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411.
The interaction of Cd2+ with uracil,2-thiouracil,4-thiouracil and 2,4-dithiouracil have been investigated by the density functional theory(DFT) calculations.For uracil and 2,4-dithiouracil,where the two basic sites are the same,Cd2+ attachment to the heteroatom at position 4 is preferred.However,for the systems where both types of basic centers,a carbonyl and a thiocarbonyl groups,are present,Cd2+ association with sulfur is favorable.The enhanced stability of these enolic and thiol forms comes from Cd2+ interaction with two basic sites simultaneously,which thereby triggers a significant aromatization of the ring.More significantly,the Cd2+ binding energy with uracil and its thio-derivatives is larger than the tautomerization barriers connecting the diketo-like forms with the corresponding enolic-like tautomers.Consequently,when associated with Cd2+,all tautomers are energetically accessible and should be observed in the gas phase. 相似文献
412.
Martín Hernndez‐Jurez Veronica Salazar‐Pereda Itzia I. Padilla‐Martínez Efrn V. García‐Bez 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(12):m367-m369
In the title complex salt, [Ir(C5H4O)(C16H22N6)(CO)](CF3O3S), the IrIII centre adopts a distorted octahedral geometry with a facial coordination of the tris(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)methane ligand. The C—C distances of the iridacycle are in agreement with its iridacyclohexa‐2,5‐dien‐4‐one nature, which presents a nonsymmetric boat‐like conformation with the C—Ir—C vertex more bent than the C—C(=O)—C vertex. The supramolecular architecture is mainly directed by CO...CO and CO...π and Csp3—H...O interactions, the arrangement of which depends on the anion. 相似文献
413.
In Lamb waves inspection, an air-coupled transmitter transducer is oriented at a specific angle such that it generates a pure Lamb mode which propagates along the structure and interacts with any existing defects. For this inspection system, amplitude losses appears when small inclinations of the tested structure occurs. An important factor which affects directly these losses has been observed, it consists of the Lamb waves beam (LWB) deviation due to this bad alignment. In this work, a simple expression of LWB deviation has been deduced. This expression includes the test structure angle, phase velocity of generated Lamb mode, and the phase velocity of waves propagating in the coupled medium. A(0) Lamb mode is generated and detected in 1 mm thick aluminium plate sample using 1 MHz PZ27 piezoelectric transducers of 20 mm of diameter. Experimental LWB deviation angles are measured for different inclination angles of the test sample. A comparative study is released with theoretical results. For 1 degree of misalignment in the aluminium plate inclination, and transducers separation distance of 35 mm, LWB deviation angle is around 7 degrees and the amplitude is reduced by around 11%. Then, for a large separation distance, we must move the receiver transducer to detect the deviated LWB. It is shown that, for both theoretical and experimental studies, the LWB deviation and its measured amplitude are very sensitive to the alignment of the tested structure with respect to the transmitter-receiver transducers plane. In metal plates it is most satisfactory to use A(0) mode compared with S(0) mode since it is easy to excite and has a large amplitude and small deviation beam angles. 相似文献
414.
Singh SB Zink DL Huber J Genilloud O Salazar O Diez MT Basilio A Vicente F Byrne KM 《Organic letters》2006,8(24):5449-5452
Inhibition of protein synthesis is one of the validated and highly successful targets for inhibition of bacterial growth; this mechanism is a target of a large number of clinical drugs. Ribosomal protein S4, a primary protein, is a potential target for the discovery of antibacterial agents. We describe, using an antisense-sensitized rpsD Streptomyces aureus strain, the discovery and activity of lucensimycins A and B. [structure: see text]. 相似文献
415.
Claudia Bueno Paulina Pavez Ricardo Salazar María Victoria Encinas 《Photochemistry and photobiology》2010,86(1):39-46
The photophysics and photochemical properties of vitamin B6 constituents and analogs were studied as function of pH and solvent. The p K of the phenolic oxygen and the pyridine ring nitrogen depends on the electron donor-acceptor ability of the 4-substituent, and agrees with the calculated proton affinity. For all studied compounds, the fluorescence properties showed that the phenolic oxygen is 8 units more acidic in the lowest singlet excited state than in the ground state. The pyridine N-atom is slightly more basic in the excited state. At pH of biological significance, pH 6–8, pyridoxamine and 4-pyridoxic acid are the more efficient chromophores with higher fluorescence yield and longer lifetime. Spectroscopic studies showed that the tautomeric equilibrium depends on the nature of the 4-substituent. The quenching of the singlet excited state of pyridoxamine and 4-pyridoxic acid by amino acids, free or in a peptide, and DNA bases at pH 7 was studied by time-resolved fluorescence techniques. The quenching rate constants are well correlated with the redox properties of the pyridoxinic compound and amino acids, and are related to the free energy change in the electron transfer process. Guanosine and pyrimidine bases also are efficient quenchers, involving an electron transfer reaction. 相似文献
416.
