Deuterated Deuterium-exchange experiments

A study of the MS" fragmentation of resveratrol and piceatannol was performed by deuterium exchange experiments and accurate mass measurements (Stella et al., 2008). The product ion spectrum of the [M-H] ion of tram-rcsvcratrol at m/z 227, is reported in Fig. 6.6, and that of piceatannol at m/z 243 are shown in Fig. 6.7. Fragmentation patterns of the [M-H] ion of two compounds are reported in Fig. 6.8. Fragmentations were confirmed with deuterium labeling experiments by dissolving the standard compounds in deuterated methanol The... 

In another series of experiments (59), toluene solutions of 1-(1,2-C B,oHu)P(CH ) were reacted with deuterium gas in the presence of (Ph3P)3RuHCl. Mass spectral evidence proved that up to eight deuterium atoms had been introduced into the phosphine. Since only four BH exchange sites could possibly be involved in deuterium exchange which proceeded only through ortho-metalation intermediates, an intermolecular, reversible oxidative addition of catalyst to terminal B—H bonds was indicated. Indeed, further work proved that under the same conditions 1,2-, 1,7-, and 1,12-C2BioHi2 carboranes could be totally deuterated at boron... 

Experiments in which azocumene was thermol.yzcd on partially deuterated silica, and experiments in which l-d was thermolyzed or photolyzed on non-deuterated silica, showed that neither cumene nor cumyl radicals exchange deuterium with the surface. With this fact established, the combined primary e-nd secondary... 

Knowles and coworkers also performed competitive deuterium washouts (i.e., an equilibrium perturbation-type washout experiments), using deuterated substrates in H2O solutions, which yielded the (V/K) values for both directions [85]. Further confirmation of these KIE values was validated by a double competitive deuterium washout experiment, in which both substrates are Ca deuterated, which yielded a ratio of the two (V/K) values. The authors were also able to perform competitive deuterium washout experiments where direct proton exchange between free enzyme forms is rate-limiting (i.e., at high substrate concentration the lower manifold of Fig. 7.16 is dominant). This experiment indicated that interconversion of free enzyme forms is very similar to the racemization manifold, in that loss of proton from one form yields the other free enzyme form, with water acting as the catalyst. Fig. 7.16. 

Modification of deuterated Raney nickel with L-glutamic acid also results in lower deuterium contents in the products but does not drastically alter deuterium distributions (experiments D28B and D28C). In contrast to other work on C=C double bonds [12], little asymmetric induction was obtained. For example, the deuteriumation of III over MRNiD(A) and IV over MRNiD(B) produced products with optical purities of 0.4 and 1.1% respectively. Low enantioselectivi-ties from these catalysts might result from processes associated with extensive exchange. 

The version of the selective-deuteration experiment most widely practiced involves the use of deuterium oxide as the solvent for n.m.r. measurements, instead of water without this procedure, the interpretation of n.m.r. spectra of sugars in aqueous media is generally diflBcult. Even so, prior deuteration of labile protons (such as those of hydroxyl and amino groups) by a series of exchange experiments is necessary before the residual-water peak can be lessened to an acceptable intensity. Other, potentially acidic protons can be similarly exchanged by deuterium through repeated lyophilization from deuterium oxide. 

The atom % 2H values of the solvent-fractionated products are also shown in Table I. In previous hydrogenation experiments conducted without the use of a donor solvent (1,18), deuterium incorporation increased from the most soluble oil fraction to the insoluble residue. In E10 and El9, contact of the coal with Tetralin resulted in a uniform incorporation of deuterium in almost all of the four product fractions. In El9, the BMI fraction s high value of 61 atom % 2H may be due to direct gas-phase exchange and deuteration. 

---