Flavonoids widely found in natural foods are characterized by acting as antioxidants compounds. There are close relationship between the antiradical activities and structural properties of flavonoids. In this work, density functional theory (DFT) methods were applied to investigate the influence of the H5⋯OC4 intramolecular hydrogen-bond (IHB) on the antiradical activity of flavonoid based on three prevalently accepted radical scavenging mechanisms: hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton-loss electron-transfer (SPLET). The thermodynamic properties: bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) related with these mechanisms were calculated to elucidate the antiradical activity. The results showed that the 5-OH group is most influenced and its antiradical capacity was weakened by the H5⋯OC4 IHB. In the gas, benzene and chloroform phases, H5⋯OC4 IHB would reduce the antiradical activity of flavonoid via increasing the bond dissociation enthalpy. While, in the DMSO and H2O phases, the opposite result occurs by lowering the proton affinity.

中文翻译：

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H5⋯O C4分子内氢键（IHB）对黄酮类抗氧化活性的影响

广泛存在于天然食物中的黄酮类化合物的特点是作为抗氧化剂化合物。黄酮类化合物的抗自由基活性与结构特性密切相关。在这项工作中，基于三种普遍接受的自由基清除机制，应用密度泛函理论 (DFT) 方法研究了 H5⋯OC4 分子内氢键 (IHB) 对黄酮类化合物抗自由基活性的影响：氢原子转移 (HAT) ，单电子转移 - 质子转移（SET-PT）和顺序质子丢失电子转移（SPLET）。计算与这些机制相关的热力学性质：键离解焓（BDE）、电离势（IP）、质子解离焓（PDE）、质子亲合力（PA）和电子转移焓（ETE）以阐明抗自由基活性。结果表明，H5⋯OC4 IHB对5-OH基团的影响最大，其抗自由基能力减弱。在气相、苯和氯仿相中，H5⋯OC4 IHB 会通过增加键离解焓来降低黄酮类化合物的抗自由基活性。而在 DMSO 和 H2O 相中，通过降低质子亲和力会出现相反的结果。