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Investigation of reaction mechanisms and kinetics of the radical scavenging ability of 5-tert-butylbenzene-1,2,3-triol and 3,5-di-tert-butylbenzene-1,2-diol compounds towards OOH radical

Posted on 26. July, 2018.

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Reactive oxygen species (ROS) is a collective term used by biologists to refer to oxygen-centred radicals, such as the superoxide (O2) and hydroxyl radical (OH•), as well as some non-radical derivatives of O2, such as hydrogen peroxide (H2O2), singlet oxygen (1O2) and hypohalites [e.g. hypochlorous acid (HOCl)] Organic derivatives of oxygen species such as alkoxyl radicals (RO•) and peroxyl radicals (ROO•) are also important examples of ROS which can seriously alter cell structures such as lipids, proteins and DNA. Thus, this phenomenon is strongly implicated in the natural aging process: cardiovascular disorder, neurodegenerative, diabetes, Alzheimer’s disease and cancer.

Antioxidants are substances that prevent free radical formation in cells. A coupling process of the antioxidant and free radical makes the latter less harmful. Aromatic ringssuch as found in phenolic compounds or polyphenols are the commonest natural antioxidant products, due to their high utilisation in several medicinal, pharmaceutical and commercial applications. Antioxidants, including biological and naturally occurring ones, are also obtained by chemical synthesis. The list of synthetic antioxidants is increasing by the day, thus Trolox (a water soluble analogue of α-tocopherol denoted α-T), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are examples of commercial synthesised antioxidants.

Recently, Guitard et al. established, using several techniques, that 5-tert-butylbenzene1,2,3-triol is an excellent DDPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenger in comparison with many antioxidants (polyphenols, synthetic phenolic compounds, tocopherols, hydroxybenzoic acid derivatives, hydroxycinnamic acid derivatives, flavonols, flavones, flavanonols, flavanones, isoflavones, catechins, stilbenes, genol and isoeugen, antioxidants in olive, lignans, carnosol and carnosic acids). Our aim in this work was to explore the antioxidant activity of the synthesised compound and compare this with that of a designed system (3,5-di-tert-butylbenzene-1,2-diol) and a reference system (α-T). For this purpose, we have chosen the hydroperoxyl radical (HOO•) due to its moderate reactivity, which is considered as an attractive characteristic for studying trends in antioxidant activities. In addition, this radical plays a central role in mediating the toxic side effects of aerobic respiration, due to its high reactivity with biomolecules and it has been established that the rate constants corresponding to the HOO• damage to polyunsaturated fatty acids are in the range 1.18 × 10– 3.05 × 103 M–1 s–1. This value has been proposed as a threshold for identifying which compounds are expected to act efficiently in retarding the oxidative degradation of lipids.

It is generally assumed that the reactions between phenolic compounds or polyphenols and ROS such as HOO• take place through three main mechanisms:
(i) The hydrogen atom transfer process/proton coupled electron transfer (HAT/PCET).
(ii) The transfer process of a single electron followed by proton transfer (SET-PT).
(iii) The radical adduct formation (RAF).

Read the full article in Progress in Reaction Kinetics and Mechanism.


Authors: Anes El-Hadj Sa—ód and Sidi Mohamed Mekelleche*
Laboratory of Applied Thermodynamics and Molecular Modelling No. 53, Department of Chemistry, Faculty of Science, University of Tlemcen, PB 119, Tlemcen, 13000, Algeria

Keywords: antioxidants, mechanism of radical scavenging ability, rate constants, density functional theory, hydroperoxyl radical 

Image: Spin density distributions on ArO• radicals in the gas phase.