Synthesis and radioprotective properties of pulvinic acid derivatives

A high-throughput screening method has highlighted the marked antioxidant activity of some pulvinic acid derivatives (PADs) towards oxidation of thymidine, under γ and UV irradiation, and Fenton-like conditions. Here, we report the synthesis of a series of new hydrophilic PADs and the evaluation of their radioprotective efficacy in cell culture. Using a cell-based fluorescent assay, we show that some of these compounds have a pronounced ability to prevent cell death caused by radiation and to allow the subsequent resumption of proliferation. Thus, PADs may be considered as a novel class of radioprotective agents.     

Rhodium‐Catalyzed Hydrogenation of Alkenes by Rhodium/Tris(fluoroalkoxy)phosphane Complexes in Fluorous Biphasic System

The reaction of [Ir(μ‐Cl)(COD)]₂ with various fluorous derivatives of triphenylphosphane containing a para‐, meta‐, or ortho‐(1H,1H‐perfluoroalkoxy)‐substituted fluorous phosphane P(C₆H₄‐ORf)₃ (Rf=CH₂C₇F₁₅, CH₂CH₂CH₂C₈F₁₇) and CO (1 atm) gives the corresponding trans‐[Ir(μ‐Cl)(CO){P(C₆H₄ORf)₃}₂]. The IR ν_CO values of these complexes give some information on the donor/acceptor properties of the phosphanes. These fluorous derivatives of triphenylphosphane, as well as a phosphane bearing two (1H,1H‐perfluoroalkyloxy) chains at the 3,5‐positions, were used in association with [Rh(μ‐Cl)(COD)]₂ or [Rh(COD)₂]PF₆ in the reduction of methyl cinnamate, 2‐cyclohexen‐1‐one, cinnamaldehyde, and methyl α‐acetamidocinnamate in a two‐phase system D‐100/ethanol under 1 bar hydrogen at room temperature. Some differences in catalytic activity were observed in the reduction of methyl cinnamate, the most active catalyst being the rhodium complex containing the phosphane with the p‐fluorous ponytail. Recycling of the fluorous catalyst was possible, particularly using the p‐substituted phosphane, where no significant loss of catalyst or activity was observed, and generally with very low leaching of rhodium or phosphane in the organic phase.     

Performance of a Single Ultrafine Particle Mass Spectrometer

We report on the performance of a rapid single particle mass spectrometer (RSMS-II), designed to obtain the size and composition of individual ultrafine particles. Particles are sized aerodynamically at the inlet using a dynamic focusing mechanism to transmit particles to the source region of a time-of-flight mass spectrometer. Since the target particles are too small to be detected optically, an excimer laser is pulsed at high frequency so that data are acquired only when a particle coincides with a laser pulse within the source region. The instrument is tested with sodium chloride and oleic acid particle standards of various sizes and the hit rate efficiency is monitored as the normalized number of particle hits per unit time. The hit rate efficiency depends on the particle flux through the active region of the laser beam, in addition to the particle size and composition, and may thus be used to determine the relative transmission efficiency and size selectivity of the inlet.     

A Technique for Rapid Estimation of the Charge Distribution of Submicron Aerosols under Atmospheric Conditions

A portable technique is presented for rapid estimation of the charge distribution of submicron aerosols under atmospheric conditions, using two Differential Mobility Analyzer (DMA) systems in parallel. Simultaneous measurement of the aerosol mobility and size distributions are made by using one DMA with a neutralizer and the other without. An estimate of the aerosol charge is obtained by a fitting procedure, in which the size distribution and an expression for the charge distribution are used to calculate the mobility distribution of the sample. The parameters in the theoretical charge distribution are varied iteratively until the calculated and measured mobility distributions match. Validation was undertaken with separate measurements of ion mobility and concentration used in the charging expression. Results are presented for ambient indoor air, unipolar ion production by an ionizer and downwind of a high-voltage overhead AC powerline.     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14–16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16–38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

A new protein folding algorithm based on hydrophobic compactness: Rigid Unconnected Secondary Structure Iterative Assembly (RUSSIA). I: Methodology

