In this thesis we describe the results of two sets of experiments on spin-polarized atomic hydrogen at temperatures below 1 K using a 115 GHz heterodyne ESR spectrometer. First, we have made measurements of the rates of the two-body recombination processes in spin-polarized atomic hydrogen gas and spin-polarized atomic deuterium gas in a 41 kG field. In the second set of experiments, we examined the ESR absorption line associated with the spin-polarized atomic hydrogen atoms adsorbed on surfaces of liquid helium. In hydrogen, a comparision of the measured recombination rates in 41 kG with the corresponding rates measured in different magnetic fields showed that an additional recombination process is activate for the conditions of these experiments. We demonstrate that this is due to a resonant recombination process via the (v,J) = (14,4) level of molecular hydrogen. In spin-polarized deuterium, we found that the recombination rate are much larger than the analogous rates in hydrogen, and therefore that atomic deuterium gas is much less stable than the hydrogen system under comparable conditions. We report the first observation and study of doubly spin-polarized deuterium, a gas in which both the deuteron and electron spins are aligned. At temperatures near 0.1 K, the absorption line of doubly spin-polarized H atoms changes drastically as a peak appears on both sides of the peak associated with the bulk atoms. We have shown that these new peaks are due to the atoms which are adsorbed onto the surface of the liquid helium film that coats the walls of the microwave cavity. The geometry dependent non-zero average magnetic dipolar field due to aligned spins on a planar surface results in a shift of the position of the ESR absorption lines. The lineshapes of the side peaks are very unusual and are best described as ramp-like. Even after extensive attempts to explain this lineshape, we still do not know what mechanism is responsible. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Dynamic nuclear polarization (DNP) is an emerging method for increasing signal-to-noise in solid-state NMR experiments by transferring polarization from electrons to nuclei. Stable nitroxide biradicals, the polarization source for the cross effect mechanism, are typically co-dissolved at millimolar concentrations with biomolecules of interest. There has been considerable recent interest, however, in co-localizing the paramagnetic polarizing agent with the analyte of interest through covalent or noncovalent interactions. In this thesis, we bound the biradical to the protein of interest through conjugation to a high affinity, non-covalent inhibitor using E.coli dihydrofolate reductase (DHFR) and its nanomolar inhibitor trimethoprim (TMP). Two different biradical affinity reagents (TMP-T and TMP-V-T) were created by covalently linking trimethoprim to the biradical polarizing agent TOTAPOL. These TMP-TOTAPOL compounds provided excellent enhancements of the DHFR NMR spectrum, comparable to when TOTAPOL is co-dissolved with the protein. In contrast to TOTAPOL, the specific interactions of these compounds enabled them to be added stoichiometrically to samples of DHFR at micromolar concentrations while retaining excellent enhancements. Benefits of lowered biradical concentration include reduced chemical perturbation of the sample and the ability to selectively enhance signals for the protein of interest in a perdeuterated solvent matrix. The binding of TMP-V-T to DHFR confines the paramagnetic TOTAPOL moiety to the protein binding pocket. We capitalized on this fact to site-specifically study paramagnet induced signal quenching in DNP samples. Using crystallography and solution NMR spectroscopy, we demonstrated that although the TMP fragment is well ordered the TOTAPOL moiety is disordered when bound to DHFR. We prepared site-specific isotpically enriched samples of DHFR and measured signal quenching in DNP samples. Intriguingly, the bleaching patterns seen in DNP samples are similar to those observed in room temperature studies. We argue that static disorder plays a role in this observation, among other contributions. Our results provide design principles for DNP experiments with affinity biradicals, and demonstrate the utility of affinity biradicals for DNP studies given the confined signal quenching. Affinity biradicals hold great promise for enabling selective DNP investigations of dilute proteins in whole cells or cellular lysates. We explored how to use TMP-T and TMP-V-T to study DHFR in whole cells and cellular lysates. We developed strategies to overcome fast chemical reduction of the nitroxide moiety in the cellular environment, and sample preparation protocols to obtain overexpressed DHFR with isotopic enrichment patterns that enable selective DNP enhancements. We demonstrate excellent enhancements of whole cell pellets by TOTAPOL, and also provide evidence for selective DHFR enhancement by TMP-V-T in cellular lysates. Our results form guidelines for future selective studies of DHFR in cellular contexts. These results collectively demonstrate the potential of the TMP-T(V-T) compounds and similar affinity biradical reagents both for mechanistic DNP studies and selective NMR studies in cellular contexts.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 207-213). Also available via the Internet

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Abstracted in Dissertation abstracts, v. 25 (1965) no. 10, p. 6015. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 180-183).

