Investigation on the formation and decay of the N,N,N′,N′-tetramethylbenzidine radical cation using various oxidants and reductants by stopped-flow spectrophotometry

N,N,N′,N′-Tetramethylbenzidine (TMB) is an aromatic amine that undergoes oxidation by various oxidizing agents such as Ce⁴⁺, MnO⁻₄, Cr₂O²⁻₇; HSO⁻₅, S₂O⁻₈, H₂O₂, Cl₂, Br₂ and I₂, thereby serving as a reducing substrate. One-electron oxidation of TMB results in a radical cation (TMB^˙+), and on further oxidation leads to the product dication (TMB⁺⁺) were monitored by stopped-flow spectrophotometer at the absorption wavelength of TMB^˙+(λ_max; 460 nm). ESR data was also provided to confirm the formation of radical cation. The rates of both the formation and decay of TMB^˙+ have been followed by a total second-order kinetics, a first-order dependence each on [TMB] (or) [TMB^˙+] and [oxidant]. The kinetic and transition state parameters have been evaluated for the effects of pH and temperature on the formation and decay of TMB^˙+ and discussed with suitable reaction mechanisms. Also, the rate constants for the reactions of the radical cation with various reducing agents such as sulfite (SO²⁻₃), thiosulfate (S₂O²⁻₃), dithionite (S₂O²⁻₄) and disulfite (S₂O²⁻₅) and ascorbic acid (vitamin C, AH₂ were determined. Besides these, this article also explains how TMB acts as a better electron relay than unsubstituted benzidine, even though both of them undergo one-electron oxidation and are used in the chemical routes to solar energy conversions. The observed rate constants for electron transfer were correlated theoretically using Marcus theory. The observed and calculated rate constants have good correlation.     

Electron transfer (oxidation) of complexes between bifunctional phenols and DMSO in non-polar surroundings

Pulse-radiolysis reactions were performed to study the effect of hydrogen bonding to dimethyl sulfoxide (DMSO) on the oxidation of dihydroxy benzene and biphenyl diols to phenoxyl radicals. It was observed that with DMSO as the hydrogen-bond acceptor, the oxidation process proceeds via proton-coupled electron transfer in the case of hydroquinone. For resorcinol, DMSO acts in a similar way as in the case of hydroquinone. For other biphenols, viz., 2,2′- and 4,4′-biphenyl diols, it was found that DMSO had no effect on the electron transfer. The results are explained based on the ionization potential and structure of the phenol derivatives which probably depends on the rotation of the OH bond causing different electron distribution in the transient conformation.     

p-硝基氯苯与α氰基乙酸乙酯-α-碳负离子的电子转移反应动力学研究: 非链式的自由基机理

在p-硝基氯苯(1)与α-氰基乙酰乙酯-α-碳负离子(2)的反应过程中, 测得了反应中间体p-硝基氯苯负离子自由基(3)的ESR谱。用ESR场/频联锁技术测定了(3)的ESR吸收强度-时间曲线, 当[1]《[2]时, 其结果与连续一级反应动力学相吻合。测得了从2向1的电子转移和3的分解反应速率常数和活化参数, 反应产物为α-氰基-α-(p-硝基苯基)乙酸乙酯和微量的硝基苯。为该反应提出了非链式的电子转移-负离子自由基分解-自由基偶合机理。     

One-electron redox reactions of troxerutin in aqueous solutions

The oxidation of flavonoids is of great interest because of their action as antioxidants with the ability to scavenge radicals by means of electron-transfer processes. The redox reactions of the flavonoid derivative troxerutin, (2-[3,4-bis-(2-hydroxyethoxy) phenyl]-3[[6-deoxy-α-L-manno-pyranosyl)-β-(D-glucopyranosyl]-oxy]-5-hydroxy-7-(2-hydroxyethoxy)-4H-1-benzo-pyran-4-one), were investigated over a wide range of conditions, using pulse radiolysis and cyclic voltammetry. The oxidation mechanism proceeds in sequential steps. One-electron redox potentials for troxerutin were found to be +1.196, +0.846 and −0.634 V vs. NHE.     

