ESR STUDIES OF A SERIES OF PHTHALOCYANINES - MECHANISM OF PHOTOTOXICITY - COMPARATIVE QUANTITATION OF O-2-CENTER-DOT(-) USING ESR SPIN-TRAPPING AND CYTOCHROME-C REDUCTION TECHNIQUES

ESR experiments with 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP) and the spin-trap 5,5-dimethyl pyrroline-N-oxide (DMPO) have been perform ed on a series of new phthalocyanines: the bis(tri-n-hexyl-siloxy) sil icon phthalocyanine ([(nhex)(3)SiO](2)SiPc), the hexadecachloro zinc p hthalocyanine (ZnPcCl16), the hexadecachloro aluminum phthalocyanine ( AlPcCl16), the hexadecachloro aluminum phthalocyanine sulfate (HSO(4)A LPcCl(16)), whose photocytotoxicity has been studied against various l eukemic and melanotic cell lines. Type I and Type II pathways occur si multaneously in DMF although the Type II seems to be prevalent. These results are not changed when the bis(tri-n-hexyl-siloxy) silicon phtha locyanine is entrapped into liposomes. By contrast, the Type I process is favored in membrane models for all the perchlorinated phthalocyani nes. This modified behavior may be accounted on a possible stacking of phthalocyanines in membranes and a preventing effect of axial ligands against aggregation in the case of the bis(tri-n-hexyl-siloxy) silico n phthalocyanine. The photodynamic action of zinc perchlorinated phtha locyanine is not dependent on singlet oxygen, phototoxicity of this mo lecule being essentially mediated by oxygen free radicals. Quantitatio n of the superoxide radical was accomplished, with good agreement, by two techniques: the cytochrome c reduction and the ESR quantitation ba sed on the double integration of the first derivative of the ESR signa l. The disproportionation of the superoxide radical or degradation of the spin-trap seem to be avoided in aprotic solvents such as DME.