Oxygen evolution on electrodes of different roughness: an electrochemical noise study

Rough and porous Ni layers have been obtained by cathodic deposition from a NiCl₂, NH₄Cl solution, at high current density. Characterisation by SEM has shown that they consisted of micro-dendrites separated by pores with a typical diameter of 1 m. In addition, circular hollows (10–100 m in diameter) were found on the deposit surface; their density varied with the deposition current density and deposition charge. The surface roughness of the Ni deposits, measured by EIS, was found to increase roughly linearly with the deposition charge, and to be little dependent on current density, provided a threshold value was exceeded. The oxygen evolution reaction has been studied on these electrodes by simultaneous real-time measurements of potential and electrolyte resistance fluctuations. The analysis of the electrochemical noise indicated that the dimensions of oxygen bubbles detaching from the electrodes slightly increased with the deposit surface roughness. It is not clear, however, whether or not this increase was associated with the effect of the small (1 m) or the large (10–100 m) features on the electrode-bubble interactions.     

Reassessment of commercially available molecular weight standards for peptide sodium dodecyl sulfate-polyacrylamide gel electrophoresis using electroblotting and microsequencing

Myoglobin CNBr peptides, constituting the commercially available molecular weight calibration kits for sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were analyzed by microsequencing after electroblotting on polyvinylidene difluoride (Immobilon) membranes. An obvious disagreement was found between peptide identification and the data provided by the manufacturers. We observed 6 peptides from Mr 2500 to 17,000 corresponding, in increasing size order, to the 3 peptides resulting from the total CNBr digestion, to 2 incompletely cleaved peptides and to the intact myoglobin. Using a corrected calibration curve, a linear relationship was established from Mr 6000 to 43,000 and a second one for shorter peptides. This method of electrophoresis and electroblotting, easily adapted for peptides, is a powerful tool for peptide identification correlated with size determination. It is especially useful for CNBr-cleaved peptides.     

Optimized simultaneous determination of several elements in human intestinal Caco-2 TC7 cells by inductively coupled plasma-mass spectrometry after closed vessel microwave digestion

A rapid procedure, based on closed vessels microwave digestion and inductively coupled plasma-mass spectrometry (ICP-MS), was evaluated to ascertain the effect of chronic exposure to cadmium on intracellular accumulation of minor and essential trace elements in cultured epithelial cells (Caco-2 TC7). For all measurements, the method of external calibration was used and 3 elements (Be, Sc, In) were selected as internal standards. Optimization procedures are discussed and results are presented for the total determination of 9 key analytes (Na, Mg, Ca, Cr, Mn, Cu, Zn, Mo, and Cd) in certified reference materials (CRMs) and 20 samples of Caco-2 TC7 cells long-term exposed to Cd. The performance characteristics of the analytical system were evaluated by calibration and linearity, limits of detection and quantitation, accuracy with spiking, trueness and repeatability with available CRMs. As a complement to the ICP-MS determinations, both available CRMs and cell samples were analyzed either by electro thermal- or flame atomic absorption spectrometry. The results were in good agreement with the ICP-MS results.     

Sugars in the gas phase: The conformational properties of erythrose, threose, and erythrulose characterized by quantum chemistry calculations

The structural properties of the three open chain C₄H₈O₄ sugars, i.e. two aldoses (erythrose and threose) and one ketose (erythrulose), have been investigated by DFT and ab initio calculations to get accurate structures and relative energies. The structure of all the conformers predicted within 10 kJ/mol has been optimized at the B3LYP/6-311++G(d,p) level of the theory. Two types of intramolecular hydrogen bonds have been clearly identified. They are related to the hydroxyl and to the carbonyl oxygen atoms and are of weak and middle strength, respectively. The most stable structures have been optimized at the B3LYP/6-311++G(2df,p) and at the MP2/6-311++G(2df,p) levels of the theory in order to calculate accurate rotational parameters and dipole moment for their future detection in the microwave range in the gas phase. Their corresponding harmonic IR spectra have also been calculated and their fingerprint signature is discussed in the region of the OH stretching vibrations, of the torsion of the C–O bonds and of the deformation of the C–C skeleton.     

