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PubMed1998

Quantitative characterization of the binding of histamine by heparin.

Tissue histamine is stored in mast cell granules, presumably as a histamine-heparin complex. Heparin is a polyelectrolyte, with a fraction of its anionic charge neutralized by condensed counterions. The interaction of heparin with histamine in aqueous solution was quantitatively characterized by 1H nuclear magnetic resonance (NMR) spectroscopy. Binding constants were determined from chemical shift-pH titration data for the C2H proton of the imidazolium ring for a wide range of histamine, heparin, and Na+ concentrations. The results indicate a binding stoichiometry of 1 histamine per heparin disaccharide repeat unit. The binding is electrostatic, as indicated by the strong dependence of the binding constant on Na+ concentration. From an analysis of the binding constants using the counterion condensation theory of polyelectrolytes, it was determined that the binding of H2A2+ results in displacement of 1.72 Na+ ions from the counterion condensation volume of heparin and that H2A2+ makes 2 ionic interactions with heparin. The displacement of Na+ from the counterion condensation volume of heparin by H2A2+ was also studied by 23Na NMR. From 23Na spin-lattice relaxation time data, it was determined directly that 1.78 Na+ ions are displaced per H2A2+ bound by heparin. The results are discussed in terms of the ion exchange process which takes place when histamine is released by mast cells.

Animals↗
PubMed2000

Influence of alkali cation nature on structural transitions and reactions of biopolyelectrolytes.

A general thermodynamic analysis is presented, describing how counterion species of different nature, but the same valency, influence polyelectrolyte transformations and reactions of the general form: PA1.B1-M(+)-->PA2.B2M+ + (B1 - B2)M+. Here PA1 and PA2 are two different states or structural forms of a polyanion, B1 and B2 are the number of M+ ions thermodynamically bound to the polyanions PA1 and PA2, respectively. The specific effects of the two counterions, M1+ and M2+, on this equilibrium can be simply related to the quotient of their selectivity constants, D2M2M1/D1M2M1, for the polyion states 1 and 2. We analyze how different monovalent counterions (particularly, sodium and potassium) affect polyelectrolyte reactions and transformations such as, e.g., the DNA helix-coil transition. Previous experimental results on the competition between DNA and the synthetic polyanion, poly(methacrylic acid), for binding to the synthetic polycation, poly(N-ethylvinylpyridinium), has been investigated with respect to sodium and potassium ion specificity, using our model. We also discuss the DNA-histone disassembly/assembly reaction modeled as a competition of two polyanions for binding to a polycation.

Acrylates↗
PubMed2001

Rheology of sodium hyaluronate under physiological conditions.

Sodium hyaluronate NaHA in phosphate-buffered saline behaves as a typical polyelectrolyte in the high-salt limit, as Newtonian viscosities are observed over a wide range of shear rates. There is no evidence of intermolecule hydrogen bonding causing gel formation in NaHA solutions without protein present. The concentration dependences of viscosity, relaxation time, and terminal modulus are consistent with observations on flexible, neutral polymers in good solvents, which are known to be in the same universality class as flexible polyelectrolytes in the presence of excess salt.

Hyaluronic Acid↗
PubMedDate not supplied

Effect of polymer ionization on the interaction with DNA in nonviral gene delivery systems.

The optimization of DNA-cationic polymer complexation is crucial for nonviral gene delivery. Although physicochemical characterization of the interaction between DNA and cationic polymers has recently attracted more attention in the nonviral DNA delivery field, the literature on the effect of varying polycation charge density on DNA-cationic polymer complexation is still scarce. Thus, the aim of this study was to systematically assess the influence of the degree of ionization of a weak cationic polyelectrolyte (poly[2-(dimethylamino)ethyl methacrylate] or DMAEMA homopolymer) on its ability to form complexes with DNA. This was achieved by varying the solution pH from 4.0 to 8.0 and analyzing the resulting effects on the binding affinity, thermodynamic properties, complex size, and morphology. Lowering the solution pH led to higher degrees of ionization for the cationic polymer and hence greater binding affinities with DNA, as judged by the increased propensity of the former to displace ethidium bromide from DNA and also by relatively low monomer:nucleotide molar ratio (0.8:1) required to retard the migration of free DNA. Isothermal titration microcalorimetry studies further confirmed that a stronger interaction occurred at low pH than at high pH. By decreasing the pH from 8.0 to 6.6, K(obs) increased from 7.8 x 10(5) to 20.4 x 10(5) M(-1). More efficient condensation at low pH was demonstrated by the reduction of ethidium bromide fluorescence in the loading wells from gel electrophoresis, decreased complex sizes without agglomeration occurring at high polymer/DNA ratios, together with discrete and dense spherical complexes observed in TEM studies. This may be attributed to the presence of electrostatic stabilization from excess cationic polymer chains, which provide a repulsive shell around the polymer/DNA complex. The physicochemical data indicate that the increased degree of ionization for the DMAEMA homopolymer at lower pH results in higher binding affinity, smaller and more compact complexes, and more efficient condensation. These findings therefore highlight the importance of the degree of ionization on DNA complex formation for weak cationic polyelectrolytes.

