Exploring the Interaction of Flavonoids Baicalein and Scutellarein With Human Serum Albumin: Spectroscopic and...

This study explores the interaction of human serum albumin (HSA) with two flavonoids (FLs), baicalein and scutellarein, and in situ formed Cu(II)-FL complexes using fluorescence spectroscopy, molecular docking, and molecular dynamics simulations. Fluorescence quenching experiments show diminished fluorescence intensity indicating that all compounds effectively bind to HSA, with free scutellarein exhibiting slightly higher affinity. Cu(II) coordination reduces quenching efficiency; however, the binding processes remain thermodynamically favorable. UV-Vis spectroscopy confirmed well-defined ground-state HSA-flavonoid complexes with minor indications of subtle protein conformational adjustments. A novel composite scoring function integrating effective free energies and thermodynamic stability was used to compute theoretical free energies. The results are in agreement with experimental results, showing that all ligands preferentially bound in Sudlow site I, while baicalein also samples site III. Per-residue energy decomposition indicates that Cu(II) complexes are stabilized by electrostatic interactions further from the intrinsic fluorophore Trp²¹⁴. Clustering analysis reveals distinct conformational landscapes, with baicalein favoring a few dominant states, whereas scutellarein adopts a more fragmented ensemble. Overall, HSA effectively accommodates both free and Cu(II)-complexed flavonoids, with metal coordination subtly modulating binding preferences and conformational dynamics.