Deuterium Substitution Research Articles

Ferroelectric Thin Films of Betaine Phosphite, Glycine Phosphite and of Their Deuterated Analogs

Results of investigation of structural and dielectric properties of thin films of betaine phosphite, glycine phosphite and of their deuterated analogs are presented. The films were obtained by the evaporation method on different substrates. The ferroelectric phase transition is followed by a strong dielectric anomaly of film structures which depend on the substrate type (piezoelectric or non-piezoelectric). A strong dielectric non-linearity was observed near the phase transition in deuterated betaine phosphite films. In the films with a high deuteration degree the substitution of deuterium by hydrogen ions on the surface and interdiffusion of these ions inside the film was analyzed on the basis of dielectric measurements. Specific features of dielectric hysteresis loops for deuterated betaine phosphite and glycine phosphite film structures are discussed.

Phase behavior of imidazolium and phosphonium tetrafluoroborates with dihydroxy alcohols

Liquid–liquid equilibrium curves for 1-ethyl-3-methylimidazolium tetrafluoroborate -[C2MIM,BF4], 1-butyl-3-methylimidazolium tetrafluoroborate -[C4MIM,BF4] and trihexyl(tetradecyl) phosphonium tetrafluoroborate -[P6,6,6,14,BF4] with chosen dihydroxy alcohols and their deuterated analogues have been determined. All fourteen obtained phase diagrams are described by the upper critical solution temperature (UCST) type behavior. The mutual solubility of 1-ethyl-3-methylimidazolium tetrafluoroborates decreases with the increase in alkyl chain of 1,2-dihydroxy alcohols but the opposite effect was observed for the ionic liquid with phosphonium cation. The impact of the hydroxyl group position in butanediol molecule on miscibility with trihexyl(tetradecyl) phosphonium tetrafluoroborate was examined. The results lead to the conclusion that vicinal(1,2 and 2,3)-butanediols are much better miscible than more polar (1,3) and (1,4) isomers. Deuterium substitution in both hydroxyl groups of investigated diols generates downward isotope shift of UCST both for phosphonium and imidazolium based ionic liquids thus making the miscibility better in each case.

Evidence for a catalytically and kinetically competent enzyme-substrate cross-linked intermediate in catalysis by lipoyl synthase.

Lipoyl synthase (LS) catalyzes the final step in lipoyl cofactor biosynthesis: the insertion of two sulfur atoms at C6 and C8 of an (N6-octanoyl)-lysyl residue on a lipoyl carrier protein (LCP). LS is a member of the radical SAM superfamily, enzymes that use a [4Fe–4S] cluster to effect the reductive cleavage of S-adenosyl-l-methionine (SAM) to l-methionine and a 5′-deoxyadenosyl 5′-radical (5′-dA•). In the LS reaction, two equivalents of 5′-dA• are generated sequentially to abstract hydrogen atoms from C6 and C8 of the appended octanoyl group, initiating sulfur insertion at these positions. The second [4Fe–4S] cluster on LS, termed the auxiliary cluster, is proposed to be the source of the inserted sulfur atoms. Herein, we provide evidence for the formation of a covalent cross-link between LS and an LCP or synthetic peptide substrate in reactions in which insertion of the second sulfur atom is slowed significantly by deuterium substitution at C8 or by inclusion of limiting concentrations of SAM. The observation that the proteins elute simultaneously by anion-exchange chromatography but are separated by aerobic SDS-PAGE is consistent with their linkage through the auxiliary cluster that is sacrificed during turnover. Generation of the cross-linked species with a small, unlabeled (N6-octanoyl)-lysyl-containing peptide substrate allowed demonstration of both its chemical and kinetic competence, providing strong evidence that it is an intermediate in the LS reaction. Mössbauer spectroscopy of the cross-linked intermediate reveals that one of the [4Fe–4S] clusters, presumably the auxiliary cluster, is partially disassembled to a 3Fe-cluster with spectroscopic properties similar to those of reduced [3Fe–4S]0 clusters.

