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Fluorescent probes for nitric oxide (NO), or more frequently for its oxidized surrogate dinitrogen trioxide (N2O3), have enabled scientists to study the contributions of this signaling molecule to many physiological processes. Seeking to improve upon limitations of other probes, we have developed a family of fluorescent probes based on a 2-amino-3′-dialkylaminobiphenyl core. This core condenses with N2O3 to form benzo[c]cinnoline structures, incorporating the analyte into the newly formed fluorophore, which results in product fluorescence with virtually no background contribution from the initial probe. We varied the substituents in the core in order to optimize both the reactivity of the probes with N2O3 and their cinnoline products' fluorescence wavelengths and brightness. The top candidates were then applied to cultured cells to verify that they could respond to NO within cellular milieus, and the top performer, NO530, was compared with a “gold standard” commercial probe, DAF-FM, in a macrophage-derived cell line, RAW 264.7, stimulated to produce NO. NO530 demonstrated similar or better sensitivity and higher selectivity for NO than DAF, making it an attractive potential alternative for NO tracking in various applications., A thorough structure-property relationship study has produced much-improved fluorescence probes for nitric oxide surrogate, e.g. N2O3, compared to the original NO550.

Dinitrogen trioxide is proposed as a precursor to forming nitrous acid, an important source of hydroxyl radicals in the atmosphere. The spectroscopy and properties of N2O3 have been studied at high pressures or low temperatures, but there are no reports of its gas-phase photodissociation. This study investigates the 355 nm photodissociation of N2O3 in a DC-sliced velocity-mapped ion imaging apparatus using linearly polarized nanosecond pump and probe lasers. The N2O3 sample was generated by expanding NO and NO2 seeded in a He carrier gas. After photodissociation, a high fraction of the available energy ends up in translation of the products. Time-dependent density functional theory calculations confirm the parallel transition dipole assignment if the dissociation occurs from a nonplanar N2O3 conformation. The vector correlations are nearly at the physical limits for a system where μ||v⊥J. The DC-sliced velocity-mapped ion imaging technique is well-suited to investigate N2O3 photodissociation since it resolves product speeds and differentiates among the sources of NO+ in an expansion containing NO, NO2, HONO, and N2O3.

A two-step procedure for preparing N-nitrosodimethylamine by direct nitrosation of aqueous solutions of dialkylamines with dinitrogen dioxide was suggested. The first step involves preparation of dialkylammonium nitrite, and in the second step, on heating to 70–90°С in a weakly acidic solution, it transforms into N-nitrosodialkylamine. The yield of N-nitrosodialkylamines is 95–98% based on the converted dialkylamine. A low-waste process for N-nitrosodimethylamine production was developed.

Dinitrogen trioxide, N2O3, is readily prepared and stabilized in high concentrations in dry organic solvents at normal working temperatures. These conditions allow for facile acid and water free nitrosation and nitration reactions for which three examples are given here: the preparation of benzenediazonium nitrite, [PhN2][NO2]; nitrosyl chloride, NOCl, and nitrosylsulfuric acid, (ONOSO3H).

The free radical nitric oxide (NO) exerts biological effects through the direct and reversible interaction with specific targets (e.g. soluble guanylate cyclase) or through the generation of secondary species, many of which can oxidize, nitrosate or nitrate biomolecules. The NO -derived reactive species are typically short-lived, and their preferential fates depend on kinetic and compartmentalization aspects. Their detection and quantification are technically challenging. In general, the strategies employed are based either on the detection of relatively stable end products or on the use of synthetic probes, and they are not always selective for a particular species. In this study, we describe the biologically relevant characteristics of the reactive species formed downstream from NO , and we discuss the approaches currently available for the analysis of NO , nitrogen dioxide (NO2 ), dinitrogen trioxide (N2O3), nitroxyl (HNO), and peroxynitrite (ONOO /ONOOH), as well as peroxynitrite-derived hydroxyl (HO) and carbonate anion (CO3) radicals. We also discuss the biological origins of and analytical tools for detecting nitrite (NO2), nitrate (NO3), nitrosyl–metal complexes, S-nitrosothiols, and 3-nitrotyrosine. Moreover, we highlight state– of–the–art methods, alert readers to caveats of widely used techniques, and encourage retirement of approaches that have been supplanted by more reliable and selective tools for detecting and measuring NO -derived oxidants. We emphasize that the use of appropriate analytical methods needs to be strongly grounded in a chemical and biochemical understanding of the species and mechanistic pathways involve Agencia Nacional de Investigación e Innovación FCE_1_2017_1_136043 Comisión Sectorial de Investigación Científica (CSIC) Universidad de la República. Espacio Interdisciplinario

