Ab-initio study on the covalent nature of hydrogen bonding in cellobiose

In this paper, a detailed ab-initio study on molecular interactions of cellobiose is presented by employing density functional theory (DFT) at the M06-2X-D3/6-31+G(d) level of theory. It is well known that hydrogen bonding plays a vital and dominating role in the dissolution of cellobiose. To understand the nature of H-bonding at the molecular level, we have considered the following solvents: water, methanol, acetate ([CH3COO](-)) propanoate ([CH3CH2COO](-)), thioglycolate ([HSCH2COO](-) and alaninate ([Ala](-)). The interaction energy, quantum theory of atom in molecules (QTAIM) analysis, natural bond orbital (NBO) and symmetry-adapted petrubation theory (SAPT0) were performed on the cellobiose-solvent complexes to get insights into the nature of H-bonding in cellobiose. It is shown that the [CH3COO](-) ion breaks the existing intra-molecular interactions in cellobiose and forms new inter-molecular interactions with it.The computed interaction energy for [cellobiose-solvent] complexes is in the following order: [CH3COO](-) > [CH3CH2COO](-) > [HSCH2COO](-) > [Ala](-) > methanol > water, which is in agreement with the experimental solubility observations. The QTAIM topological parameters indicate the polar covalent character of the [Cellobiose - acetate](-) complex, which is further confirmed by the calculated hydrogen bond energy. Furthermore, the energy components from SAPT0 calculations display that while the interaction energy is primarily dominated by the electrostatic interactions, induction force also plays a significant role, reconfirming the covalent character of the associated H-bonds. Overall, these results have profound implications on the understanding of H-bonding and dissolution of cellobiose at the molecular level.