Atomic and electronic structure of crystalline and amorphous alloys. I. Calcium-magnesium compounds.
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Journal Article↗
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Preparation of fluoride-low compounds: magnesium oxide adsorption technique.
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Adsorption↗
Syntheses and structures of magnesium pyridine thiolates--model compounds for magnesium binding in photosystem I.
Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography.
Journal Article↗
Magnesium and its combination with cinnarizine in the long-term treatment of headache.
Some of the so-called calcium antagonists are effectively applied in the prophylactic treatment of migraine. Magnesium compounds reveal some calcium- antagonistic features, which was the reason of magnesium compounds (magnesium sulphate i.m. or magnesium lactate p.o.) evaluation at chronic migraine-patients. The compounds were administered or alone or in combination with cinnarizine (in case of magnesium sulphate). Beneficial effects were registered both after application of magnesium sulphate and, more markedly, after the combination with cinnarizine. The potentiation of the effect is likely due, at least partially, to their own calcium-antagonistic features. The side-effects of the applied drugs were not registered.
Adult↗
Evaluation of buffering capacity and acid neutralizing-pH time profile of antacids.
The antacid properties of seven antacids listed in the hospital formulary of a medical center were evaluated with in vitro tests. These included not only the preliminary antacid test and acid-neutralizing capacity test as described in the United States Pharmacopeia (USP XXIII), but also a buffering pH profile test. The preliminary antacid test measured the final pH of a 10-mL solution of 0.5 N HCl 10 minutes after addition of the minimum recommended dose of an antacid, while the neutralizing capacity test measured the amount (mEq) of HCl neutralized by the minimum recommended dose in 15 minutes. The buffering pH profile recorded the pH time course of dynamic simulated gastric fluid neutralization by a dose of an antacid. In the preliminary antacid test, magnesium oxide showed the highest pH (9.52 +/- 0.14, mean +/- standard deviation, n = 3); aluminum phosphate gel yielded a final pH of 2.51 +/- 0.01, thus failing to meet the criteria of an antacid (pH > 3.5). In the acid-neutralizing capacity test, hydrotalcite had the highest neutralizing capacity (28.26 +/- 0.3 mEq), while sodium bicarbonate had the lowest (7.40 +/- 0.12 mEq). In the buffering pH profile test, aluminum-magnesium hydroxide suspensions and hydrotalcite tablets maintained a steady optimum pH (3-5) for around 1.5 hours. One tablet of calcium carbonate, sodium bicarbonate or magnesium oxide could not raise the gastric pH to above 3, but two tablets increased the pH excessively (5.3 to 8.6). The higher dose (two tablets) of aluminum hydroxide hexitol complex could not raise the pH to the optimal level. These findings demonstrate that there is disparity in the antacid effectiveness estimated by the neutralizing capacity test and the buffering pH profile test and suggest that the efficacy of an antacid cannot be accurately predicted from its acid-neutralizing capacity. The dose of antacids greatly influences the neutralizing pH profiles. Aluminum-magnesium compounds appear to provide steadier buffering than carbonate compounds or magnesium oxide.
Aluminum Compounds↗
Dual effect of magnesium on compound 48/80-induced histamine secretion from rat peritoneal mast cells.
The effect of magnesium on the secretory response to compound 48/80 from rat peritoneal mast cells was studied. The decrease in secretion caused by calcium deprivation was enlarged by magnesium. Glucose partially counteracted the decrease caused by calcium deprivation but not the one caused by magnesium. The addition of calcium to the cells simultaneously with compound 48/80 completely restored the secretory response if magnesium was present. The response was only partially restored in a magnesium- and glucose-free medium, whereas it was almost completely restored if glucose was present. Magnesium had a considerable effect on the restoration of the secretory response of EGTA-treated cells, whereas the effect of glucose was minimal indicating that an effect on the energy metabolism was of minor importance. The secretory response could also be restored by an exposure of the cells to calcium prior to stimulation with compound 48/80. This was, however, only observed if magnesium was present and glucose had no effect. The influence of magnesium on the restoration of the secretory response may partly occur by an effect on the energy metabolism, partly by an effect on the stimulus-secretion coupling. We propose that insufficient supply of Mg2+ to the G-protein during activation by compound 48/80 might cause a suboptimal signal transduction.
