Molecular Simulations to Understand the Moisture, Carbon Dioxide, and Oxygen Barrier Properties of Pectin Films.

Density functional theory and molecular dynamic simulations were used to understand the microscopic-level interactions of pectin-based thin films with moisture (H2O), carbon dioxide (CO2), and oxygen (O2). Galacturonic acid (GA), which forms ~65% of the smooth region of pectin polymer, was chosen for the current study. The electrostatic potential and Fukui function maps indicate that oxygen atoms of -OH groups of GA are the most reactive sites for electrophilic attack and hydrogen atoms on the carboxylic group (-COOH) are the reactive sites for nucleophilic attack. The GA molecule has shown strong interaction via hydrogen bonding with H2O (E= ~ 40 kJ/mol) followed by CO2 (E = ~ -13 kJ/mol). Nucleophilic O2 showed insignificant interaction with GA. Surface interaction, adsorption, and diffusion of sorbate molecules on the GA film followed the order of H2O >CO2 > O2. Molecular interaction studies provided atomistic insights into the weak moisture and high gas barrier properties of pectin films.