Qualitative Determination of Bile Acids by Fluorescence Responses of Disubstituted γ-Cyclodextrins Having 2-(1-Naphthyl) propanoyl Residues

Eight γ-cyclodextrin (γ-CyD) derivatives having two optically active (R)-or (S)-2-(1-naphthyl) propanoyl residues at the primary hydroxyl sides, which are 6A,6B-, 6A,6C-, 6A,6D-, and 6A, 6Epositions (RR-AB, RR-AC, RR-AD, RR-AE, SS-AB, SS-AC, SS-AD, and SS-AE, respectively), were synthesized for investigating their fluorescence responses towards bile acids in a 10 vol.% ethylene glycol aqueous solutions. Strong intramolecular excimer fluorescence observed for RR-AD, RR-AE, SS-AD, and SS-AE is varied either strengthened or weakened direction based on the guest species. Although RR-AB, RR-AC, SS-AB, and SS-AC showed weak or no excimer fluorescence, some bile acids changed the monomer fluorescence intensity decreased, with excimer fluorescence being induced. By taking the fluorescence intensity changes as a sensitivity factor for detecting the guests, together with the shift in peak positions of the excimer fluorescence, one may qualitatively determine the type of bile acids in a solution at 50 mmol dm-3. No simple correlation is observed between the 1: 1 host-guest binding constants and the sensing factors, which indicated that not only the binding strength but also the binding conformation governed the sensitivity and selectivity of the hosts.