Transitions dioxo species

Figure 2. The change in bonding characteristics and orbital energies in linear and bent transition metal dioxo species...

The reaction is proposed to proceed from the anion (9) of A/-aminocatbonylaspattic acid [923-37-5] to dehydrooranate (11) via the tetrahedral activated complex (10), which is a highly charged, unstable sp carbon species. In order to design a stable transition-state analogue, the carboxylic acid in dihydrooronate (hexahydro-2,6-dioxo-4-pyrimidinecarboxylic acid) [6202-10-4] was substituted with boronic acid the result is a competitive inhibitor of dibydroorotase witb a iC value of 5 ]lM. Its inhibitory function is supposedly due to tbe formation of tbe charged, but stable, tetrabedral transition-state intermediate (8) at tbe active site of tbe enzyme. 

The four most important tautomers of pyrazolo[4,3-<7]pyrimidine-5,7(477,677)-dione (52a-d) were studied using ab initio LCAO-MO methods <91CPL(181)123>. Calculation indicates that structure (52a) is the predominant form both in nonpolar and polar environments. The second most stable species, the oxo hydroxy tautomers (52b) and (52c), have relative energies of 38.7 kJ mol . For the dioxo to oxo-hydroxy transition, the calculated energy gap corresponds to an equilibrium constant... 

The vibrational energy separation between the (0 - 0) and (0 - 1) vibrational transitions in the photoluminescence spectrum was found to be 960 cm, indicating that the Cr-O bond in chromium oxide/Si02 is shorter than that in the tetrahedral Cr04 cluster ion (i.e., 850 cm ). From these considerations, a distorted monomeric four-coordinated dioxo-chromium species has been proposed as the emitting species 117, 166, 167) ... 

Consequently, in the present study, the proposed formalism is demonstrated for the rate-limiting chemical step in the OER, that is, 2[Mn=O Mn—0 ] Mn—O—O—Mn. Above, the force constants of the dioxo and peroxo species comprise fcreact and fcprod. respectively. By solving for Xjs and adding the equilibrium 0-0 bond lengths of the peroxo system, the interatomic 0-0 distance at the transition state is obtained. In what follows, the reactivity of a biomimetic binuclear molecular manganese catalyst will be contrasted by that of the binuclear Mn site supported on a magnesium oxyhydroxide rig. 

As already mentioned earlier, the chemistry of high-valent uranium is dominated by the dioxo or uranyl dication, [U02] +, which is found both in aqueous solutions and in the solid state. It is chemically robust and shows little propensity to participate in the myriad reactions that are characteristic of its Group 6 transition metal analogues, [M02] ". Furthermore, this stability coupled with its mobility in the aqueous phase means that it is a problematic environmental contaminant. There is in the literature a long range of experimental and theoretical study on actinyl, and particularly uranyl. [46,77] All of these theoretical and computational studies are focused on structure and electronic properties of actinyl using DPT and post Hartree-Fock calculations methods. But often, the theoretical studied systems are not corresponding to the real experimental one. With the increase of computational power, it is now possible to treat full experimental systems, and even more to study the reactivity of these species at the DFT level adequately. 

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