Spin-Forbidden Deprotonation of Aqueous Nitroxyl (HNO)

Shafirovich, Vladimir; Lymar, Sergei V.

doi:10.1021/ja034378j

Cited by 79 publications

(90 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…At lower pH, the monobasic NONOate will also be in equilibrium with its protonated form. This equilibrium is expressed in the pK a , based on the most stable protonated and non-protonated isomers (K a13 = [4][H + ]/ [13]). Decomposition of the protonated NONOate is also based on the equilibrium population of a metastable tautomer (K 20 = [20]/ [13]).…”

Section: The Ph-dependent Mechanism Of Primary Amine Nonoate Decomposmentioning

confidence: 99%

“…This equilibrium is expressed in the pK a , based on the most stable protonated and non-protonated isomers (K a13 = [4][H + ]/ [13]). Decomposition of the protonated NONOate is also based on the equilibrium population of a metastable tautomer (K 20 = [20]/ [13]). Compiling these pathways and other, non-productive equilibria in both the protonated and non-protonated forms, an overall kinetic model for decomposition is summarized in Figure 12 …”

Section: The Ph-dependent Mechanism Of Primary Amine Nonoate Decomposmentioning

confidence: 99%

See 1 more Smart Citation

Mechanism of pH-Dependent Decomposition of Monoalkylamine Diazeniumdiolates to Form HNO and NO, Deduced from the Model Compound Methylamine Diazeniumdiolate, Density Functional Theory, and CBS-QB3 Calculations

et al. 2006

View full text Add to dashboard Cite

Isopropylamine diazeniumdiolate, IPA/NO, the product of the reaction of isopropylamine and nitric oxide, NO, decomposes in a pH dependent manner to afford nitroxyl, HNO, in the pH range of 13 to above 5 and NO below pH 7. Theoretical studies using B3LYP/6-311+G(d) density functional theory, the PCM and CPCM solvation models and the high accuracy CBS-QB3 method on the simplified model compound, methylamine diazeniumdiolate, predict a mechanism involving HNO production via decomposition of the unstable tautomer MeNN + (O − )NHO − . The production of NO at lower pH is predicted to result from fragmentation of the amide/NO adduct upon protonation of the amine nitrogen.

show abstract

Section: The Ph-dependent Mechanism Of Primary Amine Nonoate Decomposmentioning

confidence: 99%

Section: The Ph-dependent Mechanism Of Primary Amine Nonoate Decomposmentioning

confidence: 99%

Mechanism of pH-Dependent Decomposition of Monoalkylamine Diazeniumdiolates to Form HNO and NO, Deduced from the Model Compound Methylamine Diazeniumdiolate, Density Functional Theory, and CBS-QB3 Calculations

et al. 2006

View full text Add to dashboard Cite

show abstract

“…This is indeed the case, although the spin conversion might play only a minor role in the intersystem barrier as it is proposed that nuclear reorganization energies represent most of the activation barrier. [59] It is now established that deprotonation of HNO (or protonation of 3 …”

Section: The Physiological Chemistry Of Hnomentioning

confidence: 99%

“…It should be realized, however, that if 3 NO À can be biologically generated, the slow protonation reaction allows 3 NO À to have a significant lifetime (milliseconds), even though protonation is highly favorable. [59] One-electron reduction of NO to HNO/NO À is a possible mechanism for nitroxyl generation in biological systems. Of course, the prevalence of this process in biological systems will be highly dependent on the reduction potential of NO.…”

Section: Nomentioning

confidence: 99%

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

2005

View full text Add to dashboard Cite

“…The anionic form of nitroxyl is isoelectronic with dioxygen and exists as a triplet, 3 NO − , in aqueous solutions above pH 12; at neutral pH, the protonated singlet 1 HNO dominates (12). HNO does not accumulate in aqueous solutions due its rapid dimerization producing N 2 O between pH 2 to 11 (Eq.…”

mentioning

confidence: 99%

Nitrosyl hydride (HNO) replaces dioxygen in nitroxygenase activity of manganese quercetin dioxygenase