Animals↗
PubMedDate not supplied

Surface engineering of poly(DL-lactide) via electrostatic self-assembly of extracellular matrix-like molecules.

We report the development of new biomacromolecule coatings on biodegradable biomaterials based on electrostatic assembly of extracellular matrix-like molecules. Poly(ethylene imine) (PEI) was employed to engineer poly(dl-lactide) (PDL-LA) substrate to obtain a stable positively charged surface. An extracellular matrix- (ECM-) like biomacromolecule, gelatin, was selected as the polyelectrolyte to deposit on the activated PDL-LA substrate via the electrostatic assemble technique. The extracellular matrix-like multilayer on the PDL-LA substrate was investigated by attenuated total reflection (ATR-FTIR), X-ray photoelectron spectrscopy (XPS), contact angle, and atomic force microscopy (AFM). The gradual buildup of the protein layer was investigated by UV-vis spectra, and it was further given a quantitative analysis of the protein layer on the PDL-LA substrate via the radioiodination technique. The stability of the protein layer under aqueous condition was also tested by the radiolabeling method. Chondrocyte was selected as the model system for testing the cell behavior and morphology on modified PDL-LA substrates. The chondrocyte test about cell attachment, proliferation, cell activity and cell morphology by SEM, and confocal laser scanning microscopy (CLSM) investigation on extracellular matrix-like multilayer modified PDL-LA substrate was shown to promote chondrocyte attachment and growth. Comparing conventional coating methods, polyelectrolyte multiplayers are easy and stable to prepare. It may be a good choice for the modification of 3-D scaffolds used in tissue engineering. These very flexible systems allow broad medical applications for drug delivery and tissue engineering.

Animals↗
PubMedDate not supplied

Loading the multilayer dextran sulfate/protamine microsized capsules with peroxidase.

Stable polyelectrolyte capsules were produced by the layer-by-layer (LbL) assembling of biodegradable polyelectrolytes, dextran sulfate and protamine, on melamine formaldehyde (MF) microcores followed by the cores decomposition at low pH. The mean diameter of the capsules at pH 3-5 was 8.0 +/- 0.2 microm, which is more than that diameter of the templates (5.12 +/- 0.15 microm). With pH growing up to 7-8, the capsules enlarged, swelling up to the diameter 9-10 microm. The microcapsules were loaded with horseradish peroxidase. Seemingly, peroxidase is embedded in the gellike structure in the microcapsule interior formed by MF residues in the complex with polymers used for LbL coating as proved by Raman confocal spectroscopy. The amount of finally incorporated peroxidase increased from 0.2 x 10(8) to 2.2 x 10(8) peroxidase molecules per capsule with pH growing from 5 to 8. The pH shifts causing changes in capsule swelling and the replacement of solutions without pH shifts lead to the protein loss. The encapsulated peroxidase showed a high activity (57%), which remained stable for 12 months.

Biocompatible Materials↗
PubMedDate not supplied

pH-responsive properties of multilayered poly(L-lysine)/hyaluronic acid surfaces.

