Enhancing the sensitivity of biomolecular MAS NMR by new methods of Dynamic Nuclear Polarization

本研究项目由两部分组成，以魔角旋转（MAS）核磁共振（NMR）波谱为中心主题。MAS使得在固体状态下获得复杂化学体系的高分辨率核磁共振光谱成为可能。由于不需要结晶，也不存在尺寸和复杂性上的主要限制，MAS NMR可以提供其他光谱方法几乎无法获得的系统的高分辨率结构信息，例如无定形材料，淀粉样原纤维，膜蛋白和催化位点。该项目的第一部分重点是开发新的微波脉冲序列，提供非常有效的动态核极化（DNP）。动态核极化是MAS核磁共振光谱的重要组成部分，它极大地提高了其灵敏度。我们的研究小组最近推出了两个新的DNP脉冲序列，其中一个产生了特别高的灵敏度增强因子。有趣的是，我们刚刚开始理解为什么一个DNP脉冲序列比另一个更好。因此，提出了一个研究项目，包括DNP实验和DNP过程的高级数值模拟，如果成功，将确定DNP脉冲序列的基本设计准则。第二部分，提出了利用MAS核磁共振光谱研究非晶碳酸钙（ACC）结构的方法。ACC是一个重要的前体阶段，在高度控制，但知之甚少的骨骼部分的形成由无脊椎生物。ACC含有结构水，与碳酸钙的比例约为1比1，在结晶时释放。尽管付出了巨大的努力，但关于ACC原子水平结构的光谱信息很少，因此没有很好的ACC结构模型。提案的这一部分描述了各种形式的ACC的1H-13C MAS NMR相关谱，这些ACC是由生物聚合物稳定的，可以提供ACC中结构水的化学环境的具体信息。

The research project comprises two parts, with magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy as the central theme. MAS makes it possible to acquire high-resolution NMR spectra of complex chemical systems in the solid state. Because there is no need for crystallization and no principal limitations exist on size and complexity, MAS NMR can provide high-resolution structural information on systems that are scarcely accessed with other spectroscopic methods, such as amorphous materials, amyloid fibrils, membrane proteins, and catalytic sites.The first part of the project focuses on the development of new microwave pulse sequences, which provide very efficient dynamic nuclear polarization (DNP). Dynamic nuclear polarization is an essential companion of MAS NMR spectroscopy as it strongly enhances its sensitivity. Two new DNP pulse sequences were recently introduced by our research group, one of which yielded particularly high sensitivity enhancement factors. Intriguingly, we are just beginning to understand why one DNP pulse sequence is better than the other. Hence, a research project, involving both DNP experiments and advanced numerical simulations of the DNP process, is proposed, which, if successful, will fix the basic design criteria for a DNP pulse sequence.In the second part, the use of MAS NMR spectroscopy to investigate the structure of amorphous calcium carbonate (ACC) is proposed. ACC is an essential precursor phase in the highly controlled, but poorly understood formation of skeletal parts by invertebrate organisms. ACC contains structural water, in an approximately one-on-one ratio with calcium carbonate, which is released upon crystallization. In spite of considerable effort, spectroscopic information on the atomic-level structure of ACC is scarce and, as a consequence, there exists no good structural model of ACC. This part of the proposal describes how 1H-13C MAS NMR correlation spectra of various forms of ACC, which are stabilized against crystallization by biopolymers, may provide specific information on the chemical environments of structural water in ACC.