Thermodynamics of complexation of monensin A and monensin B in methanol by titration calorimetry

Abstract

In the first reported study of the complexation behaviour of monensin B, careful titration calorimetry experiments show the following: (i) monesin B tetrabutylammonium salt (MonB^–Bu₄N⁺) is a weaker binder than monensin A anion (MonA^–Bu₄N⁺) of both Na⁺ and K⁺ in methanol; (ii) the Na⁺/K⁺ selectivity exhibited by MonB^– is diminished relative to MonA^–; and (iii) the observed differences are chiefly due to differences in entropic contributions to the binding free energy.