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 325 records · Page 18Linked to original sources
PubMed2005

Microgel-based engineered nanostructures and their applicability with template-directed layer-by-layer polyelectrolyte assembly in protein encapsulation.

A novel strategy for the fabrication of microcapsules is elaborated by employing biomacromolecules and a dissolvable template. Calcium carbonate (CaCO(3)) microparticles were used as sacrificial templates for the two-step deposition of polyelectrolyte coatings by surface controlled precipitation (SCP) followed by the layer-by-layer (LbL) adsorption technique to form capsule shells. When sodium alginate was used for inner shell assembly, template decomposition with an acid resulted in simultaneous formation of microgel-like structures due to calcium ion-induced gelation. An extraction of the calcium after further LbL treatment resulted in microcapsules filled with the biopolymer. The hollow as well as the polymer-filled polyelectrolyte capsules were characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and scanning force microscopy (SFM). The results demonstrated multiple functionalities of the CaCO(3) core - as supporting template, porous core for increased polymer accommodation/immobilization, and as a source of shell-hardening material. The LbL treatment of the core-inner shell assembly resulted in further surface stabilization of the capsule wall and supplementation of a nanostructured diffusion barrier for encapsulated material. The polymer forming the inner shell governs the chemistry of the capsule interior and could be engineered to obtain a matrix for protein/drug encapsulation or immobilization. The outer shell could be used to precisely tune the properties of the capsule wall and exterior. [Diagram: see text] Confocal laser scanning microscopy (CLSM) image of microcapsules (insert is after treating with rhodamine 6G to stain the capsule wall).

Alginates↗
PubMed2006

Protein microarrays on hybrid polymeric thin films prepared by self-assembly of polyelectrolytes for multiple-protein immunoassays.

We report here the development and characterization of protein microarrays fabricated on nanoengineered 3-D polyelectrolyte thin films (PET) deposited on glass slide by consecutive adsorption of polyelectrolytes via self-assembly technique. Antibodies or antigens were immobilized in the PET-coated glass slides by electrostatic adsorption and entrapment of porous structure of the 3-D polymer film and thus establishing a platform for parallel analysis. Both antigen and antibody microarrays were fabricated on the PET-coated slides, and direct and indirect immunoassays on protein microarrays for multiple-analyte detection were demonstrated. Microarrays produced on these PET-coated slides have consistent spot morphology and provide performance features needed for proteomic analysis. The protein microarrays on the PET films provide LOD as low as 6 pg/mL and dynamic ranges up to three orders of magnitude, which are wider than the protein microarrays fabricated on aldehyde and poly-L-lysine functionalized slides. The PET films constructed by self-assembly technique in aqueous solution is green chemistry based, cost-effective method to generate 3-D thin film coatings on glass surface, and the coated slide is well suited for immobilizing many types of biological molecules so that a wide variety of microarray formats can be developed on this type of slide.

Adsorption↗
PubMed1995

Prediction of polyelectrolyte polypeptide structures using Monte Carlo conformational search methods with implicit solvation modeling.

Many interesting proteins possess defined sequence stretches containing negatively charged amino acids. At present, experimental methods (X-ray crystallography, NMR) have failed to provide structural data for many of these sequence domains. We have applied the dihedral probability grid-Monte Carlo (DPG-MC) conformational search algorithm to a series of N- and C-capped polyelectrolyte peptides, (Glu)20, (Asp)20, (PSer)20, and (PSer-Asp)10, that represent polyanionic regions in a number of important proteins, such as parathymosin, calsequestrin, the sodium channel protein, and the acidic biomineralization proteins. The atomic charges were estimated from charge equilibration and the valence and van der Waals parameters are from DREIDING. Solvation of the carboxylate and phosphate groups was treated using sodium counterions for each charged side chain (one Na+ for COO-; two Na for CO(PO3)-2) plus a distance-dependent (shielded) dielectric constant, epsilon = epsilon 0 R, to simulate solvent water. The structures of these polyelectrolyte polypeptides were obtained by the DPG-MC conformational search with epsilon 0 = 10, followed by calculation of solvation energies for the lowest energy conformers using the protein dipole-Langevin dipole method of Warshel. These calculations predict a correlation between amino acid sequence and global folded conformational minima: 1. Poly-L-Glu20, our structural benchmark, exhibited a preference for right-handed alpha-helix (47% helicity), which approximates experimental observations of 55-60% helicity in solution. 2. For Asp- and PSer-containing sequences, all conformers exhibited a low preference for right-handed alpha-helix formation (< or = 10%), but a significant percentage (approximately 20% or greater) of beta-strand and beta-turn dihedrals were found in all three sequence cases: (1) Aspn forms supercoil conformers, with a 2:1:1 ratio of beta-turn:beta-strand:alpha-helix dihedral angles; (2) PSer20 features a nearly 1:1 ratio of beta-turn:beta-sheet dihedral preferences, with very little preference for alpha-helical structure, and possesses short regions of strand and turn combinations that give rise to a collapsed bend or hairpin structure; (3) (PSer-Asp)10 features a 3:2:1 ratio of beta-sheet:beta-turn:alpha-helix and gives rise to a superturn or C-shaped structure.