We present an algorithm that is able to propose compact modelsof protein 3D structures, only starting from the predictionof the nature and length of regular secondary structures. Helicesare modeled by cylinders and sheets by helicoid surfaces, allstrands of a sheet being considered as a single block. It meansthat relative topology of the strands inside one sheet is aprerequisite. Loops are only considered as constraints, givenby the maximal distance between their C extremities accordingto their sequence length. Unconnected regular secondary structuresare reduced to a single point, the center of their hydrophobicfaces. These centers are then repeatedly moved in order to obtaina compact hydrophobic core. To prevent secondary structuresfrom interpenetrating, a repulsive term is introduced in thefunction whose minimization leads to the compact structure.This RUSSIA (Rigid Unconnected Secondary Structure Assembly)algorithm has the advantage of relying on a small number ofvariables and therefore many initial conformations can be tested.Flexibility is produced in the following way: helices or sheetsare allowed to rotate around the direction leading to the centerof the model; residues in a sheet can slide along the main directionof the strand where they are embedded. RUSSIA is fast and simpleand it produces on a test set several neighbor good models withan r.m.s. to the native structures in the range 1.4–3.7Å. These models can be further treated by statisticalpotentials used in threading approaches in order to detect thebest candidate. The limits of the present method are the following:small proteins with few secondary structures are excluded; multidomain proteins must be split into several compact globulardomains from their sequences; sheets of more than five strandsand completely buried helices are not treated. In this firstpaper the algorithm is developed and in Part II, which follows,some applications are presented and the program is evaluated. Received July 25, 2003; revised October 25, 2003; accepted October 30, 2003     

Total fat analysis in milk- and soy-based infant formula powder by supercritical fluid extraction

A rapid method for the determination of total fat in infant formula powders using a commercially available supercritical fluid extraction (SFE) instrument was evaluated. The matrices examined were Standard Reference Material SRM 1846 Infant Formula (NIST) and commercial milk- and soybased infant formula powders. Method verification and validation were done by linear regression analysis using the Method of Standard Additions. A Data Quality Objectives (DQO) format was used to define and evaluate the performance characteristic parameters of the instrumental total fat analysis fy SFE. A peer validation study showed excellent agreement with the declared labeled percentage fat values and reproducibility among three participating laboratories. The laboratory relative SD (RSD _R %) is within Horwitz's limits of acceptability and the HORRAT ratio criteria at the level of the analyte analyzed. Linear regression analysis of all infant formula matrices spiked with added fat showed that the SFE instrument response was due only to the added analyte. By integrating the DQO process with a readily available certified reference material, along with reproducibility indicated by two outside collaborating laboratories, we established verification and validation of the accuracy of the data obtained by SFE.     

Vibration energy scavenging via piezoelectric bimorphs of optimized shapes

Compact autonomous power sources are one of the prerequisites for the development of wireless sensor networks. In this work vibration energy harvesting via piezoelectric resonant bimorph beams is studied. The available analytical approaches for the modeling of the coupled electromechanical behavior are critically evaluated and compared with a finite element (FEM) numerical model. The latter is applied to analyze thoroughly the stress and strain states, as well as to evaluate the resulting voltage and charge distributions in the piezoelectric layers. The aim of increasing the specific power generated per unit of scavenger volume is pursued by optimizing the shape of the scavengers. Two optimized trapezoidal configurations are hence identified and analyzed. An experimental set-up for the validation of the proposed numerical model and of the obtained optimized structures is developed. Results of a preliminary experimental assessment, confirming the improved performances of optimized scavengers, are finally given.     

Numerical Modeling of Electrode Degradation During Resistance Spot Welding Using CuCrZr Electrodes

Resistance spot welding is a technique widely used by the automotive industry to assemble thin steel sheets. The cyclic thermo-mechanical loading associated with the accumulation of weld spots progressively deteriorates the electrodes. This study addresses the development of a comprehensive multi-physical model that describes the sequential deterioration. Welding tests achieved on uncoated and Zn-coated steel sheets are analyzed. Finite element analysis is performed using an electrical-thermal-metallurgical model. A numerical experimental design is carried out to highlight the main process parameters and boundary conditions which affect electrode degradation.     

Fluidised bed gasification of a metallurgical coke with CO2/N2 Mixtures

The gasification of a metallurgical coke with CO₂/N₂ mixtures in a 0.1 m diameter fluidised bed has been studied over the temperature range 810–1050°C. The rate of gasification was found to be essentially kinetically controlled, with negligible influence of fluidisation parameters below 1000°C. A number of flow models were assessed. The plug flow model was found to be the simplest model which could predict the experimental results, giving similar results to the more complex two-phase flow model of Davidson and Harrison (1963). For the range of conditions studied, the simple nth order reaction model was used to determine a best value of the reaction order of 0.8. For this combination of flow and reaction models, an activation energy of 197 kJ/mol was deduced from the experiments, in agreement with packed bed results and literature data. Very simple models can be used to predict the experimental results within the range studied.