Lignin is the second most abundant biopolymer after cellulose and constitutes about 15-30 wt% of lignocellulosic biomass. Lignin is produced in large quantities as a waste from paper and pulp industries. Lignin consists of three monomer units which bond to one another through different linkages to form a complex, heterogeneous polymer. Due to lignin biocompatibility, cost effectiveness, and a growing interest in renewable energies, there has been much attention focused on converting lignin to value added products recently. Thus, structural elucidation of this complex biopolymer and its degradation products are a necessity. Many studies have been recently focused on studying lignin through synthesis and subsequent analysis of lignin oligomer model compounds using mass spectrometry with the ultimate goal of establishing mass spectrometry fragmentation rules for structure elucidation of lignin oligomers by tandem mass spectrometry. In our on-going efforts in this field, we studied the targeted-synthesis of a new tetramer lignin model compound bearing both β-O-4 and β-β bonds through a multistep reaction. In order to do so, we started with sinapyl alcohol as the starting monomer and through a series of controlled reactions, a G-(β-O-4’)-S-(β-β’)-S-(β-O-4’)-G tetramer lignin model compound was successfully synthesized and purified. Higher-energy collisional dissociation (HCD) mass spectrometry was used to generate sequence-specific ions from the synthesized model compound. Based on the structural analysis, a fragmentation pathway was proposed. Our findings support our previous observations that Li<sup>+ </sup>adduct analysis of the lignin model compounds using tandem mass spectrometry shows robust fragmentation and sequence-specific fragment ions for structural elucidation. This information can serve as a guide for better understanding of lignin’s structure and can assist researchers with structural elucidation of lignin decomposition products.

Synthesis and (+) ESI-mass spectrometry based analysis of new advanced lignin model compounds

ACS Fall 2021

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