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At least 73 records · Page 4Linked to original sources

PubMed2006

Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy.

Electrical properties of contacts formed between conducting polymers and noble metal nanoparticles have been examined using current-sensing atomic force microscopy (CS-AFM). Contacts formed between electrochemically prepared pi-conjugated polymer films such as polypyrrole (PPy), poly(3-methylthiophene) (P3MeT), as well as poly(3,4-ethylenedioxythiophene) (PEDOT) and noble metal nanoparticles including platinum (Pt), gold (Au), and silver (Ag) have been examined. The Pt nanoparticles were electrochemically deposited on a pre-coated PPy film surface by reducing a platinum precursor (PtCl62-) at a constant potential. Both current and scanning electron microscopic images of the film showed the presence of Pt islands. The Au and Ag nanoparticles were dispersed on the P3MeT and PEDOT film surfaces simply by dipping the polymer films into colloid solutions containing Au or Ag particles for specified periods (5 to approximately 10 min). The deposition of Au or Ag particles resulted from either their physical adsorption or chemical bonding between particles and the polymer surface depending on the polymer. When compared with PPy, P3MeT and PEDOT showed a stronger binding to Au or Ag nanoparticles when dipped in their colloidal solutions for the same period. This indicates that Au and Ag particles are predominantly linked with the sulfur atoms via chemical bonding. Of the two, PEDOT was more conductive at the sites where the particles are connected to the polymer. It appears that PEDOT has better aligned sulfur atoms on the surface and is strongly bonded to Au and Ag nanoparticles due to their strong affinity to gold and silver. The current-voltage curves obtained at the metal islands demonstrate that the contacts between these metal islands and polymers are ohmic.

Journal Article↗

PubMed2006

Electrochemically nanopatterned conducting coronas of a conjugated polymer precursor: SPM parameters and polymer composition.

Here we describe the formation of precisely controlled corona-type nanopatterns on electroactive polymer precursor films using scanning probe microscopy (SPM) methods. The binary composition of electroactive groups in the polymer triggers the formation of corona-type nanopatterns at particular voltages and tip writing speeds through the electrooxidation of the polymer precursor film. Various parameters such as tip speed and applied bias were explored in the nanopatterning process, and the formation of a conductive nanopattern was investigated using conducting atomic force microscopy (C-AFM). The formation of the nanopattern was attributed to the flow of electrons from the AFM tip to the polymer film in a controlled electric field distribution. We also report a new method to distinguish the polymer composition and distribution of a polymer blend film by characterizing biasing differences in the patterning of a polymer film.

Journal Article↗

PubMed2006

Mesoscale simulation of polymer reaction equilibrium: combining dissipative particle dynamics with reaction ensemble Monte Carlo. I. Polydispersed polymer systems.

We present a mesoscale simulation technique, called the reaction ensemble dissipative particle dynamics (RxDPD) method, for studying reaction equilibrium of polymer systems. The RxDPD method combines elements of dissipative particle dynamics (DPD) and reaction ensemble Monte Carlo (RxMC), allowing for the determination of both static and dynamical properties of a polymer system. The RxDPD method is demonstrated by considering several simple polydispersed homopolymer systems. RxDPD can be used to predict the polydispersity due to various effects, including solvents, additives, temperature, pressure, shear, and confinement. Extensions of the method to other polymer systems are straightforward, including grafted, cross-linked polymers, and block copolymers. To simulate polydispersity, the system contains full polymer chains and a single fractional polymer chain, i.e., a polymer chain with a single fractional DPD particle. The fractional particle is coupled to the system via a coupling parameter that varies between zero (no interaction between the fractional particle and the other particles in the system) and one (full interaction between the fractional particle and the other particles in the system). The time evolution of the system is governed by the DPD equations of motion, accompanied by changes in the coupling parameter. The coupling-parameter changes are either accepted with a probability derived from the grand canonical partition function or governed by an equation of motion derived from the extended Lagrangian. The coupling-parameter changes mimic forward and reverse reaction steps, as in RxMC simulations.

