Solvation counteracts coulombic repulsion in the binding of two cations to a model hexapeptide.

In the present paper we employ a series of dicationized (K(+)& C(+); C = H, Li, Na, or K) hexapeptide (G(6)C(+)K(+)(x), x = 1, 2, … or 5) complexes in gas phase (GP) and aqueous phase (AP) as models to mimic the key characteristics of the real biosystems. An interesting phenomenon is observed that the binding properties of K(+)(x) to G(6)C(+) species change in the two phases, i.e., those positive binding energies in the GP become negative ones in the AP. Then we probe the origin of property change of the binding energies in the two different phases and associate these changes with some biological phenomena.