Antusek, A., M. Jaszunski, et al. (2007).
"Ab initio study of interaction-induced NMR shielding constants in mixed rare gas dimers."
The Journal of Chemical Physics 126(7): 074303-9.
The interaction-induced contribution to the NMR shielding constants in homonuclear A2 and heteronuclear AB (A,B=He,Ne,Ar) dimers is obtained ab initio by employing a coupled cluster singles and doubles with perturbative treatment of triples wave function model and extended correlation-consistent basis sets. The second virial coefficients entering the expansion of the property with the density are then computed in a fully quantum mechanical approach, for temperatures ranging from the limit of dissociation of the dimer to well above standard conditions. The results can be used to describe the density and temperature dependence of the shielding constants in binary mixtures of helium, neon, and argon. The predicted effects should be observable for the interaction of 21Ne with other rare gases.
Schmidt-Rohr, K., A. Rawal, et al. (2007).
"A new NMR method for determining the particle thickness in nanocomposites, using T[sub 2,H]-selective X{[sup 1]H} recoupling."
The Journal of Chemical Physics 126(5): 054701-16.
A new nuclear magnetic resonance approach for characterizing the thickness of phosphate, silicate, carbonate, and other nanoparticles in organic-inorganic nanocomposites is presented. The particle thickness is probed using the strongly distant-dependent dipolar couplings between the abundant protons in the organic phase and X nuclei (31P, 29Si, 13C, 27Al, 23Na, etc.) in the inorganic phase. This approach requires pulse sequences with heteronuclear dephasing only by the polymer or surface protons that experience strong homonuclear interactions, but not by dispersed OH or water protons in the inorganic phase, which have long transverse relaxation times T2,H. This goal is achieved by heteronuclear recoupling with dephasing by strong homonuclear interactions of protons (HARDSHIP). The pulse sequence alternates heteronuclear recoupling for ~0.15 ms with periods of homonuclear dipolar dephasing that are flanked by canceling 90° pulses. The heteronuclear evolution of the long-T2,H protons is refocused within two recoupling periods, so that 1H spin diffusion cannot significantly dephase these coherences. For the short-T2,H protons of a relatively immobile organic matrix, the heteronuclear dephasing rate depends simply on the heteronuclear second moment. Homonuclear interactions do not affect the dephasing, even though no homonuclear decoupling is applied, because long-range 1H–X dipolar couplings approximately commute with short-range 1H–1H couplings, and heteronuclear recoupling periods are relatively short. This is shown in a detailed analysis based on interaction representations. The algorithm for simulating the dephasing data is described. The new method is demonstrated on a clay-polymer nanocomposite, diamond nanocrystals with protonated surfaces, and the bioapatite-collagen nanocomposite in bone, as well as pure clay and hydroxyapatite. The diameters of the nanoparticles in these materials range between 1 and 5 nm. Simulations show that spherical particles of up to 10 nm diameter can be characterized quite easily.
Teale, A. M., A. J. Cohen, et al. (2007).
"Transition metal NMR chemical shifts from optimized effective potentials."
The Journal of Chemical Physics 126(7): 074101-7.
Metal shielding constants and chemical shifts are determined for nine transition metal complexes using an uncoupled formalism with orbitals and eigenvalues determined using the Yang-Wu implementation [W. Yang and Q. Wu, Phys. Rev. Lett. 89, 143002 (2002)] of the optimized effective potential approach in density functional theory. Preliminary calculations using generalized gradient approximation functionals quantify the influence of the variables in the optimized effective potential implementation. In particular, a flexible potential expansion is necessary for a precise calculation of these quantities. Hybrid functionals are then considered. Expanding the potential in the primary orbital basis yields chemical shifts that are a notable improvement over conventional hybrid values, and which are a marginal improvement over those obtained using a high-quality generalized gradient approximation. Similar shifts are obtained using a more flexible potential expansion, although care is required to avoid unphysical structure in the exchange-correlation potential.
Tycko, R. (2007).
"Symmetry-based constant-time homonuclear dipolar recoupling in solid state NMR."
The Journal of Chemical Physics 126(6): 064506-9.
Constant-time dipolar recoupling pulse sequences are advantageous in structural studies by solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) because they yield experimental data that are relatively insensitive to radio-frequency pulse imperfections and nuclear spin relaxation processes. A new approach to the construction of constant-time homonuclear dipolar recoupling sequences is described, based on symmetry properties of the recoupled dipole-dipole interaction Hamiltonian under cyclic displacements in time with respect to the MAS sample rotation period. A specific symmetry-based pulse sequence called PITHIRDS-CT is introduced and demonstrated experimentally. 13C NMR data for singly-13C-labeled amino acid powders and amyloid fibrils indicate the effectiveness of PITHIRDS-CT in measurements of intermolecular distances in solids. 15N-detected and 13C-detected measurements of intramolecular 15N–15N distances in peptides with alpha-helical and beta-sheet structures indicate the utility of PITHIRDS-CT in studies of molecular conformations, especially measurements of backbone psi torsion angles in peptides containing uniformly 15N- and 13C-labeled amino acids.
Iuga, A., D. Iuga, et al. (2007).
"Observation of satellite signals due to scalar coupling to spin-1/2 isotopes in solid-state nuclear magnetic resonance spectroscopy."
The Journal of Chemical Physics 126(5): 054305-10.
A method is introduced to select the signal from a spin-1/2 nucleus I specifically bound to another spin-1/2 nucleus S for solid-state magic angle spinning nuclear magnetic resonance (NMR) spectroscopy via correlation through the heteronuclear J coupling. This experiment is analogous to the bilinear rotation decoupling (BIRD) sequence in liquid-state NMR spectroscopy which selects for signals from 1H directly bound to 13C. The spin dynamics of this modified BIRD experiment is described using the product-operator formalism, where experimental considerations such as rotor synchronization and the effect of large chemical shielding anisotropies on I and S are discussed. Two experiments are proposed that accommodate large chemical shielding anisotropies on S: (1) by stepping the inversion pulse frequency through the entire S spectral range or (2) by adiabatically inverting the S spins. Both these experiments are shown to successfully select the signal of 19F bound to 129Xe in XeF+ salts, removing the contributions from isotopomers containing non-spin-1/2 Xe isotopes. The feasibility in obtaining isotope-selective 19F spectra of inorganic fluoride compounds is discussed, and further modifications are proposed to expand the application to other chemical systems.
Monday, March 12, 2007
Thursday, March 08, 2007
JACS Journal update- January 2007 -Present, continued
J. Am. Chem. Soc., 129 (8), 2398 -2407, 2007.
Probing Hydrogen Bonding and Ion-Carbonyl Interactions by Solid-State 17O NMR Spectroscopy: G-Ribbon and G-Quartet
Irene C. M. Kwan, Xin Mo, and Gang Wu*
Abstract:
We report solid-state 17O NMR determination of the 17O NMR tensors for the keto carbonyl oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2',3',5'-O-triacetyl-[6-17O]guanosine (G2). In G1·2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6···H-N2 and N7···H-N7 hydrogen bonds in a zigzag fashion. In addition, the keto carbonyl oxygen O6 is also weakly hydrogen-bonded to two water molecules of hydration. The experimental 17O NMR tensors determined for the two independent molecules in the asymmetric unit of G1·2H2O are: Molecule A, CQ = 7.8 ± 0.1 MHz, Q = 0.45 ± 0.05, iso = 263 ± 2, 11 = 460 ± 5, 22 = 360 ± 5, 33 = -30 ± 5 ppm; Molecule B, CQ = 7.7 ± 0.1 MHz, Q = 0.55 ± 0.05, iso = 250 ± 2, 11 = 440 ± 5, 22 = 340 ± 5, 33 = -30 ± 5 ppm. In G1/K+ gel, guanosine molecules form extensively stacking G-quartets. In each G-quartet, four guanine bases are linked together by four pairs of O6···H-N1 and N7···H-N2 hydrogen bonds in a cyclic fashion. In addition, each O6 atom is simultaneously coordinated to two K+ ions. For G1/K+ gel, the experimental 17O NMR tensors are: CQ = 7.2 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2, 11 = 400 ± 5, 22 = 300 ± 5, 33 = -20 ± 5 ppm. In the presence of divalent cations such as Sr2+, Ba2+, and Pb2+, G2 molecules form discrete octamers containing two stacking G-quartets and a central metal ion, that is, (G2)4-M2+-(G2)4. In this case, each O6 atom of the G-quartet is coordinated to only one metal ion. For G2/M2+ octamers, the experimental 17O NMR parameters are: Sr2+, CQ = 6.8 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm; Ba2+, CQ = 7.0 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2 ppm; Pb2+, CQ = 7.2 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm. We also perform extensive quantum chemical calculations for the 17O NMR tensors in both G-ribbons and G-quartets. Our results demonstrate that the 17O chemical shift tensor and quadrupole coupling tensor are very sensitive to the presence of hydrogen bonding and ion-carbonyl interactions. Furthermore, the effect from ion-carbonyl interactions is several times stronger than that from hydrogen-bonding interactions. Our results establish a basis for using solid-state 17O NMR as a probe in the study of ion binding in G-quadruplex DNA and ion channel proteins.
Probing Hydrogen Bonding and Ion-Carbonyl Interactions by Solid-State 17O NMR Spectroscopy: G-Ribbon and G-Quartet
Irene C. M. Kwan, Xin Mo, and Gang Wu*
Abstract:
We report solid-state 17O NMR determination of the 17O NMR tensors for the keto carbonyl oxygen (O6) of guanine in two 17O-enriched guanosine derivatives: [6-17O]guanosine (G1) and 2',3',5'-O-triacetyl-[6-17O]guanosine (G2). In G1·2H2O, guanosine molecules form hydrogen-bonded G-ribbons where the guanine bases are linked by O6···H-N2 and N7···H-N7 hydrogen bonds in a zigzag fashion. In addition, the keto carbonyl oxygen O6 is also weakly hydrogen-bonded to two water molecules of hydration. The experimental 17O NMR tensors determined for the two independent molecules in the asymmetric unit of G1·2H2O are: Molecule A, CQ = 7.8 ± 0.1 MHz, Q = 0.45 ± 0.05, iso = 263 ± 2, 11 = 460 ± 5, 22 = 360 ± 5, 33 = -30 ± 5 ppm; Molecule B, CQ = 7.7 ± 0.1 MHz, Q = 0.55 ± 0.05, iso = 250 ± 2, 11 = 440 ± 5, 22 = 340 ± 5, 33 = -30 ± 5 ppm. In G1/K+ gel, guanosine molecules form extensively stacking G-quartets. In each G-quartet, four guanine bases are linked together by four pairs of O6···H-N1 and N7···H-N2 hydrogen bonds in a cyclic fashion. In addition, each O6 atom is simultaneously coordinated to two K+ ions. For G1/K+ gel, the experimental 17O NMR tensors are: CQ = 7.2 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2, 11 = 400 ± 5, 22 = 300 ± 5, 33 = -20 ± 5 ppm. In the presence of divalent cations such as Sr2+, Ba2+, and Pb2+, G2 molecules form discrete octamers containing two stacking G-quartets and a central metal ion, that is, (G2)4-M2+-(G2)4. In this case, each O6 atom of the G-quartet is coordinated to only one metal ion. For G2/M2+ octamers, the experimental 17O NMR parameters are: Sr2+, CQ = 6.8 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm; Ba2+, CQ = 7.0 ± 0.1 MHz, Q = 0.68 ± 0.05, iso = 232 ± 2 ppm; Pb2+, CQ = 7.2 ± 0.1 MHz, Q = 1.00 ± 0.05, iso = 232 ± 2 ppm. We also perform extensive quantum chemical calculations for the 17O NMR tensors in both G-ribbons and G-quartets. Our results demonstrate that the 17O chemical shift tensor and quadrupole coupling tensor are very sensitive to the presence of hydrogen bonding and ion-carbonyl interactions. Furthermore, the effect from ion-carbonyl interactions is several times stronger than that from hydrogen-bonding interactions. Our results establish a basis for using solid-state 17O NMR as a probe in the study of ion binding in G-quadruplex DNA and ion channel proteins.
Progress in NMR
Progress in Nuclear Magnetic Resonance Spectroscopy 50 (2007) 71–85
Solid state NMR studies of molecular recognition at protein–mineral interfaces
Gil Goobes a,1, Patrick S. Stayton b,2, Gary P. Drobny a,*
a Department of Chemistry, University of Washington, Box 351700, Seattle WA 98195, USA
b Department of Bioengineering, University of Washington, Box 355061, Seattle WA 98195, USA
Available online 26 January 2007
Keywords: Adsorbed protein; Structure determination; Recoupling; Magic angle spinning; Biomineralization
Progress in Nuclear Magnetic Resonance Spectroscopy 50 (2007) 87–174
R. Böhmer,, K.R. Jeffrey and M. Vogel
a Fachbereich Physik and Interdisziplinäres Zentrum für Magnetische Resonanz, Universität Dortmund, 44221 Dortmund, Germany
b Department of Physics, University of Guelph, Guelph, Ontario, Canada
c Institut für Physikalische Chemie, Universität Münster, 48149 Münster, Germany
Solid-state Li NMR with applications to the translational dynamics in ion conductors
Available online 9 February 2007
Keywords: Solid electrolytes; Spin–lattice relaxation; Jeener–Broekaert sequence; Stimulated echoes, Line-shape analysis; Heterogeneous relaxation; Slow
dynamics
Solid state NMR studies of molecular recognition at protein–mineral interfaces
Gil Goobes a,1, Patrick S. Stayton b,2, Gary P. Drobny a,*
a Department of Chemistry, University of Washington, Box 351700, Seattle WA 98195, USA
b Department of Bioengineering, University of Washington, Box 355061, Seattle WA 98195, USA
Available online 26 January 2007
Keywords: Adsorbed protein; Structure determination; Recoupling; Magic angle spinning; Biomineralization
Progress in Nuclear Magnetic Resonance Spectroscopy 50 (2007) 87–174
R. Böhmer,, K.R. Jeffrey and M. Vogel
a Fachbereich Physik and Interdisziplinäres Zentrum für Magnetische Resonanz, Universität Dortmund, 44221 Dortmund, Germany
b Department of Physics, University of Guelph, Guelph, Ontario, Canada
c Institut für Physikalische Chemie, Universität Münster, 48149 Münster, Germany
Solid-state Li NMR with applications to the translational dynamics in ion conductors
Available online 9 February 2007
Keywords: Solid electrolytes; Spin–lattice relaxation; Jeener–Broekaert sequence; Stimulated echoes, Line-shape analysis; Heterogeneous relaxation; Slow
dynamics
Tuesday, March 06, 2007
General Interest
1) High resolution NMR of water absorbed in single-wall carbon nanotubes
Sekhaneh, Wassef; Kotecha, Mrignayani; Dettlaff-Weglikowska, Urszula; Veeman, Wiebren S.
