Sulfate Exchange Research Articles

Effects of Fe(II) bio-oxidation rate and alkali control on schwertmannite microstructure and adsorption of oxyanions: Characteristics, performance and mechanism

Schwertmannite has attracted increasing interest for its excellent sorption of oxyanions such as AsO43−, CrO42−, and Sb(OH)6−. Controlling biomineralization by adjusting the Fe(II) oxidation rate and implementing alkali control can enhance the yield and adsorption performance of schwertmannite. However, the adsorption improvement mechanism is still unclear. The morphology, crystallinity, specific surface area (SSA) and oxyanion adsorption of schwertmannite synthesized with alkali control of solution pH and different Fe(II) oxidation rates were analyzed in this study. The differences in the adsorption mechanisms of As(V), Cr(VI) and Sb(V) on schwertmannite obtained under different synthesis conditions were also studied. Reducing the Fe(II) oxidation rate or maintaining the solution pH through alkali control significantly increased the SSA of schwertmannite and the proportion of outer-sphere sulfate. Alkali-controlled schwertmannite (Sch-C) exhibited superior As(V) and Sb(V) adsorption performance and slightly greater Cr(VI) adsorption than non-alkali-controlled schwertmannite. The As(V) and Sb(V) adsorption capacities of Sch-C greatly improved because the ultra-high SSA increased the surface hydroxyl content and reduced the passivation effect of amorphous precipitates on the mineral surface, allowing continuous sulfate exchange at inner mineral sites. An increased surface hydroxyl content had little effect on Cr(VI) adsorption, but an increased proportion of outer-sphere sulfate caused a slight increase in Cr(VI) adsorption. Sb(V) has a stronger hydroxyl exchange ability than As(V), but due to its octahedral structure, it exchanges only with outer-sphere sulfate on schwertmannite and hardly exchanges with inner-sphere sulfate.

Seed-mediated growth of schwertmannite for treatment of acid mine drainage: Improved adsorption of As(V) and Cr(VI) due to structure-related mechanisms

The biomineralization-driven formation of schwertmannite is an environmentally friendly strategy for acid mine drainage (AMD) treatment. In this study, a targeted approach using seed-mediated growth of schwertmannite was proposed. The biomineralization time was successfully shortened by one-third compared to biomineralization without seed mediation. In addition, the seed-mediated schwertmannite (S-Sch) exhibited superior adsorption performance towards As(V) and slightly improved adsorption of Cr(VI) than a non-seed-mediated schwertmannite sample (Sch). Furthermore, the whiskers that create the typical pincushion structure grew directly on the surface of the seed during the growth process with S-Sch, whereas biomineralization of Sch needed to nucleate crystals before growing the whiskers. More whiskers were found on S-Sch than on Sch, and the whiskers were arranged loosely on S-Sch while they were packed tightly on Sch. Following adsorption, As(V) is enriched at the whisker sites, where substantial > Fe–OH/OH2 existed, thereby inhibiting subsequent sulfate exchange at inner sites, the open structure of S-Sch decreases this passivation and allows continuous sulfate exchange. Cr(VI) adsorption is mainly due to sulfate exchange with little > Fe–OH/OH2 involved. Cr(VI) was distributed evenly on the surface of S-Sch, but an open mineral structure allows more inner sites to be reached, explaining the slightly better performance of S-Sch. The results suggest that the method proposed in this paper could be an effective way to shorten the biomineralization time and provide schwertmannite with excellent performance for the removal of As(V) and Cr(VI), which could lead to practical applications of biomineralization in the treatment of AMD.

