Sol-Gel Transition and Dielectric Relaxation of Poly(L-leucine) Benzene System

Abstract

In this work, dynamic behavior of poly (L-leucine) (PLL) in benzene solutions was investigated by means of the dielectric relaxation measurements in the region of the gel-to-sol transition. The real part of the dielectric constant ∈' of the gel showed a value quite similar to that for pure benzene. On the other hand, a sudden increase of ∈' occurred at the gel-to-sol transition temperature (50°C) at all frequencies measured in this work, 110 Hz∼100 kHz. These phenomena showed that the α-helical backbone becomes cooperatively free to move by the disruption of the cross-link. In the sol state, ∈' increased with an increase of PLL concentration at lower concentrations, However, it decreased at higher concentrations. The measured e' was considerably smaller than the value calculated from a theory for the dilute solution assuming no molecular association. It was suggested that PLL molecules are strongly associated in a side-by-side way with anti-parallel arrangements. Similar measurements for the random copolymer of L- and D-leucine showed that a rod-like conformation is essentially important for the gel formation.