Electrophoretic Mobility Measurements Research Articles

Surface interactions of model microplastic particles in seawater

Microplastic is classified as fragmented polymeric particles up to 500 microns in diameter. In an aqueous system, microplastic does not always present as a single particle, and these microparticles tend to aggregate and subsequently causing severe ecological risks. The exploration of the underlying mechanisms on how microplastics aggregate in seawater and freshwater enables the prediction of their diffusivity, distribution, and bioavailability in the water environment. In this study microplastic model systems of polypropylene (PP) and poly(vinyl chloride) (PVC) were used to investigate the interactions and aggregation size between microplastics in seawater and with the response anionic sodium dioctyl sulfosuccinate (AOT) surfactant dosages via electrophoretic mobility and Dynamic Light Scattering (DLS) measurements, supported by the UV-Vis spectrum analysis. This investigation revealed that mobile ions present in water ecosystems played a vital role in the surface interactions between microplastics and their aggregation behaviour. The surface charge of both PP and PVC microplastics were switched to a positive value at 5 wt.% of AOT and continued in the negative regime with increasing AOT concentration. Upon the addition of surfactant, surface charge neutralization and aggregation of PP and PVC microplastics were detected; however, the restabilization of microplastic was observed with increasing concentration of surfactant.

Relevance of zeta potential as a tool for predicting the response of controlled salinity waterflooding in oil–water-carbonate systems

Zeta potential has been proposed as a key parameter for predicting the response of controlled salinity waterflooding, as correlation with additional oil recovery has previously been established. However, it is unclear if there is a causal effect and if this parameter can be used as a unique predictive tool. We provide new insights with a detailed investigation into the role of the change of polarities of oil/water/rock interfaces on the additional oil recovery. Core flooding experiments with streaming potential and electrophoretic mobility measurements were performed to obtain insights into the electrostatic interactions that occur during oil recovery on Estaillades rock. Two different injection scenarios were followed in one crude oil/brine/rock (COBR) system: one conventional injection with decreasing salinity and one inverse injection with increasing salinity.Results indicated that oil recovery in secondary mode was more important using formation brine compared to low salinity brine. Also, almost no additional oil recovery was observed in tertiary mode irrespective of the injection scenario. Rock/water zeta potential was found positive in formation brine, and negative in the low salinity brines. The determination of oil/water polarity was more difficult as many inconsistencies between streaming potential and electrophoretic mobility measurements were observed. We propose several explanations for these discrepancies, including that the difference in zeta potential at fully water saturation and at residual saturation is not necessarily dependent on oil polarity as it can be induced by a change in rock exposed surface and in the distribution in water flow paths during measurements. The overall results suggest that zeta potential cannot be used as a unique indicator to predict the low salinity response of a COBR system.

Modification of Ti/TiO2NT with ZrO2 nanoparticles to enhance photoelectrocatalytic performance in removal of dibutyl phthalate.

This work shows that ZrO2, used as a modifier of TiO2, can be highly effective as a co-catalyst in the photoelectrocatalytic degradation of dibutyl phthalate (DBP). The monoclinic phase of ZrO2 was easily obtained by chemical deposition on TiO2 nanotubes (Ebg ~3.06 eV), increasing the occurrence of hydroxyl groups and acidity on the surface of the material, as observed by electrophoretic mobility measurements. The optimized photoelectrocatalysis conditions were bias potential of 1.5 V, 0.1 M Na2SO4 (initial pH 6) supporting electrolyte, 6 ppm of DBP, and UV/Vis irradiation. These conditions resulted in complete removal of DBP, down to the limit of detection of the chromatographic method used, with up to complete TOC removal after 60 min of treatment. The effects of pH, bias potential, DBP concentration, and applied potential were investigated. The method was compared with photocatalysis and photolysis. An oxidation mechanism is proposed, based on intermediates detected by LC-MS/MS during 10 min of photoelectrocatalysis.