Storm-driven variations in depositional environments modify pyrite sulfur isotope records

The sulfur isotopic composition of marine pyrite (δ34Spyr) is one of the major geochemical tools to reconstruct global changes in Earth's surface environment. Storm-driven variations in depositional environments, however, can play key roles in modifying the δ34Spyr signal. Here we present δ34Spyr values in a complete Holocene muddy storm deposit on the East China coastal plain, which is identified by comprehensive analyses of sediment components, organic matter composition, bulk organic carbon isotopic ratios, carbon and oxygen isotopic ratios of carbonates and trace element concentrations. We find that positive (+5.8‰ to +15.8‰) and negative (−9.0‰ to −19.7‰) δ34Spyr values were preserved in two successive intervals of the muddy storm deposit (ca. 62 cm long), corresponding to the high-energy storm peak phase (HESPP) and the waning-energy late storm phase (WELSP), respectively. We propose that the 34S enrichment in pyrite from the HESPP is most likely due to a combination of storm reworking of sediments and high sedimentation rates, which involves various physical and chemical processes leading to the accumulation of 34S-enriched pyrite, such as oxidation of near-surface sulfides, reduced exchange of sulfate between sediment pore fluids and the overlying water column, and/or input of excess reactive iron minerals. In contrast, lower sedimentation rates and limited sedimentary remobilization during the WELSP allow the isotopic signal of early-formed 32S-enriched pyrite to be preserved. The striking shift in δ34Spyr values, therefore, reflects a dramatic change in the local depositional environment between the HESPP and WELSP, suggesting that non-steady-state deposition induced by storm activity facilitates the formation of isotopically “heavy” pyrite. This sharp shift can be further generalized as a characteristic feature of δ34Spyr values in storm deposits. Our work highlights the critical impact of weather- and climate-event-driven depositional variations on δ34Spyr values, adding to the growing evidence emphasizing the local environmental and diagenetic controls on these records.

Arsenic removal and stabilization behavior of schwertmannite@BC (Sch@BC) in contaminated dual media (water/soil): Via sulfate exchange and chemical complexation

Arsenic (As) is extremely harmful to the ecological environment and human health owing to its high toxicity. The composite that biochar (BC) modified by Schwertmannite (Sch), marked as Sch@BC, were prepared to remediate As-contaminated water and soil with a high efficiency. The characterization results showed that the Sch particles were successfully loaded on the BC, providing more active sites for As(V) adsorption. Compared with the pristine BC, the adsorption capacity of Sch@BC-1 was significantly improved (50.00 mg/g), of which the adsorption capacity kept stable over a wide pH range (pH = 2–8). The adsorption process conformed to pseudo-second-order kinetics and Langmuir isotherm model, which indicated that chemical adsorption was the dominant mechanism and the adsorption rate was controlled by intraparticle diffusion. Sch@BC could adsorb As(V) through electrostatic interaction and ion exchange, forming a FeAsO4 complex and removing As(V). The 5-week soil incubation experiment showed that 3% Sch@BC showed the optimal stabilization effect, while the proportion of stable crystalline Fe/Mn-bound fractionation (F4) increased. Moreover, the results of microbial community diversity showed that Sch@BC interacted with As-resistant dominant microorganisms such as Proteobacteria in soil, promoted their growth and reproduction, and improved the stability of As in soil. In summary, Sch@BC is an excellent agent with broad application prospects for remediating As-contaminated water and soil.

Impacts of chloride-form anion exchange seawater regeneration performance

ABSTRACT Seawater was investigated as an alternative regenerant source to conventional salt-imported brine solutions in an anion exchange process treating surficial Florida coastal groundwater for the removal of sulfate and organics. Bench-scale column testing revealed that filtered Sarasota Bay seawater efficiently regenerated the anion resin media; however, sulfate exchange capacity decreased by 8.42% compared with conventional 10% salt regeneration methods. Addition of 3% sodium chloride increased regeneration efficiency, reduced exchange capacity losses to 2.4% as compared to conventional 10% salt regeneration methods. Regeneration resulted in 2.13 mg/L of bromide leakage; however, addition of 3% sodium chloride to seawater reduced bromide leakage to 1.25 mg/L. A correlation between bromide exchange and the regenerant chloride-to-bromide molar ratio (CBMR) was observed, yielding less bromide exchange at higher CBMRs. Bromide adsorption followed pseudo 2nd order kinetics and chemisorption was the rate controlling step. Increasing the CBMR of the regenerant was found to shift adsorption behaviour, allowing intra-particle diffusion to occur sooner. Bromide equilibrium appeared to follow a logarithmic decay as the CBMR of the regenerant increased. Intra-particle and film diffusion mechanisms were evaluated that indicated the presence of diffusion-based processes and more than one rate controlling step. An empirical function was derived to approximate bromide equilibrium adsorption in relation to a regenerant’s CBMR. Seawater as a regenerant when enhanced with sodium chloride shows promise as an anion exchange regenerant; additionally, classification of a seawater regenerant’s CBMR can provide insight into the kinetic and equilibrium relationships of bromide exchange.

