Presence Of Salt Ions Research Articles

Electrochemical impedance spectroscopy as a performance indicator of water dissociation in bipolar membranes

Using electrochemical impedance spectroscopy, we observed the rate of water dissociation decrease in the presence of salt ions while observing the transport of these salt ions, showing a clear link between the peaks observed in EIS and ion crossover.

Specific Ion Effects of Salt Solutions on Colloidal Properties of Octadecylamine Hydrochloride

AbstractFlotation continues to be a major technique for the production of potash from low grade, complex systems containing a variety of ores and ions. The specific ion effects on the behavior of the flotation collector in the KCl flotation system becomes important to the interpretation of the flotation mechanism. In this work, specific ion effects on the turbidity, surface tension and aggregation behavior of the common collector in KCl flotation, octadecylamine hydrochloride (ODA), have been investigated. The results from turbidity and surface tension studies of ODA solutions show that both cations and anions can affect the colloidal properties of ODA. Molecular dynamics simulations show that the binding that energy barrier between ODA headgroups and anions is principally responsible for the specific anion effect of γCAC of ODA solutions. In addition, the ion effect on the ODA aggregation particle size was also studied by using transmission electron micrographs (TEM) and dynamic light scattering. The data reveal that the presence of salt ions can induce the formation of larger ODA colloidal particles, on which the cation effect is more significant. This work provides detailed information of specific ion effect on colloidal properties of ODA, which may promote a further understanding of the flotation mechanism and help to improve the flotation of KCl from brine sources.

Membrane Deformation Induced by Cation Binding to Negatively Charged Phospholipids

The divalent cation Ca2+ plays a critical role in many cell signaling and membrane trafficking pathways, including exocytosis and membrane fusion. Ca2+ signal transduction is commonly thought to occur through interaction with protein partners; however, it may also interact with negatively charged phospholipids within the plasma membrane leading to changes in lipid behavior.Here we show that an asymmetric concentration of Ca2+ ions across the membrane can generate tubules or protrusions from membranes containing phosphatidylserine (PS) or phosphatidylinositol-4,5-bisphosphate (PIP2). We transferred single vesicles with controlled membrane tension into Ca2+ solution and observed the formation of inward tubules, indicating negative curvature generation by Ca2+. The Ca2+-induced membrane deformation is inhibited by high tension or low cation binding, in a similar manner as we have previously observed for BAR domain proteins. We propose that the membrane deformation is caused by Ca2+-induced clustering of PS and PIP2 creating negative curvature. In confirmation of this we find that Mg2+, which is known to only weakly cluster PS and PIP2, only generates curvature at relatively high concentrations and low tension. Additionally, for PS vesicles the membrane deformation requires high Ca2+ concentration (a few millimolar), while PIP2 vesicles, which are more sensitive to Ca2+-induced clustering, are deformed at lower Ca2+ concentrations. The presence of salt ions (Na+) also influences Ca2+-induced membrane curvature. High salt content can reduce Ca2+-induced curvature by shielding Ca2+ ions from the membrane. An asymmetric salt concentration can influence membrane structure and either enhance or oppose Ca2+-induced membrane curvature. The observed Ca2+-induced membrane deformation represents a new mechanism for Ca2+ signaling events. This mechanism is likely to be especially important for the role of Ca2+ in exocytosis and membrane fusion events.

Polymer Conformations in Ionic Microgels in the Presence of Salt: Theoretical and Mesoscale Simulation Results.

We investigate the conformational properties of polymers in ionic microgels in the presence of salt ions by molecular dynamics simulations and analytical theory. A microgel particle consists of coarse-grained linear polymers, which are tetra-functionally crosslinked. Counterions and salt ions are taken into account explicitly, and charge-charge interactions are described by the Coulomb potential. By varying the charge interaction strength and salt concentration, we characterize the swelling of the polyelectrolytes and the charge distribution. In particular, we determine the amount of trapped mobile charges inside the microgel and the Debye screening length. Moreover, we analyze the polymer extension theoretically in terms of the tension blob model taking into account counterions and salt ions implicitly by the Debye–Hückel model. Our studies reveal a strong dependence of the amount of ions absorbed in the interior of the microgel on the electrostatic interaction strength, which is related to the degree of the gel swelling. This implies a dependence of the inverse Debye screening length κ on the ion concentration; we find a power-law increase of κ with the Coulomb interaction strength with the exponent for a salt-free microgel and an exponent for moderate salt concentrations. Additionally, the radial dependence of polymer conformations and ion distributions is addressed.

