Andy - Some CdSe papers
Fabrication of Stable Low-Density Silica Aerogels Containing Luminescent ZnS Capped CdSe Quantum Dots.
L. Sorensen, G.F. Strouse, and A.E. Stiegman.
Advan. Mat. (2006)18, 1965.
Summary:
Luminescent CdSe quantum dots of 2.5 and 6.0 nm dimension have been incorporated into a low-density silica aerogels matrix. The aerogels are formed from the supercritical CO2 extraction of an alcogel containing quantum dots surface passivated with 3-aminopropyltriethoxysilane. The resulting aerogels (see figure and cover) are low scattering and show intense, stable luminescence.
Growth of CdSe Quantum Rods and Multipods Seeded by Noble-Metal Nanoparticles.
K.T. Yong, Y. Sahoo, M.T. Swihart and P.N. Prasad
Advan. Mat. (2006)18, 1978.
Summary:
CdSe quantum rods are prepared at much milder conditions than previously reported, using noble-metal seed particles to initiate growth. The CdSe nanocrystals initially form as multipods that cleave to yield freestanding quantum rods (see figure) with high photoluminescence quantum yields. This study provides a new direction in developing facile syntheses of semiconductor NCs with nonspherical morphology, thereby making available new building blocks for nanotechnology.
Bryan - Au Nanoparticle Stuff
Turkevich Method for Gold Nanoparticle Synthesis Revisited
J. Kimling, M. Maier, B. Okenve, V. Kotaidis, H. Ballot, and A. Plech.
J.Phys.Chem.B(2006)110,15700.
Abstract:
The growth of gold nanoparticles by reduction by citrate and ascorbic acid has been examined in detail to explore the parameter space of reaction conditions. It is found that gold particles can be produced in a wide range of sizes, from 9 to 120 nm, with defined size distribution, following the earlier work of Turkevich and Frens. The reaction is initiated thermally or in comparison by UV irradiation, which results in similar final products. The kinetics of the extinction spectra show the multiple steps of primary and secondary clustering leading to polycrystallites.
Andre
Structural, Magnetic, and Spectroscopic Studies of YAgSn, TmAgSn, and LuAgSn
C.P. Sebastian, H. Eckert, C. Fehse, J.P. Wright, J.P. Attfield, D. Johrendt, S. Rayaprol, R.D. Hoffmann, R. Pottgen.
JSolidStateChem (2006) 179, 2376.
Abstract:
The rare earth–silver–stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P63mc, Z=2, a=468.3(1), Click to view the MathML sourcepm, wR2=0.0343, 353 F2 values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a=726.4(2), Click to view the MathML source, wR2=0.0399, 659 F2 values, 15 variables for TmAgSn, and a=723.8(2), Click to view the MathML source, wR2=0.0674, 364 F2 values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with Click to view the MathML source, in order to clarify the silver–tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag–Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag–Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie–Weiss paramagnet with an experimental magnetic moment of 7.2 ?B/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by 119Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental 119Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag–Sn bonds and also significant Ag–Ag bonding in LuAgSn.
Na->Li (and Li->Na) CP/MAS
Site Discrimination in Mixed-Alkali Glasses Studied by Cross-Polarization NMR
S.P. Puls and H. Eckert.
J.Phys.Chem.B(2006)110,14253.
Abstract:
Cation-cation interactions are thought to play a significant role in shaping the nonlinear compositional dependence of ionic conductivity, known as the mixed-alkali effect (MAE) in glassy solid electrolytes. For providing a structural rationale of this effect, the discrimination of various cation sites in mixed-alkali glasses is of interest. In the present study, cross-polarization (CP) experiments have been applied to glasses in the system [(Li2O)x(Na2O)1-x]0.3[B2O3]0.7 to discriminate between alkali ions by virtue of different heteronuclear 7Li-23Na dipole-dipole coupling strengths. Cross-polarization studies involving two types of quadrupolar nuclei (both 7Li and 23Na have a spin-quantum number I = 3/2) are complicated by spin state mixing under radio frequency irradiation and magic-angle spinning (MAS). Therefore careful validation and optimization protocols are reported for the model compound LiNaSO4 prior to conducting the measurements on the glassy samples. 23Na 7Li CP/MAS NMR spectra have been obtained on glasses containing the Na+ ions as the dilute species. They reveal that those lithium species interacting particularly strongly with sodium ions have the same average 7Li chemical shift as the entire lithium population; the symmetrical situation applies to the 23Na nuclei at the sodium rich end of the composition range. On the other hand, a clear site discrimination is afforded by temperature-dependent static 23Na 7Li CP experiments, indicating that the Li ions that are most strongly interacting with sodium ions are strongly immobilized. This finding provides the first direct experimental evidence for the proposed secondary mismatch concept invoked for explaining the strong MAE in the dilute foreign ion limit
Cory - 17O NMR and Repetitive DFS experiments
Sensitivity Enhancement and Heteronuclear Distance Measurements in Biological 17O Solid-State NMR
A. Binkmann and P.M. Kentgens
J.Phys.Chem.B(2006)110,16089.
Abstract:
In this contribution we present a comprehensive approach to study hydrogen bonding in biological and biomimetic systems through 17O and 17O-1H solid-state NMR combined with density functional theory calculations of 17O and 1H NMR parameters. We explore the signal enhancement of 17O in L-tyrosine·HCl using repetitive double-frequency swept radio frequency pulses in solid-state NMR. The technique is compatible with high magnetic fields and fast magic-angle spinning of the sample. A maximum enhancement by a factor of 4.3 is obtained in the signal-to-noise ratio of the selectively excited 17O central transition in a powdered sample of 17O-L-tyrosine·HCl at an external field of 14.1 T and a spinning frequency of 25 kHz. As little as 128 transients lead to meaningful 17O spectra of the same sample at an external field of 18.8 T and a spinning frequency of 50 kHz. Furthermore we employed supercycled symmetry-based pulse sequences on the protons to achieve heteronuclear longitudinal two-spin-order (IzSz) recoupling to determine 17O-1H distances. These sequences recouple the heteronuclear dipolar 17O-1H couplings, where dipolar truncation is absent, while decoupling the homonuclear proton dipolar interactions. They can be applied at fast magic-angle-spinning frequencies up and beyond 50 kHz and are very robust with respect to 17O quadrupolar couplings and both 17O and 1H chemical shift anisotropies, which makes them suitable for the use at high external magnetic fields. The method is demonstrated by determining the 17O-1H distance in L-tyrosine·HCl at a spinning frequency of 50 kHz and an external field of 18.8 T.
Friday, August 11, 2006
Tuesday, August 08, 2006
MRC: 29Si and 27Al NMR of paramagnetic materials
Magnetic Resonance in Chemistry
Vol: 44, Issue: 9, September 2006
pp. 861 - 867
Title: Solid-state NMR spectra of paramagnetic silica-based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842‐3012, USA
Keywords: 29Si; 27Al NMR; paramagnetic solids; relaxation
Abstract (English):
Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 9, September 2006
pp. 861 - 867
Title: Solid-state NMR spectra of paramagnetic silica-based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842‐3012, USA
Keywords: 29Si; 27Al NMR; paramagnetic solids; relaxation
Abstract (English):
Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies. Copyright © 2006 John Wiley & Sons, Ltd.
MRC: 71Ga NMR; Grandinetti
Magnetic Resonance in Chemistry
Vol: 44, Issue: 9, September 2006
pp. 823 - 831
Title: Solid-state NMR characterization of 69Ga and 71Ga in crystalline solids
Authors: Ash, Jason T.a; Grandinetti, Philip J.a
Affiliations: a. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, Ohio 43210‐1173, USA
Keywords: gallium NMR; quadrupolar nuclei
Abstract (English):
Gallium model systems containing four- and six-coordinate gallium sites have been investigated using solid-state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on a-Ga2O3, b-Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic-angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor-assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four-coordinate gallium having values of approximately 50 ppm and six-coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 × 1021 Vm-2 or more, while the less strained systems have values of 1.5 × 1021 Vm-2 or less. A plot of chemical shift versus EFG suggests that solid-state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 9, September 2006
pp. 823 - 831
Title: Solid-state NMR characterization of 69Ga and 71Ga in crystalline solids
Authors: Ash, Jason T.a; Grandinetti, Philip J.a
Affiliations: a. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, Ohio 43210‐1173, USA
Keywords: gallium NMR; quadrupolar nuclei
Abstract (English):
Gallium model systems containing four- and six-coordinate gallium sites have been investigated using solid-state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on a-Ga2O3, b-Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic-angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor-assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four-coordinate gallium having values of approximately 50 ppm and six-coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 × 1021 Vm-2 or more, while the less strained systems have values of 1.5 × 1021 Vm-2 or less. A plot of chemical shift versus EFG suggests that solid-state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone. Copyright © 2006 John Wiley & Sons, Ltd.
Chem. Soc. Rev. Solid-State 17O NMR, Ashbrook and Smith
Chem. Soc. Rev., 2006, 35, 718 - 735, DOI: 10.1039/b514051j
Solid state 17O NMR—an introduction to the background principles and applications to inorganic materials
Sharon E. Ashbrook and Mark E. Smith
Oxygen is a key chemical element and solid state NMR can provide unique insight into the its local environment. In the last decade there have been significant advances (sensitivity, resolution) in the NMR methodology for non-integer spin quadrupole nuclei such as oxygen and the background to these techniques is presented in this tutorial review. The information that the NMR parameters can provide about the local environment is explained through a series of illustrations from different areas of solid state chemistry and structural science of inorganic materials.
Solid state 17O NMR—an introduction to the background principles and applications to inorganic materials
Sharon E. Ashbrook and Mark E. Smith
Oxygen is a key chemical element and solid state NMR can provide unique insight into the its local environment. In the last decade there have been significant advances (sensitivity, resolution) in the NMR methodology for non-integer spin quadrupole nuclei such as oxygen and the background to these techniques is presented in this tutorial review. The information that the NMR parameters can provide about the local environment is explained through a series of illustrations from different areas of solid state chemistry and structural science of inorganic materials.
Concepts: Structural Information from Quadrupolar Nuclei in Solid State NMR . Sharon E. Ashbrook, Melinda J. Duer.
Concepts in Magnetic Resonance Part A
Volume 28A, Issue 3 , Pages 183 - 248
Special Issue: Structural Information from Quadrupolar Nuclei in Solid State NMR . Issue Edited by Sharon E. Ashbrook, Melinda J. Duer.
Published Online: 4 May 2006
Structural information from quadrupolar nuclei in solid state NMR
Sharon E. Ashbrook 1, Melinda J. Duer 2 *
1 School of Chemistry and EaStChem, University of St. Andrews, North Haugh, St. Andrews, KY16 9ST, United Kingdom
2 Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
Keywords
solid-state NMR • quadrupole coupling • quadrupolar nuclei • structure determination • magic-angle spinning • double rotation • dynamic-angle spinning • correlation spectroscopy • multiple-quantum magic-angle spinning • satellite-transition magic-angle spinning • multiple quantum • rotational resonance • rotational-echo double resonance • J-coupling • scalar coupling • computation/calculation of NMR parameters
Abstract
Solid-state NMR has become the method of choice for determining details of molecular-level structure in heterogeneous systems. Though spin-1/2 nuclei still form the core of most such studies, quadrupolar nuclei are increasingly being used. This review assesses what is currently possible, from achieving high-resolution spectra for quadrupolar nuclei (a prerequisite for most structure determination work), to forming correlation spectra which give qualitative details of spatial proximity of nuclei and the determination of internuclear distances, between quadrupolar spins and quadrupolar and spin-1/2 nuclei. Examples are given of each method discussed, and the advantages and disadvantages of the various experiments for different possible applications are assessed. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 183-248, 2006.
