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(2R,3R,4aS,6S,7S,8aS)-4a-Fluoro-8a-hydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate  [cached]
Goverdhan Mehta,Saikat Sen
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810044314
Abstract: The title compound, C18H25FO9, exhibits a similar unit cell and packing to the α polymorph of axial 4a,8a-dihydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate. The carbonyl O atoms of two of the four acetate groups in the molecule are disordered over two sites with occupancy ratios of 0.59 (4):0.41 (4) and 0.57 (6):0.43 (6). Crystal packing is effected via intermolecular O—H...O hydrogen bonds, which link the tetraacetate molecules into tapes along the c axis.
Lead tetraacetate oxidation of the Diels-Alder adduct of 7-dehydrocholestryl acetate with maleic anhydride
LIDIJA G. BONDARENKO-GHEORGHIU,LJUBINKA B. LORENC,MIHAILO LJ. MIHAILOVIC
Journal of the Serbian Chemical Society , 2000,
Abstract: The Diels-Alder adduct (3), obtained by cycloaddition of 7-dehydrocholesteryl acetate (1) and maleic anhydride (2), was heated at ca. 90°C with a large excess of lead tetraacetate in pyridine solution for 5 h. Under these conditions, compound 3 underwent lactonization with the participation of the olefinic D6-double bond to give two isomeric monolactone derivatives, 9 and 10 (in a total yield of ca. 6%), and the bislactone product 11 (in 11.5% yield). The starting material was recovered in 36% yield.
Solvent extraction of Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Pb2+, UO22+, Mn2+, Co2+ and Ni2+ into nitrobenzene using strontium dicarbol-lylcobaltate and tetra-tert-butyl p-tert-butylcalix[4]arene tetraacetate  [PDF]
E. MAKRLíK,J. BUDKA,P. VA?URA,P. SELUCKY
Journal of the Serbian Chemical Society , 2008,
Abstract: The exchange extraction constants corresponding to the general equilibrium M2+(aq) + SrL2+(nb) D ML2+ (nb) + Sr2+ (aq) occurring in the two-phase water–nitrobenzene system (M2+ = Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Pb2+, UO22+, Mn2+, Co2+ or Ni2+; L = tetra-tert-butyl p-tert-butylcalix[4]arene tetraacetate; aq = aqueous phase; nb = nitrobenzene phase) were evaluated from extraction experiments and -activity measurements. Furthermore, the stability constants of the ML2+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the cation order Ba2+ < Mn2+ < Pb2+, Co2+ < Cu2+, Zn2+ < Cd2+, Ni2+ < UO22+ < Ca2+.
1,4,8,11-Tetrakis(carboxymethyl)-5,5,7,12,12,14-hexamethyl-4,11-diaza-1,8-diazoniacyclotetradecane dichloride dihydrate  [cached]
Shi-Fan Wang,Hai-Qing Liu,Xue-Mei Yao,Kai Yang
Acta Crystallographica Section E , 2008, DOI: 10.1107/s1600536808010532
Abstract: The title compound, C24H46N4O82+·2Cl ·2H2O, was synthesized by the hydrolysis of tetraethyl 2,2′,2′′,2′′′-(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl) tetraacetate in hydrochloric acid solution. The crystal structure of the title compound consists of a 14-membered C10N4 centrosymmetric cationic macrocycle which interacts with the chloride ions and water molecules of crystallization to give a three-dimensional hydrogen-bonded network.
(4,6-Dibromo-m-phenylenedimethylidyne) tetraacetate
Guang-Liang Song,Shan Liu,Shui-Ping Deng,Yuan-Yuan Liu
Acta Crystallographica Section E , 2008, DOI: 10.1107/s1600536807063581
Abstract: The title molecule, C16H16Br2O8, lies on a crystallographic twofold axis. Weak intramolecular C—H...O hydrogen bonds may, in part, control the conformation of the molecule. In the crystal structure, molecules are connected into a two-dimensional network via weak intermolecular C—H...O hydrogen bonds.
Lifetime Measurement of the 8s Level in Francium  [PDF]
E. Gomez,L. A. Orozco,A. Perez Galvan,G. D. Sprouse
Physics , 2004, DOI: 10.1103/PhysRevA.71.062504
Abstract: We measure the lifetime of the 8s level on a magneto-optically trapped sample of ^{210}Fr atoms with time-correlated single-photon counting. The 7P_{1/2} state serves as the resonant intermediate level for two-photon excitation of the 8s level completed with a 1300 nm laser. Analysis of the fluorescence decay through the the 7P_{3/2} level gives 53.30 +- 0.44 ns for the 8s level lifetime.