Role of Salt and Water in the Plasticization of PDAC/PSS Polyelectrolyte Assemblies.

In this work, we investigate the effect of salt and water on plasticization and thermal properties of hydrated poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate) (PSS) assemblies via molecular dynamics simulations and modulated differential scanning calorimetry (MDSC). Commonly, both water and salt are considered to be plasticizers of hydrated polyelectrolyte assemblies. However, the simulation results presented here show that while water has a plasticizing effect, salt can also have an opposite effect on the PE assemblies. On one hand, the presence of salt ions provides additional free volume for chain motion and weakens PDAC-PSS ion pairing due to electrostatic screening, which contributes toward plasticization of the complex. On the other hand, salt ions bind water in their hydration shells, which decreases water mobility and reduces the plasticization by hydration. Our MDSC results connect the findings to macroscopic PE plasticization and the glass-transition-like thermal transition Ttr under controlled PE hydration and salt content. This work identifies and characterizes the dual nature of salt both as plasticizer and hardener of PE assemblies and maps the interconnection of the influence of salt with the degree of hydration in the system. Our findings provide insight into the existing literature data, bear fundamental significance in understanding of hydrated polyelectrolyte assemblies, and suggest a direct means to tailor the mechanical characteristics of PE assemblies via interplay of water and salt.

Hygroscopic growth and cloud droplet activation of xanthan gum as a proxy for marine hydrogels

AbstractKnowledge of the physical characteristics and chemical composition of marine organic aerosols is needed for the quantification of their effects on cloud microphysical processes and solar radiative transfer. Here we use xanthan gum (XG)—a bacterial biopolymer—as a proxy for marine hydrogels. Measurements were performed for pure XG particles and mixtures of XG with sodium chloride, calcium nitrate, and calcium carbonate. The aerosol hygroscopicity parameter (κ) is derived from hygroscopic growth factor measurements (κgf) at variable water activity (aw) and from cloud condensation nuclei activation efficiency (κccn). The Zdanovskii, Stokes, and Robinson (ZSR) hygroscopicity parameter derived for multicomponent systems (κmix, sol) is used to compare measurements of κgf and κccn. Pure XG shows close agreement of κgf (at aw = 0.9) and κccn of 0.09 and 0.10, respectively. Adding salts to the system results in deviations of κgf (at aw = 0.9) from κccn. The measured κgf and ZSR‐derived hygroscopicity parameter (κmix, sol) values for different solutions show close agreement at aw > 0.9, while κgf is lower in comparison to κmix, sol at aw < 0.9. The differences between predicted κmix, sol and measured κgf and κccn values are explained by the effects of hydration and presence of salt ions on the structure of the polymer networks. Results from this study imply that at supersaturations of 0.1 and 0.5%, the presence of 30% sea salt by mass can reduce the activation diameter of pure primary marine organic aerosols from 257 to 156 nm and from 87 to 53 nm, respectively.

Freezing characteristics of air-entrained concrete in the presence of deicing salt

The interaction between a salt solution and ice formation in capillary pores might provide new insight into the salt frost scaling process. To accomplish this small prismatic specimens (10mm×10mm×90mm) were cut from air-entrained concrete, dried at 50°C until constant weight, then immersed in sodium chloride (NaCl) solutions of different concentrations (0%, 3%, 9% and 12%) until they reached full capillary saturation. They were then subjected to a freeze–thaw (F–T) cycle in a high resolution low temperature dilatometer (LTD) with the surface temperature and uniaxial length-change continuously monitored. Internal saturation of capillary pores with increasing salt solutions is found to have a profound effect on the F–T response including the temperature rise and instant dilation associated with ice nucleation. It is concluded that salt ions retard ice formation and the effect of ice-growth on pore expansion during an F–T cycle. The presence of salt ions in the concrete pores and surface liquid has a counter-balancing effect on specimen length-change associated with ice-growth, which may provide one possible explanation for the pessimum salt concentration effect. The extent of surface scaling is also affected by the intrinsic capillary transport property (i.e., sorptivity) of the porous cementitious binder. Salt scaling is exacerbated in concretes with increasing sorptivity.

