Influence of nanoparticle surface functionalization on the thermal stability of colloidal polystyrene films

The installation of large scale colloidal nanoparticle thin films is of great interest in sensor technology or data storage. Often, such devices are operated at elevated temperatures. In the present study, we investigate the effect of heat treatment on the structure of colloidal thin films of polystyrene (PS) nanoparticles in situ by using the combination of grazing incidence small-angle X-ray scattering (GISAXS) and optical ellipsometry. In addition, the samples are investigated with optical microscopy, atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). To install large scale coatings on silicon wafers, spin-coating of colloidal pure PS nanoparticles and carboxylated PS nanoparticles is used. Our results indicate that thermal annealing in the vicinity of the glass transition temperature T(g) of pure PS leads to a rapid loss in the ordering of the nanoparticles in spin-coated films. For carboxylated particles, this loss of order is shifted to a higher temperature, which can be useful for applications at elevated temperatures. Our model assumes a softening of the boundaries between the individual colloidal spheres, leading to strong changes in the nanostructure morphology. While the nanostructure changes drastically, the macroscopic morphology remains unaffected by annealing near T(g).     

Recent Advances in the Chemistry of “Clusters” and Coordination Polymers of Alkali,Alkaline Earth Metal and Group 11 Compounds

This contribution gives an overview on the different subjects treated in our group. One of our fundamental interests lies in the synthesis and study of low‐dimensional polymer and molecular solid state structures. We have chosen several synthetic approaches in order to obtain such compounds. Firstly, the concept of cutting out structural fragments from a solid state structure of a binary compound will be explained on behalf of BaI₂. Oxygen donor ligands, used as chemical scissors on BaI₂, allow obtaining three‐, two‐, one‐ and zero‐dimensional derived compounds depending on their size and concentration. Thus, a structural genealogy tree for BaI₂ can be established. This method, transferred to alkali halides using crown ethers and calix[n]arenes as delimiting ligands, leads us to the subject of one‐dimensional ionic channels. A second chapter deals with the supramolecular approach for the synthesis of different dimensional polymer structures derived from alkaline earth metal iodides, and based on the combination of metal ion coordination with hydrogen bonding between the cationic complexes and their anions. Under certain circumstances, rules can be established for the prediction of the dimensionality of a given compound, thus contributing to the fundamental problem of structure prediction in crystal engineering. A third part describes a fundamentally new synthetic pathway for generating pure alkaline earth metal cage compounds as well as alkali and alkaline earth mixed metal clusters. In a first step, different molecular precursors, such as solvated alkaline earth metal halides are investigated as a function of the ligand size and reactivity. They are then reacted with some alkali metal compound in order to partially eliminate alkali halide and to form the clusters. The so obtained unique structures of ligand stabilized metal halide, hydroxide and/or alkoxide and aryloxide aggregates are of interest as potential precursors for oxide materials. Approaches to two synthetic methods of the latter, sol‐gel and (MO)‐CVD, are investigated with our compounds. In order to generate single source precursors for oxide materials, we started to investigate transition metal ions, especially Cu and Ag, using multitopic ligands. This has led us into the fundamental problematic of “crystal engineering” and solid state structure prediction and we found ourselves confronted to numerous interesting cases of polymorphism and pseudo‐polymorphism. Weak interactions, such as π‐stacking, H‐bonding and metal‐metal interactions, and solvent, counter ion and concentration effects seem to play important roles in the construction of such low‐dimensional structures. Finally, the physical properties of some of our compounds are described qualitatively in order to show the wide spectrum of possibilities and potential applications for the chemistry in this field.     

Étude thermochimique des sels alcalins de quelques amino-acides

Standard enthalpies of formation of alkaline earth salts M(NH₂RCOO) of several amino acids

are determined by calorimetry.The thermochemical radii, the standard enthalpies of formation and the protonic affinities of ions (NH₂RCOO^?) in the gaseous state are calculated.In the case of unbranched carbon chain amino acids, the thermochemical radii are an approximately linear function of protonic affinities of their conjugate bases.     

