High Concentrations Of MgCl2 Research Articles

Rapid Synthesis of α-Hemihydrate Phosphogypsum in MgCl2 Solution by Microwave Heating.

The preparation of α-hemihydrate phosphogypsum (α-HPG) is hindered by a lengthy reaction time due to using traditional electric heating. Microwave heating was proposed for the rapid synthesis of α-HPG in MgCl2 solution. The effects of MgCl2 concentration on the heating rate of solution and conversion rate of α-HPG were investigated; the morphology of α-HPG was regulated by citric acid, and the adsorption mechanism of citric acid on the α-HPG surface was clarified. The results show that α-HPG was successfully synthesized in a MgCl2 solution by microwave heating. Increasing the MgCl2 concentration can improve both the dielectric constant and conductivity of the solution, which is advantageous for the solution to absorb more microwave energy. Consequently, the conversion rate of phosphogypsum (PG) into α-HPG was improved at higher MgCl2 concentrations. In 2.62 mol/L MgCl2 solution, the heating time is shortened to 7 min from room temperature to 95 °C, and PG was converted to α-HPG within 60 min. The morphology of α-HPG could be controlled by chemical adsorption of citric acid onto its terminal surface. In a solution containing 2.62 mol/L MgCl2 and 1.63 × 10-2 mol/L citric acid, PG was completely transformed into α-HPG at 90 min by microwave heating, whereas the reaction time was delayed to 180 min using electric heating. Accordingly, microwave heating is a highly efficient and energy-saving method for the preparation of α-HPG.

Probing molecular interactions of an anti-epileptic drug, sodium valproate in aqueous MgCl2 solutions

Study of the physicochemical properties of anti-epileptic drugs in the presence of cosolutes in aqueous solutions has been a subject of interest of researchers because of their interaction with biological membranes to employ their effect. Such properties provide complete information regarding solute-solute and solute-solvent type interactions. As electrolytes are essential components of biological systems, therefore the study of drug-electrolyte chemistry is important to understand the mechanism of drug action at the molecular level and hence useful in drug design and development processes. Therefore, in the current report, the density and sound velocity of an anti-epileptic drug sodium valproate (SV) in aqueous and in aqueous solutions of an electrolyte viz. MgCl2 (mB = 0.024, 0.047, 0.070 mol kg−1) at different temperatures (288.15, 298.15, 308.15, and 318.15 K) and at a pressure of 0.101 MPa were measured along with 1H NMR spectroscopy. Various volumetric and acoustical parameters such as apparent molar volume (Vφ) and isentropic compressibility (Kφ) of the solute, apparent molar volume (Vφ°) and isentropic compressibility (Kφ°) of solute at infinite dilution, apparent molar expansibility (Eφ°) and their double derivatives (∂2Vφ°/∂T2)P, transfer volumes (∆trVφ°), hydration number (nH), acoustic impedance (Z), intermolecular free length (Lf), Wada's constant (W) and Rao's constant (R) were calculated from density and sound velocity data. The variation in all these parameters with cosolute concentration indicates the existence of hydrophilic/ionic-ionic interactions at lower concentrations but hydrophobic-ionic interactions at higher concentrations of MgCl2. The 1H NMR spectroscopic results also support the existence of hydrophobic-ionic interactions at higher concentrations of MgCl2. The decrease in electrostriction but increase in hydrophobic hydration of solute molecules has also been seen with rise in temperature.

