Berlin 2014 – scientific programme
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MO: Fachverband Molekülphysik
MO 2: Clusters
MO 2.4: Talk
Monday, March 17, 2014, 11:15–11:30, BEBEL SR144
Microsolvation of the Formanilide Cation (FA+) in a Nonpolar Solvent: Infrared Spectra of FA+-Ln clusters (L=Ar, N2) — •Johanna Klyne1, Aude Bouchet1, Matthias Schmies1, Mitsuhiko Miyazaki2, Masaaki Fujii2, and Otto Dopfer1 — 1Institut für Optik und Atomare Physik, Technische Universität Berlin — 2Chemical Resources Laboratory, Tokyo Institute of Technology, Japan
The peptide linkage is an essential component in biochemical regognition processes since its geometry, depending on its local environment, defines the conformation of proteins. Elucidating the sequential microsolvation of peptides is therefore crucial for a full description of their behaviour in biological media. The stepwise microsolvation of cationic formanilide (FA+-Ln) is characterized by IR spectroscopy of size-selected clusters generated in a molecular beam, combined with density functional calculations. Formanilide is the simplest aromatic molecule containing a peptide linkage (-NH-CO-). The observation of size- and isomer-specific NH stretch frequencies reveals the microsolvation of FA+ in a nonpolar (L=Ar) and a quadrupolar (L=N2) solvent. Such aromatic amides exhibit at least two competing binding sites for nucleophilic ligands, namely H-bonding to the acidic N-H group of the amide and π-stacking to the the phenyl ring. The H-bound FA+-L dimer with L binding to the NH proton of the amide is the most stable isomer. Subsequent ligands are weaklier bound to the aromatic ring (π-stacking). These results demonstrate an ionization-induced change of the preferred binding motif from π-stacking to H-bonding.