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）固态NMR（SSNMR）的增强 ~（15）N-丙氨酸标记T_4溶菌酶和~（15）N-甘氨酸在冷冻条件下光谱 40：60水/甘油与自由基的水溶液 4-氨基克里思作为电子极化源。 虽然这些 CW-DNP技术提供了大幅增强（E-10），它们需要 长的极化转移时间（在自旋晶格的数量级上 弛豫时间，TJ。 这促使我们考虑脉冲 DNP的偏振转移技术，这可能是更多 比CW DNP方法更有效。 我们进行了核 旋转框架DNP（NRF-DNP）实验，其中质子NMR信号 在高场强下，单位时间内的增强系数ELT = 90 (BO= 5 T，Vp，= 139.5 GlIz），使用15 mM三苯甲基自由基，在40：60的 水/甘油冷冻溶液在11 K。电子核 在核旋转框架中执行偏振转移， 微波/RF辐射时间为100 ms。 增强归因于热混合机制。 生长 的信号增强是由旋转框架核 自旋-晶格弛豫时间（TP），在11 K下通常为10- 100 ms。由于 到快速偏振转移' * 实验可以重复使用 以大约11 T，P的速率，并且不受更长时间的限制。 实验室框架核自旋-晶格弛豫时间（T，），通常许多 在低温下几分钟。 NRF-DNP实验不需要 高微波功率;获得显著的信号增强 具有低功率（20 mW）的古恩二极管微波源和无微波 共振结构 最后，对称的三苯甲基自由基是理想的 极化剂的脉冲DNP生物系统的研究，因为 它是水溶性的，并且在一个电场处具有10 G的窄EPR线宽 5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.