Large Polyelectrolyte Research Articles

Polyamines Promote Aragonite Nucleation and Generate Biomimetic Structures.

Calcium carbonate biomineralization is remarkable for the ability of organisms to produce calcite or aragonite with perfect fidelity, where this is commonly attributed to specific anionic biomacromolecules. However, it is proven difficult to mimic this behavior using synthetic or biogenic anionic organic molecules. Here, it is shown that cationic polyamines ranging from small molecules to large polyelectrolytes can exert exceptional control over calcium carbonate polymorph, promoting aragonite nucleation at extremely low concentrations but suppressing its growth at high concentrations, such that calcite or vaterite form. The aragonite crystals form via particle assembly, giving nanoparticulate structures analogous to biogenic aragonite, and subsequent growth yields stacked aragonite platelets comparable to structures seen in developing nacre. This mechanism of polymorph selectivity is captured in a theoretical model based on these competing nucleation and growth effects and is completely distinct from the activity of magnesium ions, which generate aragonite by inhibiting calcite. Profiting from these contrasting mechanisms, it is then demonstrated that polyamines and magnesium ions can be combined to give unprecedented control over aragonite formation. These results give insight into calcite/aragonite polymorphism and raise the possibility that organisms may exploit both amine-rich organic molecules and magnesium ions in controlling calcium carbonate polymorph.

Molecular Transfer Model for pH Effects on Intrinsically Disordered Proteins: Theory and Applications.

We present a theoretical method to study how changes in pH shape the heterogeneous conformational ensemble explored by intrinsically disordered proteins (IDPs). The theory is developed in the context of coarse-grained models, which enable a fast, accurate, and extensive exploration of conformational space at a given protonation state. In order to account for pH effects, we generalize the molecular transfer model (MTM), in which conformations are re-weighted using the transfer free energy, which is the free energy necessary for bringing to equilibrium in a new environment a "frozen" conformation of the system. Using the semi-grand ensemble, we derive an exact expression of the transfer free energy, which amounts to the appropriate summation over all the protonation states. Because the exact result is computationally too demanding to be useful for large polyelectrolytes or IDPs, we introduce a mean-field (MF) approximation of the transfer free energy. Using a lattice model, we compare the exact and MF results for the transfer free energy and a variety of observables associated with the model IDP. We find that the precise location of the charged groups (the sequence), and not merely the net charge, determines the structural properties. We demonstrate that some of the limitations previously noted for MF theory in the context of globular proteins are mitigated when disordered polymers are studied. The excellent agreement between the exact and MF results poises us to use the method presented here as a computational tool to study the properties of IDPs and other biological systems as a function of pH.

Concentration-dependent and configuration-dependent interactions of monovalent ions with an RNA tetraloop.

Monovalent salt solutions have strongly coupled interactions with biopolymers, from large polyelectrolytes to small RNA oligomers. High salt concentrations have been known to induce transitions in the structure of RNA, producing non-canonical configurations and even driving RNA to precipitate out of solution. Using all-atom molecular dynamics simulations, we model a monovalent salt species (KCL) at high concentrations (0.1-3m) and calculate the equilibrium distributions of water and ions around a small tetraloop-forming RNA oligomer in a variety of structural arrangements: folded A-RNA (canonical) and Z-RNA (non-canonical) tetraloops and unfolded configurations. From these data, we calculate the ion preferential binding coefficients and Donnan coefficients for the RNA oligomer as a function of concentration and structure. We find that cation accumulation is highest around non-canonical Z-RNA configurations at concentrations below 0.5m, while unfolded configurations accumulate the most co-ions in all concentrations. By contrast, canonical A-RNA structures consistently show the lowest accumulations for all ion species. Water distributions vary markedly with RNA configuration but show little dependency on KCL concentration. Based on Donnan coefficient calculations, the net charge of the solution at the surface of the RNA decreases linearly as a function of salt concentration and becomes net-neutral near 2.5-3m KCL for folded configurations, while unfolded configurations still show a positive solution charge. Our findings show that all-atom molecular dynamics can describe the equilibrium distributions of monovalent salt in the presence of small RNA oligomers at KCL concentrations where ion correlation effects become important. Furthermore, these results provide valuable insights into the distributions of water and ions near the RNA oligomer surface as a function of structural configuration.

