Relaxation kinetics of the triple‐stranded helix ⇄ coil transition at short chain length. A model including the staggering of chains

The relaxation kinetics of a staggering zipper model are presented, in which the formation of helical nuclei is regarded to be rate‐limiting and in which the sliding of strands along the helices is prohibited. Instead a realignment of staggered chains is only possible via complete uncoiling. While maintaining the third order of the initial reaction as in an all‐or‐none mechanism, the model predicts a large range of relaxation times, which contribute to the mean relaxation time according to the stability of the individual species and which are weakly coupled in the range of small amounts of helical content. The model can easily be compared to experimental results and agrees well with relaxation data obtained from a triple‐helical peptide fragment of collagen. It may be readily expanded to other multistranded helix ⇄ coil transitions with steady‐state formation of the individual species and it suggests that the fraying of the helix ends is hidden by the fast‐relaxation times due to the equilibration of the shortest helical species.