Manganese three-dimensional structures

Because the three-dimensional structures of the peroxidase, its reductant cytochrome c, and the complex of the two (Fig. 16-9) are known, cytochrome c peroxidase is the subject of much experimental study. Other fungal peroxidases, some of which contain manganese rather than iron, act to degrade lignin (Chapter 25).218 A lignin peroxidase from the white wood-rot fungus Phanerochaete chrysosporium has a surface tryptophan with a specifically hydroxylated C(3 carbon atom which may have a functional role in catalysis.2183 0... 

Much less information is available on the manganese superoxide dismutases. No crystal structure has been reported for such an enzyme, but similarities in the three-dimensional structures can be deduced from the Cd-spectra and comparisons... 

Fig. 8. Schematic model for three-dimensional structure of yeast tRNA" showing sugar-phosphate backbone, base pairs, five magnesium-binding sites (numbered circles), manganese site, ethidium-binding site, and spermine-binding site (dark curved shape in AC stem). Partially derived from Holbrook et al. (1978) and Kim (1979).

Figure 7. Crystal structures of (a) hollandite, (b) romanechite (psilomelane), and (c) todorokite. The structures arc shown as three-dimensional arrangements of the MnO() octahedra (the tunnel-tilling cations and water molecules, respectively, are not shown in these plots) and as projections along the short axis. Small, medium, and large circles represenl the manganese atoms, oxygen atoms, and the foreign cations or water molecules, respectively. Open circles, height z. = 0 fdled circles, height z = Vi.

Figure 16. Crystal structure of a-MnOOH. The structure is shown as a three-dimensional arrangement of the Mn(0,0H)6 octahedra with the protons filling the [2 x 1] tunnels, and as a projection along the short crystallographic oaxis. Small circles, manganese atoms large circles, oxygen atoms open circles, height z - 0 filled circles, height z = A The shaded circles represent the hydrogen ions.

The coordination chemistry of oxalate (ox, C2042-) compounds provides a series of very interesting compounds from the stereochemical and magnetic points of view [197]. Most frequently the compounds form honeycomb layers in the presence of transition metal ions, in which the stereochemistry of the metal ion coordination sphere alternates between A and A. However, a three-dimensional homochiral structure is also possible. On the other hand, the negative charge of the oxalates necessitates the incorporation of cations between them, which provides the opportunity to introduce chirality and additional functionality in materials. The compound formed between homochiral manganese II oxalate and iron II tris bipyridinc (bpy) with formula [Mn oxls]2 " [Fcn(bpy)3]2+ crystallises in the space group fJ4 32. 

The LiMn204 spinel structure, shown in Figure 19, can be described as a cubic close-packed oxygen array with the manganese cations occupying one-half of the octahedral interstitial sites and the lithium cations one-eighth of the tetrahedral sites. The interstitial tetrahedral and octahedral spaces in the [Mn2]04 framework are interconnected to form three-dimensional pathways for Li+ ion diffusion (lO -lO " m s ). 

Convergent dendrimers, with their versatile three-dimensional scaffold, may be tailored to mimic, perhaps crudely, some elements of enzymatic structures. Numerous catalytic moieties, including manganese porphyrins,253,254 bis(oxazoline) copper complexes,304 305 tertiary amines,306 binaphthol titanium complexes,285 307 titanium taddolates,292,308 thiazolio-cyclophanes,309 and fullerene-bound bisoxazoline copper complexes,310 have been incorporated at the core of dendritic molecules to determine the effect of dendritic encapsulation on their catalytic activity. 

A complete crystal structure analysis has been carried out for Mn2Ru(CN)a 8 HgO, the corresponding hexacyanoferrate(II) and hexacyanoosmate(II) showing very similar lattice constants (55). This structure also consists of a three-dimensional framework with the characteristic sequence, Ru—C—N—Mn, deviating slightly from linearity. Contrary to the Prussian blue analogs, the coordination sphere of ruthenium as well as that of manganese has a definite unique composition. Moreover, the structure is ordered, and there are no fractional... 

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