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PubMed2007

Continuous polyelectrolyte adsorption under an applied electric potential.

Interactions between charged macromolecules (e.g., proteins, nucleic acids, polyelectrolytes) and charged surfaces govern many natural and industrial processes. We investigate here the influence of an applied electric potential on the adsorption of charged polymers, and report the following significant result: the adsorption of certain amine side chain-containing polycations may become continuous, i.e., asymptotically linear (or nearly linear) in time over hours, upon the application of a modest anodic potential. Employing optical waveguide lightmode spectroscopy (OWLS) and an indium tin oxide (ITO) substrate, we show that asymptotic kinetics, and the adsorbed mass at the onset of the asymptotic regime, depend sensitively on polymer chemistry (in particular, side chain volume and charge location), increase with applied potential and ionic strength (conditions favoring a thicker initial layer), and are independent of bulk polymer concentration (suggesting postadsorption events to be rate limiting). X-ray photoelectron spectra reveal a suppressed polymer charge within layers formed via continuous adsorption, but no evidence of electrochemical reactions. We propose a mechanism based on polymer-polymer binding within the adsorbed layer, enabled by suppressed electrostatic repulsion and/or enhanced ionic correlations near the conducting surface, and stabilized by short-range attractive interactions. Continuous adsorption under an applied electric potential offers the possibility of nanoscale films of tailored polymer content realized in a single step.

Adsorption↗
PubMed1984

Measurement of the repulsive force between polyelectrolyte molecules in ionic solution: hydration forces between parallel DNA double helices.

We have measured the repulsive force between B-form double helices in parallel packed arrays of polymer-condensed DNA in the presence of 0.005-1.0 M ionic solutions. Molecular repulsion is consistently exponential with a 2.5-3.5 A decay distance, when the separation between DNA surfaces is 5-15 A. Only weakly dependent on ionic strength and independent of molecular size, this intermolecular repulsion does not obey the predictions of electrostatic double-layer theory. Rather, it strongly resembles the "hydration force" first recognized and quantified between phospholipid bilayers. Only beyond 15 A separation between molecules is there evidence of electrostatic double-layer forces. The quantitative failure of electrostatic double-layer theory seen here must gravely affect accepted analyses of other polyelectrolyte systems. Because the packing of condensed DNA resembles the spacings of DNA in many bacteriophages, our results permit estimation of the "DNA pressure" in phage heads.

Anions↗
PubMed1989

Monte Carlo description of oligoelectrolyte properties of DNA oligomers: range of the end effect and the approach of molecular and thermodynamic properties to the polyelectrolyte limits.

Applications of the grand canonical Monte Carlo method demonstrate the importance of end effects on fundamental molecular and thermodynamic properties of oligoelectrolyte solutions. Simulations are carried out for a series of solutions containing double-helical DNA oligomers of varying numbers of phosphate charges N (8 less than or equal to N less than or equal to 100) and univalent electrolyte at fixed activity (a +/- = 1.76 mmol/dm3). These results are used to evaluate as follows: C+N(a), the local concentration of cations at various axial positions along the oligomer surface; C+N(a), the axial average of these concentrations; TN, the preferential interaction coefficient expressed per oligomer charge, which is directly related to the fractional thermodynamic extent of association of counterions. A sufficiently long oligomer (N greater than or equal to 48 under the conditions simulated) is characterized by an interior region over which C+N(a) is uniform and equal to C+ infinity (a), the polyion limit. This interior region is flanked by two symmetric terminal regions, in which C+N(a) varies linearly with axial position from the end of the oligomer to a distance approximately 18 monomer units (approximately 3.1 nm) from that end. For long oligomers, the characteristics of the terminal regions [length and axial profile of C+N(a)] do not vary with N and, by inference, also pertain to the polyion under the same conditions. Both C+N(a) and TN approach their polyelectrolyte limits as linear functions of 1/N. These linear dependences can be attributed to the increasing predominance of the contribution due to the polyion-like interior of the oligomer as N increases.

DNA↗
PubMed1996

Dressed polyions, counterion condensation, and adsorption excess in polyelectrolyte solutions.

The phenomenon of Manning-Oosawa counterion condensation is given an explicit statistical mechanical and qualitative basis via a dressed polyelectrolyte formalism in connection with the topology of the electrostatic free-energy surface and is derived explicitly in terms of the adsorption excess of ions about the polyion via the nonlinear Poisson-Boltzmann equation. The approach is closely analogous to the theory of ion binding in micelles. Our results not only elucidate a Poisson-Boltzmann analysis, which shows that a fraction of the counterions lie within a finite volume around the polyion even if the volume of the system tends towards infinity, but also provide a direct link between Manning's theta-the number of condensed counterions for each polyion site-and a statistical thermodynamic quantity, namely, the adsorption excess per monomer.