Volume 28A, Issue 3 , Pages 183 - 248
Special Issue: Structural Information from Quadrupolar Nuclei in Solid State NMR . Issue Edited by Sharon E. Ashbrook, Melinda J. Duer.
Published Online: 4 May 2006
Structural information from quadrupolar nuclei in solid state NMR
Sharon E. Ashbrook 1, Melinda J. Duer 2 *
1 School of Chemistry and EaStChem, University of St. Andrews, North Haugh, St. Andrews, KY16 9ST, United Kingdom
2 Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
Keywords
solid-state NMR • quadrupole coupling • quadrupolar nuclei • structure determination • magic-angle spinning • double rotation • dynamic-angle spinning • correlation spectroscopy • multiple-quantum magic-angle spinning • satellite-transition magic-angle spinning • multiple quantum • rotational resonance • rotational-echo double resonance • J-coupling • scalar coupling • computation/calculation of NMR parameters
Abstract
Solid-state NMR has become the method of choice for determining details of molecular-level structure in heterogeneous systems. Though spin-1/2 nuclei still form the core of most such studies, quadrupolar nuclei are increasingly being used. This review assesses what is currently possible, from achieving high-resolution spectra for quadrupolar nuclei (a prerequisite for most structure determination work), to forming correlation spectra which give qualitative details of spatial proximity of nuclei and the determination of internuclear distances, between quadrupolar spins and quadrupolar and spin-1/2 nuclei. Examples are given of each method discussed, and the advantages and disadvantages of the various experiments for different possible applications are assessed. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 183-248, 2006.
JMR: 2D, 1 pulse NMR (TOP NMR) of quadrupoles; Massiot and Grandinetti
Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 310-315
Title: Two-dimensional one pulse MAS of half-integer quadrupolar nuclei
Authors: Massiot, Dominiquea; Hiet, Juliana; Pellerin, Nadiaa; Fayon, Francka; Deschamps, Michaela; Steuernagel, Stefanb; Grandinetti, Philip J.c
Affiliations: a. CRMHT-CNRS, UPR4212, 45071 Orléans cedex 2, France
b. Bruker-Biospin GMBH, 76287 Rheinstetten, Germany
c. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Keywords: Solid-state NMR; Half-integer quadrupolar nuclei; Spinning sidebands
Abstract (English):
We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.
Vol: 181, Issue: 2, August, 2006
pp. 310-315
Title: Two-dimensional one pulse MAS of half-integer quadrupolar nuclei
Authors: Massiot, Dominiquea; Hiet, Juliana; Pellerin, Nadiaa; Fayon, Francka; Deschamps, Michaela; Steuernagel, Stefanb; Grandinetti, Philip J.c
Affiliations: a. CRMHT-CNRS, UPR4212, 45071 Orléans cedex 2, France
b. Bruker-Biospin GMBH, 76287 Rheinstetten, Germany
c. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Keywords: Solid-state NMR; Half-integer quadrupolar nuclei; Spinning sidebands
Abstract (English):
We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.
JMR: 2D, 1 pulse NMR (TOP NMR) of quadrupoles; Massiot and Grandinetti
Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 310-315
Title: Two-dimensional one pulse MAS of half-integer quadrupolar nuclei
Authors: Massiot, Dominiquea; Hiet, Juliana; Pellerin, Nadiaa; Fayon, Francka; Deschamps, Michaela; Steuernagel, Stefanb; Grandinetti, Philip J.c
Affiliations: a. CRMHT-CNRS, UPR4212, 45071 Orléans cedex 2, France
b. Bruker-Biospin GMBH, 76287 Rheinstetten, Germany
c. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Keywords: Solid-state NMR; Half-integer quadrupolar nuclei; Spinning sidebands
Abstract (English):
We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.
Vol: 181, Issue: 2, August, 2006
pp. 310-315
Title: Two-dimensional one pulse MAS of half-integer quadrupolar nuclei
Authors: Massiot, Dominiquea; Hiet, Juliana; Pellerin, Nadiaa; Fayon, Francka; Deschamps, Michaela; Steuernagel, Stefanb; Grandinetti, Philip J.c
Affiliations: a. CRMHT-CNRS, UPR4212, 45071 Orléans cedex 2, France
b. Bruker-Biospin GMBH, 76287 Rheinstetten, Germany
c. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Keywords: Solid-state NMR; Half-integer quadrupolar nuclei; Spinning sidebands
Abstract (English):
We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.
JMR; 13C MAS NMR of paramagnetics; Ishii
Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 233-243
Title: Sensitivity enhancement, assignment, and distance measurement in 13C solid-state NMR spectroscopy for paramagnetic systems under fast magic angle spinning
Authors: Wickramasinghe, Nalinda P.a; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, Chicago IL 60607, USA
Keywords: 13C solid-state NMR; Paramagnetic systems; Fast MAS; Sensitivity; Assignments; Distances
Abstract (English):
Despite success of previous studies, high-resolution solid-state NMR (SSNMR) of paramagnetic systems has been still largely unexplored because of limited sensitivity/resolution and difficulty in assignment due to large paramagnetic shifts. Recently, we demonstrated that an approach using very-fast magic angle spinning (VFMAS; spinning speed 20kHz) enhances resolution/sensitivity in 13C SSNMR for paramagnetic complexes [Y. Ishii, S. Chimon, N.P. Wickramasinghe, A new approach in 1D and 2D 13C high resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning, J. Am. Chem. Soc. 125 (2003) 3438–3439]. In this study, we present a new strategy for sensitivity enhancement, signal assignment, and distance measurement in 13C SSNMR under VFMAS for unlabeled paramagnetic complexes using recoupling-based polarization transfer. As a robust alternative of cross-polarization (CP), rapid application of recoupling-based polarization transfer under VFMAS is proposed. In the present approach, a dipolar-based analog of INEPT (dipolar INEPT) methods is used for polarization transfer and a 13C signal is observed under VFMAS without 1H decoupling. The resulting low duty factor permits rapid signal accumulation without probe arcing at recycle times (3ms/scan) matched to short 1H T1 values of small paramagnetic systems (1ms). Experiments on Cu(dl-Ala)2 showed that the fast repetition approach under VFMAS provided sensitivity enhancement by a factor of 8–66 for a given sample, compared with the 13C MAS spectrum under moderate MAS at 5kHz. The applicability of this approach was also demonstrated for a more challenging system, Mn(acac)3, for which 13C and 1H paramagnetic shift dispersions reach 1500 and 700ppm, respectively. It was shown that effective-evolution-time dependence of transferred signals in dipolar INEPT permitted one to distinguish 13CH, 13CH2, 13CH3, Formula Not Shown groups in 1D experiments for Cu(dl-Ala)2 and Cu(Gly)2. Applications of this technique to 2D 13C/1H correlation NMR under VFMAS yielded reliable assignments of 1H resonances as well as 13C resonances for Cu(dl-Ala)2 and Mn(acac)3. Quantitative analysis of cross-peak intensities in 2D 13C/1H correlation NMR spectra of Cu(dl-Ala)2 provided distance information between non-bonded 13C–1H pairs in the paramagnetic system.
Vol: 181, Issue: 2, August, 2006
pp. 233-243
Title: Sensitivity enhancement, assignment, and distance measurement in 13C solid-state NMR spectroscopy for paramagnetic systems under fast magic angle spinning
Authors: Wickramasinghe, Nalinda P.a; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, Chicago IL 60607, USA
Keywords: 13C solid-state NMR; Paramagnetic systems; Fast MAS; Sensitivity; Assignments; Distances
Abstract (English):
Despite success of previous studies, high-resolution solid-state NMR (SSNMR) of paramagnetic systems has been still largely unexplored because of limited sensitivity/resolution and difficulty in assignment due to large paramagnetic shifts. Recently, we demonstrated that an approach using very-fast magic angle spinning (VFMAS; spinning speed 20kHz) enhances resolution/sensitivity in 13C SSNMR for paramagnetic complexes [Y. Ishii, S. Chimon, N.P. Wickramasinghe, A new approach in 1D and 2D 13C high resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning, J. Am. Chem. Soc. 125 (2003) 3438–3439]. In this study, we present a new strategy for sensitivity enhancement, signal assignment, and distance measurement in 13C SSNMR under VFMAS for unlabeled paramagnetic complexes using recoupling-based polarization transfer. As a robust alternative of cross-polarization (CP), rapid application of recoupling-based polarization transfer under VFMAS is proposed. In the present approach, a dipolar-based analog of INEPT (dipolar INEPT) methods is used for polarization transfer and a 13C signal is observed under VFMAS without 1H decoupling. The resulting low duty factor permits rapid signal accumulation without probe arcing at recycle times (3ms/scan) matched to short 1H T1 values of small paramagnetic systems (1ms). Experiments on Cu(dl-Ala)2 showed that the fast repetition approach under VFMAS provided sensitivity enhancement by a factor of 8–66 for a given sample, compared with the 13C MAS spectrum under moderate MAS at 5kHz. The applicability of this approach was also demonstrated for a more challenging system, Mn(acac)3, for which 13C and 1H paramagnetic shift dispersions reach 1500 and 700ppm, respectively. It was shown that effective-evolution-time dependence of transferred signals in dipolar INEPT permitted one to distinguish 13CH, 13CH2, 13CH3, Formula Not Shown groups in 1D experiments for Cu(dl-Ala)2 and Cu(Gly)2. Applications of this technique to 2D 13C/1H correlation NMR under VFMAS yielded reliable assignments of 1H resonances as well as 13C resonances for Cu(dl-Ala)2 and Mn(acac)3. Quantitative analysis of cross-peak intensities in 2D 13C/1H correlation NMR spectra of Cu(dl-Ala)2 provided distance information between non-bonded 13C–1H pairs in the paramagnetic system.
JMR; SW-FAM for static NMR of quadrupolar nuclei; Madhu
Journal of Magnetic Resonance
Vol: 181, Issue: 1, July, 2006
pp. 68-78
Title: Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in static NMR of half-integer spin quadrupolar nuclei
Authors: Bräuniger, Thomasa; Hempel, Güntera; Madhu, P.K.b
Affiliations: a. Department of Physics, University of Halle, Friedemann-Bach-Platz 6, 06108 Halle, Germany
b. Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
Keywords: Static 27Al NMR; Half-integer spin; Quadrupolar nuclei; SW-FAM
Abstract (English):
In solid-state NMR of quadrupolar nuclei with half-integer spin I, fast amplitude-modulated (FAM) pulse trains have been utilised to enhance the intensity of the central-transition signal, by transferring spin population from the satellite transitions. In this paper, the signal-enhancement performance of the recently introduced SW-FAM pulse train with swept modulation frequency [T. Bräuniger, K. Ramaswamy, P.K. Madhu, Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses, Chem. Phys. Lett. 383 (2004) 403â??410] is explored in more detail for static spectra. It is shown that by sweeping the modulation frequencies linearly over the pulse pairs (SW(1/Ï?)-FAM), the shape of the frequency distribution is improved in comparison to the original pulse scheme (SW(Ï?)-FAM). For static spectra of 27Al (I=5/2), better signal-enhancement performance is found for the SW(1/Ï?)-FAM sequence, as demonstrated both by experiments and numerical simulations.
