Ionic Strenght Research Articles

Monovalent ion-mediated charge-charge interactions drive aggregation of surface-functionalized gold nanoparticles.

Monolayer-protected metal nanoparticles (NPs) are not only promising materials with a wide range of potential industrial and biological applications, but they are also a powerful tool to investigate the behaviour of matter at nanoscopic scales, including the stability of dispersions and colloidal systems. This stability is dependent on a delicate balance between attractive and repulsive interactions that occur in the solution, and it is described in quantitative terms by the classic Derjaguin-Landau-Vewey-Overbeek (DLVO) theory, that posits that aggregation between NPs is driven by van der Waals interactions and opposed by electrostatic interactions. To investigate the limits of this theory at the nanoscale, where the continuum assumptions required by the DLVO theory break down, here we investigate NP dimerization by computing the Potential of Mean Force (PMF) of this process using fully atomistic MD simulations. Serendipitously, we find that electrostatic interactions can lead to the formation of metastable NP dimers at physiological ion concentrations. These dimers are stabilized by complexes formed by negatively charged ligands belonging to distinct NPs that are bridged by positively charged monovalent ions present in solution. We validate our findings by collecting tomographic EM images of NPs in solution and by quantifying their radial distribution function, that shows a marked peak at interparticle distance comparable with that of MD simulations. Taken together, our results suggest that not only van der Waals interactions, but also electrostatic interactions mediated by monovalent ions at physiological concentrations, contribute to attraction between nano-sized charged objects at very short length scales.

Influence of pH and ionic strength on the thermal gelation behaviour of pea protein

Gelation is one of the functional properties of protein, which can be controlled by pH and ionic strength. However, kowledge related to gelation properties of emerging plant proteins is still limited. In this paper, the solubility, the thermal behaviour and gelation behaviour of pea protein were analysed. Gels were analysed rheologically measuring the elastic modulus G′25°C, the ratio of G′25°C to G′95°C, and dependence on frequency and amplitude. In addition, the stabilizing protein interactions within the gel were analysed. The stiffest gels were obtained at pH 4.5 at 0.6 M NaCl. The high G′25°C and low tan δ value indicate the inclusion of active fillers, which is proposed to be insoluble protein. Salt addition at acidic pH could protect the protein from acid denaturation leading to a low heat denaturation at 62 °C–68 °C compared to heat denaturation at neutral pH. Addition of salt at pH 3 also led to a stiffer gel with a lower G′25 °C/G′95°C ratio, which indicates more hydrophobic and covalent interactions. An increase in ionic strength at pH 7 and pH 9 led to an increase of denaturation temperature above gelation temperature and an increase of electrostatic interactions. At pH 9 at ionic strenghts of 0.9 M NaCl and 1.5 M NaCl the frequency sweep showed that an entangled solution was formed, instead of a gel. It was observed that pea protein gelation were more influenced by the ionic strength at low pH values compared to neutral or alkaline pH.

Sorption properties of carbamoylmethylphosphonated-based polymer combining both sorption and thermosensitive properties: New valuable hydrosoluble materials for rare earth elements sorption

The sorption properties of gadolinium (Gd) by an original carbamoylmethylphosphonate (cmp)-based acrylamide polymer combining both chelating and thermosensitive properties namely poly(diethyl-6-(acrylamido)hexylcarbamoyl-methylphosphonate) (P(CPAAm6C)) are presented for the first time. For pH = 1 and at 20 °C, the maximum sorption capacity reached 0.6 mmol·g−1 for the highest Gd concentrations. Different parameters influencing the sorption of Gd were studied as pH, ionic strenght and temperature. The temperature was shown to influence both the sorption and the stability of the complex cmp-Gd formed by coordination mode with CO and PO functions. The selectivity of the cmp group for Gd was demonstrated in Gd/Ni mixture and shows its thermosensitive polymer is very promising for the development of selective sorption processes.