Adsorption↗
PubMed2000

A route to hierarchical materials based on complexes of metallosupramolecular polyelectrolytes and amphiphiles.

Anisotropic thin film materials of metallosupramolecular polyelectrolyte-amphiphile complexes (denoted PACs) with structures at several length scales were fabricated through a multistep self-assembly process. Metal ion-mediated self-assembly of the ditopic ligand 1,4-bis(2,2':6',2"-terpyridine-4'-yl)benzene and electrostatic binding with the amphiphile dihexadecyl phosphate result in a PAC with tailored surface chemical properties, including solubility and surface activity. The PAC forms a stable monolayer at the air-water interface that is readily transferred and oriented on solid supports with the Langmuir-Blodgett technique. The presented strategy unifies colloid and metallosupramolecular chemistry and opens a versatile route to hierarchical materials with tailored structures and functions.

Journal Article↗
PubMed1996

The polyelectrolyte nature of F-actin and the mechanism of actin bundle formation.

Polymerized (F-)actin is induced to form bundles by a number of polycations including divalent metal ions, Co(NH3)63+, and basic polypeptides. The general features of bundle formation are largely independent of the specific structure of the bundling agent used. A threshold concentration of polycation is required to form lateral aggregates of actin filaments. The threshold concentration varies strongly with the valence of the cation and increases with the ionic strength of the solution. Polyanions such as nucleoside phosphates or oligomers of acidic amino acids disaggregate actin bundles into single filaments. These features are similar to the phenomenon of DNA condensation and can be explained analogously by polyelectrolyte theories. Similar results were found when F-actin was bundled by the peptide corresponding to the actin binding site of myristoylated alanine-rich protein kinase C substrate protein (MARCKS) or by smooth muscle calponin, suggesting that a broad class of actin bundling factors may function in a common manner. Physiologic concentrations of both small ions and large proteins can induce actin interfilament association independent of a requirement for specific binding sites.

Actins↗
PubMedDate not supplied

Cultivation and modelling of encapsulated Saccharomyces cerevisiae in NaCS-PDMDAAC polyelectrolyte complexes.

The cultivation of encapsulated S. cerevisiae in NaCS-PDMDAAC polyelectrolyte complexes was studied. The results showed that the encapsulated microorganisms had the same growth trends as in its free cell culture and, thus, NaCS-PDMDAAC microcapsules were suitable for the encapsulation of these biological substances. The encapsulated S. cerevisiae cells were fermented sequentially for 16 batches. The highest cell density in the capsules reached 2.64 x 10(10) cells mL(-1) and the ethanol concentration was 47.0 g L(-1). A model of the cultivation of the encapsulated S. cerevisiae was developed.

Capsules↗
PubMed1985

Application of polyelectrolyte theory to the study of the B-Z transition in DNA (1).

We have used the polyelectrolyte theory to study the ionic strength dependence of the B-Z equilibrium in DNA. A DNA molecule is molded as an infinitely long continuously charged cylinder of radius a with reduced linear charge density q. The parameters a and q for the B and Z forms were taken from X-ray data: aB = 1nm, qB = 4.2, aZ = 0.9 nm and qZ = 3.9. A simple theory shows that at low ionic strengths (when Debye screening length rD much greater than a) the electrostatic free energy difference FelBZ = FelZ - FelB increases with increasing ionic strength since qB greater than qZ. At high ionic strengths (when rD much less than a) the FelBZ would go on growing with increasing ionic strength if the inequality qB/aB greater than qZ/aZ were valid. In the converse case when qZ/qB greater than aZ/aB the FelBZ value decreases with increasing salt concentration at high ionic strength. Since X-ray data correspond to the latter case, theory predicts that the FelBZ value reaches a maximum at an intermediate ionic strength of about 0.1 M (where rD approximately a). We also performed rigorous calculations based on the Poisson-Boltzmann equation. These calculations have confirmed the above criterion of nonmonotonous behaviour of the FelBZ value as a function of ionic strength. Different theoretical predictions for the B-Z transition in linear and superhelical molecules are discussed. Theory predicts specifically that at a very low ionic strength the Z form may prove to be more stable than the B form.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA↗
PubMed1989

Monte-Carlo-self consistent field method in the polyelectrolyte theory.

A new time saving numerical method for calculation of equilibrium potential and density distribution of mobile ions around the polyion in a polyelectrolyte system is proposed: the region around the polyion is being divided into two zones-internal and external; in the internal zone all the ions are accounted explicity with the aid of Monte-Carlo procedure; in the external zone the combined Monte-Carlo-self consistent field method proposed earlier is applied, an exchange of ions between regions is being implied. For 1:1 electrolyte the optimal choice of the boundary between the zones has been demonstrated. As an example of a more complicated system calculation for 2:2:1:1 electrolyte was carried out.

