JET-COOLED, CONFORMER-SPECIFIC IR SPECTRA OF CYCLICALLY-CONSTRAINED β-PEPTIDES. DOES CONDENSED PHASE STRUCTURE SURVIVE THE VACUUM?

Blodgett, Karl N.

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https://hdl.handle.net/2142/104360 Copy

Description

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.

Issue Date

2019-06-18

Keyword(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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/104360

DOI

10.15278/isms.2019.TJ10

Copyright and License Information

Copyright 2019 Karl N. Blodgett

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