Substitution Of Deuterium For Hydrogen Research Articles

Geometry of bicontinuous microemulsions as revealed by SANS and simulations

Water-octane-C10E4 microemulsions in both the isotropic and lamellar phases were measured using small-angle neutron scattering. Varying the scattering length density of both the water and oil through hydrogen-deuterium substitution enabled us to isolate the scattering contributions of the surfactant monolayers and the water-surfactant and oil-surfactant interfaces. Analyses of the resulting scattering patterns allow us to directly determine the small mean curvature of the surfactant film as a function of temperature and correlate this quantity with the overall phase behavior. A simulation using a Gaussian random field yields the three-dimensional structure of the bicontinuous microemulsion having a surfactant monolayer with zero mean curvature.

Effect of tautomerization on the fast-atom bombardment tandem mass spectra of azo dyes

The effect of tautomerization on the collision-induced dissociation of negative ions produced from sulfonated azo dyes by fast-atom bombardment (FAB) was studied by analyzing the product ion spectra of several related compounds. The mechanisms by which azo dyes fragment were found to depend on the formation and stability of tautomers. The extent of tautomerization was affected by the number and location of hydroxy groups on the dye, as well as by the FAB matrix. Ions that retained a sodium were often inhibited from forming tautomers and gave different product ions. Substitution of deuterium for hydrogen on the hydroxy groups aided in the identification of ions having more than one possible structure and provided verification of proposed mechanisms. Mechanisms involving ions retaining a sodium were verified by substituting potassium for the sodium.

IMPACT OF NEUTRON SCATTERING ON THE STUDY OF WATER AND AQUEOUS SOLUTIONS

Neutron scattering is making a major impact on our physical and chemical understanding of water structure in aqueous solution. In combination with the technique of isotope substitution it can probe, via the partial pair correlation functions of the system, both the structural aspects of the water itself in solution and the correlation of water molecules with individual dissolved ions and molecules. Moreover it can also investigate the way the solute species distribute themselves in solution. The use of the so-called first-order difference method to look at the hydration of inorganic ions in solution has already been widely reported in several previous reviews, so this account concentrates largely on recent advances in the application of the second order hydrogen-deuterium substitution method to the study of water under non-ambient conditions, and to the measurement of water structure in a variety of solutions and heterogeneous media. It is also shown how the same technique can be used to investigate the nature of solute-solute correlations in solution, and the way water organizes itself around organic molecules and ions in solution.

A proton NMR investigation of rotation about the C(O)-N bonds of urea

The rates and activation energies have been determined by proton NMR for H_2^(15)N(CO)^(14)NH_2 1 and hydrogen exchange equilibrated mixtures of 1 and H_2^(15)N(CO)^(15)NH_2 2 with D_2NC(O)ND_2 3. Synthesis of 1 was achieved by the classic Wohler procedure from ^(15)NH_4 C=^(14)N=O with no detectable formation of H_2^(15)N(CO)^(15)NH_2. In the slow-rotation regime, the chemical-shift difference between the protons cis and trans to the carbonyl oxygen decreases rather rapidly with increasing temperature (0.0063 ppm/o). Coupling parameters were extracted from the rather complex six-spin system afforded by H_2^(15)NC(O)^(1)5NH_2. The activation parameters for the rotation in dimethylformamide-dimethyl sulfoxide solution were ΔG^* (245 K) = 11.2 ± 0.3 kcal/mol and E_a = 13.5 ± 0.25 kcal/mol. Significant changes in the sensitivity of the variations of the proton shifts with temperature were found with substitution of deuterium for hydrogen and addition of water to the solvent. The overall results are in accord with the resonance interpretation of the barrier to rotation about the C(O)-N bonds of amides and ureas.