Algorithms↗
PubMed1991

Comparison of different approaches for calculation of polyelectrolyte free energy.

We consider the problem of the mean field (Poisson-Boltzmann) calculation of the electrostatic free energy for a strongly charged polyelectrolyte such as DNA in a salt solution. We compare two approaches to calculate the free energy: (i) direct one starting from the statistical-mechanical expression for the electrostatic free energy and (ii) the polyion charge variation method. In the infinite dilution limit (in respect to polyion) and in excess salt (IDLES) the two approaches are fully equivalent. This is shown by straight forward algebra. We have performed specific calculations of the free energy difference for the case of B-Z transition in DNA as a function of ionic strength. As expected, the two approaches led to identical results. The ionic strength dependence of the B-to-Z free energy proves to be concaved up and as a result Z-DNA is stabilized at low ionic concentration as well as at high salt, in full agreement with our previous results (M.D.Frank-Kamenetskii et al., J. Biomol. Struct. Dyn. 3, 35-42 (1985]. Our data quantitatively agree with the results of Soumpasis (D.M.Soumpasis, J. Biomol. Struct. Dyn. 6, 563-574 (1988]. However, his claim about the absence of the effect of stabilization of Z-DNA at low salt proves to be groundless, and the criticism of our earlier approach seems to be irrelevant.

DNA↗
PubMed2002

Polyelectrolyte conditioning for iron-hydroxide-containing sludge produced from electroflocculation of fermentation wastewater.

The purpose of this study is to investigate the application of chemical conditioning method for the post-electroflocculation wastewater sludge treatment with polyelectrolytes of varying ionic characters, namely anionic, cationic and nonionic flocculating agents. Electroflocculation, a combination of the processes of electroflotation and electroprecipitation, was found effective to remove the organic and color components in monosodium glutamate fermentation wastewater. The settleability and dewaterability of the separated sludge, containing 15-20% of iron hydroxides, increased 35% and 60% due to polymer conditioning through a jar-test apparatus. The influence of shear conditions and polymer dose on the floc size, zeta potential, filterability and dewatering performance, and shear resistance of sludges was investigated. Experimental results showed that the anionic polymer acts as a better flocculating agent than both cationic and nonionic polymers, and the optimal polymer doses fall between 4.0 and 10.0 mg/g Fe sludge under corresponding shear rates of 200 300 rpm. This study also indicated that both charge neutralization and polymer bridging mechanisms operate in the sludge conditioning process.

Electrochemistry↗
PubMed2002

Immunogenic Cu2+-induced biopolymer systems comprising a steroid hormone, protein antigen, and synthetic polyelectrolytes.

We have synthesized the 17beta-estradiol comprising polycomplexes by the Cu(2+)-mediated complex formation of polyanionic polyelectrolyte (PE), [polyacrylic acid (PAA), nontoxic copolymers (CP) of acrylic acid with N-isopropylacrylamide and N-vinylpyrolidine] with BSA-estradiol covalent conjugates at the relatively low concentrations of metal ions in neutral water. Cu(2+) ions in the composition of biopolymer systems act as "fasteners" between macromolecules of same (negatively) charged polyanionic PE with protein carrier, promoting the formation of relatively stable polycomplex particles in physiological conditions. These hapten- and protein comprising Biopolymer Systems possess simultaneously highly estradiol and BSA-specific immunogenicity without traditional adjuvants after a single intravenous immunization of mice. The obtained results are of interest for the construction of polydeterminant immunogen and vaccines based on polymer derivatives of steroid hormones.

Acrylamides↗
PubMed2006

Polyelectrolyte nano-scaffolds for the design of layered cellular architectures.

The design of in vitro multilayered cellular architectures that resemble the stratified, lattice-like structure in tissues poses a significant challenge for tissue engineering. There is currently no generally applicable methodology to design multilayered cellular constructs that mimic the structure of tissues in vivo. We report a novel and generalizable approach to create multilayered cellular constructs that addresses these issues. These in vitro constructs comprise alternating layers of cells and nano-scale biocompatible polyelectrolyte (PE) scaffolds. We apply this methodology to address two specific problems in hepatic tissue engineering: the design of in vitro liver sinusoidal structures and the critical need to increase viable cell mass in extracorporeal liver-assist devices. We assembled ultrathin polymer scaffolds on the top of a confluent monolayer of cells by the sequential deposition of oppositely charged PEs. The thickness of the PE scaffold lies in the nanometer range. The PE scaffold plays a dual role. First, it is a technique to culture hepatocytes in vitro that maintains their morphology, cytoskeletal structure, and liver-specific functions. Second, the nano-scaffold provides a cell-adhesive surface on which a second layer of cells can be cultured, resulting in layered architectures. We have used this approach to design layered three-dimensional hepatocyte-PE-hepatocyte constructs, hepatocyte-PE-endothelial cell constructs, and hepatocyte-PE-fibroblast constructs. As a result of its versatility, this approach can, in principle, be used to design layered cellular constructs of any tissue type, and therefore has potentially wide applications in tissue engineering, bioreactor devices, and in drug delivery. This methodology has the potential to generate realistic in vitro constructs of any tissue type.