Cationic β-cyclodextrin polymer applied to a dual cyclodextrin polyelectrolyte multilayer system

A polyelectrolyte multilayer film (PEM) based on cationic and anionic β-cyclodextrin polyelectrolytes was coated onto a textile substrate for future drug delivery purposes. We firstly synthesized a novel cationic β-cyclodextrin polymer (polyEPG-CD) by crosslinking β-cyclodextrin (βCD) with epichlorohydrin (EP) under basic conditions, in the presence of glycidyltrimetrylammonium chloride (GTMAC) as cationizing group. The influence of preparation conditions has been investigated in order to preferably obtain a water soluble fraction whose charge density and molecular weights were optimal for the layer-by-layer (LbL) deposition process. The different cationic cyclodextrin polymers obtained were characterized by FTIR, NMR, colloidal titration, conductimetry, thermogravimetric analysis and size exclusion chromatography. Besides, the counterpart polyelectrolyte was a β-cyclodextrin polymer crosslinked with citric acid, polyCTR-CD, whose synthesis and characterization have been previously reported. Finally we realized the Layer by Layer (LbL) build-up of the PEM coating onto the textile support, using the dip coating method, by alternatively soaking it in cationic polyEPG-CD and anionic polyCTR-CD solutions. This multilayer self-assembly was monitored by SEM, gravimetry and OWLS in function of both polyelectrolytes concentrations and ratios. Solutions parameters such as pH, ionic strenght were also discussed.

Adsorption of pH-responsive polyelectrolyte chains onto spherical macroions.

The adsorption of pH-responsive polyelectrolyte chains onto oppositely charged spherical macroions is investigated through Metropolis Monte Carlo simulations and the Weighted Histogram Analysis Method. In this case, the polymer charge density is susceptible to the solution conditions, such as salt concentration and pH, as well as the presence of other charged species. Thus, the pH and ionic strength variations leads to abrupt variations of the conformational and electric properties of the chain, as a result of first-order-like transition between the adsorbed and desorbed states. The diagram of states as a function of ionic strenght and p H is provided. Despite the inhomogeneities in the polyelectrolyte charge distribution induced by the macroion presence and its dependence on ionic strength, the scaling relation between the macromolecular charge densities and the critical Debye length is obtained in agreement with experimental investigations.

Preconcentration and Determination of Lead by Solidification of Floated Organic Drop Coupled with Nanodrop Spectrophotometry

The liquid-phase microextraction based on solidification of floating organic microdrop coupled with UV-visible spectrophotometer for preconcentration and determination of lead in the aqueous samples has been developed. In this technique, 20μL of 1-undecanol containing dithizone as the chelating agent (10-3mol L-1) was transferred to the water samples containing lead ions, and the solution was stirred for 25 min. The sample vial was cooled in an ice bath for 5 min. The solidified extract was transferred into a conical vial where it melted immediately, and then the organic phase was analyzed by Nanodrop spectrophotometer. Factors that influence the extraction and complex formation, such as pH, concentration of dithizone, extraction time, effect of ionic strenght, temperature and stirring rate were optimized. Under the optimized conditions, a preconcentration factor of 356, detection limit of 0.006 μgL-1, limit of quantification 0.018 μgL-1and a good relative standard deviation of 2.1% were obtained. The procedure was applied to sea water, mineral water and well water.

Influence of ionic strenght on swelling of 2-hydroxyetylakrylate and methylmetacrylate gels

Influence of ionic strength on swelling degree of polymeric HEA-MMA hydrogels was investigated. It is shown that contraction of HEA-MMA hydrogels can be reached by variation of ionic strength and structure of initial monomeric mix.

Response surface optimization of pH and ionic strength for emulsion characteristics of egg yolk

Effects of pH (3.5, 4.5, 6.0, 7.5, and 8.5) and ionic strength (0.05, 0.15, 0.30, 0.45, and 0.55 M NaCl) on emulsion capacity, emulsion stability (ES), apparent yield stress of emulsion (AYS), and emulsion density (ED) of egg yolk were studied by using a model system. Ionic strength and pH had significant (P < 0.01) effects on the emulsion characteristics of egg yolk. Their interaction effects also have been found significant on ES, AYS, and ED. Predicted solutions of ES, emulsion capacity, and ED were minimum. The critical point of ES was determined to be at pH 6.08 and an ionic strength of 0.49 (M NaCl). Predicted solution for AYS was a maximum, which was determined to be at pH 6.04 and an ionic strength of 0.29 (M NaCl). Optimum values of pH and ionic strenght were 4.61 to 7.43 and 0.10 to 0.47, respectively.

