Electrochemical reduction of 4-thienylquinazoline in dimethylformamide

Electrochemical reduction of 4-thienylquinazoline (4-TQ) at the dropping mercury electrode in dimethylformamide solutions containing 0.1 M tetrabutyl ammonium iodide supporting electrolyte gave two well-defined diffusion-controlled waves. The first wave was found to be quasi-reversible and the second irreversible, on the basis of the usual criteria. The controlled potential electrolysis experiments carried out at the limiting regions of the frist and the total waves of 4-TQ yielded the same number of electrons, namely two, in both cases. Mechanisms corresponding to the total wave and the first wave were proposed based on the results obtained.     

Optimization of a high-performance liquid chromatography method to quantify bilirubin and separate it from its photoproducts

A rapid reversed-phase (RP) high-performance liquid chromatography method for the isolation of bilirubin from its photoproducts (e.g., biliverdin) is reported. The method is based on isocratic elution using methanol:water as the mobile phase. A 2⁴ full-factorial experimental design approach was adopted. For the optimization, the best separation was obtained using a flow rate of 1.50 mL/min, a mobile phase of 99∶1 methanol:water (v/v) at pH 3.60, and a 150×4.6 mm id RP (C₁₈) column containing 5-μm particles. These conditions produced the fastest total retention time of 3.38±0.055 min, and other chromatographic parameters were acceptable. Under the optimum conditions, a linear calibration curve for bilirubin was obtained over the 1.0–40.0 μg/L concentration range studied. The limit of quantification was 0.79 g/L and the limit of detection was 0.24 μg/L. Bilirubin in solution was monitored by ultraviolet detection at 450 nm.     

Electrochemical reduction of 1,4-dihalobutanes at carbon cathodes in dimethylformamide

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate the electrochemical behavior of 1,4-dibromo-, 1,4-diiodo-, 1-bromo-4-chloro- and 1-chloro-4-iodobutane at glassy carbon cathodes in dimethylformamide containing tetramethylammonium perchlorate. Depending on the identity of the 1,4-dihalobutane electrolyzed and the choice of potential, reduction of these compounds leads to a myriad of products including cyclobutane, n-butane, n-octane, 1-butene, cis-and trans-2-butene, 1,3-butadiene, ethylene, 1-chlorobutane, 1-bromobutane, 1-iodobutane, 1-iodooctane, 1,4-dichlorobutane, 1,8-dichlorooctane, and 1,8-diiodooctane. Experiments involving the use of proton donors (phenol and 1,1,1,3,3,3-hexafluoro-2-propanol), a radical trap (norbornylene), and several deuterium ion or atom donors have been utilized to elucidate the mechanisms by which the various electrolysis products are formed.     

Electrochemical reduction of the perfluoro-n-Hexyl iodide on mercury,in dimethylformamide

The electrochemical reduction behaviour of perfluoro-n-hexyl iodide, C₆F₁₃I, has been studied at the mercury electrode in dimethylformamide as a solvent. The major reaction product of the controlled-potential electrolysis of C₆F₁₃I is the organomercuric compound (C₆F₁₃)₂Hg. Using conventional polarography and linear sweep voltammetry, it is concluded that a chemical prereaction occurs between the perfluoro-n-hexyl iodide and polarized mercury, yielding the perfluoro-n-hexyl mercury iodide C₆F₁₃HgI, which is itself reducible in two separate steps. A detailed mechanism of the electrochemical reduction of C₆F₁₃I is proposed and discussed.     

蛋白质修饰的电化学研究

蛋白质的翻译后修饰对于生命体执行正常的生理功能具有十分重要的作用,是蛋白质科学研究的重要内容.目前研究蛋白质修饰的方法主要有质谱法、亲和层析等,然而由于蛋白质修饰研究的复杂性,迫切需要发掘新的技术手段.电化学方法理论成熟、应用广泛,在生命科学许多领域发挥着越来越重要的作用.蛋白质的体外修饰必将导致蛋白质特定位点基团的变化,可以利用巧妙设计的电化学方法予以表征和分析,以期探明修饰对蛋白质结构和功能的影响.此外,又可以利用电化学定量分析的独特优势快速准确地测定蛋白质修饰中涉及的相关酶活.正因为如此,蛋白质体外修饰的电化学研究已引起越来越多的关注.本文以作者课题组近期研究工作为主,结合国内外同行的相关代表性工作,介绍电化学方法在蛋白质修饰方面的近期研究进展,并探讨了今后的发展方向和趋势.     

