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)
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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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Biosynthesis
editThe 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]
Research
editBecause 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]
References
edit- ^ The Merck Index, 11th Edition, 243
- ^ Additives Archived 2011-04-06 at the Wayback Machine, Food Standards Australia New Zealand
- ^ Joseph P. Remington and Horatio C. Wood, ed. (1918). "Alkanet". Dispensatory of the United States of America.
- ^ H. Brockmann (1936). "Die Konstitution des Alkannins, Shikonins und Alkannans". Justus Liebigs Ann. Chem. 521 (1): 1–47. doi:10.1002/jlac.19365210102.
- ^ Shmuel Yannai (2012). Dictionary of Food Compounds. CRC Press. p. 478.
- ^ a b Vassilios P. Papageorgiou; Andreana N. Assimopoulou; Elias A. Couladouros; et al. (1999). "The Chemistry and Biology of Alkannin, Shikonin, and Related Naphthazarin Natural Products". Angew. Chem. Int. Ed. 38 (3): 270–300. doi:10.1002/(SICI)1521-3773(19990201)38:3<270::AID-ANIE270>3.0.CO;2-0. PMID 29711637.
- ^ Yazaki, Kazufumi (2017). "Lithospermum erythrorhizon cell cultures: Present and future aspects". Plant Biotechnology. 34 (3): 131–142. doi:10.5511/plantbiotechnology.17.0823a. PMC 6565996. PMID 31275019.