Charge Stoichiometry Research Articles

Fast Characterization of Polyelectrolyte Complexes by Inline Coupling of Capillary Electrophoresis to Taylor Dispersion Analysis

The inline coupling of capillary electrophoresis (CE) to Taylor dispersion analysis was used for the characterization of polyelectrolyte complexes. The charge stoichiometry and the hydrodynamic radii of the two polyelectrolyte constituents were determined in a fully automated single run using standard commercial CE apparatus with a single detection point. The proposed methodology utilizes unusual high ionic strength (1.3 M) background electrolyte to obtain the dissociation and electrophoretic separation of polyelectrolyte constituents. Such highly saline conditions in combination with neutrally coated capillary were found to avoid any polyelectrolyte interactions onto the capillary surface. This innovative methodology should greatly contribute to simplify and accelerate the characterization of polyelectrolyte complexes or polyplexes.

Effect of Polyelectrolyte Architecture and Size on Macroion–Dye Assemblies

This study describes the influence of polyelectrolyte building block nature on the formation of supramolecular polyelectrolyte-dye nanoparticles self-assembled through electrostatic interactions of the oppositely charged building units and π-π interactions in-between dye molecules ("electrostatic self-assembly"). The anionic azo dye Acid Red 26 (Ar26) is combined with cationic polyamidoamine dendrimers of generations G0, G2, G4, G6, and G8 and linear polycations polylysine (PolyLys) and polyallylamine hydrochloride (PAH). Light scattering reveals defined supramolecular particles with hydrodynamic radii R(H) = 15 nm to R(H) = 50 nm for slight excess of G2-G8 dendrimers. G0 does not yield stable assemblies. Linear polyelectrolytes form assemblies with hydrodynamic radii from R(H) = 20 nm to R(H) = 200 nm. Thermodynamic measurements by isothermal titration calorimetry (ITC) show that all macroions bind dye molecules up to about charge stoichiometry, and assembly formation is predominantly enthalpically driven. Differences in dye-dye interactions are related to structural features by analyzing endothermic heats of aggregate disruption through excess macroion addition. A simple model connects thermodynamic parameters with the internal assembly structure.

Association of a Cylindrical Polyelectrolyte Brush with Tetravalent Counterions

Cylindrical poly(styrene sulfonate) brushes were combined with a tetravalent double-DABCO based counterion. With increasing addition of counterion, hydrodynamic radius and radius of gyration decrease and AFMreveals a conformation change from wormlike to curled structures. Rg/Rh changes from 1.3 to 0.9. Above charge stoichiometry, brushes become interconnected into finite size assemblies, which are stable in aqueous solution for charge ratios (ratio of the molar concentration of charged counterion groups to the molar concentration of charged monomer units of the polymer brush) 1 < l < 1.2. They are compact and consist of the brushes in curled (bent) conformation, which is in difference to network-like aggregates from cylindrical poly(styrene sulfonate) brushes with tetravalent porphyrin counterions (Gröhn et al. Macromolecules 2009) and to a wormlike - bent conformation - helix transition found for another brush counterion system (Müller et al. Soft Matter 2009).

Influencing Particle Size and Stability of Ionic Dendrimer−Dye Assemblies

This article focuses on the physical chemical aspects of the formation of supramolecular nanoparticles with defined size and varying shape through electrostatic self-assembly of macroions and multivalent aromatic counterions. For cationic poly(amidoamine) dendrimers and different di- and trivalent sulfonate groups carrying azo dyes, the onset of interdendrimer connection and assembly size (hydrodynamic radius 20 nm < R(h) < 150 nm) depend on counterion/macroion loading ratio. Centrifugation and dialysis experiments show assemblies coexisting with individual dye-loaded dendrimers with lower dye/dendrimer ratio at small loading ratio, while around charge stoichiometry only assemblies are present. Zeta-potential measurements reveal a positive charge for samples with excess dendrimer. For excess dye, overloading to negatively charged assemblies is possible for some dyes, which is consistent with concentration-dependent stability revealing a second mode of more loosely bound dye ions. Kinetic versus thermodynamic effects are discussed based on varying the preparation route. The interaction enthalpy is an important factor in determining assembly size. Solution structures are characterized by static and dynamic light scattering, while atomic force microscopy showed that assemblies can also be deposited on surfaces.

