Minimizing 18O/16O back‐exchange in the relative quantification of ribonucleic acids

The use of isotopically labeled endonuclease digestion products allows for the relative quantification of ribonucleic acids (RNAs). This approach utilizes ribonucleases such as RNase T1 to mediate the incorporation of ¹⁸O onto the 3′‐terminus of the endonuclease digestion product from a solution containing heavy water (H₂¹⁸O). The accuracy and precision of relative quantification are dependent on the efficiency of isotope incorporation and minimizing any possible ¹⁸O to ¹⁶O back‐exchange before or during mass spectral analysis. Here, we have investigated the stability of ¹⁸O‐labeled endonuclease digestion products to back‐exchange. In particular, the effects of pH, temperature and presence of RNase on the back‐exchange process were examined using matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). We have found that back‐exchange depends on the presence of the RNase—back‐exchange was not observed once the enzyme was removed from the sample. With RNase present, at all pH values examined (from acidic to basic pH), back‐exchange was detected at incubation above room temperature. The rates and extent of back‐exchange were similar at all pH values. In contrast, back‐exchange in the presence of RNase was found to be especially sensitive to incubation temperature—at temperatures below room temperature, minimal back‐exchange was detected. However, back‐exchange increased as the incubation temperature increased. Based on these findings, appropriate sample‐handling and sample storage conditions for isotopically labeled endonuclease digestion products have been identified, and these conditions should improve the accuracy and precision of results from the relative quantification of RNAs obtained by this approach. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of homocysteine on the physical structure and molecular mobility of elastin network in cultured arteries

The thermal and dielectric properties of the elastin network were investigated in arteries cultured with physiological and pathological concentrations of homocysteine, an aminoacid responsible of histological impairments in human arteries. The glass transition of this amorphous protein was investigated by Differential Scanning Calorimetry (DSC). To explore the molecular dynamics of the elastin network in the nanometer range, we used Thermally Stimulated Currents (TSC), a dielectric technique running at low frequency and measuring the dipolar reorientations in proteins subjected to a static electrical field. Combining TSC and DSC experiments with determination of the activation parameters of relaxation times reveals the molecular mobility of the proteins. The major differences in the relaxation behavior of elastin between arteries cultured with physiological and pathological concentrations of homocysteine are discussed.     

Electrical conductivity improvement of aeronautical carbon fiber reinforced polyepoxy composites by insertion of carbon nanotubes

An increase and homogenization of electrical conductivity is essential in epoxy carbon fiber laminar aeronautical composites. Dynamic conductivity measurements have shown a very poor transversal conductivity. Double wall carbon nanotubes have been introduced into the epoxy matrix to increase the electrical conductivity. The conductivity and the degree of dispersion of carbon nanotubes in epoxy matrix were evaluated. The epoxy matrix was filled with 0.4 wt.% of CNTs to establish the percolation threshold. A very low value of carbon nanotubes is crucial to maintain the mechanical properties and avoid an overload of the composite weight. The final carbon fiber aeronautical composite realized with the carbon nanotubes epoxy filled was studied. The conductivity measurements have shown a large increase of the transversal electrical conductivity. The percolative network has been established and scanning electron microscopy images confirm the presence of the carbon nanotube conductive pathway in the carbon fiber ply. The transversal bulk conductivity has been homogenized and improved to 10^? 1 S·m^? 1 for a carbon nanotubes loading near 0.12 wt.%.     

Voice gender differences and separation of simultaneous talkers in cochlear implant users with residual hearing

Perception of a target voice in the presence of a competing talker, of same or different gender as the target, was investigated in cochlear implant users, in implant-alone and bimodal (acoustic hearing in the non-implanted ear) conditions. Recordings of two male and two female talkers acted as targets and maskers, to investigate whether bimodal benefit increased for different compared to same gender target/maskers due to increased ability to perceive and utilize fundamental frequency and spectral-shape differences. In both listening conditions participants showed benefit of target/masker gender difference. There was an overall bimodal benefit, which was independent of target/masker gender difference.     