Journal Article↗

PubMed2002

Adhesion and friction mechanisms of polymer-on-polymer surfaces.

The adhesion and friction of smooth polymer surfaces were studied below the glass transition temperature by use of a surface forces apparatus. The friction force of a crosslinked polymer was orders of magnitude less than that of an uncrosslinked polymer. In contrast, after chain scission of the outermost layers, the adhesion hysteresis and friction forces increase substantially. These results show that polymer-polymer adhesion hysteresis and friction depend on the dynamic rearrangement of the outermost polymer segments at shearing interfaces, and that both increase as a transition is made from crosslinked surfaces to surfaces with long chains to surfaces with quasi-free ends. The results suggest new ways for manipulating the adhesion and friction of polymer surfaces by adjusting the state of the surface chains.

Journal Article↗

PubMed2002

[Adsorption of neutral polymers on liposomes: investigation of the correlation between liposomes and polymers].

The characteristics of the adsorption process of neutral polymers: poly(vinyl alcohol), poly(vinyl pyrrolidone), and dextrane onto liposomes with three different lipid compositions were investigated as follows. 1 determination of the amount of polymers adsorbed on the surface of liposomes, 2 detection of the changes in the membrane structure brought by the adsorption of polymers with a high precision densimeter, 3 test dye release experiments with membrane diffusion cells after remote loading of liposomes with acridine orange (AO). The amount of polymers adsorbed on the surface of liposomes was expressed with adsorption isotherms at 25 +/- 1 degrees C. Connections were found between the lipid composition influencing the fluidity of liposome membrane, the surface charge density of liposomes, the physical-chemical properties of the polymers and the quantitative adsorption properties of the polymers. Decreasing of the molar excess volume values counted from the results of the high precision densimetric measurements revealed the compression of the membrane structure caused by polymer adsorption. We were able to influence the test dye (AO) release properties of the soy lecithin phospholipid (SLPL)/cholesterol (Chol)/dicethyl phosphate (DCP) = 25:3:2 (mol/mol) liposomes by the changing of the amount of PVA or DEX added to their dispersions.

Adsorption↗

PubMed2005

Topological polymer chemistry by dynamic selection from electrostatic polymer self-assembly.

A collection of recent developments in topological polymer chemistry is presented. First, topological isomerism occurring on randomly coiled, flexible polymer molecules having cyclic and linear structures is discussed. Second, an electrostatic self-assembly and covalent fixation strategy has been developed for the synthesis of polymeric topological isomers. These isomers have double cyclic, manacle-, and theta-shaped constructions, and are prepared by using either linear or star telechelic polymer precursors having moderately strained cyclic ammonium salt groups, which carry multifunctional carboxylate counteranions. A technique of reversed-phase chromatography (RPC) is demonstrated as an effective means to separate polymers with different topologies, especially polymeric topological isomers. A further extension of topological polymer chemistry has been observed by dynamic selection from electrostatic polymer self-assembly to enable the effective formation of tadpole-shaped, cyclic-linear hybrid topologies.

Chromatography, Liquid↗

PubMed2005

Chain-growth polycondensation for well-defined condensation polymers and polymer architecture.

The historical development of our research on polycondensation that proceeds in a chain-growth polymerization manner ("chain-growth polycondensation") for well-defined condensation polymers is described. We first studied polycondensation in which change of the substituent effect induced by bond formation drove the reactivity of the polymer end group higher than that of the monomer. In this approach, well-defined aromatic polyamides, polyesters, polyethers, and poly(ether sulfone)s were obtained. The second approach was the study of the phase-transfer polymerization of a solid monomer dispersed in an organic solvent. In this type of polymerization, the solid monomer was physically unable to react with another monomer and was carried with the phase transfer catalyst into the solution phase where it reacted with an initiator and the polymer end group in the solvent in a chain polymerization manner. We also found catalyst-transfer polycondensation as a third approach to chain-growth polycondensation. In the Ni-catalyzed polycondensation of 2-bromo-5-chloromagnesiothiophenes, the Ni catalyst transferred to the polymer end group, and a coupling reaction occurred there to yield a well-defined polythiophene. This chain-growth polycondensation was applied to the synthesis of condensation polymer architectures such as block copolymers, star polymers, graft copolymers, and so on.

