Effect Of Rare Earth Ions Research Articles

An ion‐gate response of a glutathione monolayer assembly highly sensitive to lanthanide ions

AbstractThe self‐assembled glutathione (γ‐L‐glutamyl‐L‐cysteinyl‐glycine, GSH) monolayer was formed on a gold electrode via a sulfur attachment of the cysteinyl residue. The effect of lanthanide ions (La3+, Eu3+ and Lu3+) on the ion‐gate behavior of this electrode was studied by using cyclic voltammetry (CV) and Fe(CN)63– as a probe ion. These ions were found to open the ion gate with a few micromoles, and the effect was in the order of La3+ > Eu3+ Lu3+.

The influence of the admixing of different multiplets on the spin magnetic moment and Faraday effect of rare earth ions in Garnets

The influence of the admixing of the excited multiplets of the ground configuration with the ground multiplet on the spin magnetic moment of the crystal- field- and exchange-interaction-split ground state, the Faraday rotation and the magneto-optic coefficient induced by the rare earth ions in rare-earth-substituted garnets Y3-xRxFe5O12 (R=Ce and Pr) has been calculated in this paper. It is found that, in the case of Ce3+ ions, the admixing of the 4f1 2F7/2 multiplet with the 2F5/2 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 140% and the Faraday rotation increase by 180% at 633 nm wavelength, and 150% at 1150 nm at 294 K. In the case of Pr3+ ions, the admixing of the 4f2 3H5 multiplet with the 3H4 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 34% and the Faraday rotation increase by 59% at 294 K. The admixing of different multiplets of the Ce3+ ions makes the ratio between the magneto-optic coefficients at 50 and 294 K increase by 7% at 633 nm wavelength and 15% at 1150 nm.

Influence of the A-site cation in ACoO 3 ( A = La, Pr, Nd, andGd) perovskite-type oxides on catalytic activity for methane combustion

The effect of rare-earth ions (La, Pr, Nd, and Gd) in ACoO 3 perovskites on the thermal behavior and on the catalytic activity for methane oxidation has been studied. The thermal reduction, as investigated by oxygen desorption analysis, revealed for all perovskites one evolution step occurring above 1100 K. Transmission electron micrographs at the beginning of the desorption step revealed the presence of superstructures, which are attributed to the formation of oxygen-deficient domains ( ACoO 2.5 ≤ ACoO 3- x ≤ ACoO 3) adopting perovskite-related brownmillerite-type structures. A model for the sequence of the structural changes of the perovskites during the reduction is proposed. The amount of oxygen which evolved above 1100 K increased with decreasing size of the lanthanide ion. Comparative catalytic studies were carried out in a fixed-bed microreactor at atmospheric pressure in the temperature range 600–1200 K. The activities at 830 K, expressed as reaction rates referred to the BET surface area, increased in the order PrCoO 3 ⪡ LaCoO 3 < NdCoO 3 < GdCoO 3. However, no significant influence of the A-site cations on the catalytic activity was found, with exception of praseodymium. PrCoO 3 showed a 30 times lower activity than the other samples. The catalytic activity of ACoO 3 perovskites can be markedly affected by the presence of Co 3O 4 impurity in the perovskites.

Effect of lanthanide ions on the phase behavior of dipalmitoylphosphatidylcholine multilamellar liposomes

The effect of lanthanide ions (Ln 3+) and their coordination compounds of diethylenetriamine pentaacetic acid (DTPA) on the phase behavior of dipalmitoylphosphatidycholine (DPPC) multilamellar liposomes has been studied by differential scanning calorimetry (DSC), Raman spectroscopy, and freeze-fracture electron microscopic techniques. The displacement of Ca 2+ binding on DPPC liposomes by lanthanide ions was also studied. The results show that the binding degree of four kinds of chloride salts with DPPC liposomes is: YbCl 3 > GdCl 3 > LaCl 3 > CaCl 3. Lanthanide ions increase the phase transition temperature of DPPC liposomes and decrease the membrane fluidity. Freeze-fracture electron microscopic results show that La 3+ enhances the order of DPPC membrane. The effect of coordination compounds of lanthanides with DTPA on the phase behavior of DPPC liposomes is smaller than that of their chlorides. La 3+, Gd 3+, and Yb 3+, can displace Ca 2+ binding on DPPC liposomes, but there coordination compounds of DTPA can hardly displace Ca 2+. Raman spectroscopic results show that a very slight effect in lateral packing order of DPPC liposomes was observed at various concentrations of lanthanides.

