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41.
Almodóvar I Ramírez-Rodríguez O Barriga A Rezende MC Araya-Maturana R 《Rapid communications in mass spectrometry : RCM》2011,25(2):370-378
The fragmentation patterns of nine di-, tri- and tetracyclic hydroquinones with potential antitumor activity were rationalized by invoking competing mechanisms that included sterically accelerated homolytic cleavage, Meerwein-type rearrangements and dehydrations through elimination or intramolecular nucleophilic substitution. 相似文献
42.
Regiani T Santos VG Godoi MN Vaz BG Eberlin MN Coelho F 《Chemical communications (Cambridge, England)》2011,47(23):6593-6595
Solutions of aza-Morita-Baylis-Hillman (aza-MBH) reactions were directly monitored by ESI(+)-MS(/MS) spectrometry to obtain information on their mechanism. A unique bis-sulfonamide intermediate was intercepted and characterized and, based on this novel species, a mechanism that rationalizes the uniqueness of aza-MBH reactions is proposed. 相似文献
43.
Lovelle M Mach T Mahendran KR Weingart H Winterhalter M Gameiro P 《Physical chemistry chemical physics : PCCP》2011,13(4):1521-1530
Outer membrane channels in gram-negative bacteria are implicated in the influx of the latest generation of cephalosporins. We have measured the interaction strengths of ceftriaxone, cefpirome and ceftazidime in the two most abundant outer membrane porins of Escherichia coli, OmpF and OmpC, by both ion current fluctuations through single protein channels and fluorescence quenching. Statistical analysis of individual antibiotic entry events in membrane-incorporated porins yielded the kinetic rates and the equilibrium binding constant of each antibiotic-porin pair. Affinity constants were independently obtained by measuring the static quenching of inherent tryptophan fluorescence in the porins in the presence of the antibiotics. Through an empirical inner filter effect correction we have succeeded in measuring the chemical interaction of these strongly absorbing antibiotics, and obtained a qualitative agreement with conductance measurements. The interaction of all three antibiotics is smaller for OmpC than OmpF, and in the case of each porin the interaction strength series ceftriaxone > cefpirome > ceftazidime is maintained. 相似文献
44.
Schrekker HS Gelesky MA Stracke MP Schrekker CM Machado G Teixeira SR Rubim JC Dupont J 《Journal of colloid and interface science》2007,316(1):189-195
A surface-enhanced Raman spectroscopy (SERS) study of imidazolium ionic liquid stabilized gold(0) nanoparticles (GNPs) furnished previously unknown knowledge about the coordination and stabilization mode of the imidazolium cation. GNPs were prepared by hydrazine reduction of a chloroauric acid solution in 1-triethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate 2 as ether-functionalized room-temperature ionic liquid (RTIL). UV-vis spectroscopy showed the presence of GNP aggregates as absorptions extended to the NIR region. A parallel coordination mode for the imidazolium cation of RTIL 2 on the GNP surface was observed by SERS, which occurred without the simultaneous coordination of the 1-triethylene glycol monomethyl ether-functionality. Instead of this, the ether-functionality was directed away from the GNP surface and acted as steric barrier between the GNPs/GNP aggregates, thus preventing further aggregation. These new insights suggest that the imidazolium cation is responsible for electrosteric stabilization. 相似文献
45.
Jos Bonilla‐Cruz Tania Lara‐Ceniceros Enrique Saldívar‐Guerra Enrique Jimnez‐Regalado 《Macromolecular rapid communications》2007,28(13):1397-1403
A TEMPO bromide salt is used to functionalize a silica surface with nitroxyl moieties. The functionalization reaction takes place in 48 h under mild conditions. In a second step, grafts of styrene‐maleic anhydride copolymer are grown from the functionalized silica surface by heating it in the presence of the monomers. FT‐IR and TGA analysis show that the silica was first functionalized with nitroxide moieties, and then that grafts of styrene‐maleic anhydride grew from the functionalized silica surface. A reaction mechanism is proposed in order to explain the findings. The results suggest that the oxoaminium salts are good candidates for the functionalization and grafting of surfaces that contain hydroxy groups and for the generation of hybrid materials with improved properties.
46.
