Reduction electrochimique des derives carbonyles insatures : IX. Indanones et tetralones : electrolyses mixtes en presence d'electrophiles

It is shown that activated cyclic carbonyl compounds, such as tetralones and indanones, can behave in a particular manner when they are reduced in presence of electrophiles. Two classes of electrophiles were chosen : alkyl halides and carbon dioxide. The reactivity (alkylation and carboxylation) often depends on the nature of the activated ketone used as a substrate.     

Analysis of sub-ppb levels of Fe(II), Co(II), and Ni(II) by electrokinetic supercharging preconcentration, CZE separation, and in-capillary derivatization

The analysis of sub-ppb levels of Fe(II), Co(II), and Ni(II) in heat exchanger fluids of nuclear power plants is needed to monitor corrosion. A method involving preconcentration with electrokinetic supercharging (electrokinetic injection with transient ITP), CZE separation, and in-capillary derivatization with ortho-phenanthroline (o-Phe) for direct UV detection was thus developed. First, a multizone BGE was loaded into the capillary by successive hydrodynamic introduction of zones of (i) o-Phe-containing BGE, (ii) BGE for the zonal separation, and (iii) ammonium-based leading electrolyte. Metal cations were electrokinetically injected and stacked at the capillary inlet behind this last leading zone. Finally, a terminating electrolyte zone was hydrodynamically introduced. When a constant voltage was applied, metal ions kept on concentrating isotachophoretically, then separated in CZE mode, were complexed by migrating through an o-Phe zone, and finally detected by direct absorbance. To detect extremely thin peaks, it was attempted for the first time to focus the derivatization reagent by inducing a second transient ITP, before labeling analytes, already separated in CZE mode. With this arrangement, LODs were about 30 ppt in pure water. In heat exchanger fluid matrices containing 1000 ppm bore and 2 ppm lithium, only Fe(II) cation was detected among the three cations of interest at the 1 ppb level using the present method, and its LOD was about ten times higher, due to the lower loading rate during electrokinetic injection.     

Formation and Fragmentation of Protonated Molecules after Ionization of Amino Acid and Lactic Acid Clusters by Collision with Ions in the Gas Phase

Collisions between O³⁺ ions and neutral clusters of amino acids (alanine, valine and glycine) as well as lactic acid are performed in the gas phase, in order to investigate the effect of ionizing radiation on these biologically relevant molecular systems. All monomers and dimers are found to be predominantly protonated, and ab initio quantum–chemical calculations on model systems indicate that for amino acids, this is due to proton transfer within the clusters after ionization. For lactic acid, which has a lower proton affinity than amino acids, a significant non‐negligible amount of the radical cation monomer is observed. New fragment‐ion channels observed from clusters, as opposed to isolated molecules, are assigned to the statistical dissociation of protonated molecules formed upon ionization of the clusters. These new dissociation channels exhibit strong delayed fragmentation on the microsecond time scale, especially after multiple ionization.     

Potential of long chain ionic liquids for on-line sample concentration techniques: Application to micelle to solvent stacking

The performance of micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) was improved for anionic analytes using the long chain ionic liquid type cationic surfactant 1-dodecyl-3-methylimidazolium tetrafluoroborate (C₁₂-MIM-BF₄). The peak heights and corrected peak areas of the test profens and herbicides were enhanced up to 59 and 110-fold, respectively when compared to typical injection. These were up to 10 times better compared to the surfactant cetyltrimethyl ammonium bromide as MSS carrier. This performance was attributed to the properties of C₁₂-MIM-BF₄. MSS requires micelles in the sample for transport of bound analytes to a stacking boundary that contains an organic solvent for effective electrophoretic mobility reversal. The ionic liquid micelles provided better analyte transport properties that resulted from its hydrophobic and pi–pi interaction capabilities. The good solubility of the ionic liquid in high percentages of organic solvent also facilitated a more effective reversal of mobility. The LODs obtained for the test analytes were from 0.06 to 0.12 μg/mL. The linearity R² values in terms of peak height and corrected area were ≥0.99. The interday repeatabilities (%RSD, n = 10,) were 0.5–2.2% for retention time, 1.9–4.7% for corrected areas and 4.1–6.4% for peak heights.     

