Solvation Behavior of Elastin-like Polypeptides in Divalent Metal Salt Solutions.

The effects of CaCl 2 and MgCl 2 on the cloud point temperature of two different elastin-like polypeptides (ELPs) were studied using a combination of cloud point measurements, molecular dynamics simulations, and infrared spectroscopy. Changes in the cloud point for the ELPs in aqueous divalent metal cation solutions were primarily governed by two competing interactions: the cation-amide oxygen electrostatic interaction and the hydration of the cation. In particular, Ca 2+ cations can more readily shed their hydration shells and directly contact two amide oxygens by the formation of ion bridges. By contrast, Mg 2+ cations were more strongly hydrated and preferred to partition toward the amide oxygens along with their hydration shells. In fact, although hydrophilic ELP V 5 A 2 G 3 was salted-out at low concentrations of MgCl 2 , it was salted-in at higher salt concentrations. By contrast, CaCl 2 salted the ELP sharply out of solution at higher salt concentrations because of the bridging effect.