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5,7-, 5,8-, 6,8-, 7,8-dichloro-4-quinolinol-3-carboxylic acid (5,7-, 5,8-, 6,8-, 7,8-DCQA) together with 7-chloro-4-quinolinol-3-carboxylic acid (7-CQA) and 4-quinolinol-3-carboxylic acid (QA) were synthesized to investigate the antioxidant properties. 5,7-DCQA exhibited the highest ability to scavenge 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS+.), 2,2'-diphenyl-1-picrylhydrazyl (DPPH) and galvinoxyl radicals. 6,8-DCQA possessed the highest efficacy to protect methyl linoleate against 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH)-induced oxidation. 5,7-, 5,8-DCQA and QA were able to retard the beta-carotene-bleaching in beta-carotene-linoleic acid emulsion. In addition, 5,8- and 6,8-DCQA efficiently protected DNA against hydroxyl radical (.OH)-mediated oxidation, and 5,8-DCQA and 7-CQA were active to protect DNA against AAPH-induced oxidation. Furthermore, only 7-CQA can protect DNA against Cu2+/glutathione (GSH)-mediated oxidation. Dichloro-4-quinolinol-3-carboxylic acids were potent to be antiradical drugs, and were worthy to be researched pharmacologically., (Copyright (c) 2010 Elsevier Masson SAS. All rights reserved.)

The antioxidant effects of alpha-terpinene (alpha-TH) and gamma-terpinene (gamma-TH) on the oxidation of methyl linoleate (LH), DNA, and erythrocytes induced by 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) were investigated. The results from erythrocytes and DNA were treated by means of chemical kinetic equations. It was found that either alpha- or gamma-TH was able to scavenge approximately 0.4 radicals when they protected DNA. alpha-TH can trap approximately 0.7 radicals when protecting erythrocytes and can trap approximately 0.5 radicals when protecting LH. gamma-TH can trap approximately 1.2 radicals when protecting erythrocytes and LH. Therefore, the antioxidant effectiveness of gamma-TH was higher than alpha-TH. gamma-TH contained a nonconjugated diene, and the diene in alpha-TH was conjugated. The obtained results implied that the nonconjugated diene benefited for antioxidant capacity more than a conjugated diene. Moreover, the reactions of alpha- and gamma-TH with 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cation radical (ABTS(+) (*)) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) implicated that alpha- and gamma-TH were able to scavenge radicals directly. However, alpha- and gamma-TH promoted AAPH-induced hemolysis with a high concentration employed.