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 1,063 records · Page 59Linked to original sources
PubMed1978

Mean activity coefficients for the simple electrolyte in aqueous mixtures of polyelectrolyte and simple electrolyte. V. Common counterion mixtures of alkali-metal dextransulfates with alkali metal chlorides.

Mean molal activity coefficients of simple electrolyte in aqueous solutions of Li, Na, K or Cs salts of dextransulfate (DS) with added LiCl, NaCl, KCl or CsCl are reported. The measurements were carried out by means of an electrochemical cell method using a cation exchange membrane as cation selective electrode and Ag/AgCl electrodes. For LiDS-LiCl, NaDS-NaCl and CsDS-CsCl systems the polymer concentration, mp, was varied from 0.0088 to 0.113 m and at a given mp the ratio X of the polymer to salt concentration was varied from 0.5 to 16. Due to the insolubility of KDS in high concentration of KCl, the measurements on KDS-KCl system were performed in the mp range of 0.0088--0.089 m and some of the smaller X values were omitted. The activity coefficient results are compared to Manning's limiting laws, the additivity rule, and to new limiting laws. The additivity rule can give an excellent representation of the data for all mp values when gammap is used as an adjustable parameter.

Chemical Phenomena↗
PubMed1979

Polarized fluorescence in an electric field: comparison with other electrooptical effects for rodlike fragments of DNA and the problem of the saturation of the induced moment in polyelectrolytes.

Electrical birefringence, electrical dichroism and polarisation of fluorescence in an electric field experiments have been performed at high fields on sonicated fragments of DNA labelled with Acridine Orange. The latter electrooptical effect gives access to the field dependence of the fourth moment of the orientation function while the two former give access to the field dependence of the second moment. The origin of the large departure from an E2 dependence at rather low degrees of orientation is extensively discussed. Following a suggestion of Shirai on the calculation of orientational averages for a saturated induced moment, we can show that this model rationalizes the existence of a linear E dependence of the orientation factor at intermediate fields and explains very well our experimental results. When applied to previous dichroic data at higher fields it shows that the low value of the dichroism at saturation introduced to fit with other models, in contradiction with the absence of base tilting in the B form of DNA, is not required for a quantitative fit with this new orientation mechanism. The transition from an E2 dependence at low fields to an E dependence at intermediate fields gives an estimate of the field required for the saturation of the ionic polarisation E approximately 6 kV/cm.

Acridine Orange↗
PubMed1980

Light scattering from solutions of a semi-flexible polymer and a polyelectrolyte both having sharp molecular weight distributions.

The particle scattering factor in light scattering is determined for poly(tert-butyl crotonate) in n-butyl chloride and also for partially neutralized poly (acrylic acid) in aqueous solution in the presence of added neutral salt (NaBr). The former is a wormlike chain which is extended due to stiffness of the polymer chain, while the latter is extended due to the electrostatic repulsive force which is a kind of excluded volume effect. A clear difference is found between P(theta) of both polymers.

Journal Article↗
PubMed1986

Dielectric behavior of polyelectrolytes. IV. Electric polarizability of rigid biopolymers in electric fields.

The equilibrium Kerr effect of a system of mobile charges constrained to the surface of biomacromolecules is calculated. Cylindrical and spherical geometries are considered. For the cylinder we determine the anisotropy of electric polarizability as a function of length, temperature, and number of charged species in the low-field regime, and the fraction of the maximum induced dipole in the field direction for higher electric fields. The results are compared to experimental data for DNA oligomers taken from the literature. With spherical geometry we calculate the fractional induced dipole moment as a function of electric field strength and from this deduce the orientation function. The field dependence of the orientation function is compared to experimental data in the literature for bovine disk membrane vesicles.

DNA↗
PubMed1988

Dielectric behavior of polyelectrolytes. VI. Dynamic response of cylindrical biopolymers to electric fields.

