DNP enhanced NMR with flip-back recovery

Björgvinsdóttir, Snædís; Walder, Brennan J.; Pinon, Arthur C.; Yarava, Jayasubba Reddy; Emsley, Lyndon

doi:10.1016/j.jmr.2018.01.017

Cited by 19 publications

(16 citation statements)

References 38 publications

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“…The performance of HyTEK2 was evaluated at 21.1 T. At this high magnetic field, an OE enhancement of 73 has recently been published on a solution of BDPA in OTP in a 3.2 mm rotor at 10 kHz MAS. 55 For HyTEK2 at this field we obtained an enhancement of 64 under similar experimental conditions ( Figure S44). This value is comparable to the one obtained at 18.8 T in the same rotor size (65 at 10 kHz MAS), but lower than values obtained in smaller diameter rotors.…”

Section: Acs Paragon Plus Environmentsupporting

confidence: 64%

BDPA-Nitroxide Biradicals Tailored for Efficient Dynamic Nuclear Polarization Enhanced Solid-State NMR at Magnetic Fields up to 21.1 T

et al. 2018

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Dynamic Nuclear Polarization (DNP) solid-state NMR has developed into an invaluable tool for the investigation of a wide range of materials. However, the sensitivity gain achieved with many polarizing agents suffers from an unfavorable field and Magic Angle Spinning (MAS) frequency dependence. We present a series of new hybrid biradicals, soluble in organic solvents, that consist of an isotropic narrow EPR line radical, BDPA, tethered to a broad line nitroxide. By tuning the distance between the two electrons and the substituents at the nitroxide moiety, correlations between the electron-electron interactions and the electronic spin relaxation times on one hand, and the DNP enhancement factors on the other hand are established. The best radical in this series has a short methylene linker and bears bulky phenyl spirocyclohexyl ligands. In a 1.3 mm prototype DNP probe, it yields enhancements of up to 185 at 18.8 T (800 MHz 1H resonance frequency) and 40 kHz MAS. We show that this radical gives enhancement factors of over 60 in 3.2 mm sapphire rotors at both 18.8 and 21.1 T (900 MHz 1H resonance frequency), the highest magnetic field available today for DNP. The effect of the rotor size and of the microwave irradiation inside the MAS rotor is discussed. Finally, we demonstrate the potential of this new series of polarizing agents by recording high field 27Al and 29Si DNP Surface Enhanced NMR spectra (DNP SENS) of amorphous aluminosilicates and 17O NMR on silica nanoparticles.

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Section: Acs Paragon Plus Environmentsupporting

confidence: 64%

BDPA-Nitroxide Biradicals Tailored for Efficient Dynamic Nuclear Polarization Enhanced Solid-State NMR at Magnetic Fields up to 21.1 T

et al. 2018

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“…Currently, the majority of MAS DNP-NMR experiments on materials has been carried out at B0 = 9.4 T. Nevertheless, some MAS DNP-NMR experiments on materials have been reported at 14.1 T [158,159,[190][191][192][193][194][195][196][197], 18.8 T [69,80,94,95,139,186] and 21.1 T [139,198]. DNP-NMR experiments at B0 ≥ 14.1 T benefit notably from a higher spectral resolution for the detection of half-integer quadrupolar nuclei.…”

Section: Magnetic Field Of the Nmr Magnetmentioning

confidence: 99%

Recent developments in MAS DNP-NMR of materials

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et al. 2019

Solid State Nuclear Magnetic Resonance

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Solid-state NMR spectroscopy is a powerful technique for the characterization of the atomic-level structure and dynamics of materials. Nevertheless, the use of this technique is often limited by its lack of sensitivity, which can prevent the observation of surfaces, defects or insensitive isotopes. Dynamic Nuclear Polarization (DNP) has been shown to improve by one to three orders of magnitude the sensitivity of NMR experiments on materials under Magic-Angle Spinning (MAS), at static magnetic field B0 ≥ 5 T, conditions allowing for the acquisition of high-resolution spectra. The field of DNP-NMR spectroscopy of materials has undergone a rapid development in the last ten years, spurred notably by the availability of commercial DNP-NMR systems. We provide here an in-depth overview of MAS DNP-NMR studies of materials at high B0 field. After a historical perspective of DNP of materials, we describe the DNP transfers under MAS, the transport of polarization by spin diffusion and the various contributions to the overall sensitivity of DNP-NMR experiments. We discuss the design of tailored polarizing agents and the sample preparation in the case of materials. We present the DNP-NMR hardware and the influence of key experimental parameters, such as microwave power, magnetic field, temperature and MAS frequency. We give an overview of the isotopes, which have been detected by this technique, and the NMR methods, which have been combined with DNP. Finally, we show how MAS DNP-NMR has been applied to gain new insights into the structure of organic, hybrid and inorganic materials with applications in fields, such as health, energy, catalysis, optoelectronics etc.

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“…This mechanism has recently received renewed attention aer the discovery that it was active in insulating solids using BDPA (1,3-bisdiphenylene-2-phenylallyl) radicals. 25,26 Enhancements of up to 100 and 70 have been reported in the rigid glassy solvent OTP (ortho-terphenyl), at 18.8 T 27 and 21.1 T. 28 Magnetization transfer via OE DNP requires however build-up times of several tens of seconds, which partly moderates the overall sensitivity gain. Hybrid biradicals, consisting of a radical with an isotropic g factor tethered to a broad line nitroxide have recently been explored as an alternative strategy to preserve high enhancements at high magnetic eld.…”

Section: Introductionmentioning

confidence: 99%