bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nkx2.2 Activates the Ghrelin Promoter in Pancreatic Islet Cells
Authors: Hill Jonathon T. , Chao Christina S. , Anderson Keith R. , Kaufman Fernanda , Johnson Christopher W. , Sussel Lori 
Published: December 2009

AbstractNkx2.2 is an essential regulator of pancreatic endocrine differentiation. Nkx2.2-null mice are completely devoid of β-ells and have a large reduction of α- and PP cells. In the place of these islet populations, there is a corresponding increase in the ghrelin-positive ε-cells. Molecular studies have indicated that Nkx2.2 functions as an activator and repressor to regulate islet cell fate decisions. To determine whether Nkx2.2 is solely important for islet cell fate decisions or also has the capability to control ghrelin at the promoter level, we studied the transcriptional regulation of the ghrelin promoter within the pancreas, in vitro and in vivo. These studies demonstrate that both of the previously identified transcriptional start sites in the ghrelin promoter are active within the embryonic pancreas; however, the long transcript is preferentially up-regulated in the Nkx2.2-null pancreas. We also show that the promoter region between −619 and −488 bp upstream of the translational start site is necessary for repression of ghrelin in αTC1 and βTC6 cells. Surprisingly, we also show that Nkx2.2 is able to bind to and activate the ghrelin promoter in several cell lines that do or do not express endogenous ghrelin. Together, these results suggest that the up-regulation of ghrelin expression in the Nkx2.2-null mice is not due to loss of repression of the ghrelin promoter in the nonghrelin islet populations. Furthermore, Nkx2.2 may contribute to the activation of ghrelin in mature islet ε-cells.
Relationship Between Pb2+ Adsorption and Average Mn Oxidation State in Synthetic Birnessites
Authors: Zhao Wei , Cui Haojie , Liu Fan , Tan Wenfeng , Feng Xionghan 
Published: December 2009

AbstractThe relationship between vacant Mn structural sites in birnessites and heavy-metal adsorption is a current and important research topic. In this study, two series of birnessites with different average oxidation states (AOS) of Mn were synthesized. One birnessite series was prepared in acidic media (49.6–53.6 wt.% Mn) and the other in alkaline media (50.0–56.2 wt.% Mn). Correlations between the Pb2+ adsorption capacity and the d110 interlayer spacing, the AOS by titration, and the release of Mn2+, H+, and K+ during adsorption of Pb2+ were investigated. The maximum Pb2+ adsorption by the birnessites synthesized in acidic media ranged from 1320 to 2457 mmol/kg with AOS values that ranged from 3.67 to 3.92. For birnessites synthesized in alkaline media, the maximum Pb2+ adsorption ranged from 524 to 1814 mmol/kg, with AOS values between 3.49 and 3.89. Birnessite AOS values and Pb2+ adsorption increased as the Mn content decreased. The maximum Pb2+ adsorption to the synthetic birnessites calculated from a Langmuir fit of the Pb adsorption data was linearly related to AOS. Birnessite AOS was positively correlated to Pb2+ adsorption, but negatively correlated to the d110 spacing. Vacant Mn structural sites in birnessite increased with AOS and resulted in greater Pb2+ adsorption. Birnessite AOS values apparently reflect the quantity of vacant sites which largely account for Pb2+ adsorption. Therefore, the Pb2+ adsorption capacity of birnessite is mostly determined by the Mn site vacancies, from which Mn2+, H+, and K+ released during adsorption were derived.
Origin and Mineralogy of Sepiolite and Palygorskite From the Tuluanshan Formation, Eastern Taiwan
Authors: Wang Ming Kuang , Tseng Pao Chung , Chang Shyun Sheng , Ray Dah Tong , Shau Yen Hong , Shen Yun Wei , Chen Ruey Chyong , Chiang Po Neng 
Published: December 2009

