Zeta Potential Data Research Articles

Flocculation characteristics of a biodegradable polymer based on dextran

Abstract The flocculation efficiency of a cationic polysaccharide with 1-(2-hydroxypropyl)-3-methyl imidazolium chloride groups attached to dextran (D40-MeIm36) was evaluated on synthetic wastewaters containing either inorganic particles (Zirconium silicate (kreutzonit), Kfeldspar, TiO2) or organic ones (pesticides (Decis) and (Dithane M45)). The effect of polymer dose, medium pH, its composition and contaminant concentration on the separation efficacy was followed by UV–Vis spectroscopy measurements. The interactions between D40-MeIm36 and inorganic particles led to maximum removal efficiency (of around 95%), irrespective of the medium pH and composition. The negative values of the zeta potential, at the optimum polymer doses, point to charge patch as mechanism for the particles flocculation. A good efficiency of D40-MeIm36 in separation of pesticides has been noticed; the maximum removal percent slightly increased with increasing pesticide concentration, namely, from 85% at c (v/v) = 0.01% to 92% – 94% for c (v/v) = 0.02% and 0.04% for Decis and from around 85% at c = 0.1 g L−1 to 89% at c = 0.2 g L−1 for Dithane M45. A minimum residual pesticide absorbance of about 10% has been recorded for both pesticides, at the established medium pH. Zeta potential and particle aggregates size data plead for the charge neutralization as the dominant mechanism for the flocculation of pesticide particles.

DNA-magnetic Particle Binding Analysis by Dynamic and Electrophoretic Light Scattering.

Isolation of DNA using magnetic particles is a field of high importance in biotechnology and molecular biology research. This protocol describes the evaluation of DNA-magnetic particles binding via dynamic light scattering (DLS) and electrophoretic light scattering (ELS). Analysis by DLS provides valuable information on the physicochemical properties of particles including particle size, polydispersity, and zeta potential. The latter describes the surface charge of the particle which plays major role in electrostatic binding of materials such as DNA. Here, a comparative analysis exploits three chemical modifications of nanoparticles and microparticles and their effects on DNA binding and elution. Chemical modifications by branched polyethylenimine, tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane are investigated. Since DNA exhibits a negative charge, it is expected that zeta potential of particle surface will decrease upon binding of DNA. Forming of clusters should also affect particle size. In order to investigate the efficiency of these particles in isolation and elution of DNA, the particles are mixed with DNA in low pH (~6), high ionic strength and dehydration environment. Particles are washed on magnet and then DNA is eluted by Tris-HCl buffer (pH = 8). DNA copy number is estimated using quantitative polymerase chain reaction (PCR). Zeta potential, particle size, polydispersity and quantitative PCR data are evaluated and compared. DLS is an insightful and supporting method of analysis that adds a new perspective to the process of screening of particles for DNA isolation.

Surface Zeta Potential and Diamond Seeding on Gallium Nitride Films.

The measurement of ζ potential of Ga-face and N-face gallium nitride has been carried out as a function of pH. Both of the faces show negative ζ potential in the pH range 5.5–9. The Ga-face has an isoelectric point at pH 5.5. The N-face shows a more negative ζ potential due to larger concentration of adsorbed oxygen. The ζ potential data clearly showed that H-terminated diamond seed solution at pH 8 will be optimal for the self-assembly of a monolayer of diamond nanoparticles on the GaN surface. The subsequent growth of thin diamond films on GaN seeded with H-terminated diamond seeds produced fully coalesced films, confirming a seeding density in excess of 1011 cm–2. This technique removes the requirement for a low thermal conduction seeding layer like silicon nitride on GaN.

Nanoscale zero-valent iron functionalized Posidonia oceanica marine biomass for heavy metal removal from water.