Effect of deuterium substitution for hydrogen in surface functionalisation of hydrophilic nanosilicon particles on their spectral and dynamic properties

Broadband femtosecond spectroscopy has been used to study two types of hydrophilic silicon nanoparticles: (1) photoluminescent, passivated with deuterium and oxidised in fully deuterated dimethyl sulphoxide, and (2) nonluminescent (control samples having a similar crystalline core), passivated with hydrogen and oxidised in dimethyl sulphoxide. We have found significant differences in ultrafast spectral – temporal induced absorption dynamics between the two types of nanoparticles in the energy range corresponding to their calculated band gap. The observed distinction is due to the considerably higher oxidation rate of silicon on the surface of the deuterated samples in comparison with the undeuterated ones and with the associated increase in the number of photoluminescence centres on the surface of the nanoparticles. In the samples containing self-trapped exciton (STE) energy states responsible for the photoluminescence in the red spectral region, carrier capture at these levels and carrier relaxation to the ground state have characteristic times in the femtosecond range. In the samples free of STE states, excited carriers relax to the conduction band bottom in a characteristic time of several picoseconds.

Adsorption and oxidation of formaldehyde on a polycrystalline Pt film electrode: An in situ IR spectroscopy search for adsorbed reaction intermediates.

As part of a mechanistic study of the electrooxidation of C1 molecules we have systematically investigated the dissociative adsorption/oxidation of formaldehyde on a polycrystalline Pt film electrode under experimental conditions optimizing the chance for detecting weakly adsorbed reaction intermediates. Employing in situ IR spectroscopy in an attenuated total reflection configuration (ATR-FTIRS) with p-polarized IR radiation to further improve the signal-to-noise ratio, and using low reaction temperatures (3 °C) and deuterium substitution to slow down the reaction kinetics and to stabilize weakly adsorbed reaction intermediates, we could detect an IR absorption band at 1660 cm−1 characteristic for adsorbed formyl intermediates. This assignment is supported by an isotope shift in wave number. Effects of temperature, potential and deuterium substitution on the formation and disappearance of different adsorbed species (COad, adsorbed formate, adsorbed formyl), are monitored and quantified. Consequences on the mechanism for dissociative adsorption and oxidation of formaldehyde are discussed.

Miscibility behavior of trihexyl(tetradecyl)phosphonium tetrafluoroborate with cyclic hydrocarbons

Liquid–liquid miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by trihexyl(tetradecyl)phosphonium tetrafluoroborate with cyclohexane, cycloheptane, methylcyclohexane, 1,2-dimethylcyclohexane and 1,3-dimethylcyclohexane. All the measured systems present solubility curves characterized by the asymmetry with respect to the equimolar composition and represent the phase diagrams with the upper critical solution temperatures. The effect of the deuterium substitution in cyclohexane and methylcyclohexane has also been studied revealing small upward shift of the UCSTs which means slightly worse miscibility of ILs studied with selected deuterated cycloalkanes.

Unusual behavior of the isotope effect on miscibility of 1-hexyl-3-methylimidazolium bis(trifluorosulfonyl)imide with 1-alkanols

The liquid–liquid phase diagrams of 1-hexyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide with regular and deuterated 1-alkanols (CnH2n+1OH and CnH2n+1OD, n=4–10) have been obtained. Deuteration of alcohols in the hydroxyl groups changes the upper critical solution temperatures in a very surprising way. The immiscibility region of the systems upon deuterium substitution in alcohol initially decreases (n=4, 5), then significantly enlarges (n=7), and finally practically does not change (n=8–10) in comparison with the systems with nondeuterated alcohols. This is the first time when non-monotonic change of the isotope effect on miscibility with the increase of the length of the alkyl chain was observed.