The time dependence of the orientation of a cylindrical biopolymer and the configuration of its counterion complement in the presence of an external electric field is found by solving a model forced diffusion equation. The solution is a high temperature expansion in the external field strength and is used to predict the nature of the dielectric relaxation and the dynamic Kerr effect for such systems. Specific application is made to the dynamic Kerr effect of a DNA oligomer for which experimental data appear in the literature. The analysis yields a value for the surface diffusion coefficient of a sodium ion on DNA at 20 degrees C of 3.8 x 10(-10) m2 s-1.

Biopolymers↗
PubMed1989

Conformational transition of poly(alpha-L-glutamic acid). A polyelectrolytic approach.

The charge-induced conformational transition of poly(alpha-L-glutamic acid) (PLGA) is considered in this paper from the point of view of proton dissociation. Equations for the excess electrostatic Gibbs energy of dissociation (i.e., delta pKa) are derived as a function of the degree of ionization, alpha. These analytical equations are used to describe some experimental dissociation curves at different polymer and salt concentrations. The dependence of the calculated delta pKa with respect to the ionic strength for the two conformational states, alpha-helical and extended coil, respectively, is rather satisfactorily explained. Even more interesting are the predictions which are derived from this approach for the transition point, alpha tr which is found to be ionic-strength dependent, in full agreement with the experimental results.

Kinetics↗
PubMed1992

Limiting-laws of polyelectrolyte solutions. Ionic distribution in mixed-valency counterions systems. II. A comparison of conductometric data and theoretical predictions.

The competitive binding of monovalent and divalent counterions (M+ and M2+, respectively) has been studied by a conductometric procedure as described by De Jong et al. (Biophysical Chemistry 27 (1987) 173) for aqueous solutions of alkali metal polymethacrylates in the presence of Ca (NO3)2 or Mg(NO3)2. The experimentally obtained fractions of conductometrically free counterions are compared with theoretical values computed according to a new thermodynamic model recently developed by Paoletti et al. (Biophysical Chemistry, 41 (1991) 73). For the systems studied, the fractions of free monovalent and divalent counterions can be fairly well described by the theory. In fact, the results support the assumption that under the present conditions the conductometrically obtained distribution parameters (l) and (2) approximate the equilibrium fractions of free monovalent and divalent counterions. For a degree of neutralization of 0.8 and a molar concentration ratio of divalent counterions and charged groups on the polyion up to 0.25, the mean M+/M2+, exchange ratio nu has been found to be 1.39 +/- 0.03 and 1.33 +/- 0.03 for the alkali metal/Ca/PMA and alkali metal/Mg/PMA systems, respectively. These values agree well with the theoretical value, which for this particular case is 1.38.

Journal Article↗
PubMed1995

Conformational transitions in polyelectrolyte adsorption.

The mole fraction X of nucleic acid chromophores, adsorbed on cationic and anionic exchange chromatography paper disks, was calculated [O.L. Hörer and A. Grigorescu, Rev. Roum. Med. Virol., 43 (1992) 33] in terms of the standard Debye screening length D (in the 0.01 to 1.2 M ionic strength range), using data from MLSEA (multiple light scattering enhanced absorption) measurements. In contrast to the cases of mononucleotides or double-stranded and relatively rigid DNA structures, highly polymerized and single-stranded RNA shows sigmoidal-shaped X curves, suggesting that polymer adsorption may be regarded as a conformational transition from a three-dimensional statistical coil to a two-dimensional one.

Journal Article↗
PubMed1996

Interaction of calcium ions and polyelectrolytes.

Interaction of Ca(2+) ions with poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA) was studied using a Ca(2+) ion sensitive electrode. When the PAA solution was neutralized with Ca(OH)(2), the Ca(2+) activity had a maximum around the degree of neutralization 0.5 and decreased with further increase of Ca(OH)(2), being similar to the behavior of the Ca(2+) activity in a maleic acid copolymer solution as reported previously. When the polymer concentration was as low as 0.1 mM, this peak in the Ca(2+) activity was not observed and the counterion condensation theory held. The decrease of the Ca(2+) activity in PAA solution at the degree of neutralization unity was depresseed by the presence of several millimolar KCl. The Ca(2+) activity in the PAA solution at the low degree of neutralization was increased by the presence of dilute KCl and decreased by the presence of concentrated KCl. The decrease of the Ca(2+) activity in PMA solution was observed also at the degree of neutralization unity, but its extent was small compared with that of the PAA solution and the maximum of the Ca(2+) activity was shifted to the degree of neutralization 0.75. The effects of KCl on the Ca(2+) activity in the PMA solution were almost the same as those in the PAA solution. Interpretations of the behavior of the Ca(2+) activity were discussed.