SANS characterization of time dependent, slow molecular exchange in an SDS micellar system.

We have investigated the molecular exchange of sodium dodecyl sulfate (SDS) micelles in aqueous solution by time-resolved small angle neutron scattering (TR-SANS) measurements as a function of the surfactant and salt concentration. Starting with deuterated (d-SDS) and protonated (h-SDS) SDS micelles, surfactant exchange across the micelles leads to a randomized distribution of d-SDS and h-SDS within each micelle. By employing the contrast matching technique, we have studied this randomization process which is a direct measure of the molecular exchange of this system. Our results show that the randomization of the pure h-SDS and d-SDS micelles occurs in two steps: first, an almost instantaneous drop in the scattering intensity is observed where ∼80% of the micelles are randomized (contrast matched). After this, micelle randomization progresses slowly spanning over ∼100 hours. Importantly, we show that the kinetics in the second step are dominated by the formation of domains rich in either h-SDS, d-SDS and randomized (50 : 50 h-SDS : d-SDS). The slow exchange step is modeled via a phenomenological approach by drawing analogy to the Langmuir adsorption theory. Finally, the effects of the surfactant and salt concentrations on the instantaneous, and the time dependent randomization of SDS micelles are discussed.

A thermostable extracellular α-amylase from Aspergillus flavus S2-OY: Purification, characterisation and application in raw starch hydrolysis

An amylolytic fungus was isolated locally from the soil of a cassava waste dumpsite. It was identified as Aspergillus flavus S2-OY using 18S rRNA gene sequencing with gene bank accession number MZ267053.1. α-Amylase was produced from the fungus through solid substrate fermentation of potato (Solanum tuberosum L.) peel, a cheap and renewable substrate. The fungal enzyme was purified 13.41-fold by ammonium sulphate and ion exchange chromatography (CM Sephadex C-50), with final yield of 13.41%. Apparent molecular weight of 55.0 kDa was obtained for the purified enzyme, using SDS-PAGE. Optima pH (6.0) and temperature (70 °C) of α-amylase activity were determined for the enzyme which also showed thermal stability up to 70 °C, with 80% residual activity after 120 min. The enzyme exhibited a wide range of pH stability (4.0 to 7.0). Kinetic parameters Km and Vmax values obtained with soluble starch were 158 µg/ml/min and 1.51 mg/ml, respectively. The enzyme was slightly inhibited by Mg2+. Mn2+, Zn2+, Na+, K+, Hg2+ and the chelating agent, EDTA, at 5.0 mM concentration. However, it was activated by Sn2+. The enzyme hydrolysed gelatinised and ungelatinized raw yam, corn, rice and millet starches strongly but cassava starch moderately. These results revealed that cost-effective α-amylase production from Aspergillus flavus S2-OY could be realised with the use of potato peel as a cheap substrate, under solid substrate fermentation condition. Also, the fungal α-amylase is a raw starch-hydrolysing, acid to neutral and thermostable enzyme with potential for broad biotechnological applications.

Effect of Copper Sulfate and Sulfuric Acid on Blind Hole Filling of HDI Circuit Boards by Electroplating

Here, in a certain high density interconnect (HDI) printed circuit board, the effect of copper sulfate and sulfuric acid on the filling effect of a blind hole with a certain diameter and depth was investigated by making a blind hole using a CO2 laser drilling machine, filling the blind hole via electroplating by simulating the electroplating line in a Halin cell, and observing the cross-section of a micro blind hole after polishing using metallographic microscope, as well as the effect of hole filling, are evaluated. The results show that, under the conditions of a certain plating solution formula and electroplating parameters (current density and electroplating time), the sag degree decreases with the increase in the copper sulfate concentration. When the concentration of copper sulfate increases from 210 g/L to 225 g/L, the filling effect is good and the sag degree is about 0. However, with the increase in sulfuric acid concentration, the sag increases gradually. When the sulfuric acid concentration is 25–35 g/L, both the sag and copper coating thickness are in a small range. Under appropriate electroplating conditions, a better blind hole filling effect can be obtained. The volume of blind hole has a certain effect on the diffusion and exchange of copper sulfate and sulfuric acid, as well as on the concentration distribution of additives.

