Tracer studies

Investigations with isotopic compounds have contributed greatly to the elucidation of the pathways of dissimilation of histidine. These results have been confirmed and extended by the use of purified enzyme preparations. 

Histidine is rapidly oxidized to CO2 in the animal body. Borsook et al. (240) observed that 36% of the label of an intravenous dose of l-histidine-2-C was expired in 1 hr in the rat. Similar findings have been reported by others (241). 

The demonstration that urocanic acid was an intermediate in the conversion of histidine and proof of the reaction pathway to glutamic and formic acids was first established in cell-free extracts of Pseudomonas fiuorescens. 

The formation of L-glutamate was established by isolating the crystalline hydrocholoride from the incubation mixture and establishing its identity (242). 

The correct metabolic pathway to glutamic acid and proof that urocanic acid was an intermediate in the reaction sequence was obtained by em ploying preparations of histidine labeled with N in the a-position of the side chun and N-1, or with C at C-2 of the imidazole ring (see Fig. 

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The use of tracers enables efficient and reliable measurements of oil, gas and water flow in industrial process units and pipe line systems under production conditions thus fundamentally being non-destructive testing methods. Typical problems which can be efficiently assessed by tracer studies include ... 

Tracer studies using 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element. 

Special techniques for experimentation with the actinide elements other than Th and U have been devised because of the potential health ha2ard to the experimenter and the small amounts available (15). In addition, iavestigations are frequently carried out with the substance present ia very low coaceatratioa as a radioactive tracer. Such procedures coatiaue to be used to some exteat with the heaviest actinide elements, where only a few score atoms may be available they were used ia the earHest work for all the transuranium elements. Tracer studies offer a method for obtaining knowledge of oxidation states, formation of complex ions, and the solubiHty of various compounds. These techniques are not appHcable to crystallography, metallurgy, and spectroscopic studies. 

Reactions Involving an -OOF Intermediate. In controlled reactions of O2F2 and various compounds, O tracer studies and other techniques have shown that the first step ia the reaction appears to be... 

The emitted P particles excite the organic molecules which, in returning to normal energy levels, emit light pulses that are detected by a photomultiplier tube, amplified, and electronically counted. Liquid scintillation counting is by far the most widely used technique in tritium tracer studies and has superseded most other analytical techniques for general use (70). 

Kinds oi Inputs Since a tracer material balance is represented by a linear differential equation, the response to anv one kind of input is derivable from some other known input, either analytically or numerically. Although in practice some arbitrary variation of input concentration with time may be employed, five mathematically simple input signals supply most needs. Impulse and step are defined in the Glossaiy (Table 23-3). Square pulse is changed at time a, kept constant for an interval, then reduced to the original value. Ramp is changed at a constant rate for a period of interest. A sinusoid is a signal that varies sinusoidally with time. Sinusoidal concentrations are not easy to achieve, but such variations of flow rate and temperature are treated in the vast literature of automatic control and may have potential in tracer studies. 

Tracer studies are extremely important in furthering our knowledge of atmospheric dispersion. These studies consist of release of a known quan-... 

Although extremelv useful, tracer experiments require considerable capital expenditures and personnel. In addition to the difficulties and uncertainty in making estimates of various parameters, especially cr, one of the fficulties in interpreting tracer studies is relating the atmospheric conditions under which the study was conducted to the entire spectrum of atmospheric conditions. For example, trying to interpret a series of tracer... 

The use of various statistical techniques has been discussed (46) for two situations. For standard air quality networks with an extensive period of record, analysis of residuals, visual inspection of scatter diagrams, and comparison of cumulative frequency distributions are quite useful techniques for assessing model performance. For tracer studies the spatial coverage is better, so that identification of meiximum measured concentrations during each test is more feasible. However, temporal coverage is more limited with a specific number of tests not continuous in time. 

Although many overall rearrangements can be formulated as a series of 1,2-shifts, both isotopic tracer studies and con utational work have demonstrated foe involvement of other species. These are bridged ions in which hydride or alkyl groups are partially bound to two other carbons. Such structures can be transition states for hydride and alkyl-group shifts, but some evidence indicates that these structures can also be intermediates. 

The engineer is offered a large variety of flow-modeling methods, whose complexity ranges from simple order-of-magnitude analysis to direct numerical simulation. Up to now, the methods of choice have ordinarily been experimental and semi-theoretical, such as cold flow simulations and tracer studies. 

Johnson, W. B. et al., 1975, Gas Tracer Study of Roof-Vent Effluent Diffusion at Millstone Nuclear Power Station, Atomic Industrial Forum AIF/NESP 0076. 

For the identity reactions, the intrinsic barriers are their free energies of activation, which can be determined by tracer studies or less directly by rate-equilibrium correlations. ... 

The relative natural abundance of a. stable i.sotope i.s important becau.se, in tracer studies, die amount of stable i.sotope is typically expres.sed in terms of atoms percent excess over the natural abundance of die i.sotope. 

Even though acetate units, such as those obtained from fatty acid oxidation, cannot be used for net synthesis of carbohydrate in animals, labeled carbon from " C-labeled acetate can be found in newly synthesized glucose (for example, in liver glycogen) in animal tracer studies. Explain how this can be. Which carbons of glucose would you expect to be the first to be labeled by "Relabeled acetate ... 

