High Concentrations Of Magnesium Ions Research Articles

Hydration evolution of MgO-SiO2 slurries in the presence of sodium metasilicate

In order to accelerate the formation of magnesium-silicate-hydrate gel (M-S-H), the sodium metasilicate was added into the MgO-SiO2 slurries. The effect of sodium metasilicate on the hydration process of MgO-SiO2 slurries was investigated in this work. It required a relatively small amount of sodium metasilicate to facilitate the formation of M-S-H and to surpress the brucite formation. In the early 24h, the M-S-H formed quickly due to the high concentration of magnesium ions and silicate species in solutions. With the further increasing of curing time, the M-S-H gel phase continuously grew. Furthermore, the sufficient silicate ions amount was favorable for the transformation of newly formed brucite to the M-S-H phase. The addition of sodium metasilicate influenced not only the reaction process but also the morphology of hydrates. Instead of the yolk-shell structure, the flower-like and stacked sheet-like M-S-H formed in the presence of sodium metasilicate.

Chemical and mineralogical alterations of concrete subjected to chemical attacks in complex underground tunnel environments during 20–36 years

This paper investigates the chemical and mineralogical alterations of concrete in underground tunnel structures built from 1980 to 1996, located on the China's east seashore. The underground water around the tunnels had once been treated to be not or little aggressive. However, the complex environments in the tunnels had increased the aggressiveness of certain ingredients, thus causing chemical attacks. The chlorides in the leakage underground water cause chloride attack, and the NaCl crystallizations on the surface of the C50 pre-cast concrete segments induce a deeper chloride contamination. When the concrete suffers flowing leakage water, calcium leaching also occurs, leading to decalcification and magnesium incorporation. Under this circumstance, C50 pre-cast concrete shows a higher resistance compared with C30 cast-in-place concrete, mainly due to the low water to binder ratio. Within the C30 cast-in-place concrete facing concentrated leakage water and NaCl crystallizations, a strong magnesium chloride attack is observed. Besides the materials factors, the environmental factors, including the high concentrations of both chloride and magnesium ions, the removal timing of calcium ion, and the water saturation, are believed to take responsibility for the magnesium chloride attack.

Investigating the Influence of Magnesium Ions on p53-DNA Binding Using Atomic Force Microscopy.

p53 is a tumor suppressor protein that plays a significant role in apoptosis and senescence, preserving genomic stability, and preventing oncogene expression. Metal ions, such as magnesium and zinc ions, have important influences on p53–DNA interactions for stabilizing the structure of the protein and enhancing its affinity to DNA. In the present study, we systematically investigated the interaction of full length human protein p53 with DNA in metal ion solution by atomic force microscopy (AFM). The p53–DNA complexes at various p53 concentrations were scanned by AFM and their images are used to measure the dissociation constant of p53–DNA binding by a statistical method. We found that the dissociation constant of p53 binding DNA is 328.02 nmol/L in physiological buffer conditions. The influence of magnesium ions on p53–DNA binding was studied by AFM at various ion strengths through visualization. We found that magnesium ions significantly stimulate the binding of the protein to DNA in a sequence-independent manner, different from that stimulated by zinc. Furthermore, the high concentrations of magnesium ions can promote p53 aggregation and even lead to the formation of self-assembly networks of DNA and p53 proteins. We propose an aggregation and self-assembly model based on the present observation and discuss its biological meaning.

Dual Tumor-Targeting Nanocarrier System for siRNA Delivery Based on pRNA and Modified Chitosan.

