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31.
Krishna Bisetty Francesc J. Corcho Josep Canto Hendrik G. Kruger Juan J. Perez 《Journal of Molecular Structure》2006,770(1-3):221-228
In this paper, we report on the conformational profile of the pentacyclo-undecane (PCU) cage tripeptide carried out by molecular dynamics (MD) simulation using water as an explicit solvent. The MD solution phase studies carried on the model peptide analogues (A)=Ac–Ala–Ala–Ala–NHMe; (B)=Ac–Cage–Cage–Cage–NHMe; (C)=Ac–Ala–Cage–Ala–NHMe and (D)=Ac–Ala–Pro–Ala–NHMe, are used as a complimentary technique to the corresponding gas phase simulated annealing (SA) study previously carried out in our laboratory. No significant structural changes were observed over the MD trajectories. However, the results reported here provide further evidence that the (PCU) cage amino acid exhibits C7eq, C7aq, R and L conformations, and the theoretical results suggest that the PCU cage amino acid is a strong β-turn inducer. These results support the prediction that when the PCU cage residues are in the (i) and (i+2) positions, the β-turn can be extended in either direction to form anti-parallel β-pleated sheets, thereby forming the basis of the mechanism for the folding back of the chain in a cross-β-turn structure. 相似文献
32.
Krishna Raman Surendra S. Parmar Shiva P. Singh 《Journal of heterocyclic chemistry》1980,17(5):1137-1139
A series of 1-(5-phenyl-2H-tetrazol-2-ylacetyl)-4-substituted thiosemicarbazids were prepared as possible antiinflammatory agents. Their antiproteolytic activity was reported. 相似文献
33.
Reinvestigation of the reaction of 3-aroylmethyleneindol-2-ones with hydrogen peroxide has revealed that a 1:1 isomeric mixture of spiro[3H-indole-3,2′-oxiran]-2(1H)-ones is formed. The structures of the two isomers have been confirmed by their ir, pmr and mass spectral studies. Mass fragmentation patterns of these compounds are discussed. 相似文献
34.
Reduced inorganic phosphorus in the natural environment: significance, speciation and determination 总被引:1,自引:0,他引:1
It is commonly assumed that phosphorus occurs almost exclusively in the environment as fully oxidized phosphate (primarily H2PO4− and HPO42−, where the oxidation state of phosphorus is +V). Recent developments in the field of microbiology and research on the origin of life have suggested a possibly significant role for reduced, inorganic forms of phosphorus in bacterial metabolism and as evolutionary precursors of biological phosphate compounds. Reduced inorganic forms of phosphorus include phosphorus acid (H3PO3, P(+III)), hypophosphorus acid (H3PO2, P(+I)) and various forms of phosphides (P(−III)). Reduced phosphorus has been detected in anaerobic sediments, sewage treatment facilities and in industrial and agricultural processes.Microbiological evidence suggests a significant role for reduced phosphorus species in metabolic processes and raises interesting questions regarding the biogeochemistry of this nutrient in the environment. However, the paucity of data on the presence and cycling of reduced phosphorus compounds in the environment requires attention in order to elucidate the role of these compounds in natural systems. This paper discusses the significance of reduced phosphorus in the natural environment, its speciation and methods of detection. 相似文献
35.
Summary A new colour reaction for the detection of cerram(IV) which can be carried out both in a test tube and on a spot plate has been described. The test solution is treated with methylene blue in nitric acid solution (11) to form a rose-red colour. This simple procedure has an advantage over the existing tests in that it is applicable in the presence of oxidising agents like chromium(VI), vanadium(V), nitrate, perchlorate and of coloured ions like copper(II), cobalt(II), nickel(II), chromium(III), iron(III), vanadium(IV), uranium(VI).
Zusammenfassung Eine neue, sowohl in der Eprouvette wie auf der Tüpfelplatte ausführbare Farbreaktion zum Nachweis von Cer(IV) wurde angegeben. Die Probelösung wird mit salpetersaurer Methylenblaulösung behandelt und gibt eine rosarote Färbung. Die Reaktion hat gegenüber bekannten Tests den Vorteil, in Gegenwart von Oxydationsmitteln wie Cr(VI), V(V), NO3 –, ClO4 – bzw. in Anwesenheit gefärbter Ionen wie Cu(II), Co(II), Ni(II), Cr(III), Fe(III), V(IV) oder U(VI) anwendbar zu sein.相似文献
36.
