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See detailSynthesis of New Tetraethyl(N-alkyl-1-aminoethan-1,1-diyl)bisphosphonates and ESR Analysis of Chemical Exchange of Derived Nitroxides of Acyclic Aminobisphosphonates.
Olive, Gilles ULg; Rockenbauer, Antal; Rozanska, Xavier et al

in Phosphorus, Sulfur & Silicon & the Related Elements (2007), 182(10), 2359-2369

The synthesis and the full characterization of two new linear bisphosphonates(tetraethyl(N-tert-butyl-1-aminoethan-1,1-diyl)bisphosphonate and tetraethyl(Nsec-butyl-1-aminoethan-1,1-diyl)bisphosphonate ... [more ▼]

The synthesis and the full characterization of two new linear bisphosphonates(tetraethyl(N-tert-butyl-1-aminoethan-1,1-diyl)bisphosphonate and tetraethyl(Nsec-butyl-1-aminoethan-1,1-diyl)bisphosphonate), and the first analysis of the ESR spectra of the corresponding nitroxides is reported. The preliminary results of theoretical calculations on model compounds suggest a small B0 (in the McConnell equation). The results of bisphosphonate ester and bisphosphonic acid are similar. The discrepancies of P coupling for the diphosphorus compound stems from B2 that is different when the dihedral angle is larger than 90◦. [less ▲]

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See detailESR Investigation of Chemical Exchange in Geminally Diphosphorylated Linear Nitroxide Radicals
Rockenbauer, Antal; Olive, Gilles ULg; Rozanska, Xavier et al

in Journal of Physical Chemistry A (2004), 108(25), 5484-5489

For geminally diphosphorylated linear nitroxide radicals, a marked line width alternation (LWA) can be observed. The LWA appears irrespectively whether the investigated radicals R¢¢N(O¥)C(P(O)(OEt)2)2R¢ ... [more ▼]

For geminally diphosphorylated linear nitroxide radicals, a marked line width alternation (LWA) can be observed. The LWA appears irrespectively whether the investigated radicals R¢¢N(O¥)C(P(O)(OEt)2)2R¢ contain any chiral group or not. If R¢¢ ) tert-butyl and R¢ ) H, the small â-hydrogen coupling indicates a completely blocked rotation around the N-C ó-bond and the LWA can be assigned to a chemical exchange between conformations in which the phosphoryl groups have a symmetric and a nonsymmetric geometry. The conformational change is accompanied by the deformation of the CP2 bonding angle and the rate of exchange is slowed in pentane for which the solvent molecules can be trapped by the chelating phosphoryl groups. If R¢¢ ) benzyl, both the proton hyperfine lines of the CH2 group and the phosphorus lines of the CP2 group produce a LWA; two coalescences can be observed. In the case of a chiral R¢¢ group (R¢¢ ) secondary butyl, R¢ ) methyl) a tentative four-site model can explain the highly complex LWA. [less ▲]

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See detailLarge phosphorus hyperfine coupling as a sensitive tool for studying molecular dynamics : ESR and Molecular Mechanics studies of ring interconversion in cis-2,5-diphosphoryl-2,5-dimethyl-pyrrolidinoxyl radical
Rockenbauer, Antal; Gaudel-Siri, Anouk; Siri, Didier et al

in Journal of Physical Chemistry A (2003), 107(19), 3851-3857

ESR spectra of cis- and trans-â-diphosphorylated pyrrolidine-N-oxyl radicals, c-1 and t-1, were studied in liquid and frozen solution. The expected 1:2:1 triplet (aP (2)) of the 1:1:1 triplet (aN) was ... [more ▼]

