Interaction of p-hydroxybenzoic esters with beta-cyclodextrin

Abstract

In the present investigation, the complex formation of beta-cyclodextrin (βCD) with p-hydroxybenzoic esters (parabens) was studied by mixing βCD with methyl, ethyl, propyl and butyl parabens, respectively, in aqueous solutions and subjecting the resultant mixtures individually to the following processes: occasional shaking for 24 h at 25°C, continuous shaking using shaker bath for 24 h at 25°C, intermittent ultrasonification for 90 min at 25°C, autoclaving at 115°C for 30 min and freeze-drying followed by reconstitution with distilled water. The degrees of interaction between βCD and the parabens subjected to the various processes were evaluated, using the membrane dialysis method. The difference in the method of processing did not affect the degree of interaction significantly. However, the degree of interaction was found to increase proportionally with the concentration of βCD. The alkyl group of the parabens was also found to affect the extent of interaction. Compared to methyl paraben, the degree of interaction of ethyl paraben was observed to be lower. Interestingly, further increase in the size of the alkyl group significantly enhanced the extent of interaction. Studies using 1H-NMR showed that the extent of interaction depended on how well the parabens could fit into the βCD cavity. (C) 2000 Elsevier Science B.V.