A novel fluorescent derivative of α-cyclodextrin (α-CD), possessing a pyrenylmethylamino moiety (
1), was synthesized to investigate its chiral discrimination ability for
N -octanoyltrptophan (
D-Trp-C
8 and
L-Trp-C
8). From the pH-dependent fluorescence variations, the p
Ka of
1 was determined to be 6.95. Under a weakly acidic condition (pH 5.9), although an ammonium form prevailed for
1 and, as a result, photo-induced electron transfer should be absent, the fluorescence of
1 was markedly quenched, probably due to electron or energy transfer between the pyrene residue of
1 and the indole moiety of the guests. A simple 1 : 1 host-guest complexation model was successfully applied to the guest concentration-dependent fluorescence variations, yielding 1 : 1 host-guest association constants for
D-Trp-C
8 and
L-Trp-C
8 as 2160 and 1200 M
−1, respectively, while the values were decreased to 790 and 557 M
−1, respectively, at pH 4.0, where the carboxy groups of the guests protonated. In
1H-NMR spectra measured with a mixture of
D-Trp-C
8 and
1, significant upfield shifts were observed for the aromatic signals of both
D-Trp-C
8 and
1, indicating that the two aromatic groups existed close to each other. On the other hand, no such significant upfield shifts were observed for a mixture of
L-Trp-C
8 and
1. These results indicate that the pyrene residue and the ammonium group of
1 provided effective recognition sites to
1 in addition to the α-CD cavity when
1 complexed with
D-Trp-C
8, but not with
D-Trp-C
8.
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