Investigation of design parameters in ultrasound reactors with confined channels

This paper presents a three-dimensional numercial simulation of sonochemical degradation upon cavitational activity. The model relates the simulation of the acoustic pressure distribution to the sonochemical reaction rate. As a case study, the thermal degradation of carbon tetrachloride during sonication is studied in a tubular milliscale reactor. The model is used to optimize the reactor diameter, ultrasound frequency and power dissipated to the ultrasound transducers. The results indicate that multiple transducers at a moderate power level are more efficient than one transducer with high power level. Furthermore, the average cavity volume fraction is proposed as a reaction independent parameter to estimate the optimal reactor design. Within the results obtained in this paper, it appears possible to optimise reactor design based on this parameter.     

Characterisation of Ba2In2 − x Sn x O5 + x/2 oxide ion conductors

The Ba₂In_2 − x Sn _x O_5 + x/2 solid solution was confirmed up to x = 1 by solid-state reaction. X-ray diffraction at room and at elevated temperatures, Raman scattering and impedance spectroscopy were used to characterise the samples. The structure refinement of the composition x = 0.1 from neutron diffraction data reveals that tin is preferentially located in the tetrahedral layers of the brownmillerite. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007     

Improvements in cobalt determination by thermospray flame furnace atomic absorption spectrometry using an on-line derivatization strategy

An on-line derivatization strategy was developed for improving cobalt sensitivity using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) as the analytical technique. This strategy involves the generation of a volatile cobalt compound, providing better sample vaporization efficiency. The effect of sodium diethyldithiocarbamate (DDTC) as complexing agent on the integrated absorbance signal was evaluated. Parameters including the pH of complex formation, complex concentration and volume, sample volume, flame gas composition and tube atomization configuration were optimized. A wide linear range (from 23 microg L(-1) to 3 mg L(-1); r(2)=0.9786) was obtained, with the best one (r(2)=0.9992) attained from 23 to 400 microg L(-1) with a sample throughput of 30 h(-1). The improvement in the detection power was 17-fold when compared to FAAS, which provides 7 microg L(-1) as the limit of detection when considered TS-FF-AAS technique. A relative standard deviation (n=10) of 4% for a cobalt solution containing 50 microg L(-1) was attained, and the accuracy of the procedure was evaluated through certified reference materials (IAEA-SL-1, lake sediment; and ISS-MURST-A1, Antarctic marine sediment). Good agreement between the results at the 95% confidence level was observed.     

Docking to heme proteins

In silico screening has become a valuable tool in drug design, but some drug targets represent real challenges for docking algorithms. This is especially true for metalloproteins, whose interactions with ligands are difficult to parametrize. Our docking algorithm, EADock, is based on the CHARMM force field, which assures a physically sound scoring function and a good transferability to a wide range of systems, but also exhibits difficulties in case of some metalloproteins. Here, we consider the therapeutically important case of heme proteins featuring an iron core at the active site. Using a standard docking protocol, where the iron–ligand interaction is underestimated, we obtained a success rate of 28% for a test set of 50 heme‐containing complexes with iron‐ligand contact. By introducing Morse‐like metal binding potentials (MMBP), which are fitted to reproduce density functional theory calculations, we are able to increase the success rate to 62%. The remaining failures are mainly due to specific ligand–water interactions in the X‐ray structures. Testing of the MMBP on a second data set of non iron binders (14 cases) demonstrates that they do not introduce a spurious bias towards metal binding, which suggests that they may reliably be used also for cross‐docking studies. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Advances in femto-nano-optics: ultrafast nonlinearity of metal nanoparticles

With the recent advances of experimental techniques, the nonlinear ultrafast optical response of metal nano-objects can now be investigated both on ensembles and on single nanoparticles. Its connection with the metal electronic and lattice kinetics is studied on the basis of a model describing the wavelength and time-dependent modifications of the object material dielectric function. Its application is illustrated in the case of single silver nanospheres and gold nanorods, as well as on ensembles of noble metal nanoparticles and metal-semiconductor nano-hybrids. This quantitative analysis also permits to elucidate the physical mechanisms at the origin of ultrafast nonlinearities in confined metals at different timescales.     

