Radiotracer experiments

Whereas in many metals with relatively simple and isotropic crystal structures the parameter / has values between 0.5 and 1, it can have much more extreme values in materials in which the mobile species move through much less isotropic structures with 1-D or two-dimensional (2-D) channels, as is often the case with insertion reaction electrode materials. As a result, radiotracer experiments can provide misleading information about self-diffusion kinetics in such cases. 

Pentreath RJ (1975) in Design of Radiotracer Experiments in Marine Biological Systems. IEAE, Vienna, p 137 (Tech. Rep. Series No. 167)... 

In order to estimate the flux through the SMM cycle and to explore its function, a computer model of methionine metabolism in mature Arabidopsis rosette leaves was developed based on data from radiotracer experiments and on metabolite contents. This model suggested that the cycle serves to stop accumulation of AdoMet, rather than to prevent depletion of free methionine, as proposed by Mudd and Datko.54 Because plants lack the AdoMet feedbacks on MTHFR and AdoMet synthetase that regulate AdoMet pool size in other eucaryotes, the SMM cycle may be the main mechanism whereby plants achieve short-term control of AdoMet level. MMT knockouts of maize and Arabidopsis recently became available, and these can now be used to further investigate the role of the SMM cycle, and to test the predictions of the model. 

Radiotracer experiments gave final proof of the reaction pathway. The mixture of C-labeled n-hexane with inactive 1-hexene was reacted over platinum catalyst. The same was done with the mixture of labeled n-hexane and inactive cyclohexane (52-54). 

The importance of the above radiotracer experiments is not restricted to the demonstration of the stepwise aromatization mechanism. Even more important is the evidence against the formation of any cyclohexane or cyclohexene during aromatization (55, 55, 58). 

The availability of biologically active i Sj.iabelled EPO facilitated the detection and study of cell surface receptors. In addition to erythroid precursors, various other cell lines were shown to express EPO receptors, at least when cultured in vitro. Many harboured two classes of receptors a high-affinity and a low-affinity form. Most appeared to express between 1000 and 3000 receptors/cell. Radiotracer experiments illustrated that the EPO receptor is rapidly internalized after ligand binding and the EPO-receptor complex is subsequently degraded within lysosomes. 

The authors gratefully acknowledge the help of Dr. D.G. Parker and Mr. R.A. McReddie of ICI Physics and Radioisotope Services, Billingham, in the C0 radiotracer experiment. 

Furthermore, recent radiotracer experiments have shown that metals such as Cu, Ag, and Au can diffuse into various polymers including polyimides and polycarbonates at elevated temperatures. Arrhenius type temperature dependences are not always found. This is not unexpected considering the distribution of saddle-point energies in amorphous polymers [F. Faupel, R. Willecke (1994)]. 

Concentrations of H2S typically are maintained low by a variety of reactions including oxidation, precipitation with iron, and interactions with organic matter. Sulfide may be oxidized biologically or abiotically. Elemental S reacts readily with H2S to form polysulfides (175) and is oxidized and reduced by a variety of bacteria. In radiotracer experiments, S0 was in... 

The unique advantages of radiotracer experiments include their high sensitivity, their simplicity, and small expense (compared to competing technologies such as mass spectrometry). In a well-designed experiment, the presence of radiotracers does not affect the system under study and any analysis is nondestructive. Interference from other species that may be present is not important (as compared to conventional methods of analysis where interferences may thwart the analysis). 

DESIGN OF A RADIOTRACER EXPERIMENT 4.2.1 Basic Design Criteria... 

The feasibility of radiotracer experiments is usually dependent on certain practical matters. These factors include ... 

Because only a small number of atoms are necessary to give a significant disintegration rate, there is a much better detection sensitivity in radiotracer experiments compared to conventional tracer experiments. This point is particularly important for environmental studies where high dilution factors are commonly encountered. 

Radiochemistry involves the application of the basic ideas of inorganic, organic, physical, and analytical chemistry to the manipulation of radioactive material. However, the need to manipulate radioactive materials imposes some special constraints (and features) upon these endeavors. The first of these features is the number of atoms involved and the solution concentrations. The range of activity levels in radiochemical procedures ranges from pCi to MCi. For the sake of discussion, let us assume an activity level, D, typical of radiotracer experiments of 1 p,Ci (= 3.7 x 104 dis/s = 3.7 x 104 Bq), of a nucleus with mass number A 100. If we assume a half-life for this radionuclide of 3 d, the number of nuclei present can be calculated from the equation... 

