Isotopic tracer techniques

Van Lieshout, M., West, C.E., and Van Breemen R.B., Isotopic tracer techniques for smdying the bioavaUability and bioefficacy of dietary carotenoids, particularly P-carotene, in humans a review. Am. J. Clin. Nutr, 77, 12, 2003. 

Methane emission from ruminants can be estimated by using the ERUCT technique (Emissions from Ruminants Using a Calibrated Tracer). The tracer can either be isotopic or nonisotopic. Isotopic tracer techniques generally require simple experimental designs and relatively straightforward calculations [31]. Isotopic methods involve the use of (3H-)CH4 or (14C-)CH4 and ruminally cannulated animals. 

More recently, Arnstein and Bentley66 applied the isotopic tracer technique in their studies of kojic acid. First, they investigated the mechanism of the alkaline cleavage and degradation of di-O-methylkojic acid (XXXIII).66 Yabuta4 had found that treatment of XXXIII with barium... 

Anker,3 5 using isotope tracer technique, found in a mixed laboratory strain of rats (Wistar) no significant conversion of pyruvic acid to acetic acid. This was in contrast to the results obtained with the Sprague-Dawley strain of rats in which either such a conversion did take place or else pyruvic acid was utilized directly for acetylation. Exactly what constitutes the enzymic difference between the two strains is not known, but it is clear that a striking and potentially important difference exists. From the genetic standpoint one should not expect precisely the same metabolic results from rats of different strains or even from individual rats within the same strain, but the difference here reported is perhaps more fundamental than one might anticipate. If this difference is real, presumably other differences exist which have not been looked for, and one should be extremely careful about accepting the results from one strain as applicable to another. 

Betenekov et al. [39] used an isotopic tracer technique to show that, for then-range of solution compositions, the initial deposition involved adsorption of Cd(OH)2 on the glass substrate. At the beginning of the reaction, only Cd was observed to form on the substrate and this was interpreted to be due to Cd(OH)2, since any other insoluble Cd compounds that might be formed from the deposition solution (containing CdCl2, NaOH, NH4OH, and thiourea dissolved in water) were expected to contain either S or C. However, they concluded that the deposition proceeded, not by reaction between Cd(OH)2 and sulphide formed by decomposition of thiourea, but rather by decomposition of a Cd(OH)2-thiourea complex (see Sec. 3.3.3.1). 

Such a mechanism was suggested by Betenekov et al. based on their isotopic tracer technique discussed in the previous section [39], They suggested that Cd(OH)2 forms initially on the substrate and catalyzes the thioureau decomposition. Of course the catalytic effect of the sohd surface could be to decompose thiourea to sulphide ion and not necessarily to catalyze the complex-decomposition mechanism. 

In a discussion of permeability it is important to recognize that we deal with operational definitions, since the act of measurement influences the state of the system. In your case, applying an electrical potential gradient and performing electrodialysis alter the distribution of ionophore within the membrane. I wonder whether you have attempted to measure permeability by isotopic tracer techniques In this method the distribution of ionophore would not be influenced. Furthermore, information can be obtained on the question of carriers versus channels or pores. It should not be difficult to determine the extent of possible isotope interaction between tracer species and abundant species in the membrane as discussed by Kedem and Essig [J. Gen. Physiol., 48, 1047 (1965)]. Positive isotope interaction would tend to suggest the presence of channels or pores, negative isotope interaction the presence of carriers. 

The use of isotopes in mechanistic and analytical chemistry has been known since about 1913 but it was the advent of artificially produced isotopes in the period from 1945 onwards that really marked the beginning of a wide range of isotopic tracer techniques. There is now an extensive literature on tracer techniques and a few of the more useful references are included at the end (7—5). 

The period dining which isotopic tracer techniques have developed has also seen remarkable developments in many other techniques — all forms of spectroscopy, chromatography, automated analyses, etc., and it is necessary to get isotopic techniques in their proper perspective as just another useful tool. The technique has its own unique advantages and limitations. 

Some early applications of isotopic tracer techniques to the TCA cycle led to a new generalization concerning the stereochemistry of interaction between enzymes and certain types of substrate. 

Work on the biosynthesis of cholesterol began in earnest after Rudolf Schoenheimer and David Rittenberg, at Columbia University, developed isotopic tracer techniques for the analysis of biochemical pathways. In 1941, Rittenberg and Konrad Bloch were able to show that deuterium-labeled acetate (C2H, COO ) was a precursor of cholesterol in rats and mice. In 1949, James Bonner and Barbarin Arreguin postulated that three acetates could combine to form a single five-carbon unit called isoprene. 