Structural and flow rheological properties of pumpkin pectic polysaccharide extracted by citric acid

The present study aimed to investigate the structural and physicochemical characteristics of acid-extracted pumpkin pectic polysaccharide (AcPP) and to evaluate their flow rheological properties. AcPP was extracted from pumpkin pulp using the citric acid extraction method. The physicochemical and structural properties were analyzed by chemical methods and instrumental analyses. The obtained results showed that AcPP consisted predominantly of GalA (85.99 %) and small amounts of Rha, Gal, and Ara, with the ratio of HG/RG-I being 81.39/16.75. In addition, AcPP had medium DE (45.34 %) and contained four macromolecular populations with different Mw of 106.03 (main), 10.15, 4.99, and 2.90 kDa. The NMR analysis further confirmed that AcPP contained a linear backbone consisting of α-1,4-linked GalA residues, some of which were partially methyl-esterified. Furthermore, AcPP was amorphous in nature and had favorable thermal stability. The effects of extrinsic factors on the flow rheological properties of AcPP were evaluated. In particular, the high concentrations of CaCl2 (8 mM) and MgCl2 (10 mM) were effective in enhancing the viscosity and non-Newtonian shear-thinning behavior of the AcPP solution. This study elucidates the unique molecular structure of AcPP and suggests the potential of AcPP as a rheology modifier in low-viscous and mineral-reinforced beverages.

Cathodic Polarization Behavior of Steel in Aqueous MgCl2 Solutions Containing Zn2+

So far, we have revealed that the dissolution rate of zinc is accelerated in relative high concentrations of MgCl2 in the corrosion process of galvanic couples consisting of zinc and steel. In this study, we investigated the cathodic polarization behavior of steel in MgCl2 solution containing Zn2+ and the effect of Zn2+ dissolved in the solution on the oxygen reduction reaction and hydrogen evolution reaction.The specimens used in the experiments were carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined into a 1.5×1.5×0.3 cm3. One side of the specimen was polished with SiC abrasive paper up to #2000 grit and degreased in acetone before being used for the experiment. The test solution was mixtures of 0.25 M MgCl2 + x mM ZnCl2 (x = 2.5, 5 mM, Mg/Zn molar ratio: 100, 50) at room temperature under a naturally aerated condition. As a comparison solution, 0.5 M NaCl + y mM ZnCl2 (x = 5, 10 mM, molar ratio of Na/Zn: 100, 50) with the same chloride ion concentrations were used. Cathodic polarization curves of steel were measured using a three-electrode method with a platinum wire as the counter electrode and an Ag/AgCl electrode (saturated KCl, SSE) as the reference electrode. The potential sweep rate was 0.5 mV/s. After the polarization test, the specimen surfaces were observed with a scanning electron microscope and analyzed for corrosion products formed during cathodic polarization with XRD and laser Raman spectroscopy.The cathodic polarization behavior of steel in MgCl2 solution without Zn2+ was investigated and compared with that of NaCl solution without Zn2+. Diffusion-limited currents of dissolved oxygen reduction (ORR) were observed at -0.6 V to -0.8 V in MgCl2 and NaCl solutions. Furthermore, cathodic polarization in MgCl2 and NaCl solutions showed an increase in current due to hydrogen evolution reaction (HER), and the cathodic current due to HER on steel was larger in the MgCl2 solution than in the NaCl solution. To investigate the difference in HER in both solutions, the steel surface was observed after constant polarization at -1.0 V for 20 min. Mg(OH)2 deposition was observed on the steel surface in the MgCl2 solution, but not in the NaCl solution. This indicates that the increase in pH due to ORR and HER is mitigated by the formation of Mg(OH)2 during cathodic polarization. Therefore, due to the pH buffering action of Mg2+ associated with the formation of Mg(OH)2, it can be considered that a larger HER current flowed in the MgCl2 solution than in the NaCl solution when compared at the same potential.On the other hand, cathodic polarization curves for steel in MgCl2 and NaCl solution containing Zn2+ were investigated. As a result, ORR and HER were observed at potentials down to -1 V in the MgCl2 and NaCl solutions containing Zn2+; the cathodic current due to ORR and HER in the MgCl2 and NaCl solutions containing Zn2+ was reduced compared to the solutions without Zn2+. The inhibition of ORR and HER can be attributed to the precipitation of Zn corrosion products.These results suggest that in solution environments containing Mg2+ and Zn2+, the promotion of HER by the effect of Mg2+ and the inhibition of HER and ORR by Zn corrosion products occur simultaneously.

