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

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Abstract
Flexible bis-functionalized hosts, 6A-dansyl-6X-tosyl-modified β-cyclodextrins (X = B or G, C or F, and D or E for β-1, β-2, and β-3, respectively) and γ-cyclodextrins (X = B or H, C or G, D or F, and E for γ-1, γ-2, γ-3, and γ-4, respectively) have been synthesized to investigate their chemo-sensor potential for organic compounds such as bile acids and terpenoids. These host compounds show pure monomer fluorescence, the β-analogs showing a decrease in fluorescence intensity on accommodation of all the guests examined. On the other hand, γ-analogs exhibit a decrease in intensity on complexation of bile acids and smaller guests such as bicyclic molecules, but an increase in intensity for much smaller guests such as monocyclic and non-cyclic molecules. The extent of fluorescence variation with a guest is employed to display the sensing ability of the hosts. The sensing parameter (ΔI/I0) was used to describe the sensing ability of the hosts. Host β-analogs can detect chenodeoxycholic acid, ursodeoxycholic acid, and (−)-borneol with high sensitivity. The sequence of binding ability of these hosts is β-1 > β-2 > β-3 for bile acids, and β-2 > β-1 ≥ β-3 for terpenoids. On the other hand, γ-analogs can detect lithocholic acid, chenodeoxycholic acid, ursodeoxycholic acid, and (−)-borneol with high sensitivity. The sensing parameters of β-analogs are up to almost two times larger for ursodeoxycholic acid and three times for (−)-borneol in comparison with those of γ-analogs. The behavior of the appended moieties of the hosts during host–guest complexation is studied by induced circular dichroism (ICD), fluorescence, and 1H NMR spectra. Host β- and γ-analogs show similar ICD spectral patterns. Host γ-analogs exhibit 1H NMR spectral changes after addition of ursodeoxycholic acid, whereas β-analogs indicate no change. The guest-induced variations in ICD, fluorescence, and 1H NMR spectra suggest that the dansyl and tosyl groups change their mutual relationship.

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