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PV: Plenarvorträge

PV VIII

PV VIII: Plenarvortrag

Donnerstag, 21. März 2013, 09:00–09:45, E 415

Capturing Reaction Intermediates with Cryogenic Ion Spectroscopy — •Mark Johnson — Yale University

We will describe the characterization of catalytic reaction intermediates by combining electrospray ionization with cryogenic mass spectrometry. This technique uses a cold (10-30K) RF ion trap to rapidly cool reaction partners and freeze the intermediates into well-defined structures. After mass-selection, these species occur as isomers at a particular mass, and we isolate the spectra of each using a photochemical hole burning scheme involving three stages of mass selection and two independently tunable pulsed infrared lasers. The table-top lasers yield highly resolved vibrational fingerprints of the cold chemical species in a linear action regime, which can be directly compared with theory to recover the structures at play. We will focus on a biomimetic synthetic peptide catalyst (developed at Yale) to carry out stereoselective bromination of a biaryl compound. In this case, the catalyst is first isolated and sharp features associated with particular C=O groups are identified using site-specific isotopic substitution. The catalyst is then docked to the substrate, and the geometry of the host-guest complex is unravelled, again using isotope-dependent vibrational spectrosocpy to follow how specific functional groups are attached in the non-covalent interaction. Applications of this methodology to a variety of systems, including larger peptides and organometallic homogeneous catalytic intermediates, will also be presented.