Effects of deuteration

It is the latter advantage that is valuable since it allows uniquely important, individual hydrogen atoms to be studied free from the interference of other hydrogen atom vibrations. This is why neutron spectroscopy is outstandingly suited to the study of hydrogen bonds. 

It is useful to summarise here some of the less well-publicised aspects of the isotopic substitution technique. Most obviously, the vibrations involving the substituted atoms will still change their energies and so change the neutron spectmm, although this can only be seen under suitable experimental resolution [5]. Less obviously is that the vibrations 

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Geometries, hyperfme structure, and relative stabilities of the different positional isomers of monodeuterated benzene cations have been studied theoretically by density functional theory, using the B3-LYP functional, and experimentally by ESR and ENDOR spectroscopy. A comparison between theoretical and experimental results at 30 K gives acceptable agreement, but further experiments on multiply deuterated species should improve the analysis by making the effects of deuteration larger. 

Table 5.7. Effect of Deuteration on the Triplet Lifetime of Organic Molecules<30-8°-88>...

Khaled, M., A. Hadjipetrou et al. (1990). Electrochemical and electron paramagnetic resonance studies of carotenoid cation radicals and dications Effect of deuteration. J. Phys. Chem. 94 5164—5169. 

Table I lists the excited state lifetimes for 0s(phen)3 + at three temperatures. The striking result is the lack of any significant change in the LMCT statefs lifetime on going from 295 to 10 K. Table I also presents data on the effects of deuteration on the charge transfer state lifetimes of Os(bpy) 3 /3+ complexes. The lifetimes are lengthened, but only by factors of 2 and 2.5 respectively, for Os(bpy)33+ and 0s(bpy)3 +.

The effect of deuteration, for the needs of sequence-specific resonance assignments using triple-resonance experiments, was first demonstrated by Bax and co-workers on the 19.7 kDa protein calcineurin B in 1993.56 By replacing the H spin with deuterium, the transverse relaxation time of 13C spin is increased by nearly an order of magnitude due to the 6.5 times smaller gyromagnetic ratio of 2H in comparison to in.52,56 Not surprisingly, deuteration was utilized for the aid of structure determination of several... 

Explain the effects of deuteration and heavy atoms on the relative rates of radiationless processes. 

Table 5.1 Effect of deuteration on intersystem crossing rates (k ) and triplet-state lifetimes...

McCarty LP, Malek RS, Larsen ER. 1979. The effects of deuteration on the metabolism of halogenated anesthetics in the rat. Anesthesiology 51 106-110. 

Interesting data about the effect of deuterated water molecules on electron transfer processes in reaction centres of PSl of plants have been ob-... 

Just as there can be secondary IEs on acidity and basicity, namely, on proton-transfer equilibria, so also can there be secondary IEs on Lewis acidity and basicity. All the examples though have been deuterium IEs, perhaps because heavy-atom effects are too small to measure reliably except when they are primary. Deuteration can affect not only basicity toward protonation but also basicity toward a Lewis acid. Less closely analogous but also possible is the effect of deuteration on the electrophilicity of a Lewis acid. 

Interesting data about the effect of deuterated water molecules on electron transfer processes in reaction centres of PS1 of plants have been obtained [215, 216]. Earlier [217], it was found out that, in lyophilically dried leaves of plants which were kept in the dark, there occurs a recombination of charges whose efficiency in the temperature range 77-300 K depends on the water content in the leaves. A detailed study of the effect of replacing H20 by D20 in the leaves containing 10% of the normal water content on the kinetics of recombination reaction (1) in the temperature range 77-300 K has been made [215, 216]. 

Table II. Effect of Deuteration on Cyclohexene Oxidation by Cytochrome P 450LM2...

The identification of the radical in cytochromec peroxidase proved more elusive, partly because the EPR spectrum contains no well-resolved proton couplings. However, it was possible to identify this radical as being tryptophan-based by the effect of deuterated tryptophan on the couplings observed in the ENDOR spectra [27], No effect was observed when deuterated methionine was used. 

The symbols indicate, in this order, the configuration around the C(l) = C(2) bond and the conformation of the 0=C—C(2)=C(1) moiety. e Averaged spectrum of several rotamers with E configuration in rapid equilibrium. f Total effect of deuteration at N and C(2) centers. 

Isotope effects are useful in determining chemical mechanisms. In an oxidative decarboxylation where a hydride ion is removed from one carbon and CO2 is lost from another, one can tell whether the reaction is concerted or stepwise by the effect of deuteration on the isotope effect in the CO2 (21). In a concerted mechanism, deuteration makes the chemical step more rate limiting, and one will see a larger isotope effect, or the same one if commitments were small to start with. In a stepwise mechanism, however, deuteration of the substrate makes the decarboxylation step less rate limiting and thus diminishes the size of the observed isotope effect. 

Table III. Effect of Deuteration on Properties of Piperidinium [BETA]4 Eu Chelates...

The effect of deuteration upon the rate of elimination of hydrogen halide has been studied by Good by Shilov and by Blades et In all cases... 

More interesting with regard to the effect of esterification on the rotation than with respect to the effect of deuteration are the recently synthesized optically active deuterated acid 110 and its ester 111 Generally, the rotations of acids and their corresponding esters (measured in the same solvent) differ by no more than 39 % (cf., for instance, 83 and 84,34 (Table 3) and 73). The data of 110 and 111 may be taken as a further demonstration of the role of the solvent on optical rotations of cyclopropanecarboxylic acids, in particular, steric hindrance of solvation of the COOH group. 

The curious behaviour of sulphur compounds is of great interest. This is seen in the effects of deuteration on the decay of the 2 state of xanthione °. Large deuterium effects are seen in the 1 and 0 positions. The results are ascribed to competing S2 to S, and Sj to Sg processes the latter results from motions of the C(1)-H and C(B)-H atoms towards the thionyl group. 

Within the last decade, hyphenation of LC-MS, LC-NMR, and LC-MS-NMR have become available. Because MS is destructive (in contrast to NMR) and requires far less sample than NMR, a splitter is incorporated, on-line, to direct the bulk of the sample to the less sensitive technique. In addition to the advantage of having MS and NMR information for the same chromatographic peak, the combination of these two techniques with different sensitivities must deal with other issues, such as the effect of deuterated solvents on the MS, the limitation of source of ionization on the MS compatible with low flow rates, and the timing which depends on the slower NMR technique. There is still room for improvement for LC-MS-NMR and the next decade will define the areas where this hyphenated technique is best suited. 

The effect of deuteration whose influence is independent of solvent and temperature, shows the importance of the importance of the C-H/C-D modes in promoting one or both of the triplet decay transitions. 

Mixed quantum-classical simulation using the DME method was performed in the gas phase and in a chloroform solution [34]. The effects of deuteration were also considered. The vibrational spectrum was calculated by Fourier... 

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