Theoretical and experimental investigation of carnosine and its oxygenated adducts. The reaction with the nickel ion

Abstract DFT theoretical calculations at B3LYP/TZVP or LANL2DZ level of theory, for neutral, zwitterions, protonated and anionic carnosine, were performed. Energies, the structural and spectroscopic parameters were calculated in the gas phase and aqueous medium. Additional H-bonds stabilize the ionized forms of carnosine, creating “nests” into which metal ions or bio-molecules may be sheltered. Based on Fukui functions, the reactivity of the abovementioned forms of carnosine, with 1 O 2 , may lead to oxygenated species. The theoretical spectroscopic parameters have been correlated to our experimental results. The effect of H 2 O 2 and the electrochemistry of aqueous carnosine solutions were examined. Theoretical models containing Ni(II), carnosine and water were constructed. In the isolated mauve solid, formulated [Ni(carn) 2 (H 2 O) 5 ], the COO , N π and/or NH 2 were bonded. When H 2 O 2 was added, the imidazole NMR signals disappeared. A redox couple clearly indicates one electron process, the electron coming from either the oxidation of imidazole ring or the nickel(II)/Ni(III) couple.