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Sample records for metal-binding silica materials

  1. Metal-binding silica materials for wastewater cleanup

    SciTech Connect

    Kroh, F.O.

    1997-10-01

    In this Phase I Small Business Innovation Research program, TPL, Inc. is developing two series of high-efficiency covalently modified silica materials for removing heavy metal ions from wastewater. These materials have metal ion capacities greatly exceeding those of commercial ion exchange resins. One series, containing thiol groups, has high capacity for {open_quotes}soft{close_quotes} heavy metal ions such as Hg, Pb, Ag, and Cd; the other, containing quaternary ammonium groups, has high capacity for anionic metal ions such as pertechnetate, arsenate, selenite, and chromate. These materials have high selectivity for the contaminant metals and will function well in harsh systems that inactivate other systems.

  2. Silica Materials for Medical Applications

    PubMed Central

    Vallet-Regí, María; Balas, Francisco

    2008-01-01

    The two main applications of silica-based materials in medicine and biotechnology, i.e. for bone-repairing devices and for drug delivery systems, are presented and discussed. The influence of the structure and chemical composition in the final characteristics and properties of every silica-based material is also shown as a function of the both applications presented. The adequate combination of the synthesis techniques, template systems and additives leads to the development of materials that merge the bioactive behavior with the drug carrier ability. These systems could be excellent candidates as materials for the development of devices for tissue engineering. PMID:19662110

  3. Reusable silica surface-insulation material

    NASA Technical Reports Server (NTRS)

    Goldstein, H. E.; Smith, M.; Leiser, D.

    1973-01-01

    Material was specifically developed for manufacture of insulating tiles, but it can be molded into other shapes as required. Basic raw materials are high-purity silica fiber, fumed-silica powder, and reagent-grade starch. Only purest materials are used, and care must be taken to avoid contamination during processing.

  4. Metal-silica sol-gel materials

    NASA Technical Reports Server (NTRS)

    Stiegman, Albert E. (Inventor)

    2002-01-01

    The present invention relates to a single phase metal-silica sol-gel glass formed by the co-condensation of a transition metal with silicon atoms where the metal atoms are uniformly distributed within the sol-gel glass as individual metal centers. Any transition metal may be used in the sol-gel glasses. The present invention also relates to sensor materials where the sensor material is formed using the single phase metal-silica sol-gel glasses. The sensor materials may be in the form of a thin film or may be attached to an optical fiber. The present invention also relates to a method of sensing chemicals using the chemical sensors by monitoring the chromatic change of the metal-silica sol-gel glass when the chemical binds to the sensor. The present invention also relates to oxidation catalysts where a metal-silica sol-gel glass catalyzes the reaction. The present invention also relates to a method of performing oxidation reactions using the metal-silica sol-gel glasses. The present invention also relates to organopolymer metal-silica sol-gel composites where the pores of the metal-silica sol-gel glasses are filled with an organic polymer polymerized by the sol-gel glass.

  5. Fused Silica and Other Transparent Window Materials

    NASA Technical Reports Server (NTRS)

    Salem, Jon

    2016-01-01

    Several transparent ceramics, such as spinel and AlONs are now being produced in sufficient large areas to be used in space craft window applications. The work horse transparent material for space missions from Apollo to the International Space Station has been fused silica due in part to its low coefficient of expansion and optical quality. Despite its successful use, fused silica exhibits anomalies in its crack growth behavior, depending on environmental preconditioning and surface damage. This presentation will compare recent optical ceramics to fused silica and discuss sources of variation in slow crack growth behavior.

  6. Ecodesign of ordered mesoporous silica materials.

    PubMed

    Gérardin, Corine; Reboul, Julien; Bonne, Magali; Lebeau, Bénédicte

    2013-05-07

    Characterized by a regular porosity in terms of pore size and pore network arrangement, ordered mesoporous solids have attracted increasing interest in the last two decades. These materials have been identified as potential candidates for several applications. However, more environmentally friendly and economical synthesis routes of mesoporous silica materials were found to be necessary in order to develop these applications on an industrial scale. Consequently, ecodesign of ordered mesoporous silica has been considerably developed with the objective of optimizing the chemistry and the processing aspects of the material synthesis. In this review, the main strategies developed with this aim are presented and discussed.

  7. Thermal pretreatment of silica composite filler materials

    PubMed Central

    Wan, Quan; Ramsey, Christopher

    2010-01-01

    Three different silica filler materials were thermally treated in order to effect dehydration, dehydroxylation, and rehydroxylation. Samples were characterized by thermogravimetry (TG), pycnometry, elemental analysis, and scanning electron microscopy (SEM). For all fillers, our results indicate incremental removal of silanol groups at higher heating temperatures and irreversible dehydroxylation at over 673 K. To remove the organic content and maintain adequate silanol density for subsequent silanization on Stöber-type silica, we suggest heating at 673 K followed by overnight boiling in water. PMID:20445821

  8. Improved Silica Aerogel Composite Materials

    NASA Technical Reports Server (NTRS)

    Paik, Jong-Ah; Sakamoto, Jeffrey; Jones, Steven

    2008-01-01

    A family of aerogel-matrix composite materials having thermal-stability and mechanical- integrity properties better than those of neat aerogels has been developed. Aerogels are known to be excellent thermal- and acoustic-insulation materials because of their molecular-scale porosity, but heretofore, the use of aerogels has been inhibited by two factors: (1) Their brittleness makes processing and handling difficult. (2) They shrink during production and shrink more when heated to high temperatures during use. The shrinkage and the consequent cracking make it difficult to use them to encapsulate objects in thermal-insulation materials. The underlying concept of aerogel-matrix composites is not new; the novelty of the present family of materials lies in formulations and processes that result in superior properties, which include (1) much less shrinkage during a supercritical-drying process employed in producing a typical aerogel, (2) much less shrinkage during exposure to high temperatures, and (3) as a result of the reduction in shrinkage, much less or even no cracking.

  9. Gated Silica Mesoporous Materials in Sensing Applications

    PubMed Central

    Sancenón, Félix; Pascual, Lluís; Oroval, Mar; Aznar, Elena; Martínez-Máñez, Ramón

    2015-01-01

    Silica mesoporous supports (SMSs) have a large specific surface area and volume and are particularly exciting vehicles for delivery applications. Such container-like structures can be loaded with numerous different chemical substances, such as drugs and reporters. Gated systems also contain addressable functions at openings of voids, and cargo delivery can be controlled on-command using chemical, biochemical or physical stimuli. Many of these gated SMSs have been applied for drug delivery. However, fewer examples of their use in sensing protocols have been reported. The approach of applying SMSs in sensing uses another concept—that of loading pores with a reporter and designing a capping mechanism that is selectively opened in the presence of a target analyte, which results in the delivery of the reporter. According to this concept, we provide herein a complete compilation of published examples of probes based on the use of capped SMSs for sensing. Examples for the detection of anions, cations, small molecules and biomolecules are provided. The diverse range of gated silica mesoporous materials presented here highlights their usefulness in recognition protocols. PMID:26491626

  10. Method of manufacturing silicon from powdered material containing silica

    SciTech Connect

    Santen, S.; Edstrom, J.O.

    1984-03-27

    Silicon is manufactured from powdered material containing silica by injecting this, optionally together with a reducing agent, into a gas plasma with the help of a carrier gas. Thereafter the silica material thus heated, together with the reducing agent if any and the energy-rich plasma gas, is introduced in a reaction chamber surrounded by solid reducing agent in lump form, so that the silica is caused to melt and is reduced to liquid silicon.

  11. Material Properties for Fiber-Reinforced Silica Aerogels

    NASA Technical Reports Server (NTRS)

    White, Susan; Rouanet, Stephane; Moses, John; Arnold, James O. (Technical Monitor)

    1994-01-01

    Ceramic fiber-reinforced silica aerogels are novel materials for high performance insulation, including thermal protection materials. Experimental data are presented for the thermal and mechanical properties, showing the trends exhibited over a range of fiber loadings and silica aerogel densities. Test results are compared to that of unreinforced bulk aerogels.

  12. Functionalized mesoporous silica materials for molsidomine adsorption: Thermodynamic study

    SciTech Connect

    Alyoshina, Nonna A.; Parfenyuk, Elena V.

    2013-09-15

    A series of unmodified and organically modified mesoporous silica materials was prepared. The unmodified mesoporous silica was synthesized via sol–gel synthesis in the presence of D-glucose as pore-forming agent. The functionalized by phenyl, aminopropyl and mercaptopropyl groups silica materials were prepared via grafting. The fabricated adsorbent materials were characterized by Fourier transform infrared spectroscopy (FTIR) analysis, N{sub 2} adsorption/desorption and elemental analysis methods. Then their adsorption properties for mesoionic dug molsidomine were investigated at 290–313 K and physiological pH value. Thermodynamic parameters of molsidomine adsorption on the synthesized materials have been calculated. The obtained results showed that the adsorption process of molsidomine on the phenyl modified silica is the most quantitatively and energetically favorable. The unmodified and mercaptopropyl modified silica materials exhibit significantly higher adsorption capacities and energies for molsidomine than the aminopropyl modified sample. The effects are discussed from the viewpoint of nature of specific interactions responsible for the adsorption. - Graphical abstract: Comparative analysis of the thermodynamic characteristics of molsidomine adsorption showed that the adsorption process on mesoporous silica materials is controlled by chemical nature of surface functional groups. Molsidomine adsorption on the phenyl modified silica is the most quantitatively and energetically favorable. Taking into account ambiguous nature of mesoionic compounds, it was found that molsidomine is rather aromatic than dipolar. Display Omitted - Highlights: • Unmodified and organically modified mesoporous silica materials were prepared. • Molsidomine adsorption on the silica materials was studied. • Phenyl modified silica shows the highest adsorption capacity and favorable energy. • Molsidomine exhibits the lowest affinity to aminopropyl modified silica.

  13. Non-silica aerogels as hypervelocity particle capture materials

    NASA Astrophysics Data System (ADS)

    Jones, Steven M.

    2010-01-01

    The Stardust sample return mission to the comet Wild 2 used silica aerogel as the principal cometary and interstellar particle capture and return medium. However, since both cometary dust and interstellar grains are composed largely of silica, using a silica collector complicates the science that can be accomplished with these particles. The use of non-silica aerogel in future extra-terrestrial particle capture and return missions would expand the scientific value of these missions. Alumina, titania, germania, zirconia, tin oxide, and resorcinol/formaldehyde aerogels were produced and impact tested with 20, 50, and 100μm glass microspheres to determine the suitability of different non-silica aerogels as hypervelocity particle capture mediums. It was found that non-silica aerogels do perform as efficient hypervelocity capture mediums, with alumina, zirconia, and resorcinol/formaldehyde aerogels proving to be the best of the materials tested.

  14. Water confinement in nanoporous silica materials

    SciTech Connect

    Renou, Richard; Szymczyk, Anthony; Ghoufi, Aziz

    2014-01-28

    The influence of the surface polarity of cylindrical silica nanopores and the presence of Na{sup +} ions as compensating charges on the structure and dynamics of confined water has been investigated by molecular dynamics simulations. A comparison between three different matrixes has been included: a protonated nanopore (PP, with SiOH groups), a deprotonated material (DP, with negatively charged surface groups), and a compensated-charge framework (CC, with sodium cations compensating the negative surface charge). The structure of water inside the different pores shows significant differences in terms of layer organization and hydrogen bonding network. Inside the CC pore the innermost layer is lost to be replaced by a quasi bulk phase. The electrostatic field generated by the DP pore is felt from the surface to the centre of pore leading to a strong orientation of water molecules even in the central part of the pore. Water dynamics inside both the PP and DP pores shows significant differences with respect to the CC pore in which the sub-diffusive regime of water is lost for a superdiffusive regime.

  15. Global equation of state for a glassy material: Fused silica

    SciTech Connect

    Boettger, J.C.

    1994-09-01

    A new SESAME equation of state (EOS) for fused silica has been generated using the computer program GRIZZLY and will be added to the SESAME library as material number 7387. This new EOS provides better agreement with experimental data than was achieved by all previous SESAME EOSs for fused silica. Material number 7387 also constitutes the most realistic SESAME-type EOS generated for any glassy material thus far.

  16. Silica and silica-titania sol-gel materials: synthesis and analytical application.

    PubMed

    Morosanova, Elena I

    2012-12-15

    This review describes last decade progress in the synthesis of sol-gel materials with analytically relevant properties and their application for the determination of metal ions, non-metal and organic compounds. The following types of materials are discussed: silica sol-gel materials doped with various analytical reagents, organofunctional silica sol-gel materials, and silica titania sol-gel materials. The variety of obtained materials allows their application for a wide range of analytical systems: electrochemical sensors, solid phase spectrophotometrical and SIA determination, and also for test determination including the employment of "length-of-stain" indicator tubes. This review surveys the results of studies on mentioned above subjects and summarizes the works accomplished in the field by author's team in Moscow State University.

  17. Fluorescent single walled carbon nanotube/silica composite materials.

    PubMed

    Satishkumar, B C; Doorn, Stephen K; Baker, Gary A; Dattelbaum, Andrew M

    2008-11-25

    We present a new approach for the preparation of single walled carbon nanotube silica composite materials that retain the intrinsic fluorescence characteristics of the encapsulated nanotubes. Incorporation of isolated nanotubes into optically transparent matrices, such as sol-gel prepared silica, to take advantage of their near-infrared emission properties for applications like sensing has been a challenging task. In general, the alcohol solvents and acidic conditions required for typical sol-gel preparations disrupt the nanotube/surfactant assembly and cause the isolated nanotubes to aggregate leading to degradation of their fluorescence properties. To overcome these issues, we have used a sugar alcohol modified silica precursor molecule, diglycerylsilane, for encapsulation of nanotubes in silica under aqueous conditions and at neutral pH. The silica/nanotube composite materials have been prepared as monoliths, at least 5 mm thick, or as films (<1 mm) and were characterized using fluorescence and Raman spectroscopy. In the present work we have investigated the fluorescence characteristics of the silica encapsulated carbon nanotubes by means of redox doping studies as well as demonstrated their potential for biosensing applications. Such nanotube/silica composite systems may allow for new sensing and imaging applications that are not currently achievable.

  18. Intrinsic Bistable Photonic Materials by Copper Colloid Formation in Silica

    DTIC Science & Technology

    1992-07-31

    Maximum 200 words) Eon implantation has been used to assemble planar thin films of metallic nanoclusters embedded in a dilectric. Gold and copper were...AND SUBTITLE S. FUNDING NUMBERS Intrinsic Bistable Photonic Materials by Copper Colloid C Formation in Silica DAALO3-9 IG-0028 / c. AUTHOR(S) Robert H...both found to produce nanosize metal clusters in silica. Both the size and size distribution of the metallic nanoclusters were characterized by

  19. Intrinsic Bistable Photonic Materials by Copper Colloid Formation in Silica.

    DTIC Science & Technology

    1992-07-31

    implantation has been used to assemble planar thin films of metallic nanoclusters embedded in a dilectric. Gold and copper were both found to produce nanosize...AND SUBTITLE S. FUNDING NUMBERS Intrinsic Bistable Photonic Materials by Copper Colloid Formation in Silica 6. AUTHOR(S) J Robert H. Magruder, III 7...metal clusters in silica. Both the size and size distribution of the metallic nanoclusters were characterized by transmission electron microscopy. The

  20. Nanostructured materials based on mesoporous silica and mesoporous silica/apatite as osteogenic growth peptide carriers.

    PubMed

    Mendes, L S; Saska, S; Martines, M A U; Marchetto, R

    2013-10-01

    The aim of this work was the preparation of inorganic mesoporous materials from silica, calcium phosphate and a nonionic surfactant and to evaluate the incorporation and release of different concentrations of osteogenic growth peptide (OGP) for application in bone regeneration. The adsorption and release of the labeled peptide with 5,6-carboxyfluorescein (OGP-CF) from the mesoporous matrix was monitored by fluorescence spectroscopy. The specific surface area was 880 and 484 m(2) g(-1) for pure silica (SiO) and silica/apatite (SiCaP), respectively; the area influenced the percentage of incorporation of the peptide. The release of OGP-CF from the materials in simulated body fluid (SBF) was dependent on the composition of the particles, the amount of incorporated peptide and the degradation of the material. The release of 50% of the peptide content occurred at around 4 and 30 h for SiCaP and SiO, respectively. In conclusion, the materials based on SiO and SiCaP showed in vitro bioactivity and degradation; thus, these materials should be considered as alternative biomaterials for bone regeneration.

  1. Fluorescent Functionalized Mesoporous Silica for Radioactive Material Extraction

    SciTech Connect

    Li, Juan; Zhu, Kake; Shang, Jianying; Wang, Donghai; Nie, Zimin; Guo, Ruisong; Liu, Chongxuan; Wang, Zheming; Li, Xiaolin; Liu, Jun

    2012-08-01

    Mesoporous silica with covalently bound salicylic acid molecules incorporated in the structure was synthesized with a one-pot, co-condensation reaction at room temperature. The as-synthesized material has a large surface area, uniform particle size, and an ordered pore structure as determined by characterization with transmission electron microscopy, thermal gravimetric analysis, and infrared spectra, etc. Using the strong fluorescence and metal coordination capability of salicylic acid, functionalized mesoporous silica (FMS) was developed to track and extract radionuclide contaminants, such as uranyl [U(VI)] ions encountered in subsurface environments. Adsorption measurements showed a strong affinity of the FMS toward U(VI) with a Kd value of 105 mL/g, which is four orders of magnitude higher than the adsorption of U(VI) onto most of the sediments in natural environments. The new materials have a potential for synergistic environmental monitoring and remediation of the radionuclide U(VI) from contaminated subsurface environments.

  2. Self-Assembly in Biosilicification and Biotemplated Silica Materials

    PubMed Central

    Fernandes, Francisco M.; Coradin, Thibaud; Aimé, Carole

    2014-01-01

    During evolution, living organisms have learned to design biomolecules exhibiting self-assembly properties to build-up materials with complex organizations. This is particularly evidenced by the delicate siliceous structures of diatoms and sponges. These structures have been considered as inspiration sources for the preparation of nanoscale and nanostructured silica-based materials templated by the self-assembled natural or biomimetic molecules. These templates range from short peptides to large viruses, leading to biohybrid objects with a wide variety of dimensions, shapes and organization. A more recent strategy based on the integration of biological self-assembly as the driving force of silica nanoparticles organization offers new perspectives to elaborate highly-tunable, biofunctional nanocomposites. PMID:28344249

  3. Development of novel delivery system for warfarin based on mesoporous silica: adsorption characteristics of silica materials for the anticoagulant.

    PubMed

    Dolinina, Ekaterina S; Vorobyeva, Evgeniya V; Parfenyuk, Elena V

    2016-08-01

    The adsorption of the anticoagulant warfarin onto unmodified (UMS) and modified (phenyl (PhMS), methyl (MMS), mercaptopropyl (MPMS)) mesoporous silica materials was studied at pH 1.6 and 7.4 and in the temperature range of 293-325 K. The silica materials were prepared by sol-gel method for further characterization by FTIR spectroscopy, N2 adsorption/desorption method, transmission electron microscopy and zeta potential measurements. The effects of medium pH, temperature and surface modification of mesoporous silica material on their adsorption characteristics (adsorption capacity, thermodynamic parameters of adsorption) relative to anticoagulant warfarin were investigated. It was found that medium acid-base properties strongly affect the adsorption of warfarin due to the pH-dependent structural diversity of the drug and ionization state of the silica surfaces. The adsorption capacity of the silica materials at pH 1.6 decreases in the order: MMS > MPMS > UMS > PhMS. The influence of various non-covalent interactions on the adsorption capacity of the silica materials and energy of the drug-silica interactions is discussed. These results may be useful for the development of a novel delivery system of warfarin.

  4. Solid state dye lasers: rhodamines in silica-zirconia materials.

    PubMed

    Schultheiss, Silke; Yariv, Eli; Reisfeld, Renata; Breuer, Hans Dieter

    2002-05-01

    Silica-zirconia materials as well as silica-zirconia ormosils prepared by the sol-gel technique were doped with the laser dyes Rhodamine B and Rhodamine 6G and used as solid state dye lasers. The photostability and efficiency of the solid state laser samples were measured in a transverse pumping configuration by either a nitrogen laser or the second harmonic of a Nd-YAG laser. Under the excitation of a nitrogen laser the photostability of Rhodamine B in silica-zirconia materials was low and decreased with a growing amount of zirconia. The photophysical properties of the incorporated dyes were studied by time-resolved fluorescence spectroscopy. The fluorescence lifetimes of both dyes increased when the matrix was modified by organic compounds Furthermore, the threshold energy of Rhodamine 6G in two ormosils containing 3 and 50% methylsilica was measured. The results revealed that the threshold energy was lower for the matrix with a higher amount of ormosil while the slope efficiency was higher in the matrix containing 30% ormosil.

  5. Polymer-Silica Nanocomposites: A Versatile Platform for Multifunctional Materials

    NASA Astrophysics Data System (ADS)

    Chiu, Chi-Kai

    Solution sol-gel synthesis is a versatile approach to create polymer-silica nanocomposite materials. The solution-to-solid transformation results in a solid consisting of interconnected nanoporous structure in 3D space, making it the ideal material for filtration, encapsulation, optics, electronics, drug release, and biomaterials, etc. Although the pore between nano and meso size may be tunable using different reaction conditions, the intrinsic properties such as limited diffusion within pore structure, complicated interfacial interactions at the pore surfaces, shrinkage and stress-induced cracking and brittleness have limited the applications of this material. To overcome these problems, diffusion, pore size, shrinkage and stress-induced defects need further investigation. Thus, the presented thesis will address these important questions such as whether these limitations can be utilized as the novel method to create new materials and lead to new applications. First, the behaviors of polymers such as poly(ethylene glycol) inside the silica pores are examined by studying the nucleation and growth of AgCl at the surface of the porous matrix. The pore structure and the pressure induced by the shrinkage affect have been found to induce the growth of AgCl nanocrystals. When the same process is carried out at 160 °C, silver metallization is possible. Due to the shrinkage-induced stresses, the polymer tends to move into open crack spaces and exterior surfaces, forming interconnected silver structure. This interconnected silver structure is very unique because its density is not related to the size scale of nanopore structures. These findings suggest that it is possible to utilize defect surface of silica material as the template to create interconnected silver structure. When the scale is small, polymer may no longer be needed if the diffusion length of Ag is more than the size of silica particles. To validate our assumption, monoliths of sol-gel sample containing AgNO3

  6. Solvent effects on silica domain growth in silica/siloxane composite materials

    SciTech Connect

    Ulibarri, T.A.; Bates, S.E.; Black, E.P.; Schaefer, D.W.; Beaucage, W.G.; Lee, M.K.; Moore, P.A.; Burns, G.T.

    1995-07-01

    The effect of solvent addition on the phase separation, mechanical Properties and thermal stability of silica/siloxane composite materials prepared by in situ reinforcement was examined. The addition of a solvent enhances the miscibility of the reinforcement precursor, a partial hydrolyzate of tetraethoxysilane (TEOS-PH), with the polydimethylsiloxane (PDMS) polymer. As a result, the phase separation at the micron level, termed the large-scale structure, diminished in size. This decrease in particle size resulting from the addition of moderate amounts of solvent was accompanied by an improvement in the mechanical properties. However, solvent addition in the excess of 50 weight percent led to a decrease in mechanical properties even though the large-scale structure continued to diminish in size. Small Angle X-Ray Scattering (SAXS) was used to examine the Angstrom level or small-scale structure. This small-scale structure was only affected by the presence of solvent, not the amount. The silica/siloxane composite materials showed the same thermal transition temperatures as the original PDMS material.

  7. Synthesis of mesoporous silica materials from municipal solid waste incinerator bottom ash.

    PubMed

    Liu, Zhen-Shu; Li, Wen-Kai; Huang, Chun-Yi

    2014-05-01

    Incinerator bottom ash contains a large amount of silica and can hence be used as a silica source for the synthesis of mesoporous silica materials. In this study, the conditions for alkaline fusion to extract silica from incinerator bottom ash were investigated, and the resulting supernatant solution was used as the silica source for synthesizing mesoporous silica materials. The physical and chemical characteristics of the mesoporous silica materials were analyzed using BET, XRD, FTIR, SEM, and solid-state NMR. The results indicated that the BET surface area and pore size distribution of the synthesized silica materials were 992 m2/g and 2-3.8 nm, respectively. The XRD patterns showed that the synthesized materials exhibited a hexagonal pore structure with a smaller order. The NMR spectra of the synthesized materials exhibited three peaks, corresponding to Q(2) [Si(OSi)2(OH)2], Q(3) [Si(OSi)3(OH)], and Q(4) [Si(OSi)4]. The FTIR spectra confirmed the existence of a surface hydroxyl group and the occurrence of symmetric Si-O stretching. Thus, mesoporous silica was successfully synthesized from incinerator bottom ash. Finally, the effectiveness of the synthesized silica in removing heavy metals (Pb2+, Cu2+, Cd2+, and Cr2+) from aqueous solutions was also determined. The results showed that the silica materials synthesized from incinerator bottom ash have potential for use as an adsorbent for the removal of heavy metals from aqueous solutions.

  8. Mesoporous silica as carrier of antioxidant for food packaging materials

    NASA Astrophysics Data System (ADS)

    Buonocore, Giovanna Giuliana; Gargiulo, Nicola; Verdolotti, Letizia; Liguori, Barbara; Lavorgna, Marino; Caputo, Domenico

    2014-05-01

    Mesoporous silicas have been long recognized as very promising materials for the preparation of drug delivery systems. In this work SBA-15 mesoporous silica has been functionalized with amino-silane to be used as carrier of antioxidant compound in the preparation of active food packaging materials exhibiting tailored release properties. Active films have been prepared by loading the antioxidant tocopherol, the purely siliceous SBA-15 and the aminofunctionalized SBA-15 loaded with tocopherol into LDPE matrix trough a two-step process (mixing+extrusion). The aim of the present work is the study of the effect of the pore size and of the chemical functionality of the internal walls of the mesophase on the migration of tocopherol from active LDPE polymer films. Moreover, it has been proved that the addition of the active compound do not worsen the properties of the film such as optical characteristic and water vapor permeability, thus leading to the development of a material which could be favorably used mainly, but not exclusively, in the sector of food packaging.

  9. Predicted metal binding sites for phytoremediation.

    PubMed

    Sharma, Ashok; Roy, Sudeep; Tripathi, Kumar Parijat; Roy, Pratibha; Mishra, Manoj; Khan, Feroz; Meena, Abha

    2009-09-05

    Metal ion binding domains are found in proteins that mediate transport, buffering or detoxification of metal ions. The objective of the study is to design and analyze metal binding motifs against the genes involved in phytoremediation. This is being done on the basis of certain pre-requisite amino-acid residues known to bind metal ions/metal complexes in medicinal and aromatic plants (MAP's). Earlier work on MAP's have shown that heavy metals accumulated by aromatic and medicinal plants do not appear in the essential oil and that some of these species are able to grow in metal contaminated sites. A pattern search against the UniProtKB/Swiss-Prot and UniProtKB/TrEMBL databases yielded true positives in each case showing the high specificity of the motifs designed for the ions of nickel, lead, molybdenum, manganese, cadmium, zinc, iron, cobalt and xenobiotic compounds. Motifs were also studied against PDB structures. Results of the study suggested the presence of binding sites on the surface of protein molecules involved. PDB structures of proteins were finally predicted for the binding sites functionality in their respective phytoremediation usage. This was further validated through CASTp server to study its physico-chemical properties. Bioinformatics implications would help in designing strategy for developing transgenic plants with increased metal binding capacity. These metal binding factors can be used to restrict metal update by plants. This helps in reducing the possibility of metal movement into the food chain.

  10. Structure-property relationships in silica-siloxane nanocomposite materials

    SciTech Connect

    Ulibarri, T.A.; Derzon, D.K.; Wang, L.C.

    1997-03-01

    The simultaneous formation of a filler phase and a polymer matrix via in situ sol-gel techniques provides silica-siloxane nanocomposite materials of high strength. This study concentrates on the effects of temperature and relative humidity on a trimodal polymer system in an attempt to accelerate the reaction as well as evaluate subtle process- structure-property relations. It was found that successful process acceleration is only viable for high humidity systems when using the tin(IV) catalyst dibutyltin dilaurate. Processes involving low humidity were found to be very temperature and time dependent. Bimodal systems were investigated and demonstrated that the presence of a short-chain component led to enhanced material strength. This part of the study also revealed a link between the particle size and population density and the optimization of material properties.

  11. Characterization of silica quartz as raw material in photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Boussaa, S. Anas; Kheloufi, A.; Zaourar, N. Boutarek; Kefaifi, A.; Kerkar, F.

    2016-07-01

    Raw materials are essential for the functioning of modern societies, and access to these raw materials is vital to the world economy. Sustainable development, both globally level, raises important new challenges associated with access and efficient use of raw materials. High purity quartz, is consider as a critical raw material and it is a rare commodity that only forms under geological conditions where a narrow set of chemical and physical parameters is fulfilled. When identified and following special beneficiation techniques, high purity quartz obtains very attractive prices and is applied in high technology sectors that currently are under rapid expansion such as photovoltaic solar cells, silicon metal - oxide wafers in the semiconductor industry and long distance optical fibers that are used in communication networks. Crystalline silicon remains the principal material for photovoltaic technology. Metallurgical silicon is produced industrially by the reduction of silica with carbon in an electric arc furnace at temperatures higher than 2000 °C in the hottest parts, by a reaction that can be written ideally as: SiO2 + 2C = Si + 2CO. The aim of this study has been to test experimental methods for investigating the various physical and chemical proprieties of Hoggar quartz with different techniques: X Ray Fluorescence, infra-red spectroscopy, Scanning Electron Microscopy, Optic Microscopy, Carbon Analyzer and Vickers Hardness. The results show finally that the quartz has got good result in purity but need enrichment for the photovoltaic application.

  12. Chemical Processing and Characterization of Fiber Reinforced Nanocomposite Silica Materials

    NASA Astrophysics Data System (ADS)

    Burnett, Steven Shannon

    Ultrasound techniques, acoustic and electroacoustic spectroscopy, are used to investigate and characterize concentrated fluid phase nanocomposites. In particular, the data obtained from ultrasound methods are used as tools to improve the understanding of the fundamental process chemistry of concentrated, multicomponent, nanomaterial dispersions. Silicon nitride nanofibers embedded in silica are particularly interesting for lightweight nanocomposites, because silicon nitride is isostructural to carbon nitride, a super hard material. However, the major challenge with processing these composites is retarding particle-particle aggregation, to maintain highly dispersed systems. Therefore, a systematic approach was developed to evaluate the affect of process parameters on particle-particle aggregation, and improving the chemical kinetics for gelation. From the acoustic analysis of the nanofibers, this thesis was able to deduce that changes in aspect ratio affects the ultrasound propagation. In particular, higher aspect ratio fibers attenuate the ultrasound wave greater than lower aspect fibers of the same material. Furthermore, our results confirm that changes in attenuation depend on the hydrodynamical interactions between particles, the aspect ratio, and the morphology of the dispersant. The results indicate that the attenuation is greater for fumed silica due to its elastic nature and its size, when compared to silica Ludox. Namely, the larger the size, the greater the attenuation. This attenuation is mostly the result of scattering loss in the higher frequency range. In addition, the silica nanofibers exhibit greater attenuation than their nanoparticle counterparts because of their aspect ratio influences their interaction with the ultrasound wave. In addition, this study observed how 3M NH 4 Cl's acoustic properties changes during the gelation process, and during that change, the frequency dependency deviates from the expected squared of the frequency, until the

  13. Alkoxy-Siloxide Metal Complexes: Precursors to Metal Silica, Metal Oxide Silica, and Metal Silicate Materials.

    NASA Astrophysics Data System (ADS)

    Terry, Karl William

    The alkoxy-siloxide complexes M (OSi(O ^{rm t}Bu)_3 ]_4 (M = Ti(1), Zr(2), Hf(3)), were prepared by reaction with their respective metal diethylamides. These compounds readily undergo low-temperature decomposition to their respective metal oxide silica materials rm(MO_2{cdot}4SiO_2). The volatile products of the thermolysis of 2 (ca. 200 ^circC) were isobutylene (11.7 equiv) and water (5.4 equiv). The rm ZrO _2{cdot}4SiO_2 material from the decomposition of 2 at 400^circ C was amorphous until ca. 1100^ circC where crystallization of t-ZrO _2 occurred. After thermolysis to 1500 ^circC, t-ZrO_2 and cristobalite were the major products with minor amounts of m-ZrO_2. The rm HfO_2{cdot}4SiO_2 material from the decomposition of 3 at 400^ circC was amorphous until ca. 1000 ^circC where crystallization of c/t -HfO_2 was observed. Thermolysis to 1460^circC yielded c/t -HfO_2, m-HfO_2, and minor amounts of cristobalite. The crystallization of anatase in the rm TiO_2{cdot }4SiO_2 material from decomposed 1 at 400^circC was apparent after thermolysis to 1000^circC. Thermolysis to 1400^circC gave a mixture of anatase, rutile, and cristobalite. Compound 2 was decomposed in xylenes and yielded a transparent gel which was isolated as a white powder upon drying in vacuuo. The compounds [ Me _2AlOSi(O^{t}Bu)_3] _2 (4) and [( ^{t}BuO)MeAlOSi(O^{t}Bu) _3]_2 (5) were structurally characterized and contain bent and planar rm Al_2O_2 four membered rings, respectively. Both 4 and 5 yield isobutylene upon thermolysis (ca. 200 ^circC) and the crystallization of mullite occurs at 1034^circC and 1017^circC, respectively (by DTA). The solution thermolysis of 4 in refluxing toluene yields an opaque white gel. The crystallization of mullite occurs at 1029^circC (by DTA). The compounds [ CuOSi(O ^{t}Bu)_3]_{n } (6) and [ CuOSi(O ^{t}Bu)_2Ph]_4 (7) were prepared by reaction with [ CuO^{t}Bu]_4. The thermolysis of 6 at 1000^circ C under argon gave Cu^circ and amorphous silica and thermolysis under

  14. Silica scintillating materials prepared by sol-gel methods

    SciTech Connect

    Werst, D.W.; Sauer, M.C. Jr.; Cromack, K.R.; Lin, Y.; Tartakovsky, E.A.; Trifunac, A.D.

    1993-12-31

    Silica was investigated as a rad-hard alternative to organic polymer hosts for organic scintillators. Silica sol-gels were prepared by hydrolysis of tetramethoxysilane in alcohol solutions. organic dyes were incorporated into the gels by dissolving in methanol at the sol stage of gel formation. The silica sol-gel matrix is very rad-hard. The radiation stability of silica scintillators prepared by this method is dye-limited. Transient radioluminescence was measured following excitation with 30 ps pulses of 20 MeV electrons.

  15. Synthesis of mesoporous silica materials from municipal solid waste incinerator bottom ash

    SciTech Connect

    Liu, Zhen-Shu Li, Wen-Kai; Huang, Chun-Yi

    2014-05-01

    Highlights: • The optimal alkaline agent for the extraction of silica from bottom ash was Na{sub 2}CO{sub 3}. • The pore sizes for the mesoporous silica synthesized from bottom ash were 2–3.8 nm. • The synthesized materials exhibited a hexagonal pore structure with a smaller order. • The materials have potential for the removal of heavy metals from aqueous solutions. - Abstract: Incinerator bottom ash contains a large amount of silica and can hence be used as a silica source for the synthesis of mesoporous silica materials. In this study, the conditions for alkaline fusion to extract silica from incinerator bottom ash were investigated, and the resulting supernatant solution was used as the silica source for synthesizing mesoporous silica materials. The physical and chemical characteristics of the mesoporous silica materials were analyzed using BET, XRD, FTIR, SEM, and solid-state NMR. The results indicated that the BET surface area and pore size distribution of the synthesized silica materials were 992 m{sup 2}/g and 2–3.8 nm, respectively. The XRD patterns showed that the synthesized materials exhibited a hexagonal pore structure with a smaller order. The NMR spectra of the synthesized materials exhibited three peaks, corresponding to Q{sup 2} [Si(OSi){sub 2}(OH){sub 2}], Q{sup 3} [Si(OSi){sub 3}(OH)], and Q{sup 4} [Si(OSi){sub 4}]. The FTIR spectra confirmed the existence of a surface hydroxyl group and the occurrence of symmetric Si–O stretching. Thus, mesoporous silica was successfully synthesized from incinerator bottom ash. Finally, the effectiveness of the synthesized silica in removing heavy metals (Pb{sup 2+}, Cu{sup 2+}, Cd{sup 2+}, and Cr{sup 2+}) from aqueous solutions was also determined. The results showed that the silica materials synthesized from incinerator bottom ash have potential for use as an adsorbent for the removal of heavy metals from aqueous solutions.

