Recently, it has been shown that the polymerization of lignin has considerable plasticity with respect to the incorporation of modified and engineered monolignols, enabling intriguing deviations from the conventional cross-coupling of coniferyl, sinapyl and p-coumaryl alcohols. Monolignols with desirable chemical properties may be introduced either through genetic manipulations or through incubation during cell wall growth. Such alterations which facilitate lignin decomposition chemistry impart tremendous significance to industrial applications, by reducing the recalcitrance of this polymer, and facilitating its decomposition into high-value aromatic products. Catechols, caffeoyl and 5-hydroxy coniferyl alcohol have been highlighted as promising novel monolignols for their appealing homogeneous and linear polymers, with benzodioxane linkages as the nearly exclusive connectivity. In the current paper we employ computational models using density functional theory to evaluate the thermodynamics, bond properties and energetics associated with this benzodioxane coupling mode in comparison to the common β-O-4 bonding, with emphasis on the effect of stereochemistry. A broad spectrum of homo- and heterodimers of these high-interest monolignols are compared, and further theoretical predictions of their macromolecular structures are made as a function of monolignol type and coupling mode.

Coupling and reactions of catechol monolignols

251st National Meeting (2016)

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