Magazine Articles |
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Bourguignon, B., Béroff, K., Bréchignac, P., Dujardin, G., Leach, S., & and Zehnacker-Rentien, A. (2017). In the wake of Physical Chemistry under irradiation: onward to the Institute of Molecular Sciences at Orsay. Histoire de la Recherche Contemporaine, 6, 16–27.
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Peer-reviewed Publications |
Alata, I., Perez-Mellor, A., Ben Nasr, F., Scuderi, D., Steinmetz, V., Gobert, F., Jaidane, N. E., & Zehnacker-Rentien, A. (2017). Does the Residues Chirality Modify the Conformation of a Cyclo-Dipeptide? Vibrational Spectroscopy of Protonated Cyclo-diphenylalanine in the Gas Phase. J. Phys. Chem. A, 121(38), 7130–7138.
Résumé: The structure of a protonated diketopiperazine dipeptide, cyclo-diphenylalanine, is studied by means of infrared multiple photon dissociation spectroscopy combined with quantum chemical calculations. Protonation exclusively occurs on the oxygen site and, in the most stable conformer, results to an intramolecular OH center dot center dot center dot pi interaction, accompanied by a CH-pi interaction. Higher energy conformers with free OH and NH center dot center dot center dot pi interactions are observed as well, due to kinetic trapping. Optimization of the intramolecular interactions involving the aromatic ring dictates the geometry of the benzyl substituents. Changing the chirality of one of the residues has consequences on the CH center dot center dot center dot pi interaction, which is of C alpha H center dot center dot center dot pi nature for LD, while LL shows a C beta H center dot center dot center dot pi interaction. Higher-energy conformers also display some differences in the nature of the intramolecular interactions.
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Broquier, M., Soorkia, S., Pino, G., Dedonder-Lardeux, C., Jouvet, C., & Gregoire, G. (2017). Excited State Dynamics of Cold Protonated Cytosine Tautomers: Characterization of Charge Transfer, Intersystem Crossing, and Internal Conversion Processes. J. Phys. Chem. A, 121(34), 6429–6439.
Résumé: Charge transfer reactions are ubiquitous in chemical reactivity and often viewed as ultrafast processes. For DNA, femtochemistry has undeniably revealed the primary stage of the deactivation dynamics of the locally excited state following electronic excitation. We here demonstrate that the full time scale excited state dynamics can be followed up to milliseconds through an original pump-probe photodissociation scheme applied to cryogenic ion spectroscopy. Protonated cytosine is chosen as a benchmark system in which the locally excited (1)pipi* state decays in the femtosecond range toward long-lived charge transfer and triplet states with lifetimes ranging from microseconds to milliseconds, respectively. A three-step mechanism ((1)pipi* --> (1)CT --> (3)pipi*) is proposed where internal conversion from each state can occur leading ultimately to fragmentation in the ground electronic state.
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Garcia, R. L., Nieuwjaer, N., Desfrancois, C., Lecomte, F., Leite, S. D., Manil, B., Broquier, M., & Gregoire, G. (2017). Vibronic spectra of protonated hydroxypyridines: contributions of prefulvenic and planar structures. Phys. Chem. Chem. Phys., 19(12), 8258–8268.
Résumé: Various hydroxypyridine derivatives are endogenous or synthetic photosensitizers which could contribute to solar radiation damage. The study of their excited states could lead to a better understanding of their action mechanisms. We present here the ultraviolet (UV) spectra of the protonated 2-, 3- and 4-hydroxypyridine. These spectra were obtained with an experimental device coupling an electrospray ion source with a cold quadrupole ion trap and a time of flight mass spectrometer. They display well resolved vibrational structures, with a clear influence of the position of the OH group. These results are interpreted with excited states calculations at the coupled cluster CC2 level.
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Perez-Mellor, A., & Zehnacker, A. (2017). Vibrational circular dichroism of a 2,5-diketopiperazine (DKP) peptide: Evidence for dimer formation in cyclo LL or LD diphenylalanine in the solid state. Chirality, 29(2), 89–96.
Résumé: The diastereomer diketopiperazine (DKP) peptides built on phenylalanine, namely, cyclo diphenylalanine LPhe-LPhe and LPhe-DPhe, were studied in the solid phase by vibrational circular dichroism (VCD) coupled to quantum chemical calculations. The unit structure of cyclo LPhe-LPhe in KBr pellets is a dimer bridged by two strong NH center dot center dot center dot O hydrogen bonds. The intense bisignate signature in the CO stretch region is interpreted in terms of two contributions arising from the free COs of the dimer and the antisymmetrical combination of the bound COs. In contrast, cyclo LPhe-DPhe shows no VCD signal in relation to its symmetric nature.