Infrared Vibrational Spectroscopy of [Ru(bpy)2(bpm)]2+ and [Ru(bpy)3]2+ in the Excited Triplet State

This work involved a detailed investigation into the infrared vibrational spectra of ruthenium polypyridyl complexes, specifically heteroleptic [Ru(bpy)2(bpm)](2+) (bpy = 2,2'-bipyridine and bpm = 2,2'-bipyrimidine) and homoleptic [Ru(bpy)3](2+), in the excited triplet state. Transient spectra were acquired 500 ps after photoexcitation, corresponding to the vibrational ground state of the excited triplet state, using time-resolved infrared spectroscopy. We assigned the observed bands to specific ligands in [Ru(bpy)2(bpm)](2+) based on the results of deuterium substitution and identified the corresponding normal vibrational modes using quantum-chemical calculations. Through this process, the more complex vibrational bands of [Ru(bpy)3](2+) were assigned to normal vibrational modes. The results are in good agreement with the model in which excited electrons are localized on a single ligand. We also found that the vibrational bands of both complexes associated with the ligands on which electrons are little localized appear at approximately 1317 and 1608 cm(-1). These assignments should allow the study of the reaction dynamics of various photofunctional systems including ruthenium polypyridyl complexes.

The isotopic effects of deuteration on optoelectronic properties of conducting polymers

The attractive optoelectronic properties of conducting polymers depend sensitively upon intra- and inter-polymer chain interactions, and therefore new methods to manipulate these interactions are continually being pursued. Here, we report a study of the isotopic effects of deuterium substitution on the structure, morphology and optoelectronic properties of regioregular poly(3-hexylthiophene)s with an approach that combines the synthesis of deuterated materials, optoelectronic properties measurements, theoretical simulation and neutron scattering. Selective substitutions of deuterium on the backbone or side-chains of poly(3-hexylthiophene)s result in distinct optoelectronic responses in poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) photovoltaics. Specifically, the weak non-covalent intermolecular interactions induced by the main-chain deuteration are shown to change the film crystallinity and morphology of the active layer, consequently reducing the short-circuit current. However, side-chain deuteration does not significantly modify the film morphology but causes a decreased electronic coupling, the formation of a charge transfer state, and increased electron-phonon coupling, leading to a remarkable reduction in the open circuit voltage.

Thermal Properties and Structures of CsHSO4 and CsDSO4 Crystals

Differential scanning calorimetry, thermogravimetric-differential thermal analysis, and Xray diffraction measurements were performed on cesium hydrogen sulfate (CsHSO 4) and deuterated CsDSO 4 crystals. The proton and deuterated compounds were confirmed to exhibit the superionic phase transition at 415.9 and 413.4 K, respectively. The II-III transition for the proton compound was observed in the temperature range of about 330400 K. The thermal decomposition and dehydration reactions of both compounds began at around 460 K. The decomposition continued up to around 1050 K, and the dehydration ended at around 720 K. The weight losses in the temperature ranges of 460-720 K and 720-1050 K were caused by the evaporation of H(D) 2O and SO 3, respectively. The space group symmetries and structural parameters, in phase III (monoclinic, P21/n) for CsHSO 4 and in phase II (monoclinic, P21/c) for CsHSO 4 and CsDSO 4, were determined at room temperature. The expansion of O-H-O hydrogen bond caused by the substitution of deuterium for hydrogen was observed to be 0.015(4) A. The geometric isotope effect on hydrogen-bond structure upon deuteration was realized in the CsHSO 4 crystal. The difference in morphology between as-grown CsHSO 4 and CsDSO 4 crystals was suggested to be caused by the large expansion of the O-H-O hydrogen bond upon deuteration on crystallization in D 2O aqueous solution.

