POTENTIOMETRIC AND SPECTROSCOPIC STUDY OF EQUILIBRIA IN THE AQUEOUS TERNARY-SYSTEM COPPERII-L-HISTIDINE-HA (HA = AMINOMETHANE-SULFONIC OR 2-AMINOBENZENE-SULFONIC ACID

Complexation in the ternary system CuII-L-histidine-HA [HA = aminometh anesulfonic acid (Hamsa) or 2-aminobenzenesulfonic acid (Habsa)] was i nvestigated in aqueous 0.15 mol dm-3 NaCl solution at 25-degrees-C by potentiometric and spectroscopic techniques. The results show, over th e pH range 4-8 and CuII-L-histidine-HA ratios of 1:2-8:4-12, the prese nce of the species [Cu(His)2], [Cu(HHis)(His)]+ and [Cu(His)A] [His = L-histidinate(1-)]. The log stability constants of the latter complexe s were 15.85 (A = amsa) and 17.01 (A = absa). Neither ternary species is present at neutral pH, however, they are significant at lower pHs; this point is discussed in relation to rheumatoid arthritis therapy.