Detection of nitroxyl (HNO) by a prefluorescent probe

Abstract

Recent research has shown that nitroxyl (HNO) has important and unique biological activity, especially as a potential alternative to current treatments of cardiac failure. HNO is a reactive molecule that spontaneously dimerizes and subsequently dehydrates to form nitrous oxide (N2O), making its detection in solution or biologically relevant preparations difficult. The prefluorescent probe 4‐((9‐acridinecarbonyl)amino)‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO‐9‐AC) has been used to detect HNO in aqueous solution and to differentiate it from nitric oxide (NO). TEMPO‐9‐AC reacts with HNO via a net hydrogen abstraction to produce the highly fluorescent TEMPO‐9‐AC‐H and NO. The utility of TEMPO‐9‐AC as a probe for HNO has been shown using the common HNO donors Angeli's salt and Piloty's acid (PA) along with a recently reported HNO donor, 2‐bromo‐PA. The use of TEMPO‐9‐AC is complicated by intermolecular fluorescence quenching and competitive HNO trapping by the NO produced, but nonetheless, it can be used to study HNO reactivity in aqueous solution. Copyright © 2011 John Wiley & Sons, Ltd.

The chemical biology of HNO signaling

“…$$\mathrm{R}\cdot +\mathrm{HNO}\to \mathrm{R}-\mathrm{H}+\mathrm{NO}$$$$\mathrm{R}\cdot +\mathrm{NO}\to \mathrm{R}-\mathrm{NO}$$ Thus, HNO is an efficient anti-oxidant capable of limiting free-radical chain reactions ( vide infra ) [31]. The facility of Reaction 3 is evidenced by reports that HNO can donate a hydrogen atom to even relatively stable radicals and weak oxidants such as 4-hydroxy-2,2,6,6-tetramethyl-1-piperinyloxyl and related nitroxides (R 2 NO·) generating NO and the corresponding hydroxylamine [32,33]. To be sure, the physiological/pharmacological relevance or importance of this chemical property remains to be demonstrated.…”

Recent advances in the chemical biology of nitroxyl (HNO) detection and generation

“…71 Based on this reaction, Toscano designed a nitroxide based prefluorescent probe 4-((9-acridinecarbonyl)amino)-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-9-AC, Figure 6) that demonstrates weak fluorescence. 38 Introduction of HNO from various sources transforms TEMPO-9-AC to the highly fluorescent TEMPO-9-AC-H and this probe displays selectivity for HNO over NO in aqueous solution. 38 The use of TEMPO-9-AC may be complicated by intermolecular fluorescence quenching and competitive HNO trapping by the nascent NO (a potential drawback in the Cu II probes as well) limiting its use in complicated biological environments.…”

Oxidation of N-hydroxy-l-arginine by hypochlorous acid to form nitroxyl (HNO)

“…Given its inherent reactivity, HNO has proven difficult to detect directly. Recent methods have been developed for HNO detection [8][9][10][11][12][13][14][15]; however, due to a lack of sensitivity and/or selectivity, HNO has not yet been observed in vivo.…”