The mechanism of the curing reaction between ethylene oxide as a typical epoxy function and tryptophan as an environmentally friendly curing agent was investigated by density functional theory (DFT). A transition state was identified in order to determine the activation energy for a specific reaction. The reaction energy (DH) for different steps was calculated after optimization of the reactants and products. The Mulliken and ESP-fitted charges, molecular orbitals, and Fukui indices (f) were used to determine the reactivity of a specific atom or site. The reaction was classified in four main stages with the reaction energy of 19.71 kcal mol1.
