Hydrogen bonds and twist in cellulose microfibrils

Abstract

There is increasing experimental and computational evidence that cellulose microfibrils can exist in a stable twisted form. In this study, atomistic molecular dynamics (MD) simulations are performed to investigate the importance of intrachain hydrogen bonds on the twist in cellulose microfibrils. We systematically enforce or block the formation of these intrachain hydrogen bonds by either constraining dihedral angles or manipulating charges. For the majority of simulations a consistent right handed twist is observed. The exceptions are two sets of simulations that block the O2-O6' intrachain hydrogen bond, where no consistent twist is observed in multiple independent simulations suggesting that the O2-O6' hydrogen bond can drive twist. However, in a further simulation where exocyclic group rotation is also blocked, right-handed twist still develops suggesting that intrachain hydrogen bonds are not necessary to drive twist in cellulose microfibrils.

Molecular Dynamics Study on Transmission Mechanism of Torsional Deformation in Cellulose Nanofibers with Hierarchical Structure

“…For any angular velocity condition, the shear modulus at the temperature less than 300 K is always smaller than that at 10 K. The value of shear modulus obtained here is about 1.4 GPa at 10 K, and about 0.8 -1.0 GPa between 100 and 300 K. They are somewhat smaller than the experimental value, 1.8 -3.8 GPa [15]. The calculated value reported for CMF using MD with the all atom model is 1.6 GPa [16]. This slight discrepancy is caused by inhomogeneous deformation of the whole system due to the influence of the fixed and velocity-constrained ends.…”

“…It is reported that CNF's experimental shear modulus is between 1.8 and 3.8 GPa [14], and the simulated one by all-atom model is 1.6 GPa [15]. Although knowledge on tensile properties of CMF is increasing, the material's behavior in torsion or bending deformation is quite different [13] [16]. In addition, the actual CMF is tangled complicatedly to form a hierarchical structure.…”

Moisture-related changes in the nanostructure of woods studied with X-ray and neutron scattering

“…As the relative change of L 004 with moisture content was of similar magnitude in all samples (Table 3), an increase in the twisting with drying appears a more plausible explanation. Based on molecular dynamics simulations, the twist rate of CMFs and their bundles, and thereby also the longitudinal coherence length, can be affected for instance by the fibril dimensions (Kannam et al 2017) or interactions with water (Paajanen et al 2019). However, it is not clear if the systems simulated so far are sufficiently representative of the complex, multicomponent structure of the native wood cell wall.…”

Chirality and bound water in the hierarchical cellulose structure

“…Several molecular-level mechanisms have been proposed as the driving force behind the twisting of single microfibrils. Since the phenomenon was first observed in classical MD simulations (Yui et al 2006;Matthews et al 2006;Yui and Hayashi 2007), it has been attributed, solely or in part, to (1) changes in intra and interlayer hydrogen bonding patterns (Paavilainen et al 2011) (2) attractive, interlayer, van der Waals forces (Hadden et al 2013) (3) torsional forces due to the geometry of the trans-glycosidic hydrogen bonds, especially the HO2-O6' bond (Bu et al 2015;Conley et al 2016), and (4) a joint effect of several mechanisms (Kannam et al 2017). In a related discussion (Zhao et al 2013), it has been speculated that amorphous regions repeating along the length of the fibril would be needed to release stresses involved with the twist, and to keep the cellulose I b structure intact.…”