DOI: 10.1002/cmdc.200700016 Angeli’s Salt (Na 2 N 2 O 3 ) is a Precursor of HNO and NO: a Voltammetric Study of the Reactive Intermediates Released by Angeli’s Salt Decomposition Christian Amatore,* [a] StØphane Arbault, [a] Claire Ducrocq,* [b] Shenghua Hu, [a] and Issa Tapsoba [a] Introduction The inorganic salt Na 2 N 2 O 3 , named Angeli’s salt (AS), is a well- reputed donor of nitroxyl (HNO and NO  ) species [1] and has been used for that reason in many biological and biochemical studies. From a medical point of view, AS also behaves as a nitric oxide donor, presenting both pro-inflammatory proper- ties [2] and cytotoxic effects. [3] However, the cardiovascular prop- erties of AS are discernable from those of NO. For instance there is evidence that AS, at moderate pharmacological doses, leads to vein distension and to the enhancement of myocardial contractility in failing hearts. [4] On the other hand, at high con- centrations, Angeli’s salt may induce the oxidation of DNA bases. [5] It was proposed that in the presence of oxygen, the nitroxyl anion NO  may evolve in vivo into peroxynitrite ONOO  , a reactive intermediate which, in addition to the nitra- tion of tyrosine moieties, can also oxidize nucleic bases, phos- pholipidic membranes, and thiol groups. [4] At physiological pH, HNO is the exclusive form of the nitroxyl species, as its pK a value was recently estimated at 11.3. [6] Therefore, the potential pharmacological use of Angeli’s salt, particularly in the treat- ment of heart failure, might be considered only after a precise determination of the reactive chemical intermediates released. Over the past few years, many research groups have studied the decomposition process of AS according to different meth- ods. Hence, it is generally thought that the decomposition mechanism of AS above pH 4 involves protonation of the dia- nion N 2 O 3 2 (pK a = 9.35) followed by tautomerization and het- erolytic cleavage of the N N bond to produce HNO and nitrite [Eq. (1)]. [7–11] This mechanism is supported by theoretical calculations, [7] which predict that protonation at the oxygen atom of the ni- troso group leads to the most thermodynamically stable mon- oanionic tautomer. HNO formed is also known to dimerize rap- idly (810 6 m 1 s 1 ) according to reaction (2). [8,9] HNO þ HNO ! H 2 N 2 O 2 ð2Þ The product of reaction (2) may then dehydrate into the stable N 2 O. Liochev and Fridovich showed that the reverse of reaction (1) is limited by the dimerization of HNO in the ab- sence of O 2 and furthermore by the reaction of HNO with O 2 Under physiological conditions, it is usually accepted that the aerobic decomposition of Angeli’s salt produces nitrite (NO 2  ) and nitroxyl (HNO), which dimerizes and leads to N 2 O. No con- sensus has yet been established on the formation of nitric oxide (NO) and/or peroxynitrite (ONOO  ) by Angeli’s salt. Because this salt has recently been shown to have pharmacological properties for the treatment of cardiovascular diseases, identification of its follow-up reactive intermediates is of increasing importance. In this work, we investigated the decomposition mechanism of An- geli’s salt by voltammetry performed at platinized carbon fiber microelectrodes. By following the decomposition process of An- geli’s salt, we showed that the mechanism depends on the exper- imental conditions. Under aerobic neutral and slightly alkaline conditions, the formation of HNO, NO 2  , but also of nitric oxide NO was demonstrated. In strongly alkaline buffer (pH > 10), we observed the formation of peroxynitrite ONOO  in the presence of oxygen. These electrochemical results are supported by com- parison with UV spectrophotometry data. [a] Prof. C. Amatore, Dr. S. Arbault, S. Hu, Dr. I. Tapsoba Ecole Normale SupØrieure, DØpartement de Chimie UMR CNRS-ENS-UPMC 8640 “PASTEUR”, 24 rue Lhomond, 75231 Paris Cedex 05 (France) Fax:(+ 33)1-4432-3863 E-mail:Christian.Amatore@ens.fr [b] Dr. C. Ducrocq CNRS—Institut de Chimie des Substances Naturelles—UPR 2301 Avenue de la Terrasse, 91190 Gif-sur-Yvette (France) Fax:(+ 33)1-6907-7247 E-mail:Claire.Ducrocq@icsn.cnrs-gif.fr 898 # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim ChemMedChem 2007,2,898–903 MED