Search

Acidic contaminants are one of the major pollutants that penetrate the soil through various pathways, such as breaking pipes, factory effluents, and chemical leakages. In this study, systematic static and cyclic simple shear tests were performed to explore the behavior of marine sands subjected to acidic conditions, considering the influences of the different cyclic stress ratios and acid erosion durations. The peak shear strength, pore pressure, deformation, stiffness degradation, damping ratio, and liquefaction resistance were investigated. Test results show that increasing the acid erosion duration causes an increase in the monotonic peak shear strength, a decrease in the rate of pore pressure build-up, and enhances the liquefaction resistance of marine sands. The liquefaction resistance of tested marine sands subjected to acid erosion is about 1-1.2 times greater than that of sands without acid erosion. On this basis, a modified model was established to predict the pore pressure generation of marine sands, and an assessment method of the liquefaction resistance suitable for marine sands that is independent of the acid erosion duration was obtained, providing an effective means for early evaluation of soil liquefaction in engineering practice. Furthermore, by carrying out an energy-based assessment of liquefaction behavior, a unique correlation between various cyclic behaviors and dissipated energy was revealed, indicating the potential applicability of the energy-based method for evaluating the characteristics of marine sands even under acidic conditions. [ABSTRACT FROM AUTHOR]

Electroreduction of CO2 into multi‐carbon (C2+) products (e.g. C2+ alcohols) offers a promising way for CO2 utilization. Use of strong alkaline electrolytes is favorable to producing C2+ products. However, CO2 can react with hydroxide to form carbonate/bicarbonate, which results in low carbon utilization efficiency and poor stability. Using acidic electrolyte is an efficient way to solve the problems, but it is a challenge to achieve high selectivity of C2+ products. Here we report that the amine modified copper nanoparticles exhibit high selectivity of C2+ products and carbon utilization at acidic condition. The Faradaic efficiency (FE) of C2+ products reach up to 81.8 % at acidic media (pH=2) with a total current density of 410 mA cm−2 over n‐butylamine modified Cu. Especially the FE of C2+ alcohols is 52.6 %, which is higher than those reported for CO2 electroreduction at acidic condition. In addition, the single‐pass carbon efficiency towards C2+ production reach up to 60 %. Detailed studies demonstrate that the amine molecule on the surface of Cu cannot only enhance the formation, adsorption and coverage of *CO, but also provide a hydrophobic environment, which result in the high selectivity of C2+ alcohols at acidic condition. [ABSTRACT FROM AUTHOR]

Vibrio fluvialis is an emerging foodborne pathogenic bacterium that can cause severe cholera-like diarrhea and various extraintestinal infections, posing challenges to public health and food safety worldwide. The arginine deiminase (ADI) pathway plays an important role in bacterial environmental adaptation and pathogenicity. However, the biological functions and regulatory mechanisms of the pathway in V. fluvialis remain unclear. In this study, we demonstrate that L-arginine upregulates the expression of the ADI gene cluster and promotes the growth of V. fluvialis. The ADI gene cluster, which we proved to be comprised of two operons, arcD and arcACB, significantly enhances the survival of V. fluvialis in acidic environments both in vitro (in culture medium and in macrophage) and in vivo (in mice). The mRNA level and reporter gene fusion analyses revealed that ArgR, a transcriptional factor, is necessary for the activation of both arcD and arcACB transcriptions. Bioinformatic analysis predicted the existence of multiple potential ArgR binding sites at the arcD and arcACB promoter regions that were further confirmed by electrophoretic mobility shift assay, DNase I footprinting, or point mutation analyses. Together, our study provides insights into the important role of the ArgR-ADI pathway in the survival of V. fluvialis under acidic conditions and the detailed molecular mechanism. These findings will deepen our understanding of how environmental changes and gene expression interact to facilitate bacterial adaptations and virulence. [ABSTRACT FROM AUTHOR]

Soil aggregate is the basic structural unit of soil, which is the foundation for supporting ecosystem functions, while its composition and stability is significantly affected by the external environment. This study was conducted to explore the effect of external environment (wetting-drying cycles and acidic conditions) on the soil aggregate distribution and stability and identify the key soil physicochemical factors that affect the soil aggregate stability. The yellow-brow soil from the Three Gorges Reservoir area (TGRA) was used, and 8 wetting-drying conditions (0, 1, 2, 3, 4, 5, 10 and 15 cycles) were simulated under 4 acidic conditions (pH = 3, 4, 5 and 7). The particle size distribution and soil aggregate stability were determined by wet sieving method, the contribution of environmental factors (acid condition, wetting-drying cycle and their combined action) to the soil aggregate stability was clarified and the key soil physicochemical factors that affect the soil aggregate stability under wetting-drying cycles and acidic conditions were determined by using the Pearson's correlation analysis, Partial least squares path modeling (PLS–PM) and multiple linear regression analysis. The results indicate that wetting-drying cycles and acidic conditions have significant effects on the stability of soil aggregates, the soil aggregate stability gradually decreases with increasing number of wetting-drying cycles and it obviously decreases with the increase of acidity. Moreover, the combination of wetting-drying cycles and acidic conditions aggravate the reduction in the soil aggregate stability. The wetting-drying cycles, acidic conditions and their combined effect imposes significant impact on the soil aggregate stability, and the wetting-drying cycles exert the greatest influence. The soil aggregate stability is significantly correlated with the pH, Ca2+, Mg2+, maximum disintegration index (MDI) and soil bulk density (SBD). The PLS–PM and multiple linear regression analysis further reveal that the soil aggregate stability is primarily influenced by SBD, Ca2+, and MDI. These results offer a scientific basis for understanding the soil aggregate breakdown mechanism and are helpful for clarifying the coupled effect of wetting-drying cycles and acid rain on terrestrial ecosystems in the TGRA. [ABSTRACT FROM AUTHOR]

Manganese (Mn2+) oxidation is an important phenomena in environmental and industrial processes. This study aims to shed light on the mechanism by which NaClO oxidizes Mn2+ to precipitate MnO2 in the presence of HCl. Experiments at pH = 1.5 indicated that the autocatalytic formation and the BET surface area of the MnO2 precipitates are influenced by NaClO addition speed, while further tests suggested that highly acidic conditions may promote the redissolution of the initial MnO2 crystals formed after oxidant addition. Based on these observations, a completely novel kinetic mechanism for Mn2+ oxidation with NaClO in HCl solutions was proposed. Namely: the formation of MnO2 crystal nuclei by direct oxidation, the formation of an intermediary of the MnO2•HOCl type, and the disappearance of said intermediary, which can take two competing reaction pathways. The first pathway is thought to be the autocatalytic formation of MnO2 which ultimately precipitates, whereas the second one is proposed to be the redissolution of MnO2 back into Mn2+. To validate the proposed mechanism, the experimental setup was modeled as a semi batch reactor with pulsed NaClO addition, and the ensuing system of ordinary differential equations (ODEs) was solved numerically, yielding a reasonable fitting with experimental data.

