HOMO-LUMO energy interactions between endocrine disrupting chemicals and ionic liquids using the density functional theory: Evaluation and comparison

Extraction of endocrine disrupting chemicals such as pentachlorophenol [PCP] and pthalic acid [PA] using ionic liquids (IL's) as solvents has been found to be effective for wastewater treatment. New insights are required to explain the interaction between IL's and organic compounds by quantum chemical descriptors. In this work, the parameters like global hardness and softness, chemical potential, electronegativity and electrophilicity index, HOMO/LUMO energy, and HOMO-LUMO energy gap were predicted for systems such as: [PCP] + [C4DMIM][PF6] and [PA] + [C4DMIM][PF6] and individual species. Initially geometry optimization was carried out using the DFT based B3LYP/6-31G* method for individual molecules of [PCP], [PA], cations, anions and [PCP]\[PA] + IL complexes. Thereafter, the quantum chemical descriptors were predicted and analyzed. In addition, the experimental and theoretical 1H NMR chemical shifts of [PCP] + [C4DMIM][PF6] and [PA] + [C4DMIM][PF6] were also carried out to benchmark the predictions. The highest and lowest HOMO-LUMO energy gap was obtained for [PCP] + [C4DMIM][PF6] (0.146 eV) and [PA] + [C4DMIM][PF6] (0.0597 eV) respectively. Charge distribution using the CHELPG (CHarges from Electrostatic Potentials using a Grid based method) analysis was also studied in detail.