Obtaining 1‐heptene from 1‐heptyne semihydrogenation with an anchored rhodium complex on different supports as catalyst

The complex [RhCl(NH₂(CH₂)₁₂CH₃)₃] was tested for the semihydrogenation of 1‐heptyne in homogeneous and heterogeneous conditions. γ‐Al₂O₃ and two different commercial activated carbons (RX‐3 EXTRA and GF‐45) were used as supports. The results were, then, compared with those previously reported for the [PdCl₂(NH₂(CH₂)₁₂CH₃)₂] complex supported or unsupported, and with the results obtained with the classic Lindlar catalyst. The complex was characterised by FTIR and elemental analysis. The pure species and the supported one were also characterised by X‐ray photoelectron spectroscopy. Results determined by the latter technique suggest that the active species is the complex itself, which is stable under the reaction conditions. The supported rhodium tetra‐coordinated complex shows higher activity and selectivity than the same complex unsupported, and also than the classic Lindlar catalyst. Moreover, among the rhodium‐supported complexes the one immobilised on RX‐3 EXTRA has a better performance than that heterogenised on GF‐45, and this one has a better activity and selectivity than the γ‐Al₂O₃ anchored complex. Our results also show that under the same operational conditions (temperature, hydrogen pressure and metal/substrate weight ratio) the rhodium complex, unsupported or supported, has a better performance than the corresponding palladium complex. Copyright © 2004 Society of Chemical Industry     

Unit cell thick nanosheets of zeolite H-ZSM-5: Structure and activity

Nanosheets of zeolite H-ZSM-5 were synthesized and characterized by X-ray diffraction, transmission electron microscopy (TEM), N₂-physisorption, FT-IR spectroscopy, ²⁷Al and ²⁹Si MAS NMR spectroscopy in addition to catalytic testing in conversion of methanol to hydrocarbons (MTH). It was found that Rietveld analysis, involving anisotropic broadening parameters, gave average crystallite dimensions in good agreement with TEM images. The selectivities in MTH is intact in the mesoporous nanosheet H-ZSM-5 with the largest difference being a higher C₃/C₂ ratio compared to regular H-ZSM-5.     

SUPG and discontinuity-capturing methods for coupled fluid mechanics and electrochemical transport problems

Electrophoresis is the motion of charged particles relative to the surrounding liquid under the influence of an external electric field. This electrochemical transport process is used in many scientific and technological areas to separate chemical species. Modeling and simulation of electrophoretic transport enables a better understanding of the physicochemical processes developed during the electrophoretic separations and the optimization of various parameters of the electrophoresis devices and their performance. Electrophoretic transport is a multiphysics and multiscale problem. Mass transport, fluid mechanics, electric problems, and their interactions have to be solved in domains with length scales ranging from nanometers to centimeters. We use a finite element method for the computations. Without proper numerical stabilization, computation of coupled fluid mechanics, electrophoretic transport, and electric problems would suffer from spurious oscillations that are related to the high values of the local Péclet and Reynolds numbers and the nonzero divergence of the migration field. To overcome these computational challenges, we propose a stabilized finite element method based on the Streamline-Upwind/Petrov-Galerkin (SUPG) formulation and discontinuity-capturing techniques. To demonstrate the effectiveness of the stabilized formulation, we present test computations with 1D, 2D, and 3D electrophoretic transport problems of technological interest.     

In vitro evaluation of surface topographic changes and nickel release of lingual orthodontic archwires

The objective of the article is to study surface topographic changes and nickel release in lingual orthodontic archwires in vitro. Stainless steel (SS), nickel–titanium (NiTi) and copper–nickel–titanium (CuNiTi) lingual orthodontic archwires were studied using atomic absorption spectrometry for nickel release after immersion in a saline solution. Surface roughness changes were measured using atomic force microscopy. Differences between groups were analyzed using independent sample t-tests. Statistically significant changes in roughness were seen in all archwires except NiTi. Surface changes were most severe in the CuNiTi alloy. SS archwires released the highest amount of nickel. In conclusion, only roughness changes in CuNiTi archwires seemed to be clinically significant. The amount of nickel released for all archwires tested is below the levels known to cause cell damage.     

