bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization and Transalkylation Reactions of Toluene on Cu(II)-Montmorillonite
Authors: Tipton T. , Gerdom L. E.
Published: August 2006

Products resulting from the reaction of toluene with Cu(II)-montmorillonite were analyzed using GC/MS, HPLC/MS, GPC, and FTIR methods. Numerous oligomers of toluene were observed, extending at least as high as the resolution limit (1500 g/mol) of the GPC column. The FTIR spectrum of the nonvolatile components of the extract was very similar to that of liquid toluene. GC/MS data on the volatile components revealed dimers, trimers, and a multitude of transmethylated products. Oligomerization proceeded via both ring-ring (i.e., polyphenyl) and ring-methyl linkages. The primary trans-methylated products were tert-butylbenzene and isopropylxylene, indicating a competition between ringand side-chain methylations. The side-chain substitutions cannot be explained in terms of the aromatic radical cation intermediate which typically forms in arene/clay reactions. A consideration of alkylbenzene reactions observed in various other media suggests that the present transmethylation reactions occur via a benzyl cation intermediate.
The Coordination of Aluminum Ions in the Palygorskite Structure
Authors: Güven Necip , de la Caillerie Jean-Baptiste d'Espinose , Fripiat Jose J.
Published: August 2006

NMR spectra of PF1-1 Floridan palygorskite strongly suggest that Al3+ occurs only in octahedral coordination. X-ray microanalysis of the palygorskite fibers indicate a chemical composition defined by the atomic ratios: Mg/Si = 0.34, Al/Si = 0.27, and Fe/Si = 0.04. Considering the NMR and CEC data in this report along with the previously published results of IR and Mössbauer spectroscopic studies, the following structural formula is proposed for PF1-1 palygorskite:
$${\rm{(M{g_{2.12}}A{l_{1.68}}F{e^{3 + }}_{0.24}{\square _{0.96}})S{i_8}{O_{20}}{(OH)_2}{(O{H_2})_4}}}$$
where □ represents the vacant Ml octahedral sites in the structure, and Al3+ and Fe3+ are all exclusively assigned to the octahedral sites.
The Effect of Unequal Ionic Size on the Swelling Pressure in Clays
Authors: Huerta Marlene M. , Curry Joan E. , McQuarrie Donald A.
Published: August 2006

In this paper, we use the unequal radius modified Gouy-Chapman theory to evaluate the effect of the ionic size of the electrolyte on the swelling pressures (II) in different clay systems immersed in electrolytic solutions. First the model is applied to a 1:1 electrolyte to show that the coion size is only important at surface charge densities much lower than those found in typical clay systems. The swelling pressure is calculated and the results are compared with experimental data. Literature ionic radii values are used to show the dependence of the swelling pressure on the specific counterions present. Next the model is applied to a 1:1 and 2:1 electrolyte mixture with unequal-sized counterions to show the swelling pressure is highly dependent on both counterion sizes. The unequal and same-sized cases are compared.
Reactions between Clay Volatiles and Calcite Reinvestigated
Authors: Heller-Kallai Lisa , Miloslavski Irena
Published: August 2006

Calcite crystals exposed to clay volatiles react with some components of these volatiles, giving rise to a variety of surface morphologies. F, Cl, and S in different proportions were detected by electron microprobe analysis of the calcite surfaces. Under identical experimental conditions, volatiles from every clay mineral examined caused a specific morphology and chemical composition of the calcite surfaces, but these varied with temperature of the calcite. Changes in pH values and mass spectra of the volatiles after passage through calcite demonstrate that even on rapid heating some clay volatile-calcite reactions occur at temperatures as low as 150°C. Species other than those detectable by electron microprobe analysis also participate in the reactions in which CO2 is liberated.
Influence of Fe(II) on the Formation of the Spinel Iron Oxide in Alkaline Medium
Authors: Jolivet J. P. , Belleville P. , Tronc E. , Livage J.
Published: August 2006

Fe(II) and Fe(III) in various proportions were coprecipitated by NH3 at pH ≈ 11. The Fe(II)/Fe(III) ratio (x) was varied from 0.10 to 0.50. After stabilization by aging at pH ≃ 8 in anaerobic conditions, hydrous precipitates were characterized by electron microscopy, Mössbauer spectroscopy, and kinetics of dissolution in acidic medium. At any x value, all stable products exhibited the structure of (oxidized) magnetite. For x ≤ 0.30, two distinct species were coexisting: the one (“m”) was made up of ca. 4nm-sized particles with a low Fe(II) content (Fe(II)/Fe(III) ≈ 0.07), and the other (“M”) consisted of particles of larger, more or less distributed sizes, and composition Fe(II)/Fe(III) ≈ 0.33; “M” increased relative amount with increasing x. For x ≥ 0.35, “M” was the only constituent and its Fe(II)/Fe(III) ratio was equal to x. “M” is identified with (nonstoichiometric) magnetite, whereas “m” is likely to be an oxyhydroxide. Mechanisms of formation are discussed, and a phase diagram is proposed which schematizes the evolution of the coprecipitation products with x and with time. Addition of Fe(II) after the precipitation of Fe(III), instead of coprecipitation, yielded very similar results.
The Interlayer Collapse During Dehydration of Synthetic Na0.7-Beidellite: A 23Na Solid-State Magic-Angle Spinning NMR Study
Authors: Kloprogge J. Theo , Jansen J. Ben H. , Schuiling Roelof D. , Geus John W.
Published: August 2006

