This project will involve the application of nuclear magnetic resonance (NMR) spectroscopy to the study of metal-ion complexes of the carboxylic ionophores, lasalocid A and monensin, in aqueous solvent mixtures. The long-range objective are the quantitative evaluation of the stoichiometry and the resultant net charge of the complex; the specific binding sites in the ionophore and the geometry of the complex; the specific binding sites in the ionophore and the geometry of the complex, that is, whether the metal-ion is surrounded or binds at an outer site only; the effect of metal-ion size and coordinating propensity on the type of complex formed; and the influence of anion complexing ability. The metal-ions to be used are trivalent lanthanum, lutetium, and yttrium, all strong complexing agents varying in size, and electronic and magnetic properties. A multinuclear approach using hydrogen-1, carbon-13, nitrogen-14, chlorine- 35, yttrium-89, and lanthanum-139 NMR spectroscopy will be applied in this structural study. The experiments will involve the direct observation of separate sets of resonance signals for bound and free ionophore, a condition made possible by the dissociation of its complex and subsequent ligand exchange slow enough on the NMR time scale. The objective of the project will be attained by hydrogen-1 chemical shift, relaxation time, and signal area determinations, along with chemical shift and relaxation time experiments for the other nuclei planned for study.