Nanometer‐Scale Precision Tuning of 3D Photonic Crystals Made Possible Using Polyelectrolytes with Controlled Short Chain Length and Narrow Polydispersity

Herein we report the development of an effective method which enables nanometer-scale precision tuning of prefabricated 3D colloidal photonic crystals (PCs). In our approach which involves the layer-by-layer (LbL) electrostatic assembly of polyelectrolytes in the photonic crystals, a key conceptual novelty lies in the development and utilization of polyelectrolytes with controlled short chain lengths and narrow polydispersity as the infi ltrating materials. This allows uniform deposition of the polyelectrolytes in the PCs while circumventing the leading problem in the LbL approach:blockage of the PC interstitial openings by large polyelectrolytes during the early stages of infi ltration. As a result, nanometer-scale precision tuning of photonic stopband of 10 nm or less has been achieved, which few other methods can attain. The method is facile and reproducible, and can be applied to photonic crystal lattices ranging from small to large dimensions. Photonic crystals are an interesting class of photon-control materials characterized by periodic array of dielectric lattices at the scale of light wave lengths. [ 1 ] These materials possess photo nic band gaps or stop bands where light within a range of frequencies is prohibited from propagating along specifi c lattice directions in the structure. As a result, PCs have attracted signifi cant recent attention as powerful tools for the manipulation of photons with potential applications ranging from telecommunications to optical computing. [ 2 ] Three-dimensional photonic crystals can be created by top-down methods such as holographic lithography and direct laser writing or bottom-up methods such as self-assembly of monodisperse colloidal silica or polymer spheres. [ 3 ] In both fabrication methods, the PC structures generated are of a passive nature with fi xed optical properties, and any slight change in the requirement of the photonic band gaps or stop bands, such as in solar cell, light emitting diode or lasing applications, will generally need the fabrication of a new photonic crystal. In comparison, nanometer-scale fi ne tuning of existing photo nic structures through controlled infi ltration represents an attractive and cost-effective alternative. However, since many of these photonic structures possess an interconnected pore network, control at the nanometer regime of the infi ltrated materials is a challenge for designed optical response. [ 4 ] In our efforts to develop post-fabrication strategies to tailor the optical properties of PCs, LbL assembly [ 5 ] of polyelectrolytes (PEs) [ 6 ] in preformed photonic crystal lattices [ 7 ] emerged as a promising approach. Importantly, we found that PEs which possessed controlled short chain lengths and narrow polydispersity were suitable as infi ltrating materials for the fi ne tuning of photonic stop bands. In this Communication, we report the development of the method and the precision tuning of photonic properties on the nanometer scale.

A low-cost, label-free DNA detection method in lab-on-chip format based on electrohydrodynamic instabilities, with application to long-range PCR

In order to evolve from a "chip in the lab" to a "lab on a chip" paradigm, there is still a strong demand for low-cost, portable detection technologies, notably for analytes at low concentrations. Here we report a new label-free DNA detection method with direct electronic read, and apply it to long-range PCR. This method uses a nonlinear electrohydrodynamic phenomenon: when subjected to high electric fields (typically above 100 V cm(-1)), suspensions of large polyelectrolytes, such as long DNA molecules, create "giant" dynamic concentration fluctuations. These fluctuations are associated with large conductivity inhomogeneities, and we use here a contact-mode local conductivity detector to detect these fluctuations. In order to decouple the detection electronics from the high voltage excitation one, an original "doubly symmetric" floating mode battery-operated detection scheme was developed. A wavelet analysis was then applied, to unravel from the chaotic character of the electohydrodynamic instabilities a scalar signal robustly reflecting the amplification of DNA. As a first proof of concept, we measured the products of the off-chip amplification of 10 kbp DNA from lambda phage DNA, achieving a sensitivity better than 100 fg DNA in the original 50 μl sample. This corresponds to the amplification products of less than 100 initial copies of target DNA. The companion enabling technologies developed to implement this new concept, i.e. the doubly symmetric contact conductivity detection and wavelet analysis, may also find various other applications in lab-on-chips.

