Dynamic nuclear polarization for sensitivity enhancement in modern solid-state NMR

Abstract

The field of dynamic nuclear polarization has undergone tremendous developments and diversification since its inception more than 6 decades ago. In this review we provide an in-depth overview of the relevant topics involved in DNP-enhanced MAS NMR spectroscopy. This includes the theoretical description of DNP mechanisms as well as of the polarization transfer pathways that can lead to a uniform or selective spreading of polarization between nuclear spins. Furthermore, we cover historical and state-of-the art aspects of dedicated instrumentation, polarizing agents, and optimization techniques for efficient MAS DNP. Finally, we present an extensive overview on applications in the fields of structural biology and materials science, which underlines that MAS DNP has moved far beyond the proof-of-concept stage and has become an important tool for research in these fields.

Materials Characterization by Dynamic Nuclear Polarization-Enhanced Solid-State NMR Spectroscopy

“…For example, the magnetic field strength, the sample temperature, rotor diameter, gyrotron power, pulsed vs. CW microwave output, etc., all greatly influence ε. These issues are addressed in detail elsewhere 1,5 and briefly discussed in the conclusions section. The parameters related to preparation of the sample that have the largest impact on ε and absolute sensitivity gains are described below.…”

A quasi-optical and corrugated waveguide microwave transmission system for simultaneous dynamic nuclear polarization NMR on two separate 14.1 T spectrometers

“…The commercial availability of this instrumentation has led to the wide-spread use of DNP, particularly in magic angle spinning (MAS) solids NMR experiments [18–23]. Nonetheless, DNP applications at temperatures achievable with nitrogen-based cooling (i.e.~100 K), require microwave powers in excess of 10 W. Currently, gyrotrons are the only available microwave sources that can meet these power requirements at the high magnetic fields (9–19 T) of interest to structural and material chemists.…”

Paramagnetic Metal‐Ion Dopants as Polarization Agents for Dynamic Nuclear Polarization NMR Spectroscopy in Inorganic Solids

“…When combined with magic angle spinning (MAS), as developed by Griffin et al., MAS‐DNP from nitroxide biradicals can provide sensitivity enhancement of a few orders of magnitude in solid‐state nuclear magnetic resonance (ssNMR) spectroscopy. The increased sensitivity expanded the applicability of ssNMR to many challenging systems such as membrane proteins, amyloid fibrils and heterogeneous catalysts ,,. However, in the study of inorganic particles, the use of exogenous radicals, e. g. nitroxides, introduces several constraints on the approach.…”