Carbon carriers

In the first membrane-type fuel cells, the dispersed platinum catalyst was pure metal because of its large consumption. Smaller consumption and a much more efficient utilization of the platinum catalyst were attained by depositing the metal on a highly disperse carbon carrier. The best results were attained by using Vulcan XC-72 furnace... 

It was found in the 1960s that disperse platinum catalyst supported by certain oxides will in a number of cases be more active than a similar catalyst supported by carbon black or other carbon carrier. At platinum deposits on a mixed carrier of WO3 and carbon black, hydrogen oxidation is markedly accelerated in acidic solutions (Hobbs and Tseung, 1966). This could be due to a partial spillover of hydrogen from platinum to the oxide and formation of a tungsten bronze, H WOj (0 < a < 1), which according to certain data has fair catalytic properties. 

Tests performed to determine the effectiveness of the CST system for processing shredded wood particles (simulated by sawdust) combined with a carbon-carrier medium encountered several problems, including the following ... 

Preventing the segregation of the carbon-carrier medium and shredded DPE suit material and wood dunnage in the solids feed to the CST to... 

Improved design for control of dust, especially carbon dust generated by the carbon carrier. 

Thymidylate synthase (E.C. 2.1.1.45) is the enzyme that methylates UMP to thymidine, using methylene tetrahydrofolate as the carbon carrier. The enzyme can be inhibited directly by analogues of uracil such as 5-fluorouracil (8.34, 5-FU). The antimetabolite must be in the 5-fluorodeoxyuridine monophosphate (FdUMP) form to become active, and the capability of cells to achieve this transformation is a major determinant of their sensitivity to such drugs. 

The other major class of antimalarials are the folate synthesis antagonists. There is a considerable difference in the drug sensitivity and affinity of dihydrofolate reductase enzyme (DHFR) between humans and the Plasmodium parasite. The parasite can therefore be eliminated successfully without excessive toxic effects to the human host. DHFR inhibitors block the reaction that transforms deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) at the end of the pyrimidine-synthetic pathway. This reaction, a methylation, requires N °-methylene-tetrahydrofolate as a carbon carrier, which is oxidized to dihydrofolate. If the dihydrofolate cannot then be reduced back to tetrahydrofolate (THF), this essential step in DNA synthesis will come to a standstill. 

Kiwit. A Ger chlorate expl introduced during WWI. It contains not more than 77% Na or K chlorate, carbon carriers such as paraffin, naphthalene, vaseline, meal or oil, and not more than 15% DNT. It may contain DNT, Dinitronaphthalene, NaCl and not more than 4% Guncotton... 

Ammonium nitrate based explosives are generally used for quarrying, tunnelling and mining. They are mixtures of ammonium nitrate, carbon carriers such as wood meal, oils or coal, and sensitizers such as nitro-glycol, TNT and dinitrotoluene. These compositions may also contain aluminium powder to improve their performance. 

Platinum-based bi-metallics (Pt M, M = Ti, Cr, V, Mn, Fe, Co, Ni, Cu, etc.) have been shown to exhibit enhanced activity toward the OER. Several rationales have been proposed including (1) enhanced chemisorption of intermediates (2) a lattice change of Pt that results in the shortening of Pt-Pt interatomic distances by alloying (3) the formation of skin Pt which has increased d-electron vacancy of the thin Pt surface layer caused by the underlying alloy and the anchor effect of alloy metals on a carbon carrier.93,94... 

The anomalous isotope ratio observed for the noble gases cannot be explained by any chemical process, and isotope mass effects associated with physical processes like diffusion, distillation and absorption-desorption are too small to explain what is observed. On the other hand, the carbon carrier phase is very abnormal, at least for the carbon-p phase. These facts can be explained if we accept that macroscopic amounts of interstellar carbon have survived unchanged, or at least preserved from isotopic exchange with solar system carbon. It is important to observe that a S13C = +1100%o, which corresponds to 12C/13C = 42, can be compared to the low end of the range observed for carbon in molecular clouds (60 8 or 67 10)67 K Moreover, the galactic ratio observed is now probably lower than it was 4.5 Gyr ago owing to the stellar production of 13C. 

As we have already seen, D-enriched macromolecules have a normal 513C value, but it is conceivable that the D-enriched component might come from gas-phase interstellar molecules with a normal S13C value and an abnormal 8D value. On the other hand, some carbon carrier phases could contain both polycyclic aromatic molecules (quasigraphite ) and elemental carbon with all this carbon being abnormal because it forms part of the grains. 

In archaebacteria the folic acid pathway for C-l transformations is based upon methanopterin as an ancient precursor of these important cellular interconversions. Tetrahydromethanopterin (478) has been identified as the active coenzyme and carbon carrier (479-481) in methanogenesis <84JBC(259)9447> and functions et alia as formaldehyde activation factor <84PNA(8l)l976>. 

Upon exposure to various alkanols and alkyl amines (not exceeding 4 carbons) carrier lifetimes increased up to about 50%, whereas the conductivities increased by 1%. Total conductivity was measured—i.e., bulk plus surface—and, therefore, the magnitude of the change does not reflect the true sensitivity of surface conductivity to the reaction. 

Ammonium nitrate explosives are mixtures of ammonium nitrate with carbon carriers such as wood meal, oils or coal and sensitizers such as -> Nitroglycol or -> TNT and -+ Dinitrotoluene. They also may contain -> Aluminum Powder to improve the -> Strength. Such mixtures... 

Nitrocarbonitrates are relatively low-sensitive explosives, usually based on ammonium nitrate, which do not contain any high explosives such as nitroglycerine or TNT. The components are named by nitro dinitrotoluene by carbo solid carbon carriers as fuel by nitrate ammonium nitrate. 

In these explosives, the main oxidizer is sodium, potassium, or ammonium perchlorate the combustible components consist of organic nitro compounds, hydrocarbons, waxes, and other carbon carriers. Nowadays, these explosives are uneconomical and are no longer industrially produced. 

The hydrogenolysis of acylfurans in the gas phase at 200-300°, with group VIII metal catalysts on carbon carriers, can lead to... 

Dihydrofolate Reductase Catalyzes the Regeneration of Tetrahydrofolate, a One-Carbon Carrier... 

First condense the acetyl group with a four carbon carrier to get a six carbon triacid. This is then rearranged and oxidized with loss of carbon dioxide to give a five carbon di-acid ketol very similar to pyruvate in structure. An irreversible DH Complex then creates a four carbon CoA derivative with the release of a second carbon dioxide. At this point it appears that acetyl has been released as carbon dioxide, however, the carrier has been reduced, and modified. A series of reactions now regenerates the original carrier. 

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