# Circé

The oxyde nitric or nitric oxide or nitric oxide or NR O is a chemical Composé made of a Atome of Oxygène and of an atom of Azote. It is a Gaz in the Normal conditions of pressure and temperature. It is important a Neurotransmetteur at the Mammifère S including at the Homme S, one of rare the Neurotransmetteur S gas known.

The nitric oxyde (NO), should not be confused with others Oxyde S of Azote, the such monoxide of diazotizes N2O, which one calls laughing gas, and which is a general Anesthésique, or the such Dioxide nitrogen NO2, red-brown extremely irritant and harmful gas, which is formed by fast Oxydation of NO by oxygen in air.

Its great reactivity with respect to the ridicalizing compounds as the molecular oxygen - which is a biradical - or the anion superoxyde is due to the fact that it is itself a ridicalizing compound - its Spin electronic total is worth 1/2. In biological environment, its time of half-life is estimated between 1 and 5 seconds, even 30 seconds. The Peroxynitrite S obtained are powerful oxidising agents and nitriding.

## Environmental production and effects

At high temperature, diazotizes it and the dioxygene react to give nitric oxyde, for example under the effect of the lightning. The human activity radically modified the production of nitric oxyde, which is formed in the combustion chambers of the spark-ignition engines. One of the goals of the catalytic mufflers is to reverse this reaction.

Nitric acid, which has been implicated in Acid rain. Furthermore, both NO and NO2 participate in ozone to bush-hammer depletion. -->

## Chemistry

The chemical properties of nitric oxyde are very numerous. What follows is a short overflight of its methods of preparation and its reactivity.

### Preparation

The nitric oxyde is formed starting from the elements at high temperature, as it was higher indicated.

It can be synthesized at the laboratory according to the following reactions of oxydoreduction, where a nitrogenized derivative of step oxidation higher than +II (acid nitric: +V; nitrous acid: + III) is treated by the adequate reducer:

NB: all these reactions must be implemented in the absence of oxygen, because this one quickly oxidizes nitrogen dioxide NO.

Thus the reduction of the nitric acid by copper

8HNO3 + 3Cu → 3Cu (NO3) 2 + 4:00 2O + 2NO

or that of the nitrous acid (formed in situ) by the ions iodizes or ferrous

2NaNO2 + 2NaI + 2:00 2SO4 → I2 + 4NaHSO4 + 2NO

2NaNO2 + 2FeSO4 + 3:00 2SO4 → Fe2 (SO4) 3 + 2NaHSO4 + 2:00 2O + 2NO

The preceding reaction is a simple method making it possible to obtain NO at the laboratory.

The nitric oxyde can also be obtained in anhydrous medium thanks to the nitrite and nitrate reduction by chromium III:

3KNO2 (L) + KNO3 (L) + Cr2O3 (S) → 2K2CrO4 (S) + 4NO

The industrial synthesis of NO consists of the oxidation of ammonia by oxygen in air in the presence of platinum sponge towards 750-900°C.

### Reactivity

The Diagram of Frost to pH =0 of the Nitrogen watch although the nitric oxyde is unstable and that it would owe dismuter is diazotized some and in nitric acid. It is in fact very easily oxidized out of nitrogen dioxide, more stable, by oxygen in air. This is why one observes the russet-red vapors of this last gas when one oxidizes copper by the concentrated nitric acid.

A plausible assumption is that the biradical O2 binds to two radicals NO to give ON-OO-NO, which undergoes then a homolytic rupture leading to NO2.

However, in the absence of oxygen, it dismute towards 50°C in N2O (monoxide of diazotizes or Laughing gas and NO2 (russet-red vapors). With 25°C, the reaction speed is practically null, and NO is metastable there.

In aqueous solution, NO dissolves to give nitrous acid HNO2, according to the possible reaction pathway according to:

4NO + O2 + 2:00 2O → 4HNO2

NO reacts with the difluor, the dichlore and the dibrome to give compounds of type X-NO, known under the name of halides of nitrosyle. Iodine is too not very oxidizing to give place to the iodide formation of nitrosyle.

