Transient electric optical rotation for macromolecular characterization

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Abstract
In an electric field, the optical rotation of a solution or suspension of helical molecules may be expected to change. Such changes are reported herein for solutions of poly (benzyl‐L‐glutamate) (PBLG) in ethylene dichloride using pulsed electric fields. These measurements enabled the molecular geometry to be evaluated (through the determination of a rotary diffusion constant) simultaneously with the determination of the molecular optical rotation components along the principal molecular axes. Fields were applied parallel to the light beam. Very dilute solutions were studied owing to the use of a stable laser as the light source plus the introduction of a special multiple cell in which the optical path length could be increased while maintaining the field strength. A dilute solution (0.1%) of PBLG gave rotation data in agreement with previously published data. In addition, the helical length and molecular weight were determined from the relaxation effect. Studies on concentrated solutions indicated the presence of aggregation. This highlights the need for caution in improving the observable optical rotation simply by increasing the solution concentration. The apparatus is described in outline and the advantages of this novel transieat method are listed.