Solvation and axial ligation properties of (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrinato)zinc(II)

he solvation of (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrinato)zinc(II)[Zn(obtpp)], in twelve different solvents results in large red shifts of the B and Q bands of the porphyrin accompanied by enhanced absorbance ratios of the Q bands. These observations are ascribed to the destabilisation of the highest occupied molecular orbital a2u of the porphyrin arising from a flow of charge from the axial ligand to the porphyrin ring through the zinc(II) ion. The binding constants of adducts of [Zn(obtpp)] with neutral bases have been found to be an order of magnitude greater than those observed for the corresponding adducts of (5,10,15,20-tetraphenylporphyrinato)-zinc and vary in the order piperidine > imidazole > pyridine > 3-methylpyridine > pyridine-3-carbaldehyde. The enhanced binding constants and large spectral shifts are interpreted in terms of the electrophilicity of [Zn(obtpp)] induced by the electron-withdrawing bromine substituents in the porphyrin core. The structure of [Zn(obtpp)(PrCN)2] has been determined; it reveals six-co-ordinated zinc(II) with two long Zn–N distance [2.51(4), 2.59(3)Å]. The porphyrin is non-planar and displays a saddle-shaped conformation.

Structure of pregna-4,16-diene-7[alpha],14[alpha]-diol-3,20-dione

7a,14a-Dihydroxypregna-4,16-diene-3,20- dione, C21H2804, M r = 344.45, orthorhombic, P212121, a = 7.136 (1), b = 12.342 (1), c = 20.049 (3)/k, V= 1765.7 (3)/k 3, Z = 4, Dx = 1.295 g cm -3, A(Cu Kte) = 1.5418/k, /z = 6.7 cm- a, F(000) = 744, T = 293 K, R = 0.048 for 1345 observations. The A ring may be described as in a l a,2flhalf- chair conformation or a l a-sofa conformation. The B and C rings adopt normal chair conformations and the D ring has a 14a-envelope conforma tion. The molecules are held together by a hydrogen bond [0(3)...0(7)= 2.767 A].

Synthesis of A1PO4, LaPO4 and KTiOPO4 by flash combustion

Fine particle AlPO4, LaPO4 and KTiOPO4 have been prepared by the flash combustion of aqueous solutions containing metal nitrate, ammonium hydrogen phosphate, ammonium nitrate or ammonium perchlorate and carbohydrazide or tetraformal trisazine. When rapidly heated at 400 °C, the solution containing the redox mixtures ignites to undergo self-propagating, gas-producing, exothermic reactions. Formation of crystalline phosphates was confirmed by powder X-ray diffraction patterns and IR spectra. The metal phosphates formed are fine and have 20�78 m2 g?1 surface area.

3,12-dinitro-5,10,15,20-tetraphenylporphyrin- an example of a twisted intramolecular charge-transfer system

he porphyrin ring in the title compound, 10,19-dinitro-2,7,12,17-tetraphenyl-21,22,23,24-tetraazapenta-cyclo[16.2.1.1(3,6).1(8,11).1(13,16)]tetracosa-1,3,5,7,9,11(23),-12,14,16,18(21),19-undecaene 0.5-dichloromethane solvate, C44H28N6O4.0.5CH2Cl2, adopts a saddle conformation with neighbouring pyrrole rings tilted with respect to each other. The two nitro groups are situated on alternate pyrrole rings and have their planes angled away from those of the pyrrole rings, thereby indicating that interaction between the porphyrin and nitro groups is slight.

Modified Crack Closure Integral (MCCI) For 3-D Problems Using 20-Noded Brick Elements

The Modified Crack Closure Integral (MCCI) technique based on Irwin's crack closure integral concept is very effective for estimation of strain energy release rates G in individual as well as mixed-mode configurations in linear elastic fracture mechanics problems. In a finite element approach, MCCI can be evaluated in the post-processing stage in terms of nodal forces and displacements near the crack tip. The MCCI expressions are however, element dependent and require a systematic derivation using stress and displacement distributions in the crack tip elements. Earlier a general procedure was proposed by the present authors for the derivation of MCCI expressions for 3-dimensional (3-d) crack problems modelled with 8-noded brick elements. A concept of sub-area integration was proposed to estimate strain energy release rates at a large number of points along the crack front. In the present paper a similar procedure is adopted for the derivation of MCCI expressions for 3-d cracks modelled with 20-noded brick elements. Numerical results are presented for centre crack tension and edge crack shear specimens in thick slabs, showing a comparison between present results and those available in the literature.

Modified crack closure integral (MCCI) for 3-d problems using 20 noded brick elememnts

The Modified Crack Closure Integral (MCCI) technique based on Irwin's crack closure integral concept is very effective for estimation of strain energy release rates G in individual as well as mixed-mode configurations in linear elastic fracture mechanics problems. In a finite element approach, MCCI can be evaluated in the post-processing stage in terms of nodal forces and displacements near the crack tip. The MCCI expressions are however, element dependent and require a systematic derivation using stress and displacement distributions in the crack tip elements. Earlier a general procedure was proposed by the present authors for the derivation of MCCI expressions for 3-dimensional (3-d) crack problems modelled with 8-noded brick elements. A concept of sub-area integration was proposed to estimate strain energy release rates at a large number of points along the crack front. In the present paper a similar procedure is adopted for the derivation of MCCI expressions for 3-d cracks modelled with 20-noded brick elements. Numerical results are presented for centre crack tension and edge crack shear specimens in thick slabs, showing a comparison between present results and those available in the literature.