Characterization of complexation and phase behavior of mixed systems of unmodified and hydrophobically modified oppositely charged polyelectrolytes

This paper reports turbidity, rheology, zeta potential, and rheo-small angle light scattering measurements on aqueous mixtures of oppositely charged and hydrophobically modified hydroxyethylcellulose derivatives (HM-HEC(−) and HM-HEC(+)) and mixtures of oppositely charged hydroxyethylcellulose (HEC(−) and HEC(+)). The experiments were restricted to the one-phase region, i.e., at mixing ratios before and after the two-phase area. The associative phase separation behavior usually observed when mixing oppositely charged polyelectrolytes was undetectable in the mixtures of the polyelectrolytes without attached hydrophobic groups. Upon modification of HEC by incorporation of pendant hydrophobic groups and by introducing charges of negative or positive sign (HM-HEC(−) and HM-HEC(+)), the mixtures showed phase separation over a certain mixing interval, revealing the existence of large polyelectrolyte complexes. The zero shear viscosity was strongly dependent on both the hydrophobicity of the polymers and the mixing ratio, increasing significantly with hydrophobic modification of polyelectrolytes. The strong enhancement of the turbidity and the viscosity drop as the two-phase area is approached suggest the formation of fragmented non-connected complexes. This work demonstrates that if the oppositely charged polyions have a hydrophilic character, it is not necessary that the attractive Coulombic forces induce insoluble polyelectrolyte complexes.

Electrical stimulation promotes nerve cell differentiation on polypyrrole/poly (2-methoxy-5 aniline sulfonic acid) composites

The purpose of this work was to investigate for the first time the potential biomedical applications of novel polypyrrole (PPy) composites incorporating a large polyelectrolyte dopant, poly (2-methoxy-5 aniline sulfonic acid) (PMAS). The physical and electrochemical properties were characterized. The PPy/PMAS composites were found to be smooth and hydrophilic and have low electrical impedance. We demonstrate that PPy/PMAS supports nerve cell (PC12) differentiation, and that clinically relevant 250 Hz biphasic current pulses delivered via PPy/PMAS films significantly promote nerve cell differentiation in the presence of nerve growth factor (NGF). The capacity of PPy/PMAS composites to support and enhance nerve cell differentiation via electrical stimulation renders them valuable for medical implants for neurological applications.

Electrophoretic mobility of linear and star‐branched DNA in semidilute polymer solutions

Electrophoresis of large linear T2 (162 kbp) and 3-arm star-branched (N(Arm) = 48.5 kbp) DNA in linear polyacrylamide (LPA) solutions above the overlap concentration c* has been investigated using a fluorescence visualization technique that allows both the conformation and mobility mu of the DNA to be determined. LPA solutions of moderate polydispersity index (PI approximately 1.7-2.1) and variable polymer molecular weight Mw (0.59-2.05 MDa) are used as the sieving media. In unentangled semidilute solutions (c* < c < c(e)), we find that the conformational dynamics of linear and star-branched DNA in electric fields are strikingly different; the former migrating in predominantly U- or I-shaped conformations, depending on electric field strength E, and the latter migrating in a squid-like profile with the star-arms outstretched in the direction opposite to E and dragging the branch point through the sieving medium. Despite these visual differences, mu for linear and star-branched DNA of comparable size are found to be nearly identical in semidilute, unentangled LPA solutions. For LPA concentrations above the entanglement threshold (c > c(e)), the conformation of migrating linear and star-shaped DNA manifest only subtle changes from their unentangled solution features, but mu for the stars decreases strongly with increasing LPA concentration and molecular weight, while mu for linear DNA becomes nearly independent of c and Mw. These findings are discussed in the context of current theories for electrophoresis of large polyelectrolytes.