Development of Novel Analysis and Characterization Methods Utilizing Reaction Dynamics in a Separation Capillary

Electrophoretic migration of an analyte in capillary electrophoresis (CE) reflects reaction dynamics of the analyte in solution. In affinity CE, an analyte of interest interacts with a modifier added in the separation buffer in fast equilibrium, and effective electrophoretic mobility of the analyte is contributed from its equilibrium species. Precise measurement of effective electrophoretic mobility allows analyzing the equilibrium. Analysis of equilibria under CE separation possesses several advantages against traditional analyses in homogeneous solution; coexisting substances including impurities and kinetically generated substances are resolved by CE from the equilibrium species of interest. Characteristics of the CE analysis have been applied to analyses of acid-base equilibria of degradable substances and ion-association equilibria in an aqueous solution. Since CE is operated in an open-tubular capillary, it is also suitable for the characterization of carbon nanoclusters such as graphene and carbon nanotube, and measurement of effective electrophoretic mobility helps characterization of nanoclusters. A novel analysis technique of capillary electrophoresis/dynamic frontal analysis (CE/DFA) has also been proposed for the analysis of such reactions as involving equilibria and kinetic reactions. In CE/DFA, kinetically generated product is continuously resolved from the equilibrium species, and a plateau signal would be detected when the reaction rate is constant. Michaelis-Menten constants have successfully been determined through the plateau height by CE/DFA. In this review, analysis and characterization methods utilizing reaction dynamics in a separation capillary are summarized.

Surface Charge Characteristics of Bacillus Subtilis NRS-762 Cells

Bacterial cell surface carries an electrical charge due to the myriad functional groups present, as well as assortment of ions and molecules non-specifically adsorbed to the cell surface. Thus, solution in contact with the bacterial cell surface play a critical role in influencing the overall surface charge characteristics through conferring non-specifically adsorbed ions and molecules. Various wash buffers are commonly used in removing non-specifically adsorbed ions and molecules for revealing the real surface charge of the bacterium. Using electrophoretic mobility measurement of zeta potential, this study attempted to understand the surface charge characteristics of Bacillus subtilis NRS-762 (ATCC 8473) with the help of three wash buffers: deionized (DI) water, 0.1M sodium nitrate, and 9 g/L sodium chloride. Experiment results revealed that B. subtilis NRS-762 was negatively charged over the entire pH range from 1.5 to 12. Specifically, with deionized water as wash buffer, the point-of-zero-charge (pHzpc) was at pH 1.5, which indicated that large amount of negatively charged functional groups were present on the cell surface. Comparison between the zeta potential-pH profiles of B. subtilis NRS-762 cultivated at 30 oC and 37 oC revealed that the profile for growth at 37 oC was more negatively charged over the entire pH range compared to that for growth at 30 oC. This highlighted that physiological adaptation might had occurred on the cell surface for coping with growth at a higher temperature. Zeta potential-pH profiles obtained revealed that DI water could not remove significant quantities of the non-specifically adsorbed ions and molecules. On the other hand, the zeta potential-pH profiles of cells washed with 0.1M sodium nitrate and 9 g/L sodium chloride overlapped each other substantially and were more negatively charged over the pH range from 2 to 11, compared to that of cells washed with DI water. This revealed substantial removal of non-specifically adsorbed ions and molecules with the use of 0.1M sodium nitrate (0.1M ionic strength) and 9 g/L sodium chloride (0.15M ionic strength), which helped reveal the actual surface charge of B. subtilis NRS-762 cells. Collectively, actual surface charge of B. subtilis NRS-762 was masked by non-specifically adsorbed ions and molecules, which could be removed by 0.1M sodium nitrate and 9 g/L sodium chloride wash buffer. Thus, in the case of B. subtilis NRS-762, 0.1M ionic strength wash buffer was the threshold at which there was complete removal of non-specifically adsorbed ions and molecules from the cell surface.

Magnetic response of CoFe2O4 nanoparticles confined in a PNIPAM microgel network.

