Cross Polarization for Dissolution Dynamic Nuclear Polarization Experiments at Readily Accessible Temperatures 1.2 < T < 4.2 K
Cross polarization can provide significant enhancements with respect to direct polarization of low-γ nuclei such as 13C. Substantial gains in sample throughput (shorter polarization times) can be achieved by exploiting shorter build-up times τDNP(1H) < τDNP(13C). To polarize protons rather than low-γ nuclei, nitroxide radicals with broad ESR resonances such as TEMPO are more appropriate than Trityl and similar carbon-based radicals that have narrow lines. With TEMPO as polarizing agent, the main Dynamic Nuclear Polarization (DNP) mechanism is thermal mixing (TM). Cross polarization makes it possible to attain higher polarization levels at 2.2 K than one can obtain with direct DNP of low-γ nuclei with TEMPO at 1.2 K, thus avoiding complex cryogenic technology.
KeywordsCross Polarization Dynamic Nuclear Polarization Dynamic Nuclear Polarization Enhancement Dynamic Nuclear Polarization Experiment Trityl Radical
The authors thank Dr. Jacques van der Klink for theoretical insights and Martial Rey for valuable technical assistance. This work was supported by the Swiss National Science Foundation, the Ecole Polytechnique Fédérale de Lausanne (EPFL), the Swiss Commission for Technology and Innovation (CTI), and the French CNRS.
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