Control of solute permeability based on pH‐induced reversible conformational change in block copolypeptide membrane

An ABBA‐type block copolypeptide membrane composed of L‐glutamic acid (A) and L‐leucine (B) was prepared, and a solute permeability of the membrane was studied. According to the observation of electron microscope, the membrane had the phase‐separated morphology that the domains consisting of poly(L‐glutamic acid) blocks are emebedded in a continuous matrix of the poly(L‐leucine) phase. The reversible conformational change of the poly(L‐glutamic acid) from α‐helix to random coil induced by changing the pH of the external medium was presumed to occur in the domains on the basis of the results of infrared absorption spectra. In the pH dependence of the diffusion coefficients of KCl, NaCl, and LiCl in the membrane, a considerable decrease was found at about pH 4, and thought to result from the conformational transition. In an acidic medium, the permeability of KCl, NaCl, and NiCl was higher then that of glucose, but this order was reversed in higher pHs. These results indicate that the poly(L‐glutamic acid) domains in the membrane function as channels for solute transport.