Quantification of the effects of n-π* interactions on the H-bonding properties of amide groups

Abstract

The n-π* interaction is postulated to play a key role in the folding of proteins, especially in proline-rich structures such as collagen, and cooperativity between H-bonding and the n-π* interaction has been proposed. In order to obtain experimental evidence for these cooperative effects, the H-bond acceptor properties of secondary amides with and without the capacity to form an intramolecular n-π* interaction were measured. UV-vis absorption and 13C NMR titrations were used to investigate the intermolecular H-bonded complexes formed with 2-methyl-4-nitro-phenol and perfluoro-tert-butanol, and hence quantify the H-bond acceptor properties of the amide carbonyl oxygens. For an N-acylproline derivative, the presence of an intramolecular n-π* interaction between two amide groups was confirmed by X-ray crystallography, but the solution titrations show that associated changes in the H-bond acceptor strength of the amide carbonyl oxygen group are negligible. The free energy contribution due to cooperativity between the intramolecular n-π* interaction and the intermolecular H-bond was found to be within the error of the experiment (<1 kJ mol−1). The results suggest that any contributions to the thermodynamic stability of folded proteins due to such cooperativity are small.

Graphical abstract: Quantification of the effects of n-π* interactions on the H-bonding properties of amide groups

Supplementary files

Article information

Article type
Edge Article
Submitted
09 Dec 2024
Accepted
27 Mar 2025
First published
03 Apr 2025
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2025, Advance Article

Quantification of the effects of n-π* interactions on the H-bonding properties of amide groups

F. E. Hanna, A. D. Bond and C. A. Hunter, Chem. Sci., 2025, Advance Article , DOI: 10.1039/D4SC08331H

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