Effect Of Deuterium Substitution Research Articles

Dynamic Behavior of Heavy Water Inside and Outside of Poly (N-Isopropylacrylamide) (PNIPAM) Microgel Using Broadband Dielectric Spectroscopy

One pot free radical precipitation polymerization was used to synthesize an aqueous suspension of non-ionic poly ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -isopropylacrylamide) [PNIPAM] microgel particles. For dielectric measurements in the frequency range of 100 MHz to 50 GHz and temperature range of 288 K to 323 K, 10 wt. % of freeze-dried PNIPAM microgels dispersed in heavy water were used. The relaxation process was seen at around 15 GHz, which corresponds to the entire rotational motion of the heavy water, both within and outside the microgel. Furthermore, in the high frequency relaxation spectrum, heavy water outside the microgel (h1-process with a relaxation time of h1, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h1</sub> , fixed as that of pure heavy water) and confined heavy water within the microgel (h2-process with a relaxation time of h2, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h2</sub> ) were evaluated in view of the two-water model’s assumption and contribution. Under volume phase transition temperature (VPTT), τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h2</sub> is about 4 to 5 times larger than τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h1</sub> , and it does not change much even though the temperature is raised. However, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h2</sub> rapidly increases above VPTT from 7 to 14, which reveals that the dynamics of heavy water are severely constrained inside the shrunken state of the PNIPAM microgel. The obtained results are compared to the dynamics of pure water in PNIPAM microgels aqueous suspension to better understand the effect of deuterium substitution for hydrogen on the dynamics of heavy water inside and outside of PNIPAM microgels.

Conformations and Low-Frequency Intramolecular Motions of 1-Butanol, 1-Butanethiol, Iso-butanol, and Iso-butanethiol Investigated by Fourier Transform Microwave Spectroscopy Combined with Quantum Chemical Calculations.

The rotational spectra of 1-butanol (1-BuOH), 1-butanethiol (1-BuSH), 2-methyl-1-propanol (iso-BuOH), and 2-methyl-1-propanethiol (iso-BuSH) were measured by Fourier transform microwave spectroscopy in the frequency region from 3.7 up to 25 GHz. The observed spectral lines were assigned by observation of the deuterium substitution effect and by ab initio or density functional theory calculations at the levels of MP2/6-311++G(d,p) or B3LYP and cam-B3LYP, respectively. For 1-BuOH and 1-BuSH, seven of the 14 conformations, anticipated to exist as stable, were detected, whereas four and three among the five possible conformations were identified for iso-BuOH and iso-BuSH, respectively. We further found that, of the seven conformers of 1-BuOH, five were trans and two gauche, with respect to the internal rotation axis: the C2-C3 bond, while three of iso-BuOH existed in gauche and one in trans. The most stable conformer of the two BuOH molecules was trans with respect to the C-O bond, while all the sulfur analogues were gauche to the C-S axis. The rare isotopomers examined included 13C and OD of 1-BuOH and OD of iso-BuOH, 34S, 13C, and SD of the two sulfur molecules, and the rotational constants obtained on these isotopomers were employed in the molecular structure derivation. The potential barrier to CH3 internal rotation and the deuterium quadrupole coupling constant, where available, were also derived from the spectral analysis, and the molecular parameters thus obtained were compared with those derived using quantum-chemical calculations; the values derived using cam-B3LYP/6-311++G(d,p) were in better agreement with the observed than those derived using MP2/6-311++G(d,p) and B3LYP/6-311++G(d,p). The TTg form of 1-BuOH and of 1-BuSH and the Tg form of iso-BuSH exhibited additional spectral splittings, which were interpreted as caused by the OH or SH group tunneling between the symmetric and antisymmetric states. Some of the J = 8 rotational levels of 1-BuSH happened to be near-degenerate with others, and the splittings in them caused by mutual repulsion could be precisely determined by the observation of the transitions involving those split levels. Such splittings were determined for 1-BuSH, 1-BuSD, and iso-BuSH to be 1694.1731 (22), 56.3174 (16), and 6.4678 (14) MHz, respectively. A natural bond orbital analysis was performed to show that the most stable conformation of the primary and secondary alcohols is Gt because of the charge transfer from the lone-pair electron of the oxygen atom to the antibonding orbital of the C-H bond in 1-BuOH, whereas in iso-BuOH, the charge transfer to the antibonding orbital of the C1-C2 bond.

