Preparation of amphiphilic sucrose carbamates by reaction with alkyl isocyanates in water-alcohol mixtures

The reactivity of sucrose with isocyanates in aqueous media has been studied. Mixtures of water and alcohols allow good conversion of the isocyanates to sucrose carbamates. The influence of the reaction parameters on the selectivity (degree of substitution and regioselectivity) was investigated in the case of long chain isocyanates, which have potential surfactant properties.     

Acetate- and thiol-capped monodisperse ruthenium nanoparticles: XPS, XAS, and HRTEM studies

Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.     

Reactivity of atomic cobalt with molecular oxygen: a combined IR matrix isolation and theoretical study of the formation and structure of CoO2

The reactivity of atomic cobalt toward molecular oxygen in rare gas matrices has been reinvestigated. Experiments confirm that Co atoms in their a(4)F ground state are inert toward O(2) in solid argon and neon but reactive in the b(4)F first excited state, in agreement with the previous gas-phase study of Honma and co-workers. The formation of CoO(2) starting from effusive beams of Co and O(2) has been followed by IR absorption spectroscopy, both in neon and argon matrices. Our observations show that only the dioxo form, OCoO, is stabilized in the matrix and that IR absorptions previously assigned to the peroxo and superoxo forms are due to other, larger species. The present data strongly support the linear geometry in rare gas matrices proposed by Weltner and co-workers. We report on measurements on all IR-active fundamental modes for (16)OCo(16)O, (18)OCo(18)O, and (16)OCo(18)O with additional combination transitions supplying anharmonicity correction. This allows for a 5.93 +/- 0.02 mdyne/A CoO harmonic bond force constant in solid neon. Using the empirical relationship previously optimized for the CoO diatomics, an approximate value for the CoO internuclear bond distance is proposed (1.615 +/- 0.01A). In light of recent theoretical studies predicting (2)A(1) or (6)A(1) electronic ground states, the geometry and electronic structure of the OCoO molecule has also been reconsidered. Calculations carried out at the CCSD(T)/6-311G(3df) level indicate a linear structure with an r(e) = 1.62 A bond distance, consistent with the experimental estimate. For later studies of larger systems, where CCSD(T) calculations become too time-consuming, an effective DFT-based method is proposed which reproduces the basic electronic and geometrical properties of cobalt dioxide. Quantitative results are compared to the experimental data and high-level results regarding bond length and frequencies. This DFT method is used to propose a reaction pathway.     

Experimental/theoretical electrostatic properties of a styrylquinoline-type HIV-1 integrase inhibitor and its progenitors

We have established that polyhydroxylated styrylquinolines are potent inhibitors of HIV-1 integrase (IN). Among them, we have identified (E)-8-hydroxy-2-[2-(4,5-dihydroxy-3-methoxyphenyl)-ethenyl]-7-quinolinecarboxylic acid (1) as a promising lead. Previous molecular dynamics simulations and docking procedures have shown that the inhibitory activity involves one or two metal cations (Mg2+), which are present in the vicinity of the active center of the enzyme. However, such methods are generally based on a force-field approach and still remain not as reliable as ab initio calculations with extended basis sets on the whole system. To go further in this area, the aim of the present study was to evaluate the predictive ability of the electron density and electrostatic properties in the structure-activity relationships of this class of HIV-1 antiviral drugs. The electron properties of the two chemical progenitors of 1 were derived from both high-resolution X-ray diffraction experiments and ab initio calculations. The twinning phenomenon and solvent disorder were observed during the crystal structure determination of 1. Molecule 1 exhibits a planar s-trans conformation, and a zwitterionic form in the crystalline state is obtained. This geometry was used for ab initio calculations, which were performed to characterize the electronic properties of 1. The electron densities, electrostatic potentials, and atomic charges of 1 and its progenitors are here compared and analyzed. The experimental and theoretical deformation density bond peaks are very comparable for the two progenitors. However, the experimental electrostatic potential is strongly affected by the crystal field and cannot straightforwardly be used as a predictive index. The weak difference in the theoretical electron densities between 1 and its progenitors reveals that each component of 1 conserves its intrinsic properties, an assumption reinforced by a 13C NMR study. This is also shown through an excellent correlation of the atomic charges for the common fragments. The electrostatic potential minima in zwitterionic and nonzwitterionic forms of 1 are discussed in relation with the localization of possible metal chelation sites.     

