Effect of stepwise microhydration on the imidazolium···indole interaction

The importance of non-covalent interactions has been demonstrated in many cases. Significant examples within the scope of biomolecular systems are widely known, such as ligand-receptor interactions, protein folding or molecular recognition. Among noncovalent interactions, those between cations and aromatic units are commonly observed between aromatic side chains such as those of Phe, Tyr, His or Trp and amino acids with side chains susceptible of protonation as Arg or Lys. In this work, a computational study has been carried out in systems formed by indole and imidazolium cation, in an attempt to model the interactions between the side chains of Trp and protonated His. The target of this study is to get insight on the geometric and energetic characteristics of this cation···π interaction, as well as quantifying the effect produced by the introduction of one water molecule in this system.