Spin Trapping Of Nitric Oxide (.bul.NO) by aci-Nitromethane in Aqueous Solutions

S-Nitrosothiols: Materials, Reactivity and Mechanisms

The article provides a comprehensive view of S-nitrosothiols, chemical behaviour, the pathways leading to their synthesis, their spectral properties, analytical methods of detection and determination, chemical and photochemical reactivity, kinetic aspects and suggested mechanisms. The structure parameters of S-nitrosothiols and the parent thiols are analysed with respect to their effect on the strengthening or weakening the S–NO bond, and in consequence on the S-nitrosothiol stability. This depends also on the ease of S–S bond formation in the product disulphide. These structural features seem to be crucial both to spontaneous as well as to Cu-catalysed decomposition. Principal emphasis is given here to the S-nitrosothiols’ ability to act as ligands and to the effect of coordination on the ligand properties. The chemical and photochemical behaviours of the complexes are described in more detail and their roles in chemical and biochemical systems are discussed.

The aim of the article is to demonstrate that the contribution of S-nitrosothiols to chemical and biochemical processes is more diverse than supposed hitherto. Nevertheless, their role is predictable and, based on the correlation between structure and reactivity, many important mechanisms of biochemical processes can be interpreted and various applications designed.

Detection of reactive oxygen and nitrogen species by EPR spin trapping

Electron paramagnetic resonance spin trapping has become an indispensable tool for the specific detection of reactive oxygen free radicals in biological systems. In this review we describe some of the advantages as well as some experimental considerations of this technique and how it can be applied to biological systems to measure oxidative stress.

Spin trapping of nitric oxide by aci anions of nitroalkanes

In alkaline solutions, nitroalkanes (RCH2NO2) undergo deprotonation and rearrange to an aci anion (RHC=NO2-), which may function as a spin trap. Using electron paramagnetic resonance (EPR) spectroscopy, we have investigated suitability of aci anions of a series of nitroalkanes (CH3NO2, CH3CH2NO2, CH3(CH2)2NO2, and CH3(CH2)3NO2) to spin trap nitric oxide (*NO). Based on the observed EPR spectra, the general structure of the adducts, formed by addition of *NO to RHC=NO2-, was identified as nitronitroso dianion radicals of general formula [RC(NO)NO2]*2- in strong base (0.5 M NaOH), and as a mono-anion radical [RCH(NO)NO2]*- in alkaline buffers, pH 10-13. The hyperfine splitting on 14N in the -NO2 moiety (11.2-12.48 G) is distinctly different from the splitting on 14N in the -NO moiety of the adducts (5.23-6.5 G). The structure of the adducts was verified using 15N-labeled *NO, which produced radicals, in which triplet due to splitting on 14N (I = 1) in 14NO/aci nitro adducts was replaced by a doublet due to 15N (I = 1/2) in 15NO/aci nitro adducts. EPR spectra of aci nitromethane/NO adduct recorded in NaOH and NaOD (0.5 M) showed that the hydrogen at alpha-carbon can be exchanged for deuterium, consistent with structures of the adducts being [CH(NO)NO2]*2- and [CD(NO)NO2]*2-, respectively. These results indicate that nitroalkanes could potentially be used as prototypes for development of *NO-specific spin traps suitable for EPR analysis.

Multiplicity control in the polygeminal diazeniumdiolation of active hydrogen bearing carbons: chemistry of a new type of trianionic molecular propeller

