Practice question

Hydrogen bonds in alpha helix link carbonyl oxygen of residue i to amide proton of residue i+4, shielding amides from solvent and reducing exchange with deuterium. In a 30-residue stable helix, many NH groups exhibit protection, exchanging slowly over hours versus unstructured coils exchanging within seconds to minutes. Observing slow NH to ND exchange after transferring peptide into D2O, evidenced by persistent amide resonances in successive proton spectra, indicates hydrogen-bonded, folded structure. This slow exchange corroborates NOE ladder and coupling constant data for helix stabilization and core packing.