Tuesday, December 18, 2007

Hiyam's Journal Update

Chem. Mater., 19 (25), 6277–6289 10.

Cation Ordering in Li[NixMnxCo(1–2x)]O2-Layered Cathode Materials: A Nuclear Magnetic Resonance (NMR), Pair Distribution Function, X-ray Absorption Spectroscopy, and Electrochemical Study
Dongli Zeng,† Jordi Cabana,† Julien Bréger,† Won-Sub Yoon,‡ and Clare P. Grey*†

Several members of the compositional series Li[NixMnxCo(1–2x)]O2 (0.01 ≤ x ≤ 1/3) were synthesized and characterized. X-ray diffraction results confirm the presence of the layered α-NaFeO2-type structure, while X-ray absorption near-edge spectroscopy experiments verify the presence of Ni2+, Mn4+, and Co3+. Their local environment and short-range ordering were investigated by using a combination of 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and neutron pair distribution function (PDF) analysis, associated with reverse Monte Carlo (RMC) calculations. The 6Li MAS NMR spectra of compounds with low Ni/Mn contents (x ≤ 0.10) show several well-resolved resonances, which start to merge when the amount of Ni and Mn increases, finally forming a broad resonance at high Ni/Mn contents. Analysis of the 6Li MAS NMR 6Li[Ni0.02Mn0.02Co0.96]O2 spectrum, is consistent with the formation of Ni2+ and Mn4+ clusters within the transition-metal layers, even at these low-doping levels. The oxidation state of Ni in this high Co content sample strongly depends upon the Li/transition metal ratio of the starting materials. Neutron PDF analysis of the highest Ni/Mn content sample Li[Ni1/3Mn1/3Co1/3]O2 shows a tendency for Ni cations to be close to Mn cations in the first coordination shell; however, the Co3+ ions are randomly distributed. Analysis of the intensity of the “LiCoO2” resonance, arising from Li surrounded by Co3+ in its first two cation coordination shells, for the whole series provides further evidence for a nonrandom distribution of the transition-metal cations. The presence of the insulator-to-metal transition seen in the electrochemical profiles of these materials upon charging correlates strongly with the concentration of the “LiCoO2” resonance.

Chem. Mater., 19 (25), 6088–6094
Characterization of the Phosphate Units in Rat Dentin by Solid-State NMR Spectroscopy
Yao-Hung Tseng,† Yi-Ling Tsai,† Tim W. T. Tsai,† John C. H. Chao,† Chun-Pin Lin,*‡ Shih-Hao Huang,‡ Chung-Yuan Mou,†§ and Jerry C. C. Chan*†

Dentin samples of the incisor taken from Wistar rats of different ages are studied. A series of physical techniques are used to characterize the samples, with particular emphasis on 31P solid-state nuclear magnetic resonance. The structure of incisor dentin in rats can be described as apatite crystallites embedded in an amorphous matrix. We find that 19% of the apatite crystallites contain hydroxyl groups, which are distributed near the surface of the crystallites. The internal region of the crystallites is deficient in hydroxyl groups. As rats mature with age, there are several changes in the chemical composition of the incisor dentin: (i) the water content and phosporous amount in the amorphous matrix decrease; (ii) the amount of the phosphorus species in the apatite crystallites remains the same; and (iii) the loss of phosphorus species is accompanied by approximately the same loss of the calcium content.

Chem. Mater,; 2007; 19(26) pp 6367-6369; (Communication)

First Principles Calculations of NMR Parameters in Biocompatible Materials Science: The Case Study of Calcium Phosphates, β- and γ-Ca(PO3)2. Combination with MAS-J ExperimentsFrédérique Pourpoint, Adi Kolassiba, Christel Gervais, Thierry Azaïs, Laure Bonhomme-Coury, Christian Bonhomme, and Francesco Mauri

J. Am. Chem. Soc., 129 (49), 15164 -15173, 2007. 10.1021/ja0737117 S0002-7863(07)03711-0 Web

Paramagnetic NMR Relaxation in Polymeric Matrixes: Sensitivity Enhancement and Selective Suppression of Embedded Species (1H and 13C PSR Filter)
Eduardo Fernandez-Megia, Juan Correa, Ramon Novoa-Carballal, and Ricardo Riguera*

A study of the practical applications of the addition of paramagnetic spin relaxation (PSR) ions to a variety of polymers (PLL, PAA, PGA, PVP, and polysaccharides such as hyaluronic acid, chitosan, mannan, and dextran) in solution (D2O and DMSO-d6) is described. Use of GdIII, CuII, and MnII allows a reduction of up to 500% in the 1H longitudinal relaxation times (T1), and so in the time necessary for recording quantitative NMR spectra (sensitivity enhancement) neither an increase of the spectral line width nor chemical shift changes resulted from addition of any of the PSR agents tested. Selective suppression of the 1H and 13C NMR signals of certain components (low MW molecules and polymers) in the spectrum of a mixture was attained thanks to their different sensitivity [transverse relaxation times (T2)] to GdIII (PSR filter). Illustration of this strategy with block copolymers (PGA-g-PEG) and mixtures of polymers and low MW molecules (i.e., lactose-hyaluronic acid, dextran-PAA, PVP-glutamic acid) in 1D and 2D NMR experiments (COSY and HMQC) is presented. In those mixtures where PSR and CPMG filters alone failed in the suppression of certain components (i.e., PVP-mannan-hyaluronic acid) due to their similarity of 1H T2 values and sensitivities to GdIII, use of the PSR filter in combination with CPMG sequences (PSR-CPMG filter) successfully resulted in the sequential suppression of the components (hyaluronic acid first and then mannan).

J. Am. Chem. Soc., 129 (49), 15233 -15239, 2007.
Determination of Global Structure from Distance and Orientation Constraints in Biological Solids Using Solid-State NMR Spectroscopy
Loren B. Andreas, Anil K. Mehta,* and Manish A. Mehta*

We report the results from a new solid-state NMR experiment, DANTE-REDOR, which can determine global secondary structure in uniformly (13C,15N)-enriched systems by simultaneously measuring distance and orientation constraints. Following a heteronuclear spin-pair selection using a DANTE pulse train, the magnitude and orientation of the internuclear dipole vector, within the chemical shift anisotropy (CSA) frame of the observed nucleus, are determined by tracking the dephasing of individual spinning sidebands under magic angle spinning. The efficacy of the experiment is demonstrated by measuring the imidazole side-chain orientation in U-[13C6,15N3]-L-histidine·HCl·H2O

Friday, December 14, 2007

Joel's journal updates

Advances in Structural Analysis of Fluoroaluminates Using DFT Calculations of 27Al Electric Field Gradients
M. Body, C. Legein, J.-Y. Buzaré, G. Silly, P. Blaha, C. Martineau, and F. Calvayrac
Based on the analysis of 23 aluminum sites from 16 fluoroaluminates, the present work demonstrates the strong potential of combining accurate NMR quadrupolar parameter measurements, density functional theory (DFT)-based calculations of electric field gradients (EFG), and structure optimizations as implemented in the WIEN2k package for the structural and electronic characterizations of crystalline inorganic materials. Structure optimizations are essential for compounds whose structure was refined from usually less accurate powder diffraction data and provide a reliable assignment of the 27Al quadrupolar parameters to the aluminum sites in the studied compounds. The correlation between experimental and calculated EFG tensor elements leads to the proposition of a new value of the 27Al nuclear quadrupole moment Q(27Al) ) 1.616 ((0.024)  10-29 m2. The DFT calculations provide the orientation of the 27Al EFG tensors in the crystal frame. Electron density maps support that the magnitude and orientation of the 27Al EFG tensors in fluoroaluminates mainly result from the asymmetric distribution of the Al 3p orbital valence electrons. In most cases, the definition of relevant radial and angular distortion indices, relying on EFG orientation, allows correlations between these distortions and magnitude and sign of the Vii.

K-39 Quadrupolar and Chemical Shift Tensors for Organic Potassium Complexes and Diatomic Molecules
Philip K. Lee, Rebecca P. Chapman, Lei Zhang, Jiaxin Hu, Leonard J. Barbour, Elizabeth K. Elliott, George W. Gokel, and David L. Bryce
Solid-state potassium-39 NMR spectra of two potassium complexes of crown-ether-based organic ligands (1·KI and 2) have been acquired at 11.75 and 21.1 T and interpreted to provide information on the 39K quadrupolar and chemical shift tensors. The analyses reveal a large potassium chemical shift tensor span of 75 ± 20 ppm for 1·KI. This appears to be the first such measurement for potassium in an organic complex, thereby suggesting the utility of potassium chemical shift tensors for characterizing organic and biomolecular K+ binding environments. Compound 2 exhibits a cation- interaction between K+ and a phenyl group, and therefore, the 39K NMR tensors obtained for this compound must be partly representative of this interaction. Analyses of potassium-39 spin-rotation data for gaseous 39K19F and 39K35Cl available from molecular beam experiments performed by Cederberg and co-workers reveal the largest potassium CS tensor spans known to date, 84.39 and 141 ppm, respectively. Collectively, the results obtained highlight the potential of ultrahigh-field potassium-39 solid-state NMR spectroscopy and, in particular, the wide range of the anisotropy of the potassium CS tensor when organic and diatomic systems are considered.

