Low Concentrations Of Mg Research Articles

Paleoproterozoic Dacite Dikes of the Vorontsovka Terrane, Volga–Don Orogen: Geochemistry, Age, and Petrogenesis

Metamorphosed dacitic porphyry dikes were first found in the western part of the Vorontsovka terrane, which is located in the Paleoproterozoic Volga–Don orogen at the margin of Archean Sarmatia and Volga–Ural cratons. The magmatic protolith age for the metadacites is ca. 2.07 Ga. These are ferrous, metaluminous calc-alkali I-type granitoids. The sodium specialization of the rocks and their low concentrations of Mg, Cr, Ni, and incompatible elements, with significant REE fractionation, the absence of Eu* anomalies, high Sr/Y ratio, remarkably high (Gd/Yb)n values (>10), and the radiogenic Nd isotopic composition indicate that the dacitic melts were derived from a juvenile mafic source. According to petrogenetic estimations, such conditions could be caused by the partial melting of depleted N-MORB basites in equilibrium with an eclogitic residue. The dacitic magmas were likely generated by the partial melting of mafic rocks at lower levels of the significantly thickened crust (>60 km) in relation to collision processes.

Formation of Nitrogen-Rich Hot Springs in the Water–Granite and Water–Porphyrite Systems

The processes of evolutionary transformation of solutions in crystalline rocks of different composition under formation parameters of nitrogen-bearing hot springs have been studied using physicochemical modeling. It has been established that the fundamental factor in the formation of solutions that correspond to modern nitrogen hot springs in composition is the presence of elements that produce anions in the host rocks in appropriate concentrations. They create a characteristic geochemical environment that controls their concentrations and speciation in the solutions and the crystallization/dissolution timing and amounts of secondary minerals at each step of changing the value of the rock/water ratio. Both cations and anions clearly maintain the sequence of their presence in the solution in accordance to their concentration in the rock until the time when the crystallization of secondary minerals modifies the trends of component concentrations in the solution. The reasons for low and very low mineralization of nitrogen hot springs, low concentrations of Mg, Ca, and K and high contents of Na and Si are elucidated. Modern nitrogen terms cannot be formed in rocks containing elements that form anions in an amount corresponding to their average values. Based on the revealed high discreteness of the distribution of these elements in space and their extremely poor understanding, it is concluded that the successful study of hydrogeochemical processes is impossible without taking into account the geological heterogeneity, which is a key problem of hydrogeochemistry and is not taken into account when the processes of interaction in the water/rock system are studied.

Hydrogeochemical controls and recharge-flow system of groundwater in the lowland of the Fukui-Ohno Basin, central Japan, based on carbon isotopic signatures

• River water mixing and CO 2 dissolution in groundwater was modeled with δ 13 C tracers. • Decomposition of both C3 and lacustrine organic matter was related to CO 2 dissolution. • Modeling identified similar amounts of vertical and horizontal groundwater recharge. Carbon stable isotopic compositions of dissolved inorganic carbon (δ 13 C DIC ) and chemical compositions of groundwater were used to investigate the processes of supply of DIC to groundwater in the lowland area of the Fukui-Ohno Basin and to examine constraints on the groundwater recharge-flow system. The groundwater in the basin is dominantly of Ca-HCO 3 type with relatively high concentrations of Ca 2+ and HCO 3 − and lower concentrations of Mg 2+ ; this groundwater chemistry can be attributed to weathering within the aquifer of mainly anorthite and some pyroxene at partial pressures of CO 2 that are typical of soils. The δ 13 C values of the CO 2 gas initially equilibrated with DIC in the groundwater were calculated to be −28.6‰ to −22.8‰, indicating that the groundwater in the lowland basin has two main sources of carbon: (1) C3 organic matter (δ 13 C ≈ −29‰), distributed mainly in mountains surrounding much of the basin and in aquicludes within the basin; and (2) organic matter in shallow lacustrine deposits within the lowland basin (δ 13 C ≈ −20‰). The results of modeling accounting for these two sources demonstrated that roughly equal proportions (50 ± 20%) of DIC in the groundwater are sourced from lacustrine deposits and C3 organic matter. The distributions of these types of organic matters in and around the lowland basin suggest that there are two major and roughly equal components of groundwater recharge: a vertical component of downward percolation of precipitation in the lowland area and a mainly horizontal component of groundwater flow originating in the mountains around the study area and flowing through aquifers into the lowland basin.

