Dioxygen carriers

Le Mest Y, L Her M. 1995. Electrochemical generation of a new type of dioxygen carrier complex. Reversible fixation of dioxygen by the highly electron-deficient two-electron oxidized derivative of a dicobalt face-to-face diporphyrin. J Chem Soc Chem Commun 1441. 

Attachment of the Fe(n) complex of tetraphenylporphyrin to a modified silica gel support also resulted in an efficient dioxygen carrier (Basolo, Hoffman Ibers, 1975). In this system the silica gel was modified by direct attachment of imidazoyl-propyl groups to its surface. 

R Volume 2,1993,292 pp. 109.50/ 70.00 ISBN 1-55938-272-4 CONTENTS Introduction, Robert W. Hay. Dynamics of Iron (II) and Cobalt (II) Dioxygen Carriers, P. Richard Warburton and Daryle H. Busch. Homodinuclear Metallobiosites, David... 

NMR, EPR, EXAFS, infrared, resonance Raman, and ultraviolet-visible spectroscopy should follow. Kinetic and thermodynamic information about the model complexes in comparison to that known for natural systems should be gathered. These concepts were updated in 1999 by Karlin, writing in reference 49. Model studies should provide reasonable bases for hypotheses about a biological structure and its reaction intermediates. Researchers should determine the model s competence in carrying out reactions that mimic metalloprotein chemistry. Using these methods and criteria, researchers may hope to exploit Cu-oxygen systems as practical dioxygen carriers or oxidation catalysts for laboratory and industrial purposes. 

The second class of dioxygen carriers is that of haemocyanins. These proteins, which contain a binuclear Cu(I) site (thus in the oxidized Cu(II) met form they belong to the so-called Type 3 copper proteins , which contain an EPR-silent dicopper active site), regulate dioxygen transport in the respiration of arthropods and molluscs. Figures 7 and 8 show... 

As previously discussed, the binuclear Cu(I) haemocyanins constitute another important class of dioxygen carriers. The first model compound whose structure in the oxygenated form resembles most closely that of oxyhaemocyanin is the dicopper(II) complex with the tris(3,5-diisopro-pylpyrazolyl)borate ligand shown in Figure 26.29... 

Mimoun has already pointed out clearly that dioxygen carriers, even when reversibly formed, are not different from peroxo complexes prepared from hydrogen peroxide. As a... 

Both cations play a stabilizing role in various biological structures. Calcium ions are necessary to link the 24-subunit aggregates of the dioxygen carrier hemocyanin of Limulus polyphemus into the native 48-subunit molecule.121 The divalent character of Ca2+ probably allows it to crosslink... 

Copper has an essential role in a number of enzymes, notably those involved in the catalysis of electron transfer and in the transport of dioxygen and the catalysis of its reactions. The latter topic is discussed in Section 62.1.12. Hemocyanin, the copper-containing dioxygen carrier, is considered in Section 62.1.12.3.8, while the important role of copper in oxidases is exemplified in cytochrome oxidase, the terminal member of the mitochondrial electron-transfer chain (62.1.12.4), the multicopper blue oxidases such as laccase, ascorbate oxidase and ceruloplasmin (62.1.12.6) and the non-blue oxidases (62.12.7). Copper is also involved in the Cu/Zn-superoxide dismutases (62.1.12.8.1) and a number of hydroxylases, such as tyrosinase (62.1.12.11.2) and dopamine-jS-hydroxylase (62.1.12.11.3). Tyrosinase and hemocyanin have similar binuclear copper centres. 

It was once thought that the vanadium in vanadocytes acted as dioxygen carriers but this is now known to be incorrect. Many questions remain to be answered about the role of vanadium in vanadocytes. 

Figure 52 Some synthetic iron(II) porphyrins which function as models for dioxygen carriers...

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