Charge density in crystalline citrinin from X-ray diffraction at 19 K

: En se basant sur un ensemble extensif (36 564 mesures) d'intensitks de diffraction des rayons X par un cristal unique obtenues i une tempkrature de 19 + 2 K, on a obtenu la distribution expkrimentale totale, p(r), ainsi que son laplacien, v2p(r), pour le mCtabolite de champignon citrinine, CI,H,,O5. On a ensuite analyst les 7698 donnCes indkpendantes d'intensitt k I'aide du formalisme multipble (pseudoatomes). On a determink les propriCtCs topologiques de p(r) suivant la thCorie quantique des atomes dans les molCcules. On a dCterminC les longueurs des liaisons CC et CO par leur inttgration numCrique; on a trouvt que leurs valeurs donnent une bonne corrilation avec celles obtenues i partir de la densite Clectronique des points critiques de liaison. On a utilisC des caractkristiques topologiques pour caractkriser l'extension du systtme conjuguC de la molCcule et pour confirmer la stabilitC de ses noyaux, particulibrement les deux formCs par les liaisons hydrogbnes intramoliculaires. On prisente des cartes de VZp(r) qui montrent les details de la distribution de charge de valence et qui fournissent un outil trbs sensible pour analyser la dtpendance de la densitC sur le modble adopt6 pour interpriter les donnCes de diffraction des rayons X. En se basant sur la forme de la surface molCculaire rCactive (l'enveloppe zCro du V2p(r)), on a confirm6 la rCactivitC connue de la molCcule vis-i-vis des nuclCophiles au niveau d'un atome de carbone sp2.

For the fungal metabolite citrinin, C13H14O5, the total experimental electron distribution ?(r) and its Laplacian have been obtained from an extensive set (36 564 measurements) of single-crystal X-ray diffracted intensities at a temperature of 19 ± 2 K. Relevant steps in data collection and processing are reported. The resulting 7698 independent intensity data have been analysed with a multipole (pseudoatoms) formalism. The topological properties of ?(r) have been determined according to the quantum theory of atoms in molecules. CC and CO bond path lengths have been obtained by numerical integration; their values are found to be well correlated with those of the electron density at the bond critical points. Topological features have been used to characterize the extension of the conjugated system of the molecule, and to confirm the stability of its rings, particularly the two formed by intramolecular H bonds. Maps of are presented, showing details in the valence charge distribution and providing a very sensitive tool for analysing dependence of the density on the model adopted to interpret X-ray data. The known chemical reactivity of the molecule towards nucleophiles at a Csp2 atom is confirmed by the shape of the molecular reactive surface (the zero envelope of ). Key words: experimental electron density, low-temperature X-ray diffraction, topological analysis, Laplacian of ?.