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 397 records · Page 22Linked to original sources
PubMed2002

Investigations of polyelectrolyte adsorption at the solid/liquid interface by sum frequency spectroscopy: evidence for long-range macromolecular alignment at highly charged quartz/water interfaces.

IR-visible sum frequency spectroscopy (SFS) was employed to investigate the molecular level details of the adsorption of the positively charged polyelectrolyte, polydiallyldimethylammonium chloride (PDDA), at the quartz/water interface. Below pH 9.0, signal from the interfacial water structure was visible, but none from the adsorbed polymer could be detected. This indicated that the PDDA was not well enough aligned at the interface under these conditions to elicit a sum frequency response. At more basic pH values (>or=9.6), however, adsorbed PDDA molecules became well-ordered as indicated by the presence of CH stretch peaks from methylene and methyl groups. The intensities of the CH stretch modes were independent of the adsorbed amount of PDDA at pH 12.3 but decreased as the pH of the bulk solution was lowered. The conditions for polymer alignment fell outside the parameters where layer-by-layer growth of oppositely charged polyelectrolytes was possible because the net charge on the surface under high pH conditions remained negative.

Journal Article↗
PubMed2002

Mineralization of single flexible polyelectrolyte molecules.

Conformation of a single flexible polyelectrolyte molecule with a hydrophobic backbone in aqueous solution is effected by the interplay of the short-range intramolecular attraction and the long-range Coulomb repulsion. The conformation can be frozen if the molecule is trapped by a solid substrate. With this approach, we prepared the range of single molecule templates from poly(2-vinylpyridine) (P2VP) deposited on the surface of Si-wafer or mica in different conformations from an elongated wormlike coil to compact globule. Pd(+2) was coordinated by P2VP via an ion exchange reaction exposing the samples to palladium acetate acidic aqueous solution. In the next step, Pd(+2) was reduced by dimethylamine borane. This route results in wire-shaped metallic nanoparticle assembles of about 2-5 nm in diameter and 50-700 nm in length. The conformation and size of the underlaying polyelectrolyte molecules determine the dimensions of nanoparticles.

Journal Article↗
PubMed2003

Spontaneous formation of nanoparticle vesicles from homopolymer polyelectrolytes.

Nanoparticle vesicles were spontaneously assembled from homopolymer polyamine polyelectrolytes and water-soluble, citrate-stabilized quantum dots. The further addition of silica nanoparticles to a solution of quantum dot vesicles generated stable micrometer-sized hollow spheres whose walls were formed of a thick, inner layer of close-packed quantum dots followed by an outer layer of silica. The method employed here to assemble both the nanoparticle vesicles and the hollow spheres is in direct contrast to previous syntheses that use either tailored block copolymers or oil-in-water emulsion templating. We propose that the formation of charge-stabilized hydrogen bonds between the positively charged amines of the homopolymer polyelectrolytes and the negatively charged citrate molecules stabilizing the quantum dots is responsible for the macroscopic phase separation in this completely aqueous system. The ease and processibility of the present approach gives promise for the production of a diverse array of materials ranging in applications from drug delivery to catalysis to micrometer-scale optical devices.

Journal Article↗
PubMed2003

Optically active polyelectrolyte multilayers as membranes for chiral separations.

Ultrathin films of chiral polyelectrolyte complex, prepared by the multilayering process, exhibit selectivity in the membrane separations of optically active compounds, such as l- and d-ascorbic acid. The flux through these polyelectrolyte multilayers, PEMUs, is exceptionally high and may be controlled by the concentration of salt present in the permeating solutions. Both in-situ ATR-FTIR and chiral capillary electrochromatography indicate that flux selectivity is mainly kinetically controlled, stemming from a difference in diffusion rates of various enantiomers through PEMUs, rather than a difference in partitioning.

Ascorbic Acid↗
PubMed2004

Photogenerated polyelectrolyte bilayers from an aqueous-processible photoresist for multicomponent protein patterning.

