Charge-transfer complexes of plastoquinone and α-tocopherol quinone in phosphatidylcholine and octadecane

It has been found that plastoquinone-9 and α-tocopherol quinone form charge-transfer complexes with their corresponding reduced forms in anhydrous dipalmitoyl phosphatidylcholine and octadecane throughout the whole temperature range examined, i.e. from -30 to 60°C. The charge-transfer spectra of both prenylquinones in lecithin showed the presence of only one band with λ_max in the range 520–600 nm, depending on temperature. There was a gradual long-wavelength shift of λ_max of the band observed with decrease in temperature. The intensity of the band was quite constant. Only at the lowest temperatures was a sudden intensity decrease, caused by precipitation of the hydroquinone form, observed. On the other hand, the charge-transfer spectra of both prenylquinones in octadecane showed the presence of two bands with strong temperature dependence. On freezing, the intensity of these two bands increased with a simultaneous long-wavelength shift of both maxima. The results are discussed in terms of different molecular structures of the complex in both systems.