The effect of pH on the structure of Bluetongue virus VP5.

The unenveloped Bluetongue virus capsid comprises several structural layers, the inner two comprising a core, which assembles before addition of the outer proteins, VP2 and VP5. Two symmetric trimers of VP5 fit like pegs into two distinct pits on the core and undergo pH conformational changes in the context of the virus, associated with cell entry. Here we show that in isolation VP5 alone undergoes essentially the same changes with pH and confirm a helical transition, indicating that VP5 is a motor during cell entry. In the absence of VP5 the two pits on the core differ from each other, presumably due to the asymmetric underlying structure of VP3, the innermost capsid protein. On insertion of VP5 these pits become closely similar and remain similar at low pH whilst VP5 is present. This natural asymmetry presumably destabilises the attachment of VP5, facilitating ejection upon low pH, membrane penetration and cell entry.

Equilibrium and Kinetic Studies on Adsorption of Neutral and Ionic Species of Organic Adsorbates from Aqueous Solutions on Activated Carbon.

This work presents comprehensive studies of the adsorption of neutral and ionic forms of organic adsorbates from aqueous solutions on activated carbon. The influence of pH on the equilibrium and kinetics of the adsorption of methylene blue (MB) and organic acids, benzoic (BA), 2-nitrobenzoic (2-NBA), 3-nitrobenzoic (3-NBA), and 4-nitrobenzoic (4-NBA) acid, was investigated. Experimental adsorption isotherms were analyzed using the generalized Langmuir isotherm equation (R2 = 0.932-0.995). Adsorption rate data were studied using multiple adsorption kinetics equations, of which the multi-exponential equation gave the best fit quality (R2 - 1 = (6.3 × 10-6)-(2.1 × 10-3)). The half-time was also used to represent the effect of pH on adsorption kinetics. Strong dependences of the adsorption efficiency on the solution pH were demonstrated. In the case of organic acid adsorption, the amount and rate of this process increased with a decrease in pH. Moreover, larger adsorbed amounts of methylene blue were recorded in an alkaline environment in a relatively short time. The maximum absorbed amounts were 11.59 mmol/g, 6.57 mmol/g, 9.38 mmol/g, 2.70 mmol/g, and 0.24 mmol/g for BA, 2NBA, 3-NBA, 4-NBA, and MB. The pure activated carbon and the selected samples after adsorption were investigated using thermal analysis and X-ray photoelectron spectroscopy.

Comparing the adsorption of micropollutants on activated carbon from anaerobically stored, organics-depleted, and nitrified urine.

Separate collection and treatment of urine optimizes nutrient recovery and enhances micropollutant removal from municipal wastewater. One typical urine treatment train includes nutrient recovery in three biological processes: anaerobic storage, followed by aerobic organics degradation concurrently with nitrification. These are usually followed by activated carbon adsorption to remove micropollutants. However, removing micropollutants prior to nitrification would protect nitrifiers from potential inhibition by pharmaceuticals. In addition, combining simplified biological treatment with activated carbon adsorption could offer a cheap and robust process for removing micropollutants where nutrient recovery is not the first priority, as a partial loss of ammonia occurs without nitrification. In this study, we investigated whether activated carbon adsorption could also take place between the three biological treatment steps. We tested the effectiveness of micropollutant removal with activated carbon after each biological treatment step by conducting experiments with anaerobically stored urine, organics-depleted urine, and nitrified urine. The urine solutions were spiked with 19 pharmaceuticals: amisulpride, atenolol, atenolol acid, candesartan, carbamazepine, citalopram, clarithromycin, darunavir, diclofenac, emtricitabine, fexofenadine, hydrochlorothiazide, irbesartan, lidocaine, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole, trimethoprim, venlafaxine, and two artificial sweeteners, acesulfame and sucralose. Batch experiments were conducted with powdered activated carbon (PAC) to determine how much activated carbon achieve which degree of micropollutant removal and how organics, pH, and speciation change from ammonium to nitrate influence adsorption. Micropollutant removal was also tested in granular activated carbon (GAC) columns, which is the preferred technology for micropollutant removal from urine. The carbon usage rates (CUR) per person were lower for all urine solutions than for municipal wastewater. The results showed that organics depletion would be needed when micropollutant removal was the sole aim of urine treatment, as the degradation of easily biodegradable organics prevented clogging of GAC columns. However, CUR did hardly improve with organics-depleted urine compared to stored urine. The lowest CUR was achieved with nitrified urine. This resulted from the additional organics removal during nitrification and not the lower pH or the partial conversion of ammonium to nitrate. In addition, we showed that the relative pharmaceutical removal in all solutions was independent of the initial pharmaceutical concentration unless the background organics matrix changed considerably. We conclude that removal of micropollutants in GAC columns from organics-depleted urine can be performed without clogging, but with the drawback of a higher carbon usage compared to removal from nitrified urine.

