Multivalent Anions Research Articles

Retroviral Capsid Assembly: A Role for the CA Dimer in Initiation

In maturing retroviral virions, CA protein assembles to form a capsid shell that is essential for infectivity. The structure of the two folded domains [N-terminal domain (NTD) and C-terminal domain (CTD)] of CA is highly conserved among various retroviruses, and the capsid assembly pathway, although poorly understood, is thought to be conserved as well. In vitro assembly reactions with purified CA proteins of the Rous sarcoma virus (RSV) were used to define factors that influence the kinetics of capsid assembly and provide insights into underlying mechanisms. CA multimerization was triggered by multivalent anions providing evidence that in vitro assembly is an electrostatically controlled process. In the case of RSV, in vitro assembly was a well-behaved nucleation-driven process that led to the formation of structures with morphologies similar to those found in virions. Isolated RSV dimers, when mixed with monomeric protein, acted as efficient seeds for assembly, eliminating the lag phase characteristic of a monomer-only reaction. This demonstrates for the first time the purification of an intermediate on the assembly pathway. Differences in the intrinsic tryptophan fluorescence of monomeric protein and the assembly-competent dimer fraction suggest the involvement of the NTD in the formation of the functional dimer. Furthermore, in vitro analysis of well-characterized CTD mutants provides evidence for assembly dependence on the second domain and suggests that the establishment of an NTD–CTD interface is a critical step in capsid assembly initiation. Overall, the data provide clear support for a model whereby capsid assembly within the maturing virion is dependent on the formation of a specific nucleating complex that involves a CA dimer and is directed by additional virion constituents.

From “Nano-bags” to “Micro-pouches”. Understanding and Tweaking Flocculation-based Processes for the Preparation of New Nanoparticle-Composites

The control of simple parameters involved in the process of classic bridging flocculation allow the preparation and fine-tuning a new class of hybrid nanomaterials with respect to size, composition, and morphology. The resulting nanoparticle-filled "nano-bags" are obtained in aqueous suspension by mixing three basic components, a polyelectrolyte, a multivalent ion, and nanoparticles in different ratios. The size range in which nano- and micropouches can be prepared seems to start at about 25 nm; these are oligo-nanoparticle aggregates whose size are clearly related to the size of the nanoparticles themselves and seem to extend up to about 5 microm. By controlling the stoichiometric balance between the global number of positive and negative charges on the polycation and on the multivalent anion and by controlling the absolute concentrations and the ratios, namely of the polyelectrolyte and the nanoparticles, one has access to a wide range of different nanopouch morphologies and compositions. Interestingly, the process of nanopouch formation seems not to be restricted to a single type of nanoparticles since, at least, citrate-stabilized gold and iron oxide nanoparticles showed indistinguishable results in transmission electron microscopy. The outer surface of the nanoparticle-filled nanopouches is easily functionalized further through layer-by-layer assembly. As a first example, we have enhanced the stability of nanopouch suspensions at increased ionic strength by electrostatic adsorption of a polyanion on the nanobag exterior.

Electrokinetic Properties of Vermiculite and Expanded Vermiculite: Effects of pH, Clay Concentration and Mono- and Multivalent Electrolytes

In this study, the zeta potential values of vermiculite and expanded vermiculite were measured to determine the effect of pH, clay concentration, and various mono- and multivalent electrolytes including NaCl, KCl, NH4Cl, NaNO3, NaClO4, Na2SO4, Na2CO3, Na3PO4·12H2O, MgCl2·6H2O, CaCl2·2H2O, BaCl2, SrCl2·6H2O, CuCl2·2H2O, CoCl2·6H2O, NiCl2, AlCl3, and CrCl3·6H2O on the electrokinetic properties of vermiculite samples. It was found that generally the measured zeta potential values of expanded vermiculite for the studied systems were slightly more negative than that of vermiculite. The pH profiles of vermiculite and expanded vermiculite at acidic, natural, and basic pH values were obtained to determine the effect of time on the pH values of clay suspensions. The zeta potential measurements showed that the surface charge of clay particles was negative in water. The isoelectric point of vermiculite and expanded vermiculite were determined as pH 2.30 and 2.57, respectively. Divalent cations (Mg2+, Ca2+, Sr2+, and Ba2+), heavy metal ions (Cu2+, Ni2+, and Co2+) and trivalent cations (Al3+ and Cr3+) were potential determining ions for vermiculite and expanded vermiculite particles. Moreover, divalent and trivalent cations caused the change of surface charge from negative to positive. On the other hand, monovalent cations (Na+, K+ and NH4 +), monovalent anions (Cl−, NO3 −, and ClO4 −) and multivalent anions (SO4 2−, CO3 2−, and PO4 3−) acted as indifferent ions for these clay particles.

