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 1,567 records · Page 87Linked to original sources
PubMed2003

Coagulation-flocculation pretreatment of sanitary landfill leachates.

Sanitary landfill leachates are considered as heavily polluted industrial wastewaters, presenting significant time and spatial variations of their physical-chemical parameters. Special care is required for their efficient treatment and disposal. The main aim of this work was to examine the application of coagulation-flocculation for the treatment of raw and partially stabilized leachates. Jar-test experiments were employed in order to determine the optimum conditions for the removal of organic matter and color, i.e. coagulant-flocculant combination, effective dosage and pH control. Ferric chloride, aluminium sulphate and lime were tested as conventional coagulants, whereas four commercial polyelectrolytes were co-examined: one anionic, two cationic and a non-ionic polymer. High chemical oxygen demand (COD) removal capacities (about 80%) were obtained during the addition of ferric chloride to the partially stabilized leachates, whereas low COD reductions (i.e. lower than 35%) were measured during the addition of coagulants in the raw samples. The addition of polyelectrolytes and pH adjustment in the alkaline region were found to affect slightly the removal of pollutants. The physico-chemical process may be used as a useful pretreatment step, especially for fresh leachates, prior to biological treatment, or as a post-treatment (polishing) step for partially stabilized leachates.

Alum Compounds↗
PubMed2002

Alpha-tricalcium phosphate hydrolysis to octacalcium phosphate: effect of sodium polyacrylate.

Alpha-Tricalcium phosphate (alpha-TCP) hydrolysis into octacalcium phosphate (OCP) has been investigated in phosphoric acid solution at different concentrations of sodium polyacrylate (NaPA). The hydrolysis process has been followed by powder X-ray diffraction, infrared absorption and scanning electron microscopy analyses. In the absence of the polyelectrolyte, alpha-TCP undergoes a complete transformation into OCP in 24 h. The presence of polyacrylate in solution inhibits the hydrolysis so that a NaPA concentration of 0.5 microm is sufficient to lengthen the time required to complete the hydrolysis to 4 days. The variation of Ca2+ concentration in the soaking solution suggests that the transformation occurs through alpha-TCP dissolution followed by OCP precipitation. The delayed OCP nucleation and growth in the presence of polyacrylate implies a preferential adsorption of the polyelectrolyte on the growing OCP crystals, which induces an anisotropic reduction of the coherence lengths of the perfect crystalline domains.

Acrylic Resins↗
PubMed1998

Development of glass-ionomer cement systems.

In the 1960s the idea of positive physico-chemical adhesion with tooth substance resulted in the invention of polyacrylic acid-based cements, first the zinc polycarboxylate and, subsequently, the glass-ionomer cements. These materials were shown to undergo specific adhesion with hydroxyapatite and proved to have properties satisfactory for a variety of clinical applications. The key properties of the glass-ionomer cements--fluoride release over a prolonged period and specific adhesion to enamel and dentine coupled with aesthetic qualities are related to their characteristics as aqueous polyelectrolyte systems. In order to improve toughness, speed of setting and resistance to dehydration, hybrid materials in which some of the water content of the glass-ionomer system was replaced by water-soluble polymers or monomer systems capable of ambient polymerization were formulated in the late 1980s. These materials, which have been termed resin-modified glass-ionomer cements, involve, ideally, the formation of an interpenetrating polymer network combining the acid-base cross-linking reaction of the metal ion-polyacid with the cross-linking polymerization of the monomer system or additive action of the polymers. In the predominantly resin materials there is little polyelectrolyte character and it is controversial whether such materials should be categorized as glass-ionomer cement systems. The specific advantages of these materials over traditional glass-ionomer systems and over composite restorative systems remain to be fully documented. Studies of adsorption to hydroxyapatite of typical monomers using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) indicate that resistance to water displacement decreases as hydrophobicity increases.

Biocompatible Materials↗
PubMed1998

Comparison of polymerically stabilized PEG-grafted liposomes and physically adsorbed carboxymethylchitin and carboxymethyl/glycolchitin liposomes for biological applications.

