ELECTRIC-FIELD EFFECT ON THE HELIX-COIL TRANSITION OF POLY(L-ALPHA,GAMMA-DIAMINOBUTYRIC ACID HYDROCHLORIDE) IN METHANOL-WATER MIXTURES

Transient electric birefringence of poly(L‐α,γ‐diaminobutyric acid hydrochloride) in methanol/water mixtures has been measured over a wide range of field strengths and solvent compositions and at different polymer concentrations and temperatures. The molar ellipticity at 222 nm and the specific Kerr constant underwent an abrupt change between 75 and 80 vol % methanol at 25°C, accompanied by a solvent‐induced helix–coil transition. Anomalous birefringence transients were observed between 78 and 80 vol% methanol above threshold field strengths. The double logarithmic plots of the steady‐state specific birefringence versus the square of field strength for different solvent compositions and polymer concentrations could be superimposed by shifting them horizontally along the abscissa and vertically along the ordinate except for the range where anomalous transients were observed. The threshold field strength could be estimated from the point at which a downward deviation occurred. It increased with increasing polymer concentration and with increasing methanol content on the verge of the transition region. The results were interpreted as indicating that a conformational change from the charged helix to the charged coil is induced by high fields in this system, as in the case of poly(L‐lysine hydrobromide) in methanol/water mixtures. Copyright © 1979 John Wiley & Sons, Inc.