Sunday, August 27, 2006

JPCB Update

19F Single-Quantum and 19F-33S Heteronuclear Multiple-Quantum Coherence NMR of SF6 in Thermotropic Nemtogens and in the Gas Phase.
H. Tervonen, J. Saunavaara, L.P. Ingman, and J. Jokisaari
J.Phys.Chem.B(2006)110,16232.
Abstract:
19F single-quantum (SQC) and 19F-33S heteronuclear multiple-quantum coherence (HMQC) NMR spectroscopy of sulfur hexafluoride (SF6) dissolved in thermotropic liquid crystals (TLCs) were used to investigate the properties of TLCs. On one hand, environmental effects on the NMR parameters of SF6, 19F nuclear shielding, 19F-33S spin-spin coupling, secondary isotope effects of sulfur on 19F shielding, and the self-diffusion coefficient in the direction of the external magnetic field were studied as well. The temperature dependence of the 19F shielding of SF6 in TLCs was modeled with a function that takes into account the properties of both TLC and SF6. It appears that the TLC environment deforms the electronic system of SF6 so that the 19F shielding tensor becomes slightly anisotropic, with the anisotropy being from -0.5 to -1.4 ppm, depending upon the TLC solvent. On the contrary, no sign of residual dipolar coupling between 19F and 33S was found, meaning that the so-called deformational effects, which arise from the interaction between vibrational and reorientational motions of the molecule, on the geometry of the molecule are insignificant. Diffusion activation energies, Ea, were determined from the temperature dependence of the self-diffusion coefficients. In each TLC, Ea increases when moving from an isotropic phase to a nematic phase. The spin-spin coupling constant, J(19F,33S), increases by ca. 10 Hz when moving from the gas phase to TLC solutions. The secondary isotope shifts of 19F shielding are practically independent of TLC solvent and temperature. For the first time, 19F-33S heteronuclear multiple-quantum NMR spectra were recorded for SF6 in the gas phase and in a liquid-crystalline solution.

Atomistic Origin of Germanate Anomaly in GeO2 and Na-Germanate Glasses: Insights from Two-Dimensional; 17O NMR and Quantum Chemical Calculations.
S.K. Lee and B.H. Lee
J.Phys.Chem.B (2006)110, 16408.
Abstract:
The prominent problem in archetypal germanate glasses is the germanate anomaly where the density exhibits maxima at 15-20 mol % of the alkali oxide content. Here we report 17O two-dimensional NMR spectra for GeO2 and Na-germanate glasses where the presence of both bridging oxygen linking [4]Ge and highly coordinated Ge ([5,6]Ge-O-[4]Ge) and nonbridging oxygen, and an increase in topological disorder are demonstrated at the density maximum, manifesting atomic origins of the anomaly. These densification mechanisms in germanate glasses with Na content are remarkably similar to densification in v-B2O3 with pressure.

Thermally Stable Amorphous Mesoporous Alumniophosphates with Controllable P/Al Ratio: Synthesis, Characterization and Catalytic Performance for Selective O-Methylation of Catechol.
G. Liu, Z. Wang, M. Jia, X. Zou, X. Zhu, W. Zhang, and D Jiang
J.Phys.Chem.B (2006)110, 16953.
Abstract:
Amorphous mesoporous aluminophosphates (AlPO) with P/Al molar ratio in the range 0.8-1.15 are synthesized by using the citric acid (CA) route and are systematically characterized using N2-adsorption, XRD, SEM, solid-state CP-MAS NMR, FT-IR, TG-DTA, CO2-TPD, and NH3-TPD. The characterization studies show that the change in P/Al ratio could affect the structure, texture, thermal stability, and surface acid-base properties of AlPO. Samples with a relatively low P/Al ratio (1.0) exhibit uniform amorphous mesoporous character and high thermal stability (up to 1173 K). Partial crystallization of the AlPO framework easily occurred on the sample with higher P/Al ratio (1.1), thus leading to significant decrease of surface area and formation of particle pile mesopores. Both weak acid and weak base sites are observed over AlPO materials, and the amounts of acid-base sites can be effectively controlled by adjusting the P/Al ratio. The presence of suitable interaction between citric acid and AlPO framework is critical for the formation of mesoporous structures. Both CA and PO4 units are considered to be ligands to coordinate with aluminum ions, forming relative uniform complexes (such as CA-Al-PO4) in the as-synthesized AlPO materials. The mesoporous structure of AlPO materials is obtained after the rapid decomposition of citric acid. Vapor phase selective O-methylation of catechol with methanol reaction is carried out to investigate the catalytic performances of AlPO materials with different P/Al ratios. Among them, AlP1.1O shows the highest activity (88.4% conversion of catechol) and the highest yield of guaiacol (74.3%). The presence of suitable weak acid-base pairs may play an important role on the title reaction.

Selective NMR Measurements of Homonuclear Scalar Couplings in Isotropically Enriched Solids.
S. Cadars, A. Lesarge, N. Hedin, B.F. Chmelka, and L. Emsley
J.Phys.Chem.B (2006)110, 16982.
Abstract:
Scalar (J) couplings in solid-state NMR spectroscopy are sensitive to covalent through-bond interactions that make them informative structural probes for a wide range of complex materials. Until now, however, they have been generally unsuitable for use in isotopically enriched solids, such as proteins or many inorganic solids, because of the complications presented by multiple coupled but nonisolated spins. Such difficulties are overcome by incorporating a z-filter that results in a robust method for measuring pure J-coupling modulations between selected pairs of nuclei in an isotopically enriched spin system. The reliability of the new experimental approach is established by using numerical simulations and tested on fully 13C-labeled polycrystalline L-alanine. It is furthermore shown to be applicable to partially enriched systems, when used in combination with a selective double-quantum (DQ) filter, as demonstrated for the measurement of 2J(29Si-O-29Si) couplings in a 50% 29Si-enriched surfactant-templated layered silicate lacking long-range 3D crystallinity. J-coupling constants are obtained with sufficient accuracy to distinguish between different 29Si-O-29Si pairs, shedding insight on the local structure of the silicate framework. The new experiment is appropriate for fully or partially enriched liquid or solid samples.

Sunday, August 20, 2006

Cross polarization from spins I=1/2 to spins S=1 in nuclear magnetic resonance with magic angle sample spinning

The Journal of Chemical Physics, 21 May 2006J. Chem. Phys. 124, 194311

Karthik Gopalakrishnan, Geoffrey Bodenhausen

Spin locking of the nuclear magnetization of a spin with S=1 such as deuterium in the presence of a radio-frequency field under magic angle spinning (MAS) is described in terms of adiabatic modulations of the energy levels. In a brief initial period, part of the initial density operator nutates about the Hamiltonian and is dephased. The remaining spin-locked state undergoes persistent oscillatory transfer processes between various coherences with a periodicity given by the rotation of the sample. While all crystallites in the powder undergo such periodic transfer processes, the phases of the oscillations depend on the angle of the crystallites. The angle is the azimuthal angle defining the orientation of the unique axis of the quadrupolar interaction tensor in a rotor-fixed frame. The theory is extended to describe cross-polarization between spins S=1 and I=1/2 under MAS. There are four distinct Hartmann-Hahn matching conditions that correspond to four zero-quantum matching conditions, all of which are shifted and broadened compared to their spin S=1/2 counterparts. These matching conditions are further split into a family of sideband conditions separated by the spinning frequency. The theory allows the calculation of both shifts and broadening factors of the matching conditions, as verified by simulations and experiments.

