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PubMed2005

Layered polyelectrolyte-silica coating for nanocapsules.

This paper demonstrates the ability to grow silica directly on a deposited surface of polyelectrolyte. Using this strategy, we describe the deposition of layered polyelectrolyte-silica coating on negatively charged surfaces of polystyrene particles and latex nanocapsules, which could not be coated directly with silica alone. By etching away the underlying polystyrene bead, we were able to form polyelectrolyte-silica capsules that were mechanically robust. Using scanning and transmission electron microscopy, we imaged and studied the coating after the deposition of each layer of polyelectrolyte and silica. We then applied this new coating to latex nanocapsules that were loaded with fluorescein molecules. We found that the coating procedure did not cause the loaded molecules to leak out from the capsules, and we determined that the variation in the number of loaded molecules among capsules arose from differences in the volume of the nanocavities and was not caused by the loading and coating of the capsules. This layered architecture permits the thickness of the coating to be controlled in principle over a wide dynamic range, but more importantly, this coating could act as an effective seal to prevent undesired leakage from nanocapsules and thus increase the long-term storability of loaded capsules. Over a 30-day period, we determined that leakage from uncoated capsules was significant but negligible for ones that were coated with two layers of polyelectrolyte-silica. Using single-pulse UV photolysis of individual nanocapsules, we demonstrate that the molecules contained within coated capsules could be released effectively and on demand with a single laser pulse.

Journal Article↗
PubMed2005

High catalytic activity of platinum nanoparticles immobilized on spherical polyelectrolyte brushes.

We present a study on the catalytic activity of platinum nanoparticles immobilized on spherical polyelectrolyte brushes that act as carriers. The spherical polyelectrolyte brushes consist of a solid core of poly(styrene) onto which long chains of poly(2-methylpropenoyloxyethyl) trimethylammonium chloride are grafted. These positively charged chains form a dense layer of polyelectrolytes on the surface of the core particles ("spherical polyelectrolyte brush") that tightly binds divalent PtCl6-(2) ions. The reduction of these ions within the brush layer leads to nearly monodisperse nanoparticles of metallic platinum. The average size of the particles is approximately 2 nm. The composite particles exhibit excellent colloidal stability. The catalytic activity is investigated by photometrically monitoring the reduction of p-nitrophenol by an excess of NaBH4 in the presence of the nanoparticles. The kinetic data could be explained by the assumption of a pseudo-first-order reaction with regard to p-nitrophenol. In all cases, a delay time t0 has been observed, after which the reactions start. This time is shorter when the catalyst has already been used. All data demonstrate that spherical polyelectrolyte brushes present an ideal carrier system for metallic nanoparticles.

Journal Article↗
PubMed2006

Increased layer interdiffusion in polyelectrolyte films upon annealing in water and aqueous salt solutions.

As-deposited films of multilayered polyelectrolytes are considered to be non-equilibrium structures. Due to the strong attraction between oppositely charged polyions, polyelectrolyte interdiffusion is thought to be suppressed during the adsorption process. Equilibration is promoted by a decrease of the electrostatic attraction between polyion pairs. We have used neutral impact collision ion scattering spectroscopy to investigate the influence of polyelectrolyte multilayer annealing in water and aqueous 1 M NaCl solutions at different temperatures (20 and 70 degrees C) on the increase in interpenetration of a single polyelectrolyte layer throughout the whole film. The multilayers were composed of poly(4-vinylpyridinium) and poly(4-styrenesulfonate). Contrast between neighboring layers was established by labelling the layer in question with the heavy atom ruthenium. It is found that both temperature and salt increase layer interpenetration, whereas salt has a stronger influence than temperature. From numerical simulations polyelectrolyte diffusion coefficients were evaluated for the different annealing conditions. The influence of temperature and salt on the equilibration of the film is interpreted in terms of increased screening of polyion charges and binding of small counterions to polyion monomeric units.

Journal Article↗
PubMed2004

Poisson-Boltzmann theory of the charge-induced adsorption of semi-flexible polyelectrolytes.

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson-Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Angstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson-Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)].

Adsorption↗
PubMed2005

Fluorescence correlation spectroscopy studies of diffusion of a weak polyelectrolyte in aqueous solutions.

