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We have designed and synthesized three novel twistacene-modified enlarged pentagon-containing π-systems (6 and 9) with mismatched structures. The introduction of electron-withdrawing cyclopenta rings in the parent skeleton effectively stabilizes the electron-rich arenes. Their optoelectronic properties were studied via ultraviolet-visible (UV-vis) absorption spectra, fluorescence spectra, cyclic voltammetry, and density functional theory (DFT) calculation. In addition, chemical oxidation of the as-prepared compounds with nitrosonium hexafluoroantimonate could form the corresponding cationic radicals.

It is shown that the inhalation of gaseous nitric oxide (gNO) or sprayed aqueous solutions of binuclear dinitrosyl iron complexes with glutathione or N-acetyl-L-cysteine by animals or humans provokes no perceptible hypotensive effects. Potentially, these procedures may be useful in COVID-19 treatment. The NO level in complexes with hemoglobin in blood decreases as the gNO concentration in the gas flow produced by the Plazon system increases from 100 to 2100 ppm, so that at 2000 ppm more than one-half of the gas can be incorporated into dinitrosyl complexes formed in tissues of the lungs and respiratory tract. Thus, the effect of gNO inhalation may be similar to that observed after administration of solutions of dinitrosyl iron complexes, namely, to the presence of dinitrosyl iron complexes with thiol-containing ligands in lung and airway tissues. With regard to the hypothesis posited earlier that these complexes can suppress coronavirus replication as donors of nitrosonium cations (Biophysics 65, 818, 2020), it is not inconceivable that administration of gNO or chemically synthesized dinitrosyl iron complexes with thiol-containing ligands may help treat COVID-19. In tests on the authors of this paper as volunteers, the tolerance concentration of gNO inhaled within 15 min was approximately 2000 ppm. In tests on rats that inhaled sprayed aqueous solutions of dinitrosyl iron complexes, their tolerance dose was approximately 0.4 mmol/kg body weight.

A one-pot method for the synthesis of azo compounds by the reaction of β-naphthol with aryl amines using t-BuONO as the nitrosonium source in DCM at room temperature was developed. This method features mild reaction conditions, a simple experimental procedure, and is free of acidic or alkaline additives.

The present work provides theoretical and experimental foundations for the ability of dinitrosyl iron complexes (DNICs) with thiol-containing ligands to be not only the donors of neutral NO molecules, but also the donors of nitrosonium cations (NO+) in living organisms ensuring S-nitrosation of various proteins and low-molecular-weight compounds. It is proposed that the emergence of those cations in DNICs is related to disproportionation reaction of NO molecules, initiated by their binding with Fe2+ ions (two NO molecules per one ion). At the same time, possible hydrolysis of iron-bound nitrosonium cations is prevented by the electron density transition to nitrosonium cations from sulfur atoms of thiol-containing ligands, which are included in the coordination sphere of iron. It allows supposing that iron in iron–nitrosyl complexes of DNICs has a d7 electronic configuration. This supposition is underpinned by experimental data revealing that a half of nitrosyl ligands are converted into S-nitrosothiols (RSNOs) when those complexes decompose, with the other half of those ligands released in the form of neutral NO molecules.

The synthesis of phenoxazine dyes was revisited in order to access these fluorescent N,O-heterocycles under mild conditions. The combined sequential use of nitrosonium tetrafluoroborate (NOBF4) and triphenylphosphine enables the facile conversion of bis(3-dimethylaminophenyl) ether into the methyl analog of popular laser dye oxazine 1. The ability of nitrosonium cation (NO+) to initiate the domino reaction resulting in pi-conjugated phenoxazine molecules under neutral conditions, then led us to explore the feasibility of expanding it in aqueous media. Thus, we explored the use of reactive signaling molecule nitric oxide (NO) as a biological trigger of phenoxazine synthesis in water. The implementation of a robust analytical methodology based on fluorescence assays and HPLC-fluorescence/-MS analyses, have enabled us to demonstrate the viability of this novel fluorogenic reaction-based process to selectively yield an intense "OFF-ON" response in the near-infrared (NIR-I) spectral region. This study is an important step towards the popularization of the concept of "covalent-assembly" in the fields of optical sensing, bioimaging and molecular theranostics.

In this article we minutely discuss the so-called “oxidative” mechanism of mononuclear form of dinitrosyl iron complexes (M-DNICs) formations proposed by the author. M-DNICs are proposed to be formed from their building material—neutral NO molecules, Fe2+ ions and anionic non-thiol (L−) and thiol (RS−) ligands based on the disproportionation reaction of NO molecules binding with divalent ion irons in pairs. Then a protonated form of nitroxyl anion (NO−) appearing in the reaction is released from this group and a neutral NO molecule is included instead. As a result, M-DNICs are produced. Their resonance structure is described as [(L−)2Fe2+(NO)(NO+)], in which nitrosyl ligands are represented by NO molecules and nitrosonium cations in equal proportions. Binding of hydroxyl ions with the latter causes conversion of these cations into nitrite anions at neutral pH values and therefore transformation of DNICs into the corresponding high-spin mononitrosyl iron complexes (MNICs) with the resonance structure described as [(L−)2Fe2+(NO)]. In case of replacing L− by thiol-containing ligands, which are characterized by high π-donor activity, electron density transferred from sulfur atoms to iron-dinitrosyl groups neutralizes the positive charge on nitrosonium cations, which prevents their hydrolysis, ensuring relatively a high stability of the corresponding M-DNICs with the resonance structure [(RS−)2Fe2+ (NO, NO+)]. Therefore, M-DNICs with thiol-containing ligands, as well as their binuclear analogs (B-DNICs, respective resonance structure [(RS−)2Fe2+2 (NO, NO+)2]), can serve donors of both NO and NO+. Experiments with solutions of B-DNICs with glutathione or N-acetyl-L-cysteine (B-DNIC-GSH or B-DNIC-NAC) showed that these complexes release both NO and NO+ in case of decomposition in the presence of acid or after oxidation of thiol-containing ligands in them. The level of released NO was measured via optical absorption intensity of NO in the gaseous phase, while the number of released nitrosonium cations was determined based on their inclusion in S-nitrosothiols or their conversion into nitrite anions. Biomedical research showed the ability of DNICs with thiol-containing ligands to be donors of NO and NO+ and produce various biological effects on living organisms. At the same time, NO molecules released from DNICs usually have a positive and regulatory effect on organisms, while nitrosonium cations have a negative and cytotoxic effect.

