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1.
Vivek K. Gupta Madhvi M. Lal Naresh K. Satti Prabhu Dutt Punita Sharma Musarat Amina Krishan A. Suri 《Journal of chemical crystallography》2011,41(7):1064-1070
Abstract
(5R,6S,7S,8S,9S,10R,13S,14S,17S,20R,22R)-6α,7α-epoxy-5α,17α,27-trihydroxy-1-oxo-22R-witha-2,24-dienolide has been isolated from Withania somnifera leaves. Three-dimensional X-ray intensity data were collected at 293 K on Bruker CCD area-detector diffractometer equipped with graphite-monochromated MoKα radiation (λ = 0.71073 ?). The compound crystallizes in monoclinic space group P21 with unit cell parameters: a = 6.4540(2), b = 11.3656(4), c = 17.4982(5) ?, β = 90.730 o(2), Z = 2. The crystal structure was refined to a final R-value of 0.0419 for 6122 observed reflections. One water solvent molecule was observed. All the rings of the steroid skeleton are trans connected. Rings A and B exists in a half-chair conformation, ring C a chair, and five membered ring D is intermediate between half-chair and envelope. The δ-lactone ring E adopts a distorted sofa conformation. The characteristic pattern observed in the packing diagram is the appearance of twisted chains of molecules. The packing of the molecules in the crystal is stabilized by intra- and intermolecular O–H···O and C–H···O interactions. 相似文献2.
SEARCHING FOR PHYTOCHROME MUTANTS 总被引:2,自引:0,他引:2
3.
Damanjit Kaur Punita Sharma Prasad V. Bharatam 《Journal of Molecular Structure》2010,939(1-3):118-123
The electronic structure, geometrical parameters, proton affinities, lone pair occupancies, and orbital interactions have been explored to understand the antioxidant behavior of ebselen at B3LYP/6-31+G1 level. The role of substituents in the nucleophilicity of selenium in eight model molecules containing SeN bond has been analyzed in terms of relative proton affinities. The free energy changes associated with probable catalytic reaction steps have also been evaluated. 相似文献
4.
Subbarayappa AdimurthySanjay S. Vaghela Punita V. VyasAnjani K. Bhatt Gadde RamachandraiahAshutosh V. Bedekar 《Tetrahedron letters》2003,44(34):6393-6395
A reaction of nitric acid with bromophenols and iodophenols results in substitution of the halogen with a nitro group. The study indicates moderate reactivity for bromophenols and iodophenols, while chlorophenols were found to be sluggish in this reaction. 相似文献
5.
Damanjit Kaur Punita Sharma Prasad V. Bharatam Mondeep Kaur 《International journal of quantum chemistry》2008,108(5):983-991
Density functional methods have been employed to characterize the gas phase conformations of selenocysteine. The 33 stable conformers of selenocysteine have been located on the potential energy surface using density functional B3LYP/6‐31+G* method. The conformers are analyzed in terms of intramolecular hydrogen bonding interactions. The proton affinity, gas phase acidities, and bond dissociation energies have also been evaluated for different reactive sites of selenocysteine for the five lowest energy conformers at B3LYP/6‐311++G*//B3LYP/6‐31+G* level. Evaluation of these intrinsic properties reflects the antioxidant activity of selenium in selenocysteine. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
6.
S. S. Das B. P. Baranwal S. A. Rayeeny Punita Singh Vibha Srivastava 《Progress in Crystal Growth and Characterization of Materials》2002,44(3):155-161
A number of samples of glassy sodium polyphosphate and copolyphosphates of sodium — cobalt, sodium — copper, sodium — nickel, sodium-manganese and sodium — calcium were prepared and their optical properties were investigated. The ultraviolet and visible spectra of these glasses were recorded at the room temperature. It was found that the fundamental absorption edge of these glasses usually occurs in the ultraviolet — visible region. The optical absorption edges (E0) were calculated by using the relation h ν = B (hν − E0)2 where B is constant. The linear variation of (hν)1/2 with hν where is the absorption coefficient and hν is the incident photon energy, is taken as evidence of non-direct interband transitions. The E0 values obtained for copolyphosphate glasses appeared to depend on the size of the counter cation. The infrared spectra of all these glasses appeared to be almost the same, indicating the presence of characteristic P --- O --- P linkages of linear polyphosphate chains and two non bridging oxygen atoms bonded to phosphorus atoms O --- P --- O (PO2) units in the polyphosphate tetrahedra. 相似文献
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Punita Batra 《Journal of Pure and Applied Algebra》2011,215(7):1552-1568
Inspired by recent activities on Whittaker modules over various (Lie) algebras, we describe a general framework for the study of Lie algebra modules locally finite over a subalgebra. As a special case, we obtain a very general set-up for the study of Whittaker modules, which includes, in particular, Lie algebras with triangular decomposition and simple Lie algebras of Cartan type. We describe some basic properties of Whittaker modules, including a block decomposition of the category of Whittaker modules and certain properties of simple Whittaker modules under some rather mild assumptions. We establish a connection between our general set-up and the general set-up of Harish-Chandra subalgebras in the sense of Drozd, Futorny and Ovsienko. For Lie algebras with triangular decomposition, we construct a family of simple Whittaker modules (roughly depending on the choice of a pair of weights in the dual of the Cartan subalgebra), describe their annihilators, and formulate several classification conjectures. In particular, we construct some new simple Whittaker modules for the Virasoro algebra. Finally, we construct a series of simple Whittaker modules for the Lie algebra of derivations of the polynomial algebra, and consider several finite-dimensional examples, where we study the category of Whittaker modules over solvable Lie algebras and their relation to Koszul algebras. 相似文献
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Punita Srivastava Pushpendra Kumar Kedar Singh 《Journal of nanoparticle research》2011,13(10):5077-5085
Manipulation of carrier spins in semiconductors for spintronics applications has received great attention driven by improved
functionalities and higher speed operation. Doping of semiconductor nanocrystals by transition-metal ions pronounced as diluted
magnetic semiconductors (DMS) has attracted tremendous attention. Such doping is, however, difficult to achieve in low-dimensional
strongly quantum-confined nanostructures by conventional growth procedures. In the present case, magic-sized, pure, and Cr-doped
CdS DM-QDs have been synthesized by solution phase chemistry (lyothermal method). Structural, optical, and magnetic investigation
suggest an intrinsic nature of ferromagnetism with highly quantum-confined system. Optical and magnetic results of pure and
doped QDs reveal major physical consequences of dopant localization within the capacity to engineer dopant-carrier exchange
interactions introducing magnetic functionalities within the host semiconductor lattice. Unpaired Cr ions in Cd substitutional
sites could create spin ordering and ferromagnetic coupling. The results presented herein illustrate some of the remarkable
and unexpected complexities that can arise in doped QDs. 相似文献