Molecular Dynamics in Paramagnetic Materials as Studied by Magic-Angle Spinning 2H NMR Spectra
Motohiro Mizuno,* You Suzuki, Kazunaka Endo, Miwa Murakami, Masataka Tansho, and Tadashi Shimizu
A magic-angle spinning (MAS) 2H NMR experiment was applied to study the molecular motion in paramagnetic compounds. The temperature dependences of 2H MAS NMR spectra were measured for paramagnetic [M(H2O)6][SiF6] (M = Ni2+, Mn2+, Co2+) and diamagnetic [Zn(H2O)6][SiF6]. The paramagnetic compounds exhibited an asymmetric line shape in 2H MAS NMR spectra because of the electron-nuclear dipolar coupling. The drastic changes in the shape of spinning sideband patterns and in the line width of spinning sidebands due to the 180 flip of water molecules and the reorientation of [M(H2O)6]2+ about its C3 axis were observed. In the paramagnetic compounds, paramagnetic spin-spin relaxation and anisotropic g-factor result in additional linebroadening of each of the spinning sidebands. The spectral simulation of MAS 2H NMR, including the effects of paramagnetic shift and anisotropic spin-spin relaxation due to electron-nuclear dipolar coupling and anisotropic g-factor, was performed for several molecular motions. Information about molecular motions in the dynamic range of 102 s-1 k 108 s-1 can be obtained for the paramagnetic compounds from the analysis of 2H MAS NMR spectra when these paramagnetic effects are taken into account.

Carbon-13 Chemical Shift Tensors of Disaccharides: Measurement, Computation and Assignment
Limin Shao, Jonathan R. Yates, and Jeremy J. Titman*
A recently developed chemical shift anisotropy amplification solid-state nuclear magnetic resonance (NMR) experiment is applied to the measurement of the chemical shift tensors in three disaccharides: sucrose, maltose, and trehalose. The measured tensor principal values are compared with those calculated from first principles using density functional theory within the planewave-pseudopotential approach. In addition, a method of assigning poorly dispersed NMR spectra, based on comparing experimental and calculated shift anisotropies as well as isotropic shifts, is demonstrated.

Methanol Behviour in Direct Methanol Fuel Cells

Younkee Paik, Seong-Soo Kim, Oc Hee Han
Angwandte (2007)47, 94.
Methanol crossover and reaction intermediates are studied in a direct methanol fuel cell (DMFC) by means of 2D and 13C MAS NMR spectroscopy. A membrane electrode assembly (MEA) composed of three polymer electrolyte membrane (PEM) layers is used in the DMFC, and the middle PEM film is extracted to perform the NMR measurements.

Theory and Computation of Nuclear Magnetic Resonance Parameters
J. Vaara
The art of quantum chemical electronic structure calculation has over the last 15 years reached a point where systematic computational studies of magnetic response properties have become a routine procedure for molecular systems. One of their most prominent areas of application are the spectral parameters of nuclear magnetic resonance (NMR) spectroscopy, due to the immense importance of this experimental method in many scientific disciplines. This article attempts to give an overview on the theory and state-of-the-art of the practical computations in the field, in terms of the size of systems that can be treated, the accuracy that can be expected, and the various factors that would influence the agreement of even the most accurate imaginable electronic structure calculation with experiment. These factors include relativistic effects, thermal effects, as well as solvation/environmental influences, where my group has been active. The dependence of the NMR spectra on external magnetic and optical fields is also briefly touched on.

Structural characterization of an anhydrous polymorph of paclitaxel by solid-state NMR
Elizabeth M. Heider, James K. Harper and David M. Grant
The three-dimensional structure of a unique polymorph of the anticancer drug paclitaxel (Taxol®) is established using solid state NMR (SSNMR) tensor (13C & 15N) and heteronuclear correlation (1H–13C) data. The polymorph has two molecules per asymmetric unit (Z = 2) and is thus the first conformational characterization with Z > 1 established solely by SSNMR. Experimental data are correlated with structure through a series of computational models that extensively sample all conformations. For each computational model, corresponding tensor values are computed to supply comparisons with experimental information which, in turn, establishes paclitaxels structure. Heteronuclear correlation data at thirteen key positions provide shift assignments to the asymmetric unit for each comparison. The two distinct molecules of the asymmetric unit possess nearly identical baccatin III moieties with matching conformations of the C10 acetyl moiety and, specifically, the torsion angle formed by C30–O–C10–C9. Additionally, both are found to exhibit an extended conformation of the phenylisoserine sidechain at C13 with notable differences in the dihedral angles centered around the rotation axes of O–C13, C2–C1 and C3–C2.

Microscopic Li self-diffusion parameters in the lithiated anode material Li4+xTi5O12 (0 x 3) measured by 7Li solid state NMR
Martin Wilkening, Wojciech Iwaniak, Jessica Heine, Viktor Epp, Alexandra Kleinert, Malte Behrens, Gerhard Nuspl, Wolfgang Bensch and Paul Heitjans
The microscopic Li diffusion parameters in the lithiated spinel Li4+xTi5O12, which is on its way to become a commercially used anode material in Li ion batteries, are probed for the first time via nuclear magnetic resonance spectroscopy.

A high-field solid-state 35/37Cl NMR and quantum chemical investigation of the chlorine quadrupolar and chemical shift tensors in amino acid hydrochlorides
Rebecca P. Chapman and David L. Bryce
A series of six L-amino acid hydrochloride salts has been studied by 35/37Cl solid-state NMR spectroscopy (at 11.75 and 21.1 T) and complementary quantum chemical calculations. Analyses of NMR spectra acquired under static and magic-angle-spinning conditions for the six hydrochloride salts, those of aspartic acid, alanine, cysteine, histidine, methionine and threonine, allowed the extraction of information regarding the chlorine electric field gradient (EFG) and chemical shift tensors, including their relative orientation. Both tensors are found to be highly dependent on the local environment, with chlorine-35 quadrupolar coupling constants (CQ) ranging from –7.1 to 4.41 MHz and chemical shift tensor spans ranging from 60 to 100 ppm; the value of CQ for aspartic acid hydrochloride is the largest in magnitude observed to date for an organic hydrochloride salt. Quantum chemical calculations performed on cluster models of the chloride ion environment demonstrated agreement between experiment and theory, reproducing CQ to within 18%. In addition, the accuracy of the calculated values of the NMR parameters as a function of the quality of the input structure was explored. Selected X-ray structures were determined (L-Asp HCl; L-Thr HCl) or re-determined (L-Cys HCl·H2O) to demonstrate the benefits of having accurate crystal structures for calculations. The self-consistent charge field perturbation model was also employed and was found to improve the accuracy of calculated quadrupolar coupling constants, demonstrating the impact of the neighbouring ions on the EFG tensor of the central chloride ion. Taken together, the present work contributes to an improved understanding of the factors influencing 35/37Cl NMR interaction tensors in organic hydrochlorides.

Wednesday, November 21, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (47), 14717 -14723, 2007. 10.1021/ja0749690 S0002-7863(07)04969-4 Web Release Date: November 7, 2007 Copyright © 2007 American Chemical Society
Membrane-Bound Conformation of Peptaibols with Methyl-Deuterated -Amino Isobutyric Acids by 2H Magic Angle Spinning Solid-State NMR Spectroscopy
Kresten Bertelsen, Jan M. Pedersen, Brian S. Rasmussen, Troels Skrydstrup, Niels Chr. Nielsen, and Thomas Vosegaard*
Contribution from the Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark tv@chem.au.dk.
Received July 5, 2007
We present the use of 2H magic-angle spinning (MAS) NMR on methyl-deuterated -amino isobutyric acid (Aib) as a new method to obtain fast and accurate structural constraints on peptaibols in membrane-bound environments. Using nonoriented vesicle-reconstituted samples we avoid the delicate preparation of oriented samples, and the use of MAS ensures high sensitivity and thereby very fast acquisition of experimental spectra. Furthermore, given the high content (~40%) of Aib in peptaibols and the fact that the amino acid Aib may be synthesized from cheap starting materials, even in the case of 2H, 13C, or 15N labeling, this method is ideally suited for studies of the membrane-bound conformation of peptaibols.

Thursday, November 08, 2007

Aaron's Journal Update

-Yining Huang, 23Na and 7Li NMR
J. Phys. Chem. C, 111 (36), 13427 -13436, 2007. 10.1021/jp0706275 S1932-7447(07)00627-9

Study of the Adsorption of Toluene in Zeolite LiNa-Y by Solid-State NMR Spectroscopy
Abstract: The adsorption of toluene inside partially Li+-exchanged zeolite Y (LiNa-Y) was examined by solid-state NMR spectroscopy. The environments of Li+ and Na+ ions at different sites in the framework before and after adsorption were characterized by 7Li and 23Na magic-angle-spinning (MAS) NMR. The information on the dynamic behavior of guest molecules inside the supercage of the zeolite was obtained from wide-line 2H NMR spectra. The cation-sorbate interactions were directly probed by heteronuclear dipolar coupling based double-resonance experiments such as 7Li{1H} and 23Na{1H} rotational-echo double-resonance (REDOR) experiments. Molecular modeling was also performed to assist in interpreting NMR results. The 7Li and 23Na MAS results indicate that during ion exchange the incoming Li+ ions fill the SI' sites first and then the SII sites, and the remaining Na+ ions stay mostly at SII sites. The MAS and REDOR results show that the toluene molecules are facially coordinated to the cations at SII sites in the supercage to form a -complex, resulting in a significant change in chemical shift of the Li+ ions and a dramatic reduction in the quadrupolar coupling constant (QCC) of the Na+ ions. The 2H NMR spectra indicate that at room temperature some toluene molecules reorient around the molecular long axis (two-site flip) and others undergo multiple-site jump motion, but at low temperature only two-site flip, at a much slower rate, remains. Both 2H and REDOR results show that the molecular dynamics of the guest species is also affected by the cation composition.

