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PubMed1999

The Adsorption of Polyelectrolytes on Hydroxyapatite Crystals.

The adsorption of two polyelectrolytes, poly-L-Glutamate and poly-L-Aspartate, on hydroxyapatite (HAP) crystals was studied both experimentally and theoretically. Langmuir adsorption isotherms were obtained for both these molecules, with binding constants K = 6 x 10(6) and 3 x 10(6) M-1, respectively, at 37.0 degreesC, pH 7.4, and 0.15 M ionic strength. A theoretical analysis of the data, based on a model proposed by Hesselink, suggested a "train-loop" type of adsorption with non-electrostatic energy terms 3.51 and 4.76 (kT) for poly-L-Glu and poly-L-Asp, respectively. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Ion Transport across a Polyelectrolyte-Adsorbed Cellulose Triacetate Membrane in the Multicomponent Ionic Systems.

The effects of polyelectrolyte adsorption by cellulose triacetate (CTA) membrane on ionic transport are investigated in two systems: the three-ionic-component system and the multicomponent-ionic system. In the three-ionic-component system, the permeabilities of two anions are affected by the competitive ion. Especially in the case of the albumin-adsorbed CTA membrane, there exists much greater specificity for the permeability of SO2-4 than in the case of the lysozyme-adsorbed membrane. On the other hand, in the case of the PAS-H(10L)(polydiallyldimethylammonium chloride)-adsorbed membrane, the permeability coefficient of HPO2-4 increases, though there exists the effect of a competitive ion. In a multicomponent-ionic system, the logarithmic permeability coefficient ratios (rP) of each ion in an adsorbed membrane to that in a nonadsorbed membrane decreased by PAS-H(10L) adsorption for all cations. The rP of bivalent cations decreased more than those of univalent cations because of the rejection from the positively charged adsorbed layer. On the other hand, the permeabilities slightly increase because of the attraction from the PAS-H(10L)-adsorbed layer when competitive anions exist among them. Furthermore, the increase in the HPO2-4 permeability is confirmed by PAS-H(10L)-adsorption on a CTA membrane for a case very similar to the actual anion multicomponent system. These are the most important results in the application for an approach to phosphate extraction from blood across an artificial kidney membrane. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Charge Adjustments upon Adsorption of a Weak Polyelectrolyte to a Mineral Oxide: The Hematite-Humic Acid System.

The proton adsorption to a mixture of purified Aldrich humic acid (PAHA) and hematite is investigated. Basic insight into the charge adjustment process is obtained by using a self-consistent-field lattice theory for polyelectrolyte adsorption. The calculations indicate that upon adsorption the component with the highest initial charge density tends to induce charges on the other component. The number of induced charges can show a maximum when the surface charge and the charge of the segments in direct contact with the surface roughly balance each other. Experimentally, the humic acid-hematite system is investigated by proton titrations. The alterations in charge density caused by adsorption of PAHA to hematite are investigated by comparing the proton adsorption on the individual samples with that on their mixtures. Upon adsorption a part of the functional groups of humic acid forms complexes with some of the surface sites of hematite. This interaction reduces the proton binding to the humic acid at relatively low pH and it promotes the proton adsorption on the oxide surface at relatively high pH. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Microencapsulation of Organic Solvents in Polyelectrolyte Multilayer Micrometer-Sized Shells.

Hollow-shell micrometer-sized particles were fabricated in aqueous media by stepwise deposition of oppositely charged polyelectrolytes onto melamine latex particles and biological cells with a dissolution of the core afterward. It is demonstrated that these shells can be suspended in various organic media, such as methanol, ethanol, pentanol, hexanol, octanol, octane, and decane, by a gradual solvent exchange. At this stage of the procedure the shells contain the respective organic solvent. Oil suspensions in water are then formed by transferring the particles from the organic media into water, without the use of any further surfactant addition. By an additional adsorption step employing phospholipids, it is possible to obtain a dispersion of shells in organic solvents containing an aqueous solution inside. AFM measurements are provided which show that the shells preserve their integrity in the different solvents. Confocal microscopy is employed to demonstrate encapsulation of solvents and the presence of lipids. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Binding and Ion-Exchange Analysis in the Process of Adsorption of Anionic Polyelectrolytes on Barium Sulfate.

