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

Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified 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 fluorescence whose intensity is decreased or enhanced upon addition of guest species. 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 parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host-guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host-guest complexes.