PHOTOBIOLOGY.

Molecular complexes of flavins with indoles and phenols were studied. Optical and thermodynamic properties provide insight into the role of charge transfer and other forces in these materials. The role of solvent was also investigated. The mechanism of phototaxis in Euglena was studied using a photoelectric technique. The response was shown to involve a shading from light of a photosensitive region by a carotenoid-containing organelle. The energy required to orient the organism with respect to the light source is derived from photosynthetic phosphorylation. Polarized light experiments indicate that the carotenoid molecules are aligned with their long axes parallel to the long axes of the organism. EPR and optical studies show reversible light-induced single electron transfer between chlorophyll and hydroquinone in solution. The role of oxygen and organic bases in this reaction has been elucidated. Quinones also participate in similar reactions. Studies using a variety of solvents have shown that solvent electrons are not involved in semiquinone radical formation and that carbonyl-containing solvents form complexes with the semiquinone radicals. Quenching experiments demonstrate that the chlorophyll triplet state is involved in both oxidation and reduction processes. Author