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PubMedDate not supplied

Decomposition of silicate minerals by Bacillus mucilaginosus in liquid culture.

The extraction of K(+) and SiO(2 )from silicate minerals by Bacillus mucilaginosus in liquid culture was studied in incubation experiments. B. mucilaginosus was found to dissolve soil minerals and mica and simultaneously release K(+) and SiO(2) from the crystal lattices. In contrast, the bacterium did not dissolve feldspar. B. mucilaginosus also produced organic acids and polysaccharides during growth. The polysaccharides strongly adsorbed the organic acids and attached to the surface of the mineral, resulting in an area of high concentration of organic acids near the mineral. The polysaccharides also adsorbed SiO(2) and this affected the equilibrium between the mineral and fluid phases and led to the reaction toward SiO(2 )and K(+) solubilization. These two processes led to the decomposition of silicate minerals by the bacterium.

Acids↗

PubMed2004

A disintegration method for direct counting of bacteria in clay-dominated sediments: dissolving silicates and subsequent fluorescent staining of bacteria.

The masking of bacteria by abundant microparticles of the clay and silt fraction and cell losses due to sonication hampered direct enumeration of bacteria in sediments dominated by fine sediments. These problems can be circumvented by dissolving silicate fine particles using hydrofluoric acid and subsequent staining of bacteria by DTAF. The developed disintegration method partly replaces mechanical separation of bacteria from sediment particles by chemical disintegration of the silicates. Recovery efficiency ranged from 90% to 111% for different clays and clay-dominated sediments. Especially for the analysis of fine sediments and clays, this method circumvents both strong dilution of the sediment sample and harsh sonication. The method can also therefore be used in sediments where particle abundance is several orders of magnitude higher than bacterial abundance and simple dilution would not suffice in reliably counting bacteria.

Aluminum Silicates↗

PubMed1981

Photoactivated zinc silicate in thin layer chromatography plates: a potential cause for error in liquid scintillation counting.

Thin layer chromatography plates impregnated with fluorescent indicator permit easy identification of many compounds by exposure to ultraviolet light. Exposure of zinc silicate treated plates to ultraviolet light (254 nm) for 30 seconds induced photoluminescence which persisted at significant levels for longer than 24 hours. This artifact significantly interfered with radioactivity quantitation in three commercially available liquid scintillation solutions. Chromatography plates impregnated with calcium silicate demonstrated insignificant ultraviolet light induced photoluminescence. The use of 14C rather than 3H-radiolabeled compounds, protecting the plate with aluminum foil when visualizing reference compounds with ultraviolet light, and heating the photoactivated plate to accelerate disappearance of the photoluminescence minimized the error in liquid scintillation counting.

20-Hydroxysteroid Dehydrogenases↗

PubMed2001

Sorption mechanisms of zinc to calcium silicate hydrate: X-ray absorption fine structure (XAFS) investigation.

In this study, X-ray absorption fine structure (XAFS) spectroscopy has been used to further elucidate the binding mechanisms of Zn(II) to calcium silicate hydrate (C-S-H), the quantitatively most important cement mineral. Such knowledge is essential for the assessment of the longterm behavior of cement-stabilized waste materials. XAFS spectra of the Zn(II) equilibrated with C-S-H(I) for up to 28 days are best modeled by tetrahedral coordination of Zn(II) by four O atoms in the first atomic shell. Beyond the first coordination shell, data analysis of more highly concentrated samples suggests the presence of two distinct Zn distances and possibly the presence of an Si shell. On the basis of the comparison with a set of reference compounds, this coordination environment can be reasonably related to the structure of hemimorphite, a naturally occurring zinc silicate, and/or the presence of gamma-Zn(OH)2. At the lowest Zn uptake, the above fitting approach failed and data could be described best with a Zn-Si and a Zn-Ca shell. Previous work has been able to show that Zn(II) diffuses into the C-S-H(I) particles and does not form discrete precipitates, so the findings appear to confirm the incorporation of Zn(II) in the interlayer of C-S-H(I).

