Deuterium-free samples

Deuterium-Free Samples and Solvent Suppression Techniques... 

Density. Measurement of the density of water by pycnometry is the classical method (30) for estabHshing deuterium concentrations in heavy water. Very precise measurements can be made by this method, provided the sample is prepared free of suspended or dissolved impurities and the concentration of oxygen-18 in water is about 0.2 mol %. However, in nearly all heavy water manufactured since 1950 in the United States, the... 

In a very detailed EPR study, Pakulis and Jeffries (1981) and Pakulis (1983) investigated a large number of ultra-pure germanium crystals that were grown in vacuum or in a hydrogen or deuterium atmosphere. Several of the samples were dislocation free. The sensitivity of EPR was greatly... 

Fig. 2. Deuterium (D) and free carrier concentration (n) profiles of a n-type GaAs Si bulk sample exposed to a rf deuterium plasma for 90 min. at 250°C (rf power density = 0.2W/cm2). The loss of free carriers occurring only in.the deuterated region suggests that hydrogen plays a major role in the free carrier concentration decrease. The deuterium concentration drop in the near surface region is attributed to a deuterium out-diffusion during the cooling stage of the sample with the plasma off. J. Chevallier et al., Materials Science Forum, 10-12, 591 (1986). Trans. Tech. Publications.

While checking a sample of 2,5-anhydromannose-6-P for fructose-6-P by incubating it with phosphofructokinase and MgATP, we discovered that this aldehyde, which is sterically hindered from forming an internal hemiacetal, induced an ATPase activity (6). Since aldehyde hydration shows a large inverse equilibrium isotope effect of 0.73 when the hydrogen on the carbonyl carbon is replaced by deuterium (7,8), 2,5-anhydroman-nose-6-P-l-d will be 60% hydrated, compared to 52% hydration of the unlabeled aldehyde. If the free aldehyde were the activator, 48% of the unlabeled and 40% of the deuterated compound would be active, and a normal deuterium isotope effect of 0.48/0.40 = 1.2 would be seen on V/K (the apparent first order rate constant) for the activator, while if the hydrate were the active form, an inverse isotope effect of 0.52/0.60 = 0.87 would be seen. The observed value of 1.23 0.03 showed that the free aldehyde and not the hydrate was the activator (6). 

With this method, Andersson and Rosen [169] recently investigated the adsorption of hydrogen or deuterium and oxygen on neutral platinum clusters and discovered the catal3dic water formation on the free clusters. Figure 1.30 displays mass spectra obtained with different partial pressures of hydrogen and oxygen in the separate collision gas cells. Panel a in Fig. 1.30 shows a mass spectrum of pure Pt clusters with no reactive gas in the collision cells. The mass spectrum in panel b was sampled after the cluster ions passed reaction cell 1 filled with 0.14 Pa of O2. The additional peaks in the mass spectrum... 

Equimolar mixtures of toluene and benzene were passed over beds of DHY at low temperatures (25-60°) in experiments where the two aromatics of different reactivity competed for the electrophilic deuterium (75). The distribution of deuterium between toluene and benzene (apparent ACeHsCHs/fcCeHe) and among the ring positions of the toluene-di samples was determined. A plot of log pt vs selectivity factor (St) for these data from the competitive experiments at 25-60° (Fig. 20, black circles) falls on the line obtained from a study of 47 electrophilic substitution reactions by H. C. Brown and associates (83). The partial rate factors pt and mt give the rate of substitution of the para position and one of the meta positions in toluene, relative to the rate of substitution of one of the six equivalent ring positions of benzene. Points a, b, c, d, and e fall quite close to the line, which represents a linear free energy relationship in both positional and substrate selectivity. 

The usual solvents are deuterium oxide for free cyclitols, and cliloro-form-d for their nonpolar derivatives, such as acetates. The use of methyl sulfoxide may be advantageous. When necessary, samples of one milligram or less may be examined, using special micro-cells or micro-tubes... 

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