Theoretical Study on Amino Acid-Based Ionic Pairs and Their Interaction with Carbon Nanostructures

Abstract

Quantum chemistry methods were used to analyze the properties of ionic pairs formed by combination of the 1-ethyl-3-methylimidazolium cation with anions derived from alanine, glycine, serine, and phenylalanine amino acids, which appear in the corresponding ionic liquids. Anion–cation pairs were studied from structural and energetic viewpoints using density functional theory together with the use of natural bond orbital and atoms in a molecule approaches. Interactions of the mentioned ionic pairs with carbon nanostructures carried out with graphene sheets and single-walled carbon nanotubes, with ions placed on the outer surface and when confined inside the nanotube, were analyzed from first principles. Interaction energies, density of states, and charge density allow inferring the mechanism of interaction between the ion pairs and graphene or carbon nanotubes