Solutions Of Different Ionic Strength Research Articles

Preparation and Physicochemical Characterization of Polyelectrolyte Complexes Incorporating Antitumor Peptide

In this work, tigapotide (PCK3145) was incorporated into novel block copolymer polyelectrolyte nanocarriers in order to maximize the advantages of the delivery process and possibly its biological properties. PCK3145 was incorporated into complexes with the block polyelectrolyte poly(vinyl benzyl trimethylammonium chloride)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PVBTMAC-POEGMA). Light scattering techniques (dynamic, static and electrophoretic) are used in order to examine the size, the size distribution, the morphology and the z-potential of the nanocarriers incorporating PCK3145 in different aqueous media. The concentration of PVBTMAC-POEGMA is kept constant throughout the series of aqueous solutions of different ionic strength investigated. The values of the scattering intensity, I90, which is proportional to the mass of the species in solution, increase gradually as a function of CPCK3145 providing proof of the occurring complexation. It was shown that the structure and solution behavior of the formed complexes depend on the ratio of the two components, as well as on the pH and the ionic strength of the solution. The physicochemical characteristics of the complexes, as a function of PCK concentration, remained unaffected at higher ionic strength (0.154 M). This investigation provides interesting and useful new insights into the interaction mechanism between oppositely charged block polyelectrolytes and therapeutic peptides.

Conformations of polyelectrolyte macromolecules with different charge density in solutions of different ionic strengths

Studies of charged polymer chains are interesting in both fundamental and applied aspects. Especially, polyelectrolytes attract huge attention of researchers due to their ability to form interpolymer complexes with synthetic and biopolymers. The study was carried out on the fractions of hydrophilic copolymers of N-methyl-N-vinyl acetamide and N-methyl-N-vinyl amine hydrochloride of different degrees of polymerization and of different charge density using methods of molecular hydrodynamics. Hydrodynamic and conformational characteristics as well as molar masses of isolated molecules were estimated. In addition, the intrinsic viscosity of fractions was studied at the extreme ionic strengths - in distilled water (∼10-6M) and in 6M NaCl. Scaling relations for intrinsic viscosity, sedimentation and translational diffusion coefficients with molar mass were obtained. Conformational behavior of macromolecules with different linear charge density was compared.

Solubility and hydrolysis of Np(V) in dilute to concentrated alkaline NaCl solutions: formation of Na–Np(V)–OH solid phases at 22 °C

Abstract The solubility of Np(V) was investigated at T=22±2°C in alkaline NaCl solutions of different ionic strength (0.1–5.0 M). The solid phases controlling the solubility at different –log10 mH+(pHm) and NaCl concentration were characterized by XRD, quantitative chemical analysis, SEM–EDS and XAFS (both XANES and EXAFS). Aqueous phases in equilibrium with Np(V) solids were investigated for selected samples within 8.9≤pHm≤10.3 by UV-vis/NIR absorption spectroscopy. In 0.1 M NaCl, the experimental solubility of the initial greenish NpO2OH(am) solid phase is in good agreement with previous results obtained in NaClO4 solutions, and is consistent with model calculations for fresh NpO2OH(am) using the thermodynamic data selection in NEA–TDB. Below pHm~11.5 and for all NaCl concentrations studied, Np concentration in equilibrium with the solid phase remained constant during the timeframe of this study (~2 years). This observation is in contrast to the aging of the initial NpO2OH(am) into a more crystalline modification with the same stoichiometry, NpO2OH(am, aged), as reported in previous studies for concentrated NaClO4 and NaCl. Instead, the greenish NpO2OH(am) transforms into a white solid phase in those systems with [NaCl]≥1.0 M and pHm≥11.5, and into two different pinkish phases above pHm~13.2. The solid phase transformation is accompanied by a drop in Np solubility of 0.5–2 log10-units (depending upon NaCl concentration). XANES analyses of green, white and pink phases confirm the predominance of Np(V) in all cases. Quantitative chemical analysis shows the incorporation of Na+ in the original NpO2OH(am) material, with Na:Np≤0.3 for the greenish solids and 0.8≤Na:Np≤1.6 for the white and pinkish phases. XRD data confirms the amorphous character of the greenish phase, whereas white and pink solids show well-defined but discrepant XRD patterns. Furthermore, the XRD pattern collected for one of the pink solid phases match the data recently reported for NaNpO2(OH)2(cr). UV-vis/NIR spectra collected in 0.1–5.0 M NaCl solutions show the predominance of NpO2 + (≥80%) at pHm≤10.3. This observation is consistent with the Np(V) hydrolysis scheme currently selected in the NEA–TDB. This work provides sound evidences on the formation of ternary Na–Np(V)–OH solid phases in Na-rich hyperalkaline solutions and ambient temperature conditions. Given the unexpectedly high complexity of the system, further experimental efforts dedicated to assess the thermodynamic properties of these solid phases are needed, especially in view of their likely relevance as solubility controlling Np(V) solid phases in Na-rich systems such as saline and cement-based environments in the context of the safety assessment for nuclear waste disposal.