  16. Metal binding components in human amniotic fluid

    SciTech Connect

    Paterson, P.G.; Zlotkin, S.H.; Sarkar, B. )

    1990-02-26

    Amniotic fluid is a potential source of both nutritionally essential and toxic metals for the fetus. As the binding pattern of these metals in amniotic fluid may be one of the determining factors in their availability to the fetus, the objective of this study was to investigate metal binding in vitro. The binding of six trace metals, Mn(II), Ni(II), Zn(II), Cu(II), Cd(II), and Fe(III), to components of human amniotic fluid was studied by Sephadex G-100 gel filtration at physiological pH, using radioisotopes as tracers and 50 mM TRIS/HCl as the elution buffer. The amniotic fluid was collected at 16-16.5 weeks gestation by amniocentesis and pooled for analysis. Extensive amounts of Fe, Cu, Zn, and Cd and small amounts of Mn and Ni were bound to high molecular weight proteins with elution patterns similar to those seen for the binding of these metals in serum. In addition, large amounts of Fe, Mn, Ni and Cd and small amounts of Zn and Cu were associated with low molecular weight component(s). The identity of these latter components is unknown, but they play an important biological role in amniotic fluid.

  17. Effect of Cristobalite on the Mechanical Properties of Silica RSI Materials

    NASA Technical Reports Server (NTRS)

    Khandelwal, P. K.; Scott, W. D.

    1973-01-01

    The strength of various silica surface insulation materials was measured after high temperature heat treatment to develop substantial crystalline phases, and after low temperature thermal cycling through the alpha-beta cristobalite transformation. It appears that the presence of cristobalite in the structural elements (the fibers) is highly detrimental to tensile strength. When crystallization does not occur in silica material, the strength improves with heat treatment.

  18. Impact of pore characteristics of silica materials on loading capacity and release behavior of ibuprofen.

    PubMed

    Numpilai, Thanapha; Muenmee, Suthaporn; Witoon, Thongthai

    2016-02-01

    Impact of pore characteristics of porous silica supports on loading capacity and release behavior of ibuprofen was investigated. The porous silica materials and ibuprofen-loaded porous silica materials were thoroughly characterized by N2-sorption, thermal gravimetric and derivative weight analyses (TG-DTW), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) to determine the physical properties of materials, amount of ibuprofen adsorbed and position of ibuprofen. The detailed characterization reveals that the ibuprofen molecules adsorbed inside the mesopores. Increasing the mesopore size from 5nm to 10nm increased the ibuprofen loading from 0.74 to 0.85mmol/g, respectively. Incorporation of macropore into the structure of porous silica materials enhanced the ibuprofen loading capacity of 11.8-20.3%. The ibuprofen-loaded bimodal meso-macroporous silica materials exhibited the highest dissolution of 92wt.% within an hour. The ibuprofen particles deposited on the external surface of the porous silica materials showed a lower dissolution rate than the ibuprofen adsorbed inside the mesopores due to the formation of ibuprofen crystalline.

  19. Effect of amino-modified silica nanoparticles on the corrosion protection properties of epoxy resin-silica hybrid materials.

    PubMed

    Chang, Kung-Chin; Lin, Hui-Fen; Lin, Chang-Yu; Kuo, Tai-Hung; Huang, Hsin-Hua; Hsu, Sheng-Chieh; Yeh, Jui-Ming; Yang, Jen-Chang; Yu, Yuan-Hsiang

    2008-06-01

    In this paper, a series of organic-inorganic hybrid materials consisting of epoxy resin frameworks and dispersed nanoparticles of amino-modified silica (AMS) were successfully prepared. First of all, the AMS nanoparticles were synthesized by carrying out the conventional acid-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) in the presence of (3-aminopropyl)-trimethoxysilane (APTES) molecules. The as-prepared AMS nanoparticles were then characterized by FTIR, 13C-NMR and 29Si-NMR spectroscopy. Subsequently, a series of hybrid materials were prepared by performing in-situ thermal ring-opening polymerization reactions of epoxy resin in the presence of as-prepared AMS nanoparticles and raw silica (RS) particles. The as-prepared epoxy-silica hybrid materials with AMS nanoparticles were found to show better dispersion capability than that of RS particles existed in hybrid materials based on the morphological observation of transmission electron microscopy (TEM). The hybrid materials containing AMS nanoparticles in the form of coating on cold-rolled steel (CRS) were found to be much superior in corrosion protection over those of hybrid materials with RS particles when tested by a series of electrochemical measurements of potentiodynamic and impedance spectroscopy in 5 wt% aqueous NaCI electrolyte. The increase of corrosion protection effect of hybrid coatings may have probably resulted from the enhancement of the adhesion strength of the hybrid coatings on CRS coupons, which may be attributed to the formation of Fe-O-Si covalent bond at the interface of coating/CRS system based on the FTIR-RAS (reflection absorption spectroscopy) studies. The better dispersion capability of AMS nanoparticles in hybrid materials were found to lead more effectively enhanced molecular barrier property, mechanical strength, surface hydrophobicity and optical clarity as compared to that of RS particles, in the form of coating and membrane, based on the measurements of molecular

  20. Ultrasonic cleaning of silica-coated zirconia influences bond strength between zirconia and resin luting material.

    PubMed

    Nishigawa, Goro; Maruo, Yukinori; Irie, Masao; Oka, Morihiko; Yoshihara, Kumiko; Minagi, Shogo; Nagaoka, Noriyuki; Yoshida, Yasuhiro; Suzuki, Kazuomi

    2008-11-01

    The purpose of this study was to evaluate how ultrasonic cleaning of silica-coated zirconia surfaces would influence the latter's bond strength to resin luting material. Forty zirconia specimens were divided into four groups: one air abrasion group and three silica-coated groups. Silica-coated specimens were cleaned with distilled water using an ultrasonic cleaner after tribochemical silica coating and then divided into three groups according to cleaning durations: 1 minute, 5 minutes, or without cleaning. Following which, resin luting material was polymerized against the specimens. After storage in water for 24 hours, the specimens were subjected to shear bond strength test. Shear bond strength of silica-coated group without cleaning was significantly higher than the other three groups, but there were no statistically significant differences among the three latter groups. SEM images suggested visible differences among the treatment methods. With EDXS analysis, it was revealed that ultrasonic cleaning decreased the silica content on the treated surfaces. Therefore, results showed that ultrasonic cleaning of tribochemically silica-coated zirconia surfaces decreased the adhesion efficacy to resin luting material.

  1. Bio-templated synthesis of highly ordered macro-mesoporous silica material for sustained drug delivery

    NASA Astrophysics Data System (ADS)

    Qu, Fengyu; Lin, Huiming; Wu, Xiang; Li, Xiaofeng; Qiu, Shilun; Zhu, Guangshan

    2010-05-01

    The bimodal porous structured silica materials consisting of macropores with the diameter of 5-20 μm and framework-like mesopores with the diameter of 4.7-6.0 nm were prepared using natural Manchurian ash and mango linin as macropored hard templates and P123 as mesopore soft templates, respectively. The macroporous structures of Manchurian ash and mango linin were replicated with the walls containing highly ordered mesoporous silica as well. As-synthesized dual porous silica was characterized by scanning electron microscope (SEM), powder X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption/desorption, fourier transform IR (FTIR) spectroscopy, and thermo-gravimetric analyzer (TGA). Ibuprofen (Ibu) was employed as a model drug and the release profiles showed that the dual porous material had a sustained drug delivery capability. And such highly ordered dual pore silica materials may have potential applications for bimolecular adsorption/separation and tissue repairing.

  2. Corundum ceramic materials modified with silica nanopowders: structure and mechanical properties

    NASA Astrophysics Data System (ADS)

    Kostytsyn, M. A.; Muratov, D. S.; Lysov, D. V.; Chuprunov, K. O.; Yudin, A. G.; Leybo, D. V.

    2016-01-01

    Filtering elements are often used in the metallurgy of rare earth metals. Corundum ceramic is one of the most suitable materials for this purpose. The process of formation and the properties of nanomodified ceramic materials, which are proposed as filtering materials with tunable effective porosity, are described. A silica nanopowder is used as a porosity-increasing agent. Vortex layer apparatus is used for mixing of precursor materials. The obtained results show that nanomodification with the vortex layer apparatus using 0.04 wt. % silica nanopowder as a modifying agent leads to an increase in the compression strength of corundum ceramic by the factor of 1.5.

  3. A linker peptide with high affinity towards silica-containing materials.

    PubMed

    Sunna, Anwar; Chi, Fei; Bergquist, Peter L

    2013-06-25

    A peptide sequence with affinity to silica-containing materials was fused to a truncated form of Streptococcus strain G148 Protein G. The resulting recombinant Linker-Protein G (LPG) was produced in Escherichia coli and purified to apparent homogeneity. It displayed high affinity towards two natural clinoptilolite zeolites. The LPG also displayed high binding affinity towards commercial-grade synthetic zeolite, silica and silica-containing materials. A commercial sample of the truncated Protein G and a basic protein, both without the linker, did not bind to natural or synthetic zeolites or silica. We conclude that the zeolite-binding affinity is mediated by the linker peptide sequence. As a consequence, these data may imply that the binding affinity is directed to the SiO2 component rather than to the atomic orientation on the zeolite crystal surface as previously assumed.

  4. A controlled release of ibuprofen by systematically tailoring the morphology of mesoporous silica materials

    SciTech Connect

    Qu Fengyu; Zhu Guangshan; Lin Huiming; Zhang Weiwei; Sun Jinyu; Li Shougui; Qiu Shilun . E-mail: sqiu@mail.jlu.edu.cn

    2006-07-15

    A series of mesoporous silica materials with similar pore sizes, different morphologies and variable pore geometries were prepared systematically. In order to control drug release, ibuprofen was employed as a model drug and the influence of morphology and pore geometry of mesoporous silica on drug release profiles was extensively studied. The mesoporous silica and drug-loaded samples were characterized by X-ray diffraction, Fourier transform IR spectroscopy, N{sub 2} adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. It was found that the drug-loading amount was directly correlated to the Brunauer-Emmett-Teller surface area, pore geometry, and pore volume; while the drug release profiles could be controlled by tailoring the morphologies of mesoporous silica carriers. - Graphical abstract: The release of ibuprofen is controlled by tailoring the morphologies of mesoporous silica. The mesoporous silica and drug-loaded samples are characterized by powder X-ray diffraction, Fourier transform IR spectroscopy, N{sub 2} adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The drug-loading amount is directly correlated to the Brunauer-Emmett-Teller surface area, pore geometry, and pore volume; while the drug release profiles can be controlled by tailoring the morphologies of mesoporous silica carriers.

  5. Metal-binding proteins as metal pollution indicators.

    PubMed Central

    Hennig, H F

    1986-01-01

    The fact that metal-binding proteins are a consequence of elevated metal concentration in organisms is well known. What has been overlooked is that the presence of these proteins provides a unique opportunity to reformulate the criteria of metal pollution. The detoxification effect of metal-binding proteins in animals from polluted areas has been cited, but there have been only very few studies relating metal-binding proteins to pollution. This lack is due partly to the design of most experiments, which were aimed at isolation of metal-binding proteins and hence were of too short duration to allow for correlation to adverse physiological effects on the organism. In this study metal-binding proteins were isolated and characterized from five different marine animals (rock lobster, Jasus lalandii; hermit crab, Diogenes brevirostris; sandshrimp, Palaemon pacificus; black mussel, Choromytilus meridionalis; and limpet, Patella granularis). These animals were kept under identical metal-enriched conditions, hence eliminating differences in method and seasons. The study animals belonged to different phyla; varied in size, mass, age, behavior, food requirements and life stages; and accumulated metals at different rates. It is possible to link unseasonal moulting in crustacea, a known physiological effect due to a metal-enriched environment, to the production of the metal-binding protein without evidence of obvious metal body burden. Thus a new concept of pollution is defined: the presence of metal-binding proteins confirms toxic metal pollution. This concept was then tested under field conditions in the whelk Bullia digitalis and in metal-enriched grass. PMID:3709437

  6. Metal-binding proteins as metal pollution indicators

    SciTech Connect

    Hennig, H.F.

    1986-03-01

    The fact that metal-binding proteins are a consequence of elevated metal concentration in organisms is well known. What has been overlooked is that the presence of these proteins provides a unique opportunity to reformulate the criteria of metal pollution. The detoxification effect of metal-binding proteins in animals from polluted areas has been cited, but there have been only very few studies relating metal-binding proteins to pollution. This lack is due partly to the design of most experiments, which were aimed at isolation of metal-binding proteins and hence were of too short duration to allow for correlation to adverse physiological effects on the organism. In this study metal-binding proteins were isolated and characterized from five different marine animals (rock lobster, Jasus lalandii; hermit crab, Diogenes brevirostris; sandshrimp, Palaemon pacificus; black mussel, Choromytilus meridionalis; and limpet, Patella granularis). These animals were kept under identical metal-enriched conditions, hence eliminating differences in method and seasons. The study animals belonged to different phyla; varied in size, mass, age, behavior, food requirements and life stages; and accumulated metals at different rates. It is possible to link unseasonal moulting in crustacea, a known physiological effect due to a metal-enriched environment, to the production of the metal-binding protein without evidence of obvious metal body burden. Thus a new concept of pollution is defined: the presence of metal-binding proteins confirms toxic metal pollution. This concept was then tested under field conditions in the whelk Bullia digitalis and in metal-enriched grass.

  7. Synthesis and characterization of large specific surface area nanostructured amorphous silica materials.

    PubMed

    Marquez-Linares, Francisco; Roque-Malherbe, Rolando M A

    2006-04-01

    Large specific surface area materials attract wide attention because of their applications in adsorption, catalysis, and nanotechnology. In the present study, we describe the synthesis and characterization of nanostructured amorphous silica materials. These materials were obtained by means of a modification of the Stobe-Fink-Bohn (SFB) method. The morphology and essential features of the synthesized materials have been studied using an automated surface area and pore size analyzer and scanning electron microscopy. The existence of a micro/mesoporous structure in the obtained materials has been established. It was also found that the obtained particle packing materials show large specific surface area up to 1,600 m2/g. (To our best knowledge, there is no any reported amorphous silica material with such a higher specific surface area.) The obtained materials could be useful in the manufacture of adsorbents, catalyst supports, and other nanotechnological applications.

  8. Insights into microstructure and chemistry of active fiber core material produced by the granulated silica method

    NASA Astrophysics Data System (ADS)

    Najafi, H.; Etissa, D.; Romano, V.

    2014-05-01

    The production of special fibers relies on new methods and materials to incorporate new functionalities into optical fibers by virtues of dopants and structure. In particular, the granulated silica method allows to rapidly produce active fibers with high dopant content and with virtually any microstructure. The implementation of this production method requires a multitude of process steps at various temperatures and temperature gradients that can significantly influence the optical properties of the produced preforms and fibers. To better understand and optimize the processes of active material production and fiber drawing parameters we have done a thorough analysis of microstructure, phase development, crystallinity and chemical mapping of active fiber cores produced by a combination of sol-gel process and granulated silica method with and without employment of a CO2 laser treatment. The microstructure of fibers have been analyzed with a diverse suite of techniques in Transmission Electron Microscopy (TEM), revealing formation of various silica polymorphs and distribution of active elements (i.e. Yb and P) into the core structure. Our results show the presence of another polymorph of silica with low crystallinity dispersed in the main amorphous polymorph (i.e. quartz). We conclude that in spite of importance of homogeneous distribution of Yb and P into the core, the formation of various silica polymorphs resulting from materials processing has to be considered.

  9. NiO-silica based nanostructured materials obtained by microemulsion assisted sol-gel procedure

    SciTech Connect

    Mihaly, M.; Comanescu, A.F.; Rogozea, A.E.; Vasile, E.; Meghea, A.

    2011-10-15

    Graphical abstract: TEM micrograph of NiO/SiO{sub 2} nanoparticles. Highlights: {yields} Microemulsion assisted sol-gel procedure for NiO silica nanomaterials synthesis. {yields} Controlling the size and shape of nanoparticles and avoiding their aggregation. {yields} Narrow band-gap semiconductors (energies <3 eV) absorbing VIS or near-UV light biologically and chemically inert semiconductors entrapping/coating in silica network. {yields} Low cost as the microemulsion is firstly used in water metallic cation extraction. -- Abstract: NiO-silica based materials have been synthesized by microemulsion assisted sol-gel procedure. The versatility of these soft nanotechnology techniques has been exploited in order to obtain different types of nanostructures, such as NiO nanoparticles, NiO silica coated nanoparticles and NiO embedded in silica matrix. These materials have been characterized by adequate structural and morphology techniques: DLS, HR-TEM/SAED, BET, AFM. Optical and semiconducting properties (band-gap values) of the synthesized materials have been quantified by means of VIS-NIR diffuse reflectance spectra, thus demonstrating their applicative potential in various electron transfer phenomena such as photocatalysis, electrochromic thin films, solid oxide fuel cells.

  10. Development of construction materials using nano-silica and aggregates recycled from construction and demolition waste.

    PubMed

    Mukharjee, Bibhuti Bhusan; Barai, Sudhirkumar V

    2015-06-01

    The present work addresses the development of novel construction materials utilising commercial grade nano-silica and recycled aggregates retrieved from construction and demolition waste. For this, experimental work has been carried out to examine the influence of nano-silica and recycled aggregates on compressive strength, modulus of elasticity, water absorption, density and volume of voids of concrete. Fully natural and recycled aggregate concrete mixes are designed by replacing cement with three levels (0.75%, 1.5% and 3%) of nano-silica. The results of the present investigation depict that improvement in early days compressive strength is achieved with the incorporation of nano-silica in addition to the restoration of reduction in compressive strength of recycled aggregate concrete mixes caused owing to the replacement of natural aggregates by recycled aggregates. Moreover, the increase in water absorption and volume of voids with a reduction of bulk density was detected with the incorporation of recycled aggregates in place of natural aggregates. However, enhancement in density and reduction in water absorption and volume of voids of recycled aggregate concrete resulted from the addition of nano-silica. In addition, the results of the study reveal that nano-silica has no significant effect on elastic modulus of concrete.

  11. Mixed surfactants-directed the mesoporous silica materials with various morphologies and structures

    SciTech Connect

    Lin Huiming; Qu Fengyu; Wu Xiang; Xue Ming; Zhu Guangshan; Qiu Shilun

    2011-06-15

    A new mixed surfactants system using alkyl carboxylic acids and quaternized poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl] urea] (PEPU) as the co-template was used to synthesize mesoporous silica materials with various morphologies and structures, including flakes, regular spheres, nanoparticles, and tube-spheres. The cationic polymer connected the anionic surfactant micelle to the anionic polysilicate species to induce the synthesis of the mesoporous silica materials. The structure and property of the surfactant and the cationic polymer determined the formation of mesoporous silica, and also had a signification influence on the morphology and structure of the final materials. To further explore the possible formation mechanism of these mesoporous materials, zeta potential was utilized to evaluate the interaction between the anionic surfactant and the cationic co-template. In addition, the structure, morphology, and porosity of these materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N{sub 2} adsorption-desorption measurements. - Graphical abstract: A new mixed surfactants system using alkyl carboxylic acids and PEPU as the co-template was used to synthesize mesoporous silica materials with various morphologies and structures. Highlights: {yields}A new mixed surfactants system induced the mesoporous silica materials with various morphologies and structure. > It is a development of the type S{sup -}N{sup +}I{sup -} route of the mesoporous formation. > Zeta potential was utilized to evaluate the interaction between the anionic surfactant and the cationic co-template. > The property and amount of surfactant and polymer determined the formation of the mesoporous materials.

  12. Use of ground clay brick as a pozzolanic material to reduce the alkali-silica reaction

    SciTech Connect

    Turanli, L.; Bektas, F.; Monteiro, P.J.M

    2003-10-01

    The objective of this experimental study was to use ground clay brick (GCB) as a pozzolanic material to minimize the alkali-silica reaction expansion. Two different types of clay bricks were finely ground and their activity indices were determined. ASTM accelerated mortar bar tests were performed to investigate the effect of GCB when used to replace cement mass. The microstructure of the mortar was investigated using scanning electron microscopy (SEM). The results showed that the GCBs meet the strength activity requirements of ASTM. In addition, the GCBs were found to be effective in suppressing the alkali-silica reaction expansion. The expansion decreased as the amount of GCBs in the mortar increased.

  13. Design and Construction of Synthetic Metal-Binding Proteins

    DTIC Science & Technology

    1989-06-21

    from partitioning experiments using these metallated polymers [see publications]. Synthetic metal-binding variants of bovine growth hormone yeast iso...the bovine growth hormone indicate that this His-X-X-X-His site in the helix has an affinity for Cu(II) in IDA (iminodiacetic acid) that is roughly

  14. Evaluation of the acid properties of porous zirconium-doped and undoped silica materials

    SciTech Connect

    Fuentes-Perujo, D.; Santamaria-Gonzalez, J.; Merida-Robles, J.; Rodriguez-Castellon, E.; Jimenez-Lopez, A.; Maireles-Torres, P. . E-mail: maireles@uma.es; Moreno-Tost, R.

    2006-07-15

    A series of porous silica and Zr-doped silica molecular sieves, belonging to the MCM-41 and MSU families, were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N{sub 2} adsorption at 77 K. Their acid properties have been evaluated by NH{sub 3}-TPD, adsorption of pyridine and deuterated acetonitrile coupled to FT-IR spectroscopy and the catalytic tests of isopropanol decomposition and isomerization of 1-butene. The acidity of purely siliceous solids were, in all cases, very low, while the incorporation of Zr(IV) into the siliceous framework produced an enhancement of the acidity. The adsorption of basic probe molecules and the catalytic behaviour revealed that Zr-doped MSU-type silica was more acidic than the analogous Zr-MCM-41 solid, with a similar Zr content. This high acidity observed in the case of Zr-doped silica samples is due to the presence of surface zirconium atoms with a low coordination, mainly creating Lewis acid sites. - Graphical abstract: The adsorption of basic probe molecules and the catalytic behaviour have revealed that MSU-type materials are more acidic than the analogous MCM-41 solids, mainly after the incorporation of zirconium into the silica framework.

  15. Photoluminescence properties of silica-based mesoporous materials similar to those of nanoscale silicon

    NASA Astrophysics Data System (ADS)

    Glinka, Yu. D.; Zyubin, A. S.; Mebel, A. M.; Lin, S. H.; Hwang, L. P.; Chen, Y. T.

    Photoluminescence (PL) from composites of 7- and 15-nm sized silica nanoparticles (SNs) and mesoporous silicas (MSs) induced by 266- (4.66-) and 532-nm (2.33-eV) laser light has been studied at room temperature. The multiband PL from MSs in the range of 1.0-2.1 eV is evidenced to originate from isolated bulk and surface non-bridging oxygens (NBOs) and from NBOs combined with variously placed 1-nm sized pore wall oxygen vacancies (OVs). The nature and diversity of NBO light-emitters are confirmed by ab initio calculations. The PL from SNs exhibits only a short wavelength part of the bands (1.5-2.1 eV) originated from isolated bulk and surface NBOs. This fact indicates that the highly OV-bearing structures occur only in extremely thin ( 1 nm) silica layers. The similarity of spectroscopic properties of silica-based nanoscale materials to those of surface-oxidized silicon nanocrystals and porous silicon, containing silica-passivating layers of the same width, is discussed.

  16. A silica sol-gel design strategy for nanostructured metallic materials.

    PubMed

    Warren, Scott C; Perkins, Matthew R; Adams, Ashley M; Kamperman, Marleen; Burns, Andrew A; Arora, Hitesh; Herz, Erik; Suteewong, Teeraporn; Sai, Hiroaki; Li, Zihui; Werner, Jörg; Song, Juho; Werner-Zwanziger, Ulrike; Zwanziger, Josef W; Grätzel, Michael; DiSalvo, Francis J; Wiesner, Ulrich

    2012-03-18

    Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals--including noble metals--to be combined into a library of sol-gel materials with a high degree of control over composition and structure. We demonstrate that the sol-gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the Stöber process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000 S cm(-1). This improves the electrical conductivity of porous silica sol-gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices.

  17. Kraft lignin/silica-AgNPs as a functional material with antibacterial activity.

    PubMed

    Klapiszewski, Łukasz; Rzemieniecki, Tomasz; Krawczyk, Magdalena; Malina, Dagmara; Norman, Małgorzata; Zdarta, Jakub; Majchrzak, Izabela; Dobrowolska, Anna; Czaczyk, Katarzyna; Jesionowski, Teofil

    2015-10-01

    Advanced functional silica/lignin hybrid materials, modified with nanosilver, were obtained. The commercial silica Syloid 244 was used, modified with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to increase its chemical affinity to lignin. Similarly, kraft lignin was oxidized using a solution of sodium periodate to activate appropriate functional groups on its surface. Silver nanoparticles were grafted onto the resulting silica/lignin hybrids. The systems obtained were comprehensively tested using available techniques and methods, including transmission electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, elemental analysis and atomic absorption spectroscopy. An evaluation was also made of the electrokinetic stability of the systems with and without silver nanoparticles. Conclusions were drawn concerning the chemical nature of the bonds between the precursors and the effectiveness of the method of binding nanosilver to the hybrid materials. The antimicrobial activity of the studied materials was tested against five species of Gram-positive and Gram-negative bacteria. The addition of silver nanoparticles to the silica/lignin hybrids led to inhibition of the growth of the analyzed bacteria. The best results were obtained against Pseudomonas aeruginosa, a dangerous human pathogen.

  18. Application of mesoporous silica materials for the immobilization of polyphenol oxidase.

    PubMed

    Corell Escuin, Paula; García-Bennett, Alfonso; Ros-Lis, Jose Vicente; Argüelles Foix, Angel; Andrés, Ana

    2017-02-15

    The ability of a number of mesoporous silica materials (SBA-15, SBA-3, and MCM-48) to immobilize polyphenol oxidase (PPO) at different pH has been tested. Pore size and volume are the structural characteristics with higher influence on the PPO immobilization. Mesoropous material SBA-15 adsorbs a larger quantity of PPO at pH 4.00 and offers an inhibition of enzymatic activity close the 50% in apple extracts.

  19. Microwave material characterization of alkali-silica reaction (ASR) gel in cementitious materials

    NASA Astrophysics Data System (ADS)

    Hashemi, Ashkan

    Since alkali-silica reaction (ASR) was recognized as a durability challenge in cement-based materials over 70 years ago, numerous methods have been utilized to prevent, detect, and mitigate this issue. However, quantifying the amount of produced ASR byproducts (i.e., ASR gel) in-service is still of great interest in the infrastructure industry. The overarching objective of this dissertation is to bring a new understanding to the fundamentals of ASR formation from a microwave dielectric property characterization point-of-view, and more importantly, to investigate the potential for devising a microwave nondestructive testing approach for ASR gel detection and evaluation. To this end, a comprehensive dielectric mixing model was developed with the potential for predicting the effective dielectric constant of mortar samples with and without the presence of ASR gel. To provide pertinent inputs to the model, critical factors on the influence of ASR gel formation on dielectric and reflection properties of several mortar samples were investigated at R, S, and X-band. Effects of humidity, alkali content, and long-term curing conditions on ASR-prone mortars were also investigated. Additionally, dielectric properties of chemically different synthetic ASR gel were also determined. All of these, collectively, served as critical inputs to the mixing model. The resulting developed dielectric mixing model has the potential to be further utilized to quantify the amount of produced ASR gel in cement-based materials. This methodology, once becomes more mature, will bring new insight to the ASR reaction, allowing for advancements in design, detection and mitigation of ASR, and eventually has the potential to become a method-of-choice for in-situ infrastructure health-monitoring of existing structures.

  20. Structures of alkali metals in silica gel nanopores: new materials for chemical reductions and hydrogen production.

    PubMed

    Shatnawi, Mouath; Paglia, Gianluca; Dye, James L; Cram, Kevin C; Lefenfeld, Michael; Billinge, Simon J L

    2007-02-07

    Alkali metals and their alloys can be protected from spontaneous reaction with dry air by intercalation (with subsequent heating) into the pores of silica gel (SG) at loadings up to 40 wt %. The resulting loose, black powders are convenient materials for chemical reduction of organic compounds and the production of clean hydrogen. The problem addressed in this paper is the nature of the reducing species present in these amorphous materials. The atomic pair distribution function (PDF), which considers both Bragg and diffuse scattering components, was used to examine their structures. Liquid Na-K alloys added to silica gel at room temperature (stage 0) or heated to 150 degrees C (stage I) as well as stage I Na-SG, retain the overall pattern of pure silica gel. Broad oscillations in the PDF show that added alkali metals remain in the pores as nanoscale metal clusters. 23Na MAS NMR studies confirm the presence of Na(0) and demonstrate that Na+ ions are formed as well. The relative amounts of Na(0) and Na(+) depend on both the overall metal loading and the average pore size. The results suggest that ionization occurs near or in the SiO2 walls, with neutral metal present in the larger cavities. The fate of the electrons released by ionization is uncertain, but they may add to the silica gel lattice, or form an "electride-like plasma" near the silica gel walls. A remaining mystery is why the stage I material does not show a melting endotherm of the encapsulated metal and does not react with dry oxygen. Na-SG when heated to 400 degrees C (stage II) yields a dual-phase reaction product that consists of Na(4)Si(4) and Na(2)SiO(3).

  1. Analytical Chemistry with Silica Sol-Gels: Traditional Routes to New Materials for Chemical Analysis

    NASA Astrophysics Data System (ADS)

    Walcarius, Alain; Collinson, Maryanne M.

    2009-07-01

    The versatility of sol-gel chemistry enables us to generate a wide range of silica and organosilica materials with controlled structure, composition, morphology and porosity. These materials’ hosting and recognition properties, as well as their wide-open structures containing many easily accessible active sites, make them particularly attractive for analytical purposes. In this review, we summarize the importance of silica sol-gels in analytical chemistry by providing examples from the separation sciences, optical and electrochemical sensors, molecular imprinting, and biosensors. Recent work suggests that manipulating the structure and composition of these materials at different scales (from molecular to macromolecular states and/or from micro- to meso- and/or macroporous levels) promises to generate chemical and biochemical sensing devices with improved selectivity and sensitivity.

  2. Relation between the lower consolute boundary and the structure of mesoporous silica materials.

    PubMed

    Michaux, F; Blin, J L; Stébé, M J

    2008-02-05

    In this study, we have shed some light on the relation between the position of the lower consolute boundary of various nonionic surfactants in water and the structure of the mesoporous silica materials synthesized from these surfactants-based systems. In the first part, the lower consolute boundary was shifted by adding salts. Depending on the features of the phase diagram, we have looked for either a salting out or a salting in effect. Mesoporous materials were prepared from a micellar solution of the investigated surfactants. Results clearly evidenced that the cooperative self-assembly mechanism is not favored if the lower consolute boundary is not shifted toward high temperatures. Moreover, the higher the difference between the phase separation temperature and the temperature at which the silica precursor is added to the surfactant solution, the better the mesopore ordering is. In the second part, this tendency has been confirmed by using a hydrogenated surfactant as additive.

  3. Switching behavior of thermochromic copper and silver tetraiodomercurate embedded in silica hybrid materials

    NASA Astrophysics Data System (ADS)

    Raditoiu, Valentin; Radovici, Constantin; Raditoiu, Alina; Nicolae, Cristian Andi; Culita, Daniela Cristina; Fierascu, Radu Claudiu; Amariutei, Viorica; Wagner, Luminita Eugenia

    2013-10-01

    Thermochromic silica hybrids containing copper or silver mercuric iodides and cetyltrimethylammonium bromide (CTAB) were obtained and characterized. The color and switching behavior of the materials was studied in relationship with the structure of the thermochromic composites and silica network modifiers. In order to evidence the presence of the components and possible interactions governing the thermochromic transition, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis - DR), Fourier transform infrared spectroscopy - attenuated reflection (FTIR-ATR), X-ray diffraction spectroscopy (XRD) and X-ray fluorescence (XRF) analysis were performed. The dynamic behavior was studied by UV-Vis reflectance spectra, FTIR and differential thermal analysis (DTA) analysis. Results confirm that during the embedding of thermochromic compounds in silica hybrid matrices, in the presence of CTAB, some interactions are established between thermochromic compounds and CTAB. These interactions determine the parameters of thermochromic transition in all cases of thermochromic composites. Hysteresis during the repetitive heating-cooling cycles was also observed. Thermal stability of the thermochromic compounds was enhanced after embedding in silica hybrids.

  4. Synthesis of mesoporous silica materials (MCM-41) from iron ore tailings

    SciTech Connect

    Yu Honghao; Xue Xiangxin; Huang Dawei

    2009-11-15

    Highly ordered mesoporous materials were successfully synthesized by using the iron ore tailings as the silica source and n-hexadecyltrimethyl ammonium bromide as the template. The samples were detail characterized by powder X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and N{sub 2} physisorption. The as-synthesized materials had high surface area of 527 m{sup 2} g{sup -1} and the mean pore diameter of 2.65 nm with a well-ordered two-dimensional hexagonal structure. It is feasible to prepare mesoporous MCM-41 materials using the iron ore tailings as precursor.

  5. Pharmacological activity of metal binding agents that alter copper bioavailability

    PubMed Central

    Helsel, Marian E.

    2015-01-01

    Iron, copper and zinc are required nutrients for many organisms but also potent toxins if misappropriated. An overload of any of these metals can be cytotoxic and ultimately lead to organ failure, whereas deficiencies can result in anemia, weakened immune system function, and other medical conditions. Cellular metal imbalances have been implicated in neurodegenerative diseases, cancer and infection. It is therefore critical for living organisms to maintain careful control of both the total levels and subcellular distributions of these metals to maintain healthy function. This perspective explores several strategies envisioned to alter the bioavailability of metal ions by using synthetic metal-binding agents targeted for diseases where misappropriated metal ions are suspected of exacerbating cellular damage. Specifically, we discuss chemical properties that influence the pharmacological outcome of a subset of metal-binding agents known as ionophores, and review several examples that have shown multiple pharmacological activities in metal-related diseases, with a specific focus on copper. PMID:25797044

  6. Dimensional Stability of Fused Silica, Invar, and Several Ultralow Thermal Expansion Materials

    DTIC Science & Technology

    1976-01-01

    evacuated environments at constant temperature (near 300 K). Materials were two types of fused silica, Cer-Vit, ULE, Zerodur , Invar, and Super Invar...Constant Temperature Cer-Vit ULE Zerodur Optics Interface Drift Dielectric Coating Pages: 00040 Cataloged Date: Nov 20,1992 Document Type: HC Number...changes. These include Owens-Illinois Cer-Vit C-101, Corning ULE 7971, and Schott Zerodur , whose thermal expansion coefficients are exceedingly low over a

  7. Optically transparent polyelectrolyte-silica composite materials: Preparation, characterization, and application in optical chemical sensing

    SciTech Connect

    Shi, Yining; Seliskar, C.J.

    1997-03-01

    A series of polyelectrolyte-containing silica composite materials have been prepared by sol-gel processing. These optically transparent composites have been characterized by scanning electron microscopy and UV-visible spectrophotometry. These materials can be processed into monolithic disks and thin films. The thicknesses of spin-coated films of these materials on glass can be varied from 0.13 to 3.5 {mu}m as determined by an optical interferences method. These materials are ion exchangeable and less brittle than the parent silica glass due to the incorporation of the organic polyelectrolyte. These new composites retain the nanoscale porosity and optical transparency into the ultraviolet of the parent silica sol-gel glasses, making them attractive host matrixes for the immobilization of ionizable dye molecules and chemical reagents. An optical pH sensing platform (0.9 x 2.5 cm) based on the electrostatic immobilization of HPTS (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt) in a PDMDAAC (poly(diallyldimethylammonium chloride))-silica composite film was fabricated and evaluated. The results clearly demonstrate that this platform is easy to construct with high batch reproducibility and can be regenerated by simple solution ion exchange. The platform is usable in both the modes of absorption and fluorescence, making it versatile. Having a fast response time (ca. {approximately}2 s to more than 2 units of pH change), the platform is also highly resistant to dye leaching and storage degradation over a period of months. 49 refs., 9 figs., 2 tabs.

  8. Synthesis of mesoporous SAPO-34 zeolite from mesoporous silica materials for methanol to light olefins.

    PubMed

    Kang, Eun A; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Min; Jeong, Kwang-Eun; Kim, Joo-Wan; Kim, Chul-Ung; Jeong, Soon-Yong

    2013-11-01

    Mesoporous SAPO-34 zeolites were synthesized by using as-prepared mesoporous silica material as both silica source and mesopore tailor. The mesoporous SAPO-34 zeolite materials thus obtained are characterized by a series of different techniques, including poweder X-ray diffraction pattern, nitrogen physisorption analysis, scanning electron micrograph, temperature programmed desorption of ammonia, and inductively coupled plasma atomic emission spectrometry. The resultant mesoporous SAPO-34 crystals exhibit sphere-like particle with zeolite layer units. The mesopore size distribution and particle size can be changed by amounts of silica source and water. The methanol-to-olefins (MTO) reactions using these mesoporous SAPO-34 zeolites are carried out with a fixed-bed reactor. Catalytic tests exhibit that the mesoporous SAPO-34 zeolite materials show high catalytic activity compared with the conventional SAPO-34 for MTO reaction. The better catalytic activity and longer life time of the mesoporous SAPO-34 catalysts in MTO are mainly due to the existence of the mesoporosity of SAPO-34 with small particle size.

