Increase In Ionic Strength Research Articles

Pickering Emulsions Stabilized by Tea Water-Insoluble Protein Nanoparticles From Tea Residues: Responsiveness to Ionic Strength.

Tea water-insoluble protein nanoparticles (TWIPNs) can be applied to stabilize Pickering emulsions. However, the effect of ionic strength (0–400 mmol/L) on the characteristics of Pickering emulsions stabilized by TWIPNs (TWIPNPEs) including volume-averaged particle size (d4,3), zeta potential, microstructure and rheological properties is still unclear. Therefore, this work researched the effect of ionic strength on the characteristics of TWIPNPEs. The d4,3 of TWIPNPEs in the aquatic phase increased with the increase in ionic strength (0–400 mmol/L), which was higher than that in the SDS phase. Furthermore, the flocculation index of TWIPNPEs significantly (P < 0.05) increased from 24.48 to 152.92% with the increase in ionic strength. This could be verified from the microstructure observation. These results indicated that ionic strength could promote the flocculation of TWIPNPEs. Besides, the absolute values of zeta potential under different ionic strengths were above 40 mV in favor of the stabilization of TWIPNPEs. The viscosity of TWIPNPEs as a pseudoplastic fluid became thin when shear rate increased from 0.1 to 100 s−1. The viscoelasticity of TWIPNPEs increased with increasing ionic strength to make TWIPNPEs form a gel-like Pickering emulsion. the possible mechanism of flocculation stability of TWIPNPEs under different ionic strengths was propose. TWIPNs adsorbed to the oil-water interface would prompt flocculation between different emulsion droplets under the high ionic strength to form gel-like behavior verified by CLSM. These results on the characteristics of TWIPNPEs in a wide ionic strength range would provide the theoretical basis for applying Pickering emulsions stabilized by plant proteins in the food industry.

Effect of ionic strength on the structural properties and emulsion characteristics of myofibrillar proteins from hairtail (Trichiurus haumela)

Myofibrillar proteins (MPs) are susceptibly affected by ionic strength. The effect of ionic strength on the structure and emulsifying properties of MPs from hairtail (Trichiurus haumela) is still unclear. Therefore, the effect of ionic strength on the structural properties and emulsification of myofibrillar proteins from hairtail was analyzed. The increase in ionic strength led to the increase in endogenous fluorescence intensity of MPs. The α-helix content in MPs first increased and then decreased from ionic strength of 0 to 1.0 mol/L and β-sheet content exhibited the oppositive trend, indicating that α-helix in MP transformed into β-sheet. The surface hydrophobic groups of MPs increased; however, the contact angle decreased with the increase in ionic strength of 0–0.8 mol/L and a slight rebound at 1.0 mol/L. Sulfhydryl content and electrophoretic analysis further exhibited the change of MP structure at ionic strengths of 0–1.0 mol/L. Besides, the droplet size of MP emulsions was small and evenly distributed at 0.6 mol/L. Additionally, the creaming index of MP emulsions had better stability prepared at 0.6 mol/L than the other ionic strength conditions. The apparent viscosity of MP emulsions increased with the increase in ionic strength of 0–0.8 mol/L and decreased slightly at 1.0 mol/L. The rheological behavior of MP emulsions exhibited gel-like behavior without the effect of temperatures at 20–80 °C. These results can broaden the potential application of MPs from hairtail on the emulsion-type seafood products and delivery system in the food industry.

Kinetics and Mechanism of the Reduction of Tartrazine by Nitrite Ion in Aqueous Acid Phase

Kinetics and mechanism of the reduction of tartrazine (TZ+) by nitrite ion (NO2-) was conducted in aqueous acidic phase under pseudo-first order condition in excess of [NO2-] at T = 28 ± 1°C, [H+] = 1 × 10-4 mol/dm3, λmax = 560 nm and ionic strength I = 1.0 mol/dm3 (NaCl). The stoichiometry of the reaction displayed 1:2 mole ratio for tartrazine and nitrite ion. The redox reaction was first order with respect to [TZ+] and first order with respect to [NO2-]. A second order rate constant was observed for the reaction. The rate also shows first order dependence on acid ion concentration. The overall reaction conforms to the rate law: [TZ+] = a[H+][TZ+][NO2-] Where a = 6.7343 dm6 mol-2 s-1. The rate of reaction increased with increase in ionic strength. There was no positive polymerization in the reaction. The investigation of spectroscopic and Michaelis- Mentens plot studies did not indicate any complex formation. A plausible mechanism in support of an outer-sphere mechanism is proposed for the reaction.

