Potentiometric and spectroscopic study of equilibria in the aqueous ternary system copperII–L-histidine–HA (HA = aminomethane- or 2-aminobenzene-sulfonic acid)

Abstract

Complexation in the ternary system Cu^II–L-histidine–HA [HA = aminomethanesulfonic acid (Hamsa) or 2-aminobenzenesulfonic acid (Habsa)] was investigated in aqueous 0.15 mol dm^–3 NaCl solution at 25 °C by potentiometric and spectroscopic techniques. The results show, over the pH range 4–8 and Cu^II-L–histidine–HA ratios of 1:2–8:4–12, the presence of the species [Cu(His)₂], [Cu(HHis)(His)]⁺ and [Cu(His)A][His =L-histidinate(1–)]. The log stability constants of the latter complexes 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.