  9. Adsorption of formaldehyde vapor by amine-functionalized mesoporous silica materials.

    PubMed

    Srisuda, Saeung; Virote, Boonamnuayvitaya

    2008-01-01

    The amine-functionalized mesoporous silica materials were prepared via the co-condensation reaction of tetraethoxysilane and three types of organoalkoxysilanes: 3-aminopropyl-trimethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 3-(2-(2-aminoehtylamino)ethylamino) propyl-trimethoxysilane. Cetyltrimethylammonium bromide was used as a template for forming pores. Specific surface area and pore volume of the amine-functionalized mesoporous silica materials were determined using surface area and pore size analyzer. Fourier transform infrared (FTIR) spectroscope was employed for identifying the functional groups on pore surface. In addition, the amine-functionalized mesoporous silica materials were applied as adsorbents for adsorbing formaldehyde vapor. FTIR spectra showed the evidence of the reaction between formaldehyde molecules and amine groups on pore surface of adsorbents. The equilibrium data of formaldehyde adsorbed on the adsorbents were analyzed using the Langmuir, Freundlich and Temkin isotherm. The sample functionalized from n-(2-aminoethyl)-3-aminopropyltrimethoxysilane showed the highest adsorption capacity owing to its amine groups and the large pore diameter.

  10. Enantioselectively controlled release of chiral drug (metoprolol) using chiral mesoporous silica materials

    NASA Astrophysics Data System (ADS)

    Guo, Zhen; Du, Yu; Liu, Xianbin; Ng, Siu-Choon; Chen, Yuan; Yang, Yanhui

    2010-04-01

    Chiral porous materials have attracted burgeoning attention on account of their potential applications in many areas, such as enantioseparation, chiral catalysis, chemical sensors and drug delivery. In this report, chiral mesoporous silica (CMS) materials with various pore sizes and structures were prepared using conventional achiral templates (other than chiral surfactant) and a chiral cobalt complex as co-template. The synthesized CMS materials were characterized by x-ray diffraction, nitrogen physisorption, scanning electron microscope and transmission electron microscope. These CMS materials, as carriers, were demonstrated to be able to control the enantioselective release of a representative chiral drug (metoprolol). The release kinetics, as modeled by the power law equation, suggested that the release profiles of metoprolol were remarkably dependent on the pore diameter and pore structure of CMS materials. More importantly, R- and S-enantiomers of metoprolol exhibited different release kinetics on CMS compared to the corresponding achiral mesoporous silica (ACMS), attributable to the existence of local chirality on the pore wall surface of CMS materials. The chirality of CMS materials on a molecular level was further substantiated by vibrational circular dichroism measurements.

  11. Sol-gel derived silica/siloxane composite materials: The effect of loading level and catalyst activity on silica domain formation

    SciTech Connect

    Black, E.P.; Ulibarri, T.A.; Beaucage, G.; Schaefer, D.W.; Assink, R.A.; Bergstrom, D.F.; Giwa-Agbomeirele, P.A.; Burns, G.T.

    1993-11-01

    Currently, the production of in situ reinforcement in polymeric systems by sol-gel methods is undergoing rapid development. However, understanding of synthesis/structure/property relationships is still lacking. In order to produce sol-gel derived composite materials with sufficient mechanical properties for commercial applications, this deficit of information must be addressed. We have completed a detailed investigation of in situ silica growth in polydimethylsiloxane (PDMS)/tetraethylorthosilicate (TEOS) systems. Factors which affect the domain growth, such as catalyst activity and silica loading, have been examined by solid state {sup 29}Si NMR, SEM, mechanical testing and small angle neutron scattering.

  12. Preparation of resveratrol-loaded nanoporous silica materials with different structures

    SciTech Connect

    Popova, Margarita; Szegedi, Agnes; Mavrodinova, Vesselina; Novak Tušar, Natasa; Mihály, Judith; Klébert, Szilvia; Benbassat, Niko; Yoncheva, Krassimira

    2014-11-15

    Solid, nanoporous silica-based spherical mesoporous MCM-41 and KIL-2 with interparticle mesoporosity as well as nanosized zeolite BEA materials differing in morphology and pore size distribution, were used as carriers for the preparation of resveratrol-loaded delivery systems. Two preparation methods have been applied: (i) loading by mixing of resveratrol and mesoporous carrier in solid state and (ii) deposition in ethanol solution. The parent and the resveratrol loaded carriers were characterized by XRD, TEM, N2 physisorption, thermal analysis, and FT-IR spectroscopy. The influence of the support structure on the adsorption capacity and the release kinetics of this poorly soluble compound were investigated. Our results indicated that the chosen nanoporous silica supports are suitable for stabilization of trans-resveratrol and reveal controlled release and ability to protect the supported compound against degradation regardless of loading method. The solid-state dry mixing appears very effective for preparation of drug formulations composed of poorly soluble compound. - Graphical abstract: trans-Resveratrol was stabilized in the pores of BEA zeolite, MCM-41and KIL2 mesoporous silicas. - Highlights: • BEA, KIL-2 and MCM-41 materials were used as carriers for resveratrol loading. • Resveratrol encapsulation in ethanol solution and solid state procedure were applied. • The solid-state preparation appears very effective for stabilization of trans-resveratrol.

  13. Effect of silica fume on the characterization of the geopolymer materials

    NASA Astrophysics Data System (ADS)

    Khater, Hisham M.

    2013-12-01

    The influence of silica fume (SF) addition on properties of geopolymer materials produced from alkaline activation of alumino-silicates metakaolin and waste concrete produced from demolition works has been studied through the measurement of compressive strength, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM) analysis. Alumino-silicate materials are coarse aggregate included waste concrete and fired kaolin (metakaolin) at 800°C for 3 h, both passing a sieve of 90 μm. Mix specimens containing silica fume were prepared at water/binder ratios in a range of 0.30 under water curing. The used activators are an equal mix of sodium hydroxide and silicate in the ratio of 3:3 wt.%. The control geopolymer mix is composed of metakaolin and waste concrete in an equal mix (50:50, wt.%). Waste concrete was partially replaced by silica fume by 1 to 10 wt.%. The results indicated that compressive strengths of geopolymer mixes incorporating SF increased up to 7% substitution and then decreased up to 10% but still higher than that of the control mix. Results indicated that compressive strengths of geopolymer mixes incorporating SF increases up to 7% substitution and then decreases up to 10% but still higher than the control mix, where 7% SF-digested calcium hydroxide (CH) crystals, decreased the orientation of CH crystals, reduced the crystal size of CH gathered at the interface, and improved the interface more effectively.

  14. Biomimetic synthesis of shaped and chiral silica entities templated by organic objective materials.

    PubMed

    Jin, Ren-Hua; Yao, Dong-Dong; Levi, Rumi Tamoto

    2014-06-10

    Organic molecules with accompanying self-organization have been a great subject in chemistry, material science and nanotechnology in the past two decades. One of the most important roles of organized organic molecules is the capability of templating complexly structured inorganic materials. The focus of this Minireview is on nanostructured silica with divergent morphologies and/or integrated chirality directed by organic templates of self-assembled polyamine/polypeptides/block copolymers, chiral organogels, self-organized chiral amphiphiles and chiral crystalline complexes, etc., by biomimetic silicification and conventional sol-gel reaction. Among them, biosilica (diatoms and sponges)-inspired biomimetic silicifications are particularly highlighted.

  15. Oxidation of a Silica-Containing Material in a Mach 0.3 Burner Rig

    NASA Technical Reports Server (NTRS)

    Nguyen, QuynhGiao N.; Cuy, Michael D.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    A primarily silica-containing material with traces of organic compounds, as well as aluminum and calcium additions, was exposed to a Mach 0.3 burner rig at atmospheric pressure using jet fuel. The sample was exposed for 5 continuous hours at 1370 C. Post exposure x-ray diffraction analyses indicate formation of cristobalite, quartz, NiO and Spinel (Al(Ni)CR2O4). The rig hardware is composed of a nickel-based superalloy with traces of Fe. These elements are indicated in the energy dispersive spectroscopy (EDS) results. This material was studied as a candidate for high temperature applications under an engine technology program.

  16. Preparation of resveratrol-loaded nanoporous silica materials with different structures

    NASA Astrophysics Data System (ADS)

    Popova, Margarita; Szegedi, Agnes; Mavrodinova, Vesselina; Novak Tušar, Natasa; Mihály, Judith; Klébert, Szilvia; Benbassat, Niko; Yoncheva, Krassimira

    2014-11-01

    Solid, nanoporous silica-based spherical mesoporous MCM-41 and KIL-2 with interparticle mesoporosity as well as nanosized zeolite BEA materials differing in morphology and pore size distribution, were used as carriers for the preparation of resveratrol-loaded delivery systems. Two preparation methods have been applied: (i) loading by mixing of resveratrol and mesoporous carrier in solid state and (ii) deposition in ethanol solution. The parent and the resveratrol loaded carriers were characterized by XRD, TEM, N2 physisorption, thermal analysis, and FT-IR spectroscopy. The influence of the support structure on the adsorption capacity and the release kinetics of this poorly soluble compound were investigated. Our results indicated that the chosen nanoporous silica supports are suitable for stabilization of trans-resveratrol and reveal controlled release and ability to protect the supported compound against degradation regardless of loading method. The solid-state dry mixing appears very effective for preparation of drug formulations composed of poorly soluble compound.

  17. [Dust and silica exposure on metallurgical furnace maintenance using refractory materials].

    PubMed

    Garattini, S; Barbieri, P G; Bottone, F; Brunelli, E; Carminati, F; Chiari, R; Sarnico, M

    2012-01-01

    In the metallurgical industries the silica risk has long been known, particularly for the refractoryes maintenance workers. The maintenance of furnaces, ladles and tundisches refractory linings, on the current organization of production, is provided by companies under contract. The information available about the characterization of risk for this group of workers are at present inadequate. The study investigates the exposure to dust, also containing free crystalline silica (SLC), through the analysis of samples of commercial products used in the reconstruction of refractory linings of furnaces, ladles and tundisches, materials from the demolition of refractory articles and dust from work areas. It also presents the results of an environmental investigation conducted during the demolition and reconstruction of the refractory in three steel mills. The Authors, by the numerous inspections and the systematic survey of working conditions, have formulated a SLC risk profile and some proposals for prevention.

  18. Power scaling analysis of fiber lasers and amplifiers based on non-silica materials

    SciTech Connect

    Dawson, J W; Messerly, M J; Heebner, J E; Pax, P H; Sridharan, A K; Bullington, A L; Beach, R J; Siders, C W; Barty, C P; Dubinskii, M

    2010-03-30

    A developed formalism for analyzing the power scaling of diffraction limited fiber lasers and amplifiers is applied to a wider range of materials. Limits considered include thermal rupture, thermal lensing, melting of the core, stimulated Raman scattering, stimulated Brillouin scattering, optical damage, bend induced limits on core diameter and limits to coupling of pump diode light into the fiber. For conventional fiber lasers based upon silica, the single aperture, diffraction limited power limit was found to be 36.6kW. This is a hard upper limit that results from an interaction of the stimulated Raman scattering with thermal lensing. This result is dependent only upon physical constants of the material and is independent of the core diameter or fiber length. Other materials will have different results both in terms of ultimate power out and which of the many limits is the determining factor in the results. Materials considered include silica doped with Tm and Er, YAG and YAG based ceramics and Yb doped phosphate glass. Pros and cons of the various materials and their current state of development will be assessed. In particular the impact of excess background loss on laser efficiency is discussed.

  19. Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications.

    PubMed

    Akkari, Marwa; Aranda, Pilar; Ben Haj Amara, Abdessalem; Ruiz-Hitzky, Eduardo

    2016-01-01

    In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica-organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica-organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay-SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite-silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants.

  20. Curcumin-loaded silica-based mesoporous materials: Synthesis, characterization and cytotoxic properties against cancer cells.

    PubMed

    Bollu, Vishnu Sravan; Barui, Ayan Kumar; Mondal, Sujan Kumar; Prashar, Sanjiv; Fajardo, Mariano; Briones, David; Rodríguez-Diéguez, Antonio; Patra, Chitta Ranjan; Gómez-Ruiz, Santiago

    2016-06-01

    Two different silica based (MSU-2 and MCM-41) curcumin loaded mesoporous materials V3 and V6 were synthesized and characterized by several physico-chemical techniques. Release kinetic study revealed the slow and sustained release of curcumin from those materials in blood simulated fluid (pH: 7.4). The materials V3 and V6 were found to be biocompatible in non-cancerous CHO cell line while exhibiting significant cytotoxicity in different cancer cells (human lung carcinoma cells: A549, human breast cancer cells: MCF-7, mouse melanoma cells: B16F10) compared to pristine curcumin indicating the efficacy of the mesoporous silica materials based drug delivery systems (DDSs). The generation of intracellular reactive oxygen species (ROS) and down regulation of anti-apoptotic protein leading to the induction of apoptosis were found to be the plausible mechanisms behind the anti-cancer activity of these DDSs. These results suggest that curcumin-loaded drug delivery system may be successfully employed as an alternative treatment strategy for cancer therapeutics through a nanomedicine approach in near future.

  1. Tailoring the microstructure of polyimide-silica materials using the sol-gel process

    SciTech Connect

    Schrotter, J.C.; Smaihi, M.; Guizard, C.

    1996-12-31

    Polyimide-silica materials have been prepared via the sol-gel process by mixing tetramethoxysilane with a polyamic acid. Two polyamic acids have been used. The first is obtained with an equimolar mixture of oxydianiline (ODA) and pyromellitic dianhydride (PMDA) in dimethyacetamide. The second is prepared with a mixture of PMDA with aminopropyltrimethoxysilane (APrTMOS). The microstructure of the materials obtained with these two polyamic acids are drastically different. The presence of both amino and methoxy side-groups on the APrTMOS enables a chemical bonding between the organic and the inorganic networks resulting in the formation of homogeneous films. On the other side, no chemical bond is provided by the ODA-PMDA polyamic acid resulting in a biphasic microstructure where pure silica particles are embedded in a polyimide matrix. These two types of materials have been characterized in order to point out the key parameters of their microstructure. {sup 29}Si NMR, thermogravimetric analysis, scanning electron microscopy and infra-red spectroscopy have been used to study materials containing various proportions of TMOS and prepared with various hydrolysis ratios.

  2. Hydrogen generation systems utilizing sodium silicide and sodium silica gel materials

    DOEpatents

    Wallace, Andrew P.; Melack, John M.; Lefenfeld, Michael

    2015-07-14

    Systems, devices, and methods combine reactant materials and aqueous solutions to generate hydrogen. The reactant materials can sodium silicide or sodium silica gel. The hydrogen generation devices are used in fuels cells and other industrial applications. One system combines cooling, pumping, water storage, and other devices to sense and control reactions between reactant materials and aqueous solutions to generate hydrogen. Multiple inlets of varied placement geometries deliver aqueous solution to the reaction. The reactant materials and aqueous solution are churned to control the state of the reaction. The aqueous solution can be recycled and returned to the reaction. One system operates over a range of temperatures and pressures and includes a hydrogen separator, a heat removal mechanism, and state of reaction control devices. The systems, devices, and methods of generating hydrogen provide thermally stable solids, near-instant reaction with the aqueous solutions, and a non-toxic liquid by-product.

  3. Hydrogen generation systems and methods utilizing sodium silicide and sodium silica gel materials

    DOEpatents

    Wallace, Andrew P.; Melack, John M.; Lefenfeld, Michael

    2015-08-11

    Systems, devices, and methods combine thermally stable reactant materials and aqueous solutions to generate hydrogen and a non-toxic liquid by-product. The reactant materials can sodium silicide or sodium silica gel. The hydrogen generation devices are used in fuels cells and other industrial applications. One system combines cooling, pumping, water storage, and other devices to sense and control reactions between reactant materials and aqueous solutions to generate hydrogen. Springs and other pressurization mechanisms pressurize and deliver an aqueous solution to the reaction. A check valve and other pressure regulation mechanisms regulate the pressure of the aqueous solution delivered to the reactant fuel material in the reactor based upon characteristics of the pressurization mechanisms and can regulate the pressure of the delivered aqueous solution as a steady decay associated with the pressurization force. The pressure regulation mechanism can also prevent hydrogen gas from deflecting the pressure regulation mechanism.

  4. Influence of silica-based hybrid material on the gas permeability of hardened cement paste

    NASA Astrophysics Data System (ADS)

    Li, R.; Hou, P.; Xie, N.; Zhou, Z.; Cheng, X.

    2017-03-01

    Surface treatment is one of the most effective ways to elongate the service life of concrete. The surface treatment agents, including organic and inorganic types, have been intensively studied. In this paper, the silica-based hybrid nanocomposite, which take advantages of both organic and inorganic treatment agents, was synthesized and used for surface treatment of hardened cement-based material. The effectiveness of organic and inorganic hybrid nanocomposite was evaluated through investigations on the gas permeability of cement-based materials. The results showed that SiO2/PMHS hybrid nanocomposite can greatly decrease the gas transport properties of hardened cement-based materials and has a great potential for surface treatment of cementitious materials.

  5. Design and evaluation of synthetic silica-based monolithic materials in shrinkable tube for efficient protein extraction.

    PubMed

    Alzahrani, Eman; Welham, Kevin

    2011-10-21

    Sample pretreatment is a required step in proteomics in order to remove interferences and preconcentrate the samples. Much research in recent years has focused on porous monolithic materials since they are highly permeable to liquid flow and show high mass transport compared with more common packed beds. These features are due to the micro-structure within the monolithic silica column which contains both macropores that reduce the back pressure, and mesopores that give good interaction with analytes. The aim of this work was to fabricate a continuous porous silica monolithic rod inside a heat shrinkable tube and to compare this with the same material whose surface has been modified with a C(18) phase, in order to use them for preconcentration/extraction of proteins. The performance of the silica-based monolithic rod was evaluated using eight proteins; insulin, cytochrome C, lysozyme, myoglobin, β-lactoglobulin, ovalbumin, hemoglobin, and bovine serum albumin at a concentration of 60 μM. The results show that recovery of the proteins was achieved by both columns with variable yields; however, the C(18) modified silica monolith gave higher recoveries (92.7 to 109.7%) than the non-modified silica monolith (25.5 to 97.9%). Both silica monoliths can be used with very low back pressure indicating a promising approach for future fabrication of the silica monolith inside a microfluidic device for the extraction of proteins from biological media.

  6. A new method for synthesizing fluid inclusions in fused silica capillaries containing organic and inorganic material

    USGS Publications Warehouse

    Chou, I.-Ming; Song, Y.; Burruss, R.C.

    2008-01-01

    Considerable advances in our understanding of physicochemical properties of geological fluids and their roles in many geological processes have been achieved by the use of synthetic fluid inclusions. We have developed a new method to synthesize fluid inclusions containing organic and inorganic material in fused silica capillary tubing. We have used both round (0.3 mm OD and 0.05 or 0.1 mm ID) and square cross-section tubing (0.3 ?? 0.3 mm with 0.05 ?? 0.05 mm or 0.1 ?? 0.1 mm cavities). For microthermometric measurements in a USGS-type heating-cooling stage, sample capsules must be less than 25 mm in length. The square-sectioned capsules have the advantage of providing images without optical distortion. However, the maximum internal pressure (P; about 100 MPa at 22 ??C) and temperature (T; about 500 ??C) maintained by the square-sectioned capsules are less than those held by the round-sectioned capsules (about 300 MPa at room T, and T up to 650 ??C). The fused silica capsules can be applied to a wide range of problems of interest in fluid inclusion and hydrothermal research, such as creating standards for the calibration of thermocouples in heating-cooling stages and frequency shifts in Raman spectrometers. The fused silica capsules can also be used as containers for hydrothermal reactions, especially for organic samples, including individual hydrocarbons, crude oils, and gases, such as cracking of C18H38 between 350 and 400 ??C, isotopic exchanges between C18H38 and D2O and between C19D40 and H2O at similar temperatures. Results of these types of studies provide information on the kinetics of oil cracking and the changes of oil composition under thermal stress. When compared with synthesis of fluid inclusions formed by healing fractures in quartz or other minerals or by overgrowth of quartz at elevated P-T conditions, the new fused-silica method has the following advantages: (1) it is simple; (2) fluid inclusions without the presence of water can be formed; (3

  7. Dimensional stability of fused silica, Invar, and several ultralow thermal expansion materials

    NASA Technical Reports Server (NTRS)

    Berthold, J. W., III; Jacobs, S. F.; Norton, M. A.

    1976-01-01

    A method is developed for testing the long-term dimensional stability of an iodine-stabilized He-Ne laser, using a technique whereby thermal expansion coefficients are measured by forming a Fabry-Perot etalon from the sample and monitoring the optical resonant frequencies with tunable sidebands impressed on a laser beam from a frequency-stabilized He-Ne laser. A change of 1 ppm over a 3-yr period on the part of fused silica dimensions and the differential thermal expansion of Invar LR-35 and Super Invar materials are noted. The method is of interest for the metrology of extremely stable structures such as telescopes and optical resonators.

  8. Heavy metals adsorption by novel EDTA-modified chitosan-silica hybrid materials.

    PubMed

    Repo, Eveliina; Warchoł, Jolanta K; Bhatnagar, Amit; Sillanpää, Mika

    2011-06-01

    Novel adsorbents were synthesized by functionalizing chitosan-silica hybrid materials with (ethylenediaminetetraacetic acid) EDTA ligands. The synthesized adsorbents were found to combine the advantages of both silica gel (high surface area, porosity, rigid structure) and chitosan (surface functionality). The Adsorption potential of hybrid materials was investigated using Co(II), Ni(II), Cd(II), and Pb(II) as target metals by varying experimental conditions such as pH, contact time, and initial metal concentration. The kinetic results revealed that the pore diffusion process played a key role in adsorption kinetics, which might be attributed to the porous structure of synthesized adsorbents. The obtained maximum adsorption capacities of the hybrid materials for the metal ions ranged from 0.25 to 0.63 mmol/g under the studied experimental conditions. The adsorbent with the highest chitosan content showed the best adsorption efficiency. Bi-Langmuir and Sips isotherm model fitting to experimental data suggested the surface heterogeneity of the prepared adsorbents. In multimetal solutions, the hybrid adsorbents showed the highest affinity toward Pb(II).

  9. Reflectance Spectra Diversity of Silica-Rich Materials: Sensitivity to Environment and Implications for Detections on Mars

    NASA Technical Reports Server (NTRS)

    Rice, M. S.; Cloutis, E. A.; Bell, J. F., III; Bish, D. L.; Horgan, B. H.; Mertzman, S. A.; Craig, M. A.; Renault, R. W.; Gautason, B.; Mountain, B.

    2013-01-01

    Hydrated silica-rich materials have recently been discovered on the surface of Mars by the Mars Exploration Rover (MER) Spirit, the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), and the Mars Express Observatoire pour la Mineralogie, l'Eau, les Glaces, et l'Activite'(OMEGA) in several locations. Having been interpreted as hydrothermal deposits and aqueous alteration products, these materials have important implications for the history of water on the martian surface. Spectral detections of these materials in visible to near infrared (Vis NIR) wavelengths have been based on a H2O absorption feature in the 934-1009 nm region seen with Spirit s Pancam instrument, and on SiOH absorption features in the 2.21-2.26 micron range seen with CRISM. Our work aims to determine how the spectral reflectance properties of silica-rich materials in Vis NIR wavelengths vary as a function of environmental conditions and formation. Here we present laboratory reflectance spectra of a diverse suite of silica-rich materials (chert, opal, quartz, natural sinters and synthetic silica) under a range of grain sizes and temperature, pressure, and humidity conditions. We find that the H2O content and form of H2O/OH present in silica-rich materials can have significant effects on their Vis NIR spectra. Our main findings are that the position of the approx.1.4 microns OH feature and the symmetry of the approx.1.9 microns feature can be used to discern between various forms of silica-rich materials, and that the ratio of the approx.2.2 microns (SiOH) and approx.1.9 microns (H2O) band depths can aid in distinguishing between silica phases (opal-A vs. opal-CT) and formation conditions (low vs. high temperature). In a case study of hydrated silica outcrops in Valles Marineris, we show that careful application of a modified version of these spectral parameters to orbital near-infrared spectra (e.g., from CRISM and OMEGA) can aid in characterizing the

  10. Design of ordered bimodal mesoporous silica materials by using a mixed fluorinated-hydrogenated surfactant-based system.

    PubMed

    Michaux, F; Blin, J L; Stébé, M J

    2007-02-13

    Mesoporous silica materials have been prepared using aqueous solutions of hydrogenated-fluorinated surfactant mixtures. The phase behavior of the C18H35(OC2H4)10-C6F15C2H4(OC2H4)11OH [RH18(EO)10-RF6(EO)11] mixture in aqueous solution was first established at the temperature at which the silica source is added, i.e., 20 or 40 degrees C. We have delimited the different phase domains. Concerning the mesostructured silica, whatever the temperature at which the silica source is added, mesoporous material with a hexagonal array of their channel is formed via a cooperative templating mechanism (CTM), if the content of RF6(EO)11 in the surfactant mixture is lower than 50%. Moreover, when the silica source is added at 40 degrees C, the recovered materials exhibit a bimodal pore size distribution. The appearance of this bimodality has been related to the coexistence of hydrogenated micelles with fluorinated wormlike micelles. By contrast, the bimodality is not observed when the silica source is added at 20 degrees C.

  11. Fumed silica nanoparticle mediated biomimicry for optimal cell-material interactions for artificial organ development.

    PubMed

    de Mel, Achala; Ramesh, Bala; Scurr, David J; Alexander, Morgan R; Hamilton, George; Birchall, Martin; Seifalian, Alexander M

    2014-03-01

    Replacement of irreversibly damaged organs due to chronic disease, with suitable tissue engineered implants is now a familiar area of interest to clinicians and multidisciplinary scientists. Ideal tissue engineering approaches require scaffolds to be tailor made to mimic physiological environments of interest with specific surface topographical and biological properties for optimal cell-material interactions. This study demonstrates a single-step procedure for inducing biomimicry in a novel nanocomposite base material scaffold, to re-create the extracellular matrix, which is required for stem cell integration and differentiation to mature cells. Fumed silica nanoparticle mediated procedure of scaffold functionalization, can be potentially adapted with multiple bioactive molecules to induce cellular biomimicry, in the development human organs. The proposed nanocomposite materials already in patients for number of implants, including world first synthetic trachea, tear ducts and vascular bypass graft.

  12. Influence of geometry on mechanical properties of bio-inspired silica-based hierarchical materials.

    PubMed

    Dimas, Leon S; Buehler, Markus J

    2012-09-01

    Diatoms, bone, nacre and deep-sea sponges are mineralized natural structures found abundantly in nature. They exhibit mechanical properties on par with advanced engineering materials, yet their fundamental building blocks are brittle and weak. An intriguing characteristic of these structures is their heterogeneous distribution of mechanical properties. Specifically, diatoms exhibit nanoscale porosity in specific geometrical configurations to create regions with distinct stress strain responses, notably based on a single and simple building block, silica. The study reported here, using models derived from first principles based full atomistic studies with the ReaxFF reactive force field, focuses on the mechanics and deformation mechanisms of silica-based nanocomposites inspired by mineralized structures. We examine single edged notched tensile specimens and analyze stress and strain fields under varied sample size in order to gain fundamental insights into the deformation mechanisms of structures with distinct ordered arrangements of soft and stiff phases. We find that hierarchical arrangements of silica nanostructures markedly change the stress and strain transfer in the samples. The combined action of strain transfer in the deformable phase, and stress transfer in the strong phase, acts synergistically to reduce the intensity of stress concentrations around a crack tip, and renders the resulting composites less sensitive to the presence of flaws, for certain geometrical configurations it even leads to stable crack propagation. A systematic study allows us to identify composite structures with superior fracture mechanical properties relative to their constituents, akin to many natural biomineralized materials that turn the weaknesses of building blocks into a strength of the overall system.

  13. ZnO nanoparticles embedded in UVM-7-like mesoporous silica materials: Synthesis and characterization

    NASA Astrophysics Data System (ADS)

    Haskouri, Jamal El; Dallali, Lobna; Fernández, Lorenzo; Garro, Nuría; Jaziri, Sihem; Latorre, Julio; Guillem, Carmen; Beltrán, Aurelio; Beltrán, Daniel; Amorós, Pedro

    2009-11-01

    ZnO nanodomains embedded in bimodal mesoporous silica (UVM-7) materials with high Zn content (4≤Si/Zn≤30) have been synthesized by an one-pot surfactant-assisted procedure from a hydro alcoholic medium using a cationic surfactant (CTMABr=cetyltrimethylammonium bromide) as structural directing agent, and starting from molecular atrane complexes of Zn and Si as hydrolytic inorganic precursors. This chemical procedure allows optimizing the dispersion of the ZnO particles in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N 2 adsorption-desorption isotherms. The small intra-particle mesopore system is due to the supramolecular templating effect of the surfactant, while the large pores have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. A limited pore blocking and a high accessibility to the ZnO active nanoparticles have been achieved. The effects induced by the progressive incorporation of ZnO nanoparticles into the mesostructure have been examined, including a careful optical spectroscopic study (PL and UV-visible).

  14. Rational Catalyst Design of Titanium-Silica Materials Aided by Site-Specific Titration Tools

    NASA Astrophysics Data System (ADS)

    Eaton, Todd Robert

    Silica-supported titanium materials are widely used for thermocatalytic applications such as hydroxylation of alkanes and aromatics, oxidation of alcohols and ethers, ammoximation of carbonyls, and sulfoxidations, while Ti-based materials are widely studied for photocatalytic applications such as photo-oxidation of organic substrates and photo-reduction of CO 2. However, the underlying phenomena of how to synthesize, identify, and control the active structures in these materials is not well understood because of the narrow scope of previous work. Studies of titanium-based catalysts typically focus on materials where the metal is present as either highly-dispersed Ti cations or in bulk crystalline TiO2 form, neglecting the numerous and potentially useful intermediate structures. Furthermore, these works typically focus on a single synthesis technique and rely upon bulk characterization techniques to understand the materials. Here rigorous titanium-silica synthesis-structure-function relationships are established by examining several different synthetic method and utilizing characterization techniques that enable an atomic-level understanding of the materials. The materials studied span the range from isolated Ti cations to clustered TiOx domains, polymeric TiO x domains, anatase-like 2D TiO2 domains, and 3D crystalline TiO2. Tools to quantify accessible TiO x and tetrahedral Ti sites are developed, utilizing the selective titration of titanium with phenylphosphonic acid (PPA). Catalytic properties are probed with the photocatalytic oxidation of benzyl alcohol and the thermocatalytic epoxidation of cis-cyclooctene with H2O2 . PPA titration data indicate that the rate of benzyl alcohol photo-oxidation is independent of titanium coordination, while the rate of alkene epoxidation with H2O2 is proportional to the number of tetrahedral titanium sites on the catalyst. PPA titration data also enables the estimation of TiO2 particle size and reveals an important distinction

  15. Organic/inorganic hybrid amine and sulfonic acid tethered silica materials: Synthesis, characterization and application

    NASA Astrophysics Data System (ADS)

    Hicks, Jason Christopher

    The major goals of this thesis were to: (1) create a site-isolated aminosilica material with higher amine loadings than previously reported isolation methods, (2) use spectroscopic, reactivity, and catalytic (olefin polymerization precatalysts) probes to determine isolation of amine groups on these organic/inorganic hybrid materials, (3) synthesize an organic/inorganic hybrid material capable of activating Group 4 olefin polymerization precatalysts, and (4) synthesize a high amine loaded organic/inorganic hybrid material capable of reversibly capturing CO2 in a simulated flue gas stream. The underlying motivation of this research involved the synthesis and design of novel amine and sulfonic acid materials. Traditional routes to synthesize aminosilicas have led to the formation of a high loading of multiple types of amine sites on the silica surface. Part of this research involved the creation of a new aminosilica material via a protection/deprotection method designed to prevent multiple sites, while maintaining a relatively high loading. As a characterization technique, fluorescence spectroscopy of pyrene-based fluorophores loaded on traditional aminosilicas and site-isolated aminosilicas was used to probe the degree of site-isolation obtained with these methods. Also, this protection/deprotection method was compared to other reported isolation techniques with heterogeneous Group 4 constrained-geometry inspired catalysts (CGCs). It was determined that the degree of separation of the amine sites could be controlled with protection/deprotection methods. Furthermore, an increase in the reactivity of the amines and the catalytic activity of CGCs built off of the amines was determined for aminosilicas synthesized by a protection/deprotection method. The second part of this work involved developing organic/inorganic hybrid materials as heterogeneous Bronsted acidic cocatalysts for activation of olefin polymerization precatalysts. This was the first reported organic

  16. In situ synthesis of ordered mesoporous silica materials embedded in cotton fiber and their CO2 capture properties.

    PubMed

    Ma, Li; Han, Kun-Kun; Ding, Xiao-Hua; Chun, Yuan; Zhu, Jian-Hua

    2011-05-01

    Mesoporous silica/cotton fiber composite materials have been prepared in situ by using pluronics P123 (EO20PO70EO20) as template, tetraethyl orthosilicate as silica source and degreasing cotton as supporter. In order to avoid the hydrolysis of cotton fiber in a strong acidic media during the hydrothermal treatment, two kinds of methods were used to control the acidity of the reaction media. One was to adjust the pH to 5 after self-assembly in a strong acidic media; the other was a two-step route containing the pre-hydrolysis of TEOS and self-assembly in a weak acidic media. The resulting shaped composite materials presented the morphology of cotton fiber, and the silica particles mainly covered the surfaces of cotton fibers. These silica particles possessed a slightly ordered pore structure or a well ordered SBA-15 structure according to the difference in the synthetic methods. After modification with tetraethylenepentamine, these shaped composite materials exhibited considerable CO2 adsorption capacity. The use of cotton fiber has the advantages of shaping the powdery materials, dispersing the silica particles and avoiding the formation of moisture and sticky solid surfaces by overloaded tetraethylenepentamine.

  17. Lanthano phosphomolybdate-decorated silica nanoparticles: novel hybrid materials with photochromic properties.

    PubMed

    Pinto, Tânia V; Fernandes, Diana M; Pereira, Clara; Guedes, Alexandra; Blanco, Ginesa; Pintado, Jose M; Pereira, Manuel F R; Freire, Cristina

    2015-03-14

    Novel photochromic hybrid nanomaterials were prepared through the immobilization of the lacunary Keggin-type phosphomolybdate (TBA4H3[PMo11O39]·xH2O, denoted as PMo11) and sandwich-type lanthano phosphomolybdates (K11[Ln(III)(PMo11O39)2]·xH2O, denoted as Ln(PMo11)2, where Ln(III) = Sm, Eu, Gd, Tb and Dy) onto positively-charged functionalized silica nanoparticles. The functionalized silica nanoparticles were prepared by a one-step co-condensation route between tetraethyl orthosilicate and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, presenting an average particle size of 95 ± 26 nm, a spherical morphology and a pore diameter of 13.7 nm. All characterization techniques proved the successful immobilization of the phosphomolybdates. The photochromic properties of the resulting hybrid nanomaterials in the solid state were evaluated by UV-Vis spectroscopy and colorimetry. All materials revealed promising photochromic properties under UV irradiation (λ = 254 nm). The lacunary phosphomolybdate anchored onto the silica nanoparticles, C18-SiO2@PMo11, showed the best photoswitching properties, with the color changing from green to dark-blue (ΔE* = 26.8). Among the Ln(PMo11)2-based hybrid nanomaterials, those containing higher Mo loadings--Eu(III)- and Tb(III)-based samples--presented more significant color changes from green to dark-blue (ΔE* = 18.8-18.9). These results revealed that the optical properties of the as-prepared hybrid nanomaterials did not depend directly on the type of Ln(III) cation, but only on the amount of Mo, which was the target element responsible for the photochromic behavior.

  18. Metal binding proteins, recombinant host cells and methods

    DOEpatents

    Summers, Anne O.; Caguiat, Jonathan J.

    2004-06-15

    The present disclosure provides artificial heavy metal binding proteins termed chelons by the inventors. These chelons bind cadmium and/or mercuric ions with relatively high affinity. Also disclosed are coding sequences, recombinant DNA molecules and recombinant host cells comprising those recombinant DNA molecules for expression of the chelon proteins. In the recombinant host cells or transgenic plants, the chelons can be used to bind heavy metals taken up from contaminated soil, groundwater or irrigation water and to concentrate and sequester those ions. Recombinant enteric bacteria can be used within the gastrointestinal tracts of animals or humans exposed to toxic metal ions such as mercury and/or cadmium, where the chelon recombinantly expressed in chosen in accordance with the ion to be rededicated. Alternatively, the chelons can be immobilized to solid supports to bind and concentrate heavy metals from a contaminated aqueous medium including biological fluids.

