Effect Of Salt Ions Research Articles

Thermo-pH-Salt Environmental Terpolymers Influenced by 2-((Dimethylamino)methyl)-4-methylphenyl Acrylate: A Comparative Study for Tuning Phase Separation Temperature.

This study offers a comparison between three different types of thermoresponsive (TR) and thermo-pH-salt (TPR) multiresponsive polymers including homopoly(N-isopropylacrylamide) (PNIPAAm), copolymers with three different monomers, 2-hydroxyethyl methacrylate (HEMA), N,N-dimethylacrylamide (DMAAm), and styrene (S) at three different concentrations (5, 10, and 20 mol %), and a PNIPAAm terpolymer with 5, 10, and 20 mol % 2-((dimethylamino)methyl)-4-methylphenyl acrylate (DMAMCA) and 10 mol % HEMA, DMAAm, and S monomers. All polymers were chemically analyzed with 1H NMR and Fourier transform infrared spectroscopy (FT-IR) as well as gel permeation chromatography (GPC) for the molecular weights and dispersity and differential scanning calorimeter (DSC) for the glass transition temperatures. The cloud point, also known as the phase separation temperature (Cp), was determined for all polymers by a turbidity test using a UV-vis spectrophotometer; a micro-differential scanning calorimeter was used for measuring the cloud point in deionized water. The influence of a tertiary amine cationic group of DMAMCA changed the behavior of TR copolymers into TPR by shifting the cloud point of the TPR to higher values in acidic solutions (lower pH) and to lower values in alkaline solutions. The Cp was measured at different concentrations of Hofmeister kosmotropic and chaotropic anion salt solutions in a range of pH solutions for the terpolymers. It demonstrated the same behavior as mentioned in pH solutions besides the effect of salt ions. By measuring the Tc and Cp of these polymers, we can exploit various applications of stimuli-responsive materials for sensors and biomedical technology.

On the 1H NMR spectra of weak electrolytes under the influence of strong electrolytes at low concentrations

Physical chemistry has yet to provide a convincing explanation for the many distinct ways the cosolute's properties are perturbed when under the field of action of salt ions. For that reason, a systematic and gradual approach to the problem was sought, with the present work being a step in that direction. Thus, acetic acid and n-butylamine were selected as simple models for the charged carboxyl and amine groups in more complex solutes, like proteins. The influence of the gradual addition of inorganic salts on these compounds' proton nuclear magnetic resonance spectra was analyzed. The salt concentration varied from 0.01 to roughly 100 mmol.L−1.The reported results suggest that at a low salt concentration (<c.a. 10 mmol.L−1), the effect on the properties of the weak electrolyte results from an indirect action of the salt ions. More specifically, strong electrolytes perturb the auto-dissociation of water whereby H+ or OH– ions are released. Some salts, like NaCl, releasing H+, suppress the dissociation of acetic acid and are neutral to n-butylamine. Other salts, like NaSCN, releasing OH–, shift the reaction of n-butylamine with water towards the reverse direction and are neutral to acetic acid. Moreover, the required quantity of added salt to promote the effects under consideration depends, to a considerable extent, on the valency of the salt ion, the decreasing order of efficacy being as follows: trivalent > divalent > monovalent.Therefore, the experimental facts herein reported show that the effect of salt ions at low concentrations upon the properties of other solutes can be rationalized by conventional chemical concepts, in which chemical equilibrium plays an important role. Furthermore, the results strongly support the classical interpretation of salt ions, which are charged bodies that, in solution, exert chiefly electrostatic forces.

