Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polyelectrolytes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed2003

Flocculation in mixtures of cationic polyelectrolytes and anionic surfactants.

The phase behavior of mixtures of a cationic polyelectrolyte ('Jaguar') and an anionic surfactant (either sodium dodecyl sulfate or sodium lauryl ether sulfate) has been studied. For a given polyelectrolyte (and added NaCl) concentration, with increasing surfactant concentration, three phase regions were identified. The first region is a single homogeneous phase. Within this region, at some surfactant concentration, above the critical aggregation concentration, stable open-network 'particles' form, typically approximately 100 nm in size, which are net positively charged. However, as the surfactant concentration is increased further, these particles aggregate and form a two-phase system, i.e. a separated gel phase, containing a high percentage of water, co-existing with an aqueous surfactant phase. At some higher surfactant concentration still, the particles become sufficiently negatively charged that they re-stabilize. Beyond this surfactant concentration, therefore, the system reverts to being a single, homogeneous phase. Within the two-phase (aggregated particle) region an iso-electric point for the particles has been observed at a certain surfactant concentration, by electrophoresis. Furthermore, in this aggregated, gel-phase region, there appear to be typically approximately 2-4 surfactant molecules associated with each cationic site of the polymer chains. It is postulated that association of the anionic surfactant molecules occurs within the polyelectrolyte chains, binding them together, to form the particles referred to. These associated surfactant structures have been referred to here as 'internal' micelles. A crude estimate has been made, based on turbidity/time measurements, that there may be up to approximately 1000 polymer chains in each primary particle, bound together by the internal surfactant micelles. Small-angle light scattering studies of the aggregating particles indicate a fractal dimension for the aggregates, which would correspond to a diffusion-limited aggregation process.

Anions↗
PubMed2003

Polymer-stabilized phospholipid vesicles formed on polyelectrolyte multilayer capsules.

Phospholipid vesicles on polyelectrolyte multilayer shells can be stabilized against ethanol by coating a single cationic polyelectrolyte. Confocal laser scanning microscopy (CLSM) proved that the lipids were stabilized by cationic polyelectrolytes and the permeability to small hydrophilic dyes was decreased. Measurements of fluorescence recovery after photo-bleaching (FRAP) with individual capsules enable quantification of release profiles.

Biopolymers↗
PubMed2003

Enhancing phosphate removal from wastewater by using polyelectrolytes and clay injection.

Aluminum sulfate, alum, is a common chemical coagulant used for coagulation. Recently, polymers have been utilized in coagulation/flocculation processes for water purification. In this study, the ability of two organic polymers, tannin (natural polyelectrolyte) and AN913 (synthetic anionic polyelectrolyte), and clay to act as coagulant aids was tested, in the removal of phosphate from synthetic wastewater. Contaminants in synthetic waters were coagulated using alum, alum+clay, alum+tannin, alum+AN913, alum+tannin+clay and alum+AN913+clay. Alum together with polymers as coagulant aids yielded a significant improvement in phosphate removal compared with alum alone, for initial phosphate concentrations of 5-15 mg/l PO(4)(3-). The use of clay and polyelectrolytes improved the efficiency of phosphate removal and lowered the required alum dose. Fourier transform infrared (FTIR) spectroscopy was used for the identification and characterization of the aluminum species formed during dephosphorization of the synthetic wastewater with and without tannin, AN913 and clay. Evidence from FTIR spectroscopy showed the formation of aluminum hydroxyphosphate, hydroxy-Al-tannate and aluminum complexes containing phosphorus, tannin and AN913.

Alum Compounds↗
PubMed2002

A novel method for encapsulation of poorly water-soluble drugs: precipitation in polyelectrolyte multilayer shells.

A novel method to include poorly water-soluble substances into the polyelectrolyte capsules of defined size, stability, composition and affinity properties is proposed. Encapsulation explores the polarity gradient across the capsule wall. Capsules creation makes use of electrostatic interaction and can involve many substances as layer constituents, such as synthetic polyelectrolytes, proteins, nucleic acids, lipids and multivalent dyes. Using capsules made of synthetic polyelectrolytes as a model system was demonstrated how to prepare, to measure and to use this gradient for low molecular weigh materials encapsulation.

Capsules↗
PubMed2002

Protein adsorption onto auto-assembled polyelectrolyte films.

