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飞燕草素的分子结构与抗氧化特性

Molecular structure and antioxidant properties of delphinidin.

作者信息

Estévez Laura, Mosquera Ricardo A

机构信息

Departamento de Química Física, Facultade de Química, Universidade de Vigo, Lagoas-Marcosende s/n 36310-Vigo, Galicia, Spain.

出版信息

J Phys Chem A. 2008 Oct 23;112(42):10614-23. doi: 10.1021/jp8043237. Epub 2008 Sep 27.

Abstract

Density functional theory calculations were performed to evaluate the antioxidant activity of delphinidin, taking into account its acid/base equilibrium. The conformational behavior of both the isolated and the aqueous solvation species (simulated with the polarizable continuum model) were analyzed at the B3LYP/6-31++G(d,p) level, considering the cationic, neutral, and anionic forms, the latter two forms consisting of diverse tautomers. The analysis of their electron density distributions, using the quantum theory of atoms in molecules, reveals several facts that are not in line with their usual Lewis structures. The prototropic preferences observed in the gas phase and in solution are similar. Thus, in both phases, most stable tautomer of neutral delphinidin is obtained by deprotonating the hydroxyl at C4', and the most stable tautomer of the anion is obtained by deprotonating the hydroxyls at C4' and C5. All the planar conformers obtained display an intramolecular hydrogen bond (IHB) between O3 and H6'. Furthermore, the most stable tautomers of the neutral and anionic forms display two IHBs between O4' and H3' and H5'. To obtain ionization potentials (IPs) and homolytic O-H bond dissociation enthalpies (BDEs), the corresponding radical species were optimized at the UB3LYP level. Heterolytic O-H bond dissociation enthalpies (proton dissociation enthalpies, PDEs) were also computed. The expected important antioxidant activity can be justified from these results. IP, O-H BDE, and O-H PDE values suggest that one-step H atom transfer rather than sequential proton loss-electron transfer or electron transfer-proton transfer would be the most favored mechanisms for explaining the antioxidant activity of delphinidin in nonpolar solvents as well as in aqueous solution.

摘要

考虑到飞燕草素的酸碱平衡,进行了密度泛函理论计算以评估其抗氧化活性。在B3LYP/6-31++G(d,p)水平上分析了孤立物种和水合溶剂化物种(用可极化连续介质模型模拟)的构象行为,考虑了阳离子、中性和阴离子形式,后两种形式由不同的互变异构体组成。使用分子中原子的量子理论对其电子密度分布进行分析,揭示了一些与它们通常的路易斯结构不一致的事实。在气相和溶液中观察到的质子转移偏好相似。因此,在两个相中,中性飞燕草素最稳定的互变异构体是通过使C4'位的羟基去质子化得到的,而阴离子最稳定的互变异构体是通过使C4'和C5位的羟基去质子化得到的。所有得到的平面构象异构体在O3和H6'之间都显示出分子内氢键(IHB)。此外,中性和阴离子形式最稳定的互变异构体在O4'与H3'和H5'之间显示出两个IHB。为了获得电离势(IPs)和均裂O-H键解离焓(BDEs),在UB3LYP水平上对相应的自由基物种进行了优化。还计算了异裂O-H键解离焓(质子解离焓,PDEs)。这些结果可以证明飞燕草素具有预期的重要抗氧化活性。IP、O-H BDE和O-H PDE值表明,一步氢原子转移而不是连续的质子损失-电子转移或电子转移-质子转移将是解释飞燕草素在非极性溶剂以及水溶液中抗氧化活性的最有利机制。

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