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排序方式: 共有1288条查询结果,搜索用时 62 毫秒
961.
Rodolfo Valdés Tatiana Álvarez Andrés Tamayo Eutimio G. Fernandez José Montero Déborah Geada William Ferro Yenisley Medina Yarysel Guevara Sigifredo Padilla Dobián Cecilia Lamay Dorta Marcos González Raudel Sosa Tatiana González 《Chromatographia》2008,67(11-12):923-927
This investigation sought to discover whether purification of monoclonal antibody CB.Hep-1 in ascitic fluid is possible by protein A–Sepharose affinity chromatography, for 100 runs, without pre-purification steps. Results showed that direct application of ascitic fluid to protein A–Sepharose increased monoclonal antibody recovery by 27% compared with the traditional process (control) after 100 runs. The purity of the monoclonal antibody was >95% and the cost of the purification was 15% less than that of the control process. In conclusion, monoclonal antibody CB.Hep-1 in ascitic fluid can be purified by chromatography on protein A–Sepharose, for 100 purification cycles, without the need for pre-purification steps. 相似文献
962.
Mitkina TV Zakharchuk NF Naumov DY Gerasko OA Fenske D Fedin VP 《Inorganic chemistry》2008,47(15):6748-6755
Inclusion compounds of a macrocyclic cavitand cucurbit[8]uril (CB[8]) with cobalt(III) and nickel(II) complexes of 1,3-diaminopropane (tn) and 1,3-diamino-2-propanol (tmOH) { trans-[Co(tn) 2Cl 2]@CB[8]}Cl.14H 2O ( 1), { trans-[Co(tmOH)(tmO)]@CB[8]}Cl 2.22H 2O ( 2), and { trans-[Ni(tmOH) 2]@CB[8]}Cl 2.22H 2O ( 3) were synthesized and characterized by X-ray single crystal analysis, IR spectroscopy, ESI-MS, and by solid-state stripping voltammetry. The encapsulation of trans-[Co(tn) 2Cl 2] (+) within the cavity of CB[8] stabilizes the complex toward ligand substitution reactions in aqueous solution. The electrochemical study demonstrates that CB[8] prefers the oxidized species in trans-[Co(tn) 2Cl 2] (+)/ trans-[Co(tn) 2Cl 2] (0) and trans-[Co(tmO)(tmOH) 2] (2+)/ trans-[Co(tmO)(tmOH) 2] (+) redox couples, but stabilizes the reduced form trans-[Ni(tmOH) 2] (2+) against the oxidized species. The reversibility of voltammogram shapes evidence that for the inclusion compounds 1- 3 electron transfer reactions proceed within the cavity of the host. 相似文献
963.
Poli AL Batista T Schmitt CC Gessner F Neumann MG 《Journal of colloid and interface science》2008,325(2):386-390
This paper reports on the effect of sonication on SAz-1 and SWy-1 montmorillonite suspensions. Changes in the size of the particles of these materials and modifications of their properties have been investigated. The variation of the particle size has been analyzed by DLS (dynamic light scattering). In all cases the clay particles show a bimodal distribution. Sonication resulted in a decrease of the larger modal diameter, as well as a reduction of its volume percentage. Simultaneously, the proportion of the smallest particles increases. After 60 min of sonication, SAz-1 presented a very broad particle size distribution with a modal diameter of 283 nm. On the other hand, the SWy-1 sonicated for 60 min presents a bimodal distribution of particles at 140 and 454 nm. Changes in the properties of the clay suspensions due to sonication were evaluated spectroscopically from dye-clay interactions, using Methylene Blue. The acidic sites present in the interlamellar region, which are responsible for dye protonation, disappeared after sonication of the clay. The changes in the size of the scattering particles and the lack of acidic sites after sonication suggest that sonication induces delamination of the clay particles. 相似文献
964.
965.
Revuelta J Vacas T Torrado M Corzana F Gonzalez C Jiménez-Barbero J Menendez M Bastida A Asensio JL 《Journal of the American Chemical Society》2008,130(15):5086-5103
The most significant mechanism of bacterial resistance to aminoglycosides is the enzymatic inactivation of the drug. Herein, we analyze several key aspects of the aminoglycoside recognition by the resistance enzyme ANT(4') from Staphylococcus aureus, employing NMR complemented with site-directed mutagenesis experiments and measurements of the enzymatic activity on newly synthesized kanamycin derivatives. From a methodological perspective, this analysis provides the first example reported for the use of transferred NOE (trNOE) experiments in the analysis of complex molecular recognition processes, characterized by the existence of simultaneous binding events of the ligand to different regions of a protein receptor. The obtained results show that, in favorable cases, these overlapping binding processes can be isolated employing site-directed mutagenesis and then independently analyzed. From a molecular recognition perspective, this work conclusively shows that the enzyme ANT(4') displays a wide tolerance to conformational variations in the drug. Thus, according to the NMR data, kanamycin-A I/II linkage exhibits an unusual anti-Psi orientation in the ternary complex, which is in qualitative agreement with the previously reported crystallographic complex. In contrast, closely related, kanamycin-B is recognized by the enzyme in the syn-type arrangement for both glycosidic bonds. This observation together with the enzymatic activity displayed by ANT(4') against several synthetic kanamycin derivatives strongly suggests that the spatial distribution of positive charges within the aminoglycoside scaffold is the key feature that governs its preferred binding mode to the protein catalytic region and also the regioselectivity of the adenylation reaction. In contrast, the global shape of the antibiotic does not seem to be a critical factor. This feature represents a qualitative difference between the target A-site RNA and the resistance enzyme ANT(4') as aminoglycoside receptors. 相似文献
966.
