Adaptive Aggregation of Peptide Model Systems

Abstract

Jet-cooled infrared spectra of acetylated glycine, alanine, and dialanine esters and their dimers are reported in the amide A and amide I-III regions. They serve as particularly simple peptide aggregation models and are found to prefer a single backbone conformation in the dimer that is different from the most stable monomer backbone conformation. In the case of alanine, evidence for topology-changing chirality discrimination upon dimer formation is found. The jet spectroscopic results are compared to gas phase spectra and quantum chemical calculations. They provide reliable benchmarks for the evaluation of the latter in the field of peptide interactions.

Isolated Neutral Peptides

“…Phe-containing dipeptides have been confidently assigned without relying on quantum calculations, and a ranking of the H-bonds according to their strength has been proposed (C5<NH-π<C10<C7 [34]). This pioneering work paved the way to systematic tests of quantum chemical methods in their ability to reproduce the IR spectra of these species as well as the conformer [26,28,31,46,63,95,113], although recent advances seem to be promising [147,148].…”

“…Finally, peptide dimers characterised in the supersonic expansion also provide evidence for the stabilisation of β-strands by interstrand H-bonds [31,46,64,73,90,124]. This is interesting when isolated monomers are found to adopt folded structures, thus illustrating the intrinsic flexibility of peptides and their sensitivity upon the environment.…”

“…Beyond microsolvation, peptide-peptide interactions [31,46,73,87,90,120,124] and complexation with larger molecules have also been considered by several groups, especially to describe specifically interesting interactions between a peptide and its biological environment: peptides have been complexed with pyrazole to 246 E. Gloaguen and M. Mons favour β-sheets [65,100], with sugars to describe the interactions responsible for cellular recognition in glycopeptides [114,197], or to document the anomeric effect [198].…”

“…In particular, NH, OH, and CO stretching modes appeared to be promising diagnostics, leading to an accurate H-bond network characterisation, and have therefore been explored by several groups. Although Raman absorption [22][23][24][25], FTIR [26][27][28][29][30][31] or IR/VUV [32,33] spectra can be successfully carried out in an expansion, these techniques suffer from their lack of conformer selectivity. Conversely, the selectivity of double resonance IR/UV techniques has raised considerable interest, leading laser spectroscopists to provide an accurate picture of the structure of each conformer through the IR spectra, as well as information on the conformational populations through UV spectroscopy.…”

Chirality effects in gas-phase spectroscopy and photophysics of molecular and ionic complexes: contribution of low and room temperature studies

“…This is especially true for intramolecular hydrogen bonds, which can open up if the resulting intermolecular bond leads to an energy gain [71,72]. This process and its chirality dependence have been widely documented in the case of complexes between an alcohol and an amino alcohol or in that of peptide dimers models [40,41,73]. The formation of such complexes requires deformation of the molecules and cleavage of the intramolecular hydrogen bond, which in turn introduces a barrier to the complex formation, hence the important role of temperature and kinetic factors on their formation [15,44,46].…”