Carbon shuttle

Use of the canister as an adsorption vessel without local desorption is a "carbon shuttle." It s simply a method of transporting artivated carbon from a supplier to a customer, and returning it to the supplier after it has adsorbed solvent fumes to the extent possible. Essentially, it is a system for "toll processing" " of the activated carbon, and not the solvent — because an equivalent quantity of solvent-free activated carbon is returned to the customer, but no solvent is recovered or returned to the customer. 

Slack, 1969 Johnson and Hatch, 1970 and Ting and Rocha, 1971). This protein is believed to function in part by reduction of oxalacetate to malate during C4 photosynthesis, and participates in carbon shuttles with the other MDH proteins occurring among compartments. 

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. 

Historically, polymer-matrix composite materials such as boron-epoxy and graphite-epoxy first found favor in applications, followed by metal-matrix materials such as boron-aluminum. Ceramic-matrix and carbon-matrix materials are still under development at this writing, but carbon-matrix materials have been applied in the relatively limited areas of reentry vehicle nosetips, rocket nozzles, and the Space Shuttle since the early 1970s. 

FIGURE 25.1 The citrate-malate-pyruvate shuttle provides cytosolic acetate units and reducing equivalents (electrons) for fatty acid synthesis. The shuttle collects carbon substrates, primarily from glycolysis but also from fatty acid oxidation and amino acid catabolism. Most of the reducing equivalents are glycolytic in origin. Pathways that provide carbon for fatty acid synthesis are shown in blue pathways that supply electrons for fatty acid synthesis are shown in red. 

Caibon-caibon has antigalling characteristic with the ability to slide against itself with very little wear, making it ideal for high-performance brakes. Such brakes are probably the maj or application of carbon-carbon and are found on most military aircraft, on the space shuttle. They are being introduced on civilian aircraft and racing cars. 

The space shuttle and other aerospace vehicles use carbon-carbon extensively in nose cap, leading edges, structural panels, and other components. 

Saito et al. (134) found that the cytosolic nitroreductase activity was due to DT-diaphorase, aldehyde oxidase, xanthine oxidase plus other unidentified nitroreductases. As anticipated, the microsomal reduction of 1-nitropyrene was inhibited by 0 and stimulated by FMN which was attributed to this cofactor acting as an electron shuttle between NADPH-cytochrome P-450 reductase and cytochrome P-450. Carbon monoxide and type II cytochrome P-450 inhibitors decreased the rate of nitroreduction which was consistent with the involvement of cytochrome P-450. Induction of cytochromes P-450 increased rates of 1-aminopyrene formation and nitroreduction was demonstrated in a reconstituted cytochrome P-450 system, with isozyme P-448-IId catalyzing the reduction most efficiently. 

The second-generation 02" biosensors are mainly based on the electron transfer of SOD shuttled by surface-confined or solution-phase mediators, as shown in Scheme 2(b). In 1995, Ohsaka et al. found that methyl viologen could efficiently shuttle the electron transfer between SOD and the glassy carbon electrode and proposed that such a protocol could be useful for developing 02 biosensors [125], Recently, Endo et al. reported an 02, biosensor based on mediated electrochemistry of SOD [148], In that case, ferrocene-carboxaldehyde was used as the mediator for the redox process of SOD. The as-developed 02 biosensor showed a high sensitivity, reproducibility, and durability. A good linearity was obtained in the range of 0 100 pM. In the flow cell system, tissue-derived 02 was measured. 

Ubiquinones (coenzymes Q) Q9 and Qi0 are essential cofactors (electron carriers) in the mitochondrial electron transport chain. They play a key role shuttling electrons from NADH and succinate dehydrogenases to the cytochrome b-c1 complex in the inner mitochondrial membrane. Ubiquinones are lipid-soluble compounds containing a redox active quinoid ring and a tail of 50 (Qio) or 45 (Q9) carbon atoms (Figure 29.10). The predominant ubiquinone in humans is Qio while in rodents it is Q9. Ubiquinones are especially abundant in the mitochondrial respiratory chain where their concentration is about 100 times higher than that of other electron carriers. Ubihydroquinone Q10 is also found in LDL where it supposedly exhibits the antioxidant activity (see Chapter 23). 

In 1984, the AMPTE mission launched the first carbon-foil TOF-MS into space, which would have been the second, had the Challenger shuttle disaster not delayed the Ulysses launch until 1991 (Fig. 11.2) [23]. The photons were filtered out by a traditional blackened deflection system, which directed the ions toward the 2 p,g/cm2 thick foil mounted on an 85% transparent grid almost a square centimeter in area. The grid provided the support needed to survive the launch. The foil thickness permitted >2keV/nuc ions to pass through and hit a SSD some 10 cm away. To ensure that the ions made it through the foil and also through the dead layer on the SSD (caused by the upper electrode), the foil and the entire TOF section were floated at 20 kV to post-accelerate the ions. Electrons sputtered off the carbon foil became the start, whereas electrons sputtered off the SSD became the stop pulse for the TOF. 

Following Adachi et al., aromatic compounds with similar functionalities were proposed for polymer electrolytes as redox shuttle additives, which included bipyridyl and biphenyl carbonates and di-fluoroanisoles. All these additives could protect the cathode from overcharging in the vicinity of 4.1... 

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