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41.
42.
M. P. Bccar Varela M. C. Caputo M. B. Ferraro P. Lazzeretti M. C. Mariani D. Rial 《International journal of quantum chemistry》2000,77(3):599-606
As gauge invariance of computed magnetic properties, usually partitioned into diamagnetic and paramagnetic terms, is not achieved within the algebraic approximation, unless ad hoc techniques are adopted, a general variational treatment is analyzed, attempting to minimize the term more difficult to evaluate accurately, i.e., the paramagnetic contribution to magnetic susceptibility, by means of a gauge transformation. It is shown that an absolute minimum in a variational sense cannot be determined a priori. However, a “local” minimum of the paramagnetic contribution to magnetic susceptibility can be arrived at by employing general gauge transformations of polynomial form. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 599–606, 2000 相似文献
43.
Dr. Damián Padín Prof. Jesús A. Varela Prof. Carlos Saá 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(33):7470-7478
Ruthenium vinyl carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-vinyl dihydrooxazines are preferentially obtained with the former, Z-vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η3-coordination mode of the ruthenium vinyl carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species. 相似文献
44.
L.S. Cavalcante A.Z. Simões M.R.M.C. Santos J.A. Varela 《Journal of solid state chemistry》2006,179(12):3739-3743
Ca(Zr0.05Ti0.95)O3 (CZT) thin films were grown on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates by the soft chemical method. The films were deposited from spin-coating technique and annealed at 928 K for 4 h under oxygen atmosphere. CZT films present orthorhombic structure with a crack free and granular microstructure. Atomic force microscopy and field-emission scanning electron microscopy showed that CZT present grains with about 47 nm and thickness about 450 nm. Dielectric constant and dielectric loss of the films was approximately 210 at 100 kHz and 0.032 at 1 MHz. The Au/CZT/Pt capacitor shows a hysteresis loop with remnant polarization of , and coercive field of 18 kV/cm, at an applied voltage of 6 V. The leakage current density was about at 3 V. Dielectric constant-voltage curve is located at zero bias field suggesting the absence of internal electric fields. 相似文献
45.
Franciele Maria Pelissari Paulo José do Amaral Sobral Florencia Cecilia Menegalli 《Cellulose (London, England)》2014,21(1):417-432
Cellulose nanofibers were isolated from banana peel using a combination of chemical treatments, such as alkaline treatment, bleaching, and acid hydrolysis. The suspensions of chemically treated fibers were then passed through a high-pressure homogenizer 3, 5, and 7 times, to investigate the effect of the number of passages on the properties of the resulting cellulose nanofibers. The cellulose nanofibers isolated in this study had a dry basis yield of 5.1 %. Transmission electron microscopy showed that all treatments effectively isolated banana fibers in the nanometer scale. The micrographs of the process steps used to isolate the nanofibers revealed gradual removal of amorphous components. Increasing number of passages in the homogenizer shortened the cellulose nanofibers while furnishing more stable aqueous suspensions with zeta potential values ranging from ?16.1 to ?44.1 mV. All the samples presented aspect ratio in the range of long nanofibers, hence being potentially applicable as reinforcing agents in composites. X-ray diffraction studies revealed that homogenized nanofiber suspensions were more crystalline than non-homogenized suspensions. Fourier transform infrared spectroscopy confirmed that alkaline treatment and bleaching removed most of the hemicellulose and lignin components present in the banana fibers. Thermal analyses revealed that the developed nanofibers exhibit enhanced thermal properties. In general, the nanoparticles isolated from the banana peel have potential application as reinforcing elements in a variety of polymer composite systems. 相似文献
46.
