title: Foldamers of β-peptides: conformational preference of peptides formed by rigid building blocks. The first MI-IR spectra of a triamide nanosystem.
abstract: To determine local chirality driven conformational preferences of small aminocyclobutane-1-carboxylic acid derivatives, X-(ACBA) n -Y, their matrix-isolation IR spectra were recorded and analyzed. For the very first time model systems of this kind were deposited in a frozen (~10 K) noble gas matrix to reduce line width and thus, the recorded sharp vibrational lines were analyzed in details. For cis-(S,R)-1 monomer two "zigzag" conformers composed of either a six or an eight-membered H-bonded pseudo ring was identified. For trans-(S,S)-2 stereoisomer a zigzag of an eight-membered pseudo ring and a helical building unit were determined. Both findings are fully consistent with our computational results, even though the relative conformational ratios were found to vary with respect to measurements. For the dimers (S,R,S,S)-3 and (S,S,S,R)-4 as many as four different cis,trans and three different trans,cis conformers were localized in their matrix-isolation IR (MI-IR) spectra. These foldamers not only agree with the previous computational and NMR results, but also unambiguously show for the first time the presence of a structure made of a cis,trans conformer which links a "zigzag" and a helical foldamer via a bifurcated H-bond. The present work underlines the importance of MI-IR spectroscopy, applied for the first time for triamides to analyze the conformational pool of small biomolecules. We have shown that the local chirality of a β-amino acid can fully control its backbone folding preferences. Unlike proteogenic α-peptides, β- and especially (ACBA) n type oligopeptides could thus be used to rationally design and influence foldamer's structural preferences.
authors.affiliation: Laboratory of Structural Chemistry and Biology, Institute of Chemistry, Eötvös University, P.O. Box 32, Budapest 112, 1518, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Pohl
authors.forename: Esther
authors.initials: E
authors.lastname: Gorrea
authors.forename: Vicenç
authors.initials: V
authors.lastname: Branchadell
authors.forename: Rosa M
authors.initials: RM
authors.lastname: Ortuño
authors.forename: András
authors.initials: A
authors.lastname: Perczel
authors.forename: György
authors.initials: G
authors.lastname: Tarczay
mesh_terms: D000577:Amides / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D049329:Nanostructures / Q000737:chemistry*; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry*; D017510:Protein Folding; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared
chemical_list: D000577:Amides; D010455:Peptides