Reaction Mechanisms of Transition-Metal-Catalyzed Azide-Alkyne Cycloaddition “Click” Reactions: A DFT Investigation

International audienceDFT calculations at the PBE0/LANL2DZ level have been performed on model compounds to investigate the reaction mechanism of two recently reported metal-catalyzed alkyne azide cycloaddition (MAAC). The first one, that involves a [Cu(tren)]+Br- catalyst, is shown not to proceed through a metal alkynyl intermediate, but, after precomplexation of the alkyne in an η2-mode, directly to the 1,4-disubstituted 1,2,3-triazole product, through a metallacyclic transition state. The other system, involving a rare-earth Ln[N(SiMe3)2]3 complex, is found to proceed through an alkynyl-azide complex which produces an η 2-coordinated heterocyclic ligand before protonation by an incoming alkyne molecule. Our results are discussed with respect to other computational data from the literatur

Click Metallodendrimers And Their Functions

Click chemistry involving copper-catalyzed azide-alkyne cycloaddition (CuAAC) is one of the most useful and powerful methods to construct metallodendrimers. The design of such strategies includes the choice of the copper(I) catalyst source which is critical in the case of the click synthesis of dendrimers. The 1,2,3-triazolyl-containing dendrimers that are produced provide useful intradendritic ligands that are active in supramolecular recognition and catalysis. This account dedicated to K. Peter C. Vollhardt summarizes work conducted mainly in the authors' Bordeaux laboratory. 1 Introduction 2 Click Copper Catalyzed Azide-Alkyne Cycloaddition Metallodendrimer Constructions 3 The Copper-Catalyzed Azide-Alkyne Cycloaddition Reactions in Dendrimers: Mind the Copper(I) Catalyst 4 Redox Recognition with Triazolylferrocenyl- and Triazolylbiferrocenyl-Terminated Dendrimers 5 Click Catalysis with Extremely Efficient Intradendritic Triazolyl-Copper(I) Complexes 6 Click Dendrimers as Stabilizers for Very Efficient Nanoparticle Catalysis of Cross-Coupling Carbon-Carbon Bond Formation and Redox Reactions 7 Click Dendrons and Dendrimers for Efficient Catalysis Using Magnetically Recoverable Catalysts 8 Conclusion and Prospects26111437144

Hydrolysis of Ammonia-Borane over Ni/ZIF-8 Nanocatalyst: High Efficiency, Mechanism, and Controlled Hydrogen Release

Non-noble metal nanoparticles are notoriously difficult to prepare and stabilize with appropriate dispersion, which in turn severely limits their catalytic functions. Here, using zeolitic imidazolate framework (ZIF-8) as MOF template, catalytically remarkably efficient ligand-free first-row late transition-metal nanoparticles are prepared and compared. Upon scrutiny of the catalytic principles in the hydrolysis of ammonia-borane, the highest total turnover frequency among these first-row late transition metals is achieved for the templated Ni nanoparticles with 85.7 molH2 molcat -1 min-1 at room temperature, which overtakes performances of previous non-noble metal nanoparticles systems, and is even better than some noble metal nanoparticles systems. Mechanistic studies especially using kinetic isotope effects show that cleavage by oxidative addition of an O-H bond in H2O is the rate-determining step in this reaction. Inspired by these mechanistic studies, an attractive and effective "on-off" control of hydrogen production is further proposed.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

L'électromigration appliquée à la dépollution des sols : le cas d'une pollution fluorée

International audienceL'objectif de l'étude est l'application du procédé électro cinétique à l'échelle d'un pilote. Ainsi, une méthodologie est développée afin de définir et de mettre en oeuvre des conditions adaptées à la décontamination d'un sol pollué en fluor par la technique d'électromigration. Tout d'abord, une étude expérimentale est réalisée à l'échelle du laboratoire, afin d'analyser préalablement le rôle de différents paramètres (nature de l'électrolyte uti lisé, granulométrie du sol, gradient de potentiel imposé). Puis, des travaux sont réalisés avec les conditions prédé finies, sur trois échelles différentes (0,8 et 20 litres ainsi que 1,5 m'), afin de mettre en évidence l'impact du changement d'échelle sur les paramètres: quantité de fluor récupérée, durée de traitement, consommation énergétique plus par ticulièrement. The aim of this study is to scale up the electrokinetic process. A methodology was then developed, in order to implement the adapted conditions for the fluorine polluted soil decontamination, by using an electromi gration process. First, a laboratory experimental study was carried out in order to analyse the influence of different parameters (electrolyte type, soil granulo metry, applied electrical potential). Then other studies have been performed, using three scales (0.8, 20 and 1500 litres) to observe the impact of the scale up on the removed fluorine amount, treatment time and the energy consumption parameters