Peningkatan Stabilitas Termal Enzim α-Amilase dari Bacillus subtilis ITBCCB148 dengan Amobilisasi Menggunakan Zeolit

The objective of the research is to increase the thermal stability of -amylase from Bacillus subtilis ITBCCB148 by immobilization using zeolite. For that reason, firstly we need to produce, isolate, and purify the enzyme. The purification of the enzyme was conducted by the following steps: fractionation with ammonium sulphate, dialysis, and CM-cellulose cation exchange column chromatography. The purified enzyme was immobilized using zeolite. The success in immobilization of the enzyme was evaluated by comparing the thermal stability of the enzyme before and after immobilization. Activity of α-amylase was determined by the Mandels and Fuwa method. The protein content was determined based on the method by Lowry. The results showed that the specific activity of purified enzyme was 2473.7 U / mg, increased 19 times compared to crude extract of enzyme having specific activity of 1285.9 U / mg. The purified enzyme has the optimum temperature at 65ºC, while the immobilized enzyme has the optimum temperature at 75ºC. The thermal stability test of the purified enzyme at 65ºC for 100 minutes showed the purified enzyme having residual activity of 20%; t 1 / 2 = 30 min, k i = 0.023 min -1 and ΔGi = 103.65 kJ mol -1 . The thermal stability test of the immobilized enzyme at 65ºC for 100 minutes showed that the immobilized enzyme had residual activity of 40%; t 1/ 2 = 49 min, k i = 0.014 min -1 and ΔGi = 105.03 kJ mol -1 . Immobilization using zeolite has succeeded in increasing the thermal stability of enzyme by 1.64 times compared to the purified enzyme, which is indicated by the decreasing of k i value, the increase of half-life and denaturation energy change (ΔGi).

Contrasting effects of phosphate on the rapid transformation of schwertmannite to Fe(III) (oxy)hydroxides at near-neutral pH

Schwertmannite is a metastable Fe(III)-bearing mineral that can rapidly transform to more stable Fe(III) oxides upon Fe(II) sorption, via a dissolution-reprecipitation pathway. Phosphate (PO43−) is a nutrient found in varying quantities in natural systems, but the influence of PO43− on the Fe(II) induced transformation of schwertmannite is not well characterized. Here, we aim to quantify the aqueous and mineralogical effects of varied PO43− loading, and subsequent Fe(II) loading, to schwertmannite at circumneutral pH. Phosphate was presorbed to schwertmannite at loadings of 0, 80, 400 and 800 μmoles g−1 in anoxic artificial groundwater. Fe(II) was then added at a final concentration of 12.5 mM and aqueous and mineralogical products were observed over 10 days. No transformation occurred before Fe(II) addition in the zero PO43− treatment. In contrast, the three highest PO43− treatments partially transformed to a microcrystalline Fe(III) oxyhydroxide before Fe(II) addition, possibly due to exchange of sulfate with the added PO43−. Within 1 h of subsequent Fe(II) addition in the zero PO43−treatment, all schwertmannite had transformed to goethite via the Fe(II)-induced transformation pathway. Increases in the level of PO43− loading attenuated goethite precipitation via Fe(II)-induced transformation of the precursor schwertmannite and microcrystalline Fe(III) oxyhydroxide, with 65%, 34%, and 21% solid phase Fe as goethite at day 10 in the low (80 μmoles g−1), medium (400 μmoles g−1) and high (800 μmoles g−1) PO43− treatments. Under low PO43− loading, the addition of Fe(II) induced the transformation of the microcrystalline Fe(III) oxyhydroxide and schwertmannite to a mixture of lepidocrocite and goethite. In the medium and high PO43− treatments, schwertmannite and the microcrystalline Fe(III) oxyhydroxide were instead stabilized by surface-complexation of PO43− and did not extensively transform to more crystalline phases. Overall, the results show that PO43− loadings can both drive rapid schwertmannite transformation to a new microcrystalline Fe(III) oxyhydroxide phase, and subsequently inhibit the Fe(II)-induced formation of lepidocrocite and goethite.