Effects of the ionic strength of sodium hypochlorite solution on membrane cleaning

Chemical cleaning is conducted to recover the permeability of membranes when other physical cleaning methods are not effective. This research examined cleaning by sodium hypochlorite solution with a focus on how the ionic strength of the solution affects its efficiency during flux recovery. Ultrafiltration membranes with various molecular weight cut-offs were clogged with bovine serum albumin, then flushed with sodium hypochlorite solutions of different ionic strengths. On increasing the ionic strength of the solution, the speed of flux recovery was retarded at first, before the recovery suddenly accelerated. The effects of ionic strength on both the reaction and diffusion of the cleaning process were investigated to understand the mechanism. It was inferred that the diffusivity of the foulant inside the membrane pores was altered under conditions of high ionic strength, which led to this unique tendency. This finding provides insight into the fouling mechanism and the movement of foulants inside the membrane pores.

Colloid Mobilization in a Fractured Soil: Effect of Pore-Water Exchange between Preferential Flow Paths and Soil Matrix.

Exchange of water and solutes between contaminated soil matrix and bulk solution in preferential flow paths has been shown to contribute to the long-term release of dissolved contaminants in the subsurface, but whether and how this exchange can affect the release of colloids in a soil are unclear. To examine this, we applied rainfall solutions of different ionic strength on an intact soil core and compared the resulting changes in effluent colloid concentration through multiple sampling ports. The exchange of water between soil matrix and the preferential flow paths leading to each port was characterized on the basis of the bromide (conservative tracer) breakthrough time at the port. At individual ports, two rainfalls of a certain ionic strength mobilized different amounts of colloids when the soil was pre-exposed to a solution of lower or higher ionic strength. This result indicates that colloid mobilization depended on rainfall solution history, which is referred as colloid mobilization hysteresis. The extent of hysteresis was increased with increases in exchange of pore water and solutes between preferential flow paths and matrix. The results indicate that the soil matrix exchanged the old water from the previous infiltration with new infiltrating water during successive infiltration and changed the pore water chemistry in the preferential flow paths, which in turn affected the release of soil colloids. Therefore, rainfall solution history and soil heterogeneity must be considered to assess colloid mobilization in the subsurface. These findings have implications for the release of colloids, colloid-associated contaminants, and pathogens from soils.

Electrostatics of Actomyosin Interface and the Rate of Rigor Binding

The rate of actin and myosin rigor binding depends on the ionic strength of the solution, confirming that actomyosin interaction is electrostatically driven. The dependence of the rate of actin and myosin interaction on the ionic strength of the solution reflects the charge of the interface of the interacting molecules. We used fluorescence of pyrene labeled actin to measure transient kinetics of actomyosin rigor binding in buffered solutions of different ionic strength and constant pH. We used recent data on the structure of actomyosin complex [1] to determine the charge and charge distribution of the actin binding interface of myosin head. The experimental transient kinetics data and the computational analysis were used to compare cellular and muscle myosin in terms of similarities and differences of their actin binding interface.1. Behrmann, E., et al., Structure of the rigor actin-tropomyosin-myosin complex. Cell, 2012. 150(2): p. 327-38.