Alkylidenation of Sugar Lactones and Further Transformation to C-Glycosides

ABSTRACT

The Witting reaction of (carbethoxymethylene)triphenylphosphorane with perbenzylated sugar δ-lactones and their 2-acetamido-2-deoxy derivatives is described. It is shown that this olefination occurred readily with the galacto and gluco derivatives, leading stereoselectively to Z-C-glycosylidenes in good yields. However, the same reaction with the perbenzylated 2-deoxy-D-arabino-hexono-1,5-lactone and the mannonolactones worked poorly. Reduction over Pd/C followed by acetylation of the obtained C-glycosylidenes led stereoselectively to peracetylated β-C-glycosides and amino β-C-glycosides. The olefin function could also be reduced selectively by Raney nickel or NiCl₂/NaBH₄, affording the perbenzylated C-glycosides and amino β-C-glycosides. Other transformation of the enol ether function is also reported.     

Synthesis and evaluation of C-glycosides as hydrotropes and solubilizing agents

This work presents expeditious synthesis of C-glycoside amphiphiles in aqueous media from unprotected di- or mono-saccharides. A Horner-Wadsworth-Emmons/Michael addition/Barbier allylation sequence led to C-glycosides that exhibit hydrotropic properties. The hydrotropic and solubilizing properties of these homoallylic alcohols including a β-C-glycoside moiety as well as additional β-C-glycosidic ketones with a short (C₇) alkyl chain are also described and compared with those of commercial O-glucoside references.     

Structural analysis of an unusual bioactive N-acylated lipo-oligosaccharide LOS-IV in Mycobacterium marinum

Although lipo-oligosaccharides (LOSs) are recognized as major parietal components in many mycobacterial species, their involvement in the host-pathogen interactions have been scarcely documented. In particular, the biological implications arising from the high degree of structural species-specificity of these glycolipids remain largely unknown. Growing recognition of the Mycobacterium marinum-Danio rerio as a specific host-pathogen model devoted to the study of the physiopathology of mycobacterial infections prompted us to elucidate the structure-to-function relationships of the elusive end-product, LOS-IV, of the LOS biosynthetic pathway in M. marinum. Combination of physicochemical and molecular modeling methods established that LOS-IV resulted from the differential transfer on the caryophyllose-containing LOS-III of a family of very unusual N-acylated monosaccharides, naturally present as different diastereoisomers. In agreement with the partial loss of pathogenecity previously reported in a LOS-IV-deficient M. marinum mutant, we demonstrated that this terminal monosaccharide conferred to LOS-IV important biological functions, including macrophage activating properties.     

Coupling stochastic EM and approximate Bayesian computation for parameter inference in state-space models

We study the class of state-space models and perform maximum likelihood estimation for the model parameters. We consider a stochastic approximation expectation–maximization (SAEM) algorithm to maximize the likelihood function with the novelty of using approximate Bayesian computation (ABC) within SAEM. The task is to provide each iteration of SAEM with a filtered state of the system, and this is achieved using an ABC sampler for the hidden state, based on sequential Monte Carlo methodology. It is shown that the resulting SAEM-ABC algorithm can be calibrated to return accurate inference, and in some situations it can outperform a version of SAEM incorporating the bootstrap filter. Two simulation studies are presented, first a nonlinear Gaussian state-space model then a state-space model having dynamics expressed by a stochastic differential equation. Comparisons with iterated filtering for maximum likelihood inference, and Gibbs sampling and particle marginal methods for Bayesian inference are presented.     

Asymmetric aziridination with chiral allyl aminosulfoxonium ylides: synthesis of alkenyl aziridine carboxylates and palladium-catalyzed E,trans/E,cis-isomerization of an alkenyl aziridine

Chiral cyclic and acyclic allyl aminosulfoxonium ylides have been generated from aminosulfoxonium-substituted β,γ-unsaturated α-amino acids (method A) and 1-alkenyl aminosulfoxonium salts (method B) upon treatment with DBU. Their application to the asymmetric aziridination of N-tert-butyl-sulfonyl imino ester, generated either in situ (method A) or externally added (method B), gave the corresponding alkenyl aziridine carboxylates with medium to high diastereoselectivity and enantioselectivity. A highly stereoselective Pd(0)-catalyzed isomerization of an E,trans-configured alkenyl aziridine methanol derivative to its E-cis-isomer is described, which proceeded with retention of the double bond configuration.     

Towards large amounts of Janus nanoparticles through a protection-deprotection route

Janus silica nanoparticles, regioselectively functionalized by two different chemical groups, were synthesized through a multistep procedure based on the use of a polystyrene nodule as a protecting mask.