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 (<= 2 mu M), 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 TPPS4-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 4 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 TPPS4 nanostructures might be also formed in contact with protein molecules.