Physicochemical characterization and antioxidant activity of humic acids isolated from peat of various origins

Maria V. Zykova, Igor A. Schepetkin, Michael V. Belousov, Sergey V. Krivoshchekov, Lyudmila A. Logvinova, Kristina A. Bratishko, Mekhman S. Yusubov, Sergey V. Romanenko, Mark T. Quinn

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


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.

Original languageEnglish
Article number753
Issue number4
Publication statusPublished - 1 Jan 2018


  • Antioxidant
  • Ethnopharmacology
  • Humic acid
  • Natural products
  • Peat
  • Semiquinone

ASJC Scopus subject areas

  • Analytical Chemistry
  • Chemistry (miscellaneous)
  • Molecular Medicine
  • Pharmaceutical Science
  • Drug Discovery
  • Physical and Theoretical Chemistry
  • Organic Chemistry

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