Selective complexation of alkali metal ions and nanotubular cyclopeptides: a DFT study

Abstract

A density functional theory based on interaction of alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) with cyclic peptides constructed from 3 or 4 alanine molecule (CyAla3 and CyAla4), has been investigated using mixed basis set (C, H, O, Li+, Na+ and K+ using 6-31+G(d), and the heavier cations: Rb+ and Cs+ using LANL2DZ). The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP and CAM-B3LYP functionals. The order of interaction energies were found to be Li+ > K+ > Na+ > Rb+ > Cs+ and Li+ > Na+ > K+ ≫ Rb+ > Cs+, calculated at CAM-B3LYP level for the M/CyAla3 and M/CyAla4 complexes, respectively. Their selectivity trend shows that the highest cation selectivity for Li+ over other alkali metal ions has been achieved on the basis of thermodynamic analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* of alkali metal cations.