Here we demonstrate that binuclear dinitrosyl iron complexes with thiol-containing ligands (glutathione and mercaptosuccinate, B-DNIC-GSH and B-DNIC-MS, respectively) exert cytotoxic effects on MCF7 human breast cancer cells. We showed that they are mediated by nitrosonium cations released from these complexes (NO+). This finding is supported by the cytotoxic effect of both B-DNICs on MCF7 cells evidenced to retain or was even promoted in the presence of N-Methyl-D-glucamine dithiocarbamate (MGD). MGD recruits an iron nitrosyl group [Fe(NO)] from the iron-dinitrosyl fragment [Fe(NO)2] of B-DNIC-MS forming stable mononitrosyl complexes of iron with MGD and releasing NO+ cations from a [Fe(NO)2] fragment.

The appropriateness of verification of the possible antiviral effect of dinitrosyl iron complexes with thiol-containing ligands as donors of nitrosonium cations (NO+) is argued. There is reason to hope that treatment of the human respiratory tract and lungs with sprayed solutions of dinitrosyl iron complexes with glutathione or N-acetylcysteine (NAC) ​​as NO+ donors during COVID-19 infection can initiate S-nitrosylation of cellular proteases and thereby suppress viral infection.

Nitrous acid (HONO) is a reservoir of NOx and an emerging pollutant having direct impacts on air quality, both in- and outdoors, as well as on human health. In this work, the amine-functionalized metal–organic framework (MOF), UiO-66-NH2, was investigated due to its potential to selectively decontaminate nitrous acid at environmentally relevant concentrations. UiO-66-NH2 proved to be effective in the removal of nitrous acid from a continuous gaseous stream. This is observed via the formation of an aryl diazonium salt that subsequently converts to a phenol with a concomitant release of nitrogen gas. This process is preceded via the formation of the nitrosonium cation (likely protonation from an acidic proton on the node). Thus, UiO-66-NH2 is capable of selectively converting the pollutant nitrous acid to benign products.

We report the synthesis of aryldiazonium tetrachloroaurate(III) salts [X-4-C6H4N≡N]AuCl4 (X = F, Cl, Br, I, CN, NO2) and their mild reduction to covalently functionalized nanoparticles. The synthesis of the salts was carried out by the oxidation of anilines, dissolved in HCl, using sodium nitrite followed by the exchange of the counter anion with [AuCl4]- in water. In another procedure, the anilines were protonated with H[AuCl4] in acetonitrile followed by one-electron oxidation using nitrosonium salt [NO]X (X = BF4−, PF6−). Raman and ATR-FTIR spectroscopy displayed the diazonium νN≡N and Raman showed the tetrachloroaurate νAu-Cl stretching frequencies. X-ray crystal structure of [NO2-4-C6H4N≡N]AuCl4 salt showed N≡N bond distance typical of a triple bond. Gold-aryl nanoparticles were constructed by the mild chemical reduction of the diazonium gold(III) salts using 9-borabicyclo[3.3.1]nonane (9-BBN). Nanoparticles hydrodynamic diameter, elemental composition, dynamics information, and stability data were determined. Transmission electron microscopy (TEM) measurements showed limited aggregation due to the small suppressing organic shell. However, dynamic light scattering (DLS) measurements showed considerable aggregation in acetonitrile. X-ray photoelectron spectrometry (XPS) showed the gold core in zero oxidation state and manifested the gold-organic shell connectivity. The –N=N-aryl interfacial formation on the gold surface can be ruled out since the N1s peak assigned to the diazonium moiety showed no sign in the XPS nitrogen area in addition to its absence in the ATR-FTIR spectra. Raman spectroscopy measurements showed a peak assigned to gold-carbon bonding supported by density functional calculations (DFT) on Au20-C6H4-CN model.

A simple yet robust flow set-up for the efficient desulfurization of a series of thioimidazoles is presented, which generates the corresponding imidazole derivatives in high yields. The strategic choice of peristaltic over piston pumps allowed reliable delivery of the heterogeneous stream of the thioimidazole substrate into a T-piece where it reacted with NaNO2 in the presence of acetic acid. This approach enabled the controlled and safe formation of the reactive nitrosonium species without uncontrolled exposure to hazardous nitrous oxide by-products as observed in related batch protocols. The value of the resulting imidazole products was further demonstrated by their conversion into various esters representing new derivatives of the known analgesic etomidate through an efficient one-pot Corey–Gilman–Ganem oxidation procedure.