Surface modification by deposition of ordered protein systems constitutes one of the major objectives of bio-related chemistry and biotechnology. In this respect a concept has recently been reported aimed at fabricating multilayers by the consecutive adsorption of positively and negatively charged polyelectrolytes. We investigate the adsorption processes between polyelectrolyte multilayers and a series of positively and negatively charged proteins. The film buildup and adsorption experiments were followed by Scanning Angle Reflectometry (SAR). We find that proteins strongly interact with the polyelectrolyte film whatever the sign of the charge of both the multilayer and the protein. When charges of the multilayer and the protein are similar, one usually observes the formation of protein monolayers, which can become dense. We also show that when the protein and the multilayer become oppositely charged, the adsorbed amounts are usually larger and the formation of thick protein layers extending up to several times the largest dimension of the protein can be observed. Our results confirm that electrostatic interactions dominate protein/polyelectrolyte multilayer interactions.

Adsorption↗
PubMed2003

Time evolution of the formation of different size cationic liposome-polyelectrolyte complexes.

We report on the time evolution of the aggregation behaviour of cationic liposome-polyelectrolyte complexes studied by means of dynamic light scattering technique. Pure dioleoyltrimethilammoniumpropane (DOTAP) and mixed DOTAP-dipalmitoylphosphatidylcholine (DPPC) liposomes in polyacrylate sodium salt aqueous solutions in a wide concentration range have been investigated and the size and size distributions of the resulting aggregates evaluated from the intensity autocorrelation function of the scattered light. Under appropriate conditions, we found two discrete aggregation regimes, resulting in two different structural arrangements, whose time evolution depends on the charge ratio and the polyelectrolyte molecular weight. A first small component of average size in the 100-500 range nm coexists with a larger component, whose typical size increases with time, up to some micrometers. The cluster growth from a single liposome, 70 nm in diameter, to the formation of polymer-coated liposome aggregates has been briefly discussed in the light of steric stabilization of colloids. Moreover, it has been found that the kinetics of aggregation of the larger, time-dependent, component follows a dynamical scaling within the diffusion-limited cluster aggregation (DLCA) regime. The understanding of structures resulting from interactions between polyelectrolytes with oppositely charged liposomes may help towards formulation of "lipoplexes" (cationic lipid-DNA complexes) to use as non-viral gene carriers.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Control of flow direction in microfluidic devices with polyelectrolyte multilayers.

Electroosmotic flow (EOF) is commonly utilized in microfluidics. Because the direction of the EOF can be determined by the substrate surface charge, control of the surface chemical state offers the potential, in addition to voltage control, to direct the flow in microfluidic devices. We report the use of polyelectrolyte multilayers (PEMs) to alter the surface charge and control the direction of flow in polystyrene and acrylic microfluidic devices. Relatively complex flow patterns with simple arrangements of applied voltages are realized by derivatization of different arms of a single device with oppositely charged polyelectrolytes. In addition, flow in opposite directions in the same channel is possible. A positively derivatized plastic substrate with a negatively charged lid was used to achieve top-bottom opposite flows. Derivatization of the two sides of a plastic microchannel with oppositely charged polyelectrolytes was used to achieve side-by-side opposite flows. The flow is characterized using fluorescence imaging and particle velocimetry.

Journal Article↗
PubMed2004

Chiral separations using a polypeptide and polymeric dipeptide surfactant polyelectrolyte multilayer coating in open-tubular capillary electrochromatography.

A polyelectrolyte multilayer (PEM) coating consisting of the polypeptide, poly(l-lysine) hydrobromide, poly(l-lysine) and the polymeric dipeptide surfactant, poly(sodium undecanoyl-l-leucyl-alaninate), poly(l-SULA), is investigated as a new medium for the separation of chiral analytes in open-tubular capillary electrochromatography (OT-CEC). In this approach, a stable PEM is constructed in situ by alternative rinses of the cationic polymer poly(l-lysine) and the anionic polymer poly(l-SULA). In previous studies, the PEM coating has been constructed by use of the cationic polyelectrolyte poly (diallydimethylammonium chloride), PDADMAC. In this study, we investigate the use of a biopolymer as the cationic polyelectrolyte. The results reported here indicate an increase in selectivity and resolution when poly(l-lysine) is used as the cationic polymer in place of PDADMAC. To evaluate the chromatographic performance of the PEM coating as a chiral stationary phase, the separation of the beta-blockers, labetalol and sotalol, and the binaphthyl derivatives, 1,1'-bi-2-naphthyl-2,2'-dihydrogen phosphate, 1,1'-bi-2-naphthol, and 1,1-binaphthyl-2,2'-diamine, are investigated. In addition, the effect of varying the amino acid order of the polymeric dipeptide surfactant on resolution is investigated. The number of bilayers also significantly influences the separation efficiency and resolution of enantiomers. The run-to-run and capillary-to-capillary reproducibilities are evaluated by calculating the relative standard deviations (RSDs) of the electroosmotic flow. These RSD values were found to be less than 1%. The coating is also stable and allows more than 290 runs to be performed in the same capillary. In addition, coupling of this chiral OT-CEC column with mass spectrometry is investigated.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2001

