Regio- and stereoselective complexation by a self-assembled monolayer of thiolated cyclodextrin on a gold electrode

Regio- and stereoselective complexation by a self-assembled monolayer of thiolated a-cyclodextrin (CD) derivative on a gold electrode was examined by cyclic voltammetry. Hydroquinone was included in the cavity of the surface-confined CD and reversible voltammograms were observed. In the presence of one of four stereoisomers of azo compounds, o- or p-methyl red and (R)-(+)- or (S)-(-)-1-phenylethylamine conjugates (MR-PEAs), the peak currents of the reaction were reduced. From the inhibitory effect, association constants of MR-PEAs with surface-confined CD were estimated. It was concluded that the association constants for ortho-isomers were higher than those of para-isomers (regioselective) and that the R-enantiomer of ortho-isomer more preferentially associated with CD than the S-enantiomer (stereo-selective), whereas no stereoselectivity was observed for the para-isomers.