Hydrogen movements in the oxidative half-reaction of kynurenine 3-monooxygenase from Pseudomonas fluorescens reveal the mechanism of hydroxylation

Kynurenine 3-monoxygenase (KMO) catalyzes the conversion of l-kynurenine (L-Kyn) to 3-hydroxykynurenine (3-OHKyn) in the pathway for tryptophan catabolism. We have investigated the effects of pH and deuterium substitution on the oxidative half-reaction of KMO from P. fluorescens (PfKMO). The three phases observed during the oxidative half reaction are formation of the hydroperoxyflavin, hydroxylation and product release. The measured rate constants for these phases proved largely unchanging with pH, suggesting that the KMO active site is insulated from exchange with solvent during catalysis. A solvent inventory study indicated that a solvent isotope effect of 2–3 is observed for the hydroxylation phase and that two or more protons are in flight during this step. An inverse isotope effect of 0.84 ± 0.01 on the rate constant for the hydroxylation step with ring perdeutero-L-Kyn as a substrate indicates a shift from sp2 to sp3 hybridization in the transition state leading to the formation of a non-aromatic intermediate. The pH dependence of transient state data collected for the substrate analog meta-nitrobenzoylalanine indicate that groups proximal to the hydroperoxyflavin are titrated in the range pH 5–8.5 and can be described by a pKa of 8.8. That higher pH values do not slow the rate of hydroxylation precludes that the pKa measured pertains to the proton of the hydroperoxflavin. Together, these observations indicate that the C4a-hydroperoxyflavin has a pKa ≫ 8.5, that a non-aromatic species is the immediate product of hydroxylation and that at least two solvent derived protons are in-flight during oxygen insertion to the substrate aromatic ring. A unifying mechanistic proposal for these observations is proposed.

Deuterium Kinetic Isotope Effect Studies of a Potential in Vivo Metabolic Trapping Agent for Monoamine Oxidase B

Visualizing the in vivo activity of monoamine oxidase B (MAO-B) is a valuable tool in the ongoing investigation of astrogliosis in neurodegeneration. Existing strategies for imaging changes in MAO enzyme expression or activity have utilized the irreversible suicide inhibitors or high-affinity reversibly binding inhibitors as positron emission tomography (PET) ligands. As an alternative approach, we developed 4-methyl-7-[(1-[11C]methyl-1,2,3,6-tetrahydropyridin-4-yl)oxy]-2 H-chromen-2-one ([11C]Cou) as a metabolic trapping agent for MAO-B. Trapping of [11C]Cou in rhesus monkey brain demonstrated MAO-B selectivity. In this work, we have attempted to improve on the in vivo pharmacokinetics of [11C]Cou by using the deuterium kinetic isotope effect (KIE) to slow the MAO-B-mediated oxidation step and thus reduce the rate of trapping in brain tissues. However, in vitro assays of enzyme kinetics and in vivo PET imaging of pharmacokinetics in primate brain showed no effects of deuterium substitution on the tetrahydropyridine ring of [11C]Cou. The results are possibly due to masking of the KIE by a second step in the overall metabolism of the new imaging agent.

Understanding How Isotopes Affect Charge Transfer in P3HT/PCBM: A Quantum Trajectory-Electronic Structure Study with Nonlinear Quantum Corrections.

The experimentally observed effect of selective deuterium substitution on the open circuit voltage for a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM; Nat. Commun. 2014, 5, 3180) is explored using a 221-atom model of a polymer-wrapped PCBM molecule. The protonic and deuteronic wave functions for the H/D isotopologues of the hexyl side chains are described within a quantum trajectory/electronic structure approach where the dynamics is performed with newly developed nonlinear corrections to the quantum forces, necessary to describe the nuclear wave functions; the classical forces are generated with a density functional tight binding method. The resulting protonic and deuteronic time-dependent wave functions are used to assess the effects of isotopic substitution (deuteration) on the energy gaps relevant to the charge transfer for the donor and acceptor electronic states. While the isotope effect on the electronic energy levels is found negligible, the quantum-induced fluctuations of the energy gap between the charge transfer and charge separated states due to nuclear wave functions may account for experimental trends by promoting charge transfer in P3HT:PCBM and increasing charge recombination on the donor in the deuterium substituted P3HT:PCBM.

