A molecular dynamics study of the effect of glycosidic linkage type in the hemicellulose backbone on the molecular chain flexibility

Abstract

SUMMARYThe macromolecular conformation of the constituent polysaccharides in lignocellulosic biomass influences their supramolecular interactions, and therefore their function in plants and their performance in technical products. The flexibility of glycosidic linkages from the backbone of hemicelluloses was studied by evaluating the conformational freedom of the φ and w dihedral angles using molecular dynamic simulations, additionally selected molecules were correlated with experimental data by nuclear magnetic resonance spectroscopy. Three types of b-(1?4) glycosidic linkages involving the monosaccharides (Glcp, Xylp and Manp) present in the backbone of hemicelluloses were defined. Different di-and tetrasaccharides with combinations of such sugar monomers from hemicelluloses were simulated, and free energy maps of the φ -w space and hydrogen-bonding patterns were obtained. The glycosidic linkage between Glc-Glc or Glc-Man (C-type) was the stiffest with mainly one probable conformation; the linkage from Man-Man or Man-Glc (M-type) was similar but with an increased probability for an alternative conformation making it more flexible, and the linkage between two Xyl-units (X-type) was the most flexible with two almost equally populated conformations. Glycosidic linkages of the same type showed essentially the same conformational space in both disaccharides and in the central region of tetrasaccharides. Different probabilities of glycosidic linkage conformations in the backbone of hemicelluloses can be directly estimated from the free energy maps, which to a large degree affect the overall macromolecular conformations of these polymers. The information gained contributes to an increased understanding of the function of hemicelluloses both in the cell wall and in technical products.

Regular Motifs in Xylan Modulate Molecular Flexibility and Interactions with Cellulose Surfaces

“…Since these subregions are nearly equally populated, the average value of w + c becomes ;415°, meaning that the conformation can be characterized on average as a flexible 3 1 -fold helical screw. This is in agreement with our previous observations for X 2 and X 4 , where the same simulation methodology was used as in this study (Berglund et al, 2016).…”

“…The different b-(1→4) glycosidic linkage types present in the backbone of hemicelluloses show distinct conformation flexibility in solution prone to a 3 1 -fold helix, with the xylan backbone being the most flexible compared with the (gluco)mannan and glucan (cellulose) backbone types (Berglund et al, 2016). Here, the effect of the repetitive glycosidic substituents in stabilizing the solution conformation of the xylan backbone has been evaluated.…”

“…On the other hand, the presence of a-(1→3)-Ara increases chain flexibility, which can be attributed to the hindered intramolecular hydrogen bonding possibilities of the xylan backbone caused specifically by the presence of a substituent at the O-3 position. Importantly, the presence of Ara and mGlcA side groups affects the probability of interaction with surrounding water by hydrogen bonding compared with the xylan backbone, where intermolecular hydrogen bonds also play a role (Berglund et al, 2016). Therefore, these glycosyl substitutions enhance the hydration state of the xylan macromolecule locally in these positions and prevent the possibility of intermolecular and intramolecular interactions between xylan backbone segments from the same or different macromolecules.…”

Selection of Optimal Polymerization Degree and Force Field in the Molecular Dynamics Simulation of Insulating Paper Cellulose

“…The average value of E obtained using the COMPASS force field is similar to the previously obtained E (14.24 GPa) and G (5.435 GPa) [10] and E of a cellulose amorphous region (12.79 GPa) [29], so the values conform to the actual mechanical properties of natural cellulose. The average values of E, G, v, and C12-C44 obtained using the PCFF force field differ slightly from those in References [10,29].…”

“…To determine the variation of the mechanical properties and solubility of the cellulose chain, models of 19 groups of single cellulose chains in the amorphous region with the polymerization degrees of 2,4,6,8,9,10,12,16,20,25,30,35,40,50,60,70,80,90, and 100 were constructed using COMPASS and PCFF force fields. The model density obtained by W. Chen [21] was about 1.385 g/cm 3 , while K. Mazeau and L. Heux [11] achieved a model with four different densities of 1.34-1.3927 g/cm 3 by modeling with the same method and standpoint, and proposed that the density of cellulose in the amorphous region is 1.28-1.44 g/cm 3 .…”