VOLTAMMETRIC STUDY ON A CONDENSED MONOLAYER OF A LONG ALKYL CYCLODEXTRIN DERIVATIVE AS A CHANNEL MIMETIC SENSING MEMBRANE

For a fundamental study on the development of signal-amplifying chemical sensors that mimic biological ion channels, a control of membrane permeability based on the blocking of an intramolecular channel by host-guest complexation has been Investigated for a condensed monolayer of a long alkyl derivative of beta-cyclodextrin having a channel-like structure (6A,6B,6C,6D,6E,6F,6G-heptadeoxy-6A,6B,6C,6D,6E,6F,6G-heptakis(dodecylthio)-beta-cyclodextrin tetradecaacetate). To obtain experimental evidence for such a mode of permeability control, an approach based on horizontal touch cyclic voltammetry was carried out for this condensed monolayer, which was formed at the air/water interface by applying a controlled high surface pressure to minimize the permeability through the intermolecular voids between the membranous cyclodextrin molecules. By comparing the permeabilities for three kinds of electroactive markers that differ in the steric bulkiness and/or hydrophobicity, rigid evidence was obtained for the ability of this cyclodextrin derivative to function as an intramolecular channel. The permeability of this channel for a sterically permeable marker (p-quinone) was shown to be able to be controlled by blocking the channel with a guest molecule. By using this condensed monolayer, the selectivity of permeability inhibition was examined for several organic guests. The molecular response ratio as a measure of signal transduction efficiency was up to 10.4.