Interaction of p-hydroxybenzoic esters with beta-cyclodextrin

In the present investigation, the complex formation of beta-cyclodextrin (b eta CD) with p-hydroxybenzoic esters parabens) was studied by mixing beta C D with methyl, ethyl, propyl and butyl parabens, respectively, in aqueous s olutions and subjecting the resultant mixtures individually to the followin g processes: occasional shaking for 24 h at 25 degrees C, continuous shakin g using shaker bath for 24 h at 25 degrees C, intermittent ultrasonificatio n for 90 min at 25 degrees C, autoclaving at 115 degrees C for 30 min and f reeze-drying followed by reconstitution with distilled water. The degrees o f interaction between beta CD and the parabens subjected to the various pro cesses were evaluated, using the membrane dialysis method. The difference i n the method of processing did not affect the degree of interaction signifi cantly. However, the degree of interaction was found to increase proportion ally with the concentration of beta CD. 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. Inte restingly, further increase in the size of the alkyl group significantly en hanced the extent of interaction. Studies using H-1-NMR showed that the ext ent of interaction depended on how well the parabens could fit into the bet a CD cavity. (C) 2000 Elsevier Science B.V. All rights reserved.