The electrooxidation behavior of bilirubin in DMF and DMF + H_2O mixed solvent

The electrooxidation of Bilirubin (BR) in N,N'-dimethylformamide (DMF) and DMF + H_2O mixed solvent is investigated by voltammetry techniques, in situ rapid scan thin layer spectroelectrochemistry and in situ ESR spectroscopy. The data reveal that the oxidation process of BR undergoes many stages, which are all sped up by the introduction of water. The species of bilirubin taking part in the reaction is found to be changed from BR in DMF into BR' in the mixed solvents and the anodic peak potential is shifted correspondingly from +0.58 V to +0.026-+0.35 V (vs. Ag/AgCl, 1.0 M KCl). Free radicals and the dimerization of them are observed during the oxidation.     

Modeling of biliverdin reduction process: regio-specificity and H-bonding

Octa ethyl biliverdin (OEBV) has been employed as a model for natural biliverdin and its geometry has been optimized by using semiempirical (AM1, PM3), DFT, and hybrid ONIOM methods. Geometries and energetics of formation of octa ethyl bilirubin (OEBR) formed by reduction from OEBV via three carbon sites β, γ, and δ have been obtained. It has been shown that γ-OEBR has two configurational isomers (named γ₁ and γ₂), which can convert to each other by internal 1,5-hydrogen shift. The results show that, within the accuracy level of semiempirical methods, all three isomers namely, β, γ₁, and δ-OEBR are of similar stability whereas, at higher level of theory, γ₁-OEBR is less stable than others. Moreover, γ₂-isomer with one more of its pyrrole rings being aromatic can achieve a higher symmetry, and is the most stable among others by at least 5–6 kcal mol⁻¹ based on various methods employed. It is interesting to note that the ridge-tile conformation, which has been confirmed for natural bilirubin was not observed for calculated geometries of γ₁- and γ₂-isomers. A conformational analysis show that an energy barrier of 25 kcal mol⁻¹ must be surmounted for γ₂ to obtain the ridge-tile geometry.

OEBV was synthesized and purified from octa ethyl porphyrin iron (III) chloride, and was reduced to OEBR by sodium borohydride (NaBH₄). Chemical reduction of OEBV with NaBH₄ was followed in CDCl₃ and CD₃OD solutions and the product was characterized by ¹H NMR and UV–Vis spectroscopy. The results show that γ₂-isomer as the major product, forms along with γ₁ via an equilibrium tautomerization reaction.     

Electrochemical reduction mechanism of 5(1H)-pyrromethenones in dimethylformamide on a mercury electrode

The mechanism of the electrochemical reduction of some 5(1H)-pyrromethenones and their aryl analogs (5-arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones) in dimethylformamide on a mercury electrode, using LiClO₄) as supporting electrolyte, has been investigated. Polarographic and voltammetric experimental data show that 5(1H)-pyrromethenones undergo a reductive electrodimerization only through an EC mechanism, whereas their aryl analogs can also be reduced through an ECE mechanism. This different behaviour gives information about the reactivity of the bridge carbon atom of these compounds.     

On the reduction of oxygen in dimethylformamide

The first reduction process in dimethylformamide containing 0.1 M tetraethylam-moniumperchlorate was studied. The techniques of polarography, controlled potential coulometry and potential sweep voltammetry were applied. The results obtained are consistent with the hypothesis that some chemical reactions are involved in the overall electrode process. In particular of the two chemical reactions considered, i.e. the protonation of the superoxide ion and that of its disproportion, the data seem to favour the first reaction over the second one. Evidences that the tetraethylammonium ion of the supporting electrolyte works as proton donor are provided.     

