DNA Photosensitization by an “Insider”: Photophysics and Triplet Energy Transfer of 5‐Methyl‐2‐pyrimidone Deoxyribonucleoside

The main chromophore of (6‐4) photoproducts, namely, 5‐methyl‐2‐pyrimidone (Pyo), is an artificial noncanonical nucleobase. This chromophore has recently been reported as a potential photosensitizer that induces triplet damage in thymine DNA. In this study, we investigate the spectroscopic properties of the Pyo unit embedded in DNA by means of explicit solvent molecular‐dynamics simulations coupled to time‐dependent DFT and quantum‐mechanics/molecular‐mechanics techniques. Triplet‐state transfer from the Pyo to the thymine unit was monitored in B‐DNA by probing the propensity of this photoactive pyrimidine analogue to induce a Dexter‐type triplet photosensitization and subsequent DNA damage.     

Plate coating: influence of concentrated surfactants on the film thickness

We present a large range of experimental data concerning the influence of surfactants on the well-known Landau-Levich-Derjaguin experiment where a liquid film is generated by pulling a plate out of a bath. The thickness h of the film was measured as a function of the pulling velocity V for different kinds of surfactants (C(12)E(6), which is a nonionic surfactant, and DeTAB and DTAB, which are ionic) and at various concentrations near and above the critical micellar concentration (cmc). We report the thickening factor α = h/h(LLD), where h(LLD) is the film thickness obtained without a surfactant effect, i.e., as for a pure fluid but with the same viscosity and surface tension as the surfactant solution, over a wide range of capillary numbers (Ca = ηV/γ, with η being the surfactant solution viscosity and γ its surface tension) and identify three regimes: (i) at small Ca α is large due to confinement and surface elasticity (or Marangoni) effects, (ii) for increasing Ca there is an intermediate regime where α decreases as Ca increases, and (iii) at larger (but still small) Ca α is slightly higher than unity due to surface viscosity effects. In the case of nonionic surfactants, the second regime begins at a fixed Ca, independent of the surfactant concentration, while for ionic surfactants the transition depends on the concentration, which we suggest is probably due to the existence of an electrostatic barrier to surface adsorption. Control of the physical chemistry at the interface allowed us to elucidate the nature of the three regimes in terms of surface rheological properties.     

Analytical and Preparative Chiral Separation of β-Carboline Derivatives, LDL Oxidation Inhibitors, Using HPLC and CE Methodologies: Determination of Enantiomeric Purity

In the present study, baseline separation of the enantiomers of 16 β-carboline derivatives was successfully achieved using both capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) techniques in short run times (<15?min) and thus permit the determination of enantiomeric excess. In HPLC methodology, cellulose chiral stationary phase (Chiralcel OD-H) was used with a binary mobile phase constituted of n-hexane/ethanol 85/15 leading to a resolution factor of 12.6 in 15?min. Preparative HPLC allowed to obtain pure enantiomers of two compounds. In CE, chiral selectivity was developed with an in-capillary stacking strategy using anionic (highly sulfated-γ) cyclodextrins 5% (w/v) as chiral selectors and a 60?mM phosphate buffer (pH 2.5) resulting in a resolution of 10.26 in 14?min of analysis. The analytical characteristics of the two developed methods were studied in terms of repeatability, limits of detection and limits of quantification showing their suitability to be extended to all the other molecules.     

Improving the Selectivity of the Phosphoric Acid β-Elimination on a Biotinylated Phosphopeptide

