Micellar Effects in Olefin Hydroformylation Catalysed by Neutral,Calix[4]arene‐Diphosphite Rhodium Complexes

The combination of calixarene‐derived surfactants and neutral rhodium complexes containing a hemispherical “1,3‐calix‐diphosphite” ligand led to efficient catalysts for the hydroformylation of octene and other olefins in water. While the surfactants allowed the formation of micelles that dissolve both the catalyst and the alkene, thereby resulting in high olefin:rhodium ratios, the diphosphite provided a tight envelope about the catalytic centre able to drive the reaction towards the linear aldehydes. Best results in the hydroformylation of 1‐octene were obtained when using [tetra(p‐sulfonato)]‐(tetra‐n‐butoxy)‐calix[4]arene as surfactant. With this additive remarkable linear to branched aldehyde ratios of up to 62 were obtained, the corresponding activities being higher than those observed when operating in an organic solvent [turnover frequencies (TOFs) up to 630 mol(converted 1‐octene)⋅ mol(Rh)⁻¹⋅h⁻¹].     

Anticancer activity of silver-N-heterocyclic carbene complexes: caspase-independent induction of apoptosis via mitochondrial apoptosis-inducing factor (AIF)

Fourteen silver(I) complexes bearing N-heterocyclic carbene (NHC) ligands were prepared and evaluated for anticancer activity. Some of these were found to exhibit potent antiproliferative activity toward several types of human cancer cell lines, including drug-resistant cell lines, with IC(50) values in the nanomolar range. An initial investigation into the mechanism of cell death induced by this family of silver(I) complexes was carried out. Cell death was shown to result from the activation of apoptosis without involvement of primary necrosis. In HL60 cells, silver-NHCs induce depolarization of the mitochondrial membrane potential (ΔΨ(m)) and likely allow the release of mitochondrial proteins to elicit early apoptosis. This effect is not related to the overproduction of reactive oxygen species (ROS). In addition, apoptosis is not associated with the activation of caspase-3, but is triggered by the translocation of apoptosis-inducing factor (AIF) and caspase-12 from mitochondria and the endoplasmic reticulum, respectively, into the nucleus to promote DNA fragmentation and ultimately cell death. No modification in cell-cycle distribution was observed, indicating that silver-NHCs are not genotoxic. Finally, the use of a fluorescent complex showed that silver-NHCs target mitochondria. Altogether, these results demonstrate that silver-NHCs induce cancer cell death independent of the caspase cascade via the mitochondrial AIF pathway.     

Aminolysis Reaction of Glycerol Carbonate in Organic and Hydroorganic Medium

Aminolysis reaction of glycerol carbonate with primary amine in organic and hydroorganic media leads to the formation of two hydroxyurethane isomers and a partial decomposition of glycerol carbonate into glycerol. Aminolysis with a secondary amine promotes the condensation reaction and limits the formation of glycerol. The ratio of α versus β was determined by zgig ¹³C NMR. This technique permits computing the yield of α and β products in the medium. The quantity of glycerol was determined by GC analysis. The ratio of the isomers and the amount of glycerol depend on the amine and the solvent. Kinetic investigations reveal that, in hydroorganic medium, the more the alkyl chain of the amine increased, the less glycerol was formed. On the contrary, in organic medium, the alkyl chain of the amine does not play a major role in the formation of glycerol.     

Design of semiconducting indacenodithiophene polymers for high performance transistors and solar cells

