Elementary peptide motifs in the gas phase: FTIR aggregation study of formamide, acetamide, N-methylformamide, and N-methylacetamide.
Cold, isolated peptide model compounds and their aggregates are generated in pulsed supersonic jet expansions and detected by FTIR spectroscopy in the amide-A region, complemented by amide-I spectra. The most stable, symmetric dimer of formamide is unambiguously assigned in the gas phase for the first time, also by comparison to the analogous acetamide dimer. Efficient quenching of a hot-state Fermi resonance by cooling of the dimers is invoked. As the preferred relative orientation of the C=O and N-H groups in N-methylated formamide and acetamide is trans, these compounds show a fundamentally different dimerization pattern. Their most stable dimers, which would be analogous to those of formamide and acetamide, remain undetected as a consequence of kinetic control in the jet. Accurate benchmark quantities for multidimensional vibrational treatments of these peptide models are derived, and the influence of methyl groups on the N-H stretching dynamics is discussed.
Albrecht
Merwe
M
Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, 37077 Göttingen, Germany.
Rice
Corey A
CA
Suhm
Martin A
MA
D000081:Acetamides / Q000737:chemistry*; D020816:Amino Acid Motifs; D005559:Formamides / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
D000081:Acetamides; D005559:Formamides; D005740:Gases; D010455:Peptides; C030686:acetamide; C018595:N-methylacetamide; C002950:methylformamide