Comment on "Molecular dynamics DFT:B3LYP study of guanosinetriphosphate conversion into guanosinemonophosphate upon Mg2+ chelation of alpha and beta phosphate oxygens of the triphosphate tail" by Alexander A. Tulub, Phys. Chem. Chem. Phys., 2006, 8, 2187

The mechanistic investigations of photochemical decarbonylations and oxidative addition reactions for M(CO)5 (M = Fe, Ru, Os) complexes

The mechanisms for the photochemical CO-dissociation and the oxidative addition reactions are studied theoretically using three model systems: M(CO)₅ (M = Fe, Ru, and Os) and the CASSCF/Def2-SVP (fourteen-electron/ten-orbital active space) and MP2-CAS/Def2-SVP//CASSCF/Def2-SVP methods. The structures of the intersystem crossings and the conical intersections, which play a decisive role in these CO photo-extrusion reactions, are determined. The intermediates and the transition structures in either the singlet or triplet states are also computed, in order to explain the reaction routes. These model studies suggest that after the irradiation of Fe(CO)₅ with UV light, it quickly loses one CO molecule to generate a 16-electron iron tetracarbonyl, in either the singlet or the triplet states. It is found that the triplet Fe(CO)₄ plays a vital role in the formation of the final oxidative addition product, Fe(CO)₄(H)(SiMe₃), but the singlet Fe(CO)₄ plays a relatively minor role in the formation of the final product. However, its vacant coordination site interacts weakly with solvent molecules ((Me₃)SiH) to yield the alkyl-solvated iron complexes, which are detectable experimentally. The theoretical observations show that Ru(CO)₅ and Os(CO)₅ have similar photochemical and thermal potential energy profiles. In particular, this study demonstrates that the oxidative addition yield for Fe is much greater than those for its Ru and Os counterparts, under the same chemical conditions.

New horizons of adenosinetriphosphate energetics arising from interaction with magnesium cofactor

MD DFT:B3LYP (6-31G** basis set, T = 310 K) method is used to study interactions [singlet (S) and triplet (T) reaction paths] between adenosinetriphosphate, ATP(4-), and [Mg(H(2)O)(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(H(2)O)(4 )or Mg(H(2)O)(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.