Influence of temperature and salt on coacervation in an aqueous mixture of poly-L-lysine (PLL) and poly-(sodium styrene sulfonate) (PSSNa)

The mixture of poly-L-lysine (PLL) and long-chain PSSNa can lead to the formation of soluble complexes depending on pH, PLL concentration, ionic strength, and temperature. The influence of these stimuli was studied by zetametry, dynamic and ultra-small-angle light scattering, and turbidimetric measurements. First of all, we studied the stoichiometry of complexation, and then considered the influence of salt concentration and temperature on the behavior of the mixture at different pH values. These findings have allowed us to conclude that the polyelectrolyte-polypeptide stoichiometry is controlled by electrostatic interactions between opposite charges. At mass ratios between 1.8 and 2.3 and with net charges close to neutrality, unstable complexes were formed and flocculated due to the hydrophobic attraction leading to macroscopic phase separation. The linear charge density of the complex is also controlled by the ionic strength. Higher CaCl₂ concentrations reduce the complex stability and decrease the charge density, which leads to surface patch binding (SPB) at higher pH. Finally, the electrostatic interactions and strength of hydrogen bonds increased the stabilization of the complexes formed at temperatures lower than 45 °C. At temperatures higher than 45 °C, hydrophobic interactions became more dominant, causing a destabilization of the complexes.

Modelling and predicting the interactions between oppositely and variously charged polyelectrolytes by frontal analysis continuous capillary electrophoresis

In this work, a systematic study of the interactions between poly(l-lysine) and variously charged statistical copolymers of acrylamide and 2-acrylamido-2-methyl-1-propanesulfonate (PAMAMPS) has been carried out by frontal analysis continuous capillary electrophoresis (FACCE). FACCE was successfully implemented to obtain the interaction parameters (binding constant and stoichiometry) at different ionic strengths and for different PAMAMPS charge densities varying between 15% and 100%. The range of investigated ionic strengths was carefully adjusted according to the PAMAMPS charge density to obtain measurable binding constants by FACCE (i.e. formation binding constant typically comprised between 10⁴ and 10⁶ M^-1). The number of released counter-ions during the polyelectrolyte complex formation was systematically quantified via the ionic strength dependence of the binding constant and was compared to the total condensed counter-ion reservoir according to Manning theory on counter-ion condensation. A descriptive and predictive model relating the physico-chemical properties of the two partners, the binding constant and the ionic strength is proposed in the framework of multiple independent interaction sites of equal energy.

Saloplastics: processing compact polyelectrolyte complexes

Polyelectrolyte complexes (PECs) are prepared by mixing solutions of oppositely charged polyelectrolytes. These diffuse, amorphous precipitates may be compacted into dense materials, CoPECs, by ultracentrifugation (ucPECs) or extrusion (exPECs). The presence of salt water is essential in plasticizing PECs to allow them to be reformed and fused. When hydrated, CoPECs are versatile, rugged, biocompatible, elastic materials with applications including bioinspired materials, supports for enzymes and (nano)composites. In this review, various methods for making CoPECs are described, as well as fundamental responses of CoPEC mechanical properties to salt concentration. Possible applications as synthetic cartilage, enzymatically active biocomposites, self-healing materials, and magnetic nanocomposites are presented.

Roles of hydrophobicity and charge density on the dynamics of polyelectrolyte complex formation and stability under modeled physicochemical blood conditions

To improve the understanding of the physicochemical behavior of polyplexes (DNA-polycation complexes) and to avoid the complexity of blood, the formation and stability of polyelectrolyte complexes of degradable polycations and polyanions, we previously studied under pH, temperature, and ionic strength typical of human blood. In this study, the investigation is extended to polycationic macromolecules added into mixtures of polyanions selected to mimic polyanionic species present in blood. The poly(l-lysine) polycation was added to binary mixtures of degradable polyanions with different charge densities and hydrophobicity. The polyanions were poly(l-lysine citramide imide), poly(l-lysine citramide), and poly(l-lysine citramide) partially esterified with heptyl groups. We found selectivity and fractionation in the molar mass, which depended on the structural characteristics of the polyanions. The affinity of polycationic poly(l-lysine) macromolecules to polyanions increased in the following order: poly(l-lysine citramide imide) < poly(l-lysine citramide) < hydrophobized poly(l-lysine citramide). These data complements the previous information with respect to the possibility of polyplex destabilization and/or the interactions of polycationic macromolecules in excess with the polyanionic species present in blood, depending on the physicochemical characteristics of the polyplex, the excess polycation, and blood elements.