Computer chemistry for the production, decomposition and function of woody biomass

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1. Formation of ligninThe electronic states of monolignol and the transition state during the coupling reaction were analyzed with molecular orbital calculation. It was found that the localization of unpaired electron and the reduction of negative charge at 4-oxygen encourage the production of β-O-4 structure in hydrophobic or acid environment. The charge at a-carbon of quinine methide transferred to positive value by protonation of 4-oxygen. This accounted for the easy formation of hydroxylation at a-carbon in acid environment.2. Enzymatic activity of peroxydase to syringyl compoundsA unique peroxidase isoenzyme, cationic cell-wall-bound peroxidase▲(CWPO-C), from poplar callus oxidizes sinapyl alcohol, ferrocytochrome c and synthetic lignin polymers, unlike other plant peroxidases. Modification of CWPO-C Tyr residues using tetranitromethane strongly suppressed its oxidation activities. Homology modeling revealed that Tyr-177 and Tyr-74 are located near the heme and exposed on the prot … More ein surface of CWPO-C. These results suggest that Tyr residues on the protein surface are key players in the oxidation activities of CWPO-C, and represent novel oxidation sites for the plant peroxidase family. Molecular orbital calculation also confirmed the possibility that single electron can transfer from the Tyr residue to the heme-edge of the active site of peroxidase at a distance of 14A.3. Thermal decomposition of biomassBond dissociation energy was calculated for phenolic β-O-4 type lignin model compounds and their quinone methide intermediates (QM). It was concluded that phenolic β-O-4 bond was cleaved homolytically via the quinone methide intermediate. Further, to simulate the crystal change of cellulose in high temperature water the parameters of molecular dynamics method for polysaccharide were tuned.4. Oxidation activity of white rot fungiIn the oxidation of aromatic environmental pollutants by white rot fungi, the simulation of NMR spectra by molecular orbital approach could be useful for the structural determination of oxidized products. Functions of key metabolites produced by a selective white rot fungus were analyzed. It was suggested that suppression of the Fenton reaction by extracellplar metabolites of the white rot fungus was not ascribed to HOMO energy but to the shielding effects by an alkyl side chain of the metabolites.5. Function and thermal transformation of tanninThe dipole increased with the degree of polymerization of (4α-8)-catechins. This tendency was parallel to the experimental result in the precipitation of protein by fractionated bark tannin. The equilibrium constant of (+)-catechin and (+)-epicatechin was simulated with molecular orbital calculation designated qualitatively agreement with experimental results which denotes superior of (+)-catechin and decreases with temperature. Less