Cu2+ Complexes with the Simplest Amino Acid Glycine (Gly)

Using potentiometric titrations, UV-Vis, IR and speciation diagrams, it appeared that the simplest amino acid Glycine (Gly) is not reacting in a simple manner at all with the copper metal ion (Cu 2+ ) in aqueous solutions at 25C. The potentiometric measurements indicated that Cu 2+ released a net of two protons (2H + 's) into the solution. Free Gly released one proton (H + ) into the solution from the single ammonium group. On the other hand, when Glycine hydrochloride (Gly.HCl) was used instead of free Gly, both the carboxylate and the ammonium groups released their protons. Upon the reaction of Cu 2+ with Gly.HCl in any molar ratio, a net of four protons (4H + 's) or more were released into the solution; one H + from the carboxylic acid group, the second from the ammonium group and the additional two H + 's from the Cu 2+ -aqua ligands. The proposed solution species are in a good agreement with what has been shown in the literature.