Influence of counter ions on the reverse osmosis through MFI zeolite membranes: implications for produced water desalination

Desalination of brines produced from oil and gas fields is a potential resource for potable water in the southwestern U.S. and other semi-arid areas. Oilfield brines typically contain high concentrations of Na + and Cl −, as well as other multivalent cations and anions that can reduce efficacy of reverse osmosis (RO). RO separation of NaCl solutions at existence of other co-ions or at increased ion concentration and operating pressure was experimentally tested on a pure silicalite zeolite membrane. Water fluxes increase linearly with increase of net driving force (Δ P−Σ r i RTC c,f ). Ion flux is essentially independent of the operating pressure but increases exponentially by a power factor of 1.13 as feed concentration increases from 0.001 M to 0.3 M. Inorganic cations (K +, Ca 2+, and Al 3+) and anions (Br −, and SO 4 2−), when present in a 0.01 M NaCl solution, play an important role on separation performance of the NaCl solutions. A notable variation of water flux and ion rejection in the presence of counter cations was observed, while the permeation behavior of 0.01 M NaCl solution was hardly affected by counter anions. This study is part of a broader project seeking to make desalination of oilfield-produced waters economically viable.

Polymerisation of an Anionic Monomer in a Self-Assembled M12L24 Coordination Sphere with Cationic Interior

Polymerisation within a well-defined nanocavity leads to the precise control of the rate of polymerisation and the molecular weight of the resultant polymer. We prepared a highly cationic spherical complex that was self-assembled from 12 palladium(II) ions and 24 quaternary ammonium-attached bidentate ligands. NMR experiments confirmed that this spherical complex encapsulates multivalent anions within the cavity. When the free radical polymerisation of an anionic monomer, sodium p-styrenesulphonate, was carried out in the presence of the cationic sphere as a template, acceleration of the polymerisation and control of the molecular weight of the resultant polymer were observed. The molecular weight of the polymer depends on the number of the positive charges on the template.

Removal of mono-valent oxyanions from water in an ion exchange membrane bioreactor: Influence of membrane permselectivity

The ion exchange membrane bioreactor (IEMB) proved to be an effective technology for the removal of nitrate and perchlorate from polluted drinking water when using a mono-anion permselective membrane such as Neosepta ACS. Aiming at reducing the cost of the system, this study evaluates the use of a lower-cost anion exchange membrane, which exhibits no preferential mono-anion permselective properties. With this purpose an Excellion I-200 membrane was tested, for the removal of anionic micropollutants, such as nitrate and perchlorate from drinking water supplies. The impact of the lower anion permselectivity of this membrane on the quality of the treated water was determined. It was demonstrated that differences between the membrane properties are responsible for the different permselectivities observed towards multi-valent and mono-valent anions. The use of Excellion I-200 resulted in a less selective removal of perchlorate and nitrate, allowing anions such as sulphate and phosphate species to be transported. When treating 3.1 l/m 2 h of water contaminated with 100 μg/l of perchlorate and 60 mg/l of nitrate, lower removal degrees were obtained (85% of perchlorate and 88% of nitrate), compared with 96% of perchlorate and 99% of nitrate achieved with the Neosepta ACS membrane, operating under the same conditions. However, the Excellion I-200 membrane shows no target anion flux decline during a relatively long period of operation (1 month) and no secondary contamination of the treated water by the carbon source used. These characteristics are essential for a membrane to be successfully used in the IEMB system. Additionally, the selection of the membrane depends on the latter characteristics and on the water quality requirements.

