Peptoids hold a special place in the foldamer field. They are very close mimics of peptides because their main chain is composed of glycine units. But, the peptoids main chain is deprived of N–H donors and chirality, two main features that control peptide folding. Because of these properties and the intrinsic flexibility, experimental 3D structures characterization is a difficult task. Experimentally available 3D information are mainly based on X-ray structures of medium sized molecules. NMR spectroscopy is routinely used for the chracterization of the primary sequence and, in few cases, for 3D structure determination. When chirality properties are reintroduce by side chains with asymmetric carbons appended to the nitrogen atom of the backbone, Electronic Circular Dichroism (ECD) allows to determine secondary structures. Classical Molecular Dynamics (MD) simulations combined to the quantum chemical calculations of spectroscopic data can be employed nowadays in order to obtain further insight into the three dimensional structures. The analysis of MD trajectories allows to describe specific structural characteristics. Quantum chemical structures used to reproduce experimental spectroscopic data can highlight unambiguous conformations or intramolecular interactions responsible of the ECD or NMR signatures. First, we will discuss results based on MD simulations coupled to quantum chemical calculations of 13C NMR spectra (B3LYP-GIAO) performed on mixed cis-trans α,β-oligopeptoids. This joint experimental and theoretical study has highlighted specific patterns of intramolecular weak interactions existing in this family of polypeptoids. On a second part, we will focus on the calculations of ECD spectra (TD - B3LYP) that was carried out on a set of chiral α-peptoids with tert-butylethyl side chains. This theoretical study, based on the quantitative reproduction of experimental ECD spectra of oligomers of different sizes, revealed a set of specific conformational properties to explain all the spectral characteristics.

3D structure of achiral and chiral polypeptoids by means of molecular dynamics simulations and density functional theory calculations of spectroscopic data

2019 Spring National Meeting

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