-Joel/Rob - M.E. Smith, 27Al, 29Si and 17O NMR

J. Phys. Chem. C, 111 (37), 13740 -13746, 2007. 10.1021/jp0739871 S1932-7447(07)03987-8

Structural Characterization of SiO2 and Al2O3 Zener-Pinned Nanocrystalline TiO2 by NMR, XRD and Electron Microscopy
Luke A. O'Dell, Shelley L.P. Savin, Alan V. Chadwick, and Mark E. Smith*
Abstract: Nanocrystalline TiO2 samples were prepared using sol-gel techniques in a pure form and also Zener pinned with either silica or alumina to reduce the growth of the crystallites during the annealing process and to stabilize the anatase phase at high temperatures. These samples were studied using 17O, 27Al, and 29Si nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and electron microscopy. The silica pinning phase was found to successfully restrict nanocrystal growth as well as stabilize the anatase phase at temperatures up to 800 C. The alumina phase had less of a pinning effect, and it reacted with the TiO2 to form tialite. 17O NMR relaxation time measurements on enriched samples showed that the presence of the pinning phases also reduced the activation energy for the oxygen ion diffusion mechanism.

Everyone - FAST MAS experiments to measure metal-carbon bond distances.

J. Phys. Chem. B, 111 (33), 9693 -9696, 2007. 10.1021/jp0727289 S1520-6106(07)02728-9

Elucidating Connectivity and Metal-Binding Structures of Unlabeled Paramagnetic Complexes by 13C and 1H Solid-State NMR under Fast Magic Angle Spinning
Nalinda P. Wickramasinghe, Medhat A. Shaibat, and Yoshitaka Ishii*
Abstract: Characterizing paramagnetic complexes in solids is an essential step toward understanding their molecular functions. However, methodologies to characterize chemical and electronic structures of paramagnetic systems at the molecular level have been notably limited, particularly for noncrystalline solids. We present an approach to obtain connectivities of chemical groups and metal-binding structures for unlabeled paramagnetic complexes by 13C and 1H high-resolution solid-state NMR (SSNMR) using very fast magic angle spinning (VFMAS, spinning speed 20 kHz). It is experimentally shown for unlabeled Cu(II)(Ala-Thr) that 2D 13C/1H correlation SSNMR under VFMAS provides the connectivity of chemical groups and assignments for the characterization of unlabeled paramagnetic systems in solids. We demonstrate that on the basis of the assignments provided by the VFMAS approach multiple 13C-metal distances can be simultaneously elucidated by a combination of measurements of 13C anisotropic hyperfine shifts and 13C T1 relaxation due to hyperfine interactions for this peptide-Cu(II) complex. It is also shown that an analysis of 1H anisotropic hyperfine shifts allows for the determination of electron-spin states in Fe(III)-chloroprotoporphyin-IX in solid states.


J. Phys. Chem. B, 111 (33), 9711 -9721, 2007. 10.1021/jp072112j S1520-6106(07)02112-8
High-Resolution Solid-State NMR Studies of Poly(vinyl phosphonic acid) Proton-Conducting Polymer: Molecular Structure and Proton Dynamics
Young Joo Lee,
* Bahar Bingöl, Tatiana Murakhtina, Daniel Sebastiani, Wolfgang H. Meyer, Gerhard Wegner, and Hans Wolfgang Spiess*
Abstract:The structure and the local proton mobility of poly(vinyl phosphonic acid) were studied by solid-state NMR under fast magic-angle spinning. At elevated temperatures, the signature of the hydrogen-bonded P-OH protons is observed in 1H magic-angle spinning (MAS) NMR as a single resonance at 10.5 ppm. Both 1H double-quantum NMR and variable-temperature experiments demonstrate that P-OH protons are mobile and thus able to contribute to proton conductivity. Below room temperature, two different types of hydrogen-bonded P-OH resonances are observed at 10.5 and 15 ppm, and 1H double-quantum NMR demonstrates that these protons are immobile on the NMR time scale. By means of first-principles calculations of a model polymer, we have assigned the additional hydrogen-bonded species at lower temperatures to phosphonic acid anhydride and charged anhydride. Also, in the 31P MAS NMR spectrum, two distinct resonances appear, arising from "normal" phosphonic acid and phosphonic acid anhydride. 31P double-quantum NMR experiments reveal that there is no phase segregation between normal and phosphonic acid anhydride and the condensation reaction occurs randomly throughout the system. The formation of acid anhydride leads to a decrease in proton conductivity through two mechanisms, (1) decrease in the number of charge carriers and (2) blockage of charge transport pathways through immobilization of charge carriers together with a hindered reorientation of the anhydride group. Our results provide strong evidence for these mechanisms by demonstrating that the conductivity is greatly influenced by the presence of phosphonic acid anhydride.


J. Phys. Chem. B, 111 (33), 9747 -9757, 2007. 10.1021/jp072061q S1520-6106(07)02061-5
27Al NMR Study of the Structure of Lanthanum- and Yttrium-Based Aluminosilicate Glasses and Melts
P. Florian,* N. Sadiki, D. Massiot, and J. P. Coutures
Abstract: We have investigated by 27Al nuclear magnetic resonance spectroscopy some compositions in the Ln2O3-Al2O3-SiO2 (Ln = Y or La) ternary phase diagram containing more than 60 mol % of SiO2. One- and two-dimensional high-field (17.6 T) high-speed (30 kHz) magic angle spinning experiments have been performed along with simulations of the spectra to quantify the amount of penta-coordinated aluminum present in those glasses as a function of composition. Very high-temperature experiments have allowed to follow selected samples from 2200 C down to 1700 C and hence to characterize the aluminum coordination state and dynamics in those liquids. The present study re-enforces the current view that "minor" species such as penta-coordinated aluminum are actually present in a considerable amount in aluminosilicate glasses, and high-temperature liquids at and above the charge compensation join. The high-field strength of Y3+ and La3+ reveal, for the first time in glasses, a different mean electric field gradient perceived by the tetra- and penta-coordinated aluminum environments. The movements responsible for the NMR relaxation of aluminum in the high-temperature liquid are shown to be uncorrelated with the movements responsible for the macroscopic shear viscosity. Results obtained both on glasses and in situ at high-temperature suggest a preferential localization of Ln3+ nearby tetra-coordinated aluminum species, with possible formation of tricluster and/or Ln3+ coordination changes.

-11B NMR

J. Phys. Chem. B, 111 (33), 9758 -9761, 2007. 10.1021/jp072223i S1520-6106(07)02223-7

11B MAS NMR Spectroscopic Study of Structural Relaxation, Aging, and Memory Effect at the Atomic S
cale in a Borosilicate Glass
Sezen Soyer Uzun and Sabyasachi Sen*
Abstract: Relaxation kinetics of boron coordination environments in a borosilicate glass in response to temperature jumps has been monitored using 11B magic-angle spinning (MAS) NMR spectroscopy. The relaxation time scale of the BO4/BO3 ratio is found to be closely comparable with those of the bulk properties, namely, refractive index and viscosity, showing a close connection with one another. Samples partially equilibrated at a low temperature, when subjected to a positive temperature jump, display an initial rapid decrease followed by an increase in the BO4/BO3 ratio. This reversal in the trend of the variation of the BO4/BO3 ratio has been interpreted to be the signature of a memory effect, and the implications are discussed within the framework of the potential energy landscape model of glassy dynamics.

- Calculation of C13 tensors in order to measure ordering in a liquid crystal

J. Phys. Chem. B, 111 (33), 9787 -9794, 2007. 10.1021/jp0730693 S1520-6106(07)03069-6

Orientational Order of a Liquid Crystal with Three Chiral Centers by a Combined 13C NMR and DFT Approach
R. Y. Dong,* M. Geppi, A. Marini, V. Hamplova, M. Kaspar, C. A. Veracini, and J. Zhang
Abstract: In this work, the liquid crystal (S)-2-methylbutyl-[4'-(4' '-heptyloxyphenyl)-benzoyl-4-oxy-(S)-2-((S)-2')-benzoyl)-propionyl)]-propionate (ZLL 7/*) was investigated by means of 13C NMR spectroscopy. This compound has a very peculiar mesomorphic behavior, showing the following phases: paraelectric SmA, ferroelectric SmC*, antiferroelectric SmC*A, re-entrant ferroelectric SmC*re, and ferroelectric hexatic Sm*HEX. The structural and orientational ordering properties of ZLL 7/* have been determined by exploiting the nuclear chemical shielding properties of 13C. To this aim, solid-state NMR techniques such as CP, SPINAL-64, and SUPER have been used in combination with DFT calculations. The agreement between experimental and in vacuo DFT shielding parameters appears to be satisfactory. The orientational order parameters obtained from the 13C shielding analysis have been discussed, taking into account different data analysis approaches and comparing them to those previously obtained from an independent 2H NMR study.