Frequency-selective homonuclear dipolar recoupling in solid state NMR

The Journal of Chemical Physics, 21 May 2006J. Chem. Phys. 124, 194303

Anant K. Paravastu and Robert Tycko

We introduce a new approach to frequency-selective homonuclear dipolar recoupling in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS). This approach, to which we give the acronym SEASHORE, employs alternating periods of double-quantum recoupling and chemical shift evolution to produce phase modulations of the recoupled dipole-dipole interactions that average out undesired couplings, leaving only dipole-dipole couplings between nuclear spins with a selected pair of NMR frequencies. In principle, SEASHORE is applicable to systems with arbitrary coupling strengths and arbitrary sets of NMR frequencies. Arbitrary MAS frequencies are also possible, subject only to restrictions imposed by the pulse sequence chosen for double-quantum recoupling. We demonstrate the efficacy of SEASHORE in experimental 13C NMR measurements of frequency-selective polarization transfer in uniformly 15N, 13C-labeled L-valine powder and frequency-selective intermolecular polarization transfer in amyloid fibrils formed by a synthetic decapeptide containing uniformly 15N, 13C-labeled residues.

CAESURA: Measurement of slow molecular dynamics by solid-state nuclear magnetic resonance chemical shift anisotropy modulation amplification

The Journal of Chemical Physics, 14 August 2006J. Chem. Phys. 125, 064507

Limin Shao and Jeremy J. Titman

An alternative magic angle spinning (MAS) exchange NMR experiment based on chemical shift anisotropy (CSA) amplification is described. The CSA amplification experiment correlates a standard MAS spectrum in the 2 dimension with a sideband pattern in 1 in which the intensities are identical to those expected for a sample spinning at some fraction 1/N of the actual rate r. In common with 2D-PASS, the isotropic shift appears only in the 2 dimension, and long acquisition times can be avoided without loss of resolution of different chemical sites. The new CSA amplification exchange experiment provides information about the time scale and geometry of molecular motions via their effect on the sideband intensities in a one-dimensional pattern. The one-dimensional patterns from different chemical sites are separated across two frequency dimensions according to the isotropic shifts.

The nuclear electric quadrupole moment of antimony from the molecular method

The Journal of Chemical Physics, 14 August 2006J. Chem. Phys. 125, 064301

Roberto L. A. Haiduke and Albérico B. F. da Silva

Relativistic Dirac-Coulomb (DC) Hartree-Fock calculations are employed to obtain the analytic electric field gradient (EFG) on the antimony nucleus in the SbN, SbP, SbF, and SbCl molecules. The electronic correlation contribution to the EFGs is included with the DC-CCSD(T) and DC-CCSD-T approaches, also in the four-component framework, using a finite-difference method. The total EFG results, along with the experimental nuclear quadrupole coupling constants from microwave spectroscopy, allow to derive the nuclear quadrupole moments of 121Sb and 123Sb, respectively, as –543(11) and –692(14) mb.

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

The Journal of Chemical Physics, 7 August 2006J. Chem. Phys. 125, 054905

M. Vogel, and T. Torbrügge

We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4 performing 2H and 7Li NMR line-shape analysis. Comparison of temperature dependent 7Li and 2H NMR spectra gives evidence for a coupling of ion and polymer dynamics. 2H NMR spectra for various salt concentrations reveal a strong slowdown of the polymer segmental motion when the salt content is increased. The 2H NMR line shape further indicates that the segmental motion is governed by dynamical heterogeneities. While the width of the distribution of correlation times G(log ) is moderate for low and high salt content, an extremely broad distribution exists for an intermediate salt concentration of 15:1 PPO-LiClO4. For the latter composition, a weighted superposition of two spectral components, reflecting the fast and the slow polymer segments of the distribution, describes the 2H NMR line shape over a broad temperature range. Analysis of the temperature dependent relative intensity of both spectral components indicates the existence of a continuous rather than a discontinuous distribution G(log ). Such continuous distribution is consistent with gradual fluctuations of the local salt concentration and, hence, of the local environments of the polymer segments, whereas it is at variance with the existence of large salt-depleted and salt-rich domains featuring fast and slow polymer dynamics, respectively. Finally, for all studied PPO-LiClO4 mixtures, the 2H NMR line shape strongly depends on the echo delay in the applied echo-pulse sequence, indicating that the structural relaxation of the polymer segments involves successive rotational jumps about small angles <20°.

17O nuclear quadrupole coupling constants of water bound to a metal ion: A gadolinium(III) case study

The Journal of Chemical Physics, 7 August 2006J. Chem. Phys. 125, 054503

Oleg V. Yazyev and Lothar Helm

Rotational correlation times of metal ion aqua complexes can be determined from 17O NMR relaxation rates if the quadrupole coupling constant of the bound water oxygen-17 nucleus is known. The rotational correlation time is an important parameter for the efficiency of Gd3+ complexes as magnetic resonance imaging contrast agents. Using a combination of density functional theory with classical and Car-Parrinello molecular dynamics simulations we performed a computational study of the 17O quadrupole coupling constants in model aqua ions and the [Gd(DOTA)(H2O)]– complex used in clinical diagnostics. For the inner sphere water molecule in the [Gd(DOTA)(H2O)]– complex the determined quadrupole coupling parameter of 8.7 MHz is very similar to that of the liquid water (9.0 MHz). Very close values were also predicted for the the homoleptic aqua ions of Gd3+ and Ca2+. We conclude that the 17O quadrupole coupling parameters of water molecules coordinated to closed shell and lanthanide metal ions are similar to water molecules in the liquid state.

