A solvent-dependent peptide spring unraveled by 2D-NMR

In this work, we introduce a 2D-NMR method to discriminate between the fully-extended and the 3₁₀-helical conformations for the C^α,α-diethylglycine homo-peptides in the solution phase. It is based on the observation of divergent cross-peak intensities in the NOESY spectra. In particular, any βCH₂(i-1)→NH(i) cross peak is more intense than the intraresidue βCH₂(i)→NH(i) cross peak when the peptide adopts the fully-extended conformation. In this 3D-structure a marked splitting of the chemical shifts of the two non-equivalent βCH₂ protons is also apparent. In contrast, an opposite trend of intensities of the same NOE cross-peaks indicates the occurrence of a 3₁₀-helical conformation. This 3D-structural shift is induced by a change in the nature of solvent.