Proteins and synthetic polymers that undergo aqueous phase transitions mediate self-assembly in nature and in engineered material systems. Despite this widespread interest, little is known about how phase behavior of a protein is encoded in its amino acid sequence to specify lower critical solution temperature transition (LCST) phase behavior. To address this lacuna, we synthesized intrinsically disordered peptide polymers to test motifs that we hypothesized would encode phase behavior and show that, consistent with predictions, they exhibit tunable LCST behavior in physiological solutions. These data also provide heuristics to design new LCST exhibiting peptide polymers that consist of biologically active peptide repeats. A subset of the newly discovered LCST polymers also show significant thermal hysteresis in their cloud point behavior. CD studies as function of temperature suggested that the origins of hysteresis may lie in the emergence of secondary structure upon desolvation of the more hydrophobic, hysteretic blocks. To test this hypothesis, different fractions of (Ala)25 helical domains were encoded into an ELP that show no thermal hysteresis. Consistent with our hypothesis, these polymers display varying degrees of thermal hysteresis (Tt-cooling &lt; Tt-heating) that is likely driven by inter-chain hydrogen bonding of the structured domains. We have also synthesized diblock copolymers with a hysteretic and non-hysteretic block, and have found that they show temperature triggered self-assembly into rod-like nanoparticles that retain their shape upon cooling for extended periods of time. This shape memory effect strongly depends on the degree of hysteresis exhibited by the core-forming block and persists upon prolonged incubation at temperatures below the critical assembly temperature.

Discovery of a family of new LCST peptide polymers: Coacervation behavior and self-assembly

253rd National Meeting (2017)

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