Laser- induced optical properties change in Sb10S40Se50 chalcogenide thin films: An investigation through FTIR and XPS measurements

Chalcogenide glasses are interesting materials for their infrared transmitting properties and photo-induced effects. This paper reports the influence of light on the optical properties of Sb10S40Se50 thin films. The amorphous nature and chemical composition of the deposited film was studied by X-ray diffraction and energy dispersive X-ray analysis (EDAX). The optical constants, i.e., refractive index, extinction coefficient, and optical band gap as well as film thickness are determined from the measured transmission spectra using the Swanepoel method. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The dispersion energy parameter was found to be less for the laser-irradiated film, which indicates the laser-irradiated film is more microstructurally disordered as compared to the as-prepared film. It is observed that laser-irradiation of the films leads to decrease in optical band gap (photo-darkening) while increase in refractive index. The decrease in the optical band gap is explained on the basis of change in nature of films due to chemical disorderness and the increase in refractive index may be due to the densification of films with improved grain structure because of microstructural disorderness in the films. The optical changes are supported by X-ray photoelectron spectroscopy data. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A New Mechanism For Ferromagnetism In C-60-TDAE

Based on the topology of C-60 and the resulting non-disjoint nature of the lowest unoccupied molecular orbitals, Ne propose a new model for ferromagnetic exchange in C-60-TDAE. Within the Hubbard model, we find that the ferromagnetic exchange integral is stabilized to first order in the inter-ball transfer integral, while the antiferromagnetic coupling is stabilized only to second order. This difference is adequate to counter the larger phase space available for stabilizing the antiferromagnetic state. Thus, the ground state is found to be ferromagnetic for reasonable inter-ball transfer integrals.

A.c. conductivity studies on the silver molybdo-arsenate glassy system

A new quaternary fast-ion conducting silver molybdo-arsenate [Agl-Ag2O-(MoO3 + As2O5)] (SMA) glassy system has been prepared using the melt-quenching technique for various dopant salt (Agl) concentrations by fixing the formers (MoO3 + As2O5) composition and the modifier (Ag2O) to formers (M/F) ratio. The prepared compounds were characterized by X-ray diffraction. The impedance measurements were made on different Agl compositions of the SMA glasses as a function of frequency (6.5 Hz-65 kHz) and temperature (303-343 K), using the Solatron frequency-response analyser(model 1250). The bulk conductivity and the appropriate physical model (equivalent circuit) of the SMA glass were obtained from the impedance analysis. The a.c. conductivity was calculated for different Agl compositions of SMA glasses at various temperatures and the obtained a.c. conductivity results were analysed using Jonscher's Universal Law. The conduction mechanism for the highest conducting SMA glassy compound has been explained using the diffusion path model.

Topological mimicry and epitope duplication in the guanylyl cyclase C receptor

Guanylyl cyclase C (GCC) is the receptor for the gastrointestinal hormones, guanylin, and uroguanylin, in addition to the bacterial heat-stable enterotoxins, which are one of the major causes of watery diarrhea the world over. GCC is expressed in intestinal cells, colorectal tumor tissue and tumors originating from metastasis of the colorectal carcinoma. We have earlier generated a monoclonal antibody to human GCC, GCC:B10, which was useful for the immunohistochemical localization of the receptor in the rat intestine (Nandi A et al., 1997, J Cell Biochem 66:500-511), and identified its epitope to a 63-amino acid stretch in the intracellular domain of GCC. In view of the potential that this antibody has for the identification of colorectal tumors, we have characterized the epitope for GCC:B10 in this study. Overlapping peptide synthesis indicated that the epitope was contained in the sequence HIPPENIFPLE. This sequence was unique to GCC, and despite a short stretch of homology with serum amyloid protein and pertussis toxin, no cross reactivity was detected. The core epitope was delineated using a random hexameric phage display library, and two categories of sequences were identified, containing either a single, or two adjacent proline residues. No sequence identified by phage display was identical to the epitope present in GCC, indicating that phage sequences represented mimotopes of the native epitope. Alignment of these sequences with HIPPENIFPLE suggested duplication of the recognition motif, which was confirmed by peptide synthesis. These studies allowed us not only to define the requirements of epitope recognition by GCC:B10 monoclonal antibody, but also to describe a novel means of epitope recognition involving topological mimicry and probable duplication of the cognate epitope in the native guanylyl cyclase C receptor sequence.

Facile C-O bond scission in alcohols on Zn surfaces

Interaction of methanol, ethanol, and 2-propanol with polycrystalline as well as (0001) surfaces of Zn has been investigated by photoelectron spectroscopy and vibrational energy loss spectroscopy. All the alcohols show evidence for the condensed species along with the chemisorbed species at 80 K. With increase in temperature to similar to 120 K, the condensed species desorbs, leaving the chemisorbed species which decomposes to give the alkoxy species. The alkoxy species is produced increasingly at lower temperatures as we go from methanol to 2-propanol, the 2-propoxy species occurring even at 80 K. The alkoxy species undergo C-O bond scission giving rise to a hydrocarbon species and oxygen. The C-O bond cleavage occurs at a relatively low temperature of similar to 150 K. The effect of preadsorbed oxygen is to stabilize the methoxy species and prevent C-O bond scission. On the other hand, coadsorption of oxygen with methanol favors the formation of the methoxy species and gives rise to hydrocarbon species arising from the C-O bond scission even at 80 K.

Solid state stacked trimers of 1,10-phenanthroline in a supramolecular tubular motif of C-methyl calix[4]resorcinarene

The self-assembly of bidentate ligand, 1,10-phenanthroline with C-methyl calix[4]resorcinarene (CMCR) in presence of coumarin results in a unique trimer stacking arrangement of phenanthroline molecules in a nanotubular motif generated by the supramolecular assembly of the host.

