CohomologieL 2 et parabolicité

Nous donnons ici une interprétation topologique des espaces de formes harmoniques L² de variétés riemanniennes qui sont des déformations compactes d'espaces symétriques à courbure négative ou nulle ou de groupes de Lie nilpotent simplement connexe. Nous étudions aussi la cohomologie L² des variétés dont les bouts sont paraboliques, nous retrouvons en particulier des résultats de M. Atiyah, V. Patodi, I. Singer, de W. Müller et une petite partie de résultats récents de T. Hausel, E. Hunsicker, R. Mazzeo. En mémoire d' Alain Dufresnoy     

Combined Poly(alkyl cyanoacrylate)/Cyclodextrin Nanoparticles

The use of nanoparticles is of great interest for oral or parenteral administration. In fact, nanoparticles not only can protect the active ingredient, but they confer on it a large contact surface with biological membranes and a possible improvement in bioavailability. Biodegradability of nanoparticles, which can be considered as a pre-requisite in the case of parenteral administration     

Reinforcement of an inequality due to Brascamp and Lieb

In this paper, we obtain a reinforcement of an inequality due to Brascamp and Lieb and a reinforcement of Poincaré's inequality for general logarithmical concave measures on Rd. The formula used in the proof is related to theorems concerning the integration of log-concave functions (such as results of Prékopa and of Ball, Barthe and Naor). We also obtain a lower bound for the variance of the same family of measures.     

Quantization of Γ-Lie bialgebras

We introduce the notion of Γ-Lie bialgebras, where Γ is a group. These objects give rise to cocommutative co-Poisson bialgebras, for which we construct quantization functors. This enlarges the class of co-Poisson algebras for which a quantization is known. Our result relies on our earlier work, where we showed that twists of Lie bialgebras can be quantized; we complement this work by studying the behavior of this quantization under compositions of twists.     

Synthesis of simplified analogues of eleutherobin via a Claisen rearrangement/RCM strategy

The enantioselective synthesis of a number of simplified analogues of the cytotoxic natural product eleutherobin is reported.     

Coordination and Dehydrogenation of Amine–Boranes at Metal Centers

There have been a number of approaches developed for the catalyzed dehydrogenation of amine–boranes as potential dihydrogen sources for hydrogen storage applications in recent years. Key advances in this area have been recently made thanks to catalytic and stoichiometric studies. In this Minireview, the fate of amine–boranes upon coordination to a metal center is discussed with a particular emphasis on B? H activation pathways. We focus on the few cases in which coordination of the resulting dehydrogenated product could be achieved, which includes the coordination of aminoborane, the simplest unit resulting from dihydrogen release of ammonia–borane.     

Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition processes

The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition. Unexpectedly, the starch volume fraction (as probed through thermal gravimetry) decreases with T at a higher rate than the free volume fraction (as probed through PALS).     

Preparing titania aerogel monolithic chromatography columns using supercritical carbon dioxide

The search for a method to fabricate monolithic inorganic columns has attracted significant recent attention due to their unique ability in separation applications of various biomolecules. Silica and polymer based monolithic columns have been prepared, but titania and other metal oxide monoliths have been elusive, primarily due to their fragility. This article describes a new approach for preparing nanostructured titania based columns, which offer better performance over conventional particle packed columns for separating a wide variety of biomolecules including phosphopeptides. TiO₂ monolithic aerogels were synthesized in separation columns using in situ sol‐gel reactions in supercritical carbon dioxide (scCO₂) followed by calcination, and compared to those prepared in heptanes. The characterization results show that scCO₂ is a better solvent for the sol‐gel reactions, providing lower shrinkage with the anatase TiO₂ monolith composed of nanofibers with very high surface areas. The monolithic columns show the ability to isolate phosphopeptides with little flow resistance compared to conventional titania particle based microcolumns.     

Structure of sodiated octa-glycine: IRMPD spectroscopy and molecular modeling

The structure of the sodiated peptide GGGGGGGG-Na⁺ or G₈-Na⁺ was investigated by infrared multiple photon dissociation (IRMPD) spectroscopy and a combination of theoretical methods. IRMPD was carried out in both the fingerprint and N—H/O—H stretching regions. Modeling used the polarizable force field AMOEBA in conjunction with the replica-exchange molecular dynamics (REMD) method, allowing an efficient exploration of the potential energy surface. Geometries and energetics were further refined at B3LYP-D and MP2 quantum chemical levels. The IRMPD spectra indicate that there is no free C-terminus OH and that several N—Hs are free of hydrogen bonding, while several others are bound, however not very strongly. The structure must then be either of the charge solvation (CS) type with a hydrogen-bound acidic OH, or a salt bridge (SB). Extensive REMD searches generated several low-energy structures of both types. The most stable structures of each type are computed to be very close in energy. The computed energy barrier separating these structures is small enough that G₈-Na⁺ is likely fluxional with easy proton transfer between the two peptide termini. There is, however, good agreement between experiment and computations in the entire spectral range for the CS isomer only, which thus appears to be the most likely structure of G₈-Na⁺ at room temperature.     

Thermodynamic Stability Versus Kinetic Lability of ZnS4 Core

Density Functional Theory and post‐Hartree Fock calculations reveal an unusual energy profile for Zn? S and Zn? N bond dissociation reactions in several [Zn(SR)₄]^2? and [Zn(Im)(SR)₃]^? complexes. The Zn? S bond dissociation in tetrathiolate dianions, which is highly exothermic in the gas phase, proceeds through a late transition state which can be rationalized on the basis of an avoided crossing resulting from Coulomb repulsion between the anionic fragments and ligand‐to‐metal charge‐transfer in the [Zn(SR)₄]^2? complexes. When solvation models for water, DMSO, or acetonitrile are included, some complexes become stable while others are metastable, so this constitutes the first theoretical model which is in full agreement with the experimental data for various [Zn(SR)₄]^2?, [Zn(SR)₃]^?, and [Zn(Im)(SR)₃]^? complexes. The analysis given here indicates that the Zn(Cys)₄ and Zn(His)(Cys)₃ cores of numerous proteins are metastable with respect to Zn? S and Zn? N bond dissociation, respectively. This is consistent with the kinetic lability at the zinc‐centers and illustrates that in nature, thermodynamic stability is imparted upon the zinc cores by the protein environment.