Smectites are reactive minerals that are present in surface environments. Most of the smectite dissolution kinetics reported in the literature are related to Al-rich smectites, whereas Fe(III)-rich smectites, which are commonly found in soils, have not been well studied. In this study, the impact of structural Fe(III) in smectites on the dissolution kinetics is determined under acidic conditions. The dissolution kinetics of three pure Fe(III)-rich smectites with different crystal chemistries (Si 7.16 Fe3+ 0.84)(Fe3+ 3.46 Mg 0.54)O 20 (OH) 4 Na 1.38 , (Si 6.86 Fe3+ 1.14)(Fe3+ 4)O 20 (OH) 4 Na 1.14 , and (Si 7.34 Fe3+ 0.66)(Fe3+ 4)O 20 (OH) 4 Na 0.66 are investigated at 25 °C using flow-through experiments at pH values between 1.8 and 5.5. The measured dissolution rates are compared with published rates for Al-rich smectites. The concentrations of dissolved Si, Fe and Mg are measured as a function of time, and the retrieved residual solids are analyzed via infrared spectroscopy and transmission electron microscopy. The steady-state dissolution rates of the synthetic smectites, calculated from the amount of Si release (R Si), decrease with increasing pH. A comparison of the dissolution rates as a function of pH does not allow us to observe major effects of the crystal chemistry among the synthetic smectites, demonstrating the need to develop another approach. However, the dissolution rates calculated for synthetic Fe(III)-rich smectites are systematically greater than those of Al-rich smectites. The measured dissolution rates decrease as the aqueous system approaches equilibrium. Different behaviors are observed for Fe(III)-rich (i.e., > 4 Fe(III)/O 20 (OH) 4) and Al-rich smectites as the R Si = f(ΔG) functions differ, with Fe(III)-rich smectites exhibiting greater instability than Al-rich smectites. Under the most acidic conditions investigated (pH 1.8 and 2), the crystal chemistry and mineralogy of the smectite changed during dissolution, with a relatively greater loss of tetrahedral Fe than of octahedral Fe and the formation of amorphous silica phases. These results show that the amount and location of structural Fe(III) in smectites impact the stability of the minerals. This suggests that the dissolution rate of smectites as a function of the ionic activity product classically used to describe reactive transport should consider the effects of the crystal chemistry, in particular, the amount of structural Fe(III), which is rather high, especially in soil smectites. [ABSTRACT FROM AUTHOR]

The variation of soluble soybean polysaccharides (SSPS) on pasting properties for wheat flour (WF) under acidic conditions was investigated, and its potential mechanisms were studied from the starch molecular structure changes. The SSPS decreased the pasting viscosity and elastic viscosity modulus of WF under acidic conditions and tightened the immobilized water located in the starch paste network. The ratio of 1047/1022 cm−1 and the relative crystallinity in the WF with SSPS under acidic conditions, compared with the WF sample, decreased from 0.6306 to 0.5672 and from 10.40 to 8.92%, respectively. The SSPS addition increased the thermal stability of WF under acidic conditions. This was agreed with the morphological structure characterization detected by scanning electron microscopy (SEM) and confocal laser scanning microscope (CLSM), which exhibited a more uniform structure in the sample of WF added with SSPS under acidic conditions (WF-SSPS-P). This study promoted a better understanding of the SSPS–starch interactions under acidic conditions in WF, which provided a way to enhance the quality of wheat flour-based products. [ABSTRACT FROM AUTHOR]

Streptococcus gordonii is associated with the formation of biofilms, especially those that comprise dental plaque. Notably, S. gordonii DL1 causes infective endocarditis (IE). Colonization of this bacterium requires a mechanism that can tolerate a drop in environmental pH by producing acid via its own sugar metabolism. The ability to survive acidic environmental conditions might allow the bacterium to establish vegetative colonization even in the endocardium due to inflammation-induced lowering of pH, increasing the risk of IE. At present, the mechanism by which S. gordonii DL1 survives under acidic conditions is not thoroughly elucidated. The present study was thus conducted to elucidate the mechanism(s) by which S. gordonii DL1 survives under acidic conditions. We analyzed dynamic changes in gene transcription and intracellular metabolites in S. gordonii DL1 exposed to acidic conditions, using transcriptome and metabolome analyses. Transcriptome analysis revealed upregulation of genes involved in heat shock response and glycolysis, and down regulation of genes involved in phosphotransferase systems and biosynthesis of amino acids. The most upregulated genes were a beta-strand repeat protein of unknown function (SGO_RS06325), followed by copper-translocating P-type ATPase (SGO_RS09470) and malic enzyme (SGO_RS01850). The latter two of these contribute to cytoplasmic alkalinization. S. gordonii mutant strains lacking each of these genes showed significantly reduced survival under acidic conditions. Metabolome analysis revealed that cytoplasmic levels of several amino acids were reduced. S. gordonii survives the acidic conditions by recovering the acidic cytoplasm using the various activities, which are regulated at the transcriptional level. • Transcriptome and metabolome analyses of S. gordonii DL1. • The acid tolerance mechanism of S. gordonii DL1 is similar to that of S. mutans. • Heat shock proteins- and glycolysis-related genes are upregulated under acidity. [ABSTRACT FROM AUTHOR]

The corrosion inhibition properties of Cuscuta reflexa (Amerbel) leaf extract as a green inhibitor for iron corrosion in hydrochloric acid were investigated using gravimetric and surface techniques. Results show that the extract's inhibition efficiency varied with concentration and temperature. The Langmuir adsorption isotherm model was followed, and the adsorption was physical and spontaneous. The studies suggest that Cuscuta reflexa extract exhibits great potential as a mild steel corrosion inhibitor in HCl environments. [ABSTRACT FROM AUTHOR]

Electrochemical lactate biosensors based on lactate oxidase (LOx) are used for diagnostics, sports medicine, and the food industry. However, samples from these sectors may have acidic levels at which the biocatalytic activity of LOx may be diminished. In this work, the enhancement of the bio‐electrocatalytic activity of LOx at low pH by pKa modulation of its catalytic His265 was studied by rational engineering of lactate oxidase from Aerococcus viridans (AvLOx). Several candidates based on interactions with His265 were selected by in silico structural analysis. The designed variants were heterologously produced, and the S175A mutant showed considerable improvement over its wild‐type counterpart, showing 157 % of the enzymatic activity found in the wild‐type at pH 5. Bioelectrodes were assembled based on Prussian‐blue‐modified carbon paper mediator system. The electrocatalytic performance of the amperometric biosensors of S175A variant at pH 5 exhibited a linear range of 0.2–2 mM measured at 0 V vs SCE, a sensitivity of −17.52 μA/mM ⋅ cm2, representing 240 % of the sensitivity found in the wild‐type biosensor, and a limit of detection of 38 μM, lower than observed with the wild‐type enzyme. These results show that the mutant obtained offers a significant improvement in lactate biosensing at low pH. [ABSTRACT FROM AUTHOR]