We apply fluorescent correlation spectroscopy (FCS) to investigate solution dynamics of a synthetic polyelectrolyte, i.e., a weak polycarboxylic acid in aqueous solutions. The technique brings single molecule sensitivity and molecular specificity to dynamic measurements of polyelectrolyte solutions. Translational diffusion of Alexa-labeled poly(methacrylic acid), PMAA*, chains was studied in very dilute, 10(-4) mg/ml, solutions as a function of solution pH and ionic strength. The observed changes in diffusion coefficients were consistent with about twofold expansion of PMAA* coils when pH was changed from 5 to 8, and with chain contraction for alkaline metal ion concentrations from 0.01 to 0.1 M. The dependence of the hydrodynamic size of PMAA* chains on the counterion type followed the sequence: Li(+)>Na(+) approximately equal to Cs(+)>K(+). The dependence of translational diffusion on polyacid concentration was weak at the low concentration limit, but chain motions were significantly slower at higher polymer concentrations when PMAA chains overlapped. Finally, measurements of dynamics of PMAA* chains in "salt-free" solutions showed that self-diffusion of PMAA* chains significantly slowed down when PMAA concentration was increased, probably reflecting the sensitivity of PMAA* translational motions to the onset of interchain domain formation. These results illustrate the utility of the FCS technique for studying hydrodynamic sizes of polyelectrolyte coils in response to variation in solution pH or concentration of salt and polyelectrolytes. They also suggest that FCS will be a promising technique for selective observation of the dynamics of polyelectrolyte components in complex polymer mixtures.

Colloids↗
PubMed2004

Amplified fluorescence sensing of protease activity with conjugated polyelectrolytes.

Fluorescent conjugated polyelectrolytes with pendant ionic sulfonate and carboxylate groups are used to sense protease activity. Inclusion of the fluorescent conjugated polyelectrolyte into the assay scheme leads to amplification of the sensory response. The sensing mechanism relies on an electrostatic interaction between the conjugated polyelectrolyte and a peptide substrate that is labeled with a fluorescence quencher. Enzyme activity and hydrolysis kinetics are measured in real time by using fluorescence spectroscopy. Two approaches are presented. In the first approach, a fluorescence turn-on sensor was developed that is based on the use of p-nitroanilide-labeled peptide substrates. In this system enzyme-catalyzed peptide hydrolysis is signaled by an increase in the fluorescence from the conjugated polyelectrolyte. The turn-on system was used to sense peptidase and thrombin activity when the concentrations of the enzyme and substrate are in the nanomolar regime. Kinetic parameters were recovered from real-time assays. In the second approach, a fluorescence turn-off sensor was developed that relies on a peptide-derivatized rhodamine substrate. In the turn-off system enzyme-catalyzed peptide hydrolysis is signaled by a decrease in the fluorescence intensity of the conjugated polyelectrolyte.

Endopeptidases↗
PubMed1997

On the difference in ionization properties between planar interfaces and linear polyelectrolytes.

Ionizable planar interfaces and linear polyelectrolytes show markedly different proton-binding behavior. Planar interfaces protonate in a single broad step, whereas polyelectrolytes mostly undergo a two-step protonation. Such contrasting behavior is explained using a discrete-charge Ising model. This model is based on an approximation of the ionizable groups by point charges that are treated within a linearized Poisson-Boltzmann approximation. The underlying reason as to why planar interfaces exhibit mean-field-like behavior, whereas linear polyelectrolytes usually do not, is related to the range of the site-site interaction potential. For a planar interface, this interaction potential is much more long ranged if compared with that of the cylindrical geometry as appropriate to a linear polyelectrolyte. The model results are in semi-quantitative agreement with experimental data for fatty-acid monolayers, water-oxide interfaces, and various linear polyelectrolytes.

Electrolytes↗
PubMed1991

Polyelectrolyte effects on 9-aminoacridine-DNA binding.

The 9-aminoacridine-DNA binding curve is analyzed in two ways: with polyelectrolyte effects neglected and with polyelectrolyte effects included. It is found that the analysis which includes polyelectrolyte effects is consistent with the violation of neighbor exclusion displayed by diacridine complexes as observed by Atwell et al. and by Zimmerman and coworkers. However the analysis which neglects polyelectrolyte effects is inconsistent with the diacridine results. This comparison supports the necessity of including polyelectrolyte effects in the analysis of drug-DNA binding curves.

