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Carbon monoxide
From Wikipedia, the free encyclopedia
Carbon monoxide (CO), also called carbonic oxide, is a colorless, odorless and tasteless gas which is lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions.
It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond. It is the simplestoxocarbon, and is an anhydride of formic acid.[citation needed] In coordination complexes the carbon monoxide ligand is called carbonyl.
Carbon monoxide is produced from the partial oxidation of carbon-containing compounds; it forms when there is not enough oxygen to produce carbon dioxide (CO2), such as when operating a stove or an internal combustion engine in an enclosed space. Carbon monoxide burns with a blue flame, producing carbon dioxide.[1] Coal gas, which was widely used before the 1960s for domestic lighting, cooking and heating despite its toxicity, had carbon monoxide as a primary constituent. Some processes in modern technology, such as iron smelting, still produce carbon monoxide as a byproduct.[2]
Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere which generate about 5 x 1012 kilograms per year.[3] Other natural sources of CO include volcanoes, forest fires, and other forms of combustion.
In biology, carbon monoxide is naturally produced by the action of heme oxygenase 1 and 2 on the heme from hemoglobin breakdown. This process produces a certain amount of carboxyhemoglobin in normal persons, even if they do not breathe any carbon monoxide. Following the first report that carbon monoxide is a normal neurotransmitter in 1993 [4], as well as one of three gases that naturally modulate inflammatory responses in the body (the other two being nitric oxide and hydrogen sulfide), carbon monoxide has received a great deal of clinical attention as a biological regulator. In many tissues, all three gases are known to act as anti-inflammatories, vasodilators and encouragers ofneovascular growth.[5] Clinical trials of small amounts of carbon monoxide as a drug, are on-going.
