Switchable Double Inversion of Chirality in a Helical Polyelectrolyte

Switchable inversion of chirality between opposite handedness by varying pH is discovered for a histidine pendant polymer, polymethyl (4-vinylbenzoyl) histidinate (PBHis), as demonstrated by the circular dichroism as well as the changes of hydrodynamic radius measured by fluorescence correlation spectroscopy at the single molecular level. The polyelectrolyte is found to take an M-helicity below pH 8.0 and change into P-helicity above pH 8.0. Such helicity further inverses into M-chirality above pH 10.6. All these helical structures with opposite handedness can be switched using pH variations. The mechanism of such a unique phenomenon is attributed to the protonation and deprotonation of the imidazole group and the hydroxide-ion-mediated hydrogen bonding, which determine the mutual orientation between the side under the bonds and K-K and therefore the handedness of the helical structure.

Automated summary

Switchable inversion of chirality between opposite handedness by varying pH is found in a histidine pendant polymer, PBHis. This phenomenon is demonstrated by circular dichroism and fluorescence correlation spectroscopy, which measure the changes of hydrodynamic radius at the single molecular level. Below pH 8.0, the polyelectrolyte adopts M-helicity, while above pH 8.0, it changes into P-helicity. Above pH 10.6, the helicity further inverses into M-chirality. The protonation and deprotonation of the imidazole group, as well as the hydroxide-ion-mediated hydrogen bonding, determine the mutual orientation and handedness of the helical structure.