Nucleation effects in the aggregation of water-soluble porphyrin aqueous solutions

Water soluble porphyrins bearing charged groups can be fostered to aggregate by simply screening the repulsive interactions between side-groups with the same charge. We have extensively studied the aggregation of synthetic porphyrins, which on changing the ionic strength give mesoscopic aggregates having a fractal behavior. The resulting structures can be modulated on changing the medium properties. Here we report on a kinetic study of such aggregation behavior on varying the salt concentration, the temperature and the history of the samples, showing the importance of the nucleation step in determining the growth of the aggregates.