Comparing the ion affinity of two ionophores: Theoretical study of alkali earth metal ion-nano tubular cyclic peptide complexes

The theoretical study of ion affinity of cyclic peptides containing l-proline (Cyclo(l-Pro)3 and Cyclo(l-Pro)4) with alkali earth metal ions has been carried out using the DFT methods. The metal binding affinity of these cyclic peptides has been evaluated using the binding energy. For both peptidic systems, the binding energies increased as Be2 + > Mg2 + > Ca2 + > Sr2 + > Ba2 + in the gas phase. The orbital nature of different interactions between the metal cations and the cyclic peptides has been analyzed by means of NBO. The ion affinity of both cyclic peptides in bulk water has been considered, too. In addition, the micro-solvation effect on the ion affinity of both cyclic peptides has been studied in the gas and bulk water phases. The dispersion corrected binding energies of complexes calculated and compared with uncorrected results.