Exploring exchange and transport dynamics in complex systems through nuclear magnetic resonance

Abstract

Nuclear magnetic resonance (NMR) is uniquely qualified for non-invasive studies of systems providing insights into macro-, meso-, and microscale structures. NMR relaxation and diffusion methods are applied to characterize transport and magnetization exchange dynamics in various complex systems. These techniques are highly sensitive to molecular mobility restrictions which correlate to the ability to monitor thermodynamic phase transitions and changes in molecular environment. NMR diffusion and relaxation measurements are applied to characterize the effect of xylose on transport within zeolite beads. The ability for NMR to explore the transport phenomenon on multiple length and time scales is exploited to characterize how the introduction of xylose effects the transport structure of the bead. Eigenvector simulations of magnetization evolution within a coupled pore system during multidimensional NMR measurements, T1-T2 relaxation correlation experiments, allowed for insights into complex diffusion and exchange occurring within multiple systems. Additionally, multidimensional relaxation NMR measurements, in the form of varying echo-time spin-spin relaxation dispersion T2(tau) and spin-spin relaxation exchange T2-T2 experiments, are demonstrated to successfully characterize thermodynamic structural rearrangements of two natural straight-chained hydrocarbons and a natural wax. Temperature dependent magnetization exchange was found in both the longitudinal and transverse magnetization. The results indicate the ability of NMR relaxometry to detect magnetization exchange without mass or molecular exchange, also known as spin diffusion, including in the transverse magnetization. Spatial domain extent can be inferred from the exchange timescale and an estimate of the spin diffusion coefficient. NMR relaxometry methods were extended to glycerol behenate, a common pharmaceutical component. Glycerol behenate was decomposed into its three base components to explore how polymorphic structure and exchange depend on temperature within each pure lipid through T2(tau) and T2-T2 NMR relaxation experiments. These methods allowed for in-situ monitoring of thermodynamic dependent exchange across domains in addition to decoupling of transverse and longitudinal exchange. The results allow for calculation of exchange length scales across the micro- and mesoscales within the lipids. Ultimately, multidimensional NMR relaxometry is successfully demonstrated to be an effective technique for characterizing and monitoring structural changes in lipids across various phase transition temperatures and time and length scales.