Function Of NaCl Concentration Research Articles

The selective breeding of the freshwater microalga Chlamydomonas reinhardtii for growth in salinity

The potential for Chlamydomonas reinhardtii to be utilized for biofuel production was strengthened by developing it for growth in elevated salinity via the selective breeding method of genome shuffling. A population was constructed via random mutagenesis and subjected to multiple rounds of sex and growth in increasing salinity. This sexual line was capable of growth in up to 700mM NaCl, unlike its progenitor, which could only grow in 300mM NaCl. An asexual control line was capable of growth in 500mM NaCl. Palmelloid aggregations increased in size and the concentration of final biomass decreased as a function of NaCl concentration, which poses considerations for future strain development. The sexual line maintained sexual efficiencies of up to 50% over the course of selection. This investigation achieved significant strain improvement of C. reinhardtii and demonstrated the clear advantage of its ability to participate in laboratory controlled and reproducible high efficiency sex.

Phase Diagram of Sodium Hexametaphosphate and Poly(allylamine hydrochloride) Mixtures and In Situ Monitoring of Step‐by‐Step Deposition in This Polyelectrolyte System

The step‐by‐step deposition of poly(allylamine hydrochloride) (PAH) and sodium hexameta­phosphate (PSP) leads to coatings displaying interesting intumescent properties and is a fascinating model system to understand the fundamental mechanism behind such a deposition process. In this investigation, the deposition kinetics of (PAH‐PSP)n is followed in situ by means of a quartz crystal microbalance with dissipation monitoring, as a function of NaCl concentration. The evolution of the film deposition is analyzed in detail and the data are compared with previous data obtained by ellipsometry on dried films. These results are also compared with the expectations from the PAH/PSP phase diagram. The (PAH‐PSP)n films are also able to incorporate hexacyanoferrate anions with an amount of an incorporated redox probe reflecting the film thickness as obtained in the presence of eletrolyte solutions of increasing ionic strength. The in situ measurements and the electrochemical probe experiments reveal details of the film deposition mechanism that are not accessible by dry‐state characterization methods. image

Characterization of a dielectric phantom for high-field magnetic resonance imaging applications.

In this work, a generic recipe for an inexpensive and nontoxic phantom was developed within a range of biologically relevant dielectric properties from 150 MHz to 4.5 GHz. The recipe includes deionized water as the solvent, NaCl to primarily control conductivity, sucrose to primarily control permittivity, agar-agar to gel the solution and reduce heat diffusivity, and benzoic acid to preserve the gel. Two hundred and seventeen samples were prepared to cover the feasible range of NaCl and sucrose concentrations. Their dielectric properties were measured using a commercial dielectric probe and were fitted to a 3D polynomial to generate a recipe describing the properties as a function of NaCl concentration, sucrose concentration, and frequency. Results indicated that the intuitive linear and independent relationships between NaCl and conductivity and between sucrose and permittivity are not valid. A generic polynomial recipe was developed to characterize the complex relationship between the solutes and the resulting dielectric values and has been made publicly available as a web application. In representative mixtures developed to mimic brain and muscle tissue, less than 2% difference was observed between the predicted and measured conductivity and permittivity values. It is expected that the recipe will be useful for generating dielectric phantoms for general magnetic resonance imaging (MRI) coil development at high magnetic field strength, including coil safety evaluation as well as pulse sequence evaluation (including B₁(+) mapping, B₁(+) shimming, and selective excitation pulse design), and other non-MRI applications which require biologically equivalent dielectric properties.

Centrifugation-based assay for examining nanoparticle–lipid membrane binding and disruption

Centrifugation-based assays are commonly employed to study protein-membrane affinity or binding using lipid bilayer vesicles. An analogous assay has been developed to study nanoparticle-membrane interactions as a function of nanoparticle surface functionalization, membrane lipid composition, and monovalent salt concentration (NaCl). Anionic (carboxylic acid, Ag-COOH), cationic (amine, Ag-NH), and polyethylene glycol coated (Ag-PEG) silver nanoparticles (AgNPs) were examined based on their surface plasmon resonance (SPR), which was used to determine the degree of binding to anionic, cationic, and zwitterionic membrane vesicles by analyzing supernatant and sediment phases. SPR was also used to examine AgNP aggregation in solution and at membrane-water interfaces, and direct visualization of AgNP-membrane binding, vesicle aggregation, and vesicle disruption was achieved by cryogenic transmission electron microscopy (cryo-TEM). The extent of AgNP binding, based on AgNP + vesicle heteroaggregation, and vesicle disruption was dependent upon the degree of electrostatic attraction. Because of their biological and environmental relevance, Ag-PEG + anionic vesicles systems were examined in detail. Cryo-TEM image analysis was performed to determine apparent membrane-water partition coefficients and AgNP aggregation states (in solution and bound to membranes) as a function of NaCl concentration. Despite possessing a PEG coating and exhibiting a slight negative charge, Ag-PEG was able to bind to model anionic bacterial membranes either as individual AgNPs (low salt) or as AgNP aggregates (high salt). The centrifugation assay provides a rapid and straightforward way to screen nanoparticle-membrane interactions.

