Françoise Leclercq

Synthesis of glycosylated polyethylenimine with reduced toxicity and high transfecting efficiency.

A safe and efficient synthesis of glycosylated polyethylenimine using titanium (IV) isopropoxide and sodium borohydride has been carried out as a substitute for the highly toxic sodium cyanoborohydride method currently used. Poryplexes formed between DNA and the various glycosylated polyethylenimines appeared to be much less cytotoxic than polyethylenimine (PEI)/DNA polyplexes.

Structure of powder deuteroammonia between 2 and 180 K revisited: A refinement of the neutron diffraction pattern taking into account molecular reorientations: analysis of the diffuse intensity

The standard Rietveld profile analysis is a powerful tool for refining the structure of powder crystals. Nevertheless, in case of molecular crystals, where rigid groups undergo reorientations of large amplitude in well‐defined directions, thermal ellipsoids, even with anisotropic terms, may not be sufficient to account for the motion. That is the case for deuteroammonia for which strong librations of the ND3 groups are observed even at 2 K. In this paper we present a refinement of the structure of deuteroammonia using a model allowing the ND3 group to perform reorientations about the easy C3 axis of the cubic lattice; the adjustment of diffraction patterns measured at 2, 78, and 180 K shows the temperature dependence of the librational amplitude. The geometry of the ammonia molecule in the crystal is found to be the same as in the gas phase [rN–D=1.008(4) A] and is in excellent agreement with that determined by the analysis of the intramolecular structure factor for large momentum transfers; furthermore t...

Synthesis and biological activity of a fluoroketonucleoside: 7-(3-deoxy-3-fluoro-β-d-glycero-hex-2-enopyranosyl-4-ulose)theophylline

Abstract The title compound 5 was synthesized by direct oxidation of the fluoro precursor and not from an epoxyketo intermediate according to the Paulsen procedure, which has been used until now to obtain bromo- and chloro-ketonucleosides. Antineoplastic activity and immunosuppressive effect of 5 were studied on murin splenic lymphocytes (steady state or stimulated by PHA), and on RAJI and DAUDI cells, and compared with the activity of 3-(3-deoxy-β- d -glycero-hex-2-enopyranosyl-4-ulose)thymine. IC50 values showed that the fluoroderivative 5 has a higher antineoplastic activity and a lower immunosuppressive effect.

On the structure of solid Ca(ND3)x; with x≈6

The bcc structure of Ca(ND3)5.7 is found to be stable down to He temperatures. The crystal is characterized by frozen‐in orientational disorder and also positional disorder of the ND3 molecules. The latter may be explained by a distribution of octahedrally coordinated and tetrahedrally coordinated Ca ions. The relation of occupation numbers with stoichiometry cannot be made quantitatively, however. There are no indications of a significant departure from the geometry of a free ammonia molecule in the solid.

Aminodeoxynucleosides: synthesis and conformational studies of 7-(4-amino-4-deoxy-α-d-talopyranosyl)theophylline and 7-(6-amino-6-deoxy-α-d-mannopyranosyl)theophylline, and preparation of nucleoside-amino acid derivatives

Abstract The synthesis of new aminodeoxy and amino acid nucleosides of talose and mannose is described. The unusual conformation of these hexosylpurines revealed by n.m.r. spectroscopy is reported, as well as the unexpected results of some substitution reactions.

Low-frequency Raman spectra of sub- and supercritical CO2 : Qualitative analysis of the diffusion coefficient behavior

We report the results of the low-frequency Raman experiments on CO(2) which were carried out in a wide density range, along the liquid-gas coexistence curve in a temperature range of 293-303 K, and on the critical isochore of 94.4 cm(3) mol(-1) in a temperature range of 304-315 K. In our approach, the qualitative behavior of the diffusion coefficient D is predicted, assuming the following: first, that the low-frequency Raman spectra can be interpreted in terms of the translation rotation motions; second, that the random force could be replaced by the total force to calculate the friction coefficient; and finally, that the Einstein frequency is associated with the position of the maximum of the low-frequency Raman spectrum. The results show that the diffusion coefficient increases along the coexistence curve, and its values are almost constant on the critical isochore. The predicted values reproduce qualitatively those obtained by other techniques. The values of D were also calculated by molecular-dynamics simulation and they qualitatively reproduce the behavior of D.

A precise determination of the critical index η by Small Angle Neutron Scattering (SANS)

Abstract A precise determination of the critical index η has been obtained by SANS on the sodium-ND 3 mixture. The values η = 0.0317 ± 0.0013 8 and 0.0302 ± 0.0015 7 have been found for two experiments, using the Fisher/Langer scattering formalism. These results reconciliate SANS and light scattering experiments and are in favor of renormalization group theory predictions.

Quantum Rotation of Ammonia Molecules in Disordered Ca(NH3)6

Calcium hexaammine is a low electron density, metallic compound. In this expanded metal, the ammonia molecules show important rotational and reorientational motions down to 20 K as deduced from the study of the quasielastic neutron scattering ( LECLERCQ et al./1/ ). A complete understanding of the inelastic scattering needs a simultaneous determination of the structure in the whole temperature range. Since the calcium compound crystallizes in a high symmetry group (bcc) and since no phase transition occurs as the temperature is decreased, the ammonia molecules appear to be in a frozen-in orientationally disordered state at low temperature. For temperature lower than 10 K, the Inelastic Neutron Scattering spectrum shows a very asymmetric line shape with a maximum near the energy of uniaxial rotation of the NH3 / ND3 groups. This is interpreted by quantum rotation in a (random) distribution of low hindering potentials. It is shown that these properties are very sensitive to non-stoichiometry effects.

Ammonia rotations in ytterbiumhexaammine

The results of inelastic neutron scattering experiments on ytterbiumhexaammine are presented. At temperatures below 35 K, the dominant dynamical process is a uniaxial rotation of the ammonia in hindering potentials of about 35 meV. At higher temperatures, another type of ammonia motion is observed, which is described as reorientations of entire Yb(NH3)x complexes (x≊6).