Nature and kinetic analysis of carbon-carbon bond fragmentation reactions of cation radicals derived from SET-oxidation of lignin model compounds.
Features of the oxidative cleavage reactions of diastereomers of dimeric lignin model compounds, which are models of the major types of structural units found in the lignin backbone, were examined. Cation radicals of these substances were generated by using SET-sensitized photochemical and Ce(IV) and lignin peroxidase promoted oxidative processes, and the nature and kinetics of their C-C bond cleavage reactions were determined. The results show that significant differences exist between the rates of cation radical C1-C2 bond cleavage reactions of 1,2-diaryl-(β-1) and 1-aryl-2-aryloxy-(β-O-4) propan-1,3-diol structural units found in lignins. Specifically, under all conditions C1-C2 bond cleavage reactions of cation radicals of the β-1 models take place more rapidly than those of the β-O-4 counterparts. The results of DFT calculations on cation radicals of the model compounds show that the C1-C2 bond dissociation energies of the β-1 lignin model compounds are significantly lower than those of the β-O-4 models, providing clear evidence for the source of the rate differences.
Cho
Dae Won
DW
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Parthasarathi
Ramakrishnan
R
Pimentel
Adam S
AS
Maestas
Gabriel D
GD
Park
Hea Jung
HJ
Yoon
Ung Chan
UC
Dunaway-Mariano
Debra
D
Gnanakaran
S
S
Langan
Paul
P
Mariano
Patrick S
PS
D002244:Carbon / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D008031:Lignin / Q000138:chemical synthesis / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013237:Stereoisomerism
D002412:Cations; D005609:Free Radicals; D002244:Carbon; D008031:Lignin