o,o???-Dityrosine (dityrosine), an oxidation product of tyrosine produced by reaction between tyrosyl radicals, is becoming established as a biomarker of free radical oxidative protein damage in vivo. Attempts to measure dityrosine concentrations in various physiological and pathological systems have produced varied and often contradictory results. Dityrosine concentrations in urine, plasma, cerebrospinal fluid (CSF) and brain tissue varying over three orders of magnitude have been reported, together with inconsistent claims of significant dityrosine elevation in several ageing-related pathologies. Some of these findings have contributed to the implication of free radical activity in the pathology of several neurodegenerative disorders, vascular and ocular abnormalities and in phagocyte response to infection. The aim of this study was to test the hypothesis that dityrosine levels are elevated in ageing and ageing-related disease. The study also aims to determine the utility of dityrosine measurement as an index of oxidative damage, and elucidate possible explanations for the inconsistent levels reported. An assay for the quantification of dityrosine was developed using capillary HPLC with electrospray tandem quadrupole mass spectrometry (HPLC-MS/MS). The assay was highly specific for dityrosine and has the highest absolute sensitivity for dityrosine of any method reported to date, with a detection limit of 3 femtomoles of dityrosine on-column. Urine samples from volunteers of different age and from hospital patients with various pathologies were analysed. Plasma protein hydrolysates from control, Alzheimer???s and stroke subjects were analysed, together with hydrolysates of post mortem brain tissue from Alzheimer???s and control subjects. Urinary dityrosine level is elevated in states of acute infection and inflammation, but does not correlate with age or chronic disease. Protein dityrosine in four sections of Alzheimer???s brain was not significantly different from control sections. Dityrosine was present in human plasma and tissue proteins at approximately 5-35 residues per million tyrosine residues, and in normal urine at 5-25 micromol/mol creatinine or 20-200 nM. Most of the discrepancies in the literature relate to inadequate specificity of the analytical method. Interpretation of published data with critical appraisal of measurement technology specificity is essential in developing an accurate understanding of the role of free radicals in ageing and disease.

1 v. (various pagings) : ill., plates ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1973) from the Dept. of Physical and Inorganic Chemistry, University of Adelaide

Abstract This work investigates the kinetics of the emulsion polymerization of vinyl acetate. Several aspects of this system have been clarified, including the induced decomposition of persulfate, retardation by oxygen and entry by, and analysis of, the aqueous phase oligomeric radicals. It has been shown that the retardation period observed in the emulsion polymerization of VAc can be explained by the effect of traces of oxygen (< 10-6 M) on the entry efficiency of the initiator-derived aqueous-phase oligomeric radicals. Comparison of rates of polymerization in V and persulfate -initiated polymerizations together with electrospray mass spectrometry of aqueous phase oligomers, has shown that the mechanism for the induced decomposition of persulfate by vinyl acetate is chain transfer to initiator from aqueous-phase oligomeric radicals. A value has been determined for the rate coefficient for transfer to initiator, by fitting literature data to a model based on this mechanism. The reported independence of the rate of polymerization from the monomer concentration in the emulsion polymerization of vinyl acetate has been investigated. Possible explanations for this behaviour have been proposed and tested in this work, by measuring radical-loss rates directly with y-relaxation techniques. Although the Y relaxations were found to be affected by experimental artefacts, it has been demonstrated that rapid exit is not responsible for the high radical-loss rates in this system. The major artefact identified in the y relaxations was the significant effect of relatively small exotherms on relaxation behaviour, Methodologies were developed for correcting affected data and for avoiding exotherms under certain conditions. Arrhenius parameters were determined for the rate coefficient for chain transfer to monomer using the In^M method, which utilises the whole MWD. This section of the work is incomplete, for reasons detailed in chapter 5. However, as a preliminary indication it was found that the frequency factor was 106.38 M-1 s-1 and the activation energy was 38.8 kJ mol-1.

Doctor of Philosophy (PhD) / This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.

Thesis (Ph.D.)--McMaster University (Canada), 1992. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6173. Adviser: J. Warkentin.

Thesis (Ph.D.)--McMaster University (Canada), 1995. / Source: Dissertation Abstracts International, Volume: 57-03, Section: B, page: 1801. Adviser: J. K. Terlouw.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 415-446).

Inaugural Dissertation (Ph. D.)--Universität Köln, 1976. / Includes bibliographical references (p. 161-171).

Thesis (Ph. D.)--Georgia State University, 2009. / Title from file title page. William H. Nelson, committee chair; Vadym Apalkov, Stuart A. Allison, Douglas Gies, Gary Hastings, committee members. Description based on contents viewed Nov. 5, 2009. Includes bibliographical references.

Thesis (doctoral)--Lund University, 1995. / Added t.p. with thesis statement inserted.