Abstract
Establishing structure-property relationships is always an important goal of materials research, which requires the molecular-level understanding provided by characterization tools. Popular techniques such as Raman and infrared spectroscopy are widely used, but their measurements are not quantitative. Solid-state NMR (ssNMR) has the advantages of being element selective, inherently quantitative, and equally applicable to crystalline and amorphous materials. It is also a powerful tool in the structural analysis of local symmetry, bonding patterns, and functional groups. Due to these characteristics, solid-state NMR is finding increasing use in solid-state chemistry and materials science.Nevertheless, solid-state NMR typically suffers from poor spectral resolution compared to solution NMR and low sensitivity relative to vibrational spectroscopy. Yet these challenges have been addressed in recent days with advanced NMR hardware and techniques. Materials made from isotope-enriched precursors generally provide better resolution, for example, 90-fold enrichment over the natural 13C abundance of 1.1% provides a 90-fold signal enhancement. Corresponding two-dimensional NMR based on strong dipolar couplings between enriched isotopes can be measured to determine bond connections and probe structure dynamics. In addition, reliable peak deconvolution based on spectral editing techniques assists in peak assignments and building meaningful models of complex organic materials.
My dissertation research is mainly focused on component quantification and compositional analysis of complex organic materials to understand structure-property relationships by advanced ssNMR, including but not limited to the following three categories: novel synthetic functional materials, pharmaceutical solids, and materials derived from renewable sources. Specific results include the following:
1. Novel one-dimensional sp3-hybridized nanothreads derived from modest pressure compression of 13C4-furan.
2. Functional organic linkers in canonical metal-organic frameworks with accessible benzylic amines and azides handles from post-synthetic modification.
3. Ortho-alkoxy-benzamide directed formation of a single-crystalline hydrogen-bonded crosslinked organic frameworks for boron trifluoride uptake
4. Peak assignment and quantification in hydroxyl methylcellulose acetate succinate, a cellulose-based pharmaceutical excipient.
5. Vinyl and methyl ester groups in the insoluble fluorinated polymer-drug patiromer identified and quantified by solid-state NMR