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

Ariel Pérez-Mellor , Ivan Alata (1) , Valéria Lepère (2) , Anne Zehnacker (3, 4)

1 CLUPS - Centre Laser de l'Université Paris Sud
2 LCAM - Laboratoire des collisions atomiques et moléculaires
3 ISMO - Institut des Sciences Moléculaires d'Orsay
4 SYSIPHE

The conformational landscape of the diketopiperazine (DKP) dipeptide built on tyrosine and proline, namely, cyclo Tyr-Pro, is studied by combining resonance-enhanced multiphoton ionisation, double resonance IR-UV spectroscopy, and quantum chemical calculations. Despite the geometrical constraints due the two aliphatic rings, DKP and proline, cyclo Tyr-Pro is a flexible molecule. For both diastereoisomers, cyclo LTyr-LPro and cylo LTyr-DTyr, two structural families coexist under supersonic jet conditions. In the most stable conformation, the aromatic tyrosine substituent is folded over the DKP ring (g + geometry of the aromatic ring) as it is in the solid state. The other structure is completely extended (g-geometry of the aromatic ring) and resembles that proposed for the vapor phase. IR-UV results are not sufficient for unambiguous assignment of the observed spectra to either folded or extended conformations and the simulation of the vibronic pattern of the S0-S1 transition is necessary. Still, the comparison between IR-UV results and anharmonic calculations allow explaining the minor structural differences between cyclo LTyr-LPro and cylo LTyr-DPro in terms of different NH… and CH… interactions. 2

Domaines: Chimie théorique et/ou physique

Ariel Pérez-Mellor, Ivan Alata, Valéria Lepère, Anne Zehnacker. Conformational Study of the Jet-Cooled Diketopiperazine Peptide Cyclo Tyrosyl-Prolyl. Journal of Physical Chemistry B, 2019, 123 (28), pp.6023-6033. ⟨10.1021/acs.jpcb.9b04529⟩. ⟨hal-02347969⟩