A metal adiabatic demagnetization cryostat was designed and constructed. The final-temperature dependence of a single-crystal synthetic ruby was investigated as a function of applied magnetic field. The ruby was used both as a thermometer and coolant in superconducting thin-film experiments at temperatures below 1°K. Difficulties encountered in these experiments have been discussed in detail. Further improvements on the system have been suggested in the application of thin-film superconductor studies. / Thesis / Master of Science (MS)

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Thesis (Ph. D.)--University of Chicago, Committee on Medical Physics, December 2003. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

The majority of the work in this dissertation describes the characterization of the nitrophorins (NPs) by NMR spectroscopy.NP7 was studied and compared to NP2 and relevant mutants.NP7 is shown to have three additional amino acids at the N-terminus, which contribute significantly to the protein fold stability and maintenance of NP7 function. The paramagnetic form of the protein has large 1H NMR chemical shifts and broad signals due to protein aggregation. The 1H NMR and CD spectroscopy both revealed that NP7 has mainly the A heme orientation, and the mutation of Glu27 to Val27 leads to an A:B ratio change, from mainly B to mainly or almost exclusively A.NMR investigation of the ferriheme resonances of the low-spin complexes of NP2 and mutant NP2(V24E) with imidazole (ImH), histamine (Hm) and cyanide (CN-) ligands as a function of pH has been completed. Strong chemical exchange cross peaks were observed in the NOESY/EXSY spectra at low pH (pH* 5.5 to 4.0) for the three wt NP2 complexes, which indicate an interchange between two ruffling distortions of the heme. A dramatic change of A:B ratios with pH was observed for the three NP2(V24E) ligand complexes. They both are believed to be a result of a change in protein structure near E53 when it is protonated at low pH.Homo-dimers of NP1 and NP4 were investigated. 1H{15N}-HSQC NMR experimental results revealed that holo-NP4 is a homo-dimer at low pH and a mixture of dimer and monomer at high pH. In contrast, holo-NP4-Hm is monomeric at high pH (6.5 and 7.5). A H-bond between Asp30 and the Hm ligand is responsible for destabilization of the homo-dimer. NP1 was also shown to be a mixture of dimer and monomer at high pH.Heme d1 model complexes were studied. The high-spin form and low-spin forms of the Fe(III) complexes with 2-methylimidazole or imidazole, for monooxo-octaethylchlorin, trans-dioxo-octaethylisobacteriochlorin and 2,7-dioxo-octaethyliso- bacteriochlorin, were characterized by NMR spectroscopy. Spin density maps that show the orbital used for spin delocalization have been generated from Hückel calculations.Preliminary results of additional studies of the nitrophorins and future directions of study are presented.

A detailed review and revision of the theories required to simulate the electron paramagnetic resonance (epr) spectra of S' = 1/2 transition metal monomers and dimers is undertaken. The simulation of the epr spectrum of bis(biuretato)cuprate(II), doped in its isomorphous nickel(II) complex, enables the determination of its effective spin Hamiltonian parameters, independent of PH and solvent effects. An axial bis(biuretato)cuprate(II) dimer is also detected at 110 K and its simulated spectra indicate that it is formed by the axial interaction of two monomers. / The nature of copper(II)-biuret complexes in acidic and neutral media is then investigated. Their epr spectra are shown to be deceptively simple and arise from more than one species in solution. Furthermore, in basic media the bis(biuretato)cuprate(II) and di-(mu)-hydroxo-bis(biuretato)dicuprate(II) are the predominant species. However a consideration of the structure and superexchange interactions of the latter complex indicate that it is "epr silent". / Electronic absorption and epr investigations demonstrate that polyols and carbohydrates interact axially with bis(biuretato)cuprate(II) in solution without the displacement of the equatorial biuretato ligands. / The resonance field positions and general contribution of the g tensor to the epr intensities of a preferentially oriented paramagnetic probe is derived. They are used in simulating the epr spectra of copper(II) complexes adsorbed on cellulose fibres. The results suggest that the complexes interchelate between the cellulosic sheets of the fibre. An empirical parameter describing the degree of order of the sheets, within the fibre, is defined and estimated. / Stable 9,10-anthrasemiquinone radicals are generated by carbohydrates in strictly aqueous media for the first time. They are also shown to be the predominant radicals in AQ-Soda and AQ-Kraft-Soda pulping liquors. Monitoring the radical concentrations with temperature via epr strongly suggests that they should not be disregarded as possible catalysts in these processes.

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