Electrochemical Investigation of Metal-Free and Nickel-Containing Porphyrazines Carrying Eight Tosylaminoethylthia Groups

Summary.  In this study, the electrochemical properties of metal-free and nickel-containing porphyrazines with eight tosylaminoethylthia groups were investigated using cyclic voltammetry, double potential step chronoamperometry, double potential step chronocoulometry, and controlled potential coulometry. Cyclic voltammetry measurements showed that both compounds exhibit two quasi-reversible and an irreversible reduction waves. The first electron transfer reaction was followed by an irreversible chemical reaction, the second one by a reversible chemical reaction for both species. The electrode processes of metal-free and nickel-containing porphyrazines are diffusion controlled, but the double potential step chronocoulometry measurements indicated that the nickel porphyrazine is adsorbed at the electrode. However, a small adsorption current has no significant effect on the mass transport mechanism of the system. Diffusion coefficients of both compounds were determined by both cyclic voltammetric and chronocoulometric measurements. The diffusion coefficients of the reduced forms of the porphyrazines were found to be smaller than those of the neutral forms. Received October 29, 2001. Accepted (revised) December 17, 2001     

Electrochemical Behavior of Some Thiotriazoles in Aqueous‐Alcoholic Media at GCE

An electrochemical study related to the electrooxidation of 4‐amino‐3‐thio‐5‐methyl‐1,2,4‐triazole (I), 4‐amino‐3‐thio‐5‐phenyl‐1,2,4‐triazole (II) and 3‐thio‐5‐phenyl‐1,2,4‐triazole (III), in 10% v/v methanol‐acetate buffer pH 4.6 has been performed. A variety of electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry, double‐potential step chronoamperometry, rotating‐disk electrode voltammetry and coulometry, were employed to clarify that the mechanism of the electrode process follows the oxidation of thiol compounds. All the compounds exhibit similar redox behavior under the given conditions. They display one irreversible oxidation peak, which is diffusion controlled. From the plot of current function in cyclic voltammetry and the ratio of i_c/i_a less than one in double‐potential step chronoamperometry, it was established that these compounds undergo an one electron oxidation followed by a dimerization process involving the formation of disulfide derivative (EC mechanism). The pK_a values were obtained by the dependence of limiting current and potential with in the wide pH interval. The transfer coefficients, the diffusion coefficients and rate constant of coupled chemical reaction were also reported. The substituent effects were also investigated.     

CO2在铜电极上的电还原行为

对常温常压下的MeCN, DMF和DMSO等3种有机溶剂中的CO2的电还原反应行为进行了研究, 求得了传递系数和扩散系数, 并证明了在MeCN, DMF和DMSO中, CO2的还原反应是受扩散控制的不可逆过程.     

离子液体中间硝基苯酚在玻碳电极上的电化学还原行为研究

在[EMIM]Br体系中,以玻碳为工作电极,铂丝为辅助电极,饱和甘汞电极为参比电极,研究了间硝基苯酚的电化学行为.采用循环伏安法和计时电量法,研究了扫描速度、温度和底物浓度等因素对其电化学行为的影响,求得扩散系数D为9.184×10^-7cm²/s,传递系数α为0.37,证明了在[EMIM]Br体系中,此反应是受扩散控制的不可逆反应.     

One- vs. two-electron oxidations of tetraarylethylenes in aprotic solvents

The oxidation of dimethylaminophenyl substituted ethylenes and tetra-p-anisyl ethylene at a platinum electrode in methylene chloride and acetonitrile solutions was investigated by cyclic and rotating disk electrode voltammetry, potential step chronocoulometry, controlled potential coulometry and e.s.r. spectroscopy. The results show that the oxidations occur by either two one-electron steps or by a single two-electron step depending upon the structure of the molecule. Factors influencing the reaction path are discussed.     

