Intermediate Salt Concentrations Research Articles

Property-Relaxation Correlations in 3D-Siloxane/Polyether Hybrid Polymer Electrolytes

The thermomechanical and transport properties of a series of hybrid polymer electrolytes are examined by means of differential scanning calorimetry, rheological analysis and broadband electric spectroscopy. The electrolytes are composed of 3D-oligosiloxane defect clusters grafted with polyether chains and doped with LiClO4, with concentration ranging from 0 to 1.4 mol·kg–1. The thermomechanical properties are mainly modulated by the balance of interactions taking place within the polyether domains. The materials show low Tg and no crystallization in a wide salt concentration range, while the mechanical modulus, between 104 and 105 Pa, is stable up to at least 100 °C. A detailed electric characterization, combined with the results from vibrational spectroscopy analysis, elucidates the factors influencing the transport properties. The conductivity reaches 8 × 10–5 S·cm–1 at 30 °C for intermediate salt concentrations. The sluggishness of the host matrix appears to be the limiting factor depressing the conduc...

Comparación de medios de cultivo con salinidad controlada en la enumeración de bacterias heterotróficas en una laguna costera

An efficiency comparison for counts of viable heterotrophic bacteria in a coastal lagoon was done for three media with different salinities. Water samples were taken along me salinity gradient (range 1-28 %), with and without lagoon communication with the sea. In all cases, the cstuarine mcdium wilh intermediate salt concentration gave the highest values of colony forming units and is more reliable.

Forces between silica particles in the presence of multivalent cations

Forces between negatively charged silica particles in aqueous electrolyte solutions were measured with the colloidal probe technique based on the atomic force microscope (AFM). The present study focuses on the comparison of monovalent and multivalent counterions, namely K+, Mg2+, and La3+. The force profiles can be well described with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) down to distances of about 4nm. At smaller distances, the forces become strongly repulsive due to additional non-DLVO repulsion. In the presence of La3+, one observes an additional attractive force with a range of about 1nm at intermediate salt concentrations. This force is probably related to ion-ion correlations, but could also be influenced by surface charge heterogeneities or charge fluctuation forces.

Competing salt effects on phase behavior of protein solutions: tailoring of protein interaction by the binding of multivalent ions and charge screening.

The phase behavior of protein solutions is affected by additives such as crowder molecules or salts. In particular, upon addition of multivalent counterions, a reentrant condensation can occur; i.e., protein solutions are stable for low and high multivalent ion concentrations but aggregating at intermediate salt concentrations. The addition of monovalent ions shifts the phase boundaries to higher multivalent ion concentrations. This effect is found to be reflected in the protein interactions, as accessed via small-angle X-ray scattering. Two simulation schemes (a Monte Carlo sampling of the counterion binding configurations using the detailed protein structure and an analytical coarse-grained binding model) reproduce the shifts of the experimental phase boundaries. The results support a consistent picture of the protein interactions responsible for the phase behavior. The repulsive Coulomb interaction is varied by the binding of multivalent counterions and additionally screened by any increase of the ionic strength. The attractive interaction is induced by the binding of multivalent ions, most likely due to ion bridging between protein molecules. The overall picture of these competing interactions provides interesting insight into possible mechanisms for tailoring interactions in solutions via salt effects.

Equilibrium swelling of some poly(N-IPAAm-sulfobetaine) hydrogels in water and in aqueous solutions of a single salt

The influence of single salts (either NaCl, K2CO3, KI, KSCN, KF and Na2SO4) on the degree of swelling of some copolymeric hydrogels of N-isopropyl acrylamide (N-IPAAm) and a zwitterionic comonomer sulfobetaine (=[3-(methacryloylamino) propyl] dimethyl (3-sulfopropyl) ammonium hydroxide inner salt (MPSA)) in water at 298K was investigated experimentally. As expected, the experimental results reveal that at low salt concentrations (mass fractions of salt in aqueous solution below about 10−3) none of the investigated salts has an influence on the degree of swelling. As also expected, at high salt concentrations (mass fraction above ≈10−1) the gels collapse. However, an increase of the degree of swelling at intermediate salt concentrations was found for all investigated gels in aqueous solutions of either KSCN or KI as well as for the gels with a high content of sulfobetaine in aqueous solutions of NaCl. This phenomenon is called “anti-polyelectrolyte” behavior.A previously developed thermodynamic model was extended to describe (i.e., correlate and predict) the experimental results for the swelling behavior. Calculation results for the degree of swelling are in good agreement with experimental data. In most cases the difference between the experimental and the calculation result for the degree of swelling is lower than the corresponding experimental uncertainty.