AbstractThe Tuluanshan Formation of the eastern Coastal Range of Taiwan overlies an andesitic core complex presumed to be the source of hydrothermal fluids responsible for the Si- and Mg-rich mineralization of sepiolite and palygorskite (attapulgite) which are found in veins within fissures and in fracture zones of the volcanic rocks of the region. This study was undertaken in order to understand these relationships better by characterizing sepiolite and palygorskite in this Formation and by examining their occurrence and distribution in the Tungho (TH) and Chunjih (CJ) areas. Samples were analyzed using X-ray diffraction (XRD), thermal analysis, Fourier-transform infrared (FTIR) spectroscopy, and petrographic, scanning (SEM), and transmission (TEM) electron microscopic methods. Sepiolite and palygorskite are blocky and earthy-type materials that display fibrous characteristics when viewed using TEM and SEM and occurred alone or with chalcedony in veins. The fibers of blocky sepiolite are commonly intercalated with smectite but the earthy type of sepiolite and palygorskite observed in this study displayed precipitation from fluid enriched in Si, Al, Mg, and minor Fe and depleted in other ions at an earlier stage of offset of the andesitic veins. Continuation of reverse faulting and high shearing stress caused the precipitation of a significant quantity of interlaminated sepiolite. Sepiolite and palygorskite were formed at an earlier stage of fluid interaction relative to smectite in the Tuluanshan Formation.
Partial Dissolution of Glauconitic Samples: Implications for the Methodology of K-Ar and Rb-Sr Dating
Authors: Derkowski Arkadiusz , Środoń Jan , Franus Wojciech , Uhlík Peter , Banaś Michał , Zieliński Grzegorz , Čaplovičová Maria , Franus Małgorzata 
Published: December 2009

AbstractThe K-Ar dating of glauconite has been used as an important stratigraphic tool for many decades. The application of this technique is limited to pure glauconites, free of detrital contamination by K-bearing phases, often not easy to detect. This study extends the application of isotope dating to the contaminated glauconites and offers a precise technique for detecting the detrital contamination of glauconites.The most common K-bearing detrital contaminants have smaller (K-feldspars, Al-rich dioctahedral micas) or greater (trioctahedral micas) dissolution rates than glauconite in extremely low pH solutions. The differences in the dissolution rates can be applied to evaluate the purity of the glauconite and its crystallization age.The interlaboratory GLO glauconite standard and grain-size fractions separated from glauconitic sandstones of the Paleogene (sample GL) and Jurassic (sample GW8) ages were treated with acid (3M HCl, at 99±2°C) for different reaction times (0.5–7 h) and measured for their apparent isotopic ages.Microporous amorphous silica with large specific surface area is the solid product of the reaction and its content increases with reaction time. The K-Ar dates (apparent ages) of the solid residues increase significantly with reaction time: from 44.6 to 107 Ma for the GL sample and from 125.7 to 394.7 Ma for GW8. The increase is negligible in the case of the GLO standard. The Rb-Sr data of the GL sample were modeled using initial 87Sr/Sr ratios of 0.707–0.709, which resulted in a 29.9–35.8 Ma date for the untreated portions of GL, and ∼42.6 Ma after 7 h of treatment.The increase of isotopic K-Ar date with increasing time of dissolution is interpreted to be a result of increasing concentration of detrital, acid-resistant, K-bearing minerals, observed also with the electron microscope and X-ray diffraction. Probabilistic modeling based on single (K-Ar) or double (K-Ar and Rb-Sr) isotopic systems evaluated the isotopic ages of the detrital and authigenic minerals, and their K2O and Rb concentrations. The crystallization ages computed using these two methods are: 24.0, 26.5, and 32.3 Ma for the GL material, and 117.3–121.8 Ma for the GW8 series.The proposed method based on partial dissolution is a potential tool for evaluating the reliability of glauconite dating.
Evidence of Degradation of Triarylmethine Dyes on Texas Vermiculite
Authors: Rytwo Giora , Gonen Yotam , Huterer-Shveky Reuma 
Published: December 2009