Experimental and molecular dynamics study on the deterioration mechanism of GFRP bars in distilled water and salt solution environments

The deterioration speed of glass-fibre-reinforced polymer (GFRP) bars plays an important role in their long-term application in concrete. The deterioration mechanism of GFRP bars in different salt solutions and distilled water (DW) environments was determined by conducting a combination of water uptake, microscopic, Fourier transform infrared spectroscopy, and tensile strength (TS) tests. The interaction between the epoxy resin and water molecules and the effect of salt ions on the interior of the epoxy resin system were revealed by performing molecular dynamics (MD) simulation. The results showed that the water uptake and TS losses of the GFRP bars in DW were higher than those in the salt solution environments. Moreover, the TS losses of the GFRP were mainly due to the water uptake swelling and plasticization of the resin. In addition, the MD simulation, revealed that as the moisture uptake increased, the water molecule diffusion coefficient increased and the water-water hydrogen bonding dominated, leading to the occurrence of the water-clustering phenomenon. However, the presence of salt ions led to a low transport rate of water molecules inside the resin, thereby reducing the water-molecule-clustering phenomenon. Compared with monovalent cations (Na+ and K+), multivalent Ca2+ is more likely to bind to COO− ions inside the network system, reducing the electrostatic repulsion between the COO− ions and hindering the swelling of GFRP.

Design of salt-responsive low-viscosity and high-elasticity hydrophobic association polymers and study of association structure changes under high-salt conditions

A hydrophobic associative water-soluble polymer, SRHV, was designed and synthesized in this study. The CAC of SRHV was 0.072 wt% and 0.2 wt%. The scanning electron microscopy tests showed that the polymer demonstrated a multilayer network structure. Rheological tests revealed that polymer solution exhibited low-viscosity and high-elasticity rheological behaviors under high-salinity conditions and this salt-responsive behavior persists at high temperatures. Fluorescent probe tests confirmed that salt addition promoted the formation of hydrophobic association networks. Through molecular dynamics simulation, various parameters, such as mean square displacement (MSD), radius of gyration (Rg), and radial distribution function (RDF), were analyzed to further explain the salt-tolerance mechanism of SRHV and the effect of salt ions on the hydrophobic association structure. The results showed that the viscosity and elasticity of polymers were not necessarily correlated. In addition, elasticity dominated when the positive effect of salt-promoted association exceeded the negative effect of salt-coiled molecular chains and polymer relies on elasticity to achieve an excellent sand-carrying effect at this time. In general, SRHV exhibits great potential for application in oil fields with high salt environment, which could effectively reduce the waste of freshwater resources. Furthermore, this work provides some support for suspending sand relying on elastic.

Effect of CaCl2 on 2 heat-induced whey protein concentrate fibrillation pathways: Spontaneous and nuclear induction

Amyloid fibrils have many excellent functional properties that facilitate their applications in the food industry. There are 2 pathways for whey protein concentrate (WPC) to form amyloid fibril aggregates: spontaneous pathway and nuclear induction pathway. Low ionic strength is a necessary condition for the spontaneous pathway to proceed successfully. In this paper, the effect of salt ions on 2 WPC fibrillation pathways was investigated by adding CaCl2. The results demonstrated WPC fibrils were unable to form normally through spontaneous pathway as adding CaCl2; but still could form through nuclear induction pathway with 20 to 30 mM CaCl2, the nuclei accelerated the fibrillation process led to the resistance to the disordered aggregation brought by CaCl2. Moreover, divalent cations (Ca2+, Mg2+) had much stronger effects than monovalent cations (Na+) on fibril formation, and the results of X-ray photoelectron spectrum together with Fourier-transform infrared spectroscopy suggested that Ca2+ had a greater effect on the fibril formation than Cl-.

Effect of salt ions on an ultrasonically modified soybean lipophilic protein nanoemulsion

SummarySoybean lipophilic proteins (LP) are promising emulsifiers for nanoemulsion delivery systems. We analysed the effect of common salt ions on the stability of nanoemulsion delivery systems that contained ultrasonically modified soybean LP. Moreover, explored the mechanism of influence. The LP nanoemulsions presented large absolute zeta (ζ) potentials at low salt ion concentrations, and their particle size distribution was relatively uniform. The emulsification, encapsulation efficiency and oxidation stability were superior to those of other nanoemulsions. The ultrasonically modified samples presented higher absolute ζ potentials and smaller droplet sizes than the pristine ones and formed uniform protein films at different salt ion concentrations. Therefore, ultrasonication improved the emulsification, encapsulation efficiency and oxidation stability of the emulsions, effectively improve the stability of nano‐delivery systems in different salt ion environments and maximise delivery efficiency at low salt ion concentrations. These results are helpful for the development of LP nanoemulsion systems that are stable at different salt ion concentrations.

