Reactive molecular dynamics simulations of lysozyme desorption under Ar cluster impact

Abstract

Using large gas cluster ion beams (Ar1000-5000+), it is possible to desorb and transfer non-volatile and active biomolecules (e.g. lysozymes, 14 kDa) for nanofabrication or mass spectrometry. Depending on the cluster and target characteristics, the collision may induce fragmentation and/or denaturation of the proteins. To clarify the Ar cluster-induced desorption mechanisms of proteins, molecular dynamics (MD) simulations were performed using reactive force fields (ReaxFF). First, lysozymes were adsorbed and relaxed on a gold surface with a (543) orientation and then bombarded by Ar clusters at 45° angle. The simulations consider different cluster sizes (from 1000 to 5000 atoms) and kinetic energies (from 1 to 10 eV/atom), investigating how these parameters affect desorption, and the concomitant chemical reactions and/or protein unfolding events. Three different surfaces were modelled: one single lysozyme adsorbed on gold, a lysozyme monolayer and a bilayer. The simulations show a correlation between the lysozyme fragmentation and the cluster energy per atom (E/n) but also an additional effect of the cluster size for a given E/n. The structure of the organic target influences the emission, which becomes softer when the amount of organic material increases. In the lysozyme bilayer, non-covalent aggregates were desorbed with relatively limited protein denaturation.