Dr. Graeme J. Stasiuk Dr. Florencia Minuzzi Dr. Myra Sae‐Heng Charlotte Rivas Dr. Hans‐Paul Juretschke Dr. Lorenzo Piemonti Dr. Peter R. Allegrini Dr. Didier Laurent Andrew R. Duckworth Prof. Andrew Beeby Prof. Guy A. Rutter Prof. Nicholas J. Long 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(13):5023-5033
Despite the contribution of changes in pancreatic β‐cell mass to the development of all forms of diabetes mellitus, few robust approaches currently exist to monitor these changes prospectively in vivo. Although magnetic‐resonance imaging (MRI) provides a potentially useful technique, targeting MRI‐active probes to the β cell has proved challenging. Zinc ions are highly concentrated in the secretory granule, but they are relatively less abundant in the exocrine pancreas and in other tissues. We have therefore developed functional dual‐modal probes based on transition‐metal chelates capable of binding zinc. The first of these, Gd ?1 , binds ZnII directly by means of an amidoquinoline moiety (AQA), thus causing a large ratiometric Stokes shift in the fluorescence from λem=410 to 500 nm with an increase in relaxivity from r1=4.2 up to 4.9 mM ?1 s?1. The probe is efficiently accumulated into secretory granules in β‐cell‐derived lines and isolated islets, but more poorly by non‐endocrine cells, and leads to a reduction in T1 in human islets. In vivo murine studies of Gd ?1 have shown accumulation of the probe in the pancreas with increased signal intensity over 140 minutes. 相似文献
47.
Perini Nickson Delmonde Marcelo V. F. Ranjan Chinmoy Varela Hamilton 《Journal of Solid State Electrochemistry》2020,24(8):1811-1818
Journal of Solid State Electrochemistry - The characteristics of the electrochemical oscillations that emerge along the catalytic oxidation of small organic molecules critically depend on the... 相似文献
48.
Metal‐Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons 下载免费PDF全文
Dr. Ana Sofia Varela Dr. Nastaran Ranjbar Sahraie Julian Steinberg Wen Ju Dr. Hyung‐Suk Oh Prof. Dr. Peter Strasser 《Angewandte Chemie (International ed. in English)》2015,54(37):10758-10762
This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon‐based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO2 to CO/H2 mixtures outperforming a low‐area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low‐cost, abundant electrocatalysts for synthetic fuel production from CO2. 相似文献
49.
A Simple,High‐Yield Synthesis of DNA Duplexes Containing a Covalent,Thermally Cleavable Interstrand Cross‐Link at a Defined Location 下载免费PDF全文
Jacqueline Gamboa Varela Prof. Kent S. Gates 《Angewandte Chemie (International ed. in English)》2015,54(26):7666-7669
Interstrand DNA–DNA cross‐links are highly toxic to cells because these lesions block the extraction of information from the genetic material. The pathways by which cells repair cross‐links are important, but not well understood. The preparation of chemically well‐defined cross‐linked DNA substrates represents a significant challenge in the study of cross‐link repair. Here a simple method is reported that employs “post‐synthetic” modifications of commercially available 2′‐deoxyoligonucleotides to install a single cross‐link in high yield at a specified location within a DNA duplex. The cross‐linking process exploits the formation of a hydrazone between a non‐natural N4‐amino‐2′‐deoxycytidine nucleobase and the aldehyde residue of an abasic site in duplex DNA. The resulting cross‐link is stable under physiological conditions, but can be readily dissociated and re‐formed through heating–cooling cycles. 相似文献
50.
L. C. R. Andrade M. J. M. de Almeida F. M. Fernandes Roleira C. L. Varela E. J. Tavares da Silva 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(9):o508-o510
The title compound, C19H29NO, is a C17‐oxime derivative of a potent aromatase inhibitor, which surprisingly has been found to have no inhibitory power. It crystallizes with two independent molecules in the asymmetric unit. C=N—O—H...N hydrogen bonds link pairs of molecules to form dimers almost parallel to the bc plane. Cohesion of the structure is also due to another three C—H...O hydrogen bonds directed along the a axis. This hydrogen‐bonding scheme can be correlated to the almost complete loss of inhibitory power of the title compound. 相似文献