Presence Of Multivalent Ions Research Articles

Membrane autopsy based bio-fouling investigation of distillery spent wash RO treatment plant

In this paper, a thorough investigation has been done to evaluate the effects of different pollutants on membrane performance by autopsy. Autopsy was performed on fresh and fouled reverse osmosis (RO) membrane elements from a distillery spent wash treatment plant by different analyses, such as field emission scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and X-ray diffraction, to identify the cause of poor performance of an RO plant. Results obtained from the analysis of membranes indicate that a mixture of colloids and organic matters (polysaccharides and amines) along with the presence of multivalent ions (Ca, Mg, Fe and SO4) causes membrane fouling, which in turn affects membrane performance. Possible measures to improve treated effluent quality and mitigate fouling have been suggested for this particular case study.

Interaction forces, heteroaggregation, and deposition involving charged colloidal particles.

Force profiles as well as aggregation and deposition rates are studied for asymmetrically charged particles and surfaces in aqueous electrolytes theoretically. Interactions are calculated within the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, whereby the electrostatic part is modeled at Poisson-Boltzmann (PB) level. Unequally charged surfaces are examined, from the symmetric system, where both surfaces are equally charged, to fully asymmetric systems, where the surfaces are oppositely charged. Charged-neutral systems, where one surface is charged and the other is neutral, emerge as an essential scenario. In this case, the choice of boundary conditions used for solving the PB equation is crucial, whereby constant charge and constant potential boundary conditions lead to either fully repulsive or fully attractive forces. Consequently, charge regulation has a major influence on particle aggregation and deposition rates too. In the charge-neutral case, substantial shifts in the critical coagulation concentration (CCC) are observed when the regulation properties are changed. In the presence of multivalent ions, these systems behave similarly to the symmetrically charged ones. The CCC decreases with the square of the valence in weakly charged systems, while unrealistically high charge densities are needed to recover the classical Schulze-Hardy limit, which predicts a sixth power dependence on valence.

Accurate predictions of forces in the presence of multivalent ions by Poisson-Boltzmann theory.

Forces between positively and negatively charged colloidal particles across aqueous salt solutions containing multivalent ions are measured directly with the atomic force microscope (AFM). The measurements are interpreted quantitatively with Poisson-Boltzmann (PB) theory. Thereby, the surface potentials and regulation properties of the particle surfaces are extracted from symmetric measurements between the same types of particles. This information is used to predict force profiles in the asymmetric situations involving different types of particles without any adjustable parameters. These predictions turn out to be very accurate, which demonstrates that the mean-field PB theory is reliable down to distances of about 5 nm. While various reports in the literature indicate that this theory should fail due to neglect of ion correlations, such effects seem important only at higher concentrations and smaller distances.

Monovalent-ion-selective membranes for reverse electrodialysis

Reverse electrodialysis (RED) is a process that can be used to generate energy from salinity gradients. Since its application in practice requires the use of natural seawater and river water, the presence of multivalent ions is inevitable, but this currently limits RED performance. Membranes with selectivity for monovalent ions may overcome this limitation. Standard ion exchange membranes have low monovalent-ion selectivity. We used a relatively fast method to coat a standard commercial anion exchange membrane to improve its monovalent-ion selectivity. The coating layer was formed by copolymerization of 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) as the active polymer and N,N-methylenebis(acrylamide) (MBA) as the crosslinker, using UV irradiation. The monovalent ion selectivity of the resulting membranes was comparable to that of commercial monovalent-selective membranes. Furthermore, the modified membranes with their negatively charged coating showed increased hydrophilicity and exhibited sufficient antifouling potential against organic foulants. When they were tested in an RED stack, their performance was found to depend especially on the proportion of the divalent ions (sulfate) in the river water stream. However, the use of the currently available monovalent selective membranes was not found to be very effective for obtaining higher gross power densities in RED.

