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Open Access item Structural Characterization of Wheat Straw Lignin as Revealed by Analytical Pyrolysis, 2D-NMR, and Reductive Cleavage Methods

Authors:Río Andrade, José Carlos del
Rencoret, Jorge
Prinsen, Pepijn
Martínez Ferrer, Ángel Tomás
Ralph, John
Gutiérrez Suárez, Ana
Keywords:wheat straw, Py-GC/MS, TMAH, HSQC, DFRC, milled wood lignin, p-coumarate, ferulate, coniferyl acetate, tricin
Issue Date:May-2012
Publisher:American Chemical Society
Citation:Journal of Agricultural and Food Chemistry, 60, 5922-5935
Abstract:The structure of the lignin in wheat straw has been investigated by a combination of analytical pyrolysis, 2DNMR, and derivatization followed by reductive cleavage (DFRC). It is a p-hydroxyphenyl-guaiacyl-syringyl lignin (with an H:G:S ratio of 6:64:30) associated with p-coumarates and ferulates. 2D-NMR indicated that the main substructures present are beta-O-4-ethers (ca. 75%), followed by phenylcoumarans (ca. 11%), with lower amounts of other typical units. A major new finding is that the flavone tricin is apparently incorporated into the lignins. NMR and DFRC indicated that the lignin is partially acylated (ca. 10%) at the gamma-carbon, predominantly with acetates that preferentially acylate guaiacyl (12%) rather than syringyl (1%) units; in dicots, acetylation is predominantly on syringyl units. p-Coumarate esters were barely detectable (<1%) on monomer conjugates released by selectively cleaving beta-ethers in DFRC, indicating that they might be preferentially involved in condensed or terminal structures.
Publisher version (URL):http://dx.doi.org/10.1021/jf301002n
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