The self-assembly of oppositely charged polymers provides a versatile platform to design materials for diverse applications in biology and medicine. Electrostatically-driven phase separation of oppositely charged polymers in aqueous solution gives rise to the formation of a polymer-rich phase called a polyelectrolyte complex (PEC). PECs can be in the form of liquid droplets (complex coacervates) or amorphous solid precipitates. Unlike synthetic polymers, peptides are good candidates for developing tailor-made formulations and structure-property relationships due to their biocompatibility, precise control over sequences, and ability to program hydrogen bonding interactions. However, little is known about the effect of combining additional molecular interactions with electrostatic interactions in PECs. We have created a library of oppositely charged polypeptides to examine the effect of increased hydrophobic and π-interactions on polyelectrolyte complexes. Characterization of the designed polypeptides is confirmed by matrix-assisted laser desorption ionization–time of flight mass spectroscopy, circular dichroism, and proton nuclear magnetic resonance spectroscopy. First, we discuss the role of increased hydrophobicity of the peptide pairs on complex formation. By designing a new pattern of peptide sequences, we show the experimental evidence (turbidity measurements, infrared spectroscopy, and optical microscopy) that liquid complexes form by disrupting hydrogen bonds through steric hindrance and increased hydrophobicity results in higher stability of complexes against salt and temperature. Subsequently, we address the ability of these materials to encapsulate small hydrophobic molecules. Then, we evaluate the effect of π-interactions on polypeptide complexes. π-interactions together with other forces affect the amount of hydrogen bonding in polypeptide complexes, which is correlated to the phase behavior. We discuss the stability of the complexes against different ionic strengths considering the interplay between ionic and non-ionic interactions. Finally, the encapsulation efficiency of a model molecule containing π-bonds highlights the role of the cooperative effect of ionic and π-interactions on the encapsulation properties of PECs.


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Graduation Date





Leon, Lorraine


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Materials Science and Engineering

Degree Program

Materials Science and Engineering







Release Date

December 2021

Length of Campus-only Access


Access Status

Doctoral Dissertation (Open Access)