Surface Charge Values Research Articles

Eudragit RL100 nanoparticle system for the ophthalmic delivery of cloricromene.

A Eudragit RL100 polymer nanoparticle system loaded with cloricromene was prepared and characterized on the basis of physicochemical properties, stability and drug release features. To investigate the ocular bioavailability of cloricromene after inclusion in the polymer matrix, the new nanoparticle system was topically administered in the rabbit eye and compared with an aqueous solution of the same drug. The nanoparticle system showed interesting size distribution and surface charge values, suitable for ophthalmic application. The results indicated that the dispersion of cloricromene within Eudragit RL100 polymer nanoparticles increased its ocular bioavailability and enhanced the biopharmaceutical profile. The new cloricromene-loaded nanoparticle system described here may be useful in clinical practice.

Adsorption and reduction of palladium–dimethylglyoxime complex

The voltammetric reduction of Pd II(DMGH) 2 preadsorbed on mercury in 0.2 M acetic/acetate buffer (pH 4.85) was studied. Two adsorbed surface stages could be distinguished: while a submonolayer is present molecules adsorb parallel to the electrode, but at high surface concentration perpendicular interactions between adsorbed molecules lead to bilayer or even multilayer formation. The surface charge value obtained for the reduction of a virtual monolayer is Q M = 38 μC cm −2. The electrochemical behaviour of adsorbed species under submonolayer coverage is explained in terms of an E r C i surface reaction scheme and a rate expression that takes into account attractive forces between the adsorbed reactant complex molecules.

The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Mesoporous anatase was prepared following sol–gel and using urea as template. The influence of calcination temperature on the phase stability, nanocrystal/aggregate size, pore size distribution and specific surface area as well as on the acid–base behavior in aqueous solutions was studied using X-ray diffraction, laser-Raman and diffuse reflectance spectroscopies, scanning electron microscopy and laser scattering as well as N 2 adsorption–desorption isotherms and potentiometric mass titrations. The crystal structure was kept constant upon calcination over the whole temperature range, 200–500 °C. In this range anatase is constituted from primary nanocrystals. These are assembled into larger, rather spherical, clusters of about 30–40 nm and then into aggregates of various sizes (0.2–0.3 μm and 2–100 μm) with a distribution centered at about 12 μm. Increase of the calcination temperature caused an increase in the size of the primary nanocrystals from 8.1 nm at 200 °C to 17.1 nm at 500 °C, whereas calcination does not influence the morphology at micro-scale. Moreover, increase of the calcination temperature from 200 °C to 500 °C brings about a shift in the mean pore diameter from 47 nm to 91 nm accompanied by a decrease in the specific surface area and pore volume. The above effects were related with the aforementioned increase in the size of the primary nanocrystals. The value of pzc and the values of surface charge determined at various pH do not practically depend on the calcination temperature. The absence of pore space confinement effects was explained in terms of the structure and size of the interface development between the anatase surface and the electrolytic solution.

Enhanced Intracellular Delivery of Quantum Dot and Adenovirus Nanoparticles Triggered by Acidic pH via Surface Charge Reversal

Quantum dot (QD) and adenovirus (ADV) nanoparticles were surface-modified with graft copolymers that exhibited a charge reversal behavior under acidic condition. Poly(L-lysine) (PLL) was grafted with multiple biotin-PEG chains (biotin-PEG-PLL graft copolymer), and the remaining primary amine groups in the PLL backbone were postmodified using citraconic anhydride, a pH-sensitive primary amine blocker, to generate carboxylate groups. The surfaces of streptavidin-conjugated QDs were modified with citraconylated biotin-PEG-PLL copolymer, producing net negatively charged QD nanoparticles. Under acidic conditions, citraconylated amide linkages were cleaved, resulting in the recovery of positively charged amine groups with subsequent alteration of surface charge values. Intracellular delivery of QD nanoparticles was greatly enhanced in an acidic pH condition due to the surface charge reversal. The surface of avidin-conjugated adenovirus (ADV-Avi) encoding an exogenous green fluorescent protein (GFP) gene was also modified in the same fashion. The expression extent of GFP was significantly increased at more acidic pH than pH 7.4. This study demonstrates that various nanosized drug carriers, imaging agents, and viruses could be surface-engineered to enhance their cellular uptake specifically at a low pH microenvironment like solid tumor tissue.

