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排序方式: 共有131条查询结果,搜索用时 12 毫秒
1.
Madhuri Manpadi 《Tetrahedron letters》2005,46(26):4433-4437
Various substituted arylcuprates undergo stereocontrolled additions to a d-mannitol-derived γ-alkoxy-α,β-enoate with exclusive anti-selectivity. The method is well suited for the preparation of a broad range of biologically active Amaryllidaceae alkaloids and their aromatic analogues. A model accounting for the stereochemical outcome of this process is presented. 相似文献
2.
3.
The synthesis of C1-C12 and C13-C22 fragments of (−)-callystatin A is accomplished employing desymmetrization strategy for the creation of five chiral centres of the polypropionate fragment and application of cross-metathesis (CM) reaction for the first time for this molecule. 相似文献
4.
5.
O.M. Hussain K. Srinivasa Rao K.V. Madhuri C.V. Ramana B.S. Naidu S. Pai J. John R. Pinto 《Applied Physics A: Materials Science & Processing》2002,75(3):417-422
Molybdenum trioxide thin films were prepared by reactive pulsed laser deposition on Corning 7059 glass substrates. The influence
of oxygen partial pressure and deposition temperature on the structure, surface morphology and optical properties of these
films was studied to understand the growth mechanism of MoO3 thin films. The films formed at 473 K in an oxygen partial pressure of 100 mTorr exhibited predominantly a (0k0) orientation,
corresponding to an orthorhombic layered structure of α-MoO3. The evaluated optical band gap of the films was 3.24 eV. The crystallite size increased with increase of deposition temperature.
The films formed at an oxygen partial pressure of pO2=100 mTorr and at a deposition temperature greater than 700 K exhibited both (0k0) and (0kl) orientations, representing α-β
mixed phases of MoO3. The films formed at an oxygen partial pressure less than 100 mTorr were found to be sub-stoichiometric with α-β mixed phases.
The investigation revealed the growth of polycrystalline and single-phase orthorhombic-layered-structure α-MoO3 thin films with composition nearly approaching the nominal stoichiometry at moderate substrate temperatures in an oxygen
partial pressure of 100 mTorr.
Received: 9 April 2001 / Accepted: 6 August 2001 / Published online: 17 October 2001 相似文献
6.
The present work describes an exciting method for the selective and sensitive determination of calcitonin in human blood serum samples. Adopting the surface molecular imprinting technique, a calcitonin-imprinted polymer was prepared on the surface of the zinc oxide nanostructure. Firstly, a biocompatible tyrosine derivative as a monomer was grafted onto the surface of zinc oxide nanostructure followed by their polymerization on vinyl functionalized electrode surface by activator regenerated by electron transfer–atom transfer radical polymerization (ARGET–ATRP) technique. Such sensor can predict the small change in the concentration of calcitonin in the human body and it may also consider to be as cost-effective, renewable, disposable, and reliable for clinical studies having no such cross-reactivity and matrix effect from real samples. The morphologies and properties of the proposed sensor were characterized by scanning electron microscopy, cyclic voltammetry, difference pulse voltammetry and chronocoulometry. The linear working range was found to be 9.99 ng L−1 to 7.919 mg L−1 and the detection limit as low as 3.09 ± 0.01 ng L−1 (standard deviation for three replicate measurements) (S/N = 3). 相似文献
7.
M. Ramesh B. Raju M. George K. Srinivas V. Jayathirtha Rao K. Bhanuprakash R. Srinivas 《Journal of mass spectrometry : JMS》2012,47(7):860-868
The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6‐tris(benzylamino)‐1,3,5‐triazine (1) and 2,4,6‐tris(benzyloxy)‐1,3,5‐triazine (6) show abundant product ion of m/z 181 (C14H13+). The likely structure for C14H13+ is α‐[2‐methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the ‘N’ analog (1) but low for the ‘O’ analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H‐toluene]+ and [M + H‐benzene]+ for compounds 1 and 6, respectively. The protonated 2,4,6‐tris(4‐methylbenzylamino)‐1,3,5‐triazine (4) exhibits competitive eliminations of p‐xylene and 3,6‐dimethylenecyclohexa‐1,4‐diene. Moreover, protonated 2,4,6‐tris(1‐phenylethylamino)‐1,3,5‐triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring ‘N’. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H‐shift from ring carbon to ‘O’ generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium‐labeling and CAD experiments combined with DFT calculations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
Maruthi Janaki Ram Reddy V. Venkat Reddy U. Srinivas M. Janaki Ram Reddy V. Jayathirtha Rao 《Journal of Chemical Sciences》2002,114(6):603-609
Naphthyldiene derivatives,1-4, carrying electron-donating groups at one end and electron-withdrawing groups at the other, were synthesized to study the
photoisomerization process. All the compounds showed efficient photoisomerization upon direct excitation leading to the formation
of 4-Z isomer with high selectivity. Triplet sensitization studies indicated inefficientE-Z isomerization process. Room temperature fluorescence of1 and2 displayed fine structure in hexane solvent and the same was replaced by broad or structureless fluorescence in acetonitrile
and methanol solvents. A mechanism involving a polarized or charge transfer singlet excited state is proposed for the observed
photoisomerization in these naphthyldiene derivatives. 相似文献
9.
Madhuri Mukhopadhyay Debi Banerjee Aleksander Koll Aleksander Filarowski Samaresh Mukherjee 《Chemical physics letters》2006,420(4-6):316-320
The effect of neutral, cationic and anionic micellar environments on the ground and excited state proton transfer reactions of salicylidine-3,4,7-methyl amine (SMA) in water has been studied by steady state and time resolved fluorescence spectroscopy. In the ground state, the formation of the primary form of SMA is enhanced at the expense of the zwitterionic species due to micellization. In the excited state, anion formation decreases both in the presence of Triton-X and cetyl trimethyl ammonium bromide (CTAB). However, in the presence of sodium dodecyl sulphate (SDS), the anionic emission increases after reaching a certain micellar concentration. The lifetime of the anion is significantly reduced in CTAB compared to that in the bulk water and also in the presence of Triton-X. It is proposed that the destabilization and modification of SMA anion occurs due to the different electrostatic environments produced by micellization. 相似文献
10.
The initial product ratios of several polyene nitriles, which do not have low lying n,π* states, are reported. The solvent dependent chemistry has been discussed in conjunction with the well known retinal chemistry. 相似文献