Metformin downregulates the mitochondrial carrier SLC25A10 in a glucose dependent manner

Metformin, a commonly used agent in the treatment of type 2 diabetes, is also associated with reduced risk of cancer development and improvement in cancer survival. Although much is known about metformin, the mechanisms behind its anti-cancer properties are not fully understood. In this study we addressed the role of a mitochondrial transporter commonly upregulated in cancer cells, SLC25A10, for cell survival and metabolism in the presence of metformin. SLC25A10 is a carrier in the mitochondrial inner membrane that transports malate and succinate out of the mitochondria, in exchange of phosphate and sulfate. We show that metformin treatment results in decreased gene expression of the SLC25A10 carrier both in lung cancer A549 mock cells and A549 SLC25A10 knockdown (siSLC25A10) cells. The decrease was even more pronounced when cells were grown at low glucose concentrations. The expression levels of key enzymes in glucose metabolism showed slightly altered mean values for all genes tested in both control cells and siSLC25A10 cells upon metformin treatment. The gene expression of the metabolic regulator glutamic-oxaloacetic transaminase 1 decreased in wild type cells upon metformin treatment whereas there was a trend of increased expression in the siSLC25A10 cells upon metformin treatment. In addition, the gene expression of the cyclin-dependent kinase inhibitor 1A was markedly increased in the siSLC25A10 compared to control A549 cells, and with even larger increases in the presence of metformin and at low glucose concentration. Our data show that in siSLC25A10 cell lines, metformin significantly alters the SLC25A10 carrier at both mRNA and protein levels and can thereby affect the supply of nutrients and the metabolic state of cancer cells.

Anion structural effects on interaction of rare earth element ions with Dowex 50W X8 cation exchange resin

The effect of the anion in the original rare earth element (REE) solution on the reversible ion exchange of Ce nitrate and Ce sulfate with the Dowex 50W X8 was investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, continuous flow reactor studies coupled with inductively coupled plasma mass spectroscopy (ICP-MS), and density functional theory (DFT). The simulated IR spectrum at the DFT B3LYP/6-31G(d) level was compared to the experimental results to characterize the IR spectrum, molecular interactions, and bonding of the ion exchanged species. The continuous liquid flow reactor studies show a capacity of 0.72 mmol/g sorbent for the Ce nitrateand 0.96 mmol/g sorbent for the Ce sulfate with the Dowex 50W X8. The flow reactor studies reveal the type of solute anion (SO4(2–) or NO3(−)) associated with the REE during cation exchange significantly affects the sorption capacity of the Dowex 50W X8 ion exchange resin. The calculated REE binding energy (BE) and the DFT optimized structures suggest that the differences in sorption capacity is the result of the formation of different types of partially ion-exchanged Ce2(3+)2SO4(2–) and Ce(3+) 3NO3(−). These results suggest that the solute anion affects the equilibrium constants of the Dowex resin by the formation of a charged layer capable of retaining the counterion. Modifying the sulfonic acid site (H+) in the Dowex 50W X8 with the NH4+ counterion does not affect the sorption capacity and retention times of the Ce nitrate and Ce sulfate species. These results suggest that the counterions and co-ions having a finite size, may limit access to the Dowex sulfonate active site where the type of REE cation as a nitrate or sulfate in solution may significantly modify the sorption capacity of the ion exchange resin. Similar results are obtained during sorption with nitrates and sulfates of Sm and Yb.

Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway

Microbial sulfate reduction exhibits a normal isotope effect, leaving unreacted sulfate enriched in 34S and producing sulfide that is depleted in 34S. However, the magnitude of sulfur isotope fractionation is quite variable. The resulting changes in sulfur isotope abundance have been used to trace microbial sulfate reduction in modern and ancient ecosystems, but the intracellular mechanism(s) underlying the wide range of fractionations remains unclear. Here we report the concentrations and isotopic ratios of sulfur metabolites in the dissimilatory sulfate reduction pathway of Desulfovibrio alaskensis. Intracellular sulfate and APS levels change depending on the growth phase, peaking at the end of exponential phase, while sulfite accumulates in the cell during stationary phase. During exponential growth, intracellular sulfate and APS are strongly enriched in 34S. The fractionation between internal and external sulfate is up to 49‰, while at the same time that between external sulfate and sulfide is just a few permil. We interpret this pattern to indicate that enzymatic fractionations remain large but the net fractionation between sulfate and sulfide is muted by the closed-system limitation of intracellular sulfate. This ‘reservoir effect’ diminishes upon cessation of exponential phase growth, allowing the expression of larger net sulfur isotope fractionations. Thus, the relative rates of sulfate exchange across the membrane versus intracellular sulfate reduction should govern the overall (net) fractionation that is expressed. A strong reservoir effect due to vigorous sulfate reduction might be responsible for the well-established inverse correlation between sulfur isotope fractionation and the cell-specific rate of sulfate reduction, while at the same time intraspecies differences in sulfate uptake and/or exchange rates could account for the significant scatter in this relationship. Our approach, together with ongoing investigations of the kinetic isotope fractionation by key enzymes in the sulfate reduction pathway, should provide an empirical basis for a quantitative model relating the magnitude of microbial isotope fractionation to their environmental and physiological controls.

Take a Trip Through the Plant and Fungal Transportome of Mycorrhiza.

Soil nutrient acquisition and exchanges through symbiotic plant-fungus interactions in the rhizosphere are key features for the current agricultural and environmental challenges. Improved crop yield and plant mineral nutrition through a fungal symbiont has been widely described. In return, the host plant supplies carbon substrates to its fungal partner. We review here recent progress on molecular players of membrane transport involved in nutritional exchanges between mycorrhizal plants and fungi. We cover the transportome, from the transport proteins involved in sugar fluxes from plants towards fungi, to the uptake from the soil and exchange of nitrogen, phosphate, potassium, sulfate, and water. Together, these advances in the comprehension of the mycorrhizal transportome will help in developing the future engineering of new agro-ecological systems.

Sulfate Exchange of the Nitrate-Type Layered Hydroxide Nanosheets of Ln2(OH)5NO3·nH2O for Better Dispersed and Multi-color Luminescent Ln2O3 Nanophosphors (Ln = Y0.98RE0.02, RE = Pr, Sm, Eu, Tb, Dy, Ho, Er, and Tm).

Through restricting thickness growth by performing coprecipitation at the freezing temperature of ~4 °C, solid-solution nanosheets (up to 5-nm thick) of the Ln2(OH)5NO3·nH2O layered hydroxide (Ln = Y0.98RE0.02; RE = Pr, Sm, Eu, Tb, Dy, Ho, Er, and Tm, respectively) were directly synthesized without performing conventional exfoliation. In situ exchange of the interlayer NO3− with SO42− produced a sulfate derivative [Ln2(OH)5(SO4)0.5·nH2O] of the same layered structure and two-dimensional crystallite morphology but substantially contracted d002 basal spacing (from ~0.886 to 0.841 nm). The sulfate derivative was systematically compared against its nitrate parent in terms of crystal structure and phase/morphology evolution upon heating. It is shown that the interlayer SO42−, owing to its bonding with the hydroxide main layer, significantly raises the decomposition temperature from ~600 to 1000 °C to yield remarkably better dispersed oxide nanopowders via a monoclinic Ln2O2SO4 intermediate. The resultant (Y0.98RE0.02)2O3 nanophosphors were studied for their photoluminescence to show that the emission color, depending on RE3+, spans a wide range in the Commission Internationale de l’Eclairage (CIE) chromaticity diagram, from blue to deep red via green, yellow, orange, and orange red.

MC ICP-MS δ(34)S(VCDT) measurement of dissolved sulfate in environmental aqueous samples after matrix separation by means of an anion exchange membrane.