Understanding the mechanism of CVD diamond

Abstract Recent work at GE on the chemical vapor deposition diamond process is discussed. An experimental apparatus is described which allows in situ kinetic studies of the hot filament growth of diamond. This apparatus was used to demonstrate that diamond could be formed on a graphite substrate simultaneously while etching occured. Substitution of deuterium for hydrogen decreased the deposition rate, suggesting that a C-H bond was involved in the rate-limiting step. The difficulty when using carbon filaments is discussed in terms of equilibrium analysis. Hydrogen, and especially atomic hydrogen, is critical for this process and performs several critical functions, including stabilization of the diamond surface, creation of a volatile source of carbon, formation of vacancies on the growth surface, reduction of the surface free energy, formation of carbon radicals and possibly the etching of graphite material.

An investigation of ethylene hydrogenation catalyzed by metallic molybdenum using an isolatable high-pressure reactor: Identification of the reaction site and the role of carbonaceous deposits

Ethylene hydrogenation catalyzed by a model Mo(100) single crystal catalyst is investigated using an isolatable high-pressure reactor. The observed reaction kinetics are in agreement with those measured for supported transition metal hydrogenation catalysts showing a zero-order dependence in ethylene and a first-order dependence in hydrogen partial pressures. The reaction activation energy is 8.1 ± 0.5 kcal/mol for a Mo(100) single-crystal model catalyst and for a foil and mass spectral analysis of the products formed following substitution of deuterium for hydrogen shows that a maximum of two deuterium atoms are incorporated into the ethane that is produced. Auger analysis of the surface following reaction reveals the presence of large amounts of carbon (up to ∼7 monolayers). This carbonaceous deposit decomposes on heating the surface to above 1000 K to desorb C 1 species. The experimental data suggest that either hydrogen or ethylene can permeate this layer so that hydrogen transfer takes place either at the metal surface or on top of the layer. Blocking the fourfold sites on Mo(100) by oxygen or carbon has only a marginal effect on the overall reaction kinetics, and does not substantially alter the amount of carbon deposited onto the surface during reaction. This result implies that the enhanced catalytic activity observed on metal carbide catalysts is not only due to site blocking, but also arises because of chemical modification of the catalyst by compound formation.

Geometric effects of deuteration on hydrogen-ordering phase transitions

IT has long been known that the substitution of deuterium for hydrogen in hydrogen-bonded materials can lead to a change in the geometry of the hydrogen bonds—the so-called Ubbelohde effect1. There can also be significant accompanying changes in the physical properties of the material. Among the most striking examples is the increase in the transition temperature, Tc, of hydrogen-ordering systems of the KH2PO4 type by >100K on full deuteration. In all of these systems, Tc decreases under pressure, making it possible in principle to compare protonated and deuterated forms at the same Tc by applying pressure to the latter. Here we report the results of a high-pressure neutron diffraction study of the deuterated H(D)-ordering material PbDPO4. We find that much, and possibly all, of the increase in Tc on deuteration is attributable to the accompanying changes in the hydrogen-bond dimensions. This suggests that purely mass-dependent effects on the quantum-mechanical tunnelling between the equivalent H(D) potential minima—an explanation that has been favoured previously—have little or no direct influence on Tc. Substantial revisions to the theory of this type of ordering transition are apparently required.

Synthesis of 13C and 2H‐labelled 2‐phenylcyclododecanones

Abstract13C labelled (1,2 and 1,12) and perdeuterated derivatives of 2‐phenyl cyclododecanones, as precursors for labelled triplet flexible biradicals to probe magnetic isotope effects at the radical centers on the triplet decay dynamics, were synthesized. Isotopomers of 2‐phenylcyclododecanone‐13C2‐(1,2 and 1,12) were synthesized from cyclododecanone‐13C2‐(1,2) by dibromination, followed by phenylation with lithiumdiphenylcuprate. Cyclododecanone‐13C2‐(1,2) was obtained from 1, 10‐dibromodecane via the following sequence: (1) K13CN; (2) hydrolysis; (3) esterification; (4) acyloin condensation. Perdeuterio‐2‐phenyl cyclododecanone (95% isotopic purity) was prepared from unlabelled 2‐phenyl cyclododecanone by a substitution of deuterium for hydrogen by treatment with excess D2O, catalyzed with D2‐reduced PtO2 in the presence of D2O2.