The paper addresses coupling of magnetic nanoparticles (MNPs) with the polymer matrix of temperature-sensitive microgels and their response to magnetic fields. Therefore, CoFe2O4@CA (CA = citric acid) NPs are embedded within N-isopropylacrylamid (NIPAM) based microgels. The volume phase transition (VPT) of the magnetic microgels and the respective pure microgels is studied by dynamic light scattering and electrophoretic mobility measurements. The interaction between MNPs and microgel network is studied via magnetometry and AC-susceptometry using a superconducting quantum interference device (SQUID). The data show a significant change of the magnetic properties by crossing the VPT temperature (VPTT). The change is related to the increased confinement of the MNP due to the shrinking of the microgels. Modifying the microgel with hydrophobic allyl mercaptan (AM) affects the swelling ability and the magnetic response, i.e. the coupling of MNPs with the polymer matrix. Modeling the AC-susceptibility data results in an effective size distribution. This distribution represents the varying degree of constraint in MNP rotation and motion by the microgel network. These findings help to understand the interaction between MNPs and the microgel matrix to design multi responsive systems with tunable particle matrix coupling strength for future applications.

Controlled assembly of heterogeneous aggregates of clay, iron hydr(oxydes) and polysaccharide: Effects of preparation conditions

The preparation of well-defined organo-mineral assemblies under controlled conditions is required to improve our understanding of the formation and surface reactivity of micrometric aggregates, ubiquitous in soils and continental aquatic media. We aim at investigating the building of organo-mineral assemblies with a specific focus on the assembly mode and its consequence on the final properties of the micrometric aggregates. In this work, the preparation and detailed characterization of clay-size aggregates composed of a clay mineral (illite), organic polymer (Dextran polysaccharide) and iron (hydr)oxide are reported, with a focus on the structural organization of the generated aggregates. A step-by-step strategy was developed, and three sets of clay-size composites were prepared with illite particles as a starting material. In two first steps, two distinct sets of two-component composites were obtained according to different procedures. Illite‑iron (hydr)oxide composites were obtained by alkaline hydrolysis of iron in the presence of illite particles, and illite-Dextran aggregates were obtained through the addition of Dextran polysaccharide to an illite suspension. In a third step, three-component micro-aggregates were obtained by subsequent addition of Dextran to suspensions containing the formed illite‑iron (hydr)oxide composite. The so-prepared 2- and 3- component aggregates were investigated by electrophoresis, electron microscopy, X-ray absorption and FTIR spectroscopies. For materials containing Dextran, electrophoretic mobility measurements evidenced variations of surface charge, combined with an increase of aggregate size highlighted by dynamic light scattering. Electron microscopy and EXAFS at iron K-edge evidenced the precipitation of nanoparticles of iron (hydr)oxide onto clay mineral surfaces. FTIR data in transmission and diffuse reflectance modes supported not only the adsorption of Dextran but also the preferential localization of Dextran at the external surfaces of the aggregates. All in all, data collected on the two- and three-component materials demonstrated that the presence of iron (hydr)oxide nanoparticles on the surface of illite strongly modified the organization of organic and mineral constituents.

Influence of Zwitterionic CAPB on Flocculation of the Aqueous Cationic Guar Gum/Glauconite Suspensions at Various pH.

The influence of the pseudoamphoteric zwitterionic surfactant cocamidopropylbetaine (CAPB) on the stabilizing flocculating properties of the aqueous suspensions of glauconite (GT) with cationic guar gum (CGG) at various pH values was investigated. The following techniques were used: turbidimetry, UV-VIS spectrophotometry, tensiometry, electrophoretic mobility measurements, SEM, CHN, XRD, and FT-IR. It was established that CGG is an effective glauconite flocculant. Moreover, the most probable mechanism that is responsible for flocculation is bridge flocculation resulting from polymer adsorption on the glauconite surface. The adsorption process is caused by electrostatic interactions between the negatively charged glauconite surface and the positively charged polymer. The amount of CGG adsorption increases with the increase of the pH, which was confirmed by the adsorption and zeta potential measurements. The addition of CAPB increases the amount of the polymer adsorption due to the formation of intermolecular polymer–surfactant complexes; however, it reduces flocculation effectiveness.

