TY - JOUR
T1 - Radical coupling reactions in lignin synthesis
T2 - A density functional theory study
AU - Sangha, Amandeep K.
AU - Parks, Jerry M.
AU - Standaert, Robert F.
AU - Ziebell, Angela
AU - Davis, Mark
AU - Smith, Jeremy C.
PY - 2012/4/26
Y1 - 2012/4/26
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84860305329&partnerID=8YFLogxK
U2 - 10.1021/jp2122449
DO - 10.1021/jp2122449
M3 - Article
C2 - 22475051
AN - SCOPUS:84860305329
SN - 1520-6106
VL - 116
SP - 4760
EP - 4768
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 16
ER -