The dehydration and migration of the interlayer cation of the synthetic beidellite Na0.7Al4.7Si7.3O20-(OH)4·nH2O, were studied with solid-state 23Na and 27Al MAS-NMR, heating stage XRD, and thermogravimetric analyses (TGA, DTA). The 23Na MAS-NMR of Na-beidellite at 25°C displays a chemical shift of 0.2 ppm, which indicates a configuration comparable with that of Na+ in solution. Total dehydration proceeds reversibly in two temperature ranges. Four water molecules per Na+ are gradually removed from 25° to 85°C. As a result, the basal spacing decreases from 12.54 Å to 9.98 Å and the Na+ surrounded by the two remaining water molecules is relocated in the hexagonal cavities of the tetrahedral sheet. The chemical shift of 1.5 ppm exhibited after the first dehydration stage illustrates the increased influence of the tetrahedral sheet. The high local symmetry is maintained throughout the entire first dehydration stage. During the second dehydration, which proceeds in a narrow temperature range around 400°C, the remaining two water molecules are removed reversibly without any change of the basal spacing.
Alkali Cation Selectivity and Surface Charge of 2:1 Clay Minerals
Authors: Xu Shihe , Harsh James B.
Published: August 2006

A critical demand in environmental modeling and a desirable but elusive goal of research on the ion exchange properties of the charged solid surface has been to determine the selectivity coefficient from fundamental properties of the ions and surface. We developed a Hard and Soft Acid and Base (HSAB) Model to describe exchangeable cation selectivity on solid surfaces. Our previous work has shown that the model quantitatively describes alkali cation exchange on clay minerals in terms of the absolute electronegativity and softness of the exchangeable cations and two fitting parameters:αandβ. This study was conducted to determine the relationship betweenαandβand surface charge characteristics of 2:1 clays. The layer charge and cation selectivity of seven smectites and one vermiculite were used. The regression of log Kvoagainst four combinations of charge properties was performed and the appropriate relationship betweenα,β, and surface charge was selected based on both statistical criteria (R2) and their consistency with the assumptions of the HSAB model. The selected model was then cross-validated using separate cation exchange data from the literature. It was found thatαandβare linearly related to the amount of charge arising from mineral tetrahedral and octahedral sites, respectively. These results make it possible to predict the alkali cation selectivity of 2:1 clay minerals from their chemical composition data and the alkali cation properties.
Natural and Synthetic Copper Phyllosilicates Studied by XPS
Authors: Mosser Christine , Mosser Aimé , Romeo Michelangelo , Petit Sabine , Decarreau Alain
Published: August 2006

X-ray photoelectron spectroscopy (XPS) has been used to characterize the bonding state of Cu2+, Si4+, Al3+, and O2− ions in structural (octahedral and interlamellar) or adsorbed position in phyllosilicates. Five smectites, 5 kaolinites, and 1 chrysocolla with Cu(II) in known positions (octahedral, interlamellar, or surface adsorbed) have been investigated. Their spectra were compared with those of pure Cu metal and of pure Cu(I) and Cu(II) oxides.

The line for Cu 2p3/2 (binding energy of 935.4 eV) and well-defined shake-up lines (binding energy of about 943 eV) observed after 1 hr of X-ray irradiation are characteristic of Cu(II) in phyllosilicate octahedral sites. But due to the photoreduction effect, they show Cu(I) oxidation states (Cu 2p3/2, binding energy of 933.2 eV and near absence of shake-up lines) for the phyllosilicates with adsorbed Cu or in interlamellar positions. The kinetics of photoreduction distinguishes octahedral from interlamellar positions, and the latter from a surface adsorbed position. The enlargement of the FWHM (full width at half maximum) of XPS lines has been used to describe crystallochemical parameters linked to local ordering around the probe cations. Crystallization produces decreasing O 1 s and Cu 2p (octahedral cation) line widths but has no effect on the Si 2p (tetrahedral cation) line width. The enlargement of FWHM for all ion lines of the lattice is linked to the nature (Cu > Mg > Al) and the number and amount of structural cations in the phyllosilicates.
An Electron Optical investigation of Aluminosilicate Cements in Silcretes
Authors: Singh Balbir , Gilkes R. J. , Butt C. R. M.
Published: August 2006

Silcretes developed within the in situ regolith in the Barr Smith Range, Western Australia, were investigated using optical and electron-beam techniques. One of the cementing agents in these silcretes showed gel-like optical properties and had a variable aluminosilicate chemical composition at the scale of electron microprobe analysis so that it might be considered as allophane-like material. High resolution transmission electron microscopy demonstrated that the material consists of a fine-grained and poorly ordered kaolinite embedded in a matrix of amorphous silica.
Three Zones for Illite Formation During Burial Diagenesis and Metamorphism
Authors: Eberl D. D.
Published: August 2006

Reinterpretation of published data for shale cuttings from the Gulf of Mexico sedimentary basin identifies three reaction zones for illite formation with increasing depth for well CWRU6. In a shallow zone (1.85 to 3 km), non-expanding illite-like layers formed primarily by the coalescence of smectite 2:1 layers around interlayer K+. In a middle zone (3 to 4 km), illite crystals neoformed from solution as coarser K-bearing phases and smectite were dissolved by organic acids. In the deepest zone (>4 km), illite recrystallized as less stable illite crystals dissolved, and more stable illite crystals grew during mineral ripening. The progressive loss of radiogenic argon in the deepest zone yielded a constant apparent age for the clays with depth, an effect previously attributed to “punctuated diagenesis.” The above hypothesis for illite formation emphasizes the need to establish the zone (i.e., the reaction mechanism) from which shales were derived before making detailed geologic interpretations based on illite mineralogy.
Quantitative Analysis of Mixtures of 1M And 2M1 Dioctahedral Micas by X-Ray Diffraction
Authors: Tettenhorst Rodney T. , Corbató Charles E.
Published: August 2006

