Observing Nearby Nuclei on Paramagnetic Trityls and MOFs via DNP and Electron Decoupling

Abstract

Dynamic nuclear polarization (DNP) is an NMR sensitivity enhancement technique that mediates polarization transfer from unpaired electrons to NMR-active nuclei. Despite its success in elucidating important structural information on biological and inorganic materials, the detailed polarization-transfer pathway-from the electrons to the nearby and then the bulk solvent nuclei, and finally to the molecules of interest-remains unclear. In particular, the nuclei in the paramagnetic polarizing agent play significant roles in relaying the enhanced NMR polarizations to more remote nuclei. Despite their importance, the direct NMR observation of these nuclei is challenging because of poor sensitivity. Here, we show that a combined DNP and electron decoupling approach can facilitate direct NMR detection of these nuclei. We achieved an ~80 % improvement in NMR intensity via electron decoupling at 0.35 T and 80 K on trityl radicals. Moreover, we recorded a DNP enhancement factor of 𝜀 ~ 90 and ~11 % higher NMR intensity using electron decoupling on paramagnetic metal-organic framework, magnesium hexaoxytriphenylene (MgHOTP MOF).

Efficient 18.8 T MAS-DNP NMR reveals hidden side chains in amyloid fibrils

“…The DNP sample was then degassed with at least three freeze-pump-thaw cycles using a 3-way tap, and backfilled with Argon gas. 74,86 This procedure removes the paramagnetic 11 oxygen, which reproducibly improves the DNP enhancement factor by ~10 %. We could not implement the insert/eject cycle degassing method demonstrated in Kubicki et al because the rotor is likely to be blocked in our Bruker MAS DNP probe at lower temperatures.…”

A focus on applying 63/65Cu solid-state NMR spectroscopy to characterize Cu MOFs

“…[8][9][10] On the other hand, dynamic nuclear polarization (DNP) is an NMR sensitivity enhancement technique that can usually boost the NMR signals by several orders of magnitude. [11][12][13] In conclusion, Zhang et al have shown that 63/65 Cu NMR spectroscopy is a powerful tool for probing the copper environments within MOFs. By offering site-specic information about the coordination number and geometry of copper centers, it provides crucial insights into the factors governing the properties of MOFs.…”

“…8–10 On the other hand, dynamic nuclear polarization (DNP) is an NMR sensitivity enhancement technique that can usually boost the NMR signals by several orders of magnitude. 11–13…”

In-House Fabrication of 1.3 to 7 mm MAS Drive Caps using Desktop 3D Printers

“…Although the FDM method has, in general, a poorer resolution, it is more affordable and easier to use relative to the resin-based SLA method. Both 3D printing technologies have been exploited in various NMR applications, ranging from fabricating MAS sample eject systems, 11 RF coils, [12][13][14][15] NMR sample tubes, 16 parahydrogen generator, 17 NMR sample degassing apparatus, 18,19 , NMR probeheads, 20 etc. Besides these examples, Xu et al have recently demonstrated that it is possible to fabricate MAS stator and drive caps using FDM, but only for > 3.5 mm system.…”