Effects of various salts on structural polymorphism of reconstituted type I collagen fibrils

Even though the behavior of collagen monomers self-assembling into fibrils is commonly understood in terms of hydrophobic and electrostatic interactions, the mechanisms that drive their ordered, longitudinal alignment to form a characteristic periodicity are still unclear. By introducing various salts into the collagen fibrillogenesis system, the intermolecular interactions of fibril formation were studied. We found that the pH and ion species play a critical role in forming native fibrils. Turbidity and electron microscopy revealed that collagen self-assembled into fibrils with a native banding pattern in the presence of multivalent ions. The isoelectric point of collagen in 12mM of NaCl is pH 8.9; it shifted to pH 9.4 and pH 7.0 after adding 10mM CaCl2 and Na2SO4, respectively. Native fibrils were reconstituted at pH 7.4 in salts with divalent anions and at pH 9.0 in salts with divalent cations. Circular dichroism spectroscopy showed a loss of helicity in the conditions where fibrillogenesis was unable to be achieved. The multivalent ions not only change the surface charge of collagen, but also facilitate the formation of fibrils with the native D-periodic banding pattern. It is likely that the binding multivalent ions induce the like-charge attraction and facilitate monomers’ longitudinal registration to form fibrils with the native banding.

Attractive Forces between Charged Colloidal Particles Induced by Multivalent Ions Revealed by Confronting Aggregation and Direct Force Measurements.

Interactions involving charged particles in the presence of multivalent ions are relevant in wide-range of phenomena, including condensation of nucleic acids, cement hardening, or water treatment. Here, we study such interactions by combining direct force measurements with atomic force microscopy (AFM) and aggregation studies with time-resolved light scattering for particles originating from the same colloidal suspension for the first time. Classical DLVO theory is found to be only applicable for monovalent and divalent ions. For ions of higher valence, charge inversion and additional non-DLVO attractive forces are observed. These attractive forces can be attributed to surface charge heterogeneities, which leads to stability ratios that are calculated from direct force measurements to be higher than the experimental ones. Ion-ion correlations are equally important as they induce the charge inversion in the presence of trivalent or tetravalent ions, and they enhance the surface charge heterogeneities. Such heterogeneities therefore play an essential role in controlling interactions in particle suspensions containing multivalent ions.

Structure formation in polyelectrolytes induced by multivalent ions

We review recent investigations of aqueous solutions of polyelectrolytes in presence of multivalent ions. In particular, we look into the interaction of di- and trivalent counterions with star polyelectrolytes and spherical polyelectrolyte brushes. In presence of monovalent ions these systems are dominated by the marked osmotic pressure of the confined counterions. Higher-valent counterions lead to a collapse of these structures and to precipitation if the counterion concentration is raised beyond the critical coagulation concentration. This effect can be used to switch the structure of star polyelectrolytes between an extended and a dense conformation. No overcharging occurs in these systems. This is in contrast to the behavior of bare colloids where overcharging in presence of multivalent ions is a common phenomenon. A precise monitoring of the coagulation kinetics shows that the repulsive interaction between spherical polyelectrolyte brushes can be finely tuned by addition of trivalent ions. All experimental data obtained so far are well-understood by theory, at least in a semi-quantitative fashion.

Effects of Some Multivalent Ions on Coagulation and Electrokinetic Behaviours of Colemanite Particles

The effects of magnesium, barium, aluminium, and ferric cations as multivalent ions on the coagulation and electrokinetic behaviours of colemanite have been investigated in relation to pH and cation concentration. The zero point of charge for colemanite was determined to be at pH 10.2. The positive surface charge of colemanite increased in the presence of multivalent ions at pH values below the zero point of charge. Also, these ions changed the zeta potential of colemanite from negative to positive within the pH range 10.2 to 12. In the experiments, the coagulation of colemanite with ferric ions was more efficient than with the other ions and the effect of ferric ions varied considerably depending on the concentration and pH. The coagulation recovery values of colemanite suspension increased quickly up to 2.5 × 10–3 M concentration of ferric ions and the maximum value (~93 %) was obtained at a pH of 11.5. It was also found that the coagulation behaviour of the colemanite suspension in the presence of multivalent cations was in good agreement with the electrokinetic characteristics.

Competition between Supercoils and Toroids in Single Molecule DNA Condensation

The condensation of free DNA into toroidal structures in the presence of multivalent ions and polypeptides is well known. Recent single molecule experiments have shown that condensation into toroids occurs even when the DNA molecule is subjected to tensile forces. Here we show that the combined tension and torsion of DNA in the presence of condensing agents dramatically modifies this picture by introducing supercoiled DNA as a competing structure in addition to toroids. We combine a fluctuating elastic rod model of DNA with phenomenological models for DNA interaction in the presence of condensing agents to compute the minimum energy configuration for given tension and end-rotations. We show that for each tension there is a critical number of end-rotations above which the supercoiled solution is preferred and below which toroids are the preferred state. Our results closely match recent extension rotation experiments on DNA in the presence of spermine and other condensing agents. Motivated by this, we construct a phase diagram for the preferred DNA states as a function of tension and applied end-rotations and identify a region where new experiments or simulations are needed to determine the preferred state.

