Chirality Effects in Jet-Cooled Cyclic Dipeptides

Ariel Pérez-Mellor (1) , Anne Zehnacker (1)

1 ISMO - Institut des Sciences Moléculaires d'Orsay

Jet-cooled bichromophoric cyclic dipeptides built on a diketopiperazine (DKP) ring are studied by combining conformer-specific vibrational spectroscopy with quantum chemical calculations. The dependence of the c-LL and c-LD dipeptides structure upon relative absolute configuration, L or D, of the residues is investigated for two residues: phenylalanine (Phe) and tyrosine (Tyr). A folded-extended structure is systematically observed for all systems, like in solution or in the solid. This structure is stabilized by NH…π and CH…π interactions and shows limited stereoselectivity; the only difference between c-LL and c-LD is the nature of the CH…π interaction-C α …π in c-LD and C β …π in c-LL-and a stronger NH…π interaction in c-LD. For all the studied species, the electronic excitation and the charge in the radical cation are localized on the extended ring. The c-LL diastereomer of cyclo di-tyrosyl stands out by the existence of a stacked structure, in which formation of an OH…O hydrogen bond stabilizes parallel aromatic rings orientation. In this structure, the electronic excitation and the major part of the charge in the cation are localized on the H-bond donor. The OH…O H-bond is possible in c-LL and not c-LD, which explains the high stereoselectivity.

Domaines: Chimie théorique et/ou physique

Ariel Pérez-Mellor, Anne Zehnacker. Chirality Effects in Jet-Cooled Cyclic Dipeptides. Takayuki Ebata; Masaaki Fujii. Physical Chemistry of Cold Gas-Phase Functional Molecules and Clusters, Springer Singapore, pp.63-87, 2019, 978-981-13-9370-9. ⟨10.1007/978-981-13-9371-6_3⟩. ⟨hal-03324659v2⟩