Abstract
1H MAS NMR study of water absorbed in open single-wall carbon nanotubes (SWCNTs) of average diameter 1.0 nm, synthesized with a Fe catalyst, was performed. Magic angle spinning significantly increases the spectral resolution and the spectrum shows that there are at least two distinct chemical shift regions for the water proton. From temperature dependent measurements, we assign the two chemical shift ranges to water absorbed inside and outside the nanotube. The spectra as a function of the water content show that the first water molecules that are absorbed by the dry material are absorbed inside the tubes.
CPL vol. 428 p 143
2) Characterization of violet emission from Rb optical pumping cells used in laser-polarized xenon NMR experiments
Indrajit Saha, Panayiotis Nikolaou, Nicholas Whiting, Boyd M. Goodson
Abstract
Visible emission from Rb optical pumping cells was characterized under a range of conditions relevant to the production of laserpolarized xenon (including temperature, partial pressures, and D1-resonant 795 nm laser power). Bright 421 nm (6P ! 5S) emission was consistent with energy-pooling processes of the type: Rb*(5P1/2) + Rb*(5P1/2,3/2)!Rb*(6P1/2,3/2) + Rb(5S1/2), with processes transiting through 5D states likely contributing at higher temperatures/lower N2 partial pressures. Under such conditions a number of Rb lines may be observed, indicating population of Rb states to P9D (31822 cm1). Such energies exceed those required for efficient production of laser-induced plasma.
CPL vol. 428 p 268
3) Double-quantum-filtered intermolecular single-quantum coherences in nuclear magnetic resonance spectroscopy and imaging
Zhong Chen, Xiaoqin Zhu, Bingwen Zheng, Shuhui Cai, Jianhui Zhong
Abstract
Based on the double-quantum-filtered technique, a three-pulse sequence was designed to effectively eliminate contamination of residual conventional single-quantum coherences (SQC) from intermolecular SQC signals in single-resonance spin-1/2 samples such as water. Analytical expressions were derived from the modified Bloch equations with dipolar fields. All experimental observations and numerical simulation results are in excellent agreement with the theoretical predictions. Compared to the CRAZED sequence, the sequence can effectively suppress residual conventional SQC signals even with great imperfection of radio-frequency pulse flip angles. For the first time, signals from pure intermolecular SQCs were selectively observed in forms of spectrum or image.
CPL vol 429 p 611
4) STARTMAS: A MAS-based method for acquiring isotropic NMR spectra of spin I = 3/2 nuclei in real time
Michael J. Thrippleton, Thomas J. Ball, Stefan Steuernagel, Sharon E. Ashbrook, Stephen Wimperis
Abstract
We describe a novel method, which we call STARTMAS, that allows acquisition of high-resolution or ‘isotropic’ spin I = 3/2 NMR spectra in solids in real time. Unlike the DOR technique of Samoson et al. [Mol. Phys. 65 (1988) 1013], STARTMAS is performed on a standard MAS probe and fast spinning rates are possible. The method consists of a multiple-pulse sequence interleaved with real-time data acquisition and exploits satellite (mI = ±3/2M±1/2) and double-quantum (±3/2M «1/2) transitions. We show that STARTMAS experiments can be used to obtain one-dimensional DOR-like spectra or provide an ‘ultrafast’ route to high-resolution two-dimensional spectra.
CPL vol 431 p 390
5) Improved double-quantum NMR correlation spectroscopy of dipolar-coupled quadrupolar spins
Mattias Ede´n a,*, Dan Zhou b, Jihong Yu
Abstract
We show that symmetry-based zero-quantum dipolar recoupling sequences sandwiched between central transition selective p/2-pulses may be used to excite double-quantum coherences (2QC) between the central transitions of homonuclear half-integer quadrupolar spins undergoing magic-angle spinning. The 2QC excitation is explored experimentally by 23Na and 27Al NMR on Na2SO3 and a-Al2O3 model compounds. When incorporated into 2Q–1Q 2D correlation protocols, the new recoupling method established all expected 27Al-27Al connectivities over 6A ˚ in the open-framework aluminophosphate AlPO–J19 [(NH4)2Al4(PO4)4HPO4 Æ H2O] and the layer mineral chlorite [Mg9Al6Si5O20(OH)16].
CPL vol 431 p 397
6) 27Al double rotation two-dimensional spin diffusion NMR: Complete unambiguous assignment of aluminium sites in 9Al2O3 Æ 2B2O3
I. Hung, A.P. Howes, T. Anupold, A. Samoson, D. Massiot, M.E. Smith, S.P. Brown, R. Dupree
Abstract
High-resolution two-dimensional 27Al spin diffusion NMR spectra of 9Al2O3 Æ 2B2O3 recorded under double rotation for different mixing times are presented. The two crystallographically distinct pentahedral Al sites are distinguished by the presence or absence of correlation peaks with neighboring tetrahedral sites.
CPL vol. 432 p 152
7) Solid-state 17O NMR in carbohydrates
T.H. Sefzik, J.B. Houseknecht, T.M. Clark, S. Prasad, T.L. Lowary, Z. Gan, P.J. Grandinetti
Abstract
Solid-state 17O magic-angle spinning nuclear magnetic resonance measurements at 19.5 Tesla were performed on 17O-enriched methyl a-D-galactopyranoside (4-17O), methyl b-D-glucopyranoside (2-17O), methyl a-D-glucopyranoside (4-17O), methyl a-D-glucopyranoside (6-17O), and a-D-glucopyranosyl (1 !6) a-D-glucopyranoside (6-17O). The 17O quadrupolar coupling constants and asymmetry parameters measured can be predicted with a model based entirely on the first-coordination sphere around oxygen. For the hydroxyl sites observed in the methyl glucosides, the quadrupolar coupling parameters are nearly identical, within 10% as predicted, given their nearly identical first-coordination sphere structures.
CPL 434 p 312
8) Fast adiabatic pulses for solid-state NMR of paramagnetic systems
Gwendal Kervern, Guido Pintacuda, Lyndon Emsley
Abstract
We present a simple framework for determining the parameters for efficient adiabatic pulses in solids with very large shift anisotropies under very fast MAS. We introduce the notion of the effective adiabatic quality factor to describe the spin dynamics. We then demonstrate the use of short, high-power adiabatic pulses (SHAPs) for population inversion in paramagnetic solids, and show its application to various systems with differing proton anisotropies in iron, ytterbium, and terbium complexes, from 400 to more than 1000 ppm. We then show how these pulses yield improvements in refocusing schemes and TEDOR NMR experiments on paramagnetic solids.
CPL vol 435 p 157
9) Proton-detected 14N MAS NMR using homonuclear decoupled rotary resonance
Zhehong Gan, Jean Paul Amoureux, Julien Trebosc
Abstract
A robust sensitivity-enhanced 1H/14N MAS HMQC experiment is described for proton-detected 14N NMR of solids. The sensitivity enhancement is achieved by using dipolar recoupling for coherence transfer with a so-called n = 2 rotary resonance. Rotary resonance occurs when a cw rf field matches certain ratios with the sample spinning frequency, n = x1/xr. The theory of rotary resonance for chemical shift anisotropy, heteronuclear and homonuclear dipolar interactions is presented in the irreducible representation. It is shown that the n = 2 rotary resonance decouples the homonuclear dipolar interactions while recoupling the heteronuclear dipolar interaction for proton-detected 14N NMR. The dipolar recoupling, T 02 lengthening, and 1H/14N HMQC experiment under the n = 2 rotary resonance are demonstrated.
CPL vol 435 p 163
10) High-resolution two-dimensional NMR spectra of half-integer-spin quadrupolar nuclei from one-dimensional projections
Thomas Vosegaard a,*, Dominique Massiot
Abstract
We present a technique providing high-resolution spectra of quadrupolar nuclei with half-integer nuclear spin displaying significant second-order linebroadening. The technique, dubbed chemical shift – quadrupolar projection-reconstruction of one-dimensional spectra (CQ-PRODI) exploits the different magnetic field dependence of the chemical shift and second-order quadrupolar effect. One-dimensional spectra recorded at different magnetic field strengths are represented as projections along different directions in the two-dimensional spectrum that correlates the chemical shift and the second-order quadrupolar lineshape. We present CQ-PRODI spectra for 27Al in 9Al2O3 Æ 2B2O3 and for 71Ga in b-Ga2O3 which display resolution of all sites in the chemical shift dimension.
CPL vol 437 p 120
11) Gas-Phase NMR Measurements, Absolute Shielding Scales, and Magnetic Dipole Moments
of 29Si and 73Ge Nuclei
W. Makulski, K. Jackowski, A. Antusek, and M. Jaszunski
Abstarct
New gas-phase NMR measurements of the shielding constants of 29Si, 73Ge, and 1H nuclei in SiH4 and GeH4 are reported. The results, extrapolated to zero density, provide accurate isolated molecule values, best suited for comparison with theoretical calculations. Using the recent ab initio results for these molecules and the measured chemical shifts, we determine the absolute shielding scales for 29Si and 73Ge. This allows us to provide new values of the nuclear magnetic dipole moments for these two nuclei; in addition, we examine the dipole moments of 13C and 119Sn.
JPCA vol 110 p 11462
12) An ab Initio Study of 15N-11B Spin-Spin Coupling Constants for Borazine and Selected
Derivatives
Janet E. Del Bene, Jose Elguero, Ibon Alkorta, Manuel Yanez, and Otilia Mo
Abstract
Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to investigate substituent effects on coupling constants for borazine and selected substituted borazines. For molecules in which F atoms are not bonded to adjacent atoms in the ring, F substitution increases the one-bond 11B-15N coupling constants involving the atom at which substitution occurs but leaves the remaining one-bond B-N coupling constants essentially unchanged. For these molecules, the magnitudes of one-bond B-N coupling constants are only slightly dependent on the number of F atoms present. Fluorine substitution at adjacent B and N atoms in the borazine ring further increases the one-bond B-N coupling constant involving the substituted atoms and has the same effect on the other one-bond coupling constants as observed for corresponding molecules in which substitution occurs at alternate sites. In contrast to the effect of F substitution, substitution of Li at either N or B decreases one-bond B-N coupling constants relative to borazine. The effects of F and Li substitution on one-bond B-N coupling constants for borazine are similar to F and Li substitution effects on 13C-13C coupling constants for benzene.
JPCA vol 110 p 9959
13) Proton NMR measurements of the local magnetic field in the paramagnetic metal
and antiferromagnetic insulator phases of lamda-(BETS)2FeCl4
Guoqing Wu, P. Ranin, W. G. Clark, S. E. Brown, L. Balicas, and L. K. Montgomery
Abstract
Measurements of the 1H-NMR spectrum of a small 4g single crystal of the organic conductor BETS2FeCl4 are reported with an applied magnetic field B0=9 T parallel to the a axis in the ac plane over a temperature T range 2.0–180 K. They provide the distribution of the static local magnetic field at the proton sites in the paramagnetic metal PM and antiferromagnetic insulator AFI phases, along with the changes that occur at the PM-AFI phase transition. The spectra have six main peaks that are significantly broadened and shifted at low T. The origin of these features is attributed to the large dipolar field from the
3d Fe3+ ion moments spin Sd=5/2. Their amplitude and T dependence are modeled using a modified Brillouin function that includes a mean field approximation for the total exchange interaction J0 between one Fe3+ ion and its two nearest neighbors. A good fit is obtained using J0=−1.7 K. At temperatures below the PM-AFI transition temperature TMI=3.5 K, an extra peak appears on the high frequency side of the spectrum and the details of the spectrum become smeared. Also, the rms linewidth and the frequency shift of the spectral distribution are discontinuous, consistent with the transition being first order. These measurements verify that the dominant local magnetic field contribution is from the Fe3+ ions and indicate that there is a significant change in the static local magnetic field distribution at the proton sites on traversing the PM to AFI phase transition.
PRB vol 74 p 064428
14) Structural, Solid-State NMR and Theoretical Studies of the Inverse- Coordination of Lithium Chloride Using Group 13 Phosphide Hosts
Melinda J. Duer, Felipe Garc1a, Jonathan M. Goodman, Jçrg P. Hehn, Richard A. Kowenicki, Vesal Naseri, Mary McPartlin, Matthew L. Stead, Robin Stein, and Dominic S. Wright
Abstract: The reaction of MeAlCl2 with ’PhPLi2’ in THF gives [{MeAl-(PPh)3Li4·3THF}4ACHTUNGTRENUNG(m4-Cl)]Li+ (1). The GaIII and InIII analogues, [{MeEACHTUNGTRENUNG(PPh)3Li4·3THF}4ACHTUNGTRENUNG(m4-Cl)]Li+·(THF)3 (E=Ga (2), In (3)), are obtained by the in situ reactions of MeECl2 with PhPLi2 in THF. For all of the complexes, the cage anions have an unusual cubic arrangement that is similar to a zeolite, and contain large voids (ca. 17 8). The location of the Li+ counterions in 1–3 and their coordination environment appears to subtly reflect variations in packing and lattice energy. Whereas in 1 highly mobile, loosely coordinated Li+ counterions are present, 2 and 3 contain less mobile THF-solvated counterions within the cavities. X-ray crystallographic and solid-state NMR studies are reported on 1–3, together with model DFT calculations on the selectivity of halide coordination.