A novel photoresist (PR) that can be processed under mild aqueous conditions was synthesized and used to create photogenerated polyelectrolyte bilayers. Thin films of the PR cast on polycation-coated substrates were exposed to UV irradiation to generate carboxylate groups in the photoresist. The bulk of the UV-exposed PR film was dissolved by rinsing with pH 7.4 phosphate-buffered saline, but a polyelectrolyte bilayer formed in situ at the PR/polycation interface on exposure remained bound to the substrate. The UV-exposed photoresist also exhibited pH-dependent solubility; it was soluble in water above pH 6.6, but insoluble at lower pHs. Using these unique properties, two-component protein patterning was achieved using biotinylated PR films under conditions that avoid exposing the proteins to conditions outside the narrow range of physiological pH, ionic strength, and temperature where their stability is greatest.

Biotin↗
PubMed2005

Persistence length control of the polyelectrolyte layer-by-layer self-assembly on carbon nanotubes.

We have studied layer-by-layer polyelectrolyte self-assembly on pristine individual single-wall carbon nanotubes as a function of solution ionic strength. We report the existence of an ionic strength threshold for the deposition, below which the majority of nanotubes remain uncoated. Once the ionic strength reaches the threshold value, the majority of the individual nanotubes become coated with polyelectrolytes. Our results indicate that the self-assembly process likely involves wrapping of polymer chains around nanotubes and that the polymer chain's ability to bend in order to accommodate the nanotube curvature is one of the critical parameters controlling layer-by-layer electrostatic self-assembly on these one-dimensional templates.

Electrochemistry↗
PubMed2006

Mechanical properties of reversibly cross-linked ultrathin polyelectrolyte complexes.

Tensile properties of microcoupons of polyelectrolyte complex, formed by the multilayering method, were determined using a micromechanical analysis system. The degree of internal ion-pair ("electrostatic") cross-linking was reversibly controlled by exposure to salt solution of varying concentration, which "doped" counterions into the films, breaking polymer/polymer ion pairs in the process. Linear stress-strain behavior was observed for a poly(styrene sulfonate)/poly(diallyldimethylammonium) multilayer up to 2% deformation. The dependence of modulus on cross-link density could be rationalized well by classical theories of rubber elasticity, including some insight on the topology of polyelectrolyte complexes.

Journal Article↗
PubMed2006

Control of interchain contacts, solid-state fluorescence quantum yield, and charge transport of cationic conjugated polyelectrolytes by choice of anion.

Simple procedures are provided for exchanging charge-compensating ions in conjugated polyelectrolytes by progressive dilution of the original species and for determining the degree of ion exchange by using X-ray photoelectron spectroscopy. By using these methods, the bromide ions in poly[(9,9-bis(6'-N,N,N-trimethylammoniumbromide)hexyl)fluorene-co-alt-4,7-(2,1,3-benzothiadiazole)]were exchanged with BF4-, CF3SO3-, PF6-, BPh4-, and B(3,5-(CF3)2C6H3)4- (BArF4-). Absorption, photoluminescence (PL), and PL quantum yields (Phi) were measured in different solvents and in solid films cast from methanol. Examination of the resulting trends, together with the spectral bandshapes in different solvents, suggests that increasing the counteranion (CA) size decreases interchain contacts and aggregation and leads to a substantial increase of Phi in the bulk. Size analysis of polymers containing Br- and BArF4- in water by dynamic light scattering techniques indicates suppression of aggregation by BArF4-. Nanoscale current-voltage measurements of films using conducting atomic force microscopy show that hole mobilities and, more significantly, charge injection barriers are CA dependent. These results show that it is possible to significantly modify the optoelectronic properties of conjugated polyelectrolytes by choosing different counterions. A parent conjugated backbone can thus be fine-tuned for specific applications.

Anions↗
PubMed2006

Ideal mixing in polyelectrolyte complexes and multilayers: entropy driven assembly.

Calorimetry and variable temperature equilibrium doping methods independently show complexation of common polyelectrolytes to be essentially entropy-driven. The complimentary techniques provide enthalpy and free energies of formation or mixing. These findings highlight the importance of polyelectrolyte complexes as ideally mixed polymer blends.

