(557d) Deriving Coarse-Grained Models for Crystalline Cellulose Based On Force Matching

A fundamental understanding of the intermolecular forces that bind polysaccharide chains together in cellulose is crucial for designing efficient methods to overcome the recalcitrance of lignocellulosic biomass to hydrolysis. Because the characteristic time and length scales for the degradation of cellulose by enzymatic hydrolysis or chemical pretreatment span orders of magnitude, it is important to closely integrate the molecular models used at each scale so that, ultimately, one may switch seamlessly between quantum, atomistic, and coarse-grained descriptions of the system. As a step towards that goal, multiscale coarse-grained models for polysaccharide chains in cellulose microfibers are being developed. In this work, the force matching method is used to derive effective coarse-grained forces from all-atom molecular dynamics trajectories. The force matching method systematically optimizes coarse-grained forces from all-atom simulation trajectories without fitting them to a predetermined analytical function. Several coarse-grained mapping schemes were evaluated and tested against the same all-atom reference system. The properties that were compared include crystalline lattice parameters, radial distribution functions, and root mean square fluctuations and displacements. The success of the coarse-grained molecular dynamics simulation in predicting the properties computed for the all-atom crystalline cellulose reference system was dependent on the choice of coarse-grained mapping scheme. This dependence on mapping scheme has been observed before for glucose solutions (Markutsya, et al., 2012) and it is even more pronounced for this application due to the crystalline structure. To overcome this challenge, a rationale strategy for designing coarse-grained mapping schemes in macromolecular crystals is developed and presented. Using this approach, successful agreement is observed between the coarse-grained and all-atom molecular dynamics simulations for crystalline cellulose.

S. Markutsya, Y. Kholod, A. Devarajan, T. L. Windus, M. S. Gordon, and M. H. Lamm, Theor. Chem. Accounts 131, 1162 (2012).

This research is sponsored by the U.S Department of Energy (USDOE) Scientific Discovery through Advanced Computing (SciDAC) program through USDOE's Office of Advanced Scientific Computing Research (ASCR) and Biological and Environmental Research (BER), and performed at the Ames Laboratory, FWP AL-08-330-039.