A Microscopic View of Protein Soft and Reactive Landing on Flexible Polyethylene Glycol Surfaces

The interaction of proteins with polymer surfaces is central to understanding biomaterial compatibility and developing advanced deposition techniques. In this work, we investigate the collision dynamics of lysozyme and neurotensin with polyethylene glycol (PEG) surfaces in the vacuum using the reactive force field (ReaxFF). These simulations mimic the soft and reactive landing processes encountered in electrospray ionization (ESI)-, matrix-assisted laser desorption/ionization (MALDI)- and cluster ion beam-based preparative mass spectrometry approaches. Various PEG structures, including vertically aligned chains and amorphous configurations, with or without surface chain terminations, were considered. Collision velocities ranging from 1 to 6 km/s were employed to explore structural preservation, energy transfer, and chemical bond formation between the biomolecules and the PEG. For lysozyme (∼14 kDa), where 1 km/s corresponds to approximately 74 eV, our results show that PEG acts as a soft, cushion-like substrate, effectively dissipating impact energy and preserving protein structure under most conditions. Notably, covalent bond formation was observed only at high velocity (≥5 km/s) in the amorphous PEG structure lacking surface chain terminations. The findings indicate that PEG offers a promising medium for preserving protein integrity during deposition, maintaining the capacity to build protein multilayers, and potentially facilitating controlled protein desorption in solvents when desired. Even though defining an exact energy threshold would require a more detailed investigation, our simulations also constitute a proof-of-principle that the molecular fragments also transferred in iBEAM may act as mediators to induce protein grafting at relatively low velocity (3 km/s).