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).