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 [CoIII(salen)L1][substrate = various flavonols (HL1); H2salen =N,N′-bis(salicylidene)ethane-1,2-diamine] in a model quercetinase reaction using [CoII(salen)] as catalyst has revealed that the intermediate partly undergoes ionic dissociation in dimethylformamide (dmf) to give L1 and [CoIII(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 [CoIII(salen)L2(dmf)](HL2= a depside product) which then forms L2 and [CoIII(salen)(dmf)2]+. The reaction rate was affected by the nature of the cation employed: [CoIII(salen)(dmf)2]+ is more effective than K+.