Coupling and Reactions of 5-Hydroxyconiferyl Alcohol in Lignin Formation

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• 作者：Thomas Elder ; Laura Berstis ; Gregg T. Beckham ; Michael F. Crowley
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2016
• 出版时间：June 15, 2016
• 年：2016
• 卷：64
• 期：23
• 页码：4742-4750
• 全文大小：531K
• 年卷期：0
• ISSN：1520-5118

文摘

The catechol alcohols, caffeyl and 5-hydroxyconiferyl alcohol, may be incorporated into lignin either naturally or through genetic manipulation. Due to the presence of o-OH groups, these compounds form benzodioxanes, a departure from the interunit connections found in lignins derived from the cinnamyl alcohols. In nature, lignins composed of caffeyl and 5-hydroxyconiferyl alcohol are linear homopolymers and, as such, may have properties that make them amenable for use in value-added products, such as lignin-based carbon fibers. In the current work, results from density functional theory calculations for the reactions of 5-hydroxyconiferyl alcohol, taking stereochemistry into account, are reported. Dehydrogenation and quinone methide formation are found to be thermodynamically favored for 5-hydroxyconiferyl alcohol, over coniferyl alcohol. The comparative energetics of the rearomatization reactions suggest that the formation of the benzodioxane linkage is under kinetic control. Ring-opening reactions of the benzodioxane groups show that the bond dissociation enthalpy of the α-O cleavage reaction is lower than that of the β-O reaction. The catechol lignins represent a novel form of the polymer that may offer new opportunities for bioproducts and genetic targets.