Role of the Dilution of the Gd Sublattice in Forming the Scintillation Properties of Quaternary (Gd,Lu)3Al2Ga3O12: Ce Ceramics

Technological factors and processes contributing to the scintillation mechanism have been considered in quaternary garnet ceramics doped with Ce(Gd,Lu)3Al2Ga3O12. The super-stoichiometric additive of gadolinium in the material composition or its co-doping with a low concentration of Mg were found to be effective tools to suppress phosphorescence in the quaternary garnet, confirming that it is not an intrinsic property of the material. The Monte-Carlo simulation of electronic excitation transfer demonstrates that the hopping migration along the gadolinium sublattice plays an essential role in forming the scintillation kinetic parameters. Breaking the integrity of the gadolinium sublattice by substitution with heavier lutetium ions increases the role of self-trapped states in the excitation of Ce3+ ions, which ensures both an increase in the fraction of short ~20 ns and very long ~600 ns components in the scintillation kinetics.

The magnesium isotopic compositions of the crust and mantle: A study on the Oman ophiolite

Magnesium isotope compositions (δ26Mg) can provide valuable insights into Mg cycling through surface fluid-rock interactions. Isotopic variations of Mg within the oceanic lithosphere imply incorporation of isotopically different Mg, but the underlying mechanisms remain uncertain. In this study, we measure the Mg isotopic composition of the oceanic crust (n = 32) and mantle peridotite (n = 13) from the Oman ophiolite, which has experienced magmatism at the spreading center and subduction zone. The crustal section records δ26Mg values that range from −0.58 to −0.04 ‰. In the upper crustal section, higher Mg-bearing mineral abundance tends to have lighter δ26Mg values. However, the lower crustal section has no correlation with the δ26Mg values, indicating that the hydrothermal Mg sink formed by seawater was significant within the upper 2 km of the oceanic crust. In the mantle section, the δ26Mg values range from −0.39 ‰ to −0.07 ‰. Seven peridotite samples, with a loss of MgO by up to 5.3%, have slightly higher δ26Mg values than the global mantle, which may be attributed to low-temperature weathering. In contrast, three peridotite samples with higher melting degrees (spinel Cr# = Cr/(Cr + Al) atomic ratio) than the adjacent rocks are considered to have been affected by subduction-related interactions, forming lighter δ26Mg values. The isotopically light Mg source was subducted sediments, but its low concentration of Mg requires a water/rock ratio >> 1. Therefore, we conclude that the contribution of slab-derived Mg and modification of mantle δ26Mg values were localized.

Characterization of the molten salt FMgNaK through ab initio molecular dynamics and experimental density measurements

The selection of a salt species for use in a molten salt reactor MSR is a key part of any MSR design. However, many salts have sparse or no thermophysical property data sets, especially those with higher melting points . One such salt is the eutectic mixture of (NaF)0.345(KF)0.59(MgF 2 )0.065, or FMgNaK, and is explored here through ab initio molecular dynamics (AIMD) simulation (1023-1273K) as well as experimental measurement of the liquid density using the Archimedean method (973-1223K). Predicted densities from AIMD are similar to experimentally-measured densities, though with more noise, suggesting that the small scale necessitated by AIMD simulations may be problematic for simulating FMgNaK in particular. The coefficient of thermal expansion is predicted from simulation, and salt structure is characterized. Mg-F-Mg chaining is observed in the salt network, though the low concentration of Mg inhibits chaining on the scale that is observed in (LiF) 0.67 (BeF 2 ) 0.33 , or FLiBe.

Geology, geochemistry and geochronology of Lindero porphyry gold deposit in the Southern Puna plateau, Argentina

