Tervalent Cations Research Articles

Ag1 − x Mg1 − x R1 + x (MoO4)3 Ag+-conducting NASICON-like phases, where R = Al or Sc and 0 ≤ x ≤ 0.5

Ag1 − xMg1 − xR1 + x(MoO4)3 NASICON-like solid solutions, where R = Al or Sc and 0 ≤ x ≤ 0.5, were prepared; their crystal lattice parameters and thermal stabilities were determined. Silver-ion conductivity was measured, and conductivity activation energy values were calculated for various temperature ranges. Above 400°C, Ag1 − xMg1 − xR1 + x(MoO4)3 phases have ionic conductivities comparable to the conductivities of sodium-ion and lithium-ion NASICON-like conductors. The conductivity increases as the tervalent cation radius increases or the amount of mobile silver ions increases.

Regulation of activity in vitro and in vivo of three phospholipases B from Saccharomyces cerevisiae

The genome of the yeast, Saccharomyces cerevisiae, contains three highly similar genes coding for phospholipases B/lysophospholipases. These enzymes behave differently with respect to substrate preferences in vitro and relative contributions to phospholipid catabolism in vivo [Merkel, Fido, Mayr, Pruger, Raab, Zandonella, Kohlwein and Paltauf (1999) J. Biol. Chem. 274, 28121-28127]. It is shown in the present study that, in vitro, pH markedly affects the substrate preference of Plb1p and Plb2p, but not of Plb3p. At the pH optimum of 2.5-3.5, the order of substrate preference of Plb1p and Plb2p is PtdSer (phosphatidylserine)>PtdIns>PtdCho (phosphatidylcholine>PtdEtn (phosphatidylethanolamine). At pH values of 5 and above, the substrate preferences change to PtdCho=PtdEtn for Plb1p and PtdSer=PtdEtn for Plb2p. Accordingly, with cultured cells the ratio of PtdIns/PtdCho breakdown, as reflected in the ratio of GroPIns (glycerophosphoinositol)/GroPCho (glycerophosphocholine) released into the culture medium, is inversely related to the pH of the growth medium. This effect is ascribed to the pH response of Plb1p, because Plb2p does not contribute to the degradation of PtdIns and PtdCho in vivo. Bivalent and tervalent cations activate phospholipases B at pH 5.5, but are inhibitory at pH 2.5. Al3+ at a concentration of 20 mM increases Plb1p activity in vitro by 8-fold and leads to a 9-fold increase in GroPCho release by whole cells. In vivo, cycloheximide strongly inhibits the breakdown of PtdIns, and to a lesser extent PtdCho. However, Al3+-stimulated GroPCho release is almost completely inhibited by cycloheximide. Deletion of PLB3 leads to increased sensitivity to toxic Al3+. Addition of SDS or melittin to cultured cells leads to a significant increase in phospholipid degradation, which is insensitive to inhibition by cycloheximide. Deletion mutants defective in the PLB1 gene are significantly more resistant to SDS than are wild-type cells.

Influence of the Mode of Water Coordination on the Electronic Structure of the [V(OH2)6]3+ Cation

The correlation between the stereochemistry and electronic structure of the [V(OH2)6]3+] cation has been examined using a variety of physical techniques in conjunction with angular overlap model calculations. The experimental data includes the first reported high-field, high-frequency EPR study of a vanadium(III) complex which enables a precise determination of the ground term spin-Hamiltonian parameters. The electronic structure and vibrational spectrum of the [V(OH2)6]3+ cation was studied in samples formed from the co-crystallization of RbV(SO4)2·12H2O and RbGa(SO4)2·12H2O. The structural modifications of these salts differ in terms of the orientation of the water molecules about the tervalent cation while the MIIIO6 framework remains approximately octahedral. The electronic structure of the [V(OH2)6]3+ cation in samples of Rb[Ga:V](SO4)2·12H2O is found to depend greatly on the relative proportions of gallium(III) and vanadium(III). The experimental data are in accordance with predictions based on the angular overlap model when the π-bonding normal to the plane of the water molecule is dominant over the in-plane interaction (eπ⊥−eπ∥ ca. 930 cm−1 for trigonal planar water coordination). The π-anisotropy results in a large trigonal field splitting of the 3T1g (Oh) ground term in RbV(SO4)2·12H2O (1930 cm−1) which diminishes almost to zero when [V(OH2)6]3+ is doped into RbGa(SO4)2·12H2O, on account of the change in the orientation of the water molecules imposed by hydrogen bonding constraints. This work demonstrates the strong correlation between the stereochemistry and electronic structure of the [V(OH2)6]3+ cation and accounts for the structural abnormalities reported for vanadium(III) salts of this type.