The stabilities of two types of polymerically stabilized liposomes consisting of PEG-grafted (DSPC:CHOL:DSPE-PEG1900, 5:4:1) and physically adsorbed carboxymethylchitin (CMC) and carboxymethyl/glycolchitin (CO) are compared. The polyelectrolyte is adsorbed on positive (DSPC:CHOL:DMTAP, 5:4:1) and neutral (DSPC:CHOL, 1:1) liposomes at different molecular weights (Mw). In PBS buffer (c(s) = 154 mM, pH = 7.4) the theoretical stability ratios (W) calculated using the classical DLVO Theory, indicate that the CMC-coated vesicles and the negative liposomes (DSPC:CHOL:DMPG, 5:4:1) are highly stable (W >> 1) compared to the PEG-grafted (W = 0.9511) and CO-coated (W = 0.9550) liposomes. Meanwhile, experimentally determined values of W, prove that the PEG-grafted is the most stable suspension (W = 5.5). Computation of the theoretical values of W for liposome-red blood cell and liposome-macrophage indicates that the electrosterically stabilized suspensions and the negative liposomes are stable. Light scattering results show that the flocculation of liposomes in blood and plasma depends on polymer molecular weight, type of polyelectrolyte and surface charge of the uncoated liposome. Neutral liposomes coated with CMC of Mw = 1.01 x 10(5) and negative liposomes provide a more effective barrier to plasma macromolecular protein adsorption than the grafted PEG groups and are easy to resuspend in blood.

Adsorption↗
PubMed1998

Nanocrystals of magnesium and fluoride substituted hydroxyapatite.

Hydroxyapatite nanocrystals synthetized in the presence of different concentrations of magnesium and fluoride ions in solutions--1, 5 and 10 at.% have been submitted to a structural and chemical characterization. The syntheses were carried out in the presence of low molecular weight polyacrylic acid, which has been verified to inhibit hydroxyapatite crystallization. The polyelectrolyte is adsorbed into the crystals during the synthesis and provokes a reduction of the mean crystal sizes. The reduction is greater along the direction orthogonal to the c-axis, suggesting a preferential adsorption of the polyelectrolyte on the crystalline faces parallel to the c-axis. Both magnesium and fluoride can be incorporated into the hydroxyapatite structure. On the basis of the values of the lattice constants and of the magnesium relative content of the solid phase, it can be suggested that probably just a part of magnesium is substituted for calcium, the remainder being adsorbed on the crystal surface. However, magnesium destabilizes the apatitic structure favouring its thermal conversion into beta-tricalcium phosphate, and displays an inhibiting effect on the crystallization of hydroxyapatite. This last effect is enhanced by the simultaneous presence of polyacrylic acid. Fluoride substitution for hydroxyl ions into hydroxyapatite structure induces a slight increase of the crystal sizes along the c-axis direction. The data indicate that the experimental approach can be successfully used to prepare nanoapatite with crystallinity, crystal dimensions, composition, structure and stability very close to those characteristics of biological apatites.

Durapatite↗
PubMed2001

Formation of quasi-regular compact structure of poly(methacrylic acid) upon an interaction with alpha-chymotrypsin.

Structure and dynamic properties of free poly(methacrylic acid) (PMA) and PMA complexed with alpha-chymotrypsin (CT) were studied using the time resolved fluorescence anisotropy technique. We have found that the interaction of PMA with CT induces the formation of a quasi-regular structure of PMA. At a CT/PMA weight ratio of 4:1 the interaction with CT leads to formation of approximately four equal segments of polyelectrolyte, each binding one CT molecule and characterized by an independent rotational mobility. Increase of the CT/PMA weight ratio above 8:1 gives rise to the overall rotation of the whole enzyme-polyelectrolyte complex. In water-ethanol mixtures the mobility of PMA segments containing CT decreases and the structure of the complex becomes even more rigid due to enhancement of the electrostatic interaction between CT and PMA. Formation of the compact and quasi-regular structure of the complex is perhaps the main reason behind the enhancement of enzyme stability and suppression of enzyme aggregation in water-organic cosolvent mixtures.