Journal Article↗
PubMed1996

Electric polarization of polyelectrolyte and colloid media: dielectric versus electro-optic approach.

The theories of dielectric dispersion and of electric birefringence as a representative of electro-optic methods are considered and it is shown that they both depend in a similar way simply on the real part of the complex electric polarizability of the macromolecules or the particles. The latter also contains the permanent dipole moment. Experimental data on dielectric dispersion, electric birefringence and electric light scattering of strongly elongated, rod-like poly(tetrafluoroethylene) particles are compared and an attempt is made to extend the dielectric dispersion curve to lower frequencies using electric birefringence and electric light scattering data. Further, the experimental data on dielectric dispersion, electric light scattering, electro-orientation and dipolophoresis for the more complicated Escherichia coli particles are compared. Again, the possibility to extend the 10 kHz-100 MHz dielectric dispersion curve down below 1 Hz by using electric light scattering data is examined. The good matching of the dielectric dispersion and electric light scattering frequency curves found in the overlapping frequency range (10 kHz-5 MHz) essentially enhances the chance that dielectric dispersion below 1 MHz is related to alpha dispersion and not to electrode polarization. Thus it is not only possible to obtain additional information on the mechanism of polarization at lower-frequency dielectric dispersion, but also to extend our knowledge about the effective dielectric properties of biological complex fluids to frequencies essentially below 1 MHz. This could be important for the understanding of the effect of low-frequency electromagnetic fields on living matter.

Journal Article↗
PubMed1991

A miniature Clark-type oxygen electrode using a polyelectrolyte and its application as a glucose sensor.

A miniature Clark-type oxygen electrode was fabricated by anisotropically etching silicon. A two-gold-electrode configuration was used and a double-layered gas-permeable membrane was formed directly on the electrolyte, poly(vinyl-4-ethylpyridinium bromide) in the sensitive area. These materials improved the electrode's stability in long-term storage and sterilization tolerance to a practical level. The 90% response time averaged 80 s and residual current 10%, with a good linear calibration curve. The oxygen electrode was also used to make an integrated sensor for the simultaneous determination of glucose and oxygen. The glucose sensor's response time was 50-110 s, with good linearity in glucose concentrations between 56 microM and 1.1 mM at 37 degrees C, pH 7.0.

Biosensing Techniques↗
PubMed2005

Surface modification of poly(L-lactic acid) to improve its cytocompatibility via assembly of polyelectrolytes and gelatin.

Poly(L-lactide) (PLLA) surface was modified via aminolysis by poly(allylamine hydrochloride) (PAH) at high pH and subsequent electrostatic self-assembly of poly(sodium styrenesulfonate) (PSS) and PAH, and the process was monitored by X-ray photoelectron spectroscopy (XPS) and contact angle measurement. These modified PLLAs were then used as charged substrates for further incorporation of gelatin to improve their cytocompatibility. The amphoteric nature of the gelatin was exploited and the gelatin was adsorbed to the negatively charged PLLA/PSS and positively charged PLLA/PAH at pH=3.4 and 7.4, respectively. XPS and water contact angle data indicated that the gelatin adsorption at pH=3.4 resulted in much higher surface coverage by gelatin than at pH=7.4. All the modified PLLA surfaces became more hydrophilic than the virgin PLLA. Chondrocyte culture was used to test the cell attachment, cell morphology and cell viability on the modified PLLA substrates. The results showed that the PAH and PSS modified PLLA exhibited better cytocompatibility than virgin PLLA, and the incorporation of the gelatin on these modified PLLA substrates further improved their cytocompatibility, with the PLLA/PSS substrate treated with the gelatin at pH=3.4 being the best, exceeding the chondrocyte compatibility of the tissue culture polystyrene.

