Size-Dependent Interactions of Degraded PET Nanoparticles with Human Serum Albumin: Thermodynamic and Molecular Insights

This study examines the interaction between degraded polyethylene terephthalate (PET) nanoparticles and human serum albumin (HSA), focusing on the effects of nanoparticle size and surface modifications resulting from degradation. PET degradation, induced via shock compression in water, leads to significant chemical alterations, including the formation of hydroxyl, carboxyl, and carbonyl groups. These modifications influence the hydrophilicity of PET nanoparticles and their binding behavior with HSA. The production of degraded PET nanoparticles involves subjecting pristine PET to controlled shock compression in an aqueous environment, which initiates chemical reactions similar to those that may occur during degradation. The degradation process is characterized by a progressive breakdown of polymer chains, leading to an increase in functionalized surface groups that enhanced hydrophilicity. The performed analysis of surface chemistry reveals that the introduction of oxygen-containing groups alters the interaction properties of PET nanoparticles, making them more prone to hydrogen bonding with water molecules while simultaneously reducing their affinity for HSA binding. Molecular dynamics simulations, umbrella sampling, and weighted histogram analysis are employed to investigate the thermodynamic aspects of PET-HSA interactions. The study identifies preferred binding sites of PET nanoparticles on HSA, revealing that degraded PET nanoparticles preferentially bind to Domain I and Domain III of HSA. Interaction energy analysis demonstrates that larger PET nanoparticles exhibit stronger binding, whereas small degraded nanoparticles have significantly reduced interaction energies, indicating a higher likelihood of desorption. Further structural analysis using root-mean-squared deviation (RMSD) and root-mean-squared fluctuation (RMSF) confirms that PET binding does not significantly alter HSA's secondary structure. However, degradation significantly increases PET hydrophilicity, weakening their adsorption onto HSA. Large PET nanoparticles are strongly bound, whereas small degraded nanoparticles remain unbound, raising concerns regarding their potential toxicity due to free migration in the bloodstream. These findings provide crucial insights into the biological implications of PET degradation, the role of surface chemistry in determining nanoparticle interactions, and their potential contributions to nanoplastic toxicity.