Wednesday, August 16, 2006

Sharon Ashbrook: 23Na MQMAS, Structure Determination via SSNMR and PXRD

Inorg. Chem., 45 (15), 6034 -6040, 2006. 10.1021/ic060483t S0020-1669(06)00483-6 Web Release Date: June 22, 2006 Copyright © 2006 American Chemical Society

Na2[(VO)2(HPO4)2C2O4]·2H2O: Crystal Structure Determination from Combined Powder Diffraction and Solid-State NMR

J. F. Colin, T. Bataille, S. E. Ashbrook, N. Audebrand, L. Le Pollès, J. Y. Pivan, and E. Le Fur*
Sciences Chimiques de Rennes, UMR 6226, CNRS-Université de Rennes 1-ENSCR, 35042 Rennes Cedex, France, and Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, U.K.
Received March 22, 2006

Abstract: The vanadyl oxalatophosphate Na2[(VO)2(HPO4)2C2O4]·2H2O has been synthesized by hydrothermal treatment. Its structure has been determined and refined by combining X-ray powder diffraction and solid-state NMR techniques. It crystallizes with monoclinic symmetry in space group P21, a = 6.3534(1) Å, b = 17.1614(3) Å, c = 6.5632(1) Å, = 106.597(1). The structure is related to that of (NH4)2[(VO)2(HPO4)2C2O4]·5H2O, which was previously reported. The vanadium phosphate framework consists of infinite [(VO)(HPO4)] chains of corner-sharing vanadium octahedra and hydrogenophosphate tetrahedra. The oxalate groups ensure the connection between the chains to form a 2D structure. The sodium ions and the water molecules are located between the anionic [(VO)2(HPO4)2C2O4]2- layers. The thermal decomposition has been studied in situ by temperature-dependent X-ray diffraction and thermogravimetry. It takes place in three stages, where the first two correspond to water removal and the last to the decomposition of the oxalate group and water elimination, leading to the final product NaVOPO4.

Tuesday, August 15, 2006

113Cd NMR

Dalton Trans., 2006, 3534 - 3543, DOI: 10.1039/b601665k
Cadmium-113 NMR studies on homoleptic complexes containing thioether ligands: the crystal structures of [Cd([12]aneS4)2](ClO4)2, [Cd([18]aneS4N2)](PF6)2 and [Cd([9]aneS3)2](PF6)2
Monte L. Helm, Lensey L. Hill, John P. Lee, Donald G. Van Derveer and Gregory J. Grant

We report the measurement of 113Cd NMR chemical shift data for homoleptic thioether and related aza and mixed aza/thiacrown complexes. In a series of Cd(II) complexes containing trithioether to hexathioether ligands, we observe solution 113Cd NMR chemical shifts in the range of 225 to 731 ppm. Upfield chemical shifts in these NMR spectra are seen whenever: (a) the number of thioether sulfur donors in the complex is decreased, (b) a thioether sulfur donor is replaced by a secondary nitrogen donor, or (c) the size of the macrocycle ring increases without a change in the nature or number of the donor atoms. Changes in the identity of non-coordinating anions such as perchlorate or hexafluorophosphate have little effect upon the 113Cd NMR chemical shift in solution. We report the X-ray structure of the complex [Cd([12]aneS4)2](ClO4)2 ([12]aneS4 = 1,4,7,10-tetrathiacyclododecane) (1) which shows the first example of octakis(thioether) coordination of a metal ion, forming an unusual eight-coordinate square antiprismatic structure. We report the X-ray structure of the complex [Cd([9]aneS3)2](PF6)2 ([9]aneS3 = 1,4,7-trithiacyclononane) (3a) which shows hexakis(thioether) coordination to form a distorted octahedral structure. We have also prepared and characterized the Cd(II) complex of a mixed azathiacrown, [Cd([18]aneS4N2)](PF6)2 ([18]aneS4N2 = 1,4,10,13-tetrathia-7,16-diazacyclooctadecane) (6). Its X-ray structure shows a distorted octahedral S4N2 environment around the Cd(II) with the ligand coordinated in the rac fashion. We observe a solvent- and temperature-dependent 14N–1H coupling in the 1H NMR spectrum of the complex which is not present in analogous complexes with this ligand.

A Whole Bunch of Metallocene Chemistry!! (For Those Who Care)

Dalton Trans., 2006, 3313 - 3320, DOI: 10.1039/b604640a
Complexes of a gallium heterocycle with transition metal dicyclopentadienyl and cyclopentadienylcarbonyl fragments, and with a dialkylmanganese compound
Simon Aldridge, Robert J. Baker, Natalie D. Coombs, Cameron Jones, Richard P. Rose, Andrea Rossin and David J. Willock

The reactivity of several transition metal half sandwich complexes towards an anionic gallium(I) heterocyclic complex, [K(tmeda)][Ga{[N(Ar)C(H)]2}](Ar = C6H3Pri2-2,6), has been investigated. This has led to the anionic half sandwich complexes, [K(tmeda)][(C5H4R)M(CO)n[Ga{[N(Ar)C(H)]2}]](M = V, R = H, n= 3; M = Mn, R = Me, n= 2; M = Co, R = H, n= 1), which crystallographic studies show to form dimers (M = Mn and Co) or a polymer (M = V) through bridging potassium cations. The metal–gallium bond lengths in all complexes are very short which, combined with some spectroscopic evidence, is suggestive of M–Ga -bonding. Density functional theory studies of models of all complexes indicate that the level of back-bonding in these complexes is, however, minimal and of a similar order to that seen in analogous complexes incorporating neutral N-heterocyclic carbene ligands. Reactions of the metallocenes, [M(C5H4Me)2](M = V or Cr), with the digallane(4), [Ga{[N(Ar)C(H)]2}]2, have afforded the neutral complexes, [M(C5H4Me)2[Ga{[N(Ar)C(H)]2}]], which are thought to be formed via an initial oxidative insertion of the transition metal centre into the Ga–Ga bond of the digallane. X-Ray crystallography shows the complexes to be monomeric. One (M = V) reacts with one equivalent of [K(tmeda)][Ga{[N(Ar)C(H)]2}] to give the crystallographically characterised, anionic bis(gallyl)-complex, [K(tmeda)][V(C5H4Me)2[Ga{[N(Ar)C(H)]2}]2]. For comparison, the reaction of [K(tmeda)][Ga{[N(Ar)C(H)]2}] with [Mn{CH(SiMe3)2}2] was carried out and gave the monomeric, anionic complex, [K(tmeda)][Mn{CH(SiMe3)2}2[Ga{[N(Ar)C(H)]2}]].

195Pt NMR and DFT computational methods as tools towards the understanding of speciation and hydration/solvation of [PtX6]2– (X = Cl–, Br–) anions in

Dalton Trans., 2006, 3277 - 3284, DOI: 10.1039/b605182k
195Pt NMR and DFT computational methods as tools towards the understanding of speciation and hydration/solvation of [PtX6]2– (X = Cl–, Br–) anions in solution
Klaus R. Koch, M. R. Burger, J. Kramer and A. N. Westra

195Pt NMR together with DFT calculations and MD simulations, offer a powerful toolkit with which to probe the hydration shells of the [PtCl6]2– anions, which may lead to a more profound understanding of the solute–solvent interactions of such complexes.