Removal of heavy metal(loid)s from aqueous solution by biogenic FeS–kaolin composite: Behaviors and mechanisms

In this work, a green adsorbent, biogenic FeS–kaolin composite (KL–FeS) was synthesized by sulfate–reducing bacteria (SRB) mediation, and its potential for Cd(II), Pb(II), Cu(II), Zn(II), As(III) and Sb(III) removal was evaluated. Among prepared composites, the KL–FeS synthesized at a concentration of 2 g/L kaolin performed a better removal efficiency on heavy metal(loid)s and the adsorption results followed the pseudo–second–order and Redlich−Peterson models, indicating that the adsorption was a hybrid chemical reaction–adsorption process. Additionally, the maximum adsorption capacities of Cd(II), Pb(II), Cu(II), Zn(II), As(III) and Sb(III) on KL–FeS in monocomponent system were 71.71, 133.54, 51.90, 54.41, 38.71 and 96.38 mg/g, respectively (pH = 5.0 ± 0.1, T = 25 °C). In addition, the increase of pH and ionic strength promoted the adsorption capacities of KL–FeS for metal-(loid)s. Moreover, FTIR, XPS and XRD analyses supported that surface complexation, hydrogen bonding, ion exchange, electrostatic interaction and chemical precipitation were predominately mechanisms involved in the adsorption process. Furthermore, KL–FeS displayed higher affinity for Pb(II), Sb(III) and Cu(II) in the multi–component system. This work highlighted the potential of biogenic FeS–kaolin composite for simultaneous removal of multiple heavy metal(loid)s under aerobic conditions.

Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: Effects of ionic strength, electrolyte type, and natural organic matter

Understanding the stability and aggregation of nanoparticles in aqueous milieu is critical for assessing their behavior in the natural and engineered environmental systems and establishing their threat to human and ecosystems health. In this study, the colloidal stability and aggregation kinetics of nanocrystal quantum dots (QDs) —CdSe/ZnS QDs—were thoroughly explored under a wide range of aqueous environmental conditions. The z-average hydrodynamic diameters (z-avg. HDs) and zeta potential (ξ potential) of CdSe/ZnS QDs were measured in monovalent electrolyte (NaCl) and divalent electrolyte (CaCl2) solutions in both the absence and presence of natural organic matter (NOM)—Suwannee River natural organic matter, SRNOM to assess the dynamic growth of these nanoaggregate-QD-complexes, and the evaluation of their colloidal stability. Results show that CaCl2 was more effective to destabilize the QDs compared to NaCl at similar concentrations. An increase in NaCl concentration from 0.01 to 3.5 M increased the z-avg. HD of QD aggregates from 61.4 nm to 107.2 nm. The aggregation rates of QDs increased from 0.007 to 0.042 nm·s−1 with an increase in ionic strength from 0.5 to 3.5 M NaCl solutions, respectively. In the presence of Na+ cations, the aggregation of QDs was limited as steric forces generated by the original surface coating of QDs prevailed. In the presence of CaCl2, the aggregation of QDs was observed at a low concentration of CaCl2 (0.0001 M) with a z-avg. HD of 74.2 nm that significantly increased when the CaCl2 was higher than 0.002 M. Larger sizes of QD aggregates were observed at each level of CaCl2 concentration in suspensions of 0.002–0.1 M, as the z-avg. HDs of QDs increased from 125.1 to 560.4 nm, respectively. In the case of CaCl2, an increase in aggregation rates occurred from 0.035 to 0.865 nm·s−1 with an increase in ionic strength from 0.0001 M to 0.004 M, respectively. With Ca2+ cations, the aggregation of QDs was enhanced due to the bridging effects from the formation of complexes between Ca2+ cations in solution and the carboxyl group located on the surface coating of QDs. In the presence of SRNOM, the aggregation of QDs was enhanced in both monovalent and divalent electrolyte solutions. The degree of aggregation formation between QDs through cation-NOM bridges was superior for Ca2+ cations compared to Na+ cations. The presence of SRNOM resulted in a small increase in the size of the QD aggregates for each of NaCl concentrations tested (i.e., 0.01 to 3.5 M, except 0.1 M), and induced a monodispersed and narrower size distribution of QDs suspended in the monovalent electrolyte NaCl concentrations. In the presence of SRNOM, the aggregation rates of QDs increased from 0.01 to 0.024 nm 1 with the increase of NaCl concentrations from 0.01 to 2 M, respectively. The presence of SRNOM in QDs suspended in divalent electrolyte CaCl2 solutions enhanced the aggregation of QDs, resulting in the increase of z-avg. HDs of QDs by approximately 19.3%, 42.1%, 13.8%, 1.5%, and 24.8%, at CaCl2 concentrations of 0.002, 0.003, 0.005, 0.01, and 0.1 M, respectively. In the case of CaCl2, an increase in aggregation rates occurred from 0.035 to 0.865 nm·s−1 with an increase in ionic strength from 0.0001 to 0.004 M, respectively. Our findings demonstrated the colloidal stability of QDs and cations-NOM-QD nanoparticle complexes under a broad spectrum of conditions encountered in the natural and engineered environment, indicating and the potential risks from these nanoparticles in terms of human and ecosystem health.

