Radical Coupling Reactions in Lignin Synthesis: A Density Functional Theory Study

Journal Article · Thu Apr 26 00:00:00 EDT 2012 · Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry

DOI:https://doi.org/10.1021/jp2122449· OSTI ID:1046323

Sangha, Amandeep K.; Parks, Jerry M.; Standaert, Robert F.; Ziebell, Angela; Davis, Mark; Smith, Jeremy C.

Lignin is a complex, heterogeneous polymer in plant cell walls that provides mechanical strength to the plant stem and confers resistance to degrading microbes, enzymes, and chemicals. Lignin synthesis initiates through oxidative radical-radical coupling of monolignols, the most common of which are p-coumaryl, coniferyl, and sinapyl alcohols. Here, we use density functional theory to characterize radical-radical coupling reactions involved in monolignol dimerization. We compute reaction enthalpies for the initial self- and cross-coupling reactions of these monolignol radicals to form dimeric intermediates via six major linkages observed in natural lignin. The 8-O-4, 8-8, and 8-5 coupling are computed to be the most favorable, whereas the 5-O-4, 5-5, and 8-1 linkages are less favorable. Overall, p-coumaryl self- and cross-coupling reactions are calculated to be the most favorable. For cross-coupling reactions, in which each radical can couple via either of the two sites involved in dimer formation, the more reactive of the two radicals is found to undergo coupling at its site with the highest spin density.

• Research Organization: National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy Biomass Program
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1046323
• Report Number(s): NREL/JA-5100-55132; TRN: US201216%%161
• Journal Information: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry, Vol. 116, Issue 16; ISSN 1520-6106
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALCOHOLS
COUPLING
DENSITY FUNCTIONAL METHOD
DIMERIZATION
DIMERS
ENZYMES
LIGNIN
PLANT CELLS
PLANT STEMS
POLYMERS
RADICALS
SPIN
SYNTHESIS
lignin
polymers
density functional thoery
coupling reactions