Simone Aparecida Cicillini

A new procedure to obtain Eu3+ doped oxide and oxosalt phosphors

A different route to the synthesis of Eu3+ phosphors in matrices such as Y2O3, YVO4, La(BO3)3 or YNbO4, and the characterization and luminescent properties of these compounds, were studied. The new route (Pechini method) consists of the formation of a polymeric resin obtained by polyesterification between metal chelate complexes (formed by metallic ions and α-hydroxycarboxylic acids) and a polyfunctional alcohol. Ignition of this resin at low temperature renders the selected composition of Eu3+ doped oxides or oxosalts. Luminescent and X-ray spectroscopy and thermogravimetric analysis were used to characterize the materials.

The blue phosphor Sr2CeO4 synthesized by Pechini's method

Abstract Blue emitters are very attractive research subjects because of their possible industrial applications as phosphors for field emission displays. Recently, a blue phosphor, Sr 2 CeO 4 , was identified by a combinatorial materials synthesis technique. This material was further synthesized using the chemical coprecipitation method and the decomposition of acetates, carbonates and oxalates in a tedious procedure. In this work, we present the use of Pechini’s method as an alternative for the synthesis of this promising material. When the precursor, (Sr/Ce) polymer citrate–ethylene glycol, was fired at 850°C for 2 h, a mixture of Sr 2 CeO 4 and SrCeO 3 (inactive) was obtained, whereas the amount of Sr 2 CeO 4 was increased by further heating at 1100°C for 2 h in an oxygen atmosphere, as shown by the diffraction pattern. The excitation spectra present two broad bands with maxima at 294 and 344 nm and the emission spectrum has a broad band (half width ∼80 nm) centered at ∼475 nm. The unusually long lifetime of the compound fired at 1100°C of ∼0.04 ms is in good agreement with literature data. In conclusion, the blue phosphor material Sr 2 CeO 4 synthesized at 1100°C in an oxygen flux has comparable or even better emitter properties than that prepared over several days and/or at higher temperatures. The method is very attractive for industrial purposes.

Mechanisms underlying the vascular relaxation induced by a new nitric oxide generator.

Nitric oxide (NO) is a potent vasodilator and it can be generated by the ruthenium complex cis-[Ru(H-dcbpy(-))(2)(Cl)(NO(2)(-))] (DCBPY). The present study aimed to investigate the NO specie generated and to characterize the cellular mechanisms involved on the vasodilatation induced by DCBPY. It was found that at pH 7.4 and 9.4, the NO(+) coordinated to ruthenium (Ru-NO(+)) is converted to NO(2)(-) (Ru-NO(2)(-)), which remains stable. However, the configuration Ru-NO(+) is stable at pH 5.4. It was also verified that the DCBPY complex (Ru-NO(2)(-) configuration) induces vascular relaxation of contracted rat aortic rings in a concentration-dependent manner. Therefore, the potency (pD(2) values) and the maximum relaxant effect (ME) were compared. It was observed that relaxation is more pronounced to Ru-NO(+) configuration, compared with Ru-NO(2)(-), with no difference in ME. On the other hand, the potency of DCBPY (Ru-NO(2)(-)) is lower than that of SNP and higher than that of NITRITE, with no difference in ME for all the compounds. Further experiments were conducted using DCBPY in the Ru-NO(2)(-) configuration. It was noted that the relaxation induced by DCBPY is completely blocked by the soluble guanylyl cyclase (sGC) enzyme inhibitor. The non-selective K(+) channel blocker (TEA) diminishes the potency of DCBPY, but it does not change the ME. Incubation with selective radicalar NO (NO()) and extracellular NO scavengers almost abolishes the relaxation induced by DCBPY. The use of a selective nitroxyl (NO(-)) scavenger decreases the potency of DCBPY, but it does not alter the ME. By using confocal microsopy, it was found that DCBPY, SNP, and NITRITE raise the cytosolic NO concentration and reduce the cytosolic Ca(2+) concentration [Ca(2+)]c in rat aortic smooth muscle cells. These effects are not different when DCBPY and SNP are compared, but they are lower for NITRITE. Taken together, our results demonstrate that the compound DCBPY (Ru-NO(2)(-)) is an NO generator that promotes relaxation of rat aortic rings due to a reduction in [Ca(2+)]c. The vascular smooth muscle relaxation is dependent on sGC activation.

Use of polymeric resin in the formation of SiO2 hybrid gels

Abstract A new organic–inorganic hybrid material with interpenetrating polymer networks was synthesized with a phase of SiO 2 made by sol–gel chemistry and an organic phase made from a polymeric resin obtained by polyesterification between metal chelate complexes (formed by metallic ions and α-hydroxycarboxylic acids) and a polyfunctional alcohol. One modification in this method consists in preparing organic polymers doped with europium III/dipicolinic acid or terbium III/1,2-phenylenedioxidiacetic acid complexes. Europium and terbium luminescent properties were used as probe to obtain structural information about the hybrid gel. To the organic polymers we added tetraorthosilicates to obtain transparent and luminescent organic–inorganic hybrid materials through the sol–gel process. Luminescent and infrared spectra and thermogravimetric properties were measured.

Study of the Suppression of Porphyrin Emission upon Addition of Rare Earth Ions

A topic of constant investigation in recent decades has been the study of electron and/or energy transfer reactions in supramolecular systems. The energy transfer between donor-acceptor depends on the influence of the substituent in the intersystem crossing. The competition between the radiative and non-radiative processes also depends on other factors such as temperature, solvent and energy gap. In this work, we have studied the suppression of the emission of monocarboxyphenyl porphyrins after addition of rare earth ions (RE(III)). The porphyrin emission decreases with the addition of RE(III), no matter which ion is present. When Eu(III) was used, the emission of this ion was not observed either. This suppression happens due to the effect of the heavy atom and not due to the energy transfer through electronic levels between the porphyrin and the RE(III). After the addition of RE(III), the lifetime for MCTPPH2 started to decay biexponentially, indicating the formation of a new species (MCTPPH2-RE(III)) of a shorter lifetime. The presence of NO2 groups in the ortho mesoaryl positions of MCTNPPH2 and the presence of Zn(II) in Zn(MCTPP) decreased both the porphyrin lifetime and emission due to an increase in the spin-orbit coupling.

Evaluation of Nitrosyl Ruthenium Complexes Entrapped in an Oil-In- Water Emulsion as Vasodilator Agents

Several attempts have been made toward the production of oxide (NO)- releasing agents based on metallic complexes. However, many of these agents have been shown to undergo hydroxide electrophilic attack, thus generating the corresponding nitro species. Entrapped nitrosyl ruthenium species can be stabilized in an oil-in-water (o/w) emulsion and be further used for local NO delivery. This study describes the transdermal permeation of cis and trans- (RuCl(bpy)2NO)(PF6)2 complexes as NO-donor agents from a topically applied emulsion, with NO release rates of 0.042 ± 0.002 and 0.035 ± 0.003 � mol/cm 2 .h, respectively. In vitro skin permeation studies performed with the cis and trans- (RuCl(bpy)2(NO))(PF6)2 complexes in o/w emulsion showed that they tend to accumulate in the stratum corneum (SC) and viable skin, with spontaneous NO release occurring in the viable skin only. NO release was detected by using an NO- sensor when the complexes were in contact with the sonicated skin. The vascular responses to the NO released from the cis and trans-(RuCl(bpy)2(NO))(PF6)2 complexes in o/w emulsion were also evaluated by vasodilation experiments.