Electrophoretic Mobility Values Research Articles

Surface Chemical Studies on Pyrite in the Presence of Polysaccharide-Based Flotation Depressants

The interaction of dextrin and guar gum with pyrite has been investigated through adsorption, flotation, and electrokinetic measurements. The adsorption densities of the polysaccharides onto pyrite reveal a region of higher adsorption density in the pH range 7.5–11, with a maximum around pH 10 for both polymers. The isotherms exhibit Langmuirian behavior. The adsorption density of guar gum onto pyrite is higher than that of dextrin. Electrokinetic measurements indicate a decrease in the electrophoretic mobility values in proportion to the concentration of the polymer added. Co-precipitation tests confirm polymer–ferric species interaction in the bulk solution, especially in the pH range 5.5–8.5. The pH range for higher adsorption, significant co-precipitation, and appreciable depression of pyrite encompass each other. XPS and FTIR spectroscopic studies provide evidence in support of chemical interaction between hydroxylated pyrite and the hydroxyl groups of the polymeric depressants.

Synthesis and characterization of Zn–Cd bimetallic colloids from nonaqueous solvents

Bimetallic colloids of Zn–Cd were prepared with different organic solvents, namely, THF, 2-methoxyethanol, 2-propanol, 2-butanone, 2-butanol, and acetone. The metals were evaporated to yield atoms, which were codeposited at 77 K with solvents to produce solvated metal atoms. Upon warming the matrix at room temperature, liquid colloid dispersions were formed. Different metal concentrations were used. Colloid stability was analyzed in terms of flocculation at room temperature. The lowest stability was shown for THF dispersions (2–4 h) and the highest was obtained for acetone (6–10 days) at dilute concentrations. Particle sizes were obtained by transmission electron microscopy (TEM). The particles in the bimetallic colloids had spherical shape, and average particle sizes ranged between 69 and 148 Å. The mobility of the particles was determined by electrophoresis. Particles in the Zn–Cd 2-butanone and acetone colloids had electrophoretic mobility and zeta potential values between 0.14 and 0.97 V, showing behavior typical of charged surfaces.

Physicochemical surface properties of five Listeria monocytogenes strains from a pork-processing environment in relation to serotypes, genotypes and growth temperature.

Physicochemical surface properties, related to electrostatic, van der Waals and Lewis acid-base interactions, of five Listeria monocytogenes strains isolated from pork-processing environments were determined after two subcultures at 37 degrees C and a final culture at three temperatures: 37, 10 and 4 degrees C. Three strains (Lm1, Lm114 and Lm191) were genetically related while two were unrelated (Lm25 and Lm74) according to ApaI-macrorestriction and pulsed-field gel electrophoresis (PFGE) typing. Listeria monocytogenes cell surfaces were generally negatively charged regardless of pH and tended to be hydrophilic due to a basic character. However, variable physicochemical surface properties of the five Listeria monocytogenes isolates were observed after growth at 37 degrees C. After growth at 10 degrees C, the three genetically related isolates exhibited similar surface properties and were slightly more hydrophilic and basic than the others. After growth at 4 degrees C, the five isolates displayed the same weak affinity for all kinds of solvents and low electrophoretic mobility values. A sharp decrease of temperature and subsequent growth of various Listeria monocytogenes strains resulted in loss of the physicochemical surface property variability, which may suggest the role of common chill adaptation mechanisms affecting surface properties.

Surface chemical studies on alumina suspensions using ammonium poly(methacrylate)

The interaction of α-alumina with ammonium poly(methacrylate) (APMA) has been investigated through adsorption and electrokinetic measurements. The adsorption isotherms exhibit high affinity, Langmuirian behaviour at highly acidic pH and the adsorption density is found to decrease with increasing pH. On the contrary, the percentage desorption increases with increasing pH. Electrokinetic studies indicate specific adsorption between alumina and APMA resulting in a shift of the isoelectric point to acidic pH values. Electrophoretic mobility values indicate that the alumina suspension could be well dispersed in the pH range 5–11, consequent to polymer adsorption. These results were corroborated by the dispersion tests. Dissolution tests reveal the release of aluminium species from alumina while co-precipitation experiments confirm the chemical interaction of aluminium species with APMA in the bulk solution. Hydrogen bonding, electrostatic and chemical interactive forces are postulated to govern the adsorption process. FTIR spectroscopic data lend further support to the interaction mechanisms proposed.

