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Oxidation of Polymeric Polyphenols (Tannins) in Biologically Relevent Systems

Chen, Yumin
http://rave.ohiolink.edu/etdc/view?acc_num=miami1089232925

Abstract Details

2004, Doctor of Philosophy, Miami University, Chemistry and Biochemistry.
Reactive oxygen species (ROS) are produced in human metabolic processes and uncontrolled ROS are detrimental to human health. In vitro chemical assays show that dietary tannins have potent ROS scavenging activity. My research is designed to use model systems to reveal interactions between tannins and factors (pH and protein) found in the human digestive tract where tannins work as biological antioxidants. Pentagalloyl glucose (PGG), bovine serum albumin (BSA), and NaIO4 were chosen as the model tannin, protein and oxidant, respectively. PGG was prepared from tannic acids via a methanolysis reaction. [14C]PGG was synthesized from [U-14C]-D-glucopyranose and tri-O-benzylgallic acid as a radiochemical tracer. When PGG was oxidized by NaIO4, the formation of different oxidation products was controlled by the reaction pH. PGG oxidation produced an o-semiquinone radical intermediate, which formed polymeric products at low pH (e.g. pH 2.1). The o-semiquinone radical ionized at pH > 5 and was labile to being further oxidized to o-quinone. Reaction pH similarly affected the formation of oxidation products of epicatechin16 (4→8) catechin (procyanidin) or epigallocatechin gallate (EGCG), suggesting that these three different tannins followed the same oxidation mechanism. When PGG was oxidized in the presence of BSA at various pH values, BSA promoted the formation of quinone but inhibited the formation of polymeric products. In addition to affecting PGG oxidation, BSA interacted with PGG under oxidizing conditions and formed oxidized PGG-BSA complexes. A radiochemical method was devised to quantitate oxidized PGG-BSA complexes. The complexes were treated with sodium dodecyl sulfate (SDS) to remove any non-covalently bound PGG and were co-precipitated with BSA by trichloroacetic acid (TCA) for radiochemical assessment. The molar ratio of PGG and BSA determined the solubility of oxidized PGG-BSA complexes. Soluble complexes were formed at low molar ratios (e.g. PGG/BSA=1). At high molar ratios (e.g. PGG/BSA=22), soluble complexes were rapidly converted to insoluble complexes. Besides NaIO4, 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS•+) and 2,2’-azobis(isobutyramidine) dihydrochloride (AAPH) were tested as oxidants. It was found that NaIO4 and ABTS•+ induced the formation of oxidized PGG-BSA complexes more rapidly than AAPH.
Ann Hagerman (Advisor)
Robert Minto (Other)
Christopher Makaroff (Other)
Michael Crowder (Other)
Helaine Alessiio (Other)
132 p.
Chemistry, Biochemistry
Polyphenol; Tannins; Hydrolyzable tannins; Tannin-protein interaction; Polyphenol-protein interaction; Polyphenol oxidation; Tannin oxidation; Antioxidant; Pentagalloyl glucose; Oxidized tannin-protein complexes; Oxidized polyphenol-protein comp

Recommended Citations

Citations

  • Chen, Y. (2004). Oxidation of Polymeric Polyphenols (Tannins) in Biologically Relevent Systems [Doctoral dissertation, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1089232925

    APA Style (7th edition)

  • Chen, Yumin. Oxidation of Polymeric Polyphenols (Tannins) in Biologically Relevent Systems. 2004. Miami University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1089232925.

    MLA Style (8th edition)

  • Chen, Yumin. "Oxidation of Polymeric Polyphenols (Tannins) in Biologically Relevent Systems." Doctoral dissertation, Miami University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=miami1089232925

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Miami University and OhioLINK.