Ionic Strength Of Medium Research Articles

Effect of Adsorbed Polyelectrolytes on Nanoscale Zero Valent Iron Particle Attachment to Soil Surface Models

Polyelectrolyte coatings significantly increase the mobility of nanoscale zerovalent iron (NZVI) in saturated porous media. The effect can be attributed to improved colloidal stability of NZVI suspensions, decreased adhesion to soil surfaces, or a combination of the two effects. This research explicitly examines how coatings control NZVI adhesion to model soil surfaces. NZVI was coated with three different polyeleotrolyte block copolymers based on poly(methacrylic acid), poly(methyl methacrylate or butyl methacrylate), and poly(styrenesulfonate) or with a poly(styrenesulfonate) homopolymer. SiO2 and a humic acid film served as model soil surfaces. The polyelectrolytes increased the magnitude of the electrophoretic mobility of NZVI over a broad pH range relative to unmodified NZVI and shifted the isoelectric point outside the typical groundwater pH range. Quartz crystal microgravimetry measurements indicated extensive adhesion of unmodified NZVI to SiO2. Polyelectrolyte coatings decreased adhesion by approximately 3 orders of magnitude. Adding 50 mM NaCL to screen electrostatic repulsions did not significantly increase adhesion of modified NZVI. Coated NZVI did not adhere to humic acid films for either 1 mM NaHCO3 or 1 mM NaHCO3 + 50 mM NaCl. The lack of adhesion even in a high ionic strength medium was attributed to electrosteric repulsion, as opposed to electrostatic double layer repulsion, between the polyelectrolyte-coated NZVI and the negatively charged surfaces. The lack of significant adhesion on either model surface was observed for all polymer architectures investigated.

Temperature effect on the solvent extraction of copper(II), cobalt(II) and nickel(II) with salicylideneaniline from sulphate media

The temperature effect on the solvent extraction of copper(II), cobalt(II) and nickel(II) by Schiff base salicylideneaniline (SAN) in chloroform from sulfate aqueous medium of constant ionic strength was studied. The temperature dependence of the extraction equilibrium constants were investigated to estimate the variation of enthalpy (ΔH) and entropy (ΔS). These thermodynamic functions were, as a result, calculated and discussed in conjunction with the structure of the extracted species. It was found that the extraction of each metal increased with increase in temperature. Besides ΔH and ΔS have been discussed in connection with the nature of bonding and also the symmetry of the metal complexes. It was established through this study that the types of bonding in the complexes formed in the aqueous solution are clearly reflected by the values of ΔH and ΔS for the complex formation reaction.

Influence of Low Concentration Ethanol on Membrane Permeability of E.Coli

ABSTRACTThe electric polarizability of bacteria gives information about their structure and functional state and can be measured electro-optically by orientation of the cells in electric field. The interface polarizability is two kinds: charge dependent (ChD) and Maxwell-Wagner (MW). ChD polarizability depends on the surface charge and the thickness of double electric layer. MW polarizability is determined by the electric properties of the cytoplasm and the membrane (their conductivity and dielectric permittivity). It is known that the bacteria polarizability decreases significantly by adding of ethanol; however the reason for that change is not clear. In the present work we investigate the influence of low concentration of ethanol on the polarizability of Escherichia coli K12. The results show up that the effect of ethanol is related to the cytoplasm MW polarizability which change is due to increasing the cell membrane permeability. This affect on the ionic flow through the membrane, which velocity and direction depends on the relative values of the cytoplasm and the extracellular medium ionic strength.