This study aims at improving the MALDI-TOF detection of a phosphorylated peptide containing a cysteine residue by ??-elimination of H₃PO₄ hardly enriched by classical methods. The experimental conditions were optimized on this phosphopeptide (biot-pAdd) and its nonphosphorylated counterpart (biot-Add). The major side-reactions were H₂S elimination on the cysteine residues and H₂O elimination on the non phosphorylated serine residue of biot-Add. The former dilutes the MALDI-TOF signal for the desired species. The latter gives a product similar to what is obtained by H₃PO₄ elimination and should prompt to caution when working with a mixture between phosphorylated and non phosphorylated peptides. Modifications on the solvent, the reaction temperature and time, the nature, and concentration of the base were made. Major improvement of the selectivity of the reaction was observed in 30?% ACN, at room temperature for 4?h. However, these optimizations are specific to these sequences and should be performed anew for different peptides. The selectivity of the reaction towards H₃PO₄ elimination is improved, but the persistence of side-reactions renders a previous sample fractionation necessary. In these optimized conditions, the ionization enhancement is 3-fold and the detection limits for biot-pAdd are similar to biot-Add (100?fmol).     

Asymmetric addition of a nitrogen nucleophile to an enoate in the presence of a chiral phase‐transfer catalyst: A novel approach toward enantiomerically enriched protected β‐amino acids

A proof of concept for the asymmetric organocatalytic aza‐Michael addition reaction of nitrogen nucleophiles with simple and readily available alkyl enoates as acceptor molecules in the presence of a chiral phase‐transfer catalyst has been demonstrated. The desired enantiomerically enriched β‐amino acid derivatives were obtained in up to 86% yield and with enantioselectivities of up to 37% ee. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:202–209, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21004     

A new synthesis of N‐alkyl pyrazolidine‐3,5‐diones and tetrahydropyridazine‐3,6‐diones

N‐alkyl pyrazolidine‐3,5‐diones and tetrahydropyridazine‐3,6‐diones have been synthesized by a new method in a three‐step sequence from dialkyl malonates or succinates respectively.     

Molecular Bottle Brushes with Positioned Selenols: Extending the Toolbox of Oxidative Single Polymer Chain Folding with Conformation Analysis by Atomic Force Microscopy

A synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence-controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by ¹H NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The “grafting onto” approach is performed by using triazolinedione−diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non-folded brushes show typical worm-like structures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 154–162     

Solving Maxwell equations in 3D prismatic domains

In this Note, we introduce the Fourier Singular Complement Method, for solving Maxwell equations in a 3D prismatic domain. The numerical implementation of this method provides a continuous approximation of the electromagnetic field. It can be applied to the computation of propagating and evanescent modes in prismatic stub filters, thus generalizing 2D approaches. To cite this article: P. Ciarlet, Jr., et al., C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Mass spectrometric analysis of the interactions between CP12, a chloroplast protein, and metal ions: a possible regulatory role within a PRK/GAPDH/CP12 complex

The small chloroplast protein CP12 plays the role of a protein linker in the assembly process of a PRK/GAPDH/CP12 complex that is involved in CO2 assimilation in photosynthetic organisms. The redox state of CP12 regulates its role as a protein linker. Only the oxidized protein, with two disulfide bonds, is active in complex formation. Several observations indicating that CP12 might bind a metal ion led us to screen the binding of different metal ions on oxidized or reduced CP12 using non-covalent electrospray ionization mass spectrometry (ESI-MS) experiments. The oxidized protein bound specifically Cu2+ and Ni2+ (Kd of 26+/-1 microM and 11+/-1 microM, respectively); other cations such as Fe2+ and Zn2+ did not bind, while cations such as Cd2+ formed non-specific adducts to CP12. Similar results were obtained for metal ions on screening with the reduced CP12. Interestingly, the present results suggest that Cu2+ catalyzes the re-formation of the disulfide bonds of the reduced CP12, leading to recovery of the fully oxidized CP12 that is then able to bind a Cu2+ ion. Finally the high similarity between CP12 and copper chaperones from Arabidopsis thaliana, as judged by hydrophobic cluster analysis, provides additional evidence for the relevance of metal binding for the in vivo situation. The findings that CP12 is able to bind a metal ion, and that Cu2+ catalyzes the oxidation of the thiol groups of CP12, are new characteristics of this protein that may prove to be important in the regulation of the assembly process of the PRK/GAPDH/CP12 complex.