Translocation of silver nanoparticles in the ex vivo human placenta perfusion model characterized by single particle ICP-MS

With the extensive use of silver nanoparticles (AgNPs) in various consumer products their potential toxicity is of great concern especially for highly sensitive population groups such as pregnant women and even the developing fetus. To understand if AgNPs are taken up and cross the human placenta, we studied their translocation and accumulation in the human ex vivo placenta perfusion model by single particle ICP-MS (spICP-MS). The impact of different surface modifications on placental transfer was assessed by AgNPs with two different modifications: polyethylene glycol (AgPEG NPs) and sodium carboxylate (AgCOONa NPs). AgNPs and ionic Ag were detected in the fetal circulation in low but not negligible amounts. Slightly higher Ag translocation across the placental barrier for perfusion with AgPEG NPs and higher AgNP accumulation in placental tissue for perfusion with AgCOONa NPs were observed. Since these AgNPs are soluble in water, we tried to distinguish between the translocation of dissolved and particulate Ag. Perfusion with AgNO3 revealed the formation of Ag containing NPs in both circulations over time, of which the amount and their size in the fetal circulation were comparable to those from perfusion experiments with both AgNP types. Although we were not able to clarify whether intact AgNPs and/or Ag precipitates from dissolved Ag cross the placental barrier, our study highlights that uptake of Ag ions and/or dissolution of AgNPs in the tissue followed by re-precipitation in the fetal circulation needs to be considered as an important pathway in studies of AgNP translocation across biological barriers

Translocation of silver nanoparticles in the ex vivo human placenta perfusion model characterized by single particle ICP-MS

With the extensive use of silver nanoparticles (AgNPs) in various consumer products their potential toxicity is of great concern especially for highly sensitive population groups such as pregnant women and even the developing fetus. To understand if AgNPs are taken up and cross the human placenta, we studied their translocation and accumulation in the human ex vivo placenta perfusion model by single particle ICP-MS (spICP-MS). The impact of different surface modifications on placental transfer was assessed by AgNPs with two different modifications: polyethylene glycol (AgPEG NPs) and sodium carboxylate (AgCOONa NPs). AgNPs and ionic Ag were detected in the fetal circulation in low but not negligible amounts. Slightly higher Ag translocation across the placental barrier for perfusion with AgPEG NPs and higher AgNP accumulation in placental tissue for perfusion with AgCOONa NPs were observed. Since these AgNPs are soluble in water, we tried to distinguish between the translocation of dissolved and particulate Ag. Perfusion with AgNO3 revealed the formation of Ag containing NPs in both circulations over time, of which the amount and their size in the fetal circulation were comparable to those from perfusion experiments with both AgNP types. Although we were not able to clarify whether intact AgNPs and/or Ag precipitates from dissolved Ag cross the placental barrier, our study highlights that uptake of Ag ions and/or dissolution of AgNPs in the tissue followed by re-precipitation in the fetal circulation needs to be considered as an important pathway in studies of AgNP translocation across biological barriers

Dentromers, a Family of Super Dendrimers with Specific Properties and Applications

Dentromers (from dentro, δεντρο: tree in Greek), and meros (μεροσ, in greek: part) are introduced as a family of dendrimers constructed according to successive divergent 1 → 3 branching. The smaller dentromers have 27 terminal branches. With alcohol termini they were originally named arborols by Newkome, who pioneered 1 → 3 constructions of dendrimers and dendrons. Giant dentromers have been constructed and decorated in particular with ferrocene and other redox active groups. The synthesis, specific properties, and applications are examined in this mini review article dedicated to Don Tomalia, with an emphasis on dense peripheral packing favoring the functions of encapsulation, redox sensing, and micellar template for catalysis in water and aqueous solvents