Heavy Water Molecules Research Articles

2H-NMR study of molecular reorientation of D2O confined into the slit-shaped micropores of activated carbon fiber

Herein, the reorientation of heavy water (D2O) molecules adsorbed in the slit-type micropores of activated carbon fibers is investigated using the 2H-nuclear magnetic resonance technique. The rotational correlation times (τc) of D2O are evaluated from the 2H spin–lattice relaxation time (T1). The obtained τc values are significantly influenced by both the pore-filling ratio (ϕ) and temperature, thus suggesting that the adsorption of D2O into activated carbon fibers (ACF) effectively influences the reorientation of the D2O molecules within the ACF. The reorientational motion of D2O is examined by the extended jump model. According to this model, the nanoconfinement effect, which results from the reduction in free volume around D2O, is attributed to the transition-state excluded volume effect, whereas the effect of hydrogen bonding between the D2O and surface functional groups is attributed to the transition-state hydrogen bonding effects. Furthermore, the dependence of τc on ϕ is explained by the chemical exchange between the pore surface adsorption sites and the central space of the pore. Thus, the dynamic behavior of adsorbed D2O molecules reveals the mechanism of D2O adsorption into the ACF micropores.

Water isotopic characterisation of the cloud–circulation coupling in the North Atlantic trades – Part 1: A process-oriented evaluation of COSMOiso simulations with EUREC4A observations

Abstract. Naturally available, stable, and heavy water molecules such as HDO and H218O have a lower saturation vapour pressure than the most abundant light water molecule H216O; therefore, these heavy water molecules preferentially condense and rain out during cloud formation. Stable water isotope observations thus have the potential to provide information on cloud processes in the trade-wind region, in particular when combined with high-resolution model simulations. In order to evaluate this potential, nested COSMOiso (isotope-enabled Consortium for Small Scale Modelling; Steppeler et al., 2003; Pfahl et al., 2012) simulations with explicit convection and horizontal grid spacings of 10, 5, and 1 km were carried out in this study over the tropical Atlantic for the time period of the EUREC4A (Elucidating the role of clouds-circulation coupling in climate; Stevens et al., 2021) field experiment. The comparison to airborne in situ and remote sensing observations shows that the three simulations are able to distinguish between different mesoscale cloud organisation patterns as well as between periods with comparatively high and low rain rates. Cloud fraction and liquid water content show a better agreement with aircraft observations with higher spatial resolution, because they show strong spatial variations on the scale of a few kilometres. A low-level cold-dry bias, including too depleted vapour in the subcloud and cloud layer and too enriched vapour in the free troposphere, is found in all three simulations. Furthermore, the simulated secondary isotope variable d-excess in vapour is overestimated compared to observations. Special attention is given to the cloud base level, which is the formation altitude of shallow cumulus clouds. The temporal variability of the simulated isotope variables at cloud base agrees reasonably well with observations, with correlations of the flight-to-flight data as high as 0.7 for δ2H and d-excess. A close examination of isotopic characteristics under precipitating clouds, non-precipitating clouds, clear-sky and dry-warm patches at the altitude of cloud base shows that these different environments are represented faithfully in the model with similar frequencies of occurrence, isotope signals, and specific-humidity anomalies as found in the observations. Furthermore, it is shown that the δ2H of cloud base vapour at the hourly timescale is mainly controlled by mesoscale transport and not by local microphysical processes, while the d-excess is mainly controlled by large-scale drivers. Overall, this evaluation of COSMOiso, including the isotopic characterisation of different cloud base environments, suggests that the simulations can be used for investigating the role of atmospheric circulations on different scales for controlling the formation of shallow cumulus clouds in the trade-wind region, as will be done in part 2 of this study.

Exploring the dynamic changes in hydrogen bond structure of water and heavy water under external perturbation of DMF

The Raman spectra of DMF-water/heavy water binary solutions at different volume ratios are measured to investigate the hydrogen bond structure between N, N-dimethylformamide (DMF) and water/heavy water. It was observed that when VDMF below 40 %, DMF reinforces the hydrogen bond among water molecules through the substitution of a small amount of water molecules within the tetrahedral structure. However, a similar enhancement phenomenon is not observed in heavy water. When VDMF is less than 60 %, the hydrogen bonds among DMF and heavy water molecules affect the symmetry of OD covalent bond. Furthermore, as VDMF exceeds 40 %/60 %, the tetrahedral structures of water and heavy water are gradually replaced by DMF·3H2O/3D2O, DMF·2H2O/2D2O, and DMF·H2O/D2O clusters. The transition point of hydrogen bond structure in DMF- aqueous solution moved to VDMF = 15 % under the influence of under the influence of dynamic high pressure caused by pulsed laser beam. This study provides valuable insights into the microstructure of water/heavy water clusters.

