1,721,586 research outputs found
Coppola y su yo melómano
Full text linkQuintana, A. (1998). Coppola y su yo melómano. La madriguera. (9):72-72. https://riunet.upv.es/handle/10251/41686.Importación Masiva7272
Electrocatalytic oxidation of styrene by a high valent ruthenium porphyrin cation radical
No full text[[abstract]]A sterically-hindered carbonylruthenium(II) porphyrin Ru-II(CO)(TMP) (where TMP = meso-tetramesitylporphyrinato dianion) has been synthesized. Chemical oxidation of Ru-II(CO)(TMP) by m-chloroperbenzoic acid (m-CPBA) gives the dioxoruthenium(VI) porphyrin (Ru-VI(O)(2)TMP). Cyclic voltammograms show that Ru-VI(O)(2)TMP is reversibly oxidized at E-1/2 = +1.24 V in CH2Cl2. Thin-layer absorption spectra for oxidation of Ru-VI(O)(2)TMP at + 1.32 V indicates that the product is a porphyrin cation radical (Ru-VI(O)(2)TMP+.). Electrogenerated Ru-VI(O)(2)TMP+. reacts selectively with styrene to give phenylacetaldehyde (96%) and benzaldehyde (4%). We report the first case of styrene oxidation by high valent ruthenium porphyrin under electrochemical conditions. An electrocatalytic oxidation reaction scheme is proposed. (C) 2000 Elsevier Science S.A. All rights reserved.[[note]]SC
Hydrogen gas-rechargeable metal hydride electrode for Ni-MH battery
No full text[[abstract]]Some nonbreakable pellets made of an AB(5) alloy and metallic powder Ag or Ni were used as the anode in a Ni-MH battery such that the anode could be charged in hydrogen gas and discharged in electrolyte. The performance is influenced by the alloy properties, electrode porosity, hydrogen pressure, discharge current, electrolyte polarization, and contamination in the system. For the pellet Ag/AB(5) = 10, continuous discharge can proceed but only for a limited time. The lower porosity of the pellet may be the main problem. For the pellet Ni/AB(5) = 25, it can be discharged unlimitedly at a constant hydrogen pressure of 20 atm. When discharged with a fixed amount of hydrogen gas, the adsorbed hydrogen is immediately discharged on the surface rather than being absorbed into the bulk, and the discharge capacity comes mostly from the gaseous hydrogen rather than from the hydrogen already dissolved in the bulk of alloy. Therefore, the pellet acts more like a catalyst for hydrogen dissociation than as an absorbent. Furthermore, a minimum of similar to 7 atm of hydrogen pressure is required for the system to operate properly. It is suggested that, in order for such a system to operate better under the wet condition, a higher hydrogen gas pressure be maintained to accelerate the hydrogenation rate and more porous pellets be used for faster reaction kinetics. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1938087] All rights reserved.[[note]]SC
Spectral and redox properties of zinc porphyrin core dendrimers with triarylamines as dendron
No full text[[abstract]]The first and second generation of zinc porphyrin core dendrimers (3 and 4) with triarylamine as dendron have been synthesized via Ullmann coupling reaction. Their absorption and emission spectra indicate that there are strong interactions between zinc porphyrin core and triarylamine dendrons. Zinc porphyrin links with triarylamine causes Soret band broadening and Q band shift as compared with ZnTPP. Because of the antenna effect on these dendrimers, the fluorescence quantum yields were strongly enhanced when more triarylamine moieties were linked. Cyclic voltammetry and spectroelectrochemical methods were used to investigate the redox properties of dendrimers. Axial ligation of zinc porphyrin with N-methylimidazole is useful in differentiating the oxidation site of dendrimers. For the first generation dendrimer (3), porphyrin ring oxidation potential shifts cathodically because the periphery dendrons are strong electron-donating groups. On the other hand, the dendrons of the second generation (4) are oxidized first and generate an atmosphere of eight positive charges. The porphyrin ring core is then oxidized with an anodic shift in potential due to the electron-withdrawing effect of the oxidized substituents.[[note]]SC
