CO2 reduction over NaNbO3 and NaTaO3 perovskite photocatalysts.

The activity of NaNbO3 and NaTaO3 perovskites for the photocatalytic reduction of CO2 is studied in this work. For this purpose, sodium niobate and tantalate have been prepared using solid-state reactions, extensively characterised by means of powder X-ray diffraction, UV-vis, photoluminescence and Raman spectroscopies and N2 adsorption isotherms, and tested in the gas-phase reduction of CO2 under UV light in a continuous flow photoreactor. NaNbO3 is constituted of an orthorhombically distorted perovskite structure, while a ca. 4.5 : 1 combination of the orthorhombic and monoclinic modifications is found in the tantalate. Both catalysts exhibit interesting intrinsic activities, with the tantalate material giving rise to a slightly higher performance. This is attributed to a compromise situation between electron-hole recombination and the reducing potential of conduction band electrons. In addition, a decrease in the competition of water protons for photogenerated electrons is observed with both catalysts with respect to TiO2.

Revisiting the BaO2/BaO redox cycle for solar thermochemical energy storage.

The barium peroxide-based redox cycle was proposed in the late 1970s as a thermochemical energy storage system. Since then, very little attention has been paid to such redox couples. In this paper, we have revisited the use of reduction-oxidation reactions of the BaO2/BaO system for thermochemical heat storage at high temperatures. Using thermogravimetric analysis, reduction and oxidation reactions were studied in order to find the main limitations associated with each process. Furthermore, the system was evaluated through several charge-discharge stages in order to analyse its possible degradation after repeated cycling. Through differential scanning calorimetry the heat stored and released were also determined. Oxidation reaction, which was found to be slower than reduction, was studied in more detail using isothermal tests. It was observed that the rate-controlling step of BaO oxidation follows zero-order kinetics, although at high temperatures a deviation from Arrhenius behaviour was observed probably due to hindrances to anionic oxygen diffusion caused by the formation of an external layer of BaO2. This redox couple was able to withstand several redox cycles without deactivation, showing reaction conversions close to 100% provided that impurities are previously eliminated through thermal pre-treatment, demonstrating the feasibility of this system for solar thermochemical heat storage.

X-ray diffraction, and Raman scattering study of nanostructured ZrO2-TiO2 oxides prepared by sol-gel.

In the present work, we study the phase composition of ZrO2-TiO2 system by means of XRD and Raman spectroscopy, using also TG-ATD, and N2 adsorption isotherms as complementary characterization techniques. TiO2-ZrO2 samples of selected compositions (0, 10, 90, 50 and 100% in weight of TiO2) were prepared by sol-gel method and annealed at three different temperatures (400, 600 and 800 degrees C). Structural characterization reveals that only the pure oxides are crystalline at 400 degrees C: TiO2 as anatasa with a minor brookite component, and ZrO2 as a mixture of tetragonal (majority) and monoclinic phases. Following the 600 degrees C calcination, the TiO2-ZrO2 50-50% sample forms the ZrTiO4 mixed oxide, although this materials remains partly amorphous. In contrast, samples with higher and lower TiO2 content form solid solutions with, respectively, anatasa and tetragonal ZrO2 structures. Zirconium incorporation into the TiO2 lattice leads to the expansion of the unit cell parameters, and it stabilizes the anatase phase, hindering its transformation into rutile. Similarly, dissolving titanium atoms into the ZrO2 structure delays the transformation from the tetragonal to the monoclinic polymorph.

A novel target of lithium therapy.

Phosphatases converting 3'-phosphoadenosine 5'-phosphate (PAP) into adenosine 5'-phosphate are of fundamental importance in living cells as the accumulation of PAP is toxic to several cellular systems. These enzymes are lithium-sensitive and we have characterized a human PAP phosphatase as a potential target of lithium therapy. A cDNA encoding a human enzyme was identified by data base screening, expressed in Escherichia coli and the 33 kDa protein purified to homogeneity. The enzyme exhibits high affinity for PAP (K(m)<1 microM) and is sensitive to subtherapeutic concentrations of lithium (IC(50)=0.3 mM). The human enzyme also hydrolyzes inositol-1, 4-bisphosphate with high affinity (K(m)=0.4 microM), therefore it can be considered as a dual specificity enzyme with high affinity (microM range) for both PAP and inositol-1,4-bisphosphate. Hydrolysis of inositol-1,4-bisphosphate was also inhibited by lithium (IC(50)=0.6 mM). Thus, we present experimental evidence for a novel target of lithium therapy, which could explain some of the side effects of this therapy.

Revisiting the hydrothermal synthesis of titanate nanotubes: new insights on the key factors affecting the morphology.

