H2O Incorporation Research Articles

Water Enhancement of Si Self‐Diffusion in Wadsleyite

AbstractWe investigated the H2O‐content dependence of Si self‐diffusion coefficient in Fe‐free wadsleyite using multi‐anvil experiments at pressures of 19–20 GPa, temperatures of 1573–1873 K, and H2O‐content ranging from ∼10 to 5,300 wt. ppm by the isotopic thin‐film diffusion‐couple method. The 29Si‐doped diffusion profiles were measured by nanoscale secondary ion mass spectrometry in the depth profiling mode. The H2O contents in the samples were analyzed by Fourier transformation infrared spectroscopy. The experimental results show a H2O enhancement of Si diffusion coefficient with a H2O content exponent of 0.8 ± 0.1. The activation enthalpy was found to be 270 ± 40 kJ/mol. The diffusion coefficients in the [100], [010], and [001] directions are indistinguishable. The temperature and H2O‐content dependences of Si diffusion indicate that H2O incorporation dramatically reduces the rheological strength of wadsleyite, whereas temperature has a relatively small effect. The viscosity in the mantle transition zone could be significantly reduced by H2O incorporation in wadsleyite. The viscosity contrast between mantle plumes and surroundings may control the evolution of plume shapes at 410–660 km depths.

The Polymorphic Nature of M3BiBr6 Halides (M=Cs, Rb) and their Reversible Intercalation with Water to Isomorphous Hydrates at Room Temperature

AbstractBismuthates with composition M3BiBr6 (M=Rb, Cs) form series of polymorphs capable of reversible H2O incorporation at room temperature. The host compounds were synthesized by annealing mixtures of MBr/BiBr3, or by precipitation from acidic solution and removing water molecules from the host framework of the hydrates in a thermal dehydration reaction. While the compound oP‐Rb3BiBr6 (space group Pbnm) is known from previous work, mP‐Rb3BiBr6 crystallizes with a new type of structure (space group P21/c). For Cs3BiBr6, the oP‐phase crystallizes isostructural to Cs3NdCl6 (space group Pbcm), the mC‐phase isostructural to Cs3BiCl6 (space group C2/c) and the tP‐phase isostructural to Tl3BiCl6 (space group P42/m). All crystal structures were refined from single crystal X‐ray diffraction data. In both systems, the crystal structures of orthorhombic and the monoclinic phases are polytypes and differ by stacking sequence only. By intercalation of water molecules, all polytypes of M3BiBr6 transform to semi‐hydrates M3BiBr6 ⋅ H2O. Both, the incorporation of water and the reverse process proceed without the host structure being changed. The inclusion of crystal water was also confirmed by IR‐spectroscopy, thermal gravimetric analysis and mass spectrometry. The modification tP‐Cs3BiBr6 features a crystal structure with higher density and does not accommodate water.

The Effect of Water on Ionic Conductivity in Olivine

AbstractHigh‐temperature ionic conductivity in olivine single crystals has been measured in the [100], [010], and [001] crystallographic orientations as a function of pressure from 2 to 10 GPa, temperature from 1450 to 2180 K, and H2O content from 20 to 580 wt. ppm using multianvil presses with in situ impedance analyses. The experimental results yield an activation energy, activation volume, and H2O content exponent of 250–405 kJ/mol, 3.2–5.3 cm3/mol, and 1.3 ± 0.2, respectively, for the high‐temperature ionic conduction regime. Olivine ionic conductivity has negative pressure and positive temperature dependences and is significantly enhanced by H2O incorporation. The [001] direction is more conductive than the [100] and [010] directions. The H2O‐enhanced ionic conductivity may contribute significantly to the electrical conductivity profile in the asthenosphere, especially in the regions under relatively high‐temperature and low‐pressure conditions.

Rod-like anhydrous V2O5 assembled by tiny nanosheets as a high-performance cathode material for aqueous zinc-ion batteries.