The current perspective holds that the generation of secondary signaling mediators from nitrite (NO2(-)) requires acidification to nitrous acid (HNO2) or metal catalysis. Herein, the use of stable isotope-labeled NO2(-) and LC-MS/MS analysis of products reveals that NO2(-) also participates in fatty acid nitration and thiol S-nitrosation at neutral pH. These reactions occur in the absence of metal centers and are stimulated by autoxidation of nitric oxide ((•)NO) via the formation of symmetrical dinitrogen trioxide (nitrous anhydride, symN2O3). Although theoretical models have predicted physiological symN2O3 formation, its generation is now demonstrated in aqueous reaction systems, cell models and in vivo, with the concerted reactions of (•)NO and NO2(-) shown to be critical for symN2O3 formation. These results reveal new mechanisms underlying the NO2(-) propagation of (•)NO signaling and the regulation of both biomolecule function and signaling network activity via NO2(-)-dependent nitrosation and nitration reactions.

4-Nitrofuroxans (4-nitro-1,2,5-oxadiazole 2-oxides) were prepared by a dinitrogen trioxide–mediated domino reaction of acrylic acids under the action of NaNO2 excess in AcOH at room temperature. The reaction proceeds completely regioselectively and presents a new, simple, general, and safe method for the preparation of both 3-aryl- and 3-alkyl-4-nitrofuroxans available with difficulty before. A mechanism for the furoxan ring construction through a four-step one-pot protocol is proposed. The synthesized nitrofuroxans have been characterized by multinuclear NMR spectroscopy and X-ray powder diffraction.

Biological nitrogen oxide signalling and stress is an area of extreme clinical, pharmacological, toxicological, biochemical and chemical research interest. The utility of nitric oxide and derived species as signalling agents is due to their novel and vast chemical interactions with a variety of biological targets. Herein, the chemistry associated with the interaction of the biologically relevant nitrogen oxide species with fundamental biochemical targets is discussed. Specifically, the chemical interactions of nitrogen oxides with nucleophiles (e.g. thiols), metals (e.g. hemeproteins) and paramagnetic species (e.g. dioxygen and superoxide) are addressed. Importantly, the terms associated with the mechanisms by which NO (and derived species) react with their respective biological targets have been defined by numerous past chemical studies. Thus, in order to assist researchers in referring to chemical processes associated with nitrogen oxide biology, the vernacular associated with these chemical interactions is addressed.

Nitrosation of thiols is thought to be mediated by dinitrogen trioxide (N 2 O 3 ) or by nitrogen dioxide radical ( NO 2 ). A kinetic study of glutathione (GSH) nitrosation by NO donors in aerated buffered solutions was undertaken. S -nitrosoglutathione (GSNO) formation was assessed spectrophotometrically and by chemiluminescence. The results suggest an increase in the rate of GSNO formation with an increase in GSH with a half-maximum constant EC 50 that depends on NO concentration. Our observed increase in EC 50 with NO concentration suggests a significant contribution of NO 2 -mediated nitrosation with the glutathiyl radical as an intermediate in the production of GSNO.