Vol: 181, Issue: 1, July, 2006
pp. 68-78
Title: Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in static NMR of half-integer spin quadrupolar nuclei
Authors: Bräuniger, Thomasa; Hempel, Güntera; Madhu, P.K.b
Affiliations: a. Department of Physics, University of Halle, Friedemann-Bach-Platz 6, 06108 Halle, Germany
b. Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
Keywords: Static 27Al NMR; Half-integer spin; Quadrupolar nuclei; SW-FAM
Abstract (English):
In solid-state NMR of quadrupolar nuclei with half-integer spin I, fast amplitude-modulated (FAM) pulse trains have been utilised to enhance the intensity of the central-transition signal, by transferring spin population from the satellite transitions. In this paper, the signal-enhancement performance of the recently introduced SW-FAM pulse train with swept modulation frequency [T. Bräuniger, K. Ramaswamy, P.K. Madhu, Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses, Chem. Phys. Lett. 383 (2004) 403â??410] is explored in more detail for static spectra. It is shown that by sweeping the modulation frequencies linearly over the pulse pairs (SW(1/Ï?)-FAM), the shape of the frequency distribution is improved in comparison to the original pulse scheme (SW(Ï?)-FAM). For static spectra of 27Al (I=5/2), better signal-enhancement performance is found for the SW(1/Ï?)-FAM sequence, as demonstrated both by experiments and numerical simulations.
JMR: CSA recoupling; Duer
Journal of Magnetic Resonance
Vol: 181, Issue: 1, July, 2006
pp. 1-8
Title: Recoupling of chemical-shift anisotropy powder patterns in MAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
Keywords: Solid-state NMR; Magic-angle spinning; Chemical-shift anisotropy; Recoupling
Abstract (English):
A comparison of three different implementations of the chemical-shift recoupling experiment of Tycko et al. [R. Tycko, G. Dabbagh, P.A. Mirau, Determination of chemical-shift-anisotropy lineshapes in a two-dimensional magic-angle-spinning NMR experiment, J. Magn. Reson. 85 (1989) 265â??274] is presented. The methods seek to reduce the effects of artefacts resulting from pulse imperfections and residual C-H dipolar coupling in organic solids. An optimised and constant time implementation are shown to give well-defined and artefact free powder pattern lineshapes in the indirectly observed dimension for both sp2 and sp3 carbon sites. Experimental setup is no more demanding than for the original experiment, and can be implemented using standard commercial hardware.
Vol: 181, Issue: 1, July, 2006
pp. 1-8
Title: Recoupling of chemical-shift anisotropy powder patterns in MAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
Keywords: Solid-state NMR; Magic-angle spinning; Chemical-shift anisotropy; Recoupling
Abstract (English):
A comparison of three different implementations of the chemical-shift recoupling experiment of Tycko et al. [R. Tycko, G. Dabbagh, P.A. Mirau, Determination of chemical-shift-anisotropy lineshapes in a two-dimensional magic-angle-spinning NMR experiment, J. Magn. Reson. 85 (1989) 265â??274] is presented. The methods seek to reduce the effects of artefacts resulting from pulse imperfections and residual C-H dipolar coupling in organic solids. An optimised and constant time implementation are shown to give well-defined and artefact free powder pattern lineshapes in the indirectly observed dimension for both sp2 and sp3 carbon sites. Experimental setup is no more demanding than for the original experiment, and can be implemented using standard commercial hardware.
MRC: 31P-71Ga MAS HMQC experiments; gallophosphates; Massiot
Magnetic Resonance in Chemistry
Vol: 44, Issue: 8, August 2006
pp. 770 - 775
Title: Toward a better description of gallo-phosphate materials in solid-state NMR: 1D and 2D correlation studies
Authors: Montouillout, Valériea; Morais, Cláudia M.a; Douy, Andréa; Fayon, Francka; Massiot, Dominiquea
Affiliations: a. CRMHT—CNRS UPR4212 1D, Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
Keywords: NMR; 71Ga; 31P; HMQC experiment; gallo-phosphates
Abstract (English):
We show that weak 2J(71Ga—O—31P), typically 12 Hz in GaPO4, can be used to efficiently establish heteronuclear 31P—71Ga correlation using a MAS HMQC experiment in gallo-phosphate materials. The experiment demonstrated for cristobalite GaPO4 is then applied to Ga(PO3)3, where it allows the differentiation of the signature of three different Ga sites overlapping in the 1D spectrum. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 8, August 2006
pp. 770 - 775
Title: Toward a better description of gallo-phosphate materials in solid-state NMR: 1D and 2D correlation studies
Authors: Montouillout, Valériea; Morais, Cláudia M.a; Douy, Andréa; Fayon, Francka; Massiot, Dominiquea
Affiliations: a. CRMHT—CNRS UPR4212 1D, Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
Keywords: NMR; 71Ga; 31P; HMQC experiment; gallo-phosphates
Abstract (English):
We show that weak 2J(71Ga—O—31P), typically 12 Hz in GaPO4, can be used to efficiently establish heteronuclear 31P—71Ga correlation using a MAS HMQC experiment in gallo-phosphate materials. The experiment demonstrated for cristobalite GaPO4 is then applied to Ga(PO3)3, where it allows the differentiation of the signature of three different Ga sites overlapping in the 1D spectrum. Copyright © 2006 John Wiley & Sons, Ltd.
MRC: 33S NMR of ethanesulfonates, plus DFT and NBO methods
Magnetic Resonance in Chemistry
Vol: 44, Issue: 8, August 2006
pp. 753 - 760
Title: 33S NMR spectroscopy 3. substituent effects on 33S NMR parameters in 2-substituted ethanesulfonates
Authors: Musio, Robertaa; Sciacovelli, Oronzoa
Affiliations: a. Istituto C.N.R. di Chimica dei Composti Organo‐Metallici—Sezione di Bari and Dipartimento di Chimica, Università degli Studi di Bari, Via E. Orabona 4, 70126 Bari, Italy
Keywords: NMR; 33S NMR; 33S chemical shift; 33S nuclear shielding calculations; 33S nuclear quadrupole coupling constant; substituent effect; 2-substituted ethanesulfonates
Abstract (English):
33S NMR parameters (chemical shifts and linewidths) in 2-substituted sodium ethanesulfonates, XCH2CH2SO3Na (X = H, CH3, OH, SH, NH2, Cl, Br, NH3+) depend upon the electronic properties of substituents. To explain experimental results and obtain additional information on the origin of the observed substituent effect (SE), sulfur isotropic absolute shielding constants have been calculated at DFT level of theory (B3LYP/6-311 + + G(2d,p)) by gauge-including atomic orbitals (GIAO) method. Data have been interpreted with the aid of natural bond orbital (NBO) method and natural chemical shielding (NCS) analysis. It has been demonstrated that in the class of compounds considered the diamagnetic contribution to sulfur-shielding constant is constant and the observed upfield shift of 33S resonance induced by electron-withdrawing substituents (reverse chemical shift effect) can be related to variations of the paramagnetic contribution. Substituents with different electronic properties cause variations in the polarization of S—C and S—O bonds of the —C—SO3- moiety thus determining changes of the electron density at sulfur nucleus and consequently the expansion or contraction of 3p sulfur orbitals. Also oxygen lone-pairs and sulfur core 2p electrons can play an active role in determining the paramagnetic contribution to sulfur shielding. With regard to linewidth variations, they can be ascribed primarily to changes in the nuclear quadrupole coupling constant values. B3LYP/6-311 + + G(2d,p) method allows obtaining a good reproducibility of SE on the electric field gradient (EFG) at sulfur, although its values tend to be underestimated significantly. Moreover, 17O shielding constants have been calculated. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 8, August 2006
pp. 753 - 760
Title: 33S NMR spectroscopy 3. substituent effects on 33S NMR parameters in 2-substituted ethanesulfonates
Authors: Musio, Robertaa; Sciacovelli, Oronzoa
Affiliations: a. Istituto C.N.R. di Chimica dei Composti Organo‐Metallici—Sezione di Bari and Dipartimento di Chimica, Università degli Studi di Bari, Via E. Orabona 4, 70126 Bari, Italy
Keywords: NMR; 33S NMR; 33S chemical shift; 33S nuclear shielding calculations; 33S nuclear quadrupole coupling constant; substituent effect; 2-substituted ethanesulfonates
Abstract (English):
33S NMR parameters (chemical shifts and linewidths) in 2-substituted sodium ethanesulfonates, XCH2CH2SO3Na (X = H, CH3, OH, SH, NH2, Cl, Br, NH3+) depend upon the electronic properties of substituents. To explain experimental results and obtain additional information on the origin of the observed substituent effect (SE), sulfur isotropic absolute shielding constants have been calculated at DFT level of theory (B3LYP/6-311 + + G(2d,p)) by gauge-including atomic orbitals (GIAO) method. Data have been interpreted with the aid of natural bond orbital (NBO) method and natural chemical shielding (NCS) analysis. It has been demonstrated that in the class of compounds considered the diamagnetic contribution to sulfur-shielding constant is constant and the observed upfield shift of 33S resonance induced by electron-withdrawing substituents (reverse chemical shift effect) can be related to variations of the paramagnetic contribution. Substituents with different electronic properties cause variations in the polarization of S—C and S—O bonds of the —C—SO3- moiety thus determining changes of the electron density at sulfur nucleus and consequently the expansion or contraction of 3p sulfur orbitals. Also oxygen lone-pairs and sulfur core 2p electrons can play an active role in determining the paramagnetic contribution to sulfur shielding. With regard to linewidth variations, they can be ascribed primarily to changes in the nuclear quadrupole coupling constant values. B3LYP/6-311 + + G(2d,p) method allows obtaining a good reproducibility of SE on the electric field gradient (EFG) at sulfur, although its values tend to be underestimated significantly. Moreover, 17O shielding constants have been calculated. Copyright © 2006 John Wiley & Sons, Ltd.
MRC; DFT of 53Cr chemical shielding; Buhl
Magnetic Resonance in Chemistry
Vol: 44, Issue: 7, July 2006
pp. 661 - 668
Title: Density-functional computation of 53Cr NMR chemical shifts
Author: Bühl, Michaela
Affiliations: a. Max‐Planck Institut für Kohlenforschung, Kaiser‐Wilhelm Platz 1, D‐45470 Mülheim an der Ruhr, Germany
Keywords: NMR; 53Cr; density-functional calculations; chemical-shift computations; electric field gradients
Abstract (English):
53Cr chemical shifts of CrO42-, Cr2O72-, CrO3X-, CrO2X2(X = F, Cl), and Cr(CO)5L (L = CO, PF3, CHNH2, CMeNMe2) are computed, using geometries optimized with the gradient-corrected BP86 density functional, at the gauge-including atomic orbitals (GIAO)-, BPW91-, and B3LYP levels. For this set of compounds, substituent effects on d(53Cr) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. For selected cases, 53Cr NMR line widths can be rationalized in terms of electric field gradients (EFGs) computed with the BPW91 functional, but in general other factors such as molecular correlation times appear to be dominating. 53Cr chemical shifts and EFGs are predicted for CrO3, Cr(C6H6)2, Cr(C6H6)CO3, and, with reduced reliability, for Cr2(m2-O2CH)4. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 7, July 2006
pp. 661 - 668
Title: Density-functional computation of 53Cr NMR chemical shifts
Author: Bühl, Michaela
Affiliations: a. Max‐Planck Institut für Kohlenforschung, Kaiser‐Wilhelm Platz 1, D‐45470 Mülheim an der Ruhr, Germany
Keywords: NMR; 53Cr; density-functional calculations; chemical-shift computations; electric field gradients
Abstract (English):
53Cr chemical shifts of CrO42-, Cr2O72-, CrO3X-, CrO2X2(X = F, Cl), and Cr(CO)5L (L = CO, PF3, CHNH2, CMeNMe2) are computed, using geometries optimized with the gradient-corrected BP86 density functional, at the gauge-including atomic orbitals (GIAO)-, BPW91-, and B3LYP levels. For this set of compounds, substituent effects on d(53Cr) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. For selected cases, 53Cr NMR line widths can be rationalized in terms of electric field gradients (EFGs) computed with the BPW91 functional, but in general other factors such as molecular correlation times appear to be dominating. 53Cr chemical shifts and EFGs are predicted for CrO3, Cr(C6H6)2, Cr(C6H6)CO3, and, with reduced reliability, for Cr2(m2-O2CH)4. Copyright © 2006 John Wiley & Sons, Ltd.