Engineering noble metal‐based electrocatalysts (NMEs) with high activity is of vital importance to accelerate the hydrogen production from proton exchange membrane water electrolyzers (PEMWEs). However, the poor stability and high price of NMEs greatly restrict the practical application. In this review, a series of strategies are summarized to boost the activity and reduce the cost of NMEs under acidic condition from the perspective of composition and structure optimization. The composition regulation through doping of metals or nonmetals can effectively inspire alloy effect or cocktail effect of NMEs, which provides an essential guidance to reduce the cost and enhance the stability of NMEs. Meanwhile, the structure optimization also directly improves the intrinsic activity of NMEs, which is comprehensively elaborated based on size, defect, and geometric effects. In addition, to extend the industrial application of PEMWEs, critical scientific issues behind the formulating of electrocatalyst slurry and coating method–PEMWEs performance relationships are fully clarified. Finally, the challenges for survivability of active center, catalytic mechanism research, and construction of membrane electrode are concluded. This review offers comprehensive and targeted guidelines for the rational design of NMEs for PEMWEs application. [ABSTRACT FROM AUTHOR]

Vibrio fluvialis is an emerging foodborne pathogenic bacterium that can cause severe cholera-like diarrhea and various extraintestinal infections, posing challenges to public health and food safety worldwide. The arginine deiminase (ADI) pathway plays an important role in bacterial environmental adaptation and pathogenicity. However, the biological functions and regulatory mechanisms of the pathway in V. fluvialis remain unclear. In this study, we demonstrate that L-arginine upregulates the expression of the ADI gene cluster and promotes the growth of V. fluvialis. The ADI gene cluster, which we proved to be comprised of two operons, arcD and arcACB, significantly enhances the survival of V. fluvialis in acidic environments both in vitro (in culture medium and in macrophage) and in vivo (in mice). The mRNA level and reporter gene fusion analyses revealed that ArgR, a transcriptional factor, is necessary for the activation of both arcD and arcACB transcriptions. Bioinformatic analysis predicted the existence of multiple potential ArgR binding sites at the arcD and arcACB promoter regions that were further confirmed by electrophoretic mobility shift assay, DNase I footprinting, or point mutation analyses. Together, our study provides insights into the important role of the ArgR-ADI pathway in the survival of V. fluvialis under acidic conditions and the detailed molecular mechanism. These findings will deepen our understanding of how environmental changes and gene expression interact to facilitate bacterial adaptations and virulence.

Abstract Electrochemical lactate biosensors based on lactate oxidase (LOx) are used for diagnostics, sports medicine, and the food industry. However, samples from these sectors may have acidic levels at which the biocatalytic activity of LOx may be diminished. In this work, the enhancement of the bio‐electrocatalytic activity of LOx at low pH by pKa modulation of its catalytic His265 was studied by rational engineering of lactate oxidase from Aerococcus viridans (AvLOx). Several candidates based on interactions with His265 were selected by in silico structural analysis. The designed variants were heterologously produced, and the S175A mutant showed considerable improvement over its wild‐type counterpart, showing 157 % of the enzymatic activity found in the wild‐type at pH 5. Bioelectrodes were assembled based on Prussian‐blue‐modified carbon paper mediator system. The electrocatalytic performance of the amperometric biosensors of S175A variant at pH 5 exhibited a linear range of 0.2–2 mM measured at 0 V vs SCE, a sensitivity of −17.52 μA/mM ⋅ cm2, representing 240 % of the sensitivity found in the wild‐type biosensor, and a limit of detection of 38 μM, lower than observed with the wild‐type enzyme. These results show that the mutant obtained offers a significant improvement in lactate biosensing at low pH.

Engineering noble metal‐based electrocatalysts (NMEs) with high activity is of vital importance to accelerate the hydrogen production from proton exchange membrane water electrolyzers (PEMWEs). However, the poor stability and high price of NMEs greatly restrict the practical application. In this review, a series of strategies are summarized to boost the activity and reduce the cost of NMEs under acidic condition from the perspective of composition and structure optimization. The composition regulation through doping of metals or nonmetals can effectively inspire alloy effect or cocktail effect of NMEs, which provides an essential guidance to reduce the cost and enhance the stability of NMEs. Meanwhile, the structure optimization also directly improves the intrinsic activity of NMEs, which is comprehensively elaborated based on size, defect, and geometric effects. In addition, to extend the industrial application of PEMWEs, critical scientific issues behind the formulating of electrocatalyst slurry and coating method–PEMWEs performance relationships are fully clarified. Finally, the challenges for survivability of active center, catalytic mechanism research, and construction of membrane electrode are concluded. This review offers comprehensive and targeted guidelines for the rational design of NMEs for PEMWEs application.

This work examines the transformation of iron-bearing precursors to jarosite-like minerals in the absence of bacteria or other organic compounds. The composition of the aqueous solution determines the transformation, through which crystallinity and long-term stability ofjarosite increase, whereas the temperature of the environment affects the kinetics of the process. Spectroscopic techniques (FTIR and XPS) were used to characterize the chemical species present on the transformed mineral surfaces. Schwertmannite is the first phase to precipitate as a result of homogeneous nucleation and growth in the bulk of the supersaturated solution. This metastable phase transforms into a crystalline Na-rich member of the (Na,H30)Fe3(S04)(0H)6 solid-solution family after aging for either 3 h at 70 °C or 1 day at 20 °C. XRD analyses show that the crystallinity of natrojarosite increases progressively with reaction time, although its cell parameters and crystallite size remain nearly constant during aging, which reveals the stability of the crystal structure of this secondary phase. Interestingly, the mechanisms governing the transformation from aggregates of schwertmannite into natrojarosite crystals consist of interface-coupled dissolution-precipitation reactions that involve an internal structural reorganization within the individual nanoparticles of the secondary phase, in which Fe3+ is transferred from the solid to the solution while S04-, 0H-, and Na+ move in the opposite direction. The spectroscopic study confirms the mineralogical results and suggests that the crystal structure of jarosite-like minerals may offer interesting geochemical information about the aqueous solutions where they were formed. The transformation kinetics and the apparent activation energy (Ea = 52.1 kJ/mol) of the transformation were estimated using the so-called "time to a given fraction" method, and a temperature-transformation-time (TTT) diagram was established in the range 20-70 °C to define the reaction pathways during the process. [ABSTRACT FROM AUTHOR]

Abstract Background D-allulose, a hexulose monosaccharide with low calorie content and high sweetness, is commonly used as a functional sugar in food and nutrition. However, enzyme preparation of D-allulose from D-frutose was severely hindered by the non-enzymatic browning under alkaline and high-temperature, and the unnecessary by-products further increased the difficulties in separation and extraction for industrial applications. Here, to address the above issue during the production process, a tandem D-allulose 3-epimerase (DPEases) isomerase synergistic expression strategy and an auto-inducible promoter engineering were levered in Bacillus subtilis 168 (Bs168) for efficient synthesis of D-allulose under the acidic conditions without browning. Results First, based on the dicistron expression system, two DPEases with complementary functional characteristics from Dorea sp. CAG:317 (DSdpe) and Clostridium cellulolyticum H10 (RCdpe) were expressed in tandem under the promoter HpaII in one cell. A better potential strain Bs168/pMA5-DSdpe-RCdpe increases enzyme activity to 18.9 U/mL at acidic conditions (pH 6.5), much higher than 17.2 and 16.7 U/mL of Bs168/pMA5-DSdpe and Bs168/pMA5-RCdpe, respectively. Subsequently, six recombinant strains based on four constitutive promoters were constructed in variable expression cassettes for improving the expression level of protein. Among those engineered strains, Bs168/pMA5-PspoVG-DSdpe-PsrfA-RCdpe exhibited the highest enzyme activity with 480.1 U/mL on fed-batch fermentation process in a 5 L fermenter at pH 6.5, about 2.1-times higher than the 228.5 U/mL of flask fermentation. Finally, the maximum yield of D-allulose reached as high as 163.5 g/L at the fructose concentration (50% w/v) by whole-cell biocatalyst. Conclusion In this work, the engineered recombinant strain Bs168/pMA5-PspoVG-DSdpe-PsrfA-RCdpe was demonstrated as an effective microbial cell factory for the high-efficient synthesis of D-allulose without browning under acidic conditions. Based on the perspectives from this research, this strategy presented here also made it possible to meet the requirements of the industrial hyper-production of other rare sugars under more acidic conditions in theory.