The role of salt ions and organic molecules in the self-assembled nanolayering

This study investigated effects of polyacrylic acid (PAA) on nanolayering self-assembly, and effects of salt ions on the formation of nanolayering after their chemical interaction with 10-methacryloyloxydecyl dihydrogen phosphate (MDP). ACP–MDP suspension was prepared by dispersing 0.01 g ACP nanoparticles in 4 mL of a 5 wt% MDP solution. Then a PAA solution (100 or 500 μg/mL) was mixed into ACP–MDP suspension. The reaction products were analyzed by transmission electron microscope (TEM). After one of the following metal chlorides (each 0.076 mM of CaCl2, BaCl2, AlCl3, FeCl2, FeCl3, MnCl2, CuCl2, ZnCl2, or MgCl2) was dispersed in a 4 mL MDP solution, they were further analyzed by X-ray diffraction (XRD) and TEM. ACP nanoparticles in the MDP solution could self-assemble into ACP–MDP nanolayering composites. The TEM images show that an amount of ACP nanoparticles were aggregated and fused together after the addition of PAA into ACP–MDP suspensions, while no nanolayering was found. The XRD data and TEM images reveal that nanolayering was self-assembled after the chemical interaction of MDP with some metal chlorides (CaCl2, BaCl2, AlCl3, FeCl2, FeCl3, MnCl2), but not with the others (ZnCl2, CuCl2, MgCl2). PAA could inhibit the self-assembly of nanolayering. Some salt ions play an important role in highly ordered, self-assembled nanostructure after their chemical interaction with MDP. The finding is helpful for functional materials fabrication.

Effects of salt ions and heating on the behaviour of whey protein particle dispersions

We investigated the aggregation stability of whey protein isolate (WPI) particles in the presence of different salts (NaCl, MgCl2, and AlCl3) and the heat stability of dispersions in the presence of protein (native WPI) and polysaccharides (dextran and gum Arabic, GA). WPI particles coagulated either at pH values close to the iso-electric point of proteins or at high salt concentrations. Critical coagulation concentration (CCC) for different salts decreased with increasing valence of ions. CCC values for colloidal WPI particle dispersions closely followed the Schulze-Hardy rule, which is derived from the DLVO theory; however, deviations from the theory, particularly in the case of multivalent ions, showed that the specific ion adsorption also played a role. To investigate the heat stability of WPI particles, particle size and viscosities of dispersions containing different biopolymers were measured. Using dynamic viscosity of dilute dispersions, with the assumption of no particle aggregation after heating, swelling ratio (SR) of particles was estimated. Increasing concentrations of biopolymers decreased the SR of particles, and the presence of GA totally inhibited the swelling. Shear viscosity of concentrated dispersions showed an increase and shear-thickening behaviour after heating, when native WPI or dextran was present, whereas viscosity did not change when GA was present in the continuous phase. At low volume fractions, swelling was more likely to occur; whereas at high volume fractions, possibly both swelling and aggregation occurred. In addition, concentration and type of biopolymer were found to be important for the heat stability of dispersions.

Assessment of the Rheological Behavior of Polymer–Oxidant Mixtures and the Influence of the Groundwater Environment on Their Properties