Peptide hormone covalently bound to polyelectrolytes and embedded into multilayer architectures conserving full biological activity.

We report the development of new bioactive coatings of biomaterials based on the alternate deposition of oppositely charged polyelectrolytes. We selected polylysine (PLL) and poly(glutamic acid) (PGA) for the polyelectrolytes and murine melanoma cells as a biological test model system. These cells respond specifically to a small peptide hormone, alpha-melanocortin, which is a potent stimulator of melanogenesis. We show that a synthetic alpha-melanocortin derivative, covalently coupled to PLL forming the outer layer of a multilayer film remains as biologically active as the free hormone. Furthermore, the long time activity of the hormone is maintained when embedded in multilayer architectures whereas its short time activity depends on integration depth. The embedding of bioactive molecules not only anchors them irreversibly on the biomaterial, but opens also the possibility to control their activity. In comparison to conventional coating methods, polyelectrolyte multilayers are easy to prepare and retain their biological activity after storage as dry material. These very flexible systems allow broad medical applications for implant and tissue engineering.

Animals↗
PubMedDate not supplied

Ionic strength dependence of protein-polyelectrolyte interactions.

The effect of univalent electrolyte concentration on protein-polyelectrolyte complex formation has been measured by frontal analysis continuous capillary electrophoresis (FACCE) and turbidimetry for the interaction of bovine serum albumin (BSA) with a synthetic hydrophobically modified polyacid, for BSA with (porcine mucosal) heparin (Hp), a highly charged polyanion, and for Hp and insulin. All three highly diverse systems display maxima or plateaus in complex formation in the range of ionic strength 5 < I < 30 mM, confirmed in the case of BSA-Hp by multiple techniques. Similar maxima are reported in the literature, but with little discussion, for BSA-poly(dimethyldiallylammonium chloride), lysozyme-hyaluronic acid, and lysozyme-chondroitin sulfate, always in the I range 5-30 mM. While inversion of salt effect has been discussed specifically for the interaction of gelatin and sodium polystyrenesulfonate with gelatin(28) and with beta-lactoglobulin,(10) the general nature of this phenomenon, regardless of polyelectrolyte origin, molecular weight, and charge sign has not been recognized. The position of the maxima and their occurrence when protein and polyelectrolyte have the same net charge imply that they arise when Debye lengths extend, at low I, beyond half the protein diameter so that addition of salt screens repulsions, as well as attractions. This appears to be a general effect caused by electrostatic repulsions that can coexist simultaneously with hydrophobic interactions. Modeling of protein electrostatics via Delphi is used to visualize this effect for BSA, lysozyme, insulin, and beta-lactoglobulin.

Electrolytes↗
PubMedDate not supplied

Freeze-fracture electron microscopy of lipid membranes on colloidal polyelectrolyte multilayer coated supports.

Lipid membranes were assembled on polyelectrolyte (PE)-coated colloidal particles. The assembly was studied by means of confocal microscopy, flow cytometry, scanning force microscopy, and freeze-fracture electron microscopy. A homogeneous lipid coverage was established within the limits of optical resolution. Flow cytometry showed that the lipid coverage was uniform. Freeze-fracture electron microscopy revealed that the lipid was adsorbed as a bilayer, which closely followed the surface profile of the polyelectrolyte support. Additional adsorption of polyelectrolyte layers on top of the lipid bilayer introduced inhomogeneities as evident from jumps in the fracture plane. Characteristic lipid multilayers have not been seen with freeze-fracture electron microscopy.

Colloids↗
PubMed2006

Real-time assessment of spatial and temporal coupled catalysis within polyelectrolyte microcapsules containing coimmobilized glucose oxidase and peroxidase.

