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Title:JET-COOLED, CONFORMER-SPECIFIC IR SPECTRA OF CYCLICALLY-CONSTRAINED β-PEPTIDES. DOES CONDENSED PHASE STRUCTURE SURVIVE THE VACUUM?
Author(s):Blodgett, Karl N.
Contributor(s):Zwier, Timothy S.
Subject(s):Conformers and isomers
Abstract:We present laser-desorbed, jet-cooled, conformation-specific UV and IR data on a series of increasingly complex $\beta$-peptide oligomers: Ac-(ACHC)$_{2}$-NHBn, Ac-ACHC-m$_{4}$ACHC-NHBn, Ac-m$_{5}$ACHC-m$_{4}$ACHC-NHBn, Ac-m$_{4}$ACHC-ACHC-NHBn, Ac-m$_{4}$ACHC-m$_{5}$ACHC-NHBn, Ac-(ACHC)$_{3}$-NHBn, and Ac-(ACHC)$_{4}$-NHBn. Synthetic foldamers are polymers composed of non-natural building blocks which either mimic, or expand upon, nature’s preferred secondary structures which are accessible to pure $\alpha$-amino acid sequences. The ring-constrained $\beta$-amino acid, \textit{cis}-2-aminocyclohexanecarboxylic acid (ACHC), is one such non-natural building block which when polymerized with alternating chirality has been shown to adopt both right- and left-handed 12/10 mixed helices in solution and crystalline form. ACHC may adopt two local minima conformations: one in which the NH is axial (ax) with respect to the cyclohexane chair and the C=O is equatorial (eq), and vice versa. In poly-ACHC sequences, the cooperative conformational isomerization between these two minima switches the screw-sense of the 12/10 helix. The use of the more rigid $\beta$-amino acids, \textit{cis}-2-amino-\textit{cis}-4-methylcyclohexanecarboxylic acid (m$_{4}$ACHC) and \textit{cis}-2-amino-\textit{cis}-5-methylcyclohexanecarboxylic acid (m$_{5}$ACHC) sterically lock the ACHC residue into one of its two minima, depending on the stereochemical patterning at the ring’s three stereocenters. The isolated, solvent-free conformational preferences will be compared with condensed phase data, and the energetic impact of the benzyl chromophore on preferred structure will be discussed.
Issue Date:2019-06-18
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Type:Text
Language:English
URI:http://hdl.handle.net/2142/104360
DOI:10.15278/isms.2019.TJ10
Rights Information:Copyright 2019 Karl N. Blodgett
Date Available in IDEALS:2019-07-15
2020-01-25


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