Red Shift of the Zero Crossing in the CD Spectra of the LH2 Antenna Complex of Rhodopseudomonas acidophila: A Structure-Based Study

The published crystal structure of the LH2 complex of Rhodopseudomonas acidophila is used to calculate absorption and CD spectra of this system. An important parameter, the zero crossing of the CD spectrum with respect to the absorption maximum, is shown to be sensitive to structural changes. The changes in spectral properties as a function of varying excited state energy, variation in the dielectric properties of the surrounding medium, and changes in relative orientations of the chromophores are also investigated. It is shown that the experimentally observed red shift of the zero crossing can be explained by lifting the degeneracy of the excited state of the monomers and taking into account more than half of the LH2 ring.