Spectroscopic and thermoanalytical studies on bincichoninic acid and its copper (I) complexes

Abstract: Bicinchoninic acid (H(2)BCA H(2)L) has been characterized in aqueous solution, by UV spectrophotometry, to establish the presence of the various protonated forms and in the solid state, by thermoanalytical techniques, to determine the behaviour of its thermal decomposition. The reaction in aqueous solution of H(2)BCA with cupric ions in the presence of some reducing agents [ascorbic acid, hydroxylamine hydrochloride, hydrazine sulphate] was studied varying time, temperature, pH, metal/ligand and metal/reducing agent mole ratio. At pH greater than or equal to 7, with an excess of reducing agent compared to the metal ion concentration, if C-L/C-M > 5, copper(II) is wholly reduced to copper(I) which forms [CuL(2)](3-) chelate complex. This complex, precipitated as [CuH(3)L(2)], was characterized by spectroscopic and thermoanalytical techniques. The reducing agent concentration can be determined, indirectly, if an excess of copper(II), compared to the reducing agent, is used and if the stoichiometry of the redox reaction is known. At last, when C-L/C-M less than or equal to 2, the reaction is not quantitative and the colour of the solution is not stable.