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Issue 4, 2017
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A tendril perversion in a helical oligomer: trapping and characterizing a mobile screw-sense reversal

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Abstract

Helical oligomers of achiral monomers adopt domains of uniform screw sense, which are occasionally interrupted by screw-sense reversals. These rare, elusive, and fast-moving features have eluded detailed characterization. We now describe the structure and habits of a screw-sense reversal trapped within a fragment of a helical oligoamide foldamer of the achiral quaternary amino acid 2-aminoisobutyric acid (Aib). The reversal was enforced by compelling the amide oligomer to adopt a right-handed screw sense at one end and a left-handed screw sense at the other. The trapped reversal was characterized by X-ray crystallography, and its dynamic properties were monitored by NMR and circular dichroism, and modelled computationally. Raman spectroscopy indicated that a predominantly helical architecture was maintained despite the reversal. NMR and computational results indicated a stepwise shift from one screw sense to another on moving along the helical chain, indicating that in solution the reversal is not localised at a specific location, but is free to migrate across a number of residues. Analogous unconstrained screw-sense reversals that are free to move within a helical structure are likely to provide the mechanism by which comparable helical polymers and foldamers undergo screw-sense inversion.

Graphical abstract: A tendril perversion in a helical oligomer: trapping and characterizing a mobile screw-sense reversal

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Supplementary files

Article information


Submitted
15 Dec 2016
Accepted
24 Jan 2017
First published
25 Jan 2017

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2017,8, 3007-3018
Article type
Edge Article

A tendril perversion in a helical oligomer: trapping and characterizing a mobile screw-sense reversal

M. Tomsett, I. Maffucci, B. A. F. Le Bailly, L. Byrne, S. M. Bijvoets, M. G. Lizio, J. Raftery, C. P. Butts, S. J. Webb, A. Contini and J. Clayden, Chem. Sci., 2017, 8, 3007
DOI: 10.1039/C6SC05474A

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