Two approaches to the synthesis of dinitrosyl iron complexes (DNIC) with glutathione and l -cysteine in aqueous solutions based on the use of gaseous NO and appropriate S-nitrosothiols, viz., S-nitrosoglutathione (GS-NO) or S-nitrosocysteine (Cys-NO), respectively, are considered. A schematic representation of a vacuum unit for generation and accumulation of gaseous NO purified from the NO 2 admixture and its application for obtaining aqueous solutions of DNIC in a Thunberg apparatus is given. To achieve this, a solution of bivalent iron in distilled water is loaded into the upper chamber of the Thunberg apparatus, while the thiol solution in an appropriate buffer (рН 7.4) is loaded into its lower chamber. Further steps, which include degassing, addition of gaseous NO, shaking of both solutions and formation of the Fe 2+ -thiol mixture, culminate in the synthesis of DNIC. The second approach consists in a stepwise addition of Fe 2+ salts and nitrite to aqueous solutions of glutathione or cysteine. In the presence of Fe 2+ and after the increase in рН to the physiological level, GS-NO or Cys-NO generated at acid media (pH The pattern of spin density distribution in iron-dinitrosyl fragments of DNIC characterized by the d 7 electronic configuration of the iron atom and described by the formula Fe + (NO + ) 2 is unique in that it provides a plausible explanation for the ability of DNIC to generate NO and nitrosonium ions (NO + ) and the peculiar characteristics of the EPR signal of their mononuclear form (M-DNIC).

Carboxyl and nitrite functionalized graphene quantum dots (CNGQDs) was used for the efficient synthesis of α-oximinoketones under free mineral acid conditions at room temperature. CNGQDs was prepared via o-nitrozation of carboxyl and hydroxyl graphene quantum dots (CHGQDs) and used as a nitrosonium source and also as an efficient acidic catalyst for the synthesis of α-oximinoketones. The structure of the catalyst was characterized by FT-IR, XRD, TGA and photoluminescence techniques. The structures of the synthesized products were confirmed by FT-IR, 1H-NMR and 13C-NMR spectroscopic techniques. Stability and recyclability of the prepared homogeneous catalyst was studied in details. Reaction times and yields of the products were compared with previous reported methods resulting high yields and also shorter reaction times.

This study aimed to discover chemiluminescent analogues of luminol, understand their molecular binding to hemoglobin of bloodstains in the household crime, and the mechanism of chemiluminescence. Similarity and clustering analyses of luminol analogues were conducted, and molecular docking was carried out on hemoglobin from Homo sapiens and other four domestic organism namely Gallus gallus, Drosophila melanogaster, Rattus norvegicus, and Canis familiaris. The results show that the order of overall binding score is D. melanogaster > H. sapiens > C. familiaris > R. norvegicus > G. gallus. Seven compounds namely ZINC16958228, ZINC17023010, ZINC19915427, ZINC34928954, ZINC19915369, ZINC19915444, and ZINC82294978, were found to be consistently stable in binding to diverse hemoglobin and possibly have chemiluminescence than luminol. The amino acid residues involved in the interaction of human hemoglobin with the 30 test compounds, show that His45, Lys61, Asn68, Val73, Met76, Pro77, Ala79, Ala82, Leu83, Pro95, Phe98, Lys99, Ser102, Ser133, Ala134, and Thr134 are significant in the mechanism of action of presumptive test compounds. The improved mechanism of chemiluminescent identification of blood hypothesized that nitrite interact with the Fe(II) heme, with the cleavage of a hydroxide ion and the formation of the nitrosonium cation in peroxidase reaction. It was proposed that degradation of rhombic heme complex to fluorescent products is possibly inhibited by nitric oxide from the test compound luminol. This study provides novel insight on the luminol and its actual mechanism for broader possible applications of luminol with careful development of new methodologies.

Natural purified mordenite from Palmarito de Cauto (ZP) deposit, Cuba, was subjected to a hydrothermal ion exchange process in acid medium with Fe2+ or Fe3+ salts (Fe2+ZP and Fe3+ZP). The set of samples was characterized regarding their textural properties, morphology, and crystallinity, and tested in the NO reduction with CO/C3H6. Infrared spectroscopy coupled with NO as a probe molecule was used to give a qualitative description of the Fe species&rsquo, nature and distribution. The exchange process caused an increase in the iron loading of the samples and a redistribution, resulting in more dispersed Fe2+ and Fe3+ species. When contacted with the NO probe, Fe2+ZP showed the highest intensity of nitrosyl bands, assigned to NO adducts on isolated/highly dispersed Fe2+/Fe3+ extra-framework sites and FexOy clusters. This sample is also characterized by the highest NO sorption capacity and activity in NO reduction. Fe3+ZP showed a higher intensity of nitrosonium (NO+) species, without a correlation to NO storage and conversion, pointing to the reactivity of small FexOy aggregates in providing oxygen atoms for the NO to NO+ reaction. The same sites are proposed to be responsible for the higher production of CO2 observed on this sample, and thus to be detrimental to the activity in NO SCR.