Journal Article↗
PubMed2005

Water-soluble full-length single-wall carbon nanotube polyelectrolytes: preparation and characterization.

HiPco single-wall carbon nanotubes (SWNTs) have been noncovalently modified with ionic pyrene and naphthalene derivatives to prepare water-soluble SWNT polyelectrolytes (SWNT-PEs), which are analogous to polyanions and polycations. The modified nanotubes have been characterized with UV-vis-NIR, fluorescence, Raman and X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The nanotube-adsorbate interactions consist of pi-pi stacking interactions between the aromatic core of the adsorbate and the nanotube surface and specific contributions because of the substituents. The interaction between nanotubes and adsorbates also involves charge transfer from adsorbates to SWNTs, and with naphthalene sulfonates the role of a free amino group was important. The ionic surface charge density of the modified SWNTs is constant and probably controlled by electrostatic repulsion between like charges. The linear ionic charge density of the modified SWNTs is similar to that of common highly charged polyelectrolytes.

Journal Article↗
PubMed2005

Dynamics and lithium binding energies of polyelectrolytes based on functionalized poly(para-phenylene terephthalamide).

Polyelectrolyte materials are an interesting class of electrolytes for use in fuel cell and battery applications. Poly(para-phenylene terephthalamide) (PPTA, Kevlar) is a liquid crystalline polymer that, when sulfonated, is a polyelectrolyte that exhibits moderate ion conductivity at elevated temperatures. In this work, quasi-elastic neutron scattering (QENS) experiments were performed to gain insight into the effect of the presence of lithium counterions on the chain dynamics in the material. It was found that the addition of lithium ions decreases the dynamics of the chains. Additionally, the binding of lithium ions to the sulfonic acids groups was investigated by density functional theory (DFT) calculations. It was found that the local surroundings of the sulfonic acid group have very little effect on the lithium-ion binding energy. Binding energies for a variety of different systems were all calculated to be around 150 kcal/mol. The DFT calculations also show the existence of a structure in which a single lithium ion interacts with two sulfonic acid moieties on different chains. The formation of such "electrostatic cross-links" is believed to be the source of the increased tendency to aggregate and the reduced dynamics in the presence of lithium ions.

Journal Article↗
PubMed2005

A modified box model including charge regulation for protein adsorption in a spherical polyelectrolyte brush.

Recent experiments showed significant adsorption of bovine serum albumin (BSA) in spherical polyelectrolyte brushes (SPB) consisting of polyacrylic acid, even for pH values above the isoelectric point of the protein, when both protein and polyion are negatively charged. To describe these experimental findings theoretically, we have constructed a spherical box model for an annealed brush consisting of a weak polyelectrolyte that includes the adsorption of BSA. At equilibrium the chemical potential of BSA in solution equals that at each location in the brush, while the net force on the polyions (including osmotic, stretching, and excluded volume terms) is zero at each location. Protein adsorption is predicted above the isoelectric point and--in agreement with experimental data--is a strong function of ionic strength and pH. Adsorption of protein in the brush is possible because the pH in the brush is below the isoelectric point and protein reverses its charge from negative to positive when it adsorbs.

Adsorption↗
PubMed2005

Simple model for overcharging of a sphere by a wrapped oppositely charged asymmetrically neutralized polyelectrolyte: Possible effects of helical charge distribution.

We investigate the complexation of a polyelectrolyte bendable rod with an oppositely charged spherical macroion. We take into account electrostatic bending of the rod and its asymmetric charge neutralization by sphere charges. The spontaneous curvature of the rod toward the sphere results in a substantial overcharging of such polyelectrolyte complex with a possible phase transition. Assuming a discrete helical charge distribution on the rod surface, we calculate the electrostatic energy of the helix and the electrostatic contribution to its bending and twisting elasticity. We show that the latter may change sign when the helical pitch is changed. For a DNA-relevant case, these corrections appear to be small compared to the corresponding mechanical elastic moduli. We discuss possible applications of our results to the description of overcharging of the nucleosome core particles.

