NAMS 2002 Workshop - ICOM 2008

Nanostructured Membranes II – 6
Tuesday July 15, 11:30 AM-12:00 PM, Moloka’i
Fixed-Charge Group-like Behavior of the Captured Ion By Crown Ether and
Its Effect on the Response of a Molecular Recognition Ion Gating
Membrane
T. Ito (Speaker), Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama,
Japan
T. Yamaguchi, Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama,
Japan, yamag@res.titech.ac.jp
We have suggested the concept of a molecular recognition ion gating membrane,
which can open and close its pores automatically in response to the specific ion
signals such as Ba 2+ and K + , and have showed various functions of the gating
effect to control pressure-driven permeation, osmotic pressure, and diffusion.
These response behaviors of the gating membrane mainly depend on the
swelling and shrinking of the grafted poly- NIPAM(N-isopropylacrylamide)-co-
BCAm (Benzo- [18]-crown-6-acrylamide). The grafted copolymer have crown
ether moieties, which can capture specific ion species and trigger the swelling of
the grafted polymer. This swelling and shrinking of the grafted copolymer also
accompany the change of water hydration onto the copolymer. These
phenomena were thought to control the membrane responses. However, we
recently found some interesting gating behaviors, which can’t be explained by
swelling and shrinking only. For instance, the permeability change of a small
molecular weight drug in response to ion stimulations was larger than that of high
molecular weight drug. The difference between these drugs was whether the
drugs have charges or not. Second, ion concentration gradient through the gating
membrane generated osmotic pressure, even though the size of ions was small
enough and water content of the grafted copolymer was high enough. Based on
these phenomena, the captured ions by crown ether moieties behave like fixed-
charge groups, and the molecular recognition ion gating membrane has the
aspect of a charged membrane, which can change its fixed charge density in
response to the specific ion signals. We conclude that combination of hydration
effect and charge effect of the grafted copolymer can make the sophisticated
functions of the molecular recognition ion gating membrane.