Deuterium, natural abundance

Keywords NMR spectroscopy isotope effects carbon 13C deuterium natural abundance theoretical calculations reaction mechanisms... 

Deuterium is abundant in and easily separated from water. There is enough deuterium on earth to provide power for geological time scales. In contrast, tritium is not available in nature, but can be produced from n+ lithium reactions (see Lithium and lithium compounds). Natural Hthium is exhaustible, but sufficient tritium can be provided from it until fusion energy production is efficient enough to involve only D-D reactions ... 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

The overall reaction releases 3 X 108 kj for each gram of deuterium consumed. That energy corresponds to the energy generated when the Hoover Dam operates at full capacity for about an hour. Additional tritium is supplied to facilitate the process. Because tritium has a very low natural abundance and is radioactive, it is generated by bombarding lithium-6 with neutrons in the immediate surroundings of the reaction zone ... 

Yakir, D. 1992 Variations in the natural abundance of oxygen-18 and deuterium in plant carbohydrates. Plant, Cell, and Environment 15 1005-1020. 

In order to obtain more insights into the biosynthetic mechanism, [Me- C-Me-d ] double-labeled methionine was fed to the organism. The C-NMR spectrum of resulting neosaxitoxin showed a clean triplet for C-13 beside the natural abundance singlet. The result indicated that only one deuterium was left on the methylene carbon. 

Water is a mixture of varying isotopic composition (Franks, 2000). In addition to the two most common isotopes, 160 and there are two stable oxygen isotopes (170, lsO), one stable hydrogen isotope (2H, deuterium), and one radioactive hydrogen isotope (3H, tritium, half-life = 12.6 years). Water also contains low concentrations of hydronium (H30+) and hydroxide ions (OH-) and their isotopic variants. In total, water consists of more than 33 chemical variants of HOH however, these variants occur in relatively minor amounts (Fennema, 1996). Table II gives the natural abundance isotopic composition of the four major water species. 

N.m.r. spectroscopy T.l.c.-m.s. analysis of oligosaccharides coupled to a lipid amine (neoglycolipids) H n.m.r. spectrum in D20 after exchange of free protons with deuterium Experiments conducted at 295 K, with acetone as the internal standard (set at 2.225 p.p.m. from 4,4-dimethyl-4-silapentane-1-sulfonate) Results compared, to within 0.005 p.p.m. (laboratory-to-la-boratory variation) of data in the literature Conformational studies by n.O.e. experiments Natural-abundance-13C analysis Chemical-shift assignment by 2D H- H and H-13C n.m.r. spectroscopy... 

Deuterium nmr spectroscopy has been utilized for the last decade to determine large (primary deuterium) KIEs in reactions with isotopes present at the natural abundance level (Pascal et al., 1984,1986 Zhang, 1988). A great advantage of this approach is that labelled materials do not have to be synthesized. Neither is there any need for selective degradation procedures, which are often necessary to produce the molecules of low mass, e.g. C02, acceptable for isotope ratio mass spectrometry. Moreover, the KIEs for several positions can be determined from one sample. However, until quite recently the relatively low precision of the nmr integrations that are used for the quantitative assessment of the amount of deuterium at specific molecular sites has limited the applicability of this technique for determining small (secondary deuterium) KIEs. 

This period also focuses on the discovery of isotopes of light weight elements some of which have such low natural abundance that they could not be detected by the mass spectrographs available in the early part of the twentieth century, but which may be very desirable for study because isotope effects involving lightweight elements tend to be much larger than those for heavier elements. A prime example is the discovery of deuterium in 1932, one of the major events in isotope chemistry during this time period. 

The very low D/H natural abundance ratio (0.015% = 150 ppm) is responsible for the high cost of heavy water. Materials balance requires a minimum of 7x 103 mol feed per mol of product, and that increases even more for reasonable values of tails analysis (in some plants the feed/product ratio has reached nearly 4 x 104). At peak Canadian production, 800t year-1, this amounted to feeds of 3 x 107t year-1. Clearly that figure demands a cheap and easily accessible feed (i.e. water), or alternatively, requires deuterium production to be parasitic on some large industrial process, for example the production of NH3 for fertilizer, or petrochemical processing. 

An isotope of hydrogen having a nucleus (referred to as the deutron) consisting of one proton and one neutron. Deuterium is a stable isotope (symbolized by or D) having an atomic weight of 2.0140 amu and a natural abundance of 0.015% relative to all hydrogen isotopes. 

The only drawback to NMR is its low sensitivity. Concentrations in the millimolar range are sometimes required, although with computer enhancement techniques (such as Fourier transform) signals at 10 -10 M concentrations can be detected. This is especially important for nuclei that have a low natural abundance, such as (1.1%) or deuterium, (0.015%). 

Martin GJ, Martin ML (1981) Deuterium labeling at the natural abundance level as studied by high field quantitative H NMR. Tetrahedron Lett 22 3525... 

To measure isotope effects it is not always necessary to prepare deuterium-enriched starting compounds. It can also be done by measuring the change in deuterium concentration at specific sites between a compound containing deuterium in natural abundance and the reaction product, using a high field nmr instrument.59... 

Although you would expect deuterium (D) NMR to be every bit as useful as NMR, it is not carried out routinely as deuterium has a natural abundance of 0.015% and very low sensitivity. Furthermore, as the spin is greater than %, it is a quadrupolar nucleus and the signals are usually broad. Deuterium shows signals in the same chemical shift range as H (5 0-12), and NMR is most often used in experiments using D-labelled compounds to investigate reaction mechanisms. 

All of the H-n.m.r. spectra, and most of the 13C-n.m.r. spectra, were recorded for solutions in deuterium oxide, on the tacit assumption that the composition in that solvent would be the same as that in natural-abundance water. It is by no means certain that this assumption is valid,... 

Deuterium (2H). The natural abundance is very low so that use of 2H-labeled compounds is practical for study of metabolism, e.g., for following an 2H label in glucose into products of fermentation455 or in mammalian blood flow 456 Deuterium NMR has been used extensively to study lipid bilayers (Chapter 8). 

Deuterium is abundant, naturally occurring and in wide use now as D20 in heavy-water-mo derated reactors. Tritium is a radioactive isotope with a 12.3-year half-life and does not occur in natnre. Tritium emits an electron and decays to stable helium-3. 

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