“…In the present paper, we describe our findings about the photodynamic action of some porphyrin derivatives on amino acids and proteins. Porphyrins were chosen because the photochemistry of tetrapyrrolic molecules has been investigated in great detail (Robinson, 1964;Goedheer, 1966;Azizova et al, 1966); in particular, it has been demonstrated that the chelation of metal ions to the porphyrin molecules greatly affects the yield of the intersystem crossing from the first excited singlet state to the first triplet state, which is the reactive one in photoreactions involving porphyrins (Fujimori and Livingston, 1957); the lifetime of the triplet state is also appreciably affected (Livingston and Pugh, 1959). As far as we know, however, only very few and qualitative experiments concerning the use of porphyrins as sensitizers for the photodamage of proteins are reported in the literature (Spikes and Glad, 1964;Della Pietra and Dose, 1965).…”