[Todos] Seminario INQUIMAE / DQIAQF - 9 de agosto - 13 hs.

[Gabriel Gordillo]

Seminarios DQIAQF - INQUIMAE,  9 de agosto de 2010- 13 hs.
 
Aula de Seminarios INQUIMAE - DQIAQF
Facultad de Ciencias Exactas y Naturales
Ciudad Universitaria - Pab. 2  -  Piso 3

Structure of reactive species in the gas phase using Infrared spectroscopy coupled with tandem mass spectrometry
 
Philippe Maître

Laboratoire de Chimie Physique, UMR8000  CNRS/Université Paris Sud 11,
Faculté des Sciences, bâtiment 350, 91405 Orsay Cedex, France
 
 
Resumen:
Gas phase mid-infrared spectroscopy of molecular ions can nowadays be performed with high performance tandem mass spectrometers, thus offering an interesting opportunity for the direct 3D structural characterization of mass-selected ions.[1]  The free-electron lasers (FELs) are particularly interesting since they produce tunable mid-IR radiation in a broad wavenumber range covering the so-called molecular fingerprint region (typically 600-2000 cm-1), and their high intensity makes them very suitable for IRMPD spectroscopy of gas phase molecular ions. 
Experiments are performed using a quadrupole ion-trap (QIT)[2] or a 7 teslas Fourier Transform Ion Cyclotron Resonance (FT-ICR)[3] mass spectrometer coupled with the IR FEL based in Orsay, France. In addition, IR spectra recorded in the NH and OH stretching region using an optical parametric oscillator/amplifier (OPO/OPA) laser system will also be presented.[4, 5] Comparison of the experimental spectrum with calculated IR absorption spectra of the low-lying isomers allows for an unambiguous characterization of the molecular structure.[1]  
Two types of applications will be given. Examples of characterization of organometallic reactive intermediates will be first presented.[1] Two examples of palladium catalyzed reactions will be presented. We will then turn our attention on the structure of N-terminal CID fragments of peptides, [6, 7] with a special focus on doubly protonated tryptic peptides whose fragmentation behaviours are of particular interest. We will see that the 1600-2000 cm-1 spectral range is the most diagnostically useful part of the IR spectrum, especially for distinguishing oxazolone from other isomers of bn+ ions. Whereas it has been suggested that b2+ fragments of doubly protonated tryptic peptides may have a diketopiperazine structure, we will provide spectroscopic evidence of an oxazolone structure. IR spectra of larger bn+ ions will also be presented providing evidence of the formation of a macro-cyclic structure competing with oxazolone as in the case of the b5+ fragment of G5RH+ which has been characterized as a 15-membered ring cyclic.[7] In addition to IR fingerprint spectra, we will also present IR spectra of b2+ recorded in the NH and OH stretching region which may allow for the characterization of the protonation site of oxazolone.

1. MacAleese, L.; Maitre, P., Infrared spectroscopy of organometallic ions in the gas phase: From model to real world complexes. Mass Spectrom. Rev. 2007, 26, (4), 583-605.
2. Mac Aleese, L.; Simon, A.; McMahon, T. B.; Ortega, J. M.; Scuderi, D.; Lemaire, J.; Maitre, P., Mid-IR spectroscopy of protonated leucine methyl ester performed with an FTICR or a Paul type ion-trap. Int. J. Mass Spectrom. 2006, 249, 14-20.
3. Bakker, J. M.; Besson, T.; Lemaire, J.; Scuderi, D.; Maitre, P., Gas-phase structure of a p-allyl-palladium complex: Efficient infrared Spectroscopy in a 7 T Fourier transform mass spectrometer. J. Phys. Chem. A 2007, 111, (51), 13415-13424.
4. Bakker, J. M.; Sinha, R. K.; Besson, T.; Brugnara, M.; Tosi, P.; Salpin, J. Y.; Maitre, P., Tautomerism of Uracil Probed via Infrared Spectroscopy of Singly Hydrated Protonated Uracil. J. Phys. Chem. A 2008, 112, (48), 12393-12400.
5. Bakker, J. M.; Salpin, J. Y.; Maitre, P., Tautomerism of cytosine probed by gas phase IR spectroscopy. Int. J. Mass Spectrom. 2009, 283, (1-3), 214-221.
6. Bythell, B. J.; Erlekam, U.; Paizs, B.; Maitre, P., Infrared Spectroscopy of Fragments from Doubly Protonated Tryptic Peptides. ChemPhysChem 2009, 10, (6), 883-885.
7. Erlekam, U.; Bythell, B. J.; Scuderi, D.; Van Stipdonk, M.; Paizs, B.; Maitre, P., Infrared Spectroscopy of Fragments of Protonated Peptides: Direct Evidence for Macrocyclic Structures of b(5) Ions. J. Am. Chem. Soc. 2009, 131, (32), 11503-11508.
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