Shear-thinning polymers have been introduced to contaminant remediation in the subsurface as a mobility control method applied to mitigate the inefficient delivery of remedial agents caused by geological heterogeneity. Laboratory experiments have been conducted to assess the compatibility of polymers (xanthan and hydrolyzed polyacrylamide (HPAM)) and oxidants (KMnO4 and Na2S2O8) through quantitative evaluation of the viscosity maintenance, shear-thinning performance, and oxidant consumption. The mechanism that causes viscosity loss and the influence of the groundwater environment on the mixture viscosity were also explored. The xanthan–KMnO4 mixture exhibited the best performance in both viscosity retention and shear-thinning behavior with retention rates higher than 75% and 73.5%, respectively. Furthermore, the results indicated that xanthan gum has a high resistance to MnO4− and that K+ plays a leading role in its viscosity reduction, while HPAM is much more sensitive to MnO4−. The viscosity responses of the two polymers to Na2S2O8 and NaCl were almost consistent with that of KMnO4; salt ions displayed an instantaneous effect on the solution’s viscosity, while the oxide ions could cause the solution’s viscosity to decrease continuously with time. Since xanthan exhibited acceptable oxidant consumption as well, xanthan–KMnO4 is considered to be the optimal combination. In addition, the results implied that the effects of salt ions and the water pH on the mixture solution could be acceptable. In the 2D tank test, it was found that when xanthan gum was introduced, the sweeping efficiency of the oxidant in the low-permeability zone was increased from 28.2% to 100%. These findings demonstrated the feasibility of using a xanthan–KMnO4 mixture for actual site remediation.

A Theoretical Investigation on the pH Responses of Strong Polyelectrolyte Brushes

The pH responsive properties of poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC) brushes have been manifested in an experiment carried out by Liu et al. (2017). In this paper, we have employed a molecular theory to study the pH response of strong polyelectrolyte brushes (SPBs), by considering both strong polyelectrolyte-OH− (P–O) hydrogen bonds and polyelectrolyte-counterions (P–C) bonds and their explicit coupling to the SPB conformation. It is found that, when at lower salt concentrations, the combination of P–O hydrogen bonds and P–C bonds results in the pH-responsive properties of a SPB, which are governed by the formation of interchain hydrogen bonds, while at higher salt concentrations, the pH response of the SPB is suppressed by the effect of salt ions. This finding agrees well with the experimental observation. We also investigate the OH−-mediated bridging effect on the structure of a SPB. Based on this theoretical perspective, we predict that the pH response of a SPB will depend on the identity of salt, and the OH−-mediated bridging interactions can induce a vertically phase segregation in a SPB.

Effects of Salt Ions on the Methane Hydrate Formation and Dissociation in the Clay Pore Water and Bulk Water

Gas hydrates in marine sediments are promising energy resources, while an effective recovery of methane from clay pores relies on a comprehensive appreciation of the hydrate evolution inside and outside the pore especially at a saline environment. Molecular dynamics simulations were conducted to investigate the methane hydrate formation and dissociation in the sodium montmorillonite (Na-MMT) interlayer with fresh water and saline water, respectively, by characterizing the distribution and transportation of methane and ions (K+, Na+, and Ca2+), the overall and local four-body structural order parameter, and the radial distribution functions. Results indicated that it was much easier to form methane hydrates in the bulk water than in the pore water, while the hydrates in the pore region were more readily dissociated than in the bulk region. The effects of salt ions on the hydrate formation were opposite in these two regions, which highlighted the role of the salting-out effect and the ion exchange between b...

Effects of salt ions on rheological properties of SPI-GG hybrid system

The rheological characteristic of soy protein isolate (SPI), is one of the most important properties in its application in food industry. The effects of different concentrations of guar gum (GG, polysaccharide) and sodium chloride (salt ion) on the rheological properties of SPI were studied in this research. Steady-state shear, strain sweep and frequency sweep tests (static and dynamic rheological tests) were performed, and the following phenomenon and conclusions were drawn: (1) The viscosity of the hybrid system increases with the GG addition. This trend could also be seen with the appropriate adding of salt ion; (2) As the applied frequency increases, the storage modulus G′ and the loss modulus G″ of the hybrid system increase at a similar rate. And the frequency sweep parameters of the hybrid system rise significantly with the increase of both GG and ionic concentration; The frequency dependence of the system varies significantly with the addition of salt ion; (3) With the concentration of the salt ion increase, the storage module G′ of the hybrid system decrease indicating that salt ion destroyed the network structure of hybrid dispersion to a certain extent. Keywords: guar gum, salt ions, soy protein isolate, rheological property, frequency dependence, food additive DOI: 10.25165/j.ijabe.20171005.3245 Citation: Bi C H, Zhang Y L, Wu M, Ni Z J, Li G, Liu Y, et al. Effects of salt ions on rheological properties of SPI-GG hybrid system. Int J Agric & Biol Eng, 2017; 10(5): 234–241.