AbstractSynthetic dyes in industrial effluents pose a significant risk to human health and the environment, so much effort has been expended to degrade them using various methods, including the use of clay minerals as catalysts. The purpose of this study was to advance understanding of the mechanisms for clay-catalyzed degradation of crystal violet (CV) and other triarylmethine dyes using three different vermiculite clays (Llano, Texas, VTx-1; Ojen, OV; and Russian, RV), a montmorillonite (SWy-1), and a Spanish sepiolite (SEP). While OV, RV, SWy-1, and SEP showed almost no activity with respect to dye degradation, VTx-1 caused complete removal of the dye from solution up to the equivalent of 200% of the cation exchange capacity of the clay. While large amounts of dye were removed from the solution, no change in basal spacing was observed by X-ray diffraction. The kinetics of removal of CV from solution began after a lag period of >10 days in a process that can be described by pseudo-second order kinetics. By comparison, adsorption of CV onto SWy-1 and SEP was immediate, without any lag period. Sonication treatment of the VTx-1 vermiculite suspension caused the CV removal process to begin immediately. Fourier-transform infrared measurements of adsorption of CV on clays revealed that for the OV and RV vermiculites, SEP sepiolite, and SWy-1 montmorillonite the spectra were similar to the original dye; the spectra of the VTx-1-dye differed considerably, however, exhibiting vibrations of methylene groups (—CH2—) which were not present in the CV molecule. The significant changes in the IR spectrum indicated that CV underwent degradation on the surface of the VTx-1 vermiculite. Carbon-content analysis led to the conclusion that degradation products remained bound to the clay. Similar effects were observed for two other triarylmethine dyes (malachite green and methyl green) added to VTx-1, indicated that it may, therefore, be considered suitable as a sorbent to remove and decompose such dyes from industrial effluents. Pretreatment by sonication would remove the need for long incubation times.
Progressive Formation of Halloysite From the Hydrothermal Alteration of Biotite and the Formation Mechanisms of Anatase in Altered Volcanic Rocks From Limnos Island, Northeast Aegean Sea, Greece
Authors: Papoulis Dimitrios , Tsolis-Katagas Panagiota , Kalampounias Angelos G. , Tsikouras Basilios 
Published: December 2009

AbstractOccurrences of halloysite-rich material in altered volcanic rocks, principally trachyandesites, dacites, and tuffs, extend over an area of ∼1 km2 in the southwestern part of Limnos, Island, northeast Aegean Sea, Greece. The present study was designed to investigate the alteration processes which acted on the biotite in these volcanic rocks, to describe in detail the mechanism of formation of the halloysite, and to specify the mechanisms of formation of anatase during the alteration processes. Samples were examined using polarized-light microscopy, X-ray powder diffraction, scanning electron microscopy, scanning electron microscopy-energy dispersive spectroscopy, and Fourier-transform-Raman techniques. The extensive alteration of the parent rocks, triggered by the circulation of hydrothermal fluids through faults and fractures, resulted in the alteration of biotite to halloysite. Six stages of alteration were recognized. Nanoparticles of halloysite were initially formed on the mica layers, which progressively grew through short-tubular to well formed tubular halloysite, with increasing alteration. In the most altered samples, laths and interconnected laths with the composition (Al3.96Fe0.04)Si4O10(OH)8, were the dominant halloysite morphologies. Anatase was encountered as an alteration product of both ilmenite and biotite. Ilmenite was altered to anatase and Fe oxides. The altered ilmenite crystals constrained most of the newly formed anatase within the space occupied previously by ilmenite, leading to the formation of skeletal anatase. The layered structure of the micas was the main factor governing the morphology of newly formed anatase developed outside ilmenite margins in the form of layers parallel to those of mica. An unusual ring-like structure of anatase was thought to be the result of the uncommon alteration of inner parts of mica folia to tubular halloysite oriented perpendicular to the mica layers. The detachment of the halloysite tubes by circulating hydrothermal fluids was considered to be the reason for the creation of holes which were subsequently surrounded by the anatase ring forms.
Effect of Silica Polymerization on the Oxalate-Promoted Dissolution of Goethite
Authors: Eick Matthew J. , Luxton Todd P. , Welsh Holly A. 
Published: December 2009