Models, Molecular↗

PubMed1994

Measurement of the hemoglobin concentration in deoxyhemoglobin S polymers and characterization of the polymer water compartment.

Biological polymers contain freely exchangeable water within intermolecular crevices with restricted access to large extrapolymer solutes. Our recent studies highlighted large osmotic effects of such polymer water compartments (PWCs), and their substantial physiological and pathophysiological relevance. The size and accessibility of the PWC are critical parameters determining the polymers' osmotic properties. We report here a new experimental approach to investigate these parameters in deoxyhemoglobin S polymers. The size of the PWC is inversely related to the deoxyhemoglobin S concentration in the polymer (CP). Only an approximation of CP (approximately 69 g/dl) was previously available. By analyzing the distributions of soluble hemoglobin and a large molecular weight (MW) marker (14C-dextran, MW approximately 70kDa) in the supernatant and pellet of centrifuged gels, we obtained a reproducible value of CP, 54.7 (+/- 0.7)g/dl. This indicates that 60% of the polymer is composed of a water compartment inaccessible to soluble Hb and other non-interactive macromolecules. The accessibility properties of this PWC to smaller molecules were explored with markers of different MW. Non-interactive markers with MW < 200 kDa diffused freely in the PWC, whereas those with 300 kDa < MW < 1000 kDa showed partial exclusion. Higher MW markers were generally excluded, except molecules with elongated (rather than spherical) shapes or possible interactivity with hemoglobin. These results predict that dense sickle cells would significantly dehydrate on deoxygenation, generating a PWC of up to 60% to 80% of the cell water. Soluble enzymes would concentrate in the residual cytosol. For osmotic equilibrium, most of the ions and low MW substrates would concentrate in the PWC. Oxygenation-deoxygenation would thus cause dynamic oscillations in cell hydration and between states of single and double cytoplasmic water phases, the latter with a substantially altered internal environment. The relevance of such oscillations to the membrane and metabolic abnormalities of dense sickle cells requires further investigation.

Anemia, Sickle Cell↗

PubMed2005

Novel mucoadhesion tests for polymers and polymer-coated particles to design optimal mucoadhesive drug delivery systems.

To design an effective particulate drug delivery system having mucoadhesive function, several mucoadhesion tests for polymers and the resultant particulate systems were developed. Mucin particle method is a simple mucoadhesion test for polymers, in which the commercial mucin particles are used. By measuring the change in particle size or zeta potential of the mucin particle in a certain concentration of polymer solution, we could estimate the extent of their mucoadhesive property. BIACORE method is also a novel mucoadhesion test for polymers. On passing through the mucin suspension on the polymer-immobilized chip of BIACORE instrument, the interaction was quantitatively evaluated with the change in its response diagram. By using these mucoadhesion tests, we detected a strong mucoadhesive property of several types of chitosan and Carbopol. Evaluation of mucoadhesive property of polymer-coated particulate systems was demonstrated with the particle counting method developed by us. To detect the mucoadhesive phenomena in the intestinal tract, we observed the rat intestine with the confocal laser scanning microscope (CLSM) after oral administration of the particulate systems. The resultant photographs clearly showed a longer retention of submicron-sized chitosan-coated liposomes (ssCS-Lip) in the intestinal tract than other liposomal particles tested such as non-coated liposomes and chitosan-coated multilamellar one. These observations explained well the superiority of the ssCS-Lip as drug carrier in oral administration of calcitonin in rats than other liposomal particles.

Adhesiveness↗

PubMed2005

Ophthalmic delivery systems based on drug-polymer-polymer ionic ternary interaction: in vitro and in vivo characterization.

