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Chemical compound From Wikipedia, the free encyclopedia
Alkannin is a natural dye that is obtained from the extracts of the plant dyer's alkanet (Alkanna tinctoria) which is found in the Mediterranean region. The dye is used as a food coloring and in cosmetics; within the European E number schedule, it is numbered E103. It is used as a red-brown food additive in regions such as Australia.[2] Alkannin is deep red in an acid and blue in an alkaline environment.[3] The chemical structure as a naphthoquinone derivative was first determined by Hans Brockmann in 1936.[4] The (R)-enantiomer of alkannin is known as shikonin, and the racemic mixture of the two is known as shikalkin.[5][6]
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Names | |
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Preferred IUPAC name
5,8-Dihydroxy-2-[(1S)-1-hydroxy-4-methylpent-3-en-1-yl]naphthalene-1,4-dione | |
Other names
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Identifiers | |
3D model (JSmol) |
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ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.007.497 |
E number | E103 (colours) |
KEGG | |
PubChem CID |
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UNII | |
CompTox Dashboard (EPA) |
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Properties[1] | |
C16H16O5 | |
Molar mass | 288.299 g·mol−1 |
Appearance | Red-brown crystalline prisms |
Density | 1.15 g/mL |
Melting point | 149 °C (300 °F; 422 K) |
Boiling point | 567 °C (1,053 °F; 840 K) |
Sparingly soluble | |
Hazards | |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
3.0 g/kg (mice) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The enzyme 4-hydroxybenzoate geranyltransferase utilizes geranyl diphosphate and 4-hydroxybenzoic acid to produce 3-geranyl-4-hydroxybenzoic acid and diphosphate. These compounds are then used to form alkannin.[6]
Because the root bark (cork layers) of Alkanna tinctoria contains large amounts of red naphthoquinone pigments, including alkannin, the roots of these plants are red-purple. When extracted from fresh tissues, the pigment gradually darkens over several days, finally forming black precipitates, which are thought to be polymers.[7]
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