A Uniform Benchmark for Testing SsrA-Derived Degrons in the Escherichia coli ClpXP Degradation Pathway

The ssrA degron is commonly used in fusion proteins to control protein stability in bacteria or as an interaction module. These applications often rely on the modular activities of the ssrA tag in binding to the SspB adaptor and in engaging the ClpXP protease. However, a comparison of these activities for a substantial standard set of degron variants has not been conducted previously, which may hinder the development of new variants optimized exclusively for one application. Here, we strive to establish a benchmark that will facilitate the comparison of ssrA variants under uniform conditions. In our workflow, we included methods for expression and purification of ClpX, ClpP, SspB and eGFP-degrons, assays of ClpX ATPase activity, of eGFP-degron binding to SspB and for measuring eGFP-degron degradation in vitro and in vivo. Using uniform, precise and sensitive methods under the same conditions on a range of eGFP-degrons allowed us to determine subtle differences in their properties that can affect their potential applications. Our findings can serve as a reference and a resource for developing targeted protein degradation approaches.     

Electrochemical Synthesis and Characterisation of Alternating Tripyridyl–Dipyrrole Molecular Strands with Multiple Nitrogen‐Based Donor–Acceptor Binding Sites

Synthesis of alternating pyridine–pyrrole molecular strands composed of two electron‐rich pyrrole units (donors) sandwiched between three pyridinic cores (acceptors) is described. The envisioned strategy was a smooth electrosynthesis process involving ring contraction of corresponding tripyridyl–dipyridazine precursors. 2,6‐Bis[6‐(pyridazin‐3‐yl)]pyridine ligands 2 a – c bearing pyridine residues at the terminal positions were prepared in suitable quantities by a Negishi metal cross‐coupling procedure. The yields of heterocyclic coupling between 2‐pyridyl zinc bromide reagents 12 a – c and 2,6‐bis(6‐trifluoromethanesulfonylpyridazin‐3‐yl)pyridine increased from 68 to 95 % following introduction of electron‐donating methyl groups on the metallated halogenopyridine units. Favorable conditions for preparative electrochemical reduction of tripyridyl–dipyridazines 2 b , c were established in THF/acetate buffer (pH 4.6)/acetonitrile to give the targeted 2,6‐bis[5‐(pyridin‐2‐yl)pyrrol‐2‐yl]pyridines 1 b and 1 c in good yields. The absorption behavior of the donor–acceptor tripyridyl–dipyrrole ligands was evaluated and compared to theoretical calculations. Highly fluorescent properties of these chromophores were found (ν_em≈2×10⁴ cm^?1 in MeOH and CH₂Cl₂), and both pyrrolic ligands exhibit a remarkable quantum yield in CH₂Cl₂ (?_f=0.10). Structural studies in the solid state established the preferred cis conformation of the dipyrrolic ligands, which adopting a planar arrangement with an embedded molecule of water having a complexation energy exceeding 10 kcal mol^?1. The ability of the tripyridyl–dipyrrole to complex two copper(II) ions in a pentacoordinate square was investigated.     

Diffraction microtomography with sample rotation: influence of a missing apple core in the recorded frequency space

Diffraction microtomography in coherent light is foreseen as a promising technique to image transparent living samples in three dimensions without staining. Contrary to conventional microscopy with incoherent light, which gives morphological information only, diffraction microtomography makes it possible to obtain the complex optical refractive index of the observed sample by mapping a three-dimensional support in the spatial frequency domain. The technique can be implemented in two configurations, namely, by varying the sample illumination with a fixed sample or by rotating the sample using a fixed illumination. In the literature, only the former method was described in detail. In this report, we precisely derive the three-dimensional frequency support that can be mapped by the sample rotation configuration. We found that, within the first-order Born approximation, the volume of the frequency domain that can be mapped exhibits a missing part, the shape of which resembles that of an apple core. The projection of the diffracted waves in the frequency space onto the set of sphere caps covered by the sample rotation does not allow for a complete mapping of the frequency along the axis of rotation due to the finite radius of the sphere caps. We present simulations of the effects of this missing information on the reconstruction of ideal objects.      

Contribution to the research on cellulose diacetate as a solid state track detector

Abstract

While having a similar composition to Cellulose Triacetate, Cellulose Diacetate is a less sensible heavy ions detector. With a 0.9 N potash etching at 20°C, ions which have higher Z than Carbon are not recorded and the Etch Rate Ratio is about 1 to 2 for Cu and Kr ions. The study of the infrared absorption spectra shows a decrease of the v(O-H) band intensity at 3500 cm^?1 for CDA, when it increases for CTA.     

Invariant Mass Spectroscopy of 23O via the (p, p′) Reaction in Inverse Kinematics

The neutron-rich oxygen isotope ²³O has been investigated via proton inelastic scattering on a liquid hydrogen target at 63.5 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum. A sharp resonance state was observed at 42(5) keV above the neutron threshold. A comparison of the differential cross section leading to this state with a microscopic DWBA calculation allowed a J ^π assignment of 5/2⁺ for this state.