Mg-assisted reduced graphene oxide fabrication under microwave irradiation of a natural source of carbon

Chemical reduction of graphene oxide to form reduced graphene oxide (rGO) is a long process that needs time and energy. In this work, we present a facile one-step method to produce rGO using a domestic microwave oven for 2 min. The chemical composition is studied by X-Ray Photoelectron Spectroscopy (XPS), Raman and X-Ray diffraction (XRD) that confirm the formation of rGO. They reveal also the benifit effect of MgCl2 addition towards the rGO formation. Different amounts of MgCl2 are added to polyethylene glycol (PEG) and a natural source of carbon (glucose) is used to form rGO. The rGO yield is successfully enhanced by addition of MgCl2 low concentration. The oxygen concentration decreases with Mg addition which means that Mg atoms replaced oxygen or simply adsorbed at the edge sites. Moreover, carbon concentration increases with MgCl2 addition, which means that Mg acts as an activator of rGO formation. At high MgCl2 concentration, Mg(OH)2-rGO is formed and has a lot of applications.

Durability of concretes exposed to high concentrations of CaCl2 and MgCl2.

In cold regions, calcium and magnesium chloride deicing salts damage concrete pavements due to the formation of certain deleterious chemical phases, including calcium oxychloride. While there is much research at a cement paste-scale, damage in concrete has been less studied. In this study, we evaluate concrete damage due to calcium and magnesium chloride and explain the roles of supplementary cementitious materials (SCM) replacement level, air entrainment, salt type, and exposure conditions in damage development. Various non-destructive test methods including bulk resistivity, mass change, and visual damage assessment were used to monitor the damage over time. Damage was reduced as the SCM replacement level and air content increased, regardless of exposure conditions. Bulk resistivity and visual assessment were promising indicators of damage. The product of 91-day bulk resistivity and the air content predicted concrete performance when exposed to concentrated deicing salts. Based on several criteria, mixtures with 20% fly ash replacement level or 35% slag mitigated damage significantly when the air content was greater than 5% by concrete volume. Damage mitigation mechanisms of SCM and air are discussed.Supplementary InformationThe online version contains supplementary material available at 10.1617/s11527-022-01992-y.

HwMR is a novel magnesium-associated protein

Microbial rhodopsins (MRho) are vital proteins in Haloarchaea for solar light sensing in extreme living environments. Among them, Haloquadratum walsbyi (Hw) is a species known to survive high MgCl2 concentrations, with a total of three MRhos identified, including a high-acid-tolerance light-driven proton outward pump, HwBR, a chloride-insensitive chloride pump, HwHR, and a functionally unknown HwMR. Here, we showed that HwMR is the sole magnesium-sensitive MRho among all tested MRho proteins from Haloarchaea. We identified at least D84 as one of the key residues mediating such magnesium ion association in HwMR. Sequence analysis and molecular modeling suggested HwMR to have an extra H8 helix in the cytosolic region like those in signal-transduction-type MRho of deltarhodopsin-3 (dR-3) and Anabaena sensory rhodopsin (ASR). Further, HwMR showed a distinctly prolonged M-state formation under a high concentration of Mg2+. On the other hand, an H8 helix truncated mutant preserved photocycle kinetics like the wild type, but it led to missing M-state structure. Our findings clearly suggested not only that HwMR is a novel Mg2+-associated protein but that the association with both Mg2+ and the H8 domain stabilizes M-state formation in HwMR. We conclude that Mg2+ association and H8 are crucial in stabilizing HwMR M state, which is a well-known photoreceptor signaling state.

Elevation of Hyaluronan Synthase by Magnesium Supplementation Mediated through the Activation of GSK3 and CREB in Human Keratinocyte-Derived HaCaT Cells.

