Interaction of a Model Hydrophobic Drug Dimethylcurcumin with Albumin Nanoparticles

The aim of present study was to investigate the binding interactions of a model hydrophobic molecule, dimethylcurcumin (DMC) with nanoparticle form of bovine serum albumin (BSA) using fluorescence spectroscopy techniques. For this, BSA nanoparticles (size = 62.0 ± 3.5 nm, molecular weight = 11,243 ± 3445 kD) prepared by thermal denaturation method was mixed with DMC in solution and monitored for fluorescence emission of tryptophan (Trp) residue as well as DMC separately. The emission maximum of DMC in nanoparticles form exhibited more blue sift and quenched the excited state of tryptophan (Trp) by six fold higher than in the native form of BSA. By analyzing Trp fluorescence, the mean binding constant (K) estimated for the interaction of DMC with native and nanoparticles forms of BSA was 2.7 ± 0.4 × 10⁴ M^-1 and 1.5 ± 0.5 × 10⁵ M^-1 respectively. Together these results suggested that DMC experienced a more rigid environment in nanoparticles than in native form of BSA. Additionally the above determined K values were in agreement with those reported previously by absorption techniques. Further direct energy transfer was observed between Trp and DMC, using which the distance (r) calculated between them was 28.25 ± 0.27 Ǻ in BSA native. Similar analysis involving BSA nanoparticle and DMC revealed a distance of 24.25 ± 1.05 Ǻ between the hydrophobic core and the ligand. Finally interaction of DMC with BSA was validated through molecular docking studies, which indicated sub-domain IIA as the binding site of DMC. Thus it is concluded that intrinsic fluorescence of protein can be utilized to study the interaction of its different physical forms with any hydrophobic ligand.