Insight into interactions between cellulose model D-cellobiose and fourteen selected sodium salts using FT-IR, thermogravimetry, and computational analysis tools

Abstract

Understanding intermolecular interactions between cellulose and metal salts, and in particularly with anions, is crucial in development of cellulose composites and processing methods. Intermolecular interactions between cellulose model compound D-cellobiose and 14 sodium salts were evaluated using Fourier-Transform Infrared (FT-IR) spectroscopy, thermogravimetric (TG), and computational analysis tools. In FT-IR, shifts in 10 distinct bands in the D-cellobiose spectra were monitored to evaluate interactions between D-cellobiose and sodium salts. Na₂B₄O₃ and Na₃PO₄ caused the highest total shifts of 61.85 and 34.08 cm⁻¹, respectively. Mixing with salt caused lowering the initial decomposition temperatures in 10 out of the 14 salts. In density functional theory (DFT) study, Na₂B₄O₇ and D-cellobiose mixture showed negative binding energies of −11.18, −25.3, −30.9, and −12.2 kJ/mol in approaching α- and β-D-cellobiose from up and down faces. In addition, FT-IR data showed the strong interaction between borate anion and carbohydrate, where mixing Na₂B₄O₇ with D-cellobiose resulted in the largest total shift of 61.85 cm⁻¹ in the ten IR bands monitored. The strong interactions between Na₂B₄O₇ and D-cellobiose were explained as a result of Lewis acidity of boron, as well as multiple B and O atoms present in the anion and strong hydrogen bonding and dipolar interactions between B and O atoms.