-23Na and 95 Mo NMR

J. Phys. Chem. B, 111 (34), 10109 -10117, 2007. 10.1021/jp072883n S1520-6106(07)02883-0

Structural Studies of NaPO3-MoO3 Glasses by Solid-State Nuclear Magnetic Resonance and Raman Spectroscopy
Silvia H. Santagneli, Carla C. de Araujo, Wenzel Strojek, and Hellmut Eckert*
Gaël Poirier, Sidney J. L. Ribeiro, and Younes Messaddeq
Abstract: Vitreous samples were prepared in the (100 - x)% NaPO3-x% MoO3 (0 x 70) glass-forming system by a modified melt method that allowed good optical quality samples to be obtained. The structural evolution of the vitreous network was monitored as a function of composition by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), Raman scattering, and solid-state nuclear magnetic resonance (NMR) for 31P, 23Na, and 95Mo nuclei. Addition of MoO3 to the NaPO3 glass melt leads to a pronounced increase in the glass transition temperatures up to x = 45, suggesting a significant increase in network connectivity. For this same composition range, vibrational spectra suggest that the Mo6+ ions are bonded to some nonbridging oxygen atoms (Mo-O- or Mo=O bonded species). Mo-O-Mo bond formation occurs only at MoO3 contents exceeding x = 45. 31P magic-angle spinning (MAS) NMR spectra, supported by two-dimensional J-resolved spectroscopy, allow a clear distinction between species having two, one, and zero P-O-P linkages. These sites are denoted as Q(2)2Mo, Q(2)1Mo, and Q(2)0Mo, respectively. For x < n =" 0," x =" 45">

- Learn all about membrane proteins

J. Phys. Chem. B, 111 (35), 10340 -10351, 2007. 10.1021/jp073652j S1520-6106(07)03652-8

Structure, Topology, and Dynamics of Membrane Peptides and Proteins from Solid-State NMR Spectroscopy
Mei Hong
Abstract:The high-resolution structure of membrane proteins is notoriously difficult to determine due to the hydrophobic nature of the protein-membrane complexes. Solid-state NMR spectroscopy is a unique and powerful atomic-resolution probe of the structure and dynamics of these important biological molecules. A number of new solid-state NMR methods for determining the depth of insertion, orientation, oligomeric structure, and long-range (10-15 Å) distances of membrane proteins are summarized. Membrane protein depths can now be determined using several complementary techniques with varying site-specificity, distance precision, and mobility requirement on the protein. Membrane protein orientation can now be determined with or without macroscopic alignment, the latter providing a novel alternative for orientation determination of intrinsically curvature-inducing proteins. The novel analyses of -sheet membrane protein orientation are described. The quaternary structure of membrane peptide assemblies can now be elucidated using a 19F spin diffusion technique that simultaneously yields the oligomeric number and intermolecular distances up to 15 Å. Finally, long-range distances up to ~10 Å can now be measured using 1H spins with an accuracy of better than 1 Å. These methods are demonstrated on several -sheet membrane peptides with antimicrobial activities and on two -helical ion-channel proteins. Finally, we show that the nearly ubiquitous dynamics of membrane proteins can be readily examined using 2D correlation experiments. An intimate appreciation of molecular motion in these systems not only leads to important insights into the specific function of these membrane proteins but also may be exploited for other purposes such as orientation determination.

-27Al{19F} and 23Na{19F} REDOR experiments

J. Phys. Chem. B, 111 (35), 10402 -10412, 2007. 10.1021/jp072725w S1520-6106(07)02725-3

Structural Role of Fluoride in Aluminophosphate Sol-Gel Glasses: High-Resolution Double-Resonance NMR Studies
Long Zhang, Carla C. de Araujo, and Hellmut Eckert*
Abstract: The local structure of Na-Al-P-O-F glasses, prepared by a novel sol-gel route, was extensively investigated by advanced solid-state NMR techniques. 27Al{19F} rotational echo double resonance (REDOR) results indicate that the F incorporated into aluminophosphate glass is preferentially bonded to octahedral Al units and results in a significant increase in the concentration of six-coordinated aluminum. The extent of Al-F and Al-O-P connectivities are quantified consistently by analyzing 27Al{31P} and 27Al{19F} REDOR NMR data. Two distinct types of fluorine species were identified and characterized by various 19F{27Al}, 19F{23Na}, and 19F{31P} double resonance experiments, which were able to support peak assignments to bridging (Al-F-Al, -140 ppm) and terminal (Al-F, -170 ppm) units. On the basis of the detailed quantitative dipole-dipole coupling information obtained, a comprehensive structural model for these glasses is presented, detailing the structural speciation as a function of composition.

-27Al, 23Na, 19F, 29Si Solids NMR

J. Phys. Chem. B, 111 (35), 10413 -10420, 2007. 10.1021/jp073687j S1520-6106(07)03687-5

Preferential Binding of Fluorine to Aluminum in High Peralkaline Aluminosilicate Glasses
N. G. Karpukhina, U. Werner-Zwanziger, J. W. Zwanziger,* and A. A. Kiprianov
Abstract: For two series of fluoride-containing aluminosilicate glasses of high peralkaline type, we apply 27Al, 19F, 29Si, and 23Na NMR spectroscopy to understand the structural changes introduced by the addition of alkali fluorides. Adding fluoride in concentrations above the solubility limit causes crystallization of different phases in sodium and potassium glasses despite identical composition. However, the NMR spectra reveal that the structural evolution of the precrystallized states is similar in both series. In particular, fluorine coordinates exclusively to alkaline cations and aluminum. No indication of direct bonding with silicon was found from 19F 29Si cross-polarization experiments. In contrast to other glass systems, double resonance experiments in these peralkaline systems show that halide addition produces at most a minor fraction of tetrahedral aluminum containing fluorine in its coordination sphere. Instead, the fluorine addition prior to crystallization converts up to about 20% of the initial tetrahedral aluminum (1 mol % in absolute units) to 5- and 6-fold coordinated aluminum. A minor portion of five-coordinated aluminum groups is considered as the intermediate to the growing fraction of octahedral aluminum in the silicate matrix. The initialization of the crystallization process is correlated with the saturation of the silicate matrix by octahedral aluminum clusters segregating out under further doping by fluoride. It is suggested that the formation of the nonframework Al-F bonds is responsible for structural relaxation, reflected by the reduction of the glass transition temperature.

J. Phys. Chem. B, 111 (36), 10671 -10680, 2007. 10.1021/jp072001k S1520-6106(07)02001-9

Initio Calculation of Solid-State NMR Spectra for Different Triazine and Heptazine Based Structure Proposals of g-C3N4
Jan Sehnert, Kilian Baerwinkel, and Juergen Senker*
Abstract: We present a comprehensive theoretical study of the structure and NMR parameters of a large number of triazine and heptazine based structure proposals for g-C3N4 in different condensation states. This approach includes a detailed investigation of cyclic melon which tends toward the formation of densely packed hydrogen bonded meshes. In all of the investigated systems, we found planar layers to represent saddlepoints on the energy surface, whereas corrugated species were identified as minima. The corrugation source was linked to the repulsion of nitrogen lone pairs in close NN contacts. A linear dependency of the corrugation energy from the number of NN interactions in the investigated clusters was found. Heptazine based systems gain about twice as much energy per NN close contact in comparison to triazine structures which could be understood in terms of the distortion mechanism in the investigated structures. Furthermore, a full study of the 15N and 13C chemical shift tensors was performed for the different C/N layers. The description of the NMR parameters required dividing the investigated systems into subclusters for which the NMR tensors were calculated with density functional theory (DFT) methods. A statistical analysis of these entities allowed for the investigation of the change in the chemical shift upon corrugation and, in the case of the cyclic melon system, hydrogen bonding. With the here presented study, the most prominent structure models for g-C3N4 are characterized in terms of the 15N and 13C NMR parameters which now can directly be compared to experimental spectra.