Spectroscopic study on deuterated benzenes. I. Microwave spectra and molecular structure in the ground state.

We observed microwave absorption spectra of some deuterated benzenes and accurately determined the rotational constants of all H/D isotopomers in the ground vibrational state. Using synthetic analysis assuming that all bond angles are 120°, the mean bond lengths were obtained to be r0(C-C) = 1.3971 Å and r0(C-H) = r0(C-D) = 1.0805 Å. It has been concluded that the effect of deuterium substitution on the molecular structure is negligibly small and that the mean bond lengths of C-H and C-D are identical unlike small aliphatic hydrocarbons, in which r0(C-D) is about 5 mÅ shorter than r0(C-H). It is considered that anharmonicity is very small in the C-H stretching vibration of aromatic hydrocarbons.

Keto-Enol Tautomeric Equilibrium of Acetylacetone Solution Confined in Extended Nanospaces.

We aim to clarify the effects of size confinement, solvent, and deuterium substitution on keto-enol tautomerization of acetylacetone (AcAc) in solutions confined in 10-100 nm spaces (i.e., extended nanospaces) using (1)H NMR spectroscopy. The keto-enol equilibrium constants of AcAc (K(EQ) = [keto]/[enol]) in various solvents confined in extended nanospaces of 200-3000 nm were examined using the area ratios of -CH3 peaks in keto to enol forms. The results showed that the keto form of AcAc in hydrogen-bonded solvents such as water and ethanol increased drastically with decreasing space sizes below about 500 nm, but the size confinement did not induce equilibrium shifts in aprotic solvents such as DMSO. The magnitudes of K(EQ) enhancement were well correlated with solvent proton donicity. It followed from the determination of thermodynamic parameters that the stabilization of intermolecular interactions between protons in water and carbonyl oxygen (C═O) in the keto form of AcAc were promoted by size-confinement, and that the keto form could be energetically and structurally favored in extended nanospaces vis-à-vis the bulk space. Furthermore, the measurements of deuterium dependence of the K(EQ) values verified that the nanoconfinement-induced shifts of keto-enol tautomerization of AcAc are attributable to high proton mobility via a proton hopping mechanism of the confined water.

Phase behavior of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide with chloroform and/or chloroform/carbon tetrachloride mixed solvent

The phase behavior of liquid mixtures of the ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C2MIM][NTf2]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C4MIM][NTf2]), 1-pentyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C5MIM][NTf2]) with chloroform and chloroform/carbon tetrachloride mixed solvent including the effect of deuterium substitution in chloroform has been studied. Using the cloud point method the phase diagrams were obtained showing very complicated miscibility behavior. Thus phase diagrams with the upper critical solution temperature (UCST) were obtained in most cases however under some conditions the phase diagrams with the lower critical solution temperature (LCST) or even with the both (UCST and LCST) were also observed. The “hourglass” type of the phase diagrams constitutes another type of the phase behavior observed in this study. Deuterium substitution affects the miscibility very seriously, in particular in the systems with the mixed solvent (CHCl3/CCl4). In general the worse miscibility is observed, and deuteration induces large isotope shifts of the UCST and LCST, provoking in some cases the transfer from the UCST/LCST behavior to the “hourglass” phase diagram.

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.

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.

ChemInform Abstract: Hydrogen Bonding in the Symmetry-Equivalent C2h Dimer of 2-Pyridone in Its S0 and S2 Electronic States. Effect of Deuterium Substitution.