Facilitation of Fenton-Like Reaction of Copper-Nitrogen-Doped Carbon-Based Nanocatalysts by Enhancing Hydroxyl Adsorption on Single-Atom Cu-NxC4- x Sites.

Copper-nitrogen-doped carbon-based nanocatalysts (Cu-NCs), containing atomically dispersed Cu-NxC4- x sites, are efficient in boosting the Fenton-like reaction. However, the mechanisms of the Fenton-like reaction, including the pH effect on the products and the effect of the coordination environment on catalytic activity, remain controversial, restricting the development of Cu-NCs. Cu-NCs are experimentally synthesized with Cu-N4 sites and prove that the Fenton-like reaction generates mainly hydroxyl radicals (·OH) in the acidic but ·OH and superoxide radicals (·O2 -) in the neutral. The density functional theory (DFT) calculations reveal that the catalytic activity of Cu-NCs in the Fenton-like reaction is associated with the adsorption strength of ·OH at the Cu site. Further investigation of the effect of the coordination environment of Cu-NCs indicates that the Cu-N2C2 site, which can enhance the ·OH adsorption strength, is an ideal catalyst site for the Fenton-like reaction. These results open the way to facilitating the catalytic activity of Cu-NCs in the Fenton-like reaction.

Effect of Copper-Modification of g-C3N4 on the Visible-Light-Driven Photocatalytic Oxidation of Nitrophenols.

Graphitic carbon nitride (g-C3N4) has proved to be a promising heterogeneous photocatalyst in the visible range. It can be used, among others, for the oxidative conversion of environmentally harmful nitrophenols occurring in wastewater. However, its photocatalytic activity needs to be enhanced, which can be achieved by modification with various dopants. In our work, copper-modified g-C3N4 was prepared by ultrasonic impregnation of the pristine g-C3N4 synthesized from thiourea. The morphology, microstructure, and optical properties of the photocatalysts were characterized by XRD, FT-IR, DRS, SEM, XPS, and TEM. DRS analysis indicated a slight change in both the CB and the VB energies of Cu/g-C3N4 compared to those of g-C3N4. The efficiency of the photocatalysts prepared was tested by the degradation of nitrophenols. Copper modification caused a sevenfold increase in the rate of 4-nitrophenol degradation in the presence of H2O2 at pH = 3. This dramatic enhancement can be attributed to the synergistic effect of copper and H2O2 in this photocatalytic system. A minor Fenton reaction role was also detected. The reusability of the Cu/g-C3N4 catalyst was demonstrated through five cycles. Copper-modified g-C3N4 with H2O2 proved to be applicable for efficient visible-light-driven photocatalytic oxidative degradation of nitrophenols.

Extended X-ray Absorption Fine Structure Revealed the Mechanism of Arsenate Removal by the Fe/Mn Oxide-Based Composite under Conditions of Fully Saturated Sorption Sites.

Molecular mechanism of arsenate removal by a promising inorganic composite based on Fe/Mn oxides and MnCO3 was studied under the rarely investigated conditions of fully saturated sorption sites (characteristic of dynamic sorption, such as water treatment plants) at the pH of 4/6/7/8 using As K-edge extended X-ray absorption fine structure (EXAFS)/X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). Comparison of arsenic speciation in the initial adsorbate solution (calculated by Visual MINTEQ) and after sorption (determined by As 3d XPS) allowed the interpretation of the initializing forces of the interfacial processes. Contribution of various solid phases of this composite anion exchanger to the removal of arsenate was disclosed by examining the Fe 2p3/2 and Mn 2p3/2 XPS spectra supported by FTIR. As K-edge EXAFS simulation not only proved the chemisorptive binding of aqueous As(V) anions to the Fe/Mn oxide-based adsorbent but also demonstrated the presence of a variety of sorption sites in this complex structured porous material, which became available step-wise upon an increasing pressure on the interface with high arsenate loading during the long-term sorption process. The type of inner-sphere complexation of As(V) on the saturated surface discovered by As K-edge EXAFS modeling was a function of pH. Analysis of EXAFS fitting data resulted in suggestion of a methodological idea on how the EXAFS-derived coordination numbers can be used to distinguish the localization of adsorbed ions (surface versus structure emptiness). This work also provides more insights into the superiority of composite adsorbents (compared to the materials based on individual compounds) in terms of their capability to adapt/change the molecular sorption mechanism in order to inactivate (remove) more toxic aqueous anions.

