Computational simulation study on the anion recognition properties of functionalized tetraphenyl porphyrins
The anion recognitions of tetra-(2-formamido) phenyl porphyrin (APP), tetra-(2-ureido) phenyl porphyrin (UPP), and their zinc derivatives (ZnAPP and ZnUPP) to three anions (Cl(-), H2PO4 (-), CH3COO(-)) were studied using quantum mechanical calculations (QM) and molecular dynamics (MD) simulations. The density functional theory (DFT) calculations at M06-2X/6-31G (d, p) level indicated that the anion recognition ability of ZnAPP was better than that of APP, and the anion selectivity was in the order Cl(-) < H2PO4 (-) < CH3COO(-). The selectivity trends for ZnUPP and UPP were found to be H2PO4 (-) < Cl(-) < CH3COO(-). The structures, thermodynamic properties, and recognition mechanisms were discussed in detail. The 2 ns MD simulations were then carried out for anion@ZnAPP and anion@ZnUPP complexes in mixed solvent DMSO/water. The MD simulation results showed that anion@ZnUPP complexes exhibited higher stability than anion@ZnAPP, which was in good agreement with QM results. H-bonds formed between the anions and the side-chains of receptors, and zinc coordination bonds with anions contributed significantly to the stability of complexes. The anion selectivity of ZnAPP and ZnUPP in the solvent phase were also discussed and compared with those in the gas phase.