Residence time distribution in the chromatographic column: Applications in the separation engineering of DNA

Experimental and theoretical works were performed for the separation of large polyelectrolyte, such as DNA, in a column packed with gel particles under the influence of an electric field. Since DNA quickly orient in the field direction through the pores, this paper presents how intraparticle convection affects the residence time distribution of DNAs in the column. The concept is further illustrated with examples from solid-liquid systems, for example, from chromatography showing how the column efficiency is improved by the use of an electric field. Dimensionless transient mass balance equations were derived, taking into consideration both diffusion and electrophoretic convection. The separation criteria are theoretically studied using two different Peclet numbers in the fluid and solid phases. These criteria were experimentally verified using two different DNAs via electrophoretic mobility measurements, which showed how the separation position of the DNAs varies in the column in relation to the Peg/Pef values of an individual DNA. The residence time distribution was solved by an operator theory and the characteristic method to yield the column response.

Transport modelling of a polyelectrolyte in membrane chromatography under an electric field

Electrophoretic separations were theoretically performed for large polyelectrolytes such as DNA in the membrane chromatography. This paper deals with the study of the mass transfer involved in multi-layered membrane chromatography in the presence of an electric field. The different contributions to mass transfer were considered in order to establish a relationship providing intramembrane convection effects as a function of an electric field since a polyelectrolyte is quickly oriented through pores in the field direction. Dimensionless transient mass balance equations were derived considering diffusion and electrophoretic convection, and the mass transfer was theoretically studied using two different Peclet numbers in the fluid and solid phases, showing how the concentration profiles of polyelectrolyte inside a membrane varies in the membrane according to values of Peclet number of an individual polyelectrolyte. Governing equations were solved by an operator theory.

Separation of DNA by mass-transfer properties in the presence of an electric field

Experimental and theoretical works were performed for the separation of large polyelectrolyte such as DNA in the column packed with gel particles under influence of an electric field. Since DNA quickly orients through the pores in the field direction, this paper presents how intraparticle convection affects the separation of DNAs in the column. Dimensionless transient mass balance equations were derived considering diffusion and electrophoretic convection. The separation criteria are theoretically studied using two different Peclet numbers in the fluid and solid phases and these criteria were verified using two different DNAs by electrophoretic mobilities measured experimentally, showing how the separation position of DNAs varies in the column according to values of Pe f/ Pe g of individual DNA. Governing equations are solved by an operator theory and the characteristic method to yield the column response.

Separation of ϕX HAE III DNA with electrochromatography

Experimental and theoretical works were performed for the separation of large polyelectrolytes such as DNA in the column packed with gel particles under an electric field. This paper shows how intraparticle convection effects the separation of DNAs in the column because DNAs quickly oriented through the pores in the field direction. Dimensionless transient mass balance equations were derived considering diffusion and electrophoretic convection. The separation criteria is theoretically studied using two different Peclet numbers in the fluid and solid phases and these criteria were verified uing two different DNAs by electrophoretic mobilities measured experimentally, showing how the separation position of DNAs varies in the column according to values ofPe f/Peg of individual DNA. Governing equations are simultaneously solved by operator theoretic and characteristic methods to yield the column response.

Stability of colloidal silica, sikron and polystyrene latex influenced by the adsorption of polycations of different charge density

In order to describe the influence of cationic polyelectrolytes (PEs) on the stability and flocculation of dispersed particles the adsorption of statistic copolymers of diallyl-dimethyl-ammonium-chloride (DADMAC) and of N-methyl- N-vinylacetamide (NMVA) and of the corresponding homopolymers was investigated on particles of colloidal silica, quartz powder Sikron and polystyrene latex. The adsorbed amounts and the hydrodynamic thicknesses of the polymer layers and furthermore the surface charge densities and the electrophoretic mobilities of the bare and covered particles have been measured. On silica and latex the adsorbed amounts and the layer thicknesses increase with ionic strength and pH (only silica), with decreasing chain charge density of the polycations and at high electrolyte concentration with the molar mass of the polymers. The zero point of charge (zpc), and the shape of the zeta potential-pH plots vary with the coverage of the surface by the polycations. The zpc-values are independent of the ionic strength. Zeta potentials, diffusion coefficients and flocculation rates measured in dependence of the adsorbed amount of the different charged copolymers at various salt concentration and pH demonstrate fast flocculation by van der Waals attraction at small zeta potentials because of screening of the repulsive surface charges at high ionic strength and by adsorbed polycations. Additional with high molecular polycations slow mosaic flocculation is observed at low PE concentrations at still higher surface charge and slow bridging flocculation at approach of plateau adsorption. Stabilization is accomplished at low salt concentration at full coverage by electrostatic repulsion because of charge reversal. At large ionic strength high molar mass PEs are necessary to stabilize the particles sterically by osmotic repulsion of the long tails. For Sikron particles optimum flocculation is obtained at about 30% of plateau adsorption of poly(diallyl-dimethyl-ammonium-chloride) (PDADMAC) and the size of the flocs increase with molar mass.

