Free radical versus electron-transfer routes of oxidation of hydrocarbons by laccase/mediator systems catalytic or stoichiometric procedures
Free radical versus electron-transfer routes of oxidation of hydrocarbons by laccase/mediator systems catalytic or stoichiometric procedures
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DOI：
10.1016/s1381-1177(03)00014-6
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发表时间：
2003-06-02
影响因子：
--
通讯作者：
Gentili, P
中科院分区：
文献类型：
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作者：
Cantarella, G;Galli, C;Gentili, P
在酚氧化酶漆酶的催化下，只要加入合适的介体化合物，烷基芳烃中C-H键的氧化可以通过分子氧发生。在非酶促步骤中，通过介体的氧化形式进行底物的实际氧化。评价了四种>N-OH型介体（HBT、HPI、VLA、NHA）的相对效率，并与结构不同的介体ABTS的相对效率进行了比较。漆酶/介体催化的非酚类底物的氧化可以通过两种不同的机制进行。通过介体ABTS的氧化形式，或者通过>N-O-夺取氢原子，在单电子氧化上。自由基物种来源于>N-OH型介质。前一种机制需要具有低氧化电位的底物;后一种机制需要具有相对弱的C-H键的底物。电化学和热化学的证据提供（i）解释失败的氧化特定的烷基芳烃和（ii）在支持的合理化的实验结果。特别强调的是给讨论的效果的介体-底物的摩尔比后的氧化过程的效率。为了解释为什么，在以前的文献研究中，更好的结果可能已经通过使用更多的介质，化学计量的量，我们提出了从介质，这可能是负责替代氧化途径的发病降解产物的同时形成。本研究对漆酶在木材木质素氧依赖性降解中的天然作用有了更好的认识。(C)2003 Elsevier Science B. V.保留所有权利。
The oxidation of C-H bonds in alkylarenes can take place by dioxygen, under catalysis by the phenol-oxidase enzyme laccase, provided that suitable mediator compounds are added. The actual oxidation of the substrate is carried out by the oxidised form of the mediator, in a non-enzymatic step. The relative efficiency of four >N-OH-type mediators (HBT, HPI, VLA, NHA) has been evaluated, and compared with that of the structurally different mediator ABTS. Laccase/mediator catalysed oxidations of non-phenolic substrates can proceed via two different mechanisms. Either on monoelectronic oxidation, by the oxidised form of mediator ABTS, or, by abstraction of hydrogen atom, by a >N-O-. radical species derived from the >N-OH-type mediators. The former mechanism requires substrates with a low oxidation potential; the latter mechanism requires substrates with relatively weak C-H bonds. Electrochemical and thermochemical evidence is provided (i) to explain the failure in the oxidation of specific alkylarenes and (ii) in support to the rationalisation of the experimental findings. Particular emphasis is given to discuss the effect of the mediator-to-substrate molar ratio upon the efficiency of the oxidation procedure. In order to explain why, in previous literature studies, better results may have been obtained by using the mediator in more that stoichiometric amounts, we propose the concurrent formation of degradation products from the mediator, which could be responsible for the onset of alternative oxidation pathways. A better understanding of the natural role of laccase in the oxygen-dependent degradation of lignin in wood emerges from this study. (C) 2003 Elsevier Science B.V. All rights reserved.