CEJ vol 13 p 1251
JACS Journal update- January 2007 -Present
J. Am. Chem. Soc., 129 (5), 1386 -1392, 2007.
Structures of Alkali Metals in Silica Gel Nanopores: New Materials for Chemical Reductions and Hydrogen Production
Mouath Shatnawi, Gianluca Paglia, James L. Dye,* Kevin C. Cram, Michael Lefenfeld,* and Simon J. L. Billinge*
Abstract:
Alkali metals and their alloys can be protected from spontaneous reaction with dry air by intercalation (with subsequent heating) into the pores of silica gel (SG) at loadings up to 40 wt %. The resulting loose, black powders are convenient materials for chemical reduction of organic compounds and the production of clean hydrogen. The problem addressed in this paper is the nature of the reducing species present in these amorphous materials. The atomic pair distribution function (PDF), which considers both Bragg and diffuse scattering components, was used to examine their structures. Liquid Na-K alloys added to silica gel at room temperature (stage 0) or heated to 150 C (stage I) as well as stage I Na-SG, retain the overall pattern of pure silica gel. Broad oscillations in the PDF show that added alkali metals remain in the pores as nanoscale metal clusters. 23Na MAS NMR studies confirm the presence of Na0 and demonstrate that Na+ ions are formed as well. The relative amounts of Na0 and Na+ depend on both the overall metal loading and the average pore size. The results suggest that ionization occurs near or in the SiO2 walls, with neutral metal present in the larger cavities. The fate of the electrons released by ionization is uncertain, but they may add to the silica gel lattice, or form an "electride-like plasma" near the silica gel walls. A remaining mystery is why the stage I material does not show a melting endotherm of the encapsulated metal and does not react with dry oxygen. Na-SG when heated to 400 C (stage II) yields a dual-phase reaction product that consists of Na4Si4 and Na2SiO3.
J. Am. Chem. Soc., 129 (5), 1293 -1303, 2007.
Structure of Molecular Tweezer Complexes in the Solid State: NMR Experiments, X-ray Investigations, and Quantum Chemical Calculations
Torsten Schaller,* Uta P. Büchele, Frank-Gerrit Klärner, Dieter Bläser, Roland Boese, Steven P. Brown, Hans Wolfgang Spiess, Felix Koziol, Jörg Kussmann, and Christian Ochsenfeld
Abstract:
The structure of supramolecular complexes formed by a naphthalene-spaced tweezer molecule as host and 1,4-dicyanobenzene (DCNB), 1,2,4,5-tetracyanobenzene (TCNB), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as aromatic, electron-deficient guests is investigated by solid-state NMR and X-ray diffraction measurements. Quantum chemical calculations using linear scaling methods are applied to predict and to assign the 1H NMR chemical shifts of the complexes. By combining experiment and theory, insights into intra- and intermolecular effects influencing the proton chemical shifts of the host-guest system are provided in the solid state.
J. Am. Chem. Soc., 129 (4), 839 -845, 2007.
Rotational Dynamics in a Crystalline Molecular Gyroscope by Variable-Temperature 13C NMR, 2H NMR, X-Ray Diffraction, and Force Field Calculations
Tinh-Alfredo V. Khuong, Hung Dang, Peter D. Jarowski, Emily F. Maverick, and Miguel A. Garcia-Garibay*
Abstract:
A combination of solid-state 13C CPMAS NMR, 2H NMR, X-ray-determined anisotropic displacement parameters (ADPs), and molecular mechanics calculations were used to analyze the rotational dynamics of 1,4-bis[3,3,3-tris(m-methoxyphenyl)propynyl]benzene (3A), a structure that emulates a gyroscope with a p-phenylene group acting as a rotator and two m-methoxy-substituted trityl groups acting as a stator. The line shape analysis of VT 13C CPMAS and broad-band 2H NMR data were in remarkable agreement with each other, with rotational barriers of 11.3 and 11.5 kcal/mol, respectively. The barriers obtained by analysis of ADPs obtained by single-crystal X-ray diffraction at 100 and 200 K, assuming a sinusoidal potential, were 10.3 and 10.1 kcal, respectively. A similar analysis of an X-ray structure solved from data acquired at 300 K suggested a barrier of only 8.0 kcal/mol. Finally, a rotational potential calculated with a finite cluster model using molecular mechanics revealed a symmetric but nonsinusoidal potential that accounts relatively well for the X-ray-derived values and the NMR experimental results. It is speculated that the discrepancy between the barriers derived from low and high-temperature X-ray data may be due to an increase in anharmonicity, or to disorder, at the higher temperature values.
J. Am. Chem. Soc., 129 (4), 728 -729, 2007.
Proton Assisted Insensitive Nuclei Cross Polarization
Józef R. Lewandowski, Gaël De Paëpe, and Robert G. Griffin*
Abstract:
This Communication presents a solid-state NMR 15N-13C polarization transfer scheme applicable at high B0 and high MAS frequencies, requiring moderate rf powers and mixing time (1-6 ms). The sequence, PAIN-CP, involves the abundant nearby protons in the heteronuclear recoupling dynamics and provides a new tool for obtaining long distance 15N-13C contacts. It should be of major interest for biomolecular structural studies.
J. Am. Chem. Soc., 129 (3), 470 -471, 2007.
Simultaneous Supralinear Line-Narrowing and Sensitivity Enhancement at High Fields in Magic Angle Spinning NMR of Spin-1/2 Nuclei in Solids
Riqiang Fu,* Ozge Gunaydin-Sen, and Naresh S. Dalal*
Abstract:
We report that, in the 15N CP/MAS NMR measurements on NH4H2AsO4 (ADA), the line widths decrease nonlinearly on going from 7.0 to 21.1 T (0.260 to 0.071 ppm, respectively), which can be attributed to an increase in the spin-spin relaxation time, T2. Additionally, besides the expected (B0)3/2 effect, the sensitivity is further enhanced by a factor of 1.6 from 7.0 to 14.1 T, and 2.7 on going to 21.1 T. The enhanced resolution and sensitivity at 21.1 T have enabled us to probe the nature of the antiferroelectric transition at 215 K in ADA to a depth not possible at lower fields.
J. Am. Chem. Soc., 129 (3), 462 -463, 2007.
NMR Detection of Protein 15N Spins near Paramagnetic Lanthanide Ions
Michael John, Ah Young Park, Nicholas E. Dixon, and Gottfried Otting*
Abstract:
Pronounced paramagnetic relaxation enhancement (PRE) due to paramagnetic metal ions prevents the observation of NMR signals from 1H spins near the metal. While 15N spins are less prone to PRE, the intrinsic sensitivity of 15N NMR spectroscopy is low. This Communication presents a 1H detected out-and-back Nz-exchange experiment which allows the measurement of pseudocontact shifts of 15N spins located as close as 6 Å from a Dy3+ ion in a 30 kDa protein complex. The experiment relies on the chemical exchange between paramagnetic and diamagnetic metal ions during two mixing times during which the 15N magnetization is stored as PRE-insensitive longitudinal magnetization. It is demonstrated with the complex between the subunit and the N-terminal domain of the subunit of E. coli DNA polymerase III, prepared with a mixture of Dy3+ and La3+. Pseudocontact shifts were measured for 61 15N spins which were not observable in a conventional 15N-HSQC spectrum.
J. Am. Chem. Soc., 129 (2), 335 -346, 2007.
17O Magic Angle Spinning NMR Studies of Brnsted Acid Sites in Zeolites HY and HZSM-5
Luming Peng, Hua Huo, Yun Liu, and Clare P. Grey*
Abstract:
High-resolution 17O/1H double resonance NMR spectra were obtained for two zeolites, one with a low Si/Al ratio (zeolite HY) and one with a high Si/Al ratio (HZSM-5), to investigate their local structure and Brnsted acidity. Two different oxygen signals, corresponding to Brnsted acid sites in supercages and sodalite cages of zeolite HY were readily resolved in the two-dimensional (2-D) 1H-17O heteronuclear correlation (HETCOR) NMR spectra allowing the 17O isotropic chemical shift (CS) and quadrupolar coupling parameters (quadrupolar coupling constant, QCC, and asymmetry parameter, ) for the two oxygen atoms to be extracted. Similar experiments for HZSM-5 showed that the sites in this system are associated with a much larger distribution in NMR parameters than found in HY. 17O-1H rotational echo double resonance (REDOR) NMR was applied to probe the O-H distances in zeolites HY and HZSM-5. Weaker 17O-1H dephasing was observed for zeolite HZSM-5 in comparison to that of HY, consistent with longer O-H bonds and/or increased proton mobility.
Structures of Alkali Metals in Silica Gel Nanopores: New Materials for Chemical Reductions and Hydrogen Production
Mouath Shatnawi, Gianluca Paglia, James L. Dye,* Kevin C. Cram, Michael Lefenfeld,* and Simon J. L. Billinge*
Abstract:
Alkali metals and their alloys can be protected from spontaneous reaction with dry air by intercalation (with subsequent heating) into the pores of silica gel (SG) at loadings up to 40 wt %. The resulting loose, black powders are convenient materials for chemical reduction of organic compounds and the production of clean hydrogen. The problem addressed in this paper is the nature of the reducing species present in these amorphous materials. The atomic pair distribution function (PDF), which considers both Bragg and diffuse scattering components, was used to examine their structures. Liquid Na-K alloys added to silica gel at room temperature (stage 0) or heated to 150 C (stage I) as well as stage I Na-SG, retain the overall pattern of pure silica gel. Broad oscillations in the PDF show that added alkali metals remain in the pores as nanoscale metal clusters. 23Na MAS NMR studies confirm the presence of Na0 and demonstrate that Na+ ions are formed as well. The relative amounts of Na0 and Na+ depend on both the overall metal loading and the average pore size. The results suggest that ionization occurs near or in the SiO2 walls, with neutral metal present in the larger cavities. The fate of the electrons released by ionization is uncertain, but they may add to the silica gel lattice, or form an "electride-like plasma" near the silica gel walls. A remaining mystery is why the stage I material does not show a melting endotherm of the encapsulated metal and does not react with dry oxygen. Na-SG when heated to 400 C (stage II) yields a dual-phase reaction product that consists of Na4Si4 and Na2SiO3.
J. Am. Chem. Soc., 129 (5), 1293 -1303, 2007.
Structure of Molecular Tweezer Complexes in the Solid State: NMR Experiments, X-ray Investigations, and Quantum Chemical Calculations
Torsten Schaller,* Uta P. Büchele, Frank-Gerrit Klärner, Dieter Bläser, Roland Boese, Steven P. Brown, Hans Wolfgang Spiess, Felix Koziol, Jörg Kussmann, and Christian Ochsenfeld
Abstract:
The structure of supramolecular complexes formed by a naphthalene-spaced tweezer molecule as host and 1,4-dicyanobenzene (DCNB), 1,2,4,5-tetracyanobenzene (TCNB), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as aromatic, electron-deficient guests is investigated by solid-state NMR and X-ray diffraction measurements. Quantum chemical calculations using linear scaling methods are applied to predict and to assign the 1H NMR chemical shifts of the complexes. By combining experiment and theory, insights into intra- and intermolecular effects influencing the proton chemical shifts of the host-guest system are provided in the solid state.
J. Am. Chem. Soc., 129 (4), 839 -845, 2007.
Rotational Dynamics in a Crystalline Molecular Gyroscope by Variable-Temperature 13C NMR, 2H NMR, X-Ray Diffraction, and Force Field Calculations
Tinh-Alfredo V. Khuong, Hung Dang, Peter D. Jarowski, Emily F. Maverick, and Miguel A. Garcia-Garibay*
Abstract:
A combination of solid-state 13C CPMAS NMR, 2H NMR, X-ray-determined anisotropic displacement parameters (ADPs), and molecular mechanics calculations were used to analyze the rotational dynamics of 1,4-bis[3,3,3-tris(m-methoxyphenyl)propynyl]benzene (3A), a structure that emulates a gyroscope with a p-phenylene group acting as a rotator and two m-methoxy-substituted trityl groups acting as a stator. The line shape analysis of VT 13C CPMAS and broad-band 2H NMR data were in remarkable agreement with each other, with rotational barriers of 11.3 and 11.5 kcal/mol, respectively. The barriers obtained by analysis of ADPs obtained by single-crystal X-ray diffraction at 100 and 200 K, assuming a sinusoidal potential, were 10.3 and 10.1 kcal, respectively. A similar analysis of an X-ray structure solved from data acquired at 300 K suggested a barrier of only 8.0 kcal/mol. Finally, a rotational potential calculated with a finite cluster model using molecular mechanics revealed a symmetric but nonsinusoidal potential that accounts relatively well for the X-ray-derived values and the NMR experimental results. It is speculated that the discrepancy between the barriers derived from low and high-temperature X-ray data may be due to an increase in anharmonicity, or to disorder, at the higher temperature values.
J. Am. Chem. Soc., 129 (4), 728 -729, 2007.
Proton Assisted Insensitive Nuclei Cross Polarization
Józef R. Lewandowski, Gaël De Paëpe, and Robert G. Griffin*
Abstract:
This Communication presents a solid-state NMR 15N-13C polarization transfer scheme applicable at high B0 and high MAS frequencies, requiring moderate rf powers and mixing time (1-6 ms). The sequence, PAIN-CP, involves the abundant nearby protons in the heteronuclear recoupling dynamics and provides a new tool for obtaining long distance 15N-13C contacts. It should be of major interest for biomolecular structural studies.
