Magnesium Hexahydrate Research Articles

DESULFURIZATION OF FLUE GASES OF THERMAL POWER PLANTS WITH OBTAINING POTASSIUM-MAGNESIUM FERTILIZER (KALIMAGNESIA)

A new method of flue gas desulfurization with the production of a valuable is proposed. The essence of the method is to pass flue gases through a scrubber (Venturi) filled with magnesium hydroxide suspension. At the same time, SO2 of the flue gases will react with magnesium hydroxide according with the formation of magnesium sulfite. Crystals of magnesium sulfite are able to interact with new portions of SO2 and turn into hydrosulfite. As a result of such "washing" of flue gases, a suspension of sparingly soluble salt MgSO3∙6H2O in a 12-15% solution of MgSO4 is obtained. Magnesium hexahydrate will precipitate as large crystals and be separated in a hydrocyclone. Separated crystals of magnesium sulfite will be oxidized under the influence of air oxygen to magnesium sulfate.

Serum and urine uric acid level may have different predictive value for urinary stone composition: a retrospective cohort study of 718 patients in Chinese population.

We launched a retrospective cohort study to explore the interactions among serum uric acid (UA), urine UA, and stone types. Clinical characteristics of urolithiasis patients in Beijing Tsinghua Changgung Hospital from October 2015 to August 2017 were retrospectively collected. Participants were categorized according to the quartiles of SUA and UUA respectively. Logistic regression model was built to identify the relationship between stone composition and UA level. Cubic spline was fitted to explore the correlation between 24-h urine UA and serum UA. 718 hospitalized patients (51.1 ± 14.3years, male 63.4%) with urinary calculi were included. Higher serum UA is associated with male, alcohol use, multiple serum and urine electrolytes (e.g. potassium, chloride, calcium, phosphorus), and lower estimated glomerular filtration rate. The risk of UA stone and carbonate apatite stone was associated with serum UA while the risk of calcium oxalate (CaOx) stone and ammonium magnesium hexahydrate (AMH) was dependent on urine UA. In the unadjusted model (Model 1), higher risks of UA stones were observed in the third quartile (OR 3.26, 95% CIs 1.63-6.53, P = 0.001) and the fourth quartile (OR 3.55, 95% CIs 1.78-7.08, P < 0.001) of serum UA compared with the first quartile. The risks of carbonate apatite stone were lowered in the third (OR 0.48, 95% CIs 0.31-0.73, P = 0.001) and fourth quartile (OR 0.40, 95% CIs 0.42-0.98, P = 0.042) of serum UA. The risk of CaOx stone was increased in the fourth quartile (OR 2.14, 95% CIs 1.15-3.99, P = 0.017) while the risk of AMH stone was decreased in the third (OR 0.46, 95% CIs 0.22-0.94, P = 0.034) and fourth quartile (OR 0.35, 95% CIs 0.16-0.78, P = 0.009) of urine UA. The elevated risks of UA stones in high levels of serum UA were demonstrated in the adjusted model (Model 2). An M-shaped association was found between serum UA and urine UA in our population. Serum UA and urine UA might cast different impact on urinary calculus composition. Proper control of the parameters should be considered based on different predisposing factors in individual patients.

Structural and Optical Properties of Struvite. Elucidating Structure of Infrared Spectrum in High Frequency Range.

Study of structure and optical properties of magnesium ammonium phosphate hexahydrate crystal known as struvite is presented. Experimentally determined infrared (IR) and ultraviolet–visible (UV–vis) spectra are compared with the theoretical predictions of density functional methods. Examination of the interatomic bond lengths, Mulliken atomic charges, and binding energies of water in the magnesium hexahydrate cation, together with the analysis of the hydrogen bond pattern have allowed us to explain a special feature of the IR spectrum of struvite, a blueshift of the band corresponding to the O–H stretching mode. This mode has been assigned to a “dangling” hydroxyl group in one of the water molecules in magnesium hexahydrate. Using experimentally obtained UV–vis spectrum and performing Tauc plots analysis, optical bandgap of struvite has been narrowed to a range from 5.92 to 6.06 eV.

