Solvation properties of natural and synthetic ionophores. I. Stoichiometry of complexes with alkali and alkaline earth cations in aprotic organic solvents

Abstract

Ion-solvent interactions play a very important role in the studies of stoichiometry, structure, and stability of complexes of cations with natural and synthetic ionophores. These compounds are extremely useful in study of the interaction of neutral salts with macromolecules and the mechanism of cation transport across biological membranes. Knowledge of the ionophore solvation properties enables one to choose a suitable solvent for complexation studies and to obtain detailed information on the solvent effect. We would like to present in this paper a very simple method of estimating the solvation properties of ionophores. We treat the ligand as an assembly of individual noninteracting binding sites. The solvation properties of solvents can be used to represent the solvation sites in natural and synthetic ligands. The solvation properties are represented by the Gutmann donor number (DN) of the model solvent. We can define the solvation ability of a ligand binding site be "donor number of binding site" (DN binding site), which in turn can be represented by the DN of the appropriate model solvent. The average DN of the ligand (DN average) is defined as [xi ni-1 (DN binding site)i]/n, where n is the number of the ligand binding sites. Comparison of the DN average with the DN solvent, together with the knowledge of the composition of the system, characterizes remarkably well the solvation properties of the ligand. This model explains (a) the stoichiometry of many alkali and alkaline earth cation complexes with natural and synthetic ligands in aprotic organic solvents, (b) the transport of alkali and alkaline earth cations across lipid bilayers, and (c) how polypeptides and proteins interact with neutral salts in solutions.

Extraordinary swelling behavior of poly(AMPS) organogel in solvent/DMSO binary mixed media

“…6). The DN values are not reported for ethylene glycol and glycerol, however, DN values are expected to be higher than those of methanol and ethanol 38. If so, the solvation interaction (6) will be logically promoted to the right side resulted in easier SO 3 H dissociation and wide‐ranged overentrant behavior.…”

Kinetics and equilibria of alkaline-earth-metal complex formation with cryptands in methanol

“…In some cases an acid-catalyzed dissociation of the cryptates was observed. The overall observed rate constant is then given by eq 5, where kd is the uncatalyzed dissociation rate constant of the ke = kd + & +[ +]/ ±4 (5) cryptate and kH+ the rate constant for the acid-catalyzed pathway.…”

Coordination chemistry of lithium ion: a crystal and molecular structure review

“…13,14 In addition, complexation of a cation by a ligand is affected by the nature of the solvent24 and the anion present. [23][24][25][26] The complex which is formed in biological and artificial membranes results from the simultaneous interaction of the cation with ligand, solvent, and anion binding sites.13,14,23-26 Thus, solvent molecules and counterions in addition to ligands are regarded as containing possible binding sites in the Li+ complexes. Li+ which is already bonded to a ligand molecule might interact with additional solvent mole-cule^) and/or the counterion in order to saturate its coordination sphere.…”