Showing papers on "Nitroso published in 2000"

N-NO bond dissociation energies of N-nitroso diphenylamine derivatives (or analogues) and their radical anions: implications for the effect of reductive electron transfer on N-NO bond activation and for the mechanisms of NO transfer to nitranions

Abstract: The heterolytic and homolytic N−NO bond dissociation energies [i.e., ΔHhet(N−NO) and ΔHhomo(N−NO)] of 12 N-nitroso-diphenylamine derivatives (1−12) and two N-nitrosoindoles (13 and 14) in acetonitrile were determined by titration calorimetry and from a thermodynamic cycle, respectively. Comparison of these two sets of data indicates that homolysis of the N−NO bonds to generate NO• and nitrogen radical is energetically much more favorable (by 23.3−44.8 kcal/mol) than the corresponding heterolysis to generate a pair of ions, giving hints for the driving force and possible mechanism of NO-initiated chemical and biological transformations. The first (N−NO)- • bond dissociation energies [i.e., ΔH(N−NO)- • and ΔH‘(N−NO)- •] of radical anions 1- •−14- • were also derived on the basis of appropriate cycles utilizing the experimentally measured ΔHhet(N−NO) and electrochemical data. Comparisons of these two quantities with those of the neutral N−NO bonds indicate a remarkable bond activation upon a possible one-ele...

On the Chemical Reactions of Diphenylamine and its Derivatives with Nitrogen Dioxide at Normal Storage Temperature Conditions

Abstract: The chemical reactions between nitrogen dioxide vapour and diphenylamine (DPA), some of its nitro/nitroso derivatives and between their consecutive products have been studied at temperatures of about 23 °C, whereby cellulose was used as substrate material. The following stabilizer compounds were used as starting components: DPA, N-NO-DPA, 2-NO2-DPA and 4-NO2-DPA. Concentration profiles as function of added nitrogen dioxide have been measured by HPLC. These profiles are similar to the ones obtained by accelerated aging, and the typical consecutive stabilizer products have been formed. The profiles are interpreted in terms of possible reactions. Furthermore, the influences of time and light on the decomposition of the mono-nitro-N-nitroso compounds have been investigated. The consequences of these reactions are discussed to explain differences between the storage aging at ambient temperatures and the higher temperature induced accelerated aging. The reactivity towards nitrogen dioxide for each stabilizer compound was obtained by a kinetic model for the decrease of the starting component.

Structure and Reactivity of Amphoteric Oxygen Species

Abstract: The structure and chemical properties of 1,3-dipolar peroxidic species (X+-O-O-) such as ozone (X = O), nitroso oxides or nitrenium peroxides (X = RN), carbonyl oxides or carbenium peroxides (X = R2C), and persulfoxides or sulfonium peroxides (X = R2S) have been attracting much attention from synthetic, biological, and theoretical standpoints. These active oxygen species can be classified into two types depending on whether the X+ is an enium (carbenium, nitrenium, silylenium etc.) ion or an onium (ammonium, oxonium, phosphonium, sulfonium etc.) ion, and their reactivities are quite different depending on the nature of X. The individual features as well as the overviews of structure and reactivities of these X-O-O species are reviewed. Ozone and nitroso oxides have an electrophilic character while carbonyl oxides usually act as a nucleophilic oxygen transfer agent, their reactivities being controlled by substituents. It is important to see whether or not XOO species can isomerize to the cyclic isomers. Al...

N-Nitroso-N,O-dialkylhydroxylamines: preparation, structure, and mechanism of the hydronium ion catalysed solvolytic nitrous oxide extrusion reaction

