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1.
The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br2/I2) and water were efficiently carried out in aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diastereoselectivities. The alkenoyl, cinnamoyl and electron-deficient cinnamoyl substrates smoothly underwent bromohydrin reaction in aqueous acetone but no iodohydrin reaction, where as electron-rich cinnamoyl substrates preferred to undergo iodohydrin reaction in aqueous acetone with moderate diastereoselectivity and enhanced diastereoselectivity was observed in aqueous THF. 相似文献
2.
Chloramphenicol and thiamphenicol have been enantioselectively synthesized using an asymmetric halohydrin reaction as a key step. In particular, halomethoxylation reaction was used, where O-methyl functions as a hydroxyl protecting group and eliminates an additional protection step. 相似文献
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R. Yimnirun A. Ngamjarurojana R. Wongmaneerung S. Wongsaenmai S. Ananta Y. Laosiritaworn 《Applied Physics A: Materials Science & Processing》2007,89(3):737-741
The temperature scaling of the ferroelectric hysteresis was investigated in hard lead zirconate titanate (PZT) bulk ceramic.
The power-law temperature scaling relations were obtained for hystersis area 〈A〉, remnant polarization Pr, and coercivity EC in the forms of 〈A〉∝T-0.9650, Pr∝T-0.0261, and EC∝T-0.8823, respectively, which are mostly comparable to those of its soft counterpart. The observation that Pr decayed more slowly with temperature than in soft PZT was attributed to the presence of the complex defects in hard PZT.
However, the product of Pr and EC still provided the similar scaling law on the T dependence in comparison with 〈A〉.
PACS 77.80.-e; 77.80.Fm; 77.84.-s; 77.84.Dy 相似文献
5.
Ghosh AK Ghoshal D Zangrando E Ribas J Chaudhuri NR 《Dalton transactions (Cambridge, England : 2003)》2006,(12):1554-1563
Three new polymeric squarato-bridged manganese complexes {[Mn(H(2)O)(2)(bpe)(sq)].bpe.H(2)O}(n) (1), [Mn(2)(H(2)O)(4)(phen)(2)(sq)(2)](n) (2) and [Mn(2)(H(2)O)(2)(phen)(4)(sq)].(sq).8(H(2)O) (3) [bpe, 1,2-bis(4-pyridyl)ethane; phen, 1,10-phenanthroline; sq, squarate dianion] have been synthesized and characterized by single crystal X-ray diffraction analysis and variable temperature magnetic studies. Complex 1 is a 2D rectangular grid-like structure, achieved through flexible bpe bridging ligands and squarate dianions. On the other hand the use of chelating phen instead of bpe gives rise to a 1D polymeric chain in complex 2 and to a dinuclear entity in 3. In all the three complexes weak interactions play a vital role in stabilizing the solid-state structure. Variable temperature (2-300 K) magnetic studies indicate weak antiferromagnetic coupling between the metal centres in all the complexes. 相似文献
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Ananta Karmakar Mushkin Basha G.T. Venkatesh Babu Murali Botlagunta Noormohamed Abdul Malik Richard Rampulla Arvind Mathur Arun Kumar Gupta 《Tetrahedron letters》2018,59(48):4267-4271
A number of cyanomethyl esters of natural/unnatural aminoacids with un-protected amino functionality were synthesized because of their synthetic and medicinal importance. Critical N-Boc deprotection methods in the presence of labile (hydrolytic sensitivity) cyanomethyl functionality were screened thoroughly and it was found that readily available 4M HCl in 1,4-dioxane solution (2–4 equiv); acetonitrile, 0?°C, 2–4?h was a suitable condition. This condition was generalized and successfully applied to a variety of alkyl, alkynyl, aryl, heteroaryl, benzyl, azido, spiro amino acid cyanomethylesters irrespective of the nature of the amine (primary or secondary) and the distance between the amine and ester group to achieve final deprotected amino esters with high yield, and purity compared to other commonly known N-protecting groups (Cbz, Fmoc, Ac, Bn, Bz etc.). It was also demonstrated that N-Boc protected aminoacid cyanomethylesters are stable enough to carry out further functionalization compared to N-unprotected counterparts. 相似文献
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A Gaussian kernel approximation algorithm for a feedforward neural network is presented. The approach used by the algorithm, which is based on a constructive learning algorithm, is to create the hidden units directly so that automatic design of the architecture of neural networks can be carried out. The algorithm is defined using the linear summation of input patterns and their randomized input weights. Hidden-layer nodes are defined so as to partition the input space into homogeneous regions, where each region contains patterns belonging to the same class. The largest region is used to define the center of the corresponding Gaussian hidden nodes. The algorithm is tested on three benchmark data sets of different dimensionality and sample sizes to compare the approach presented here with other algorithms. Real medical diagnoses and a biological classification of mushrooms are used to illustrate the performance of the algorithm. These results confirm the effectiveness of the proposed algorithm. 相似文献
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Ananta Kumar Ghosh Debajyoti Ghoshal Michael G. B. Drew Golam Mostafa Nirmalendu Ray Chaudhuri 《Structural chemistry》2006,17(1):85-90
Two new cadmium (II) complexes [Cd(hmt)(dca)2]
n
(1) and [Cd3(hmt)2(SeCN)6(H2O)2]
n
(2) (hmt=hexamethylenetetramine, dca=dicyanamide) have been synthesized and characterized by X-ray single-crystal analysis.
The complex 1 is a 2D rectangular grid of octahedral cadmium (II) with CdN6 chromophore where cadmium centers are doubly bridged by dicyanamide and hmt along a-axis, which are interlinked by dicyanamide running along c-axis. Whereas, complex 2 is a 1D chain of octahedral cadmium (II) with a three-leg ladder topology running along a-axis. The Cd(II) centers are doubly bridged through SeCN (infinite rail) along a-axis and singly bridged by hmt (two-step rung) along c-axis, having cadmium centers with CdSe2N3O and CdSe2N4 chromophores. The adjacent chains through H-bonding between coordinated water and hmt, and SeSe interaction are extended to 2D supramolecular architecture. 相似文献
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More Krantiveer V. Dhodamani Ananta G. Dongale Tukaram D. Panda Dillip K. Delekar Sagar D. 《Journal of Solid State Electrochemistry》2022,26(4):1075-1084
Journal of Solid State Electrochemistry - Ti1-xFexO2-δ nanoparticles (NPs) with varying content of Fe (III) ions (x = 0.008 to 0.024 and δ =0.5x) were synthesized using sol-gel method at... 相似文献
10.
Mantosh K. Sinha Ofer Reany Dr. Galit Parvari Ananta Karmakar Dr. Ehud Keinan Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9056-9067
4‐Aminobipyridine derivatives form strong inclusion complexes with cucurbit[6]uril, exhibiting remarkably large enhancements in fluorescence intensity and quantum yields. The remarkable complexation‐induced pKa shift (ΔpKa=3.3) highlights the strong charge–dipole interaction upon binding. The reversible binding phenomenon can be used for the design of switchable beacons that can be incorporated into cascades of binding networks. This concept is demonstrated herein by three different applications: 1) a switchable fluorescent beacon for chemical sensing of transition metals and other ligands; 2) direct measurement of binding constants between cucurbit[6]uril and various nonfluorescent guest molecules; and 3) quantitative monitoring of biocatalytic reactions and determination of their kinetic parameters. The latter application is illustrated by the hydrolysis of an amide catalyzed by penicillin G acylase and by the elimination reaction of a β‐cabamoyloxy ketone catalyzed by aldolase antibody 38C2. 相似文献