Interactions between metal cations and the ionophore lasalocid. Part 4.—ΔH⊖ and ΔS⊖ for formation of 1–1 and 2–1 complexes of the lasalocid anion and salicylate with alkaline-earth metal cations in methanol
Abstract
Enthalpies of formation of 1–1 and 2–1 complexes of the lasalocid anion and salicylate with alkaline-earth metal cations in methanol have been obtained from calorimetric measurements. The corresponding entropies were obtained from previously determined stability constants. Involvement in the complexation of the salicylate part of the lasalocid anion was thereby assessed. For 1–1 complexes, the results point to a transition from an extended conformation for the lasalocid anion in the magnesium complex to a folded one in the barium complex. For 2–1 complexes bonding of the second lasalocid anion may not be solely due to the salicylate moiety. Finally, the ionophoric power of lasalocid with respect to alkaline-earth metal cations is discussed.