Caffeine
Note: some carbon and hydrogen atoms are omitted in this diagram. |
In this diagram, black is carbon, blue is nitrogen, red is oxygen, and white is hydrogen. |
Caffeine is a chemical compound found naturally in such foods as coffee beans, tea, cacao beans (chocolate), kola nuts, and guarana. It is well known for its characteristic, intensely bitter taste, and as a stimulant of the central nervous system, heart, and respiration. It is also a diuretic. It is added to some soft drinks such as colas and Mountain Dew.
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2 Physical properties 3 Sources 4 Metabolism and toxicology 5 External Links |
Caffeine is an alkaloid of the methylxanthine family, which also includes the similar compounds theophylline and theobromine. In its pure state it is an intensely bitter white powder. Its chemical formula is C8H10N4O2, its systematic name is 1,3,7-trimethylxanthine or 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, and its structure is shown below.
Pure caffeine occurs as odorless, white, fleecy masses, glistening needles or powder.
One dose of caffeine is generally considered to be 200 mg, delivered by one standard cup of coffee or one caffeine tablet. Real-world coffee varies considerably in caffeine content per cup, from about 75 - 250 mg.
Tea and cola contain somewhat less caffeine per serving than coffee, while yerba mate contains significantly more.
The amount of caffeine in some common consumables is approximately as follows:
Caffeine is thought to act on the brain by blocking adenosine receptors. Adenosine, when bound to receptors of nerve cells, slows down nerve cell activity; this happens, among other times, during sleep. The caffeine molecule, being similar to adenosine, binds to the same receptors but doesn't cause the cells to slow down; instead, the caffeine blocks the receptors and thereby the adenosine action. The resulting increased nerve activity causes the release of the hormone epinephrine, which in turn leads to several effects such as higher heart rate, increased blood pressure, increased blood flow to muscles, decreased blood flow to the skin and inner organs, and release of glucose by the liver. In addition, caffeine, similar to amphetamines, increases the levels of the neurotransmitter dopamine in the brain.
Caffeine is quickly and completely removed from the brain and, unlike alcohol or other CNS stimulants, its effects are short lived. In addition, caffeine does not affect concentration or higher mental functions, and hence caffeinated drinks are often consumed in the course of work.
Continued consumption of caffeine can lead to tolerance. Upon withdrawal, the body becomes oversensitive to adenosine, causing the blood pressure to drop dramatically, leading to headache and other symptoms.
Recent studies suggest that caffeine intake (in coffee) may decrease the risk of developing Parkinson's disease, but additional study is needed.
Too much caffeine can lead to caffeine intoxication. The symptoms of this disorder are restlessness, nervousness, excitement, insomnia, flushed face, diuresis, and gastrointestial complaints. They can occur in some people after as little as 250 mg/d. More than 1 g/d may result in muscle twitching, rambling flow of thought and speech, cardiac arrythmia, and psychomotor agitation. Caffeine intoxication can lead to symptoms similar to panic disorder and generalized anxiety disorder. The LD50 is estimated to be about 10 /kg of body mass, or about 3,750 cups of coffee for an average adult.
Chemical properties
Physical properties
BOILING POINT: 178 °C (sublimes)
MELTING POINT: 238 °C
SPECIFIC GRAVITY: 1.2
VOLATILITY: 0.5%
VAPOR PRESSURE: 760 mm Hg @ 178 °C
pH: 6.9 (1% solution)
SOLUBILITY IN WATER: 2.17% VAPOR DENSITY: 6.7
MOLECULAR WEIGHT: 194.19
Sources
Metabolism and toxicology
External LinksCaffeine Content of Foods