High-temperature deformation processing of Ti-24Al-20Nb

Power dissipation maps have been generated in the temperature range of 900 degrees C to 1150 degrees C and strain rate range of 10(-3) to 10 s(-1) for a cast aluminide alloy Ti-24Al-20Nb using dynamic material model. The results define two distinct regimes of temperature and strain rate in which efficiency of power dissipation is maximum. The first region, centered around 975 degrees C/0.1 s(-1), is shown to correspond to dynamic recrystallization of the alpha(2) phase and the second, centered around 1150 degrees C/0.001 s(-1), corresponds to dynamic recovery and superplastic deformation of the beta phase. Thermal activation analysis using the power law creep equation yielded apparent activation energies of 854 and 627 kJ/mol for the first and second regimes, respectively. Reanalyzing the data by alternate methods yielded activation energies in the range of 170 to 220 kJ/mol and 220 to 270 kJ/mol for the first and second regimes, respectively. Cross slip was shown to constitute the activation barrier in both cases. Two distinct regimes of processing instability-one at high strain rates and the other at the low strain rates in the lower temperature regions-have been identified, within which shear bands are formed.

Determination of coefficient of consolidation from early stage of log t plot

The standard curve-fitting methods, Casagrande's log t method and Taylor's root t method, for the determination of the coefficient of consolidation use the later part of the consolidation curve and are influenced by secondary compression effects. Literature shows that secondary compression is concurrent with primary consolidation and that its effect is to decrease the value of the coefficient of consolidation. If the early part of the time-compression data is used, the values obtained will be less influenced by secondary compression effects. A method that uses the early part of the log t plot is proposed in this technical note. As the influence of secondary compression is reduced, the value obtained by this method is greater than that yielded by both the standard methods. The permeability values computed from C-v (obtained from the proposed method) rue more in agreement with the measured values than the standard methods showing that the effects of secondary compression are minimized. Time-compression data for a shorter duration is sufficient for the determination of C-v if the coefficient of secondary compression is not required.

Guanylyl Cyclase C Receptor: Regulation of Catalytic Activity by ATP

Guanylyl cyclase C (GCC), a member of the family of membrane bound guanylyl cyclases is the receptor for the heat-stable enterotoxin (ST) peptides and the guanylin family of endogenous peptides. GCC is activated upon ligand binding to increase intracellular cGMP levels, which in turn activates other downstream signalling events in the cell. GCC is also activated in vitro by nonionic detergents. We have used the T84 cell line as a model system to investigate the regulation of GCC activity by ATP. Ligand-stimulated GCC activity is potentiated in the presence of ATP, whereas detergent-stimulated activity is inhibited. The potentiation of GCC activity by ATP is dependent on the presence of Mg2+ ions, and is probably brought about by a direct binding of Mg-ATP to GCC. The protein kinase-like domain of GCC, which has earlier been shown to play a critical role in the regulation of GCC activity, may be a possible site for the binding of Mg-ATP to GCC.

Highly efficient C-8 oxidation of substituted xanthines with substitution at the 1-, 3-, and 7- positions using biocatalysts

A bacterial consortium consisting of strains belongings to the genus Klebsiella and Rhodococcus quantitatively converts 1-, 3- and 7-substituted xanthines to their respective 8-oxo compounds.

Synthesis of Unnatural C-2 Amino Acid Nucleosides Using NIS-Mediated Ring Opening of 1,2-Cyclopropane Carboxylated Sugar Derivatives

We have developed a general and efficient method for the stereoselective construction of pyrimidine-based pyranosyl C-2 amino acid nucleosides using NIS-mediated ring opening of 1,2-cyclopropanated sugar derivatives. This methodology has been successfully extended to the synthesis of furanosyl nucleosides, Which have potential applications in the development of novel, nontoxic antifungal therapeutics.

Determination of beta-turn conformation by laser Raman spectroscopy

To correlate the Raman frequencies of the amide I and III bands to beta-turn structures, three peptides shown to contain beta-turn structure by x-ray diffraction and NMR were examined. The compounds examined were tertiary (formula: see text). The amide I band of these compounds is seen at 1,668, 1,665, and 1,677 cm-1, and the amide III band appears at 1,267, 1,265, and 1,286 cm-1, respectively. Thus, it is concluded that the amide I band for type III beta-turn structure appears in the range between 1,665 and 1,677 cm-1 and the amide III band between 1,265 and 1,286 cm-1.

Crystalline A-DNA: The X-Ray Analysis of the Fragment d(G-G-T-A-T-A-C-C)

An A-DNA type double helical conformation was observed in the single crystal X-ray structure of the octamer d(G-G-T-A-T-A-C-C), 1, and its 5-bromouracil-containing analogue, 2. The structure of the isomorphous crystals (space group P61) was solved by a search technique based on packing criteria and R-factor calculations, with use of only low order data. At the present stage of refinement the R factors are 31 % for 1 and 28 % for 2 at a resolution of 2.25 A (0.225 nm). The molecules interact through their minor grooves by hydrogen bonding and base to sugar van der Waals contacts. The stable A conformation observed in the crystal may have some structural relevance to promoter regions where the T-A-T-A sequence is frequently found.

Molecular-Conformation of 1,3-Pyridylphenylureas by H-1 and C-13 NMR-study

1H and 13C NMR spectra are reported for several 1,3-pyridylphenyl ureas. Analysis of the spectra yielded the chemical shifts. The variations in the chemical shifts have been discussed in terms of the molecular conformations.