Aqueous zinc-ion batteries offer a low-cost and high-safety alternative for next-generation electrochemical energy storage, whereas suitable cathode materials remain to be explored. Herein, rod-like anhydrous V2O5 derived from a vanadium-based metal–organic framework is investigated. Interestingly, this material is assembled by tiny nanosheets with a large surface area of 218 m2 g−1 and high pore volume of 0.96 cm3 g−1. Benefiting from morphological and structural merits, this material exhibits excellent performances, such as high reversible capacity (449.8 mA h g−1 at 0.1 A g−1), good rate capability (314.3 mA h g−1 at 2 A g−1), and great long-term cyclability (86.8% capacity retention after 2000 cycles at 2 A g−1), which are significantly superior to the control sample. Such great performances are found to derive from high Zn2+ ion diffusion coefficient, large contribution of intercalation pseudocapacitance, and fast electrochemical kinetics. The ex situ measurements unveil that the intercalation of Zn2+ ion is accompanied by the reversible V5+ reduction and H2O incorporation. This work discloses a direction for designing and fabricating high-performance cathode materials for zinc-ion batteries and other advanced energy storage systems.

Mechanism of Carbon Dioxide and Water Incorporation in Ba2TiO4: A Joint Computational and Experimental Study

CO2 incorporation in solids is attracting considerable interest in a range of energy-related areas. Materials degradation through CO2 incorporation is also a critical problem with some fuel cell materials, particularly for proton conducting ceramic fuel cells. Despite this importance, the fundamental understanding of the mechanism of CO2 incorporation is lacking. Furthermore, the growing use of lower temperature sol gel routes for the design and synthesis of new functional materials may be unwittingly introducing significant residual carbonate and hydroxyl ions into the material, and so studies such as the one reported here investigating the incorporation of carbonate and hydroxyl ions are important, to help explain how this may affect the structure and properties. This study on Ba2TiO4 suggests highly unfavorable intrinsic defect formation energies but comparatively low H2O and CO2 incorporation energies, in accord with experimental findings. Carbonate defects are likely to form in both pristine and undo...

Density of hydrous magma

Magmas in the interior of the Earth have been geophysically observed. The generation of magmas is closely related to H2O because the water-induced decrease in the melting temperature of mantle rocks is an essential process, which forms hydrous magmas due to H2O incorporation into the molten rocks. Knowledge on physical properties of hydrous magmas, such as density, can give us better understanding of the magma behavior inside the Earth. The density of hydrous magma can be controlled by the partial molar volume of H2O (V¯H2O) and its pressure- and temperature-dependences. The new compression behavior of V¯H2O using Vinet equation of state is proposed based on compiled data. Since H2O is one of the most compressible oxides in the magma at lower pressure, a rapid densification of hydrous magma can be observed at shallower mantle. The dense hydrous magma can be gravitational stable above and below mantle transition zone.

Water transport by subduction: Clues from garnet of Erzgebirge UHP eclogite

Abstract A key question concerning the water budget of Earth’s mantle is how much water is actually recycled into the mantle by the subduction of eclogitized oceanic crust. Hydrous phases are stable only in quartz eclogite not coesite eclogite so that water transport to greater depths is mainly governed by structural water in omphacite and garnet. Here we explore if garnet can be used as a proxy to assess the amount of this water. Available data on the water contents of garnet in coesite eclogite vary over orders of magnitude, from a few up to ca. 2000 ppm. By implication, the maximum bulk-rock water contents are unrealistically high (wt% level). New data from the Erzgebirge indicate moderate amounts of structural H2O stored in garnet (43–84 ppm), omphacite (400–820 ppm), and in the bulk coesite eclogite (ca. 280–460 ppm). Higher garnet water contents occur, but these are not primary features. They are related to molecular water in fluid inclusions that can be attributed to eclogite-facies fluid influx postdating the metamorphic peak. Fluid influx also caused the uptake of additional structural water in garnet domains close to fluid inclusions. Such secondary H2O incorporation is only possible in the case of primary water-deficiency indicating that garnet hosted less water than it was able to store. This is insofar astonishing as comparably high H2O amounts are liberated by the breakdown of prograde eclogite-facies hydrous minerals as a result of ultrahigh-pressure (UHP) metamorphism. Judging from Erzgebirge quartz eclogite, dehydration of 5–10% hydrous minerals (±equal portions of zoisite+calcic amphibole) produces 1500–3000 ppm water. We infer that the largest part of the liberated water escaped, probably due to kinetic reasons, and hydrated exhuming UHP slices in the hanging-wall. Depending on the physical conditions, water influx in eclogite during exhumation (1) produces fluid inclusions and simultaneously enhances the structural water content of nominally anhydrous minerals—as in the Erzgebirge—and/or (2) it may give rise to retrograde hydrous minerals. We conclude that eclogite transports moderate quantities of water (several hundred parts per million) to mantle depths beyond 100 km, an amount equivalent to that in ca. 1% calcic amphibole.

