Phenolic antioxidants chemical structures

Polyhydroxy phenols. Representative chemical structures of the various phenolic antioxidants are shown in Figure 2. 

Among the plant phenols, the flavonoids and the anthocyanidins, belonging to the 1,3-diphenylpropans, have been studied in most detail, mainly because of their potential health benefits. With more than 4,000 different flavonoids known, systematic studies of the effects of variation in molecular structure on physico-chemical properties of importance for antioxidative effects have also been possible (Jovanovic et al, 1994 Seeram and Nair, 2002). Flavonoids were originally found not to behave as efficiently as the classic phenolic antioxidants like a-tocopherol and synthetic phenolic antioxidants in donating... 

After benzoylation, it was possible to analyze together the food substances of varying chemical structures, such as alcohols, esters of 4-hydroxybenzoic acid, phenolic antioxidants, saccharides, and sugar alcohols. The method allowed the determination of these substances in different matrices by the same analytical procedure, using the same cleanup. The preservatives were separated on an RP-18 column. Acetonitrile-water (50 35) or acetonitrile-water-butylmethyl ether (110 35 40) were used as mobile phases. Detection was UV at 230 nm (71). 

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).

Sudjaroen,Y., Haubner, R., Wilrtele, C., Hull, W.E., Erben, G., Spiegelhalder, B., Changbumrung, S., Bartsch, H.and Owen, R.W. (2005) Isolation and structure elucidation of phenolic antioxidants from Tamarind (Famarindus indica L.) seeds and pericarp. Food and Chemical Toxicology 43(11), 1673-1682. 

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

Figure 16. Chemical structures of antioxidative phenolic acids.

The main function of metal deactivators (MD) is to retard efficiently metal-catalyzed oxidation of polymers. Polymer contact with metals occur widely, for example, when certain fillers, reinforcements, and pigments are added to polymers, and, more importantly when polymers, such as polyolefins and PVC, are used as insulation materials for copper wires and power cables (copper is a pro-oxidant since it accelerates the decomposition of hydroperoxides to free radicals, which initiate polymer oxidation). The deactivators are normally poly functional chelating compounds with ligands containing atoms like N, O, S, and P (e.g., see Table 1, AOs 33 and 34) that can chelate with metals and decrease their catalytic activity. Depending on their chemical structures, many metal deactivators also function by other antioxidant mechanisms, e.g., AO 33 contains the hindered phenol moiety and would also function as CB-D antioxidants. 

Bungert K. and Eichner K. (2000) Radical scavenging and antioxidative properties of phenolic compounds in relation to their chemical structure Am. Chem. Soc. Symp. Ser. (Caffeinated Beverages) Chem. Abstr. 13, 88522)754, 119 134. 

This review analyzes the data on most important antioxidants for polyolefins, i. e. the data on phenols. To learn consistently the whole mechanism of polyolefin stabilization, it is not possible to consider only the facts about the kinetics of the process and relationships between the chemical structure of stabilizers and their observed efficiency. It is necessary to understand the mechanism of stabilizer action on the basis of knowledge of transformations which occur in the inhibited oxidation and of properties of resulting products. The product analyses were obtained above all from the study of models and from independent syntheses. The confirmation of results under real conditions cannot be always carried out consistently because of low concentrations, difficult isolation, and reactivity of transformation products. It is also difficult to analyze such reaction mixtures directly in a polymer6 ... 

The most obvious feature of Pycnogenol, owing to the basic chemical structure of its components, is its strong antioxidant activity. Phenolic acids, polyphenols, and in particular flavonoids are composed of one (or more) aromatic rings bearing one or more hydroxyl groups and are therefore potentially able to quench free radicals by forming resonance-stabilized phenoxyl radicals. " The ability to quench the reactivity of... 

Consumption of diets rich in fruits is associated with a lowered risk of cancer and cancer mortahty [1], Antioxidants in fruits contribute to their protective effect as anticarcinogens. These protective effects are attributed chiefly by ubiquitous groups of plant secondary metabolites such as phenolic compounds in addition to antioxidant vitamins C and E. Polyphenols or phenolic compounds are a widespread group of ph3dochemicals that are shown to possess different physiological activities associated with their chemical structures. In plants, phenolic compounds are generally involved in protection or defense... 

In the present chapter, we showed that boldine is the main alkaloidal constituent of the Chilean medicinal plant, boldo. Boldine shows potent antioxidant activity and free radical scavenging effects both imder in vitro and in vivo conditions. We also showed that the antioxidant activity of boldine is due to the presence of phenol groups in the aporphine ring of its chemical structure. In view of the multiple applications of boldo in the traditional medicine, it can be concluded that boldine causes no adverse effects and therefore it could be used as antioxidant for mitigation of oxidative stress. Nevertheless, there is no clinical study... 

Representative chemical structures of the various amine antioxidant types are shown in Figure 1. Similarly, phenolic antioxidants can also be subdivided by basic chemical types ... 

In addition to the use of the above phenolic and amine type antioxidants, peroxide decomposers are used to harmlessly decompose the peroxides, which otherwise could decompose to give free radical propagating species, e.g., R-0 or H-0 . Examples of such peroxide decomposers, which act synergisticaUy with the phenolic or amine antioxidants, are dilauryl- 3, 3-thiodiproprionate and tris(p-nonylphenyl)phosphite. These and others are also listed in Table 4.10, with their chemical structures being listed in Table 4.11. We note that some of the peroxide decomposers are also accelerators for sulfur vulcanization. 

---