Voies d'accès à un analogue pyrannique de la puromycine

In a continuation of our studies with methyl 3-amino-3,4-dideoxypetopyranosides, two pyranic analogues of puromycin 3A and 3b have been synthesized by two routes starting from methyl 2,3-anhydro-4-deoxy-or D, L -erythro-pentopyranosides. In the first one, both amino group and erythro stereochemistry have been introduced before the introduction of the purine moiety; in the second one the introduction of the erythro stereochemistry and of the 3-butrigeb atom has, more advantageously, been performed in the same step using an intermediate (22) with a suitable conformation. The two diastereoisomerws 3A and 3B have been separated and, after assignment of absolute configuration and the heterocyclic studies, will permit and evaluation of the role plays played by the heterocyclic oxygen atom by comparison with previous studies on cyclohexyl puromycin analogues (Vince et al.).     

Metal–ligand bond strength determines the fate of organic ligands on the catalyst surface during the electrochemical CO2 reduction reaction

Colloidally synthesised nanocrystals (NCs) are increasingly utilised as catalysts to drive both thermal and electrocatalytic reactions. Their well-defined size and shape, controlled by organic ligands, are ideal to identify the parameters relevant to the activity, selectivity and stability in catalysis. However, the impact of the native surface ligands during catalysis still remains poorly understood, as does their fate. CuNCs are among the state-of-the-art catalysts for the electrochemical CO₂ reduction reaction (CO₂RR). In this work, we study CuNCs that are capped by different organic ligands to investigate their impact on the catalytic properties. We show that the latter desorb from the surface at a cathodic potential that depends on their binding strength with the metal surface, rather than their own electroreduction potentials. By monitoring the evolving surface chemistry in situ, we find that weakly bound ligands desorb very rapidly while strongly bound ligands impact the catalytic performance. This work provides a criterion to select labile ligands versus ligands that will persist on the surface, thus offering opportunity for interface design.

The metal–ligand binding strength is a key parameter in determining the role and fate of the surface ligands on nanoparticle catalysts during the electrochemical CO₂ reduction reaction.     

Interaction of microwaves with atmospheric pressure plasmas

In this paper, the interaction of microwaves with a plasma, generated at atmospheric pressure, is studied. The refractive index, attenuation index, skin depth, attenuation coefficient, phase coefficient, and reflectivity are investigated as functions of the plasma number density, the wave frequency and type of polarization, and the grazing angle. It is found that two frequency regimes characterize these type of plasmas. The first is a range where the phase velocity and attenuation of the wave both increase with frequency. The second is a frequency range in which the phase velocity and attenuation of the wave remain constant. It is also found that to have a shallow skin depth, the plasma number density has to be in the 10¹³ cm^–3 range. The reflectivity is found to be an increasing function of the number density. In horizontal polarization, the reflectivity is a decreasing function of the grazing angle. But in vertical polarization and for grazing angle less than 20°, the reflectivity has a maximum at a frequency , where f_pe is the electron plasma frequency and v is the collision frequency.     

Useful spectrokinetic methods for the investigation of photochromic and thermo-photochromic spiropyrans

This review reports on the main results of a set of kinetic elucidation methods developed by our team over the last few years. Formalisms, procedures and examples to solve all possible AB photochromic and thermophotochromic kinetics are presented. Also, discussions of the operating conditions, the continuous irradiation experiment, the spectrokinetic methods testing with numerical integration methods, and the identifiability/distinguishability problems, are included.     

Modeling membranes under a transmembrane potential

Accurate modeling of ion transport through synthetic and biological transmembrane channels has been so far a challenging problem. We introduce here a new method that allows one to study such transport under realistic biological conditions. We present results from molecular dynamics simulations of an ion channel formed by a peptide nanotube, embedded in a lipid bilayer, and subject to transmembrane potentials generated by asymmetric distributions of ions on both sides of the membrane. We show that the method is efficient for generating ionic currents and allows us to estimate the intrinsic conductance of the channel.     

Morphology control of poly(lactic) acid/polypropylene blend composite by using silanized cellulose fibers extracted from coir fibers

The objective of this work is the use of cellulose fibers extracted from coir fibers as Janus nanocylinders to suppress the phase retraction and coalescence in poly(lactic) acid/polypropylene bio-blend polymers via prompting the selective localization of cellulose fibers at the interface using chemical modification. The untreated and modified cellulose fibers extracted from coir fibers using a silane molecule (tetraethoxysilane) were used as reinforcement and as Janus nanocylinder at two weight contents (2.5 wt% and 5 wt%) to manipulate the morphology of the bio-blends. Their bio-composites with PLA-PP matrix were prepared via melt compounding (at PLA/PP: 50/50). The treatment effect on component interaction and the bio-composites properties have been studied via Scanning electron microscopy, infrared spectroscopy, and differential calorimetry analysis. The mechanical and rheological properties of nanocomposites were similarly assessed. Young's modulus and tensile strength of PLA-PP nanocomposites reinforced by silanized cellulose fibers show a great enhancement as compared to a neat matrix. In particular, there was a gain of 18.5% in Young's modulus and 11.21% in tensile strength for silanized cellulose fiber-based bio-blend composites at 5 wt%. From the rheological point of view, it was found that the silanized cellulose fibers in PLA-PP at both fibers loading enhances the adhesion between both polymers leading to tuning their morphology from sea-island to the continuous structures with the appearance of PLA microfibrillar inside of bio-composites. This change was reflected in the relaxation of the chain mobility of the bio-blend composites.

     

A convenient synthesis of linear pyridinoimidazo[1,2-a]pyridine and pyrroloimidazo[1,2-a]pyridine cores

Two new imidazo[1,2-a]pyridine derivatives, pyridinoimidazo[1,2-a]pyridine (10) and pyrroloimidazo[1,2-a]pyridine (16), were synthesised from 2-amino-4-methyl-5-nitropyridine (1) by linear cyclisation, making use of dimethylformamide dimethylacetal (DMFDMA) as an agent of vinylamine functionalisation. This report describes first the formation of pyridine and pyrroloimidazopyridine from (1), and then the formation of pyridine-fused and pyrrolo-fused pyridine by the Friedländer method and reductive cyclisation followed by treatment of the resulting adduct with chloroacetaldehyde.     

Energetics of ion transport in a peptide nanotube

Ion channels constitute an important family of integral membrane proteins responsible for the regulation of ion transport across the cell membrane. Yet, the underlying energetics of the permeation events and how the latter are modulated by the environment, specifically near the mouth of the pore, remain only partially characterized. Here, a synthetic membrane channel formed by cyclic peptides of alternated d- and l-hydrophobic alpha-amino acids was considered. The free energy delineating the translocation of a sodium ion was measured along the conduction pathway by means of molecular dynamics simulations. The free-energy profiles that underly the permeation of the open-ended tubular structure are shown to not only depend on the characteristics of the latter but also inherently on the location of the mouth of the synthetic channel with respect to the membrane surface.     

All-fiber acousto-optic polarization monitor

We describe the operational principle of and experimentally demonstrate a narrowband, wavelength-tunable polarization monitor based on a fiber acousto-optic tunable filter. Two orthogonally vibrating acoustic waves are used to create a variable polarizer that can be used to measure the state of polarization of an incident narrowband light source. The accuracy of the polarization monitor is measured at two different wavelengths in reference to a commercial polarimeter and is shown to be within 5%.