Polyelectrolyte Hydrogels as Draw Agents for Desalination of Solutions with Multivalent Ions

We model a process of seawater desalination that employs compression of a weak polyelectrolyte hydrogel as the drawing force for ion transfer. We model seawater as an aqueous solution containing mono- and divalent ions, Na+, Cl–, and Ca2+. We demonstrate that the compression of hydrogel in equilibrium with a bath containing such a solution creates two types of ion flow. The first type is the exchange of divalent Ca2+ by monovalent Na+. The charge density during this process is preserved, so that per one absorbed Ca2+ two Na+ are released. The second type is the desalination itself which leads to the uptake of Na+ and Cl– pairs from the surrounding solution. The first flow predominates when Ca2+ are in excess; however, as their fraction in the solution decreases, desalination flow becomes more significant. We have shown that although the gel is a weak polyelectrolyte, its compression in the presence of divalent ions does not influence its ionization degree. This is caused by a significant screening of electrostatic interactions by divalent ions. When the density of Ca2+ is small, the gel compression may lead to its discharge and to the release of counterions, which shows up in an increase of the solution ionic strength.

Lanthanum and Gadolinium availability in aquatic mediums: New insights to ecotoxicology and environmental studies

Studies dealing with Rare Earth Elements (REE) ecotoxicological behavior are scattered and with potential conflicting results. Climate change impacts on aquatic biota and is known to modify contaminants toxicokinetic. Nevertheless, the current knowledge on the potential interactions between climate change and REE is virtually non-existent. Therefore, we focus our research on La and Gd as representatives of Light and Heavy REE that also are of great environmental concern. Experiments on different mediums (fresh-, brackish- and seawater) were designed to run at present-day and near-future conditions (T°=+4 °C, pH=△-0.4). Sampling was taken at different time scales from minutes to hours for one day. The main challenge was to evaluate the availability of La and Gd under environmental conditions closely related to climate changes scenarios. Furthermore, this study will contribute to the baseline knowledge by which future research towards understanding REE patterns and toxicity will build upon. Lanthanum and Gd behave differently with salinity. Temperature also affects the availability of dissolved La in freshwater. On the other hand, pH reduction causes the decrease of Gd in freshwater. In this medium, concentrations reduce sharply, presumably due to sorption processes or precipitates. In the brackish water experiment only the dissolved La levels in the Warming (T°=+4 °C) and Warming & Acidification (T°=+4 °C, pH=△0.4) diminished significantly through time. Dissolved La and Gd levels in seawater were relatively constant with time. The speciation of both elements is also of great relevance for ecotoxicological experiments. The trivalent free ions (La3+ and Gd3+) were the most common species in the trials. However, as ionic strength increases, the availability of other complexes rose, which should be subject of great attention for upcoming ecotoxicological studies.

Visualizing RNA Structures by SAXS-Driven MD Simulations.