Algorithms↗
PubMed1997

Frequency Behavior of the Electro-optical Effect from Colloid Particles in Polyelectrolyte Solutions with Counterion Mixtures

The electric light scattering method was used to investigate the frequency behavior of ferric oxide particles in carboxymethylcellulose solutions containing mono- and divalent counterion mixtures. The dispersion curves of suspensions, stabilized by polyelectrolyte adsorption, were analyzed in terms of three relaxations: rotational relaxation of the polymer-coated particles (at frequencies below 1 kHz), low-frequency relaxation of the bound counterions polarization (at frequencies from 1 kHz to 10 kHz) and high-frequency relaxation of the free counterions polarization (at frequencies above 60 kHz) along the particle axis. The frequency behavior of the electro-optical effect from suspensions containing polyelectrolyte with counterions mixtures was explained in accordance with the theory that the fraction of free (mono- and divalent) counterions increases with increasing the equivalent fraction of divalent ions in the mixture. Immobility of the strongly bound divalent counterions at low field strengths is supposed to reduce their contribution in the low-frequency effect in comparison to the effect from the less bound monovalent counterions.

Journal Article↗
PubMed1997

Polyelectrolyte Complex Formation in Lamellar Liquid Crystalline Systems

The influence of polyelectrolytes on structure formation in liquid crystalline Na-dodecylsulfate/decanol/water systems was investigated by means of small angle X-ray diffraction, rheology, NMR spectroscopy, and microscopy. By adding Na-polyacrylate (PAA) into the mesophase, the one-phase region is left and phenomena of phase separation into a solvent-rich and a polymer/surfactant-rich phase occurs. By incorporating an anionic and cationic polyelectrolyte step by step the tendency of phase separation is increased drastically. The self-organization process can be regulated directly by varying the water content of the system. However, at a water content of 30% the properties of the resulting liquid crystal were changed drastically. X-ray diffraction shows a multitude of Bragg peaks, NMR shows a peak-splitting, and rheology shows a change from non-Newtonian to Newtonian-flow behavior. On the basis of the experimental results an ordered multilayer associate structure can be assumed.

Journal Article↗
PubMed1997

Measurement of Colloidal Stability in Solutions of Simple, Nonadsorbing Polyelectrolytes

The stability of a solution of charged polystyrene particles in the presence of nonadsorbing polyelectrolyte macromolecules is measured using optical light scattering. The particles were negatively charged polystyrene latex spheres (0.5-1 &mgr;m diameter) while the macromolecules were simulated using negatively charged colloidal silica spheres (5-7 nm diameter). Because of the electrostatic repulsion between the particles, the solution is found to be stable against primary flocculation (irreversible flocculation into a primary energy minima). However, because of long-range attractive depletion forces, reversible secondary flocculation of the particles occurs into a local potential energy minimum. As observed with uncharged macromolecules, the polyelectrolyte first induces flocculation at a critical flocculation concentration (v *), but later restabilizes the system at a critical restabilization concentration (v **). These critical concentrations are found to decrease with decreasing macromolecule size and increasing particle size. The restabilized solutions are found to remain suspended for periods greater than 20 days. Comparison of the measured flocculation and restabilization results to predictions made using a recently developed force-balance model show qualitative agreement.