Aminacrine↗
PubMed2003

A physico-chemical approach of polyanion-polycation interactions aimed at better understanding the in vivo behaviour of polyelectrolyte-based drug delivery and gene transfection.

Polyanions and polycations are known to interact electrostatically and form soluble or insoluble polyelectrolyte complexes. Body fluids, blood and cells are composed of many polyelectrolytic systems such as proteins, glycoproteins, poly(glycosamino glycane)s, polynucleotides, etc. under physiological conditions. Nowadays synthetic polyelectrolytes are proposed as carriers of bioactive compounds, such as drugs and genes, and are thus to be injected into body fluids. For the sake of better understanding the complex behaviour of such artificial polyelectrolytic systems in the pool of natural polyelectrolytes forming living systems, interactions of bi- and multi-components mixtures of synthetic polyanions with the same synthetic polycation, namely poly[(dimethylaminoethyl) methacrylate], HCl, were investigated under the conditions imposed by physiological media, namely pH = 7.4, ionic strength mu = 0.15 and T = 37 degrees C. The selected artificial polyanions were the sodium salts of poly(acrylic acid), poly(methacrylic acid), poly(L-lysine citramide) and poly(styrene sulfonic acid) which have different acid strength, charge density and ionogenic group. The influence of ionic strength and pH on complex formation and stability was investigated by turbidimetry at lambda = 520 nm. Phase separation occurred regardless of ionic strength in the case of sodium polystyrene sulfonate. For the other polyanions, redissolution was observed at critical NaCl concentrations much higher than the physiological ionic strength. In the case of mixtures of two or three polyanions with the polycation, the complex formation appeared polyanion-selective at physiological ionic strength. Data are discussed with regard to phenomena that can occur in vivo.

Acrylic Resins↗
PubMed2001

Spherical polyelectrolyte brushes: comparison between annealed and quenched brushes.

We report on a study of spherical polyelectrolyte brushes that consist of a solid core onto which linear polyelectrolyte chains are chemically grafted. The core particles are made up of solid poly(styrene) and have a radius R of ca. 50 nm. As polyelectrolyte chains the weak polyelectrolyte poly(acrylic acid) or the strong polyelectrolyte poly(styrenesulfonate) was used. These chains were generated directly on the surface of the core particles by a grafting-from technique. Hence, the chains are chemically bound to the surface but can be cleaved off and analyzed separately. The contour length L(c) and the number of grafted chains per unit area sigma can thus be determined accurately. The thickness L of the brush layer on the surface has been determined by dynamic light scattering. It is measured for different L(c)/R as a function of pH, ionic strength, and valency of counterions. Annealed brushes exhibit a transition with increasing pH in which the chains are stretched to nearly full length. This can be traced back to the building up of the osmotic pressure of the counterions. The brush height L decreases considerably with increasing ionic strength, most notably when adding divalent ions. The entire set of L as a function of R, L(c), and sigma can be fully explained in terms of a simple two-parameter theory developed by Hariharan et al. [Macromolecules 31, 7514 (1998)].

Journal Article↗
PubMed2002

Conformation of a polyelectrolyte complexed to a like-charged colloid.

We report results from a molecular dynamics simulation on the conformations of a long flexible polyelectrolyte complexed to a charged sphere, both negatively charged, in the presence of neutralizing counterions in the strong Coulomb coupling regime. The structure of this complex is very sensitive to the charge density of the polyelectrolyte. For a fully charged polyelectrolyte the polymer forms a dense two-dimensional "disk," whereas for a partially charged polyelectrolyte the monomers are spread over the colloidal surface. A mechanism involving the overcharging of the polyelectrolyte by counterions is proposed to explain the observed conformations.

Colloids↗
PubMed2002

Dissolution of a polyelectrolyte-macroion complex by addition of salt.

The dissolution of complexes formed by a linear polyelectrolyte and oppositely charged macroions by addition of salt has been examined by employing a simple model with focus on the electrostatic interactions and solved by Monte Carlo simulations. In the absence of salt an overcharged complex appears. Upon addition of salt, the number of complexed macroions is continuously decreasing, the effect being similar for flexible and stiff polyelectrolytes. Regarding the flexible polyelectrolyte, the number of polyelectrolyte-macroion contacts is reduced, whereas it remains nearly constant for the stiff polyelectrolyte as the salt content is increased. A screened Coulomb potential of the Debye-Hückel type, in which the small ions are only indirectly described, displays a good representation of the system.

