Plant biomass recalcitrance, a major
obstacle to achieving sustainable
production of second generation biofuels, arises mainly from the amorphous
cell-wall matrix containing lignin and hemicellulose assembled into
a complex supramolecular network that coats the cellulose fibrils.
We employed the statistical-mechanical, 3D reference interaction site
model with the Kovalenko–Hirata closure approximation (or 3D-RISM-KH
molecular theory of solvation) to reveal the supramolecular interactions
in this network and provide molecular-level insight into the effective
lignin–lignin and lignin–hemicellulose thermodynamic
interactions. We found that such interactions are hydrophobic and
entropy-driven, and arise from the expelling of water from the mutual
interaction surfaces. The molecular origin of these interactions is
carbohydrate−π and π–π stacking forces,
whose strengths are dependent on the lignin chemical composition.
Methoxy substituents in the phenyl groups of lignin promote substantial
entropic stabilization of the ligno-hemicellulosic matrix. Our results
provide a detailed molecular view of the fundamental interactions
within the secondary plant cell walls that lead to recalcitrance