Electrokinetic properties of barite nanoparticles suspensions in different electrolyte media

In this study, electrokinetic properties of barite nanoparticles have been investigated in water. A series of systematic zeta potential measurements have been performed to determine the isoelectric point (iep) and potential-determining ions (pdi), and the effect of mono-, di-, and trivalent anions sodium salts such as NaCl, NaNO3, NaCH3COO, Na2SO4, Na2CO3, and Na3PO4 on the zeta potential of barite nanoparticles. Barite nanoparticles yields an isoelectric point at pH 7.8. The zeta potential for the barite nanoparticles has ranged from +15.5 mV at pH ∼ 3 to −19.8 mV at pH ∼ 9.5 at 25 ± 1 °C in water. It is proved that the valency of the ions greatly influence on the electrokinetic behavior of the suspension. Monovalent anions were found to have a weak effect on the zeta potentials. The negative zeta potentials were observed in the presence of di- and trivalent anions. Charge reversal was observed for divalent anions at 1 × 10−2 M and for trivalent anions at 1 × 10−1 M. It was considered that monovalent anions are indifferent ions and di- and trivalent anions are potential-determining ions. A schematic adsorption model which accounts for the adsorption of mono- and multivalent anions in the electrical double layer of barite nanoparticles is proposed.

Adsorption and ion-pairing interactions of phospholipids in the system of two immiscible electrolyte solutions. Part II: The formation and behaviour of a lecithin layer at the water/1,2-dichloroethane interface in the presence of multivalent anions in the aqueous phase

The present paper investigates voltammetrically the properties of the layers formed, whereas Part I of this series studied the electrochemical formation of l-α-lecithin (dipalmitoyl, DPPC) adsorbed layers at the water/1,2-dichloroethane interfaces. These are primarily determined by ion pairing between the positively charged layer and the anions present on the aqueous side of the interface. Cerium(IV) sulfate has been used as the source of the model anion and a five-step mechanism proposed for the formation and behaviour of DPPC layers. For the sake of comparison, the same experiments have been carried out with trimethyloctadecylammonium cation (TODA+) which have helped in elucidation of certain parts of the mechanism. In the absence of anions of higher charges, both DPPC and TODA+ form monolayers at the interface and the process involves simple free diffusion transport of the layer components through the bulk of the solution. In their presence, both DPPC and TODA+ form multilayers, the transport of the components is slower and is given by lateral diffusion along the layer surface and diffusion through the layer. The passage of ions across the interface is virtually not hindered by the monolayers, unless the ions are very large. However, DPPC and TODA+ multilayers strongly slow down or even prevent passage of larger ions (trimetylammonium (TMA+), PF6- and K+ ions assisted by a crown compound were used in the study).

Effect of Inorganic Ions on Gelation, Particle Morphology, and Texture of Solo-Gel-Derived Silica Nanospheres

The gelation process is of importance for the structure and texture of the silica particle and further functionalization in the area of biomedical application. In a base-catalysis process the sodium phosphate or plus calcium nitrate salts could be added to induce the gelling velocity and particle size distribution. Multivalent anions (phosphate ions) or dication (calcium ions) induce the microscopic phase separation and accelerate gelation of silica sol. Furthermore, the composite silica nanospheres show excellent monodispersibility as well as pH-stability in the simulated body fluids or Tris-HCl buffer solution, which will help to surface modification and functionalization in the biomolecule-existing environments.

Nanoparticle-Assembled Capsule Synthesis: Formation of Colloidal Polyamine−Salt Intermediates

There is current interest in developing new synthesis strategies for multifunctional hollow spheres with tunable structural properties that would be useful in encapsulation and controlled release applications. A new route was reported recently, in which the sequential reaction of polyamines, multivalent anions, and charged nanoparticles leads to the formation of polymer-filled and water-filled organic/inorganic micron-sized structures known as nanoparticle-assembled capsules. This technique is unique among other capsule preparation routes, as it allows the rapid and scalable formation of robust shells at room temperature, in near-neutral water, and with readily available precursors. This nanoparticle assembly synthesis route involves two steps: the formation of polymer aggregates and the subsequent deposition of particles around the aggregates. The purpose of this paper is to understand in greater detail the noncovalent chemistry of the polymer-salt aggregation step. With poly(allylamine hydrochloride) (PAH) as the model polymer, aggregate formation was investigated as a function of charge ratio, pH, and time through dynamic light scattering, electrophoretic mobility measurements, chloride ion measurements, and optical microscopy. PAH formed aggregates by the cross-linking action of divalent and higher-valent anions above a critical charge ratio and in a pH range defined by the pKa values of PAH and the anion. The aggregates grew in size through coalescence and with growth rates that depended on their surface charge. Controlling polymer aggregate growth provided a direct and simple means to adjust the size of the resultant capsule materials.

