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21.
Casas JS Castaño MV García-Tasende MS Rodríguez-Castellón E Sánchez A Sanjuán LM Sordo J 《Dalton transactions (Cambridge, England : 2003)》2004,(13):2019-2026
Zinc(II) and cadmium(II) acetates were reacted in methanol under various experimental conditions with thiosemicarbazones derived from beta-keto amides or beta-keto esters (HTSC). Some of these reactions afforded thiosemicarbazonate complexes [M(TSC)2] with IR and NMR spectra compatible with N,S-coordination, but most gave complexes [ML2], where HL is a substituted 2,5-dihydro-5-oxo-1H-pyrazole-1-carbothioamide resulting from cyclization of the HTSC. Some of these pyrazolonates and two of the HL ligands were studied by X-ray diffractometry, and their structures are discussed. Surprisingly, the reactions of zinc(II) acetate with HTSC in 1:1 mol ratio usually gave a third, previously unreported type of complex with a dideprotonated ligand, [Zn(L-H)], which was also formed when [ZnL2] and Zn(OAc)2 interacted at room temperature in 1:1 mol ratio. These L-H complexes are highly insoluble in all common solvents, which hinders their characterization but suggests that they are polymeric in nature. 相似文献
22.
Fernando Castañeda Paul Silva M. Teresa Garland Ata Shirazi Clifford A. Bunton 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):2152-2168
The phosphonium ylidic diesters, methyl and ethyl isopropyl and, methyl and ethyl t-butyl triphenylphosphoranylidene malonates, 1a,b and 2a,b , respectively, have the syn-anti conformation in solution, as in the crystal, and the bulkier alkoxy group is oriented towards phosphorus. The 1 H NMR spectra show that in 1a,b , the isopropyl group is oriented towards the face of a phenyl group, consistent with π shielding in the 1 H signals, and examination of the 1 H coupled 13 C NMR spectra allows assignment of the acyl carbon signals. Computed bond lengths and angles for isolated molecules are similar to those in the crystal, and the geometry and the NMR spectra indicate extensive ylidic resonance. Estimated partial atomic charges on the ester oxygens are more negative when they are oriented towards, rather than away from, phosphorus. 相似文献
23.
Téllez CA Hollauer E Giannerini T da Silva MI Mondragón MA Rodríguez JR Castaño VM 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(8-9):2171-2180
Fourier transform infrared and Raman spectra of dimethylterephthalate (DMT), as microcrystalline powder, have been investigated. The vibrational spectra were calculated using the AM1 and PM3 semi empirical procedures, and the M?ller-Plesset (MP2/DZV), and the Becke-Lee, Yang and Parr gradient-corrected correlation functional: B3LYP/6-31G(d) ab initio calculations. On this basis, and assisted with the FT-IR and Raman spectra of the terephthalic acid, an assignment of the vibrational spectra of dimethylterephthalate was proposed. In the calculations, remarkable differences concerning the assignments of the vibrational spectra were noted between the AM1 and PM3 methods. Also, the ab initio procedure shows differences in interpreting the spectra compared with the semi empiric procedures, and among themselves. Calculated geometrical parameters were compared with the experimental values of dimethylterephthalate, diethylterephthalate and terephthalic acid. 相似文献
24.
Mínguez JM Castellote MI Vaquero JJ García-Navio JL Alvarez-Builla J Castaño O Andrés JL 《The Journal of organic chemistry》1996,61(14):4655-4665
A new synthesis of the pyrrolo[1,2-a]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on this heterocyclic system some of its basic chemistry was investigated and included electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1,2-a]pyrazines, pyrazolo[1,5-a]-pyrrolo[2,1-c]pyrazines, and heterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions are also reported. 相似文献
25.
Masashi Shiotsuki Atsushi Nakagawa Jesus Rodriguez Castañon Naoya Onishi Tatsurou Kobayashi Fumio Sanda Toshio Masuda 《Journal of polymer science. Part A, Polymer chemistry》2010,48(23):5549-5556
End‐functionalized poly(phenylacetylene)s were synthesized by the polymerization of phenylacetylene (PA) using the well‐defined palladium catalysts represented as [(dppf)PdBr(R)] {dppf = 1,1′‐bis(diphenylphosphino)ferrocene}. The Pd catalysts having a series of R groups such as o‐tolyl, mesityl, C(Ph)?CPh2, C6H4‐o‐CH2OH, C6H4‐p‐CN, and C6H4‐p‐NO2 in conjunction with silver triflate polymerized PA to give end‐functionalized poly(PA)s bearing the corresponding R groups in high yields. The results of IR and NMR spectroscopies and MALDI‐TOF mass analyses proved the introduction of these R groups at one end of each polymer chain. The poly(PA) bearing a hydroxy end group was applied as a macroinitiator to the synthesis of a block copolymer composed of poly(PA) and poly(β‐propiolactone) moieties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
26.
