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Coacervation of oppositely charged macromolecules, micelles and proteins: Disproportionation and hierarchical structures
Analogous disproportionation processes lead to similarities in the structures present at incipient coacervation to those within the subsequent dense phase. Coacervation in polyelectrolyte/mixed micelle system is induced by temperature to explore structural evolution before, during and after coacervation. Assemblies of polyelectrolyte-micelle primary complexes appear to be governed by the interparticle interaction, a delicate balance between short-range attraction and long-range repulsion. Dilution-induced coacervation in opposite to self-suppression is facilitated by the presence of smaller particles in size but larger in number as a result of the favourable interparticle interaction. While dilution leads to formation of smaller particles that can phase separate easily, larger particles can achieve coacervation by increase in temperature, a greater entropy contribution. Dynamic light scattering reveals a progressive increase in aggregate size with temperature up to the phase transition at Tphi;, followed by splitting of these aggregates into respectively smaller and larger particles. The fact that the process of coacervation itself is accompanied by the expulsion of smaller aggregates to form near-neutral aggregates is known as a type of macroion disproportionation. At incipient coacervation, the transfer among soluble complexes of excess macroions to achieve near-neutrality is found to be analogous to the expulsion (with counterions) of excess macroions into dilute domains in the coacervates. The driving forces of ion-pairing and counterion release, in one-phase and dense phase states, use similar strategies of disproportionation and local charge neutralization to form analogous transient structures. The transient nature of coacervate structure is further investigated by rheology and total internal reflection microscopy in PDADMAC/BSA coacervates. While polyelectrolyte-colloid coacervates exhibit structural rearrangement in the coacervate correlated with the compositional difference between supernatant and coacervate, heteroprotein coacervation appears to have a fixed stoichiometry in both phases. The absence of disproportionation is suggested to be responsible for the highly limited conditions of pH, ionic strength I, total protein concentration Cp, and BLG:LF stoichiometry under which Lactoferrin (LF) and B-lactoglobulin (BLG) form optically clear coacervates. These constraints on conditions for pure coacervation were also attributed to the requirements for the formation of a basic primary unit, LF(BLG)4 , characterized in the supernatant and coacervate. Coacervate is characterized as a solidlike transient network of primary units embedded into a viscoelastic suspending fluid.^
Kizilay, Ebru, "Coacervation of oppositely charged macromolecules, micelles and proteins: Disproportionation and hierarchical structures" (2013). Doctoral Dissertations Available from Proquest. AAI3615426.