顺、反丁烯二酸在铅电极上的电还原特性

采用循环伏安、计时电量及电化学阻抗等方法, 研究了顺、反丁烯二酸在铅电极上的电化学还原行为, 获取了传递系数、表观活化能和扩散系数等动力学参数, 并讨论了电化学还原机理. 结果表明, 顺、反丁烯二酸在铅电极上的电还原过程均为二电子不可逆反应, 扩散过程是速率控制步骤; 反丁烯二酸(FA)的还原电位要比顺丁烯二酸(MA)高约0.1 V, 较顺丁烯二酸难还原; 0.04 mol·L-1顺、反丁烯二酸在0.1 mol·L-1硫酸介质中的扩散系数分别为7.96×10^-6和6.72×10^-6 cm2·s-1. 电化学阻抗研究表明, 在铅电极上顺丁烯二酸较反丁烯二酸有更好的反应活性, 在较低偏置电压下FA和MA的电化学还原过程受电子转移控制, 随着偏置电压的增加, 逐渐转变为扩散控制. 顺丁烯二酸和反顺丁烯二酸的不同空间结构, 使顺、反丁烯二酸在铅电极表面电还原行为存在差异.     

The electrochemistry of proteins and related substances part III. Bovine serum albumin

The electroreduction of bovine serum albumin (BSA) in pH 7.4 solution was studied at the hanging mercury drop electrode by double potential step chronocoulometry and cyclic voltammetry, and at a mercury pool electrode by controlled potential coulometry. The proposed mechanism involves reduction of an adsorbed monolayer of BSA (maximum coverage 3.3 μC^?2); at short times 3 or 4 disulfide bonds are reduced, the product remains adsorbed and may be reoxidized. On the coulometric time scale (hours) 8 or 9 of the total 17 disulfide bonds are broken and an insoluble product which cannot be oxidized is formed.     

Electrocatalysis of the SiC Particle‐Modified Glassy Carbon Electrode for the Oxidation of Adrenaline

The electrocatalytic properties of the SiC particle‐modified glassy carbon electrode (MGC) for adrenaline oxidation were studied by cyclic voltammetry (CV), double‐potential step chronocoulometry (DPSCC), and electrochemical impedance spectroscopy (EIS) techniques in McIlvaine buffer solution. It was shown that the electrode modified with SiC particles markedly displayed an electrocatalytic effect on the process of the electrochemical reaction of adrenaline, i.e., the activity and the reversibility of the MGC electrode has been significantly improved. This was attributed to the adsorption effect of the electroactive adrenaline molecules on the MGC electrode surface.     

2，3—二氨基吩嗪的薄层光谱电化学研究

研究了2，3—二氨基吩嗪(DAP)在金圆盘电极、金超微电极上的循环伏安行为 和在金网栅电极上的薄层循环伏安行为．在pH2．0的B—R缓冲溶液中的2，3—二氨 基吩嗪在金圆盘电极上为准可逆氧还过程；以超微电极法求得了2，3—二氨基吩嗪 在pH2．0的B—R缓冲溶液中的扩散系数，由耗竭性库仑电解和循环伏安法求得其电 极反应电子转移数和H+反应级数均为2，实验说明参与电极反应的H+也为2，并用循 环伏安法求得其标准电极反应速率常数．采用紫外—可见薄层光谱电化学方法测得 2，3—二氨基吩嗪的克式量电位和电子转移数，与电化学实验结果一致；双电位阶 跃—计时吸收紫外—可见薄层光谱电化学实验说明，2，3—二氨基吩嗪电还原无随 后化学反应，其在电极上经历了H+eH+e的两步一电子过程，生成产物2，3—二氨基 -5，10-二氢吩嗪．     

Electrochemical characterization of phthalocyanine derivatives carrying a bulky triester unit on each benzo group

The focus of the present work is to gain more insight into the electrochemical behavior of newly synthesized Co^II, Zn^II, Cu^II, and Pd^II phthalocyanines with tetra-tricarbethoxyethyl substituents at the peripheral position. A more exhaustive electrochemical study of the complexes was done to determine the desired wisdom for the usage of the complexes as a functional material. A comparative study of the voltammetric measurements of these complexes showed that while Zn^II, Cu^II, and Pd^II phthalocyanines exhibited up to four common phthalocyanine ring reductions, Co^II phthalocyanine gave a metal-centered oxidation, a reduction and a ligand-centered reduction process. By contrast observation of the splitting of the second reduction process of Pd^II phthalocyanine suggests aggregation of the complex. Diffusion coefficients of all complexes were determined by both the cyclic voltammetry and the potential step chronocoulometry techniques. Diffusion coefficients of the reduced and oxidized forms of the redox couples of the complexes were also calculated by the potential step chronocoulometry technique. Diffusion coefficients of the reduced forms of the electrode products of the complexes were found to be slightly higher than that of the oxidized forms.     

