Xenon polarizer characterization and biological studies

Abstract

I will describe a low-pressure flow-through 129Xe polarizer and report its performance by examining both the output 129Xe and in situ Rb polarization. The 129Xe polarization was made using standard NMR techniques, and the Rb polarization measurement was made using optically detected electron paramagnetic resonance. I compared the results of these measurements to a one-dimensional numerical model of the system. While we qualitatively understand the behavior of the system, the comparison between measurement and model reveals several inadequacies in our understanding of many important physical mechanisms. I will discuss the relevant physics necessary to qualitatively understand the system's behavior and suggest what mechanisms may cause the discrepancies in the modeled and measured behavior. I will demonstrate the utility of this Xe polarizer by measuring xenon's chemical shift dependence on the concentration of Bovine Pancreatic Trypsin Inhibitor (BPTI) and some of its mutants. Mutants Y23A and F45G have measured dependence of 0.56±0.05 ppm/mM and 0.47±0.07 ppm/mM, respectively, which is consistent with relatively strong, manufactured binding sites in the structure. Wild type BPTI has a measured dependence of only 0.15±0.02 ppm/mM, suggesting that there exists no specific binding site to which Xe can bind. Finally, the mutant Y35G has a dependence of 0.10±0.07 ppm/mM. This, with previous data, suggests that a large fraction of solution-phase Y35G does not exist in a conformation that allows Xe access to its binding cavity.