title: Reaction pH and protein affect the oxidation products of beta-pentagalloyl glucose.
abstract: To better understand the biochemical consequences when polymeric polyphenols serve as biological antioxidants, we studied how reaction pH (pH 2.1-7.4) and protein affected the oxidation of pentagalloyl glucose (PGG) by NaIO4 in aqueous solution. PGG oxidation produced an o-semiquinone radical intermediate, which tended to form polymeric products at pH values below 5, and o-quinones at higher pH. The model protein bovine serum albumin promoted the formation of quinone even at low pH. Two other polyphenols, procyanidin (epicatechin16-(4-->8)-catechin) and epigallocatechin gallate, had similar pH-dependent oxidation patterns.
authors.affiliation: Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
authors.forename: Yumin
authors.initials: Y
authors.lastname: Chen
authors.forename: Ann E
authors.initials: AE
authors.lastname: Hagerman
mesh_terms: D044946:Biflavonoids / Q000737:chemistry; D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D047348:Hydrolyzable Tannins / Q000737:chemistry*; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010504:Periodic Acid / Q000737:chemistry; D044945:Proanthocyanidins / Q000737:chemistry; D011809:Quinones / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D044946:Biflavonoids; D005609:Free Radicals; D047348:Hydrolyzable Tannins; D044945:Proanthocyanidins; D011809:Quinones; D010504:Periodic Acid; D012710:Serum Albumin, Bovine; C435084:pentagalloylglucose; C017674:procyanidin; D002392:Catechin; C009288:metaperiodate; C045651:epigallocatechin gallate; D015032:Zinc