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281.
Nail M. Suleimanov Sergey M. Khantimerov Robert Scheuermann Dierk Herlach Alexandr A. Loschin Oleg I. Gnezdilov Yurii A. Sakhratov Vadim L. Matukhin 《Journal of Solid State Electrochemistry》2013,17(8):2115-2121
In situ muSR and nuclear magnetic resonance (NMR) experiments on the investigation of methanol decomposition on Pt-Ru nanoscaled catalyst supported on Vulcan XC-72 carbon black (Pt-Ru/Vulcan XC-72) are presented. Avoided-level-crossing muon spin resonance measurements reveal the resonance line at magnetic field 2.018 T, we assign to transient CH2?OMu? formaldehyde muonated radical. Results obtained allow us to estimate the contribution of chemical decomposition reaction process for the formaldehyde—carbon oxide—hydrogen conversion on Pt-Ru/Vulcan XC-72 catalytic material. NMR spectrum of the methanol covered Pt-Ru/Vulcan XC-72 consists of three broad resonance lines. Two of them are assigned to OH and CH3 groups of methanol bound to the carbon black surface. Following the existing literature, which indicates that polymerization of formaldehyde readily takes place when the monomer is adsorbed on some active surface, the third one is assigned to the resonance signal of oligomeric species of formaldehyde. Taking into account the results of our experiments on electrochemical hydrogenation of carbon nanotubes, we do not exclude that the hydrogen arising as a result of methanol decomposition would also contribute to this signal. The high surface area of amorphous carbon nanoparticles of Vulcan XC-72 is favourable to adsorb the hydrogen on their surface. 相似文献
282.
283.
Back Cover: Dimers of Nineteen‐Electron Sandwich Compounds: Crystal and Electronic Structures,and Comparison of Reducing Strengths (Chem. Eur. J. 47/2014)
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284.
Identification and specificity profiling of protein prenyltransferase inhibitors using new fluorescent phosphoisoprenoids 总被引:4,自引:0,他引:4
Dursina B Reents R Delon C Wu Y Kulharia M Thutewohl M Veligodsky A Kalinin A Evstifeev V Ciobanu D Szedlacsek SE Waldmann H Goody RS Alexandrov K 《Journal of the American Chemical Society》2006,128(9):2822-2835
Posttranslational modification of proteins with farnesyl and geranylgeranyl isoprenoids is a widespread phenomenon in eukaryotic organisms. Isoprenylation is conferred by three protein prenyltransferases: farnesyl transferase (FTase), geranylgeranyl transferase type-I (GGTase-I), and Rab geranylgeranyltransferase (RabGGTase). Inhibitors of these enzymes have emerged as promising therapeutic compounds for treatment of cancer, viral and parasite originated diseases, as well as osteoporosis. However, no generic nonradioactive protein prenyltransferase assay has been reported to date, complicating identification of enzyme-specific inhibitors. We have addressed this issue by developing two fluorescent analogues of farnesyl and geranylgeranyl pyrophosphates {3,7-dimethyl-8-(7-nitro-benzo[1,2,5]oxadiazol-4-ylamino)-octa-2,6-diene-1}pyrophosphate (NBD-GPP) and {3,7,11-trimethyl-12-(7-nitro-benzo[1,2,5]oxadiazo-4-ylamino)-dodeca-2,6,10-trien-1} pyrophosphate (NBD-FPP), respectively. We demonstrate that these compounds can serve as efficient lipid donors for prenyltransferases. Using these fluorescent lipids, we have developed two simple (SDS-PAGE and bead-based) in vitro prenylation assays applicable to all prenyltransferases. Using the SDS-PAGE assay, we found that, in contrast to previous reports, the tyrosine phosphatase PRL-3 may possibly be a dual substrate for both FTase and GGTase-I. The on-bead prenylation assay was used to identify prenyltransferase inhibitors that displayed nanomolar affinity for RabGGTase and FTase. Detailed analysis of the two inhibitors revealed a complex inhibition mechanism in which their association with the peptide binding site of the enzyme reduces the enzyme's affinity for lipid and peptide substrates without competing directly with their binding. Finally, we demonstrate that the developed fluorescent isoprenoids can directly and efficiently penetrate into mammalian cells and be incorporated in vivo into small GTPases. 相似文献
285.