Development of a sensitive MEKC-LIF method for synthetic cathinones analysis

Synthetic cathinones are phenylalkylamine compounds related to natural cathinone from Catha edulis leaves. Due to their sympathomimetic effects comparable to common illicit drugs, these substances are mainly drugs of abuse and constitute the second most frequently seized group of new psychoactive substances. In order to ensure their regulation and to promote public health, reliable analytical tools are required to track these substances. In the present study, we developed a CE hyphenated to laser-induced fluorescence detection method to demonstrate its suitability to perform fast and cost-effective synthetic cathinones analysis. Fourteen compounds including isobaric compounds and position isomers were selected to encompass the large panel of chemical structures. To separate the FITC-labeled analytes (presenting the same negative charge and close mass to charge ratios), MEKC separation mode was selected. Method selectivity was not suitable using common surfactants. In this context, alkyl polyethylene glycol ether surfactants were successfully used as neutral surfactant to overcome this analytical challenge. The effect of surfactant nature on separation performances and migration behaviors of the analytes was also studied. Optimal BGE composition included 75 mM borate buffer at pH 9.3 and 0.4 mM of C12E10 surfactant. Final MEKC separation conditions were proposed to analyze a large panel of synthetic cathinones. This method helped to reach a sensitivity with LOD from 0.1 to 0.4 nM (pg/mL order).     

Maytansinol Derivatives: Side Reactions as a Chance for New Tubulin Binders

Maytansinol is a valuable precursor for the preparation of maytansine derivatives (known as maytansinoids). Inspired by the intriguing structure of the macrocycle and the success in targeted cancer therapy of the derivatives, we explored the maytansinol acylation reaction. As a result, we were able to obtain a series of derivatives with novel modifications of the maytansine scaffold. We characterized these molecules by docking studies, by a comprehensive biochemical evaluation, and by determination of their crystal structures in complex with tubulin. The results shed further light on the intriguing chemical behavior of maytansinoids and confirm the relevance of this peculiar scaffold in the scenario of tubulin binders.     

High selectivities in electrophilic additions to cyclobutene compounds

Epoxidation of 2, 3, 4 with m-CPBA mainly led to the cis-attack products whereas 1 and 6 led to the other selectivity. The result was reversed, from 4, with Payne's reagent. Bromohydroxylation of 4 involved an intermediate bromonium ion syn to the substituents. Haloselenylations occurred with the syn-selectivity from 1, 2, 3 and 4, to the anti-selectivity from 6, and without selectivity from 5. NOE enhancement measurements and several chemical correlations led to the stereochemical assignments. Formation of the intramolecular reaction products 24 and 25 was also pointed out.     

Synthesis of new acyclonucleosides comprising unexpected regioisomers in the case of purines

Acyclonucleosides 4 have been obtained by a short way starting from ethyl 2-hydroxymethyl acrylate 5. The key intermediate was acetate 9. Its reaction with free or protected nucleic bases gave either the expected compounds or unusual regioisomers.     

Laser optogalvanic spectroscopy of N2 from the AΣu metastable state in a corona excited supersonic expansion

A hollow cathode combined with a corona excited supersonic expansion has proven to be an efficient method of producing a stable discharge in a N₂/Ar gas mixture. A high-resolution and rotationally cold absorption spectrum of the well-known (2,0) and (8,7) bands of the B³Π_g ← A³Σ_u⁺ first positive system of N₂ was recorded. It illustrates the sensitivity of the laser optogalvanic detection technique coupled to such an apparatus. A significant reduction of the linewidth and an enhancement of the signal-to-noise ratio were obtained. A high variational excitation process has been observed and is discussed.