Adenosine Triphosphate↗
First principles density functional study of the adsorption and dissociation of carbonyl compounds on magnesium oxide nanosurfaces.
The adsorption and dissociation of three carbonyl compounds, formaldehyde, acetaldehyde, and acetone, on the magnesium oxide nanosurface, consisting of four stacked (MgO)3 hexagons, is investigated by first principles density functional theory (DFT). In the case of formaldehyde, strongly chemisorbed species, with carboxylate-like structures, are initially formed. These may subsequently undergo heterolytic cleavage of an aldehyde C-H bond to form formate ions involving a surface oxide ion and a hydride ion adsorbed over the magnesium dication [(MgH+)(HCOO-)]. For acetaldehyde, besides this reaction leading to the formation of acetate, the methyl hydrogen of the adsorbed species also tends to attach itself to a surface oxide ion, yielding surface hydroxyl ions and adsorbed [CH2=C(H)OMg]+. These results are in accord with our previous experimental and theoretical results. In particular, the shift of the aldehyde C-H vibration band to higher frequency and the appearance of OH bands in the infrared spectrum are clearly accounted for. For acetone, the mechanism is found to be similar, i.e., a methyl hydrogen shift to yield surface enolate. Again, this is in agreement with experimental studies.
Journal Article↗
Solid-state 25Mg QCPMG NMR of bis(cyclopentadienyl)magnesium.
Application of the "quadrupolar Carr-Purcell Meiboom-Gill" (QCPMG) sequence permits the first natural abundance solid-state 25Mg NMR study of an organometallic magnesium compound, bis(cyclopentadienyl)magnesium. Analytical and numerical simulations of both static and magic-angle spinning QCPMG NMR spectra beget an axially symmetric 25Mg electric field gradient (EFG) tensor (quadrupolar asymmetry parameter, eta(Q)=0.01(1)) with a nuclear quadrupole coupling constant of C(Q)=5.80(5)MHz. Restricted Hartree-Fock and hybrid density functional theory (B3LYP) calculations are in good agreement with experimental EFG values and predict a chemical shielding anisotropy of about 40-50 ppm, which we attempt to elucidate by numerical simulations. The parameters and orientation of the 25Mg EFG tensor are rationalized from examination of the crystal structure and molecular symmetry. The NMR properties of the cyclopentadienyl rings are examined by 13C[1H] CPMAS NMR, RHF and hybrid-DFT (B3LYP) calculations, and simulations of the effects of chemical exchange on the 13C powder pattern.
Journal Article↗
Functionalized magnesium organometallics as versatile intermediates for the synthesis of polyfunctional heterocycles.
In the last few years, we have demonstrated that the halogen/magnesium-exchange reaction is a unique method for preparing a variety of new functionalized aryl, alkenyl, heteroaryl magnesium compounds which has considerably extended the range of functionalized Grignard reagents available for synthetic purposes. A variety of functional groups such as an ester, nitrile, iodide, imine and even sensitive groups like nitro, hydroxyl and boronic ester can be tolerated in these organomagnesium compounds. We wish to describe the application of this halogen/magnesium-exchange reaction for the preparation of a broad range of five- and six-membered functionalized heteroaryl magnesium compounds and their reactions with various electrophiles providing a new entry to a range of polyfunctional heterocycles such as thiophene, furan, pyrrole, imidazole, thiazole, antipyrine, pyridine, quinoline and uracil derivatives.
Antipyrine↗
Stoichiometric compounds of magnesium dichloride with ethanol for the supported Ziegler-Natta catalysis: first recognition and multidimensional MAS NMR study.