An investigation of Cu(II) adsorption by raw and acid-activated bentonite: A combined potentiometric, thermodynamic, XRD, IR, DTA study

Adsorption of Cu(II) by raw bentonite (RB) and acid-activated bentonite (AAB) samples was investigated as a function of the initial Cu(II) concentration, solution pH, ionic strenght, temperature, the competitive and complexation effects of ligands (Cl −, SO 4 2−, PO 4 3−). Langmuir monolayer adsorption capacity of the RB (42.41 mg g −1) was found greater than that of the AAB (32.17 mg g −1). The effect of structural charges on the reactivity of the edge groups was evidenced by the particular proton adsorption behaviour of the bentonite samples. The spontaneity of the adsorption process is established by decrease in Δ G which varied from −0.34 to −0.71 kJ mol −1 (RB), −1.13 to −1.49 kJ mol −1 (AAB) in temperature range 303–313 K. Infrared (IR) spectra of the bentonite samples showed that the positions and shapes of the fundamental vibrations of the OH and Si–O groups were influenced by the adsorbed Cu(II) cations. Differential thermal analysis (DTA) results showed that adsorbed Cu(II) cations have a great effect on the thermal behaviour of the bentonite samples. The X-ray diffraction (XRD) spectra indicated that the Cu(II) adsorption onto the bentonite samples led to changes in unit cell dimensions and symmetry of the parent bentonites.

Polymethylene-co-guanidine based capsules: A mechanistic study of the formation using alginate and cellulose sulphate

Capsules have been prepared based on a polyanion blend of sodium alginate and sodium cellulose sulphate, gelled in the presence of calcium chloride and sodium chloride. In a second step a membrane was formed via the addition of polymethylene-co-guanidine (PMCG), an oligocation. A mechanistic study examined the influences of pH, ionic strenght, gelation and reaction times as well as the molar mass of the polyanions on the transport and mechanical properties. The ratio of alginate-to-cellulose sulphate in the polyanion blend was also varied and it was found that both mechanical resistance to compression as well as the pore size of the membrane decreased as the percentage of cellulose sulphate was reduced. The maximum mechanical strength was observed to correspond to the minimum in viscosity of the polyanion blend with, for low NaCl levels, a 3:1 alginate:cellulose sulphate level providing the largest resistance to deformation. The ability to decouple the molar mass cut-off and mechanical resistance is viewed as an important advantage of alginate/cellulose sulphate/PMCG capsules. Capsules were transplanted into mice to a maximum of 102 days, after which animals were sacrificed and capsules retrieved. Over 90% of the capsules were recovered from the peritoneal cavity with the mechanical properties of the explanted capsules observed to decrease as a function of implantation time, likely as a result of ion exchange. The capsules were, however, relatively free from any rejection which is a quite unusual result for cation containing systems. It is believed that the reason PMCG-based microcapsules function well in vivo is that they provide a net negative charge on the surface. Higher molar mass polycations such as poly-L-lysine provide a net positive charge, inducing inflammation.

Enraizamento in vitro de Anthurium andraeanum Lindl. cv. Eidibel e aclimatização com fungos micorrízicos arbusculares

The aim of the present study was to evaluate A. andraeanum in vitro rooting and acclimatization with arbuscular mycorrhizal fungi (AMF). In order to induce rooting, the consistence and ionic strenght of MS medium modified (5,71 µM de NAA) were tested: solid MS; liquid MS; solid half-strenght MS and liquid half-strength MS. After 60 days, plants were acclimatized in association with the AMF Gigaspora albida, Glomus etunicatum, Acaulospora longula, multiple inoculum or without AMF (control treatment). The liquid nutritive medium containing the complete concentration of MS salts induced better plant development, specially with regard to root number. Mycorrhization reduced the acclimatization impact, favoring water and phosphorus absorption, as well as plant growth, specially those associated with multiple inoculum.

Potentiometric, NMR, and Fluorescence‐Emission Studies on the Binding of Adenosine 5′‐Triphosphate (ATP) by Open‐Chain Polyamine Receptors Containing Naphthylmethyl and/or Anthrylmethyl Groups