J. Am. Chem. Soc., 129 (3), 470 -471, 2007.
Simultaneous Supralinear Line-Narrowing and Sensitivity Enhancement at High Fields in Magic Angle Spinning NMR of Spin-1/2 Nuclei in Solids
Riqiang Fu,* Ozge Gunaydin-Sen, and Naresh S. Dalal*
Abstract:
We report that, in the 15N CP/MAS NMR measurements on NH4H2AsO4 (ADA), the line widths decrease nonlinearly on going from 7.0 to 21.1 T (0.260 to 0.071 ppm, respectively), which can be attributed to an increase in the spin-spin relaxation time, T2. Additionally, besides the expected (B0)3/2 effect, the sensitivity is further enhanced by a factor of 1.6 from 7.0 to 14.1 T, and 2.7 on going to 21.1 T. The enhanced resolution and sensitivity at 21.1 T have enabled us to probe the nature of the antiferroelectric transition at 215 K in ADA to a depth not possible at lower fields.
J. Am. Chem. Soc., 129 (3), 462 -463, 2007.
NMR Detection of Protein 15N Spins near Paramagnetic Lanthanide Ions
Michael John, Ah Young Park, Nicholas E. Dixon, and Gottfried Otting*
Abstract:
Pronounced paramagnetic relaxation enhancement (PRE) due to paramagnetic metal ions prevents the observation of NMR signals from 1H spins near the metal. While 15N spins are less prone to PRE, the intrinsic sensitivity of 15N NMR spectroscopy is low. This Communication presents a 1H detected out-and-back Nz-exchange experiment which allows the measurement of pseudocontact shifts of 15N spins located as close as 6 Å from a Dy3+ ion in a 30 kDa protein complex. The experiment relies on the chemical exchange between paramagnetic and diamagnetic metal ions during two mixing times during which the 15N magnetization is stored as PRE-insensitive longitudinal magnetization. It is demonstrated with the complex between the subunit and the N-terminal domain of the subunit of E. coli DNA polymerase III, prepared with a mixture of Dy3+ and La3+. Pseudocontact shifts were measured for 61 15N spins which were not observable in a conventional 15N-HSQC spectrum.
J. Am. Chem. Soc., 129 (2), 335 -346, 2007.
17O Magic Angle Spinning NMR Studies of Brnsted Acid Sites in Zeolites HY and HZSM-5
Luming Peng, Hua Huo, Yun Liu, and Clare P. Grey*
Abstract:
High-resolution 17O/1H double resonance NMR spectra were obtained for two zeolites, one with a low Si/Al ratio (zeolite HY) and one with a high Si/Al ratio (HZSM-5), to investigate their local structure and Brnsted acidity. Two different oxygen signals, corresponding to Brnsted acid sites in supercages and sodalite cages of zeolite HY were readily resolved in the two-dimensional (2-D) 1H-17O heteronuclear correlation (HETCOR) NMR spectra allowing the 17O isotropic chemical shift (CS) and quadrupolar coupling parameters (quadrupolar coupling constant, QCC, and asymmetry parameter, ) for the two oxygen atoms to be extracted. Similar experiments for HZSM-5 showed that the sites in this system are associated with a much larger distribution in NMR parameters than found in HY. 17O-1H rotational echo double resonance (REDOR) NMR was applied to probe the O-H distances in zeolites HY and HZSM-5. Weaker 17O-1H dephasing was observed for zeolite HZSM-5 in comparison to that of HY, consistent with longer O-H bonds and/or increased proton mobility.
Saturday, March 03, 2007
Angewandte Update from Jan. 07 - Present
Secondary Structure, Dynamics, and Topology of a Seven-Helix Receptor in Native Membranes, Studied by Solid-State NMR Spectroscopy
Manuel Etzkorn, Swetlana Martell, Ovidiu C. Andronesi, Karsten Seidel, Martin Engelhard, Marc Baldus
Angewandte (2007) 46, 459.
Summary:
In the loop: High-resolution solid-state NMR spectroscopy is used to study the secondary structure, dynamics, and membrane topology of an entire seven-helix receptor, sensory rhodopsin II from Natronomonas pharaonis. The experiments are carried out on a single isotope-labeled sample in a native membrane environment.
Solid-State NMR Spectroscopy of a Paramagnetic Protein: Assignment and Study of Human Dimeric Oxidized CuII-ZnII Superoxide Dismutase (SOD)
Guido Pintacuda, Nicolas Giraud, Roberta Pierattelli, Anja Böckmann, Ivano Bertini, Lyndon Emsley
Angewandte (2007)46,1079.
Summary:
A solid story: The paramagnetic form of the protein superoxide dismutase (SOD; see portion of structure in upper right corner of picture with detectability sphere in blue) is shown to be accessible to high-resolution solid-state magic angle spinning NMR studies when in microcrystalline form. A nearly complete assignment of the signals of this 32-kDa dimer has been achieved.
Manuel Etzkorn, Swetlana Martell, Ovidiu C. Andronesi, Karsten Seidel, Martin Engelhard, Marc Baldus
Angewandte (2007) 46, 459.
Summary:
In the loop: High-resolution solid-state NMR spectroscopy is used to study the secondary structure, dynamics, and membrane topology of an entire seven-helix receptor, sensory rhodopsin II from Natronomonas pharaonis. The experiments are carried out on a single isotope-labeled sample in a native membrane environment.
Solid-State NMR Spectroscopy of a Paramagnetic Protein: Assignment and Study of Human Dimeric Oxidized CuII-ZnII Superoxide Dismutase (SOD)
Guido Pintacuda, Nicolas Giraud, Roberta Pierattelli, Anja Böckmann, Ivano Bertini, Lyndon Emsley
Angewandte (2007)46,1079.
Summary:
A solid story: The paramagnetic form of the protein superoxide dismutase (SOD; see portion of structure in upper right corner of picture with detectability sphere in blue) is shown to be accessible to high-resolution solid-state magic angle spinning NMR studies when in microcrystalline form. A nearly complete assignment of the signals of this 32-kDa dimer has been achieved.
PCCP Update from Jan. 07 - Present
NMR measurements of scalar-coupling distributions in disordered solids
Sylvian Cadars, Anne Lesage, Michel Trierweiler, Laurent Heux and Lyndon Emsley
PCCP(2007)9,92.
Abstract:
The measurement of scalar (J) couplings by solid-state NMR is a field of great interest, since this interaction is a rich source of local structural information, complementary to dipolar and chemical shift interactions. Here, we first demonstrate that J-coupling distributions exist and can be observed in disordered solids, as illustrated with the observation of a pair-specific distribution of 2J(31P–N–31P) couplings in a bis-phosphino amine, and we investigate the potential effects of such distributions on the measurement of average J-coupling constants. Second, we show that the measurement of two-dimensional (2D) distributions of J-couplings provides a much richer probe of local structural disorder than one-dimensional distributions, and we introduce new methods that provide different (selective or non-selective) ways of measuring 2D J distributions in a wide range of disordered systems. These methods are finally applied to a slightly disordered polymorphic sample of fully 13C-enriched cellulose, and then to the bis-phosphino amine sample, from which 2D 2JPP-coupling distributions are clearly identified and interpreted
NMR crystallography of oxybuprocaine hydrochloride, Modification II°
Robin K. Harris, Sylvian Cadars, Lyndon Emsley, Jonathan R. Yates, Chris J. Pickard, Ram K. R. Jetti and Ulrich J. Griesser
PCCP(2007)9,360.
Abstract:
The 13C CPMAS spectrum is presented for the polymorph of oxybuprocaine hydrochloride which is stable at room temperature, i.e. Mod. II°. It shows crystallographic splittings arising from the fact that there are two molecules, with substantially different conformations, in the asymmetric unit. An INADEQUATE two-dimensional experiment was used to link signals for the same independent molecule. The chemical shifts are discussed in relation to the crystal structure. Of the four ethyl groups attached to NH+ nitrogens, one gives rise to unusually low chemical shifts, very different from those of the other three ethyl groups. This is attributed empirically to -gauche conformational effects, as is confirmed by shielding computations. These considerations allow 13C signals to be assigned to specific carbons in the two crystallographically inequivalent molecules in the crystal structure. Indeed, information about the conformations is inherent in the NMR spectrum, which thus provides data of crystallographic significance. A 13C/1H HETCOR experiment enabled resolution to be obtained in the 1H dimension and allowed 1H and 13C signals for the same independent molecule to be linked.
Experimental and quantum-chemical determination of the 2H quadrupole coupling tensor in deuterated benzenes
Anu M. Kantola, Susanna Ahola, Juha Vaara, Jani Saunavaara and Jukka Jokisaari
PCCP(2007)9,481.
Abstract:
Deuterium Quadrupole Coupling Constant (DQCC) in benzene was determined both experimentally by Nuclear Magnetic Resonance spectroscopy in Liquid Crystalline solutions (LC NMR) and theoretically by ab initio electronic structure calculations. DQCCs were measured for benzene-d1 and 1,3,5-benzene-d3 using several different liquid crystalline solvents and taking vibrational and deformational corrections into account in the analysis of experimental dipolar couplings, used to determine the orientational order parameter of the dissolved benzene. The experimental DQCC results for the isotopomers benzene-d1 and 1,3,5-benzene-d3 are found to be 187.7 kHz and 187.3 kHz, respectively, which are essentially equal within the experimental accuracy (±0.4 kHz). Theoretical results were obtained at different C–D bond lenghts, and by applying corrections for electron correlation and rovibrational motion on top of large-basis-set Hartree–Fock results. The computations give a consistent DQCC of ca. 189 kHz for three different isotopomers; benzene-d1, 1,3,5-benzene-d3, and benzene-d6, revealing that isotope effects are not detectable within the present experimental accuracy. Calculations carried out using a continuum solvation model to account for intermolecular interaction effects result in very small changes as compared to the data obtained in vacuo. The comparison of theoretical and experimental results points out the selection of the underlying molecular geometry as the most likely source of the remaining discrepancy of less than 2 kHz. Such an agreement between the calculated and the experimental DQCC results can only be achieved if rovibrational effects are considered on one hand in the experimental direct dipolar coupling data, and on the other hand in the theoretical property calculation, as is done presently.
A double quantum 129Xe NMR experiment for probing xenon in multiply-occupied cavities of solid-state inclusion compounds
Darren H. Brouwer, Saman Alavi and John A. Ripmeester
PCCP(2007)9,1093.
Abstract:
A method is presented for detecting multiple xenon atoms in cavities of solid-state inclusion compounds using 129Xe double quantum NMR spectroscopy. Double quantum filtered 129Xe NMR spectra, performed on the xenon clathrate of Dianins compound were obtained under high-resolution Magic-Angle Spinning (MAS) conditions, by recoupling the weak 129Xe–129Xe dipole–dipole couplings that exist between xenon atoms in close spatial proximity. Because the 129Xe–129Xe dipole–dipole couplings are generally weak due to dynamics of the atoms and to large internuclear separations, and since the 129Xe Chemical Shift Anisotropy (CSA) tends to be relatively large, a very robust dipolar recoupling sequence was necessary, with the symmetry-based SR26114 dipolar recoupling sequence proving appropriate. We have also attempted to measure the 129Xe–129Xe dipole–dipole coupling constant between xenon atoms in the cavities of the xenon–Dianins compound clathrate and have found that the dynamics of the xenon atoms (as investigated with molecular dynamics simulations) as well as 129Xe multiple spin effects complicate the analysis. The double quantum NMR method is useful for peak assignment in 129Xe NMR spectra because peaks arising from different types of absorption/inclusion sites or from different levels of occupancy of single sites can be distinguished. The method can also help resolve ambiguities in diffraction experiments concerning the order/disorder in a material.
A solid-state 55Mn NMR spectroscopy and DFT investigation of manganese pentacarbonyl compounds
Kirk W. Feindel, Kristopher J. Ooms and Roderick E. Wasylishen
PCCP(2007)9, 1226.
Abstract:
Central transition 55Mn NMR spectra of several solid manganese pentacarbonyls acquired at magnetic field strengths of 11.75, 17.63, and 21.1 T are presented. The variety of distinct powder sample lineshapes obtained demonstrates the sensitivity of solid-state 55Mn NMR to the local bonding environment, including the presence of crystallographically unique Mn sites, and facilitates the extraction of the Mn chemical shift anisotropies, CSAs, and the nuclear quadrupolar parameters. The compounds investigated include molecules with approximate C4v symmetry, LMn(CO)5(L = Cl, Br, I, HgMn(CO)5, CH3) and several molecules of lower symmetry (L = PhCH2, Ph3–nClnSn (n= 1, 2, 3)). For these compounds, the Mn CSA values range from <100>
Ultraslow Li diffusion in spinel-type structured Li4Ti5O12—A comparison of results from solid state NMR and impedance spectroscopy
Martin Wilkening, Roger Amade, Wojciech Iwaniak and Paul Heitjans
PCCP(2007)9,1239.
Abstract:
The cubic spinel oxides Li1+xTi2–xO4 (0 x 1/3) are promising anode materials for lithium-ion rechargeable batteries. The end member of the Li–Ti–O series, Li4Ti5O12, can accommodate Li ions up to the composition Li7Ti5O12. Whereas a number of studies focus on the electrochemical behaviour of Li insertion into and Li diffusion in the Li intercalated material, only few investigations about low-temperature Li dynamics in the non-intercalated host material Li4Ti5O12 have been reported so far. In the present paper, Li diffusion in pure-phase microcrystalline Li4Ti5O12 with an average particle size in the µm range was probed by 7Li solid state NMR spectroscopy using spin-alignment echo (SAE) and spin–lattice relaxation (SLR) measurements. Between T = 295 K and 400 K extremely slow Li jump rates –1 ranging from 1 s–1 to about 2200 s–1 were directly measured by recording the decay of spin-alignment echoes as a function of mixing time and constant evolution time. The results point out the slow Li diffusion in non-intercalated Li4Ti5O12·–1 (1/T) follows Arrhenius behaviour with an activation energy EASAE of about 0.86 eV. Interestingly, EASAE is comparable to activation energies deduced from conductivity measurements (0.94(1) eV) and from SLR measurements in the rotating frame (0.74(2) eV) rather than from those performed in the laboratory frame, EAlow-T = 0.26(1) eV at low T.
Sylvian Cadars, Anne Lesage, Michel Trierweiler, Laurent Heux and Lyndon Emsley
PCCP(2007)9,92.