The adsorption of poly(acrylic acid) and poly(styrenesulfonic acid) (PSS) is studied on a barium sulfate powder. Comparison of the polyelectrolytes shows that the difference in binding strength corroborates the difference between the ligand strengths with barium ions. The surface excess dependence on pH correlates with the density of the ionized groups. The electrokinetic potential follows the surface coverage and the ionization ratio of the polymer up to the onset of the adsorption plateau, but continues to increase above that point. This peculiarity is explained by the release of barium ions from the adsorption layer into the solution. The phenomenon is attributed to the complexing power of unadsorbed molecules. Analysis of the displacement of small ions (Na(+), SO(2-)(4)) shows that adsorbed PSS releases sulfate ions from the surface and sodium counterions from the polymer. The displacement ratio for sulfate ions (SO(2-)(4)/PSS monomer units) remains constant over the adsorption isotherm, but that for sodium ions is constant only up to about two-thirds of the maximum coverage. From the data we deduced that about half of the monomer units of the adsorbed PSS molecules bind with surface barium ions. The other half form barium and sodium sulfonates whose ratio varies with the concentration of unadsorbed molecules. Copyright 1999 Academic Press.

Journal Article↗
PubMed2001

Adsorption Kinetics of Complexes Formed by Oppositely Charged Polyelectrolytes.

The objective of this study is to gain an understanding of the kinetics of adsorption of complexes formed in aqueous solution by oppositely charged polyelectrolytes. The properties of the complexes were characterized by means of dynamic light scattering and electrophoretic mobility and the reaction stoichiometry was studied by titration. The stoichiometry in the complexes depends on the polymer weight ratio w(p). Their point of zero charge (pzc) is shifted toward lower w(p) when simple cations of higher valence are added to the solution. The adsorption kinetics of the complexes on silica was studied by stagnation point reflectometry. The sign of charge of the complexes as well as the valence and concentration of simple cations governs the occurrence of adsorption in the electrolytes studied. Five different types of adsorption kinetics were found. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Electrochemistry and Electrocatalysis with Myoglobin in Biomembrane-Like DHP-PDDA Polyelectrolyte-Surfactant Complex Films.

The polyelectrolyte-surfactant complex DHP-PDDA was prepared by reacting the anionic surfactant dihexadecylphosphate (DHP) with polycationic poly(diallyldimethylammonium) (PDDA). Thin films made from DHP-PDDA on solid substrates demonstrated an ordered multibilayer structure by XRD and DSC. Incorporated myoglobin (Mb) in DHP-PDDA films on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible cyclic voltammetric peaks for the Mb Fe(III)/Fe(II) couple at about -0.3 V vs SCE in pH 7.0 buffers. Electron transfer between Mb and PG electrodes was greatly facilitated in the film microenvironment. The positions of the Soret absorption band suggest that Mb maintains its secondary structure similar to its native state in DHP-PDDA films in the medium pH range. Mb could act as an enzyme-like catalyst in DHP-PDDA films as demonstrated by catalytic reduction of trichloroacetic acid, nitrite, and oxygen with a decrease in the electrode potentials required. Mb-DHP-PDDA films may thus have potential application as biosensors. Copyright 2001 Academic Press.

Journal Article↗
PubMed2002

The relationship between polymer/substrate charge density and charge overcompensation by adsorbed polyelectrolyte layers.

