Laboratory for Epigenomics, Division of Molecular Medicine, Ruđer Bošković Institute, P.O. Box 180, HR-10002 Zagreb, Croatia.
Food Chem. 2013 Nov 15;141(2):1562-70. doi: 10.1016/j.foodchem.2013.03.072. Epub 2013 Mar 29.
Notwithstanding multiple mechanisms of radical scavenging (RS), measured RS activities (RSA) of flavonoids are usually related to O-H bond dissociation enthalpy (BDE) for hydrogen atom transfer (HAT). For 12 flavonoids the reaction free energies were calculated for: (1) HAT, (2) single electron transfer-proton transfer (SET-PT) and (3) sequential proton loss electron transfer (SPLET) in gas and aqueous phases. Aqueous free energies, like bond dissociation (BDFEaq), ionisation (IFEaq) and deprotonation (ΔGdeprot,aq) free energies were estimated using thermochemical cycles. While in gas HAT is a RS mechanism (BDFEg<IFEg<ΔGdeprot,g), in water SPLET can be concurrent or dominant mechanism depending upon pH since ΔGdeprot,aq<BDFEaq and ETFEaq⩽BDFEaq. For 12 flavonoids, BDFEaq has been correlated with ΔGdeprot,aq and ETFEaq with r=0.74 and 0.87 respectively. This reveals why BD(F)E parameter explains most of variance in variously measured RSA data even if the underlying mechanism is SPLET.
尽管黄酮类化合物具有多种清除自由基（RS）的机制，但测得的 RS 活性（RSA）通常与氢原子转移（HAT）的 O-H 键离解焓（BDE）有关。对于 12 种黄酮类化合物，在气相和水相条件下分别计算了 HAT、单电子转移-质子转移（SET-PT）和顺序质子丢失电子转移（SPLET）的反应自由能。水相自由能，如键离解（BDFEaq）、离解能（IFEaq）和去质子化（ΔGdeprot,aq）自由能，是通过热化学循环来估算的。虽然在气相中 HAT 是一种 RS 机制（BDFEg<IFEg<ΔGdeprot,g），但在水中 SPLET 可以是并发或主导机制，这取决于 pH 值，因为 ΔGdeprot,aq<BDFEaq 且 ETFEaq⩽BDFEaq。对于 12 种黄酮类化合物，BDFEaq 与 ΔGdeprot,aq 呈正相关，ETFEaq 与 ΔGdeprot,aq 呈正相关，相关系数分别为 0.74 和 0.87。这揭示了为什么 BD（F）E 参数可以解释大多数不同测量 RSA 数据中的差异，即使潜在的机制是 SPLET。