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Shafizadeh, N., Soorkia, S., Gregoire, G., Broquier, M., Crestoni, M. E., & Soep, B. (2017). Dioxygen Binding to Protonated Heme in the Gas Phase, an Intermediate Between Ferric and Ferrous Heme. Chem.-Eur. J., 23(54), 13493–13500.
Résumé: With a view to characterizing the influence of the electronic structure of the Fe atom on the nature of its bond with dioxygen (O-2) in heme compounds, a study of the UV/Vis action spectra and binding energies of heme-O-2 molecules has been undertaken in the gas phase. The binding reaction of protonated ferrous heme [Fe-II-hemeH](+) with O-2 has been studied in the gas phase by determining the equilibrium of complexed [Fe-II-hemeH(O-2)](+) with uncomplexed protonated heme in an ion trap at controlled temperatures. The binding energy of O-2 to the Fe atom of protonated ferrous heme was obtained from a van't Hoff plot. Surprisingly, this energy (1540 +/- 170 cm(-1), 18.4 +/- 2 kJmol(-1)) is intermediate between those of ferric heme and ferrous heme. This result is interpreted in terms of a delocalization of the positive charge over the porphyrin cycle, such that the Fe atom bears a fractional positive charge. The resulting electron distribution on the Fe atom differs notably from that of a purely low-spin ferrous heme [Fe-II-heme(O-2)] complex, as deduced from its absorption spectrum. It also differs from that of ferric heme [Fe-III-heme(O-2)](+), as evidenced by the absorption spectra. Protonated heme creates a specific bond that cannot accommodate strong sigma donation.
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Szczepaniak, U., Kolos, R., Gronowski, M., Chevalier, M., Guillemin JC., Turowski M., Custer, T., & Crépin, C. (2017). Cryogenic Photochemical Synthesis and Electronic Spectroscopy of Cyanotetracetylene. JOURNAL OF PHYSICAL CHEMISTRY A, 121(39), 7374–7384.
Résumé: HC9N is a molecule of astrochemical interest. In this study, it was produced in cryogenic Ar and Kr matrices from UV-photolyzed diacetylene/cyanodiacetylene mixtures. Its strong phosphorescence was discovered and served for the identification of the compound. Vibrationally resolved phosphorescence excitation spectra gave insight into excited singlet electronic states. Two electronic systems were observed around 26 00034 000 cm(-1) and 35 000-50 000 cm(-1). Energies of the second excited singlet and the lowest triplet state were derived from analysis of these systems. Vibrational and electronic spectroscopic features were assigned with the assistance of density functional theory calculations. Some trends concerning the electronic spectroscopy of HC2+1N family molecules are presented.
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Thon, R., Chin, W., Chamma, D., Gutiérrez-Quintanilla, A., Chevalier, M., Galaup, J. - P., & Crépin, C. (2017). W(CO) 6 in cryogenic solids: A comparative study of vibrational properties. Journal of Luminescence, 191, 78–86.
Résumé: A comparative study of the vibrational properties of W(CO)6 has been performed in different solids at cryogenic temperatures focusing on the IR absorption and the vibrational dynamics of the CO stretching mode of the organometallic compound. Guest-host interactions are investigated in doped solids through the linear IR spectroscopy and four-wave mixing techniques at different temperatures. We show how the host nature, the trapping site, the crystallographic ordering affect the properties of the guest molecule and in particular its vibrational dynamics.
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Uriarte, I., Ecija, P., Lozada-Garcia, R., Carcabal, P., & Cocinero, E. J. (2017). Investigating the Conformation of the Bridged Monosaccharide Levoglucosan. Chemphyschem, , 01242.
Résumé: Levoglucosan is one of the main products of the thermal degradation of glucose and cellulose and is commonly used as a tracer for biomass burning. Herein we report a conformational analysis of levoglucosan under isolation conditions, by means of microwave spectroscopy coupled with ultrafast laser vaporization in supersonic expansions. We observed three different conformations of levoglucosan in the gas phase. They all share a common heavy atom rigid bicyclic structure. The difference between the three of them lies in the network of intramolecular hydrogen bonds that arises from the OH groups at positions 2, 3 and 4. The different combinations of H-bonds give richness to the conformational landscape of levoglucosan. The gas phase conformers obtained in this work are compared to the crystal structure of levoglucosan previously reported. Although the heavy atom frame remains unchanged, there are significant differences in the positions of the H-atoms. In addition, the levoglucosan structure can be compared to the related glucose, for which gas phase conformational studies exist in the literature. In this case, in going from glucose to levoglucosan, there is an inversion in the chair conformation of the pyranose ring. This forces the OH groups to adopt axial positions (instead of the more favorable equatorial positions in glucose) and completely changes the pattern of intramolecular H-bonds.
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