THERMODYNAMICS OF REACTION IN HETEROGENEOUS SYSTEMS (WATER ORGANIC PHASES) BETWEEN THE IONOPHORE MONENSIN AND ALKALI-METAL CATIONS

Gibbs functions, enthalpies, entropies, and volumes of reaction for the reaction of the bacterial ionophore monensin with alkali-metal cations in various water-organic biphasic solvent systems are obtained by using various experimental methods. In addition, weak but perceptible solubilization of the complexes formed is shown to occur in the aqueous phase. Their dissociation in water is studied. All the data are discussed in terms of structure and solvation of the various species. The selectivity sequence is not solvent dependent though the enthalpic and entropic contributions for different cations vary with the solvent system involved. On the basis of these data, both biological functional aspects and analytical aspects relevant to the testing of such ionophores are discussed.