Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed July 22, 2008). PDF text: xiv, 137 p. : ill. (some col.) ; 11 Mb. UMI publication number: AAT 3302727. Includes bibliographical references. Also available in microfilm and microfiche formats.

Through the use of laser flash photolysis and product studies, the photochemistry of dibenzyl ketone and its derivatives in SDS micelles shows that these aggregates impart some constraint on the dynamics of benzylic radical pairs. The enhancement of the geminate/cross-termination product occurring within the micellar interior is termed the geminate cage effect. Under conditions where all radicals exit from the supramolecular system, a substantial amount of the cross-termination product is observed in the product studies. This experimental evidence cannot be explained with conventional models, and a new proposal is put forth which suggests that some of the cross-termination product arises from radicals that exit the micelle and then recombine upon re-entry. This new approach is based on the binding of solutes to the micelle and is called the partition effect. Two sizes of DODAC vesicles were investigated. In small unilamellar vesicles with a diameter of 30 nm, the cage effect derived from product studies showed a significant enhancement of the cross-termination product. Time-resolved experiments showed that all radicals separate, which implies that all of the enhanced cross-termination reactions from the product studies are derived from random radical encounters. Product studies in large vesicles (∼150 nm diameter) demonstrated that the cross-termination product is enhanced, but not to the same extent as for SDS micelles or small vesicles. Calculations reveal that a significant proportion of the random encounters occur in the bulk aqueous phase. The proposed model suggests that it is not necessary to generate a triplet radical pair in order to observe a magnetic field effect on product distribution. In summary, this new proposal predicts that magnetic field effects in biological systems can be observed as long as mobility between different solubilization sites occurs. / Graduate

The work described in this thesis is concerned with the development of new applications of the photo-CIDNP (photochemically induced dynamic nuclear polarization) technique to aspects of protein structure and folding. Chapters 1 and 2 are introductory chapters; Chapter 1 describes the theoretical basis of the CIDNP phenomenon in terms of the underlying spin chemistry of the radical pair mechanism, while Chapter 2 presents the apparatus, photosensitizer and pulse sequences used, along with some important experimental considerations. Chapter 3 describes how ¹⁵N CIDNP can be used to probe the accessibility of tryptophan side-chains in both native and denatured states of proteins. The polarization of indole nitrogens in uniformly ¹⁵N labeled protein is detected in a two-dimensional ¹⁵N-¹ H NMR heteronuclear correlation experiment. Chapter 4 describes two new techniques offering considerable improvements in the quality of photo-CIDNP spectra of proteins. Both focus on the problem of progressive photo-degradation of the flavin dye and in both cases a larger number of scans can be accumulated before the flavin is exhausted than would otherwise be possible. In Chapter 5, the potential of stopped-flow photo-CIDNP spectroscopy for the study of protein folding is explored. Rapid dilution of denatured protein into a buffer solution is used to initiate a refolding process which is followed using short laser pulses to generate ¹H CIDNP in the side-chains of exposed aromatic residues. In Chapter 6, the field dependence of amino acid photo-CIDNP intensities is investigated using a stopped-flow CIDNP device that allows sample irradiation over a range of magnetic fields (0.1-7 T) within the bore of a 9.4 T NMR magnet and rapid transfer into the NMR tube for detection. Finally, in Chapter 7 two photo-CIDNP techniques that probe the exposure of aromatic residues in partially folded states are described. Both involve transfer of polarization to the native state for detection. One approach achieves this kinetically by rapid refolding, and the other involves monitoring exchange cross peaks in a two-dimensional CIDNP spectrum under conditions where the two states are interconverting.

Thesis (M. Sc.)--York University, 2001. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 85-90). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71609.

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Thesis (Ph.D.)--McMaster University, 2006. / Supervisor: William J. Leigh. Includes bibliographical references (leaves 236-246).

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 198-205).

Tightly focused femtosecond laser pulses are widely used in the biomedical field due to their nonlinear multiphoton precision and minimal thermal side effects. Below the threshold of optical breakdown, light energy contributes to photochemical reactions that introduce more chemical bonding in the form of collagen crosslinking (CxL) in extracellular matrices of transparent tissues such as corneal stroma. Previously, based on the principles of ultrafast laser-tissue interaction, a novel collagen CxL method relying on low-density plasma (LDP) generating reactive oxygen species (ROS) was proposed and applied to cornea tissue for vision correction by the Vukelic Group and extended to articular cartilage tissue for early osteoarthritis treatment in collaboration with Musculoskeletal Biomechanics Research Laboratory. Despite the efficiency and safety of the procedure, LDP was elusive and challenging to control due to its potential dependence on a cascade of intertwining factors such as ultrafast laser wavelength, power, pulse duration, repetition rate, and ionization resonance. This thesis has two aims: the first is to investigate the photochemical laser-tissue interaction with femtosecond nanojoule energy pulses, and the second is to develop robust and practical laser parameter envelopes for treating corneal ectatic diseases and osteoarthritis. Chapter 2 proposes a corneal epithelium-stromal level wound healing treatment. Relying on the interaction between reactive oxygen species (ROS) created by low-density plasma (LDP) therapy and inflammatory cytokines, epithelium recovery is accelerated on in vivo rabbit corneas. Chapters 3 to 5 focus on photochemical reaction-based morphological correction and biomechanical enhancement for corneal diseases such as keratoconus and astigmatism. A wavelength-independent, nonenzymatic CxL technique based on oxygen-independent, pentose-mediated glycation and ROS acceleration is developed; collagen CxL efficiency is tested through autofluorescence microscopy and nanoindentation. Subsequently, the combined effects of simultaneous external mechanical loading and nonenzymatic collagen CxL, achieved by both traditional CxL that involves soaking eyes with riboflavin solution, a photosensitizer, and then activating it with ultraviolet A light (UVA-Riboflavin-CxL) and new ROS catalyzed glycation CxL (ROS-Glycation-CxL) techniques, are investigated on ex vivo rabbit corneas. Through X-Ray Diffraction, permanent adjustments to the ultrastructure of collagen fibril packing are observed, ultimately contributing to refractive power changes in corneal topography. Furthermore, with the addition of melanin application that increases absorption and ionization efficiency, a robust method for generating plasma and reactive oxygen species (ROS) is proposed and implemented on ex vivo corneas to address ectatic diseases. Chapter 6 discusses the effect of plasma-guided laser collagen CxL on articular cartilages’ compressive equilibrium modulus and chondrocyte viability. Stemming from the melanin-assisted protocol and ultrafast pulses' high peak power, a plasma spark-mediated laser treatment is hypothesized to biomechanically enhance both bovine and human articular cartilage superficial zone for the treatment of osteoarthritis. Chapter 7 concludes this thesis and proposes future directions.