Hemicelluloses as Recalcitrant Components for Saccharification in Wood

Abstract

Cellulose is a linear polymer consisting of more than 2,000 1,4-β-glucopyranosyl residues. The glucosyl residues form intramolecular hydrogen bonds at O3–O5′ and O6–O2′. Therefore, each glucosyl residue is bound to its neighbors by three bonds consisting of one covalent bond at C1β–C4′ and two hydrogen bonds at O3–O5′ and O6–O2′. Each glucosyl residue is oriented at an angle of 180° to the next residue of the chain, which might be synthesized from two residues at a time during cellulose biosynthesis. Since individual strands of cellulose are intrinsically less hydrophilic than other soluble polysaccharides, crystals tend to form with extensive intra- and intermolecular hydrogen bonds and complex, three-dimensional structures. In these crystals, each parallel glucan strand is situated between hydrophobic ribbon faces by both hydrophobic bonds and intermolecular hydrogen bonds (O6–O3′). Glucan forms a nanofiber, which associates to form bundles of compact lattices made up of hydrophobic and hydrogen bonds. In the natural crystals (cellulose I), the cellulose strands are parallel and form monoclinic cellulose I (Iβ) (Hackney et al.1994).