The biological role of biomolecules is intimately linked to their structural dynamics. Experimental or computational techniques alone are often insufficient to determine accurate structural ensembles in atomic detail. We use all-atom molecular dynamics (MD) simulations and couple it to small-angle X-ray scattering (SAXS) experiments to resolve the structural dynamics of RNA molecules. To accomplish this task, we utilize a set of re-weighting and biasing techniques tailored for RNA molecules. To showcase our approach, we study two RNA molecules: a riboswitch that shows structural variations upon ligand binding, and a two-way junction RNA that displays structural heterogeneity and sensitivity to salt conditions. Integration of MD simulations and experiments allows the accurate construction of conformational ensembles of RNA molecules. We observe a dynamic change of the SAM-I riboswitch conformations depending on its binding partners. The binding of SAM and Mg2+ cations stabilizes the compact state. The absence of Mg2+ or SAM leads to the loss of tertiary contacts, resulting in a dramatic expansion of the riboswitch conformations. The sensitivity of RNA structures to the ionic strength demonstrates itself in the helix junction helix (HJH). The HJH shows non-monotonic compaction as the ionic strength increases. The physics-based picture derived from the experimentally guided MD simulations allows biophysical characterization of RNA molecules. All in all, SAXS-guided MD simulations offer great prospects for studying RNA structural dynamics.

OXIDATION KINETICS OF ANILINE BY ZINC DICHROMATE

The kinetics of oxidation of aniline by Zinc Dichromate (ZDC) has been studied in 50% acetic acid-water medium. The reaction shows unit order dependence each with respect to oxidant and substrate. The rate of reaction increases with increase in the [H+]. The rate of oxidation increases with decrease in dielectric constant of solvent suggests ion-dipole interaction. Increase in ionic strength by the addition of sodium perchlorate has no effect on the rate constant. There is no polymerization with acrylonitrile and absence of free radical is proved. The rate of the reaction has been conducted at four different temperatures. Thermodynamic parameters have been calculated. Based on the kinetics results, a suitable mechanism has been proposed.

Enzyme-assisted dewatering of oil sands tailings: Significance of water chemistry and biological activity

Remediation of oil sands tailings is a crucial environmental aspect of the Canadian oil sands industry. Because of the poor released water quality and slow consolidation of tailings, engineered non-natural strategies to improve the consolidation of tailings are warranted. Here, we investigated enzymatic treatment (using cellulase, protease, and lysozyme) to accelerate the dewatering of fluid fine tailings (FFT). Our findings illustrated that lysozyme (0.5% and 1%) significantly improved FFT dewatering by increasing the water recovery (WR) up to 20% compared with the other enzymes (up to 12%) or the control (2%). Moreover, lysozyme treatment resulted in the highest increase in ionic strength (0.038 to 0.1 mol L−1), decrease in diffuse double layer (DDL) thickness (1.54 × 10−7 to 9.40 × 10−8 cm), and increase in zeta potential (−34.7 to −14.8 mV). Increased methane production was observed for cellulase (0.5% and 1%), lysozyme (0.5% and 1%), and protease (0.5%). The enhanced dewatering could be linked to the ebullition of methane gas resulting from the methanogenic activity, which created pathways for the trapped water release. In addition, the dissolution of carbonate minerals during the release of methane gas increased ionic strength and decreased the DDL of the FFT. Lysozyme 1% treatment was also the most effective in reducing naphthenic acid fractions (1934.6 to 243 ng mL−1); however, the released water had high toxicity toward Vibrio fischeri and had a slight decrease in microbial populations. This study provides a fundamental insight into enzymatic treatment for oil sand tailings.

Discrepant effects of monovalent cations on membrane fouling induced by colloidal polymer: Evaluation and mechanism investigation

Understanding how ionic conditions affect membrane fouling induced by anionic polyacrylamide (APAM) is important for achieving long-term and stable operation of a polymer flooding produced wastewater (PFPW) membrane separation process. However, there is lack of studies on the effects of monovalent cations (Na+ and K+) on APAM-based membrane fouling. In this work, the effects of Na+ and K+ on filtration efficiency, flux decline behavior, fouling resistance, and cleaning efficiency were studied through a series of microfiltration tests. Moreover, the influencing mechanism of membrane fouling was further comprehensively revealed from the aspects of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the hydration force, and the microstructure characterizations. The XDLVO theory agreed well with membrane fouling behavior at various ionic strengths. The increase in ionic strength (0–10,000 mg/L) of Na+ and K+ exacerbated the reduction of relative flux (J/J0) and the accumulation of fouling resistance, as well as made the porous APAM-induced fouling layer denser and more compact, boosting removal efficiency. Furthermore, K+ had a stronger aggravating effect on membrane fouling than Na+. Specifically, the final value of J/J0 for APAM+K+ (0.08) was lower than that for APAM + Na+ (0.12), and the fouling resistance for APAM+K+ (12.25 × 1011 m−1) was higher than that for APAM + Na+ (12.01 × 1011 m−1) at an ionic strength of 10,000 mg/L, which was owing to the larger hydration force caused by Na+ with a smaller ionic radius. This research offers practical guidance for the PFPW membrane filtering process.

