Stabilities and spectroscopy of hydrogen bonding complexes formed by 2,4-bis(acrylamido)pyrimidines

Hydrogen bonds play important roles to living organisms containing pyrimidine-based derivatives. The electronic structures of the hydrogen bonding complexes formed by 2,4-bis(acrylamido)pyrimidine (2,4-BAAP) derivatives with 1-substituted uracil were studied using Austin Model 1 (AM1) and density function theory (DFT) methods. The UV and NMR spectra of the complexes were calculated with the INDO/CIS (configuration interaction for singlet in intermediate neglect of differential overlap) and B3LYP/6-31G(d) methods. It was shown that the complexes could be formed via the triple hydrogen bonding between two monomers owing to the negative binding energies. The binding energies of the complexes were weakened in the presence of substituents, but this weakening effect depended on the simultaneous influence of the electronic and steric effects. The binding energies of the complexes were also decreased owing to the formation of the isomeric complexes in the presence of piperidyl on 2,4-BAAP. The energy gaps of the complexes were lessened in the presence of electron-donating groups. Holes and electrons were easily injected to the complexes due to the extension of the conjugation chain. The first UV absorptions of the complexes relative to those of the parent compound were red-shifted because of the narrow energy gaps. The chemical shifts of the carbon atoms on the C=O bonds in the complexes were changed downfield.