Multicomponent kinetic analysis and theoretical studies on the phenolic intermediates in the oxidation of eugenol and isoeugenol catalyzed by laccase.
Multicomponent kinetic analysis and theoretical studies on the phenolic intermediates in the oxidation of eugenol and isoeugenol catalyzed by laccase.
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漆酶催化丁香酚和异丁香酚氧化过程中酚类中间体的多组分动力学分析及理论研究
DOI：
10.1039/c5cp03475b
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发表时间：
2015-11
影响因子：
3.3
通讯作者：
Zhao Yi-Lei
中科院分区：
文献类型：
--
作者：
Qi Yan-Bing;Wang Xiao-Lei;Shi Ting;Liu Shuchang;Xu Zhen-Hao;Li Xiqing;Shi Xuling;Xu Ping;Zhao Yi-Lei
漆酶催化天然酚类的氧化，从而被认为是木质化和脱木质化中的初始化反应。许多酚类介体也被应用于漆酶-介体体系。然而，苯酚的初级O-H断裂后的反应细节仍然不清楚。本研究以丁香酚（EUG）和异丁香酚（ISO）两种异构体酚为探针，结合时间分辨紫外-可见吸收光谱、MCR-ALS、HPLC-MS和量子力学（QM）计算等方法，对酶促反应途径进行了研究。结果表明，EUG的消耗速率与其浓度成线性关系，而ISO则不成线性关系。通过UV-Vis光谱、质谱和TD-DFT计算，证实了EUG反应中存在邻甲氧基醌甲基化中间体（E/Z）-4-亚丙基-2-甲氧基环己-2，5-二烯酮;而ISO反应中存在异丙基苯氧基自由基（E/Z）-2-甲氧基-4-（丙-1-烯-1-基）苯氧基自由基。此外，QM计算表明，EUG生成的苯氧基自由基（O-中心自由基）可以通过氢原子转移（HAT）容易地转化为烯丙基自由基（C-中心自由基），其活化焓为5.3 kcal mol（-1），然后被快速氧化为所观察到的丁香醌甲基化物，而不是O-自由基烯烃加成，其势垒高于12.8 kcal mol（-1）。相比之下，ISO生成的苯氧基自由基直接经历自由基偶联（RC）过程，势垒为4.8 kcal mol（-1），而O-和C-中心自由基之间的HAT异构化具有更高的反应势垒8.0 kcal mol（-1）。苄基型自由基和芳香族烯丙基自由基的电子共轭导致这两种途径的区别。这些结果表明，竞争性反应途径存在的新生的活性中间体在漆酶催化氧化天然酚类，这是重要的了解木质素聚合，并可能揭示了一些光的发展，有效的漆酶介体系统。
Laccase catalyzes the oxidation of natural phenols and thereby is believed to initialize reactions in lignification and delignification. Numerous phenolic mediators have also been applied in laccase-mediator systems. However, reaction details after the primary O-H rupture of phenols remain obscure. In this work two types of isomeric phenols, EUG (eugenol) and ISO (trans-/cis-isoeugenol), were used as chemical probes to explore the enzymatic reaction pathways, with the combined methods of time-resolved UV-Vis absorption spectra, MCR-ALS, HPLC-MS, and quantum mechanical (QM) calculations. It has been found that the EUG-consuming rate is linear to its concentration, while the ISO not. Besides, an o-methoxy quinone methide intermediate, (E/Z)-4-allylidene-2-methoxycyclohexa-2,5-dienone, was evidenced in the case of EUG with the UV-Vis measurement, mass spectra and TD-DFT calculations; in contrast, an ISO-generating phenoxyl radical, a (E/Z)-2-methoxy-4-(prop-1-en-1-yl) phenoxyl radical, was identified in the case of ISO. Furthermore, QM calculations indicated that the EUG-generating phenoxyl radical (an O-centered radical) can easily transform into an allylic radical (a C-centered radical) by hydrogen atom transfer (HAT) with a calculated activation enthalpy of 5.3 kcal mol(-1) and then be fast oxidized to the observed eugenol quinone methide, rather than an O-radical alkene addition with barriers above 12.8 kcal mol(-1). In contrast, the ISO-generating phenoxyl radical directly undergoes a radical coupling (RC) process, with a barrier of 4.8 kcal mol(-1), while the HAT isomerization between O- and C-centered radicals has a higher reaction barrier of 8.0 kcal mol(-1). The electronic conjugation of the benzyl-type radical and the aromatic allylic radical leads to differentiation of the two pathways. These results imply that competitive reaction pathways exist for the nascent reactive intermediates generated in the laccase-catalyzed oxidation of natural phenols, which is important for understanding the lignin polymerization and may shed some light on the development of efficient laccase-mediator systems.
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影响因子：
--
作者：
Hernandez-Vazquez, Liliana;de Jesus Olivera-Flores, Ma Teresa;Navarro-Ocana, Arturo
通讯作者：
Navarro-Ocana, Arturo
影响因子：
3.6
作者：
Brandi, P;Galli, C;Gentili, P
通讯作者：
Gentili, P
影响因子：
7.4
作者：
Gang, DR;Wang, JH;Pichersky, E
通讯作者：
Pichersky, E
DOI：
10.1021/jo202082v
发表时间：
2012-01
期刊：
The Journal of organic chemistry
影响因子：
--
作者：
Szilvia Hajdok;J. Conrad;U. Beifuss
通讯作者：
Szilvia Hajdok;J. Conrad;U. Beifuss
影响因子：
3.3
作者：
Sangha, Amandeep K.;Parks, Jerry M.;Smith, Jeremy C.
通讯作者：
Smith, Jeremy C.