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排序方式: 共有1117条查询结果,搜索用时 15 毫秒
11.
12.
The microwave-assisted dry media technology was utilized for the synthesis of some novel derivatives in the Hantzsch—Biginelli reaction. In this eco-friendly approach, the usage of organic solvents and hazardous reagents resulting in corrossion of materials was minimized, giving high yields of products within a short reaction time. 相似文献
13.
Kim SY Saxena A Kwak G Fujiki M Kawakami Y 《Chemical communications (Cambridge, England)》2004,(5):538-539
Cooperative amplification of the C-F...Si weak interaction between side chains and the main chain was found to afford rigid rodlike helical polysilanes with a preferential screw sense. 相似文献
14.
Ashok K. Singh Amar Singh Ranjana Gupta Madhu Saxena Bharat Singh 《Transition Metal Chemistry》1992,17(5):413-416
The kinetics of oxidation of three aldoses (glucose, mannose and galactose) byN-bromoacetamide (NBA) in the presence of an alkaline solution of RuO4 as catalyst and Hg(OAc)2 as co-catalyst and as a scavenger for bromide have been investigated. The main products of the oxidation are the corresponding
aldonic acids. The reaction is zero order with respect to aldose and OH−. First order dependence of the reaction on both NBA and RuO4 at low concentrations shifts to zero order at higher concentrations. Addition of acetamide decreases the reaction rate, while
addition of Hg(OAc)2 has the opposite effect. No significant effect of ionic strength was observed. OBr− is postulated as the reactive oxidising species and a mechanism involving co-catalysis by RuO4 and HgII is proposed.
TMC 2588 相似文献
15.
Saxena C Wang H Kavakli IH Sancar A Zhong D 《Journal of the American Chemical Society》2005,127(22):7984-7985
In this communication, we report the ultrafast dynamics of resonance energy transfer in a blue-light photoreceptor, Vibrio cholerae cryptochrome. The transfer was observed to occur in 60 ps. We also studied the local rigidity and solvation around the binding site of the photoantenna molecule. The results for the first time show energy transfer in cryptochrome suggesting some mechanistic similarities between photolyase that repairs damaged DNA and cryptochrome that mediates blue-light signaling. 相似文献
16.
Reactions of dimethyl acetylenedicarboxylate—VI : Reaction with aldehyde and ketone phenylhydrazones
Benzaldehyde phenylhydrazone with dimethyl acetylenedicarboxylate gives dimethyl 1,3-diphenylpyrazoline-4,5-dicarboxylate, dimethyl 1,3-diphenylpyrazole-4,5-dicarboxylate and trimethyl 1-phenylpyrazole-3,4,5-tricarboxylate; p-chlorobenzaldehyde phenylhydrazone gives trimethyl 1-phenyl-3,4,5-tricarboxylate and 1,2-(bis-phenylazo)-1,2-di-p-chlorophenylethane. Under similar conditions, p-tolualdehyde phenylhydrazone gives only trimethyl 1-phenylpyrazole-3,4,5- tricarboxylate. Acetophenone phenylhydrazone with dimethyl acetylenedicarboxylate gives dimethyl 1,3-diphenylpyrazole-4,5-dicarboxylate. Benzophenone phenylhydrazone, on the other hand, gives a mixture of dimethyl 1,3-diphenylpyrazoline-4,5-dicarboxylate and dimethyl 1,3-diphenylpyrazole-4,5- dicarboxylate. Benzyl methyl ketone and dimethyl acetylenedicarboxylate gives an enamine maleate, which is the Michael addition product. 相似文献
17.
A general formulation has been developed for the evaluation of the total electron spin-spin contact interaction in many-electron atoms, including both the intra- and inter-shell contributions. Calculations have been carried out, using existing analytical Hartree-Fock functions, for the positive ions, neutral systems, and negative ions for all the atoms from He to Kr.
This work has been supported in part by the National Research Council of Canada. 相似文献
Zusammenfassung Es wird ein allgemeiner Formalismus zur Berechnung der gesamten Elektronen-Spin-Spin-Kontakt-Wechselwirkung in Vielelektronen-Atomen angegeben, der sowohl die Anteile der Wechselwirkung innerhalb einer Schale als auch zwischen einzelnen Schalen berücksichtigt. Berechnungen wurden unter Benutzung vorhandener analytischer Hartree-Fock-Funktionen für die positiven Ionen, die neutralen Systeme und die negativen Ionen aller Atome von He bis Kr durchgeführt.
