Hommage à Henri-Edouard Audier du "Journal of mass spectrometry"

vendredi 13 janvier 2017
par  Administrateur

Henri Edouard Audier was born on February 18, 1940 in La Ciotat, a city on the French Mediterranean coast where he later returned every summer. He obtained his first scientific degree at the Ecole Normale Supérieure in 1962. Henri began research as “attaché de recherches” in the team of Marcel Fétizon at the Institut de Chimie des Substances Naturelles (ICSN) in the Centre National de la Recherche scientifique (CNRS) in Gif sur Yvette. In 1966, Henri presented his thesis on the use of mass spectrometry for the structural determination of natural products. In 1970, Marcel Fétizon created the “Laboratoire de Synthèse Organique” at the University of Orsay, which later moved to the Ecole Polytechnique in Palaiseau in 1974. Henri-Edouard Audier directed the mass spectrometry group in this laboratory until 1985. During the reorganization of the chemistry laboratories at the Ecole Polytechnique, the “Laboratoire des Mécanismes Réactionnels” was created. Henri was first co-director of this new entity and was made full director in 1989, a position he held until his retirement in 2002 with the title of “Directeur de Recherches émérite”. Over the course of his forty yearlong scientific career, Henri directed ten Ph.D. students (Yannik Hoppilliard, Guy Bouchoux, Jean-Claude. Tabet, Chaid Moustapha, Dorothée Robin-Berthomieux, Candida Monteiro, Piétrick Hudhomme, Valérie Troude, Guillaume van der Rest, Hristo Nedev) and the same number of post-doctoral fellows. Henri published over 200 articles and established scientific collaborations and strong friendships with numerous foreign colleagues including : Steen Hammerum (University of Copenhagen), Robert Flammang and André Maquestiau (University of Mons), Thomas Morton (University of California, Riverside), and Terry McMahon (University of Waterloo).

During his time at the ICSN, Henri employed mass spectrometry to determine the structure of various natural products such as terpenes, steroids, flavonoids and alkaloids. Among his most prominent results was the demonstration of the influence of stereochemistry on the fragmentation of ethylenic or polycyclic saturated ring systems. Henri also pioneered the introduction by microderivatization of appropriate functional groups, such as ethylene acetals, intomolecules such as keto-steroïds and keto-terpenes, in order to simplify their mass spectra. In 1969, Henri published a paper (Organic Mass Spectrometry, 2, 283–298) where he demonstrated the applicability of Stevenson’s rule to fragmentations leading to neutral and ionized molecular species. The corresponding fragmentations included McLafferty and retro-Diels-Alder rearrangements, cross-cleavage of four membered rings, and retro-ene fragmentation. This generalization of the Stevenson’s rule is now known as the “Stevenson-Audier” rule.

In 1977, Henri had the opportunity to use chemical ionization on one of the mass spectrometers at the ICSN where he performed a series of studies on simplemolecules including aldehydes, ketones, esters, oxiranes, oxetanes, alcohols, ethers, and aromatics. Henri demonstrated the occurrence of several types of molecular rearrangements on the corresponding protonated species, in particular processes involving hydrogen, alkyl group and aryl group migrations.

The year 1980 saw the arrival of one of the first VG ZAB 2F mass spectrometers at the Ecole Polytechnique. This was for Henri the starting point of series of studies on metastable ions using MIKE and CID-MIKE techniques on ions coming from various classes of molecules such as amines, ethers, carboxylic acids, esters, aromatics, and furans. Most of these molecules, and their isotopically substituted variants, were prepared by close collaborators of Henri : Arielle Milliet, Jean-Pierre Denhez, and Georges Sozzi. From the important amount of results accumulated during this period,
Henri was able to show that extensive skeletal rearrangements may occur in cations of lowinternal energy. He proposed isomerization mechanisms involving hydrogen migrations, reversible ring expansion-contraction, and reaction steps (substitutions, additions, exchanges) occurring inside isomeric forms such as ion-neutral complexes and distonic ions.

For several years, Henri championed a project to buy a Fourier transform ion cyclotron resonance mass spectrometer. This was accomplished in 1989, when a Bruker CMS 47X mass spectrometer equipped with an external EI/CI source and controlled gas inlets was installed at the Palaiseau laboratory. Until 2002, this new equipment was an opportunity for Henri to improve and complete previous studies and to examine new ion-molecule systems. Danielle Leblanc and Philippe Mourgues were key participants in these experiments as well as Julia Chamot-Rooke and Jacques Fossey who, in parallel, performed quantum chemical computations. Among the various ion-molecule reactions studied by Henri during this period one may cite alkene displacements, nucleophilic substitutions, hydrogen exchanges between oxonium, carbonium or carbene cations and small monofunctional molecules such as alkenes, alcohols, ethers, and benzene. Henri’s final work included studies on the chemistry occurring inside protonated adducts (for example water elimination from (ROH)2H+ complexes), or onthe strange reactivity of the [H2O, NH3]+• complex, and selective preparation and examination of the reactivity of monoand di-solvated ions (a typical example is the solvent catalyzed keto-enol tautomerisation).

Guy Bouchoux

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Journal of MASS SPECTROMETRY : Hommages à Henri-Edouard AUDIER

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