Regioselectively hetero-labeled hosts, 6
A-pyrenebutylate-6
X-tosyl-modified
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), were synthesized in order to investigate their chemo-sensor properties for applications to organic compounds, such as bile acids and terpenes. The hosts (
γ-
1,
γ-
2,
γ-
3, and
γ-
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 (Δ
I/I0, where
I and
I0 are the fluorescence intensities in the presence and absence of a guest and Δ
I =
I0-
I) was used to describe the sensing ability of these hosts. Host
γ-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
γ-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.
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