Temperature Study of Nonionic Polymers Adsorption at the Alumina—Solution Interface

The temperature influence of the structures of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) adsorption layers on the alumina surface was studied. The amount of polymer adsorbed, the surface and diffuse layer charge of Al2O3 particles in the absence and presence of the polymer, and the thickness of polymer adsorption layers were determined in the 5°–40°C temperature range. An increase of PVA and PEG adsorption with an increase of temperature was observed. It is caused by conformation changes of polymer macromolecules from the coil structure to more and more stretched conformation when the temperature increases. Such a behavior was confirmed by the parameters calculated from the experimental data (Rh—hydrodynamic radius of a polymer coil in the solution, δ—thickness of the polymer adsorption layer, Rs—radius of a sphere equivalent to the volume that falls per a macromolecule in the adsorbed layer). From the comparison of the values of diffuse layer charge and surface charge, the main factor influencing the ζ potential changes was determined. The free energy of PVA and PEG adsorption was calculated using the ζ potential data.

The effect of intercultivar substitution of wheat Triticum aestivum L. chromosomes on lipoxygenase activity and its correlation with the technological properties of flour

The effects of intercultivar substitution of individual chromosome pairs (except for 1B, 6D, and 7A) in the wheat cultivars Saratovskaya 29 and Janetzkis Probat, differing in quality, on specific lipoxygenase activity, the grain yield per spike, and the main technological properties of flour and dough were studied. It was demonstrated that the substitution of individual chromosomes of the recipient cultivar Saratovskaya 29 with the homologous chromosomes of the donor cultivar Janetzkis Probat caused significant changes in lipoxygenase activity and several other quality characteristics. The correlations between the lipoxygenase activity and the parameters of physical dough properties were determined. Three molecular forms of lipoxygenase (Lpx-1, Lpx-2, and Lpx-3), differing in the value of surface charge and enzymatic activity, were detected by native PAGE.

Attachment of Shiga toxigenic Escherichia coli to stainless steel

Shiga toxigenic Escherichia coli (STEC) are important foodborne pathogens causing gastrointestinal disease worldwide. Bacterial attachment to food surfaces, such as stainless steel may lead to cross contamination of foods and subsequent foodborne disease. A variety of STEC isolates, including E. coli O157:H7/H− strains, were grown in planktonic (broth) and sessile (agar) culture, following which initial attachment to stainless steel was determined using epifluorescence microscopy. Experiments were performed to determine whether the number of bacteria attached to stainless steel differed between STEC strains and between the two modes of growth. No relationship was found between STEC strains and the number of bacteria attached to stainless steel. Five STEC strains, including one non-toxigenic O157 isolate, attached in significantly greater ( p < 0.05) numbers to stainless steel following growth in planktonic culture compared to sessile culture. In contrast, two clinical strains of O157:H7 attached in significantly greater ( p < 0.05) numbers following growth in sessile culture compared to planktonic culture. Thirteen out of twenty E. coli strains showed no significant difference ( p > 0.05) in attachment when grown in planktonic or sessile culture. The change of interfacial free energy between the bacterial strains and stainless steel was calculated and the influence of free energy in attachment was determined. Although a significant variation ( p < 0.05) in free energy values was found between STEC strains, no correlation was found between free energy values and bacterial counts on stainless steel. In addition, no correlation was also found between bacterial hydrophobicity and surface charge values or production of surface structures (type I fimbriae or flagella) (previously determined) with the number of bacteria attached to stainless steel. The results of this study suggest that different growth conditions (planktonic and sessile) can influence the attachment of STEC to stainless steel. Factors other than bacterial physicochemical properties and these surface structures may also influence STEC attachment to stainless steel.

Tuning of shell and core characteristics of chitosan-decorated acrylic nanoparticles

The aim of the work was to develop a new family of chitosan-coated acrylic nanoparticles to increase the specificity of absorption of drugs associated given by the mucosal route. To achieve this goal, techniques of radical and anionic emulsion polymerisation of isobutylcyanoacrylate (IBCA) were used. Changes in the shell composition were made by using chitosan of different molecular weight and thiolated chitosan to modify the particle surface properties in order to vary the mucosae–nanoparticle interactions. The core was also modified by the inclusion of methyl methacrylate (MMA) as second monomer potentially able to improve the control of drug release. Finally, the labelling of nanoparticles core with a fluorophore, methacryloxyethyl thiocarbamoyl rhodamine B (Polyfluor™), was successfully achieved, necessary for the in vitro and in vivo evaluation of the systems created. Results showed that nanoparticle size varied from 200 to 500 nm, depending on the molecular weight of chitosan used. Positive surface charge values were obtained in all cases. In addition, evidences of the presence of thiol groups were obtained (0.03–0.16 × 10 −3 μmol/cm 2 of nanoparticle).