Highly specific and efficient delivery of siRNA is still unsatisfactory. Herein, a dual tumor-targeting siRNA delivery system combining pRNA dimers with chitosan nanoparticles (CNPPs) was designed to improve the specificity and efficiency of siRNA delivery. In this dual delivery system, folate-conjugated and PEGylated chitosan nanoparticles encapsulating pRNA dimers were used as the first class of delivery system and would selectively deliver intact pRNA dimers near or into target cells. pRNA dimers simultaneously carrying siRNA and targeting aptamer, the second class of delivery system, would specifically deliver siRNA into the target cells via aptamer-mediated endocytosis or proper particle size. To certify the delivering efficiency of this dual system, CNPPs, pRNA dimers alone, chitosan nanoparticles containing siRNA with folate conjugation and PEGylation (CNPS), and chitosan nanoparticles containing pRNA dimers alone (CN) were first prepared. Then, we observed that treatment with CNPPs resulted in increased cellular uptake, higher cell apoptosis, stronger cell cytotoxicity, and more efficacious gene silencing compared to the other three formulations. Higher accumulation of siRNA in the tumor site, stronger tumor inhibition, and longer circulating time were also observed with CNPPs compared to other formulations. In conclusion, this dual nanocarrier system showed high targeting and favorable therapeutic efficacy both in vitro and in vivo. Thereby, a new approach is provided in this study for specific and efficient delivery of siRNA, which lays a foundation for the development of pRNA hexamers, which can simultaneously carry six different substances.

ВИВЧЕННЯ УМОВ ОТРИМАННЯ СПОЛУК МАГНІЮ ОСОБЛИВОЇ ЧИСТОТИ З ЙОГО ХЛОРИДУ

In the article questions of providing quality of important for new technology Chloride compounds and Magnesium oxide of high level of purity are considered.The processes of magnesium ions alkaline hydrolysis and its features within the borders of high concentration of magnesium ions are studied. It is shown that in such conditions alkaline solutions are formed, which contain magnesium complexes that can form magnesium hydroxide sediment with special properties: high sorption capacity to impurity ions of 3-d elements and significant filtration rate, which areespecially important in the technology of separation of such sediment. Based on results obtained in the study the recommendationson the technology of obtaining high-purity Chloride and Magnesium oxide are given. Recommendations regarding applicability of the research results andtechnological techniques for other high-purity compounds such as: Sodium chloride,Potassium and Calcium are given.

An Open and Shut Case: The Interaction of Magnesium with MST Enzymes.

The shikimate pathway of bacteria, fungi, and plants generates chorismate, which is drawn into biosynthetic pathways that form aromatic amino acids and other important metabolites, including folates, menaquinone, and siderophores. Many of the pathways initiated at this branch point transform chorismate using an MST enzyme. The MST enzymes (menaquinone, siderophore, and tryptophan biosynthetic enzymes) are structurally homologous and magnesium-dependent, and all perform similar chemical permutations to chorismate by nucleophilic addition (hydroxyl or amine) at the 2-position of the ring, inducing displacement of the 4-hydroxyl. The isomerase enzymes release isochorismate or aminodeoxychorismate as the product, while the synthase enzymes also have lyase activity that displaces pyruvate to form either salicylate or anthranilate. This has led to the hypothesis that the isomerase and lyase activities performed by the MST enzymes are functionally conserved. Here we have developed tailored pre-steady-state approaches to establish the kinetic mechanisms of the isochorismate and salicylate synthase enzymes of siderophore biosynthesis. Our data are centered on the role of magnesium ions, which inhibit the isochorismate synthase enzymes but not the salicylate synthase enzymes. Prior structural data have suggested that binding of the metal ion occludes access or egress of substrates. Our kinetic data indicate that for the production of isochorismate, a high magnesium ion concentration suppresses the rate of release of product, accounting for the observed inhibition and establishing the basis of the ordered-addition kinetic mechanism. Moreover, we show that isochorismate is channeled through the synthase reaction as an intermediate that is retained in the active site by the magnesium ion. Indeed, the lyase-active enzyme has 3 orders of magnitude higher affinity for the isochorismate complex relative to the chorismate complex. Apparent negative-feedback inhibition by ferrous ions is documented at nanomolar concentrations, which is a potentially physiologically relevant mode of regulation for siderophore biosynthesis in vivo.