The structure of aqueous tetramethylammonium dodecylsulphate solutions at the air-water interface studied by the specular reflection of neutrons

The technique of specular reflection of neutrons has been used to investigate the adsorption of tetramethylammonium dodecylsulphate (TMDS) at the aqueous solution/air interface over the concentration range 0·0004–0·0118 M. Hydrogen-deuterium substitution in both surfactant and solvent has been used to highlight different features of the adsorbed layer, and to distinguish between solvent and solute in this layer. The structure of the layer consists of three regions, the first, nearest the vapour, containing only hydrocarbon chains, the second containing a small fraction of chains, the head groups, water and a fraction of counterions, and the third containing water and a diffuse atmosphere of counterions. The area per molecule at completion of the monolayer is 60 ± 2 Å2. At this point the thickness of the chain region is 14·5 ± 1 Å and the thickness of the head group region 10 ± 1 Å. The fraction of chains incorporated into the head group region is 0·15, corresponding to about 2 CH2 groups, and the fraction of bound ions is 0·25. Simple geometrical constraints, in conjunction with the reflectivity results, indicate that the head groups are arranged on a single plane in the complete TMDS monolayer unlike the situation found for decyl trimethyl ammonium bromide. At coverages down to about half a monolayer there is no significant change in the geometry of the layer other than the increase in the area per molecule. For the isotopic composition dTMhDS in null reflecting water the diffuse layer of counterions contributes significantly to the reflectivity. This is the first time that a direct measurement has been made on the diffuse double layer. However, although the width of the diffuse layer scales with the Debye length, the shape of the distribution is not consistent with the Stern layer model.

High temperature lubricants from biodeuterated materials produced by algae

The substitution of deuterium for hydrogen in a lubricating hydrocarbon base oil imparts improved oxidation stability and wear performance as a result of a kinetic isotope effect. In this investigation a biotechnological approach was applied to the production of deuterated compounds suitable for lubricant synthesis. From algae grown in heavy water (D 2O) and supplied only with mineral salts, carbon dioxide, and light, it was possible to isolate fatty acids which were over 98% deuterated and constituted 50%–60% of the dry weight of the organisms. By appropriate choices of organism and growth conditions, fatty acids could be obtained with suitable deuterocarbon chain length and double bond density for the syntheses of a variety of lubricants. Thermogravimetric analysis, differential scanning calorimetry, and microsample friction and wear tests showed that a pentaerythritol perdeutero-tetrahexanoate ester base oil was significantly more resistant to high temperature oxidation and produced substantially less wear than the undeuterated hydrogen analog.

Hydrogen-induced phase separation in amorphous Cu0.5Ti

The influence of hydrogen on the structure of an amorphous ${\mathrm{Cu}}_{0.5}$${\mathrm{Ti}}_{0.5}$ alloy has been studied by means of x-ray and neutron scattering. These experiments include large-angle x-ray and neutron scattering and small-angle neutron scattering with hydrogen-deuterium substitution. The results indicate that large hydrogen contents (hydrogen-to-metal ratio of 0.84) induce a phase separation into Cu and ${\mathrm{TiH}}_{\mathrm{x}}$ regions on a scale of about 10--15 A\r{}. Experiments on samples loaded with hydrogen by electrolysis or from the gas phase show that such a phase separation does not depend on the method of hydrogen loading. The results of a computer simulation with nearest-neighbor Cu-Ti permutations reproduce the main features of the diffraction data and confirm the large change of chemical ordering between Cu and Ti atoms upon hydrogen absorption.

