Synthese et reactivite d'organomagnesiens perfluores. V.[1] Synthese et identification de nouveaux composes perfluoroalkyles du mercure a chaine longue.

The reaction of mercuric salts HgY₂ or organic mercuric compounds R_HHgX with long chain perfluorinated Grignard reagents R_FMgBr leads to a series of new perfluoroalkyl mercury derivatives with the general formula R_FHgZ (R_F=C₄F₉, C₆F₁₃, C₈F₁₇ ; Z=R_F,R_H,Y with Y = I,Br,Cl, NO₃,OCOCH₃,OCOCF₃).The synthesis of these organomercuric compounds is described, and their spectroscopic properties are reported.     

Remodeling of ordered membrane domains by GPI-anchored intestinal alkaline phosphatase

Glycosylphosphatidyl-inositol (GPI)-anchored proteins preferentially localize in the most ordered regions of the cell plasma membrane. Acyl and alkyl chain composition of GPI anchors influence the association with the ordered domains. This suggests that, conversely, changes in the fluid and in the ordered domains lipid composition affect the interaction of GPI-anchored proteins with membrane microdomains. Validity of this hypothesis was examined by investigating the spontaneous insertion of the GPI-anchored intestinal alkaline phophatase (BIAP) into the solid (gel) phase domains of preformed supported membranes made of dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DOPC/DPPC), DOPC/sphingomyelin (DOPC/SM), and palmitoyloleoylphosphatidylcholine/SM (POPC/SM). Atomic force microscopy (AFM) showed that BIAP inserted in the gel phases of the three mixtures. However, changes in the lipid composition of membranes had a marked effect on the protein containing bilayer topography. Moreover, BIAP insertion was associated with a net transfer of phospholipids from the fluid to the gel (DOPC/DPPC) or from the gel to the fluid (POPC/SM) phases. For DOPC/SM bilayers, transfer of lipids was dependent on the homogeneity of the gel SM phase. The data strongly suggest that BIAP interacts with the most ordered lipid species present in the gel phases of phase-separated membranes. They also suggest that GPI-anchored proteins might contribute to the selection of their own microdomain environment.     

Detection of genetically modified corn (Bt176) in spiked cow blood samples by polymerase chain reaction and immunoassay methods

The fate of DNA and protein transgenic sequences in products derived from animals fed transgenic crops has recently raised public interest. Sensitive molecular tests targeting the Bt176 genetic construct and the transgenic Cry1Ab protein were developed to determine whether plant sequences, especially transgenic sequences, are present in animal products. A protocol for total DNA extraction and purification from cow whole blood samples was first drawn up and assessed by spiking with known amounts of DNA from Bt176 maize. The limit of detection for transgenic sequences (35S promoter and Bt176-specific junction sequence) was determined by both the polymerase chain reaction-enzyme-linked immunosorbent assay (PCR-ELISA) and the 5'-nuclease PCR assay. Four additional PCR systems were built to substantiate the results. The first detects a mono-copy maize-specific sequence (ADH promoter). Two others target multi-copy sequences from plant nucleus (26S rRNA gene) and chloroplast (psaB gene). The last one, used as a positive control, targets a mono-copy animal sequence (alpha(s1)-casein gene). Both methods detected a minimum spiking at 25 copies of Bt176 maize/mL in 10 mL whole blood samples. The sandwich ELISA kit used detected down to 1 ng transgenic Cry1Ab protein/mL spiked whole blood.     

Asymmetric Synthesis. 39.(1) Synthesis of 2-(1-Aminoalkyl)piperidines via 2-Cyano-6-phenyl Oxazolopiperidine

The asymmetric synthesis of a series of 2-(1-aminoalkyl) piperidines using (-)-2-cyano-6-phenyloxazolopiperidine 1 is described. LiAlH(4) reduction of 1 followed by hydrogenolysis led to the diamine 3. The same strategy applied to C-2-methylated compound 7 afforded [(2S)-2-methylpiperidin-2-yl]methanamine (9). Addition of lithium derivatives to the cyano group of 1 resulted in the formation of an intermediate imino bicyclic system (11a-c) which could be diastereoselectively reduced to substituted diamino alcohols 13a-c. The addition of an excess of PhLi to 1 in the presence of LiBr furnished disubstituted amine 19, the precursor of diphenyl[(2S)-piperidin-2-yl]methanamine (22).     

Syntheses and configurations of some heterocyclic amidoximes. X-Ray crystal structure of 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime

O-Methyl-α-ketophenylacetohydroximoyl chloride ( 1 ) was prepared by the reaction of O-methyl-α-methoxyphenylacetohydroximoyl chloride ( 5 ) with N-bromosuccinimide and concentrated hydrobromic acid. Reaction of 1 with ethylenediamine gave 3-phenyl-5,6-dihydro-2(1H)-pyrazinone-O-methyloxime ( 6 ). 3-Phenyl-5,6-cyclohexano-5,6-dihydro-2(1H)-pyrazininone-O-methyloxime ( 7 ) was prepared by reaction of 1 with trans-1,2-diaminocyclohexane. The X-ray structure of 6 has been determined. The crystals are orthorhombic, space group Pbca with a = 10.264(3), b = 18.262(4), c = 23.530(4)Å, V = 4411(2)ų, and Z = 16. The structure, which was refined to R = 0.038 using 1652 observed reflections, shows the amidoxime moiety to be the Z configuration. Reaction of benzohydroximoyl chloride with aziridine gave (Z)-aziridinylbenzaldoxime ( 16a ). Ultraviolet irradiation of a benzene solution of 16a gave a mixture of the Z and E isomers 16a and 16b . The E isomer 16b underwent thermal isomerization to 16a at 100°. Reaction of 16a with dimethyl sulfate in sodium hydroxide solution gave (Z)-O-methylaziridinylbenzaldoxime ( 17a ). Photoisomerization of a hexane solution of 17a gave a mixture of the Z and E isomers 17a and 17b which were separated by preparative glc. The isomers 17a and 17b are resistant to thermal Z = E isomerization. The mechanisms of thermal isomerization of benzamidoximes are discussed.     

