  The surface of Titan, Saturn's largest moon, is rich in organics and is often
suggested to model early Earth environments. Titan's surface is cold, at a
temperature of approximately 90 K, which prohibits most thermally activated
chemical reactions. However, quantum effects become more important at low
temperatures and reactions that are classically prohibited can often proceed
through quantum mechanical pathways. Using path integral molecular dynamics
simulations, we investigate nuclear quantum effects on the thermodynamics of
model proton transfer reactions in liquid ethane. We find that proton transfer
can occur at Titan surface conditions through quantum tunneling. Consequently,
we estimate that nuclear quantum effects can enhance reaction rates by many
orders of magnitude. Our results suggest that nuclear quantum effects could
facilitate prebiotic chemistry on Titan, and quantum effects should be
considered in future investigations.
