Synthesis, X-ray structure and ascorbic oxidation properties of ternary α-amino acid Schiff base-bipy Cu(II) complexes as functional models for ascorbic oxidase

Three ternary copper(II) complexes [Cu(5-bromo-salTyr)(bipy)]·½CH3OH (1), [Cu(5-bromo-salLue)(bipy)]·CH3OH (2) and [Cu(5-bromo-salTrp)(bipy)]·3CH3OH (3) (where 5-bromo-salTyr, 5-bromo-salLue and 5-bromo-salTrp are tridentate Schiff base ligands derived from the condensation of 5-bromosalicylaldehyde with tyrosine, leucine and tryptophan, respectively, and bipy is 2,2′-bipyridine) have been prepared and characterized by elemental analysis, electronic, IR spectroscopies, magnetic measurement and cyclic voltammetry. The complexes, 1 and 3 have been also structurally characterized by X-ray diffraction technique. Crystal structures of 1 and 3 complexes displayed a distorted square-pyramidal geometry around Cu(II). The complexes are one-electron paramagnetic and show one d–d transition and one LMCT bands near 664 and 378 nm in aqueous methanol, respectively. The electrochemical studies of 1–3 in DMF medium exhibit an irreversible Cu(II)/Cu(I) redox couple in the potential range of −0.3 to 0.5 V and one additional irreversible anodic wave associated with oxidation of ligands about 0.8 V. These complexes are also catalytically active in oxidation of ascorbic acid in presence of dioxygen, models the ascorbate oxidation property of the Cu(II) sites in ascorbate oxidase. The catalytic cycle is effective for a [H2A]:[complex] mole ratio of about 100 for 1–3.

Three new ternary copper(II) complexes have been prepared and characterized. Synthesized compounds are found to be catalytically active in oxidation of ascorbic acid in presence of dioxygen which models the ascorbate oxidation property of the Cu(II) sites in ascorbate oxidase.Figure optionsDownload as PowerPoint slide