Dynamics on Cellulose Show Two Important Populations from Neutron Scattering and Simulations

Elastic Intensity Scans
Elastic intensity scans of dry and hydrated cellulose. Dashed lines denote inflection points in the curves at 220 and 260 K, the temperatures at which the surface water (nonfreezing) and interfibrillar water (freezing) become mobile in the hydrated cellulose sample, respectively. Inset illustration depicts water populations associated with cellulose. [Adapted from O’Neill, H., et al. “Dynamics of Water Bound to Crystalline Cellulose.” Sci. Rep. 7, 11840 (2017). [DOI:10.1038/s41598-017-12035-w]. Reused under a Creative Commons license (CC BY 4.0, https://creativecommons.org/licenses/by/4.0/). Curve colors were modified, and additional labels and inset added.]
Biomass pretreatment is necessary to make cellulose accessible to hydrolysis for conversion to biofuels. Understanding water’s role in cellulose reactivity will aid discovery of the underlying processes that change biomass morphology and reactivity during different pretreatment regimes for biofuels production. In this study, cellulose-water interactions were examined using neutron scattering supported by molecular dynamics simulation. The data show two distinct populations of water molecules—one tightly “bound” to the surface and the other interfibrillar and translationally mobile. Accurate models of hydration water in the cell wall can address fundamental questions about cellulose-water interactions. The mobility of the interfibrillar water is also important to enzyme and chemical attack and is distinct from the bound and bulk water.

O’Neill, H. M., et al. “Dynamics of Water Bound to Crystalline Cellulose.” Sci. Rep. 7, Article 11840 (2017). [DOI:10.1038/s41598-017-12035-w].

Instruments and Facilities Used: Deuterium labeling, neutron scattering, and molecular dynamics simulation; quasi-elastic neutron scattering (QENS) using BASIS, the Backscattering Spectrometer, at Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS). Structural characterization using small-angle neutron scattering (SANS) CG-3 Bio-SANS instrument at High Flux Isotope Reactor (HFIR) facility of ORNL and X-ray diffraction (XRD) analysis combined with SANS. Wide-Angle X-ray Diffraction (WAXD) using theta-theta goniometer Bruker D5005 instrument; quasi-elastic neutron scattering (QENS) using BASIS, the Backscattering Spectrometer at ORNL SNS; Molecular Dynamics (MD) Simulations (GROMACS software and the CHARMM C36 carbohydrate force field); and TIP4P water model.