Surface Charge Concentration Research Articles

A Gel Filtration-Based Method for the Purification of Infectious Rotavirus Particles for Environmental Research Applications.

This article describes a rapid method for purifying infectious rotavirus particles from cell culture for environmental research. The method is based on size-exclusion chromatography using TOSOH TSKgel® G5000PWXL-CP with a TSKgel® Size Exclusion G2500PWxl guard column, set up on an AKTA Explorer10. Four peaks were identified from the chromatogram and the corresponding fractions were collected and analysed by electron microscopy, 1-step quantitative reverse transcription polymerase chain reaction (RT-PCR) and qNano measurement. Infectivity potential of the recovered virus particles was determined using cell culture. Our analysis reveals that the first fraction contains majority of the intact triple-layered infectious virions while the other three fractions contain mixtures of empty capsids and intact infectious virions. Our results also indicate that there is a gross overestimation of rotaviruses in crude extracts due to encapsidated RNA in the order of 2.3×1011 particles and we note that estimates by qNano are similarly skewed (1.36×1013 particle) possibly due to empty capsids and cellular debris. In summary we present a method for purification (~12h) of rotaviruses for a more robust and accurate quantification of virus size, surface charge and particle concentration in environmental contexts.

Geometrical parameters controlled focusing and enhancing near field in infinite circular metal-dielectric multilayered cylinder

The plasmon resonance-induced near electric field focusing and enhancement of three-layered silver nano-cylinder has been studied by quasi-static electricity. A field enhancement factor of more than 102 times can be obtained in the middle dielectric wall between the inner silver wire and outer tube around the resonance wavelengths of 400–500 nm. Because of the anti-symmetric coupling between the bonding tube plasmon and the wire plasmon, the incident electric field could be fine focused between the two metallic surfaces by decreasing the middle wall thickness. As a result of the curvature-dependent surface charge concentration, thinner dielectric wall with small diameter provides stronger local field enhancement. It provides the potential applications of plamonic nano-structures for high-density and high-contrast optical data storage under the diffraction limit.

In situmagnetometry studies of magnetoelectric LSMO/PZT heterostructures

In order to identify and quantify characteristics of the magnetoelectric coupling at ferromagnetic/ferroelectric interfaces, epitaxial La${}_{1\ensuremath{-}x}$Sr${}_{x}$MnO${}_{3}$/Pb(Zr,Ti)O${}_{3}$ (LSMO/PZT) heterostructures were deposited by large-distance magnetron sputtering. The remarkably high lateral uniformity achieved in such films allowed for a ferroelectric device area of more than 6 mm${}^{2}$. This has enabled for superconductive quantum interference device (SQUID) measurements of the magnetic response to the systematically, completely in situ, varied remanent ferroelectric polarization. Temperature dependence of the magnetic modulation upon charging and the magnetic response to the ferroelectric stimulation indicate a field-effect dominated coupling mechanism and generally confirm the concept of electrostatic hole (${h}^{+}$) doping of LSMO. The modulation of magnetization was comprehensively analyzed for a broad range of electrostatically induced surface charge concentrations. For small charge modulations at low temperature a linear tuning coefficient of $\ensuremath{\approx}\ensuremath{-}3.6\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/{h}^{+}$ has been determined. This suggests the activation of an antiferromagnetic coupling, even for very small surface charge densities. Simultaneously, a shift in the magnetic transition temperature at higher surface charge concentration indicates the presence of a ferromagnetic phase at the LSMO/PZT interface. Eventually, a physical picture of magnetoelectric coupling is proposed in which these quantitative results are consistently interpreted, in terms of a surface-charge dependent electronic phase separation with the coexistence of antiferromagnetic and ferromagnetic regions at the ferromagnetic/ferroelectric interface.

Adsorbent for chromium removal based on graphene oxide functionalized with magnetic cyclodextrin–chitosan

A simple chemical bonding method to synthesize magnetic cyclodextrin–chitosan/graphene oxide (CCGO) was reported. The adsorption behaviors of Cr(VI) in aqueous solution on CCGO were systematically investigated. As the results shown that, with the advantage of high surface area, abundant hydroxyl and amino groups of CCGO, and the magnetic property of Fe3O4, the Cr(VI) can be easily and rapidly extracted from the water by magnetic attraction under investigation. The adsorption equilibrium of CCGO for Cr(VI) corresponded with Langmuir isotherm, and the novel adsorbent exhibited better Cr(VI) removal efficiency in solutions with low pH. It was found that the Cr(VI) adsorption performance of CCGO strongly depends on their surface charge concentration and specific surface area. These results provide evidences for estimating and optimizing the removal of metal ions from the wastewater by using of CCGO composites in the future.

