MD DFT:B3LYP (6-31G*z.ast;basis set, T = 310 K) method is used to study interactions [singlet (S) and triplet (T) reaction paths] between adenosinetriphosphate, ATP^4-, and [Mg(H₂O) ₆]²⁺ in water environment, modeled with 78 water molecules. Computations reveal the appearance of low and high-energy states (stable, quasi-stable, and unstable), assigned to different spin symmetries. At the initial stage of interaction, ATP donates a part of its negative charge to the Mg complex making the Mg slightly charged. As a result, the original octahedral Mg complex loses two (S state) or four (T state) water molecules. Moving along S or T potential energy surfaces (PESs), Mg(H₂O) ₄ or Mg(H₂O)₂ display different ways of complexation with ATP. S path favors the formation of a stable chelate with the O1-O2 fragment of ATP triphosphate tail, whereas T path favors producing a single-bonded complex with the O2. The latter, being unstable, undergoes a further conversion into a spin-separated complex, also unstable, and two metastable S complexes, which finally arise in two stable, low-energy and high-energy, chelates. The spin-separated complex experiences rapid decomposition resulting in the production of a highly reactive adenosinemonophosphate ion-radical •AMP, early observed in the CIDNP experiment (Tulub 2006). Biological consequences of the findings are discussed.