Chiral synthons from carvone .20. Stereo- and enantiospecific total synthesis of (-)-valeranone

Stereo- and enantiospecific total synthesis of the irregular sesquiterpene, valeranone, starting from S-6-methylcarvone employing a hydrindanone to decalone ring expansion methodology, is described.

Structural and optical properties of nonpolar (11-20) a-plane GaN grown on (1-102) r-plane sapphire substrate by plasma-assisted molecular beam epitaxy

We report the structural and optical properties of a-plane GaN film grown on r-plane sapphire substrate by plasma-assisted molecular beam epitaxy. High resolution X-ray diffraction was used to determine the out-of-plane and in-plane epitaxial relation of a-plane GaN to r-plane sapphire. Low-temperature photoluminescence emission was found to be dominated by basal stacking faults along with near-band emission. Raman spectroscopy shows that the a-GaN film is of reasonably good quality and compressively strained. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Nucleation and growth characteristics of cavities during the early stages of tensile creep deformation in a superplastic zirconia-20 wt% alumina composite

Constant-stress tensile creep experiments on a superplastic 3-mol%-yttria-stabilized tetragonal zirconia composite with 20 wt% alumina revealed that cavities nucleate relatively early during tensile deformation. The number of cavities nucleated increases with increasing imposed stress. The cavities nucleate at triple points associated largely with an alumina grain, and then grow rapidly in a cracklike manner to attain dimensions on the order of the grain facet size. It is suggested that coarser-grained superplastic ceramics exhibit lower ductility due to the ease in formation of such grain boundary facet-cracks and their interlinkage to form a macroscopic crack of critical dimensions.

Influence of synthesis route on structural phase transition in YBa2−xLaxCu3Oy (0

The compounds YBa2−xLaxCu3Oy, with compositions (0

Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85-xAgx (0≤x≤0.20) glasses

Temperature modulated alternating differential scanning calorimetric studies show that Se rich Ge0.15Se0.85−xAgx (0 x 0.20) glasses are microscopically phase separated, containing Ag2Se phases embedded in a Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase percolates in the Ge–Se matrix, with a well-defined percolation threshold at x = 0.10. A signature of this percolation transition is shown up in the thermal behavior, as the appearance of two exothermic crystallization peaks. Density, molar volume, and microhardness measurements, undertaken in the present study, also strongly support this view of percolation transition. The superionic conduction observed earlier in these glasses at higher silver proportions is likely to be connected with the silver phase percolation.

Thermodynamic, Raman and electrical switching studies on Si15Te85-xAgx (4 <= x <= 20) glasses

We have investigated thermal properties of bulk Si15Te85-xAgx (4 <= x <= 20) glasses in detail, through alternating differential scanning calorimetry experiments. The composition dependence of thermal parameters reveal the signatures of rigidity percolation and chemical threshold at compositions x = 12 and x = 19, respectively. The stability and glass forming ability of these glasses have also been determined using the data obtained from different thermodynamic quantities and it is found that the Si15Te85-xAgx glasses in the region 12 <= x <= 17 are more stable when compared to other glasses of the same series. Further, the blueshift observed in Raman spectroscopy investigations, in the composition range 12 <= x <= 13, support the occurrence of stiffness threshold in this composition range. All Si15Te85-xAgx (4 <= x <= 20) glasses are found to exhibit memory type switching (for sample thickness 0.25 mm) in the input current range 3-9 mA. The effect of rigidity percolation and chemical thresholds on switching voltages are observed at x = 12 and 19, respectively. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682759]

Monsoon circulation interaction with Western Ghats orography under changing climate - Projection by a 20-km mesh AGCM

In this study, the authors have investigated the likely future changes in the summer monsoon over the Western Ghats (WG) orographic region of India in response to global warming, using time-slice simulations of an ultra high-resolution global climate model and climate datasets of recent past. The model with approximately 20-km mesh horizontal resolution resolves orographic features on finer spatial scales leading to a quasi-realistic simulation of the spatial distribution of the present-day summer monsoon rainfall over India and trends in monsoon rainfall over the west coast of India. As a result, a higher degree of confidence appears to emerge in many aspects of the 20-km model simulation, and therefore, we can have better confidence in the validity of the model prediction of future changes in the climate over WG mountains. Our analysis suggests that the summer mean rainfall and the vertical velocities over the orographic regions of Western Ghats have significantly weakened during the recent past and the model simulates these features realistically in the present-day climate simulation. Under future climate scenario, by the end of the twenty-first century, the model projects reduced orographic precipitation over the narrow Western Ghats south of 16A degrees N that is found to be associated with drastic reduction in the southwesterly winds and moisture transport into the region, weakening of the summer mean meridional circulation and diminished vertical velocities. We show that this is due to larger upper tropospheric warming relative to the surface and lower levels, which decreases the lapse rate causing an increase in vertical moist static stability (which in turn inhibits vertical ascent) in response to global warming. Increased stability that weakens vertical velocities leads to reduction in large-scale precipitation which is found to be the major contributor to summer mean rainfall over WG orographic region. This is further corroborated by a significant decrease in the frequency of moderate-to-heavy rainfall days over WG which is a typical manifestation of the decrease in large-scale precipitation over this region. Thus, the drastic reduction of vertical ascent and weakening of circulation due to `upper tropospheric warming effect' predominates over the `moisture build-up effect' in reducing the rainfall over this narrow orographic region. This analysis illustrates that monsoon rainfall over mountainous regions is strongly controlled by processes and parameterized physics which need to be resolved with adequately high resolution for accurate assessment of local and regional-scale climate change.