Nitrosonium Research Articles

Sucrose tricarboxylate by sonocatalysed TEMPO-mediated oxidation

Oxidation of sucrose by the NaOCl/TEMPO system provided sucrose tricarboxylate without the addition of sodium bromide as co-catalyst when high-frequency (500 kHz) ultrasound was applied, in contrast to very limited conversion without sonication. In the presence of sodium bromide, sonication also caused acceleration of the oxidation. The rate increase due to sonication of the oxidant system prior to sucrose addition suggests that ultrasound acts at the level of the formation of the nitrosonium ion, the active oxidising species in the catalytic cycle.

Effects of Interferon-γ and Lipopolysaccharide on Macrophage Iron Metabolism Are Mediated by Nitric Oxide-induced Degradation of Iron Regulatory Protein 2

Iron regulatory proteins (IRP-1 and IRP-2) control the synthesis of transferrin receptors (TfR) and ferritin by binding to iron-responsive elements, which are located in the 3'-untranslated region and the 5'-untranslated region of their respective mRNAs. Cellular iron levels affect binding of IRPs to iron-responsive elements and consequently expression of TfR and ferritin. Moreover, NO(*), a redox species of nitric oxide that interacts primarily with iron, can activate IRP-1 RNA binding activity resulting in an increase in TfR mRNA levels. Recently we found that treatment of RAW 264.7 cells (a murine macrophage cell line) with NO(+) (nitrosonium ion, which causes S-nitrosylation of thiol groups) resulted in a rapid decrease in RNA binding of IRP-2 followed by IRP-2 degradation, and these changes were associated with a decrease in TfR mRNA levels (Kim, S., and Ponka, P. (1999) J. Biol. Chem. 274, 33035-33042). In this study, we demonstrated that stimulation of RAW 264.7 cells with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) increased IRP-1 binding activity, whereas RNA binding of IRP-2 decreased and was followed by a degradation of this protein. Moreover, the decrease of IRP-2 binding/protein levels was associated with a decrease in TfR mRNA levels in LPS/IFN-gamma-treated cells, and these changes were prevented by inhibitors of inducible nitric oxide synthase. Furthermore, LPS/IFN-gamma-stimulated RAW 264.7 cells showed increased rates of ferritin synthesis. These results suggest that NO(+)-mediated degradation of IRP-2 plays a major role in iron metabolism during inflammation.

Nitrosation of anisole, stability constants of complexes of the nitrosonium ion with aromatic nitroso compounds, and NMR studies of restricted rotation in the complexes

Anisole can be nitrosated in good yield under the acidic and anaerobic conditions previously reported for methylbenzenes. The product, 4-nitrosoanisole, is slowly converted into 4-nitrosophenol in acetic–sulfuric acid mixtures. The decrease in the rate constant for this reaction with increasing concentration of nitrosonium ion leads to an estimate of the stability constant of the complex between 4-nitrosoanisole and nitrosonium ion. Stability constants for the similar complexes formed by 4-nitrosotoluene and 1,3-dimethyl-4-nitrosobenzene with nitrosonium ion in trifluoroacetic acid have been determined by UV spectroscopy. Restricted rotation about the bond between nitrogen and aromatic carbon is evident from the 1H NMR spectra of the complexes; activation parameters for the rotation are reported and compared with similar data in the literature for restricted rotation in uncomplexed aromatic nitroso compounds.

Gas‒phase reactions of NO+ with Glu and γ‒Glu–Met

The reactivity of the nitrosonium ion, NO+, with the amino acid Glu and the dipeptide γ‒Glu–Met in the gas phase has been investigated using the combination of chemical ionisation mass spectrometry and MS/MS. It is shown that NO+ reacts efficiently with both Glu and Glu–Met leading to the formation of the nitroso‒group containing ions at m/z 159 and 288.The formation of m/z 159, (GluNO‒18)+, is rationalized by a mechanism involving an electrophilic attack of NO+ upon the carbonyl oxygen atom of one of the carboxylic groups of Glu and the N‒terminal carboxylic group of Glu–Met leading to the neutral losses of H2O and Met, respectively. The unimolecular decompositions of the metastable and collisionally activated m/z 159 ions lead primarily to the elimination of the neutral species HNO (major) and the (Glu‒18) residue (minor). The formation of the m/z 288 ions can be described by a mechanistic scheme which involves the ion‒molecule interaction of m/z 159 with Glu and Glu–Met and subsequent losses of H2O and Met, respectively. Unimolecular and collisionally activated dissociations of m/z 288 suggest the formation of the proton‒bridged ion‒neutral complex [(GluNO‒18)···H+···(Glu‒18)].