AbstractNumerous studies have investigated the ligand-promoted dissolution of Fe (oxyhydr)oxides. In natural environments, inorganic ligands can compete with organic ligands for surface sites on (oxyhydr)oxides which may influence dissolution rates. Published research of this interaction and its effect on the dissolution of (oxyhydr)oxides is rare. The objective of the present study was to examine the extent to which silica, as a naturally occurring competitive ligand added in the form of silicic acid, impacts the oxalate-promoted dissolution of the common soil Fe (oxyhydr)oxide goethite. Sorbed silica reduced the oxalate-promoted dissolution rate of goethite at all surface coverages investigated. As initial silica solution concentrations increased from 0.50 mM to 5.0 mM, relatively little change in the dissolution rate was observed. Fourier-transform infrared (FTIR) spectra indicated that, as silica-surface coverages increased, the silica underwent polymerization on the goethite surface. Initially, silicate was associated with surface functional groups, but as polymerization occurred some of the silica appeared to desorb from the goethite surface without being released into the bulk solution, suggesting that silica polymers formed discrete islands or surface clusters that grew away from the goethite surface rather than expanding epitaxially across the surface. Minimal changes were observed in the quantity of reactive goethite surface, which is responsible for the observed dissolution rates, as silica-surface coverages increased.
Effect of the Size of Aggregates on Pore Characteristics of Minerals Measured by Mercury Intrusion and Water-Vapor Desorption Techniques
Authors: Jozefaciuk Grzegorz 
Published: December 2009

AbstractThe size, shape, and continuity of pores in mineral solids greatly influence the behavior of percolating liquids and solids in porous media, which has significant practical environmental implications. In order to expand understanding of these properties in soil minerals, the present study was undertaken to analyze the pore characteristics of bentonite, illite, and kaolinite in the forms of powder and aggregates of different dimensions, combining water-vapor desorption and mercury-intrusion techniques. Different granulometric fractions of milled quartz glass were also studied. With increasing aggregate size of the minerals, larger pore volumes (up to 25%), smaller surface areas (down to 15%), larger average radii (up to 15%), and smaller fractal dimensions (down to 6%) were measured using water-vapor adsorption-desorption data. The differences were smallest for bentonite, possibly due to the smallest particle size of this mineral and/or to its very large water-vapor adsorption capacity. The degree of water-vapor adsorption on quartz was too small to rely on the data obtained.The pore volumes and average radii, measured by mercury-intrusion porosimetry, were up to few times larger for the mineral powders than for their aggregate counterparts. Similar values were noted for aggregates >1 mm in diameter, for which the input of interaggregate spaces into total porosity of the sample bed was negligible. Two pathways of mercury intrusion were detected in porosimetric curves: filling of interaggregate spaces, and penetration into aggregates. Similar penetration thresholds into aggregates of different sizes were calculated. With increasing size of quartz grains, the pore volume of the quartz bed decreased whereas the average pore radius increased. Mercury intrusion detected pore-fractal behavior of bentonite and kaolinite, but for aggregated minerals the calculated values of fractal dimensions were >3, values which increased with increasing aggregate size. Very similar pore parameters were measured for aggregates prepared from a natural deposit of kaolinite and for artificially prepared aggregates from powder of the same mineral, indicating that artificial aggregation can simulate natural processes.Both water desorption and mercury intrusion detected fractal behavior in the limited range of pores. A test to find fractal build up of the aggregates in extended scales based on a dependence of surface area of unit volume of aggregate bed on aggregate size showed no fractal-aggregate build-up.
Clayey Cap-Rock Behavior in H2O-CO2 Media at Low Pressure and Temperature Conditions: An Experimental Approach
Authors: Kohler Eric , Parra Teddy , Vidal Olivier 
Published: December 2009