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

The hetero ring in 4-(l -hydroxyalkylidene)-5-oxazolones is cleaved by alcoholic HCl to form alkyl a-acylaminoacylacetates, which cyclize to oxazole-4-carboxylates [Eq. (25)]. This rearrangement occurs directly in alkali, and a carbon-14 tracer study has substantiated a mechanism involving ring opening followed by the alternative ring closure. ... 

Early studies on oxide films stripped from iron showed the presence of chromium after inhibition in chromate solutionand of crystals of ferric phosphate after inhibition in phosphate solutions. More recently, radio-tracer studies using labelled anions have provided more detailed information on the uptake of anions. These measurements of irreversible uptake have shown that some inhibitive anions, e.g. chromateand phosphate are taken up to a considerable extent on the oxide film. However, other equally effective inhibitive anions, e.g. benzoate" pertechnetate and azelate , are taken up to a comparatively small extent. Anions may be adsorbed on the oxide surface by interactions similar to those described above in connection with adsorption on oxide-free metal surfaces. On the oxide surface there is the additional possibility that the adsorbed anions may undergo a process of ion exchange whereby... 

Plug-flow behaviour has been shown in this type of reactor by the use of tracer studies (Table 8.6). 

Additional 14C-tracer studies were conducted to determine the specific isomer participation for TeNMe formation. In the dinitration mixt there are six isomers present 2,4-, 2,6-, 2,3-, 2,5-, 3,4- and 3,5-Dinitrotoluene (DNT). It was observed that 83% of the TeNMe formed from carbon-1 came from the DNT isomers derived from m-Nitrotoluene. The relative participation of DNT isomers for TeNMe formation is summarized in Table 1... 

Tracer Studies on the Nitro lysis of Hexamine to RDX and HMX. The formation of RDX and/or HMX molecules from the nitration or nitrolysis of Hexamethylenetetramine (Hexamine) is a complex process and has been postulated to take place via two separate paths. One involves the selective cleavage of the Hexamine molecule to the appropriate cyclic nitramine (RDX, HMX or both) depending on the specific... 

The following very brief discussion on synthesis of cyclic polynitramines is given merely to provide the historical background necessary to discuss the tracer studies ... 

In conclusion, there appears to be some supporting evidence, other than these tracer studies, that the synthesis of HMX and RDX molecules can be accomplished thru a build-up from single methylene-containing spedes or other small molecules, and that this route can also take place via a total degradation and resynthesis from molecules such as Hexamine. However, die development of an economical process for the large scale production of these expl nitramines, in particular HMX, via a method precluding the use of Hexamine, is vet to be accomplished... 

Radio tracer studies, and adsorption of perchlorate ions on copper, 94 Raman s scattering, and differential capacitance, 80... 

Equipment, The reactor was 1.523 liter, 316 stainless steel cylindrical, jacketed vessel equipped with two multiblade, paddle-type agitators. Tracer studies showed the reactor was well-mixed. A thermocouple measured temperature and was recorded continuously. Feed tanks, tubing, pumps and valves were made of stainless steel and had teflon seals. 

Steele, K.W. and Daniel, R.M. 1978 Fractionation ofnitrogen isotopes by animals as further complication to the use of variations in the natural abundance of for tracer studies. JoMJTja/... 

Boutton, T.W. 1991 Tracer studies with C-enriched substrates humans and large animals. In Coleman, D.W. and Fry, B., eds.. Carbon Isotope Techniques. Academic Press, San Diego 219-242. 

Neopterin cyclic phosphate (92) has been isolated as an intermediate in the biosynthesis of pteridines from GTP in Comamonas Tracer studies show that the phosphoryl group in (92) originates from the... 

Stable and radioactive tracers have been used extensively in catalysis to validate reaction networks, test for intermediates, confirm reaction orders, distinguish between intra- and inter-molecular mechanisms, establish rate limiting steps, docviment direct participation of surface atoms in fluid-solid reactions, etc. A unique feature of tracer studies is that Individual reaction steps can be followed in a complicated set of reactions without perturbing the chemical composition of the... 

Kung H-F, L Tsai, TC Stadtman (1971) Nicotinic acid metabolism. VIII. Tracer studies on the intermediary roles of a-methyleneglutarate, methylitaconate, dimethymaleate and pyruvate. J Biol Chem 246 6444-6451. 

Isab, A.A., Shaw, C.E. Ill and Locke, J. (1988) GC-MS and oxygen-17 NMR tracer studies of triethylphosphine oxide formation from auranofin and water- O in the presence of bovine serum albumin an in vitro model for auranofin metabolism. Inorganic Chemistry, 27, 3406-3409. 

Hintelmann H, Evans RD. 1997. Application of stable isotopes in environmental tracer studies — measurement of monomethyhnercury (CKjEg ) by isotope dilution ICP-MS and detection of species transformation. Fresenius J Anal Chem 358 378-385. 

Sensitive analytic procedures enable detection and measurement of very low tracer levels. In tracer studies, an identifiable tracer material is injected through one or more injection wells into the reservoir being studied. Water or other fluid is then injected to push the tracer to one or more recovery wells in the reservoir. The output of the recovery wells is monitored to determine tracer breakthrough and flow through the recovery wells. Analysis of the breakthrough times and the flows yields important information regarding how to perform the secondary or enhanced recovery processes. 

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