A Modified Cyclodextrin with a Fully Encapsulated Dansyl Group: Self‐Inclusion in the Solid State and in Solution

Abstract

A monofunctionalized p-cyclodextrin containing a dansyl moiety, 6-cyclodextrin (CD-en-DNS, 2), was synthesized and its crystal structure determined. It was shown that the dansyl group is fully encapsulated within the cyclodextrin cavity, with the dimethylamino and sulfonyl groups emerging from opposite sides. The shape of the cavity is considerably flattened, since O(4)-0(4) distances parallel to the naphthalene ring were found to be longer than the others. The conformation of the diaminoethane linker was found to be determined by the inclusion of the dansyl group and by a hydrogen bond between the sulfonamide NH and one of the O(6)-H groups on the cyclodextrin rim. The self-inclusion features of the aromatic moiety were found to be consistent with the solution data: 'H NMR ROESY spectra suggested that the orientation of the dansyl moiety observed in the solid state was retained in aqueous solution; the circular dichroism spectrum was consistent with an axial complexation model. Fluorescence spectra showed that the inclusion of the dansyl group in the cyclodextrin cavity considerably increases the quantum yield; time-resolved fluorescence experiments showed the presence of a long-lifetime component (16.1 ns), which was attributed to the included fluorophore. The ability of 2 to act as a fluorescence sensor was evaluated by the addition of several guests of different shape: fluorescence intensity was lowered, especially upon addition of adamantanecarboxylic acid. All the data obtained were consistent with the model of the inout movement of the dansyl group from the self-included conformation observed in the solid state to a position more exposed to the bulk solvent. Copper(I1) was shown to enhance the difference in the fluorescence of 2 in the presence of guests by additional static quenching.

Cyclodextrins as templates for the presentation of protease inhibitors

“…In recent years extensive investigations have been performed by NMR and X-ray analysis on methylated and unmethylated 13-cyclodextrin monosubstituted at the C6 of the cyclomaltoheptaose with aromatic chromophores [6], amino acids, related derivatives and dipeptides [7][8][9][10]. Self-inclusion of the grafted moieties was found to depend critically upon *Corresponding author.…”

Design and synthesis of fluorescent ?-cyclodextrins for the enantioselective sensing of ?-amino acids

“…27,28 In the last few years we have developed a model of fluorescent sensors based on modified ␤-cyclodextrins containing a binding site for copper(II) and a dansyl fluorophore. 29,30 Similar systems were also designed for enantiomeric recognition of unmodified amino acids. The design is described in Figure 1 and takes into account the following elements: 1) a cyclodextrin as a rigid scaffold; 2) a Cu(II) coordinating side arm similar to those used as selectors in ligand exchange chromatography [31][32][33][34][35] ; 3) a dansyl group as fluorophore, able to interact with both the cyclodextrin cavity and the Cu(II) ion; 4) an additional chiral center in the side arm, which could enhance enantioselectivity.…”

Synthesis of novel dansyl appended cyclodextrins. Self-inclusion and sensor properties

“…Soc., Perkin Trans. 2,1997 600-500-400-2 300- Desilylation of the protected intermediates 15, 13 and 23 by tetrabutylammonium fluoride (TBAF) in refluxingTHF finally yielded the desired products 4, 5 and 6 in 63, 76 and 79% yields, respectively. The compounds were purified by dissolving them in a small volume of ethanol-water (2 : 1, v/v) followed by pre cipitation with ethyl acetate.…”