Structural and functional comparison of manganese-, iron-, cobalt-, nickel-, and copper-containing biomimic quercetinase models

Abstract

A series of divalent transition metal (Mn, Fe, Co, Ni, and Cu) flavonolate (Fla) complexes MII(Fla)(L1), and MII(Fla)(L2)X (X=Cl or ClO4) with the ligands N-propanoate-N,N-bis(2-pyridylmethyl)amine (L1=HPBMPA) and N-methylpropanoate-N,N-bis(2-pyridylmethyl)amine (L2=MPBMPA) have been prepared and characterized by spectroscopic methods and two cases by X-ray crystal analysis. The coordination sphere of the central ions is distorted octahedral with N3 or N3O donor sets, which are good structural models for the cupin-type metal-containing flavonol 2,4-dioxygenases (FDO). The dioxygenation of the metal flavonolate complexes results in the oxidative cleavage of the heterocyclic ring to give the corresponding O-benzoylsalicylate complexes and carbon monoxide as biomimic FDO models. The bathochromic shift of the absorption band I (π–π∗) of the coordinated flavonolate is influenced by the metals, and a linear correlation was observed between the logarithm of the reaction rate constant with O2 and the degree of the bathochromic shift (Δλ), providing a mechanistic insight into the stoichiometric dioxygenation reactions.