Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior

This work reports the energy transfer mechanism process of [Eu(TTA)(2)(NO(3))(TPPO)(2)] (bis-TTA complex) and [Eu(TTA)(3)(TPPO)(2)] (tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA = 2-thienoyltrifluoroacetone and TPPO = triphenylphosphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogavimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA)(3)(TPPO)(2)] and [Gd(TTA)(2) (NO(3))(TPPO)(2)] complexes are associated to T -> S(0) transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters Omega(lambda)(lambda = 2 and 4), spontaneous emission rates (A(rad)), luminescence lifetime (tau), emission quantum efficiency (eta) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(Ill) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA)(2)(NO(3))(TPPO)(2)] complexes are discussed in terms of ligand-to-metal energy transfer. (c) 2007 Elsevier B.V. All fights reserved.

Efficient Phosphodiester Hydrolysis by Luminescent Terbium(III) and Europium(III) Complexes

The synthesis and structures of two new isostructural mononuclear [Ln(L)(NO(3))(H(2)O)(3)](NO(3))(2) complexes, with Ln = Tb (complex 1) and Eu (complex 2), which display high activity in the hydrolysis of the substrate 2,4-bis(dinitrophenyl)phosphate, are reported. These complexes displayed catalytic behavior similar to the mononuclear gadolinium complex [Gd(L)(NO(3))(H(2)O)(3)](NO(3))(2) previously reported by us (lnorg. Chem. 2008, 47, 2919-2921); one hydrolysis reaction in two stages where the diesterase and monoesterase activities could be monitored separately, with the first stage dependent on and the second independent of the complex concentration. Through potentiometric studies, electrospray ionization mass spectrometry (ESI-MS) analysis, and determination of the kinetic behaviors of 1 and 2 in acetonitrile/water solution, the species present in solution could be identified and suggested a dinuclear species, with one hydroxo group, as the most prominent catalyst under mild conditions. The complexes show high activity (k(1)= 7 and 18 s(-1) for 1 and 2, respectively) and catalytic efficiency. Complexes 1 and 2 were found to be active toward the cleavage of plasmid DNA, and complete kinetic studies were carried out. Studies with a radical scavenger (dimethylsulfoxide) confirmed the hydrolytic action of 1 and 2 in the cleavage of DNA. Studies on the incubation of distamycin with plasmid DNA suggested that 1 and 2 are regio-specific, interacting with the minor groove of DNA. These complexes displayed luminescent properties. Complex 1 showed higher emission intensity than 2 due to a more efficient energy transfer between triplet and emission levels of terbium (T -> (5)D(4)), along with nonradiative deactivation mechanisms of the excited states of europium via multiphonon decays and the ligand-to-metal charge transfer state. Lifetime measurements of the (5)D(4) and (5)D(0) excited levels for 1 and 2, respectively, indicated the numbers of coordinated water molecules for the complexes.

Effect of Eu(2)O(3) doping on Ta(2)O(5) crystal growth by the laser-heated pedestal technique

High energy band gap hosts doped with lanthanide ions are suitable for optical devices applications To study the potential of Ta(2)O(5) as a host compound pure and Eu(2)O(3)-doped Ta(2)O(5) crystal fibers were grown by the laser-heated pedestal growth technique in diameters ranging from 250 to 2600 pm and in lengths of up to 50 mm The axial temperature gradient at the solid/liquid interface of pure Ta(2)O(5) fibers revealed a critical diameter of 2200 gm above which the fiber cracks X-ray diffraction measurements of the pure Ta(2)O(5) single crystals showed a monoclinic symmetry and a growth direction of [1 (1) over bar 0] An analysis of the pulling rate as a function of the fiber diameter for Eu(2)O(3)-doped Ta(2)O(5) fibers indicated a well defined region in which constitutional supercooling is absent Photoluminescence measurements of pure Ta(2)O(5) crystals using excitation above the band gap (3 8 eV) were dominated by a broad unstructured green band that peaked at 500 nm Three Eu(3+)-related optical centers were identified in the doped samples with nominal concentrations exceeding 1 mol% Two of these centers were consistent with the ion in the monoclinic phase with different oxygen coordinations The third one was visible in the presence of the triclinic phase (C) 2010 Elsevier B V All rights reserved

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE(3+) = Eu(3+), Gd(3+) and Tb(3+)) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H(2)O)(2)], [RE(TLA)(H(2)O)(4)] and [RE(TMA)(H(2)O)(G)], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd(3+)-(BTC) complexes showed that the triplet states (T) of the BTC(3-) anions have energy higher than the main emitting states of the Eu(3+) ((5)D(0)) and Tb(3+) ((5)D(4)), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Omega(2)) of Eu(3+)-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited (5)D(0) and (5)D(4) levels of the Eu(3+) and Tb(3+) ions is discussed. The emission quantum efficiencies (eta) of the (5)D(0) emitting level of the Eu(3+) ion have been also determined. In the case of the Tb(3+) ion, the photoluminescence data show the high emission intensity of the characteristic transitions (5)D(4) -> (7)F(J) (J=0-6), indicating that the BTC ligands are good sensitizers. The RE(3+)-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials. (C) 2009 Elsevier B.V. All rights reserved.

