Equilibrium and kinetic studies of the aggregation of porphyrins in aqueous solution

Abstract

An investigation of the behavior of protoporphyrin IX, deuteroporphyrin IX, haematoporphyrin IX and coproporphyrin III in aqueous solution revealed extensive and complex aggregation processes. Protoporphyrin appears to be highly aggregated under all conditions studied. At concentrations below 4 muM, aggregation of deutero-, haemato- and coproporphyrin is probably restricted to dimerization. At approx. 4muM each of these three porphyrins exhibits sharp changes in spectra consistent with a "micellization" process to form large aggregates of unknown size. This critical concentration increases with increasing temperature and pH, but is not very sensitive to variation in ionic strength. Temperature-jump kinetic studies on deuteroporphyrin also imply an initial dimerization process, the rate constants for which are comparable with those for various synthetic porphyrins, followed by a further extensive aggragation. The ability of a particular porphyrin to dimerize appears to parallel that of the corresponding iron(III) complexes (ferrihaems), although it is thought that ferrihaems do not exhibit further aggregation under these conditions.

Spectroscopic studies of self-assembled TPPS4nanostructures in aqueous solutions: The role of serum albumin and pH

“…The efficiency of PDT is highly dependent on the photophysical properties of the sensitizers, such as their intensive absorbance in the far red spectral region and high quantum yields for triplet state population and singlet oxygen generation. However, these properties can vary with the aggregation state of the porphyrins [1][2][3][4][5][6][7].…”

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

“…13,18 The spectrum observed in HP showed a marked decrease in the intensity of the Soret band, being blueshifted to 374 nm, which was a typical spectrum assigned as a dimeric form. 13 The spectrum of MP was similar to that of HP, though the intensity of the Soret band somewhat decreased, showing that most of the MP was present as a dimer, like HP. These porphyrins produced rather small amounts of H2O2.…”

“…We were interested in the degree of aggregation of porphyrins, because some porphyrins are known to take mainly dimeric forms in aqueous solutions. 13,18 Figure 5 shows the absorption spectra of porphyrins under the same conditions as used in the photochemical experiments. Most of the obtained spectra were consistent with previous results.…”

“…The absorption spectrum of PP was extremely broadened, showing a highly aggregated form, as previously reported. 13 It is interesting that PP produced much greater amounts of H2O2 than any dimer of porphyrins. In general, H2O2 is effectively photogenerated on the surface of solid-phase porphyrins.…”

“…In this study, we used a luminol chemiluminescence method 9,10 and found that it could quantify H2O2 even in the presence of a high concentration of porphyrin. Using the present method, we demonstrated how the chemical properties of porphyrins, especially their aggregation in an aqueous solution, [11][12][13] influenced the photogeneration of H2O2.…”