Effects of salt ions on rheological properties of SPI-GG hybrid system

The rheological characteristic of soy protein isolate (SPI), is one of the most important properties in its application in food industry. The effects of different concentrations of guar gum (GG, polysaccharide) and sodium chloride (salt ion) on the rheological properties of SPI were studied in this research. Steady-state shear, strain sweep and frequency sweep tests (static and dynamic rheological tests) were performed, and the following phenomenon and conclusions were drawn: (1) The viscosity of the hybrid system increases with the GG addition. This trend could also be seen with the appropriate adding of salt ion; (2) As the applied frequency increases, the storage modulus G′ and the loss modulus G″ of the hybrid system increase at a similar rate. And the frequency sweep parameters of the hybrid system rise significantly with the increase of both GG and ionic concentration; The frequency dependence of the system varies significantly with the addition of salt ion; (3) With the concentration of the salt ion increase, the storage module G′ of the hybrid system decrease indicating that salt ion destroyed the network structure of hybrid dispersion to a certain extent. Keywords: guar gum, salt ions, soy protein isolate, rheological property, frequency dependence, food additive DOI: 10.25165/j.ijabe.20171005.3245 Citation: Bi C H, Zhang Y L, Wu M, Ni Z J, Li G, Liu Y, et al. Effects of salt ions on rheological properties of SPI-GG hybrid system. Int J Agric & Biol Eng, 2017; 10(5): 234–241.

The effects of salt ions on the dynamics and thermodynamics of lysozyme unfolding

ABSTRACTClassical molecular dynamics (MD) simulations coupled with metadynamics (MTD) simulations were used to investigate lysozyme unfolding in physiological 0.154 M NaCl salt concentration as well as in 0.5 and 1 M NaCl salt solutions. It was found that lysozyme unfolding dynamics is strongly dependent on the salt concentration. Moreover, the stable low energy denatured states are also different in different salt concentrations. Salt ion−protein interaction seems to stabilize both the native and denatured states, but their relative stability depends on salt concentration. Our simulation results and complementary experimental measurements demonstrate that salt ion−protein interactions facilitate lysozyme unfolding.

Effect of Salt Ions on the Proton-Transfer Rate in 3-Hydroxyflavone

The effects of lithium and chloride ions on the spectral characteristics of the two-band fluorescence of 3-hydroxyflavone solutions were studied. The obtained absorption, emission, and fluorescence excitation spectra showed that the salt ions effectively modulated intramolecular proton transfer in the excited state, which led to increases in the shortwavelength band intensity and the fluorescence quantum yield. Thus, the quantum yield for 3-hydroxyflavone in acetonitrile with salt concentrations 0.005, 0.01, and 0.02 M increased by 1.5, 2.0, and 3.0 times, respectively, with standard excitation in the principal absorption band. The intensity ratio of the short-wavelength and longwavelength bands also increased as the salt concentration increased. The increase was so significant that the color change of the fluorescence was easily noticed visually. The good sensitivity of the fluorescence-band intensity ratio to the salt concentration could provide a basis for solving the inverse problem, i.e., determining the salt concentration in solutions and biological objects. An explanation allowing the obtained changes in the fluorescence spectral properties after adding LiCl to the solution to be interpreted was proposed.

Key factors influencing water diffusion in aromatic PA membrane: Hydrates, nanochannels and functional groups

Desalination by aromatic polyamide (PA) composite membranes is currently the most important technology of solving the global freshwater crisis. However, understanding the main factors influencing water diffusion in the desalination process remains a major hurdle in designing new membrane materials. Here, we investigate the key roles of the hydrates, the nanochannels in a PA membrane and the functional groups of the membrane on water diffusion by molecular dynamic simulations. Results show that the membrane can strongly hinder the diffusions of water molecules via both geometrical obstruction and water–membrane interaction when the radius of the water diffusion channel in the membrane is less than 8.75Å. Conversely, the membrane has little influence on water diffusion. In a dilute NaCl solution, the effect of salt ions on the overall diffusion behavior of water can be neglected because only a small quantity of water molecules form hydrates. Almost all Na+ and Cl−, on the contrary, can form hydrates, which could explain why the PA membrane has a higher rejection level to salt ions rather than to water in seawater.