Nitration of arachidonic and linoleic acids was performed with nitronium tetrafluroborate, nitrogen dioxide, and dinitrogen trioxide. The nitro compounds were separated on HPLC and characterized further on mass spectrometry. Formation of nitro arachidonic acid m/z 348 and nitro linoleic acid m/z 324 were observed with all the reagents. Interestingly, MS/MS of nitro AA and nitro LA showed specific ions m/z 142, m/z 193, and m/z 206 for nitro arachidonic and m/z 156 and m/z 196 for linoleic acid that were common in all three reactions.

Since oxidative/nitrosative stress cause diabetes, can we prevent this chemistry generating the disease? Streptozotocin causes diabetes by entering the pancreatic beta cell generating excessive nitric oxide which reacts with oxygen creating a toxin possibly peroxynitrite, dinitrogen trioxide, dinitrogen tetraoxide and so forth. The toxic compounds damage the DNA causing beta cell death. This prevents insulin synthesis, storage and release. By using antioxidant substances that destroy the nitric-oxide-based toxins (e.g., carboxy-PTIO (oxidizes nitric oxide), polyphenolic-quercetin and monophenolic acetaminophen (Tylenol)) which are oxidation and nitration targets can the diabetes I causing toxins in animals be destroyed? Will this tri-drug combination completely prevent the deleterious effects of diabetes namely poor blood glucose control and blindness from cataracts for the entire length of the experiment (one year). These disease reversal experiments were accomplished in rats where the streptozotocin-diabetic effects were completely thwarted. In vitro experiments were accomplished to provide the scientific basis for the experimental results in animals.

The kinetics of synthesizing methyl nitrite via the gas–liquid reaction of N2O3 with methanol was studied in a double-stirred cell reactor with a plane, horizontal gas–liquid interface, in the temperature range of 278–298 K. Since N2O3 is stable only below 0 °C, a mixture of NO and NO2 with the ratio of 1:1 behaves chemically like N2O3 and replaces it. The Henry's constants and diffusion coefficients of NO and NO2 in the liquid phase were estimated, and it was found that the generating rate of methyl nitrite was only affected by the partial pressure of NO in the gas phase. The reaction between N2O3 and methanol was fast pseudo-first order, and a kinetic equation was obtained as follows: R MN = 2 P NO H NO C 0 D NO × 6.546 × 10 9 exp − 57 , 416 R T × C 0

The geometrical, electronic, and thermodynamic parameters of three known isomers of dinitrogen trioxide N2O3 were calculated by the density functional theory DFT/B3LYP method using the 6-311++G(3df) basis. The structure of the new isomer, NONO2, was calculated. From the calculation of vibrational frequencies it follows that the structure of NONO2 has a local potential energy minimum and corresponds to the stationary state of the N2O3 isomer. The molecular structure of NONO2 is characterized by a substantial negative charge on the NO2 fragment and positive charge on the NO fragment. The electronic structure of the NO+NO 2 − isomer can be characterized as nitrosonium nitrite, which can be oxidized to nitrite and participate in nitrosylation in accordance with the biogenic characteristics of the NO x intermediate, assumed to be formed in biological systems during the oxidation of NO.

Nitrite reacts with deoxyhemoglobin to form nitric oxide (NO) and methemoglobin. Though this reaction is experimentally associated with NO generation and vasodilation, kinetic analysis suggests that NO should not be able to escape inactivation in the erythrocyte. We have discovered that products of the nitrite-hemoglobin reaction generate dinitrogen trioxide (N2O3) via a novel reaction of NO and nitrite-bound methemoglobin. The oxygen-bound form of nitrite-methemoglobin shows a degree of ferrous nitrogen dioxide (Fe(II)-NO2*) character, so it may rapidly react with NO to form N2O3. N2O3 partitions in lipid, homolyzes to NO and readily nitrosates thiols, all of which are common pathways for NO escape from the erythrocyte. These results reveal a fundamental heme globin- and nitrite-catalyzed chemical reaction pathway to N2O3, NO and S-nitrosothiol that could form the basis of in vivo nitrite-dependent signaling. Because the reaction redox-cycles (that is, regenerates ferrous heme) and the nitrite-methemoglobin intermediate is not observable by electron paramagnetic resonance spectroscopy, this reaction has been 'invisible' to experimentalists over the last 100 years.