ChemInform Abstract: A Quantitative Discrimination Between Reversible Li+-Insertion and Irreversible Solvent Oxidation at a Lithium/Manganese-Spinel Electrode.

Abstract Oxidic Li + -insertion compounds of the donor type in aprotic Li + -electrolytes are of high practical importance as positives in rechargeable Li + -ion batteries. The manganese oxides MnO x are of special interest as host lattices due to their high reversibility and to the relatively positive potentials. However, these materials may induce irreversible anodic decomposition of the organic solvent molecules, especially towards the end of the charging process. Protons are injected into the electrolyte in this case. It is possible to evaluate these side reactions quantitatively through a measurement at the rotating ring/disk-electrode (RRDE). The disk was made of a 1 μm thick layer of MnO 2 (anodic deposit) on Pt (I) or a ceramic layer of the spinel LiMn 2 O 4 on Ti, which was fabricated after Beers’s method at a firing temperature of 400 (II) and 600°C (III). The ring was made of Pt. At the ring, protons were reduced to H 2 at a half wave potential of −0.25 V versus saturated sodium chloride electrode (SSCE). The electrolytes were 0.1 M LiClO 4 in propylenecarbonate (PC) and acetonitrile (MeCN). These measurements showed that the novel MnO x -layers behave similar to the conventional porous battery electrodes which are much thicker and are made of powdery materials. Charge stoichiometry y in Li y Mn 2 O 4 is found to increase from I to III from 0.2 to 2.0. No solvent oxidation could be detected at the potentials of the reversible Li + -intercalation peaks in cyclic voltammogram. The irreversible side reaction can be excluded therefore with a margin of error of 1–2%. This is in contrast to the former results obtained from the graphite intercalation compounds of the acceptor type (A-GIC), albeit at potentials more positive by 1 V. However, just behind the reversible Li + -deintercalation peak, i.e. charge direction, the positive end of the electrochemical window is attained. The current rises steeply. Abundant protons are injected into the electrolyte. The potentials are by 0.5–1 V more negative than at Pt due to the electrocatalytic activity of MnO x with respect to the irreversible anodic oxidation of the solvent molecules PC and MeCN.

Kinetics of Complex Formation between DNA and Cationically Charged Cylindrical Brush Polymers Observed by Stopped Flow Light Scattering

The complex formation of pUC19 DNA and a cylindrical brush polymer with quaternized poly(vinyl pyridinium) side chains is investigated by stopped flow light scattering (LS). In highly dilute solutions up to two kinetic processes are observable, depending on the mole fraction of anionic charges, x(anion) . For x(anion) < 0.2 and x(anion) > 0.4-0.5 only one kinetic process was identified leading to the largest complexes at x(anion) = 0.4 well below charge stoichiometry. For 0.2 < x(anion) < 0.4 two kinetic growth processes were identified: The initially formed complexes on the time scale of a few hundred milliseconds keep growing by an unusual fractal growth process until after several minutes they become stable. This last fractal process does not follow the classical Smoluchowski coagulation theory as monitored by LS up to 90 s after mixing.

Interaction of sodium dodecyl sulfate and high charge density comb polymers at the silica/water interface