The encapsulation of biological enzymes within polyelectrolyte microcapsules is an important step toward microscale devices for processing and analytical applications, one which could be applied to the realization of minimally invasive sensing technology. In this work, the encapsulation and functional characterization of a bienzymatic coupled catalytic system within polyelectrolyte microcapsules is described. The two components, glucose oxidase (GOx) and horseradish peroxidase (HRP), were coprecipitated with calcium carbonate microspheres, followed by layer-by-layer assembly to form ultrathin polymer film coatings that act as capsule walls after removal of the sacrificial carbonate cores. Encapsulated concentrations of GOx and HRP were determined to be 19.7 +/- 1.0 and 29.4 +/- 3.6 mg/mL, respectively. An 85% decrease in the rate of glucose consumption relative to GOx and HRP in free solution was observed, which is attributed to substrate diffusion limitations. To further understand the temporal and spatial dynamics of the two-step reaction, a technique for monitoring microscale glucose consumption was developed using confocal imaging techniques. Time-based acquisition of capsule/Amplex Red suspensions was performed, from which it was observed that the high concentration of enzyme immobilized within the capsule walls resulted in a greater rate and quantity of glucose consumption at the capsule periphery when compared to glucose consumption within the capsule interior. These findings demonstrate the function of a bienzymatic catalytic system within the controlled environment of polyelectrolyte microspheres and a novel approach to analysis of the internal reactions using confocal imaging that will allow direct comparison with reaction-diffusion modeling and further explorations to optimize the distribution and activity of the encapsulated species.

Aspergillus niger↗
PubMed2006

Biorecognition through layer-by-layer polyelectrolyte assembly: in-situ hybridization on living cells.

Encapsulated cells were formed from the assembly of cationic and anionic alternating layers using a number of polyelectrolyte-based systems. Chitosan, alginate, hyaluronic acid, and oligonucleotides were used as polyelectrolytes to encapsulate individual E. coli cells, which were used as a model. Zeta potential measurements taken for both chitosan/alginate and chitosan/hyaluronic acid systems indicate successful layer-by-layer (LbL) deposition and gave full reversal of the surface change eight times. Layer adsorption was further observed by fluorescence microscopy, and, through a newly developed protocol for sample preparation, transmission electron microscopy micrographs clearly showed the presence of LbL assembly on the outer layer of the cell membrane, in the nanometer range. A second generation of E. coli cells could be grown from encapsulated first generation cells, demonstrating that the cellular activity was not affected by the presence of polyelectrolyte multilayers. Hybridization between attached oligonucleotide sequences and the complementary sequence was demonstrated by both fluorescence spectroscopy and microscopy. Fluorescence energy transfer data recorded after hybrid formation showed that at a molar ratio of 10:20 (donor:acceptor), Q and I were 92.3% and 52.5%, respectively, which suggests that fluorescein fluorescence was quenched by 92.3% and that the fluorescence of rhodamine was enhanced by 52.5%. Oligonucleotide incorporation was stabilized by deposition of four alternating layers, hence offering not only the potential use of the encapsulated cell as a bio-recognition system but also its application in a number of fields such as oligonucleotide delivery, gene therapy, and the use of DNA as an immunocompatible coating.

Biocompatible Materials↗
PubMed2003

Highly flexible polyelectrolyte nanotubes.

A pressure-filter-template approach was employed to prepare polyelectrolyte nanotubes through layer-by-layer deposition in the alumina template. With the thicker wall, the ordered polymer nanotubes possess a high flexibility. The results demonstrate that the electrostatic interactions of polyelectrolytes play a key role in fabricating water-soluble charged polymer nanotubes. The structure of the polyelectrolyte nanotube was confirmed by SEM, TEM, and UV, respectively.

Journal Article↗
PubMed2004

Selective hydrogenation by Pd nanoparticles embedded in polyelectrolyte multilayers.

Alternating adsorption of poly(acrylic acid) and a polyethylenimine-Pd(II) complex on alumina and subsequent reduction of Pd(II) by NaBH4 yield catalytic Pd nanoparticles embedded in multilayer polyelectrolyte films. The polyelectrolytes limit aggregation of the particles and impart catalytic selectivity in the hydrogenation of alpha-substituted unsaturated alcohols by restricting access to catalytic sites. Hydrogenation of allyl alcohol by encapsulated Pd(0) nanoparticles can occur as much as 24-fold faster than hydrogenation of 3-methyl-1-penten-3-ol. Additionally, the nanoparticle/polyelectrolyte system suppresses unwanted substrate isomerization, when compared to a commercial palladium catalyst. Selective diffusion through poly(acrylic acid)/polyethlyenimine membranes suggests that hydrogenation selectivities are due to different rates of diffusion to nanoparticle catalysts. First-order kinetics are also consistent with a diffusion-limited mechanism. Further exploitation of the versatility of polyelectrolyte films should increase selectivity in hydrogenation as well as other reactions.