Investigation of a naturally occurring mixture of dioctahedral micas prompted an examination of X-ray diffraction (XRD) techniques for obtaining quantitative estimates of 1M and 2M1 mica proportions. A method for determining quantitative estimates has been developed that includes the effect of preferred orientation of mica particles as described by the March function. A diagram is presented from which the percentage of 2Mı and the March parameter (r) can be obtained from two peak-area ratios: 2.80 Å/5.0 Å and 2.80 Å/2.58 Å, which are measured on observed XRD patterns of mica mixtures. The ability of this peak-area ratio diagram to predict reasonably accurate proportions of 1M and 2Mı micas was tested by comparing calculated and observed XRD patterns over a range of 2θ values from 16° to 40° for size-fractionated mixtures. Lack of accurate crystal-structure data for dioctahedral 1M mica proved an impediment to obtaining improved quantitative estimates of mica proportions.
Chemisorption of Benzene on Cu-Montmorillonite as Characterized by FTIR and 13C MAS NMR
Authors: Hinedi Z. R. , Johnston C. T. , Erickson C.
Published: August 2006

Sorption of benzene onto Cu-montmorillonite was characterized by Fourier transform infrared (FTIR) spectroscopy and 13C magic angle spinning nuclear magnetic resonance (MAS NMR). Under anhydrous conditions, chemisorption of benzene in the interlamellar region of Cu-montmorillonite led to the formation of a dark red surface complex that exhibited a vibrational spectrum similar to that of doped poly-p-phenylene. When the benzene sorption reaction was carried out under high relative humidity conditions, polymerization of benzene did not occur. The FTIR spectrum of the surface complex formed under wet conditions exhibited vibrational bands that could not be assigned to those of the parent benzene molecule or to those of previously observed chemisorbed Type I or Type II complexes. 13C MAS NMR spectra of 13C-enriched benzene sorbed onto Cu-montmorillonite powder showed the presence of two groups of peaks that could be assigned to aromatic and aliphatic carbon respectively.
Considerations and Applications of the Illite/Smectite Geothermometer in Hydrocarbon-Bearing Rocks of Miocene to Mississippian Age
Authors: Pollastro Richard M.
Published: August 2006

Empirical relationships between clay mineral transformations and temperature provide a basis for the use of clay minerals as geothermometers. Clay-mineral geothermometry has been applied mainly to diagenetic, hydrothermal, and contact- and burial-metamorphic settings to better understand the thermal histories of migrating fluids, hydrocarbon source beds, and ore and mineral formation.

Quantitatively, the most important diagenetic clay mineral reaction in sedimentary rocks is the progressive transformation of smectite to illite via mixed-layer illite/smectite (I/S). Changes in both the illite/smectite ratio and ordering of I/S, as determined from X-ray powder diffraction profiles, correlate with changes in temperature due to burial depth. Although the smectite-to-illite reaction may be influenced by several factors, reaction progress appears to be strongly controlled by temperature. Studies show that the model proposed by Hoffman and Hower in 1979 is applicable in burial diagenetic settings from about 5 to 330 Ma, and includes most rocks about Miocene to Mississippian in age. Reliability of the I/S geothermometer is, however, dependent upon a good understanding of the rock's original clay-mineral composition.

Changes in the ordering of I/S are particularly useful in the exploration for hydrocarbons because of the common coincidence between the temperatures for the conversion from random-to-ordered I/S and those for the onset of peak, or main phase, oil generation. Here, the utility of the I/S geothermometer is reviewed in hydrocarbon-bearing rocks of Miocene to Mississippian age. Using three common applications, the I/S geothermometer is compared to other mineral geothermometers, organic maturation indices, and grades of indigenous hydrocarbons. Good agreement between changes in ordering of I/S and calculated maximum burial temperatures or hydrocarbon maturity suggests that I/S is a reliable semiquantitative geothermometer and an excellent measures of thermal maturity.
An Experimentally Derived Kinetic Model for Smectite-to-Illite Conversion and Its Use as a Geothermometer
Authors: Huang Wuu-Liang , Longo John M. , Pevear David R.
Published: August 2006

The smectite-to-illite conversion during shale diagenesis has recently been used to constrain the estimate of a basin's thermal history. We have systematically investigated the kinetics for the conversion of a Na-saturated montmorillonite (SWy-1) to a mixed-layer smectite/illite as a function of KCl concentration (from 0.1 to 3 moles/liter) over a temperature range of 250° to 325°C at 500 bars in cold-seal pressure vessels using gold capsules. The results show that the conversion rate can be described by a simple empirical rate equation

-dS/dt = A · exp(-Ea/RT) · [K+] · S2

where S = fraction of smectite layers in the I/S, t = time in seconds, A = frequency factor = 8.08 × 10-4 sec-1, exp = exponential function, Ea = activation Energy = 28 kcal/mole, R = gas constant, 1.987 cal/deg-mole, T = temperature (degree Kelvin), [K+] = K+ concentration in molarity (M) in the fluid.

The results also show that Ca2+ in solutions barely affects the illitization rate, whereas Mg2+ significantly retards the rate. The retardation, however, is not as severe as previously reported. Na+ ion can significantly retard the rate only if the concentration is high.