AbstractThe storage of CO2 in geological reservoirs requires an understanding of the impact of CO2 on clay-rich sealing cap-rocks to identify and explore critical parameters that modify petrophysical properties such as permeability and fracturing. The purpose of this study was to investigate the effect of heating, under different hydrated-CO2 partial pressures, on the chemical compositions and relative amounts of mineral phases in the Saint Martin de Bossenay (SMB, Paris Basin, France) cap-rock in order to identify possible mineral-phase transitions and to estimate reaction kinetics induced by the presence of excess dissolved CO2.X-ray diffraction, transmission electron microscopy, and electron microprobe analyses were employed to study mineral alteration, with particular attention given to visualization and quantification of the mineral evolution of clay minerals. In all the altered mixtures investigated, the illitization of clays was combined with the formation of anhydrite. These changes were accompanied by a dolomitization and a slight increase in the quartz content. The CO2-rich samples crystallized Fe2+-and K+-enriched illites, whereas the CO2-free experiments precipitated Al3+-deprived and Mg2+-enriched illites. Advanced characterizations of cap-rock material allowed reaction paths, induced by the increase in dissolved CO2 in the porous media, to be determined precisely. The results place strong constraints on numerical models aimed at evaluating the safety of an SMB site.
Functionalization of the Interlayer Surfaces of Kaolinite by Alkylammonium Groups From Ionic Liquids
Authors: Letaief Sadok , Detellier Christian 
Published: December 2009

AbstractThe objective of this study was to design new, functional, nanostructured materials from the abundant clay mineral kaolinite, in spite of development problems with the interlayer chemistry of kaolinite because of its non-swelling properties. A particular goal of this work was to graft, in a controlled way, alkylammonium groups onto the aluminol interlayer surfaces of kaolinite. This was successfully achieved by soft-chemical approaches, more specifically by the melting intercalation process of alkylammonium ionic liquids which were synthesized for this purpose. The resulting nanohybrid materials were characterized chemically and structurally by X-ray diffraction analysis, thermal analysis (TG/DTA), 13C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy, and Fourier-transform infrared spectroscopy. The amount of grafted organic material was quantified from TGA results. Alkylammonium salts with a short alkyl chain were grafted directly using a melting reaction at 180°C under N2 involving the in situ displacement of dimethylsulfoxide (DMSO) from a DMSO-kaolinite pre-intercalate; for longer alkyl chains, the grafting was done in two steps. In the first step, the corresponding amino-alcohol was grafted into the kaolinite by displacement of DMSO from the interlayer space. The second step consisted of quaternarization of the grafted material by reaction with iodomethane or iodoethane.
The Charge of Component Layers of Illite-Smectite in Bentonites and the Nature of End-Member Illite
Authors: Środoń Jan , Zeelmaekers Edwin , Derkowski Arkadiusz 
Published: December 2009

AbstractThe nature of component layers of mixed-layer illite-smectite and their possible evolution in the course of illitization have been debated since the 1960s. The present study is a new attempt to solve these problems, using samples collected from diverse geological formations around the world. Twenty three purified illite-smectites from bentonites and hydrothermal rocks, covering the complete range of expandability, were analyzed chemically, including NH4+\$\end{document} determination, and their structural formulae were calculated. The exchangeable cations (EXCH) were plotted vs. the fixed cations (FIX) yielding the following experimental regression:
EXCH=−0.43×FIX+0.41(R2=0.98)\$\end{document}FIX and EXCH depend on the charge of the illite (Qi) and smectite (Qs) interlayers, and the fractions of these interlayers in the bulk clay leading to:
EXCH=−Qs/Qi×FIX+Qs\$\end{document}Analysis of these relations and independent measurements of the total specific surface area (TSSA) indicate that the layer charges of both types do not change in the course of illitization. The smectite layer charge is equal to 0.41 and the illite layer charge is equal to 0.95 per O10(OH)2. End-member illite has a well defined composition that is close to intermediate between muscovite and phengite, with fixed cations content greater than that specified in the AIPEA classification of layer silicates:
FIX0.95(Si3.25Al0.75)(Al1.81Fe0.01Mg0.19)O10(OH)2\$\end{document}The established relationship allows the calculation of the mean number (N) of 2:1 layers in all fundamental particles and also the fraction of smectitic layers (fs) from FIX:
N=Qi/(Qi−FIX)fs=(Qi−FIX)/Qi\$\end{document}N and fs can be used to calculate TSSA, and all three parameters can also be calculated from cation exchange capacity and from X-ray diffraction peak positions, utilizing the regressions established here.