Increasing Magnesium Ion Concentration Research Articles

Influence of Mg doping on the structural, electrical and dielectric properties of Co-Zn nanoferrites

Mg-Co-Zn nanoferrites of composition MgxCo0.5Zn0.5Fe2−xO4 (x = 0.25, 0.5, 0.75 and 1.0) were successfully synthesized by using a citrate precursor method. After synthesis, the samples were examined using different techniques for structural, morphological, electrical and dielectric characterizations. All the samples were found to have single phase spinel cubic structure with Fd-3m space group in the X-ray diffraction spectroscopy (XRD) investigation. The value of average crystallite size ranged from 37 to 47 nm with the increase in Mg ion concentration from x = 0.25 to 1.0. The hopping lengths at tetrahedral and octahedral sites showed an increasing behaviour with increasing magnesium ion concentration. The presence of tensile strain in the samples was confirmed by W-H plots. The dielectric behaviour of the prepared nanoferrites was recorded at room temperature in the frequency range 10 kHz–10 MHz. The real part and imaginary part of the dielectric constant were found to be in the range 3.80–7.93 and 0.0036–0.644 at 1 MHz frequency and the value of loss tangent was 0.00095–0.081 at 1 MHz for the magnesium doped Co-Zn nanoferrites. The value of loss tangent decreased very sharply to remarkably low values at 10 MHz frequency. The dc resistivity value was found very low in the range 3.2 × 108 Ω-cm to 4.0 × 109 Ω-cm for different concentrations of Mg2+ ions in the samples. Due to such low losses at high frequency region and high value of dc resistivity, these materials can be considered as potential candidate for high frequency applications.

Comprehensive Study of the Impact of Mg2+ Doping on Optical, Structural, and Magnetic Properties of Copper Nanoferrites

Cu1-xMgxFe2O4 (x = 0.2, 0.4, 0.6, 0.8, and 1.0) nanoferrites were synthesized by co-precipitation technique. The substitution of Mg2+ in Cu1-xMgxFe2O4 leads to the decrease of crystallite size from 17.4 to 10.2 nm. In addition, the lattice constant reduced from 8.465 A to 8.334 A with increasing the Mg2+ concentration. The particle size obtained from TEM micrographs is consistent with the size of the crystallite determined from XRD results. The band gap energy will increase from 2.82 eV to 3.31 eV with increasing the ratio of Mg2+ content. It has been observed that the luminescence intensity of copper nanoferrite decreases with increasing the ratio of Mg2+. The saturation magnetization decreases with increasing magnesium ion concentration as indicated in the M-H loops.

Peptide Formation by N-Methyl Amino Acids in Translation Is Hastened by Higher pH and tRNAPro

Applications of N-methyl amino acids (NMAAs) in drug discovery are limited by their low efficiencies of ribosomal incorporation, and little is known mechanistically about the steps leading to incorporation. Here, we demonstrate that a synthetic tRNA body based on a natural N-alkyl amino acid carrier, tRNA(Pro), increases translation incorporation rates of all three studied NMAAs compared with tRNA(Phe)- and tRNA(Ala)-based bodies. We also investigate the pH dependence of the incorporation rates and find that the rates increase dramatically in the range of pH 7 to 8.5 with the titration of a single proton. Results support a rate-limiting peptidyl transfer step dependent on deprotonation of the N-nucleophile of the NMAA. Competition experiments demonstrate that several futile cycles of delivery and rejection of A-site NMAA-tRNA are required per peptide bond formed and that increasing magnesium ion concentration increases incorporation yield. Data clarify the mechanism of ribosomal NMAA incorporation and provide three generalizable ways to improve incorporation of NMAAs in translation.

Exciton-magnon interactions in NicMg1−c O single crystals

The effect of chemical composition and temperature on exciton-magnon interactions in NicMg1−cO single crystals was studied using optical absorption spectra in the region of the magnetic-dipole 3A2g(G)→3T2g(F) and electric-dipole 3A2g(F)→1Eg(D) transitions. The two zero-phonon lines at ∼7800 and ∼7840 cm−1 on the low-energy side of the magnetic-dipole transition band were assigned to a pure exciton transition and an exciton-one-magnon transition at the center of the Brillouin zone. The intensity of the exciton-one-magnon peak decreases rapidly with increasing magnesium ion concentration and/or temperature, to vanish altogether at T=6 K for c<0.95 and at T=130 K for c≥0.99. Thus, the contribution of long-wavelength magnons in optical absorption spectra of NicMg1−cO becomes negligible at temperatures substantially lower than the Neel point TN (the antiferromagnetic ordering temperature). This observation can be explained as being due to a substantial decrease in the characteristic spin-spin interaction length with increasing concentration of the diamagnetic magnesium impurity ions (static disorder) and/or with increasing amplitude of thermal atomic vibrations (dynamic disorder). At the same time, the peak at ∼14500 cm−1, which lies in the electric-dipole transition region and corresponds to excitation of an exciton and two magnons at the Brillouin zone edge, remains visible up to the Neel temperature. This is accounted for by the short-wavelength magnons being sensitive to short-range magnetic order, which persists up to TN.

Interaction of Alkaline Earth Metal Ions with Carboxylic Acids in Aqueous Solutions studied by 13C NMR Spectroscopy

Abstract 13C NMR spectroscopic measurements of aqueous solutions containing alkaline earth metal chloride and a carboxylic acid have been carried out to acquire some insight into the coordination manners of various carboxylic acids to alkaline earth metal ions. The dependence of the 13C NMR signal positions of the carboxylate carbons on the magnesium ion concentration in a magnesium carboxylate system is a good index to understand the coordination manner of the carboxylate ion. The upfield shift of the carboxylate carbon signal with increasing magnesium ion concentration indicates that the carboxylate ion acts as a bidentate ligand to form a ring structure. Only in the citrate systems, the existence of a relatively stable complex is evidenced in which the citrate ion is expected to act as a tridentate ligand.

