Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA-02139, USA.
Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA-02139, USA.
Chemistry. 2022 Dec 6;28(68):e202202556. doi: 10.1002/chem.202202556. Epub 2022 Oct 11.
Dynamic nuclear polarization (DNP) is an NMR sensitivity enhancement technique that mediates polarization transfer from unpaired electrons to NMR-active nuclei. Despite its success in elucidating important structural information on biological and inorganic materials, the detailed polarization-transfer pathway from the electrons to the nearby and then the bulk solvent nuclei, and finally to the molecules of interest-remains unclear. In particular, the nuclei in the paramagnetic polarizing agent play significant roles in relaying the enhanced NMR polarizations to more remote nuclei. Despite their importance, the direct NMR observation of these nuclei is challenging because of poor sensitivity. Here, we show that a combined DNP and electron decoupling approach can facilitate direct NMR detection of these nuclei. We achieved an ∼80 % improvement in NMR intensity via electron decoupling at 0.35 T and 80 K on trityl radicals. Moreover, we recorded a DNP enhancement factor of ∼90 and ∼11 % higher NMR intensity using electron decoupling on paramagnetic metal-organic framework, magnesium hexaoxytriphenylene (MgHOTP MOF).
动态核极化 (DNP) 是一种 NMR 灵敏度增强技术，可介导未成对电子向 NMR 活性核的极化转移。尽管它在阐明生物和无机材料的重要结构信息方面取得了成功，但从电子到附近溶剂核，然后再到感兴趣的分子的详细极化转移途径仍不清楚。特别是，顺磁极化剂中的核在将增强的 NMR 极化传递到更远的核方面起着重要作用。尽管它们很重要，但由于灵敏度差，直接进行这些核的 NMR 观察具有挑战性。在这里，我们展示了一种结合 DNP 和电子去耦的方法可以促进这些核的直接 NMR 检测。我们在 0.35 T 和 80 K 下通过电子去耦实现了三苯甲基自由基的 NMR 强度提高约 80%。此外，我们在使用电子去耦的顺磁金属有机骨架（镁六氧三苯并菲（MgHOTP MOF）上）记录到 DNP 增强因子提高了约 90%和 NMR 强度提高了约 11%。