Skin barrier damage is present in the patients with hereditary disorders of the magnesium channel, but the molecular mechanism has not been fully understood. We found that the expressions of hyaluronan synthase (HAS), HAS2 and HAS3 are influenced by MgCl2 concentration in human keratinocyte-derived HaCaT cells. The exposure of cells to a high concentration (5.8 mM) of MgCl2 induced the elevation of HAS2/3 expression, which was inhibited by mRNA knockdown of nonimprinted in Prader-Willi/Angelman syndrome-like domain containing 4 (NIPAL4). Similarly, the content of hyaluronic acid (HA) was changed according to MgCl2 concentration and the expression of NIPAL4. The MgCl2 supplementation increased the reporter activities of HAS2/3, which were inhibited by NIPAL4 knockdown, indicating that the expressions of HAS2/3 are up-regulated at the transcriptional level. The reporter activities and mRNA levels of HAS2/3, and the production of HA were inhibited by CHIR-99021, a glycogen synthase kinase-3 (GSK3) inhibitor, and naphthol AS-E, a cyclic AMP-response element binding protein (CREB) inhibitor. Furthermore, the mutation in putative CREB-binding sites of promoter region in HAS2/3 genes inhibited the MgCl2 supplementation-induced elevation of promoter activity. Our results indicate that the expressions of HAS2/3 are up-regulated by MgCl2 supplementation in HaCaT cells mediated through the activation of GSK3 and CREB. Magnesium may play a pivotal role in maintaining the skin barrier function and magnesium supplementation may be useful to enhance moisturization and wound repair in the skin.

Magnesium in Combinatorial With Valproic Acid Suppressed the Proliferation and Migration of Human Bladder Cancer Cells.

Magnesium, the second most predominant intracellular cation, plays a crucial role in many physiological functions; magnesium-based biomaterials have been widely used in clinical application. In a variety of cancer types, the high intracellular concentration of magnesium contributes to cancer initiation and progression. Therefore, we initiated this study to investigate the likelihood of confounding magnesium with cancer therapy. In this study, the anti-tumor activity of magnesium and underlying mechanisms were assessed in bladder cancer both in vitro and in vivo. The results indicated that the proliferation of bladder cancer cells was inhibited by treatment with a high concentration of MgCl2 or MgSO4. The apoptosis, G0/G1 cell cycle arrest, autophagy, and ER stress were promoted following treatment with MgCl2. However, the migratory ability of MgCl2 treated cells was similar to that of control cells, as revealed by the trans-well assay. Besides, no significant difference was observed in the proportion of CD44 or CD133 positive cells between the control and MgCl2 treated cells. Thus, to improve the therapeutic effect of magnesium, VPA was used to treat cancer cells in combination with MgCl2. As expected, combination treatment with MgCl2 and VPA could markedly reduce proliferation, migration, and in vivo tumorigenicity of UC3 cells. Moreover, the Wnt signaling was down-regulated, and ERK signaling was activated in the cells treated with combination treatment. In conclusion, the accurate utilization of MgCl2 in targeting autophagy might be beneficial in cancer therapy. Although further studies are warranted, the combination treatment of MgCl2 with VPA is an effective strategy to improve the outcome of chemotherapy.

DNA-Biofunctionalization of CTAC-Capped Gold Nanocubes.

