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PubMed2006

Water-dissolvable sodium sulfate nanowires as a versatile template for the fabrication of polyelectrolyte- and metal-based nanotubes.

This study presents the synthesis of water-dissolvable sodium sulfate nanowires, where Na(2)SO(4) nanowires were produced by an easy reflux process in an organic solvent, N,N-dimethylformamide (DMF) and formed from the coexistence of AgNO(3), SnCl(2), dodecylsodium sulfate (SDS), and cetyltrimethylammonium bromide (CTAB). Na(2)SO(4) nanowires were derived from SDS, and the morphology control of the Na(2)SO(4) nanowires was established by the cooperative effects of Sn and NO(3)(-), while CTAB served as the template and led to homogeneous nanowires with a smooth surface. Since the as-synthesized sodium sulfate nanowires are readily dissolved in water, these nanowires can be treated as soft templates for the fabrication of nanotubes by removing the Na(2)SO(4) core. This process is therefore significantly better than other reported methodologies to remove the templates under harsh condition. We have demonstrated the preparation of biocompatible polyelectrolyte (PE) nanotubes using a layer-by-layer (LbL) method on the Na(2)SO(4) nanowires and the formation of Au nanotubes by the self-assembly of Au nanoparticles. In both nanotube synthesis processes, PEI (polyethylenimine), PAA (poly(acrylic acid)), and Au nanoparticles served as the building blocks on the Na(2)SO(4) templates, which were then rinsed with water to remove the core templates. This unique water-dissolvable template is anticipated to bring about versatile and flexible downstream applications.

Coated Materials, Biocompatible↗
PubMed2006

Aggregation-mediated optical properties of pH-responsive anionic conjugated polyelectrolytes.

Conjugated polyelectrolyte copolymers containing 2,1,3-benzothiadiazole- (BT) and oligo(ethylene oxide)-substituted fluorene and phenylene units have been designed and synthesized. The phenylene pendent groups also have carboxylic acid functionalities, which allow probing the effect of pH on optical properties. The BT content in the backbone can be regulated at the synthesis stage. Dynamic light scattering studies show that polymers aggregate in water at low pH. Increased interchain contacts give rise to a lowering of the photoluminescence (PL) efficiency via self-quenching when the BT units are absent and increased levels of FRET from the phenylene-fluorene segments to BT. Furthermore, the PL efficiency of BT increases in the aggregated structures. Examination of solvent effects indicates that the increased BT efficiencies are likely due to decreased contact with water. The changes in PL efficiencies are reversible, showing that the aggregates are dynamic and not kinetically constrained.

Anions↗
PubMed1982

Carboxyimamidate, a low-molecular-weight polyelectrolyte with antitumor properties and low toxicity.

A new polyelectrolyte was synthesized and evaluated for antitumor activity. The product is a derivative of ethylene/maleic anhydride copolymer of low molecular weight (Mn approximately equal to 1100). The anhydride groups were first converted to the half-amide, half-ammonium salt by reaction with ammonia. A percentage (14-25 wt %) of these groups was further converted to the imide by heating. The product, carboxyimamidate (Carbethimer, N-137) inhibited the growth of a number of solid tumors in vivo. Sensitive tumor models included Lewis lung carcinoma, Madison 109 lung carcinoma, M5076 ovarian tumor, colon carcinoma 26, B16 melanoma, and P815 mastocytoma. Activity was dose related between nontoxic dose levels of 300 and 2000 mg/kg ip.

Animals↗
PubMed2005

Loading and release behaviors of compressed polyelectrolyte multilayers for small dye molecules.

Loading and release behaviors of compressed polyelectrolyte multilayers composed of poly(styrenesulfonate sodium salt) and poly(diallyldimethylammonium chloride) were investigated using fluorescein and rhodamine 6G as indicators by confocal laser scanning microcopy, fluorescence spectroscopy, and UV-vis spectroscopy. Compression of the multilayers resulted in a more densely packed microstructure, leading to the decrease of fluorescence intensity of the incorporated probes to 80% of its initial value, and much slower releasing rate as well as smaller releasing amount regardless of the types of the probes and the presence of salt. Utilizing the difference of loading and release rates between the compressed and the uncompressed regions, arrays of dye reservoirs have been fabricated on a chemical homogeneous but physical heterogeneous multilayer film.