Salt effects on hydrophobic-core formation in folding of a helical miniprotein studied by molecular dynamics simulations

We have investigated effects of salt ions on folding events of a helical miniprotein chicken villin headpiece subdomain HP36. Low concentrations of ions alter electrostatic interactions between charged groups of a protein and can change the populations of conformers. Here, we compare two data sets of folding simulations of HP36 in explicit water solvent with or without ions. For efficient sampling of the conformational space of HP36, the multicanonical replica-exchange molecular dynamics method was employed. Our analyses suggest that salt alters salt-bridging nature of the protein at later stages of folding at room temperature. Especially, more nonnative, nonlocal salt bridges are formed at near-native conformations in pure water. Our analyses also show that such salt-bridge formation hinders the fully native hydrophobic-core packing at the final stages of folding.

Freezing and Melting of Salt Hydrates Next to Solid Surfaces Probed by Infrared–Visible Sum Frequency Generation Spectroscopy

Understanding the freezing of salt solutions near solid surfaces is important in many scientific fields. Here we use sum frequency generation (SFG) spectroscopy to study the freezing of a NaCl solution next to a sapphire substrate. During cooling we observe two transitions. The first corresponds to segregation of concentrated brine next to the sapphire surface as we cool the system down to the region where ice and brine phases coexist. At this transition, the intensity of the ice-like peak decreases, suggesting the disruption of hydrogen-bonding by sodium ions. The second transition corresponds to the formation of NaCl hydrates with abrupt changes in both the SFG intensity and the sharpness of spectral peaks. The similarity in the position of the SFG peaks with those observed using IR and Raman spectroscopy indicates the formation of NaCl·2H2O crystals next to the sapphire substrate. The melting temperatures of the hydrates are very similar to those reported for bulk NaCl·2H2O. This study enhances our understanding of nucleation and freezing of salt solutions on solid surfaces and the effects of salt ions on the structure of interfacial ice.

Effect of salt ions on protein layers at the air–water interface under a crystallization condition

The density profiles of lysozyme layers at the air–water interface before and after adding salt were determined by X-ray reflection. After adding salt, the density of the lysozyme (LSZ) layers decreases, whereas the thickness drastically increases. The salt ions are considered to increase the LSZ–LSZ interaction, and consequently decrease the surface activity of LSZ, allow adsorbed lysozyme molecules crystallize.

The Effects of NaCl on Oxidized Lipid Bilayers

Lipid peroxidation plays an important role in cell membrane damage in which the polyunsaturated lipids are the main target for free radicals. The lipid bilayer systems of 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphatidylcholine (PLPC) and its 4 main oxidation products, namely 9-tc-hydroperoxide linoleic acid, 13-tc-hydroperoxide linoleic acid, 9-oxononanoic acid, and 12-oxo-9-didecadienoic acid were used to study the properties of oxidized lipid bilayer {Wong-ekkabut J., et al., Biophys. J., 2007 }. Our study showed that the oxidized lipid molecules were able to change the physical and mechanical properties of lipid bilayer. The effect of salt ions, important in living cells, have not been studied previously. Here, the effects of NaCl on the properties of oxidized lipid bilayers were studied by using molecular dynamics simulations. We found that the effects of the oxidized lipids in the bilayer were in good agreement with the previous studies {Wong-ekkabut J., et al., Biophys. J., 2007 }. The increasing concentrations of the oxidized lipids caused an increase of the area per lipid and a decrease of the bilayer thickness. A stable water defect was formed in the bilayer at a high concentration of oxidized lipids because the polar group in the oxidized lipid tail attracted the water dipoles. When salt molecules were added, sodium ions permeated into the head group region leading to a decrease of the area per lipid and an increase of the bilayer thickness. Our results show that salt ions decrease membrane fluidity and water permeability of the oxidized lipid bilayer.