Chemical Depolymerization of Recycled PET to Oxadiazole and Hydrazone Derivatives: Synthesis, Characterization, Molecular Docking and DFT study

Abstract The extensive use of polyethylene terephthalate (PET)-based packaging materials has increased the desire to focus on their recycling. In this study, a chemical depolymerization method is proposed for synthesizing terephthalic dihydrazide (TDH) via the aminolysis of post-consumed PET. TDH is further used as a precursor along with 2-chlorobenzoic acid and 4-hydroxybenzoic acid to synthesize aromatic compounds, such as two oxadiazole derivatives, with potential applications. TDH is also used along with 2-chlorobenzaldehyde, benzaldehyde, and 4-hydroxybenzaldehyde to synthesize three hydrazone derivatives. The five compounds (the oxadiazoles and hydrazones) are well characterized by ultraviolet–visible (UV–Vis) spectroscopy, elemental analysis, fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and thermal analysis. The theoretical parameters of the compounds are studied by abinitio density functional theory (DFT). The DFT calculations are conducted at Becke’s three parameter and Lee–Yang–Parr(B3LYP) functional level of calculation with 631-G basis set. Moreover, several thermodynamic parameters at the ground state, such as the point group symmetry, dipole moment, and vibrational frequency, are calculated. The study of molecular docking of the synthesized compounds with target proteins (glucosamine-6-phosphate synthase (GlcN-6-P) and sterol 14α-demethylase (CYP51)) is conducted. Further, different parameters, such as the binding energy (BE), inhibition constant, internal energy, total intermolecular vander Waals forces, unbound energy, and hydrogen bond energy, are calculated. The three of the synthesized compounds are evaluated for antifungal and antibacterial activities using agar well diffusion method. The study of such compounds can offer a good prospective as potential antimicrobial and antifungal leads.