Nitrogen natural abundance

Although the natural abundance of nitrogen-15 [14390-96-6] leads to lower sensitivity than for carbon-13, this nucleus has attracted considerable interest in the area of polypeptide and protein stmcture deterrnination. Uniform enrichment of is achieved by growing protein synthesi2ing cells in media where is the only nitrogen source. reverse shift correlation via double quantum coherence permits the... 

Binkley, D., Sollins, P. and McGill, W.B. 1985 Natural abundance ofnitrogen-15 as a tool fortracing alder-fixed nitrogen. Soil Science Society of America Journal 49 444-447. 

Handley, L.L. and Raven, J.A. 1992 The use of natural abundance of nitrogen isotopes in plant physiology and ecology. Plant Cell Environment 15 965-985. 

Steele, K.W. and Daniel, R.M.J 1978 Fractionation of nitrogen isotopes by animals a further complication to the use of variations in the natural abundance of for tracer studies. Journal of Agricultural Science, Cambridge 90 7-9. 

Nitrogen-14, with its natural abundance of 99.6%, is one of the most ubiquitous and, until recently, least studied NMR-active nuclei. Due to the integer spin number (/ = 1), its single-quantum transitions are affected by first-order quadrupolar broadening, which in most materials is on the order of a few megahertz. A new class of 2D HETCOR protocols has been recently developed, which makes it possible to indirectly observe well-resolved 14N sites via their spin-1/2 neighbors and obtain the related parameters of the quadrupolar tensors. 

Rennie, D. A., Paul E. A. Johns, L. E., Natural Nitrogen-15 Abundance in a Wide Variety of Soils, Canadian Journal of Social Science, 1976, 56, 43-50. 

Nitrogen is an A + 1 element, while the natural abundance of 15N isotope constitutes about 0.4% of 14N. Since besides nitrogen only carbon contributes notably to the intensity of the A + 1 peak, it is possible to estimate the number of nitrogen atoms in the molecule on the basis of the nitrogen mle and the differences in the abundances of 13C ii 15N isotopes. 

The elements whose isotopes are routinely measured with gas inlet mass spectrometers are carbon (12C and 13C, but not 14C), oxygen (160, 170, l80), hydrogen ( H, 2H, but not 3H), nitrogen (14N and 1SN) and sulphur (32S, 33S, 34). Stable isotopes of H, C, N, O, and S occur naturally throughout atmosphere, hydrosphere, lithosphere, and biosphere. They are atoms of the same elements with a different mass. Each element has a dominant light isotope with the nominal atomic weight (I2C, 160,14N, 32S, and H) and one or two heavy isotopes (l3C, nO, 180, 15N, 33S, 34S, and, 2H) with a natural abundance of a few percent or less Table 1). 

The nitrogen kinetic isotope effect of 1.0197 found using the substrate with the natural abundance of nitrogen isotopes corresponds to an isotope effect of 1.04 for the reaction of the doubly labelled compound. Thus, the nitrogen isotope effects found using two different analytical techniques to measure the isotope effect are in excellent agreement. 

ISOTOPES There are 19 isotopes of nitrogen, two of which are stable. The stable ones and their proportion to the natural abundance of nitrogen on Earth follow N-14 = 99.634% and N-15 = 0.366%. The other 17 isotopes are radioactive and man-made in nuclear reactors and have half-lives ranging from a few nanoseconds to 9.965 minutes. 

Hoering TC (1955) Variations in nitrogen-15 abundance in naturally occuring substances. Science 122 1233... 

Saino T, Hattori A (1987) Geophysical variation of the water column distribution of suspended particulate organic nitrogen and its N natural abundance in the Pacific and its marginal seas. Deep Sea Res 34 807-827... 

Sweeney RE, Kaplan IR (1980) Natural abundance of as a source indicator for near-shore marine sedimentary and dissolved nitrogen. Mar Chem 9 81-94 Sweeney RE, Liu KK, Kaplan IR (1978) Oceanic nitrogen isotopes and their use in determining the source of sedimentary nitrogen. In Robinson BW (ed.) DSIR Bull 220 9-26 Swihart GH (1996) Instrumental techniques for boron isotope analysis. Rev Miner 33 845-862 Swihart GH, Moore PB (1989) A reconnaissance of the boron isotopic composition of tourmaline. Geochim Cosmochim Acta 53 911-916... 

The two isotopes N (7 = 1) and N (7 = 1/2) both have only small values of S and thus belong to the class of insensitive nuclides. Although the electric quadrupole moment of N is relatively small and the signals are therefore not very greatly broadened, the overwhelming majority of nitrogen NMR studies are now performed on N using natural abundance samples, despite the difficulties involved. The spread of chemical shifts for... 

For the much less sensitive 15N nucleus HSQC (preferred over HMQC for nitrogen) is often the only way to obtain spectra at natural abundance. 

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