We found that by assuming a range 0.0026-0.0052 moles/liter (100-200 ppm) of K+, concentrations similar to the value typically reported in oil field brines, the present kinetic model can reasonably predict the extent of the smectite-to-illite conversion for a number of basins from various depths and age. This narrow range of potassium concentrations, therefore, is used to model the smectite-to-illite conversion in shale when the actual chemical information of pore fluid is not available.

The kinetic equation has been tested using field data from a large variety of geologic settings worldwide (i.e., the Gulf of Mexico, Vienna Basin, Salton Trough Geothermal Area, East Taiwan Basin, Huasna Basin, etc). The results show that the equation reasonably predicts the extent of the reaction within our knowledge of the variables involved, such as burial history, thermal gradients, and potassium concentration.
Chlorite Geothermometry: A Review
Authors: de Caritat Patrice , Hutcheon Ian , Walshe John L.
Published: August 2006

Chlorite minerals, found in a great variety of rocks and geological environments, display a wide range of chemical compositions and a variety of polytypes, which reflect the physicochemical conditions under which they formed. Of particular importance for studies dealing with ore deposit genesis, metamorphism, hydrothermal alteration or diagenesis is the paleotemperature of chlorite crystallization. However, in order to understand the relationship between chlorite composition and formation temperature and hence use chlorite as a geothermometer, one must determine how other parameters influence chlorite composition. These parameters may include fO2 and pH of the solution and Fe/(Fe + Mg) and bulk mineral composition of the host rock.

Four approaches to chlorite geothermometry, one structural and three compositional, have been proposed in the past: 1) a polytype method based on the (largely qualitative) observation that structural changes in chlorite may be partly temperature-dependent (Hayes, 1970); 2) an empirical calibration between the tetrahedral aluminum occupancy in chlorites and measured temperature in geothermal systems (Cathelineau, 1988), which has subsequently been modified by several workers; 3) a six-component chlorite solid solution model based upon equilibrium between chlorite and an aqueous solution, which uses thermodynamic properties calibrated with data from geothermal and hydrothermal systems (Walshe, 1986); and 4) a theoretical method based on the intersection of chlorite-carbonate reactions and the CO2-H2O miscibility surface in temperature-XCO2 space, which requires that the composition of a coexisting carbonate phase (dolomite, ankerite, Fe-calcite or siderite) be known or estimated (Hutcheon, 1990). These four approaches are reviewed and the different calculation methods for the compositional geothermometers are applied to a selection of chlorite analyses from the literature. Results of this comparative exercise indicate that no single chlorite geothermometer performs satisfactorily over the whole range of natural conditions (different temperatures, coexisting assemblages, Fe/(Fe + Mg), fO2, etc.). Therefore, chlorite geothermometry should be used with caution and only in combination with alternative methods of estimating paleotemperatures.
Origin, Diagenesis, and Mineralogy of Chlorite Minerals in Devonian Lacustrine Mudrocks, Orcadian Basin, Scotland
Authors: Hillier S.
Published: August 2006

Chlorite and corrensite are common clay minerals in lacustrine mudrocks from the Devonian Orcadian Basin, Scotland. The relationship of their occurrence to vitrinite reflectance data demonstrate that they are authigenic minerals, formed during burial diagenesis/metamorphism at temperatures of ≥120°C. Whole rock mineralogical and chemical analyses show that chlorite authigenesis occurred by reactions between the detrital dioctahedral clay mineral assemblage and dolomite that was formed under early evaporitic conditions in the lacustrine environment.

XRD and electron microprobe analyses indicate that phases intermediate between corrensite and chlorite are probably mixed-layer chlorite/corrensite with a tendency towards segregation of layer types. Chemically, the conversion of corrensite to chlorite involves an increase in Al for Si substitution in tetrahedral sites, but there is no change in the Fe/Mg ratio of octahedral cations. There is also no relationship of mixed-layer proportions to paleotemperature; only a general paleotemperature interval of approximately 120° to 260°C in which a range of phases between corrensite and chlorite occurs. Chlorite polytypes are exclusively IIb, indicating the formation of this polytype at diagenetic temperatures.

The occurrence of corrensite and Mg-rich chlorite in evaporite and carbonate successions is probably a reliable indicator of diagenetic alteration at temperatures of ≥ 100°C. Burial diagenetic reactions between dioctahedral clay minerals and Mg-rich carbonates may possibly explain many occurrences of corrensite and Mg-rich chlorite in such rocks.
Chlorite Polytype Geothermometry
Authors: Walker Jeffrey R.
Published: August 2006

Since the initial studies of chlorite polytypes, it has been suggested that the stability of the various polytypes may be a function of the temperature at which the mineral formed; however, few studies have been performed in which polytypes of chlorite in a specific suite of samples have been determined and correlated with temperature. A review of the reported occurrences of type I chlorite indicates that other factors, including grain size of the host rock, may be at least as important as temperature in controlling the stability of these polytypes. Results of systematic studies in areas of diagenesis and very low-grade metamorphism suggest that type-II chlorite is stable at temperatures well below 200°C and that it can form as the initial chlorite phase without passing through any intermediate polytypic stages. The conditions under which type-I polytypes occur are somewhat restricted, and cognizance of those restrictions will help to direct future studies of chlorite polytype transformations. These studies should focus on the structural details of polytype transformations; on the relationship of polytype stability to pressure, composition and kinetics; and on experimental calibration of the transformations.
Dimepiperate Adsorption and Hydrolysis on Al3+-, Fe3+-, Ca2+-, and Na+-Montmorillonite
Authors: Pusino A. , Liu W. , Gessa C.
Published: August 2006