Ferrous nitrosylated cytochrome c: The unusual strength of the proximal His18-Fe bond.

NO binding to horse heart cytochrome c (hhcyt c) has been investigated as a function of pH by both optical absorption and EPR spectroscopies. Lowering pH from 3.5 to 1.5 induces: (i) a blue-shift of the maximum of the optical absorption spectrum in the Soret region from 415 to about 404 nm, and (ii) the appearance of a strong three hyperfine splitting in the gz region of the EPR spectrum. Both spectroscopic features indicate the cleavage of the proximal His18-Fe(II)-NO bond giving rise to the five-coordinated Fe(II)-NO species. By quantification of the relative weight for the six- and the five-coordinated component in the EPR spectra, the pKa value was determined. The apparent pKa of the proximal His Nε atom (1.8 ±â€¯0.1) is unusually low for a ferrous nitrosylated form since in all investigated ferrous NO-bound heme-proteins the pKa value for the cleavage of the proximal His-Fe(II) bond ranges between 3.7 and 5.8. The pKa value of ferrous nitrosylated hhcyt c indicates that the strength of the proximal His18-Fe(II) bond (= 27.9 kJ/mol) is about 10-22 kJ/mol higher than that observed in all investigated heme-proteins. The strong coordination of the heme-Fe atom by His18 is extremely important to maintain the redox efficiency of cyt c and to keep apoptosis under control. This is a crucial point in tissues, such as retina, where apoptosis might trigger macular degenerative processes.

Self-Standing Pd-Based Nanostructures for Electrocatalytic CO Oxidation: Do Nanocatalyst Shape and Electrolyte pH Matter?

Tailoring the shape of Pd nanocrystals is one of the main ways to enhance catalytic activity; however, the effect of shapes and electrolyte pH on carbon monoxide oxidation (COOxid) is not highlighted enough. This article presents the controlled fabrication of Pd nanocrystals in different morphologies, including Pd nanosponge via the ice-cooling reduction of the Pd precursor using NaBH4 solution and Pd nanocube via ascorbic acid reduction at 25 °C. Both Pd nanosponge and Pd nanocube are self-standing and have a high surface area, uniform distribution, and clean surface. The electrocatalytic CO oxidation activity and durability of the Pd nanocube were significantly superior to those of Pd nanosponge and commercial Pd/C in only acidic (H2SO4) medium and the best among the three media, due to the multiple adsorption active sites, uniform distribution, and high surface area of the nanocube structure. However, Pd nanosponge had enhanced COOxid activity and stability in both alkaline (KOH) and neutral (NaHCO3) electrolytes than Pd nanocube and Pd/C, attributable to its low Pd-Pd interatomic distance and cleaner surface. The self-standing Pd nanosponge and Pd nanocube were more active than Pd/C in all electrolytes. Mainly, the COOxid current density of Pd nanocube in H2SO4 (5.92 mA/cm2) was nearly 3.6 times that in KOH (1.63 mA/cm2) and 10.3 times that in NaHCO3 (0.578 mA/cm2), owing to the greater charge mobility and better electrolyte-electrode interaction, as evidenced by electrochemical impedance spectroscopy (EIS) analysis. Notably, this study confirmed that acidic electrolytes and Pd nanocube are highly preferred for promoting COOxid and may open new avenues for precluding CO poisoning in alcohol-based fuel cells.

Controlled release of MT-1207 using a novel gastroretentive bilayer system comprised of hydrophilic and hydrophobic polymers.

