Surface treatment of nanoporous silicon with noble metal ions and characterizations

A very large surface to volume ratio of nanoporous silicon (PS) produces a high density of surface states, which are responsible for uncontrolled oxidation of the PS surface. Hence it disturbs the stability of the material and also creates difficulties in the formation of a reliable electrical contact. To passivate the surface states of the nanoporous silicon, noble metals (Pd, Ru, and Pt) were dispersed on the PS surface by an electroless chemical method. GIXRD (glancing incidence X-ray diffraction) proved the crystallinity of PS and the presence of noble metals on its surface. While FESEM (field emission scanning electron microscopy) showed the morphology, the EDX (energy dispersive X-ray) line scans and digital X-ray image mapping indicated the formation of the noble metal islands on the PS surface. Dynamic SIMS (secondary ion mass spectroscopy) further confirmed the presence of noble metals and other impurities near the surface of the modified PS. The variation of the surface roughness after the noble metal modification was exhibited by AFM (atomic force microscopy). The formation of a thin oxide layer on the modified PS surface was verified by XPS (X-ray photoelectron spectroscopy).     

Improvement of the scintillation properties of Gd3Ga3Al2O12:Ce,B single crystals having tailored defect structure

A novel approach is reported to minimize various defect centers in Ce doped Gd₃Ga₃Al₂O₁₂ single crystals to improve the scintillation properties. The crystals of Gd₃Ga₃Al₂O₁₂ codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma‐rays from a ¹³⁷Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post‐growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

In situ SEM,TEM and AFM studies of the antimicrobial activity of lemon grass oil in liquid and vapour phase against Candida albicans

Inhibition of Candida albicans growth was shown by lemon grass oil (LGO) and lemon grass oil vapour (LGO vapour) at 288 μg/ml and 32.7 μg/ml concentration, respectively. The assessment of cell damage by LGO and LGO vapour was done through scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) observations. SEM analysis showed complete rupture of C. albicans cells treated with LGO vapour while in those treated with LGO in broth, only shrinkage was observed. TEM study showed the alterations in morphology upon treatment with LGO while complete degradation of the Candida cells was observed in case of LGO vapour. Further three dimensional morphological changes and roughness of the cells have also been evaluated with AFM after the treatment with LGO & LGO vapour. Roughness (root mean square value) was significantly higher in control C. albicans cells (211.97 nm) than LGO (143 nm) and LGO vapour (5.981 nm) treated cells. The results for the first time demonstrate relatively higher efficacy of LGO vapours for inhibition and cellular damage of C. albicans cells as compared to the LGO in liquid phase. This suggests the potential application of LGO vapour phase against infections caused by C. albicans.     

Oxidation of gas-phase protactinium ions, Pa+ and Pa2+: formation and properties of PaO2(2+)(g), protactinyl

Oxidation reactions of bare and ligated, monopositive, and dipositive Pa ions in the gas phase were studied by Fourier transform ion cyclotron resonance mass spectrometry. Seven oxidants were employed, ranging from the thermodynamically robust N(2)O to the relatively weak CH(2)O-all oxidized Pa(+) to PaO(+) and PaO(+) to PaO(2)(+). On the basis of experimental observations, it was established that D[Pa(+)-O] and D[OPa(+)-O] > or = 751 kJ mol(-1). Estimates for D[Pa(+)-O], D[OPa(+)-O], IE[PaO], and IE[PaO(2)] were also obtained. The seven oxidants reacted with Pa(2+) to produce PaO(2+), indicating that D[Pa(2+)-O] > or = 751 kJ mol(-1). A particularly notable finding was the oxidation of PaO(2+) by N(2)O to PaO(2)(2+), a species, which formally comprises Pa(VI). Collision-induced dissociation of PaO(2)(2+) suggested the protactinyl connectivity, {O-Pa-O}(2+). The experimentally determined IE[PaO(2)(+)] approximately 16.6 eV is in agreement with self-consistent-field and configuration interaction calculations for PaO(2)(+) and PaO(2)(2+). These calculations provide insights into the electronic structures of these ions and indicate the participation of 5f orbitals in bonding and a partial "6p hole" in the case of protactinyl. It was found that PaO(2)(2+) catalyzes the oxidation of CO by N(2)O-such O atom transport via a dipositive metal oxide ion is distinctive. It was also observed that PaO(2)(2+) is capable of activating H(2) to form the stable PaO(2)H(2+) ion.     

