Cobalt specific activity

Single compact sources of Cobalt-60 vary from about 1 to 10/curie, depending on quantity and specific activity. 

Throughout these studies, no product other than propane was observed. However, subsequent studies by Sinfelt et al. [249—251] using silica-supported Group VIII metals (Co, Ni, Cu, Ru, Os, Rh, Ir, Pd and Pt) have shown that, in addition to hydrogenation, hydrocracking to ethane and methane occurs with cobalt, nickel, ruthenium and osmium, but not with the other metals studied. From the metal surface areas determined by hydrogen and carbon monoxide chemisorption, the specific activities of... 

The cost of irradiation—i.e., the cost of the curies—depends greatly on which reactor the cobalt is irradiated in. If irradiated in a reactor at high flux, the high specific activity material would be irradiated in 10 cans for... 

Zinc(II) and Co(II) are the only cations found to reactivate apophos-phatase to any appreciable extent (120). The Co(II) enzyme follows the same formal mechanism as the native enzyme, but has a lower specific activity (113, 121). It lacks the phosphotransferase activity (113, 119, 121) observed for the native enzyme, for example in Tris buffers. This was taken to imply that the lower activity of the cobalt enzyme is due to a lower rate of phosphorylation, so that this step becomes rate-limiting also below f>H 7 (113). Stopped-flow experiments by Gottesman etal. (121) show, however, that a very fast burst of -nitrophenol occurs in the cobalt alkaline phosphatase-catalyzed hydrolysis of -nitrophenyl phosphate over a wide pH region. These results strongly suggest that a step subsequent to the phosphorylation is rate-limiting in this metal derivative. 

The specific activities of penicillolysin for clupeine and casein hydrolysates were 3.04 x 10 1 and 5.23 x 10 3 katal/kg protein at pH 7.0, respectively (Table 9) [69], The rate of clupeine hydrolysis was 60-fold greater than that for casein hydrolysis. When zinc is removed, the enzyme is completely inactive, and readdition of zinc restores the dual activities towards clupeine and casein (Table 9). Depending on the casein substrate, the cobalt-penicillolysin (Co-penicillolysin) could be up to ca 1.6 times more active than the native zinc enzyme. On the other hand, in clupeine-hydrolysis, the cobalt enzyme is about 70% as active as the native enzyme. Thus, replacement of the zinc-penicillolysin with cobalt markedly decreases the activity towards clupeins while increases it towards casein. 

According to Vannice s data, ruthenium is about six times more active than nickel and about three times more active than iron. As ruthenium is not only much more expensive than nickel but is also in very short supply, it is very improbable that it will ever be used as a catalyst in any large-scale process. Iron and cobalt (which have similar specific activities for methanation to that... 

Hutchings (170) plotted (Figure 31) the activity against the surface area for a number of promoted catalysts and deduced that most of the catalysts conform to a linear correlation. The only enhancement of the specific activity was observed for the cerium-promoted catalyst. This result shows that care must be taken in the interpretation of the catalyst performance data, particularly when catalysts prepared by different methods are compared. In a separate study, Hutchings and Higgins (171) found that chromium, niobium, palladium, antimony, ruthenium, thorium, zinc, and zirconium each had very little effect on the specific activity of (VO)2P207. A significant increase in surface area was observed with zirconium, zinc, and chromium, which could be of use as structural promoters. Iron-, cesium-, and silver-doped catalysts decreased the specific activity, and cobalt and molybdenum were the only promoters found to increase the specific activity. 

Electronic promoters, for example, the alkali oxides, enhance the specific activity ofiron-alnmina catalysts. However, they rednce the inner snrface or lower the thermal stability and the resistance to oxygen-containing catalyst poisons. Promoter oxides that are rednced to the metal during the activation process, and form an alloy with the iron, are a special group in which cobalt is an example that is in industrial use. Oxygen-containing compounds such as H2O, CO, CO2, and O2 only temporarily poison the iron catalysts in low concentrations. Sulfur, phosphorus, arsenic, and chlorine compounds poison the catalyst permanently. 

Cyanombalamln Radioactive Cobalt ( Co) Capsules, USP. Cyanocobalamin Co capsules contain cyanocobaJ-amin in which some of the molecules contain radioactive cobalt ( Co), Each microgram of this cyanocobalamin preparation has a specific activity of not less than 0.02 MBq (0.. i Ci). The USP cautions that in making dosage calculations one. should correct for radioactive decay. The radioactive half-life of Co is 270 days. 

