Study on molecular recognition of para-aminobenzoic acid species by α-, β- and hydroxypropyl-β-cyclodextrin

The molecular recognition interaction of alpha-cyclodextrin, beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin by para-aminobenzoic acid (PABA) species was studied by using steady-state fluorescence measurements. PABA can exist as one of three species (an anionic, neutral on cationic species) due to its amphoteric property. The various factors affecting the inclusion process were examined in detail. The type of species depended on the pH value in the medium. The results suggested that cyclodextrins (CDs) were most suitable for inclusion of the uncharged species of PABA and could cause enhanced fluorescence emission of PABA. A mechanism is proposed to explain the inclusion process. (C) 2002 Elsevier Science B.V. All rights reserved.