Equilibrium properties and crystal growth of D2O + cyclopentane hydrate for sustainable tritium separation

This study reports thermodynamic properties and crystal growth observations of D₂O + cyclopentane hydrate toward the development of a hydrate-based tritium separation process. We employed D₂O as a host of hydrate with respect to the investigation into the formation of D₂O hydrate substrate, which is a core component of the tritium separation process. The hydrate phase equilibrium temperature in the liquid D₂O + liquid cyclopentane system was 3.2°C higher than the corresponding H₂O hydrate. Experiments on crystal growth were conducted at temperatures ranging from 5.1 to 8.5°C under atmospheric pressure. Under each thermodynamic condition, polygonal hydrate crystals appeared, growing along the D₂O/cyclopentane interface. The geometric shape and size of the crystals varied depending on the temperature. The variation in crystal morphology was comparable to that of the H₂O + cyclopentane hydrate. Implications based on the obtained results for the hydrate-based isotopic water separation process design are discussed.     

The Mechanism for the Selective Oxidation of CO Enhanced by H2O on a Novel PROC Catalyst

Preferential oxidation (PROX) reaction of CO in H₂ catalyzed by a new catalyst of FeO _x /Pt/TiO₂ (Fe: Pt: TiO₂ = 100: 1: 100) was studied by dynamic in-situ DRIFT-IR spectroscopy. The oxidation of CO is markedly enhanced by H₂ and H₂O, and the enhancement by H₂/D₂ and H₂O/D₂O takes a common hydrogen isotope. Dynamics of DRIFT-IR spectroscopy suggests that the oxidation of CO with O₂ in the absence of H₂ proceeds via bicarbonate intermediate. In contrast, rapid oxidation of CO in the presence of H₂ proceeds via HCOO intermediate and the subsequent oxidation of HCOO by the reaction with OH, that is, CO + OH→ HCOO and HCOO + OH → CO₂ + H₂O. The latter reaction is a rate determining step being responsible for a common hydrogen isotope effect by H₂/D₂ and H₂O/D₂O.     

Isotope effects in the desaturation of stearic to oleic acid

Comparisons have been made of the rates of desaturation of stearic to oleic acid using a series of differently labeled forms of the substrate and two different methods of assay. The reaction has been measured either by analyzing the amount of labeled oleic acid produced, or by analyzing the amount of tritium released into water from [9,10-³H₂]-labeled substrates. The rate of desaturation of [1-¹⁴C] stearic acid has been compared with that of [threo-9,10-³H₂] and [erythro-9,10-³H₂] stearic acids in which about 99% of the label was at the 9 and 10 positions and in which most of the labeled molecular species contained two tritium atoms. A further series of [erythro-9,10-³H₂] stearates was used in which there was a greater proportion of tritium at positions other than 9 and 10 or a greater proportion of species containing only one tritium atom, or both. In the tritium release assay the enzyme discriminated against the tritium substrates, the discrimination being greater witherythro-ditritio-compounds than with monotritio orthreo-ditritio-compounds. The isotope effect was also observed when [³H] stearoyl-CoA thiol esters were the substrates, and when the source of the enzyme was the green algaChlorella vulgaris. Despite the isotope effect, the release of tritiated water can be used as an assay of desaturase activity. If the absolute value of enzymic activity is required, however, the location and stereochemistry of the tritium atoms should be known or the method standardized against [1-¹⁴C] stearic acid.     

Molecular Hydrogen as a Potential Clinically Applicable Radioprotective Agent

Although ionizing radiation (radiation) is commonly used for medical diagnosis and cancer treatment, radiation-induced damages cannot be avoided. Such damages can be classified into direct and indirect damages, caused by the direct absorption of radiation energy into DNA and by free radicals, such as hydroxyl radicals (•OH), generated in the process of water radiolysis. More specifically, radiation damage concerns not only direct damages to DNA, but also secondary damages to non-DNA targets, because low-dose radiation damage is mainly caused by these indirect effects. Molecular hydrogen (H₂) has the potential to be a radioprotective agent because it can selectively scavenge •OH, a reactive oxygen species with strong oxidizing power. Animal experiments and clinical trials have reported that H₂ exhibits a highly safe radioprotective effect. This paper reviews previously reported radioprotective effects of H₂ and discusses the mechanisms of H₂, not only as an antioxidant, but also in intracellular responses including anti-inflammation, anti-apoptosis, and the regulation of gene expression. In doing so, we demonstrate the prospects of H₂ as a novel and clinically applicable radioprotective agent.     