ESR spectra of cis- and trans-â-diphosphorylated pyrrolidine-N-oxyl radicals, c-1 and t-1, were studied in liquid and frozen solution. The expected 1:2:1 triplet (aP (2)) of the 1:1:1 triplet (aN) was observed for t-1; however, for c-1, the inner lines of the 1:2:1 triplet showed a dramatic broadening characteristic of chemical exchange between two equivalent conformations. Owing to the large difference in the hyperfine splitting constants (hfsc) of the exchanging phosphorus (¢aP 21 G), the coalescence temperature was unusually high (193 K, in n-pentane), and the potential barrier for ring interconversion (10.5 kJ mol-1) was easily obtained from the temperature dependence of the exchange rate. This value was in very good agreement with the value obtained for an empirical pseudorotational potential (11 kJ mol-1) that was adjusted to fit the temperature dependence of the phosphorus hfsc. For c-1, molecular mechanics calculations gave similar characteristics for the pseudorotational potential and indicated the existence of two identical minima with distorted geometries lying between 3T4 and 3E or 4T3 and E3. For t-1, only the 3T4 conformer was found to be significantly populated. Frozen solution spectra showed that the phosphorus hfsc anisotropy is higher when the C-P bond is pseudoaxial; this result can be explained by a geometry-dependent delocalization of the unpaired electron into the phosphorus 3p orbitals. [less ▲]

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See detail2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-1-oxide: evaluation of the spin trapping properties
Olive, Gilles ULg; Mercier, Anne; Le Moigne, François et al

in Free Radical Biology & Medicine (2000), 28(3), 403-408

The 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-l-oxide (EMPO), an easily prepared pyrroline-Noxide has been tested as a free radical scavenger. Spin adducts of superoxide, hydroxyl radical, and ... [more ▼]

The 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-l-oxide (EMPO), an easily prepared pyrroline-Noxide has been tested as a free radical scavenger. Spin adducts of superoxide, hydroxyl radical, and other free radicals were characterized in phosphate buffer at pH 7.0 and 5.6. At pH 7 in phosphate buffer, the EMPO/O2 2• spin adduct was estimated to be about five times more persistent than its DMPO analogue. Furthermore, its decay does not produce the EMPO/HO• adduct. [less ▲]

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See detailSynthesis of Tetraalkyl(Pyrrolidine-2,2-diyl)bisphosphonates and 2,2-Bis(diethoxyphosphoryl)-3,4-dihydro-2H-pyrrole 1-Oxide; ESR Study of Derived Nitroxides
Olive, Gilles ULg; Le Moigne, François; Mercier, Anne et al

in Journal of Organic Chemistry (1998), 63(24), 9095-9099

Synthesis of Tetraalkyl (Pyrrolidine-2,2-diyl)bisphosphonates and 2,2-Bis(diethoxyphosphoryl)-3,4-dihydro-2Hpyrrole 1-Oxide; ESR Study of Derived Nitroxides

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See detailCombined Ring Inversion and Side Group Rotation in Geminal Diphosphoryl Substituted Pyrrolinoxyl Radicals: ESR Analysis of Chemical Exchange between Four Nonequivalent Sites
Rockenbauer, Antal; Mercier, Anne; Le Moigne, François et al

in Journal of Physical Chemistry A (1997), 101(43), 7965-7970

The ESR spectra of three diphosphorylated pyrrolidinoxyl radicals have been studied over a large temperature range. While for the trans 2,5-disubstituted compound 1 no line width alternation was found ... [more ▼]

The ESR spectra of three diphosphorylated pyrrolidinoxyl radicals have been studied over a large temperature range. While for the trans 2,5-disubstituted compound 1 no line width alternation was found, for the 2,2-disubstituted compounds 2 and 3, dramatic changes in the spectra were observed as a function of the temperature. These changes were explained by a four-site chemical exchange model including both ring inversion and hindered rotation around the carbon-phosphorus bonds. For radical 3, the presence of additional 5,5-dimethyl substitution can completely block rotations around carbon-phosphorus bonds for certain ring geometries, while for other ring conformations chemical exchange still occurs through combined inversionrotation processes. An effective two-site model composed of nonequivalent sites and a superposition model composed of a pair of exchanging conformers and a pair of nonexchanging conformers were used to simulate spectrum variations. A satisfactory fit was obtained over the entire temperature range investigated. From the temperature dependence of the exchange frequencies the potential barriers for ring inversion (27 kJ/mol), for combined inversion-rotation (11 kJ/mol), and for rotation around the carbon-phosphorus bonds (14 kJ/mol) were estimated. [less ▲]

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