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

1. 用分子轨道计算方法分析了单分子木质素的电子态和偶联反应中的过渡态。发现在疏水或酸性环境下，未配对电子的定位和4-氧负电荷的减少促进了β-O-4结构的产生。奎宁甲碳上的电荷通过4-氧的质子化转移到正电荷上。这就解释了在酸性环境中a-碳上容易形成羟基化。杨树愈伤组织中一种独特的过氧化物酶同工酶，阳离子细胞壁结合过氧化物酶▲（CWPO-C），与其他植物过氧化物酶不同，它可以氧化sinapyl醇、铁细胞色素c和合成木质素聚合物。利用四硝基甲烷对CWPO-C - Tyr残基进行改性，可明显抑制其氧化活性。同源性分析表明，tyr177和tyr74位于血红素附近，暴露在CWPO-C的蛋白表面。这些结果表明，蛋白质表面的Tyr残基是CWPO-C氧化活性的关键参与者，代表了植物过氧化物酶家族的新氧化位点。分子轨道计算也证实了单个电子可以从Tyr残基转移到距离为14a的过氧化物酶活性位点血红素边缘的可能性。计算了酚类β-O-4型木质素模型化合物及其醌类中间体（QM）的键解离能。结果表明，酚类β-O-4键是通过醌类中间体进行均裂的。此外，为了模拟纤维素在高温水中的结晶变化，调整了多糖分子动力学方法的参数。白腐真菌的氧化活性在白腐真菌对芳香环境污染物的氧化过程中，利用分子轨道法模拟核磁共振光谱可用于氧化产物的结构测定。分析了一株选择性白腐菌产生的关键代谢物的功能。结果表明，白腐菌胞外代谢物对Fenton反应的抑制不是由于HOMO能量，而是由于代谢物的烷基侧链的屏蔽作用。单宁偶极子的功能和热转化随(4α-8)-儿茶素聚合程度的增加而增加。这种趋势与树皮单宁分馏沉淀蛋白质的实验结果相似。用分子轨道计算方法模拟了(+)-儿茶素和(+)-表儿茶素的平衡常数，与实验结果定性一致，表明(+)-儿茶素的平衡常数优于(+)-儿茶素，并随温度的升高而降低。少

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