Comparative study of Mg/Al and Mg/Ga layered double hydroxides

Three brucite-like layered Mg 2+/M 3+ (M=Al or Ga) double hydroxides were synthesized by the coprecipitation method. The hydroxides and the mixed oxides obtained by thermal decomposition at 773 K were characterized by X-ray diffraction, infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy and thermogravimetric analysis. These techniques allowed us to confirm that double hydroxides possess a brucite-like structure where tervalent cations are octahedrally arranged and that the calcination products contain a periclase MgO phase and an amorphous Al 2O 3 or Ga 2O 3 phase. The surface properties of the mixed oxides and their basicities were also determined by temperature-programmed desorption of carbon dioxide. The calcination at 773 K of synthetic LDHs gave aluminum or gallium magnesium double oxides with basic sites and high specific surface areas.

Thermal decomposition of Mg/Al and Mg/Ga layered-double hydroxides: a spectroscopic study

M. A. Aramendía, Y. Avilés, V. Borau, J. M. Luque, J. M. Marinas, J. R. Ruiz and F. J. Urbano, J. Mater. Chem., 1999, 9, 1603 DOI: 10.1039/A900535H

Cooperative Jahn-Teller Effect in Titanium Alum

A low-temperature (ca. 12 K) cubic (Pa3) to orthorhombic (Pbca) phase transition of the β-alum CsTi(SO4)2·12H2O has been characterized by High Resolution Powder Neutron Diffraction and EPR measurements. Single crystal Raman spectra of the corresponding rubidium alum, RbTi(SO4)2·12H2O, show that a phase transition from the β-alum structure also occurs over the temperature range 5−15 K, with the spectroscopic changes remarkably similar for the caesium and rubidium salts. The structural instability of the titanium(III) alums is not evident in the corresponding salts of larger or smaller tervalent cations and hence is interpreted in terms of the electronic structure of [Ti(OH2)6]3+. It is proposed that in the high-temperature cubic phase the S6 site symmetry lifts the degeneracy of the t2g (Oh) orbitals to leave the eg (S6) orbital set lowest lying. The resultant 2Eg (S6) ground term is subject to Jahn-Teller coupling with Eg phonon modes. The phase transition is interpreted as arising from a long-range inte...

Single-Crystal Raman Spectroscopy of the Rubidium Alums RbM(III)(SO(4))(2).12H(2)O (M(III) = Al, Ga, In, Ti, V, Cr, Fe) between 275 and 1200 cm(-)(1): Correlation between the Electronic Structure of the Tervalent Cation and Structural Abnormalities.

Low-temperature single-crystal Raman spectra for RbM(III)(SO(4))(2).12H(2)O (M(III) = Al, Ga, In, Ti, V, Cr, Fe) and RbM(III)(SO(4))(2).12D(2)O (M(III) = Al, V) have been collected and assigned in the range 275-1200 cm(-)(1). These results permit classification of the Ti and V rubidium sulfate alums to the beta modification, whereas the remaining tervalent cations give the expected alpha modification. The dimorphism of the rubidium sulfate alums is explained in terms of the electronic structure of the tervalent cation, where the observation of the beta modification is associated with unequal occupancy of the t(2g) (O(h)()) orbitals. For the rubidium vanadium alums the (3)E(g) <-- (3)A(g) electronic Raman (eR) transition permits quantification of the trigonal field splitting of the t(2g) (O(h)()) orbitals (ca. 1940 cm(-)(1)). The profile of the eR band is sensitive both to changes in temperature and to deuteration. Analysis of the eR band profile suggests a reduced spin-orbit splitting of the (3)E(g) manifold, this being ascribed to excited state Jahn-Teller (J-T) effects. The similarity of the Raman spectra of the cesium and rubidium titanium sulfate alums suggest that they exhibit closely related structural chemistry, with both subject to phase transitions below 80 K. The observation that modes of E(g) symmetry are coupled to the structural change is consistent with the interpretation that the trigonal field leaves an orbital doublet ground term for titanium(III), leading to a cooperative J-T effect.

