Electrophoretic Properties Research Articles

Multidisciplinary determination of the phase distribution for VOX–ZrO2–SO42−–sepiolite catalysts for NH3-SCR

A series of V2O5–ZrO2–SO42−–sepiolite mixtures were extruded, calcined and characterised. NH3-SCR activity was found to be related to the content of the active VOX–ZrO2–SO42− phase (VSZ). The distribution of sepiolite and VSZ at the surface of the mechanical mixtures was studied by the electrophoretic migration technique. The samples were further characterised by nitrogen adsorption, NH3-TPD, XRD and scanning electron micrography techniques. The electrophoretic migration results showed that the addition of sepiolite to VSZ, by kneading in water, had a dramatic effect on the quantity of VOX–ZrO2–SO42− present at the support's surface, both strongly decreasing the molar fraction of zirconia at the surface, and altering the electrophoretic properties of the mixtures.The SEM micrographs, XRD patterns and activity measurements of the water-kneaded samples supported the electrophoretic migration results. Furthermore, it was verified by electrophoretic migration experiments that up until a composition of 75% VOX–ZrO2–SO42−, the sepiolite fibers coats the zirconia particles. This has a slightly negative influence on the overall SCR activity of fresh catalysts.

Colored nanoparticles dispersions as electronic inks for electrophoretic display

Phthalocyanine green (CuPcCl) nanoparticles was successfully prepared by anti-solvent recrystallization method and combined with in situ modification to improve the electrophoretic properties and dispersion ability in organic medium. The produced particles were characterized by SEM, FT-IR and ζ-potential test. It was found that the particles exhibited 120 nm with spherical shape and narrow size distribution when the modifier was mixture of CTAB and PVP. Sedimentation ratio of the prepared CuPcCl particles in tetrachloroethylene was nearly down to zero within 30 days and the ζ-potential was 26.8 mV. In addition, stable TiO 2/C 2Cl 4 dispersion was prepared by coated TiO 2 surface with trimethoxyoctylsilane. The sedimentation ratio of the modified TiO 2 was nearly 7.6% within 30 days, and the ζ-potential value was −28.9 mV. The particle size was about 300 nm with spherical morphology. The results demonstrated that green CuPcCl and white TiO 2 dispersions were suitable as electronic ink and showed potential value in the application of electrophoretic display.

The Effect of Ultrasound on the Functional Properties of Wheat Gluten

In this study, the effect of ultrasound on the foaming and emulsifying properties of wheat gluten as well as its electrophoretic and rheology properties were investigated. The foam capacity and foam stability of ultrasound treated wheat gluten proteins gradually increased as the treatment power increased, and were more pronounced at 100% power level. Excluding those of the raw wheat gluten, the lowest emulsifying capacity values and emulsifying stability were obtained with the samples ultrasound treated at 60% power level. In general, ultrasound treatment did not cause major changes on the protein electrophoretic patterns of gluten samples at the power levels used. Ultrasound affected the storage and the loss moduli with typical U-shape alteration.

Calcium-induced Folding of Intrinsically Disordered Repeat-in-Toxin (RTX) Motifs via Changes of Protein Charges and Oligomerization States

Ligand-induced disorder-to-order transition plays a key role in the biological functions of many proteins that contain intrinsically disordered regions. This trait is exhibited by so-called RTX (repeat-in-toxin) motifs found in many virulence factors secreted by numerous gram-negative pathogenic bacteria: RTX proteins are natively disordered in the absence of calcium but fold upon calcium binding. The adenylate cyclase toxin (CyaA) produced by Bordetella pertussis, the causative agent of whooping cough, contains ∼40 RTX motifs organized in five successive blocks separated by non-RTX flanking regions. This RTX domain mediates toxin binding to its eukaryotic cell receptor. We previously showed that the last block of the RTX domain, block V, which is critical for CyaA toxicity, exhibits the hallmarks of intrinsically disordered proteins in the absence of calcium. Moreover, the C-terminal flanking region of CyaA block V is required for its calcium-induced folding. Here, we describe a comprehensive analysis of the hydrodynamic and electrophoretic properties of several block V RTX polypeptides that differ in the presence and/or length of the flanking regions. Our results indicate that the length of the C-terminal flanking region not only controls the calcium-induced folding but also the calcium-induced multimerization of the RTX polypeptides. Moreover, we showed that calcium binding is accompanied by a strong reduction of the net charge of the RTX polypeptides. These data indicate that the disorder-to-order transition in RTX proteins is controlled by a calcium-induced change of the polypeptide charges and stabilized by multimerization.