Thermodynamic characterization of the interaction between a peptide-drug complex and serum proteins.

The interaction between a peptide-based drug delivery system and two serum proteins, bovine serum albumin (BSA) and immunoglobulin G (IgG), is investigated using fluorescence quenching and calorimetric techniques. An ionic-complementary self/co-assembling peptide, EAR8-II, is employed to encapsulate the hydrophobic anticancer drug pirarubicin (THP) and stabilize it in protein environments. Self/co-assembling properties of the peptide-drug complex (EAR8-II-THP) are shown to be different while interacting with serum proteins compared with the properties of the isolated complex. The results from thermodynamic studies suggest that the drug delivery system has a strong binding affinity (K(SV) 1689 M(-1)), exothermic and enthalpy-driven interaction, with BSA and a relatively weak affinity with IgG (K(SV) 295.2 M(-1)). In the presence of salt ions, the enthalpy and binding affinity remain unchanged, implying other interactions such as hydrogen bonding and Van der Waals interactions are present that are not affected by reduced polarity. This work forms the basis for further studies of EAR8-II-THP complexes in the presence of important proteins and for further evaluation of the complexes' immune response and anticancer activity.

Conformational, thermal, and ionic conductivity behavior of PEO in PEO/PMMA miscible blend: Investigating the effect of lithium salt

AbstractIn this research, influence of incorporating LiClO4 salt on the crystallization, conformation, and ionic conductivity of poly(ethylene oxide) (PEO) in its miscible blend with poly(methyl methacrylate) (PMMA) is studied. Differential scanning calorimetry showed that the incorporation of salt ions into the blend suppresses the crystallinity of PEO. The X‐ray diffraction revealed that the unit‐cell parameters of the crystals are independent of the LiClO4 concentration despite of the existence of ionic interactions between PEO and Li cations. In addition, the complexation of the Li+ ions by oxygen atoms of PEO is investigated via Fourier transform infrared spectroscopy. The conformational changes of PEO segments in the presence of salt ions are studied via Raman spectroscopy. It is found that PEO chains in the blend possess a crown‐ether like conformation because of their particular complexation with the Li+ ions. This coordination of PEO with lithium cations amorphize the PEO and is accounted for suppressed crystallinity of PEO in the presence of salt ions. Finally, electrochemical impedance spectroscopy is used to characterize the ionic conductivity of PEO in the PEO/PMMA/LiClO4 ternary mixture at various temperatures. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A dielectric relaxation study of nanocomposite polymer electrolytes

(PEO)4:LiClO4 and the effect of δ-Al2O3 nano-fillers on the polymer electrolyte have been investigated by differential scanning calorimetry (DSC) and dielectric relaxation studies. The DSC studies indicated a decrease in the glass transition temperature of (PEO)4:LiClO4 in the presence of fillers. The polymer–salt complex exhibited a conductivity of σD.C.=4.0×10−7Scm−1 at room temperature (298K). In the presence of 4wt% δ-Al2O3 fillers, the ionic conductivity increased by almost two orders of magnitude and exhibited a value of σD.C.=1.5×10−5Scm−1 (298K). By comparing the conductivity data with the calorimetric glass transition it is evident that the enhanced conductivity can be attributed to a speeding up of the segmental polymer dynamics. Hence, the combined data indicate a direct coupling between Li+ ion motions and polymer segmental dynamics, even when 4wt% nano-fillers have been introduced. From the temperature dependence of the conductivity relaxation time, which, thus, is coupled to the structural (α) relaxation time, it is understood that the fragility of the polymer electrolytes decreases with increasing filler concentration. The decrease in Tg and fragility suggests that the interaction between the nano-fillers and polymer is mainly non-attractive in nature. Moreover, the dielectric relaxation studies show that the β-relaxation speeds up with increasing concentration of filler particles. However, this speeding up is probably of less importance for the ionic conductivity. It was also found that the activation energy of the β-relaxation of PEO decreases in the presence of δ-Al2O3 nano-fillers and lithium salt. The strength of the β-relaxation increases also in the presence of salt ions. The γ-relaxation seems to be unaffected by the salt and fillers.