N-Heterocyclic phosphenium (NHP) and nitro-sonium (NO+) ligands are often viewed as isolobal analogues that share the capability to switch between different charge states and thus display redox "noninnocent" behavior. We report here on mixed complexes [(NHP)M(CO)(n)(NO)] (M = Fe, Cr; n = 2, 3), which permit evaluating the donor/acceptor properties of both types of ligands and their interplay in a single complex. The crystalline target compounds were obtained from reactions of N-heterocyclic phosphenium triflates with PPN[Fe(CO)(3)(NO)] or PPN[Cr(CO)(4)-(NO)], respectively, and fully characterized (PPN = nitride-bistriphenylphosphonium cation). The structural and spectroscopic (IR, UV-vis) data support the presence of carbene-analogue NHP ligands with an overall positive charge state and pi-acceptor character. Even if the structural features of the M-NO unit were in all but one product blurred by crystallographic CO/NO disorder, spectroscopic studies and the structural data of the remaining compound suggest that the NO units exhibit nitroxide (NO-) character. This assignment was validated by computational studies, which reveal also that the electronic structure of iron NHP/ NO complexes is closely akin to that of the Hieber anion, [Fe(CO)(3)(NO)](-). The electrophilic character of the NHP units is further reflected in the chemical behavior of the mixed complexes. Cyclic voltammetry and IR-SEC studies revealed that complex [(NHP)Fe(CO)(2) (NO)] (4) undergoes chemically reversible one-electron reduction. Computational studies indicate that the NHP unit in the resulting product carries significant radical character, and the reduction may thus be classified as predominantly ligand-centered. Reaction of 4 with sodium azide proceeded likewise under nucleophilic attack at phosphorus and decomplexation, while super hydride and methyl lithium reacted with all chromium and iron complexes via transfer of a hydride or methyl anion to the NHP unit to afford anionic phosphine complexes. Some of these species were isolated after cation exchange or trapped with electrophiles (H+, SnPh3(+)) to afford neutral complexes representing the products of a formal hydrogenation or hydrostannylation of the original M=P double bond.

Nitrosonium ions are versatile and mild oxidants, which were successfully employed in organic transformations. The applications cover different fields, such as the functionalization of carbon-carbon and carbon-heteroatom bonds, functionalization of unsaturated bonds and the oxidative coupling of arenes, catalyzed by nitrosonium ions. Due to the ability of nitrosonium ions to modify various types of bonds with different modes of action, a variety of applications has been established, which addresses current challenges in organic chemistry research. By considering additional points, such as safety of reagents, by-product formation, employed solvents and energy consumption, several aspects of green and sustainable chemistry can be addressed. Within this review, synthetic applications of nitrosonium ions under transition metal-free reaction conditions are summarized.

Solar emission produces copious nitrosonium ions (NO(+)) in the D layer of the ionosphere, 60 to 90 km above the Earth's surface. NO(+) is believed to transfer its charge to water clusters in that region, leading to the formation of gaseous nitrous acid (HONO) and protonated water cluster. The dynamics of this reaction at the ionospheric temperature (200-220 K) and the associated mechanistic details are largely unknown. Using ab initio molecular dynamics (AIMD) simulations and transition-state search, key structures of the water hydrates-tetrahydrate NO(+)(H2O)4 and pentahydrate NO(+)(H2O)5-are identified and shown to be responsible for HONO formation in the ionosphere. The critical tetrahydrate NO(+)(H2O)4 exhibits a chain-like structure through which all of the lowest-energy isomers must go. However, most lowest-energy isomers of pentahydrate NO(+)(H2O)5 can be converted to the HONO-containing product, encountering very low barriers, via a chain-like or a three-armed, star-like structure. Although these structures are not the global minima, at 220 K, most lowest-energy NO(+)(H2O)4 and NO(+)(H2O)5 isomers tend to channel through these highly populated isomers toward HONO formation.

The formation of electron donor-acceptor complexes is studied with global and local charge transfer partitionings. The 1-parabola model is applied to the bromination reaction of alkenes and the correlations found between the global and local charge transferred with the transition energy of the charge transfer bands and the kinetic rate constants indicate that the nucleophilic attack of alkenes to bromine is the electronic process controlling the reactivity in the formation of the electron donor-acceptor complexes in this reaction. The 2-parabolas model is used in studying the nitrosation of aromatic compounds where colorful electron donor-acceptor complexes are formed. In this case, and like previous applications of the 2-parabolas model, the consistent usage of the model mandates the explicit consideration of reaction conditions in preparing the reactants to have a direction of electron transfer that is consistent with the chemical potential differences. For the nitrosation reaction this implies considering the nitrosonium cation as the charge acceptor. Both applications support that the charge transferred predicted from chemical reactivity models can be used as a scale to measure the nucleophilicity in reactivity trends. Graphical Abstract ᅟ.

The susceptibility of the nitrosonium ligand (NO+) of metal nitrosyls to nucleophilic attack has been reviewed. The reactions of nitroprusside with thiolate (RS−) nucleophiles (H2S, cysteine, glutathione, N-acetylcysteine and others) have been covered, albeit the main focus is on the reactivity of ruthenium nitrosyl ammines (trans-[Ru(NH3)4(L)NO+]n+) with cysteine and glutathione. Kinetic aspects and reaction products are discussed. Nitric oxide (NO) and nitroxyl (HNO) are the primary and main nitrogen-based products of the reactions with RS−. The final nitrogen based product N2O is identified and suggested as the direct product from the dimerization reaction of HNO. The accumulated data strongly suggest that the ratio of [NO]/[HNO] formed is dependent on the [RS−]/[RSH] ratio, which can be controlled by the experimental conditions. Some aspects of thiol-responsive nitric oxide-releasing materials are also discussed.

