Interaction of copper(II) with imidazole pyridine nitrogen-containing ligands in aqueous medium: a spectroscopic...

UV (300-400 nm) and FT/IR (4000-850 cm(-1)) spectra were considered for a structural discussion of the copper(II) complexes formed with a series of imidazole-containing ligands (namely L-histidine, N-acetyl-L-histidine, histamine, L-histidine methyl ester and carnosine) in aqueous solution (T=25 degrees C, I=0.1 M). A shoulder at 330 nm was recorded for the main copper(II) complexes with all the ligands considered with the exception of carnosine: this singularity is discussed and a spectrum-structure correlation is proposed. epsilon(330) values were evaluated for CuL (59 M(-1) cm(-1)) and Cu(2)L(2)H(-2) (577 M(-1) cm(-1)) complexes with histamine and for CuL(2) (49 M(-1) cm(-1)) and CuL(3) (163 M(-1) cm(-1)) with N-acetyl-L-histidine, thus indicating the usefulness of UV spectra in the explored region for the purpose of structural definition. FT/IR spectra (recorded both in aqueous solution and on the residue of evaporated solutions of carnosine and N-acetyl-L-histidine only) help to reveal a significant conformational rearrangement of the ligand, corresponding to complex formation in solution: in fact, modifications in the fingerprint region of the FT/IR spectrum for the dimer of carnosine are observed. Indications of a copper(II)-imidazole nitrogen interaction are also obtained from FT/IR data in the 1000-1100 cm(-1) range.