Microelectrophoretic Mobility Measurements Research Articles

The Modulating Effect of p-Coumaric Acid on The Surface Charge Density of Human Glioblastoma Cell Membranes.

p-Coumaric acid (p-CoA), a phenolic acid belonging to the hydroxycinnamic acids family, is a compound with tentative anticancer potential. Microelectrophoretic mobility measurements conducted at various pH values of electrolyte solution were applied to study p-CoA effects on electrical properties of human glioblastoma cell membranes. The obtained results demonstrated that after the p-CoA treatment, the surface charge density of cancer cells changed in alkaline pH solutions, while no noticeable changes were observed in cell membranes incubated with p-CoA compared to control at acidic pH solutions. A four-equilibrium model was used to describe the phenomena occurring on the cell membrane surface. The total surface concentrations of both acidic and basic functional groups and their association constants with solution ions were calculated and used to define theoretical curves of membrane surface charge density versus pH. The resulting theoretical curves and the experimental data were compared to verify the reliability and validity of the adopted model. The deviation of both kinds of data obtained at a higher pH may be caused by disregarding interactions between the functional groups of cancer cells. Processes occurring in the cell membranes after their incubation with p-CoA can lead to disorders of existing equilibria, which result in changes in values of the parameters describing these equilibria.

The modulating effect of lipid bilayer/p-coumaric acid interactions on electrical properties of model lipid membranes and human glioblastoma cells

Biological membranes are one of the most important elements of living cells determining their permeability to the active compounds. Still, little is known about the drug-membrane interactions in terms of pharmacological properties of potential drugs. Chemoprevention based on natural compounds is becoming a strong trend in modern oncopharmacology, and p-coumaric acid (p-CoA) is one such compound with tentative anticancer activity. The microelectrophoretic mobility measurements and electrochemical impedance spectroscopy were applied to study the effects of p-CoA on electrical properties of liposomes, spherical bilayers, and human glioblastoma cell membranes. Our results demonstrated that after treatment with p-CoA, the surface charge of LBC3, LN-229 and LN-18 cell lines was significantly changed in alkaline pH solutions, but not in acidic pH solutions. In contrast, no changes in surface charge density values were registered for phosphatidylethanolamine liposomal membranes and A172 cell membranes after p-CoA treatment. The impedance data showed an increase in values of both the electrical capacitance and the electrical resistance, indicating that p-CoA can be partially inserted into the phosphatidylcholine bilayers. The MTT assay showed cell line-dependent cytotoxic effect of p-CoA. Further molecular analyses revealed the ATP depletion and gene transcription modulation, which might indicate organelle membrane-crossing potential of p-CoA. These results suggest, that changes in surface charge of membranes of living cells not only might be potential predictor of membrane permeability, but also indicate differential composition of cell membranes in various cell lines. Thus further multidirectional analyses are required to implement electrochemical methods as standard testing procedures during drug development process.

The effect of quercetin on the electrical properties of model lipid membranes and human glioblastoma cells

Quercetin is a naturally-occurring flavonoid claimed to exert many beneficial health effects. In this report, the influence of quercetin on the surface charge of phosphatidylcholine liposomes and human glioblastoma LN-229 and LN-18 cells was studied using microelectrophoretic mobility measurements. The effect of quercetin on the electrical resistance and capacitance of bilayer lipid membranes was analyzed via electrochemical impedance spectroscopy. The results showed that after flavonoid treatment, the cell lines demonstrated changes in surface charge only in alkaline pH solutions, whereas there were no significant alterations in quercetin-treated vs. control cells in acidic pH solutions. The same tendency was found for liposomal membranes proving that quercetin insertion into membranes is strongly pH-dependent. Capacitance and resistance measurements conducted in acidic electrolyte solutions demonstrated an increase in both electrical parameters, indicating an increased amount of quercetin inserted into the bilayers. Moreover, the cytotoxic effect of quercetin confirms that the flavonoid enters the cells and perturbs the proliferation of LN-229 and LN-18 glioblastoma cell lines. As such, our results indicate that the specific localization of quercetin, membrane-bound or cell-entering, might be crucial for its pharmacological activity. However, further studies are necessary prior to applying these physicochemical measurements as standard methods of evaluating drug activity.