On the Benefits of Rubbing Salt in the Cut: Self‐Healing of Saloplastic PAA/PAH Compact Polyelectrolyte Complexes

The inherent room temperature mending and self-healing properties of saloplastic PAA/PAH CoPECs are studied. After ultracentrifugation of PAA/PAH polyelectrolyte complexes, tough, elastic materials are obtained that undergo self-healing facilitated by salt. At intermediate salt concentrations the CoPECs remain elastic enough to recover their original shape while the chains are mobile enough to repair the cut, thus leading to actual self-healing behavior.

Phase Boundaries for Fibril and Metastable Oligomer Formation of Lysozyme

Deposition of protein fibers with a characteristic cross-beta sheet structure is the molecular marker for many human disorders including Alzheimer's disease, type II diabetes and rheumatoid arthritis. Given the large number of proteins and peptides beyond those associated with diseases that have been shown to form amyloid fibrils in vitro, it has been suggested that amyloid fibril formation represents a generic protein phase transition. Mapping out the corresponding phase boundaries is complicated by the presence of least two distinct fibril assembly pathways. One pathway is characterized by the nucleation of long, rigid fibrils common to the late stages of amyloid diseases. A second pathway involves the formation of globular oligomeric species and curvilinear protofibril. The relation of this latter pathway to the mature fibrils is not entirely clear. Intriguingly, it is these latter oligomers and protofibrils that have been implicated as the molecular species mediating the cellular toxicity associated with amyloid diseases.For the amyloidogenic protein lysozyme, we have systematically mapped out the combination of protein and salt concentrations resulting in the formation of either long rigid or oligomeric amyloid aggregates for fixed temperature and pH. Using dynamic light scattering, thioflavin fluorescence spectroscopy, atomic force microscopy and infrared spectroscopy, we detected three distinct types of aggregates. Growth of long straight fibrils prevailed at either low salt or protein concentrations. At intermediate salt and protein concentration oligomer formation with subsequent protofibril nucleation prevailed. Oligomers and protofibrils represent metastable phases that are kinetically favored, while long straight fibrils are the thermodynamically stable state. Eventually, fibril formation gives way to amorphous precipitation. This phase behavior shows intriguing similarities with the phase diagram for protein crystallization where a metastable liquid-liquid phase is located within the stable coexistence region for protein crystals.

Study on interaction of bile salts with curcumin and curcumin embedded in dipalmitoyl-sn-glycero-3-phosphocholine liposome

Curcumin, often used as a food spice, is a natural polyphenol that has various medicinal benefits such as anti-cancer, anti-amyloid, anti-oxidant, and anti-inflammatory properties, among others. The interaction between bile salts having physiological significance and curcumin suggests the aggregation of bile salts dramatically alters the absorption and fluorescence parameters of curcumin. The fluorescence emission maximum as well as the intensity can easily detect critical micellar concentration of sodium cholate and sodium deoxycholate respectively to be 16 and 6mM at room temperature. The mechanism of interaction of curcumin with bile salts has been presented at low, intermediate and high bile salt concentrations and depends on temperature. In the presence of bile salts the DPPH scavenging activity was preserved, though less than in the presence of curcumin alone. The effect of submicellar concentration, 5–50μM, of bile salt with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes in solid gel and liquid crystalline phases has been investigated using curcumin as an embedded probe in the membrane. The curcumin based fluorescence probing method indicates even at very low concentration, ∼5μM, incorporation of monomeric bile salt molecules disorders the membrane properties. Expulsion of curcumin from the membrane in the presence of bile salt is ruled out, suggesting wetting of membrane. Alteration of membrane fluidity by bile salts is found to have an opposing effect in the liquid crystalline phase compared to in the solid gel phase, and is sensitive to the nature of bile salt. The permeability in the liquid crystalline phase decreases in the presence of bile salt. The phase transition temperature of the membrane is influenced by bile salt.