The properties of the two intermolecular N–H⋅⋅⋅O bonds that are responsible for the formation of the cis‐peptide‐like dimer of 2‐pyridone (2PY) have been examined using deuterium substitution of the bridging hydrogen atoms as a probe. Studies of the fully resolved S2←S0 electronic spectrum of (2PY)2 in a molecular beam show that the protonated dimer has a symmetry‐equivalent planar C2h structure in its S0(1Ag) and S2(1Bu) states. Analogous studies of (2PY)2–d1 and (2PY)2–d2 show that (2PY)2 and (2PY)2–d2 are energy delocalized dimers in their S2 states, with an exciton splitting of less than 20 cm−1. Effective structures of the symmetric dimers in both states are derived from the measured rotational constants. A comparison of these structures shows that there is a distortion of the hydrogen‐bonding geometry when hydrogen is replaced by deuterium, along both in‐plane and out‐of‐plane coordinates. ΔR(N–H⋅⋅⋅O)=0.008 A, Δθ[C=O⋅⋅⋅(H)–N]=0°, and Δφ (the dihedral angle)=0.96° in S0 (2PY)2–d2 and ΔR=0.003 A, Δθ=0...

Effect of Deuterium Substitution on the Physical Properties of Polymer Melts and Blends

Using our simple lattice-based equation of state, we capture the effect of deuterium substitution in polystyrene (PS), predicting both the pure component melt properties and the remarkable shift in...

The effect of deuterium substitution in the amino group on the internal-rotation barrier of acetamide

Peptide molecules XCO–NYY′ are characterized by low potential barrier V 3 to internal rotation of a methyl group substituted for X and/or Y. A most conspicuous example is acetamide, for which V 3 was previously reported to be 25.043857(19) cm −1 [8]. The present study intended to clarify why V 3 is so low in acetamide, by examining the effect of the out-of-plane bending or inversion of the amino group on the molecular structure through deuterium substitution for amino hydrogens. The potential barrier V 3 in acetamide was found to decrease by 2.630, 2.986, and 5.532 cm −1, when H′s at cis, trans, and both positions in the amino group were replaced by deuterium atoms, respectively. The reduction was proportional to the effective mass of the out-of-plane bending mode of the amino group (hereafter referred to as the amino inversion), which was in turn ascribed to the change in electronic resonance character of the peptide linkage. The amino inversion is coupled with the CH 3 internal rotation, producing an interaction term proportional to τ sin 3 α, where τ and α denote the amino inversion and methyl internal rotation angles, respectively. This coupling term, when the inversion is treated by second-order perturbation, yields a V 6 term in the internal-rotation potential function of the methyl group, in agreement with the finding of Ilyushin et al. [8], who derived an unusually large V 6 term of −10.044874(73) cm −1. It is quite interesting that even a small perturbation such as deuterium substitution causes a substantial change in electronic structure of the peptide linkage.

Densities, Viscosities, and Speeds of Sound of the Nitromethane + 1-Pentanol System near the Critical Demixing Temperature: Effect of Deuterium Substitution

Densities, viscosities, and speeds of sound were measured for the binary mixtures of nitromethane and 1-pentanol and their deuterated forms in the vicinity of the upper critical solution temperature. The excess molar volumes and excess isentropic compressibilities as well as the deviations of viscosity were determined. The influence of the deuterium substitution was analyzed and discussed.

The Totally Symmetric Vibrations of NH3···HF and NH3···HCN: a CCSD(T) Study Including Anharmonicity Effects

Abstract The coupled cluster variant CCSD(T) has been employed to calculate potential energy and dipole moment surfaces for the hydrogen-bonded complexes NH3···HF and NH3···HCN, restricting the treatment to the totally symmetric coordinates. Both complexes have C 3ν symmetry, with equilibrium dissociation energies (D e) predicted to be 52.1 and 27.1 kJ mol−1, respectively. Vibrational term energies and wavefunctions as well as absolute IR intensities are calculated under inclusion of anharmonicity effects. In contrast to previous theoretical work for NH3···HF, the umbrella bending vibration of this complex as well as for NH3···HCN is found to be rather anharmonic. The familiar double harmonic approximation fails to yield reliable values for the IR intensities of the NH3 (ND3) symmetric stretching vibrations of either NH3···HF or ND3···DF. The wavenumbers of the intermolecular stretching vibrations are predicted as ν4 = 277 cm−1 (NH3···HF) and ν5 = 154 cm−1 (NH3···HCN). Owing to a large quadratic coupling term in the electric dipole moment function, the band ν4(NH3···HF) has virtually zero intensity. The effects of deuterium substitution on wavenumbers and IR intensities have been studied for both complexes.