MRC: 13C SSNMR of taxol
Magnetic Resonance in Chemistry
Vol: 44, Issue: 6, May 2006
pp. 581 - 585
Title: Solid-state NMR studies of the molecular structure of Taxol
Authors: Ho, Yua; Tzou, Der-Lii M.; Chu, Feng-Ia
Affiliations: a. Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China
Keywords: NMR; 13C; Taxol; molecular conformation
Abstract (English):
Solid-state 13C{1H} cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 6, May 2006
pp. 581 - 585
Title: Solid-state NMR studies of the molecular structure of Taxol
Authors: Ho, Yua; Tzou, Der-Lii M.; Chu, Feng-Ia
Affiliations: a. Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China
Keywords: NMR; 13C; Taxol; molecular conformation
Abstract (English):
Solid-state 13C{1H} cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol. Copyright © 2006 John Wiley & Sons, Ltd.
MRC; ssnmr of nanocrystalline hydroxyapatite; Jäger
Magnetic Resonance in Chemistry
Vol: 44, Issue: 6, May 2006
pp. 573 - 580
Title: A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite
Authors: Jäger, Christiana; Welzel, Theab; Meyer-Zaika, Wolfgangb; Epple, Matthiasb
Affiliations: a. Federal Institute for Materials Research and Testing, Division I.3, Working Group NMR Spectroscopy, Richard Willstaetter Str. 11, D‐12489 Berlin, Germany
b. Institute of Inorganic Chemistry, University Duisburg‐Essen, Universitaetsstr. 5‐7, D‐45117 Essen, Germany
Keywords: NMR; 1H; 31P; biomineralization; hydroxyapatite; calcium phosphate; nanoparticles
Abstract (English):
Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30–50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 44, Issue: 6, May 2006
pp. 573 - 580
Title: A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite
Authors: Jäger, Christiana; Welzel, Theab; Meyer-Zaika, Wolfgangb; Epple, Matthiasb
Affiliations: a. Federal Institute for Materials Research and Testing, Division I.3, Working Group NMR Spectroscopy, Richard Willstaetter Str. 11, D‐12489 Berlin, Germany
b. Institute of Inorganic Chemistry, University Duisburg‐Essen, Universitaetsstr. 5‐7, D‐45117 Essen, Germany
Keywords: NMR; 1H; 31P; biomineralization; hydroxyapatite; calcium phosphate; nanoparticles
Abstract (English):
Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30–50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd.
Progress in NMR: 13C of columnar liquid crystals
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 48, Issue: 2-3, May 30, 2006
pp. 85-107
Title: Carbon-13 NMR spectroscopy applied to columnar liquid crystals
Authors: Dvinskikh, Sergey V.a, b; Sandström, Dickb; Zimmermann, Herbertc; Maliniak, Arnoldb
Affiliations: a. Institute of Physics, St Petersburg State University, Ulianovskaia 1, 198504 St Petersburg, Russian Federation
b. Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden
c. Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany
Keywords: Columnar liquid crystals; Solid-state NMR; Carbon-13 NMR; Dipolar coupling; Chemical shift anisotropy
Vol: 48, Issue: 2-3, May 30, 2006
pp. 85-107
Title: Carbon-13 NMR spectroscopy applied to columnar liquid crystals
Authors: Dvinskikh, Sergey V.a, b; Sandström, Dickb; Zimmermann, Herbertc; Maliniak, Arnoldb
Affiliations: a. Institute of Physics, St Petersburg State University, Ulianovskaia 1, 198504 St Petersburg, Russian Federation
b. Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden
c. Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany
Keywords: Columnar liquid crystals; Solid-state NMR; Carbon-13 NMR; Dipolar coupling; Chemical shift anisotropy
SSNMR; 19F NMR of polymers; Hazendonk
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123
Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):
Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123
Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):
Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.
SSNMR; 17O NMR, Exchange; Zr-tungstate
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105
Title: Quantitative analysis of 17O exchange and ... relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):
The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105
Title: Quantitative analysis of 17O exchange and ... relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):
The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).
SSNMR; 17O-enriched pyrophosphates; Freude
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74
Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):
For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74
Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):
For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.
SSNMR: 14N NQR of sulfa drugs
Solid-State NMR:
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68
Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):
The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68
Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):
The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.
SSNMR journal update - Rob - Vol 30, i.2 Sept. 2006
Solid-State NMR:
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68
Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):
The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.
---
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74
Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):
For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.
---
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105
Title: Quantitative analysis of 17O exchange and Formula Not Shown relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):
The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).
---
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123
Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):
Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68
Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):
The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.
---
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74
Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):
For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.
---
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105
Title: Quantitative analysis of 17O exchange and Formula Not Shown relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):
The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).
---
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123
Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):
Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.
JMR; pressurized glass inserts for MAS rotors
Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 229-232
Title: An easy way to prepare pressurized glass inserts for MAS rotors
Authors: Tallavaara, Pekkaa; Jokisaari, Jukkaa
Affiliations: a. NMR Research Group, Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 University of Oulu, Finland
Keywords: MAS rotor insert; Xenon; Liquid crystal; Porous material; Pressurised sample
Abstract (English):
A novel technique to prepare pressurized glass insert samples for MAS rotors is described. In this technique, a small drop of epoxy is added to the tip of a piston and the gas is squeezed into the insert by pressing the piston. The amount of gas, i.e., pressure, in the sample can be controlls doing it better, it's all over.
I have a post up on the Killer Year Blog on the subject. It deals with writing, but the message applies to any kind of hula hoop you're trying to keep in the air.
Vol: 181, Issue: 2, August, 2006
pp. 229-232
Title: An easy way to prepare pressurized glass inserts for MAS rotors
Authors: Tallavaara, Pekkaa; Jokisaari, Jukkaa
Affiliations: a. NMR Research Group, Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 University of Oulu, Finland
Keywords: MAS rotor insert; Xenon; Liquid crystal; Porous material; Pressurised sample
Abstract (English):
A novel technique to prepare pressurized glass insert samples for MAS rotors is described. In this technique, a small drop of epoxy is added to the tip of a piston and the gas is squeezed into the insert by pressing the piston. The amount of gas, i.e., pressure, in the sample can be controlls doing it better, it's all over.
I have a post up on the Killer Year Blog on the subject. It deals with writing, but the message applies to any kind of hula hoop you're trying to keep in the air.
Thursday, August 03, 2006
natural abundance 43Ca SSNMR
Chemical Physics Letters
Volume 427, Issues 1-3 , 18 August 2006, Pages 201-205
Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials
Abstract
As a first step for probing Ca sites in biomolecules using solid-state 43Ca NMR spectroscopy, natural abundance 43Ca NMR data of calcium-containing organic solids is reported. The 43Ca NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found: the 43Ca shift increases as the mean Ca–O distance decreases, with a strong deshielding being observed for calcium with strong Ca–O bonds (distance <2.4>
Volume 427, Issues 1-3 , 18 August 2006, Pages 201-205
Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials
Abstract
As a first step for probing Ca sites in biomolecules using solid-state 43Ca NMR spectroscopy, natural abundance 43Ca NMR data of calcium-containing organic solids is reported. The 43Ca NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found: the 43Ca shift increases as the mean Ca–O distance decreases, with a strong deshielding being observed for calcium with strong Ca–O bonds (distance <2.4>
new heteronuclear decoupling sequence
Chemical Physics Letters
Volume 426, Issues 4-6, 4 August 2006, Pages 459-463
Swept-frequency two-pulse phase modulation for heteronuclear dipolar decoupling in solid-state NMR
Rajendra Singh Thakura, Narayanan D. Kurur, 1, a, and P.K. Madhu
Abstract
We introduce a heteronuclear dipolar decoupling sequence for application in solid-state nuclear magnetic resonance. The sequence, called swept-frequency two-pulse phase modulation (SWf-TPPM), is based on one of the decoupling sequences, TPPM. The sequence is robust in performance with respect to various experimental parameters, such as, the pulse flip angle, pulse phase, and offset and a comparison is made with other decoupling schemes, namely TPPM, SPINAL, and XiX, on a sample of U–13C-labelled tyrosine for magic-angle spinning speeds up to 14 kHz.
Volume 426, Issues 4-6, 4 August 2006, Pages 459-463
Swept-frequency two-pulse phase modulation for heteronuclear dipolar decoupling in solid-state NMR
Rajendra Singh Thakura, Narayanan D. Kurur, 1, a, and P.K. Madhu
Abstract
We introduce a heteronuclear dipolar decoupling sequence for application in solid-state nuclear magnetic resonance. The sequence, called swept-frequency two-pulse phase modulation (SWf-TPPM), is based on one of the decoupling sequences, TPPM. The sequence is robust in performance with respect to various experimental parameters, such as, the pulse flip angle, pulse phase, and offset and a comparison is made with other decoupling schemes, namely TPPM, SPINAL, and XiX, on a sample of U–13C-labelled tyrosine for magic-angle spinning speeds up to 14 kHz.
13C DQ under moderate MAS
Chemical Physics Letters
Volume 426, Issues 1-3 , 26 July 2006, Pages 187-191
Multiple-quantum 13C solid-state NMR spectroscopy under moderate magic-angle spinning
Sungsool Wia, , and Son-Jong Hwangb
Abstract
A new experimental scheme for the excitation and detection of 13C multiple-quantum (MQ) NMR signals in solids under magic-angle spinning (MAS) condition is presented. Symmetry-based dipolar DQ recoupling sequences have been concatenated by π/2 pulses to generate high-order 13C MQ coherences in dipolar coupled networks. This approach generates every order of MQ coherences at moderate MAS frequencies.
Volume 426, Issues 1-3 , 26 July 2006, Pages 187-191
Multiple-quantum 13C solid-state NMR spectroscopy under moderate magic-angle spinning
Sungsool Wia, , and Son-Jong Hwangb
Abstract
A new experimental scheme for the excitation and detection of 13C multiple-quantum (MQ) NMR signals in solids under magic-angle spinning (MAS) condition is presented. Symmetry-based dipolar DQ recoupling sequences have been concatenated by π/2 pulses to generate high-order 13C MQ coherences in dipolar coupled networks. This approach generates every order of MQ coherences at moderate MAS frequencies.