Adsorption↗
PubMed2004

Polyelectrolyte multilayer films with pegylated polypeptides as a new type of anti-microbial protection for biomaterials.

Adhesion of bacteria at the surface of implanted materials is the first step in microbial infection, leading to post-surgical complications. In order to reduce this adhesion, we show that poly(L-lysine)/poly(L-glutamic acid) (PLL/PGA) multilayers ending by several PLL/PGA-g-PEG bilayers can be used, PGA-g-PEG corresponding to PGA grafted by poly(ethylene glycol). Streaming potential and quartz crystal microbalance-dissipation measurements were used to characterize the buildup of these films. The multilayer films terminated by PGA and PGA-g-PEG were found to adsorb an extremely small amount of serum proteins as compared to a bare silica surface but the PGA ending films do not reduce bacterial adhesion. On the other hand, the adhesion of Escherichia coli bacteria is reduced by 72% on films ending by one (PLL/PGA-g-PEG) bilayer and by 92% for films ending by three (PLL/PGA-g-PEG) bilayers compared to bare substrate. Thus, our results show the ability of PGA-g-PEG to be inserted into multilayer films and to drastically reduce both protein adsorption and bacterial adhesion. This kind of anti-adhesive films represents a new and very simple method to coat any type of biomaterials for protection against bacterial adhesion and therefore limiting its pathological consequences.

Adsorption↗
PubMed2004

A preliminary study on chitosan and gelatin polyelectrolyte complex cytocompatibility by cell cycle and apoptosis analysis.

In this study, L929 cell adhesion, proliferation and apoptosis were investigated on chitosan (CS) and chitosan-gelatin (CS-Gel) membranes having different degrees of deacetylation (DD). The mitochondrial activity [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay results demonstrated that the DD played a key role in the L929 cell adhesion. Indeed, the higher the DD of a CS membrane, the stronger the cell adhesion. The cell cycle analysis showed that the CS surface inhibits most of the cells entering the cell cycle and the DD of CS had little effect on the cell cycle progression. On the other hand, this study also confirmed that CS, blended with Gel, induced L929 cells to enter the cell cycle, encouraged proliferation, decreased the degree of apoptosis on the CS membranes, and are comparable to the results from L929 cells on tissue culture plates. In brief, CS modified with Gel improves cytocompatibility by shielding the positively charged CS with a high charge density.

Animals↗
PubMed2005

An investigation on the physicochemical properties of chitosan/DNA polyelectrolyte complexes.

In this work, to eliminate the effect of the hydrophobicity of N-acetyl groups in chitosan on the interaction between chitosan and DNA, a water soluble chitosan with molecular weight of 5000 and deacetylated degree of 99% was selected to complex with DNA at varied charged ratios. The physicochemical properties of chitoplexes were investigated by means of FTIR, circular dichroism (CD), static fluorescence spectroscopy, and atomic force microscopy (AFM). The results indicated that upon interacting with chitosan, the DNA molecules saved a B conformation, and the binding affinity of chitosan to DNA was dependent on pH of media. At pH 5.5, highly charged chitosan had a strong binding affinity with DNA; whereas in pH 12.0 medium, only weak interactions existed. The CD spectra of Hoechst 33258 competitive displacement revealed that chitosan was partially bound to the minor groove of DNA. The morphology of chitosan/DNA complexes was strongly dependent upon the charge ratios. At charge ratio (+/-) of 1:4, not all DNA could be entrapped in the complex; at ratio of 8:1, the spherical complexes with mean size of nanoscale were formed without free DNA, but no typical toroid patterns were observed, which might stem from the strong compact of DNA caused by highly charged chitosan. It was supposed that the strong interaction of chitosan with DNA possibly prevented gene unpacking from chitosan vector, consequently restraining gene expression in nucleus.

