Rapidly converging lattice sums for nonelectrostatic interactions

The relative energies of one-, two-, and three-dimensional Bravais lattice Lennard-Jones particles can be calculated by lattice sums. The expression of lattice sums over a Lennard-Jones potential can be manipulated into a form that converges rapidly. A formalism capable of calculating the lattice potential at arbitrary points of a completely general lattice has been developed. This method provides an alternative way to calculate the relative energies from the surface and the interior bulk sites of many chemical systems. The method is illustrated with application to hcp and fcc Lennard-Jonesium, both for the relative binding energy and for calculating the potential along the geometric diffusion pathway between tetrahedral and octahedral interstitial sites. Diffusion from the tetrahedral site to the octahedral site experiences a barrier of 752.600 in units of 4 epsilon. The reverse pathway experiences a barrier of 1035.614 in units of 4 epsilon.     

层状LiMnO2的固相合成及电化学性能

以Mn₂O₃和氢氧化锂为原料，通过焙烧合成出o-LiMnO₂。用X射线衍射和扫描电镜对不同温度下合成的粉末样品进行了表征，并研究了材料的电化学性能。通过对不同温度条件下烧结样品的晶胞参数、布拉格(110)晶面峰半高宽及电化学性能研究发现：600 ℃下合成样品的半高宽最大，堆垛层错率高，同时电化学性能也最好，首次放电容量达到156 mAh·g^-1，20次循环后仍保持在140 mAh·g^-1以上。中高温固相合成的o-LiMnO₂材料，在晶粒范围大小相近时，材料电化学性能与材料堆垛层错率相关。     

Ab initio excited-state dynamics of the photoactive yellow protein chromophore

The photoisomerization mechanism of the neutral form of the photoactive yellow protein (PYP) chromophore is investigated using ab initio quantum chemistry and first-principles nonadiabatic molecular dynamics (ab initio multiple spawning or AIMS). We identify the nature of the two lowest-lying excited states, characterize the short-time behavior of molecules excited directly to S2, and explain the origin of the experimentally observed wavelength-dependent photoisomerization quantum yield.     

Human topoisomerase I poisoning: docking protoberberines into a structure-based binding site model

Summary Using the X-ray crystal structure of the human topoisomerase I (top1) – DNA cleavable complex and the Sybyl software package, we have developed a general model for the ternary cleavable complex formed with four protoberberine alkaloids differing in the substitution on the terminal phenyl rings and covering a broad range of the top1-poisoning activities. This model has the drug intercalated with its planar chromophore between the −1 and +1 base pairs flanking the cleavage site, with the nonplanar portion pointing into the minor groove. The ternary complexes were geometry-optimized and relative interaction energies, computed by using the Tripos force field, were found to rank in correct order the biological potency of the compounds; in addition, the model is also consistent with the top1-poisoning inactivity of berberine, a major prototype of the protoberberine alkaloids. The model might serve as a rational basis for elaboration of the most active compound as a lead structure, in order to develop more potent top1 poisons as next generation anti-cancer drugs.     

ATRP grafting of styrene from benzyl chloride functionalized polysiloxanes: An AFM and TGA study of the Cu(0)/bpy catalyst

Various combinations of Cu(0), CuCl, 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) were used as catalysts for the grafting polymerizations of styrene from polysiloxane macroinitiators functionalized with benzyl chloride. While Cu(0)/bpy alone promotes the grafting, narrower polydispersities were obtained in the presence of CuCl. Analysis of the Cu(0) surface before and after polymerization by a combination of AFM, TGA and FTIR investigations reveals the formation of bpy or phen films on Cu(0). In the presence of CuCl, the ligand film appears decorated with CuCl particles which increase in size with increasing the CuCl concentration. The initial layer occurs most likely as a result of complexation between the ligands and the Cu(0) surface and acts as a support for the rest of the film. These observations are consistent with the film formation on Cu(0) from related nitrogen donors and indicate that the reactivity of the Cu surface may depend not only on its prior treatment but also on the deposition of ligands from the reaction mixture.     

Synthesis of new vitamin D3 analogues with a decalin-type CD-ring

Vitamin D analogues, characterized by a decalin CD-ring fragment are described.     

catena‐Poly[[copper(II)‐μ‐2‐[bis­(2‐pyridylmeth­yl)amino]butyrato‐κ4N,N′,N′′,O:κO′] perchlorate]

The copper(II) ion in the syn–anti carboxyl­ate‐bridged one‐dimensional zigzag chain title complex, {[Cu(C₁₆H₁₈N₃O₂)]ClO₄}_n, exhibits a distorted trigonal–bipyramidal environment. Two N atoms and one carboxyl­ate O atom of the ligand form the basal plane, while the axial positions are filled by an N atom of the ligand and one O atom belonging to the carboxyl­ate group of an adjacent mol­ecule. The crystal packing is enhanced by C—H⋯O(perchlorate) hydrogen bonds.     

Long-range interaction in the D and D′ states of H2

The interaction energy between two hydrogen atoms in the D and D′ ¹Π_u states of the hydrogen molecule has been calculated for large internuclear distances (12 ? R ? 25 bohr). The variational method and a very flexible trial wave-function were used. The results indicate that for the states under consideration the Rayleigh-Schrödinger perturbation theory with the multipole expansion of the interaction hamiltonian gives reliable results only for R > 25 bohr i.e. in the region where the interaction energies are practically negligible.     

Simple Method for Simultaneous Determination of Selenium and Arsenic in Human Hair by Means of Atomic Fluorescence Spectrometry with Hydride Generation Technique

This study describes a simple, rapid and reliable method for simultaneous determination of selenium and arsenic in human hair by means of atomic fluorescence spectrometry combined with a hydride generation technique (HG-AFS). The procedure developed encompasses microwave digestion of a sample in the nitric acid environment only. The interferences caused by nitrous oxides are eliminated by removing a gas from above the digested solution with a stream of argon. The sample is then chemically treated in a flow-through hydride generation system and exposed to measurements in a double-channel atomic fluorescence spectrometer. The method permits determining both analytes in the linear range of 0.5–100µgL^–1 with a detection limit equal to 0.2µgL^–1, as well as with very good repeatability not exceeding 1% for Se and 2% for As. No mutual interferences from either of the analytes in the concentrations ranges matching the hair composition were found. The method was verified in terms of accuracy with the use of a reference material and then applied to the analysis of the natural samples of human hair.