In the present study, novel gastroretentive bilayer tablets were developed that are promising for the once-a-day oral delivery of the drug candidate MT-1207. The gastroretentive layer consisted of a combination of hydrophilic and hydrophobic polymers, namely polyethylene oxide and Kollidon® SR. A factorial experiment was conducted, and the results revealed a non-effervescent gastroretentive layer that, unlike most gastroretentive layers reported in the literature, was easy to prepare, and provided immediate tablet buoyancy (mean floating lag time of 1.5 s) that lasted over 24 h in fasted state simulated gastric fluid (FaSSGF) pH 1.6, irrespective of the drug layer, thereby allowing a 24-hour sustained release of MT-1207 from the drug layer of the tablets. Furthermore, during in vitro buoyancy testing of the optimised bilayer tablets in media of different pH values (1.0, 3.0, 6.0), the significant difference (one-way ANOVA, p < 0.001) between the respective total floating times indicated that stomach pH effects on tablet buoyancy are important to be considered during the development of non-effervescent gastroretentive formulations and the choice of dosing regimen. To the best of our knowledge, this has not been reported before, and it should probably be factored in when designing dosing regimens. Finally, a pharmacokinetic study in Beagle dogs indicated a successful in vivo 24-hour sustained release of MT-1207 from the optimised gastroretentive bilayer tablet formulations with the drug plasma concentration remaining above the estimated minimum effective concentration of 1 ng/mL at the 24-hour timepoint and also demonstrated the gastroretentive capabilities of the hydrophilic and hydrophobic polymer combination. The optimised formulations will be forwarded to clinical development.

Growth performance of Listeria monocytogenes and background microbiota from mushroom processing environments.

Interaction between Listeria monocytogenes and resident background microbiota may occur in food processing environments and may influence the survival of this pathogen in a factory environment. Therefore the aim of this study was to characterize the growth performance of microbiota isolated from the processing environments of frozen sliced mushrooms, and to investigate the competitive performance of L. monocytogenes when co-cultured with accompanying environmental microbiota. Acinetobacter, Enterobacteriaceae, Lactococcus and Pseudomonas were the most prominent background microbiota isolated from the processing environment of frozen sliced mushrooms. All individual microbiota strains were able to grow and form biofilm in filter-sterilized mushroom medium, with the mannitol-consumers Raoultella and Ewingella as top performers, reaching up to 9.6 and 9.8 log CFU/mL after 48 h incubation at room temperature. When L. monocytogenes mushroom isolates were co-cultured with the microbiota strains, L. monocytogenes counts ranged from 7.6 to 8.9 log CFU/mL after 24 h of incubation, while counts of the microbiota strains ranged from 5.5 to 9.0 log CFU/mL. Prolonged incubation up to 48 h resulted in further increase of L. monocytogenes counts when co-cultured with non-acidifying species Pseudomonas and Acinetobacter reaching 9.1 to 9.2 log CFU/mL, while a decrease of L. monocytogenes counts reaching 5.8 to 7.7 log CFU/mL was observed in co-culture with Enterobacteriaceae and acidifying Lactococcus representatives. In addition, L. monocytogenes grew also in spent mushroom media of the microbiota strains, except in acidified spent media of Lactococcus strains. These results highlight the competitive ability of L. monocytogenes during co-incubation with microbiota in fresh and in spent mushroom medium, indicative of its invasion and persistence capacity in food processing factory environments.

Providing New Insights on the Molecular Properties and Thermal Stability of Ovotransferrin and Lactoferrin.

Ovotransferrin (OVT) is a multi-functional protein showing over 50% homology with Bovine lactoferrin (BLF) and human lactoferrin (HLF), which have the potential to be a substitute for lactoferrin (LF) due to the limited production of LF. To explore the substitutability of OVT, the molecular properties and thermal stability of OVT, BLF and HLF were characterized because these properties will affect the processing quality and biological activities of protein products when exposed to different processing conditions (e.g., temperature, pH, ion strength). The results showed that although obviously different isoelectric point (5.31, 9.12 and 8.75 for OVT, BLF and HLF, respectively), particle size distribution and hydrophobicity were found, they exhibited good dispersity because of high potential value. They showed an endothermic peak at 80.64 °C, 65.71 °C and 90.01 °C, respectively, and the denaturation temperature varied at different pH and ionic strength. OVT and BLF were more susceptible to heating at pH 5.0 as reflected by the decline of denaturation temperature (21.78 °C shift for OVT and 5.81 °C shift for BLF), while HLF could remain stable. Compared with BLF, OVT showed higher secondary structure stability at pH 7.0 and 9.0 with heating. For example, the α-helix content of OVT changed from 20.35% to 15.4% at pH 7.0 after heating, while that of BLF changed from 20.05% to 6.65%. The increase on fluorescence intensity and redshifts on the maximum wavelength after heating indicated the changes of tertiary structure of them. The turbidity measurements showed that the thermal aggregation degree of OVT was lower than BLF and HLF at pH 7.0 (30.98%, 59.53% and 35.66%, respectively) and pH 9.0 (4.83%, 12.80% and 39.87%, respectively). This work demonstrated the similar molecular properties and comparable thermal stability of OVT to BLF and HLF, which can offer a useful reference for the substitute of LF by OVT.

