[82] Linear dichroism studies in the visible, UV, and IR on oriented rod suspensions

Publisher Summary This chapter discusses the linear dichroism (LD) studies in the visible, ultraviolet (UV), and infrared (IR) on oriented rod suspensions. The observation that rod outer segments (ROS) orient in magnetic fields of a few kilogauss, combined with the availability of elasto-optic quartz modulators such as those used in commercial circular dichrographs, opened the way to a new technical approach in the visible and UV: instead of working with micro-optics on a single rod, one studies the LD of an oriented suspension containing about 10 rods. In diluted suspensions of ROS, contaminating cells do not perturb the orientation of the ROS. These contaminants, if unoriented, do not give a LD signal and the only limitation is that they should not attenuate the beam too much. As the LD signal is collected from a large number of rods, bleaching by the dichrograph beam can be reduced to a very low level and repetitive scanning can be used to study the dichroism of the photobleaching intermediates.