Magneto-optics of Ferritin

Abstract

Measurements of Rayleigh light scattering, nonlinear light scattering in DC magnetic fields, and the Cotton–Mouton effect were carried out for 15 mM NaCl and water solutions of ferritin at room temperature. The spherical geometry of the molecule implies that it is optically isotropic. Such a macromolecule should not manifest magnetic anisotropy; however, in solution it shows induced magnetic birefringence (Cotton–Mouton effect) and changes in the intensity of the scattered light components. The analysis of the obtained results indicates the deformation of linear optical polarizability induced in the ferritin by a magnetic field as the main source of the magneto-optical phenomena observed. Light scattering and the CM effects theoretically depend on the linear magneto-optical polarizability, χ, and the nonlinear magneto-optical polarizability, η. Using the theory describing the phenomena as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizability components, χ ‖−χ ⊥=−(1.3±0.7)×10 −22 [cm 3] (in SI units χ ‖−χ ⊥=−(2.0±1.2)×10 −33 [m 3]), the linear optical polarizability, α=(α ‖+2α ⊥)/3=(3.9±1.0)×10 −20 [cm 3] (in SI units α=(3.52±0.09)×10 −4 [Cm 2V −1]), and its anisotropy, κ α=(α ‖−α ⊥)/3α=−(0.06±0.03), nonlinear magneto-optical polarizability, η=(η ‖+2η ⊥)/3=−(4.7±0.9)×10 −30 [cm 3Oe −2] (in SI units η=−(6.7±1.3)×10 −18 [Cm 4V −1A −2]) and its anisotropy, κ η=(η ‖−η ⊥)/3η=−(0.15±0.10), were deduced. Here α ‖, η ‖, α ⊥, η ⊥ are the optical and magneto-optical polarizability components along the parallel and the perpendicular axes of the axially symmetric molecule, respectively.