Chemically modified polybenzimidazole nanofiltration membrane for the separation of electrolytes and cephalexin

A novel chemical modification process has been proposed to prepare polybenzimidazole (PBI) nanofiltration membrane with desirable pore sizes and pore-size distribution. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis have verified the proposed chemical modification reaction between the PBI membrane and p-xylylene dichloride. Depending on the post-treatment process in the p-xylylene dichloride/heptane solution, one can finely control the pure water permeability of the modified membrane. The modified PBI membranes have a decreased effective mean pore size, a narrowed pore size distribution, and demonstrate superior ion rejection performance for liquid separation, especially for the fractionation of multivalent cations and anions from monovalent ions. It is also found that the charge characteristics of PBI membrane may vary with the solution pH, which is reflected by the rejection of NaCl under different pH. Particularly, this modified PBI NF membrane can be employed for the separation and concentration of cephalexin with impressive high rejection rates under a wide range of pH.

Sulfonium and phosphonium, new ion-pairing agents with unique selectivity towards polarizable anions

Ion-pair chromatography (IPC) almost universally relies upon ammonium-based ion-pairing agents (IPAs) for anion separations. This work compares tetrabutylammonium (TBA) with tetrabutylphosphonium (TBP) and tributylsulfonium (TBS). To best understand the retention behavior analytes used for characterization of the IPAs spanned the Hofmeister series; from kosmotropic monoanions (iodate, chloride, nitrite) and intermediate anions (nitrate, bromide) to chaotropic ions (perchlorate, thiocyanate, iodide). The studies demonstrate that tetrabutylphosphonium is the most chaotropic IPA, followed by tetrabutylammonium and finally tributylsulfonium is the least chaotropic. In the case of the chaotropic anions, the retention of perchlorate was least with tributylsulfonium, and greatest for tetrabutylphosphonium, with tetrabutylammonium being intermediate. The multivalent kosmotropic anions (sulfate, chromate, thiosulfate) demonstrated unique selectivity changes depending on the kosmotropic/chaotropic nature of the IPA. Demonstrating increases in retention with increasing IPA concentration only with tributylsulfonium, whereas the more chaotropic IPAs universally decreased the retention of the multivalent anions.

Proton-conducting ionic liquids based upon multivalent anions and alkylimidazolium cations

Alkylimidazolium type ionic liquids have been prepared with acidic anions derived from multivalent anions with the expectation of excellent thermal properties and ionic conductivity, including proton conduction.

Synthesis and characterization of nickel–copper hydroxide acetate, NiCu(OH) 3.1(OCOCH 3) 0.9 · 0.9H 2O

Nickel–copper hydroxide acetate with a chemical composition of NiCu(OH) 3.1(OCOCH 3) 0.9 · 0.9H 2O was synthesized by hydrothermal heating of an aqueous solution containing nickel acetate, copper acetate, and hydrogen peroxide to 423 K for 4 h. The crystal structure of this compound can be described as brucite-type octahedral (Ni,Cu)(OH) 2 layers, where a part of OH sites are replaced by acetate ions located in the interlayer. This compound is stable below about 455 K except that the reversible dissociation and association of the water molecules from/with the interlayer acetate ions occur depending upon the surrounding conditions. Above 455 K, a part of the interlayer acetate ions are released from the solid phase. The solid phase is decomposed to nickel and copper oxides above about 500 K. The synthesized nickel–copper hydroxide acetate takes up little or no Cl − and NO 3 - but shows high selectivity for multivalent anions such as SeO 3 2 - and AsO 4 3 - . The uptake of multivalent anions proceeds on the basis of exchange with the acetate ions but may also involve exchange with the hydroxide ions in the matrix hydroxide layers.