The structures of interfacial layers formed from mixtures of comb polymers, comprising a high charge density cationic backbone and poly(ethylene oxide) (PEO) side-chains, with the anionic surfactant sodium dodecyl sulfate (SDS) at the silica/water interface, have been determined using neutron reflectivity measurements. The use of mixtures in which only the isotopic composition of the surfactant is changed has made it possible to determine the interfacial volume fraction profiles for both the polymer and the surfactant. For the polymer with 90% of the segments charged and 10% of the segments carrying PEO side-chains, there are four regimes of interfacial behavior with increasing surfactant composition of the bulk solution. First there is adsorption of surfactant to the polymer-covered surface, then, slightly above polymer charge stoichiometry, there is adsorption of near-neutral polymer/surfactant complexes followed by the adsorption of polymer/surfactant aggregates, with a well-defined internal structure. If the concentration of SDS is increased directly from below polymer charge stoichiometry to above the cmc, micelles or polymer/micelle complexes interact with the pre-existing polymer layer. Increasing the fraction of segments carrying PEO side-chains to 25% suppresses the formation of charge-neutral polymer/surfactant complexes at the interface. There is an increase in the adsorption of surfactant, which interacts with the pre-existing layer of polymers. This results in the surface aggregation of SDS and a swelling of the PEO side-chains from a mushroom to a brush-like configuration.

Polyelectrolyte−Macroion Complexation in 1:1 and 3:1 Salt Contents: A Brownian Dynamics Study

On the basis of the coarse-grained model, we performed Brownian dynamics simulations to investigate behavior of the polyelectrolyte (PE)-macroion complexations in 1:1 and 3:1 salt contents. Our simulation results show that in 3:1 salt content there exists a critical salt concentration (CSC), which is determined by the charge stoichiometry, for the breakup of the PE-macroion complexations. Beyond the CSC concentration, an obvious depletion appears in the macroion-macroion and macroion-PE interactions, which is absent in 1:1 salt content. Both the mobilities of macroions and PEs increase monotonically with increasing the salt concentration in 1:1 and 3:1 salt contents. And the mobility in 3:1 salt content is always larger than that in corresponding 1:1 salt content, which is due to the fact that in 3:1 salt content the PE-macroion complexations are looser than those in 1:1 salt content. Moreover, we observed the collapse and re-expansion of PE chains with the increase of the salt concentration in the PEs-macroions systems of 3:1 salt content, which is due to the charge inversion of PE chains induced by the adsorption of trivalent cations. In addition, we also explored the effects of salt concentration and the length and charge density of PE chains. Our simulation results show that the effects of the length and charge density of PE chains in both salt contents on the radial distribution functions (RDFs) between macroions and between a macroion and a PE segment are similar to these in salt free solution basically. However, we observed an interesting phenomenon that the gyration radius of PE chains in the system of 3:1 salt content is not affected significantly by its charge density, while that in 1:1 salt content increases monotonically.

Gel particles from spray-dried disordered polysaccharides

The formation of gel particles from alginate and ι-carrageenan was studied through a novel pathway of formation via an amorphous spray-dried intermediate. Dried biopolymer particles were suspended in solutions of different Ca 2+ concentration. Particle size ranges and microscopic observation demonstrated that a range of swelling behaviour could be induced, with lower calcium concentrations resulting in more expanded particles, until a lower limit is reached below which particles initially dissolve. For the same calcium charge stoichiometry, larger swollen gel particles were obtained for alginate than for ι-carrageenan. The ability to produce a range of swollen biopolymer gel particle sizes, on the order of 1–600 μm, is attributed to the balance between gelation and dissolution kinetics, with fast gelation kinetics and slow dissolution promoting production of small gel particles whilst fast dissolution with slow gelation leads to larger gel particles. By controlling the solution environment in which rehydration is carried out, it is therefore possible to produce particles with desired degrees of swelling from a single starting material.

Colloidal Complexes from Poly(vinyl amine) and Carboxymethyl Cellulose Mixtures

The phase behaviors of polyelectrolyte complexes formed from dilute solutions of poly(vinyl amine) (PVAm) and carboxymethyl cellulose (CMC) were determined as a function of overall composition and pH. The phase diagram included regions with soluble complexes, colloidal complexes, and macroscopic precipitates. Colloidal complexes were stable when either polymer was in sufficient excess to give electrosteric stabilization. The polymer mixing ratios giving complexes with an isoelectric point of 7 could be predicted from a simple model using the degree of ionization vs pH data for PVAm and CMC. The model failed at extreme pH values because not all added polymer was incorporated into the complexes. At pH 7, essentially all the added polymer was incorporated into the colloidal complex or precipitate, as long as the mixing ratio was within +/-10% of charge stoichiometry. The interaction of PVAm and CMC at pH 7 was endothermic, supporting the generally accepted viewpoint that the interaction of oppositely charged polyelectrolytes is entropy-driven. Although the colloidal complexes had a broad particle size distribution, the average particle size was rather insensitive to mixing ratio. By contrast, complex size was sensitive to electrolyte concentration with no complex formation when the NaCl concentration was > or =2 M.