Through the use of cyclic beta-diketones as supporting ligands, the copper-catalyzed coupling of aryl iodides with aliphatic amines occurs at room temperature in as little as 1 h. These high reaction rates allow for the coupling of a wide range of aryl and heteroaryl iodides at room temperature. This method is highly tolerant of a number of reactive functional groups, including -Br and aromatic -NH2 as well as phenolic and aliphatic -OH. The high selectivity of the CuI-beta-diketone catalyst for aliphatic amines represents a useful complement to the palladium-based methods. 相似文献
286.
Talyzin AV Tsybin YO Purcell JM Schaub TM Shulga YM Noréus D Sato T Dzwilewski A Sundqvist B Marshall AG 《The journal of physical chemistry. A》2006,110(27):8528-8534
Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C(60)H(x) (x > 36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da) hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation pathways are discussed. 相似文献
287.
Fedor I. Zubkov Julya D. Ershova Vladimir P. Zaytsev Alexandr S. Peregudov Roman S. Borisov Abel M. Maharramov 《Tetrahedron》2009,65(18):3789-9163
The interaction between 1-furyl-1,2,3,4-tetrahydroisoquinolines and unsaturated acids derivatives (acryloyl, methacryloyl, and crotonoyl chloride, maleic and citraconic anhydride) was studied. It was shown that the reaction proceeds via amide formation and subsequent intramolecular Diels-Alder reaction of the furan (IMDAF). The [4+2] cycloaddition proceeded under mild reaction conditions (25-80 °C) and afforded only the exo-adduct in a high yield. With this method, a new approach to the isoindolo[1,2-a]isoquinoline system, the basic structural element of alkaloids Jamtine, Hirsutine, and Nuevamine, is proposed. 相似文献
288.
For every graph G, let . The main result of the paper says that every n-vertex graph G with contains each spanning subgraph H all whose components are isomorphic to graphs in . This generalizes the earlier results of Justesen, Enomoto, and Wang, and is a step towards an Ore-type analogue of the Bollobás-Eldridge-Catlin Conjecture. 相似文献
289.
Henry A. Kierstead Alexandr V. Kostochka Marcelo Mydlarz Endre Szemerédi 《Combinatorica》2010,30(2):217-224
A proper vertex coloring of a graph is equitable if the sizes of color classes differ by at most one. The celebrated Hajnal-Szemerédi Theorem states: For every positive integer
r, every graph with maximum degree at most r has an equitable coloring with r+1 colors. We show that this coloring can be obtained in O(rn
2) time, where n is the number of vertices. 相似文献
290.
The dynamic behavior of thermodynamic system, described by one order parameter and one control parameter, in a small neighborhood of ordinary and bifurcation equilibrium values of the system parameters is studied. Using the general methods of investigating the branching (bifurcations) of solutions for nonlinear equations, we performed an exhaustive analysis of the order parameter dependences on the control parameter in a small vicinity of the equilibrium values of parameters, including the stability analysis of the equilibrium states, and the asymptotic behavior of the order parameter dependences on the control parameter (bifurcation diagrams). The peculiarities of the transition to an unstable state of the system are discussed, and the estimates of the transition time to the unstable state in the neighborhood of ordinary and bifurcation equilibrium values of parameters are given. The influence of an external field on the dynamic behavior of thermodynamic system is analyzed, and the peculiarities of the system dynamic behavior are discussed near the ordinary and bifurcation equilibrium values of parameters in the presence of external field. The dynamic process of magnetization of a ferromagnet is discussed by using the general methods of bifurcation and stability analysis presented in the paper. 相似文献