Chitosan↗
PubMed2006

Layer-by-layer self-assembled multilayer films of carbon nanotubes and platinum nanoparticles with polyelectrolyte for the fabrication of biosensors.

Platinum nanoparticle-doped chitosan (CHIT) solution can be easily prepared by treating the CHIT solution with aqueous H2PtCl6 solution followed by chemical reduction of Pt(IV) with NaBH4. Multiwalled carbon nanotubes (MWCNT) are then dispersed in the nanoparticle-doped solution. The resulting Pt-CNT-CHIT material brings new capabilities for electrochemical devices by using the synergistic action of Pt nanaoparticles and CNT. Positively charged Pt-CNT-CHIT solution and negatively charged poly(sodium-p-styrenesulfonate) salt (PSS) have been employed to fabricate stable ultrathin multilayer films on gold electrode and quartz glass slides in a layer-by-layer fashion. Cyclic voltammetric and UV-vis adsorption spectroscopy confirms the consecutive growth of the multilayer films. The modified gold electrode allows low-potential detection of hydrogen peroxide with high sensitivity and fast response time. With the immobilization of cholesterol oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to cholesterol has been constructed. In pH 6.98 phosphate buffer, almost interference free determination of cholesterol has been realized at 0.1 V vs. SCE with a linear range from 0.01 to 3mM and response time<30s. With the immobilization of another cholesterol esterase enzyme layer, the biosensor was used to determine total cholesterol in serum samples with satisfactory results.

Biosensing Techniques↗
PubMed2005

Dynamics of complex formation between biological and luminescent conjugated polyelectrolytes--a surface plasmon resonance study.

A water-soluble polythiophene, POWT, with zwitterionic peptide like side chains possess good characteristics for biosensor applications. The zwitterionic side chains of the polymer can couple to biomolecules via electrostatic and hydrogen bonding. This creates possibilities to imprint biomolecules to spin-coated polymer films with maintained functionality, and use the resulting matrix as a biosensor. Polymer-biomolecular interaction studies done with surface plasmon resonance (SPR) reveal a well performing sensor matrix with high affinity for DNA hybridizations as well as for protein detection. The responses are distinct and very specific. A directional dependence of antibodies binding to POWT layer has also been observed. The polymer films have also been characterized by optical methods. Emission and absorption measurements in different buffer systems confirm that the polymer matrix can undergo structural and conformational changes on surfaces. The dielectric function in the interval 300-800 nm of POWT is reported, based on variable angle spectroscopic ellipsometry. This modeling reveals that a considerable amount of water is included in the material. The polymer layer possesses the characteristics needed for biochip applications and micro array techniques.

Biocompatible Materials↗
PubMed2005

Effects of polyelectrolytes on reduction of model compounds via coagulation.

The objective of this research work was to evaluate the performance of enhanced coagulation by alum and polymer. Synthetic source waters containing high molecular weight humic acids, medium molecular weight tannic acids and low molecular weight p-hydroxybenzoic acid were formulated by adjusting the concentration of turbidity and pH; and jar tests were used to study the effect of various types and dosages of polymer on reducing the above model compounds. At a specific pH condition, the applied alum dosage would efficiently decrease the turbidity to 2 NTU follows the order: humic>tannic>p-hydroxybenzoic acid. Adjustment of pH influenced the performance of alum obviously but not of p-DADMAC. High p-DADMAC dosage overwhelming the effects of alum is less affected by pH adjustment. The results of this investigation reveal that enhanced coagulation with p-DADMAC was founded to be very effective for removing high-molecular-weight THM precursors, i.e., humic acid and tannic acid, and markedly reduced the alum dosages required for turbidity removal. The other two polymers, i.e., cationic PAM and non-ionic PAM, which had higher molecular weight but lower charge density than p-DADMAC, were not capable of removing organic precursors. It was thus concluded that enhanced coagulation with polymer, p-DADMAC, could be considered as a promising technique for removal of NOMs with hydrophobic and higher-molar-mass (>1K) in water treatment plants.

Air Pollutants↗