-Calculation of J-couplings in DNA

J. Phys. Chem. B, 111 (36), 10813 -10824, 2007. 10.1021/jp072822p S1520-6106(07)02822-2

Theoretical Study of the Scalar Coupling Constants across the Noncovalent Contacts in RNA Base Pairs: The cis- and trans-Watson-Crick/Sugar Edge Base Pair Family
Zuzana Vok ov , Ji í poner, Judit E. poner, and Vladimír Sychrovsk *
Abstract:The structure and function of RNA molecules are substantially affected by non-Watson-Crick base pairs actively utilizing the 2'-hydroxyl group of ribose. Here we correlate scalar coupling constants across the noncovalent contacts calculated for the cis- and trans-WC/SE (Watson-Crick/sugar edge) RNA base pairs with the geometry of base to base and sugar to base hydrogen bond(s). 23 RNA base pairs from the 32 investigated were found in RNA crystal structures, and the calculated scalar couplings are therefore experimentally relevant with regard to the binding patterns occurring in this class of RNA base pairs. The intermolecular scalar couplings 1hJ(N,H), 2hJ(N,N), 2hJ(C,H), and 3hJ(C,N) were calculated for the N-H···N and N-H···O=C base to base contacts and various noncovalent links between the sugar hydroxyl and RNA base. Also, the intramolecular 1J(N,H) and 2J(C,H) couplings were calculated for the amino or imino group of RNA base and the ribose 2'-hydroxyl group involved in the noncovalent interactions. The calculated scalar couplings have implications for validation of local geometry, show specificity for the amino and imino groups of RNA base involved in the linkage, and can be used for discrimination between the cis- and trans-WC/SE base pairs. The RNA base pairs within an isosteric subclass of the WC/SE binding patterns can be further sorted according to the scalar couplings calculated across different local noncovalent contacts. The effect of explicit water inserted in the RNA base pairs on the magnitude of the scalar couplings was calculated, and the data for discrimination between the water-inserted and direct RNA base pairs are presented. The calculated NMR data are significant for structural interpretation of the scalar couplings in the noncanonical RNA base pairs.

-35/37Cl NMR of Ionic Liquids

J. Phys. Chem. B, 111 (40), 11619 -11621, 2007. 10.1021/jp0756449 S1520-6106(07)05644-1

Hydrogen Bonds in Ionic Liquids Revisited: 35/37Cl NMR Studies of Deuterium Isotope Effects in 1-n-Butyl-3-Methylimidazolium Chloride
Richard C. Remsing, Jayme L. Wildin, Ashleigh L. Rapp, and Guillermo Moyna*
Abstract: Detailed knowledge of the structure, dynamics, and interionic interactions of ionic liquids (ILs) is critical to understand their physicochemical properties. In this letter, we show that deuterium isotope effects on the chloride ion 35/37Cl NMR signal represent a useful tool in the study of interionic hydrogen bonds in imidazolium chloride ILs. Sizable 35/37Cl(H,D) values obtained for the model system 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl) upon deuteriation of the imidazolium C-2 and C-2,4,5 positions, of nearly 1 and 2 ppm, respectively, show that the approach can readily identify and differentiate Cl···H hydrogen bonds between the anion and cation. Our study is one of a few examples in which hydrogen-bonding in ILs has been investigated using deuterium isotope effects and, to our knowledge, the only one employing 35/37Cl NMR to detect these interactions. The methodology described could be easily extended to the study of other systems bearing NMR-active nuclei.

-The title says it all

J. Phys. Chem. B, 111 (42), 12088 -12096, 2007. 10.1021/jp073682m S1520-6106(07)03682-6

Provides Checklist of Generic Properties for Atomic-Scale Models of Periodic Mesoporous Silicas
Ilja G. Shenderovich,* Daniel Mauder, Dilek Akcakayiran, Gerd Buntkowsky, Hans-Heinrich Limbach,* and Gerhard H. Findenegg
Abstract:MCM-41 and SBA-15 silicas were studied by 29Si solid-state NMR and 15N NMR in the presence of 15N-pyridine with the aim to formulate generic structural parameters that may be used as a checklist for atomic-scale structural models of this class of ordered mesoporous materials. High-quality MCM-41 silica constitutes quasi-ideal arrays of uniform-size pores with thin pore walls, while SBA-15 silica has thicker pore walls with framework and surface defects. The numbers of silanol (Q3) and silicate (Q4) groups were found to be in the ratio of about 1:3 for MCM-41 and about 1:4 for our SBA-15 materials. Combined with the earlier finding that the density of surface silanol groups is about three per nm2 in MCM-41 (Shenderovich, et al. J. Phys. Chem. B 2003, 107, 11924) this allows us to discriminate between different atomic-scale models of these materials. Neither tridymite nor edingtonite meet both of these requirements. On the basis of the hexagonal pore shape model, the experimental Q3:Q4 ratio yields a wall thickness of about 0.95 nm for MCM-41 silica, corresponding to the width of ca. four silica tetrahedra. The arrangement of Q3 groups at the silica surfaces was analyzed using postsynthesis surface functionalization. It was found that the number of covalent bonds to the surface formed by the functional reagents is affected by the surface morphology. It is concluded that for high-quality MCM-41 silicas the distance between neighboring surface silanol groups is greater than 0.5 nm. As a result, di- and tripodical reagents like (CH3)2Si(OH)2 and CH3Si(OH)3 can form only one covalent bond to the surface. The residual hydroxyl groups of surface-bonded functional reagents either remain free or interact with other reagent molecules. Accordingly, the number of surface silanol groups at a given MCM-41 or SBA-15 silica may not decrease but increase after treatment with CH3Si(OH)3 reagent. On the other hand, nearly all surface silanol groups could be functionalized when HN(Si(CH3)3)2 was used.

J. Phys. Chem. B, 111 (42), 12097 -12102, 2007. 10.1021/jp074517+ S1520-6106(07)04517-8

Rotation and Diffusion of H2 in Hydrogen-Ice Clathrate by 1H NMR
Lasitha Senadheera and Mark S. Conradi*
Abstract:A recently reported hydrogen-ice clathrate carries up to four H2 in each large cage and one H2 in each small cage. We report pulsed proton NMR line shape measurements on H2-D2O clathrate formed at 1500 bar and 250 K. The behavior of the two-pulse spin-echo amplitude with respect to the nutation angle of the refocusing pulse shows that intramolecular dipolar broadening, modulated by H2 molecular reorientations, dominates the line width of the ortho-H2. Dipolar interaction between H2 guests and host D atoms explains the echo variation with the relative phases of the pulses. From 12 to 120 K, the line width varies as 1/T, demonstrating that the three sublevels of J = 1 are split by a constant energy, . The splitting arises from distortion in the otherwise high-symmetry cages from frozen-out D2O orientational disorder. Above 120 K, further line-narrowing signals the onset of H2 diffusion from cage to cage. At the lowest temperature, 1.9 K, the spectrum has Pake powder doublet-like features; the doublet is not fully developed, indicating a broad distribution of order parameters and energies .

J. Phys. Chem. B, 111 (42), 12119 -12123, 2007. 10.1021/jp076046x S1520-6106(07)06046-4

Solid-State 13C NMR Studies on Organic-Inorganic Hybrid Zeolites
Katsutoshi Yamamoto, Yasuyuki Sakata, and Takashi Tatsumi*
Abstract:A novel type of organic-inorganic hybrid zeolite with organic lattice (ZOL) is studied in detail by solid-state 13C magic angle spinning nuclear magnetic resonance (MAS NMR). The 13C MAS NMR measurements employing several pulse sequences quantitatively demonstrate that methylene groups are really incorporated in the framework, although they are partially cleaved into methyl groups. The organic species in ZOL materials are open for adsorbates, which is evidenced by the 13C MAS NMR measurements for an n-hexane-adsorbing ZOL material. This finding strongly suggests that organic moieties are incorporated as a zeolite framework, indicating that ZOL is not a physical mixture of a carbon-containing amorphous aggregate and a conventional zeolite but a true organic-inorganic hybrid zeolite.

-Massiot: 27Al NMR
J. Phys. Chem. B, 111 (44), 12707 -12714, 2007. 10.1021/jp072620t S1520-6106(07)02620-X
Cation Sublattice Disorder Induced by Swift Heavy Ions in MgAl2O4 and ZnAl2O4 Spinels: 27Al Solid-State NMR Study
Nadia Pellerin,* Catherine Dodane-Thiriet, Valérie Montouillout, Michel Beauvy, and Dominique Massiot
Abstract: MgAl2O4 and ZnAl2O4 spinels have been irradiated by swift heavy ions (86Kr and 36S) simulating the irradiation by fission products for applications in the transmutation targets. The structures of unirradiated and irradiated spinel samples have been studied by NMR spectroscopy, with 27Al magic angle spinning and multiple-quantum magic angle spinning experiments. The parameters of fluence and electronic stopping power have been compared. For 86Kr ions, the obtained spectra are modified by irradiation: we observe a rise of the amount of aluminum in tetrahedral sites and a widening of the lines associated with the different aluminum environments compared with those of the pristine samples. Site exchange in the cationic sublattice is then observed and can be quantified from NMR spectra, determining the inversion parameter. An inversion parameter of 0.77 is estimated for the MgAl2O4 spinel irradiated with 1013 Kr ions/cm2, for a value of 0.275 in the pristine samples. Moreover, a line attributed to aluminum in 5-fold coordination with oxygen is observed in irradiated spinel samples at the maximum fluence for krypton. These new aluminum environments can characterize a transition layer which could change toward an amorphous layer, increasing the electronic stopping power and/or the fluence.