Because of the excellent reducing capacity of nanoscale zero-valent iron (NZVI), it can be used as alternative materials for the removal of a variety of reducible water contaminants including toxic metals. The current paper reports the research results obtained for self-prepared biosorbent, Posidonia oceanica biomass, activated in alkaline medium and functionalized with NZVI particles. The structural characteristics, surface morphology, and binding properties of the resulting nanobiosorbent are presented. Batch comparative adsorption trials including adsorption kinetics and isothermals onto raw Posidonia, Posidonia-OH and Posidonia-OH-NZVI were investigated on three heavy metal ions: Cd(II), Pb(II), and Cu(II). The nanobiosorbent showed better properties, such as high reactivity and high uptake rate through the sorption process. The toxic metal removal has been monitored in terms of pseudo-first- and pseudo-second-order kinetics, and both Langmuir- and Freundlich-type isotherm models have been used to describe the sorption mechanism. The experimental data of all studied systems showed that the uptake kinetics follow the pseudo-second-order kinetic model and the equilibrium uptake can adopt the Langmuir-type isotherm model which assumes a monolayer coverage as the adsorption saturates and no further adsorption occurs. The thermodynamic results confirm that all sorption processes were feasible, spontaneous and thermodynamically favorable. Zeta potential data displayed that Cd(II), Pb(II), and Cu(II) tend to be reduced after exposure on the Posidonia-OH-NZVI surface. Furthermore, sorption competitions of the metals from binary and ternary systems were carried out onto Posidonia-OH-NZVI in order to gain further insight into the sorption efficiency of this material. Therefore, as a result, the proposed new nanobiosorbent could offer potential benefits in remediation of heavy metal-contaminated water as a green and environmentally friendly bionanocomposite.

Magnetic nanohydrogel obtained by miniemulsion polymerization of poly(acrylic acid) grafted onto derivatized dextran

This study describes the synthesis of magnetic nanohydrogels by miniemulsion polymerization technique. Dextran was derivatized by the glycidyl methacrylate to anchor vinyl groups on polysaccharides backbone, allowing its use as a macromonomer for miniemulsion polymerization, as confirmed by proton nuclear magnetic resonance spectroscopy (13C NMR). Magnetite nanoparticles were synthesized by coprecipitation, followed by air oxidation to maghemite. The results of X-ray diffractometry (XRD), Raman and transmission electron microscopy (TEM) analysis showed that maghemite nanoparticles were obtained with a diameter of 5.27nm. The entrapment of iron oxide nanoparticles in a dextran nanohydrogel matrix was confirmed by thermogravimetric analysis (TGA), scanning transmission electron microscopy (STEM) and Zeta potential data. The magnetic nanohydrogels presented superparamagnetic behavior and were colloidal stable in physiological during 30days. Our findings suggest that the synthesized magnetic nanohydrogel are potential candidates for use in drug delivery systems due to its physicochemical and magnetic properties.

PH-sensitive polymersomes: controlling swelling via copolymer structure and chemical composition

pH-sensitive vesicles used as drug delivery systems (DDSs) are generally composed of protonable copolymers. The disaggregation of these nanoparticles (NPs) during drug release implies the dispersion of positively charged cytotoxic polyelectrolytes in the human body. To alleviate such issue, we synthesised A(BC)n amphiphilic block copolymers with linear (n = 1) and branched (n = 2) architectures to obtain pH-sensitive vesicles capable of releasing drugs in acidic conditions via controlled swelling instead of disaggregation. We obtained this feature by fine-tuning the relative amount of pH-sensitive and hydrophobic monomers. We studied pH-driven swelling by measuring NPs size in neutral and acidic conditions, the latter typical of tumours or inflamed tissues (pH∼6) and lysosomes (pH∼4.5). Dynamic light scattering (DLS) and zeta potential data provided useful indications about the influence of architecture and chemical composition on NPs swelling, stability and polycation release. Results demonstrated that vesicles made of linear copolymers with ∼22–28% in mol of protonable monomers in the ‘BC’ block swelled more than other species following a pH change from pH 7.4 to pH 4.5. We finally evaluated the cytotoxicity of vesicles composed of linear species, and paclitaxel (PTX) release from the latter in both cancer and normal cells.

