Conjugation of steroids with PAMAM nanoparticles

We studied the binding process between polyamidoamine PAMAN-G4 dendrimer and testosterone and its aliphatic (alip) and aromatic (arom) dimers in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize the steroid binding process to PAMAM-G4 nanoparticles. Thermodynamic parameters ΔS, ΔH and ΔG showed steroid-PAMAM bindings occur via hydrophobic, H-bonding and van der Waals contacts. The binding affinity is testosterone>testosterone-aromatic dimer>testosterone-aliphatic dimer. Transmission electron microscopy showed significant changes in carrier morphology with major changes in the diameter of the polymer aggregate as steroid encapsulation occurred. Modeling also showed that testosterone is located in the interior cavity of PAMAM with the free binding energy of -9.36 kcal/mol, indicating of spontaneous steroid-polymer interaction at room temperature.