Surface, core, and structure modifications of phosphorus-containing dendrimers. Influence on the thermal stability

Three new series of phosphorus-containing dendrimers are described. Their solubility depends on the type of end groups they bear. Perfluoroalkyl chains give dendrimers soluble in chlorofluorocarbons, whereas guanidinium and pyridinium derivatives give water-soluble compounds. The thermal stability of these compounds, as well as of 19 other dendrimers of various generations, having various cores, or various end groups, or branching points is studied. The main feature of this study is that the internal structure of these dendrimers is thermally stable at least up to 376°C. The number of the generation has practically no influence, whereas the principal criterion influencing the thermal stability is the type of end groups. The water-soluble cationic dendrimers are the least stable, but even those are stable up to 225°C. For most of these dendrimers, an important percentage of mass (around 50%) is retained even at a temperature as high as 1000°C. In the best case, up to 70% of the initial mass is retained at 1000°C.     

Flame holding downstream from a co-flow injectorAccrochage d'une flamme en aval d'un injecteur co-courant

We present numerical results on the flame attachment in the downstream vicinity of the co-flow injector lip that separates the reactive fluids at injection. Two stability diagrams show the domains where the flame is anchored, blown off, or extinguished, in terms of separating plate thickness and injection velocities of both fluids. Different anchoring modes—stagnation point counter-flow holding or edge flame anchorage—are described, depending particularly on the plate rim thickness. To cite this article: C. Nicoli et al., C. R. Mecanique 334 (2006).     

Trivalent lanthanide interactions with a terdentate bis(dialkyltriazinyl)pyridine ligand studied by electrospray ionization mass spectrometry

The 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridines (DATPs) belong to a new family of extracting agents recently developed in the framework of nuclear fuel reprocessing. These molecules exhibit exceptional properties to separate actinides(III) from lanthanides(III) in nitric acid solutions. A previous work showed that electrospray ionization mass spectrometry (ESI-MS) is a reliable technique to provide solution data such as stoichiometries and conditional stability constants of various DATP complexes with europium and evidenced the unusual capability of DiPTP [bis(di-iso-propyltriazinyl)pyridine] ligand to form 1:3 complexes in nitric acid solution. This latter result is further investigated by considering DiPTP complexation features with the complete lanthanide family. As a starting point of the experimental procedure used for stability constant evaluation, the intensity distribution of ions detected by ESI-MS is studied for solutions containing Ln(NO(3))(3) in water/methanol (1:1 v/v) with the pH value set at 2.8 and 4.6 by HNO(3) additions. At pH 2.8, the nitrate anions are found to prevent lanthanides from processes occurring within the ion source: redox phenomena or gas-phase reactions with methanol which give species such as [Ln(MeO)(2)](+). Thus, the total intensity of MS signals from [Ln(NO(3))(2)(H(2)O)(p)(MeOH)(n)](+) ions is found proportional to the metal ion concentration. At pH 4.6, with lower nitrate concentration, the nature of the species identified on mass spectra depends on the electronic properties of the lanthanide elements. It is shown that Ln(III) complexation with DiPTP leads to the exclusive formation of 1:3 complexes with the whole lanthanide series which may be due not only to the hydrophobic exterior of the ligand but also to the unusual electronic density distribution in DATP ligands as compared with other aza-aromatic ligands. The conditional stability constants of the 1:3 lanthanide(III) complexes with DiPTP have been determined at pH 2.8 and are found to increase almost regularly from La (log beta(3)(app) = 11.7 +/- 0.1) to Lu (log beta(3)(app) = 16.7 +/- 0.8). Moreover, the kinetic stability of the gas-phase 1:3 complexes obtained by electrospray has been investigated by energy-resolved collision-induced dissociation and provides useful information on the bonding and structure.     

AlFe-pillared clay catalyst for phenol oxidation in water solution

Catalytic wet peroxide oxidation of phenol over AlFe-pillared montmorillonites, with different iron contents, was carried out at room temperature, in a glass batch reactor, under constant airflow and halogen lamp light. At lower concentration (0.5 mg phenol/100 cm³ water) a phenol conversion of 100% was achieved independently of the iron content in pillared clay catalyst. However, at higher phenol concentration (5.0 mg phenol/100 cm³ water) retardation of the catalyst activity was observed. This revised version was published online in June 2006 with corrections to the Cover Date.