Multilayer films have been prepared by the sequential electrostatic adsorption of poly(L-lysine) and hyaluronic acid onto charged silicon surfaces from dilute aqueous solutions under various pH conditions. Microelectrophoresis was used to examine the local acid-base equilibria of the polyelectrolytes within the films as a function of the total number of layers in the film and the assembly solution pH. The acid-base dissociation constants were observed to deviate significantly from dilute solution values upon adsorption, to be layer dependent only within the first 3-4 layers, and to show sensitivity to the assembly solution pH. As a result, some of the physicochemical properties of the films have also been found to exhibit pH-responsive behavior. For example, the thickest films result when at least one of the polyelectrolytes is only partially dissociated in solution. As well, the pH-dependent degree of dissociation of the surface functional groups can be used to vary the contact angle of a water droplet by as much as 25 degrees and the coefficient of friction by up to an order of magnitude. In addition, the extent to which PLL/HA films can be made to swell in solution can be varied by a factor of 7 depending on the assembly solution and swelling solution pH. The anomalies found in the dissociation constants account for the trends in these pH-dependent properties. Here, we demonstrate that knowledge of the acid-base dissociation behavior in multilayer films is key to understanding and controlling the physical properties of the films, particularly surface friction and wettability, which are fundamentally important factors for many biomaterials applications. For example, we outline a mechanism whereby biopolymer thin films can be electrostatically adsorbed under highly charged "sticky" conditions and then quickly transformed into stable low-friction films simply by altering the pH environment.

Biocompatible Materials↗
PubMedDate not supplied

Characterization of nanostructure of stimuli-responsive polymeric composite membranes.

To elucidate the mechanism of stimuli-responsive permeability and to optimize the design, the nanostructure of polymeric composite membranes, developed in our laboratory, was characterized. The membranes were prepared to contain various amounts of stimuli-responsive nanoparticles of poly(N-isopropylacrylamide-co-methacrylic acid), with or without polyelectrolyte coating. Scanning electron microscopy and X-ray photoelectron spectroscopy were used respectively to examine the morphology and surface chemical composition, whereas atomic force microscopy and laser scanning confocal microscopy were employed to characterize the in situ surface and internal structure of the membranes in aqueous media of various pHs. The porous structure was evidenced in the presence of the nanoparticles. The surface content of the nanoparticles increased with increasing particle concentration while the polyelectrolyte coating was nearly undetectable. AFM images revealed that the particles in the membranes shrank with a concomitant increase in pore size as the buffer pH decreased. LSCM results indicated that particles were distributed through the membrane as interconnected clusters.

Acrylamides↗
PubMedDate not supplied

Ultrathin antibiotic walled microcapsules.

Ultrathin microcapsules comprised of anionic polyelectrolytes (PE) and a polycationic aminoglycoside (AmG) antibiotic drug were prepared by depositing PE/AmG multilayers on zinc oxide (ZnO) colloid particles using the layer-by-layer self-assembly technique and subsequently dissolving the ZnO templated cores. The polyelectrolytes, dextran sulfate sodium (DxS) and poly(styrenesulfonate) (PSS), were selected owing to their different backbone structure. An aminoglycoside, tobramycin sulfate (TbS), was used for studying DxS/TbS or PSS/TbS multilayer films. The multilayer growth on ZnO cores was characterized by alternating zeta potential values that were different for the DxS/TbS and PSS/TbS multilayers due to the PE chemistry and its interaction with Zn(2+) ions. Transmission and scanning electron microscopy provide evidence of PE/TbS multilayer coating on ZnO core particles. The slow acid-decomposition of the ZnO cores using weak organic acids and the presence of sufficient quantity of Zn(2+) in the dispersion were required to produce antibiotic multilayer capsules. There was no difference in the morphological characteristics of the two types of capsules; although, the yield for [PSS/TbS](5) capsules was significantly higher than for [DxS/TbS](5) capsules which was related to the physicochemical properties of DxS/TbS/Zn(2+) and PSS/TbS/Zn(2+) complexes forming the capsule wall. The TbS quantity in the multilayer films was determined using a quartz crystal microbalance and high performance liquid chromatography techniques which showed less TbS loading in both, capsules and multilayers on planar gold substrate, than the theoretical DxS:TbS or PSS:TbS stoichiometric ratio. The decomposition of the [PE/TbS](6) multilayers was fastest in physiological buffer followed by mannitol and water. The decomposition rate of the [PSS/TbS](6) multilayers was slower than [DxS/TbS](6) monolayers. The incomplete decomposition of DxS/TbS under saline conditions suggests the major role of hydrogen bonding for stability of DxS/TbS multilayers. A combination of hydrogen bonding and hydrophobic interaction between phenyl rings in PSS was responsible for PSS/TbS multilayer stability. In vivo studies in rabbits highlight the safety and sustained drug delivery potential of the PE/AmG microcapsules. The antibiotic walled ultrathin capsules presented here are suitable for sustained ophthalmic antibiotic delivery.

