イオン認識ゲート膜の開発 Development of an a Molecular Recognition Ion Gating Membrane
Biomembranes, typified by an ion channel such as a K<sup>+</sup> channel, can recognize a specific ion, and can control the transport of recognized ions by themselves. Inspired by the functions of biomembranes, we have fabricated a molecular recognition ion gating membrane. The membrane was prepared by plasma graft copolymerization, which filled the pores of porous polyethylene film with a copolymer of NIPAM (N-isopropylacrylamide) and BCAm (benzocrown-6-acrylamide). NIPAM is well known to have an LCST (lower critical solution temperature), at which its volume changes dramatically in water. The crown receptor of the BCAm traps a specific ion, and causes a shift in the LCST. Therefore, selectively responding to either K<sup>+</sup> or Ba<sup>2+</sup>, the grafted copolymer swelled and shrank in the pores at a constant temperature between two LCSTs. <br>We have been studying the interesting functions of the membrane. The membrane changed its permeation flux in response to the ion signals. The solution flux in the absence of Ba<sup>2+</sup> decreased by about two orders of magnitude over a solution flux containing Ba<sup>2+</sup>. Osmotic pressure through the membrane was changed in response to the ion signals. The membrane controlled the diffusion of model drugs in response to the ion signals. Due to its stability, the membrane also showed responding function in the mixture of ethanol and water. As typified by Hodgkin-Huxley equation, excitation of neuron synapses is an interesting phenomenon of biomembranes. Three ion channels work cooperatively and make dynamics of membrane potential. Theorell made the oscillator of the artificial glass membrane, hinted by neurons. Inspired by Theorell oscillator, we combined hydrodynamic pressure-driven permeation and osmotic permeation through the membrane. We finally found that the membrane showed autonomous oscillation in response to Ba<sup>2+</sup> only.
膜 37(3), 140-145, 2012-05-01