Gene pacA+ codes for the multiple active forms of Pi-repressible acid phosphatase in the mould Aspergillus nidulans

The acid phosphatase secreted by the biA1 strain of the mould Aspergillus nidulans was separated into at least nine isoforms by isoelectric focusing (IEF). The components visualized by activity were predominantly acidic proteins with isoelectric points ranging from pH 4.0 to 6.5. Almost the same isoforms were secreted by strains pabaA1 and palD8 biA1. Furthermore, the isoforms secreted by strain pacA1 biA1 were not visualized by staining after IEF, indicating that these isoforms are encoded by gene pacA. Treatment of the secreted enzyme with endoglycosidase H also reduced the number of isoforms visualized by staining after IEF and enhanced the Rf (electrophoretic mobility) value of this enzyme visualized after PAGE.

Electrophoretic mobility of some tropical soil clays: effect of iron oxides and organic matter

The effect of organic matter and iron oxides on the electrophoretic mobility (EM) behaviour of some colloidal clay fractions of some tropical soils was studied. The clays from the A-horizon of the soils were treated to remove organic matter (oxidation by Na hypochlorite treatment), ferrihydrite (by acid ammonium oxalate) and better crystalline iron oxides (reductive dissolution by dithionite–citrate–bicarbonate treatment). Organic matter and iron oxides particularly better crystalline ones contributed to the pH-dependent charge. The removal of organic matter resulted in an increase in the EM and isoelectric point (iep). Deferration decreased both the EM and iep of the soil clays. Increase in pH resulted in negative EM while salt concentration did not have consistent effect on the EM and iep values.

Correlations Between the Charge of Proteins and the Number of Ionizable Groups They Incorporate: Studies Using Protein Charge Ladders, Capillary Electrophoresis, and Debye−Hückel Theory

The values of electrophoretic mobility, μelectro, of bovine carbonic anhydrase II, human carbonic anhydrase II, cytochrome c, lysozyme, superoxide dismutase, ovalbumin, and derivatives of these proteins produced by partial neutralization of Lys e-NH3+ and/or Asp and Glu carboxyl groups were measured using capillary electrophoresis (CE). For derivatives of these proteins with the lowest overall values of net charge (either positive or negative), the values of μelectro and the values of charge measured by CE, ZCE, demonstrate a linear correlation with the number of charged groups, n, converted to neutral derivatives. For derivatives of these proteins with larger values of net charge, the values of μelectro and ZCE demonstrate a nonlinear correlation with n. Several observations made in this work suggest that shifts in the values of pka of the ionizable groups on these proteins likely contribute to the observed nonlinear correlation. Debye−Huckel theory was used to calculate values of electrostatic potential...

Surface properties of monodisperse poly(acrylamide- co-acrylic acid) hydrogel microspheres prepared by a membrane emulsification technique

Monodisperse poly(acrylamide- co-acrylic acid) hydrogel microspheres of different average sizes were prepared using a membrane emulsification technique. The average diameters of the microspheres were dependent on the pore sizes (0.33, 0.73, 1.15, and 1.70 μm) of SPG membranes used in the preparation procedure. The surface properties of microspheres have been studied from their electrophoretic mobility values. The mobility values of poly(acrylamide- co-acrylic acid) microspheres were negative at pH 7.4 with ionic strengths between 0.005 and 0.154 at 25°C. More negative mobility values were obtained with smaller poly (acrylamide- co-acrylic acid) microspheres than with the larger ones. By analyzing the data with an electrokinetic theory for `soft' surfaces, it was found that copolymerization of acrylamide monomers and acrylic acid monomers does not proceed homogeneously within a microsphere. The density of polymer networks composed of both monomers is higher in the core region than in the surface layer of the microspheres. This is not the case for smaller microspheres, hence their electrophoretic mobility becomes more negative.

