Synthesis and fluorescence properties of six fluorescein-nitroxide radical hybrid-compounds

Shingo Sato; Susumu Endo; Yusuke Kurokawa; Masaki Yamaguchi; Akio Nagai; Tomohiro Ito; Tateaki Ogata

doi:10.1016/j.saa.2016.06.021

Synthesis and fluorescence properties of six fluorescein-nitroxide radical hybrid-compounds

Spectrochim Acta A Mol Biomol Spectrosc. 2016 Dec 5:169:66-71. doi: 10.1016/j.saa.2016.06.021. Epub 2016 Jun 16.

Authors

Shingo Sato¹, Susumu Endo², Yusuke Kurokawa², Masaki Yamaguchi², Akio Nagai², Tomohiro Ito², Tateaki Ogata²

Affiliations

¹ 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.
² Graduate School of Science and Engineering, Yamagata University, Jonan 4-3-16, Yonezawa-shi, Yamagata 992-8510, Japan.

PMID: 27337053
DOI: 10.1016/j.saa.2016.06.021

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.

Keywords: Ascorbic acid; ESR; Fluorescein; Fluorescence intensity; Nitroxide-radical.