The Lindero gold deposit is located in the Southern Puna plateau, northwest Argentina. The deposit is centered in a cluster of six subvolcanic intrusions emplaced at the margin of the Arizaro Basin. Three alteration types were recognized: (i) Ca–Na silicate (clinopyroxene + magnetite + K-feldspar + quartz + calcite ± plagioclase), (ii) K-silicate (K-feldspar + quartz + magnetite ± biotite ± anhydrite) and (iii) chlorite-calcite alteration. The highest ore grades are linked to the K-silicate alteration. The proven plus probable reserves of Lindero are 84,226 t with average grades of 0.63 g/t Au and 0.11% Cu. A previous study assigned Lindero to the iron oxide copper-gold (IOCG) deposit type but many features of Lindero suggest that it is a porphyry gold deposit, including (i) the temporal and spatial link between alteration and the intrusive bodies, (ii) the alteration distribution pattern, particularly the small volume of rock affected by Ca–Na silicate alteration, (iii) the Au-rich and Cu-poor mineralization style.The magmatic complex at Lindero comprises an early-mineral unit (FPD), four inter-mineral units (CPD1, PBFD, CPD2 and DDP) and one post-mineral unit (PMI). In-situ U/Pb SIMS dating of the oldest (FPD), an intermediate (PBFD) and the youngest (DDP) intrusive units, confirms a middle Miocene age. The weighted mean ages of the oldest and youngest units are indistinguishable, with 15.36 ± 0.13 Ma (n = 21) and 15.47 ± 0.11 Ma (n = 16), respectively. Individual ages from each unit range by ~1 m.y. and the overall spread of zircon ages is 15.92 ± 0.23 to 14.44 ± 0.33 Ma. We suggest that emplacement of the subvolcanic stocks took place within this span time, likely at the lower end of this range (15.0–14.4 Ma). Two 40Ar/39Ar ages of hydrothermal biotites from the K-silicate alteration (14.99 ± 0.16 Ma and 14.93 ± 0.12 Ma) indicate that hydrothermal alteration began practically simultaneously with the emplacement of the porphyry units.All of the intrusive units are similar compositionally. They show a fine- to medium-grained porphyric texture (1–4 mm) comprising plagioclase, amphibole, clinopyroxene and scarce quartz phenocrysts (40–55 vol % of phenocrysts) in a K-feldspar ± quartz microcrystalline (0.02–0.07 mm) groundmass, except in the post-mineral unit which has a cryptocrystalline groundmass. Whole-rock analyses reveal a narrow range of dioritic composition (58.6–61.9 wt % SiO2) and high-K calc-alkaline character for all units. Trace element features (low Ba/Nb ratios, high Nb) of the Lindero magmas indicate a back-arc affinity, similar to those from the Southern Puna and distinct from the Central Volcanic Zone (CVZ) frontal arc. The Sr and Nd isotope ratios (87Sr/86Sr = 0.706042 to 0.706607; 143Nd/144Nd = 0.512501 to 0.512582) from Lindero intrusives are also similar to Southern Puna back-arc volcanic rocks. The Pb isotope ratios of Lindero (206Pb/204Pb = 18.79 to 18.83; 207Pb/204Pb = 15.60 to 15.63; 208Pb/204Pb = 38.66 to 38.74) overlap with both back-arc and arc magmas in the CVZ. The narrow age range, spatial association and uniform chemical and isotopic composition of Lindero porphyry units suggest that were derived from a common magma source, which underwent fractionation and/or crustal assimilation before emplacement as suggest by the low concentrations of Mg, Cr, Ni and Sr. The Lindero porphyry units show chemical and isotopic similarities with those from porphyry gold deposits in the Maricunga belt, Chile, and with the porphyry copper deposits of Argentina located in a back-arc setting; however, they differ from porphyry copper deposits in the frontal-arc setting of Chile, notably by the lack of an adakite-like signature (high Sr/Y ratio).

Analysis of Na, Mg, Al and Cl in archaeological glass and pottery: comparison of PIGE with low energy deuteron activation analysis

Na, Mg, Al and Cl in Roman glasses and pottery were analyzed by PIGE with 2.5 MeV protons and 2.0 MeV deuteron activation analysis. Both methods are simple and rapid. For Na, Mg and Al in glasses, the detection limits with PIGE and deuteron activation are: 40, 800, 300 (µg/g) and 120, 110, 100 (µg/g), respectively. PIGE is not suitable for trace analysis of chlorine. The detection limit of Cl is 500 µg/g for 2 MeV deuteron activation. PIGE is a sensitive method for Na analysis. At low concentrations of Mg and Al, deuteron activation with its higher sensitivity and improved photopeak-to-background ratios, gives more precise and accurate results than PIGE.

