4-Aminobenzoic acid
IUPAC name	4-Aminobenzoic acid
Other names	para-Aminobenzoic acid; p-Aminobenzoic acid; PABA; Vitamin Bx; Bacterial vitamin H1
Identifiers
CAS number	150-13-0 Y
PubChem	978
SMILES	O=C(O)c1ccc(N)cc1
InChI	1/C7H7NO2/c8-6-3-1-5(2-4-6)7(9)10/h1-4H,8H2,(H,9,10)
InChI key	ALYNCZNDIQEVRV-UHFFFAOYAH
ChemSpider ID	953
Properties
Molecular formula	C7H7NO2
Molar mass	137.14 g mol−1
Appearance	White crystals
Density	1.374 g/mL
Melting point	187–189 °C
Solubility in water	1 g/170 mL (25 °C) 1 g/90 mL (90 °C)
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

4-Aminobenzoic acid (also known as para-aminobenzoic acid or PABA) is an organic compound with the formula H₂NC₆H₄CO₂H. PABA is a white crystalline substance that is only slightly soluble in water. It consists of a benzene ring substituted with an amino group and a carboxyl group.

Contents 1 Production and occurrence 2 Biology 2.1 Biochemistry 2.2 Medical use 2.3 Nutritional supplement 3 Commercial and industrial use 4 Safety considerations 5 References 6 External links

[edit] Production and occurrence

Industrially, PABA is mainly prepared by two routes: reduction of para-nitrobenzoic acid and the Hoffman degradation of the monoamide derived from terephthalic acid.^[1]

Food sources of PABA include liver, brewer's yeast (and unfiltered beer), kidney, molasses, and whole grains.^[2]

[edit] Biology

[edit] Biochemistry

PABA is an intermediate in the bacterial synthesis of folate. It has been referred to as Vitamin B_x.^[3] Some bacteria in the human intestinal tract such as E. coli^[4] require PABA^[5]. Humans require folate since we lack the enzymes to convert PABA to folate. Therefore in humans PABA is not a vitamin and is considered nutritionally unimportant.^[6]

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.

[edit] Medical use

The potassium salt is used as a drug against fibrotic skin disorders, such as Peyronie's disease, under the trade name Potaba.^[7] 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.

[edit] 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 (vitiligo), and premature grey hair.^[8]

[edit] 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. ^[9] Patented in 1943, PABA was one of the first active indregients to be used in sunscreen. ^[10] Initially, in vivo studies on mice showed that PABA reduced UV damage. Additionally, PABA was shown to protect against skin tumors in rodents. ^[11] Animal and in vitro studies in the early 1980's suggested PABA might increase the risk of cellular UV damage.^[12] 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 octyl dimethyl PABA (padimate O) are currently used in some products.

[edit] Safety considerations

PABA is largely nontoxic, the LD50 of PABA in dogs (oral) is 2 g/kg.^[1] Allergic reactions to PABA can occur. PABA is formed in the metabolism of certain ester local anesthetics, and many allergic reactions to local anesthetics are the result of reactions to PABA.^[13]

[edit] References

[edit] External links

• PABA Cancer link

v • d • e Sunscreening agents approved by the US FDA or other agencies UVA: 400–315 nm • UVB: 315–290 nm • chemical agents unless otherwise noted UVA filters Avobenzone (Parsol 1789) • Bisdisulizole disodium (Neo Heliopan AP) • Diethylamino hydroxybenzoyl hexyl benzoate (Uvinul A Plus) • Ecamsule (Mexoryl SX) • Methyl anthranilate UVB filters 4-Aminobenzoic acid (PABA) • Cinoxate • Ethylhexyl triazone (Uvinul T 150) • Homosalate • 4-Methylbenzylidene camphor (Parsol 5000) • Octyl methoxycinnamate (Octinoxate) • Octyl salicylate (Octisalate) • Padimate O (Escalol 507) • Phenylbenzimidazole sulfonic acid (Ensulizole) • Polysilicone-15 (Parsol SLX) • Trolamine salicylate UVA+UVB filters Bemotrizinol (Tinosorb S) • Benzophenones 1–12 • Dioxybenzone • Drometrizole trisiloxane (Mexoryl XL) • Iscotrizinol (Uvasorb HEB) • Octocrylene • Oxybenzone (Eusolex 4360) • Sulisobenzone • hybrid (chemical/physical): Bisoctrizole (Tinosorb M) • physical: Titanium dioxide, Zinc oxide See also: Photoprotection • Sunburn • Sun protective clothing