Study on the Correlation between Lateral Diffusion Effect and Effective Charge in Neutral Liposomes

An experimental investigation is described on the variables that affect the lateral diffusion coefficient (D(lat)) of dimyristoylphosphatidylcholine, a zwitterionic phospholipid, and the effective charge (Z(ef)) on liposomes. The lateral diffusion coefficient was obtained from the dielectric relaxation time of the zwitterionic phospholipids in the bilayer, and the effective charge on the external monolayer was estimated from microelectrophoretic mobility measurements by means of the Henry and Coulomb equations. The measurements were performed at different pH values and salt (KBr) concentrations as well as in two physical states of the phospholipid: the liquid-crystalline phase and gel phase. The Z(ef) and D(lat) values in the gel phase are always lower than those in the fluid phase. A very small change of pH (approximately 0.5 pH units) caused a pronounced variation of the effective charge and the lateral diffusion coefficient. Both variations are correlated, which demonstrates that the adsorption of the ions that determine the electrokinetic potential also controls the lateral diffusion of dipolar phospholipids in the bilayer and the effective charge on the external surface of the liposomes.

Deposition of colloid particles on polyelectrolyte multilayers

Deposition of negatively and positively charged latex particles onto polyelectrolyte multilayers adsorbed at mica was studied experimentally by using the impinging-jet cell. These data were complemented by streaming potential measurements in the parallel-plate channel arrangement. Two types of polyelectrolytes were used: polyallylamine hydrochloride (PAH), of a cationic type and polysodium 4-styrenesulfonate (PSS) of an anionic type. The bulk characteristics of polymers is represented by the zeta potential values obtained from microelectrophoretic mobility measurements. It was shown that the initial deposition rates of polystyrene latex on oppositely charged polyelectrolyte layer attained the limiting value characteristic for homogeneous surface. On the other hand, the initial deposition rate in case of similarly charged polyelectrolyte layer and colloid particles was negligible. Periodic variations in particle deposition rate correlated well with periodic changes in apparent zeta potential of the mica substrate covered by polyelectrolyte layers. These results suggested that in the case of PAH/PSS multilayers adsorbed from polyelectrolyte solutions of high concentrations there was little chain interpenetration between adjacent polyelectrolyte layers.

Investigation of Rutile, Anatase, and Industrial Titania/Water Solution Interfaces using Potentiometric Titration and Microelectrophoresis

The rutile, anatase, and industrial titania (used in catalysis as support and consisting of rutile and anatase)-water solution interfaces were studied using potentiometric titration and microelectrophoretic mobility measurements. Concerning the simple oxides it was found that specific adsorption of the ions of the background electrolyte (NH4NO3) does not take place. The electrical double layer developed in the anatase/aqueous solution and rutile/aqueous solution interfaces is described by the diffuse layer model. On the basis of this model the surface acidity constants, the point of zero charge, and the concentration of the various surface hydroxyls in the pH range 4-8 were calculated using a computer program called SURFEQL. It was confirmed that the surface of rutile is more acidic than the surface of anatase. Concerning industrial titania used in catalysis as support it was demonstrated that its surface has a patchwise structure consisting of rutile (10%) and anatase (90%) regions. The acid-base behavior of this material is identical to a mechanical mixture of rutile and anatase of the same composition. Taking into account its patchwise structure we calculated the variation, with pH, of the concentration of each surface hydroxyl of industrial titania [TirOH+2, TiIOH, TirO-, TiaOH+2, TiaOH, and TiaO-; a, r stand for anatase and rutile, respectively]. These variations allow one to model the deposition of species containing catalytically active ions on the surface of industrial titania.

Evaluation of Drug-Lipid Association Constants from Microelectrophoretic Mobility Measurements

Electrophoretic mobilities of negatively charged lipid vesicles were measured after incubation with cationic drugs (adriamycin, celiptium, ethidium bromide, tetracaine) at different drug concentrations. We show here that comparison of the measured electrophoretic mobility with adsorption isotherms allows calculation of the drug-binding constants over a large range of drug concentrations, whatever the structure of the drug, its topology into the lipid bilayer, or its aggregation state

Mechanistic aspects of the deposition of the Cr(VI) species on the surface of TiO 2 and SiO 2

The deposition of the negatively charged Cr(VI) species on TiO 2 and SiO 2 surfaces suspended in aqueous electrolyte media has been studied in the pH range 3.0–8.0. The investigation included deposition isotherm and microelectro-phoretic mobility measurements. From the experimental results and a theoretical analysis of the deposition isotherms, it was concluded that the Cr x O y z− ions taken up were located in energetically equivalent sites at the inner Helmholtz plane (IHP) of the electric double layer that had developed between the support particles and the impregnating solution. The deposition sites were mainly created by protonated surface hydroxyl groups in the case of SiO 2 and by protonated and undissociated surface hydroxyl groups in the case of TiO 2. The lateral interactions operative among the deposited Cr(VI) species were, in general, strong, being stronger in SiO 2 supports in comparison with those of TiO 2. Moreover, it was found that upon a pH decrease from 6.0 to 3.0, the extent of deposition of the Cr(VI) species on silica increased from 0.01 to 0.13 μmol Cr(VI) m −2. The extent of deposition of the Cr(VI) species on titania increased also from 0.23 to 1.68 μmol Cr(VI) m −2 with a pH decrease from 8.0 to 4.8. Further decrease in the pH in the case of titania resulted in a considerable decrease in the extent of deposition.