Chem. Mater. 45Sc NMR of Solid Oxides and Stablized Zirconia, Stebbins

Chem. Mater., 18 (16), 3855 -3859, 2006. 10.1021/cm060590lS0897-4756(06)00590-4
Web Release Date: July 7, 2006

Scandium Coordination in Solid Oxides and Stabilized Zirconia: 45Sc NMR

Namjun Kim, Cheng-Han Hsieh, and Jonathan F. Stebbins

Departments of Geological and Environmental Sciences and Materials Science and Engineering, Stanford University, Stanford, California 94305

Abstract:

45Sc NMR isotropic chemical shifts and quadrupole coupling constants of several scandium-containing solid oxides have been measured. Both parameters prove to be sensitive to local structure. In particular, in these materials the 45Sc isotropic chemical shift appears to be dominated by the first neighbor coordination environment, i.e., the coordination number. The difference in the isotropic shifts between six-coordinated and eight-coordinated scandium is more than 150 ppm, suggesting that this parameter may be especially useful in studying the scandium coordination in oxide materials, disordered solids in particular. Quadrupole coupling constants are sensitive to the nature of the second coordination cation, although many other structural details may play a role. The chemical shift correlation was applied to scandia-stabilized zirconia, (ZrO2)0.92(Sc2O3)0.08, and the mean coordination number obtained appears to be close to seven, which suggests the possibility of two scandium cations pairing with one vacancy.

Friday, August 11, 2006

Joel's Monthly Journal Update

Andy - Some CdSe papers
Fabrication of Stable Low-Density Silica Aerogels Containing Luminescent ZnS Capped CdSe Quantum Dots.
L. Sorensen, G.F. Strouse, and A.E. Stiegman.
Advan. Mat. (2006)18, 1965.
Summary:
Luminescent CdSe quantum dots of 2.5 and 6.0 nm dimension have been incorporated into a low-density silica aerogels matrix. The aerogels are formed from the supercritical CO2 extraction of an alcogel containing quantum dots surface passivated with 3-aminopropyltriethoxysilane. The resulting aerogels (see figure and cover) are low scattering and show intense, stable luminescence.

Growth of CdSe Quantum Rods and Multipods Seeded by Noble-Metal Nanoparticles.
K.T. Yong, Y. Sahoo, M.T. Swihart and P.N. Prasad
Advan. Mat. (2006)18, 1978.
Summary:
CdSe quantum rods are prepared at much milder conditions than previously reported, using noble-metal seed particles to initiate growth. The CdSe nanocrystals initially form as multipods that cleave to yield freestanding quantum rods (see figure) with high photoluminescence quantum yields. This study provides a new direction in developing facile syntheses of semiconductor NCs with nonspherical morphology, thereby making available new building blocks for nanotechnology.

Bryan - Au Nanoparticle Stuff
Turkevich Method for Gold Nanoparticle Synthesis Revisited
J. Kimling, M. Maier, B. Okenve, V. Kotaidis, H. Ballot, and A. Plech.
J.Phys.Chem.B(2006)110,15700.
Abstract:
The growth of gold nanoparticles by reduction by citrate and ascorbic acid has been examined in detail to explore the parameter space of reaction conditions. It is found that gold particles can be produced in a wide range of sizes, from 9 to 120 nm, with defined size distribution, following the earlier work of Turkevich and Frens. The reaction is initiated thermally or in comparison by UV irradiation, which results in similar final products. The kinetics of the extinction spectra show the multiple steps of primary and secondary clustering leading to polycrystallites.

Andre
Structural, Magnetic, and Spectroscopic Studies of YAgSn, TmAgSn, and LuAgSn
C.P. Sebastian, H. Eckert, C. Fehse, J.P. Wright, J.P. Attfield, D. Johrendt, S. Rayaprol, R.D. Hoffmann, R. Pottgen.
JSolidStateChem (2006) 179, 2376.
Abstract:
The rare earth–silver–stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P63mc, Z=2, a=468.3(1), Click to view the MathML sourcepm, wR2=0.0343, 353 F2 values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a=726.4(2), Click to view the MathML source, wR2=0.0399, 659 F2 values, 15 variables for TmAgSn, and a=723.8(2), Click to view the MathML source, wR2=0.0674, 364 F2 values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with Click to view the MathML source, in order to clarify the silver–tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag–Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag–Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie–Weiss paramagnet with an experimental magnetic moment of 7.2 ?B/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by 119Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental 119Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag–Sn bonds and also significant Ag–Ag bonding in LuAgSn.

Na->Li (and Li->Na) CP/MAS
Site Discrimination in Mixed-Alkali Glasses Studied by Cross-Polarization NMR
S.P. Puls and H. Eckert.
J.Phys.Chem.B(2006)110,14253.
Abstract:
Cation-cation interactions are thought to play a significant role in shaping the nonlinear compositional dependence of ionic conductivity, known as the mixed-alkali effect (MAE) in glassy solid electrolytes. For providing a structural rationale of this effect, the discrimination of various cation sites in mixed-alkali glasses is of interest. In the present study, cross-polarization (CP) experiments have been applied to glasses in the system [(Li2O)x(Na2O)1-x]0.3[B2O3]0.7 to discriminate between alkali ions by virtue of different heteronuclear 7Li-23Na dipole-dipole coupling strengths. Cross-polarization studies involving two types of quadrupolar nuclei (both 7Li and 23Na have a spin-quantum number I = 3/2) are complicated by spin state mixing under radio frequency irradiation and magic-angle spinning (MAS). Therefore careful validation and optimization protocols are reported for the model compound LiNaSO4 prior to conducting the measurements on the glassy samples. 23Na 7Li CP/MAS NMR spectra have been obtained on glasses containing the Na+ ions as the dilute species. They reveal that those lithium species interacting particularly strongly with sodium ions have the same average 7Li chemical shift as the entire lithium population; the symmetrical situation applies to the 23Na nuclei at the sodium rich end of the composition range. On the other hand, a clear site discrimination is afforded by temperature-dependent static 23Na 7Li CP experiments, indicating that the Li ions that are most strongly interacting with sodium ions are strongly immobilized. This finding provides the first direct experimental evidence for the proposed secondary mismatch concept invoked for explaining the strong MAE in the dilute foreign ion limit

Cory - 17O NMR and Repetitive DFS experiments
Sensitivity Enhancement and Heteronuclear Distance Measurements in Biological 17O Solid-State NMR
A. Binkmann and P.M. Kentgens
J.Phys.Chem.B(2006)110,16089.
Abstract:
In this contribution we present a comprehensive approach to study hydrogen bonding in biological and biomimetic systems through 17O and 17O-1H solid-state NMR combined with density functional theory calculations of 17O and 1H NMR parameters. We explore the signal enhancement of 17O in L-tyrosine·HCl using repetitive double-frequency swept radio frequency pulses in solid-state NMR. The technique is compatible with high magnetic fields and fast magic-angle spinning of the sample. A maximum enhancement by a factor of 4.3 is obtained in the signal-to-noise ratio of the selectively excited 17O central transition in a powdered sample of 17O-L-tyrosine·HCl at an external field of 14.1 T and a spinning frequency of 25 kHz. As little as 128 transients lead to meaningful 17O spectra of the same sample at an external field of 18.8 T and a spinning frequency of 50 kHz. Furthermore we employed supercycled symmetry-based pulse sequences on the protons to achieve heteronuclear longitudinal two-spin-order (IzSz) recoupling to determine 17O-1H distances. These sequences recouple the heteronuclear dipolar 17O-1H couplings, where dipolar truncation is absent, while decoupling the homonuclear proton dipolar interactions. They can be applied at fast magic-angle-spinning frequencies up and beyond 50 kHz and are very robust with respect to 17O quadrupolar couplings and both 17O and 1H chemical shift anisotropies, which makes them suitable for the use at high external magnetic fields. The method is demonstrated by determining the 17O-1H distance in L-tyrosine·HCl at a spinning frequency of 50 kHz and an external field of 18.8 T.