Aminoglycosides↗
PubMed2006

Coating of DNA/poly(L-lysine) complexes by covalent attachment of poly[N-(2-hydroxypropyl)methacrylamide].

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers (pHPMA) containing 4-nitrophenyl ester (ONp) or thiazolidine-2-thione (TT) reactive groups in side chains and telechelic/semitelechelic pHPMA with TT groups were designed as highly hydrophilic biocompatible polymers suitable for chemical coating of polyelectrolyte-based DNA-containing nanoparticles bearing amino groups on the surface. The course of the coating reaction carried out in aqueous solution was evaluated on model self-assembling polyelectrolyte DNA/poly(L-lysine) (DNA/PLL) complexes either by monitoring the amount of residual polymer reactive groups by UV spectroscopy or by monitoring changes in the weight-average molecular weight and hydrodynamic size of the complexes using light scattering methods. Physicochemical stability of the coated complexes in buffered saline solution was also investigated. Contrary to uncoated particles, the coated complexes showed remarkable stability to aggregate in 0.15 M NaCl. Coating with pHPMA had practically no effect on the size distribution of the most stable complexes prepared by complexation of DNA with high-molecular-weight PLL (M(w) = 134 000) as shown by dynamic light scattering. The coating reaction was faster and more efficient with multivalent HPMA copolymers containing TT reactive groups than that with HPMA copolymers containing ONp groups.

Amination↗
PubMed2006

Effect of polycation length on its complexation with DNA and with poly(oxyethylene-block-sodium methacrylate).

Polyelectrolyte complexes of a synthetic polycation with either a genomic DNA or a synthetic poly(oxyethylene-block-sodium methacrylate), POE-b-PMANa, have been studied in aqueous solutions as a function of cation:anion ratio, the degree of polymerization of the polycation, the ionic strength, and temperature using dynamic light scattering and turbidity measurements. The polycation was a copolymer of methacryl oxyethyl trimethylammonium chloride and poly(oxyethylene) monomethyl ether monomethacrylate with 4-5 oxyethylene repeating units, PMOTAC-g-POE. The molar masses of the polycations in a homological series were 0.3, 0.9, and 2.1 x 10(6) g/ mol. The amount of comonomers with poly(oxyethylene) tails in the copolymers was 15 mol %. The molar mass of the POE-b-PMANa was 75000 g/mol and that of the POE-block was 5000 g/mol. The molar mass of the polycation was shown to have a dramatic effect on the stability and size of the complexes formed by either of the polyanions. An increase in the polycation molar mass shifts the cloud point toward the lower polycation content in the complexes, and a macro phase separation occurs in the solutions with the cation to anion molar ratios much below than 1:1. Increasing the ionic strength has a similar effect. Further addition of salt to turbid and phase-separated solutions results in dissociation of the complexes, and the polyions dissolve as individual macromolecules. The effect of POE on the stability of polyelectrolyte complexes is discussed as well.

Cations↗
PubMedDate not supplied

Fine tuning of physical properties of designed polypeptide multilayer films by control of pH.

Adjustment of pH can alter the ensemble of three-dimensional structures of a polypeptide in solution by changing the distribution of charge and Coulombic interactions. The role of pH in layer-by-layer self-assembly (LbL) of designed 32mer peptides containing the amino acid cysteine has been investigated using a combination of physical methods. Results show that pH can have a substantial influence on the mass of adsorbed peptide, surface roughness, and film density over a range of 1.5 pH units. Peptide film thickness depends on the number of layers, as with "conventional" polyelectrolytes. Film density and morphology, however, vary more with pH than does thickness, translating into a change in density on the order of 70% over the pH range 7.4-8.9. Results of this work provide insight on the physical basis of LbL and suggest that peptides are a promising class of polyelectrolytes for the creation of designer thin films for applications in biotechnology and other areas.

