Browsing by Author "Parish, Christopher"
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Item Chemical Physics and Applications of Dynamic Nuclear Polarization-enhanced Nuclear Magnetic Resonance(2019-04-23) Parish, Christopher; Lumata, LloydNuclear magnetic resonance (NMR) spectroscopy of nuclei with low magnetic moments such as 13C spins can be quite challenging and time-consuming. Dynamic nuclear polarization (DNP) via the dissolution method greatly alleviates this sensitivity problem by enhancing the NMR signals of these insensitive nuclei by several thousand-fold. Dissolution DNP thus allows 13C NMR tracking of cellular metabolism in living cells in real-time with superb sensitivity and high specificity. Herein, the bulk of my PhD dissertation work has been devoted to the elucidation and optimization of chemical physics of DNP technology in pursuit of attaining the highest NMR signal enhancements. One finding highlighted in this dissertation is the confirmation that the solidstate 13C DNP efficiency is affected by the isotopic location of the 13C label within the target molecule. Such can be explained via the thermal mixing model of DNP. Another major work in this dissertation is the investigation of the effects of 2H enrichment of the glassing solvents on the solid-state 13C spin-lattice T1 relaxation times of hyperpolarized 13C acetate. It is reported herein that glassing solvent deuteration elongates the 13C T1 relaxation times significantly, indicative of reduced intermolecular dipolar interaction of 13C spins with 2H spins compared to coupling with 1H spins. Next, this dissertation also encompasses two studies regarding the effect upon DNP of doping samples with mixtures of two different free radicals as opposed to doping them with one type of free radical. In one of the two studies, it was determined that a mixture of the wide EPR width 4-oxo-TEMPO and narrow EPR width trityl OX063 yields interesting 13C DNP results. There appears to be competing effects when the microwave irradiation frequency was set to the negative polarization peak of trityl OX063 which coincides with the positive polarization peak of 4-oxo-TEMPO. On the other hand, a mixture of both narrow EPR widths trityl and BDPA free radicals yields an additive effect. Finally, this dissertation also details the use of 13C NMR in the characterization of 13C-labelled amino acids and their application in investigating cancer cell metabolism. 13C-labeled amino acids are potential hyperpolarized 13C NMR spectroscopy and imaging (MRI) metabolic probes for cancer because a number of metabolic pathways that involve these biomolecules are abnormal in tumors. For instance, the enzyme branched chain amino acid transferase (BCAT), which catalyzes the conversion of branched chain amino acids (BCAA) to their ketoacid counterparts or vice versa, is overexpressed in several cancers. In this project, [1- 13C] L-leucine and [1- 13C] alpha-ketoisocaproate (KIC) were used to study the aberrant BCAT metabolic activity in glioblastoma. SfXL glioblastoma cells appear to preferentially convert 13CKIC to 13C leucine rather than vice versa. Western blot experiments confirmed that BCAT expression is higher in SfXL cells than in normal astrocytes. Overall, this dissertation details the chemical tuning methods in DNP that I have unraveled in pursuit of attaining the highest 13C NMR signal enhancements. These optimized DNP signals are crucial to the success of in vivo NMR or MRI studies, particularly in probing the hyperactive metabolism of cancer.Item Influence of Dy³⁺ and Tb³⁺ Doping on ¹³C Dynamic Nuclear Polarization(American Institute of Physics Inc, 2017-01-03) Niedbalski, Peter; Parish, Christopher; Kiswandhi, Andhika; Fidelino, L.; Khemtong, C.; Hayati, Z.; Song, L.; Martins, Andr©; Sherry, A. Dean; Lumata, Lloyd L.; Niedbalski, Peter; Parish, Christopher; Kiswandhi, Andhika; Martins, Andr©; Sherry, A. Dean; Lumata, LloydDynamic nuclear polarization (DNP) is a technique that uses a microwave-driven transfer of high spin alignment from electrons to nuclear spins. This is most effective at low temperature and high magnetic field, and with the invention of the dissolution method, the amplified nuclear magnetic resonance (NMR) signals in the frozen state in DNP can be harnessed in the liquid-state at physiologically acceptable temperature for in vitro and in vivo metabolic studies. A current optimization practice in dissolution DNP is to dope the sample with trace amounts of lanthanides such as Gd3+ or Ho3+, which further improves the polarization. While Gd³⁺ and Ho³⁺ have been optimized for use in dissolution DNP, other lanthanides have not been exhaustively studied for use in ¹³C DNP applications. In this work, two additional lanthanides with relatively high magnetic moments, Dy³⁺ and Tb³⁺, were extensively optimized and tested as doping additives for ¹³C DNP at 3.35 T and 1.2 K. We have found that both of these lanthanides are also beneficial additives, to a varying degree, for ¹³C DNP. The optimal concentrations of Dy³⁺ (1.5 mM) and Tb³⁺ (0.25 mM) for ¹³C DNP were found to be less than that of Gd³⁺ (2 mM). W-band electron paramagnetic resonance shows that these enhancements due to Dy³⁺ and Tb³⁺ doping are accompanied by shortening of electron T₁ of trityl OX063 free radical. Furthermore, when dissolution was employed, Tb³⁺-doped samples were found to have similar liquid-state ¹³C NMR signal enhancements compared to samples doped with Gd³⁺, and both Tb³⁺ and Dy³⁺ had a negligible liquid-state nuclear T₁ shortening effect which contrasts with the significant reduction in T₁ when using Gd³⁺. Our results show that Dy³⁺ doping and Tb³⁺ doping have a beneficial impact on ¹³C DNP both in the solid and liquid states, and that Tb³⁺ in particular could be used as a potential alternative to Gd³⁺ in ¹³C dissolution DNP experiments.Item Influence of ¹³C Isotopic Labeling Location on Dynamic Nuclear Polarization of Acetate(Amer Chemical Soc, 2017-05-19) Niedbalski, Peter; Parish, Christopher; Kiswandhi, Andhika; Kovacs, Zoltan; Lumata, Lloyd L.; Niedbalski, Peter; Parish, Christopher; Kiswandhi, Andhika; Lumata, Lloyd L.Dynamic nuclear polarization (DNP) via the dissolution method has alleviated the insensitivity problem in liquid-state nuclear magnetic resonance (NMR) spectroscopy by amplifying the signals by several thousand-fold. This NMR signal amplification process emanates from the microwave-mediated transfer of high electron spin alignment to the nuclear spins at high magnetic field and cryogenic temperature. Since the interplay between the electrons and nuclei is crucial, the chemical composition of a DNP sample such as the type of free radical used, glassing solvents, or the nature of the target nuclei can significantly affect the NMR signal enhancement levels that can be attained with DNP. Herein, we have investigated the influence of ¹³C isotopic labeling location on the DNP of a model ¹³C compound, sodium acetate, at 3.35 T and 1.4 K using the narrow electron spin resonance (ESR) line width free radical trityl OX063. Our results show that the carboxyl ¹³C spins yielded about twice the polarization produced in methyl ¹³C spins. Deuteration of the methyl ¹³C group, while proven beneficial in the liquid-state, did not produce an improvement in the ¹³C polarization level at cryogenic conditions. In fact, a slight reduction of the solid-state ¹³C polarization was observed when ²H spins are present in the methyl group. Furthermore, our data reveal that there is a close correlation between the solid-state ¹³C T₁ relaxation times of these samples and the relative ¹³C polarization levels. The overall results suggest the achievable solid-state polarization of ¹³C acetate is directly affected by the location of the ¹³C isotopic labeling via the possible interplay of nuclear relaxation leakage factor and cross-talks between nuclear Zeeman reservoirs in DNP.