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301.
Thallium cation complexation by calix[4]tubes has been investigated by a combination of (205)Tl, (1)H NMR and ES MS demonstrating the solution formation of a dithallium complex in which the cations are held in the calix[4]arene cavities. In addition, the structure of the complex has been determined in the solid state revealing the cations to be held exclusively by pi-cation interactions. Furthermore, this crystal structure has been used as the basis for molecular dynamics simulations to confirm that binding of the smaller K(+) cation in the calix[4]tube cryptand like array occurs via the axial route featuring a pi-cation intermediate. 相似文献
302.
Adams H Amado AM Félix V Mann BE Antelo-Martinez J Newell M Ribeiro-Claro PJ Spey SE Thomas JA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(7):2031-2046
The synthesis of a series of RuII complexes incorporating thiacrown ligands ([12]ane-S4, [14]ane-S4, [16]ane-S4), as well as 2,2'-bipyridine (bpy) or pyridine, is reported. Structural studies on these complexes have been carried out using a variety of techniques. Detailed 1H NMR spectroscopic studies on the previously reported [Ru([12]ane-S4)(bpy)]2+ (1) reveal that-contrary to earlier reports-the observed fluxional 1H NMR behavior is not due to chemical exchange involving cleavage of the bpy Ru--N bond but is, in fact, due to lone-pair inversion of coordinated macrocyclic sulfur donor atoms. This phenomenon is also observed for the [14]ane-S4 and [16]ane-S4 analogues of 1. For the first time, using a combination of X-ray crystallography, more detailed 1H NMR experiments, and computational methods, an in-depth study on the energetics and dynamics of invertomer formation and conversion for macrocyclic coordination complexes has been carried out. These studies reveal that the steric constraints of assembling each sulfur macrocycle and bpy ligand around the octahedral Ru(II) center lead to close intramolecular contacts. These contacts are largely dependent on the orientation of the electron lone pairs of equatorial sulfur donor atoms and correlate with the comparative stability of the different invertomeric forms. Thus, the conformational preferences of the three macrocyles in [Ru([n]ane-S4)(bpy)]2+ complexes are determined by steric rather than electronic effects. 相似文献
303.
Webber PR Beer PD Chen GZ Felix V Drew MG 《Journal of the American Chemical Society》2003,125(19):5774-5785
A new class of redox-active ionophore comprised of two calix[4]diquinone moieties connected through either alkylene or pyridylene linkages has been developed. Spectroscopic and electrochemical investigations, X-ray crystal structure analyses, and molecular modeling studies show butylene- and propylene-linked members of this family of redox-active receptors exhibit remarkable selectivity preferences and substantial electrochemical recognition effects toward cesium and rubidium cations. 相似文献
304.
Leonardo S. G. Teixeira A. C. Spinola Costa Adriana S. Queiroz Adelaide M. M. Amorim Osvaldo N. Bomfim Sérgio L. C. Ferreira 《Mikrochimica acta》1998,129(1-2):103-106
The present work describes the use of 2-(2-thiazolylazo)-p-cresol (TAC) as a spectrophotometric reagent for vanadium determination. TAC reacts with vanadium(IV) in the presence of ascorbic acid, forming a red complex with absorption maximum at 525 nm. The following parameters were studied: complex stability, pH effect, amount of TAC, amount of acetate buffer, HEDTA effect, order of addition of reagents and Beer's law validity. TAC can be used for vanadium determination in the pH range 4.6–6.0, with molar absorptivity of 2.11 × 104Lmole–1 cm–1 (at525nm). Beer's law is obeyed up to 2.0 g mL–1. Many cation interferences can be easily eliminated by using HEDTA as a masking agent. Steel reference standards were used to test the proposed procedure and the accuracy and precision obtained were satisfactory. 相似文献
305.
Thermal analysis of the rice and by-products 总被引:2,自引:0,他引:2
J. A. Amorim S. A. Eliziário D. S. Gouveia A. S. M. Simőes J. C. O. Santos M. M. Conceiçăo A. G. Souza M. F. S. Trindade 《Journal of Thermal Analysis and Calorimetry》2004,75(2):393-399
The thermogravimetry (TG) is a technique used in the quality control of foods. In this work the moisture and ash contents
in the rice and by-products (bran and husk), the thermal stability and the gelatinization process by conventional, thermogravimetric
and calorimetric methods were studied. The moisture and ash contents obtained by TG and conventional methods did not present
significant differences. The rice presented higher starch content, while the bran presented higher protein content. The thermogravimetric
data presented the following thermal stability order: rice>bran>husk. The calorimetric curves indicated the gelatinization
of the starch. The kinetic parameters were compatible.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
306.
