DENSITY FUNCTIONAL THEORY (DFT) AND NATURAL BOND ORBITAL (NBO) INVESTIGATION OF INTRA/INTERMOLECULAR HYDROGEN BOND INTERACTION IN SULFONATED NATA-DE COCO-WATER (NDCS-(H2O)N)

Abstract

This research aim to study the conformation, hydrogen bonding network, and stability of all possible molecular interactions between sulfonated nata-de-coco membranes with water (NDCS-(H₂O)n,n=1-5) as well as associate them with results of phosphorylated nata-de-coco reported previously, to determine the potential of proton transfer within both systems. The calculations used DFT method at the B3LYP/6-311G** level as well as NBO analysis. The strongest hydrogen bonds were found among sulfonic group in NDCS-(H₂O)₅ and the oxygen in the water molecules. The stabilization energy of NDCS-(H₂O)₅ is 98.9 kcal/mol, That is much greater than that found in NDCP-(H₂O)₅. This suggests that the NDCS was more easily to donate its lone pair and that the hydrogen bonds between sulfonic group and water molecule were stronger, so that it was easier to transfer protons to another sulfonic group than to NDCP. The energy profile showed that barrier energy was roughly 58.1 kcal/mol and 138.6 kcal/mol for NDCS-(H₂O)₅ and NDCP-(H₂O)₅, respectively. Proton transfer in NDCS-(H₂O)₅ generated a lower energy-barrier than the one in NDCP-(H₂O)₅.