Molecular and crystal structure of tetrahydroneosophoramine

The structure of tetrahydroneosophoramine has been studied by x-ray structural analysis. Rings A, B, and C have the chair conformation, and ring D the half-chair conformation. On the basis of a semiquantitative analysis it has been shown that the strains in the molecules of tetrahydroneosophoramine and of matrine are of the same order of magnitude.     

Intermolecular interaction potentials for the Ar-C2H2, Kr-C2H2, and Xe-C2H2 weakly bound complexes: information from molecular beam scattering, pressure broadening coefficients, and rovibrational spectroscopy

Integral cross sections and pressure broadening coefficients have been measured for the acetylene-krypton complex, by molecular beam scattering and by high resolution IR spectroscopy, respectively. A new potential energy surface (PES) is proposed to describe structure and dynamical properties of this prototypical weakly bound complex. The PES has been parametrized exploiting a novel atom-bond pairwise additive scheme and has been fitted to the experimental data. A similar PES has been obtained for the acetylene-xenon system by a proper scaling of the interaction parameters of the krypton case, based on empirical considerations. These PESs together with that recently proposed by the same authors [J. Phys. Chem. 109, 8471 (2005)] for the acetylene-argon case have been employed for close coupling calculations of the pressure broadening cross sections and for a characterization of the rovibrational structure of the complexes.     

TiO2-Based Porous Materials Obtained from Gels, in Different Experimental Conditions

The gels which are precursors of TiO₂ porous materials are prepared by the controlled hydrolysis-condensation of titanium isopropoxide by polymeric method. In the present work, a study of the influence of different experimental conditions (water/alkoxide ratio, solvent/alkoxide ratio and temperature) on the structure and texture of the polymeric gels obtained with the same type of alkoxide has been investigated. The structural and textural modifications for the unsupported materials have been detected using DTA/TGA, XRD, specific surface area and pore size computerized measurements. The optical properties of the supported materials deposited on silicon wafers have been investigated using ellipsometric method. Supported and unsupported porous materials with different structure and texture have been obtained depending on different experimental and thermal treatment conditions.     

Thermal properties of fibres from a new polymer of the polyimideamide group

The paper presents the thermal properties of fibres made of a modified polyimideamide. The effects of as-spun draw ratio and deformation during the fibre drawing stage on the structure, thermal properties, moisture absorption and tenacity of the obtained fibres have been determined. Based on the findings obtained by the DTA and DSC methods, it has been found that the modification of the polymer under investigation causes its glass transition temperature to decrease through the increase of molecular mobility. At the same time, the heat-resistant fibres with the amorphous oriented structure are characterized by a tenacity of 16 cN/tex, good absorption properties and increased porosity. The thermal stability indices of the examined fibres have been determined on the basis of thermogravimetric curves obtained both under air and inert gas. This revised version was published online in July 2006 with corrections to the Cover Date.     

The improvement of Cα atom positions of trichosanthin—–An application of phase filtering procedure to three-dimensional structure determination of protein

Wang's phase filtering procedure has been applied to the structure study of trichosanthin crystals belonging to space group C2. The MIR phases at 3Å resolution have been improved with the accumulative phase shift of 31.8° and the figure of merit has been improved from 0.54 to 0.84. The resulted electron density map at 3Å resolution has been much improved with a higher ratio of the electron density of the protein to the noise in the solvent region. The minimap has been interpreted more reasonably than the previous maps, giving the overall course of the polypeptide chain substantially the same as previously reported except for containing more secondary structure and a few short segments traced differently. The first 85 C_α atoms of the polypeptide chain are located in about the same positions as determined previously with an exception of a short segment but the amino acid residues after that shift along the chain with a maximum shift of about 15 residues. The electron density of side chains agrees better with the primary structure. The conformation and the three-dimensional structure as well as the major heavy-atom binding sites for the two molecules in an asymmetric unit are substantially the same. The structure of trichosanthin shows more similarity to ricin A chain than that reported previously.     

Optical properties of Yeast Cytochrome c monolayer on gold: an in situ spectroscopic ellipsometry investigation

The adsorption of Yeast Cytochrome c (YCC) on well defined, flat gold substrates has been studied by Spectroscopic Ellipsometry (SE) in the 245-1000 nm wavelength range. The investigation has been performed in aqueous ambient at room temperature, focusing on monolayer-thick films. In situ δΨ and δΔ difference spectra have shown reproducibly well-defined features related to molecular optical absorptions typical of the so-called heme group. The data have been reproduced quantitatively by a simple isotropic optical model, accounting for the molecular absorption spectrum and film-substrate interface effects. The simulations allowed a reliable estimate of the film thickness and the determination of the position and the shape of the so-called Soret absorption peak that, within the experimental uncertainty, is the same found for molecules in liquid. These findings suggest that YCC preserves its native structure upon adsorption. The same optical model was able to reproduce also ex situ results on rinsed and dried samples, dominated by the spectral features associated to the polypeptide chain that tend to overwhelm the heme absorption features.     

