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71.
An improved, isomer-free synthesis of Tetrahydrometinoxocrinine () is described. 相似文献
72.
Figliozzi P Sun L Jiang Y Matlis N Mattern B Downer MC Withrow SP White CW Mochán WL Mendoza BS 《Physical review letters》2005,94(4):047401
Optical second-harmonic generation (SHG) is used as a noninvasive probe of the interfaces of Si nanocrystals (NCs) embedded uniformly in an SiO2 matrix. Measurements of the generated SH mode verify that the second-harmonic polarization has a nonlocal dipole form proportional to (E x Delta inverted) E that depends on inhomogeneities in the incident field E, as proposed in recent models based on a locally noncentrosymmetric dipolar response averaged over the spherical NC interfaces. A two-beam SHG geometry is found to enhance this polarization greatly compared to single-beam SHG, yielding strong signals useful for scanning, spectroscopy, and real-time monitoring. This configuration provides a general strategy for enhancing the second-order nonlinear response of centrosymmetric samples, as demonstrated here for both Si nanocomposites and their glass substrates. 相似文献
73.
P.?SantiagoEmail author J.A.?Ascencio D.?Mendoza M.?Pérez-Alvarez A.?Espinosa C.?Reza-SanGermán P.?Schabes-Retchkiman G.A.?Camacho-Bragado M.?José-Yacamán 《Applied Physics A: Materials Science & Processing》2004,78(4):513-518
In the present work we report the synthesis of MoS2 nanotubes with diameters greater than 10 nm using a template method. The length and properties of these nanotubes are a direct result of the preparation method. High-resolution transmission electron microscopy is used to study the structure of these highly curved entities. Molecular dynamics simulations of MoS2 nanotubes reveal that one of the stable forms of the nanotubes is a twisted one. The twisting of the nanotubes produces a characteristic contrast in the images, which is also studied using simulation methods. The analysis of the local contrast close to the perpendicular orientation shows geometrical arrays of dots in domain-like structures, which are demonstrated to be a product of the atomic overlapping of irregular curvatures in the nanotubes. The configuration of some of the experimentally obtained nanotubes is demonstrated to be twisted with a behavior suggesting partial plasticity. PACS 61.16.Bg; 79.60.Jv; 61.46.+w; 61.50.Ah 相似文献
74.
Duarte MF Martins F Fernandez MT Langley GJ Rodrigues P Barros MT Costa ML 《Rapid communications in mass spectrometry : RCM》2003,17(9):957-962
A series of derivatives of 2-azidoacetic acid and 2-azidoacetone were synthesized and their behaviour under electron ionization conditions was investigated. This paper reports the electron ionization fragmentation mechanisms for five aliphatic alpha-carbonyl azides, which were clarified by accurate mass measurements and B/E linked scans. The substituent influences the abundance and the nature of the ions resulting from the molecular ion fragmentation. 相似文献
75.
Kleij AW Souto B Pastor CJ Prados P de Mendoza J 《The Journal of organic chemistry》2003,68(22):8711-8714
The selective preparation and complete structural characterization of a small series of 1,2-anti-heterodisubstituted calix[4]arenes has been accomplished. These compounds were obtained in two steps from unsubstituted p-tert-butylcalix[4]arene by tribenzoylation and a subsequent one-pot, two-step sequence involving alkylation with simultaneous partial deacylation, resulting in heterodisubstituted calixarenes carrying an alkyl and an aroyl group. The monoalkyl-tribenzoyl intermediate, prior to in situ deprotection, could also be isolated. 相似文献
76.
Solladié N Walther ME Gross M Duarte TM Bourgogne C Nierengarten JF 《Chemical communications (Cambridge, England)》2003,(19):2412-2413
In addition to the ammonium-crown ether recognition, pi-stacking interactions between the C60 sphere and the porphyrin moiety have been evidenced in a supramolecular complex obtained from a porphyrin-crown ether conjugate and a fullerene derivative bearing an ammonium unit. 相似文献
77.
78.
do Nascimento Hederson Majela dos Santos Andressa Duarte Vitor Anthony Bittencourt Paulo Rodrigo Stival Radovanovic Eduardo Fávaro Silvia Luciana 《Cellulose (London, England)》2021,28(9):5477-5492
Cellulose - In this work lignocellulosic fibers were obtained from Yucca aloifolia L. leaves and their chemical, morphological, thermal and mechanical properties were studied. The fibers were... 相似文献
79.
Karla Calfumán María Jesus Aguirre Diego Villagra Claudia Yañez Carmen Arévalo Betty Matsuhiro Leonora Mendoza Mauricio Isaacs 《Journal of Solid State Electrochemistry》2010,14(6):1065-1072
In this work, the modification of a glassy carbon electrode with tetraruthenated porphyrins electrostatically assembled onto
a Nafion film, previously adsorbed on the electrode surface, is reported. This modified electrode was characterized by scanning
electron microscopy–energy-dispersive X-ray, Raman spectroscopy, UV-Vis spectroelectrochemistry, and cyclic voltammetry. The
Nafion film onto the glassy carbon electrode shows a smooth disposition; when the tetraruthenated porphyrin is incorporated
on the Nafion film, the complex is adsorbed in a homogeneous way. The modified electrode catalyzes HSO3− oxidation in water–ethanol solutions and shows an enhanced stability compared with the electrode modified with the dip coating
method. Rotating disk electrode experiments showed a kinetic limitation to the electron transfer controlled by charge propagation
in the film. I/E curves show a Tafel slope of 120 mV/decade corresponding to a first electron-transfer reaction, depending on the potential,
as the determining step. Spectroelectrochemical experiments demonstrated that Ru(II) is the active site for the electrocatalysis. 相似文献
80.
J. A. M. S. Duarte 《Zeitschrift für Physik B Condensed Matter》1990,80(2):299-304
A method for conversion of directed site animals to their bond counterparts is used to significantly extend the number of such configurations in 2, 3, 4 dimensions, obtain their loop partition and study the singularity structure (for both dominant and subdominant singularities) of the corresponding dilute polymer transitions. A special property of bond directed configurations (equivalence lence of loop and bond perimeter partition) is exploited to obtain longer susceptibility series in 3 and 4 dimensions and the gap exponent estimate is refined into the intervals TANOPartly funded by SBF 341 (Aachen-Julich-Koln) and Reitoria Uni. Porto (Project 1-87) 相似文献