Theoretical Analysis of Hydrogen-Bonded Structures of the Enhanced Green Fluorescent Protein with Multi-Component Density Functional Theory

Abstract Recently, neutron crystallography of the enhanced green fluorescent protein (EGFP) has revealed that a heavy water molecule directly hydrogen-bonded to the chromophore of EGFP, DOD323, has a longer bond length than other heavy water molecules. This remarkable elongation of bond length is because of intrinsic electrostatic potential inside EGFP, but its physicochemical origin has not been fully understood, yet. To clarify the phenomenon, we theoretically investigated the effect of residues surrounding the chromophore on the hydrogen-bonded structure around the chromophore with multi-component density functional theory. We focused on Arg96, Thr203, and Glu222, which are directly hydrogen-bonded to the chromophore. We theoretically confirmed that Arg96 and Thr203 affect the geometric asymmetrization of DOD323 quantitatively. Arg96 and Thr203 also stabilize the anionic (deprotonated) form of the chromophore, and the absence of even one of the residues causes proton/deuteron transfer from the neighboring His148. Our results suggest that Arg96 and Thr203 have a significant effect on the charge states of the chromophore and His148.

Effect of hydrostatic pressure on the quantum paraelectric state of dipolar coupled water molecular network

We measure the real part ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ of the dielectric permittivity of beryl crystals with heavy water molecules ${\mathrm{D}}_{2}\mathrm{O}$ confined in nanosized cages formed by an ionic crystal lattice. The experiments are performed at a frequency of 1 MHz in the temperature interval from 300 down to 4 K under different hydrostatic pressures up to $P=6.3$ GPa. At high temperatures, a Curie-Weiss-like increase of ${\ensuremath{\epsilon}}^{\ensuremath{'}}(T)$ is observed upon cooling. Application of pressure leads to flattening of ${\ensuremath{\epsilon}}^{\ensuremath{'}}(T)$ at low temperatures due to quantum effects, i.e., tunneling of deuterium atoms in the hexagonal localizing potential. Analyzing the temperature behavior of ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ with the Barrett expression allows us to obtain pressure dependencies of the quantum temperature ${T}_{1}$, the Curie-Weiss temperature ${T}_{C}$, and the Barrett constant $C$. The increase of ${T}_{1}$ observed up to 4 GPa is associated with an enhanced azimuthal tunneling of the confined water molecules through the barriers of the potential. For $P>4$ GPa, ${T}_{1}(P)$ levels off since the barriers disappear. Any further pressure increase does not affect the tunneling rate because of the absence of a barrier. The behavior is modeled by solving the Schr\"odinger equation for the water molecule in the azimuthal potential numerically. Small negative values of ${T}_{C}\ensuremath{\approx}\phantom{\rule{4pt}{0ex}}\ensuremath{-}10$ K obtained for $P<4$ GPa indicate the antiferroelectric ordering tendency of the water dipoles localized in the crystalline nanochannels. For higher pressure, a strong decrease of ${T}_{C}$ toward negative values is observed that would correspond to the enhanced interdipole coupling strength, which is however hard to explain in the present case, and thus calls for additional theoretical and experimental studies.

Study of IR Spectroscopy of Crystalline Materials Structure Used in Laser Shutters

The IR absorption spectra of hexagonal crystals of lithium iodate α-LiIO3, used in laser shutters for ship wiring, where the quality, transparency and power of laser radiation are of great importance, are studied. The transmission spectra allowed us to determine the width of the crystal band gap 4.37 eV along the Z-axis (C6 [0001]) and 4.46 eV along the axis perpendicular to the Z axis. The activation energies and the wavelength of the vibrational centers associated with the vibrations of the H3O+, OH-, H2O groups, heavy D2O and semi-heavy molecules HDO are determined. It is established that the band 1450-1650 cm-1 is a superposition of at least two broad absorption maxima centered at ~1550 and ~1600 cm-1. It was experimentally established that the ratio of the absorption coefficients of these bands was ~1:1 (75:74 cm-1) for crystals grown in H2O, and ~2:1 (161:84 cm-1) – for crystals grown in D2O. This allows us to assume that in a lithium iodate crystal grown in D2O, the bands 1550 cm-1 and 1600 cm-1 correspond to the vibrations of the bound HDO and H2O molecules, the band 1150 cm-1 corresponds to the vibrations of heavy water molecules. The results of the study allowed us to propose a mechanism of transport and translational diffusion of protons and to determine the presence of heavy water molecules in crystalline materials, as well as to diagnose the quality of laser crystals.