3T3 Cells↗
PubMed1999

Vertical free-standing films of amphiphilic associating polyelectrolytes.

Hydrophobically modified poly(acrylic acid) sodium salt (HMPAANa) copolymers are known to provide a huge stabilization of oil in water macroemulsions. An interstitial HMPAANa film is formed between the oil droplets, thus creating repulsion between them. We present an x-ray reflectivity study of vertical free-standing films drawn from aqueous solutions of HMPAANa copolymers. The vertical HMPAANa films are model systems for the interstitial films between oil droplets and the description of their behavior provides information about the stabilization process. Their thickness was investigated as a function of various parameters such as the solution concentration, the degree of grafting, the length of the grafts, and the backbone molecular weight. Below a solution concentration threshold (C(t)), the film thickness scales like the square root of the molecular weight and is independent of the degree of grafting and the length of the grafts. Polyelectrolyte chains adopt a self-screened coil conformation within the films and the thickness is governed by the radius of gyration of the coils. Above C(t), a transition from a bimolecular film to a physical gel is observed and the thickness then increases with concentration. Finally, we propose an explanation for the stabilization of macroemulsions by HMPAANa copolymers.

Journal Article↗
PubMed2001

Liquid crystals of polyelectrolyte networks.

The Onsager theory of nematic liquid crystals is extended to rigid polyelectrolytes cross-linked by polyvalent ions. Recent synchrotron x-ray diffraction experiments showed that dilute, birefringent networks are formed under these conditions. The application of Onsager theory to this system leads to the prediction of the existence of a range of exotic mesophases such as the "cubatic," the "tetratic," and the "trigatic." The exotic network phases appear on the border of regions of phase coexistence of network phase with isotropic material (at low polyvalent ion concentration) and with dense bundles (at high polyvalent ion concentration).

Journal Article↗
PubMed2002

Rodlike polyelectrolyte solutions: effect of the many-body Coulomb attraction of similarly charged molecules favoring weak nematic ordering at very small polymer concentration.

The correlation free energy of the many-body Coulomb interactions in the solution of rodlike polyelectrolytes with counterions is calculated. For this purpose a theory of the Debye-Hückel type, based on the density functional approach, is developed. We have shown that for all the analyzed regimes electrostatic interactions of similarly charged rods are attractive independent of their mutual orientation. Coexistence of weakly and highly ordered nematic phases at intermediate degrees of ionization of the molecules is predicted. It is shown that the electrostatic attractive forces favor liquid-crystalline ordering and stabilize a weakly ordered nematic phase at very small polymer concentrations. In other words, isotropic solutions of charged rods are in many cases intrinsically unstable with respect to orientational ordering.

Journal Article↗
PubMed2003

Counterion penetration and effective electrostatic interactions in solutions of polyelectrolyte stars and microgels.

Counterion distributions and effective electrostatic interactions between spherical macroions in polyelectrolyte solutions are calculated via second-order perturbation (linear response) theory. By modeling the macroions as continuous charge distributions that are permeable to counterions, analytical expressions are obtained for counterion profiles and effective pair interactions in solutions of star-branched and microgel macroions. The counterions are found to penetrate stars more easily than microgels, with important implications for screening of bare macroion interactions. The effective pair interactions are Yukawa in form for separated macroions, but are softly repulsive and bounded for overlapping macroions. A one-body volume energy, which depends on the average macroion concentration, emerges naturally in the theory and contributes to the total free energy.

Journal Article↗
PubMed2003

Persistence length of a strongly charged rodlike polyelectrolyte in the presence of salt.

The persistence length of a single, intrinsically rigid polyelectrolyte chain, above the Manning condensation threshold is investigated theoretically in the presence of added salt. Using a loop expansion method, the partition function is consistently calculated, taking into account corrections to mean-field theory. Within a mean-field approximation, the well-known results of Odijk, Skolnick, and Fixman are reproduced. Beyond mean field, it is found that density correlations between counterions and thermal fluctuations reduce the stiffness of the chain, indicating an effective attraction between monomers for highly charged chains and multivalent counterions. This attraction results in a possible mechanical instability (collapse), alluding to the phenomenon of DNA condensation. In addition, we find that more counterions condense on slightly bent conformations of the chain than predicted by the Manning model for the case of an infinite cylinder. Finally, our results are compared with previous models and experiments.

Journal Article↗