In an acidic environment, the mineral components in rock begin to break down. As a result, the microstructure will be damaged, and then the mechanical properties will deteriorate, which will eventually have a negative effect on engineering stability. In order to study acid damage's effect on this kind of rock, limestone samples were acidified for 0 days, 5 days, 10 days, 15 days, and 20 days. The microstructure changes in the limestone after acidification were studied via the wave velocity test and electron microscope scanning, and the damage deterioration mechanism was revealed. The results show that the acoustic signal of acidified samples has an obvious absorption effect at high frequency, and the surface pore structure of acidified samples shows fractal characteristics. The P-wave velocity, main peak amplitude, and fractal dimension of the acidified samples did not gradually decrease with time; however, there was a short-term strengthening phenomenon during immersion, which was mainly caused by the formation of CaSO4 crystals. [ABSTRACT FROM AUTHOR]

Aiming to design a catalyst for stable electrooxidation of water at low pH, the present work explores the properties and structural features of electrodeposited composite oxides based on Bi and Co, which were anticipated to provide stability and catalytical activity, respectively. Materials deposited as very thin (ca 50 nm) films on F‐doped SnO2 (FTO) substrate do not initially exhibit high activity in 0.1 M H2SO4, but are activated during operation through the electrooxidatively‐induced enrichment of the catalytic surface with Co and Sn oxides. The latter originate from the FTO support and are identified as an important component of the catalyst through control experiments with a Sn‐free substrate and with Sn2+ intentionally added at the electrodeposition stage. A distinctive feature of the Co−Bi−Sn‐based electrocatalyst is the slow but persistent improvement in the activity during operation in 0.1 M H2SO4 at both ambient and elevated (60 °C) temperatures, which contrasts with the continuously degrading behaviour of state‐of‐the‐art oxygen evolution catalysts at low pH. This is demonstrated by 9‐day‐long galvanostatic tests at 10 mA cm−2, during which the Co−Bi−Sn‐based thin film catalyst shows no degradation and sustains stable water oxidation at ca 1.9 V vs. reversible hydrogen electrode. The effects of tin leaching from the support detected herein might have implications to other acidic water oxidation catalysts supported on high‐surface area doped SnO2 materials. [ABSTRACT FROM AUTHOR]

Fast and real-time detection of trace Hg(Ⅱ) by fluorescent probes under acidic conditions is urgently required due to the high toxicity and accessibility to creatures and human being. However, fluorescent probes for Hg(Ⅱ) detection in environmental samples are rarely reported due to the protonation potential of acidic mercury sources. In this study, the SD probe was developed by 5-(p-dimethylaminobenzylidene) rhodanine (DMABR) loaded on sepiolite by hydrothermal treatment, and showed excellent Hg(Ⅱ) detection performances for mercury sources at pH 4–10 due to buffering ability of the hyperconjugated lactam rings. Sepiolite functioned as the support skeleton to decrease intermolecular transition, and thus increased the sensitivity. At pH 4, the SD probe showed high selectivity and sensitivity for Hg(Ⅱ) among various species, with low LOD and binding constant of 4.78 × 10−9 M and 1.34 × 106 M−1, respectively. Through DFT calculations, MAS 1H NMR and 2D-COS analysis, the detection mechanism was demonstrated as S N1 substitution of the spontaneous leaving H on amino groups in the transient state during tautomeric equilibrium, rather than the expected high-affinity sulphydryl. Additionally, the SD probe exhibited promising potential in quantifying water-soluble and bioavailable Hg(Ⅱ) in acidic polluted soil and water samples. Moreover, real-time detection was realized by paper-based strips. [Display omitted] • The SD probe exhibited excellent performance in Hg(Ⅱ) detection pH 4-10. • Bioavailable Hg(Ⅱ) in soil and water samples was accurately detected by SD probe. • Real-time detection of Hg(Ⅱ) by SD probe was achieved by paper-based strips. • pH-induced tautomeric equilibrium posed the mechanism as S N1 substitution on N-H. [ABSTRACT FROM AUTHOR]

Background: D-allulose, a hexulose monosaccharide with low calorie content and high sweetness, is commonly used as a functional sugar in food and nutrition. However, enzyme preparation of D-allulose from D-frutose was severely hindered by the non-enzymatic browning under alkaline and high-temperature, and the unnecessary by-products further increased the difficulties in separation and extraction for industrial applications. Here, to address the above issue during the production process, a tandem D-allulose 3-epimerase (DPEases) isomerase synergistic expression strategy and an auto-inducible promoter engineering were levered in Bacillus subtilis 168 (Bs168) for efficient synthesis of D-allulose under the acidic conditions without browning. Results: First, based on the dicistron expression system, two DPEases with complementary functional characteristics from Dorea sp. CAG:317 (DSdpe) and Clostridium cellulolyticum H10 (RCdpe) were expressed in tandem under the promoter HpaII in one cell. A better potential strain Bs168/pMA5-DSdpe-RCdpe increases enzyme activity to 18.9 U/mL at acidic conditions (pH 6.5), much higher than 17.2 and 16.7 U/mL of Bs168/pMA5-DSdpe and Bs168/pMA5-RCdpe, respectively. Subsequently, six recombinant strains based on four constitutive promoters were constructed in variable expression cassettes for improving the expression level of protein. Among those engineered strains, Bs168/pMA5-PspoVG-DSdpe-PsrfA-RCdpe exhibited the highest enzyme activity with 480.1 U/mL on fed-batch fermentation process in a 5 L fermenter at pH 6.5, about 2.1-times higher than the 228.5 U/mL of flask fermentation. Finally, the maximum yield of D-allulose reached as high as 163.5 g/L at the fructose concentration (50% w/v) by whole-cell biocatalyst. Conclusion: In this work, the engineered recombinant strain Bs168/pMA5-PspoVG-DSdpe-PsrfA-RCdpe was demonstrated as an effective microbial cell factory for the high-efficient synthesis of D-allulose without browning under acidic conditions. Based on the perspectives from this research, this strategy presented here also made it possible to meet the requirements of the industrial hyper-production of other rare sugars under more acidic conditions in theory. [ABSTRACT FROM AUTHOR]

