Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
J Magn Reson. 2012 Aug;221:5-10. doi: 10.1016/j.jmr.2012.05.017. Epub 2012 Jun 6.
We have performed dynamic nuclear polarization (DNP) experiments at liquid helium temperatures using a low-power (<70 mW) solid-state diode microwave source at 200 GHz-the electron paramagnetic resonance frequency of stable radicals at 7 T. We employed a home-built Alderman-Grant probe for the detection of ¹H NMR signal at 300 MHz, as such coils are well suited for higher frequency NMR detection. The Alderman-Grant coil is inductively coupled to the rest of the radiofrequency (rf) circuit, whose design allows probe components to be placed away from the sample area, and also enables easy switching of coils with different diameters and resonance frequencies. We have tested our DNP instrument on a frozen nitroxide model system consisting of 4-Amino TEMPO dissolved in a glycerol:water mixture. The largest nuclear spin polarization observed was 61 ± 2% with a sample containing 20 mM 4-Amino TEMPO dissolved in deuterated glycerol (d-glycerol):D₂O:H₂O (50:40:10), amounting to record polarization measured to date at an easily amenable temperature of 4 K.
我们在液氦温度下使用功率低于 70mW 的 200GHz 固态二极管微波源进行了动态核极化（DNP）实验——在 7T 下稳定自由基的电子顺磁共振频率为 200GHz。我们采用了自制的 Alderman-Grant 探头来检测 300MHz 的 ¹H NMR 信号，因为这种探头非常适合更高频率的 NMR 检测。Alderman-Grant 探头与射频（rf）电路的其余部分感应耦合，其设计允许探头组件放置在远离样品区域的位置，并且还可以轻松切换具有不同直径和共振频率的线圈。我们在由溶解在甘油：水混合物中的 4-氨基 TEMPO 组成的冷冻氮氧化物模型系统上测试了我们的 DNP 仪器。在含有 20mM 4-氨基 TEMPO 的样品中观察到的最大核自旋极化度为 61±2%，该样品溶解在氘化甘油（d-甘油）：D₂O：H₂O（50：40：10）中，这是迄今为止在易于实现的 4K 温度下测量到的记录极化度。
