Self-diffusion of supercritical water in extremely low-density region

The self-diffusion coefficient D for super- and subcritical water is determined by using the proton pulsed-field-gradient spin echo method at high temperatures and low densities. The density of water is ranged in the steamlike region from 0.0041 to 0.0564 g [corrected] cm(-3) at a supercritical temperature of 400 degrees C, also at 0.0041-0.0079 and 0.0041-0.0462 g [corrected] cm(-3) (the steam-branch densities on the coexistence curve and lower) at 200 and 300 degrees C, respectively. The density is precisely determined on the basis of the PVT dependence of the proton chemical shift. The density-diffusivity products in the zero-density limit divided by the square root of the temperature, (rho D)0/square root of T, are 0.94, 1.17, and 1.35 mg m(-1) s(-1) K(-1/2) (mg=10(-3)g) [corrected] at 200, 300, and 400 degrees C, respectively. The (rhoD)0/square root of T obtained decreases with decreasing temperature and is significantly smaller than the temperature-independent value from the hard sphere model, 1.95 mg [corrected] m(-1) s(-1) K(-1/2). The marked temperature dependence reflects the presence of the strong attractive interaction between a pair of water molecules. The magnitude of the experimental D values and the temperature dependence are well reproduced by the molecular dynamics simulation using TIP4P-FQ model. The initial slope of the product rhoD/square root of T against rho is slightly negative at 300 and 400 [corrected] degrees C.     

Fast thermal desorption spectroscopy study of H/D isotopic exchange reaction in polycrystalline ice near its melting point

Using fast thermal desorption spectroscopy, a novel technique developed in our laboratory, we investigated the kinetics of HD isotopic exchange in 3 microm thick polycrystalline H2O ice films containing D2O layers at thicknesses ranging from 10 to 300 nm at a temperature of -2.0+/-1.5 degrees C. According to our results over the duration of a typical fast thermal desorption experiment (3-4 ms), the isotopic exchange is confined to a 50+/-10 nm wide reaction zone located at the boundary between polycrystalline H2O and D2O ice. Combining these data with a theoretical analysis of the diffusion in polycrystalline medium, we establish the range of possible values for water self-diffusion coefficients and the grain boundary widths characteristic of our ice samples. Our analysis shows that for the grain boundary width on the order of a few nanometers, the diffusivity of D2O along the grain boundaries must be at least two orders of magnitude lower than that in bulk water at the same temperature. Based on these results, we argue that, in the limit of low concentrations of impurities, polycrystalline ice does not undergo grain boundary premelting at temperatures up to -2 degrees C.     

Mechanisms and kinetics of noncatalytic ether reaction in supercritical water. 1. Proton-transferred fragmentation of diethyl ether to acetaldehyde in competition with hydrolysis

Noncatalytic reaction pathways and rates of diethyl ether in supercritical water are determined in a quartz capillary by observing the liquid- and gas-phase 1H and 13C NMR spectra. The reaction is investigated at two concentrations (0.1 and 0.5 M) in supercritical water at 400 degrees C and over a water-density range of 0.2-0.6 g/cm3, and in subcritical water at 300 and 350 degrees C. The neat reaction (in the absence of solvent) is also studied for comparison at 0.1 M and 400 degrees C. The ether is found to decompose through (i) the proton-transferred fragmentation to ethane and acetaldehyde and (ii) the hydrolysis to ethanol. Acetaldehyde from reaction (i) is consecutively subjected to the unimolecular and bimolecular redox reactions: (iii) the unimolecular proton-transferred decarbonylation forming methane and carbon monoxide, (iv) the bimolecular self-disproportionation producing ethanol and acetic acid, and (v) the bimolecular cross-disproportionation yielding ethanol and carbonic acid. Reactions (ii), (iv), and (v) proceed only in the presence of hot water. Ethanol is produced through the two types of disproportionations and the hydrolysis. The proton-transferred fragmentation is the characteristic reaction at high temperatures and is much more important than the hydrolysis at densities below 0.5 g/cm3. The proton-transferred fragmentation of ether and the decarbonylation of aldehyde are slightly suppressed by the presence of water. The hydrolysis is markedly accelerated by increasing the water density: the rate constant at 400 degrees C is 2.5 x 10(-7) s(-1) at 0.2 g/cm3 and 1.7 x 10(-5) s(-1) at 0.6 g/cm3. The hydrolysis becomes more important in the ether reaction than the proton-transferred fragmentation at 0.6 g/cm3. In subcritical water, the hydrolysis path is dominant at 300 degrees C (0.71 g/cm3), whereas it becomes less important at 350 degrees C (0.57 g/cm3). Acetic acid generated by the self-disproportionation autocatalyzes the hydrolysis at a higher concentration. Thus, the pathway preference can be controlled by the water density, reaction temperature, and initial concentration of diethyl ether.     

