In an aqueous solution, water solvent molecules form structures around the compound present in that solution. These structures may either prevent or stimulate intermolecular interactions between solvated species such as chemical groups, whole molecules, or side chains within a receptor protein. The possible scenarios for the involvement of different kinds of groups in dimer interactions as compared to their interaction with water molecules are considered: two ions, two inverse charged groups, an ion group with a dipole (polar) group, and two dipole groups. The interaction energies favor charged groups to come into direct contact in an aqueous solution, whereas for dipole groups, the advantages of direct contact are not so pronounced. Ligands of the melatonin receptor have a weaker affinity owing to the presence of extra charged groups, thus preventing desolvation and therefore weakening the interaction of the ligand with its receptor.