The rotational spectra of the ground vibrational state and the ν 9 = 1 torsional state have been reinvestigated and accurate spectroscopic constants have been determined. The torsional frequency, ν 9 = 70(15) cm −1 , has been determined by relative intensity measurements. The assignment of the infrared spectrum has been slightly revised and an accurate harmonic force field has been calculated. The equilibrium structure has been determined using different, complementary methods: experimental, semi-experimental and ab initio , leading to r (NN) = 1.870(2) A, in particular.

The bonding between anionic nucleophiles and the nitroso group has been studied in the common nitrosating agents nitroso chloride (ONCl), nitroso bromide (ONBr), nitroso thiocyanate (ONSCN), and dinitrogen trioxide (N2O3) in aqueous solution. A variety of theoretical methods were employed, including ab initio, density functional theory (DFT), and composite theoretical techniques, with solvent effects described using the polarizable continuum model (PCM). Experimental nitroso bond heterolytic dissociation free energies were accurately reproduced with a number of composite theoretical methods, the most successful being CBS-Q and G2MP2, with average errors of 3.1 and 3.4 kJ mol-1, respectively. Using the MP2 and B3LYP methods, calculations were made with correlation consistent basis sets up to quadruple-ζ, extrapolated to the complete basis set (CBS) limit. The MP2/CBS calculations were accurate to around 10 kJ mol-1, while the B3LYP/CBS calculations routinely overpredicted experimental bond free energies by...

The nitrosation reactions of both thiourea and ammonia have been investigated, owing to their interesting kinetic behaviour and their industrial importance in the sensitisation of emulsion explosives. Kinetic experiments were conducted using a well-mixed aqueous reactor, from which samples were periodically removed, quenched, and then analysed for nitrite concentration using ion chromatography. We derived a number of plausible rate equations for both the ammonia and thiourea gassing processes, which we subsequently tested against experimental results to determine the operating kinetic mechanism, under a range of conditions. The reaction between ammonia and nitrite was seen to proceed by way of the nitrosating agent dinitrogen trioxide. In the presence of thiocyanate, however, dinitrogen trioxide was replaced by the thermodynamically more powerful nitrosating agent nitrosyl thiocyanate. Both reaction mechanisms exhibited relatively similar temperature dependencies, with respective activation energies of 56 and 68kJmol-1, determined between 25 and 45 °C, indicating reaction-controlled regimes. The effects of pH, temperature and ammonium nitrate concentration on the rate of thiourea nitrosation were studied. The rate of reaction was independent of ammonium nitrate concentration, while decreasing the pH of the reaction medium resulted in significant increases in the rate of reaction. The activation energy was evaluated as being 61kJmol-1 in the temperature range of 25 to 45 °C. Theoretical evidence at the G2MP2 level of theory supports a mechanism of thiourea nitrosation involving rapid deprotonation of S-nitrosothiourea, followed by rate-limiting S to N migration of the nitroso group.

