Evaluation of OH···O type hydrogen bond energy in native cellulose by quantum chemical calculations

Intrasheet interaction of native cellulose was investigated at the MP2 and DFT(B3LYP) levels of theory, employing various one-sheet crystalline models. Our MP2//DFT(B3LYP) calculations for the smallest two dimensional dimeric system possessing a short O6-H···O3' hydrogen bond and a long O6-H···O2' one indicated that the interaction energy between the two dimers (cellobiose) was 8.4 kcal/mol per one glucosyl residue. Energy contribution of the short O6-H···O3' hydrogen bond was estimated to be 5.8 kcal/mol, which was ∼70 % of the total interaction energy, on the assumption that all part of the intrasheet interaction energy was derived from the intermolecular hydrogen bond energy. Interestingly, the long O6-H···O2' hydrogen bond provided somewhat large contribution of 2.6 kcal/mol, ∼30 % of the total interaction energy. The DFT(B3LYP) method presented similar results. The DFT(B3LYP) method was then applied to larger crystalline sheet models, whose degree of polymerization was up to 8 with the chain dimension being up to 3. Their intrasheet interaction energies per one glucosyl residue did not significantly depend on the degree of polymerization and the chain dimension, which suggests that the above interaction energy can be applied to discuss the stabilization of the real native cellulose. © 2020 The Society of Materials Science, Japan.