Adsorption of Binary Mixture of Highly Positively Charged PTMA5M and Partially Negatively Charged PAA onto PSL Particles Studied by Means of Brownian Motion Particle Tracking and Electrophoresis

Effects of ionic strength on the adsorption of highly charged polycationic ((2-dimethylamino)ethyl methacrylate) methyl chloride quaternary salt (PTMA5M) individually as well as in a binary mixture with polyanionic acrylic acid (PAA) onto polystyrene sulfate latex (PSL) particles with negative charges were investigated by means of Brownian movement particle tracking and measurement of electrophoretic mobility. In addition, the adsorption mechanism was confirmed by Fourier transform infrared (FT-IR) and energy-dispersive X-ray (EDX) spectroscopic methods. The hydrodynamic thickness of the adsorbed polyelectrolyte layer (δH) and electrophoretic mobility (EPM) of particles as a function of concentration ratios of the two polyelectrolytes were measured to clarify the effect of negatively charged molecules on the structure of the positively charged adsorbed layer at various ionic strengths. Extremely thick δH was confirmed for the case of excess dosage of polycations. The δH decreased more significantly with the addition of PAA than increasing ionic strength. Interestingly, in the presence of PAA, the adsorbed layer thickness increased more at lower ionic strength than at higher ionic strength. In addition, the initial δH decreases remarkably after a time lapse of 1 h. Contrary to the decrease of the δH, almost all EPM either remained unchanged or increased over time depending on the concentration ratio of the two polyelectrolytes. Constant charge density, desorption of polyanions, and then reconformation of the adsorbed polycationic layer are proposed model components.

Controlling the surface charge of simple viruses.

The vast majority of plant viruses are unenveloped, i.e., they lack a lipid bilayer that is characteristic of most animal viruses. The interactions between plant viruses, and between viruses and surfaces, properties that are essential for understanding their infectivity and to their use as bionanomaterials, are largely controlled by their surface charge, which depends on pH and ionic strength. They may also depend on the charge of their contents, i.e., of their genes or–in the instance of virus-like particles–encapsidated cargo such as nucleic acid molecules, nanoparticles or drugs. In the case of enveloped viruses, the surface charge of the capsid is equally important for controlling its interaction with the lipid bilayer that it acquires and loses upon leaving and entering host cells. We have previously investigated the charge on the unenveloped plant virus Cowpea Chlorotic Mottle Virus (CCMV) by measurements of its electrophoretic mobility. Here we examine the electrophoretic properties of a structurally and genetically closely related bromovirus, Brome Mosaic Virus (BMV), of its capsid protein, and of its empty viral shells, as functions of pH and ionic strength, and compare them with those of CCMV. From measurements of both solution and gel electrophoretic mobilities (EMs) we find that the isoelectric point (pI) of BMV (5.2) is significantly higher than that of CCMV (3.7), that virion EMs are essentially the same as those of the corresponding empty capsids, and that the same is true for the pIs of the virions and of their cleaved protein subunits. We discuss these results in terms of current theories of charged colloidal particles and relate them to biological processes and the role of surface charge in the design of new classes of drug and gene delivery systems.

Efficient Wood Hydrophobization Exploiting Natural Roughness Using Minimum Amounts of Surfactant-Free Plant Oil Emulsions.

Wood in service requires protection from excessive moisture. Herein, we demonstrate that efficient surface hydrophobization can be provided with small amounts of biobased oils, benefitting from the hierarchical roughness inherent to wood surfaces. The developed technique involves coating spruce wood with surfactant-free emulsions based on tung oil, linseed oil, or a linseed oil-based long oil alkyd resin. The ζ-potential of the emulsions was determined by electrophoretic mobility measurements. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and spectrophotometry were used to study coated surfaces. XPS measurements confirmed the presence of the tung oil coatings. Tung oil emulsions were effective at concentration levels as low as 0.04 wt % oil content, roughly equivalent to 0.04 g m–2 and led to static water contact angles reaching up to >130°. SEM imaging and AFM measurements provide evidence that the micro- and nanostructures inherent to wood enhance the hydrophobization effect of the obtained coatings. A further benefit of the method lies in only minimal effects of the coating on the surface color and gloss. Thus, the mass-efficient process following several of the principles of green engineering led to improved water repellency while not affecting the visual appearance of the coated wood.

