Interactions between metal cations and the ionophore lasalocid. Part 9. Structural study of the free acid, anion and potassium complex salt in chloroform and methanol, using 13C and 1H nuclear magnetic resonance spectroscopy

From two-dimensional NMR experiments, complete and unequivocal assignment of the proton and carbon resonance shifts is independently obtained for the free acid, anion, and potassium salt of lasalocid in both chloroform and methanol. Variation of the 1H and 13C chemical shifts of the anion and the potassium salt in chloroform as a function of their concentration afforded both their dimerization constants and the NMR parameters specific to both monomers and dimers. From the present results, mainly 1H and 13C chemical shifts and 1H–1H coupling constants, and other data involving various methods, the state and structure of the various species formed in the two solvents (conformation of lasalocid, co-ordination sites of the cation, solvation, etc.) are discussed. The high flexibility and adaptability of lasalocid is stressed.