Removal of Cadmium(II) by hydrated manganese dioxide: behaviour and mechanism at different pH.

Homogeneous precipitation was proposed to prepare hydrated manganese dioxide (HMO) with KMnO4 as oxidant, NaCl as reductant and HNO3 as reaction auxiliary. HMO was applied to remove Cd(II) and the effect of contact time, initial concentration, adsorbent dose and pH value on adsorption efficiency were investigated. The removal mechanisms at various pH values were analysed in detail. Adsorption thermodynamics parameters were calculated as ΔG < 0, ΔH > 0 and ΔS > 0, which meant that the adsorption process was endothermic. The result of adsorption kinetics indicated the adsorption process conformed to pseudo-second-order kinetics. When adsorbing Cd(II) with initial concentration equaling 100 mg·L-1, the activation energy (Ea) was 62.740 kJ·mol-1. The Langmuir model could describe adsorption behaviour on HMO better than the Freundlich model, indicating that the adsorption sites of HMO were homogeneous and that single-layer adsorption was a dominant way in this process. The maximum adsorption capacity of Cd(II) on MnO2 calculated by the Langmuir model was 267 mg·g-1. The adsorbent HMO could be recycled and reused for several times with a high efficiency above 70% by adding HCl. SEM, EDS, FTIR and XPS were used to analyse the mechanisms of removal of Cd(II) at pH = 3,7 and 10. The mechanisms included electrostatic attraction, ion exchange and chemical precipitation. With pH increasing, the zeta potential decreased and the surface negative charge increased, promoting Cd(II) removal through enhanced electrostatic attraction. Meanwhile, ion exchange mechanisms including inner-sphere complexation and outer-sphere complexation occurred during adsorption process at different pH.

Viscoelastic Analysis of Pectin Hydrogels Regenerated from Citrus Pomelo Waste by Gelling Effects of Calcium Ion Crosslinking at Different pHs.

Pectin was extracted from citrus pomelo waste, and the effects of calcium ions (Ca2+) on the gelation and hydrogels properties were investigated over a pH range of 3.2-8 by using viscoelastic analysis. The gelatinization of Ca2+-pectin was examined at concentrations of 0.9, 1.8, 2.4, and 3.6 M of Ca2+ in aqueous pectin solutions of 1%, 2%, 3%, and 4%. The gel transition of Ca2+-pectin solution to hydrogels was determined by measuring the storage modulus (G') and loss modulus (G") under mechanical strain from 0.01 to 100%. In a hydrogel of 3% pectin at Ca2+ = 2.4 M, as pH increased to 7, the G' at 0.01 strain % was 3 × 104 Pa, and 3 × 103 Pa at pH 5, indicating that the crosslinking weakened at acidic pH. Due to the crosslinking between the calcium ions and the ionized carboxylic acid groups of pectin, the resulting hydrogel became stiff. When the mechanical strain % was in the range of 0.01-1%, G' was unchanged and G" was an order of magnitude smaller than G', indicating that the mechanical stress was relieved by the gel. In the range of 1-100%, the gel deformation progressed and both the moduli values were dropped. Collapse from the gel state to the solution state occurred at 1-10 strain %, but the softer hydrogels with G' of 103 Pa had a larger strain % than the stiffer hydrogels with G' of 104 Pa.

Effects of Neutralization on the Physicochemical, Mechanical, and Biological Properties of Ammonium-Hydroxide-Crosslinked Chitosan Scaffolds.

