Interactions and conformations of polyelectrolytes in solutions, thin films, and complexes.

摘要

Polyelectrolyte complexes have gained great attention over the past few decades for their applications in materials science, engineering, and medicine. They can be assembled into thin films via the layer-by-layer deposition of oppositely charged polyelectrolytes or transformed into moldable complexes, or hydrogels, through their controlled mixing. The properties of the resulting materials are highly tunable depending on the nature and composition of the system at hand; of great importance are the polyelectrolytes' interactions and their conformations. In this dissertation, we walk through several chemiscapes revealing the properties of synthetic, biocompatible, and biological polyelectrolytes and their complexes.;Polynucleotides are the focus herein; they have been used as materials in biocompatible polyelectrolyte composites for the many controllable properties they offer: hydrogen bonding, electrostatic interactions, and conformational changes depending on pH, ionic strength and temperature. DNAs have also caught the attention of theoretical investigators; they are used as model polyelectrolytes due to their defined structure and charge density. On the other hand most of the studies have been conducted under conditions far from physiological while the applications are targeted for medicinal purposes as implants or for drug and/or gene delivery.;The first section of the manuscript describes the studies conducted on the isothermal pairing of oligonucleotides in solutions under molecular crowding conditions and different ionic strengths mimicking physiological conditions where polyethylene glycol is used as crowder. The osmotic properties of polyethylene glycol and sodium chloride solutions were investigated to establish the thermodynamics of the DNA pairing while spectroscopy was used to monitor the conformational changes and the binding properties of the strands under these conditions.;In the following section, the discussion extends to the hybridization of polynucleotides incorporated into polyelectrolyte multilayers. Biodegradable capsules of polynucleotides based on the layer-by-layer technique are candidates for gene delivery. It is therefore important to understand the properties and stability of polynucleotides in polyelectrolyte matrices. We employed surface characterization and spectroscopic methods to establish the polynucleotides' hydrogen bonding efficacy under varying ionic and temperature conditions.;Polyelectrolyte thin films are also promising coatings as anti-fouling, anti-corrosion, and anti-sticking agents. To improve these characteristics it is necessary to have a clear vision of the composition of the thin films to better control their chemical, physical and mechanical properties. In this dissertation, scintillation counting using radiolabeled ions is described for the determination of the ionic content of the polyelectrolyte films and the extent of polyelectrolyte interpenetration and charge overcompensation, the driving forces of the layer-by-layer technique.;Finally, we present the synthesis and analysis of polyelectrolyte complexes which have gained attention as materials for bio-implants and cell culture scaffolds. This section details the methods used for the synthesis of stoichiometric complexes followed by their characterization by neutron scattering methods where the conformation of individual polyelectrolyte chains is explored under different ionic conditions presenting a first study of the structural properties of the charged polymers in these compact matrices.