Influence of the A-site cation in AMnO3+x and AFeO3+x (A = La, Pr, Nd and Gd) perovskite-type oxides on the catalytic activity for methane combustion

The effect of rare-earth ions (La, Pr, Nd and Gd) in AMnO3+x and AFeO3+x perovskites on the thermal behavior and on the catalytic activity for the deep oxidation of methane has been studied. AMnO3+x perovskites showed after preparation an oxidative non-stoichiometry. Oxygen desorption analysis revealed for the four manganites different desorption steps occurring between 930 and 1370 K. Stoichiometry was reached after the first desorption step. Heating the samples at temperatures above 1300 K resulted in phase segregation to the simple oxides. AFeO3+x perovskites were more stable towards thermal decomposition than the Mn-perovskites, showing no oxygen evolution up to 1400 K. The reducibility of these perovskites in hydrogen correlated inversely with the relative effective ionic radii of the trivalent rare-earth cations. Comparative catalytic studies were carried out in a fixed-bed microreactor at atmospheric pressure in the temperature range 600–1200 K. The activities at 770 K, expressed as reaction rates referred to the BET surface area, varied between 1.4 × 10−7 and 2.9 × 10−7 mol s−1 m−7 for the AMnO3+x, and between 1.1 × 10−7 and 1.6 × 10−7 mols−1m−2for the AFeO3+x perovskites.

The effect of rare earth ions on the thermal stability of AlF3-based glasses

Abstract The effect of rare earth ions on the thermal stability of AlF 3 -based glasses has been investigated. Different concentrations of NdF 3 , ErF 3 and PrF 3 ranging from 0.25 to 2.0 wt% have been added to a well characterized base glass. Differential scanning calorimetry (DSC) measurements were carried out to determine the time-temperature-transformation (TTT) curves, critical cooling rates and Hruby parameters for both the base glass as well as for the selectively doped glasses. It was found that the thermal stability of AlF 3 -based glasses actually increased following the addition of the above rare earth ions up to certain concentrations and then started to gradually decrease but still remained higher than the original base glass. This behavior of AlF 3 -based glasses is in contrast to those based on ZrF 4 and may offer certain advantages in the fabrication of active fiber devices.

Effect of rare earth ions on the phase transition of Na 2SO 4 crystals

The V ⇄ I phase transition of Na 2SO 4 crystals was investigated on a sample of pure Na 2SO 4 and on rare-earth-ion ( Ln 3+ = La 3+, Eu 3+, Tm 3+)-doped Na 2SO 4 samples in various ambient gases (O 2, N 2, NH 3) with high temperature X-ray diffraction and differential thermal analysis. On heating in N 2 flow, the initiating temperature for the V → I transition was lowered by doping with Ln 3+ ion and the doping effect was enhanced by an increase in the ionic size ratio r Ln 3+ r Na + . The low temperature form of the solid solution (LSS) Na 2SO 4 and rare earth sulfate, which was a by-product in the preparation of the Ln 3+-doped samples, transformed to a high temperature form (HSS) after the V → I transition, and the initiating temperature for the LSS → HSS transition was highest in the Eu 3+-doped sample ( r Ln 3+ r Na + ⋍ 1 ). On the other hand, on cooling in N 2 flow, the HSS was stable until room temperature in the La 3+- or Eu 3+-doped sample ( r Ln 3+ r Na + ≧ 1 ), but transformed to LSS in the Tm 3+-doped sample ( r Ln 3+ r Na + < 1 ). The results obtained in other ambient gas flows (O 2, NH 3) were considerably affected by the sorption of ambient gas into Na 2SO 4 crystals and/or the reaction between ambient gas and Na 2SO 4 and were different from those obtained in N 2 flow.

Effect of Lanthanide Ions on the Properties of Ln1Ba2Cu3O7 Thin Films

Ln1Ba2Cu3Oy thin films with nine different lanthanide ions were prepared by a laser ablation method. Systematic changes in the structure and superconducting properties were observed in regard to the difference of the lanthanide ion radii. Smaller lanthanide ions were found to be suitable for the formation of a superconducting film with orthorhombic structure.

Effect of rare-earth ions on the photoelectric properties of garnets

The study of the photoelectric properties of nominally pure crystals of the complex oxides R/sub 3/Ga/sub 5/O/sub 12/ (R - Nd, Sm, Gd), Gd/sub 3/Sc/sub 2/Ga/sub 3/O/sub 12/, Y/sub 2.75/Er/sub 0.25/Sc/sub 2/Ga/sub 3/O/sub 12/ with the structure of garnet revealed the formation of a photoelectric state (PES) which persists for a long time at room temperature. The spectral sensitivity (SS) of the PES is manifested in the UV region of the spectrum (210 nm > lambda > 400 nm) and repeats the behavior of the optical absorption curve, corresponding to intraconfigurational (4f-4f) transitions of rare-earth (RE) ions. In the case of Cd/sub 3/Sc/sub 2/Ga/sub 3/O/sub 12/ the photosensitivity is red-shifted with the formation of a peak at 450 nm. Comparison of the spectral sensitivity curves for the PES according to the corresponding optical absorption spectra suggests that the most extreme peak in the short-wavelength region corresponds to the fundamental absorption edge and is attributable to band-band transitions.

Effect of rare earth ions on the catalytic activity of Ln2MnNiO6 perovskites

A series of rare earth transition metal perovskites has been synthesized and the catalytic activity tested for 2-propanol decomposition. The effect of rare earth ions on the catalytic activity can been understood from the correlations obtained between the physico-chemical properties and the catalytic activity of the perovskites.

