385767 Restraint-Free Coarse-Grain Modeling of a Crystalline Cellulose Fibril Based on Force Matching

Thursday, November 20, 2014: 3:15 PM
212 (Hilton Atlanta)
Sergiy Markutsya, Department of Chemical and Biological Engineering and Ames Laboratory, Iowa State University, Ames, IA, Ajitha Devarajan, Ames Laboratory, Iowa State University, Ames, IA, Mark S. Gordon, Chemistry, Iowa State University, Ames, IA, Theresa L. Windus, Department of Chemistry, Iowa State University, Ames, IA and Monica H. Lamm, Department of Chemical and Biological Engineering, Iowa State University, Ames, IA

As a major component of ligno-cellulosic biomass, crystalline cellulose fibrils are resistant to hydrolysis (biomass recalcitrance) and this is a bottle neck for any process that hopes to decompose cellulosic feedstocks into glucose that can later be converted to bio-fuels. To design efficient processes to degrade the biomass, it is important to understand the molecular forces that bind the cellulosic units. Coarse-grained simulations are useful to explore the residue scale motions in large molecules for long periods of time. The multi-scale coarse-graining (MS-CG) method based on force matching is used to derive effective coarse-grained forces from all-atom molecular dynamics trajectories to model a crystalline cellulose fibril. Unlike for many coarse-graining methods, the force matching method systematically optimizes coarse-grained forces from all-atom simulation trajectories without fitting them to a predetermined analytical function. Two restraint-free coarse-grained mapping schemes with two and eight unique coarse-grain bead types are evaluated and tested against the same all-atom reference system. For the performance analysis of coarse-grained models such properties as crystalline lattice parameters, radial distribution functions, and root mean square fluctuations and displacements are compared. The choice of coarse-grained mapping scheme significantly influences the performance of the coarse-grained molecular dynamics simulation in predicting the properties computed for the reference all-atom crystalline cellulose. A rationale strategy for designing two-type and eight-type coarse-grained mapping schemes in a crystalline cellulose fibril is developed and presented.  Using this approach, both CG mapping schemes predicted the sheet structure of a cellulose fibril well, while only eight-type CG model is capable to accurately represent the intersheet ordering and therefore a complete crystalline structure for a crystalline cellulose fibril.

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