Complexation between polyallylammonium cations and polystyrenesulfonate anions: the effect of ionic strength and the electrolyte type

Specific ion effects on the aggregation of polysaccharide-based polyelectrolyte complex particles induced by monovalent ions within Hofmeister series

Polysaccharide-based polyelectrolyte complex (PEC) particles have been utilized as carriers for drug delivery systems (DDS) and as building components for material development. Despite their versatility, the aggregation mechanism of PEC particles in the presence of salts remains unclear. To clarify the aggregation mechanism, the specific ion effects of monovalent salts within the Hofmeister series on the aggregation behavior of PEC particles composed of chitosan and chondroitin sulfate C, which are often used as DDS carriers and materials, were studied. Here, we found that weakly hydrated chaotropic anions promoted the aggregation of positively charged PEC particles. The hydrophobicity of the PEC particles was increased by these ions. Strongly hydrated ions such as Cl^- are less likely to accumulate in these particles, whereas weakly hydrated chaotropic ions such as SCN^- are more likely to accumulate. Molecular dynamics simulations suggested that the hydrophobicity of PECs might be strengthened by ions due to changes in intrinsic and extrinsic ion pairs and hydrophobic interactions. Based on our results, it is expected that the control of surface hydrophilicity or hydrophobicity is an effective approach for controlling the stability of PEC particles in the presence of ions.

Applicability of the Generalized Stokes-Einstein Equation of Mode-Coupling Theory to Near-Critical Polyelectrolyte Complex Solutions

We examine whether the mode-coupling theory of Kawasaki and Ferrell (KF) [Kawasaki, K. Kinetic Equations and Time Correlation Functions of Critical Fluctuations. Ann. Phys. 1970, 61 (1), 1-56; Ferrell, R. A. Decoupled-Mode Dynamical Scaling Theory of the Binary-Liquid Phase Transition. Phys. Rev. Lett. 1970, 24 (21), 1169-1172] can describe dynamic light scattering (DLS) measurements of the dynamic structure factor of near-critical polyelectrolyte complex (PC) solutions that have been previously shown to exhibit a theoretically unanticipated lower critical solution temperature type phase behavior, i.e., phase separation upon heating, and a conventional pattern of static critical properties (low angle scattering intensity and static correlation, ξ_s) as a function of reduced temperature. Good qualitative accord is observed between our DLS measurements and the KF theory. In particular, we observe that the collective diffusion coefficient D_c of the PC solutions obeys the generalized Stokes-Einstein equation (GSE), D_c = k_BT/6πηξ_s, where ξ_s is specified from our previous measurements and where η is measured by capillary rheometry under the same thermodynamic conditions as in our previous study of these solutions, allowing for a no-free-parameter test of the GSE. We also find that even the wavevector (q)-dependent collective diffusion coefficient D_c(q), measured by varying the scattering angle in the DLS measurements over a large range, is also well-described by the mean-field version of the KF theory. We find it remarkable that the KF theory provides such a robust description of collective diffusion in these complex charged polyelectrolyte blends under near-critical conditions given that charge fluctuations and association of the polymers might be expected to lead to physical complications that would invalidate the standard model of uncharged fluid mixtures.

Polyelectrolyte Complexes as Desiccants: Thirsty Saloplastics

Desiccants or drying agents are used extensively to remove water from liquids and gases. Many organic reactions, from the laboratory to the industrial scale, are sensitive to even trace amounts of water. A new class of desiccants made from complexed polyelectrolytes, PECs, is described here, exploiting the affinity of charged polymer repeat units for water. The enthalpy of hydration of dry PECs was used for the first time as a quantitative measure of PEC water affinity. Several combinations of positive, Pol+, and negative, Pol-, polymers were used to prepare PECs. All of these displayed significant exothermic (favorable) enthalpies of hydration, measured at room temperature using solution calorimetry. A PEC made from poly(diallyldimethylammonium) and poly(styrene sulfonate) was extruded into convenient shapes. This PEC was used to dry three common solvents, acetonitrile, tetrahydrofuran, and toluene, representing a range of polarities. Added water was radiolabeled with tritium to provide accurate and sensitive detection of residual water after treatment. This PEC was almost as efficient as the comparison desiccants, molecular sieve 3A and calcium sulfate, after 3 days of static drying but could be regenerated at a lower temperature (120 °C) and shed far fewer dust particles.