Abstract:
The measurement of scalar (J) couplings by solid-state NMR is a field of great interest, since this interaction is a rich source of local structural information, complementary to dipolar and chemical shift interactions. Here, we first demonstrate that J-coupling distributions exist and can be observed in disordered solids, as illustrated with the observation of a pair-specific distribution of 2J(31P–N–31P) couplings in a bis-phosphino amine, and we investigate the potential effects of such distributions on the measurement of average J-coupling constants. Second, we show that the measurement of two-dimensional (2D) distributions of J-couplings provides a much richer probe of local structural disorder than one-dimensional distributions, and we introduce new methods that provide different (selective or non-selective) ways of measuring 2D J distributions in a wide range of disordered systems. These methods are finally applied to a slightly disordered polymorphic sample of fully 13C-enriched cellulose, and then to the bis-phosphino amine sample, from which 2D 2JPP-coupling distributions are clearly identified and interpreted
NMR crystallography of oxybuprocaine hydrochloride, Modification II°
Robin K. Harris, Sylvian Cadars, Lyndon Emsley, Jonathan R. Yates, Chris J. Pickard, Ram K. R. Jetti and Ulrich J. Griesser
PCCP(2007)9,360.
Abstract:
The 13C CPMAS spectrum is presented for the polymorph of oxybuprocaine hydrochloride which is stable at room temperature, i.e. Mod. II°. It shows crystallographic splittings arising from the fact that there are two molecules, with substantially different conformations, in the asymmetric unit. An INADEQUATE two-dimensional experiment was used to link signals for the same independent molecule. The chemical shifts are discussed in relation to the crystal structure. Of the four ethyl groups attached to NH+ nitrogens, one gives rise to unusually low chemical shifts, very different from those of the other three ethyl groups. This is attributed empirically to -gauche conformational effects, as is confirmed by shielding computations. These considerations allow 13C signals to be assigned to specific carbons in the two crystallographically inequivalent molecules in the crystal structure. Indeed, information about the conformations is inherent in the NMR spectrum, which thus provides data of crystallographic significance. A 13C/1H HETCOR experiment enabled resolution to be obtained in the 1H dimension and allowed 1H and 13C signals for the same independent molecule to be linked.
Experimental and quantum-chemical determination of the 2H quadrupole coupling tensor in deuterated benzenes
Anu M. Kantola, Susanna Ahola, Juha Vaara, Jani Saunavaara and Jukka Jokisaari
PCCP(2007)9,481.
Abstract:
Deuterium Quadrupole Coupling Constant (DQCC) in benzene was determined both experimentally by Nuclear Magnetic Resonance spectroscopy in Liquid Crystalline solutions (LC NMR) and theoretically by ab initio electronic structure calculations. DQCCs were measured for benzene-d1 and 1,3,5-benzene-d3 using several different liquid crystalline solvents and taking vibrational and deformational corrections into account in the analysis of experimental dipolar couplings, used to determine the orientational order parameter of the dissolved benzene. The experimental DQCC results for the isotopomers benzene-d1 and 1,3,5-benzene-d3 are found to be 187.7 kHz and 187.3 kHz, respectively, which are essentially equal within the experimental accuracy (±0.4 kHz). Theoretical results were obtained at different C–D bond lenghts, and by applying corrections for electron correlation and rovibrational motion on top of large-basis-set Hartree–Fock results. The computations give a consistent DQCC of ca. 189 kHz for three different isotopomers; benzene-d1, 1,3,5-benzene-d3, and benzene-d6, revealing that isotope effects are not detectable within the present experimental accuracy. Calculations carried out using a continuum solvation model to account for intermolecular interaction effects result in very small changes as compared to the data obtained in vacuo. The comparison of theoretical and experimental results points out the selection of the underlying molecular geometry as the most likely source of the remaining discrepancy of less than 2 kHz. Such an agreement between the calculated and the experimental DQCC results can only be achieved if rovibrational effects are considered on one hand in the experimental direct dipolar coupling data, and on the other hand in the theoretical property calculation, as is done presently.
A double quantum 129Xe NMR experiment for probing xenon in multiply-occupied cavities of solid-state inclusion compounds
Darren H. Brouwer, Saman Alavi and John A. Ripmeester
PCCP(2007)9,1093.
Abstract:
A method is presented for detecting multiple xenon atoms in cavities of solid-state inclusion compounds using 129Xe double quantum NMR spectroscopy. Double quantum filtered 129Xe NMR spectra, performed on the xenon clathrate of Dianins compound were obtained under high-resolution Magic-Angle Spinning (MAS) conditions, by recoupling the weak 129Xe–129Xe dipole–dipole couplings that exist between xenon atoms in close spatial proximity. Because the 129Xe–129Xe dipole–dipole couplings are generally weak due to dynamics of the atoms and to large internuclear separations, and since the 129Xe Chemical Shift Anisotropy (CSA) tends to be relatively large, a very robust dipolar recoupling sequence was necessary, with the symmetry-based SR26114 dipolar recoupling sequence proving appropriate. We have also attempted to measure the 129Xe–129Xe dipole–dipole coupling constant between xenon atoms in the cavities of the xenon–Dianins compound clathrate and have found that the dynamics of the xenon atoms (as investigated with molecular dynamics simulations) as well as 129Xe multiple spin effects complicate the analysis. The double quantum NMR method is useful for peak assignment in 129Xe NMR spectra because peaks arising from different types of absorption/inclusion sites or from different levels of occupancy of single sites can be distinguished. The method can also help resolve ambiguities in diffraction experiments concerning the order/disorder in a material.
A solid-state 55Mn NMR spectroscopy and DFT investigation of manganese pentacarbonyl compounds
Kirk W. Feindel, Kristopher J. Ooms and Roderick E. Wasylishen
PCCP(2007)9, 1226.
Abstract:
Central transition 55Mn NMR spectra of several solid manganese pentacarbonyls acquired at magnetic field strengths of 11.75, 17.63, and 21.1 T are presented. The variety of distinct powder sample lineshapes obtained demonstrates the sensitivity of solid-state 55Mn NMR to the local bonding environment, including the presence of crystallographically unique Mn sites, and facilitates the extraction of the Mn chemical shift anisotropies, CSAs, and the nuclear quadrupolar parameters. The compounds investigated include molecules with approximate C4v symmetry, LMn(CO)5(L = Cl, Br, I, HgMn(CO)5, CH3) and several molecules of lower symmetry (L = PhCH2, Ph3–nClnSn (n= 1, 2, 3)). For these compounds, the Mn CSA values range from <100>
Ultraslow Li diffusion in spinel-type structured Li4Ti5O12—A comparison of results from solid state NMR and impedance spectroscopy
Martin Wilkening, Roger Amade, Wojciech Iwaniak and Paul Heitjans
PCCP(2007)9,1239.
Abstract:
The cubic spinel oxides Li1+xTi2–xO4 (0 x 1/3) are promising anode materials for lithium-ion rechargeable batteries. The end member of the Li–Ti–O series, Li4Ti5O12, can accommodate Li ions up to the composition Li7Ti5O12. Whereas a number of studies focus on the electrochemical behaviour of Li insertion into and Li diffusion in the Li intercalated material, only few investigations about low-temperature Li dynamics in the non-intercalated host material Li4Ti5O12 have been reported so far. In the present paper, Li diffusion in pure-phase microcrystalline Li4Ti5O12 with an average particle size in the µm range was probed by 7Li solid state NMR spectroscopy using spin-alignment echo (SAE) and spin–lattice relaxation (SLR) measurements. Between T = 295 K and 400 K extremely slow Li jump rates –1 ranging from 1 s–1 to about 2200 s–1 were directly measured by recording the decay of spin-alignment echoes as a function of mixing time and constant evolution time. The results point out the slow Li diffusion in non-intercalated Li4Ti5O12·–1 (1/T) follows Arrhenius behaviour with an activation energy EASAE of about 0.86 eV. Interestingly, EASAE is comparable to activation energies deduced from conductivity measurements (0.94(1) eV) and from SLR measurements in the rotating frame (0.74(2) eV) rather than from those performed in the laboratory frame, EAlow-T = 0.26(1) eV at low T.
Monday, February 26, 2007
Concepts in NMR - update to Dec. 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 6, November 2006
pp. 369 - 383
Title: Operator formalisms: An overview
Author: Bain, Alex D.a
Affiliations: a. Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1
Keywords: operators; density matrix theory; spherical tensors; Cartesian tensors; single transition operators; quadrupolar echo; pulse sequences
Abstract (English):
Operator formalisms are mathematical recipes for simplifying the manipulations of the density matrix. Because the density matrix is a vital tool in describing and analyzing magnetic resonance experiments, many approaches have been developed. This article gives an overview of a number of different methods: spherical tensors, fictitious spin-1/2, single-transition operators, product operators, superspin methods, and others. In principle, they all must give the same answer, because an exact description of magnetic resonance phenomena is usually within reach. The choice of the formalism for the user, therefore, depends on various personal decisions. Among these decisions is the choice between spherical and Cartesian tensors, between Hilbert space and Liouville space, between commutators and matrix elements, and so on. We do not go into the details of any of the formalisms but rather try to compare their approaches at a fairly general level. The quadrupolar echo pulse sequence is used as an example of the application of the formalisms. The aim of this overview is to give readers enough of a picture so that they can make an intelligent choice for themselves. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 369–383, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 6, November 2006
pp. 384 - 409
Title: On the physical interpretation of density operators at the atomic scale: A thorough analysis of some simple cases
Author: Paniagua, Juan C.a
Affiliations: a. Departament de Química Física, Universitat de Barcelona, C. Martí i Franquès 1, E‐08028 Barcelona, Spain
Keywords: density operator; density matrix; coherences; phase coherence; physical interpretation
Abstract (English):
The physical meaning of the concepts underlying the density operator formalism are analyzed from different points of view. In particular, the diversity of ways of expressing the density operator of the simplest NMR sample is exploited to show that there are many molecular-scale physical pictures compatible with each macroscopic state, some of them being more useful than others for specific aims. Those corresponding to diagonal representations of the density matrix conform closely to classical-like pictures, which allow us to ignore the subtle effects of quantum interferences that are implicit in the concept of coherence. A widespread biconical picture that does not rely on a sound physical basis is shown to be quantitatively valid provided that ad hoc populations are chosen for the involved quantum states. The interpretation of the coefficients of the density operator expansion in terms of observable-related basis elements is discussed to show that the identification of these with the corresponding physical properties can be misleading in certain cases. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 384–409, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 5, September 2006
pp. 307 - 320
Title: A simple analytical model to describe dynamic magic-angle spinning experiments
Author: Hirschinger, Jérômea
Affiliations: a. Institut de Chimie, UMR 7177 CNRS, Université Louis Pasteur, BP 296, 67008 Strasbourg Cedex, France
Keywords: memory-function approach; Anderson-Weiss theory; magic-angle spinning; molecular motion; rotational-echo double-resonance (REDOR); solid-state NMR
Abstract (English):
A simple analytical method based on the memory-function approach and the Anderson-Weiss theory is presented for studying in a uniform way the spin dynamics in several NMR experiments performed under the conditions of magic-angle spinning (MAS). A series of 1H MAS spectra of adamantane serve as an example for a sample with homogeneous line broadening. A good agreement between experimental and calculated integral spinning sideband intensities for a spinning frequency ranging from 5 to 33 kHz is obtained using a sixth-order approximation of the theory. Moreover, this model, which is able to describe the NMR spectra in the presence of a rotationally diffusive isotropic and anisotropic Gaussian-Markoff process, allows the treatment of the combined effects of sample spinning and molecular motion. Finally, the application of MAS recoupling methods in the intermediate motional regime is examined by using the concept of refocusing pulses. It is shown that recoupling experiments such as rotational-echo double-resonance (REDOR) can still be applied in the presence of anisotropic molecular motion. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A, 28A: 307–320, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 5, September 2006
pp. 347 - 368
Title: The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations
Author: Stueber, Dirka
Affiliations: a. Department of Chemistry, Washington University, St. Louis, Missouri 60607‐7061
Keywords: NMR; nuclear magnetic shielding tensor; quantum mechanical shielding calculations; embedded ion method (EIM); intermolecular interactions; Ewald method; point charge arrays; electrostatic; crystal lattice effects
Abstract (English):
The nuclear magnetic shielding anisotropy of NMR active nuclei is highly sensitive to the nuclear electronic environment. Hence, measurements of the nuclear magnetic shielding anisotropy represent a powerful tool in the elucidation of molecular structure for a wide variety of materials. Quantum mechanical ab initio nuclear magnetic shielding calculations effectively complement the experimental NMR data by revealing additional structural information. The accuracy and capacity of these calculations has been improved considerably in recent years. However, the inherent problem of the limitation in the size of the systems that may be studied due to the relatively demanding computational requirements largely remains. Accordingly, ab initio shielding calculations have been performed predominantly on isolated molecules, neglecting the molecular environment. This approach is sufficient for neutral nonpolar systems, but leads to serious errors in the shielding calculations on polar and ionic systems. Conducting ab initio shielding calculations on clusters of molecules (i.e., including the nearest neighbor interactions) has improved the accuracy of the calculations in many cases. Other methods of simulating crystal lattice effects in shielding calculations that have been developed include the electrostatic representation of the crystal lattice using point charge arrays, full ab initio methods, ab initio methods under periodic boundary conditions, and hybrid ab initio/molecular dynamics methods. The embedded ion method (EIM) discussed here follows the electrostatic approach. The method mimics the intermolecular and interionic interactions experienced by a subject molecule or cluster in a given crystal in quantum mechanical shielding calculations with a large finite, periodic, and self-consistent array of point charges. The point charge arrays in the EIM are generated using the Ewald summation method and embed the molecule or ion of interest for which the ab initio shielding calculations are performed. The accuracy with which the EIM reproduces experimental nuclear magnetic shift tensor principal values, the sensitivity of the EIM to the parameters defining the point charge arrays, as well as the strengths and limitations of the EIM in comparison with other methods that include crystal lattice effects in chemical shielding calculations, are presented. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 347–368, 2006
Vol: 28A, Issue: 6, November 2006
pp. 369 - 383
Title: Operator formalisms: An overview
Author: Bain, Alex D.a
Affiliations: a. Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4M1
Keywords: operators; density matrix theory; spherical tensors; Cartesian tensors; single transition operators; quadrupolar echo; pulse sequences
Abstract (English):
