(149h) Grazing-Incidence Diffraction Reveals Cellulose Lattice Contraction with Dehydration of Plant Primary Cell Wall

Cellulose, a major structural component of plant cell wall, is an essential feedstock biopolymer in industries such as paper, textiles, and renewable energy. It natively exists in the form of semi-crystalline cellulose microfibrils, which are important in the mechanics of primary cell wall expansion. Characterization of the crystalline properties of cellulose is crucial in understanding plant growth, as well as the degradation of cellulosic biomass for industrial applications. The plant primary cell wall is highly hydrated in its native state, yet most X-ray scattering studies of this system have been conducted in the dried state. To study primary cell walls under hydrated conditions, we employ grazing-incidence wide-angle X-ray scattering (GIWAXS) with a humidity chamber. GIWAXS near the critical angle for total external reflection provides enhanced scattering and signal-to-noise, while a humidity chamber keeps the sample hydrated with minimal interference from water. Onion outer epidermal peels were used as model system for primary cell walls. After sample dehydration, we observed cellulose crystal lattice contraction and changes in the relative intensities of diffraction peaks. We attribute these changes to the removal of water that, while in the hydrated state, interacts with the hydrogen bonding network within the cellulose crystal. Density functional theory (DFT) models of hydrated and dry cellulose microfibrils qualitatively support our hypothesis. These results elucidate the influence of water on native cellulose crystal structure and by extension, the material properties of primary cell walls.