Coloring Agents↗
PubMed2005

Salt effect on the complex formation between polyelectrolyte and oppositely charged surfactant in aqueous solution.

The complex formation between sodium carboxymethylcellulose (NaCMC) and dodecyltrimethylammonium bromide (DTAB) at various sodium bromide concentrations (C(NaBr)) has been studied by microcalorimetry, turbidimetric titration, steady-state fluorescence measurements, and the fluorescence polarization technique. The addition of salt is found to influence the formation of NaCMC/DTAB complexes markedly. At C(NaBr) = 0.00, 0.01, 0.02, 0.10, and 0.20 M, DTAB monomers form micelle-like aggregates on NaCMC chains to form NaCMC/DTAB complexes above the critical surfactant concentration (C1). At C(NaBr) = 0.23 M, DTAB molecules first form micelles above a 2.46 mM DTAB concentration prompted by the added salt, and then, above C1 = 4.40 mM, these micelles can aggregate with NaCMC chains to form NaCMC/DTAB complexes. However, at C(NaBr) = 0.25 M, there is no NaCMC/DTAB complex formation because of the complete salt screening of the electrostatic attraction between DTAB micelles and NaCMC chains. It is also surprisingly found that the addition of NaBr can bring out a decrease in C1 at C(NaBr) < 0.20 M. Moreover, the addition of NaBr to a mixture of 0.01 g/L NaCMC and 3.6 mM DTAB can directly induce the formation of NaCMC/DTAB complexes. This salt-enhancing effect on the complex formation is explained as the result of competition between the screening of interaction of polyelectrolyte with surfactant and the increasing of polyelectrolyte/surfactant interaction owing to the growth of micelles by added salt. When the increasing of polyelectrolyte/surfactant interaction exceeds the screening of interaction, the complex formation can be enhanced.

Journal Article↗
PubMed2005

Structure-selective dye uptake into an aggregate of a copolymer with linear polyelectrolyte block and hydrophobic block carrying pendant dendritic moiety in water.

Selective uptake of various dyes into an aggregate of amphiphilic copolymer consisting of a hydrophilic linear polyelectrolyte block and hydrophobic block carrying pendant dendritic moiety has been investigated in water. The copolymer associated into an aggregate with a hydrophobic interior at concentrations above 0.2 mg cm(-3). The uptake (23 and 36 molecules per aggregate, respectively) of pyrene and Oil Yellow in an aggregate was one order higher than that of benzo[a]pyrene and SudanIII. The hydrophobic dyes are always doped in the interior of the aggregate, but the difference in uptake among dyes may depend on their structure. Even if a large number of guest molecules was doped into the interior of an aggregate, the size of the sphere-like aggregate was conserved. It is suggested that guest molecules are encapsulated into the persisting cavity within and between hydrophobic dendron moieties in an aggregate. Structure-selective uptake reported in this investigation is a unique character of an aggregate of copolymer with dendron moiety because the dendron moiety offers a large void for doping.

Journal Article↗
PubMed2005

Thermodynamic characterization of the interaction behavior of a hydrophobically modified polyelectrolyte and oppositely charged surfactants in aqueous solution: effect of surfactant alkyl chain length.

We have used a precision isothermal titration microcalorimeter (ITC) to measure the enthalpy curves for the interaction of a hydrophobically modified polyelectrolyte (D40OCT30) with oppositely charged surfactants (SC(n)S) in aqueous solution. D40OCT30 is a newly synthesized polymer based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-octylammonium chloride groups randomly distributed along the polymer backbone with degree of substitution of 28.1%. The employed anionic surfactants are sodium octyl sulfate (SC(8)S) and sodium tetradecyl sulfate (SC(14)S). Microcalorimetric results along with turbidity and kinematic viscosity measurements demonstrate systematically the thermodynamic characterization of the interaction of D40OCT30/SC(n)S. A three-dimensional diagram with the derived phase boundaries is drawn to describe the effect of the alkyl chain length of surfactant and of the ratio between surfactant and pendant groups on the interaction. A more complete picture of the interaction mechanism for D40OCT30/SC(n)S systems is proposed here.