Sonocatalysis of the TEMPO-mediated oxidation of glucosides

Ultrasound is shown to increase the rate of the TEMPO-mediated oxidation of methyl α- d-glucopyranoside or sucrose in the presence of stoichiometric amounts of sodium hypochlorite in basic aqueous medium. The reaction can then occur without the usually necessary sodium bromide, showing that ultrasound acts at the level of the formation of the nitrosonium ion, the active oxidizing species in the catalytic cycle.

Exposure of Mn and FeSODs, but not Cu/ZnSOD, to NO leads to nitrosonium and nitroxyl ions generation which cause enzyme modification and inactivation: an in vitro study

The effect of NO treatment in vitro on structural and functional alterations of Cu/Zn, Mn, and Fe type of SODs was studied. Significant difference in response to NO of Cu/ZnSOD compared to the Mn and Fe types was demonstrated. Cu/ZnSOD was shown to be stable with respect to NO: even on prolonged exposure, NO produced negligible effect on its structure and activity. In contrast, both Mn and Fe types were found to be NO-sensitive: exposure to NO led to their fast and extensive inactivation, which was accompanied by extensive structural alterations, including (in some of the samples tested) the cleavage of enzyme polypeptide chains, presumably at His residues of the enzyme metal binding sites. The generation of nitrosonium (NO +) and nitroxyl (NO −) ions in NO treated Mn and FeSODs, which produce enzyme modifications and inactivation, was demonstrated. The physiological and biomedical significance of described findings is briefly discussed.

Reactions of peroxynitrite with N,N-dimethyl- p-toluidine and 1,4-naphthoquinone. Evidence for heterolytic cleavage of a nitrogenoxygen bond in peroxynitrous acid

Peroxynitrite (ONOO −) has been found to react with the title amine 1 and quinone 5 to form N-nitrosoamine 2 and 2,3-epoxide 6, respectively, in accord with the in situ generation of the nitrosonium and hydroperoxide ions as the respective reactive species.

Intracellular redox state determines whether nitric oxide is toxic or protective to rat oligodendrocytes in culture.

We found that several nitric oxide donors had similar potency in killing mature and immature forms of oligodendrocytes (OLs). Because of the possibility of interaction of nitric oxide with intracellular thiols, we tested the effect of the nitrosonium ion donor S-nitrosylglutathione (SNOG) in OL cultures in the setting of cystine deprivation, which has been shown to cause intracellular glutathione depletion. Surprisingly, the presence of 200 microM SNOG completely protected OLs against the toxicity of cystine depletion. This protection appeared to be due to nitric oxide, because it could be blocked by hemoglobin and potentiated by inclusion of superoxide dismutase. We tested the effect of three additional NO* donors and found that protection was not seen with diethylamine NONOate, a donor with a half-life measured in minutes, but was seen with dipropylenetriamine NONOate and diethylaminetriamine NONOate, donors with half-lives measured in hours. This need for donors with longer half-lives for the protective effect suggested that NO* was required when intracellular thiol concentrations were falling, a process evolving over hours in medium depleted of cystine. These studies suggest a novel protective role for nitric oxide in oxidative stress injury and raise the possibility that intracerebral nitric oxide production might be a mechanism of defense against oxidative stress injury in OLs.

An FTIR Study on the Mechanism of the Reaction between Nitrogen Dioxide and Propene over Acidic Mordenites

Nitrosonium ions, NO+, are formed upon reaction between NO, NO2, and the Brønsted acid sites of H–MOR. It is shown that the NO+ ions are highly reactive towards propene, forming propenal oxime at 120°C. At temperatures above 170°C, propenal oxime is dehydrated to acrylonitrile. A mechanism is proposed to explain the acrylonitrile formation. The nitrile can be hydrolysed to yield adsorbed ammonium ions, which are known to be efficient in reducing nitrogen oxides to nitrogen. The dehydration of propenal oxime appears to be the rate determining step in nitrile formation.

Targeting cysteine residues of human immunodeficiency virus type 1 protease by reactive free radical species.