Electrocatalytic reactions of nitric oxide on Prussian blue film modified electrodes
No full text[[abstract]]The electrocatalytic reduction and oxidation of nitric oxide on electrodes modified with Prussian blue (PB) films in acidic aqueous buffer solutions has been studied. The cyclic voltammetry and spectroelectrochemistry results show that Prussian white, the reduced form of Prussian blue, acted as an electrocatalyst toward NO reduction. The reduction current started at - 0.4 V and became higher at more negative potentials. Bulk electrolysis of nitrite solution at PB-modified electrodes at - 0.7 V led to the formation of NH3 and NH2OH. Berlin green, the oxidized form of PB, has the activity to catalyze NO oxidation to yield nitrate at + 1. 3 V. The reactivity of PB is discussed and the reaction schemes are presented. (C) 2001 Elsevier Science B.V. All rights reserved.[[note]]SC
Electrochemical characterization and electrocatalysis of high valent manganese meso-tetrakis(N-methyl-2-pyridyl)porphyrin
No full text[[abstract]]Electrochemical oxidation of water-soluble manganese(III) meso-tetrakis(N-methyl-2-pyridyl)porphyrin (Mn-III(2-TMPyP)) generates stable Mn-IV and Mn-V porphyrins. Speciation of various oxidation states of the porphyrin are characterized by spectroelectrochemical methods. The acid dissociation constants (pK(a)s) for Mn-III(2-TMPyP)(H2O)(2) are 9.6 and 10.7, respectively. Spectroelectrochemical results of the one-electron oxidation of Mn-III(2-TMPyP) exhibit different forms of oxomanganese(IV) porphyrin, depending on the pH of the solution and the applied potential. The pK(a) for O=Mn-IV(2-TMPyP)(H2O) is 10.5. The axial oxygen atom ligated to the Mn(IV) center is protonated in acidic solution (pK(a) 3.4). Further one-electron oxidation generates dioxomanganese(V) porphyrin, (O)(2)Mn-V(2-TMPyP), which is stable in alkaline solution at room temperature. No oxidation wave is observed in the cyclic voltammograms, indicating the slow heterogeneous electron transfer rate of these oxidation reactions. The electrogenerated dioxomanganese(V) porphyrin exhibits higher reactivity toward olefin oxidation than oxomanganese(IV) porphyrin in basic solutions. (C) 1999 Elsevier Science S.A. All rights reserved.[[note]]SC
Electrochemically controlled ligand shuttling between zinc porphyrin and meso-phenylenediamine substituent
No full text[[abstract]]ZnTMP-PD was synthesized and fully characterized; by using electrochemical and spectroelectrochemical methods, ligand shuttling between the zinc porphyrin and the meso-phenylenediamine substituent could be monitored; EPR results indicated that the charge was delocalized on ZnTMP-PD.[[note]]SC
Strain-enhanced arsenic precipitation in GaAs-based quantum-well structures grown by low-temperature molecular beam epitaxy
No full text[[abstract]]The precipitation of arsenic in InGaAs/GaAs and GaAs/AlGaAs multiple-quantum-well (MQW) structures grown by molecular-beam epitaxy at 230 degrees C has been studied by transmission electron microscopy. For InGaAs/GaAs MQWs with strained InGaAs wells, upon annealing at 500 and 600 degrees C, arsenic precipitates tend to be completely confined in InGaAs wells near the InGaAs/GaAs interfaces, resulting in dual two-dimensional planes of precipitates in each InGaAs well. In contrast, this strong confinement of precipitates does not exist in InGaAs/GaAs MQWs with partially or totally strain-relieved InGaAs wells and in unstrained AlGaAs/GaAs MQWs. The present results suggest that the As precipitation process in strained GaAs-based MQWs is not only driven by the bond strength in different materials, but also by the lattice-mismatch-induced strain.[[note]]SC
- …
