Dynamics of energy transfer in peptide - Surface collisions

Classical trajectory simulations are performed to study energy transfer in collisions of protonated triglycine (Gly)₃ and pentaglycine (Gly)₅ ions with n-hexyl thiolate self-assembled monolayer (SAM) and diamond {111} surfaces, for a collision energy E_i in the range of 10-110 eV and a collision angle of 45°. Energy transfer to the peptide ions' internal degrees of freedom is more efficient for collision with the diamond surface; i.e., 20% transfer to peptide vibration/rotation at E_i = 30 eV. For collision with diamond, the majority of E_i remains in peptide translation, while the majority of the energy transfer is to surface vibrations for collision with the softer SAM surface. The energy-transfer efficiencies are very similar for (Gly)₃ and (Gly)₅. Constraining various modes of (Gly)₃ shows that the peptide torsional modes absorb ∼80% of the energy transfer to the peptide's internal modes. The energy-transfer efficiencies depend on E_i. These simulations are compared with recent experiments of peptide SID and simulations of energy transfer in Cr(CO)₆⁺ collisions with the SAM and diamond surfaces.