Animals↗
PubMed2000

DNA delivery systems based on complexes of DNA with synthetic polycations and their copolymers.

Block and graft copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) with 2-(trimethylammonio)ethyl methacrylate were synthesised and used for preparation of polyelectrolyte complexes with calf thymus DNA intended for targeted delivery of genes in vivo. In this study the effects of the speed of component mixing, total concentration of polymers, ionic strength of solvents, copolymer structure and content of HPMA in the copolymers on parameters of the polyelectrolyte complexes was investigated. Static and dynamic light scattering methods were used as a main tool for characterising these complexes. The presence of HPMA units in the polycation had no significant effect on its ability to form complexes with DNA, but did affect molecular parameters and aggregation (precipitation) of the complexes. The size of the complexes increases whereas their molecular weight decreases with increasing content of HPMA units. The density of the complexes decreases with increasing HPMA content independently of the copolymer structure. In order to prepare stable DNA complexes containing single DNA molecule, the following rules should be observed: (1) copolymers should have a content of HPMA units higher than 40%; (2) the DNA concentrations in solutions should be kept below 4 x 10(-5) g/ml and (3) both components should be mixed together in deionized water. The stability of the complexes against precipitation in 0.15 M NaCl and the resistance of the complexed DNA to the action of nucleases was also studied. Whereas DNA complexes of all copolymers showed very good nuclease stability, the presence of a sufficiently high content of HPMA is necessary for their good stability in 0.15 M NaCl. The investigation of the stability and the interaction of DNA complexes in aqueous solutions of serum albumin and dilute human blood serum revealed adsorption of biomacromolecules on DNA complexes accompanied by significant changes in the zeta-potential which finally resulted in formation of a "protein layer" and in undesirable precipitation of DNA complexes. In in vitro transfection experiments, the transfection efficiency of DNA complexes with copolymers was always higher than that of the cationic homopolymer slightly increasing with increasing content of HPMA in the copolymers but being about 10-100-times lower than the complexes DNA-poly(L-lysine. In the cytoplasmic injections, it was observed that DNA complexes produced greater gene expression than a direct microinjection of free DNA. The block copolymer complexes were also found to be more efficient than the corresponding simple polycation complexes. In the nuclear microinjection, precisely the opposite behaviour was observed.

Acrylamides↗
PubMed2000

Analytical ultracentrifugation and the characterization of chromatin structure.

This mini review consists of two parts. The first part will provide a brief overview of the theoretical aspects involved in the two kinds of experiments that can be conducted with the analytical ultracentrifuge (sedimentation velocity and sedimentation equilibrium) as they pertain to the study of chromatin. In the following sections, I describe the analytical ultracentrifuge experiments which, in my opinion, have contributed the most to our understanding of chromatin. Few other biophysical techniques, with the exception of X-ray scattering and diffraction, have contributed as extensively as the analytical ultracentrifuge to the characterization of so many different aspects of chromatin structure. In the course of his scientific career, Professor Henryk Eisenberg has made many important contributions to the theoretical aspects underlying ultracentrifuge analysis, especially in the analysis of solutions of polyelectrolytes and biological macromolecules [H. Eisenberg, Biological macromolecules and polyelectrolytes in solution, Clarendon Press, Oxford, 1976]. As an example he has devoted some of his research effort to the characterization of chromatin in solution. This review includes these important contributions.

Animals↗
PubMed2002

Electrostatic free energy of the DNA double helix in counterion condensation theory.

