Self-discrimination of enantiomers in hydrogen-bonded dimers

The homochiral and heterochiral hydrogen-bonded (HB) dimers of a set of small model molecules (alpha-amino alcohols) have been studied by means of ab initio methods. The gas-phase calculations have been carried out with the hybrid HF/DFT B3LYP method and the 6-311 ++G** basis set. The electron density of the complexes has been analyzed using the atoms in molecules (AIM) methodology, which allows characterization of the HB interactions and additional intermolecular contacts. To take into account the water solvation effect, the polarized continuum model (PCM) method has been used to evaluate the DeltaG(solv). The gas-phase results show that the heterochiral dimers are the most stable ones for each case studied, while in solution for several cases, the relative stability is reversed and the homochiral dimers become more stable. The AIM analysis shows the typical bond critical points characteristic of the HB and additional bond critical points denoting, in this case, destabilization of intermolecular interaction as CF3...F3C and CH3...H3C contacts.