The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel.
Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853-1301, USA.
Solid State Nucl Magn Reson. 2018 Feb;89:35-44. doi: 10.1016/j.ssnmr.2017.11.001. Epub 2017 Nov 21.
We report on a new approach to the analysis of dynamic NMR lineshapes from polycrystalline (i.e., macroscopically disordered) samples in the presence of Magic Angle Spinning (MAS). This is an application of the Stochastic Liouville Equation developed by Freed and co-workers for treating restricted (i.e., microscopically ordered) motions. The H nucleus in an internally-mobile C-CD moiety serves as a prototype probe. The acronym is H/MOMD/MAS, where MOMD stands for "microscopic-order-macroscopic-disorder." The key elements describing internal motions - their type, the local spatial restrictions, and related features of local geometry - are treated in MOMD generally, within their rigorous three-dimensional tensorial requirements. Based on this representation a single physically well-defined model of local motion has the capability of reproducing experimental spectra. There exist other methods for analyzing dynamic H/MAS spectra which advocate simple motional modes. Yet, to reproduce satisfactorily the experimental lineshapes, one has either to use unusual parameter values, or combine several simple motional modes. The multi-simple-mode reasoning assumes independence of the constituent modes, features ambiguity as different simple modes may be used, renders inter-system comparison difficult as the overall models differ, and makes possible model-improvement only by adding yet another simple mode, i.e., changing the overall model. H/MOMD/MAS is free of such limitations and inherently provides a clear physical interpretation. These features are illustrated. The advantage of H/MOMD/MAS in dealing with sensitive but hardly investigated slow-motional lineshapes is demonstrated by applying it to actual experimental data. The results differ from those obtained previously with a two-site exchange scheme that yielded unusual parameters.
我们报告了一种新的方法，用于分析存在魔角旋转（MAS）的多晶（即宏观无序）样品的动态 NMR 线宽。这是由 Freed 及其同事为处理受限（即微观有序）运动而开发的随机刘维尔方程的应用。内部移动的 C-CD 部分中的 H 核用作原型探针。缩写是 H/MOMD/MAS，其中 MOMD 代表“微观有序-宏观无序”。描述内部运动的关键要素 - 它们的类型、局部空间限制以及局部几何的相关特征 - 在 MOMD 中通常按照其严格的三维张量要求进行处理。基于这种表示，单个物理上定义良好的局部运动模型具有重现实验光谱的能力。存在其他用于分析动态 H/MAS 光谱的方法，这些方法提倡简单的运动模式。然而，为了令人满意地重现实验线宽，要么必须使用不寻常的参数值，要么必须组合几种简单的运动模式。多简单模式推理假设组成模式的独立性，特征模糊性，因为可以使用不同的简单模式，使得不同系统之间的比较变得困难，因为总体模型不同，并且只能通过添加另一个简单模式来改进模型，即改变总体模型。H/MOMD/MAS 没有这些限制，并且固有地提供了清晰的物理解释。这些功能进行了说明。通过将其应用于实际实验数据，证明了 H/MOMD/MAS 在处理敏感但几乎未被研究的缓慢运动线宽方面的优势。结果与以前使用产生不寻常参数的两个站点交换方案获得的结果不同。
