Gases nitric oxide

We have not yet distinguished the gases nitric oxide, hydrogen, and oxygen. Nitric oxide has its own personality. Immediately upon exposure to air, the colorless nitric oxide becomes reddish-brown—exactly the color of nitrogen dioxide. Neither oxygen nor hydrogen behaves this way. 

Reiativeiy recentiy, the gases nitric oxide (NO) and carbon monoxide (CO) have been found to act as neurotransmitters in the nervous system. Nitric oxide is synthesized from L-arginine via nitric oxide synthase, requiring NADPH as a co-enzyme and tetrahydrobiopterin as a cofactor. Unlike other neurotransmitters, NO is a smaii, very soiubie moiecuie and cannot be stored in synaptic vesicles. Rather, it is synthesized on demand and freeiy diffuses through membranes. It is not broken down enzymaticaiiy because it is unstabie and degrades rapidiy. NO may have several actions, one of which is to increase the production of cGMP by guanyiyi... 

Concern over the role of nitrogen oxides in air pollution. This has stimulated the development of catalysts for the removal of nitrogen oxides from exhaust gases. Nitric oxide is thermodynamically unstable with respect to decomposition to its elements at 25°C and 1 atm ... 

Priestley used mercury instead of water in a pneumatic trough and he was thus able to isolate gases which until then could not be isolated (because they dissolve in water). Priestley was the firstto isolate and characterisethe gases nitric oxide, carbon monoxide, sulphur dioxide, hydrogen chloride and ammonia. 

The complicated redox chemistry of NO c species is both a blessing and a curse in this endeavor, as is illustrated in Figure 4. i. Unlike SO c chemistry, many NO c species are stable and may be used directly as substrates or analyzed for as products these include nitrate, nitrite, hydroxylamine, and ammonia and the gases nitric oxide, nitrous oxide, and dinitrogen. Still, there remains much confusion about NO c chemistry, for example the potential of the simple one-electron reduction of nitric oxide (NO) to the nitroxyl (NO ) state has been widely misrepresented, a recent re-evaluation has set it at ca. -800 mVNHE, a revision of more than one volt from previously cited values. Likewise, the pA"a of the... 

This group of nitrogen-o gen compounds includes the gases nitric oxide, nitrogen dioxide, and nitrous oxide. Natural sources of nitrogen oxides are forest fires, lightning. 

The particles, or molecules, of the gas nitric oxide cannot be exactly like those of nitrogen dioxide. There must be differences that account for the fact that one gas is colorless and the other reddish-brown. Yet, when nitric oxide and air are mixed, color appears, suggesting that nitrogen dioxide has been formed. Apparently molecules present in air somehow combine with the molecules of nitric oxide to form molecules of nitrogen dioxide. We would like to develop our picture of molecules so it will aid us in discussing these changes. 

Seif-Test 12.1A Copper reacts with dilute nitric acid to form copper(II) nitrate and the gas nitric oxide, NO. Write the net ionic equation for the reaction. 

Quite unexpectedly, EDRF was found to be the gas nitric oxide (NO). NO is formed by the action of the enzyme NO synthase, which is cytosolic. The endothe-hal and neuronal forms of NO synthase are activated by Ca + (Table 49-8). The substrate is arginine, and the products are citmUine and NO ... 

The results of a number of studies demonstrate that the gas nitric oxide (NO) plays a functional role in the central nervous system. This all originated with the discovery that the so-called endothelium-derived relaxing factor (EDRF), found in blood vessels, and thought to be a peptide, was in fact NO. The potential roles of this freely diffusible gas have subsequently been extended to many other tissues and organs but we will concentrate on the possible neuronal roles of what is obviously a novel mediator. There are also suggestions that the closely related carbon monoxide may also have a function in the central nervous system. 

NO (molecular weight = 30) is small but plays a big role in physiological regulation, not least in the vasculature where its effects were first seen (see Chapter 4). Endothelium-derived relaxation factor (EDRF) was discovered its ability to cause dilatation of vessels by relaxing the arterial muscle layer. Only much later was EDRF discovered to be a gas, nitric oxide. More recent interest in NO is based on the evidence that it is antiatherogenic. The pathogenesis of atherosclerosis is complex but many of the known effects of NO can be implicated in this common and serious condition. 