Alginate Oligoguluronates as a Tool for Tailoring Properties of Ca‐Alginate Gels

AbstractAlginates represent a family of structural polysaccharides derived from either seaweeds or bacteria. They readily form ionotropically‐induced physcial gels in aqueous solution in the presence of multivalent ions. In this study, the homogeneous release of Ca2+ from Ca‐ethylene glycol tetraacetic acid (Ca‐EGTA) within an alginate solution is utilized to prepare homogeneous gelation conditions. The pH‐dependence of the multiple equilibria involved, i.e. between Ca2+, the various states of EGTA, the alginate and its protonation and ion binding, is modeled and used as a basis for designing the glucono‐δ‐lactone concentration to reduce the pH. This method is used for the perturbation of the Ca‐induced gelation of alginates in the presence of oligoguluronate oligomers. These oligoguluronate oligomers are able to be involved in the binding of Ca2+, but sufficiently short not to mediate connectivity through their chains. The results indicate that the oligoguluronate oligomers perturb the gelation of alginate differently in the Ca2+‐limited and non‐Ca2+‐limited regimes. In the calcium limited regime, the oligoguluronate oligomers appear to sequester calcium either by binding to oligoguluronate sequences of the network, or between the free oligoguluronates, yielding an overall net effect of reduced gel strength. In the non‐Ca2+ limited regime, the experimental data shows increased gel strength in the presence of oligoguluronate blocks. These results show that oligoguluronates can be used as modulators of gelation kinetics as well as local network structure formation and equilibrium properties in alginate gels.

Characterization of the binding of multivalent ions to modified pluronic micelles by isothermal titration calorimetry and modified conductometry

CAE surfactants ( carboxylic acid end-standing triblock copolymers of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide)) are amphiphiles that are able to bind multivalent cations thermoreversibly; a property that can be used to develop new environmentally friendly separation and ion exchange applications. The analysis of the binding of multivalent ions to CAE micelles is more difficult as compared to conventional surfactants because of its thermo-responsive micellization behavior and its low CMC at room temperature. Conventional analysis techniques like conductometry and surface tensiometry are highly sensitive to temperature and are therefore very difficult to apply in surfactant solutions with strong temperature dependent micellization behavior. For this reason, binding of multivalent ions to CAE micelles has been investigated using isothermal titration calorimetry (ITC) and an alternative conductometric analysis method. Conductometry was used to construct ‘Eisenberg’ plots, which show the binding and release behavior of monovalent ions in the presence of multivalent ions. Regarding the CAE-85 (modified Pluronic P85) micellar system, both methods provide information about the exchange of multivalent cations for monovalent ions above the critical micellization temperature (CMT) of CAE-85. ITC results confirm that dehydration of multivalent ions plays a dominant role in the observed heat effect during the titration of multivalent chloride salts to CAE-85 solutions. The multivalent ions investigated in this study are Ca 2+, Cu 2+, Zn 2+, Co 2+, Mg 2+, Ba 2+, Mn 2+ and La 3+. Additionally, using the alternative conductivity approach a change in micellar shape was observed upon the addition of multivalent ions when the molar amount of cationic charges balances the molar amount of anionic carboxylate end groups of the surfactant.

Effects of pH, Ca- and SO4-concentration on surface charge and colloidal stability of goethite and hematite – consequences for the adsorption of anionic organic substances

AbstractSoil solution chemistry, especially pH and the presence of multivalent ions, affects the surface charge (SC) of Fe oxides and accordingly colloidal stability and sorption properties. The SC of synthetic goethite and hematite was quantified in the presence of different electrolytes (NaCl, CaCl2, Na2SO4and CaSO4) by combining the streaming potential with polyelectrolyte titration. The point of zero charge (PZC) for goethite was observed at pH 8.2 and the stability field around the PZC, where colloids are flocculated, is more extended (±1 pH unit) than that of hematite with a PZC at pH 7.1 (±0.5 pH unit). The SC decreases with increasing SO4concentration, indicating adsorption of SO4on the oxide, whereas the presence of Ca increases the SC. At pH 4, the addition of 0.1 mmol l–1Na2SO4induced a decrease in SC from 1.5 to 0.380 μmolcm–2for goethite and from 0.85 to 0.42 μmolcm–2for hematite. In a suspension with 0.1 mmol l–1Na2SO4, the number of colloids is already reduced, and both oxides flocculate rapidly and completely at >0.5 mmol l–1Na2SO4. While the addition of SO4did not affect charge titrations with the cationic polyelectrolyte, the anionic polyelectrolyte formed complexes with Ca, resulting in an overestimation of positive SC. The electrolyte CaSO4is most efficient at keeping goethite and hematite in the pH range 4–10 in the flocculated state. Besides pH, the presence of multivalent ions should also be considered when predicting colloid mediated transport and adsorption properties of anionic substances by Fe oxides in soil systems.

