Cononsolvency of Elastin-like Polypeptides in Water/Alcohol Solutions.

Elastin-like polypeptides (ELPs) are one of the most widely-studied classes of protein material because of their lower critical solution temperature (LCST)-like thermoresponsive behavior in aqueous solutions. Here, it is shown that ELPs also exhibit cononsolvency effects, similar to many other water-soluble polymers. The effect of solvent composition on the dilute solution phase behavior of an elastin-like polypeptide is studied here in water/alcohol blends that contain 0-40 vol % methanol, ethanol, isopropanol, or 1-propanol. In all systems studied, the ELP exhibits cononsolvency behavior at low alcohol content, as indicated by a decrease in the transition temperature of the ELP. When the alcohol added is ethanol, isopropanol, or 1-propanol, the decrease in transition temperature is followed by a region of complete ELP insolubility, and, finally, the emergence of upper-critical solution transition (UCST)-like behavior. The ELP is completely soluble at all temperatures measured at alcohol contents above 40 vol %. The effect of sodium chloride on this ELP cononsolvency in water/ethanol blends was also studied. Unlike the previously studied polymer poly( N-isoropylacrylamide) (PNIPAM), ELP exhibits nonmonotonic changes in transition temperature with the addition of sodium chloride at ethanol contents that produce UCST-like transitions of the ELP. This discovery of ELP cononsolvency in water/alcohol systems introduces a new handle with which the solubility of ELPs can be tuned.