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Université de Fribourg

Hydrogen bond stabilization in Diels–Alder transition states: The cycloaddition of hydroxy-ortho-quinodimethane with fumaric acid and dimethylfumarate

Tamilmani, Venkatachalam ; Daul, Claude A. ; Lage Robles, Jaime ; Bochet, Christian G. ; Venuvanalingam, P.

In: Chemical Physics Letters, 2005, vol. 406 (4-6), p. 355-359

DFT investigations on the mechanism of Diels–Alder reactions of a hydroxy-ortho-quinodimethane with fumaric acid derivatives were performed to understand the origin of the syn or anti configuration of the adducts. The diene hydroxyl group and the dieneophile carboxyl group show hydrogen bonding in the transition state, significantly favouring the syn product. This reaction is poorly...

Université de Fribourg

Chromatic Orthogonality in Organic Synthesis

Bochet, Christian G.

In: Synlett, 2004, p. 2268-2274

A major challenge in organic synthesis is the selective reaction of a functional group in the presence of others. This can be achieved by using an appropriate reagent, tuned to react exclusively at the desired center. An alternate approach would be to use a single reagent, and to transmit from the outside the information as to where it should react. This account describes the use of light as a...

Université de Fribourg

Geometry determination of tetrasubstituted stilbenes by proton NMR spectroscopy

Fluxá, Viviana S. ; Jenny, Titus A. ; Bochet, Christian G.

In: Tetrahedron Letters, 2005, vol. 46(2), p. 3793-3795

A simple spectroscopic method was applied to determine the geometry of tetrasubstituted alkenes. The observation of the ⁵J-coupling constants in proton NMR spectra on the ¹³C satellite signals could confirm the previous misassignment of 2,3-diphenylbutene. Hence, the (E)-isomer showed a 1.5 Hz coupling constant, whereas the (Z)-isomer showed a 1.1 Hz coupling constant. Based on this new...

Université de Fribourg

Electron collisions with NO: Elastic scattering, vibrational excitation, and ²Πi1/2 ⇌ ²Π3/2 transitions

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2005, vol. 38, p. 603

Absolute differential elastic and vibrational excitation cross sections have been measured for NO at 135° with resolution of the ²Π1/2 and ²Π3/2 spin-orbit components of the ground electronic term. The electronic fine structure excitation is dominated by the ³Σ⁻ and the ¹Δ resonances of NO⁻, the nonresonant contribution is very small. The cross section is very large, it has about the...

Université de Fribourg

Transitions between the ²Π₁͵₂ and ²Π₁͵₃ spin-orbit components of NO induced by impact of slow electrons

Allan, Michael

In: Physical Review Letters, 2004, vol. 93, p. 063201-63204

The electron impact cross section for the transition between the ²Π₁͵₂ and ²Π₁͵₃ spin-orbit components of the ground electronic term of nitric oxide, separated by 15 meV, has been measured as a function of electron energy at a scattering angle of Θ= 135°. It is dominated by the ³Σ⁻ and the ¹Δ resonances. Its magnitude is very large, at peak about equal to that of the elastic...

Université de Fribourg

Excitation of the four fundamental vibrations of CH₄ by electron impact near threshold

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2005, vol. 38, p. 1679

Absolute differential elastic and vibrational excitation cross sections have been measured for CH₄ at 90° and from 0.1 to 1.5 eV, with the resolution of all four vibrational modes. Threshold peaks were observed in the excitation of the ν1, ν3 and ν4 modes, but not in the ν2 mode. These results are in good agreement with the recent calculation of Nishimura and Gianturco (2002 J. Phys. B:...

Université de Fribourg

Facteurs influençant le transfert d'électron photoinduit

Muller, Pierre-Alain ; Haselbach, Edwin (Dir.) ; Vauthey, Eric (Codir.)

Thèse de doctorat : Université de Fribourg, 2001 ; no 1341.

Le sujet de cette thèse est l’étude de différents facteurs influençant le transfert d’électron photoinduit ou la recombinaison des charges et qui ne sont pas liés à la force motrice thermodynamique. Un grand nombre de techniques expérimentales ont été utilisées, allant de la spectroscopie photoélectronique pour la mesure des potentiels d’ionisation à la spectroscopie des...

Université de Fribourg

Complexation and protonation behaviour of chiral tetradentate polypyridines derived from α-Pinene

Düggeli, Mathias ; Schläpfer, Carl-Willhelm (Dir.) ; Zelewsky, Alexander von (Codir.) ; Belser, Peter (Codir.) ; Stoeckli-Evans, Helen (Codir.)

Thèse de doctorat : Université de Fribourg, 2002 ; Nr. 1382.

Im Rahmen der vorliegenden Arbeit wurden neue enantiomerenreine 5’- und 6’- substituierte, mit Pinen annellierte Bipyridin- (Pinen-bpy Derivate) und N-Pyridin- Liganden (Pinen-N-py Derivate) hergestellt. Die 6’-Brom substituierten Pinen-bpy Derivate stellen dabei geeignete Zwischenstufen für die Synthese von weiteren 6’- substituierten Pinen-bpy Derivate dar. Tetradentate Liganden...

Université de Fribourg

Glycosylphosphatidylinositol membrane anchors in "Saccharomyces cerevisiae" : characterization of proteins involved in side chain modifications

Flury, Isabelle ; Conzelmann, Andreas (Dir.) ; Aebi, Markus (Codir.) ; Puoti, Alessandro (Codir.)

Thèse de doctorat : Université de Fribourg, 2001 ; Nr. 1361.

Die Verankerung von bestimmten Proteinen an der Aussenseite der Plasmamembran mittels eines Glycosylphosphatidylinositol (GPI)-Ankers ist in eukaryontischen Zellen weit verbreitet. Es gibt Hinweise, dass GPI-Anker neben ihrer Funktion als stabiler Anker auch eine wichtige Rolle in der Uebertragung von Signalen und in der Sortierung von Proteinen spielen. Sowohl die Biosynthese des GPI-Ankers als...

Université de Genève

Rigid-rod β-barrel pores as enzyme sensors

Sordé, Nathalie ; Matile, Stefan (Dir.)

Thèse de doctorat : Université de Genève, 2004 ; Sc. 3575.