Carboxymethyl Cellulose:Polyvinylamine Complex Hydrogel Swelling

The swelling behavior of the polyelectrolyte complex films made from polyvinylamine (PVAm) or poly(vinylformamide-co-vinylamine) copolymers and carboxymethyl cellulose (CMC) was studied as a function of polymer composition, pH, and salt concentration. Swelling is determined by the balance between ionic cross-link density, opposing swelling, with solvation and Donnan effects promoting swelling. Films containing excess ammonium groups gave the greatest swelling at low pH, whereas excess carboxyl groups enhanced swelling at high pH. Films with balanced charge stoichiometry (CMC:PVAm 3:1 w:w) gave the minimum swelling. High concentrations of sodium chloride increased swelling due to the decomposition (screening) of ionic cross-links, whereas calcium ion decreased swelling possibly because of calcium dicarboxylate cross-links. A simple swelling model based on the ionization behavior of dilute polymers and ionic cross-linking predicted the major swelling behaviors, including the effects of pH and polymer compos...

One- versus two-electron reaction pathways in the electrocatalytic reduction of benzyl bromide at silver cathodes

The electrocatalytic reduction of benzyl bromide at a silver cathode has been investigated in acetonitrile in the absence and presence of acids, using cyclic voltammetry (CV) and controlled-potential electrolysis (CPE). CV gives rise to two reduction waves, which represent the dissociative 1e − reduction of PhCH 2Br to PhCH 2 and Br − followed by a further reduction of the benzyl radical to PhCH 2 - at more negative potentials. The charge stoichiometry (1e − vs 2e −/molecule) and product distribution depend on the applied potential and reaction medium. In the absence of added acids, the reduction of PhCH 2Br at potentials of the first wave is a 1e − process mainly yielding bibenzyl, whereas toluene becomes the principal product at potentials beyond the second wave. The addition of acids strongly modifies the dependence of selectivity on the applied potential. The presence of a strong acid changes the mechanism of the process, which now becomes a 2e − reduction to toluene, even at potentials corresponding to the first reduction wave.

Adsorption of toluidine blue on pulp fibers

How pulp fibers interact with salt is important for fiber swelling, water retention and drainage. The dye toluidine blue is a salt, consisting of a chloride anion and an aromatic cation, which can be easily detected by light absorbance measurements. In distilled water, toluidine blue adsorption on fibers proceeds up to charge stoichiometry, provided the accessible lignin content is below a critical level. Thus, toluidine blue adsorption provides a convenient alternative method to determine the charge of fibers. The adsorption of toluidine blue, on thermomechanical and kraft pulp fibers, was found to depend strongly on pH and ionic strength. The data for thermomechanical pulp (TMP) fibers can be explained by a model in which the dye can adsorb on fibers in two ways: physisorption on lignin and by ion-exchange with cations inside the fiber wall. For fibers with a low charge density, and for ionic strengths larger than about 0.1 mM, an adsorption plateau is reached which corresponds to maximum toluidine blue adsorption on lignin. At lower ionic strengths the adsorption is increased due to ion-exchange up to charge stoichiometry, i.e. the (positive) charge of the adsorbed dye equals the (negative) charge of the fiber wall. For highly charged fibers, more lignin becomes accessible due to fiber swelling, and toluidine adsorption on lignin can exceed stoichiometry, resulting in positively charged fibers. For kraft fibers, which contain very little lignin, adsorption is governed by ion-exchange only. Despite the fact that the fibers are subjected to shear, the rate of adsorption is determined by diffusion, due to the small size of the dye molecules.

On the Indirect Polyelectrolyte Titration of Cellulosic Fibers. Conditions for Charge Stoichiometry and Comparison with ESCA

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration.

