Sequence Effect in the Cononsolvency of Elastin-like Polypeptides in Water, Ethanol, and Sodium Chloride Solutions

Elastin-like polypeptides (ELPs) are a family of recombinant biopolymers that offer precise sequence control. Six ELP sequences with systematically varied hydrophobicity and charge were designed to investigate how hydrophobicity and charge influence dilute solution phase behavior in 0-40 mol % ethanol and 0-200 mM sodium chloride. Both hydrophobic and hydrophilic ELPs in this study display four characteristic regimes in their phase diagrams: lower critical solution temperature (LCST)-like transitions at low ethanol concentrations, a one-phase region at low-to-moderate ethanol concentrations, upper critical solution temperature (UCST)-like transitions at intermediate ethanol concentrations, and full miscibility at high ethanol concentrations. Despite an identical overall composition with a previously studied ELP sequence, differences in sequence and molecular weight significantly impact phase behavior in ethanol/water mixtures. These results reveal both sequence dependence in the phase behavior of ELPs and universal cononsolvency behavior in uncharged hydrophobic and hydrophilic ELPs.