Pd/C-H2-Catalysed Deuterium Exchange Reaction of the Benzylic Site in D2O
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Abstract:
Pd/C is found to catalyse efficient and chemoselective exchange of deuterium derived from D2O with hydrogens on a benzylic carbon in the presence of a catalytic amount of hydrogen at room temperature.Keywords:
Hydrogen–deuterium exchange
Carbon fibers
Kinetic isotope effect
Interstitial defect
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Hydrogen–deuterium exchange
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Pyrrole
Hydrogen–deuterium exchange
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The ion-induced release of hydrogen and deuterium from AXF-5Q graphite has been measured for hydrogen and deuterium ions with energies near 200 eV. The experimental data obtained are analyzed to determine the ion-induced release cross section and the location and release of the additional retained hydrogen (i.e., that not retained in the surface layer). Two different approaches were used to model the release of the additional hydrogen. The model that treats the additional retained hydrogen (deuterium) as having migrated deeper into the graphite on grain surfaces produces results that are consistent with experimental data, whereas the model that treats the additional retained hydrogen as being trapped in a codeposited layer produces results that are inconsistent with experimental data. The ion-induced release cross section is determined to be in the range (1–2)×10−17 cm2.
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An apparatus for measuring exchange equilibria and rates of exchange of molecular deuterium with hydrogen containing compounds is described. The gas density balance is used to analyze the hydrogen-deuterium mixtures. Results on the equilibria H2+2DCl = D2+2HCl, H2+DCl = HD+HCl are reported which check the theoretical values to within the limits of the experimental errors.
Hydrogen–deuterium exchange
Hydrogen chloride
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We discuss the variant of a method for the determination of absolute hydrogen atom densities based on the absorption of the hydrogen Lyman-alpha line. Previously, we demonstrated that by using a simple vacuum ultraviolet spectrometer with low resolution an accuracy of better than 50% for the determined hydrogen atom densities can be obtained for transmissions ranging from 10% to 90%. For transmissions outside of this range excessive errors occur, thus, limiting the usefulness of the method to a certain range of hydrogen atom densities, depending on absorber length and temperature. This range of atomic hydrogen densities accessible to the measurement can be extended by the new method that consists of using well-defined mixtures of hydrogen and deuterium in the absorber. Using a source of either hydrogen or deuterium Lyman-alpha radiation, only one sort of atoms contributes to the absorption. Thus, by selecting an appropriate mixture of hydrogen and deuterium, the range of atom densities accessible to the measurement can be extended to higher densities. Using well-defined mixtures ranging from 1% hydrogen in deuterium to 2% deuterium in hydrogen as absorbers, we were able to determine hydrogen atom densities up to a factor 100 higher than those measured previously in pure hydrogen. Using mixtures down to the natural abundance of deuterium in hydrogen, the measurement of even higher atom densities seems possible. The effect of the difference of the energies of dissociation of hydrogen and deuterium has been investigated using a computer model of relevant chemical processes. In most situations, this effect is smaller than the experimental error. The main limitation of the method is its sensitivity to absorption by impurities, as many molecular gases absorb Lyman-alpha radiation.
Hydrogen atom
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Pd/C is found to catalyse efficient and chemoselective exchange of deuterium derived from D2O with hydrogens on a benzylic carbon in the presence of a catalytic amount of hydrogen at room temperature.
Hydrogen–deuterium exchange
Carbon fibers
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Deuterium/hydrogen exchange in combination with mass spectrometry (DH MS) is a sensitive technique for detection of changes in protein conformation and dynamics. Since temperature, pH and timing control are the key elements for reliable and efficient measurement of hydrogen/deuterium content in proteins and peptides, we have developed a small, semiautomatic interface for deuterium exchange that interfaces the HPLC pumps with a mass spectrometer. This interface is relatively inexpensive to build, and provides efficient temperature and timing control in all stages of enzyme digestion, HPLC separation and mass analysis of the resulting peptides. We have tested this system with a series of standard tryptic peptides reconstituted in a solvent containing increasing concentration of deuterium. Our results demonstrate the use of this interface results in minimal loss of deuterium due to back exchange during HPLC desalting and separation. For peptides reconstituted in a buffer containing 100% deuterium, and assuming that all amide linkages have exchanged hydrogen with deuterium, the maximum loss of deuterium content is only 17% of the label, indicating the loss of only one deuterium molecule per peptide.
Hydrogen–deuterium exchange
Amide
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Abstract Dimethylpyridines undergo deuterium‐hydrogen exchange when heated in deuterium oxide containing potassium carbonate at ring positions 2 and 6 when these positions are unsubstituted and at methyl groups located at ring positions 2,4, and 6 exclusively.
Hydrogen–deuterium exchange
Potassium carbonate
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We present the investigation of hydrogen/deuterium (H/D) exchange of carbohydrates ions occurring in the electrospray ion source. The shape of the deuterium distribution was observed to be considerably dependent on the temperature of the ion transfer tube and the solvent used. If deuterated alcohol (EtOD or MeOD) or D2O/deuterated alcohol is used as an electrospray solvent, then for high temperatures (>350 °C), intensive back exchange is observed, resulting in ∼30% depth of the deuterium exchange. At low temperatures (<150 °C), the back exchange is weaker and the depth of the deuterium exchange is ∼70%. In the intermediate temperature region (∼250 °C), the deuterium distribution is unusually wide for methanol and bimodal for ethanol. The addition of 1% formic acid results in low (∼30%) depth of the deuterium exchange for any temperature in the operating region. The bimodal distribution for the ethanol can be possibly explained by the presence of differently folded gas-phase ions of carbohydrates.
Hydrogen–deuterium exchange
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