Circulating Ca and its relationship with serum minerals, metabolic and nutritional profiles, health disorders, and productive and reproductive outcomes in dairy cows

The objectives were to (1) investigate factors associated with serum Ca concentration, and (2) examine its relationship with serum analytes, incidence of health disorders, and productive and reproductive outcomes in dairy cows. Serum concentrations of macro minerals, metabolites, liver enzymes, β-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA), and haptoglobin were determined between 2 and 7 days in milk (DIM) in 398 Holstein cows from 11 dairy herds in Alberta, Canada. Cows were categorized into either Low- (≤2.10 mmol/L; n = 136) or High- (>2.10 mmol/L; n = 262) Ca groups. Concentrations of Ca were affected by herd, calf sex and number, and DIM at sample collection. Low-Ca cows had lower concentrations of Mg, Na, K, albumin, globulin, total protein and cholesterol, and greater concentrations of urea, aspartate aminotransferase, BHB, NEFA and haptoglobin than High-Ca cows. Low-Ca cows had greater incidence of health disorders compared to High-Ca cows, with the exception of mastitis and displaced abomasum. Low-Ca cows had lower milk yield only by 25 DIM compared to High-Ca cows, with no difference in later milk yield measurements. The proportion of cows cyclic at 35 DIM and pregnant to first artificial insemination tended to be lesser for Low-Ca cows compared to High-Ca cows, with no difference in the proportion of cows pregnant by 150 DIM. In summary, cows categorized as Low-Ca had lower serum concentrations of macro minerals, greater concentrations of markers for fat mobilization and inflammation, greater incidence of postpartum health disorders and poorer reproductive outcomes compared to those categorized as High-Ca.

Petrogenesis of leucogranites in collisional orogens

Abstract Leucogranites are a characteristic feature of collisional orogens. Their generation is intimately related to crustal thickening and the active deformation and metamorphism of metapelites. Data from Proterozoic to present day orogenic belts show that collisional leucogranites (CLGs) are peraluminous, with muscovite, biotite and tourmaline as characteristic minerals. Isotopic ratios uniquely identify the metapelitic sequences in which CLGs occur as sources. Organic material in pelitic sources results in f O 2 in CLGs that is usually below the fayalite–magnetite–quartz buffer. Most CLGs form under vapour-poor conditions with melting involving a peritectic breakdown of muscovite. The low concentrations of Mg, Fe and Ti that characterize CLGs are largely related to biotite–melt equilibria in the source rocks. Concentrations of Zr, Th and rare earth elements are lower than expected from zircon and monazite saturation models because these minerals often remain enclosed in residual biotite during melting. Melting involving muscovite may limit the temperatures achieved in the source regions. A lack of nearby mantle heat sources in thick collisional orogens has led to thermal models for the generation of CLGs that involve flux melting, or large amounts of radiogenic heat generation, or decompression melting or shear heating, the last one emphasizing the link of leucogranites and their sources to crustal-scale shear zone systems.

Ion substitution induced formation of spherical ceramic particles

How to precipitate ceramic nano- and microspheres in water based solutions only using inorganic ions is a challenge. In this study, spherical particles of alkaline earth phosphates and fluorides were synthesized using a precipitation reaction. Substituting ions, through inhibition of crystal growth, was used to induce sphere formation and to alter the morphology, size and composition of the spheres. The difference in ionic radius between the substituting ion (Mg, Ca and Sr) and the main cation (Sr and Ba) influenced the critical concentration to allow for sphere formation as well as the crystallinity. The larger difference, the lower was the concentration needed to form spheres. Low concentrations of Mg was enough to generate amorphous spheres of Sr- and Ba-phosphates whereas higher concentrations were needed if the radius difference were smaller. An increasing degree of substitution leads to a decrease in crystallinity of precipitated particles. The degree of substitution was determined to 16–55% where a low degree of ion substitution in the phosphates resulted in the formation of spheres (500–800 nm) with rough surfaces composed of apatite like phases. A higher degree of substitution resulted in amorphous spheres (500 nm- 1 μm) with smooth surfaces.

