Structural elucidation of lignin–carbohydrate complex (LCC) preparations and lignin from Arundo donax Linn

Abstract

Lignin carbohydrate complex (LCC) impedes the industrial application of plant fibers but also displays diverse pharmacological activities. In the present study, lignin chemical linked LCC preparations were subsequently isolated from energy crop Arudo donax Linn., and chemically characterized by using GPC, HPAEC, FT-IR, and 2D HSQC NMR spectroscopy. The results indicated that the isolated LCC preparations were xylan-rich and exhibited relatively narrow molecular weight distribution (PI<2.0). 2D HSQC NMR analysis showed direct evidences that the carbohydrate and lignin constituents in each LCC preparation were chemically bonded. Specially, Björkman LCC preparation was rich in phenyl glycoside, benzyl ether, and benzyl ester LCC linkages, indicating that the classic Björkman LCC preparation was preferable for the analysis of LCC linkages in A. donax. Moreover, lowest “concentration” of benzyl ether LCC linkage was found in CEL preparation. Further lignin characterization demonstrated that β-O-4′ alkyl ether linkages (77–100%) were predominant. With respect to the hydroxycinnamates, p-coumarate was incorporated into all LCC preparations, whereas ferulate existed mainly in Björkman LCC and may ether link to lignin. These findings will provide a theoretical basis for biofuels and biomedicine production.