Resonant vibrational excitation of the NO ground state by electron impact in the 0.1-3 eV energy range

Tronc, M.; Huetz, A.; Landau, M.; Pichou, F.; Reinhardt, Joachim

doi:10.1088/0022-3700/8/7/021

Cited by 70 publications

(39 citation statements)

References 17 publications

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“…Assuming, therefore, that these measurements pertain to the NO reduction in the ground 3 NO Ϫ state, ⌬ f G 0 ( 3 NO aq Ϫ ) Ϸ180 kJ͞mol can be estimated. Finally, the values for ⌬ f G 0 ( 3 HNO aq ) Ϸ190 kJ͞mol and for ⌬ f G 0 ( 1 NO aq Ϫ ) Ϸ248 kJ͞mol can be assigned under a reasonable presumption that hydration does not appreciably alter the gas-phase energy gaps of 75 kJ͞mol between 3 HNO and 1 HNO (9) and 68 kJ͞mol between 1 NO Ϫ and 3 NO Ϫ (10).…”

Section: Resultsmentioning

confidence: 96%

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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.

400

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: Resultsmentioning

confidence: 96%

“…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).…”

mentioning

confidence: 73%

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.

400

496

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“…However, this is not the case and the most significant uncertainty concerns the energy gap between 1 NO -and 3 NO -that was taken from the gas-phase measurements by Tronc and co-workers. 35 They noted that their measurements could possibly pertain to the first vibrationally excited level of 1 NO -that is 18 kJ/mol above the zero-point energy. If so, the value -∆ r4 G°would decrease to about 35 kJ/mol and become sufficiently close to the observed E a , considering other uncertainties in nitroxyl energetics in water.…”

Section: Discussionmentioning

confidence: 99%

Spin-Forbidden Deprotonation of Aqueous Nitroxyl (HNO)

Shafirovich

Lymar

2003

J. Am. Chem. Soc.

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The first mechanistic study of a spin-forbidden proton-transfer reaction in aqueous solution is reported. Laser flash photolysis of alkaline trioxodinitrate (N(2)O(3)(2)(-), Angeli's anion) is used to generate a nitroxyl anion in its excited singlet state ((1)NO(-)). Through rapid partitioning between protonation by water and electronic relaxation, (1)NO(-) produces (1)HNO (ground state, yield 96%) and (3)NO(-) (ground state, yield 4%), which comprise a unique conjugate acid-base couple with different ground-state multiplicities. Using the large difference between reactivities of (1)HNO and (3)NO(-) in the peroxynitrite-forming reaction with (3)O(2), the kinetics of spin-forbidden deprotonation reaction (1)HNO + OH(-) --> (3)NO(-) + H(2)O is investigated in H(2)O and D(2)O. Consistent with proton transfer, this reaction exhibits primary kinetic hydrogen isotope effect k(H)/k(D) = 3.1 at 298 K, which is found to be temperature-dependent. Arrhenius pre-exponential factors and activation energies of the second-order rate constant are found to be: log(A, M(-)(1) s(-)(1)) = 10.0 +/- 0.2 and E(a) = 30.0 +/- 1.1 kJ/mol for proton transfer and log(A, M(-)(1) s(-)(1)) = 10.4 +/- 0.1 and E(a) = 35.1 +/- 0.7 kJ/mol for deuteron transfer. Collectively, these data are interpreted to show that the nuclear reorganization requirements arising from the spin prohibition necessitate significant activation before spin change can take place, but the spin change itself must occur extremely rapidly. It is concluded that a synergy between the spin prohibition and the reaction energetics creates an intersystem barrier and is responsible for slowness of the spin-forbidden deprotonation of (1)HNO by OH(-); the spin prohibition alone plays a minor role.

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“…3 [32]. The gas-phase energy gaps are 75 kJ/mol between 3 HNO and 1 HNO [33], and 68 kJ/mol between 1 NO À and 3 NO À [34]. The spin state barrier slows the proton exchange considerably such that the triplet state anion, if generated directly, would have a lifetime of seconds in pH 7 buffer.…”

Section: Hno Revisitedmentioning

confidence: 99%

Coordination chemistry of the HNO ligand with hemes and synthetic coordination complexes

Farmer

Sulc

2005

Journal of Inorganic Biochemistry

138

179

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Resonant vibrational excitation of the NO ground state by electron impact in the 0.1-3 eV energy range

Cited by 70 publications

References 17 publications

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

Spin-Forbidden Deprotonation of Aqueous Nitroxyl (HNO)

Coordination chemistry of the HNO ligand with hemes and synthetic coordination complexes

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