The major role of London dispersion interaction in the assembly of cellulose, chitin, and chitosan

Noncovalent interactions are vitally important to understand the structural stability and molecular assembly of cellulose and its analog molecules. Using density functional theory in conjunction with three popular generations of dispersion correction (D2, D3, D4), we systematically estimate the strength of inter-chain interaction for several β-1,4-linked crystalline polysaccharides (cellulose Iα, Iβ, II, III I , α-chitin, β-chitin, chitosan) and their building block monomers (glucose, cellobiose). Switching on and off dispersion correction and combining the calculation of condensed and isolated chains allow the extraction of the intra- and inter-chain London dispersion interactions and the inter-chain electrostatic interaction. Regardless of the generations of dispersion correction and allomorphs, the estimated inter-chain London dispersion interaction is 45 ~ 74 kJ/mol per pyranose ring comparable to the inter-chain electrostatic interaction (47 ~ 88 kJ/mol). The upper limit of the strength of inter- or intra-chain hydrogen bonds is estimated to be 27 ~ 50 or 21 ~ 53 kJ/mol, respectively, based on energy profiles of hydroxy rotation. Our work quantitatively highlights that it is the London dispersion interaction rather than the hydrogen bonding interaction dominating in the tight assembly of polymer chains for β-1,4-linked crystalline polysaccharides, regardless of the crystal allomorph and types as well as the generations of dispersion correction of DFT. Thus, London dispersion interaction should be preferentially considered during their deconstruction, defibrillation, or dissolution processes.