Thin‐Layer Cyclic Voltammetric and Scanning Electrochemical Microscopic Study of Antioxidant Activity of Ascorbic Acid at Liquid/Liquid Interface

An electron transfer reaction between ascorbic acid (H₂A) in an aqueous solution and oxidizing agent in an organic solution immiscible with water has been studied by thin‐layer cyclic voltammetry (TLCV) for charge transfer at the interface between two immiscible electrolyte solutions (ITIES). As an antioxidant, H₂A provide electrons through the aqueous/organic interface to reduce Fc⁺ and the procedure has been proved to be a one electron process again. In this work, the first combination of TLCV and scanning electrochemical microscopy (SECM) was achieved and showed a reasonable agreement between the results from the two different approaches. Otherwise, lower concentration ratios Kr of aqueous to organic reactants was adopted, which is given as evidence to the proposed procedure of Barker.     

苯并三氮唑及其羧酸酯衍生物对铜缓蚀机理的分子动力学模拟研究

用分子动力学(MD)方法, 模拟计算了5种铜缓蚀剂[苯并三氮唑(BTA)、苯并三氮唑-5-羧酸甲酯(MBTC)、苯并三氮唑-5-羧酸丁酯(BBTC)、苯并三氮唑-5-羧酸己酯(HBTC)、苯并三氮唑-5-羧酸辛酯(OBTC)]与Cu₂O晶体的相互作用. 结果发现, 中性条件下缓蚀剂分子与Cu₂O晶体的结合能均大于酸性条件下的数值, 但两种条件下结合能的大小排序均为OBTC＞HBTC＞BBTC＞MBTC＞BTA. 对体系各种相互作用以及对关联函数g(r)的分析表明, 体系结合能主要由库仑作用提供, Cu₂O晶体中的Cu原子与缓蚀剂分子中的N原子之间形成了配位键. 在与Cu₂O(001)晶面结合过程中, BTA及其衍生物分子发生了扭曲变形, 但形变能远小于体系的非键相互作用能.     

Sulfide ion electrooxidation catalysed by cobalt phthalocyanine microcrystals

Electrooxidation of sulfide ion catalysed by microcrystals of cobalt phthalocyanine was investigated by cyclic voltammetry in 0.5M KNO₃ at pH 9.22. Traces of catalyst were immobilized at the surface of a paraffin-impregnated graphite electrode by the mechanical transfer of its powder. The electro-oxidation of HS^– proceeds in two irreversible steps, with the first peak between 0 V and –0.12 V and the second at 0.17 V. The first step is second order in HS^– and its product is the adsorbed disulfide, which may further dissociate to give adsorbed sulfur atoms. The reduction of sulfur occurs at –0.1 V.     

Absolute Rate Constants for the Addition of the 1‐(tert‐Butoxy)carbonylethyl Radical onto Cyclic Alkenes in Solution

Absolute rate constants are reported for the addition of the 1‐[(tert‐butoxy)carbonyl]ethyl (= 2‐(1,1‐dimethylethoxy)‐1‐methyl‐2‐oxoethyl) radical ^.CHMeCO₂(t‐Bu) to several cyclic and monosubstituted alkenes in MeCN as obtained by time‐resolved electron paramagnetic resonance (EPR). The activation energies for the addition of this alkyl radical are mainly governed by the addition enthalpy but are also substantially lowered by the ambiphilic effect and by relief of cyclic strain.     