AbstractThe interaction in aqueous solution of adenosine 5′‐triphosphate (ATP) with a series of open‐chain polyamines linked at one or both ends to anthrylmethyl or naphthylmethyl fragments was followed by potentiometric titration, 1H‐, 13C‐, and 31P‐NMR spectroscopy, and by steady‐state fluorescence measurements. The results revealed greater stabilities for the compounds containing one anthracene moiety than for those with one naphthalene moiety, the stabilities of the compounds with both ends N‐substituted with naphthylmethyl groups being close to those containing just one anthrylmethyl unit. The 1H‐NMR spectra showed that in all systems, there is involvement of π‐π stacking interactions in the stabilization of the adduct species. The competitive effect of the anions afforded by the supporting electrolyte was checked in some of the studied systems working at two different ionic strenghts (0.15M and 1.0M NaCl). The joint analysis of the spectrofluorimetric titrations and pH‐metric species‐distribution curves showed that for all the ATPreceptor systems, a quenching of the fluorescence occurred upon protonation of the adenine N(1)atom. Steady‐state fluorescence and time‐correlated single‐photon‐counting analysis of a system made up of ATP and a bis‐chromophoric polyamine receptor containing anthracene and naphthalene fluorophores established that the energy‐transfer process between the naphthalene and anthracene moieties is still operative despite the presence of ATP.

Monitoring of oxidation steps of ascorbic acid redox reaction by kinetics-sensitive voltcoulometry in unsupported and supported aqueous solutions and real samples.

Aqueous solutions of ascorbic acid in unsupported and supported aqueous solutions and real samples were studied by the kinetics-sensitive double-step voltcoulommetric method with the aim to contribute to a better understanding of its behavior in biological systems. The data obtained from measurements made on analytes prepared in the laboratory, as well as those made on real samples (some commercial orange drinks, flash of the fresh fruits) point to the redox reaction of L-ascorbic acid (L-AH2) being very sensitive to both the presence of dissolved gaseous species (O2, CO2) and the ionic strenght in the analyte. Either the dissolved gaseous species, or the higher ionic strength caused by both the presence of supporting electrolyte and increased total concentration of ascorbic acid, respectively, give birth to the degradation of L-AH2. Naturally, the highest percentage of L-AH2 was spotted in fresh fruit.

Polycation graft copolymers accelerating DNA strand exchange: involvement of ionic interaction.

In the previous study (Chem. Eur. J., 7, 176 (2001)) we demonstrated that the comb-type polycationic copolymer (PLL-g-Dex) which is composed of poly (L-lysine) backbone and dextran graft chains expedited the DNA strand exchange reaction. In this study, fluorescence resonance energy transfer (FRET) was employed to explore the copolymer-mediated DNA strand exchange with higher time-resolution. To initiate strand exchange reaction the duplex prepared from 3'-fluorescein isothiocyanate (FITC)--and 5'-carboxytetramethylrhodamine(TAMRA)-labeled complementary DNAs was added to its non-labeled complementary single strand. DNA strand exchange was monitored by observing the recovery of the FITC quenching. More than 20,000 times increase in strand exchange rate at 37 degrees C by the copolymer was estimated. To investigate the accelerating mechanisms of the copolymer, the same reactions but at various ionic strenghts were studied. With increasing ionic strengths the strand exchange rate in the absence of the copolymer increased, suggesting that ionic repulsion among DNAs is unfavorable for the strand exchange to occur. Hence, alleviation of the electrostatic repulsion through interpolyelectrolyte complex formation is probably a role of the copolymer for accelerating the strand exchange reaction.

Spontaneous precipitation of struvite from aqueous solutions

The kinetics of the spontaneous precipitation of struvite was investigated in aqueous supersaturated solutions containing stoichiometric concentrations of Mg 2+, NH 4 + and PO 4 3− ions, ionic strenght 0.15 M NaCl and at 25°C in a batch, stirred reactor at constant supersaturation. The induction times preceding the onset of struvite precipitation and the initial rates of precipitation were measured directly from the traces of titrants added in order to maintain the solution supersaturation. From the measurement of the induction times as a function of the solution supersaturation, the stability diagram of the system was constructed. In all cases the only solid-phase forming was identified as struvite. Kinetic analysis of the rates, which depended strongly on the solution supersaturation yielding a second-order dependence, suggested a surface diffusion mechanism. The precipitated struvite crystals showed a high negative charge which increased as a function of the solution pH while the presence of magnesium ions affected the microelectrophoretic mobility of struvite dispersions yielding an isoelectric point at pMg of 1.75.