Influence of multivalent ions on power production from mixing salt and fresh water with a reverse electrodialysis system

Reverse electrodialysis is a membrane-based technique for production of sustainable electricity from controlled mixing of a diluted electrolyte solution (e.g., river water) and a concentrated electrolyte solution (e.g., sea water). Reverse electrodialysis has been investigated with pure sodium chloride solutions. In practice, however, in most cases also other ions are present in both feed solutions. In the present paper, the effect of multivalent ions on the performance of a reverse electrodialysis stack was investigated. Results show that, besides a higher stack resistance in presence of multivalent ions, especially the presence of multivalent ions in the dilute solution has a lowering effect on the stack voltage. This can be explained by an observed transport of these ions from the diluted electrolyte solution to the concentrated electrolyte solution. In order to prevent or hamper this transport against the activity gradient, monovalent-selective membranes can be used. This shows indeed better results with respect to the stack voltage. Therefore, it would be beneficial to use monovalent-selective membranes in reverse electrodialysis, especially in the case of a relatively high content of multivalent ions in the dilute (i.e., in the first stages of the installation where the sodium chloride content in the dilute is still relatively low).

Equation of state of looped DNA

We derive the equation of state of DNA under tension that features a loop. Such loops occur transiently during DNA condensation in the presence of multivalent ions or permanently through sliding protein linkers such as condensin. The force-extension relation of such looped-DNA modeled as a wormlike chain is calculated via path integration in the semiclassical limit. This allows us to rigorously determine the high stretching asymptotics. Notably the functional form of the force-extension curve resembles that of straight DNA, yet with a strongly renormalized apparent persistence length. We also present analogous results for DNA under tension with several protein-induced kinks and/or loops. That means that the experimentally extracted single-molecule elasticity does not necessarily only reflect the bare DNA stiffness, but can also contain additional contributions that depend on the overall chain conformation and length.

Coil-globule Coexistence and Compaction of DNA Chains

In this work we discuss different factors governing coil-globule coexistence in the compaction process of DNA. We initially analyse the role played by fluctuations in the degree of binding of an external compacting agent in the conformational behavior of the chain backbone. The analysis relies both on Monte Carlo simulation results and simple statistical approaches. Compacting agents of various binding characteristics are taken into consideration and the degree of charge neutralization upon the chain is related to conformational indicators. Selected model systems comprising stiff chains in the presence of multivalent ions are employed to assess intrinsic single-chain conformational fluctuation, in the presence of external agents but not resulting from differences in binding. It is shown that trends found for a variety of compacting agents, including the extension of the coil-globule coexistence regions, can be rationalised on the basis of this analysis.

Chemical characterization of pitch deposits produced in the manufacturing of high-quality paper pulps from hemp fibers

The composition of pitch deposits occurring in pulp sheets and mill circuits during soda/anthraquinone pulping and elemental chlorine-free pulp bleaching of bast fibers of industrial hemp ( Cannabis sativa) was studied. Pitch deposits were extracted with acetone, and the extracts analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Acetone extracts (15–25% of pitch deposits) were constituted by the defoamers used at the mill and by lipophilic extractives from hemp fibers. Acetone-insoluble residues (75–85% of pitch deposits) were analyzed by pyrolysis–GC/MS in the presence and absence of tetramethylammonium hydroxide. These residues were constituted by salts of fatty acids (arising from hemp fibers) with calcium, magnesium, aluminum and other cations that were identified in the deposits. It was concluded that inappropriate use of defoamer together with the presence of multivalent ions seemed to be among the causes of hemp extractives deposition in the pitch problems reported here.

