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

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