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Assignment of vibrational circular dichroism cross-referenced electronic circular dichroism spectra of flexible foldamer building blocks: towards assigning foldamers’ pure chiroptical properties

Farkas, Viktor and Nagy, Adrienn and Menyhárd, Dóra K. and Perczel, András (2019) Assignment of vibrational circular dichroism cross-referenced electronic circular dichroism spectra of flexible foldamer building blocks: towards assigning foldamers’ pure chiroptical properties. CHEMISTRY-A EUROPEAN JOURNAL. ISSN 0947-6539 (In Press)

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Abstract

The assignment of the most established ECD spectra of polypeptides and foldamers is either “evidence based” or rely on the 3D-structures of longer oligomers of limited internal dynamics, derived from NMR (or X-ray) data. Critics warn that using NMR and ECD side by side have severe limitations for flexible molecules as the explicit knowledge of the conformational ensembles is a challenge. Herein we present the old-new method of comparing ab initio computed and measured VCD data to validate both structures and, conf(i), and their relative weights, c(i), making up the conformational ensemble. Based on the array of {conf(i), c(i)} the pure ECD spectra, g(i)conf(i), can be ab initio calculated. The reconstructed spectrum Σc(i)*g(i)conf(i) can thus help to assign any experimental ECD counterpart. Here we present such a protocol successfully applied for flexible foldamer building blocks of sugar β-amino acid diamides. The epimeric pair of our model system was selected because these molecules are conformationally tunable by simple chemical modification (N-methylation) and thus, the robustness of our current approach could be probed. The initial H-bond (NH..O) eliminated by N-methylation reorients the amide plain influencing the chiroptical properties of the foldamer building block, a structural change successfully monitored by the VCD- and ECD-transition changes now assigned to pure conformers. The current method seems general and effective without requiring extensive CPU and spectroscopic resources.

Item Type: Article
Subjects: Q Science / természettudomány > QD Chemistry / kémia
Depositing User: Viktor Farkas
Date Deposited: 24 Sep 2019 17:36
Last Modified: 24 Sep 2019 17:36
URI: http://real.mtak.hu/id/eprint/101008

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