Anionic poly(amino acid)s dissolve F-actin and DNA bundles, enhance DNase activity, and reduce the viscosity of cystic fibrosis sputum

Bundles of F-actin and DNA present in the sputum of cystic fibrosis (CF) patients but absent from normal airway fluid contribute to the altered viscoelastic properties of sputum that inhibit clearance of infected airway fluid and exacerbate the pathology of CF. Previous strategies to remove these filamentous aggregates have focused on DNase to enzymatically depolymerize DNA to constituent monomers and gelsolin to sever F-actin to small fragments. The high densities of negative surface charge on DNA and F-actin suggest that the bundles of these filaments, which alone exhibit a strong electrostatic repulsion, may be stabilized by multivalent cations such as histones, antimicrobial peptides, and other positively charged molecules prevalent in airway fluid. This study reports that bundles of DNA or F-actin formed after addition of histone H1 or lysozyme are efficiently dissolved by soluble multivalent anions such as polymeric aspartate or glutamate. Addition of poly-aspartate or poly-glutamate also disperses DNA and actin-containing bundles in CF sputum and lowers the elastic moduli of these samples to levels comparable to those obtained after treatment with DNase I or gelsolin. Addition of poly-aspartic acid also increased DNase activity when added to samples containing DNA bundles formed with histone H1. When added to CF sputum, poly-aspartic acid significantly reduced the growth of bacteria, suggesting activation of endogenous antibacterial factors. These findings suggest that soluble multivalent anions have potential alone or in combination with other mucolytic agents to selectively dissociate the large bundles of charged biopolymers that form in CF sputum.

Multivalent Ion/Polyelectrolyte Exchange Processes in Exponentially Growing Multilayers

We show, in this paper that multivalent ferrocyanide anions can penetrate into exponentially growing (PGA/PAH)n multilayer films whatever the nature of the last deposited layer. These ions are not able to diffuse out of the film when it is brought in contact with a pure buffer solution. However, the contact of this film with a poly(allylamine) (PAH) or a poly(L-glutamic acid) (PGA) solution leads to the release of ferrocyanide ions from the multilayer. It is shown that the release of ferrocyanide anions, when the film is in contact with a PGA solution, is due to the diffusion of the PGA chains into the film so that an exchange between ferrocyanide ions and PGA chains takes place inside the film. On the other hand, PAH chains do not diffuse into PGA/PAH multilayers. When the film is then brought in contact with a PAH solution, the PAH chains from the solution are expected to strongly interact with the ferrocyanide ions and thus induce a diffusion mechanism of the multivalent anions out of the film, the film/solution interface playing the role of a sink for these ions. This work thus shows that interactions between multivalent ions and exponentially growing films are much more complex than expected at first sight and that polyelectrolyte multilayers must be seen as dynamic entities in which diffusion and exchange processes can take place.

Thermodynamic Properties of the Unique Self-Assembly of {Mo72Fe30} Inorganic Macro-Ions in Salt-Free and Salt-Containing Aqueous Solutions

Static and dynamic laser light scattering techniques are used to monitor the slow self-assembly of 2.5-nm-diameter, hollow spherical, fully hydrophilic heteropolyoxometalate {Mo72Fe30} macro-ions into single-layer vesicle-like "blackberries" (averaging approximately 50-60 nm in diameter) in dilute salt-free and salt-containing aqueous solutions, to obtain the thermodynamic properties of the unique self-assembly. A very high activation energy is observed during the transition from the single ion (general solute state) to blackberries (so-called "second solute state"), which might be responsible for the interestingly slow self-assembly process in dilute solutions. The thermodynamic parameters of the blackberry formation can be affected by adding simple electrolytes into the solution, because the electrostatic interactions are responsible for the unique self-assembly, and the effects of various anions and cations (in the low salt concentration regimes) are discussed. Multivalent anions make the single {Mo72Fe30} macro-ions more stable and make the blackberry formation more difficult. Small cations carrying more charges tend to accelerate the self-assembly process. This is the first study on the thermodynamic properties of the novel self-assembly in dilute solutions and the equilibrium and transition between the two solute states of macro-ions in solution.