Acidic oxygen reduction is vital for renewable energy devices such as fuel cells. However, many aspects of the catalytic process are still uncertain—especially the large difference in activity in acidic and alkaline media. Thus, the design and synthesis of model catalysts to determine the active centers and the inactivation mechanism are urgently needed. We report a pyrolysis‐free synthesis route to fabricate a catalyst (CPF‐Fe@NG) for oxygen reduction in acidic conditions. By introducing a deprotonation process, we extended the oxygen reduction reaction (ORR) activity from alkaline to acidic conditions. CPF‐Fe@NG demonstrated outstanding performance with a half‐wave potential of 853 mV (vs. RHE) and good stability after 10000 cycles in 1 M HClO4. The pyrolysis‐free route could also be used to assemble fuel cells, with a maximum power density of 126 mW cm−2. Our findings offer new insights into the ORR process to optimize catalysts for both mechanistic studies and practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Mining Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O 2 − during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (∼56 μmol g−1 h−1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition. [Display omitted] • Bifunctional CN with K, S co-doping is synthesized via a facile calcination process. • Acidic cellobiose photoreforming to simultaneously obtain gluconic acid and syngas. • Cellobiose conversion (>80%) and gluconic acid selectivity (>70%) can be achieved. • Favorable generation of •O 2 − proved by DFT is essential for gluconic acid production. [ABSTRACT FROM AUTHOR]

This article overviews the acylation methods of α-chitin developed over the last four decades. The acylation of polysaccharides has been identified as a useful approach for conferring properties such as thermoplasticity. Owing to the poor solubility of α-chitin, its acylation using acid anhydrides and acyl chlorides has been traditionally investigated under heterogeneous conditions in strong acidic media. Although chitin chains depolymerize under acidic conditions, the resultant derivatives exhibit certain properties and functions. Solvents, such as LiCl/ N , N -dimethyladcetamide, ionic liquids, and deep eutectic solvents, are suitable for α-chitin dissolution; therefore, acylation methods for α-chitin under homogeneous conditions have been developed using these solvents as reaction media. The functional materialization of the resultant derivatives was achieved by introducing appropriate substituents and controlling their ratios. [ABSTRACT FROM AUTHOR]

Utilization of lignin-rich side streams has been a focus of intensive studies recently. Combining biocatalytic methods with chemical treatments is a promising approach for sustainable modification of lignocellulosic waste streams. Laccases are catalysts in lignin biodegradation with proven applicability in industrial scale. Laccases directly oxidize lignin phenolic components, and their functional range can be expanded using low-molecular-weight compounds as mediators to include non-phenolic lignin structures. In this work, we studied in detail recombinant laccases from the selectively lignin-degrading white-rot fungus Obba rivulosa for their properties and evaluated their potential as industrial biocatalysts for the modification of wood lignin and lignin-like compounds. We screened and optimized various laccase mediator systems (LMSs) using lignin model compounds and applied the optimized reaction conditions to biorefinery-sourced technical lignin. In the presence of both N–OH-type and phenolic mediators, the O. rivulosa laccases were shown to selectively oxidize lignin in acidic reaction conditions, where a cosolvent is needed to enhance lignin solubility. In comparison to catalytic iron(III)–(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) oxidation systems, the syringyl-type lignin units were preferred in mediated biocatalytic oxidation systems.

Proteolytic enzymes are used for proteolysis and peptide synthesis which can be run in various conditions including low pH value and the presence of ethanol. The most common cysteine protease applied in acidic–alcoholic conditions is well-characterized papain. Ficin, which is closely related to papain in terms of proteolytic activity and substrate specificity, could potentially be applied in the alcoholic beverage industry and peptide synthesis. The aim of this study was to compare papain and ficin stability in process conditions. Comparative stability study showed that ficin as a mixture of different isoforms has a broader range of stability in respect of pH and cold storage stability, in comparison to papain. It retains about 70% of initial activity after 3-week cold storage at low pH and in the presence of ethanol. Unlike ficin, papain loses about 70% of initial activity in the same incubation period as it is more prone to non-native aggregation that was confirmed by FTIR analysis. The presence of multiple isoforms of ficin stabilizes the protease against cold denaturation and aggregation, making it more suitable for biotechnological and laboratory usage than single papain isoform. It is more cold-stable in alcoholic–acidic and acidic conditions suggesting possible replacement of papain with even lower enzyme concentration. [ABSTRACT FROM AUTHOR]

Efficient, earth‐abundant, and acid‐stable catalysts for the oxygen evolution reaction (OER) are missing pieces for the production of hydrogen via water electrolysis. Here, we report how the limitations on the stability of 3d‐metal materials can be overcome by the spectroscopic identification of stable potential windows in which the OER can be catalyzed efficiently while simultaneously suppressing deactivation pathways. We demonstrate the benefits of this approach using gamma manganese oxide (γ‐MnO2), which shows no signs of deactivation even after 8000 h of electrolysis at a pH of 2. This stability is vastly superior to existing acid‐stable 3d‐metal OER catalysts, but cannot be realized if there is a deviation as small as 50‐mV from the stable potential window. A stable voltage efficiency of over 70 % in a polymer–electrolyte membrane (PEM) electrolyzer further verifies the availability of this approach and showcases how materials previously perceived to be unstable may have potential application for water electrolysis in an acidic environment. Window of opportunity: Spectroscopic measurements allowed the identification of a stable potential window in which γ‐MnO2 is able to catalyze the oxygen evolution reaction under acidic conditions for more than 8000 hours. This shows how the limitations on the stability of 3d‐metal materials acting as electrocatalysts can be overcome. [ABSTRACT FROM AUTHOR]

Abstract This work aims to compare the use of olive mill solid waste as substrate in pH-controlled fermentation at acid (pH = 5), neutral (uncontrolled, pH ≈ 7) and alkaline (pH = 9) operating pH levels. The results obtained in this study indicate that operating pH strongly affected the anaerobic microorganisms and, hence, different target compounds could be obtained by adjusting the operating pH. Fermentation at neutral pH resulted in the conversion of 93.5% of the fed chemical oxygen demand to methane. However, fermentations at pH 5 and 9 resulted in the inhibition of the methanogenic activity. At pH 9, volatile fatty acids reached a maximum concentration of 3.69 g O 2 /L, where acetic acid represented up to 79.3% of the total volatile fatty acids. Unlike volatile fatty acid production, an optimal operation of fermentation at pH 5 could allow the recovery of phenols such as vanillin. Graphical abstract Unlabelled Image Highlights • Olive mill solid waste was fermented at acidic, neutral and alkaline conditions. • More than 90% of the organic matter was biomethanized at neutral pH. • Volatile fatty acids reached a maximum concentration of 3.69 g COD/L at pH 9. • The highest phenolic compounds accumulation occurred at pH 5. [ABSTRACT FROM AUTHOR]

