Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
Bruker BioSpin Corporation, Billerica, MA 01821, United States.
J Magn Reson. 2021 Aug;329:107012. doi: 10.1016/j.jmr.2021.107012. Epub 2021 Jun 7.
We present the results of an experimental pulsed DNP study at 1.2 T (33.5 GHz/51 MHz electron and H Larmor frequencies, respectively). The results include a comparison of constant-amplitude NOVEL (CA-NOVEL), ramped-amplitude NOVEL (RA-NOVEL) and the frequency-swept integrated solid effect (FS-ISE) experiments all of which were performed at the NOVEL matching condition, ω=ω, where ω is the electron Rabi frequency andω the proton Larmor frequency. To the best of our knowledge, this is the first pulsed DNP study carried out at field higher than X-band (0.35 T) using the NOVEL condition. A combination of high microwave power (∼150 W) and a microwave cavity with a high Q (∼500) allowed us to satisfy the NOVEL matching condition. We also observed stretched solid effect (SE) contributions in the Zeeman field profiles when chirped pulses are applied. Furthermore, the high quality factor of the cavity limits the concentration of the radical to ∼5 mM and generates a hysteresis in the FS-ISE experiments. Nevertheless, we observe very high DNP enhancements that are comparable to the results at X-band. These promising outcomes suggest the importance of further studies at even higher fields that delineate the instrumentation and methods required for time domain DNP.
我们展示了在 1.2 T（33.5 GHz/51 MHz 电子和 H 拉莫尔频率，分别）下进行的实验脉冲 DNP 研究结果。结果包括对恒定幅度 NOVEL（CA-NOVEL）、斜坡幅度 NOVEL（RA-NOVEL）和频率扫描集成固态效应（FS-ISE）实验的比较，所有这些实验都是在 NOVEL 匹配条件下进行的，ω=ω，其中ω是电子拉莫尔频率，ω是质子拉莫尔频率。据我们所知，这是首次在 NOVEL 条件下使用高于 X 波段（0.35 T）的场进行脉冲 DNP 研究。高微波功率（约 150 W）和 Q 值较高（约 500）的微波腔的结合，使我们能够满足 NOVEL 匹配条件。当应用啁啾脉冲时，我们还观察到在磁场分布中出现拉伸固态效应（SE）贡献。此外，腔的高品质因数将自由基的浓度限制在约 5 mM，并在 FS-ISE 实验中产生滞后现象。尽管如此，我们观察到非常高的 DNP 增强，与 X 波段的结果相当。这些有希望的结果表明，在更高的场强下进行进一步研究的重要性，以描绘出用于时域 DNP 的仪器和方法。