- Speiss 13C NMR Studies of Polymers
Macromolecules, 40 (17), 6249 -6256, 2007. 10.1021/ma0706531 S0024-9297(07)00653-5 Chain Dynamics in Poly(n-alkyl acrylates) by Solid-State NMR, Dielectric, and Mechanical Spectroscopies
Marianne Gaborieau,* Robert Graf, Stefan Kahle, Tadeusz Pakula, and Hans W. Spiess*
Abstract:A relaxation process was detected and quantified for the first time in various poly(n-alkyl acrylates) in the melt by a solid-state NMR method, NOE with dipolar filter. By comparison with dielectric spectroscopy and dynamic mechanical measurements carried out on the same samples, the relaxation process detected by NMR occurs at a higher temperature than the simple -relaxation and on a longer time scale than the -relaxation (cooperative -relaxation). This relaxation process could be the isotropization of the main chain (by analogy with structurally similar polymethacrylates), but it is more probably a local relaxation within the alkyl side chain that is usually detected only at significantly lower temperatures. The fact that this side-chain motion is slower than the cooperative main-chain -relaxation of restricted amplitude can be rationalized in the context of restricted amplitude main-chain motions in the local nanostructure present in the samples, as NMR and dielectric spectroscopy detect motions in different frames.

Wednesday, November 07, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (45), 13806 -13807, 2007.
Probing Spatially-Resolved Pt Distribution in PtRu Nanoparticles with 195Pt EC-NMR
Aaron L. Danberry, Bingchen Du, In-Su Park, Yung-Eun Sung, and YuYe Tong*

We report the first quantitative analysis of spatially resolved local Pt distribution in graphite and carbon nanofibers supported PtRu alloy nanoparticles using slow-beat measurements by in situ 195Pt electrochemical NMR. While the two samples had the same nominal 1:1 atomic ratio and similar average particle size, it was found that the former had a rather homogeneous Pt distribution but not the latter, which had Pt segregation at the core and depletion at the surface of the nanoparticles.

Friday, November 02, 2007

Hiyam's Journal Update

Phys. Rev. Lett. 99, 187003 (2007)
NMR Relaxation and Resistivity from Rattling Phonons in Pyrochlore Superconductors
Thomas Dahm1,2 and Kazuo Ueda1
(Received 13 June 2007; published 30 October 2007)

We calculate the temperature dependence of the NMR relaxation rate and electrical resistivity for coupling to a local, strongly anharmonic phonon mode. We argue that the two-phonon Raman process is dominating NMR relaxation. Due to the strong anharmonicity of the phonon an unusual temperature dependence is found having a low temperature peak and becoming constant towards higher temperatures. The electrical resistivity is found to vary like T2 at low temperatures and following a behavior at high temperatures. Both results are in qualitative agreement with recent observations on -pyrochlore oxide superconductors.

Phys. Rev. Lett. 99, 187601 (2007)

Stochastic Dipolar Recoupling in Nuclear Magnetic Resonance of Solids
Robert Tycko
(Received 1 August 2007; published 2 November 2007)

I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body systems.

Wednesday, October 31, 2007

Hiyam's Journal Update

Phys. Rev. B 76, 165122 (2007)
Spin and orbital magnetic response in metals: Susceptibility and NMR shifts
Mayeul d'Avezac, Nicola Marzari, and Francesco Mauri
(Received 12 July 2007; published 23 October 2007)
A DFT-based method is presented which allows the computation of all-electron NMR shifts of metallic compounds with periodic boundary conditions. NMR shifts in metals measure two competing physical phenomena. Electrons interact with the applied magnetic field (i) as magnetic dipoles (or spins), resulting in the Knight shift, and (ii) as moving electric charges, resulting in the chemical (or orbital) shift. The latter is treated through an extension to metals of the gauge-invariant projector augmented wave developed for insulators. The former is modeled as the hyperfine interaction between the electronic spin polarization and the nuclear dipoles. NMR shifts are obtained with respect to the computed shieldings of reference compounds, yielding fully ab initio quantities which are directly comparable to experiment. The method is validated by comparing the magnetic susceptibility of interacting and noninteracting homogeneous gas with known analytical results, and by comparing the computed NMR shifts of simple metals with experiment.

Phys. Rev. B 76, 155201 (2007)

Long-lived spin echoes in a magnetically dilute system: An NMR study of Ge single crystals
A. M. Panich, N. A. Sergeev, and I. Shlimak
(Received 22 March 2007; revised 1 August 2007; published 1 October 2007)

Owing to the well-developed technology, isotopic engineering of Si and Ge semiconductors permits one to control the density of nuclear spins and vary the spin coherence time, a crucial parameter in spintronics and quantum computing where nuclear spin is used as a qubit. In the present paper, we report on the NMR study of 73Ge nuclear spin decoherence in germanium single crystals with different abundances of the 73Ge isotope. Our measurements of Hahn- and solid-echo decays show that they are well fit by a superposition of two exponentials; at that, the deviation from the single exponential is more pronounced in the more spin-diluted sample, causing long-lived echoes. We show that the decay of these echoes becomes slower with the reduction of 73Ge abundance and is therefore caused by dipole-dipole interaction, reflecting the fundamental decoherence process in the spin system. The fast decay at the beginning of the relaxation process is shown to be mainly caused by the quadrupole interaction. Our experimental findings are supported by the calculations of Hahn- and solid-echo decays in the germanium crystals under study. Quite good agreement between the theory and experiment is demonstrated.

Hiyam's Journal Update

Phys. Rev. B 76, 132510 (2007)
77Se NMR measurements of the -d exchange field in the organic conductor -(BETS)2FeCl4
Guoqing Wu, W. G. Clark, S. E. Brown, J. S. Brooks, A. Kobayashi, and H. Kobayashi
(Received 6 June 2007; published 26 October 2007)

77Se-NMR spectrum and frequency shift measurements in the paramagnetic metal and antiferromagnetic insulating phases are reported for a small single crystal of the organic conductor -(BETS)2FeCl4 as a function of temperature (T) and field alignment for an applied magnetic field B0=9 T. The results show that in the low T limit, where the localized Fe3+ spins (Sd=5/2) are almost fully polarized, the conduction electrons (Se electrons, spin s=1/2) in the BETS molecules experience an exchange field (Bd) from the Fe3+ spins with a value of −32.7±1.5 T at 5 K and 9 T aligned opposite to B0. This large negative value of Bd is consistent with that predicted by the resistivity measurements and supports the Jaccarino-Peter internal field-compensation mechanism being responsible for the origin of field-induced superconductivity.

Phys. Rev. B 76, 144511 (2007)
11B NMR in the layered diborides OsB2 and RuB2
B. J. Suh, X. Zong, Y. Singh, A. Niazi, and D. C. Johnston
(Received 4 June 2007; published 23 October 2007)

11B nuclear magnetic resonance (NMR) measurements have been performed on 11B enriched OsB2 and RuB2 polycrystalline powder samples in an external field of 4.7 T and in the temperature range, 4.2 K
Phys. Rev. B 76, 144405 (2007)
Multiple quantum NMR dynamics in dipolar ordered spin systems

S. I. Doronin, E. B. Fel'dman, and E. I. Kuznetsova G. B. Furman and S. D. Goren
(Received 6 December 2006; revised 28 August 2007; published 2 October 2007)

We investigate analytically and numerically the multiple-quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole interactions in the case of the dipolar ordered initial state. We suggest two different methods of MQ NMR. One of them is based on the measurement of the dipolar temperature in the quasiequilibrium state which is established after the time of order (loc is the dipolar local field) after the MQ NMR experiment. The other method uses an additional resonance (/4)y pulse after the preparation period of the standard MQ NMR experiment in solids. Many-spin clusters and correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

Phys. Rev. B 76, 144433 (2007)
NMR study of ordered states in NpFeGa5: Orbitally related ordering below 78 K
S. Kambe,H. Sakai, Y. Tokunaga, R. E. Walstedt, D. Aoki, Y. Homma, and Y. Shiokawa
(Received 18 July 2007; published 29 October 2007)

We report NMR studies on a single crystal of NpFeGa5, which has the tetragonal HoCoGa5(115) structure and exhibits two antiferromagnetically ordered states. In the antiferromagnetic I phase below 118 K, the observed internal field at the Ga(2) (4i) site is consistent with the ordered structure revealed by neutron diffraction measurements. Below 78 K in the antiferromagnetic II phase, two different Ga(2) sites with different electric field gradient tensors appear, which indicates an orbitally related ordering. A possible quadrupolar ordering in the antiferromagnetic II phase is discussed.

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (44), 13396 -13397, 2007. 10.1021/ja0761636 S0002-7863(07)06163-X

Characterization of Chemical Exchange Using Residual Dipolar Coupling
Tatyana I. Igumenova, Ulrika Brath, Mikael Akke, and Arthur G. Palmer, III*

NMR line shape analysis and relaxation dispersion measurements for N,N-dimethyltrichloroacetamide (DMTCA) weakly aligned using poly--benzyl-L-glutamate, which forms a lyotropic nematic phase when dissolved in chloroform, were used to characterize chemical exchange kinetics for the rotation around the C-N amide bond. At low temperatures (<312>312 K), a single population-averaged 13C methyl quartet is observed; in this regime, the differences in RDCs contribute to differential line broadening of the quartet components. Self-consistent measurements of the difference in RDCs are obtained from both line shape and relaxation dispersion techniques. The results show that NMR spectroscopy of weakly aligned molecules allows complete characterization of chemical exchange processes using RDCs, even if exchange broadening is absent in isotropic samples.

