DEVELOPMENT OF HIGH-RESOLUTION SOLID-STATE NMR

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。在过去的20年里，交叉极化的灵敏度和魔角旋转（偶极去耦）的分辨率相结合，使13 C NMR成为表征固体聚合物的标准工具。局部结构揭示了13 C化学位移和本地动态从各种弛豫测量在实验室和旋转参考系。在将这些微观参数与聚合物的宏观性质联系起来方面已经取得了一些成功。然而，这一重要的连接是阻碍了传统的13 C NMR谱必须解释主要是在一个单一的链与间接推断的相邻链的影响。然而，在固体，玻璃状聚合物的链间包装的准确，直接的表征是至关重要的聚合物的机械性能的理解。今天，堆积链之间的距离可以通过为蛋白质和蛋白质复合物开发的相同类型的旋转回波双共振（REDOR）NMR实验来确定。用于I-S自旋对的REDOR NMR涉及通过转子同步的I-自旋π脉冲使横向S-自旋磁化失相。使用第三射频通道去除与大量质子的耦合。REDOR实验的结果直接导致了异源I-S偶极耦合的强度，从而导致了I-S核间距。在玻璃状聚合物的应用中，具有13 C标记的聚碳酸酯链已与具有2 H标记的链混合。由13 C-2 H REDOR NMR确定的所得距离定义了衍射实验不可能的系统上的局部堆积几何形状。如下图所示，多相聚合物（如聚（对氟苯乙烯）和13 C标记的聚碳酸酯）的共混物的界面也可以通过REDOR NMR定量准确地表征。全氘代聚合物中的剩余质子表现为罕见的自旋，并且全氘代聚碳酸酯中孤立的1H-13 C对之间的REDOR揭示了玻璃态聚碳酸酯中普遍存在的0.3%（按重量计）水的平均位置。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the last 20 years, the combination of cross polarization for sensitivity and magic-angle spinning (with dipolar decoupling) for resolution has made 13C NMR a standard tool for the characterization of solid polymers. Local structure is revealed by 13C chemical shifts and local dynamics from a variety of relaxation measurements in both the laboratory and rotating reference frames. Some success has been achieved in relating these microscopic parameters to macroscopic properties of the polymers. Nevertheless, this important connection is hampered by the fact that conventional 13C NMR spectra must be interpreted primarily in terms of a single chain with the effects of neighboring chains inferred indirectly. However, an accurate, direct characterization of the interchain packing in solid, glassy polymers is crucial to the understanding of the mechanical properties of the polymers. Today, the distances between packed chains can be determined by the same types of rotational-echo double resonance (REDOR) NMR experiments developed for proteins and protein complexes. REDOR NMR for an I-S spin pair involves the dephasing of transverse S-spin magnetization by rotor-synchronized I-spin pi pulses. Coupling to abundant protons is removed using a third radio frequency channel. The results of REDOR experiments lead directly to the strength of the heteronuclear I-S dipolar coupling and hence I-S internuclear distances. In applications on glassy polymers, polycarbonate chains with 13C labels have been mixed with chains having 2H labels. The resulting distances determined by 13C-2H REDOR NMR define local packing geometry on a system for which diffraction experiments are impossible. Interfaces of blends of heterogeneous polymers like poly(p-fluorostyrene) and 13C-labeled polycarbonate can also be characterized quantitatively and accurately by REDOR NMR as shown in the figure below. The residual protons in perdeuterated polymers behave as a rare spin, and REDOR between isolated 1H-13C pairs in perdeuterated poly-carbonate reveals the average location of the ubiquitous 0.3% (by weight) water in glassy polycarbonate.