Bruna Botteon Della Coletta Thiago Borges Jacob Luana Aparecida de Carvalho Moreira Karina Torres Pomini Daniela Vieira Buchaim Rachel Gomes Eleutrio Eliana de Souza Bastos Mazuqueli Pereira Domingos Donizeti Roque Marcelie Priscila de Oliveira Rosso Joo Vitor Tadashi Cosin Shindo Marco Antnio Húngaro Duarte Murilo Priori Alcalde Rui Seabra Ferreira Júnior Benedito Barraviera Jefferson Aparecido Dias Jesus Carlos Andreo Rogrio Leone Buchaim 《Molecules (Basel, Switzerland)》2021,26(4)
The aim is to evaluate the effects of photobiomodulation therapy (PBMT) on the guided bone regeneration process (GBR) in defects in the calvaria of rats filled with biphasic calcium phosphate associated with fibrin biopolymer. Thirty male Wistar rats were randomly separated: BMG (n = 10), defects filled with biomaterial and covered by membrane; BFMG (n = 10), biomaterial and fibrin biopolymer covered by membrane; and BFMLG (n = 10), biomaterial and fibrin biopolymer covered by membrane and biostimulated with PBMT. The animals were euthanized at 14 and 42 days postoperatively. Microtomographically, in 42 days, there was more evident bone growth in the BFMLG, limited to the margins of the defect with permanence of the particles. Histomorphologically, an inflammatory infiltrate was observed, which regressed with the formation of mineralized bone tissue. In the quantification of bone tissue, all groups had a progressive increase in new bone tissue with a significant difference in which the BFMLG showed greater bone formation in both periods (10.12 ± 0.67 and 13.85 ± 0.54), followed by BFMG (7.35 ± 0.66 and 9.41 ± 0.84) and BMG (4.51 ± 0.44 and 7.11 ± 0.44). Picrosirius-red staining showed greater birefringence of collagen fibers in yellow-green color in the BFMLG, showing more advanced bone maturation. PBMT showed positive effects capable of improving and accelerating the guided bone regeneration process when associated with biphasic calcium phosphate and fibrin biopolymer. 相似文献
307.
The sulfate anion's templating role in catenane formation is demonstrated for the first time; a novel bis-pyridinium nicotinamide [2]catenane is prepared in a remarkable high yield and is shown to exhibit selectivity for sulfate, the templating anion. 相似文献
308.
Amorim R 《Physical review letters》2008,101(8):081602
Some consequences of promoting the object of noncommutativity theta(ij) to an operator in Hilbert space are explored. Its canonical conjugate momentum is also introduced. Consequently, a consistent algebra involving the enlarged set of canonical operators is obtained, which permits us to construct theories that are dynamically invariant under the action of the rotation group. In this framework it is also possible to give dynamics to the noncommutativity operator sector, resulting in new features. 相似文献
309.
Vitor M. Souza Daiki Koga Walter D. Gonzalez Flavia R. Cardoso 《Brazilian Journal of Physics》2017,47(4):447-459
Magnetic field reconnection has shown to be the dominant process in the solar wind-Earth’s magnetosphere interaction. It enables mass, momentum, and energy exchange between different plasma regimes, and it is regarded as an efficient plasma acceleration and heating mechanism. Reconnection has been observed to occur in laboratory plasmas, at planetary magnetospheres in our Solar System, and the Sun. In this work, we focus on analyzing the characteristics of magnetic reconnection at the Earth’s magnetosphere according to spaceborne observations in the vicinity of our planet. Firstly, the locations where magnetic field reconnection are expected to occur within the vast magnetospheric region are addressed, and is shown how they are influenced by changes in the interplanetary magnetic field direction. The main magnetic field and plasma signatures of magnetic reconnection are discussed from both theoretical and observational points of view. Spacecraft observations of ion inertial length scale reconnection are also presented. 相似文献