Magic angle spinning NMR below 6 K with a computational fluid dynamics analysis of fluid flow and temperature gradients

Sesti, Erika L.; Alaniva, Nicholas; Rand, Peter W.; Choi, Eun A; Albert, Brice J.; Saliba, Edward P.; Scott, Faith J.; Barnes, Alexander B.

doi:10.1016/j.jmr.2017.11.002

Cited by 36 publications

(32 citation statements)

References 29 publications

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“…62 Second, several groups are developing helium cooled DNP systems. [63][64][65][66] Reducing the sample temperature to less than 30 K can potentially provide further absolute sensitivity gains of one to two orders of magnitude by increasing both DNP enhancements and thermal nuclear polarization. [63][64][65][66] Third, the development of coherent, pulsed microwave sources for time-domain high-field DNP could revolutionize the field in much the same way that pulsed methods revolutionized NMR spectroscopy.…”

Section: Acs Paragon Plus Environmentmentioning

confidence: 99%

“…[63][64][65][66] Reducing the sample temperature to less than 30 K can potentially provide further absolute sensitivity gains of one to two orders of magnitude by increasing both DNP enhancements and thermal nuclear polarization. [63][64][65][66] Third, the development of coherent, pulsed microwave sources for time-domain high-field DNP could revolutionize the field in much the same way that pulsed methods revolutionized NMR spectroscopy. Pulsed DNP will improve polarization transfer efficiency and make it possible to use simple monoradical PA. 67,68 It may also be possible to eliminate deleterious paramagnetic broadening effects with electron decoupling.…”

Section: Acs Paragon Plus Environmentmentioning

confidence: 99%

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

Rossini

2018

J. Phys. Chem. Lett.

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High-resolution solid-state NMR spectroscopy is a powerful tool for the study of organic and inorganic materials because it can directly probe the symmetry and structure at nuclear sites, the connectivity/bonding of atoms and precisely measure inter-atomic distances. However, NMR spectroscopy is hampered by intrinsically poor sensitivity, consequently, the application of NMR spectroscopy to many solid materials is often infeasible. High-field dynamic nuclear polarization (DNP) has emerged as a technique to routinely enhance the sensitivity of solid-state NMR experiments by one to three orders of magnitude. This perspective gives a general overview of how DNP enables advanced solid-state NMR experiments on a variety of materials. DNP-enhanced solid-state NMR experiments provide unique insights into the molecular structure, which makes it possible to form structure-activity relationships that ultimately assist in the rational design and improvement of materials. Disciplines Materials Chemistry | Physical Chemistry CommentsThis document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in The Journal of Physical Chemistry Letters, copyright © American Chemical Society after peer review. To access the final edited and published work see doi: 10.1021/acs.jpclett.8b01891. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Abstract High-resolution solid-state NMR spectroscopy is a powerful tool for the study of organic and

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Section: Acs Paragon Plus Environmentmentioning

confidence: 99%

Section: Acs Paragon Plus Environmentmentioning

confidence: 99%

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

Rossini

2018

J. Phys. Chem. Lett.

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“…Thecurrently available electron nutation frequency of 0.7 MHz, predicted with 15 W of incident microwave power, [29,31] yields electron spin control only sufficient to decouple weaker hyperfine interactions. [50] RF and microwave pulses were controlled with aT ecmag Redstone spectrometer (Tecmag,H ouston, TX). Figure 3c ompares aH ahn echo to aB loch decay,b oth with electron decoupling and aD NP period of 10 ms.T he Hahn echo significantly improves the baseline.Anexpansion around the NMR resonances is shown in Figure 3b.B road features,which relax on atimescale faster than the echo delay, are filtered out with aH ahn echo.F urther improvements to microwave technology will enable electron decoupling of the stronger hyperfine interactions manifested in these broad features.T he performance of electron decoupling with Bloch decay acquisition is further described in the Supporting Information.…”

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Electron Decoupling with Chirped Microwave Pulses for Rapid Signal Acquisition and Electron Saturation Recovery

