pH‐controlled uphill transport of ammonium ions through polymer membranes with sulfonic acid groups

Abstract

Uphill transport of ammonium ions through a membrane with sulfonic acid groups were investigated with pH-controllers which keep the solution at a constant pH. A membrane with sulfonic acid groups was prepared by casting an aqueous solution containing poly(styrenesu1fonic acid) and poly(viny1 alcohol) on a glass plate. When a membrane with one side alkaline and the other acidic was fixed as a diaphragm in a cell, ammonium ions were transported from the alkaline side to the acidic side through the membrane against the concentration gradient of the adjacent solutions. Uphill transport of ammonium ions with pHcontrollers was more efficient than without, thus keeping the pH difference between both sides of the membrane constant, which is a driving force for the uphill transport. Furthermore, the effect of pH of the acidic side on the uphill transport was investigated and the mechanism of the pHcontrolled uphill transport is discussed.

pH and Ionic Strength Effects on Amino Acid Transport through Au-Nanotubule Membranes Charged with Self-Assembled Monolayers

“…In any case, the experimental results show that the electrostatic interaction between the amino acid and the nanopore charges significantly influence the transport through the hydrophilic nanopores. The key role of the membrane-charge density has been emphasized previously for the case of uphill transport of ions through ion-exchange membranes (see also refs and ). Also, the pH and ionic strength effects have recently been found to dominate protein transport in the same charged nanopores employed here …”

“…There is clear experimental evidence that electrical charge effects play a key role in the amino acid transport through hydrophilic charged pores. ,− ,− In particular, these effects are theoretically predicted to be crucial for amino acid transport at a zero concentration gradient and against its external concentration difference (uphill transport 33 ). This transport should occur for certain combinations of the pH and salt concentration in the external solutions and has previously been studied for small ions in fixed-charge membranes. , Uphill transport is also typical of biological membranes because of the coupling of the flux of the species being transported to other processes (e.g., hydrogen transport due to a pH gradient). We report here preliminary experimental data showing nonzero values of the flux at zero amino acid concentration difference when a pH difference is imposed in the external solutions.…”

“…This transport should occur for certain combinations of the pH and salt concentration in the external solutions and has previously been studied for small ions in fixed-charge membranes. 38,39 Uphill transport is also typical of biological membranes because of the coupling of the flux of the species being transported to other processes (e.g., hydrogen transport due to a pH gradient). We report here preliminary experimental data showing nonzero values of the flux at zero amino acid concentration difference when a pH difference is imposed in the external solutions.…”