Fluorescent nitric oxide detection by copper complexes bearing anthracenyl and dansyl fluorophore ligands

Abstract

Anthrancenyl and dansyl fluorophore ligands [AnCH2pipCS 2K (1), Ds-Hen (2), Ds-HAMP (3), Ds-HAQ (4), and Ds-HAPP (5)] were prepared for coordination to CuII. Five Cu complexes, [Cu(AnCH 2pipCS2)2] (6), [Cu(Ds-en)2] (7), [Cu(Ds-AMP)2] (8), [Cu(Ds-AQ)2] (9), and [Cu(Ds-APP)(OTf)] (10), were synthesized as candidates for detecting nitric oxide (NO) by fluorescence and characterized by X-ray crystallography. A decrease in fluorescence compared to that of the free ligands (1-5) was measured following the formation of the corresponding five CuII complexes 6-10. Fluorescence was restored in the presence of NO in CH3OH/CH 2Cl2 solutions of the compounds. Complexes 7, 8, and 10 exhibited a fluorescence response to NO in pH 7.0 or 9.0 buffered aqueous solutions. Spectroscopic studies revealed that NO-induced fluorescence enhancement in these CuII complexes occurs by reduction to Cu I. The present studies demonstrate that CuII complexes are effective as fluorescent probes for detecting NO in both organic and aqueous environments.