This work examines polyelectrolyte adsorption (exclusively driven by electrostatic attractions) for a model system (DMAEMA, polydimethylaminoethyl methacrylate, adsorbing onto silica) where the adsorbing polycation is more densely charged than the substrate. Variations in the relative charge densities of the polymer and substrate are accomplished by pH, and the polycation is of sufficiently low molecular weight that the adsorbed conformation is generally flat under all conditions examined. We demonstrate, quantitatively, that the charge overcompensation observed on the isotherm plateau can be attributed to the denser positive charge on the adsorbing polycation and that the ultimate coverage obtained corresponds to the adsorption of one oligomer onto each original negative silica charge, when the silica charge is most sparse, at pH 6. This limiting behavior breaks down at higher pHs where the greater silica charge density accommodates single chains adsorbing onto multiple negative sites. As a result of the greater substrate charge density and reduced polycation charge at higher pHs, the extent of charge overcompensation diminishes while the coverage increases on the plateau of the isotherm. Ultimately at the highest pHs, a regime is approached where the coil's excluded surface area, not surface charge, limits the ultimate coverage. In addition to quantifying the crossover from the charge-limiting to the area-limiting behaviors, this paper quantitatively reports adsorption-induced changes in bound counterion density and ionization at the interface, which were generally found to be independent of coverage for this model system.

Journal Article↗
PubMed2002

Precipitation of inorganic salts inside hollow micrometer-sized polyelectrolyte shells.

Hollow polymer shells formed by layer-by-layer adsorption of oppositely charged polyelectrolytes onto micrometer-sized colloidal particles with subsequent decomposition of the colloidal core were employed as a model system for the study of inorganic crystallization reactions in restricted volumes. The size-selective permeability of shells is used for spatially controlling the precipitation of inorganic salts CaCO3 and BaCO3 into the shell interior. Outside the shells the precipitation was suppressed by the polymers, which are unable to penetrate the shell wall. The precipitates were studied by scanning electron microscopy and atomic force microscopy. The fundamental and applied aspects of research on spatially confined synthesis of inorganic particles are under discussion.

Journal Article↗
PubMed2002

Specific counterion effects on the competitive co-adsorption of polyelectrolytes and ionic surfactants.

Counterions affect not only the bulk and interfacial self-assembly of ionic surfactants but also their competitive adsorption with similarly charged polyelectrolytes. Here, we explore the specific effects of bromide, chloride, and the bulky, somewhat hydrophobic tosylate counterion on the adsorption of hexadecyltrimethylammonium surfactants (CTA(+)), the adsorption of polylysine (PL), and the co-adsorption of CTA(+) and PL on negatively charged silica surfaces. Similar to bulk self-assembly, increasing the micellar binding affinity of the counterion from chloride to bromide to tosylate promoted interfacial self-assembly in the absence of polylysine. During co-adsorption, the presence of the polylysine decreased the adsorbed amount of CTA(+) in all cases. Polylysine was more effective at hindering CTA(+) adsorption when the surfactant concentration was below the critical micelle concentration. Although these systems were strongly influenced by persistent nonequilibrium states, it was possible to demonstrate that polylysine was able to prevent CTA(+) admicelle formation below the cmc only when the thermodynamic driving forces for adsorption of the polymer and the surfactant were comparable. Solution compositions where that condition was met depended on the identity of the counterion. Below the bulk cmc, CTAT adsorption displayed the greatest degree of cooperativity, and it also was the most susceptible to hindered adsorption by polylysine.

Journal Article↗
PubMed2002

Formation and structure of polyelectrolyte and nanoparticle multilayers: effect of particle characteristics.

The formation and structure of multilayer films containing a cationic polyelectrolyte and anionic silica nanoparticles were studied by means of ellipsometry and atomic force microscopy. Three types of silica particles of different sizes were examined. The density and thickness of the films as well as the adsorption kinetics appear to be strongly dependent on the choice of particle; smaller particles favor the formation of smooth and dense films with a higher content of the inorganic component.

Journal Article↗
PubMed1988

Phase I trial of the polyelectrolyte carbetimer administered i.v. once every four weeks.