The importance of catalyst acidity is emphasised by comparisons between initial coke formation on cobalt molybdate based catalysts and on sodium molybdate based systems [24]. In the latter case, the acidity is low, the steady state specific activity is not too dissimilar from cobalt molybdate and the initial deactivation is very much less. 

While Co " competes with Zn for binding at both sites in bovine lens leucine aminopeptidase, Mg " " competes for only one of the sites. When cobalt(ii) is substituted at site 1, the specific activity with L-leucine-p-nitroanilide is increased by more than ten-fold. Cobalt(ii) has been replaced for zinc in thermolipin and simultaneously terbium(iii) for calcium the observed visible fluorescence (excitation at 280 nm) provided quantum yield measurements which indicated that the terbium-cobalt distance was 13.7 A, in good agreement with the Ca—Zn distance determined from a recent crystal structure. Vallee and co-workers suggest that this technique... 

The catalytic performance of the Co-doped catalysts was compared to that of an undoped VPO catalyst activated for the same time period. The results of our analysis are presented in Table 2, where it is clear that the addition of Co in all cases has a beneficial effect on both the selectivity to maleic anhydride production and the specific activity of the VPO catalyst. The most significant improvement, however, was noted for the catalyst with the lowest cobalt loading. 

A controversial issue related to cobalt catalysts in Fisher-Tropsch synthesis is the structure-sensitive character of this reaction. Iglesia and co-workers [126,127] reported a large increase in activity when the cobalt particle size was decreased from 200 nm to 9 nm, whereas the specific activity [turnover frequency (TOF)] was not influenced by the cobalt particle size. However, other authors have reported that the TOF suddenly decreased for catalysts with cobalt particle sizes smaller than 10 nm [122,128]. Bezemer et al. [125] were the first to investigate the influence of cobalt particle size in the range 2.6 to 27 nm on performance in Fischer-Tropsch synthesis on well-defined catalysts supported on carbon nanofibers. It was found that the TOF for CO hydrogenation was independent of cobalt particle size for catalysts with particles larger then 6 nm (at atmospheric pressure) or 8 nm (at 35 bar). But both the TOF and the C5+ selectivity decreased for catalysts with smaller particles. It was proposed that the cobalt particle size effects could be attributed to a strucmre-sensitivity characteristic of the reaction, together with a CO-indnced reconstmction of the cobalt surface. 

A radioactive solution containing Co of the total radioactivity of ca. 4000 counts/100 sec was anployed as a radioactive feed. The respective radioactivity counting rate (pulse/sec), treated as the intensity of the y-radiation of a 5 cm liquid sample containing Co, was measured by a y-analyzer, LG-IB (INCT). The obtained values were compared with the radiation intensity of the Co standard sample. Therefore, the specific activity of the feed (Ap), the retentate (Ar), and the permeate (Ap) were calculated. The parameters (/ ), (DF), and if) were determined when the radioactive solutions were treated. In all the experiments, the transman-brane hydrostatic pressure was maintained at 0.22 MPa and the feed flow rate at 401/h. Substantially high DFs for radioactive Co were obtained for the SMM-modified membranes used in the UF/complexation process 223 for SMM3/PES and 163 for SMM41/PES (Table 1.2). For the unmodified membranes, the DFs were lower 44 for the commercial PES membrane and 75 for the prepared unmodified PES membrane. Additionally, the SMM-modified membranes showed smaller adsorption of the radioactive cobalt than the modified membranes, which was beneficial, taking into account the considered applications. After a 2 h operation, the adsorption of Co by the SMM-modified membranes was four to five times smaller than that of the unmodified PES membrane. 

Tritium and iodine 125 are the tags most often used for RIA. Certain assays, e.g., vitamin B-12, require the use of cobalt 57. Except for a few special cases it is not possible to use a carbon-14 tag since a sufficiently high specific activity can not be obtained owing to the long half life of carbon 14. Although iodine 131 has enjoyed widespread use as a tag for protein in years past it has been replaced almost entirely by the 60-day half life of the mass 125 isotope. 

The requirement of high specific activity restricts the choice of nuclide principally to tritium, iodine 125 and cobalt 57. A high specific activity is required because the nuclide must serve as a tracer to a trace amount of analyte. Carbon 14 and other nuclides commonly used as tracers are generally not satisfactory for RIA applications. 

---