Solvothermal reduction of graphene oxide in dimethylformamide

The reduction of graphene oxide (G-O) is one of the most promising methods for the large scale production of graphene-based materials. In this paper, we report a simple and non-toxic method to produce reduced graphene oxide (rG-O) by refluxing G-O in N, N-dimethylformamide without the aid of a reducing agent. The rG-O materials with high degrees of reduction are prepared and the levels of reduction are controlled using reflux time. Successful reduction is confirmed by combustion-based elemental analysis and X-ray photoelectron and Fourier transform infrared spectroscopy.     

A full conformational space analysis of bilirubin

Ab initio methods were utilized in a gas-phase systematic conformational search of bilirubin conformers. The whole molecule was divided into four fragments. Most stable conformers of them were employed to build 196 conformers of the complete bilirubin molecule. Initial geometries were optimized using HF/3-21G level of theory and the minimum energy conformers were then reoptimized at B3LYP/6-31G(d) level. Ridge-tile conformer was the most stable one, in perfect agreement with X-ray data. We found that while tetrapyrrole backbone shows some flexibility, propionic acid side chains have a greater influence in bilirubin conformation because they can interact through different hydrogen bond patterns with the backbone and between them.     

探讨电化学界面的原子－分子世界（厦门大学电化学研究工作简介之一）

探讨电化学界面的原子－分子世界（厦门大学电化学研究工作简介之一）田昭武（固体表面物理化学国家重点实验室,厦门大学化学系,厦门３６１００５）厦门大学电化学研究工作内容包括：基础研究、新研究方法与仪器的研制以及应用研究。拟在本刊陆续予以介绍。作为厦门大学...     

胆红素的伏安特性及其微分脉冲伏安法测定

建立中成药中胆红素定量测定的微分脉冲伏安法。在多种介质中研究胆红素在玻碳电极上的电化学行为 ,全面优化条件后 ,采用标准加入法对中成药中胆红素进行测定 ,并通过与药典中标准方法对照和干扰实验及回收率实验对本方法进行评价。在 0 .2mol·L-1HAc NaAc 5 0 %EtOH和 1 1 5mol·L-1KH2 PO4 Na2 HPO4 溶液中 ,峰电流与胆红素浓度分别在 6.2 5× 1 0 -7～ 1 .0 0× 1 0 -5mol·L-1(r=0 .9976)和 5 .0 0× 1 0 -8～ 3.0 0× 1 0 -6mol·L-1(r=0 .9939)范围内呈良好的线性关系 ,检测下限分别为 5 .0× 1 0 -8mol·L-1和 5 .0× 1 0 -9mol·L-1。众生丸和牛黄解毒片中胆红素的质量分数分别为 0 .0 86%和 0 .1 0 9% ,RSD分别为 3 4%和 3.0 % ,回收率为 96.6%～ 1 0 4 .1 % ,其结果与药典中标准方法测定结果基本一致。     

Electrochemical dechlorination of some derivatives of 1-chlorophthalazine in dimethylformamide

The electrochemical reduction of some chlorophthalazine derivatives that differ with respect to the nature of the substituent and the heteroring (phthalazines, phthalazones, and 1,2,4-triazolo[3,4-a]phthalazines) on a dropping mercury electrode in dimethylformamide was studied by polarography, coulometry, and preparative electrolysis with isolation and identification of the electrolysis products. It is shown that the carbon-chlorine bond is cleaved initially in the cathode reduction of the investigated compounds to give the corresponding dehalogenated heterocycles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 541–544, April, 1979.     

肾上腺素电氧化生成肾上腺素醌的反应动力学

使用以铂片为工作电极的长光程薄层电化学池,采用单电位阶跃计时吸收法测定了1．0mol·L^-1H2SO4和冰醋酸中,肾上腺素电氧化生成肾上腺素醌的动力学参数．实验结果表明：肾上腺素在1．0mol·L^-1H2SO4介质中比在冰醋酸中容易被氧化．