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.