Chirality and bound water in the hierarchical cellulose structure

Abstract

The origins of the unique properties of natural fibres have remained largely unresolved because of the complex interrelations between structural hierarchy, chirality and bound water. In this paper, analysis of the melting endotherms for bleached hardwood pulps indicates that the amount of nonfreezing bound water (0.21 g/g) is roughly half of the amount of freezing bound water (0.42 g/g). We link this result to the two smallest constitutive units, microfibrils and their bundles, using molecular dynamics simulations at both hierarchical levels. The molecular water layers found in the simulations correspond quite accurately to the measured amount of non-freezing and freezing bound water. Disorder that results from the microfibril twist and amphiphilicity prevents co-crystallisation, leaving routes for water molecules to diffuse inside the microfibril bundle. Moreover, the simulations predict correctly the magnitude of the right-handed twist at different hierarchical levels. Significant changes in hydroxymethyl group conformations are seen during twisting that compare well with existing experimental data. Our findings go beyond earlier modelling studies in predicting the twist and structure of the microfibril bundle.

Preferred crystallographic orientation of cellulose in plant primary cell walls

“…Twisting of microfibrils has been observed through simulations 25,26,[68][69][70][71][72][73][74] and experiments 12,18,25 . The twist observed in simulations has been attributed to van der Waals interactions that aid in packing of crystals between layers 75 or trans-glycosidic linkages due to hydrogen bonds 76 .…”

A novel supra coarse-grained model for cellulose

“…The right-hand twist of cellulose was observed and discussed in many experimental and simulation studies (Matthews et al 2006;Conley et al 2016;Paajanen et al 2019;Paavilainen et al 2011;Zhao et al 2013;Hadden et al 2013;Hanley et al 1997;Arcari et al 2019). Although the twist can be clearly seen in TEM (Conley et al 2016) and AFM (Hanley et al 1997;Arcari et al 2019) pictures, it is difficult to deduce exactly how much is the twist per length of fibril.…”

“…Cellulose has been the subject of many molecular simulation studies. Some of these studies focus only at the surface phenomena and modifications of CNC, (Chen et al 2017;Zhou et al 2015;Bergenstråhle et al 2008;Paajanen et al 2016;Chundawat et al 2011) while many others simulate whole CNC, both at atomistic (Chen et al 2017;Zhou et al 2015;Bergenstråhle et al 2008;Paajanen et al 2016;Chundawat et al 2011;Matthews et al 2006;Conley et al 2016;Oehme et al 2015;Djahedi et al 2015;Paajanen et al 2019;Ciesielski et al 2019) and coarsegrained representations (López et al 2009;Wohlert and Berglund 2011;López et al 2015;Mehandzhiyski and Zozoulenko 2019;Glass et al 2012;Fan and Maranas 2015;Markutsya et al 2013;Shishehbor et al 2018;Shishehbor and Zavattieri 2019;Ramezani and Golchinfar 2019;Srinivas et al 2011;Poma et al 2015Poma et al , 2016Poma et al , 2017. All-atom molecular dynamics (AA-MD) studies are able to simulate the crystal structure of cellulose in a perfect agreement with the experimental crystal structure of different cellulose allomorphs and provide a detailed atomistic picture for the structure and dynamics of CNC (Chundawat et al 2011).…”

“…Therefore, it is of the crucial importance for the CG models to be carefully parameterized and to reproduce key aspects of CNC structure and interactions. Most commonly the parameterization of CG models is based of AA-MD, which is shown to reproduce experiments very well (Zhou et al 2015;Chundawat et al 2011;Oehme et al 2015;Paajanen et al 2019).…”

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.…”