Study of the relationship between electrophoretic mobility of the diabetic red blood cell and hemoglobin A1c by using a mini-cell electrophoresis apparatus

A mini-cell electrophoresis system using capillary tubing (50 microm inner diameter, length ca. 10 mm and volume ca. 20 nL) was applied to measure the electrophoretic mobility of red blood cells of 89 patients with diabetes on single cell level. A significant negative correlation was observed between hemoglobin A1c and the average electrophoretic mobility, with a correlation coefficient of 0.793. By statistically processing the electrophoretic mobility of each single red blood cell, it became clear that the reduction of the average value of electrophoretic mobility was caused by the reduction of the relative frequency of the red blood cell with high mobility. The cause of the average reduction was not the shift of electrophoretic mobility of all red blood cells to the lower mobility.

Electrophoretic Mobility of Colloidal Particles in Weak Electrolyte Solutions

The analytical theory of the thin double layer concentration polarization in suspensions of colloidal particles is generalized to the case of weak electrolyte solutions, i.e., when the dissociation–recombination equilibrium and rate constants have both finite values. It is shown that under the action of a static applied field, regions near the particle appear where there is departure from the dissociation–recombination equilibrium. The resulting ion and ion-pair sources have a strong bearing on their flows, leading to a change of the electrolyte concentration gradients around the particle. This phenomenon also modifies the value of the particle electrophoretic mobility, which is dependent on the concentration polarization. At constant ionic strength, the theoretical maximum of the electrophoretic mobility versus ζ potential curve can substantially surpass in weak electrolyte solutions the corresponding value attained in strong electrolytes.

Capillary electrophoresis of subcellular-sized particles

Utilization of capillary electrophoresis (CE) for characterization and analytical separation of submicron- and micron-sized organic and inorganic particles as well as biological vesicles is reviewed. CE has been applied to charged polystyrene size standards, inorganic and organic colloidal particles, lipoprotein particles, liposomes, microsomes and viruses. These particle separations generally occur in a size-dependent manner and provide values of electrophoretic mobility which are in good agreement with those obtained by other electrophoretic techniques.

Electrokinetic demixing of aqueous two-phase systems. 3. Drop electrophoretic mobilities and demixing rates

Scale-up of aqueous two-phase extraction, which is useful in the isolation and purification of certain bioproducts, is limited by the slow demixing rates of the two aqueous phases. Electrokinetic demixing has been shown to increase by more than 5-fold the demixing rates of systems up to 100 mL in volume in a manner that depends on field strength, field polarity, pH, and phase composition. The present study is an attempt to relate demixing rates to droplet electrokinetic mobilities which were measured microscopically and inferred from demixing data. A clear dependence of demixing rate was observed on drop electrophoretic mobility and pH. The electrophoretic mobility of individual phase droplets suspended in the other phase was measured for poly(ethylene glycol)/Dextran systems using a microelectrophoresis unit and compared with mobilities predicted by electrokinetic theory. We confirmed earlier reports that the droplet electrophoretic mobility increased with increasing drop diameter and explained this increase on the basis of an internal electroosmotic flow model. Effective electrophoretic mobilities were estimated from electrokinetic demixing data in a 100-mL column and compared with predicted as well as experimentally measured values of electrophoretic mobility. The mobilties increased with increased phosphate ionization due to change in pH irrespective of the sign (or polarity) of the applied electric field. The electroosmotic flow model could explain satisfactorily the following two paradoxes: (1) the direction of migration of drops is the opposite of that predicted by colloid electrokinetics and (2) the phase demixing rate increased irrespective of the sign of the applied electric field.

Method for the Elimination of Chromatographic Bias from Measured Capillary Electrophoretic Effective Mobility Values

A method based on a modified version of pressure-mediated capillary electrophoresis (PreMCE) has been developed for the elimination of the chromatographic bias inherent in effective electrophoretic mobilities measured by capillary electrophoresis. This new five-band PreMCE method can be readily executed on most commercial capillary electrophoresis instruments. It yields not only precise but also accurate effective mobilities and electroosmotic flow rates, even when the analytes and electroosmotic flow markers are strongly retained on the coated fused-silica capillary wall.