Effect of lanthanide ions on histamine secretion from rat peritoneal mast cells.

1 Ions of the lanthanide series (lanthanum-lutetium) inhibit histamine release induced by allergen and anti-IgE in the presence of extracellular calcium. The inhibition is dose-dependent in the range 10(-6) to 10(-9) M and there is no marked difference in potency between the lanthanides. 2 The response to lanthanum is biphasic and higher concentrations (10(-4) M) potentiate the release. Maximal concentrations (10(-3) M) again abolish secretion. 3 The effect of concanavalin A is weakly antagonized by lanthanum but strongly inhibited by higher lanthanides. 4 Inhibition of histamine release evoked by basic agents is markedly dependent on the ionic radius of the lanthanide. In the presence of extracellular calcium, dysprosium is the most effective inhibitor. Similar results are observed with dextran. In the absence of calcium, there is a regular increase in inhibition with decreasing ionic radius. 5 Inhibition of release in the presence of calcium is immediate and does not require preincubation with the lanthanide. The antagonism due to lanthanum is competitive and the pA2 values vary with the secretagogue. In contrast, the inhibitory effect in the absence of extracellular calcium increase progressively with time. 6 These results are discussed in terms of the calcium-pools important in histamine release and the mode of action of different secretagogues.

The effect of lanthanide ions on enteropeptidasecatalyzed activation of trypsinogen

Rare earths were found to be powerful inhibitors of enteropeptidase-catalyzed (enterokinase, EC 3.4.21.9) activation of trypsinogen. Inhibition was complete at a La 3+ concentration of 12.5 · 10 −6 M in the assay system used and still detectable at a concentration of 1.25 · 10 −6 M. Inhibition was observed with all lanthanides tested. No significant differences between individual metals could be established under the conditions of the inhibition assay. Increasing ionic strength decreased enzyme activity and progressively diminished the inhibitory effect of rare earth ions suggesting an electrostatic basis for the mechanism of this inhibition. La 3+ did not significantly affect enteropeptidase-mediated hydrolysis of N benzoyl- l- arginine ethyl ester. Its inhibitory effect on activation of trypsinogen by enteropeptidase, therefore, must be attributed to interaction with the zymogen rather than the enzyme. Kinetic measurements show that inhibition by rare earths is noncompetitive in nature. Binding of lanthanides to the tetraaspartyl sequence near the aminoterminus of trypsinogen may prevent this group from interacting with a critical specificity subsite on the enzyme.

Structure of a Phosphonomannan, as Determined by the Effect of Lanthanide Ions on Its Carbon-13 Magnetic Resonance Spectrum

The carbon-13 magnetic resonance spectrum of phosphonomannan 2 in deuterium oxide expands on addition of europium and praseodymium chlorides. With the aid of a parallel study on structurally related α-D-mannose-1-phosphate and α-D-mannose-6-phosphate the signal displacements were interpreted in terms of chemical structure. Both ions cause predominantly contact shifts, and in general addition of praseodymium ion produces a downfield shift of the 13C.m.r. signal of the esterified 13C nucleus, which is accompanied by a smaller downfield shift of that of the adjacent carbon. Europium ion produces smaller and approximately equal shifts of signals of the corresponding α-13C and β-13C nuclei, but in the opposite direction and with less broadening. Displacements produced by neodymium chloride were comparable in size and downfield. Other lanthanide chlorides, namely those of ytterbium, holmium, neodymium, and gadolinium, broadened the signal of the 13C nucleus attached to the phosphodiester group without displacement. Changes produced in proton nuclear magnetic resonance spectra of the phosphates and phosphodiester 2 are more difficult to interpret in terms of structure.

The effect of lanthanide ions on the conformation of adenine mononucleotides and dinucleotides.

1 The binding of lanthanide ions to the pyrophosphate portion of NAD and AppA causes conformational changes, monitored by circular dichroism, which involve a perturbation of the population distribution of these flexible molecules generating new conformations. 2 Binding occurs to both stacked and unstacked states; the former probably involves a change in the relative orientation of the nucleotide chromophores without a fundamental change in overall symmetry; and the latter, by analogy with weaker binding to mononucleotides, changes in glycosidic angle, χ. 3 The implications are discussed for the use of lanthanide probes in high-resolution molecular magnetic resonance studies of small molecules possessing conformational flexibility.

Evaluation of the effect of rare-earth ions on the properties of magnesium ferrite

Analysis of all geometric and energetic factors shows that a partial replacement of the Mg2+ ions by REM ions is possible, but is hindered mainly by the high thermal stability of MgO. A partial replacement of the Fe3+ ions by REM ions is also possible. It may be assumed that REM cations will occupy preferentially the octahedral positions. REM cations entering the ferrite lattice would be expected to alter the conditions of indirect exchange reaction and the overall magnetic moment of the ferrite, thereby strongly affecting the magnetic characteristics of the material. The electrical resistivity of magnesium ferrite alloyed with REM ions varies depending on the positions occupied in the lattice by valency electrons released from linkage.