Carbetimer, a new synthetic low molecular weight polyelectrolyte with a novel structure displayed antitumor activity in a number of animal tumor model systems and in vitro investigations. Based on these findings it was brought to a phase I clinical trial in patients with advanced malignant disease after failure of conventional treatment or with no conventional treatment available. Forty-eight patients received 98 courses. The schedule was a one hour i.v. infusion every four weeks. The starting dose was 180 mg/m2 and dose escalation was performed according to a modified Fibonacci formula up to 16,690 mg/m2. At least three patients were treated at each dose level and each patient was eligible to receive repeat courses at the same dose, until progressive disease or dose-limiting toxicity intervened. No hematological toxicity was encountered. Some adverse effects such as reversible proteinuria, hypercalcaemia, pain at infusion site, nausea and vomiting and fatigue were seen partly in a dose-related manner but did not represent the maximum tolerated dose (MTD). The limiting toxicity at the highest dose level of 16,690 mg/m2 consisted of ocular symptoms ('light flashes') accompanied by a modest decrease of blood pressure and nausea or vomiting during a one hour infusion. 16,690 mg/m2/1 hour was considered the MTD. There were four deaths on study, all considered disease-related. Fourteen patients had stable disease for more than two courses, which, however, could also be explained by the natural course of disease. No clear-cut antitumor responses were noted in our study center. The recommended dose for phase II trials derived from our results is 12,550 mg/m2/2 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Poly-L-arginine and an N-formylated chemotactic peptide act synergistically with lectins and calcium ionophore to induce intense chemiluminescence and superoxide production in human blood leukocytes. Modulation by metabolic inhibitors, sugars, and polyelectrolytes.

Various cationic polyelectrolytes (poly-alpha-amino acids and histones), lectins, the chemotactic peptide, f-methionyl-leucyl-phenylalanine (fMLP), the calcium ionophore A23187, and phorbol myristate acetate (PMA) were investigated regarding their capacity to induce luminol-dependent chemiluminescence (LDCL) and superoxide production by human blood leukocytes. Although when tested individually, poly-L-arginine (PARG), phytohemagglutinin (PHA), concanavalin A (Con A), or fMLP induced only a low to moderate LDCL response, very intense synergistic CL reactions were obtained by mixtures of PARG + PHA, PARG + Con A, PARG + PHA + fMLP, Ca2 + ionophore + PARG + PHA + fMLP, and PARG + PMA. The sequence of addition of the various agents to WBC in the presence of luminol absolutely determined the intensity of the LDCL signals obtained, the highest reactions being achieved when the WBC were preincubated for 2-3 min with A23187 followed by the sequential addition of fMLP, PARG, and PHA. These "multiple hits" induced CL reactions which were many times higher than those obtained by each factor alone. On the other hand, neither poly-L-lysine, poly-L-ornithine, poly-L-histidine, nor poly-L-asparagine, when employed at equimolar concentrations, cooperated efficiently with PHA and fMLP to trigger synergistic LDCL responses in leukocytes. Concomitantly with the induction of LDCL, certain ligand mixtures also triggered the production of superoxide. The LDCL which was induced by the "cocktail" of agents was markedly inhibited by sodium azide (93% inhibition), but to a lesser extent by catalase (10% inhibition) or by superoxide dismutase (20%-60% inhibition). On the other hand, scavengers of singlet oxygen and OH (sodium benzoate, histidine) did not affect the synergistic LDCL responses induced by these multiple ligands. Cytochalasin B also markedly inhibited the LDCL responses induced either by soluble stimuli or by streptococci preopsonized either with histone or with polyanethole sulfonate. The LDCL responses which were induced by mixtures of PARG and concanavalin A were also strongly inhibited by mannose, alpha-methyl mannoside, and poly-L-glutamic acid. The data suggest that the LDCL responses induced by the soluble ligands involved a myeloperoxidase-catalyzed reaction. The possible employment of "cocktails" of ligands to enhance the bactericidal effects of PMNs, macrophages, and natural killer cells on microbial cells and mammalian targets is discussed.

Antimetabolites↗
PubMed1977

Effect of leukocyte hydrolases on bacteria. X. The role played by leukocyte factors, cationic polyelectrolytes, and by membrane-damaging agents in the lysis of Staphylococcus aureus: relation to chronic inflammatory processes.