Silk–elastinlike protein polymer hydrogels: Influence of monomer sequence on physicochemical properties

Silk–elastinlike protein polymer, SELP-815K, with eight silk and fifteen elastin units and a lysine (K) modified elastin, was genetically engineered with longer silk and elastin units compared to existing hydrogel forming analogs (SELP-415K and SELP-47K). Hydrogels of the three SELPs (with similar MWs) were investigated for their structure–function relationships. Results indicate that equilibrium swelling ratio in these hydrogels is a function of polymer structure, concentration, cure time and ionic strength of media. Swelling was not influenced by the changes in pH. Storage moduli observed by dynamic mechanical analysis and the Debye–Bueche correlation length obtained from small-angle neutron scattering provided structural insight that suggests the cross-linking densities in these hydrogels follow the order SELP-47K>SELP-815K>SELP-415K. These results allude to the importance of the length of elastin blocks in governing the spacing of the cross-linked hydrogel network and that of silk in governing the stiffness of their 3-dimensional structures.

4‐Aminothiophenol Self‐Assembled Monolayer for the Development of a DNA Biosensor Aiming the Detection of Cylindrospermopsin Producing Cyanobacteria

AbstractThe development of a DNA biosensor for the detection of cylindrospermopsin, based on self‐assembled monolayers (SAMs) of 4‐aminothiophenol, is investigated. SAMs were characterized by electrochemical reductive desorption. Detection of probe immobilization and hybridization has been achieved by cyclic and square‐wave voltammetry (SWV), using methylene blue (MB) as electroactive indicator. The SWV data obtained in phosphate buffer, with and without NaCl, after MB accumulation, revealed an increase of the redox indicator current peaks after the hybridization step. This behavior is consistent with MB intercalation into DNA, for high ionic strength media and attributed to electrostatic interactions in the absence of salt. Evidence for surface modification is also provided by atomic force microscopy and ellipsometry.

Influence of ethanol on the high frequency electric polarizability of E. coli

The interface electric polarizability of bacteria (charge dependent (ChD) and Maxwell–Wagner (MW) polarizabilities) gives information about their electric charge, determined by the structure and functional state. It is well known that the polarizability could be changed significantly by adding some substances to the suspension, and can be measured using an electro-optical (EO) method. There are some literature data, according to which the adding of ethanol decreases the electric polarizability of the cells. However the reason for the change in this parameter is not clear, as well as which component (ChD and/or MW) of polarizability has the main contribution. Generally the present work shows that the effect of ethanol is connected to the change of the internal (cytoplasm) MW polarizability and is mainly caused by increasing the cell membrane permeability. This results in an ionic flow through the membrane, which velocity and direction depends on the relative values of the inner (cytoplasm) and the outer medium ionic strength.

Electrochemical generation of H2O2 in low ionic strength media on gas diffusion cathode fed with air

Abstract The electrogeneration of hydrogen peroxide in solution with low ionic strength using a gas diffusion cathode fed with air was investigated by linear sweep voltammetries and bulk electrolyses. The effect of applied current (15–45 mA cm −2 ), solution pH (4–10), temperature (15–60 °C) and cell configuration (divided or undivided) on the H 2 O 2 generation rate and current efficiency was evaluated. Experimental results showed that in Na 2 SO 4 0.05 M H 2 O 2 can be produced with a satisfactory efficiency, i.e. 53%. Higher production rate was obtained in a two-compartment cell by increasing current density and pH and by decreasing solution temperature. A much lower efficiency (i.e. 30%) was obtained using the undivided cell, because, under these conditions, electrogenerated hydrogen peroxide was decomposed by anodic oxidation on Pt electrode.

Observations and analysis of electrokinetically driven particle trapping in planar microelectrode arrays

AbstractIn situ observations of submicron fluorescent tracers suspended in high ionic strength media sealed in a confined geometry are combined with 3‐D simulations in order to provide a better understanding of the synergism between dielectrophoresis and electrothermal flows that cause rapid particle transport and trapping on the surface of planar quadrupolar microelectrodes. The influence of electrode design on the microfluidic patterns and observed particle collection is examined by employing two different types of microelectrodes in the experiments. The potential use of quadrupolar microelectrodes as means for achieving accelerated sampling and signal amplification in future surface based biosensor devices is illustrated with an experiment involving stable capture of antigen‐coated polystyrene particles on the surface of an antibody‐functionalized microelectrode array.