Protonation and Solvation Thermodynamics of Some Naphthol Derivatives in KCl Aqueous Solution of Different Ionic Strengths

The acid-base properties of naphthalen-1-ol (L1), naphthalene-1,5-diol (L2), and 4-amino-3-hydroxynaphthalene-1-sulphonic acid (L3) were characterized from pH-metric measurements in pure water and in different concentrations (0–4 mol kg−1) of aqueous KCl solutions at the temperature range ofT= (293.15 to 213.15) K at 5 K intervals. The results reveal that naphthalen-1-ol and naphthalene-1,5-diol molecules have two ionisable protons (of the hydroxyl groups) while 4-amino-3-hydroxynaphthalene-1-sulphonic acid has three ionisable protons (hydrogen ion of the hydroxyl group, SO3H, andNH3+). Modeling of the data was done by applying Debye-Hückel model. The protonation and the solvation processes of all studied ligands are spontaneous and endothermic processes. Also the solubilities of naphthalen-1-ol, naphthalene-1,5-diol, and 4-amino-3-hydroxynaphthalene-1-sulphonic acid were determined. The data were analyzed using Setschenow equation and the values of Setschenow coefficients (km) were determined. From the solubility data, the activity coefficients were obtained. The values of the total solubilities (ST) for naphthalen-1-ol and naphthalene-1,5-diol were found equal to the values of their neutral species (S0). On the other hand, the total solubility for 4-amino-3-hydroxynaphthalene-1-sulphonic acid is different from that of its neutral species. The results also indicate solubility decrease in pure water from L1-L2-L3.

Joule heating monitoring in a microfluidic channel by observing the Brownian motion of an optically trapped microsphere.

Electric fields offer a variety of functionalities to Lab-on-a-Chip devices. The use of these fields often results in significant Joule heating, affecting the overall performance of the system. Precise knowledge of the temperature profile inside a microfluidic device is necessary to evaluate the implications of heat dissipation. This article demonstrates how an optically trapped microsphere can be used as a temperature probe to monitor Joule heating in these devices. The Brownian motion of the bead at room temperature is compared with the motion when power is dissipated in the system. This gives an estimate of the temperature increase at a specific location in a microfluidic channel. We demonstrate this method with solutions of different ionic strengths, and establish a precision of 0.9 K and an accuracy of 15%. Furthermore, it is demonstrated that transient heating processes can be monitored with this technique, albeit with a limited time resolution.

Aquaphotomics: Near Infrared Spectroscopy and Water States in Biological Systems.

Aquaphotomics is a new discipline that provides a framework for understanding changes in water molecular system presented as a water spectral pattern, to mirror the rest of the solution and to give a holistic description related to system functionality. One of its main purposes is to identify water bands as main coordinates of future absorbance patterns to be used as a system biomarker. This chapter presents the Aquaphotomics methodology and illustrates a way to identify specific water bands using temperature change and addition of solutions of different ionic strength as perturbations. Rapid and precise measurement of low concentration solutes has been given as a strong evidence of the vast information that "the water spectral pattern as molecular mirror" approach provides. Few applications using near infrared spectroscopy and multivariate analysis as main tools of Aquaphotomics have been presented.

Stretching of DNA confined in nanochannels with charged walls.

There is currently a growing interest in control of stretching of DNA inside nanoconfined regions due to the possibility to analyze and manipulate single biomolecules for applications such as DNA mapping and barcoding, which are based on stretching the DNA in a linear fashion. In the present work, we couple Finite Element Methods and Monte Carlo simulations in order to study the conformation of DNA molecules confined in nanofluidic channels with neutral and charged walls. We find that the electrostatic forces become more and more important when lowering the ionic strength of the solution. The influence of the nanochannel cross section geometry is also studied by evaluating the DNA elongation in square, rectangular, and triangular channels. We demonstrate that coupling electrostatically interacting walls with a triangular geometry is an efficient way to stretch DNA molecules at the scale of hundreds of nanometers. The paper reports experimental observations of λ-DNA molecules in poly(dimethylsiloxane) nanochannels filled with solutions of different ionic strength. The results are in good agreement with the theoretical predictions, confirming the crucial role of the electrostatic repulsion of the constraining walls on the molecule stretching.

