Selective Binding of Cyclic Nanopeptide with Halides and Ion Pairs; a DFT-D3 Study

In this article, theoretical studies on the selective complexation of the halide ions (f^-, cl^- and br^-) and ion pairs (na^+f-, na^+cl- and na^+br^-) with the cyclic nano-hexapeptide (cp) composed of l-proline have been performed in the gas phase. to calculate the dispersion interaction energies of the cp and ions, dft-d3 calculations at the m05-2x-d3/6-31g(d) level were employed. based on the results, fand na^+f^- make the most stable complex with the cp. the dispersion interactions between the ions and the cp are small while the electrostatic interactions are a driving force for the complex formation. finally, natural bond orbital (nbo) and quantum theory of atoms in molecules (qtaim) analyses indicate that f^- makes the most stable complex with cp due to more charge transfer and stronger bond formation in comparison to other ions.