Tuesday, August 08, 2006

MRC: 29Si and 27Al NMR of paramagnetic materials

Magnetic Resonance in Chemistry
Vol: 44, Issue: 9, September 2006
pp. 861 - 867

Title: Solid-state NMR spectra of paramagnetic silica-based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions
Authors: Bakhmutov, Vladimir I.a; Shpeizer, Boris G.a; Clearfield, Abrahama
Affiliations: a. Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842&hyphen;3012, USA
Keywords: 29Si; 27Al NMR; paramagnetic solids; relaxation
Abstract (English):

Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies. Copyright © 2006 John Wiley & Sons, Ltd.

MRC: 71Ga NMR; Grandinetti

Magnetic Resonance in Chemistry
Vol: 44, Issue: 9, September 2006
pp. 823 - 831

Title: Solid-state NMR characterization of 69Ga and 71Ga in crystalline solids
Authors: Ash, Jason T.a; Grandinetti, Philip J.a
Affiliations: a. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, Ohio 43210‐1173, USA
Keywords: gallium NMR; quadrupolar nuclei
Abstract (English):

Gallium model systems containing four- and six-coordinate gallium sites have been investigated using solid-state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on a-Ga2O3, b-Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic-angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor-assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four-coordinate gallium having values of approximately 50 ppm and six-coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 × 1021 Vm-2 or more, while the less strained systems have values of 1.5 × 1021 Vm-2 or less. A plot of chemical shift versus EFG suggests that solid-state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone. Copyright © 2006 John Wiley & Sons, Ltd.

Chem. Soc. Rev. Solid-State 17O NMR, Ashbrook and Smith

Chem. Soc. Rev., 2006, 35, 718 - 735, DOI: 10.1039/b514051j
Solid state 17O NMR—an introduction to the background principles and applications to inorganic materials

Sharon E. Ashbrook and Mark E. Smith
Oxygen is a key chemical element and solid state NMR can provide unique insight into the its local environment. In the last decade there have been significant advances (sensitivity, resolution) in the NMR methodology for non-integer spin quadrupole nuclei such as oxygen and the background to these techniques is presented in this tutorial review. The information that the NMR parameters can provide about the local environment is explained through a series of illustrations from different areas of solid state chemistry and structural science of inorganic materials.

Concepts: Structural Information from Quadrupolar Nuclei in Solid State NMR . Sharon E. Ashbrook, Melinda J. Duer.

Concepts in Magnetic Resonance Part A
Volume 28A, Issue 3 , Pages 183 - 248

Special Issue: Structural Information from Quadrupolar Nuclei in Solid State NMR . Issue Edited by Sharon E. Ashbrook, Melinda J. Duer.

Published Online: 4 May 2006

Structural information from quadrupolar nuclei in solid state NMR

Sharon E. Ashbrook 1, Melinda J. Duer 2 *
1 School of Chemistry and EaStChem, University of St. Andrews, North Haugh, St. Andrews, KY16 9ST, United Kingdom
2 Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom

Keywords
solid-state NMR • quadrupole coupling • quadrupolar nuclei • structure determination • magic-angle spinning • double rotation • dynamic-angle spinning • correlation spectroscopy • multiple-quantum magic-angle spinning • satellite-transition magic-angle spinning • multiple quantum • rotational resonance • rotational-echo double resonance • J-coupling • scalar coupling • computation/calculation of NMR parameters

Abstract
Solid-state NMR has become the method of choice for determining details of molecular-level structure in heterogeneous systems. Though spin-1/2 nuclei still form the core of most such studies, quadrupolar nuclei are increasingly being used. This review assesses what is currently possible, from achieving high-resolution spectra for quadrupolar nuclei (a prerequisite for most structure determination work), to forming correlation spectra which give qualitative details of spatial proximity of nuclei and the determination of internuclear distances, between quadrupolar spins and quadrupolar and spin-1/2 nuclei. Examples are given of each method discussed, and the advantages and disadvantages of the various experiments for different possible applications are assessed. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 183-248, 2006.

JMR: 2D, 1 pulse NMR (TOP NMR) of quadrupoles; Massiot and Grandinetti

Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 310-315

Title: Two-dimensional one pulse MAS of half-integer quadrupolar nuclei
Authors: Massiot, Dominiquea; Hiet, Juliana; Pellerin, Nadiaa; Fayon, Francka; Deschamps, Michaela; Steuernagel, Stefanb; Grandinetti, Philip J.c
Affiliations: a. CRMHT-CNRS, UPR4212, 45071 Orléans cedex 2, France
b. Bruker-Biospin GMBH, 76287 Rheinstetten, Germany
c. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Keywords: Solid-state NMR; Half-integer quadrupolar nuclei; Spinning sidebands
Abstract (English):

We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.

JMR: 2D, 1 pulse NMR (TOP NMR) of quadrupoles; Massiot and Grandinetti

Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 310-315

Title: Two-dimensional one pulse MAS of half-integer quadrupolar nuclei
Authors: Massiot, Dominiquea; Hiet, Juliana; Pellerin, Nadiaa; Fayon, Francka; Deschamps, Michaela; Steuernagel, Stefanb; Grandinetti, Philip J.c
Affiliations: a. CRMHT-CNRS, UPR4212, 45071 Orléans cedex 2, France
b. Bruker-Biospin GMBH, 76287 Rheinstetten, Germany
c. Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Keywords: Solid-state NMR; Half-integer quadrupolar nuclei; Spinning sidebands
Abstract (English):

We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.

JMR; 13C MAS NMR of paramagnetics; Ishii

Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 233-243

Title: Sensitivity enhancement, assignment, and distance measurement in 13C solid-state NMR spectroscopy for paramagnetic systems under fast magic angle spinning
Authors: Wickramasinghe, Nalinda P.a; Ishii, Yoshitakaa
Affiliations: a. Department of Chemistry, University of Illinois at Chicago, Chicago IL 60607, USA
Keywords: 13C solid-state NMR; Paramagnetic systems; Fast MAS; Sensitivity; Assignments; Distances
Abstract (English):