  19. Medical applications of organic-inorganic hybrid materials within the field of silica-based bioceramics.

    PubMed

    Vallet-Regí, María; Colilla, Montserrat; González, Blanca

    2011-02-01

    Research on bioceramics has evolved from the use of inert materials for mere substitution of living tissues towards the development of third-generation bioceramics aimed at inducing bone tissue regeneration. Within this context hybrid bioceramics have remarkable features resulting from the synergistic combination of both inorganic and organic components that make them suitable for a wide range of medical applications. Certain bioceramics, such as ordered mesoporous silicas, can exhibit different kind of interaction with organic molecules to develop different functions. The weak interaction of these host matrixes with drug molecules confined in the mesoporous channels allows these hybrid systems to be used as controlled delivery devices. Moreover, mesoporous silicas can be used to fabricate three (3D)-dimensional scaffolds for bone tissue engineering. In this last case, different osteoinductive agents (peptides, hormones and growth factors) can be strongly grafted to the bioceramic matrix to act as attracting signals for bone cells to promote bone regeneration process. Finally, recent research examples of organic-inorganic hybrid bioceramics, such as stimuli-responsive drug delivery systems and nanosystems for targeting of cancer cells and gene transfection, are also tackled in this tutorial review (64 references).

  20. Thermal expansion coefficient prediction of fuel-cell seal materials from silica sand

    NASA Astrophysics Data System (ADS)

    Hidayat, Nurul; Triwikantoro, Baqiya, Malik A.; Pratapa, Suminar

    2013-09-01

    This study is focused on the prediction of coefficient of thermal expansion (CTE) of silica-sand-based fuel-cell seal materials (FcSMs) which in principle require a CTE value in the range of 9.5-12 ppm/°C. A semi-quantitative theoretical method to predict the CTE value is proposed by applying the analyzed phase compositions from XRD data and characterized density-porosity behavior. A typical silica sand was milled at 150 rpm for 1 hour followed by heating at 1000 °C for another hour. The sand and heated samples were characterized by means of XRD to perceive the phase composition correlation between them. Rietveld refinement was executed to investigate the weight fraction of the phase contained in the samples, and then converted to volume fraction for composite CTE calculations. The result was applied to predict their potential physical properties for FcSM. Porosity was taken into account in the calculation after which it was directly measured by the Archimedes method.

  1. Comparison of mesoporous silicon and non-ordered mesoporous silica materials as drug carriers for itraconazole.

    PubMed

    Kinnari, Päivi; Mäkilä, Ermei; Heikkilä, Teemu; Salonen, Jarno; Hirvonen, Jouni; Santos, Hélder A

    2011-07-29

    Mesoporous materials have an ability to enhance dissolution properties of poorly soluble drugs. In this study, different mesoporous silicon (thermally oxidized and thermally carbonized) and non-ordered mesoporous silica (Syloid AL-1 and 244) microparticles were compared as drug carriers for a hydrophobic drug, itraconazole (ITZ). Different surface chemistries pore volumes, surface areas, and particle sizes were selected to evaluate the structural effect of the particles on the drug loading degree and on the dissolution behavior of the drug at pH 1.2. The results showed that the loaded ITZ was apparently in amorphous form, and that the loading process did not change the chemical structure/morphology of the particles' surface. Incorporation of ITZ in both microparticles enhanced the solubility and dissolution rate of the drug, compared to the pure crystalline drug. Importantly, the physicochemical properties of the particles and the loading procedure were shown to have an effect on the drug loading efficiency and drug release kinetics. After storage under stressed conditions (3 months at 40 °C and 70% RH), the loaded silica gel particles showed practically similar dissolution profiles as before the storage. This was not the case with the loaded mesoporous silicon particles due to the almost complete chemical degradation of ITZ after storage.

  2. Sorptive removal of trinitroglycerin (TNG) from water using nanostructured silica-based materials.

    PubMed

    Saad, Rabih; Thibutot, Sonia; Ampleman, Guy; Hawari, Jalal

    2010-01-01

    Trinitroglycerin (TNG), a nitrate ester, is widely used in the pharmaceutical industry for the treatment of angina pectoris (chest pain) and by the military for the manufacturing of dynamite and propellants. Currently, TNG is considered as a key environmental contaminant due to the discharge of wastewater tainted with the chemical from various military and pharmaceutical industries. The present study describes the use of a nanostructured silica material (Mobil Composite Material no. 48 [MCM-48]) prepared by mixing tetraethylorthosilicate (TEOS) and cetyltrimethylammonium bromide (CTAB) to remove TNG from water. The sorption of TNG onto MCM-48 rapidly reached equilibrium within 1 h. Sorption kinetics were best described using a pseudo-second order model, whereas sorption isotherms were best interpreted using the Langmuir model. The latter gave a maximum sorption capacity of 55.2 mg g(-1) at 40 degrees C. The enthalpy and entropy of TNG sorption onto MCM-48 were 1.89 kJ mol(-1) and 79.0 J mol(-1).K(-1), indicating the endothermic nature of the TNG sorption onto MCM-48. When MCM-48 was heated at 540 degrees C for 5 h, the resulting calcined material (absence of the surfactant) did not sorb TNG, suggesting that the surfactant component of the nanomaterial was responsible for TNG sorption. Finally, we found that MCM-48 lost approximately 30% of its original sorption capacity after five sorption-desorption cycles. In conclusion, the nanostructured silica based sorbent, with high sorption capacity and remarkable reusability, should constitute the basis for the development of an effective technology for the removal of TNG from contaminated water.

  3. A novel silica alumina-based backfill material composed of coal refuse and fly ash.

    PubMed

    Yao, Yuan; Sun, Henghu

    2012-04-30

    In this paper, a systematic study was conducted to investigate a novel silica alumina-based backfill material composed of coal refuse and fly ash. The coal refuse and fly ash had different properties under various thermal activation temperatures (20 °C, 150 °C, 350 °C, 550 °C, 750 °C and 950 °C). It is known that a thermal activation temperature ranging from 20 °C to 950 °C significantly increases the flowability and pozzolanic properties of the coal refuse; however, the flowability of fly ash decreases when the activation temperature is higher than 550 °C because of a severe agglomeration phenomenon on its surface. An optimal design for this backfill material was determined to include an activated portion composed of 5% coal refuse at 750 °C and 15% fly ash at 20 °C. This combination yields the best performance with excellent flowability, a high compressive strength and a low bleeding rate. The microanalysis results corresponded well with the performance tests at different activation conditions. In the coal refuse, kaolinite peaks began to decrease because of their transformation into metakaolin at 550 °C. Chlorite peaks disappeared at 750 °C. Muscovite peaks decreased at 750 °C and disappeared at 950 °C. During this process, muscovite 2M(1) gradually dehydroxylated to muscovite HT. Furthermore, this paper examined the environmental acceptance and economic feasibility of this technology and found that this silica alumina-based backfill material composed of coal refuse and fly ash not only meets EPA requirements but also has several advantages in industry feasibility when compared with hydraulic backfill, rock backfill and paste backfill.

  4. Material removal and surface figure during pad polishing of fused silica

    SciTech Connect

    Suratwala, T I; Feit, M D; Steele, W A

    2009-05-04

    The material removal and surface figure after ceria pad polishing of fused silica glass have been measured and analyzed as a function of kinematics, loading conditions, and polishing time. Also, the friction at the workpiece/lap interface, the slope of the workpiece relative to the lap plane, and lap viscoelastic properties have been measured and correlated to material removal. The results show that the relative velocity between the workpiece & lap (determined by the kinematics) and the pressure distribution determine the spatial and temporal material removal and hence the final surface figure of the workpiece. In the case where the applied loading and relative velocity distribution over the workpiece are spatially uniform, a significant non-uniform spatial material removal from the workpiece surface is observed. This is due to a non-uniform pressure distribution resulting from: (1) a moment caused by a pivot point and interface friction forces; (2) viscoelastic relaxation of the polyurethane lap; and (3) a physical workpiece/lap interface mismatch. Both the kinematics and these contributions to the pressure distribution are quantitatively described, and then combined to form a spatial and temporal Preston model & code for material removal (called Surface Figure or SurF{copyright}). The surface figure simulations are consistent with the experiment for a wide variety of polishing conditions. This study is an important step towards deterministic full-aperture polishing, which would allow optical glass fabrication to be performed in a more repeatable, less iterative, and hence more economical manner.

  5. Entrapping quercetin in silica/polyethylene glycol hybrid materials: Chemical characterization and biocompatibility.

    PubMed

    Catauro, Michelina; Bollino, Flavia; Nocera, Paola; Piccolella, Simona; Pacifico, Severina

    2016-11-01

    Sol-gel synthesis was exploited to entrap quercetin, a natural occurring antioxidant polyphenol, in silica-based hybrid materials, which differed in their polyethylene glycol (PEG) content (6, 12, 24 and 50wt%). The materials obtained, whose nano-composite nature was ascertained by Scanning Electron Microscopy (SEM), were chemically characterized by Fourier Transform InfraRed (FT-IR) and UV-Vis spectroscopies. The results prove that a reaction between the polymer and the drug occurred. Bioactivity tests showed their ability to induce hydroxyapatite nucleation on the sample surfaces. The direct contact method was applied to screen the cytotoxicity of the synthetized materials towards fibroblast NIH 3T3 cells, commonly used for in vitro biocompatibility studies, and three nervous system cell lines (neuroblastoma SH-SY5Y, glioma U251, and pheochromocytoma PC12 cell lines), adopted as models in oxidative stress related studies. Using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay NIH 3T3 proliferation was assessed and the morphology was not compromised by direct exposure to the materials. Analogously, PC-12, and U-251 cell lines were not affected by new materials. SH-SY5Y appeared to be the most sensitive cell line with cytotoxic effects of 20-35%.

  6. Synthesis of new water-soluble metal-binding polymers: Combinatorial chemistry approach. 1997 mid-year progress report

    SciTech Connect

    Smith, B.F.

    1997-06-01

    'The first objective of this research is to develop rapid discovery and optimization approaches to new water-soluble chelating polymers. A byproduct of the development approach will be the new, selective, and efficient metal-binding agents. The second objective is to evaluate the concept of using water and organic soluble polymers as new solid supports for combinatorial synthesis. The technology under development, Polymer Filtration (PF), is a technique to selectively remove or recover hazardous and valuable metal ions and radionuclides from various dilute aqueous streams. Not only can this technology be used to remediate contaminated soils and solid surfaces and treat aqueous wastes, it can also be incorporated into facilities as a pollution prevention and waste minimization technology. Polymer Filtration uses water-soluble metal-binding polymers to sequester metal ions in dilute solution. The water-soluble polymers have a sufficiently large molecular size that they can be separated and concentrated using commercial ultrafiltration technology. Water, small organic molecules, and unbound metals pass freely through the ultrafiltration membrane while concentrating the metal-binding polymer. The polymers can then be reused by changing the solution conditions to release the metal ions. The metal-ions are recovered in concentrated form for recycle or disposal using a diafiltration process. The water-soluble polymer can be recycled for further aqueous-stream processing. To advance Polymer Filtration technology to the selectivity levels required for DOE needs. fixture directions in Polymer Filtration must include rapid development, testing, and characterization of new metal-binding polymers. The development of new chelating molecules can be equated to the process of new drugs or new materials discovery. Thus, the authors want to build upon and adapt the combinatorial chemistry approaches developed for rapid molecule generation for the drug industry to the rapid

  7. Catalytic performance of subtilisin immobilized without covalently attachment on surface-functionalized mesoporous silica materials

    NASA Astrophysics Data System (ADS)

    Murai, K.; Nonoyama, T.; Ando, F.; Kato, K.

    2011-10-01

    Mesoporous silica (MPS) materials were synthesized using cetyltrimethylammonium bromide or amphiphilic pluronic polymer P123 (EO20PO70EO20) as structure-directing agent. MPS samples were characterized by FE-SEM and N2 adsorption-desorption isotherms, respectively. Subtilisin from Bacillus licheiformis (4.1 × 7.8 × 3.7 nm) was easily immobilized by a direct one-step immobilization process onto MPS with different organo-functinalized surfaces. However, enzyme immobilized on MPS modified with 3-mercaptopropyl group strongly reduced its enantioselectivity. Denaturation temperature of immobilized subtilisin shifted to a high temperature compared to free-enzyme. These biocatalysts on MPS particles retained about 30% of original activity even after 5 cycles of recycle use.

  8. Monodisperse hollow silica nanospheres for nano insulation materials: synthesis, characterization, and life cycle assessment.

    PubMed

    Gao, Tao; Jelle, Bjørn Petter; Sandberg, Linn Ingunn C; Gustavsen, Arild

    2013-02-01

    The application of manufactured nanomaterials provides not only advantages resulting from their unique properties but also disadvantages derived from the high energy use and CO(2) burden related to their manufacture, operation, and disposal. It is therefore important to understand the trade-offs of process economics of nanomaterial production and their associated environmental footprints in order to strengthen the existing advantages while counteracting disadvantages. This work reports the synthesis, characterization, and life cycle assessment (LCA) of a new type of superinsulating materials, nano insulation materials (NIMs), which are made of hollow silica nanospheres (HSNSs) and have great flexibility in modifying their properties by tuning the corresponding structural parameters. The as-prepared HSNSs in this work have a typical inner pore diameter of about 150 nm and a shell thickness of about 10-15 nm and exhibit a reduced thermal conductivity of about 0.02 W/(m K) because of their size-dependent thermal conduction at the nanometer scale. The energy and raw material consumption related to the synthesis of HSNSs have been analyzed by the LCA method. The results indicate that the recycle of chemicals, up-scaling production, and use of environmentally friendly materials can greatly affect the process of environmental footprints. New synthesis routes for NIMs with improved thermal performance and energy and environmental features are also recommended on the basis of the LCA study.

  9. Mesoporous silica materials modified with alumina polycations as catalysts for the synthesis of dimethyl ether from methanol

    SciTech Connect

    Macina, Daniel; Piwowarska, Zofia; Tarach, Karolina; Góra-Marek, Kinga; Ryczkowski, Janusz; Chmielarz, Lucjan

    2016-02-15

    Highlights: • Deposition of alumina ologoctaions on mesoporous silicas modified with surface −SO{sub 3}H groups. • Alumina aggregates generated acid properties in the silica supports. • Alumina modified SBA-15 and MCF were active and selective catalysts in DME synthesis. - Abstract: Mesoporous silica materials (SBA-15 and MCF) were used as catalytic supports for the deposition of aggregated alumina species using the method consisting of the following steps: (i) anchoring 3-(mercaptopropyl)trimethoxysilane (MPTMS) on the silica surface followed by (ii) oxidation of −SH to−SO{sub 3}H groups and then (iii) deposition of aluminum Keggin oligocations by ion-exchange method and (iv) calcination. The obtained samples were tested as catalysts for synthesis of dimethyl ether from methanol. The modified silicas were characterized with respect to the ordering of their porous structure (XRD), textural properties (BET), chemical composition (EDS, CHNS), structure ({sup 27}Al NMR, FTIR) and location of alumina species (EDX-TEM), surface acidity (NH{sub 3}-TPD, Py-FTIR) and thermal stability (TGA). The obtained materials were found to be active and selective catalysts for methanol dehydration to dimethyl ether (DME) in the MTD process (methanol-to-dimethyl ether).

  10. Identification and characterization of a novel high affinity metal-binding site in the hammerhead ribozyme.

    PubMed Central

    Hansen, M R; Simorre, J P; Hanson, P; Mokler, V; Bellon, L; Beigelman, L; Pardi, A

    1999-01-01

    A novel metal-binding site has been identified in the hammerhead ribozyme by 31P NMR. The metal-binding site is associated with the A13 phosphate in the catalytic core of the hammerhead ribozyme and is distinct from any previously identified metal-binding sites. 31P NMR spectroscopy was used to measure the metal-binding affinity for this site and leads to an apparent dissociation constant of 250-570 microM at 25 degrees C for binding of a single Mg2+ ion. The NMR data also show evidence of a structural change at this site upon metal binding and these results are compared with previous data on metal-induced structural changes in the core of the hammerhead ribozyme. These NMR data were combined with the X-ray structure of the hammerhead ribozyme (Pley HW, Flaherty KM, McKay DB. 1994. Nature 372:68-74) to model RNA ligands involved in binding the metal at this A13 site. In this model, the A13 metal-binding site is structurally similar to the previously identified A(g) metal-binding site and illustrates the symmetrical nature of the tandem G x A base pairs in domain 2 of the hammerhead ribozyme. These results demonstrate that 31P NMR represents an important method for both identification and characterization of metal-binding sites in nucleic acids. PMID:10445883

  11. A Short Overview on the Biomedical Applications of Silica, Alumina and Calcium Phosphate-based Nanostructured Materials.

    PubMed

    Ellahioui, Younes; Prashar, Sanjiv; Gómez-Ruiz, Santiago

    2016-01-01

    This article reviews the use of silica, alumina and calcium phosphate-based nanostructured materials with biomedical applications. A short introduction on the use of the materials in Science, Nanotechnology and Health is included followed by a revision of each of the selected materials. A description of the principal synthetic methods used in the preparation of the materials in nanostructured form is included. The most widely used applications in biomedicine are reviewed including, for example drug-delivery, bone regeneration, imaging, sensoring amongst others. Finally, a short description of the toxicity and cytotoxicity associated with each of the materials of this revision is presented. This short literature revision serves to demonstrate the very promising future ahead of nanosystems based on silica, alumina and calcium phosphate for biological and biomedical applications.

  12. Challenges in the size analysis of a silica nanoparticle mixture as candidate certified reference material

    NASA Astrophysics Data System (ADS)

    Kestens, Vikram; Roebben, Gert; Herrmann, Jan; Jämting, Åsa; Coleman, Victoria; Minelli, Caterina; Clifford, Charles; De Temmerman, Pieter-Jan; Mast, Jan; Junjie, Liu; Babick, Frank; Cölfen, Helmut; Emons, Hendrik

    2016-06-01

    A new certified reference material for quality control of nanoparticle size analysis methods has been developed and produced by the Institute for Reference Materials and Measurements of the European Commission's Joint Research Centre. The material, ERM-FD102, consists of an aqueous suspension of a mixture of silica nanoparticle populations of distinct particle size and origin. The characterisation relied on an interlaboratory comparison study in which 30 laboratories of demonstrated competence participated with a variety of techniques for particle size analysis. After scrutinising the received datasets, certified and indicative values for different method-defined equivalent diameters that are specific for dynamic light scattering (DLS), centrifugal liquid sedimentation (CLS), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), particle tracking analysis (PTA) and asymmetrical-flow field-flow fractionation (AF4) were assigned. The value assignment was a particular challenge because metrological concepts were not always interpreted uniformly across all participating laboratories. This paper presents the main elements and results of the ERM-FD102 characterisation study and discusses in particular the key issues of measurand definition and the estimation of measurement uncertainty.

  13. Challenges in the size analysis of a silica nanoparticle mixture as candidate certified reference material.

    PubMed

    Kestens, Vikram; Roebben, Gert; Herrmann, Jan; Jämting, Åsa; Coleman, Victoria; Minelli, Caterina; Clifford, Charles; De Temmerman, Pieter-Jan; Mast, Jan; Junjie, Liu; Babick, Frank; Cölfen, Helmut; Emons, Hendrik

    A new certified reference material for quality control of nanoparticle size analysis methods has been developed and produced by the Institute for Reference Materials and Measurements of the European Commission's Joint Research Centre. The material, ERM-FD102, consists of an aqueous suspension of a mixture of silica nanoparticle populations of distinct particle size and origin. The characterisation relied on an interlaboratory comparison study in which 30 laboratories of demonstrated competence participated with a variety of techniques for particle size analysis. After scrutinising the received datasets, certified and indicative values for different method-defined equivalent diameters that are specific for dynamic light scattering (DLS), centrifugal liquid sedimentation (CLS), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), particle tracking analysis (PTA) and asymmetrical-flow field-flow fractionation (AF4) were assigned. The value assignment was a particular challenge because metrological concepts were not always interpreted uniformly across all participating laboratories. This paper presents the main elements and results of the ERM-FD102 characterisation study and discusses in particular the key issues of measurand definition and the estimation of measurement uncertainty.

  14. Barcoded materials based on photoluminescent hybrid system of lanthanide ions-doped metal organic framework and silica via ion exchange.

    PubMed

    Shen, Xiang; Yan, Bing

    2016-04-15

    A multicolored photoluminescent hybrid system based on lanthanide ions-doped metal organic frameworks/silica composite host has potential in display and barcode applications. By controlling the stoichiometry of the lanthanides via cation exchange, proportional various lanthanide ions are successfully introduced into metal organic frameworks, whose emission intensity is correspondingly proportional to its amount. The resulting luminescent barcodes depend on the lanthanide ions ratios and compositions. Subsequently, the lanthanide ions located in the channels of metal organic frameworks are protected from any interaction with the environment after the modification of silica on the surface. The optical and thermal stability of the hybrid materials are improved for technological application.

  15. QM/MM Molecular Dynamics Studies of Metal Binding Proteins

    PubMed Central

    Vidossich, Pietro; Magistrato, Alessandra

    2014-01-01

    Mixed quantum-classical (quantum mechanical/molecular mechanical (QM/MM)) simulations have strongly contributed to providing insights into the understanding of several structural and mechanistic aspects of biological molecules. They played a particularly important role in metal binding proteins, where the electronic effects of transition metals have to be explicitly taken into account for the correct representation of the underlying biochemical process. In this review, after a brief description of the basic concepts of the QM/MM method, we provide an overview of its capabilities using selected examples taken from our work. Specifically, we will focus on heme peroxidases, metallo-β-lactamases, α-synuclein and ligase ribozymes to show how this approach is capable of describing the catalytic and/or structural role played by transition (Fe, Zn or Cu) and main group (Mg) metals. Applications will reveal how metal ions influence the formation and reduction of high redox intermediates in catalytic cycles and enhance drug metabolism, amyloidogenic aggregate formation and nucleic acid synthesis. In turn, it will become manifest that the protein frame directs and modulates the properties and reactivity of the metal ions. PMID:25006697

  16. Metals and Neuronal Metal Binding Proteins Implicated in Alzheimer's Disease.

    PubMed

    Cristóvão, Joana S; Santos, Renata; Gomes, Cláudio M

    2016-01-01

    Alzheimer's disease (AD) is the most prevalent age-related dementia affecting millions of people worldwide. Its main pathological hallmark feature is the formation of insoluble protein deposits of amyloid-β and hyperphosphorylated tau protein into extracellular plaques and intracellular neurofibrillary tangles, respectively. Many of the mechanistic details of this process remain unknown, but a well-established consequence of protein aggregation is synapse dysfunction and neuronal loss in the AD brain. Different pathways including mitochondrial dysfunction, oxidative stress, inflammation, and metal metabolism have been suggested to be implicated in this process. In particular, a body of evidence suggests that neuronal metal ions such as copper, zinc, and iron play important roles in brain function in health and disease states and altered homeostasis and distribution as a common feature across different neurodegenerative diseases and aging. In this focused review, we overview neuronal proteins that are involved in AD and whose metal binding properties may underlie important biochemical and regulatory processes occurring in the brain during the AD pathophysiological process.

  17. Prototype of low thermal expansion materials: fabrication of mesoporous silica/polymer composites with densely filled polymer inside mesopore space.

    PubMed

    Kiba, Shosuke; Suzuki, Norihiro; Okawauchi, Yoshinori; Yamauchi, Yusuke

    2010-09-03

    A prototype of novel low thermal expansion materials using mesoporous silica particles is demonstrated. Mesoporous silica/polymer composites with densely filled polymer inside the mesopore space are fabricated by mechanically mixing both organically modified mesoporous silica and epoxy polymer. The mesopores are easily penetrated by polymers as a result of the capillary force during the mechanical composite processing. Furthermore, we propose a new model of polymer mobility restriction using mesoporous silica with a large pore space. The robust inorganic frameworks covering the polymer effectively restrict the polymer mobility against thermal energy. As a result, the degree of total thermal expansion of the composites is drastically decreased. From the mass-normalized thermal mechanical analysis (TMA) charts of various composites with different amounts of mesoporous silica particles, it is observed that the coefficient of thermal expansion (CTE) values gradually increase with an increase of the polymer amount outside the mesopores. It is proven that the CTE values in the range over the glass-transition temperatures (T(g)) are perfectly proportional to the outside polymer amounts. Importantly, the Y-intercept of the relation equation obtained by a least-square method is the CTE value and is almost zero. This means that thermal expansion does not occur if no polymers are outside the mesopores. Through such a quantative discussion, we clarify that only the outside polymer affects the thermal expansion of the composites, that is, the embedded polymers inside the mesopores do not expand at all during the thermal treatment.

  18. Impact of physicochemical properties of porous silica materials conjugated with dexamethasone via pH-responsive hydrazone bond on drug loading and release behavior

    NASA Astrophysics Data System (ADS)

    Numpilai, Thanapha; Witoon, Thongthai; Chareonpanich, Metta; Limtrakul, Jumras

    2017-02-01

    The conjugation of dexamethasone (DEX) onto modified-porous silica materials via a pH-responsive hydrazone bond has been reported to be highly efficient method to specifically deliver the DEX to diseased sites. However, the influence of physicochemical properties of porous silica materials has not yet been fully understood. In this paper, the impact of pore sizes, particle sizes and silanol contents on surface functionalization, drug loading and release behavior of porous silica materials conjugated with dexamethasone via pH-responsive hydrazone bond was investigated. The grafting density was found to relate to the number of silanol groups on the surface of porous silica materials. The particle size and macropores of the porous silica materials played an vital role on the drug loading and release behavior. Although the porous silica materials with larger particle sizes possessed a lower grafting density, a larger amount of drug loading could be achieved. Moreover, the porous silica materials with larger particle sizes showed a slower release rate of DEX due to a longer distance for cleaved DEX diffusion out of pores. DEX release rate exhibited pH-dependent, sustained release. At pH 4.5, the amount of DEX release within 10 days could be controlled in the range of 12.74-36.41%, depending on the host material. Meanwhile, less than 1.5% of DEX was released from each of type of the porous silica materials at pH 7.4. The results of silica dissolution suggested that the degradation of silica matrix did not significantly affect the release rate of DEX. In addition, the kinetic modeling studies revealed that the DEX releases followed Korsmeyer-Peppas model with a release exponent (n) ranged from 0.3 to 0.47, indicating a diffusion-controlled release mechanism.

  19. Concentrated polymer brush-modified silica particle coating confers biofouling-resistance on modified materials.

    PubMed

    Yoshikawa, Chiaki; Qiu, Jun; Shimizu, Yoshihisa; Huang, Chih-Feng; Gelling, Onko-Jan; van den Bosch, Edith

    2017-01-01

    Biofouling, an undesired adsorption of biological material to otherwise inert surfaces, is detrimental in medical, pharmaceutical, and other sectors. Concentrated polymer brushes (CPB) confer non-biofouling properties on modified surfaces but are cumbersome to fabricate. Here, a simple and versatile method of fabricating non-biofouling coatings for various substrates was developed using CPB-modified silica nanoparticles (SiPs). Concentrated poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) brushes were grafted on SiPs by surface-initiated atom transfer radical polymerization. CPB-SiPs were spin-coated onto silicon wafers or quartz crystal microbalance (QCM) sensor chips with phenyl azido cross-linkers. SiP cross-linking was then performed by ultra violet irradiation for 20s, or by heating at 120°C for 12h. Protein adsorption to coatings was studied by QCM approach and human umbilical vein endothelial cell adhesion to coatings was examined. SiP to cross-linker weight ratios were varied from 2.0/0.5 to 9.0/0.5 (wt/wt%) and the coatings almost completely suppressed protein adsorption and cell adhesion to treated surfaces. The coating was also applied to polymeric films, rendering these materials biofouling-resistant.

  20. Multifunctional mesoporous silica catalyst

    DOEpatents

    Lin, Victor Shang-Yi; Tsai, Chih-Hsiang; Chen, Hung-Ting; Pruski, Marek; Kobayashi, Takeshi

    2015-03-31

    The present invention provides bifunctional silica mesoporous materials, including mesoporous silica nanoparticles ("MSN"), having pores modified with diarylammonium triflate and perfluoroaryl moieties, that are useful for the acid-catalyzed esterification of organic acids with organic alcohols.

  1. Silica/quercetin sol–gel hybrids as antioxidant dental implant materials

    PubMed Central

    Catauro, Michelina; Papale, Ferdinando; Bollino, Flavia; Piccolella, Simona; Marciano, Sabina; Nocera, Paola; Pacifico, Severina

    2015-01-01

    The development of biomaterials with intrinsic antioxidant properties could represent a valuable strategy for preventing the onset of peri-implant diseases. In this context, quercetin, a naturally occurring flavonoid, has been entrapped at different weight percentages in a silica-based inorganic material by a sol–gel route. The establishment of hydrogen bond interactions between the flavonol and the solid matrix was ascertained by Fourier transform infrared spectroscopy. This technique also evidenced changes in the stretching frequencies of the quercetin dienonic moiety, suggesting that the formation of a secondary product occurs. Scanning electron microscopy was applied to detect the morphology of the synthesized materials. Their bioactivity was shown by the formation of a hydroxyapatite layer on sample surface soaked in a fluid that simulates the composition of human blood plasma. When the potential release of flavonol was determined by liquid chromatography coupled with ultraviolet and electrospray ionization tandem mass spectrometry techniques, the eluates displayed a retention time that was 0.5 min less than quercetin. Collision-activated dissociation mass spectrometry and untraviolet-visible spectroscopy were in accordance with the release of a quercetin derivative. The antiradical properties of the investigated systems were evaluated by DPPH and ABTS methods, whereas the 2,7-dichlorofluorescein diacetate assay highlighted their ability to inhibit the H2O2-induced intracellular production of reactive oxygen species in NIH-3T3 mouse fibroblast cells. Data obtained, along with data gathered from the MTT cytotoxicity test, revealed that the materials that entrapped the highest amount of quercetin showed notable antioxidant effectiveness. PMID:27877802

  2. Silica/quercetin sol-gel hybrids as antioxidant dental implant materials

    NASA Astrophysics Data System (ADS)

    Catauro, Michelina; Papale, Ferdinando; Bollino, Flavia; Piccolella, Simona; Marciano, Sabina; Nocera, Paola; Pacifico, Severina

    2015-06-01

    The development of biomaterials with intrinsic antioxidant properties could represent a valuable strategy for preventing the onset of peri-implant diseases. In this context, quercetin, a naturally occurring flavonoid, has been entrapped at different weight percentages in a silica-based inorganic material by a sol-gel route. The establishment of hydrogen bond interactions between the flavonol and the solid matrix was ascertained by Fourier transform infrared spectroscopy. This technique also evidenced changes in the stretching frequencies of the quercetin dienonic moiety, suggesting that the formation of a secondary product occurs. Scanning electron microscopy was applied to detect the morphology of the synthesized materials. Their bioactivity was shown by the formation of a hydroxyapatite layer on sample surface soaked in a fluid that simulates the composition of human blood plasma. When the potential release of flavonol was determined by liquid chromatography coupled with ultraviolet and electrospray ionization tandem mass spectrometry techniques, the eluates displayed a retention time that was 0.5 min less than quercetin. Collision-activated dissociation mass spectrometry and untraviolet-visible spectroscopy were in accordance with the release of a quercetin derivative. The antiradical properties of the investigated systems were evaluated by DPPH and ABTS methods, whereas the 2,7-dichlorofluorescein diacetate assay highlighted their ability to inhibit the H2O2-induced intracellular production of reactive oxygen species in NIH-3T3 mouse fibroblast cells. Data obtained, along with data gathered from the MTT cytotoxicity test, revealed that the materials that entrapped the highest amount of quercetin showed notable antioxidant effectiveness.

  3. Crosslinking Amine-Modified Silica Aerogels with Epoxies: Mechanically Strong Lightweight Porous Materials

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Fabrizio, Eve F.; Ilhan, Faysal; Dass, Amala; Zhang, Guo-Hui; Vassilaras, Plousia; Johnston, J. Chris; Leventis, Nicholas

    2005-01-01

    The mesoporous surfaces of TMOS-derived silica aerogels have been modified with amines by co-polymerization of TMOS with APTES. The amine sites have become anchors for crosslinking the nanoparticles of the skeletal backbone of the aerogel by attachment of di-, tri and tetra-functional epoxies. The resulting conformal coatings increase the density of the native aerogels by a factor of 2-3 but the strength of the resulting materials may increase by more than two orders of magnitude. Processing variables such as amount of APTES used to make the gels, the epoxy type and concentration used for crosslinking, as well as the crosslinking temperature and time were varied according to a multivariable design-of-experiments (DOE) model. It was found that while elastic modulus follows a similar trend with density, maximum strength is attained neither at the maximum density nor at the highest concentration of -NH2 groups, suggesting surface saturation effects. Aerogels crosslinked with the tri-functional epoxide always show improved strength compared with aerogels crosslinked with the other two epoxides under identical conditions. Solid C-13 NMR studies show residual unreacted epoxides, which condense with ne another by heating crosslinked aerogels at 150 C.

  4. Nonionic fluorinated-hydrogenated surfactants for the design of mesoporous silica materials.

    PubMed

    Michaux, F; Blin, J L; Stébé, M J

    2008-09-25

    We have investigated the influence of the ratio between the volume of the hydrophilic head (VA) and the volume of the hydrophobic part (VB) of the surfactant on the mesopore ordering. To understand the difference of behavior we have performed a complete study dealing with fluorinated [Rm(F)(EO)n] and hydrogenated [Rm(H)(EO)n] surfactants. Their mixtures have also been taken into account. Here only the phase diagrams and the structural parameters of the liquid crystal phases of the mixed systems are reported. We have shown that the mutual or partial miscibility of the fluorinated and the hydrogenated surfactants depends on the number of oxyethylene units of each surfactant. To follow, various systems were used for the preparation of silica mesoporous materials via a cooperative templating mechanism (CTM). Results clearly reveal that VA/VB ratios in the range between 0.95 and 1.78 lead to the formation of well-ordered mesostructures. Wormhole-like structures are obtained for higher or lower values. Moreover, results show that from the VA/VB point of view, polyoxyethylene fluoroalkyl ether surfactants behave like their hydrogenated analogues.

  5. Organoclay hybrid materials as precursors of porous ZnO/silica-clay heterostructures for photocatalytic applications

    PubMed Central

    Akkari, Marwa; Aranda, Pilar; Ben Haj Amara, Abdessalem

    2016-01-01

    In this study, ZnO/SiO2-clay heterostructures were successfully synthesized by a facile two-step process applied to two types of clays: montmorillonite layered silicate and sepiolite microfibrous clay mineral. In the first step, intermediate silica–organoclay hybrid heterostructures were prepared following a colloidal route based on the controlled hydrolysis of tetramethoxysilane in the presence of the starting organoclay. Later on, pre-formed ZnO nanoparticles (NP) dispersed in 2-propanol were incorporated under ultrasound irradiation to the silica–organoclay hybrid heterostructures dispersed in 2-propanol, and finally, the resulting solids were calcinated to eliminate the organic matter and to produce ZnO nanoparticles (NP) homogeneously assembled to the clay–SiO2 framework. In the case of montmorillonite the resulting materials were identified as delaminated clays of ZnO/SiO2-clay composition, whereas for sepiolite, the resulting heterostructure is constituted by the assembling of ZnO NP to the sepiolite–silica substrate only affecting the external surface of the clay. The structural and morphological features of the prepared heterostructures were characterized by diverse physico-chemical techniques (such as XRD, FTIR, TEM, FE-SEM). The efficiency of these new porous ZnO/SiO2-clay heterostructures as potential photocatalysts in the degradation of organic dyes and the removal of pharmaceutical drugs in water solution was tested using methylene blue and ibuprofen compounds, respectively, as model of pollutants. PMID:28144545

  6. Silica-Ceria Hybrid Nanostructures

    SciTech Connect

    Munusamy, Prabhakaran; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Baer, Donald R.; Thevuthasan, Suntharampillai

    2012-04-25

    A new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ~50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ~2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states.

  7. Optical and spectroscopic characterizations of Algerian silica raw material to predict high quality solar-grade silicon

    NASA Astrophysics Data System (ADS)

    Kheloufi, A.; Bobocioiu, E.; Kerkar, F.; Kefaifi, A.; Anas, S.; Medjahed, S. A.; Belkacem, Y.; Keffous, A.

    2017-03-01

    We assess the potential use as raw material for photovoltaics of Algerian silica samples from the quartz veins of the Tirek deposit and quartz sandstones of the Ain Barda deposit. With 97-98% purity, they all require enrichment before their industrial utilization. Acid leaching and gravimetric separation are used to remove the impurities at the grain boundaries and within the crystal lattice. We obtain course, middle, and fine products. The acid leaching process and the gravimetric separation increase the content of SiO2 up to 99.68%; the residue concentration of iron, alumina and zirconium is decreased to 70, 72 and 58 ppm respectively. These values are in agreement with requirements for silica as raw material destined for solar-grade silicon production.