Molecular Insights into Roles of Dissolved Organic Matter in Cr(III) Immobilization by Coprecipitation with Fe(III) Probed by STXM-Ptychography and XANES Spectroscopy.

The coprecipitation of heavy metals (HMs) with Fe(III) in the presence of dissolved organic matter (DOM) is a crucial process to control the mobility of HMs in the environment, but its underlying immobilization mechanisms are unclear. In this study, Cr(III) immobilization by coprecipitation with Fe(III) in the presence of straw-derived DOMs under different Fe/C molar ratios, pHs, and ionic strengths was investigated using scanning transmission X-ray microscopy (STXM) and ptychography and X-ray absorption near-edge structure (XANES) spectroscopy. The results showed that Cr(III) retention was enhanced in the presence of DOM, a maximum of which was achieved at an Fe/C molar ratio of 0.5. The increase of pH and ionic strength could also promote Cr(III) immobilization. Cr K-edge XANES results indicated that Fe (oxy)hydroxide fractions, instead of organics, provided the predominant binding sites for Cr(III), which was directly confirmed by high spatial resolution STXM-ptychography analysis at the sub-micron- and nanoscales. Moreover, organics could indirectly facilitate Cr immobilization by improving the aggregation and deposition of coprecipitate particles through DOM bridging or electrostatic interactions. Additionally, C K-edge XANES analysis further indicated that the carboxylic groups of DOM were complexed with Fe (oxy)hydroxides, which probably contributed to DOM bridging. This study provides a new insight into Cr(III) immobilization mechanisms in its coprecipitation with Fe(III) and DOM, which could have important implications on the management of Cr(III)-enriched soils, particularly with crop straw returning.

Co-transport of bentonite colloid and U(VI) in particulate granite column: role of colloid concentration, ionic strength, pH and flow rate

Abstract China is considering Beishan granitic formation (Gansu Province, China) as the site for high-level radioactive waste (HLW) repositories. Thus, it is crucial to understand the transport behavior of radionuclide in Beishan granitic media under disposal conditions. In this context, the co-transport of U(VI) (as the representative of radionuclides) and bentonite colloid (BC, from erosion of compacted bentonite) in particulate Beishan granite was studied as a function of important in-situ factors, such as BC concentration, ionic strength, pH and flow rate. We found that the increase of BC concentration (BC = 240–480 mg/L) did not affect the transport of individual BC, whereas it significantly facilitated the transport of U(VI). The increase of ionic strength (I = 0.001–0.01 M NaCl) or decrease of pH (pH = 7.50–5.40) obviously inhibited the BC transport, where these inhibiting effects were relatively slight for the transport of U(VI). The increase of flow rate significantly facilitated both the transport of BC and U(VI). Finally, a two-site kinetic attachment/detachment model was applied to describe the breakthrough curves of individual and co-transport of BC. The experimental and modeling results of this study have a significant implication on the safety assessment of HLW repositories built in granitic formation.

Magnetic Fe3O4/TiO2/graphene sponge for the adsorption of methylene blue in aqueous solution

Graphene adsorbents are widely applied in pollutant removal with high adsorption capacities. However, the contradiction between high capacity and poor regeneration hinders the practical applications of graphene adsorbents in aqueous systems. In this study, we designed a magnetic Fe3O4/TiO2/graphene sponge (MFTGS) for dye adsorption in aqueous solution. Small Fe3O4 and TiO2 nanoparticles were decorated on the graphene sheets. MFTGS could be magnetically separated in aqueous systems with a saturated magnetization of 17.0 emu/g. MFTGS showed a moderately large capacity of 224 mg/g for methylene blue (MB). The adsorption could reach the equilibrium within 10 min with a k2 constant of 4.48 × 10−4 g/mg∙min−1. The adsorption of MB on MFTGS was driven by entropy production, so the capacity increased at higher temperature. The decrease of pH value and increase of ionic strength slightly lowered the adsorption capacity of MFTGS. MFTGS could be easily regenerated by ethanol washing, where 80% of the capacity retained after 4 cycles. Our results provided high-performance magnetic graphene adsorbents for dye removal and would benefit the development of graphene nanotechnology.