Operator formalisms are mathematical recipes for simplifying the manipulations of the density matrix. Because the density matrix is a vital tool in describing and analyzing magnetic resonance experiments, many approaches have been developed. This article gives an overview of a number of different methods: spherical tensors, fictitious spin-1/2, single-transition operators, product operators, superspin methods, and others. In principle, they all must give the same answer, because an exact description of magnetic resonance phenomena is usually within reach. The choice of the formalism for the user, therefore, depends on various personal decisions. Among these decisions is the choice between spherical and Cartesian tensors, between Hilbert space and Liouville space, between commutators and matrix elements, and so on. We do not go into the details of any of the formalisms but rather try to compare their approaches at a fairly general level. The quadrupolar echo pulse sequence is used as an example of the application of the formalisms. The aim of this overview is to give readers enough of a picture so that they can make an intelligent choice for themselves. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 369–383, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 6, November 2006
pp. 384 - 409
Title: On the physical interpretation of density operators at the atomic scale: A thorough analysis of some simple cases
Author: Paniagua, Juan C.a
Affiliations: a. Departament de Química Física, Universitat de Barcelona, C. Martí i Franquès 1, E‐08028 Barcelona, Spain
Keywords: density operator; density matrix; coherences; phase coherence; physical interpretation
Abstract (English):
The physical meaning of the concepts underlying the density operator formalism are analyzed from different points of view. In particular, the diversity of ways of expressing the density operator of the simplest NMR sample is exploited to show that there are many molecular-scale physical pictures compatible with each macroscopic state, some of them being more useful than others for specific aims. Those corresponding to diagonal representations of the density matrix conform closely to classical-like pictures, which allow us to ignore the subtle effects of quantum interferences that are implicit in the concept of coherence. A widespread biconical picture that does not rely on a sound physical basis is shown to be quantitatively valid provided that ad hoc populations are chosen for the involved quantum states. The interpretation of the coefficients of the density operator expansion in terms of observable-related basis elements is discussed to show that the identification of these with the corresponding physical properties can be misleading in certain cases. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 384–409, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 5, September 2006
pp. 307 - 320
Title: A simple analytical model to describe dynamic magic-angle spinning experiments
Author: Hirschinger, Jérômea
Affiliations: a. Institut de Chimie, UMR 7177 CNRS, Université Louis Pasteur, BP 296, 67008 Strasbourg Cedex, France
Keywords: memory-function approach; Anderson-Weiss theory; magic-angle spinning; molecular motion; rotational-echo double-resonance (REDOR); solid-state NMR
Abstract (English):
A simple analytical method based on the memory-function approach and the Anderson-Weiss theory is presented for studying in a uniform way the spin dynamics in several NMR experiments performed under the conditions of magic-angle spinning (MAS). A series of 1H MAS spectra of adamantane serve as an example for a sample with homogeneous line broadening. A good agreement between experimental and calculated integral spinning sideband intensities for a spinning frequency ranging from 5 to 33 kHz is obtained using a sixth-order approximation of the theory. Moreover, this model, which is able to describe the NMR spectra in the presence of a rotationally diffusive isotropic and anisotropic Gaussian-Markoff process, allows the treatment of the combined effects of sample spinning and molecular motion. Finally, the application of MAS recoupling methods in the intermediate motional regime is examined by using the concept of refocusing pulses. It is shown that recoupling experiments such as rotational-echo double-resonance (REDOR) can still be applied in the presence of anisotropic molecular motion. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A, 28A: 307–320, 2006
Concepts in Magnetic Resonance Part A
Vol: 28A, Issue: 5, September 2006
pp. 347 - 368
Title: The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations
Author: Stueber, Dirka
Affiliations: a. Department of Chemistry, Washington University, St. Louis, Missouri 60607‐7061
Keywords: NMR; nuclear magnetic shielding tensor; quantum mechanical shielding calculations; embedded ion method (EIM); intermolecular interactions; Ewald method; point charge arrays; electrostatic; crystal lattice effects
Abstract (English):
The nuclear magnetic shielding anisotropy of NMR active nuclei is highly sensitive to the nuclear electronic environment. Hence, measurements of the nuclear magnetic shielding anisotropy represent a powerful tool in the elucidation of molecular structure for a wide variety of materials. Quantum mechanical ab initio nuclear magnetic shielding calculations effectively complement the experimental NMR data by revealing additional structural information. The accuracy and capacity of these calculations has been improved considerably in recent years. However, the inherent problem of the limitation in the size of the systems that may be studied due to the relatively demanding computational requirements largely remains. Accordingly, ab initio shielding calculations have been performed predominantly on isolated molecules, neglecting the molecular environment. This approach is sufficient for neutral nonpolar systems, but leads to serious errors in the shielding calculations on polar and ionic systems. Conducting ab initio shielding calculations on clusters of molecules (i.e., including the nearest neighbor interactions) has improved the accuracy of the calculations in many cases. Other methods of simulating crystal lattice effects in shielding calculations that have been developed include the electrostatic representation of the crystal lattice using point charge arrays, full ab initio methods, ab initio methods under periodic boundary conditions, and hybrid ab initio/molecular dynamics methods. The embedded ion method (EIM) discussed here follows the electrostatic approach. The method mimics the intermolecular and interionic interactions experienced by a subject molecule or cluster in a given crystal in quantum mechanical shielding calculations with a large finite, periodic, and self-consistent array of point charges. The point charge arrays in the EIM are generated using the Ewald summation method and embed the molecule or ion of interest for which the ab initio shielding calculations are performed. The accuracy with which the EIM reproduces experimental nuclear magnetic shift tensor principal values, the sensitivity of the EIM to the parameters defining the point charge arrays, as well as the strengths and limitations of the EIM in comparison with other methods that include crystal lattice effects in chemical shielding calculations, are presented. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 347–368, 2006
JMR: Journal of Magnetic Resonance update to February 2007
Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 322-329
Title: Improved resolution in 13C solid-state spectra through spin-state-selection
Authors: Verel, Renéa; Manolikas, Theofanisa; Siemer, Ansgar B.a; Meier, Beat H.a
Affiliations: a. Physical Chemistry, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
Keywords: Solid-state NMR; Spin-state selection; High resolution
Abstract (English):
The application of a spin-state-selective coherence transfer experiment (INADEQUATE-SSS) to solid-state NMR spectroscopy is described. Two-dimensional 13C double-quantum/single-quantum spectra without J splittings in both dimensions lead to enhanced spectral resolution. The method is demonstrated to significantly improve the spectral resolution of the crowded C’–Ca region of two proteins.
Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 350-356
Title: Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation
Authors: Wickramasinghe, Nalinda P.a; Kotecha, Mrignayania; Samoson, Agob; Past, Jaanb; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, 845 W Taylor St., Chicago, IL 60607, USA
b. National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Keywords: Solid-state NMR; Protein microcrystal; T1 relaxation; Paramagnetic doping; 13C CPMAS
Abstract (English):
We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4–0.8s to 60–70ms for ubiquitin and lysozyme in D2O in the presence of 10mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4–2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0–8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 1-14
Title: HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids
Authors: Amoureux, J.P.a; Trebosc, J.a; Wiench, J.b; Pruski, M.b
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, Fr-59652 Villeneuve d’Ascq, France
b. Ames Laboratory, Iowa State University, Ames, IA 50011, USA
Keywords: Solid-state NMR; J-coupling; R-INEPT; HMQC; Quadrupolar nuclei; MAS; MQMAS; STMAS
Abstract (English):
Hetero-nuclear coherence transfers in HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids are analyzed. 1D and 2D schemes are considered under MAS for the general case of multi-spin systems SIn (n4), where S is an observed nucleus. These results are also discussed in the context of high-resolution schemes featuring MQMAS or STMAS. The theoretical predictions are verified experimentally in a series of 1D and 2D experiments performed at 9.4 and 18.8T.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 15-19
Title: Three-dimensional through-bond homonuclear–heteronuclear correlation experiments for quadrupolar nuclei in solid-state NMR applied to 27Al–O–31P–O–27Al networks
Authors: Deschamps, Michaëla; Massiot, Dominiquea
Affiliations: a. CRMHT-CNRS, 1D Avenue de la Recherche Scientifique, 45071 ORLEANS cedex 2, France
Keywords: 3D; J-coupling; Quadrupolar nuclei; Aluminium; Phosphate
Abstract (English):
We present here the first 3D homonuclear/heteronuclear correlation experiment applied to quadrupolar nuclei and making use of the sole scalar J-coupling. This experiment, based on the 2D-Homonuclear–Heteronuclear Single Quantum Correlation (H–HSQC) experiment, uses a relayed transfer from the 27Al central transition to neighbouring 31P spins and to the central transition of a second 27Al. It confirms the correlation map characterizing the two 27Al and the 31P NMR signatures of 27Al–O–31P–O–27Al chemically bonded molecular motifs.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 39-43
Title: 13C/14N heteronuclear multiple-quantum correlation with rotary resonance and REDOR dipolar recoupling
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: 13C/14N Correlation; HMQC; Dipolar recoupling; MAS; Rotary resonance; REDOR
Abstract (English):
A two-dimensional 13C/14N heteronuclear multiple quantum correlation (HMQC) experiment using dipolar recoupling under magic-angle spinning (MAS) is described. The experiment is an extension of the recent indirect 13C detection scheme for measuring 14N quadrupolar coupling under MAS. The recoupling allows the direct use of the much larger dipolar interaction instead of the small J and residual dipolar couplings for establishing 13C/14N correlations. Two recoupling methods are incorporated into the HMQC sequence, both applying rf only to the observed 13C spin. The first one uses the REDOR sequence with two p-pulses per rotor cycle. The second one uses a cw rf field matching the spinning frequency, known as rotary resonance. The effects of CSA, Formula Not Shown signal loss, MAS frequency and stability and t1-noise are compared and discussed.
Journal of Magnetic Resonance
Vol: 183, Issue: 2, December, 2006
pp. 235-241
Title: Rotary resonance echo double resonance for measuring heteronuclear dipolar coupling under MAS
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: Rotary resonance; R-REDOR; REDOR; MAS; Dipolar coupling
Abstract (English):
A rotary resonance echo double resonance (R-REDOR) experiment is described for measuring heteronuclear dipolar coupling under magic-angle spinning. Rotary resonance reintroduces both dipolar coupling and chemical shift anisotropy with an rf field matching the spinning frequency. The resonance effect from chemical shift anisotropy can be refocused with a rotary resonance echo. The R-REDOR experiment thus measures the dephasing of the rotary resonance echo from the heteronuclear dipolar coupling to determine the dipolar coupling constant. The rotary resonance experiment is suitable for measuring dipolar coupling with quadrupolar nuclei because it applies the recoupling rf only to the observed spin-1/2. The rotary resonance scheme has the advantages of a long Formula Not Shown and susceptible to spinning frequency fluctuation.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 68-76
Title: Polarization transfer from remote protons in 13C CP/MAS
Authors: Tripon, Carmena; Aluas, Mihaelab; Filip, Xeniaa; Filip, Claudiua
Affiliations: a. National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania
b. Physics Department, Babes-Bolyai University, Cluj, Romania
Keywords: Solid-state NMR; Cross-polarization; CP/MAS; Spin dynamics
Abstract (English):
An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C–1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH2 and CH3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of l-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 123-133
Title: Bayesian and information theory analysis of MAS sideband patterns in spin 1/2 systems
Author: Sachleben, Joseph R.a
Affiliations: a. Department of Chemistry, Otterbein College, Westerville, OH 43081, USA
Keywords: Magic angle spinning; Errors; Bayesian analysis; Chemical shift tensor
Abstract (English):
Bayesian statistics and information theory are used to analyze the reliability of extracting chemical shift parameters from spinning sideband patterns of spin 1/2 systems. Efficient code has been written to calculate the two-dimensional posterior probability as a function of the chemical shift anisotropy, d, and the asymmetry parameter, , given the sideband intensities and the signal-to-noise ratio. This method has the advantage of assuming only that the noise in the sideband intensities is distributed as a Gaussian. It assumes nothing about the distribution of the values of parameters d and , which are shown in some cases to be highly non-Gaussian. The utility of Bayesian analysis is demonstrated on 1D slow-spinning MAS spectra and on sideband patterns extracted from 2D PASS spectra. Previous investigations have shown that there is an optimal range of spinning frequencies for determining d. In this study, information theory is used to determine the signal-to-noise ratio dependence of the entropy in d, , and total entropy in spinning sideband spectra. The entropy is a measure of the information content of a probability distribution. When the entropy is zero, there is perfect information on a system, while if it is infinite, there is no information on the system. It is found that for all values of and for signal-to-noise ratios in the range 50–1000, an entropy minimum in nd/nr occurs for values 1.5nd/nr3. In the same range of signal-to-noise ratios, the entropy in is a monotonically decreasing function of nd/nr. The global information content of a spinning sideband pattern (i.e., the total entropy) is dependent on the signal-to-noise ratio and has an optimal value at nd/nr2 at a signal-to-noise ratio of 50 and increasing to 2.5 for signal-to-noise ratios of 1000. Finally, the increase of information in a sideband pattern as a function of the number of sidebands used in the analysis is examined. Most of the information about d and is contained in the five central sidebands; i.e., sidebands -2 to 2.
Vol: 184, Issue: 2, February, 2007
pp. 322-329
Title: Improved resolution in 13C solid-state spectra through spin-state-selection
Authors: Verel, Renéa; Manolikas, Theofanisa; Siemer, Ansgar B.a; Meier, Beat H.a
Affiliations: a. Physical Chemistry, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
Keywords: Solid-state NMR; Spin-state selection; High resolution
Abstract (English):
The application of a spin-state-selective coherence transfer experiment (INADEQUATE-SSS) to solid-state NMR spectroscopy is described. Two-dimensional 13C double-quantum/single-quantum spectra without J splittings in both dimensions lead to enhanced spectral resolution. The method is demonstrated to significantly improve the spectral resolution of the crowded C’–Ca region of two proteins.