1,4—二氢吡啶及其衍生物电化学反应机理的研究

研究了１１种１，４－二氢吡啶及其衍生物在乙腈溶剂中和铂盘电极上的电化学行为。实验结果表明：１，４－二氢吡啶及其衍生物在铂盘电极上的反应是受扩散和化学反应速率控制的两电子不可逆氧化过程，经连续两步失电子脱氢后形成相应的吡啶。用紫外吸收光谱电化学方法观测了电化学氧化过程。并与化学氧化产物的紫外光谱作了比较，证明１，４－二氢吡啶的电化学氧化产物与化学氧化产物一致。因此，电化学氧化是一种不需加化学试剂可使     

1,3-二甲基-5-亚硝基-6-氨基脲嘧啶铂电极电化学加氢机理研究

采用稳态极化法、循环伏安法和恒电位库仑法对1,3-二甲基-5-亚硝基-6-氨基脲嘧啶在铂电极上的电化学加氢机理进行了研究,研究介质为硫酸和硫酸钾水溶液.结果表明,pH=3时,1,3-二甲基-5-亚硝基-6-氨基脲嘧啶在铂电极析氢电位(-600～-800mV,vs.饱和硫酸钾的硫酸亚汞参比电极)前,发生加氢还原反应,氢离子在铂电极表面得到电子生成原子态的氢参与反应.随着pH值降低,加氢反应速度增大,还原电位正移.在铂电极上的电化学加氢过程受扩散控制,增大搅拌速度和提高温度都可提高反应速度.     

Electrochemical reduction of the lanthanide ions: Part I. First reduction step of ytterbium(III) in acidic 1 M NaClO4 solution

The reduction of Yb(III) to Yb(II) in 1 M NaClO₄ in the pH range 1.9–6.6 was studied by d c. polarography, cyclic voltammetry and electrode impedance measurements as a function of frequency and electrode potential. It results that the d.c. reversible reduction is followed by a homogeneous chemical reaction and is accompanied, by an irreversible process which is attributed to a lowering of the overpotential of the reduction of the hydrogen ions. Values of the rate constant and transfer coefficient pertaining to the charge transfer step were deter mined.     

Kinetics of the Electrocatalytic Oxidation of 2,2-Dimethylolpropionaldehyde

A new method of synthesis 2,2-dimethylolpropionic acid from 2,2-dimethylolpropionaldehyde was put forward. The electrochemical oxidation behavior of 2,2-dimethylolpropionaldehyde has been investigated on a Ti/SnO₂ + Sb₂O₄/PbO₂ electrode by cyclic voltammetry (CV) and stable polarization curves in sulfuric acid. The results showed that it was an irreversible reaction controlled by diffusion. The formation mechanism of 2,2-dimethylolpropionic acid in the sulfuric acid was then proposed and the transfer coefficients of the reaction were calculated. It was concluded that RCHO+ỌH_ads→RCHOỌH_ads was the rate-determining step in the electrolysis process. The rate of this step obtained from the assumed process agrees well with experiment.     

酸性介质中碘离子在铂电极上的电化学氧化行为

采用循环伏安法研究了酸性介质中碘离子在铂电极上不同电位区间, 不同酸度下的电化学反应行为. 结果表明, 当极化电位较低(小于0.6 V(vs Hg/Hg2SO4))时, 碘离子在铂电极上发生2I--2e→I2电氧化反应, 反应产物通过I2+I-=I-3被进一步溶解, 整个反应属于E-C(electrochemical-chemical)模式. 电氧化过程中可以形成碘膜, 其也可以被碘离子溶解. 当极化电位升高至0.6 V(vs Hg/Hg2SO4)或以上时, 碘离子会直接电氧化为高价态碘化合物, I-+3H2O→IO-3+6H++6e, 而析出的碘膜并不发生再氧化反应; 在电化学还原过程中, 出现了两个还原峰, 分别对应于I2、I-3的还原反应; 在无碘膜时, 碘离子电氧化过程受溶液中碘离子的液相扩散步骤控制; 碘膜形成后, 主要受碘膜中碘离子的固相扩散控制; 酸度对于碘离子的电化学氧化过程有很大的影响, 其线性极化曲线的起峰电位及电流峰值电位均随酸浓度升高而负移.     