Atomic Mechanism of Arsenic Monolayer Doping on oxide-free Silicon(111)

AbstractThe reaction pathway for shallow arsenic doping of silicon by methylarsenic acid molecules directly grafted on oxide-free, H-terminated Si(111) surfaces is unraveled combining Infrared absorption spectroscopy, X-ray Photoelectron Spectroscopy, Low Energy Ion Scattering and ab initio Molecular Dynamics simulations. The overall driving force is identified as a thermodynamic instability of As+5 in contact with silicon, which initiates a self-decomposition of chemisorbed methylarsenic molecules at ∼600 K. As the temperature is increased, the As-C bond breaks -- the weakest link of the adsorbed molecule -- with release of the organic ligand and a rearrangement from a monodentate to a bidentate bonding configuration. In this process, oxygen atoms evolve by partial desorption as H2O and partial incorporation into the surface Si atom backbonds. At ∼1050 K, diffusion of As into the sub-surface region of silicon is observed. There is no evidence for As desorption and no remaining C contamination.

Degradation mechanism of CH3NH3PbI3 perovskite materials upon exposure to humid air

Low stability of organic-inorganic perovskite (CH3NH3PbI3) solar cells in humid air environments is a serious drawback which could limit practical application of this material severely. In this study, from real-time spectroscopic ellipsometry characterization, the degradation mechanism of ultra-smooth CH3NH3PbI3 layers prepared by a laser evaporation technique is studied. We present evidence that the CH3NH3PbI3 degradation in humid air proceeds by two competing reactions of (i) the PbI2 formation by the desorption of CH3NH3I species and (ii) the generation of a CH3NH3PbI3 hydrate phase by H2O incorporation. In particular, rapid phase change occurs in the near-surface region and the CH3NH3PbI3 layer thickness reduces rapidly in the initial 1 h air exposure even at a low relative humidity of 40%. After the prolonged air exposure, the CH3NH3PbI3 layer is converted completely to hexagonal platelet PbI2/hydrate crystals that have a distinct atomic-scale multilayer structure with a period of 0.65 ± 0.05 nm. We find that conventional x-ray diffraction and optical characterization in the visible region, used commonly in earlier works, are quite insensitive to the surface phase change. Based on results obtained in this work, we discuss the degradation mechanism of CH3NH3PbI3 in humid air.

Isotopomer-selective spectra of a single intact H2O molecule in the Cs(+)(D2O)5H2O isotopologue: Going beyond pattern recognition to harvest the structural information encoded in vibrational spectra.

We report the vibrational signatures of a single H2O molecule occupying distinct sites of the hydration network in the Cs(+)(H2O)6 cluster. This is accomplished using isotopomer-selective IR-IR hole-burning on the Cs(+)(D2O)5(H2O) clusters formed by gas-phase exchange of a single, intact H2O molecule for D2O in the Cs(+)(D2O)6 ion. The OH stretching pattern of the Cs(+)(H2O)6 isotopologue is accurately recovered by superposition of the isotopomer spectra, thus establishing that the H2O incorporation is random and that the OH stretching manifold is largely due to contributions from decoupled water molecules. This behavior enables a powerful new way to extract structural information from vibrational spectra of size-selected clusters by explicitly identifying the local environments responsible for specific infrared features. The Cs(+)(H2O)6 structure was unambiguously assigned to the 4.1.1 isomer (a homodromic water tetramer with two additional flanking water molecules) from the fact that its computed IR spectrum matches the observed overall pattern and recovers the embedded correlations in the two OH stretching bands of the water molecule in the Cs(+)(D2O)5(H2O) isotopomers. The 4.1.1 isomer is the lowest in energy among other candidate networks at advanced (e.g., CCSD(T)) levels of theoretical treatment after corrections for (anharmonic) zero-point energy. With the structure in hand, we then explore the mechanical origin of the various band locations using a local electric field formalism. This approach promises to provide a transferrable scheme for the prediction of the OH stretching fundamentals displayed by water networks in close proximity to solute ions.