ESR and polarography of nitroazoles. 7. Anion-radicals of isomers of N-methyl-C-nitro-1,2,4-triazole

The anion-radicals of N-methyl-substituted 3-nitro-1,2,4-triazole have been studied by polarography, ESR, and quantum-chemical methods. The difference in electrochemical behavior of the N-methyl isomers of 3-nitro-1,2,4-triazole has been analyzed. The spin distributions in their anion-radicals have been investigated by quantum-chemical methods. The theoretical data obtained are in poor agreement with experiment. By varying the structural characteristics of the anion-radicals internal geometric parameters have been separated out which prove to have the greatest effect on spin distributions. Geometric structures were established for the investigated isomers by minimizing the functional describing the disagreement of the theoretical and experimental spin distributions on the magnetic nuclei. The calculated hyperfine structure constants for the magnetically active nuclei for the structures obtained were in good agreement with experiment. The influence of solvation effects on the electronic structure parameters of the nitrotriazole anion-radicals has been investigated. Hydrated complexes containing four molecules of water proved to be the most stable. Structural deformation of the solvated anion-radicals occurs in the same direction as on minimizing the functional.For part 6 see [1].Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk 664033, Russia; e-mail: vti@irioch.irk.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 193–202, February, 2000.     

Spectroscopic investigations and quantum chemical computational study of (E)-4-methoxy-2-[(p-tolylimino)methyl]phenol

In this work the electronic structure of (E)-4-methoxy-2-[(p-tolylimino)methyl]phenol has been characterized by the B3LYP/6-31G(d) level by using density functional theory. The experimental infrared and electronic absorption spectra have been obtained and compared with the theoretically obtained ones. Molecular electrostatic potential map has been evaluated; natural bond orbital and frontier molecular orbitals analysis have been performed from the optimized geometry. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model. The non-linear optical properties have been computed with the same level of theory. In addition, the changes of thermodynamic properties have been obtained in the range of 100-500 K.     

菁染料薄膜的光谱性能及稳定性的研究

本文研究了6种长链菁染料薄膜的光谱特性与光稳定性,以及两种抗氧剂对其薄膜光稳定性的影响。研究表明,结构相近的菁染料利用旋涂法成膜后,光稳定性与其母核的结构有关,依吲哚>喹啉> 唑>噻唑>硒唑顺序而变,与溶液状态下相类似,两种抗氧剂均为有效的单重态氧猝灭剂,都能提高菁染料的光稳定性。且抗氧剂的用量对染料的稳定性也会产生一定的影响     

分子动力学模拟研究熔盐中的局部结构

我们用分子动力学(MD)方法通过计算机模拟研究了熔盐中的键取向序和局部结构。描述局部结构的简单方法是计算键角分布几率,但它不能给出键取向序的三维空间描述。有的文献采用Direchlet-Voroitol(DV)多面体处理MD模拟产生的瞬态构型,但DV     

Insulated copper(I) "wires": structural variations and photoluminescence

An unprecedented "molecular wire" type of structure for the copper(I) carboxylate family has been synthesized by utilizing copper-copper interactions and controllable switch of copper-oxygen interactions. Several modifications of the same complex, copper(I) 2,4,6-triisopropylbenzoate, have been isolated to allow evaluation of the structural variation effects on photoluminescent behavior.     

Modification of Activated Carbon Fibers and Their Characterizes of Adsorption for Xenon

Activated carbon fibers (ACFs) are characterizes by their highly developed internal surface area and porosity. Especially the development of micro- and mesopores is of great importance because it allows the carbons to adsorb large amounts and various types of chemicals from gases or liquids. Due to such a valuable feature, activated carbon fibers have been in use for many years. Porous carbon materials have now become extremely versatile adsorbents of major industrial significance. The high surface area and porosity of activated carbon fibers are the result of the activation process; physical or chemical activation. However, the complexity of the carbon structure, although voluminous research has been done and great effort has been made toward the control of pore size and its distribution^[1-3]. The recent development of industrial technology provides new application fields for porous carbons and,at the same time, requires the carbon to have a desired pore structure. To meet such a requirement, many novel approaches to control pore structure have been proposed.     

Synthesis, structural determination and dynamic behavior of 2-chloro-4,6-bis(pyrazolylamino)-1,3,5-triazines

A series of 2-chloro-4,6-bis(pyrazolylamino)-1,3,5-triazines with applications in crystal engineering have been prepared. At low temperature, the presence of two or three isomers has been detected and these assigned to 4,6-diamino-1,3,5-triazine structures on the basis of comparison with model compounds. 2D-Exchange spectroscopy studies in various solvents and at different temperatures have been used to determine the equilibrium constants and the activation free energies of the restricted rotation about the amino-triazine bond. A plot of the activation free energy versus temperature showed a good linear correlation and confirmed that the same process is present in all of the compounds under investigation. Comparison with model compounds also confirmed both the occurrence of the restricted rotation and the 4,6-diamino-1,3,5-triazine tautomerism for triazines 1-4 in solution. The structure of compound 1 has been determined in the solid state by X-ray crystallography and consists ofa 4,6-diamino- 1,3,5-triazine structure stabilized by intra and intermolecular hydrogen bonds.     