聚苯胺修饰超微盘电极上镉(Ⅱ)的表面络合吸附波

用直径7 μm的碳纤维组合成超微圆盘电极,以聚苯胺修饰电级.以阶梯扫描法、循环伏安法、双阶跃计时电量法和交流阻抗法等,研究了Cd2＋在该电极上的表面络合吸附特性和电极过程.在循环伏安图上出现两个还原峰,实验和理论都证明,由于电极表面的聚苯胺对Cd2＋的特性吸附,形成电活性的表面吸附态络合物.因此,这种表面络合物首先被还原,形成峰电位－0.90 V处的表面络合吸附波,还原峰电位比Cd2＋直接还原电位（－0.98 V）正移,循环反扫时,氧化波无峰形.根据实验数据推测了电极过程的反应机理,证实该还原波具有扩散和表面反应同时控制的表面络合吸附波的特性.理论计算与实验基本一致,并求得了表面吸附态配合物的形成常数、吸附量和表面络合反应的动力学参数.实验还证实,在峰电位－1.06 V 处的还原波,是Cd2＋的表面吸附还原态诱导而产生的催化氢波.     

A study on electrochemistry of histidine and its metabolites based on the diazo coupling reaction

The diazo coupling reaction of diazotized p-aminoacetophenone (DPAAP) with histidine and its metabolites form the basis of the differential pulse adsorption stripping voltammetry (DPASV) method for determination of histidine and its metabolites. The adsorption and electrochemical reaction mechanism of the coupling products were studied in detail by structure analysis, cyclic voltammetry, chronocoulometry, control potential electrolysis, electrocapillary curves, UV spectroscopy and the effect of temperature and surfactants. The adsorption of azo-histidine was found to obey Frumkin adsorption isotherm. The calculation results of the maximum surface excess (Gamma(m)=3.08x10(-11) mol cm(2)), diffusion coefficient (D=2.27x10(-6) cm(2) s(-1)), adsorption coefficient (beta=1.06x10(7)) and interactive factor (gamma=0.9900) showed that the azo-histidine conjugation molecules adsorbed on the mercury electrode surface were attracted each other and the electrode process was adsorption controlled.     

二茂铁基超支化聚氨酯的电化学性能

通过循环伏安法(CV)测定了二茂铁基超支化聚氨酯(HAPE-Fc)的电化学性能.结果表明:HPAE-Fc表现为单对氧化还原峰,在二茂铁接枝到超支化聚氨酯上以后,二茂铁基团依然保持着自身的氧化还原独立性,具有较强的电子转移速率,这是其具有电化学特性和催化作用的前提条件.通过分析扫描速率与HPAE-Fc电化学行为之间的关系,发现HPAE-Fc的电极过程既受扩散控制,同时也受电极反应的控制.     

玻碳电极表面因瓦合金的电化学成核机理

在弱酸性因瓦合金(含镍质量分数为32~36 % 的镍铁合金)镀液中, 以线性扫描伏安法、循环伏安法和恒电位阶跃法对因瓦合金在玻碳电极表面的电沉积过程及其成核机理进行研究. 结果表明, 在该体系下, 因瓦合金在玻碳电极表面的电结晶属于扩散控制下的不可逆电极过程. 运用Scharifker-Hills理论模型(SH)拟合实验数据表明, 因瓦合金在玻碳电极表面的共沉积更加符合三维瞬时成核的成核规律. 运用Heerman-Tarallo理论模型(HT)分析得到因瓦合金在玻碳电极表面的成核生长的动力学参数, 当阶跃电位从-1.11 V变化至-1.17 V (vs SCE), 成核密度数(N₀)由0.72×10⁵ cm^-2提高至1.91×10⁵ cm^-2, 成核速率常数(A)从 40.35 s^-1增至 194.38 s^-1, 扩散系数(D)为(7.67±0.15)×10^-5 cm²•s^-1, 变化不大.     

Kinetic analysis of a slow electron transfer coupled with a father—son reaction

The electrode reaction mechanism involving interaction of the products of a slow, rate-determining electron transfer with the parent molecule (father—son reaction) has been examined theoretically under the conditions of cyclic voltammetry. The kinetic analysis indicates how to determine the correct values of the kinetic parameters for both the heterogeneous charge transfer and the homogeneous chemical step. The irreversible cathodic reaction of diphenylmethylphenylsulphide in anhydrous DMF provides a good example of this mechanism, since the diphenylmethyl carbanion resulting from the irreversible two-electron reduction undergoes proton transfer from the parent molecule (self-protonation mechanism).