A computational study on the complexation of Bisbenzimidazolyl derivatives with cucurbituril and cyclohexylcucurbituril

The binding properties of 1,ω-bisbenzimidazolyl derivatives with cucurbit[6]uril (Q[6]) and cyclohexanocucurbit[6]uril (Cy6Q[6]) host, for 1:1 stoichiometry, have been studied using density functional theory. The distance between the two benimidazole acidic hydrogen’s along with the flexible butyl spacer group play a vital role in the complexation with host. The energetic analysis exhibits strong complexation ability of guests with Q[6] than Cy6Q[6] host. The computed enthalpy and free energy change were negative indicating the encapsulation process to be spontaneous and thermodynamically favorable and enthalpy driven. The global reactivity descriptors based charge transfer calculations show that charge transfer occurs from the guest to host molecule which was supported by the electron density difference map. The main factors for the higher stability of stable complex was the presence of C–H····O=C hydrogen bonding interactions in addition to the weak C···O, C···N, N···O, C···H, H···N type of interactions. AIM topological parameters and NCI analysis reveals the existence of weak interaction, mainly of electrostatic in nature and more number of hydrogen bonds are present in stable complexes. EDA analysis demonstrates the presence of noncovalent and electrostatic interaction with partial covalent character in the encapsulated complexes. The lower stability of Cy6Q[6] complexes compare to Q[6] are due to the presence of positive Vs,max values of cyclohexanone methylene hydrogen’s on Cy6Q[6] host.