Abstract: Eleven N-nitroso-N,O-dialkylhydroxylamines, RN(NO)OR′, have been prepared and the mechanisms of their hydronium ion catalysed solvolyses in aqueous solution which liberate nitrous oxide have been investigated. All reactions are first-order in substrate and first-order in hydronium ion, and the second-order rate constants at 25 °C vary over a range of less than 140 in spite of considerable variation in substrate structure (R ranges from methyl to 4-methoxybenzyl to 2-adamantyl, for example) and changes in solvent composition (water with up to 50% methanol or 66% acetonitrile). Enthalpies and entropies of activation are qualitatively similar throughout the range (ΔH‡ = 72–93 kJ mol−1 and ΔS‡ = −19 to −57 J K−1 mol−1) which, with the product analyses, are accommodated by a mechanism involving pre-equilibrium protonation of the substrates followed by rate-limiting dissociation to give RN2O+ and HOR′. The oxodiazonium ion intermediate, RN2O+, then dissociates further to give the carbenium ion intermediate, R+, or suffers direct nucleophilic displacement of N2O by solvent (the external nucleophile) or by R′OH (the internal nucleophile liberated in the initial fragmentation). The carbenium ion, R+ (if formed), suffers nucleophilic capture either by solvent or by R′OH. When acetonitrile is the co-solvent (rather than methanol) for the N-(2-adamantyl) substrate 3g, the product of the Ritter reaction, 2-acetamidoadamantane, is detected. These nitrous oxide liberating reactions are compared with the nitric oxide liberating reactions of related N-nitrosohydroxylamines, and the origin of the difference between them is identified. The N(1)-nitroso group in the N,O-dibenzyl compound 3c is shown by X-ray crystallography to be essentially coplanar with the C and O atoms also bonded to N(1).

Lipid radicals: properties and detection by spin trapping.

Abstract: Unsaturated lipids are rapidly oxidized to toxic products such as lipid hydroperoxides, especially when transition metals such as iron or copper are present. In a Fenton-type reaction Fe2+ converts lipid hydroperoxides to the very short-lived lipid alkoxyl radicals. The reaction was started upon the addition of Fe2+ to an aqueous linoleic acid hydroperoxide (LOOH) emulsion and the spin trap in the absence of oxygen. Even when high concentrations of spin traps were added to the incubation mixture, only secondary radical adducts were detected, probably due to the rapid re-arrangement of the primary alkoxyl radicals. With the commercially available nitroso spin trap MNP we observed a slightly immobilized ESR spectrum with only one hydrogen splitting, indicating the trapping of a methinyl fragment of a lipid radical. With DMPO or 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) adducts were detected with carbon-centered lipid radical, with acyl radical, and with the hydroxyl radical. We also synthesized lipophilic derivatives of the spin trap DEPMPO in order to detect lipid radical species generated in the lipid phase. With all spin traps studied a lipid-derived carbon-centered radical was obtained in the anaerobic incubation system Fe2+/LOOH indicating the trapping of a lipid radical, possibly generated as a secondary reaction product of the primary lipid alkoxyl radical formed. Under aerobic conditions an SOD-insensitive oxygen-centered radical adduct was formed with DEPMPO and its lipophilic derivatives. The observed ESR parameters were similar to those of alkoxyl radical adducts, which were independently synthesized in model experiments using Fe3+-catalyzed nucleophilic addition of methanol or t-butanol to the respective spin trap.

From mutagenic to non-mutagenic nitroarenes: effect of bulky alkyl substituents on the mutagenic activity of 4-nitrobiphenyl in Salmonella typhimurium. Part I. Substituents ortho to the nitro group and in 2'-position.

Abstract: Eleven alkyl substituted derivatives of 4-nitrobiphenyl (4NBp) and two corresponding nitroso compounds were synthesised and tested for mutagenic potency in strains TA98 and TA100 of Salmonella typhimurium . The mutagenicity of compounds substituted ortho to the nitro group (3-methyl-, 3-ethyl-, 3- iso propyl-, 3- tert butyl-, 3,5-diethyl-, 3,5-di iso propyl-, and 3,5-di tert butyl-4NBp) decreased with growing steric demand of the alkyl substituents in both tester strains. The most sterically hindered compounds were non-mutagenic even at highest concentrations. This reduction of mutagenicity is correlated with deviations from the coplanar orientation of the nitro group relative to the aromatic plane. Since a comparable decrease of mutagenicity for the nitroso compounds (4NOBp and 3- tert butyl-4NOBp) was not observed, the first reduction step of non-planar nitro groups must be inhibited. Alkyl groups in the 2′-position of 4NBp (2′-methyl-, 2′-ethyl-, 2′- iso propyl-, and 2′,4′,6′-trimethyl-4NBp) also reduced mutagenic activity with increasing size and removed it completely for the most sterically hindered species (2′- iso propyl-, 2′,4′,6′-trimethyl-4NBp). In this case, the co-planarity of the nitro group is not affected but the twisting of the two aromatic rings, which is associated with a less effective charge delocalisation of the nitrenium ion. The experimental mutagenicities of all nitro compounds were compared to predicted values, that are based on recently developed empirical equations. While there was reasonable correspondence for the parent compound (4NBp), its ortho methylated derivative (3-methyl-4NBp) and two highly hydrophobic dialkylated species (3,5-di iso propyl- and 3,5-di tert butyl-4NBp), predictions for all other alkyl substituted compounds were too high. Thus, steric parameters should be included to improve the general validity of predictions by means of quantitative structure–activity relationships (QSAR).

