Magnesium-Catalyzed Tandem Dehydrogenation-Dehydrocoupling: An Atom Economical Access to Alkynylboranes

Owing to the unusual reactivity of sterically hindered amine–borane complexes, a catalytic system based on magnesium salts was designed to perform a tandem dehydrogenation–dehydrocoupling between terminal alkynes and boranes. The reaction is providing pure alkynylboranes within few minutes at room temperature, with only two molecules of hydrogen as a byproduct.     

Rapid Assembly of Oligosaccharides: Total Synthesis of a Glycosylphosphatidylinositol Anchor of Trypanosoma brucei

Six building blocks, six reaction steps : The recently developed innovative methodology facilitated the convergent synthesis of the complex oligosaccharide core 1 (shown here with protecting groups) for the total synthesis of a glycosylphosphatidylinositol (GPI) anchor. The key factors are the tuning of the reactivity of the building blocks by using 1,2-diacetal protecting groups and the desymmetrization of glycerol and myo-inositol with a chiral bis(dihydropyran).     

Discrete spectrum of a model Schr?dinger operator on the half-plane with Neumann conditions

We study the eigenpairs of a model Schr?dinger operator with a quadratic potential and Neumann boundary conditions on a half-plane. The potential is degenerate in the sense that it reaches its minimum all along a line that makes the angle ?? with the boundary of the half-plane. We show that the first eigenfunctions satisfy localization properties related to the distance to the minimum line of the potential. We investigate the densification of the eigenvalues below the essential spectrum in the limit ?? ?? 0, and we prove a full asymptotic expansion for these eigenvalues and their associated eigenvectors. We conclude the paper by numerical experiments obtained by a finite element method. The numerical results confirm and enlighten the theoretical approach.     

Electrolytic Cell Design to Simulate the Electrochemical Skin Response

Small fiber peripheral neuropathy is an early complication of diabetes. Electric skin response to some stimulus, as electrochemical skin conductance ECS, is a promising route in the early follow‐up of such diseases. It is related to sweat gland innervations and their permeability to chlorides and protons; it is non‐invasive, quantitative and reproducible. In routine clinical use, it could allow to better adapt the treatments and improve the adhesion for preventing pathological progress, thus reducing colossal healthcare costs. To optimize the measurements and understand the electrochemical behavior of electrodes, an original electrolytic cell was designed in lab scale. Thereby, an electrolyte is chosen to mimic sweat composition. For achieving currents range of ESC in vivo measurements, the original idea was to play on electrolyte viscosity by adding sucrose. In this paper, the novel electrolytic lab cell is presented with its limiting kinetics processes. A model of chloride migration to the anode and global electric model dedicated to the cell are proposed. Cell parameters are thoroughly studied, e. g. the resistance, which is equivalent to the inverse of ESC, by exploiting the models and through in vitro experiments, with protocols focusing on reproducibility. This original approach establishes, inter alia, an important result: the resistance is accurately retrieved using linear voltammetry, whereas single voltage measurement fails notably and is, therefore, unsatisfactory.     

Image processing for the study of bedload transport of two-size spherical particles in a supercritical flow

Bedload sediment transport of two-size coarse spherical particle mixtures in a turbulent supercritical flow was analyzed with image and particle tracking velocimetry algorithms in a two-dimensional flume. The image processing procedure is entirely presented. Experimental results, including the size, the position, the trajectory, the state of movement (rest, rolling, and saltation), and the neighborhood configuration of each bead, were compared with a previous one-size experiment. Analysis of the solid discharge along the vertical displayed only one peak of rolling in the two-size bed, whereas three peaks of rolling appeared in the one-size case due to a larger collective motion. The same contrast is evidenced in spatio-temporal diagrams where the two-size mixtures are characterized by the predominance of saltation and a smaller number of transitions between rest and rolling. The segregation of fine particles in a bed formed by larger particles was analyzed taking into account the neighborhood configurations.     

