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

A series of divalent transition metal (Mn, Fe, Co, Ni, and Cu) flavonolate (Fla) complexes M-II(Fla)(L-1), and M-II(Fla)(L-2)X (X = Cl or ClO4) with the ligands N-propanoate-N,N-bis(2-pyridylmethyl)amine (L-1 = HPBMPA) and N-methylpropanoate-N,N-bis(2-pyridylmethyl)amine (L-2 = 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 N-3 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 (pi-pi*) of the coordinated flavonolate is influenced by the metals, and a linear correlation was observed between the logarithm of the reaction rate constant with O-2 and the degree of the bathochromic shift (Delta lambda), providing a mechanistic insight into the stoichiometric dioxygenation reactions. (C) 2013 Elsevier Ltd. All rights reserved.