H/D exchange, reactions

Solvent for Base-Catalyzed Reactions. The abihty of hydroxide or alkoxide ions to remove protons is enhanced by DMSO instead of water or alcohols (91). The equiUbrium change is also accompanied by a rate increase of 10 or more (92). Thus, reactions in which proton removal is rate-determining are favorably accompHshed in DMSO. These include olefin isomerizations, elimination reactions to produce olefins, racemizations, and H—D exchange reactions. 

TABLE 11. Relative stabilities derived from H/D exchange reactions of a-sulfinyl carbanions... 

One commonly used procedure for studying the steric stability of the carbanion is comparison of the rate of base-catalyzed H/D exchange reaction (kel) on the chiral carbon with the rate of racemization (fcrac). By this comparison, inversion, racemization or... 

TABLE 16. Base-catalyzed H/D exchange reactions of sulfonyl compounds 70-73... 

The hydrogenase-like proteins are known to catalyze the H/D exchange reaction, typical of hydrogenase (58). It remains to be determined to what extent the hydrogen binding site of these proteins re-... 

Some representative data on base-catalyzed H/D exchange reactions of several optically active sulfonyl compounds 70-73 are listed in Table 16. In all these reactions, 10. 

N. A. Zorin, B. Dimon, J. Gagnon, J. Gaillard, P. Carrier, P. M. Vignais (1996) Inhibition by iodoacetamide and acetylene of the H-D exchange reaction catalyzed by Thiocapsa roseopersicina hydrogenase. Eur. J. Biochem., 241 675-681... 

The ESR signal due to 02 demonstrates that the heterolytic activation of R-H has occurred. An interesting feature of the H-D exchange reactions over the MgO surface is the low activation energy, i.e., Ea 2 kcal/mol. This is lower than the gas phase for the reaction H + D2 —> 2 D + HD. The high activity of the ionic oxides has been attributed to the presence of basic sites and in particular to defect sites that are formed during the oxide preparation that persist even at elevated temperatures.41 42... 

Elimination Reactions, Cleavage and Rearrangement Reactions, Isomerism and H/D Exchange Reactions... 

Hydro gen-deuterium exchange in chiral ion—dipole complexes. The rates of gas phase H/D exchange reactions are most conveniently measured in a FT-ICR cell in which the ions can be trapped for extended periods of time in the presence of a fixed... 

Vignais, P. M., Dimon, B., Zorin, N. A., Colbeau, A. and Elsen, S. (1997) HupUV proteins of Rhodobacter capsulatus can bind H2 Evidence from the H-D exchange reaction. J. Bacteriol., 179, 290-2. 

To initiate an H/D exchange reaction, a protein sample, initially in non-deuterated buffer, is incubated in a buffer with 50-90% mole fraction deuterated water. There are almost no restrictions on reaction conditions which allow exchange behavior to be studied as a function of protein and buffer composition, solution pH, and in the presence and absence of ligands. To follow the deuterium buildup of individual amide hydrogen or sets of hydrogens, several on exchange time points are sampled for each condition. 

The exponential decay of the strongest carbonyl absorption is presented in Figure 6.16A. The natural logarithm of the relative absorption of the carbonyl frequency at 2020 cm versus time is presented in Figure 6.16B, indicative of first-order kinetics in the rhodium concentration and the pressure of FI2 and the H/D exchange rate was 1140 h Although the H/D exchange reaction was very... 

The formation of a considerable amount of HDCO(g) suggests that the H-D exchange reaction via CHO(a) species. 

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