Synthesis, Assembly, and Image Analysis of Spheroidal Patchy Particles

We report a method to synthesize and image Janus spheroid and "kayak" shaped patchy particles that combine both shape and interaction anisotropy. These particles are fabricated by sequentially combining evaporative deposition of chrome and gold with the uniaxial deformation of the colloidal particles into spheroids. We introduce combined reflection and fluorescence confocal microscopy to image each component of the patchy particle. Image analysis algorithms that resolve patch orientation from these image volumes are described and used to characterize self-assembly behavior. Assemblies of the Janus spheroid and kayak particles produced at different salt concentrations demonstrate the functional nature of the patch-to-patch interactions between the particles. Selective gold-to-gold patch bonding is observed at intermediate salt concentrations, while higher salt concentrations yield gel-like structures with nonselective patch-to-patch bonding. At intermediate salt concentrations, differences in the orientational order of the assemblies indicate that both the preferential gold-to-gold patch bonding and the particles' shape anisotropy influence the self-assembled structure.

Theory and simulations of crystalline control via salinity and pH in ionizable membranes

Many amphiphilic molecules with ionizable charged groups self-assemble into membranes. Their degree of ionization is a function of the pH and salt concentration in the solution, and it can also be suppressed or enhanced depending on the local crystalline structure on the membrane, which must be computed self-consisitently via the competition of short range and electrostatic interactions. We consider here a dense two-dimensional binary mixture consisting of positive and negative species of equal concentration. Each particle may be either charged according to its type or neutral, specifying its ionization state. We analyze this co-assembled system by numerically exact optimization and by continuum Monte Carlo simulations including short range and electrostatic interactions among all the particles. We find the optimal structure to be a triangular lattice for high salt concentrations, a face-centered rectangular lattice for intermediate salt concentrations, and a square lattice for low salt concentrations. At neutral pH, this crossover occurs gradually over a wide range of salt concentrations, while for highly acidic or basic solutions, it is much more abrupt. At intermediate values of pH, the unit cells become more complicated, causing the dissociation curve to follow a staircase function.

Conformation of polyelectrolytes using cellular automata techniques

A cellular automata model of polyelectrolytes is studied using NetLogo, a multi-agent modelling environment based on the Java virtual machine. NetLogo allows easy construction of cellular automata models, is free to use and has a detailed documentation and examples library. In order to illustrate the working principles of NetLogo, we study polyelectrolyte conformations in a liquid salt solution using the so called cluster entropy S_C as an order parameter. Our results predict the correct evolution of polyelectrolyte conformations, from collapsed clustered structures, at low charge/high salt concentration conditions, to elongated chains, at high charge/low salt concentration, as had been reported in the literature. In both of these situations the cluster entropy is approximately zero S_C ≈ 0. In intermediate charge and salt concentration conditions the well-known pearl necklace structure is observed, in this case the values of S_{C} reach a maximum. The use of NetLogo modelling environment along the cluster entropy concept, permits quick and objective descriptions of the spatial properties of polyelectrolytes.

Ion exchange membrane adsorption of bovine serum albumin—Impact of operating and buffer conditions on breakthrough curves

Abstract The relevant phenomena underlying the adsorption of proteins on ion exchange membranes with grafted polymer layers are not well understood yet. In this work the influence of operating and buffer conditions on the adsorption of bovine serum albumin (BSA) on anion and cation exchange membrane adsorbers is systematically investigated in order to find indications on the relevant mechanisms. The experimental results obtained at different buffer conditions are analyzed using the steric mass action model. Large differences were observed between the adsorption behavior of BSA on anion and cation exchange membranes. On the anion exchange membranes the dynamic binding capacity at 10% breakthrough was independent of the applied flow rate and decreased with increasing salt concentration. This in contrast to the cation exchange membranes, for which the dynamic binding capacity was strongly dependent on the flow rate and for which an optimum in binding capacity was observed at an intermediate salt concentration. Especially, the results obtained on cation exchange suggest a strong role of non-ideal effects such as steric hindrance and electrostatic repulsion in membrane adsorption. An improved understanding of these effects is required for further optimization of membrane adsorber materials.

Double Inversion of Emulsions Induced by Salt Concentration

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements.

Anomalous Pull-Off Forces between Surfactant-Free Emulsion Drops in Different Aqueous Electrolytes

A systematic study of collisions between surfactant-free organic drops in aqueous electrolyte solutions reveals the threshold at which continuum models provide a complete description of thin-film interactions. For collision velocities above ~1 μm/s, continuum models of hydrodynamics and surface forces provide a complete description of the interaction, despite the absence of surfactant. This includes accurate prediction of coalescence at high salt concentration (500 mM). In electrolyte solutions at intermediate salt concentration (50 mM), drop-drop collisions at lower velocity (<1 μm) or extended time of forced drop-drop interaction exhibit a strong pull-off force of systematically varying magnitude. The observations have implications on the effects of ion-specificity and time-dependence in drop-drop interactions where kinetic stability is marginal.