Clinical diagnostics and disease control are fields that strongly depend on technologies for rapid, sensitive, and selective detection of biological or chemical analytes. Nanoparticles have become an integral part in various biomedical detection devices and nanotherapeutics. An increasing focus is laid on gold nanoparticles as they express less cytotoxicity, high stability, and hold unique optical properties with the ability of signal transduction of biological recognition events with enhanced analytical performance. Strong electromagnetic field enhancements can be found in close proximity to the nanoparticle that can be exploited to enhance signals for e.g., metal-enhanced fluorescence or Raman spectroscopy. Even stronger field enhancements can be achieved with sharp-edged nanoparticles, which are synthesized with the help of facet blocking agents, such as cetyltrimethylammonium bromide/chloride (CTAB/CTAC). However, chemical modification of the nanoparticle surface is necessary to reduce the particle’s cytotoxicity, stabilize it against aggregation, and to bioconjugate it with biomolecules to increase its biocompatibility and/or specificity for analytical applications. Here, a reliable two-step protocol following a ligand exchange with bis (p-sulfonatophenyl) phenyl phosphine (BSPP) as the intermediate capping-agent is demonstrated, which results in the reliable biofunctionalization of CTAC-capped gold nanocubes with thiol-modified DNA. The functionalized nanocubes have been characterized regarding their electric potential, plasmonic properties, and stability against high concentrations of NaCl and MgCl2.

Effect of Zn2+ on Cathodic Reaction of Carbon Steel in Aqueous MgCl2 Solutions

We have shown that zinc dissolution is accelerated in relatively high concentrations of MgCl2 during the galvanic corrosion process consisting of zinc and carbon steel. In this study, in order to understand further the galvanic corrosion process of zinc and carbon steel in MgCl2, the cathode reaction on carbon steel was investigated in MgCl2 aqueous solution with and without Zn2+ which is generated during the galvanic corrosion process.The sample used for the experiment was carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined to a shape of 1.5 × 1.5 × 0.3 cm3. One side of this sample was ground up to #2000 grit with SiC abrasive papers and then degreased and washed in acetone before use in the following experiments. The test solutions were mixtures of 0.25 M MgCl2 and x mM ZnCl2 (x = 2.5, 5 mM, Mg / Zn molar ratio: 100, 50) and they were used at room temperature under a naturally aerated condition. As reference solutions, the mixtures of 0.5 M NaCl and y mM ZnCl2 (x = 5, 10 mM, Na / Zn molar ratio: 100, 50) with the same Cl- concentration were used. The cathodic polarization curve measurements were done by a conventional three-electrode method with a platinum wire as a counter electrode and an Ag / AgCl electrode (saturated KCl, SSE) as a reference electrode. The potential sweep rate was 0.5 mV/sOn the cathodic polarization curves for carbon steel measured in an aqueous MgCl2 solution containing Zn2+, the diffusion-limiting current region due to the cathodic reduction reaction of dissolved oxygen (ORR) was observed from -0.6 V to -0.8 V, and the magnitude of the limiting currents were almost the same regardless of the Zn2+ concentration. Furthermore, the cathodic polarization curves showed that an increase in the current due to the hydrogen evolution reaction (HER) occurred in the MgCl2 solution without Zn2+. By comparison with the cathodic polarization curve measured in the NaCl solution without Zn2+ showed a diffusion-limiting current of ORR was comparable to that in the MgCl2 solution, but the overvoltage of HER was increased by about 0.1 V. These results indicated that in the MgCl2 solution, HER on carbon steel was enhanced more than that in NaCl aqueous solution.On the other hand, in the MgCl2 solutions containing Zn2+, a shoulder was observed in the cathode polarization curve at around -0.95 V, and the the current due to HER was decreased with increasing the Zn2+ concentration. It was shown that HER was suppressed in MgCl2 solutions by the presence of Zn2+. This may be attributed to the precipitation of zinc corrosion products formed during cathodic polarization.