  8. Influence of sulfhydryl sites on metal binding by bacteria

    NASA Astrophysics Data System (ADS)

    Nell, Ryan M.; Fein, Jeremy B.

    2017-02-01

    The role of sulfhydryl sites within bacterial cell envelopes is still unknown, but the sites may control the fate and bioavailability of metals. Organic sulfhydryl compounds are important complexing ligands in aqueous systems and they can influence metal speciation in natural waters. Though representing only approximately 5-10% of the total available binding sites on bacterial surfaces, sulfhydryl sites exhibit high binding affinities for some metals. Due to the potential importance of bacterial sulfhydryl sites in natural systems, metal-bacterial sulfhydryl site binding constants must be determined in order to construct accurate models of the fate and distribution of metals in these systems. To date, only Cd-sulfhydryl binding has been quantified. In this study, the thermodynamic stabilities of Mn-, Co-, Ni-, Zn-, Sr- and Pb-sulfhydryl bacterial cell envelope complexes were determined for the bacterial species Shewanella oneidensis MR-1. Metal adsorption experiments were conducted as a function of both pH, ranging from 5.0 to 7.0, and metal loading, from 0.5 to 40.0 μmol/g (wet weight) bacteria, in batch experiments in order to determine if metal-sulfhydryl binding occurs. Initially, the data were used to calculate the value of the stability constants for the important metal-sulfhydryl bacterial complexes for each metal-loading condition studied, assuming a single binding reaction for the dominant metal-binding site type under the pH conditions of the experiments. For most of the metals that we studied, these calculated stability constant values increased significantly with decreasing metal loading, strongly suggesting that our initial assumption was not valid and that more than one type of binding occurs at the assumed binding site. We then modeled each dataset with two distinct site types with identical acidity constants: one site with a high metal-site stability constant value, which we take to represent metal-sulfhydryl binding and which dominates under low

  9. A New Phase Change Material Based on Potassium Nitrate with Silica and Alumina Nanoparticles for Thermal Energy Storage.

    PubMed

    Chieruzzi, Manila; Miliozzi, Adio; Crescenzi, Tommaso; Torre, Luigi; Kenny, José M

    2015-12-01

    In this study different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (KNO3 selected as phase change material) with nanoparticles using the direct synthesis method. The thermal properties of the nanofluids obtained were investigated. Following the improvement in the specific heat achieved, these nanofluids can be used in concentrating solar plants with a reduction of storage material. The nanoparticles used (1.0 wt.%) were silica (SiO2), alumina (Al2O3), and a mix of silica-alumina (SiO2-Al2O3) with an average diameter of 7, 13, and 2-200 nm respectively. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements of the thermophysical properties were performed by DSC analysis, and the dispersion of the nanoparticles was analyzed by SEM microscopy. The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of about 5-10 % in solid phase and of 6 % in liquid phase. In particular, this research shows that the addition of silica nanoparticles has significant potential for enhancing the thermal storage characteristics of KNO3. The phase-change temperature of potassium nitrate was lowered up to 3 °C, and the latent heat was increased to 12 % with the addition of silica nanoparticles. These results deviated from the predictions of theoretical simple mixing model used. The stored heat as a function of temperature was evaluated for the base salt, and the nanofluids and the maximum values obtained were 229, 234, 242, and 266 J/g respectively. The maximum total gain (16 %) due to the introduction of the nanoparticles (calculated as the ratio between the total stored heat of the nanofluids and the base salt in the range of temperatures 260-390 °C) was also recorded with the introduction of silica. SEM and EDX analysis showed the presence of aggregates in all nanofluids: with silica nanoparticles they were homogenously present while with

  10. A New Phase Change Material Based on Potassium Nitrate with Silica and Alumina Nanoparticles for Thermal Energy Storage

    NASA Astrophysics Data System (ADS)

    Chieruzzi, Manila; Miliozzi, Adio; Crescenzi, Tommaso; Torre, Luigi; Kenny, José M.

    2015-06-01

    In this study different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (KNO3 selected as phase change material) with nanoparticles using the direct synthesis method. The thermal properties of the nanofluids obtained were investigated. Following the improvement in the specific heat achieved, these nanofluids can be used in concentrating solar plants with a reduction of storage material. The nanoparticles used (1.0 wt.%) were silica (SiO2), alumina (Al2O3), and a mix of silica-alumina (SiO2-Al2O3) with an average diameter of 7, 13, and 2-200 nm respectively. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements of the thermophysical properties were performed by DSC analysis, and the dispersion of the nanoparticles was analyzed by SEM microscopy. The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of about 5-10 % in solid phase and of 6 % in liquid phase. In particular, this research shows that the addition of silica nanoparticles has significant potential for enhancing the thermal storage characteristics of KNO3. The phase-change temperature of potassium nitrate was lowered up to 3 °C, and the latent heat was increased to 12 % with the addition of silica nanoparticles. These results deviated from the predictions of theoretical simple mixing model used. The stored heat as a function of temperature was evaluated for the base salt, and the nanofluids and the maximum values obtained were 229, 234, 242, and 266 J/g respectively. The maximum total gain (16 %) due to the introduction of the nanoparticles (calculated as the ratio between the total stored heat of the nanofluids and the base salt in the range of temperatures 260-390 °C) was also recorded with the introduction of silica. SEM and EDX analysis showed the presence of aggregates in all nanofluids: with silica nanoparticles they were homogenously present while with alumina and

  11. High surface area Au-SBA-15 and Au-MCM-41 materials synthesis: tryptophan amino acid mediated confinement of gold nanostructures within the mesoporous silica pore walls.

    PubMed

    Selvakannan, Pr; Mantri, Kshudiram; Tardio, James; Bhargava, Suresh K

    2013-03-15

    Advantages of confining the gold nanostructures formation within the mesoporous silica pore walls during its silica condensation and consequent improvement in the textural properties such as specific surface area, pore volume, pore diameter have been demonstrated, while retaining gold nanostructures within the silica walls. This has been achieved by tryptophan mediated confinement of gold nanoparticles formation within the condensing silica framework, to obtain Au-SBA-15 (SSA 1247 m(2)/g, V(t)~1.37 cm(3)/g) and Au-MCM-41 (SSA 1287 m(2)/g, V(t)~1.1 cm(3)/g), mesoporous silica materials having the combination of very high surface area from the porous support as well as gold nanoparticles infiltrated silica walls. Choice of tryptophan for this purpose is that it has an indole group, which was known to reduce gold ions to form gold nanoparticles and its amine and carboxylic acid groups, catalyze the hydrolysis of silica precursors in a wide range of pH. These properties have been utilized in restricting the gold nanostructures formation inside the condensing silica phase without affecting the self assembly between the silica precursors and the triblock copolymer (for SBA-15) or cetyltrimethylammonium bromide template (for MCM-41). The polytryptophan and the gold nanostructures, which were encapsulated within the silica framework and upon removal of the template by calcination resulting in the formation mesoporous materials wherein the silica walls become microporous due to the removal of occluded polytryptophan and the resulting microchannels contain very small gold nanostructures. Hence, the resulting materials have very high surface area, high pore volume and narrow pore size distribution as compared to their parent SBA-15, MCM-41 and SBA-15, MCM-41 post functionalized with gold nanoparticles inside the pores.

  12. The effects of surface chemistry of mesoporous silica materials and solution pH on kinetics of molsidomine adsorption

    SciTech Connect

    Dolinina, E.S.; Parfenyuk, E.V.

    2014-01-15

    Adsorption kinetics of molsidomine on mesoporous silica material (UMS), the phenyl- (PhMS) and mercaptopropyl-functionalized (MMS) derivatives from solution with different pH and 298 K was studied. The adsorption kinetics was found to follow the pseudo-second-order kinetic model for all studied silica materials and pH. Effects of surface functional groups and pH on adsorption efficiency and kinetic adsorption parameters were investigated. At all studied pH, the highest molsidomine amount is adsorbed on PhMS due to π–π interactions and hydrogen bonding between surface groups of PhMS and molsidomine molecules. An increase of pH results in a decrease of the amounts of adsorbed molsidomine onto the silica materials. Furthermore, the highest adsorption rate kinetically evaluated using a pseudo-second-order model, is observed onto UMS and it strongly depends on pH. The mechanism of the adsorption process was determined from the intraparticle diffusion and Boyd kinetic film–diffusion models. The results showed that the molsidomine adsorption on the silica materials is controlled by film diffusion. Effect of pH on the diffusion parameters is discussed. - Graphical abstract: The kinetic study showed that the k{sub 2} value, the rate constant of pseudo-second order kinetic model, is the highest for molsidomine adsorption on UMS and strongly depends on pH because it is determined by availability and accessibility of the reaction sites of the adsorbents molsidomine binding. Display Omitted - Highlights: • The adsorption capacities of UMS, PhMS and MMS were dependent on the pH. • At all studied pH, the highest molsidomine amount is adsorbed on PhMS. • The highest adsorption rate, k{sub 2}, is observed onto UMS and strongly depends on pH. • Film diffusion was the likely rate-limiting step in the adsorption process.

  13. Facile and tunable synthesis of hierarchical mesoporous silica materials ranging from flower structure with wrinkled edges to hollow structure with coarse surface

    NASA Astrophysics Data System (ADS)

    Hao, Nanjing; Li, Laifeng; Tang, Fangqiong

    2016-11-01

    Mesoporous silica materials have attracted great attention in many fields. However, facile and tunable synthesis of hierarchical mesoporous silica structures is still a big challenge, and thus the development of them still lags behind. Herein, well-defined mesoporous silica flower structure with wrinkled edges and mesoporous silica hollow structure with coarse surface were synthesized simply by using poly(vinylpyrrolidone) and hexadecylamine as cotemplates in different water/ethanol solvent systems. The shape evolution from flower to hollow can be easily realized by tuning the volume ratio of water to ethanol, and the yields of both materials can reach gram scale. The formation mechanisms of mesoporous silica flower and hollow structures were also experimentally investigated and discussed. These novel hierarchical structures having unique physicochemical properties may bring many interesting insights into scientific research and technological application.

  14. Combination of porous silica monolith and gold thin films for electrode material of supercapacitor

    NASA Astrophysics Data System (ADS)

    Pastre, A.; Cristini-Robbe, O.; Boé, A.; Raulin, K.; Branzea, D.; El Hamzaoui, H.; Kinowski, C.; Rolland, N.; Bernard, R.

    2015-12-01

    An all-solid electrical double layer supercapacitor was prepared, starting from a porous silica matrix coated with a gold thin-film. The metallization of the silica xerogel was performed by an original wet chemical process, based on the controlled growth of gold nanoparticles on two opposite faces of the silica monolith as a seed layer, followed by an electroless deposition of a continuous gold thin film. The thickness of the metallic thin film was assessed to be 700 nm. The silica plays two major roles: (1) it is used as a porous matrix for the gold electrode, creating a large specific surface area, and (2) it acts as a separator (non-metallized part of the silica). The silica monolith was soaked in a polyvinyl alcohol and phosphoric acid mixture which is used as polymer electrolyte. Capacitance effect was demonstrated by cyclic voltammetry experiments. The specific capacitance was found to be equal to 0.95 mF cm- 2 (9.5 F g-1). No major degradation occurs within more than 3000 cycles.

  15. Influence of Environmental Factors on the Adsorption Capacity and Thermal Conductivity of Silica Nano-Porous Materials.

    PubMed

    Zhang, Hu; Gu, Wei; Li, Ming-Jia; Fang, Wen-Zhen; Li, Zeng-Yao; Tao, Wen-Quan

    2015-04-01

    In this work, the influence of temperature and humidity environment on the water vapor adsorption capacity and effective thermal conductivity of silica nano-porous material is conducted within a relative humidity range from 15% to 90% at 25 °C, 40 °C and 55 °C, respectively. The experiment results show that both the temperature and relative humidity have significant influence on the adsorption capacity and effective thermal conductivity of silica nano-porous materials. The adsorption capacity and effective thermal conductivity increase with humidity because of the increases of water vapor concentration. The effective thermal conductivity increases linearly with adsorption saturation capacity at constant temperature. Because adsorption process is exothermic reaction, the increasing temperature is not conducive to the adsorption. But the effective thermal conductivity increases with the increment of temperature at the same water uptake because of the increment of water thermal conductivity with temperature Geometric models and unit cell structure are adopted to predict the effective thermal conductivity and comparisons with the experimental result are made, and for the case of moist silica nano-porous materials with high porosity no quantitative agreement is found. It is believed that the adsorbed water will fill in the nano-pores and gap and form lots of short cuts, leading to a significant reduction of the thermal resistance.

  16. Interplay of carbon-silica sources on the formation of hierarchical porous composite materials for biological applications such as lipase immobilization.

    PubMed

    Higuita, Mario; Bernal, Claudia; Mesa, Monica

    2014-10-01

    The porous inorganic materials, with hierarchical structures, find application in many processes where the chemical stability and pore connectivity are key points, such as separation, adsorption and catalysis. Here, we synthesized carbon-silica composite materials, which combine hydrolytic stability of the carbon with the surface chemical reactivity of silica in aqueous media. The polycondensation of carbonaceous and siliceous species from sucrose, Triton X-100 surfactant and tetraethylortosilicate during the hydrothermal synthesis led to the formation of hydrochar composite materials. The subsequent carbonization process of these composite hydrochars gave carbon-silica hierarchical porous materials. The study of the micellar reaction system and the characterization of the derivate materials (carbon-silica composite, carbon and silica) were carried out. The results indicate that synthesis conditions allowed the formation of a silica network interpenetrated with a carbon one, which is produced from the incorporated organic matter. The control of the acidity of the reaction medium and hydrothermal conditions modulated the reaction yield and porous characteristics of the materials. The composite nature in conjunction with the hierarchical porosity increases the interest of these materials for future biological applications, such as lipase immobilization.

  17. Models of metal binding structures in fulvic acid from the Suwannee River, Georgia

    USGS Publications Warehouse

    Leenheer, J.A.; Brown, G.K.; MacCarthy, P.; Cabaniss, S.E.

    1998-01-01

    Fulvic acid, isolated from the Suwannee River, Georgia, was assessed for its ability to bind Ca2+, Cd2+, Cu2+, Ni2+, and Zn2+ ions at pH 6 before and after extensive fractionation that was designed to reveal the nature of metal binding functional groups. The binding constant for Ca2+ ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purpose of building quantitative average model structures. The 'metal binding' fraction was characterized by quantitative 13C NMR, 1H NMR, and FT-1R spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that carboxyl groups were clustered in short- chain aliphatic dibasic acid structures. The Ca2+ binding data suggested that ether-substituted oxysuccinic acid structures are good models for the metal binding sites at pH 6. Structural models were derived based upon oxidation and photolytic rearrangements of cutin, lignin, and tannin precursors. These structural models rich in substituted dibasic acid structures revealed polydentate binding sites with the potential for both inner-sphere and outer-sphere type binding. The majority of the fulvic acid molecule was involved with metal binding rather than a small substructural unit.Fulvic acid, isolated from the Suwannee River, Georgia, was assessed for its ability to bind Ca2+, Cd2+, Cu2+, Ni2+, and Zn2+ ions at pH 6 before and after extensive fractionation that was designed to reveal the nature of metal binding functional groups. The binding constant for Ca2+ ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purpose of building quantitative average model structures. The `metal binding' fraction was characterized by quantitative 13C NMR, 1H NMR, and FT-IR spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that

  18. Silylated melamine and cyanuric acid as precursors for imprinted and hybrid silica materials with molecular recognition properties.

    PubMed

    Arrachart, Guilhem; Carcel, Carole; Trens, Philippe; Moreau, Jöel J E; Wong Chi Man, Michel

    2009-06-15

    Two monotrialkoxysilylated compounds that consist of complementary fragments of melamine (M) and cyanuric acid (CA) have been synthesised. The molecular recognition properties of the M and CA fragments through complementary hydrogen bonds (DAD and ADA; D=donor, A=acceptor) are the key factor used to direct the formation of hybrid silica materials by using a sol-gel process. These materials were synthesised following two methods: First, an organo-bridged silsesquioxane was obtained by the hydrolysis of the two complementary monotrialkoxysilylated melamine and cyanuric acid derivatives, with fluoride ions as a catalyst. The hydrogen-bonding interactions between the two organic fragments are responsible for the formation of the bridging unit. The transcription of the assembly into the hybrid material was characterised and evidenced by solid-state NMR (29Si, 13C) and FTIR spectroscopic experiments. Second, the molecular recognition was exploited to synthesise an imprinted hybrid silica. This material was prepared by co-condensation of tetraethyl orthosilicate (TEOS) with the monosilylated cyanuric acid derivative (CA) templated by nonsilylated melamine. The melamine template was completely removed by treating the solid material with hydrochloric acid. The reintroduction of the template was performed by treating the resulting material with an aqueous suspension of melamine. These steps were monitored and analysed by several techniques, such as solid-state NMR (29Si, 13C) and FTIR spectroscopic analysis and nitrogen adsorption-desorption isotherms.

  19. Development of UHPC Mixtures Utilizing Natural and Industrial Waste Materials as Partial Replacements of Silica Fume and Sand

    PubMed Central

    2014-01-01

    In the exploratory study presented in this paper, an attempt was made to develop different mixtures of ultrahigh performance concrete (UHPC) using various locally available natural and industrial waste materials as partial replacements of silica fume and sand. Materials such as natural pozzolana (NP), fly ash (FA), limestone powder (LSP), cement kiln dust (CKD), and pulverized steel slag (PSS), all of which are abundantly available in Saudi Arabia at little or no cost, were employed in the development of the UHPC mixtures. A base mixture of UHPC without replacement of silica fume or sand was selected and a total of 24 trial mixtures of UHPC were prepared using different percentages of NP, FA, LSP, CKD, and PSS, partially replacing the silica fume and sand. Flow and 28-d compressive strength of each UHPC mixture were determined to finally select those mixtures, which satisfied the minimum flow and strength criteria of UHPC. The test results showed that the utilization of NP, FA, LSP, CKD, and PSS in production of UHPC is possible with acceptable flow and strength. A total of 10 UHPC mixtures were identified with flow and strength equal to or more than the minimum required. PMID:25197709

  20. Development of UHPC mixtures utilizing natural and industrial waste materials as partial replacements of silica fume and sand.

    PubMed

    Ahmad, Shamsad; Hakeem, Ibrahim; Maslehuddin, Mohammed

    2014-01-01

    In the exploratory study presented in this paper, an attempt was made to develop different mixtures of ultrahigh performance concrete (UHPC) using various locally available natural and industrial waste materials as partial replacements of silica fume and sand. Materials such as natural pozzolana (NP), fly ash (FA), limestone powder (LSP), cement kiln dust (CKD), and pulverized steel slag (PSS), all of which are abundantly available in Saudi Arabia at little or no cost, were employed in the development of the UHPC mixtures. A base mixture of UHPC without replacement of silica fume or sand was selected and a total of 24 trial mixtures of UHPC were prepared using different percentages of NP, FA, LSP, CKD, and PSS, partially replacing the silica fume and sand. Flow and 28-d compressive strength of each UHPC mixture were determined to finally select those mixtures, which satisfied the minimum flow and strength criteria of UHPC. The test results showed that the utilization of NP, FA, LSP, CKD, and PSS in production of UHPC is possible with acceptable flow and strength. A total of 10 UHPC mixtures were identified with flow and strength equal to or more than the minimum required.

  1. Magnetic Memory from Site Isolated Dy(III) on Silica Materials

    PubMed Central

    2017-01-01

    Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy(III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy(III) siloxide complex on partially dehydroxylated silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, “bare” Dy(III) sites bound to the silica surface. During the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence. PMID:28386602

  2. Effects of quenching, irradiation, and annealing processes on the radiation hardness of silica fiber cladding materials (I)

    NASA Astrophysics Data System (ADS)

    Wen, Jianxiang; Gong, Renxiang; Xiao, Zhongyin; Luo, Wenyun; Wu, Wenkai; Luo, Yanhua; Peng, Gang-ding; Pang, Fufei; Chen, Zhenyi; Wang, Tingyun

    2016-07-01

    Silica optical fiber cladding materials were experimentally treated by a series of processes. The treatments involved quenching, irradiation, followed by annealing and subsequent re-irradiation, and they were conducted in order to improve the radiation hardness. The microstructural properties of the treated materials were subsequently investigated. Following the treatment of the optical fiber cladding materials, the results from the electron spin resonance (ESR) analysis demonstrated that there was a significant decrease in the radiation-induced defect structures. The ESR signals became significantly weaker when the samples were annealed at 1000 °C in combination with re-irradiation. In addition, the microstructure changes within the silica optical fiber cladding material were also analyzed using Raman spectroscopy. The experimental results demonstrate that the Sisbnd Osbnd Si bending vibrations at ω3 = 800-820 cm-1 and ω4 = 1000-1200 cm-1 (with longitudinal optical (LO) and transverse optical (TO) splitting bands) were relatively unaffected by the quenching, irradiation, and annealing treatments. In particular, the annealing process resulted in the disappearance of the defect centers; however, the LO and TO modes at the ω3 and ω4 bands were relatively unchanged. With the additional support of the ESR test results, we can conclude that the combined treatment processes can significantly enhance the radiation hardness properties of the optical fiber cladding materials.

  3. Effect of silica coating and silane surface treatment on the bond strength of soft denture liner to denture base material

    PubMed Central

    ATSÜ, Saadet; KESKİN, Yasemin

    2013-01-01

    Objective This study investigated the effects of different surface treatments on the tensile bond strength of an autopolymerizing silicone denture liner to a denture base material after thermocycling. Material and Methods Fifty rectangular heat-polymerized acrylic resin (QC-20) specimens consisting of a set of 2 acrylic blocks were used in the tensile test. Specimens were divided into 5 test groups (n=10) according to the bonding surface treatment as follows: Group A, adhesive treatment (Ufi Gel P adhesive) (control); Group S, sandblasting using 50-µm Al2O3; Group SCSIL, silica coating using 30-µm Al2O3 modified by silica and silanized with silane agent (CoJet System); Group SCA, silica coating and adhesive application; Group SCSILA, silica coating, silane and adhesive treatment. The 2 PMMA blocks were placed into molds and the soft lining materials (Ufi Gel P) were packed into the space and polymerized. All specimens were thermocycled (5,000 cycles) before the tensile test. Bond strength data were analyzed using 1-way ANOVA and Duncan tests. Fracture surfaces were observed by scanning electron microscopy. X-ray photoelectron spectrometer (XPS) and Fourier Transform Infrared spectrometer (FTIR) analysis were used for the chemical analysis and a profilometer was used for the roughness of the sample surfaces. Results The highest bond strength test value was observed for Group A (1.35±0.13); the lowest value was for Group S (0.28±0.07) and Group SCSIL (0.34±0.03). Mixed and cohesive type failures were seen in Group A, SCA and SCSILA. Group S and SCSIL showed the least silicone integrations and the roughest surfaces. Conclusion Sandblasting, silica coating and silane surface treatments of the denture base resin did not increase the bond strength of the silicone based soft liner. However, in this study, the chemical analysis and surface profilometer provided interesting insights about the bonding mechanism between the denture base resin and silicone soft liner

  4. Models of metal binding structures in fulvic acid from the Suwannee River, Georgia

    SciTech Connect

    Leenheer, J.A.; Brown, G.K.; Cabaniss, S.E.; MacCarthy, P.

    1998-08-15

    Fulvic acid, isolated from the Suwannee River, Georgia, was assessed for its ability to bind Ca{sup 2+}, Cd{sup 2+}, Cu{sup 2+}, Ni{sup 2+}, and Zn{sup 2+} ions at pH 6 before and after extensive fractionation that was designed to reveal the nature of metal binding functional groups. The binding constant for Ca{sup 2+} ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purpose of building quantitative average model structures. The metal binding fraction was characterized by quantitative {sup 13}C NMR, {sup 1}H NMR, and FT-IR spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that carboxyl groups were clustered in short-chain aliphatic dibasic acid structures. The Ca{sup 2+} binding data suggested that ether-substituted oxysuccinic acid structures are good models for the metal binding sites at pH 6. Structural models were derived based upon oxidation and photolytic rearrangements of cutin, lignin, and tannin precursors. These structural models rich in substituted dibasic acid structures revealed polydentate binding sites with the potential for both inner-sphere and outer-sphere type binding. The majority of the fulvic acid molecule was involved with metal binding rather than a small substructural unit.

  5. Metal-binding sites are designed to achieve optimal mechanical and signaling properties

    PubMed Central

    Dutta, Anindita; Bahar, Ivet

    2010-01-01

    Many proteins require bound metals to achieve their function. We take advantage of increasing structural data on metal-binding proteins to elucidate three properties: the involvement of metal-binding sites in the global dynamics of the protein, predicted by elastic network models, their exposure/burial to solvent, and their signal-processing properties indicated by Markovian stochastics analysis. Systematic analysis of a dataset of 145 structures reveals that the residues that coordinate metal ions enjoy remarkably efficient and precise signal transduction properties. These properties are rationalized in terms of their physical properties: participation in hinge sites that control the softest modes collectively accessible to the protein and occupancy of central positions minimally exposed to solvent. Our observations suggest that metal-binding sites may have been evolutionary selected to achieve optimum allosteric communication. They also provide insights into basic principles for designing metal-binding sites, which are verified to be met by recently designed de novo metal-binding proteins. PMID:20826340

  6. Subunit dissociation and metal binding by Escherichia coli apo-manganese superoxide dismutase.

    PubMed

    Whittaker, Mei M; Lerch, Thomas F; Kirillova, Olga; Chapman, Michael S; Whittaker, James W

    2011-01-15

    Metal binding by apo-manganese superoxide dismutase (apo-MnSOD) is essential for functional maturation of the enzyme. Previous studies have demonstrated that metal binding by apo-MnSOD is conformationally gated, requiring protein reorganization for the metal to bind. We have now solved the X-ray crystal structure of apo-MnSOD at 1.9Å resolution. The organization of active site residues is independent of the presence of the metal cofactor, demonstrating that protein itself templates the unusual metal coordination geometry. Electrophoretic analysis of mixtures of apo- and (Mn₂)-MnSOD, dye-conjugated protein, or C-terminal Strep-tag II fusion protein reveals a dynamic subunit exchange process associated with cooperative metal binding by the two subunits of the dimeric protein. In contrast, (S126C) (SS) apo-MnSOD, which contains an inter-subunit covalent disulfide-crosslink, exhibits anti-cooperative metal binding. The protein concentration dependence of metal uptake kinetics implies that protein dissociation is involved in metal binding by the wild type apo-protein, although other processes may also contribute to gating metal uptake. Protein concentration dependent small-zone size exclusion chromatography is consistent with apo-MnSOD dimer dissociation at low protein concentration (K(D)=1×10⁻⁵ M). Studies on metal uptake by apo-MnSOD in Escherichia coli cells show that the protein exhibits similar behavior in vivo and in vitro.

  7. Validating metal binding sites in macromolecule structures using the CheckMyMetal web server

    PubMed Central

    Zheng, Heping; Chordia, Mahendra D.; Cooper, David R.; Chruszcz, Maksymilian; Müller, Peter; Sheldrick, George M.

    2015-01-01

    Metals play vital roles in both the mechanism and architecture of biological macromolecules. Yet structures of metal-containing macromolecules where metals are misidentified and/or suboptimally modeled are abundant in the Protein Data Bank (PDB). This shows the need for a diagnostic tool to identify and correct such modeling problems with metal binding environments. The "CheckMyMetal" (CMM) web server (http://csgid.org/csgid/metal_sites/) is a sophisticated, user-friendly web-based method to evaluate metal binding sites in macromolecular structures in respect to 7350 metal binding sites observed in a benchmark dataset of 2304 high resolution crystal structures. The protocol outlines how the CMM server can be used to detect geometric and other irregularities in the structures of metal binding sites and alert researchers to potential errors in metal assignment. The protocol also gives practical guidelines for correcting problematic sites by modifying the metal binding environment and/or redefining metal identity in the PDB file. Several examples where this has led to meaningful results are described in the anticipated results section. CMM was designed for a broad audience—biomedical researchers studying metal-containing proteins and nucleic acids—but is equally well suited for structural biologists to validate new structures during modeling or refinement. The CMM server takes the coordinates of a metal-containing macromolecule structure in the PDB format as input and responds within a few seconds for a typical protein structure modeled with a few hundred amino acids. PMID:24356774

  8. Subunit Dissociation and Metal Binding by Escherichia coli apo-Manganese Superoxide Dismutase

    PubMed Central

    Whittaker, Mei M.; Lerch, Thomas F.; Kirillova, Olga; Chapman, Michael S.; Whittaker, James W.

    2010-01-01

    Metal binding by apo-manganese superoxide dismutase (apo-MnSOD) is essential for functional maturation of the enzyme. Previous studies have demonstrated that metal binding by apo-MnSOD is conformationally gated, requiring protein reorganization for the metal to bind. We have now solved the X-ray crystal structure of apo-MnSOD at 1.9 Å resolution. The organization of active site residues is independent of the presence of the metal cofactor, demonstrating that protein itself templates the unusual metal coordination geometry. Electrophoretic analysis of mixtures of apo- and (Mn2)-MnSOD, dye-conjugated protein, or C-terminal Strep-tag II fusion protein reveals a dynamic subunit exchange process associated with cooperative metal binding by the two subunits of the dimeric protein. In contrast, (S126C) (SS) apo-MnSOD, which contains an inter-subunit covalent disulfide crosslink, exhibits anticooperative metal binding. The protein concentration dependence of metal uptake kinetics implies that protein dissociation is involved in metal binding by the wild type apo-protein, although other processes may also contribute to gating metal uptake. Protein concentration dependent small-zone size exclusion chromatography is consistent with apo-MnSOD dimer dissociation at low protein concentration (KD = 1×10−6 M). Studies on metal uptake by apo-MnSOD in Escherichia coli cells show that the protein exhibits similar behavior in vivo and in vitro. PMID:21044611

  9. Development of cholesterol biosensor with high sensitivity using dual-enzyme immobilization into the mesoporous silica materials

    NASA Astrophysics Data System (ADS)

    Murai, Kazuki; Kato, Katsuya

    2011-12-01

    Mesoporous silica (MPS) materials with different pore diameters were synthesized by a sol-gel method where organic templates such as cationic surfactant (cetyltrimethylammonium bromide) and triblock co-polymer of (poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (Pluronic P123, EO 20PO 70EO 20)), were used. MPS surface was organo-functionalized using a silane coupling reagent (ethyl-, phenyl-, or 3-mercaptpropyltriethoxysilane). Dual-enzyme, cholesterol esterase (10.0 nm × 5.4 nm × 11.0 nm) and cholesterol oxidase (6.8 nm × 8.5 nm × 8.8 nm), was immobilized on MPS materials by physical adsorption. Amount of dual-enzyme immobilized on all MPS materials, having a different pore size (2.7, 6.4, 12.4, 14.7, and 22.6 nm), and organo-functionalized MPS was similar (CE: 1.5 mg/mg silica and CO: 0.01 mg/mg silica). High activity of dual-enzyme was obtained by adjacently immobilizing on MPS materials. Its activity on MPS-2 (pore diameter: 6.4 nm) or MPS-5 (pore diameter: 22.6 nm) showed approximately 60% of native activity. Moreover, dual-enzyme immobilized on MPS with highly hydrophobic organo-functional groups (phenyl- or mercaptopropyl-group) exhibited higher activity than that on no-substituted MPS. Relative activity of dual-enzyme immobilized on organo-functionalized MPS-2 increased from 58% to 93%, under the optimum conditions.

  10. Preparation of antibacterial composite material of natural rubber particles coated with silica and titania

    NASA Astrophysics Data System (ADS)

    Wisutiratanamanee, Apisit; Poompradub, Sirilux; Poochinda, Kunakorn

    2014-06-01

    Silica coating, followed by titania coating, was performed over spray-dried natural rubber (NR) compound for physical and anti-bacterial characterizations. Titania has a strong photo-oxidative catalytic property, which can disinfect bacteria, but may degrade NR. Therefore, silica coating was intended to form a barrier between NR and titania. First, NR particles were prepared by spray-drying of NR compound latex, formulated for household glove products, mixed with sodium dodecyl sulfate (SDS) to reduce particle agglomeration. The factorial experimental design was employed to investigate the effects of nozzle flow rate (500-700 Lh-1), inlet air temperature (110-150 °C), SDS content (35-55 phr) and mass flow rate (1.2-1.7 g rubber/min) on NR yield and moisture content. Then, the NR compound particles prepared at the optimum condition were coated with silica, using tetraethoxysilane (TEOS) as the precursor, by chemical vapor deposition (CVD) at 60 °C for 2-48 hours. Next, the particles were coated with titania using titanium tetrafluoride (TiF4) by liquid phase deposition (LPD) at 60 ºC for 4-8 hours. The NR composites were characterized for surface morphology by SEM, silica and titania content by TGA and EDX. The NR composites were found to cause more than 99% reduction of Escherichia coli and Staphylococcus aureus under 1-hour exposure to natural light.

  11. Single Source Molecular Precursors to Niobia-Silica and NiobiumPhosphate Materials

    SciTech Connect

    Lugmair, Claus G.; Tilley, T. Don

    2006-01-13

    The molecular precursors Nb(OiPr)2[OSi(OtBu)3]3 and {l_brace}Nb(OiPr)4[O2P(OtBu)2]{r_brace}2 have been prepared. The first compound undergoes facile thermal conversion to high surface area, acidic niobia silica, whereas the second one thermally decomposes to a low surface area niobium phosphate.

  12. Synthesis of Silica-Carbon Nanotube Composite Materials and Their Application for Laser Systems

    NASA Astrophysics Data System (ADS)

    Pilipavicius, J.; Sakalauskas, D.; Beganskiene, A.; Kareiva, A.

    2012-08-01

    Currently, fabrication of CNT and polymer composites for saturable absorbers is very popular. But due to nature of organic polymer matrix, these composites are unstable on higher temperatures or in high energy light exposition. Therefore a sol-gel process for the fabrication for inorganic (i.e. silica) or semi-organic (organic-modified silica) matrix can be a promising way to produce photo-chemically and thermally stable CNT composites. In this work we investigated SWCNT's solubility in ethanol using different surfactants - Triton, polyvinylpyrrolidone, and Poly(4-vinylpyridine). Most stable colloidal solution was obtained using a P4VP as surfactant - solutions were stable up to 6 weeks. Therefore this surfactant was used for the fabrication of SWCNT/Silica composite coatings. SWCNT's was directly dispensed in a colloidal silica sol and coatings made by spin-coating technique. Samples were investigated under optical, atomic force microscopy methods, and optical non-linearity was measured. Thermal stability was investigated using Raman spectroscopy.

  13. Naphthopyran-Based Silica Nanoparticles as New High-Performance Photoresponsive Materials.

    PubMed

    Pinto, Tânia V; Costa, Paula; Sousa, Céu M; Sousa, Carlos A D; Monteiro, Andreia; Pereira, Clara; Soares, Olívia Salomé G P; Silva, Carla S M; Pereira, Manuel Fernando R; Coelho, Paulo J; Freire, Cristina

    2016-03-23

    Hybrid nanomaterials based on the covalent grafting of silylated naphthopyrans (NPTs) onto silica nanoparticles (SiO2 NPs) were successfully prepared and studied as new photochromic materials. They were prepared by a two-step protocol consisting of (i) NPTs (derivatives from 2H-naphtho[1,2-b]pyran (2H-NPT) and 3H-naphtho[2,1-b]pyran (3H-NPT)) silylation by a microwave-assisted reaction between hydroxyl-substituted NPTs and 3-(triethoxysilyl)propyl isocyanate, followed by (ii) covalent post-grafting onto SiO2 NPs. In order to study the role of the silylation step, the analogous non-silylated nanomaterials were also prepared by direct adsorption of NPTs. The characterization techniques confirmed the successful NPTs silylation and subsequent grafting to SiO2 NPs. All SiO2-based nanomaterials revealed photoswitching behavior, following a biexponential decay. The SiO2 NPs functionalized with silylated 3H-NPTs (SiO2@S3 and SiO2@S4) presented the most promising photochromic properties, showing fast coloration/decoloration kinetics (coloring in 1 min under UV irradiation and fading in only 2 min) and high values of total color difference (ΔE*ab = 30-50). Also, the 2H-NPTs-based SiO2 NPs (SiO2@S1 and SiO2@S2) presented fast coloration and good color contrasts (ΔE*ab = 54), but slower fading kinetic rates, taking more than 2 h to return to their initial color. In contrast, the SiO2 NPs functionalized with non-silylated NPTs (SiO2@1 and SiO2@3) showed weaker color contrasts (ΔE*ab = 6-10) and slower fading kinetics, proving that the NPT silylation step was crucial to enhance the photochromic behavior of SiO2 NPs based on NPTs. Furthermore, the silylated-based nanomaterials showed good photostability upon prolonged UV light exposure, keeping their photochromic performance unchanged for at least 12 successive UV/dark cycles, anticipating interesting technological applications in several areas.

