Microwave-assisted selective deoxygenation of layer- and chain-containing oxides

Very rapid (within 5 min), selective, single-step deoxygenation of layer- and chain-containing oxides, MoO3, CrO3, V2O5, alpha-VOPO4 . 2H(2)O and Ag6Mo10O33 has been accomplished using graphitic carbon in a microwave-assisted reaction. The products were found to be MoO2, Cr2O3, VO2, VPO4 and a mixture of (Ag + MoO2), respectively. Products were characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), IR and electron paramagnetic resonance (EPR) spectroscopies. Although conventional methods of preparing these materials are tedious, the present method is simple, fast and yields very homogeneous products of good crystallinity. Our results reveal that while layer- and chain-containing oxides undergo rapid microwave-assisted carbothermal reduction, the non-layered materials do not. The high structural selectivity of these reactions is suggestive of the topochemical nature of the fast reduction process.

Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 x 10(-2) Omega cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide. (C) 2011 Elsevier B.V. All rights reserved.

Crystal growth and defects characterization of zinc tris (thiourea) sulfate: a novel metalorganic nonlinear optical crystal

Single crystals of the metalorganic nonlinear optical material zinc tris (thiourea) sulfate (ZTS) were grown from aqueous solution. The morphology of the crystals was indexed. The grown crystals were characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. Spectrophotometric studies on ZTS reveal that it has good transparency for the Nd: YAG laser fundamental wavelength. Differential thermal analysis of ZTS indicates that the material does not sublime before melting but decomposes immediately after melting. The defect content of the crystals was estimated using etching and X-ray topography. The mechanical hardness anisotropy was evaluated in the (100) plane, which indicates the presence of soft directions.

Self-similar solutions of laser produced blast waves

The aerodynamics of the blast wave produced by laser ablation is studied using the piston analogy. The unsteady one-dimensional gasdynamic equations governing the flow an solved under assumption of self-similarity. The solutions are utilized to obtain analytical expressions for the velocity, density, pressure and temperature distributions. The results predict. all the experimentally observed features of the laser produced blast waves.

Synthesis of taxanes - The carvone approach; A simple, efficient stereo- and enantio-selective synthesis of the functionalised A ring

A highly stereo- and enantio-selective methodology for the construction of the chiral functionalised A-ring of taxanes, starting from (R)-carvone employing a short, simple and efficient sequence is described.

Application of selective F-1 decoupled H-1 NMR for enantiomer resolution and accurate measurement of enantiomeric excess at low chiral substrate/auxiliary concentration

The higher substrate and chiral auxiliary concentration is a pre-requisite to obtain efficient separation of H-1 NMR signals of enantiomers. The higher concentration of chiral lanthanide shift reagents provides broadened spectral lines resulting in a severe loss of resolution between the enantiomer resonances. In order to circumvent such difficulties, herein we present the application and the usefulness of a selective F-1 decoupled correlation (COSY) experiment which yields proton decoupled proton spectra in the indirect dimension. The potentiality of the experiment is demonstrated on several chiral compounds possessing different functional groups, employing either a lanthanide shift reagent or a solvating reagent as chiral auxiliaries. (C) 2011 Elsevier B.V. All rights reserved.

Selective immunoneutralization of luteinizing hormone results in the apoptotic cell death of pachytene spermatocytes and spermatids in the rat testis

The selective withdrawal of pituitary gonadotropins through specific antibodies is known to cause disruption of spermatogenesis. The cellular mechanism responsible for the degenerative changes under isolated effect of luteinizing hormone (LH) deprivation is not clear. Using antibodies specific to LH we have investigated the effect of immunoneutralization of LH on apoptotic cell death in the testicular cells of the immature and the adult rats. Specific neutralization of LH resulted in apoptotic cell death of germ cells, both in the immature and the adult rats. The germ cells from control animals showed predominantly high molecular weight DNA, while the antiserum treated group showed DNA cleavage into low molecular weight DNA ladder characteristic of apoptosis. This pattern could be observed within 24 h of a/s administration and the effect could be reversed by testosterone. The germ cells were purified by centrifugal elutriation and the vulnerability of germ cell types to undergo apoptosis under LH deprivation was investigated. The round spermatids and the pachytene spermatocytes were found to be the most sensitive germ cells to lack of LH and underwent apoptosis. Interestingly, spermatogonial cells were found to be the least sensitive germ cells to the lack of LH in terms of apoptotic cell death. Results show that LH, in addition to being involved in the germ cell differentiation, is also involved in cell survival and prevent degeneration of germ cells during spermatogenesis. Apoptotic DNA fragmentation may serve as a useful marker for the study of hormonal regulation of spermatogenesis and the specific neutralization of gonadotropic hormones can be a reliable model for the study of the molecular mechanism of apoptosis.

