4Aminobenzoesäure

4-Aminobenzoesäure, also known as para-aminobenzoic acid or PABA, is an organic compound with the chemical formula C7H7NO2. It is a white crystalline solid that is sparingly soluble in water. Structurally, it consists of a benzene ring substituted with an amino group (-NH2) and a carboxyl group (-COOH) in opposite (para) positions.

PABA is an important component of the folic acid molecule, which is a B vitamin essential for cell growth and metabolism. While not a vitamin itself in humans, it is synthesized by many bacteria and plants as a precursor to folate. This metabolic pathway is targeted by certain antibiotics, such as sulfonamides, which act as competitive inhibitors of the enzyme that incorporates PABA into folic acid, thus disrupting bacterial growth.

Historically, PABA was considered a vitamin for humans and was sometimes included in vitamin supplements. However, it is now understood that humans obtain sufficient folate from their diet or through the action of gut bacteria, and direct PABA supplementation is not generally required. PABA has also been used in sunscreen lotions due to its ability to absorb ultraviolet (UV) radiation, although its use in this application has decreased due to concerns about skin sensitivity and the availability of more effective UV filters.