DEVELOPMENT OF HIGH-RESOLUTION SOLID-STATE NMR

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。在过去的20年里，交叉极化用于灵敏度和魔角旋转(带有偶极去耦合)用于分辨的组合使13C核磁共振成为表征固体聚合物的标准工具。在实验室和旋转参考系中的各种弛豫测量中，通过13C化学位移和局部动力学揭示了局域结构。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，这一重要的联系受到以下事实的阻碍，即传统的13C核磁共振谱必须主要根据单链来解释，并间接推断相邻链的影响。然而，准确、直接地表征固体玻璃聚合物中的链间堆积对于了解聚合物的机械性能是至关重要的。今天，填充链之间的距离可以通过为蛋白质和蛋白质复合体开发的相同类型的旋转回波双共振(REDOR)核磁共振实验来确定。I-S自旋对的Redor核磁共振涉及到转子同步的i-自旋pi脉冲对横向S自旋磁化的退相作用。使用第三个射频通道去除与丰富质子的耦合。REDOR实验的结果直接导致了异核I-S偶极耦合的强度，从而导致了I-S的核间距离。在玻璃聚合物上的应用中，具有13C标记的聚碳酸酯链与具有2H标记的链混合。由~(13)C-~2H红外线核磁共振确定的结果距离定义了一个不可能进行衍射实验的系统上的局部堆积几何。多相聚合物如聚对氟苯乙烯和~(13)C标记聚碳酸酯的共混物的界面也可以用红外线核磁共振定量和准确地表征，如下图所示。过氢聚合物中的剩余质子表现为罕见的自旋，而过氢聚碳酸酯中孤立的1H-13C对之间的红色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.