Three Mutations in the BIN1 N-BAR Domain Impair Membrane Curvature Generation via Different Mechanisms

Cellular signaling and membrane transport are tightly coupled to membrane curvature. Bin/Amphiphysin/Rvs (BAR) domain-containing proteins are key players in regulating membrane shapes. Particularly, BIN1, an N-BAR domain containing protein is believed to be essential in initiating and maintaining plasma membrane invaginations (T-tubules) in muscle cells. Three mutations, K35N, D151N and R154Q, have been discovered so far in the BAR domain of BIN1 in patients with centronuclear myopathy (CNM), where biogenesis of T-tubules is compromised. However, the molecular mechanisms remain elusive. Here, we demonstrate that all CNM-related mutations lead to loss of membrane tubule generation in C2C12 myoblasts. We also use several in vitro assays to characterize the differences among BIN1 N-BAR variants with respect to membrane association affinities and membrane tubulation potential. We find that the mutations-D151N and R154Q in the BAR domain reduce membrane binding affinities and membrane-bound protein densities especially on highly curved liposomes, whereas the K35N mutation in the N-terminal inserting helix binds membranes similarly as the wild type protein (WT). We observe that both WT and K35N can deform vesicles into ∼ 30nm wide tubules and tubulation capacity is dependent on membrane surface charge and protein concentration. Contrarily, D151N and R154Q show limited ability to induce membrane curvature. Equilibrium tube-pulling force measurements report on mechanical effects of proteins on established membrane tethers and suggest that only WT and K35N oligomerize on membrane tethers. R154Q barely causes a tether pulling force reduction, consistent with the observation that R154Q shows the weakest membrane binding affinity. We hypothesize that the D151N mutation impairs protein oligomerization interface and is deficient in membrane-mediated protein lattice formation, thus defective curvature induction. Taken together, our results provide new insights into the membrane-involved pathophysiological mechanisms leading to human disease.

Synthesis of self-assembled sphingolipid conjugates and their morphology effect on anticancer therapeutic potency

The shape of self-assembling polymer–drug conjugates, influencing the cellular uptake, is one of the important factors to be considered for effective drug delivery. In this study, we described synthesis of polymeric drug conjugates of different morphologies with phytosphingosine (PHS) as a hydrophobic model drug and poly(amino acid) as a hydrophilic host polymer. By varying the amount of PHS grafted to poly(amino acid), PHS–poly(amino acid) conjugates exhibited morphological transition from spherical to worm-like micellar aggregates in the aqueous media. We investigated the physicochemical properties of self-assembled structures in terms of hydrodynamic size, surface charge, and critical aggregation concentration. The anticancer therapeutic potency of these self-assembled structures was also discussed in terms of cellular uptake and cytotoxicity of prodrug micelles as a function of dose and time by in vitro cell study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Solvated calcium ions in charged silica nanopores

Hydroxyl surface density in porous silica drops down to nearly zero when the pH of the confined aqueous solution is greater than 10.5. To study such extreme conditions, we developed a model of slit silica nanopores where all the hydrogen atoms of the hydroxylated surface are removed and the negative charge of the resulting oxygen dangling bonds is compensated by Ca(2+) counterions. We employed grand canonical Monte Carlo and molecular dynamics simulations to address how the Ca(2+) counterions affect the thermodynamics, structure, and dynamics of confined water. While most of the Ca(2+) counterions arrange themselves according to the so-called "Stern layer," no diffuse layer is observed. The presence of Ca(2+) counterions affects the pore filling for strong confinement where the surface effects are large. At full loading, no significant changes are observed in the layering of the first two adsorbed water layers compared to nanopores with fully hydroxylated surfaces. However, the water structure and water orientational ordering with respect to the surface is much more disturbed. Due to the super hydrophilicity of the Ca(2+)-silica nanopores, water dynamics is slowed down and vicinal water molecules stick to the pore surface over longer times than in the case of hydroxylated silica surfaces. These findings, which suggest the breakdown of the linear Poisson-Boltzmann theory, provide important information about the properties of nanoconfined electrolytes upon extreme conditions where the surface charge and ion concentration are large.