Spin-Selective Correlation Experiment for Measurement of Long-Range J Couplings and for Assignment of (R/S) Enantiomers from the Residual Dipolar Couplings and DFT

We report the C-HETSERF experiment for determination of long- and short-range homo- and heteronuclear scalar couplings ((n)J(HH) and (n)J(XH), n >= 1) of organic molecules with a low sensitivity dilute heteronucleus in natural abundance. The method finds significant advantage in measurement of relative signs of long-range heteronuclear total couplings in chiral organic liquid crystal. The advantage of the method is demonstrated for the measurement of residual dipolar couplings (RDCs) in enantiomers oriented in the chiral liquid crystal with a focus to unambiguously assign R/S designation in a 2D spectrum. The alignment tensor calculated from the experimental RDCs and with the computed structures of enantiomers obtained by DFT calculations provides the size of the back-calculated RDCs. Smaller root-mean-square deviations (rmsd) between experimental and calculated RDCs indicate better agreement with the input structure and its correct designation of the stereogenic center.

Photoinduced transparency of effective three-photon absorption coefficient for femtosecond laser pulses in Ge16As29Se55 thin films

We report a dramatic change in effective three-photon absorption coefficient of amorphous Ge16As29Se55 thin films, when its optical band gap decreases by 10 meV with 532 nm light illumination. This large change provides valuable information on the higher excited states, which are otherwise inaccessible via normal optical absorption. The results also indicate that photodarkening in chalcogenide glasses can serve as an effective tool to tune the multiphoton absorption in a rather simple way. (C) 2011 American Institute of Physics.

Inverse surface melting in confined clusters: Ar-13 in zeolite L

Monte Carlo and molecular dynamics simulations on an Ar-13 cluster in zeolite L have been carried out at a series of temperatures to understand the rigid-nonrigid transition corresponding to the solid-liquid transition exhibited by the free Ar-13 cluster. The icosahedral geometry of the free cluster is no longer preferred when the cluster is confined in the zeolite. The root-mean-squared pair distance fluctuation, delta, exhibits a sharp, well-defined rigid-nonrigid transition at 17 K as compared to 27 K for the free cluster. Multiple peaks in the distribution of short-time averages of the guest-host interaction energy indicate coexistence of two phases.; It is shown that this transition is associated with the inner atoms becoming mobile at 17 K even while the outer layer atoms, which are in close proximity to the zeolitic wall, continue to be comparatively immobile. This may be contrasted with the melting of large free clusters of 40 or more atoms which exhibit surface melting. Guest-host interactions seem to play a predominant role in determining the properties of confined clusters. We demonstrate that the volume of the cluster increases rather sharply at 17 and 27 K respectively for the confined and the free cluster. Power spectra suggest that the motion of the inner atoms is generally parallel to the atoms which form the cage wall.

Selective deprotection of propargyl ethers using tetrathiomolybdate

Benzyltriethylammonium tetrathiomolybdate, [PhCH2NEt3](2)MoS4, 1 deprotects propargyl ethers of alcohols and phenols in a selective manner in high yields. Easily reducible groups like nitro, aldehyde, keto and allyl are not affected.

Antiferroelectric lead zirconate thin films by pulsed laser ablation

Lead Zirconate (PbZrO3) thin films were deposited by pulsed laser ablation method. Pseudocubic (110) oriented in-situ films were grown at low pressure. The field enforced anti-ferroelectric (AFE) to ferroelectric (FE) phase transformation behaviour was investigated by means of a modified Sawyer Tower circuit as well as capacitance versus applied voltage measurements. The maximum polarisation obtained was 36 mu C cm(-2) and the critical field to induce ferroelectric state and to reverse the antiferroelectric slates were 65 and 90 kV cm(-1) respectively. The dielectric properties were investigated as a function of frequency and temperature. The dielectric constant of the AFE lead zirconate thin him was 190 at 100 kHz which is more than the bulk ceramic value (120) with a dissipation factor of less than 0.07. The polarisation switching kinetics of the antiferroelectric PbZrO3 thin films showed that the switching time to be around 275 ns between antipolar state to polar states. (C) 1999 Elsevier Science S.A. All rights reserved.

Study of the electrical properties of pulsed laser ablated (Ba0.5Sr0.5)TiO3 thin films

The laser ablated barium strontium titanate (BST) thin films were characterized in terms of composition, structure, microstructure and electrical properties. Films deposited at 300 degrees C under 50 mTorr oxygen pressure and 3 J cm(-2) laser fluence and further annealed at 600 degrees C in flowing oxygen showed a dielectric constant of 467 and a dissipation factor of 0.02. The room-temperature current-voltage characteristics revealed a space charge limited conduction (SCLC) mechanism, though at low fields the effect of the electrodes was predominant. The conduction mechanism was thoroughly-investigated in terms of Schottky emission at low fields, and bulk-limited SCLC at high fields. The change over to the bulk-limited conduction process from the electrode-limited Schottky emission was, attributed to the process of tunneling through the electrode interface at high fields resulting into the lowering of the electrode contact resistance and consequently giving rise to a bulk limited conduction process. The predominance of SCLC mechanism in the films suggests that the bulk properties are only revealed if the depletion width at the electrode interface is thin enough to allow the tunneling process to take place. This condition is only favorable if the him thickness is high or if the doping concentration is high enough. In the present case the film thickness ranged from 0.3 to 0.7 mu m which was suitable to show the transition mentioned above. (C) 1999 Elsevier Science S.A. All rights reserved.