This work has been supported in part by the National Research Council of Canada. 相似文献
18.
Ravi Shankar Anubhav Saxena Ajaib S. Brar 《Journal of organometallic chemistry》2002,650(1-2):223-230
New functional polysilanes [R2R1Si(CH2)2SiH]n (R=Me, R1=H (1); R=R1=Et (2); R=Me, R1=Ph (3)) bearing carbosilyl side chains have been synthesized by catalytic dehydropolymerization of precursor carbosilanes R2R1SiCH2CH2SiH3 using Cp2TiCl2–BuLi as a catalyst. These polymers are characterized by 1H, 13C, 29Si, {1H–29Si} HSQC NMR spectroscopy, GPC and TGA. Attempts to delineate the tacticity from the analysis of deconvoluted 29Si{1H}-NMR signals associated with the side chain silicon atoms reveal that the triad concentration ratio follows a Bernoullian statistical model for polymers 1 and 2 only. 相似文献
19.
Zusammenfassung Wir untersuchten auf polarographischem Wege die Kinetik der Entladung von Zn2+ und Ni2+ an der Quecksilbertropfelektrode in einem Thiomalatmedium konstanter Ionenstärke (=0,5). Wir stellten fest, daß die Reduktion von Zn2+ und Ni2+ irreversibel verläuft und berechneten daher die kinetischen Parameter (Übertragungskoeffizient , Geschwindigkeitskonstante der HinreaktionK
f,h
o
) nach dem theoretischen Verfahren vonKoutecky in der vonMeites undIsrael erweiterten Form.
Mit 2 Abbildungen 相似文献
Kinetics of discharge of Zn2+ and Ni2+ at the D.M.E. in thiomalate media
Kinetics of discharge of Zn2+ and Ni2+ have been studied polarographically in thiomalate media of constant ionic strength (=0.5) at the dropping mercury electrode. The reduction of both Zn2+ and Ni2+ was found to be irreversible. Hence, the kinetic parameters (transfer coefficient , and forward rate constantK j,h o ) have been calculated byKoutecky's theoretical treatment as extended byMeites andIsrael.
Mit 2 Abbildungen 相似文献
20.
Effect of M. tuberculosis infection was studied on the expression of intercellular adhesion molocule-1 (ICAM-1) and Mac-1 markers on murine peritoneal macrophages. Intraperitoneal administration of M. tuberculosis resulted in a marked increase in the proportion of Mac-1(+) cells whereas the proportion of ICAM-1(+) cells declined sharply 4 h post infection. Absolute numbers of Mac-1(+) and ICAM-1(+) cells however increased at all time points after the infection. Comparison of kinetics of changes observed in Mac-1(+) and ICAM-1(+) cell populations with differential leukocyte counts in peritoneal cells indicated that these alterations could be due to cellular influx, especially that of neutrophils, or up regulation of these markers on macrophages and other peritoneal cells. In adherent peritoneal macrophages infected in vitro with M. tuberculosis, proportion of Mac-1(+) and ICAM-1(+) cells increased markedly within 24 h of infection. Mean expression of these markers on per cell basis also increased significantly. Similar results were obtained by using RAW 264.7 mouse macrophage cell line, suggesting that the enhanced expression of Mac-1 and ICAM-1 markers was a direct effect of M. tuberculosis infection and not mediated by contaminating cell types present in adherent macrophage preparations. Mac-1 and ICAM-1 expression was further studied on macrophages that had actually engulfed M. tuberculosis and compared with bystander macrophages without intracellular M. tuberculosis. For this purpose M. tuberculosis pre-stained with DilC18 fluorescent dye were used for infecting adherent peritoneal macrophages. Mac-1 and ICAM-1 expression on gated DilC18 positive and negative cell populations was analyzed. Our results indicate that the expression of Mac-1 and ICAM- 1 markers was significantly enhanced on all macrophages incubated with M. tuberculosis but was more pronounced on macrophages with internalized mycobacteria. Taken together, our results suggest that the expression of Mac-1 and ICAM-1 markers is significantly up regulated as a result of exposure and infection with M. tuberculosis. Since these markers play important role in the uptake of mycobacteria as well as in the process of antigen presentation by macrophages, their upregulation may be beneficial for generation of a protective immune response to M. tuberculosis. 相似文献