The adsorption of the herbicide dimepiperate S-(α;α-dimethylbenzyl)-1-piperidinecarbothioate on homoionic Fe3+-, Al3+-, Ca2+-, and Na+-montmorillonite was studied in aqueous medium. The adsorption is described well by the Freundlich equation. The adsorption capacity decreases in the order Fe3+ > Al3+ > Ca2+ > Na+ clay. The dimepiperate adsorption from chloroform solution was also investigated by analytical, spectroscopic, and X-ray powder diffraction techniques. IR results suggest that the adsorption involves the interaction of the thioester carbonyl group of dimepiperate possibly with the surrounding water of metal ions. On Al3+ and Fe3+ clays, this interaction leads to hydrolysis of the thioester bond and formation of the thiol and carbamic acid derivatives that yield α-methylstyrene and piperidine, respectively.
Formation of Clay Minerals During Low Temperature Experimental Alteration of Obsidian
Authors: Kawano Motoharu , Tomita Katsutoshi , Kamino Yoshitaka
Published: August 2006

Experimental alteration of obsidian in distilled-deionized water at 150°, 175°, 200°, and 225°C was studied. The alteration products were examined by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX) to evaluate the formation process of clay minerals. The surface composition of obsidian before and after alteration was examined by X-ray photoelectron spectroscopy (XPS), and concentrations of released elements in solution were measured to elucidate alteration and dissolution processes. TEM clearly showed that allophane appeared as the first reaction product in each experiment. With increasing reaction length, noncrystalline straight fibrous material was formed in the aggregates of allophane particles as a metastable transitional phase, and tended to form curled or wavy bundles of fibers with longer reaction. The non-crystalline fibers were transformed into highly curled smectite exhibiting small circular forms less than 1.0 µm in diameter as reaction progressed. EDX confirmed that the smectite consisted mainly of Si, Al, and small amounts of Ca, K, and Fe. XPS revealed the formation of a dealkalized leached layer on the surface of obsidian during the reaction. The concentration of released elements suggested that nonstoichiometric dissolution proceeded during the reaction.
Some Colloidal Properties of Beidellite: Comparison with Low and High Charge Montmorillonites
Authors: Hetzel Frederic , Doner Harvey E.
Published: August 2006

Recent evidence of the occurrence of beidellite in many soils around the world necessitates a better understanding of the role of charge location on the colloidal behavior of this smectite as compared to the more frequently studied montmorillonites. Clay suspension stability and sorption of an organic polymer, two properties sensitive to surface charge characteristics, were selected to examine the differences in colloidal behaviors of these smectites. The Otay montmorillonite was shown to have a higher charge than either the beidellite or the SWy-1 montmorillonite. Even though structural formulae resulted in a higher permanent charge for the beidellite as compared to the SWy-1, effective charge of these two smectites is the same. The pH dependency of the critical coagulation concentration of the smectites could not be explained based only on edge charge considerations, and it is proposed that tetrahedral charge location enhances the pH effect on the CCC. Decreased poly(vinyl) alcohol sorption with either increasing surface charge or tetrahedral charge location was observed. Both parameters affect the ease of replacement of water molecules by PVA on the surface of smectites.
Properties and Characterization of Al2O3 and SiO2-TiO2 Pillared Saponite
Authors: Malla P. B. , Komarneni S.
Published: August 2006

A saponite pillared with a single (Al2O3) or a mixed (SiO2-TiO2) oxide exhibited basal spacings of 16–19 and 30–40Å, respectively. The pillared structures were found to be stable up to 700°C. Water, nitrogen, and high resolution argon adsorption were used to study the effect of thermal treatments on surface chemistry, pore structure, and surface area of these pillared clays. The pillared saponites exhibited a hydrophobic behavior at temperatures > 500°C, whereas such behavior was observed at ≥300°C for montmorillonite. Most of the micropores in the Al2O3 pillared clays were < 10 Å, whereas the SiO2-TiO2 pillared clays showed a broad distribution of pores in both micropore and mesopore regions. The SiO2-TiO2 pillared samples possessed higher surface area compared with Al2O3 pillared clays. The percent decrease in surface area was smaller for pillared saponites compared with pillared montmorillonites when calcined from 300° to 700°C, indicating a higher thermal stability of the former. The pillared clays were also characterized by solid state 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS/NMR) spectroscopy. There was no direct evidence of cross-linking (covalent bonding between the clay layer and pillar) in montmorillonite irrespective of the types of pillars. In saponite, however, a significant structural modification took place. 27Al spectra of Al2O3 pillared saponite heated at ≥300°C appear to indicate an increase in AlVI as a result, at least in part, of initiation of hydrolytic splitting of Si-O-Al bonds. The actual release of Al from the tetrahedral sheet probably occurred at a temperature > 500°C and completed around 700°C with the formation of Si-O-Si linkages. The decreased intensity of peak due to Si(1Al) in 29Si spectra of the sample heated at 700°C corroborates the 27Al MAS/NMR results. Additionally, the 29Si spectra indicated a cross-linking between SiO4 (clay sheet) with Al2O3 pillars, which could be achieved by inverting some silica tetrahedra into the interlayer. 27Al and 29Si spectra of SiO2TiO2 pillared saponite also showed the trend similar to that exhibited by Al2O3 pillared saponite, indicating that the crystal chemistry of the host may be more important than the nature of pillars in the structural modification and cross-linking behavior of thermally treated pillared clays.
Characterization of Hydroxy-Interlayered Vermiculite and Illite/Smectite Interstratified Minerals from the Weathering of Chlorite in a Cryorthod
Authors: Righi Dominique , Petit Sabine , Bouchet Alain
Published: August 2006

