Structural, thermodynamic, and kinetic analysis of CO2 binding with cucurbiturils (CB[4], CB[5], CB[6]): A DFT computational study

Abstract

The adsorption characteristics and structural dynamics of CO₂ within the cavities of three cucurbiturils—CB[4], CB[5], and CB[6]—have been examined using DFT calculations, specifically APF-D and ωB97XD functionals with the 6-31+G(d) and aug-cc-pVTZ basis sets. The CO₂ adsorption configurations reveal two minimal-energy poses: a vertical alignment at the entrance and a horizontal alignment at the center of the host molecule. The quantum chemical results suggest a stronger affinity for CO₂ adsorption in the larger cucurbiturils compared to their smaller counterparts. The strongest interaction energy among all binding sites is observed for CO₂ located at the portal of CB[5], with an interaction energy of approximately −40 kJ/mol. At the center of host molecules, CB[6] demonstrates the strongest attractive energy toward CO₂ and achieves the highest adsorption rate. Conversely, CO₂ capture in smaller cucurbiturils, such as CB[4], is less effective due to their smaller cavity size. The encapsulation efficiency follows the trend CB[6] > CB[5] > CB[4]. The interaction between the host and guest is identified as van der Waals, as indicated by natural bond orbital (NBO) analysis.