|Primary and secondary structures of peptoids as probed by Ion Mobility Mass Spectrometry
|Ion Mobility - Mass Spectrometry (BMSS)
|Mrs Emilie Halin
Abstract Information :
Poly-N-substituted glycines, called peptoids, constitute an emerging class of biomimetic foldamers. The peptoid specificity, compared to the classic peptides, lies in the position of the side chain present on the nitrogen atom rather than the δ carbon, classifying them as peptide regioisomers . This particularity prevents two amide functions from interacting by hydrogen bonding as in the peptide case . However, highly structured peptoids, essentially presenting helicoidal folding, have been identified both in organic and aqueous media . A great care has been paid to the peptoid structural investigation especially since the helicoidal folding has been recognized to be at the origin of enantioselective properties exploited in catalytic reaction or in chiral chromatography. Numerous studies report that the helical structure of peptoid macromolecules is mostly related to the combination of the CIS-TRANS conformations of the amide bonds all along the peptoid backbone. Nuclear Magnetic Resonance (NMR) and Circular Dichroism (CD) are widely used to evaluate the helicoidal character of peptoid polymers. Nevertheless, the information relative to the peptoid secondary structure is averaged over all the stereoisomers present in solution. Mass Spectrometry (MS) techniques a priori represent a great opportunity in this context for their ability to analyze isolated - ionized - compounds in the gas phase. Recently, the investigation of primary/secondary structure relationship has largely benefited from the coupling between MS and Ion Mobility technology (IMMS). We then undertake a large study aiming at developing state-of-the-art MS-based methods for defining that primary structures as well as the secondary structures of peptoids and peptoid ions.
In the present communication, we report on the association between Collision-induced Dissociation (CID) and Ion mobility (IM) experiments for the primary and secondary structure assessment of peptoid ions. We here describe our results related to protonated N-(S)-phenylethyl peptoid monomer and dimer on a Waters Synapt G2-Si mass spectrometer. We first demonstrate that the ion dissociation reaction upon CID is dependent (i) on the nature of the side-chain and (ii) the position along the backbone. We also use IMMS to localize a specific fragmentation in MSMS experiments to establish the primary structure. The potential of IMMS technology is further exploited to decipher the secondary structure of ionized peptoids in the gas phase.