Calcium activation of silica surfaces with sodium oleate collector

In the Florida phosphate industry, fatty acid collectors are used to separate phosphate ore from silica during the rougher flotation stage. However, the presence of multivalent ions (in particular Ca++) in the processing water has been reported to result in the activation of silica with respect to oleate adsorption, rendering it floatable. Hence, adequate separation may not be achieved during the rougher flotation stage. In this study, the direct measurement of surface interaction forces via atomic force microscopy was used to delineate possible mechanisms for calcium activation under phosphate flotation conditions at oleate/calcium concentrations both above and below the calcium dioleate precipitation limit.

Polyelectrolytes in the presence of multivalent ions: gelation versus segregation.

We analyze solutions of strongly charged chains bridged by linkers such as multivalent ions. The gelation induced by the strong short range electrostatic attractions is dramatically suppressed by the long range electrostatic correlations due to the charge along the non-cross-linked monomers and ions. A modified Debye-Hückel approach of cross-linked clusters of charged chains is used to determine the mean field gelation transition self-consistently. Highly dilute polyelectrolyte solutions tend to segregate macroscopically. Semidilute solutions can form gels if the Bjerrum length l(B) and the distance between neighboring charged monomers along the chain b are both greater than the ion size a.

DNA-lipid systems. A physical chemistry study.

It is well known that the interaction of polyelectrolytes with oppositely charged surfactants leads to an associative phase separation; however, the phase behavior of DNA and oppositely charged surfactants is more strongly associative than observed in other systems. A precipitate is formed with very low amounts of surfactant and DNA. DNA compaction is a general phenomenon in the presence of multivalent ions and positively charged surfaces; because of the high charge density there are strong attractive ion correlation effects. Techniques like phase diagram determinations, fluorescence microscopy, and ellipsometry were used to study these systems. The interaction between DNA and catanionic mixtures (i.e., mixtures of cationic and anionic surfactants) was also investigated. We observed that DNA compacts and adsorbs onto the surface of positively charged vesicles, and that the addition of an anionic surfactant can release DNA back into solution from a compact globular complex between DNA and the cationic surfactant. Finally, DNA interactions with polycations, chitosans with different chain lengths, were studied by fluorescence microscopy, in vivo transfection assays and cryogenic transmission electron microscopy. The general conclusion is that a chitosan effective in promoting compaction is also efficient in transfection.

Cation-mediated interaction of dextran sulfate with phospholipid vesicles: binding, vesicle surface polarity, leakage and fusion

The interaction of dextran sulfate (DS) with dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles was investigated. DS of different molecular weights (1, 8, 40 and 500 kDa) and divalent cations (Ca2+, Mg2+ and Mn2+) and the trivalent cation La3+ were used in the experiments. Binding of DS was studied by use of the microelectrophoresis and monolayer technique. Binding depends strongly on cation and NaCl concentrations in the medium and does not occur in the absence of multivalent cations. Binding is modulated by the molecular weight of the polymers; DS with lower molecular weights lead to less negative zeta potentials at identical concentrations. A comparable monomer of DS, glucose-6-sulfate, does not change the zeta potential of DMPC vesicles. Monolayer experiments revealed a decrease in surface pressure after addition of multivalent cations and DS, indicating a stronger interaction of the cation–polymer complex with the phosphatidylcholine headgroups than its penetration into the phospholipid (PL) bilayer. The cation-mediated binding of DS to the vesicles leads to aggregation of the vesicles. The tendency to promote aggregation of DMPC vesicles is La3+>Ca2+>Mn2+≥ Mg2+. The aggregated vesicles show a stacklike arrangement of the bilayers as shown by freeze-fracture electron microscopy. The strong aggregation is accompanied by lipid mixing measured by the 1,4-nitrobenzo-2-oxa-1,3-diazole–phosphatidylethanolamine (PE)/lissamine rhodamine B sulfonyl-PE assay. At low ionic strength substantial lipid mixing can be observed in the previously mentioned order of the cations. This lipid mixing is accompanied by an increase in the permeability of the vesicles as revealed by the 1-aminonaphthalene-3,6,8-trisulfonic acid/p-xylenebis (pyridiium bromide) assay. The extent of leakage is determined by the cation used and the DS molecular weight. These interaction processes between the opposing bilayers are connected with a decrease in the water content in the gap between the opposing PL bilayers. As a measure for the change of the polar properties of the vesicle surface the shift of the emission wavelength of the fluorescent probe dansylphosphatidylethanolamine was measured. The effectiveness of divalent/trivalent cations to decrease the surface dielectric constant of DMPC vesicles also followed the sequence of ions as found for binding, PL mixing and leakage. The results are discussed in terms of the changed hydration at the bilayer surface induced by DS in the presence of multivalent ions.