The effect of electrophoretic convection for the separation of solute in the chromatography column (I)

A theoretical model has been derived in an electrophoretic packed column where an electric potential is applied to a column in the axial direction. The effect of electrophoretic convection in gel particles packed in the column significantly contributes to the separation of large polyelectrolytes because the conformation of polyelectrolyte quickly orients in the field direction. The dependence of the transport in the gel particle upon field intensity and molecular size aids in understanding the transport of polyelectrolyte in the packed column, since the convective velocity of polyelectrolyte is accelerated inside a porous gel particle. There are few convection studies of large poly-electrolyte in a column packed with porous gel particles under an electric field for the separation. Convective-diffusive transport of a large polyelectrolyte is analyzed using Peclet number described by electrophoretic mobility and diffusion coefficient measured experimentally. The separation of two different polyelectrolytes in the packed column is performed using a value ofPe f/Peg of individual polyelectrolyte by molecular size and an electric field. The purpose of this paper is to study the separation of solute from a mixture in the column using the physicochemical properties in the gel particle which are measured experimentally.

Scaling and scale breaking in polyelectrolytes

We consider the thermodynamics of a uniformly charged polyelectrolyte with harmonic bonds. For such a system there is at high temperatures an approximate scaling of global properties like the end-to-end distance and the interaction energy with the chain length divided by the temperature. This scaling is broken at low temperatures by the ultraviolet divergence of the Coulomb potential. By introducing a renormalization of the strength of the nearest-neighbor interaction the scaling is restored, making possible an efficient blocking method for emulating very large polyelectrolytes using small systems. The high temperature behavior is well reproduced by the analytical high-T expansions even for fairly low temperatures and system sizes. In addition, results from low-T expansions, where the coefficients have been computed numerically, are presented. These results approximate well the corresponding Monte Carlo results at realistic temperatures. A corresponding analysis of screened chains is performed. The situation here is complicated by the appearance of an additional parameter, the screening length. A window is found in parameter space, where scaling holds for conformational as well as thermodynamical properties. This window corresponds to situations where the range of the potential interpolates between the bond length and the size of the chain. This scaling behavior, which is verified by Monte Carlo results, is, for the end-to-end distance, consistent with Flory scaling. Also for the screened chain a blocking approach can be devised, that performs well for low temperatures, whereas the low-T expansion is inaccurate at realistic temperatures.

Blocking technique for emulating very large polyelectrolytes.

A new Monte Carlo method for computing thermodynamical properties of very large polyelectrolytes is presented. It is based on a renormalization group relating the original polymer to a smaller system, where, in addition to the naively rescaled forces, a corrective nearest-neighbor interaction originating from the short distance Coulomb cutoff is introduced. The method is derived for low T but is in the unscreened case valid for all T. Large polymers with N monomers are emulated by Monte Carlo calculations on smaller systems, $K\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}N/Q$. The computational gain of the method is ${Q}^{3}$ and is explored with emphasis on room temperature.

Protected amino acids as novel low‐molecular‐weight displacers in cation‐exchange displacement chromatography

Although the ability to carry out simultaneous concentration and purification in a single displacement step has significant advantages for downstream processing of pharmaceuticals, a major impediment to the implementation of displacement chromatography has been the lack of suitable displacer compounds. An important recent advance in the state of the art of displacement chromatography has been the discovery that low-molecular-weight dendritic polymers can be successfully employed as displacers for protein purification in ion-exchange systems. In this article, protected amino acid esters (based on arginine and lysine) are shown to be useful displacers for protein purification in cation-exchange systems. A dynamic affinity plot is employed to evaluate the affinity of these low-molecular-weight compounds under dis-placement conditions. In contrast to large polyelectroyte displacers, the efficacy of these low-molecular-weight displacers was shown to be dependent on both the initial carrier salt concentration and the displacer concentration. In addition to the funcamental interest generated by low-molecular-weight displacers, it is likely that these displacers will have significant operatioal advantages as compared with large polyelectrolyte displacers. (c) 1995 John Wiley & Sons, Inc.

