Free radical scavenging potency of quercetin catecholic colonic metabolites: Thermodynamics of 2H + /2e - processes.

•Catecholic metabolites possess higher radical scavenging potency than quercetin.•They have potential to inactivate free radicals of different characteristics.•Second HAT and SPLET mechanisms enable this potency.•Abundant colonic metabolites could be at least in situ efficient antioxidants.•Direct free radical inactivation by metabolites may be of biological significance.