Labeling techniques, hydrogen isotope

Kingston, L. P., Lockley, W. J. S., Mather, A. N., Spink, E., Thompson, S. P., Wilkinson, D. J., Hydrogen isotope labelling novel applications of parallel chemistry techniques, International Isotope Society Symposium, Dresden, June 2000. 

Tobias et al. [665] have described a method in which the GC effluent is passed into a combustion furnace to convert the organic hydrogen content into water, which is then selectively reduced to hydrogen in a reduction furnace containing Ni metal. The final stream is transmitted to the IRMS via a heated Pd filter, which passes only hydrogen isotopes to the ion source. For a benzene sample a precision of < 5 %o was obtained for <52HSMOw> which approaches the performance of off-line techniques and the requirements for studies of natural variability. This already meets requirements for analysis of D-labeled compounds used in tracer studies [666,667]. 

The development of modern spectroscopic techniques (IR, NMR, mass spectroscopy), in addition to facilitating the characterization of deuterium-labeled products, has also helped to establish a demand for these compounds. Mass spectroscopy, for example, played an important role in the history of deuterium, beginning with the discovery of hydrogen isotopes in 1931.172... 

One particular strength of SANS over SAXS is the differing scattering behaviour of isotopes towards neutrons, which is particularly pronounced for the hydrogen isotopes H and D. The true value of the SANS technique for structure analysis of dendrimers is due to this phenomenon. Thus, by deuterium label-... 

The mechanism of hydrazine decomposition has been studied much less than that of hydrogen peroxide, and the mechanism actually is not known. We may take some clues however from studies of its oxidation in aqueous solution by metal salts, in which kinetic and isotope labelling techniques were used. As the main mechanism for the oxidation of hydrazine by ferric ion the following was proposed 57) ... 

Small isotope-effects can be detected by double-labeling techniques, in which the carbon skeleton is labeled with 14C, and the ratio of 14C to tritium is measured both in the substrate and the product. Care must be taken in the observation and interpretation of isotope effects determined from the hydrogen-isotope content of the product. Just as in non-enzymic reactions (see p. 154), discrimination against the substrate containing deuterium or tritium leads to an increase in the isotopic content of the substrate, and this decreases the apparent isotope-effect towards the end of the reaction. 

Spin contrast variation will probably bear fruit in in situ structure determinations of arbitrary parts of biological structures. For this purpose a selected region of the macromolecular structure has to have the usual hydrogen isotope H whereas the larger remainder is preferably completely deuterated. This technique of specific isotopic labelling is now well established with ribosomes and other subcellular particles which allow in vitro recombination of the constituents... 

A short overlook on transverse relaxation-optimized spectroscopy (TROSY) in combination with various isotope-labelling techniques has been published by Fernandez and Wider. The method improves, among others, the detection of scalar couplings across hydrogen bonds, providing crucial information on the determination of solution structures of large proteins and oligonucleotides. 

Radiochemical analysis relies on the assumption that different isotopes of the same element exhibit the same properties in any macroscopic physical or chemical process, and that radioactive labeling does not influence the other properties of a chemical species. This is generally the case, with deviations below 1% (with exception of hydrogen isotopes) owing to isotopic fractionation or radiation effects. For analytical purposes, the radiotracer and the analyte must be present in the same chemical form. This is usually easy to achieve, but specialized preparative techniques may be necessary for radioactive labeling of more complex organic compounds. 

Purpose. This experiment illustrates a selective cross-coupUng reaction between an alkyl Grignard reagent and an aryl halide in the presence of a nickel phosphine catalyst to form a C—C bond. The reaction is also used to demonstrate the technique of "labeling" specific hydrogen atoms with an isotope for identification purposes. 

To understand the mechanism, chemists have used an important technique called isotopic labeling. AH elements have isotopes (for example, deuterium is an isotope of hydrogen because deuterium has an extra neutron in the nucleus). Carbon also has some important isotopes. is an important isotope because we can easily determine the position of a atom in a compound using NMR spectroscopy. So if we enrich a specific spot with then we can follow where that carbon atom goes during the reaction. For example, let s say we take chlorobenzene, and we enrich one particular site with... 

Also present in the first test tube is a synthetic analog of ATP in which both the 2 and 3 hydroxyl groups have been replaced by hydrogens This compound is called 2 3 dideoxyadenosme triphosphate (ddATP) Similarly ddTTP is added to the second tube ddGTP to the third and ddCTP to the fourth Each tube also contains a primer The primer is a short section of the complementary DNA strand which has been labeled with a radioactive isotope of phosphorus ( P) When the electrophoresis gel is examined at the end of the experiment the positions of the DNAs formed by chain extension of the primer are located by a technique called autoradiography which detects the particles emitted by the P isotope... 

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