Thursday, October 25, 2007

New neuron-rich elements

C&EN Latest News, Oct 24, 2007
Nuclear Chemistry
by Jyllian Kemsley

Neutron-Rich Isotopes Discovered
Magnesium-40 and aluminum-42 push the limits of nuclear stability

Friday, October 19, 2007

Hiyam's Journal Update

Chem. Mater., ASAP Article 10.1021/cm0715388 S0897-4756(07)01538-4 Web Release Date: October 19, 2007 Copyright © 2007 American Chemical Society
Vacancy and Cation Distribution in Yttria-Doped Ceria: An 89Y and 17O MAS NMR Study
Namjun Kim* and Jonathan F. Stebbins

The local structure and dynamics of oxide ions in yttria-doped ceria (YDC, 5 to 30% Y2O3) were studied using high-resolution 89Y and 17O MAS NMR spectroscopy at ambient temperature and high temperatures to 500 C. Eight-, seven-, and six-coordinated yttrium cations are clearly resolved in 89Y MAS NMR spectra, and their relative populations were measured. The derived average coordination number of yttrium is smaller than that for a random distribution of oxygen vacancies, suggesting that there is strong association between yttrium cations and vacancies and there is the possibility of pairing of two yttrium cations with one vacancy. In the 17O MAS NMR spectra, resonances for oxygens with different coordination environments are resolved and are assigned to oxygens with different numbers of yttrium cations in the first coordination sphere. The relative intensities of the 17O resonances also deviate from those expected from a random distribution, again indicating possible pairing of yttrium cations. High-temperature 17O MAS NMR shows coalescence among various peaks. The exchange between oxygen sites with yttrium neighbors appears to occur at a lower temperature (about 100 C) than the exchange that involves the sites without yttrium neighbors; rapid exchange of all oxide anions throughout the structure occurs above 400 C.

Hiyam's Journal Update

Chem. Mater., ASAP Article 10.1021/cm070496k S0897-4756(07)00496-6 Web Release Date: October 18, 2007 Copyright © 2007 American Chemical Society
NMR Structural Study on the As-P-S Glassy System
S. H. Santagneli, I. Skripatchev, S. J. L. Ribeiro, and Y. Messaddeq,J. Schneider

Glasses having the composition As2S3(1-x)-P2S5(x) with x ranging from 0 to 0.7 have been investigated to determine the compositional effect on properties and local structure. Glass transition temperature (Tg) decreases and molar volume (Vm) increases with an increase in P content. Using 31P NMR, we measured the strength of the 31P-31P magnetic dipolar interaction in the glass samples and the AsPS4 crystallized phase. Based on these data, we observed the formation of the As2P2S8 network, which reflects an increase in the average coordination number and a decrease in the degree of rigidity.

Friday, October 12, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021/ja073170l S0002-7863(07)03170-8 Web Release Date: October 6, 2007 Copyright © 2007 American Chemical Society

Internuclear 31P-51V Distance Measurements in Polyoxoanionic Solids Using Rotational Echo Adiabatic Passage Double Resonance NMR Spectroscopy
Wenlin Huang, Alexander J. Vega,* Terry Gullion, and Tatyana Polenova*

We report the first results establishing rotational echo adiabatic passage double resonance (REAPDOR) experiments for distance measurements between a spin-1/2 (31P) and spin-7/2 (51V) pair in a series of vanadium-substituted polyoxoanionic solids from the Keggin and Wells-Dawson families. We have quantitatively measured 31P-51V distances in monovanadium substituted K4PVW11O40, 1-K7P2VW17O62, and 4-K7P2VW17O62. Numerical simulations of the experimental data yield very good agreement with the averaged P-W/P-V distances determined from the X-ray diffraction measurements in the same or related compounds. REAPDOR is therefore a very sensitive P-V distance probe anticipated to be especially useful in the absence of long-range order. Our results suggest that REAPDOR spectroscopy could be broadly applicable for interatomic distance measurements in other spin-7/2-spin-1/2 nuclear pairs.

J. Am. Chem. Soc., ASAP Article 10.1021/ja074428a S0002-7863(07)04428-9 Web Release Date: October 9, 2007 Copyright © 2007 American Chemical Society
17O and 29Si NMR Parameters of MgSiO3 Phases from High-Resolution Solid-State NMR Spectroscopy and First-Principles Calculations
Sharon E. Ashbrook,* Andrew J. Berry, Daniel J. Frost, Alan Gregorovic, Chris J. Pickard, Jennifer E.

The 29Si and 17O NMR parameters of six polymorphs of MgSiO3 were determined through a combination of high-resolution solid-state NMR and first-principles gauge including projector augmented wave (GIPAW) formalism calculations using periodic boundary conditions. MgSiO3 is an important component of the Earth's mantle that undergoes structural changes as a function of pressure and temperature. For the lower pressure polymorphs (ortho-, clino-, and protoenstatite), all oxygen species in the 17O high-resolution triple-quantum magic angle spinning (MAS) NMR spectra were resolved and assigned. These assignments differ from those tentatively suggested in previous work on the basis of empirical experimental correlations. The higher pressure polymorphs of MgSiO3 (majorite, akimotoite, and perovskite) are stabilized at pressures corresponding to the Earth's transition zone and lower mantle, with perovskite being the major constituent at depths >660 km. We present the first 17O NMR data for these materials and confirm previous 29Si work in the literature. The use of high-resolution multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments allows us to resolve distinct oxygen species, and full assignments are suggested. The six polymorphs exhibit a wide variety of structure types, providing an ideal opportunity to consider the variation of NMR parameters (both shielding and quadrupolar) with local structure, including changes in coordination number, local geometry (bond distances and angles), and bonding. For example, we find that, although there is a general correlation of increasing 17O chemical shift with increasing Si-O bond length, the shift observed also depends upon the exact coordination environment.

J. Am. Chem. Soc., ASAP Article 10.1021/ja075272h S0002-7863(07)05272-9 Web Release Date: October 9, 2007 Copyright © 2007 American Chemical Society
Conformational Preferences of Chondroitin Sulfate Oligomers Using Partially Oriented NMR Spectroscopy of 13C-Labeled Acetyl Groups
Fei Yu, Jeremy J. Wolff, I. Jonathan Amster, and James H. Prestegard*

A new method is presented for the retrieval of information on the conformation of glycosaminoglycan oligomers in solution. The method relies on the replacement of acetyl groups in isolated native oligomers with 13C labeled acetyl groups and the extraction of orientational constraints from residual dipolar couplings (RDCs) and chemical shift anisotropy (CSA) offsets observed in NMR spectra of partially oriented samples. A novel method for assignment of resonances based on the correlation of resonance intensities with isotope ratios determined from mass spectrometric analysis is also presented. The combined methods are used in conjunction with more traditional NMR structural data to determine the solution structure of a pentasaccharide, GalNAc6S(1-4)GlcA(1-3)GalNAc4S(1-4)GlcA(1-3)GalNAc4S-ol, derived by enzymatic hydrolysis of chondroitin sulfate. The geometry derived is compared to that for similar molecules that have been reported in the literature, and prospects for use of the new types of data in the study of protein-bound oligosaccharides are discussed.

J. Am. Chem. Soc., ASAP Article 10.1021/ja075768z S0002-7863(07)05768-X Web Release Date: October 10, 2007 Copyright © 2007 American Chemical Society
Hyperpolarized 89Y Offers the Potential of Direct Imaging of Metal Ions in Biological Systems by Magnetic Resonance
Matthew E. Merritt, Crystal Harrison, Zoltan Kovacs, Preeti Kshirsagar, Craig R. Malloy, and A. Dean Sherry*

Hyperpolarization of 89YCl3 and three 89Y-complexes was achieved by dynamic nuclear polarization of aqueous samples. The long T1s of 89Y make its application as an NMR imaging probe extremely promising. In addition, the wide chemical shift range for various chelates of 89Y means that agents sensitive to their biological/chemical milieu could serve as exquisite sensors of important biological events.

Wednesday, October 10, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (41), 12406 -12407, 2007.
2H Solid-State NMR of Mobile Protons: It Is Not Always the Simple Way
Young Joo Lee, Tatiana Murakhtina, Daniel Sebastiani, and Hans Wolfgang Spiess

A combined study of 2H line-shape analysis and ab initio molecular dynamics simulations was carried out on poly[vinyl phosphonic acid] (a water-free proton conducting material). We can elucidate the geometry and even time scale of the complex motional process, where dynamical proton motion occurs via the rearrangement of H-bonding networks, involving both intra- and interchain transfers.

Tuesday, October 09, 2007

Hiyam's Journal Update

Chem. Mater., 19 (21), 5067 -5073, 2007.
Synthesis, Crystal Structure, and Characterization (Vibrational and Solid-State 31P MAS NMR Spectroscopy) of the High-Temperature Modification of Calcium catena-Polyphosphate(V)

The metastable high-temperature modification of calcium catena-polyphosphate, -Ca(PO3)2, was obtained by quenching the recrystallized sample from a temperature shortly below the melting point. The novel crystal structure [Cc, Z = 16, a = 13.6835(14) Å, b = 19.981(2) Å, c = 6.7535(7) Å, = 94.514(2), V = 1840.7(3) Å3, 4929 structure factors, 326 parameters, R[F2 > 2(F2)] = 0.0561] was determined from a combined X-ray diffraction and solid-state 31P NMR study. The unit cell features a pseudoinversion center. The structure contains 4 Ca, 8 P, and 24 O atoms in the asymmetric unit and is composed of two different kinds of polyphosphate chains, with one helical chain running with a periodicity P of 12 parallel to [101], whereas the second chain is corrugated and directed parallel to [001] with a periodicity P of 4. 31P chemical shift parameters were determined for all eight phosphorus positions, and peaks were assigned to the two different polyphosphate chains. -(CaPO3)2 was further characterized by IR and Raman spectroscopy.

