In this work an investigation of the photodynamic efficiency of octaethylporphyrin (OEP), vanadyl octaethylporphyrin (VOOEP), and meso-tetramesitylporphyrin (m-TMP) was done. This study was performed by the determination of photoxidation rate constants (k f) of the tryptophan amino acid (Trp). The mechanism involved in the photoxidation of Trp was also studied using sodium azide (singlet oxygen scavenger) and deuterium oxide. The values of k f/10-4s-1 for Trp photoxidation demonstrated that OEP (2.80 ± 0.05) is more efficient than m-TMP (1.62 ± 0.07) and VOOEP (0.81 ± 0.08). The values of k f were reduced by the presence of sodium azide and increased by deuterium oxide indicating that singlet oxygen is responsible by OEP, VOOEP, and m-TMP photoactivity. These results indicated that differences in the photodynamic activity between porphyrins could be associated with differences in their molecular structures. The presence of vanadyl group (V=O) interferes clearly in the photodynamic activity of OEP causing a considerable reduction in its efficiency.
photodynamic therapy; porphyrins; singlet oxygen
