D2O Molecules Research Articles

State-selected photodissociation of D2O

The effect of selective vibrational preparation of the parent on its absorption cross section and on the vibrational distribution of the photofragments is studied in D2O. Rovibrationally excited D2O molecules are prepared in the | 03 〉− state by infrared excitation and photolyzed via the A(1B1) state by 193 nm photons. The OD fragments are detected by laser-induced fluorescence. The ≈ 1 eV vibrational excitation of D2O results in a five orders of magnitude increase in the absorption cross section and its subsequent photolysis yields OD with (v = 1)/(v = 0) = 0.39±0.07. The significant population of both vibrational states of OD may help in testing quantitative agreement between experiment and future theoretical studies of state-selected photodissociation.

Static and Dynamic Behaviour of the Crystal Water Molecules in the Normal Phase of Deuterated Betaine Calciumchloride Dihydrate

AbstractThe static and dynamic behaviour of the deuterated crystal water molecules in the normal (N) phase of betaine calciumchloride dihydrate (BCCD) single crystals is investigated by means of quadrupolar perturbed 2H NMR. The temperature dependence both of the 2H NMR spectra and of the 2H spin‐lattice relaxation time 7i can be interpreted consistently by a thermally activated exchange process of the deuterons within the D2O molecule. At 170 K, under the condition of slow exchange, the electric field gradient (EFG) tensors of both deuterium sites are determined. From their principal axes and the quadrupole coupling constants information is derived about the structure of the C1D2O unit in BCCD in comparison with previous X‐ray studies.

STUDIES ON THE DEUTERATION OF AROMATIC ORGANOSULFUR COMPOUNDS USING AQUEOUS TRANSITION METAL SPECIES

Abstract Reaction of benzenethiols and benzo[b]thiophene (BT) with D2O solutions of trichlorides of Ru, Fe or Cr at elevated temperatures (200–315°C) constitutes a simple method for the preparation of per-deuterated derivatives. Substitution patterns observed for partially deuterated products imply that D-incorporation occurs by standard electrophilic processes. Reactions with benzenethiols produced diaryl sulfides as by-products although these compounds were deuterated to the same extent as the thiols. Experimental observations and the known behaviour of aqueous transition metal species indicate that D+ is furnished by the hydrolysis of D2O molecules in the solvation sphere of the metal ion. Complete deuteration of the organosulfur substrates was achieved using a 100: 1 organosulfur/metal chloride mole ratio. Hydrodesulfurization of per-deuteroBT under standard conditions afforded perdeuteroethylbenzene in good yield.

The Crystal Structure of α- and β-Cs2U2O7

The structure of anhydrous β-Cs2U2O7 has been redetermined. The compound is stabilized by water, and the structure of the stable compound in air, α-Cs2U2O7 · 0.4D2O, has been determined with neutron powder diffraction data. Infrared spectra show these D2O molecules to be chemically bonded.

Energy partitioning in the reaction 2H2+ O2? 2H2O on Pd(111)

(2 + 1)-Photon resonance-enhanced multiphoton ionization (REMPI) has been used to detect desorbed H2O molecules in a state-specific manner. We have studied the reaction on Pd(111) at temperatures between 500 and 700 K in the regime of low oxygen coverages ( <0.05 ML) resulting from adsorption of ambient O2. D2 is dosed using a supersonic molecular beam with pulse fluxes resulting in stoichiometric coverages of D and O atoms. We find that D2O molecules are desorbed with a translational energy of ca. 300 K with weak, if any, dependence on the surface temperature. The angular distribution is nearly cosine in form. The spectroscopic data indicate that the D2O is desorbed with an average energy in the rotational degree of freedom close to the surface temperature. Experiments probing vibrationally excited states yielded negative results setting an upper limit for their population. These data show that most of the excess energy of the final OD + D reaction step of ca. 100 kJ mol–1 is not channelled into any of the degrees of freedom of the desorbed molecules. The data are interpreted such that the product water molecules reside on the surface for a time sufficient to dissipate most of the energy.

FTIR evidence for alcohol binding and dehydration in phospholipid and ganglioside micelles.

