The reactivity of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine towards copper(II) ions

The acid–base properties of the N-substituted amino acid HL HL = N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine] and its reactivity towards the Cu^II ion have been measured by potentiometric and spectrophotometric techniques in aqueous solution at 25 °C and 0.1 M KCl ionic strength. These studies show that the neutral HL compound is present in aqueous solution (3–7 pH range) in the zwitterionic form with the diprotonated imidazolic residue. Studies of HL/Cu^II mixtures reveal the existence of complex species with the neutral ligand, HL and containing the deprotonated L ligand. By controlling the reaction conditions, four solid phases of stoichiometry: CuLCl(H₂O)₆, Cu₂LCl₃(H₂O)₈, CuL₂(H₂O)₆ and Cu(HL)₂Cl₂(H₂O)₆ were isolated and characterised by i.r. and electronic spectroscopy, thermal techniques and magnetic measurements.