Oxo-/hydroxo-group

According to the most familiar one-site/two-pK model [14] only one generic kind of oxo-/hydroxo-groups is developed on the surface of an oxide in contact with water. Depending on the pH of the impregnating solution these groups may be protonated/deprotonated. 

Only one generic kind of surface of oxo-/hydroxo-groups is also assumed in the context of the one-site/one-pK model [15-17]. 

The much more realistic multisite surface complexation (music) model recognizes that different kinds of oxo-/hydroxo-groups are developed on the surface of the oxidic supports [18], Thus, single MO(H), double M20(H) and/or triple MjO coordinated oxo-/hydroxo-groups may be developed on the surface. Moreover, this model provides a very simple formula for estimating the surface charge of the surface oxo-/hydroxo-groups. 

In principle, a more reliable value for the charge of an oxo/hydroxo-group could be obtained by performing ab-initio calculations in the frame of the density Junctional theory. The first example of catalytic interest, recently reported, concerns the oxo/hydroxo-groups developed on anatase (23). 

An even more realistic deposition mode for the ions of the second kind and most of the catalytic supports is the electrostatic adsorption through ion-pair formation at plane 2. The only difference between this deposition mode and the simple electrostatic adsorption is that the ions located at the front end of the diffuse part of the interface form ion pairs with the surface oxo/hydroxo-groups of opposite charge. The cations involved in the ion pairs retain their hydration sphere. The model related with this deposition mode is called basic Stem [32] and, as the Stem-Gouy—Chapmann model, it involves only two planes (the surface plane and the plane 2). 

HF/STO-3G Amber - for R2met only). In all models the QM part consists of the two Fe centers and the first shell ligands of four formates, two imidazoles, and a few oxo, hydroxo, and/or aquo groups (see Figure 2-4). 

There is evidence that in the oxidized form, an oxo or hydroxo group bridges the Ni and Fe atoms, which should be absent in the enzymatically active reduced form. 

We define "oxo-lron aggregates" as a collection of three or more iron ions linked continuously by bridging oxo-, hydroxo- or alkoxo groups. The aggregates are labelled according to their nuclearlty. Undoubtedly the molecular structures of the aggregates represent the key to understanding their properties and therefore they will be discussed first. 

This approach emphasizes the role of water as a source of 0X0 ligands. It is important to note that crystalline tetranuclear 4B and undecanuclear 11 aggregates form only if the amounts and concentrations of water vary within certain narrow limits. Perhaps the number of potentially bridging oxo and hydroxo groups that can form in solution determine the nuclearity of the aggregates. 

Many common acids are oxoacids, i.e., molecules with the central atom surrounded by =0 (oxo) and -OH (hydroxo) groups. Perchloric (HC104), chloric (HC103), chlorous (HC102), and hypochlorous (HC10) acids... 

The term molybdenum cofactor (or Moco) refers to the metal center and its inner coordination sphere. Moco is not a single, unique, moiety, rather it is a diverse collection of protein-bound sites that have certain common features. Thus, one or two MPTs are coordinated to the metal via the dithiolene group and the remainder of the metal s coordination sphere is taken up by non-protein ligands (e.g., oxo, hydroxo, water, or sulfido groups) and, in some cases, an amino acid side chain is coordinated. Hille (1) has shown that the mononuclear Mo—MPT enzymes of molybdenum can be classified into three families, on the basis of the nature of the inner coordination sphere of the oxidized form of the enzyme (Fig. 2). 

The combined results of EXAFS and Mossbauer effect spectroscopies have been used to deduce the oxidation state and local structure of iron in iron containing Na, K- and H-chabazites. In the mineral Na,K(Fe) chabazite iron is found to be present as oxo- or hydroxo-bridged Fe(III) oligimers, while in the H-chabazite it is found to be present as Fe(III) ions bridged by oxo- or hydroxo-groups to the zeolite frameworks... 

If, on the other hand, the number of water molecules found for M,AaH A is hi2, then h/2 oxo group(s) should be involved in the extracted species instead of h hydroxo group(s). In that case, following equilibrium becomes relevant to the extraction ... 

---