A Comparative Study of the 1-Hexene Hydroformylation Either Under Syngas Conditions or with Paraformaldehyde Catalyzed by Rhodium/Diphosphine Systems

In order to carry out a comparison, the hydroformylation of 1-hexene to their corresponding aldehydes (heptanal and 2-methyl-hexanal) was studied both under syngas conditions and with paraformaldehyde using the catalytic rhodium/diphosphine precatalysts; the catalytic systems were formed in situ by the addition of one or two equivalents of the corresponding diphosphine, Ph₂P(CH₂)_nPPh_2, n = 2 (dppe), 3 (dppp) and 4 (dppb), to the carbonyl complex Rh(acac)(CO)₂. For the hydroformylation reactions under syngas conditions, the more active systems were the ones containing one equivalent of the diphosphine, which produce trigonal bipyramidal species like RhH(CO)₂(diphos). The activity and selectivity of these systems strongly depend on the bite angle of the ligand: when the bite angle increases both parameters are higher (dppb > dppp > dppe). Contrary to these results, for the reaction with paraformaldehyde, the systems containing two equivalents of the diphosphine ligand, which produce the cationic square planar species [Rh (diphos)₂]⁺, were more active than those containing one equivalent; the reaction rate decreases with the enlargement of the carbon chain of the bridge between the two phosphorous atoms of the diphosphine (dppe > dppp > dppb). These results may be explained by a higher steric effect on the metal center, which probably produces a decreasing of the rate of the CH₂O oxidative addition reactions. For both reactions, these effects were explained through DFT calculations of the corresponding resting states.     

Liquid crystals ‘made of gold’

The simple linear coordination of gold(I) helps in the understanding of structure-property relationships in liquid crystals based on metal-containing molecules. This simple geometry also allows the preparation of materials showing a range of mesophases, based on both rod-like and disc-like molecules.     

Electrochemical insight into the mechanism of electron transport in biofilms of Geobacter sulfurreducens

Electroactive bacterial biofilms can be produced on a polarized electrode by forcing its use as the final electron acceptor for bacterial respiration. This strategy offers the researcher the unique possibility to control the respiration process with extreme precision. The production of current, the accumulation of charge and the conducting properties of electroactive biofilms has been interrogated in this work through very basic electrochemical techniques including chronopotentiometry, chronoamperometry and cyclic voltammetry. Presented results indicate that charge can be accumulated in the biofilm conductive network, that network conductivity does not represent a limit for current production and that both the steady state current and the amount of accumulated charge depend on the redox state of cytochromes wiring the cells to the electrode. A model of biofilm conduction is presented as well.     

Cell Lines as In Vitro Models for Drug Screening and Toxicity Studies

ABSTRACT

Cell culture is highly desirable, as it provides systems for ready, direct access and evaluation of tissues. The use of tissue culture is a valuable tool to study problems of clinical relevance, especially those related to diseases, screening, and studies of cell toxicity mechanisms. Ready access to the cells provides the possibility for easy studies of cellular mechanisms that may suggest new potential drug targets and, in the case of pathological-derived tissue, it has an interesting application in the evaluation of therapeutic agents that potentially may treat the dysfunction. However, special considerations must be addressed to establish stable in vitro function. In primary culture, these factors are primarily linked to greater demands of tissue to adequately survive and develop differentiated conditions in vitro. Additional requirements include the use of special substrates (collagen, laminin, extracellular matrix preparations, etc.), growth factors and soluble media supplements, some of which can be quite complex in their composition. These demands, along with difficulties in obtaining adequate tissue amounts, have prompted interest in developing immortalized cell lines which can provide unlimited tissue amounts. However, cell lines tend to exhibit problems in stability and/or viability, though they serve as a feasible alternative, especially regarding new potential applications in cell transplant therapy. In this regard, stem cells may also be a source for the generation of various cell types in vitro. This review will address aspects of cell culture system application, with focus on immortalized cell lines, in studying cell function and dysfunction with the primary aim being to identify cell targets for drug screening.