Guest-responsive fluorescence variations of gamma-cyclodextrins labeled with hetero-functionalized pyrene and tosyl...

Regioselectively hetero-labeled hosts, 6A-pyrenebutylate-6X-tosyl-modified gamma-cyclodextrins (X = B or H, C or G, D or F, and E for gamma-1, gamma-2, gamma-3, and gamma-4, respectively), were synthesized in order to investigate their chemo-sensor properties for applications to organic compounds, such as bile acids and terpenes. The hosts (gamma-1, gamma-2, gamma-3, and gamma-4) exhibit pure monomer fluorescence. The guest-induced fluorescence emissions of these hosts were suppressed in the presence of guests. The extent of fluorescence variations of these hosts with guests was recognized as a manifestation of the sensing ability of the hosts. A sensing parameter (deltaI/I0, where I and I0 are the fluorescence intensities in the presence and absence of a guest and deltaI = I0-I) was used to describe the sensing ability of these hosts. Host gamma-analogs were able to detect progesterone, ursodeoxycholic acid, chenodeoxycholic acid, and (-)-borneol with high sensitivity. The behaviors of the appended moieties of these hosts during the formation of host-guest complexes were studied using induced circular dichroism (ICD) spectra, fluorescence spectra and the MM2-energy-minimized structure. The host gamma-analogs exhibited different ICD spectra patterns before and after the addition of ursodeoxycholic acid. The guest-induced variations of ICD and the fluorescence spectra and MM2-minimized structures suggest that the pyrene and tosyl moieties move by altering the spatial relationship between them, in which the pyrene moiety works as a hydrophobic cap and the tosyl moiety is speculated to act as a spacer.