Age distribution and composition analysis of 198 female cases with urinary calculi

Objective To analyze the age distribution and stone composition of female patients with urinary calculi, and to provide the direction and ideas for clinical treatment. Methods 198 patients with urinary calculi were selected.The age, stone parts of patients were recorded, the stone composition was analyzed. Results In this study, there were 198 female patients with urinary calculi, 2 cases≤25 years old, accounting for 1.01%, 20 patients >25~45 years, accounting for 10.10%, 109 patients >45~65 years, accounting for 55.05 %, >65 years old patients in 67 cases, accounting for 33.84%.The main components of calcium stones were calcium carbonate components, carbonated apatite components, magnesium hexahydrate phosphate components, uric acid components, cystine components.The calcium oxalate composition stone in 158 cases, accounting for 79.80%.There were 135 cases (68.18%) of carbonate-containing apatite.8 cases of magnesium sulfate hexahydrate, accounting for 4.04%.40 cases of uric acid-containing stones, accounting for 20.20%.12 cases of cystic acid containing stones, accounting for 6.06%.198 female cases with stones were divided into mixed stones and simple stones.The mixed stones were mainly calcium oxalate + carbonate apatite, calcium oxalate + urate, calcium oxalate + cystine, carbonate apatite + magnesium phosphate hexahydrate, calcium oxalate + carbonated apatite + uric acid, calcium oxalate + carbonate apatite + cystine, carbonate apatite + magnesium phosphate hexahydrate + uric acid) .The simple stones were mainly calcium oxalate, carbonated apatite, uric acid and uric acid.According to the main components of the stone, they were divided into 131 cases of calcium oxalate, uric acid-based 23 cases, cystine-based 8 cases, 21 cases of carbonate apatite, magnesium phosphate hexahydrate mainly in 15 cases.According to the position of urinary tract stones, they were divided into upper urinary tract stones in 171 cases, 27 cases of lower urinary tract stones. Conclusion Female urinary tract stones in patients with high incidence in postmenopausal and old age, according to different components of stones should avoid the relevant dietary intake in order to avoid recurrence. Key words: Urinary calculi; Age distribution; Principal component analysis; Female

Effect of in situ generated nascent magnesia and alumina from nitrate precursor on reaction sintered magnesium aluminate spinel

Synthesis of dense magnesium aluminate spinel using a single stage solid oxide reaction is difficult owing to volume expansion associated with spinel formation. In the present work, reaction sintered magnesium aluminate spinel was prepared using commercial grade oxide in a single stage solid oxide reaction reactants. The effect of incorporation of nascent MgO and Al2O3 from nitrate precursor additives was studied. Aluminium nitrate nonahydrate and magnesium hexahydrate were used up to 2wt.% as a source of nascent Al2O3 and MgO respectively. Sintering of the mixed oxide compositions was done in the temperature range 1200–1600°C after compaction under a uniaxial pressure of 150MPa. The dilatometry study was used as a tool to observe the spinel formation reaction. Sintered products were characterised by densification study, flexural strength, thermal shock resistance measurement, phase analysis and microstructural development. The presence of excess MgO and Al2O3 enhanced the spinel formation reaction and densification of spinel at a higher temperature. The template mechanism of spinel formation was observed in the microstructures. The addition of excess alumina and magnesia was found to increase strength values. Also, much higher strength retainment even after 6–8cycles of thermal shock was observed in additive contained batches.

