The structure of some methyl and benzyl malonate derivatives of pyrimidine

Reaction of 2,4,6-trichloropyrimidine with sodium dibenzylmalonate in p-dioxane gave 4,6-dichloro-2-(dibenzylmalonyl)pyrimidine, while reaction of 2,4,6-trichloropyrimidine with sodium dimethylmalonate yielded both 4,6-dichloro-2-(dimethylmalonyl)pyrimidine and 2,2-bis-(4,6-dichloropyrimidin-2-yl)dimethylmalonate. Structural studies using nmr, ir and uv spectroscopy indicate that for the former two compounds in basic solvent, an equilibrium exists between the keto forms and resonance-stabilized enolate ions.     

Inductive limits and partitions of unity

Let E be the inductive limit of a family of locally convex topological vector spaces E_l. We introduce the concept of partitions of unity in E, which extends the usual partitions of unity in function spaces. Inductive limits admitting such a partition of unity have many interesting properties, similar to those of the strict inductive limits.They also have rather unusual properties concerning duals and spaces of mappings, which seem to be unknown, even in spaces likeD() andE().Some examples of such inductive limits are quoted at the end of the paper.     

Photoluminescence from E band centers in amorphous and crystalline SiO2

Photoluminescence (PL) originating from intrinsic defects in neutron-irradiated crystalline (x-) SiO₂ is observed and compared with that from amorphous (a-) SiO₂. The PL and photoluminescence excitation (PLE) spectra of x-SiO₂ are qualitatively similar to those of a-SiO₂. This suggests that PL centers, similar to those found in amorphous systems, are present in ordered systems. In addition, the PL and PLE spectra a-SiO₂ and a-As₂S₃ scale with energy band gap, suggesting that the radiative processes in a-SiO₂ and semiconducting chalcogenide glasses are alike. The similarity of the PL from x-SiO₂ to that from a-SiO₂ and the scaling of the PL from a-SiO₂ and a-As₂S₃ with energy band gap strongly suggest that PL centers are unique bonding configurations which primarily depend on the chemistry of the system rather than on the degree of long range order.     

Physicochemical Properties of Deuterated Compounds. 7th Communication. The H/D exchange between hydrogen and methane over Ni Catalyst

The isotopic exchange between hydrogen and methane over Ni catalyst has been studied as a function of temperature, isotopic substitution, and ratio of hydrogen to methane. The experimental results can be described by means of a model in which methane is adsorbed either as methyl or as methylene. The adsorbed species undergo one or several exchanges. The four required parameters are adjusted to the experimental results. The exchange of partially deuterated methane with H₂ or D₂ allowed us to study the isotopic effect on the adsorption and the exchange processes.     

Electrical manipulation of oligonucleotides grafted to charged surfaces

The electrical manipulation of short DNA molecules on surfaces offers novel functionalities with fascinating possibilities in the field of bio-interfaces. Here we present systematic investigations of the electrical interactions which govern the structure of oligonucleotides on charged gold surfaces. Successively, we address influences of the applied field strength, the role of DC electrode potentials, in particular for polycrystalline surfaces, as well as screening effects of the surrounding electrolyte solution. Data obtained for single and double stranded DNA exhibit differences which can be attributed to the dissimilar flexibility of the different molecular conformations. A comparison of the experimental results with a basic model shows how the alignment of the molecules adjusts according to a balance between electrically induced ordering and stochastic thermal motions. The presented conclusions are expected to be of general relevance for the behaviour of polyelectrolytes exposed to localized electric fields at interfaces.     

Novel Helmholtz-based photoacoustic sensor for trace gas detection at ppm level using GaInAsSb/GaAlAsSb DFB lasers

A new and compact photoacoustic sensor for trace gas detection in the 2-2.5 microm atmospheric window is reported. Both the development of antimonide-based DFB lasers with singlemode emission in this spectral range and a novel design of photoacoustic cell adapted to the characteristics of these lasers are discussed. The laser fabrication was made in two steps. The structure was firstly grown by molecular beam epitaxy then a metallic DFB grating was processed. The photoacoustic cell is based on a Helmholtz resonator that was designed in order to fully benefit from the highly divergent emission of the antimonide laser. An optimized modulation scheme based on wavelength modulation of the laser source combined with second harmonic detection has been implemented for efficient suppression of wall noise. Using a 2211 nm laser, sub-ppm detection limit has been demonstrated for ammonia.