Article pubs.acs.org/JAFC
Structural Characterization of Wheat Straw Lignin as Revealed by Analytical Pyrolysis, 2D-NMR, and Reductive Cleavage Methods José C. del Río,*,† Jorge Rencoret,†,‡ Pepijn Prinsen,† Á ngel T. Martínez,§ John Ralph,‡ and Ana Gutiérrez† †
Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, PO Box 1052, E-41080 Seville, Spain Departments of Biochemistry and Biological Systems Engineering, the Wisconsin Bioenergy Initiative, and the DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53706, United States § Centro de Investigaciones Biológicas (CIB), CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain ‡
S Supporting Information *
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 β-O-4′ethers (∼75%), followed by phenylcoumarans (∼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 (∼10%) at the γ-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 (
