The host–guest interactions of cucurbit[7]uril (CB[7]) as host and amphetamine (AMP), methamphetamine (MET) and their enantiomeric forms (S-form and R-form) as guests were computationally investigated using density functional theory calculations with the recent D4 atomic-charge dependent dispersion corrections. The analysis of energetic, structural and electronic properties with the aid of frontier molecular orbital analysis, charge decomposition analysis (CDA), extended charge decomposition analysis (ECDA) and independent gradient model (IGM) approach allowed to characterize the host–guest interactions in the studied systems. Energetic results indicate the formation of stable non-covalent complexes where R-AMP@CB[7] and S-AMP@CB[7] are more stable thermodynamically than R-MET@CB[7] and S-MET@CB[7] in gas phase while the reverse is true in water solvent. Based on structural analysis, a recognition mechanism is proposed, which suggests that the synergistic effect of van der Waals forces, ion–dipole interactions, intermolecular charge transfer interactions and intermolecular hydrogen bonding is responsible for the stabilization of the complexes. The geometries of the complexes obtained theoretically are in good agreement with the X-ray experimental structures and indicate that the phenyl ring of amphetamine and methamphetamine is deeply buried into the cavity of CB[7] through hydrophobic interactions while the ammonium group remains outside the cavity to establish hydrogen bonds with the portal oxygen atoms of CB[7].

Density functional theory (DFT) calculations based on the BLYP-D4 and PBEh-3c composite methods were performed for investigating the encapsulation mode of pentachlorophenol (PCP) inside the cavity of β-cyclodextrin (β-CD). Different quantum chemical parameters such as HOMO, LUMO, and HOMO–LUMO gap were calculated. Complexation energies were computed at the molecular level to provide insight into the inclusion of PCP inside the β-CD cavity. The Independent gradient model (IGM) approach was applied to characterize the non-covalent interactions that occurred during the complex (PCP@β-CD) formation. Two modes of inclusion were considered in this work (modes A and B). Calculated complexation energies as well as the changes in enthalpy, entropy, and free Gibbs energy exhibit negative values for both modes A and B, indicating a thermodynamically favorable process. Weak Van der Waals interactions and one strong intermolecular hydrogen bond act as the main driving forces behind the stabilization of the formed most stable complex. This study was carried out to explore the potential use of the β-CD as a host macrocycle for sensing and capturing pentachlorophenol.