Generic pathways to stability in concentrated protein mixtures

We present a series of experimental results that disclose the crucial role of ionic strength and partial volume fractions in the control of the phase behaviour of binary protein mixtures. Our findings can be understood as that the ionic strength determines the relative contribution of the entropy of the protein counter-ions to the overall thermodynamics of the system. Associative phase separation and crystallization observed at, respectively, low and high ionic strength are suppressed at intermediate salt concentrations, where the entropy gain upon releasing the counter-ions from the double layer of the proteins is negligible and the entropy loss upon confining the counter-ions within the protein crystal phase significant. Moreover, we find that the partial volume fraction of the protein prone to crystallize determines the crystallization boundary and that the presence of other proteins strongly delays crystallization, leading to temporarily stable mixtures. These findings suggest that stability in more complex protein mixtures, such as the cytosol, relates to the ionic strength and protein composition rather than to protein specific properties.

Partition of Pepsinogen from the Stomach of Red Perch (Sebastes marinus) by Aqueous Two Phase Systems: Effects of the Salt Type and Concentration

An important acidic protease, pepsin is synthesized and secreted in the gastric membrane in an inactive state called pepsinogen (PG) and has applications in the food and manufacturing industries, collagen extraction, gelatin extraction and in regulating digestibility. Fish processing waste can be used to produce commercially valuable byproducts such as pepsinogen. In the present study, the purification of pepsinogen from the stomach of red perch using aqueous two phase systems (ATPS) formed by polyethylene glycol (PEG) and salt at 4°C was optimized. The effects of salt type (MgSO4, (NH4)2SO4, Na3C6H5O7 and K2HPO4) and concentration (6, 7, 8, 9, 10, 11, 12, 13, 15, 17, 19%) on the partitioning of PG were studied and parameters including total volume (TV), volume ratio (VR), enzyme activity (AE), protein content (Cp), specific activity (SA), partition coefficient (Kp), purification fold (PF) and recovery yield (RY) were evaluated. Salt type and salt concentration had significant effects on each parameter. MgSO4, (NH4)2SO4, Na3C6H5O7 and K2HPO4 required different critical salt concentrations (9, 12, 12 and 10%, respectively) to form biphasic systems. TV and VR decreased with increased salt concentration since salt formed hydrogen bonds with water molecules and created a more compact and ordered water structure. AE, CP, SA, PF and RY showed a maximum increase with intermediate salt concentration, while KP had the opposite pattern. The highest TV and AE values were obtained at 12% (NH4)2SO4 while the highest SA and PF values were obtained at 12% MgSO4. The highest TV and Cp values were obtained at 12 and 15% Na3C6H5O7, respectively. (NH4)2SO4 at 15% concentration gave the highest RY (71.7%) and was selected as the optimum salt type and concentration. Thus, 15% (NH4)2SO4 18% PEG 1500 was the optimal ATPS combination and presented the best partition. The values of SA and PF and RY obtained with ATPS method were two fold higher than those obtained with the ammonium sulphate fractionation (ASF) method.

Collapse of a weak polyelectrolyte star in a poor solvent

We present a theory of intramolecular collapse transition in a weak (pH sensitive) polyelectrolyte (PE) star induced by a decrease in the solvent strength and/or variation in the ionic strength in the solution. Our system mimics conformational coil-to-globule transitions in individual star-shaped thermo- and pH-sensitive (e.g. poly(dimethylaminoethyl methacrylate)) macromolecules in dilute aqueous solutions. Systematic comparison with the behaviour of non-ionic and strong (quenched) polyelectrolyte stars in poor solvents enables us to unravel specific features of the collapse transition in weak polyelectrolyte stars. We demonstrate that, depending on temperature and the ionic strength of the solution, a vast diversity of different scenarios for the salt- or temperature-induced collapse transitions may take place. Both at high or low ionic strength a collapse transition induced by a decrease in the solvent strength occurs continuously resembling the collapse of a neutral polymer star. On the contrary, at intermediate salt concentrations the collapse of a weak polyelectrolyte star may feature a first order phase transition, which involves the co-existence of a collapsed, weakly ionized state with a swollen, strongly ionized state. At a fixed temperature the collapse transition can be triggered by an increase in salt concentration. In the latter case the transition may occur via a sequence of two co-existence regimes separated by continuous though non-monotonous variation in the star dimensions as a function of salt concentration.

