Oxidative degradation of lipids, not only leads to the quality deterioration in foodstuffs but also associates with a multitude of physiological processes. One of the causations involved in these damaging effects is the generation of reactive carbonyl species (RCS) in lipid peroxidation process. RCS are notorious toxins that possess reactivity towards biological nucleophiles (such as proteins and DNA) with potential functional alternation in these biomolecules. Therefore, the exogenous intervention is required to inhibit the toxicity related to RCS/lipid peroxidation. In present study, the screening for effective natural polyphenols to trap two representative RCS, acrolein (ACR) and 4-hydroxy-trans-2-nonenal (HNE), was performed with mechanism elucidation. It was found that the polyphenols from the categories of flavan-3-ols, theaflavins, cyanomaclurins and dihydrochalcones were effective scavengers of ACR/HNE. Subsequently, facilitated by HPLC, LC-MS/MS and NMR analysis, the characterization of polyphenols’ as sacrificial nucleophiles towards these two electrophiles products was accomplished. Michael addition at A ring of polyphenols’ to the C=C bond of ACR/HNE was suggested to be responsible for trapping of these two RCS and thus render their active sites unavailable to covalently modify critical biomolecules. Further investigation of phloretin’s effect to attenuate ACR-induced modification on lysine residue and proteins was carried out. Phloretin’s protective effect against ACR’s toxicity was clearly reflected by its inhibition of the formation of Nε-(3-formyl-3,4-dehydropiperidino) lysine (FDP-lysine), blocking the electrophilic site in FDP-lysine, lowering protein carbonylation in bovine serum albumin (BSA) and lessening protein oligomerization in bovine pancreas ribonuclease A. Such protection might be mediated by phloretin’s directly trapping of ACR and consequently deactivation of ACR in covalent modification of amino acids and proteins. The biological relevance of polyphenols’ trapping activity of ACR was explored in a cell culture model. Natural polyphenols including phloretin, EGCG and quercetin were proved to be active to inhibit ACR-induced cytotoxicity in human neuroblastoma SH-SY5Y cells. The cytoprotection of phloretin (as the most potent one in alleviation of ACR stress) was suggested to be achieved through the reduction of the increased cellular protein carbonyl level as revealed by Western blotting analysis. In the final part of this study, an in vitro system containing metal-catalyzed fatty acids and BSA was established to study the modification on protein induced by lipid peroxidation and possible inhibitory effects conferred by some natural polyphenols. The protective effects of these polyphenols against lipid peroxidation-induced modification on BSA was manifested by the observation of reduced levels of high-molecular-weight proteins, MDA-related fluorescent substances and protein carbonylation. However, poor correlations were found between such protection and antioxidant activities, suggesting alternative mechanisms were existed such as carbonyl-scavenging. In conclusion, findings from the present study highlighted certain kinds of natural polyphenols as promising agents in counteracting RCS/lipid peroxidation-induced toxicity in amino acid, protein and cell models. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

No description available.

The reaction of ((eta)-Arene)Cr(CO)(,2)(CX) (X = S, Se) complexes with excess (RO)(,3)P (R = Me, Et, n-Bu, Ph) yields Cr(CO)(,2)(CX) (RO)(,3)P (,3), predominantly as the mer I isomer, in which a phosphite ligand is trans to CX. Arene displacement from ((eta)-C(,6)H(,6))Cr(CO)(,2)(CX) by tridentate phosphine ligands L-L-L L-L-L = (Me)C(CH(,2)P(Ph)(,2))(,3), (Ph(,2)PCH(,2)CH(,2))(,2)PhP gives fac-(L-L-L)Cr(CO)(,2)(CX) products. The molecular structures of Cr(CO)(,2)(CX) (MeO)(,3)P (,3) have been determined by single crystal X-ray diffraction. Intramolecular isomerization of these complexes as well as their tricarbonyl analogue has been demonstrated and activation parameters have been calculated for the rearrangement processes. Two-dimensional ('31)P NMR spectroscopy has provided evidence that isomerization occurs via trigonal prismatic intermediates. Kinetic investigations of the reaction of ((eta)-C(,6)H(,6))Cr(CO)(,2)(CX) with (MeO)(,3)P have established a first-order rate dependence on both the complex and the entering ligand. The faster reaction rate of the selenocarbonyl derivative relative to its thiocarbonyl analogue originates in a lower entropy of activation in the former case. The effect on the reaction rate of variation in the nature of the arene and of the entering ligand has been investigated. / An approach to hormonal receptor assay involving the detection by FT-IR spectroscopy of Cr(CO)(,3)-labelled modified estradiol bound to estrogen receptors in target tissue is reported. / The FT-IR spectra of FeTPP(CX) FeTPP = (5,10,15,20-tetraphenyl-porphinato)Fe(II); X = S, Se and FeTPP(CX)L (X = S, Se; L = pyridine, ethanol) have been obtained. Some changes in the porphyrin spectrum were observed with variation or removal of L, but not with variation of X.

No description available.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 230-243).

Thesis (Ph. D.)--University of Hong Kong, 1995. / Includes bibliographical references (leaf 320-343).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1973. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Marie E. Krafft, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed June 13, 2006). Document formatted into pages; contains xix, 119 pages. Includes bibliographical references.