Guaiacol oxidation: theoretical insight into thermochemistry of radical processes involving methoxy group demethylation.

IF 3.6 3区 生物学 Q2 BIOCHEMISTRY & MOLECULAR BIOLOGY
Monika Biela, Andrea Kleinová, Erik Klein
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引用次数: 0

Abstract

Guaiacol (2-methoxyphenol) is naturally occurring phenolic compound essential in various research areas. Oxidative transformation of guaiacol can lead to the formation of various products, including 1,3-benzodioxole or ortho-quinone. Therefore, this study is focused on the investigation of the reaction enthalpies of experimentally observed guaiacol oxidation pathways in gas-phase, as well as in non-polar environment and aqueous solution. Corresponding Density Functional Theory (DFT) calculations were carried out using two hybrid functionals (M06-2X and B3LYP-D3). All reaction enthalpies, as well as Gibbs free energies, were also calculated using composite ab initio G4 method. M06-2X and G4 results show mutual agreement and the best accordance with available experimentally determined reaction enthalpies. Obtained Gibbs free reaction energies indicate that formation of ortho-quinone is thermodynamically preferred to formation of 1,3-benzodioxole at 298 K in studied environments. Moreover, all computational methods confirm that the reaction enthalpy of methoxy group demethylation, i.e. O-C bond dissociation enthalpy (BDE), is substantially lower in comparison to the enthalpy of hydrogen atom transfer from phenolic OH group. In the case of phenoxide anion of guaiacol, which can be formed in ionization supporting solvents, O-C BDE shows further significant decrease, exceeding 50 kJ mol-1, in comparison to parent molecule.HIGHLIGHTSReaction enthalpies and Gibbs free energies of individual steps of guaiacol transformation to 1,3-benzodioxole or ortho-quinone are studied in three environments.M06-2X functional and composite ab initio G4 methods provide reliable O-H and O-C bond dissociation enthalpies.Dissociation enthalpy of methoxy group O-C bond is lower by ca. 100 kJ mol-1 in comparison to phenolic O-H bond.Phenoxide anion of guaiacol shows substantially lower O-C BDE than parent molecule.

愈创木酚氧化:涉及甲氧基去甲基化的自由基过程的热化学理论见解。
愈创木酚(2-甲氧基酚)是一种天然存在的酚类化合物,在许多研究领域都是必不可少的。愈创木酚的氧化转化可导致各种产物的形成,包括1,3-苯二酚或对醌。因此,本研究的重点是研究实验观察到的愈创木酚在气相、非极性环境和水溶液中氧化途径的反应焓。使用两个混合泛函(M06-2X和B3LYP-D3)进行相应的密度泛函理论(DFT)计算。所有反应焓和吉布斯自由能也用复合从头算G4方法计算。M06-2X和G4的结果基本一致,且与实验测定的反应焓最吻合。得到的吉布斯自由反应能表明,在所研究的环境中,在298 K下,对醌的生成比1,3-苯并二唑的生成更有利。此外,所有的计算方法都证实,甲氧基去甲基化的反应焓,即O-C键离解焓(BDE),与酚羟基的氢原子转移焓相比,要低得多。愈创木酚的苯氧阴离子可在电离支持溶剂中形成,与母体分子相比,O-C BDE进一步显著降低,超过50 kJ mol-1。研究了愈创木酚在三种环境下转化为1,3-苯并二唑或对醌的反应焓和吉布斯自由能。M06-2X功能和复合从头算G4方法提供可靠的O-H和O-C键解离焓。甲氧基O-C键的解离焓比酚类O-H键低约100 kJ mol-1。愈创木酚酚阴离子的O-C BDE明显低于母体分子。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Free Radical Research
Free Radical Research 生物-生化与分子生物学
CiteScore
6.70
自引率
0.00%
发文量
47
审稿时长
3 months
期刊介绍: Free Radical Research publishes high-quality research papers, hypotheses and reviews in free radicals and other reactive species in biological, clinical, environmental and other systems; redox signalling; antioxidants, including diet-derived antioxidants and other relevant aspects of human nutrition; and oxidative damage, mechanisms and measurement.
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