The Application of Nuclear Magnetic Resonance to Molecules Undergoing Rapid Axial Reorientation
The cell membrane is critical for life. The functionality of this membrane is dependent on the interactions between the many different molecules found within and connected to the cell membrane. Proteins and peptides are responsible for a variety of biological activities including signal transmission and ion movement. Membrane proteins can be associated very closely with the membrane (known as integral membrane proteins) or loosely with the membrane (peripheral proteins). The functionality of these membrane proteins depends on their structure, which can be studied using nuclear magnetic resonance (NMR). In structural studies, protons present themselves as desirable nuclei for detection, owing to their high abundance in biological systems. However, strong homonuclear dipolar interactions often lead to broad signals and obscured details. This thesis describes the study and development of NMR pulse sequences that can be used to investigate model membrane systems that include small molecules. Beginning with a leucine-rich peptide P0813, proton suppression techniques were developed using a unique gradient probe assembly. The addition of pulsed field gradients within the pulse sequences resulted in significant proton coherence suppression in a sample composed of protonated lipid and peptide. Gramicidin-A was used in the development of proton-detected correlation experiments. These experiments were further studied with Conolysin-Mt1, a natural cytolytic peptide found in sea snails. Cholesterol was employed in the study of how the nuclear Overhauser effect can be used to probe molecular structure and dynamics. Finally, the majority of the modified experiments were tested on a synthetic peptide ALGA, which was originally designed to produce well-resolved proton spectra. Throughout the studies performed on the five different small molecules, new proton detection techniques were investigated, with varying degrees of success. In addition, different sample preparations were explored to help determine how changes in sample composition can affect sample stability.