RESUMO
In this work, we have investigated the crystal and electronic structure of the orthorhombic phase of BaPbxBi1-xO3(BPBO) forx = 0.7 (BPBO70), 0.75 (BPBO75) and 1.0 (BPO), using temperature dependent x-ray diffraction measurements, photoemission spectroscopy, and electronic structure calculations. Our results show the importance of particle size and strain in governing superconductivity. Interestingly, the temperature evolution of the structural parameters in the case of BPBO70 is similar to that of BPBO75 but the magnitude of the change is diminished. The BPBO75 and BPO compounds exhibit metallic nature, which is corroborated by the core level studies. The electronic structure calculations in conjunction with the core level studies suggest that oxygen vacancies play an important role for metallicity observed in the end compound. The exponent to the spectral line shape close to the Fermi level suggests the origin of pseudogap to be due to other contributions in addition to disorder in the case of BPBO70 and BPO. The core level studies also show that as one goes fromx = 0.70 to 1.0, there occurs chemical potential shift towards the valence band suggesting hole doping. Our results open the venue to further study these compounds as a function of particle size, nature of carriers for its transport behaviour, electronic structure belowTC, composition at the grain boundaries and microscopic origin of pseudogap in the non-superconducting phase. We believe that our results call for a revision of the temperature-doping phase diagram of BPBO to include the pseudogap phase.
RESUMO
Arsenic transforming bacterial strains belong to genus Pseudomonas sp.AK9 (KY569424), were isolated from the middle Gangetic plains of Bihar, India. The Pseudomonas sp. AK9 strains were able to transform toxic arsenite to a less toxic arsenate. In the present work, the presence of different arsenic resistance genes (aoxB, arsB, acr3 and aoxAB) were observed in isolated strain. Furthermore, the aoxB gene was amplified from genomic DNA of AK9, cloned in E.coli/DH5αcells, and sequenced. The BLASTn results and phylogenetic study of the aoxB gene showed 95.32 % and 90.07 % identity with the large subunit of aoxB gene of previous reported Thiomonas arsenivorans strain DSM16361 and Thiomonas arsenivorans strain b6, respectively. Further overhang primers were designed for amplifications of full length aoxB gene (â¼1200 bp), and cloned in to the expression vector and host E.coli/BL21 cells. The GST-aoxB gene was expressed in BL21 cells, and a profound expression product of â¼ 72 kDa was observed in SDS PAGE. The detection of a large subunit (aoxB) of arsenate oxidase protein in western blotting assay affirmed the expression of aoxB gene in recombinant E.coli/BL21 clone. Further, the recombinant E.coli/BL21cells showed increased growth than the normal E.coli/BL21 cells against As (III). Thus, this study showed the presence of aoxB gene in Pseudomonas sp. AK9 genome which regulates the resistant ability to arsenic toxicity.