Electrochemistry of lumiflavin adsorbed at mercury acidic aqueous solution interface

Abstract The adsorption of the oxidized and the reduced forms of lumiflavin (−0.150 V and −0.450 V, respectively) at pH 4.5, and the electrochemical conversion of them were investigated. Two adsorbed surface stages could be distinguished for each oxidation state. Vertical interactions between adsorbed molecules lead to bilayer formation at high surface concentration. These interactions are stronger for the reduced form (H 2 LF) than the corresponding oxidized (LF) molecule. Surface charge values for a virtual monolayer of Q M = 17 μC cm −2 for both, LF and H 2 LF, and the corresponding capacitances of 16 μF cm −2 and 11 μF cm −2 were obtained, respectively. The electrochemical behaviour of adsorbed species under sub-monolayer coverage is characterized as a quasi-reversible redox process conditioned by molecular lateral interactions. The apparent standard rate constant for the overall two-electron process, k 0 = 295 s −1 , and a transfer coefficient, α = 0.5, were estimated from square wave voltammetry.

Attachment of Shiga Toxigenic Escherichia coli to Beef Muscle and Adipose Tissue

Shiga toxigenic Escherichia coli (STEC) serotypes are important foodborne pathogens that cause gastrointestinal disease worldwide. An understanding of how STEC strains attach to surfaces may provide insight into the potential persistence of and contamination with STEC in food environments. The initial attachment of a selection of STEC serotypes to beef muscle and adipose tissue was evaluated for isolates grown in planktonic and sessile culture. Initial experiments were performed to determine whether attachment differed among STEC strains and between the two modes of growth. Viable counts were obtained for loosely and strongly attached cells, and the strength of attachment (Sr) was calculated. All bacterial isolates grown in sessile culture attached in higher numbers to muscle and adipose tissue than did bacteria in planktonic cultures. For all attachment assays performed, mean concentrations for loosely attached cells were consistently higher than concentrations for strongly attached cells. The mean concentrations for strongly attached bacteria for planktonic and sessile cultures were significantly higher (P < 0.05) on adipose than on muscle tissue. However, some strains of STEC, particularly those from sessile culture, did not differ in their attachment to muscle or adipose tissue. Sr values were not significantly different (P > 0.05) among STEC isolates for all assays. No correlation was found between bacterial hydrophobicity and surface charge values (previously determined) and production of surface structures, viable counts, and Sr values. STEC grown in planktonic and sessile culture seems to behave differently with respect to attachment to muscle and adipose tissue. Cells in sessile culture may have a greater potential to strongly attach to meat surfaces.

Electrokinetic behavior and colloidal stability of polystyrene latex coated with ionic surfactants

This work is focused on analyzing the electrokinetic behavior and colloidal stability of latex dispersions having different amounts of adsorbed ionic surfactants. The effects of the surface charge sign and value, and the type of ionic surfactant were examined. The analysis of the electrophoretic mobility ( μ e ) versus the electrolyte concentration up to really high amounts of salt, much higher than in usual studies, supports the colloidal stability results. In addition, useful information to understand the adsorption isotherms was obtained by studying μ e versus the amount of the adsorbed surfactant. Aggregation studies were carried out using a low-angle light scattering technique. The critical coagulation concentrations (ccc) of the particles were obtained for different surfactant coverage. For latex particles covered by ionic surfactants, the electrostatic repulsion was, in general, the main contribution to the colloidal stability of the system; however, steric effects played an important role in some cases. For latices with not very high colloidal stability, the adsorption of ionic surfactants always improved the colloidal stability of the dispersion above certain coverage, independently of the sign of both, latex and surfactant charge. This was in agreement with higher mobility values. Several theoretical models have been applied to the electrophoretic mobility data in order to obtain different interfacial properties of the complexes (i.e., zeta potential and density charge of the surface charged layer).