Journal Article↗
PubMed2005

Ultrathin free-standing polyelectrolyte nanocomposites: a novel method for preparation and characterization of assembly dynamics.

We present a new opportunity for the investigation of the dynamics of electrostatic ultrathin-film assembly and the elucidation of time scales required for layer-by-layer adsorption of polyelectrolytes using a novel pendant drop technique which allows for the synthesis of free-standing nanocomposites. In short, a charged molecular template, i.e., a lipid monolayer, is deposited on a pendant drop and compressed to present a defined surface charge density to the subphase of the drop. The subphase is then cycled alternatively between solutions of polycations, saline, and polyanions by injection and withdrawal of liquid from coaxial capillaries on which the drop was formed, resulting in encapsulation of the drop volume by a polymeric composite membrane. The in situ dynamics of the process are followed by axisymmetric drop shape analysis. As a model, nanocomposites of dimyristoyl phosphatidyl glycerol-(polyallylamine hydrochloride/polystyrene sulfonate)(n=1-3) were prepared. The characteristic time scales for assembly range from 1 to 4 min and increase with film thickness. It is also demonstrated that small-amplitude (>1%) perturbations in the film density during adsorption prolong the assembly. Both these results underscore the nonequilibrium nature of these materials.

Letter↗
PubMed2005

Fabrication, characterization, and application in SERS of self-assembled polyelectrolyte-gold nanorod multilayered films.

An effective and facile approach for the preparation of multilayered nanostructure of gold nanorods (Au NRs) has been demonstrated. Linear polyethylenimine (LPEI) was selected as a polymeric adhesive layer, and an anionic polyelectrolyte poly(sodium styrenesulfonate) (PSS) was used as the linker of the positively charged Au NRs in multilayered nanostructure. They were deposited onto the LPEI-modified indium-doped tin oxide (ITO) substrate alternately using the layer-by-layer assembly technique via electrostatic interactions. The plasmonic property of the multilayered nanostructure of Au NRs is tunable by the controlled self-assembly process. FE-SEM was used to study the morphologies of the resulted substrates with Au NRs monolayer membrane and with Au NRs multilayered membrane. More importantly, it was found that the multilayered NRs films could be used as a surface-enhanced Raman spectroscopy (SERS) substrate for probing 4-aminothiophenol (4-ATP).

Journal Article↗
PubMed2006

Redox processes of cytochrome c immobilized on solid supported polyelectrolyte multilayers.

The heme protein cytochrome c (Cyt-c), immobilized on polyelectrolyte multilayers on a silver electrode, was studied by stationary and time-resolved surface-enhanced resonance Raman (SERR) spectroscopy to probe the redox site structure and the mechanism and dynamics of the potential-dependent interfacial processes. The layers were built up by sequential adsorption of polycations (poly[ethylene imine] (PEI); polyallylamine hydrochloride (PAH)) and polyanions (poly[styrene sulfonate] (PSS)). All multilayers terminated by PSS electrostatically bind Cyt-c. On PEI/PSS coatings, Cyt-c is peripherally bound and fully redox-active. Due to the interfacial potential drop, the apparent redox potential is lowered by 40 mV compared to that in solution. The rate constant for the heterogeneous electron transfer (ET) of ca. 0.1 s(-1) is consistent with electron tunneling through largely ordered PEI/PSS layers. ET is coupled to a reversible conformational transition of Cyt-c that involves a change of the coordination pattern of the heme. Additional (PAH/PSS) double layers cause a broadening of the redox transition and a drastic negative shift of the redox potential, which is attributed to the formation of PSS/Cyt-c complexes. It is concluded that Cyt-c can effectively compete with PAH for binding of PSS, resulting in a rearrangement of the layered structure and a penetration of the PSS-bound Cyt-c into the PAH/PSS double layers. This conclusion is consistent with SERR intensity and quartz microbalance measurements. ET was found to be overpotential-independent and faster than that for PEI/PSS coatings, which is interpreted in terms of specific PSS/Cyt-c complexes serving as gates for the heterogeneous ET.