Low‐temperature polarized single‐crystal Raman spectra of the β‐alums CSM(SO4)2. 12H2O (M = Mo or Ru) between 275 and 1200 cm−1

AbstractLow‐temperature, polarized, single‐crystal Raman spectra of the β‐alums CsM(SO4)2. 12H2O (M = Mo or Ru) and their deuterated analogues were recorded between 275 and 1200 cm−1. The internal modes of sulphate and [M(OH2)6]3+ and the external modes of water coordinated to the mono‐ and tervalent cation were assigned. This allowed a comparison between the wavenumbers of the internal modes of second‐ and first‐row transition metal hexaaquacations. The relationship between v1(MO6) and the MIII—O bond length is similar for the first‐row transition and Group 13 metals, but is significantly different for the second‐row transition metals. This suggests a non‐ionic contribution to the metal‐water bonding in the latter case. The relative intensities of the v1(MO6) modes are highly dependent on the identity of the metal; however, the trend in this property is not simply related to either the bond strength, the polarizing power of the cation or the covalent interaction.

Localization of polyvalent cations in pentasil catalysts modified by metal oxides

Polyvalent cations in HZSM-5 zeolites were found to be preferentially localized at the outer surface of microcrystallites (for Me3+) or inside the channels of the zeolite structure (for Me2+). This difference was explained by both steric and electrostatic hindrances arising for the tervalent cations.

Single-crystal Raman spectroscopy of the α alums CsM(SO4)2· 12H2O (M = Co or Ir) between 275 and 1200 cm–1

Low-temperature polarised single-crystal Raman spectra of CsM(SO4)2·12H2O (M = Co or Ir) have been recorded between 275 and 1200 cm–1. A full assignment of the spectra has been completed, including all the Raman-active internal modes of the tervalent hexaaqua cation [ν1(MO6) 548 (Co) and 554 (Ir), ν2(MO6) 509 (Co) and 540 (Ir) and ν5(MO6) 332 av. (Co) and 314 av. cm–1(Ir)]. The relationship between the wavenumber of the ν1(MO6) mode and the metal–oxygen bond length is significantly different for the tervalent cations of the second- and third-row transition metals than for those of first-row transition metals and Group 13 metals. Solution Raman spectra of [Ir(OH2)6]3+ have enabled determination of ν1(MO6)aq(536 cm–1); the relationship between this value and that obtained at low temperature in the solid state closely follows that found previously for the chromium(III) and rhodium(III) aqua ions. The external modes of water co-ordinated to the tervalent cation are highly sensitive to the alum type, the metal–ligand bond length, and the stereochemistry of water co-ordination and provide additional insight into the metal–water interaction. This, in turn, casts light on the assignment of the external modes to particular molecular motions.

Thermodynamic relationships of complex formation: Part II. Enthalpy-entropy interdependence in hard-hard interactions in aqueous solution

Thermodynamic data for hard-hard interactions in stepwise complex formation in aqueous solution between UO 2(II), Th(IV) or tervalent cations and carboxylate ligands are inspected for the occurrence of enthalpy-entropy relationships. Such relationships are found in the first complexation of UO 2(II) and in all the stepwise complex formations between Ln(III) (Ln = lanthanide) and acetate, propionate, isobutyrate, lactate, or α-hydroxyiso-butyrate. Weaker correlations occur in the Th(IV) complex formation and in the Ln(III)-glycolate systems. The enthalpy-entropy susceptibilities are different for the various complexation reactions.

Relationship between the electronic and molecular structure of tervalent aqua ions: low-temperature neutron diffraction structure of CsCr(SO4)2·12H2O

The alum CsCr(SO4)2·12H2O has been investigated by single-crystal neutron diffraction at 15 K. The structure, which conforms to the β modification, was refined using a total of 651 unique reflections to give a weighted R value of 0.041. The stereochemistry of water co-ordination to chromium(III) is trigonal planar, with the Cr–O bond vector making an angle of 0.8(6)° with the plane of the co-ordinated water molecule. The angle between the plane of the co-ordinated water molecule and the CrO6 framework, φ, is –19.0(4)°, similar to that found for the corresponding iron salt [–19.4(3)°], but smaller than found for the corresponding ruthenium [–22.0(3)°] and vanadium [–22(1)°] salts. The relationship between φ and the splitting of the t2g(Oh) orbital energies is described using the angular overlap model. Accordingly, the preferred value of φ depends on the occupancy of the t2g orbitals. Using this approach the φ values found for the caesium sulphate β alums are explained, and the electronic structures of the titanium and vanadium hexaaqua cations are discussed. The general features of the site of the tervalent cation in the alum lattice are described, these being important owing to the extensive use of the alum lattice for the spectroscopic study of tervalent aqua ions.

