STRUCTURAL ELUCIDATION OF LIGNOCELLULOSE AND WETLAND SOIL BY SOLID-STATE NMR AND DYNAMIC NUCLEAR POLARIZATION

Solid-state Nuclear Magnetic Resonance (ssNMR) is a powerful analytical technique that has emerged as a versatile tool for high-resolution detection and characterization of biosolids, such as carbohydrates, proteins, nucleic acids, and organic matter, in their native state. By harnessing the principles of NMR spectroscopy, ssNMR provides detailed insights into the atomic-level structure, dynamics, and interactions of these biomolecules, making it an invaluable resource for advancing our understanding of complex biological systems. This work is dedicated to addressing fundamental yet profoundly significant questions in the fields of sustainable bioenergy development and coastal wetland ecosystem preservation by ssNMR. Firstly, we have unraveled the intricate packing of lignin and carbohydrates within plant cell walls, a critical inquiry that underpins our ability to engineer plants for improved biofuel and materials production. This research holds exceptional significance within the field of bio-renewable energy. Leveraging the power of ssNMR, we have achieved atomic-resolution characterization of the polymorphic structure, dynamical behavior, hydration profiles, and physical arrangement of lignin and polysaccharides. The findings uncover that the extent of glycan-aromatic association increases sequentially across grasses, hardwoods, and softwoods; and lignin principally packs with the xylan in a non-flat conformation via electrostatic interactions and partially binds the junction of flat-ribbon xylan and cellulose surface as a secondary site. Another exciting development in our research is the integration of the sensitivity-enhancing Dynamic Nuclear Polarization (DNP) technique. This innovative approach holds immense promise for the investigation of natural abundance samples. We have successfully demonstrated the feasibility of combining traditional ssNMR with DNP methods to probe the structure and dynamics of carbohydrates in natural abundance rice stems. This streamlined approach enables the efficient screening of a diverse array of biomass materials without the need for labeling. Furthermore, the application of ssNMR and DNP has facilitated the rapid acquisition of 2D 13C/1H-13C correlation spectra to detail the molecular fingerprint and spatial organization of biopolymers in unlabeled wetland soil obtained from a brackish island situated along the Gulf of Mexico coastline. Surprisingly, the lignocellulosic core identified in the plants grown on this island was found to be preserved in the surface layer of soil formed in the brackish marshes, but with tighter physical packing between molecules. Extending the depth from the surface to 2 m covers a geological timeline of eleven centuries, where we found sophisticated changes in the molecular structure and composition of organic matter as well as the bulk properties of the wetland soil. These findings offer a promising avenue toward addressing pressing environmental challenges, including coastal wetland loss and the impact of sea-level rise. Additionally, statistical approaches for the analysis of carbohydrate composition and structure using high-resolution ssNMR data have been introduced. We generate simulated spectra (density maps) using data deposited in our developed and maintained Complex Carbohydrates Magnetic Resonance Database (CCMRD, www.ccmrd.org), to demonstrate the chemical shift dispersion and to aid in the fast identification of important fungal and plant polysaccharides in cell walls. By comparing the projected spectra with experimental data, we highlight the challenges of assigning resonances because distinct carbohydrates from different organisms can produce nearly identical signals.