  The Schlegel-Frisch ab initio molecular dynamics (ADMP) (DFT:B3LYP), T = 310
K, is used to study complexation between adenosinetriphosphate (ATP), ATP
subsystem, and magnesium cofactor [Mg(H2O)6]2+, Mg subsystem, in a water pool,
modeled with 78 water molecules, in singlet (S) and triplet (T) states. The
computations prove that the way of ATP cleavage is governed by the electron
spin of Mg. In the S state Mg prefers chelation of \gamma-\beta-phosphate
oxygens (O1-O2), whereas in the T state it chelates \beta-\alpha-phosphate
oxygens (O2-O3) or produces a single-bonded intermediate. Unlike the chelates,
which initiate ionic reaction paths, the single-bonded intermediate starts off
a free-radical path of ATP cleavage, yielding a highly reactive
adenosinemonophosphate ion-radical, .AMP-, earlier observed in the CIDNP
(Chemically Induced Dynamic Nuclear Polarization) experiment (A.A. Tulub,
2006). The free-radical path is highly sensitive to Mg nuclear spin, which
through a hyperfine interaction favors the production of unpaired electron
spins. The unique role of Mg in ATP cleavage comes through its ability to serve
as a unique redox center, initially accepting an electron from ATP and then
giving it back to products. Redox activity of Mg differs for T and S states and
affects the number of coordinated water molecules. The findings give a new
insight into the NTP (N = nucleoside) energetics and assembly of NTP-operating
molecules, including proteins.
