Inhibition of aggregation of meso-tetra(4-sulfonatophenyl) porphyrin (H4TPPS) by urea

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 mu M 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 x 10(5)M(-1).cm(-1). No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 mu M concentration range. Aggregated H4TPPS (10 mu M) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65 degrees C. In D2O at pH 2, no aggregation is observed. These spectral observations suggest that the H4TPPS aggregation involves intermolecular hydrogen bonding. Copyright (c) 2007 Society of Porphyrins & Phthalocyanines.