Tagging isotopes

Tracer Diffusivity Tracer diffusivity, denoted by D g is related to both mutual and self-diffusivity. It is evaluated in the presence of a second component B, again using a tagged isotope of the first component. In the dilute range, tagging A merely provides a convenient method for indirect composition analysis. As concentration varies, tracer diffusivities approach mutual diffusivities at the dilute limit, and they approach selr-diffusivities at the pure component limit. That is, at the limit of dilute A in B, D g D°g and... 

Nucleotide tags Peptide tags Haloaromatic tags Secondary amine tags Isotopic tags Autotagging... 

NUCLEOTIDE TAGS PEPTIDE TAGS HALOAROMATIC TAGS SECONDARY AMINE TAGS ISOTOPIC TAGS AUTOTAGGING... 

Different combinations of stable xenon isotopes have been sealed into each of the fuel elements in fission reactors as tags so that should one of the elements later develop a leak, it could be identified by analyzing the xenon isotope pattern in the reactor s cover gas (4). Historically, the sensitive helium mass spectrometer devices for leak detection were developed as a cmcial part of building the gas-diffusion plant for uranium isotope separation at Oak Ridge, Tennessee (129), and heHum leak detection equipment is stiU an essential tool ia auclear technology (see Diffusion separation methods). 

Birds and animals are tagged so that their wanderings and ultimate fate can be followed. To do the same for nitrogen fertilizer, we use the heavy isotope of nitrogen, as a tag or label . This is a safe isotope to use because it is not radioactive. The of the label is taken up by the crop, incorporated in the soil s... 

Generally, methylation of enolate ions with isotopically tagged methyl iodide is a satisfactory labeling procedure. For example, application of this method has given the C-18 labeled steroids, (244) and (245) (see above), 17 -acetoxy-4jS-trideuteriomethyl-4a-methyl-l9-norandrost-5-en-3-one (264) and 19- C-testosterone acetate (268). Methylation of the anion derived from 17jS-acetoxy-4-methyl-l9-norandrost-4-en-3-one (263) with d3-methyl iodide occurs predominantly at C-4, yielding mainly the 4)S-trideuterio-methyl derivative (264) and about 10% of the corresponding C-4 epimer... 

Another widely used approach to the elucidation of metabolic sequences is to feed cells a substrate or metabolic intermediate labeled with a particular isotopic form of an element that can be traced. Two sorts of isotopes are useful in this regard radioactive isotopes, such as and stable heavy isotopes, such as or (Table 18.3). Because the chemical behavior of isotopically labeled compounds is rarely distinguishable from that of their unlabeled counterparts, isotopes provide reliable tags for observing metabolic changes. The metabolic fate of a radioactively labeled substance can be traced by determining the presence and position of the radioactive atoms in intermediates derived from the labeled compound (Figure 18.13). 

The recent rise in the use of expolosives in terrorist activity poses new challenges to industry and law enforcement. This challenge is being met by the use of sophisticated chemical detection devices to screen for bombs and more rigorous explosive inventory safeguards and controls. Plans have also been proposed to tag explosives with isotopes to make them easier to trace if misused. 

Much work has been invested to reveal the mechanism by which propylene is catalytically oxidized to acrolein over the heterogeneous catalyst surface. Isotope labeling experiments by Sachtler and DeBoer revealed the presence of an allylic intermediate in the oxidation of propylene to acrolein over bismuth molybdate. In these experiments, propylene was tagged once at Ci, another time at C2 and the third time at C3. 

Tao WA, Aebersold R (2003) Advances in quantitative proteomics via stable isotope tagging and mass spectrometry. Curr Opin Biotechnol 14 110-118... 

In vitro labeling of proteins using isotope-coded affinity tags... 

Gygi, S. P., Rist, B., Gerber, S. A., Turecek, F., Gelb, M. H., and Aebersold, R. (1999). Quantitative analysis of complex protein mixtures using isotope-coded affinity tags. Nat. Biotechnol. 17, 994-999. 

The 0(1D) + HD reaction was also studied using the same Rydberg tagging TOF technique described above. The experiment was carried out at a collision energy of 1.7kcal/mol, which is below the 1.8 kcal/mol barrier for the abstraction mechanism inferred from previous experimental studies.63 The purpose of this experimental study is to investigate the isotope effect on this reaction. 

Von Haller, P.D., Yi, E., Donohoe, S., Vaughn, K., Keller, A., Nesvizhskii, A.I., Eng, J., Li, X.J., Goodlett, D.R., Aebersold, R., Watts, J.D. (2003). The Application of New Software Tools to Quantitative Protein Profiling Via Isotope-coded Affinity Tag (ICAT) and Tandem Mass Spectrometry II. Evaluation of Tandem Mass Spectrometry Methodologies for Large-Scale Protein Analysis, and the Application of Statistical Tools for Data Analysis and Interpretation. Mol. Cell. Proteomics 2, 428 -42. 

By coupling GC with MS as the detection system (either ion trap or quadrupole mass spectrometer), structural information can be obtained regarding unknown or unexpected components. Another advantage of using mass spectrometric detection is that it can distinguish analytes tagged with stable isotopes, offering the possibility to use them as... 

Figure 16.1 The general design of an ICAT reagent consists of a biotinylation compound with a spacer arm containing stable isotope substitutions. The reactive group is used to label proteins or peptides at particular functional groups and the biotin affinity tag is used to isolate labeled molecules using immobilized (strept)avidin.

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