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首页> 外文期刊>Pigment cell research >Dopaquinone redox exchange with dihydroxyindole and dihydroxyindole carboxylic acid
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Dopaquinone redox exchange with dihydroxyindole and dihydroxyindole carboxylic acid

机译：多巴醌与二羟基吲哚和二羟基吲哚羧酸的氧化还原交换

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A pulse radiolytic investigation has been conducted to establish whether a redox reaction takes place between dopaquinone and 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA) and to measure the rate constants of the interactions. To obviate possible confounding reactions, such as nucleophilic addition, the method employed to generate dopaquinone used the dibromide radical anion acting on dopa to form the semiquinone which rapidly disproportionates to dopaquinone. In the presence of DHI the corresponding indole-5,6-quinone (and/or tautomers) was also formed directly but, by judicious selection of suitable relative concentrations of initial reactants, we were able to detect the formation of additional indolequinone from the redox exchange reaction of DHI with dopaquinone which exhibited a linear dependency on the concentration of DHI. Computer simulation of the experimental time profiles of the absorption changes showed that, under the conditions chosen, redox exchange does proceed but not quite to completion, a forward rate constant of 1.4 x 10(6)/M/s being obtained. This is in the same range as the rate constants previously established for reactions of dopaquinone with cyclodopa and cysteinyldopa. In similar experiments carried out with DHICA, the reaction more obviously does not go to completion and is much slower, k (forward) =1.6 x 10(5)/M/s. We conclude that, in the eumelanogenic pathway, DHI oxidation may take place by redox exchange with dopaquinone, although such a reaction is likely to be less efficient for DHICA.
机译：已经进行了脉冲辐射分解研究，以确定在多巴醌和5,6-二羟基吲哚（DHI）及其2-羧酸（DHICA）之间是否发生了氧化还原反应，并测量了相互作用的速率常数。为了消除可能的混淆反应，例如亲核加成反应，用于生成多巴醌的方法是使用作用于多巴的二溴化物自由基阴离子形成半醌，该醌迅速歧化成多巴醌。在DHI存在下，也直接形成了相应的吲哚5,6-醌（和/或互变异构体），但通过明智地选择合适的初始反应物相对浓度，我们能够从氧化还原中检测到其他吲哚醌的形成。 DHI与多巴醌的交换反应对DHI浓度呈线性关系。吸收变化的实验时间曲线的计算机模拟表明，在所选条件下，氧化还原交换确实在进行，但还没有完全完成，正向速率常数为1.4 x 10（6）/ M / s。该范围与先前为多巴醌与环多巴和半胱氨酰多巴的反应建立的速率常数在同一范围内。在用DHICA进行的类似实验中，更明显的是反应没有完全完成，并且慢得多，k（正向）= 1.6 x 10（5）/ M / s。我们得出的结论是，虽然在Eumelanogenic途径中，DHI氧化可能是通过与多巴醌的氧化还原交换而发生的，尽管这种反应对DHICA的效率可能较低。

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