Using Deuterated Probes

The necessity to label (deuterate) the systems under study may often appear as a disadvantage, since it prevents working with real (industrially designed) materials. A way to circumvent this drawback is to use labelled (deuterated) molecules as 2H NMR probes of material properties [67]. 

The uniaxial contribution to the stress-induced orientation (the second term in Equation 15.4) has been attributed mainly to orientational interactions between chain segments. When guest molecules are introduced in a rubber matrix, these interactions take place between network chain segments and guest molecules as well. This effect has been recognised earlier, and may be used to study indirectly the behaviour of the matrix. Two types of guest molecules have been used for this purpose. 

The orientation of the swelling agent (solvent or free chains) has to be taken into account in the analysis of the stress-optical behaviour of swollen networks. Specifically, the segment polarisability (relative to the network chains or to the diluent chains), as currently derived from stress-optical coefficients [33], may not be representative of intrinsic properties of isolated chains. Short-range orientational interactions between the probe molecules and network chains (and between the chains of the matrix itself) must be considered in the interpretation of opticoelastic properties of swollen (and dry) rubbers [67]. 

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The difference in the electron affinity between light and heavy isotopic isomers is, in other words, the difference in the stability of their anion-radicals. Such a difference gives a valuable tool for use in probing the chemistry of anion-radicals. The difference in the stability of the ring-deuterated and ring-nondeuterated arene anion-radicals has been employed to examine the transition states for the one-electron-promoted cleavage of naphthyl methyl phenyl ether and naphthyl benzyl ether (Guthrie and Shi 1990). In this reaction, the potassium salt of fluoranthene anion-radical was an electron donor ... 

Probing for proton transfer in the rate-determining step can be accomplished using deuterated compounds or solvents [63,86,91,138,140], If the deuterated explosive is available, it can be examined neat and in solution. If no deuterium kinetic isotope effect (DKIE) is exhibited by the neat deuterated explosive, then hydrogen transfer can be ruled out in the... 

Drawn isotactic polypropylene (iPP) fibres have been studied by using deuterated n-decane as a 2H NMR probe of the chain deformation ratio in the amorphous regions. It is observed that the slope P=A/(X2-X 1) (defined in the limit of low deformations) indeed depends on the annealing temperature [82]. Thus, annealing above the melting temperature Tm of the crystallites allows chains to relax to some extent. Then, the local deformation ratio in the amorphous phase Xt becomes lower than the macroscopic one X and depends on the annealing temperature, i.e., on the amount of chain relaxation. Therefore, such systems have strongly non-affine deformation at the chain scale. 

Polyamide-polyether (PA-PEG) block copolymers have been studied using deuterated water (2H20) molecules as 2H NMR probes [85, 86, 87]. Well resolved doublets are observed on 2H20 on stretching the samples at room temperature. At a given elongation ratio X, the splitting depends on the water concentration c. The linewidth is that of a liquid and becomes comparable to that in bulk water for c=0.6. This confirms that water... 

Various types of neutron scattering can be utilized to extract data on structure and dynamics for novel catalytic materials. By selectively deuterating an SSZ-13 zeolite, Cheetham and others" used ND performed on the Dual Beam Neutron Spectrometer (DUALSPEC) diffractometer at the Chalk River Laboratories and found that two acid sites are present in the unit cell of the zeohte. INS can be used to probe the mechanism of the catalytic reaction by looking at the change in the vibrational modes of the adsorbed molecules on the surface. Lennon et alP found that the interaction of HCl with a ]-alumina catalyst results in the dissociative adsorption of HCl, in which the hydroxyl groups terminally bound to A1 are replaced by chlorine. INS spectra reveal an in-plane deformation mode, 5 (OH), that can be resolved into two bands located at 990 and 1050 cm. ... 

Incoherent quasielastic neutron scattering measured as a function of hydration for powders of deuterated phycocyanin has been used to probe water motions (Middendorf et al., 1984). The simplest model accounting for the data was jump diffusion of water molecules between localized-sorption sites and the development of clusters of surface water at higher hydration (half-coverage of the surface, 0.15 h). This model is consistent with the picture developed from sorption thermodynamics. 

The nature of OA interaction with SC lipids in vivo was of significant interest, particularly in light of the IR results above. Reflectance IR spectroscopy in conjunction with the use of a deuterated probe once again proved to be a valuable approach for the noninvasive evaluation of this enhancer in humans [153]. Prior to treatment, test sites on the inner ventral forearm of volunteers were cleansed with water, after which the subject remained at constant temperature and relative humidity, while three pretreatment spectra were collected. The experimental site on one arm was treated with a 5% v/v solution of perdeuterated oleic acid ( H-OA) in ethanol, while the control site, on the contralateral arm, was treated with ethanol alone. Both formulations were applied under occlusion for 16 hours posttreatment, the sites were swabbed clean with ethanol and then air-exposed for 2 hours to allow the occluded skin to dry. An ATR-IR spectmm of the dosed site was then obtained. This site was then tape stripped once and a second spectral examination was made. This sequential tape stripping and spectral acquisition was repeated -20 times in order to obtain an incremental spectral profile as a function of SC depth (defined by the cumulative weight of SC removed with tape stripping). IR spectra thus collected yielded the following information (a) the distribution... 

Chemical ionization MS, with various deuterated reagent gases, has been used to probe the number and nature of active hydrogens in a molecule. For example, based on the mass shifts of the protonated ions that are observed when switching from ammonia (NH3) to deuterated ammonia (ND3), the number of active hydrogens in morphine and several other drugs have been demonstrated. 

Deuterated testosterone has been used to probe the catalytic mechanism of P450 3A4 [1372] (Fig. 9.19). Abstraction of the 6[ hydrogen of testosterone is highly stereoselective, with the oxygen rebound also going only to the po-sitioa The use of both 6-deuterated and 6-triti-ated testosterone led to the conclusion that the 6y -hydroxylation step has a high intrinsic kinetic deuterium isotope effect, which is considerably attenuated in the steady state [1372]. The conclusion is that steps other than C-H bond breaking hmit rates of the steady-state reaction. 

The stereochemistry of aminopalladation, as is involved in the initial step of the aza-Wacker reaction, is still a subject of ongoing research. A particularly extensive mechanistic study by Stahl and Liu uncovered the stereochemical aspects of intramolecular aminopalladation under Wacker-type conditions. Here, the selectively deuterated compound 46 was used to probe the overall mechanism through product evaluation. It turned out that, for almost all common catalyst combinations, the reaction led to two deuterated alkenes, which were identified as product 47 and its regioisomer. As the final step of 3-hydride elimination must be a syn-selective... 

Experimentally, we do not have any data on the diffusion of trapped chains in a network. What is available is the diffusion coefficient of a labeled chain in polyethylene melts, measured by two techniques 1) from nuclear spin resonance data, and 2) using deuterated chains as labels, the local concentrations of deuterated/protonated species being probed by infrared measurements. ... 

Fig. 17 Schematic drawing (only illustrative) of the (a) side-chain and (b) main-chain LCEs used in this study together with the chemical formulas of the LCE components and deuterated probe molecules. The various crosslinkers are denoted as V6, V3 and HD5...

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