Characteristics of the Porous Structure of Cement Stone

The complex study of filtration and electric properties of the samples of cement stone with different water-cement ratios is performed. It is established that filtration coefficient decreases by 4–6 times with an increase in a pressure drop and becomes constant at pressure drops above 3–3.5 MPa. The observed effect is interpreted as a reversible change in the internal structure of cement stone upon the filtration of a liquid through the stone. It is revealed that the filtration coefficient and porosity of samples decrease with time. Total open porosity and the most probable pore radius are determined by mercury porosity technique. Coefficients of structural resistance and pore tortuosity of the samples are determined from the comparison of through and total porosity. The values of streaming potential are measured and values of surface charge and potential of the samples of cement stone are calculated.

Small high density lipoprotein subclasses: some of their physico-chemical properties and stability in solution.

Small high density lipoproteins (SHDL) contribute to the protection from atherosclerosis, but detailed information about their properties is not available yet. We isolated four of the smallest HDL subclasses that contain apoA-I alone, the small lipoprotein A-I (SLpAI), by their separation on gradient polyacrylamide gel followed by electroelution. Their physico-chemical properties were calculated from their displacement in non-denaturing gradient polyacrylamide gel under the effect of electrical potential. The properties are: Stokes' radii 2.96-3.56 nm; molecular masses 42-70 kDa; net negative charge 7.2-13.5; surface charge densities 3139-4069 -esu.cm(-2); surface potentials 10.6-15.7 -mV; coefficients of friction 5.74-6.90 x 10(-8) g.s(-1); and diffusion coefficients 5.76-6.94 x 10(-7) cm(2).s(-1). We found that these particles were of low stability as they underwent molecular transformation into larger particles on storage. The estimated dimensions of these particles do not support ellipsoidal shape, therefore, the most probable shape is spherical; consequently, their hydrated characteristics were estimated. We conclude that these particles have high values of negative surface charge and diffusion coefficients, and are of low stability. Their small Stokes' radii were similar to each other and they are spherical and highly hydrated.

Self-Association of Potassium Nonanoate Molecules in Aqueous Aerosil Dispersions:13C NMR Data

The association of potassium nonanoate molecules in aqueous Aerosil dispersions at high and low surface charges of its particles are studied by the 13C NMR technique at frequencies of 75 and 125 MHz with the rotation of a sample at a magic angle. It is shown that, using the chemical shifts and spin–lattice relaxation times of 13C nuclei of single segments of the hydrophobic chain of a surfactant molecule, one can determine whether the segments are located in the adsorption layer on a solid surface or in the associates formed in the bulk solution. The values of the chemical shift and spin–lattice relaxation time depend, above all, on the value of the surface charge. The NMR parameters of two carbon atoms in the hydrophobic chain nearest to the polar group of the surfactant molecule appeared to be the most sensitive to the value of the adsorbent surface charge. It is discovered that, upon adsorption of potassium nonanoate from solutions with concentrations of 1.5–3 wt % and pH 6, the surfactant molecules are located in the adsorption layer parallel to the surface. At a higher surface charge, adsorption in the same concentration range occurs mainly on the hydroxyl groups; in this case, adsorbed molecules are arranged mostly along the normal to the surface. At surfactant concentrations much higher than the CMC (10–20%), the values of the chemical shift and relaxation time become closer to those measured in surfactant solutions in the absence of Aerosil.

Improving the Accuracy of Nondestructive Electromagnetic Method of Determining the Strength of Composite Dielectric Materials

A method of improving the accuracy of nondestructive electromagnetic emission method of determining the strength of materials is proposed and tested experimentally. A new method of determining the value and sign of the effective surface charge in dielectrics on the basis of parameters of the electromagnetic response on their impact excitation is also proposed.

Dynamic electrophoretic mobility of spherical colloidal particles in a salt-free medium

A theory is proposed for the dynamic electrophoretic mobility μ( ω) of spherical colloidal particles in a salt-free medium containing only counterions in an oscillating electric field of frequency ω. The dynamic mobility depends on the frequency ω of the applied electric field and on the particle volume fraction as well as on the particle surface charge. It is found that as in the case of the static electrophoretic mobility μ(0) in salt-free media, there is a certain critical value of the particle surface charge separating two cases, that is, the low-surface-charge case and the high-surface-charge case (in the latter case the counterion condensation takes place near the particle surface). For the low-surface-charge case, the dynamic mobility agrees with that of a sphere in an electrolyte solution in the limit of very low electrolyte concentrations κa→0 (Hückel's limit), where κ is the Debye–Hückel parameter and a is the particle radius. For the high-surface-charge case, however, the dynamic mobility becomes constant independent of the particle surface charge, because of the counterion condensation effects. A simple expression for the ratio μ( ω)/ μ(0) applicable for all cases is given.