High frequency electric polarizability of bacteria E. coli: Dependence on the medium ionic strength

There are two main kinds of electric polarizability of bacteria: surface charge dependent (SChD) and Maxwell–Wagner (MW) polarizability. The aim of this article is to distinguish SChD and MW components on the external bacteria surface. An electro-optic method (electric turbidity) was used to study the polarizability of E. coli fixed by formaldehyde at the frequency range 20 kHz to 20 MHz. According to the literature the SChD polarization disappears at such high frequencies and MW one gives the main contribution. However we found unexpected dependence on the outer medium electrolyte concentration, which cannot be explained by MW polarization. The results show that the polarizability decreases by ionic strength increasing in the same way as the double electric layer thickness does. Such behaviour is a characteristic for SChD polarizability, which allows us to conclude that this component has the main contribution on the external bacteria surface at the experimental frequencies mentioned.

Non-electrolyte permeability of deoxygenated sickle cells compared

The passive permeability pathways of red cells are poorly defined, with the exception of the Gardos channel. Several cation and anion pathways can be induced by a variety of manoeuvres, however, including treatment with oxidants, low ionic strength (LIS), shrinkage, swelling and also infection with the intra-erythrocytic malaria parasite. Several of these stimuli (malaria, swelling, LIS), in addition, also activate a non-electrolyte this permeability. Sickle cells uniquely show a deoxygenation-induced pathway, which is termed P sickle and is usually considered to be a conductive cationic pathway. In this report, we explore further the extent to which this permeability pathway of deoxygenated sickle cells is available for non-electrolyte transport. We show that a number of solutes are permeable, with greater permeability to sugars (notably lactose and maltose) and smaller molecules, and less to charged or zwitterionic species. Red cells from heterozygous HbSC patients also showed deoxygenation-induced haemolysis in isosmotic sucrose solution, though to a slightly lesser extent than for red cells from homozygous sickle cell patients. In contrast to sickle cells, red cells from β-thalassaemic patients did not show haemolysis in isosmotic sucrose solutions, regardless of the O 2 tension. Of the secondary cellular changes resulting from incubation in non-electrolyte solutions (which include imposition of a highly positive membrane potential, marked intracellular alkalinisation and cell shrinkage), none appear to correlate with activation of the non-electrolyte permeability. Rather, findings indicate that it is low ionic strength per se that is responsible. Normal red cells also show changes in ionic and non-electrolyte permeability in low ionic strength media, and these permeabilities are compared to those found in deoxygenated sickle cells. The extent to which these different permeabilities in normal and sickle red cells can be ascribed to one or more common pathways remains to be determined.

NADPH oxidase involvement in cellular integrity

NADPH oxidase activity is involved in plant adaptation and development. The reactive oxygen species sourced by NADPH oxidase activity may contribute to wall strength and protoplast volume adjustment. Root hair bulge apices of the NADPH oxidase mutant rhd2/Atrbohc were more robust than the kjk cellulose synthase mutant, but burst more readily than the wild type (WT). Root epidermal wall appeared impaired in rhd2/Atrbohc, as revealed by the number of protoplasts released by wall-degrading enzymes. Root hair bulges of rhd2/Atrbohc burst more than the WT when challenged in situ with hypo-osmotic low ionic strength medium. Inhibition of NADPH oxidase activity with diphenylene iodonium caused WT to phenocopy the rhd2/Atrbohc bursting in response to hypo-osmotic shock. This implicates RHD2/AtRBOHC in softening the cell wall to permit protoplast expansion. Overall, the results point to a role for RHD2/AtRBOHC in contributing to wall strength.