Metal ion-binding studies highlight important differences between flaviviral RNA polymerases

West Nile virus (WNV) is a member of the Flaviviridae family which includes a number of important human pathogens. The WNV NS5 protein harbors an RNA-dependent RNA polymerase activity which is required both for replication and transcription of the viral genome. To extend our studies on the role of metal ions in the activity of flaviviral polymerases, we have used fluorescence spectroscopy, circular dichroism, and a combination of chemical and thermal denaturation assays to monitor the consequences of metal ion binding to the enzyme. We demonstrate that the binding of magnesium is not critical for the structural stabilization of the enzyme. Moreover, structural studies indicate that the protein does not undergo conformational change upon the binding of magnesium ions. Additional binding assays also indicate that the interaction of magnesium ions with the enzyme does not significantly stimulate the interaction with the RNA or NTP substrates. The inability of cobalt hexamine, an exchange-inert metal complex structurally analogous to magnesium hexahydrate, to support the catalytic activity also allowed us to demonstrate a direct role of magnesium ions in the catalytic activity of the enzyme. Finally, a three-dimensional structural model of the active center of the enzyme was generated which highlighted the importance of two aspartate residues involved in the coordination of two metal ions. Mutational analyses confirmed the importance of these two amino acids for the binding of magnesium ions. Our data provide further insight into the precise role of magnesium ions for the RNA polymerase activity of the protein, and more importantly, highlight key differences between the RNA polymerases of the Flaviviridae family.

Structural Roles of Monovalent Cations in the HDV Ribozyme

The hepatitis delta virus (HDV) ribozyme catalyzes viral RNA self-cleavage through general acid-base chemistry in which an active-site cytidine and at least one metal ion are involved. Monovalent metal ions support slow catalysis and were proposed to substitute for structural, but not catalytic, divalent metal ions in the RNA. To investigate the role of monovalent cations in ribozyme structure and function, we determined the crystal structure of the precursor HDV ribozyme in the presence of thallium ions (Tl(+)). Two Tl(+) ions can occupy a previously observed divalent metal ion hexahydrate-binding site located near the scissile phosphate, but are easily competed away by cobalt hexammine, a magnesium hexahydrate mimic and potent reaction inhibitor. Intriguingly, a third Tl(+) ion forms direct inner-sphere contacts with the ribose 2'-OH nucleophile and the pro-S(p) scissile phosphate oxygen. We discuss possible structural and catalytic implications of monovalent cation binding for the HDV ribozyme mechanism.

The effect of ions at the surface of calcium oxalate monohydrate crystals on cell-crystal interactions.

Magnesium is an abundant ion in biologic systems, including renal tubular fluid; however, the precise role of magnesium during the interaction of calcium oxalate crystals with cells has not been previously defined. In addition, the respective roles of calcium and hydrogen ions during the cell-crystal bonding interaction remain poorly defined. Here we report an atomic level three-dimensional study of a single crystal of calcium oxalate monohydrate (COM; whewellite) which was bathed in a solution of magnesium hexahydrate for 1 year. Magnesium was not incorporated into the structure of whewellite to any significant degree. Instead, COM accepted magnesium primarily as an adsorbate in a binding configuration which, as a surface phenomenon, is controlled by localized charge effects. The effect of magnesium and calcium on the efficiency of calcium oxalate crystal binding to renal cells was also investigated. When present in supraphysiologic concentrations (greater than 0.1 M), magnesium progressively inhibited adhesion of pre-formed COM crystals to cultured renal cells. Therefore, even though magnesium does not incorporate into the crystal structure of calcium oxalate, magnesium can exert important surface effects and change the interaction of pre-formed COM with molecules anchored on the cell surface. Similarly, binding was nearly blocked when the exogenous calcium concentration was > or =0.1 M (supraphysiologic range), although in lower concentrations (within the physiologic range) exogenous calcium promoted crystal adhesion. Finally, the ambient hydrogen ion concentration also influenced calcium oxalate crystal interactions with renal cells, with maximal binding occurring at a pH of 4. Therefore, hypercalciuria and/or an acidic urine could each promote renal stone formation via increased crystal adhesion to renal cells, a previously under-appreciated potential mechanism.

