Gold Nanoparticle Plasmonic Field Effect on the Primary Step of the Other Photosynthetic System in Nature, Bacteriorhodopsin

Abstract

In regards to the effect of the surface plasmon field of gold nanospheres on the rate of primary steps leading to retinal photoisomerization in the photosynthesis of bacterirhodopsin (bR), it is believed that the light absorption of bR that leads to its retinal isomerization first involves the formation of a highly polar electronic excited state (I460) of the all-trans isomer which strongly polarizes the protein around it. This is followed by its decay to a viibrationally excited 13-cis isomer (J625). The effect of plasmonic field of gold nanospheres of different sizes and concentrations is found to slow down the rate of the isomerization of the polar electronic excited-state to the J625 but has no effect on the vibration relaxation of the isomeric state itself. This is consistent with the electrostatic nature of the plasmonic field.