Fragmentation of realgar,As4S4, controlled by transition metalligand systems

The chemical behavior of the realgar molecule, As₄S₄, toward various (triphos)M moieties has been investigated. The reaction of As₄S₄ with [{MCl(cod)}₂] (M=Rh or Ir; cod=1,5-cyclooctadiene) in the presence of the ligand triphos [triphos=1,1,1- tris(diphenylphosphinomethyl)ethane] yields compounds of formula [(triphos)M(η³-As₃S₃)]·C₆H₆ containing the new As₃S₃ unit, which is trihapto bonded to the metal atom through one sulfur and two arsenic atoms. Such a As₃S₃ fragment is the largest one so far extruded from the realgar molecule. The As₄S₄ molecule undergoes more drastic disruptions in the reactions with Co(BF₄)₂·6H₂O and Ni(BF₄)₂·6H₂O in the presence of triphos. These results suggest that the fragmentation of the As₄S₄ molecule is controlled by the nature of the metal atom involved in the reaction.     

中国蚊类新纪录,4.Aedes(S.)galloisi Yamada,1921

本种伊蚊采自黑龙江省(许荣满、刘泉等);在吉林省(苏龙)和辽宁省(陈继寅)也有发现。它可以根据下列特征和我国复蚊亚属(Stegomyia)的其它种类相区别。成蚊盾片有一中央白纵条,沿盾角有侧纵条;后附节Ⅲ和Ⅳ几乎全白,节Ⅴ深褐色;雄蚊小抱器末端膨大,膨大部分有很多弯曲细刚毛和一些     

Unusual NMR, EPR, and M?ssbauer properties of Chromatium vinosum 2[4Fe-4S] ferredoxin.

The ferredoxin from Chromatium vinosum (CvFd) exhibits sequence and structure peculiarities. Its two Fe4S4(SCys)4 clusters have unusually low potential transitions that have been unambiguously assigned here through NMR, EPR, and M?ssbauer spectroscopy in combination with site-directed mutagenesis. The [4Fe-4S]2+/1+ cluster (cluster II) whose coordination sphere includes a two-turn loop between cysteines 40 and 49 was reduced by dithionite with an E degrees ' of -460 mV. Its S = 1/2 EPR signal was fast relaxing and severely broadened by g-strain, and its M?ssbauer spectra were broad and unresolved. These spectroscopic features were sensitive to small perturbations of the coordination environment, and they were associated with the particular structural elements of CvFd, including the two-turn loop between two ligands and the C-terminal alpha-helix. Bulk reduction of cluster I (E degrees ' = -660 mV) was not possible for spectroscopic studies, but the full reduction of the protein was achieved by replacing valine 13 with glycine due to an approximately 60 mV positive shift of the potential. At low temperatures, the EPR spectrum of the fully reduced protein was typical of two interacting S = 1/2 [4Fe-4S]1+ centers, but because the electronic relaxation of cluster I is much slower than that of cluster II, the resolved signal of cluster I was observed at temperatures above 20 K. Contact-shifted NMR resonances of beta-CH2 protons were detected in all combinations of redox states. These results establish that electron transfer reactions involving CvFd are quantitatively different from similar reactions in isopotential 2[4Fe-4S] ferredoxins. However, the reduced clusters of CvFd have electronic distributions that are similar to those of clusters coordinated by the CysIxxCysIIxxCysIII.CysIVP sequence motif found in other ferredoxins with different biochemical properties. In all these cases, the electron added to the oxidized clusters is mainly accommodated in the pair of iron ions coordinated by CysII and CysIV.     

Structural and electronic properties of 4H-cyclopenta[2,1-b,3;4-b′]dithiophene S-oxide (BTO) derivatives with an S, S=O, O, SiH2, or BH2 bridge: semi-empirical and DFT study

In this paper, we theoretically studied the geometries, stabilities, and the electronic and thermodynamic properties of 4H-cyclopenta[2,1-b,3;4-b']dithiopene S-oxide derivatives (BTO-X, with X = BH(2), SiH(2), S, S=O, or O) using semi-empirical methods, ab initio methods, and density functional theory. The geometries and thermodynamic parameters calculated by PM3 were in good agreement with those calculated with B3LYP/6-31 G*. The band gap calculated using B3LYP/6-31 G* ranged from 3.94 eV (BTO-O) to 3.16 eV (BTO-B). The absorption λ(max) calculated using B3LYP/6-31 G* was shifted to longer wavelengths when X = BH(2), SiH(2), or S=O (due to their electron-withdrawing effects) and to shorter wavelengths for BTO-S and BTO-O as compared to the λ(max) for the thiophene S-oxide (2TO) dimer. The changes in ΔH°, ΔS°, and ΔG° calculated using both semi-empirical and DFT methods were quite similar.     

四通4S高级科技编排系统简介

四通4S(Super Sclenc Setting System)高级科技书刊编排系统,是专门为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。 4S系统具有文字、图片、数学、化学,乐谱、表格、杂志、造字等直观排版功能,可在24针打印机,不同精度激光印字机及激光照排机,输出与版式一致的样张,目前可提供包     

四通4S高级科技编排系统简介

四通4S(Super Science setting system)高级科技书刊编排系统,是专门为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。 4S系统具有文字、图片、数学、化学、乐谱、表格、杂志、造字等直观排版功能,可在24针打印机、不同精度激光印字机及激光照捧机,输出与版式一致的样张,目前可提供包括宋、楷、黑、仿宋、魏碑、隶书、中圆、细圆、标宋等丰富的汉     