Journal Article↗
PubMed2005

Spatial distribution of protein molecules adsorbed at a polyelectrolyte multilayer.

The spatial distribution of protein molecules interacting with a planar polyelectrolyte multilayer was determined using neutron reflectometry. Staphylococcal nuclease (SNase) was used as model protein that was adsorbed to the multilayer at 22 degrees C and 42 degrees C. At each temperature, the protein solution was adjusted to pD -values of 4.9 and 7.5 to vary the net charge of the protein molecules. The multilayer was built up on a silicon wafer by the deposition of poly(ethylene imine) (PEI), poly(styrene sulfonate) (PSS), and poly(allylamine hydrochloride) (PAH) in the order Si-PEI-PSS- (PAH-PSS)(5). Applying the contrast variation technique, two different neutron reflectivity curves were measured at each condition of temperature and pD -value. From the analysis of the curves, protein density profiles normal to the interface were recovered. Remarkably, it has been found that SNase is partially penetrating into the polyelectrolyte multilayer after adsorption at all conditions studied. The measured neutron reflectivities are consistent with a penetration depth of 50 A at pD=4.9 and 25 A at pD=7.5. Since SNase has an isoelectric point of pH=9.5, it carries a net positive charge at both pD -values and interacts with the PSS final layer under electrostatic attraction conditions. However, when increasing the temperature, the amount of adsorbed protein is increasing at both pD -values indicating the dominance of entropic driving forces for the protein adsorption. Interestingly, at pD=4.9 where the protein charge is relatively high, this temperature-induced mass increase of immobilized protein is more pronounced within the polyelectrolyte multilayer, whereas at pD=7.5, closer to the isoelectric point of SNase, raising the temperature has mainly the effect to accumulate protein molecules outside the polyelectrolyte multilayer at the water interface. It is suggested that the penetration of SNase into the polyelectrolyte multilayer is related to a complexation mechanism. The complexation is essentially entropic in nature due to the release of counterions.

Adsorption↗
PubMed2005

Solvent quality influence on the dielectric properties of polyelectrolyte solutions: a scaling approach.

The dielectric properties of polyelectrolytes in solvent of different quality have been measured in an extended frequency range and the dielectric parameters associated with the polarization induced by counterion fluctuation over some peculiar polyion lengths have been evaluated. Following the scaling theory of polyelectrolyte solutions and the recent models developed by Dobrynin and Rubinstein that explicitly take into account the quality of the solvent on the polyion chain conformation, we have reviewed and summarized a set of scaling laws that describe the dielectric behavior of these systems in the dilute and semidilute regime. Moreover, for poorer solvents, where theory of hydrophobic polyelectrolytes predicts, and computer simulation confirms, a particular chain structure consisting of partially collapsed monomers (beads) connected by monomer strings, we derived a scaling law. These predictions are compared with the results obtained from the dielectric parameters (the dielectric increment delta epsilon and the relaxation time tau(ion)) of the "intermediate" frequency relaxation of two partially charged polymers, which possess a carbon-based backbone for which water is a poor solvent and ethylene glycol is a good solvent. By varying the solvent composition (a water-ethylene glycol mixture), we have tuned the quality of the solvent, passing from poor to good condition and have observed the predicted scaling for all the systems investigated. These findings give a further support to the scaling theory of polyelectrolyte solutions and to the necklace model for hydrophobic polyelectrolytes in poor solvents.

Journal Article↗
PubMed2002

Polyelectrolyte multilayer films modulate cytoskeletal organization in chondrosarcoma cells.