Pharmaceutical suspensions: micro electrophoretic properties.

The microelectrophoretic properties of the drugs griseofulvin, betamethasone, nalidixic acid and thiabendazole in aqueous dispersion have been examined and the zeta potentials calculated from the measured mobilities. Variation in magnitude of particle charge with pH of dispersion is reported and related to the chemical structure and the surface characteristics. The effect of adding anionic (sodium dodecyl sulphate) cationic (dodecyl trimethyl bromide) and non-ionic (polyoxyethylene glycol monoethers of hexadecanol) surface-active agents, and mixtures of these ionic and non-ionic species, on the electrophoretic properties of the drug dispersions has been measured. The results reported agree with those found previously for a model polystyrene latex suspension system under the same conditions.

FRET-Based Biosensor for Oleic Acid in Nanomolar Range with Quantum Dots As an Energy Donor

A self-assembling sensor for oleic acid has been developed. The sensor consists of a self-assembling fluorescent dye labeled BSA and quantum dots CdSe/ZnS capped with 3-mercaptopropionic acid. The detection limit of the new sensor is 10-1000 nM. The influence of the quantum dot size on the FRET efficiency in the course of the interaction of the sensor system with the analyte has been studied. The pH dependence, aggregation stability. and electrophoretic properties of the sensor have been examined. The data suggest a new approach for the development of nanoscale FRET-based sensors operating effectively due to unique fluorescent properties of quantum dots as well as due to selective protein-ligand interactions.

Single Cell Sensing and Manipulation by Scanning Nanopore Microscopy

Signal Transduction by Ion Nano-Gating (STING) technology is a label-free biosensor based on quartz nanopipettes capable of detecting DNA and proteins. Using conical quartz nanopipettes a Scanning Ion Conductance Microscope (SICM) was developed and used for single cell imaging, sensing and manipulation. The height of the nanopore above a surface can be accurately controlled by measuring the ionic current through the pore as it approaches a surface. By maintaining a predefined distance from a surface and raster scanning the pore, a topographical image can be acquired. Additionally, material can be ejected through nanopipette using electrophoretic and electroosmotic properties. The cost of fabrication and ease of use of nanopipettes provides an ideal system for developing cellular systems for both cell detection and control. We demonstrate the capability of this sensor to image living cells, deposit material for controlled single cell growth on a substrate, and a platform for single cell injection and detection using an integrated microfluidic chip. The combination of STING technology with traditional SICM technology can be leveraged to acquire both topographical data and functional data, such as local ion concentration. This form of complementary microscopy is henceforth termed functional Scanning Ion Conductance Microscopy (fSICM). Preliminary fSICM results will be presented. This work illustrates the applicability of the STING sensor to a variety of applications, from single cell detection to definition of cellular circuits.

Characterization of Asphaltenes by Nonaqueous Capillary Electrophoresis

Nonaqueous capillary electrophoresis was used for the separation and characterization of asphaltene samples from different sources. For the separation medium (background electrolyte), mixtures of tetrahydrofuran and a high-permittivity organic solvent could be used. The best results were obtained with an 80:20 mixture of tetrahydrofuran and acetonitrile, containing 1−10 mM of lithium perchlorate. In this separation medium, asphaltene samples were found to be composed of two fractions that could be clearly separated: one fraction of neutral species and a fraction that carries a positive charge in the solvent mixture employed. Between samples of different origin, differences were found in the relative amounts of the neutral and the charged fractions and in the average electrophoretic mobility of the charged components. Taylor dispersion analysis was applied to estimate the average diffusion coefficient of the asphaltene species in the solvent mixture used. From the results, it is concluded that the asphaltenes are present as nanoaggregate clusters of 3000−4000 Da and that the charged aggregates carry a net charge of approximately +1. The possible correlation between the electrophoretic properties of asphaltenes in crudes of different origin and their field behavior is discussed.

