Micelas de polieletrólitos: caracterização, propriedades e aplicações para encapsulamento de enzimas

Author(s)

Júlia Bonesso Sabadini

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2024-06-06

Examining board members

Watson Loh; Leandro Ramos Souza Barbosa; Juliana da Silva Bernardes; Denise Freitas Siqueira Petri; Fernando Luis Barroso da Silva

• Advisor: Watson Loh; Sarah Louise Perry

Abstract

Complex coacervates result from an associative liquid-liquid phase separation commonly involving oppositely charged polyelectrolytes. When this associative interaction occurs between a charged neutral diblock copolymer and an oppositely charged homopolymer, a nanometric core-shell aggregate called Complex Coacervate Core Micelle (C3M) is formed. Recent studies have addressed the issue of C3M’s thermodynamic or kinetic stability, without a clear consensus yet. To further investigate this question, we studied C3Ms formed by the combination of poly(diallyldimethylammonium) and the poly(acrylamide)-b-poly(acrylate) copolymer, using different preparation routes and evaluating the structure of the resulting C3Ms over time. The results suggest that it is an aggregate in the equilibrium condition. In this way, the thermodynamic and kinetic stability frontier was also evaluated through the variation of structural parameters and external conditions such as the length and density of the neutral block in the shell and the ionic strength of the medium. It was observed that by decreasing the shell density, the C3Ms reached a metastable state, eventually resulting in phase separation. The stability boundary of C3M was also reached above the NaCl concentration of 100 mmol L?1, obtaining a rapid increase in the hydrodynamic radius of the aggregates. The nature of the neutral block was also assessed by substituting the polyacrylamide neutral block with a copolymer containing a poly(ethylene oxide) (PEO) block. Similar to ethoxylated surfactant micelles, the thermoresponsive properties of C3Ms with PEO shells were investigated based on the packaging of the polymeric species and the morphology of the aggregate. It was observed that the increase in the size of C3M with temperature was a consequence of a morphological transition: from spherical to elongated aggregates. However, these structural changes were dependent on the length of the PEO block. Thus, despite differences in the driving forces between classical ethoxylated surfactant micelles and coacervated micelles, our results suggest that the critical packing parameter is universally applicable in both systems. Considering the various structures that could be obtained, their stability, and the resemblance of coacervates' properties to the interior of cells, C3Ms were utilized as a platform to encapsulate a model protein. In this context, this work suggests the potential to shed light on the biophysical mechanisms through which cells may regulate protein absorption in coacervate-like granules. All systems were primarily investigated using light scattering and low-angle X-ray scattering measurements, along with transmission electron cryomicroscopy and confocal microscopy. Additionally, since the intracellular space contains various proteins and nucleic acids, the formation of subcompartments with specific species must be related to different affinities. In this context, we propose a novel approach to understanding polyelectrolyte complex strength based on affinity, specifically the association constant between the polyelectrolyte species involved obtained by Isothermal titration calorimetry (ITC). By employing peptides with systematically controlled size, sequence, and composition, we offer a perspective on comprehending the interaction strength between oppositely charged polyelectrolytes and the formation of multiphase coacervates (AU)

• FAPESP's process: 20/11735-5 - Polyelectrolyte micelles: characterization, properties and applications for enzymes encapsulation
• Grantee: Julia Bonesso Sabadini
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)