Insights into Crystalline and Material Solids from Ultrafast Magic Angle Spinning NMR Spectroscopy

Nuclear Magnetic Resonance;Magic Angle Spinning;Chemistry;Science;Chemistry

Damron, JoshuaMatzger, Adam J ;

University of Michigan

关键词: Nuclear Magnetic Resonance;    Magic Angle Spinning;    Chemistry;    Science;    Chemistry;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/144002/jtda_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

While tremendous progress has been made in the development of tools used to probe the molecular world, a number of shortcoming persist in many of the commonly used techniques highlighting the importance for the development of new approaches for molecular inquiry. For example, X-ray diffraction, which is considered to be the gold standard for probing molecular structure, is limited in its ability to achieve atomic resolution for non-crystalline or heterogeneous systems including intrinsically disordered proteins, amorphous polymers or other multiphase systems. In addition, only limited dynamic information can be obtained by X-ray diffraction. Solution-state Nuclear Magnetic Resonance (NMR) is a complementary technique which can address a number of these issues including the ability to probe dynamics and detect disordered systems with high resolution. However, this requires good solubility of the sample and is limited by molecular size before spectral line-widths become too broad to be detected for slow-tumbling macromolecules. Magic Angle Spinning (MAS) NMR is not bound by the limitation of molecular size, opening up many new avenues for applications including the ability to detect signals from solid or semi-solid systems. In contrast to solution NMR, orientation dependent contributions to the spin state are present in solids which reflect structural characteristics at the atomic and molecular levels. While the increased complexity of solid-state systems provides an opportunity for rich insight, the spectral resolution is limited by the MAS frequency. Until recently, solid-state NMR spectra have rarely achieved the resolution obtained in solution. Simultaneously addressing sensitivity and resolution is a major goal in modern solid-state NMR spectroscopy. Recent innovations in MAS technology combined with refined approaches for pulse sequence design have made a substantial impact to this end. The topic of this dissertation focuses on the application of these approaches to crystalline and material systems. The main thrust of the work describes 1H-based techniques under fast MAS frequencies. Under these spinning speeds, 1H/1H dipolar couplings are suppressed thereby reducing spectral broadening and achieving chemical shift resolution to render ;;solution-like” proton NMR spectra. It is advantageous to detect protons as the large gyromagnetic ratio and near 100% natural-abundancedramatically reduce the experimental time or required sample quantity. New approaches utilizing 1H-detected fast MAS are presented for the interrogation of structural differences in crystalline polymorphs and hydrates with a focus on 1H chemical shift anisotropy tensors. Valuable insights are gleaned from experimentally measured NMR parameters reflective of the distinct structural features complementing X-ray data. In the second part, novel dynamic insights were found using13C-detected slow MAS approaches in Metal-Organic Frameworks (MOFs). The quantification of 13C-1H heteronuclear dipolar couplings is used to probe dynamics in the microporous structure. This was completed for a series of Zr, terephthalate based MOFs (UiO66) with different chemical functionalization on the terephthalate ring. The dynamic evolution of the rings is shown to span several orders of magnitude depending on the nature of the functional group. The dramatic reduction in the required sample quantity and considerable enhancements in spectral resolution and sensitivity by ultrafast-MAS are bound to enable a plethora of investigations on numerous exciting classes of chemical and biological materials without any constraints on the molecular size and nature of the sample. Therefore, we believe that the methods and results reported in this thesis will be useful for a variety of other systems as well.