Copper(II) triflate-catalyzed reduction of carboxylic acids to alcohols and reductive etherification of carbonyl compounds

A protocol is described for the reduction of carboxylic acids to primary alcohols using 1,1,3,3-tetramethyldisiloxane (TMDS) and a catalytic amount of Cu(OTf)₂. Aliphatic as well as aromatic carboxylic acids are reduced in high selectivity and good yields. TMDS/Cu(OTf)₂ has also been found to be an efficient catalytic reducing system for the preparation of symmetrical ethers from carbonyl compounds under mild conditions.     

Engineering the Donor Selectivity of D‐Fructose‐6‐Phosphate Aldolase for Biocatalytic Asymmetric Cross‐Aldol Additions of Glycolaldehyde

D ‐Fructose‐6‐phosphate aldolase (FSA) is a unique catalyst for asymmetric cross‐aldol additions of glycolaldehyde. A combination of a structure‐guided approach of saturation mutagenesis, site‐directed mutagenesis, and computational modeling was applied to construct a set of FSA variants that improved the catalytic efficiency towards glycolaldehyde dimerization up to 1800‐fold. A combination of mutations in positions L107, A129, and A165 provided a toolbox of FSA variants that expand the synthetic possibilities towards the preparation of aldose‐like carbohydrate compounds. The new FSA variants were applied as highly efficient catalysts for cross‐aldol additions of glycolaldehyde to N‐carbobenzyloxyaminoaldehydes to furnish between 80–98 % aldol adduct under optimized reaction conditions. Donor competition experiments showed high selectivity for glycolaldehyde relative to dihydroxyacetone or hydroxyacetone. These results demonstrate the exceptional malleability of the active site in FSA, which can be remodeled to accept a wide spectrum of donor and acceptor substrates with high efficiency and selectivity.     

Excitation of theΔ (1232)-resonance in proton-nucleus collisions

The excitation of theΔ resonance is observed in proton collisions on C, Nb and Pb targets at 0.8 and 1.6 GeV incident energies. The mass E₀ and widthΓ of the resonance are determined from the invariant mass spectra of correlated (p, π^±)-pairs in the final state of the collision: The mass E₀ is smaller than that of the free resonance, however by comparing to intra-nuclear cascade calculations, this reduction is traced back to the effects of Fermi motion, NN scattering and pion reabsorption in nuclear matter.     

Radial and time resolved measurement of electron density in a copper vapour laser

The electron density (n_e) is determined by measuring the associated microscopic Stark effect on the Balmer emission lines of atomic hydrogen present as a trace in the laser active volume. We deduce the radial and temporal evolution of n_e and suggest the main physical processes leading to this evolution.     

Waveguide and diode heterodyne measurements with CO2 laser and assignment of the CW FIR laser emission of OCS

Heterodyne spectra of carbonyl sulfide have been obtained with saturation in a CO₂ waveguide laser and without saturation with a diode laser. The absolute uncertainties of the measured positions lie between 10⁻⁴ and 7 × 10⁻⁶ cm⁻¹. The CW submillimeter laser line of OCS at 378 μm has been assigned to the J = 65 → 64 transition in the 02²0e state of ¹⁶O¹²C³²S, with a pumping through the R(64) line of 02²0e ← 00⁰0, a Δ-Σ transition weakly allowed by the l-type resonance.     

Absolute diode-laser frequency calibration using varactor mixing with a stabilized CO2 laser. Ozone spectrum near the 9R6 CO2 frequency

Efficient infrared varactor mixing near 9 μm has been performed between diode-laser and CO₂ laser. Difference frequency up to 17 GHz has been detected using non linear mixing between the two radiations and the first four harmonics of a microwave frequency (f = 4.2 GHz). As a result, the absorption spectrum of ozone near the 9R₆ CO₂ line is frequency scaled over a 1.7 cm^-1 range with microwave accuracy.     

Invar properties in the rare earth-3d transition metal alloys

The RCo₂ and R₂Fe₁₇ compounds (R = rare earth) exhibit Invar-like thermal expansion anomalies below their ordering temperatures. These spontaneous volume magnetostrictions are discussed by considering their magnetic properties. In RCo₂ compounds there is no intrisinc Co-moment is induced by the exchange and applied fields. The volume expansion anomaly is associated with the onset of the 3d magnetic moment. IN R₂Fe₁₇ compounds there is an intrisinc Fe- moment. Magnetic structures give evidence for positive and negative exchange interactions between Fe atoms which are strongly distance dependent. The thermal expansion anomaly is a result of this distance of the magnetic interactions.     

Measurement of infrared transition of NH3 from a microwave line shift due to a non-resonance infrared field

An i.r. spectroscopic technique is proposed which may be useful for the determination of i.r. transitions and for the assignment of molecular spectra. This method is based on the microwave line shift in the presence of a non-resonant laser field. For NH₃ gas, the accuracy is of about the same order of magnitude as the one obtained from the i.r. Stark spectroscopy technique.