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Author ORCID Identifier

https://orcid.org/0000-0002-2586-2470

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemical Engineering

Year Degree Awarded

2020

Month Degree Awarded

May

First Advisor

Sarah Perry

Subject Categories

Biochemical and Biomolecular Engineering | Polymer Science | Thermodynamics

Abstract

Complex coacervation is a liquid-liquid phase separation driven by the complexation of oppositely charged polyelectrolytes. The resulting coacervate phase has been used for many applications, such as underwater adhesives, drug delivery, food and personal care products. There also has been increasing interest in coacervate-like droplets occurring in biological systems. The majority of these “membraneless organelles” involve a combination of intrinsically-disordered proteins and RNA, and phase separate due to long-range charge effects and short-range hydrophobic effects. While evolution has optimized the self-assembly of these types of biological polymers, our ability to design such materials remains limited, in part because the relevant interactions that occur over a wide range of different length scales. The goal of this research is to establish molecular-level design rules as to how chemical sequence can modulate the formation and properties of complex coacervates. While studies to date have focused on the effect of parameters such as the charge stoichiometry, temperature, pH, salt concentration, stereochemistry, polymer architecture, and the density of charges present, the ability to pattern the sequence of charges and other chemistries has been rarely studied. However, polypeptides represent a model platform for the synthesis and study of polyelectrolytes with precisely controlled polymer architecture and sequence patterning at the molecular level, while retaining relevance to a variety of biological, medical, and industrial applications. Experimental measures such as turbidimetry and optical microscopy, coupled with isothermal titration calorimetry were used to study how variations in the patterning and overall fraction of charged groups along the polymer affect coacervate phase behavior. Increasing the number of charged residues increased the salt resistance and the size of the two-phase region. More interestingly, a comparison between polypeptides with the same overall charge fraction, but different periodic repeating patterns of charged monomers showed an increase in coacervate stability with increasing charge block size. Thermodynamic data, coupled with insights from simulation showed that the increase in stability was entropic in nature, resulting from differences in the one-dimensional confinement of counterions along the patterned polymer. We have also explored arbitrary sequences, hydrophobicity, and the identity of salt, as well as the self-coacervation of polyampholytes.

Available for download on Saturday, May 08, 2021

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