Chapter 17: Fast 2D NMR to Study Microstructures

In addition to standard solution state chemical analysis, NMR spectroscopy is also a powerful method for the studies of microstructures of solid materials. In addition to solid-state NMR, solid materials can be studied by solution state NMR techniques using either inherent or external probe fluids. This chapter is devoted to fast solution state NMR methods for studying microstructures of hard and soft matter. The first part concentrates on methods relying on chemical shift contrast. Particularly, it focuses on ¹²⁹Xe NMR of xenon gas, which is broadly used in the investigations of porous materials as well as biosensor applications. It describes how spin exchange optical pumping and chemical exchange saturation transfer (CEST) techniques can be exploited to enhance the sensitivity of experiment up to seven orders of magnitude. Furthermore, it explains how CEST spectra can be measured in a single scan using spatial encoding. The second part is devoted to relaxation and diffusion contrast. It elucidates the principles of ultrafast multidimensional relaxation and diffusion experiments and describes how those experiments can be exploited in the studies of porous materials, aggregation of surfactants, intra- and extracellular metabolites in cancer cell suspensions, etc., even with low field single sided NMR devices.