Ethanol associates easily with MgCl(2) to form adducts of complex architecture, but until now available characterization methods have failed to identify the pure stoichiometric compounds and their structures. To remedy this, we set about applying homonuclear and heteronuclear 2D correlated solid-state NMR spectroscopy to identify the pure compounds and the ethanol-to-magnesium coordination pattern. High spinning speed and Lee-Goldburg sequences were able to reduce the hydrogen spin-diffusion and homonuclear coupling in the crystalline solid, thus achieving high resolution also in the hydrogen domain. On this basis, the pure adducts, of interest as catalyst supports for Ziegler-Natta polymerization, were isolated for the first time. Magnesium coordination sites with given numbers of ligands and their multiplicity in the crystal cells were determined in the new-found stoichiometric complexes. Variable temperature and 2D carbon-carbon exchange NMR, as well as relaxation times in the fast motion regime, revealed the disordering phenomena generated by ethanol dynamics in the crystal. Decoding the intriguing polymorphism of the precursors permits to trace the genealogy of tailored MgCl(2) titanate granules, active as highly productive catalysts for the stereospecific polymerization of olefins.
Journal Article↗
[Mg(XeF(2))(n)()](AsF(6))(2) (n = 4, 2): first compounds of magnesium with XeF(2).
The reaction between Mg(AsF(6))(2) and XeF(2) in anhydrous HF (aHF) at room temperature yields two compounds with XeF(2) bonded directly to the Mg(2+) cation: [Mg(XeF(2))(4)](AsF(6))(2); [Mg(XeF(2))(2)](AsF(6))(2). The 1:4 compound is obtained with excess XeF(2) while the 1:2 compound is prepared from stoichiometric amounts of Mg(AsF(6))(2) and XeF(2). [Mg(XeF(2))(4)](AsF(6))(2) crystallizes in an orthorhombic crystal system, space group P2(1)2(1)2(1), with a = 8.698(15) A, b = 14.517(15) A, c = 15.344(16) A, V = 1937(4) A(3), and Z = 4. The octahedral coordination sphere of Mg consists of one fluorine atom from each of the four XeF(2) molecules and two fluorine atoms from the two AsF(6) units. [Mg(XeF(2))(2)](AsF(6))(2) crystallizes in the orthorhombic crystal system, space group Pbam, with a = 8.9767(10) A, b = 15.1687(18) A, c = 5.3202(6) A, V = 724.42(14) A(3), and Z = 2. The octahedral coordination sphere consists of two fluorine atoms, one from each of the two XeF(2) molecules and four fluorine atoms from the four bridging AsF(6) units.
Journal Article↗
[On the pharmacotherapy of children and adolescents with behavior disorders. Experience with the magnesium-bromine compound Psicosoma].
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Adolescent↗
The neutralizing capacity and sodium content of antacid brands on the Kenyan market.
Seventeen brands of antacid products available on the Kenya market were investigated for their acid neutralising capacity and sodium content. Thirteen tablet products gave neutralising capacity per tablet of between 4.7 to 14.12 mMol hydrochloric acid. The neutralising capacities for the suspensions ranged between 11.97 to 34.32 mMol hydrochloric acid for 10ml suspension. The lowest neutralising capacities were obtained for products based on compound magnesium trisilicate and higher capacities for those containing magaldrate, or magnesium hydroxide or magnesium carbonate in combination with other ingredients. The fastest rate of neutralization was obtained with preparations containing carbonates and the lowest by compound magnesium trisilicate. The sodium content for the preparations was between < 0.001 mEq to 0.732 mEq sodium per minimum recommended dose. The study shows a high degree of variation in both the acid neutralising capacities and the sodium content of the different brands investigated.
Antacids↗
[Absorption of complex compounds of magnesium and amino acids in the small intestine].
In chronic experiments on 12 dogs, absorption of manganese complexes and amino acids proceeded more intensively than absorption of each of them separately. In acute experiments on 48 dogs, absorption of glycine and alanine complexes of manganese proceeded with an increase in oxygen utilization and in the rate of the intestinal motility.