High-temperature behaviour of lithium borates:: Part I: Characterization and thermal stability

Nine compounds, namely Li₃BO₃, -Li₄B₂O₅, β-Li₄B₂O₅, Li₆B₄O₉, -LiBO₂, Li₂B₄O₇, Li₃B₇O₁₂, LiB₃O₅ and Li₂B₈O₁₃ in the Li₂O–B₂O₃ system have been synthesized and characterized. The unit-cell parameters, density and solubility in water at room temperature of all the compounds are reported. The densities of the compounds were found to be in the 1.90–2.50 g cm⁻³ range, while their solubility in water at room temperature was in the 0.91–8.64×10⁻² g cm⁻³ range. Determination of the thermal stability of the compounds by quenching and differential thermal analysis (DTA) showed that only -LiBO₂ and Li₂B₄O₇ retained their original symmetry up to their congruent melting at 1121 and 1188 K, respectively, in air.     

A facile synthesis and spectral (ir, 1H, 13C, 31P nmr) studies of 2,10-dichloro-6-aryloxy-12H-dibenzo[d,g][1,3,2]dioxaphosphocin 6-sulfides

The synthesis of new 2,10-dichloro-6-aryloxy-12H-dibenzo[d,g][1,3,2]dioxaphosphocin 6-sulfides 4 was achieved in two steps with high yields from the simple materials 5,5′-dichloro-2,2′-dihydroxydiphenyl-methane (1) and thiophosphoryl chloride (2) which produced the key intermediate 2,6,10-trichloro-12H-dibenzo[d,g][1,3,2]dioxaphosphocin 6-sulfide (3) . Treatment of 3 with substituted phenols under phase transfer catalytic (PTC) conditions led to members of 4 . Long range coupling [⁵J_(P,H) = 3.6 Hz] was observed between phosphorus and one of the bridged methylene protons in 4 . A ¹³C nmr analysis revealed ²J_(P,O,C), ³J_(P,O,C) ⁴J(P,O,C) and ⁵J(P,O,C) couplings. All ³¹P nmr chemical shifts for thirteen members of these new heterocycles are reported for the first time. The nmr data are not totally definitive to confirm a boat-chair as the major conformer for the central eight-membered dioxaphosphocin ring, but such a conformer is tentatively suggested as favored.     

The enhanced green fluorescent protein as a tool for the analysis of protein dynamics and localization: local fluorescence study at the single-molecule level

The green fluorescent protein (GFP) has emerged, in recent years, as a powerful reporter molecule for monitoring gene expression, protein localization and protein-protein interaction. Several mutant variants are now available differing in absorption, emission spectra and quantum yield. Here we present a detailed study of the fluorescence properties of the Phe-64-->Leu, Ser-65-->Thr mutant down to the single molecule level in order to assess its use in quantitative fluorescence microscopy and single-protein trafficking. This enhanced GFP (EGFP) is being used extensively as it offers higher-intensity emission after blue-light excitation with respect to wild-type GFP. By means of fluorescence spectroscopy we demonstrate the absence of the neutral form of the chromophore and the lack of photobleaching recovery after ultraviolet light irradiation. Furthermore, we show that the EGFP spectral properties from isolated to densely packed molecules are highly conserved. From these experiments EGFP emerges as an ideal molecule for quantitative studies of intra and intercellular tagged-protein dynamics and fluorescence-activated cell sorting, but not for monitoring single-protein trafficking over extended periods of time.     

Construction and assessment of some perchlorate-selective liquid membrane electrodes

Perchlorate-selective liquid membrane electrodes were developed by incorporating the ion-pair complexes of perchlorate with brucine, cinchonidine, emetine and benzyldimethyltetradecylammonium chloride (zephiramine) in nitrobenzene. The electrodes, which respond to perchlorate ion over the concentration range 1.0–5.0 × 10^?4 M ClO^?₄, have a fast response and wide pH range. The zephiramine-perchlorate electrode was the best in terms of its fast response, wide pH range and high reproducibility of potentials. Most common inorganic and organic anions, except permanganate, do not cause significant interference. Electrodes based on brucine-, emetine- and zephiramine-perchlorate were successfully employed for the direct potentiometric determination of perchlorate in the presence of halides, sulphate, nitrate and chlorate. The cinchonidine-perchlorate electrode showed comparatively poor selectivity.