Cytochromes c↗
PubMed2006

Solubilization of polyelectrolytic hairy-rod polyfluorene in aqueous solutions of nonionic surfactant.

We report on the solubilization, phase behavior, and self-organized colloidal structure of a ternary water-polyfluorene-surfactant (amphiphile) system comprised of polyelectrolytic poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) in nonionic pentaethylene glycol monododecyl ether (C12E5) at 20 degrees C. We show in particular how a high amount (milligrams per milliliter) of polyfluorene can be solubilized by aqueous C12E5 via aggregate formation. The PBS-PFP and C12E5 concentrations of 0.31 x 10(-4)-5 x 10(-4) M and 2.5 x 10(-4)-75 x 10(-4) M, respectively, were used. Under the studied conditions, the photoluminescence (PL), surface tension, static contact angle, and (pi-A) isotherm measurements imply that D2O-PBS-PFP(C12E5)x realizes three phase regimes with an increasing molar ratio of surfactant over monomer unit (x). First, for x < or = 0.5, the mixture is cloudy. In this regime polymer is only partially dissolved. Second, for 1 < or = x < or = 2, the solution is homogeneous. In this regime polymer is dissolved down to the colloidal level. Small-angle neutron scattering (SANS) patterns indicate rigid elongated (polymer-surfactant) aggregates with a diameter of 30 A and mean length of approximately 900 A. The ratio between contour length and persistence length is less than 3. Third, for x > or = 4, the solution is homogeneous and there is cooperative binding between polymer and surfactant. Surface tension, contact angle, and surface pressure remain essentially constant with increasing x. A PL spectrum characteristic of single separated polyfluorene molecules is observed. SANS curves show an interference maximum at q approximately 0.015 A(-1), indicating an ordered phase. This ordering is suggested to be due to the electrostatic repulsion between polymer molecules adsorbed on or incorporated into the C12E5 aggregates (micelles). On dilution the distance between micelles increases via 3-dimensional packing. In this regime the polymer is potentially dissolved down to the molecular level. We show further that the aggregates (x = 2) form a floating layer at the air-water interface and can be transferred onto hydrophilic substrates.

Fluorenes↗
PubMed2006

Modelling layer-by-layer assembly of flexible polyelectrolytes.

We have modelled the layer-by-layer assembly process of flexible polyelectrolytes on flat surfaces. The multilayer has a three-zone structure. An exponential growth is found for the first several layers, followed by a linear growth for subsequent layers evolving toward a steady state. While adjacent layers are highly interpenetrating, stratification can be seen for every four or more layers. The effects of surface charge density, bulk salt concentration, and solvent quality on the thickness and internal structure of the multilayer are also studied. Our results agree with experimental findings.

Letter↗
PubMed2006

Ionization equilibria and conformational transitions in polyprotic molecules and polyelectrolytes.

The coupling between proton binding and conformational degrees of freedom in polyprotic molecules and polyelectrolytes is studied theoretically. Our approach combines the classical rotational isomeric state (RIS) model developed by Flory and the site binding (SB) model used to treat proton binding equilibria. The properties of the resulting SBRIS model, which treats conformational degrees of freedom and proton binding on equal footing, are studied with statistical mechanical techniques. Quantities of interest, such as titration curves, conformational probabilities, or macroscopic binding constants, are expressed as thermal averages and are evaluated by direct enumeration of states or by transfer matrix techniques. We further demonstrate that in the SBRIS model conformational degrees of freedom can be averaged out, leading to the contracted description within the SB model. In most cases, this contraction leads to higher order interactions, which may not be present at the SBRIS level (e.g., triplet interactions). Several examples are discussed to illustrate the concepts developed. The case of succinic acid exemplifies the situation in its simplest form. The model can further rationalize the very different titration behavior of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). In particular, the characteristic "jump" in the titration curve of PMAA is described quantitatively and is interpreted in terms of a conformational transition.

