Orientation–deformation electro-optical effect in water suspension of purple membranes

Electro-optical methods of light scattering (LS) and dichroism (D) are used to investigate water suspension of purple membranes (PM). The transient processes upon electric pulse turn on and off were measured as well as the field strength dependence of the stationary electro-optic effect (EOE). At fields under 2.5 kV cm−1, the PM behaves as rigid particles and the EOE is due to PM orientation. When 5 kV cm−1 electric pulse is switched off a fast relaxation process of microsecond kinetics and a millisecond relaxation process of disorientation are registered at LS. A process with similar amplitude is absent at D. That fast process is explained with electrically and/or hydrodynamically induced changes in PM form and size, without perceptible changes in membrane internal structure. A conclusion is drawn that the EOE of PM suspension in high electric field has orientation–deformational mechanism.