Aggregation phenomena in porphyrin aqueous solutions

The aggregation of porphyrins is a well-known behavior of this class of com pounds. Aggregated porphyrins play a key role in man!: systems related to m edicine and biology, e.g., the bacteriochlorophyll dimer, known as the "spe cial pair", is the main electron donor in the bacterial reaction center. Th e large surface and planarity of the porphyrin chromophore favor strong van der Waals stacking interactions which lead to very large aggregates. Recen tly, we have studied the aggregation of a synthetic water soluble porphyrin (trans-H2Pagg), which on salt addition gives mesoscopic aggregates having a fractal structure mainly driven by a diffusion limited kinetic (DLA). Her e we are reporting a study of such aggregation property on varying the salt concentration, obtaining evidences that differ ent dynamics of aggregation exist in different ionic strength regimes.