Polymorphic Protein Crystal Growth: Influence of Hydration and Ions in Glucose Isomerase.

Crystal polymorphs of glucose isomerase were examined to characterize the properties and to quantify the energetics of protein crystal growth. Transitions of polymorph stability were measured in poly(ethylene glycol)/NaCl solutions, and one transition point was singled out for more detailed quantitative analysis. Single crystal x-ray diffraction was used to confirm space groups and identify complementary crystal structures. Crystal polymorph stability was found to depend on the NaCl concentration, with stability transitions requiring > 1 M NaCl combined with a low concentration of PEG. Both salting-in and salting-out behavior was observed and was found to differ for the two polymorphs. For NaCl concentrations above the observed polymorph transition, the increase in solubility of the less stable polymorph together with an increase in the osmotic second virial coefficient suggests that changes in protein hydration upon addition of salt may explain the experimental trends. A combination of atomistic and continuum models was employed to dissect this behavior. Molecular dynamics simulations of the solvent environment were interpreted using quasi-chemical theory to understand changes in protein hydration as a function of NaCl concentration. The results suggest that protein surface hydration and Na+ binding may introduce steric barriers to contact formation, resulting in polymorph selection.

Effect of Organic Additives on the Solubility Behavior and Morphology of Calcium Sulfate Dihydrate (Gypsum) in the Aqueous Sodium Chloride System and Physicochemical Solution Properties at 35 °C

The effect of the addition of organic solvents, such as ethyl acetate (EA), glycerol (GLY), isopropyl alcohol (IPA), dimethylformamide (DMF), oxalic acid (OA), and propylamine (PA), on the solubility behavior of calcium sulfate dihydrate (gypsum, CaSO4·2H2O) in aqueous NaCl solutions has been examined at 35 °C. Compared to organic solvent free system, the addition of EA slightly increased CaSO4·2H2O solubility, whereas only a little alteration in solubility was found with the addition of GLY. CaSO4·2H2O solubility decreased significantly and to nearly same extent with the addition of IPA or DMF. In the solutions containing PA or OA, CaSO4·2H2O dissolution was very limited probably due to precipitation of highly stable Ca salts of these organic solvents. Except OA, where no solubility maximum was observed, the addition of organic solvents did not shift the solubility maximum of CaSO4·2H2O as a function of NaCl concentration in solution, and the solubility pattern remained similar. Accurate data on density (ρ) and speed of sound (u) data have been recorded for the quaternary systems (CaSO4·2H2O + NaCl + H2O + organic solvent) at 35 °C. Measurements of u and ρ have been used to determine the solution isentropic compressibility (κS). Empirical equations describing the solubility, density, speed of sound, and isentropic compressibility in these systems are presented. The morphology of CaSO4·2H2O recrystallized from different aqueous–organic solvent solutions and aqueous-NaCl-organic solvent solutions has also been examined from scanning electron microscopy (SEM).

Salt-tuned phase separation of poly(S-co-Nipam) core-shell particles via interfacial in situ polymerization

In this study, temperature-sensitive amphiphilic core-shell nanoparticles of N-isopropylacrylamide (NIPAM) were prepared via interfacial in situ polymerization of styrene (S) and NIPAM. Oil soluble cumene hydroperoxide (CHPO) oxidizer and water soluble reductant iron(II) sulfate (FS), polyurethane and hexadecane were used as interfacial initiation pair, surfactant and co-stabilizer, respectively. Radicals are produced and initiate polymerization only when the CHPO and FS are present at oil/water interface. FT-IR and 1H NMR spectroscopy confirmed the co-polymerization of these monomers. The core-shell structure with a diameter 150 nm was corroborated by TEM and FESEM. DSC analysis showed the existence of two glassytransition temperatures of the resulting particles. Salt-tuned phase separation behavior of poly(S-co-NIPAM) core-shell particles has been studied by dynamic light scattering. The lower critical solution temperature of the core-shell particles decreased linearly as a function of NaCl concentration that was attributed to the “salt out effect”. The variation of particle diameter showed a sigmoidal plot as a function of temperature regardless of the salt concentration.

