Single-Conformation Spectroscopy of Capped Aminoisobutyric Acid Dipeptides: The Effect of C-Terminal Cap Chromophores on Conformation.

Aminoisobutyric acid (Aib) oligomers are known to form racemic mixtures of enantiomeric left- and right-handed structures. The introduction of a chiral cap converts the enantiomeric structures into diastereomers that, in principle, afford spectroscopic differentiation. Here, we screen different C-terminal caps based on a model Aib dipeptide using double resonance laser spectroscopy in the gas phase to record IR and UV spectra of individual conformations present in the supersonic expansion: NH-benzyl (NHBn) as a reference structure because of its common use as a fluorophore in similar studies, NH- p-fluorobenzyl (NHBn-F), and α-methylbenzylamine (AMBA).