Porphyrin-Induced Photogeneration of Hydrogen Peroxide Determined Using the Luminol Chemiluminescence Method in Aqueous Solution: A Structure-Activity Relationship Study Related to the Aggregation of Porphyrin

The Influence of Aggregation of Porphyrins on the Efficiency of Photogeneration of Hydrogen Peroxide in Aqueous Solution

“…8) In brief, a 5-ml volume of a 50 mM porphyrin solution was put in a cylindrical glass vessel and photo-irradiated by a 1 kW tungsten projector lamp (Rikagaku Seiki, Tokyo, Japan) for 10 min with stirring at 25°C. Subsequently, 0.5 ml of the solution was pipetted into a plastic cell and the amount of H 2 O 2 produced was determined by a luminol chemiluminescence method as described below.…”

“…8) Using this method, we found that highly aggregated porphyrin was much more active in producing H 2 O 2 than the dimer and concluded that a highly aggregated form of porphyrin had a semiconductorlike role, causing effective charge separation, leading to a larger amount of H 2 O 2 . 8) As a continuation and extension of this work, we examined the effect of pH on the photogeneration of H 2 O 2 , because porphyrins are known to take different aggregated forms depending on their environment, including the pH of solution. [9][10][11][12] Coproporphyrin (CP) and uroporphyrin (UP) were chosen, because these porphyrins are known to photogenerate sufficient amounts of H 2 O 2 .…”

“…Although H 2 O 2 has usually been determined with a colorimetric method based on an enzymatic reaction using peroxidase coupled with phenol and 4-aminoantipyrine, there is a large degree of interference from strong absorbance due to porphyrin itself. 8) Thus, we employed a luminol chemiluminescence method making it possible to detect down to 1 mM of H 2 O 2 even in the presence of a high concentration of porphyrin. 8) Using this method, we found that highly aggregated porphyrin was much more active in producing H 2 O 2 than the dimer and concluded that a highly aggregated form of porphyrin had a semiconductorlike role, causing effective charge separation, leading to a larger amount of H 2 O 2 .…”

“…8) Thus, we employed a luminol chemiluminescence method making it possible to detect down to 1 mM of H 2 O 2 even in the presence of a high concentration of porphyrin. 8) Using this method, we found that highly aggregated porphyrin was much more active in producing H 2 O 2 than the dimer and concluded that a highly aggregated form of porphyrin had a semiconductorlike role, causing effective charge separation, leading to a larger amount of H 2 O 2 . 8) As a continuation and extension of this work, we examined the effect of pH on the photogeneration of H 2 O 2 , because porphyrins are known to take different aggregated forms depending on their environment, including the pH of solution.…”

“…[9][10][11][12] Coproporphyrin (CP) and uroporphyrin (UP) were chosen, because these porphyrins are known to photogenerate sufficient amounts of H 2 O 2 . [6][7][8] It was found that the efficiency in producing H 2 O 2 was strongly dependent on the aggregation of CP and UP mediated by changes in the pH of the solution, with a dimer suppressing, and a highly aggregated form enhancing, the production of H 2 O 2 . The increased efficiency with which the highly aggregated porphyrin produced H 2 O 2 was further demonstrated using a different type of aggregate 13) whose formation was driven by the electrostatic interaction of cationic tetrakis-5,10,15,20-(N-methyl-4-pyridyl)porphin (TMPyP) with anionic tetrakis-5,10,15,20-(4-sulfonatophenyl)porphin (TSPP).…”