Journal of Magnetic Resonance
Vol: 184, Issue: 2, February, 2007
pp. 350-356
Title: Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation
Authors: Wickramasinghe, Nalinda P.a; Kotecha, Mrignayania; Samoson, Agob; Past, Jaanb; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, 845 W Taylor St., Chicago, IL 60607, USA
b. National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia
Keywords: Solid-state NMR; Protein microcrystal; T1 relaxation; Paramagnetic doping; 13C CPMAS
Abstract (English):
We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T1 values can be reduced from 0.4–0.8s to 60–70ms for ubiquitin and lysozyme in D2O in the presence of 10mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T1 attained by paramagnetic doping provided sensitivity enhancements of 1.4–2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0–8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 1-14
Title: HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids
Authors: Amoureux, J.P.a; Trebosc, J.a; Wiench, J.b; Pruski, M.b
Affiliations: a. UCCS, CNRS-8181, ENSCL-USTL, Fr-59652 Villeneuve d’Ascq, France
b. Ames Laboratory, Iowa State University, Ames, IA 50011, USA
Keywords: Solid-state NMR; J-coupling; R-INEPT; HMQC; Quadrupolar nuclei; MAS; MQMAS; STMAS
Abstract (English):
Hetero-nuclear coherence transfers in HMQC and refocused-INEPT experiments involving half-integer quadrupolar nuclei in solids are analyzed. 1D and 2D schemes are considered under MAS for the general case of multi-spin systems SIn (n4), where S is an observed nucleus. These results are also discussed in the context of high-resolution schemes featuring MQMAS or STMAS. The theoretical predictions are verified experimentally in a series of 1D and 2D experiments performed at 9.4 and 18.8T.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 15-19
Title: Three-dimensional through-bond homonuclear–heteronuclear correlation experiments for quadrupolar nuclei in solid-state NMR applied to 27Al–O–31P–O–27Al networks
Authors: Deschamps, Michaëla; Massiot, Dominiquea
Affiliations: a. CRMHT-CNRS, 1D Avenue de la Recherche Scientifique, 45071 ORLEANS cedex 2, France
Keywords: 3D; J-coupling; Quadrupolar nuclei; Aluminium; Phosphate
Abstract (English):
We present here the first 3D homonuclear/heteronuclear correlation experiment applied to quadrupolar nuclei and making use of the sole scalar J-coupling. This experiment, based on the 2D-Homonuclear–Heteronuclear Single Quantum Correlation (H–HSQC) experiment, uses a relayed transfer from the 27Al central transition to neighbouring 31P spins and to the central transition of a second 27Al. It confirms the correlation map characterizing the two 27Al and the 31P NMR signatures of 27Al–O–31P–O–27Al chemically bonded molecular motifs.
Journal of Magnetic Resonance
Vol: 184, Issue: 1, January, 2007
pp. 39-43
Title: 13C/14N heteronuclear multiple-quantum correlation with rotary resonance and REDOR dipolar recoupling
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: 13C/14N Correlation; HMQC; Dipolar recoupling; MAS; Rotary resonance; REDOR
Abstract (English):
A two-dimensional 13C/14N heteronuclear multiple quantum correlation (HMQC) experiment using dipolar recoupling under magic-angle spinning (MAS) is described. The experiment is an extension of the recent indirect 13C detection scheme for measuring 14N quadrupolar coupling under MAS. The recoupling allows the direct use of the much larger dipolar interaction instead of the small J and residual dipolar couplings for establishing 13C/14N correlations. Two recoupling methods are incorporated into the HMQC sequence, both applying rf only to the observed 13C spin. The first one uses the REDOR sequence with two p-pulses per rotor cycle. The second one uses a cw rf field matching the spinning frequency, known as rotary resonance. The effects of CSA, Formula Not Shown signal loss, MAS frequency and stability and t1-noise are compared and discussed.
Journal of Magnetic Resonance
Vol: 183, Issue: 2, December, 2006
pp. 235-241
Title: Rotary resonance echo double resonance for measuring heteronuclear dipolar coupling under MAS
Author: Gan, Zhehonga
Affiliations: a. Center of Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA
Keywords: Rotary resonance; R-REDOR; REDOR; MAS; Dipolar coupling
Abstract (English):
A rotary resonance echo double resonance (R-REDOR) experiment is described for measuring heteronuclear dipolar coupling under magic-angle spinning. Rotary resonance reintroduces both dipolar coupling and chemical shift anisotropy with an rf field matching the spinning frequency. The resonance effect from chemical shift anisotropy can be refocused with a rotary resonance echo. The R-REDOR experiment thus measures the dephasing of the rotary resonance echo from the heteronuclear dipolar coupling to determine the dipolar coupling constant. The rotary resonance experiment is suitable for measuring dipolar coupling with quadrupolar nuclei because it applies the recoupling rf only to the observed spin-1/2. The rotary resonance scheme has the advantages of a long Formula Not Shown and susceptible to spinning frequency fluctuation.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 68-76
Title: Polarization transfer from remote protons in 13C CP/MAS
Authors: Tripon, Carmena; Aluas, Mihaelab; Filip, Xeniaa; Filip, Claudiua
Affiliations: a. National Institute for R&D of Isotopic and Molecular Technologies, P.O. Box 700, 400293 Cluj, Romania
b. Physics Department, Babes-Bolyai University, Cluj, Romania
Keywords: Solid-state NMR; Cross-polarization; CP/MAS; Spin dynamics
Abstract (English):
An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C–1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH2 and CH3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of l-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.
Journal of Magnetic Resonance
Vol: 183, Issue: 1, November, 2006
pp. 123-133
Title: Bayesian and information theory analysis of MAS sideband patterns in spin 1/2 systems
Author: Sachleben, Joseph R.a
Affiliations: a. Department of Chemistry, Otterbein College, Westerville, OH 43081, USA
Keywords: Magic angle spinning; Errors; Bayesian analysis; Chemical shift tensor
Abstract (English):
Bayesian statistics and information theory are used to analyze the reliability of extracting chemical shift parameters from spinning sideband patterns of spin 1/2 systems. Efficient code has been written to calculate the two-dimensional posterior probability as a function of the chemical shift anisotropy, d, and the asymmetry parameter, , given the sideband intensities and the signal-to-noise ratio. This method has the advantage of assuming only that the noise in the sideband intensities is distributed as a Gaussian. It assumes nothing about the distribution of the values of parameters d and , which are shown in some cases to be highly non-Gaussian. The utility of Bayesian analysis is demonstrated on 1D slow-spinning MAS spectra and on sideband patterns extracted from 2D PASS spectra. Previous investigations have shown that there is an optimal range of spinning frequencies for determining d. In this study, information theory is used to determine the signal-to-noise ratio dependence of the entropy in d, , and total entropy in spinning sideband spectra. The entropy is a measure of the information content of a probability distribution. When the entropy is zero, there is perfect information on a system, while if it is infinite, there is no information on the system. It is found that for all values of and for signal-to-noise ratios in the range 50–1000, an entropy minimum in nd/nr occurs for values 1.5nd/nr3. In the same range of signal-to-noise ratios, the entropy in is a monotonically decreasing function of nd/nr. The global information content of a spinning sideband pattern (i.e., the total entropy) is dependent on the signal-to-noise ratio and has an optimal value at nd/nr2 at a signal-to-noise ratio of 50 and increasing to 2.5 for signal-to-noise ratios of 1000. Finally, the increase of information in a sideband pattern as a function of the number of sidebands used in the analysis is examined. Most of the information about d and is contained in the five central sidebands; i.e., sidebands -2 to 2.
MRC: Magnetic Resonance in Chemitry - Update to February 2007
Magnetic Resonance in Chemistry
Vol: 45, Issue: 2, February 2007
pp. 118 - 122
Title: Structure of a paramagnetic supermicroporous silica-based material via a multinuclear solid-state NMR monitoring
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&hyphen;3012, USA
Keywords: 29Si; 27Al; 1H; 13C MAS NMR; paramagnetic solids; T1 relaxation; porous materials
Abstract (English):
The paramagnetic Si/Al material doped with 19.8% (weight) of Mn2+ has been characterized by the 1H, 13C, 27Al, 29Si MAS NMR spectra and the 1H, 29Si T1MAS relaxation measurements as a gel dried at 130 °C and as samples calcined at 504, 540 and 650 °C. It has been demonstrated that in spite of strong paramagnetic effects, NMR monitoring in combination with 29Si T1 relaxation experiments can be successful for structural descriptions of porous materials. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 45, Issue: 1, January 2007
pp. 5 - 23
Title: Structural elucidation of nitro-substituted five-membered aromatic heterocycles utilizing GIAO DFT calculations
Authors: Katritzky, Alan R.a; Akhmedov, Novruz G.a; Doskocz, Jacekb; Hall, C. Dennisa; Akhmedova, Rena G.a; Majumder, Sumana
Affiliations: a. Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611‐7200, USA
b. Faculty of Bioorganic Chemistry, Department of Chemistry, Wroclaw University of Technology, Wybrzeże Wyspiańkiego 27, 50‐370, Wroc3aw, Poland
Keywords: GIAO; long-range coupling constants; five-membered heterocycles; proton-coupled 13C NMR spectra
Abstract (English):
The GIAO (Gauge Including Atomic Orbitals) DFT (Density Functional Theory) method is applied at the B3LYP/6–31+G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311++G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311+G (2d,p)//B3LYP/6–31+G(d) and B3LYP/6–311++G(d,p)//B3LYP/6–311++G(d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants for 25 nitro-substituted five-membered heterocycles. Difference (1D NOE) spectra in combination with long-range gHMBC experiments were used as tools for the structural elucidation of nitro-substituted five-membered heterocycles. The assigned NMR data (chemical shifts and coupling constants) for all compounds were found to be in good agreement with theoretical calculations using the GIAO DFT method. The magnitudes of one-bond (1JCH) and long-range (nJCH, n > 1) coupling constants were utilized for unambiguous differentiation between regioisomers of nitro-substituted five-membered heterocycles. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 985 - 988
Title: 29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, College Station, Texas 77842&hyphen;3012, USA
Keywords: 29Si MAS NMR; T1 relaxation; microporous materials
Abstract (English):
The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1–6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2–4 with relatively small Mn2+ contents. Because the relaxation curves for 1–6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (£2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 989 - 1007
Title: Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac—[Ru(CO)3I3]-
Authors: Autschbach, Jochena; Zheng, Shaohuia
Affiliations: a. Department of Chemistry, 312 NSC, State University of New York at Buffalo, Buffalo, NY 14260‐3000, USA
Keywords: density functional theory; computational chemistry; ruthenium; solvent effects; relativistic effects
Abstract (English):
Solvent effects on the 99Ru NMR chemical shift of the complex fac—[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac—[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 10, October 2006
pp. 909 - 916
Title: 7Li and 13C solid-state NMR spectra of lithium cuprates
Authors: Jost, Steffena; Kühnen, Martina; Günther, Haralda
Affiliations: a. University of Siegen, FB 8, OC II, D‐57068 Siegen, Germany
Keywords: NMR; solid-state NMR; 7Li NMR; 13C NMR; quadrupole interaction; ion pairs; SIP; CIP; organolithium compounds
Abstract (English):
7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures—lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4-[tris(trimethylsilyl) methyl]2 cuprate (3)—have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, c(7Li), and the asymmetry parameters of the quadrupolar interactions, (7Li), as well as the 6, 7Li and 13C chemical shifts. The c(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd.
