Reaction mechanism and thermodynamics of the elimination of peroxy radicals by an antioxidant enzyme inhibitor complex

•An antioxidant enzyme inhibitor to retard coal oxidation was proposed;•The mechanism of peroxy radical generation in the initial stage of coal self-oxidation was delineated;•Disproportionation between Cu,Zn superoxide dismutase and peroxy radical was described;•Disproportionation between Mn catalase and hydrogenperoxide was analyzed. An antioxidant enzyme inhibitor composed of polyethylene glycol-Cu,Zn superoxide dismutase and Mn catalase is proposed to eliminate peroxy radical (OO). The mechanism of the initial OO generation during coal self-oxidation was delineated. Three reactions were analyzed by quantum chemical. For the acylation reaction, the active sites of succinic acid and lysine have been identified through natural bond orbital and frontier molecular orbital analyses; pathways and mechanisms of the respective reactions have been proposed; the reaction involved two transition states and was associated with an activation energy (Ea) of 4.65 kJ/mol and an enthalpy change of −58.03 kJ/mol. For the disproportionation reaction between Cu,Zn-SOD and ROO, it was divided into four steps with an overall rate of 2.009 × 109m−1s−1; the first step was endothermic by 11.23 kJ/mol and needed to surmount an Ea of 31.3 kJ/mol; the second step was accompanied by a maximum heat release of 137.23 kJ/mol; the Cu2+ in the active center was reduced to Cu+ by consuming OO/H+, and then the Cu+ was oxidized to Cu2+ by again consuming OO. For the disproportionation reaction between Mn catalase and H2O2, it was divided into five steps with an overall rate of 3.267 × 106m−1 s−1; the first and fourth steps were endothermic by 22.74 and 19.72 kJ/mol, respectively; for the fourth step, under the exothermic process, an Ea of 47.21 kJ/mol needed to be surmounted; the reaction mechanism involved mutual conversion between Mn(II) in the reduced state and Mn(III) in the oxidized state to consume hydrogen peroxide.