Groundwater contamination sourced from the main cemetery of Tabriz, Iran

ABSTRACTSitting on porous and highly permeable volcanic tuffs, the main cemetery of Tabriz (Vadi-e Rahmat) poses a high potential risk to groundwater quality. To investigate the potential pollution, groundwater was sampled in the fall of 2011 and spring of 2012 around the cemetery and analyzed for major physicochemical and microbial parameters by standard methods. The results indicated relatively high concentrations of calcium, magnesium, sulfate, nitrate, and fluoride ions and microbial colonies in the aquifer samples; nitrate:sodium and chloride:sodium ratios as well as good correlation between nitrate and fluoride concentrations confirmed the source of contamination to be the cemetery. These releases from the cemetery have also contaminated local qanats, traditional Iranian horizontal channels that are used for irrigation and drinking water. The main factors that increase the risk of groundwater pollution from the cemetery are the relatively shallow groundwater table, the relatively high permeability of the aquifer, and the high rate of burials.

Phase transformation of Mg-calcite to aragonite in active-forming hot spring travertines

A travertine specimen collected from the western part of Yunnan Province of China was subjected to microstructural analysis by powder X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. A new formation mechanism was proposed whereby polycrystalline rhombohedral particles of magnesium-containing calcite underwent a phase transformation into sheaf-like clusters of aragonite microrods. It is proposed that a high concentration of magnesium ions and embedded biological matter poisoned the growth of calcite and therefore instigated the phase transformation of the core of the rhombohedral calcite particles to an aragonite phase with a higher crystallinity. The single crystalline aragonite microrods with a higher density than the Mg-calcite nanocrystallites grew at the expense of the latter to generate sheaf-like clusters. This newly discovered formation mechanism is expected to enhance previous knowledge on this geologically important phase transformation from a morphology point of view.

Biodegradation of metallic magnesium elicits an inflammatory response in primary nasal epithelial cells

Resorbable magnesium-based implants hold great promise for various biomedical applications, such as osteosynthesis and coronary stenting. They also offer a new therapeutic option for the treatment of chronic rhinosinusitis, but little data is yet available regarding the use of magnesium in the nasal cavity. To model this field of application, primary porcine nasal epithelial cells were used to test the biocompatibility of degrading pure magnesium and investigate whether the degradation products may also affect cellular metabolism. Magnesium specimens did not induce apoptosis and we found no major influence on enzyme activities or protein synthesis, but cell viability was reduced and elevated interleukin 8 secretion indicated proinflammatory reactions. Necrotic damage was most likely due to osmotic stress, and our results suggest that magnesium ion build-up is also involved in the interleukin 8 release. Furthermore, the latter seems to be mediated, at least in part, by the p38 signaling pathway. These effects probably depended on the accumulation of very high concentrations of magnesium ions in the in vitro set-up, which might not be achieved in vivo, although we cannot exclude that further, as yet unknown, factors played a role in the inflammatory response during the degradation process. In conclusion, the biocompatibility of pure magnesium with cells in the immediate vicinity appears less ideal than is often supposed, and this needs to be considered in the evaluation of magnesium materials containing additional alloying elements.

The Effect of Magnesium Ion Concentration on the Fibrocartilage Regeneration Potential of Goat Costal Chondrocytes

Magnesium has recently been explored as a potential biomaterial for degradable orthopedic implants but its effect on fibrocartilage remains unknown. The objective of this study was to assess the effect of high concentrations of magnesium ions on the matrix production of goat costal fibrochondrocytes in vitro. Cells were cultured using a scaffoldless approach with media containing magnesium chloride (MgCl(2)) or magnesium sulfate (MgSO(4)) at concentrations of 20, 50, and 100 mM in addition to the baseline magnesium concentration of 0.8 mM MgSO(4). At 4 weeks, there were no significant differences in compressive tangent modulus and total matrix production between constructs cultured in 20 mM Mg(2+) and the 0.8 mM Mg(2+) control (435 ± 47 kPa). There was a significant decrease in compressive tangent modulus compared to the 0.8 mM Mg(2+) constructs in the 50 mM MgCl(2) and MgSO(4) groups, while the 100 mM groups were not mechanically testable (p < 0.05). The collagen and glycosaminoglycan (GAG) content of the 50 and 100 mM MgCl(2) and MgSO(4) constructs was significantly lower than the control (6.9 ± 0.5% and 16.5 ± 1.3% per dry weight, respectively) (p < 0.05). The results show that goat costal fibrochondrocytes exhibit a high degree of resiliency to magnesium ion concentrations up to 20 mM in vitro.