Polyelectrolyte theory based on counterion condensation is extended from the standard line charge model to helical and double helical charge arrays. The number of condensed counterions turns out to be the same as for a line charge with charge density equal to the axial charge density of the helix. Also, the logarithmic salt dependence of the electrostatic free energy is the same in the range of lower salt concentration, so that the limiting laws remain unchanged. However, the internal free energy of the condensed layer of counterions and the overall electrostatic free energy depend on the helical parameters. At higher salt, the free energies of both single and double helix are negative, indicating electrostatic stabilization of the helical charge lattices due to the mixing entropy of the condensed counterions. Except at very low salt, the free energy of a single helix is higher than the free energy of a double helix with twice the charge density. With B-DNA parameters and single strands modeled as single helices, the predicted salt dependence of the free energy of transition from double helix to separated single strands has a maximum at approximately 0.2 M salt, close to the location in the laboratory of this well-known feature of the DNA strand separation transition. We also calculate the electrostatic free energy for the transition of the DNA double helix from the B to the A conformation. The B form is electrostatically stable over most of the salt range, but there is a spontaneous electrostatic transition to A near 1 M salt. The electrostatic free energy values are close to the experimental values of the overall (electrostatic plus non-electrostatic) transition free energies for A-philic base pair sequences. We are led to suggest that the experimentally observed B-to-A transition for A-philic sequences near 1 M salt in water is governed by the polyelectrolyte properties of these two conformations of the DNA double helix. The effect of ethanol, however, cannot be attributed to lowering of the bulk dielectric constant.

DNA↗
PubMed2003

Static material properties of the tectorial membrane: a summary.

The tectorial membrane (TM) is a polyelectrolyte gel. Hence, its chemical, electrical, mechanical, and osmotic properties are inextricably linked. We review, integrate, and interpret recent findings on these properties in isolated TM preparations. The dimensions of the TM in alligator lizard, chick, and mouse are sensitive to bath ion concentrations of constituents normally present in the cochlear fluids - an increase in calcium concentration shrinks the TM, and an increase in sodium concentration swells the TM in a manner that depends competitively on the calcium concentration. The sodium-induced swelling is specific; it does not occur with other alkali metal cations. We interpret these findings as due to competitive binding of sodium and calcium to TM macromolecules which causes a change in their conformation that leads to a change in mechanical properties. In mouse TM, decreasing the bath pH below 6 or increasing it above 7 results in swelling of the TM. Electric potential measurements are consistent with the notion that the swelling is caused by a pH-driven increase in positive fixed charge at low pH and an increase in the magnitude of the negative fixed charge at high pH which is consistent with the known protonation pattern of TM macromolecules. Increasing the osmotic pressure of the bathing solution with polyethylene glycol shrinks the TM and decreasing the ionic strength of the bathing solution swells the TM. Both results are qualitatively consistent with predictions of a polyelectrolyte gel model of the TM.

Animals↗
PubMed2001

Microgravimetric DNA sensor based on quartz crystal microbalance: comparison of oligonucleotide immobilization methods and the application in genetic diagnosis.

We report on the study of immobilization DNA probes onto quartz crystal oscillators by self-assembly technique to form variety types of mono- and multi-layered sensing films towards the realization of DNA diagnostic devices. A 18-mer DNA probe complementary to the site of genetic beta-thalassaemia mutations was immobilized on the electrodes of QCM by covalent bonding or electrostatic adsorption on polyelectrolyte films to form mono- or multi-layered sensing films by self-assembled process. Hybridization was induced by exposure of the QCMs immobilized with DNA probe to a test solution containing the target nucleic acid sequences. The kinetics of DNA probe immobilization and hybridization with the fabricated DNA sensors were studied via in-situ frequency changes. The characteristics of QCM sensors containing mono- or multi-layered DNA probe constructed by direct chemical bonding, avidin-biotin interaction or electrostatic adsorption on polyelectrolyte films were compared. Results indicated that the DNA sensing films fabricated by immobilization of biotinylated DNA probe to avidin provide fast sensor response and high hybridization efficiencies. The effects of ionic strength of the buffer solution and the concentration of target nucleic acid used in hybridization were also studied. The fabricated DNA biosensor was used to detect a set of real samples. We conclude that the microgravimetric DNA sensor with its direct detection of amplified products provide a rapid, low cost and convenient diagnostic method for genetic disease.

Biosensing Techniques↗
PubMed2002

Nanoencapsulated microcrystalline particles for superamplified biochemical assays.

