Electron Spin Resonance of Triplet States and Free Radicals Appearing in Porphyrins, Aromatic Amino‐acids and Proteins Under the Effect of Light

Abstract

The electron paramagnetic resonance (EPR) of the triplet excited state of solutions of a series of porphyrins and aromatic amino-acids has been studied at 77°K. It has been shown that for some of the compounds it is possible to observe EPR for transitions with It has been shown that photoreactions in solid solutions of porphyrins and aromatic Reactions of photosensitized deamination of aliphatic amino-acids in solid aqueous A M = & l , &2. amino-acids proceed through the triplet excited state. solutions at 77°K by aromatic compounds have been studied.

Photodynamic action of porphyrins on amino acids and proteins. I. Selective photooxidation of methionine in aqueous solution

“…This is to be expected if the triplet state is the reactive one in porphyrin-sensitized photochemical processes, it has been suggested by several authors (Fujimori and Livingston, 1957; Pekkarinen and Linschitz, 1960). Actually, it has been shown that porphyrins containing diamagnetic metal ions have a stronger phosphorescence than the corresponding free compounds (Allison and Becker, 1963), as well as a much higher steady-state triplet population and a longer triplet lifetime (Azizova et al, 1966), due to the lowering of the rate of nonradiative decay. Accordingly, one could assume in the present case that the introduction of the Mg2+ ion into the chlorophyll molecule leads to a high population of the triplet state of the dye, which in turn increases the efficiency of the photodynamic process.…”

“…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).…”

ON THE LUMINESCENCE OF L‐TRYPTOPHANE AND l‐TYROSINE IN AQUEOUS SOLUTION AT 77dK INDUCED BY X‐RAYS AND U.V.‐LIGHT

“…The G-value of the X-ray induced luminescence was about 10 for both tryptophane and tyrosine. Thus, about 30 per cent of the total energy absorbed from X-rays in these compounds was re-emitted as light.…”