Electronic and topological analyses of C–O bonds in carbohydrates and lignin-carbohydrate complexes: An atomistic understanding of refractory molecules in agro-industrial waste

Theoretical calculations were employed to investigate carbohydrates and model molecules representing lignin-carbohydrate complexes (LCCs). These complexes exhibit resistance to chemical transformation due to specific C–O chemical bonds, being a part of certain agro-industrial waste. Enthalpy values for C–O bonds at different positions in carbohydrates unveiled distinct stabilities. Calculations of bond orders and topological properties were performed to better understand the properties of carbohydrates. Model molecules of LCCs were also analyzed to explore primary lignin-carbohydrate (LC) linkages. The enthalpy values of C–O bonds were found to be closely tied to the functional group nature in LCCs—ether, ester, or aromatic bonding. Bond orders revealed crucial features influencing the stability of these complexes. Particularly noteworthy, topological properties unveiled the covalency inherent in the C–O bond within specific LC linkages, contributing to the refractory nature of these complexes. This study provides analytical insights into the recalcitrant characteristics of LCCs.