We theorize that intoxicants and modern anesthetics bind at the membrane-water interface and displace (dehydrate) bound water molecules by breaking the hydrogen bonds. We tested this hypothesis by examining the effect of butanol on the binding of water to the polar regions of lipids in reversed micelles. Understanding the mechanisms of intoxication requires studies in physiologically relevant systems such as systems containing sialoglycoconjugates, especially gangliosides, which concentrate in the synapses of neural tissue. Therefore, we compared butanol effects on phospholipid with effects on ganglioside. Hydrogen-bond breaking activity of 1-butanol was studied in reversed micelles made of dipalmitoylphosphotidylcholine (DPPC), ganglioside (GM1 and GT1b) or the lipid mixture in a D2O-CCl4 medium. Fourier transform infrared spectroscopy (FTIR) data indicated that 1-butanol binds to DPPC and to gangliosides. Adding GM1 to the DPPC micelles introduces a new binding site for the alcohol. GT1b binds more butanol than GM1, because of more binding sites provided by extra sialic acid moieties. Spectral red shifts indicate that both water and butanol bind to the C = O group of sialic acid. Butanol partially releases the surface-bound water by disrupting hydrogen bonds, as indicated by an appearance of a sharp new free OD stretching band of the released D2O molecules. However, control studies with lipid-free systems in CCl4 revealed that a free OD peak could occur from a deuterium exchange reaction between D2O and 1-butanol(ol-h).(ABSTRACT TRUNCATED AT 250 WORDS)

The Intramolecular Structure of Oxonium Ion in Concentrated Aqueous Deuterochloric Acid Solutions

Abstract Time-of-flight (TOP) neutron diffraction experiments have been carried out for pure liquid D2O and concentrated aqueous deuterochloric acid solutions (DCl)x(D2O)1−x (x = 0.10, 0.23). The errors due to the inelasticity effect on the molecular structure in the solution were markedly reduced by the TOF measurement at the small scattering angle (2θ=44°). From the least square fit of the theoretical intramolecular interference function to the observed one, the internuclear distances, rOD and rDD, and the root mean square displacements, lOD and lDD, in both D3O+ and D2O molecules were determined as follows; rOD = 1.04(4) Å, rDD = 1.63(5) Å, lOD = 0.07(2) Å and lDD = 0.12(6) Å for D3O+, and rOD = 0.983(5) Å, rDD = 1.55(4) Å, lOD = 0.067(8) Å, and lDD = 0.12(4) Å for D2O. The bond angle ∠DOD in D3O+ was also calculated to be 103°. The trigonal pyramidal structure of oxonium ion in the liquid phase has been lead through this investigation.

Experimental and simulated vibrational spectra of H2 absorbed in amorphous ice: Surface structures, energetics, and relaxations

Infrared spectra are reported for thin films of deuterated microporous amorphous ice formed at 12 K and saturated with absorbed molecular hydrogen. This paper focuses on both the influence of the surface-bound H2 on the absorption bands of the OD groups that dangle from the micropore surfaces and the behavior of the induced infrared bands of the stretching mode of H2 itself. Both structural changes and the relaxation of ortho-H2 to para-H2 are apparent from variations in the observed spectra with time and temperature. A reasonably detailed interpretation of the complex spectral behavior has been possible through simulation of spectra for H2 interacting with the surface of amorphous ice clusters generated previously in a classical trajectory study of the cluster growth through the accumulation and relaxation of individual water molecules. Potential minima were calculated with respect to H2 coordinates on the cluster surface and a qualitative interpretation of adsorbate–surface bonding provided via the partitioning of the H2⋅⋅D2O interactions into relatively weak van der Waals interactions, and stronger electrostatic interactions between the H2 quadrupole and the H2O dipole and quadrupole. The net binding of H2 to the surface is dominated by several van der Waals interactions with neighboring D2O molecules, but in most of the calculated minima, H2 also forms a single electrostatic bond to a surface molecule. While such electrostatic bonds provide only a small fraction of the binding energy, they appear to influence strongly the observed spectra. Observed H2-induced shifts in the dangling OD bands appear to be caused by electrostatic bonding of H2 to a D atom of a dangling OD and a significant fraction of the H2 intensity is proposed to originate from H2 molecules which are electrostatically bonded to dangling oxygen atoms on the surface. Calculations (which do not contain adjustable parameters) reproduce quite well several features of the measured spectra, including the splitting of the dangling OD band, the shift of this band due to binding of H2, and the frequency and the width of the H2 band.

