An angular trinuclear copper(II) complex as a model for the active site of multicopper oxidases

Abstract

A new angular trinuclear copper(II) complex [Cu₃L¹L²(1-MeIm)(H₂O)](ClO₄) (1), where H₃L¹ and H₂L² are penta and tetra-dentate Schiff base ligands, is prepared from a reaction of [CuL²] and [Cu₂L¹(μ-Br)] in the presence of 1-methylimidazole (1-MeIm) and isolated as a perchlorate salt. The complex which crystallizes in the monoclinic space group P2₁/n shows the presence of a discrete angular trinuclear copper(II) core in which the monomeric precursor is linked with the dimeric precursor through phenoxo bridges. The core structure resembles well with the active site structure of blue multicopper oxidases. The Cu...Cu separations of ca. 3.3 Å in the angular unit is 0.4 Å shorter than those observed in the active site of the oxidized form of ascorbate oxidase. The complex displays a visible band at 620 nm (ε=500 M^-1 cm^-1) in DMSO. It shows magnetic moment values of 3.07 and 2.18 μ_B at 300 and 18 K, respectively, for the Cu₃ cluster. The complex models the structural and magnetic properties of the trinuclear active site of blue copper oxidases. An angular copper(II) complex [Cu₃L¹L²(1-MeIm)(H₂O)](ClO₄) has been synthesized by reacting type-2 and type-3 mimic precursor complexes, where H₃L¹ and H₂L² are penta and tetradentate Schiff base ligands. The complex, characterized by X-ray diffraction, models the active site structural features and magnetic properties of blue copper oxidases.