Exploring interactions of copper hybrid surfactants with calf thymus-DNA

The efficacy of copper functionalized surfactant cetylpyridinium chloride (CPC) to bind with Calf- thymus DNA was evaluated using different physicochemical and spectroscopic techniques. The two surfactant moieties viz. [CPC]+[CuCl3]− and [CPC]2+[CuCl4]2− were synthesized and a thorough approach has been made to understand the binding interface between CT-DNA and synthesized surfactants. Binding saturation point (BSP) of negatively charged CT-DNA with positively charged copper metallosurfactants was estimated from Zeta potential and conductivity data. Cyclic voltammetry and Zeta potential variations inferred electrostatic interaction between CT-DNA and metal hybrid surfactants. Fluorescence emission spectrscopy also points out that functionalized surfactants adopted a partial mode of binding through ionic interactions with moderate binding constant values. Circular Dichroism analysis lends us on the ground of non-covalent binding between CT-DNA and surfactant complexes. Conformational changes in the molecule under investigation have also been visualized through fluorescence microscopy imaging.

A sorption model for alkalis in cement-based materials – Correlations with solubility and electrokinetic properties

In cement-based materials, radionuclide uptake is mainly controlled by calcium silicate hydrates (C-S-H). This work presents an approach for defining a unique set of parameters of a surface complexation model describing the sorption behavior of alkali ions on the C-S-H surface. Alkali sorption processes are modeled using the CD-MUSIC function integrated in the Phreeqc V.3.0.6 geochemical code. Parameterization of the model was performed based on (1) retention, (2) zeta potential, and (3) solubility experimental data from the literature. This paper shows an application of this model to sodium ions. It was shown that retention, i.e. surface interactions, and solubility are closely related, and a consistent sorption model for radionuclides in cement-based materials requires a coupled surface interaction/chemical equilibrium model. In case of C-S-H with low calcium-to-silicon ratios, sorption of sodium ions on the C-S-H surface strongly influences the chemical equilibrium of the C-S-H + NaCl system by significantly increasing the aqueous calcium concentration. The close relationship between sorption and chemical equilibrium was successfully illustrated by modeling the effect of the solid-to-liquid ratio on the calcium content in solution in the case of C-S-H + NaCl systems.

Biological interactions of fluorinated chalcones: Stimulation of tyrosinase activity and binding to bovine serum albumin

The evaluation of tyrosinase activity of CH, CH3F, CH4F, CH23F, CH25F, CH35F and CH2356F as well as of the interactions of CH and fluorinated chalcones CH3F, CH4F and CH2356F with bovine serum albumin (BSA) in a PBS buffer solution (pH=7.4), at 288K, 293K and 298K, were investigated by using spectroscopic techniques, zeta potential and computational methods. Tyrosinase enzymatic activity was measured by UV–vis spectrometry of the oxidation of l-DOPA in the presence of the enzyme and chalcones: the unsubstituted chalcone inhibits tyrosinase activity, whereas its fluorinated derivatives showed the opposite effect, whose sample CH2356F showed the highest percentage activation. Studies of quenching of the BSA fluorescence by CH, CH3F, CH4F and CH2356F show a combination of static and dynamic quenching mechanisms. In addition FRET mechanism can occurs with high probability. For CH the binding constant (Ka) is in the range of 105M−1 indicating a moderate association between chalcone and BSA. On the other hand, for the fluorinated derivatives CH3F, CH4F and CH2356F Ka=104M−1, which indicates that the presence of fluorine atoms on the chalcone structure decreases the binding ability. The thermodynamic parameters ΔH° and ΔS° show that the BSA:CH association is enthalpically and entropically driven, whereas for fluorinated derivatives it is only entropically driven. The negative ΔG° values found in all cases are consistent with a spontaneous albumin:chalcone association. Circular dichroism and zeta potential data show that the binding does not affect significantly the albumin structure. The binding site study clearly indicates that the main binding pocket for the samples is the Trp-212-containing binding site. The largest docking score values also suggest the same binding site. Molecular docking results suggested that the presence of fluorine atoms decrease the number of amino acid residues that can stabilize the interaction of the fluorinated chalcones with BSA. For CH3F and CH2356F the type of interaction between the amino acid residues and ligand structure did not change significantly.

