Acceleration of particles by nonrotating charged black holes?

Recently, in the series of works a new effect of acceleration of particles by black holes has been found. Under certain conditions, the energy in the center-of-mass system can become infinitely large. The essential ingredient of such effect is the rotation of a black hole. In this work, it has been argued that the similar effect exists for a nonrotating but charged black hole even for the simplest case of radial motion of particles in the Reissner-Nordstrom background. All main features of the effect under discussion due to rotating black holes have their counterpart for the nonrotating charged ones.