Background: Earthworm hemoglobin (LtHb) is a potential blood substitute. Results: LtHb can generate nitric oxide (NO) and preserve NO bioactivity. Conclusion: LtHb reactions with nitrite and NO are indicative of therapeutic possibilities. Significance: The results further highlight the potential role of hemoglobins in NO homeostasis., The giant extracellular hemoglobin (erythrocruorin) from the earth worm (Lumbricus terrestris) has shown promise as a potential hemoglobin-based oxygen carrier (HBOC) in in vivo animal studies. An important beneficial characteristic of this hemoglobin (LtHb) is the large number of heme-based oxygen transport sites that helps overcome issues of osmotic stress when attempting to provide enough material for efficient oxygen delivery. A potentially important additional property is the capacity of the HBOC either to generate nitric oxide (NO) or to preserve NO bioactivity to compensate for decreased levels of NO in the circulation. The present study compares the NO-generating and NO bioactivity-preserving capability of LtHb with that of human adult hemoglobin (HbA) through several reactions including the nitrite reductase, reductive nitrosylation, and still controversial nitrite anhydrase reactions. An assignment of a heme-bound dinitrogen trioxide as the stable intermediate associated with the nitrite anhydrase reaction in both LtHb and HbA is supported based on functional and EPR spectroscopic studies. The role of the redox potential as a factor contributing to the NO-generating activity of these two proteins is evaluated. The results show that LtHb undergoes the same reactions as HbA and that the reduced efficacy for these reactions for LtHb relative to HbA is consistent with the much higher redox potential of LtHb. Evidence of functional heterogeneity in LtHb is explained in terms of the large difference in the redox potential of the isolated subunits.

Although the nitric oxide (⋅NO)-mediated nitrosation of thiol-containing molecules is increasingly recognized as an important post-translational modification in cell signaling and pathology, little is known about the factors that govern this processin vivo. In the present study, we examined the chemical pathways of nitrosothiol (RSNO) production at low micromolar concentrations of ⋅NO. Our results indicate that, in addition to nitrosation by the ⋅NO derivative dinitrogen trioxide (N2O3), RSNOs may be formed via intermediate one-electron oxidation of thiols, possibly mediated by nitrogen dioxide (⋅NO2), and the subsequent reaction of thiyl radicals with ⋅NO. In vitro, the formation ofS-nitrosoglutathione (GSNO) from ⋅NO and excess glutathione (GSH) was accompanied by the formation of glutathione disulfide, which could not be ascribed to the secondary reaction of GSH with GSNO. Superoxide dismutase significantly increased GSNO yields and the thiyl radical trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), inhibited by 45 and 98% the formation of GSNO and GSSG, respectively. Maximum nitrosation yields were obtained at an oxygen concentration of 3%, whereas higher oxygen tensions decreased GSNO and increased GSSG formation. When murine fibroblasts were exposed to exogenous ⋅NO, RSNO formation was sensitive to DMPO and oxygen tension in a manner similar to that observed with GSH alone. Our data indicate that RSNO formation is favored at oxygen concentrations that typically occur in tissues. Nitrosothiol formation in vivo depends not only on the availability of ⋅NO and O2 but also on the degree of oxidative stress by affecting the steady-state concentration of thiyl radicals.

A method for the kinetic study of amino acid nitrosation reactions whose products are unstable is described. The reactions of NaNO2 with α-, β-, and γ-amino acids with a primary amino group in acidic media were studied spectrophotometrically by monitoring the absorbance of the nitrite. The experimental rate equation r=k3exp[amino acid][nitrite]2 was found. The second-order with respect to the nitrite concentration implies that dinitrogen trioxide would be the main nitrosating agent.

