We study the role of quantum fluctuations of atomic nuclei in the real-time
dynamics of non-equilibrium macro-molecular transitions. To this goal we
introduce an extension of the Dominant Reaction Pathways (DRP) formalism, in
which the quantum corrections to the classical overdamped Langevin dynamics are
rigorously taken into account to order h^2 . We first illustrate our approach
in simple cases, and compare with the results of the instanton theory. Then we
apply our method to study the C7_eq to C7_ax transition of alanine dipeptide.
We find that the inclusion of quantum fluctuations can significantly modify the
reaction mechanism for peptides. For example, the energy difference which is
overcome along the most probable pathway is reduced by as much as 50%.Comment: Final version, to appear in the Journal of Chemical Physic