Substrate interactions in the human type IIa sodium-phosphate cotransporter (NaPi-IIa)

We have characterized the kinetics of substrate transport in the renal type IIa human sodium-phosphate cotransporter (NaPi-IIa). The transporter was expressed in Xenopus laevis oocytes, and steady-state and pre-steady-state currents and substrate uptakes were characterized by voltage-clamp and isotope flux. First, by measuring simultaneous uptake of a substrate (32Pi, 22Na) and charge in voltage-clamped oocytes, we established that the human NaPi-IIa isoform operates with a Na:Pi:charge stoichiometry of 3:1:1 and that the preferred transported Pi species is HPO4(2-). We then probed the complex interrelationship of substrates, pH, and voltage in the NaPi-IIa transport cycle by analyzing both steady-state and pre-steady-state currents. Steady-state current measurements show that the apparent HPO4(2-) affinity is voltage dependent and that this voltage dependency is abrogated by lowering the pH or the Na+ concentration. In contrast, the voltage dependency of the apparent Na+ affinity increased when pH was lowered. Pre-steady-state current analysis shows that Na+ ions bind first and influence the preferred orientation of the transporter in the absence of Pi. Pre-steady-state charge movement was partially suppressed by complete removal of Na+ from the bath, by reducing extracellular pH (both in the presence and absence of Na+), or by adding Pi (in the presence of 100 mM Na). None of these conditions suppressed charge movement completely. The results allowed us to modify previous models for the transport cycle of NaPi-II transporters by including voltage dependency of HPO4(2-) binding and proton modulation of the first Na+ binding step.

Polyelectrolyte complex formation between iota-carrageenan and poly( l-lysine) in dilute aqueous solutions: a spectroscopic and conformational study

The polyelectrolyte complex formation between iota- (ι-)carrageenan and poly( l-lysine) (PLL) has been investigated in HEPES 5 mM, NaCl 150 mM pH 6.5 at 25 °C, in dilute conditions. After building of the ternary phase diagram of the system, the formation of soluble polyelectrolyte complexes in transparent systems has been evidenced by means of spectroscopic techniques. Absorption spectrum of methylene blue (MB +) interacting with ι-carrageenan chains, in presence of increasing amounts of the polypeptide, as well as fluorescence polarization of a FITC-labeled PLL and circular dichroism spectrum of PLL, in presence of increasing amounts of the polysaccharide, have been studied. In all cases, the endpoint occurred for a peptide to polysaccharide weight ratio of about 0.82, indicating an approximate 1/1 charge stoichiometry of the polyelectrolyte complex formed. Furthermore, the polyelectrolyte complex formation process was proved to be conformation-directing as PLL adopts a right-handed α-helical conformation when mixed with ι-carrageenan.

Polyelectrolytes. 2. Intrinsic or Extrinsic Charge Compensation? Quantitative Charge Analysis of PAH/PSS Multilayers

Floating multilayers of polyallylamine/polystyrenesulfonate (PAH/PSS) adsorbed to a dimethyldioctadecylammonium bromide (DODAB) monolayer at the air/water interface (at pH 5.5) are analyzed quantitatively with respect to the internal charge stoichiometry of the polyelectrolytes. To this end the adsorbed amount of polymer is translated into charge per area. It is postulated that the strong acid PSS is fully charged (fully dissociated). The weak polyelectrolyte PAH is also assumed to be fully dissociated. This is vindicated by theoretical considerations and deduced from pH-dependent studies of the isotherms of Langmuir monolayers of negatively charged dimyristoylphosphatidic acid (DMPA) with PAH adsorbed from the subphase. With both polyelectrolytes fully charged the PAH charges significantly overcompensate the PSS charges. The polyelectrolyte charge stoichiometry is not 1:1, and the multilayer must contain some small counterions (Cl-) for charge compensation. It is suggested that this “extrinsic compensation” occurs when the charge density of the polyelectrolytes exceeds a certain threshold. If the distance between the charges is less than the Bjerrum length, the strong binding of the counterions (“Manning condensation”) prevents their release upon multilayer formation. This explains why multilayers with PAH with its unusually high charge density contain counterions whereas other polyelectrolyte films are ion-free. Literature data support this hypothesis.

