Spectroscopic and molecular modeling of the binding of meso-tetrakis(4-hydroxyphenyl)porphyrin to human serum albumin

The binding of meso-tetrakis(4-hydroxyphenyl)porphyrin to human serum albumin has been investigated by the combination of fluorescence, UV–vis absorption, Fourier transform infrared, circular dichroism spectroscopies and molecular modeling. Fluorescence and UV–vis data indicated that hydrophobic interaction is the main driving force for binding and that aggregation of the colorant plays a major role in the affinity of the dye for the serum. The dye–serum distance, r, was determined to be ∼4 nm based on Förster non-radiative energy transfer theory. FT-IR and CD spectral examinations revealed that binding induces a conformational change in the serum which reduces the α-helix structure of the protein. Molecular modeling suggested that the colorant can partially insert into the site II of subdomain IIIA via hydrophobic and hydrogen bonding interactions.