Discriminating factors affecting incorporation: comparison of the fate of Eu3+-Cm3+ in the Sr carbonate-sulfate system

The aim of this work is to assess the effect of ligand strength, symmetry, and coordination number on solid solution formation of trivalent actinides and lanthanides in carbonate and sulfate minerals. This is of particular importance in radionuclide migration where trivalent actinides such as Pu, Am, and Cm are responsible for the majority of radiotoxicity after 1000 years. Time-resolved laser fluorescence spectroscopy was used to study trace concentrations of the dopant ion after interaction with the mineral phase. This study expands on previous work with aragonite and gypsum where it was found that aragonite incorporates Eu(3+) and Cm(3+) while only surface sorption is observed in gypsum. This study uses isostructural minerals strontianite (SrCO(3)) and celestite (SrSO(4)) to decouple the effect of structure from that due to the anion. It is demonstrated that while distribution coefficients can predict the amount of dopant ion associated with the mineral phase, they do not have any correlation with solid solution formation. This substitution mechanism is most likely dictated by the symmetry of the site being substituted and the electronic structure of the dopant atom.     

Tailoring metal-organic framework catalysts by click chemistry

We successively introduce new catalytic centers through click reaction into MOFs and modify their environment by addition of lipophilic groups. The resulting bifunctionalized MOF provides an optimized balance between basicity and lipophilicity and shows outstanding performance for the transesterification reaction.     

Synthesis of protected 2-pyrrolylalanine for Peptide chemistry and examination of its influence on prolyl amide isomer equilibrium

Protected enantiopure 2-pyrrolylalanine was synthesized for application in peptide science as an electron-rich arylalanine (histidine) analog with π-donor capability. (2S)-N-(Boc)-N'-(Phenylsulfonyl)-, (2S)-N,N'-bis-(phenylsulfonyl)-, and (2S)-N,N'-bis-(Boc)-3-(2-pyrrolyl)alanines (10, 3, and 14, respectively) were made in 13-17% overall yields and six to seven steps from oxazolidine β-methyl ester 4. Homoallylic ketone 5 was prepared by a copper-catalyzed cascade addition of vinylmagnesium bromide to ester 4 and converted to pyrrolyl amino alcohol 7 by olefin oxidation and Paal-Knorr condensation. Protecting group shuffle and oxidation of the primary alcohol enabled the synthesis of pyrrolylalanines. The bis-Boc analog 14 proved useful in peptide chemistry and was employed to make N-acetyl-pyrrolylalaninyl-proline N'-methylamide 25. A study of the influence of the pyrrole moiety on the prolyl amide isomer equilibrium of 25 using (1)H NMR spectroscopy in chloroform, DMSO, and water demonstrated that the pyrrolylalanine peptide exhibited behavior and conformations different from those of other arylalanine analogs.     

Techniques for generating centimetric drops in microgravity and application to cavitation studies

This paper describes the techniques and physical parameters used to produce stable centimetric water drops in microgravity, and to study single cavitation bubbles inside such drops (Parabolic Flight Campaigns, European Space Agency ESA). While the main scientific results have been presented in a previous paper, we shall herein provide the necessary technical background, with potential applications to other experiments. First, we present an original method to produce and capture large stable drops in microgravity. This technique succeeded in generating quasi-spherical water drops with volumes up to 8 ml, despite the residual g-jitter. We find that the equilibrium of the drops is essentially dictated by the ratio between the drop volume and the contact surface used to capture the drop, and formulate a simple stability criterion. In a second part, we present a setup for creating and studying single cavitation bubbles inside those drops. In addition, we analyze the influence of the bubble size and position on the drop behaviour after collapse, i.e., jets and surface perturbations.