Becke Surface Studies on the Interaction Mechanism

We have presented a benchmark study of binding energies for dioxin-imprinted polymer 11 complexes. A density functional theory (DFT) approach was used for screening the polymerization 12 precursors in the rational design of molecularly imprinted polymers (MIPs). The 13 tetrachlorodibenzo-p-dioxin (TCDD) was taken as an imprinted molecule. The geometry 14 optimization, natural bond orbital (NBO) charge, and molecular electrostatic potential (MEP) of 15 TCDD and AM were studied at the M062X level and 6-31g (d,p) belonging to one of the hybrid 16 density functional theories. The results of MEP and NBO charge analysis were comparable. Among 17 functional monomers: acrylamide (AM), methacrylic acid (MAA), itaconic acid (IA), and 4-Vinyl 18 pyridine (VP); acrylamide (AM) was confirmed as the best functional monomer, because the 19 strongest interaction (the maximum number of hydrogen bonds and the lowest binding energy) 20 occurs between TCDD and AM. The stability property was excellent when the ratio of TCDD and 21 AM was 1:4. The polarizable continuum model (PCM) was used for solvent calculations. 22 Computational results showed that acetonitrile plays an important role in the MIP formation, as it 23 seems to control the size and the shape of the cavity. The atoms in molecule (AIM) and Becke 24 surface method have also been applied to understand the nature and strength of the hydrogen 25 bonding interactions in complexes. TCDD-AM complexes were found involving C-O···Cl and 26 N-H···Cl hydrogen bonds. Good correlations have been established between hydrogen bond 27 lengths versus AIM topological parameter like electron density (ρ (r)) and its Laplacian (▽2ρ (r)) at 28 the bond critical points. On ground of theoretical results, a series of MIPs were synthesized. The 29 MIP prepared using TCDD as the template, the functional monomer (AM), and the cross-linker 30 (TRIM) in acetonitrile solvent exhibited the highest adsorption capacity for TCDD. The maximum 31 binding capacity of TCDD on the MIP was 3.7 μg/mg. This research work can provide a theoretical 32 reference for the fabrication and characterization of novel TCDD-MIPs for environmental 33 applications. 34