Biological Activities of Phthalocyanines—vi. Photooxidation of L‐tryptophan by Selectively Sulfonated Gallium Phthalocyanines: Singlet Oxygen Yields and Effect of Aggregation

Abstract

Abstract— The photosensitized oxidation of L‐tryptophan by gallium phthalocyanines sulfonated to different degrees is studied as a function of both substrate and sensitizer concentrations in water and 50% MeOH‐H2O solutions. The maximum quantum yield of singlet oxygen was found to be nearly 0.5 for all sulfonated gallium complexes. The effect of adding sulfonate groups in the phthalocyanine backbone is to change the tendency of dye molecules to dimerize or aggregate in a particular solvent. A shift in the chemical equilibrium away from the monomeric state, which occurs at high dye concentrations and at lower degrees of dye sulfonation, results in a reduced photochemical yield. The variation of quantum yields in different solvent systems and at several wavelengths is similarly accounted for by the fraction of light absorbed by the productive monomer state.

Peripheral and Axial Substitution of Phthalocyanines with Solketal Groups: Synthesis and In Vitro Evaluation for Photodynamic Therapy

“…25,33 Singlet oxygen quantum yields have been shown to be directly related to the aggregation state of the PS, that is, the quantum yield is low when the sensitizer is in an aggregated form. 34,35 Also, the fluorescence of the PS will be reduced accordingly. Substitution of the macrocycle with bulky groups can reduce aggregation tendency by shielding of the Pc core.…”

Tryptophan Photo-Oxidation by Clay-Adsorbed Sensitizers

“…MB forms dimers on the clay surface even at the low loadings used for the present experiments (Cenens & Schoonheydt, 1988). These dye aggregates enhance the decay of the singlet state: the emission quantum yield of proflavine on clays is quenched by proflavine dimers (Cenens et al, 1987); the TRP sensitized degradation by phthallocyanines decreases with increasing dye aggregation (Wagner et al, 1987). By increasing the MB loading on LAP, the fraction of monomers with sensitizing capacitie s diminishes, as is reflected in the reduced rate of TRP degradation (Fig.…”

“…The value for the pseudo-first order constant kso of 102 in water is 5 • 105 s -1 . The value for the total quenching rate k, + kq of TRP with 102 in water is 6 x 107 mo1-1 s -1 (Wagner et al, 1987). Assuming that all TRP in solution (2 x 10 -4 mole dm -3) is available for reaction, a maximum pseudo-firstorder rate constant of 1.2 x 104 s -1 is expected when no physical quenching takes place.…”

Biological Activities of Phthalocyanines‐x. Syntheses and Analyses of Sulfonated Phthalocyanines

“…1) have received increasing attention as sensitizers for photodynamic therapy of cancer [for recent reviews, see Spikes (1986), Ben-Hur (19871, van Lier et al (1988)]. The degree of sulfonation affects the tendency of the SPC to aggregate, and thus changes their ability to generate lo2 (Wagner et a)., 1987). and to be transported through cell membranes which are important factors of their photocytotoxicity (Brasseur et ul., 1987a).…”