Endohedral gas adsorption by cucurbit[7]uril: a theoretical study

Abstract

The selectivity of cucurbit[7]uril (CB[7]) towards adsorbing a series of 14 molecules encompassing four hydrocarbons (C₂H₂, C₂H₄, C₂H₆, and CH₄), diatomic molecules of halogens (F₂ and Cl₂), nitrogen oxides (NO₂ and NO), carbon oxides (CO₂ and CO), SO₂, H₂S, N₂, and H₂ is explored via a density functional theory based study. CB[7] is noted to have high selectivity towards adsorbing SO₂ over the other considered molecules, highlighting its probable utility to separate SO₂ from flue gas or other gas mixtures containing these molecules. The nature of bonding is deciphered via the computations of non-covalent interaction indices and energy decomposition analysis. Although in all cases the dispersion interaction turns out to be the most dominating contributor in stabilizing these complexes, the electrostatic contribution is also considerable. In fact, the combined effect of these two energy terms in SO₂@CB[7] is responsible for the obtained selectivity.