In previous experiments that simulated conditions on primordial volcanic islands, we demonstrated the abiotic formation of hydrophobic porphyrins. The present study focused on the question whether such porphyrins can be metalated by prebiotically plausible metal ion sources. We used water-insoluble octaethylporphyrin (H2oep) as a model compound. Experiments were conducted in a nitrogen atmosphere under cyclic wet–dry conditions in order to simulate the fluctuating environment in prebiotic rock pools. Wetting–drying proved to be a crucial factor. Significant yields of the metalloporphyrins (20–78% with respect to H2oep) were obtained from the soluble salts MCl2 (M = Mg, Fe, Co, Ni and Cu) in freshwater. Even almost insoluble minerals and rocks metalated the porphyrin. Basalt (an iron source, 11% yield), synthetic jaipurite (CoS, 33%) and synthetic covellite (CuS, 57%) were most efficient. Basalt, magnetite and FeCl2 gave considerably higher yields in artificial seawater than in freshwater. From iron sources, the highest yields, however, were obtained in an acidic medium (hydrochloric acid with an initial pH of 2.1). Under these conditions, iron meteorites also metalated the porphyrin. Acidic conditions were considered because they are known to occur during eruptions on volcanic islands. Octaethylporphyrinatomagnesium(II) did not form in acidic medium and was unstable towards dissolved Fe2+. It is therefore questionable whether magnesium porphyrins, i.e. possible ancestors of chlorophyll, could have accumulated in primordial rock pools. However, abiotically formed ancestors of the modern cofactors heme (Fe), B12 (Co), and F430 (Ni) may have been available to hypothetical protometabolisms and early organisms. [ABSTRACT FROM AUTHOR]

This article, published in ChemElectroChem, discusses the development of bioengineered lactate oxidase mutants for use in biosensors that detect lactate in sweat. The mutants were designed to have improved catalytic activity and electrochemical response at low pH. Through in silico analysis, the researchers found that the S175A variant exhibited 240% higher sensitivity than the wild-type biosensor at pH 5. This research has potential applications in the field of biosensing and could contribute to advancements in healthcare and sports performance monitoring. [Extracted from the article]

This comprehensive study summarizes kinetic data from experiments performed over a wide temperature range that overlaps the physiological operating temperature windows for most mesophilic Fe-oxidizers. Three acidophilic autotrophic bacterial strains Acidithiobacillus (At.) ferrivorans, At. ferrooxidans and Leptospirillum (L.) ferriphilum were investigated in this work in order to compare their growth and iron oxidation kinetics over a temperature range of 5–45 °C. On-line gas analysis was applied to determine the O 2 and CO 2 consumption rates during the culture incubation. Despite the genotypic differences these three strains share many common physiological traits. At t = 30 °C, the specific growth rate (μ) at all three species reached 0.11 h−1 which is equivalent to generation time 6.5 h. Maximum ferrous‑iron oxidation rate per unit of biomass was achieved with L. ferriphilum at t = 40 °C and approached 10 mmol Fe2+ (C-mmol) h−1. The temperature of incubation had a profound effect on the specific rates, while the kinetic parameter Ks / Ki at the Acidithiobacilli strains remained unaffected. Cultures with Leptospirillum incubated at temperatures >35 °C were capable of iron oxidation at redox potentials close to +950 mV and kept constant specific rates until Fe2+ depletion. The parameter Ks/Ki at L. ferriphilum was two order of magnitude lower than for the Acidithiobacilli. However, this feature disappears at temperatures below 30 °C, where Ks / Ki has a value comparable to Acidithiobacilli , which suggests that L. ferriphillum uses different Fe oxidation systems depending on temperature conditions. Strong correlation was observed between ferrous iron oxidation, and carbon dioxide fixation in the exponentially growing cultures with the yield coefficient (Y SX) approaching 14 μmol C fixed per mmol Fe2+ oxidized. The kinetic parameters differed significantly between bacterial strains under "extreme" temperatures (t < 10 °C; t > 35 °C). All three bacterial strains were capable of oxidizing iron over the entire range (5–45 °C) of incubation temperatures. Neither At. ferrivorans nor At. ferrooxidans showed exponential growth at the temperature 40 °C. Bacterial iron oxidation not associated with growth was observed during incubation at 5 °C. At. ferrivorans , was the only species that can grow exponentially at a temperature of 5 °C. Moreover, it differed from the other species by greater sensitivity to low pH which seems to be more pronounced at temperatures t < 10 °C, with minimum of pH 1.9 for growth. • Bacteria oxidized Fe2+ to Fe3+ in the temperature range of 5–45 °C. • Significant differences in growth and Fe2+ oxidation rate at t < 10 °C, t > 30 °C. • A. ferrivorans showed exponential growth at 5 °C, pH > 1.9, sensitivity to low pH. • Bacterial Fe2+ oxidation not associated with cell growth at suboptimal temperatures. • L. ferriphilum manifest different Fe oxidation systems depending on the temperature. [ABSTRACT FROM AUTHOR]

The development of antibiotic resistance among hospital pathogens has provided a great need for new antimicrobial agents. Zinc oxide nanoparticles (ZnO NPs) in combination with various antibiotics can act as a reducing agent for antibiotic resistance. The aim of this study was to investigate the influence and the mechanism of ZnO NPs on the antimicrobial activity of ciprofloxacin (CP) and ceftazidime (CAZ) against Enterococcus faecalis (E. faecalis) and Acinetobacter baumannii (A. baumannii) bacteria in acidic conditions (pH 5.5). ZnO NPs were synthesised using the solvothermal method and characterised. The MIC90 value of ZnO NPs against A. baumannii was 0.25 mg ml−1 and its highest growth‐inhibitory activity was observed at 0.125 mg ml−1 for E. faecalis. The Fourier transform infrared spectroscopy spectra of ZnO NPs treated with antibiotics showed the interaction between ZnO NPs and each of the two antibiotics. ZnO NPs at a sub‐inhibitory concentration had no effect on the antibacterial activity of CP and CAZ against E. faecalis and CP against A. baumannii. The action mechanism of ZnO NPs for enhancing the antibacterial efficacy of CAZ against A. baumannii was evaluated. ZnO NPs caused to increase in the antibacterial activity of CAZ against A. baumannii, possibly through the release of Zn2+ and increasing of membrane permeability. [ABSTRACT FROM AUTHOR]

Ammonium nitrate (AN) can decompose and further detonate under some conditions, e.g., in the presence of impurities which act as promoters. Its reactive hazards have been widely studied for several years. However, many large accidents involving AN still happened frequently in the recent years. It is found that, for accidents in storage or transportation, the thermal runaway is a major factor. The main objective of the research is to examine the effect of potassium chloride (KCl) on the thermal stability of AN under acidic conditions. The thermal stability of samples was investigated by differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), the Cook-off test and the Dewar test. The results indicate that KCl can significantly reduce the thermal stability of AN under acidic conditions. The catalytic effect of KCl on the decomposition of AN is limited without acidic conditions. The scale effect also is important factor to influence the thermal stability of AN. [ABSTRACT FROM AUTHOR]

