Electric-field orientation of charged helical polypeptides in solution

Abstract

The electric birefringence of charged polypeptides, including poly(L-lysine hydrobromide), poly(L-ornithine hydrobromide), poly (L-α,γ-diaminobutyric acid hydrochloride) and sodium poly(L-glutamate), in aliphatic alcohol/water mixtures has been measured at various solvent compositions. The field strength dependence of the steady-state birefringence, for both helical and coil conformations, resembled that expected for permanent dipole moment orientation. On the other hand, the transient behaviour indicated a mechanism of induced dipole moment orientation. This conflict can be resolved if saturation of the counterion-induced dipole moment is taken into account. The field strength dependence of the counterion-induced dipole moment and the orientation function is discussed in terms of the one-dimensional lattice model.