Structural and functional analogue of the active site of polysulfide reductase from Wolinella succinogenes

Synthesis of [PPh4]2[Mo(SPh)2(S2C2(CN)2)2] (2) from [PPh4]2[MoO(S2C2(CN)2)2] (1) has been achieved to mimic the postulated [Mo(S)6] core of polysulfide reductase with two thiolates and two bis(ene-dithiolate) ligands. Compound 2 reacts with polysulfide to yield H2S, modeling the function of polysulfide reductase. The facile conversion of 2 back to 1 in moist solvent suggests that the interconversion of the [MoIV = O] and [MoIV - X] (X = O-Ser, S-Cys, Se-Cys) moieties might occur in the DMSO reductase class of enzymes under appropriate hydrophobic/hydrophilic conditions.     

Determination of 2-hydroxy-4-methoxybenzaldehyde in roots of Decalepis hamiltonii (Wight & Arn.) and Hemidesmus indicus R.Br

The roots of Decalepis hamiltonii and Hemidesmus indicus are aromatic and possess the crystalline compound 2-hydroxy-4-methoxybenzaldehyde as the major compound (> 90%) in their volatile oils. A gas chromatographic procedure was developed for the assay of 2-hydroxy-4-methoxybenzaldehyde in both fresh and dried roots of different origin. Benzyl butyrate was used as the internal standard. Among the methods tried, steam hydrodistillation was suitable for extraction of the volatile oils. The quantity of this aromatic compound varied from 0.03 to 0.54%.     

Measurement of internal stresses via the polarization in epitaxial ferroelectric films

The relations between electrical and mechanical properties of constrained ferroelectric films are analyzed. It is shown that the internal stresses and the elastic constants can be determined through the measurement of the electrical response. The change in the polarization is proportional to internal stresses due to film-substrate misfit, whereas the linear electrical and electromechanical responses to external field do not depend on the misfit and are determined by the film constraint. The theoretical results are successfully applied to PbZr 0.2Ti 0.8O (3) films on (001) LaAlO (3) substrate which exhibit a considerable increase in the saturation polarization due to epitaxial stresses. Significant recovery in the piezoelectric constant and susceptibility is theoretically predicted and experimentally verified for specific film configurations which reduce the degree of constraint. The concept presented in this Letter can be expanded to constrained ferromagnetic and superconductor films.     

Strong phase separation in a model of sedimenting lattices

We study the steady state resulting from instabilities in crystals driven through a dissipative medium, for instance, a colloidal crystal which is steadily sedimenting through a viscous fluid. The problem involves two coupled fields, the density and the tilt; the latter describes the orientation of the mass tensor with respect to the driving field. We map the problem to a one-dimensional lattice model with two coupled species of spins evolving through conserved dynamics. In the steady state of this model each of the two species shows macroscopic phase separation. This phase separation is robust and survives at all temperatures or noise levels- hence the term strong phase separation. This sort of phase separation can be understood in terms of barriers to remixing which grow with system size and result in a logarithmically slow approach to the steady state. In a particular symmetric limit, it is shown that the condition of detailed balance holds with a Hamiltonian which has infinite-ranged interactions, even though the initial model has only local dynamics. The long-ranged character of the interactions is responsible for phase separation, and for the fact that it persists at all temperatures. Possible experimental tests of the phenomenon are discussed.     

The use of fractional orders in the determination of birefringence of highly dispersive materials by the channelled spectrum method

The channelled spectrum employing polarized light interference is a very convenient method for the study of dispersion of birefringence. However, while using this method, the absolute order of the polarized light interference fringes cannot be determined easily. Approximate methods are therefore used to estimate the order. One of the approximations is that the dispersion of birefringence across neighbouring integer order fringes is negligible. In this paper, we show how this approximation can cause errors. A modification is reported whereby the error in the determination of absolute fringe order can be reduced using fractional orders instead of integer orders. The theoretical background for this method supported with computer simulation is presented. An experimental arrangement implementing these modifications is described. This method uses a Constant Deviation Spectrometer (CDS) and a Soleil Babinet Compensator (SBC).     

Studies on the hydrolysis of {Cu[Al(OPri)4]2}, a single source precursor for CuAl2O4 spinel

Controlled hydrolysis experiments of the heterobimetallic alkoxide {Cu[Al(OPrⁱ)₄]₂}, were investigated. The progress of hydrolysis was monitored by the FT-IR and NMR spectroscopy. A blue colored gel appeared after four days of hydrolysis and the hydrolysis experiments were continued up to ten days. The elemental analysis and FT-IR spectrum revealed the presence of isopropoxy group in the gel obtained even after ten days of hydrolysis. The presence of carbon was further confirmed from the presence of a weak signal at 3.351 ppm in the ¹³C CP-NMR spectrum. The thermal analysis of the hydrolyzed gels in air also suggested that they were not simple hydroxides of copper and aluminum. The gels on one time heat treatment at 900 °C in air yielded inverse spinel CuAl₂O₄ as shown by the PXRD patterns. CuO was observed along with CuAl₂O₄ in the case of the fired product of the gel obtained after five or six days of hydrolysis which was absent in the fired product of ten days hydrolyzed gel. The phase pure spinel was nanocrystalline in nature as revealed by the analysis of PXRD pattern. TEM images revealed porous structured nanocrystallites. The optical property of the spinel was evaluated by the diffuse reflectance spectroscopy. Raman spectrum showed five bands at 767, 698, 595, 450 and 356 cm^?1 conforming to the spinel structure.     

Effect of phenyl group on the structure and formation of transitional alumina from Al (OPh)<Subscript>3</Subscript>

The structure of freshly prepared Al(OPh)₃, its decomposition product, the hydrolyzed products and their structural evolution were investigated employing ²⁷Al MAS NMR spectroscopy, PXRD, TGA/DTA/DSC/FTIR techniques. In the ²⁷Al MAS NMR spectrum of the aluminium phenoxide, three signals with the chemical shift at 3.78, 21 and 45 ppm were observed. The chemical shift at 3.78 and 45 ppm revealed the presence of four and sixfold coordinated aluminum. The signal at 21 ppm corresponded to fivefold coordinated aluminium. When the aluminium phenoxide was directly decomposed in air at 600 °C, it resulted in amorphous product as evidenced from the PXRD pattern. The observed signals with chemical shifts at 10.1, 42, 73.6 ppm in the ²⁷Al MAS NMR spectrum indicated the presence of 6, 5 and 4 coordination for the aluminium atoms suggesting disordered transitional γ-alumina to be the product. The hydrolysis studies of Al(OPh)₃ with excess of water at 70 °C yielded bohemite (γ-AlOOH). The alumina obtained after dehydration at 600 °C was X-ray amorphous. The dehydrated product at 600 °C showed the presence of four and six coordinated aluminium atoms in the ²⁷Al MAS NMR spectrum confirming it to be ordered γ-Al₂O₃. Crystalline γ-Al₂O₃ was obtained on further heating at 800 °C.