Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
J Magn Reson. 2012 Oct;223:170-9. doi: 10.1016/j.jmr.2012.07.008. Epub 2012 Jul 20.
We described a versatile spectrometer designed for the study of dynamic nuclear polarization (DNP) at low temperatures and high fields. The instrument functions both as an NMR spectrometer operating at 212 MHz ((1)H frequency) with DNP capabilities, and as a pulsed-EPR operating at 140 GHz. A coiled TE(011) resonator acts as both an NMR coil and microwave resonator, and a double balanced ((1)H, (13)C) radio frequency circuit greatly stabilizes the NMR performance. A new 140 GHz microwave bridge has also been developed, which utilizes a four-phase network and ELDOR channel at 8.75 GHz, that is then multiplied and mixed to obtain 140 GHz microwave pulses with an output power of 120 mW. Nutation frequencies obtained are as follows: 6 MHz on S=1/2 electron spins, 100 kHz on (1)H, and 50 kHz on (13)C. We demonstrate basic EPR, ELDOR, ENDOR, and DNP experiments here. Our solid effect DNP results demonstrate an enhancement of 144 and sensitivity gain of 310 using OX063 trityl at 80 K and an enhancement of 157 and maximum sensitivity gain of 234 using Gd-DOTA at 20 K, which is significantly better performance than previously reported at high fields (≥3 T).
我们描述了一种多功能光谱仪，专为低温和高场下的动态核极化 (DNP) 研究而设计。该仪器既可以作为具有 DNP 功能的工作在 212 MHz（(1)H 频率）的 NMR 光谱仪，也可以作为工作在 140 GHz 的脉冲 EPR 光谱仪。一个螺旋 TE(011) 谐振器同时充当 NMR 线圈和微波谐振器，双平衡 ((1)H, (13)C) 射频电路极大地稳定了 NMR 性能。还开发了一种新的 140 GHz 微波桥，它利用四相网络和 8.75 GHz 的 ELDOR 通道，然后进行倍频和混频，以获得输出功率为 120 mW 的 140 GHz 微波脉冲。得到的旋进频率如下：S=1/2 电子自旋为 6 MHz，(1)H 为 100 kHz，(13)C 为 50 kHz。我们在此演示了基本的 EPR、ELDOR、ENDOR 和 DNP 实验。我们的固态效应 DNP 结果表明，在 80 K 下使用 OX063 三苯甲基时，增强倍数为 144，灵敏度增益为 310，在 20 K 下使用 Gd-DOTA 时，增强倍数为 157，最大灵敏度增益为 234，这比以前在高场（≥3 T）下报道的性能要好得多。
