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

Abstract

Dispersion corrected M06-2X based density functional theory has been employed to characterize electronic structures, UV–visible and 1H 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⋯O interactions. Furthermore the ABZ and CBZ complexes possess N–H⋯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⋯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 1H NMR chemical shifts has been simulated through the self-consistent reaction field theory. Calculated 1H 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 196nm) in UV–visible spectra to longer wavelengths.