Biomimetic Membranes without Proteins but with Aqueous Nanochannels and Facilitated Transport. Minireview

Imitation of biological membranes and aqueous channels attracts more and more attention. In this review, we mention both the early and very recent papers in this area. Still, we concentrate our attention on less known biomimetic membranes, which are commercial nitrocellulose ultrafilters, impregnated by esters of fatty acids. Pores in filters are filled with lipid-like oils, but aqueous nanochannels are spontaneously formed on the inner pore surfaces with carboxylic groups fixed on nitrocellulose. This combination imitates the most fundamental barrier properties of biological membranes, including specific (per unit thickness) permeability of respiratory gases, transport of nonelectrolytes, water, and ions, cation/anion selectivity, electric impedance, etc. The activation energy for water transport in nanochannels is similar to that in aquaporin. In the presence of fatty acids and other carriers, it is possible to observe facilitated and coupled active counter transport of different metal cations in exchange to H(+) and without any transmembrane pressure, voltage or ATP. When quinones are dissolved in oils, light-sensitive co-transport of electrons and H(+) through oil is possible. In this case, redox-active substances are separated by the membrane. They are not mixed, but they still react. Small biomimetic membranes can be used as electrochemical drug sensors in drug detection and screening, medium size membranes—for smart transdermal drug -delivery, and large membranes—for industrial separation and purification. For example, after small modifications, they can be used for metal recovery, including radioactive strontium removal from nuclear waste accumulated and stored since the Cold War.