On the mechanism of a model quercetinase reaction using a cobalt Schiff-base complex

Abstract

Cyclic voltammetry of a substrate anion–catalyst binary complex intermediate [Co^III(salen)L¹][substrate = various flavonols (HL¹); H₂salen =N,N′-bis(salicylidene)ethane-1,2-diamine] in a model quercetinase reaction using [Co^II(salen)] as catalyst has revealed that the intermediate partly undergoes ionic dissociation in dimethylformamide (dmf) to give L¹ and [Co^III(salen)(dmf)₂]⁺. Dioxygen is then incorporated into the flavonolate anion in a non-radical manner, which is promoted by the counter cobalt cation complex, finally to give [Co^III(salen)L²(dmf)](HL²= a depside product) which then forms L² and [Co^III(salen)(dmf)₂]⁺. The reaction rate was affected by the nature of the cation employed: [Co^III(salen)(dmf)₂]⁺ is more effective than K⁺.