Protein induced formation of porphyrin (TPPS₄) nanostructures

The stimulating effect of two cationic proteins lysozyme and serum albumin on TPPS₄ aggregation was studied in aqueous acidic solution (pH 1) by means of absorption and fluorescence spectroscopy. At low TPPS₄ concentrations (⩽2μM), the presence of both proteins significantly increased formation of TPPS₄ J-aggregates as compared with pure TPPS₄ solution. The absorption intensity of protein-induced J-aggregates was found being dependent on protein nature, TPPS₄ concentration and TPPS₄/protein molar ratio. J-aggregates formed in mixed TPPS -protein solutions had a broader absorption band (490 nm), except for TPPS₄:BSA at a ratio 1:10, when it was even narrower and bathochromically shifted. The formation of a new absorption band at 426 nm was also observed for both Lys and BSA at certain molar ratios. The presence of a similar absorption band at 423 nm in the pure highly concentrated TPPS solutions, in which nanotube-like structures were identified on AFM images, suggests that ordered TPPS nanostructures might be also formed in contact with protein molecules.