Nitric oxide (NO) is a naturally occurring free radical with many functions. The oxidized form of NO, the nitrosonium ion, reacts with the thiol group of cysteine residues resulting in their modification to S-nitrosothiols. The human immunodeficiency virus type 1 (HIV-1) protease (HIV-PR) has two cysteine residues that are conserved amongst different viral isolates found in patients with acquired immunodeficiency syndrome (AIDS). In an active dimer, these residues are located near the surface of the protease. We have found that treatment of HIV-PR with different NO congeners results in loss of its proteolytic activity and simultaneous formation of S-nitrosothiols. Sodium nitroprusside inhibited HIV-PR up to 70% and S-nitroso-N-acetylpenicillamine completely inhibited the protease within 5 min of treatment. The pattern of inhibition by NO donors is comparable to its inhibition by N-acetyl pepstatin. Using electrospray ionization-mass spectrometry, we identified the modification of HIV-PR by NO as that of S-nitrosation. Our findings point towards a possible role of NO in mediating resistance to HIV-1 infection.

Kinetics and mechanism of nitrosation of toluene, o-xylene, and m-xylene in trifluoroacetic acid, or in acetic–sulfuric acid mixtures, under nitric oxide

The title reactions give good yields with m-xylene, and modest yields with toluene and o-xylene which are successfully directly nitrosated for the first time. The advantages of purging with nitric oxide are demonstrated and discussed. The kinetics have been successfully interpreted in terms of a mechanism in which both the aromatic substrate and the nitrosoaromatics form, reversibly, complexes with nitrosonium ion. The nitrosoaromatics are unstable under the acid conditions and the method is successful only because of the protective complexation with the nitrosonium ion.

Response to reactive nitrogen intermediates in Mycobacterium tuberculosis: induction of the 16-kilodalton alpha-crystallin homolog by exposure to nitric oxide donors.

In contrast to the apparent paucity of Mycobacterium tuberculosis response to reactive oxygen intermediates, this organism has evolved a specific response to nitric oxide challenge. Exposure of M. tuberculosis to NO donors induces the synthesis of a set of polypeptides that have been collectively termed Nox. In this work, the most prominent Nox polypeptide, Nox16, was identified by immunoblotting and by N-terminal sequencing as the alpha-crystallin-related, 16-kDa small heat shock protein, sHsp16. A panel of chemically diverse donors of nitric oxide, with the exception of nitroprusside, induced sHsp16 (Nox16). Nitroprusside, a coordination complex of Fe2+ with a nitrosonium (NO+) ion, induced a 19-kDa polypeptide (Nox19) homologous to the nonheme bacterial ferritins. We conclude that the NO response in M. tuberculosis is dominated by increased synthesis of the alpha-crystallin homolog sHsp16, previously implicated in stationary-phase processes and found in this study to be a major M. tuberculosis protein induced upon exposure to reactive nitrogen intermediates.

Nitrogen Monoxide Sensing with Nitrosonium Ion Conducting Solid Electrolytes

Nitrogen Monoxide Sensing with Nitrosonium Ion Conducting Solid Electrolytes

Nitrosonium Nitrate, an Isomer of N2O4 in IF5

N2O4 dissolves in IF5 as NO+NO3–, as established by n.m.r spectroscopy, and in the solid state the solvate complex NO+NO3– · IF5 is formed. This contains a double chain of alternating NO+ cations and NO3– anions. (a = 483.4(2), b = 773.9(1), c = 932.6(3) pm, (α = 70.18(2)°, β = 80.90(3)°, (γ = 87.34(2)°, space group P1, Z = 2). Nitrosoniumnitrat, ein Isomer des N2O4 in Gegenwart von IF5 N2O4 lost sich in IF5 als NO+NO3–, wie mit der Kernresonanzspektroskopie bewiesen wird. Im festen Zustand bildet sich ein Solvatkomplex der Formel NO+NO3– · IF5, welcher eine Doppelkette alternierender NO+-Kationen und NO3–-Anionen enthalt (a = 483.4(2), b = 773.9(1), c = 932.6(3) pm, (α = 70.18(2)°, β = 80.90(3)°, (γ = 87.34(2)°, Raumgruppe P1, Z = 2).

Spectroelectrochemical Detection of an Intermediate in the Alcohol Oxidation Process with a Nitroxyl Radical

Abstract A spectroelectrochemical study revealed the formation of an adduct of nitrosonium ion with 4-methoxybenzyl alcohol as an intermediate in the alcohol oxidation process.

