Anisotropic photoselection of the bacteriorhodopsin molecules in the purple membrane with hexagonal crystalline lattice of trimers


Introduction. In the purple membrane fragment, bacteriorhodopsin (BR) molecules are arranged at 120 degrees into trimers forming a two-dimensional hexagonal crystalline lattice with a space of 62 Å. BR has gained acceptance as the multifunctional nanomaterial. However, the potentials of a light impact on the creation of nanostructures with BR were not considered previously. 
Purpose. The aim of this work is to develop a method of the directed photobleaching of one, two or three molecules in the BR trimer through the variation of intensity of linearly polarized light beam. 
Methods. We experimentally studied the optical density changes and photoinduced dichroism in the BR films as a function of the intensity of linearly polarized light beam which excites the initial form of photocycle bR570. 
Results. An experimental dependence of the macroscopic photoinduced dichroism was modeled taking into account the trimer orientation angle relatively to the direction of the exciting beam polarization. From a value of the macroscopic photoinduced dichroism, we determine a quantity of the photobleaching BR molecules in trimers at given light intensity. 
Conclusion. Thus a probability of a transformation to the intermediate M412 of one, two or three molecules in BR trimers is a function of intensity of the linearly polarized exciting light beam. We found that control of a quantity of BR molecules in the M412 intermediate at sites in the hexagonal crystalline lattice with a space of 62 Å could be performed by the low-power cw He-Ne laser irradiance


Keywords: organic nanomaterial, bacteriorhodopsin, nonlinear optical methods, linearly polarized light, nanostructure anisotropy