Interactions between metal cations and the ionophore lasalocid. Part 2.—Gibbs functions, enthalpies and entropies for complexation of alkali-metal cations by lasalocid and bromolasalocid

Abstract

The nature and stability of the complexes formed in methanol through interaction of the ionophore lasalocid, and its 5-bromo-derivative, with alkali-metal cations were studied by a potentiometric method. The involvement of the salicylate group of the ionophore in the complexation process is discussed in the light of u.v.–visible spectra and of literature data. Enthalpies and (from the Gibbs functions) entropies for anionic 1 : 1 metal–ionophore complexes were obtained from calorimetric measurements. The results are discussed in terms of competition between complexation and solvation of the ions. It is shown that the variations observed with different metal cations are a fairly regular function of the size of the cation, suggesting a progressive adaptation of the ionophore with no conspicuous selectivity for any particular cation.