Discriminative determination of hydrogen gas formed from tandem CO2 reforming and shift reaction by isotope labeling followed by cryogenic gas chromatography

Cryogenic gas chromatography (GC) combined with isotope labeling was applied to discriminative determination of hydrogen gas formed through consecutive CO₂ reforming of methane and water–gas shift reaction. First, hydrogen gas was obtained by using a tandem reaction system, where reforming and shift reaction occurred consecutively. Here, D₂O instead of H₂O was used for shift reaction to label hydrogen gas generated there. Then, the resulting hydrogen isotopes were analyzed by a cryogenic GC system, in which an oven temperature was maintained at −196 °C by immersing a separation column into liquid nitrogen. On the chromatograms, the peaks of H₂ and D₂ generated from reforming and shift reaction, respectively, were clearly observed as well-separated peaks. Based on their peak intensities, hydrogen gas formed through the tandem reaction system was precisely determined with differentiating its sources.     

Effect of single water adsorption on the bond order of calcium silicates and its implication for hydration variation

The differences in hydration between β-C₂S and M3-C₃S, the main phases of silicate cement, have not been fully investigated. In this study, density functional theory calculations were used to investigate the structure and bond order of β-C₂S and M3-C₃S before and after the molecular and dissociative adsorption of single water atoms. The unit cell of M3-C₃S was found to have some O atoms with lower bond orders than those in β-C₂S, implying higher chemical reactivity of O atoms in M3-C₃S. The total bond orders of water atoms generally decreased after molecular adsorption, but reductions were minimal, and there were even increases, when the hydrogen bonding among H and surface O atoms was very weak in several M3-C₃S surfaces. In the case of dissociative adsorption, the bond orders of water O–H hydroxyl tended to increase, and the other bond orders among water atoms decreased sharply, even to zero in some cases. Moreover, the bond order variations of water atoms of β-C₂S and M3-C₃S in molecular adsorption were highly correlated with the adsorption energy, with correlation coefficients of 0.9070 and 0.8330, respectively. In both molecular and dissociative adsorption of β-C₂S and M3-C₃S, the total bond order among Ca atoms with other surface atoms decreased after the Ca atoms adsorbed water atoms. This phenomenon also appeared in the dissociative adsorption of surface O atoms. In M3-C₃S, the total strength of the surface O atom bonded to other surface atoms after dissociative adsorption was similar to the strength of the surface O–H hydroxyl bond. The special O atoms in M3-C₃S showed a clear layered arrangement on the surfaces. In the case of dissociative adsorption, H atoms were preferentially adsorbed to special O atoms in the surface layer.     

Deuterium tracer studies of the mechanism of homogeneous catalytic hydrogenation of sorbic acid with pentacyanocobaltate II

Exchange of deuterium and hydrogen during homogeneous catalytic reduction of sorbic acid with pentacyanocobaltate II has been investigated three ways: isotopic exchange between D₂ and H₂O, H₂-D₂O exchange, and D₂-anhydrous methanol exchange. In contrast to experiments with heterogeneous catalysts, where complete exchange and equilibration occur readily, mass spectrometric analysis of the gas phase above the pentacyanocobaltate II shows slow, incomplete exchange during the course of reduction of either catalyst alone or catalyst and substrate. Mass spectra of methyl hexenoates from the deuterium exchange experiments have been examined. The fragmentation patterns of the esters reduced in the presence of D₂O were compared with those reduced in H₂O and with authentic 2-, 3-, and 4-hexenoates. Little or no exchange occurred with the hydrogen of valeric acid in the presence of pentacyanocoblatate deuteride ion [DCo(CN₅)]³⁻ and deuterium oxide. Experimental results indicate that either the hydrogen or deuterium that adds to the double bond originates predominantly from the solvent. It appears that the hydrogen atoms on the δ-carbon atoms in both 2- and 3-hexenoates exchange with deuterium during reduction in heavy water solutions. Presented at the AOCS meeting. Minneapolis, 1963. A laboratory of the No. Utiliz. Res. and Dev. Div., ARS, USDA.     

