Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Call number: LD2668 .T4 1984 G86 / Master of Science

The gaseous free radicals, alkaline-earth metal monoalkylamides, monoacetylides, monoformamidates and monopyrrolidates, consisting of a metal atom (Ca or Sr) bonded to a single ligand, were synthesized in a Broida oven. The electronic and vibrational structures of these molecules were studied by low-resolution laser spectroscopy techniques. These inorganic molecules are ionic, well represented by the structure M⁺L⁻ (M = Ca, Sr: L = ligand). Three electronic transitions were identified for the metal monoalkylamides and the metal monoformamidates. The formamidate anion bonds to the metal in a bidentate fashion through the oxygen and nitrogen atoms. Two electronic transitions were observed for the metal monopyrrolidates. The pyrrolide anion ring bonds to the metal to provide these "open-faced sandwich" type molecules with pseudo-C₅ᵥ symmetry. For the metal monoacetylide molecules, only one electronic transition (Ā²Π-Ẋ²Σ⁺) was observed. Several vibrational frequencies were determined for these inorganic molecules from the low-resolution spectra. The Ā²Π-Ẋ²Σ⁺ transition of the calcium monoacetylide molecule was rotationally analyzed at high-resolution using the filtered laser excitation spectoscopy technique. The rotational line positions were fitted to a ²Π-²Σ⁺ Hamiltonian to obtain several rotational constants. The calcium-carbon bond length in CaCCH was calculated for the ground (2.248 Å) and excited (2.200 Å) electronic states. The vibration-rotation spectra of the gaseous bismuth hydride and bismuth deuteride molecules were recorded, using a diode laser system. The 1-0 fundamental band and several hot bands with Δv-1 were rotationally analyzed. The rotational line positions were fitted first, to a Dunham energy expression and then to a ³Σ⁻ Hamiltonian, to obtain ground state rotational constants. The bismuth-hydrogen (deuterium) bond distance was calculated to be 1.809 Å (1.807 Å).

The addition of benzyltrimethylsilane to maleic anhydride mediated by TiO2 photocatalysis was initially investigated. The affect of changing the catalyst, the radical trap loading and the substitution of the benzyltrimethylsilane molecule was assessed. Cyclisation precursors based on benzyltrimethylsilane were prepared, but were found not to cyclise via TiO2 photocatalysis. A number of other systems were assessed for their ability to cyclise under TiO2 photocatalysis; tertiary amines, aminomethyltrimethylsilanes, phenoxymethyltrimethylsilanes and phenoxyacetic acids. Phenoxymethyltrimethylsilane and phenoxyacetic acid were found to add effectively to maleic anhydride under TiO2 photocatalysis conditions, however they were unreactive with regards to cyclisation. EPR spectroscopy has been employed to characterise further the reaction of benzylsilanes with maleic anhydride under TiO2 photocatalytic conditions. A number of EPR active species were observed; trapped holes and electrons, which reside within the TiO2 catalyst. In addition, methyl and benzyl radicals were observed and were found to originate from the oxidation of the benzylsilanes by trapped holes in the TiO2 catalyst. However, no radical species were observed from the maleic anhydride. These observations had the following consequences for the currently proposed reaction mechanism for the addition of benzyltrimethylsilane with maleic anhydride under TiO2 photocatalysis.  The observation of the benzyl radical definitely proved that the reactive intermediate was indeed the proposed benzyl radical  The absence of any maleic anhydride EPR active species cast doubt on the role of maleic anhydride as an electron trap. Moreover when maleic anhydride is removed from the reaction system, interstitial Ti3+ species is absent from the EPR spectra, indicating that maleic anhydride is in fact acting as a hole trap.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by John Wesley Frost. / Ph.D.