A comparative study of the adsorption of uranium on commercial and natural (Cypriot) sea sand samples

The adsorption of hexavalent uranium on two different types of sea sand [e.g. a local, Cypriot (N_SS) and a commercially available marine sediment (C_SS)] has been investigated as a function of pH, initial metal concentration, ionic strength and contact time under normal atmospheric conditions. Before carrying out the adsorption experiments, the sea sand samples have been characterized by XRD, XRF, N2-adsorption, acid/base titrations and FTIR spectroscopy. Sample characterization showed clearly that the two sea sand types differ significantly in their composition, particularly in their calcite and FeOOH content. According to experimental data obtained from acid/base titrations and adsorption batch experiments sea sand composition affects the acid/base and the adsorption properties of the adsorbents. The extraordinary high affinity of N_SS for hexavalent uranium in the alkaline pH region can be attributed to the formation of mixed U(VI)–carbonato surface species on the FeOOH crystall phases present in N_SS, which effectively compete the formation of U(VI)–carbonato complexes in solution. On the other hand, data obtained by adsorption experiments carried out in solution of different ionic strengths don’t differ significantly from one another indicating the formation of inner-sphere complexes. Finally, the adsorption on sea sands is a relatively fast two-step process.

Lead Uptake in Diverse Plant Families: A Study Applying X-ray Absorption Near Edge Spectroscopy

The chemical environment of lead in roots and leaves of plants from four different plant families and a lichen from a former lead mining site in the Eifel Mountains in Germany was determined by Pb L3-edge XANES measurements using solid reference compounds and also aqueous solutions of different ionic strength simulating the plant environment. Pb(2+) ions in the plants were found to have two major coordinations, one with nine oxygen atoms in the first coordination shell similar to outer-sphere complexation and a second coordination with just three oxygen atoms similar to inner-sphere complexation. This can be interpreted assuming that lead is sorbed on the surface of cell walls depending on the concentration of lead in the soil solution. Pb L3-edge XANES spectra of dried and fresh plant samples are very similar because sorption does not change with removal of water but only because of the initial ionic strength. No bonding to biologically important groups (-S, - N) or precipitation (-PO4) was found.

Characteristic features of the behavior of charged hydrophilic and hydrophobic macromolecules in solutions of different ionic strength

Characteristic features of the behavior of charged hydrophilic and hydrophobic macromolecules in solutions of different ionic strength

Characterisation of hydrogen bond perturbations in aqueous systems using aquaphotomics and multivariate curve resolution-alternating least squares

Aquaphotomics is a new discipline that provides a framework for understanding changes in the structure of water caused by various perturbations, such as variations in temperature or the addition of solutes, using near infrared spectroscopy (NIRS). One of the main purposes of aquaphotomics is to identify water bands as main coordinates of future absorbance patterns to be used as biomarkers. These bands appear as consequence of perturbations in the NIR spectra. Curve resolution techniques may help to resolve and find new water bands or confirm already known bands. The aim of this study is to investigate the application of multivariate curve resolution-alternating least squares (MCR-ALS) to characterise the effects of various perturbations on the NIR spectra of water in terms of hydrogen bonding. For this purpose, the perturbations created by temperature change and the addition of four solutions of different ionic strength and Lewis acidity were studied (NaCl, KCl, MgCl2 and AlCl3, with concentrations ranging from 0.2 to 1molL−1 in steps of 0.2molL−1). Transmission spectra of all salt solutions and pure water were obtained at temperatures ranging from 28 to 45°C. We have found that three distinct components with varying temperature dependence are present in water perturbed by temperature. The salt solutions studied exhibited similar trends with respect to the temperature perturbation, while the peak locations of their MCR-ALS pure components varied according to the ionic strength of the salt used.

