Synthése d'époxydes et d'éthers glycidiques á chaîne chlorofluorée

Epoxides of general formula

(II, V) (R_F,Cl = Cl ; CF₃ ; Cl(CFClCF₂)_n?) are prepared from chlorohydrines R_F,ClCCl₂CH₂CHClCH₂OH (I).These chlorhydrines are monoadducts of carbon tetrachloride 1,1,1 trichlorotrifluoroethane, telomers Cl(CFClCF₂)_nCCl₃, with allyl alcohol.Reactions of these epoxides with lithium aluminium hydride and/or sulfuric acid lead to corresponding secondary alcohols and/or diols. Glycidyl ethers of (I) and (II,n) with epichlorhydrin could not be obtained. However, epichlorhydrin reacts with the more acidic chlorofluorinated alcohol CFCl₂CF₂CH₂OH. Thus, the glycidyl ether

is prepared.     

All-optical orientation of photoisomerizable octupolar zinc(II) complexes in polymer films

A new type of 4,4'-bis(styryl)-2,2'-bipyridine functionalized by a dialkylamino-azobenzene group has been prepared. This ligand has allowed the preparation of photoisomerizable octupolar tris(bipyridyl)zinc(II) complexes and the corresponding star-shaped polymer by atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). The photoisomerization properties of such new metallo-chromophores have been studied. The macroscopic molecular orientation of the corresponding doped and grafted NLO-polymer films is reported for the first time.     

Norbornane: an investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories

We report on the results of an exhaustive study of the valence electronic structure of norbornane (C(7)H(12)), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-zeta quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a(2) (-1) one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at approximately 25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at approximately 26 eV.     

Diastereoselective hydroxylation of 6-substituted piperidin-2-ones. An efficient synthesis of (2S,5R)-5-hydroxylysine and related alpha-amino acids

The synthesis of (2S,5R)-5-hydroxy-6-oxo-1,2-piperidinedicarboxylates (5) and related (3S,6R)-3-hydroxy-6-alkyl-2-oxo-1-piperidinecarboxylates has been developed. The approach is based on the asymmetric hydroxylation of enolates generated from the corresponding N-protected-6-substituted piperidin-2-ones. The utility of 5a as a precursor in the synthesis of (2S,5R)-5-hydroxylysine (1), an amino acid unique to collagen and collagen-like proteins, has also been demonstrated. (2S)-6-oxo-1,2-piperidinedicarboxylates (6) required for hydroxylation studies were prepared in 38-74% yield, starting from conveniently protected aspartic acid as inexpensive chiral adduct. Hydroxylation of 6 to 5 proceeds in high yield and excellent diastereoselectivity by treatment of their Li-enolate with (+)-camphorsulfonyloxaziridine at -78 degrees C. Ring opening of di-tert-butyl (2S,5R)-6-oxo-1,2-piperidinedicarboxylate ((5R)-5a) under reductive conditions afforded the corresponding 1,2-diol (17) in 91%, which was further transformed to (2S,5R)-5-hydroxylysine in four steps (84%). 17 is also a versatile intermediate in the preparation of tert-butyl (2S,5R)-2-[(tert-butoxycarbonyl)amino]-5-hydroxy-6-iodohexanoate (3) and tert-butyl (2S)-2-[(tert-butoxycarbonyl)amino]-4-[(2R)-oxiranyl]butanoate (4), two amino acid derivatives used in the total synthesis of the bone collagen cross-link (+)-pyridinoline (2a).     

Virtual Screening and Structure Generation Applied to Drug Design

The methods of computer-aided drug design can be divided into two categories according to whether or not the structures of receptors are known1, corresponding to two principal strategies: (1) searching the bio-active ligands against virtual combinatorial libraries and calculating the affinity energy between ligand and receptor by docking ; (2) QSAR and 3D-structure data-mining. 3D-QSAR method is now applied widely to drug discovery, but this method is generally limited to refine the structu…     

2,3-di-n-decyloxy-6,7-dichloroanthracene (Cl2DDOA), a new low-molecular-mass fluorescent organogelator: physical properties and structures

To extend the family of 2,3-didecyloxyanthracene (DDOA, 1), an organogelator having a rodlike shape, a high polarity, and fluorescing properties, the 6,7-dichloro derivative (Cl2DDOA, 2), was designed and prepared. Compound 2 forms gels in alcohols, nitriles, and alkanes. The electronic absorption spectra of the gel show a finer structure than those of the isotropic solutions, pointing to a specific degree of packing of the molecules; such an aggregation mode is also supported by fluorescence data. The gel-to-sol temperatures (Tm) were determined as a function of gelator concentration and the corresponding enthalpies (DeltaHm) were extracted. Scattering experiments have shown that the molecular packing in aggregates of 2 organogels is less reminiscent of the crystalline state than was the situation with DDOA gels. 2 organogels in butanol are made up of 120 A radius fibers much thinner than those observed in DDOA gels (r ca. 300 A) and with rather monodisperse cross sections. In 1-octanol, dodecane, or cyclohexane, the fibrillar organogel networks involve a broader distribution of the related cross sections through anisometric sections of the fibers and/or formation of bundles.     

Metric homology

Metric homology is a homology theory constructed on semialgebraic (or compact subanalytic) sets with singularities. Metric homology is an invariant under semialgebraic (subanalytic) bi‐Lipschitz homeomorphisms and not a topological invariant. As in intersection homology theory, classes of admissible chains are defined using a semialgebraic stratification and a perversity function. In contrast to intersection homology, the perversity is a rational‐valued function. Instead of the topological dimension of the intersection of a chain with a stratum, we consider the so‐called volume‐growth number. This number is a sort of generalization of Hausdorff dimension. In the second part of the paper we describe one‐dimensional metric homology for spaces with isolated singularities and calculate some concrete examples. © 2000 John Wiley & Sons, Inc.     

A study of the spectral emissions in laser-irradiated microdot targets at 0.53 and 0.27 μm wavelengths with micron resolution

Using a knife-edge technique, we have determined the spatial extension of H-like and He-like emissions and the time-integrated axial electron density profile in laser-irradiated aluminium microdot targets at 0.53 and 0.25 μm wavelengths with about 3 μm resolution.     

On the uniqueness of bivariant Chern class and bivariant Riemann–Roch transformations

The existence of bivariant Chern classes was conjectured by W. Fulton and R. MacPherson and proved by J.-P. Brasselet for cellular morphisms of analytic varieties. However, its uniqueness has been unsolved since then. In this paper we show that restricted to morphisms whose target varieties are possibly singular but (rational) homology manifolds (such as orbifolds), the bivariant Chern classes (with rational coefficients) are uniquely determined. We also discuss some related results and problems.     

Emittance measurements of a laser-wakefield-accelerated electron beam

The transverse emittance of a relativistic electron beam generated by the interaction of a high-intensity laser with an underdense plasma has been measured with the "pepper-pot" method. For parameters pertaining to the forced laser wakefield regime, we have measured an emittance as low as (2.7+/-0.9) pi mm mrad for (55+/-2) MeV electrons. These measurements are consistent with 3D particle-in-cell simulations of the experiment, which additionally show the existence of a relatively large halo around the beam core.