Synthesis and Conformations of Dendronized Poly(L-lysine)

Dendronized polymers based on a poly(L-lysine) backbone have been synthesized up to the fourth generation. The hydroxyl-terminated polymers are completely water-soluble, which makes them good candidates for drug delivery applications. The dendronized polypeptide backbones are helical at lower generations, but undergo a dramatic conformational change from alpha-helical to disordered upon increasing the dendron size to the third generation. This conformational change, attributed to steric repulsions between dendrons, is supported by spectroscopic measurements while chain extension upon dendronization is confirmed by scanning force microscopy.     

The third industrial fluid properties simulation challenge

The third industrial fluid properties simulation challenge was held from March to September 2006. As in the previous two events contestants were challenged to predict specific, industrially relevant, properties of fluid systems. Their efforts were judged based on the agreement of the predicted values with previously unpublished experimental data (provided by researchers at ExxonMobil and DuPont). The focus of this contest was on the transferability of modeling methods—the ability to predict properties for materials that are chemically different, or at different state points, to those used in model parameterization and validation. Nine groups attempted to compute bubble point pressures for mixtures of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) and ethanol at 343 K, given data for mixtures at 283 K, and given the pure component vapor pressures. They used a range of different techniques including statistical mechanical and molecular simulations-based approaches. Four of the groups were recognized for providing predictions that were significantly more accurate than would be obtained by extrapolation using the NRTL model (the standard engineering approach). Three groups undertook the more challenging “molecular transferability” problem, attempting to predict shear viscosities at two different state points for a range of diols and triols for which little experimental data was available.     

Curve veering and mode localization in a buckling problem

Summary It is shown on a simple example that small disorder, or mistuning, may alter drastically the eigensolution of buckling problems in nearly periodic structures with weak internal coupling. Specifically, the phenomena of eigenvalue loci veering and mode shape localization, which are known to occur for free vibration problems, are evidenced in the case of structural buckling as well.     

The application of strictly localized geminals to the description of chemical bonds

A theory is developed in which closed-shell molecules are viewed as systems of weakly interacting chemical bonds. Composite-particle creation operators obtained by an appropriate quasiparticle transformation are used to create the wave function of two-electron bonds. These quasiparticles are bosons, since they are composed of two electrons, but the total many-electron wave function is properly antisymmetric. The internal structure of the quasi-Bose-particles is affected by inductive interbond interactions. Delocalization and dispersion interactions between different bonds are neglected, thus the approach corresponds to a first-order many-body PT (Perturbation Theory) with a correlated, but fully localized, reference state. The whole formalism is developed ab initio. The nonorthogonality problem is handled by a biorthogonal formulation. To illustrate the effectiveness of the model, numerical calculations are reported.     

Improved interface conditions for a non-overlapping domain decomposition of a non-convex polygonal domain

We propose a local improvement of domain decomposition methods which fits with the singularities occurring in the solutions of elliptic equations in polygonal domains. This short presentation focuses on a model elliptic problem with the decomposition of a non-convex polygonal domain into convex polygonal subdomains. After explaining the strategy and the theoretical design of adapted interface conditions at the corner, we present numerical experiments which show that these new interface conditions satisfy some optimality properties. To cite this article: C. Chniti et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Preliminary Communications Thermotropic liquid crystal behaviour of 5,5'-[(4-hexadecyloxyphenyl)ethynyl]-2,2'-bipyridine

5,5'-[(4-Hexadecyloxyphenyl)ethynyl]-2,2'-bipyridine was synthesized by a palladium(O) cross-coupling reaction. Its thermotropic liquid crystalline behaviour was analysed using differential scanning calorimetry, polarizing microscopy, and X-ray diffraction. Three enantiotropic tilted smectic phases were identified upon heating: S_F, S_I, and S_C.     

Cuprate-catalyzed Three-Component Couplings of Functionalized Organozinc Reagents

Organozinc reagents FG-(CH₂)_nZnX containing electrophilic centers (FG) upon conversion to their corresponding zincates (FG-(CH₂)_nZnMe₂Li) and in the presence of 5–8 mol % MeCu(CN)Li, undergo 1,4-additions to cyclic conjugated enones. The intermediate zinc enolates can be trapped with aldehydes to afford products of three-component couplings.     

Correlation Functions and Boundary Conditions in Rational Conformal Field Theory and Three-Dimensional Topology

We give a general construction of correlation functions in rational conformal field theory on a possibly nonorientable surface with boundary in terms of three-dimensional topological field theory. The construction applies to any modular category in the sense of Turaev. It is proved that these correlation functions obey modular invariance and factorization rules. Structure constants are calculated and expressed in terms of the data of the modular category.