Precise measurement of the self-diffusion coefficient for poly(ethylene glycol) in aqueous solution using uniform oligomers

Uniform poly(ethylene glycol) (PEG) oligomers, with a degree of polymerization n=1-40, were separated by preparative supercritical fluid chromatography from commercial monodispersed samples. Diffusion coefficients, D, for separated uniform PEG oligomers were measured in dilute solutions of deuterium oxide (D(2)O) at 30 degrees C, using pulsed-field gradient nuclear magnetic resonance. The measured D for each molecular weight was extrapolated to infinite dilution. Diffusion coefficients obtained at infinite dilution follow the scaling behavior of Zimm-type diffusion, even in the lower molecular weight range. Molecular-dynamics simulations for PEG in H(2)O also showed this scaling behavior, and reproduced close hydrodynamic interactions between PEG and water. These findings suggest that diffusion of PEG in water is dominated by hydrodynamic interaction over a wide molecular weight range, including at low molecular weights around 1000.     

Temperature dependence of ion and water transport in perfluorinated ionomer membranes for fuel cells

To clarify the mechanisms of transport of ions and water molecules in perfluorosulfonated ionomer membranes for fuel cells, the temperature dependence of their transport behaviors was investigated in detail. Two types of Flemion membranes having different equivalent weight values (EW) were utilized along with Nafion 117 as the perfluorinated ionomer membranes, and H-, Li-, and Na-form samples were prepared for each membrane by immersion in 0.03 M HCl, LiCl, and NaCl aqueous solutions, respectively. The ionic conductivity, water self-diffusion coefficient (D(H)(2)(O)), and DSC were measured in the fully hydrated state as a function of temperature. The ionic conductivity of the membranes was reflected by the cation transport through the intermediary of water. Clearly, H(+) transports by the Grotthuss (hopping) mechanism, and Li(+) and Na(+) transport by the vehicle mechanism. The differences of the ion transport mechanisms were observed in the activation energies through the Arrhenius plots. The D(H)(2)(O) in the membranes exhibited a tendency similar to the ionic conductivity for the cation species and the EW value. However, no remarkable difference of D(H)(2)(O) between H- and the other cation-form membranes was observed as compared with the ionic conductivity. It indicates that water in each membrane diffuses almost in a similar way; however, H(+) transports by the Grotthuss mechanism so that conductivity of H(+) is much higher than that of the other cations. Moreover, the D(H)(2)(O) and DSC curves showed that a part of water in the membranes freezes around -20 degrees C, but the nonfreezing water remains and diffuses below that temperature. This fact suggests that completely free water (bulk water) does not exist in the membranes, and water weakly interacting with the cation species and the sulfonic acid groups in secondary and higher hydration shells freezes around -20 degrees C, while strongly binding water in primary hydration shells does not freeze. The ratio of freezing and nonfreezing water was estimated from the DSC curves. The D(H)(2)(O) in the membranes was found to be influenced by the ratio of freezing and nonfreezing water. DFT calculation of the interaction (solvation) energy between the cation species and water molecules suggested that the water content and the ratio of freezing and nonfreezing water depend strongly on the cation species penetrated into the membrane.     