Effects of biochar on transport and retention of phosphorus in porous media: Laboratory test and modeling

Given the complexity of soil components, a detailed understanding of the effects of single factors on phosphorus transport and retention will play a key role in understanding the environmental effects of phosphorus. In this work, quartz sand columns (considering five factors: doping rate, pH, particle size, ionic strength and cation type), combined with a two-site nonequilibrium transport model (TSM), were used to investigate phosphate (P) transport behavior. The results show that changes in doping ratio (0.4%–1.6%) and pH (5–9) have a notable effect on the transport of P, while, particle size of quartz sand hardly impacts the transport. When biochar was added at 1.6%, the surface of biochar increased the P fixation rate by about 37% through direct interaction with phosphate and bridging action with metal ions. As the morphology of P changed under different pH conditions, a part of P was immobilized in the form of precipitation. The immobilization of P was further enhanced with the increase of ionic strength. Compared with the direct interaction of P with biochar in Na+ solution, Ca2+ and Mg2+ solutions are more likely to adsorb P. Meanwhile, the TSM model also fits the transport behavior well. This study provides a perspective for evaluating the environmental behavior of P in the porous media interaction with biochar.

EFFECT OF IONIC STRENGTH AND ACTIVE ACIDITY OF THE MEDIUM ON THE STABILITY OF VITAMIN E NANOEMULSIONS (ALPHA-TOCOPHEROL ACETATE)

In this work, the influence of the ionic strength and active acidity of the medium on the stability of vitamin E (alpha-tocopherol acetate) nanoemulsions was studied. Vitamin E nanoemulsions were obtained by mixing an aqueous solubilizer solution with vitamin E. Nonionic surfactants Tween 80 and Kolliphor HS 15 were used as solubilizers. The obtained samples were studied by dynamic light scattering on a Photocor-Complex device. It has been established that samples of vitamin E nanoemulsions have a monomodal size distribution. The hydrodynamic radius of vitamin E micelles obtained with Kolliphor HS 15 is 12 ± 4 nm, and with Tween 80 it is 160 ± 21 nm. The study of the influence of ionic strength on the stability of vitamin E nanoemulsions showed that in the range of ionic strength from 0.1 to 3.0 mol/dm3, there are no significant changes in the hydrodynamic radius of vitamin E micelles, and with an increase in ionic strength up to 5.0 mol/dm3 “jumping” change in the hydrodynamic radius of vitamin E micelles when using both nonionic surfactants. It has been shown that at pH &gt; 9, the hydrodynamic radius of micelles of vitamin E nanoemulsion obtained using Kolliphor HS 15 increases from 12 to 255 nm, which is associated with alkaline hydrolysis of ether groups of Kolliphor HS 15. Nanoemulsions of vitamin E solubilized in Tween 80 micelles are stable over the entire pH range from 1.65 to 12.43.

NaCl induces flocculation and lipid oxidation of soybean oil body emulsions recovered by neutral aqueous extraction.

Soybean oil bodies (SOB) are naturally pre-emulsified lipid droplets recovered directly from soybean seeds. Almost all food emulsions contain salts. However, it was not clear how the incorporation of salts affected the physicochemical stability of SOB. This study investigated the effect of NaCl (0-1.2%) on the physical and oxidative stability of SOB emulsions under neutral (pH7) and acidic (pH3) conditions. In the presence of NaCl, the SOB emulsion (pH7) showed strong flocculation during storage due to electrostatic screening. The NaCl-induced flocculation of SOB was attenuated at pH3, which may be due to the difference in conformation or interaction of the protein interfaces covering SOB at different pH values. The increase in ionic strength or acid conditioning treatment resulted in a remarkable increase in the stability of SOB emulsions against coalescence. The confocal laser scanning microscopy images also confirmed the NaCl-induced changes in the flocculation/coalescence properties of SOB. The oxidative behavior tests indicated that SOB emulsions containing NaCl were more susceptible to lipid oxidation but protein oxidation was inhibited due to electrostatic screening, which reduced pro-oxidant accessibility of unadsorbed proteins in the emulsion. This oxidative behavior was attenuated at pH3. The incorporation of NaCl significantly reduced the physical and oxidative stability of the SOB emulsion, and acidic pH mitigated NaCl-induced flocculation and lipid oxidation of SOB. © 2021 Society of Chemical Industry.