Synthesis and characterization of Mg, Zn and Sr-incorporated hydroxyapatite whiskers by hydrothermal method

The feasibility of incorporating high (M/M+Ca = 16 mol. %) and low (M/M+Ca = 4.76 mol. %) concentrations of Mg2+, Zn2+ and Sr2+, as divalent cations with interesting biological properties, into the structure of well-known bioceramic: hydroxyapatite (HA) was carefully assessed. An established hydrothermal synthesis method was employed for preparation of HA in whisker-like morphology. Consequently, the possibility of synthesizing HA whiskers (HAWs) with cationic substitutions and effects of the introduced ions on morphology, structure and composition of HA products were evaluated. Almost, all the cation-substituted preparations could maintain the apatite phase, while the decrease in crystallite size and crystallinity was obvious. Lattice parameters (a, c) of the hexagonal system of HA were also affected in accordance with the type and amount of substituting cation. Zn2+ and high amounts of Mg2+ dramatically inhibited formation of whisker-like apatite and promoted formation of a mixture of hexagonal prism-like and flaky bundles, or hexagonal and multifaceted morphologies, respectively. However, Sr2+ exhibited minimum inhibitory effect on HAWs formation. Therefore, Sr- and Mg-substituted (low concentration of Mg) HAWs could be prepared for their potential biomedical applications.

Magnesium Is a Key Regulator of the Balance between Osteoclast and Osteoblast Differentiation in the Presence of Vitamin D3

Magnesium (Mg) is crucial for bone health. Low concentrations of Mg inhibit the activity of osteoblasts while promoting that of osteoclasts, with the final result of inducing osteopenia. Conversely, little is known about the effects of high concentrations of extracellular Mg on osteoclasts and osteoblasts. Since the differentiation and activation of these cells is coordinated by vitamin D3 (VD3), we investigated the effects of high extracellular Mg, as well as its impact on VD3 activity, in these cells. U937 cells were induced to osteoclastic differentiation by VD3 in the presence of supra-physiological concentrations (>1 mM) of extracellular Mg. The effect of high Mg concentrations was also studied in human bone-marrow-derived mesenchymal stem cells (bMSCs) induced to differentiate into osteoblasts by VD3. We demonstrate that high extra-cellular Mg levels potentiate VD3-induced osteoclastic differentiation, while decreasing osteoblastogenesis. We hypothesize that Mg might reprogram VD3 activity on bone remodeling, causing an unbalanced activation of osteoclasts and osteoblasts.

POSTTRAUMATIC SYNDROME DURING PREGNANCY: EXPECTATIONS AND REALITY

Aim of the research is to study identification of peculiar issues associated with psycho-emotional state and the related stress-associated hormones and micronutrients in pregnant-displace individuals for further improvement of programmes for antenatal research. Materials and methods. In order to reach the research objective, a dynamic prospective clinical-paraclinical examination of 96 pregnant women (experimental group) – temporary displaced individuals with gestation period of more than 22 weeks who have been treated and gave birth to their children in the Central Municipal Hospital in Rubizhne and Perinatal Centre in Severodonetsk, Lugansk region. The control group consists of 39 randomly selected pregnant women for the purposes of prospective research that are living in the areas under the control of Ukraine government. All pregnant women were examined (clinical-laboratory and special midwifery examinations), the evaluation of psycho-emotional state of examined pregnant women was conducted with the help of screening by performing clinical interviews together with routine questioning. The questionnaires that contained the questions of Spielberg’s tests in the modification of Khanin were composed in advance. Concentration of stress-associated hormones in the blood serum, Ca and Mg was identified using the method of solid-phase immuno-ferment analysis. Results. According to the Spielberg’s test, the average score of reactive anxiety in the experimental group exceeded the analogous indicator in the control group by 1.6 times. The indicators of personal anxiety exceeded the normal indicator in the control group by 2.2 times. Of the pregnant women in the experimental group had the concentration of cortisol in the blood serum exceeded the upper physiological standard by 5.5 % and exceeded the analogous indicator in the control group by 43.4 %. The increase concentration of prolactin was yet observed in the II trimester of pregnancy if compared to the upper level of physiological standard by 13.3 %; if compared to the average indicator of this hormone in the control group - by 20.3 %. In the III trimester - concentration in both groups was within normal ranges, but in the experimental group this indicator was higher by 10.5 %. In the experimental group of pregnant women the concentration of Ca in the blood serum in comparison to the physiological standard was higher by 19.2 % and by 9.6 % higher if compared to the analogous indicator in the control group of pregnant women. At the same time, the pregnant women in the experimental group have low concentration of Mg. Conclusions. Taking into account the identified patterns, it is useful to categorise the pregnant women from among the internally displaced individuals as the group of high risk with respect to the development of obstetric and perinatal complications.

Toxic Metal and Trace Element Concentrations in Blood and Outcome of In Vitro Fertilization in Women.