Necessity and feasibility of improving the residual resistance factor of polymer flooding in heavy oil reservoirs

The efficiency of water flooding in heavy oil reservoirs would be improved by increasing the viscosity of the displacing phase, but the sweep efficiency is not of significance due to the low mobility of the vicious oil. On the basis of mobility control theory, increasing the residual resistance factor not only reduces the water-oil mobility ratio but also decreases the requirement for viscosity enhancement of the polymer solution. The residual resistance factor caused by hydrophobic associating polymer solution is higher than that caused by polyacrylamide solution in brine containing high concentrations of calcium and magnesium ions. The results of numerical simulations show that the polymer flooding efficiency improved by increasing the residual resistance factor is far better than that by only increasing solution viscosity. The recovery factor of heavy oil reservoirs (70 mPa·s) can be enhanced by hydrophobic associating polymer solution of high residual resistance factor (more than 3) and high effective viscosity (24 mPa·s). Therefore, increasing the residual resistance factor of the polymer solution not only decreases the requirement for the viscosity of polymer solution injected into heavy oil reservoirs but also is favorable to enhanced oil recovery during polymer flooding.

Structural Diversity of Triplet Repeat RNAs

Tandem repeats of various trinucleotide motifs are present in the human transcriptome, but the functions of these regular sequences, which likely depend on the structures they form, are still poorly understood. To gain new insight into the structural and functional properties of triplet repeats in RNA, we have performed a biochemical structural analysis of the complete set of triplet repeat transcripts, each composed of a single sequence repeated 17 times. We show that these transcripts fall into four structural classes. The repeated CAA, UUG, AAG, CUU, CCU, CCA, and UAA motifs did not form any higher order structure under any analyzed conditions. The CAU, CUA, UUA, AUG, and UAG repeats are ordered according to their increasing tendency to form semistable hairpins. The repeated CGA, CGU, and all CNG motifs form fairly stable hairpins, whereas AGG and UGG repeats fold into stable G-quadruplexes. The triplet repeats that formed the most stable structures were characterized further by biophysical methods. UV-monitored structure melting revealed that CGG and CCG repeats form, respectively, the most and least stable hairpins of all CNG repeats. Circular dichroism spectra showed that the AGG and UGG repeat quadruplexes are formed by parallel RNA strands. Furthermore, we demonstrated that the different susceptibility of various triplet repeat transcripts to serum nucleases can be explained by the sequence and structural features of the tested RNAs. The results of this study provide a comprehensive structural foundation for the functional analysis of triplet repeats in transcripts.

Calcium ion release from calcium hydroxide stimulated fibronectin gene expression in dental pulp cells and the differentiation of dental pulp cells to mineralized tissue forming cells by fibronectin

The effect of calcium ions on dental pulp cells was examined and the mechanism of dentine bridge formation by calcium hydroxide was investigated. Human dental pulp cells were treated with high concentration of calcium or magnesium ions for 24 h and fibronectin gene expression was measured by the quantitative PCR method. Human dental pulp cells were then cultured on fibronecin-coated dishes for 24 h, and osteocalcin and osteopontin gene expression, which are typical phenotypes of mineralized tissue forming cells, were measured by the quantitative PCR method. Fibronectin gene expression was stimulated by calcium ions dose-dependently. On the other hand, magnesium ions did not influence fibronectin gene expression. Furthermore, pulp cells cultured on fibronectin-coated dishes enhanced the expression of phenotypes of mineralized tissue forming cells. Calcium ions released from calcium hydroxide stimulates fibronectin synthesis in dental pulp cells. Fibronectin might induce the differentiation of dental pulp cells to mineralized tissue forming cells that are the main cells to form dentine bridges, via contact with cells.

