STRUCTURE OF THE IONOPHORE LASALOCID TETRAMETHYLAMMONIUM SALT IN THE GASEOUS STATE AND IN AQUEOUS-SOLUTION - A COMPUTATIONAL STUDY OF THE MONOMERIC SPECIES

A sampling of the conformational space of the lasalocid tetramethylamm onium salt combined with molecular dynamics simulation and AM1 semiemp irical quantum calculations show that in vacuo this salt exists as ion pairs in which the most energetically favored conformations of the la salocid anion are the closed conformations. In aqueous solutions, two molecular dynamics simulations differing in their initial conformation s and simulation times, as well as Monte-Carlo statistical mechanics s imulations, show that the lasalocid anion has a high flexibility and t hat the equilibrium conformations are unfolded in such a way that all of the anion oxygens are readily accessible to water molecules.