  14. Silver-coated silica beads applicable as core materials of dual-tagging sensors operating via SERS and MEF.

    PubMed

    Kim, Kwan; Lee, Yoon Mi; Lee, Hyang Bong; Shin, Kuan Soo

    2009-10-01

    We have developed dual-tagging sensors, operating via both surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF), composed of silver-coated silica beads onto which were deposited SERS markers and dye-grafted polyelectrolytes, for multiplex immunoassays. Initially, a very simple electroless-plating method was applied to prepare Ag-coated silica beads. The Raman markers were then assembled onto the Ag-coated silica beads, after which they were brought to stabilization by the layer-by-layer deposition of anionic and cationic polyelectrolytes including a dye-grafted polyelectrolyte. In the final stage, the dual-tagging sensors were assembled onto them with specific antibodies (antihuman-IgG or antirabbit-IgG) to detect target antigens (human-IgG or rabbit-IgG). The MEF signal was used as an immediate indicator of molecular recognition, while the SERS signals were subsequently used as the signature of specific molecular interactions. For this reason, these materials should find wide application, especially in the areas of biological sensing and recognition that rely heavily on optical and spectroscopic properties.

  15. CheckMyMetal: a macromolecular metal-binding validation tool

    PubMed Central

    Porebski, Przemyslaw J.

    2017-01-01

    Metals are essential in many biological processes, and metal ions are modeled in roughly 40% of the macromolecular structures in the Protein Data Bank (PDB). However, a significant fraction of these structures contain poorly modeled metal-binding sites. CheckMyMetal (CMM) is an easy-to-use metal-binding site validation server for macromolecules that is freely available at http://csgid.org/csgid/metal_sites. The CMM server can detect incorrect metal assignments as well as geometrical and other irregularities in the metal-binding sites. Guidelines for metal-site modeling and validation in macromolecules are illustrated by several practical examples grouped by the type of metal. These examples show CMM users (and crystallographers in general) problems they may encounter during the modeling of a specific metal ion. PMID:28291757

  16. CheckMyMetal: a macromolecular metal-binding validation tool.

    PubMed

    Zheng, Heping; Cooper, David R; Porebski, Przemyslaw J; Shabalin, Ivan G; Handing, Katarzyna B; Minor, Wladek

    2017-03-01

    Metals are essential in many biological processes, and metal ions are modeled in roughly 40% of the macromolecular structures in the Protein Data Bank (PDB). However, a significant fraction of these structures contain poorly modeled metal-binding sites. CheckMyMetal (CMM) is an easy-to-use metal-binding site validation server for macromolecules that is freely available at http://csgid.org/csgid/metal_sites. The CMM server can detect incorrect metal assignments as well as geometrical and other irregularities in the metal-binding sites. Guidelines for metal-site modeling and validation in macromolecules are illustrated by several practical examples grouped by the type of metal. These examples show CMM users (and crystallographers in general) problems they may encounter during the modeling of a specific metal ion.

  17. A systematic typology for negative Poisson's ratio materials and the prediction of complete auxeticity in pure silica zeolite JST.

    PubMed

    Siddorn, M; Coudert, F-X; Evans, K E; Marmier, A

    2015-07-21

    Single crystals can commonly have negative Poisson's ratio in a few directions; however more generalised auxeticity is rarer. We propose a typology to distinguish auxetic materials. We characterise numerous single crystals and demonstrate that partial auxeticity occurs for around 37%. We find average auxeticity to be limited to α-cristobalite and no example of complete auxeticity. We simulate two hundreds pure silica zeolites with empirical potentials and quantum chemistry methods, and for the first time identify complete auxeticity in a zeolite network, JST.

  18. Shock-wave compression of silica gel as a model material for comets

    NASA Astrophysics Data System (ADS)

    Arasuna, Akane; Okuno, Masayuki; Chen, Liliang; Mashimo, Tsutomu; Okudera, Hiroki; Mizukami, Tomoyuki; Arai, Shoji

    2016-07-01

    A shock-wave compression experiment using synthesized silica gel was investigated as a model for a comet impact event on the Earth's surface. The sample shocked at 20.7 GPa showed considerable structural changes, a release of water molecules, and the dehydration of silanol (Si-OH) that led to the formation of a new Si-O-Si network structure containing larger rings (e.g., six-membered ring of SiO4 tetrahedra). The high aftershock temperature at 20.7 GPa, which could be close to 800 °C, influenced the sample structure. However, some silanols, which were presumed to be the mutually hydrogen-bonded silanol group, remained at pressures >20.7 GPa. This type of silanol along with a small number of water molecules may remain even after shock compression at 30.9 GPa, although the intermediate structure of the sample recovered was similar to that of silica glass.

  19. Synthesis and physicochemical study of ZSM-5 high-silica zeolite from natural raw materials

    NASA Astrophysics Data System (ADS)

    Aliev, A. M.; Mamedova, U. A.; Samedov, Kh. R.; Sarydzhanov, A. A.; Agaeva, R. Yu.

    2011-02-01

    ZSM-5 high-silica zeolite was obtained from metakaolinite, Dzhenranchel'sk volcanic ash, and silica gel at T = 150-220°C, pH 9-13, and τ = 48-240 h with the use of an organic structure-forming additive, butanediol-1,4, in an alkaline solution. Optimum conditions for the synthesis of ZSM-5 zeolite were found ( T = 200°C, pH 10, τ = 144 h). The catalytic properties of its H-form in vapor-phase esterification of acetic acid ( I) with ethanol ( II) were studied at 140-180°C and a I: II molar ratio from 1 to 2. Synthesized HZSM-5 showed high activity and selectivity in this reaction.

  20. Raspberry-like PS/CdTe/Silica Microspheres for Fluorescent Superhydrophobic Materials.

    PubMed

    Chang, Jinghui; Zang, Linlin; Wang, Cheng; Sun, Liguo; Chang, Qing

    2016-12-01

    Superhydrophobic particulate films were fabricated via deposition of raspberry-like fluorescent PS/CdTe/silica microspheres on clean glass substrates and surface modification. Particularly, the fluorescent microspheres were prepared by a kind of modified strategy, namely introducing poly (acrylic acid)-functionalized polystyrene microspheres and thiol-stabilized CdTe quantum dots into a hydrolysis reaction of tetraethoxysilane simultaneously. And through adjusting the reaction parameters, the polystyrene spheres with two particle sizes and three colors of CdTe quantum dots aqueous solution were obtained. Consequently, raspberry-like microspheres consist of polystyrene cores and the composite shells of CdTe quantum dots and silica. These microspheres possess a fluorescent characteristic and form a hierarchical dual roughness which was conductive to superhydrophobicity, and the hydrophobic tests also showed the contact angles of water droplets on the surface of the raspberry-like microspheres which were over 160° at room temperature.

  1. Raspberry-like PS/CdTe/Silica Microspheres for Fluorescent Superhydrophobic Materials

    NASA Astrophysics Data System (ADS)

    Chang, Jinghui; Zang, Linlin; Wang, Cheng; Sun, Liguo; Chang, Qing

    2016-02-01

    Superhydrophobic particulate films were fabricated via deposition of raspberry-like fluorescent PS/CdTe/silica microspheres on clean glass substrates and surface modification. Particularly, the fluorescent microspheres were prepared by a kind of modified strategy, namely introducing poly (acrylic acid)-functionalized polystyrene microspheres and thiol-stabilized CdTe quantum dots into a hydrolysis reaction of tetraethoxysilane simultaneously. And through adjusting the reaction parameters, the polystyrene spheres with two particle sizes and three colors of CdTe quantum dots aqueous solution were obtained. Consequently, raspberry-like microspheres consist of polystyrene cores and the composite shells of CdTe quantum dots and silica. These microspheres possess a fluorescent characteristic and form a hierarchical dual roughness which was conductive to superhydrophobicity, and the hydrophobic tests also showed the contact angles of water droplets on the surface of the raspberry-like microspheres which were over 160° at room temperature.

  2. Catalyst free silica templated porous carbon nanoparticles from bio-waste materials.

    PubMed

    Kumar, Anuj; Hegde, Gurumurthy; Manaf, Shoriya Aruni Bt Abdul; Ngaini, Z; Sharma, K V

    2014-10-28

    Porous Carbon Nanoparticles (PCNs) with well-developed microporosity were obtained from bio-waste oil palm leaves (OPL) using single step pyrolysis in nitrogen atmosphere at 500-600 °C in tube-furnace without any catalysis support. The key approach was using silica (SiO2) bodies of OPL as a template in the synthesis of microporous carbon nanoparticles with very small particle sizes of 35-85 nm and pore sizes between 1.9-2 nm.

  3. Electrospun Ultrafine Fiber Composites Containing Fumed Silica: From Solution Rheology to Materials with Tunable Wetting.

    PubMed

    Dufficy, Martin K; Geiger, Mackenzie T; Bonino, Christopher A; Khan, Saad A

    2015-11-17

    Fumed silica (FS) particles with hydrophobic (R805) or hydrophilic (A150) surface functionalities are incorporated in polyacrylonitrile (PAN) fibers by electrospinning to produce mats with controlled wettability. Rheological measurements are conducted to elucidate the particle-polymer interactions and characterize the system while microscopic and analytic tools are used to examine FS location within both fibers and films to aid in the fundamental understanding of wetting behavior. Unlike traditional polymers, we find these systems to be gel-like, yet electrospinnable; the fumed silica networks break down into smaller aggregates during the electrospinning process and disperse both within and on the surface of the fibers. Composite nanofiber mats containing R805 FS exhibit an apparent contact angle over 130° and remain hydrophobic over 30 min, while similar mats with A150 display rapid surface-wetting with a static contact angle of ∼30°. Wicking experiments reveal that the water absorption properties can be further manipulated, with R805 FS-impregnated mats taking up only 8% water relative to mat weight in 15 min. In contrast, PAN fibers containing A150 FS absorb 425% of water in the same period, even more than the pure PAN fiber (371%). The vastly different responses to water demonstrate the versatility of FS in surface modification, especially for submicron fibrous mats. The role of fumed silica in controlling wettability is discussed in terms of their surface functionality, placement on nanofibers and induced surface roughness.

  4. Titania-silica materials from the molecular precursor Ti[OSi(O{sup t}Bu){sub 3}]{sub 4}: Selective epoxidation catalysts

    SciTech Connect

    Coles, M.P.; Lugmair, C.G.; Terry, K.W.; Tilley, T.D.

    2000-01-01

    The tris(tert-butoxy)siloxy complex Ti[OSi(O{sup t}Bu){sub 3}]{sub 4} was pyrolytically converted at low temperatures to the theoretical yield of homogeneous TiO{sub 2}{center{underscore}dot}4SiO{sub 2} materials. The complex also serves as a soluble model for isolated, tetrahedral titanium atoms in a silica matrix. The molecular route to homogeneous titania-silica materials described here represents an alternative to the sol-gel method, affording materials with surface areas comparable to those of related aerogels and moderate-to-excellent activities for the epoxidation of cyclohexene.

  5. Adsorption of CO{sub 2} on microporous materials. 1: On activated carbon and silica gel

    SciTech Connect

    Berlier, K.; Frere, M.

    1997-05-01

    Adsorption isotherms of carbon dioxide (CO{sub 2}) at temperatures ranging from 278 K to 328 K (seven temperatures) and at pressures up to 3300 kPa on activated carbon and on silica gel are presented. These experimental results are useful as they allow one to broaden, the T, P domain of CO{sub 2} adsorption. These data, together with more classical ones (obtained at low temperature and low pressure (Berlier and Frere, 1996)), will make possible the test of theoretical developments for the prediction of adsorption isotherms in a range of temperature and pressure conditions never studied before.

  6. Metal binding studies and EPR spectroscopy of the manganese transport regulator MntR.

    PubMed

    Golynskiy, Misha V; Gunderson, William A; Hendrich, Michael P; Cohen, Seth M

    2006-12-26

    Manganese transport regulator (MntR) is a member of the diphtheria toxin repressor (DtxR) family of transcription factors that is responsible for manganese homeostasis in Bacillus subtilis. Prior biophysical studies have focused on the metal-mediated DNA binding of MntR [Lieser, S. A., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2003) Biochemistry 42, 12634-12642], as well as metal stabilization of the MntR structure [Golynskiy, M. V., Davis, T. C., Helmann, J. D., and Cohen, S. M. (2005) Biochemistry 44, 3380-3389], but only limited data on the metal-binding affinities for MntR are available. Herein, the metal-binding affinities of MntR were determined by using electron paramagnetic resonance (EPR) spectroscopy, as well as competition experiments with the fluorimetric dyes Fura-2 and Mag-fura-2. MntR was not capable of competing with Fura-2 for the binding of transition metal ions. Therefore, the metal-binding affinities and stoichiometries of Mag-fura-2 for Mn2+, Co2+, Ni2+, Zn2+, and Cd2+ were determined and utilized in MntR/Mag-fura-2 competition experiments. The measured Kd values for MntR metal binding are comparable to those reported for DtxR metal binding [Kd from 10(-)7 to 10(-4) M; D'Aquino, J. A., et al. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 18408-18413], AntR [a homologue from Bacillus anthracis; Sen, K. I. et al. (2006) Biochemistry 45, 4295-4303], and generally follow the Irving-Williams series. Direct detection of the dinuclear Mn2+ site in MntR with EPR spectroscopy is presented, and the exchange interaction was determined, J = -0.2 cm-1. This value is lower in magnitude than most known dinuclear Mn2+ sites in proteins and synthetic complexes and is consistent with a dinuclear Mn2+ site with a longer Mn...Mn distance (4.4 A) observed in some of the available crystal structures. MntR is found to have a surprisingly low binding affinity (approximately 160 microM) for its cognate metal ion Mn2+. Moreover, the results of DNA binding studies in

  7. Flexibility of the metal-binding region in apo-cupredoxins

    PubMed Central

    Zaballa, María-Eugenia; Abriata, Luciano A.; Donaire, Antonio; Vila, Alejandro J.

    2012-01-01

    Protein-mediated electron transfer is an essential event in many biochemical processes. Efficient electron transfer requires the reorganization energy of the redox event to be minimized, which is ensured by the presence of rigid donor and acceptor sites. Electron transfer copper sites are present in the ubiquitous cupredoxin fold, able to bind one or two copper ions. The low reorganization energy in these metal centers has been accounted for by assuming that the protein scaffold creates an entatic/rack-induced state, which gives rise to a rigid environment by means of a preformed metal chelating site. However, this notion is incompatible with the need for an exposed metal-binding site and protein–protein interactions enabling metallochaperone-mediated assembly of the copper site. Here we report an NMR study that reveals a high degree of structural heterogeneity in the metal-binding region of the nonmetallated CuA-binding cupredoxin domain, arising from microsecond to second dynamics that are quenched upon metal binding. We also report similar dynamic features in apo-azurin, a paradigmatic blue copper protein, suggesting a general behavior. These findings reveal that the entatic/rack-induced state, governing the features of the metal center in the copper-loaded protein, does not require a preformed metal-binding site. Instead, metal binding is a major contributor to the rigidity of electron transfer copper centers. These results reconcile the seemingly contradictory requirements of a rigid, occluded center for electron transfer, and an accessible, dynamic site required for in vivo copper uptake. PMID:22645370

  8. New nanostructured silica incorporated with isolated Ti material for the photocatalytic conversion of CO2 to fuels

    PubMed Central

    2014-01-01

    In this work, new nanoporous silica (Korea Advanced Institute of Science and Technology-6 (KIT-6)-dried or KIT-6-calcined) incorporated with isolated Ti materials with different Si/Ti ratios (Si/Ti = 200, 100, and 50) has been synthesized and investigated to establish photocatalytic reduction of CO2 in the presence of H2O vapors. The properties of the materials have been characterized through N2 adsorption/desorption, UV-vis, TEM, FT-IR, and XPS analysis techniques. The intermediate amount of the isolated Ti (Si/Ti = 100) has resulted to be more uniformly distributed on the surface and within the three-dimensional pore structure of the KIT-6 material, without its structure collapsing, than the other two ratios (Si/Ti = 200 and 50). However, titania agglomerates have been observed to have formed due to the increased Ti content (Si/Ti = 50). The Ti-KIT-6 (calcined) materials in the reaction showed higher activity than the Ti-KIT-6 (dried) materials, which produced CH4, H2, CO, and CH3OH (vapors) as fuel products. The Ti-KIT-6 (Si/Ti = 100) material also showed more OH groups, which are useful to obtain a higher production rate of the products, particularly methane, which was even higher than the rate of the best commercial TiO2 (Aeroxide P25, Evonik Industries AG, Essen, Germany) photocatalyst. PMID:24690396

  9. Oxidized dextran facilitated synthesis of a silica-based concanavalin a material for lectin affinity enrichment of glycoproteins/glycopeptides.

    PubMed

    Liu, Yujie; Fu, Dongmei; Yu, Long; Xiao, Yuansheng; Peng, Xiaojun; Liang, Xinmiao

    2016-07-15

    Lectin affinity chromatography (LAC) is an important enrichment technique in glycoproteomics analysis. In order to improve the effectiveness of enrichment, it is necessary to develop LAC materials with high specificity and efficiency. Herein, using oxidized dextran as the spacer, a silica-based concanavalin A material (SiO2-ODex Con A) was synthesized to enrich glycoproteins/glycopeptides. For comparison, the SiO2-Ald Con A material was synthesized using conventional (3-glycidoxypropyl) triethoxysilane (GPMS) as the initial spacer arm. The analytical merits of both Con A materials, such as non-specific adsorption, binding capacity and trapping efficiency, have been evaluated using ovalbumin. Under high performance liquid affinity chromatography (HPLAC) mode, the SiO2-ODex Con A material was highly effective in the enrichment of glycoproteins/glycopeptides attached to high-mannose-type and bi-antennary complex-type glycans. The promising potential of the SiO2-ODex Con A material was demonstrated by selective fractionation of glycoproteins from complex biological samples for glycosylation analysis.

  10. Time-Resolved Imaging of Material Response Following Laser-Induced Breakdown in the Bulk and Surface of Fused Silica

    SciTech Connect

    Raman, R N; Negres, R A; DeMange, P; Demos, S G

    2010-02-04

    Optical components within high energy laser systems are susceptible to laser-induced material modification when the breakdown threshold is exceeded or damage is initiated by pre-existing impurities or defects. These modifications are the result of exposure to extreme conditions involving the generation of high temperatures and pressures and occur on a volumetric scale of the order of a few cubic microns. The response of the material following localized energy deposition, including the timeline of events and the individual processes involved during this timeline, is still largely unknown. In this work, we investigate the events taking place during the entire timeline in both bulk and surface damage in fused silica using a set of time-resolved microscopy systems. These microscope systems offer up to 1 micron spatial resolution when imaging static or dynamic effects, allowing for imaging of the entire process with adequate temporal and spatial resolution. These systems incorporate various pump-probe geometries designed to optimize the sensitivity for detecting individual aspects of the process such as the propagation of shock waves, near-surface material motion, the speed of ejecta, and material transformations. The experimental results indicate that the material response can be separated into distinct phases, some terminating within a few tens of nanoseconds but some extending up to about 100 microseconds. Overall the results demonstrate that the final characteristics of the modified region depend on the material response to the energy deposition and not on the laser parameters.

  11. Method 1664, Revision A: n-hexane extractable material (HEM; oil and grease) and silica gel treated n-hexane extractable material (SGT-HEM; non-polar material) by extraction and gravimetry

    SciTech Connect

    Not Available

    1999-02-01

    This method is for determination of n-hexane extractable material (HEM; oil and grease) and n-hexane extractable material that is not adsorbed by silica gel (SGT-HEM; non-polar material) in surface and saline waters and industrial and domestic aqueous wastes. Extractable materials that may be determined are relatively non-volatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, greases, and related materials. This method is capable of measuring HEM and SGT-HEM in the range of 5 to 1000 mg/L, and may be extended to higher levels by analysis of a smaller sample volume collected separately.

  12. Imaging System to Measure Kinetics of Material Cluster Ejection During Exit-Surface Damage Initiation and Growth in Fused Silica

    SciTech Connect

    Raman, R N; Negres, R A; Demos, S G

    2009-10-29

    Laser-induced damage on the surface of optical components typically is manifested by the formation of microscopic craters that can ultimately degrade the optics performance characteristics. It is believed that the damage process is the result of the material exposure to high temperatures and pressures within a volume on the order of several cubic microns located just below the surface. The response of the material following initial localized energy deposition by the laser pulse, including the timeline of events and the individual processes involved during this timeline, is still largely unknown. In this work we introduce a time-resolved microscope system designed to enable a detailed investigation of the sequence of dynamic events involved during surface damage. To best capture individual aspects of the damage timeline, this system is employed in multiple imaging configurations (such as multi-view image acquisition at a single time point and multi-image acquisition at different time points of the same event) and offers sensitivity to phenomena at very early delay times. The capabilities of this system are demonstrated with preliminary results from the study of exit-surface damage in fused silica. The time-resolved images provide information on the material response immediately following laser energy deposition, the processes later involved during crater formation or growth, the material ejecta kinetics, and overall material motion and transformation. Such results offer insight into the mechanisms governing damage initiation and growth in the optical components of ICF class laser systems.

  13. Parameters affecting the efficient delivery of mesoporous silica nanoparticle materials and gold nanorods into plant tissues by the biolistic method.

    PubMed

    Martin-Ortigosa, Susana; Valenstein, Justin S; Sun, Wei; Moeller, Lorena; Fang, Ning; Trewyn, Brian G; Lin, Victor S-Y; Wang, Kan

    2012-02-06

    Applying nanotechnology to plant science requires efficient systems for the delivery of nanoparticles (NPs) to plant cells and tissues. The presence of a cell wall in plant cells makes it challenging to extend the NP delivery methods available for animal research. In this work, research is presented which establishes an efficient NP delivery system for plant tissues using the biolistic method. It is shown that the biolistic delivery of mesoporous silica nanoparticle (MSN) materials can be improved by increasing the density of MSNs through gold plating. Additionally, a DNA-coating protocol is used based on calcium chloride and spermidine for MSN and gold nanorods to enhance the NP-mediated DNA delivery. Furthermore, the drastic improvement of NP delivery is demonstrated when the particles are combined with 0.6 μm gold particles during bombardment. The methodology described provides a system for the efficient delivery of NPs into plant cells using the biolistic method.

  14. Hydrophilic solid-phase extraction of melamine with ampholine-modified hybrid organic-inorganic silica material.

    PubMed

    Wang, Tingting; Zhu, Yiming; Ma, Junfeng; Xuan, Rongrong; Gao, Haoqi; Liang, Zhen; Zhang, Lihua; Zhang, Yukui

    2015-01-01

    In this work, an ampholine-functionalized hybrid organic-inorganic silica sorbent was successfully used to extract melamine from a milk formula sample by a hydrophilic interaction solid-phase extraction protocol. Primary factors affecting the extraction efficiency of the material such as extraction solvent, elution solvent, sample loading volume, and elution volume have been thoroughly optimized. Under the optimized hydrophilic solid-phase extraction conditions, the recoveries of melamine spiked in milk formula samples ranged from 86.2 to 101.8% with relative standard deviations of 4.1-9.4% (n = 3). The limit of detection (S/N = 3) was 0.32 μg/g. The adsorption capacity toward melamine was 30 μg of melamine per grams of sorbent. Due to its simplicity, rapidity and cost effectiveness, the newly developed hydrophilic solid-phase extraction method should provide a promising tool for daily monitoring of doped melamine in milk formula.

  15. Influence of polymer matrix and adsorption onto silica materials on the migration of alpha-tocopherol into 95% ethanol from active packaging.

    PubMed

    Heirlings, L; Siró, I; Devlieghere, F; Van Bavel, E; Cool, P; De Meulenaer, B; Vansant, E F; Debevere, J

    2004-11-01

    In this study, the effect of polymer materials with different polarity, namely low density polyethylene (LDPE) and ethylene vinyl acetate (EVA), on the migration behaviour of alpha-tocopherol from active packaging was investigated. The antioxidant was also adsorbed onto silica materials, namely SBA-15 (Santa Barbara-15) and Syloblock, in order to protect the antioxidant during extrusion and to ensure a controlled and sufficient release during the shelf-life of the food product. Migration experiments were performed at 7.0 +/- 0.5 degrees C and 95% ethanol was used as fatty food simulant. All films contained a high concentration of alpha-tocopherol, approximately 2000 mg kg(-1), to obtain an active packaging. Polymer matrix had a small influence on the migration profile. The migration of 80% of total migrated amount of antioxidant was retarded for 2.4 days by using LDPE instead of EVA. When alpha-tocopherol was adsorbed onto both silica materials, the migration of 80% of total migrated amount of antioxidant was retarded for 3.4 days in comparison to pure alpha-tocopherol. No difference was seen between the migration profiles of alpha-tocopherol adsorbed onto both silica materials. In the case of pure alpha-tocopherol, 82% of the initial amount of alpha-tocopherol in the film migrated into the food simulant at a rather fast migration rate. In the case of adsorption on silica materials, a total migration was observed. These antioxidative films can have positive food applications.

  16. Tuning of the vinyl groups' spacing at surface of modified silica in preparation of high density imprinted layer-coated silica nanoparticles: a dispersive solid-phase extraction materials for chlorpyrifos.

    PubMed

    Lu, Qing; Chen, Xuemei; Nie, Li; Luo, Jing; Jiang, Huijun; Chen, Lina; Hu, Qin; Du, Shuhu; Zhang, Zhongping

    2010-05-15

    This paper reports the preparation of high density imprinted layer-coated silica nanoparticles toward selective recognition and fast enrichment of chlorpyrifos (CP) from complicated matrices. The molecularly imprinted polymers (MIPs) were successfully coated at the surface of modified silica through using the chemical immovable vinyl groups at the nanoparticles' surface, followed by the graft copolymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) in the presence of templates CP. It has been demonstrated that the space of end vinyl groups at the surface of silica can be controlled by changing the condition of chemical modification, regulating the thickness of imprinted shells and the density of efficient imprinted sites. After removal of templates by solvent extraction, the recognition sites of CP were created in the polymer coating layer. The CP-imprinted nanoparticles exhibited high recognition selectivity and binding affinity to CP analyte. When the CP-imprinted nanoparticles were used as dispersive solid-phase extraction (dSPE) materials, the high recovery yields of 76.1-93.5% from various spiked samples with only 1microg/mL analyte were achieved by one-step extraction. These results reported herein provide the possibility for the separation and enrichment of CP from complicated matrices by the molecular imprinting modification at the surface of common silica nanoparticles.

  17. Performance and mechanism on a high durable silica alumina based cementitious material composed of coal refuse and coal combustion byproducts

    NASA Astrophysics Data System (ADS)

    Yao, Yuan

    Coal refuse and combustion byproducts as industrial solid waste stockpiles have become great threats to the environment. Recycling is one practical solution to utilize this huge amount of solid waste through activation as substitute for ordinary Portland cement. The central goal of this dissertation is to investigate and develop a new silica-alumina based cementitious material largely using coal refuse as a constituent that will be ideal for durable construction, mine backfill, mine sealing and waste disposal stabilization applications. This new material is an environment-friendly alternative to ordinary Portland cement. The main constituents of the new material are coal refuse and other coal wastes including coal sludge and coal combustion products (CCPs). Compared with conventional cement production, successful development of this new technology could potentially save energy and reduce greenhouse gas emissions, recycle vast amount of coal wastes, and significantly reduce production cost. A systematic research has been conducted to seek for an optimal solution for enhancing pozzolanic reactivity of the relatively inert solid waste-coal refuse in order to improve the utilization efficiency and economy benefit for construction and building materials. The results show that thermal activation temperature ranging from 20°C to 950°C significantly increases the workability and pozzolanic property of the coal refuse. The optimal activation condition is between 700°C to 800°C within a period of 30 to 60 minutes. Microanalysis illustrates that the improved pozzolanic reactivity contributes to the generated amorphous materials from parts of inert aluminosilicate minerals by destroying the crystallize structure during the thermal activation. In the coal refuse, kaolinite begins to transfer into metakaol in at 550°C, the chlorite minerals disappear at 750°C, and muscovite 2M1 gradually dehydroxylates to muscovite HT. Furthermore, this research examines the environmental

  18. Thermolytic Conversion of a bis(alkoxy)tris(siloxy)tantalum(V)Single-Source Molecular Precursor to Catalytic Tantala-SilicaMaterials

    SciTech Connect

    Brutchey, Robert L.; Lugmair, Claus G.; Schebaum, Lugmair O.; Tilley, T. Don

    2004-10-13

    The new complex ({sup i}PrO){sub 2}Ta[OSi(O{sup t}Bu){sub 3}]{sub 3} (1) was prepared via silanolysis of Ta(O{sup i}Pr){sub 5} with ({sup t}BuO){sub 3}SiOH and is a useful structural and spectroscopic (NMR, FTIR) model of Ta(V) on silica. The complex was also used to prepare tantalum-containing silica materials, via the thermolytic molecular precursor method (yielding Ta{sub 2}O{sub 5}{center_dot}6SiO{sub 2} and Ta{sub 2}O{sub 5}{center_dot}18SiO{sub 2}) or by grafting 1 onto mesoporous SBA-15 silica (yielding a surface-supported tantala species, TaSBA-15). The solution phase thermolysis of 1 in nonpolar media afforded homogeneous, high-surface-area (ca. 450 m{sup 2} g{sup -1}) xerogels (Ta{sub 2}O{sub 5}{center_dot}6SiO{sub 2}) that are amorphous up to approximately 1100 C. A more silica-rich tantala-silica material (Ta{sub 2}O{sub 5}{center_dot}18SiO{sub 2}) was prepared via a solution-phase co-thermolytic route with 1 and HOSi(O{sup t}Bu){sub 3}, to yield a material with a Si/Ta ratio of 9/1. It was demonstrated that tantala-silica materials are active as catalysts for cyclohexene oxidation.

  19. Biosynthesis of metal-binding polypeptides and their precursors in response to cadmium in Datura innoxia

    SciTech Connect

    Jackson, P.J.; Delhaize, E.; Kuske, C.R.

    1991-01-01

    Metal-tolerant Datura innoxia cells synthesize large amounts of a class of metal-binding polypeptides, poly({gamma}-glutamylcysteinyl) glycines (({gamma}-EC){sub n}G, n=2-5), when exposed to Cd. These polypeptides have a high affinity for Cd (2) and certain other metal ions and are thought to play a role in metal tolerance in higher plants. ({gamma}-EC){sub n}G is biosynthetically derived from glutathione. Therefore, the response of Datura cells to Cd must include an increase in production of glutathione and its precursors, since cells rapidly accumulate very high concentrations of these metal-binding polypeptides. The biosynthesis of ({gamma}-EC){sub n}Gs, glutathione, and cysteine in response to Cd exposure is described. The physiological significance of the synthesis of these polypeptides and their precursors and its relevance to Cd tolerance and metal homeostasis are discussed. 34 refs., 6 figs., 1 tab.

  20. Metal binding spectrum and model structure of the Bacillus anthracis virulence determinant MntA.

    PubMed

    Vigonsky, Elena; Fish, Inbar; Livnat-Levanon, Nurit; Ovcharenko, Elena; Ben-Tal, Nir; Lewinson, Oded

    2015-10-01

    The potentially lethal human pathogen Bacillus anthracis expresses a putative metal import system, MntBCA, which belongs to the large family of ABC transporters. MntBCA is essential for virulence of Bacillus anthracis: deletion of MntA, the system's substrate binding protein, yields a completely non-virulent strain. Here we determined the metal binding spectrum of MntA. In contrast to what can be inferred from growth complementation studies we find no evidence that MntA binds Fe(2+) or Fe(3+). Rather, MntA binds a variety of other metal ions, including Mn(2+), Zn(2+), Cd(2+), Co(2+), and Ni(2+) with affinities ranging from 10(-6) to 10(-8) M. Binding of Zn(2+) and Co(2+) have a pronounced thermo-stabilizing effect on MntA, with Mn(2+) having a milder effect. The thermodynamic stability of MntA, competition experiments, and metal binding and release experiments all suggest that Mn(2+) is the metal that is likely transported by MntBCA and is therefore the limiting factor for virulence of Bacillus anthracis. A homology-model of MntA shows a single, highly conserved metal binding site, with four residues that participate in metal coordination: two histidines, a glutamate, and an aspartate. The metals bind to this site in a mutually exclusive manner, yet surprisingly, mutational analysis shows that for proper coordination each metal requires a different subset of these four residues. ConSurf evolutionary analysis and structural comparison of MntA and its homologues suggest that substrate binding proteins (SBPs) of metal ions use a pair of highly conserved prolines to interact with their cognate ABC transporters. This proline pair is found exclusively in ABC import systems of metal ions.

  1. The structure of the Helicobacter pylori ferric uptake regulator Fur reveals three functional metal binding sites.

    PubMed

    Dian, Cyril; Vitale, Sylvia; Leonard, Gordon A; Bahlawane, Christelle; Fauquant, Caroline; Leduc, Damien; Muller, Cécile; de Reuse, Hilde; Michaud-Soret, Isabelle; Terradot, Laurent

    2011-03-01

    Fur, the ferric uptake regulator, is a transcription factor that controls iron metabolism in bacteria. Binding of ferrous iron to Fur triggers a conformational change that activates the protein for binding to specific DNA sequences named Fur boxes. In Helicobacter pylori, HpFur is involved in acid response and is important for gastric colonization in model animals. Here we present the crystal structure of a functionally active HpFur mutant (HpFur2M; C78S-C150S) bound to zinc. Although its fold is similar to that of other Fur and Fur-like proteins, the crystal structure of HpFur reveals a unique structured N-terminal extension and an unusual C-terminal helix. The structure also shows three metal binding sites: S1 the structural ZnS₄ site previously characterized biochemically in HpFur and the two zinc sites identified in other Fur proteins. Site-directed mutagenesis and spectroscopy analyses of purified wild-type HpFur and various mutants show that the two metal binding sites common to other Fur proteins can be also metallated by cobalt. DNA protection and circular dichroism experiments demonstrate that, while these two sites influence the affinity of HpFur for DNA, only one is absolutely required for DNA binding and could be responsible for the conformational changes of Fur upon metal binding while the other is a secondary site.

  2. Structural characterization of metal binding to a cold-adapted frataxin.

    PubMed

    Noguera, Martín E; Roman, Ernesto A; Rigal, Juan B; Cousido-Siah, Alexandra; Mitschler, André; Podjarny, Alberto; Santos, Javier

    2015-06-01

    Frataxin is an evolutionary conserved protein that participates in iron metabolism. Deficiency of this small protein in humans causes a severe neurodegenerative disease known as Friedreich's ataxia. A number of studies indicate that frataxin binds iron and regulates Fe-S cluster biosynthesis. Previous structural studies showed that metal binding occurs mainly in a region of high density of negative charge. However, a comprehensive characterization of the binding sites is required to gain further insights into the mechanistic details of frataxin function. In this work, we have solved the X-ray crystal structures of a cold-adapted frataxin from a psychrophilic bacterium in the presence of cobalt or europium ions. We have identified a number of metal-binding sites, mainly solvent exposed, several of which had not been observed in previous studies on mesophilic homologues. No major structural changes were detected upon metal binding, although the structures exhibit significant changes in crystallographic B-factors. The analysis of these B-factors, in combination with crystal packing and RMSD among structures, suggests the existence of localized changes in the internal motions. Based on these results, we propose that bacterial frataxins possess binding sites of moderate affinity for a quick capture and transfer of iron to other proteins and for the regulation of Fe-S cluster biosynthesis, modulating interactions with partner proteins.

  3. Periodic mesoporous hydridosilica--synthesis of an "impossible" material and its thermal transformation into brightly photoluminescent periodic mesoporous nanocrystal silicon-silica composite.

    PubMed

    Xie, Zhuoying; Henderson, Eric J; Dag, Ömer; Wang, Wendong; Lofgreen, Jennifer E; Kübel, Christian; Scherer, Torsten; Brodersen, Peter M; Gu, Zhong-Ze; Ozin, Geoffrey A

    2011-04-06

    There has always been a fascination with "impossible" compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these "impossible" materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such "impossible" material is periodic mesoporous hydridosilica (meso-HSiO(1.5)). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO(1.5) can be synthesized by template-directed self-assembly of HSi(OEt)(3) under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO(2), a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.

  4. Mechanochemical synthesis of maghemite/silica nanocomposites: advanced materials for aqueous room-temperature catalysis.

    PubMed

    Ojeda, Manuel; Pineda, Antonio; Romero, Antonio A; Barrón, Vidal; Luque, Rafael

    2014-07-01

    A simple, environmentally friendly, and highly reproducible protocol has been developed for the mechanochemical preparation of advanced nanocatalytic materials in a one-pot process. The materials proved to have unprecedented activities in aqueous Suzuki couplings at room temperature, paving the way for a new generation of highly active and stable advanced nanocatalysts.