The methods described so far for studying self-diffusion are essentially based on an observation of the diffusion paths, i.e. on the application of Einstein s relation (eq 3). Alternatively, molecular self-diffusion may also be studied on the basis of the Fick s laws by using iso-topically labeled molecules. As in the case of transport diffusion, the diffusivities are determined by comparing the measured curves of tracer exchange between the porous medium and the surroundings with the corresponding theoretical expressions. As a basic assumption of the isotopic tracer technique for studying self-diffusion, the isotopic forms are expected to have... 

Imai, T., Guto, H., Matsumura, H., and Yasuda, S., 1998, Determination of the distribution and reaction of polysaccharides in wood cell-walls by the isotope tracer techniques. VII. Double radiolabeling of xylan and pectin in magnolia Magnolia kobus DC) and comparison of their behaviors during kraft pulping by radiotracer technique. J. Wood Sci. 44 106-110. 

Steroid hormones by the application of isotope tracer techniques 3I8-321]. Lieberman and co-workers undertook urinary metabolic studies [304,325] by administration of isotopically labeled steroids followed by the determination of specific activities of urinary metabolites derived only from the administered substance. Mathematical analyses were performed by compartmentalization of the metabolism [385]. One- or two-compartment systems are most frequently used [304,306,384,386,387]. A compartment is defined as a particular species (e.g., dehydroepiandro-sterone sulfate) in a particular space (e.g., peripheral organ). It is assumed that a species entering a compartment mixes immediately with the whole compartment. Two factors were responsible for the institution of com-partmental analysis ... 

Various isotope applications are used to monitor the quality of materials and structures. Isotopic tracer techniques measure wear, corrosion, moisture, leakage, and many other factors. Neutron radiography creates images of materials that are not as dense as those captured in X-ray photos. This method is used chiefly to check uranium fuel in nuclear reactors for flaws, to find cracks in the inner plastic or aluminium parts of airplanes, or to detect tiny fissures in gas turbine blades. Californium-252 is used for neutron radiography and neutron activation analyses. 

A number of other reactions have been studied using orthodox isotopic tracer techniques for which complete exchange in the time of separation was observed. The lower limits for the specific rates that can be calculated are considerably smaller than those to which we have referred, and since in many cases no proof could be adduced that the separation method did not cause the exchange, these results are not reported. The review by Amphlett (5) gives references to many of the literature reports on these and other reactions in the entire field. 

The mechanism of osazone formation has been studied by the isotopic-tracer technique, by using an N -labeled arylhydrazone, treating it with an unlabeled arylhydrazone, and making an isotopic assay of the reaction products. The results were characteristic of Weygand s mechanism involving the oxidation of the hydrazone to a l-imino-lV -2-keto derivative (40) and subsequent osazone formation with the elimination of ammonia-iV . 

Ogston, A. G. Interpretation of experiments on metabolic processes, using isotopic tracer techniques. Nature (London) 162, 963 (1948). 

Different isotopes of the same element have, by definition, the same electronic configuration, and hence similar chemical properties. This similarity is the basis of the isotopic tracer technique (Sec. 3.29) one isotope docs pretty much what another will do, but, from its radioactivity or unusual mass, can be traced through a chemical sequence. 

Ni, J. et al., Characterization of benzimidazole and other oxidative and conjugative metabolites of brimonidine in vitro and in rats in vivo using on-line HID exchange LC-MS/MS and stable-isotope tracer techniques, Xenobiotica, 37(2), 205, 2007. 

In 1911 Ernest Rutherford asked a student, George de Hevesy, to separate a lead impurity from a decay product of uranium, radium-D. De Hevesy did not succeed in this task (we now know that radium-D is the radioactive isotope °Pb), but this failure gave rise to the idea of using radioactive isotopes as tracers of chemical processes. With Friedrich Paneth in Vieima in 1913, de Hevesy used °Pb to measure the solubifity of lead salts—the first appfication of an isotopic tracer technique. De Hevesy went... 

In chemical reaction kinetics, isotope-labelled reactants are frequently employed to follow a reaction pathway and to determine the reaction mechanism (see Chapter 7.6). The isotopic tracer technique is a useful tool in catalyst surface analysis, because it enables determination of whether the adsorbed species present on the surface during the reaction are by-products or reaction intermediates. One of the adsorbed species is labelled by an isotope atom and its rate of disappearance is followed by surface spectroscopy. Simultaneously, its rate of appearance in the product molecule is followed by mass spectrometry. When both rates are identical, it can be concluded that the observed adsorbed species is the reaction intermediate. 

A wide range of techniques are used to determine catabolic nitrate reduction rates. These include mass balance methods using input-outputs, acetylene inhibition techniques, dinitrogen production rates, nitrate consumption rates, nitrate pore water profiles, and stable isotope tracer techniques. The limitations and advantages of these methods are discussed by Seitzinger (1988) and Herbert (1999). 

It is also used in carrying out the studies on the biotransformation of paeonol by means of isotope tracer techniques. 

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