Catalysis of water molecules acting as Brönsted acids at Lewis acid sites on niobium oxide

The effects of water addition on cumene cracking over niobium oxide and H-ZSM-5 are investigated in order to clarify the behavior of water molecules on solid acid catalysts. The activity of niobium oxide was improved in the presence of water vapor although H-ZSM-5 showed constant activity. When heavy water was introduced into the reaction over niobium oxide, the hydrogen atoms were substituted with the deuterium atoms in about 85 % of the produced benzene. The heavy water molecule on niobium oxide acts as the catalyst for cumene cracking, resulting in the formation of benzene containing D atoms. In addition, the Lewis acid on the niobium oxide was observed to change reversibly to the Brönsted acid in the presence of water using IR of adsorbed pyridine. We propose a mechanism that water behaves as Brönsted acid, which was clarified by repeating adsorption and desorption on Lewis acid sites of niobium oxide.

Wet surface sightings in clusters

Water Structure In principle, the surface structure of water (H2O) should be discernable from the O–H vibrations. In practice, however, so many configurations rapidly interconvert that the bands are bewilderingly broad. Yang et al. studied a cluster of 20 H2O surrounding a cesium ion, using isotopomers that vary in the position of one H2O amid 19 heavy water (D2O) molecules. Precisely assigned spectral features from contributing configurations mapped well onto a bulk surface spectrum. Science , this issue p. [275][1] [1]: /lookup/doi/10.1126/science.aaw4086

Studies on helium-3 separation at Cernavoda nuclear power plant

Helium-3 is a rare isotope of helium (1.37 ppm as fraction of total helium – natural abundance), with applications in medicine, industry, security, and science. The world is experiencing nowadays a shortage of helium-3, related to its high request and to the scarce availability of tritium, which is the most common source of helium-3. Tritium is an unstable isotope of hydrogen because it undergoes a beta-decay with a half-life of 12.3 years, and is a by-product in CANDU type nuclear reactors. Tritium is found mostly in the heavy water from the moderator circuit. It is produced by the thermal neutron activation of deuterium atoms from the heavy water molecules. It can be also found in the cover gas used to control the pressure in the calandria and to provide a non-corrosive, non-radioactive atmosphere in parts of the system not filled with water.In the first part, the paper presents an analysis regarding the feasibility of helium-3 extraction from the cover gas used in Cernavoda Nuclear Power Plant. A theoretical calculation of the amount of helium-3 produced so far is presented. The production rate of helium-3 is related to the concentration of tritium in the heavy water from the moderator circuit. The solubility of helium-3 in water is very low, therefore almost all of it will be found in the moderator cover gas.The second part of the paper presents a technological solution for separation of helium-3 from helium gas by cryogenic distillation that permits obtaining a purity of the distillate of 99.1%, while the raffinate contains only 0.03% helium-3.

Validation of Thermal Neutron Scattering Cross Sections for Heavy Water based on Molecular Dynamics Simulation

Recently, the thermal scattering libraries of ENDF/B-VIII.0 and JEFF-3.3 for light and heavy water were released with a new water model (CAB model) proposed by Damian. For the CAB model, the molecular dynamics code GROMACS was used to more accurately describe the realistic motions of water molecules. In this paper, to consider the coherent component we also generated the thermal scattering cross section of the deuterium and oxygen bound in the heavy water molecules using the GROMACS code and EPSR code. In addition, the frequency spectrum was also calculated using the GROMACS code. Thermal scattering cross sections based on the newly calculated Sköld correction factor and the frequency spectrum were generated by NJOY2016 code. Finally, the performance of the generated thermal scattering cross sections were validated by performing an ICSBEP benchmark simulation using MCNPX code.