Aim of the work was to develop mucoadhesive eyedrops containing tetrahydrozoline hydrochloride (TZ), a decongestant drug, and based on a ternary interaction drug-polymer-polymer. The anionic polymers assessed were the anionic hyaluronic acid (HA) and polyacrylic acid (PAA), the cationic chitosan (HCS) and the polyelectrolyte gelatin (G). Formulations based on the ternary systems TZ/G/HA, TZ/HCS/HA, TZ/G/PAA and TZ/HCS/PAA at the stoichiometry ratios between cationic and anionic polymers and containing a 10 and 20 fold excess of the anionic polymers were prepared. The formulations were characterized for in vitro mucoadhesive and release properties. The ex vivo/in vivo residence properties were assessed for the formulations that combined the better in vitro mucoadhesive and release properties. The physical stability of the formulations selected was determined following steam sterilization and storage at 25 and 40 degrees C. The synergistic effect of G with HA and PAA improves the mucoadhesion of the formulations while the interaction of HCS with HA and PAA is likely to produce higher neutralization of the anionic polymer charge and minor chain flexibility resulting in a limited mucoadhesion improvement. Both G and HCS participate to control drug release. The selected formulations demonstrate to possess consistency (viscosity) sensitive to the ions of the medium, and probably for this reason the ex vivo/in vivo residence properties could not directly correlated to mucoadhesion and to drug release control properties. However, the formulations are able to maintain levels of TZ detectable until 20 min after the instillation in rabbits, while TZ was not detectable since 3 min after instillation of the drug solution. The physical stability, following steam sterilization and storage, the low viscosity combined with good residence time in conjunctival sac make the TZ/G/20HA the more promising formulation.

Acrylic Resins↗

PubMed1994

Interaction of Cibacron blue with polymers: implications for polymer-shielded dye-affinity chromatography of phosphofructokinase from baker's yeast.

Interactions between Cibacron Blue F3GA and water-soluble non-ionic polymers were investigated by monitoring the spectral shift that accompanies the binding phenomena. Polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) were the only polymers among those tested found to interact effectively with the dye. The difference spectra for the PVP-dye complex was typical of "electrostatic interaction spectra" at low ionic strength and typical of "hydrophobic interaction spectra" in the presence of 1.5 M KCl. The binding constant and the number of binding sites per polymer molecule were calculated using the simplest model of independent binding sites. One dye molecule was bound by a PVP segment with a molecular mass of 1000-1300. Regardless of the size of the polymer molecules, the binding constants were in the micromolar range. Poly(vinyl alcohol) bound less efficiently to Cibacron Blue than PVP. One dye molecule was bound by a polymer segment with a molecular mass of about 10,000. The data on PVP complexing with Cibacron Blue were used to develop the concept of polymer-shielded dye-affinity chromatography. This concept was successfully applied to the chromatography of phosphofructokinase (EC 2.7.1.11) from baker's yeast. Specific elution of the bound enzyme from PVP-shielded column resulted in an efficient process with 27-fold purification.

Chromatography, Affinity↗

PubMedDate not supplied

Poly[Lys-(AEDTP)]: a cationic polymer that allows dissociation of pDNA/cationic polymer complexes in a reductive medium and enhances polyfection.

Polyplexes of high stability resulting from the condensation of a plasmid DNA by a cationic polymer are widely used to develop polymer-based gene delivery systems. However, the plasmid must be released from its vector once inside the cells for an efficient expression of the exogenous gene in the cell nucleus. We have designed a disulfide-containing cationic polymer termed poly[Lys-(AEDTP)] which allowed for the formation of polyplexes and the release of the plasmid in a reductive medium. The amino groups of polylysine were substituted with 3-(2-aminoethyldithio)propionyl residues in order to have each amino group of poly[Lys-(AEDTP)] interacting with a phosphate DNA linked to the polymer backbone via a disulfide bond. As evidenced by agarose gel electrophoresis and ethidium bromide/pDNA fluorescence restoration, poly[Lys-(AEDTP)] polyplexes were decondensed and the plasmid released upon treatment with either dithiothreitol, glutathione in the presence of glutathione reductase, or the thioredoxin reductase. Electron microscopy showed that polyplexes exhibiting spherical particles of a mean size at about 100 nm were decondensed in the presence of glutathione and exhibited filamentous aggregates. Finally, we found that the transfection of 293T7 and HepG2 cells was 10- and 50-fold more efficient with poly[Lys-(AEDTP)] polyplexes, respectively, than with poly[Lys] polyplexes. These results indicate that disulfide-containing cationic polymers must be borne in mind for developing polymer-base gene delivery systems.