Diode array detectors in flow injection analysis. Simultaneous determination of rare earth metals with Arsenazo III

A flow injection spectrophotometric procedure for the simultaneous determination of rare earths with Arsenazo III is reported. The spectrum of the sample is recorded by using a diode array detector and the mixed spectra are resolved with the aid of a multicomponent analysis program based on a least-squares fitting algorithm. Binary mixtures of tervalent cations at concentrations between 0.5 and 2.5 μg/g and uranyl in the range 1.4–4.3 μg/g were accurately resolved by univariate calibration. The presence of thorium (2.8–7.0 μ/g) required the use of multivariate calibration in order to obtain accurate results. Tervalent cations were globally determined as lanthanum. The sampling rate was about 60 samples/h. The results obtained in the analysis of U and Th in a pitchblende agree well with the certified values.

Stereochemistry of tervalent aqua ions: low-temperature neutron diffraction structures of CsFe(SO4)2·12H2O and CsFe(SeO4)2·12H2O

The structures of CsFe(SO4)2·12H2O and CsFe(SeO4)2·12H2O have been investigated by neutron diffraction at 15 K. Both alums crystallise in the cubic space group Pa3, Z= 4, with a= 12.354(6)A for the sulphate and 12.593(10)A for the selenate. The structures were refined using 802 [CsFe(SO4)2·12H2O] and 1 059 [CsFe(SeO4)2·12H2O] inequivalent reflections to give weighted R factors of 0.029 and 0.028 respectively. In agreement with prior X-ray crystallographic determinations, CsFe(SO4)2·12H2O gives the β alum modification whereas CsFe(SeO4)2·12H2O forms an α alum. The stereochemistry of water co-ordination to FeIII differs in the two alums, with the angle between the metal (III)–water bond and the plane of the co-ordinated water molecule being 0.6(10)° for the sulphate and 18.6(10)° for the selenate. This tilting of the plane of the co-ordinated water molecule is shown to be related to the alum type. The iron(III)–water bond distance shows some sensitivity to the tilt of the co-ordinated water molecule, lengthening from 1.994(1) to 2.002(1)A as the plane of the water molecule is tilted by 18.6°. The sensitivity of the alum type to the size of the constituent ions, and to the stereochemistry of water co-ordination to the tervalent cation, is discussed in light of the hydrogen bonding in the alum structures.

Vibrational spectroscopic studies of tervalent hexa-aqua cations: oriented single-crystal Raman spectra between 275 and 1 200 cm–1of the caesium rhodium alums, CsRh(SO4)2·12H2O, CsRh(SeO4)2·12H2O, and CsRh(SO4)2·12D2O

Oriented single-crystal Raman spectra of the caesium α-alums CsRh(SO4)2·12H2O, CsRh(SeO4)2·12H2O, and CsRh(SO4)2·12D2O have been recorded at or below 80 K. The external modes of water co-ordinated to the mono- and ter-valent cations as well as the internal modes of S(Se)O42– and [Rh{OH(D)2}6]3+ are found in the spectral region 275–1 200 cm–1. A full assignment of the spectra in this region has been completed and the results are in close agreement with the predictions of factor group analysis. This work provides the first full vibrational characterisation of the Raman-active modes of the sulphate α-alum lattice. The site and factor group splitting of the XO42– vibrational modes is independent of the identity of X but highly dependent on the alum type, with the internal modes of SO42– in the caesium rhodium sulphate α-alums giving similar Raman band profiles to those of SeO42– in the caesium selenate α-alums. The internal modes of [Rh(OH2)6]3+ are found at 548[ν1(RhO6)], 533 [ν2(RhO6)], and 315 cm–1[ν5(RhO6)] in the low-temperature single-crystal spectra, while the ν1(Rho6) mode occurs at 529 cm–1 in solution (300 K, 1 mol dm–3 H2SO4). The relationship between the wavenumber of the ν1(RhO6) mode and the Rh–O bond length is significantly different compared with that obtained for the first-row transition-metal tervalent hexa-aqua ions.

Distribution coefficients of lanthanide elements and some separations on layered hydrous titanium dioxide

Distribution coefficients /Kd/ of lanthanide elements on layered hydrous titanium dioxide, H2Ti4O9.nH2O /where n=1.2–1.3/, have been determined as a function of the pH of the aqueous phase. The plots of 1g Kd vs. pH gave straight lines with slopes equal to +3 except for the data for heavier lanthanides, suggesting ideal ion-exchange equilibria between tervalent cations in the aqueous phase and hydrogen ions in the hydrous oxide. Mutual separations of La−Cs and La−Ba have been achieved on a column of this material on the basis of large differences in affinities between the metal ion pairs.