Effect of ion species on change in particle electrophoresis caused by change in applied electric field

The effects of ion species (Li+, Na+, NH4+, Cs+, guanidinium (Gdm+), and tetraphenylarsonium (Ph4As+)) and applied electric fields on the electrophoretic mobility of hydrophobic sulfate polystyrene latex particles were experimentally investigated via direct measurements based on microscopic electrophoresis. At a high electrolyte concentration (50 mM), as the applied electric field increased, the electrophoretic mobility increased and the fraction of charge in the slipping layer (FOC) decreased, before converging to certain constant values for each cation; thus, the ion accumulation was weak, and the amount of cations in the slipping layer decreased as the applied electric field increased. Furthermore, FOC was smaller for cations with higher hydrophilicity, indicating that higher-hydration ions are less likely to accumulate in the slipping layer. These results can be useful for evaluating the ion-accumulation state around particles based on electrophoretic mobility measurements wherein the applied electric field is controlled as an operational parameter.

New perspectives in iron ore flotation: Use of collector reagents without depressants in reverse cationic flotation of quartz

The reverse flotation of the iron ore with etheramine collector is significantly impacted when the iron-bearing silicates and the kaolinite are present in the silicates gangue mineral complex. This paper aims to propose a new amidoamine collector N-[3-(Dimethylamino)propyl]dodecanamide for iron ore reverse flotation with a potential of removing the iron oxides depressant. The contact angle and electrophoretic mobility measurements as well as the flotation experiments were performed on the pure quartz, kaolinite and hematite samples to compare its effect with the etheramine which is widely used as collector in reverse flotation of iron ores. Infrared spectroscopy was performed to study the adsorption of the amidoamine collector on the surface of the minerals studied.Amidoamine collector showed a significant selectivity towards quartz while the flotation of hematite and kaolinite were inhibited at pH 10 without the presence of a depressor. A total floatability of quartz was explained by increased contact angle from 10° to about 50° without impacting significantly the contact angle measured on the hematite (9.4° to 17°). Surface hindrance effect caused by the structure of the N-[3-(Dimethylamino)propyl]dodecanamide collector on the hematite surface is the most suitable hypothesis concerning the high selectivity regarding the iron ore reverse flotation process.

Enhanced photocatalytic activity of accordion-like layered Ti3C2 (MXene) coupled with Fe-modified decahedral anatase particles exposing {1 0 1} and {0 0 1} facets

New composites consisting of decahedral anatase particles exposing {001} and {101} facets coupled with accordion-like layered Ti3C2 with boosted photocatalytic activity towards phenol and carbamazepine degradation were investigated. The photocatalysts were characterized with X-ray diffraction (XRD), diffuse reflectance spectroscopy (DR/UV–Vis), Brunauer-Emmett-Teller (BET) specific surface area, Raman spectroscopy, scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) spectroscopy, emission spectroscopy, luminescence decay analysis, electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and electrophoretic mobility measurements. The effect of hydrothermal reaction parameters on physicochemical, structural, and photocatalytic properties was studied. In all photodegradation processes, ortho-hydroxyphenol and para-hydroxyphenol were detected as the first intermediates of phenol decomposition. For the TiO2/Ti3C2(140,12) sample containing VTi, a higher concentration of para-hydroxyphenol than ortho-hydroxyphenol was observed, whereas for sample TiO2/Ti3C2(220,24) higher concentration of ortho-hydroxyphenol was noticed. The formation of surface heterojunction between {101} and {001} facets of decahedral anatase particles grown on Ti3C2 surface led to improved photoelectron transfer and enhanced photocatalytic activity towards degradation of carbamazepine - non-biodegradable and susceptible to bioaccumulation in living organisms commonly used pharmaceutical agent. Moreover, modification of TiO2/Ti3C2 surface with iron by magnetron sputtering deposition markedly improved photocatalytic activity in carbamazepine decomposition, with nearly 100% degradation in 60 min of irradiation under simulated solar light.