Preparation of monodisperse poly(acrylamide-co-acrylic acid) hydrogel microspheres by a membrane emulsification technique and their size-dependent surface properties

Monodisperse poly(acrylamide-co-acrylic acid) hydrogel microspheres with different polymer compositions (0–10 mol% acrylic acid and 90–100 mol% acrylamide) and with different sizes have been prepared from w/o emulsion using microporous glass membranes with average pore sizes of 0.33, 0.73, 1.15, and 1.70 μm. The broader size distribution was observed in the microspheres composed of hydrogel containing more acrylic acid. The size distribution was not affected by the membrane pore size. The microsphere size on the other hand was dependent on both the membrane pore size and the polymer composition. As the membrane with a larger pore size was used, larger microspheres were obtained. When the membrane with a pore size of 1.70 μm was used, the microsphere size clearly increased as the acrylic acid concentration in the monomer mixture increased, while it decreased as the acrylic acid concentration increased when the membranes with smaller pore sizes were used. The surface properties of the microspheres have been studied from their electrophoretic mobility values. The electrophoretic mobility values of poly(acrylamide-co-acrylic acid) microspheres were negative at pH 7.4 with ionic strengths between 0.005 and 0.154 at 25°C, although those of poly(acrylamide) microspheres were almost zero. The electrophoretic mobility of the microspheres became more negative as the acrylic acid concentration increased, with two exceptions. Only two types of poly(acrylamide-co-acrylic acid) microspheres prepared with the membrane of the largest pore size (1.70 μm) showed the same electrophoretic mobility values at all ionic strengths, although they were composed of hydrogels of different acrylic acid concentrations (5 and 10 mol%). The electrophoretic mobility values of the microspheres were also size dependent. More negative mobility values were obtained with smaller microspheres than larger ones. By analyzing the data with an electrokinetic theory for “soft” surfaces, it was found that the microsphere surface becomes softer by the addition of acrylic acid. It was also suggested that the microspheres with smaller sizes have higher surface charge density than those with larger sizes, although the microspheres were prepared from solutions with the same monomer composition. From this, it is found that copolymerization of acrylamide monomers and acrylic acid monomers does not proceed homogeneously within a single microsphere. The density of polymer networks composed of both monomers is higher in the core region than in the surface layer of the microspheres. The accumulation of polymers in the core region of a microsphere explains the decrease in microsphere size with the increase in acrylic acid concentration observed in smaller microspheres. When microspheres are relatively large, enough volume is available for 10 mol% acrylic acid inside a microsphere and the polymer networks are looser than in smaller microspheres, which causes the increase in microsphere size depending on the acrylic acid concentration. This volume increase explains the same electrophoretic mobility values observed in two types of large microspheres containing different concentrations of acrylic acid (5 and 10 mol%).

Protein Charge Ladders, Capillary Electrophoresis, and the Role of Electrostatics in Biomolecular Recognition

Introduction Life rests on a web of molecular recognition;1,2 the folding of proteins, the hybridization of nucleic acids, the recognition of signaling molecules by receptors, and the interaction of enzymes with substrates and cofactors all require molecular recognition. Molecular recognition is based on shape-sensitive, noncovalent interactions between molecules or fragments of molecules.3-6 The energetics of molecular recognition can reflect van der Waals, hydrophobic, hydrogen bonding, and electrostatic interactions; all include both enthalpic and entropic contributions. The role of van der Waals interactions in molecular recognition in aqueous ionic solutions is well understood; they contribute to molecular recognition primarily through unfavorable steric interactions that exclude ligands with noncomplementary shapes from the recognition site of the protein. Hydrophobic interactions, although still a challenge to describe theoretically, can be estimated empirically from the observed partitioning of model compounds between aqueous and hydrocarbon solvents.7 Hydrogen bonds are best thought of as a specific type of localized electrostatic interaction;8 they are also well understood qualitatively. Although much theoretical and experimental work has gone into understanding the electrostatic properties and interactions that are central to biomolecular recognition events9-11(for a review, see ref 12), it has been difficult to measure and evaluate these interactions quantitatively. One of the central electrostatic properties of proteins is their charge, which is determined, in principle, by the sequence and structure of the protein and the properties of the solvent. Although one can measure the isoelectric point of proteins (the value of pH at which the charge of the protein is zero), there has been no general way of measuring the charge of a protein at other values of pH or as a function of the properties of the solution. Previous attempts to estimate the effects of electrostatic interactions on the affinities of proteins for ligands have focused on the use of site-directed mutagenesis.10,13-15 This technique, although powerful, is labor intensive, and the number of mutated sites that can be explored practically is limited. In this Account we describe the use of protein charge ladders in combination with capillary electrophoresis (CE) as a new biophysical tool with which to measure the electrostatic properties and interactions that are central to biomolecular recognition events involving proteins. The partial acetylation of amino groups on a protein changes the charge of the protein and generates a protein charge ladder, that is, a series of derivatives of a protein differing in values of charge but having similar coefficients of friction. The distribution of protein derivatives group, in terms of their values of electrophoretic mobility, into the “rungs” of a charge ladder, which appear in CE as a set of peaks; each successive peak in the charge ladder differs incrementally in the number of acetylated amino groups (Scheme 1). Charge ladders in combination with CE have been used to estimate the charge of the unmodified protein16 and the values of pKa of individual ionizable groups.17,18 Charge ladders in combination with affinity capillary electrophoresis (ACE) make it possible to quantify the contributions of electrostatics to the free energies of binding of charged ligands to proteins.19 Although we have developed this approach primarily using charge ladders of bovine carbonic anhydrase II (BCA II, EC 4.2.1.1.) as a model system (Figure 1),16,19 we have demonstrated the formation of charge ladders with a range of other proteins and biological molecules.17,18,20-23