The prospect of using low cost, high throughput material deposition processes to fabricate organic circuitry and solar cells continues to drive research towards improving the performance of the semiconducting materials utilized in these devices. Conjugated aromatic polymers have emerged as a leading candidate semiconductor material class, due to their combination of their amenability to processing and reasonable electrical and optical performance. Challenges remain, however, to further improve the charge carrier mobility of the polymers for transistor applications and the power conversion efficiency for solar cells. This optimization requires a clear understanding of the relationship between molecular structure and both electronic properties and thin film morphology. In this Account, we describe an optimization process for a series of semiconducting polymers based on an electron rich indacenodithiophene aromatic backbone skeleton. We demonstrate the effect of bridging atoms, alkyl chain functionalization, and co-repeating units on the morphology, molecular orbital energy levels, charge carrier mobility, and solar cell efficiencies. This conjugated unit is extremely versatile with a coplanar aromatic ring structure, and the electron density can be manipulated by the choice of bridging group between the rings. The functionality of the bridging group also plays an important role in the polymer solubility, and out of plane aliphatic chains present in both the carbon and silicon bridge promote solubility. This particular polymer conformation, however, typically suppresses long range organization and crystallinity, which had been shown to strongly influence charge transport. In many cases, polymers exhibited both high solubility and excellent charge transport properties, even where there was no observable evidence of polymer crystallinity. The optical bandgap of the polymers can be tuned by the combination of the donating power of the bridging unit and the electron withdrawing nature of co-repeat units, alternating along the polymer backbone. Using strong donors and acceptors, we could shift the absorption into the near infrared.     

Design and Synthesis of Metabolically Stable tRNA Synthetase Inhibitors Derived from Cladosporin

Selective and specific inhibitors of Plasmodium falciparum lysyl-tRNA synthetase represent promising therapeutic antimalarial avenues. Cladosporin was identified as a potent P. falciparum lysyl-tRNA synthetase inhibitor, with an activity against parasite lysyl-tRNA synthetase >100-fold more potent than that of the activity registered against the human enzyme. Despite its compelling activity, cladosporin exhibits poor oral bioavailability; a critical requirement for antimalarial drugs. Thus, the quest to develop metabolically stable cladosporin-derived analogues, while retaining similar selectivity and potency to that of the natural compound, has begun. Chemogenomic profiling of a designed library allowed an entirely innovative structure–activity relationship study to be initiated; this shed light on structural evidence of a privileged scaffold with a unique activity against tRNA synthetases.     

Preparation of Tetradentate Copper Chelators as Potential Anti‐Alzheimer Agents

The uncontrolled redox activity of metal ions, especially copper, in the brains of patients with Alzheimer's disease (AD) should be considered the origin of intense oxidative damage to neurons in the AD brain. To obtain low‐molecular‐weight copper chelators that act as tetradentate ligands, we designed new compounds based on an 8‐aminoquinoline motif with a lateral chain attached at the 2‐position of the aromatic ring. Some of these new ligands, termed TDMQ for TetraDentate MonoQuinolines, are specific for copper chelation. Full characterization of these ligands is reported, as well as their affinities for Cu^II, and their capacities to inhibit oxidative stress induced by copper–amyloids activated by a reductant. Such metal ligands can be considered as potential anti‐AD agents, as they should be able to regulate the homeostasis of copper in brain tissue.     

Influence of the gel on the morphology of a thermoset polymerized into a thermoplastic matrix, under shear

The relation between the gel point of the thermosetting dispersed phase and the coarsening of the morphology of a thermoplastic/thermoset blend reacted under shear has been investigated. The model system was composed of 60 wt% of polystyrene (PS) and 40 wt% of an epoxy-amine system (diglycidyl ether of bisphenol A — 4,4′-methylenebis [2,6-diethylaniline]). This blend is initially homogeneous and phase separates upon polymerization. The reactive blending process consisted of a sequence of dynamic and static blending modes imposed into an internal mixer. The observation of the morphology before and after the transition from the static to the dynamic mode allowed showing that a short period of time, corresponding to a limited evolution of the conversion around the gel point, influences drastically the development of the morphology. The coalescence and agglomeration phenomena that play a determinant role at low and intermediate epoxy conversion, are stopped when the epoxy drops gel, resulting in a stabilization of the morphology. The transition from a static mode to a blending under shear has also revealed the existence of a distribution of conversion among the epoxy-rich domains, caused by the competition between the continual nucleation process of the epoxy droplets and their growth.