A DFT study of the domino inter

Abstract: The molecular mechanism of the domino inter [4 + 2]/intra [3 + 2] cycloaddition reactions of nitroalkenes with enol ethers to give nitroso acetal adducts has been characterized using density functional theory methods with the B3LYP functional and the 6-31G* basis set. The presence of Lewis acid catalyst and solvent effects has been taken into account to model the experimental environment. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular [4 + 2] cycloaddition of the enol ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intramolecular [3 + 2] cycloaddition reaction. The intermolecular [4 + 2] cycloaddition can be considered as a nucleophilic attack of the enol ether to the conjugated position of the nitroalkene, with concomitant ring closure and without intervention of an intermediate. For this cycloaddition process, the presence of the Lewis acid favors the delocalization of t...

Nitroso esters of β-oxo-amides and aryl propionic acid derivatives of non-steroidal antiinflammatory drugs

Abstract: A compound comprising a non-steroidal antiinflammatory agent to which is directly or indirectly linked an NO group, a pharmaceutical composition including the compounds and methods of treatment of pain and/or inflammation using the compounds and compositions are disclosed. Also disclosed is a composition comprising a non-steroidal antiinflammatory agent and a compound that donates, transfers or releases nitric oxide.

From mutagenic to non-mutagenic nitroarenes: effect of bulky alkyl substituents on the mutagenic activity of nitroaromatics in Salmonella typhimurium. Part II. Substituents far away from the nitro group.

Abstract: Derivatives of 4-nitrobiphenyl, 4-nitrosobiphenyl, 2-phenyl-5-nitropyridine (2-aza-4-nitrobiphenyl) and 2-nitrofluorene, bearing various alkyl substituents far away from the nitro group (4′-position in nitrobiphenyls, 7-position in 2-nitrofluorenes) were synthesised and tested for mutagenic potency in strains TA98 and TA100 of Salmonella typhimurium. In the absence of S9 in both strains, mutagenicity of all compounds decreased with increasing steric demand of the attached alkyl groups as, e.g., for the 4-nitrobiphenyl series in the order 4′-H>4′-Me>4′-Et>4′-nBu>4′-iPr>4′-tBu>4′-Ad (Ad=adamantyl). Changes of the molecular shape from ‘planar’ to non-planar caused by the bulk of the introduced substituents (without influencing the twisting of the nitro substituent or the phenyl rings in the biphenyl compounds) may be responsible for this effect by interfering with an efficient intercalation into DNA. A comparison between experimental and theoretical values as calculated from recently developed equations (QSAR) confirmed our previous results (see the preceding paper) that mutagenicity of alkyl-substituted nitroaromatics cannot be predicted by hydrophobicity and LUMO-energies alone without including steric parameters.

Pseudophase Approach to the Transfer of the Nitroso Group in Water/AOT/SDS/Isooctane Quaternary Microemulsions

Abstract: The kinetics of the transfer of the nitroso group from N-methyl-N-nitroso-p-toluenesulfonamide to each of three secondary amines (piperazine, N-methylbenzylamine, and morpholine) was studied using a wide variety of water/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/sodium dodecyl sulfate/isooctane quaternary microemulsions as reaction media. The diverse kinetic behavior of these amines can be explained quantitatively on the basis of a single model taking into account the distribution of the amine between the aqueous and isooctane phases and their mutual interface (surfactant film); the reaction always takes place at the surfactant film. The reactivities of the amines are discussed in comparison with the behavior observed in water and in AOT/isooctane/water ternary microemulsions.