PH-responsive aminolipid nanocarriers for antimicrobial peptide delivery

HypothesispH-responsive aminolipid self-assemblies are promising platforms for the targeted delivery of antimicrobial peptides (AMPs), with the potential to improve their therapeutic efficiency and physico-chemical stability. ExperimentspH-sensitive nanocarriers based on dispersed self-assemblies of 1,2-dioleoyl-3-dimethylammonium-propane (DODAP) with the human cathelicidin LL-37 in excess water were characterized at different pH values using small-angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. Fluorescence and electrophoretic mobility measurements were used to probe the encapsulation efficiency of LL-37 and the nanocarriers’ surface potential. FindingsUpon decreasing pH in the DODAP/water systems, normal oil-in-water emulsions at pH ≥ 5.0 transitioned to emulsions encapsulating inverse hexagonal and cubic structures at pH between 4.5 and 4.0, and mostly positively-charged vesicles at pH < 4.0. These colloidal transformations are driven by the protonation of DODAP upon pH decrease. The larger lipid-water interfacial area provided by the DODAP self-assemblies at pH ≤ 4.5 allowed for an adequate encapsulation efficiency of LL-37, favouring the formation of vesicles in a concentration-dependent manner. Contrary, LL-37 was found to dissociate from the emulsion droplets at pH 6.0. The knowledge on the pH-triggered self-assembly of LL-37 and DODAP, combined with the results on peptide release from the structures contribute to the fundamental understanding of lipid/peptide self-assembly. The results can guide the rational design of future pH-responsive AMP delivery systems.

Formation of Myoglobin Corona at Polymer Microparticles

Adsorption of myoglobin molecules at negatively charged polystyrene microparticles was studied using the dynamic light scattering (DLS), electrophoresis (LDV) and the solution depletion method involving atomic force microscopy (AFM). The measurements were carried out at pH 3.5 and NaCl concentration of 10−2 and 0.15 M. Initially, the stability of myoglobin solutions and the particle suspensions as a function of pH were determined. Afterward, the formation of myoglobin molecule corona was investigated via the direct electrophoretic mobility measurements, which were converted to the zeta potential. The experimental results were quantitatively interpreted in terms of the general electrokinetic model. This approach yielded the myoglobin corona coverage under in situ conditions. The maximum hard corona coverage was determined using the AFM concentration depletion method. It was equal to 0.9 mg m−2 for the NaCl concentration in the range 0.01 to 0.15 M and pH 3.5. The electrokinetic properties of the corona were investigated using the electrophoretic mobility measurements for a broad pH range. The obtained results confirmed that thorough physicochemical characteristics of myoglobin molecules can be acquired using nM amounts of the protein. It was also argued that this method can be used for performing electrokinetic characteristics of other proteins such as the SARS-Cov-2 spike protein exhibiting, analogously to myoglobin, a positive charge at acidic pHs.

Complex coacervate formation between hemp protein isolate and gum Arabic: Formulation and characterization

In this study, intermolecular interactions and structure formation between hemp protein isolate (HPI) and gum Arabic (GA) were investigated to unravel their complexation mechanisms. For this purpose, structural transition as a function of pH (2.0–7.0) and protein to polysaccharide ratio (HPI:GA, R = 0.5:1–13:1 w/w) was evaluated via turbidimetric analysis, ζ-potentiometry, state diagram construction and coacervate yield. It was proved that critical phase transition pH shifted to higher values with R increase, until reaching a plateau at ratio 10:1, with complexes to be formed even at pH region where both biopolymers were negatively charged. The shift of pH value, where maximum turbidity was noticed (pHopt), was well in accordance with net charge neutrality of HPI-GA mixtures found by electrophoretic mobility measurements. Maximum coacervation, occurred at ratio R = 2:1 and pHopt = 3.5, was depicted by the highest yield (92%), while morphological characteristics of liquid as well as freeze-dried HPI-GA coacervates, obtained through optical and scanning electron microscope measurements, gave a further perception of the associative processes during complex coacervation. Additionally, the molecular interactions between HPI and GA were confirmed by Fourier transform infrared spectroscopy (FTIR) revealing primarily electrostatic interactions with secondary stabilization of hydrogen bonds. Therefore, these findings could provide useful information for the development of HPI – GA coacervates as a potential bioactive encapsulation means.

