Photolysis of the nitrogen-nitrogen double bond in trioxodinitrate: reaction between triplet oxonitrate(1-) and molecular oxygen to form peroxonitrite

Donald, Caroline E.; Hughes, Martin N.; Thompson, Janet M.; Bonner, Francis T.

doi:10.1021/ic00236a004

Cited by 103 publications

(57 citation statements)

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“…6, which is published as supporting information on the PNAS web site, www.pnas.org). This result is in qualitative accord with the previous communication (13). The same spectral changes were observed in O 2 -saturated solutions.…”

Section: Resultssupporting

confidence: 93%

“…This result was interpreted as evidence against the occurrence of reaction 2. On the other hand, the same researchers reported peroxynitrite formation during N 2 O 3 2Ϫ photolysis in alkaline solution (13). To reconcile the data, it was suggested that thermal reaction 1 followed by deprotonation of HNO produces singlet NO Ϫ , which is the ground state in water, and that 1 3 Ϫ upon completion of the reaction (16).…”

mentioning

confidence: 97%

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Nitroxyl and its anion in aqueous solutions: Spin states, protic equilibria, and reactivities toward oxygen and nitric oxide

Shafirovich

Lymar

2002

Proc. Natl. Acad. Sci. U.S.A.

402

496

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The thermodynamic properties of aqueous nitroxyl (HNO) and its anion (NO ؊ ) have been revised to show that the ground state of NO ؊ is triplet and that HNO in its singlet ground state has much lower acidity, pKa( 1 HNO͞ 3 NO ؊ ) Ϸ 11.4, than previously believed. These conclusions are in accord with the observed large differences between 1 HNO and 3 NO ؊ in their reactivities toward O2 and NO. Laser flash photolysis was used to generate 1 HNO and 3 NO ؊ by photochemical cleavage of trioxodinitrate (Angeli's anion). The spin-allowed addition of 3 O2 to 3 NO ؊ produced peroxynitrite with nearly diffusion-controlled rate (k ‫؍‬ 2.7 ؋ 10 9 M ؊1 ⅐s ؊1 ). In contrast, the spin-forbidden addition of 3 O2 to 1 HNO was not detected (k Ͻ Ͻ 3 ؋ 10 5 M ؊1 ⅐s ؊1 N itroxyl (HNO, also known as nitrosyl hydride) and its anion, NO Ϫ , are the simplest molecules with nitrogen in the ϩ1 oxidation state and yet their aqueous chemistry is not well understood. Recent suggestions that these redox neighbors of the biologically important NO radical may play a role in cellular metabolism (1-4) and in aerobic environments may be precursors to cytotoxic peroxynitrite, ONOO Ϫ , (5, 6) have engendered considerable interest in the chemistry of HNO͞NO Ϫ . The characterization of these species is complicated by their instability with respect to formation of nitrous oxide (7,8). In most cases where nitroxyl has been invoked as an intermediate, the rate-determining step was its generation, a situation that allows little insight into the properties and reactivities of HNO͞NO Ϫ themselves. The NO Ϫ anion is isoelectronic with O 2 and, like O 2 , should have a triplet ground state, whereas the ground state of HNO should be a singlet. Indeed, these ground state assignments have been well established for HNO͞NO Ϫ in the gas phase (9, 10).A frequently used source for aqueous HNO͞NO Ϫ is trioxodinitrate (N 2 O 3 2Ϫ , also known as Angeli's anion), whose conjugate acid (H 2 N 2 O 3 ) has consecutive pKa values of 2.5 and 9.7 (11). It is widely accepted (7, 8) that slow decomposition of the monoprotonated anion occurs through heterolytic NON bond cleavageSubsequent addition of O 2 could yield peroxynitriteHowever, nitrate, which is the peroxynitrite decomposition product, was not detected among the end products of HN 2 O 3 Ϫ decay (12). This result was interpreted as evidence against the occurrence of reaction 2. On the other hand, the same researchers reported peroxynitrite formation during N 2 O 3 2Ϫ photolysis in alkaline solution (13). To reconcile the data, it was suggested that thermal reaction 1 followed by deprotonation of HNO produces singlet NO Ϫ , which is the ground state in water, and that 1 NO Ϫ is unreactive toward O 2 . In contrast, photochemical cleavage of N 2 O 3 2Ϫ was thought to generate the long-lived triplet excited state of NO Ϫ , which reacted with O 2 . However, it seems unlikely that hydration can reverse a gas-phase energy gap of about 70 kJ͞mol between the ground state 3 NO Ϫ and the excited state 1 NO Ϫ (10). Moreover, by ana...

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Section: Resultssupporting

confidence: 93%

mentioning

confidence: 97%

Nitroxyl and its anion in aqueous solutions: Spin states, protic equilibria, and reactivities toward oxygen and nitric oxide

Shafirovich

Lymar

2002

Proc. Natl. Acad. Sci. U.S.A.

