On the double peak of NMR in the helix—coil transition region

Abstract

AbstractTo attempt to resolve the controversy over “fast” and “slow” helix–coil transition rates in polypeptides, nuclear magnetic resonance spectra were measured for monodisperse poly‐γ‐benzyl‐L‐glutamate (PBLG). These results were compared with simulated line spectra which were computed by taking the molecular‐weight distribution into consideration. Broad but single peaks have been observed in 220 mHz nmr for the α‐CH and NH proton resonance spectra in the transition region. The shape of the line changes with the extent of polydispersity. Assuming a fast conversion rate, a molecular model of the helix–coil transition simulates these results. Consequently, the double peak which has been observed in the nmr of polypeptides at the helix–coil transition region is shown to result from the polydispersity in molecular weight.