O/W nano-emulsions with tunable PIT induced by inorganic salts

Paraffin oil/water nano-emulsions stabilized by Tween 80/Span 80 were prepared using the phase inversion temperature (PIT) method in the presence of inorganic salts. The influence of different kinds of inorganic salts on the PIT, electrophoretic properties and long-term stability of the nano-emulsions was studied by conductivity measurements, zeta potential measurement and dynamic light scattering. It was found that, for a system with high PIT, an optimum PIT can be obtained in the presence of salting-out salts, and thus a stable emulsion can be prepared. The salts reduce the absolute value of the zeta potential of the nano-emulsion droplets and influence their long term stability. By analyzing the evolution of emulsion droplet size with time, the main instability mechanisms of the nano-emulsions were found to be Ostwald ripening and/or coalescence.

Calibrative approaches to protein solubility modeling of a mutant series using physicochemical descriptors.

A set of physicochemical properties describing a protein of known structure is employed for a calibrative approach to protein solubility. Common hydrodynamic and electrophoretic properties routinely measured in the bio-analytical laboratory such as zeta potential, dipole moment, the second osmotic virial coefficient are first estimated in silico as a function a pH and solution ionic strength starting with the protein crystal structure. The utility of these descriptors in understanding the solubility of a series of ribonuclease Sa mutants is investigated. A simple two parameter model was trained using solubility data of the wild type protein measured at a restricted number of solution pHs. Solubility estimates of the mutants demonstrate that zeta potential and dipole moment may be used to rationalize solubility trends over a wide pH range. Additionally a calibrative model based on the protein’s second osmotic virial coefficient, B 22 was developed. A modified DVLO type potential along with a simplified representation of the protein allowed for efficient computation of the second viral coefficient. The standard error of prediction for both models was on the order of 0.3 log S units. These results are very encouraging and demonstrate that these models may be trained with a small number of samples and employed extrapolatively for estimating mutant solubilities.

Chemical and electrophoretic properties of Holstein cow milk as affected by somatic cell count

Chemical and electrophoretic properties of raw milk samples with different somatic cell counts (SCCs)(<200 000, 200 000–800 000 and >800 000 cells/mL) were determined. Milk was analysed for fat, lactose, total nitrogen (TN), non‐casein nitrogen (NCN), ratio of casein nitrogen to total nitrogen (CN/TN), pH, titratable acidity (TA), solid‐non‐fat (SNF), total solid (TS), the amount of α s ‐casein and β‐casein. Milk SCC had no significant effect (P ≥ 0.05) on fat and TN. An increase in the SCC resulted in an increase in pH and NCN content, and a significant decrease in lactose, TA, SNF, CN/TN, αs‐casein and β‐casein. Milk quality of Holstein dairy cattle deteriorate due to higher proteolytic activity associated with high SCC.

Identification and properties of insect resistance-associated maize anionic peroxidases

Previous studies with transgenic plants have indicated a tobacco anionic peroxidase can confer enhanced resistance to a variety of insects when expressed in different plant species. Tissue that expresses high levels of this enzyme often browns rapidly when damaged. Maize roots damaged under sterile conditions browned and had an anionic peroxidase induced. When introduced biolistically, maize callus transformants expressing a maize peroxidase gene with a predicted isoelectric point of ca. 5.1 produced browner callus compared to a corresponding β-glucuronidase (GUS) transformant as callus aged. Higher production of only one isozyme of ca. pI 4.5 was noted. When the callus was fed to two maize pest caterpillar species, growth rates were slower (as reflected by weights) relative to the GUS callus. Based on examination of published information and electrophoretic properties, this gene appears to code for Px11, a peroxidase isozyme that is primarily produced in root tissue and callus. When sequence of the gene in several inbreds was examined, coding variations were noted, and abilities to utilize ferulic and p-coumaric acids differed. These coding differences may influence the ability of corresponding forms of the peroxidase to promote resistance. In addition to potential use in marker assisted breeding, enhanced expression of this anionic peroxidase through breeding or genetic engineering may lead to enhanced insect or disease resistance.

Separation and recovery of nucleic acids with improved biological activity by acid‐degradable polyacrylamide gel electrophoresis

One of the fundamental challenges in studying biomacromolecules (e.g. nucleic acids and proteins) and their complexes in a biological system is isolating them in their structurally and functionally intact forms. Electrophoresis offers convenient and efficient separation and analysis of biomacromolecules but recovery of separated biomacromolecules is a significant challenge. In this study, DNAs of various sizes were separated by electrophoresis in an acid-degradable polyacrylamide gel. Almost 100% of the nucleic acids were recovered after the identified gel bands were hydrolyzed under a mildly acidic condition and purified using anion exchange resin. Further concentration by centrifugal filtration and a second purification using ion exchange column chromatography yielded 44-84% of DNA. The second conventional (non-degradable) gel electrophoresis confirmed that the nucleic acids recovered from acid-degradable gel bands preserved their electrophoretic properties through acidic gel hydrolysis, purification, and concentration processes. The plasmid DNA recovered from acid-degradable gel transfected cells significantly more efficiently than the starting plasmid DNA (i.e. improved biological activity via acid-degradable PAGE). Separation of other types of nucleic acids such as small interfering RNA using this convenient and efficient technique was also demonstrated.