Variations in the interaction of human defensins with Escherichia coli: Possible implications in bacterial killing.

Human α and β-defensins are cationic antimicrobial peptides characterized by three disulfide bonds with a triple stranded β-sheet motif. It is presumed that interaction with the bacterial cell surface and membrane permeabilization by defensins is an important step in the killing process. In this study, we have compared interactions of three human α-defensins HNP3, HNP4, HD5 and human β-defensins HBD1-4 that are active against Escherichia coli, with its cell surface and inner membrane as well as negatively charged model membranes. We have also included the inactive α-defensin HD6 in the study. Among the α-defensins, HNP4, HD5 and HD6 were more effective in increasing the zeta potential as compared to HNP3. Among the β-defensins, HBD1 was the least effective in increasing the zeta potential. The zeta potential modulation data indicate variations in the surface charge neutralizing ability of α- and β-defensins. Comparison of E. coli inner membrane and model membrane permeabilizing abilities indicated that HD5, HD6 and HBD1 do not permeabilize membranes. Although HBD4 does not permeabilize model membranes, considerable damage to the inner membrane of E. coli is observed. Our data indicate that mammalian defensins do not kill E. coli by a simple mechanism involving membrane permeabilization though their antibacterial potencies are very similar.

Ligand-Promoted Photoreductive Dissolution of Goethite by Atmospheric Low-Molecular Dicarboxylates.

Recent evidence suggested that organic ligands in atmosphere water play an important role in the mobilization of iron from mineral aerosol. In this study, the dissolution of goethite (α-FeOOH) was investigated in the presence of three low-molecular dicarboxylates enriched in the atmosphere, as well as a reference organic acid of methanesulfonate (MSA), which is especially abundant in marine atmospheric boundary layer. Iron mobilized from α-FeOOH was promoted under the irradiation and the deaerated condition, and the soluble Fe(II) concentration was enhanced greatly in the ligand-containing suspensions exposed to light. Irrespective of the reaction conditions, the capacities of the dicarboxylates on Fe mobilization were in the following order: oxalate > malonate > succinate, which were closely correlated with the carbon chain length of dicarboxylates: n = 2 > 3 > 4. The space barrier action of carbon atoms inhibited ligand-promoted Fe dissolution by affecting the structure and stability of the complexes. MSA also acted as an organic ligand to mobilize iron and showed weak capacity to reduce Fe(III) under the irradiation. The reactive oxygen species (ROS) analysis indicated that ·OH, O2·-, and H2O2 could be involved in the Fe(II)-Fe(III) redox circle, and the ligand-promoted photoreductive dissolution process could be an important source of ROS in atmosphere water. Both transmission electron microscopy analysis and zeta potential data supported that the adsorption of oxalate molecules onto the surface would change the aggregation state of goethite nanoparticles, which increased the effective surface area, and therefore facilitated Fe mobilization from the oxide. The data shown herein deepens our understanding on the ligand-promoted dissolution mechanisms, which could be an important formation pathway of bioavailable Fe in the atmosphere.

