The synthesis of a fluorescent chemo-sensor system based on regioselectively dansyl-tosyl-modified beta- and gamma-cyclodextrins

Flexible bis-functionalized hosts, 6(A)-dansyl-6(X)-tosyl-modified beta-cyc lodextrins (X=B or G, C or F, and D or E for beta-1, beta-2, and beta-3, re spectively) and gamma-cyclodextrins (X=B or H, C or G, D or F, and E for ga mma-1, gamma-2, gamma-3, and gamma-4, respectively) have been synthesized t o investigate their chemo-sensor potential for organic compounds such as bi le acids and terpenoids. These host compounds show pure monomer fluorescenc e, the beta-analogs showing a decrease in fluorescence intensity on accommo dation of all the guests examined. On the other hand, gamma-analogs exhibit a decrease in intensity on complexation of bile acids and smaller guests s uch as bicyclic molecules, but an increase in intensity for much smaller gu ests such as monocyclic and non-cyclic molecules. The extent of fluorescenc e variation with a guest is employed to display the sensing ability of the hosts. The sensing parameter (Delta I/I-0) was used to describe the sensing ability of the hosts. Host beta-analogs can detect chenodeoxycholic acid, ursodeoxycholic acid, and (-)-borneol with high sensitivity. The sequence o f binding ability of these hosts is beta-1 >beta-2 >beta-3 for bile acids, and beta-2 >beta-1 greater than or equal to beta-3 for terpenoids. On the o ther hand, gamma-analogs can detect lithocholic acid, chenodeoxycholic acid , ursodeoxycholic acid, and (-)-borneol with high sensitivity. The sensing parameters of beta-analogs are up to almost two times larger for ursodeoxyc holic acid and three times for (-)-borneol in comparison with those of gamm a-analogs. The behavior of the appended moieties of the hosts during host-g uest complexation is studied by induced circular dichroism (ICD), fluoresce nce, and H-1 NMR spectra. Host beta- and gamma-analogs show similar ICD spe ctral patterns. Host gamma-analogs exhibit H-1 NMR spectral changes after a ddition of ursodeoxycholic acid, whereas beta-analogs indicate no change. T he guest-induced variations in ICD, fluorescence, and H-1 NMR spectra sugge st that the dansyl and tosyl groups change their mutual relationship.