A surface complexation model of YREE sorption on Ulva lactuca in 0.05–5.0 M NaCl solutions

We present distribution coefficients, logiKS, for the sorption of yttrium and the rare earth elements (YREEs) on BCR-279, a dehydrated tissue homogenate of a marine macroalga, Ulva lactuca, resembling materials featured in chemical engineering studies aimed at designing renewable biosorbents. Sorption experiments were conducted in NaCl solutions of different ionic strength (0.05, 0.5, and 5.0M) at T=25°C over the pH range 2.7–8.5. Distribution coefficients based on separation of the dissolved and particulate phase by conventional filtration (<0.22μm) were corrected for the effect of colloid-bound YREEs (>3kDa) using an existing pH-dependent model. Colloid-corrected values were renormalized to free-cation concentrations by accounting for YREE hydrolysis and chloride complexation. At each ionic strength, the pH dependence of the renormalized values is accurately described with a non-electrostatic surface complexation model (SCM) that incorporates YREE binding to three monoprotic functional groups, previously characterized by alkalimetric titration, as well as binding of YREE–hydroxide complexes (MOH2+) to the least acidic one (pKa∼9.5).In non-linear regressions of the distribution coefficients as a function of pH, each pKa was fixed at its reported value, while stability constants of the four YREE surface complexes were used as adjustable parameters. Data for a single fresh U. lactuca specimen in 0.5M NaCl show generally the same pH-dependent behavior but a lower degree of sorption and were excluded from the regressions. Good linear free-energy relations (LFERs) between stability constants of the YREE–acetate and YREE–hydroxide solution complex and surface complexes with the first and third functional group, respectively, support their prior tentative identifications as carboxyl and phenol. A similar confirmation for the second group is precluded by insufficient knowledge of the stability of YREE–phosphate complexes and a perceived lack of YREE binding in 0.05M NaCl; this issue awaits further study. The results indicate that SCMs can be successfully applied to sorbents as daunting as marine organic matter. Despite remnant challenges, for instance resolving the contributions of individual groups to the aggregate sorption signal, our approach helps formalize seaweed’s avowed promise as an ideal biomonitor or biofilter of metal pollution in environments ranging from freshwaters to brines by uncovering what chemical mechanisms underlie its pronounced affinity for YREEs and other surface-reactive elements.

SYBR Green I: Fluorescence Properties and Interaction with DNA

In this study, we have investigated the fluorescence properties of SYBR Green I (SG) dye and its interaction with double-stranded DNA (dsDNA). SG/dsDNA complexes were studied using various spectroscopic techniques, including fluorescence resonance energy transfer and time-resolved fluorescence techniques. It is shown that SG quenching in the free state has an intrinsic intramolecular origin; thus, the observed >1,000-fold SG fluorescence enhancement in complex with DNA can be explained by a dampening of its intra-molecular motions. Analysis of the obtained SG/DNA binding isotherms in solutions of different ionic strength and of SG/DNA association in the presence of a DNA minor groove binder, Hoechst 33258, revealed multiple modes of interaction of SG inner groups with DNA. In addition to interaction within the DNA minor groove, both intercalation between base pairs and stabilization of the electrostatic SG/DNA complex contributed to increased SG affinity to double-stranded DNA. We show that both fluorescence and the excited state lifetime of SG dramatically increase in viscous solvents, demonstrating an approximate 200-fold enhancement in 100% glycerol, compared to water, which also makes SG a prospective fluorescent viscosity probe. A proposed structural model of the SG/DNA complex is compared and discussed with results recently reported for the closely related PicoGreen chromophore.

Chelating DTPA amphiphiles: ion-tunable self-assembly structures and gadolinium complexes

