Analysisof Solvation and Gelation Behavior of MethylcelluloseUsing Atomistic Molecular Dynamics Simulations.

Weadopt atomistic molecular dynamics (MD) simulations to studythe solvation and gelation behavior of homogeneous methylcellulose(MC) and model random oligomers that represent the commercial cellulosicpolymer product METHOCEL A in water and acetone solvents. We demonstratethat the two carbohydrate-specific GROMOS force fields, GROMOS 45A4and 56Acarbo, are capable of reproducing characteristic angle distributionsand the persistence length of MC chains reported in the literature.We then use the GROMOS 56Acarbo force field in both single-chain andmultiple-chain simulations to characterize their solvation behaviorthrough radial distribution functions, hydrogen-bond counts, and contactmap analyses. We find that the un-methylated O6 position on the cellulosering forms the most hydrogen bonds, followed by O2 and O3, implyingthat methylation at the 6 position reduces hydrogen bonding more thandoes methylation at other positions. O6–O6 is the most probableintermolecular hydrogen bond between different MC molecules. Dimethylatedand trimethylated MCs form aggregated structures at low temperaturesand precipitate-like structures at high temperatures in water butdisperse randomly in acetone. This is consistent with experimentalobservations of gelation at elevated temperatures in water. The heterogeneousMETHOCEL A model shows increased aggregation of trimethylated monomerunits at elevated temperatures, suggesting that hydrophobic interactionis the main factor that induces the gelation, rather than hydrogenbonding. [ABSTRACT FROM AUTHOR]