Photoluminescence study of new lanthanide complexes with benzeneseleninic acids

New lanthanide complexes with benzeneseleninic (ABSe) and 4-chloro-benzeneseleninic (ABSeCl) acids have been synthesized and characterized by elemental analysis, infrared and UV-visible spectroscopies. The emission spectra of the trivalent europium complexes presented the typical electronic (5)D(0) -> (7)F(j) transitions of the ion (J = 0-4). The ground-state geometries of the europium complexes have been calculated by using the Sparkle/AM1 model. From these results, the 4f-4f intensity parameters and energies of the ligand singlet and triplet excited states have been obtained. The lower emission quantum yield for the [Eu(ABSe)(3)(H(2)O)(2)](H(2)O)(2) compound, as compared to the [Eu(Al(3)SeCl)(3)(H(2)O)(2)] one, can be associated to the higher numbers of water molecules, in the first and second coordination spheres, that contribute to the luminescence quenching. The [Eu(Al(3)Se)(3)(H(2)O)(2)](H(2)O)(2) complex presents an intermediate state whose energy difference with respect to the first excited singlet state is resonant with three phonons from the water molecules, favouring a multiphonon relaxation process from the singlet state followed by a fast internal conversion process; this effect is less pronounced in the complex with the ABSeCl ligand. The luminescence decay curves of the gadolinium complexes indicate that the level responsible for the intramolecular energy transfer process has a triplet character for both compounds. The nephelauxetic effect in these compounds was investigated under the light of a recently proposed covalency scale based on the concept of overlap polarizability of the chemical bond. (C) 2009 Elsevier B.V. All rights reserved.

New Relativistic Atomic Natural Orbital Basis Sets for Lanthanide Atoms with Applications to the Ce Diatom and LuF3

New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are inluded as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.

Physiological implications of the regulation of vacuolar H+-ATPase by chloride ions

Vacuolar H+-ATPase is a large multi-subunit protein that mediates ATP-driven vectorial H+ transport across the membranes. It is widely distributed and present in virtually all eukaryotic cells in intracellular membranes or in the plasma membrane of specialized cells. In subcellular organelles, ATPase is responsible for the acidification of the vesicular interior, which requires an intraorganellar acidic pH to maintain optimal enzyme activity. Control of vacuolar H+-ATPase depends on the potential difference across the membrane in which the proton ATPase is inserted. Since the transport performed by H+-ATPase is electrogenic, translocation of H+-ions across the membranes by the pump creates a lumen-positive voltage in the absence of a neutralizing current, generating an electrochemical potential gradient that limits the activity of H+-ATPase. In many intracellular organelles and cell plasma membranes, this potential difference established by the ATPase gradient is normally dissipated by a parallel and passive Cl- movement, which provides an electric shunt compensating for the positive charge transferred by the pump. The underlying mechanisms for the differences in the requirement for chloride by different tissues have not yet been adequately identified, and there is still some controversy as to the molecular identity of the associated Cl--conducting proteins. Several candidates have been identified: the ClC family members, which may or may not mediate nCl-/H+ exchange, and the cystic fibrosis transmembrane conductance regulator. In this review, we discuss some tissues where the association between H+-ATPase and chloride channels has been demonstrated and plays a relevant physiologic role.

Photolysis of ferric ions in the presence of sulfate or chloride ions: implications for the photo-Fenton process

The photo-Fenton process (Fe(2+)/Fe(3+), H(2)O(2), UV light) is one of the most efficient and advanced oxidation processes for the mineralization of the organic pollutants of industrial effluents and wastewater. The overall rate of the photo-Fenton process is controlled by the rate of the photolytic step that converts Fe(3+) back to Fe(2+). In this paper, the effect of sulfate or chloride ions on the net yield of Fe(2+) during the photolysis of Fe(3+) has been investigated in aqueous solution at pH 3.0 and 1.0 in the absence of hydrogen peroxide. A kinetic model based on the principal reactions that occur in the system fits the data for formation of Fe(2+) satisfactorily. Both experimental data and model prediction show that the availability of Fe(2+) produced by photolysis of Fe(3+) is inhibited much more in the presence of sulfate ion than in the presence of chloride ion as a function of the irradiation time at pH 3.0.

Theory of small-signal ac response of a dielectric liquid containing two groups of ions

The analysis of Macdonald for electrolytes is generalized to the case in which two groups of ions are present. We assume that the electrolyte can be considered as a dispersion of ions in a dielectric liquid, and that the ionic recombination can be neglected. We present the differential equations governing the ionic redistribution when the liquid is subjected to an external electric field, describing the simultaneous diffusion of the two groups of ions in the presence of their own space charge fields. We investigate the influence of the ions on the impedance spectroscopy of an electrolytic cell. In the analysis, we assume that each group of ions have equal mobility, the electrodes perfectly block and that the adsorption phenomena can be neglected. In this framework, it is shown that the real part of the electrical impedance of the cell has a frequency dependence presenting two plateaux, related to a type of ambipolar and free diffusion coefficients. The importance of the considered problem on the ionic characterization performed by means of the impedance spectroscopy technique was discussed. (c) 2008 American Institute of Physics.

