LAUSR

In this work, the encapsulations of halide ions including F−, Cl−, and Br− by cyclic peptide nanocapsule as ion carrier (F−, Cl−, and Br− @(Ala4...Ala4)) were investigated using the dispersion corrected density functional theory (DFT) employing CAM-B3LYP functional and the 6–311 + G (d, p) basis set in the gas phase. The electronic binding energy (Ebind), binding enthalpy (Hbind), and binding Gibbs free energy (Gbind) for each anion were calculated and showed that the stability order of the complexes based on their calculated Ebind is F− > Cl− > Br− @(Ala4...Ala4). The calculated value of Gbind for F− @(Ala4...Ala4) was − 29.77 kcal/mol showing the formation of this complex is thermodynamically favorable while the formation of Br− @(Ala4...Ala4) is 14.35 kcal/mol which shows that the encapsulation of Br− is not possible. The calculated value of Gbind for Cl− @(Ala4...Ala4) was − 0.57 kcal/mol which shows that Cl− ion can be reversibly stored inside the nanocapsule. The NBO analysis was also performed to investigate the charge transfer between two cyclic peptides in the complexes and also between the anion and the nanocapsule. The NBO analysis showed that the strongest hydrogen bonds between two cyclic peptides are in the complex.