et al. 2019

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Dynamic nuclear polarization (DNP) increases NMR sensitivity by transferring polarization from electron to nuclear spins.Herein, we demonstrate that electron decoupling with chirped microwave pulses enables improved observation of DNP-enhanced 13 Cs pins in direct dipolar contact with electron spins,t herebyl eading to an optimal delay between transients largely governed by relatively fast electron relaxation. We report the first measurement of electron longitudinal relaxation time (T 1e )d uring magic angle spinning (MAS) NMR by observation of DNP-enhanced NMR signals (T 1e = 40 AE 6ms, 40 mm trityl, 4.0 kHz MAS,4 .3 K). With a5ms DNP period, electron decoupling results in a195 %increase in signal intensity.MAS at 4.3 K, DNP,electron decoupling,and short recycle delays improve the sensitivity of 13 Cinthe vicinity of the polarizing agent. This is the first demonstration of recovery times between MAS-NMR transients being governed by short electron T 1 and fast DNP transfer.Magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy reveals structure and dynamics on ar ange of molecular architectures,i ncluding membrane proteins, [1][2][3][4][5][6] fibrils, [7][8][9][10] and interfaces. [11][12][13][14] Mechanical rotation of the sample about the magic angle of 54.78 8 with respect to the magnetic field partially averages anisotropic interactions of the magnetic resonance Hamiltonian, improving spectral resolution and sensitivity. [15][16][17][18] Often, sensitivity is also increased through the transfer of polarization from spins with stronger Zeeman interactions by radiofrequency [16,19] or microwave irradiation. In the case of dynamic nuclear polarization (DNP), hyperfine interactions are required to transfer spin polarization from electron to nuclear spins. [20][21][22][23][24][25] DNP transfer mechanisms require polarizing agents exhibiting electron paramagnetic resonance (EPR). [26] Here, we use as table organic monoradical, trityl (Finland radical), which has ar elatively narrow EPR lineshape. [27] Then arrow electron spin resonance and high-power microwave chirps generated by ac ustom-built frequency-agile gyrotron enable time-domain manipulation of electronic and hyperfine interactions. [28,29] We have shown that chirped microwave pulses can partially decouple the electron-nuclear spin interaction after DNP in am ethod known as electron decoupling,w ith amore pronounced effect on observed nuclear spins in direct proximity to electron spins. [30,31] DNP experiments typically require seconds to hours to spread enhanced polarization via nuclear spin diffusion to chemical sites of interest. [32][33][34] This slow spin diffusion significantly limits experiments.D NP is faster if nuclear spins proximal to the electron are polarized directly through hyperfine interactions.H owever,s uch direct DNP requires electron decoupling after the polarization transfer period to mitigate the detrimental effects of hyperfine interactions on NMR signatures. [31,35] Theo ptimal repetition time for direct DNP is li...

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“…55 With this substitution, sample temperatures below 6 K are attainable while maintaining spinning of 6 kHz. Computational fluid dynamics (CFD) was used to optimize the fluid flow, minimize sample temperatures, and also provide a means to measure the sample temperature.…”

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“…(b) Heat exchanger that is used to cool drive, bearing, and VT fluids to 80–100 K. These figures were reproduced with permission from the Journal of Magnetic Resonance. 32,55 …”

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Pulsed Electron Decoupling and Strategies for Time Domain Dynamic Nuclear Polarization with Magic Angle Spinning

Saliba

Sesti

Alaniva

et al. 2018

J. Phys. Chem. Lett.

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Magic angle spinning (MAS) dynamic nuclear polarization (DNP) is widely used to increase nuclear magnetic resonance (NMR) signal intensity. Frequency-chirped microwaves yield superior control of electron spins and are expected to play a central role in the development of DNP MAS experiments. Time domain electron control with MAS has considerable promise to improve DNP performance at higher fields and temperatures. We have recently demonstrated that pulsed electron decoupling using frequency-chirped microwaves improves MAS DNP experiments by partially attenuating detrimental hyperfine interactions. The continued development of pulsed electron decoupling will enable a new suite of MAS DNP experiments that transfer polarization directly to observed spins. Time domain DNP transfers to nuclear spins in conjunction with pulsed electron decoupling is described as a viable avenue toward DNP-enhanced, high-resolution NMR spectroscopy over a range of temperatures from <6 to 320 K.

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Magic angle spinning NMR below 6 K with a computational fluid dynamics analysis of fluid flow and temperature gradients

Cited by 36 publications

References 29 publications

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

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

Electron Decoupling with Chirped Microwave Pulses for Rapid Signal Acquisition and Electron Saturation Recovery

Pulsed Electron Decoupling and Strategies for Time Domain Dynamic Nuclear Polarization with Magic Angle Spinning

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Magic angle spinning NMR below 6 K with a computational fluid dynamics analysis of fluid flow and temperature gradients

Cited by 36 publications

References 29 publications

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

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

Electron Decoupling with Chirped Microwave Pulses for Rapid Signal Acquisition and Electron Saturation Recovery

Pulsed Electron Decoupling and Strategies for Time Domain Dynamic Nuclear Polarization with Magic Angle Spinning

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Magic angle spinning NMR below 6 K with a computational fluid dynamics analysis of fluid flow and temperature gradients