Anomalous X-ray diffraction study of Pr-substituted BaCeO3 - δ.

The effect of Pr doping on the crystal structure and site occupancy was studied for the nominally synthesized BaCe1 - xPrxO3 - δ (x = 0, 0.2, 0.4, 0.6 and 0.8) perovskites using anomalous X-ray powder diffraction (AXRD) data and Rietveld analysis. Crystal structure parameters were accurately determined using 10,000 eV photons, and the Pr occupancy was refined using data collected with 5962 eV photons, close to the Pr LIII absorption edge. BaCe1 - xPrxO3 - δ crystallizes in the Pnma (No. 62) space group for all x values. Pr cations are mainly located at the Ce sites (perovskites B site), but a small fraction of them increasingly substitute some of the Ba ions at the A site as Pr content increases. The Pr doping introduces electronic defects (Pr(+3)/Pr(+4)) and oxygen vacancies needed for H2O incorporation and H-ionic conductivity. A decrease in the orthorhombic distortion would produce the opposite effects on the electronic and ionic mobility. The electronic mobility should increase due to an improvement in the overlap of the (Ce/Pr)4f-O2p orbital, while the proton mobility should decrease as a consequence of a larger hopping distance.

Activation of PPARα Ameliorates Hepatic Insulin Resistance and Steatosis in High Fructose–Fed Mice Despite Increased Endoplasmic Reticulum Stress

Endoplasmic reticulum (ER) stress is suggested to cause hepatic insulin resistance by increasing de novo lipogenesis (DNL) and directly interfering with insulin signaling through the activation of the c-Jun N-terminal kinase (JNK) and IκB kinase (IKK) pathway. The current study interrogated these two proposed mechanisms in a mouse model of hepatic insulin resistance induced by a high fructose (HFru) diet with the treatment of fenofibrate (FB) 100 mg/kg/day, a peroxisome proliferator–activated receptor α (PPARα) agonist known to reduce lipid accumulation while maintaining elevated DNL in the liver. FB administration completely corrected HFru-induced glucose intolerance, hepatic steatosis, and the impaired hepatic insulin signaling (pAkt and pGSK3β). Of note, both the IRE1/XBP1 and PERK/eIF2α arms of unfolded protein response (UPR) signaling were activated. While retaining the elevated DNL (indicated by the upregulation of SREBP1c, ACC, FAS, and SCD1 and [3H]H2O incorporation into lipids), FB treatment markedly increased fatty acid oxidation (indicated by induction of ACOX1, p-ACC, β-HAD activity, and [14C]palmitate oxidation) and eliminated the accumulation of diacylglycerols (DAGs), which is known to have an impact on insulin signaling. Despite the marked activation of UPR signaling, neither JNK nor IKK appeared to be activated. These findings suggest that lipid accumulation (mainly DAGs), rather than the activation of JNK or IKK, is pivotal for ER stress to cause hepatic insulin resistance. Therefore, by reducing the accumulation of deleterious lipids, activation of PPARα can ameliorate hepatic insulin resistance against increased ER stress.

Anaerobic and aerobic cleavage of the steroid core ring structure by Steroidobacter denitrificans

The aerobic degradation of steroids by bacteria has been studied in some detail. In contrast, only little is known about the anaerobic steroid catabolism. Steroidobacter denitrificans can utilize testosterone under both oxic and anoxic conditions. By conducting metabolomic investigations, we demonstrated that S. denitrificans adopts the 9,10-seco-pathway to degrade testosterone under oxic conditions. This pathway depends on the use of oxygenases for oxygenolytic ring fission. Conversely, the detected degradation intermediates under anoxic conditions suggest a novel, oxygenase-independent testosterone catabolic pathway, the 2,3-seco-pathway, which differs significantly from the aerobic route. In this anaerobic pathway, testosterone is first transformed to 1-dehydrotestosterone, which is then reduced to produce 1-testosterone followed by water addition to the C-1/C-2 double bond of 1-testosterone. Subsequently, the C-1 hydroxyl group is oxidized to produce 17-hydroxy-androstan-1,3-dione. The A-ring of this compound is cleaved by hydrolysis as evidenced by H2(18)O-incorporation experiments. Regardless of the growth conditions, testosterone is initially transformed to 1-dehydrotestosterone. This intermediate is a divergence point at which the downstream degradation pathway is governed by oxygen availability. Our results shed light into the previously unknown cleavage of the sterane ring structure without oxygen. We show that, under anoxic conditions, the microbial cleavage of steroidal core ring system begins at the A-ring.