  5. Fungus-Mediated Preferential Bioleaching of Waste Material Such as Fly - Ash as a Means of Producing Extracellular, Protein Capped, Fluorescent and Water Soluble Silica Nanoparticles

    PubMed Central

    Khan, Shadab Ali; Uddin, Imran; Moeez, Sana; Ahmad, Absar

    2014-01-01

    In this paper, we for the first time show the ability of the mesophilic fungus Fusarium oxysporum in the bioleaching of waste material such as Fly-ash for the extracellular production of highly crystalline and highly stable, protein capped, fluorescent and water soluble silica nanoparticles at ambient conditions. When the fungus Fusarium oxysporum is exposed to Fly-ash, it is capable of selectively leaching out silica nanoparticles of quasi-spherical morphology within 24 h of reaction. These silica nanoparticles have been completely characterized by UV-vis spectroscopy, Photoluminescence (PL), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Energy dispersive analysis of X-rays (EDAX). PMID:25244567

  6. Thermolytic Molecular Precursor Route to Site-IsolatedVanadia-Silica Materials and Their Catalytic Performance in MethaneSelective Oxidation

    SciTech Connect

    Ruddy, Daniel A.; Ohler, Nicholas L.; Bell, Alexis T.; Tilley, T.Don

    2005-11-23

    The thermolytic molecular precursor (TMP) method was used to prepare site-isolated, high-surface area vanadia-silica (V/SBA15) materials of various V loadings via the grafting of two precursors, OV[OSi(O{sup t}Bu){sub 3}]{sub 3} (1) and Ov(O{sup t}Bu){sub 3} (2). Spectroscopic analysis indicates that excellent synthetic control was established for the exclusive formation of a pseudotetrahedral monovanadate (VO4) structure on all catalyst surfaces. Another V/SBA15 catalyst was prepared via conventional incipient wetness impregnation (WI) with aqueous NH4VO3. A spectroscopic investigation of this catalyst revealed the presence of monovanadate and polyvanadate species along with small domains of V2O5. The TMP materials behave as single-site catalysts in the selective oxidation of methane to formaldehyde up to a V coverage of 0.47 Vnm-2 and demonstrate superior activity compared with the WI catalyst. A space-time yield of 5.84 kgCH2Okg-1cat h-1 was observed, more than twice the highest value previously reported.

  7. Emergence of Zeolite Analogs and other Microporous Crystals in an Atomic Lattice Model of Silica and Related Materials.

    PubMed

    Jin, Lin; Auerbach, Scott M; Monson, Peter A

    2012-03-15

    The potential of tailored nanopores to transform technologies such as drug delivery, biofuel production, and optical-electronic devices depends on fundamental knowledge of the self-assembly of ordered nanoporous solids. Atomic-level geometries of critical nuclei that lead to such solids have remained hidden in the nanoscale blind spot between local (<0.5 nm) and collective (>5 nm) probes of structure. Heroic efforts at molecular simulation of nanopore formation have provided massive libraries of hypothetical structures; (1-5) however, to date no statistical simulation has generated a crystallization pathway from random initial condition to ordered nanoporous solid, until now. In this work, we show that a recently developed atomic lattice model of silica and related materials can form ordered nanoporous solids with a rich variety of structures including known chalcogenides, zeolite analogs, and layered materials. We find that whereas canonical Monte Carlo simulations of the model consistently produce the amorphous solids studied in our previous work, parallel tempering Monte Carlo gives rise to ordered nanoporous solids. The utility of parallel tempering highlights the existence of barriers between amorphous and crystalline phases of our model. Moreover, the self-assembly or nanoporous crystalline phases in the model open the door to detailed understanding of nanopore nucleation.

  8. Electrochemical Sensors: Functionalized Silica

    SciTech Connect

    Fryxell, Glen E.; Lin, Yuehe; Yantasee, Wassana

    2009-03-24

    This chapter summarizes recent devellopment of electrochemical sensors based on functionlized mesoporous silica materials. The nanomatrials based sensors have been developed for sensitive and selective enrironmental detection of toxic heavy metal and uranium ions.

  9. The accelerating effect of chitosan-silica hybrid dressing materials on the early phase of wound healing.

    PubMed

    Park, Ji-Ung; Jung, Hyun-Do; Song, Eun-Ho; Choi, Tae-Hyun; Kim, Hyoun-Ee; Song, Juha; Kim, Sukwha

    2016-05-24

    Commercialized dressing materials with or without silver have played a passive role in early-phase wound healing, protecting the skin defects from infections, absorbing exudate, and preventing dehydration. Chitosan (CTS)-based sponges have been developed in pure or hybrid forms for accelerating wound healing, but their wound-healing capabilities have not been extensively compared with widely used commercial dressing materials, providing limited information in a practical aspect. In this study, we have developed CTS-silica (CTS-Si) hybrid sponges with water absorption, flexibility, and mechanical behavior similar to those of CTS sponges. In vitro and in vivo tests were performed to compare the CTS-Si sponges with three commercial dressing materials [gauze, polyurethane (PU), and silver-containing hydrofiber (HF-Ag)] in addition to CTS sponges. Both in vitro and in vivo tests showed that CTS-Si sponges promoted fibroblast proliferation, leading to accelerated collagen synthesis, whereas the CTS sponges did not exhibit significant differences in fibroblast proliferation and collagen synthesis from gauze, PU, and HF-Ag sponges. In case of CTS-Si, the inflammatory cells were actively recruited to the wound by the influence of the released silicon ions from CTS-Si sponges, which, in return, led to an enhanced secretion of growth factors, particularly TGF-β during the early stage. The higher level of TGF-β likely improved the proliferation of fibroblasts, and as a result, collagen synthesis by fibroblasts became remarkably productive, thereby increasing collagen density at the wound site. Therefore, the CTS-Si hybrid sponges have considerable potential as a wound-dressing material for accelerating wound healing. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2016.

  10. Selective enrichment of metal-binding proteins based on magnetic core/shell microspheres functionalized with metal cations.

    PubMed

    Fang, Caiyun; Zhang, Lei; Zhang, Xiaoqin; Lu, Haojie

    2015-06-21

    Metal binding proteins play many important roles in a broad range of biological processes. Characterization of metal binding proteins is important for understanding their structure and biological functions, thus leading to a clear understanding of metal associated diseases. The present study is the first to investigate the effectiveness of magnetic microspheres functionalized with metal cations (Ca(2+), Cu(2+), Zn(2+) and Fe(3+)) as the absorbent matrix in IMAC technology to enrich metal containing/binding proteins. The putative metal binding proteins in rat liver were then globally characterized by using this strategy which is very easy to handle and can capture a number of metal binding proteins effectively. In total, 185 putative metal binding proteins were identified from rat liver including some known less abundant and membrane-bound metal binding proteins such as Plcg1, Acsl5, etc. The identified proteins are involved in many important processes including binding, catalytic activity, translation elongation factor activity, electron carrier activity, and so on.

  11. Spacing and Site Isolation of Amine Groups in 3-Aminopropyl-Grafted Silica Materials - The Role of Protecting Groups

    SciTech Connect

    Hicks, Jason C; Dabestani, Reza T; Buchanan III, A C; Jones, Christopher W

    2006-01-01

    The relative spacing of amines in 3-aminopropylsilyl-grafted silica is studied by solid-state fluorescence spectroscopy of 1-pyrenecarboxylic acid (PCA) and 1-pyrenebutyric acid (PBA) bound to traditionally prepared, deprotected benzyl- or deprotected trityl-spaced aminosilicas. Thermogravimetric analysis and FT-Raman spectroscopy results show evidence that the protected imine can be cleaved to yield the corresponding amine in essentially quantitative yield. The steady-state fluorescence spectroscopic data of either PCA or PBA indicate that the number of amine pairs on the surface separated by a distance of 1 nm or less decreases as the total amine loading decreases. Both the intensity ratio of the excimer band to the monomer band (I{sub 470}/I{sub 384} or I{sub exc}/I{sub mon}) and lifetime decay studies of the fluorophore are useful probes of the amine spacing. Separation of amines on the surface can be achieved by either use of a protected synthesis route or through reduction of the concentration of the unprotected 3-aminopropyltrimethoxysilane used in the grafting solution. However, the two routes lead to materials with significantly different average amine spacings. Due to clustering of unprotected amines in solution before grafting or on the surface during the grafting process, amine-amine distances on the surface of materials prepared by an unprotected synthesis are on average smaller than when a protected synthesis is used. With the protected synthesis, evidence suggests that the amines are more isolated, with larger average amine-amine distances when compared to corresponding materials with a similar amine loading prepared via an unprotected synthesis. This is attributed to both the steric influence of the protecting groups and a reduction in silane clustering in solution due to protection of the amines before grafting. Thus, the mechanism of surface amine spacing when using the protection-deprotection strategy appears to involve both of these factors

  12. Formation of Mach angle profiles during wet etching of silica and silicon nitride materials

    NASA Astrophysics Data System (ADS)

    Ghulinyan, M.; Bernard, M.; Bartali, R.; Pucker, G.

    2015-12-01

    In integrated circuit technology peeling of masking photoresist films is a major drawback during the long-timed wet etching of materials. It causes an undesired film underetching, which is often accompanied by a formation of complex etch profiles. Here we report on a detailed study of wedge-shaped profile formation in a series of silicon oxide, silicon oxynitride and silicon nitride materials during wet etching in a buffered hydrofluoric acid (BHF) solution. The shape of etched profiles reflects the time-dependent adhesion properties of the photoresist to a particular material and can be perfectly circular, purely linear or a combination of both, separated by a knee feature. Starting from a formal analogy between the sonic boom propagation and the wet underetching process, we model the wedge formation mechanism analytically. This model predicts the final form of the profile as a function of time and fits the experimental data perfectly. We discuss how this knowledge can be extended to the design and the realization of optical components such as highly efficient etch-less vertical tapers for passive silicon photonics.

  13. Structure and metal binding properties of ZnuA, a periplasmic zinc transporter from Escherichia coli

    PubMed Central

    Yatsunyk, Liliya A.; Easton, J. Allen; Kim, Lydia R.; Sugarbaker, Stacy A.; Bennett, Brian; Breece, Robert M.; Vorontsov, Ivan I.; Tierney, David L.

    2009-01-01

    ZnuA is the periplasmic Zn2+-binding protein associated with the high-affinity ATP-binding cassette ZnuABC transporter from Escherichia coli. Although several structures of ZnuA and its homologs have been determined, details regarding metal ion stoichiometry, affinity, and specificity as well as the mechanism of metal uptake and transfer remain unclear. The crystal structures of E. coli ZnuA (Eco-ZnuA) in the apo, Zn2+-bound, and Co2+-bound forms have been determined. ZnZnuA binds at least two metal ions. The first, observed previously in other structures, is coordinated tetrahedrally by Glu59, His60, His143, and His207. Replacement of Zn2+ with Co2+ results in almost identical coordination geometry at this site. The second metal binding site involves His224 and several yet to be identified residues from the His-rich loop that is unique to Zn2+ periplasmic metal binding receptors. Electron paramagnetic resonance and X-ray absorption spectroscopic data on CoZnuA provide additional insight into possible residues involved in this second site. The second site is also detected by metal analysis and circular dichroism (CD) titrations. Eco-ZnuA binds Zn2+ (estimated Kd < 20 nM), Co2+, Ni2+, Cu2+, Cu+, and Cd2+, but not Mn2+. Finally, conformational changes upon metal binding observed in the crystal structures together with fluorescence and CD data indicate that only Zn2+ substantially stabilizes ZnuA and might facilitate recognition of ZnuB and subsequent metal transfer. PMID:18027003

  14. Cucumber Metallothionein-Like 2 (CsMTL2) Exhibits Metal-Binding Properties

    PubMed Central

    Pan, Yu; Pan, Yanglu; Zhai, Junpeng; Xiong, Yan; Li, Jinhua; Du, Xiaobing; Su, Chenggang; Zhang, Xingguo

    2016-01-01

    We identified a novel member of the metallothionein (MT) family, Cucumis sativus metallothionein-like 2 (CsMTL2), by screening a young cucumber fruit complementary DNA (cDNA) library. The CsMTL2 encodes a putative 77-amino acid Class II MT protein that contains two cysteine (Cys)-rich domains separated by a Cys-free spacer region. We found that CsMTL2 expression was regulated by metal stress and was specifically induced by Cd2+ treatment. We investigated the metal-binding characteristics of CsMTL2 and its possible role in the homeostasis and/or detoxification of metals by heterologous overexpression in Escherichia coli cells. Furthermore, we produced a deletion mutant form of the protein, CsMTL2m, that contained the two Cys-rich clusters but lacked the spacer region, in E. coli. We compared the metal-binding properties of CsMTL2 with those of CsMTL2m, the β domain of human metallothionein-like protein 1 (HsMTXb), and phytochelatin-like (PCL) heterologously expressed in E. coli using metal-binding assays. We found that E. coli cells expressing CsMTL2 accumulated the highest levels of Zn2+ and Cd2+ of the four transformed cell types, with levels being significantly higher than those of control cells containing empty vector. E. coli cells expressing CsMTL2 had a higher tolerance for cadmium than for zinc ions. These findings show that CsMTL2 improves metal tolerance when heterologously expressed in E. coli. Future studies should examine whether CsMTL2 improves metal tolerance in planta. PMID:27916887

  15. Characterization of Two Metal Binding Lipoproteins as Vaccine Candidates for Enterococcal Infections

    PubMed Central

    Romero-Saavedra, Felipe; Laverde, Diana; Budin-Verneuil, Aurélie; Muller, Cécile; Bernay, Benoit; Benachour, Abdellah; Hartke, Axel; Huebner, Johannes

    2015-01-01

    Background Enterococcus faecium and faecalis are Gram-positive opportunistic pathogens that have become leading causes of nosocomial infections over the last decades. Especially multidrug resistant enterococci have become a challenging clinical problem worldwide. Therefore, new treatment options are needed and the identification of alternative targets for vaccine development has emerged as a feasible alternative to fight the infections caused by these pathogens. Results We extrapolate the transcriptomic data from a mice peritonitis infection model in E. faecalis to identify putative up-regulated surface proteins under infection conditions in E. faecium. After the bionformatic analyses two metal binding lipoproteins were identified to have a high homology (>72%) between the two species, the manganese ABC transporter substrate-binding lipoprotein (PsaAfm,) and the zinc ABC transporter substrate-binding lipoprotein (AdcAfm). These candidate lipoproteins were overexpressed in Escherichia coli and purified. The recombinant proteins were used to produce rabbit polyclonal antibodies that were able to induce specific opsonic antibodies that mediated killing of the homologous strain E. faecium E155 as well as clinical strains E. faecium E1162, Enterococcus faecalis 12030, type 2 and type 5. Mice were passively immunized with the antibodies raised against recombinant lipoproteins, showing significant reduction of colony counts in mice livers after the bacterial challenge and demonstrating the efficacy of these metal binding lipoproteins as promising vaccine candidates to treat infections caused by these enterococcal pathogens. Conclusion Overall, our results demonstrate that these two metal binding lipoproteins elicited specific, opsonic and protective antibodies, with an extensive cross-reactivity and serotype-independent coverage among these two important nocosomial pathogens. Pointing these two protein antigens as promising immunogens, that can be used as single

  16. Graphene-coated materials using silica particles as a framework for highly efficient removal of aromatic pollutants in water.

    PubMed

    Yang, Kaijie; Chen, Baoliang; Zhu, Lizhong

    2015-06-29

    The substantial aggregation of pristine graphene nanosheets decreases its powerful adsorption capacity and diminishes its practical applications. To overcome this shortcoming, graphene-coated materials (GCMs) were prepared by loading graphene onto silica nanoparticles (SiO2). With the support of SiO2, the stacked interlamination of graphene was held open to expose the powerful adsorption sites in the interlayers. The adsorption of phenanthrene, a model aromatic pollutant, onto the loaded graphene nanosheets increased up to 100 fold compared with pristine graphene at the same level. The adsorption of GCMs increased with the loading amount of the graphene nanosheets and dramatically decreased with the introduction of oxygen-containing groups in the graphene nanosheets. The highly hydrophobic effect and the strong π-π stacking interactions of the exposed graphene nanosheets contributed to their superior adsorption of GCMs. An unusual GCM peak adsorption coefficient (Kd) was observed with the increase in sorbate concentration. The sorbate concentration at peak Kd shifted to lower values for the reduced graphene oxide and graphene relative to the graphene oxide. Therefore, the replacement of water nanodroplets attached to the graphene nanosheets through weak non-hydrogen bonding with phenanthrene molecules via strong π-π stacking interactions is hypothesized to be an additional adsorption mechanism for GCMs.

  17. Preparation and adsorption behavior of berberine hydrochloride imprinted polymers by using silica gel as sacrificed support material

    NASA Astrophysics Data System (ADS)

    Li, Hui; Li, Yuzhuo; Li, Zhiping; Peng, Xiyang; Li, Yanan; Li, Gui; Tan, Xianzhou; Chen, Gongxi

    2012-03-01

    Preparation of berberine hydrochloride (B-Cl) imprinted polymers (MIPs) based on surface imprinting technique with silica gel as sacrificial support material was performed successfully by using B-Cl as template, methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as functional monomer and cross-linker, respectively. The prepared polymers were characterized by Fourier transmission infrared spectrometry (FTIR) and scanning electron microscopy (SEM). Adsorption behavior of the MIPs for the template and its structural analogues was investigated. Sites distribution on the surface of MIPs was explored by using different isotherm adsorption models and thermodynamic parameters for the adsorption of B-Cl on the MIPs determined. Sample application and reusability for the MIPs was also evaluated. Results indicated the strong adsorption and high selectivity of the MIPs for B-Cl. Saturated adsorption capacity reached 27.2 μmol g-1 and the selectivity coefficient of the MIPs for B-Cl relative to jatrorrhizine hydrochloride (J-Cl) and palmatine palmatus hydrochloride (P-Cl) are 3.70 and 6.03, respectively. In addition, the MIPs were shown with good reusability and selectively retention ability in sample application.

  18. Graphene-coated materials using silica particles as a framework for highly efficient removal of aromatic pollutants in water

    NASA Astrophysics Data System (ADS)

    Yang, Kaijie; Chen, Baoliang; Zhu, Lizhong

    2015-06-01

    The substantial aggregation of pristine graphene nanosheets decreases its powerful adsorption capacity and diminishes its practical applications. To overcome this shortcoming, graphene-coated materials (GCMs) were prepared by loading graphene onto silica nanoparticles (SiO2). With the support of SiO2, the stacked interlamination of graphene was held open to expose the powerful adsorption sites in the interlayers. The adsorption of phenanthrene, a model aromatic pollutant, onto the loaded graphene nanosheets increased up to 100 fold compared with pristine graphene at the same level. The adsorption of GCMs increased with the loading amount of the graphene nanosheets and dramatically decreased with the introduction of oxygen-containing groups in the graphene nanosheets. The highly hydrophobic effect and the strong π-π stacking interactions of the exposed graphene nanosheets contributed to their superior adsorption of GCMs. An unusual GCM peak adsorption coefficient (Kd) was observed with the increase in sorbate concentration. The sorbate concentration at peak Kd shifted to lower values for the reduced graphene oxide and graphene relative to the graphene oxide. Therefore, the replacement of water nanodroplets attached to the graphene nanosheets through weak non-hydrogen bonding with phenanthrene molecules via strong π-π stacking interactions is hypothesized to be an additional adsorption mechanism for GCMs.

  19. Graphene-coated materials using silica particles as a framework for highly efficient removal of aromatic pollutants in water

    PubMed Central

    Yang, Kaijie; Chen, Baoliang; Zhu, Lizhong

    2015-01-01

    The substantial aggregation of pristine graphene nanosheets decreases its powerful adsorption capacity and diminishes its practical applications. To overcome this shortcoming, graphene-coated materials (GCMs) were prepared by loading graphene onto silica nanoparticles (SiO2). With the support of SiO2, the stacked interlamination of graphene was held open to expose the powerful adsorption sites in the interlayers. The adsorption of phenanthrene, a model aromatic pollutant, onto the loaded graphene nanosheets increased up to 100 fold compared with pristine graphene at the same level. The adsorption of GCMs increased with the loading amount of the graphene nanosheets and dramatically decreased with the introduction of oxygen-containing groups in the graphene nanosheets. The highly hydrophobic effect and the strong π-π stacking interactions of the exposed graphene nanosheets contributed to their superior adsorption of GCMs. An unusual GCM peak adsorption coefficient (Kd) was observed with the increase in sorbate concentration. The sorbate concentration at peak Kd shifted to lower values for the reduced graphene oxide and graphene relative to the graphene oxide. Therefore, the replacement of water nanodroplets attached to the graphene nanosheets through weak non-hydrogen bonding with phenanthrene molecules via strong π-π stacking interactions is hypothesized to be an additional adsorption mechanism for GCMs. PMID:26119007

  20. Metal-binding proteins in eggs of various sea urchin species.

    PubMed

    Scudiero, R; Capasso, C; De Prisco, P P; Capasso, A; Filosa, S; Parisi, E

    1994-01-01

    Metallothionein presence and amount were determined in the unfertilized eggs of six sea urchin species by silver saturation assay and gel-chromatography of cell extracts. The results showed high levels of metallothionein in the egg cytoplasm of the two Mediterranean species Paracentrotus lividus and Sphaerechinus granularis. No metallothionein was found either in the eggs of Arbacia lixula, or in those of the three Eastern species Strongylocentrotus intermedius, Temnopleurus hardwickii and Clypeaster japonicus. However, the extracts of the latter three species revealed the presence of zinc bound in a macromolecular form, thus suggesting the existence of metal-binding proteins distinct from metallothioneins.

  1. Synthesis of mesoporous silica-alumina materials via urea-templated sol-gel route and their catalytic performance for THF polymerization

    NASA Astrophysics Data System (ADS)

    Ge, Yuanyuan; Jia, Zhiqi; Gao, Chunguang; Gao, Pengfei; Zhao, Lili; Zhao, Yongxiang

    2014-10-01

    A series of mesoporous silica-alumina materials was successfully synthesized by using urea as a low-cost template via sol-gel routes. The characterization results showed that the employ of urea enhanced the porosity of the silica-alumina materials and made the pore size distributions become narrower. The specific surface area, pore volume and pore diameter of SAU-X firstly increased and then decreased as the urea concentration increased from 0 to 60 wt %, and the maximums were obtained at 40 wt % urea concentration. All samples were tested for the THF polymerization. Among them, SAU-40 exhibited the highest activity and the longest catalyst life due to its superior porosity.

  2. Immobilization of Lactobacillus rhamnosus in mesoporous silica-based material: An efficiency continuous cell-recycle fermentation system for lactic acid production.

    PubMed

    Zhao, Zijian; Xie, Xiaona; Wang, Zhi; Tao, Yanchun; Niu, Xuedun; Huang, Xuri; Liu, Li; Li, Zhengqiang

    2016-06-01

    Lactic acid bacteria immobilization methods have been widely used for lactic acid production. Until now, the most common immobilization matrix used is calcium alginate. However, Ca-alginate gel disintegrated during lactic acid fermentation. To overcome this deficiency, we developed an immobilization method in which Lactobacillus rhamnosus cells were successfully encapsulated into an ordered mesoporous silica-based material under mild conditions with a high immobilization efficiency of 78.77% by using elemental analysis. We also optimized the cultivation conditions of the immobilized L. rhamnosus and obtained a high glucose conversion yield of 92.4%. Furthermore, L. rhamnosus encapsulated in mesoporous silica-based material exhibited operational stability during repeated fermentation processes and no decrease in lactic acid production up to 8 repeated batches.

  3. Ampholine-functionalized hybrid organic-inorganic silica material as sorbent for solid-phase extraction of acidic and basic compounds.

    PubMed

    Wang, Tingting; Chen, Yihui; Ma, Junfeng; Chen, Mingliang; Nie, Chenggang; Hu, Minjie; Li, Ying; Jia, Zhijian; Fang, Jianghua; Gao, Haoqi

    2013-09-20

    A novel sorbent for solid-phase extraction (SPE) was synthesized by chemical immobilization of ampholine on hybrid organic-inorganic silica material. The ampholine-functionalized hybrid organic-inorganic silica sorbent is consisted of aliphatic amine groups, carboxyl groups and long carbon chains, allowing for extraction of both acidic and basic compounds. The retention properties of the developed sorbent were evaluated for 1-hydroxy-2-naphthoic acid (HNA), 1-naphthoic acid (NA), 3-hydroxybenzoic acid (HBA), benzoic acid (BA), sorbic acid (SA), vanillic aldehyde (VA), butyl 4-hydroxybenzoate (BHB), propyl 4-hydroxybenzoate (PHB), ethyl 4-hydroxybenzoate (EHB), and methyl 4-hydroxybenzoate (MHB). The results show that such a sorbent has three types of interaction, i.e., electrostatic interaction, hydrophobic interaction, and hydrogen bonding, exhibiting high extraction efficiency towards the compounds tested. The adsorption capacities of the analytes ranged from 0.61 to 6.54μgmg(-1). The reproducibility of the sorbent preparation was evaluated at three spiking concentration levels, with relative standard deviations (RSDs) of 1.0-10.5%. The recoveries of ten acidic and basic compounds spiked in beverage Coca-Cola(®) sample ranged from 82.5% to 98.2% with RSDs less than 5.8%. Under optimum conditions, the ampholine-functionalized hybrid organic-inorganic silica sorbent rendered higher extraction efficiency for acidic compounds than that of the commercially available ampholine-functionalized silica particles, and was comparable to that of the commercial Oasis WAX and Oasis WCX.

  4. MamO Is a Repurposed Serine Protease that Promotes Magnetite Biomineralization through Direct Transition Metal Binding in Magnetotactic Bacteria

    SciTech Connect

    Hershey, David M.; Ren, Xuefeng; Melnyk, Ryan A.; Browne, Patrick J.; Ozyamak, Ertan; Jones, Stephanie R.; Chang, Michelle C. Y.; Hurley, James H.; Komeili, Arash

    2016-03-16

    Many living organisms transform inorganic atoms into highly ordered crystalline materials. An elegant example of such biomineralization processes is the production of nano-scale magnetic crystals in magnetotactic bacteria. Previous studies have implicated the involvement of two putative serine proteases, MamE and MamO, during the early stages of magnetite formation in Magnetospirillum magneticum AMB-1. Here, using genetic analysis and X-ray crystallography, we show that MamO has a degenerate active site, rendering it incapable of protease activity. Instead, MamO promotes magnetosome formation through two genetically distinct, noncatalytic activities: activation of MamE-dependent proteolysis of biomineralization factors and direct binding to transition metal ions. By solving the structure of the protease domain bound to a metal ion, we identify a surface-exposed di-histidine motif in MamO that contributes to metal binding and show that it is required to initiate biomineralization in vivo. Finally, we find that pseudoproteases are widespread in magnetotactic bacteria and that they have evolved independently in three separate taxa. In conclusion, our results highlight the versatility of protein scaffolds in accommodating new biochemical activities and provide unprecedented insight into the earliest stages of biomineralization.

  5. MamO Is a Repurposed Serine Protease that Promotes Magnetite Biomineralization through Direct Transition Metal Binding in Magnetotactic Bacteria

    DOE PAGES

    Hershey, David M.; Ren, Xuefeng; Melnyk, Ryan A.; ...

    2016-03-16

    Many living organisms transform inorganic atoms into highly ordered crystalline materials. An elegant example of such biomineralization processes is the production of nano-scale magnetic crystals in magnetotactic bacteria. Previous studies have implicated the involvement of two putative serine proteases, MamE and MamO, during the early stages of magnetite formation in Magnetospirillum magneticum AMB-1. Here, using genetic analysis and X-ray crystallography, we show that MamO has a degenerate active site, rendering it incapable of protease activity. Instead, MamO promotes magnetosome formation through two genetically distinct, noncatalytic activities: activation of MamE-dependent proteolysis of biomineralization factors and direct binding to transition metal ions.more » By solving the structure of the protease domain bound to a metal ion, we identify a surface-exposed di-histidine motif in MamO that contributes to metal binding and show that it is required to initiate biomineralization in vivo. Finally, we find that pseudoproteases are widespread in magnetotactic bacteria and that they have evolved independently in three separate taxa. In conclusion, our results highlight the versatility of protein scaffolds in accommodating new biochemical activities and provide unprecedented insight into the earliest stages of biomineralization.« less

  6. Copper-doped silica materials silanized with bis-(triethoxy silyl propyl)-tetra sulfide for mercury vapor capture

    SciTech Connect

    D.E. Meyer; N. Meeks; S. Sikdar; N.D. Hutson; D. Hua; D. Bhattacharyya

    2008-07-15

    The use of Cu-S sites for Hg capture from the gas phase has been successfully applied to a silica-based platform using an S4 organic polysulfane and copper sulfate. The maximum fixed-bed equilibrium capacity achieved using these materials was 19 789 {mu}g Hg.g{sup -1} sorbent for a material with 2.5 wt % Cu and 6 wt % S. An optimal S level was determined to be around 3 wt % because enhancement of capacity was only 18% when increasing from this 3 to 6 wt %. The rate of adsorption in pure beds ranged from 0.6 to 1.6 {mu}g Hg.min{sup -1} depending on the inlet concentration. Differences in breakthrough times suggest that material deposition is not uniform. When compared to two other platforms, commercially available Darco HG-LH and previously tested Fe-Cu-S4 nanoaggregates, the Si-1 material performed the best in fixed-bed testing. During entrained-flow testing, a steady-state Hg removal of 82% was achieved using Si-1 at injection rates of both 6 x 10{sup -5} and 1.2 x 10{sup -4} g.L{sup -1}.h{sup -1}. The lack of increase in Hg removal when the injection rate is doubled suggests that pore accessibility is the rate-controlling step during dynamic Hg capture. A calculation of the approximate pore usage based on injection testing helped confirm this observation. During injection testing, the performance of Si-1 was only diminished 10% when exposed to 20 ppm SO{sub 3}. This is an encouraging result for flue-gas applications where SO{sub 3} levels range from 1 to 40 ppm. Testing demonstrated that Si-1 is stable when exposed to leaching conditions after concrete blending and cement impregnation. This is an important aspect to consider for injection because the sale of fly ash for concrete is a key cost-recovery tool for power plants. 27 refs., 8 figs., 5 tabs.

  7. Chromatographic determination of the differential isosteric adsorption enthalpies and differential entropies on ordered silica materials.

    PubMed

    Grajek, H; Paciura-Zadrozna, J; Witkiewicz, Z

    2008-06-13

    The adsorption properties of the ordered mesoporous siliceous materials: MCM-41C16 (denoted as C16), MCM-41C16-SH and MCM-41C16-NH(2) (known as MCMs) having different surface functionalities were studied by inverse gas chromatography to assess their suitability for adsorption of analytes from gas and liquid phases. Polar and non-polar adsorbates were employed. The differential isosteric enthalpies, -DeltaH(ads), and differential entropies, -DeltaS(ads), of adsorption of different 'molecular probes' were determined chromatographically. A mathematical link between the -DeltaH(ads), and -DeltaS(ads) magnitudes and experimental data was derived through an Antoine-type equation. The present studies have been entirely restricted to the region of low adsorbate concentration. The problem of the interrelationship between the -DeltaH(ads), and -DeltaS(ads) values, known as the 'thermodynamic compensation effect', and interpretation of chromatographic data for the adsorption of different adsorbates on the MCMs have been considered in the light of both experimental data obtained in the present studies and the data available in the literature for siliceous adsorbents with randomly ordered structures. It was shown chromatographically that there is substantial parallelism between the magnitudes of the differential isosteric enthalpy and differential entropy for some 'molecular probes' chromatographed on C16 and its derivatives. Complementary information was obtained by atomic-force microscopy (AFM), X-ray photoelectron spectroscopy and X-ray diffraction (XRD) spectroscopy.

  8. Heavy metal binding capacity (HMBC) of municipal solid waste landfill leachates.

    PubMed

    Ward, Marnie L; Bitton, Gabriel; Townsend, Timothy

    2005-07-01

    This research describes the use of a toxicity assay for the identification of metal toxicity, bioavailability and heavy metal binding capacity (HMBC) of municipal solid waste (MSW) landfill leachates. MetPLATE, an assay specific for heavy metal toxicity, was used to determine the HMBC of MSW leachates collected from 14 sites in Florida, with a wide range of chemical and physical characteristics. The leachates displayed a low toxicity which was attributed to the site-specific parameters, including, high concentrations of both organic and inorganic ligands. The HMBC test was undertaken to measure the effect of these site-specific parameters on metal toxicity. The potential for MSW leachate to bind and, thus, detoxify heavy metals was investigated with copper, zinc, and mercury. The HMBC values obtained ranged from 3 to 115, 5 to 93 and 4 to 101 for HMBC-Cu+2, HMBC-Zn+2, and HMBC-Hg+2, respectively. Additionally, the high strength leachates displayed the highest binding capacities, although the landfills sampled represented a wide range of characteristics. For comparison, the HMBC values reported with local lake water, Lake Alice and Lake Beverly, and a wastewater treatment plant effluent were all below 3. A partial fractionation of MSW leachate samples from sites 1, 5 and 8, was conducted to further investigate the influence of selected site-specific physico-chemical parameters on metal binding. The fractionation revealed that the HMBC of the leachate samples was heavily influenced by the concentration of solids, organics and hardness.

  9. Metal-binding characteristics of the gamma-glutamyl capsular polymer of Bacillus licheniformis ATCC 9945

    SciTech Connect

    McLean, R.J.C.; Beauchemin, D.; Clapham, L.; Beveridge, T.J. Univ. of Guelph, Ontario )

    1990-12-01

    The metal-binding affinity of the anionic poly-{gamma}-D-glutamyl capsule of Bacillus licheniformis was investigated by using Na{sup +}, Mg{sup 2+}, Al{sup 3+}, Ca{sup 2+}, Cr{sup 3+}, Mn{sup 2+}, Fe{sup 3+}, Ni{sup 2+}, and Cu{sup 2+}. Exposure of purified capsule to excess concentrations of Na{sup +} revealed it to contain 8.2 {mu}mol of anionic sites per mg on the basis of Na binding. Other metal ions were then added in ionic concentrations equivalent to 25, 50, 75, 100, 200, and 400% of the available anionic sites. The binding characteristics varied with the metal being investigated. Addition of Cu{sup 2+}, Al{sup 3+}, Cr{sup 3+}, or Fe{sup 3+} induced flocculation. These metal ions showed the greatest affinity for B. licheniformis capsule in competitive-binding experiments. Flocculation was not seen with the addition of other metal ions. With the exception of Ni{sup 2+} and Fe{sup 3+} all capsule-metal-binding sites readily saturated. Ni{sup 2+} had low affinity for the polymer, and its binding was increased at high metal concentrations. Fe{sup 3+} binding resulted in the development of rust-colored ferrihydrite which itself could bind additional metal.

  10. Exploring the Influence of the Protein Environment on Metal-Binding Pharmacophores

    PubMed Central

    2015-01-01

    The binding of a series of metal-binding pharmacophores (MBPs) related to the ligand 1-hydroxypyridine-2-(1H)-thione (1,2-HOPTO) in the active site of human carbonic anhydrase II (hCAII) has been investigated. The presence and/or position of a single methyl substituent drastically alters inhibitor potency and can result in coordination modes not observed in small-molecule model complexes. It is shown that this unexpected binding mode is the result of a steric clash between the methyl group and a highly ordered water network in the active site that is further stabilized by the formation of a hydrogen bond and favorable hydrophobic contacts. The affinity of MBPs is dependent on a large number of factors including donor atom identity, orientation, electrostatics, and van der Waals interactions. These results suggest that metal coordination by metalloenzyme inhibitors is a malleable interaction and that it is thus more appropriate to consider the metal-binding motif of these inhibitors as a pharmacophore rather than a “chelator”. The rational design of inhibitors targeting metalloenzymes will benefit greatly from a deeper understanding of the interplay between the variety of forces governing the binding of MBPs to active site metal ions. PMID:25116076

  11. A New Metal Binding Domain Involved in Cadmium, Cobalt and Zinc Transport

    SciTech Connect

    Smith, Aaron T.; Barupala, Dulmini; Stemmler, Timothy L.; Rosenzweig, Amy C.

    2015-07-20

    In the P1B-ATPases, which couple cation transport across membranes to ATP hydrolysis, are central to metal homeostasis in all organisms. An important feature of P1B-ATPases is the presence of soluble metal binding domains (MBDs) that regulate transport activity. Only one type of MBD has been characterized extensively, but bioinformatics analyses indicate that a diversity of MBDs may exist in nature. Here we report the biochemical, structural and functional characterization of a new MBD from the Cupriavidus metallidurans P1B-4-ATPase CzcP (CzcP MBD). The CzcP MBD binds two Cd2+, Co2+ or Zn2+ ions in distinct and unique sites and adopts an unexpected fold consisting of two fused ferredoxin-like domains. Both in vitro and in vivo activity assays using full-length CzcP, truncated CzcP and several variants indicate a regulatory role for the MBD and distinct functions for the two metal binding sites. Moreover, these findings elucidate a previously unknown MBD and suggest new regulatory mechanisms for metal transport by P1B-ATPases.