Inhibition of the Self-cleavage Reaction of the Human Hepatitis Delta Virus Ribozyme by Antibiotics

Human hepatitis δ virus (HDV) poses a health threat in populations where chronic hepatitis B is endemic. It is a single-stranded RNA virus of 1700 nucleotides and both genomic and antigenomic sequences contain ribozymes which are important for viral replication. Using ribozyme constructs we show that several classes of antibiotics inhibit the self-cleavage reaction of the HDV ribozyme. Antibiotics of the aminoglycoside, peptide and tetracycline classes all inhibit HDV cleavage in vitroat micromolar concentrations. Neomycin (an aminoglycoside) inhibits HDV self-cleavage with a K Ivalue of 28 (±10) μM. Neomycin inhibition can be reversed by increasing magnesium ion concentration in a competitive manner. Lead acetate cleaves positions G76, A42 and G28, which surround the ribozyme cleavage site. Both Mg 2 +and neomycin prevent lead cleavage. Footprinting experiments using base-specific chemical probes revealed enhanced modifications of a set of bases by neomycin, overlapping with the above mentioned lead cleavages. These observations may indicate that neomycin directly displaces divalent metal ions essential for catalysis.

Effects of mono- and divalent ions on the binding of the adenosine analogue CGS 21680 to adenosine A 2 receptors in rat striatum

The effect of monovalent and divalent cations on equilibrium binding of the adenosine A 2-selective agonist ligand CGS 21680 (2-[ p-(2-carbonylethyl)phenylethylamino]-5′- N-ethylcarboxamidoadenosine) to membranes prepared from rat striatum was examined. Competition experiments with cyclohexyladenosine, 2-chloroadenosine, N-ethylcarboxamidoadenosine and CGS 21680 suggest that at 2 nM [ 3H]CGS 21680 binds to a single site with the pharmacology of an A 2a receptor. Magnesium and calcium ions caused a concentration-dependent increase in binding that reached about 10-fold at 100 mM. Manganese ions had a biphasic effect on binding with a maximal increase at 5 mM. Lithium, sodium and potassium ions all caused a concentration-dependent decrease of binding. Sodium was most potent, potassium least. At 200 mM ion concentration, the inhibition of binding was 88% by sodium, 47% by lithium and 29% by potassium ions. The effect of sodium chloride was the same as that of sodium acetate. The effect of sodium ions was essentially similar to that of Gpp(NH)p. However, sodium ions produced a larger effect than even maximally effective concentrations of Gpp(NH)p. The maximal inhibition by Gpp(NH)p was about 55% at 2 nM radioligand concentration irrespective of the magnesium concentration. The maximal effect of sodium ions was reduced by increasing concentrations of magnesium ions. Increasing magnesium ion concentration from 1 to 100 mM increased the half-maximally effective concentration of Gpp(NH)p almost 10-fold and that of sodium ions less than 2-fold. Furthermore, sodium ions and Gpp(NH)p had additive effects. The binding of an agonist to striatal A 2a receptors shows an unusually large dependence on both divalent and monovalent cations that can only partly be explained by a change in the coupling to G s proteins.

EFFECT OF MAGNESIUM COMPLEXATION ON THE31P MIDDLE-GROUP CHEMICAL SHIFTS OF CHAIN AND RING PHOSPHATES

Abstract For pure sodium polyphosphates, Na n + 2P n O3n + 1, exhibiting 3 through 6 phosphorus atoms per molecule, the 31P chemical shift of the middle group phosphorus atoms as measured in aqueous solution (0.1 M in P) at pH 7 was seen to increase with increasing magnesium ion concentration until there was one Mg atom per polyphosphate molecule, after which the chemical shift decreased. Finally the rate of decrease diminishes and precipitation occurs. For the longer-chain phosphates, Na n + 2P n O3n + 1 with n = 8, 9, 10, or an average of 100, as well as for the ring phosphates, Na n P n O3n for n ranging from 3 through 10, an increase in magnesium concentration simply leads to a decrease in chemical shift which diminishes at the higher concentrations. These data lend additional support to the concept that polymerized phosphate anions in solution exist in preferred conformations which depend on the nature of the counteraction.

FURTHER CHEMICAL ASPECTS OF THE SENSITIZATION AND ACTIVATION REACTIONS OF NEREIS EGGS

1. Inhibition of activation of Nereis eggs by trinitrophenol, with concurrent sensitization of the eggs to subsequent stimulation, appears to depend on the nitrogroup in the para-position on the phenol.2. The rate of the sensitization process is enhanced by anoxia, CO2, inhibitors of the cytochrome system, or increased potassium ion concentration, but is insensitive to several other inhibitors, narcotics, stimulating agents, and to calcium ion deprivation.3. The immediate initiation of activation by various chemical procedures requires the presence of the calcium ion, is assisted by the potassium ion, `and slightly depressed by increasing magnesium ion concentration, but is not affected by anoxia or by various metabolic poisons.4. Subsequent nuclear and cytoplasmic reorganization, ensuing some minutes after the initial disturbance, is reversibly inhibited by anoxia, inhibitors of the cytochrome system, or diethyl ether.5. Urethane and iodoacetate activate the eggs; this activation is inhibited by trinitrophenol. Cupric ion and p-chloromercuribenzoate also activate the eggs, but only at nearly lytic concentrations, and the activation is not affected by trinitrophenol.6. These data are partly interpreted in relation to the hypothesis of an activator metabolite produced within the egg.