Cations↗

PubMedDate not supplied

Delivery of antisense oligonucleotides using HPMA polymer: synthesis of A thiol polymer and its conjugation to water-soluble molecules.

Here, we report the synthesis and characterization of an HPMA-based polymer for use as a carrier for the delivery of water soluble drugs. The polymer contains active-sulfhydryl groups for coupling of ligands through a disulfide linkage. The polymer can also be prepared containing pendant amino groups in addition to the active-sulfhydryl moiety. This allows the use of different chemistries to conjugate a variety of ligands to the polymer. We demonstrate that a sulfhydryl-terminated antisense oligonucleotide can be efficiently and rapidly conjugated to the polymer. The polymer-oligonucleotide conjugate is efficiently taken up by cultured cells.

Cells, Cultured↗

PubMed1990

Heparin promotes the binding of thrombin to fibrin polymer. Quantitative characterization of a thrombin-fibrin polymer-heparin ternary complex.

The binding of human alpha-thrombin (IIa) to fibrin polymer (FnIIp) was studied in the presence and absence of a high affinity 20,300 Mr heparin (H) at pH 7.4, I 0.15, and 23 degrees C. In the absence of heparin, thrombin interacts with a high affinity class of binding sites on fibrin polymer with a dissociation constant of 301 +/- 36 nM in a manner which is independent of the enzyme active site. Studies of thrombin binding as a function of heparin and fibrin polymer concentrations imply that a ternary thrombin-fibrin polymer-heparin complex (IIa.FnIIp.H) is formed. Assembly of the ternary complex occurs randomly through the interactions of all three possible intermediate binary complexes; IIa.H, IIa.FnIIp, and FnIIp.H. Using an independently determined value of 280 +/- 35 nM for the FnIIp.H dissociation constant, global fits of the binding data yield a dissociation constant of 15 +/- 6 nM for the IIa.H interaction and 47 +/- 9 nM for the IIa.H intermediate binary complex interaction with FnIIp. These studies indicate that heparin enhances the binding of thrombin to fibrin polymer 6.4-fold with an overall dissociation constant for ternary complex formation of 705 nM2. The effect of heparin molecular weight on ternary complex formation has also been investigated. Heparins of molecular weights 11,200-20,300 behave similarly with respect to their influence on ternary complex formation, whereas heparins of lower molecular weight are less effective in promoting thrombin binding to fibrin polymer. This effect of heparin is also independent of whether it has high or low affinity for antithrombin III. The demonstration of the formation of a ternary IIa.FnIIp.H complex complements kinetic evidence indicating the formation of an analogous ternary complex with fibrin II monomer (Hogg, P. J., and Jackson, C. M. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 3619-3623). The possible implications of these findings for the in vivo distribution and actions of thrombin and the clinical efficacy of heparin are also discussed.

Antithrombin III↗

PubMed2001

Preparation and Properties of Polymer-Wrapped Single-Walled Carbon Nanotubes We would like to acknowledge the following agencies and foundations for supporting various aspects of this work: the polymer synthesis and spectroscopic characterization of the nanotube-polymer complex was funded by ONR; the chemical preparation and AFM analysis of these materials was supported by the NSF; device fabrication and charge-transport measurements were funded by DARPA and ONR; and the nonlinear microscopy experiments were supported by DARPA and the Keck Foundation.