The iodotrifluorocarbone reacts with NO to give one of rare known water gas, the nitrosotrifluorocarbone:

NO + CF3I → I2 + CF3NO

The speed of formation of the ion Peroxynitrite starting from nitric oxyde and of the ion superoxyde is of 1,9.1010 mol-1s-1, which implies the presence of Peroxynitrite in vitro and in vivo to the least excess of its two precursors.

### The nitric oxyde is also a ligand

The nitric oxyde molecule is related with that of the Carbon monoxide CO, with the difference which it comprises an additional electron, which occupies orbital a $p$ antiliante. Thus NO forms complexes of the same type as those formed with CO, the angle of connection M-N=O being practically equal to 180° - actually this angle varies between 160° and 180°.

These complexes are thus regarded as linear. In this case, the nitrogen formally engages its free doublet in the connection of coordination. However, the nitrogen is oxidized because it gives its lone electron to metal that it coordinate and who are thus reduced. Thus the complexes tétracarbonylonickel, nitrosylotricarbonylocobalt and dicarbonylodinitrosylofer are isostructuraux (tetrahedral) because isoelectronic.

NR O can form complexes by giving one electron to metal. That led to a group M-N-O where the angle of connection lies between 120° and 140°.

It can also play the part of bridge between two metal centers by the means of nitrogen.

#### Reactions of the complexes nitrosyle

The chemistry of composed of coordination of NO is vast and will be approached only briefly. For example NO forms part between niobium and a ligand methyl of the following reaction:

#### Characterization of coordinate NO

Final NO can be recognized by their intense infra-red absorption with 1610 cm-1. The numbers of wave of absorption IR of the angular derivatives are lower.

## Quantitative analysis

The quantitative analysis of nitric oxyde implements a simple reaction chemiluminescente with ozone.

A sample containing NO is mixed with a quantity of ozone in excess. The nitric oxyde reacts by forming Oxygène and di Oxyde of Azote. The reaction also releases from energy in the form of electromagnetic waves in the visible one: it is the chemiluminescence. The intensity of the produced light, measured thanks to a photodetector, is proportional to the quantity of nitric oxyde.

One can also proportion by various electrochemical methods (potentiometry with the potassium permanganate, polarography)

## Technical applications

Semiconductor industry for various processes. In one off its applications it is used along with Nitrous oxide to form oxynitride spoil in CMOS devices. Intermediate It is year off the Ostwald process, which converts Ammonia into Nitric acid.

Nitric oxide edge Be used for detecting surface radicals one polymers. Radical Quenching off surface S with nitric oxide results in incorporation off nitrogen, which edge Be quantified by means off X-ray photoelectron spectroscopy.

Because off its production in allergic reactions, there is research one using levels off exhaled nitric oxide to optimize treatment off Asthma.

It has also recently been seeing uses ace has supplement in Bodybuilding. It is believed that it' S dialation off the blood vessels (vasodilation) increases blood flow to the muscles, which in turn leads to increased strength, endurance and muscle size. Ace it has fairly new product one the market, there is ace off yet little research to conclusivley prove gold disprove thesis claims. Nitric oxide supplements C not actually contain nitric oxide, goal rather arginine and other precursors such ace citrulline, Pycnogenol, L-aspartic acid, and ginsenosides which the body synthesizes into nitric oxide. -->

## Biological functions

NO is a Molécule Endogène released by the cells endothéliales, the Macrophage S, the cells of the liver and the Neuron S.

It is synthesized starting from the L Arginine and of the Oxygène by several Enzyme S known as NO Synthase S (OUR), which are Hémoprotéine S close relations of the Cytochrome P450. The Catalyseur of the Oxydation by the oxygen of the grouping iminourée of the arginine is thus the Fer of the Hème which passes from the oxidation step + II to the degree + III and vice versa.

The connection of NO to the Thiol S of bottom molecular weight - such as the Glutathion - led to the formation of S-nitrosothiols which would constitute an important determinant for the activity and the transport of NO These compounds can subsequently act like donors of NO and thus increase its half-life substantially.