Predicting the outcomes of interpolyelectrolyte neutralization at surfaces on the basis of complexation experiments and vice versa

This study was carried out with the aim of establishing how the outcomes of polyelectrolyte multilayer formation can be predicted on the basis of the results of complexation studies in solution and vice versa. For this purpose, the correlation between the processes of complex and multilayer formation involving three pairs of vinylic polyions in solutions of binary 1 : 1 sodium salts (NaX; X = F, Cl, Br, I, NO₃, ClO₄) was explored by means of dynamic and electrophoretic light scattering, potentiometry, microcalorimetry, spectrophotometry and quartz crystal microbalance. The gradual reactant mixing in solution at lower salt concentrations resulted in a Fuoss-Sadek sequence of events (primary complexes → secondary complexes → 1 : 1 flocculate), whereby the obtained nano-complexes could be successively overcharged. At high salt concentration and with excess polycation present, metastable nano-complexes and precipitates containing surplus of positively charged monomers were formed. The amount of extrinsically compensated charge was in accord with the polycation affinities toward counteranions, established by monitoring the electrolyte-induced aggregation of positively charged nano-complexes. Perfect analogy with respect to counteranion influence on the amount of adsorbed polycation was noticed for corresponding multilayers. Aside from providing a deeper understanding of interpolyelectrolyte neutralization, the gained insights can also be used to steer the polyelectrolyte multilayer composition and properties.

Ion-Specific and Solvent Effects on PDADMA–PSS Complexation and Multilayer Formation

Among various parameters that influence the formation of polyelectrolyte complexes and multilayers, special emphasis should be placed on ion-specific and solvent effects. In our study, we systematically examined the above-mentioned effects on poly(diallyldimethylammonium chloride) (PDADMACl)-sodium poly(4-styrenesulfonate) (NaPSS) complexation in solution and at the surface by means of dynamic light scattering, ellipsometry and atomic force microscopy measurements. As solvents, we used water and water/ethanol mixture. The obtained results confirm the importance of ion-specific and solvent effects on complexes prepared in solution, as well as on multilayers built up on a silica surface. The experiments in mixed solvent solution showed that at a higher ethanol mole fraction, the decrease in monomer titrant to titrand ratio, at which the increase in the size of complexes is observed, takes place. The difference between chloride and bromide ions was more pronounced at a higher mole fraction of ethanol and in the case of positive complex formation, suggesting that the larger amount of bromide ions could be condensed to the polycation chain. These findings are in accordance with the results we obtained for polyelectrolyte multilayers and could be helpful for designing polyelectrolyte multilayers with tuned properties needed for various applications, primarily in the field of biomedicine.

Overcharging of polyelectrolyte complexes: an entropic phenomenon

Overcharging in complex coacervation, in which a polyelectrolyte complex coacervate (PEC) initially containing equal moles of the cationic and anionic monomers absorbs a large excess of one type of polyelectrolyte species, is predicted using a recently developed thermodynamic model describing complexation through a combination of reversible ion binding on the chains and long-range electrostatic correlations. We show that overcharging is favored roughly equally by the translational entropy of released counterions and the binding entropy of polyelectrolytes in the polyelectrolyte complex, thus helping resolve competing explanations for overcharging in the literature. We find that the extent of overcharging is non-monotonic in the concentration of added salt and increases with both strength of ion-pairing between polyions and chain hydrophobicity. The predicted extent of overcharging of the PEC is directly compared with that of multilayers made of poly(diallyldimethylammonium), PDADMA, and poly(styrene-sulfonate), PSS, overcompensated by the polycation in two different salts: KBr and NaCl. Accounting for the specificity of salt ion interactions with the polyelectrolytes, we find good qualitative agreement between theory and experiment.