Stereospecificity for the hydrogen transfer of pyridoxal enzyme reactions

We have studied the stereospecificities of various pyridoxal 5'-phosphate dependent enzymes for the hydrogen transfer between the C-4' of a bound coenzyme and the C-2 of a substrate in the transamination catalyzed by the enzymes. Prior to our studies, pyridoxal enzymes so far studied were reported to catalyze the hydrogen transfer only on the si-face of the planar imine intermediate formed from substrate and coenzyme. This finding had been considered as the evidence that pyridoxal enzymes have evolved divergently from a common ancestral protein, because identity in the stereospecificity reflects the similarity in the active-site structure, in particular in the geometrical relationship between the coenzyme and the active site base participating in the hydrogen transfer. However, we found that D-amino acid aminotransferase, branched-chain L-amino acid aminotransferase, and 4-amino-4-deoxychorismate lyase catalyze the re-face specific hydrogen transfer, and that amino acid racemases catalyze the nonstereospecific hydrogen transfer. These findings suggest the convergent evolution of pyridoxal enzymes. Crystallographical studies have shown that the stereospecificity reflects the active-site structure of the enzymes, and that the enzymes with the same fold exhibit the same stereospecificity. The active site structure with the catalytic base being situated on the specific face of the cofactor has been conserved during the evolution among the pyridoxal enzymes of the same family.     

Amino acid sequences of sturin A and of nudiventrin A

Nudiventrin and sturin have been fractionated and it has been shown that each of them consists of two components, A and B, their ratio in sturin being 10:1. The amino acid sequences of these proteins have been determined and it has been shown that they have the same primary structure.M. V. Lomonosov Moscow State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 76–82, January–February, 1980.     

Synthesis and characterization of transition metal-vitamin B13 complexes mixed with a co-vitamin

The synthesis and structural characterization of mixed vitamin-metal complexes are reported. A complex bearing two vitamins (B3 and B13) on the same metal centre, nicotinamide(orotato)nickel(II) pentahydrate, has been prepared and characterised by single-crystal X-ray diffraction methods. A complex of Cr(III) with vitamins C and B13, bis(ascorbato)orotatochromium(III) dihydrate, has been isolated and its nature investigated by means IR, ¹³C?NMR, API-ES and thermogravimetric measurements. Theoretical calculations have been performed to propose a structure in accord with results obtained.     

藏药五脉绿绒蒿碱结构和性质的理论研究

五脉绿绒蒿碱是一种从藏药五脉绿绒蒿中提取并已确认结构的新的生物碱. 采用密度泛函理论(DFT)和从头算(ab initio)方法, 在HF/6-31G*和B3LYP/6-31G*水平下全优化计算了该化合物的分子几何构型和电子结构; 依据Onsager自恰反应场(SCRF)模型考察了五脉绿绒蒿碱在氯仿、丙酮、二甲亚砜及水等溶剂中的溶剂化作用; 基于气相优化结构进行了B3LYP/6-31G*振动分析与红外光谱计算, 进一步按照统计力学原理求得了298～1500 K温度范围内该化合物的热力学性质. 此外, 还讨论了五脉绿绒蒿碱的分子结构与药效的关系.     

耐蚀合金Al3Ni和Ni3Al液态冷凝过程的比较研究

采用F-S多体势对液态合金Al3Ni和Ni3Al在不同冷却速度下的微观结构及其转变机制进行了分子动力学模拟,得到了不同冷速下各温度的双体分布函数;采用HA键型指数法对其结构进行了分析,结果表明: Al3Ni在两种冷速下均以非晶的形式出现,只是慢冷时体系的有序度略有升高;而Ni3Al的结构及能量转变受冷速影响较大,快冷时形成非晶,而慢冷时出现明显结晶;同样冷速下Al含量较少的Ni3Al体系的有序度高,更易形成晶体,晶体的形成过程中有能量突变.     

Divergent synthesis of segmented carbosilane dendrimers

A number of carbosilane copolymers of the first through third generations has been synthesized via the divergent approach. Each molecule of these compounds contains two pairs of dendrons—segments that have the same poly(propylenesilyl) carbosilane dendritic architecture but differ in the generation number and the amount and type of terminal groups (n-decyl or allyl). The target dendrimers have been isolated as individual compounds via preparative gel-permeation chromatography, and their structure has been studied by ¹H NMR spectroscopy.