Direct Observation of Spin Forbidden Proton-Transfer Reactions:  3NO- + HA → 1HNO + A-

Janaway, Gordon A.; Brauman, John I.

doi:10.1021/jp992511h

Cited by 28 publications

(17 citation statements)

References 26 publications

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“…This report not only revised the pK a but also indicated that the relevant equilibrium was between singlet HNO and the triplet anion [Eq. (3)] (a conclusion already drawn by Janaway and Brauman for the gas phase [56] ). Subsequent experimental work by Shafirovich and Lymar [58] and theoretical re-evaluation by Bartberger and co-workers [57] have now provided a consensus agreement that the pK a of HNO is approximately 11.4.…”

Section: Nosupporting

confidence: 52%

The Chemistry and Biology of Nitroxyl (HNO): A Chemically Unique Species with Novel and Important Biological Activity

2005

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Section: Nosupporting

confidence: 52%

The Chemistry and Biology of Nitroxyl (HNO): A Chemically Unique Species with Novel and Important Biological Activity

2005

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“…However, whereas the NO À anion has a triplet ground state (DE S-T ¼ 18 kcal/mol), the conjugate acid, HNO, is a ground state singlet (DE S-T ¼ 18.1 kcal/mol) (Janaway & Brauman, 2000). Therefore, adiabatic proton transfer requires intersystem crossing from the triplet to the singlet surface (Ellis & Ellison, 1983;Tennyson & Noble, 1986;Szmytkowski & Maciag, 1991).…”

Section: B Proton Transfer Reagentsmentioning

confidence: 99%

“…Therefore, adiabatic proton transfer requires intersystem crossing from the triplet to the singlet surface (Ellis & Ellison, 1983;Tennyson & Noble, 1986;Szmytkowski & Maciag, 1991). On the other hand, diabatic proton transfer, where spin is conserved, requires an additional 18 kcal/mol to overcome the singlet-triplet splitting in HNO (Janaway & Brauman, 2000) and is only energetically allowed for reagents with gas phase acidities lower than ca. 343 kcal/mol.…”

Section: B Proton Transfer Reagentsmentioning

confidence: 99%

“…Brauman and co-workers have examined reactions of triplet NO À with a series of acids, including CF 3 CO 2 H, HCl, CH 3 CO 2 H, H 2 S, (CH 3 ) 3 CSH, CH 3 NO 2 , CH 3 SH, CF 3 (CH 3 )CHOH, CFH 2 CH 2 OH, and CH 3 OH by using FT-ICR mass spectrometry (Janaway & Brauman, 2000). Triplet nitric oxide anion was found to react with most acids with gas-phase acidities less than 352.0 kcal/mol even though reaction in many cases required spin conversion to the singlet (Eq.…”

Section: B Proton Transfer Reagentsmentioning

confidence: 99%

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The negative ion chemistry of nitric oxide in the gas phase

Chacko¹,

Wenthold²

2005

Mass Spectrometry Reviews

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Nitric oxide is not only an important biological molecule with varied indispensable physiological roles but also shows interesting chemical reactivity both in gas-phase and solution phase. Even though it is a small molecule with an extremely low electron affinity, the reactivity of NO in the gas-phase is not just limited to electron-transfer or adduct formation. NO can behave both as an electrophile with closed-shell anions or as a radical with open-shell anions. Its reactivity with open-shell anions is characteristic and varied leading to interesting rearrangements. Nitric oxide anion undergoes spin-forbidden proton transfer with strong acids. Also, the ability of NO to serve both as one-electron or three-electron donor ligand can result in adduct formation or substitution reactions with transition metal complexes.

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“…1 (9,19). In the original study by Grätzel et al (4), difficulty in obtaining an accurate NO Ϫ concentration measurement directly after the radiolysis pulse (25,26) that the process of proton transfer involving spin state interconversion is slowed by as much as 10 7 , as compared with spin-conserving proton transfers.…”

Section: Nomentioning

confidence: 99%

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

Bartberger

Fukuto

Houk

2001

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

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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Direct Observation of Spin Forbidden Proton-Transfer Reactions: ³NO^- + HA → ¹HNO + A^-

Cited by 28 publications

References 26 publications

The Chemistry and Biology of Nitroxyl (HNO): A Chemically Unique Species with Novel and Important Biological Activity

The Chemistry and Biology of Nitroxyl (HNO): A Chemically Unique Species with Novel and Important Biological Activity

The negative ion chemistry of nitric oxide in the gas phase

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

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