Is there a redox reaction between Cu(II) and gallic acid?

Free Radic Res. 2011 Feb;45(2):115-24. doi: 10.3109/10715762.2010.515220. Epub 2010 Oct 13.

Abstract

Interactions between transition metal ions and polyphenols can result in complexation, redox or polymerization, but the relative importance of these reactions is unclear. The present paper reports results from the reaction of gallic acid (GA) with Cu(II) using electron paramagnetic resonance (EPR) and UV/visible spectroscopy for various relative concentrations and pH values. Reduction of Cu(II) by GA does not occur under strongly acidic or strongly alkaline conditions. Di- or polymerization reactions between Cu(II) and carboxylate groups of GA dominate the results at acidic pH, whereas mononuclear complexes increase in importance at higher pH and GA concentrations. There was no evidence for any redox reaction between Cu(II) and GA and free radical formation from GA at high pH was shown to be the consequence of auto-oxidation, which was inhibited by Cu(II). Serious questions are thus raised about the existence of the frequently assumed redox reactions between Cu(II) and polyphenols.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Benzoquinones / chemistry
  • Coordination Complexes / chemistry*
  • Coordination Complexes / metabolism
  • Copper / chemistry*
  • Copper / metabolism
  • Electron Spin Resonance Spectroscopy
  • Gallic Acid / chemistry*
  • Gallic Acid / metabolism
  • Hydrogen-Ion Concentration
  • Oxidation-Reduction
  • Polymerization
  • Spectrum Analysis

Substances

  • Benzoquinones
  • Coordination Complexes
  • semiquinone radicals
  • Gallic Acid
  • Copper