HIGH FREQUENCY DYNAMIC NUCLEAR POLARIZATION IN NUCLEAR ROTATING FRAME

利用连续波DNP技术，我们最近获得了大信号 魔角旋转(MAS)固体核磁共振(SS核磁共振)的改进 15N-丙氨酸标记T4溶菌酶和“C-甘氨酸”在冷冻状态下的光谱 含有自由基的40：60水/甘油水溶液 4-氨基TEMPO作为电子极化的来源。尽管这些 CW-DNP技术提供了很大的增强(E-10)，他们需要 长偏振转移时间(自旋晶格数量级 放松时间，TJ。这促使我们考虑PULSE DNP的偏振转移技术，可能更多 比CW DNP方法更有效。我们已经完成了一次核爆炸 旋转坐标系DNP(NRF-DNP)实验，其中质子核磁共振信号 在高场下获得了单位时间ELT=90的增强 (BO=5 T，VP，=139.5格利兹)在40：60中使用15 mM三叔丁基自由基 水/甘油冷冻溶液在11K下的电子-核 偏振转移是在原子核的旋转框架中进行的 微波/射频照射时间为100ms。大多数人 增强作用归因于热混合机制。增长 的信号增强是由旋转框架核控制的 自旋-晶格弛豫时间(TP)，通常为10-100毫秒 对于快速偏振传输，实验可以循环使用 在大约11T，P的速率下，并且不受更长的 实验室框架核自旋-晶格弛豫时间(T，，，)，通常为 在低温下只需几分钟。NRF-DNP实验不需要 高微波功率；信号得到显著增强 采用低功率(20 MW)耿氏二极管微波源，无微波炉 谐振式结构。最后，对称的三叔丁基是一种理想的 用于生物体系脉冲DNP研究的偏振剂 它是水溶性的，在一场比赛中具有10G的窄EPR线宽 5个特斯拉。

Using CW DNP techniques we have recently obtained large signal enhancements in magic-angle spinning (MAS) solid-state NMR (SSNMR) spectra of 15N-alanine labeled T4 lysozyme and "C-Glycine in frozen aqueous solutions of 40:60 water/glycerol with the free radical 4-amino TEMPO as the source of electron polarization. Although these CW-DNP techniques provide large enhancements (E-10), they requires long polarization transfer times (on the order of the spin-lattice relaxation time, TJ. This has motivated us to consider pulsed polarization transfer techniques for DNP, which might be more efficient than the CW DNP methods. We have performed a Nuclear Rotating Frame DNP (NRF-DNP) experiment in which a proton NMR signal enhancement per unit time of elt = 90 has been obtained at high field (BO = 5 T, Vp, = 139.5 GlIz) using 15 mM trityl radical in a 40:60 water/glycerol frozen solution at 11 K. The electron-nuclear polarization transfer is performed in the nuclear rotating frame with microwave/RF irradiation times of 100 ms. A majority of the enhancement is attributed to the thermal mixing mechanism. The growth of the signal enhancement is governed by the rotating frame nuclear spin-lattice relaxation time (TP), typically 10- 100 ms at I I K. Due to the rapid polarization transfer' * the experiment can be recycled at a rate of approximately 11T,P and is not limited by the much longer lab frame nuclear spin-lattice relaxation time (T,,,), typically many minutes at low temperatures. The NRF-DNP experiment does not require high microwave power; significant signal enhancements were obtained with a low power (20 mW) Gunn diode microwave source and no microwave resonant structure. Finally, the symmetric trityl radical is an ideal polarization agent for pulsed DNP studies of biological systems since it is water-soluble and has a narrow EPR line width of 10 G at a field of 5 Tesla.