A pulse radiolysis investigation of the oxidation of indolic melanin precursors: evidence for indolequinones and subsequent intermediates.
A pulse radiolysis investigation of the oxidation of indolic melanin precursors: evidence for indolequinones and subsequent intermediates.
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吲哚黑色素前体氧化的脉冲放射分解研究：吲哚醌和后续中间体的证据。
DOI：
10.1016/0304-4165(89)90136-0
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发表时间：
1989
期刊：
影响因子：
--
通讯作者：
Truscott,TG
中科院分区：
文献类型：
--
作者：
Lambert,C;Chacon,JN;Chedekel,MR;Land,EJ;Riley,PA;Thompson,A;Truscott,TG
用脉冲辐解法研究了黑色素前体化合物5，6-二羟基吲哚（DHI）、5，6-二羟基吲哚-2-羧酸（DHICA）和模型化合物N-甲基-5，6-二羟基吲哚（NMDHI）的单电子氧化引发的一系列瞬态反应的速率常数。在pH7.3 -7.4范围内，N3氧化反应产生的初始过渡产物被归属为相应的半醌类化合物。在每一种情况下，这些自由基衰变，可能是通过反硝化作用，在400-430 nm区域最容易监测到的产品。对于DHI，该区域的衰减可以用两个与母体浓度无关的一级过程来拟合。这些可能对应于5，6-吲哚醌，其醌亚胺和醌甲基化物互变异构体之间的转换。与NMDHI，另一方面，一个单一的较长寿命的产品与峰约430 nm的相应的自由基衰减后占主导地位，由于几乎肯定N-甲基-5，6-吲哚醌。这些数据似乎排除了通过半醌缩合、半醌与二羟基吲哚反应、吲哚醌或互变异构体的自加成、或吲哚醌或互变异构体与母体二羟基吲哚反应而引起的显著黑色素聚合。有人建议，黑色素的聚合，而可能会发生逐步加入吲哚醌甲基化物/亚胺减少低聚物物种。
The rate constants associated with the series of successive transient absorptions initiated by one-electron oxidation of 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-car☐ylic acid (DHICA), precursors of melanin, andN-methyl-5,6-dihydroxyindole (NMDHI), a model compound, have been studied by pulse radiolysis. The initial transient species resulting from N3oxidation reaction at pH 7.3–7.4 are assigned as the corresponding semiquinones. In each case, these radicals decayed, probably by disproportionation, into products most readily monitored in the 400–430 nm region. For DHI, the decay in this region could be fitted by two parent concentration independent first-order processes. These may correspond to transformations between 5,6-indolequinone, and its quinone-imine and quinone-methide tautomers. With NMDHI, on the other hand, a single longer-lived product with a peak around 430 nm predominated after decay of the corresponding radical, due almost certainly toN-methyl-5,6-indolequinone. The data appear to exclude significant melanin polymerisation by condensation of semiquinones, reaction of semiquinones with dihydroxyindoles, self-addition of indolequinones or tautomers, or reaction of indolequinones or tautomers with the parent dihydroxyindoles. It is suggested that polymerisation of melanin may rather occur by stepwise addition of indolequinone methide/imine to reduced oligomeric species.