Biophysics↗
PubMed2005

Controlling ionic conductivity in lipid polyelectrolyte composite capsules by cholesterol.

The effect of cholesterol on the formation and properties of bilayer lipid membranes deposited on polyelectrolyte multilayered capsules was studied. The permeability of lipid/cholesterol coated capsules for NaCl was derived from osmotic response experiments and ranged from 1.45 x 10(-8) to 2.9 x 10(-8) m.s(-1), which corresponds to a lipid layer conductivity of (0.7-1.4) x 10(-8) S.m(-1). These conductivity values were in good agreement with the value of 0.8 x 10(-8) S.m(-1) obtained by electrorotation and were by 3 orders of magnitude lower than those found earlier for lipid layers on polyelectrolyte capsules in the absence of cholesterol.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2006

Similarity of salt influences on the pH of buffers, polyelectrolytes, and proteins.

Changes in pH induced by the addition of electrolytes to buffers, polyelectrolytes (a polycarboxy polymethylene and a polyethyleneimine), and proteins (casein, whey, and lysozyme) solutions are explored systematically. The two buffer systems are triethanolamine/triethanolammonium chloride and citric acid/sodium citrate. These are chosen because of the similarity of their acid-base equilibria with those of amino acids predominant in most proteins, that is, amino acids that include carboxylate or ammonium groups in their structures. The pH of triethanolamine and of citrate buffers respectively increases and decreases when salt is added. At low electrolyte concentrations (<0.15 mol/kg), the phenomenon is well accounted for by standard electrostatic theories. pH values at higher salt concentrations are not reliable when measured with a commercial glass electrode without cross-checking by a standard hydrogen electrode. The changes of the pH values of polyelectrolyte and protein solutions with added salts turn out to be remarkably similar to the salt induced pH changes in the buffer solutions. It is even possible to qualitatively predict these changes in protein solutions simply from the primary protein structure. At least in the systems considered here, the specific ion effects on pH seem to correlate with the bulk activity coefficients of the added electrolytes, at least at moderate salt concentrations.

Buffers↗
PubMed2006

Balance of hydrophobic and electrostatic forces in the pH response of weak polyelectrolyte capsules.

A detailed study of the role of solution pH and ionic strength on the swelling behavior of capsules composed of the weak polyelectrolytes poly(4-vinylpyridine) (P4VP) and poly(methacrylic acid) (PMA) with different numbers of layers was carried out. The polyelectrolyte layers were assembled onto silicon oxide particles and multilayer formation was followed by zeta-potential measurements. Hollow capsules were investigated by scanning electron microscopy and atomic force microscopy. The pH-dependent behavior of P4VP/PMA capsules was probed in aqueous media using confocal laser scanning microscopy. All systems exhibited a pronounced swelling at the edges of stability, at pHs of 2 and 8.1. The swelling degree increased when more polymer material was adsorbed. The swollen state can be attributed to uncompensated positive and negative charges within the multilayers, and it is stabilized by counteracting hydrophobic interactions. The swelling was related to the electrostatic interactions by infrared spectroscopy and zeta-potential measurements. The stability of the capsules as well as the swelling degree at a given pH could be tuned, when the ionic strength of the medium was altered.

Biophysics↗
PubMed2004

Formation of weak polyelectrolyte multilayers studied by spin labeling.

Multilayers of alternately adsorbing poly(allylamine) (PAH) and poly(acrylic acid) (PAA) of opposite charges on silica have been studied by the spin labeling technique, as a function of pH. The two polyelectrolytes have been labeled independently by a nitroxide free radical. Its electron paramagnetic resonance spectrum is mainly sensitive to the local Brownian motion and shows lines typical of two different environments, namely, loops protruding in solution with a fast motion and trains adsorbed on the solid with a hindered motion. These two parts have been evaluated for each of the polymer layers separately, and the thickness of the coatings has been described more precisely by characterizing the four contributions existing, for example, for a bilayer. Complexation is demonstrated by the loss of loops and tails belonging to the first polyelectrolyte. The overall picture emerging from the data is explained in terms of compensation of charges and entropy of confinement.

Journal Article↗