Physicochemical stability of oleogel-in-water emulsions loaded with β-carotene against environmental stresses

Oleogel-in-water emulsions were prepared using monoglyceride (GMS) oleogel as the oil phase and tween-20 (TW) as the emulsifier. The roles of TW content in the emulsions over the change in temperature, ionic strength, pH and against freeze-thawing were evaluated. Particle size of the emulsions decreased with the increase in emulsifier content. With the development of GMS structures in emulsions, both shearing viscosity and storage modulus of the systems were enhanced. Only minor size changes in emulsions with higher TW content were observed after thermal treatment. The increase in ionic strength of emulsions led to increase in droplet size, but the presence of TW inhibited phase separation. All the emulsions were stable by changing pH from 6 to 10. Significant increases in droplet size were observed when the emulsions were subjected to three cycles of freeze-thawing, but only slight oiling off was detected. When β-carotene (3% in the emulsion) was incorporated within oleogel-in-water emulsions, it was better retained in the systems with higher TW content, either subjected to thermal treatment or light exposure. These findings suggested that oleogel-in-water emulsions had good physical stability over changes in pH, ionic strength, and temperature, and were able to protect high loading of lipophilic bioactives.

The influence of pH and ionic strength on the interactions between human serum albumin and magnetic iron oxide nanoparticles

Human serum albumin (HSA) is a very well-characterized protein, which has already been used for many biocompatible coatings. We hypothesized binding between HSA and magnetic iron oxide nanoparticles (MNPs) as well as HSA coating stability to be pH- and ionic strength-dependent. The impact of phosphate buffer on protein coating was studied at varying pH (6.0, 6.6, and 7.5) and ionic strengths (0.15 and 0.30 M NaCl) using different physicochemical methods. In addition, the stability of HSA coatings on MNPs was studied by means of UV/visible spectrophotometry, dynamic light scattering, and electron magnetic resonance. We used differential scanning calorimetry (DSC) to determine the differences in the change of enthalpies and denaturation temperatures of HSA in various buffer conditions and on the surface of the particles. The binding thermodynamics of HSA and MNPs were determined by isothermal titration calorimetry (ITC), and it was also dependent on pH and ionic strength. The stability of adsorbed layer on MNPs decreases with increasing pH [from weakly acidic (pH 6.0–6.6) to slightly alkaline (pH 7.5)], as well as with an increase of ionic strength. This study develops stable HSA coating on MNPs which might be applied to a wide range of biomedical applications.

KINETICS AND MECHANISM OF THE OXIDATION OF TANNIC ACID BY POTASSIUM TRISOXALATOFERRATE (III) IN AQUEOUS HYDROCHLORIC ACID MEDIUM

The kinetics of the redox reaction between tannic acid (TA) and potassium trisoxalatoferrate (III) trihydrate, (K3[Fe(C2O4)3].3H2O) has been studied in aqueous hydrochloric acid medium. The stoichiometry of the reaction determined by the mole ratio method was observed to be 1:1. The kinetic results showed first order dependence with respect to complex and tannic acid concentrations. The experimental data for the reaction system are consistent with the following rate law:where a = 2.0 × 10-3 mol-1 dm3 s-1 and b = 2.1 × 10-3 mol-2 dm6 s-1 at 420 nm and 27.0 ± 1.0 ºC. The rate of reaction was found to increase with increase in [H+] in the acid range used, but decreased with increase in ionic strength of the reaction medium. While the rate of reaction was observed to decrease with increasing dielectric constant of the reaction medium, the addition of CH3COO-, HCOO-, Ni2+and K+ catalyzed the rate of the reaction. The Michaelis-Menten plot of 1/kobs versus 1/[oxidant] gave a straight line with an insignificant positive intercept. The addition of acrylamide to the partially oxidized reaction mixture did gave a gel in the presence of excess methanol. Based on the experimental data, a plausible mechanism involving outer sphere electron transfer has been proposed for the redox reaction between tannic acid and potassium trisoxalatoferrate (III) trihydrate.