Solubility and molar enthalpy of solution of sucralose in H2O and D2O

The solubility of sucralose, a chlorinated derivate of sucrose was measured for the first time in D2O over a range of temperatures. The results are important to verify the effect of substitution of OH by Cl in the structure of sucrose and the consequent interaction with the heavy water molecules. Our findings indicated that in the temperature range measured, the solubility of sucralose in D2O is 23.3% lower than in H2O. Based on such measurements, the dissolution Gibbs free energy, enthalpy and entropy were then determined. The values of solubility and the mentioned thermodynamic parameters were compared to the ones for sucralose in H2O. Beside the determination of dissolution enthalpy by using the van't Hoff Equation, this thermodynamic property was also measured for the two solvents in an isoperibol solution-reaction calorimeter.

The impact of adsorption on the localization of spins in graphene oxide and reduced graphene oxide, observed with electron paramagnetic resonance

We report the observations of electronic properties of graphene oxide and reduced graphene oxide, performed with electron paramagnetic resonance technique in a broad temperature range. Both materials were examined in pure form and saturated with air, helium, and heavy water molecules. We show that spin localization strongly depends on the type and amount of molecules adsorbed at the graphene layer edges (and possible in-plane defects). Physical and chemical states of edges play crucial role in electrical transport within graphene-based materials, with hopping as the leading mechanism of charge carrier transport. Presented results are a good basis to understand the electronic properties of other carbon structures made of graphene-like building blocks. Most active carbons show some degree of functionalization and are known of having good adsorptive properties; thus, controlling both phenomena is important for many applications. Sample treatment with temperature, vacuum, and various adsorbents allowed for the observation of a possible metal-insulator transition and sorption pumping effects. The influence of adsorption on the localization phenomena in graphene would be very important if to consider the graphene-based material as possible candidates for the future spintronics that works in ambient conditions.

Neutron structure of the T26H mutant of T4 phage lysozyme provides insight into the catalytic activity of the mutant enzyme and how it differs from that of wild type.

T4 phage lysozyme is an inverting glycoside hydrolase that degrades the murein of bacterial cell walls by cleaving the β‐1,4‐glycosidic bond. The substitution of the catalytic Thr26 residue to a histidine converts the wild type from an inverting to a retaining enzyme, which implies that the original general acid Glu11 can also act as an acid/base catalyst in the hydrolysis. Here, we have determined the neutron structure of the perdeuterated T26H mutant to clarify the protonation states of Glu11 and the substituted His26, which are key in the retaining reaction. The 2.09‐Å resolution structure shows that the imidazole group of His26 is in its singly protonated form in the active site, suggesting that the deprotonated Nɛ2 atom of His26 can attack the anomeric carbon of bound substrate as a nucleophile. The carboxyl group of Glu11 is partially protonated and interacts with the unusual neutral state of the guanidine moiety of Arg145, as well as two heavy water molecules. Considering that one of the water‐binding sites has the potential to be occupied by a hydronium ion, the bulk solvent could be the source for the protonation of Glu11. The respective protonation states of Glu11 and His26 are consistent with the bond lengths determined by an unrestrained refinement of the high‐resolution X‐ray structure of T26H at 1.04‐Å resolution. The detail structural information, including the coordinates of the deuterium atoms in the active site, provides insight into the distinctively different catalytic activities of the mutant and wild type enzymes.

Розрахунок константи рівноваги димерізації молекул насиченої пари важкої води

The magnitude and the temperature dependence of the equilibrium constant of dimerization of heavy water molecules in saturated vapor in terms of the second virial coefficient of the equation of state have been determined. An expression is found for the equilibrium dimerization constant of water vapor molecules, which contains terms involving the monomer–monomer, monomer–dimer, and dimer–dimer interaction. The obtained results are compared with experimental data. The equilibrium constant of dimerization in heavy water vapor is shown to exceed that in light water vapor within the whole temperature interval.

Signatures of quantum phase transitions and excited state quantum phase transitions in the vibrational bending dynamics of triatomic molecules

Signatures of quantum phase transitions (QPTs) and excited state quantum phase transitions (ESQPTs) in the bending motion of eight XYZ triatomic molecules (HCN, HNC, NiCN; CaOH, CaOD, MgOH, MgOD and OCS), the large-amplitude bending degree of freedom of a tetratomic molecule (HNCS), and four symmetric XY2 triatomic molecules (H2O,D2O,H2S,H2Se) are investigated in an attempt to understand their dependence on the composition of the molecular species. It is shown that the isomerizing HCN/HNC system leads to quasi-linearity, that the water molecule H2O displays a dramatic effect at Ex∼11,000cm−1 with clear indication of an ESQPT at about vibrational quantum number υb=8, and that the heavy water molecule D2O is expected to undergo an ESQPT at υb=10.