Irina V. Lijanova Ivana Moggio Eduardo Arias Tatiana Klimova Marcos Martínez-García 《Tetrahedron》2008,64(44):10258-10266
Dendrimers with resorcinarene core and π-conjugated dendron branches with 16 and 32 stilbene groups have been synthesized and characterized by 1H and 13C NMR, FTIR, UV–vis, fluorescence spectroscopy, MALDI-TOF, electrospray or FAB+ mass spectrometry, and elemental analysis. Homogeneous thin films of resorcinarene-dendrimers deposited on quartz, glass or ITO substrates were prepared by spin-coating. All the materials showed absorption in the UV region in both chloroform solutions and thin films. The band gap energies (Eg) determined from both UV–vis spectroscopy and voltammetry were in the semiconducting range. A slight decrease in the Eg values was observed when passing from the first generation of dendrimers to the second one, which can be attributed to an increase in the π-conjugated system. The fluorescence quantum yield of the molecules in solution was low and practically null in the solid state. Nevertheless, a very interesting behavior was observed in the reductive voltammetric cycle, where electrochromism from transparent to blue forms occurred in the film by n-doping process; property that makes these materials suitable for the development of electrochromic devices such as smart windows. 相似文献
967.
Electrolysis of aromatic aldehydes, malononitrile and malonate in methanol in an undivided cell in the presence of sodium bromide-sodium methoxide as double mediatory system results in the stereoselective formation of methyl (1R∗,5R∗,6R∗) 6-substituted 5-cyano-4,4-dialkoxy-2-oxo-3-azabicyclo[3.1.0]hexane-1-carboxylates in 50-70% yields. 相似文献
968.
Heider Nasser ákos Rédey Tatiana Yuzhakova József Kovács 《Reaction Kinetics and Catalysis Letters》2008,94(1):165-173
A kinetic study of the homogeneous catalytic hydrogenation of avermectins is reported for a series of isosteric p-substituted
arylphosphines as ligands. The activity of the rhodium complexes formed in situ from [RhCl(COD)]2 increased with increasing the electron-donor capacity of the P(p-XC6H4)3: P(p-ClC6H4)3 < P(C6H5)3 < P(p-CH3C6H4)3 < P(p-OCH3C6H4)3. As expected, this trend was also observed when using preformed complexes thereof. Linear correlations based on Hammett and
Kabachnik treatments are provided as useful tools to guide the exploration work towards improved [RhCl(COD)]2/P(p-XC6H4)3 catalytic systems. 相似文献
969.
It has been reported that cellulose is better dissolved in NaOH-water when a certain amount of urea is added. In order to
understand the mechanisms of this dissolution and the interactions between the components, the binary phase diagram of urea/water,
the ternary urea/NaOH/water phase diagram and the influence of the addition of microcrystalline cellulose in urea/NaOH/water
solutions were studied by DSC. Urea/water solutions have a simple eutectic behaviour with a eutectic compound formed by pure
urea and ice (one urea per eight water moles), melting at −12.5 °C. In the urea/NaOH/water solutions, urea and NaOH do not
interact, each forming their own eutectic mixtures, (NaOH + 5H2O, 4H2O) and (urea, 8H2O), as found in their binary mixtures. When the amount of water is too low to form the two eutectic mixtures, NaOH is attracting
water at the expense of urea. In the presence of microcrystalline cellulose, the interactions between cellulose and NaOH/water
are exactly the same as without urea, and urea is not interacting with cellulose. A tentative explanation of the role of urea
is to bind water, making cellulose-NaOH links more stable.
Member of the European Polysaccharide Network of Excellence (EPNOE), 相似文献
970.
Egorova-Zachernyuk T van Rossum B Erkelens C de Groot H 《Magnetic resonance in chemistry : MRC》2008,46(11):1074-1083
In this investigation we report a complete assignment of (13)C, (1)H and (15)N solution and solid state chemical shifts of two bacterial photosynthetic pigments, bacteriochlorophyll (BChl) a and bacteriopheophytin (BPheo) a. Uniform stable-isotope labelling strategies were developed and applied to biosynthetic preparation of photosynthetic pigments, namely uniformly (13)C, (15)N labelled BChl a and BPheo a. Uniform stable-isotope labelling with (13)C, (15)N allowed performing the assignment of the (13)C, (15)N and (1)H resonances. The photosynthetic pigments were isolated from the biomass of photosynthetic bacteria Rhodopseudomonas palustris 17001 grown in uniformly (13)C (99%) and (15)N (98%) enriched medium. Both pigments were characterised by NMR in solution (acetone-d(6)) and by MAS NMR in solid state and their NMR resonances were recorded and assigned through standard liquid 2D (13)C-(13)C COSY, (1)H-(13)C HMQC, (1)H-(15)N HMBC and solid 2D (13)C-(13)C RFDR, (1)H-(13)C FSLG HETCOR and (1)H-(15)N HETCOR correlation techniques at 600 MHz and 750 MHz. The characterisation of pigments is of interest from biochemical to pharmaceutical industries, photosynthesis and food research. 相似文献