The relationship between inner surface potential and electrokinetic potential from an experimental and theoretical point of view

Environmental contextInterfacial properties of colloid and nanoparticles are directly related to the reactivity and surface densities of existing surface sites. Surface characterisation of particles provides only some kind of average surface properties. Analysis of well-defined monocrystal surfaces, which form the surface of the single particle, leads to a better understanding of surface reactions and mutual interactions of adjacent crystal planes on average surface properties. AbstractThe contact of small solid particles and macroscopic flat planes with aqueous electrolyte solutions results in the accumulation of ions at the interface and the formation of the electrical interfacial layer. Analysis of well-defined monocrystal surfaces, which are the building blocks of a single particle, leads to a better understanding of surface reactions and mutual interactions of adjacent crystal planes on average surface properties of particles. We analyse inner surface potential (obtained by single-crystal electrode) and zeta-potential data (obtained by streaming potential measurements) that were obtained on identical samples. Among the systems for which comparable surface and zetapotentials are available, measured inner surface potential data for sapphire (0001), haematite (0001) and rutile (110) show the expected behaviour based on the face-specific surface chemistry model, whereas the slopes for rutile (110) and quartz (0001) do not. Isoelectric points for sapphire (0001), haematite (0001) and rutile (100) are in conflict with the standard model that implies consistent behaviour of surface potential and diffuse layer potential. For the two former systems, previous results from the literature suggest that the charge of interfacial water can explain the discrepancy. The water layer could also play a role for quartz (0001), but in this case, the discrepancy would simply not be noticed, because both point of zero potential and isoelectric point are low. Along with data on silver halides, it can be concluded that six-ring water structures on solids may generate the electrokinetic behaviour that is typical of inert surfaces like Teflon.

Synthesis of A12O3 Nanoparticles from Local Bauxite for Water- A12O3 Nanofluids egy

A study on synthesis and characterization of A12O3 nanoparticles from bauxite for water-A12O3 nanofluids as an alternative coolant for nuclear and non-nuclear applications has been done. The A12O3 nanoparticles were synthesized by heating AlOOH as a precursor derived from local bauxite. The Al2O3 nanoparticles were dispersed in water and ultrasonicated to produce nanofluids. XRD data showed that the A12O3 nanoparticles crystallized in gamma alumina with crystallite size of 4.5 nm (Debye Scherrer method). Surface area of the A12O3 nanoparticles was 195 m2/gram. Data of TEM showed that the particle size was smaller than 10 nm. According to zeta potential data, the nanofluids were stable at neutral pH of 7.3 with zeta potential of 28-51 mV. The height of the nanofluid surface decreased about 13 % after 6 days. In addition, the CHF of the water-A12O3 nanofluids produced in this study increased about 55-161 % compared to that of water.

On the driving forces for complexation of methyl orange with polycations

HypothesisComplexation between Methyl orange and polycations involves multiple interactions dictated by molecular structure, composition (D/P), pH and ionic strength. The effect of ionic strength is considered a generic effect. By step-wise construction of complexes, we expect to gain insight in the nature of interactions and whether displacement by competing ions is a generic effect. ExperimentsWe step-wise constructed complexes of methyl orange with two model polycations, whilst recording visible light spectra, size and electrophoretic mobility in buffered solution. MO organization was derived from discrete spectral changes, whereas complexes were described in terms of size and zeta-potential data. Spectral data were used to study the effect of competing ions, both potassium halides and polyanions, using a manual titration method. FindingsSpectral and size data reveal a complex stoichiometry of D/P=2.2 and 4.6 for poly(ethylenimine hydrochloride)(PEI) and poly(di allyldimethyl amine hydrochloride) PDADMAC, respectively. Contrary to PEI-MO, the formation of PDADMAC-MO complexes is driven by hydrophobic rather than electrostatic interactions. Organization of PDADMAC-MO complexes also shows a strong dependency on the order of construction and polycation concentration. Displacement of MO by halides shows no effect of ion size for PEI, whereas Hofmeister series ordering was found for PDADMAC. The displacement by polyanions is shown to be charge-stoichiometric.