Despite success of previous studies, high-resolution solid-state NMR (SSNMR) of paramagnetic systems has been still largely unexplored because of limited sensitivity/resolution and difficulty in assignment due to large paramagnetic shifts. Recently, we demonstrated that an approach using very-fast magic angle spinning (VFMAS; spinning speed 20kHz) enhances resolution/sensitivity in 13C SSNMR for paramagnetic complexes [Y. Ishii, S. Chimon, N.P. Wickramasinghe, A new approach in 1D and 2D 13C high resolution solid-state NMR spectroscopy of paramagnetic organometallic complexes by very fast magic-angle spinning, J. Am. Chem. Soc. 125 (2003) 3438–3439]. In this study, we present a new strategy for sensitivity enhancement, signal assignment, and distance measurement in 13C SSNMR under VFMAS for unlabeled paramagnetic complexes using recoupling-based polarization transfer. As a robust alternative of cross-polarization (CP), rapid application of recoupling-based polarization transfer under VFMAS is proposed. In the present approach, a dipolar-based analog of INEPT (dipolar INEPT) methods is used for polarization transfer and a 13C signal is observed under VFMAS without 1H decoupling. The resulting low duty factor permits rapid signal accumulation without probe arcing at recycle times (3ms/scan) matched to short 1H T1 values of small paramagnetic systems (1ms). Experiments on Cu(dl-Ala)2 showed that the fast repetition approach under VFMAS provided sensitivity enhancement by a factor of 8–66 for a given sample, compared with the 13C MAS spectrum under moderate MAS at 5kHz. The applicability of this approach was also demonstrated for a more challenging system, Mn(acac)3, for which 13C and 1H paramagnetic shift dispersions reach 1500 and 700ppm, respectively. It was shown that effective-evolution-time dependence of transferred signals in dipolar INEPT permitted one to distinguish 13CH, 13CH2, 13CH3, Formula Not Shown groups in 1D experiments for Cu(dl-Ala)2 and Cu(Gly)2. Applications of this technique to 2D 13C/1H correlation NMR under VFMAS yielded reliable assignments of 1H resonances as well as 13C resonances for Cu(dl-Ala)2 and Mn(acac)3. Quantitative analysis of cross-peak intensities in 2D 13C/1H correlation NMR spectra of Cu(dl-Ala)2 provided distance information between non-bonded 13C–1H pairs in the paramagnetic system.

JMR; SW-FAM for static NMR of quadrupolar nuclei; Madhu

Journal of Magnetic Resonance
Vol: 181, Issue: 1, July, 2006
pp. 68-78

Title: Fast amplitude-modulated pulse trains with frequency sweep (SW-FAM) in static NMR of half-integer spin quadrupolar nuclei
Authors: Bräuniger, Thomasa; Hempel, Güntera; Madhu, P.K.b
Affiliations: a. Department of Physics, University of Halle, Friedemann-Bach-Platz 6, 06108 Halle, Germany
b. Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
Keywords: Static 27Al NMR; Half-integer spin; Quadrupolar nuclei; SW-FAM
Abstract (English):

In solid-state NMR of quadrupolar nuclei with half-integer spin I, fast amplitude-modulated (FAM) pulse trains have been utilised to enhance the intensity of the central-transition signal, by transferring spin population from the satellite transitions. In this paper, the signal-enhancement performance of the recently introduced SW-FAM pulse train with swept modulation frequency [T. Bräuniger, K. Ramaswamy, P.K. Madhu, Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses, Chem. Phys. Lett. 383 (2004) 403â??410] is explored in more detail for static spectra. It is shown that by sweeping the modulation frequencies linearly over the pulse pairs (SW(1/Ï?)-FAM), the shape of the frequency distribution is improved in comparison to the original pulse scheme (SW(Ï?)-FAM). For static spectra of 27Al (I=5/2), better signal-enhancement performance is found for the SW(1/Ï?)-FAM sequence, as demonstrated both by experiments and numerical simulations.

JMR: CSA recoupling; Duer

Journal of Magnetic Resonance
Vol: 181, Issue: 1, July, 2006
pp. 1-8

Title: Recoupling of chemical-shift anisotropy powder patterns in MAS NMR
Authors: Orr, Robin M.a; Duer, Melinda J.a
Affiliations: a. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
Keywords: Solid-state NMR; Magic-angle spinning; Chemical-shift anisotropy; Recoupling
Abstract (English):

A comparison of three different implementations of the chemical-shift recoupling experiment of Tycko et al. [R. Tycko, G. Dabbagh, P.A. Mirau, Determination of chemical-shift-anisotropy lineshapes in a two-dimensional magic-angle-spinning NMR experiment, J. Magn. Reson. 85 (1989) 265â??274] is presented. The methods seek to reduce the effects of artefacts resulting from pulse imperfections and residual C-H dipolar coupling in organic solids. An optimised and constant time implementation are shown to give well-defined and artefact free powder pattern lineshapes in the indirectly observed dimension for both sp2 and sp3 carbon sites. Experimental setup is no more demanding than for the original experiment, and can be implemented using standard commercial hardware.

MRC: 31P-71Ga MAS HMQC experiments; gallophosphates; Massiot

Magnetic Resonance in Chemistry
Vol: 44, Issue: 8, August 2006
pp. 770 - 775

Title: Toward a better description of gallo-phosphate materials in solid-state NMR: 1D and 2D correlation studies
Authors: Montouillout, Valériea; Morais, Cláudia M.a; Douy, Andréa; Fayon, Francka; Massiot, Dominiquea
Affiliations: a. CRMHT—CNRS UPR4212 1D, Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
Keywords: NMR; 71Ga; 31P; HMQC experiment; gallo-phosphates
Abstract (English):

We show that weak 2J(71Ga—O—31P), typically 12 Hz in GaPO4, can be used to efficiently establish heteronuclear 31P—71Ga correlation using a MAS HMQC experiment in gallo-phosphate materials. The experiment demonstrated for cristobalite GaPO4 is then applied to Ga(PO3)3, where it allows the differentiation of the signature of three different Ga sites overlapping in the 1D spectrum. Copyright © 2006 John Wiley & Sons, Ltd.

MRC: 33S NMR of ethanesulfonates, plus DFT and NBO methods

Magnetic Resonance in Chemistry
Vol: 44, Issue: 8, August 2006
pp. 753 - 760

Title: 33S NMR spectroscopy 3. substituent effects on 33S NMR parameters in 2-substituted ethanesulfonates
Authors: Musio, Robertaa; Sciacovelli, Oronzoa
Affiliations: a. Istituto C.N.R. di Chimica dei Composti Organo‐Metallici—Sezione di Bari and Dipartimento di Chimica, Università degli Studi di Bari, Via E. Orabona 4, 70126 Bari, Italy
Keywords: NMR; 33S NMR; 33S chemical shift; 33S nuclear shielding calculations; 33S nuclear quadrupole coupling constant; substituent effect; 2-substituted ethanesulfonates
Abstract (English):

33S NMR parameters (chemical shifts and linewidths) in 2-substituted sodium ethanesulfonates, XCH2CH2SO3Na (X = H, CH3, OH, SH, NH2, Cl, Br, NH3+) depend upon the electronic properties of substituents. To explain experimental results and obtain additional information on the origin of the observed substituent effect (SE), sulfur isotropic absolute shielding constants have been calculated at DFT level of theory (B3LYP/6-311 + + G(2d,p)) by gauge-including atomic orbitals (GIAO) method. Data have been interpreted with the aid of natural bond orbital (NBO) method and natural chemical shielding (NCS) analysis. It has been demonstrated that in the class of compounds considered the diamagnetic contribution to sulfur-shielding constant is constant and the observed upfield shift of 33S resonance induced by electron-withdrawing substituents (reverse chemical shift effect) can be related to variations of the paramagnetic contribution. Substituents with different electronic properties cause variations in the polarization of S—C and S—O bonds of the —C—SO3- moiety thus determining changes of the electron density at sulfur nucleus and consequently the expansion or contraction of 3p sulfur orbitals. Also oxygen lone-pairs and sulfur core 2p electrons can play an active role in determining the paramagnetic contribution to sulfur shielding. With regard to linewidth variations, they can be ascribed primarily to changes in the nuclear quadrupole coupling constant values. B3LYP/6-311 + + G(2d,p) method allows obtaining a good reproducibility of SE on the electric field gradient (EFG) at sulfur, although its values tend to be underestimated significantly. Moreover, 17O shielding constants have been calculated. Copyright © 2006 John Wiley & Sons, Ltd.

