Probing the influence of solvent effect on the lithium ion binding affinity of 12-crown-O3N derivatives with unsaturated side arms: A computational study

Abstract

Molecular structures of crown ether derivatives play a crucial role in complexing and transporting alkali metal ions such as lithium ion. The complexation of such ions take place in solution, hence it is important to examine the complexation behavior of host systems in solution. We have investigated employing quantum chemical calculations the stable conformations of 12-crown-O3N derivatives with unsaturated side-arms and its corresponding Li+ ion complexation in low polar to high polar solvent medium. The General Gradient Approximation (GGA) using PW91 functional with DNP basis set calculated results show that the side-arms contribute via cation-π interaction in the complexation of lithium ion with the receptor molecules 2 and 3 quite effectively in the gas phase and in low polar solvent medium (CHCl3). The vinyl and acetylene groups attached to the receptor molecules are away from the cavity of the crown ether, however, orients toward the cavity while complexing with the lithium ion. The auxiliary effect of such side-arms to augment the binding affinity of Li+ ion is reduced in the high polar solvent medium. The side-arms also orient away from the complexed Li+ ion in relatively more polar solvents. These calculated results indicate that the complexing ability of aza-crowns toward the Li+ ion can be enhanced with the unsaturated side-arms in low polar solvent medium, which however, is less effective in more polar mediums.