Permeability characteristic of polyelectrolyte complex capsule membranes: Effect of preparation condition on permeability

Because polyelectrolyte complex formation is known to depend on charge densities of polyelectrolytes, influence of pH condition in the preparation of the polyelectrolyte complex capsules on their permeability characteristic for phenylethylene glycol was examined. Partly crosslinked polyelectrolyte complex capsules were prepared by addition of an aqueous poly(acrylic acid) solution into an aqueous poly(ethylenimine) or L-histidine attached poly(ethylenimine) (ethylenimine unit/L-histidine residue: 5/1, mol/mol) solution and subsequent crosslinking under various pH conditions. Although poly(acrylic acid) and poly(ethylenimine) change their charge density depending on pH in an aqueous solution, the resultant capsules prepared at pHs 7, 6, and 5 show similar permeation properties under neutral and acidic conditions. By contrast, when L-histidine-attached poly(ethylenimine) was used instead of the unmodified polymer as the capsule membrane component, the resultant capsules prepared at pHs 8, 7, and 6 revealed remarkable difference in the permeability under neutral and acidic conditions. Because the ionization of an imidazolyl group, whose pKa is 6, on the L-histidine-attached poly(ethylenimine) is influenced significantly by pH near its pKa, such situation might affect density of networks formed by the ionic bonds in the polyelectrolyte complex membrane and resulted in the permeability difference. © 1996 John Wiley & Sons, Inc.