Comparison of electrical conductivities of various brain phantom gels: Developing a ‘brain gel model’

The use of conducting gels to mimic brain and other tissues is of increasing interest in the development of new medical devices. Currently, there are few such models that can be utilized at physiologic temperatures. In this work, the conductivities of agar, agarose and gelatin gels were manipulated by varying NaCl concentration from 0–1mg/ml. The AC conductivity was measured at room and physiological temperatures (37°C) in the 100–500Hz frequency range. Conductivity (σ) was nearly independent of frequency but increased linearly with NaCl concentration and was higher at physiological temperatures in these gels. A formula for predicting conductivity as a function of NaCl concentration was derived for each gel type. The overall goal is to develop a ‘brain gel model’, for studying low frequency electrical properties of the brain and other tissues at physiological temperatures.

Distinct neural ensembles in the rat gustatory cortex encode salt and water tastes

The gustatory cortex (GC) is important for perceiving the intensity of tastants but it remains unclear as to how single neurons in the region carry out this function. Previous studies have shown that taste-evoked activity from single neurons in GC can be correlated or anticorrelated with tastant concentration, yet whether one or both neural responses signal intensity is poorly characterized because animals from these studies were not trained to report the intensity of the concentration that they tasted. To address this issue, we designed a two-alternative forced choice (2-AFC) task in which freely licking rats distinguished among concentrations of NaCl and recorded from ensembles of neurons in the GC. We identified three neural ensembles that rapidly (<300 ms or ∼2 licks) processed NaCl concentration. For two ensembles, their NaCl evoked activity was anticorrelated with NaCl concentration but could be further distinguished by their response to water; in one ensemble, water evoked the greatest response while in the other ensemble the lowest tested NaCl concentration evoked the greatest response. However, the concentration sensitive activity from each of these ensembles did not show a strong association with the behaviour of the rat in the 2-AFC task, suggesting a lesser role for signalling tastant intensity. Conversely, for a third neural ensemble, its neural activity was well correlated with increases in NaCl concentration, and this relationship best matched the intensity perceived by the rat. These results suggest that this neuronal ensemble in GC whose activity monotonically increases with concentration plays an important role in signalling the intensity of the taste of NaCl.

Water-Diesel Microemulsions Stabilized by an Anionic Extended Surfactant and a Cationic Hydrotrope

Alcohol-free microemulsions were formulated using mixtures of extended surfactant (C12-14-PO14-EO2SO4Na), sodium dodecyl benzene sulfonic acid and cationic hydrotropes with equal amounts of water and diesel. The cationic hydrotropes had short hydrocarbon or propylene oxide chain. The formulation included sodium carbonate to convert naphthenic acids in diesel to soaps. The phase behavior at ambient temperature of oil-free mixtures as a function of NaCl concentration was investigated. Visual inspection as well as cross polarizers were used to detect anisotropy. The microemulsion fish phase diagram and solubilization ratios for diesel and brine in the middle phases were determined. The minimum surfactant concentration needed to initiate middle phase formation was 0.10 wt%. Salinity scans revealed that optimal salinity can be adjusted according to the hydrophilic/lipophilic nature of the hydrotrope used. Interfacial tension measurements using a spinning drop tensiometer showed a minimum value of 0.0015 mN/m between middle phase microemulsion and excess brine and a value of 0.032 mN/m between diesel and brine.

Formation of Polyelectrolyte Multilayers by Flexible and Semiflexible Chains

Poly(sodium 4-styrene sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) are flexible polyelectrolytes, whereas sulfated chitosan (SC) and cationic guar gum (CGG) are semiflexible polyelectrolytes. By use of a quartz crystal microbalance with dissipation (QCM-D), a zeta potential analyzer (ZPA), and atomic force microscopy (AFM), we have investigated the growth of PSS/PDDA, PSS/CGG, SC/PDDA, and SC/CGG multilayers as a function of NaCl concentration (C(NaCl)). For the same layer number, the changes of frequency (-Δf) and dissipation (ΔD) regarding PSS/PDDA multilayer increase with C(NaCl), whereas -Δf and ΔD for SC/CGG multilayer increase at C(NaCl) < 0.1 M and decrease at C(NaCl) > 0.1 M as C(NaCl) increases. In the cases of PSS/CGG and SC/PDDA multilayer, for the same layer number, -Δf and ΔD increase with C(NaCl) in the range of C(NaCl) < 0.5 M, and they decrease with the increasing C(NaCl) in the case of SC/PDDA multilayer but slightly change for the PSS/CGG multilayer at C(NaCl) > 0.5 M. QCM-D studies indicate that the growth of multilayers as a function of salt concentration is determined by the delicate balance between the weakening of electrostatic repulsion between identically charged groups and the decrease of electrostatic attraction between neighboring layers. ZPA and AFM measurements demonstrate that the extent of surface charge overcompensation and the surface morphology of the multilayers are controlled by the chain conformation.

