COMPARISON OF THE PHOTOSENSITIZING EFFICIENCIES OF HEMATOPORPHYRIN (HP) AND ITS DERIVATIVE (HPD) WITH THAT OF FREE-BASE TETRASULFOPHTHALOCYANINE (TSPC-H2) IN HOMOGENEOUS AND MICROHETEROGENEOUS MEDIA

Using solutions of different polarity and various reducing (oxidizing) substrates, the type I (free radical) and type II (singlet oxygen) photosensitizing efficiencies of haematoporphyrin (HP), haematoporphyrin derivative (HPD, Photofrin II) and free-base tetrasulphophthalocyanine (TSPC-H2) were investigated. The quantum yields of 1O2-mediated oxidation of 2,2,6,6-tetramethyl-4-oxopiperidine (TEMP) followed the order QHP>QHPD>QTSPC-H in all the reaction media investigated. Monomeric TSPC-H2 effectively generates Oa2 . ̄ as shown by spin-trapping measurements. It is probable that both HPD and TSPC-H2 can oxidize l-tryptophan (Trp) via a mixed type I and type II mechanism, depending on the polarity of the medium. Both HP and TSPC-H2 in the monomeric form can be readily photoreduced by mild electron donors (ethylenediaminetetraacetic acid (EDTA), cysteine, sodium ascorbate, etc.). However, the reaction efficiencies differ because of the higher net negative electrical charge of TSPC-H2. © 1990.