Miriam Martín Dr. Alejandro González Orive Prof. Pablo Lorenzo‐Luis Prof. Alberto Hernández Creus Prof. José Luis González‐Mora Dr. Pedro Salazar 《Chemphyschem》2014,15(17):3742-3752
Novel core‐shell quinone‐rich poly(dopamine)–magnetic nanoparticles (MNPs) were prepared by using an in situ polymerization method. Catechol groups were oxidized to quinone by using a thermal treatment. MNPs were characterized by using X‐ray diffraction, X‐ray photoelectron spectroscopy, atomic force microscopy, magnetic force microscopy, UV/Vis, Fourier‐transform infrared spectroscopy, and electrochemical techniques. The hybrid nanomaterial showed an average core diameter of 17 nm and a polymer‐film thickness of 2 nm. The core‐shell nanoparticles showed high reactivity and were used as solid supports for the covalent immobilization of glucose oxidase (Gox) through Schiff base formation and Michael addition. The amount of Gox immobilized onto the nanoparticle surface was almost twice that of the nonoxidized film. The resulting biofunctionalized MNPs were used to construct an amperometric biosensor for glucose. The enzyme biosensor has a sensitivity of 8.7 mA M ?1 cm?2, a low limit of detection (0.02 mM ), and high stability for 45 days. Finally, the biosensor was used to determine glucose in blood samples and was checked against a commercial glucometer. 相似文献
417.
Verónica Salazar Gloria Sánchez-Cabrera Julián Cruz Martín Hernández Celia Maya María J. Rosales-Hoz 《Journal of organometallic chemistry》2011,696(3):748-757
The thermally unstable adduct TpMe2Ir(C2H4)(DMAD), which was generated “in situ” by the reaction of DMAD with TpMe2Ir(C2H4)2 (1) at low temperature, reacted with different carboxylic acids to produce the following compounds: TpMe2Ir(E-C(CO2Me)CH(CO2Me))(H2O)(OC(O)C6H4R), (R = H, 2a; o-OH, 2b; o-Cl, 2c; m-Cl, 2d; o-NO2, 2e; m-NO2, 2f;o-Me, 2g;p-Me, 2h) and TpMe2Ir(E-C(CO2Me)CH(CO2Me))(H2O)(OC(O)Me) 3. In the reaction of derivative 2a with Lewis bases, TpMe2Ir(E-C(CO2Me)CH(CO2Me))(L)(OC(O)C6H5), (L = Py, 4a; m-Br-Py, 4b; m-Cl-Py, 4c; NCMe, 5) were obtained, of which 4b and 4c were isolated as a mixture of two isomers in which the substituted pyridine ring was present at different rotational orientations. All new compounds prepared were characterized by 1H and 13C{1H} NMR spectroscopy, the structure of compounds 2d, 2h and 4a being determined by X-ray diffraction analysis. DFT was used to analyze the relative stability and the structural orientation of the isomers. 相似文献
418.
M. I. Barrena J. M. Gómez de Salazar L. Pascual A. Soria 《Journal of Thermal Analysis and Calorimetry》2013,113(2):713-720
The effects of ageing treatment on phase transformations in Mg–Al alloy have been assessed. The techniques of scanning and transmission electron microscopy, microhardness and differential scanning calorimetric tests were used to characterize the materials obtained after application of artificial ageing. An ageing treatment at 175 °C causes the β-Mg17Al12 precipitation to become evenly distributed along the grain boundary and within the grain together with precipitation of the Al6Mn and the Τ-Mg32(Al,Zn)49 phases. The transformation processes are associated with increased hardness values. The hardness value increases with the ageing time and attains maximum value after 10 h of ageing time. The presence of the β-Mg17Al12 phase acts as an effective barrier to dislocation motion, thus improving the mechanical properties of the alloy. Analysing the DSC data it is found a shift of peak temperatures to higher temperatures with increasing heating rates, which suggests that the solid state reactions are thermally activated and kinetically controlled. The fraction and the rate of transformation, the transformation function and the kinetic parameters such as activation energy and frequency factor for the alloy in artificial ageing conditions were determined. 相似文献
419.
Lara P Paneque M Poveda ML Salazar V Santos LL Carmona E 《Journal of the American Chemical Society》2006,128(11):3512-3513
2,6-Dimethyl-substituted anisoles can be converted into the corresponding 2-ethyl-6-methylphenols in a several-step reaction mediated by a TpMe2Ir(III) complex; use of the 13C-enriched anisoles, ArO13CH3, shows that the 13C label distributes across the two ethyl sites with a preference for the terminal position. 相似文献
420.
Aamodt K Abelev B Abrahantes Quintana A Adamová D Adare AM Aggarwal MM Aglieri Rinella G Agocs AG Agostinelli A Aguilar Salazar S Ahammed Z Ahmad N Ahmad Masoodi A Ahn SU Akindinov A Aleksandrov D Alessandro B Alfaro Molina R Alici A Alkin A Almaráz Aviña E Alme J Alt T Altini V Altinpinar S Altsybeev I Andrei C Andronic A Anguelov V Anielski J Antičić T Antinori F Antonioli P Aphecetche L Appelshäuser H Arbor N Arcelli S Arend A Armesto N Arnaldi R Aronsson T Arsene IC Arslandok M Asryan A 《Physical review letters》2012,108(9):092301
The yield of charged particles associated with high-p(t) trigger particles (8
3 GeV/c on the away side drops to about 60% of that observed in pp collisions, while on the near side a moderate enhancement of 20%-30% is found. 相似文献