Effects of pH, NaCl, ethanol, and drying methods on the solubility of Saccharomyces cerevisiaeproteins

Proteins were produced by fed-batch fermentation of Saccharomyces cerevisiaecultivated on date solution. Protein content was 52.5% (dry basis). Protein solubility was studied as a function of pH, NaCl concentration, and solvent. The minimum protein solubility was at pH 4 and the maximum was at pH 12. As a function of NaCl concentration, protein solubility was 647.6 g/kg for 1 M. The best solubility was 916.3 g/kg under pH 12 and 1 M NaCl. Solubility was very low, 2.1 g/kg, when ethanol was used as a solvent. Biomass was dried by air drying, vacuum drying, and freeze drying. The best solubility of 937.5 g/kg was obtained using freeze and vacuum drying methods.

Galvanic Corrosion of a Zn/steel Couple in Aqueous NaCl

Galvanic corrosion of a model Zn/steel couple was investigated in aqueous NaCl solutions by measuring open circuit potentials (OCPs), potential and current distributions, and galvanic currents. The OCP transient of the Zn/steel couple was divided into two stages. The first stage consisted of sacrificial dissolution of zinc. At low concentrations of NaCl (0.01 mol/dm3), the cathodic reaction on the couple surface was an oxygen reduction reaction (ORR). With increasing concentrations of NaCl, the cathodic reaction at the steel surface changed from an ORR to the combination of an ORR and hydrogen evolution reaction (HER). In addition, the precipitation morphology of zinc corrosion products differed as a function of NaCl concentration, suggesting that the pH distribution on the couple surface depended on the relationship between the cathodic reactions and the hydrolysis of Zn2+. Furthermore, the findings demonstrated that both the ORR and HER were inhibited at the steel underlying precipitated zinc corrosion products. The second stage consisted of steel corrosion. The location of the onset of steel corrosion was related to the pH distribution just prior to the extinction of the galvanic action of zinc.

Sedimentation of Polyelectrolyte Chains in Aqueous Solutions

We have investigated the dynamics of poly(sodium styrenesulfonate) (PSSNa) in aqueous solutions with and without added salt (NaCl) by use of analytical ultracentrifuge (AUC) via sedimentation velocity (SV) as a function of NaCl concentration (Cs) or PSSNa concentration (Cp). As Cs increases, the sedimentation coefficient monotonically increases, whereas the diffusion coefficient shows a minimum. On the other hand, as Cp increases, the sedimentation coefficient decreases while the diffusion coefficient exhibits a minimum at Cs < 1.0 × 10−3 M. However, they linearly vary with Cp at Cs > 1.0 × 10−3 M. The scaling relation between the molar mass and sedimentation coefficient or diffusion coefficient at infinite dilution indicates that PSSNa chain changes from an extended conformation to a random coil as NaCl concentration increases. Our experiments demonstrate that the dynamics of polyelectrolyte chains is mediated by interchain electrostatic repulsion, hydrodynamic interactions, and intrinsic excluded volume effect.

Changes of zeta potential and particles size of silica caused by DPPC adsorption and enzyme phospholipase A2 presence

The changes in electrokinetic properties of silica suspensions in the presence of 1,2-dipalmitoyl-sn-glycero-3-phospshocholine (DPPC) were investigated via zeta potential, mean diameter and transmittance determinations. Silica particles were precovered with monolayer (ML) or bilayer (BL) of the phospholopid from chloroform solution (SiO2/DPPC) or covered by DPPC adsorption from aqueous solution (SiO2+DPPC). The zeta potential and mean diameter of SiO2/DPPC suspension were measured as a function of NaCl concentration and due to the phospholipase A2(PLA2) action in 10−3 M NaCl solution and buffer Tris at pH=8 and 9. It was found that the DPPC adsorption onto silica surface decreases its the zeta potential, however the suspensions were stable during the experiment time, probably because of steric stabilization. During PLA2 enzyme action the changes in zeta potential were observed, which were caused by the hydrolysis products, especially palmitic acid molecules, which also had influence on the stability of these systems.