Alanine↗
Experimental studies on the intestinal uptake of organic and inorganic magnesium and potassium compounds given alone or simultaneously.
The peroral administration of magnesium and potassium compounds in effective doses (ED50) to rats yielded the following results: 1. Magnesium or potassium given as chlorides are significantly better absorbed than the corresponding aspartates. 2. In the presence of aspartate in higher concentrations the absorption of both magnesium and potassium is inhibited to a certain degree. 3. Increasing amounts of chloride cannot abolish the inhibitory effect of aspartate on potassium absorption, in contrast magnesium, which, in the presence of aspartate is better taken up when chloride is provided. 4. High concentrations of magnesium may perhaps impede the uptake of potassium to a small degree but not vice versa. 5. Magnesium losses from the body--induced by treatment with 9-alpha-fluorocortisol-acetate--can be effectively substituted by peroral administration of chloride-containing magnesium compounds over a reasonable time. The simultaneously occurring loss of potassium cannot be corrected correspondingly by potassium supplements.
Animals↗
Synthesis and characterization of an unsolvated dimeric diarylmagnesium compound and its magnesium iodide byproducts.
The Grignard reagent 2,6-Et(2)C(6)H(3)MgI(THF)(n), 1, undergoes rapid aryl exchange in THF solution at room temperature to afford the diorganomagnesium compound (2,6-Et(2)C(6)H(3))(2)Mg(THF)(n), 2, and the sparingly soluble salt Mg(THF)(6)I(2), 5. Removal of the coordinated THF in 2 under reduced pressure and elevated temperature affords the unique diorganomagnesium species [2,6-Et(2)C(6)H(3)Mg(mu-C(6)H(3)Et(2)-2,6)](2), 3, which features three-coordinate magnesium. Compound 3 is fluxional in benzene or toluene solution at room temperature and dissociates into monomeric (2,6-Et(2)C(6)H(3))(2)Mg around 115 degrees C. Recrystallization of crude 5 from benzene solution gave large well-shaped crystals of MgI(2)(THF)(3), 4, and 5. Benzene solutions of 4 and 5 are remarkably easily oxidized by laboratory air to MgI(THF)(5)I(3), 6. Compound 3 has been characterized by variable-temperature (1)H NMR spectroscopy and X-ray crystallography, and compounds 4-6 have been characterized by X-ray crystallography.
Journal Article↗
Synthesis and degradation of nucleic Acid components by formamide and cosmic dust analogues.
We show the unprecedented one-pot synthesis of a large suite of pyrimidines (including cytosine and uracil) and purines from formamide in the presence of cosmic-dust analogues (CDAs) of olivines. Since the major problem in the origin of informational macromolecules is the instability of their precursors, we also investigate the stabilizing effect of CDAs on the intrinsic instability of oligonucleotides in formamide.
Catalysis↗
Physical, X-ray diffraction and scanning electron microscopic studies of uroliths.
Identification of chemical constituents of calculus is important in the diagnosis and management of urolithiasis. The compositional variability of uroliths has different etiologies and requires various modes of treatment and prophylaxis. In the present study, we report the chemical compositional analyses of calculi recovered from buck and bullock by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) techniques and ultra-structure examination by scanning electron microscopy (SEM). XRD and EDX investigations conclusively established the chemical compositions of urinary calculi under investigation. The calculus from buck (sample I) had calcium oxalate monohydrate, a dominant salt phase and magnesium compound in significant amount. The calculus from bullock (sample II) had magnesium ammonium phosphate phase, with significant amount of calcium in apatite form and K+ ions. SEM study at higher magnification (X 1000) showed bipyramidal crystals in external zones of urolith (sample I). The struvite apatite calculus showed that basic unit of structure was lamination and the laminitis appeared to be made up of fine granules and high porosity. The bio-mineralization process of calculus formation was also studied, with a view to take preventive and therapeutic measures for amelioration of urinary stone diseases in animals and humans.
Animals↗