Hydration of Cm3+ in aqueous solution from 20 to 200 degrees C. A time-resolved laser fluorescence spectroscopy study

Time-resolved laser fluorescence spectroscopy (TRLFS) is used to study the hydration of the Cm3+ ion in acidified (0.1 M perchloric acid) H2O and D2O from 20 to 200 degrees C. Strong temperature dependency is found for several of the spectroscopic quantities associated with the 6D'(7/2) --> 8S'(7/2) photoemission spectra, with similar relative changes in both solvents. The emission band shifts to lower energy with increasing temperature, which is attributed to an equilibrium between hydrated Cm3+ ions with different numbers of water molecules in the first coordination sphere, namely [Cm(H2O)9]3+ and [Cm(H2O)8]3+. Comparison with crystalline reference compounds and the analysis of hot bands corroborates the assignment of these species. The molar fraction of the octahydrated species increases from approximately 10% at room temperature to approximately 40% at 200 degrees C, indicating an entropy driven reaction. The corresponding thermodynamic parameters are obtained as Delta H degrees = + 13.1 +/- 0.4 kJ mol(-1), Delta S degrees = + 25.4 +/- 1.2 J mol(-1) K(-1), and Delta G298 = + 5.5 +/- 0.6 kJ mol(-1). Both the emission intensity and lifetime decrease with increasing temperature. The temperature dependency of the nonradiative decay rate of the emitting 6D'(7/2) level follows an Arrhenius equation with the activation energy 26.5 kJ mol(-1) (2250 cm(-1)) in both H2O and D2O, which is somewhat lower than the energy gap between 6D'(7/2) and 6P'(5/2) exited state levels.     

Neutron and beta/gamma radiolysis of water up to supercritical conditions. 1. beta/gamma yields for H(2), H(.) atom, and hydrated electron

Yields for H2, H(.) atom, and hydrated electron production in beta/gamma radiolysis of water have been measured from room temperature up to 400 degrees C on a 250 bar isobar, and also as a function of pressure (density) at 380 and 400 degrees C. Radiolysis was carried out using a beam of 2-3 MeV electrons from a van de Graaff accelerator, and detection was by mass spectrometer analysis of gases sparged from the irradiated water. N2O was used as a specific scavenger for hydrated electrons giving N2 as product. Ethanol-d(6) was used to scavenge H(.) atoms, giving HD as a stable product. It is found that the hydrated electron yield decreases and the H(.) atom yield increases dramatically at lower densities in supercritical water, and the overall escape yield increases. The yield of molecular H2 increases with temperature and does not tend toward zero at low density, indicating that it is formed promptly rather than in spur recombination. A minimum in both the radical and H2 yields is observed around 0.4 kg/dm(3) density in supercritical water.     

Different properties of H2O- and D2O-containing phospholipid-based reverse micelles near a critical temperature

Dipalmitoylphosphatidylcholine (DPPC)/water/pyridine reverse micelles have been found to transform from a clear liquid into a glass when the DPPC-to-water volume fraction is in the 0.78-0.89 range at 28 or 26 degrees C depending on whether water is H2O or D2O. Their study by SANS, FT-IR, and 1H NMR for this composition has shown remarkable effects of the isotopic nature of water on their structural and dynamic properties. By SANS, between 38 and 43.5 degrees C, micelles appear as either flexible polymer-like cylinders or short rods depending on whether water is H2O or D2O. On the basis of this dual aspect, micelles have been visualized as branched cylinders whose quasi-spherical branching points would be prone to assemble into short rods. In addition, when water contains more than 40% of D2O, a Bragg reflection emerges at 0.12 A(-1) on SANS spectra, evidencing an organization of micelles. In addition, FT-IR spectra show that DPPC phosphate groups are D bonded only when water is D2O. Consequently, we assumed that forces prone to organize the D2O-containing micelles are D-bonded water bridges between neighboring micelles at the level of their branching points. In fact, ab initio calculations have shown that water dimers are more stable when the bridging atom is D rather than H. These water bridges could be formed due to the fact that branching points, able to slide along micelles, keep close for a longer time when water is D2O than when it is H2O. Indeed, it has been shown experimentally that the lateral diffusion of phospholipid molecules in any layer is slower in the first case. Formation of such bridges triggers a deuteron migration between micelles evidenced by the 1/T1 relaxation rate of deuterons of water in D2O-containing micelles measured at 43 degrees C by 1H NMR.     

