Fluorescent molecular recognition and sensing system of bis-dansyl modified gamma-cyclodextrins

Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modifie d gamma-cyclodextrins (gamma-1, gamma-2, gamma-3, and gamma-4, respectively ) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluores cence whose intensity is decreased or enhanced upon addition of guest speci es. The value Delta I/I-0, where I and I-0 are fluorescence intensities in the presence and absence of a guest and Delta I is I-0 - I, was used as a p arameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeo xycholic acid, and ursodeoxycholic acid. The behaviors of the appended moie ties of these hosts when host-guest complexation occurs are studied by indu ced circular dichroism (ICD) spectra and fluorescence spectral change on ac commodation of a guest. The ICD pattern of these hosts alone or on accommod ation of a guest is very similar, indicating that the behavior of the appen ded moieties are very similar. The guest-induced variations in the fluoresc ence or ICD intensity suggest that the appended moieties act as a hydrophob ic cap that enables the cyclodextrin to form 1 : 1 host-guest complexes.