Journal article
Free radicals produced by the oxidation of gallic acid: An electron paramagnetic resonance study
Chemistry Central journal, Vol.4(1), pp.15-15
12/2010
DOI: 10.1186/1752-153X-4-15
PMCID: PMC2924338
PMID: 20687941
Abstract
Background: Gallic acid (3,4,5-trihydroxybenzoic acid) is found in a wide variety of plants; it is extensively used in tanning, ink dyes, as well as in the manufacturing of paper. The gallate moiety is a key component of many functional phytochemicals. In this work electron paramagnetic spectroscopy (EPR) was used to detect the free radicals generated by the air-oxidation of gallic acid.
Results: We found that gallic acid produces two different radicals as a function of pH. In the pH range between 7-10, the spectrum of the gallate free radical is a doublet of triplets (aH = 1.00 G, aH = 0.23 G, aH = 0.28 G). This is consistent with three hydrogens providing hyperfine splitting. However, in a more alkaline environment, pH >10, the hyperfine splitting pattern transforms into a 1:2:1 pattern (aH (2) = 1.07 G). Using D2O as a solvent, we demonstrate that the third hydrogen (i.e. aH = 0.28 G) at lower pH is a slowly exchanging hydron, participating in hydrogen bonding with two oxygens in ortho position on the gallate ring. The pKa of this proton has been determined to be 10.
Conclusions: This simple and novel approach permitted the understanding of the prototropic equilibrium of the semiquinone radicals generated by gallic acid, a ubiquitous compound, allowing new insights into its oxidation and subsequent reactions.
Details
- Title: Subtitle
- Free radicals produced by the oxidation of gallic acid: An electron paramagnetic resonance study
- Creators
- Angelique C Eslami - Free Radical and Radiation Biology, Med Labs B180, The University of Iowa, Iowa City, IA 52242-1181, USAWanvimol Pasanphan - Department of Applied Radiation and Isotopes, Faculty of Science, Kasetsart University, Bangkok 10900, ThailandBrett A Wagner - Free Radical and Radiation Biology, Med Labs B180, The University of Iowa, Iowa City, IA 52242-1181, USAGarry R Buettner - Free Radical and Radiation Biology, Med Labs B180, The University of Iowa, Iowa City, IA 52242-1181, USA
- Resource Type
- Journal article
- Publication Details
- Chemistry Central journal, Vol.4(1), pp.15-15
- DOI
- 10.1186/1752-153X-4-15
- PMID
- 20687941
- PMCID
- PMC2924338
- NLM abbreviation
- Chem Cent J
- ISSN
- 1752-153X
- eISSN
- 1752-153X
- Publisher
- BioMed Central
- Language
- English
- Date published
- 12/2010
- Academic Unit
- Radiation Oncology
- Record Identifier
- 9984046817202771
Metrics
27 Record Views