Experimental and theoretical study on the β-FeOOH nanorods: growth and conversion

This study presents an experimental and theoretical study on the growth of monodispersed akaganeite (β-FeOOH) nanorods with tunable aspect ratios (longitudinal to transversal) under mild conditions (80 °C, aqueous solution). The synthesis of β-FeOOH nanorods is highly influenced by the presence of salt ions, and thus, the effect of various anions (e.g., NO3 −, SO4 2−, F−, Cl−, and Br−) were investigated on the microstructure, morphology, and size of the nanoparticles. It was found that these anions could interact strongly or weakly with the FeO6 octahedral unit in the ferric oxyhydroxides, hence greatly affect the morphology, crystallization, and structure of the iron oxide/oxyhydroxide nanoparticles under the reported conditions. Moreover, these nanorods could be converted into magnetite (Fe3O4) through the reduction of hydrazine, which provides a new template approach to prepare magnetite nanorods with shape and size control at ambient conditions. The microstructure, composition, and structural transformation of the as-synthesized nanoparticles were characterized by various techniques, such as transmission electron microscopy (TEM and HRTEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The possible formation and growth mechanism of akaganeite nanorods were discussed. Finally, the influence of anions on the β-FeOOH(100), (110), and (001) surfaces was further understood by theoretical simulations (e.g., molecular dynamics method).

Poly(triazine imide) with Intercalation of Lithium and Chloride Ions [(C3N3)2(NHxLi1−x)3⋅LiCl]: A Crystalline 2D Carbon Nitride Network

Poly(triazine imide) with intercalation of lithium and chloride ions (PTI/Li(+)Cl(-)) was synthesized by temperature-induced condensation of dicyandiamide in a eutectic mixture of lithium chloride and potassium chloride as solvent. By using this ionothermal approach the well-known problem of insufficient crystallinity of carbon nitride (CN) condensation products could be overcome. The structural characterization of PTI/Li(+)Cl(-) resulted from a complementary approach using spectroscopic methods as well as different diffraction techniques. Due to the high crystallinity of PTI/Li(+)Cl(-) a structure solution from both powder X-ray and electron diffraction patterns using direct methods was possible; this yielded a triazine-based structure model, in contrast to the proposed fully condensed heptazine-based structure that has been reported recently. Further information from solid-state NMR and FTIR spectroscopy as well as high-resolution TEM investigations was used for Rietveld refinement with a goodness-of-fit (χ(2)) of 5.035 and wRp=0.05937. PTI/Li(+)Cl(-) (P6(3)cm (no. 185); a=846.82(10), c=675.02(9) pm) is a 2D network composed of essentially planar layers made up from imide-bridged triazine units. Voids in these layers are stacked upon each other forming channels running parallel to [001], filled with Li(+) and Cl(-) ions. The presence of salt ions in the nanocrystallites as well as the existence of sp(2)-hybridized carbon and nitrogen atoms typical of graphitic structures was confirmed by electron energy-loss spectroscopy (EELS) measurements. Solid-state NMR spectroscopy investigations using (15)N-labeled PTI/Li(+)Cl(-) proved the absence of heptazine building blocks and NH(2) groups and corroborated the highly condensed, triazine-based structure model.

Spectroscopic investigations of CdTe quantum dot stability in different aqueous media

For the successful use of quantum dots (QDs) in biomedicine their chemical and optical stability is of great importance. In this study the changes of photoluminescence parameters of CdTe QDs coated with mercaptopropionic acid (MPA) dependently on time and environment are presented. The presence of salt ions in the QD water solution decreases photoluminescence band intensity and induces red shift. The pH value of the solution also influences spectroscopic properties of QDs. In the pH range from 2.5 to 9 a decrease of photoluminescence intensity is observed. The fastest one, leading to the complete luminescence bleaching, occurs in the most acidic medium. Changes of QD spectral properties in cell growth media were studied as well. The results imply that spectroscopic changes of CdTe‐MPA QDs are caused by the interactions between the ions present in the solution and ligand coating of QDs. The model of possible processes is proposed.

Probing Interactions between Aggrecan and Mica Surface by the Atomic Force Microscopy.

