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

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⁺, Ca²⁺, and Ba²⁺ 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 Ba²⁺ > 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.