The cellular activity of nitric oxyde passes by two essential ways, that which consists of the intracellular production of Guanosine monophosphate cyclic (GMPc) starting from the Guanosine triphosphate (GTP), and the cytotoxic formation of peroxynitrites.

In the organization the oxyde nitric (NO) fulfills several functions:

#### vasodilator

The Endothélium of the Blood-vessels makes use of the NO to start the relaxation of its tunic of Smooth muscle, thus causing a vasodilatation and an increase in the blood flow and a reduction in the aggregation of the blood plates (thrombocytes). It is thought that this mechanism is essential to the safeguarding of the endothelium. At a great proportion the human ones, this synthesis of NO appears insufficient, increasing their risk consequently to present a Cardiovascular disease. This mechanism explains the use of the derivatives nitrated like the Trinitrine in the treatment of these same cardiac diseases: These drugs are transformed into NO , in a way not yet completely elucidated, which in its turn dilates the coronary arteries, blood-vessels irrigating the heart, increasing its blood contribution.

#### microbicide

The Macrophage S, cells of the Immune system, produce NO with an aim of eliminating from the pathogenic Bactéries, NO which can, in certain circumstances, to cause harmful side effects: it is the case in fulminant the infections known as Septicémie S, where the excessive production of NO by the macrophages leads to a massive vasodilatation, main cause of the Hypotension met in the septic Choc.

#### neuro-transmitter

The NO plays the part of a Neurotransmetteur between cells nervous S. With the difference of the majority of the other neuro-transmitters, whose action in the synaptic slit has as a single target the post-synaptic neuron, the small molecule of NO diffuses widely and can reach several surrounding neurons, including neurons not inter connected by synapses. It is thought that this process is implied in the memorizing by ensuring the long-term memorizing.

#### releasing smooth muscles

The NO is present in several bodies of the digestive Tract like neuro-transmitter non-adrenergic, not-cholinergic. It is responsible for the relieving of the smooth muscles of the gastro-intestinal apparatus. In particular it increases the capacity of the Estomac to store food liquids.

#### regulator of the apoptose

The nitric oxyde is an essential regulator of the cellular Apoptose. It can have an effect antiapoptotic, or, conversely, an effect apoptotic.

In the presence of an high rate of ion Superoxyde O2-, the nitric oxyde allows the formation of ion Peroxynitrite, probably person in charge of the modification of the Potentiel of membrane mitochondrial as well as many phenomena of cellular Apoptose, in particular that of the cells of the immune system.

## Therapeutic uses

• It is used in medicine as inhaled vasodilator. The use of inhaled vasodilators allows vasodilater in a selective way the capillaries of the well broken down pulmonary zones. This makes it possible to reduce the pulmonary arterial Hypertension related to the hypoxic vasoconstriction and to increase the oxygenation of blood.
• a compound named Dimethyl-Arginine Asymmetrical (ADMA) is an inhibiting known of the synthesis of NO , and is thus regarded as a biological marker of cardiovascular dysfonction.
• the production of NO also plays a big role in obtaining and the conservation of a durable erection. Increased concentrations of GMPc lead to a vasodilatation and an erection of better quality. It is thought that the effect of the “Poppers” is also obtained via the NO , causing a relieving of the smooth muscle fibers which surround the small arteries irrigating the cavernous Corps Pénis and increase the blood surge. The Sildénafil (Viagra) and the Tadalafil (Cialis), are inhibiting competitive of the standard Enzyme Phosphodiestérase 5 (PDE5) responsible for the inactivation of the cyclic GMP in GMP.

The discovery of the biological properties of the NO in the Années 1980 was completely unexpected and caused a certain agitation. The newspaper Science named the NO “Molecule of the year” in 1992, a Learned society of the NO was created and an scientific magazine entirely devoted to the NO appeared. The Nobel Prize of Medicine and Physiology was given in 1998 to Ferid Murad, Robert F. Furchgott, and Louis J. Ignarro for their work on the functions of neurotransmission of the NO . This work is at the origin of the foundation of the French pharmaceutical company Nicox. One estimates at 3000 per annum the publication of scientific articles on the role in Biologie of nitric oxyde.

## Sources

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