Nano modification of NZVI with an aquatic plant Azolla filiculoides to remove Pb(II) and Hg(II) from water: Aging time and mechanism study

This paper reports the preparation and stabilization of nano zero valent iron (NZVI) on a modified aquatic plant, Azolla filiculoides, and investigates its potential for the adsorption/reduction of Pb(II) and Hg(II) ions from aqueous media even after six months of storage in the lab condition. XRD, TEM and zeta potential results demonstrated that the Azolla-NaOH could be a good stabilizer of aged NZVI (six months) and the green support suppressed the oxidation and aggregation of immobilized NZVI. Kinetic and equilibrium models for lead and mercury ions uptake were developed by considering the effect of the initial Pb(II) and Hg(II) concentrations, contact time, adsorbent dosage, initial pH and effect of temperature. The contact time to obtain equilibrium for maximum uptake by Azolla-OH-NZVI was 20min. The removal of toxic metal ions has been monitored in terms of pseudo-first- and -second-order kinetics, and the Freundlich and Langmuir isotherms models have also been utilized to the equilibrium uptake results. The uptake kinetics followed the mechanism of the pseudo-second-order equation for all systems studied, confirming chemical sorption as the rate-limiting step of adsorption mechanisms and not involving a mass transfer in solution. The thermodynamic results confirmed that the uptake of Pb(II) and Hg(II) ions were feasible, spontaneous and endothermic at 25–80°C. XRD and zeta potential data displayed the existence of Pb(0) and Hg(0) on the Azolla-OH-NZVI surface. The nanobioadsorbent revealed high recyclability due to its reasonable uptake efficiency after 7th adsorption–desorption cycles. The proposed nano biocomposite could also be utilized to uptake Pb(II) and Hg(II) ions from the real water (Anzali lagoon water). However, coated NZVI with Azolla filiculoides as a green and environmentally friendly support suppressed rapid oxidation and aggregation of the immobilized NZVI, therefore vastly enhancing the probability of environmental transport and reducing the sedimentation and potential for toxicity.

Zeta-potential data reliability of gold nanoparticle biomolecular conjugates and its application in sensitive quantification of surface absorbed protein

Zeta potentials (ZP) of gold nanoparticle bioconjugates (AuNP-bios) provide important information on surface charge that is critical for many applications including drug delivery, biosensing, and cell imaging. The ZP measurements (ZPMs) are conducted under an alternative electrical field at a high frequency under laser irradiation, which may strongly affect the status of surface coating of AuNP-bios and generate unreliable data. In this study, we systemically evaluated the ZP data reliability (ZPDR) of citrate-, thiolated single stranded DNA-, and protein-coated AuNPs mainly according to the consistence of ZPs in the repeated ZPMs and the changes of the hydrodynamic size before and after the ZPMs. We found that the ZPDR was highly dependent on both buffer conditions and surface modifications. Overall, the higher ionic strength of the buffer and the lower affinity of surface bounders were related with the worse ZPDR. The ZPDR of citrate-coated AuNP was good in water, but bad in 10mM phosphate buffer (PB), showing substantially decrease of the absolute ZP values after each measurement, probably due to the electrical field facilitated adsorption of negatively charged phosphate ions on AuNPs. The significant desorption of DNAs from AuNP was observed in the PB containing medium concentration of NaCl, but not in PB. The excellent ZPDR of bovine serum albumin (BSA)-coated AuNP was observed at high salt concentrations and low surface coverage, enabling ZPM as an ultra-sensitive tool for protein quantification on the surface of AuNPs with a single molecule resolution.

