From subtle to substantial: role of metal ions on π−π interactions

Quantum chemistry calculations reveal that the subtle π−π 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 a π−π dimer compared to a single π-moiety. Considering the widespread occurrence of cation−π−π 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−π and π−π, work in concert