Effect of Plastic Type and Salt Concentration on Interactions Between Nanoscale Plastic and Amino Acids in Solution Using Saturation-Transfer Difference NMR Spectroscopy

We have used saturation-transfer difference nuclear magnetic resonance (STD-NMR) spectroscopy to examine binding between amino acids and nanoparticles that are composed of different kinds of plastic. We also examined how the presence of salt influences these interactions. We find that the presence of salt decreases binding that is primarily due to electrostatic interactions. Additionally, phenylalanine binding to polyethylene and polypropylene nanoparticles is negligible compared to binding to polystyrene nanoparticles. Lysine and leucine exhibit binding to polypropylene nanoparticles, and this binding is due to electrostatic interactions. Last, we have shown that these experiments can be done in natural water samples including lake and river water, by adding a minimal amount of D2O to the natural water. The results of these studies can be applied to understanding the fundamental interactions that are responsible for binding between nanoplastics and biological macromolecules or between nanoplastics and small-molecule xenobiotics. This work has implications in the study of nanoscale plastic pollution, as nanoscale plastic pollution can absorb toxic small molecule contaminants in the environment.