Journal Article↗
PubMed1997

Suspension Flocculation by Polyelectrolytes: Experimental Verification of a Developed Mathematical Model

Using experimental data of AgI sol and poly(2-methyl-5-vinylpyridine) chloride, we show that there is good agreement between the developed mathematical model of suspension flocculation by polyelectrolytes and the experimental data. The rate constants of bridging and nonbridging aggregation of particles and of floc breakup, as well as their ratios, have been determined. It has been shown that the role of the nonbridging mechanism, as compared with that of the bridging one, diminishes when molecular mass of polyelectrolyte increases from 1.4 x 10(5) to 9.3 x 10(5).

Journal Article↗
PubMed1997

Interfacial State Change of Cellulose Triacetate Membrane by Adsorption of Polyelectrolyte

Lysozyme, albumin, and PAS-H (poly diallyl dimethyl ammonium chloride), which are positively and negatively charged proteins, and cationic polysulfones, respectively, were adsorbed by a cellulose triacetate (CTA) membrane to investigate their effects on ionic transport through the membrane. The interface states between the membrane and the adsorption layer are discussed based on the measurements of contact angle and membrane potential and atomic force microscopy (AFM). The contact angle shows that the membrane changed from hydrophobic to hydrophilic due to adsorption of the above substances. AFM imaged the aggregates on the surface and showed that lysozyme, in particular, penetrates the membrane pores, making them shallower and decreasing their porosity. The results of membrane potential measurements showed that lysozyme and albumin did not change the membrane charge state, but PAS-H changed it from negative to positive. The permeability coefficients of KCl and K2HPO4 varied significantly with the adsorption of each polyelectrolyte. In particular, the permeability coefficient of phosphate through the lysozyme-adsorbed membrane increased to twice that of the nonadsorbed membrane. Such polyelectrolyte adsorption on the membrane surface can be used for the modification of commercial artificial kidney phosphate extraction.

Journal Article↗
PubMed1998

Surface Tension of Biological Polyelectrolyte Solutions.

Surface tensions, gamma, of biological polyelectrolytes in aqueous solutions are studied systematically as possible at the air-water interface by the Wilhelmy method. The polyelectrolytes measured are sodium chondroitin sulfates A (NaCRA) and C (NaCRC), sodium poly-alpha,l-glutamate (NaPGA), poly-l-lysine hydrobromide (PLL . HBr), deoxyribonucleic acid (DNA), lysozyme (LZ), and bovine serum albumin (BSA). Linear-type macroions such as NaCR, NaPGA, PLL . HBr, and DNA have no surface activity in a wide range of polymer concentrations below the critical polymer concentration, m*, and increases as the concentration increases above m*. Surface activity of the undissociated state of macroions is rather high in general. Globule-like macroions such as LZ and BSA show high surface activity at isoelectric point above m* accompanied with orientation of the molecules along the air-water interface. Separation into the hydrophobic and hydrophilic parts at the interface and balancing in their strength are important for appearance of surface activity. Copyright 1998 Academic Press.

Journal Article↗
PubMed2000

Investigation of Structure and Growth of Self-Assembled Polyelectrolyte Layers by X-ray and Neutron Scattering under Grazing Angles.

The structure of self-assembled polyelectrolyte thin films on float glass has been investigated by interface sensitive X-ray and neutron scattering methods. Special emphazis was given to the adsorption process of poly (ethylene imine) and polystyrole sulfonate as an important model system which is often used as a basis for subsequent multilayer buildup. From complementary X-ray and neutron reflectivity data, the vertical film density profile was derived for various growth parameters, including kinetic effects of different adsorption times. In addition to specular reflectivity, we have for the first time employed nonspecular X-ray scattering to study lateral structure parameters in self-assembled polyelectrolyte films. Furthermore, the technique of time-resolved in situ X-ray reflectivity during film growth has been demonstrated and is discussed in view of its future potential. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Assembly of Alternated Multivalent Ion/Polyelectrolyte Layers on Colloidal Particles. Stability of the Multilayers and Encapsulation of Macromolecules into Polyelectrolyte Capsules.