Covalent Binding of Proteins to Acetal-Functionalized Latexes. I. Physics and Chemical Adsorption and Electrokinetic Characterization

In this work the interaction of an a-CRP IgG protein with functionalized latexes that have acetal groups on their surfaces has been studied. Two acetal latexes with similar amounts of surface acetal groups but different surface charge densities were used. Some experiments on the physical and chemical adsorption of the IgG onto these polystyrene beads have been performed, and several latex–protein complexes with the IgG physically or chemically bound to the surface were obtained by modifying the incubation conditions. In the covalent coupling experiments of the IgG, the physically adsorbed protein was removed by redispersion of the complexes in the presence of a nonionic surfactant (Tween 20). After this treatment the final amount of protein on the latex surface was around 80% of the total protein initially adsorbed. The latex–protein complexes that formed were characterized from the electrokinetic point of view by measuring their electrophoretic mobilities versus the pH, in order to detect any difference between the particles when the protein is physically or chemically coupled. The isoelectric point (iep) of the complexes was around pH 4, where they will be unstable because the electrostatic repulsion cannot stabilize the particles. At neutral and basic pH, the electrophoretic mobility values of the latex–protein particles seem to predict a good colloidal stability which is a very important aspect when looking for its application in the field of the clinical diagnostic. The redispersion of the complexes in the presence of Tween 20 modified the electrokinetic behavior of the particles, especially at pH 4 and 5, which seems to indicate an interaction between the surfactant and the protein molecules which could reduce the immunoreactivity of the latex–protein complexes.

Effects of gamma-irradiation on the electrokinetic properties of purple membranes.

The effect of gamma-irradiation (5, 10 and 15 Gy) on the kinetic surface charge of purple membranes (PM) was followed by means of particle microelectrophoresis. The changes in electrophoretic mobility (EPM) were examined at 2, 5 and 26 h, respectively, following irradiation of native PM, and at 2, 26, 50 h and 5 days following irradiation of delipidated PM. It was concluded that the high inhomogeneity of the suspension, even after sonication, largely affects the measured zeta-potential. The 15-Gy treatment significantly increased the net negative surface charge density at 5 and 26 h after irradiation of native PM. However, the opposite effect of approximately twofold reduction of EPM values was derived from simultaneous studies concerning their delipidated form. Low irradiation doses clearly induced an enhancement of negative surface charge density at 2 h post-exposure as well as the formation of unstable structures of delipidated PM. The changes in electrokinetic properties might reflect the specific aggregate formation in both native and delipidated PM. It was suggested that the effect observed of both types of PM was mainly a structural phenomenon possibly related to the modification of functionally active residues.

Affinity capillary electrophoresis: a physical-organic tool for studying interactions in biomolecular recognition.