Emulsion stabilisation by complexes of oppositely charged synthetic polyelectrolytes

We investigate the possibility of stabilising oil-water emulsions from the polyelectrolyte complexes (PEC) obtained in mixtures of a strong cationic polyelectrolyte (poly(diallyldimethylammonium chloride), PDADMAC) and a weak anionic one (poly(acrylic acid)sodium salt, PAANa). Unlike other previous work however, both polyelectrolytes (PEL) are chosen as they are completely water-soluble and possess no surface activity when present alone over nearly all the pH range. In water, the effects of PEL concentration, PEL mixing ratio and pH on the formation of PEC are studied in detail. At low pH where the anionic PEL is uncharged, complex coacervation occurs in which droplets rich in both polymers are dispersed in water. At intermediate pH, the PEC comprise a mixture of coacervate droplets and solid particles. At high pH where the anionic PEL is significantly charged, only complex coacervation is observed. On addition of dodecane followed by homogenisation, no stable emulsions arose from dispersions containing solid particle PEC due to either the large precursor particle aggregates or their inherent hydrophilicity. By contrast, oil-in-water emulsions stable to coalescence could be prepared from coacervate dispersions. We discuss the feasibility of the coacervate phase spreading at the oil-water interface in terms of the relevant spreading coefficients and compare the predictions with experiment for a range of oils. We encounter oils whose drops become engulfed by the coacervate phase as well as oils where no engulfing occurs.

Repulsion between oppositely charged rod-shaped macromolecules: Role of overcharging and ionic confinement

The interaction between two oppositely charged rod-shaped macro-ions in a micro-ion solution is investigated via Monte Carlo simulations of the primitive model. The focus is on the asymmetry in rod and/or ion charge, i.e., conditions where oppositely charged objects can repel one another. For equally and oppositely charged rods with asymmetric z:1 micro-ions, repulsion may be induced by overcharging one of the rods with the z valent ions. For asymmetrically charged rods in a symmetric z:z micro-ion solution, a repulsive interaction-at separation of the order of one ion diameter-can arise via an unbalanced osmotic pressure contribution from the ionic atmosphere in the inter-rod space, and an attractive interaction-at a smaller separation-may occur due to a "squeezing out" of the micro-ions from the space between the rods (with a consequent gain in entropy). The thermodynamics of each mechanism is investigated in terms of rod charge and size and micro-ion valence, size, and concentration. Our findings contribute to the understanding of the complex role of charge asymmetry on the interaction of, for example, oppositely charged polyelectrolytes, functionalized nanotubes, and rod-like biomolecules, e.g., viruses.

Influence of Polyelectrolyte Multilayer Properties on Bacterial Adhesion Capacity

Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity were determined by atomic force microscopy and tensiometry. The surface charge was examined by the zeta potential measurements of silica particles covered with polyelectrolyte multilayers, whereby ionic strength and polyelectrolyte concentrations significantly influenced the build-up process. For adhesion experiments, we used the bacterium Pseudomonas aeruginosa. The extent of adhered bacteria on the surface was determined by scanning electron microscopy. The results showed that the extent of adhered bacteria mostly depends on the type of terminating polyelectrolyte layer, since relatively low differences in surface roughness and hydrophobicity were obtained. In the case of polyelectrolyte multilayers terminating with a positively charged layer, bacterial adhesion was more pronounced than in the case when the polyelectrolyte layer was negatively charged.

Submicron-sized hydrogels incorporating cyclic dinucleotides for selective delivery and elevated cytokine release in macrophages

Despite the emerging evidences supporting the potential of cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) as a vaccine adjuvant, few properly designed micro-/nanocarriers for the delivery of cyclic dinucleotides have been developed. In this study, we formulated cGAMP within linear polyethyleneimine (LPEI)/hyaluronic acid (HA) hydrogels via inverse water-in-oil (W/O) emulsion/crosslinking. Spherical and cationic LPEI/HA hydrogels (LH gels) with a size of 455.3±3.1nm and a surface charge of 48.7±3.7mV were selectively and efficiently delivered into phagocytic macrophage cells, which are one type of antigen-presenting cells (APCs), but not into non-phagocytic fibroblast cells. LH gels incorporating cGAMP (LH/cGAMP gels) elicited excellent induction of the cytokines interferon-β (IFN-β) and interleukin-6 (IL-6). In particular, the amount of IFN-β released by LH hydrogels was significantly increased by 2.5-fold compared to that released by conventional cationic liposomes, such as Lipofectamine. In addition, fabricated LH gels showed superior biocompatibility in phagocytic cell lines and primary bone marrow-derived macrophages (BMDMs). After intramuscular injection with ovalbumin into C57BL/6 mice, LH/cGAMP gels exhibited significantly elevated levels of anti-ovalbumin total IgG in serum and IFN-β mRNA in spleens. Thus, the newly designed cGAMP-incorporating hydrogels can serve as safe and potent adjuvants for vaccination and immunotherapy.

