Origin of multipeak behavior in the NMR spectra of poly(L‐glutamic acid)

Abstract

SynopsisThe previous report that poly (L-glutamic acid) exhibits doubled resonances in the helix-coil transition region by either proton or carbon-13 nmr resolves the question of whether or not this behavior is limited to uncharged polypeptides in organic solvents, as had been previously thought. In the present work, we show that the underlying principle causing this anomalous double-peak behavior is due to molecular-weight polydispersity of the sample. The molecular-weight range in which this phenomenon is observed is largely dependent on the values of u, the nucleation or cooperativity factor. The principles developed are shown to encompass all classes of polypeptides in a very natural way and to explain the key experimental data in the literature.