Analysis of the alcohol biomarker phosphatidylethanol by NACE with on‐line ESI‐MS

Phosphatidylethanol (Peth), a group of aberrant phospholipids formed in cell membranes in the presence of ethanol, has been recently proposed as biomarker of chronic alcohol abuse. The aim of this study was to develop a new analytical method, based on NACE online coupled with a mass spectrometer for the analysis of Peth in blood. For this purpose an ion-trap mass spectrometer equipped with an orthogonal ESI source operating in negative ion mode was used. An alkaline solution of ammonium acetate 5 mM (pH 9) in water/methanol (MeOH) (80:20 v/v) was delivered as coaxial sheath liquid. All experiments were performed using an uncoated fused-silica capillary (90 cm x 75 microm id). The effects of variable percentages of ACN, MeOH, 2-propanol, dichloromethane, along with variable concentrations of ammonium acetate were investigated for the separation of Peth. Collectively, a separation medium composed of ACN (45% v/v), 2-propanol (20% v/v), dichloromethane (20% v/v), MeOH (10% v/v), water (5% v/v), and ammonium acetate (25 mM) was chosen. The estimated LOD was 0.1 microM, while LOQ was 0.4 microM. Within-run (intra-day) and between-run (inter-day) precision was always lower than 15%. The method proved to be robust and reliable. The MS detector allowed the simultaneous identification of several Peth homologues, and the use of an internal standard (phosphatidylbutanol) with similar electrophoretic properties of that of Peth increased quantitation effectiveness.

Resolution and characterization of the structural polymorphism of a single quadruplex-forming sequence

The remarkable structural polymorphism of quadruplex-forming sequences has been a considerable impediment in the elucidation of quadruplex folds. Sequence modifications have commonly been used to perturb and purportedly select a particular form out of the ensemble of folds for nuclear magnetic resonance (NMR) or X-ray crystallographic analysis. Here we report a simple chromatographic technique that separates the individual folds without need for sequence modification. The sequence d(GGTGGTGGTGGTTGTGGTGGTGGTGG) forms a compact quadruplex according to a variety of common biophysical techniques. However, NMR and chromatography showed that this oligonucleotide produces at least eight monomeric quadruplex species that interconvert very slowly at room temperature. We have used a combination of spectroscopic, hydrodynamic and thermodynamic techniques to evaluate the physicochemical properties of the mixture and the individual species. These species have almost identical thermodynamic, hydrodynamic and electrophoretic properties, but significantly different NMR and circular dichroism (CD) spectra, as well as kinetic stability. These results demonstrate that simple standard low-resolution techniques cannot always be used for quadruplex fold determination or quality control purposes, and that simple thermodynamic analysis does not directly provide interpretable thermodynamic parameters.

The preparation and TD-DFT studies of 1-[(4-methyl-2-nitrophenyl) azo]-2-naphthalenol (C.I. Pigment Red 3) nanoparticles

Nanosized 1-[(4-methyl-2-nitrophenyl)azo]-2-naphthalenol (C.I. Pigment Red 3) particles were prepared using a facile liquid precipitation method. The morphology and electrical properties of the produced particles were characterized by SEM, ζ-potential and electrophoretic display device. The particles were ∼80 nm in size within a narrow particle size distribution and displayed excellent electrophoretic properties. The structure and geometry of 1-[(4-methyl-2-nitrophenyl)azo]-2-naphthalenol were investigated using density functional theory, for which, calculated results indicated that the compound possessed both trans- and cis- conformers. UV–vis spectroscopy of the two conformers was evaluated using time-dependent density functional theory taking bulk solvent effects into account by means of the polarizable continuum model. Vertical excitation energies and oscillator strengths were determined for the lowest-energy electronic transitions. The calculated results reproduced the experimental data and corroborated the reliability of the structural characterization of the pigment.

