Encapsulation of benzimidazole derivatives within cucurbit[7]uril: Density functional investigations

Dispersion corrected M06-2X based density functional theory has been employed to characterize electronic structures, UV-visible and H-1 NMR spectra of inclusion complexes between cucurbit[7]uril (CB[7]) and biologically important guest molecules viz., benzimidazole (BZ), albendazole (ABZ), carbendazim (CBZ), thiabendazole (TBZ) and fuberidazole (FBZ). The lowest energy ABZ, CBZ, TBZ and FBZ complexes reveal partial encapsulation of the guest with benzimidazole ring bound within the host cavity through N-H center dot center dot center dot O interactions. Furthermore the ABZ and CBZ complexes possess N-H center dot center dot center dot O interactions from the carbamate substituent with ureido oxygens on the CB[7] portals. On the other hand FBZ and TBZ complexes render C-H center dot center dot center dot O interactions from the furanyl and thiazole substituent. The strength of host-guest binding follows the order: ABZ > CBZ >BZ > FBZ TBZ. Underlying hydrogen bonding interactions are analyzed through (QTAIM) approach and natural bond orbital (NBO) analyses. Effect of solvent (water) on H-1 NMR chemical shifts has been simulated through the self-consistent reaction field theory. Calculated H-1 NMR spectra revealed that aromatic protons confined within CB[7] macrocycle exhibit up-field signals as opposed to those interacting with the portals of the host in the complex relative to the isolated guest. Time dependent density functional theory (TDDFT) demonstrates that substitution on benzimidazole ring shifts its wavelength maximum (at 196 nm) in UV-visible spectra to longer wavelengths. (C) 2015 Elsevier B.V. All rights reserved.