In situ incorporation of arsenic, molybdenum, and selenium during precipitation of hydrotalcite-like layered double hydroxides

Magnesium (Mg2+) and iron (Fe3+) are common cations and their precipitation as MgFeCO3-type hydrotalcite-like layered double hydroxide (HTlc) may influence contaminant mobilization in, for example, mine drainage sites. The extent of As(V), Mo(VI), and Se(VI) incorporation during HTlc precipitation in alkaline media under normal atmospheric conditions was evaluated and its effect on physico-chemical properties was examined. Even after solute entrapment, the HTlcs were characterized by strong agglomeration. The affinity for solute inclusion in the HTlcs varied in the order As(V)>Mo(VI)>Se(VI). The incorporation of solutes resulted in slight decreases in interlayer thickness, degree of crystallinity, and crystallite size compared to the solute-free MgFeCO3-type HTlc. Open air conditions allowed a substantial mass of CO32− to occupy the HTlc interlayer together with the metal(loid)ic oxyanions. The incorporation of As(V), Mo(VI), and Se(VI) into the HTlcs resulted in the addition of Raman spectral vibrations at ~810, ~898, and ~835cm−1, respectively. With solute incorporation, additional mass loss occurred in multiple stages upon heating; however, the thermal stability of the solute-incorporated HTlcs was unchanged compared to solute-free counterpart. Additional surface absorption of H2O and structural incorporation of CO32− were evident in the solute-incorporated HTlcs.

Oxygen isotopic composition of nitrate and nitrite produced by nitrifying cocultures and natural marine assemblages

The δ18O value of nitrate produced during nitrification (δ18ONO3,nit) was measured in experiments designed to mimic oceanic conditions, involving cocultures of ammonia‐oxidizing bacteria or ammonia‐oxidizing archaea and nitrite‐oxidizing bacteria, as well as natural marine assemblages. The estimates of ranged from −1.5‰ ± 0.1‰ to +1.3‰ ± 1.4‰ at δ18O values of water (H2O) and dissolved oxygen (O2) of 0‰ and 24.2‰ vs. Vienna Standard Mean Ocean Water, respectively. Additions of 18O‐enriched H2O allowed us to evaluate the effects of oxygen (O) isotope fractionation and exchange on . Kinetic isotope effects for the incorporation of O atoms were the most important factors for setting overall values relative to the substrates (O2 and H2O). These isotope effects ranged from +10‰ to +22‰ for ammonia oxidation (O2 plus H2O incorporation) and from +1‰ to +27‰ for incorporation of H2O during nitrite oxidation. values were also affected by the amount and duration of nitrite accumulation, which permitted abiotic O atom exchange between nitrite and H2O. Coculture incubations where ammonia oxidation and nitrite oxidation were tightly coupled showed low levels of nitrite accumulation and exchange (3% ± 4%). These experiments had values of −1.5‰ to +0.7‰. Field experiments had greater accumulation of nitrite and a higher amount of exchange (22% to 100%), yielding an average value of +1.9‰ ± 3.0‰. Low levels of biologically catalyzed exchange in coculture experiments may be representative of nitrification in much of the ocean where nitrite accumulation is low. Abiotic oxygen isotope exchange may be important where nitrite does accumulate, such as oceanic primary and secondary nitrite maxima.