Investigation of the association in water of sodium dodecyl sulfate with a positively charged copolymer based on N -isopropylacrylamide

The interactions of sodium dodecyl sulfate with a positively charged copolymer based on N-isopropylacrylamide (NIPAM) have been investigated in aqueous solution by turbidimetric and viscometric measurements. The copolymer contains mainly NIPAM and only 5 mol % of the charged comonomer [3-(methacryloylamino)propyl]-dimethyloctylammonium bromide. The polymer–surfactant complex is insoluble for mixture compositions near to the charge stoichiometry, while it exhibits lower critical solution temperature behavior for mixtures with an excess of polymer or surfactant. In the case of surfactant excess, the transition from an expanded coil to a globular state upon heating has been observed by viscometry.

A quantitative discrimination between reversible Li +-insertion and irreversible solvent oxidation at a lithium/manganese-spinel electrode

Oxidic Li +-insertion compounds of the donor type in aprotic Li +-electrolytes are of high practical importance as positives in rechargeable Li +-ion batteries. The manganese oxides MnO x are of special interest as host lattices due to their high reversibility and to the relatively positive potentials. However, these materials may induce irreversible anodic decomposition of the organic solvent molecules, especially towards the end of the charging process. Protons are injected into the electrolyte in this case. It is possible to evaluate these side reactions quantitatively through a measurement at the rotating ring/disk-electrode (RRDE). The disk was made of a 1 μm thick layer of MnO 2 (anodic deposit) on Pt (I) or a ceramic layer of the spinel LiMn 2O 4 on Ti, which was fabricated after Beers’s method at a firing temperature of 400 (II) and 600°C (III). The ring was made of Pt. At the ring, protons were reduced to H 2 at a half wave potential of −0.25 V versus saturated sodium chloride electrode (SSCE). The electrolytes were 0.1 M LiClO 4 in propylenecarbonate (PC) and acetonitrile (MeCN). These measurements showed that the novel MnO x -layers behave similar to the conventional porous battery electrodes which are much thicker and are made of powdery materials. Charge stoichiometry y in Li y Mn 2O 4 is found to increase from I to III from 0.2 to 2.0. No solvent oxidation could be detected at the potentials of the reversible Li +-intercalation peaks in cyclic voltammogram. The irreversible side reaction can be excluded therefore with a margin of error of 1–2%. This is in contrast to the former results obtained from the graphite intercalation compounds of the acceptor type (A-GIC), albeit at potentials more positive by 1 V. However, just behind the reversible Li +-deintercalation peak, i.e. charge direction, the positive end of the electrochemical window is attained. The current rises steeply. Abundant protons are injected into the electrolyte. The potentials are by 0.5–1 V more negative than at Pt due to the electrocatalytic activity of MnO x with respect to the irreversible anodic oxidation of the solvent molecules PC and MeCN.

Layer-by-layer deposition of oppositely charged polyelectrolytes on the surface of condensed DNA particles.

DNA can be condensed with an excess of poly-cations in aqueous solutions forming stable particles of submicron size with positive surface charge. This charge surplus can be used to deposit alternating layers of polyanions and polycations on the surface surrounding the core of condensed DNA. Using poly-L-lysine (PLL) and succinylated PLL (SPLL) as polycation and polyanion, respectively, we demonstrated layer-by-layer architecture of the particles. Polyanions with a shorter carboxyl/backbone distance tend to disassemble binary DNA/PLL complexes by displacing DNA while polyanions with a longer carboxyl/backbone distance effectively formed a tertiary complex. The zeta potential of such complexes became negative, indicating effective surface recharging. The charge stoichiometry of the DNA/PLL/SPLL complex was found to be close to 1:1:1, resembling poly-electrolyte complexes layered on macrosurfaces. Recharged particles containing condensed plasmid DNA may find applications as non-viral gene delivery vectors.