Multiscale theory, modelling, and simulation of hemicellulose and lignin in solution

Abstract

This review examines multiscale modelling approaches for cellulose nanocrystals (CNCs) and lignocellulosic plant cell walls, with a focus on hemicellulose and lignin interactions in aqueous environments. The three-dimensional reference interaction site model with the Kovalenko-Hirata closure (3D-RISM-KH) is highlighted as a powerful molecular solvation theory applied in nanochemistry and biomolecular simulations. The method has been successfully employed to investigate hemicellulose hydrogels, the influence of hemicellulose composition on nanoscale forces in primary cell walls, and lignin-lignin and lignin-hemicellulose interactions. Findings indicate that these interactions are predominantly hydrophobic and entropy-driven, arising from water exclusion effects. Insights gained through this modeling framework deepen the understanding of molecular-scale forces in plant cell walls and inform strategies for biomass valorization, including genetic engineering and pretreatment technologies aimed at enhancing cellulose extraction and utilization.

Figures (7)

• Figure 1: (Colour online) Potential of mean force $W_{\rm PMF}(d)$ and aggregation free energy $\Delta G_{\rm agg}$59. Disaggregation of CNs in hemicellulose hydrogels through the disruption of hydrophilic ( a) and hydrophobic ( b) interactions. PMF profiles along these disaggregation pathways ( c) and ( d) are shown for glucuronate molar fractions ranging from $x=0.0$ to $0.1$ (legend in ( c). PMF variations with glucuronate concentration are indicated by grey arrows. $G_{\rm agg}$ for hydrophilic and hydrophobic contacts in hemicellulose hydrogels is displayed in ( e) and ( f), respectively. The sum of arabinose and acetate curves is represented by a grey dotted line.
• Figure 2: (Colour online) 3D site density distributions $g({\bf r})$ of aggregated CNs 51. ( a) highlights the hydrogen bond donor and acceptor sites within the CN structure. $g({\bf r})$ of hemicellulose carbon atoms from arabinose ( b), glucuronic acid ( c), glucuronate ( d), and acetate ( e) monomers in proximity to the CNs. The isosurfaces of $g({\bf r}) = 1.4$ are displayed in the same colors as the corresponding atoms, except for the glucuronate C6 atom which is represented at $g({\bf r}) = 2.0$.
• Figure 3: (Colour online) Isosurfaces of the 3D solvation free energy density of glucuronate around cellulose nanocrystals 59. ( a) Localized regions of strong hydrogen bonding are shown in green (larger negative isovalue). ( b) Diffuse second-layer distributions with weaker interactions, shown in blue (smaller negative isovalue), represent hemicellulose–cellulose stacking.
• Figure 4: (Colour online) Hemicellulose and lignin oligomers 60. ( a) Lignin residues, with substituents R$_1$ and R$_2$ highlighted in red. ( b) Lignin dimer containing a $\beta$-O-4$'$ bond (light-blue background). ( c) Lignin monomer with hydroxyl groups replaced by methoxy groups. ( d) Stick model of lignin and hemicellulose oligomers, with $\beta$-O-4$'$ bonding in blue.
• Figure 5: (Colour online) Solvation free energies of ( a) hemicellulose and ( b) lignin oligomers in aqueous solutions containing H, G, or S monomers at molar fractions $x = 0.0-0.1$, relative to pure water 60. Interaction strength increases in the order H < G < S.