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21.
J. A. Kanters F. H. Van Der Steen A. Schouten Pushpa Bagdi N. S. Poonia 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(3):225-233
NH4(Pic)(DB18C6) (Pic=picrate and DB18C6=dibenzo-18-crown-6), (C26H30N4O13) FW 606.56, arthorhombic,Pmn21,a=26.045(5),b=12.055(3),c=8.982(3) Å,V=2820(1) Å3,Z=4,D
c
=1.429 g/cm3, CuK, =1.54184 Å, (CuK)=9.5 cm–1,F(000)=1272,T=298 K. The structure has been refined toR=0.0475 for 2617 unique observed reflections. In the lattice the 1:1 complex exists as a 2:2 dimer in which the crown are coupled through the Pic anions and NH4
+ cations. The asymmetric unit consists of two independent half crown ethers of which two opposite O atoms are on the mirror plane, two half ammonium cations of which the N and two H atoms are also on the mirror plane while the Pic anion is in a general position. Relative to each other, the corwn ethers are shifted by about 7.3 Å alongb and 1 Å alongc. The 1:1 sandwich of NH4 with DB18C6 and Pic on dimerisation becomes a club pseudo-sandwich with three phenyl rings on either side of the mirror plane, thus forming a nearly parallel stack with a 3.6 Å inter-ring distance. The NH4 ions hold the structure; two H atoms on the mirror plane are hydrogen-bonded to the opposite oxygens of the crown located on the purely aliphatic part of the ring (2.10(1), 2.06(3) and 2.26(3), 2.05(1) Å) for the two independent crowns, respectively, while the other two H atoms form mirror-related bifurcated hydrogen bonds with the phenoxide oxygen (1.99(1) and 2.01(1) Å) and theo-nitrogen oxygen (2.44(2) and 2.34(1) Å) of the picrates.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82037 (29 pages) 相似文献
22.
Hypervalent iodine oxidation of ketoximes (1) using iodosobenzene diacetate leads to cleavage of 1 with the formation of corresponding ketones (2) under neutral conditions in good yields. The scope and limitations of the reaction are discussed as well as the mechanism. 相似文献
23.
Eight cryopreservation protocols were assessed for their effects on the viability and phenotypic stability of the yeast Saccharomyces cerevisiae during a five-year study. It is found that viability and phenotypic features have remained largely unchanged when the yeast was preserved in glycerol, dimethyl sulphoxide, or sucrose at -80 degrees C or in liquid nitrogen. When sorbitol was used as a cryoprotectant, yeast cells frozen and stored at -80 degrees C manifested great decreases in viability after six months in storage and concomitantly large fluctuations in the rate of the trpl auxotrophic reversion. This phenotypic reversion was stable passage after passage. Such a degree of phenotypic fluctuations, however, was not observed for yeast cells preserved in the same sorbitol solution that went through a controlled freezing program and were subsequently stored in liquid nitrogen. These results indicate that some combinations of cryoprotective agent, freezing program, and storage temperature disturb biomaterials more profoundly during cryopreservation and imply a genetic basis of this phenotypic change. 相似文献
24.
Symmetries, vibrational instabilities, and routes to stable structures of clusters of Al, Sn, and As 总被引:2,自引:0,他引:2
We investigate the stability of small clusters using density functional theory to compute the total energy, forces, and vibrational frequencies using linear response. We exhibit an efficient and computationally low-cost route to finding stable structures, by starting with high-symmetry structures and distorting them according to their unstable modes. We illustrate this by application to 4-, 6-, and 13-atom clusters of Al, Sn, and As. This technique also naturally elucidates the origins of stability of the lower symmetry structures, which is variously due to the linear or pseudo Jahn-Teller effect, combined with a lowering of various contributions to the total energy. We show that the situation is more complex than has generally been appreciated. 相似文献
25.
Novel LC‐ ESI‐MS/MS method for desvenlafaxine estimation human plasma: application to pharmacokinetic study
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Pushpa Kumari Kancharla Venu Gopal Raju Kondru Gowri Sankar Dannana 《Biomedical chromatography : BMC》2016,30(2):249-255
A simple, sensitive and specific liquid chromatography tandem mass spectrometry (LC‐ESI‐MS/MS) method was developed for the quantification of desvenlafaxine in human plasma using desvenlafaxine d6 as an internal standard (IS). Chromatographic separation was performed using a Thermo‐BDS hypersil C8 column (50 × 4.6 mm, 3 µm) with an isocratic mobile phase composed of 5 mM ammonium acetate buffer: methanol (20:80, v/v), at a flow rate of 0.80 mL/min. Desvenlafaxine and desvenlafaxine d6 were detected with proton adducts at m/z 264.2/58.1 and 270.2/ 64.1 in multiple reaction monitoring positive mode, respectively. Liquid–liquid extraction was used to extract the drug and the IS. The method was linear over the concentration range 1.001–400.352 ng/mL with a correlation coefficient of ≥0.9994. This method demonstrated intra and inter‐day precision within 0.7–5.5 and 1.9–6.8%, and accuracy within 95.3–107.4 and 93.4–99.5%. Desvenlafaxine was found to be stable throughout the freeze–thaw cycles, bench‐top and long‐term matrix stability studies. The developed and validated method can be successfully applied for the bioequivalence/pharmacokinetic studies of desvenlafaxine in pharmaceutical dosage forms. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
26.
27.
K. Pushpa P. S. Bisht O. P. S. Negi 《International Journal of Theoretical Physics》2014,53(7):2222-2230
Generators of \(\operatorname{SO}(8)\) group have been described by using direct product of the Gamma matrices and the Pauli Sigma matrices. We have obtained these generators in terms of generalized split octonion also. These generators have been used to describe the rotational transformation of vectors in \(\operatorname{SO}(7)\) symmetry group. 相似文献
28.
Raji Thomas Joseph P. Nelson Ramchand T. Pardasani Pushpa Pardasani Tulsi Mukherjee 《Helvetica chimica acta》2013,96(9):1740-1749
Organotin complexes 1 – 6 of the general formula [SnR2L] and [(SnR3)2L] (L=phenanthrenequinone dioximato – a bidentate ligand, R=Me, Bu, and Ph) were synthesized by the reaction of the sodium salt of the ligand H2L (prepared in situ with MeONa) and SnR2Cl2/SnR3Cl in 1 : 1 and 1 : 2 molar ratios. The physical and spectral properties of the newly synthesized complexes 1 – 6 are described. DFT and HF Calculations were performed to confirm the proposed structures. 相似文献
29.
The exact 1P-state wavefunction R
1P
(r) is obtained for the potential 相似文献
30.
N. Pushpa A. P. Gnana Prakash K. C. Praveen John D. Cressler D. Revannasiddaiah 《辐射效应与固体损伤》2013,168(10):592-603
Abstract The effects of 8 MeV electrons and 60 and 95 MeV oxygen ions on the electrical properties of Si npn RF power transistors have been investigated as a function of fluence. The dc current gain (h FE), displacement damage factor, excess base current (Δ I B=I Bpost?I Bpre), excess collector current (Δ I C=I Cpost?I Cpre), collector saturation current (I CS) and deep level transient spectroscopy trap signatures of the irradiated transistors were systematically evaluated. 相似文献