AbstractA convergent synthesis of the southern furan segment of novel furanocembranoids from Croton oblongifolius has been accomplished involving silver-catalyzed cyclization of alkynyl diol as the key step towards 2, 5-disubstituted furan ring formation. 相似文献
37.
Rajuru R. Reddy Agarala S. R. Reddy Vanka Krishna Reddy 《Theoretical chemistry accounts》1985,67(3):187-191
The bond dissociation energies for Alkali halides have been estimated based on the derived relations: $$\begin{gathered} D_{AB} = \bar D_{AB} + 31.973{\text{ e}}^{0.363\Delta x} {\text{ and}} \hfill \\ D_{AB} = \bar D_{AB} (1 - 0.2075\Delta xr_e ) + 52.29\Delta x, \hfill \\ \end{gathered} $$ where \(\bar D_{AB} = (D_{AA} \cdot D_{BB} )^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} \) , Δx represents Pauling electronegativity differences x(A ?xB) and r e is the internuclear distance. A simplified formula relating bond orders, q, to spectroscopic constants is suggested. The formula has the form q = 1.5783 × 10?3 (ω e 2 re/ Be)1/2. The ambiguity arising from the Parr and Borkman relation is discussed. The present study supports the view of Politzer that q/(0.5r e)2 is the correct definition of bond order. The estimated bond energies and bond orders are in reasonably good agreement with the literature values. The bond energies estimated with the relations we suggested, for alkali halides give an error of 4.5% and 5.3%, respectively. The corresponding error associated with Pauling's equation is 40.2%. 相似文献
38.
Ramaswamy K Saito H Murakami H Shiba K Suga H 《Journal of the American Chemical Society》2004,126(37):11454-11455
Fx3 is an artificial ribozyme with the ability to aminoacylate various tRNAs with phenylalanine and its nonnatural derivatives. Herein we report a simple strategy to build tRNA specificity into the generic Fx3, by appending to its 3'-end a tRNA-specific sequence (TSS), which is complementary to the acceptor stem of the cognate tRNA. This new designer ribozyme, referred to as Fx10, is able to recognize its cognate tRNA via a 10-base-pair interaction that is formed after the invasion of the tRNA acceptor stem by the TSS. We have demonstrated that Fx10 can aminoacylate its cognate tRNA with a high degree of specificity and also discriminate against the noncognate tRNAs. Because the tRNA specificity can be easily programmed into Fx10, it is a custom-made catalyst to generate nonnatural aminoacyl-tRNAs. 相似文献
39.
Krishna C. Joshi Renuka Jain Anshu Dandia Vandana Sharma 《Journal of heterocyclic chemistry》1986,23(1):97-99
A novel system 2-oxo-1′,2′,4′,5′-tetrahydrospiro[3H-indole-3,3′-1,2,4,5-tetrazine]-6′-thione has been synthesized by the treatment of fluorinated isatins with thiocarbohydrazide in aqueous ethanolic medium. Under exactly similar conditions, N-acetylisatin gave exclusively thiocarbohydrazone. The spiro product, on treatment with acetic acid, gave fluorinated isoindigo. Characterization of these products have been done by elemental analyses, ir, pmr and mass spectral studies. 相似文献
40.
Abstract— Recently, a new technique of 1O2 generation has been described by Midden and Wang. The sensitizer is immobilized on silica gel particles which are attached on one surface of a glass plate which is placed, sensitizer-side down, above a solution leaving a small air space between the sensitizer and the solution. Applying the principle of the technique, i.e. generation of 1O2 in the gas phase above the solution, we first improved the long-term stability of the dye (rose bengal) by using double stock transparent tape instead of rubber cement. Under these conditions, although the initial rate of production was higher in rubber cement, the rate of production reached a plateau after 30 min, whereas with double stick transparent tape, the rate of generation was linear up to 100 min. This result was explained by the fact that silica glass beads are embedded in the cement which could lead to the bleaching reaction of the dye. Different reactions have been investigated, the bleaching of N,N-dimethyl-4-nitrosoaniline (RNO) in the presence of imidazole, destruction of anthracenedipropionic acid, formation of a stable nitroxide from a sterically hindered secondary amine and the influence of pH on the nitroxide yield. The yield was measured to be 5 × 1012 molecules of singlet oxygen produced per second per cm2 from the surface of the plate using the RNO bleaching reaction. This method of generating 1O2 also seems promising for studying the killing of mammalian cells by 1O2 as the sole damaging species. 相似文献