Pressure effect on hydrogen isotope exchange kinetics in chymotrypsinogen investigated by FT-IR spectroscopy

Hydrogen/deuterium (H/D) exchange rate constants in chymotrypsinogen have been determined at several pressures up to 28.9 kbar by FTIR spectroscopy. The secondary structure of the protein molecules was monitored simultaneously at the corresponding pressures by the intensity redistribution of the infrared amide I band at these pressures. As in other proteins, the labile protons on the amide groups in chymotrypsinogen can, to a good approximation, be separated into two classes, each with distinct first order H/D exchange rates constants in the time period from 10 min to ~24 h. The fast exchange rate constant increases while the slow exchange rate constant decreases with increasing pressure. The increase in the fast exchange rate constant at high pressure is largely associated with the pressure-induced unfolding of the protein molecules. At extremely high pressure (12.8 kbar), in addition to the unfolding of protein molecules, pressure induced a distortion and weakening of the hydrogen bonds of the fold protein segments also contribute to an increase in the overall H/D exchange rate. The present results confirm that when chymotrypsinogen is dissolved in D2O, a considerable amount of D2O molecules is bound to the protein molecules on the surface as well as in the interior cavities of the molecules. The H/D exchange takes place between these bound D2O and the protons in the protein molecules. The mechanism of the H/D exchange and the interior dynamics in proteins are discussed on the basis of the present results. Key words: hydrogen/deuterium exchange, exchange kinetics, rate constant, pressure effects, infrared spectroscopy, protein, conformation structure, bound water.

Phases and phase transitions in a nematic lyotropic system with a biaxial phase

Abstract NMR spectroscopy and optical microscopy have been used to study phase transitions and structure in nematic lyotropic mesophases formed by potassium laurate, decylammonium hydrochloride and water. The different mesophases obtained in a well-defined composition range have been characterized, by deuterium NMR, following the evolution of the D2O spectra as a function of temperature and of the orientation of the samples with respect to the magnetic field. Wide ranges of biaxiality have been found and the asymmetry parameter of the averaged electrical field gradient tensor on the deuterium of the D2O molecule has been determined. The presence of the different mesophases has always been confirmed by observing oriented samples under the polarizing optical microscope.

NMR Studies on Reorientational Motion of Hydrated D2O Molecules of Halaide Ions (F−, Cl−, Br−, and I−) in Dilute Aqueous Solutions

Abstract The spin–lattice relaxation rates of the D and 17O nuclei of D2O molecules have been measured for dilute aqueous solutions of potassium halides (KF, KBr, KCl, KI) in the concentration range below 1.0 mol kg−1 at 25°C. The agreement between the B\barx′ coefficients of the spin–lattice relaxation rate (reorientational motion) and the B− coefficients of the solution viscosity of the anions is somewhat better than that of the cations. The reorientational motion of hydration for D2O molecules of Cl−, Br−, and I− ions was anisotropic; this anisotropic motion is enhanced with increasing ion radius. On the other hand, the hydration D2O molecule of the F− ion was approximately isotropic.

Reactions of silicon cluster ions, Si+n (n=10–65), with water

The chemical reactions of size selected Si+n (n=10–65) with D2O have been studied using injected ion drift tube techniques between temperatures of 258 and 404 K. The only products detected were a series of Sin(D2O)+m adducts. Large variations in reactivity were observed for the smaller clusters (n&amp;lt;40) that diminish with increasing cluster size. Si+11, Si+13, Si+14, Si+19, and Si+23 are particularly unreactive compared to their neighbors. At room temperature the larger clusters (n&amp;gt;40) are a factor of ∼10–1000 (depending on the bulk surface) less reactive towards water than bulk silicon. The reaction rates for all clusters exhibit an unusually strong negative temperature dependence but are independent of the buffer gas pressure. These results suggest that the reaction mechanism probably involves two steps. In the first step, a weakly bound molecularly adsorbed Si+n⋅⋅⋅D2O adduct is produced. The second step involves rearrangement to give a more strongly bound (and probably dissociatively adsorbed) SinD2O+ product. It appears that the reaction rates for some of the smaller clusters show a faster than linear dependence on D2O pressure. One possible explanation for this unusual observation is that a second D2O molecule solvates the transition state and significantly lowers the activation barrier for dissociative adsorption.

Isotope Effects on the Reorientational Motion of Hydrated H2O Molecules in Alkali Metal Bromide Dilute Aqueous Solutions Studied by NMR Spectroscopy

Abstract The spin-lattice relaxation times of 1H and 17O nuclei of hydrated H2O molecules in alkali metal bromide (LiBr, NaBr, KBr, and CsBr) dilute aqueous solutions in the concentration range from 0.2 to 1.0 mol kg−1 at 25 °C were measured by NMR spectroscopy. The reorientational correlation times for the intramolecular 1H–1H (τHH+) and 1H–17O (τOH+) axes, as well as the perpendicular axis (17O nuclei, τ17O+) to the molecular plane of a hydrated H2O molecule were determied. The two reorientational correlation times (τHH+ and τOH+) of pure H2O and hydrated H2O molecules in Li+, Na+, K+, and Cs+ ions were equal, respectively. Comparing previous data for hydrated D2O molecules with that calculated by using correction values (rHH, rOH, and quadrupolar constant) for H2O molecules, the ratios of τD+(D2O)/τOH(H2O) and τ17O+(D2O)/τ17O+(H2O) were found to be of the same order as η(D2O)/η(H2O), except for the τ17O+(D2O)/τ17O+(H2O) value for the Li+ ion.