MRC; DFT of 53Cr chemical shielding; Buhl

Magnetic Resonance in Chemistry
Vol: 44, Issue: 7, July 2006
pp. 661 - 668

Title: Density-functional computation of 53Cr NMR chemical shifts
Author: Bühl, Michaela
Affiliations: a. Max‐Planck Institut für Kohlenforschung, Kaiser‐Wilhelm Platz 1, D‐45470 Mülheim an der Ruhr, Germany
Keywords: NMR; 53Cr; density-functional calculations; chemical-shift computations; electric field gradients
Abstract (English):

53Cr chemical shifts of CrO42-, Cr2O72-, CrO3X-, CrO2X2(X = F, Cl), and Cr(CO)5L (L = CO, PF3, CHNH2, CMeNMe2) are computed, using geometries optimized with the gradient-corrected BP86 density functional, at the gauge-including atomic orbitals (GIAO)-, BPW91-, and B3LYP levels. For this set of compounds, substituent effects on d(53Cr) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. For selected cases, 53Cr NMR line widths can be rationalized in terms of electric field gradients (EFGs) computed with the BPW91 functional, but in general other factors such as molecular correlation times appear to be dominating. 53Cr chemical shifts and EFGs are predicted for CrO3, Cr(C6H6)2, Cr(C6H6)CO3, and, with reduced reliability, for Cr2(m2-O2CH)4. Copyright © 2006 John Wiley & Sons, Ltd.

MRC: 13C SSNMR of taxol

Magnetic Resonance in Chemistry
Vol: 44, Issue: 6, May 2006
pp. 581 - 585

Title: Solid-state NMR studies of the molecular structure of Taxol
Authors: Ho, Yua; Tzou, Der-Lii M.; Chu, Feng-Ia
Affiliations: a. Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China
Keywords: NMR; 13C; Taxol; molecular conformation
Abstract (English):

Solid-state 13C{1H} cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol. Copyright © 2006 John Wiley & Sons, Ltd.

MRC; ssnmr of nanocrystalline hydroxyapatite; Jäger

Magnetic Resonance in Chemistry
Vol: 44, Issue: 6, May 2006
pp. 573 - 580

Title: A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatite
Authors: Jäger, Christiana; Welzel, Theab; Meyer-Zaika, Wolfgangb; Epple, Matthiasb
Affiliations: a. Federal Institute for Materials Research and Testing, Division I.3, Working Group NMR Spectroscopy, Richard Willstaetter Str. 11, D‐12489 Berlin, Germany
b. Institute of Inorganic Chemistry, University Duisburg‐Essen, Universitaetsstr. 5‐7, D‐45117 Essen, Germany
Keywords: NMR; 1H; 31P; biomineralization; hydroxyapatite; calcium phosphate; nanoparticles
Abstract (English):

Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30–50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd.

Progress in NMR: 13C of columnar liquid crystals

Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 48, Issue: 2-3, May 30, 2006
pp. 85-107

Title: Carbon-13 NMR spectroscopy applied to columnar liquid crystals
Authors: Dvinskikh, Sergey V.a, b; Sandström, Dickb; Zimmermann, Herbertc; Maliniak, Arnoldb
Affiliations: a. Institute of Physics, St Petersburg State University, Ulianovskaia 1, 198504 St Petersburg, Russian Federation
b. Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden
c. Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany
Keywords: Columnar liquid crystals; Solid-state NMR; Carbon-13 NMR; Dipolar coupling; Chemical shift anisotropy

SSNMR; 19F NMR of polymers; Hazendonk

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123

Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):

Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.

SSNMR; 17O NMR, Exchange; Zr-tungstate

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105

Title: Quantitative analysis of 17O exchange and ... relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):

The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).

SSNMR; 17O-enriched pyrophosphates; Freude

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74

Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):

For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.

SSNMR: 14N NQR of sulfa drugs

Solid-State NMR:

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68

Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):

The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.

SSNMR journal update - Rob - Vol 30, i.2 Sept. 2006

Solid-State NMR:

Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006
pp. 61-68

Title: 14N nuclear quadrupole resonance of some sulfa drugs
Authors: Blinc, Roberta, b; Seliger, Janeza, c; Zidansek, Aleksandera, b; Zagar, Veselkoa; Milia, Fanid; Robert, Hectore
Affiliations: a. J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
b. Jožef Stefan International Postgraduate School, Jamova 39, 1000 Ljubljana, Slovenia
c. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
d. NCSR Demokritos, Aghia Paraskevi Attikis, Athens, Greece
e. GE Security, Quantum Magnetics, Inc, 15175 Innovation Dr, San Diego, CA 92128, USA
Keywords: Polymorphs; Sulfa drugs; 14N nuclear quadrupole resonance
Abstract (English):

The 14N nuclear quadrupole double resonance spectra of different polymorphs of sulfanilamide, sulfadiazine, sulfamerazine and sulfamethazine have been measured and the 14N quadrupole coupling tensors have been determined. The obtained 14N spectra are compared with those of other sulfa drugs like sulfathiazole. It is shown that different polymorphs can be easily discriminated. The application of this technique for non-destructive analysis, polymorph determination and quality control in the production of pharmaceuticals is stressed.

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Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 69-74

Title: Solid-state NMR studies of 17O-enriched pyrophosphates
Authors: Prochnow, Daniela; Grimmer, Arnd-Rüdigerb; Freude, Dietera
Affiliations: a. Abteilung Grenzflächenphysik, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany
b. Institut für Chemie, Fachinstitut für Anorganische und Allgemeine Chemie, Humboldt-Universität zu Berlin, Rudower Chaussee 5, Haus 3.51, Berlin, Germany
Keywords: NMR; Multiple quantum MAS; Double-rotation; Inorganic phosphates; Crystalline pyrophosphates; 17O
Abstract (English):

For the first time, 17O NMR studies were performed on 17O-enriched crystalline pyrophosphates (magnesium-, sodium- and barium-pyrophosphate) by means of triple-quantum magic-angle spinning (3QMAS) and double-rotation (DOR) in the high external field of 17.6T. Oxygen atoms in bridging positions (P–OB–P) exhibit a significant higher quadrupole coupling constant compared to oxygen atoms in terminal positions (P–OT). With increasing cationic radius a higher value of the chemical shift of the terminal oxygen atoms is observed.

