The interaction of metallic iron with a model asphaltene molecule in the presence of water and electron-donor additives was modeled by using a quantum mechanics parametric method, CATIVIC. Results of Fe-asphaltene interactions show the formation of bonds on aromatic rings and directly on heteroatoms and so a decrease of C-C, N-C, and S-C bond energies (bond activations) and the formation of metal-asphaltene complexes. Values of diatomic energies (DE), equilibrium bond distances (EBD), and diatomic bond energies (DBE) show that the most significant bonds arise when the interaction is directly on heteroatoms (N, S) and the highest activation is in the C-S bonds. Electronic charge transfer occurs from the metal to hydrocarbon, except when interaction is on the N atom. Important metal-O bond is observed when water interacts with Fe-asphaltene complex, leading to some activation of O-H bonds. Negative charge on the system, in the presence of H2O, will decrease Fe-O and Fe-N bonds and will reinforce Fe-S ones. Comparison with previous work shows that, in general, hydrogenation and carbon-heteroatom bond activations due to metal interaction in the presence of water follow the trend: nickel > iron. (c) 2005 Elsevier B.V. All rights reserved.