The unimolecular chemistry of [Zn(amino acid)2-H]+ in the gas phase: H2 elimination when the amino acid is a secondary amine

The unimolecular chemistry of the [Zn(Pro-H)(Pro)](+) complex following collisional or infrared multiple photon activation was studied, and interestingly was found to lose H2 as one of the main dissociation pathways. Furthermore a second dehydrogenation step, forming [Zn(Pro-H)(Pro)-2H2](+), was also observed. When proline was substituted for sarcosine, also a secondary amine, a single dehydrogenation was observed. In contrast, [Zn(Gly-H)(Gly)](+) and [Zn(Ala-H)(Ala)](+) were found to lose H2O as their primary fragmentation route with no dehydrogenation observed. Tandem mass spectrometry, deuterium substitution, and infrared spectroscopy were used to determine the origin of the H atoms in the losses of H2, as well as for other fragmentation routes, including the loss of H2O. The hydrogen atoms for H2 loss from [Zn(Pro-H)(Pro)](+) was found to originate on the amine group and primarily from C5 on the non-deprotonated proline, with a smaller contribution from the C2 hydrogen. Both hydrogens for H2O loss were determined to be from labile hydrogens. Potential energy surfaces were computed for the H2 loss and H2O loss routes for both [Zn(Pro-H)(Pro)](+) and [Zn(Gly-H)(Gly)](+) and were compared. For [Zn(Pro-H)(Pro)](+), H2 loss was found to be the pathway with the lower energy requirement than for H2O loss, and the opposite was found for [Zn(Gly-H)(Gly)](+). The greater basicities of proline and sarcosine are most likely responsible for stabilizing the 3 coordinate Zn(2+) transition states en route to H2 loss, compared to those complexes formed with the much less basic glycine or alanine.

Novel nitro-PAH formation from heterogeneous reactions of PAHs with NO2, NO3/N2O5, and OH radicals: prediction, laboratory studies, and mutagenicity.

The heterogeneous reactions of benzo[a]pyrene-d12 (BaP-d12), benzo[k]fluoranthene-d12 (BkF-d12), benzo[ghi]perylene-d12 (BghiP-d12), dibenzo[a,i]pyrene-d14 (DaiP-d14), and dibenzo[a,l]pyrene (DalP) with NO2, NO3/N2O5, and OH radicals were investigated at room temperature and atmospheric pressure in an indoor Teflon chamber and novel mono-NO2-DaiP and mono-NO2-DalP products were identified. Quartz fiber filters (QFF) were used as a reaction surface and the filter extracts were analyzed by GC/MS for nitrated-PAHs (NPAHs) and tested in the Salmonella mutagenicity assay, using Salmonella typhimurium strain TA98 (with and without metabolic activation). In parallel to the laboratory experiments, a theoretical study was conducted to rationalize the formation of NPAH isomers based on the thermodynamic stability of OH-PAH intermediates, formed from OH-radical-initiated reactions. NO2 and NO3/N2O5 were effective oxidizing agents in transforming PAHs to NPAHs, with BaP-d12 being the most readily nitrated. Reaction of BaP-d12, BkF-d12, and BghiP-d12 with NO2 and NO3/N2O5 resulted in the formation of more than one mononitro isomer product, while the reaction of DaiP-d14 and DalP resulted in the formation of only one mononitro isomer product. The direct-acting mutagenicity increased the most after NO3/N2O5 exposure, particularly for BkF-d12 in which di-NO2-BkF-d10 isomers were measured. The deuterium isotope effect study suggested that substitution of deuterium for hydrogen lowered both the direct and indirect acting mutagenicity of NPAHs and may result in an underestimation of the mutagencity of the novel NPAHs identified in this study.

Rotational spectroscopy of pyridazine and its isotopologs from 235–360 GHz: Equilibrium structure and vibrational satellites

