Purpurin

Purpurin, or 1,2,4-trihydroxyanthraquinone, is a naturally occurring red/yellow dye in the roots of the plant madder (or known as Rubia tinctorum L). Purpurin also occurs in madder with alizarin. Purpurin is a crystalline compound with the formula of C14H5O2(OH)3 that is colorless until dissolved in alkalic solutions. It is soluble in ethanol (becomes red) and is soluble in water at boiling and alkalis water (becomes yellow). It has the appearance of dark red needles. It is also called Verantin, Smoke Brown G, Hydroxylizaric acid, and C.I. 58205.

Purpurin is a fast dye for cotton printing and forms complexes with various metal ions.

As relating to biochemistry, purpurin is a glycosaminoglycan binding protein as well as a retinol binding protein. Purpurin's pattern of sequences has shown it to belong to the lipocalin family of proteins.