AbstractThe mechanisms for the electron transfer between the indole side chain and phenol side chain of peptides involving tryptophan and tyrosine have been studied by ab initio calculation in this work. The solvent effect has been considered by using the conductor‐like screening model (COSMO). Three mechanisms including the two‐proton elimination mechanism, the hole transfer without proton deprotonation, and the step‐by‐step mechanism for the electron transfer processes between indole and phenol have been discussed. From the theoretical calculations, we can conclude that, for the electron transfer between indole and phenol, and consequently between tryptophan and tyrosine, a deprotonation process is necessary, otherwise the ET process is difficult to proceed. There are two deprotonation cases that make the successive electron transfer feasible: one is that both the proton attached to indole N and that attached to phenol O, are removed before the ET process, the other is that the proton attached to indole N is first removed, then the proton attached to O of phenol group transfers to the indole group, and the ET follows. The comparison between our theoretical predication and the experimental conclusion has been made. The influence of the donor‐acceptor distance on the ET rate constant for the intramolecular electron transfer has been investigated in solution. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1067–1081, 2001