Free radicals produced by the oxidation of gallic acid: An electron paramagnetic resonance study
نویسندگان
چکیده
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.
منابع مشابه
Study of the Structure of Free Radicals in Gamma – Irradiated Amino Acid Derivatives
Electron paramagnetic resonance spectroscopy has been used for the study of the free radicals produced in the powders of L-arginine monohydrochloride, ala-ala and DL-β-leucine gamma-irradiated at room temperature. The structures of the radicals formed in compounds were determined as NH2(NH)NHĊHCH2CH2CH(NH2)COOH, CH3ĊHCOOH and (CH3)2ĊCH(NH2)CH2COOH respectively. The paramagnetic species were fou...
متن کاملDemystifying EPR: A Rookie Guide to the Application of Electron Paramagnetic Resonance Spectroscopy on Biomolecules
Electron Paramagnetic Resonance (EPR) spectroscopy, also known as Electron Spin Resonance(ESR) especially among physicists, is a strong and versatile spectroscopic method forinvestigation of paramagnetic systems, i.e. systems like free radicals and most transition metalions, which have unpaired electrons. The sensitivity and selectivity of EPR are notable andintriguing as compared to other spec...
متن کاملThe reduction of cytochrome c by enzyme-generated ascorbic free radical.
The reduction of cytochrome c during peroxidatic oxidation has been observed, and it has been suggested that free radicals derived from hydrogen donors are the reductants (1, 2). The formation of these free radicals during peroxidatic oxidation has been confirmed recently by means of electron paramagnetic resonance spectroscopy (3). Since it has been found that a free radical mechanism is also ...
متن کاملInvestigation of ethyl radical quenching by phenolics and thiols in model wine.
In the present study, the reaction between 1-hydroxyethyl radicals (1-HER) and various wine-related phenolics and thiols, including gallic acid, caffeic acid, ferulic acid, 3-mercaptohexan-1-ol (3MH), cysteine (Cys), and glutathione (GSH), was studied using competitive spin trapping with electron paramagnetic resonance (EPR) and mass spectrometry. Previous studies have reported several importa...
متن کاملIon-exchange in melanin: an electron spin resonance study with lanthanide probes.
Changes are induced in the electron spin resonance signal amplitude and microwave power saturation of the naturally occurring free radical in melanin by bound paramagnetic ions. The changes serve as experimental observables in competition experiments between diamagnetic and paramagnetic metal ions for melanin binding sites and between melanin and ethylenediaminetetraacetic acid for paramagnetic...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره 4 شماره
صفحات -
تاریخ انتشار 2010