The aim of this study was to investigate the association of trace element and toxic metal concentrations in blood and the outcome of in vitro fertilization (IVF). The study included 104 consecutive patients that underwent assisted reproductive technology (ART) procedures. The following parameters were determined: cadmium (Cd), mercury (Hg), arsenic (As), and lead (Pb); and copper (Cu), zinc (Zn), selenium (Se), and magnesium (Mg). Serum samples were obtained before commencing stimulation. Patients with smoking habit had significantly higher Pb concentrations (P = 0.022), as well as higher concentrations of As and Hg but not significantly. All subjects were divided into groups of pregnant and nonpregnant patients. Pregnant patients had lower mean values of Mg (P = 0.009), As (P < 0.05), and Pb (P = 0.034), compared to nonpregnant, and a significant correlation between pregnancy outcome and concentrations of Mg, Cd, and Pb was found. Women who had had delivered had lower Mg (P = 0.009) and Cd (P = 0.014) concentrations. There was a significant correlation of the negative outcome of IVF procedure with higher concentrations of Pb (P = 0.046) and Cd (P = 0.012). In conclusion, our results suggest that there is a difference in Mg, Pb, and Cd concentrations between pregnant and nonpregnant women. There was no association between toxic metals and number and quality of oocytes and embryos, while there was with fertilization rate. Concerning trace elements, we did not find the correlation of trace elements with oocyte number and quality, nor with a number of fertilized oocytes, except for Cu. Patients who were pregnant had lower concentrations of Mg.

Development and studies of Cd1−xMgxTe thin films with varying band gaps to understand the Mg incorporation and the related material properties

In this paper we report a systematic work involving the development of Cd1−xMgxTe thin films by co-evaporation of CdTe and Mg. The evaporation rate of both materials were adjusted to obtain ternary films of varying stoichiometry and hence the band gap. We have deposited films with band gap ranging from 1.47 to 2.41eV. The films were characterized for structural, morphological, optical, opto-electronic, and spectroscopic properties. The film stoichiometry was studied across the thickness using SIMS data. SEM images showed that the grain size has a dependence on Mg content in the film, which inhibits the grain growth. The structural parameters showed a systematic dependence on Mg content in the film, however, there was no noticeable change in the XRD reflections with respect that of pure CdTe for lower concentrations of Mg. XPS analysis shed light on the incorporation of Mg further supporting the band gap variations observed with the UV–Vis spectroscopic studies. The photoresponse of the film was affected by Mg incorporation. Prototype devices of the type Cd1−XMgxTe/CdS were fabricated and the results are discussed.

High hole mobility p-type GaN with low residual hydrogen concentration prepared by pulsed sputtering

We have grown Mg-doped GaN films with low residual hydrogen concentration using a low-temperature pulsed sputtering deposition (PSD) process. The growth system is inherently hydrogen-free, allowing us to obtain high-purity Mg-doped GaN films with residual hydrogen concentrations below 5 × 1016 cm−3, which is the detection limit of secondary ion mass spectroscopy. In the Mg profile, no memory effect or serious dopant diffusion was detected. The as-deposited Mg-doped GaN films showed clear p-type conductivity at room temperature (RT) without thermal activation. The GaN film doped with a low concentration of Mg (7.9 × 1017 cm−3) deposited by PSD showed hole mobilities of 34 and 62 cm2 V−1 s−1 at RT and 175 K, respectively, which are as high as those of films grown by a state-of-the-art metal-organic chemical vapor deposition apparatus. These results indicate that PSD is a powerful tool for the fabrication of GaN-based vertical power devices.

Magnesium pyrophosphates in enzyme mimics of nucleotide synthases and kinases and in their prebiotic chemistry

Derivatives of ribosyl pyrophosphate have been synthesized, and examined with magnesium salts in the coupling of the ribose unit to various nucleophiles, including pyrazole and 2-chloroimidazole. Only with the magnesium salt present did they generate the ribosyl cation by binding to the leaving group and then couple the ribose derivative with nucleophiles. The role of magnesium salts in phosphorylation of methanol by ATP was also examined. Here a remarkable effect was seen: phosphorylation by ATP was slowed with low concentrations of Mg(2+) but accelerated by higher concentrations. Related effects were also seen in the effect of Mg(2+) on phosphorylation by ADP. The likely mechanisms explain these effects.