Effect of ionic strength and presence of serum on lipoplexes structure monitorized by FRET

BackgroundSerum and high ionic strength solutions constitute important barriers to cationic lipid-mediated intravenous gene transfer. Preparation or incubation of lipoplexes in these media results in alteration of their biophysical properties, generally leading to a decrease in transfection efficiency. Accurate quantification of these changes is of paramount importance for the success of lipoplex-mediated gene transfer in vivo.ResultsIn this work, a novel time-resolved fluorescence resonance energy transfer (FRET) methodology was used to monitor lipoplex structural changes in the presence of phosphate-buffered saline solution (PBS) and fetal bovine serum. 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/pDNA lipoplexes, prepared in high and low ionic strength solutions, are compared in terms of complexation efficiency. Lipoplexes prepared in PBS show lower complexation efficiencies when compared to lipoplexes prepared in low ionic strength buffer followed by addition of PBS. Moreover, when serum is added to the referred formulation no significant effect on the complexation efficiency was observed. In physiological saline solutions and serum, a multilamellar arrangement of the lipoplexes is maintained, with reduced spacing distances between the FRET probes, relative to those in low ionic strength medium.ConclusionThe time-resolved FRET methodology described in this work allowed us to monitor stability and characterize quantitatively the structural changes (variations in interchromophore spacing distances and complexation efficiencies) undergone by DOTAP/DNA complexes in high ionic strength solutions and in presence of serum, as well as to determine the minimum amount of potentially cytotoxic cationic lipid necessary for complete coverage of DNA. This constitutes essential information regarding thoughtful design of future in vivo applications.

Prediction of calibration curves in ria of digoxin: Influence of some variables

Background Competitive protein binding radioimmunoassay (CPB-RIA) is a principal method for quantifying serum digoxin concentration. The accuracy of this method is critically dependent on factors that influence the substitution reaction between unlabelled (Q) antigen (digoxin) with 125I-labelled antigen (M) bound to anti-digoxin antibody (P). We studied the influence of initial concentration of M, ionic strength, and viscosity on the substitution reaction between M and Q. In addition, we propose a kinetic model for this reaction. Methods We used a commercially available CPB-RIA for digoxin, a gamma counter, and a viscosimeter to study the effect of initial concentration of M, ionic strength, viscosity, and temperature on the substitution reaction between M and Q. Data were analyzed using Statistica software. Results The apparent rate constant for the reaction between M and Q in the formation of PM is dependent on the initial concentration of M, and the ionic strength, viscosity, and temperature of the reaction medium, and independent of the concentration of Q. Conclusion A kinetic model for the displacement of the 125I-digoxin by the digoxin in its union to a specific antibody is proposed. Such model adjusts satisfactorily to the results and allows the prediction of the calibration curves of RIA (activity bound to the antibody vs. concentration of digoxin) showing the influence of the concentration of both species, the time of incubation, the viscosity and the ionic strength of the medium, on the sensitivity of the method of RIA on which the analytical determination of the digoxin is based.

Effect of pH, ionic strength, fulvic acid and humic acid on sorption of Th(IV) on Na-rectorite

Sorption of Th(IV) on Na-rectorite as a function of pH, ionic strength, soil humic acid (HA) and fulvic acid (FA) are studied under ambient conditions by using a batch technique. The results indicate that the sorption of Th(IV) on Na-rectorite is not only dependent on medium pH values, but also dependent on medium ionic strength and humic substances. Surface complexation and cation competition exchange account for Th(IV) sorption on Na-rectorite. The sorption of Th(IV) on Na-rectorite decreases with the increase on the concentration of NaNO3, Mg(NO3)2 and Ca(NO3)2, and increases with the increasing amount of HA/FA in the suspension/adsorbed on rectorite. Soil HA/FA enhances the sorption of Th(IV) on rectorite at medium pH 6, and HA has no effect on Th(IV) sorption at medium pH>6. An interpretation for the results is attempted, considering the occurrence of different sorption mechanisms.