Electroreduction of Nitroaryl‐1,4‐dihydropyridines on a Mercury Pool Electrode in Mixed Media Analysis of the Reaction Products and Their Reactivity with Biomolecules

Abstract: The electroreduction of a series of nitroaryl-1,4-dihydropyridines has been studied in mixed media. Controlled potential electrolyses using a mercury pool electrode at three different reduction potentials were carried out. Voltammetric (polarography and cyclic voltammetry) and chromatographic studies, showed that these nitro compounds were transformed into their corresponding hydroxylamine derivatives at the end of the electrolysis. On the other hand, early in the electrolysis it was possible to detect the formation of the nitro radical anion in the bulk solution which through a dismutation reaction produces the nitroso compound which is reduced to the final product, a hydroxylamine derivative. When different biomolecules like glutathione, cysteamine, adenine, and uracil were added, a direct reaction with the nitro radical anion derivative was detected. The parent nitro compound and the final product, the hydroxylamine derivative, did not react with the biomolecules.

Sensitized Photoreduction of Nitrosoazoles on Titanium Dioxide

Abstract: The photosensitized reduction of some 4-nitrosopyrazoles and 4nitrosoimidazoles using titanium dioxide as a photocatalyst has been investigated. The photoreaction produces the corresponding 4-aminoazoles and assumes an initial electron transfer from the conduction band of the excited titanium dioxide to the nitroso compound, followed by hydrogen transfer from the solvent. The photoreduction reaction takes also place by irradiating nitrosoazoles in the presence of triethylamine in acetonitrile, pointing out the electron transfer also to occur from a ground state donor to the excited nitrosoazole. The photocatalytic reactions at semiconductor particles have been receiving increasing attention for synthetic projects: their use in processes involving functional group modifications constitutes a new tool for the organic chemist.1-8 On the other hand, an interesting point of view regards the question of photodegradation of organic substrates,3 particularly heterocyclic compounds which are widely used in medicinal and agricultural chemistry. In the frame of our researches regarding the photochemical behavior of five-membered heterocycles,9 we became interested in the photochemistry of nitrosoazoles, namely nitrosopyrazoles for which an antifungal activity is recognised10 and nitrosoimidazoles which are considered active form of nitroimidazole drugs used therapeutically.11 In particular, aiming to exploit semiconductor catalysts in heterocyclic chemistry that is oxidation, reduction, functionalization, we looked at the behavior of these nitrosoazoles toward a semiconductor-assisted photoreduction. As for nonphotochemical methods, it is worthy noting that the reduction of 4-nitrosopyrazoles into the corresponding amino compounds is reported to occur by using hydrazine in ethanolic solution,12 or, in some case, tin and hydrochloric acid;13 in turn, the reduction of the nitroso-diphenylimidazole (7) into the amino compound (8) is easily accomplished by using stannous chloride in hydrochloric acid, or ammonium sulfide in ethanol.14 The use of a semiconductor catalyst in a photoreduction reaction has been reported for aliphatic and aromatic nitro compounds which were transformed into the amino compounds.7 The reaction is accomplished by using titanium dioxide (TiO2; anatase) in alcoholic solvent, and has been interpreted as proceeding through the corresponding nitroso and hydroxylamino derivatives as intermediates. In a generalized pattern of the photoreduction process, irradiation of titanium dioxide promotes one electron from the valence band to the conduction band.7,8 The electron in the conduction band is readily available for transference and then the acceptor will be reduced, while the electron hole in the valence band is open for donation and then the donor will be oxidized. In the above cited case, the photoreduction of the nitro compound is coupled with the oxidation of the alcoholic solvent, while concomitant formation of molecular hydrogen takes place.7 In this note we report preliminary results concerning with the photoreduction of 4nitrosopyrazoles (1-3) and 4-nitroso-diphenylimidazole (7) on semiconductor photocatalyst (TiO2). In addition, a preliminary assay of the photoreduction of nitrosoazoles by using ground state electron donor (e.g. triethylamine) is also presented. RESULTS AND DISCUSSION Irradiation (with RPR-3500A Hg lamps) of a suspension of titanium dioxide in ethanol containing the 1,5diphenyl-3-methyl-4-nitrosopyrazole (1) produces the corresponding 1,5-diphenyl-3-methyl-4aminopyrazole (4). Similarly, the 1-phenyl-3,5-dimethyl(2) and the 3,5-dimethyl-4-nitrosopyrazole (3) give the corresponding 4-aminopyrazoles (5) and (6), respectively. When comparatively irradiated in the absence of TiO2, compounds (1-3) remained unchanged, thus indicating that the semiconductor really acts as a photosensitizer in the photoreduction reaction.

