Proton transfer and dissociation of GlyLysH ⁺ following O-H and N-H stretching mode excitations: Dynamics simulations

Proton transfer and dissociation processes following excitation of the OH or NH stretching modes of the proton-bound complex GlyLysH ⁺ are studied by classical trajectories. "On the fly" simulations with the PM3 semiempirical electronic structure method for the potential surface are used. Initial conditions are sampled to correspond to the v=1 excited state of the OH or NH stretching modes. Five different conformers of the complex are studied as initial structures. The main findings are (1) Photoinduced proton transfer is on the picosecond time scale. (2) Proton transfer is much faster than the processes of dissociation. (3) Proton transfer involves different sites. Most trajectories show sequences of two proton transfer events. (4) The proton transfer events show high selectivity with regard to the initially excited vibration and the initial structure. (5) Photodissociation of the complex occurs on a typical time scale of 100 ps. (6) Conformational transitions are found to be often faster than proton transfer. These results have implications for the mass spectrometry of complexes, for dynamics of proton wires, and for proton migration in proteins.