From subtle to substantial:: Role of metal ions on π-π interactions

Quantum chemistry calculations reveal that the subtle pi-pi interactions. usually in the range 2-4 kcal/mol, will become substantially significant, from 6 to 17 kcal/mol, in the presence of metal ion. The metal ions have higher affinity toward pi-pi dimer compared to a single pi-moiety. Considering the widespread occurrence of cation-pi-pi motifs in chemistry and biology, as evident from the database analysis, we propose that the two key noncovalent forces, which govern the macromolecular structure. cation-pi and pi-pi, work in concert.