Cryptate compounds and methods for diagnosis and therapy

Abstract: The present invention relates to cryptate compounds useful as chelating agents. In particular, the present invention relates to functionalised derivatives of certain cryptate compounds. These functionalised derivatives are suitable for use in radiolabelling and similar applications. The present invention also relates to a method for diagnosis or therapy of a disease utilising functionalised derivatives of cryptase compounds. In one embodiment, the present invention relates to a compound which is capable of being radiolabelled of general formula (I) in which n represents an integer from 2 to 4, where each R?4 and R5? is independently selected from -H, CH?3?, COOH, NO2, CH2OH, H2PO4, HSO3, CN, C=ONH2 and CHO; X and Y are the same or different and are selected from the group of C-R, N, P and C-Z in which R represents a hydrogen or halogen atom or a hydroxyl, nitro, nitroso, amino, optionally substituted alkyl, optionally substituted aryl, optionally substituted aralkyl or cyano group, or a group of the formula -COOR', COCOOR', NH-COCH2Br, -NH-CO-CH=CH-COOR' in which R' is a hydrogen atom or alkyl group; or; W is selected from the group of NH, S and O; and Z is a functionalised linkage group which is capable of binding said compound of formula (I) to a molecular recognition unit and wherein at least one of X and Y is C-Z; or a pharmaceutically acceptable salt thereof.

Synthetic Procedures Yielding Targeted Nitro and Nitroso Derivatives of the Propellant Stabilisers Diphenylamine, N‐Methyl‐4‐nitroaniline, and N,N′‐Diethyl‐N,N′‐diphenylurea

Abstract: Synthetic methodologies have been developed which yield a variety of diphenylamine (DPA) and 1,3-diethyl-l,3-diphenylurea (ethylcentralite or EC) propellant stabiliser degradation derivatives in high yield. The N-alkyl nitroanilines (N-methyl-2,4,6-trinitroaniline; N-methyl-2,4-dinitroaniline; N-ethyl-2,4,6-trinitroaniline; N-ethyl-2,4-dinitroaniline; N-ethyl-4-nitroaniline; N-ethyl-2-nitroaniline) have been obtained either by reaction of the parent aniline with the required alkyl halide under mild conditions or via Ullmann type chemistry. A robust and high yielding approach for the synthesis of di, tri and tetranitrodiphenylamines (2,2′,4,4′-tetranitrodiphenylamine; 2,4,4′-trinitrodiphenylamine; 2,2′,4-trinitrodiphenylamine; 2,4,6-trinitrodiphenyl-amine; 2,4-dinitrodiphenylamine) is reported which involves passing the nitroanilines and chloronitrobenzenes down a base activated alumina column. The N-nitroso-N-alkyl compounds (N-nitroso-N-ethyl-4-nitroaniline; N-nitroso-N-ethyl-2-nitroaniline; N-nitroso-N-Methyl-4-nitroaniline; N-ethyl-N-nitrosoaniline; N-nitroso-2-nitrodiphenylamine) have been synthesised using nitrosyl acetate in acetic acid as the N-nitrosating agent.

Decomposition of H2O2 using ion exchange resin with a spacer containing α-nitroso-β-naphthol as a functional group

Abstract: Catalytic activity of some transition metal complexes derived from crosslinked styrene–divinylbenzene copolymer with spacer containing α-nitroso-β-naphthol as a functional group (Ps-ANBN) have been used for the decomposition of hydrogen peroxide (H 2 O 2 ) The decomposition of H 2 O 2 was investigated by measuring evolution of oxygen at different time intervals Kinetic and thermodynamic parameters have been evaluated Various metal complexes were used to study the effect of the nature of metal ion on decomposition of H 2 O 2 Scanning electron microscopy (SEM) have been used to study the morphological variation between Ps-ANBN and Ps-ANBN-Cu II The Ps-ANBN-Cu II is found to be thermodynamically more stable than Ps-ANBN