CHEMICAL RELEVANCE OF THE COPPER(II) L-CARNOSINE SYSTEM IN AQUEOUS-SOLUTION - A THERMODYNAMIC AND SPECTROPHOTOMETRIC STUDY

The copper(II)-L-carnosine (L-) system has been re-investigated in aqueous solution, at I = 0.1 mol dm-3, different temperatures (5 less-than-or-equal-to t less-than-or-equal-to 45-degrees-C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH]2+, [CuL]+, [CuLH-1]-degrees, [Cu2L2H-2]-degrees and [Cu2LH-1]2+ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of DELTAH-degrees and good estimates of DELTAC(p)-degrees. From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.