NMR Studies on Reorientational Motion of Hydrated D2O Molecules in Tetraalkylammonium Bromide Dilute Aqueous Solutions

Abstract The spin-lattice relaxation times of D and 17O nuclei of hydrated D2O molecules in tetraalkylammonium bromide (Me4NBr, Et4NBr, Pr4NBr, and Bu4NBr) dilute aqueous solutions in the concentration range of 0.2 to 1.0 mol kg−1 at 25°C were measured by NMR spectroscopy. The relaxation rates of D and 17O nuclei varied linearly with increasing the concentration below 1.0 mol kg−1. The dynamic hydration number, Bx+, is defined by Bx+=(k·τx+⁄τx0−1)nx+⁄50.0, where τx+ and τx0 (X=D or 17O) are the reorientational correlation times of hydrated D2O molecules (nx+) in R4N+ (R: alkyl group) and pure D2O molecule. The Bx+ increases with increasing the alkyl chain length of R4N+ ions. The abnormally large Bx+ values, compared with those of alkali metal ions, are caused by the hydrophobic hydration around the alkyl group of the R4N+ ion. The reorientational motion of a hydrated D2O molecule in the hydration sphere of R4N+ ions is isotropic, though the motion of a D2O molecule in the ionic hydration of alkali metal ions is anisotropic.

NMR Studies on the Rotational Motion of Coordinated D2O Molecules in MBr (M=Li+, Na+, K+, Cs+) Dilute Aqueous Solutions

Abstract The parallel (D,τ⁄⁄) and perpendicular (17O,τ⊥) rotational correlation times of coordinated D2O molecules in MBR (M=Li+, Na+, K+, Cs+ aqueous solutions in the concentration range of 0.2 to 1.0 molkg−1 at 25 °C were determined by NMR. The spin-lattice relaxation rates (R1) varied linearly with increase in concentration up to 1.0 molkg−1. The ratios (τ⁄⁄/τ⊥) of the rotational correlation times of coordinated D2O molecules in Li+, Na+, K+, and Cs+ ions were 1.12, 1.13, 0.89, and 0.92, respectively. These results indicate that for coordinated D2O molecules in Li+ and Na+ ions, the perpendicular rotational motion is 10% faster than the parallel one. On the other hand, for coordinated D2O molecules in K+ and Cs+ ions, the tendency was reversed. These results are explained in terms of both the Eulerian angle β between the diffusion tensors with the molecular plane and the intermolecular interactions between the ions and D2O molecules.

Nuclear Quadrupole Coupling Tensors of 2H in the a-Alum RbAl(SO4)2 · 12D2O and the Dynamical Behaviour of the D2O Molecules. An Investigation by NMR and IR

Abstract By single crystal NMR the nuclear quadrupole coupling constants eQΦzz h-1 (2H), the asymmetry parameters η(2H) and the direction cosines of the principal axes of the electric field gradient tensors of the 2H atoms of the two kinds of D2O molecules have been determined at 295 K in RbAl(SO4)2 · 12D2O. The results show that the D2O molecules surrounding the ion Al3+ are “static” within the time scale of the 2H nuclear quadrupole interaction while the D2O belonging to the octahedron around the Rb+ undergoes fast reorientations around the twofold molecular axis. For the two kinds of D2O in the alum we found: eQΦzz (1)h-1 (2H) = 186.5 kHz, η(1),(2H) = 0.1234; eQΦzz (2)h-1 (2H) = 169.7 kHz,η (2)(2H) = 0.1297; eQΦzz (3)h-1(2H) = 122.1 kHz, (2H) = 0.8087. eQΦzz (1) and eQΦzz (2) belong to the "static" D2O molecules and an assignment to the two different 2H atoms has been performed. The IR spectra of RbAl(SO4)2 · 12(H1-xDx)2O have been investigated, and for the O - D stretching frequencies values of 2145 cm-1 , 2235 cm-1 , 2470 cm-1 and 2525 cm -1 have been obtained. They agree well with the relations between ṽOD and eQΦzz h-1(2H) given in the literature.