Detection and mechanism of formation of the potent direct-acting mutagen 2-bromoacrolein from 1,2-dibromo-3-chloropropane

The nematocide 1,2-dibromo-3-chloropropane (DBCP) was converted to products which are mutagenic for Salmonella typhimurium TA 100 in the presence of rat liver microsomes, NADPH, and oxygen. Typical in vivo and in vitro inhibitors of cytochrome P-450 decreased DBCP mutagenicity in the presence of microsomes. Addition of glutathione to cytosolic preparations failed to bioactivate DBCP to mutagenic metabolites. Mutagenicity studies with selectively deuterated analogs showed that substitution of deuterium for hydrogen at C-1 or C-3 of DBCP modestly decreased mutagenicity, but that deuteration at both C-1 and C-3 markedly decreased mutagenicity. The formation rates of the potent direct-acting mutagen, 2-bromoacrolein (2-BA), in incubations of DBCP and its deuterated analogs with rat liver microsomes, correlated with the isotope effects on mutagenicity. Characterization of 2-BA was accomplished by gas chromatography-mass spectrometry using positive-ion chemical ionization. Mass spectral analysis of 2-BA formed from specifically deuterated analogs of DBCP indicated that initial oxidative dehalogenation at C-1 followed by a spontaneous β-elimination reaction was the preferred pathway in the formation of 2-BA from DBCP. These results demonstrate that mutagenic metabolites of DBCP are formed by cytochrome P-450-mediated oxidative metabolism, and that 2-BA is a major mutagen formed.

Multinuclear magnetic resonance studies of the hydrolysis of aluminium(III). Part 8. Base hydrolysis monitored at very high magnetic field

New studies of base-hydrolysed aluminium(III) solutions were made using high-field 1H and 27Al n.m.r. spectroscopy. The increased sensitivity of the modern equipment has allowed data to be obtained at concentrations as low as 1 × 10–3 mol dm–3, some of it quantitative, and the 1H n.m.r. spectra of solutes transferred to non-aqueous solvents has provided new structural data. The results enable it to be stated quite unequivocally that the tridecameric cation [AlO4Al12(OH)24(H2O)12]7+ is the principal species formed at lower concentrations, and is virtually the only one formed below 20 × 10–3 mol dm–3. At concentrations higher than this, and at intermediate levels of hydrolysis, an oligomeric mixture is formed with a stoicheiometry close to {[Al(OH)2.5]1/2+}n and which could be composed of species such as [Al2(OH)5]+, [Al3(OH)8]+, [Al4(OH)10]2+, and [Al5(OH)13]2+. Partial deuteriation produces isotopic splitting of the proton resonances of bound water which allows these to be distinguished from the resonances of OH-bridge protons. An indication of fine structure due to hydrogen–deuterium substitution on AlO6 fragments is also obtained which favours the more condensed structures and this is in accord with the ease with which the oligomer is converted into the tridecamer on simple dilution. It is now certain that the dihydroxo-bridged dimer found in the solid state is not a significant constituent of these solutions. Oxygen-17 n.m.r. data are also briefly reported.

Radical transformation kinetics in irradiated acetyl- L-leucine single crystals at room temperature

It has been found that the radical (CH 3) 2C̊CH 2CH(NHCOCH 3)CO 2H transforms into (CH 3) 2CHCH 2C̊(NHCOCH 3)CO 2H at temperatures of 293–315 K by the first-order reaction. The kinetic parameters determined for this reaction are k 0 = 9.2 × 10 9s −1 and E‡ = 20.0 ±0.6 kcal/mole. The substitution of deuterium for hydrogen in α-carbon does not affect the kinetic parameters which proves the absence of isotropic effects.

Tetrahydroboratobis(triphenylphosphine)copper(I): a vibrational spectroscopic study

Application of infrared and Raman spectroscopy together with hydrogen—deuterium substitution has allowed identification of at least seven of the twelve fundamental vibrational frequencies expected for the double bridge CuBH 4 unit in tetrahydroboratobis(triphenylphosphine)copper(I). Limited assignments for the AgBH 4 unit in the analogous silver compound, based on infrared data for the hydride deuteride, are also presented.