The rotational spectrum of pyridazine (o-C4H4N2), the ortho disubstituted nitrogen analog of benzene, has been measured and analyzed in the gas phase. For the ground vibrational state of the normal isotopolog, over 2000 individual rotational transitions have been identified between 238 and 360 GHz and have been fit to 13 parameters of a 6th-order centrifugal distortion Hamiltonian. All transitions in this frequency region can now be predicted from this model to near experimental accuracy, i.e., well enough for the purpose of any future radio-astronomical search for this species. Three isotopologs, [3-(13)C]-C4H4N2, [4-(13)C]-C4H4N2, and [1-(15)N]-C4H4N2, have been detected in natural abundance, and several hundred lines have been measured for each of these species and fit to 6th-order Hamiltonians. Ten additional isotopologs were synthesized with enhanced deuterium substitution and analyzed to allow for a complete structure determination. The equilibrium structure (Re) of pyridazine was obtained by correcting the experimental rotational constants for the effects of vibration-rotation coupling using interaction constants predicted from CCSD(T) calculations with an ANO0 basis set and further correcting for the effect of electron mass. The final Re structural parameters are determined with excellent accuracy, as evidenced by their ability to predict 28 independent moments of inertia (Ia and Ib for 14 isotopologs) very well from 9 structural parameters. The rotational spectra of the six lowest-energy fundamental vibrational satellites of the main isotopolog have been detected. The rotational spectra of the five lowest-energy vibrational satellites have been assigned and fit to yield accurate rotational and distortion constants, while the fit and assignment for the sixth is less complete. The resultant vibration-rotation interaction (α) constants are found to be in excellent agreement with ones predicted from coupled-cluster calculations, which proved to be the key to unambiguous assignment of the satellite spectra to specific vibration modes.

Vibrational Properties of the Isotopomers of the Water Dimer Derived from Experiment and Computations

The water dimer and its 11 deuterated isotopomers are investigated utilizing coupled cluster theory and experimental data as input for a perturbational determination of the isotopomer frequencies. Deuterium substitution reduces the H-bond stretching frequency by maximally 12 cm–1 from 143 to 131 cm–1, which makes a spectroscopic differentiation of H- and D-bonds difficult. However, utilizing the 132 frequencies obtained in this work, the identification of all isotopomers is straightforward. The CCSD(T)/CBS value of the binding energy De is 5.00 kcal mol–1. The binding energy D0 of the water dimer increases upon deuterium substitution from 3.28 to maximally 3.71 kcal mol–1 reflecting a decrease in the zero point energy contribution. The entropy values of the D-isotopomers increase from 73 to 77 entropy units in line with the general observation that a mass increase leads to larger entropies. All 12 isotopomers possess positive free binding energies at 80 K and a reduced pressure of 110 Pa, which means that they can be spectroscopically observed under these conditions.

The electrooxidation mechanism of formic acid on platinum and on lead ad-atoms modified platinum studied with the kinetic isotope effect

Kinetics and mechanism of formic acid (FA) oxidation on platinum and upd-lead ad-atoms modified platinum electrodes have been studied using unlabelled and deuterated compounds. Poisoning of the electrode surface by CO-like species was prevented by suppression of dissociative chemisorption of FA due to a fast competitive underpotential deposition of lead ad-atoms on the Pt surface from an acidic solution containing Pb2+ cations. Modification of the Pt electrode with upd lead induced a catalytic effect in the direct electrooxidation of physisorbed FA to CO2. With increasing degree of H/D substitution, the rate of this reaction decreased in the order: HCOOH > DCOOH ≥ HCOOD > DCOOD. HCOOH was oxidized 8.5-times faster on a Pt/Pb electrode than DCOOD. This primary kinetic isotope effect proves that the C–H- and O–H-bonds are simultaneously cleaved in the rate determining step. A secondary kinetic isotope effect was found in the dissociative chemisorption of FA in the hydrogen adsorption–desorption range on a bare Pt electrode after H/D exchange in the C–H bond, wherein the influence of deuterium substitution in the O–H group was negligibly small. Thus the C–H bond cleavage is accompanied by the C–OH and not the O–H bond split in the FA decomposition, producing CO-like species on the Pt surface sites.

