The formation of covalent linkages via the oxocarbenium intermediate in lignocellulosic biomass
Bibliographic record
Abstract
Elucidating molecular origins of plant recalcitrance is critical for developing novel and atom-efficient strategies for lignocellulosic biomass (LCB) valorization. In particular, understanding the formation of covalent, lignin-carbohydrate complex (LCC) linkages is crucial because these interactions are known to significantly contribute to plant recalcitrance. In this work, a new mechanism for the formation of LCC linkages in LCB is explored. Our proposal is based on the formation of the oxocarbenium intermediate in sugar moieties in hemicellulose and the subsequent formation of glycosidic bonds between polysaccharides and lignin. We applied density functional theory calculations to monosaccharides and monolignol molecules serving as model precursors for LCB. Namely, mannopyranose, xylopyranose, arabinofuranose, and glucopyranuronic acid were used as hemicellulose models; p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol were employed as lignin models. Computations without the presence of explicit water molecules predict the stable formation of the proposed glycosidic bonds between all lignin and all sugar models, with some exceptions for mannopyranose and arabinofuranose. Whereas including explicit water molecules showed that, for all systems, the formation of LCC bonds is more thermodynamically favourable than in the absence of water or when using implicit solvent models. In addition, the explicit solvent models indicate that hydrogen bonding between water and organic molecules promotes the formation of more stable LCC bonds. Finally, transition states and intermediates associated with the formation of oxocarbenium ions were computationally found for mannopyranose and xylopyranose, allowing us to evaluate the kinetics of LCC linkage formation for major components of hemicellulose in the secondary cell walls of plants. These results, in combination with recent experimental evidence on hemicellulose-lignin interactions in native biomass, suggest that glycosylation reactions via the oxocarbenium intermediate can occur in the secondary cell walls of plants. Specifically, the hydrated nature of the hemicellulose matrix and the proximity of lignin to hemicellulose in native LCB provides the necessary conditions for the formation of the LCC linkages proposed herein. Overall, this study provides further evidence for the formation of covalent LCC linkages in LCB.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".