Redox pathways in the carnosine–manganese system mediated by semiquinone radicals Scientific paper

Abstract

The interaction of carnosine histidine-containing dipeptide with the semiquinone radical of 3,4-dihydroxybenzoic dianion in dimethyl sulfoxide sol­ution under aerobic conditions was investigated in the present study. The inter­action of dipeptide–manganese system with the same semiquinone was also stu­died under the identical conditions. The metal-binding and redox chemistry of these systems were investigated using electronic, ESR, ¹H-NMR spectroscopies and cyclic voltammetry. The in situ formal semiquinone radicals (extensively studied in previous works) were significantly modified upon addition of carno­sine, as evidenced by the redistribution of the visible absorption bands and the change of the redox couples of the catecholic product. Subsequent influence of Mn ions induced further spectral and electrochemical changes, consistent with metal centered oxidation and formation of ligand-stabilized manganese spe­cies. Paramagnetic broadening in the ¹H-NMR spectra supported the presence of higher-valent Mn intermediates in solution. The combined data support a cooper­ative redox pathway in which semiquinone species mediate both peptide oxid­ation and Mn centered electron transfer. These results provide chem­ical insight into the understanding of multicomponent systems usually present in nature.