DIFFUSION IMAGING OF LIPID MEMBRANES: DEVELOPING MULTI-PULSE NMR TO IMAGE STATIC MEMBRANES SAMPLES

A multi-pulse (MP), pulsed-field gradient (PG) stimulated echo (STE) nuclear magnetic resonance (NMR) pulse program was constructed and refined using ethylene glycol (EG), with\ud the goal of providing a detailed diffusion image of a lipid membrane. This MP PGSTE NMR technique offers a useful combination of magnetic resonance imaging (MRI) and NMR tools that may provide images of lipid rafts at a length scale that is not restricted by the diffraction limit. MP NMR was used to provide homonuclear dipole-dipole decoupling, directly replacing magic-angle spinning (MAS), in a PGSTE NMR pulse program. Optimizing the use of MP NMR for EG and lipids, it was found that moving the carrier frequency ~2.5 kHz off resonance and shortening the cycle time to the minimum allowed by the probe hardware (in this case 43.2 μs at a power level of 139 kHz) produced the best results. By eliminating the use of magic-angle spinning (MAS), the gradient coils in the NMR diffusion-imaging probe may be placed closer to the sample, increasing their effect. Future work is needed to apply MP PGSTE NMR to static lipid samples. A basic PGSTE NMR diffusion measuring pulse program was used to determine the self-diffusion coefficient, D, of EG with the results showing Dself for EG was 6.5 x 10^-11 m^2 s^-1