Adsorption↗

PubMed1997

Modelling of the prebiotic synthesis of oligopeptides: silicate catalysts help to overcome the critical stage.

On the basis of experimental studies of the initial stages of glycine oligomerization in aqueous suspension of zeolite and kaolinite catalysts, a model is suggested for the prebiotic synthesis of oligopeptides from alpha-amino acids. The formation of linear dipeptides by hydrolysis of one amide bond in the cyclic piperazinedione intermediate (formed from glycine spontaneously) is found to be the critical stage of the reaction. This stage is base catalyzed and its rate increases when pH of the medium goes up. The linear glycyl-glycine yield rises under effect of hydroxyl anions generated from different sources including insoluble silicates and soluble sodium bicarbonate. During prebiotic evolution silicates capable of cation-exchange can serve as local sources of the hydroxyl anions which dramatically accelerate formation of linear dipeptides from cyclic ones. Oligopeptides of higher molecular weight are then easily formed from the linear dipeptides at neutral pH, even in the absence of catalysts or sources of energy (e.g. such as light). The described catalytic synthesis could occur in the proximity of submarine hydrothermal vents.

Aluminum Silicates↗

PubMed2003

Highly stabilized amorphous 3-bis(4-methoxyphenyl)methylene-2-indolinone (TAS-301) in melt-adsorbed products with silicate compounds.

3-Bis(4-Methoxyphenyl)methylene-2-indolinone (TAS-301) is a poorly water-soluble drug showing low oral bioavailability in rats and dogs. Previously, we reported that when a physical mixture of TAS-301 and a porous calcium silicate, Florite RE (FLR), was heated at high temperature (250 degrees C), the drug melted and was adsorbed by the FLR in an amorphous state, and that the preparation (melt-adsorbed product) showed a significantly increased solubility and dissolution rate, and a significantly enhanced oral bioavailability of the drug. The aim of the present study was to elucidate important factors for preparing a melt-adsorbed product showing greater stability of drug in an amorphous state. We examined the effects of the kind of adsorbent, drug/adsorbent ratio, heating conditions, and drug particle size on converting drug crystal into an amorphous state, the stability of amorphous state, and chemical stability of the drug in the melt-adsorbed products under a high temperature and high humidity condition (60 degrees C/80% RH, open). FLR, light anhydrous silicic acid and two types of hydrated silicon dioxides were tested as adsorbents. For the batch method, TAS-301 was converted into an amorphous state by heating TAS-301/adsorbents physical mixtures above the melting point of TAS-301 for more than 2 min. The amorphous state was most stabilized when FLR was used as an adsorbent and drug/FLR ratio was 1:0.5 and more. For the continuous method using the twin screw extruder that enables significantly larger scale manufacturing than batch method, TAS-301 melt-adsorbed products were able to produce when only FLR was used as adsorbent. The heating temperature was needed to be set above the melting point of TAS-301 to convert it into an amorphous state as well as batch method. The amorphous state was stabilized when drug/FLR ratio was 1:2 and more. The micronization of the drug decreased the stability of the amorphous state. These results indicate the importance of optimizing the above factors in the preparation of melt-adsorbed product.

Adsorption↗

PubMed1996

Apatite-forming ability of silicate ion dissolved from silica gels.

It is known that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces, and a certain type of hydrated silica developed on their surfaces plays an important role in nucleating the apatite. In the present study, the apatite-forming ability of silicate ion dissolved from different silica materials into a simulated body fluid was examined as follows. Polyether sulfone substrates pretreated with O2 plasma were placed in parallel to plates of three kinds of silica gels prepared in different media and silica glass, with a distance of 0.5 mm between them in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for 4 days, and then soaked in a solution with ion concentrations 1.5 times those of the simulated body fluid for 6 days. After the first soaking, silicon combined with oxygen was detected on the surfaces of the substrates faced to all the silica gels, whereas it was not detected on that faced to the silica glass. After the second soaking, the former formed a bonelike apatite layer on their surfaces, but the latter did not. These results indicate that silicate ion which is dissolved from the silica gels and adsorbed on the substrates has an apatite-forming ability, irrespective of the microstructure of the original silica gels.

