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11.
Sai Chodavarapu Seshatalpa Hela Pamidipati Gayatri Sridhar Yeleswarapu Anipindi Nageswara Rao 《Transition Metal Chemistry》1998,23(3):249-252
The reaction of the Cr(xx)2(H2O)2
− (xx = oxalate, malonate and methylmalonate) complexes with dissolved CO2 was studied by stopped-flow spectrophotometry in the 7 < pH < 9 range and between 20 to 30°C at an ionic strength of 0.5
mol dm−3 (NaCl). Under the experimental conditions the aqua complex ion consists of a pH-dependent mixture of Cr(xx)2(H2O)2
−, Cr(xx)2(OH) (H2O)2− and Cr(xx)2(OH)2
3−. The monohydroxo and dihydroxo species undergo CO2 uptake and subsequent intramolecular carbonate ligand chelation independently, at rates which are readily distinguishable
and are governed by the uptake rate constants k
1 and k
2 and chelation rate constants k
3 and k
4, respectively. Only the k
1 values for oxalato, malonato and methylmalonato complexes could be calculated; k
1 = 1084 and 1333 and 1650 mol−1 dm3 s−1, respectively. The results obtained were compared with those obtained from other systems that have either cobalt(III), iridium(III)
or rhodium(III) as central atoms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
This study deals with the use of ethanol as washing solvent in the preparation of the silica gels from sodium silicate in order to enhance the textural properties, especially surface area. We here examined the effect of ethanol-washing on surface area, micro- and mesopore volume, and average pore size. The silica xerogels prepared from sodium silicate solution exhibited an extremely high surface area of 1139 m2/g by washing their hydrogels with ethanol. Compared to water-washed xerogels, ethanol-washed xerogels showed higher surface areas, total pore volumes, and larger average pore sizes. Unlike the surface area of water-washed xerogel, that of the ethanol-washed xerogel was not affected by the silica concentration of initial solution. This study indicates that the textural properties of sodium silicate-derived xerogels are further enhanced by using ethanol as washing solvent. 相似文献
13.
A number of beta-d-glycosyl azide derivatives undergo reduction on treatment with tetrathiomolybdate to produce the corresponding beta-d-glycosylamines exclusively without anomerization under very mild and neutral reaction conditions. Acetyl, allyl, benzoyl, and benzyl protective groups are left untouched under the reaction conditions. An exclusive selectivity in the reduction of anomeric azides is observed, while the C-2 and C-6 azides are left untouched. 相似文献
14.
B. Sridhar K. Ravikumar Y. S. Sadanandam 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(12):o687-o690
The title compound, C22H19N3O2S, crystallizes in two polymorphic forms having the same space group, viz. P, with Z′ = 2 and Z′ = 1. In both polymorphs, the planar thiazole ring is fused cis with the dihydropyrimidine ring, the carbamoyl group is in an extended conformation with an anticlinal orientation with respect to the pyrimidine ring, and the phenyl ring is attached to the pyrimidine ring approximately at a right angle. The two polymorphs have different interplanar angles between the phenyl and thiazole rings. The molecules are linked by N—H⋯O and C—H⋯O hydrogen bonds. 相似文献
15.
Chary KV Sagar GV Naresh D Seela KK Sridhar B 《The journal of physical chemistry. B》2005,109(19):9437-9444
A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2. 相似文献
16.
I. Sridhar Reddy P. Chandrasekhar Reddy B. Rangamannar 《Journal of Radioanalytical and Nuclear Chemistry》1991,153(5):333-338
An accurate and rapid radiochemical method has been developed for the determination of silver based on the substoichiometric extraction of its complex with potassium 3-phenylmethyldithiocarbazate into chloroform from pH 5.5 acetate buffer. Microgram amounts of silver could be determined with an average error of ±1.1% and the effect of diverse metal ions was critically examined. The method developed was applied to evaluate the silver content of photofilm washings. 相似文献
17.
In this note we show that the characterization results for P-matrices due to K.G. Murty and A. Tamir which state that a given square matrixM of ordern is a P-matrix if and only if the linear complementarity problem (q, M) has a unique solution for allq in a specified finite subset of
n
depending onM are incorrect whenn > 3.Research supported by Dr. K.S. Krishnan (DAE) fellowship for research in Mathematics and Computer Science, Bombay, India. 相似文献
18.
19.
Mahendra Madegowda Doreswamy Beeranahally H. Sridhar Mandayam A. Prasad Javaregowda S. Khanum Shaukath A. Shashikanth Sheena Sudha Belagur S. 《Structural chemistry》2004,15(3):211-214
Benzophenone analog 3 has been synthesized and characterized by the X-ray diffraction (XRD) method. The compound crystallizes in a monoclinic space group P21/c with cell parameters a = 7.701(8) Å, b = 7.151(5) Å, c= 28.323(3) Å, = 104.639(4)°, Z = 4. The structure exhibits intra- and intermolecular hydrogen bonding of the type N–HO, C–HO, and N–HN. The molecules are interlinked through hydrogen bonds forming an infinite chain. This polymeric-like structure may play an important role in biological activity. 相似文献
20.
Kloprogge JT Komarneni S Yanagisawa K Fry R Frost RL 《Journal of colloid and interface science》1999,212(2):562-569
The structural changes of synthetic and natural beidellites during dehydroxylation have been studied using infrared emission spectroscopy of the OH-stretching and bending regions. The OH-stretching region is characterized by two OH-stretching modes around 3600-3615 cm-1 and around 3650 cm-1. These bands strongly decrease in intensity upon dehydroxylation up to 600 degrees C for the natural beidellite and 700-750 degrees C for the synthetic ones. The differences in bandwidth, intensity, and dehydroxylation behavior are interpreted as due to differences in crystallinity with crystallinity increasing in the order natural beidellite < synthetic beidellite BSK3 < synthetic beidellite E498. Above 400 degrees C a new band attributed to silanol groups becomes visible in all samples due to transfer of the hydroxyls from the octahedral layer to the siloxane layer before they are lost. The broad band around 3300-3400 cm-1 is assigned to both H-bonding in H2O and H-bonding to Si-O-Al linkages. The presence of two different OH groups is also reflected in the OH-bending modes around 875-895 cm-1 and 915-925 cm-1 and in the OH-libration modes around 780 and 800-820 cm-1. These bands show a decrease in intensity upon heating and dehydroxylation of the clay structure. Here again the same order can be observed for the disappearance of the bands as for the OH-stretching region. Copyright 1999 Academic Press. 相似文献