p-Hydroxyphenyl (H) Units Lower the Degree of Polymerization in Lignin: Chemical Control in Lignin Biosynthesis

Conference · Tue Jan 01 04:00:00 EST 2013

OSTI ID:1087245

Sangha, A. K.; Parks, J. M.; Davis, M. F.; Smith, J. C.

Lignin, composed predominantly of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) subunits, is a major component of plant cell walls that imparts resistance toward chemical and microbial deconstruction of plant biomass, rendering its conversion inefficient and costly. Previous studies have shown that alterating lignin composition, i.e., the relative abundance of H, G and S subunits, promises more efficient extraction of sugars from plant biomass. Smaller and less branched lignin chains are more easily extracted during pretreatment, making cellulose more readily degradable. Here, using density functional theory calculations, we show that the incorporation of H subunits into lignin via b-b and b-5 interunit linkages reduces the degree of polymerization in lignin. Frontier molecular orbital analyses of lignin dimers and trimers show that H as a terminal subunit on a growing lignin polymer linked via b-b and b-5 linkage cannot undergo radical formation, preventing further chain growth by endwise polymerization resulting in lignin polymers with lower degree of polymerization. These results indicate that, for endwise polymerization in lignin synthesis, there exists a chemical control that may lay a significant role in determining the structure of lignin.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO.
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy Biomass Program
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1087245
• Country of Publication: United States
• Language: English

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