title: Tricin-lignins: occurrence and quantitation of tricin in relation to phylogeny.
abstract: Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as an authentic monomer in grass lignification that likely functions as a nucleation site. It is linked onto lignin as an aryl alkyl ether by radical coupling with monolignols or their acylated analogs. However, the level of tricin that incorporates into lignin remains unclear. Herein, three lignin characterization methods: acidolysis; thioacidolysis; and derivatization followed by reductive cleavage; were applied to quantitatively assess the amount of lignin-integrated tricin. Their efficiencies at cleaving the tricin-(4'-O-β)-ether bonds and the degradation of tricin under the corresponding reaction conditions were evaluated. A hexadeuterated tricin analog was synthesized as an internal standard for accurate quantitation purposes. Thioacidolysis proved to be the most efficient method, liberating more than 91% of the tricin with little degradation. A survey of different seed-plant species for the occurrence and content of tricin showed that it is widely distributed in the lignin from species in the family Poaceae (order Poales). Tricin occurs at low levels in some commelinid monocotyledon families outside the Poaceae, such as the Arecaceae (the palms, order Arecales) and Bromeliaceae (Poales), and the non-commelinid monocotyledon family Orchidaceae (Orchidales). One eudicotyledon was found to have tricin (Medicago sativa, Fabaceae). The content of lignin-integrated tricin is much higher than the extractable tricin level in all cases. Lignins, including waste lignin streams from biomass processing, could therefore provide a large and alternative source of this valuable flavone, reducing the costs, and encouraging studies into its application beyond its current roles.
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, WI, USA.|Department of Biological System Engineering, University of Wisconsin, Madison, WI, USA.
authors.forename: Wu
authors.initials: W
authors.lastname: Lan
authors.affiliation: Instituto de Recursos Naturales y Agrobiologia de Sevilla (IRNAS), CSIC, Avenida de la Reina Mercedes, 10, 41012, Seville, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Rencoret
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, WI, USA.|Department of Biochemistry, University of Wisconsin, Madison, WI, USA.|State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, China.
authors.forename: Fachuang
authors.initials: F
authors.lastname: Lu
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, WI, USA.|Department of Biochemistry, University of Wisconsin, Madison, WI, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Karlen
authors.affiliation: School of Chemical Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: Bronwen G
authors.initials: BG
authors.lastname: Smith
authors.affiliation: School of Biological Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Harris
authors.affiliation: Instituto de Recursos Naturales y Agrobiologia de Sevilla (IRNAS), CSIC, Avenida de la Reina Mercedes, 10, 41012, Seville, Spain.
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Del Río
authors.affiliation: DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, WI, USA.|Department of Biological System Engineering, University of Wisconsin, Madison, WI, USA.|Department of Biochemistry, University of Wisconsin, Madison, WI, USA.
authors.forename: John
authors.initials: J
authors.lastname: Ralph
mesh_terms: D002853:Chromatography, Liquid; D005419:Flavonoids / Q000378:metabolism*; D008031:Lignin / Q000378:metabolism*; D013058:Mass Spectrometry; D010802:Phylogeny; D006109:Poaceae / Q000145:classification / Q000378:metabolism
chemical_list: D005419:Flavonoids; D008031:Lignin; C017769:tricin
keywords: Poaceae; acidolysis; derivatization followed by reductive cleavage; liquid chromatography-mass spectrometry; multiple reaction monitoring; stable isotopically labeled internal standard; thioacidolysis; tricin-d6