Hydroxyl radical reactivity with nitrobenzene in subcritical and supercritical water

The bimolecular rate constants of the addition reaction between hydroxyl radical (*OH) and nitrobenzene (C(6)H(5)NO(2)) were measured in subcritical and supercritical water (SCW) at temperatures between ambient and 390 degrees C. The measured bimolecular rate constants showed distinctly non-Arrhenius behavior (i.e., essentially no increase with temperature) from ambient to 350 degrees C, but increased in the slightly subcritical and supercritical region between 350 and 390 degrees C. These data were modeled reasonably well over the entire temperature range with a three-step reaction mechanism, originally proposed by Ashton et al.(1) This model includes the formation of a pi-complex intermediate as the precursor of the nitrohydroxycyclohexadienyl radical.     

Rotational dynamics of water and benzene controlled by anion field in ionic liquids: 1-butyl-3-methylimidazolium chloride and hexafluorophosphate

The rotational correlation time (tau(2R)) is determined for D(2)O (polar) and C(6)D(6) (apolar) in 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF(6)]) by measuring (2)H (D) nuclear magnetic resonance spin-lattice relaxation time (T(1)) in the temperature range from -20 to 110 degrees C. The tau(2R) ratio of water to benzene (tau(WB)) was used as a measure of solute-solvent attraction. tau(WB) is 0.73 and 0.52 in [bmim][Cl] and [bmim][PF(6)], respectively, whereas the molecular volume ratio is as small as 0.11. The slowdown of the water dynamics compared to the benzene dynamics in ionic liquids is interpreted by the Coulombic attractive interaction between the polar water molecule and the anion. As for the anion effect, the rotational dynamics of water solvated by Cl(-) is slower than that solvated by PF(6) (-), whereas the rotational dynamics of benzene is similar in the two ionic liquids. This is interpreted as an indication of the stronger solvation by the anion with a larger surface charge density. The slowdown of the water dynamics via Coulombic solvation is actually significant only at water concentrations lower than approximately 9 mol dm(-3) at room temperature, and it is indistinguishable at temperatures above approximately 100 degrees C. The quadrupolar coupling constants determined for D(2)O and C(6)D(6) in the ionic liquids were smaller by a factor of 2-3 than those in the pure liquid state.     

The water/n-octane/octyl-beta-D-glucoside/1-octanol system: phase diagrams and phase properties

The partial phase diagram of D2O/n-octyl-beta-D-alkyl-glucoside(C8G1)/n-octane has been determined at T=25 degrees C. The diagram contains a funnel-shaped micellar phase originating from the water corner of the phase diagram D2O/C8G1 with the stem forming a narrow three-phase region, in which the three phases in equilibrium are two microemulsions of similar composition and an excess oil phase. The microemulsions have been characterized with NMR self-diffusion measurements. At high surfactant concentration and no or low n-octane content, branched micelles exist. As the n-octane content is increased, discrete micelles are formed. Upon further addition of n-octane, the phase separation into two microemulsion phases is induced. Possible mechanisms causing the phase separation are discussed. The phase diagram of D2O/(C8G1)/1-octanol has been determined at 25 degrees C. Ten different phase regions were identified. The phases have been characterized with SAXS and deuterium heavy water NMR, and the swelling of the lamellar phase was investigated with SAXS.     

Unravelling micellar structure and dynamics in an unusually extensive DDAB/bile salt catanionic solution by rheology and NMR-diffusometry

The mixed didodecyldimethylammonium bromide (DDAB)-sodium taurodeoxycholate (STDC)-(2)H(2)O catanionic system forms a large isotropic (L(1)) phase at 25 degrees C. The evolution of microstructure along different dilution lines has been followed by means of rheology and NMR diffusometry. In general, the L(1) phase is characterised by a weak viscoelasticity and Newtonian response. In the STDC-rich regime (W(s)=[DDAB]/[STDC]=0.2), 5 wt% is an overlapping concentration at which the discrete-to-rodlike micellar transition occurs as indicated from the total surfactant concentration (C(s)) dependency of both zero-shear viscosity (eta(0) approximately C(s)(3.7)) and surfactant self-diffusion (D(s) approximately C(s)(-3.0)). As the surfactant molar ratio (W(s)1) increases, i.e., DDAB concentration increases, and at constant C(s), eta(0) decreases and D(s) increases, indicating the formation of a multiconnected micellar network.     

