Deciphering the Unique Structure and Acylation Pattern of <i>Posidonia oceanica</i> Lignin
Jorge Rencoret, Gisela Marques, Óscar Serrano, Joeri Kaal, Ángel T. Martı́nez, José C. del Rı́o, Ana Gutiérrez
Abstract
Lignins from different parts of the seagrass Posidonia oceanicanamely sheaths, rhizome, and rootsas well as from fibrous balls from P. oceanica detritus were isolated and thoroughly characterized by pyrolysis coupled with gas chromatography/mass spectrometry, derivatization followed by reductive cleavage, two-dimensional nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The lignins of P. oceanica were enriched in guaiacyl (G) over syringyl (S) units, with S/G ratios ranging from 0.1 (fibrous balls) to 0.5 (rhizome). -O-4 ethers and phenylcoumarans were the most abundant lignin substructures, followed by resinols, and minor amounts of dibenzodioxocins and spirodienones. Moreover, all lignins were found to be highly -acylated (up to 44% of total units), mainly with p-hydroxybenzoates but also, to a lesser extent, with acetates. The data indicated that this acylation extensively occurred in both G-and S-lignin units, contrary to what happens in palms, poplar, and willow, where p-hydroxybenzoates overwhelmingly appear at the -position of S-units.