A series of chelating amphiphiles and their gadolinium (Gd(III)) metal complexes have been synthesized and studied with respect to their neat and lyotropic liquid crystalline phase behavior. These amphiphiles have the ability to form ion-tunable self-assembly nanostructures and their associated Gd(III) complexes have potential as magnetic resonance imaging (MRI) contrast enhancement agents. The amphiphiles are composed of diethylenetriaminepentaacetic acid (DTPA) chelates conjugated to one or two oleyl chain(s) (DTPA-MO and DTPA-BO), or isoprenoid-type chain(s) of phytanyl (DTPA-MP and DTPA-BP). The thermal phase behavior of the neat amphiphiles was examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross polarizing optical microscopy (POM). Self-assembly of neat amphiphiles and their associated Gd complexes, as well as their lyotropic phase behavior in water and sodium acetate solutions of different ionic strengths, were examined by POM and small and wide angle X-ray scattering (SWAXS). All neat amphiphiles exhibited lamellar structures. The non-complexed amphiphiles showed a variety of lyotropic phases depending on the number and nature of the hydrophobic chain in addition to the ionic state of the hydration. Upon hydration with increased Na-acetate concentration and the subtle changes in the effective headgroup size, the interfacial curvature of the amphiphile increased, altering the lyotropic liquid crystalline structures towards higher order mesophases such as the gyroid (Ia3d) bicontinuous cubic phase. The chelation of Gd with the DTPA amphiphiles resulted in lamellar crystalline structures for all the neat amphiphiles. Upon hydration with water, the Gd-complexed mono-conjugates formed micellar or vesicular self-assemblies, whilst the bis-conjugates transformed only partially into lyotropic liquid crystalline mesophases.

Adsorption of nucleic acids on collodion films

Adsorption of nucleic acids on collodion films from solutions of different ionic strengths was studied, and the adsorption equilibrium constants were determined. The primary adsorption of DNA samples on collodion films was examined depending on various factors. A comparative analysis of different techniques (vacuum drying, UV irradiation) employed for immobilization of DNA samples on collodion films was carried out.

Soil properties affect the availability, movement, and virulence of entomopathogenic fungi conidia against puparia of Ceratitis capitata (Diptera: Tephritidae)

The Mediterranean fruit fly, Ceratitis capitata Wiedemann (Diptera: Tephritidae), is the major tephritid pest in the Mediterranean region. This insect may overwinter as pupae inside fruits or in soil. Therefore, infection with entomopathogenic fungi is a potentially useful control technique during the insect’s soil-dwelling stage. Entomopathogenic fungi have an important role in Integrated Pest Management programs as an alternative to conventional chemical control, but they have been usually selected on the basis of laboratory results with little regard to fungal ecology. In this work, we designed several experiments to study the availability and movement of the EF Beauveria bassiana (Balsamo) Vuill. and Metarhizium anisopliae (Metsch.) conidia in 16 soils differing widely in pH, texture, organic matter, and carbonate contents. Experiments of adsorption and drag of conidia by soil particles suspended in CaCl 2 solutions of different ionic strength showed B. bassiana conidia to be retained by clay particles, and this effect disappeared with increasing ionic strength. The availability of M. anisopliae conidia in the suspension tended to be lower for sandy than for clayey soils and was not influenced by ionic strength. Regardless of soil properties, over 90% of the added fungal propagules were recovered from the surface layer of columns of packed soils representing model combinations of texture (sandy or clayey) and pH values (acid or alkaline). However, retention of B. bassiana conidia in the surface layer was higher in clayey than in sandy soils, and the retention of M. anisopliae conidia in the surface layer was higher in sandy than in clayey soils. Finally, neither soil texture nor ionic strength affected the infectivity of conidia of both fungal strains to C. capitata puparia.

Synthesis and properties of sodium alginate/Na +rectorite grafted acrylic acid composite superabsorbent via 60Coγ irradiation

Sodium alginate/Na +rectorite-graft-poly acrylic acid (SA/Na +REC-g-PAA) composite superabsorbent was prepared via 60Coγ irradiation in methanol solution and nitrogen protection. The effect of the preparation conditions on graft ratio, graft efficiency and absorption of water were investigated. The structure and morphology were analyzed by IR, XRD, TEM and SEM. The results showed that the optimal condition was that the amount of Na +REC was 2 wt%, the ratio of SA/Na +REC to AA was 10 wt%, total dose was 9.0 kGy and volume ratio of methanol to water was 8:2. SEM showed that it is much easier to obtain porous products through 60Coγ irradiation than chemical initiator. The mechanism of graft copolymerization via 60Coγ irradiation was discussed. The water absorption of the graft copolymer in salt solutions of different ionic strengths was also measured, from which the superabsorbent properties are found to be saline sensitive. Ionic strength markedly decreased the water absorption of the sodium alginate grafted superabsorbent composites.