Achieving high resolution dipolar NMR information without fast sample spinning: combining magic angle turning with dipolar based NMR methods

HR-MAS DREAMTIME NMR for Slow Spinning ex Vivo and in Vivo Samples

HR-MAS NMR is a powerful tool, capable of monitoring molecular changes in intact heterogeneous samples. However, one of the biggest limitations of 1H NMR is its narrow spectral width which leads to considerable overlap in complex natural samples. DREAMTIME NMR is a highly selective technique that allows users to isolate suites of metabolites from congested spectra. This permits targeted metabolomics by NMR and is ideal for monitoring specific processes. To date, DREAMTIME has only been employed in solution-state NMR, here it is adapted for HR-MAS applications. At high spinning speeds (>5 kHz), DREAMTIME works with minimal modifications. However, spinning over 3-4 kHz leads to cell lysis, and if maintaining sample integrity is necessary, slower spinning (<2.5 kHz) is required. Very slow spinning (≤500 Hz) is advantageous for in vivo analysis to increase organism survival; however, sidebands from water pose a problem. To address this, a version of DREAMTIME, termed DREAMTIME-SLOWMAS, is introduced. Both techniques are compared at 2500, 500, and 50 Hz, using ex vivo worm tissue. Following this, DREAMTIME-SLOWMAS is applied to monitor key metabolites of anoxic stress in living shrimp at 500 Hz. Thus, standard DREAMTIME works well under MAS conditions and is recommended for samples reswollen in D2O or spun >2500 Hz. For slow spinning in vivo or intact tissue samples, DREAMTIME-SLOWMAS provides an excellent way to target process-specific metabolites while maintaining sample integrity. Overall, DREAMTIME should find widespread application wherever targeted molecular information is required from complex samples with a high degree of spectral overlap.

Development and application of novel NMR methodologies for the in situ characterization of crystallization processes of metastable crystalline materials

In this contribution we report on the development and application of modern NMR approaches for the in situ characterization of the crystallization of metastable materials. The work was performed within the framework of the DFG priority programme SPP 1415 “Crystalline Non-Equilibrium Phases”. As one of the goals of this project, the development of a NMR methodology which enables an analysis of local structural motifs on short (1–2 Å) and extended (2–6 Å) length scales without the need for fast magic angle spinning (MAS) has been defined, since the enormous centripetal forces which occur during fast sample rotation (up to 107 g) may intervene with the chemical or physical process which is being monitored. To achieve this goal, we developed a magic angle turning probe and pulse sequences allowing to trace the isotropic chemical shifts and heteronuclear dipolar couplings and hence the determination of structural motifs on short and intermediate length scales. With the implementation of novel inductive heating approaches the range of accessible rotation frequencies for in situ high temperature NMR measurements has been enlarged, now covering the ν MAS range of 0–10 kHz with an accessible temperature of up to 700°C. Application of NMR methodologies for the characterization of crystallization processes and the structure and dynamics of novel phases, partially in joint collaborations within the priority program, are also reported.