Characteristic monomials with chirality fittingness for combinatorial enumeration of isomers with chiral and achiral ligands

A new method of combinatorial enumeration based on characteristic monomials with chirality fittingness (CM-CFs) has been proposed in order to enumerate isomers with chiral ligands as well as with achiral ones. The CM-CFs have been defined as monomials that consist of three kinds of dummy variables in light of the subduction of the Q-conjugacy representations for chiral and achiral cyclic groups. A procedure of calculating CM-CFs for cyclic groups and finite groups has been discribed so as to tabulate them as CM-CF tables. Then the CM-CF method has been applied to the enumeration of isomers with achiral ligands as well as chiral ones.     

Stochastic behavior of the dynamic stokes shift in rhodamine 6G

Transient behavior of the fluorescence spectrum has been investigated in rhodamine 6G in ethanol at low temperatures by means of a time-resolved luminescence technique. The width of the fluorescence spectrum as well as its peak position has been found to change with time. These characteristics are shown to be well explained by a stochastic model.     

Reactions of radical cations of acetals: Evidence for unimolecular decomposition

The thermal and photochemical reactions of the methylal radical cation /I/ in freon matrices were studied using selective deuteration for elucidating the structure of the resulting species. /I/ has been shown to decay by unimolecular reaction upon heating to 140 K as well as upon photolysis in CFCl₃ matrix and the product of decay has been assumed to be the complex of formaldehyde radical cation with CFCl₃. Such decay reaction has been demonstrated for 1,3-dioxolan radical cation as well.     

Hydrophobic agglomeration kinetics of fine kaolinite particles in aqueous suspensions

The hydrophobic agglomeration kinetics of kaolinite has been studied through the in-situ turbidity meter measurement system. The effects of surfactant dosage, stirring rate and particle size on the hydrophobic agglomeration dynamics have been investigated. Appropriate surfactant concentrations provided the strongest hydrophobicity, modest stirring rate offered a higher agglomerates formation rate and a lower disruption rate, and smaller particles had lower energy barrier and higher attachment efficiency. The best hydrophobic agglomeration conditions have been determined and a kinetic model of hydrophobic agglomeration has been proposed by experimental results. The kinetic model has been turned out to be fitted to the dynamic process well and can characterize as well as assess the hydrophobic agglomeration kinetics appropriately.     

Encapsulation of functional moieties within branched star polymers: effect of chain length and solvent on site isolation

Porphyrin and pyrene photoactive cores have been encapsulated within an isolating polymeric shell using an efficient and general strategy based on the use of dendritic initiators for the ring-opening polymerization of epsilon-caprolactone to yield functional core star polymers. The isolation of the core functionalities has been studied using fluorescence quenching and fluorescence resonance energy transfer (FRET) techniques as well as solvatochromic probes. With increasing chain length as well as solvent polarity, enhanced site isolation of the core has been observed. These findings have been correlated to actual molecular dimensions independently measured by pulsed field gradient spin-echo (PGSE) NMR. The developed synthetic methodology offers a rapid route to efficient encapsulation of functional moieties and therefore has potential for the design of new materials.     

Iron compounds in controlled radical polymerization: Ferrocenes, (clathro)chelates,and porphyrins

Experimental data on the application of metal complexes in radical polymerization of vinyl monomers collected over the recent 15 years have been analyzed and generalized. Special attention has been given to (un)substituted ferrocenes, macrocyclic (clathro)chelates, and iron porphyrinates as well as to the approaches to enhance their catalytic activity in controlled synthesis of macromolecules. The mentioned systems have been compared with each other as well as with selected complexes of other transition metals. It has been shown that the electronic and spatial structures of the metal complexes are related to their efficiency in the radical polymerization reactions.     

Enantiorecognition of profens by capillary electrophoresis using a novel chiral selector eremomycin

The evaluation of a macrocyclic glycopeptide antibiotic, eremomycin, as a chiral selector in capillary electrophoresis (CE) has been performed. The stability of eremomycin in solution and capillary electrolyte, as well as its optical and electrophoretic properties have been discussed. The effect of experimental parameters influencing the enantioseparation of several profens has been studied. Excellent enantioseparation of profens has been achieved and migration order has been validated. Comparison of enantioseparations of profens in CE by using eremomycin-mediated electrolytes and in HPLC with eremomycin immobilized on silica has revealed similar trends for both methods.     

Straightforward synthesis and crystal structures of the 3-piperazine-bisbenzoxaboroles and their boronic acid analogs

The straightforward synthesis of a highly biologically active 3-piperazine-bisbenzoxaborole and its fluorine analog has been described. The obtained bisbenzoxaboroles have been used in the synthesis of their phenylboronic acids analogs. One diboronic acid has been also isolated as hydrochloride salt as well as its methyl monoester. All the described compounds display unique molecular architectures, which have been determined by X-ray measurements.     

肽链体系中的长程电子转移: 多肽构象和旁链间距对电子转移矩阵元的影响

用AM1半经验方法,优化了吲哚和苯酚中性分子、正离子自由基和负离子自由基的几何构型。用线性反应坐标近似和溶剂效庆的类导体屏蔽模型（COSMO）构造吲哚正离子和苯酚中性分子间电子转移的双势阱,用以估算多肽链中色氨酸和酪氨酸之间的电子转移的反应热和内重组能。优化TrpH-(Pro)n-TyrOH(n=0-3)多肽模型分子的结构和构象,用能级分裂因子的极小值方法计算了这些多肽体系的电子转移矩阵元。     

Monitoring Method for Airborne Polycyclic Aromatic Hydrocarbons

Abstract

This paper describes a method for the determination of airborne polycyclic aromatic hydrocarbons (PAH), which has been employed in routine analysis of a large number of samples. The method is in principle based on well known techniques, but some improvements have been made in order to reduce the analysis time and the cost without lowering the quality of the analytical results. Recovery studies have been made for some important steps of the procedure, and the reproducibility of the sampler has been tested. The method has proved to be suitable for monitoring of PAH in highly polluted as well as pristine areas.     