Apatites↗

PubMed2004

First preparation of nanocrystalline zinc silicate by chemical vapor synthesis using an organometallic single-source precursor.

A method is presented to prepare nanocrystalline alpha-Zn(2)SiO(4) with the smallest crystal size reported so far for this system. Our approach combines the advantages of organometallic single-source precursor routes with aerosol processing techniques. The chemical design of the precursor enables the preferential formation of pure zinc silicates. Since gas-phase synthesis reduces intermolecular processes, and keeps the particles small, zinc silicate was synthesized from the volatile organometallic precursor [[MeZnOSiMe(3)](4)], possessing a Zn-methyl- and O-silyl-substituted Zn(4)O(4)-heterocubane framework (cubane), under oxidizing conditions, using the chemical vapor synthesis (CVS) method. The products obtained under different process conditions and their structural evolution after sintering were investigated by using various analytical techniques (powder X-ray diffraction, transmission electron microscopy, EDX analysis, solid-state NMR, IR, Raman, and UV/Vis spectroscopy). The deposited aerosol obtained first (processing temperature 750 degrees C) was amorphous, and contained agglomerates with primary particles of 12 nm in size. These primary particles can be described by a [Zn-O-Si] phase without long-range order. The deposit obtained at 900 degrees C contained particles with embedded nanocrystallites (3-5 nm) of beta-Zn(2)SiO(4), Zn(1.7)SiO(4), and ZnO in an amorphous matrix. On further ageing, the as-deposited particles obtained at 900 degrees C form alpha-Zn(2)SiO(4) imbedded in amorphous SiO(2). The crystallite sizes and primary particle sizes in the formed alpha-Zn(2)SiO(4) were found to be below approximately 50 nm and mainly spherical in morphology. A gas-phase mechanism for the particle formation is proposed. In addition, the solid-state reactions of the same precursor were studied in detail to investigate the fundamental differences between a gas-phase and a solid-state synthesis route.

Organometallic Compounds↗

PubMed1981

Effect of poly-2-vinylpyridine-N-oxide and sucrose on silicate-induced hemolysis of erythrocytes.

The biological activity of montmorillonite, palygorskite, kaolinite, chrysotile, and silica was examined using in vitro hemolysis of erythrocytes. The hemolytic potency was in the order montmorillonite greater than silica greater than palygorskite greater than chrysotile greater than kaolinite. The polymer poly-2-vinylpyridine-N-oxide inhibited hemolysis caused by montmorillonite, palygorskite, kaolinite, and silica, but it was less effective with chrysotile. The extent of polymer binding to the silicates and red blood cells was measured by UV spectroscopy. When sucrose was substituted for the saline solution as the incubating medium, hemolysis was eliminated in all systems except chrysotile-erythrocyte, where it was enhanced. The results indicate that both hydrogen bonding and ionic interactions between silicate surfaces and the erythrocyte membrane are important in the hemolytic process.

Animals↗

PubMed2006

An investigation into the structure and reactivity of calcium-zinc-silicate ionomer glasses using MAS-NMR spectroscopy.

The suitability of Glass Polyalkenoate Cements (GPCs) for orthopaedic applications is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium-free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. However there is no data available on the structure of these glasses. (29)Si MAS-NMR, differential thermal analysis (DTA), X-ray diffraction (XRD), and network crosslink density (CLD) calculations were used to characterize the structure of five calcium zinc silicate glasses and relate glass structure to reactivity. The results indicate that glasses capable of forming Zn-GPCs are predominantly Q(2)/Q(3) in structure with corresponding network crosslink densities greater than 2. The correlation of CLD and MAS-NMR results indicate the primary role of zinc in these simple glass networks is as a network modifier and not an intermediate oxide; this fact will allow for more refined glass compositions, with less reactive structures, to be formulated in the future.