Salts ofmolybdenum(Vl) fluoride, [MoFy]" were prepared by reaction of [MoFe] with F under appropriate conditions. These anions have capped octahedral stmctures in agreement with theoretical predictions. Radiotracer experiments using... 

Pool Sizes Metabolic tracers can in principle be used to estimate the size of various body pools for trace elements It is somewhat analogous to making specific activity measurements in radiotracer experiments ... 

Like other dissolved organic nutrients, the chemical composition of organic P is relatively unknown. Marine dissolved organic phosphorus (DOP) composition has been mostly identified as particular compound classes such as monophosphate esters, phosphonucleotides, nucleic acids, phospholipids, phosphonates and polyphosphates (Benitez-Nelson, 2000). Kolowith et al. (2001) found that monophosphate esters and phosphonates are major components in the Pacific Ocean, the Atlantic Ocean and the North Sea. ATP (adenosine triphosphate), ubiquitous in aU living cells, has been used as a model DOP compound in radiotracer experiments to obtain information on P sources and fluxes in natural environments (Bjorkman et al., 2000 Karl and Bossard, 1985) and cyanobacterial cultures (Fu et al., 2006). 

For the determination of antimony, the digestion efficiency of particulate matter, collected on Whatman 41 cellulose filters, was evaluated by means of radiotracer experiments [6], A quantitative recovery was obtained using 8 ml sulfuric acid and 4 ml hydrogen peroxide, when applied to a quarter fraction of the filter. For the dissolution of residual silicates 0.5 to 4 ml of hydrofluoric acid were added, which were later on evaporated. After digestion the solution was filtered if needed and diluted appropriately. 

A rapid technique has been developed for quantitatively concentrating several trace metals from aqueous solution. The metals are co-precipitated as dithiocarbamate chelates by adding an excess of another dissolved metal. This technique has been coupled with atomic absorption analysis for the precise determination of nmol/kg quantities of copper in seawater. Radiotracer experiments show that nickel, iron, and cadmium are also co-precipUated by this technique under proper experimental conditions. 

Radiotracer experiments, using and Needle s Eye humic substances have also shed light upon changes in U binding which take place following an initial, fairly rapid complexing step. The pattern represents the end result of a long... 

Very few non-oxo Movl halides are known. These include Cs[MoF7] and NO[MoF7]-MeCN, prepared by reacting MoF6 with CatF 520 the anions exhibit capped octahedral structures in line with theoretical predictions.521 18F-radiotracer experiments have revealed rapid and complete intermolecular fluoride exchange between [MF7]- and MF6 (M = Mo, W).522... 

In radiotracer experiments conducted in the authors laboratories, deposition of Polymer-JR was found to be almost 2.3 times greater for bleached hair than for virgin hair, indicating a greater number of negative binding sites on the former (Table 10.16). 

Araki, H., and Terashima, N. (1981) Radiotracer Experiments on Lignin Reactions VII. The origins of low molecular weight compounds formed during kraft cooking. Mokuzai Gakkaishi 27(5), 414-418. 

H Araki, Y Tomimura, N Terashima. Radiotracer experiments on lignin reactions. V. The behaviour of lignin in kraft pulping process. Mokuzai Gakkaishi 23 378-382, 1977. 

Radiotracer experiments were used to elucidate the biosynthetic precursors to eudistomin H (7) and I (8) in Floridian collections of Eudistoma olivaceum. Both radiolabeled tryptophan and proline were incorporated by E. olivaceum into eudistomins H and I and tryptamine was incorporated into eudistomin I, to the exclusion of eudistomin H. Bromotryptamine and bromotryptophan are incorporated into eudistomin H (Scheme 30). These results suggest eudistomin biosynthesis proceeds from the amino acids via decarboxylation, halogenation, then condensation with proline. 

Mn oxidation and scavenging in plumes appear to be dominated by microbial activity (see review in Winn etal., 1995). Plume bacteria are often characterised by capsules of abundant extracellular polymer matrices that are believed to scavenge Mn from solution (e.g. Cowen etal., 1986, 1999). Radiotracer experiments (54Mn uptake) and elevated microbial biomass at plume depths suggest that microbial metabolic activity enhances Mn scavenging (Cowen etal., 1986). However, it is not clear if this activity includes active Mn2+ oxidation or is simply due to non-enzymatic processes. 

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