锰卟啉一次氯酸钠模拟体系中由芳醛制备相应羧酸

前文报道了在金属卟啉-次氯酸钠模拟体系中氧化苯甲醛时,金属卟啉结构与其催化性能的关系,结果表明:四(2.6-二氯)苯基卟啉合锰是稳定性能最好及活性较高的催化剂。本文进一步报道各种因素对反应的影响,并在此基础上提出了由芳醛合成相应羧酸的新方法。     

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二苯硒醚(TPDASe)间光诱导电子转移过程的激光光解研究

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二 苯硒醚(TPDASe)间在激光光诱导条件下，发生了分子间的电子转移过程．在可见- 近红外区(600-1200nm)，观测到了TPDASe阳离子自由基、富勒烯(C60／C70)激发三 线态和阴离子自由基，在苯腈溶液中，观测瞬态谱测定了电子从TPDASe转移到富勒 烯(C60／C70)激发三线态的量子转化产率(Φet^T)和电子转移常数(Ket)．     

[Co(C~5H~5)~2]~n.[M(dmit)~2](M=Ni,Pd;n=0,1,2)型配合物的合成及表征

二茂金属[M'(C~5H~5)~2]^1^+的盐与(NBu~4)~n[M(dmit)~2](M=Ni, Pd; N=1,2)反应, 当M'=Fe, Ni; n=1时, 分别得到了导电配合物[Ni(dmit)~2]和[Pd(dmit)~2]; 当M'=Co, n=1,2时, 分别得到的是电荷几乎不转移的4个盐[Co(C~5H~5)~2]~n[Ni(dmit)~2]和[Co(C~5H~5)~2]~n[Pd(dmit)~2]。用ESCA、Raman谱及循环伏安图讨论了上述化合物形成时的电荷转移量。尽管[M(dmit)~2]的室温电导率相当大, 但其电导率随温度的变化曲线表明它们属于半导体。EHCO能带计算给出[Ni(dmit)~2]的能隙0.112eV, 与实测的电导活化能相当接近。     

In situ polymer nanocomposites: Effect of nanoparticles on the interfacial region

Composites based on the blends of polyurethane and poly(methyl methacrylate) of various composition were synthesized in situ in the presence of various amounts of nanoparticles (fumed silica). From thermophysical measurements it was found that, during reaction, phase separation and evolution of two phases occur. The temperature transitions in the systems and their positions depend on the blend composition and on various amounts of nanoparticles. Using scanning differential calorimetry from the changing of heat capacity increments the fraction of an intermediate region between two main phases has been estimated. For the first time it was observed that in nanocomposites in the temperature region between two main relaxation transitions, there appears a third transition, which was related to the adsorption layers formed by both components at the interface of the nanoparticles. The appearance of such intermediate regions increases essentially the fraction of an interfacial region in the system.     

Reaction-Induced Phase Separation and Structure Formation in Polymer Blends

The peculiarities of reaction-induced phase separation and the structure formation in semi- and full interpenetrating polymer networks and in the blends of linear polymers formed in situ are analyzed. It is shown that for most of these systems phase separation proceeds viathe spinodal decomposition mechanism resulting in the formation of interconnected spatially periodic structures. The possible ways for the structure regulation of the composites produced are considered.     

Thermal behavior of chemically treated and untreated sisal fiber reinforced composites fabricated by resin transfer molding

Using thermogravimetric analysis (TGA), the thermal behavior of sisal fibers and sisal/polyester composites, fabricated by resin transfer molding (RTM), has been followed. Chemical treatments have been found to increase the thermal stability, which has been attributed to the resultant physical and chemical changes. Scanning electron microscopy (SEM) and infrared (FT-IR) studies were also performed to study the structural changes and morphology in the sisal fiber during the treatment. The kinetic studies of thermal degradation of untreated and treated sisal fibers have been performed using Broido method. In the composites, as the fiber content increases, the thermal stability of the matrix decreases. The treated fiber reinforced composites have been found to be thermally more stable than the untreated derivatives. The increased thermal stability and reduced moisture behavior of treated composites have been correlated with fiber/matrix adhesion.