Analysis of the relationship between the blood concentration of several metals, macro- and micronutrients and endocrine disorders associated with male aging.

Beyond 30years of age, men experience a decline in the production of testosterone, yet only a few develop late-onset hypogonadism. This study was designed to determine the relationship between blood concentrations of metals, macro- and micronutrients and age-related testosterone deficiency and associated hormonal changes in aging men. The research involved 313 men aged 50-75years. We used ELISA to determine the concentrations of total testosterone (TT), free testosterone (FT), estradiol (E2), dehydroepiandrosterone sulfate (DHEAS) and sex hormone-binding globulin (SHBG). We calculated free androgen index (FAI). With the use of emission spectrometry in inductively coupled argon plasma, we determined the whole-blood concentrations of lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As) and tungsten (W), as well as serum concentrations of magnesium (Mg), iron (Fe), calcium (Ca), copper (Cu), zinc (Zn), selenium (Se), chromium (Cr), manganese (Mn) and molybdenum (Mo). The study showed no relationship between TT and FT and the concentrations of metals. Men with TT deficiency had significantly lower concentrations of Mg and Fe and increased Mn. Men with FT deficiency had higher W and Cr levels and lower Fe. Assessing the correlation between the concentrations of hormones, SHBG and FAI, and the concentration of metals and macro- and microelements in the blood of the men, we found positive correlations between the concentrations of TT-Mg, TT-Fe, TT-Mo, FT-Fe, E2-As, SHBG-Mn, FAI-W, FAI-As, FAI-Zn and FAI-Ca, and negative correlations between the concentrations of TT-Mn, FT-Cd, FT-Cr, E2-Hg, E2-Cr, SHBG-W, SHBG-As, SHBG-Zn, SHBG-Ca, FAI-Pb and FAI-Mn. Positive correlations between As and E2 and between As and FAI may suggest a lack of association between this metal and hypogonadism in people not exposed to excess As levels. Our research indicates a positive relationship between the concentrations of Mg, Fe and Zn and endocrine system in aging men, in contrast to Mn and Cr. Toxic metals (Cd, Pb) seemed to negatively affect the level of bioavailable testosterone. In persons not exposed to As, As does not contribute late-onset hypogonadism. Heavy metals (Pb, Cd, Hg and W) may contribute to a lower concentration of DHEAS. The role of W in men with LOH was found to be ambiguous, as on the one hand its concentration was higher in men with FT deficiency, and on the other hand it positively correlated with FAI, which in turn indirectly indicates testosterone availability. Copper and selenium do not seem to play any significant role in the occurrence of TT deficiency in aging men.

Thermite reactions with oxides of iron and silicon during combustion of magnesium with lunar and Martian regolith simulants

It has been shown recently that mixtures of JSC-1A lunar regolith simulant with magnesium are combustible. Thermite-type reactions in these mixtures could be used for in situ production of construction materials on the Moon. Because of complex composition of lunar regolith, however, the mechanisms of these reactions are not well understood. Also, for Mars mission applications, it is important to explore the possibility of using Martian regolith in such mixtures. In the present paper, combustion of two Martian regolith simulants (JSC-Mars-1A and Mojave Mars) with magnesium is studied using thermodynamic calculations and combustion experiments. To understand the reaction mechanisms in these mixtures as well as in the mixtures of JSC-1A lunar regolith simulant with magnesium, thermoanalytical experiments are also conducted. It has been shown that the Martian regolith simulants form combustible mixtures with magnesium. The measured combustion temperatures and identified product compositions are in reasonable agreement with thermodynamic predictions. The mixtures of JSC-Mars-1A with magnesium at 20–30wt% Mg exhibit higher temperatures and burn more vigorously than mixtures based on Mojave Mars, which is explained by the higher content of iron oxide in JSC-Mars-1A. For Mojave Mars, combustion is accompanied by oscillations in the front motion and by the formation of a layered structure of the product. This effect is more significant at lower concentrations of Mg. Thermoanalytical studies have shown that iron oxide plays a dominant role in the combustion of JSC-Mars-1A simulant with magnesium. However, Mg/SiO2 mixture ignites at a temperature lower by approximately 100°C than for Mg/Fe2O3. For Mojave Mars material and JSC-1A lunar regolith simulant, which include more silica and less iron oxide, silica exhibits a significant effect on the combustion, promoting reactions at lower temperatures.