JCPA update
J. Phys. Chem. A, ASAP Article 10.1021/jp061350w S1089-5639(06)01350-8
Web Release Date: August 2, 2006
Alan Wong, Ramsey Ida, Xin Mo, Zhehong Gan, Jennifer Poh, and Gang Wu*
Abstract:
We report a solid-state 25Mg NMR spectroscopic study of two magnesium-containing organic compounds: monopyridinated aqua(magnesium) phthalocyanine (MgPc·H2O·Py) and chlorophyll a (Chla). Each of these compounds contains a Mg(II) ion coordinating to four nitrogen atoms and a water molecule in a square-pyramidal geometry. Solid-state 25Mg NMR spectra for MgPc·H2O·Py were obtained at 11.7 T (500 MHz for 1H) for a 25Mg-enriched sample (99.1% 25Mg atom) using both Hahn-echo and quadrupole Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences. Solid-state 25Mg NMR spectra for Chla were recorded at 25Mg natural abundance (10.1%) at 19.6 T (830 MHz for 1H). The 25Mg quadrupole parameters were determined from spectral analyses: MgPc·H2O·Py, CQ = 13.0 ± 0.1 MHz and Q = 0.00 ± 0.05; Chla, CQ = 12.9 ± 0.1 MHz and Q = 1.00 ± 0.05. This work represents the first time that Mg(II) ions in a square-pyramidal geometry have been characterized by solid-state 25Mg NMR spectroscopy. Extensive quantum mechanical calculations for electric-field-gradient (EFG) and chemical shielding tensors were performed at restricted Hartee-Fock (RHF), density functional theory (DFT), and second-order Mller-Plesset perturbation theory (MP2) levels for both compounds. Computed 25Mg nuclear quadrupole coupling constants at the RHF and MP2 levels show a reasonable basis-set convergence at the cc-pV5Z basis set (within 7% of the experimental value); however, B3LYP results display a drastic divergence beyond the cc-pVTZ basis set. A new crystal structure for MgPc·H2O·Py is also reported.
Web Release Date: August 2, 2006
Alan Wong, Ramsey Ida, Xin Mo, Zhehong Gan, Jennifer Poh, and Gang Wu*
Abstract:
We report a solid-state 25Mg NMR spectroscopic study of two magnesium-containing organic compounds: monopyridinated aqua(magnesium) phthalocyanine (MgPc·H2O·Py) and chlorophyll a (Chla). Each of these compounds contains a Mg(II) ion coordinating to four nitrogen atoms and a water molecule in a square-pyramidal geometry. Solid-state 25Mg NMR spectra for MgPc·H2O·Py were obtained at 11.7 T (500 MHz for 1H) for a 25Mg-enriched sample (99.1% 25Mg atom) using both Hahn-echo and quadrupole Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences. Solid-state 25Mg NMR spectra for Chla were recorded at 25Mg natural abundance (10.1%) at 19.6 T (830 MHz for 1H). The 25Mg quadrupole parameters were determined from spectral analyses: MgPc·H2O·Py, CQ = 13.0 ± 0.1 MHz and Q = 0.00 ± 0.05; Chla, CQ = 12.9 ± 0.1 MHz and Q = 1.00 ± 0.05. This work represents the first time that Mg(II) ions in a square-pyramidal geometry have been characterized by solid-state 25Mg NMR spectroscopy. Extensive quantum mechanical calculations for electric-field-gradient (EFG) and chemical shielding tensors were performed at restricted Hartee-Fock (RHF), density functional theory (DFT), and second-order Mller-Plesset perturbation theory (MP2) levels for both compounds. Computed 25Mg nuclear quadrupole coupling constants at the RHF and MP2 levels show a reasonable basis-set convergence at the cc-pV5Z basis set (within 7% of the experimental value); however, B3LYP results display a drastic divergence beyond the cc-pVTZ basis set. A new crystal structure for MgPc·H2O·Py is also reported.
Sunday, July 30, 2006
Organometallics, 25 (9), 2248 -2252, 2006
A 13C CP/MAS NMR Study of the Structure and Dynamics of [(5-C5H5)2Fe2(CO)4] Included in -Cyclodextrin: Evidence for Terminal-Bridging Exchange in the cis Isomer
Holly C. Canuto, Admir Masic, Nicholas H. Rees, Stephen J. Heyes, Roberto Gobetto, and Silvio Aime
Abstract:
The novel inclusion compound of -cyclodextrin with the binuclear metal carbonyl complex (5-C5H5)2Fe2(CO)4 as guest molecule is reported. 13C CP/MAS NMR spectroscopy, in the temperature range 100 to 353 K, is used to probe the structure and dynamics of the included molecules. Specifically, below ca. 240 K evidence is presented for the existence of both cis and trans isomers of included (5-C5H5)2Fe2(CO)4. Analysis of the temperature-dependence of the NMR line shapes shows that the microenvironment provided by the -cyclodextrin cavity allows much more extensive dynamic rearrangements of the guest molecules, in comparison to pure cis- or trans-(5-C5H5)2Fe2(CO)4, for which no isomerization or bridging-terminal carbonyl exchange processes are observed in this temperature regime. Notably, even at 100 K, bridging-terminal carbonyl exchange for the included trans isomer is rapid on the exchange-broadening time scale. However, the inclusion cavity is still more dynamically restrictive than a solution environment, and the rates of various exchange processes are usefully modified compared to those detected in solution. For (5-C5H5)2Fe2(CO)4 included in -cyclodextrin, contrary to the situation found in solution, the rate of bridging-terminal carbonyl exchange in the cis isomer is greater than the rate of cis-trans isomerization; in solution direct bridging-terminal exchange in the cis isomer could not be studied because indirect exchange via isomerization to the trans form, which undergoes rapid bridging-terminal exchange, is always significantly faster. By restricting isomerization, the inclusion environment thus confirms for the first time that the cis isomer is capable of carbonyl exchange and would allow the study of its rate and activation parameters.
Holly C. Canuto, Admir Masic, Nicholas H. Rees, Stephen J. Heyes, Roberto Gobetto, and Silvio Aime
Abstract:
The novel inclusion compound of -cyclodextrin with the binuclear metal carbonyl complex (5-C5H5)2Fe2(CO)4 as guest molecule is reported. 13C CP/MAS NMR spectroscopy, in the temperature range 100 to 353 K, is used to probe the structure and dynamics of the included molecules. Specifically, below ca. 240 K evidence is presented for the existence of both cis and trans isomers of included (5-C5H5)2Fe2(CO)4. Analysis of the temperature-dependence of the NMR line shapes shows that the microenvironment provided by the -cyclodextrin cavity allows much more extensive dynamic rearrangements of the guest molecules, in comparison to pure cis- or trans-(5-C5H5)2Fe2(CO)4, for which no isomerization or bridging-terminal carbonyl exchange processes are observed in this temperature regime. Notably, even at 100 K, bridging-terminal carbonyl exchange for the included trans isomer is rapid on the exchange-broadening time scale. However, the inclusion cavity is still more dynamically restrictive than a solution environment, and the rates of various exchange processes are usefully modified compared to those detected in solution. For (5-C5H5)2Fe2(CO)4 included in -cyclodextrin, contrary to the situation found in solution, the rate of bridging-terminal carbonyl exchange in the cis isomer is greater than the rate of cis-trans isomerization; in solution direct bridging-terminal exchange in the cis isomer could not be studied because indirect exchange via isomerization to the trans form, which undergoes rapid bridging-terminal exchange, is always significantly faster. By restricting isomerization, the inclusion environment thus confirms for the first time that the cis isomer is capable of carbonyl exchange and would allow the study of its rate and activation parameters.
Organometallics, 25 (14), 3428 -3434, 2006
Convergent Synthesis and Characterization of Organotin Dendrimers Sn{(CH2)nSn[(CH2)4SnPh3]3}4 (n = 3, 4)
Abstract:
The reaction of the haloalkyltin trihalides Br(CH2)3SnBr3 and Br(CH2)4SnBr3 with 3 equiv of but-3-enylmagnesium bromide yielded Br(CH2)3Sn(CH2CH2CH=CH2)3 (3) and Br(CH2)4Sn(CH2CH2CH=CH2)3 (4). Both dendritic branches can be converted into their corresponding Grignard reagents, whose consequent treatment with 0.25 M amounts of SnCl42)3Sn(CH2CH2CH=CH2)3]4 (5) and Sn[(CH2)4Sn(CH2CH2CH=CH2)3]4 (6), respectively. The subsequent hydrostannation of 5 and 6 delivered Sn{(CH2)3Sn[(CH2)4SnPh3]3}4 (7) and Sn{(CH2)4Sn[(CH2)4SnPh3]3}4 (8) as dendrimers of the second generation. All compounds were characterized by elemental analysis, 1H, 13C, and 119Sn NMR spectroscopy, and MALDI-TOF mass spectrometry. resulted in the formation of the dendrimers Sn[(CH
Organometallics, 25 (14), 3370 -3378, 2006
Comment P-31 NMR and p31-pt J-coupling
Platinum(II) Phosphido Complexes as Metalloligands. Structural and Spectroscopic Consequences of Conversion from Terminal to Bridging Coordination
Abstract:
Treatment of the terminal phosphido complexes Pt(dppe)(Me)(PPh(R)) (R = Ph (1), i-Bu (6)) with Pt(dppe)(Me)(OTf) gave the cationic phosphido complexes [(Pt(dppe)(Me))2(PPh(R))][OTf] (R = Ph (7), i-Bu (8)). Similarly, Pt((R,R)-Me-Duphos)(Me)(PPh(i-Bu)) (10) was converted to [(Pt((R,R)-Me-Duphos)(Me)) 2 (PPh(i-Bu))][OTf] (11). A fluxional process in 8 and 11, presumably involving hindered rotation about the Pt-PPh(i-Bu) bonds, was observed by NMR spectroscopy; it resulted in two diastereomers for 8 and four for 11 at low temperature. Coordination of the metalloligand 10 to the [Pt((R,R)-Me-Duphos)(Me)]+11, resulted in structural changes at the Pt-phosphido group, whose geometry changed from distorted pyramidal to tetrahedral. Decomposition of 6 also gave the cation 8, while oxidation of 6 with H2O2 gave the crystallographically characterized phosphido oxide complex Pt(dppe)(Me)(P(O)Ph(i-Bu)) (12).
Saturday, July 29, 2006
Chemistry - A European Journal, Volume: 12, Issue: 20 , pp. 5282 - 5292
Solid-State NMR and EXAFS Spectroscopic Characterization of Polycrystalline Copper(I) O,O’-Dialkyldithiophosphate Cluster Compounds: Formation of Copper(I) O,O’-Diisobutyldithiophosphate Compounds on the Surface of Synthetic Chalcocite I) Rusanova, Daniela; Pike, Kevin J.; Persson, Ingmar; Hanna, John V.; Dupree, Ray; Forsling,
Abstract: A number of polycrystalline copper(i) O,O’-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy.The structural relationship of these compounds is discussed. The polyACHTUNGTRENUNGcrystalline copper(i) O,O’-diisobutyl ACHTUNG- TRENUNGdithiophosphate cluster compounds,[Cu8ACHTUNGTRENUN {S2PACHTUNG- TRENUNG(OiBu)2}6(S)]and [Cu6ACHTUNGTRENUNG{S2PACHTUNGTRENUNG(OiBu)2}6], were also characterized by using 31P CP/MAS NMR CP = cross polarization, MAS =magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shifttensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR
spectra of the polycrystalline copper(i) cluster compounds, are presented. The adsorption mechanism of the potassium O,O’-diACHTUNGTRENUNGisobutyldithiophosphate collector, KACHTUNGTRENUNG[S2PACHTUNGTRENUNG(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8ACHTUNGTRENUNG {S2PACHTUNGTRENUNG (OiBu)2}- 6(S)]and [Cu6- ACHTUNGTRENUNG{S2PACHTUNGTRENUNG(OiBu)2}6]compounds .