We report a mechanistic DRIFTS in-situ study of NO2, NO + O2 and NO adsorption on a commercial Cu-CHA catalyst for NH3-SCR of NOx. Both pre-reduced and pre-oxidized catalyst samples were investigated with the aim of clarifying mechanistic aspects of the NO oxidation to NO2 as a preliminary step towards the study of the Standard SCR reaction mechanism at low temperatures. Nitrosonium cations (NO+, N formal oxidation state = +3) were identified as key surface intermediates in the process of NO (+2) oxidation to NO2 (+4) and nitrates (+5). While NO+ and nitrates were formed simultaneously upon catalyst exposure to NO2, nitrates evolved consecutively to NO+ when the catalyst was exposed to NO + O2, suggesting that nitrite-like species, and not NO2, are formed as the primary products of the NO oxidative activation over Cu-CHA. Upon catalyst exposure to NO only, i.e. in the absence of gaseous O2, NO+ and then nitrates were formed on a pre-oxidized sample but not on a pre-reduced one, which demonstrates the red-ox nature of the NO oxidation mechanism. The negative effect of H2O on NO+ and nitrates formation was also clearly established. Assuming Cu dimers as the active sites for NO oxidation to NO2, we propose a mechanism which reconciles all the experimental observations. In particular, we show that such a mechanism also explains the observed kinetic effects of H2O, O2 and NO2 on the NO oxidation activity of the investigated Cu zeolite catalyst.

The development of rechargeable Ca-ion batteries as an alternative to Li systems has been limited by the availability of suitable electrolyte salts. We present the synthesis of complexes of Ca(PF6)2 (a key potential Ca battery electrolyte salt) via the treatment of Ca metal with NOPF6, and explore their conversion to species containing PO2F2− under the reaction conditions.

The Na2[Ru(NO)Cl3 (df)] (I) and cis-[Ru(NO)(df)(cyclen)]Cl2 (II) complexes (df=diflunisal (5-(2,4-difluorophenyl)-2-hydroxybenzoic acid, cyclen=1, 4, 7, 10-tetraazacyclododecane) have been synthesized and characterized by elemental analysis, electronic (UV-Vis) and vibrational (FTIR) spectroscopic techniques. FTIR data suggests different modes of coordination of the ligand diflunisal in these complexes, i.e., coordinated in the bidentate form in the compound I and in the monodentate form in the compound II, and that df is coordinated to ruthenium by carboxylate group in a monodentate mode for both complexes. The FTIR spectra also display v(NO) at 1880 cm-1 and 1892 cm-1 for I and II, respectively, indicating a nitrosonium (NO+) character. Electronic spectra suggest that df is coordinated to the metal center in both complexes in catecholate form. Detailed electrochemical studies showed that complexes I and II display {RuNO}6/7 process at -420 mV and at -400 mV (vs. Ag/AgCl) respectively, and df ligand is oxidized at 1120 mV and at 770 mV, respectively. Controlled potential electrolysis at -750 mV or chemical reduction with Zn(Hg) amalgam results in NO release from both complexes.

The reduction of trans- [Ru(NO)(NH 3 ) 4 (P(OEt) 3 )] 3+ ion was investigated in aqueous medium. Due to the phosphite ligand trans -effect and trans -influence, this complex selectively releases NO or HNO after one or two electrons reduction centered at the nitrosonium ligand (NO + ). These reactions were carried out through electrochemical reduction and using Eu 2+ and zinc amalgam, and the products were identified using electrochemical and spectroscopic techniques. Only the reduction of the nitrosonium ligand to nitric oxide is observed when europium is used as reductant. When the reaction is carried out with Zn(Hg), nitric oxide formation was not observed and N 2 O, an indirect marker of HNO, is detected in solution.

The B3LYP density functional method with the expanded 6-311++G(3df,3pd) basis was used to calculate the energy profiles of the reaction 2NO2 + H2O→HNO2 + HNO3 in the gas phase and in the presence of water. The acid formation process should proceed through prior dimerization of ∙NO2 radicals to give an asymmetrical trans isomer of ONONO2 in the rate-limiting step with subsequent formation of nitrosonium nitrate $ {\mathrm{N}}{{\mathrm{O}}^{+} }{\mathrm{NO}}_3^{-} $ .

The cis to trans isomerizations during the syntheses of trans-[Ru(NO)(OH)(cyclam)](PF6)2, from cis-[RuCl2(cyclam)]Cl, and [Ru(NO)Cl(cyclam)] (PF6)2, from cis-[RuCl2(dmso)4], are reported. The novel trans-[Ru(NO)(OH)(cyclam)](PF6)2 complex was characterized by X-ray crystallography and vibrational infrared and nuclear magnetic resonance spectroscopies. The Ru–N–O bond angle (176.75o) and ν(NO) (1835 cm− 1) suggest a nitrosonium character for this hydroxo complex. The crystal and molecular structure of trans-[Ru(NO)Cl(cyclam)](ClO4)2·2 H2O is also reported. Results presented here support the cis–trans isomerization observed for the first time with ruthenium cyclam complexes.

An improved method for the synthesis of nitrosoarenes has been developed using a new nitrite ionic liquid (IL-ONO) and immobilized nitrite ionic liquid. These ionic liquids play as nitrosonium sources for electrophilic aromatic nitrosation of active aromatics at 0–5 °C. Their action was accomplished in water and the satisfactory results were obtained under the mild conditions in short reaction time.

[Bmim]NO 2 /H 3 BO 3 was used as a nitrosonium source for the efficient synthesis of nitrosoarenes. The reaction was accomplished under MW irradiation at 60 W in a solventless system. Side processes such as oxidation or dealkylation were not observed during the nitrosation of alkyl phenyl ethers in the presence of this new reagent. The satisfactory results were obtained with very short reaction time, simplicity in the experimental procedure and good to excellent yields.