Dynamic structures of aqueous oxalate and the effects of counterions seen by 2D IR

Two dimensional vibrational echo spectra of oxalate in the carboxylate asymmetric stretch region in D(2)O show two transitions having anomalously slow spectral diffusion and a third transition having relaxation properties typical of the free carboxylate ion. Quantitative analysis of the frequency shifts of the carboxylate asymmetric stretch modes caused by a singly charged cation in the oxalate hydration shell supports that ion pairs can be responsible for these new transitions. Experimental evidence and DFT calculations are consistent with oxalate forming a mixture of "side-on" and "end on" contact ion pairs wherein the carboxylate groups are protected from mobile heavy water molecules.

2H NMR Spectroscopy and Multiquantum Relaxometry as a Probe of the Magnetic-Field-Induced Ordering of Clay Nanoplatelets within Aqueous Dispersions

2H NMR spectroscopy and relaxometry were used to investigate the orientation of nontronite clay nanoplatelets induced by the static magnetic field within dilute aqueous dispersions by exploiting the residual quadrupolar splitting resulting from the specific orientation of heavy water molecules physisorbed at the clay surface. A careful analysis of the variation of the residual 2H splitting as a function of clay concentration and magnetic field strength was required to extract the intrinsic clay ordering induced by the magnetic field. The variation of clay ordering as a function of clay concentration clearly indicated two concentration regimes, corresponding to free and collective orientations of the clay platelets, respectively. Multiquantum NMR relaxation measurements were further used to identify the main NMR relaxation mechanism whose temperature variation is compatible with a fast exchange, at the NMR time scale, between free and physisorbed water molecules.

Heavy water hydration of mannose: the anomeric effect in solvation, laid bare

The presence and consequences of the anomeric effect have been explored and directly exposed, through an investigation of the vibrational spectroscopy of the doubly and triply hydrated α and β anomers of phenylD-mannopyranoside, (PhMan) isolated under molecular beam conditions in the gas phase. The experiments have been aided by the simple trick of substituting D2O for H2O, which has the advantage of isotopically isolating the carbohydrate (OH) bands from the water (OD) bands. Recording the double resonance, IR-UV ion dip spectra of the hydrated complexes, α- and β-PhMan·(D2O)2,3 in a series of ‘proof of principle’ experiments, revealed that these heavy water molecules engage the key endocyclic oxygen atom, O5, allowing the anomeric effect to be probed through a combination of vibrational spectroscopy and quantum chemical calculations. Importantly, in the dihydrates, both anomers adopt the same conformation and the two water molecules occupy the same template. One of them acts as a remarkably sensitive reporter, able to sense and expose subtle stereoelectronic changes through the resulting changes in its hydrogen-bonded interaction with the substrate.

First Principles Simulations of the Structural and Dynamical Properties of Hydrated Metal Ions Me2+and Solvated Metal Carbonates (Me = Ca, Mg, and Sr)

The structural and dynamical properties of the alkaline earth metal ions Mg2+, Ca2+, and Sr2+ and their carbonate and bicarbonate complexes in aqueous solution are examined through first principles molecular dynamics simulations based on the density functional theory. Calculations were conducted in explicit heavy water molecules and at the average temperature of 400 K, conditions which are necessary to obtain a liquid-like water structure and diffusion time-scales when using gradient corrected density functionals. According to these simulations, the magnesium ion undergoes a significant contraction of its coordination sphere in the Mg(H)CO3(+) aqueous complex, whereas calcium and strontium increase their average first shell coordination number when coordinated to HCO3− or CO32−. The analysis of the water exchange processes in the hydration shells of the metals suggests the following order for metal reactivity in solution: Mg2+ < Ca2+ < Sr2+. Moreover, our simulations suggest that the structures of the mos...

Quadrupolelike electrostatic guiding for cold polar molecules

We demonstrate electrostatic guiding of cold heavy water (D(2)O) molecules over a distance of 44.5 cm by using a quadrupolelike electrostatic field, which is generated by the combination of two parallel charged poles and two grounded metal plates. We measure the transverse spatial distribution of the guided D(2)O molecular beam and study the dependence of the relative guiding efficiency and the transverse temperature of the guided molecular beam on the guiding voltage. Our study shows that the maximum guiding efficiency of approximately 50% can be obtained, and our experimental results are in good agreement with ones of theoretical calculation and Monte Carlo simulations, and this guiding scheme has some potential applications in molecule optics, such as molecular-beam splitter, integrated molecular optics, etc.