|Molar mass||430.71 g/mol|
|Appearance||yellow-brown viscous liquid|
|Melting point||2.5 to 3.5 °C (36.5 to 38.3 °F; 275.6 to 276.6 K)|
|Boiling point||200 to 220 °C (392 to 428 °F; 473 to 493 K) at 0.1 mmHg|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is: / ?)(|
α-Tocopherol is a form of vitamin E that is preferentially absorbed and accumulated in humans. The measurement of "vitamin E" activity in international units (IU) was based on fertility enhancement by the prevention of spontaneous abortions in pregnant rats relative to alpha-tocopherol.
There are three stereocenters in alpha-tocopherol, so this is a chiral molecule. The eight stereoisomers of alpha-tocopherol differ in the arrangement of groups around these stereocenters. In the image of RRR-alpha-tocopherol, all three stereocenters are in the R form. However, if the middle of the three stereocenters were changed (so the hydrogen was now pointing down and the methyl group pointing up), this would become the structure of RSR-alpha-tocopherol. RSR-alpha-tocopherol and RRR-alpha-tocopherol are diastereomers of each other. These stereoisomers can also be named in an alternative older nomenclature, where the stereocenters are either in the d or l form.
1 IU of tocopherol is defined as ⅔ milligrams of RRR-alpha-tocopherol (formerly named d-alpha-tocopherol or sometimes ddd-alpha-tocopherol). 1 IU is also defined as 1 milligram of an equal mix of the eight stereoisomers, which is a racemic mixture called all-rac-alpha-tocopheryl acetate. This mix of stereoisomers is often called dl-alpha-tocopheryl acetate, even though it is more precisely dl,dl,dl-alpha-tocopheryl acetate). However, 1 IU of this racemic mixture is not now considered equivalent to 1 IU of natural (RRR) α-tocopherol, and the Institute of Medicine and the USDA now convert IU's of the racemic mixture to milligrams of equivalent RRR using 1 IU racemic mixture = 0.45 "milligrams α-tocopherol".
- Merck Index, 11th Edition, 9931.
- Rigotti A (2007). "Absorption, transport, and tissue delivery of vitamin E". Mol. Aspects Med. 28 (5–6): 423–36. doi:10.1016/j.mam.2007.01.002. PMID 17320165.
- Jensen SK, Lauridsen C (2007). "Alpha-tocopherol stereoisomers". Vitam. Horm. 76: 281–308. doi:10.1016/S0083-6729(07)76010-7. PMID 17628178.
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- Composition of Foods Raw, Processed, Prepared USDA National Nutrient Database for Standard Reference, Release 20 USDA, February 2008