Dynamic and 2D NMR studies on hydrogen-bonding aggregates of cholesterol in low-polarity organic solvents

Self-diffusion coefficients (D) are measured for normal (nondeuterated) and deuterated cholesterol-d(6) (C26 and C27 methyl groups deuterated) in 1-octanol, chloroform, and cyclohexane at concentrations of 1-700 mM by varying the impurity water concentration (>2 mM) and temperature (30-50 degrees C). The pulsed field gradient spin-echo (PGSE) (1)H and (2)H NMR were used, respectively, at 600 and 92 MHz. At 30 degrees C, the hydrodynamic radius (R) obtained at 20 mM from the D value and solvent viscosity is 5.09, 7.07, and 6.17 A, respectively, in 1-octanol, chloroform, and cyclohexane when the impurity water is negligible. The R value in 1-octanol is the smallest and comparable with the average length of the molecular axes for the cholesterol molecule. In 1-octanol, R is invariant against the concentration variation, whereas in chloroform, R is larger and increases almost linearly with cholesterol concentration. At the highest concentration, 700 mM, the R in chloroform is 13.5 and 16.7 A, respectively, when the impurity water is at negligible and saturated concentrations. The R value larger than that in hydrogen-bonding 1-octanol indicates that cholesterol forms an aggregate through hydrogen bonding. The aggregate structure is confirmed by comparing NOESY spectra in chloroform and 1-octanol. The NOESY analysis reveals the presence of one extra cross peak (C4-C19) in chloroform compared to 1-octanol. Because the carbon atoms related to the cross peak are close to the hydroxyl group (C3-OH), cholesterol molecules are considered to be not piled but are found to be OH-centered in the aggregate. This is supported also by larger rotational hydrodynamic radii measured on cholesterol deuterated at positions C2, C3, C4, and C6. This shows that the aggregate formation is driven by the hydrogen-bonding between cholesterol molecules.     

Properties of poly(styrene/alpha-tert-butoxy-omega-vinylbenzyl-polyglycidol) microspheres suspended in water. Effect of sodium chloride and temperature on particle diameters and electrophoretic mobility

Hydrodynamic and electrophoretic properties of core-shell poly(styrene/alpha- tert-butoxy-omega-vinylbenzyl-polyglycidol) (P(S/PGL)) microspheres suspended in water are described. The microspheres were obtained by surfactant-free emulsion copolymerization of styrene and alpha- tert-butoxy-omega-vinylbenzyl-polyglycidol macromonomer ( M n = 2800, M w/ M n = 1.05). The process yielded microspheres with number average diameter D n = 270 nm and with low diameter dispersity index D w/ D n = 1.01. Shells of P(S/PGL) microspheres were enriched in polyglycidol. Molar fraction of polyglycidol monomeric units in the shells (determined by X-ray photoelectron spectroscopy) was equal to 0.34, which is much higher than the average molar fraction of polyglycidol monomeric units in whole particles of 0.048. Influences of NaCl concentration and temperature on P(S/PGL) microsphere diameters and on their electrophoretic mobility were investigated. It was found that hydrodynamic diameter of P(S/PGL) microspheres, determined by photon correlation spectroscopy, decreased significantly when temperature did exceed a certain value (transition temperature, T t). It has been found that the decrease is more pronounced for higher concentrations of NaCl in the medium. For microspheres suspended in 10 (-1) M NaCl, the hydrodynamic diameter decreased by 8% whereas for the same particles in pure water the diameter decreased by 5.2%. The process of shrinkage was fully reversible. Values of T t for P(S/PGL) microspheres were lower for higher concentrations of NaCl. Adjustment of salt concentration allowed controlling T t in a range from 44.4 to 49.9 degrees C. 13C NMR relaxation time measurements (T 1) for carbon atoms in polyglycidol macromonomer revealed that T 1 did increase with increasing temperature (in temperature range from 25 to 75 degrees C) indicating higher motion of chains at higher temperature. Addition of NaCl did not induce a substantial change of T 1 in the mentioned temperature range. The swelling-deswelling properties of P(S/PGL) microspheres' interfacial layer affected adsorption of P(S/PGL) particles on modified with (3-aminopropyl)triethoxysilane mica. It was shown that the deposition of P(S/PGL) microspheres at 25 degrees C on mica led to formation of two-dimensional crystal-shape assemblies, whereas at 60 degrees C (far above T t = 49.8 degrees C in H2O) the microspheres were randomly adsorbed without formation of colloidal crystal assemblies.     