I. E. Castañeda J. G. Gonzalez-Rodriguez J. Colin M. A. Neri-Flores 《Journal of Solid State Electrochemistry》2010,14(7):1145-1152
An investigation about the corrosion resistance of Ni-Al-Fe intermetallic alloys in simulated human body fluid environments
has been carried out using electrochemical techniques. Tested alloys included 57 (wt%) Ni-(20 to 30) Al-(12 to 23) Fe using
the Hank's solution because the high corrosion resistance provided by protective Al2O3 external layer. For comparison, AISI 316L type stainless steel has also been used. Electrochemical techniques included potentiodynamic
polarization curves, electrochemical impedance spectroscopy, and electrochemical noise measurements. The different techniques
have shown that these alloys showed a similar or higher corrosion resistance than conventional AISI 316L type stainless steel,
and this corrosion resistance decreased as the Al content in the alloy increased. The alloys were susceptible to pitting type
of corrosion on the interdendritic Ni-rich phases. 相似文献
27.
V. Torres-Zúñiga O. G. Morales-Saavedra E. Rivera R. Castañeda-Guzmán J. G. Bañuelos R. Ortega-Martínez 《Journal of Sol-Gel Science and Technology》2010,56(1):7-18
SiO2-based bulk and film sol–gel hybrid materials were prepared with a family of novel liquid crystalline (LC) amphiphilic azo-dyes
bearing oligo(ethylene glycol) spacers (named here RED-PEG-n, n = 2, 3, 4, 6). The catalyst-free-sonogel route was implemented to produce optically active hybrid monoliths and spin-coated
films with these materials. Comprehensive morphological, thermal, photo-acoustic and spectroscopic sample characterizations
were performed in order to elucidate the physical properties of these novel compounds within the sonogel environment. Film
samples were also studied via the nonlinear optical (NLO) second harmonic generation (SHG)-Maker fringes technique. Results
show that the chromophores were homogeneously embedded within the highly pure SiO2-sonogel network, showing a clear thermotropic mesogenic behavior. The push–pull structure of the implemented azo-dyes allowed
effective electrically-induced monomeric alignment within the sonogel confinement; thus, stable quadratic NLO-SHG-activity
in the organic–inorganic film samples was achieved despite the lack of glass transition temperature (T
g
) of the guest LC-compounds. 相似文献
28.
A new graphite-epoxy composite electrode (GECE) containing Bi(NO(3))(3) as a built-in bismuth precursor for simultaneous and individual anodic stripping analysis of heavy trace metals like lead and cadmium is reported. The developed Bi(NO(3))(3)-GECE is compatible with bismuth film electrodes reported previously including the composite electrodes (Bi-GECE) recently reported by our group. Bi(NO(3))(3)-GECE displays the ability for the detection of both individual and simultaneous determination of heavy trace metals and exhibits well defined, reproducible and sharp stripping signals. The sensitive response is combined with the minimal toxicity of Bi(NO(3))(3). This novel sensor would be an appropriate alternative tool to sensors using bismuth in solution during their utilization in environmental quality monitoring as well as other applications. 相似文献
29.
Hernández FE Yu S García M Campiglia AD 《The journal of physical chemistry. B》2005,109(19):9499-9504
We present for the first time experimental evidence of fluorescence lifetime enhancement of organic chromophores attached to metal nanospheres via radiative decay engineering. The hybrid system (HS) was a modified "diconjugated" molecular probe, 4-acetamido-4'-maleimidylstilbene-2,2'-dithiol (AMDT), covalently bound to the surface of 5-nm-diameter Au nanospheres by its two sulfur atoms, at a distance d < 1 nm and with its molecular axis parallel to the surface of the nanoparticle surface. We measured a fluorescence lifetime increase of a factor of 2 at room temperature (tau(AMDT) = (4.32 +/- 0.10) ns and tau(HS) = (8.73 +/- 0.23) ns) and a factor of 3.4 at 4.2 K (tau(AMDT) = (2.64 +/- 0.07) ns and tau(HS) = (7.96 +/- 0.14) ns). We also found that the fluorescence quantum yield of this hybrid system is not reduced, proof of a weak energy transfer between the molecular probe and the nanoparticle. These results demonstrate that a molecular dipole oriented parallel to the metal surface tends to be reduced by the coupling with its image. 相似文献
30.