二价金属离子萃取速率常数与软硬酸碱规则

用上升液滴法测定了２－乙基己基膦酸单（２－乙基己基）酯－正辛烷从硝酸介质中萃取镁、钙、锌、镍、铜和铅等二价金属离子的正向初始速率，建立了速率方程，计算出正向萃取反应的速率常数、活化能及活化熵，首次将软硬酸碱规则与金属溶萃取速率常数关联。结果表明，在萃取机理相同时，萃取速率常数的大小与金属离子的软硬酸碱标度一致，即萃取过程中，作为酸的被萃取金属离子，其硬度越大，萃取速率常数亦越大，萃取反应的活化能…     

锚联膦,胺配体对胶体钯的配位俘获及其负载催化剂的催化性能

本文继采用含硫配体(-SH,-SR)对高分子保护金属胶体的配位俘获之后,采用锚联在SiO_2表面的较含硫配体配位能力弱的P,N配体分别与聚乙烯吡咯烷酮(PVP)保护的胶体钯在室温下反应,在P/Pd大于3.5,N/Pd大于7时,可以实施对保护金属胶体的配位俘获,证实了配位俘获法是一种具有普遍意义的方法,经原子吸收光谱分析,溶液中残留的金属钯的量小于0.36 ppm(P/Pd=3.5)。经电子能谱证实,锚联膦胺配体与金属钯之间存在配位作用,这是实施保护胶体负载化的关键。透射电镜分析表明,在整个配位俘获的过程中,无论是在载体上或是在溶液中,胶体钯的颗粒大小与分布均保持不变。因此,配位俘获法是一种能控制多相催化剂中金属颗粒大小与分布的有效方法。由此合成的钯催化剂具有很高的催化活性,良好的选择性和稳定性,在对Cis,Cis-1,3-环辛二烯的选择性加氢中,其活性仅比均相的PVP-Pd胶体催化剂稍低,选择性达100％。在周转数达12,000次/个钯原子后,其催化活性仍保持不变,随着P/Pd比的增大,催化活性迅速下降。     

邻近C-H键对中心金属原子的配位作用—[Fe(PH3)3(C8H13)]+的定域分子轨道研究

采用INDO方法计算了{Fe[P(OMe)_3]_3(C_8H_(13))}~+的简化离子[Fe(PH_3)_3(C_8H_(13))]~+,将正则分子轨道用Edmiston-Ruedenberg定域化方法变换为定域分子轨道,结果表明:在对应C_1-H_(1A)键的定域分子轨道中,明显包含有铁原子轨道成分(7.8％),Fe-H_(1A)和Fe—C_1键级分别为0.190和0.302。指出C_1-H_(1A)键是以一对成键σ电子配位到铁原子上的。C_8H_(13)环以包含三个碳原子的η~4—共轭体系与铁原子相互作用。铁以二价(d~6-Fe(Ⅱ)的形式存在于该离子中。C_1-H_(1A)键的配位满足了文献[15]提出的Fe(Ⅱ)的共价12价。     

Thermochemistry of adducts of some bivalent transition metal bromides with 4-chloroaniline

The compounds [MBr₂(p-clan)₂] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II); p-clan = 4-chloroaniline) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of solution of the adducts, metal(II) bromides and 4-chloroaniline in methanol, 1.2 M aqueous HCl or 25% (v/v) 1.2 M aqueous HCl in methanol were measures and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH°), the standard enthalpies of formation (Δ_fH°), the standard enthalpies of decomposition (Δ_DH°), the lattice standard enthalpies (Δ_MH°) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH°(g)). The mean bond dissociation enthalpies of the metal(II)-nitrogen coordinated bonds and the enthalpies of adduct formation in the gaseous phase have been estimated.     

A simple and simultaneous determination of acyclovir and ganciclovir in human plasma by high-performance liquid chromatography

A simple high-performance liquid chromatographic method was developed for the simultaneous determination of the therapeutic levels of acyclovir and ganciclovir in human plasma. After precipitation of plasma proteins with 6% perchloric acid, acyclovir and ganciclovir were simultaneously determined by reversed-phase chromatography with spectophotometric detection at 254 nm. The peak heights for acyclovir and ganciclovir were linearly related to their concentrations ranging from 0.063 to 2.080 micro g/mL. The recovery was 100.48-102.84% for acyclovir and 99.26-103.07% for ganciclovir. The intra- and inter-day relative standard deviation values were in the range 0.186-8.703% for acyclovir and 0.137-6.424% for ganciclovir. The detection limits for both compounds were 0.01 micro g/mL determined as the signal-to-noise ratio of 3. The present method is applicable to therapeutic monitoring during antiviral medication.     

