Linear Dichroism (250-700 nm) of Chlorophyll a and Pheophytin a Oriented in a Lamellar Phase of Glycerylmonooctanoate / H2O. Characterization of Electronic Transitions

Journal article, 1988

We determined the polarized and isotropic visible/UV absorption spectra of chlorophyll a (Chi a) and pheophytin a (Pheo a) oriented in the lamellar phase of glycerylmonooctanoate/H2O. Resolution into mutually perpendicular X- and Y-polarized absorption spectra of the pigments was achieved assuming that the transition moments of Chi a and Pheo a are located in the plane of the chromophores. The polarized spectra were deconvoluted into harmonic progressions and the resultant assignment of band positions in the long-wavelength region was found to correlate well with independent spectral measurements, such as the polarisation of fluorescence. However, the correlation of the experimentally determined transitions with the results of theoretical calculations is not straightforward. The overall conclusions are of fundamental interest in the determination of orientations of the tetrapyrrole macrocycle in lipid lamellae and pigment-protein structures of photosynthetic membranes.