Triplet excited fluoroquinolones as mediators for thymine cyclobutane dimer formation in DNA

A series of fluoroquinolones (FQs), including enoxacin (ENX), pefloxacin (PFX), norfloxacin (NFX), its N(4')-acetyl derivative (ANFX), ofloxacin (OFX), and rufloxacin (RFX) have been investigated to determine their potential as DNA photosensitizers via thymine cyclobutane dimer (T<>T) formation in DNA. At fluoroquinolone concentrations and light doses insufficient to produce direct single strand breaks, ENX, PFX, and NFX were able to produce T<>T dimers in DNA, revealed by enzymatic treatment with T4 endonuclease V. By contrast, ANFX, OFX, and RFX were inefficient in this assay. The absolute values of the triplet energies of ENX, PFX, NFX, ANFX, OFX, and RFX were estimated by means of laser flash photolysis, using flurbiprofen, 4-biphenylcarboxylic acid, and naproxen as energy acceptors. They were found to be 273, 269, 269, 265, 262, and 253 kJ/mol, respectively. Other triplet excited state properties of the FQs, including quantum yields and lifetimes, were also studied. All the results indicate that the threshold ET value required for a given compound to become a potential DNA photosensitizer via T<>T formation is in the range defined by the triplet energies of NFX and ANFX (265-269 kJ/mol). This provides the basis for an alert rule: any chemical (drugs, cosmetics, pesticides, etc.) with higher ET has to be considered with regard to its potential photogenotoxicity.     

An Analytical Model of Porosity–Permeability for Porous and Fractured Media

The classic Kozeny–Carman equation (KC) uses parameters that are empirically based or not readily measureable for predicting the permeability of unfractured porous media. Numerous published KC modifications share this disadvantage, which potentially limits the range of conditions under which the equations are applicable. It is not straightforward to formulate non-empirical general approaches due to the challenges of representing complex pore and fracture networks. Fractal-based expressions are increasingly popular in this regard, but have not yet been applied accurately and without empirical constants to estimating rock permeability. This study introduces a general non-empirical analytical KC-type expression for predicting matrix and fracture permeability during single-phase flow. It uses fractal methods to characterize geometric factors such as pore connectivity, non-uniform grain or crystal size distribution, pore arrangement, and fracture distribution in relation to pore distribution. Advances include (i) modification of the fractal approach used by Yu and coworkers for industrial applications to formulate KC-type expressions that are consistent with pore size observations on rocks. (ii) Consideration of cross-flow between pores that adhere to a fractal size distribution. (iii) Extension of the classic KC equation to fractured media absent empirical constants, a particular contribution of the study. Predictions based on the novel expression correspond well to measured matrix and fracture permeability data from natural sandstone and carbonate rocks, although the currently available dataset for fractures is sparse. The correspondence between model calculation results and matrix data is better than for existing models.     

Polysulfurated pyrene-cored dendrimers: luminescent and electrochromic properties

We have synthesized a novel class of dendrimers, consisting of a polysulfurated pyrene core with appended poly(thiophenylene) dendrons (PyG0, PyG1, and PyG2, see Scheme 1), which exhibit remarkable photophysical and redox properties. In dichloromethane or cyclohexane solution they show a strong, dendron-localized absorption band with a maximum at around 260 nm and a band in the visible region with a maximum at 435 nm, which can be assigned to the pyrene core strongly perturbed by the four sulfur substituents. The dendrimers exhibit a strong (Phi=0.6), short-lived (tau=2.5 ns) core-localized fluorescence band with maximum at approximately 460 nm in cyclohexane solution at 293 K. A strong fluorescence is also observed in dichloromethane solution at 293 K, in dichloromethane/chloroform rigid matrix at 77 K, and in the solid state (powder) at room temperature. The dendrimers undergo reversible chemical and electrochemical one-electron oxidation with formation of a strongly colored deep blue radical cation. A second, reversible one-electron oxidation is observed at more positive potential values. The photophysical and redox properties of the three dendrimers are finely tuned by the length of their branches. The strong blue fluorescence and the yellow to deep blue color change upon reversible one-electron oxidation can be exploited for optoelectronic devices.