Mimicking the first turn of an α-helix with an unnatural backbone: conformation-specific IR and UV spectroscopy of cyclically constrained β/γ-peptides.

摘要: The folding preferences of two capped, constrained β/γ-dipeptide isomers, Ac-βACPC-γACHC-NHBn and Ac-γACHC-βACPC-NHBn, (designated βγ γβ, respectively), have been investigated using single- double-resonance ultraviolet infrared spectroscopy in the gas phase. These capped β/γ-dipeptides same number backbone atoms between their N- C-termini as a α-tripeptide thus serve minimal structural unit on which to test ability mimic formation first turn an α-helix. Resonant two-photon ionization UV–UV hole-burning were performed S0–S1 region, revealing presence three unique conformations single conformation γβ. ion-dip spectra obtained NH stretch region from 3300 3500 cm–1 both amide I II regions 1400 1800 cm–1. compared computational predictions density functional theory calculations at M05-2X/6-31+G(d) l...