Radical amination with sulfonyl azides: a powerful method for the formation of C-N bonds

A novel reaction for the introduction of an azide moiety by means of a mild radical process is currently under development. Sulfonyl azides are suitable azidating agents for nucleophilic radicals, such as secondary and tertiary alkyl radicals. More electrophilic radicals, such as enolate radicals, do not react with sulfonyl azides. This feature allowed the development of efficient intra- and intermolecular carboazidations of olefins. Due to the versatility of the azido group, this reaction has an important synthetic potential, as already demonstrated by the preparation of the core of several alkaloids, particularly those containing an amino-substituted quaternary carbon center, such as FR901483.     

Parity-broken chiral spin dynamics in Ba₃NbFe₃Si₂O₁₄

The spin-wave excitations emerging from the chiral helically modulated 120° magnetic order in a langasite Ba?NbFe?Si?O?? enantiopure crystal were investigated by unpolarized and polarized inelastic neutron scattering. A dynamical fingerprint of the chiral ground state is obtained, singularized by (i) spectral weight asymmetries answerable to the structural chirality and (ii) a full chirality of the spin correlations observed over the whole energy spectrum. The intrinsic chiral nature of the spin waves' elementary excitations is shown in the absence of macroscopic time-reversal symmetry breaking.     

Separation of saponins and determination of quinovic acid 3-O-α-L-rhamnopyranoside fromNauclea diderrichii (de Wild) Merr. Bark by high performance liquid chromatography

Summary A reversed-phase HPLC determination of 11 saponins and an alkaloid glycoside inNauclea diderrichii bark is described. Quantitative analysis of quinovic acid 3-0-α-L-rhamnopyranoside which is one of the main saponins was determined, using Chrysanthelline A as internal standard. The complete separation was achieved in 47 minutes. The method of quantification was validated.     

Effondrement de quotients aléatoires de groupes hyperboliques avec torsion

We show that random quotients of hyperbolic groups with ‘harmful’ torsion collapse at densities smaller than expected. To cite this article: Y. Ollivier, C. R. Acad. Sci. Paris, Ser. I 341 (2005).     

Adductor spasmodic dysphonia: case reports withacoustic analysis following botulinum toxin injection and acupuncture

We analyzed frequency and duration parameters of voice and speech in two men with adductor spasmodic dysphonia (SD). One was treated with botulinum toxin injection; the other received acupuncture therapy. Im provement after acupuncture therapy in terms of standard deviation of fundamental frequency, acoustic perturbation measurements, durational measurements of voice and speech, and spectrographic analysis was comparable to the results achieved with botulinum toxin injection. Voice and speech parameters were stable I year after acupuncture therapy.     

Gluco-indole alkaloids from the bark of Nauclea diderrichii. 1H and 13C NMR assignments of 3alpha-5alpha-tetrahydrodeoxycordifoline lactam and cadambine acid

Detailed (1)H and (13)C NMR assignments of 3alpha-5alpha-tetrahydrodeoxycordifoline lactam and cadambine acid, isolated from the bark of the Nauclea diderrichii (de Wild.) Merr. (Rubiaceae) were achieved by 1D and 2D techniques such as DEPT, HMBC, HMQC, COSY and NOESY.     

Comparison of the dynamics of MIL-53(Cr) and MIL-47(V) frameworks using neutron scattering and DFT methods

The low-frequency modes of MIL-47(V) and MIL-53(Cr) frameworks have been measured by inelastic neutron scattering. The librational modes of benzene are very close in frequency in the two structures. First-principles calculations have been performed to assign the measured spectra. The calculated values of the rotational barriers of the benzene rings are in reasonable agreement with experimental data. The relatively large barriers (413–588 meV) explain the absence of quasi-elastic broadening on the neutron time scale.     

Changes in silicon elastomeric surface properties under stretching induced by three surface treatments

Poly(dimethylsiloxane) (PDMS) substrates are used in many applications where the substrates need to be elongated and various treatments are used to regulate their surface properties. In this article, we compare the effect of three of such treatments, namely, UV irradiation, water plasma, and plasma polymerization, both from a molecular and from a macroscopic point of view. We focus our attention in particular on the behavior of the treated surfaces under mechanical stretching. UV irradiation induces the substitution of methyl groups by hydroxyl and acid groups, water plasma leads to a silicate-like layer, and plasma polymerization causes the formation of an organic thin film with a major content of anhydride and acid groups. Stretching induces cracks on the surface both for silicate-like layers and for plasma polymer thin coatings. This is not the case for the UV irradiated PDMS substrates. We then analyzed the chemical composition of these cracks. In the case of water plasma, the cracks reveal native PDMS. In the case of plasma polymerization, the cracks reveal modified PDMS. The contact angles of plasma polymer and UV treated surfaces vary only very slightly under stretching, whereas large variations are observed for water plasma treatments. The small variation in the contact angle values observed on the plasma polymer thin film under stretching even when cracks appear on the surface are explained by the specific chemistry of the PDMS in the cracks. We find that it is very different from native PDMS and that its structure is somewhere between Si(O2) and Si(O3). This is, to our knowledge, the first study where different surface treatments of PDMS are compared for films under stretching.