An intramolecular electron transfer reaction modulated by proton motion in a hydrogen-bonded interface immersed in a polar-polarizable solvent is studied theoretically. The role of the proton interface is to modulate the electronic matrix element, V, that permits the electron transfer, and this modulation provides a mechanism for a proton-coupled electron transfer (PCET) reaction. We use ab initio, methods to obtain V as a function of the proton configuration in the interface and find that it increases by a factor of about 4 (from about 1.8 cm(-1)), as the protons move from their equilibrium to their transition-state positions. Molecular dynamics simulations are performed to obtain the free energy surfaces that characterize the activation energy for the electron transfer. The charge recombination reaction, occurring from the charge transfer state to the neutral ground state, has an activation energy of a few kilocalories/mole.