Controlled incorporation of deuterium into bacterial cellulose

Isotopic enrichment has been widely used for investigating the structural and dynamic properties of biomacromolecules to provide information that cannot be carried out with molecules composed of natural abundance isotopes. A media formulation for controlled incorporation of deuterium in bacterial cellulose synthesized by Gluconacetobacter xylinus subsp. sucrofermentans is reported. The purified cellulose was characterized using Fourier Transform Infra-Red spectrophotometry and mass spectrometry which revealed that the level of deuterium incorporation in the perdeuterated cellulose was greater than 90 %. Small-angle neutron scattering analysis demonstrated that the overall structure of the cellulose was unaffected by the substitution of deuterium for hydrogen. In addition, by varying the amount of D-glycerol in the media it was possible to vary the scattering length density of the deuterated cellulose. A large disk model was used to fit the curves of bacterial cellulose grown using 0 and 100 % D-Glycerol yielding a lower bound to the disk radii, R min = 1,132 ± 6 and 1,154 ± 3 A and disk thickness, T = 128 ± 1 and 83 ± 1 A for the protiated and deuterated forms of the bacterial cellulose, respectively. This agrees well with the scanning electron microscopy analysis which revealed stacked sheets in the cellulose pellicles. Controlled incorporation of deuterium into cellulose will enable new types of experiments using techniques such as neutron scattering to reveal information about the structure and dynamics of cellulose and its interactions with proteins and other (bio) polymers.

Saturation recovery electron spin–lattice relaxation studies on benzene anion radical and its derivatives: application of Kivelson–Orbach mechanism of electron spin relaxation

The role of low-lying excited states on the spin–lattice relaxation times (T1) of organic radicals has been investigated. To test the applicability of Kivelson's electric field fluctuation model (D. Kivelson, J. Chem. Phys. 45, 1324 (1966)), based on the Orbach mechanism of spin relaxation, the T1s of the anion radicals of benzene, benzene-1-d, toluene, ethyl benzene, isopropyl benzene, t-butyl benzene, p-xylene, 1,2,4-trimethyl benzene and 1,3,5-trimethyl benzene in liquid solutions, with potassium cation as the counter ion, have been measured by the pulse saturation recovery technique. The energy gap between the ground and the first excited electronic states changed with the substitutions to different extent. The spin–lattice relaxation rates showed correlation with this energy gap. Anion radicals of benzene and benzene-1-d showed the shortest T1 among the radicals studied here. A small but measurable energy splitting due to the deuterium substitution in benzene-1-d radical was obtained from the temperature dependence of T1. Spin–lattice relaxation times of benzene anion measured here decreased monotonically in the range of −60 to −125 °C, in contrast to some reported claims of very unusual temperature dependence, based on the continuous wave microwave power saturation studies. Our results also showed that the ion pairing between benzene anion and potassium cation did not significantly influence the spin–lattice relaxation times.

Structural studies of biological membranes using ESEEM spectroscopy of spin labels and deuterium substitution

Electron Spin Echo Envelope Modulation (ESEEM) spectroscopy in conjunction with biochemical techniques of site-directed spin labeling and deuterium substitution in molecules or parts of molecules can be used to gain insights into supramolecular structure of biological membranes. The review covers the applications of this approach to study water penetration into the hydrophobic part of model phospholipid membranes and into the ion channels of biological membranes, to determine the localization and orientation of peptide antibiotics in membranes, and to investigate the conformations of enzymes and membrane proteins.

Effect of deuteration on the metabolism and clearance of some pharmacologically active compounds—synthesis and in vitro metabolism of deuterated derivatives of dronedadrone

The synthesis and in vitro metabolism studies of a family of specifically deuterated derivatives of dronedarone are described. Metabolic stability and clearance of the parent compound are not sensitive to deuterium substitution, irrespective of the position of the heavy label.

Raman Spectra of Deuterated Potassium Dihydrogen Phosphate Crystals with Different Degrees of Deuteration

The polarized Raman spectra of deuterated potassium dihydrogen phosphate crystals with different deuterium concentrations are measured. With the increasing deuterium concentration, the Raman peaks which are assigned as the internal vibrations of the (H/D)2PO−4 anion shift to lower wavenumbers. This red-shift contributes to the decrease in the bonding force of the P—O bond as a result of the substitution of deuterium for hydrogen. Moreover, the intensity of the strongest peak of these crystals decreases first, and reaches the minimum value while the mole percentage of the deuterium content in the crystal is about 74%. After that, the intensity increases with the increase of the deuterium concentration in the crystal.