Quantitating the Effect of Solvent Type on Neutral Macrocycle‐Mediated Cation Transport in Liquid Membranes

Abstract

AbstractThe recently confirmed diffusion‐limited transport model for neutral macrocyle‐mediated cation transport in membranes has been used to quantify the membrane solvent effects on the fundamental parameters in the model and their relative importance. The fundamental parameters involved are the extraction equilibrium constant, macrocycle partition coefficient, and diffusion coefficient. Experimental measurements and predictive correlation calculations have been made to quantify these fundamental parameters. Membrane stability has also been quantified by looking at solvent solubilities and solvent compatibility with various membrane types. It was found that membrane stability vs. rapid transport is the major choice to be made in choosing a membrane solvent. Retention of the macrocycle in the membrane and diffusion coefficients are greatest with short carbon chain solvents containing few chlorine atoms. On the other hand, high boiling points and low water solubility are obtained with long carbon chain solvents containing increasing numbers of chlorine atoms. Extraction equilibrium constants also decrease with increasing carbon chain lengths and increasing chlorination, but the decrease is not uniform like the changes in the other parameters. Little effect of solvent type on membrane selectivity was observed. The transport model and quantification of these fundamental parameters should allow for accurate predictions in the choice of solvent in designing stable membranes with optimal transport properties.