Narrow Results

The inhibition of the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)-porphyrin (H₄TPPS) by urea is investigated spectroscopically by absorbance, fluorescence, and fluorescence lifetime techniques. In 8 M urea at pH 2 with 0.1 M NaCl, diacid TPPS (H₄TPPS) exists as a monomer up to 75 μM H₄TPPS where the absorbance is linearly dependent on porphyrin concentration. The extinction coefficient of monomeric H₄TPPS in 8 M urea at pH 2 with 0.1 M NaCl at 438 nm is 4.43 × 10⁵M^-1.cm^-1. No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 μM concentration range. Aggregated H₄TPPS (10 μM) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65°C. In D₂O at pH 2, no aggregation is observed. These spectral observations suggest that the H₄TPPS aggregation involves intermolecular hydrogen bonding.