HIGH FIELD DNP & ELECTRON CROSS RELAXATION IN INHOMOGENEOUSLY BROADENED EPR LINE

我们提出了一个分析偏振光传输的模型 热混合动态核极化(DNP)机制 解释电子-电子的高磁场强度 在非均匀加宽的EPR线内的交叉弛豫 应用该模型对DNP和Eldor实验进行了模拟 4-氨基TEMPO/水/甘油体系。这些研究表明， 40 mm 4-氨基节拍EPR线处于中等交叉松弛状态 政权。因此，以前使用的三浴热混合模型 描述低场实验，没有充分解释 高场下系统的偏振动力学。给出了一些 基本参数，如EPR线条形状和自旋晶格 松弛时间，本文建立的模型可以用来预测 DNP在更高磁场强度下的效率，其中 热混合将由于更大的 光谱色散，因此交叉弛豫速率较慢，并且随着 除4-氨基TEMPO自由基外的极化剂。使用这个 通过这种方法，有可能开发出最佳的顺磁系统 用于在适合以下条件的实验条件下执行DNP 生物样品的固体核磁共振研究。

We have presented a model for analyzing polarization transfer via the thermal mixing dynamic nuclear polarization (DNP) mechanism at high magnetic field strengths that accounts for electron-electron cross-relaxation within an inhomogeneously broadened EPR line and have applied this model to simulate DNP and ELDOR experiments in the 4-amino TEMPO/water/glycerol system. These studies indicate that the 40 mM 4-amino TEMPO EPR line is in the intermediate cross-relaxation regime. Thus, the three-bath thermal mixing model, used previously to describe low field experiments, does not adequately explain the.polarization dynamics of the system at high fields. Given some basic parameters, such as the EPR line shape and spinlattice relaxation times, the model developed here can be used to predict the efficiency of DNP at even higher magnetic field strengths, where thermal mixing will be more severely attenuated due to the greater spectral dispersion and hence slower cross-relax ation rate , and with polarization agents other than the 4-amino TEMPO radical. Using this approach, it may be possible to develop optimal paramagnetic systems for performing DNP under experimental conditions suited for solid-state NMR studies of biological samples.