Carbon dioxide clusters

A substantial fraction of the named enzymes are oxido-reductases, responsible for shuttling electrons along metabolic pathways that reduce carbon dioxide to sugar (in the case of plants), or reduce oxygen to water (in the case of mammals). The oxido-reductases that drive these processes involve a small set of redox active cofactors , that is, small chemical groups that gain or lose electrons. These cofactors include iron porjDhyrins, iron-sulfur clusters and copper complexes as well as organic species that are ET active. 

Ozone and carbon dioxide demonstrate that p orbitals can overlap side by side with more than one neighbor. This feature can lead to a system of 7r bonds that can extend over many atoms. Extended systems can be long chains, or they can be more compact clusters or rings. We begin by describing two examples of four-atom tt systems, butadiene and the carbonate anion. 

The formation of carbido-carbonyl cluster compounds with ruthenium and osmium appears to be common in pyrolysis reactions the basic reaction may be viewed as the transformation of the coordinated carbon monoxide to carbide and carbon dioxide. Small variations in... 

Scheme 106 Fe4S4 cubane cluster for the cathodic fixation of carbon dioxide.

Finally, the PFR of 1-naphthyl acetate has been used to demonstrate the occurrence of solvent-solute clustering in supercritical carbon dioxide. This is... 

M,S4 preparation, 38 28 (M4S31 inverted clusters, 38 28-29 M—S(thioether bond), 35 3 Multalin (software), 47 86 Multi-electron reduction, carbon dioxide, 43 423-426... 

Catalysis may be of interest even on Mars. The Martian atmosphere consists of 95% carbon dioxide and Breedlove et al. (2001) have presented that nickel cluster catalysts could be used in a photoelectrochemical process to split carbon dioxide, according to the reaction... 

Gas products from the alkylation of acetonitrile were regularly analysed using the same column as used for the side-chain alkylation of toluene. Liquid products were also collected every 30 minutes in an acetone-ice bath, but were analysed using a Porapak Q column at 150-180 °C with a helium carrier gas flow rate of 30 ml/min. To investigate the effect of carbonated catalysts, especially that with the excess cesium cation "clusters", carbon dioxide was introduced to the fresh CsNaX-CsOH at the reaction temperature, 350 °C, for 30 minutes before the alkylation of acetonitrile was carried out in a flow of helium. The cesium clusters of treated catalysts were presumed to be fully carbonated (CS2CO3) clusters and the activity of this catalyst was compared with the untreated CsNaX-CsOH. 

One of the simplest biochemical addition reactions is the hydration of carbon dioxide to form carbonic acid, which is released from the zinc-containing carbonic anhydrase (left, Fig. 13-1) as HC03-. Aconitase (center, Fig. 13-4) is shown here removing a water molecule from isocitrate, an intermediate compound in the citric acid cycle. The H20 that is removed will become bonded to an iron atom of the Fe4S4 cluster at the active site as indicated by the black H20. An enolate anion derived from acetyl-CoA adds to the carbonyl group of oxaloacetate to form citrate in the active site of citrate synthase (right, Fig. 13-9) to initiate the citric acid cycle. 

KH(S03N)2Hg(Hg.0H)2,H20, is obtained. Complete saturation with carbon dioxide under press, gives finally the free acid, (HS03.N)2Hg,0H)2. Sodium mercuric amidosulphonate, NHg.S03Na, is prepared similarly to the potassium salt it forms radiating clusters, or often felted masses, of slender, colourless needles. It differs from the potassium salt in that it is soluble in water on heating, whereas the addition of alkali is necessary to dissolve readily the former salt. 

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