TY - JOUR
T1 - Pulse-Shaped Dynamic Nuclear Polarization under Magic-Angle Spinning
AU - Equbal, Asif
AU - Tagami, Kan
AU - Han, Songi
N1 - Funding Information:
We thank Dr. Yangping Liu (Tianjin Medical University, China) for providing us with the TEMTriPol-1 radical. Part of the AWG-DNP instrument development was supported by the National Institute of Health through Grant No. R21EB022731 awarded to S.H. The Binational Science Foundation through Grant No. 2014149 provided partial support for A.E. K.T. was partially supported by the John H. Tokuyama Memorial Fellowship. We thank David Lewis and Ed Twehouse from Revolution NMR, LLC for collaboration on designing and operating the low-temperature MAS-DNP probe. A.E. also thanks Akiva Feintuch and Shimon Vega for helpful advise on MAS-DNP during a research visit to Weizmann Institute of Science.
Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2019/12/19
Y1 - 2019/12/19
N2 - 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.
AB - 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.
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U2 - 10.1021/acs.jpclett.9b03070
DO - 10.1021/acs.jpclett.9b03070
M3 - Article
C2 - 31790265
AN - SCOPUS:85076243658
SN - 1948-7185
VL - 10
SP - 7781
EP - 7788
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 24
ER -