It has been reported that chitosan scaffolds, due to their physicochemical properties, stimulate cell proliferation in different tissues of the human body. This study aimed to determine the physicochemical, mechanical, and biological properties of chitosan scaffolds crosslinked with ammonium hydroxide, with different pH values, to better understand cell behavior depending on the pH of the biomaterial. Scaffolds were either neutralized with sodium hydroxide solution, washed with distilled water until reaching a neutral pH, or kept at alkaline pH. Physicochemical characterization included scanning electron microscopy (SEM), elemental composition (EDX), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), and mechanical testing. In vitro cytotoxicity was assessed via dental-pulp stem cells' (DPSCs') biocompatibility. The results revealed that the neutralized scaffolds exhibited better cell proliferation and morphology. It was concluded that the chitosan scaffolds' high pH (due to residual ammonium hydroxide) decreases DPSCs' cell viability.

Efficient Mesoporous MgO/g-C3N4 for Heavy Metal Uptake: Modeling Process and Adsorption Mechanism.

Removing toxic metal ions arising from contaminated wastewaters caused by industrial effluents with a cost-effective method tackles a serious concern worldwide. The adsorption process onto metal oxide and carbon-based materials offers one of the most efficient technologies adopted for metal ion removal. In this study, mesoporous MgO/g-C3N4 sorbent is fabricated by ultrasonication method for the uptake Pb (II) and Cd (II) heavy metal ions from an aqueous solution. The optimum conditions for maximum uptake: initial concentration of metal ions 250 mg g-1, pH = 5 and pH = 3 for Pb++ and Cd++, and a 60 mg dose of adsorbent. In less than 50 min, the equilibrium is reached with a good adsorption capacity of 114 and 90 mg g-1 corresponding to Pb++ and Cd++, respectively. Moreover, the adsorption isotherm models fit well with the Langmuir isotherm, while the kinetics model fitting study manifest a perfect fit with the pseudo-second order. The as fabricated mesoporous MgO/g-C3N4 sorbent exhibit excellent Pb++ and Cd++ ions uptake and can be utilized as a potential adsorbent in wastewater purification.

Influence of key operational parameters on biohydrogen production from fruit and vegetable waste via lactate-driven dark fermentation.

This study aims at investigating the influence of operational parameters on biohydrogen production from fruit-vegetable waste (FVW) via lactate-driven dark fermentation. Mesophilic batch fermentations were conducted at different pH (5.5, 6.0, 6.5, 7.0, and non-controlled), total solids (TS) contents (5, 7, and 9%) and initial cell biomass concentrations (18, 180, and 1800 mg VSS/L). Higher hydrogen yields and rates were attained with more neutral pH values and low TS concentrations, whereas higher biomass densities enabled higher production rates and avoided wide variations in hydrogen production. A marked lactate accumulation (still at neutral pH) in the fermentation broth was closely associated with hydrogen inhibition. In contrast, enhanced hydrogen productions matched with much lower lactate accumulations (even it was negligible in some fermentations) along with the acetate and butyrate co-production but not with carbohydrates removal. At pH 7, 5% TS, and 1800 mg VSS/L, 49.5 NmL-H2/g VSfed and 976.4 NmL-H2/L-h were attained.

What Are the Oxidizing Intermediates in the Fenton and Fenton-like Reactions? A Perspective.

The Fenton and Fenton-like reactions are of major importance due to their role as a source of oxidative stress in all living systems and due to their use in advanced oxidation technologies. For many years, there has been a debate whether the reaction of FeII(H2O)62+ with H2O2 yields OH• radicals or FeIV=Oaq. It is now known that this reaction proceeds via the formation of the intermediate complex (H2O)5FeII(O2H)+/(H2O)5FeII(O2H2)2+ that decomposes to form either OH• radicals or FeIV=Oaq, depending on the pH of the medium. The intermediate complex might also directly oxidize a substrate present in the medium. In the presence of FeIIIaq, the complex FeIII(OOH)aq is formed. This complex reacts via FeII(H2O)62+ + FeIII(OOH)aq → FeIV=Oaq + FeIIIaq. In the presence of ligands, the process often observed is Ln(H2O)5-nFeII(O2H) → L•+ + Ln-1FeIIIaq. Thus, in the presence of small concentrations of HCO3- i.e., in biological systems and in advanced oxidation processes-the oxidizing radical formed is CO3•-. It is evident that, in the presence of other transition metal complexes and/or other ligands, other radicals might be formed. In complexes of the type Ln(H2O)5-nMIII/II(O2H-), the peroxide might oxidize the ligand L without oxidizing the central cation M. OH• radicals are evidently not often formed in Fenton or Fenton-like reactions.

pH-Dependent Photophysical Properties of Metallic Phase MoSe2 Quantum Dots.

