Science Fair Project Encyclopedia
|Molecular mass||162.23 g/mol|
|Melting point||-7.9 °C|
|Boiling point||247 °C|
Nicotine is an organic compound, an alkaloid found naturally throughout the tobacco plant, with a high concentration in the leaves. It is considered a carcinogen, and constitutes 0.3 to 5% of the plant by dry weight. The biosynthesis takes place in the roots and it is accumulated in the leaves. It is a potent nerve poison and is included in many insecticides. In lower concentrations, the substance is a stimulant and is one of the main factors leading to the pleasure and habit-forming qualities of tobacco smoking. In addition to the tobacco plant, nicotine is also found in lower quantities in other members of the Solanaceae (nightshade) family, which includes tomato, potato, eggplant (aubergine), and green pepper. Nicotine alkaloids are also found in the leaves of the coca plant.
Nicotine is a hygroscopic oily liquid that is miscible with water in its base form. As a nitrogenous base, nicotine forms salts with acids that are usually solid and water soluble. Nicotine easily penetrates the skin and forms vapors at elevated temperature.
Effects on the body
In small doses nicotine has a stimulating effect, increasing activity, alertness and memory. Repeat users report a pleasant relaxing effect. It also increases the heart rate and blood pressure and reduces the appetite. In large doses it may cause vomiting and nausea. The LD50 is 50 mg/kg for rats and 3 mg/kg for mice. 40-60 mg can be a lethal dosage for adult human beings.
Repeat users of nicotine often develop a physical dependency to the chemical. A report released on May 16, 1988 by United States Surgeon General C. Everett Koop stated that the addictive properties of nicotine are similar to those of heroin and cocaine; although many people do not agree with such a comparison. Physical withdrawal symptoms include irritability, headaches, anxiety, cognitive disturbances and sleep disruption. These symptoms may last for months or years, although they peak at around 48-72 hours, and generally cease after two to six weeks.
Although the amount of nicotine inhaled with tobacco smoke is quite small (most of the substance is destroyed by the heat) it is still sufficient to cause dependence. The amount of nicotine absorbed by the body from smoking depends on many factors, including the type of tobacco, whether the smoke is inhaled, and whether a filter is used. For chewing tobacco, which is held in the mouth between the cheek and gum, the amount released into the body tends to be much greater than smoked tobacco.
As nicotine enters the body, it quickly gets distributed through the bloodstream and can cross the blood-brain barrier. On average it takes about seven seconds for the substance to reach the brain. It acts on the nicotinic acetylcholine receptors. In small concentrations it increases the activity of these receptors, among other things leading to an increased flow of adrenaline, a stimulating hormone. The release of adrenaline causes an increase in heart rate, blood pressure and respiration, as well as higher glucose levels in the blood. Cotinine is a break-down product of nicotine which remains in the blood for up to 48 hours, and so can be used as an indicator of a person's exposure to smoke. In high doses, nicotine blocks the nicotinic acetylcholine receptor, which is the reason for its toxicity and its effectiveness as an insecticide.
In addition, nicotine increases dopamine levels in the reward circuits of the brain. Studies have shown that smoking tobacco inhibits monoamine oxidase (MAO), an enzyme responsible for breaking down monoaminergic neurotransmitters such as dopamine, in the brain. It is currently believed that nicotine by itself does not inhibit the production of monoamine oxidase (MAO), but that other ingredients in inhaled tobacco smoke are believed to be responsible for this activity. Thus it generates feelings of pleasure. This reaction is similar to that caused by cocaine and heroin, and is another reason people keep smoking: to sustain high dopamine levels.
It has been noted that the majority of people diagnosed with schizophrenia smoke tobacco. Estimates for the number of schizophrenics that smoke range from 75% to 90%. It is argued that the increased level of smoking in schizophrenia may be due to a desire to self-medicate with nicotine.  
It has long been thought that tar and other chemicals in tobacco were the main cause of cancer but recent studies showed that nicotine alone has carcinogenic properties by inhibiting the natural ability of the body to get rid of cells with significant genetic damage before they turn cancerous.
History and name
Nicotine is named after the tobacco plant Nicotiana tabacum which in turn is named after Jean Nicot, who sent tobacco seeds from Portugal to Paris in 1550 and promoted its medicinal use. It was first isolated in 1828; its molecular formula was established in 1843 and it was first synthesized in 1904.
- Guardian article: "Nicotine could soon be rehabilitated as a treatment for schizophrenia, Alzheimer's and Parkinson's diseases, as well as hyperactivity disorders."
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details