Chemical Structures of Antioxidants

Fig. 9.6 Chemical structures of antioxidants in phase III clinical trials. Tirilazad mesylate (a) ...

Figure 16. Chemical structures of antioxidative phenolic acids.

Figure 20. Chemical structure of antioxidative sterols identified from (a) oats, and (b) rice and corn fiber.

Fig. 9.4 Chemical structures of cellular lipids that act as endogenous antioxidants. Choline plasmalogens (a) ethanolamine plasmalogens (b) ganglioside (c) and vitamin E (a-tocopherol) (d)...

Fig. 9.5 Chemical structures of low molecular weight antioxidants Melatonin (a) ascorbic acid (Vitamin C) (b) glutathione (c) lipoic acid (d) a-tocopherol (Vitamin E) (e) and a-tocotrienol (f)...

Knowledge about the chemical structure of the antioxidative MRP is very limited. Only a few attempts have been made to characterize them. Evans, et al. (12) demonstrated that pure reductones produced by the reaction between hexoses and secondary amines were effective in inhibiting oxidation of vegetable oils. The importance of reductones formed from amino acids and reducing sugars is, however, still obscure. Eichner (6) suggested that reductone-like compounds, 1,2-enaminols, formed from Amadori rearrangement products could be responsible for the antioxidative effect of MRP. The mechanism was claimed to involve inactivation of lipid hydroperoxides. 

The health benefits explain the growth in interest concerning the characterization and evaluation of phenolics and antioxidant capacity in food-related products. The chemical structures of the main polyphenols found in Madeira table wines are summarized in Fig. 7.13. 

Figure 2. The chemical structures of the two different types of antioxidants used in gasoline are phenylenediamines (PDA) and hindered phenols (such as BHT).

Figure 11-3 Chemical Structure of the Active Antioxidant Principles in Rosemary...

Fig. 1. Chemical structures of some important antioxidants and their transient radical species.

The trace element selenium plays an essential role in the activity of some bacterial and eukaryotic antioxidant enzymes (34). Selenium is incorporated into proteins in the form of the so-called twenty-first amino acid selenocysteine, which is encoded by a UGA stop codon. Although the chemical structure of selenocysteine differs from cysteine only by the replacement of the sulfur atom with selenium, the lower pKa of selenocysteine (5.2) allows for ionization of selenocysteine at physiological pH (35). To read through the UGA stop codon selectively, selenocysteine insertion requires a variety of proteins and RNA stmctures. 

Figure 4. Chemical structures of synthetic phenolic antioxidants commonly used in fats and oils.

Hopia, A.I., Huang, S.-W., Schwarz, K., German, J.B. and Frankel, E.N. 1996. Effect of different lipid systems on antioxidant activity of rosemary constituents camosol and camosic acid with and without alpha-xocopherol. J. Agric. Food Chem. 44 2030-2036. Houlihan, C.M., Ho, C.-T. and Chang, S.S. 1984 Elucidation of the chemical structure of a novel antioxidant, rosmaridiphenol, isolated from rosemary. J. Am. Oil Chem. Soc. 61 1036-1039. 

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