Interactions of tervalent lanthanide ions with bacterial collagenase (clostridiopeptidase A).

Tervalent cations of the lanthanide (rare-earth) elements reversibly inhibit bacterial collagenase (clostridiopeptidase A; EC 3.4.24.3). Sm(3+), whose ionic radius is closest to that of Ca(2+), is the most effective inhibitor, completely suppressing clostridiopeptidase activity at a concentration of 100mum in the presence of 5mm-Ca(2+). Er(3+) and Lu(3+), which both have ionic radii smaller than either Ca(2+) or Sm(3+), inhibit less efficiently, and La(3+), which is slightly larger than Ca(2+) or Sm(3+), inhibits only weakly. These findings indicate a closely fitting, stereospecific, Ca(2+)-binding pocket in clostridiopeptidase, which excludes ions that are only slightly larger than Ca(2+) [ionic radius 0.099nm (0.99 A)]. By contrast, trypsin, an enzyme whose activity does not depend on Ca(2+), requires lanthanide concentrations 50-100-fold greater for inhibition. Furthermore, the relative efficiency of inhibition of trypsin by lanthanides increases as the lanthanide ions become smaller and the charge/volume ratio increases. At a concentration of 50mum, Sm(3+) lowers the apparent K(m) for the hydrolysis of Pz-peptide by clostridiopeptidase from 5.4mm to 0.37mm and the apparent V(max.) from 0.29 Wünsch-Heidrich unit to 0.018 unit. Thus Sm(3+) enhances the affinity of this enzyme for its substrate; inhibition of hydrolysis of Pz-peptide may result from the excessive stability of the enzyme-Sm(3+)-substrate complex. Inhibition by Sm(3+) is competitive with regard to Ca(2+). The apparent dissociation constant, K(d), of Ca(2+) is 0.27mm, where the K(i) for Sm(3+) is 12mum. Clostridiopeptidase is more thermolabile in the absence of Ca(2+). With Sm(3+), thermoinactivation of the enzyme at 53 degrees C or 60 degrees C is initially accelerated, but then becomes retarded as heating continues. Lanthanide ions bind to gelatin and collagen. In so doing, they appear to protect these substrates from lysis by clostridiopeptidase through mechanisms additional to supplanting Ca(2+) at its binding site on the enzyme. Collagen and gelatin sequester sufficient lanthanide ions to gain partial protection from clostridiopeptidase in the absence of an extraneous source of these inhibitors.

Studies with inorganic ion exchange membranes—a membrane selective to strontium ion

Strontium tungstoarsenate membrane shows response for Sr2+ and can be used to determine the activity of these ions. The response time of the membrane is a few seconds and the potentials generated are reproducible. The membrane electrode can be used for one year without any drift in potentials. The membrane was found to be more selective to Sr2+ ions than to many other of univalent, bivalent and tervalent cations. Anions also show no interference.

Studies with inorganic ion exchange membranes—a membrane selective to strontium ion

AbstractStrontium tungstoarsenate membrane shows response for Sr2+ and can be used to determine the activity of these ions. The response time of the membrane is a few seconds and the potentials generated are reproducible. The membrane electrode can be used for one year without any drift in potentials. The membrane was found to be more selective to Sr2+ ions than to many other of univalent, bivalent and tervalent cations. Anions also show no interference.

Transfer rate of some tervalent cations in the biphasic system HClO 4, water-dinonylnaphthalenesulfonic acid, toluene—III : Transfer rate at t≠0 determined by both chemical reactions and diffusion processes

Concentration vs time data for the transfer of Fe(III), Ce(III), Eu(III), Gd(III), Tm(III) from aqueous perchloric acid solutions to toluene solutions of dinonylnaphthalenesulfonic acid have been obtained as function of the chemical composition of the system and in some cases of the stirring speed of the phases. A model, coupling together both chemical reactions and diffusion processes, obtained through the elaboration of models previously developed has been proved to explain well the experimental data in a wide range of stirring speeds and for times ranging from zero to about 300 min (near equilibrium). A complete description of the diffusion processes and interfacial chemical reactions taking place in the system as well as numerical values of the rate constants are reported.