Isotope effect of H2/D2 and H2O/D2O for the PROX reaction of CO on the FeOx/Pt/TiO2 catalyst

The oxidation reaction of CO with O₂ on the FeOx/Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O, but no such enhancement occurs on the Pt/TiO₂ catalyst. Isotope effects were studied by H₂/D₂ and H₂O/D₂O on the FeOx/Pt/TiO₂ catalyst, and almost the same magnitude of isotope effect of ca. 1.4 was observed for the enhancement of the CO conversion by H₂/D₂ as well as by H₂O/D₂O at 60 °C. This result suggests that the oxidation of CO with O₂ via such intermediates as formate or bicarbonate in the presence of H₂O, in which H₂O or D₂O acts as a molecular catalyst to promote the oxidation of CO as described below.      

Mechanistic Aspects of Hydrogen Production by Partial Oxidation of Methanol Over Cu/ZnO Catalysts

In this work, mechanistic aspects of the partial oxidation of methanol (POM) to hydrogen and carbon dioxide over Cu/ZnO catalysts have been investigated. The data obtained with different catalyst compositions and different Cu^o metal surface areas showed that the reaction depends on the presence of both the phases ZnO and Cu^o. On the other hand, for catalysts with Cu concentrations in the range 40-60 wt%, the copper metal surface area seems to be the main factor determining the reaction rate. Kinetic isotope effects using CH₃OH and CH₃OD showed that both C–H and O–H bonds are at least partially involved in the rate-limiting step. TPD experiments with pure Cu^o, pure ZnO and the catalyst Cu/ZnO showed that methanol can be activated by both ZnO and copper. On the ZnO surface methanol can form intermediates which in the presence of copper might react and desorb more easily probably via a reverse spillover process. The isotopic product distribution of H₂, HD, D₂, H₂O, HDO and D₂O in the temperature-programmed reaction of CH₃OD revealed a slight enrichment of the products with H, suggesting that during methanol activation on the ZnO some of the D atoms might be retained by the support. The effect of oxygen partial pressure suggests that oxygen atoms on the copper surface strongly promote methanol activation and H₂ and CO₂ formation. It is proposed that oxygen atoms participate in methanol activation by the abstraction of the hydroxyl H atom to form methoxide and OH_surf. This OH_surf species rapidly loses H to the surface regenerating the O_surf.     

The Degradation of Polyglycolide in Water and Deuterium Oxide. Part II: Nuclear Reaction Analysis and Magnetic Resonance Imaging of Water Distribution

Magnetic resonance imaging (MRI) and scanning microbeam nuclear reaction analysis (NRA) were used to monitor changes of water ingress into polyglycolide (PGA) disks with degradation time. MRI detects H₂O, whereas NRA is sensitive to D₂O. The acid-catalysed hydrolysis of the ester is significantly slower in D₂O than H₂O because of the kinetic isotope effect. This behaviour was investigated in Part I. In this paper, NRA was used to investigate PGA hydration in buffers made from D₂O, and NRA and MRI experiments were performed on samples degraded buffers made from a 50% mixture of D₂O and H₂O (D₂O/H₂O 50:50) to allow a comparison between the two techniques. The NRA and MRI results provide direct evidence in support of the four-stage reaction-erosion model reported in previous literature, and show that this model applies to polymer degradation in heavy water and in a buffer made from D₂O/H₂O 50:50. It is believed that this is the first time that NRA and MRI have been compared for the same hydrating system.     

In situ comparison of diffusivities for hydrogen and deuterium in palladium

An electrochemical permeation method was employed to study the diffusion behaviour of hydrogen and deuterium in palladium. Solutions of 0.1 m LiOD (in D₂O) and 0.1 m LiOH (in H₂O) and their mixtures were used as the catholytes. More than one hundred diffusivity data from 20 palladium membranes were collected. Statistical analysis of these data was made to examine the validity of the reversed isotope dependence for hydrogen diffusion in palladium. It was concluded that the effective diffusivities increased with the concentration of deuterium in the electrolyte. In addition, an in situ experiment was also performed by adding to the cathodic cell an equivalent amount of LiOD solution to the original LiOH solution, or vice versa. Graphical comparison of the corresponding permeation transients showed that the permeation rate increased when deuterium was added to the solution of H₂O, and the rate decreased when hydrogen was added to the solution of D₂O. This constitutes direct evidence for the higher diffusivity of deuterium than that of hydrogen in palladium.     