A heat-stable factor present in extracts of human blood leukocytes is capable of lysing young Staphylococcus aureus at pH 5.0. Lysis is characterized by breakdown of cell-wall components as judged by electron microscopic and biochemical analysis. The leukocyte extracts can be replaced by a variety of agents known to injure cell membranes, e.g., leukocyte cationic protein histone, polymyxin B, colimycin, phospholipase A, and lysolecithin. The mechanisms by which all these agents bring about the degradation of the staphylococcal walls was studied. By using 14C-labeled cell walls devoid of cytoplasmic structures, it was demonstrated that none of the above-mentioned agents had a direct lytic effect on purified cell walls. On the other hand, when any of these agents first interacted with intact staphylococci, a factor (presumably an autolysin) was generated that directly lysed the cell walls. Lysis of cell walls in the presence of intact staphylococci used as a source of autolysin was strongly inhibited by a variety of anionic polyelectrolytes such as heparine and liquoid. The possible role played by bacterial autolysins in the generation of microbial cell-wall components capable of triggering chronic inflammation is discussed.

Bacteriolysis↗
PubMed1981

Modulation of the formation of the human C-3 amplification convertase of complement by polyelectrolytes.

Heparin in the fluid phase inhibits generation of the C3 amplification convertase of complement C3b,Bb. The anticomplementary activity requires the presence of O-sulfate groups on the molecule and is suppressed when the negative charges of heparin are neutralized with positive charges on polycations. In the absence of heparin, polycations inhibit generation of the cell-bound or fluid phase amplification convertase at final concentrations of 1 to 2 x 10(-8) M for poly-L- lysine 50,000 (PLL). PLL is more active on the D-dependent convertase C3b,Bb than in preventing generation of C3b,B; it does not alter the stabilizing effect of properdin. As for heparin, the major site of the inhibitory action of polycations is on the binding capacity of C3b for B. The low affinity interaction of C3b and B is a privileged site for potential pharmacologic modulation of the amplification convertase of complement by polyelectrolytes.

Binding Sites↗
PubMed1989

The dual role of polyelectrolytes and proteins as mineralization promoters and inhibitors of calcium oxalate monohydrate.

Polyelectrolytes and protein molecules appear to be able to act not only as crystallization inhibitors when present in solution, but also as promoters of crystal growth when immobilized onto surfaces. Because this is especially relevant for systems in which heterogeneous nucleation can occur, the influence of poly-L-glutamic (PGlu) acid, poly-L-aspartic (PAsp) acid, and human serum albumin (HSA) on the nucleation and growth inhibition of calcium oxalate monohydrate (COM) was studied using the Constant Composition (CC) kinetics technique. The overgrowth of COM on hydroxyapatite (HAP) seed crystals pretreated with HSA was also investigated. Pronounced differences in inhibiting and nucleating potential were found for the various additives. HSA, a relatively poor growth inhibitor when present in solution, was found to nucleate very regular, hexagonal COM crystals when immobilized on a surface and to enhance the overgrowth of COM when adsorbed on HAP surfaces.

Calcium Oxalate↗
PubMed1987

Counterion condensation in polyelectrolyte theory.

Condensation of counterions to a single, highly charged polyelectrolyte is formulated in terms of the two-dimensional coulomb gas theory of Kosterlitz and Thouless. The critical condensation criterion is calculated and is shown to vary as a function of the added salt concentration.

Electrolytes↗
PubMed2003

Application of polyelectrolyte complexes as novel pseudo-stationary phases in MEKC.

Polyacrylic acid (PAA) and polymethacrylic acid (PMAA) with carboxyl groups partially blocked by dodecyltrimethylammonium bromide (DTAB) and tetrabutylammonium bromide (TBAB) were tested as new pseudo-stationary phases in micellar electrokinetic chromatography (MEKC). The separation of was examined using PAA and PMAA. Excellent resolution of the substituted phenols and derivatized amino acids was demonstrated using additives of PAA-DTAB polyelectrolyte complex in the running phosphate buffer. It was found that the capacity factors were proportional to the concentration of the complex PAA/DTAB. Critical micelle concentration was effectively zero. It was found that the migration times and efficiency of separation of phenols and derivatives of amino acids depended on the type of polymers and alkyltrimethylammonium salts used.

Journal Article↗