Thesis (M.A.)--Ohio University, June, 2002. / Title from PDF t.p. Includes bibliographical references (leaves 223-228)

The Green's function method is applied to investigate the magnetic spin resonance spectra of three-dimensional and two-dimensional spin-polarized quantum gases. The Hartree-Fock approximation is employed to calculate the one-particle Green's function of the atoms, then this one-particle Green's function is used for the calculation of the vertex part of the Green's function. Such a combination yields a self-consistent result. The absorption spectra are obtained from the calculation of the susceptibility in terms of the two-particle Green's function (bubble diagram). Some general expressions for the dispersion relation, for the effective mass of a spin wave, and for the dipolar frequency shift are given in the calculation. In order to estimate the shift of the electron-spin-resonance (ESR) frequency, the effective dipole-dipole interactions among the hydrogen atoms are included in the calculation. These effective interactions are deduced from the ladder approximation, and hence are characterized by the scattering amplitude. The scattering amplitude is calculated numerically. The result shows that the theoretical value of the shift is smaller than the experimentally observed value by about 35%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

The solid/liquid intermolecular transfer (SLIT) flow dynamic nuclear polarization (DNP) experiment potentially provides new methodology for studying interfacial phenomena (e.g., weak hydrogen bonding). In addition, the high efficiency of the transfer also ensures dramatically enhanced NMR signals. These large DNP enhancements could alleviate sensitivity limitations in various flow NMR experiments. Previous studies have established that silica phase immobilized nitroxide (SPIN) radical system are advantageous in the SLIT experiment. In favorable cases (e.g. DCCI₃/SPIN system) a ¹³C DNP enhancement 60 times in excess of the high magnetic field (4.7 T) magnetization has been achieved.¹² However a number of factors still limit the SPIN system presently available. For example, low magnetogyric ratio nuclides, ¹³C, ¹⁵N, which are not dominated by scalar relaxation mechanism require high surface radical concentrations. The focal point of the present study is the preparation and characterization of several new SPIN radical systems and can be divided into two parts: 1). Preparation, EPR, and DNP Characterization of Achiral SPIN Radicals: a number of SPIN samples were prepared in order to examine the dependence of the observed SLIT DNP enhancements as a function of the surface spin concentration and also isotope-substitution of the immobilized radicals. The SPIN samples were characterized by EPR and DNP. The results show that the increase in the spin concentration does not offer any advantage for ¹H DNP studies. In contrast, ¹³C SLIT DNP results in improved SPIN sample demonstrate the possibility of monitoring dipolar dominated ¹³C DNP enhancements as a result of better leakage factors and suppressed three-spin effects at higher radical concentration. The effect of substitution of deuterons for protons in the immobilized radical also suggest an appreciable contribution of a solid-state three-spin effect. 2). Preparation, EPR, and DNP Characterization of Chiral SPIN Samples: This part of the study provides a chiral SPIN radical suitable for monitoring enantioselective ¹³C DNP enhancements. The DNP results suggest that selective enantiomer/chiral SPIN interactions are feasible. Specifically, differences in the ¹³C DNP enhancements for a model system: (R)- and (S)- enantiomers of bromocamphor, and a (R) chiral SPIN sample were observed. / Ph. D.

A flow solid/liquid intermolecular transfer (SLIT) ¹H dynamic nuclear polarization (DNP) experiment is described. The SLIT ¹H DNP results are reported for the case of flowing benzene over silica gel surfaces prepared with stable immobilized nitroxide and phenoxy spin labels. The advantages of the flow SLIT DNP experiment in comparison with the recently reported flow liquid/liquid intermolecular transfer (LLIT) ¹H DNP experiment are discussed. The results suggest that the flow SLIT DNP experiment provides a new method for monitoring liquid/surface intermolecular interactions, since the reporter group (flowing benzene) reflects properties of the surface. Potential applications such as: 1) observation of enhanced NMR signals without detrimental line broadening due to the presence of stable free radicals in the NMR detection region, and 2) independent optimization of the "EPR" and "NMR" portions of the DNP experiment, are discussed. The thrust of this thesis was twofold: 1) to synthesize immobilized free radical systems appropriate for the SLIT DNP measurements, and 2) to establish the factors influencing DNP mechanism(s) for these systems. The resulting ¹H DNP line shapes imply that both Overhauser effect and solid- state effect are effective mechanisms for the DNP enhancements. The results suggest that the relatively low magnitude of the enhancements can be attributed to the longer molecular correlation times of the solid/liquid systems studied. Also, the EPR spectra and the corresponding number of unpaired spins were measured for these immobilized systems. / M.S.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Kirby W. Kemper, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Nov. 20, 2003). An arrow pointed to the right over the Li in title. Includes bibliographical references.