Investigation of the binding interactions between dimethyl phthalate and its metabolite with bovine serum albumin by multispectroscopy.

To understand the behavior of dimethyl phthalate (DMP) and realize the effect of DMP and its metabolite, monomethyl phthalate (MMP), on the conformation changes of bovine serum albumin (BSA), the interaction mechanisms of DMP and MMP with BSA were investigated by multispectroscopy and molecular docking. The results of the fluorescence quenching experiment showed that the fluorescence quenching of BSA by DMP and MMP was due to the formation of a complex though static quenching, which was also confirmed by time-resolved fluorescence measurements. The binding constants were 8.06 × 104 M-1 and 4.74 × 104 M-1 for DMP-BSA and MMP-BSA, respectively, and the number of binding sites were 1.20 (DMP) and 1.18 (MMP). The thermodynamic parameters showed different binding forces for DMP and MMP with BSA. The binding of DMP to BSA was driven mainly by hydrophobic interactions and hydrogen bonding, and MMP bound to BSA by van der Waals forces and hydrogen bonding, which were in accordance with the results from the molecular docking. The conformation and structural alterations of BSA upon DMP or MMP binding were studied by UV-vis spectroscopy, circular dichroism spectroscopy and synchronous fluorescence spectroscopy. The presence of metabolite did not change the quenching mechanism but decreased the binding affinity of DMP toward BSA as well as shortened the binding distance, which may be attributed to the competition between DMP and MMP for binding to BSA. This study revealed the combined effects of DMP and its metabolite on BSA at the molecular level.