title: Nature and kinetic analysis of carbon-carbon bond fragmentation reactions of cation radicals derived from SET-oxidation of lignin model compounds.
abstract: 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.
authors.affiliation: Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Cho
authors.forename: Ramakrishnan
authors.initials: R
authors.lastname: Parthasarathi
authors.forename: Adam S
authors.initials: AS
authors.lastname: Pimentel
authors.forename: Gabriel D
authors.initials: GD
authors.lastname: Maestas
authors.forename: Hea Jung
authors.initials: HJ
authors.lastname: Park
authors.forename: Ung Chan
authors.initials: UC
authors.lastname: Yoon
authors.forename: Debra
authors.initials: D
authors.lastname: Dunaway-Mariano
authors.forename: S
authors.initials: S
authors.lastname: Gnanakaran
authors.forename: Paul
authors.initials: P
authors.lastname: Langan
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Mariano
mesh_terms: 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
chemical_list: D002412:Cations; D005609:Free Radicals; D002244:Carbon; D008031:Lignin