Deuterium enrichment

Fig. 6. Deuterium enrichment through a conceptual trophic chain.

Sandford S. A. (2002). Interstellar processes leading to molecular deuterium enrichment and their detection. Planetary and Space Science 50 1145-1154... 

Dual Temperature Exchange The GS Process for Deuterium Enrichment... 

Two mechanisms have been proposed to account for the deuterium enrichment (1) for organic molecules, high D/H ratios can be explained by ion molecule reactions that occur in interstellar space and (2) for the phyllosilicates the enrichment can be produced via isotope exchange between water and hydrogen (Robert et al. 2000). 

Deuterium-enriched water in Martian meteorites (Leshin et al., 1996 Leshin, 2000) indicates that some water has been lost from the atmosphere, but the fate of most of the... 

Delsemme, A. H. (1999) The deuterium enrichment observed in recent comets is consistent with the cometary origin of seawater. Planetary and Space Science, 47, 125-131. 

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... 

Originally it was stated that the formation of 2-bromo-l,8-naphthyridine from 8-bromo-1,8-naphthyridine occurred for 27% via the SN(AE) ek mechanism.10-29 However, when the isotope effect—calculated from the deuterium enrichment in the recovered starting material-was taken into consideration, 45% of telesubstitution was found.21-24... 

The naphthalene cation radical can react with the hydrogen atom. The 1-hydronaphthalene cation resulting from this reaction is more stable than the reactants. This process has no activation barrier. After its formation, the 1-hydronaphthalene cation can absorb a photon and lose one of the two hydrogen atoms on carbon 1, since these hydrogens are more weakly bound than the aromatic hydrogens. Because the C-D bond is slightly stronger than the C-H bond, the reaction mentioned here can lead to some deuterium enrichment (Bauschlicher 1998). 

It is the position ortho to the maximum number of substituents that is most electron-rich in an anion radical of a starting aromatic compound. Being less basic species, anion radicals exhibit a more selective primary isotope effect than their more basic (and therefore more reactive) carbanion counterparts. As a consequence, the deuterium enrichment in the me la position is usually higher than in the ortho position. 

C60 and C70 fullerenes were obtained from Southern Chemical L.L.C. and were both 99.9+% pure grade. Toluene and n-hexane were purchased from Aldrich as well as DC1 37% in D20 (deuterium enrichment 99%). Zn dust was from Aldrich as well and was characterized by a particle size <10 pm. 

As we will see, some anomalies in the isotopic composition of carbon, hydrogen and oxygen can be explained on the basis of this assumption, and we will start the discussion with the deuterium-rich matter in carbonaceous chondrites. This deuterium-rich matter is essentially present as complex macromolecules 70 73 96 97). The carbon in these samples is essentially normal 76,98). For some polymer-type fractions, the deuterium content is up to 32 times higher than the galactic value (D/H 2 x 10s in the number of atoms per cubic centimeter). High deuterium enrichments are known in interstellar molecules and the mechanism of this enrichment is fully understood. For an excellent review dealing with interstellar chemistry, see the paper by Winnewisser 99) and the previously mentioned book by Duley and Williams 13). 

In 1981, Geiss and Reeves 100) suggested that the deuterium enrichment observed in the organic macromolecular compounds could be explained on the basis of a suggestion made by the same authors in 1972 101 , i.e. the survival of interstellar molecules [synthesised at low temperatures (10—50 K) by ion-molecule gas-phase reaction] in chondritic matter. 

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