Thermodynamic isotope effect in partial oxidation of methane to syngas

AbstractThermodynamic deuterium substitution effects on reactant conversion and product selectivity were investigated by computer simulation for the stoichiometric partial oxidation of methane. Methane conversion shows a normal deuterium isotope effect, whereas CO selectivity shows an inverse deuterium isotope effect. H2 selectivity exhibits a large normal deuterium effect. Moreover, deuterium isotope effects are dependent on reaction temperatures and pressures. When reaction pressure is very low, such as 0.001 MPa, all thermodynamic deuterium isotope effects are negligible at 650°C or above. Three criteria, based on the deuterium‐isotope effects, were proposed to determine whether a partial oxidation reaction of methane is kinetically controlled without accurately measured reaction temperatures.

Quantifying the effects of deuterium substitution on phospholipid mixing in bilayer membranes. A nearest-neighbor recognition investigation.

Nearest-neighbor recognition measurements have established that the effects of deuterium substitution on phospholipid mixing are exceedingly small. Thus, the mixing behavior of an exchangeable phospholipid bearing two stearoyl chains with a homologue containing two myristoyl chains in gel-fluid bilayers, fluid bilayers, cholesterol-rich fluid bilayers, and gel-fluid bilayers that have been enriched with cholesterol correspond to a difference in the free energy of mixing that is less than 2.2 cal/mol of hydrogen in all cases. These findings provide the strongest evidence to date in support of the use of deuterated phospholipids as "nonperturbing" probes for structural and dynamic studies of bilayer membranes.

Reactivity of methanol on clean Ru( [formula omitted]) studied by RAIRS: effect of deuterium substitution

The effect of deuteration on the reactivity of methanol on clean Ru(0 0 1) has been studied by comparing the adsorption and decomposition of methanol (CH 3OH), methanol- d 3 (CD 3OH) and methanol- d 4 (CD 3OD) on that surface, using reflection–absorption infrared spectroscopy (RAIRS). At 90 K and low exposure, the three methanol isotopomers adsorb dissociatively as methoxide (CH 3O– or CD 3O–), in a tilted geometry. The isotope effect is revealed by a lower coverage of CD 3O– for methanol- d 4, reflecting the higher O–D versus O–H bond enthalpy. The deuterated alcohols undergo C–D bond scission at 110 K, leaving mostly CO (ads), whereas CH 3OH does not undergo C–H bond cleavage bellow 120 K. This higher reactivity of the deuterated alcohols was interpreted in terms of a surface assisted mechanism. No isotope effect is observed upon adsorption above 120 K. At 190 K, all the methanol isotopomers decompose into stable η 2-formaldehyde (H 2CO or D 2CO, respectively) on passivated Ru(0 0 1) surfaces, obtained by sequential dosing.

Deuterium isotope effect on enantioselectivity in the Comamonas testosteroni quinohemoprotein alcohol dehydrogenase-catalyzed kinetic resolution of rac-2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane, solketal

Isotopic substitution provides an effective tool to probe the mechanism of enzyme-catalyzed reactions. To our knowledge, kinetic isotope effects on the enantioselectivity of enzymes have not been reported. We investigated the effect of deuterium substitution on the enantiomeric ratio, E, of PQQ-containing quinohemoprotein alcohol dehydrogenase, QH-ADH, from Comamonas testosteroni in the ferricyanide-coupled kinetic resolution of rac-2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane, solketal. Under otherwise identical conditions, we measured E=30 for solketal and E=6 for rac-2,2-dimethyl-4-[1,1- 2H]hydroxymethyl-1,3-[5,5,4- 2H]dioxolane, d 5-solketal. It is proposed that isotopic substitution affects the relative kinetic weights of the initial hydron/deuteron transfer from substrate to cofactor and the subsequent proton/deuteron shift in the cofactor–product complex. The latter step becomes more important in the deuterated complex to the extent that the enantiomer discrimination in the first step is partially overruled.