We report on the preparation and utilization of a novel class of particulate labels based on nanoencapsulated organic microcrystals with the potential to create highly amplified biochemical assays. Labels were constructed by encapsulating microcrystalline fluorescein diacetate (FDA; average size of 500 nm) within ultrathin polyelectrolyte layers of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) via the layer-by-layer technique. Subsequently, the polyelectrolyte coating was used as an "interface" for the attachment of anti-mouse antibodies through adsorption. A high molar ratio of fluorescent molecules present in the microcrystal core to biomolecules on the particle surface was achieved. The applicability of the microcrystal-based label system was demonstrated in a model sandwich immunoassay for mouse immunoglobulin G detection. Following the immunoreaction, the FDA core was dissolved by exposure to organic solvent, leading to the release of the FDA molecules into the surrounding medium. Amplification rates of 70-2000-fold (expressed as an increase in assay sensitivity) of the microcrystal label-based assay compared with the corresponding immunoassay performed with direct fluorescently labeled antibodies are reported. Our approach provides a general and facile means to prepare a novel class of biochemical assay labeling systems. The technology has the potential to compete with enzyme-based labels as it does not require long incubation times, thus speeding up bioaffinity tests.

Animals↗
PubMed2006

Structure and thickness dependence of "molecular wiring" in nanostructured enzyme multilayers.

Supramolecular organized multilayers composed of glucose oxidase (GOx) and osmium-derivatized poly(allylamine) redox polymer have been self-assembled electrostatically from Os-polyelectrolyte solutions of variable pH (5.5-8.8) leading to a decrease of the linear charge density in the PAH-Os with increasing pH. The layer-by-layer enzyme multilayers were studied by ellipsometry, quartz crystal microbalance, AFM, cyclic voltammetry, and electrocatalytic oxidation of beta-D-glucose. At higher adsorption solution pH, an increase in the film thickness, enzyme loading, and redox charge was observed. While the electrocatalytic response increases with the increase of the adsorption solution pH (decrease of the polyelectrolyte linear charge), the FADH2 oxidation bimolecular rate constant has a maximum in the pH range 7.0-7.5 where a change in the film growth mechanism is observed.

Electrochemistry↗
PubMed2006

Electrostatic switching of biopolymer layers. Insights from combined electrokinetics and reflectometric interference.

Structural integrity and functional characteristics of biomacromolecules are largely defined by electrostatic forces between ionized moieties, which are often altered at interfaces. Unraveling these changes requires access to charge state and structure of surface-confined biopolymers in aqueous environments. We therefore combined electrokinetic measurements of interfacial electrical potentials with the simultaneous determination of the optical layer thickness by reflectometric interference spectroscopy. Two examples are summarized to demonstrate the resulting options: The pH-switching of grafted poly(l-glutamic acid) layers caused by dissociation-dependent helix-coil transitions was studied; potential distribution and ion mobility within the grafted polyelectrolyte were unraveled using an new theoretical model for the charging of polyelectrolyte layers. The charge-driven modulation of biopolymers at interfaces was furthermore analyzed in the adsorption of fibronectin onto polymer substrates with varied charge density; the results permit us to reach a conclusion about the relevance of electrostatic matching for orientation and anchorage of the protein. Altogether, the introduced methodology was found suitable to follow the electrosurface characteristics of biomacromolecules in situ.

Biopolymers↗
PubMed2006

Biomolecular sensing using near-null single wavelength arrayed imaging reflectometry.

We use reflectivity changes at an interface functionalized with molecular probes to detect label-free biomolecular binding. Attachment of the target molecules to the surface alters the effective thickness of an antireflective coating formed by thermal oxidation of a silicon wafer to remove destructive interference of the reflected waves. The thermal oxide thickness is adjusted for precise interference using electrostatic layer-by-layer self-assembly of polyelectrolytes to which the molecular probes can be bound covalently. Reflectivity increases of over a factor of 100 are observed for binding of 2.5 nm of streptavidin to biotinylated polyelectrolytes, considerably more sensitive than surface plasmon resonance detection. Theoretical modeling is in agreement with the experimentally observed reflectivity increases and suggests the sensitivity is at present limited by the roughness of the oxide.

