Radical chemistry of epigallocatechin gallate and its relevance to protein damage

A Hagerman, Roger Dean, Michael Davies

Research output: Contribution to journalArticle

75 Citations (Scopus)

Abstract

The radical chemistry of the plant polyphenolics epigallocatechin gallate (EGCG) and epigallocatechin (EGC) were investigated using electron paramagnetic resonance spectroscopy. Radical species formed spontaneously in aqueous solutions at low pH without external oxidant and were spin stabilized with Zn(II). The spectra were assigned to the gallyl radical and the anion gallyl radical, with only 10% of the signal assigned to a radical from the galloyl ester. Spectral simulations were used to establish a pKa of 4.8 for the EGCG radical and a pKa of 4.4 for the EGC radical. The electrochemical redox potentials of EGCG and EGC varied from 1000 mV at pH 3 to 400 mV at pH 8. The polyphenolics did not produce hydroxyl radicals unless reduced metal ions such as iron(II) were added to the system. Zinc(II)-stabilized EGCG radicals were more effective protein-precipitating agents than unoxidized EGCG and produced irreversibly complexed protein. EGCG and other naturally occurring polyphenolics are effective radical scavengers but their radical products have the potential to damage biological molecules such as proteins.
Original languageEnglish
Pages (from-to)115-120
Number of pages6
JournalArchives of Biochemistry and Biophysics
Volume414
DOIs
Publication statusPublished - 2003

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Proteins
Electron Spin Resonance Spectroscopy
Oxidants
Hydroxyl Radical
Oxidation-Reduction
Anions
Metal ions
Paramagnetic resonance
epigallocatechin gallate
Zinc
Spectrum Analysis
Esters
Iron
Metals
Spectroscopy
Ions
Molecules
gallocatechol

Cite this

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abstract = "The radical chemistry of the plant polyphenolics epigallocatechin gallate (EGCG) and epigallocatechin (EGC) were investigated using electron paramagnetic resonance spectroscopy. Radical species formed spontaneously in aqueous solutions at low pH without external oxidant and were spin stabilized with Zn(II). The spectra were assigned to the gallyl radical and the anion gallyl radical, with only 10{\%} of the signal assigned to a radical from the galloyl ester. Spectral simulations were used to establish a pKa of 4.8 for the EGCG radical and a pKa of 4.4 for the EGC radical. The electrochemical redox potentials of EGCG and EGC varied from 1000 mV at pH 3 to 400 mV at pH 8. The polyphenolics did not produce hydroxyl radicals unless reduced metal ions such as iron(II) were added to the system. Zinc(II)-stabilized EGCG radicals were more effective protein-precipitating agents than unoxidized EGCG and produced irreversibly complexed protein. EGCG and other naturally occurring polyphenolics are effective radical scavengers but their radical products have the potential to damage biological molecules such as proteins.",
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Radical chemistry of epigallocatechin gallate and its relevance to protein damage. / Hagerman, A; Dean, Roger; Davies, Michael.

In: Archives of Biochemistry and Biophysics, Vol. 414, 2003, p. 115-120.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Radical chemistry of epigallocatechin gallate and its relevance to protein damage

AU - Hagerman, A

AU - Dean, Roger

AU - Davies, Michael

PY - 2003

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AB - The radical chemistry of the plant polyphenolics epigallocatechin gallate (EGCG) and epigallocatechin (EGC) were investigated using electron paramagnetic resonance spectroscopy. Radical species formed spontaneously in aqueous solutions at low pH without external oxidant and were spin stabilized with Zn(II). The spectra were assigned to the gallyl radical and the anion gallyl radical, with only 10% of the signal assigned to a radical from the galloyl ester. Spectral simulations were used to establish a pKa of 4.8 for the EGCG radical and a pKa of 4.4 for the EGC radical. The electrochemical redox potentials of EGCG and EGC varied from 1000 mV at pH 3 to 400 mV at pH 8. The polyphenolics did not produce hydroxyl radicals unless reduced metal ions such as iron(II) were added to the system. Zinc(II)-stabilized EGCG radicals were more effective protein-precipitating agents than unoxidized EGCG and produced irreversibly complexed protein. EGCG and other naturally occurring polyphenolics are effective radical scavengers but their radical products have the potential to damage biological molecules such as proteins.

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DO - 10.1016/S0003-9861(03)00158-9

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JF - Archives of Biochemistry and Biophysics

SN - 0003-9861

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