Solution chemistry of oxidovanadium(IV) complexes with two bis-kojic acid derivatives

Despite the recognized importance of vanadium compounds in biological systems, including insulin-mimetic properties of oxidovanadium(IV) complexes, namely those with two units of natural occurring mono-hydroxypyrone ligands, as kojic acid, few is known about the vanadium complexation properties with bis-hydroxypyrones ones. We describe herein detailed solution equilibrium studies of the V^IVO²⁺ complexes with two bis-kojic acid derivatives, L1 and L8, containing, respectively, a methylenic (–CH₂-) and 1-ethylenic (–CH(CH₃)-) linkage between the kojic units. The set of the results obtained from potentiometry, UV–Vis spectrophotometry and EPR spectroscopy studies allowed to conclude that they both can form stable binuclear species due to their capacity to bind simultaneous two oxidovanadium(IV) ions. The structures and coordination modes of the binuclear complexes species were mainly based on the EPR results, and also supported by DFT calculations. Molecular docking of the complexes with hen egg white lysozyme showed an efficient hydrogen binding interaction, a relevant feature for potential beneficial effects on the complex transport or even on the inhibition of its enzymatic activity.