Electrophoretic mobility of a liquid drop in a salt-free medium

A theory is proposed for the electrophoretic mobility μ of dilute spherical liquid drops of radius a in salt-free media containing only counterions (e.g., nonaqueous media). As in the case of the electrophoretic mobility of rigid particle in salt-free media, there is a certain critical value of the drop surface charge separating two cases, that is, the low-surface-charge case and the high-surface-charge case. For the low-surface-charge case, μ coincides with that of a drop in an electrolyte solution in the limit of very low electrolyte concentrations κa→0 (Hückel's limit), where κ is the Debye–Hückel parameter. For the high-surface-charge case, however, μ becomes constant independent of the drop surface charge, since the counterion condensation takes place near the drop surface.

Effects of different crystal faces on the surface charge of colloidal goethite (α-FeOOH) particles: an experimental and modeling study

The surface charge of colloidal particles is usually determined by potentiometric titration. These acid-base titrations make it possible to measure the pH of point-of-zero charge (pzc) for oxide minerals. This macroscopic property is the most important parameter used in surface complexation modeling to reproduce experimental data. The pzc values of goethite reported in the literature vary between 7.0 and 9.5. Carbonate adsorption and/or surface morphology are thought to account for this wide range. We demonstrate a procedure for the removal of the carbonate ions that initially adsorb on goethite and strongly affect the titration curves and pzc determination. We also investigated the crystal-face-specific reactivity of two morphologically different goethites. The z-profiles obtained from atomic force microscopy (AFM) images showed that the goethite with the smallest specific surface area ( S = 49 m 2/g, denoted G49) exhibits 70% of the (001) face, whereas this value is only 30% for the goethite with largest specific surface area ( S = 95 m 2/g, denoted G95). This morphologic difference results in slightly different pzc values: 9.0 for G49 goethite and 9.1 for G95 geothite. These experimental pzc values have been correlated with multisite complexation calculations using both the full-site and the 1-pK approaches. We used the full-site approach to consider all of the configurations of hydrogen bond interactions with surface site. The resulting mean charges gave estimated pzc values of 8.9 and 9.2 for the (001) and (101) faces, respectively. Considering these theoretical pzc values for individual faces and the face distributions obtained from AFM analysis, the calculated pzc values are in full agreement with the experimental pzc values. However, this morphologic difference is more expressed in surface charge values than in the pzc values. Indeed, the surface charge of G49 goethite is much higher than that of G95 goethite, and the 1-pK calculations make it possible to fit the titration data satisfactorily.

Role of Electrosurface Properties of Thiobacteria and Galenite in Ore Microbial Leaching

Electrokinetic properties of thiobacteria in the process of galenite microbial leaching were studied by microelectrophoresis method. It was shown that, in the region of acidic pH, precipitates of oxidized galenite and thiobacterium cells possess low negative electrokinetic potential. The analysis of the contribution of electrostatic and molecular forces, as well as of biospecific factor to the efficiency of interaction between the cell and sulfide mineral was performed. It was assumed that, after the attachment at the sulfide surface, the cells generate a microenvironment with high redox potential and buffer properties that promotes the highest oxidation activity of cells and optimal conditions for sulfide oxidation. With the accumulation of Fe(III) in the environment and the aging of culture, its surface charge grows and the cell tends to leave the microenvironment to find new accessible substrate. Changes in the value of cell surface charge can be of adaptation character and promote optimal functioning of its bioenergetic systems in the redox medium including sulfur and iron.

The Charge of the Pores of Poly(ethylene terephthalate) Nucleopore Membranes

The electrosurface properties of nucleopore membranes are studied by the streaming potential and EPR spectroscopy methods. Large differences between the values of surface charge of pores obtained by these methods are disclosed. This effect can be explained by the presence of the developed gel-layer on the pore surface.