Characterization and examination of the H2O2 and O2- reactivity of a copper(II) complex with a N4 -Schiff-base ligand

FERREYRA, JOAQUÍN; PUZZOLO, JUAN; PALOPOLI, CLAUDIA M.; SIGNORELLA, SANDRA R.; RICHEZZI, MICAELA; MORENO, DIEGO

Congreso; VII LATIN AMERICAN MEETING ON BIOLOGICAL INORGANIC CHEMISTRY; 2021

Copper plays a rich variety of roles in nature. Due to its normally accessible CuI/CuII redox couple and its bioavailability, it is found as a constituent of natural enzymes which catalyze a broad range of chemical reactions, including O2 and H2O2 activation and the disproportionation of superoxide ion. A good strategy for gaining some insight into the mechanisms through which these reactions proceed involves the study of the interactions between bioinspired copper(II) complexes and H2O2/O2-, as well as a detailed characterization of the structures, reactivity and physicochemical properties of the copper-bound oxygen species which are implied as active intermediates in these processes.In this work, the [CuII(pyrprn)]2+ complex (pyrprn = N,N?-bis(2-pyridinylmethylene)propanediamine) was prepared and fully characterized, and its chemical reactivity towards O2- and H2O2 was examined. The results of the SOD-like activity measurements indicate that [CuII(pyrprn)]2+ has a higher ability to catalyze O2- disproportionation than most Cu(II) complexes of N4-amine/pyridine ligands, which is even greater than Cu(II) complexes of N2O2-Schiff-base ligands. The electron transfer reaction takes place through an inner-sphere mechanism within a [(pyrprn)CuII-η1-O2]+ adduct, which was characterized at low temperature by UV/Vis spectroscopy and simulated by DFT calculations. On the other hand, the reaction of [CuII(pyrprn)]2+ with an excess of H2O2 occurs through EPR silent intermediates. Low temperature spectroscopy and kinetic data suggest that, at higher complex concentrations (> 1 mM), the reaction proceeds by a mechanism which involves the formation of a peroxo-bridged dicopper intermediate. Conversely, at lower concentrations, the Cu(II) complex reacts with excess H2O2 to give an [(pyrprn)CuII-OOH]+ adduct, which could be stabilized and detected spectroscopically at low temperature in basic medium. The geometry of this intermediate was optimized by DFT calculations, and the simulated electronic spectrum was in good agreement with the experimentally observed value.