四通4S高级科技编排系统简介

四通4S(Super Science Setting System)高级科技书刊编排系统,是专门为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。 4S系统具有文字、图片、数学、化学、乐谱表格、杂志、造字等直观排版功能,可在24针打印机、不同精度激光印字机及激光照排机,输出与版式一致的样张,目前可提供包括宋、楷、黑、仿宋、魏碑、隶书、中圆、细圆、标宋等丰富的汉字字体。 四通4S先后荣获第37届尤里卡世界发明博览会金奖、北京首届国际博览会金奖、广州     

四通4S高级科技编排系统简介

四通4S(Super Science Setting System)高级科技书刊编排系统,是专门为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。     

四通4S高级科技编排系统简介

四通4S(Super Science Setting System)高级科技书刊编排系统,是专门为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。 4S系统具有文字、图片、数学、化学、乐谱、表格、杂志、造字等直观排版功能,可在24针打印机、不同精度激光印字机及激光照排机,输出与版式一致的样张,目前可提供包     

S100A4 在胰腺癌中的研究进展

胰腺癌最重要的生物学特性是容易发生转移和侵袭,致使很多患者无法得到根治性治疗。外科手术是胰腺癌惟一可能治愈的手段,但仅有10-20%的患者有机会手术治疗。错过早期诊断、常规疗法普遍不明显及快速肿瘤扩散共同导致患者的预后不良。胰腺癌的发生、发展受多基因调控。S100A4基因是近几年发现的一种具有促肿瘤作用的基因,目前研究认为该蛋白在胰腺癌的侵袭和转移中起重要作用.本文主要就S100A4与胰腺癌的有关研究进展加以综述。     

S100A4在胰腺癌中的研究进展

胰腺癌最重要的生物学特性是容易发生转移和侵袭,致使很多患者无法得到根治性治疗。外科手术是胰腺癌惟一可能治愈的手段,但仅有10-20%的患者有机会手术治疗。错过早期诊断、常规疗法普遍不明显及快速肿瘤扩散共同导致患者的预后不良。胰腺癌的发生、发展受多基因调控。S100A4基因是近几年发现的一种具有促肿瘤作用的基因,目前研究认为该蛋白在胰腺癌的侵袭和转移中起重要作用.本文主要就S100A4与胰腺癌的有关研究进展加以综述。     

四通4S高级科技编排系统简介

<正> 四通4S(Super Science Setting System)高级科技书刊编排系统,是专为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。 4S系统具有文字、图片、数学、化学、乐谱、表格、杂志、造字等直观排版功能,可在24针打印机、不同精度激光印字机及激光照排机,输出与版式一致的样张,目前可提供包括宋、楷、黑、仿宋、魏碑、隶书、中圆、细圆、标宋等丰富的汉字字体。     

四通4S高级科技编排系统简介

四通4S(super science setting system)高级科技书刊编排系统,是专门为科技类书刊文献的编排而设计的,排版功能实用性很强,采用即打即排的操作界面,直观形象,从根本上解决了科技书刊排版的难题。4S系统具有文字、图片、数学、化学、乐谱、表格、杂志、造字等直观排版功能,可在24针打印机、不同精度激光印字机及激光照排机,输出与版式一致的样张,目前可提供包括宋、楷、黑、仿宋、     

4-[(R,S)-1-氨基(2’,4’-二甲氧苄基)]苯氧乙酸的合成

合成了４－［（Ｒ,Ｓ）－１－氨基（２’,４’－二甲氧苄基）］苯氧乙酸以及４个中间体,其结构分别通过红外光谱、核磁共振、折光率、熔点等测试手段得到确证。     

(2R,3S,4S)-2-(N,N-二乙氨基)甲酰氧基-3-苯基-4-苯甲酰基-N-甲基-Y-内酰胺的合成及工艺研究

目的:通过对黄皮酰胺全合成中间体(2R,3s,4S)-2-羟基-3-苯基-4-苯甲酰基-N-甲基-Y-内酰胺(化合物A)2位羟基的酯化,提高脂水分配系数(1gP),考察对谷丙转氨酶活性的影响。方法:以化合物A为原料,通过酰化反应合成(2R,3S,4S)-2-(N,N-二乙氨基)甲酰氧基-3-苯基-4-苯甲酰基-N-甲基-Y-内酰胺(化合物B),重点考察了摩尔比、反应温度、反应时间等条件对反应的影响。化合物B结构已经元素分析、红外光谱、质谱及核磁共振氢谱确证。结果:化合物A和酰化剂以摩尔比2:3,在160℃下反应1h,目标化合物B,收率78．42%。结论:本合成路线及具体反应方法,具有试剂廉价易得、反应条件温和、后处理简便等优点,是一种较为实用的合成方法。     

(2R,3S,4S)-2-(N,N-二乙氨基)甲酰氧基-3-苯基-4-苯甲酰基-N-甲基-γ-内酰胺的合成及工艺研究

目的：通过对黄皮酰胺全合成中间体（2R,3S,4S）-2-羟基-3-苯基-4-苯甲酰基-N-甲基-γ-内酰胺（化合物A）2位羟基的酯化,提高脂水分配系数（kP）,考察对谷丙转氨酶活性的影响。方法：以化合物A为原料,通过酰化反应合成（2R,3S,4S）-2-（N,N-二乙氨基）甲酰氧基-3-苯基-4-苯甲酰基-N-甲基-γ-内酰胺（化合物B）,重点考察了摩尔比、反应温度、反应时间等条件对反应的影响。化合物B结构已经元素分析、红外光谱、质谱及核磁共振氢谱确证。结果：化合物A和酰化剂以摩尔比2：3,在160℃下反应1h,目标化合物B。收率78．42％。结论：本合成路线及具体反应方法,具有试剂廉价易得、反应条件温和、后处理简便等优点,是一种较为实用的合成方法。