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Molecules 2018, 23(4), 753; https://doi.org/10.3390/molecules23040753

Physicochemical Characterization and Antioxidant Activity of Humic Acids Isolated from Peat of Various Origins

1
Department of Chemistry, Siberian State Medical University, Tomsk 634050, Russia
2
Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA
3
Department of Pharmaceutical Analysis, Siberian State Medical University, Tomsk 634050, Russia
4
Research School of Chemical and Biomedical Technologies, Tomsk Polytechnic University, Tomsk 634050, Russia
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editor: Susana M. Cardoso
Received: 5 March 2018 / Revised: 20 March 2018 / Accepted: 22 March 2018 / Published: 24 March 2018
(This article belongs to the Special Issue The Antioxidant Capacities of Natural Products)
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Abstract

Although humic acids (HAs) from peat exhibit various therapeutic properties, there is little information available concerning their physicochemical and antioxidant properties. To address this issue, nine different types of peat, including oligotrophic, mesotrophic, and minerotrophic peat samples, were used for isolation of HA fractions by basic (HAb) and pyrophosphate (HAp) extractions. Physical parameters of the HAs were analyzed by UV-Vis, fluorescent, infrared (IR), and electron paramagnetic resonance (EPR) spectroscopy. Average Mr of the fractions ranged from 17.2 to 39.7 kDa, while their humification index (HIX) varied from 0.49 to 1.21. HAp fractions had a higher content of aromatic structures compared to HAb fractions. Moreover, HAp fractions had a significantly higher content of phenolic OH groups (3.6 ± 0.5 mmol/g) versus HAb (3.1 ± 0.5 mmol/g). All HA fractions exhibited antioxidant activity in radical scavenging and electrochemical assays, and their EPR signal had a single line with g = 2.0035, which is consistent with semiquinone type radicals. Furthermore, the HIX was found to be important in determining the number of semiquinone-type free radicals in the HA structures. Overall, these data provide a molecular basis to explain at least part of the beneficial therapeutic properties of peat-derived HAs. View Full-Text
Keywords: peat; humic acid; antioxidant; ethnopharmacology; semiquinone; natural products peat; humic acid; antioxidant; ethnopharmacology; semiquinone; natural products
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Zykova, M.V.; Schepetkin, I.A.; Belousov, M.V.; Krivoshchekov, S.V.; Logvinova, L.A.; Bratishko, K.A.; Yusubov, M.S.; Romanenko, S.V.; Quinn, M.T. Physicochemical Characterization and Antioxidant Activity of Humic Acids Isolated from Peat of Various Origins. Molecules 2018, 23, 753.

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