Deuterium uptake

The rate of hydrogen (or deuterium) uptake with homogeneous catalysts is usually faster in benzene-alcohol (methanol or ethanol) solvent systems or in acetone than in tetrahydrofuran or in benzene alone. Whereas... 

The rhodium catalyst (46 mg) is dissolved in acetone (10 ml) in a microhydrogenation apparatus which is then flushed three times with deuterium gas. After stirring the solution in an atmosphere of deuterium for about 1 hr the deuterium uptake ceases and constant pressure is attained. 5a-Cholest-2-ene (136, 19.5 mg) is added and the stirring continued until deuterium uptake ceases (about 3/4 hr). The solvent is evaporated to dryness and the residue is extracted with hexane and the resulting solution filtered through a small alumina column (3 g, activity 111). Evaporation of the hexane gives 2, 3 -d2-5oc-cholestane (137) 18 mg, 92% mp 78-79° isotope composition 94%d2,5%d, andl%do. ... 

Some other work of a semi-quantitative nature has been carried out using hydrogen bromide but none of it yields usable rates. For example, the relative rates of deuterium uptake in phenylated alkanes was measured and showed the expected decrease in reactivity with increasing phenyl group substitution580. 

CH2 groups are not acidic enough for this base (2) recovered 18 was racemized 20 is symmetrical and can be attacked equally well from either side (3) when the experiment was performed in deuterated solvent, the rate of deuterium uptake was equal to the rate of racemization and (4) recovered 18 contained up to three atoms of deuterium per molecule, though if 19 were the only ion, no more than two could be taken up. Ions of this type, in which a negatively charged carbon is stabilized by a carbonyl group two carbons away, are called homoenolate ions. 

Coal Products Isotopic Distribution by Structural Position. Other workers have also investigated deuterium uptake in coal pro-ducts by structural position. Schweighardt, et al. (26) examined a centrifuged liquid product from a Synthoil run which was heated to 450°C with deuterium gas, Kershaw and Barrass (27) examined the products from the reaction of coal with deuterium gas using SnCl2 as catalyst, and Franz (10) examined the products from the reaction of a subbituminous coal with Tetralin-1,l-d2 at 427°C and 500°C. 

Despite its smaller cross section, the other nuclear reaction used for deuterium analysis, the (2H,p) reaction, can be made extremely sensitive, as Myers (1987) has shown. The key is that the proton is emitted with such high energy, 15 MeV, that the detector can be mounted behind the sample wafer (Fig. 1) ensuring a very low background count rate and hence good sensitivity. Myers measured deuterium amounts as low as 1012 atoms/cm2 in his study of deuterium uptake by Si02. However, the depth resolution of this measurement was poor, l jum. 

Figure 3. Hydrogen/deuterium uptake during nitrosobenzene hydrogenation...

Hydrogenation was a zero order reaction in the olefin over each catalyst up to more than 60% conversion in complete agreement with the observation of Boudart et al [11,12]. For 1-hexene hydrogenation no turnover frequency data were found over any of the transition metal catalysts and under comparable conditions. For 1-hexene initial rates were determined, because isomerization occurs over Pd [13] and the non-terminal olefins hydrogenate slower. Indeed, deuterium uptake decreased appreciably after a short initial period. A similar effect was found for Rh as well, but over Ft, no decrease in rate was observed in complete accordance what was expected [13]. The hydrogenation of both olefins showed mild structure sensitivity over Pd catalysts, with an apparent maximum in hydrogenation rate at 65% dispersion. 

Figure 10.6 (a) Deuterium uptake D/M versus the number of metal atoms for clusters of Pt , Ni +, and Rh . With permission from Springer Science and Business Media [39] (b) largest number of hydrogen atoms present in... 

Deuterium chemisorption on platinum clusters is difficult to observe by product analysis due to the high IP (> 6.42 eV) of the clusters, the high mass of the metal, and the large number of naturally occurring isotopes of Pt. The amount of deuterium uptake is estimated from the increase in the widths of the observed mass peaks. No reaction is observed on the atom through the tetramer either by depletion of the metal ion signal or by product formation. 

Protein-ligand interactions can also be detected by comparison method as long as there is change in the deuterium uptake.162 The baseline HX data for individual proteins are obtained first and compared to similar data for those proteins in the complex. The location of changes due to complex formation is identfied by digesting the proteins and comparing the deuterium uptake for the two sets of peptides. 

Whatever approach is taken to characterising a gravimetric system, comparison with deuterium uptake by the same sample is a valuable check on the measured uptake of protium. 

Time (min) Centroid (m/z) Centroid (Da) Reiative deuterium uptake ... 

Figure 1.10 MS spectra of a peptide (displaying EX2 kinetics) from an HX-MS experiment with horizontal lines indicating the centroid m/z value at three labeling time points, (b) tabulated results for deuterium uptake of peptide In (a),(c) deuterium uptake plot displaying relative deuterium content of peptide In (a)...

The relative deutraium uptake is determined by the dififa-ence in the average mass at each time point and the undeutraated control. To determine the absolute deuterium uptake. Equation 1.14 is used where the deutraium uptake is adjusted according to the back-exchange during HX-MS analysis ... 

Figure 4,2 The repeatability and intermediate measurement precision IMP) of a robotic HX-MS apparatus. The study is based on replicant measurements of bovine ubiquitin deuterium uptake after 30s immersion in D O. (a) The peptide map of ubiquitin, comprising 29 peptides (100% protein coverage) observed in 39 analyzed peptide ions, used for the HX-MS analyses (see footnotes 2, 3 and Ref [27]). (b) The average fractional D uptake observed for each of the 39 analyzed peptide ions. As shown in the key, each symbol presents the average of 20 measurements conducted on Day 1, 2, and 37. Bars on each symbol indicate the standard deviation (SD) when it exceeds the symbol size, (c) Repeatability and IMP for each peptide set, plotted as the SD of the D fraction measurements obtained for each peptide. The horizontal solid line in each group indicates the mean SD of the peptide set (780 measurements)...

The graphs in Figure 4.2 illustrate the terms repeatability and IMP. These data were obtained by the authors during an evaluation of their robotic HX-MS system. - The experiments measured the deuterium uptake by bovine ubiquitin after immersion in D O for 30 s. This short exchange period... 

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