Fluorescent Fatty Acid Transfer from Bovine Serum Albumin to Phospholipid Vesicles: Collision or Diffusion Mediated Uptake

The extent of palmitate uptake by hepatocytes is dependent upon the surface charge of the extracellular binding protein. Specifically, hepatocyte uptake is greater when palmitate is bound to cationic binding proteins than when it is bound to anionic proteins. To further understand the role of protein surface charge on the uptake process of protein-bound ligands, we examined the rate of transfer of fluorescent anthroyloxy palmitic acid (AOPA) in the presence of anionic and cationic extracellular proteins to model membranes containing different surface charged groups. AOPA transfer rate in the presence of bovine serum albumin (ALB; isoelectric point pI = 4.8-5.0) or modified ALB (ALBe; pI = 7.0-7.5) to negative, positive and neutral lipid vesicles was investigated using a fluorescence resonance energy transfer assay. The rate of AOPA transfer from both proteins was decreased when ionic strength was increased; directly dependent on the concentration of acceptor lipid vesicles; and was affected by both the lipid membrane surface charge and protein-bound concentration. The data support the notion that AOPA transfer from binding proteins to lipid membranes occurred through two concomitant processes, aqueous diffusion of the unbound ligand (diffusion-mediated process) and a collisional interaction between the protein-ligand complex and acceptor membrane. The contribution of diffusional mediated transfer to the overall uptake process was determined to be 3 to 4 times less than the contribution of a collisional interaction. This study strengthened the hypothesis that charged amino acid residues on proteins are important for effective collisional interaction between protein-ligand complexes and cell membranes through which more free ligand could be supplied for the uptake process.

Effective Interaction between Two Ion-Adsorbing Plates: Hofmeister Series and Salting-In/Salting-Out Phase Diagrams from a Global Mean-Field Analysis

Interactions between ions and solutes are key to ion-specificity. A generic model in which ions interact via square well potentials of finite range with charged plates is solved analytically on the Poisson-Boltzmann level and analyzed globally for varying surface charge, salt concentration, and ion-surface affinity. Ion adsorption as well as depletion can lead to stably bound plates at finite separation, relevant for the equilibrium salting-out of small solutes such as proteins. The interplate pressure at large plate separation, relevant for aggregation kinetics of large solutes, exhibits direct as well as indirect Hofmeister ordering, depending on surface charge and salt concentration. A simple method for mapping explicit ion-surface potentials of mean force as obtained from solvent-explicit molecular dynamics simulations onto square-well potential parameters is demonstrated.

Graphene sponge for efficient and repeatable adsorption and desorption of water contaminations

Seeking highly-efficient, low-cost and robust methods to disinfect and decontaminate water from source to point-of-use is very much in demand. Here, we developed a new material, graphene sponge (GS), for water treatment, which was assembled with graphene oxide sheets by hydrothermal treatment with the assistance of thiourea. These GSs show a tunable pore structure and surface properties, and are mechanically strong. They show high adsorption ability for various water contaminations such as dyes, oils and many other organic solvents. The adsorption capacity of methylene blue and diesel oil in GSs can reach 184 mg g−1 and 129 g g−1, respectively. Moreover, the GSs can be repeatedly used by simple treatment without obvious structure and performance degradation. Additionally, we studied the relationship between the structure and contamination adsorption performance of GSs. It was found that the dye adsorption performance of GSs strongly depends on their surface charge concentration and specific surface area, but the oil adsorption capacity is mainly related to their specific surface area, indicating the different adsorption mechanism. These findings open up many possibilities for the use of graphene in water cleaning, including disinfection, decontamination, re-use, reclamation and desalination.

Direct quantification of negatively charged functional groups on membrane surfaces

Surface charge plays an important role in membrane-based separations of particulates, macromolecules, and dissolved ionic species. In this study, we present two experimental methods to determine the concentration of negatively charged functional groups at the surface of dense polymeric membranes. Both techniques consist of associating the membrane surface moieties with chemical probes, followed by quantification of the bound probes. Uranyl acetate and toluidine blue O dye, which interact with the membrane functional groups via complexation and electrostatic interaction, respectively, were used as probes. The amount of associated probes was quantified using liquid scintillation counting for uranium atoms and visible light spectroscopy for the toluidine blue dye. The techniques were validated using self-assembled monolayers of alkanethiols with known amounts of charged moieties. The surface density of negatively charged functional groups of hand-cast thin-film composite polyamide membranes, as well as commercial cellulose triacetate and polyamide membranes, was quantified under various conditions. Using both techniques, we measured a negatively charged functional group density of 20–30 nm −2 for the hand-cast thin-film composite membranes. The ionization behavior of the membrane functional groups, determined from measurements with toluidine blue at varying pH, was consistent with published data for thin-film composite polyamide membranes. Similarly, the measured charge densities on commercial membranes were in general agreement with previous investigations. The relative simplicity of the two methods makes them a useful tool for quantifying the surface charge concentration of a variety of surfaces, including separation membranes.