A new ionic liquid 1-(3-trimethoxysilylpropyl)-3-methylimidazolium nitrite was synthesized. This ionic liquid was used as a convenient nitrosonium source in diazotization of arylamines into their corresponding diazonium salts which were converted into their related azo dyes via the in situ azo-coupling with aniline derivatives or phenolic compounds. The diazotization of anilines in this ionic liquid and subsequent azo-coupling generated the related azo dyes in good to excellent yields at 0–5 °C in short reaction times via a simple experimental procedure.

Efficient transformation of alcohols to the corresponding aldehydes is an important process in organic synthesis and industry. In the absence of transition metal ion, an acid-activated NO x has been explored for the catalytic oxidation of benzyl alcohol. Under the optimal conditions, 95% yield of benzyl aldehyde could be achieved at room temperature with dioxygen as the terminal oxidant. The reaction mechanism was investigated through UV–visible spectrometry and cyclic voltammetry, and the key active species for oxidation have been assigned to the nitrosonium cation.

It's the Network Numerous reactions of small molecules and ions in the atmosphere take place in the confines of watery aerosols. Relph et al. (p. 308 ; see the Perspective by Siefermann and Abel ) explored the specific influence of a water cluster's geometry on the transformation of solvated nitrosonium (NO + ) to nitrous acid (HONO). The reaction involves (O)N–O(H) bond formation with one water molecule, concomitant with proton transfer to additional, surrounding water molecules. Vibrational spectroscopy and theoretical simulations suggest that certain arrangements of the surrounding water network are much more effective than others in accommodating this charge transfer, and thus facilitating the reaction.

This work reviews the use of pyrrole, chloroform, methanol, as well as methoxy and nitrosonium groups generated ‘in situ’, as infrared and NMR probe molecules to characterize zeolites basicity. The main results reported in the bibliography about the correlation of the spectroscopic properties of the adsorbed molecule with the framework basicity, the host–guest interactions, and the limitations in the use of these molecules as probes for zeolite basicity are discussed. Special attention is paid to the results reported for the adsorption of pyrrole and halocarbons, most specially CHCl3 and CHClF2 over alkali-exchanged FAU-type zeolites using IR and NMR spectroscopies.

The specific behavior of HY in some steps that possibly occurred in the selective catalytic reduction of NO by hydrocarbon (HC-SCR) was investigated. Experimental results indicated that the activity of HY for NO oxidation to NO 2 was much lower than those of the pentasil zeolites (HZSM-5, HFER and HMOR). In addition, FTIR measurements showed that both nitrosonium ions (NO + ) and nitrate species were remarkably produced at 300 °C over the pentasil zeolites and they were highly active towards hydrocarbons at the temperature. On the contrary, no NO + species could be detected over HY and the nitrate species produced over the zeolite were almost inactive towards reduction at the same reaction condition. It is proposed that the low amount of strong Bronsted acids of HY accounts for the above inferior founctions of the zeolite required by HC-SCR, leading to the low NO reduction activity.

Selective catalytic reduction of NO with acetylene (C2H2-SCR) over mordenite-based catalysts (HMOR, 0.5% Mo/HMOR and NaMOR) was investigated by in situ Fourier transform infrared spectroscopy. A possible mechanism was proposed to explain catalytic performance of the mordenite-based catalysts in the C2H2-SCR: Nitrosonium ions (NO+) and bidentate nitrate are reactive nitric species towards acetylene at 250 °C. Isocyanate species thus formed are then hydrolyzed to acid amide species that are crucial intermediate of the C2H2-SCR. Bridging nitrate species become reactive towards the reductant when reaction temperature increased to 300 °C. Molybdenum loading on HMOR zeolite considerably increased the population of bridging nitrate species and therefore enhanced the title reaction above 300 °C.

The geometric, electronic, and thermodynamic parameters of six known isomers of the molecular structure of dinitrogen tetraoxide N2O4 were calculated by the quantum-chemical DFT/B3LYP density functional method with the 6-311++G(3df) basis set. The structure of a new isomer of dinitrogen tetraoxide NONO3, which is characterized by a local potential energy minimum and corresponds to a stationary state of the N2O4 isomer, was calculated. The DFT calculations showed that this structure NONO3 is characterized by a significant negative charge on the NO3 fragment and a positive charge on the NO fragment. The calculated dipole moment of nitrosonium nitrate NO+NO 3 − in the gas phase is 4.13 D.

The interaction of benzoate-type ultraviolet absorbers (UVA) with hindered amine light stabilizers (HALS) was investigated. Benzoate-type UVA showed antagonism or synergism with HALS, depending on the chemical structures of the UVA. p-Aminobenzoates exhibited antagonism with HALS to accelerate the photo-oxidation, despite absorbing UV rays with considerably high absorption coefficients. In contrast, p-hydroxybenzoates showed synergistic photo-antioxidant activity with HALS, despite no or little absorption of ultraviolet rays. The synergism has been ascribed to conversion into benzophenone-type UVA by a photo-Fries rearrangement. This mechanism can explain the photo-antioxidant ability of substituted phenyl p-hydroxybenzoates, but not that of alkyl p-hydroxybenzoates not undergoing the photo-Fries rearrangement. This study proposes a new and comprehensive synergism in which the photo-antioxidant activity of p-hydroxybenzoate is due to the formation of a UV-absorbing intermediate and a photo-antioxidant compound with a catechol structure from the reaction of the benzoate with HALS nitrosonium.