Absence of Minor Groove Monovalent Cations in the Crosslinked Dodecamer C-G-C-G-A-[formula omitted]-T-T-C-G-C-G

The structure of a crosslinked B -DNA dodecamer of sequence C-G-C-G-A-A-T-T-C-G-C-G has been solved to a resolution of 1.43Å. The dithiobis-propane crosslink, -CH2-CH2-CH2-S-S-CH2-CH2-CH2-, bridges N7 atoms of adenine bases 6 and 18 in the two central base-pairs within the major groove. The crosslink is sufficiently long that no bending is induced in the helix, which is essentially isostructural with the native unlinked dodecamer at 1.9Å. A constellation of solvent peaks tentatively fitted as a spermine molecule in that earlier analysis is now seen at higher resolution to be a well-defined octahedral magnesium hexahydrate complex in the major groove. One end of the duplex curves around that complex to produce a roll-bend near base-pairs 3-5, and an overall bend in helix axis, as has long been noted. Two other magnesium complexes connect the helices and help to knit the crystal lattice together. No evidence exists for partial sodium or potassium ion substitution for solvent water molecules within the minor groove spine of hydration, as had been suggested previously: not coordination geometry and environment, nor B values, nor calculated valence values, nor difference map analyses. Indeed, the very numbers that have been claimed in support of partial substitution by sodium or potassium ions are reproduced with the present crystals, which by chemical analysis contains only one trace sodium ion per 160bp, and one potassium ion per 41bp. In contrast, our crystals contain one Mg2+per base-pair, meaning that phosphate group charge neutrality is accomplished by divalent cations, not monovalent ions. Three of these magnesium cations per duplex are localized and visible in the X-ray analysis, and nine are disordered and invisible. Hence although binding of monovalent cations within the minor groove of A -tracts on occasion may be a consequence of groove narrowing, it cannot be the cause of that narrowing. Cations, contrary to what has been claimed, are not in charge.

An Adduct of Magnesium Sulfate with a Member of the Quinolone Family (Ciprofloxacin)

In the title compound, 4-(3-carboxy-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-quinolinyl)-1- piperazinium—magnesium hexahydrate—sulfate—water(1/0.5/1/3), (C17H19FN3O3)[Mg(H2O)6]0.5SO4.3H2O, the Mg2+ ion lies on a twofold axis and adopts a nearly regular octahedral geometry. The quinolone is protonated at the terminal N atom of the piperazine residue. The H atom of the carboxylic group is hydrogen bonded to the carbonyl O atom, thus preventing the bonding of the metal to this part of the molecule.

Structure of a B-DNA decamer with a central T-A step: C-G-A-T-T-A-A-T-C-G

The X-ray crystal structure analysis of the decamer C-G-A-T-T-A-A-T-C-G has been carried out to a resolution of 1.5 Å. The crystals are space group P2 12 12 1, cell dimensions a = 38.60 A ̊ , b = 39.10 A ̊ , c = 33.07 A ̊ . The structure was solved by molecular replacement and refined with X-PLOR and NUCLSQ. The final R factor for a model with 404 DNA atoms, 108 water molecules and one magnesium hexahydrate cation is 15.7%. The double helix is essentially isostructural with C-G-A-T-C-G-A-T-C-G, with closely similar local helix parameters. The structure of the T-T-A-A center differs from that found in C-G-C-G-T-T-A-A-C-G-C-G in that the minor groove in our decamer is wide at the central T-A step rather than narrow, and the twist angle of the T-A step is small (31.1 °) rather than large. Whereas the tetrad model provides a convenient framework for discussing local DNA helix structure, it cannot be the entire story. The articulated helix model of DNA structure proposes that certain sequence regions of DNA show preferential twisting or bending properties, whereas other regions are less capable of deformation, in a manner that may be useful in sequence recognition by drugs and protein. Further crystal structure analyses should help to delineate the precise nature of sequence-dependent articulation in the DNA double helix.