Salt-modulated structure of polyelectrolyte-macroion complex fibers

The structure and stability of strongly charged complex fibers, formed by complexation of a single long semi-flexible polyelectrolyte chain and many oppositely charged spherical macroions, are investigated numerically at the ground-state level using a chain-sphere cell model. The model takes into account chain elasticity as well as electrostatic interactions between charged spheres and chain segments. Using a numerical optimization method based on a periodically repeated unit cell, we obtain fiber configurations that minimize the total energy. The optimal fiber configurations exhibit a variety of helical structures for the arrangement of macroions including zig-zag, solenoidal and beads-on-a-string patterns. These structures result from the competition between attraction between spheres and the polyelectrolyte chain (which favors chain wrapping around the spheres), chain bending rigidity and electrostatic repulsion between chain segments (which favor unwrapping of the chain), and the interactions between neighboring sphere-chain complexes which can be attractive or repulsive depending on the system parameters such as salt concentration, macroion charge and chain length per macroion (linker size). At about physiological salt concentration, dense zig-zag patterns are found to be energetically most stable when parameters appropriate for the DNA-histone system in the chromatin fiber are adopted. In fact, the predicted fiber diameter in this regime is found to be around 30 nanometers, which roughly agrees with the thickness observed in in vitro experiments on chromatin. We also find a macroion (histone) density of 5-6 per 11nm which agrees with results from the zig-zag or cross-linker models of chromatin. Since our study deals primarily with a generic chain-sphere model, these findings suggest that structures similar to those found for chromatin should also be observable for polyelectrolyte-macroion complexes formed in solutions of DNA and synthetic nano-colloids of opposite charge. In the ensemble where the mean linear density of spheres on the chain is fixed, the present model predicts a phase separation at intermediate salt concentrations into a densely packed complex phase and a dilute phase.

Transferability of Coarse Grained Potentials: Implicit Solvent Models for Hydrated Ions.

Understanding the relation between structural and thermodynamic quantities obtained with simplified-e.g., coarse-grained (CG) or implicit-solvent-models is an ongoing challenge in the field of multiscale simulation. Assessing the transferability of such models to state points that differ from the one where the model was parametrized is important if one wants to apply these models to complex systems, which, for example, exhibit spatially varying compositions. Here, we investigate the transferability of CG (in this case implicit-solvent) ion models with effective pair potentials derived at very low concentrations to different ion concentrations in aqueous solution. We evaluate both thermodynamic and structural properties of systems of NaCl in aqueous solution both in atomistic explicit-solvent and CG simulations. For the explicit solvent simulations, osmotic coefficients have been calculated at a wide range of salt concentrations and agree very well with experimental data. It had been shown previously that a concentration-dependent dielectric permittivity can be used to make effective implicit-solvent pair potentials transferable since it accounts for the effect of ion concentration on solvent properties, resulting in very good osmotic properties of these models for a certain range of salt concentrations. We investigate the explicit and implicit solvent models also in terms of structural properties, where we can show how with a concentration-dependent dielectric constant one obtains very good structural agreement at low and intermediate salt concentrations, while for larger salt concentrations, multibody ion-ion correlations put a limit to straightforward transferability. We show how-guided by this structural analysis-the transferability of the implicit-solvent model can be improved for high ion concentrations. Doing so, we obtain transferable implicit-solvent effective pair potentials which are both structurally and thermodynamically consistent with an explicit solvent reference model.

The Effect of Salt on the Water Structure at a Charged Solid Surface: Differentiating Second- and Third-order Nonlinear Contributions

We have used visible-infrared sum-frequency generation spectroscopy to reveal fundamental characteristics of water structure at the fused silica surface. By studying a wide range of ionic strengths, from 0.05 mM to 4 M, we are able to comment on the contributions of second- and third-order nonlinearities to the spectroscopic response. Spectra obtained from extremely dilute salt concentrations provide evidence of the previously sought increasing surface charge with ionic strength. This is followed by a screening regime where the extent to which the surface field penetrates into the bulk is limited by the electrolyte. Data from intermediate salt concentrations reveal a few strongly ordered layers of water immediately adjacent to the surface. At high concentrations, we observe a significant disruption of solvent ordering. Together, the observation of these four distinct regimes provides a unified understanding of interfacial water structure in the presence of salt that consolidates previous reports in the literature.