Abstract: A number of polycrystalline copper(i) O,O’-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy.The structural relationship of these compounds is discussed. The polyACHTUNGTRENUNGcrystalline copper(i) O,O’-diisobutyl ACHTUNG- TRENUNGdithiophosphate cluster compounds,[Cu8ACHTUNGTRENUN {S2PACHTUNG- TRENUNG(OiBu)2}6(S)]and [Cu6ACHTUNGTRENUNG{S2PACHTUNGTRENUNG(OiBu)2}6], were also characterized by using 31P CP/MAS NMR CP = cross polarization, MAS =magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shifttensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR
spectra of the polycrystalline copper(i) cluster compounds, are presented. The adsorption mechanism of the potassium O,O’-diACHTUNGTRENUNGisobutyldithiophosphate collector, KACHTUNGTRENUNG[S2PACHTUNGTRENUNG(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8ACHTUNGTRENUNG {S2PACHTUNGTRENUNG (OiBu)2}- 6(S)]and [Cu6- ACHTUNGTRENUNG{S2PACHTUNGTRENUNG(OiBu)2}6]compounds .
Friday, July 28, 2006
J. Chem. Phys. 125, 044510
Description of depolarization effects in double-quantum solid state nuclear magnetic resonance experiments using multipole-multimode Floquet theory
Ramesh Ramachandran and Robert G. Griffin
Using an analytical model based on multipole-multimode Floquet theory (MMFT), we describe the polarization loss (or depolarization) observed in double-quantum (DQ) dipolar recoupling magic angle spinning (MAS) experiments. Specifically, the factors responsible for depolarization are analyzed in terms of higher order corrections to the spin Hamiltonian in addition to the usual phenomenological decay rate constant. From the MMFT model and the effective Hamiltonians, we elucidate the rationale behind the inclusion of a phenomenological damping term in DQ recoupling experiments. As a test of this theoretical approach, the recoupling efficiency of one class of 13C–13C and 13C–15N resonance width dipolar recoupling experiments are investigated at different magnetic field strengths and compared with the more exact numerical simulations. In contrast to existing analytical treatments, the role of higher order corrections is clearly explained in the context of the MMFT approach leading to a better understanding of the underlying spin physics. Furthermore, the analytical model presented herein provides a general framework for describing coherent and incoherent effects in homonuclear and heteronuclear DQ MAS recoupling experiments.
Ramesh Ramachandran and Robert G. Griffin
Using an analytical model based on multipole-multimode Floquet theory (MMFT), we describe the polarization loss (or depolarization) observed in double-quantum (DQ) dipolar recoupling magic angle spinning (MAS) experiments. Specifically, the factors responsible for depolarization are analyzed in terms of higher order corrections to the spin Hamiltonian in addition to the usual phenomenological decay rate constant. From the MMFT model and the effective Hamiltonians, we elucidate the rationale behind the inclusion of a phenomenological damping term in DQ recoupling experiments. As a test of this theoretical approach, the recoupling efficiency of one class of 13C–13C and 13C–15N resonance width dipolar recoupling experiments are investigated at different magnetic field strengths and compared with the more exact numerical simulations. In contrast to existing analytical treatments, the role of higher order corrections is clearly explained in the context of the MMFT approach leading to a better understanding of the underlying spin physics. Furthermore, the analytical model presented herein provides a general framework for describing coherent and incoherent effects in homonuclear and heteronuclear DQ MAS recoupling experiments.
J. Chem. Phys. 125, 034507
Heteronuclear isotropic mixing separated local field NMR spectroscopy
Sergey V. Dvinskikh, Kazutoshi Yamamoto and Ayyalusamy Ramamoorthy
This paper presents a theoretical, numerical, and experimental study of a new class of separated local field (SLF) techniques. These techniques are based on the heteronuclear isotropic mixing leading to spin exchange via the local field (HIMSELF). It is shown that highly efficient and robust SLF experiments can be designed based on double channel windowless homonuclear decoupling sequences. Compared to rotating frame techniques based on Hartmann-Hahn cross polarization, the new approach is less susceptible to the frequency offset and chemical shift interaction and can be applied in the structural studies of macromolecules that are uniformly labeled with isotopes such as 13C and 15N. Furthermore, isotropic mixing sequences allow for transfer of any magnetization component of one nucleus to the corresponding component of its dipolar coupled partner. The performance of HIMSELF is studied by analysis of the average Hamiltonian and numerical simulation and is experimentally demonstrated on a single crystalline sample of a dipeptide and a liquid crystalline sample exhibiting motionally averaged dipolar couplings.
Sergey V. Dvinskikh, Kazutoshi Yamamoto and Ayyalusamy Ramamoorthy
This paper presents a theoretical, numerical, and experimental study of a new class of separated local field (SLF) techniques. These techniques are based on the heteronuclear isotropic mixing leading to spin exchange via the local field (HIMSELF). It is shown that highly efficient and robust SLF experiments can be designed based on double channel windowless homonuclear decoupling sequences. Compared to rotating frame techniques based on Hartmann-Hahn cross polarization, the new approach is less susceptible to the frequency offset and chemical shift interaction and can be applied in the structural studies of macromolecules that are uniformly labeled with isotopes such as 13C and 15N. Furthermore, isotropic mixing sequences allow for transfer of any magnetization component of one nucleus to the corresponding component of its dipolar coupled partner. The performance of HIMSELF is studied by analysis of the average Hamiltonian and numerical simulation and is experimentally demonstrated on a single crystalline sample of a dipeptide and a liquid crystalline sample exhibiting motionally averaged dipolar couplings.
J. Chem. Phys. 124, 204717
Nuclear magnetic resonance structural investigations of ammonia-doped fullerides
T. Shiroka, G. Fumera, O. Ligabue, and M. Riccò G. C. Antonioli
The dynamic and structural properties of the ammonia-doped superconducting fulleride (NH3)xNaK2C60 (0.5x1), well known for its anomalous decrease of transition temperature with doping, have been investigated using sodium and deuterium solid-state NMR techniques. The independence of 23Na quadrupole splitting from the ammonia content x, which, at the same time, substantially affects Tc, suggests a marginal role of the cation position in the superconducting mechanism. On the other hand, a strong reduction of the deuterium quadrupole coupling with respect to the free ammonia value denotes the presence of weak hydrogen bonds between the deuterium atoms and fullerene orbitals. Despite the bond weakness, as evinced by the lively ammonia rotational dynamics even at very low temperatures, the resulting electron localization could explain the observed Tc anomaly. The motion of the ND3–Na group (located in the compound's octahedral voids), as well as the evolution of the ammonia dynamics as a function of temperature, were determined from deuterium NMR line shape analysis and from detailed numerical simulations. While at the lowest measured temperatures only the ammonia rotation around its own C3 axis takes place, above ~25 and 70 K, respectively, also the wobbling of the C3 axis and the ND3 relocation become active, successfully modeled by a strongly correlated motion involving two different time scales
T. Shiroka, G. Fumera, O. Ligabue, and M. Riccò G. C. Antonioli
The dynamic and structural properties of the ammonia-doped superconducting fulleride (NH3)xNaK2C60 (0.5x1), well known for its anomalous decrease of transition temperature with doping, have been investigated using sodium and deuterium solid-state NMR techniques. The independence of 23Na quadrupole splitting from the ammonia content x, which, at the same time, substantially affects Tc, suggests a marginal role of the cation position in the superconducting mechanism. On the other hand, a strong reduction of the deuterium quadrupole coupling with respect to the free ammonia value denotes the presence of weak hydrogen bonds between the deuterium atoms and fullerene orbitals. Despite the bond weakness, as evinced by the lively ammonia rotational dynamics even at very low temperatures, the resulting electron localization could explain the observed Tc anomaly. The motion of the ND3–Na group (located in the compound's octahedral voids), as well as the evolution of the ammonia dynamics as a function of temperature, were determined from deuterium NMR line shape analysis and from detailed numerical simulations. While at the lowest measured temperatures only the ammonia rotation around its own C3 axis takes place, above ~25 and 70 K, respectively, also the wobbling of the C3 axis and the ND3 relocation become active, successfully modeled by a strongly correlated motion involving two different time scales
Phys. Chem. Chem. Phys., 2006, 8, 3552 - 3556
Reactions of alkyl-radicals with gold and silver nanoparticles in aqueous solutions
Tomer Zidki, Haim Cohen and Dan Meyerstein
Comment: This paper doen not have NMR in it.
Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 × 108 M–1 s–1 and 1.4 × 109 M–1 s–1, respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.
Tomer Zidki, Haim Cohen and Dan Meyerstein
Comment: This paper doen not have NMR in it.
Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 × 108 M–1 s–1 and 1.4 × 109 M–1 s–1, respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.
Phys. Chem. Chem. Phys., 2006, 8, 3510 - 3519
Solid state NMR studies of photoluminescent cadmium chalcogenide nanoparticles
Christopher I. Ratcliffe, Kui Yu, John A. Ripmeester, Md. Badruz Zaman, Cristina Badarau and Shanti Singh
Solid state 113Cd, 77Se, 13C and 31P NMR have been used to study a number of Cd chalcogenide nanoparticles synthesized in tri-n-octyl-phosphine (TOP) with different compositions and architectures. The pure CdSe and CdTe nanoparticles show a dramatic, size-sensitive broadening of the 113Cd NMR line, which can be explained in terms of a chemical shift distribution arising from multiple Cd environments. From 13C NMR, it has been discovered that TOP, or its derivatives such as TOPO (trioctylphosphine oxide), is rapidly moving about the surface of the nanoparticles, indicating that it is relatively weakly bound as compared to other materials used as surface ligands, such as hexadecylamine. 31P NMR of the nanoparticles shows at least five species arising from coordination of the ligands to different surface sites. 113Cd NMR of CdSeTe alloy and layered nanoparticles has provided crucial information which, in conjunction with results from other techniques (especially optical characterization), has made it possible to develop a detailed picture of the composition and structure of these materials: (i) a true CdSeTe homogeneous alloy nanoparticle, (ii) a nanoparticle segregated into an alloy core region rich in Te, with a CdSeTe (close to 1 : 1 Se : Te) alloy shell and (iii) a CdSe/CdTe/CdSe layered nanoparticle in which the CdTe layer contains a small amount of Se and which forms a Quantum Dot Quantum Well (QDQW) system. The results demonstrate that solid state NMR is a vital tool in the arsenal of characterisation techniques available for nanomaterials.
Christopher I. Ratcliffe, Kui Yu, John A. Ripmeester, Md. Badruz Zaman, Cristina Badarau and Shanti Singh
Solid state 113Cd, 77Se, 13C and 31P NMR have been used to study a number of Cd chalcogenide nanoparticles synthesized in tri-n-octyl-phosphine (TOP) with different compositions and architectures. The pure CdSe and CdTe nanoparticles show a dramatic, size-sensitive broadening of the 113Cd NMR line, which can be explained in terms of a chemical shift distribution arising from multiple Cd environments. From 13C NMR, it has been discovered that TOP, or its derivatives such as TOPO (trioctylphosphine oxide), is rapidly moving about the surface of the nanoparticles, indicating that it is relatively weakly bound as compared to other materials used as surface ligands, such as hexadecylamine. 31P NMR of the nanoparticles shows at least five species arising from coordination of the ligands to different surface sites. 113Cd NMR of CdSeTe alloy and layered nanoparticles has provided crucial information which, in conjunction with results from other techniques (especially optical characterization), has made it possible to develop a detailed picture of the composition and structure of these materials: (i) a true CdSeTe homogeneous alloy nanoparticle, (ii) a nanoparticle segregated into an alloy core region rich in Te, with a CdSeTe (close to 1 : 1 Se : Te) alloy shell and (iii) a CdSe/CdTe/CdSe layered nanoparticle in which the CdTe layer contains a small amount of Se and which forms a Quantum Dot Quantum Well (QDQW) system. The results demonstrate that solid state NMR is a vital tool in the arsenal of characterisation techniques available for nanomaterials.
