(589b) Breaking Lignin: First-Principles Steered Dynamics for Studying Lignin Depolymerization

Lignin is a highly heterogeneous biopolymer comprising 20-30% of all biomass by weight. We present here the results of a first-principles steered molecular dynamics approach to studying the depolymerization of representative lignin repeats under force.  Our constant force molecular dynamics runs are both representatitive of experimental mechanochemical degradation (e.g. via ball milling) as well as a useful screening tool to identify the dynamics behind depolymerization during pyrolysis or other high temperature, high energy conditions.  In our simulations, we pull various points of dimeric, trimeric, and hexameric repeats of coniferyl alcohols (a representative monolignol) and examine how and when select linkages break apart.  We then follow the dynamics that occurs after this initial break to see if there are additional bond-breaking events and fragmentation.  Finally, we analyze whether this degradation occurs via a homolytic or heterolytic mechanism and hypothesize that heterolytic bond-breaking events could be advantageous to promote in order to ensure that recombination does not occur. Overall, our screening approach, which is accelerated through the use of stream-processors (i.e. graphical processing units), can pave the way for identifying which reaction paths are most critical to catalyze in order to selectively depolymerize lignin into value-added products.