Anaerobic digestion and bioelectrochemical systems have great potential to recover energy from waste streams and help overcome common hurdles associated with this process, as integrated technologies. In this study, the benefit of integrating an electrogen-enriched bioanode in a batch anaerobic digester was explored under ambient temperature conditions associated with organic overloading and reactor acidity. An increase in CH4 production was observed in the electrode-containing reactors (0.56 L CH4 kgVS-1 h-1) in comparison with the conventional anaerobic digester (0.14 L CH4 kgVS-1 h-1) during the initial stages of operation. In addition, the mere presence of electrodes operating in open circuit mode resulted in a delay in volatile fatty acid (VFA) build-up. This seems to be associated with the enhancement in VFA consumption due to biomass proliferation on the electrode surface, rather than on electrochemical activity. [ABSTRACT FROM AUTHOR]

Mounting evidence suggests that amphibians are globally and currently the most threatened group of vertebrates and different causes might be responsible for this phenomenon. Acidification of water bodies is a global environmental issue that has been proposed as a possible cause for amphibian populations decline. Indeed, it has been widely demonstrated that low pH may exert harmful effects on amphibians, either directly or by increasing the adverse effects of other stressors. Surprisingly only few studies documented the response of amphibian integument to acidic pH conditions and no data are available on the effects of a non-lethal level of pH onto the amphibian larval epidermis. The present study showed that acidic pH (4.5) condition has severe effects on the epidermis of the Italian newt ( Lissotriton italicus , formerly Triturus italicus ) inducing both morphological and functional alterations. The increase of mucus is the first evident effect of acid injury, followed by the flattening of the epithelium and the appearance of a keratinized shedding layer. The immunolabeling of cytokeratins substantially changes acquiring an adult-like pattern. Also aquaporin 3 and iNOS expression modify their distribution according to a change of the histological features of the epidermis. These results clearly indicate that a short-term exposure to a sub-lethal pH disrupts the epidermis morphology and function in L. italicus larvae. Since the skin exerts a prominent role in both respiration and osmoregulation, the described alterations may adversely affect the overall ionic balance, with a long chain of cascading effects significantly decreasing newts survival probabilities when environmental pH lowering occurs. [ABSTRACT FROM AUTHOR]

Development of first-row transition-metal-based catalysts for oxygen evolution is a desirable goal due to the low cost and abundance of transition metals, relative to iridium. However, low stability of first-row transition metal catalysts in acidic electrolytes has impeded practical application. In this work, we proposed the role of Sb in metal oxide which enhance electrochemical stability in acid media. While a Co-Fe mixed oxide exhibited poor stability in acid, a FeCoSbO x electrode demonstrate superior stability of over 70 h under the same conditions. In-situ/Operando analysis results suggest that distortion occurred in the FeCoO x electrode under acidic conditions for oxygen evolution, while the structure of the FeCoSbO x electrode was maintained. As compared to an SbO x electrode, Sb in an FeCoSbO x electrode had a higher oxidation state and shorter lattice distance, indicating strong Sb-O bonding. Given the stronger oxide bond, we anticipated that incorporation of Sb would enhance stability in acidic media not only via greater thermodynamic stability but by inhibiting distortion during the reaction. A more stable structure prevents participation by lattice oxygen, resulting in enhanced electrode stability. This demonstration of a stabilizing structural element in a transition metal oxide offers new principles for designing electrocatalysts that are stable in acidic media. [Display omitted] • Mixed transition metal oxide electrodes were prepared by dip coating and heat treatment. • Sb incorporated CoFe oxides electrodes shows good stability for OER in acid media. • Distortion occurred in the FeCoO x electrode under acidic conditions for OER. • Structure of the FeCoSbO x electrode was maintained for OER in acidic media. • Strong Sb O bond prevents participation by lattice oxygen, resulting enhanced stability. [ABSTRACT FROM AUTHOR]

Aluminium (Al) is one of the major stressors for plants in acidic soils, negatively affecting plant growth and nutrient balances. Significant efforts have been undertaken to understand mechanisms of Al tolerance in plants. However, little is known of the relevance of iron (Fe) and silicon (Si) nutrition under Al stress conditions. The objectives of this study were to determine whether effects induced by Fe and Si are of importance for limitation of Al moving via xylem in plants ( Cucumis sativus L.). Cucumber plants (cv. Phoenix and Solovei) were grown (i) hydroponically in a complete nutrient solution at pH 4.0, either with (+Fe) or in Fe-free (−Fe) nutrient solution, without (−Si) or with (+Si) supply of Si, without (−Al) or with (+Al) exposure of Al and (ii) in soil. Xylem sap concentrations of Al, Fe and Si were measured. To characterise the pattern of xylem sap transport of Al and Fe, metabolomic changes of root tissues were investigated. Although the growth of cucumber plants was not significantly affected by Al 3+ (Al-tolerant), Al exposure decreased xylem sap Fe (+Fe plants) and increased ferric chelate reductase (FC-R) activity of roots (−Fe plants). On the other hand, Fe supply greatly mitigated the Al-induced increase in xylem sap Al. The ameliorative effect of Fe depended on plant genotypes and was more pronounced in the more Fe-efficient cultivar Phoenix, which presented the highest level of xylem sap Fe. Xylem sap Fe was positively correlated with root serine, succinic and fumaric acids, suggesting that a probable underlying mechanism of Al tolerance might involve the chelation of Fe by biosynthesis of these chelating compounds. The Si-modulated root succinate increase appears to be of great importance for facilitating long-distance transport of Fe, thereby hindering Al transport from roots to shoots. The results highlight for the first time the importance of both Fe and Si supply in plant exclusion of Al under acidic conditions. [ABSTRACT FROM AUTHOR]

The presence of swelling clay minerals, such as smectites, is known to be one of the main parameters controlling the mobility of radium in natural environments due to the high adsorption capacities of these materials. However, experimental data and modeling from literature allowing to investigate the adsorption properties of radium towards smectite in a wide range of acidic conditions (2 < 7) are scarce. Moreover, the role of the smectite crystal chemistry (charge location in the layer) remains unclear. Therefore, experimental data for the adsorption of radium onto a swelling clay mineral with a tetrahedral charge (beidellite) are presented here in the 2–7 pH range. Different batch experiments were conducted in order to investigate the effects of both ionic strength (i.e., from 0.027 to 0.11 M in sodium chloride medium) and presence of competing major cations (i.e., magnesium). Experimental data were interpreted using a multi-site ion-exchange model that takes into account the adsorption of major cations (including H + ), which usually compete with trace elements for sorption onto mineral surfaces in natural environments. The ability of the proposed model to predict experimental distribution coefficient (K d ) values under various conditions of ionic strength and aqueous cation compositions was tested, and results were compared with those obtained using previously published models. The evolution of radium adsorption on beidellite with pH variation is better reproduced by using a multi-site ion-exchange model, as proposed in this study, than by using a single-site model as that reported in literature. Finally, the implication of the results obtained in this study for the mobility of radium in natural environments was discussed. The significant role of smectites in the adsorption of radium at low pH conditions (pH ≤ 6) in complex mixtures, which are representative of natural matrices, was demonstrated based on comparison with experimental data previously obtained on organic material and Fe(III)-oxy/hydroxides. The multi-site model proposed in this study for beidellite, coupled with a model from literature for organic matter, was applied in order to predict the role played by the beidellite in the adsorption properties of a virtual complex mixture containing various proportions of beidellite and organic matter. The model shows that smectite can contribute from 80 to 100% to the total adsorption of radium of the complex mixture for pH < 3. Moreover, the predicted results were in good agreement with experimental data from literature obtained with natural peat. Finally, the multi-site ion-exchange model proposed in this study for beidellite could be applied in many natural environments characterized by acidic pH, such as naturally acidic soils (pH ≤ 5) and acid mining environments (pH ≤ 1), where predicting 226 Ra exchange onto swelling clay minerals requires accounting for the effects of the major cations present in these systems. [ABSTRACT FROM AUTHOR]