Alternating adsorption of multivalent ions and oppositely charged polyelectrolytes on colloid particles has been investigated. Multilayer films composed of Tb(3+)/polysterene sulfonate (PSS) and 4-pyrene sulfate/polyallylamine (PAH) were successfully assembled on polysterene sulfonate (PS) and melamine formaldehyde (MF) latex particles. The amount of assembled material was estimated by fluorescence and the linear growth of the film versus the number of layers was demonstrated. These multilayers are not stable and can be decomposed by salt and temperature. Dissolution of MF particles leads to formation of hollow capsules consisting of multivalent ion/polyelectrolyte multilayers. Comparative analysis of the capsules was done by confocal and scanning force microscopy. Complex hollow spheres consisting of Tb(3+)/PSS or 4-PS/PAH as an inner shell and stable PSS/PAH as an outer shell were produced. Due to selective permeability of the outer shell after degradation of the inner shell the multivalent ions are released out of the capsule while the polyelectrolytes fill the capsule interior. This is indicative of swelling of the capsule by osmotic pressure. The filled capsules were studied by confocal and scanning electron microscopy. Possibilities of encapsulating macromolecules in defined amounts per capsule are discussed. Copyright 2000 Academic Press.

Journal Article↗
PubMed2001

Adsorption of Polyelectrolyte and Nanoparticles at the Silica-Aqueous Solution Interface: Influence of the History of Additions of the Two Components.

The interfacial properties of a mixed system of low-charged cationic polyelectrolyte and silica nanoparticles has been studied by means of ellipsometry. Special attention was devoted to the effect that the order of addition of the two components has on the adsorption behavior of the mixed system. Adsorption on silica was in one case studied after simultaneous addition of the components to the aqueous solution. The measured adsorption rates were then much slower than expected for a mass-transfer limited process. This behavior signifies the presence of an electrosteric barrier arising due to preadsorbed polymer-particle complexes. Interfacial layers containing particles were at plateau conditions shown to be highly swollen, whereas the cationic polymer in the particle-free systems adopted a more flat surface conformation. The layer thickness was observed to monotonously increase with an increasing presence of nanoparticles in solution, while the surface excess showed a maximum at intermediate values. The finding was rationalized by the competition between particles and the surface for polymer charges leading to swelling and a decreased effective interaction between polymer and surface. In the other case studied, when polyelectrolyte and nanoparticles were added sequentially, a much more rapid concentration-dependent adsorption was observed. The kinetic adsorption barrier for nonassociated particles was clearly negligible compared with that for the polymer-particle complex. The surface excess did not exhibit an adsorption maximum as a function of added nanoparticles in this situation, indicating that the polymer layer to some degree is irreversibly anchored at the silica surface. Some implications of the above findings for practical papermaking using multicomponent retention systems are put forward. Copyright 2001 Academic Press.

Journal Article↗
PubMed1977

Dynamic properties of polyelectrolyte calcium membranes.

Shashoua observed spontaneous oscillations in a polyelectrolyte membrane formed by interfacial precipitates of polyacid and polybase. We have here undertaken experimental and theoretical studies of polyglutamic acid-Ca++ membrane in order to clarify the processes involved in this dynamic behavior. We find a region of distinct hysteresis in the voltage current curve for this system. A sharp transition from a state of low membrane resistance to one of high resistance occurs at a current density different from that of inverse transition. This membrane system is modeled as a two layer structure: a negatively charged layer alpha made of ionized polyelectrolyte in series with a neutral region beta in which the polymeric ionic sites are masked by calcium ion. This structure results in a difference in the transference number for the mobile ions, causing salt accumulation at the interfacial region during a current flow in the alpha to beta direction. This altered salt concentration induces a change of polymeric conformation, which in turn affects the membrane permeability and the rate of accumulation. Based upon nonequilibrium thermodynamic flow equations, and a two-state representation of membrane macromolecular conformation, this model displays a region of hysteresis in the current range of experimental observations.

Calcium↗
PubMed2003

Composite lipid polyelectrolyte capsules templated on red blood cells: fabrication and structural characterisation.