Fluorescence properties of quantum dots (QDs) are critically affected by their redox states, which is important for practical applications. In this study, we investigated the optical properties of MoSe2-metallic phase quantum-dots (MoSe2-mQDs) depending on the pH variation, in which the MoSe2-mQDs were dispersed in water with two sizes (Φ~3 nm and 12 nm). The larger MoSe2-mQDs exhibited a large red-shift and broadening of photoluminescence (PL) peak with a constant UV absorption spectra as varying the pH, while the smaller ones showed a small red-shift and peak broadening, but discrete absorption bands in the acidic solution. The excitation wavelength-dependent photoluminescence shows that the PL properties of smaller MoSe2-mQDs are more sensitive to the pH change compared to those of larger ones. From the time-resolved PL spectroscopy, the excitons dominantly decaying with an energy of ~3 eV in pH 2 clearly show the shift of PL peak to the lower energy (~2.6 eV) as the pH increases to 7 and 11 in the smaller MoSe2-mQDs. On the other hand, in the larger MoSe2-mQDs, the exciton decay is less sensitive to the redox states compared to those of the smaller ones. This result shows that the pH variation is more critical to the change of photophysical properties than the size effect in MoSe2-mQDs.

Isolation and Characterization of Chicken Serum Albumin (Hen Egg Alpha-Livetin, Gal d 5).

Chicken serum albumin, i.e., hen egg alpha-livetin, is a recognized food allergen in chicken meat and hen eggs. Currently, there is no immunoassay available for its detection from food matrices. The characterization of chicken serum albumin-specific antibodies and the extraction of the target protein are essential for immunoassay development. One monoclonal antibody (mAb), 3H4, was used in this study due to its selectivity to a linear epitope on avian serum albumin. To study the extraction of chicken serum albumin, phosphate-buffered saline (PBS) with two additives, i.e., sodium dodecyl sulfate (SDS) and dithiothreitol (DTT), was used for its extraction from chicken blood plasma and hen egg yolk. SDS and DTT improved the chicken serum albumin's recovery and enhanced chicken serum albumin's immunodetection. In addition, chicken serum albumin retained the best solubility and immunoreactivity after heat treatment in a neutral condition. It experienced degradation and aggregation in acidic and alkaline conditions, respectively. Overall, PBS containing 0.1% SDS and 1 mM DTT (pH 7.2) was a better extraction buffer for chicken serum albumin. However, the complexity of the food matrix and elevated temperature could reduce its solubility and immunoreactivity.

Coagulation behavior of polyaluminum-titanium chloride composite coagulant with humic acid: A mechanism analysis.

The hydrolysate species of metal-based coagulants and the binding sites of humic acid (HA) are highly dependent on the pH conditions. Exploring the binding sites and modes between coagulant hydrolysates and HA molecules is critical to understanding the coagulation mechanism. In this paper, the binding behavior between HA molecules and the hydrolysates of a polyaluminum-titanium chloride composite coagulant (PATC) was investigated under different pH conditions by semi-quantitative FTIR and XPS. It was found that oligomeric and mesopolymeric hydrolysates were the dominant species under acid conditions, which could complex with the hydroxyl and carboxyl groups of HA by forming COAl/Ti coordinate bonds. However, large amounts of H+ could compete with Al3+ and weaken the removal efficiency of HA. With the increase of pH, the hydrolysis process of the PATC and the deprotonation of HA were simultaneously underway. Under weakly acid conditions, the complexation of the aluminum hydrolysates with carboxyl groups was improved due to the gradually diminishing competition of H+ and the enhanced charge neutralization of the further polymerized hydrolysates. Consequently, the maximum UV254 removal by adding PATC was observed at pH 6. Under alkaline conditions, the sweeping effect of amorphous hydroxide dominated the HA removals, which was accompanied by the surface complexation of Al/Ti nuclear with carboxyl groups as well as the hydrogen bonds between hydroxyl and hydroxide. This study provides a new clue for the interaction mechanisms between the hydrolysates of composite coagulants and the dominant functional groups of HA at various pH conditions.