Chain elongations by three carbon atoms at a time in the boron-catalyzed polymerization of methallyltriphenylarsonium ylide

Methallyltriphenylarsonium ylide polymerized in the presence of catalytic amounts of trialkylboranes. Linear polymers containing a terminal alcohol function were obtained after alkaline hydrogen peroxide oxidation. The chain of these polymers is constituted of methyl-substituted double bonds, separated by one methylene group. Their structure is related to that of natural rubber, in which the double bonds are separated by two methylene groups. These polymers arise from successive chain elongations of three carbon atoms at a time. A cyclic, polymeric ketone was also prepared from a cyclic trialkylborane. The mechanism, which involves a boratropic rearrangement after every insertion of a monomer, is discussed.     

Unusual effects in the pd-catalyzed asymmetric allylic alkylations: synthesis of chiral chromans

An examination of earlier reports of poor-to-modest results using Pd-catalyzed asymmetric allylic alkylations (AAA) to effect cyclization to form tetrasubstituted carbons reveals several novel factors that can influence this class of reactions. Thus, carboxylate has a major effect on such cyclizations wherein the ee increases from 14% ee favoring the S with no carboxylate to 84% ee favoring the R enantiomer in the presence of 1 equiv of carboxylate. Changing the double bond geometry from E to Z further increases the ee to 97%. Furthermore, the chiral catalyst that forms the R enantiomer with the E-alkene forms the S enantiomer with the Z alkene. In contrast to trisubstituted alkene substrates, disubstituted ones show a decrease in ee in going from the E to Z alkenes. The role of carboxylate appears to be a ligand to Pd during the catalytic cycle, a previously unsuspected phenomenon since such reactions are generally believed to involve pi-allylpalladium cationic complexes. The dependence upon alkene geometry helps define the nature of the chiral pocket which better accommodates a Z alkene compared to an E alkene. The results are compatible with the enantiodiscriminating step being ionization which occurs by coordination of the palladium to one of the two prochiral faces of the double bond. A synthesis of (+)-clusifoliol, a constituent of a folk medicine for treatment of malignant tumors, which also assigns the absolute configuration, illustrates the utility of the method.     

A microfluidic array with cellular valving for single cell co-culture

We present a highly parallel microfluidic approach for contacting single cell pairs. The approach combines a differential fluidic resistance trapping method with a novel cellular valving principle for homotypic and heterotypic single cell co-culturing. Differential fluidic resistance was used for sequential single cell arraying, with the adhesion and flattening of viable cells within the microstructured environment acting to produce valves in the open state. Reversal of the flow was used for the sequential single cell arraying of the second cell type. Plasma stencilling, along the linear path of least resistance, was required to confine the cells within the trap regions. Prime flow conditions with minimal shear stress were identified for highly efficient cell arraying (～99%) and long term cell culture. Larger trap dimensions enabled the highest levels of cell pairing (～70%). The single cell co-cultures were in close proximity for the formation of connexon structures and the study of contact modes of communication. The research further highlights the possibility of using the natural behaviour of cells as the working principle behind responsive microfluidic elements.     

New multiresidue analytical method dedicated to trace level measurement of brominated flame retardants in human biological matrices

A new method has been developed for the multi-residue measurement of the main brominated flame retardants (alpha- and gamma-hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBP-A) and polybrominated diphenyl ethers including decabromodiphenyl ether) in human biological matrices (serum, adipose tissue and breast milk). The proposed sample preparation procedure focused on reduced solvent and consumable consumption and associated procedural contamination, as well as reduced sample size. This protocol was fully validated and was proved to be suitable for identification of brominated flame retardant residues at ultra-trace level, as attested by preliminary results on real samples.     

Palladium-catalyzed synthesis of 3-trifluoromethylated 1,3-dienes from acrylate derivatives and BTP

Here we reported a Pd-catalyzed coupling reaction between acrylate derivatives and BTP (2-bromo-3,3,3-trifluoropropene) to access 3-trifluoromethylated 1,3-dienes. The reaction allows the formation of the corresponding products in good to excellent yields and moderate Z/E diastereoisomeric ratios. This method broadens the current toolbox to access 3-trifluoromethylated 1,3-dienes.     