Over a century ago, Traube reported the reaction of four nitric oxides with acetone and sodium ethoxide to yield sodium methanebis(diazene-N-oxide-N'-hydroxylate) and sodium acetate. However, when this reaction is carried out in the presence of nitric oxide at slightly elevated pressures (35-40 psi), a product corresponding to the addition of six nitric oxides, sodium methanetris(diazene-N-oxide-N'-hydroxylate), forms as the main product in addition to a trace of the previously observed sodium methanebis(diazene-N-oxide-N'-hydroxylate) and sodium acetate. The corresponding potassium salts form when potassium hydroxide is employed as the base, while lithium hydroxide results in the formation of lithium methanebis(diazene-N-oxide-N'-hydroxylate) exclusively. Nitric oxide reacts with 3,3-dimethylbutan-2-one in the presence of sodium and potassium hydroxide in methanol to yield sodium and potassium 3,3-dimethylbutan-2-one-1,1,1-tris(diazene-N-oxide-N'-hydroxylate), respectively. In contrast, the reaction in the presence of lithium hydroxide forms lithium methanebis(diazene-N-oxide-N'-hydroxylate) and lithium pivalate. The differential reactivity of nitric oxide with acetone and 3,3-dimethylbutan-2-one in the presence of the three bases is attributed to competing hydrolytic reactions of the acetyl and trimethylacetyl group-containing intermediates. A mechanism is proposed for the nitric oxide addition to active methyl groups in these reactions, where the product distribution between the di- and trisubstituted methanes is under kinetic control of the competing reactions. The products are characterized by NMR and IR spectroscopy, differential scanning calorimetry, and elemental analysis. Two differentially hydrated forms of potassium methanetris(diazene-N-oxide-N'-hydroxylate) are characterized by single-crystal X-ray diffraction. From the metathesis reaction of the silver salt of methanetris(diazene-N-oxide-N'-hydroxylate) with ammonium iodide, the corresponding ammonium salt is isolated in 59% yield, but only trace amounts of methylated products form in the reaction of the silver salt with methyl iodide. Density functional calculations (B3LYP/6-311++G) are used to evaluate the bonding, ground-state structures, and energy landscape for the different conformers of methanetris(diazene-N-oxide-N'-hydroxylate)(3-) trianion, a new type of a molecular propeller, and its corresponding triprotonated acid.

Continuous monitoring of cellular nitric oxide generation by spin trapping with an iron-dithiocarbamate complex

Nitric oxide (NO) generation in murine macrophages was determined in real time using the electron paramagnetic resonance (EPR) spin trapping method. An iron complex of N-methyl D-glucamine dithiocarbamate was utilized as the spin trap. This spin trapping compound reacts with NO in solution to form a specific room-temperature stable, mononitrosyl complex which is readily detected and identified by EPR spectroscopy. Mouse peritoneal macrophages were placed in an EPR sample-cell and activated by lipopolysaccharide and gamma-interferon at 37 degrees C, followed by an additional incubation in oxygenated medium without these activation agents. After various incubation periods, spin trap solution was infused to replace the medium in the sample-cell, and the time-evolution of the EPR signal of the spin adduct (NO-complex) was recorded. Rates of NO generation were calculated based upon the initial slopes of the increase in the EPR intensity with time. In comparison to the NO (or NO2-) generation rate obtained under similar experimental conditions using the Griess reaction assay, the spin trapping method was found to be more sensitive, with a lowest limit of the detection of 3 pmol/min. In addition, by using the spin trapping method, NO generation from the same cells could be measured consecutively during various stages of activation, because infusion of the spin trap solution did not affect the viability of macrophages.

Spin trapping isotopically-labelled nitric oxide produced from [15N]L-arginine and [17O]dioxygen by activated macrophages using a water soluble Fe(++)-dithiocarbamate spin trap

The unique capabilities of EPR spin trapping of nitric oxide based on a ferrous-dithiocarbamate spin trap have been demonstrated in a study verifying the source of the nitrogen and oxygen atoms in nitric oxide produced from activated macrophages. Spin trapping experiments were performed during nitric oxide generation from activated mouse peritoneal macrophages using the ferrous complex of N-methyl D-glucamine dithiocarbamate as a spin trap. When 15N-substituted arginine was given to the activated macrophages in the presence of the spin trap, a characteristic EPR spectrum of the nitric oxide spin adduct was obtained, which indicates the presence of the 15N atom in the nitric oxide molecule. The hyperfine splitting (hfs) constant of the 15N nucleus was 17.6 gauss. When 17O-containing dioxygen (55%) was supplied to the medium, an EPR spectrum consistent with the 17O-substituted nitric oxide spin adduct was observed in the composite spectrum. The hfs of 17O was estimated to be 2.5 gauss. The 14NO spin adduct observed after prolonged incubation in the medium which contains [15N]L-arginine as the only extracellular source of arginine demonstrates that arginine is recycled through its metabolite in activated macrophages.