The Separation of Polyelectrolyte Using an Electric Field in a Packed Column

Abstract The effect of electrophoretic convection in a packed column is presented. When an electric field is applied, the conformation of polyelectrolyte quickly orients in the field direction. The convective velocity of polyelectrolyte inside a porous gel particle is accelerated. The dependence of the transport in the gel particle upon field intensity and molecular size aids in understanding the transport of polyelectrolyte in the packed column. To date, few dynamic studies of polyelectrolyte in a porous gel particle have been attempted for the separation of polyelectrolyte in a packed column. A large polyelectrolyte like DNA will separate due to conformation changes in the presence of the electric field. Convective-diffusive transport of DNA is analyzed by physical properties measured experimentally, such as the diffusion coefficient, the electrophoretic convection, and the gel porosity. The purpose of this study is to show how the variation of physicochemical properties in the gel particle affects the separation of DNA from a mixture in a packed column. A theoretical model using the characteristic method is used to calculate the separation point in a packed column.

Antibiotics as low-molecular-mass displacers in ion-exchange displacement chromatography

While the ability to carry out simultaneous concentration and purification in a single displacement step has significant advantages for downstream processing of pharmaceuticals, a major impediment to the implementtion of displacement chromatography has been the lack of suitable displacer compounds. An important recent advance in the state-of-the-art of displacement chromatography has been the discovery that low-molecular-mass dendritic polymers and protected amino acids can be successfully employed as displacers for protein purification in ion-exchange systems. In this paper, the efficacy of aminoglycosidic antibiotic displacers are investigated for protein purification in cation-exchange systems. The displacers neomycin B and streptomycin A are employed with model feed mixtures containing moderately to very strongly retained proteins. These experiments demonstrate that this new class of low-molecular-mass antibiotic displacers can indeed act as efficient protein displacers. In fact, the displacer neomycin B is the first low-molecular-mass displacer reported i the literature which can readily displace very strongly retained proteins such as lysozyme. In addition to the fundamental interest generaed by low-molecular-mass displacers, it is likely that these displacers will have significant operational advantages as compared to large polyelectrolyte displacers.

Ion-exchange displacement chromatography of proteins Dendritic polymers as novel displacers

While the ability to carry out simultaneous concentration and purification in a single displacement step has significant advantages for downstream processing of biopharmaceuticals, a major obstacle to the implementation of displacement chromatography has been the lack of appropriate displacer compounds. All protein displacement separations reported to date have employed relatively high-molecular-mass (> 2000) polyelectrolyte displacers. In this paper, results are presented on the discovery that low-molecular-mass dendritic polymers can be successfully employed as efficient displacers for protein purification in ion-exchange systems. Pentaerythritol-based dendritic polyelectrolytes ranging in molecular mass from 480 to 5100 were investigated as potential displacers for the purification of proteins in cation-exchange systems. The adsorption properties of these dendrimers were investigated using the steric mass action (SMA) model of non-linear ion-exchange chromatography. An analysis of the resulting SMA parameters using a dynamic affinity plot indicated that these dendrimers should have sufficient affinity to act as protein displacers. Displacement separations of protein mixtures in cation-exchange systems were carried out using zero-, first- and second-generation dendrimers. These experiments demonstrate that this new class of dendritic polyelectrolytes can indeed act as efficient protein displacers. The ability of a low-molecular-mass compound such as the “zero”-generation dendrimer ( M r 480) to displace proteins is very significant in that it represents a major departure from the conventional wisdom that large polyelectrolyte polymers are required to displace proteins in ion-exchange systems. In addition to the fundamental interest generated by low-molecular-mass displacers, it is likely that these displacers will have significant operational advantages as compared to large polyelectrolyte displacers.