Modulating the activity of membrane-active peptides through Zn(II) complexation

Seeking to increase the selectivity of antimicrobial peptides for prokaryotic cells, we incorporated a bis-dipicolyl amine (bis-DPA) ligand at the N-terminus of de novo designed model peptides. The Zn₂·bisDPA complex increases the interaction of peptides with anionic model membranes, while decreasing interactions with zwitterionic model membranes. Further, it improves the peptides’ antimicrobial activity and decreases their hemolytic activity without substantial changes to their secondary structure. Therefore, incorporating a Zn₂·bisDPA complex is a useful strategy to enhance the selectivity of antimicrobial peptides.     

Existence of secondary bifurcations or isolas for PDEs

In this paper, we introduce a method to conclude about the existence of secondary bifurcations or isolas of steady state solutions for parameter dependent nonlinear partial differential equations. The technique combines the Global Bifurcation Theorem, knowledge about the non-existence of nontrivial steady state solutions at the zero parameter value and explicit information about the coexistence of multiple nontrivial steady states at a positive parameter value. We apply the method to the two-dimensional Swift-Hohenberg equation.     

Tumor targeting in photodynamic therapy. From glycoconjugated photosensitizers to glycodendrimeric one. Concept, design and properties

In this paper, we discuss the evolution over the last 15 years in the Curie Institute of the concept, the development of the design and some properties of glycoconjugated photosensitizers with the aim to optimize the tumor targeting in photodynamic therapy. By this research, we have shown that specific interactions between a mannose-lectin and trimannosylglycodendrimeric porphyrins contributed to a larger extent than non-specific ones to the overall interaction of a glycosylated tetraarylporphyrin with a membrane. The studies of in vitro photocytotoxicity showed the relevance of the global geometry of the photosensitizer, the number and position of the linked glycopyranosyl groups on the chromophore and their lipophilicity. The two best compounds appeared to be porphyrins bearing three α-glycosyl groups on para-position of meso-phenyl via a flexible linker. Compound bearing α-manosyl moieties was evaluated successfully in two in vivo xenografted animal models of human retinoblastoma and colorectal cancers. Conversely, the presence on the chromophore of three sugars via a glycodendrimeric moiety induced a potential cluster effect, but decreased the in vitro photoefficiency despite a good affinity for a mannose-lectin.     

Schrödinger Equations on Damek–Ricci Spaces

In this paper we consider the Laplace–Beltrami operator Δ on Damek–Ricci spaces and derive pointwise estimates for the kernel of e ^τΔ, when τ ∈ ?* with Re τ ≥0. When τ ∈i?*, we obtain in particular pointwise estimates of the Schrödinger kernel associated with Δ. We then prove Strichartz estimates for the Schrödinger equation, for a family of admissible pairs which is larger than in the Euclidean case. This extends the results obtained by Anker and Pierfelice [4 Anker , J.-P. , Pierfelice , V. ( 2009 ). Nonlinear Schrödinger equation on real hyperbolic spaces . Ann. Inst. H. Poincaré (C) Non Linear Analysis 26 : 1853 – 1869 . [Google Scholar]] on real hyperbolic spaces. As a further application, we study the dispersive properties of the Schrödinger equation associated with a distinguished Laplacian on Damek–Ricci spaces, showing that in this case the standard L ¹ → L ^∞ estimate fails while suitable weighted Strichartz estimates hold.     

Economic value of greenhouse gases and nitrogen surpluses: Society vs farmers’ valuation

Livestock supply must challenge the growth of final demand in the developing countries. This challenge has to take into account its ecological effects since the dairy and livestock sectors are clearly pointed out as human activities which contribute significantly to environmental deterioration. Therefore, livestock activity models have to include desirable and undesirable outputs simultaneously. Using this perspective, we implement a Data Envelopment Analysis model to evaluate shadow prices of outputs under contradictory objectives between the society and the farmers. We show that farmers are able to reduce pollution significantly if society accepts to balance farmers’ opportunity cost. Finally, we observe that initial levels of the CO₂ tax implemented in European countries are in line with farmers’ valuation while the current level of the CO₂ tax tends to reach the value of pollution targeted by the society.