X-ray diffraction, FTIR, and chemical analyses were performed on clay fractions (1–2 µm, <0.1 µm), separated by means of size fractionations and high-gradient magnetic separation techniques, from a Cryorthod developed in a chlorite-mica schist saprolite. Weathering of large phyllosilicates pre-existing in the saprolite involves physical fragmentation and mineralogical transformations. Chloritic minerals in the coarse fractions were the most affected by physical breakdown, while micas were generally preserved. As a consequence, a concentration of mica layers occurred in the coarse clay fraction, while chloritic residues accumulated in the fine clays. These residues exhibited the typical XRD pattern of hydroxy-interlayered intergrade minerals, but the interlayered contaminants were found to be mainly hydroxy-Mg cations. Further mineralogical transformations of the intergrade minerals involved the progressive removal of the hydroxide interlayered sheet and dissolution of chloritic layers. Illite/smectite mixed-layers were formed in the surface horizon of the soil profile. These processes were associated with a strong decrease in Fe and Mg contents in the clay fractions.
The Al Pillaring of Clays. Part I. Pillaring with Dilute and Concentrated Al Solutions
Authors: Schoonheydt Robert A. , van den Eynde J. , Tubbax H. , Leeman H. , Stuyckens M. , Lenotte I. , Stone W. E. E.
Published: August 2006

Saponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemistry or Al. Pillared saponite is obtained after exchange with refluxed Al solutions; while for hectorite, Al solutions treated with ammonium acetate give a pillared product with 1.8–1.9 nm spacing and thermal stability up to 873 K. In both types of solutions, the Keggin ion Al cluster is a minority species or totally absent. The typical 1.8–1.9 nm spacing is only obtained after washing. The quality of the pillared material can be judged from its thermal stability, its surface area, and the width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. The latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated conditions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.
Weathering of Spodumene to Smectite in a Lateritic Environment
Authors: Singh Balbir , Gilkes R. J.
Published: August 2006

Weathering of spodumene in a lateritized pegmatite in Western Australia was studied by investigating in situ samples by electron-beam techniques. The spodumene had mostly altered to smectite. However, some non-crystalline material adjacent to smectite and intermixed with smectite was also observed. No crystallographic orientation between spodumene and smectite was observed by high resolution techniques. The spodumene dissolved to produce etch pits similar to those observed on hornblende grains. The etch pits were almost completely filled with smectite. Most of the Li in the spodumene was lost during its weathering to smectite.
Synthesis of Smectite from Volcanic Glass at Low Temperature
Authors: Tomita Katsutoshi , Yamane Hisanori , Kawano Motoharu
Published: August 2006

Smectite and zeolites were formed from a volcanic glass as the products of reaction with NaOH solution at 90°C and 100°C under atmospheric pressure. Formation conditions of smectite and various zeolites were determined by the ratio of the amounts of volcanic glass (g) to NaOH (g) in the solution. Smectite was formed under the condition that the values of weight of volcanic glass (g)/(NaOH(g)/40) are between 0.5 and 6. Fe was an important constituent of the octahedral layer of smectite.
Rietveld Refinement of the Kaolinite Structure at 1.5 K
Authors: Bish David L.
Published: August 2006

The crystal structure of Keokuk kaolinite, including all H atoms, was refined in space group C1 using low-temperature (1.5 K) neutron powder diffraction data (λ = 1.9102 Å) and Rietveld refinement/difference-Fourier methods to Rwp = 1.78%, reduced χ2 = 3.32. Unit-cell parameters are: a = 5.1535(3) Å, b = 8.9419(5) Å, c = 7.3906(4) Å, α = 91.926(2)°, β = 105.046(2)°, γ = 89.797(2)°, and V = 328.70(5) Å3. Unit-cell parameters show that most of the thermal contraction occurred along the [001] direction, apparently due to a decrease in the interlayer distance. The non-H structure is very similar to published C1 structures, considering the low temperature of data collection, but the H atom positions are distinct. The inner OH group is essentially in the plane of the layers, and the inner-surface OH groups make angles of 60°–73° with the (001) plane. Difference-Fourier maps show minor anisotropy of the inner-OH group in the [001] direction, but the inner-surface OH groups appear to have their largest vibrational (or positional disorder) component parallel to the layers. Although no data indicate a split position of any of the H sites in kaolinite, there is support for limited random positional disorder of the H atoms. However, these data provided no support for a space group symmetry lower than C1.
A Prospective Analysis of the Prognostic Value of Biomarkers (FibroTest) in Patients with Chronic Hepatitis C
Authors: Ngo Yen , Munteanu Mona , Messous Djamila , Charlotte Frederic , Imbert-Bismut Françoise , Thabut Dominique , Lebray Pascal , Thibault Vincent , Benhamou Yves , Moussalli Joseph , Ratziu Vlad , Poynard Thierry
Published: August 2006

Background: FibroTest, a noninvasive method of measuring biomarkers of liver fibrosis, is an alternative to liver biopsy for determining the severity of chronic hepatitis C virus (HCV) infection. We compared the 5-year prognostic value of the FibroTest with biopsy staging for predicting cirrhosis decompensation and survival in patients with chronic HCV infection.

Methods: Fibrosis stage was assessed on the same day by FibroTest and biopsy in a prospective cohort of 537 patients. Disease classification at baseline was 157 patients with severe fibrosis (FibroTest >0.58), 137 with moderate fibrosis (FibroTest 0.32–0.58), and 243 with no or minimal fibrosis (FibroTest <0.32).

