Intercalation Route to Complex Perovskites AM_0.2Ta_0.8O_2.8N_0.2 (A = Sr, Ba; M = Li, Na): Neutron Diffraction and Nuclear Magnetic Resonance Study

Oxynitride-type complex perovskites, AM_0.2Ta_0.8O_2.8N_0.2 (A = Sr, Ba; M = Li, Na), were synthesized by the ammonolytic heating of a layered perovskite, A₅Ta₄O₁₅, with 0.5M₂CO₃. A Rietveld refinement of the synchrotron X-ray and neutron powder diffraction patterns confirmed the complete structural transformation from a hexagonal layered-perovskite to a three-dimensional perovskite type, as well as the stabilization of alkali cations on the octahedral sites rather than on the dodecahedral sites in the latter. In all four compounds, M⁺ and Ta⁵⁺ were disordered completely despite a charge difference as much as 4. The crystal symmetry of the average structure depended on the size of the dodecahedral cation: simple cubic for BaM_0.2Ta_0.8O_2.8N_0.2 and body-centered tetragonal for SrM_0.2Ta_0.8O_2.8N_0.2. This trend coincides with the symmetry transition from BaTaO₂N (<i>Pm</i>3̅<i>m</i>) to SrTaO₂N (<i>I</i>4/<i>mcm</i>). In both SrM_0.2Ta_0.8O_2.8N_0.2, nitrogen atoms preferentially occupied the <i>c</i>-axial 4a site of the tetragonal cell. Solid state magic angle spinning nuclear magnetic resonance spectroscopy showed that SrNa_0.2Ta_0.8O_2.8N_0.2 and BaNa_0.2Ta_0.8O_2.8N_0.2 exhibited marked downfield shifts of ²³Na, manifesting an octahedral coordination. On the other hand, the ⁷Li NMR of SrLi_0.2Ta_0.8O_2.8N_0.2 and BaLi_0.2Ta_0.8O_2.8N_0.2 indicated a highly symmetrical coordination environment of Li

The Application of REDOR NMR to Understand the Conformation of Epothilone B

The structural information of small therapeutic compounds complexed in biological matrices is important for drug developments. However, structural studies on ligands bound to such a large and dynamic system as microtubules are still challenging. This article reports an application of the solid-state NMR technique to investigating the bioactive conformation of epothilone B, a microtubule stabilizing agent, whose analog ixabepilone was approved by the U.S. Food and Drug Administration (FDA) as an anticancer drug. First, an analog of epothilone B was designed and successfully synthesized with deuterium and fluorine labels while keeping the high potency of the drug; Second, a lyophilization protocol was developed to enhance the low sensitivity of solid-state NMR; Third, molecular dynamics information of microtubule-bound epothilone B was revealed by high-resolution NMR spectra in comparison to the non-bound epothilone B; Last, information for the macrolide conformation of microtubule-bound epothilone B was obtained from rotational-echo double-resonance (REDOR) NMR data, suggesting the X-ray crystal structure of the ligand in the P450epoK complex as a possible candidate for the conformation. Our results are important as the first demonstration of using REDOR for studying epothilones

SYNTHESIS OF HIGHLY CRYSTALLINE OLIVINE-TYPE LiFePO4 NANOPARTICLES BY SOLUTION-BASED REACTIONS

LiFePO4 nanocrystals were synthesized in various polyol media without any further post-heat treatment. The LiFePO4 samples synthesized using three different polyol media namely, diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TTEG), exhibited plate and rod-shaped structures with average sizes of 50–500 nm. The X-ray diffraction (XRD) patterns were indexed on the basis of an olivine structure (space group: Pnma). The samples prepared in DEG, TEG, and TTEG polyol media showed reversible capacities of 123, 155, and 166 mAh/g, respectively, at current density of 0.1 mA/cm2 with no capacity fading and exhibited excellent capacity retention up to the 50th cycle. In particular, the samples showed excellent performances at high rates of 30 and 60 C with high capacity retention. It is assumed that the nanometer size materials (~50 nm) possessing a highly crystalline nature may generate improved performance at high rate current densities.Lithium ion battery, LiFePO4, nanocrystal, cathode, polyol