Analysis of 34S/32S of sulfate in rainwater and soil solutions can be seen as a powerful tool for the study of the sulfur cycle. Therefore, it is considered as a useful means, e.g., for amelioration and calibration of ecological or biogeochemical models. Due to several analytical limitations, mainly caused by low sulfate concentration in rainwater, complex matrix of soil solutions, limited sample volume, and high number of samples in ecosystem studies, a straightforward analytical protocol is required to provide accurate S isotopic data on a large set of diverse samples. Therefore, sulfate separation by anion exchange membrane was combined with precise isotopic measurement by multicollector inductively coupled plasma mass spectrometry (MC ICP-MS). The separation method proved to be able to remove quantitatively sulfate from matrix cations (Ca, K, Na, or Li) which is a precondition in order to avoid a matrix-induced analytical bias in the mass spectrometer. Moreover, sulfate exchange on the resin is capable of preconcentrating sulfate from low concentrated solutions (to factor 3 in our protocol). No significant sulfur isotope fractionation was observed during separation and preconcentration. MC ICP-MS operated at edge mass resolution has enabled the direct 34S/32S analysis of sulfate eluted from the membrane, with an expanded uncertainty U (k = 2) down to 0.3 ‰ (a single measurement). The protocol was optimized and validated using different sulfate solutions and different matrix compositions. The optimized method was applied in a study on solute samples retrieved in a beech (Fagus sylvatica) forest in the Vienna Woods. Both rainwater (precipitation and tree throughfall) and soil solution δ34SVCDT ranged between 4 and 6 ‰, the ratio in soil solution being slightly lower. The lower ratio indicates that a considerable portion of the atmospherically deposited sulfate is cycled through the organic S pool before being released to the soil solution. Nearly the same trends and variations were observed in soil solution and rainwater δ34SVCDT values showing that sulfate adsorption/desorption are not important processes in the studied soil.Graphical abstractSulfate separation by means of an anion exchange resin on a plastic membraneElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-015-9053-z) contains supplementary material, which is available to authorized users.

Controlled Synthesis of Layered Rare‐Earth Hydroxide Nanosheets Leading to Highly Transparent (Y0.95Eu0.05)2O3 Ceramics

Chemical precipitation at the freezing temperature of ~4°C has directly yielded layered rare‐earth hydroxide [LRH, Ln2(OH)5NO3·nH2O, Ln = Y0.95Eu0.05] nanosheets (up to 7 nm thick) for the Y/Eu binary system, with the interlayer NO3− exchangeable with SO42−. Calcining the sulfate derivative at 1100°C for 4 h produces well‐dispersed and readily sinterable Ln2O3 red phosphor powders (~14.8 m2/g) that can be densified into highly transparent ceramics via optimized vacuum sintering at the relatively low temperature of 1700°C for 4 h (average grain size ~14 μm; in‐line transmittance ~80% at the 613 nm Eu3+ emission or ~99% of the theoretical transmittance of Y2O3 single crystal). Our systematic studies also found that (1) the extent of SO42− exchange and the interlayer distance of LRH are both affected by the SO42−/Ln3+ molar ratio (R), and an almost complete exchange is achievable at R = 0.25 as expected from the chemical formula (one SO42− replaces two NO3− for charge balance). The optimal R value for sintering, however, was found to be 0.03; (2) The Ln3+ concentration for LRH synthesis substantially affects properties of the resultant oxides, and hard agglomeration has been significantly reduced at the optimized Ln3+ concentration of 0.05–0.075 mol/L; (3) Sulfate exchange significantly alters the thermal decomposition pathway of LRH, and was found essential to produce well‐dispersed and highly sinterable oxide powders; (4) Both the oxide powders and transparent ceramics exhibit the typical red emission of Eu3+ at ~613 nm (the 5D0→7F2 transition) under charge‐transfer (CT) excitation. Red‐shifted CT band center, stronger excitation/emission, and shorter fluorescence lifetime were, however, observed for the transparent ceramics.