402

496

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“…Donald et al originally suggested that the triplet forms of HNO should possess enhanced acidity versus the singlet state (42). We predict that the excited triplet state of HNO is an extremely potent acid in aqueous solution, with a pK a of about Ϫ2 based on the spectroscopically determined singlet-triplet gap of HNO.…”

Section: Nomentioning

confidence: 81%

On the acidity and reactivity of HNO in aqueous solution and biological systems

Bartberger

Fukuto

Houk

2001

Proc. Natl. Acad. Sci. U.S.A.

162

163

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The gas phase and aqueous thermochemistry and reactivity of nitroxyl (nitrosyl hydride, HNO) were elucidated with multiconfigurational self-consistent field and hybrid density functional theory calculations and continuum solvation methods. The pK a of HNO is predicted to be 7.2 ؎ 1.0, considerably different from the value of 4.7 reported from pulse radiolysis experiments. The ground-state triplet nature of NO ؊ affects the rates of acid-base chemistry of the HNO͞NO ؊ couple. HNO is highly reactive toward dimerization and addition of soft nucleophiles but is predicted to undergo negligible hydration (Keq ‫؍‬ 6.9 ؋ 10 ؊5 ). HNO is predicted to exist as a discrete species in solution and is a viable participant in the chemical biology of nitric oxide and derivatives.T he discoveries of nitric oxide (NO) biosynthesis in mammalian cells and the diverse biological activity associated with NO and NO-derived species (1) have brought intense interest in the physiological chemistry of nitrogen oxides. The chemistry of NO and its biologically accessible oxidized congeners nitrogen dioxide (NO 2 ), nitrite (NO 2 Ϫ ), peroxynitrite (ONOO Ϫ ), dinitrogen trioxide (N 2 O 3 ), and nitrate (NO 3 Ϫ ) is fairly well established (2). By contrast, the reduced congeners such as nitroxyl (HNO) and its conjugate base (NO Ϫ ) are less well understood, and consequently their role in biology is not clear. The importance of HNO or NO Ϫ in biology has often been neglected or dismissed, in part because NO metabolism is thought to be primarily oxidative in nature (3), and because HNO is thought to be only metastable (3), a strong acid (4), and to dimerize readily (5). NO Ϫ is known to react rapidly and irreversibly with NO (6), making the examination of NO Ϫ in the presence of NO difficult. Additionally, HNO might be expected to be electrophilic, and hydration under physiological conditions would serve to attenuate its aqueous reactivity.Nitroxyl (HNO), or its conjugate base, NO Ϫ , is known to be formed under physiological conditions; for example, oxidation of N-hydroxy-L-arginine (an intermediate in NO biosynthesis) (7), reaction of S-nitrosothiols with thiols (8, 9), nitric oxide synthase (10-12), and even direct reduction of NO by mitochondrial cytochrome c (13), may all generate HNO. Nitroxyl has been generated via the interaction of NO with manganese superoxide dismutase (14) and with ubiquinol (15). HNO has biological activity; it can act as a potent cytotoxic agent that causes double-stranded breaks in DNA, depletion of cellular glutathione (16), as well as elicitation of smooth muscle relaxation (17). HNO has been found to be a potent inhibitor of thiol-containing enzymes (18,19) and attenuates the activity of the NMDA receptor via thiol modification, thus providing neuroprotection (20).Much of the fundamental biological chemistry associated with HNO is unknown, aside from the rate constant for dimerization is a typical nucleophile, yet several studies find that HNO generated at physiological pH reacts readily as an electrophile, par...

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“…It has often been suggested that these two molecules, both having a triplet ground state (64), react with each other, thereby directly generating ONOO Ϫ (24,30,32,36,56,65).…”

Section: Putative Mechanism By Which Nitroxyl Anion Generates Peroxynmentioning

confidence: 99%

Formation of Peroxynitrite from Reaction of Nitroxyl Anion with Molecular Oxygen

Kirsch

Groot

2002

Journal of Biological Chemistry

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Photolysis of the nitrogen-nitrogen double bond in trioxodinitrate: reaction between triplet oxonitrate(1-) and molecular oxygen to form peroxonitrite

Cited by 103 publications

References 1 publication

Nitroxyl and its anion in aqueous solutions: Spin states, protic equilibria, and reactivities toward oxygen and nitric oxide

Nitroxyl and its anion in aqueous solutions: Spin states, protic equilibria, and reactivities toward oxygen and nitric oxide

On the acidity and reactivity of HNO in aqueous solution and biological systems

Formation of Peroxynitrite from Reaction of Nitroxyl Anion with Molecular Oxygen

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