Computational Unravelling of the Role of Alkyl Groups on the Host-Guest Complexation of Pillar[5]arenes with Neutral Dihalobutanes

摘要

Density Functional Theory (DFT) calculations have been carried out to understand the electronic structure and non-covalent interactions within host-guest complexes between 1,4-dihalobutanes (DHBs) and alkylated pillar[5]arenes (P5 A). Binding energies show that the propyl substituted P5 A are found to have greater binding abilities than that of P5 A with smaller alkyl chains. Among the halogens, dibromobutane is found to have higher binding energy compared to difluoro and dichloro butanes respectively. Contribution of different molecular units towards the frontier molecular orbitals has been studied to gain insights into the role of each segment at the molecular level. Electrostatic potential maps are examined to draw clues on the nature of active sites for the inclusion phenomena. Noncovalent interactions (NCI) present in these host-guest complexes are addressed from NCI analysis based reduced density gradient method. In order to characterize these weak interactions, Bader's Quantum Theory of Atoms In Molecules (QTAIM) analysis is utilized. Our results reveal that though the hydrogen bonding patterns in P5 A inclusion complexes are collapsed upon alkylation, a new set of X-H-C interactions stabilize these DHBs along with other C-H-π interactions in the alkylated P5 A inclusion complexes. Overall, the present study sheds light on the importance of the alkyl chain and handling non-covalent interactions carefully to tune the binding ability of P5 A.