The interaction of water with cellulose stages many unresolved questions. Here 2H MAS NMR and IR spectra recorded under carefully selected conditions in 1H-2H exchanged, and re-exchanged, cellulose samples are presented. It is shown here, by a quantitative and robust approach, that only two of the three available hydroxyl groups on the surface of cellulose fibrils are exchanging their hydrogen with the surrounding water molecules. This finding is additionally verified and explained by MD simulations which demonstrate that the 1HO(2) and 1HO(6) hydroxyl groups of the constituting glucose units act as hydrogen-bond donors to water, while the 1HO(3) groups behave exclusively as hydrogen-bond acceptors from water and donate hydrogen to their intra-chain neighbors O(5). We conclude that such a behavior makes the latter hydroxyl group unreactive to hydrogen exchange with water.

During autocatalyzed steam explosion of lignocellulose, polysaccharides in the cell wall are hydrolyzed and dehydrated to form various furaldehydes. In addition to furfural, 5-methylfurfural and 2-acetylfuran were identified in condensates from autocatalyzed steam explosion of Scandinavian softwood (Norway spruce, Picea abies). The presence of 5-methylfurfural can be explained by an acid-catalyzed dehydration of 6-deoxyaldohexoses, which are known to be present in lignocellulosic biomass. However, the presence of 2-acetylfuran cannot be explained by previously published reaction mechanisms since the required substrate (a 1-deoxyhexose or a 1-deoxyhexosan) is not known to be present in lignocellulosic biomass. In model experiments, it was shown that 2-acetylfuran is formed from rhamnose and fucose upon heating in the presence of the Lewis acid Cr3+. Possible reaction pathways for the formation of 2-acetylfuran from 6-deoxyaldohexoses are suggested. This reaction can potentially enable the targeted production of 2-acetylfuran from renewable biomass feedstocks. © 2022 The Authors

The structures of water-soluble birch and beech xylans, extracted from holocellulose using dimethyl sulfoxide, were determined employing 1H and 13C NMR spectroscopy together with chemical analysis. These polysaccharides were found to be O-acetyl-(4-O-methylglucurono)xylans containing one 4-O-methylglucuronic acid substituent for approximately every 15 D-xylose residues. The average degree of acetylation of the xylose residues in these polymers was 0.4. The presence of the structural element → 4)[4-O-Me-α-D-GlcpA-(1 → 2)][3-O-Ac]-β-D-Xylp-(1 → was demonstrated. Additional acetyl groups were present as substituents at C-2 and/or C-3 of the xylopyranosyl residues. Utilizing size-exclusion chromatography in combination with mass spectroscopy, the weight-average molar masses (and polydispersities) were shown to be 8000 (1.09) and 11,100 (1.08) for birch and beech xylan, respectively.