Journal Article↗
PubMed2005

Adsorption of atomic hydrogen at a nanostructured electrode of polyacrylate-capped Pt nanoparticles in polyelectrolyte.

Atomic hydrogen electrosorption is reported at crystallite sites of polyacrylate-capped Pt nanoparticles (d = 2.5 +/- 0.6 nm), by assembling nanostructured electrodes of polyacrylate-Pt nanocrystallites layer-by-layer in a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). Cyclic voltammetry in 1 M H2SO4 revealed a strongly adsorbed hydrogen state and a weakly adsorbed hydrogen state assigned to adsorption at (100) and (110) sites of the modified nanocrystallites, respectively. Resolving hydrogen adsorption states signifies that surface capping by the carboxylate groups is not irreversibly blocking hydrogen adsorption sites at the modified Pt nanoparticle surface. Adsorption peak currents increased with increasing the number of layers up to 16 bilayers, indicating the feasibility of nanoparticle charging via interparticle charge hopping and the accessibility of adsorption states within the thickness of the nanoparticle/polyelectrolyte multilayers. Despite similarity in hydrogen adsorption in the cyclic voltammorgrams in 1 M H2SO4, negative shifts in adsorption potentials were measured at the nanocrystallite Pt-polyelectrolyte multilayers relative to a polycrystalline bulk Pt surface. This potential shift is attributed to a kinetic limitation in the reductive hydrogen adsorption as a result of the Pt nanoparticle surface modification and the polyelectrolyte environment.

Absorption↗
PubMed2005

Thermal behavior of polyelectrolyte multilayer microcapsules. 1. The effect of odd and even layer number.

The temperature-dependent behavior of hollow polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) with a different number of layers was investigated in aqueous media using confocal laser scanning microscopy, scanning and transmission electron microscopy, atomic force microscopy, and elemental analysis. Capsules with an even number of layers exhibited a pronounced shrinking at elevated temperature resulting in a transition to a dense sphere, whereas capsules with an odd number of layers swelled during heating to 5-fold of their initial size followed by their rupture. This effect increases for odd layer numbers and decreases for even layer numbers with increasing layer number. According to elemental analysis, an excess of PDADMAC monomers exists within the multilayers of capsules with an odd number of layers leading to a repulsion between the positive charges, whereas shells with an even number of layers have a balanced ratio between the oppositely charged polyions, so that the temperature-dependent behavior is controlled by the different interactions between polyelectrolytes and the bulk water. At a certain temperature, the polyelectrolyte material softens thus facilitating any rearrangement. Besides incubation temperature, the duration of heating has an influence on the restructuring of the multilayers.

Electrolytes↗
PubMed2005

Effective charges of polyelectrolytes in a salt-free solution based on counterion chemical potential.

The phenomenon of counterion condensation around a flexible polyelectrolyte chain with N monomers is investigated by Monte Carlo simulations in terms of the degree of ionization alpha, which is proportional to the effective charge. It is operationally defined as the ratio of observed to intrinsic counterion concentration, alpha = co/ci. The observed counterion concentration in the dilute polyelectrolyte solution is equivalent to an electrolyte solution of concentration co with the same counterion chemical potential. It can be determined directly by thermodynamic experiments such as ion-selective electrode. With the polyelectrolyte fixed at the center of the spherical Wigner-Seitz cell, the polymer conformation, counterion distribution, and chemical potential can be obtained. Our simulation shows that the degree of ionization rises as the polymer concentration decreases. This behavior is opposite to that calculated from the infinitely long charged rod model, which is often used to study counterion condensation. Moreover, we find that, for a specified line charge density, alpha decreases with an increment in chain length and chain flexibility. In fact, the degree of ionization is found to decline with increasing polymer fractal dimension, which can be tuned by varying bending modulus and solvent quality. Those results can be qualitatively explained by a simple model of two-phase approximation.

Electrolytes↗