Nonaqueous CE using contactless conductivity detection and ionic liquids as BGEs in ACN

N,N'-Alkylmethylimidazolium cations have been separated in NACE when one of the N,N'-dialkylimidazolium salts (ionic liquids (ILs)) was used as an electrolyte additive to the organic solvent separation medium. The separated species were 1-methyl-, 1-ethyl-, 1-butyl-, 1-octyl-, 1-decyl-3-methylimidazolium and N-butyl-3-methylpyridinium cations and BGE composed of 1-ethyl-3-methylimidazolium ethylsulfate or 1-butyl-3-methylimidazolium trifluoroacetate [BMIm][FAcO] (A6; B2) diluted in ACN. It was demonstrated that contactless conductivity detection (CCD) may be applied to monitoring the separation process in nonaqueous separation media, allowing to use the UV light-absorbing imidazolium-based electrolyte additives. There could be marked three concentration regions of added ILs; at first ionic strength of BGE below 1-2 mM, and then the actual electrophoretic mobility of analytes rises from 0. At concentrations above 1-2 mM, the added IL facilitated separation. In concentration region of 1-20 mM, the actual electrophoretic mobility of analyzed imidazolium cations was increasing with decrease in separation medium ionic strength. At higher concentrations of BGE (above 30 mM), the conductivity of the separation media became too high for this detector. Some organic dyes were also successfully separated and detected by contactless conductivity detector in a 20 mM A6 separation electrolyte in ACN.

Natural variation of Arabidopsis thaliana reveals that aluminum resistance and proton resistance are controlled by different genetic factors

Root growth of Arabidopsis thaliana is inhibited by proton rhizotoxicity in low ionic strength media when the pH of the medium is lower than 5.0. QTL analysis at pH 4.7 revealed that two major QTLs on chromosome 2 and 5 and an additional six epistatic interacting loci pairs control proton resistance in the Ler/Col recombinant inbred population. These genetic factors are independently associated with proton resistance in comparison to the known Al resistant QTL and epistases detected in the same RI population at 4 microM Al at pH 5.0. This indicates that different genetic factors regulate mechanisms of resistance to each stress in this plant species. No correlation was observed between proton resistance and Al resistance among 260 accessions indicating that there is no simple relationship between the genetic factors controlling each trait. Several accessions with different combinations of proton (pH 4.7) and Al (4 microM Al at pH 5.0) resistances were identified by phenotypic cluster analysis. Although this grouping was performed using root growth data, the degree of resistance was correlated with their sensitivity to short-term damage in the root tip, indicating that the same resistance mechanism controls proton resistance at different time scales. Resistant accessions grew better than sensitive ones in acid soil culture. This suggests that proton resistance in hydroponic conditions could be an important index in breeding programs to improve productivity in acid soil, at least in acid sensitive plant species.

Thermal Field-Flow Fractionation of Charged Submicrometer Particles in Aqueous Media

Thermal field-flow fractionation (ThFFF) of various types of submicrometer silica particles in aqueous media is experimentally investigated under an extended range of medium ionic strengths with and without the presence of surfactant. The experiments were designed to examine the applicability to submicrometer particles of the theory of charged nanoparticles thermodiffusion recently proposed by Parola and Piazza (Parola, A.; Piazza, R. Eur. Phys. J. E. 2004, 15, 255-263). In particular, the expression for the calibration function in terms of particle radius and channel temperature is derived and experimentally verified. Moreover, retention is expected to be dependent on particle surface potential and charge, and on ionic strength. These dependences are experimentally investigated and the pertinent relationships and correlations derived. The effect of heavy metal adsorption on the silica surface was investigated, and significant ThFFF retention changes were measured. Independent measurements of the zeta potential (zeta-potential) indicated that a decrease in the surface charge of a silica particle is a consequence of heavy metal adsorption, which is, in turn, correlated to the observed decrease in ThFFF retention.

