Structure-based rational design, synthesis, crystal structure, DFT and molecular docking of 1,4-benzene dicarboxamide isomers with application as hardeners

Abstract

N,N′-Di-n-propyl (nPA) and N,N′-di-iso-propyl 1,4-benzene dicarboxamides (iPA), two structural isomers, have been successfully synthesized through aminolysis of poly(ethylene) terephthalate (PET) waste under catalyst free and ambient conditions. The compounds were characterized by elemental analysis, UV-visible spectroscopy, FTIR, ¹H-NMR, ¹³C-NMR, mass spectrometry, Raman spectroscopy and SEM/EDX analysis. Single crystals of the isomers were grown in dimethylsulfoxide (DMSO) and analyzed through single crystal XRD to gain insight into the crystal structure of the compounds (bond lengths and bond angles). An ab initio Density Functional Theory (DFT) study has been executed at B3LYP (Becke's three parameter functional and Lee–Yang–Parr functional) using the 6-31G basis set to investigate the physical parameters and for theoretical calculation of crystal structures. The vibrational frequencies were optimized by DFT and were found to be in close agreement with the experimental vibrational frequencies. The isomers crystallize in triclinic systems and the bond lengths and bond angles obtained from DFT calculations were in agreement with single crystal experimental data. The thermal characteristics of the derivatives were studied through TGA/DTA and DSC. The antimicrobial activity of the two isomers was assessed through molecular docking study with target proteins sterol 14 α-demethylase and glucosamine-6-phosphate synthase. In order to validate isomers as hardeners for epoxy systems, curing kinetic parameters were determined based on the isothermal method using the DSC823^e kinetic software.