title: Synthesis and fluorescence properties of six fluorescein-nitroxide radical hybrid-compounds.
abstract: Six fluorescein-nitroxide radical hybrid-compounds (2ab, 3ab, 4, and 5) were synthesized by the condensation of 5- or 6-carboxy-fluorescein and 4-amino-TEMPO (2ab), 5- or 6-aminofluorescein and 4-carboxy-TEMPO (3ab), and fluorescein and 4-carboxy-TEMPO (4), or by reaction of the 3-hydroxyl group of fluorescein with DPROXYL-3-ylmethyl methanesulfonate (5). Fluorescence intensities (around 520nm) after reduction of the radical increased to 1.43-, 1.38-, and 1.61-folds for 2a, 2b and 3b respectively; 3a alone exhibited a decrease in intensity on reduction. Since 4 was readily solvolyzed in PBS or even methanol to afford fluorescein and 4-carboxy-TEMPO, its fluorescence change could not be measured. Hybrid compound 5 containing an ether-linkage between the fluorescein phenol and 3-hydroxymethyl-DPROXYL hydroxyl centers, was stable and on reduction, showed a maximum increase (3.21-fold) in relative fluorescence intensity in PBS (pH5.0), despite its remarkably low absolute fluorescence intensity.
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan. Electronic address: shingo-s@yz.yamagata-u.ac.jp.
authors.forename: Shingo
authors.initials: S
authors.lastname: Sato
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Endo
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kurokawa
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Nagai
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Ito
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.
authors.forename: Tateaki
authors.initials: T
authors.lastname: Ogata
keywords: Ascorbic acid; ESR; Fluorescein; Fluorescence intensity; Nitroxide-radical