Studies on the mechanism of MPTP oxidation by human liver monoamine oxidase B

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its deuterated analogues were oxidized to their corresponding dihydropyridinium species (MPDP +) by preparations of pure human liver MAO B : monoclonal antibody complex to investigate the mechanism of MPTP activation. Lineweaver-Burk plots of initial reaction rates revealed that the K m,app values for the various deuterated MPTP analogues were similar to those of MPTP. In contrast, V max,app values were substantially decreased by substitution of deuterium for hydrogen on the tetrahydropyridinium ring, especially at C-6. Deuterium substitution on the N-methyl group alone did not significantly reduce V max,app. These studies support the interpretation that oxidation of MPTP at the C-6 position on the tetrahydropyridine ring is a major rate-determining step in its biotransformation by MAO B.

The isotope study of the SiH absorption peaks in the FZSi grown in hydrogen atmosphere

The isotope effects of hydrogen and silicon prove that all the four intense i.r. absorption peaks 2210, 1946, 812 and 791 cm −1 in the floating zone melted silicon crystal grown in hydrogen atmosphere (FZSi:H) are the vibration peaks of SiH bonds. The experiment of the partial substitution of deuterium for hydrogen demonstrates that the hydrogen-defect complex corresponding to 2210 cm −1 peak possesses Td symmetry, while that corresponding to 1946 cm −1 peak is of SiH 1 structure. The fine structure of 2210 cm −1 peak found in the FZSi:H samples at low temperature is shown to be caused by the natural isotopes of silicon.

Time resolved measurements of methanol decomposition on Ni(100) utilizing laser induced desorption

A new method utilizing laser induced desorption (LID) is used to study the decomposition of methanol on Ni(100) in real time. The dependence of the rate of decomposition on surface coverage and on surface temperature is measured. The decomposition rate decreases during reaction in a manner characteristic of a self-poisoned reaction. The rate data are fit to a model in which the energy barrier to reaction increases in proportion to the coverage of the CH 3O product. The energy barrier obtained is 9 kcal mol −1 plus 4 kcal mol −1 monolayer −1 of CH 3O. The frequency factor of 2×10 9 s −1 suggests there is significant entropy barrier to decomposition. Substitution of deuterium for the alcoholic hydrogen alters de decomposition rate appreciably and identifies the breaking of the OH bond as the rate determining step.

Time resolved measurements of methanol decomposition on Ni(100) utilizing laser induced desorption

A new method utilizing laser induced desorption (LID) is used to study the decomposition of methanol on Ni(100) in real time. The dependence of the rate of decompositition on surface coverage and on surface temperature is measured. The decomposition rate decreases during reaction in a manner characteristic of a self-poisoned reaction. The rate data are fit to a model in which the energy barrier to reaction increases in proportion to the coverage of the CH 3O product. The energy barrier obtained is 9 kcal mol −1 plus 4 kcal mol −1 monolayer −1 of CH 3O. The frequency factor of 2 × 10 9 s −1 suggests there is significant entropy barrier to decomposition. Substitution of deuterium for the alcoholic hydrogen alters de decomposition rate appreciably and identifies the breaking of the OH bond as the rate determining step.

Cholesterol metabolism: use of D2O for determination of synthesis rate in cell culture.

Cholesterol synthesis in cell culture in the presence of D2O yields a spectrum of enriched molecules having a relative abundance that indicates random substitution of deuterium for hydrogen. Quantitation of the absolute rate of cholesterol synthesis is obtained by isotope ratio mass spectrometry. Mevinolin and 26-hydroxycholesterol both decrease cholesterol synthesis rate but have a discordant effect on HMG-CoA reductase activity.