Vol: 45, Issue: 2, February 2007
pp. 118 - 122
Title: Structure of a paramagnetic supermicroporous silica-based material via a multinuclear solid-state NMR monitoring
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&hyphen;3012, USA
Keywords: 29Si; 27Al; 1H; 13C MAS NMR; paramagnetic solids; T1 relaxation; porous materials
Abstract (English):
The paramagnetic Si/Al material doped with 19.8% (weight) of Mn2+ has been characterized by the 1H, 13C, 27Al, 29Si MAS NMR spectra and the 1H, 29Si T1MAS relaxation measurements as a gel dried at 130 °C and as samples calcined at 504, 540 and 650 °C. It has been demonstrated that in spite of strong paramagnetic effects, NMR monitoring in combination with 29Si T1 relaxation experiments can be successful for structural descriptions of porous materials. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 45, Issue: 1, January 2007
pp. 5 - 23
Title: Structural elucidation of nitro-substituted five-membered aromatic heterocycles utilizing GIAO DFT calculations
Authors: Katritzky, Alan R.a; Akhmedov, Novruz G.a; Doskocz, Jacekb; Hall, C. Dennisa; Akhmedova, Rena G.a; Majumder, Sumana
Affiliations: a. Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611‐7200, USA
b. Faculty of Bioorganic Chemistry, Department of Chemistry, Wroclaw University of Technology, Wybrzeże Wyspiańkiego 27, 50‐370, Wroc3aw, Poland
Keywords: GIAO; long-range coupling constants; five-membered heterocycles; proton-coupled 13C NMR spectra
Abstract (English):
The GIAO (Gauge Including Atomic Orbitals) DFT (Density Functional Theory) method is applied at the B3LYP/6–31+G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311++G(d,p)//B3LYP/6–31+G(d), B3LYP/6–311+G (2d,p)//B3LYP/6–31+G(d) and B3LYP/6–311++G(d,p)//B3LYP/6–311++G(d,p) levels of theory for the calculation of proton and carbon chemicals shifts and coupling constants for 25 nitro-substituted five-membered heterocycles. Difference (1D NOE) spectra in combination with long-range gHMBC experiments were used as tools for the structural elucidation of nitro-substituted five-membered heterocycles. The assigned NMR data (chemical shifts and coupling constants) for all compounds were found to be in good agreement with theoretical calculations using the GIAO DFT method. The magnitudes of one-bond (1JCH) and long-range (nJCH, n > 1) coupling constants were utilized for unambiguous differentiation between regioisomers of nitro-substituted five-membered heterocycles. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 985 - 988
Title: 29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, College Station, Texas 77842&hyphen;3012, USA
Keywords: 29Si MAS NMR; T1 relaxation; microporous materials
Abstract (English):
The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1–6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.8 (4), 15 (5) and 19.8 wt% (6). It has been found that the central lines, corresponding to isotropic chemical shifts, and their sidebands relax differently in samples 2–4 with relatively small Mn2+ contents. Because the relaxation curves for 1–6 are nonexponential and identical for 6 at spinning rates of 5, 10 and 12 kHz, dipolar relaxation via the paramagnetic centers is dominant. The relaxation data have been interpreted as a function of Mn2+ concentrations in terms of incorporation of the Mn2+ ions into the silica lattice when their concentration is small (£2.5 wt%). At higher concentrations, most of the manganese is located on the surface of the silica. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 11, November 2006
pp. 989 - 1007
Title: Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac—[Ru(CO)3I3]-
Authors: Autschbach, Jochena; Zheng, Shaohuia
Affiliations: a. Department of Chemistry, 312 NSC, State University of New York at Buffalo, Buffalo, NY 14260‐3000, USA
Keywords: density functional theory; computational chemistry; ruthenium; solvent effects; relativistic effects
Abstract (English):
Solvent effects on the 99Ru NMR chemical shift of the complex fac—[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac—[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional. Copyright © 2006 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Vol: 44, Issue: 10, October 2006
pp. 909 - 916
Title: 7Li and 13C solid-state NMR spectra of lithium cuprates
Authors: Jost, Steffena; Kühnen, Martina; Günther, Haralda
Affiliations: a. University of Siegen, FB 8, OC II, D‐57068 Siegen, Germany
Keywords: NMR; solid-state NMR; 7Li NMR; 13C NMR; quadrupole interaction; ion pairs; SIP; CIP; organolithium compounds
Abstract (English):
7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures—lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4-[tris(trimethylsilyl) methyl]2 cuprate (3)—have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, c(7Li), and the asymmetry parameters of the quadrupolar interactions, (7Li), as well as the 6, 7Li and 13C chemical shifts. The c(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd.
Progress in NMR - update to Jan. 30, 2007
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 50, Issue: 1, January 30, 2007
pp. 1-50
Title: NMR in chiral and achiral smectic phases: Structure, orientational order and dynamics
Authors: Domenici, Valentinaa; Geppi, Marcoa; Veracini, Carlo Albertoa
Affiliations: a. Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy
Keywords: Smectic; NMR; Carbon 13; Proton; Deuterium; Liquid crystals; Chirality; Relaxation
Abstract: No Abstract
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 49, Issue: 3-4, November 30, 2006
pp. 169-206
Title: The use of NMR spectroscopy to study tautomerism
Authors: Claramunt, R.M.a; López, C.a; Santa María, M.D.a; Sanz, D.a; Elguero, J.a
Affiliations: a. Departamento de Quı´mica Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey, 9, E-28040 Madrid, Spain
Keywords: NMR; Tautomerism; Prototropy; CPMAS NMR
Vol: 50, Issue: 1, January 30, 2007
pp. 1-50
Title: NMR in chiral and achiral smectic phases: Structure, orientational order and dynamics
Authors: Domenici, Valentinaa; Geppi, Marcoa; Veracini, Carlo Albertoa
Affiliations: a. Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy
Keywords: Smectic; NMR; Carbon 13; Proton; Deuterium; Liquid crystals; Chirality; Relaxation
Abstract: No Abstract
Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 49, Issue: 3-4, November 30, 2006
pp. 169-206
Title: The use of NMR spectroscopy to study tautomerism
Authors: Claramunt, R.M.a; López, C.a; Santa María, M.D.a; Sanz, D.a; Elguero, J.a
Affiliations: a. Departamento de Quı´mica Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey, 9, E-28040 Madrid, Spain
Keywords: NMR; Tautomerism; Prototropy; CPMAS NMR
Solid-State NMR Update - October 2006
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 125-129
Title: 3-Methylglutaric acid as a 13C solid-state NMR standard
Authors: Barich, Dewey H.a; Gorman, Eric M.a; Zell, Mark T.b; Munson, Eric J.a
Affiliations: a. Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Ave., Lawrence, KS 66047, USA
b. Pfizer Global Research and Development, Analytical Research and Development, 2800 Plymouth Road, Ann Arbor, MI 48105, USA
Abstract (English):
The calibration of a solid-state NMR spectrometer requires setting the magic angle, setting the reference and decoupler frequencies, ensuring that the magnetic field is homogeneous across the sample volume, optimizing the signal-to-noise ratio, determining the p/2 pulse durations, and optimizing the Hartman–Hahn matching condition. Each task has one or more widely accepted standards, such as potassium bromide for setting the magic angle, adamantane for optimizing magnet homogeneity, and hexamethylbenzene or glycine for measuring the signal-to-noise ratio. We show that all of these tasks can be performed using 3-methylglutaric acid (MGA). In the case of high-powered decoupling, the CH2 and CH carbon peaks of MGA provide an opportunity to evaluate the decoupling in a manner that is superior to any of the commonly used standard compounds. Thus, MGA can be used as a single solid-state NMR standard compound to perform all calibration steps except for magnet shimming.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 130-134
Title: Decoupling residual dipolar coupling between 13C and14N spin pairs in CPMAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
Abstract (English):
Decoupling of the residual dipolar coupling between 13C and14N nuclei is investigated experimentally in a triple resonance experiment. It is shown that pulsed decoupling can be used to give enhanced sensitivity and reduced line widths and the technique is illustrated using short peptides.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 162-170
Title: Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline g-glycine
Authors: Yamada, Kazuhikoa; Honda, Hisashib; Yamazaki, Toshioa; Yoshida, Mitsuruc
Affiliations: a. NMR Spectroscopy Team, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama-shi, Kanagawa-ken 230-0045, Japan
b. International Graduate School of Arts and Sciences, Yokohama City University, 22-2 Seto, Kanawaza, Yokohama 236-0027, Japan
c. Analytical Science Division, National Food Research Institute, 2-1-12 Kannondai, Tsukuba 305-8642, Japan
Keywords: Solid-state 17O NMR; Chemical shielding tensor; Electric-field-gradient tensor; g-glycine
Abstract (English):
We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline g-glycine. Analysis of magic-angle spinning (MAS) and stationary 17O NMR spectra of [17O]-g-glycine obtained at 9.4, 14.1, 16.4, and 18.8T yields the magnitudes of the 17O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree–Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that 17O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary 17O NMR spectra.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 171-181
Title: Vanadium-51 solid-state NMR electric field gradient tensors: A DFT-embedded ion and isolated cluster study of crystalline vanadium oxides
Author: Gee, Becky A.a
Affiliations: a. Department of Chemistry and Biochemistry, 1 University Plaza, Long Island University, Brooklyn Campus, Brooklyn, NY 11201, USA
Keywords: Vanadium-51; Nuclear magnetic resonance (NMR); Density functional theory (DFT); Embedded ion; Embedded cluster; Electric field gradient (EFG); Quadrupole coupling; Orthovanadates; Vanadium oxides
Abstract (English):
Density functional theory (DFT) calculations (6–311+G(2d,p)/B3LYP level of theory) of 51V electric field gradient (EFG) tensor elements are performed for embedded and isolated cluster models of orthovanadates. The structural models used to calculate the EFGs of 51V are (I) an isolated H4VO4+ cluster, (II) an isolated HnVO4n-3 cluster (n=number of next-neighbor cations) (III) an isolated orthovanadate anion, VO4-x, and (IV) a VO4-x ion embedded in a finite point-charge array whose electrostatic potential, at the embedded ion, is equivalent to that of the infinite lattice. For models III and IV, a charge x is assigned estimating the covalence of the system. Models III and IV provide results in good agreement with the experiment. Calculations, employing the embedded and isolated VO4-x models, are used to discuss site assignments for AlVO4. Correlations between quadrupole coupling parameters and deviations of the orthovanadate structure from ideal tetrahedral symmetry are shown.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 198-202
Title: First evidence of multiple Ca sites in amorphous slag structure: Multiple-quantum MAS NMR spectroscopy on calcium-43 at high magnetic field
Authors: Shimoda, Keijia; Tobu, Yasuhiroa; Kanehashi, Kojia; Nemoto, Takahirob; Saito, Kojia
Affiliations: a. Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Japan
b. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
Abstract: No Abstract
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.
Vol: 30, Issue: 3-4, October, 2006
pp. 125-129
Title: 3-Methylglutaric acid as a 13C solid-state NMR standard
Authors: Barich, Dewey H.a; Gorman, Eric M.a; Zell, Mark T.b; Munson, Eric J.a
Affiliations: a. Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Ave., Lawrence, KS 66047, USA
b. Pfizer Global Research and Development, Analytical Research and Development, 2800 Plymouth Road, Ann Arbor, MI 48105, USA
Abstract (English):
The calibration of a solid-state NMR spectrometer requires setting the magic angle, setting the reference and decoupler frequencies, ensuring that the magnetic field is homogeneous across the sample volume, optimizing the signal-to-noise ratio, determining the p/2 pulse durations, and optimizing the Hartman–Hahn matching condition. Each task has one or more widely accepted standards, such as potassium bromide for setting the magic angle, adamantane for optimizing magnet homogeneity, and hexamethylbenzene or glycine for measuring the signal-to-noise ratio. We show that all of these tasks can be performed using 3-methylglutaric acid (MGA). In the case of high-powered decoupling, the CH2 and CH carbon peaks of MGA provide an opportunity to evaluate the decoupling in a manner that is superior to any of the commonly used standard compounds. Thus, MGA can be used as a single solid-state NMR standard compound to perform all calibration steps except for magnet shimming.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 130-134
Title: Decoupling residual dipolar coupling between 13C and14N spin pairs in CPMAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
Abstract (English):
Decoupling of the residual dipolar coupling between 13C and14N nuclei is investigated experimentally in a triple resonance experiment. It is shown that pulsed decoupling can be used to give enhanced sensitivity and reduced line widths and the technique is illustrated using short peptides.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 162-170
Title: Solid-state 17O NMR study of the electric-field-gradient and chemical shielding tensors in polycrystalline g-glycine
Authors: Yamada, Kazuhikoa; Honda, Hisashib; Yamazaki, Toshioa; Yoshida, Mitsuruc
Affiliations: a. NMR Spectroscopy Team, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama-shi, Kanagawa-ken 230-0045, Japan
b. International Graduate School of Arts and Sciences, Yokohama City University, 22-2 Seto, Kanawaza, Yokohama 236-0027, Japan
c. Analytical Science Division, National Food Research Institute, 2-1-12 Kannondai, Tsukuba 305-8642, Japan
Keywords: Solid-state 17O NMR; Chemical shielding tensor; Electric-field-gradient tensor; g-glycine
Abstract (English):
We report the first experimental determination of the carboxylate oxygen electric-field-gradient (EFG) and chemical shielding (CS) tensors in polycrystalline g-glycine. Analysis of magic-angle spinning (MAS) and stationary 17O NMR spectra of [17O]-g-glycine obtained at 9.4, 14.1, 16.4, and 18.8T yields the magnitudes of the 17O EFG and CS tensors and the relative orientations between the two tensors. Extensive quantum chemical calculations at both the restricted Hartree–Fock and density functional levels have been performed to present the absolute tensor orientations in term of the molecular frame. We have demonstrated that 17O NMR tensor information could be unambiguously derived by the multiple field analyses of stationary 17O NMR spectra.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 171-181
Title: Vanadium-51 solid-state NMR electric field gradient tensors: A DFT-embedded ion and isolated cluster study of crystalline vanadium oxides
Author: Gee, Becky A.a
Affiliations: a. Department of Chemistry and Biochemistry, 1 University Plaza, Long Island University, Brooklyn Campus, Brooklyn, NY 11201, USA
Keywords: Vanadium-51; Nuclear magnetic resonance (NMR); Density functional theory (DFT); Embedded ion; Embedded cluster; Electric field gradient (EFG); Quadrupole coupling; Orthovanadates; Vanadium oxides
Abstract (English):
Density functional theory (DFT) calculations (6–311+G(2d,p)/B3LYP level of theory) of 51V electric field gradient (EFG) tensor elements are performed for embedded and isolated cluster models of orthovanadates. The structural models used to calculate the EFGs of 51V are (I) an isolated H4VO4+ cluster, (II) an isolated HnVO4n-3 cluster (n=number of next-neighbor cations) (III) an isolated orthovanadate anion, VO4-x, and (IV) a VO4-x ion embedded in a finite point-charge array whose electrostatic potential, at the embedded ion, is equivalent to that of the infinite lattice. For models III and IV, a charge x is assigned estimating the covalence of the system. Models III and IV provide results in good agreement with the experiment. Calculations, employing the embedded and isolated VO4-x models, are used to discuss site assignments for AlVO4. Correlations between quadrupole coupling parameters and deviations of the orthovanadate structure from ideal tetrahedral symmetry are shown.
Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 3-4, October, 2006
pp. 198-202
Title: First evidence of multiple Ca sites in amorphous slag structure: Multiple-quantum MAS NMR spectroscopy on calcium-43 at high magnetic field
Authors: Shimoda, Keijia; Tobu, Yasuhiroa; Kanehashi, Kojia; Nemoto, Takahirob; Saito, Kojia
Affiliations: a. Advanced Technology Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu 293-8511, Japan
b. JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
Abstract: No Abstract
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.
Monday, December 04, 2006
Hiyam's Journal Update
Chemistry - A European Journal Volume: 12, Issue: 33 November 15, 2006
Computational Modeling of Polyoxotungstates by Relativistic DFT Calculations of 183W NMR Chemical Shifts 183W NMR Chemical Shifts.
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