I Isotope Enrichment

Carnivores rely on a protein-rich diet and produce new biomass primarily from dietary amino acids, although the enzymes required for de novo amino acid synthesis are present (Garmes et al., 1998). Bone collagen, muscle (meat) and apatite were analyzed for a set of modern southern African herbivores and carnivores (Lee-Thorp et al., 1989). The isotopic analyses showed i C enrichment in bone collagen, apatite and muscle, and depletion in lipids. Difference in values between herbivores and carnivores indicates a trophic effect, which for carbon in bone collagen is 2.5-3%o (Fig. 2). 

The [NiFe] hydrogenase from D. gigas has been used as a prototype of the [NiFe] hydrogenases. The enzyme is a heterodimer (62 and 26 kDa subunits) and contains four redox active centers one nickel site, one [3Fe-4S], and two [4Fe-4S] clusters, as proven by electron paramagnetic resonance (EPR) and Mosshauer spectroscopic studies (174). The enzyme has been isolated with different isotopic enrichments [6 Ni (I = I), = Ni (I = 0), Fe (I = 0), and Fe (I = )] and studied after reaction with H and D. Isotopic substitutions are valuable tools for spectroscopic assignments and catalytic studies (165, 166, 175). 

The benefits of using ionic compounds in microwave-enhanced reactions led us to explore the possibility of using ionic solvents i.e. ionic liquids, as donors for both deuterium and tritium. Whilst D20 is now relatively inexpensive and available at high isotopic enrichment, tritiated water is usually employed, for safety reasons, at low isotopic incorporation (we typically use HTO at 5 or 50 Ci mLT1 specific activity corresponding to 0.2-2% isotopic incorporation). This is a serious limitation when there is a need to provide compounds at high specific activity. 

C is present in 1.1% natural abundance and so approximately n% of a M (CO) complex is isotopically labelled. General infrared instrumental improvements have made studies on such natural-abundance species perfectly feasable, for most i>(CO) infrared peaks are rather narrow in hydrocarbon solvents. The commercial availability of 13 CO and C180 (substitution by either of which has very similar frequency perturbation consequences) has led to studies of isotopically enriched species. Perhaps because of the emphasis on studies of v(CO) vibrations, little work has been reported... 

I 1 Modern Methods for the Expression of Proteins in Isotopically Enriched Form... 

I 7 7 MAS Solid-State NMR of Isotopically Enriched Biological Sample. ... 

The primed or unprimed symbols refer to isotope fractions. The single stage separation factor for infinitesimal product removal (yi/zj 0), (rj)0, is given the symbol a . The i s index the stage number. Most often a is close to unity and it is convenient to define the isotope enrichment factor (the single stage enrichment factor), e, between the i th and (i + l) th stage... 

Regardless of the ultimate sources of these compositions, these results clearly show that strongly isotopically fractionated Li from crustal sources plays a role in the mantle. Processes active in subduction zones appear to be cardinal in the control of the Li isotopic composition of different parts of the mantle. The results to date imply that both isotopically enriched (8 Li > MORE) and depleted (5T i < MORE) material are available for deep subduction, and that areas of the continental lithosphere may retain these records on long time scales. 

Figure 2.3 Changes in the heavy isotope content of oxygen and hydrogen in the urine with time after administration of The and 0 are diluted by the formation of H2O from oxidation of fuels and particularly that ingested in food and drink. The 0 in water is diluted from the production of CO2 via the oxidation of the fuels. The difference in the slopes indicates the rate of CO2 production. The label heavy isotope content is actually the isotopic enrichment. Physical activity, for example, increases fuel oxidation (i.e. respiration) and therefore greater dilution of...

Os-191 is produced by neutron irradiation of isotopically enriched 0s-190 (isotopic composition 0s-190, 97.8 o Os-188, 0.47 o Os-192, 1. 02 o). Irradiations are currrently performed at the Oak Ridge National Laboratory in the High Flux Isotope Reactor (HFIR) at a neutron flux of 2.5 x 10 n/cm -s. The routes to the various nuclides produced during irradiation of the 0s-190 target and the neutron cross-section values (2 ) are summarized below (Scheme I). 

Typical results for the overall isotopic separation for Linde X exchanged essentially completely with praseodymium are shown in Table I. Generally, 50-60% of the neutron capture product, 142Pr, was eluted from the zeolite, along with about 1% of the unreacted 141Pr target. In most cases, the isotopic enrichment factor (the ratio of specific activity of metal in the eluate to the average specific activity of all the metal) was in the... 

Fyfe et al. (354) have combined 31P and 13C CP/MAS NMR studies first to identify the polymer-immobilized catalyst (Scheme 4, compound ii) formed from the precursor i by treatment with Pd(PPh3)4 and, second, to monitor the carbonyl insertion reaction using 13C-enriched CO to yield iii. The use of isotopically enriched CO was required so as to record meaningful signals above those emerging from the carbon-rich polymer background. 

Gallagher, R. T., Wilson, I. D., and Hobby, K. (2008). New approach for identification of metabolites of a model drug Partial isotope-enrichment combined with novel mass spectral modeling software. In Proceedings of the 56th ASMS Conference on Mass Spectrometry and Allied Topics. ASMS, Denver, CO. 

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