Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

Electrostatic interactions encoded in the monomer sequence play an important role in the structure and function of many biomacromolecules. Ionic block copolymers (BCPs) comprise an ionizable hydrophilic segment and a non-ionizable hydrophobic segment, which can self-assemble into core-shell type structures with varying geometries (e.g., spheres, cylinders, bilayer structures, lamellae, vesicles, etc.) in selective solvents. Micellar structures can be influenced by numerous factors, including electrostatic repulsion, counterion condensation, and osmotic swelling. Polypeptoids, structural mimics of polypeptides with N-substituted glycine backbone and make them free of hydrogen bonding and secondary structures, have attracted significant interests due to their broad applications (e.g., drug delivery carrier, theragnostic agent, tissue engineering matrices, etc.). In this study, we synthesized a series of amphoteric polypeptoid BCPs with one fixed ionizable monomer in the hydrophobic segment and another ionizable monomer positioned either at the hydrophilic segment terminus or at the hydrophilic-and-hydrophobic segment junction. These BCPs formed a core-shell ellipsoidal structure in aqueous solutions and exhibited that the electrostatic interaction encoded in the polymer block sequence have a dominant effect on solution micellar structures. Furthermore, the end-group structure of the polypeptoid significantly affects the hybridization of the N-terminus nitrogen atom and enhances the crystalline interactions within the micelles. By end-capping the N-terminus of the polypeptoid BCPs, the micellar structure was rapidly transformed from ellipsoidal structure to nanosheet structure. Crystlline interactions are expected to have a pronounced effect on modulating the micellar structure. However, it remains ambiguous how the charge pattern affects the solution micellar structure. Combining small-angle scattering (SANS and SAXS) with microscopic analyses revealed that the micelles formed two sets of nanosheet structures with different dimensional sizes and predominantly formed large nanosheet structures below pKa, while small nanosheet structures became dominant above pKa. This study highlights the role of electrostatic interactions and crystalline interactions in modulating micellar structures in aqueous solutions.

Date

11-15-2023

Committee Chair

Zhang, Donghui

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Available for download on Friday, November 15, 2030

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