Condition of Soils and Vegetation Along Roads Treated with Magnesium Chloride for Dust Suppression

Investigations of vegetation stress along non-paved roads treated with a range of magnesium chloride (MgCl2) application rates utilized 60 roadside and 79 drainage plots on 15 and 18 roads, respectively. Evaluations were completed of foliar damage, plant health, biotic and abiotic damage incidence and severity, soil and foliar chemistry and other common site and stand characteristics of Pinus contorta, Populus tremuloides, Picea engelmannii, Abies lasiocarpa, and lower elevation plots dominated by shrubs and grasses. High concentrations of soil magnesium and chloride (400–500 ppm), high foliar chloride (2,000–16,000 ppm depending on species) and high incidence of foliar damage were measured in roadside plots along straight road segments in the first 3 to 6.1 m adjacent to treated roads. In drainage plots, where water is channeled off roads, high concentrations of both magnesium and chloride ions and associated foliar damage were measured between 3 and 98 m from the road. High incidence of foliar damage and elevated ion concentrations were not apparent in control plots along non-treated roads. Lodgepole pine appeared to be the most sensitive species, while aspen accumulated the most chloride and exhibited the least amount of damage. Foliar chloride concentrations strongly correlated with percent foliar damage for all species (r = 0.53 to 0.74, p < 0.0001) while the incidence of biotic damages did not correlate well. Positive relationships between foliar chloride and magnesium chloride application rates were strong and can be used to predict foliar concentrations and subsequent damage to roadside trees.

Concentrations of Nitrate, Organic Acids, Free Amino Acids, Cations and Sugars in Komatsuna (Brassica campestris var. perviridis) Grown with Carbonate, Sulfate and Chloride Application

This study compared the concentrations of components such as nitrate, organic acids, free amino acids, cations and sugars in komatsuna (Brassica campestris var. perviridis) grown with carbonate, sulfate and chloride application (CO3-TK, SO4-TK and Cl-TK, respectively). The komatsuna was cultivated in 1/2000-a Wagner pots (6 hills per pot) filled with light-colored Andosol in a glasshouse for 37 days at soil water potential (SWP) right before harvesting of −6.2 and −62 kPa. And 26.5 mmolc of carbonate, sulfate or chloride in the form of potassium salts was applied to each pot. Chloride application to the komatsuna induced relatively high concentrations of potassium, calcium and magnesium ions, and the low concentrations of malate, glucose and fructose on a dry weight basis (DWB). Carbonate application induced relatively high concentrations of malate and low concentrations of nitrate. Sulfate was almost between chloride and carbonate. Concentration variation was not substantial in free amino acids. Those tendencies were almost the same in both SWPs. Most of the variations in component concentrations were attributed to the regulation of ionic and osmotic balance to respond to chloride, nitrate and sulfate absorption, as judged from quantitative relationships among the components and water in the komatsuna. It seems that the absorption of nitrate is influenced by the pH of the soil. There were clear differences in glucose, fructose and malate concentrations among CO3-TK, SO4-TK and Cl-TK on a fresh weight basis just as on a DWB.

Mutational analysis on the S-domain of bacterial ribonuclease P ribozyme

We have prepared a temporal engineering template for Escherichia coli RNase P RNA that has additional restriction sites on the S-domain region. We have prepared several deletion variants of S-domain region. The results showed the P12 and P13 domains are necessary for efficient enzymatic reactions and the absence of P14 and P17 domains are easily rescued by the presence of high concentration of magnesium ions.