Based on the previous report of McCord and co-workers (Crow, J. P., Beckman, J. S., and McCord, J. M. (1995) Biochemistry 34, 3544-3552), the zinc dithiolate active site of alcohol dehydrogenase (ADH) has been studied as a target for cellular oxidants. In the nitrogen monoxide ((*NO)/superoxide (O(2)) system, an equimolar generation of both radicals under peroxynitrite (PN) formation led to rapid inactivation of ADH activity, whereas hydrogen peroxide and ( small middle dot)NO alone reacted too slowly to be of physiological significance. 3-Morpholino sydnonimine inactivated the enzyme with an IC(50) value of 250 nm; the corresponding values for PN, hydrogen peroxide, and (*NO) were 500 nm, 50 microm, and 200 microm. When superoxide was generated at low fluxes by xanthine oxidase, it was quite effective in ADH inactivation (IC(50) (XO) approximately 1 milliunit/ml). All inactivations were accompanied by zinc release and disulfide formation, although no strict correlation was observed. From the two zinc thiolate centers, only the zinc Cys(2)His center released the metal by oxidants. The zinc Cys(4) center was also oxidized, but no second zinc atom could be found with 4-(2-pyridylazo)resorcinol (PAR) as a chelating agent except under denaturing conditions. Surprisingly, the oxidative actions of PN were abolished by a 2-3-fold excess of (*)NO under generation of a nitrosating species, probably dinitrogen trioxide. We conclude that in cellular systems, low fluxes of (*)NO and O(2) generate peroxynitrite at levels effective for zinc thiolate oxidations, facilitated by the nucleophilic nature of the complexed thiolate group. With an excess of (*)NO, the PN actions are blocked, which may explain the antioxidant properties of (*)NO and the mechanism of cellular S-nitrosations.

Tempol is a stable nitroxide radical that has been shown to protect laboratory animals from the injury associated with conditions of oxidative and nitrosoactive stress. Tempol's protective mechanisms against reactive oxygen species have been extensively studied, but its interactions with reactive nitrogen species remain little explored. Recently, it has been shown that tempol is a potent inhibitor of peroxynitrite-mediated phenol nitration while it increases phenol nitrosation by a complex mechanism [Carrol et al. (2000) Chem. Res. Toxicol. 13, 294]. To obtain further mechanistic insights, we reexamined the interaction of peroxynitrite with tempol in the absence and presence of carbon dioxide. Stopped-flow kinetic studies confirmed that tempol does not react directly with peroxynitrite but levels off the amount of oxygen (monitored with an oxygen electrode) and nitrite (monitored by chemiluminescence) produced from peroxynitrite in the presence and absence of carbon dioxide to about 30% and 70% of the initial oxidant concentration at pH 5.4, 6.4, and 7.4. Tempol inhibited phenol nitration while increasing the amounts of 4-nitrosophenol, that attained yields close to 30% of the peroxynitrite in the presence of carbon dioxide at pH 7.4. Fast-flow EPR experiments showed detectable changes in the instantaneous tempol concentration (maximum of 15%) only in the presence of carbon dioxide. Under these conditions, the instantaneous concentration of the carbonate radical anion was reduced by tempol in a concentration-dependent manner. The results indicate that tempol is oxidized by peroxynitrite-derived radicals (*OH and CO(3)(*-), in the absence and presence of carbon dioxide, respectively) to the oxoammonium cation which, in turn, is reduced back to tempol while oxidizing peroxynitrite to oxygen and nitric oxide. The latter reacts rapidly with peroxynitrite-derived nitrogen dioxide to produce the nitrosating species, dinitrogen trioxide. Overall, the results support a role for peroxynitrite and its derived radicals in the tissue pathology associated with inflammatory conditions.

Oxidative stress arises from the uncontrolled actions of reactive oxygen species (ROS) that originate from O2 taken into the cells. Following the discovery of versatile functions for the radical nitric oxide (NO) in mammals, research has focused on the roles played by reactive nitrogen species (RNS), including NO, in disorders and diseases associated with oxidative stress. Previously, the nitric oxide synthase (NOS) system was thought to be the sole enzymatic mechanism for NO production in mammals. More recently, accumulating evidence has revealed the nitrite-dependent NO production pathway to be another important mechanism. This chapter provides an overview of our current knowledge of NO production from nitrite with emphasis on the features that distinguish it from NOS-catalyzed l-arginine-dependent NO synthesis.