Saturday, October 06, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021/ja073234s S0002-7863(07)03234-9
Combined Analysis of 15N Relaxation Data from Solid- and Solution-State NMR Spectroscopy
Veniamin Chevelkov, Anastasia V. Zhuravleva, Yi Xue, Bernd Reif, and Nikolai R. Skrynnikov

It is well-known that structures of globular proteins in liquid and in crystalline solid are essentially identical. Many lines of evidence suggest that internal dynamics are also similar (assuming that the solid sample is well-hydrated and the measurements are conducted at the same temperature). On the basis of this premise, we undertake a combined analysis of solid- and liquid-state 15N relaxation data from a small globular protein, -spectrin SH3 domain. The interpretation using the extended Lipari-Szabo model demonstrates that liquid R1, R2, NOE, and solid R1 data measured at multiple fields are mutually consistent. To validate these results, we prepared a series of samples where the protein is dissolved in a water-glycerol solvent. The presence of glycerol ensures that the overall protein tumbling is slowed, thus increasing the visibility of nanosecond time-scale internal motions. When additional data are included in the fitting procedure, a credible picture of protein dynamics is obtained. In particular, the analysis suggests that ns time-scale motions with very low amplitude, S2 0.95, are present throughout the protein. It is envisaged that combined analyses of liquid- and solid-state data can provide an efficient method for detailed characterization of internal dynamics in proteins at multiple time scales.

J. Am. Chem. Soc., ASAP Article 10.1021/ja075846i S0002-7863(07)05846-5
Probing Supramolecular Structure from Measurement of Methyl 1H-13C Residual Dipolar Couplings
Remco Sprangers and Lewis E. Kay

A simple NMR experiment is presented for the measurement of methyl 1H-13C residual dipolar couplings in fractionally aligned supramolecular protein complexes. The approach makes use of methyl-TROSY spectroscopy that significantly increases the lifetime of the NMR signal, along with highly deuterated, methyl-protonated samples that minimize relaxation contributions from protons external to the methyl group probes. An application to a 360 kDa half-proteasome complex is presented, establishing the methodology.

Friday, October 05, 2007

A new renewable energy source

C&EN, latest news (Oct 4, 2007)
Title: Turing Water Into Fuel
by Mitch Jacoby

A new silicide semiconductor was discovered. It can be used with sunlight and oxygen to generate H2 from H2O.

Tuesday, October 02, 2007

interesting article

Clarifying HIV Entry Process
New details of virus's embrace with cell surface
By Stu Borman

C&EN, October 1, 2007
Volume 85, Number 40
p. 7

Friday, September 28, 2007

Sept 28, 2007 - Journal Updates

Aluminum Siting in Silicon-Rich Zeolite Frameworks: A Combined High-Resolution 27Al NMR Spectroscopy and Quantum Mechanics / Molecular Mechanics Study of ZSM-5
Stepan Sklenak, Jií Ddeek, Chengbin Li, Blanka Wichterlová, Vendula Gábová, Marek Sierka, Joachim Sauer
Angewandte (2007)46, 7286.
Finding Al: The distribution of catalytically active sites over crystallographic positions in zeolites is not random but controlled by synthesis. For differently synthesized ZSM-5 samples, distinct 27Al resonances have been identified by NMR spectroscopy. Shift calculations by DFT show that the observed resonances belong to Al in different crystallographic sites.

Structural and dynamical properties of guest molecules confined in mesoporous silica materials revealed by NMR
Gerd Buntkowsky, Hergen Breitzke, Anna Adamczyk, Frank Roelofs, Thomas Emmler, Egbert Gedat, Bob Grünberg, Yeping Xu, Hans-Heinrich Limbach, Ilja Shenderovich, Anastasia Vyalikh and Gerhard Findenegg
In the last fifteen years several novel porous silica materials, which are periodically structured on the mesoscopic length scale, have been synthesized. They are of broad interest for fundamental studies of surface–substrate interactions, for studies of the dynamics of guest molecules in confinement and for studies of the effect of confinement on the structural and thermophysical properties of fluids. Examples of such confinement effects include the change of the freezing and melting points or glass transitions of the confined liquids. These effects are studied by combinations of several NMR techniques, such as 15N- and 2H-solid-state NMR line shape analysis, MAS NMR and NMR diffusometry with physico-chemical characterization techniques such as nitrogen adsorption and small angle diffraction of neutrons or X-rays. This combination does not require crystalline samples or special clean and well defined surfaces such as conventional surface science techniques, but can work with typical ill-defined real world systems. The review discusses, after a short introduction, the salient features of these materials and the applied NMR experiments to give the reader a basic knowledge of the systems and the experiments. The rest of the review then focuses on the structural and dynamical properties of guest molecules confined in the mesoporous silica. It is shown that the confinement into the pores leads to fascinating new features of the guests, which are often not known for their bulk phases. These features depend strongly on the interplay of the their interactions with the silica surface and their mutual interactions.

Solid-state NMR opf endoheral hydrogen-fullerene complexes
M. Carravetta, A. Danquigny, S. Mamone, F. Cuda, O. G. Johannessen, I. Heinmaa, K. Panesar, R. Stern, M. C. Grossel, A. J. Horsewill, A. Samoson, M. Murata, Y. Murata, K. Komatsu and M. H. Levitt
We present an overview of solid-state NMR studies of endohedral H2-fullerene complexes, including 1H and 13C NMR spectra, 1H and 13C spin relaxation studies, and the results of 1H dipole–dipole recoupling experiments. The available data involves three different endohedral H2-fullerene complexes, studied over a wide range of temperatures and applied magnetic fields. The symmetry of the cage influences strongly the motionally-averaged nuclear spin interactions of the endohedral H2 species, as well as its spin relaxation behaviour. In addition, the non-bonding interactions between fullerene cages are influenced by the presence of endohedral hydrogen molecules. The review also presents several pieces of experimental data which are not yet understood, one example being the structured 1H NMR lineshapes of endohedral H2 molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H2-fullerene complexes, especially in the cryogenic regime.

Friday, September 21, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021

Chemical Shift Correlation NMR Spectroscopy with Indirect Detection in Fast Rotating Solids: Studies of Organically Functionalized Mesoporous Silicas
Jerzy W. Wiench, Charles E. Bronnimann, Victor S.-Y Lin, and Marek Pruski*

The first indirectly detected 13C-1H solid-state NMR correlation spectra of species bound to a surface are reported. The experiments were performed at 14.1 T under fast (40 kHz) MAS. The sensitivity gain was demonstrated on a mesoporous silica sample containing approximately 300 g of covalently bound allyl groups, in the absence of templating molecules and without isotope enrichment. A well-resolved two-dimensional spectrum was acquired in 15 min, which is more than 10 times faster than using direct detection of 13C nuclei.

Wednesday, September 19, 2007

Hiyam's Journal Update

Proton-Detected Solid-State NMR Spectroscopy of Fully Protonated Proteins at 40 kHz Magic-Angle Spinning
Donghua H. Zhou, Gautam Shah, Mircea Cormos, Charles Mullen, Dennis Sandoz, and Chad M. Rienstra

Remarkable progress in solid-state NMR has enabled complete structure determination of uniformly labeled proteins in the size range of 5-10 kDa. Expanding these applications to larger or mass-limited systems requires further improvements in spectral sensitivity, for which inverse detection of 13C and 15N signals with 1H is one promising approach. Proton detection has previously been demonstrated to offer sensitivity benefits in the limit of sparse protonation or with ~30 kHz magic-angle spinning (MAS). Here we focus on experimental schemes for proteins with ~100% protonation. Full protonation simplifies sample preparation and permits more complete chemical shift information to be obtained from a single sample. We demonstrate experimental schemes using the fully protonated, uniformly 13C,15N-labeled protein GB1 at 40 kHz MAS rate with 1.6-mm rotors. At 500 MHz proton frequency, 1-ppm proton line widths were observed (500 ± 150 Hz), and the sensitivity was enhanced by 3 and 4 times, respectively, versus direct 13C and 15N detection. The enhanced sensitivity enabled a family of 3D experiments for spectral assignment to be performed in a time-efficient manner with less than a micromole of protein. CANH, CONH, and NCAH 3D spectra provided sufficient resolution and sensitivity to make full backbone and partial side-chain proton assignments. At 750 MHz proton frequency and 40 kHz MAS rate, proton line widths improve further in an absolute sense (360 ± 115 Hz). Sensitivity and resolution increase in a better than linear manner with increasing magnetic field, resulting in 14 times greater sensitivity for 1H detection relative to that of 15N detection.