Amino Acid Sequence↗
PubMed1999

Strategies for recombinant protein recovery from canolaby precipitation

Transgenic plants may prove to be one of the most economical systems for the large-scale production of proteins and peptides. Our goal is to develop an approach for protein recovery from canola that will be adaptable to a wide variety of recombinant proteins. For recombinant protein recovery, the two downstream processes considered were extraction of target protein and purification of recombinant protein from host proteins and other impurities. In these experiments, T4 lysozyme has been added to the canola extracts as an example protein to simulate recovery of recombinant proteins while evaluating the merits of several candidate precipitation strategies to understand selectivity behavior and how it might be affected by the presence of canola components. The ability of precipitating agents, such as acid and the polyelectrolytes Glass H and poly(acrylic acid) (PAA), was investigated. Approximately 70% of extracted canola proteins were precipitated by acid addition to pH 5, leaving about 90% of T4 lysozyme still in solution. Targeting T4 lysozyme for the precipitate phase by addition of oppositely charged polyelectrolyte was not successful in the presence of canola components. Addition of 2.5 times the PAA dosage required to precipitate pure T4 lysozyme to the spiked canola extract brought down only 40% of the T4 lysozyme. For the comparable result with Glass H, a 9 times higher dosage was required.

Journal Article↗
PubMed2002

Analysis of trace metal humic acid interactions using counterion condensation theory.

Recent extensions of counterion condensation theory, originally developed for well-defined linear polyelectrolytes, enable us to analyze the interaction of trace metals with humic acid. In the present model, the heterogeneity of the macromolecule is taken into account as well as the chemical binding of the considered metal ions to the humic material. Experimentally, potentiometric titrations have been performed for humic acid in solution in the presence of different environmentally important (heavy) metals (Ca, Cd, Cu, Ni, and Pb) at various metal concentrations by titrating with potassium hydroxide without additional salt. From proton release data obtained for the initial point in the titration, it was estimated that the interaction of the different metals with the humic acid in terms of binding strength increased in the order Ca < Cd approximately = Ni < Pb approximately = Cu. These results were confirmed by model analysis. Experimentally obtained apparent dissociation constants were in good agreement for the humic acid systems containing Ca, Cd, and Ni at concentrations ranging from 0 up to 0.75 x 10(-3) mol L(-1) and polymer dissociation degree from about 0.1 up to approximately 0.8. Also for the Cu/humic acid and Pb/humic acid systems, the agreement between experimental data and calculated data was satisfactory atthe lowest metal concentrations over the complete titration curve. For elevated levels of Cu and Pb, the agreement between experimental data and theoretical calculations becomes less satisfactory at low degrees of dissociation of the humic acid. This distortion of the potentiometric curves is probably due to changes in the intrinsic pK of the functional groups due to metal binding. This complex process is not included in present polyelectrolytic models.

Chemical Phenomena↗
PubMed2001

Salinity effect on mechanical dewatering of sludge with and without chemical conditioning.

The salinity levels of wastewater and sludge are relatively high in some coastal cities as they may use saline water for toilet flushing, and as such,the sludge dewaterability can be affected by it. The salinity effect on sludge dewaterability was therefore investigated through experimental testing of specific resistance in filtration (SRF), time to filter (TTF), and final solid content of sludge. SRF and TTF were determined using Buchner funnel tests. The final solid content was estimated by centrifuging the sludge at four levels of rotational speed. Sludge with three salinity levels (5,000, 10,000 and 20,000 ppm) were considered in this study. Coagulants such as alum, iron(II) sulfate, and organic polyelectrolytes were added to the sludgetostudythe dewaterability of such sludge with chemical conditioning. Experimental results show that doubling the salinity level of the sludge from 10,000 to 20,000 ppm shows not much change in SRF and TTF. Compared with the sludge without chemical conditioning, the addition of the coagulants to the sludge at a salinity level of 5,000 ppm drastically reduces its SRF and TTF. However, sludge with and without chemical conditioning at a salinity of 20,000 ppm has similar SRF and TTF. The final solid content of sludge increases almost linearly with salinity. Among the coagulants used in this study, the cationic polyelectrolyte is found to be better in improving sludge dewaterability, while iron(II) sulfate performs slightly better in enhancing the final solid content of the sludge.