Phys. Chem. Chem. Phys., 2006, 8, 3423 - 3431
23Na multiple-quantum MAS NMR of the perovskites NaNbO3 and NaTaO3
Sharon E. Ashbrook, Laurent Le Pollès, Régis Gautier, Chris J. Pickard and Richard I. Walton
The distorted perovskites NaTaO3 and NaNbO3 have been studied using 23Na multiple-quantum (MQ) MAS NMR. NaTaO3 was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO3 were studied. The first, a commercially available sample which was annealed at 900 °C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.
Sharon E. Ashbrook, Laurent Le Pollès, Régis Gautier, Chris J. Pickard and Richard I. Walton
The distorted perovskites NaTaO3 and NaNbO3 have been studied using 23Na multiple-quantum (MQ) MAS NMR. NaTaO3 was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO3 were studied. The first, a commercially available sample which was annealed at 900 °C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state.
Phys. Chem. Chem. Phys., 2006, 8, 3418 - 3422
Assigning powders to crystal structures by high-resolution 1H–1H double quantum and 1H–13C J-INEPT solid-state NMR spectroscopy and first principles computation. A case study of penicillin G
Nicolas Mifsud, Bénédicte Elena, Chris J. Pickard, Anne Lesage and Lyndon Emsley
We show how powder samples at natural isotopic abundance can be assigned to crystal structures by using high-resolution proton and carbon-13 solid-state NMR spectra in combination with first principles calculations. Homonuclear proton double-quantum spectra in combination with through-bond proton–carbon HSQC spectra are used to assign the NMR spectra. We then show that the proton chemical shifts can be included in the process of assigning the spectra to a crystal structure using first principles calculations. The method is demonstrated on the K salt of penicillin G.
Nicolas Mifsud, Bénédicte Elena, Chris J. Pickard, Anne Lesage and Lyndon Emsley
We show how powder samples at natural isotopic abundance can be assigned to crystal structures by using high-resolution proton and carbon-13 solid-state NMR spectra in combination with first principles calculations. Homonuclear proton double-quantum spectra in combination with through-bond proton–carbon HSQC spectra are used to assign the NMR spectra. We then show that the proton chemical shifts can be included in the process of assigning the spectra to a crystal structure using first principles calculations. The method is demonstrated on the K salt of penicillin G.
Phys. Chem. Chem. Phys., 2006, 8, 3379 - 3382
Spin–spin coupling constants in homonuclear polynitrogen species
David L. Bryce
Quantum chemical calculations provide new insights into the dependence of J(N,N) coupling tensors on bonding environment in a series of polynitrogen species including N5+.
David L. Bryce
Quantum chemical calculations provide new insights into the dependence of J(N,N) coupling tensors on bonding environment in a series of polynitrogen species including N5+.
Phys. Chem. Chem. Phys., 2006, 8, 2733 - 2743
An NMR and relativistic DFT investigation of one-bond nuclear spin–spin coupling in solid triphenyl group-14 chlorides
Mathew J. Willans, Bryan A. Demko and Roderick E. Wasylishen
A solid-state nuclear magnetic resonance and zeroth-order regular approximation density functional theory, ZORA-DFT, study of one-bond nuclear spin–spin coupling between group-14 nuclei and quadrupolar 35/37Cl nuclei in triphenyl group-14 chlorides, Ph3XCl (X = C, Si, Ge, Sn and Pb), is presented. This represents the first combined experimental and theoretical systematic study of spin–spin coupling involving spin-pairs containing quadrupolar nuclei. Solid-state NMR spectra have been acquired for all compounds in which X has a spin-1/2 isotope—13C, 29Si, [117/119]Sn and 207Pb—at applied magnetic fields of 4.70, 7.05 and 11.75 T. From simulations of these spectra, values describing the indirect spin–spin coupling tensor—the isotropic indirect spin–spin coupling constant, 1J(X,35/37Cl)iso and the anisotropy of the J tensor, 1J(X,35/37Cl)—have been determined for all but the lead–chlorine spin-pair. To better compare the indirect spin–spin coupling parameters between spin-pairs, 1Jiso and 1J values were converted to their reduced coupling constants, 1Kiso and 1K. From experiment, the sign of 1Kiso was found to be negative while the sign of 1K is positive for all spin-pairs investigated. The magnitude of both 1Kiso and 1K was found to increase as one moves down group-14. Theoretical values of the magnitude and sign of 1Kiso and 1K were obtained from ZORA-DFT calculations and are in agreement with the available experimental data. From the calculations, the Fermi-contact mechanism was determined to provide the largest contribution to 1Kiso for all spin-pairs while spin-dipolar and paramagnetic spin–orbit mechanisms make significant contributions to the anisotropy of K. The inclusion of relativistic effects was found to influence K(Sn,Cl) and K(Pb,Cl).
Mathew J. Willans, Bryan A. Demko and Roderick E. Wasylishen
A solid-state nuclear magnetic resonance and zeroth-order regular approximation density functional theory, ZORA-DFT, study of one-bond nuclear spin–spin coupling between group-14 nuclei and quadrupolar 35/37Cl nuclei in triphenyl group-14 chlorides, Ph3XCl (X = C, Si, Ge, Sn and Pb), is presented. This represents the first combined experimental and theoretical systematic study of spin–spin coupling involving spin-pairs containing quadrupolar nuclei. Solid-state NMR spectra have been acquired for all compounds in which X has a spin-1/2 isotope—13C, 29Si, [117/119]Sn and 207Pb—at applied magnetic fields of 4.70, 7.05 and 11.75 T. From simulations of these spectra, values describing the indirect spin–spin coupling tensor—the isotropic indirect spin–spin coupling constant, 1J(X,35/37Cl)iso and the anisotropy of the J tensor, 1J(X,35/37Cl)—have been determined for all but the lead–chlorine spin-pair. To better compare the indirect spin–spin coupling parameters between spin-pairs, 1Jiso and 1J values were converted to their reduced coupling constants, 1Kiso and 1K. From experiment, the sign of 1Kiso was found to be negative while the sign of 1K is positive for all spin-pairs investigated. The magnitude of both 1Kiso and 1K was found to increase as one moves down group-14. Theoretical values of the magnitude and sign of 1Kiso and 1K were obtained from ZORA-DFT calculations and are in agreement with the available experimental data. From the calculations, the Fermi-contact mechanism was determined to provide the largest contribution to 1Kiso for all spin-pairs while spin-dipolar and paramagnetic spin–orbit mechanisms make significant contributions to the anisotropy of K. The inclusion of relativistic effects was found to influence K(Sn,Cl) and K(Pb,Cl).
Phys. Chem. Chem. Phys., 2006, 8, 2635 - 2641
Phys. Chem. Chem. Phys., 2006, 8, 2635 - 2641, DOI: 10.1039/b601539e
Magnetic alignment of aqueous CTAB in nematic and hexagonal liquid crystalline phases investigated by spin-1 NMR
Jacalyn S. Clawson, Gregory P. Holland and Todd M. Alam
Spin-1 NMR has been used to characterize the magnetically aligned nematic and hexagonal liquid crystalline phases of aqueous cetyltrimethylammonium bromide (CTAB). A nematic/hexagonal biphasic region has been identified for the first time in this system. The nematic phase is characterized by an order parameter of smaller magnitude and greater temperature dependence. Magnetic alignment kinetic rates of the two phases differ greatly, with the nematic phase showing magnetic alignment much faster than the hexagonal phase. Equilibration has been monitored over time by measuring the change in quadrupole splitting as a function of temperature. As the sample equilibrates the temperature dependence of the splitting decreases logarithmically. This work also demonstrates how the phase and order of the liquid crystal can be manipulated during the early part of equilibration.
Magnetic alignment of aqueous CTAB in nematic and hexagonal liquid crystalline phases investigated by spin-1 NMR
Jacalyn S. Clawson, Gregory P. Holland and Todd M. Alam
Spin-1 NMR has been used to characterize the magnetically aligned nematic and hexagonal liquid crystalline phases of aqueous cetyltrimethylammonium bromide (CTAB). A nematic/hexagonal biphasic region has been identified for the first time in this system. The nematic phase is characterized by an order parameter of smaller magnitude and greater temperature dependence. Magnetic alignment kinetic rates of the two phases differ greatly, with the nematic phase showing magnetic alignment much faster than the hexagonal phase. Equilibration has been monitored over time by measuring the change in quadrupole splitting as a function of temperature. As the sample equilibrates the temperature dependence of the splitting decreases logarithmically. This work also demonstrates how the phase and order of the liquid crystal can be manipulated during the early part of equilibration.
Friday, July 14, 2006
Joel - Monthly Journal Update
Probing Local Environments in Paramagnetic Europium-Substituted Keggin Solids by 31P Magic Angle Spinning NMR Spectroscopy
W. Huang et al.
J.Phys.Chem.B(2006)110,12340.
Abstract:
Paramagnetic Eu-substituted Keggin oxopolytungstates crystallize in different forms, determined by the nature of the counterions. The crystal packing is in turn responsible for the variations in the geometry of paramagnetic Eu sites with respect to the anion core. We probed the paramagnetic environments in a series of Eu-substituted Keggin solids, by 31P magic angle spinning NMR spectroscopy. 31P spinning sideband envelopes are dominated by the electron-nuclear dipolar interaction. For the compounds under investigation, both the magnitude and the asymmetry parameter of the electron-nuclear dipolar coupling tensor are sensitive to the mutual arrangements of paramagnetic Eu sites in the crystal lattice. and also report on the stoichiometry of the anion. The electron-nuclear dipolar coupling tensors were calculated from the crystallographic coordinates and the experimentally determined effective magnetic moments, assuming a point dipole approximation. The computed tensors are in very good agreement with the experimental spectra. Furthermore, the P-Eu distance estimates, accurate to within 0.06-0.12 A, can be obtained directly from the magnitude of the electron-nuclear dipolar coupling. This work demonstrates that 31P MAS NMR spectroscopy is a useful probe for investigating local environments in paramagnetic Keggin solids.
Cory
Oxygen Sites and Network Coordination in Sodium Germanate Glasses and Crystals: High Resolution Oxygen-17 and Sodium-23 NMR.
L.S. Du and J.F. Stebbins
J.Phys.Chem.B(2006)110,12427.
Abstract:
Sodium germanate glasses are well-studied materials in which, unlike silicates but analogous to borates, the major structural consequence of alkali addition is generally thought to involve a coordination number increase of the network-forming Ge cations. However, the nature of this change, in particular quantifying fractions of nonbridging oxygens and of five- and/or six-coordinated Ge, has remained unresolved. We present here highresolution 17O results, including triple-quantum MAS NMR (3QMAS), on a series of crystalline model compounds that allow the definition of ranges of chemical shifts corresponding to oxygens bonded to various coordinations of Ge. These include quartz- and rutile-structured GeO2, Na4Ge9O20, Na2Ge4O9, and Na2GeO3 (germanium dioxide, sodium enneagermanate, sodium tetragermanate, and sodium metagermanate). 3QMAS spectra of Na-germanate glasses ranging from 0% to 27% Na2O clearly show the development of partially resolved peaks as alkali is added, corresponding to signals from nonbridging oxygens (in the highest Na glasses) and to oxygen bridging between one four-coordinated and one higher coordinated Ge. As in conventional models of this system, nonbridging oxygen contents are much lower than in corresponding silicates. Although we do not directly distinguish between five- and six-coordinated Ge, modeling of bridging oxygen populations and comparison with measured speciation suggest that substantial proportions of both species are likely to be present. High-field 23Na MAS NMR shows systematic decreases in mean Na-O bond distance and/or coordination number with increasing alkali content that can be compared with published results for high-temperature liquids. These results, as well as comparison of molar volumes of glasses and high-temperature liquids, suggest the possibility of significant temperature effects on liquid structure.