During the course of the systematic study, it was also discovered that doubly-protonated diarginated peptides containing multiple glutamic acid residues (E) (n>4) could suppress the backbone fragmentation of [M+2H]+· . Together with the results obtained from conformational searches, it was hypothesized that the interactions between carboxylic oxygens of E side chains and backbone amide hydrogens could stabilize the radical intermediate and thereby inhibiting the usual N-Calpha cleavages and H · loss from [M+2H]+·. / In order to ascertain the impacts of the structural features of polypeptide and oligosaccharide ions on the dissociation of these biomolecules under typical collision induced dissociation (CID) and electron capture dissociation (ECD) conditions, the dissociation patterns of even-electron precursor ions generated by protonation ([M+nH]n+)/metalation ([Metal+M]n+), odd-electron hydrogen-deficient precursor ions (M+·) generated by SORI-CID of [Cu(Tpy)M]2+ and odd-electron hydrogen-surplus precursor ions ([M+2H]+·) generated by ECD of [M+2H] 2+ were examined. It was found that backbone cleavages, with the generation of b/y and c/z ions, were dominant in the dissociation of [M+H]+ and [M+2H]+· respectively. Whilst in the dissociation of M+·, side chain loss reactions were the major fragments generated. For post translational modification (PTM)-containing peptides, the labile PTM groups were found to cleave preferentially in the dissociation of M+· and [M+H]+, but were found to be retained in the intact peptides and peptide fragments in the dissociation of [M+2H]+·. It is hypothesized that the different dissociation pathways is attributed to the different nature of radicals. Further to these, it was found that in the dissociation of oligosaccharides, similar cleavage patterns (glycosidic and cross-ring cleavages) were obtained regardless of the nature of the precursor ions (i.e. whether odd- or even-electron) and the ion activation conditions. / Chan, Wai Yi. / Adviser: T.W. Dominic Chan. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 145-152). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Stable radicals have enjoyed widespread use in a variety of fields including synthetic chemistry, materials chemistry, energy storage, and biochemistry. This thesis outlines our investigations of cyclopropenium-based stable radicals and their application as redox mediators, redox-active ligands, catalysts, and materials for energy storage. The first chapter gives a brief overview of the use of radicals in synthetic chemistry. The principles that govern the stability of radicals is discussed and notable examples are highlighted. The second section of the first chapter reviews the aromatic platforms that have been developed by the Lambert group and how they might be converted into stable radical species. The second chapter details our study of 2,3-diaminocyclpropenones as stable radicals. These electron rich cyclopropenium derivatives undergo facile oxidation to yield a radical cation species. The origin of the stability of this oxygen-centered radical was elucidated by density functional theory calculations and analysis of the crystal structure. Diaminocyclopropenones were also found to be effective neutral L-type ligands in Ce(IV) complexes. EPR and UV-VIS experiments revealed that these complexes exhibited reversible homolytic dissociation of their diaminocyclopropenone ligands. The third chapter describes the use of trisaminocyclopropeniums as catholytes for nonaqueous redox flow batteries. A newly designed trisaminocyclopropenium structure could be accessed in large quantities and showed long lasting stability in its oxidized state. A new composite polyionic material was developed for use as a membrane suitable for organic solvent and high voltages. Cycling in combination with a perylenediimide anolyte yielded a 1.7 V battery that exhibited excellent coulombic efficiency and capacity retention. Using a spiro-bis(phthalimido) anolyte afforded a battery with an open circuit voltage of 2.8 V. The fourth chapter details how our battery studies with trisaminocyclopropenium radical dications led us to discover their photoinduced reactivity. We developed an electrophotocatalytic platform using trisaminocyclopropeniums as a species capable of being activated by both photochemical and electrochemical energy. The excited state oxidation potential of the doubly activated species was found to be +3.33 V, which was capable of effecting oxidative coupling reactions using both arenes and ethers as substrates. Density functional theory calculations and spectroscopic experiments revealed that the photoreactivity was due to a SOMO-inversion event. The trisaminocyclopropenium radical dication could be prepared on scale via direct electrolysis and subsequently used in high throughput screening.

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.

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.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.