Gaseous [N2O5]H+, [N2O4]H+, and Related Species from the Addition of NO2+ and NO+ Ions to Nitric Acid and Its Derivatives

Gaseous [HN2O5]+ ions formed upon addition of NO2+ to nitric acid have been studied by mass spectrometric and computational methods. The results from MIKE, CAD and FT-ICR spectrometry and calculations at the B3LYP 6-311++G(3df, 3dp)//6-311G(d,p) level of theory show that the most stable adduct formed is an electrostatic HNO3·NO2+ complex where NO2+ is coordinated to the nitro group of nitric acid. Consequently, the nitro group is the energetically preferred protonation site of N2O5, whose experimental proton affinity (PA) amounts to 189.8 ± 2 kcal mol-1, vs theoretically computed values ranging from 182 to 188 kcal mol-1. Addition of NO2+ to XNO2 molecules (X = CH3O, C2H5O and NH2) also yields electrostatic complexes where the nitronium ion is coordinated to the NO2 group. The most stable [HN2O4]+ ion from the addition of NO+ to HNO3 is also identified as a cluster characterized by coordination of the nitrosonium ion to the nitro group, whose almost thermoneutral isomerization into a cluster where a nitronium ion is coordinated to the nitroso group of HNO2 is characterized by a sizable barrier. The larger PA of N2O5 than of H2O and HNO3 is of interest in atmospheric chemistry, pointing to protonation by H3O+ and/or H2NO3+ ions as the first step of the N2O5 destruction in ionic clusters and aerosols.

Nitrous and nitric acid ionisation equilibria and nitrous acid-catalysed nitration of 4-fluorophenol, in aqueous trifluoroacetic acid

The acidity dependencies of the equilibria between nitrous acid and nitrosonium ion, and between nitrate ion and nitric acid in aqueous trifluoroacetic acid (TFA) have been investigated. The decomposition of nitrous acid in air-saturated aqueous TFA has been studied and is considerably faster than in dilute HCl. Nitrous acid and 4-fluorophenol in TFA react to give quantitatively 4-fluoro-2-nitrophenol. The kinetics are shown to be consistent with the mechanism previously proposed for similar substrates in dilute aqueous acid.

The oxidation of octacyanomolybdate(IV) and octacyanotungstate(IV) by nitrous acid

The kinetics of the oxidation of octacyanomolybdate(IV) by nitrous acid has been studied in aqueous perchloric acid medium. An equilibrium concentration of the nitrosonium ion, NO +, has been proposed as the active oxidizing species. An acid dissociation constant for H[Mo(CN) 8] 3−, K a = 0.47 ± 0.05 M at 25°C and I = 1.0 M has been obtained from the kinetic data.

Mesencephalic neuron death induced by congeners of nitrogen monoxide is prevented by the lazaroid U-83836E

We explored the effects of congeners of nitrogen monoxide (NO) on cultured mesencephalic neurons. Sodium nitroprusside (SNP) was used as a donor of NO, the congeners of which have been found to exert either neurotoxic or neuroprotective effects depending on the surrounding redox milieu. In contrast to a previous report that suggests that the nitrosonium ion (NO+) is neuroprotective to cultured cortical neurons, we found that the nitrosonium ion reduces the survival of cultured dopamine neurons to 32% of control. There was a trend for further impairment of dopamine neuron survival, to only 7% of untreated control, when the cultures were treated with SNP plus ascorbate, i.e. when the nitric oxide radical (NO.) had presumably been formed. We also evaluated the effects of an inhibitor of lipid peroxidation, the lazaroid U-83836E, against SNP toxicity. U-83836E exerted marked neuroprotective effects in both insult models. More than twice as many dopamine neurons (75% of control) survived when the lazaroid was added to SNP-treated cultures and the survival was increased eight-fold (to 55% of control) when U-83836E was added to cultures treated with SNP plus ascorbate. We conclude that the congeners of NO released by SNP are toxic to mesencephalic neurons in vitro and that the lazaroid U-83836E significantly increases the survival of dopamine neurons in situations where congeners of NO are generated.

A new method for incorporation of nitroxyl radicals into the polypyrrole matrix

In presence of protons nitroxyl radicals (NR) cause polymerization of pyrrole (Py) to polypyrrole (PPy) with incorporated reduced (hydroxylamine) form and oxidized (nitrosonium ion) form of nitroxyl radical in polymer matrix. In electrochemical oxidation of pyrrole in the presence of NR a coupled electrochemical-chemical (ECH-CH) synthesis produces PPy films with incorporated nitrosonium ions. They can be reduced to NR by partial film reduction. The pattern of polymer ESR signal strongly depends on the extent of film reduction and reflects the ratio of NR and polaron concentrations. The type and the chain length of soluble pyrrole oligomers accumulated in the solution during the chemical or ECH-CH oxidation of pyrrole by NR strongly depend on the experimental conditions. At least two different radical species have been identified in the reaction mixture using UV-Vis-NIR and ESR spectroscopy.