A COMPARISON OF THE PHOTOPROPERTIES OF ZINC PHTHALOCYANINE AND ZINC NAPHTHALOCYANINE TETRASULFONATES - MODEL SENSITIZERS FOR THE PHOTODYNAMIC THERAPY OF TUMORS

Phthalo- and naphthalocyanines are of interest as sensitizers for the photodynamic therapy of tumors because of their strong absorption in the 680 and 760 nm ranges respectively. Both zinc phthalocyanine and naphthalocyanine tetrasulfonates (ZnPcS(4) and ZnNcS(4)) were aggregated and photochemically inactive in aqueous buffer of pH 7.4, while in 10 mM cetyl pyridinium chloride in buffer they were monomeric and active. Therefore all these studies were carried out using the buffered detergent. The triplet lifetimes of ZnPcS(4) and ZnNcS(4) under argon were 490 and 110 mu s respectively, with oxygen bimolecular quenching constants of 4.2 X 10(9) and 2.0 X 10(8) M(-1) s(-1) respectively. Triplet decay curves in argon, air and 100% oxygen were first order, suggesting that there was little back reaction of the triplet states with oxygen as has been observed with some naphthalocyanines. The quantum yield of singlet oxygen generation by ZnPcS(4) was 0.70 and that for ZnNcS(4) was 0.25. Both compounds sensitized the photo-oxidation of furfuryl alcohol, cysteine, histidine, methionine, tryptophan, tyrosine and guanosine; ZnPcS(4) was three times more efficient than ZnNcS(4). These reactions were 50% inhibited by about 0.5 mM azide, suggesting the involvement of singlet oxygen. Both sensitizers photobleached on illumination, with quantum yields of 1.7 X 10(-5) for ZnPcS(4) and 4.2 X 10(-3) for ZnNcS(4).