Structural transitions of sword bean canavalin in response to different salt concentrations

Canavalin is the major storage protein in sword beans (Canavalia gladiata) and belongs to the 7S seed globulin class. Canavalin solubility can be reversibly altered via the addition of MgCl2 and CaCl2 at different concentrations; specifically, it is insoluble at lower concentrations and soluble at higher concentrations. However, the addition of NaCl does not induce the insolubilization of canavalin. In this study, it was determined that the addition of NaCl causes the nearly complete solubilization of MgCl2-precipitated canavalin in the presence of high concentrations. Moreover, using gel filtration we examined the quaternary structures of soluble canavalin in the bean extract and in the presence of high-concentration salts. Results indicated that canavalin was present in the monomer form within crude extracts with distilled water. Alternatively, we identified trimeric soluble canavalin in the presence of high concentrations of NaCl or MgCl2. Our study revealed that the quaternary structures of sword bean soluble proteins differ in crude extract compared to those in high-concentration salt solutions. The three-dimensional structure of β-conglycinin, which is a typical 7S-seed globulin in soybean, has a trimer form in the presence of high concentrations of NaCl. However, it remains unclear whether β-conglycinin is present as trimers in soybean seed. Our findings serve as an important reference to analyze 7S globulin characteristics.

Multiple uses of magnesium chloride during waste activated sludge alkaline fermentation

Multiple uses of magnesium chloride during waste activated sludge (WAS) alkaline fermentation was investigated. The results revealed that a higher MgCl2 concentration inhibited acidogenesis, while the purity of volatile fatty acids (VFAs) improved and the maximum percentage of VFAs accounted for 52.92% (w/w) of soluble chemical oxygen demand (SCOD) at 120 mmol/L Mg2+. A phosphate removal efficiency of 81.22% was obtained at 15 mmol/L MgCl2 concentration, while only a 14.77% increase was observed when further MgCl2 was added (120 mmol/L MgCl2). Capillary suction time (CST) values decreased sharply from 4410.20 s to 207.30 s with the increase of MgCl2. A similar trend was observed in bound water and the minimum value was 85.56 ± 0.06%. The distribution of extracellular polymeric substances (EPS) and rheological profiles of the fermented sludge were also analyzed and the results confirmed that a high MgCl2 concentration had a positive effect on sludge dewatering.

Insights Into the Microbiology of the Chaotropic Brines of Salar de Atacama, Chile.

Microbial life inhabiting hypersaline environments belong to a limited group of extremophile or extremotolerant taxa. Natural or artificial hypersaline environments are not limited to high concentrations of NaCl, and under such conditions, specific adaptation mechanisms are necessary to permit microbial survival and growth. Argentina, Bolivia, and Chile include three large salars (salt flats) which globally, represent the largest lithium reserves, and are commonly referred to as the Lithium Triangle Zone. To date, a large amount of information has been generated regarding chemical, geological, meteorological and economical perspectives of these salars. However, there is a remarkable lack of information regarding the biology of these unique environments. Here, we report the presence of two bacterial strains (isolates LIBR002 and LIBR003) from one of the most hypersaline lithium-dominated man-made environments (total salinity 556 g/L; 11.7 M LiCl) reported to date. Both isolates were classified to the Bacillus genera, but displayed differences in 16S rRNA gene and fatty acid profiles. Our results also revealed that the isolates are lithium-tolerant and that they are phylogenetically differentiated from those Bacillus associated with high NaCl concentration environments, and form a new clade from the Lithium Triangle Zone. To determine osmoadaptation strategies in these microorganisms, both isolates were characterized using morphological, metabolic and physiological attributes. We suggest that our characterization of bacterial isolates from a highly lithium-enriched environment has revealed that even at such extreme salinities with high concentrations of chaotropic solutes, scope for microbial life exists. These conditions have previously been considered to limit the development of life, and our work extends the window of life beyond high concentrations of MgCl2, as previously reported, to LiCl. Our results can be used to further the understanding of salt tolerance, most especially for LiCl-dominated brines, and likely have value as models for the understanding of putative extra-terrestrial (e.g., Martian) life.

Phenomics and Genomics Reveal Adaptation of Virgibacillus dokdonensis Strain 21D to Its Origin of Isolation, the Seawater-Brine Interface of the Mediterranean Sea Deep Hypersaline Anoxic Basin Discovery.

