Electron spin density matching for cross-effect dynamic nuclear polarization

Equbal, Asif; Tagami, Kan; Han, Songi

doi:10.1039/c9cc03499d

Cited by 15 publications

(11 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The operational DNP mechanism directly guides the rational design principle of optimal PAs. To date, PA and DNP experimental design has been focused around optimizing the SE and CE mechanisms, ,,− given the in-depth understanding of the two mechanisms that can be illustrated with coupled two-spin e–n or three-spin e–e–n model systems, respectively. ,, However, the intrinsic problem of SE and CE is that the polarization transfer efficiencies are significantly impaired at high B 0 .…”

mentioning

confidence: 99%

¹H Thermal Mixing Dynamic Nuclear Polarization with BDPA as Polarizing Agents

Equbal

Tabassum

Han

2020

J. Phys. Chem. Lett.

Self Cite

View full text Add to dashboard Cite

Dynamic Nuclear Polarization (DNP) is a sensitivity enhancing technique for Nuclear Magnetic Resonance. A recent discovery of Overhauser Effect (OE) DNP in insulating systems under cryogenic conditions using 1,3-bisdiphenylene-2-phenylallyl (BDPA) as the polarizing agent (PA) has caught attention due to its promising DNP performance at a high magnetic field and under fast magic angle spinning conditions. However, the mechanism of OE in insulating-solids/BDPA is unclear. We present an alternative explanation that the dominant underlying DNP mechanism of BDPA is Thermal Mixing (TM). This is ascertained with the discovery that TM effect is enhanced by multi-electron spin coupling, which is corroborated by an asymmetric electron paramagnetic resonance line shape signifying the coexistence of clustered and isolated BDPA species, and by hyperpolarized electron spin populations giving rise to an electron spin polarization gradient which are characteristic signatures of TM DNP. Finally, quantum mechanical simulations using spatially asymmetrically coupled three electron spins and a nuclear spin demonstrate that triple-flip DNP, with hyperfine fluctuations turned off, can yield the 1 H DNP profile as observed with BDPA. Clarifying the DNP mechanism is critical to develop design principles for optimizing the PA for achieving optimal DNP efficiency.

show abstract

mentioning

confidence: 99%

¹H Thermal Mixing Dynamic Nuclear Polarization with BDPA as Polarizing Agents

Equbal

Tabassum

Han

2020

J. Phys. Chem. Lett.

Self Cite

View full text Add to dashboard Cite

show abstract

“…In contrast, AWG permits enhanced control over the manipulation of e spin polarization, granted sufficient knowledge of the e spin system and necessary μw technology. Taken together, AWG MAS-DNP should be able to (a) help saturate e spins at a much faster rate than MAS alone can do and importantly (b) mitigate the e spin orientation dependence on saturation 43 A simulated EPR spectrum for this mixture is shown in Figure 1D, which clearly shows the separation of spin populations. In Figure 1E, the normalized 1 H-ε DNP procured using AWG irradiation at ν r = 3 kHz is plotted as a function of the sweep width, Δν AWG .…”

Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 94%

“…TEMPO–Trityl Physical Mixture . To test AWG-DNP under MAS by exploiting nonoverlapping spin populations for CE DNP, we chose the physical mixture of 4-Amino TEMPO and Trityl-OX063 in a 2:1 ratio as optimized by Li et al in a recently published study . A simulated EPR spectrum for this mixture is shown in Figure D, which clearly shows the separation of spin populations.…”

mentioning

confidence: 99%

Pulse-Shaped Dynamic Nuclear Polarization under Magic-Angle Spinning

Equbal

Tagami

Han

2019

J. Phys. Chem. Lett.

Self Cite

View full text Add to dashboard Cite

Dynamic nuclear polarization (DNP) under magic-angle spinning (MAS) is transforming the scope of solid-state NMR by enormous signal amplification through transfer of polarization from electron spins to nuclear spins. Contemporary MAS-DNP exclusively relies on monochromatic continuous-wave (CW) irradiation of the electron spin resonance. This limits control on electron spin dynamics, which renders the DNP process inefficient, especially at higher magnetic fields and non cryogenic temperatures. Pulse-shaped microwave irradiation of the electron spins is predicted to overcome these challenges but hitherto has never been implemented under MAS. Here, we debut pulse-shaped microwave irradiation using arbitrary-waveform generation (AWG) which allows controlled recruitment of a greater number of electron spins per unit time, favorable for MAS-DNP. Experiments and quantum mechanical simulations demonstrate that pulse-shaped DNP is superior to CW-DNP for mixed radical system, especially when the electron spin resonance is heterogeneously broadened and/or when its spin−lattice relaxation is fast compared to the MAS rotor period, opening new prospects for MAS-DNP.

show abstract

“…Details on this commercially available package can be found in the original paper by Veshtort et al, 25 in the well maintained online resource (https:// spinevolution.com/), as well as in several recent publications from our own group that made extensive use of this simulation package for DNP studies. 20,22,[26][27][28] All spin polarization values were calculated with respect to thermal Boltzmann polarization of 1 H nuclear spins.…”

Section: Simulation Packagementioning

confidence: 99%