Collaborative Research: The chemistry of lignin's photochemical transformation in the environment: implications for global carbon cycling

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In this project funded by the Environmental Chemical Sciences program of the Chemistry Division, Drs. Patrick Hatcher of Old Dominion University, Satish Myneni of Princeton University, and Christopher Hadad of The Ohio State University employ a multidisciplinary approach to study lignin, a complex organic polymer deposited in the cell walls of many plants, making them rigid and woody. Lignin is an Earth abundant organic biopolymer that provides the starting point to recycle carbon from plants into the environment. In this project, the researchers explore pathways for the molecular rearrangement of lignin to form the molecules present in soil, water and sediments. A postdoctoral associate, graduate students, and several undergraduates are trained to combine geochemistry, fundamental molecular studies, advanced analytical techniques, and modern computational modeling of complex reaction pathways. This training provides these future scientists with an interdisciplinary experience. Undergraduate and high school engagement, including diversified recruitment, is included.In this research project, lignin is subjected to oxidative degradation by reactive oxygen species (ROS) to partially reorganize and polymerize to form humic substances. These humic substances may effectively sequester lignin-derived carbon in contrast to the theory that lignin is completely oxidized to carbon dioxide and contribute to greenhouse warming. This research subjects both synthesized and natural lignin to oxidative decomposition by ROS in the presence of aqueous iron species, mimicking environmental oxidation. The study employs Fourier transform ion cyclotron resonance mass spectrometry, multidimensional liquids and solids NMR, and synchrotron-based X-ray absorption spectroscopy to discern molecular transformation pathways. The research also provides new information regarding both the pathways and magnitude with which photochemistry and ROS affect the cycling of terrestrial carbon among Earth's large reservoirs of carbon, impacting the chemistry of terrestrial systems and oceans.