Affinity capillary electrophoresis (ACE) is a technique that is used to measure the binding affinity of receptors to neutral and charged ligands. ACE experiments are based on differences in the values of electrophoretic mobility of free and bound receptor. Scatchard analysis of the fraction of bound receptor, at equilibrium, as a function of the concentration of free ligand yields the dissociation constant of the receptor-ligand complex. ACE experiments are most conveniently performed on fused silica capillaries using a negatively charged receptor (molecular mass < 50 kDa) and increasing concentrations of a low molecular weight, charged ligand in the running buffer. ACE experiments that involve high molecular weight receptors may require the use of running buffers containing zwitterionic additives to prevent the receptors from adsorbing appreciably to the wall of the capillary. This review emphasizes ACE experiments performed with two model systems: bovine carbonic anhydrase II (BCA II) with arylsulfonamide ligands and vancomycin (Van), a glycopeptide antibiotic, with D-Ala-D-Ala (DADA)-based peptidyl ligands. Dissociation constants determined from ACE experiments performed with charged receptors and ligands can often be rationalized using electrostatic arguments. The combination of differently charged derivatives of proteins - protein charge ladders - and ACE is a physical-organic tool that is used to investigate electrostatic effects. Variations of ACE experiments have been used to estimate the charge of Van and of proteins in solution, and to determine the effect of the association of Van to Ac2KDADA on the value of pKa of its N-terminal amino group.

Complex electrosurface investigations of dispersed microphases

The structure of the electrical double layer (EDL) of colloidal systems is discussed. The methods of determination of the most important parameters of the EDL, i.e. the value of the surface-potential ψ 0, the Stern-potential ψ δ and the electrokinetic-potential ζ, the surface charge density σ 0, the electrokinetic charge σ ζ, as well as the specific surface conductance κ σ and Rel parameter are described. The application of the theory of non-linear electrosurface phenomena developed by Dukhin, Derjaguin and Shilov for calculation of the EDL parameters is discussed. The above data of the EDL characteristics for polystyrene and melamin-formaldehyde latices, suspensions of AgI, Sb 2S 3, Fe 2O 3, ZrO 2, hydromica, palygorskyte, yeast cells as well as kerosene-in-water, ET grade lubricating oil technical emulsions in different electrolyte solutions are discussed. It has been shown that in the most of cases (with the exception of AgI solution) ψ 0 or ψ δ>ζ and σ 0≫σ ζ. It indicates the presence of a considerable free charge between the surface and slipping plane due to the formation of hydrodynamically immobile water layers on the surface in which the ions retain high mobility. The necessity of complex (integrated) electrosurface measurements for the description of the electrical double layer structure is stressed. A new kind of non-linear electrokinetic phenomena, namely the superfast electrophoresis is described. The phenomenon was predicted theoretically by Dukhin and Mishchuk and investigated experimentally in detail in the author's laboratory. It has been shown that the electrophoretic mobility of large (hundreds μm) ion-type conducting particles like ion-exchanger grains/fibres or electron-type conducting particles like Al/Mg alloy, graphite and activated carbon in strong electric fields (100–1000 V/cm) exceeds the electrophoretic mobility values typical for non-conducting particles by 1–2 orders of magnitude. The mobility of such particles depends on the conductivity ratio between the particles and medium and strongly increases with the electric field gradient and the particle size. This is in contrast to classical electrophoresis. The superfast electrophoresis is due to the interaction of a strong electric field with the space charge near the surface of unipolar conducting particles. This space charge is induced by the strong external field because of the concentration polarisation.

Formation of Protein Charge Ladders by Acylation of Amino Groups on Proteins

The values of charge and electrophoretic mobility of a protein are changed upon acylation of its α- and Lys ε-NH3+ groups. Partial acylation of the amino groups of a protein results in a set of derivatives that is often resolved by capillary electrophoresis into a set of distinct peaksthe “rungs” of a protein charge ladderthat differ incrementally in the number of residues modified. Proteins that have values of MW < 50 kD usually form resolved charge ladders when allowed to react with acetic anhydride, while proteins that have values of MW > 50 kD form broad unresolved peaks. Resolved charge ladders of proteins that have values of MW > 50 kD may be formed using acylating agents that introduce several charges upon acylation of each of their Lys ε-NH3+ groups. As an example, l-lactate dehydrogenase (MW = 147 kD) does not form a resolved charge ladder when modified with acetic anhydride. When it is acylated with either 1,2,4-benzenetricarboxylic anhydride, 3, or 1,2,4,5-benzenetetracarboxylic dianhydride, 4, however, it forms charge ladders in which each of the first several pairs of adjacent rungs are separated by approximately 3 or 4 units of charge, respectively. The procedures described in this paper were used to form resolved charge ladders from 25 proteins differing in pI and in MW.