Theoretical binding affinities and spectroscopy of complexes formed by cyclobis(paraquat-p-anthracene) with amino acids

The electronic structures and spectroscopy of the complexes formed by cyclobis(paraquat-p-anthracene) with amino acids have been studied using the semi-empirical AM1 method and density function theory. Based on the B3LYP/3-21G optimized geometries, the energies of the complexes have been calculated at B3LYP/6-31G(d) level. The binding energies of the complexes have been obtained after the correction of basis set superposition error. The energy gaps of the complexes are decreased due to the formation of hydrogen bonds. The stretching vibration frequencies of the C-H bonds in the IR spectra of the complexes calculated with AM1 method are red shifted as compared with those of the host. The chemical shifts of the carbon atoms adjacent to the hydrogen bonds, calculated at B3LYP/3-21G level, generally move downfield, whereas those of the carbon atoms next to the nitrogen atoms move upfield. Most of the complexes are less aromatic than the host, based on the nuclear independent chemical shifts calculated at B3LYP/3-21G level.