The role of hydroxyl groups in interchain interactions in cellulose Iα and Iβ

Complex networks of hydrogen bonds within the cellulose I and I contribute greatly to cellulose's anisotropic physical properties such as material stiffness. The interchain hydrogen bonding interactions through hydroxyl groups are isolated in each of the three lattice planes of the adjacent chains within the unit cell of two allomorphs of natural cellulose. In our density function theory study with dispersion corrected Perdew-Burke-Ernzerhof (PBE-D2) functional, these hydroxyl groups participate in strong hydrogen bonding interactions (-24.8 and -24.8 kcal/mol for cellulose I and I, respectively) in the side-to-side lattice plane. Unexpectedly, the hydroxyl groups also participate significantly in hydrogen bonding interactions (-11.0 and -12.4 kcal/mol for cellulose I and I, respectively) in one of the diagonal lattice planes in both cellulose I and I. Both PM7 and PBE-D2 method predict that the overall interaction is asymmetric and stronger in the right diagonal lattice plane. While hydrogen bonding interactions are strongest in side-to-side lattice plane as expected, the role of hydrogen bonding interactions for keeping the sheet together is more significant than previously thought.