Solvent isotope effect on sol–gel transition of methylcellulose studied by DSC

Methylcellulose (MC), a hydrophobically modified cellulose derivative, in an aqueous solution undergoes sol-to-gel and gel-to-sol transitions on heating and cooling, respectively. Using differential scanning calorimetry, MC in light (H₂O) and heavy (D₂O) water solutions has been investigated to elucidate the solvent isotope effect on the transitions. As a result, their transition temperatures are higher in H₂O by about 4 °C than D₂O. This phenomenon is rationalized in terms of the strength of the hydrophobic attractive interaction; the strength is enhanced by D₂O. We discuss the reason for the enhancement and the difference in the isotope effect between MC and a poly(N-isopropylacrylamide) polymer which shows an opposite trend to MC.     

ESR study of reactions of cellulose with ·OH generated by Fe+2/H2O2

It was demonstrated by ESR spectroscopy that the Fe⁺²/H₂O₂ system gave a reactive species which generated an ESR triplet spectrum or sorbitol similar to that generated by hydroxyl radicals from the Ti⁺³/H₃O₂ system. An ESR spectrum was obtained for the hydroxyl radicals generated by the latter system. However, the lifetime of hydroxyl radicals, generated by the Fe⁺²/H₂O₂ system, was apparently very short, and an ESR spectrum for the hydroxyl radicals, generated by this system, was not observed. The Fe⁺²/H₂O₂ system also generated triplet spectra with cotton cellulose I, cotton cellulose II, and microcrystalline cellulose, suggesting that a hydrogen atom had been abstracted from the hydroxyl group on carbon C₆, or possibly the hydrogen atom on carbon C₅. The ESR spectrum generated on microcrystalline cellulose was less intense than those generated on cellulose I and II. On initiation of graft polymerization of the activated cellulose with acrylonitrile, the triplet spectrum disappeared and was replaced by two strong singlet spectra. One of the singlet spectra was likely generated on carbon C₁ or C₄ on depolymerization of the cellulose molecule, and the other was probably generated on the end of the growing polyacrylonitrile molecular chain. The absence of a triplet spectrum gave direct evidence for the order in which the acrylonitrile monomer was being grafted onto the cellulose molecule. The mechanisms proposed by Haber and Weiss for the reactions generated in the Fe⁺²/H₂O₂ system were generally supported.     

Thermodynamic evaluation of steam gasification mechanisms of carbonaceous materials

Reactions of water with clean, oxidized, and hydrogenated carbon surfaces were investigated using density functional theory. It was confirmed that H₂O can dissociatively chemisorb through highly exothermic reactions on the active sites of clean zigzag and armchair carbonaceous models to yield stable intermediates such as hydroxyl, semiquinone, and cyclic ether functional groups. Since the main products of the carbon-steam gasification process are molecular hydrogen and carbon monoxide, several pathways for their evolution are proposed, all of which are endothermic reactions. The interaction of H₂O with an oxidized surface in some cases is even more exothermic than the interaction with the active sites of a clean surface. However, it becomes endothermic when H₂O interacts with a hydrogen saturated surface. Thus, the presence of hydrogen hinders the gasification reactions by blocking of the active sites rather than by removing surface oxygen.     

Water-gas shift: steady state isotope switching study of the water-gas shift reaction over Pt/ceria using in-situ DRIFTS

The stability of surface formates generated by reaction of bridging OH groups with CO is an important first criterion supporting the idea that the rate limiting step of WGS involves formate decomposition. The second important factor is that, in the presence of water, shown directly by the measurements obtained during this steady state isotope switching study, the forward decomposition of surface formates to CO₂ and H₂ is strongly auto-catalyzed by H₂O, in agreement with the findings of Shido and Iwasawa. Based on a normal kinetic isotope effect previously observed with H₂O:D₂O switching and the response of surface formate coverages to the WGS rate under steady state conditions when a high H₂O:CO ratio is employed, the conclusion is drawn that a surface formate mechanism is likely operating for the low temperature water gas shift reaction.     

