THERMODYNAMICS OF COMPLEXATION OF MONOVALENT METAL-CATIONS BY THE IONOPHORE MONENSIN FREE ACID IN ACETONITRILE

The standard Gibbs functions, enthalpies, and entropies for the format ion of the complexes of monensin acid with monovalent metal cations in acetonitrile were obtained using various methods (conductometry, pote ntiometry, and calorimetry). Complexation is appreciable (from 2.0 to 4.5 in terms of association constant logarithm) and controlled mainly by the enthalpic effect. Comparison with formation of the correspondin g neutral complexes permits a comparison to the process of monensin me diated transport of cation in membranes. A two-step process involving first the formation of the acidic complex is suggested.