CHIRAL MOLECULAR RECOGNITION IN POLYMER LANGMUIR-BLODGETT-FILMS CONTAINING AXIALLY CHIRAL BINAPHTHYL GROUPS

Axially chiral binaphthalene chromophores (BN) can be incorporated into polymer Langmuir-Blodgett (LB) films as comonomers of N-alkylacrylamides which have an excellent ability to form stable monolayers and LB multilayers. The spreading behavior of the copolymers of (S)-2-methoxy-1,1'-binaphthalen-2'-yl methacrylate ((S)-MeBN) or (S)-2-hydroxy-1,1'-binaphthalen-2'-yl methacrylate ((S)-HOBM) with N-decyl- (DA), dodecyl- (DDA), or tetradecylacrylamide (TDA) was investigated by a measurement of the surface pressure-area isotherms. The isotherms show that the copolymers, especially DDA copolymers, form a stable condensed monolayer on pure water and the axially chiral binaphthalene chromophore is dispersed uniformly, having its own surface area on water when the mole fraction of BN is less than ca. 20 mol %. The copolymer monolayers could be transferred onto solid supports successively by the Langmuir-Blodgett technique (Y-type deposition). The strong CD (circular dichroism) spectra consisting of positive first and negative second Cotton effects were observed for the LB films, supporting the (S)-configuration of the chiral binaphthyl chromophore. The enantioselective response of the chiral copolymer LB films to optically active 1-phenylethylamine (PEA) was investigated by an electrochemical potentiometric method. The electrodes modified with the copolymer monolayers induced a very sensitive potential change on addition of PEA. The electrode with (S)-HOBN copolymer monolayers showed a large chiral discrimination to distinguish between (R)- and (S)-PEA, whereas the (S)-MeBN copolymers showed no discrimination. The mechanism for the chiral molecular recognition is discussed.