|French, Alfred - Al|
Submitted to: Journal of the American Chemical Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2009
Publication Date: 9/29/2009
Citation: Shen, T., Langan, P., French, A.D., Johnson, G.P., Gnanakaran, S. 2009. Conformational Flexibility of Soluble Cellulose Oligomers: Chain Length and Temperature Dependence. Journal of the American Chemical Society. 131(41):14786-14794 Interpretive Summary: Cellulose molecules are the primary constituents of plant cell walls, and their properties are of interest to scientists of many disciplines. For example, biologists trying to understand how the plants make cell walls, cotton textile scientists and cellulose-to-ethanol researchers all have a stake in the properties of cellulose and the action mechanisms of enzymes that create or break down cellulose molecules. This paper investigates the properties of fragments of cellulose molecules that could interfere with enzymatic processes, and also should suggest properties of cellulose itself in an environment with lots of water. The variation in properties was also investigated at different temperatures, all with a computer modeling method that had not been previously applied to cellulose-like molecules. The information is mostly of interest to those studying enzymatic breakdown of cellulose, cell wall structure, and to those carrying out molecular modeling studies of other carbohydrate materials.
Technical Abstract: Structures, dynamics, and stabilities of different sized cellulosic oligomers need to be considered when designing enzymatic cocktails for the conversion of biomass to biofuels since they can be both productive substrates and inhibitors of the overall process. In the present work, the conformational variability, hydrogen bonding and mechanical properties of short, soluble cellulose chains are investigated as a function of chain length. Cellulose oligomers consisting of 2, 4, and 6 '-D glucose units are examined in explicit solvent using the replica exchange molecular dynamics (REMD) which provides a rigorous evaluation of the relative stabilities of different conformations and their temperature dependence. This application of REMD to oligosaccharides in solution also allows evaluation of the quality of the force-field and its suitability for sampling carbohydrates efficiently. Simulation results are analyzed in synergy with polymer theory and compared to known measurements of oligomers and crystals. As chain length is increased, the conformations of the oligomers become more rigid and likely to form intra-chain hydrogen bonds, like those found in crystals. Several other conformations and hydrogen bonding patterns distinguish these short cellulose chains from those in cellulose crystals. These studies have also addressed the key role played by solvent on shifting the conformational preferences of the oligosaccharides with respect to vacuum and crystals. Correlation between pyranose ring flipping and the conformation of the 1,4-glycosidic bond was observed.