Results: In 64 untreated patients with severe fibrosis, survival without HCV complications was 73% [95% confidence interval (CI), 59%–086%; 13 complications], and survival without HCV-related death was 85% (95% CI, 73%–96%; 7 HCV deaths). Survival rates were higher in patients with moderate fibrosis, [99% (95% CI, 97%–100%; 1 complication; P <0.001) and 100% (no HCV death; P <0.001) for patients with and without HCV-related complications, respectively], and in patients with minimal fibrosis [100% (no complication; P <0.001 vs severe) and 100% (no HCV death; P <0.001 vs severe), respectively]. FibroTest was a better predictor than biopsy staging for HCV complications, with area under the ROC curves (AUROC) = 0.96 (95% CI, 0.93%–0.97%) vs 0.91 (95% CI, 0.85%–0.94%; P = 0.01), respectively; it was also a better predictor for HCV deaths: AUROC = 0.96 (95% CI, 0.93%–0.98%) vs 0.87 (95% CI, 0.70%–0.94%; P = 0.046), respectively. The prognostic value of FibroTest was still significant (P <0.001) in multivariate analyses after taking into account histology, treatment, alcohol consumption, and HIV coinfection.

Conclusion: The FibroTest measurement of HCV biomarkers has a 5-year prognostic value similar to that of liver biopsy.
Colloid‐Facilitated Solute Transport in Variably Saturated Porous Media: Numerical Model and Experimental Verification
Authors: Šimůnek Jirka , He Changming , Pang Liping , Bradford S. A.
Published: August 2006

Strongly sorbing chemicals (e.g., heavy metals, radionuclides, pharmaceuticals, and explosives) in porous media are associated predominantly with the solid phase, which is commonly assumed to be stationary. However, recent field‐ and laboratory‐scale observations have shown that in the presence of mobile colloidal particles (e.g., microbes, humic substances, clays, and metal oxides), colloids can act as pollutant carriers and thus provide a rapid transport pathway for strongly sorbing contaminants. To address this problem, we developed a one‐dimensional numerical model based on the HYDRUS‐1D software package that incorporates mechanisms associated with colloid and colloid‐facilitated solute transport in variably saturated porous media. The model accounts for transient variably saturated water flow, and for both colloid and solute movement due to advection, diffusion, and dispersion, as well as for solute movement facilitated by colloid transport. The colloid transport module additionally considers the processes of attachment/detachment to/from the solid phase and/or the air–water interface, straining, and/or size exclusion. Various blocking and depth dependent functions can be used to modify the attachment and straining coefficients. The solute transport module uses the concept of two‐site sorption to describe nonequilibrium adsorption–desorption reactions to the solid phase. The module further assumes that contaminants can be sorbed onto surfaces of both deposited and mobile colloids, fully accounting for the dynamics of colloid movement between different phases. Application of the model is demonstrated using selected experimental data from published saturated column experiments, conducted to investigate the transport of Cd in the presence of Bacillus subtilis spores in alluvial gravel aquifer media. Numerical results simulating bacteria transport, as well as the bacteria‐facilitated Cd transport, are compared with experimental results. A sensitivity analysis of the model to various parameters is also presented.
IMPORTANCE OF LOCUS OF HELP INITIATION AND TYPE OF OUTCOME AS DETERMINANTS OF REACTIONS TO ANOTHER'S HELP ATTEMPT
Authors: Greenberg Martin S. , Saxe Leonard
Published: August 2006

The present study examined the effect on a recipient of another's effort to provide help. Two variables, locus of responsibility for initiating a help attempt (Requested, Offered, and Imposed) and type of outcome resulting from the help attempt (Successful and not costly, and Unsuccessful
and costly for the help-giver), were manipulated in a 3 × 2 factorial design. Subjects were asked to place themselves in the role of a hypothetical student who was confronted with a particular situation and to answer a series of questions regarding their reactions to that situation.
Results indicated that the Requested help condition yielded the strongest obligation to help Other as well as the greatest liking for Other. With regard to type of outcome, successful help produced greater obligation to help Other and greater liking for Other. Successful help also resulted
in a greater willingness to assist Other when the locus of help initiation was either Offered or Imposed. However, when the locus of help initiation was internal (i.e., Requested), success of the outcome had no effect on willingness to assist Other.
Regulation of Renal Fatty Acid and Cholesterol Metabolism, Inflammation, and Fibrosis in Akita and OVE26 Mice With Type 1 Diabetes
Authors: Proctor Gregory , Jiang Tao , Iwahashi Mieko , Wang Zhuowei , Li Jinping , Levi Moshe
Published: August 2006

In Akita and OVE26 mice, two genetic models of type 1 diabetes, diabetic nephropathy is characterized by mesangial expansion and loss of podocytes, resulting in glomerulosclerosis and proteinuria, and is associated with increased expression of profibrotic growth factors, proinflammatory cytokines, and increased oxidative stress. We have also found significant increases in renal triglyceride and cholesterol content. The increase in renal triglyceride content is associated with 1) increased expression of sterol regulatory element–binding protein (SREBP)-1c and carbohydrate response element–binding protein (ChREBP), which collectively results in increased fatty acid synthesis, 2) decreased expression of peroxisome proliferator–activated receptor (PPAR)-α and -δ, which results in decreased fatty acid oxidation, and 3) decreased expression of farnesoid X receptor (FXR) and small heterodimer partner (SHP). The increase in cholesterol content is associated with 1) increased expression of SREBP-2 and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, which results in increased cholesterol synthesis, and 2) decreased expression of liver X receptor (LXR)-α, LXR-β, and ATP-binding cassette transporter-1, which results in decreased cholesterol efflux. Our results indicate that in type 1 diabetes, there is altered renal lipid metabolism favoring net accumulation of triglycerides and cholesterol, which are driven by increases in SREBP-1, ChREBP, and SREBP-2 and decreases in FXR, LXR-α, and LXR-β, which may also play a role in the increased expression of profibrotic growth hormones, proinflammatory cytokines, and oxidative stress.
Analysis of T-Cell Assays to Measure Autoimmune Responses in Subjects With Type 1 Diabetes
Authors: Seyfert-Margolis Vicki , Gisler Trang D. , Asare Adam L. , Wang Richard S. , Dosch H. Michael , Brooks-Worrell Barbara , Eisenbarth George S. , Palmer Jerry P. , Greenbaum Carla J. , Gitelman Stephen E. , Nepom Gerald T. , Bluestone Jeffrey A. , Herold Kevan C.
Published: August 2006

