The effect of substituents on aromatic ring on antioxidant capacity of phenolic substances

English. This study comprises thirteen selected phenolic antioxidants as follows: vanillin, acetosyringone, eugenol, isoeugenol, 4-ethylguaiacol, guaiacol and acids: gentisic, 4-hydroxybenzoic, protocatechuic, ferulic, syringic, coffee, chlorogenic. For each of the phenolic substances, total antioxidant capacity (TAC) was measured using the FRAP and DPPH method expressed as TEAC (Trolox Equivalent Antioxidant Capacity); antioxidants with the concentration of 20 mg/l were compared with each other as well as against Trolox. It was found based on the results of measurements that the presence and position of some substitution groups on fenolic ring significantly affect the antioxidant capacity of these substances. Larger antioxidant capacity was measured in multiple hydroxylated substances. An effect was also observed of the type of the functional group where substances possessing a hydroxyl group instead of the methoxyl group featured significant antioxidant capacity. Similar was seen for substances possessing a carboxyl group instead of acetyl group. An effect was also observed immediately between the ortho and para positions of hydroxyl groups in aromatic ring. Examples include gentisic and protocatechuic acid, where while either of the acids has the identical molecular formula, i.e., C7H6O4, for the hydroxyl group the antioxidant capacity is 1.2 to 1.7 times higher in case of the ortho position in gentisic acid than in the para position in protocatechuic acid.

English. phenols, antioxidant capacity, functional group, FRAP, DPPH

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