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Antioxidant Capacity of Soil Humic Substances: TEAC vs. ORAC Approachтезисы доклада
- Авторы: Klein O.I., Kulikova N.A., Perminova I.V.
- Сборник: Book of Abstracts. Fourth International Conference of CIS IHSS on Humic Innovative Technologies «From Molecular Analysis of Humic Substances – to Nature-like Technologies» (HIT-2017)
- Тезисы
- Год издания: 2017
- Место издания: ООО "КЛУБ ПЕЧАТИ" Москва
- Первая страница: 59
- Последняя страница: 59
- Аннотация: Humic substances (HS) play important functions in the environment by radical scavenging in biogeochemical redox reactions and thus influencing behavior of pollutants and preventing damage to cell membranes; this is due to antioxidant properties of HS. Phenolic moieties formed from more complex plant precursor molecules, such as lignin and tannins, have been suggested as the major electron-donating moieties of HS, and thus are thought to provide their antioxidant activity [1, 2]. However, due to difficulties in measuring the individual antioxidant components of a complex mixture such as HS, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid)-equivalency is mainly used as a measure for the antioxidant capacity (AOC) of HS. Trolox-equivalent antioxidant capacity (TEAC) is most often measured using the ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6- sulfonic acid)). Nevertheless, the ABTS cation-radical is a synthetic one, so the antioxidant effect cannot be clearly interpreted in terms of biological systems. Besides, antioxidant interaction with ABTS both involves electro- and proton-donating mechanisms, whilst interaction of antioxidant with biologically relevant radicals such as the peroxyl radical could be realized only through proton donation. Consequently, it is important to compare data obtained by this method with data obtained by methods based on the use of the peroxyl radical such as oxygen radical absorbance capacity (ORAC) approach. In our study we measured AOC of 9 soil HS both by TEAC and ORAC methods. A set of HS included 3 samples of fulvic acids (FA) extracted from sod-podzolic soils and 6 samples of humic acids (HA) obtained from sod-podzolic soils and chenozems. Both FA and HA were characterized by elemental analysis and 13C NMR spectroscopy. Evaluation of AOC using TEAC approach was conducted according [2] at pH 6.8 using 40 min as the end point. ORAC measurements were performed according to [3] at pH 7.4. To compare the obtained values of AOC, they were expressed in Trolox equivalents (TE) normalized to weight. Values of measured AOC varied in the range 0.3–1.4 mol/mg HS in case of ORAC and in the range 0.2–1.5 mol/mg HS when TEAC was used. Antioxidant properties of FA were usually more pronounced than those of HA. Though similar ranges of AOC values for ORAC and TEAC methods were observed for the studied set of HS, AOC values obtained by ORAC were usually lower than those obtained using TEAC. The latter might be most likely explained by realization of two mechanism of radical scavenging (electron and proton donation) under TEAC conditions when only scavenging via electron donation could occur in case of ORAC. Surprisingly, there were two exceptions, namely, HA derived from chernozems when ORAC values were greater than TEAC. As compared to the other studied HS, chernozemic HA possessed the highest content of aromatic moieties (both non-substituted and oxygen-substituted carbon) and the lowest ratios O/C and H/C. As a short-term assay using the ABTS•+ is recommended for the evaluation of fast constituents, rather than for determination of the end-point AOCs of HS [2], our results allowed to conclude that humic materials of high aromaticity and low oxygen content have relatively low content of fast constituents demonstrating antioxidant activity. References 1. Aeschbacher et al. // Environ. Sci. Technol. 2012. 46:4916–4925. 2. Klein et al. // J. Soil Sediments. 2016. https://doi.org/10.1007/s11368-016-1538-7. 3. Cao et al. // Free Radic. Biol. Med. 1993. 14(3): 303–311.
- Добавил в систему: Куликова Наталья Александровна