Lipid nanoparticles as vitamin matrix carriers in liquid food systems: On the role of high-pressure homogenisation, droplet size and adsorbed materials

Twelve oil-in-water nano-emulsions were prepared using a melt high-pressure homogenisation process (HPH) at 300, 800 or 1200 bar. The resulting emulsions containing 20 wt% palm oil in the absence or presence of α-tocopherol were stabilised by whey proteins alone or in mixture with lecithin. Lipid nanoparticles in these emulsions were characterized for their particle size, surface charge and protein surface concentration (PSC) in relation to their stability against aggregation and coalescence, and to their ability for encapsulation and protection of α-tocopherol against chemical degradation. Increasing HPH values were accompanied by the formation of lipid nanoparticles with decreasing size and PSC, but increasing long-term stability against aggregation and coalescence in parallel with an increase in α-tocopherol degradation (up to 15 wt% for 1200 bar). Presence of α-tocopherol, led to increasing (or decreasing) PSC values with increasing (or decreasing) HPH values for lipid nanoparticles stabilised by proteins alone (or in mixture with lecithins). In addition to these structural properties, the ability for α-tocopherol long-term stability of nanoparticles in emulsions was shown to differ more depending on their adsorbed materials (protein alone, or in mixture with lecithin) than on their particle size values. After 2 months storage, α-tocopherol in emulsions prepared at 300, 800 or 1200 bar was protected against chemical degradation at 79, 77, 67 wt%, respectively, when whey proteins were used alone, instead of 66, 63, 48 wt% when proteins were used in mixture with lecithins. These results indicated the dominant role of adsorbed proteins on the protection of vitamin models by nanoemulsions. They are of a great technological importance for production of lipid nanoparticles presenting a high volume-to-diameter ratio values and consequently high exchange surfaces between the matrix carrier and water and oxygen environmental factors.

Density functional theory for differential capacitance of planar electric double layers in ionic liquids

The differential capacitance of electric double layers in ionic liquids and its correlation with the surface charge density, ion size and concentration are studied within the framework of the classical density functional theory (DFT). As prescribed by previous analytical theories, DFT is able to reproduce the transition in the differential capacitance versus the surface potential curve from the ‘camel’ shape to the ‘bell’ shape when the ionic density increases. However, DFT predicts alternating layers of cations and anions at the charged surface that cannot be described by the classical Gouy–Chapman–Stern model and its modifications.

Selective electret charging method for energy harvesters using biased electrode

A lot of energy harvesting devices using electret material has been developed. Since the power from the electret energy harvester is proportional to the surface charge concentration, i.e. charged voltage on the electret, frequency and dynamic range of the capacitance change. To fabricate the electret, the corona discharge is a very popular charging method that consists of a high voltage needle for corona ions generation, and a grid electrode applying a bias voltage that implants the electrons from corona ions to the electret material. In this study, we introduce a novel charging method with fine patterns using the buried gridelectrodes applied with a bias voltage. We also describe FEM analysis and experimental results.

DNA nanowire translocation phenomena in nanopores

One recent application of nanopores is to use them as detectors and analyzers for fast DNA sequencing. To better understand the DNA electrokinetic transport through a nanopore, a hydrodynamic model is developed to investigate the flow field, the resistive forces acting on the DNA, the DNA velocity and the ionic current through the nanopore. The numerical results reveal the relation between the DNA velocity and various parameters such as nanopore surface charge and solution concentration. The model is validated by comparing the numerical results with the experimental data for both DNA velocity and ionic current through the nanopore.

Reduction of protein adsorption on silica and polystyrene surfaces due to coating with Complex Coacervate Core Micelles

The reduction of protein adsorption by a polymer brush formed upon adsorption of Complex Coacervate Core Micelles (C3Ms), consisting of a charged copolymer containing a neutral block and an oppositely charged homopolymer, on silica and polystyrene surfaces has been studied in situ using fixed angle optical reflectometry. Four proteins were used: lysozyme, β-lactoglobulin, bovine serum albumin, and fibrinogen. The C3M coating is responsive to changes in pH and salt concentration, and can be completely removed from the surface by rinsing with a concentrated salt solution (>2 M NaCl) or an acidic solution (pH < 2). The same surface can be subsequently coated with a fresh micellar layer. The reduction of protein adsorption by C3Ms was found to be influenced by the surface chemical composition, surface charge, hydrophobicity and salt concentration. C3M adsorption was higher on hydrophobic polystyrene than on hydrophilic silica, but stronger reduction of protein adsorption was observed on silica. The protein resistance of the brush is enhanced by increasing the salt concentration from 5 to 100 mM as a consequence of the stronger screening of excess charges. The stoichiometric charge composition, at which stable C3Ms are formed in bulk, is not the optimal one to create an effective coating on charged surfaces. On the silica surface higher reduction of protein adsorption was observed when micelles carry an excess charge opposite to the charge of the native surface.

