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

In this work, we introduce a 2D-NMR method to discriminate between the fully-extended and the 3(10)-helical conformations for the C-alpha,C-alpha-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 beta CH2(i-1)-> NH(i) cross peak is more intense than the intraresidue beta CH2(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 beta CH2 protons is also apparent. In contrast, an opposite trend of intensities of the same NOE cross-peaks indicates the occurrence of a 3(10)-helical conformation. This 3D-structural shift is induced by a change in the nature of solvent.