Truncated Cross Effect Dynamic Nuclear Polarization: An Overhauser Effect Doppelgänger

作者：A. Equbal, Yuanxin Li, Alisa Leavesley, Shengdian Huang, Suchada Rajca, A. Rajca, Songi Han · 发表于：Journal of Physical Chemistry Letters · 年份：2018 · DOI：10.1021/acs.jpclett.8b00751 · 被引用次数：36 · 研究领域：Chemistry、Medicine

The discovery of a truncated cross-effect in dynamic nuclear polarization (DNP) NMR that has the features of an Overhauser-effect DNP (OE-DNP) is reported here. The apparent OE-DNP, where minimal μw-power achieved optimum enhancement, was observed when doping Trityl-OX063 with a proline nitroxide radical that possesses electron withdrawing, tetracarboxylate substituents (tetracarboxylate-ester-proline or TCP) in vitrified water/glycerol at 6.9 T and at 3.3 to 85 K, in apparent contradiction to expectations. While the observations are fully consistent with OE-DNP, we discover that a truncated cross-effect (tCE) is the underlying mechanism, owing to TCP’s shortened T1e. We take this observation as a guideline, and demonstrate that a crossover from CE to tCE can be replicated by simulating CE of a narrow-line (Trityl-OX063) and a broad-line (TCP) radical pair, with a significantly shortened T1e of the broad-line radical.