The binding and catalytic properties of a positively charged cyclodextrin

Abstract

In order to learn the significance of electrostatic interactions between charged groups in an enzymatic process, a positively charged cyclodextrin, mono-(6-trimethylammonio-6-deoxy)-β-cyclodextrin hydrogencarbonate (βCDtma), was prepared as a simple enzyme model, and its binding and catalytic properties were examined. The dissociation constant for an inclusion complex of βCDtma with an azo dye, sodium 4-(4-hydroxy-1-naphthylazo)-1-naphthalenesulfonate (1), was found to be 5.4 × 10-5 mol/dm3 in an alkaline solution (pH 10.5, Ic = 0.0 mol/dm3) at 25 °C, the value being smaller than that for an inclusion complex of the parent β-cyclodextrin (βCD) with 1 by a factor of ca. 4. The catalytic effect of βCDtma on the alkaline hydrolyses of o-, m-, and p-acetoxybenzoic acids was significantly different from that of βCD. These observations were explained in terms of electrostatic and hydrophobic interactions between βCDtma and a guest molecule.