Journal Article↗
PubMed2006

Charge stoichiometry inside polyelectrolyte-protein complexes: a direct SANS measurement for the PSSNa-lysozyme system.

We study by small angle neutron scattering and UV titration how the ratio of negative to positive charges, [-]/[+](intro), acts on the structure of complexes formed by short negatively charged polyelectrolyte chains (PSS) and globular positively charged proteins (lysozyme). The range of [-]/[+](intro) lies between 0.65 and 3.33. In all ratios, dense primary complexes are formed with radii around 10 nm. The species composition and the water content of the primary complexes are precisely obtained by the systematic use of the contrast matching of (deuterated) polymer or protein in SANS, yielding the compactness and the inner charge ratio [-]/[+](inner). The primary complexes have (i) an inner charge ratio [-]/[+](inner) close to 1 whatever [-]/[+](intro), (ii) a high total volume fraction (0.25-0.4), (iii) a constant radius (75 A) for [-]/[+](intro) 1, and (iv) a shell of PSS chains when [-]/[+](intro) > 1. Moreover, UV titration shows that there are free proteins if [-]/[+](introduced) < 1 and free PSS chains if [-]/[+](intro) is largely superior to 1. Hence, we observe that the primary complexes reach a finite size, controlled by electrostatic repulsion, and then aggregate at a higher scale with a fractal dimension of 2.1 characteristic of reaction-limited colloidal aggregation.

Electrolytes↗
PubMed2004

Electrochemical polymerization of aniline monomers infiltrated into well-ordered truncated eggshell structures of polyelectrolyte multilayers.

The use of nanosphere lithography to construct two-dimensional arrays of polystyrene (PS) particles coated with multilayered polyelectrolyte (PE) shells and truncated eggshell structures composed of PE thin layers is reported. The truncated eggshell PE structures were produced by extraction of the PS particle cores with toluene. The core-extraction process ruptures the apex of the PE coating and causes a slight expansion of the PE thin layers. Aniline hydrochloride was infiltrated into the PE shells and subsequently electropolymerized to yield an array of a composite containing polyaniline (PAni) and PE thin shells. Voltammetric, quartz crystal microbalance, and reflectance Fourier transform infrared spectroscopic measurements indicate that aniline monomers were confined within the thin PE shells and the electropolymerization occurred in the interior of the PE shell. The PE thickness governs the amount of infiltrated monomer and the ultimate loading of the PAni in the truncated eggshell structure. Surface-structure imaging by atomic force microscopy and scanning electron microscopy, carried out after each step of the fabrication process, shows the influence of the PE thickness on the organization and dimensions of the arrays. Thus, the PE thin shells composed of different layers can function as nanometer-sized vessels for the entrapment of charged species for further construction of composite materials and surface modifications. This approach affords a new avenue for the synthesis of new materials that combine the unique properties of conductive polymers and the controllability of template-directed surface reactions.

Aniline Compounds↗
PubMed2004

Synthesis of hydrophilic polymer-grafted ultrafine inorganic oxide particles in protic media at ambient temperature via atom transfer radical polymerization: use of an electrostatically adsorbed polyelectrolytic macroinitiator.

A new approach for the surface grafting of polymer chains to colloidal substrates is described. A cationic macroinitiator has been designed for the surface polymerization of a wide range ofhydrophilic methacrylates from ultrafine inorganic oxide sols by atom transfer radical polymerization in protic media at ambient temperature. One advantage of this approach is that it allows one-pot syntheses: the macroinitiator is adsorbed onto the sol, followed by an in situ polymerization. Nonionic, cationic, and betaine monomers can be polymerized directly by this protocol, with reasonably high conversions being obtained, as judged by 1H NMR spectroscopy. Anionic monomers such as sodium 4-styrenesulfonate cannot be polymerized directly due to incompatibility problems with the cationic macroinitiator-coated sol. However, hydroxylated monomers such as glycerol monomethacrylate can be surface-polymerized and then converted to anionic polyelectrolytes by reaction with succinic anhydride under mild conditions. This derivatization was confirmed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic analysis. Thermogravimetry was used to assess the degree of polymer grafting. Higher target degrees of polymerization led to increased grafted polymer loadings, as expected. Particle morphologies and relative degrees of dispersion in aqueous solution were assessed by transmission electron microscopy and dynamic light scattering, respectively. Surface characterization of the polymer-grafted sols was achieved by X-ray photoelectron spectroscopy and aqueous electrophoresis measurements. Most of the data reported in this study concern surface polymerizations from ultrafine silica sols, but some preliminary data for ultrafine tin(IV) oxide sols are also presented. Since most surfaces are negatively charged, this cationic macroinitiator approach can, in principle, be extended to include a wide range of sols, latexes, and planar substrates without requiring a separate surface functionalization step.