Precipitation behavior of highly Sr-doped LaPO4 in phosphoric acid solutions

The precipitation condition of LaPO4 in phosphoric acid solution was investigated under both atmospheric and humidified conditions. The crystal morphology, Sr doping level, H2O incorporation, and high temperature stability of Sr-doped LaPO4 precipitates were also analyzed. Increasing pH2O from 0.01 to 1 atm extends the precipitation region of LaPO4 in phosphoric acid solutions toward higher temperatures by nearly 100 °C. Under such conditions (e.g. T = 250 °C and pH2O = 1 atm), it is possible to obtain aggregated crystals up to 200 μm. The Sr doping level in LaPO4 shows a strong dependence on the precipitation ratio of La, XLa. The Sr doping level is higher in the low XLa region, reaching 20 mol% at maximum. This value is one order of magnitude higher than the previously reported solubilities. It was confirmed H2O is certainly incorporated in the bulk by Sr doping. The solubility of Sr in LaPO4 would be sufficiently high (at least 20.1%) even at 600 °C; however, it becomes considerably lower at 1200 °C.

Properties of La-silicate high-K dielectric films formed by oxidation of La on silicon

In this article, we present data on the properties of La-based high-k dielectric films prepared by oxidation of La deposited by physical vapor deposition on silicon. Films are characterized by x-ray photoelectron spectroscopy, infrared absorption, and capacitance versus voltage analysis. We find that when we oxidize La metal sputter deposited on Si substrates, it reacts with the silicon substrate to form La silicate. La films as thick as 300 Å will react completely with Si under moderate oxidation conditions (900 °C for 10 min) suggesting a very rapid silicidation reaction between La and Si. Under some processing conditions the as-deposited films contain a small La2O3 component that reduces to La silicate upon anneal at high temperatures. La-silicate films do not phase separate into La2O3 and SiO2 upon annealing at 1050 °C, and their resistance to H2O incorporation depends critically on the oxidation temperature. Electrical measurements show a high concentration of positive fixed charge.

The Distribution of H2O between Cordierite and Granitic Melt: H2O Incorporation in Cordierite and its Application to High-grade Metamorphism and Crustal Anatexis

Experiments defining the distribution of H2O [Dw = wt % H2O(melt)/wt % H2O(crd)]) between granitic melt and coexisting cordierite over a range of melt H2O contents from saturated (i.e. coexisting cordierite + melt + vapour) to highly undersaturated (cordierite + melt) have been conducted at 3–7 kbar and 800–1000°C. H2O contents in cordierites and granitic melts were determined using secondary ion mass spectrometry (SIMS). For H2O vapour-saturated conditions Dw ranges from 4·3 to 7 and increases with rising temperature. When the system is volatile undersaturated Dw decreases to minimum values of 2·6–5·0 at moderate to low cordierite H2O contents (0·6–1·1 wt %). At very low aH2O, cordierite contains less than 0·2–0·3 wt % H2O and Dw increases sharply. The Dw results are consistent with melt H2O solubility models in which aH2O is proportional to Xw2 (where Xw is the mole fraction of H2O in eight-oxygen unit melt) at Xw ≤ 0·5 and 0·25kw{exp[(6·52 − (2667/T)) × Xw]} at Xw > 0·5, coupled with cordierite hydration models in which aH2O is proportional to n/(1 − n), where n is the number of molecules of H2O per 18-oxygen anhydrous cordierite formula unit (n < 1). Combination of our 800–1000°C cordierite H2O saturation results with previous cordierite hydration data leads to the following geohydrometer relation, applicable for temperatures in the range 500–1000°C: \[ \ln K_{\rm eq} = [4203(\pm 320)/\hbox{T}]- 11\cdot75 (\pm 0\cdot33) \] where Keq = [nsat/(1 − nsat)]/fH2O(P,T), nsat is the saturation value of n for the P–T condition of interest, and T is in Kelvin. Moderate to high aH2O (0·4–0·9) are calculated for H2O-rich cordierites in several pegmatites and zones of hydrous fluid infiltration in high-grade terrains in Antarctica and central Australia, whereas aH2O calculated from the measured H2O contents in cordierites from several granulite migmatites are lower and in the range 0·1–0·4. Calculated H2O contents of melts that equilibrated with low-H2O (0·6–1·2 wt %) cordierites in several migmatite terrains are in the range 2·8–4·4 wt %, consistent with dehydration-melting reactions involving biotite (± sillimanite). Calculated melt H2O contents that in other studied migmatites are unrealistically low for the specified temperature conditions of melting probably reflect post-equilibrium H2O loss from the cordierites.

Hepatitis A virus capsid protein VP1 has a heterogeneous C terminus.

