RSI Research Seminar

Join us every other Monday at noon for lunch and a 30-minute research talk, presented by Resnick Sustainability Institute Graduate Fellows and Caltech researchers funded by the Resnick Sustainability Institute. To see the full schedule of speakers, visit the RSI Research Seminar web page. Seminars currently take place in a hybrid format, both in-person (in the new Resnick Sustainability Center building!) and via Zoom. For more information and to get the Zoom login info, please reach out to ramonae@caltech.edu

Isotopic fingerprints of the mechanisms of lignin destruction in the environment

One of the families of strategies for removing CO2 from the atmosphere and oceans involves sequestering biomass in forms and/or locations where it resists re-oxidation; examples include deposition of plant litter or algae in anoxic waters and sediments, introduction of 'biochar' into soils, and reforestation.  Engineering of these processes are aided by laboratory and field studies of rates of degradation, but involve a complex mix of physical, chemical and biological mechanisms that interact with one another and play out over a range of timescales, making them challenging to predict or monitor.  In this study, we develop a tool for determining the mechanism and reaction progress of organic matter degradation, based on the distinctive effects various processes have on the isotopic structures of the residues — i.e., the atomic positions of natural rare isotope substitutions within individual molecular structures. Here we apply this method to lignin compounds (arguably the most abundant and resistant long-lived component of plant matter), first focusing on vanillin as a model system that captures some of the essential features of lignin chemistry.  We demonstrate that measurements of molecular isotopic structure using Fourier-transform mass spectrometry are able to forensically discriminate among sources of vanillin, and to both identify and measure the progress of different biological, thermal and photolytic destruction processes. This measurement is suitable for application to small, compositionally complex environmental samples, can be paired with known chemical preparation procedures for application to a variety of more complex lignin compounds, and could be adapted to other components of biomass, such as cellulose and lipids.