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

• Study on models of neutral cations and anions of carnosine at the B3LYP/TZVP level.
• The 1O2-adducts of these models resulted in oxygenated carnosine.
• Theoretical parameters correlated to experimental results for carn and carn-H2O2.
• Theoretical models of Nickel-carn complexes have been investigated.
• Isolation and characterization of the solid [Ni(carn)2(H2O)5] have been performed.

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 1O2, may lead to oxygenated species. The theoretical spectroscopic parameters have been correlated to our experimental results. The effect of H2O2 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(H2O)5], the COO, Nπ and/or NH2 were bonded. When H2O2 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.

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