Aggrecan is a bottlebrush shaped macromolecule found in the extracellular matrix of cartilage. The negatively charged glycosaminoglycan (GAG) chains attached to its protein backbone give aggrecan molecules a high charge density, which is essential for exerting high osmotic swelling pressure and resisting compression under external load. In solution aggrecan assemblies are insensitive to the presence of calcium ions, and show distinct osmotic pressure versus concentration regimes. The aim of this study is to investigate the effect of ionic environment on the structure of aggrecan molecules adsorbed onto well-controlled mica surfaces. The conformation of the aggrecan were visualized using Atomic Force Microscopy. On positively charged APS mica the GAG chains of the aggrecan molecules are distinguishable, and their average dimensions are practically unaffected by the presence of salt ions. With increasing aggrecan concentration they form clusters, and at higher concentrations they form a continuous monolayer of conforming molecules. On negatively charged mica, the extent of aggrecan adsorption varies with salt composition. Understanding aggrecan adsorption onto a charged surface provides insight into its interactions with bone and implant surfaces in the biological milieu.

Surface chemistry aspects of coal flotation in bore water

Several theories have been proposed to explain enhancement of coal flotation in salt solutions. In this paper, surface chemistry aspects of coal flotation in bore (hypersaline) water were examined using bubble-particle attachment time experiments, zeta potential measurements, cyclic measurements of contact angle and Atomic Force Microscopy (AFM). The attachment time experiments showed that the bubble-particle attachment in deionized water was instantaneous and independent of the particle size. The attachment in bore water required longer time, which increased with increasing particle size. The cyclic measurements of contact angle on a flat coal surface showed that the coal hydrophobicity as measured by the advancing (maximum) and receding (minimum) contact angle did not change in the presence of salt ions. The zeta potential measurements show that both the coal particles and air bubbles were negatively charged in bore water. The AFM studies showed that bore water reduced repulsive surface forces between the coal particles and air bubbles but had little effect on the force of adhesion. The overall results suggest that enhancement of coal flotation in hypersaline water is not entirely attributed to the surface chemistry aspects as previously proposed.

Decoupling of the Nernst−Planck and Poisson Equations. Application to a Membrane System at Overlimiting Currents

This paper deals with one-dimensional stationary Nernst-Planck and Poisson (NPP) equations describing ion electrodiffusion in multicomponent solution/electrode or ion-conductive membrane systems. A general method for resolving ordinary and singularly perturbed problems with these equations is developed. This method is based on the decoupling of NPP equations that results in deduction of an equation containing only the terms with different powers of the electrical field and its derivatives. Then, the solution of this equation, analytical in several cases or numerical, is substituted into the Nernst-Planck equations for calculating the concentration profile for each ion present in the system. Different ionic species are grouped in valency classes that allows one to reduce the dimension of the original set of equations and leads to a relatively easy treatment of multi-ion systems. When applying the method developed, the main attention is paid to ion transfer at limiting and overlimiting currents, where a significant deviation from local electroneutrality occurs. The boundary conditions and different approximations are examined: the local electroneutrality (LEN) assumption and the original assumption of quasi-uniform distribution of the space charge density (QCD). The relations between the ion fluxes at limiting and overlimiting currents are discussed. In particular, attention is paid to the "exaltation" of counterion transfer toward an ion-exchange membrane by co-ion flux leaking through the membrane or generated at the membrane/solution interface. The structure of the multi-ion concentration field in a depleted diffusion boundary layer (DBL) near an ion-exchange membrane at overlimiting currents is analyzed. The presence of salt ions and hydrogen and hydroxyl ions generated in the course of the water "splitting" reaction is considered. The thickness of the DBL and its different zones, as functions of applied current density, are found by fitting experimental current-voltage curves.

Carboxymethyl cellulose (CMC) based semi-IPNs as carriers for controlled release of ciprofloxacine: an in-vitro dynamic study

Semi-interpenetrating polymer networks (IPNs) of carboxymethyl cellulose (CMC) and polyacrylic acid were prepared and its potential for controlled release of ciprofloxacine (Cfx) was assessed. The IPNs were characterized by IR spectral analysis and Environmental scanning electron microscopy (ESEM). The entrapped drug was examined for its antibacterial activity and chemical stability. The effects of experimental parameters such as varying chemical composition of the IPNs, percent loading of Cfx, pH and temperature of release medium and presence of salt ions in outer solution were examined on the release profile of the drug. On the basis of Fick's power law equations, the diffusion exponents (n) and diffusion constant (D) were evaluated for different IPNs compositions. From the kinetic parameter data, an attempt was made to resolve the mechanism of the release process of Cfx.