Aluminum↗

PubMed2006

Kinetics and mechanisms of the conversion of silicate (45S5), borate, and borosilicate glasses to hydroxyapatite in dilute phosphate solutions.

Bioactive glasses with controllable conversion rates to hydroxyapatite (HA) may provide a novel class of scaffold materials for bone tissue engineering. The objective of the present work was to comprehensively characterize the conversion of a silicate bioactive glass (45S5), a borate glass, and two intermediate borosilicate glass compositions to HA in a dilute phosphate solution at 37 degrees Celsius. The borate glass and the borosilicate glasses were derived from the 45S5 glass by fully or partially replacing the SiO(2) with B(2)O(3). Higher B(2)O(3) content produced a more rapid conversion of the glass to HA and a lower pH value of the phosphate solution. Whereas the borate glass was fully converted to HA in less than 4 days, the silicate (45S5) and borosilicate compositions were only partially converted even after 70 days, and contained residual SiO(2) in a Na-depleted core. The concentration of Na(+) in the phosphate solution increased with reaction time whereas the PO(4) (3-) concentration decreased, both reaching final limiting values at a rate that increased with the B(2)O(3) content of the glass. However, the Ca(2+) concentration in the solution remained low, below the detection limit of atomic absorption, throughout the reaction. Immersion of the glasses in a mixed solution of K(2)HPO(4) and K(2)CO(3) produced a carbonate-substituted HA but the presence of the K(2)CO(3) had little effect on the kinetics of conversion to HA. The kinetics and mechanisms of the conversion process of the four glasses to HA are compared and used to develop a model for the process.

Borates↗

PubMed1983

Isolation of silicate ionophore(s) from the apochlorotic diatom Nitzschia alba.

An organic extract of Nitzschia alba cells possesses ionophoretic activity towards silicate, as it induces silicate transport across an organic phase or across synthetic lipid membranes. The activity is dependent upon Na+ and prefers silicon to germanium, a congener. The activity can be resolved into two apparently pure fractions by a combination of high performance liquid chromatography and thin-layer chromatography. Preliminary characterization indicates that the compound(s) contains vicinal hydroxyl groups but is devoid of amino, sugar or phosphate groups.

Animals↗

PubMed1991

Diffusion of a multi-species component and its role in oxygen and water transport in silicates.

An important but poorly understood factor that affects diffusion rates is the role of speciation during diffusion of a multi-species component. The diffusion of such a component is complicated by the different diffusion coefficient of each species and the interconversion reactions among the species. These complexities can be treated by a diffusion equation that incorporates the diffusive fluxes of all species contributing to the concentration of the component. The effects of speciation on the diffusion of the component can be investigated experimentally in some simple cases by measuring concentration profiles of all species developed during diffusion experiments or by studying some of their other consequences. Experimental data on water diffusion in rhyolitic glasses indicate that although dissolved water is present as two species, H2O molecules and OH groups, molecular H2O is the dominant diffusing species at very low to high water concentrations. This explains the apparently complex behavior of water diffusion. Experimental data on oxygen diffusion in some silicates using 18O tracers in the form of H2(18O) are consistent with the idea that 18O transport is dominated by diffusion of H2O molecules even at lower water contents (ppm or less). This explains why oxygen transport depends on the presence of water and generally depends on water fugacity linearly. For this mode of oxygen transport, there is a simple theoretical relationship between the effective total oxygen diffusion coefficient and the total water diffusion coefficient that is a function of only the water concentration of the silicate at low water content. This relationship appears to describe quantitatively the existing data over a wide range in water contents and diffusion coefficients in several phases.

Diffusion↗

PubMed1982

Dissolution rates of silicate cements.

