Birefringence of Purple Membranes

An investigation of the electric birefringence of aqueous suspensions of purple membrane fragments was carried out. We have determined values for the permanent dipole moment ( p ∼ 10 -24 C m) and for the membrane polarizability (Δγ ∼ 10 -28 F m 2) of the purple membrane fragment. These values are in agreement with previous measurements made by other authors using different electro-optical techniques. In addition, we have determined that the optical anisotropy Δ g of the purple membranes is ≈ 10 -3. We have probed the nature of the electric field orientation function for the purple membrane fragments, and we suggest a method for determination of p and Δγ based on an experimentally measured value of the orienting dc electric field strength at which the electro-optic effect goes to zero.