Particle Size↗
PubMed2001

Two modes of linear layer-by-layer growth of nanoparticle--polylectrolyte multilayers and different interactions in the layer-by-layer deposition.

The structure of the multilayer assemblies of yttrium iron garnet nanoparticles (YIG) with polyelectrolytes was investigated with the emphasis on the control of the particle density in the adsorption layers. It was found that the growth of YIG films prepared by the layer-by-layer assembly can occur via two deposition modes: (1) sequential adsorption of densely packed adsorption layers (normal growth mode) and (2) in-plane growth of isolated particle domains (lateral expansion mode). Importantly, the dependence of the optical density on the number of deposition cycles remains linear in both cases. Microscopy results indicate that the origin of the lateral growth is in the interplay of particle/particle and particle/polyelectrolyte interactions rather than in a substrate effect. The lateral expansion mode is a general attribute of the layer-by-layer deposition and can be observed for various aqueous colloids. For the preparation of sophisticated multifunctional assemblies on nanoparticles, the film growth via domain expansion should be avoided, and therefore, one must be able to control the growth pattern. The switch from lateral to normal growth mode can be effected by grafting charged organic groups to YIG nanoparticles. Hydrophobic interactions between the hydrocarbon groups of the modified YIG and polyelectrolyte significantly increase the attractive component of the particle/polyelectrolyte and particle/particle interactions. The films from modified YIG display densely packed nanoparticle layers with a greatly reduced number of defects.

Journal Article↗
PubMed2002

Superquenching in cyanine pendant poly(L-lysine) dyes: dependence on molecular weight, solvent, and aggregation.

A series of poly(L-lysines) ranging in number of repeat units (N(PRU)) from 6 to 900 has been synthesized and the photophysics of the series and monomer cyanine dye have been studied in solution. In water or aqueous dimethyl sulfoxide, the oligomers and polymers exhibit high sensitivity to fluorescence quenching by oppositely charged electron acceptors; in this study, 9,10-anthraquinone-2,6-disulfonate was used as a quencher for the cationic fluorescent polyelectrolytes. Quenching constants (K(SV)) measured in 50:50 (v/v) dimethyl sulfoxide-water increase monotonically with increase in N(PRU) ranging from 630 M(-1) for monomer to 1.2 x 10(9) M(-1) for dilute solutions of the polymer having N(PRU) approximately 900. The polymers having N(PRU) > 100 exhibit predominantly J-aggregate absorption and fluorescence and enhanced susceptibility to quenching. For the polymers exhibiting strong J-aggregation, the effective exciton domain quenched by a single quencher reaches approximately 100 PRU. The results of this study permit a semiquantitative analysis of superquenching of fluorescent polyelectrolytes in solution and the factors that control it.

Carbocyanines↗
PubMed2002

The structure of self-assembled multilayers with polyoxometalate nanoclusters.

Using electrostatic layer-by-layer self-assembly (ELSA), the formation of multilayers with polyelectrolytes and nanoscopic polyoxometalate (POM) clusters of different sizes and charges is investigated. The multilayers are characterized by UV-vis absorption spectroscopy, optical ellipsometry, cyclic voltammetry, and atomic force microscopy. In all cases, it is possible to find experimental conditions to achieve irreversible adsorption and regular multilayer deposition. Most importantly, the surface coverage is directly related to the total charge of the POM anion and can be controlled from submonolayer to multilayer coverage by adjusting the ionic strength of the dipping solutions. Imaging the interfaces after POM deposition by atomic force microscopy reveals a granular surface texture with nanometer-sized features. The average interfacial roughness amounts to approximately 1 nm. Cyclic voltammetry indicates that the electrochemical properties of the POM clusters are fully maintained in the polyelectrolyte matrix, which opens a route toward practical applications such as sensors or heterogeneous catalysts. Moreover, the permeability toward electrochemically active probe molecules can be tailored through the multilayer architecture and deposition conditions. Finally, we note that despite the low total charge and comparably small size of the discrete POM anions, the multilayers are remarkably stable. This work provides basic guidelines for the assembly of POM-containing ELSA multilayers and provides detailed insight into characteristic surface coverage, permeability, and electrochemical properties.

Journal Article↗