Anisotropic Circular Dichroism of Light-Harvesting Complex II in Oriented Lipid Bilayers: Theory Meets Experiment

Abstract

Anisotropic circular dichroism (ACD) spectroscopy of macroscopically aligned molecules reveals additional information about their excited states that is lost in the CD of randomly-oriented solutions. ACD spectra of light-harvesting complex II (LHCII)-the main peripheral antenna of photosystem II in plants-in oriented lipid bilayers, were recorded from the far-UV to the visible wavelength region. The ACD spectra show a drastically enhanced magnitude and level of detail compared to the isotropic CD spectra, resolving a greater number of bands and weak optical transitions. Exciton calculations show that the spectral features in the chlorophyll Q y region are well reproduced by an existing Hamiltonian for LHCII, providing further evidence for the identity of energy sinks at chlorophylls a603 and a610 in the stromal layer and chlorophylls a604 and a613 in the luminal layer. We propose ACD spectroscopy to be a valuable tool linking the threedimensional structure and the photophysical properties of pigment-protein complexes.

Circular Polarization of Luminescence as a Tool To Study Molecular Dynamical Processes

“…The degree of circular polarization is actually a tensorial quantity that can vary strongly depending on the direction of propagation of the photon. [190][191][192][193] Hence degrees of circular polarization from immobile molecules differ considerably from the results in solution. [194] In fact it has been realized early on that anisotropy can play a role in CPL measurements especially under where photoselection in excitation occurs and where tumbling is slow.…”

An Exciton Dynamics Model of Bryopsis corticulans Light-Harvesting Complex II

“…It is also interesting to note that the same Chls were identified as likely candidates for the a/b exchange based on the anisotropic circular dichroism spectra of LHCII from B. corticulans. 12,25 On the other hand, the Hamiltonian from Novoderezhkin et al 24 suggests the replacement of Chl a602 and either Chl a612 or a611 (Figure 7b), while the replacement of Chl a610 in this case is not probable since it does not cause a spectral blue shift (Supplementary Figure S8). Thus, it can be seen that the predictions of pigment identities vary with the Hamiltonian used.…”

Differential Polarization Imaging of Plant Cells. Mapping the Anisotropy of Cell Walls and Chloroplasts

“…In all cases, full information on the orientation of the transition dipoles can be obtained from two measurements, determining the difference between the transmitted intensities in the horizontal and vertical directions and between the +45° and −45°, respectively. On the other hand, in (FD)CD and CPL measurements, the microscopic alignments may complicate the picture because of the emergence of anisotropic CD (ACD), also known as oriented CD (OCD) [ 21 , 22 ].…”