Alisi Ikechukwu Ogadimma, Uzairu Adamu, Abechi Stephen Eyije
Department of Applied Chemistry, Federal University Dutsinma, Katsina State, Nigeria.
Department of Chemistry, Ahmadu Bello University Zaria, Kaduna State, Nigeria.
Heliyon. 2020 Mar 31;6(3):e03683. doi: 10.1016/j.heliyon.2020.e03683. eCollection 2020 Mar.
The thermodynamics of free radical scavenge of 1,3,4-oxadiazole derivatives towards oxygen-centred free radicals were investigated by the density functional theory (DFT) method in the gas phase and aqueous solution. Three mechanisms of free radical scavenge namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were considered. The antioxidant descriptors that characterize these mechanisms such as, bond dissociation enthalpy (BDE), adiabatic ionization potential (AIP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) were evaluated. The sequence of electron donation as predicted by the HOMO results were in good agreement with the sequence of ETE for the considered molecules at their favoured sites of free radical scavenge. The reaction Gibbs free energy for inactivation of the selected peroxyl radicals, show that 1,3,4-oxadiazole antioxidants are more efficient radical scavengers by HAT and SPLET mechanisms than SET-PT mechanism in vacuum. In aqueous solution, the SET-PT mechanism was observed to be the dominant reaction pathway.
采用密度泛函理论（DFT）方法在气相和水溶液中研究了1,3,4-恶二唑衍生物对以氧为中心的自由基的自由基清除热力学。考虑了自由基清除的三种机制，即氢原子转移（HAT）、单电子转移后质子转移（SET-PT）和顺序质子损失电子转移（SPLET）。评估了表征这些机制的抗氧化剂描述符，如键解离焓（BDE）、绝热电离势（AIP）、质子解离焓（PDE）、质子亲和势（PA）和电子转移焓（ETE）。由最高占据分子轨道（HOMO）结果预测的电子供体顺序与所考虑分子在其有利的自由基清除位点处的ETE顺序高度一致。所选过氧自由基失活的反应吉布斯自由能表明，在真空中，1,3,4-恶二唑抗氧化剂通过HAT和SPLET机制比SET-PT机制更有效地清除自由基。在水溶液中，观察到SET-PT机制是主要的反应途径。
