Aggregation of tetrakis(4-methylpyridyl)porphyrin and tetrakis(4-sulphonatophenyl)porphyrin in water

The homo- and heteroaggregation of two oppositely charged water soluble porphyrins, tetrakis(4-methylpyridyl)porphyrin, TMPyP and tetrakis(4-sulphonatophenyl) porphyrin, TSPP has been studied by means of absorption and fluorescence spectroscopy in phosphate buffered saline. All experimental results on TSPP are consistent with a monomerdimer equilibrium (Delta H = -19.6 and Delta S = 19.3 kJ mole(-1)). The absorption spectrum of the TSPP dimer was obtained from a global fit of a set of spectra to the monomer dimer model. TMPyP does not aggregate at concentrations up to 10(-4)M. Changes in the fluorescence spectrum of TMPyP upon dilution are due to adsorption phenomena. 1:1 heteroagregates of both porphyrins cannot be characterized in water solution due to extreme small solubility. A 2:1 heteroaggregate is detectable in solution. It is prpoosed to exploit the extreme small solubility of heteroaggregated oppositely charged porphyrins to increase the selective retention of porphyrins provided there is an initial selectivity of ether component.