Anion translocation through an Slc26 transporter mediates lumen expansion during tubulogenesis

Lumen formation is a critical event in biological tube formation, yet its molecular mechanisms remain poorly understood. Specifically, how lumen expansion is coordinated with other processes of tubulogenesis is not well known, and the role of membrane transporters in tubulogenesis during development has not been adequately addressed. Here we identify a solute carrier 26 (Slc26) family protein as an essential regulator of tubulogenesis using the notochord of the invertebrate chordate Ciona intestinalis as a model. Ci-Slc26aα is indispensable for lumen formation and expansion, but not for apical/luminal membrane formation and lumen connection. Ci-Slc26aα acts as an anion transporter, mediating the electrogenic exchange of sulfate or oxalate for chloride or bicarbonate and electroneutral chloride:bicarbonate exchange. Mutant rescue assays show that this transport activity is essential for Ci-Slc26aα's in vivo function. Our work reveals the consequences and relationships of several key processes in lumen formation, and establishes an in vivo assay for studying the molecular basis of the transport properties of SLC26 family transporters and their related diseases.

Dynamic sulfur and carbon cycling through the end-Ordovician extinction revealed by paired sulfate–pyrite δ34S

Geochemical records of the end-Ordovician Hirnantian Stage show parallel positive excursions in the stable isotope compositions of sedimentary pyrite sulfur (δ34Spyr), organic carbon (δ13Corg), and carbonate carbon (δ13Ccarb); these isotope excursions coincide with the end Ordovician glaciation and mass extinction. A relative increase in pyrite burial (fpyr) attributed to marine anoxia has been invoked to explain the sulfur isotope excursion and link oceanic redox conditions to the extinction of marine fauna. An increase in fpyr would necessarily generate a parallel excursion of equal magnitude in the isotopic composition of coeval marine sulfate (δ34SSO4). Here we present new high-resolution paired sulfur isotope data from carbonate-associated sulfate (δ34SCAS) and pyrite from the Hirnantian Stage of western Anticosti Island (Québec, Canada). These data document a positive 20‰ enrichment in δ34Spyr (comparable in magnitude to previous reports), but no parallel excursion in δ34SCAS. This pattern provides new constraints on the origin of the δ34Spyr excursion and the nature of carbon–sulfur coupling through Hirnantian time. Specifically, these observations preclude enhanced pyrite burial as the cause of the Hirnantian δ34Spyr excursion and suggest the possible role of anoxia in the mass extinction may need to be reevaluated. Rather, the global δ34Spyr excursion is best explained by a transient reduction in the isotopic fractionations expressed during microbial sulfur cycling (εpyr). The εpyr record shows a strong inverse correlation with δ13C, suggesting a mechanistic link between carbon cycling and processes controlling εpyr during the Hirnantian. Changes in sea level or marine redox state associated with glaciation could further impact the expression of the biological fractionation (e.g., through syndepositional sediment reworking and/or chemocline migration and resultant restricted exchange of porewater sulfate). The magnitude of isotopic fractionation during microbial sulfate reduction is partially controlled by metabolic rates, which are sensitive to the abundance, type, and lability of metabolically relevant substrates. Environmental change associated with the end Ordovician glaciation may have elevated the flux of organic material to marine sediments or caused an increase in physical reworking of sediments, leading to increased microbial sulfate reduction rates and reduced εpyr. As such, the Hirnantian δ34Spyr excursion may be viewed as a dynamic biological response to global climate change, highlighting the connections between the carbon and sulfur biogeochemical cycles.

Comparison of arsenate, chromate and molybdate binding on schwertmannite: Surface adsorption vs anion-exchange

The presence of iron oxides may play an important role in controlling the mobility and availability of contaminants in soils and waters affected by acid mine drainage. The present study describes the uptake of arsenate, chromate and molybdate from solution by synthetic schwertmannite. Batch experiments were performed at different pH values in order to obtain the adsorption isotherms for the three oxyanions. In addition to the formation of surface complexes between the oxyanions and the iron surface reactive groups, it is also expected that anion exchange will occur between sulphate anions from the schwertmannite structure and the oxyanions present in the solid/solution interface. Comparison of the experimental adsorption results for the different oxyanions showed large differences, not only the amount adsorbed, which was much higher for arsenate, but also in the sulphate exchange with the anions in solution. In case of chromate, the main mechanism of adsorption process is the exchange reaction with the sulphate groups present in the schwertmannite. The observed results suggest a different adsorption mechanisms for each of the three oxyanions, with important implications for the mobility of these anions in acid mine drainage systems.