Molybdenum-oxo species deposited on titania by adsorption: Mechanism of the adsorption and characterization of the calcined samples

The mechanism of the adsorption of molybdates on the titania surface has been investigated using adsorption equilibrium experiments, potentiometric titrations, and microelectrophoretic mobility measurements. Comparison of adsorption data with the surface charge of titania, regulated by changing the pH of the impregnating solution, demonstrated that the groups responsible for the creation of the adsorption sites are mainly the protonated surface hydroxyls of titania in addition to the neutral sites. Moreover, the results obtained by the combination of potentiometric titrations and microelectrophoretic mobility measurements, and the variation of pH before and after adsorption with the Mo( vI) concentration suggested that the MoO 2 2− ions are adsorbed on the Inner Helmholtz Plane (IHP) of the electrical double layer, which is developed between the surface of the titania particles and the impregnating solution. Finally, from the analysis of the isotherms obtained it was concluded that the adsorbed MoO 2 − ions are located on energetically equivalent sites of the IHP and that relatively weak lateral interactions are exerted. On the basis of the abovementioned menhanism, an explanation of the dependence of the sorptive capacity of titania on the pH of the impregnating solution is provided. The combined use of NO and CO 2 adsorption, as well as XPS, RAMAN spectroscopy, and temperature programmed reduction measurements, showed that at pH 7.3, corresponding to about 2 wt% MoO 3, the titania surfaceis completely covered and the active surface reaches its maximum value. At pH values lower than 7.3, a second molybdena layer starts to form until the Mo03 content reaches the 5.4 wt% MoO 3, a point at which Mo03 crystallites are formed.

Functionalization of colloidal silica and silica surfaces via silylation reactions

A series of trialkoxysilane compounds tipped with primary amine groups were used to functionalize the surfaces of glass and colloidal silica. Streaming potential and microelectrophoretic mobility measurements were used to monitor the stability of the functionalized surfaces. Hydrolytic breakdown of the surface-to-silane coupling was induced by either successively increasing and decreasing the pH of the solution in contact with the surface, or by aging the derivatised surfaces in aqueous solution over prolonged periods of time. The chemistry of the spacer units between the trialkoxysilane group and the primary amine tip had a major influence on the subsequent hydrolytic stability. Large hydrophobic spacer groups showed small changes in the electrokinetic properties on storage, but large changes when successively titrated with acid and base through the pH range. The behavior observed with small hydrophobic spacer groups was that large changes in electrokinetic properties were obtained on storage and with pH titration.

Determination of the surface coverage of oxidic supports by oxidic and non-oxidic supported phases using potentiometric titration and electrophoretic mobility data. A study of Fe2O3/Al2O3 supported catalysts

The point of zero charge (p.z.c.) and the isoelectric point (i.e.p.) of a series of Fe2O3/Al2O3 catalysts of varying iron contents, used as a model system, have been determined using potentiometric titrations and microelectrophoretic mobility measurements, respectively. Simple equations allowing the calculation of the percentage surface coverage (p.s.c.) by determing p.z.c. or i.e.p. values have been derived. Although the p.z.c. was found to differ from the i.e.p., both techniques provided similar, although not identical, p.s.c. values. These values correlated very well with X-ray photoelectron spectroscopy results. This fact suggests that both potentiometric titrations and microelectrophoretic mobility measurements can be used to estimate the variation in p.s.c. of a supported-metal oxide catalyst caused by the variation of a preparative parameter. The main advantage of these two methods is the low cost involved. The present work suggests that the combination of the above-mentioned electrochemical techniques could prove extremely useful in investigating the formation of small amounts of non-oxidic supported phases hardly detectable by X-ray spectroscopy. Finally, it has been concluded that three iron-supported phases are formed on the surface of alumina: (i) small amounts of a non-oxidic supported phase (e.g. adsorbed Fe3+ or iron aluminate), (ii) loosely bound α-Fe2O3 and (iii) strongly associated α-Fe2O3.

Coagulation of Colloidal Hydrous Manganese Dioxide

The objective of this study was to explore the factors governing the destabilization and precipitation of colloidal hydrous manganese dioxide in water treatment practice. Particular emphasis is placed on evaluation of appropriate coagulation controls that might permit more effective removal of this material from water supplies. A chemical determination of residual MnO2 concentration to measure the progress of coagulation and sedimentation is presented, and the orthotolidine method was found to be quite suitable for this purpose. Interference of iron was eliminated by masking with phosphoric acid. Absorbance measurements were made with a spectrophotometer. For several experiments, the analytic determinations were supplemented by microelectrophoretic mobility measurements, after a procedure described by Black and Smith.