Andy
Photochemical Fine-Tuning of Luminescent Coloout on Cadmium Selenide Nanoparticles: Fabricating a Single-Source Multicolor Luminophore.
T. Torimoto et al.
J.Phys.Chem.B(2006)110,13314.
Abstract:
Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/ CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.
Josh, Andy
Synthesis, crystal structure and magnetic properties of an alternating manganese chain.
M.R. Silva et al.
JSolidStateChem (2006) 179, 2054.
Abstract:
A new 1D complex has been prepared and characterized. X-ray single crystal structure con.rms that the Mn(II) ions assemble in alternating chains with Mn–Mn distances of 3.8432(13) and 4.4428(14)A . A 3D network of hydrogen bonds links the chains together. The temperature dependence of the magnetic susceptibility reveals that this compound undergoes a magnetic transition and exhibits an antiferromagnetic interaction in the low-temperature phase with two alternating exchange interactions of -2.32(1) and -5.55(1)cm-1.
Rob
Sr4PbPt4O11, the first platinum oxide containing Pt2 6+ ions.
C. Renard et al.
JSolidStateChem (2006) 179, 2054.
Abstract:
We report the synthesis and crystal structure of the new compound Sr4PbPt4O11, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R = 0.0260 and wR = 0.0262. The symmetry is triclinic, space group P1¯ , with a = 5.6705(6) A, b = 9.9852(5) A, c = 10.0889(5) A, alpha = 90.421(3), beta = 89.773(8), gamma = 90.140(9) and Z = 2. The structure is built from dumbell-shaped Pt2O9 entities formed by a dinuclear metal–metal bonded Pt2 6+ ion with asymmetric environments of the two Pt atoms, classical PtO4 square plane and unusual PtO5 square pyramid. Successive Pt2O9 entities deduced from 901 rotations are connected through the oxygens of the PtO4 basal squares to form (Pt4O10)-8 columns further connected through Pb2+ and Sr2+ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.
Structural and 31P NMR investigation of Bi(MM')2PO6 statistic solid solutions: Deconvolution of lattice constrants and cationic influences.
M. Colmont et al.
JSolidStateChem (2006) 179, 2111.
Abstract:
Two solid solutions BiMxMg(2-x)PO6 (with M2+ = Zn or Cd) have been studied through 31P MAS NMR. The analysis has been performed on the basis of re.ned crystal structures through X-ray diffraction and neutron diffraction. The BiZnxMg(2-x)PO6 does not provide direct evidence for sensitive changes in the phosphorus local symmetry. This result is in good agreement with structural data which show nearly unchanged lattices and atomic separations through the Zn2+ for Mg2+ substitution. On the other hand, the Cd2+ for Mg2+ substitution behaves differently. Indeed, up to five resonances are observed, each corresponding to one of the five first-cationic neighbour distributions, i.e. 4Mg/0Cd, 3Mg/1Cd, 2Mg/2Cd, 1Mg/3Cd and 0Mg/4Cd. Their intensities match rather well the expected weight for each con.guration of the statistical Cd2+/Mg2+ mixed occupancy. The match is further improved when one takes into account the in.uence of the 2nd cationic sphere that is available from high-.eld NMR data (18.8 T). Finally, the fine examination of the chemical shift for each resonance versus x allows to de-convolute the mean Z/a2 effective field into two sub-effects: a lattice constraint only term and a chemical-only term whose effects are directly quantifiable.
W. Huang et al.
J.Phys.Chem.B(2006)110,12340.
Abstract:
Paramagnetic Eu-substituted Keggin oxopolytungstates crystallize in different forms, determined by the nature of the counterions. The crystal packing is in turn responsible for the variations in the geometry of paramagnetic Eu sites with respect to the anion core. We probed the paramagnetic environments in a series of Eu-substituted Keggin solids, by 31P magic angle spinning NMR spectroscopy. 31P spinning sideband envelopes are dominated by the electron-nuclear dipolar interaction. For the compounds under investigation, both the magnitude and the asymmetry parameter of the electron-nuclear dipolar coupling tensor are sensitive to the mutual arrangements of paramagnetic Eu sites in the crystal lattice. and also report on the stoichiometry of the anion. The electron-nuclear dipolar coupling tensors were calculated from the crystallographic coordinates and the experimentally determined effective magnetic moments, assuming a point dipole approximation. The computed tensors are in very good agreement with the experimental spectra. Furthermore, the P-Eu distance estimates, accurate to within 0.06-0.12 A, can be obtained directly from the magnitude of the electron-nuclear dipolar coupling. This work demonstrates that 31P MAS NMR spectroscopy is a useful probe for investigating local environments in paramagnetic Keggin solids.
Cory
Oxygen Sites and Network Coordination in Sodium Germanate Glasses and Crystals: High Resolution Oxygen-17 and Sodium-23 NMR.
L.S. Du and J.F. Stebbins
J.Phys.Chem.B(2006)110,12427.
Abstract:
Sodium germanate glasses are well-studied materials in which, unlike silicates but analogous to borates, the major structural consequence of alkali addition is generally thought to involve a coordination number increase of the network-forming Ge cations. However, the nature of this change, in particular quantifying fractions of nonbridging oxygens and of five- and/or six-coordinated Ge, has remained unresolved. We present here highresolution 17O results, including triple-quantum MAS NMR (3QMAS), on a series of crystalline model compounds that allow the definition of ranges of chemical shifts corresponding to oxygens bonded to various coordinations of Ge. These include quartz- and rutile-structured GeO2, Na4Ge9O20, Na2Ge4O9, and Na2GeO3 (germanium dioxide, sodium enneagermanate, sodium tetragermanate, and sodium metagermanate). 3QMAS spectra of Na-germanate glasses ranging from 0% to 27% Na2O clearly show the development of partially resolved peaks as alkali is added, corresponding to signals from nonbridging oxygens (in the highest Na glasses) and to oxygen bridging between one four-coordinated and one higher coordinated Ge. As in conventional models of this system, nonbridging oxygen contents are much lower than in corresponding silicates. Although we do not directly distinguish between five- and six-coordinated Ge, modeling of bridging oxygen populations and comparison with measured speciation suggest that substantial proportions of both species are likely to be present. High-field 23Na MAS NMR shows systematic decreases in mean Na-O bond distance and/or coordination number with increasing alkali content that can be compared with published results for high-temperature liquids. These results, as well as comparison of molar volumes of glasses and high-temperature liquids, suggest the possibility of significant temperature effects on liquid structure.
Andy
Photochemical Fine-Tuning of Luminescent Coloout on Cadmium Selenide Nanoparticles: Fabricating a Single-Source Multicolor Luminophore.
T. Torimoto et al.
J.Phys.Chem.B(2006)110,13314.
Abstract:
Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/ CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.
Josh, Andy
Synthesis, crystal structure and magnetic properties of an alternating manganese chain.
M.R. Silva et al.
JSolidStateChem (2006) 179, 2054.
Abstract:
A new 1D complex has been prepared and characterized. X-ray single crystal structure con.rms that the Mn(II) ions assemble in alternating chains with Mn–Mn distances of 3.8432(13) and 4.4428(14)A . A 3D network of hydrogen bonds links the chains together. The temperature dependence of the magnetic susceptibility reveals that this compound undergoes a magnetic transition and exhibits an antiferromagnetic interaction in the low-temperature phase with two alternating exchange interactions of -2.32(1) and -5.55(1)cm-1.
Rob
Sr4PbPt4O11, the first platinum oxide containing Pt2 6+ ions.
C. Renard et al.
JSolidStateChem (2006) 179, 2054.
Abstract:
We report the synthesis and crystal structure of the new compound Sr4PbPt4O11, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R = 0.0260 and wR = 0.0262. The symmetry is triclinic, space group P1¯ , with a = 5.6705(6) A, b = 9.9852(5) A, c = 10.0889(5) A, alpha = 90.421(3), beta = 89.773(8), gamma = 90.140(9) and Z = 2. The structure is built from dumbell-shaped Pt2O9 entities formed by a dinuclear metal–metal bonded Pt2 6+ ion with asymmetric environments of the two Pt atoms, classical PtO4 square plane and unusual PtO5 square pyramid. Successive Pt2O9 entities deduced from 901 rotations are connected through the oxygens of the PtO4 basal squares to form (Pt4O10)-8 columns further connected through Pb2+ and Sr2+ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.
Structural and 31P NMR investigation of Bi(MM')2PO6 statistic solid solutions: Deconvolution of lattice constrants and cationic influences.
M. Colmont et al.
JSolidStateChem (2006) 179, 2111.
Abstract:
Two solid solutions BiMxMg(2-x)PO6 (with M2+ = Zn or Cd) have been studied through 31P MAS NMR. The analysis has been performed on the basis of re.ned crystal structures through X-ray diffraction and neutron diffraction. The BiZnxMg(2-x)PO6 does not provide direct evidence for sensitive changes in the phosphorus local symmetry. This result is in good agreement with structural data which show nearly unchanged lattices and atomic separations through the Zn2+ for Mg2+ substitution. On the other hand, the Cd2+ for Mg2+ substitution behaves differently. Indeed, up to five resonances are observed, each corresponding to one of the five first-cationic neighbour distributions, i.e. 4Mg/0Cd, 3Mg/1Cd, 2Mg/2Cd, 1Mg/3Cd and 0Mg/4Cd. Their intensities match rather well the expected weight for each con.guration of the statistical Cd2+/Mg2+ mixed occupancy. The match is further improved when one takes into account the in.uence of the 2nd cationic sphere that is available from high-.eld NMR data (18.8 T). Finally, the fine examination of the chemical shift for each resonance versus x allows to de-convolute the mean Z/a2 effective field into two sub-effects: a lattice constraint only term and a chemical-only term whose effects are directly quantifiable.
JACS - Volume 128, Issue 27
Cory's Comment: small coils = super high (600 kHz) proton decoupling fields!
Title: Microcoil High-Resolution Magic Angle Spinning NMR Spectroscopy
Authors: Hans Janssen, Andreas Brinkmann, Ernst R. H. van Eck, P. Jan M. van Bentum, and Arno P. M. Kentgens
Page #: 8722
Abstract: We report the construction of a dual-channel microcoil nuclear magnetic resonance probehead allowing magic-angle spinning for mass-limited samples. With coils down to 235 m inner diameter, this allows high-resolution solid-state NMR spectra to be obtained for amounts of materials of a few nanoliters. This is demonstrated by the carbon-13 spectrum of a tripeptide and a single silk rod, prepared from the silk gland of the Bombyx mori silkworm. Furthermore, the microcoil allows for radio frequency field strengths well beyond current probe technology, aiding in getting the highest possible resolution by efficiently decoupling the observed nuclei from the abundantly present proton nuclei.
Thursday, July 13, 2006
Cory's Journals - June 2006
Does anyone use this thing anymore???
As per usual, by the end of today, I will have the journal articles that I collected in June 2006 available in their usual spot.
Peace.
As per usual, by the end of today, I will have the journal articles that I collected in June 2006 available in their usual spot.
Peace.
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