Host–guest binding selectivity of ethylated pillar[5]arene (EtP5A) towards octane, 1,7-octadiene, and 1,7-octadiyne: a computational investigation

Host–guest binding selectivity of the perethylated pillar[5]arene (EtP5A) macrocycles with aliphatic modified hydrocarbons, i.e., octane, 1,7-octadiene, and 1,7-octadiyne as guests, has been investigated computationally employing molecular docking simulations. Density functional theory (DFT) investigations were also performed on these host–guest complexes using the dispersion-corrected approach BLYP-D3(BJ)/TZP/COSMO calculations as implemented in the ADF program and two dispersion-corrected density functionals, ωB97XD and B97D, along with the 6-311G* basis set, coupled with the PCM solvation model as implemented in the Gaussian software. We performed analysis of the frontier molecular orbitals (FMO) and natural bond orbitals (NBO), energy decomposition analysis (EDA), and noncovalent interaction (NCI-RDG) analysis. The study sheds light on the structures and binding energetics of EtP5A with the above-mentioned guests as well as on the physicochemical nature of the noncovalent interactions involved in these host–guest inclusion complexes. Based on the docking simulations, the EtP5A host revealed slightly better binding ability in the complex with the alkyne guest than with the octane and alkene, as corroborated by the EDA analysis. The results showed that the complexation of EtP5A with the hydrocarbons is mainly governed by the interplay of electrostatic interactions and dispersive noncovalent interactions. These results agree well with NCI-RDG and NBO analysis showing that host–guest binding interactions result predominantly from electrostatic C-H···π and van der Waals interactions, the H-bonding being weak or not observed. The results obtained using different computational methods were found to be in good agreement and complementary.