Aquation and Base Hydrolysis of trans-Tetraammine(methylamine)sulfatocobalt(III) Complex Ion

The kinetics of aquation and base hydrolysis reactions of fmns-[Co(NH 3 ) 4 (NH 2 CH 3 )(OSO 3 )] + have been studied. In acid solution the aquation rate, R aq , follows the equation R aq /[complex] = k s + k c [H + ], at constant ionic strenght μ = 1.0Μ. The activation parameters are ΔΗ* = 88.8 kj mol -1 , ΔS* = - 50.5 JK -1 mol -1 , ΔΗ* = 96.7 kj mol -1 and ΔS* =-23 JK -1 mol -1 . The rate constants at 25°C are k s = 4.15 χ 10 -6 s -1 and k c = 4.52M -1 s -1 . The rate of base hydrolysis, R OH , follows the equation R OH/ complex] = k 0H [OH - ]. The activation parameters are ΔΗ* OH =74.9kJmol -1 and ΔS* OH = 2JK -1 mol -1 and the rate constant is k OH = 0.58M 1 s -1 at 25°C and μ, = 0.15 Μ. The stereochemistry of the hidroxo product has been determined (cis-[Co(NH 3 ) 4 (NH 2 CH 3 )- (OH)] 2+ =9%). The results are discussed in the light of the reaction mechanisms proposed so far.

Prediction of swelling behaviour of hydrogels containing diprotic acid moieties

Prediction of swelling behaviour of hydrogels containing diprotic acid moieties, sensitive to pH and ionic strenght changes of the swelling medium, was investigated. The equations derived for the prediction of the theoretical swelling curves are based on the phantom network theory of Erman et al. and the approaches of Peppas et al. For all predictions, a number of polymer-based parameters, solution property parameters and polymer-solvent combination type parameters were evaluated typical of dicarboxylated copolymers. The advantages of the derived equations for the determinations of average molecular weight between the cross-links and also a polymer-solvent interaction parameter have been exemplified.

Mediated reagentless enzyme inhibition electrodes

We have investigated the use of the copper-containing oxygenase enzymes, laccase, tyrosinase and ceruloplasmin as reagentless enzyme activity sensors. The system is based on the mediated reduction of oxygen by the enzymes co-immobilized in an osmium redox polymer hydrogel on glassy carbon electrode surfaces. Both laccase and tyrosinase present rapid homogeneous second-order rate constants for the interaction with a model monomer, [Os(2,2′-bipyridine) 2(N-methylimidazole)Cl] + (OsMeIm). Ceruloplasmin rates are several orders of magnitude slower and no catalytic currents are observed upon co-immobilization of this enzyme in the redox hydrogel. The activity of the immobilized laccase and tyrosinase sensors is shown to be influenced by the enzyme loading in the deposition solution, the electrolyte pH and ionic strenght. The immobilized sensors can be utilized for the detection of modulators of enzyme activity, such as the respiratory poison azide. Reproducible inhibition curves can be obtained by normalization of the sensor response. The resulting enzyme inhibition biosensors can detect levels of azide as low as 1 μM in solution and may be useful as an early warning sensor for the presence of such respiratory toxins.

Formation of Phenolate Complexes of Some First-Row Transition Metal Cations

We report in the present paper the result of our potentiometric studies on the complexation tendency of phenolate anion with divalent manganese, cobalt, nickel, and copper ions in aqueous sodium pperchlorate solutions of 0.1 M ionic strenght at 25.0°

Indirect ultraviolet detection of biologically relevant organic acids by capillary electrophoresis

Indirect UV detection of fourteen short-chain organic acids (e.g., oxalic acid, citric acid, malonic acid, tartaric acid, methylmalonic acid, α-ketoglutaric acid, succinic acid, ethylmalonic acid, methylsuccinic acid, glutaric acid, apidic acid, methylglutaric acid, lactic acid and pyruvic acid) by capillary electrophoresis is described. The method used phthalate as the UV-absorbing additive in carbonate buffer and the non-absorbing analytes were detected indirectly at 230 nm. The influences of buffer pH, ionic strenght, concentration of phthalate and organic modifier on indirect signal response and migration behavior of the organic acids were investigated. Comparisons of reproducibility on migration time, limit of detection and separation efficiency among three types of capillary (e.g., polyacrylamide-coated, myristyltrimethylammonium bromide-coated and uncoated capillaries) were conducted. The method developed was applied to detect succinic acid, methylmalonic acid, citric acid, glutaric acid and lactic acid in human body fluids, and preliminary results were provided.