The effect of oxygen on the chemisorption on polycrystalline silver surface

The adsorption of oxygen(O₂) and the effect of oxygen on the chemisorption of water(D₂O) and hydrogen(D₂) on polycrystalline silver surface have been studied using the technique of thermal desorption spectroscopy(TDS) under ultra-high vacuum(UHV) condition. Three different states of adsorbed oxygen are observed on the surface. The adsorptions and reactions of water and hydrogen on the oxygendosed surface are strongly affected by the pre-adsorbed oxygen. Water on the oxygen-dosed surface shows a maximum desorption at 430K. During the adsorption of hydrogen on the oxygen-dosed surface, hydrogen is rapidly oxidized by a stepwise reaction in which hydrogen reacts first with O(a) to yield hydroxyl intermediate[OD(a)] and then this intermediate reacts to form water. The rate-determining step in this reaction is desorption of water.     

Water diffusion in Zr-containing fiberglass materials at room temperature

Diffusion of water into Zr-containing silica fiberglass materials was studied at room temperature by infrared spectroscopy. Several types of experiments were performed: (a) rehydration with H₂O of fiberglass materials previously calcined in air at 450°C and under vacuum at 180°C; (b) isotopic experiments for uncalcined fiberglass materials using D₂O with and without the presence of sodium. Water diffusion coefficients were determined in each case. It was suggested that the transfer of the protons and water molecules occurred by different mechanisms: the protons diffused through the hydroxyl groups via the relay mechanism like in liquid water, whereas water diffused more slowly in the form of molecular water.     

Analysis of Water and Hydroxyl Species in Soda Lime Glass Surfaces Using Attenuated Total Reflection (ATR)‐IR Spectroscopy

ATR‐IR spectroscopy is a useful and convenient method for evaluation of local structure and concentration of water and hydroxyl species in glass because it can be more surface sensitive than reflection or transmission IR analysis. In this work, a semiquantitative analysis of the ATR spectra of OH groups and interstitial molecular water species in glass surfaces after various surface treatments is presented. Both hydroxyl groups and interstitial molecular water exist in the hydrated surfaces but the relative water speciation varies with surface treatment. The SiOH and H₂O species in the glass surface showed a wide range of hydrogen bonding interactions and their distributions varied with the SO₂, polishing, acid leaching, thermal tempering, and chemical strengthening treatments. SIMS analysis of the hydrogen concentration — depth profiles for the acid‐leached samples was used to provide independent information to validate and quantify the ATR signal.     

The γ-radiolysis of zeocarb 225 cation-exchange resins

Irradiation of Zeocarb 225 cation-exchange resin leads to a loss of exchange capacity and the formation of SO₄^2? ions. G(SO₄^2?) is dependent upon the relative amount of water associated with the resin and may be reduced by the addition of scavengers, reactive towards hydroxyl radicals. The results suggest that both direct and indirect radiolyses are able to bring about desulphonation and that hydroxyl radicals are responsible for the indirect radiolysis.     

Low-dimensional compounds containing bioactive ligands. Part VI. Spectral and structural characterizations of a unique zinc(II) compound with biologically active ligand — clioquinol

The investigated compound of {[Zn(CQ)₂(H₂O)₂]₂[Zn(CQ)₂(H₂O)]₃}·5DMF·2H₂O (1) composition (where CQ = 5-chloro-7-iodo-quinolin-8-ol, DMF = N,N-dimethylformamide) was prepared by simple mixing of ZnCl₂ and CQ. Infrared spectroscopy confirmed the presence of CQ, DMF and H₂O molecules in the prepared compound. X-ray structural analysis revealed that the structure of the title compound consists of five independent Zn(II) atoms, which are coordinated by two bidentately coordinated molecules of CQ. Three of these central atoms are also coordinated by one water molecule, while the other two have two water molecules in the coordination sphere. The structure of 1 also includes five solvated DMF and two water molecules involved in thirteen hydrogen bonds, which interconnect different complex species to form four “triplets”, in the centre of which are units with hexacoordinated Zn atoms surrounded by two units with pentacoordinated Zn atoms. These triplets are linked together to chains parallel with the b axis by two kinds of π–π interactions.