Charged phospholipids and mixtures of charged phospholipids with zwitterionic lipids were adsorbed onto polyelectrolyte capsules templated on erythrocytes. The assembly was proved by means of electrophoretic mobility measurements, confocal laser scanning microscopy and flow cytometry. Freeze-fracture electron microscopy proved that the phospholipids assemble as bilayers or multilayers. Single particle light scattering showed that bilayers composed of anionic lipids can be intercalated between subsequent polyelectrolyte inter-layers in a regular manner. Neutral lipids can form multilayers. A pronounced decrease in capsule permeability for small polar dyes upon lipid adsorption was followed by confocal laser scanning microscopy.

Adsorption↗
PubMed2002

Artificial cell based on lipid hollow polyelectrolyte microcapsules: channel reconstruction and membrane potential measurement.

A new model system as an artificial cell based on hollow polyelectrolyte microcapsules (HPM), fabricated by step-wise adsorption of polyelectrolytes and phospholipids, was proposed. To demonstrate the feasibility of the functioning of HPM coated with lipid layers as a model biosystem, the membrane permeability for ions and the channel reconstruction were examined by measuring the membrane potential as one of the most important cell parameters. The membrane potential was measured by confocal microscopy using the potentiometric fluorescent dye tetramethylrhodamine ethyl ester perchlorate (TMRE). The influence of the lipid composition (phosphatidylcholine--DPPC-HPM, phosphatidylcholine/phosphatidic acid 9/1-(DPPC/DPPA)-HPM) and metal cations (Na+, K+, Ca2+) on the membrane potential was shown. Addition of DPPA was found to lead to an increase of the negative membrane potential value. To investigate the ion-transport activity of the lipid-HPM, the ion channel-forming peptides valinomycin and gramicidin were used. The selectivity of the valinomycin and gramicidin channels for K+ and for K+, and Na+ ions, respectively, and the tolerance for Ca2+ ions is evidence that lipid-HPM functions as an artificial cell.

Biomimetic Materials↗
PubMed2003

The hydration dynamics of polyelectrolyte gels with applications to cell motility and drug delivery.

We combine the physics of gels with the hydrodynamics of two-phase fluids to construct a set of equations that describe the hydration dynamics of polyelectrolyte gels. We use the model to address three problems. First, we express the effective diffusion constants for neutral and charged spherically distributed gels in terms of microscopic parameters. Second, we use the model to describe the locomotion of nematode sperm cells. Finally, we describe the swelling dynamics of polyelectrolyte gels used for drug release.

Animals↗
PubMed2005

Mesoscopic simulation study on a weakly charged block polyelectrolyte in aqueous solution.

In this paper, we use density functional theory to study the effect of the charge of solvophilic beads and concentration on the mesoscale structures of polyelectrolyte solution. The polyelectrolyte A6B12A6 was selected as the triblock polymer, and the solvophobic B blocks have no charges, while the solvophilic A blocks are charged. The simulation results showed: at higher concentration (above 50% systems), relatively small charges on the solvophilic block do not alter the bicontinuous phase inherent to uncharged solution, but at moderate concentrations (50% system), even though the charge per solvophilic bead is very small, the order lamellar structures become disturbed. [Figure: see text].

Computer Simulation↗
PubMed2005

Macroporous hydrogels based on 2-hydroxyethyl methacrylate. Part II. Copolymers with positive and negative charges, polyelectrolyte complexes.

Crosslinked macroporous hydrogels based on 2-hydroxyethyl methacrylate (HEMA)-[2-(methacryloyloxy)ethyl]trimethylammonium chloride (MOETACl) copolymer, HEMA-MOETACl-methacrylic acid (MA) terpolymer, and on a polyelectrolyte complex of HEMA-MA copolymer with poly(MOETACl) were prepared. All the hydrogels were prepared in the presence of fractionated sodium chloride particles. The hydrogels were characterized by the number of pores and the total volume of all pores in unit volume, the average volume and the average diameter of single pore. Morphology of the hydrogels was investigated by confocal and scanning electron microscopy. The hydrogels based on polyelectrolyte complexes were also characterized by chemical composition. Homogeneous (non-porous) hydrogels with the same composition as macroporous hydrogels were prepared and characterized by their biocompatibility.

Animals↗