Absorption and linear dichroism spectroscopy at room and low temperatures of single crystals of the B800-850 light-harvesting complex from Rhodopseudomonas acidophila strain 10050.

The absorbance, polarized absorbance and linear dichroism spectra of single crystals of the B800-850 light-harvesting complex from Rhodopseudomonas acidophila strain 10050 taken at room (298 K) and low (85 K) temperatures are presented. The spectra are compared and contrasted with random phase solution spectra from the same complex. The single crystal spectra display a spectral narrowing at low temperatures in the BChl Qx (550-650 nm) and carotenoid (450-550 nm) regions similar to that observed from the random phase solution. The single crystal absorption spectra in the BChl Qy (750-900 nm) region are broader than the solution spectra and remain broad as the temperature is lowered. It is suggested that this broadening is the result of specific exciton interactions between the BChl chromophore Qy transition dipoles and is a molecular feature which occurs only in the crystalline complex.