Deuterium oxide , inhibition

Thiols can also be converted to disulfides, as in the CdS-photocatalyzed conversion of cysteine to cystine In the latter reaction, the uptake of oxygen was pH dependent. Since the reaction rate was not increased in deuterium oxide and was not decreased by added azide, the authors conclude that singlet oxygen is not involved. Since superoxide dismutase inhibited the conversion, a photoinduced electron transfer is probably responsible for the observed transformations. Such organosulfide oxidations may be environmentally important since naturally occurring hematite suffers a photoassisted dissolution in the presence of thiols... 

Reaction with deuterium oxide, O-deuterated alcohols or acids is commonly used to provide evidence for the formation of organomagnesium compounds (e.g. see Ref. [3]). Although the presence of water normally inhibits the reaction of organic halides with magnesium, it is noteworthy that under appropriate conditions a Barbier procedure was successful [4] ... 

The pathway by which the hydrogen chloride inhibits the telomerization and thus produces mono-ethylcyclohexane was supported by use of a solution of deuterium chloride (38%) in heavy water (99% deuterium oxide) as promoter under the standard conditions. The reaction mixture included 1.15 mols of cyclohexane and... 

An indication of the importance of the steric inhibition of resonance in aromatic substitution reactions has been gained by a study of the exchange reaction of dialkylanilines with deuterium oxide.21 With di-methylaniline, for example, the ortho and para hydrogen atoms equilibrate readily with deuterium oxide. This reaction, like most aromatic substitution reactions (see Chapter 13), is believed to proceed by the attack of a positively charged fragment (in this case a hydrogen or deuterium ion) at a point of high electron density. Consequently, the ease with which equilibration occurs can be taken as an approximate measure of the contribution of forms such as XLV or XLVI to the structure of the... 

This notion was supported by additional studies in which platelet water was totally exchanged with deuterium oxide (D2O) (29). D2O had been previously shown to block the release of Ca2 from the sarcoplasmic reticulum of barnacle muscle and inhibit muscular contraction (30). Since the... 

Osaki and Walaas (171) have observed that the oxidase activity of ceruloplasmin was reduced 42—43% in 66% deuterium oxide when Fe + was used as substrate. The authors suggested that proton-transfer may be involved in the rate limiting step, but since the effect of D2O on real acidity was not evaluated it cannot be excluded that the inhibition merely reflects a change in acidity this is an interesting observation. 

Deuterium oxide was known to stabilize microtubules and, when applied to pancreatic endocrine cells, resulted in a dose-dependent inhibition of secretion which eventually reached complete cessation of insulin release. Pretreatment of cells with D2O protected them from the effects of colchicine or vinblastine when D2O was removed from the incubation media. Similarly, pretreatment of cells with cytocholasin B protected the cells from the effects of D2O. 

Alkali metal benzhydrolate oxidizes in toluene [111] and benzene [112] as well as in f-butanol [113] with autocatalysis that is produced by the K02 formed in the oxidation [113]. The induction period disappears when K02 is added to a solution of potassium benzhydrolate. The kinetics of oxidation of sodium benzhydrolate was studied by Pereshein et al. [111]. The maximum oxidation rate appears to be approximately proportional to [RONa] [02]/[ROH],the activation energy being 12 kcal mole-1. The inhibiting action of alcohol (benzhydrol and t-butanol) on the oxidation of metal benzhydrolates was noted by Russell et al. [110], No deuterium exchange was observed during the oxidation of potassium benzhydrolate in t-butanol. Thus no dianions are produced from benzhydrolate ion by the equilibrium reaction... 

However, Boozer and Hammond [7] have obtained additional support for the postulated chain termination via reaction (9) as opposed to reaction (5) on the basis of isotopic labelling experiments and from the inhibiting effect of amines not possessing a labile N—H function in their structure [8]. The use of deuterium-labelled methyl aniline and diphenyl-amine as inhibitors in the oxidation of tetralin and cumene did not show the isotope effect which would be expected if reaction (5) was important. Similarly, both AT-dimethylaniline and AT,AP-tetramethyl-p-phenylene-diamine have measurable inhibitory activity despite the fact that neither has a labile hydrogen [8]. However, it has been argued [12] that neither a kinetic isotope effect nor a labile hydrogen is necessary if inhibition results from an electron transfer reaction of the type... 

The calculated values are those obtained by assuming the ratedetermining step to be abstraction of an allylic hydrogen with an isotope effect equal to the discrimination effect obtained from the retention of deuterium in the products. The observed kinetic isotope effects show clearly that this first abstraction is the slow step. The good agreement with the discrimination values gives excellent confirmation for the stepwise mechanistic scheme proposed. In the tracer experiments using deuterium it was found that appreciable propylene isomerization occurred unless ammonia was present. The oxidation rate was unaffected by the ammonia. This was taken to indicate that the initial oxidative abstraction reaction had no carbonium ion characteristic. However, this conclusion does not apply in the case of cuprous oxide, where ammonia very severely inhibited the oxidation reaction. 

There are few reports of alkene-deuterium reactions on bimetallic catalysts, but those few contain some points of interest. On very dilute solutions of nickel in copper (as foil), the only product of the reaction with ethene was ethene-di it is not clear whether the scarcity of deuterium atoms close to the presumably isolated nickels inhibits ethane formation, so that alkyl reversal is the only option, or whether (as with nickel film, see above) the exchange occurs by dissociative adsorption of the ethene. Problems also arise in the use of bimetallic powders containing copper plus either nickel, palladium or platinum. Activation energies for the exchange of propene were similar to those for the pure metals (33-43 kJ mol ) and rates were faster than for copper, but the distribution of deuterium atoms in the propene-di clearly resembled that shown by copper. It was suggested that the active centre comprised atoms of both kinds. On Cu/ZnO, the reaction of ethene with deuterium gave only ethane-d2. as hydrogens in the hydroxylated zinc oxide surface did not participate by reverse spillover. ... 

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