Fluorescence detection of the electrostatic interactions in the molecular recognition between protonated amino-cyclodextrins and some anilinonaphthalenesulfonate anions

Abstract

Strong fluorescence enhancements have been observed when some anilinonaphthalenesulfonate anions formed inclusion complexes with protonated amino-cyclodextrins in aqueous solution. The role of electrostatic interactions between anilinonaphthalenesulfonate anions and chemically modified β-cyclodextrin such as mono(6-aminoethylamino-6-deoxy)-β-cyclodextrin and mono(6-N,N dibutylaminoethylamino-6-deoxy)-β-cyclodextrin was clarified by fluorescence spectroscopy. Modified β-cyclodextrins could become positively charged by the protonation of their amino group in some pH regions. Stability constants of the formed inclusion complexes were found to be increased by electrostatic interactions and in some cases the extension of the hydrophobic environment at the periphery of the inclusion site. The possible structure of the inclusion complexes was also discussed in detail.