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

我们提出了一个分析偏振传输的模型， 热混合动态核极化（DNP）机制 更高的磁场强度， 在非均匀加宽的EPR谱线内的交叉弛豫， 应用该模型模拟DNP和ELDOR实验， 4-氨基克里思/水/甘油体系。 这些研究表明， 40 mM 4-氨基克里思EPR线处于中间交叉弛豫 政权 因此，三浴热混合模型，以前用于 描述了低场实验，没有充分解释 系统在高场下的极化动力学。 给他些 基本参数，如EPR线型和自旋晶格 弛豫时间，这里开发的模型可以用来预测 DNP在更高磁场强度下的效率，其中 热混合将更严重地衰减， 光谱色散和因此较慢的交叉弛豫速率， 除了4-氨基克里思基团之外的极化剂。 使用此 通过这种方法，有可能开发出最佳的顺磁系统， 用于在适合于以下的实验条件下进行DNP： 生物样品的固态核磁共振研究。

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.