The aim of this study was to evaluate polyelectrolyte multilayer films as interfaces for implants. Polyelectrolyte multilayers were built up with different terminating layers by alternate deposition of oppositely charged polyelectrolytes on which chondrosarcoma (HCS-2/8) cells were grown in the presence of serum. Films formed by an increasing number of layers were investigated. The terminating layer was made of one of the following polyelectrolytes: poly-sodium-4-styrenesulfonate (PSS), poly-L-glutamic acid (PGA), poly-allylamine hydrochloride (PAH), or poly(L-lysine) (PLL). Cell viability, inflammatory response, adherence, and cytoskeletal organization were studied. Induction of interleukin-8 (IL-8) secretion was detected on PAH and PLL ending polyelectrolyte films. Early cellular adherence was enhanced with PGA, PAH, PLL, and, to a lower extent, PSS terminating layers. Adherence was independent of the number of layers constituting the films. The presence of actin filaments and vinculin focal adhesion spots was observed on PSS or PAH ending films. They were respectively partially and totally absent on PGA and PLL terminating multilayer architectures. For PLL ending films, vinculin and actin organization was clearly dependent on the number of deposited layers. The results of this study suggest that PSS ending multilayered films constitute a good interfacial micro-environment at the material surface for HCS-2/8 cells.

Actins↗
PubMed2005

Drug release from complexes with a series of poly(carboxyalkyl methacrylates), a new class of weak polyelectrolytes.

Carboxyalkyl methacrylates, a new class of non-cross-linked, hydrophobic weak polyelectrolytes, were synthesized, and then bound to cationic drugs (propranolol.HCl, diltiazem.HCl and verapamil.HCl) to form water-insoluble complexes that release the bound drug only in ionic media (pH 7.4). Compressed tablets were prepared from these cation exchange polyelectrolytes. Release profiles followed zero order kinetics (n>0.90; n is the release exponent). As the hydrophobicity of the polyelectrolytes increased, the rate of release decreased and deviated from linearity (n=0.7). Both the ionic strength of the medium as well as the solubility of the drug affected the rate of release. In acidic media (pH 1.2) a burst of drug was released but the release was halted by a layer of non-ionized polymer precipitated on the surface of the tablets. The results indicate that it is possible to "tailor-make" the release kinetics by using a polyelectrolyte from the series with the suitable hydrophobicity.

Cations↗
PubMed2004

Novel formulations of vitamins and insulin by nanoengineering of polyelectrolyte multilayers around microcrystals.

Microcapsules loaded with vitamin K3 (VK3), biotin, or insulin were prepared by using a novel coating technology based on the layer-by-layer (LbL) deposition of oppositely charged polyelectrolytes onto microcrystal templates. This produced multilayered, polymeric shells of varying thickness around the crystalline cores. Dissolution of the core material (VK3 with ethanol, biotin with basic solution, and insulin with acidic solution), resulted in its release through the shells. Microelectrophoresis was employed to monitor the microcrystal coating process; confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) were used to verify multilayer coating and the formation of hollow polymer shells following removal of the microcrystal templates. The release rates of both VK3 and insulin decreased as the wall thickness (the number of polyelectrolyte layers deposited onto the microcrystal cores), increased. The release time could be varied by a factor of more than ten, depending on the number of polyelectrolyte layers applied. Following the addition of 70 mass % ethanol, the solubility of VK3 increased by as much as 170-fold, resulting in an increased rate of VK3 release. By selecting appropriate polymer materials for the shells, and by controlling the number of polyelectrolyte layers applied, shells of various thickness, stiffness, aqueous solubility, dispersibility, biocompatibility, and permeability can be constructed.

Insulin↗
PubMed2003

Towards a microchip-based chromatographic platform. Part 2: sol-gel phases modified with polyelectrolyte multilayers for capillary electrochromatography.

The potential for using polyelectrolyte multilayers (PEMs) to provide chromatographic functionality on continuous silica networks created from sol-gel chemistry has been evaluated by capillary electrochromatography (CEC). Construction of the PEM was achieved by flushing the column with polyelectrolytes of alternative charge, with variation of the properties of the exposed polyelectrolyte providing a unique means to vary the chromatographic surface. Variation of the exposed polyelectrolyte from poly(diallyldimethylammonium chloride) (PDDAC) to dextran sulfate (DS) allowed the direction of the electroosmotic flow (EOF) to be changed and also provided a means to vary the chromatographic capacity. Variation of negative polymer from DS to poly(styrene sulfonate) (PSS) significantly altered the EOF and the migration of peptides, with both the reversed-phase and ion-exchange capacities increasing. An alternative method for changing the column capacity was to change the thickness of the PEM, which was evaluated by anion-exchange CEC. A 70-80% increase in retention was observed for all anions without any increase in EOF suggesting significant penetration of the analytes through the PEM and interaction with buried charges within the PEM.

Dextran Sulfate↗