Electrodiffusive Transport in Charged Porous Media: From the Particle-Level Scale to the Macroscopic Scale Using Volume Averaging

The Poisson-Nernst-Planck (PNP) system of equations can be used to describe electro-diffusive multi-ion transport through uncharged porous materials. Phenomenological formulations have been proposed for charged porous media (e.g. clays), usually disregarding links to the particle level scale. However using volume averaging of microscale governing equations, we derive a new set of up-scaled generalized (macroscopic) PNP equations that are valid for both charged and uncharged porous materials. These equations consistently account for non-homogeneous ionic distributions at the microscale, but reduce standard phenomenological PNP equations for the special case of uncharged porous materials. With this approach we can estimate macroscopic parameters such as effective diffusion coefficients for individual charged species, and the effective fixed charge concentration, based on microscale quantities. It is shown that effective ion diffusion coefficients are functions of ion self-diffusion coefficients, the tortuosity of the porous material, and effective concentrations, which depend on surface charge density and concentration of background electrolyte. We apply the proposed method to electro-diffusive transport of a binary electrolyte through a thin charged porous membrane containing cylindrical pores. This allows estimation of the derived generalized effective diffusion coefficient in two ways, i.e., based on the derived formula and from the ion flux equations.

Computer Simulation of Edge Effects in a Small-Area Mesa N-P Junction Diode

AbstractThe influence of edges on the performance of small-area solar cells is determined using a modified commercial, finite-element software package. The n+/p mesa device is modeled as having a sub-oxide layer on the edges, which acquires positive charges that result in development of an electric field within the device. Our computer simulations include generation/ recombination at the diode edges as well as the influence of light on the recombination characteristics of the edges. We present a description of our model, dark and illuminated characteristics of devices with various surface charge concentrations, and the dynamics of carrier generation/recombination. The influence of edge geometry on diode performance is determined.

Channel width effect on the spin-orbit interaction parameter in a two-dimensional electron gas

The spin splitting energy obtained from the Shubnikov–de Haas oscillation increases with decreasing channel width (w) of the InAs-based heterostructure. Since the surface charge concentration depends only weakly on w, the channel width dependence of the spin splitting energy is attributed to variations in the spin-orbit interaction strength. The spin-orbit interaction parameter was found to be inversely proportional to w in the range of w=2–64μm. Our findings indicate that a strong spin-orbit interaction is induced in a narrow channel due to suppression of the spin precession length for a thin quantum well layer system.

Biodegradable Self-Assembling PEG-Copolymer as Vehicle for Poorly Water-Soluble Drugs

To develop self-assembling systems increasing the solubility of poorly water-soluble drugs. Low molecular weight liquid biodegradable copolymers were synthesized by ring-opening polymerization using caprolactone (CAP) and trimethylenecarbonate (TMC) as monomers. Various initiators were evaluated. The emulsifying and self-assembling properties were investigated by a water titration method. The self-assembling systems were characterized for size, shape, isotropic behavior, cloud point, surface charge, and critical micellar concentration in order to optimize the polymer synthesis. Finally, the improvement of solubility of model drugs was assessed. Only diblock monomethyl ether PEG-CAP/TMC copolymers synthesized with monomethyl ether polyethyleneglycol 550 to 2000 as initiator have shown self-assembling properties: upon dilution, these copolymers formed an isotropically clear solution with droplet sizes in the range of 20 to 100 nm. The hypothesis that these diblock polymers form micelles was confirmed by their low critical micellar concentration (10(-5) g/ml). The copolymers initated with mmePEG750 had a higher cloud point and better colloidal stability than those initiated with mmePEG 550. The solubility of the poorly water-soluble drugs was increased by 1 to 2 orders of magnitude. Good reproducibility was observed from batch to batch. The polyester diblock copolymer mmePEG750-CAP/TMC forms spontaneously stable micelles in aqueous medium and increases the solubility of lipophilic drugs. They are very promising vehicles for the oral delivery of poorly water-soluble drugs.