Applications and associated processing technologies of lignocellulosic biomass are becoming increasingly important as we endeavor to meet societal demand for fuels, chemicals, and materials from renewable resources. Meanwhile, the rapidly expanding availability and capabilities of high-performance computing present an unprecedented opportunity to accelerate development of technologies surrounding lignocellulose utilization.In order to realize this potential, suitable modeling frameworks must be constructed that effectively capture the multiscale complexity and tremendous variety exhibited by lignocellulosic materials. In our assessment of previous endeavors toward this goal, several important shortcomings have been identified: (1) the lack of multiscale integration strategies that capture emergent properties and behaviors spanning different length scales and (2) the inability of many modeling approaches to effectively capture the variability and diversity of lignocellulose that arise from both natural and process-induced sources. In this Perspective, we survey previous modeling approaches for lignocellulose and simulation processes involving its chemical and mechanical transformation and suggest opportunities for future development to enhance the utility of computational tools to address barriers to widespread adoption of a renewable bioeconomy.

The mechanistic underpinnings of the complex process of plant polysaccharide biosynthesis are poorly understood, largely due to the resistance of glycosyltransferase (GT) enzymes to structural characterization. In Arabidopsis thaliana, a glycosyl transferase family 37 (GT37) fucosyltransferase-1 (AtFUT1) catalyzes the regiospecific transfer of terminal 1,2-fucosyl residues to xyloglucan side chains – a key step in the biosynthesis of fucosylated sidechains of galactoxyloglucan. We unravel the mechanistic basis for fucosylation by AtFUT1 with a multipronged approach involving protein expression, X-ray crystallography, mutagenesis experiments and molecular simulations. Mammalian cell culture expressions enable sufficient production of the enzyme for X-ray crystallography, which reveals the structural architecture of AtFUT1 in complex with bound donor and acceptor substrate analogs. The lack of an appropriately positioned active site residue as a catalytic base leads us to propose an atypical water-mediated fucosylation mechanism facilitated by an H-bonded network, which is corroborated by mutagenesis experiments as well as detailed atomistic simulations.

Technologies surrounding utilization of cellulosic materials have been integral to human society for millennia. In many materials, controlled introduction of defects provides a means to tailor properties, introduce reactivity, and modulate functionality for various applications. The importance of defects in defining the behavior of cellulose is becoming increasingly recognized. However, fully exploiting defects in cellulose to benefit biobased materials and conversion applications will require an improved understanding of the mechanisms of defect induction and corresponding molecular-level consequences. We have identified a fundamental relationship between the macromolecular structure and mechanical behavior of cellulose nanofibrils whereby molecular defects may be induced when the fibrils are subjected to bending stress exceeding a certain threshold. By nanomanipulation, imaging, and molecular modeling, we demonstrate that cellulose nanofibrils tend to form kink defects in response to bending stress, and that these macromolecular features are often accompanied by breakages in the glucan chains. Direct observation of deformed cellulose fibrils following partial enzymatic digestion reveals that processive cellulases exploit these defects as initiation sites for hydrolysis. Collectively, our findings provide a refined understanding of the interplay between the structure, mechanics, and reactivity of cellulose assemblies.

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A major challenge for the utilization of lignocellulosic feedstocks for liquid fuels and other value added chemicals has been the recalcitrant nature of crystalline cellulose to various hydrolysis techniques. Ionic liquids (ILs) are considered to be a promising solvent for the dissolution and conversion of cellulose to simple sugars, which has the potential to facilitate the unlocking of biomass as a supplement and/or replacement for petroleum as a feedstock. Recent studies have revealed that the orientation of the hydroxymethyl group, described via the ω dihedral, and the glycosidic bond, described via the φ-ψ dihedrals, are significantly modified in the presence of ILs. In this study, we explore the energetics driving the orientational preference of the ω dihedral and the φ-ψ dihedrals for glucose and cellobiose in water and three imidazolium based ILs. It is found that interactions between the cation and the ring oxygen in glucose directly impact the conformational preference of the ω dihedral shifting the distribution towards the gauche-trans (GT) conformation and creating an increasingly unfavorable gauche-gauche (GG) conformation with increasing tail length. This discovery modifies the current hypothesis that intramolecular hydrogen bonding is responsible for the shift in the ω dihedral distribution and illuminates the importance of the cation's character. In addition, it is found that the IL's interaction with the glycosidic bond results in the modification of the observed φ-ψ dihedrals, which may have implications for hydrolysis in the presence of ILs. The molecular level information gained from this study identifies the favorable IL-sugar interactions that need to be exploited in order to enhance the utilization of lignocellulosic biomass as a ubiquitous feedstock.