Conformational Study of the Jet-Cooled Diketopiperazine Peptide Cyclo Tyrosyl-Prolyl

• DOI: 10.1021/acs.jpcb.9b04529
• Publication Date: 2019-06-21T18:36:39Z
• Authors: Ariel Pérez-Mellor; Ivan Alata; Valeria Lepère; Anne Zehnacker
• Keywords: Cyclic peptide; Diketopiperazines

The conformational landscape of the diketopiperazine (DKP) dipeptide built on tyrosine and proline, namely, cyclo Tyr-Pro, is studied by combining resonance-enhanced multiphoton ionization, double resonance infrared ultraviolet (IR-UV) spectroscopy, quantum chemical calculations. Despite geometrical constraints due two aliphatic rings, DKP Tyr-Pro a flexible molecule. For both diastereoisomers, LTyr-LPro LTyr-DPro, structural families coexist under supersonic jet conditions. In most stable conformation, aromatic substituent folded over ring (g+ geometry ring) as it in solid state. other structure completely extended (g– resembles that proposed for vapor phase. IR-UV results are not sufficient unambiguous assignment observed spectra to either or conformations simulation vibronic pattern S0–S1 transition necessary. Still, comparison between anharmonic calculations allows explanation minor differences LTyr-DPro terms different NH···π CH···π interactions.