Stimulation of P2 receptors causes release of IL-1β–loaded microvesicles from human dendritic cells

AbstractDendritic cells (DCs) are professional antigen-presenting cells that initiate the immune response by activating T lymphocytes. DCs express plasma membrane receptors for extracellular nucleotides named P2 receptors (P2Rs). Stimulation of P2Rs in these cells is known to cause chemotaxis, cytokine release, and cell death and to modulate LPS-dependent differentiation. Here we show that stimulation of the P2X7 receptor subtype (P2X7R) causes fast microvesicle shedding from DC plasma membrane. Vesicle release occurs from both immature and mature DCs; however, only vesicles from mature DCs, due to their previous exposure to LPS, contain IL-1β. Microvesicles, whether from immature or mature DCs, also contain caspase-1 and -3 and cathepsin D. They also express the P2X7R in addition to other P2Rs and known markers of immune cells such as major histocompatibility complex II (MHC II) and CD39. Activation of the P2X7R by extracellular ATP causes IL-1β release from the vesicle lumen. Previous studies demonstrated that high extracellular K+ inhibits IL-1β processing and release; here we show that high ionic strength reduces microvesicle shedding when compared with a low ionic strength medium but strongly increases microvesicle IL-1β loading.

Core−Shell Au Nanoparticle Formation with DNA−Polymer Hybrid Coatings Using Aqueous ATRP

We report here a direct surface-grafting approach to forming DNA-containing polymer shells outside of Au nanoparticles using aqueous atom transfer radical polymerization (ATRP). In this approach, DNA molecules were immobilized on Au particles to introduce ATRP initiators on the surface. The same DNA molecules also acted as particle stabilizers through electrostatic repulsion and allowed particles to stay suspended in water. The immobilized ATRP initiators prompted polymer chain growth under certain conditions to form thick polymer shells outside of the particles. The formation of DNA-polymer hybrids outside of Au nanoparticles was characterized using absorption spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and gel electrophoresis. The presence of thick polymer shells improved particle stability in high ionic strength media, whereas particles with the DNA coating only aggregated. A visible color difference between these two particle solutions was clearly observed, providing the basis for DNA sensing in homogeneous solutions.

Structure of flexible and semiflexible polyelectrolyte chains in confined spaces of slit micro/nanochannels

Understanding the behavior of a polyelectrolyte in confined spaces has direct relevance in design and manipulation of microfluidic devices, as well as transport in living organisms. In this paper, a coarse-grained model of anionic semiflexible polyelectrolyte is applied, and its structure and dynamics are fully examined with Brownian dynamics (BD) simulations both in bulk solution and under confinement between two negatively charged parallel plates. The modeling is based on the nonlinear bead-spring discretization of a continuous chain with additional long-range electrostatic, Lennard-Jones, and hydrodynamic interactions between pairs of beads. The authors also consider the steric and electrostatic interactions between the bead and the confining wall. Relevant model parameters are determined from experimental rheology data on the anionic polysaccharide xanthan reported previously. For comparison, both flexible and semiflexible models are developed accompanying zero and finite intrinsic persistence lengths, respectively. The conformational changes of the polyelectrolyte chain induced by confinements and their dependence on the screening effect of the electrolyte solution are faithfully characterized with BD simulations. Depending on the intrinsic rigidity and the medium ionic strength, the polyelectrolyte can be classified as flexible, semiflexible, or rigid. Confined flexible and semiflexible chains exhibit a nonmonotonic variation in size, as measured by the radius of gyration and end-to-end distance, with changing slit width. For the semiflexible chain, this is coupled to the variations in long-range bond vector correlation. The rigid chain, realized at low ionic strength, does not have minima in size but exhibits a sigmoidal transition. The size of confined semiflexible and rigid polyelectrolytes can be well described by the wormlike chain model once the electrostatic effects are taken into account by the persistence length measured at long length scale.