Hydrogen bonding in vitamin B6

Double-well potential energy surfaces for hydrogen bonding in crystalline vitamin B₆ have been associated with molecular environmental effects. New calculations, involving improved representations of a fragmentation model, include the introduction of a second pyridoxinium chloride system within the model in a “dimer-like” configuration. The new results confirm the double-well potential and the prediction of the experimentally observed position for the proton as being due essentially to environmental effects. Atomic difference maps are presented for the charge density distributions, which reflect the nature of the bonding as it depends on the proton position. Mulliken populations are examined particularly in relation to the “intermolecular” transfer of electrons.     

A non local density functional calculation of the diamagnetic susceptibilities and other electronic properties of noble gases and closed-shell ions

The non local weighted-density approximation (WDA) to the exchange-correlation potentialV _xc (r) is used to compute electron densities, ionization potentials and electron affinities of several atoms and ions. Especial care is taken in calculating and discussing 〈r ²〉 in noble gas atoms. Good results are obtained for all those quantities, but it is critical that the WDA is applied in such a way that it preserves the correct larger behaviour ofV _xc (r). A comparison of the calculated electron density with that of the Hartree-Fock method shows the effects of coulomb correlation. The density rearrangements upon the introduction of correlation agree qualitatively with the results of Configuration-Interaction calculations     

Crystal structure of 1-[N-2-aminoethyl)-aminopropyl]silatrane

The crystal structure of 1-[N-(2-aminoethyl)aminopropyl]silatrane has been determined by x-ray diffraction at room temperature. The Si←N bond distance (2.165(2) Å) is in the range observed for other 1-X-propylsilatranes (X = CN, OH, SH, Cl and SCN). The structure is partially disordered: the silatrane moiety displays a disorder that is typical for silatranes and the aminoethyl group terminating the planar chain linked to silicon is rotationally disordered.     

Second-order relativistic electron capture

Starting with the impulse approximation, we analyse second-order effects in relativistic electron capture. The relation of this model with relativistic distorted-wave approximations is clarified. In particular it is shown that the second-order spin-coupling terms in the RCDW theory are consistent with the correct form given by perturbation theory. In the semirelativistic limit, the RCDW results are shown to accord with the formulae of Moiseiwitsch for flip and nonflip transitions in the ultra-relativistic limit. This confirms that the continuum-distorted-wave model generalises to relativistic spinors, and highlights the defects of scalar models. We also present a new symmetric eikonal theory which gives reliable results for capture without change of spin, but leads to a divergent total cross section for spin-flip transitions in the second-order term. This effect, which is quite distinct from the spurious spin-flip amplitudes of the scalar symmetric eikonal theory, is taken as further evidence that the eikonal approximation is not valid for magnetic transitions.     

An attempt to prepare and characterize a soil reference material for Cr(VI) and Cr(III)

Reference materials for the speciation and quantification of chromium in contaminated soils were prepared by impregnating diatomaceous earth with BaCrO₄ and Cr₂O₃. The chronium concentrations of these materials were confirmed to be 200 mg/kg both by atomic absorption spectrometry and by instrumental neutron activation analysis, but monthly assays over two calendar quarters of the reference material impregnated with BaCrO₄ revealed the hexavalent chromium was not stable in this matrix.     

Trace aluminum determination and sampling problems of archeological bone employing destructive neutron activation analysis

A destructive neutron activation analysis procedure was developed for determining trace aluminum content in bone. It was found that soil contamination can influence the aluninum bone levels in prehistoric bone specimens. These maximum aluninum content values for prehistoric bone are larger than those of modern bone and comparable to aluminum levels present in bone from renal patients.     

Recherches en série triazepine-1,2,4: 1 - détermination de la structure de la triazolotriazépinone obtenue par action de l'acétylacétate d'éthyle sur le diamino-3,4 triazole-1,2,4

The condensation of 3,4-diamino 1,2,4-triazole with ethyl aceloacelate gave 6-methyl-8,9-dihydro(7H)-s-triazolo[4,3-b]-1,2,4-triazepin-8-one ( 2 ); 2 has been caracterized by nmr spectroscopy and by comparison with its methylated derivative prepared in an unambigous manner.     

Etude de la microstructure des oligomeres desactives du butadiene-1,3

Oligomers of butadiene have been prepared in hydrocarbons in the presence of butyllithium isomers. Nuclear magnetic resonance (NMR), gas chromatography and i.r. spectroscopy allowed the study of the microstructures of the products. Various parameters (nature of the deactivator, the solvent and the initiator as well as the monomer/initiator ratio) influence the microstructure. All the results may be explained on the basis of delocalized living species in anionic polymerization of conjugated dienes.     

Thermal properties of tetrahydroperparine derivatives

The thermal behaviour of tetrahydroperparine (THP) and its derivatives with various acids has been investigated. The acid is liberated from the formate derivative basically in two steps, while the other aliphatic acids are released quantitatively before the thermal decomposition of the THP molecule. The thermoanalytical curves, electrical conductivity data measured in the molten phase, and infrared spectra prove that while part of the formic acid is hydrogen-bonded the other part is bound ionically in the molecule. It may be assumed that the marked biological activity of the compound can be explained by this difference in the nature of the bonds.     

Glass forming ability and thermal stability in the system ZrF46BaF26PrF3

New glasses have been synthesized in the system ZrF₄6BaF₂6PrF₃. Glasses were prepared by conventional fusion method and the vitreous domain was established. For vitreous samples the thermal stability parameters were determined, so that the best compositions could be selected according to a compromise between high glass forming ability and thermal stability vs. crystallization.