Role of chain stiffness on the conformation of single polyelectrolytes in salt solutions

Conformation of single polyelectrolytes in tetravalent salt solutions is investigated under the framework of a coarse-grained model, using Langevin dynamics simulations. The chain size, studied by the radius of gyration, shows three different variational behaviors with salt concentration, depending on the chain stiffness. According to the size variations, polyelectrolytes of fixed chain length are classified into three categories: (1) flexible chain, for which the variation shows a curve similar to a tilted L, (2) semiflexible chain, whose curve resembles U, and (3) rigid chain, for which the curve is a straight line. The wormlike chain model with persistence length predicted by the Odijk-Skolnick-Fixman theory is found to be able to qualitatively describe the end-to-end distance at low salt concentration not only for semiflexible and rigid chains but also for flexible chain. In a low salt region, a flexible polyelectrolyte extends more significantly than a semiflexible chain, in reference of the size of their uncharged counterparts, and in a high salt region, regardless of chain stiffness, a chain attains a dimension comparable to that of its neutral polymer. The chain stiffness influences both the local and the global chain structures. A flexible chain exhibits a zigzagged local structure in the presence of salt ions, and the condensed structure is a disordered, random globule. A semiflexible chain is locally smooth, and the condensed structure is orderly packed, taking a form such as hairpin or toroid. Moreover, the chain stiffness can also affect the nature of the coil-globule transition. The transition occurred in a discrete manner for semiflexible chain, whereas it occurred in a continuous way for flexible chain. This discrete feature happened not only at low salt concentration when a semiflexible chain collapsed but also at high salt concentration when the collapsed chain is reexpanded. At the end, the effects of chain stiffness and salt concentration on the conformation of single polyelectrolytes are summarized in a schematic state diagram.

Enhanced Heating of Salty Ice and Water Under Microwaves: Molecular DynamicsStudy

Through the use of molecular dynamics simulations, we have studied the enhanced heating of salty ice and water by the electric field of applied microwaves at 2.5 GHz, and in the range of 2.5–10 GHz for the frequency dependence. We show that water molecules in salty ice are allowed to rotate in response to the microwave electric field to the extent comparable to those in pure water because the molecules in salty ice are loosely tied by hydrogen bonds with adjacent molecules unlike rigidly bonded pure ice. The weakening of hydrogen-bonded network of molecules in salty ice is mainly due to the electrostatic effect of salt ions rather than the short-range geometrical (size) effect of salt since the presence of salt ions with small radii causes similar enhanced heating.

Effects of Contact Force and Salt Concentration on the Unbinding of a DNA Duplex by Force Spectroscopy

We report that varying the contact force in force spectroscopy results in a significant shift in DNA unbinding forces, measured from short oligonucleotides using a PicoForce microscope. The contact force between a 30-mer complementary DNA-coated probe and surface was varied from 100 pN to 10 nN, resulting in a significant shift in the most abundant unbinding force measured between the duplex. When contact forces were set at 200 pN or less, which is generally considered to be a low contact force region for biomolecular force spectroscopy studies, the shift in DNA unbinding forces was significant with changes in contact force. The effect of the salt concentration on the DNA unbinding forces was also examined for a range of salt concentrations from 5 to 500 mM because the presence of salt ions is necessary to facilitate the hybridization process. Although an increase in salt concentration resulted in the facilitation of DNA multiple binding events during force spectroscopy measurements, no significant shift in unbinding forces was observed. Our experiment demonstrates that the wide variation in DNA unbinding forces reported in the literature (50-600 pN) for short oligonucleotides can be accounted for by the different contact forces used and shows little or no effect of the salt concentration used in those studies. Furthermore, this study demonstrates the importance of reporting contact forces in force spectroscopy measurements for quantitative comparisons between different biomolecular systems, especially for noncovalent-type interactions.