Lignin–carbohydrate complexes (LCCs) are covalent assemblies that contribute substantially to biomass recalcitrance, yet their tissue-dependent structural diversity in softwood and their fate during oxidative depolymerization remain insufficiently understood. In this exploratory study based on one larch tree, MWL and LCC-enriched fractions were sequentially isolated from the heartwood, sapwood, and bark of larch and characterized by FT-IR, UV–vis, GPC, TG/DTG, and 2D HSQC NMR. Clear tissue specificity was observed. Among the MWL fractions, HMWL showed the highest β-O-4 content (77.5%), whereas among the LCC fractions, BLCC exhibited the highest phenyl glycoside (PhGlc) content (5.4%). The LCC fractions possessed larger molecular weights than the corresponding MWLs, and an apparent positive relationship was observed between β-O-4 abundance and molecular weight across tissues, with HLCC showing the highest apparent molecular weight among the isolated LCC-rich fractions. To probe oxidative structural evolution, SLCC was selected as a representative substrate because of its relatively abundant LCC linkages and typical lignin interunit distribution. Under optimized conditions over H₃PMo₁₂O₄₀ in methanol/water (8:2, v/v) at 140 °C for 2 h, the monomer yield reached 9.1 wt%. HSQC analysis of residual solids after mild and severe treatments indicated progressive loss of carbohydrate-associated signals and LCC-related correlations, together with substantial depletion of lignin side-chain signals. These observations provide an exploratory, spectroscopically based description of the transformation of a representative sapwood LCC fraction under oxidative conditions. • Larch LCCs exhibited distinct tissue-dependent structural features. • Heartwood MWL showed the highest β-O-4 content. • Bark LCC showed the highest phenyl glycoside content. • SLCC underwent stepwise oxidative disassembly under H 3 PMo 12 O 40 /O 2 .
Shan et al. (2026) studied this question.