Mobility field induced shift

Thylakoid membrane as a Molecular Voltmeter and Ammeter. The antibiotic valinomycin was found in 1964 by Moore and Pressman to affect ion transport across the mitochondrial membrane. Subsequently, Pressman and coworkers proposed that valinomycin is an ionophore and acts as a mobile ion carrier across the lipid membrane [cf. sectionlll.B. above]. Since the light-induced FIAC in thylakoid membrane appears to be an electrochromic band shift in pigments produced by an electric field, Boeck and Witt °, Junge and Schmid used this unique effect to probe the effect of compounds such as the ionophore, valinmycin, on the voltage and current density generated across the membrane. 

An electric field in a material causes polarization, as summarized in Fig. 4.171. The polarization may have different origins (1) Electron polarization, an interaction that shifts the electrons with respect to the center of the atom. (2) Atom polarization, caused by shift of relative positions of bonded atoms. (3) Dipole or orientation polarization, the effect to be discussed. The first two types of polarization involve fast displacement of positive and negative charges relative to each other within a time-scale of about 10" s. Both are usually treated together as induced polarization and are related to the refractive index, n, by the equation of Maxwell (see also the discussions of light scattering. Sect. 1.4.2 and Appendix 3). The time scale of dipole polarization is 10 to 10" s for mobile dipoles, but may become seconds and longer... 

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