María Inés Flores‐Conde Fabiola N. de la Cruz Julio López J. Óscar C. Jiménez‐Halla Eduardo Peña‐Cabrera Marcos Flores‐Álamo Francisco Delgado Miguel A. Vázquez 《应用有机金属化学》2018,32(3)
The unprecedented reaction of ketone‐containing aromatic pyridinium salts 3a ‐ e and alkynyl Fischer complexes 1a ‐ f proceeds via a mild domino process to provide 4,6‐disubstituted pyran‐2‐ones 5a ‐ k and 2,3,5‐trisubstituted furans 6a ‐ h (45‐97%). According of the results of isotopic labeling experiments, a mechanism involving an initial Michael addition appears to be the key step, obtaining a mesomeric structure responsible for the formation of both products. 相似文献
47.
de Oliveira Elcio Cruz de Santana Maia Lúcio Abdala da Costa Lívio Garcia Lourenço Túlio Campos 《Accreditation and quality assurance》2018,23(6):365-369
Accreditation and Quality Assurance - In any commercial transaction, the presence of tolerances from specification limits is essential to ensure that the true value of the property of interest is... 相似文献
48.
Hiren Solanki Carlos Angulo-Preckler Kevin Calabro Navdeep Kaur Perrine Lasserre Bastien Cautain Mercedes de la Cruz Fernando Reyes Conxita Avila Olivier P. Thomas 《Tetrahedron letters》2018,59(36):3353-3356
Following ecological and chemical screenings, the Antarctic sponge Phorbas areolatus was chemically investigated for the first time. Three new suberitane derivatives named isosuberitenone B, 19-episuberitenone B, and isoxaspirosuberitenone were identified together with the known compounds suberitenones A and B, and oxaspirosuberitenone after a thorough inspection of their NMR data. These compounds were found to exhibit moderate cytotoxic activity and their presence in this sponge rules out their use as a chemotaxonomic marker for Suberites sponges. 相似文献
49.
Y. Leyet F. Guerrero J. Anglada-Rivera R. F. B. de Souza W. R. Brito L. Aguilera L. A. Pocrifka R. Peña-Garcia E. Padrón-Hernández J. de la Cruz Pérez 《Journal of Solid State Electrochemistry》2018,22(5):1315-1319
Na2Ti3O7 ceramic materials have been widely used in sodium-ion battery applications with relative good results; however, there are still several studies that might be carried out in the improvement of the Na2Ti3O7 properties and the overall batteries’ performance. In this direction, we used sonochemical method following a thermal treatment in order to synthetized pure phase Na2Ti3O7 nanopowders. X-ray diffraction characterization revealed that Na2Ti3O7 is the primary phase in nanopowders and ceramic sample; although, a high level of amorphization was observed in the sonicated nanopowder without heat treatment process. Nanopowder-prepared ceramic sample showed a crystallite size of 50 nm after sintering at 900 °C for 1 h. The specific surface area, pore volume, and pore size were obtained from the B.E.T. measurements, being 51 m2 g?1, 0.07 cm3 g?1, and 55 Å, respectively. The capacitance values of the nanopowder-prepared ceramic sample were in the order of microfarad. The total energy of the system was used to determine relaxation time of the sample (τ 0 = 31 ms). 相似文献
50.
Laíse Oliveira Resende Ana Cristina Honorato de Castro Adriano O. Andrade João Marcos Madurro Ana Graci Brito-Madurro 《Journal of Solid State Electrochemistry》2018,22(5):1365-1372
Epidemiological studies have demonstrated an association between the risk of cardiovascular events and increasing C-reactive protein (CRP) concentration. This paper reports the development of an immunosensor for the assessment of the cardiovascular process using anti-C-reactive protein antibody immobilized onto a gold-printed screen electrode. Positive and negative human sera were successfully evaluated using electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and atomic force microscopy (AFM). EIS results show that, after the incubation with positive serum for myocardial infarction, the resistance increased about two times in relation to the negative serum. A linear range from 6.25 to 50 μg mL?1 and detection limit of 0.78 μg mL?1 using DPV were obtained. The immunosensor developed for the CRP detection using gold electrode revealed efficacy and a potential use for the diagnosis and monitoring of the progression of cardiovascular diseases. 相似文献