Spectroscopic study of TPPS4nanostructures in the presence of bovine serum albumin

Abstract

The influence of bovine serum albumin (BSA) on the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS₄) in aqueous acid solution (pH 1.3) has been investigated by means of absorption and fluorescence spectroscopy. TPPS₄ concentration was kept constant at 2 μM while BSA concentration was varied to get TPPS₄ : BSA molar ratios from 1 : 0.005 to 1 : 20. In the presence of protein at all used concentrations the intensity of J-aggregates absorption band was higher than that in the pure solution. Spectral changes indicated that the dynamic equilibrium of the aggregated TPPS₄ species was highly dependent on the molar ratio between TPPS₄ and BSA. Small relative concentrations of BSA (TPPS₄ : BSA, 1 : 0.005–1 : 0.1) had a stimulating effect on formation of J-aggregates. Several fractions of J-aggregates located in protein and aqueous moieties were detected in mixed solutions at intermediate BSA concentrations (TPPS₄ : BSA, 1 : 0.5–1 : 8), when the absorbance intensity of the J-aggregates was the highest. At the highest used BSA concentrations (TPPS₄ : BSA, 1 : 10–1 : 20) the spectral properties of the remaining J-aggregates were similar to those typical for pure porphyrin solution. Additionally, the split of the Soret band into two with peaks at 440 nm and 423 nm was followed by the simultaneous appearance of Q bands and reflected the formation of TPPS₄–BSA complexes including both protonated and deprotonated TPPS₄ forms.