Overtone spectroscopy of chlorine substituted benzene derivatives

The absorption spectra of di-, tri- and tetra-derivatives of chlorobenzene have been studied in their pure form in the spectral range 400-20,000 cm(-1). A large number of bands associated with the fundamental, the overtones and the combination frequencies of C-H stretching mode have been observed. Vibrational frequencies, anharmonicity constants and dissociation energies, for the C-H stretch vibrations for the six molecules have been determined using local mode model. The C-H stretch frequencies obtained from experiments are compared with the corresponding frequency determined theoretically using RHF and DFT methods with same 6-31+G* basis set. This information has been used for the assignment of several combination bands as well as some weak overtone bands. Effect of hydrogen atom substitution by chlorine atom has been studied by measuring changes in the vibrational frequency of the C-H stretching mode and the C-H bond length. Frequency changes have been well correlated with the change in charge density on carbon as well as chlorine atoms.     

Competitive wetting of acetonitrile and dichloromethane in comparison to that of water on functionalized carbon nanotube surfaces

Differential wetting of pristine and ozonized carbon nanotubes has been studied using solvents like acetonitrile and dichloromethane in comparison to the well-known wetting behavior of water. Based on their unique structural and physical properties, functionalized CNT substrates have been used due to the fact that independent variation in molecular as well as electronic properties could be controlled by understanding the wetting of these liquids on carbon nanotubes (CNTs), both pristine as well as ozone treated. The sensitivity of the wetting behavior with respect to molecular interactions has been investigated using contact angle measurements while Raman and XPS studies unravel the differential wetting behavior. Charge-transfer between adsorbed molecules and CNTs has been identified to play a crucial role in determining the interfacial energies of these two liquids, especially in the case of acetonitrile. Ozone treatment has been observed to affect the surface properties of pristine CNTs along with a concomitant change in the wetting dynamics.     

Regioselective Iodination of Activated Arenes Using Phenyl Trimethylammonium Dichloroiodate in Ionic Liquid Under Microwave Irradiation

Abstract

The regioselective iodination of activated arenes has been achieved in the presence of phenyltrimethylammonium dichloroiodate and ionic liquid. The reaction has been carried out by both conventional heating as well as by microwave irradiation.     

LiF-KF熔盐溶液局部结构的计算机模拟研究

本文用Monte Carlo法对同离子系LiF-KF熔盐溶液的局部结构进行了计算机模拟,介绍了计算方法和模型。计算了LiF, KF及Lif-KF混合前后正-正离子, 正-负离子, 负-负离子间位能变化, 各类离子的近邻离子排布规律, 以及各种形式离子团的组成比例。本文还讨论了在熔盐瞬时结构中存在的静电场的微区涨落。     

Flammability of macrocyclic polymers and their complexes with metals

The peculiarities of thermal degradation and the flammability of nitrogen-containing macrocyclic polymers have been investigated. It has been shown that the thermal and thermo-oxidative stability of these polymers depend on the structure of the macrocycle, the type of organic radicals of the main unit and the metal nature. The effect of the type of n-conjugated macromolecules, as well as of the planarity and symmetry of macrocycle, on thermal stability as well as flammability of macrocyclic polymers has been studied. Metals (Cu, Co, Ni) in the coordination sphere increase the thermal stability and decrease the thermo-oxidative degradation of macrocyclic polymers.     

Deduction of an improved formula for coincidence counting and its experimental verification

An improved accurate coincidence correction formula has been deduced on the basis of Cox's theory considering the complex situations of differences in pulse shaping width as well as a relative delay existing between the two channels. The correctness has been examined by experiments.     

Facile synthesis of N-aryl pyrroles via Cu(II)-mediated cross coupling of electron deficient pyrroles and arylboronic acids

N-Arylation of electron-deficient pyrroles has been achieved by cross-coupling with arylboronic acids at room temperature in the presence of stoichiometric amounts of copper(II) acetate. The generality of this reaction has been established with variously substituted pyrroles as well as boronic acids. A key intermediate in the synthesis of a matrix metalloprotease inhibitor has been achieved using this methodology.     

Ab initio characterization of XH3 (X = N,P). Part II. Electric, magnetic and spectroscopic properties of ammonia and phosphine

The coupled cluster theory in conjunction with core valence triple and quadruple zeta basis sets has been employed for investigating electric, magnetic and spectroscopic properties of ammonia and phosphine. Namely molecular dipole and quadrupole moments, NMR shielding and spin-rotation constants, as well as spectroscopic properties such as rotational and centrifugal distortion constants as well as harmonic and anharmonic frequencies of NH₃ and PH₃ have been determined at a high level of accuracy. To obtain parameters directly comparable to experiment, vibrational effects have also been taken into account. In addition, the basis set convergence has been investigated for the molecular dipole moment.     

化学药品杂质控制的现状与展望

对药品中杂质的控制是保证药品用药安全的重要环节.伴随着对药品杂质特性的深入了解,依据杂质的生理活性逐一制定每一个杂质限度的"杂质谱控制"理念已经被国内外普遍接受.与"杂质谱控制"相关的关键技术问题可概括为:复杂体系样本的分离分析、微量组分的结构分析和微量组分的毒性评价三方面.本文从杂质控制理念和杂质分析技术两方面,综述了化学药品杂质控制的现状,并就今后的发展提出自己的观点.