Apparent and standard partial molar volumes of NaCl, NaOH, and HCl in water and heavy water at T = 523 K and 573 K at p = 14 MPa

Apparent molar volumes, Vphi,2, of aqueous NaCl, NaOH, NaOD, HCl, and DCl in water and heavy water were determined at T = 523 and 573 K and p = 14 MPa with a high-temperature platinum vibrating-tube densimeter in the aquamolality range 0.25 相似文献   

Slowdown of H/D exchange reaction rate and water dynamics in ionic liquids: deactivation of solitary water solvated by small anions in 1-butyl-3-methyl-imidazolium chloride

The H/D exchange reaction and the rotational dynamics of heavy water (D2O) are studied at 50 degrees C in the ionic liquid, 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), in the [D2O] range of 3-55 M. The initial H/D exchange rates are observed as 1.0 x 10(-7), 4.5 x 10(-6), 1.0 x 10(-5), 4.1 x 10(-5), 1.1 x 10(-4), and 3.7 x 10(-4) s(-1), respectively, at [D2O] of 2.8, 7.1, 8.1, 11, 15, and 25 M. The rate is very slow and less than 10(-5) s(-1) at [D2O] below approximately 7 M. It steeply increases to the order of 10(-4)s(-1) for 7 M < [D2O] < 10 M, and linearly increases with [D2O] in the more water-rich region. The intercept of the linear region at [D2O] = approximately 9 M is interpreted by considering that each chloride anion deactivates 1.6 equiv water molecules due to the strong solvation. Correspondingly, the rotational correlation time of D2O at [D2O] < 7 M is 1 order of magnitude larger than that in water-rich conditions.     

Formation and reactivity of Ir(III) hydroxycarbonyl complexes

Kinetic studies show that the reaction of [TpIr(CO)2] (1, Tp = hydrotris(pyrazolyl)borate) with water to give [TpIr(CO2H)(CO)H] (2) is second order (k = 1.65 x 10(-4) dm(3) mol(-1) s(-1), 25 degrees C, MeCN) with activation parameters DeltaH++= 46+/-2 kJ mol(-1) and DeltaS++ = -162+/-5 J K(-1) mol(-1). A kinetic isotope effect of k(H2O)/k(D2O) = 1.40 at 20 degrees C indicates that O-H/D bond cleavage is involved in the rate-determining step. Despite being more electron rich than 1, [Tp*Ir(CO)2] (1*, Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) reacts rapidly with adventitious water to give [Tp*Ir(CO2H)(CO)H] (2*). A proposed mechanism consistent with the relative reactivity of 1 and 1* involves initial protonation of Ir(I) followed by nucleophilic attack on a carbonyl ligand. An X-ray crystal structure of 2* shows dimer formation via pairwise H-bonding interactions of hydroxycarbonyl ligands (r(O...O) 2.65 A). Complex 2* is thermally stable but (like 2) is amphoteric, undergoing dehydroxylation with acid to give [Tp*Ir(CO)2H]+ (3*) and decarboxylation with OH- to give [TpIr(CO)H2] (4*). Complex 2 undergoes thermal decarboxylation above ca. 50 degrees C to give [TpIr(CO)H2] (4) in a first-order process with activation parameters DeltaH++ = 115+/-4 kJ mol(-1) and DeltaS++ = 60+/-10 J K(-1) mol(-1).     

