Theoretical binding affinities and spectroscopy of complexes formed by cyclobis(paraquat-p-anthrancene) with some pharmaceutical molecules

Theoretical investigation on the stabilities and spectroscopic properties of the complexes formed by cyciobis(paraquat-p-anthracene) with pharmaceutical molecules were performed using the semi-empirical PM3 and B3LYP/3-21G methods. Based on the B3LYP/3-21G optimized geometries, the energies of the complexes were calculated at B3LYP/6-31G(d) level. The binding energies of the complexes were computed after the correction of basis set superposition error (BSSE). The energy gaps of the complexes are decreased due to the formation of the hydrogen bonds. The stretching vibrations of the C-H bonds adjacent to the hydrogen bonds in the IR spectra of the complexes calculated with PM3 method are red-shifted compared with those of the host. The chemical shifts of alpha-C and beta-C atoms in the complexes calculated at B3LYP/3-21G level are shifted downfield due to the formation of the hydrogen bonds and the electron-withdrawing effect of the nitrogen atoms. The aromaticities of the complexes are improved because of the enlargement of the conjugation system and the overlap of electron cloud based on the nuclear independent chemical shifts (NICS) calculated at B3LYP/3-21G level.