The adaptation of sporeformers to extreme environmental conditions is frequently questioned due to their capacity to produce highly resistant endospores that are considered as resting contaminants, not representing populations adapted to the system. In this work, in order to gain a better understanding of bacterial adaptation to extreme habitats, we investigated the phenotypic and genomic characteristics of the halophile Virgibacillus sp. 21D isolated from the seawater-brine interface (SBI) of the MgCl2-saturated deep hypersaline anoxic basin Discovery located in the Eastern Mediterranean Sea. Vegetative cells of strain 21D showed the ability to grow in the presence of high concentrations of MgCl2, such as 14.28% corresponding to 1.5 M. Biolog phenotype MicroArray (PM) was adopted to investigate the strain phenotype, with reference to carbon energy utilization and osmotic tolerance. The strain was able to metabolize only 8.4% of 190 carbon sources provided in the PM1 and PM2 plates, mainly carbohydrates, in accordance with the low availability of nutrients in its habitat of origin. By using in silico DNA-DNA hybridization the analysis of strain 21D genome, assembled in one circular contig, revealed that the strain belongs to the species Virgibacillus dokdonensis. The genome presented compatible solute-based osmoadaptation traits, including genes encoding for osmotically activated glycine-betaine/carnitine/choline ABC transporters, as well as ectoine synthase enzymes. Osmoadaptation of the strain was then confirmed with phenotypic assays by using the osmolyte PM9 Biolog plate and growth experiments. Furthermore, the neutral isoelectric point of the reconstructed proteome suggested that the strain osmoadaptation was mainly mediated by compatible solutes. The presence of genes involved in iron acquisition and metabolism indicated that osmoadaptation was tailored to the iron-depleted saline waters of the Discovery SBI. Overall, both phenomics and genomics highlighted the potential capability of V. dokdonensis 21D vegetative cells to adapt to the environmental conditions in Discovery SBI.

Evolved tolerance to freshwater salinization in zooplankton: life-history trade-offs, cross-tolerance and reducing cascading effects.

Recent discoveries have documented evolutionary responses to freshwater salinization. We investigated if evolutionary responses to salinization exhibit life-history trade-offs or if they can mitigate ecological impacts such as cascading effects through mechanisms of tolerance and cross-tolerance. We conducted an outdoor mesocosm experiment using populations of Daphnia pulex-a ubiquitous algal grazer-that were either naive or had previously experienced selection to become more tolerant to sodium chloride (NaCl). During the initial phase of population growth, we discovered that evolved tolerance comes at the cost of slower population growth in the absence of salt. We found evolved Daphnia populations maintained a tolerance to NaCl approximately 30 generations after the initial discovery. Evolved tolerance to NaCl also conferred cross-tolerance to a high concentration of CaCl2 (3559 µS cm-1) and a moderate concentration of MgCl2 (967 µS cm-1). A higher concentration of MgCl2 (2188 µS cm-1) overwhelmed the cross-tolerance and killed all Daphnia Tolerance to NaCl did not mitigate NaCl-induced cascades leading to phytoplankton blooms, but cross-tolerance at moderate concentrations of MgCl2 and high concentrations of CaCl2 mitigated such cascading effects caused by these two salts. These discoveries highlight the important interplay between ecology and evolution in understanding the full impacts of freshwater salinization.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Damage in cement pastes exposed to MgCl2 solutions