Elution of Propranolol as an Ion-Pair Complex by Buffer Solutions on C18-Silica

Propranolol (pK(a) = 9.4) was eluted on C(18)-bonded Kromasil, equilibrated with buffer solutions of methanol and water (40/60, v/v) containing a constant concentration of a counteranion (12 mM). Nine different counteranions were studied: Cl(-), I(-), NO(3)(-), SO(4)(2-), CH(3)COO(-), HOOCC(2)H(4)COO(-), (-)OOCC(2)H(4)COO(-), HOOCCOHCOOHCOO(-), HOOCCOHCOO(-)COO(-), and (-)OOCCOHCOO(-)COO(-). The co-cation was K(+) or Na(+). Vacancy perturbations were measured on three concentration plateaus of propranolol hydrochloride, at 1.2, 12, and 24 mM, by injecting 100 microL of a pure mixture of methanol and water (40/60, v/v). Indirect detection of the solvent, the counteranion, the co-cation, and the chloride ion was carried out at 325 nm, a wavelength at which only propranolol responds. In a 1.2 mM propranolol hydrochloride solution, there is a 10-fold excess of counteranions and only a positive perturbation peak, due to the excluded co-cation and eluting before the column hold-up time, and a large vacancy peak, associated with propranolol, were recorded. Association between propranolol and the counteranion in excess determines the retention time of this second perturbation. The hydrophobicity of the complexes increases in the order Cl(-) < CH(3)COO(-) approximately HOOCC(2)H(4)COO(-) < NO(3)(-) < I(-) < HOOCCOHCOOHCOO(-) < (-)OOCC(2)H(4)COO(-) < SO(4)(2-) approximately HOOCCOHCOO(-)COO(-) < (-)OOCCOHCOO(-)COO(-). Propranolol retention is larger in the presence of the trivalent citrate anion than in that of the bivalent citrate, succinate, or sulfate anions. It is larger with these bivalent anions than with any monovalent anion. Equal concentration of propranolol hydrochloride and buffer in the mobile phase reveals five system peaks associated with the five components (solvent, counteranion, co-cation, chloride, propranolol molecules). In contrast with monovalent anions, bivalent anions (sulfate, succinate, citrate) or trivalent anions (citrate) cause a reversal of the elution order of the perturbation peaks of chloride anions and buffer molecules. This confirms a competition between chloride and buffer anions to form ion pairs with propranolol. The retention of the perturbation signal of the buffer increases with increasing anion charge because multivalent anions can bind to several molecules of propranolol. The perturbation measurements demonstrate the influence of the valence and hydrophobicity of the buffer on the retention of ionizable compounds. The inverse method allowed the derivation of the isotherm parameters from the overloaded band profiles of propranolol. These values confirm that adsorbate-adsorbate interactions increase with increasing valence of the anions.

Further investigations on a poly(vinyl alcohol)- polyelectrolyte chemically selective optical film.

The ionomer poly(vinylbenzyltrimethylammonium chloride) has been blended with cross-linked poly(vinyl alcohol) to form optically clear composites that can be covalently linked as thin films to oxide surfaces. Films are characterized using spectroscopic ellipsometry with refractive index (n) and extinction coefficient (k) data presented for wavelengths 300 to 1100 nm. A refractive index of 1.54 and average thickness of 709 nm are typical of an air dry film prepared by spin-coating. Dynamic in situ ellipsometry results for films exposed to 0.1 M KNO(3) and 1.0 mM Fe(CN)(6)(-3) are presented. Upon initial exposure to 0.1 M KNO(3), an air dry film expands by about 160% and stabilizes in size and refractive index at about 18 hours. Ion exchange of film cationic groups with ferricyanide is marked by slight film contraction, presumably due to electrostatic cross-linking by the multivalent anion. These films are useful in the spectroelectrochemical sensor with our newly developed fluorescence detection mode, as demonstrated by results of the reversible incorporation of the fluorescent anion fluorescein.

Biomimetic synthesis of silica nanospheres depends on the aggregation and phase separation of polyamines in aqueous solution

Long-chain polyamines extracted from the highly siliceous cell walls of diatoms are known to precipitate silica nanospheres from aqueous, silicic-acid containing solutions at near-neutral pH in vitro. The same is true for synthetic polyamines such as polyallylamine. In the present contribution we show that the microscopic phase separation of polyallylamine in aqueous solution is strictly correlated with the silica precipitation activity of polyallylamine/silicic acid solutions. Multivalent anions such as phosphate or sulfate efficiently induce this microscopic phase separation. At higher anion concentrations, macroscopic phase separation occurs. In contrast to the multivalent phosphate and sulfate ions, the monovalent chloride ions are much less efficient in polyallylamine aggregate formation.