Vibrational study on the cobalt binding mode of carnosine

The Co(II)-L-Carnosine (Carnos) system was investigated at different pH and metal/ligand molar ratios by Raman and IR spectroscopy. Raman spectra present some marker bands yielding information on the ability of the Co(II)/Carnos system to bind molecular oxygen and to identify the metal co-ordination site of the imidazole ring (Np or Nt atom) of Carnos. The existence of different oxygenated species is greatly affected by pH and the structure of the predominant complexes depends on the available nitrogen atoms. Under basic conditions, binuclear complexes binding molecular oxygen are the predominant species and two forms (monobridged and dibridged) were identified by the Raman nO-O band (750-850 cm21). Decreasing pH to 7, the species present in the system are less able to bind oxygen. Hydrogen peroxide and a Co(III) chelate not binding O2, were formed with a significant conversion of peroxo into superoxo complexes. A slight excess of Carnos does not enhance metal chelation. In slightly acidic conditions,