Interaction of the Cationic Peptide Bactenecin with Phospholipid Monolayers at the Air−Water Interface: I Interaction with 1,2-Dipalmitoyl-sn-Glycero-3-Phosphatidilcholine

In this work we have investigated the influence of NaCl on the adsorption of the antimicrobial cationic peptide bactenecin in the monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at the air-water interface, as a function of NaCl concentrations in the subphase. We show that the effect of the salt concentration on DPPC monolayers is a monotonic decrease of the liquid-condensed-liquid-expanded (LC-LE) coexistence region. By contrast, the effect of the bactenecin adsorption at the DPPC monolayer not only removed the LC-LE coexistence region plateau, but also shifted the DPPC isotherms to higher pressures and increased the compressibility of the DPPC/bactenecin monolayers with respect to the pure DPPC monolayer around the LC phase. Analysis of the domain structure, obtained by Brewster angle and atomic force microscopes, indicates that the salt concentration in the subphase builds an electrostatic barrier, increasing the rigidity of DPPC monolayers and limiting the bactenecin adsorption at the LC-LE phase coexistence.

Electrostatic Interactions Contribute to the Folded-back Conformation of Wild Type Human Factor H

Factor H (FH), a major serum regulator of C3b in the complement alternative pathway, is composed of 20 short complement regulator (SCR) domains. Earlier solution structures for FH showed that this has a folded-back domain arrangement and exists as oligomers. To clarify the molecular basis for this, analytical ultracentrifugation and X-ray scattering studies of native FH were performed as a function of NaCl concentration and pH. The sedimentation coefficient for the FH monomer decreased from 5.7 S to 5.3 S with increase in NaCl concentration, showing that weak electrostatic inter-domain interactions affect its folded-back structure. FH became more elongated at pH 9.4, showing the involvement of histidine residue(s) in its folded-back structure. Similar studies of partially deglycosylated FH suggested that oligosaccharides were not significant in determining the FH domain structure. The formation of FH oligomers decreased with increased NaCl concentration, indicating that electrostatic interactions also affect this. X-ray scattering showed that the maximum length of FH increased from 32 nm in low salt to 38 nm in high salt. Constrained X-ray scattering modelling was used to generate significantly improved FH molecular structures at medium resolution. In 50 mM NaCl, the modelled structures showed that inter-SCR domain contacts are likely, while these contacts are fewer in 250 mM NaCl. The results of this study show that the conformation of FH is affected by its local environment, and this may be important for its interactions with C3b and when bound to polyanionic cell surfaces.

Solubility and Acid–Base Properties of Ethylenediaminetetraacetic Acid in Aqueous NaCl Solution at 0 ≤ I ≤ 6 mol·kg−1 and T = 298.15 K

Solubility and protonation constants of ethylenediaminetetraacetic acid (EDTA) were determined in aqueous NaCl solutions at different ionic strengths (0 ≤ I ≤ 6.0 mol·kg−1), at T = 298.15 K. Dependence on the ionic strength of protonation constants was modeled by the modified SIT approach on the molal concentration scale. From total solubility, we calculated the solubility of the neutral species S0, and from these values, as a function of NaCl concentration, the Setschenow (km) coefficient was obtained, together with the values of KS0.

Effects of Ionic Strength and Denaturation Time on Polyethyleneglycol Self-Diffusion in Whey Protein Solutions and Gels Visualized by Nuclear Magnetic Resonance

Pulsed field gradient NMR spectroscopy was used to determine the poly(ethylene glycol) (PEG) self-diffusion coefficient (D(PEG)) as a function of NaCl concentration (C(NaCl)) and denaturation time (t(D)) in whey protein solutions and gels. D(PEG) in the gel decreased with increasing C(NaCl) concentrations and increased with increasing t(D); the increase ceased for all PEGs when the gel was fixed. This increase was more pronounced for the 82250 g/mol PEG than the 1080 g/mol PEG. Moreover, the diffusion coefficient of nonaggregated whey protein was measured and an increase for longer t(D) was also observed. Scanning electron microscopy images and (1)H spectra demonstrated that D(PEG) were related to the structure changes and to the percentage of beta-lactoglobulin denaturation.

Effect of Salt and Temperature on Visco-Elasticity of Gelatin Hydrogels

Rheology studies, on aqueous gelatin gels, were performed below gelation temperature (T g ≈ 28°C) in the temperature range, T= 5-25°C as a function of NaCl concentration (0.01-0.1M). In the low frequency domain and at a given temperature, both the storage (G') and loss (G) modulii exhibited power-law frequency dependence, G' ∼ ω 0.02±0.005 and ∼ ω 0.8±0.2 . The network size, ξ estimated from low-frequency relaxation modulus, G 0 ≈ K B T/ξ 3 increased three fold as the temperature was increased from 5 to 25°C indicating thermal swelling of the network. The strain peaks were observed to shift to higher frequency as the temperature was lowered. Higher salt concentration had the same effect on the gel as higher temperature.