Magnesium chloride (MgCl2) reacts with cement pastes resulting in calcium leaching and the formation of calcium oxychloride, which can cause damage. This paper examines the damage in different cement pastes exposed to MgCl2 solutions. Volume change measurement and low temperature differential scanning calorimetry are used to characterize the formation of calcium oxychloride. Thermogravimetric analysis and X-ray fluorescence are used to quantify calcium leaching from Ca(OH)2 and C-S-H. The ball-on-three-balls test is used to quantify the flexural strength reduction. Calcium oxychloride can form in cement pastes exposed to MgCl2 solutions with a (Ca(OH)2/MgCl2) molar ratio larger than 1. As the MgCl2 concentration increases, two-stages of flexural strength reduction are observed in the plain cement pastes, with the initial reduction primarily due to calcium leaching from Ca(OH)2 and the additional reduction due to the calcium leaching from C-S-H (at MgCl2 concentrations above 17.5 wt%). For the cement pastes containing fly ash, there is a smaller reduction in flexural strength as less Ca(OH)2 is leached, while no additional reduction is observed at high MgCl2 concentrations due to the greater stability of C-S-H with a lower Ca/Si ratio. The addition of fly ash can mitigate damage in the presence of MgCl2 solutions.

Accurate fidelity analysis of the reverse transcriptase by a modified next-generation sequencing

We evaluated fidelity of various reverse transcriptases (RTs) by a novel method with modified next-generation sequencing (NGS). In the optimized condition, one NGS run could handle cDNA products from multiple cDNA synthesis reactions performed at different conditions. This was achieved using a primer containing not only the tag of 14 randomized bases to label each cDNA molecule but also a tag of five bases to label each reaction condition. With this method, we quantitated the error rates of 44 cDNA synthesis reactions by retroviral RTs or genetically engineered DNA polymerases with RT activity under different conditions. The results indicated that high concentrations of MgCl2, Mn(OCOCH3)2, and dNTP decrease the fidelity and that these effects are more pronounced in reactions using RT from human immunodeficiency virus type 1. This is the first report about a precise fidelity monitoring of various RTs by a direct sequence determination.

Volumetric, Viscometric, and1H NMR Studies on Caffeine, Theophylline, and Theobromine in Aqueous Solutions of MgCl2at TemperaturesT= (288.15 to 318.15) K and at Pressurep= 101.3 kPa

Apparent molar volumes (V2,ϕ) and viscosity B-coefficients for xanthine drugs (caffeine, theophylline, and theobromine) in aqueous (0.09999–0.99989) mol·kg–1 MgCl2 solutions have been determined from measured densities ρ and viscosities η, respectively at T = (288.15 to 318.15) K and at pressure p = 101.3 kPa. These studies indicate the decrease in solubilization of xanthine drugs with increasing ionic strengths of MgCl2 solutions. The results have also been interpreted in terms of structure making/breaking ability of solutes. Spectroscopic studies also support that hydrophilic–ionic interactions are greater at lower concentrations of MgCl2, which descend and finally become weaker at higher concentrations of MgCl2. This type of behavior may also be understood in terms of a large dehydration effect.

Prokaryotic diversity and community composition in the Salar de Uyuni, a large scale, chaotropic salt flat.

Salar de Uyuni (SdU), with a geological history that reflects 50000 years of climate change, is the largest hypersaline salt flat on Earth and is estimated to be the biggest lithium reservoir in the world. Its salinity reaches saturation levels for NaCl, a kosmotropic salt, and high concentrations of MgCL2 and LiCl, both salts considered important chaotrophic stressors. In addition, extreme temperatures, anoxic conditions, high UV irradiance, high albedo and extremely low concentrations of phosphorous, make SdU a unique natural extreme environment in which to contrast hypotheses about limiting factors of life diversification. Geophysical studies of brines from different sampling stations show that water activity is rather constant along SdU. Geochemical measurements show significant differences in magnesium concentration, ranging from 0.2 to 2M. This work analyses the prokaryotic diversity and community structure at four SdU sampling stations, selected according to their location and ionic composition. Prokaryotic communities were composed of both Archaea (with members of the classes Halobacteria, Thermoplasmata and Nanohaloarchaea, from the Euryarchaeota and Nanohaloarcheota phyla respectively) and Bacteria (mainly belonging to Bacteroidetes and Proteobacteria phyla). The important differences in composition of microbial communities inversely correlate with Mg2+ concentration, suggesting that prokaryotic diversity at SdU is chaotropic dependent.