Electroreduction of Aryldiazonium Ion at the Polar and Non-Polar Faces of ZnO: Characterisation of the Grafted Films and Their Influence on Near-Surface Band Bending

ZnO is a strong candidate for transparent electronic devices due to its wide band gap and earth-abundance, yet its practical use is limited by its surface metallicity arising from a surface electron accumulation layer (SEAL). The SEAL forms by hydroxylation of the surface under normal atmospheric conditions, and is present at all crystal faces of ZnO, although with differing hydroxyl structures. Multilayer aryl films grafted from aryldiazonium salts have previously been shown to decrease the downward bending at O-polar ZnO thin films, with Zn−O−C bonds anchoring the aryl films to the substrate. Herein we show that the Zn-polar (0001), O-polar (000 ), and non-polar m-plane (10 0) faces of ZnO single crystals, can also be successfully electrografted with nitrophenyl (NP) films. In all cases, X-ray photoelectron spectroscopy (XPS) measurements reveal that the downward surface band bending decreases after modification. XPS provides strong evidence for Zn−O−C bonding at each face. Electrochemical reduction of NP films on O-polar ZnO single crystals converts the film to a mainly aminophenyl layer, although with negligible further change in band bending. This contrasts with the large upward shifts in band bending caused by X-ray induced reduction.     

Reactions of trialkylalanes with cyclic acetals and orthoformates in CH2Cl2 and ClCH2CH2Cl as solvents

Under mild conditions, trialkylalanes (Et₃Al and Buⁱ ₃Al) in chlorine-containing solvents (CH₂Cl₂ or ClCH₂CH₂Cl) react with cyclic acetals and orthoformates to form glycol monoethers and dialkylacetals, respectively, in high yields. The ¹H NMR spectroscopic data demonstrate that CH₂Cl₂ or ClCH₂CH₂Cl interacts with Buⁱ ₃Al.     

pH值对聚四氨基酞菁钴膜电化学和紫外光谱性质的影响

用循环伏安法在导电玻璃(ITO)和玻碳电极(GC)上制备了聚氨基酞菁钴(CoTAPc)修饰电极(CoTAPc/GC)。探讨了pH值对CoTAPc膜的光谱和电化学性质的影响，发现其氧化还原电位与pH值有线性关系，电催化活性也随酸度的增加而增加。CoTAPc膜的紫外吸收带变化与溶液pH值及在溶液中浸泡时间有关。     

Some chemical transformations of the neo-clerodane diterpene teubotrin

Starting from the natural neo-clerodane diterpenoid teubotrin (1) several neo-clerodane derivatives (3-7,9-11) have been obtained. The naturally occurring diterpenoid teuscordinon (12) has also been synthesized from teubotrin (1), showing thereby how some of these transformations can be useful for the synthesis of other natural neo-clerodane diterpenes. The latter are of interest due to their activity as insect antifeedants and other important biological properties.     

Deformation calorimetry of polyurethane block-copolymers

A thermodynamic analysis of the uniaxial stretching of polyurethanes of various compositions and mechanical histories was carried out by using deformation calorimetry. The initial small strain deformations were found to result from the volume elasticity of the hard phase. The intramolecular energy contributions of the soft blocks were estimated. The hard block contributions were shown to depend on their content and on the degree of sample stretching. The predominant role of the soft component is proved to be manifested only in softened samples with a hard block content not exceeding 30%. The thermodynamics of the softening and hysteresis phenomena were studied. The dependence of the deformation mechanism on the hard block content and mechanical history is discussed.The authors express their thanks to Dr. A. R. Korigodsky and Dr. M. P. Letunovsky for the PU samples.     

Oxidation of theexo- andendo-phenylcyclohexadienyl iron complexes Fe(η5-6-PhC6H6) (η5- C5H5)

The roe of oxidatively induced homolyhc scission a the C(sp³)-H bonds in the iron phenykychhexadienyl complexes Fe(⁵-6-PhC₆H₆)(⁵-C₅H₅) (1) depends on the spatial orientation of the Ph substitutent. In the case of the (1 _endo ⁺) radical cation this process, resulting in the cationic biphenyl complex (Fe(⁶ -C₆H₅C₆H₅)(⁵-C₅H₅)]⁺ (2 ⁺), is fast and proceeds for several minutes. In the case of the more stable radical cation (1 _exo ⁺) the formation of 2⁺ is slow and takes tens minutes to complete.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1698–1700, July, 1996.