Determination de la structure de perfluoroalcenes a chaines longues par R.M.N. du19F : lère Partie : pefluoroalcenes-1

After a review of 1-perfluoroalkene R_FCFCF₂ synthesis, with R_FC₄F₉, C₅F₁₁, C₆F₁₃, we have studied their fine structures by ¹⁹F N.M.R. This study has led us to first generalize the rules set for the chemical shifts and coupling constants of olefinic fluorine atoms of fluoropropene and their derivatives. Then, we have been able to determinate unambiguously the chemical shifts of the difluoromethylene groups of the perfluorinated chains. We have thus shown, by irradiation, that inversions may take place in the chemical shifts of the CF₂ groups at the β and γ position of the double bond.     

HCl adsorption on ice at low temperature: a combined X-ray absorption, photoemission and infrared study

The reaction of HCl on water ice provides a simple case for understanding dissociation and proton transfer in this non-optimal, incomplete solvation environment, playing a central role in atmospheric chemistry. This reaction has been repeatedly reported as thermally dependent, whereas the theoretical models predict a spontaneous dissociation. We examine the adsorption of HCl on ice at low temperature (50 K and 90 K) via a combination of near-edge X-ray absorption spectroscopy (NEXAFS) at the chlorine L-edge, photoemission (XPS and UPS), and reflection-adsorption infrared spectroscopy (FT-RAIRS). We show the complete dissociation of HCl into Cl(-) and H(+) through 3 hydrogen bonds, predominantly by direct reaction with water (80%) and by self-solvation (20%), in full agreement with the prediction of a barrierless process.     

Conformation and distribution of groups on the surface of amphiphilic polyether-co-polyester dendrimers: effect of molecular architecture

Amphiphilic polyester-co-polyether (PEPE) dendrimers synthesized from poly(ethylene glycol) (PEG) were examined to understand the influence of alterations in the architecture of dendrimers on their conformation at interfaces and distribution of various groups on their surface. Effect of changes in the number of branching points, type of terminal functional groups and generation of dendrimer was primarily evaluated. Dendrimers were deposited on mica by spin coating at 0.1 mg/mL. Tapping mode atomic force microscopy (AFM) was employed for the visualization of dendrimer topographies while, X-ray photoelectron spectroscopy (XPS), AFM phase and force imaging were used as the tools for characterization of their surfaces. Individual dendrimer molecules could be imaged by AFM, which showed that they are round or oval in topography. Dendrimers were also flattened on mica but the extent of flattening differed with the chemical structure; for instance, third generation dendrimers were more flattened than second generation dendrimers whereas, dendrimers with higher number of branches had greater height above the mica surface. Hydrophilic and hydrophobic groups present towards the aerial interface existed in distinct zones rather than being distributed randomly, except in dendrimer with higher number of branches. The percentage of various hydrophobic groups on the surface of dendrimer was enhanced by increase in the number of branches but, was lowered by the presence of hydroxyl groups as the pendant terminal groups. Furthermore, the core of dendrimers was not always located towards the centre, its position was found to be altered by the number of branching points, type of terminal functional groups and the generation of dendrimer.     

The excited state dipole moments of betaine pyridinium investigated by an innovative solvatochromic analysis and TDDFT calculations

This work reports on the solvatochromic properties of a simple heterocyclic betaine pyridinium, 2-(1-pyridinio)benzimidazolate (SBPa), having promising potentialities in non-linear optics. From advanced PCM-TDDFT calculations, the solvatochromism of SBPa was found to be unusual, involving two different electronic states for absorption (S(0)→ S(2)) and emission (S(1)→S'(0)). To account for this behavior, we developed an innovative physical treatment which consists in a non-linear fit of the solvatochromic data using the Bilot-Kawski theoretical model and visualizing the least-square coefficient χ(2) on a 2D map as a function of the solute polarizability and gas phase absorption energy. In parallel, Kamlet-Taft correlations were undertaken to select a propitious set of electrostatic solvents usable in this treatment. Protic solvents that lead to specific interactions and nonpolar solvents that favor dimerization processes were excluded. From a choice of aprotic solvents with sufficiently high polarity, 4 dipole moments μ(g)(S(0)) = +9.1 D, μ(e)(S(2)) = -1.5 D, μ(e)(S(1)) = 0 D and μ(g)(S'(0)) = +3.31 D were determined, the 3 former values being in close agreement with TDDFT values, although the solute polarizability values seem underestimated. Anyhow, disregarding this discrepancy, we evaluated the static hyperpolarizability to β(0) = -64 × 10(-30) esu from the solvatochromic data in close agreement with DFT calculations.