Plants transmit a variety of signaling molecules from roots to aerial parts, and vice-versa, in response to their growth conditions (environment, nutrients, stress factors etc.). A signaling molecule should be produced quickly, induce a defined effect within the cell and be removed or metabolized rapidly when not required. Nitric oxide (NO) plays significant signaling roles in plant cells since it has all the above-stated features. It is a gaseous free radical, can gain or lose an electron, has short half-life (I´ 30 sec) and it can exist in three interchangeable forms, namely the radical (NO•), the nitrosonium cation (NO+) and as nitroxyl radical (NO). NO is soluble in aqueous as well as lipid phases. It rapidly reacts with oxygen to form NO2 and can react with other potential signaling molecules as well (eg. superoxide anions (O2•¯). In the recent past, NO has been observed to regulate various growth and developmental processes.

This chapter is aimed at providing an overview of the up-to-now published literature on resorc[4]arene macrocycles exploited as artificial receptors for surface recognition and host-guest chemistry. A concise illustration of the main synthetic strategies developed to afford the resorc[4]arene scaffold is followed by a report on the principles of the investigation of recognition phenomena by nuclear magnetic resonance (NMR), in particular the study of protein-small molecule interactions. Emphasis will be placed on the literature taken largely from our own works on the inhibition of chymotrypsin by suitable N-linked peptidoresorc[4]arenes. Then, the attention was moved towards host-guest studies relying on the entrapment of nitrosonium (NO+) cation inside the cavities of ad hoc functionalized resorc[4]arenes, which yielded both complexes and covalent products. Finally, some recent intriguing resorc[4]arene architectures built up by olefin metathesis reaction occurring between side chains ending with vinylidene groups are presented.

Gas-phase nitrosation of amines implies a nonionic pathway different from the nitrosonium nitrosation via acidification of nitrite. Electronic structure calculations discussed in this work suggest a free radical mechanism, in which NO2 abstracts a hydrogen atom from the nitrogen in primary and secondary amines to form an intermediate complex of an aminyl radical and nitrous acid. The aminyl radical intermediate is then quenched by nitric oxide, leading to the formation of nitrosamine. High-level calculations (CBS-QB3) show that alkyl substitutions on amines can activate the H-abstraction reaction. Thus, while H-abstraction from NH3 was found to exhibit a reaction barrier (DeltaH) of 106 kJ/mol, similar calculations indicate that the corresponding barriers decrease to 72 and 45 kJ/mol for methylamine and dimethylamine, respectively. Heterocyclic secondary amines have also been investigated in a similar manner. The five-membered-ring (5-m-r) amine appears to be the most reactive: pyrrolidine (DeltaH=30 kJ/mol), azetidine (DeltaH=44 kJ/mol), piperidine (DeltaH=44 kJ/mol), and aziridine (DeltaH=74 kJ/mol). The reaction barrier for 1H-pyrrole, an aromatic 5-m-r secondary amine, was found to be 59 kJ/mol. The origin of the high activity for the 5-m-r alkylamine stems from a hydrogen-bond-like interaction between the aminyl radical and the nascent nitrous acid molecule. This theoretical study suggests that, in the presence of nitrogen oxides, the gas-phase nitrosation of secondary amines is feasible.

The antagonism between nitroxides of hindered amine light stabilizers (HALS NO) and phenolic antioxidants, such as 2,6-di-t-butyl-4-methylphenol (BHT), was investigated. Identification of the reaction products of HALS NO and BHT clarified the formation of HALS hydroxylamine (HALS NOH) and HALS amine (HALS NH) by the reduction of HALS NO, and the formation of quinone methide and stilbene quinone by the oxidation of BHT. The identification of these products in the reaction of HALS NO with BHT suggests a new antagonism between HALS NO and BHT: two molecules of HALS NO form HALS nitrosonium by electron transfer. The nitrosonium has strong oxidation power, and uselessly oxidizes a phenol such as BHT to quinone methide and finally stilbene quinone, while the nitrosonium and HALS NO are reduced to HALS NOH and HALS NH.

The effect of acidic compound on the formation of active species in homolytic hydroperoxide decomposition by hindered amine light stabilizers (HALS) was studied. The hydroperoxide decomposition activity of HALS is an important to characteristics of HALS. HALS Ammonium salt, which is a fundamental compound involved in the antagonism between HALS and acidic compounds including phenolic antioxidants, was found to be a key compound for the formation of HALS nitrosonium salt, which was identified as the active species of hydroperoxide decomposition. HALS Nitrosonium salt was not formed from active species for polymer stabilization, such as nitroxide, alkoxide, or hydroxylamine of HALS, but from HALS salt. A formation mechanism of HALS nitrosonium salt is proposed. Furthermore, molecular aggregates formed between HALS and acid compounds are discussed to be important for HALS properties.

[reaction: see text] Alpha-tocopherol (alpha-TOH), the main oil component making up vitamin E, and its nonnatural solid 6-hydroxy-2,2,5,7,8-pentamethylchroman and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid structurally related analogues were oxidized quantitatively with 2 mol equiv of NO+ SbF6(-) in CH3CN at 233 K to form phenoxonium cations (alpha-TO+ SbF6(-)) in a chemically reversible two-electron/one-proton process. Solution-phase infrared spectroscopy, 1H and 13C NMR spectroscopy, and corresponding theoretical calculations of the spectroscopic data using density-based and wave-function-based models support the identity of the remarkably stable phenoxonium cations. The presence of an oxygen atom in the para position to the hydroxyl group and the chromanol ring structure appear to be important factors in stabilization of the phenoxonium ions, which raises the interesting possibility that the cations play a crucial role in the mode of action of vitamin E in biological systems. Although the phenoxonium cations are reactive toward nucleophiles such as water, they may be moderately stable in the hydrophobic (lipophilic) environment where vitamin E is known to occur naturally.