The literature relating to the dissolution of the silicate cements is reviewed, including the methodology, intrinsic factors relating to composition and method of mixing, curing etc. and extrinsic factors, i.e. the medium, pH, ionic strength etc. to which the sample of cement is exposed. New experimental data is shown relating the dissolution rate to solution composition and ionic strength. It is seen that samples of silicate cement can take up phosphate from solution as well as releasing this species and a dissolution process based on a reversible equilibrium is advanced. Also considered are the effects of sample volume:area ratio and the effect of agitation.

Buffers↗

PubMed1984

Degradation of DNA by silicic acid.

S1 nuclease hydrolysis and hydroxyapatite chromatography were used to study the effect of silicic acid on DNA. Native calf thymus DNA was incubated with increasing concentrations of silicic acid (DNA nucleotide/silicic acid molar ratios of 1:0.25, 1:0.5 and 1:1) and subjected to S1 nuclease hydrolysis. An increasing degree of DNA degradation was seen suggesting a destabilization of the secondary structure. A decrease in melting temperature was also observed. Hydroxyapatite chromatography indicated that incubation at the molar ratio of 1:1 resulted in denaturation and degradation of DNA.

Animals↗

PubMed1981

Enzyme-mimicking properties of silicates and other minerals.

The adsorptive and/or catalytic properties of clays, silicates in general, and other minerals are well known. More recently, their probable role in prebiotic syntheses of bio-organic compounds has become a matter of record. We demonstrate that, in addition to their role in de novo formation of important biomolecules, clays, micas, fibrous silicates and other minerals mimic the activities of contemporary enzymes including oxidases, esterases, phosphatases and glucosidases. The existence of such capabilities in substances likely to be represented on the surfaces of Earth-like planets may offer a challenge to the technology and design of remote life detection systems which must then distinguish between bona fide biological chemistry and mineral-base pseudometabolism. It also raises questions about the importance of mineral surfaces in post-mortem transformations of organic metabolites in our own biosphere.

Catalysis↗

PubMed1993

Cytotoxicity of aluminum silicates in primary neuronal cultures.

To study their cytotoxicity, clays containing aluminum silicates were added to cultures of primary murine spinal cord neurons and differentiated N1E-115 neuroblastoma cells. Bentonite (0.1 mg/ml) and montmorillonite (0.1 mg/ml) rapidly associated with the outer membrane of both N1E-115 and neuronal cells. Erionite (0.1 mg/ml) was randomly distributed throughout the culture. Both bentonite and montmorillonite caused complete cell lysis in the neuronal cultures within 60 min following addition. Erionite had no effect. None of the clays appeared to be cytotoxic to the differentiated N1E-115 cells even though bentonite and montmorillonite were closely associated with the cell membrane. N1E-115 cell lysis did not occur up to 18 h after addition of the clay. Aluminum silicate-containing clays caused a rapid lysis of primary neuronal cells. Differentiated N1E-115 neuroblastoma cells were not susceptible to clay-induced lysis, suggesting that the lytic mechanism is not a general phenomenon that affects all cell types equally.

Aluminum Silicates↗

PubMed1994

Structure of hydrated layers on silicate electrode glasses.

The structural changes of the silicate framework in hydrated layers of silicate electrode glasses compared with untreated glasses as well as the quality and quantity of water and its ionic species stored in the layer have been investigated by high-resolution solid-state nuclear magnetic resonance (NMR) techniques [29Si magic-angle spinning (MAS), 29Si cross-polarization (CP) MAS, 1H high-speed MAS, 1H CRAMPS and 1H Echo NMR]. To support the results, infrared (IR) spectroscopy, thermal analysis and sodium ion concentration analyses were used. It was found that at least two different water species exist in the hydrated layer: SiOH groups and not very mobile hydrogen-bonded molecular water. Concerning the framework modified, Q3 groups [(SiO)3SiOH] were formed in the hydrated glass. During the swelling process a condensation of silanol groups formed took place to a great extent.

Electrodes↗