Biosensing Techniques↗
PubMed1993

Betaine can eliminate the base pair composition dependence of DNA melting.

We show that the amino acid analogue betaine shares with small tetraalkylammonium ions [Melchior, W. B., Jr., & von Hippel, P. H. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 298-302] the ability to reduce or even eliminate the base pair composition dependence of DNA thermal melting transitions. The "isostabilizing" concentration of betaine (at which AT and GC base pairs are equally stable) is approximately 5.2 M. Betaine exerts its isostabilizing effect without appreciably altering the conformation of double-stranded DNA from the B form. The presence of > 5 M betaine also does not greatly change the behavior of DNA as a polyelectrolyte; this lack of effect on electrostatic interactions is expected because betaine exists as a zwitterion near neutral pH. Study of DNA melting transitions in high concentrations of betaine thus allows the experimental separation of compositional and polyelectrolyte effects on DNA melting. As a consequence, betaine solutions can also be used to investigate DNA-protein interactions under isostabilizing (or close to isostabilizing) conditions, which has not been possible using isostabilizing salts. This potential is illustrated by examining the highly salt concentration-dependent interaction of ribonuclease A with DNA in concentrated betaine solutions.

Base Composition↗
PubMed2001

Thermodynamic basis for sequence-specific recognition of ssDNA by an autoantibody.

11F8 is a sequence-specific DNA binding monoclonal autoantibody previously isolated from an autoimmune lupus-prone mouse [Stevens, S. Y., and Glick, G. D. (1999) Biochemistry 38, 560-568]. This antibody, like many other lupus anti-DNAs, localizes to kidney tissue and eventually leads to renal damage through a process that first involves the binding of DNA antigens. A series of experiments were conducted to investigate the thermodynamic and structural basis by which this antibody discriminates between specific, noncognate, and nonspecific sequences. Sequence-specific binding occurs with a minimal dependence on the polyelectrolyte effect along with a favorable binding enthalpy reflecting the presence of base stacking and contacts to DNA bases. This favorable binding enthalpy apparently is derived from desolvation at the binding interface and is consistent with recent models of the nonclassical hydrophobic effect. Noncognate recognition is also driven by the nonclassical hydrophobic effect, but is accompanied by highly unfavorable entropies that are responsible for reduced affinity relative to the high-affinity consensus sequence. Nonspecific recognition is driven completely by the polyelectrolyte effect involving extensive electrostatic interactions with the phosphate backbone. Collectively, the data demonstrate the ability of 11F8 to adapt its mode of binding to the available DNA surface and provide a thermodynamic model for sequence-specific recognition of single-stranded DNA. The salient features of this model employ the paradigms invoked to explain protein.dsDNA, protein.RNA, and antibody.antigen binding.

Animals↗
PubMed2006

Anisotropic nucleation growth of actin bundle: a model for determining the well-defined thickness of bundles.

Biopolymers such as DNA, F-actins, and microtubules, which are highly charged, rodlike polyelectrolytes, are assembled into architectures with defined morphology and size by electrostatic interaction with multivalent cations (or polycations) in vivo and in vitro. The physical origin to determine their morphology and size is not clearly understood yet. Our results show that the actin bundle formation consists of two stages: the thickness of actin bundles is determined nearly at the initial stage, while the length of actin bundles is determined later on. It is also found that the thickness of actin bundles decreases with the increase of polycation-mediated attraction between F-actins. From these results, we propose the anisotropic nucleation-growth mechanism, in which the thickness of actin bundles is determined by critical nucleus size, whereas the length of actin bundles is determined by the concentration of free actins relative to nucleus concentration. Observing that polycations are concentrated in some sites of actin bundles, which are thought to be nucleation sites to initiate the formation of actin bundles, supports this model. This anisotropic nucleation-growth mechanism of actin bundles can be broadly applied to the self-assembly of rodlike polyelectrolytes.

Actins↗