Simulations of photopumping in doubly illuminated liquid membranes containing photoactive carriers

A steady-state model used to simulate photofacilitated active transport against a concentration gradient, called photopumping, is described. Central to this model is the idea that the carrier can be in either a strongly binding or a weakly binding form and light can be used to control the interconversion rate between the two forms. Most experimental and theoretical studies have focused on systems in which only one side of the membrane is illuminated at a time to form singly illuminated liquid membranes. This study explores membranes in which both the feed and the sweep side are illuminated simultaneously with light of different wavelengths to form doubly illuminated liquid membranes. Doubly illuminated liquid membranes can sustain transport against concentration gradients in which the solute concentration in the sweep is a factor of 10 or more higher than that in the feed, while transport in singly illuminated liquid membranes falls off at lower concentration gradients. In addition, carrier properties that are important in single illumination such as the interconversion rates between the weakly and the strongly binding forms of the carrier are not important for doubly illuminated membranes, meaning that the range of suitable carriers will be much greater for double illumination than for single illumination.