Pnicogen-π complexes: theoretical study and biological implications.

The energetic and geometric features of pnicogen-π complexes involving different types of aromatic rings (benzene, trifluorobenzene, hexafluorobenzene and s-triazine) and the heavier pnicogenes (ECl(3), E = As, Sb, Bi) are investigated using theoretical methods (ab initio and DFT-D3). We have analyzed how the interaction energy is affected by the π-acidity of the aromatic moieties and the pnicogen used. In addition, we have found several examples in the Protein Databank where pnicogen-π interactions are present. This likely indicates the potential use of this interaction in the design and synthesis of potential inhibitors of enzymatic reactions. Moreover, in order to know the reliability of the latest version of dispersion termed corrected DFT-D3, we have also compared the energies obtained using the ab initio MP2 method with those obtained using BP86-D3. We have also computed and analyzed the dispersion contribution to the total interaction energy in order to know if it is crucial for the favourable binding. This allows a better understanding of the physical nature of the interaction. Finally, we have used the Bader's theory of "atoms-in-molecules" to demonstrate that the electron density computed at the bond critical point that emerges upon complexation can be used as a measure of bond order in this noncovalent interaction.