Dynamic Nuclear Polarization Enhanced NMR in the Solid-State

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is one of the most commonly used spectroscopic techniques to obtain information on the structure and dynamics of biological and chemical materials. A variety of samples can be studied including solutions, crystalline solids, powders and hydrated protein extracts. However, biological NMR spectroscopy is limited to concentrated samples, typically in the millimolar range, due to its intrinsic low sensitivity compared to other techniques such as fluorescence or electron paramagnetic resonance (EPR) spectroscopy.Dynamic nuclear polarization (DNP) is a method that increases the sensitivity of NMR by several orders of magnitude. It exploits a polarization transfer from unpaired electrons to neighboring nuclei which leads to an absolute increase of the signal-to-noise ratio (S/N). Consequently, biological samples with much lower concentrations can now be studied in hours or days compared to several weeks.This chapter will explain the different types of DNP enhanced NMR experiments, focusing primarily on solid-state magic angle spinning (MAS) DNP, its applications, and possible means of improvement.

Small is Beautiful: Challenges and Perspectives of Nano/Meso/Microscience

“…[ 51 ] Here, NMR is already bringing in a rich harvest for biostructures, but of course this could be applied to many organic and inorganic nanomaterials, too, resolving detailed functional neighborhood relations. As everything, in principle, exists, progress here is a matter of the right people and the right projects.…”

Persistent Radicals of Self‐assembled Benzophenone bis‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

“…1–3 In material science, solid-state DNP methods primarily rely on exogenous radicals, such as TOTAPOL and AMUPol, which are typically introduced by incipient wetness impregnation in mM concentrations. 4 Recent work suggests that high field DNP enhancement may also be observed with endogenous radicals. 5 This manuscript probes the structure of an unusually persistent endogenous radical in bis -urea macrocycle 1 and its use as a polarizing agent for DNP enhancement.…”

“…Solutions of exogenous stable radicals such as AMUPol, known as “DNP juice”, are typically used in mM concentration as polarizing agents for solid-state DNP MAS NMR at ~100 K. 1, 4 Under microwave irradiation, the exogenous radical transfers its spin polarization to neighbouring protons. The large spin polarization of the protons generates a spin polarization gradient leading to spin diffusion to nearby protons resulting in a uniform proton hyperpolarization throughout the sample.…”

Ultra-Low Temperature Nuclear Magnetic Resonance

“…This hyperpolarization of nuclei, known as dynamic nuclear polarization (DNP), has only recently started to be routinely exploited [3][4][5][6][7]. This is due to the technological breakthroughs resulting from the intra-MIT collaboration and perseverance of Griffin, Temkin, and coworkers [8,9], as well as the subsequent commercialization of the necessary hardware [10].…”

“…This is due to the technological breakthroughs resulting from the intra-MIT collaboration and perseverance of Griffin, Temkin, and coworkers [8,9], as well as the subsequent commercialization of the necessary hardware [10]. Nowadays, high-resolution spectra, recorded under magic angle sample spinning (MAS) conditions, can be acquired in a fraction of the previously required experimental time for a large variety of systems ranging from biomolecules [4,5] to functional materials [6,7]. The boundaries of the technique still strive to be pushed further.…”