Type 1 diabetes is a chronic autoimmune disease mediated by autoreactive T-cells. Several experimental therapies targeting T-cells are in clinical trials. To understand how these therapies affect T-cell responses in vivo, assays that directly measure human T-cell function are needed. In a blinded, multicenter, case-controlled study conducted by the Immune Tolerance Network, we tested responses in an immunoblot and T-cell proliferative assay to distinguish type 1 diabetic patients from healthy control subjects. Peripheral blood cells from 39 healthy control subjects selected for DR4 and 23 subjects with recently diagnosed type 1 diabetes were studied. Autoantibody responses were measured in serum samples. Positive responses in both assays were more common in peripheral blood mononuclear cells from new-onset type 1 diabetic patients compared with control subjects. The proliferative, immunoblot, and autoantibody assays had sensitivities of 58, 91, and 78% with specificities of 94, 83, and 85%, respectively. When cellular assays were combined with autoantibody measurements, the sensitivity of the measurements was 75% with 100% specificity. We conclude that cellular assays performed on peripheral blood have a high degree of accuracy in discriminating responses in subjects with type 1 diabetes from healthy control subjects. They may be useful for assessment of cellular autoimmune responses involved in type 1 diabetes.
Fibroblast Growth Factor-21 Improves Pancreatic β-Cell Function and Survival by Activation of Extracellular Signal–Regulated Kinase 1/2 and Akt Signaling Pathways
Authors: Wente Wolf , Efanov Alexander M. , Brenner Martin , Kharitonenkov Alexei , Köster Anja , Sandusky George E. , Sewing Sabine , Treinies Iris , Zitzer Heike , Gromada Jesper
Published: August 2006

Fibroblast growth factor-21 (FGF-21) is a recently discovered metabolic regulator. Here, we investigated the effects of FGF-21 in the pancreatic β-cell. In rat islets and INS-1E cells, FGF-21 activated extracellular signal–regulated kinase 1/2 and Akt signaling pathways. In islets isolated from healthy rats, FGF-21 increased insulin mRNA and protein levels but did not potentiate glucose-induced insulin secretion. Islets and INS-1E cells treated with FGF-21 were partially protected from glucolipotoxicity and cytokine-induced apoptosis. In islets isolated from diabetic rodents, FGF-21 treatment increased islet insulin content and glucose-induced insulin secretion. Short-term treatment of normal or db/db mice with FGF-21 lowered plasma levels of insulin and improved glucose clearance compared with vehicle after oral glucose tolerance testing. Constant infusion of FGF-21 for 8 weeks in db/db mice nearly normalized fed blood glucose levels and increased plasma insulin levels. Immunohistochemistry of pancreata from db/db mice showed a substantial increase in the intensity of insulin staining in islets from FGF-21–treated animals as well as a higher number of islets per pancreas section and of insulin-positive cells per islet compared with control. No effect of FGF-21 was observed on islet cell proliferation. In conclusion, preservation of β-cell function and survival by FGF-21 may contribute to the beneficial effects of this protein on glucose homeostasis observed in diabetic animals.
Glucose Toxicity Is Responsible for the Development of Impaired Regulation of Endogenous Glucose Production and Hepatic Glucokinase in Zucker Diabetic Fatty Rats
Authors: Fujimoto Yuka , Torres Tracy P. , Donahue E. Patrick , Shiota Masakazu
Published: August 2006

The effect of restoration of normoglycemia by a novel sodium-dependent glucose transporter inhibitor (T-1095) on impaired hepatic glucose uptake was examined in 14-week-old Zucker diabetic fatty (ZDF) rats. The nontreated group exhibited persistent endogenous glucose production (EGP) despite marked hyperglycemia. Gluconeogenesis and glucose cycling (GC) were responsible for 46 and 51% of glucose-6-phosphatase (G6Pase) flux, respectively. Net incorporation of plasma glucose into hepatic glycogen was negligible. Glucokinase (GK) and its inhibitory protein, GK regulatory protein (GKRP), were colocalized in the cytoplasm of hepatocytes. At day 7 of drug administration, EGP was slightly reduced, but G6Pase flux and GC were markedly lower compared with the nontreated group. In this case, GK and GKRP were colocalized in the nuclei of hepatocytes. When plasma glucose and insulin levels were raised during a clamp, EGP was completely suppressed and GC, glycogen synthesis from plasma glucose, and the fractional contribution of plasma glucose to uridine diphosphoglucose flux were markedly increased. GK, but not GKRP, was translocated from the nucleus to the cytoplasm. Glucotoxicity may result in the blunted response of hepatic glucose flux to elevated plasma glucose and/or insulin associated with impaired regulation of GK by GKRP in ZDF rats.