An online method combining a thermal conversion elemental analyzer with isotope ratio mass spectrometry for the determination of hydrogen isotope composition and water concentration in geological samples

An online continuous-flow method, combining a thermal conversion elemental analyzer (TC/EA) with isotope ratio mass spectrometry (MS), is evaluated for the determination of both the hydrogen isotope composition and the water concentration of hydrous and nominally anhydrous minerals. The technique involves reduction of hydrous minerals or nominally anhydrous minerals by reaction with glassy carbon at 1450 degrees C in a helium stream. The product gases, H2 and CO, are separated on a gas chromatographic column prior to analysis in the mass spectrometer. Calibration curves for the H concentration analysis were generated from a standard of benzoic acid (C7H6O2) that has an H concentration of 5.0 wt%; the analytical uncertainties were better than +/-0.05% in our runs. Two standards of material with given D values, polyethylene IAEA-CH-7 and biotite NBS-30, were tested for the purpose of calibrating a natural garnet 04BXL02 representing nominally anhydrous minerals. Preheating at 90 degrees C for 12 h was found to be suitable for removing adsorption water on the sample surface. This results in constant D values and total H2O contents for the garnet, with weighted means of -94 +/- 1 and 522 +/- 11 ppm (wt), respectively. The TC/EA-MS technique allows routine analysis of sample sizes as small as 0.01 microL H2O. For natural minerals, absolute reproducibilities for D values are +/-0.5 to +/-2 (1) and relative uncertainties for total H2O concentrations are at levels of +/-1% to +/-3% (1). Therefore, this online method can be used for the quantitative determination of H isotope composition and H2O concentration of either hydrous or anhydrous minerals.     

Ion conduction mechanisms and thermal properties of hydrated and anhydrous phosphoric acids studied with 1H, 2H, and 31P NMR

To understand the behaviors of phosphoric acids in fuel cells, the ion conduction mechanisms of phosphoric acids in condensed states without free water and in a monomer state with water were studied by measuring the ionic conductivity (sigma) using AC impedance, thermal properties, and self-diffusion coefficients (D) and spin-lattice relaxation times (T1) with multinuclear NMR. The self-diffusion coefficient of the protons (H+ or H3O+), H2O, and H located around the phosphate were always larger than the diffusion coefficients of the phosphates and the disparity increased with increasing phosphate concentration. The diffusion coefficients of the samples containing D2O paralleled those in the protonated samples. Since the 1H NMR T1 values exhibited a minimum with temperature, it was possible to determine the correlation times and they were found to be of nanosecond order for a distance of nanometer order for a flip. The agreement of the ionic conductivities measured directly and those calculated from the diffusion coefficients indicates that the ion conduction obeys the Nernst-Einstein equation in the condensed phosphoric acids. The proton diffusion plays a dominant role in the ion conduction, especially in the condensed phosphoric acids.     

Conformations, protonation sites, and metal complexation of benzohydroxamic Acid. A theoretical and experimental study

A theoretical and experimental study on the structure and deprotonation of benzohydroxamic acid (BHA) has been performed. Calculations at the RHF/cc-pVDZ level, refined by the B3LYP/AUG-cc-pVDZ method, indicate that, in the gas phase, Z amide is the most stable structure of both neutral and deprotonated BHA. (1)H-(1)H nuclear Overhauser enhancement spectroscopy and (1)H-(1)H correlation spectroscopy spectra in acetone, interpreted with ab initio interatomic distances, reveal that BHA is split into the Z and E forms, the [E]/[Z] ratio being 75:25 at -80 degrees C. The formation of E-E, Z-Z, and E-Z dimers has been detected; in the presence of water, the dimers dissociate to the corresponding monomers. The rates of proton exchange within the Z and E forms and between E and Z were measured by dynamic (1)H NMR in the -60 to 40 degrees C temperature range; an increase in water content lowers the rate of exchange of the E isomer. The effect of D(2)O on the NMR signals indicates a fast hydrogen exchange between D(2)O and the E and Z amide forms. The sequence of the acid strength at low temperatures is (N)H(E)) approximately (O)H(E) < (O)H(Z) approximately (N)H(Z). The kinetics of complex formation between BHA and Ni(2+), investigated by the stopped-flow method, show that both neutral BHA and its anion can bind Ni(2+). Whereas the anion reacts at a "normal" speed, the rate of water replacement from Ni(H(2)O)(6)(2+) by neutral BHA is about 1 order of magnitude less than expected. This behavior was interpreted assuming that, in aqueous solution, BHA mainly adopts a closed (hydrogen-bonded) Z configuration, which should open (with an energy penalty) for the metal binding process to occur.