N-H•••X interactions stabilize intra-residue C5 hydrogen bonded conformations in heterocyclic ccamino α-acid derivatives

Nature makes extensive and elaborate use of hydrogen bonding to assemble and stabilize biomolecular structures. The shapes of peptides and proteins rely significantly on N-H center dot center dot center dot O=C interactions, which are the linchpins of turns, sheets and helices. The C5 H-bond, in which a single residue provides both donor and acceptor, is generally considered too weak to force the backbone to adopt extended structures. Exploiting the synergy between gas phase (experimental and quantum chemistry) and solution spectroscopies to decipher IR spectroscopic data, this work demonstrates that the extended C5-based conformation in 4-membered ring heterocyclic alpha-amino acid derivatives is significantly stabilized by the formation of an N-H center dot center dot center dot X H-bond. In this synergic system the strength of the C5 interaction remains constant while the N-H center dot center dot center dot X H-bond strength, and thereby the support provided by it, varies with the heteroatom.

Automated summary

Nature utilizes hydrogen bonding extensively to assemble and stabilize biomolecular structures, with the shapes of peptides and proteins relying significantly on N-H···O=C interactions. While the C5 hydrogen bond is generally considered too weak to force extended structures, this work demonstrates that an N-H···X hydrogen bond significantly stabilizes the extended C5-based conformation in specific derivatives.