Vanadate structures

Proposed mechanism for the catalytic hydrolysis of the sulfate ester bond by the active form of aryl sulfatase-B (AS-B), and the structure (right) of the active centre of the vanadate AS-B complex, otherwise containing the substrate sulfate. The active centre also accommodates a seven-coordinated calcium ion, ligated to three aspartates (one of which is in the Y-mode), an asparagine and two 0X0 anions of the sulfate/vanadate. Structure modified from that provided in ref. 95. 

Tetrahedral VO4 units are rare for poly vanadate structures, and the current anions are the first examples of a heteropolyvanadate that is exclusively made up of such... 

Smith, C. A., Rayment, 1. X-ray structure of the magnesium (11). ADP-vanadate complex of the Dictyostelium discoideum myosin motor domain to 1.9 A resolution. Biochemistry 35 5404-5407, 1996. 

There are several theories about the chemistry of vanadium poisoning. The most prominent involves conversion of VjOj to vanadic acid (H-iVO ) under regenerator conditions. Vanadic acid, through hydrolysis, extracts the tetrahedral alumina in the zeolite crystal structure, causing it to collapse. 

Vanadium and sodium neutralize catalyst acid sites and can cause collapse of the zeolite structure. Figure 10-5 shows the deactivation of the catalyst activity as a function of vanadium concentration. Destruction of the zeolite by vanadium takes place in the regenerator where the combination of oxygen, steam, and high temperature forms vanadic acid according to the following equations ... 

The produced vanadic acid, VO (OH)3, is mobile. Sodium tends to accelerate the migration of vanadium into the zeolite. This acid attacks the catalyst, causing collapse of the zeolite pore structure. 

Vanadate, dioxybis(oxamato)-bond-length ratios, 1,57 Vanadate, heptacyano-potassium salt structure, I, 72 Vanadate, hexafluoro-dipotassium salt history, I, 21 potassium salt history, 1,21 tripotassium salt history, 1,21 Vanadate, pentachloro-stereochemistry, 1,40 Vanadate, pentafluorooxy-stereochemistry, I, 50 Vanadates biochemistry, 3,456 calcium/magnesium ATPase inhibition, 6, 567 competition with phosphates physiology, 6,665 protonation, 3,1026 sodium pump, 6, 557 in uranium purification from ore, 6, 899 Vanadates, hexafluoro-, 3. 482,531 Vanadates, oxoperoxo-, 3,501 Vanadates, pentacarbonyl-, 3, 457 Vanadium biology, 6,665 determination, 1. 548 extraction... 

Layered Perrhenate and Vanadate Hybrid Solids On the Utility of Structural Relationships... 

This highhght examines several new hybrid layered structures in the hetero-metallic perrhenate and vanadate families, whereby the late transition-metals are incorporated and their roles probed in the structures of layered solids. From these two families, new structural principles have emerged that not only help us understand key stractural features and correcdy forecast new compositions, but equally, have yielded many surprises (chirality, reduced phases) that show some of the most exciting chemistry is still waiting to be discovered or even imagined ... 

Fig. 4. Tentative allocation of probe binding sites within the three-dimensional structure of Ca -ATPase derived from vanadate-induced E2-type crystals. The top picture is the projection view of the Ca -ATPase down the x-axis, revealing the pear-shaped contours of ATPase molecules. The maximum length of the cytoplasmic domain to the tip of the lobe is =r65A. In the middle and bottom pictures the same structure is viewed down the x-axis, revealing the gap between the bridge and the bilayer surface and the connections between ATPase molecules in neighboring dimer chains. The proposed binding sites for lAEDANS and FITC are indicated. The bottom right picture is the same structure viewed down the y-axis. Adapted from Taylor et al. [90].

The target of vanadate-catalyzed photolysis is presumably an amino acid near the catalytic site of the Ca " -ATPase. The vanadate-catalyzed photocleavage at the V cleavage site in the absence of Ca " is 500 amino acids away from the C cleavage site which is attacked in the presence of Ca. Both sites are probably adjacent in the native structure to the catalytic site of the Ca -ATPase. 

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