The Schrödinger Equation Type with a Nonelliptic Operator

We consider some linear Schrödinger equation with variable coefficients associated to a smooth symmetric metric g which can be degenerate, without sign and such that g has a submatrix of fixed rank v which is uniformly nondegenerate. In this general setting we prove Strichartz estimates with a loss of derivative on the solution. We also discuss the problem of the control of high frequencies. In particular, we prove that if the equation preserves the H ^s norm for all s ≥ 0, then we obtain almost the same Strichartz estimates as those for the Schrödinger equation associated to a Riemannian metric of dimension 2d ? v.     

Approximation locale précisée dans des problèmes multi-échelles avec défauts localisés

We proceed here with our systematic study, initiated in [3], of multiscale problems with defects, within the context of homogenization theory. The case under consideration here is that of a diffusion equation with a diffusion coefficient of the form of a periodic function perturbed by an $L^r({\mathbb{R}}^d)$, $1<r<+\infty$, function modelling a localized defect. We outline the proof of the following approximation result: the corrector function, the existence of which has been established in [3], [4], allows us to approximate the solution to the original multiscale equation with essentially the same accuracy as in the purely periodic case. The rates of convergence may however vary, and are made precise, depending upon the $L^r$ integrability of the defect. The generalization to an abstract setting is mentioned. Our proof exactly follows, step by step, the pattern of the original proof of Avellaneda and Lin in [1] in the periodic case, extended in the works of Kenig and collaborators [12], and borrows a lot from it. The details of the results announced in this Note are given in our publications [2], [11].     

Rapid Generation and Safe Use of Carbenes Enabled by a Novel Flow Protocol with In‐line IR spectroscopy

A powerful new continuous process for the formation and use of donor/acceptor‐substituted carbenes is described. The safety profile of diazo group transfer on methyl phenylacetate was determined including kinetic studies in batch and in flow using in‐line IR analysis. Batch work‐up and liquid chromatography were circumvented by developing an optimized liquid/liquid flow separation method providing aryl diazoacetates in high purity. Fast screening of reaction conditions in flow with in‐line IR analysis allowed rapid reaction optimization. Finally, a multistep process of diazo group transfer, extraction, separation and subsequent diazo decomposition combined with multiple X?H insertion reactions was established.     

Mechanism of nanocapsules formation by the emulsion-diffusion process

A detailed investigation into the mechanisms of nanocapsule formation by means of the two stages "emulsion-diffusion" process is reported. Such widely used process is still poorly understood. An emulsion of oil, polymer and ethyl acetate is fabricated as a first step; dilution with pure water allows ethyl acetate to diffuse out from the droplets, leaving a suspension of nanocapsules at the end. It has been shown that the size of nanocapsules was related to the chemical composition of the organic phase and the size of primary emulsion through a simple geometrical relationship. As a consequence, most of the properties of the nanocapsules were decided at the emulsification step. The influence of several formulation and processing parameters of the primary emulsion was studied accordingly. The thin polymer membrane of nanocapsules was observed by means of cryo-fracture electron microscopy. Finally two experiments were designed for a mechanistic investigation of the diffusion step. A step-by-step diffusion of the organic solvent takes place by successive partition equilibria of ethyl acetate between the droplets and aqueous phase. A time-resolved experiment shows the fast diffusion (less than 20 ms) related to the small droplet size of the emulsion.     

Elaboration,characterization and study of a new hybrid chitosan/ceramic membrane for affinity membrane chromatography

A new kind of metal affinity membrane based on a ceramic support was prepared. It was elaborated in four steps: (i) deposition of a chitosan layer in order to functionalize the ceramic support, (ii) cross-linking with epichlorohydrin to stabilise the polymer layer and to enable the grafting, (iii) iminodiacetic acid grafting, (iv) Cu²⁺ adsorption. Due to the ceramic support, this membrane is highly resistant and the chitosan layer brings its biocompatibility properties. Each step of the membrane elaboration was studied and the membrane structure was characterized. Both thin coating of the polymer on the alumina grains of the support and the chemical modification of the membrane were proved. Then, bovine serum albumin (BSA) was used as a model protein to test protein retention of the affinity membrane. The protein/membrane interactions were investigated showing that some non-specific ones are involved. Finally, the effect of buffer concentration was checked and it appears that, in the studied range, an increase of the buffer concentration entailed a limitation of the non-specific interactions inducing a better BSA recovering and a higher selectivity.