Interactions between metal cations and the ionophore lasalocid. Part 5.—A potentiometric, polarographic and electron spin resonance study of copper(II)–lasalocid equilibria in methanol

The complexation of Cu2+ by lasalocid and the model compound salicylic acid, AH, has been studied in methanol. The stability constants of species ACu+ and A2Cu were obtained from potentiometric measurements using a pH glass electrode and a copper-selective electrode, and by polarographic determinations. The stability of these copper(II) complexes was shown to be higher than that of the analogous complexes of the other transition-metal cations of the first row and very similar for lasalocid and salicylic acid. The e.s.r. spectra suggest that the structures of the species formed with the two ligands differ; the oxygen of the backbone probably participates in complexation with lasalocid. In addition, other complexes possibly involving the methoxide ion, formed in more basic media, were characterised.