The decomposition of S-nitrosothiols (RSNO) in solution under oxidative conditions is significantly faster than can be accounted for by homolysis of the S-N bond. Here we propose a cationic chain mechanism in which nitrosation of nitrosothiol produces a nitrosated cation that, in turn, reacts with a second nitrosothiol to produce nitrosated disulfide and the NO dimer. The nitrosated disulfide acts as a source of nitrosonium for nitrosothiol nitrosation, completing the catalytic cycle. The mechanism accounts for several unexplained facets of nitrosothiol chemistry in solution, including the observation that the decomposition of an RSNO is accelerated by O(2), mixtures of O(2) and NO, and other oxidants, that decomposition is inhibited by thiols and other antioxidants, that decomposition is dependent on sulfur substitution, and that decomposition often shows nonintegral kinetic orders.

The reactivity of a nitrosating agent (N2O3) on oxidations of alcohols and the methyl group of acetophenone were tested. Active electrophylic surface nitrosonium ions (NO+) was detected on H2SO4/SiO2 catalysts by Raman spectroscopy, suggesting a surface ionic mechanism of oxidation in agreement with the one proposed in acid aqueous solutions. Alcohols are selectively oxidized to ketones and aldehydes in high yield, useful for synthetic applications, at 25 °C in 1,2-dichlorethane and using commercial sulfonated styrene divinyl benzene resins (Amberlyst 15®) as catalysts. In addition, nitrous acid ester has been observed as intermediates according to an ionic mechanism by surface NO+. Under the same reaction conditions, acetophenone is selectively oxidized to benzoyl cyanide in high yield and selectivity. The comparison with oxidation carried out in aqueous solution of HNO2, where benzoyl formic acid was obtained, suggests that the differences in the final products are likely due to the specific stabilizing effect of each solvent. Moreover, the reactivity of the intermediates isolated in aqueous systems implies that α-nitroso-acetophenone is a probable reaction intermediate also in aprotic heterogeneous systems.

2-(4-Azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (14), 2-(4-azidophenyl)benzimidazole-1-oxide-3-oxyl (16), 2-(4-azidophenyl)-1,2,6-triphenylverdazyl (19), 2-(3-azidophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (21), and (3-azidophenyl)-N-tert-butyl-N-aminoxyl (25) were photolyzed in frozen solution to give S = 3/2 state ESR spectra of the corresponding nitrenophenyl radicals with the following zero-field splitting parameters: |D/hc| = 0.277 cm(-1), |E/hc| < or = 0.002 cm(-1) (7 from 14); |D/hc| = 0.256 cm(-1), |E/hc| < or = 0.002 cm(-1) (8 from 16); |D/hc| = 0.288 cm(-1), |E/hc| < or = 0.002 cm(-1) (9 from 19); |D/hc| = 0.352 cm(-1), |E/hc| = 0.006 cm(-1) (10 from 21); |D/hc| = 0.336 cm(-1), |E/hc| = 0.004 cm(-1) (11 from 25). UB3LYP/6-31G computations and ESR spectroscopic analyses suggest that these are nitreno radicals, even para-linked systems with possible quinonoidal resonance forms. Neat samples of azidophenyl radicals 14 and 21 showed bulk paramagnetic behavior, consistent with the lack of close contacts in their crystal structures. Efforts to make photolabile coordination complexes of 14 and 21 with paramagnetic transition metal ions were unsuccessful: Cu(ClO4)2 x 6H2O instead oxidized them to the corresponding diamagnetic nitrosonium perchlorate salts.

A selected ion flow tube (SIFT) study has been carried out of the reactions of hydrated nitrosonium ions, NO+H2O, which theory has equated to protonated nitrous acid ions, H2ONO+. One objective of this study was to investigate if this ion exhibits the properties of both a cluster ion and a protonated acid in their reactions with a variety of organic molecules. The chosen reactant molecules comprise two each of the following types—amines, terpenes, aromatic hydrocarbons, esters, carboxylic acids, ketones, aldehydes and alcohols. The reactant H2ONO+ (NO+H2O) ions are formed in a discharge ion source and injected into helium carrier gas where they are partially vibrationally excited and partially dissociated to NO+ ions. Hence, the reactions of the H2ONO+ ions had to be studies simultaneously with NO+ ions, the reactions of the latter ions readily being studied by selectively injecting NO+ ions into the carrier gas. The results of this study indicate that the H2ONO+ ions undergo a wide variety of reaction processes that depend on the properties of the reactant molecules such as their ionisation energies and proton affinities. These processes include charge transfer with compounds, M, that have low ionisation energies (producing M+), proton transfer with compounds possessing large proton affinities (MH+), hydride ion transfer (MH+), alkyl radical (MR+), alkoxide radical transfer (MOR+), ion–molecule association (NO+H2OM) and ligand switching (NO+M), producing the ions given in parentheses.

[reaction: see text] A novel class of stable, mild, and size-shape-selective nitrosating agents for secondary amides is introduced. These are based on reversible entrapment and release of reactive nitrosonium species by calix[4]arenes. The NO(+) encapsulation controls the reaction selectivity.