An isotopic effect in the dielectric spectra of Ark. 9/water systems

Abstract Dielectric spectra of H2O and D2O molecules in the Lα liquid crystalline phase of nonylphenoxy-poly(ethylenoxy)ethanol(Ark. 9)/water lyotropic systems have been investigated by dielectric time domain spectroscopy in the frequency range from 10 MHz to 10 GHz. By fitting the Cole-Cole formula to the dielectric spectra, obtained at different temperatures the dielectric increments, the relaxation times and the distribution parameters have been calculated. A strong retardation of water molecules has been found for the lamellar phase with low water content, i.e. 10 water molecules (H2O or D2O) per one Ark. 9 molecule. The relaxation times obtained at room temperature for the light and heavy water are 63 and 93 ps, respectively. It means that the retardation factor for D2O molecules in the Lα phase is close to 1.5 and higher than that found for pure heavy water (1.25). Any decomposition of the dielectric spectra obtained seems to be unsubstantiated. The temperature dependences of the relaxation times ac...

The reactions of iron clusters with water

The reactions of neutral iron clusters Fe7–27 with water are studied in a laser-vaporization cluster source coupled to a continuous-flow reactor. Reaction products are detected via laser ionization and time-of-flight mass spectrometry. The reactions of room-temperature clusters with H2O show adsorbate decomposition and hydrogen desorption, as do the reactions with D2O at elevated temperatures. The room-temperature reaction with D2O appears not to involve any decomposition, and is at equilibrium under the conditions of these experiments. The dependence of reaction extent on D2O pressure yields equilibrium constants for the addition of the first and second D2O molecules. The analysis is complicated by the presence of two-photon ionization processes that are treated quantitatively with a rate-equation model. This treatment also yields estimates for cluster photoabsorption cross sections, which are found to be approximately linear in cluster size, having a magnitude of 2.3×10−17 cm2 per iron atom. From the derived equilibrium constants and estimated adsorption entropies, approximate D2O–cluster binding energies are determined. They range from 0.42 to 0.59 eV, and their dependence on cluster size shows a remarkable similarity to the dependence of the rate constants for reaction of iron clusters with H2. The implications of this similarity are discussed.

The intra-molecular structure of a water molecule in hydrated and incompletely hydrated LiCl solutions

Time-of-flight neutron diffraction measurements were carried out on the hydrated and incompletely hydrated solutions (LiCl)x(D2O)1-x for x=0.20, 0.27, 0.32 and 0.35. The data for the high-Q region observed at the high scattering angle 2 theta =91 degrees have been analysed in terms of intra-molecular interference, including an inelasticity correction, to determine the intra-molecular distances of a water molecule, rOD and RDD. The former shows no composition dependence within experimental error; the distance rOD=0.970+or-0.006 AA is equal to that in pure D2O. On the other hand, the distance rDD=1.59+or-0.02 AA in the solutions with above 20 mol.% LiCl is 0.04 AA longer than that of liquid D2O because of the strong interaction between the D2O molecule and the ions. The conclusion reached in this work suggests that the results of the molecular dynamics simulation are not reasonable.

Proton trapping and defect energetics in ice from FT-IR monitoring of photoinduced isotopic exchange of isolated D2O

The photoexcitation of 2-naphthol as a trace impurity in ice results in the injection of excess protons into the ice network. These protons are immobile at temperatures &amp;lt;100 K but warming to ∼120 K generates a near steady-state concentration of mobile protons which decays slowly. This behavior confirms the existence of shallow proton traps in ice which, following Kunst and Warman, are presumed to be intrinsic and, most probably, Bjerrum L defects. The quantity of mobile protons at a given temperature, in a pseudoequilibrium with immobile protons bound to the L defects, is controlled by the temperature coefficients of (a) the pseudoequilibrium constant and (b) the L-defect concentration. Since both the L and D defects are immobile below ∼130 K, the L-defect concentration can be taken to be temperature independent. Consequently, the temperature dependence of the rate at which D2O molecules isolated in H2O cubic ice are converted to (HOD)2 units by mobile protons is a direct measure of the binding energy between the excess protons and the L defects. This binding energy has been estimated at 10.0 kcal/mol. At the completion of each kinetic experiment at T&amp;lt;126 K, the predominant deuterated species is (HOD)2. Such samples are ideal for observation of the ice L-defect activity which is thermally activated by warming to above 130 K. By following the rate of conversion of (HOD)2 to isolated HOD for the range 134 to 150 K, the activation energy for the L-defect formation and mobility has been determined to be 12.2 kcal for cubic ice. This is close to the value of 12.0 kcal previously determined for cubic ice from isotopic exchange rates, but is less than the accepted value for hexagonal ice of 13.1 kcal/mol. Further, the enthalpy change for ice self-ionization has been estimated as 16.8 kcal from a combination of the activation energies for proton transport (9.5 kcal) and L-defect formation (7.8 kcal) with the L-defect–proton binding energy of 10.0 kcal.