Four cyclodextrins (CDs) including heptakis-O-(2-hydroxypropyl)-β-cyclodextrin (HP-β-CD), heptakis-O-(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD) were evaluated for their ability to enhance the aqueous solubility of kaempferol (Kae). Phase solubility studies indicated that these four CDs can form 1:1 type complexes with Kae and that HP-β-CD demonstrated the most significant solubilizing effect on Kae. Among the CDs tested, HP-β-CD demonstrated the most significant solubilizing effect on Kae. With an HP-β-CD concentration of 5.00 × 10⁻³ mol·L⁻¹, the concentration of Kae reached 4.56 × 10⁻⁵ mol·L⁻¹, which is 12.7 times greater than its solubility in water. Characterization of the HP-β-CD/Kae complex was performed using empirical methods. Molecular docking indicated that the A and C rings of Kae fit into the hydrophobic cavity of HP-β-CD, while the B ring remained at the rim. Six hydrogen bonds were found between HP-β-CD and the -OH groups of Kae. The negative complexation energy (ΔE) suggests the complex formation was exergonic. A 30-ns molecular dynamics simulation revealed no significant structural changes, with average root-mean-square deviation RMSD values of 2.230 Å for HP-β-CD and 0.786 Å for Kae, indicating high stability of the complex.

Icariin (ICA) is widely recognized for its health benefits. In this work, we examined the intermolecular interactions between ICA and proteinase K (PK) via multi-spectroscopic techniques and molecular simulations. The experimental findings revealed that ICA quenched the fluorescence emission of PK by forming a noncovalent complex. Both hydrogen bonding and van der Waals interactions are essential for the complex’s formation. Then Förster resonance energy transfer (FRET), competitive experiments, and synchronous fluorescence spectroscopy were adopted to verify the formation of the complex. Molecular docking studies demonstrated that ICA could spontaneously bind to PK by hydrogen bonding and hydrophobic interactions, which is consistent with the spectroscopic results. The PK-ICA complex’s dynamic stability was evaluated using a 50 ns molecular dynamics (MD) simulation. The simulation results revealed no significant structural deformation or positional changes throughout the entire simulation period. The complex appears to be rather stable, as seen by the average root-mean-square deviation (RMSD) fluctuations for the host protein in the PK-ICA complex of 1.08 Å and 3.09 Å. These outcomes of molecular simulations suggest that ICA interacts spontaneously and tightly with PK, consistent with the spectroscopic findings. The approach employed in this research presents a pragmatic and advantageous method for examining protein–ligand interactions, as evidenced by the concordance between empirical and theoretical findings.