Inclusion Effects of Cyclodextrin on the Intramolecular Fluorescence Quenching of Naphthylalanine Derivatives

Ken-ichiro MIYOSHI, Kanji KUBO, Tetsutaro IGARASHI and Tadamitsu SAKURAI*

Department of Applied Chemistry, Faculty of Engineering, Kanagawa University; Kanagawa-ku, Yokohama-shi 221-8686 Japan
Institute of Advanced Material Study, 86, Kyushu University; Kasuga-koen, Kasuga-shi 816-0811 Japan

We analyzed UV absorption, fluorescence and circular dichroism spectra of the title compounds, as well as their fluorescence lifetimes, in the presence of β-cyclodextrin (β-CDx) or γ-cyclodextrin (γ-CDx). The β-CDx cavity turned out to axially incorporate the naphthalene ring of the model 2-naphthylalanine derivative to exert its effect so as to significantly decrease the fluorescence quenching rate. This finding provides a strong piece of evidence for a “through space” mechanism by which the emission quenching occurs. On the other hand, the naphthalene ring of the 1-naphthylalanine derivative was suggested to be immersed into the γ-CDx cavity in both axial and equatorial modes resulting in a less significant decrease of the fluorescence quenching rate.

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