An active transport mimetic system based on thioctic acid as carrier for alkaline earth metal ions

Abstract

Liquid membranes incorporating thioctic acid as a carrier to mimic an active transport system for alkaline earth metals has been described. A transport cell, operating on the same principle as the Schulman Bridge was used. It has been demonstrated that such a system is capable of transporting alkaline earth metals against a proton gradient, as driving force. The potential of thioctic acid to complex and transport these metal ions particularly Mg2+, Ca 2+, and Ba 2+ was verified. Furthermore, this transport phenomenon was extended to some different barium salts (Cl-, Br-, NO3-, and SCN-) to determine the effect of nature of anion on the transport of the Ba2+ions. The order of the transport rate was found to be Ba 2+> Ca2+> Mg2+ which is inconsistent with the stability of coordination to the carboxyl group. The rate of transport of Ba2+ ions were found to decrease with the anion type in the order SCN-> Br-> NO3-> Cl-which is related to the extent of hydration of the anions