A novel mechanism for the rate of growth during the crystallisation of salts and the precipitation of minerals

A kinetic mechanism is proposed for the rate of growth during the crystallisation of salts and the precipitation of minerals. This mechanism envisages the deposition of constituent anions and cations onto the surface in separate parallel reactions, each of which is referred to as a ‘partial reaction’. The rate of deposition is dependent on the potential difference across the Stern layer. The action of deposition of ions onto the surface both causes this potential and influences the rate of deposition. The resulting rate expression reduces to four limiting cases: (i) equilibrium, (ii) crystallisation far from equilibrium, (iii) “partial equilibrium” due to the cation, and (iv) “partial equilibrium” due to the anion. The proposed mechanism is shown to be widely applicable, with examples from sulphide, carbonate and fluoride systems being discussed. The correspondence between the rate expression for crystallisation and dissolution is clearly delineated for the proposed mechanism. The implications of the mechanism for the interpretation of zeta potential data are discussed.

A novel radiation-induced grafting methodology to synthesize stable zerovalent iron nanoparticles at ambient atmospheric conditions

A novel method was developed to synthesize air-stable zerovalent iron nanoparticles (hereafter nZVI) utilizing a radiation grafting technique. The nZVI were synthesized by borohydrate reduction of FeCl3 and stabilized on a radiation grafted copolymer matrix. Polyacrylic acid (PAA) grafted non-woven polyethylene/polypropylene (NWPE/PP-g-PAA) was used as the copolymer matrix and Co-60 γ-radiation was applied. The nZVI adsorbed NWPE/PP-g-PAA (hereafter nZVI-Ads-NWP) polymer composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrational spectroscopy, scanning electron microscopy (SEM), Mossbauer spectroscopy, proton titrations, and zeta potential techniques. The SEM images showed that PAA was properly grafted onto the NWPE/PP fabric during irradiation and that the nZVI were well dispersed and stabilized on the fabric surface. Vibrational spectroscopy showed supplementary evidence for the proper grafting of PAA onto the base polymer and suggested a monodentate configuration as the primary interaction between the carboxylate groups of PAA and the nZVI surface. XRD, XPS, and Mossbauer analyses revealed core zerovalent iron with a shell mainly consisting of iron oxides. The pHZPC and pHIEP values of nZVI–NaCl suspensions were 7.3. Zeta potential and surface charge data were modeled using the 1-pK Stern layer model with two dissimilar sites for electrolyte and proton binding to account for the observed charge asymmetry.

Some properties of xanthan gum in aqueous solutions: effect of temperature and pH

The properties of xanthan gum (XG) aqueous solutions were investigated by using viscometric, electrokinetic and surface tension measurements. The effects of polymer concentration, temperature and pH on the viscosity of the XG solutions were evaluated and discussed. Zeta potential data determined for XG solutions in water in the temperature range of 15–45 °C corroborated with the results obtained from the viscometric investigations suggest the occurence of conformational changes above 36 °C. The activation energy of flow and that associated with the electrophoretic migration of the charged particles were estimated for XG solutions in water. In acid medium, xanthan gum determines a slight decrease of the surface tension of pure water at all investigated temperatures.

Nanoemulsions of thymol and eugenol co-emulsified by lauric arginate and lecithin

Lauric arginate (LAE) is a cationic surfactant with excellent antimicrobial activities. To incorporate essential oil components (EOCs) in aqueous systems, properties of EOC nanoemulsions prepared with a LAE and lecithin mixture were studied. The LAE–lecithin mixture resulted in stable translucent nanoemulsions of thymol and eugenol with spherical droplets smaller than 100nm, contrasting with the turbid emulsions prepared with individual emulsifiers. Zeta-potential data suggested the formation of LAE–lecithin complexes probably through hydrophobic interaction. Negligible difference was observed for antimicrobial activities of nanoemulsions and LAE in tryptic soy broth. In 2% reduced fat milk, nanoemulsions showed similar antilisterial activities compared to free LAE in inhibiting Listeria monocytogenes, but was less effective against Escherichia coli O157:H7 than free LAE, which was correlated with the availability of LAE as observed in release kinetics. Therefore, mixing LAE with lecithin improved the physical properties of EOC nanoemulsions but did not improve antimicrobial activities, especially against Gram-negative bacteria.