Thursday, January 17, 2008

Hiyam's Journal Update

J. Am. Chem. Soc., ASAP Article 10.1021/ja0759949 S0002-7863(07)05994-X Web Release Date: January 4, 2008 Copyright © 2008 American Chemical Society
NMR Investigations of the Static and Dynamic Structures of Bisphosphonates on Human Bone: a Molecular Model
Sujoy Mukherjee, Yongcheng Song, and Eric Oldfield*

We report the results of an investigation of the binding of a series of bisphosphonate drugs to human bone using 2H, 13C, 15N, and 31P nuclear magnetic resonance spectroscopy. The 31P NMR results show that the bisphosphonate groups bind irrotationally to bone, displacing orthophosphate from the bone mineral matrix. Binding of pamidronate is well described by a Langmuir-like isotherm, from which we deduce an ~30-38 Å2 surface area per pamidronate molecule and a G = -4.3 kcal mol-1. TEDOR of [13C3, 15N] pamidronate on bone shows that the bisphosphonate binds in a gauche [N-C(1)] conformation. The results of 31P as well as 15N shift and cross-polarization measurements indicate that risedronate binds weakly, since it has a primarily neutral pyridine side chain, whereas zoledronate (with an imidazole ring) binds more strongly, since the ring is partially protonated. The results of 2H NMR measurements of side-chain 2H-labeled pamidronate, alendronate, zoledronate, and risedronate on bone show that all side chains undergo fast but restricted motions. In pamidronate, the motion is well simulated by a gauche+/gauche- hopping motion of the terminal -CH2-NH3+ group, due to jumps from one anionic surface group to another. The results of double-cross polarization experiments indicate that the NH3+-terminus of pamidronate is close to the bone mineral surface, and a detailed model is proposed in which the gauche side-chain hops between two bone PO43- sites.

J. Am. Chem. Soc.,

Local Environments and Lithium Adsorption on the Iron Oxyhydroxides Lepidocrocite
(-FeOOH) and Goethite (-FeOOH): A 2H and 7Li Solid-State MAS NMR Study
Jongsik Kim, Ulla Gro Nielsen, and Clare P. Grey*

2H and 7Li MAS NMR spectroscopy techniques were applied to study the local surface and bulk environments of iron oxyhydroxide lepidocrocite (-FeOOH). 2H variable-temperature (VT) MAS NMR experiments were performed, showing the presence of short-range, strong antiferromagnetic correlations, even at temperatures above the Néel temperature, TN, 77 K. The formation of a Li+ inner-sphere complex on the surface of lepidocrocite was confirmed by the observation of a signal with a large 7Li hyperfine shift in the 7Li MAS NMR spectrum. The effect of pH and relative humidity (RH) on the concentrations of Li+ inner- and outer-sphere complexes was then explored, the concentration of the inner sphere complex increasing rapidly above the point of zero charge and with decreasing RH. Possible local environments of the adsorbed Li+ were identified by comparison with other layer-structured iron oxides such as -LiFeO2 and o-LiFeO2. Li+ positions of Li+-sorbed and exchanged goethite were reanalyzed on the basis of the correlations between Li hyperfine shifts and Li local structures, and two different binding sites were proposed, the second binding site only becoming available at higher pH.

J. Am. Chem. Soc., 130 (1), 288 -299, 2008.

Tuning the Structural and Physical Properties of Cr2Ti3Se8 by Lithium Intercalation: A Study of the Magnetic Properties, Investigation of Ion Mobility with NMR Spectroscopy and Electronic Band Structure Calculations
Joseph Wontcheu, Wolfgang Bensch,* Martin Wilkening, Paul Heitjans, Sylvio Indris, Paul Sideris, Clare P. Grey, Sergiy Mankovsky, and Hubert Ebert

The room temperature intercalation of Cr2Ti3Se8 with butyl lithium yields a phase mixture of the starting material and of the new trigonal phase with composition Li0.4Cr0.5Ti0.75Se2. The phase pure fully intercalated trigonal phase is obtained at elevated temperature (80 C) with the final composition Li0.62Cr0.5Ti0.75Se2. The line profile analysis (LPA) of the powder patterns shows that pronounced strain occurs in the intercalated material. The deintercalation of the material is realized by treatment of the fully intercalated sample with distilled water leading to the composition Li0.15Cr0.5Ti0.75Se2. The intercalation is accompanied by an electron transfer from the guest Li to the host material, and as a consequence significant changes of the interatomic distances are observed. The local environment and the dynamics of the Li+ ions in the fully intercalated sample were studied with 7Li magic angle spinning (MAS) NMR investigations. These reveal different environments of transition metal neighbors for the Li sites and a high mobility of the Li ions. Magnetic measurements show that in the pristine material antiferromagnetic interactions are dominating ( = -113.5 K) with no long-range order at low temperatures. The magnetic ground state is characterized by a spin-glass behavior. With increasing Li content the antiferromagnetic character vanishes progressively, and the fully intercalated phase exhibits a positive Weiss constant ( = 12 K) indicating dominating ferromagnetic exchange interactions; i.e., the magnetic properties can be significantly altered by lithiation. The interpretation of our experimental findings is supported by the results of accompanying band structure calculations done within the framework of local spin density functional theory. These demonstrate in particular the role of the charge transfer between the constituents as a function of the Li concentration and its impact on the exchange coupling.

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