TMDS-Pd/C: a convenient system for the reduction of acetals to ethers

A simple and practical procedure for the reduction of acetals to ethers is described. It is based on the use of a 1,1,3,3-tetramethyldisiloxane (TMDS)-Pd/C system in the presence of a Brønsted acid as the co-catalyst. The reaction occurs under mild conditions and ethers are obtained in high yields.     

Practical synthesis of (2'R)-2'-deoxy-2'-C-methyluridine by highly diastereoselective homogeneous hydrogenation

Diastereoselective hydrogenation of 2'-deoxy-2'-exo-methyleneuridine was carried out under homogeneous conditions using a low loading of a chiral Rh catalyst. This, coupled with improvements in the synthesis of the substrate, allowed the smooth pilot plant preparation of the title compound on >10 kg scale.     

Changes in the morphology of interstellar ice analogues after hydrogen atom exposure

The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H(2) formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H(2) is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of ?(0) = 2 × 10(16) D-atoms cm(-2) per layer of H(2)O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D(2) formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous.     

Zur Untersuchung von Arzneimitteln

Ohne Zusammenfassung     

Statistical mechanics of aliphatic chain layers,influence of chain-length mixing

A molecular model is used to simulate interfaces composed of surfactants and cosurfactants in microemulsions where molecules are anchored at the surface of spherical micelles. A Monte Carlo calculation of the conformational properties of the aliphatic layer is carried out taking into account the rotational isomerism of the chains and the binary random distribution of chain lengths. The thermodynamic behavior and the main structural features of the monolayer are analyzed in relation to some micellar properties.     

Doppler-free two-photon spectroscopy of the 2ν3 band of SF6

The assignments of most of the observed Doppler-free two-photon spectra of the 2ν₃ band of SF₆ near the P(14)–P(20) lines of a 10-μm CO₂ waveguide laser are reported. The rovibrational and anharmonic constants for this band were obtained, along with ground state constants determined from observed “forbidden” transitions.     

Polarographie radiochimique des solutions acides de TeIV

With ¹²¹Te (T_1/2=17 days) radiochemical polarography of [Te^IV]≤10^?9M is possible with negligible surface coverage. Deposition of Te is diffusion controlled. The potential range of Te⁰ formation is limited at negative potential by its reduction to HTe^?.     

Observation of Lamb dips by infrared fluorescence detection in D2CO

Fluorescence detected Lamb dips have been observed in D₂CO. The D₂CO was placed inside a CO₂ waveguide laser cavity and fluorescence detection was performed with a InSb detector. Possible explanations for this observation are discussed.     

Composite particle emission in relativistic heavy ion collisions

Inclusive spectra of d, t, and ³He have been measured over a wide range of fragment angles and energies. The observed spectra are well reproduced by the “coalescence model” with a coalescence radius p₀ which is independent of beam energies and which decreases as the sizes of the target-projectile combinations increase. The sizes of the interaction regions have been derived from these p₀ values. The experimental cross sections generally deviate from predictions of the firestreak model.