Journal Article↗
PubMed2004

Fibronectin adsorption onto polyelectrolyte multilayer films.

The Layer-by-layer deposition of positively and negatively charged macromolecular species is an ideal method for constructing thin films incorporating biological molecules. We investigate the adsorption of fibronectin onto polyelectrolyte multilayer (PEM) films using optical waveguide lightmode spectroscopy (OWLS) and atomic force microscopy (AFM). PEM films are formed by adsorption onto Si(Ti)O2 from alternately introduced flowing solutions of anionic poly(sodium 4-styrenesulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH). Using OWLS, we find the initial rate and overall extent offibronectin adsorption to be greatest on PEM films terminated with a PAH layer. The polarizability density of the adsorbed protein layer, as measured by its refractive index, is virtually identical on both PAH- and PSS-terminated films; the higher adsorbed density on the PAH-terminated film is due to an adsorbed layer of roughly twice the thickness. The binding of monoclonal antibodies specific to the protein's cell binding site is considerably enhanced to fibronectin adsorbed to the PSS layer, indicating a more accessible adsorbed layer. With increased salt concentration, we find thicker PEM films but considerably thinner adsorbed fibronectin layers, owing to increased electrostatic screening. Using AFM, we find adsorbed fibronectin layers to contain clusters; these are more numerous and symmetric on the PSS-terminated film. By considering the electrostatic binding of a segmental model fibronectin molecule, we propose a picture of fibronectin adsorbed primarily in an end-on-oriented monolayer on a PAH-terminated film and as clusters plus side-on-oriented isolated molecules onto a PSS-terminated film.

Adsorption↗
PubMed2004

Controlling mammalian cell interactions on patterned polyelectrolyte multilayer surfaces.

A newly discovered class of cell resistant surfaces, specifically engineered polyelectrolyte multilayers, was patterned with varying densities of adhesion ligands to control attachment of mammalian cells and to study the effects of ligand density on cell activity. Cell adhesive patterns were created on cell resistant multilayer films composed of poly(acrylic acid) and polyacrylamide through polymer-on-polymer stamping of poly(allylamine hydrochloride) PAH and subsequent reaction of the amine functional groups with an adhesion ligand containing RGD (Arg-Gly-Asp). These cell patterns demonstrated great promise for long-term applications since they remained stable for over 1 month, unlike ethylene glycol functional surfaces. By changing the stamping conditions of PAH, it was possible to alter the number of available functional groups in the patterned regions, and as a result, control the ligand density. Cell spreading, morphology, and cytoskeletal organization were compared at four different RGD densities. The highest RGD density, approximately 152 000 molecules/microm2, was created by stamping PAH at a pH of 11.0. Lowering the stamping ink pH led to patterns with lower ligand surface densities (83 000 molecules/microm2 for pH 9.0, 53,000 molecules/ microm2 for pH 7.0, and 25 000 molecules/microm2 for pH 3.5). An increasing number of cells attached and spread as the RGD density of the patterns increased. In addition, more cells showed well-defined actin stress fibers and focal adhesions at higher levels of RGD density. Finally, we found that pattern geometry affected cytoskeletal protein organization. Well-formed focal adhesions and cell-spanning stress fibers were only found in cells on wider line patterns (at least 25 microm in width).

Acrylic Resins↗