Recently, titanate nanotubes have attracted a significant deal of interest, but the mechanism of formation as well as some structural aspects of these materials is still under debate. In this context, the main goal of the present study is to identify the key factors affecting the morphology of the titanate nanostructures during hydrothermal synthesis in order to increase the homogeneity and control, as finely as possible, the dimensions of the nanotubes. Previous studies also analyzed the influence of synthesis conditions but, unlike other works, the simultaneous assessment of the influence of parameters such as the phase and crystal size of the TiO(2) used as precursor, and the time and temperature of the hydrothermal treatment has been now analyzed under the same experimental context. The characterization of the prepared materials by means of TEM, XRD, N(2) adsorption isotherms and Raman spectroscopy was performed to establish correlations between the structural features and the preparation conditions. In this research, special attention has been paid to study the non-washed materials, which most of the previous studies have excluded from characterization. After hydrothermal treatment amorphous particles with different morphologies are isolated before acidification, which seems to be a crucial stage in controlling nanotube formation. Besides, the obtained data indicate that some characteristics of the nanotubes, such as the degree of conversion, the homogeneity and crystallinity of the structures or the aspect ratio, can be easily selected by adjusting the synthesis parameters.

A novel mammalian lithium-sensitive enzyme with a dual enzymatic activity, 3'-phosphoadenosine 5'-phosphate phosphatase and inositol-polyphosphate 1-phosphatase.

We report the molecular cloning in Rattus norvegicus of a novel mammalian enzyme (RnPIP), which shows both 3'-phosphoadenosine 5'-phosphate (PAP) phosphatase and inositol-polyphosphate 1-phosphatase activities. This enzyme is the first PAP phosphatase characterized at the molecular level in mammals, and it represents the first member of a novel family of dual specificity enzymes. The phosphatase activity is strictly dependent on Mg2+, and it is inhibited by Ca2+ and Li+ ions. Lithium chloride inhibits the hydrolysis of both PAP and inositol-1,4-bisphosphate at submillimolar concentration; therefore, it is possible that the inhibition of the human homologue of RnPIP by lithium ions is related to the pharmacological action of lithium. We propose that the PAP phosphatase activity of RnPIP is crucial for the function of enzymes sensitive to inhibition by PAP, such as sulfotransferase and RNA processing enzymes. Finally, an unexpected connection between PAP and inositol-1,4-bisphosphate metabolism emerges from this work.

The Arabidopsis HAL2-like gene family includes a novel sodium-sensitive phosphatase.

The yeast HAL2 gene encodes a lithium- and sodium-sensitive phosphatase that hydrolyses 3'-phosphoadenosine-5'-phosphate (PAP). Salt toxicity in yeast results from Hal2 inhibition and accumulation of PAP, which inhibits sulphate assimilation and RNA processing. We have investigated whether the model plant Arabidopsis thaliana contains sodium-sensitive PAP phosphatases. The Arabidopsis HAL2-like gene family is composed of three members: AtAHL and AtSAL2, characterized in the present work, and the previously identified AtSAL1. The AtAHL and AtSAL2 cDNAs complement the auxotrophy for methionine of the yeast hal2 mutant and the recombinant proteins catalyse the conversion of PAP to AMP in a Mg(2+)-dependent reaction sensitive to inhibition by Ca2+ and Li+. The PAP phosphatase activity of AtAHL is sensitive to physiological concentrations of Na+, whereas the activities of AtSAL1 and AtSAL2 are not. Another important difference is that AtAHL is very specific for PAP while AtSAL1 and AtSAL2 also act as inositol polyphosphate 1-phosphatases. AtAHL constitutes a novel type of sodium-sensitive PAP phosphatase which could act co-ordinately with plant sulphotransferases and serve as target of salt toxicity in plants.

The yeast HAL1 gene improves salt tolerance of transgenic tomato.

Overexpression of the HAL1 gene in yeast has a positive effect on salt tolerance by maintaining a high internal K(+) concentration and decreasing intracellular Na(+) during salt stress. In the present work, the yeast gene HAL1 was introduced into tomato (Lycopersicon esculentum Mill.) by Agrobacterium tumefaciens-mediated transformation. A sample of primary transformants was self-pollinated, and progeny from both transformed and non-transformed plants (controls) were evaluated for salt tolerance in vitro and in vivo. Results from different tests indicated a higher level of salt tolerance in the progeny of two different transgenic plants bearing four copies or one copy of the HAL1 gene. In addition, measurement of the intracellular K(+) to Na(+) ratios showed that transgenic lines were able to retain more K(+) than the control under salt stress. Although plants and yeast cannot be compared in an absolute sense, these results indicate that the mechanism controlling the positive effect of the HAL1 gene on salt tolerance may be similar in transgenic plants and yeast.