DEVELOPMENT OF HIGH-RESOLUTION SOLID-STATE NMR

高分辨率固态核磁共振的发展

• 批准号: 7355294
• 负责人: JACOB SCHAEFER
• 金额: $ 0.03万
• 依托单位: WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-02-01 至 2007-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7355294
• 关键词: DEVELOPMENT; RESOLUTION; SOLID; STATE; NMR

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.

该子项目是利用 NIH/NCRR 资助的中心拨款提供的资源的众多研究子项目之一。子项目和研究者 (PI) 可能已从另一个 NIH 来源获得主要资金，因此可以在其他 CRISP 条目中得到体现。列出的机构是中心的机构，不一定是研究者的机构。在过去 20 年中，交叉极化的灵敏度和魔角旋转（偶极去偶）的分辨率相结合，使 13C NMR 成为固体聚合物表征的标准工具。局部结构通过实验室和旋转参考系中各种弛豫测量的 13C 化学位移和局部动力学来揭示。在将这些微观参数与聚合物的宏观性能联系起来方面已经取得了一些成功。然而，这种重要的联系受到以下事实的阻碍：传统的 13C NMR 光谱必须主要根据单链进行解释，并间接推断相邻链的影响。然而，准确、直接地表征固体玻璃状聚合物中的链间堆积对于理解聚合物的机械性能至关重要。如今，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。 I-S 自旋对的 REDOR NMR 涉及通过转子同步的 I-自旋 pi 脉冲对横向 S-自旋磁化进行移相。使用第三射频通道消除与丰富质子的耦合。 REDOR 实验的结果直接导致异核 I-S 偶极耦合的强度，从而导致 I-S 核间距离。在玻璃状聚合物的应用中，具有 13C 标记的聚碳酸酯链与具有 2H 标记的链混合。由 13C-2H REDOR NMR 确定的所得距离定义了系统上的局部堆积几何形状，而对于该系统来说，衍射实验是不可能的。聚（对氟苯乙烯）和 13C 标记的聚碳酸酯等非均质聚合物共混物的界面也可以通过 REDOR NMR 定量、准确地表征，如下图所示。全氘化聚合物中的残余质子表现为稀有自旋，全氘化聚碳酸酯中孤立的 1H-13C 对之间的 REDOR 揭示了玻璃状聚碳酸酯中普遍存在的 0.3%（按重量计）水的平均位置。