Subject nitrogen monoxide

The biological importance of nitrogen monoxide (NO) as a messenger substance was originally recognized in coimection with contraction and relaxation of blood vessels. In the meantime, it has become clear that NO is a universal messenger substance that takes part in diverse forms in intercellular and intracellular commimication. Practically every cell in mammals is subject to regulation by NO in one form or another. 

S. M. Aldoshin (Director). This session included four presentations. Professor N.P. Konovalova reported on antioxidants and donors of nitrogen monoxide (antitumor effects of nitroxides and NO-donors) the report of N.A. Sanina and S.M. Aldoshin was concerned with a new class of NO-donors (synthesis, structure, properties, and practical use of sulfur-nitrosyl complexes of iron). Free-radical mechanisms of induction and development of secondary necrosis after gun wounds were the subject of the lecture by G.N. Bogdanov L.D. Smirnov reported on pharmacological properties and promising clinical application of antioxidants of the heteroaromatic array. 

Metal- and proton-exchanged zeolites have been recently attracted much attention because of their selective catalytic activity to efficiently reduce nitrogen monoxide (NO) by hydrocarbon in an 02-rich atmosphere [1]. The formation of nitrogen dioxide (NO2) from NO and O2 has been suggested as an important step in the selective reduction [2, 3] NO2 is one of rare stable paramagnetic gaseous molecules and has been subjected to electron spin resonance (ESR) studies [4-7]. The ESR parameters and their relation/to the electronic structure have been well established [4] and NO2 can be used as a "spin probe" for the study of molecular dynamics at the gas-solid interface by ESR. 

With the commission directive 91/322/EEC, released in May 1991, a first fist of 27 chemical substances with indicative limit values was published [6-9], and these are listed in the annex of this directive. In February 2006, directive 91/322/EEC was amended by the new directive 2006/15/EC [6-41]. In accordance with this directive, 17 substances were taken out and transferred into the new directive, leaving 10 substances in the annex of 91/322/EC. In Ikble 6.6, the remaining 10 chemical agents together with their indicative Hmit values are shown. They are still the subject of further evaluation, but the insufficient scientific data did allow for setting a provisional lOELV. In the case of nitrogen monoxide, it is expected that additional data will be available in the near future. Until then, aU values remain in force. 

For many years nitrogen monoxide was a molecule with an unsavoury reputation a destroyer of ozone, a supposed carcinogen and precursor of acid rain. However, in a remarkable Cinderella story, we now realize that NO, despite its simplicity, is one of the most important functional molecules in our bodies. In fact, when its numerous biochemical roles were established, the prestigious monthly journal Science named NO its molecule of the year for 1992, and the oxide was the subject of a BBC TV Horizon programme the following year. 

Whilst carbon monoxide and nitrogen oxides are the toxic products of explosives, other constituents of the fume cause a characteristic smell. As the nitroglycerine content of explosives is reduced, this smell tends to become rather unpleasant. Subjective tests must be used for its estimation. 

In one study,human subjects were tested in a controlled-environ-ment chamber with a high (summer) temperature and with ozone, nitrogen dioxide, and carbon monoxide as pollutants. Performance on a divided-attention task given at the end of the exposure period and the subjects heartrate variability (a potential psychophysiologic measure of attention) were evaluated. The subjects displayed a significant decrement in peripheral attention associated with increased ambient temperature. Effects attributable to pollutant gases were variable. 

Adult male volunteers were exposed to purified air,2 -2 - to ozone alone, or to ozone in combination with nitrogen dioxide and carbon monoxide. No additional effects were detected when nitrogen dioxide at 0.3 ppm was added to ozone. The addition of carbon monoxide at 30 ppm to the ozone-nitrogen dioxide mixture produced no additional effects, other than a slight increase in blood carboxyhemoglobin content and small decreases in psychomotor performance, which were not consistent in different subject groups. 

In ambient air, the primary removal mechanism for acrolein is predicted to be reaction with photochemically generated hydroxyl radicals (half-life 15-20 hours). Products of this reaction include carbon monoxide, formaldehyde, and glycolaldehyde. In the presence of nitrogen oxides, peroxynitrate and nitric acid are also formed. Small amounts of acrolein may also be removed from the atmosphere in precipitation. Insufficient data are available to predict the fate of acrolein in indoor air. In water, small amounts of acrolein may be removed by volatilization (half-life 23 hours from a model river 1 m deep), aerobic biodegradation, or reversible hydration to 0-hydroxypropionaldehyde, which subsequently biodegrades. Half-lives less than 1-3 days for small amounts of acrolein in surface water have been observed. When highly concentrated amounts of acrolein are released or spilled into water, this compound may polymerize by oxidation or hydration processes. In soil, acrolein is expected to be subject to the same removal processes as in water. 

In many cases the molecular orbitals for a heteronuclear diatomic molecule may be worked out in a straightforward manner as for hydrogen chloride. In others, however, certain difficulties arise and we shall take as an example the case of carbon monoxide, the structure of which has been the subject of much controversy. In carbon monoxide, as in the nitrogen molecule, there are fourteen valency electrons and Mullikan has formulated the structure of both molecules as... 

Potassium forms explosive mixmres with halogenated hydrocarbons, carbon tetrachloride, carbon dioxide (dry ice), carbon monoxide, and carbon disulfide, resulting in explosions when subjected to shock. With carbon monoxide, it forms potassium carbonyl, which explodes on exposure to air. It ignites in nitrogen dioxide, sulfur dioxide, and phosphine. 

The question arises as to what the effect of these changes will be on the composition of exhaust gas from vehicles, which plays such a large part in determining the quality of air in our cities. Much work has been done to demonstrate the relatively small effect of fuel quality and composition on the gaseous exhaust components currently subject to legislation, namely carbon monoxide, hydrocarbons and nitrogen oxides, but the effect on other components of exhaust has been less well characterized. 

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