The mechanism by which organic nitrates relieve the pain of angina pectoris was not discovered until nitric oxide was identified as the agent which was responsible for vasodilation of arteries. It was known for many years that endothelial cells released a factor that resulted in vasodilation a factor appropriately called endothelial relaxing factor (EDRF). It was, however, some time before the factor was identified, probably because it turned out to be a gas - nitric oxide - which was totally unexpected. Nitric oxide is now known to be a very important messenger molecule involved in the regulation of many other systems. The mechanism by which it causes vasodilation is described in Chapter 13. 

Dalton s work provided a system for representing chemical reactions, but inevitably, conflicts arose when trying to resolve Dalton s idea on chemical combination with experimental evidence. According to Dalton, one volume of nitrogen gas combined with one volume of oxygen to give one volume of nitrous gas (nitric oxide). Dalton referred to combination of atoms as compound atoms. Using Dalton s symbols, this reaction would be represented as... 

When combustion takes place in a stream of gas, nitric oxide is formed after the fuel has completely burned. 

For years, articles in the medical literature detailed the activities and the functions of EDRF. Even before scientists knew what it was, they recognized the enormous importance of EDRF. Despite the difficulty of isolating and identifying something that appeared and disappeared in a nanosecond, EDRF was discovered to be a gas, nitric oxide (NO). That discovery earned three doctors the Nobel Prize in medicine in 1998. 

Izquierdo, M.T. and Rubio, B. (1998). Influence of char physicochemical features on the flue gas nitric oxide reduction with chars. Environ. Sci. TechnoL, 32, 4017-22. 

One gas, nitric oxide (whose chemical symbol is NO ), serves the body in a host of useful ways. Scientists were rather surprised not many years ago when they discovered that the gas NO is a chemical messenger. Tiny and hard to study in the laboratory, NO eluded scientists for many years. Other molecular messengers—such as neurotransmitters and larger proteins—can be relatively easily extracted from body fluids and studied in a test tube, where they can remain intact for minutes or even hours at body temperatures. NO, on the other hand, vanishes in seconds. While this property makes it horrendously difficult to study, such volatility renders NO a molecule with extraordinary versatility. In a snap, NO can open blood vessels, help pass electrical signals between nerves, or fight infections. 

In effect, the reactions in Eqns 7.3 and 7.4 bring about the reverse ofEqns 7.1 and 7.2. Another anthropogenic gas, nitric oxide (NO), scavenges ozone in a similar way (to form nitrogen dioxide, N02) and is produced by the dissociation of N20, which can be generated from fossil fuel combustion and from the decomposition... 

The amino acid Arginine is a precursor to a novel second messenger and neurotransmitter, which is a gas, nitric oxide. Nitric oxide is produced from arginine in an unusual five-electron oxidation that also yields citrulline (see Figure 21.3). The enzyme catalyzing the reaction, nitric oxide synthase, contains bound FMN, FAD, non-heme iron, and tetrahydrobiopterin. 

Characters and Tests.—Colourless liquid. Sp. gr. 1 42 boiling-point 250 F. Exposed to air, it emits acrid and corrosive fumes. Copper dropped into a mixture of equal parts of the add and water causes the evolution of a colourless gas (nitric oxide), which, as it mixes with the oxygen of the air, forms ruddy fumes (nitric trioxide and nitric peroxide). A crystal of ferrous sulphate dropped into the add, diluted with an equal bulk of water, becomes surrounded by a brown cloud if the mixture be cold. The add should leave no residue on evaporation. Diluted with six times its volume of distilled water, it should give no precipitate with barium nitrate or silver nitrate, showing the absence of sulphuric and hydrochloric acids. 

The gas nitric oxide (NO) was first identified as a putative neurotransmitter substance in the mammalian brain by Garthwaite et al. in 1988 (1). In 1990, the enzyme responsible for synthesis of NO in the brain, NO synthase (NOS), was purified and antibodies to it were used to establish the distribution of NO-producing neurons in the rat brain (2). NOS was also found to be responsible for an enzyme activity in the brain known as NADPH diaphorase that was first described by Thomas and Pearse in 1961 (2—5). 

Nitric oxide at room temperature is a colorless, nonflammable, toxic gas. Nitric oxide in the presence of air forms brown fumes of nitrogen dioxide, which is extremely reactive and a strong oxidizing agent. The conversion of nitric oxide to nitrogen dioxide is rate dependent on the concentration of oxygen and the square of the concentration of nitric oxide. It also reacts vigorously with fluorine oxides and, when moisture is present, chlorine. Nitric oxide is shipped in a nonliquefied form at a cylinder pressure of 514.7 psia (3549 kPa abs) at 70°F (21.1°C). 

---