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Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 98-105

Title: Quantitative analysis of 17O exchange and Formula Not Shown relaxation data: Application to zirconium tungstate
Authors: Hodgkinson, Paula; Hampson, Matthew R.a
Affiliations: a. Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Keywords: Solid-state; NMR; Exchange; Relaxation; O-17; Quadrupole
Abstract (English):

The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175–15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid Formula Not Shown relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with Formula Not Shown values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40–226°C).

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Solid State Nuclear Magnetic Resonance
Vol: 30, Issue: 2, September, 2006 Bibliographic Page
pp. 114-123

Title: Fluorine-19 solid state NMR study of vinylidenefluoride polymers using selective relaxation filters
Authors: Wormald, Philipa; Ameduri, Brunob; Harris, Robin K.c; Hazendonk, Pauld
Affiliations: a. School of Chemistry, University of St Andrews, Purdie Building, St. Andrews KY16 9ST, UK
b. Laboratory of Macromolecular Chemistry, Ecole Nationale de Chimie de Montpellier, Unite Mixte Recherche CNRS 5076, 8 rue de l’Ecole Normale, F 34296 Montpellier, Cedex 5, France
c. Department of Chemistry, University of Durham Science Laboratories, South Road, Durham DH1 3LE, UK
d. Department of Chemistry and Biochemistry, 4401 University Drive, University of Lethbridge, Alberta, Canada
Keywords: 19F solid-state NMR; Relaxation filters; Fluoropolymers; High-speed MAS; Vinylidene fluoride; Telomer
Abstract (English):

Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1r filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to b PVDF, whereas the PVDF contained crystallites of the a form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately -115 and approximately -117ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.




JMR; pressurized glass inserts for MAS rotors

Journal of Magnetic Resonance
Vol: 181, Issue: 2, August, 2006
pp. 229-232

Title: An easy way to prepare pressurized glass inserts for MAS rotors
Authors: Tallavaara, Pekkaa; Jokisaari, Jukkaa
Affiliations: a. NMR Research Group, Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 University of Oulu, Finland
Keywords: MAS rotor insert; Xenon; Liquid crystal; Porous material; Pressurised sample
Abstract (English):

A novel technique to prepare pressurized glass insert samples for MAS rotors is described. In this technique, a small drop of epoxy is added to the tip of a piston and the gas is squeezed into the insert by pressing the piston. The amount of gas, i.e., pressure, in the sample can be controlls doing it better, it's all over.

I have a post up on the Killer Year Blog on the subject. It deals with writing, but the message applies to any kind of hula hoop you're trying to keep in the air.

Thursday, August 03, 2006

Andy's literature search is updated

natural abundance 43Ca SSNMR

Chemical Physics Letters
Volume 427, Issues 1-3 , 18 August 2006, Pages 201-205

Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials

Abstract
As a first step for probing Ca sites in biomolecules using solid-state 43Ca NMR spectroscopy, natural abundance 43Ca NMR data of calcium-containing organic solids is reported. The 43Ca NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the 43Ca isotropic chemical shift with Ca–O distance is found: the 43Ca shift increases as the mean Ca–O distance decreases, with a strong deshielding being observed for calcium with strong Ca–O bonds (distance <2.4>

new heteronuclear decoupling sequence

Chemical Physics Letters
Volume 426, Issues 4-6, 4 August 2006, Pages 459-463

Swept-frequency two-pulse phase modulation for heteronuclear dipolar decoupling in solid-state NMR

Rajendra Singh Thakura, Narayanan D. Kurur, 1, a, and P.K. Madhu

Abstract
We introduce a heteronuclear dipolar decoupling sequence for application in solid-state nuclear magnetic resonance. The sequence, called swept-frequency two-pulse phase modulation (SWf-TPPM), is based on one of the decoupling sequences, TPPM. The sequence is robust in performance with respect to various experimental parameters, such as, the pulse flip angle, pulse phase, and offset and a comparison is made with other decoupling schemes, namely TPPM, SPINAL, and XiX, on a sample of U–13C-labelled tyrosine for magic-angle spinning speeds up to 14 kHz.

13C DQ under moderate MAS

Chemical Physics Letters
Volume 426, Issues 1-3 , 26 July 2006, Pages 187-191

Multiple-quantum 13C solid-state NMR spectroscopy under moderate magic-angle spinning

Sungsool Wia, , and Son-Jong Hwangb

Abstract
A new experimental scheme for the excitation and detection of 13C multiple-quantum (MQ) NMR signals in solids under magic-angle spinning (MAS) condition is presented. Symmetry-based dipolar DQ recoupling sequences have been concatenated by π/2 pulses to generate high-order 13C MQ coherences in dipolar coupled networks. This approach generates every order of MQ coherences at moderate MAS frequencies.

JCPA update

J. Phys. Chem. A, ASAP Article 10.1021/jp061350w S1089-5639(06)01350-8
Web Release Date: August 2, 2006

Alan Wong, Ramsey Ida, Xin Mo, Zhehong Gan, Jennifer Poh, and Gang Wu*

Abstract:

We report a solid-state 25Mg NMR spectroscopic study of two magnesium-containing organic compounds: monopyridinated aqua(magnesium) phthalocyanine (MgPc·H2O·Py) and chlorophyll a (Chla). Each of these compounds contains a Mg(II) ion coordinating to four nitrogen atoms and a water molecule in a square-pyramidal geometry. Solid-state 25Mg NMR spectra for MgPc·H2O·Py were obtained at 11.7 T (500 MHz for 1H) for a 25Mg-enriched sample (99.1% 25Mg atom) using both Hahn-echo and quadrupole Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences. Solid-state 25Mg NMR spectra for Chla were recorded at 25Mg natural abundance (10.1%) at 19.6 T (830 MHz for 1H). The 25Mg quadrupole parameters were determined from spectral analyses: MgPc·H2O·Py, CQ = 13.0 ± 0.1 MHz and Q = 0.00 ± 0.05; Chla, CQ = 12.9 ± 0.1 MHz and Q = 1.00 ± 0.05. This work represents the first time that Mg(II) ions in a square-pyramidal geometry have been characterized by solid-state 25Mg NMR spectroscopy. Extensive quantum mechanical calculations for electric-field-gradient (EFG) and chemical shielding tensors were performed at restricted Hartee-Fock (RHF), density functional theory (DFT), and second-order Mller-Plesset perturbation theory (MP2) levels for both compounds. Computed 25Mg nuclear quadrupole coupling constants at the RHF and MP2 levels show a reasonable basis-set convergence at the cc-pV5Z basis set (within 7% of the experimental value); however, B3LYP results display a drastic divergence beyond the cc-pVTZ basis set. A new crystal structure for MgPc·H2O·Py is also reported.