Influence of surfactants with different ionic character on the structure of poly(acrylic acid) adsorption layer on the activated biocarbons surface – electrokinetic and stability studies

Two samples of activated biocarbons obtained from corncobs and peanut shells precursors were applied for poly(acrylic acid) – PAA macromolecules adsorption from the aqueous solutions containing surfactants with different ionic character (non-ionic Triton X-100, cationic CTAB and anionic SDS). The effects of biocarbon structure, solution pH and surfactant type were examined. The structure of PAA adsorption layer without and with surfactant molecules on the activated carbons surface was described based on the adsorption, electrokinetic and stability results obtained from the spectrophotometric experiments, potentiometric titrations, electrophoretic mobility measurements and stability tests. It was shown that the presence of surfactant influences significantly the adsorption affinity of PAA macromolecules for the micro/mesoporous biocarbons and causes changes in both solid suspensions stability.

Experimental and Theoretical Study of Morphological and Charging Properties of Truncated Octahedron and Cubic Ceria Nanoparticles: Implications for Biomedical Applications

Ceria (CeO2) nanoparticles are known to be very often used in various applications from biomedicine to fuel cells. To optimize the applications, detailed information about the physicochemical properties such as size, shape, and charge of nanoparticles should be available. Therefore, in our study we performed a systematic study of ceria nanoparticles ranging from synthesis to comprehensive experimental and theoretical characterization. We synthesized ceria nanoparticles using two synthesis paths which led to the formation of two types of ceria nanoparticles. The structure and charging properties of both types of ceria nanoparticles were studied by using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), particle charge detector (PCD) for surface charge density, and a ZetaPlus instrument for electrophoretic mobility measurements. The results suggested that in the case where hydrolysis of Ce(NO3)3 at room temperature was applied nanoparticles with morphology close to a spherical, more exactly truncated octahedron were synthesized. On the other hand, nanoparticles obtained by hydrothermal synthesis had characteristic cube-like morphology. Finally, for more complete understanding and interpretation of the studied system, we prepared a theoretical model based on the classical density functional theory for electrolyte solutions coupled with the surface charge regulation via the law of mass action. Even without using fitting parameters, the theory adequately describes the experimental data. All the results obtained in our study could serve as a basis for obtaining tuned and engineered ceria nanoparticles with optimized physicochemical properties which could lead to the improved applications of the nanotechnology in the biomedical research.

A physico-chemical study of the interaction of ethanolic extracts of propolis with bacterial cells

In the present study, an effort has been made to understand the interaction mode of propolis, a natural substance produced by honey bees, with gram-positive and gram-negative bacterial cells by measuring alterations in cell surface physico-chemical properties following the incubation of the cells with different sub-inhibitory concentrations of this antimicrobial agent. Electrophoretic mobility and surface hydrophobicity measurements revealed for the first time that propolis induced substantial changes in the volumetric charge density, electrophoretic softness and degree of hydrophobicity characterizing the outermost surface layer of cells. These changes, which appear to be dose-dependent, seem to be consistent with the increasing accumulation and penetration of the propolis antimicrobial components through the cells extracellular layer. Moreover, electron microscopy observation and the determination of the cell constituents’ release demonstrated that propolis at sub-bactericidal concentrations already provoked (at least localized) cell wall damage and/or perturbations. These findings thus suggest that the initial mechanism of action of propolis is most likely structural, resulting from sufficient interaction between the different propolis components and bacterial cell wall structures.