The reaction force and the electron localization function (ELF) have been used to investigate the mechanism that promote the metal chelation in the formation of the Mg(II)-thymine enol bi-coordinated complex. Energy and reaction force profiles together with ELF isosurfaces reveal that the intramolecular hydrogen transfer activates the metal chelation process through a concentration of electron population in the monosynaptic valence basin associated to the hydrogen donor atom. Moreover, the ELF analysis suggest that the metal chelation proceeds via electrostatic interaction and the new Mg-N bond in the product complex being of ionic character. (c) 2007 Elsevier B.V. All rights reserved.