Solvent Reorganization Energy of Intramolecular Electron Transfer in Peptides Involving Tryptophan and Tyrosine

Intramolecular electron transfer (ET) from tyrosine to tryptophan within peptide Trp-(Pro)(n)-Tyr (n= 1, 2) has been investigated by ab initio calculation associated with a proper consideration of solvent effect by a continuum model. After geometry optimizations of the charge-localized reactant and product, double-well potentials have been constructed by adopting the linear reaction coordinate. The transition state has been determined by finding the crossing point of the potential energy curves. The realistic ET reaction was found complicated in polar solvent, hence the solvent reorganization energy of the electron transfer has received especial attention in this work. Applying the nonequilibrium solvation procedure implemented based on the polarizable continuum model by the authors, the solvent. reorganization energy was estimated to be 87.36 kJ/mol for the ET in Trp-Pro-Tyr system and 105.80 kJ/mol for Trp-(Pro)(2)-Tyr.