4-Aminobenzoic acid
Encyclopedia
4-Aminobenzoic acid is an organic compound
with the formula
H2NC6H4CO2H. PABA is a white grey crystalline substance that is only slightly soluble in water. It consists of a benzene ring substituted with an amino
group and a carboxyl group.
and the Hoffman degradation of the monoamide derived from terephthalic acid
.
Food sources of PABA include liver, brewer's yeast (and unfiltered beer), kidney, molasses, mushrooms, and whole grains.
PABA is an intermediate in the bacteria
l synthesis of folate. It has been referred to as Vitamin Bx
.
Some bacteria in the human intestinal tract such as E. coli
generate PABA from chorismate. However, humans lack the enzymes to convert PABA to folate, and therefore require a dietary supply of folate, unless they have E. coli that produce folate from PABA. In humans that have E. coli that produce both PABA and folate, PABA is considered nonessential and is not recognized as a vitamin
.
Sulfonamide drugs
are structurally similar to PABA, and their antibacterial activity is due to their ability to interfere with the conversion of PABA to folate by the enzyme dihydropteroate synthetase
. Thus, bacterial growth is limited through folate deficiency without effect on human cells.
, under the trade name Potaba. PABA is also occasionally used in pill form by sufferers of irritable bowel syndrome
to treat its associated gastrointestinal symptoms, and in nutritional epidemiological studies to assess the completeness of 24-hour urine collection for the determination of urinary sodium, potassium, or nitrogen levels.
), and premature grey hair.
Oral supplements of PABA can make the skin less sensitive to sun damage.
In the past, PABA was widely used in sunscreens as a UV filter. It is a UVB absorber, meaning that it can absorb wavelengths between 290-320 nm. Patented in 1943, PABA was one of the first active ingredients to be used in sunscreen. The first in vivo studies on mice showed that PABA reduced UV damage. In addition, PABA was shown to protect against skin tumors in rodents.
Animal and in vitro studies in the early 1980s suggested PABA might increase the risk of cellular UV damage. On the basis of these studies as well as problems with allergies and clothing discoloration, PABA fell out of favor as a sunscreen. However, water-insoluble PABA derivatives such as padimate O are currently used in some products.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
H2NC6H4CO2H. PABA is a white grey crystalline substance that is only slightly soluble in water. It consists of a benzene ring substituted with an amino
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
group and a carboxyl group.
Production and occurrence
In industry, PABA is prepared mainly by two routes: reduction of 4-nitrobenzoic acidNitrobenzoic acid
Nitrobenzoic acids are derivatives of benzoic acid. Two are commercially important. They are about ten times more acidic than the parent benzoic acid .*2-Nitrobenzoic acid is prepared by oxidation of 2-nitrotoluene....
and the Hoffman degradation of the monoamide derived from terephthalic acid
Terephthalic acid
Terephthalic acid is the organic compound with formula C6H42. This colourless solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several billion kilograms are produced annually...
.
Food sources of PABA include liver, brewer's yeast (and unfiltered beer), kidney, molasses, mushrooms, and whole grains.
Biochemistry
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l synthesis of folate. It has been referred to as Vitamin Bx
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
.
Some bacteria in the human intestinal tract such as E. coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
generate PABA from chorismate. However, humans lack the enzymes to convert PABA to folate, and therefore require a dietary supply of folate, unless they have E. coli that produce folate from PABA. In humans that have E. coli that produce both PABA and folate, PABA is considered nonessential and is not recognized as a vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
.
Sulfonamide drugs
Sulfonamide (medicine)
Sulfonamide or sulphonamide is the basis of several groups of drugs. The original antibacterial sulfonamides are synthetic antimicrobial agents that contain the sulfonamide group. Some sulfonamides are also devoid of antibacterial activity, e.g., the anticonvulsant sultiame...
are structurally similar to PABA, and their antibacterial activity is due to their ability to interfere with the conversion of PABA to folate by the enzyme dihydropteroate synthetase
Dihydropteroate synthetase
Dihydropteroate synthetase is an enzyme classified under . It produces dihydropteroate in bacteria, but it is not expressed in most eukaryotes including humans...
. Thus, bacterial growth is limited through folate deficiency without effect on human cells.
Medical use
The potassium salt is used as a drug against fibrotic skin disorders, such as Peyronie's diseasePeyronie's disease
Peyronie's Disease Peyronie's Disease Peyronie's Disease (also known as "Induratio penis plastica", or more recently Chronic Inflammation of the Tunica Albuginea (CITA), is a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis affecting up to 10% of men...
, under the trade name Potaba. PABA is also occasionally used in pill form by sufferers of irritable bowel syndrome
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...
to treat its associated gastrointestinal symptoms, and in nutritional epidemiological studies to assess the completeness of 24-hour urine collection for the determination of urinary sodium, potassium, or nitrogen levels.
Nutritional supplement
Despite the lack of any recognized syndromes of PABA deficiency in humans, many claims of benefit are made by commercial suppliers of PABA as a nutritional supplement. Benefit is claimed for fatigue, irritability, depression, weeping eczema (moist eczema), scleroderma (premature hardening of skin), patchy pigment loss in skin (vitiligoVitiligo
Vitiligo is a condition that causes depigmentation of sections of skin. It occurs when melanocytes, the cells responsible for skin pigmentation, die or are unable to function. The cause of vitiligo is unknown, but research suggests that it may arise from autoimmune, genetic, oxidative stress,...
), and premature grey hair.
Oral supplements of PABA can make the skin less sensitive to sun damage.
Commercial and industrial use
PABA mainly finds use in the biomedical sector. Other uses include its conversion to specialty azo dyes and crosslinking agents.In the past, PABA was widely used in sunscreens as a UV filter. It is a UVB absorber, meaning that it can absorb wavelengths between 290-320 nm. Patented in 1943, PABA was one of the first active ingredients to be used in sunscreen. The first in vivo studies on mice showed that PABA reduced UV damage. In addition, PABA was shown to protect against skin tumors in rodents.
Animal and in vitro studies in the early 1980s suggested PABA might increase the risk of cellular UV damage. On the basis of these studies as well as problems with allergies and clothing discoloration, PABA fell out of favor as a sunscreen. However, water-insoluble PABA derivatives such as padimate O are currently used in some products.