An apparatus for in situ spectroscopy of radiation damage of polymers by bombardment with high-energy heavy ions

A new target station providing Fourier transform infrared (FT-IR) spectroscopy and residual gas analysis (RGA) for in situ observation of ion-induced changes in polymers has been installed at the GSI Helmholtz Centre for Heavy Ion Research. The installations as well as first in situ measurements at room temperature are presented here. A foil of polyimide Kapton HN (R) was irradiated with 1.1 GeV Au ions. During irradiation several in situ FT-IR spectra were recorded. Simultaneously outgassing degradation products were detected with the RGA. In the IR spectra nearly all bands decrease due to the degradation of the molecular structure. In the region from 3000 to 2700 cm(-1) vibration bands of saturated hydrocarbons not reported in literature so far became visible. The outgassing experiments show a mixture of C(2)H(4), CO, and N(2) as the main outgassing components of polyimide. The ability to combine both analytical methods and the opportunity to measure a whole fluence series within a single experiment show the efficiency of the new setup. (C) 2011 American Institute of Physics. [doi:10.1063/1.3571301]

Intermolecular energy transfer and photostability of luminescence-tuneable multicolour PMMA films doped with lanthanide-beta-diketonate complexes

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)(3)(H(2)O)(2)] and [Tb(acac)(3)(H(2)O)(3)] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln(3+)-beta-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand-Ln(3+) intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the (5)D(4) emitting level of the Tb(3+) ion to the excited triplet state T(1) of the tta ligand coordinated to the Eu(3+) ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.

Strong reduction of V(4+) amount in vanadium oxide/hexadecylamine nanotubes by doping with Co(2+) and Ni(2+) ions: Electron paramagnetic resonance and magnetic studies

In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VO(x)/Hexa NT's) doped with Co(2)+ and Ni(2+) ions. The morphology of the NT's has been characterized by transmission electron microscopy, while the metallic elements have been quantified by the instrumental neutron activation analysis technique. The static and dynamic magnetic properties were studied by collecting data of magnetization as a function of magnetic field and temperature and by electron paramagnetic resonance. At difference of the majority reports in the literature, we do not observe magnetic dimers in vanadium oxide nanotubes. Also, we observed that the incorporation of metallic ions (Co(2+), S = 3/2 and Ni(2+), S = 1) decreases notably the amount of V(4+) ions in the system, from 14-16% (nondoped case) to 2%-4%, with respect to the total vanadium atoms (fact corroborated by XPS experiments) anyway preserving the tubular nanostructure. The method to decrease the amount of V(4+) in the nanotubes improves considerably their potential technological applications as Li-ion batteries cathodes. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3580252]

Effect of cerium (IV) ions on the anticorrosion properties of siloxane-poly(methyl methacrylate) based film applied on tin coated steel

This work investigates the influence of the addition of cerium (IV) ions on the anticorrosion properties of organic-inorganic hybrid coatings applied to passivated tin coated steel. In order to evaluate the specific effect of cerium (IV) addition on nanostructural features of the organic and inorganic phases of the hybrid coating, the hydrolytic polycondensation of silicon alkoxide and the radical polymerization of the methyl methacrylate (MMA) function were induced separately. The corrosion resistance of the coatings was evaluated by means of linear polarization, Tafel type curves and electrochemical impedance measurements. The impedance results obtained for the hybrid coatings were discussed based on an electrical equivalent circuit used to fit the experimental data. The electrochemical results clearly showed the improvement of the protective properties of the organic-inorganic hybrid coating mainly when the cerium (IV) was added to the organic phase solution precursor, which seemed to be due to the formation of a more uniform and densely reticulated siloxane-PMMA film. (C) 2010 Elsevier Ltd. All rights reserved.

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Biogenic modified silica as a sorbent of cadmium ions: Preparation and characterization

This work describes the preparation and characterization of biogenic modified silica from rice hull ash and its use as a sorbent of cadmium ions. Thus, an agro-industrial residue has been used to produce a new adsorbent product which is able to remove toxic elements. Mesoporous biogenic silica was obtained by alkaline extraction of sodium silicate by hydrolysis with the sol-gel process, and it was modified with salen using 1,2-dichloroethane as a spacer. The surface area of the silica was measured by nitrogen adsorption/desorption analysis. Surface modification was measured by Fourier transform infrared spectroscopy. The degree of functionalization was obtained by elemental analysis. This work showed that biogenic modified silica can be produced in aqueous media from rice hull ash using a simple method, providing an alternative method for adsorbent preparation. Thermogravimetric analysis showed that the salen-modified silica is stable up to 209 C. The modified silica displays appropriate structural characteristics for an adsorbent. The cylindrical pores, open at both ends, allow free diffusion of cadmium ions to the adsorption sites on the silica surface. The surface modification increases cadmium adsorption on the silica surface 100-fold. The salen-modified silica showed specific adsorption for Cd2+ of 44.52 mg/g SiO2 at cadmium concentration of 100 mg/l.