Comprehensive explanation of Cross Effect DNP under MAS is provided using the Landau-Zener model. Recommendations and guiding principles for the development of a polarizing agent are also provided.
A dual EPR-DNP probe design for high magnetic field is presented. This probe works in the temperature range of 8 - 100 kelvin.
Three strategies to understand and engineer a DNP experiment are presented.
1) Smart non-cw microwave irradiation 2) Electron spin dynamics detection using EPR 3) Quantum mechanical modelling
A recent discovery of Overhauser Effect (OE) like DNP in insulating systems under cryogenic conditions using 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).
The efficiency of CE-DNP depends on the strength of the electron-electron coupling in biradical polarizing agents. Hence, the focus lately has been on designing biradicals with a large net exchange (J) and dipolar (D) coupling. In this study, we reveal that the crucial factor for CE-DNP is not the large sum, J+D, but rather the relative magnitude ofJ and D, expressed as the ratio J/D.
Trityl-OX063 is a narrow-line, water-soluble, and biocompatible polarizing agent, widely used for dynamic nuclear polarization (DNP) amplified NMR of 13C, but not of the abundant 1H nuclear spin, for which the ineffective solid effect (SE) is expected to be operational. Surprisingly, we observed a crossover from SE to thermal mixing (TM) DNP of 1H with increasing Trityl-OX063 concentration at 7 T.
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.
A new design principle for a mixed broad (TEMPO) and narrow (Trityl) line radical to boost the dynamic nuclear polarization efficiency is electron spin density matching, suggesting a polarizing agent of one Trityl tethered to at least two TEMPO moieties.
Nuances of cross effect dynamic nuclear polarization is explained using effective Hamiltonian formalism.
Role of T1e on nuclear depolarization under MAS was varified experimentally.
The discovery of a truncated cross-effect in DNP NMR that has the features of an Overhauser-effect DNP is reported.
REversal of PRE by electron Spin SaturatION (REPRESSION) as a result of shortening of electron Tm of any paramagnetic system is discovered.
