FLUORESCENT CYCLODEXTRINS FOR MOLECULE SENSING - FLUORESCENT PROPERTIES, NMR CHARACTERIZATION, AND INCLUSION PHENOMENA OF N-DANSYLLEUCINE-MODIFIED CYCLODEXTRINS

Fluorophore-amino acid-cyclodextrin (CD) triad systems, N-dansyl-L-leu cine-modified and N-dansyl-D-leucine-modified beta-CD (1, 2) and N-dan syl-L-leucine-modified and N-dansyl-D-leucine-modified gamma-CD (3, 4) , were synthesized and characterized as fluorescent indicators of mole cular recognition. Fluorescence decay analyses of these CD derivatives indicated that there exist two lifetime components, being in equilibr ium with each other in aqueous solution, with the dansyl moiety includ ed in its own cavity (self-inclusion) for the larger lifetime componen t while located outside the cavity for the shorter lifetime one. The s tructural analyses of beta-CD derivatives 1 and 2 undertaken by combin ed use of 1D and 2D MVIR spectra indicate that the dansyl moiety of 2 is more deeply included in the CD cavity than that of 1. The leucine r esidue between the dansyl and the CD moieties of these hosts was more effective in enhancing the binding abilities for various guests when c ompared with the glycine residue of the corresponding hosts; The diffe rence in the enantiomeric configuration of the leucine residue caused the difference in the binding constants with larger values for 1 than 2 and with the opposite trend for the gamma-CD derivatives 3 and 4. Up on guest addition, the fluorescence intensities of 1 and 2 decreased, reflecting the exclusion of the dansyl moiety from inside to outside o f the beta-CD cavity, while the fluorescence intensities of the gamma- CD derivatives 3 and 4 depended on the guest as shown by the increase induced by cyclohexanol and the decrease by (-)-borneol and other larg er guests. These guest-responsive variations of the fluorescence inten sity enabled these hosts to be used as effective fluorescent indicator s of molecular recognition.