Fluorescent Carrier Ampholytes Assay for Portable, Label-Free Detection of Chemical Toxins in Tap Water

We present a novel method for fluorescence-based indirect detection of analytes and demonstrate its use for label-free detection of chemical toxins in a hand-held device. We fluorescently label a mixture of low-concentration carrier ampholytes and introduce it into an isotachophoresis (ITP) separation. The carrier ampholytes provide a large number of fluorescent species with a wide range of closely spaced effective electrophoretic mobilities. Analytes focus under ITP and displace subsets of these carrier ampholytes. The analytes are detected indirectly and quantified by analyzing the gaps in the fluorescent ampholyte signal. The large number (on the order of 1000) of carrier ampholytes enables detection of a wide range of analytes, requiring little a priori knowledge of their electrophoretic properties. We discuss the principles of the technique and demonstrate its use in the detection of various analytes using a standard microscope system. We then present the integration of the technique into a self-contained hand-held device and demonstrate detection of chemical toxins (2-nitrophenol and 2,4,6-trichlorophenol) in tap water, with no sample preparation steps.

The RNA strands of the plus and minus polarities of peach latent mosaic viroid fold into different structures

It is believed that peach latent mosaic viroid (PLMVd) strands of both the plus and minus polarities fold into similar secondary and tertiary structures. In order to verify this hypothesis, the behavior of both strands in three biophysical assays was examined. PLMVd transcripts of plus and minus polarity were found to exhibit distinct electrophoretic mobility properties under native conditions, to precipitate differently in the presence of lithium chloride, and to possess variable thermal denaturation profiles. Subsequently, the structure of PLMVd transcripts of minus polarity was elucidated by biochemical methods, thereby permitting comparison to the known structure of the plus polarity. Specifically, enzymatic probing, electrophoretic mobility shift assay, and ribonuclease H hydrolysis were performed in order to resolve the secondary structure of the minus polarity. The left domains of the strands of both polarities appear to be similar, while the right domain exhibited several differences even though they both adopted a branched structure. The pseudoknot P8 formed in the plus strand seemed not formed in the minus strands. The structural differences between the two polarities might have important implications in various steps of the PLMVd life cycle.

Formation and properties of paraffin wax submicron emulsions prepared by the emulsion inversion point method

Paraffin wax-in-water submicron emulsions stabilized by Span 80/Tween 80 were prepared by the emulsion inversion point (EIP) method. Stable emulsions with droplet diameters about 700 nm could be formed when the hydrophilic–lipophilic balance (HLB) values are between 9.5 and 10.3 and the surfactant-to-oil ratio is above 0.2. Increased emulsification temperature and cooling rate were found to improve the emulsion properties. Either mixing all components together or addition of oil to the aqueous surfactant dispersion could not produce stable emulsions. Optical microscopy and scanning electron microscopy (SEM) were used to study the morphology of the emulsion droplets. The droplets were solid at room temperature, showing bright spots under polarized light and an irregular spheres shape under SEM. Due to homogeneous nucleation in the finely dispersed emulsion droplets, the emulsion shows a large degree of undercooling (15 °C) in the differential scanning calorimetry (DSC) thermogram. The emulsions became unstable with heating, but remained stable under cooling. The electrophoretic properties of emulsion droplets showed a negative zeta potential, which was increased with the pH of the system due to the adsorption of hydroxyl groups.

Preparation of Polymer-Coated TiO<sub>2</sub> Particles for Electronic Paper Based on Electrophoresis

The preparation and characterization of TiO2 particles coated with an electrophoretic polymer using silane coupling agents and highly hydrophilic monomers (methyl methacrylate) are presented in this article. The organic layer was formed by radical polymerization and bonded to the surface of inorganic TiO2 with a silane coupling agent. The polymer-coated particles were characterized by Fourier transform infrared spectrometry, field emission scanning electron microscopy, and thermogravimetric analysis. The size distribution and charge properties of the polymer-coated particles were measured, and the optical response of electrophoretic image display cells, containing the particles, was also investigated. It was found that coating materials having a branched alkyl side chain structure endowed the final polymer-coated particles with good stability and favorable electrophoretic properties in an electrophoretic medium. In addition, the charge polarity of the polymer-coated particles could be controlled using different silanizing reagents and polymers. Furthermore, electrophoretic image display cells, containing such particles, demonstrated good response and high reflectance in their white state.