Effects of high magnesium ion concentration on KCl flotation: Part II – Plant research

There appears to be several mechanisms affecting the recovery of coarse KCl particles as they flow through the flotation circuit of the Taquari Vassouras mine (Companhia Vale do Rio Doce; CVRD), Aracaju, Brazil in the presence of continually increasing concentrations of carnallite. The increase in carnallite assists in the deposition of fine NaCl and KCl crystals on the surface of the coarse KCl particles. The effect seems to be a slight net improvement in the surface hydrophobicity and therefore flotation recovery of the coarse KCl particles. As the concentration of Mg 2+ ions increase, the precipitation of fine crystals of NaCl and KCl starts to increase. These NaCl crystals appear to have fine inclusions of KCl on the surface (and vice versa) which appear to attract collector, thus reducing hydrophobicity and flotation recovery of the coarse KCl feed. It is at this stage that the removal of fine precipitates appears to become critical in order to provide enough collector coverage of the coarse KCl particles to keep them floating.

Increased Water Hardness and Magnesium Levels May Increase Occurrence of Urolithiasis in Cows from the Burdur Region (Turkey)

Objectives of the study were to measure water hardness in Burdur, and to establish its possible association with urolithiasis in cattle. Water samples were obtained from different stables (n = 15). Water hardness and the concentrations of potassium, calcium, magnesium, sodium, iron, zinc, manganese and copper ions were calculated from these water samples. Total hardness of the samples (mean 285 ppm) exceeded the standards and the water was characterized by high content of magnesium ions. Kidneys (n = 500) were collected randomly from slaughterhouses and examined for urolithiasis. Urolithiasis was observed in 102 kidneys (20.4%). The weights of the stones were between 0.02 and 237.44 g and the colour varied from white to brown. The calculi collected had various shapes and composed of calcium apatite (42.45%), struvite (20.15%), magnesium carbonate (15.15%), calcium carbonate (12.12%), and calcium phosphate cystine (10.13%). It was concluded that high water hardness with high magnesium ion concentrations in water may contribute to urolithiasis and needs to be investigated further in future studies.

Group II Intron Folding under Near-physiological Conditions: Collapsing to the Near-native State

The folding of group II intron ribozymes has been studied extensively under optimal conditions for self-splicing in vitro (42 °C and high magnesium ion concentrations). In these cases, the ribozymes fold directly to the native state by an apparent two-state mechanism involving the formation of an obligate intermediate within intron domain 1. We have now characterized the folding pathway under near-physiological conditions. We observe that compaction of the RNA proceeds slowly to completion, even at low magnesium concentration (3 mM). Kinetic analysis shows that this compact species is a “near-native” intermediate state that is readily chased into the native state by the addition of high salt. Structural probing reveals that the near-native state represents a compact domain 1 scaffold that is not yet docked with the catalytic domains (D3 and D5). Interestingly, native ribozyme reverts to the near-native state upon reduction in magnesium concentration. Therefore, while the intron can sustain the intermediate state under physiological conditions, the native structure is not maintained and is likely to require stabilization by protein cofactors in vivo.

A New Protein Engineering Approach Combining Chemistry and Biology, Part I; Site‐Specific Incorporation of 4‐Iodo‐L‐phenylalanine in vitro by Using Misacylated Suppressor tRNAPhe

An Escherichia coli suppressor tRNA(Phe) (tRNA(Phe) (CUA)) was misacylated with 4-iodo-L-phenylalanine by using the A294G phenylalanyl-tRNA synthetase mutant (G294-PheRS) from E. coli at a high magnesium-ion concentration. The preacylated tRNA was added to an E. coli cell-free system and a Ras protein that contained the 4-iodo-L-phenylalanine residue at a specific target position was synthesized. Site-specific incorporation of 4-iodo-L-phenylalanine was confirmed by using LC-MS/MS. Free tRNA(Phe) (CUA) was not aminoacylated by aminoacyl-tRNA synthetases (aaRSs) present in the E. coli cell-free system. Our approach will find wide application in protein engineering since an aryl iodide tag on proteins can be used for site-specific functionalization of proteins.