Kumar

Zapata

Ramirez

et al. 2011

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

View full text Add to dashboard Cite

Quercetin dioxygenase (QDO) catalyzes the oxidation of the flavonol quercetin with dioxygen, cleaving the central heterocyclic ring and releasing CO. The QDO from Bacillus subtilis is unusual in that it has been shown to be active with several divalent metal cofactors such as Fe, Mn, and Co. Previous comparison of the catalytic activities suggest that Mn(II) is the preferred cofactor for this enzyme. We herein report the unprecedented substitution of nitrosyl hydride (HNO) for dioxygen in the activity of Mn-QDO, resulting in the incorporation of both N and O atoms into the product. Turnover is demonstrated by consumption of quercetin and other related substrates under anaerobic conditions in the presence of HNO-releasing compounds and the enzyme. As with dioxygenase activity, a nonenzymatic base-catalyzed reaction of quercetin with HNO is observed above pH 7, but no enhancement of this basal reactivity is found upon addition of divalent metal salts. Unique and regioselective N-containing products ( 14 N∕ 15 N) have been characterized by MS analysis for both the enzymatic and nonenzymatic reactions. Of the several metallo-QDO enzymes examined for nitroxygenase activity under anaerobic condition, only the Mn(II) is active; the Fe(II) and Co(II) substituted enzymes show little or no activity. This result represents an enzymatic catalysis which we denote nitroxygenase activity; the unique reactivity of the Mn-QDO suggests a metalmediated electron transfer mechanism rather than metal activation of the substrate's inherent base-catalyzed reactivity.nitroxyl | quercetinase D ioxygenases are enzymes that incorporate both atoms of dioxygen into a targeted substrate, e.g., the enzyme catechol 1,2-dioxygenase cleaves the C-C bond between catechol's two hydroxyl groups forming the dicarboxylate cis,cis-muconic acid (1). Although highly divergent, there are two broadly defined classes of nonheme dioxygenases: those that directly bind dioxygen at the metal center or those in which dioxygen binds to the substrate that has been activated by interaction with the metal center (2). Such questions also apply to quercetin dioxygenase (QDO), which catalyzes the oxidation of the flavonol quercetin (1) with dioxygen ( Fig. 1). During turnover, QDO cleaves the central heterocyclic ring of quercetin, releasing CO, and yielding the corresponding depside. The QDO from Bacillus subtilis is unusual in that it has been shown to be active with several divalent metal cofactors such as Cu, Fe, Mn, and Co. Comparison of the catalytic activities suggest that Mn(II) is the preferred cofactor for this enzyme (3).The simple molecule nitrosyl hydride (HNO) is the singly reduced and protonated form of nitric oxide, NO. HNO has garnered much interest because it demonstrates a physiological reactivity distinctly different from its congener nitric oxide (4, 5). In a series of papers, we have reported the preparation and characterization of the HNO adduct of myoglobin (HNO-Mb) by reduction of 7) and by trapping of free HNO by deoxymyoglobin (Mb-Fe II ) (8)...

show abstract

Spin-Forbidden Deprotonation of Aqueous Nitroxyl (HNO)

Cited by 79 publications

References 36 publications

Mechanism of pH-Dependent Decomposition of Monoalkylamine Diazeniumdiolates to Form HNO and NO, Deduced from the Model Compound Methylamine Diazeniumdiolate, Density Functional Theory, and CBS-QB3 Calculations

Mechanism of pH-Dependent Decomposition of Monoalkylamine Diazeniumdiolates to Form HNO and NO, Deduced from the Model Compound Methylamine Diazeniumdiolate, Density Functional Theory, and CBS-QB3 Calculations

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

Nitrosyl hydride (HNO) replaces dioxygen in nitroxygenase activity of manganese quercetin dioxygenase

Contact Info

Product

Resources

About