Hepatitis A virus (HAV) encodes a single polyprotein which is posttranslationally processed into the functional structural and nonstructural proteins. Only one protease, viral protease 3C, has been implicated in the nine protein scissions. Processing of the capsid protein precursor region generates a unique intermediate, PX (VP1-2A), which accumulates in infected cells and is assumed to serve as precursor to VP1 found in virions, although the details of this reaction have not been determined. Coexpression in transfected cells of a variety of P1 precursor proteins with viral protease 3C demonstrated efficient production of PX, as well as VP0 and VP3; however, no mature VP1 protein was detected. To identify the C-terminal amino acid residue of HAV VP1, we performed peptide sequence analysis by protease-catalyzed [18O]H2O incorporation followed by liquid chromatography ion-trap microspray tandem mass spectrometry of HAV VP1 isolated from purified virions. Two different cell culture-adapted isolates of HAV, strains HM175pE and HM175p35, were used for these analyses. VP1 preparations from both virus isolates contained heterogeneous C termini. The predominant C-terminal amino acid in both virus preparations was VP1-Ser274, which is located N terminal to a methionine residue in VP1-2A. In addition, the analysis of HM175pE recovered smaller amounts of amino acids VP1-Glu273 and VP1-Thr272. In the case of HM175p35, which contains valine at amino acid position VP1-273, VP1-Thr272 was found in addition to VP1-Ser274. The data suggest that HAV 3C is not the protease responsible for generation of the VP1 C terminus. We propose the involvement of host cell protease(s) in the production of HAV VP1.

Psyllium Feeding Increases the Rates of Hepatic and Intestinal Sterol Biosynthesis While Lowering the Plasma and Hepatic Cholesterol Levels in Rats

Previous studies have shown that psyllium (PS) lowers plasma cholesterol and alters hepatic sterol metabolism. We conducted a dose response study to further explore the effects of PS on hepatic and intestinal sterol biosynthesis. Forty five male Sprague-Dawley rats, aged 90 days, were divided into three treatment groups (15 rats/group). Rats were fed ad libitum diets (isocaloric and isonitrogenous) and had free access to deionized water. Rats in group 1 (control) were fed a diet containing 10% cellulose as the source of dietary fiber; group 2 rats received a diet containing 5% PS and 5% cellulose; and group 3 rats were given a diet containing 10% PS. After 21 days of treatment, at the midpoint of the dark cycle, within a 1-h period, rats were lightly anesthetized and were rapidly injected with 1.85 GBq (50 mCi) of tritiated water ([3H]H2O) in 0.5ml of isotonic NaCl into the femoral artery of each rat. Sixty minutes later, the animals were anesthetized and blood was collected from the abdominal aorta for measuring plasma water activity and lipid and cholesterol analyses. The liver and intestine were immediately removed for determining the rates of [3H]H2O incorporation into digitonin-precipitable sterols (DPS). Liver total cholesterol and total lipids were significantly lower in rats fed the diet containing either 5% or 10% PS compared with those of the 10% cellulose. Animals fed both the 5% and 10% PS diets had significantly lower serum total cholesterol (126±4.6, 103±7.0, 101±5.7mg/dl, respectively, for the 10% cellulose, 5 and 10% PS diets), but not serum HDL or triglyceride levels, than the 10% cellulose diet. Hepatic rates of sterol biosynthesis were significantly higher with PS feeding in a dose-dependent manner (21±2, 312±34.6, 463±40.0, nmol [3H]H2O incorporation into DPS/g liver per hour for 0, 5 and 10% PS in diets, respectively). The effect of PS on intestinal biosynthesis of sterols was less pronounced (68±26, 86±34.5, 113±54.5nmol [3H]H2O incorporation into DPS/g intestine per hour for 0, 5 and 10% PS in diets, respectively). The results of this study indicate that the presence of PS in the diet may cause depletion of liver cholesterol, conceivably, by enhancing bile acid synthesis, and/or increasing fecal elimination of acidic and neutral sterols, thus resulting in higher rates of sterol biosynthesis. Although the maximal effect on plasma cholesterol levels was observed with 5% PS, further enhancement of hepatic sterol biosynthesis by 10% PS demonstrates the sensitivity of liver to changes in PS levels.