Antioxidant properties of bee propolis and an important component, galangin, described by X-ray crystal structure, DFT-D and hydrodynamic voltammetry

PLoS One. 2022 May 18;17(5):e0267624. doi: 10.1371/journal.pone.0267624. eCollection 2022.

Abstract

Propolis is produced by honeybees and used to seal their hives for defensive purposes and has been used in ethnopharmacology since ancient times. It is a lipophilic material containing a large collection of naturally produced plant organic molecules, including flavonoids. The flavonoid galangin is consistently found in propolis, independent of the hive geographical location and its X-ray crystal and molecular structure is reported. The antioxidant scavenging of superoxide by galangin and propolis is here presented. Using a cyclic voltammetry technique developed in our lab, we show that galangin is an excellent scavenger of the superoxide radical, perhaps even better than quercetin. Our results show that galangin displays a Superoxide Dismutase (SOD) function. This is described experimentally and theoretically (DFT). Two modes of scavenging superoxide are seen for galangin: (1) superoxide radical extraction of H atom from the hydroxyl moieties located in position 3 and 5 of galangin, which are also associated with proton incorporation defining the SOD action; (2) π-π interaction among several superoxide radicals and the galangin polyphenol ring that evolve towards release of O2 and H2O2. We describe these two actions separately as their relative sequence, and/or combination, cannot be defined; all these processes are thermodynamically spontaneous, or subjected to mild barriers.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antioxidants / pharmacology
  • Flavonoids / pharmacology
  • Hydrodynamics
  • Hydrogen Peroxide
  • Propolis* / chemistry
  • Superoxide Dismutase
  • Superoxides
  • X-Rays

Substances

  • Antioxidants
  • Flavonoids
  • Superoxides
  • galangin
  • Propolis
  • Hydrogen Peroxide
  • Superoxide Dismutase

Grants and funding

MR received funding for X-ray diffractometer obtained from NSF Grant Number 051237. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.