STATEMENT OF SIGNIFICANCE

Since cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) was first found as a second messenger of immune signaling in human systems in February 2013 (Science, 15, 826), several scientific studies have been reported related to the potential of cGAMP as a vaccine adjuvant or additive for immunotherapy. However, only naked cGAMP without carriers were studied via intramuscular or intranasal administration so far. In our study, we first investigated the feasibility of polymeric hydrogels incorporating cGAMP in terms of selective uptake into phagocytic antigen presenting cells (APCs), induction of cytokines, production of target antibodies, and biocompatibility for vaccination and immunotherapy in vitro and in vivo. Therefore, we believe this manuscript would be of great interest to the biomaterial communities especially who are studying immunotherapy.

Effects of salt on intermolecular polyelectrolyte complexes formation between cationic microgel and polyanion

The study of interpolyelectrolyte complex (IPEC) formation between cationic microgel and polyanion was presented. The size and molecular weight of cationic microgel are much larger than those of linear anionic polyelectrolyte. The resulting IPEC was divided by dynamic light scattering (DLS), static light scattering (SLS), and turbidity or spectrometry; (i) water-soluble intra-particle complexes consisting of one microgel to which linear polyelectrolytes bind; (ii) complex coacervates (inter-particle complexes composed of aggregated intra-particle complexes); and (iii) insoluble amorphous precipitates. These types depended on not only the mixing ratio of polyanion to cationic microgel but also salt concentration. This trend was discussed from IPEC's composition, thermodynamics of IPEC formation and the salt effect on intermolecular interactions which were expected in IPEC formation. The results obtained from the use of microgel in IPEC's study suggested that not only electrostatic interaction but also hydrophobic interaction play an important role in the aggregation or association of IPEC.

Polymeric stabilizers for protection of soil and ground against wind and water erosion

The article is devoted to the design, development and application of a new generation of binders for various dispersed systems, including soil, ground, sand, waste rock and others. The binders are formed by interaction of oppositely charged polyelectrolytes, both chemically stable and (bio)degradable. The fundamental aspects of interpolyelectrolyte reactions are discussed; the IPC structure and properties of the resulting interpolyelectrolyte complexes (IPCs) allow considering them as unique and universal binders. Numerous results of laboratory experiments and field trials of the IPC formulations are presented. In particular, large-scale tests have been done in the Chernobyl accident zone where the IPC binders were shown to be effective means to suppress water and wind erosion thereby preventing a spread of radioactive particles (radionuclides) from contaminated sites. Ecologically friendly IPC compositions are described, including those based on commercially available polymers; prospects for improving their efficiency and extending the range of their possible use are discussed.

The influence of ionic strength and mixing ratio on the colloidal stability of PDAC/PSS polyelectrolyte complexes

Polyelectrolyte complexes (PECs) form by mixing polycation and polyanion solutions together, and have been explored for a variety of applications. One challenge for PEC processing and application is that under certain conditions the as-formed PECs aggregate and precipitate out of suspension over the course of minutes to days. This aggregation is governed by several factors such as electrostatic repulsion, van der Waals attractions, and hydrophobic interactions. In this work, we explore the boundary between colloidally stable and unstable complexes as it is influenced by polycation/polyanion mixing ratio and ionic strength. The polymers examined are poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate) (PSS). Physical properties such as turbidity, hydrodynamic size, and zeta potential are investigated upon complex formation. We also perform detailed molecular dynamics simulations to examine the structure and effective charge distribution of the PECs at varying mixing ratios and salt concentrations to support the experimental findings. The results suggest that the colloidally stable/unstable boundary possibly marks the screening effects from added salt, resulting in weakly charged complexes that aggregate. At higher salt concentrations, the complexes initially form and then gradually dissolve into solution.