Rooperol tetraacetate decreases cytokine mRNA levels and binding capacity of transcription factors in U937 cells  [cached]
A. Guzdek,H. Rokita,J. Cichy,A. C. Allison
Mediators of Inflammation , 1998, DOI: 10.1080/09629359891324
Abstract:
Ground state splitting of ^8S rare earth ions in semiconductors  [PDF]
A. Lusakowski
Physics , 2005, DOI: 10.1103/PhysRevB.72.094429
Abstract: We propose a new mechanism leading to the ground state splitting for the rare earth ^8S ions in semiconductor crystals. The resulting splitting is due to three effects, the first is the intra atomic 4f-5d spin-spin interaction, the second one is the spin - orbit interaction for 5d electrons and the third one is their hybridization with the valence band states of semiconductors host. The resulting splitting significantly depends on the relative position of 5d level with respect to semiconductor host band structure. We also discuss different model, already known in the literature, which is also based on ion - band states hybridization. For both models, as an example, we present results of numerical calculations for rare earth ion in IV-VI semiconductor PbTe.
Crystal structures of Burkholderia cenocepacia dihydropteroate synthase in the apo-form and complexed with the product 7,8-dihydropteroate
Rachel E Morgan, Ga?lle O Batot, Jennifer M Dement, Vincenzo A Rao, Thomas C Eadsforth, William N Hunter
BMC Structural Biology , 2011, DOI: 10.1186/1472-6807-11-21
Abstract: An efficient recombinant protein expression system for DHPS from B. cenocepacia (BcDHPS) was prepared, the dimeric enzyme purified in high yield and crystallized. The structure of the apo-enzyme and the complex with the product 7,8-dihydropteroate have been determined to 2.35 ? and 1.95 ? resolution respectively in distinct orthorhombic crystal forms. The latter represents the first crystal structure of the DHPS-pterin product complex, reveals key interactions involved in ligand binding, and reinforces data generated by other structural studies. Comparisons with orthologues identify plasticity near the substrate-binding pocket and in particular a range of loop conformations that contribute to the architecture of the DHPS active site. These structural data provide a foundation for hit discovery. An intriguing observation, an artifact of the analysis, that of a potential sulfenamide bond within the ligand complex structure is mentioned.Structural similarities between BcDHPS and orthologues from other Gram-negative species are evident as expected on the basis of a high level of sequence identity. The presence of 7,8-dihydropteroate in the binding site provides details about ligand recognition by the enzyme and the different states of the enzyme allow us to visualize distinct conformational states of loops adjacent to the active site. Improved drugs to combat infections by Burkholderia sp. and related Gram-negative bacteria are sought and our study now provides templates to assist that process and allow us to discuss new ways of inhibiting DHPS.Dihydropteroate synthase (DHPS, EC: 2.5.1.15) catalyses the reaction of 6-hydroxymethyl-7,8-dihydropterin-pyrophosphate with p-aminobenzoic acid (p-ABA) to yield 7,8-dihydropteroate and pyrophosphate (Figure 1). In so doing the enzyme supports the biosynthesis of folate, a key metabolite required to support the synthesis of DNA, and proteins. The provision of folates, either by synthesis in plants and microorganisms or as acquire
7,8-secolignans from Schisandra neglecta and their anti-HIV-1 activities
Gao, Xuemei;Mu, Huaixue;Wang, Ruirui;Hu, Qiufen;Yang, Liumeng;Zheng, Yongtang;Sun, Handong;Xiao, Weilie;
Journal of the Brazilian Chemical Society , 2012, DOI: 10.1590/S0103-50532012005000054
Abstract: four new 7,8-secolignans (neglectahenols a-d), together with two known 7,8-secolignans, were isolated from leaves and stems of schisandra neglecta. the structures were elucidated by spectroscopic methods, including extensive one and two dimension nmr (nuclear magnetic resonance) techniques. 7,8-secolignans and neglectahenols a-d were also tested for their anti-hiv-1 (human immunodeficiency virus type 1) activities, and all of them showed modest activities.
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