Fluorescence response mechanism of D-glucose selectivity for supramolecular probes composed of phenylboronic-acid-modified beta-cyclodextrin and styrylpyridinium dyes.

Supramolecular complex formation of phenylboronic-acid-modified beta-cyclodextrin (1) with 1-methyl-4-(4-dimethylaminostyryl)pyridinium (C1SP) in aqueous solutions containing saccharides was fully clarified to gain an insight into the observed D-glucose (D-glc) selectivity of a supramolecular fluorescent probe composed of 1 and the 1-heptyl analogue of C1SP (Chem. Commun., 2006, 4319). At pH 9.6, where 1 was in its anionic form, both the stability and the fluorescence of the 1/C1SP complex were reduced by the formation of boronate esters of 1 with saccharides. Among the saccharides, D-glc had the smallest effect on destabilization of the 1/C1SP complex, almost completely retaining the fluorescence of the 1/C1SP complex that was reduced by other saccharides by approximately 2/3. Under neutral conditions, D-glc enhanced the fluorescence of the 1/C1SP complex by increasing the fraction of anionic 1 while minimally decreasing the stability and fluorescence of the 1/C1SP complex. Although other saccharides also increased the fraction of the anionic 1, their relatively large effects on the destabilization and reduction of fluorescence of the 1/C1SP complex limited the enhancement of the fluorescence of the 1-C1SP system under neutral conditions.

Greater fluorescence from styrylpyridinium dye upon complexation with cyclodextrin derivatives through a pi-pi interaction.

The fluorescence of 4-(4'-dimethylamino)styryl-1-methylpyridinium (C1SP) was enhanced by more than 33-fold by complexation with beta-cyclodextrin (beta-CD) bearing a naphthalene, pyrene, or phenylboronic acid group. The great enhancement of the fluorescence of C1SP was due to a pi-pi stacking interaction, by which the bond rotation of C1SP was effectively suppressed. The results indicate that C1SP and structurally related hemicyanine dyes potentially become powerful fluorescent indicators for aromatic compounds through the pi-pi stacking interaction in water.

Pseudorotaxane-type fluorescent receptor exhibiting unique response to saccharides.

Pseudorotaxane formed by reacting beta-cyclodextrin bearing a phenylboronic acid residue with 1-heptyl-4-(4'-dimethylaminostyryl)pyridinium functioned as a novel fluorescent saccharide receptor having unique responses.