Aggregation behavior of a tetracarboxylic porphyrin in aqueous solution.

The aggregation of 3,8,13,18-tetramethyl-21H,23H-porphine-2,7,2,17-tetrapropionic acid (Coproporphyrin-I) has been investigated by UV–vis spectroscopy in aqueous solutions. The aggregation occurred by total neutralization of propionic groups and can be induced by alkaline salts, hydrogen peroxide or acidification. The hydrogen peroxide effect is investigated in the presence of different concentrations and it has been observed that only high concentrations favour the formation of H-aggregates. The dimerization constants in the several experimental conditions are reported. The H-dimers of Coproporphyrin-I in particular experimental conditions formed highly aggregate species depending on the pH. The kinetic of aggregation has been studied at different pHs and the results have showed that the log of kinetic constants kP were linearly dependent on the pH. The morphology of these aggregates, investigated by SEM spectroscopy, showed that the solvent polarity influenced their structures.