Synthesis of a novel rigid molecule family for the investigation of electron and energy transfer

Three new rigid bridging ligands for metal complexation (7=bmb, 8=bqb and 11=btb) were prepared from a rigid triptycene spacer connected to two bipyridine ligands using a Horner–Emmons type reaction. The triptycene spacer is substituted by methoxy groups in the case of bmb and in the case of bqb by a benzoquinone substituent. The corresponding metal complexes (ruthenium and/or osmium) were synthesised and the different luminescence behaviour was tested. They show great potential for the investigation of intramolecular electron and energy transfer reactions. The dinuclear metal complex Ru---bqb---Os is an interesting system in which the bridging ligand bqb acts as a redox switch, able to tune the conductivity for energy or electrons across the bridge.     

Polarography in solution of some problems in organic chemistry: recent applications

Applications of chromatographic and atomic absorption methods are compared with those of electroanalytical techniques. The limitations of electroanalytical procedures and their advantages, such as speed, sensitivity and speciation are discussed. Among applications of polarography and voltammetry to a solution of basic problems, attention has been paid to the possibility to distinguish the degree of conjugation (e.g. of compounds containing the grouping CNNC), to a contribution to understanding of solution chemistry of mitomycin C and to processes involved in the reduction of cephalosporins. Among practical applications, the possibility to analyze suspensions, which can be carried out without separation offers advantages. Examples are interactions in suspensions of bile salts in the presence of metal (II) ions, adsorptions of various pesticides and other toxic materials on lignin and the possibility to follow alkaline cleavage of lignin in buffers pH 8-12 at 25 °C. Most of these studies would not be possible to carry out using other techniques.     

Enzyme inhibitors as chemical tools to study enzyme catalysis: rational design, synthesis, and applications

Carefully designed molecules that are intimately related to the reaction mechanism of enzymes are often highly selective and potent inhibitors that serve as extremely useful chemical probes for understanding the reaction mechanism and structure of enzymes. This article describes the design, synthesis, and applications of specific inhibitors of two mechanistically distinct groups of enzymes, ATP-dependent amide ligases and Ser- and Thr-hydrolases. Our strategy is based on the premise that stable analogues of the transition state (transition-state analogues) are highly potent inhibitors that serve as good mechanistic probes, and that a key structure of a good inhibitor of one enzyme is also utilized for the inhibitors of other enzymes that share the same chemistry in their catalyzed reactions, irrespective of the degree of structural similarity and evolutionary link between the enzymes. According to these principles, we designed and synthesized a series of phosphinate- and sulfoximine-based transition-state analogue inhibitors of glutathione synthetase, gamma-glutamylcysteine synthetase and asparagine synthetase. For the second group of enzymes, we synthesized a gamma-monofluorophosphono glutamate analogue for mechanism-based affinity labeling of gamma-glutamyltranspeptidase and fluorescent phosphonic acid esters for the active-site titration of lipase. These inhibitors were used successfully as ligands for detailed kinetic analyses, X-ray crystallography, and mass analysis of the enzymes to identify the key amino acid residues responsible for catalysis and substrate recognition in the transition state.     

Speciation of chromium in waste waters by coupled column ion chromatography-inductively coupled plasma mass spectrometry

An application of coupled column ion chromatography (IC)-inductively coupled plasma mass spectrometry (ICP-MS) is presented for speciation of chromium in waste waters. By coupling an anion column with a cation column, both the cationic Cr(III) and anionic Cr(VI) species can be analyzed with detection limits below 0.5 μg/1. The separation of the interfering ions (chloride, chlorate, perchlorate, sulphate, sulphite, sulphide, thiosulphate, carbonate, cyanide and some organic compounds) from the chromium peaks is discussed, and the use of different chromium isotopes for data acquisition is compared. Based on the results, m/z 52 was considered as an ideal isotope for speciation of chromium in waste waters by the coupled column IC-ICP-MS, because it did not suffer from polyatomic interferences and due to the high sensitivity for chromium. The analysis of the waste water samples should be performed as soon as possible after sampling according to the stability tests of the species.     

硝酸镧与冠醚(2, 2)配合物的晶体及电子结构研究

用X-射线单晶衍射法测定了硝酸镧与冠醚(2,2)配合物的晶体结构,发现其具有与报道的Eu(NO_3)_3(2,2)配合物不同的配位方式.晶体属于三斜晶系,空间群P(?),晶胞参数为a=10.312(2)(?);b=12.745(3)(?);c=8.917(2)(?);α=103.79(2)°;β=112.73(2)°;γ=83.68(2)°;V=1049.5(5)(?)~3;F(000)=587.88;Z=2.结构用重原子法解出;R值为0.0292.用INDO法计算了配合物的净电荷分布,电子结构、键级.结果表明,镧与配位原子间的键具有一定程度的共价性.镧的5d轨道对共价性的贡献最大,而4f轨道基本上不参与成键.La-N比La-O(醚)间存在较强的作用,增大了配合物的稳定性.