In this work, the effect of the usual acidic conditions of dry-cured fermented foods (pH values between 4.5 and 6), on the growth and expression of the virulence genes, hly and inlA , of Listeria monocytogenes serotype 4b, was evaluated. To analyse the expression of the inlA gene, a novel real-time PCR (qPCR) method using SYBR® Green methodology was developed. L. monocytogenes levels increased as the pH did and they were kept constant throughout incubation time at pH 4.5. However, a significant increase in the relative expression of the virulence genes was detected in most of the acidic conditions in all the incubation times. The most pronounced upregulation of the relative expression of the virulence genes was found at pH 4.5. The efficient inlA -based qPCR method could be of interest to check changes in the expression of such virulence gene of this pathogenic bacterium in acidic environments. [ABSTRACT FROM AUTHOR]

Soil water erosion is frequently reported as serious problem in soils in Southeast Asia with tropical climates, and the variations in pH affect the development of the erosion. This study investigated the effects of changes in pH on soil water erosion based on changes in the physical properties of the simulated soils with pH adjusted from 2.0 to 10.0 through artificial rainfall tests. The zeta potential was entirely shifted to positive direction at each pH condition due to Al, Ca, and Mg. In the pH range of 6.0 to 2.0, the aggregation of soil particles resulting from the release of Al3+ from clay minerals and/or molecular attraction between soil particles caused the plastic index (IP) of the soil to decrease. The decrease in IP led to the development of soil water erosion at the pH range. When the pH exceeded 6.0, the repulsive force generated by the negative charges on soil particles decreased IP, resulting in accelerated erosion by water. The results suggest that changes in pH causes physical properties of the soil to change through changes of the zeta potential in the clayey soil rich in Al, Ca, and Mg, leading to the development of soil water erosion.

Anaerobic digestion and bioelectrochemical systems have great potential to recover energy from waste streams and help overcome common hurdles associated with this process, as integrated technologies. In this study, the benefit of integrating an electrogen-enriched bioanode in a batch anaerobic digester was explored under ambient temperature conditions associated with organic overloading and reactor acidity. An increase in CH4 production was observed in the electrode-containing reactors (0.56 L CH4 kgVS−1 h−1) in comparison with the conventional anaerobic digester (0.14 L CH4 kgVS−1 h−1) during the initial stages of operation. In addition, the mere presence of electrodes operating in open circuit mode resulted in a delay in volatile fatty acid (VFA) build-up. This seems to be associated with the enhancement in VFA consumption due to biomass proliferation on the electrode surface, rather than on electrochemical activity.

Development of a highly efficient trifunctional electrocatalyst for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential in a variety of energy conversion technologies, such as H 2 -O 2 fuel cell and overall water splitting. However, state-of-the-art electrocatalysts (Pt, Ir, Ru) for these electrochemical reactions suffer from high cost. Therefore, search for novel and cost-effective metal-based catalysts have gained tremendous attention. In this work, we investigated a novel Cd based electrocatalysts as efficient trifunctional electrocatalysts by density functional theory analysis. An in-depth reaction mechanism of CdN 4 C 0 -gra and CdN 0 C 4 -gra structure in acidic conditions had been investigated. After a detailed and systematic analysis by partial densities of states (PDOS) and Gibbs free energy (ΔG) of various modeled catalytic systems, the catalysts system composed of CdN 4 C 0 -gra showed excellent electrocatalytic properties with an overpotential of (ƞHER = 0.05 V, ƞOER = 0.48 V, and ƞORR = 0.75 V). [Display omitted] • The catalytic mechanism of Cd–N–C-doped graphene system for OER, ORR and HER reactions were investigated for the first time. • Catalytic performance of CdN 4 C 0 -gra is better, when Cd is coordinated by four N atoms (Cd-N 4 -C). • In the acidic conditions, water molecules influence the adsorption of OH*,and improve the catalytic performance. • The overpotentials of trifunctional electrocatalyst CdN 4 C 0 -gra (PH=0) are ƞHER = 0.05 V, ƞOER = 0.48 V and ƞORR = 0.75 V. [ABSTRACT FROM AUTHOR]

• Assessed soluble soybean polysaccharides (SSPS), acidic condition on bread quality. • SSPS and acidic condition decreased the staling rate of bread. • SSPS and acidic condition delayed the water migration in bread. • SSPS and acidic conditions provide more volatile organic compounds in bread. Effect of soluble soybean polysaccharides (SSPS) and acidic condition on the bread staling of crumb and crust were evaluated in bread characteristics, water migration, starch retrogradation, and flavor. Bread characteristic analysis showed SSPS and acidic conditions significantly improved bread quality during storage, maintaining crumb softness. The staling rate of the synergistic group under SSPS and acidic condition decreased by 49.46% compared to the control group. This retardation was associated with water migration and starch retrogradation. SSPS and acidic conditions restricted the water migration from crumb to crust. A synergy between SSPS and acidification restrained the relative crystallinity and retrogradation enthalpy in bread crumbs and crust during storage. The scores plot and heat map analysis indicated SSPS and acidic condition was facilitated the flavors retention in the crumb and crust after stored 7-days. This study suggested SSPS and acidic conditions might be beneficial for extending bread shelf-life. [ABSTRACT FROM AUTHOR]

We investigated the influence of pH and sodium chloride concentration on aggregation kinetics of a monoclonal antibody. Aggregation was induced by sodium chloride addition at low pH. Protein conformation before and after salt addition was determined as well as the reversibility of aggregation. Aggregation was monitored at pH values between 2 and 7 with NaCl up to 1.5 M by turbidity measurement and size-exclusion chromatography. Particle size distribution was assessed by using size-exclusion chromatography as well as nanoparticle tracking analysis and flow imaging microscopy. Structural changes were monitored by circular dichroism, Fourier transform infrared and fluorescence spectroscopy. Thermal stability was measured by differential scanning fluorimetry. Aggregation propensity was maximal at low pH and high ionic strength. While thermal stability decreased with pH, the secondary structure remained unchanged down to pH 3.5 and up to 1.5 M NaCl. Precipitated protein could be largely reverted to monomers by dilution into salt-free buffer. The re-solubilized antibody was indistinguishable in structure, solubility and monodispersity from the unstressed protein. Also, binding to Protein A was steady. Aggregation could be reduced in the presence of trehalose. The results suggest a reversible aggregation mechanism characterized by a limited change in tertiary structure at low pH and a subsequent loss of colloidal stability resulting from electrostatic repulsion once salt is added to the sample. The experimental setup is robust and allows high-throughput quantification of the effect of additives on aggregation kinetics. [ABSTRACT FROM AUTHOR]