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Journal Article↗

PubMed2006

Protein-imprinted polymer with immobilized assistant recognition polymer chains.

Here we introduce a new method for preparing a protein-imprinted polymer with immobilized assistant recognition polymer chains as an additional element of monomer to create effective recognition sites. In this work the bovine serum albumin was used as template and the template protein was selectively assembled with immobilized assistant recognition polymer chains from their library, numerous limited length polymer chains with randomly distributed recognition sites and immobilizing sites. These assemblies of protein and immobilized assistant recognition polymer chains would be adsorbed by the macro porous adsorbent spheres and immobilized by cross-linking polymerization. After removing the template, binding sites that were complementary to the target protein in size, shape and position of recognition groups were exposed, and their confirmation was preserved by the cross-linked structure. The synthesized imprinted polymer was used to adsorb BSA from protein mixtures, and showed a high selectivity.

Biocompatible Materials↗

PubMed2002

Control of polymer topology through transition-metal catalysis: synthesis of hyperbranched polymers by cobalt-mediated free radical polymerization.

A novel approach was demonstrated for the synthesis of hyperbranched polymers by direct free radical polymerization of divinyl monomers controlled by a cobalt chain transfer catalyst (1). By controlling the competition between propagation and chain transfer with 1, the free radical polymerization of ethylene glycol dimethacrylate (3) afforded soluble hyperbranched polymers in one pot. The structure of the hyperbranched polymers was confirmed by (1)H and (13)C NMR. The molecular weight and intrinsic viscosity of the hyperbranched polymers were measured by matrix-assisted laser desorption ionization (MALDI) mass spectrometry and size exclusion chromatography (SEC) equipped with triple detectors. The intrinsic viscosities of the hyperbranched polymers are much lower than those of their linear analogues and do not show molecular weight dependence. The unique structure and properties of these hyperbranched polymers combined with the commercial availability of many divinyl monomers and the robustness of free radical polymerization make this new approach attractive for the preparation of new functional materials.

Journal Article↗

PubMed2003

Conducting polymers as driving electrodes for Polymer-Dispersed Liquid-Crystals display devices: on the electro-optical efficiency.

Intrinsically conducting polymer (ICP) thin films are used as driving electrodes for Polymer-Dispersed Liquid-Crystals (PDLC) display devices. In order to investigate the electro-optical efficiency of these organic electrodes, three different kinds of conducting polymers, i.e. polyaniline doped with 10-camphorsulfonic acid (PANI(HCSA)), polypyrrole doped with dodecylbenzenesulfonic acid (PPY(DBSA)), and polyethylenedioxythiophene doped with polystyrenesulfonate (PEDOT(PSS)), were prepared or purchased, and coated either on glass or plastic substrates. Optical absorption studies in the UV-Vis range of the conducting polymer-coated substrates were first performed showing the presence of conducting species for the three types of polymers. The electrical characteristics of the resulting films were measured with the four-probes technique. PANI(HCSA) exhibits a higher conductivity sigma approximately 122 S x cm(-1) (RS=1.2x10(3) Omega x (-1)) compared to PPY(DBSA) sigma approximately 2.6 S x cm(-1) (RS=150.7x10(3) Omega x (-1)), and PEDOT(PSS) sigma approximately 1.6 S x cm(-1) (RS=637.3x10(3) Omega x (-1)). It is also shown that for a given conducting polymer, its electrical conductivity decreases when a plastic substrate is used. These observations have been related to significant morphological changes observed by scanning electron microscopy (SEM). A mixture of Norland Optical Adhesive 65 and nematic liquid-crystal E7 in the weight ratio (35:65) was used as precursor of the PDLC material. Better electro-optical responses (transmission properties, drive voltages and switching times) of PDLC films were obtained for devices prepared with (PPY(DBSA))-based electrodes. The electro-optical performances of the PDLC display devices also depend on the nature of the ICP substrate used.

Journal Article↗