The free radical nitric oxide (NO) has emerged in recent years as a fundamental signaling molecule for the maintenance of homeostasis, as well as a potent cytotoxic effector involved in the pathogenesis of a wide range of human diseases. Although this paradoxical fate has generated confusion, separating the biological actions of NO on the basis of its physiologic chemistry provides a conceptual framework which helps to distinguish between the beneficial and toxic consequences of NO, and to envision potential therapeutic strategies for the future. Under normal conditions, NO produced in low concentration acts as a messenger and cytoprotective (antioxidant) factor, via direct interactions with transition metals and other free radicals. Alternatively, when the circumstances allow the formation of substantial amounts of NO and modify the cellular microenvironment (formation of the superoxide radical), the chemistry of NO will turn into indirect effects consecutive to the formation of dinitrogen trioxide and peroxynitrite. These "reactive nitrogen species" will, in turn, mediate both oxidative and nitrosative stresses, which form the basis of the cytotoxicity generally attributed to NO, relevant to the pathophysiology of inflammation, circulatory shock, and ischemia-reperfusion injury.

A reanalysis of the absolute shielding tensors for the two nitrogens in N 2 O 3 is made using results from recent calculations to fix the out-of-plane component of the tensor. The recalculated experimental values and theoretical values from density functional and multi-configurational methods are now in good agreement for the nitro nitrogen. Agreement for the nitroso nitrogen is not so good and suggests that multiconfigurational calculations with larger basis sets are required. Remeasurement of the microwave spectrum with greater resolution of the spin–rotation fine structure is needed to provide good experimental values for the absolute shielding tensor elements. Measurement of the 15 N NMR spectrum of N 2 O 3 would also be useful to obtain a more accurate value of the 15 N chemical shifts.

The kinetics and mechanism of the reaction between nitrous acid and bromine are studied in dilute sulfuric acid medium, using both the stopped-flow method and conventional spectrophotometry. The partial reaction order with respect to Br2 moderately differs from 1, showing a saturation at a higher concentration of bromine. The second order of the reaction towards nitrous acid has been observed. Hydrogen and bromide ions significantly suppress the rate of reaction. Despite the apparent simplicity, the mechanism is rather complex, with two reaction pathways proposed. The first one is represented by the reaction of bromine with the intermediate dinitrogen trioxide. A direct nucleophilic attack of NO2− ion towards the bromine molecule is suggested as the second pathway. The proposed mechanism accounts for the observed behavior; in almost all cases a satisfactory quantitative agreement with the experiments is obtained. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 279–285, 2000

Conventional N234 carbon black was chemically modified by a low temperature treatment with dinitrogen trioxide (N 2 O 3 ), nitrogen oxide (NO) and dinitrogen tetroxide (N 2 O 4 ). The purpose of this treatment was to increase significantly the fraction of polymer chain segments chemically linked to the filler surface in comparison to a conventional CB after compounding with rubber. The theoretical expectation was to reduce the mechanical hysteresis of a rubber compound. The chemical structure of the resulting carbon black (CB) was studied by FT-IR spectroscopy which revealed that an extensive surface chemical modification had occurred. In fact, extensive surface nitration, nitrosation and oxidation had taken place. Raman spectroscopy of treated CB reveals that the bulk structure of the CB remained substantially unchanged after the treatment. The modified CB was tested in practice in a rubber tread compound formulation, and has substantially confirmed the theoretical expectations by reducing the tan 6 at 70°C by about 14%, which correlates with tire rolling resistance without significant losses in traction performances (as estimated on lab scale by tan 6 at 0°C).

In order to clarify the role of oxygen in the reaction of amines with nitric oxide, secondary amines were allowed to react with nitric oxide in the presence of oxygen. Although N-nitrosamines were obtained as the main products in every case, the yields depended on the substituents and reaction solvents. Detailed investigation revealed that the reaction proceeded by at least two pathways: one involving oxygen as a catalyst, and the other consuming the stoichiometric amount of oxygen. Both paths afforded the same nitroso adducts. It was suggested that a third path, a catalytic process via Drago’s salts was also possible. The same reaction was applied to a tertiary amine, and it was found that the oxygen was consumed stoichiometrically in this case.