  12. Influence of chemical and environmental stresses on metal-binding proteins: Species-dependent effects

    SciTech Connect

    Baer, K.N.

    1988-01-01

    The development of tolerance to cadmium toxicity was investigated in mammals. In adult mice pretreated with 20 mg Cd/kg, no mortality was observed following administration of a 100 mg/kg cadmium challenge dose. In animals receiving prior exposure to cold stress a mortality of 40% was observed, while in animals receiving no pretreatment an 80% mortality was observed following cadmium challenge. Analysis of the metal-binding proteins using G-75 gel-filtration chromatography revealed that MT-like protein was responsible, in part, for the observed tolerance to cadmium toxicity. For example, following 20 mg Cd/kg and cold pretreatment, the MT-like reserve capacity was 56 and 42 nmoles cadmium, respectively, compared to a control value of 12 nmoles cadmium. The influence of pretreatments on the subcellular distribution of cadmium was also examined. The influence of chemical and environmental stresses on metal-binding proteins in teleosts was investigated. Following cadmium exposure, cadmium increased in the MT fraction in both the gill and liver. However, following exposure to environmental stresses such as cold and hypoxia, significant decreases in zinc and copper were observed in the gill MT fraction, as compared to control. In the liver, no significant alterations were observed in the MT fraction, as compared to control.

  13. Halophilic properties of metal binding protein characterized by high histidine content from Chromohalobacter salexigens DSM3043.

    PubMed

    Yamaguchi, Rui; Arakawa, Tsutomu; Tokunaga, Hiroko; Ishibashi, Matsujiro; Tokunaga, Masao

    2012-02-01

    Periplasmic metal binding protein characterized by high histidine content was cloned from moderate halophile, Chromohalobacter salexigens. The protein, termed histidine-rich metal binding protein (HP), was expressed in and purified from E. coli as a native form. HP bound to Ni- and Cu-loaded chelate columns with high affinity, and Co- and Zn-columns with moderate affinity. Although the secondary structure was not grossly altered by the addition of 0.2-2.0 M NaCl, the thermal transition pattern was considerably shifted to higher temperature with increasing salt concentration: melting temperature was raised by ~20 °C at 2.0 M NaCl over the melting temperature at 0.2 M NaCl. HP showed reversible refolding from thermal melting in 0.2-1.15 M NaCl, while it formed irreversible aggregates upon thermal melting at 2 M NaCl. Addition of 0.01-0.1 mM NiSO₄ stabilized HP against thermal melting with high reversibility, while addition above 0.5 mM resulted in irreversible melting due to aggregation.

  14. Exploring the influence of the protein environment on metal-binding pharmacophores.

    PubMed

    Martin, David P; Blachly, Patrick G; McCammon, J Andrew; Cohen, Seth M

    2014-08-28

    The binding of a series of metal-binding pharmacophores (MBPs) related to the ligand 1-hydroxypyridine-2-(1H)-thione (1,2-HOPTO) in the active site of human carbonic anhydrase II (hCAII) has been investigated. The presence and/or position of a single methyl substituent drastically alters inhibitor potency and can result in coordination modes not observed in small-molecule model complexes. It is shown that this unexpected binding mode is the result of a steric clash between the methyl group and a highly ordered water network in the active site that is further stabilized by the formation of a hydrogen bond and favorable hydrophobic contacts. The affinity of MBPs is dependent on a large number of factors including donor atom identity, orientation, electrostatics, and van der Waals interactions. These results suggest that metal coordination by metalloenzyme inhibitors is a malleable interaction and that it is thus more appropriate to consider the metal-binding motif of these inhibitors as a pharmacophore rather than a "chelator". The rational design of inhibitors targeting metalloenzymes will benefit greatly from a deeper understanding of the interplay between the variety of forces governing the binding of MBPs to active site metal ions.

  15. Kinetic Analysis of the Metal Binding Mechanism of Escherichia coli Manganese Superoxide Dismutase

    PubMed Central

    Whittaker, Mei M.; Mizuno, Kazunori; Bächinger, Hans Peter; Whittaker, James W.

    2006-01-01

    The acquisition of a catalytic metal cofactor is an essential step in the maturation of every metalloenzyme, including manganese superoxide dismutase (MnSOD). In this study, we have taken advantage of the quenching of intrinsic protein fluorescence by bound metal ions to continuously monitor the metallation reaction of Escherichia coli MnSOD in vitro, permitting a detailed kinetic characterization of the uptake mechanism. Apo-MnSOD metallation kinetics are “gated”, zero order in metal ion for both the native Mn2+ and a nonnative metal ion (Co2+) used as a spectroscopic probe to provide greater sensitivity to metal binding. Cobalt-binding time courses measured over a range of temperatures (35–50°C) reveal two exponential kinetic processes (fast and slow phases) associated with metal binding. The amplitude of the fast phase increases rapidly as the temperature is raised, reflecting the fraction of Apo-MnSOD in an “open” conformation, and its temperature dependence allows thermodynamic parameters to be estimated for the “closed” to “open” conformational transition. The sensitivity of the metallated protein to exogenously added chelator decreases progressively with time, consistent with annealing of an initially formed metalloprotein complex (kanneal = 0.4 min−1). A domain-separation mechanism is proposed for metal uptake by apo-MnSOD. PMID:16258041

  16. Development and evaluation of a new multi-metal binding biosorbent.

    PubMed

    Abdolali, A; Ngo, H H; Guo, W S; Lee, D J; Tung, K L; Wang, X C

    2014-05-01

    A novel multi-metal binding biosorbent (MMBB) was developed by combining a group of three from the selective natural lignocellulosic agro-industrial wastes for effectively eliminating lead, cadmium, copper and zinc from aqueous solutions. Four MMBBs with different combinations (MMBB1: tea waste, corncob, sugarcane bagasse; MMBB2: tea waste, corncob and sawdust; MMBB3: tea waste, corncob and apple peel; MMBB4: tea waste, corncob and grape stalk) were evaluated. FTIR analysis for characterizing the MMBB2 explored that the MMBB2 contains more functional groups available for multi-metals binding. Comparing among the MMBBs as well as the single group biosorbents, MMBB2 was the best biosorbent with the maximum biosorption capacities of 41.48, 39.48, 94.00 and 27.23 mg/g for Cd(II), Cu(II), Pb(II) and Zn(II), respectively. After 5 times of desorption with CaCl2, CH3COOH and NaCl as eluent, the MMBB2 still remained excellent biosorptive capacity, so as it could be well regenerated for reuse and possible recovery of metals.

  17. Synthesis Mechanism and Thermal Optimization of an Economical Mesoporous Material Using Silica: Implications for the Effective Removal or Delivery of Ibuprofen

    PubMed Central

    Kittappa, Shanmuga; Cui, Mingcan; Ramalingam, Malarvili; Ibrahim, Shaliza; Khim, Jeehyeong; Yoon, Yeomin; Snyder, Shane A.; Jang, Min

    2015-01-01

    Mesoporous silica materials (MSMs) were synthesized economically using silica (SiO2) as a precursor via a modified alkaline fusion method. The MSM prepared at 500°C (MSM–500) had the highest surface area, pore size, and volume, and the results of isotherms and the kinetics of ibuprofen (IBP) removal indicated that MSM–500 had the highest sorption capacity and fastest removal speed vs. SBA–15 and zeolite. Compared with commercial granular activated carbon (GAC), MSM–500 had a ~100 times higher sorption rate at neutral pH. IBP uptake by MSM–500 was thermodynamically favorable at room temperature, which was interpreted as indicating relatively weak bonding because the entropy (∆adsS, –0.07 J mol–1 K–1) was much smaller. Five times recycling tests revealed that MSM–500 had 83–87% recovery efficiencies and slower uptake speeds due to slight deformation of the outer pore structure. In the IBP delivery test, MSM–500 drug loading was 41%, higher than the reported value of SBA–15 (31%). The in vitro release of IBP was faster, almost 100%, reaching equilibrium within a few hours, indicating its effective loading and unloading characteristics. A cost analysis study revealed that the MSM was ~10–70 times cheaper than any other mesoporous silica material for the removal or delivery of IBP. PMID:26161510

  18. Development of bacterium-based heavy metal biosorbents: Enhanced uptake of cadmium and mercury by Escherichia coli expressing a metal binding motif

    SciTech Connect

    Pazirandeh, M.; Wells, B.M.; Ryan, R.L.

    1998-10-01

    A gene coding for a de novo peptide sequence containing a metal binding motif was chemically synthesized and expressed in Escherichia coli as a fusion with the maltose binding protein. Bacterial cells expressing the metal binding peptide fusion demonstrated enhanced binding of Cd{sup 2+} and Hg{sup 2+} compared to bacterial cells lacking the metal binding peptide. The potential use of genetically engineered bacteria as biosorbents for the removal of heavy metals from wastewaters is discussed.

  19. Preparation and physical characterization of calcium sulfate cement/silica-based mesoporous material composites for controlled release of BMP-2

    PubMed Central

    Tan, Honglue; Yang, Shengbing; Dai, Pengyi; Li, Wuyin; Yue, Bing

    2015-01-01

    As a commonly used implant material, calcium sulfate cement (CSC), has some shortcomings, including low compressive strength, weak osteoinduction capability, and rapid degradation. In this study, silica-based mesoporous materials such as SBA-15 were synthesized and combined with CSC to prepare CSC/SBA-15 composites. The properties of SBA-15 were characterized by X-ray diffraction, transmission electron microscopy, and nitrogen adsorption–desorption isotherms. SBA-15 was blended into CSC at 0, 5, 10, and 20 wt%, referred to as CSC, CSC-5S (5% mass ratio), CSC-10S (10% mass ratio), and CSC-20S (20% mass ratio), respectively. Fourier-transform infrared spectroscopy and compression tests were used to determine the structure and mechanical properties of the composites, respectively. The formation of hydroxyapatite on composite surfaces was analyzed using scanning electron microscopy and X-ray diffraction after soaking in simulated body fluid. BMP-2 was loaded into the composites by vacuum freeze-drying, and its release characteristics were detected by Bradford protein assay. The in vitro degradation of the CSC/SBA-15 composite was investigated by measuring weight loss. The results showed that the orderly, nanostructured, mesoporous SBA-15 possessed regular pore size and structure. The compressive strength of CSC/SBA-15 increased with the increase in SBA-15 mass ratio, and CSC-20S demonstrated the maximum strength. Compared to CSC, hydroxyapatite that formed on the surfaces of CSC/SBA-15 was uniform and compact. The degradation rate of CSC/SBA-15 decreased with increasing mass ratio of SBA-15. The adsorption of BMP-2 increased and released at a relatively slow rate; the release rate of BMP-2 in CSC-20S was the slowest, and presented characteristics of low doses of release. In vitro experiments demonstrated that the physical properties of pure CSC incorporated with SBA-15 could be improved significantly, which made the CSC/SBA-15 composite more suitable for bone repair

  20. Silica-polyamine composite materials for heavy metal ion removal, recovery, and recycling. 2. Metal ion separations from mine wastewater and soft metal ion extraction efficiency

    SciTech Connect

    Fischer, R.J.; Pang, D.; Beatty, S.T.; Rosenberg, E.

    1999-12-01

    Silica-polyamine composites have been synthesized which have metal ion capacities as high as 0.84 mmol/g for copper ions removed from aqueous solutions. In previous reports it has been demonstrated that these materials survive more than 3,000 cycles of metal ion extraction, elution, and regeneration with almost no loss of capacity (less than 10%). This paper describes two modified silica-polyamine composite materials and reveals the results of tests designed to determine the effectiveness of these materials for extracting and separating metal ions from actual mining wastewater samples. Using these materials, the concentration of copper, aluminum, and zinc in Berkeley Pit mine wastewater is reduced to below allowable discharge limits. The recovered copper and zinc solutions were greater than 90% pure, and metal ion concentration factors of over 20 for copper were realized. Further, the ability of one of these materials to decrease low levels of the soft metals cadmium, mercury, and lead from National Sanitation Foundation recommended challenge levels to below Environmental Protection Agency allowable limits is also reported.

  1. The effect of various naturally occurring metal-binding compounds on the electrochemical behavior of aluminum

    SciTech Connect

    Hansen, D.C.; McCafferty, E.

    1996-01-01

    Naturally occurring biological molecules are of considerable interest as possible corrosion inhibitors because of increased attention on the development of environmentally compatible, nonpolluting corrosion inhibitors. A hydroxamate yeast siderophore (rhodotorulic acid), a catecholate bacterial siderophore (parabactin), an adhesive protein from the blue mussel Mytilus edulis, and two metal-binding compounds isolated from the tomato and sunflower roots, namely, chlorogenic and caffeic acid, respectively, were adsorbed from solution onto pure aluminum (99.9995%) and their effect on the critical pitting potential and polarization resistance in deaerated 0.1 M NaCl was measured. These measurements were made using anodic polarization and ac impedance spectroscopy. The catechol-containing siderophore has an inhibitive effect on the critical pitting potential of aluminum in 0.1 M NaCl and increases the polarization resistance of the metal over time. The adhesive protein from the blue mussel is also effective in inhibiting the pitting of aluminum.

  2. Structure and Synaptic Function of Metal Binding to the Amyloid Precursor Protein and its Proteolytic Fragments

    PubMed Central

    Wild, Klemens; August, Alexander; Pietrzik, Claus U.; Kins, Stefan

    2017-01-01

    Alzheimer’s disease (AD) is ultimately linked to the amyloid precursor protein (APP). However, current research reveals an important synaptic function of APP and APP-like proteins (APLP1 and 2). In this context various neurotrophic and neuroprotective functions have been reported for the APP proteolytic fragments sAPPα, sAPPβ and the monomeric amyloid-beta peptide (Aβ). APP is a metalloprotein and binds copper and zinc ions. Synaptic activity correlates with a release of these ions into the synaptic cleft and dysregulation of their homeostasis is linked to different neurodegenerative diseases. Metal binding to APP or its fragments affects its structure and its proteolytic cleavage and therefore its physiological function at the synapse. Here, we summarize the current data supporting this hypothesis and provide a model of how these different mechanisms might be intertwined with each other. PMID:28197076

  3. The properties of silica-gelatin composites

    NASA Astrophysics Data System (ADS)

    Stavinskaya, O. N.; Laguta, I. V.

    2010-06-01

    Silica-gelatin composites with various silica-to-gelatin ratios were obtained. The influence of high-dispersity silica on the swelling of composites in water and desorption of pyridoxine and thiamine vitamins incorporated into the material was studied. The addition of silica to gelatin was shown to increase the time of the dissolution of the materials in aqueous medium and decelerate the desorption of vitamins.

  4. Absorption Spectroscopy Study of Acid-Base and Metal-Binding Properties of Flavanones

    NASA Astrophysics Data System (ADS)

    Shubina, V. S.; Shatalina, Yu. V.

    2013-11-01

    We have used absorption spectroscopy to study the acid-base and metal-binding properties of two structurally similar flavanones: taxifolin and naringenin. We have determined the acid dissociation constants for taxifolin (pKa1 = 7.10 ± 0.05, pKa2 = 8.60 ± 0.09, pKa3 = 8.59 ± 0.19, pKa4 = 11.82 ± 0.36) and naringenin (pKa1 = 7.05 ± 0.05, pKa2 = 8.85 ± 0.09, pKa3 = 12.01 ± 0.38). The appearance of new absorption bands in the visible wavelength region let us determine the stoichiometric composition of the iron (II) complexes of the flavanones. We show that at pH 5, in solution there is a mixture of complexes between taxifolin and iron (II) ions in stoichiometric ratio 2:1 and 1:2, while at pH 7.4 and pH 9, we detect a 1:1 taxifolin:Fe(II) complex. We established that at these pH values, naringenin forms a 2:1 complex with iron (II) ions. We propose structures for the complexes formed. Comprehensive study of the acid-base properties and the metal-binding capability of the two structurally similar flavanones let us determine the structure-properties relation and the conditions under which antioxidant activity of the polyphenols appears, via chelation of variable-valence metal ions.

  5. Catalytic reduction of organic dyes at gold nanoparticles impregnated silica materials: influence of functional groups and surfactants

    NASA Astrophysics Data System (ADS)

    Azad, Uday Pratap; Ganesan, Vellaichamy; Pal, Manas

    2011-09-01

    Gold nanoparticles (Au NPs) in three different silica based sol-gel matrixes with and without surfactants are prepared. They are characterized by UV-vis absorbance and transmission electron microscopic (TEM) studies. The size and shape of Au NPs varied with the organo-functional group present in the sol-gel matrix. In the presence of mercaptopropyl functionalized organo-silica, large sized (200-280 nm) spherical Au NPs are formed whereas in the presence of aminopropyl functionalized organo-silica small sized (5-15 nm) Au NPs are formed inside the tube like organo-silica. Further, it is found that Au NPs act as efficient catalyst for the reduction of organic dyes. The catalytic rate constant is evaluated from the decrease in absorbance of the dye molecules. Presence of cationic or anionic surfactants greatly influences the catalytic reaction. The other factors like hydrophobicity of the organic dyes, complex formation of the dyes with anionic surfactants, repulsion between dyes and cationic surfactant, adsorption of dyes on the Au NPs also play important role on the reaction rate.

  6. Sol-gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure-activity correlations in hybrid materials targeting Zn(II) antibacterial use.

    PubMed

    Halevas, E; Nday, C M; Kaprara, E; Psycharis, V; Raptopoulou, C P; Jackson, G E; Litsardakis, G; Salifoglou, A

    2015-10-01

    In the emerging issue of enhanced multi-resistant properties in infectious pathogens, new nanomaterials with optimally efficient antibacterial activity and lower toxicity than other species attract considerable research interest. In an effort to develop such efficient antibacterials, we a) synthesized acid-catalyzed silica-gel matrices, b) evaluated the suitability of these matrices as potential carrier materials for controlled release of ZnSO4 and a new Zn(II) binary complex with a suitably designed well-defined Schiff base, and c) investigated structural and textural properties of the nanomaterials. Physicochemical characterization of the (empty-loaded) silica-nanoparticles led to an optimized material configuration linked to the delivery of the encapsulated antibacterial zinc load. Entrapment and drug release studies showed the competence of hybrid nanoparticles with respect to the a) zinc loading capacity, b) congruence with zinc physicochemical attributes, and c) release profile of their zinc load. The material antimicrobial properties were demonstrated against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus) and negative (Escherichia coli, Pseudomonas aeruginosa, Xanthomonas campestris) bacteria using modified agar diffusion methods. ZnSO4 showed less extensive antimicrobial behavior compared to Zn(II)-Schiff, implying that the Zn(II)-bound ligand enhances zinc antimicrobial properties. All zinc-loaded nanoparticles were less antimicrobially active than zinc compounds alone, as encapsulation controls their release, thereby attenuating their antimicrobial activity. To this end, as the amount of loaded zinc increases, the antimicrobial behavior of the nano-agent improves. Collectively, for the first time, sol-gel zinc-loaded silica-nanoparticles were shown to exhibit well-defined antimicrobial activity, justifying due attention to further development of antibacterial nanotechnology.

  7. MODELING OF METAL BINDING ON HUMIC SUBSTANCES USING THE NIST DATABASE: AN A PRIORI FUNCTIONAL GROUP APPROACH

    EPA Science Inventory

    Various modeling approaches have been developed for metal binding on humic substances. However, most of these models are still curve-fitting exercises-- the resulting set of parameters such as affinity constants (or the distribution of them) is found to depend on pH, ionic stren...

  8. Silica, hybrid silica, hydride silica and non-silica stationary phases for liquid chromatography.

    PubMed

    Borges, Endler M

    2015-04-01

    Free silanols on the surface of silica are the "villains", which are responsible for detrimental interactions of those compounds and the stationary phase (i.e., bad peak shape, low efficiency) as well as low thermal and chemical stability. For these reasons, we began this review describing new silica and hybrid silica stationary phases, which have reduced and/or shielded silanols. At present, in liquid chromatography for the majority of analyses, reversed-phase liquid chromatography is the separation mode of choice. However, the needs for increased selectivity and increased retention of hydrophilic bases have substantially increased the interest in hydrophilic interaction chromatography (HILIC). Therefore, stationary phases and this mode of separation are discussed. Then, non-silica stationary phases (i.e., zirconium oxide, titanium oxide, alumina and porous graphitized carbon), which afford increased thermal and chemical stability and also selectivity different from those obtained with silica and hybrid silica, are discussed. In addition, the use of these materials in HILIC is also reviewed.

  9. Extraction-spectrophotometric determination of trace phosphorus in chromium-bearing materials which may contain silica, niobium, tantalum, zirconium, titanium, and hafnium

    SciTech Connect

    Zatka, V.J.; Zelding, N.

    1984-08-01

    In this paper, a general extraction-spectrophotometric molybdenum blue method is described for the determination of phosphorus in chromium-bearing materials, e.g., chromite ore, complex nickel alloys, stainless and speciality steels, magnetic alloys, etc. Refractory elements and silica do not interfere. To avoid low recoveries, phosphorus must be extracted from chromium-free solutions. The separation is achieved by precipitating ferric or zirconium phosphate after all chromium has been oxidized to the hexavalent form. Selective fluoride complexation controlled by boric acid is used to eliminate interference by Nb, Ta, Zr, Hf, or Ti. 17 references, 3 tables.

  10. A Rapid and Sensitive Strip-Based Quick Test for Nerve Agents Tabun, Sarin, and Soman Using BODIPY-Modified Silica Materials.

    PubMed

    Climent, Estela; Biyikal, Mustafa; Gawlitza, Kornelia; Dropa, Tomáš; Urban, Martin; Costero, Ana M; Martínez-Máñez, Ramón; Rurack, Knut

    2016-08-01

    Test strips that in combination with a portable fluorescence reader or digital camera can rapidly and selectively detect chemical warfare agents (CWAs) such as Tabun (GA), Sarin (GB), and Soman (GD) and their simulants in the gas phase have been developed. The strips contain spots of a hybrid indicator material consisting of a fluorescent BODIPY indicator covalently anchored into the channels of mesoporous SBA silica microparticles. The fluorescence quenching response allows the sensitive detection of CWAs in the μg m(-3) range in a few seconds.

  11. Heavy metal binding to heparin disaccharides. II. First evidence for zinc chelation.

    PubMed

    Whitfield, D M; Sarkar, B

    1992-06-01

    To map out the heavy metal binding sites of iduronic acid containing oligosaccharides isolated from human kidneys, we studied Zn(II) binding by nuclear magnetic resonance (NMR) and molecular modeling to two disaccharides isolated after nitrous acid depolymerization of heparin and two synthetic disaccharides representative of the heparin structure, namely, IdopA2S (alpha 1,4)AnManOH, 1 alpha, IdopA2S (alpha 1,4)AnManOH6S, 1b, IdopA2S-(alpha 1,4)GlcNS alpha Me, 2a, and IdopA2S (alpha 1,4)GlcNS6S alpha Me, 2b (see previous article in this series). A conformational analysis of the metal free and metal bound solutions was made by comparing calculated [(NOE)]s, [T1]s, and [J]s to experimental values. The 1C4, 4C1, and 2S0 conformations of the L-idopyranosiduronate ring and the 4E and 4T3 of the anhydro-D-mannitol ring are evaluated as are rotations about the C5-C6 hydroxymethylene of the AnManOH(6S) or GlcNS (6S) residues. The NOE between IdopA2S H1 and H3 and the known NOE between H2 and H5, as well as the T1 of IdopA2S H3, are introduced as NMR observables sensitive to the IdopA2S ring conformation. Similarly, a NOE between IdopA2S H5 and AnManOH(6S) or GlcNS(6S) H3 was observed that directly restricts the allowed interglycosidic conformational space. For all disaccharides, the Zn(II) bound spectral data are consistent with models in which these motions are partially "frozen" such that the 1C4 conformation of the IdopA2S is stabilized along with the 4T3 conformation of the AnManOH(6S) ring. The interglycosidic conformation is also stabilized in one of two minima. Electrostatic potential energy calculations gave the best overall agreement with experiment and suggest metal binding conformations with the carboxylate and ring oxygen of the IdopA2S residues (1C4 conformation) and either O3 of the GlcNS(6S) residues or the sulfate oxygens of the 6-sulphate for 2b providing additional chelating sites. These chelation models concur with the observation of marked 13C and 1H NMR

  12. Designed synthesis of carbon-functional magnetic graphene mesoporous silica materials using polydopamine as carbon precursor for the selective enrichment of N-linked glycan.

    PubMed

    Sun, Nianrong; Yao, Jizong; Deng, Chunhui

    2016-02-01

    Glycosylation, which has been confirmed to be associated with many diseases, is an important protein post-translation modification. Taking into account the low abundant of glycan, the purification of complex biological samples is considered to be very significant before mass spectrometry detection. In this work, carbon-functionalized magnetic graphene /mesoporous silica materials (C-Mag G@mSiO2 materials) with high content of carbon were designed and synthesized by using polydopamine as carbon precursor. Taking advantage of the special interaction between carbon and glycan, C-Mag G@mSiO2 materials were successfully applied to enrich N-linked glycans in different complex samples, such as standard glycoprotein digestion, the mixture of standard glycoprotein digestion, glycoprotein and non-glycoprotein, and human serum.

  13. The Fungus Tremella mesenterica Encodes the Longest Metallothionein Currently Known: Gene, Protein and Metal Binding Characterization

    PubMed Central

    Lin, Weiyu; Calatayud, Sara; Palacios, Òscar; Capdevila, Mercè; Atrian, Sílvia

    2016-01-01

    Fungal Cu-thioneins, and among them, the paradigmatic Neurospora crassa metallothionein (MT) (26 residues), were once considered as the shortest MTs -the ubiquitous, versatile metal-binding proteins- among all organisms, and thus representatives of their primeval forms. Nowadays, fungal MTs of diverse lengths and sequence features are known, following the huge heterogeneity of the Kingdom of Fungi. At the opposite end of N. crassa MT, the recently reported Cryptococcus neoformans CnMT1 and CnMT2 (122 and 186 aa) constitute the longest reported fungal MTs, having been identified as virulence factors of this pathogen. CnMTs are high-capacity Cu-thioneins that appear to be built by tandem amplification of a basic unit, a 7-Cys segment homologous to N. crassa MT. Here, we report the in silico, in vivo and in vitro study of a still longer fungal MT, belonging to Tremella mesenterica (TmMT), a saprophytic ascomycete. The TmMT gene has 10 exons, and it yields a 779-bp mature transcript that encodes a 257 residue-long protein. This MT is also built by repeated fragments, but of variable number of Cys: six units of the 7-Cys building blocks-CXCX3CSCPPGXCXCAXCP-, two fragments of six Cys, plus three Cys at the N-terminus. TmMT metal binding abilities have been analyzed through the spectrophotometric and spectrometric characterization of its recombinant Zn-, Cd- and Cu-complexes. Results allow it to be unambiguous classified as a Cu-thionein, also of extraordinary coordinating capacity. According to this feature, when the TmMT cDNA is expressed in MT-devoid yeast cells, it is capable of restoring a high Cu tolerance level. Since it is not obvious that T. mesenterica shares the same physiological needs for a high capacity Cu-binding protein with C. neoformans, the existence of this peculiar MT might be better explained on the basis of a possible role in Cu-handling for the Cu-enzymes responsible in lignin degradation pathways. PMID:26882011

  14. The Fungus Tremella mesenterica Encodes the Longest Metallothionein Currently Known: Gene, Protein and Metal Binding Characterization.

    PubMed

    Iturbe-Espinoza, Paul; Gil-Moreno, Selene; Lin, Weiyu; Calatayud, Sara; Palacios, Òscar; Capdevila, Mercè; Atrian, Sílvia

    2016-01-01

    Fungal Cu-thioneins, and among them, the paradigmatic Neurospora crassa metallothionein (MT) (26 residues), were once considered as the shortest MTs--the ubiquitous, versatile metal-binding proteins--among all organisms, and thus representatives of their primeval forms. Nowadays, fungal MTs of diverse lengths and sequence features are known, following the huge heterogeneity of the Kingdom of Fungi. At the opposite end of N. crassa MT, the recently reported Cryptococcus neoformans CnMT1 and CnMT2 (122 and 186 aa) constitute the longest reported fungal MTs, having been identified as virulence factors of this pathogen. CnMTs are high-capacity Cu-thioneins that appear to be built by tandem amplification of a basic unit, a 7-Cys segment homologous to N. crassa MT. Here, we report the in silico, in vivo and in vitro study of a still longer fungal MT, belonging to Tremella mesenterica (TmMT), a saprophytic ascomycete. The TmMT gene has 10 exons, and it yields a 779-bp mature transcript that encodes a 257 residue-long protein. This MT is also built by repeated fragments, but of variable number of Cys: six units of the 7-Cys building blocks--CXCX3CSCPPGXCXCAXCP-, two fragments of six Cys, plus three Cys at the N-terminus. TmMT metal binding abilities have been analyzed through the spectrophotometric and spectrometric characterization of its recombinant Zn-, Cd- and Cu-complexes. Results allow it to be unambiguous classified as a Cu-thionein, also of extraordinary coordinating capacity. According to this feature, when the TmMT cDNA is expressed in MT-devoid yeast cells, it is capable of restoring a high Cu tolerance level. Since it is not obvious that T. mesenterica shares the same physiological needs for a high capacity Cu-binding protein with C. neoformans, the existence of this peculiar MT might be better explained on the basis of a possible role in Cu-handling for the Cu-enzymes responsible in lignin degradation pathways.

  15. ETMB-RBF: Discrimination of Metal-Binding Sites in Electron Transporters Based on RBF Networks with PSSM Profiles and Significant Amino Acid Pairs

    PubMed Central

    Ou, Yu-Yen; Chen, Shu-An; Wu, Sheng-Cheng

    2013-01-01

    Background Cellular respiration is the process by which cells obtain energy from glucose and is a very important biological process in living cell. As cells do cellular respiration, they need a pathway to store and transport electrons, the electron transport chain. The function of the electron transport chain is to produce a trans-membrane proton electrochemical gradient as a result of oxidation–reduction reactions. In these oxidation–reduction reactions in electron transport chains, metal ions play very important role as electron donor and acceptor. For example, Fe ions are in complex I and complex II, and Cu ions are in complex IV. Therefore, to identify metal-binding sites in electron transporters is an important issue in helping biologists better understand the workings of the electron transport chain. Methods We propose a method based on Position Specific Scoring Matrix (PSSM) profiles and significant amino acid pairs to identify metal-binding residues in electron transport proteins. Results We have selected a non-redundant set of 55 metal-binding electron transport proteins as our dataset. The proposed method can predict metal-binding sites in electron transport proteins with an average 10-fold cross-validation accuracy of 93.2% and 93.1% for metal-binding cysteine and histidine, respectively. Compared with the general metal-binding predictor from A. Passerini et al., the proposed method can improve over 9% of sensitivity, and 14% specificity on the independent dataset in identifying metal-binding cysteines. The proposed method can also improve almost 76% sensitivity with same specificity in metal-binding histidine, and MCC is also improved from 0.28 to 0.88. Conclusions We have developed a novel approach based on PSSM profiles and significant amino acid pairs for identifying metal-binding sites from electron transport proteins. The proposed approach achieved a significant improvement with independent test set of metal-binding electron transport proteins

  16. Novel silica surface charge density mediated control of the optical properties of embedded optically active materials and its application for fiber optic pH sensing at elevated temperatures.

    PubMed

    Wang, Congjun; Ohodnicki, Paul R; Su, Xin; Keller, Murphy; Brown, Thomas D; Baltrus, John P

    2015-02-14

    Silica and silica incorporated nanocomposite materials have been extensively studied for a wide range of applications. Here we demonstrate an intriguing optical effect of silica that, depending on the solution pH, amplifies or attenuates the optical absorption of a variety of embedded optically active materials with very distinct properties, such as plasmonic Au nanoparticles, non-plasmonic Pt nanoparticles, and the organic dye rhodamine B (not a pH indicator), coated on an optical fiber. Interestingly, the observed optical response to varying pH appears to follow the surface charge density of the silica matrix for all the three different optically active materials. To the best of our knowledge, this optical effect has not been previously reported and it appears universal in that it is likely that any optically active material can be incorporated into the silica matrix to respond to solution pH or surface charge density variations. A direct application of this effect is for optical pH sensing which has very attractive features that can enable minimally invasive, remote, real time and continuous distributed pH monitoring. Particularly, as demonstrated here, using highly stable metal nanoparticles embedded in an inorganic silica matrix can significantly improve the capability of pH sensing in extremely harsh environments which is of increasing importance for applications in unconventional oil and gas resource recovery, carbon sequestration, water quality monitoring, etc. Our approach opens a pathway towards possible future development of robust optical pH sensors for the most demanding environmental conditions. The newly discovered optical effect of silica also offers the potential for control of the optical properties of optically active materials for a range of other potential applications such as electrochromic devices.

  17. Evolutionary history of redox metal-binding domains across the tree of life.

    PubMed

    Harel, Arye; Bromberg, Yana; Falkowski, Paul G; Bhattacharya, Debashish

    2014-05-13

    Oxidoreductases mediate electron transfer (i.e., redox) reactions across the tree of life and ultimately facilitate the biologically driven fluxes of hydrogen, carbon, nitrogen, oxygen, and sulfur on Earth. The core enzymes responsible for these reactions are ancient, often small in size, and highly diverse in amino acid sequence, and many require specific transition metals in their active sites. Here we reconstruct the evolution of metal-binding domains in extant oxidoreductases using a flexible network approach and permissive profile alignments based on available microbial genome data. Our results suggest there were at least 10 independent origins of redox domain families. However, we also identified multiple ancient connections between Fe2S2- (adrenodoxin-like) and heme- (cytochrome c) binding domains. Our results suggest that these two iron-containing redox families had a single common ancestor that underwent duplication and divergence. The iron-containing protein family constitutes ∼50% of all metal-containing oxidoreductases and potentially catalyzed redox reactions in the Archean oceans. Heme-binding domains seem to be derived via modular evolutionary processes that ultimately form the backbone of redox reactions in both anaerobic and aerobic respiration and photosynthesis. The empirically discovered network allows us to peer into the ancient history of microbial metabolism on our planet.

  18. Computational approaches for de novo design and redesign of metal-binding sites on proteins.

    PubMed

    Akcapinar, Gunseli Bayram; Sezerman, Osman Ugur

    2017-04-28

    Metal ions play pivotal roles in protein structure, function and stability. The functional and structural diversity of proteins in nature expanded with the incorporation of metal ions or clusters in proteins. Approximately one-third of these proteins in the databases contain metal ions. Many biological and chemical processes in nature involve metal ion-binding proteins, aka metalloproteins. Many cellular reactions that underpin life require metalloproteins. Most of the remarkable, complex chemical transformations are catalysed by metalloenzymes. Realization of the importance of metal-binding sites in a variety of cellular events led to the advancement of various computational methods for their prediction and characterization. Furthermore, as structural and functional knowledgebase about metalloproteins is expanding with advances in computational and experimental fields, the focus of the research is now shifting towards de novo design and redesign of metalloproteins to extend nature's own diversity beyond its limits. In this review, we will focus on the computational toolbox for prediction of metal ion-binding sites, de novo metalloprotein design and redesign. We will also give examples of tailor-made artificial metalloproteins designed with the computational toolbox.

  19. Similarities in the HIV-1 and ASV Integrease Active Site Upon Metal Binding

    SciTech Connect

    Lins, Roberto D.; Straatsma, TP; Briggs, J. M.

    2000-04-05

    The HIV-1 integrase, which is essential for viral replication, catalyzes the insertion of viral DNA into the host chromosome thereby recruiting host cell machinery into making viral proteins. It represents the third main HIV enzyme target for inhibitor design, the first two being the reverse transcriptase and the protease. We report here a fully hydrated 2 ns molecular dynamics simulation performed using parallel NWChem3.2.1 with the AMBER95 force field. The HIV-1 integrase catalytic domain previously determined by crystallography (1B9D) and modeling including two Mg2+ ions placed into the active site based on an alignment against an ASV integrase structure containing two divalent metals (1VSH), was used as the starting structure. The simulation reveals a high degree of flexibility in the region of residues 140-149 even in the presence of a second divalent metal ion and a dramatic conformational change of the side chain of E152 when the second metal ion is present. This study shows similarities in the behavior of the catalytic residues in the HIV-1 and ASV integrases upon metal binding. The present simulation also provides support to the hypothesis that the second metal ion is likely to be carried into the HIV-1 integrase active site by the substrate, a strand of DNA.

  20. Metal Binding in Photosystem II Super- and Subcomplexes from Barley Thylakoids1

    PubMed Central

    Persson, Daniel Pergament; Powikrowska, Marta

    2015-01-01

    Metals exert important functions in the chloroplast of plants, where they act as cofactors and catalysts in the photosynthetic electron transport chain. In particular, manganese (Mn) has a key function because of its indispensable role in the water-splitting reaction of photosystem II (PSII). More and better knowledge is required on how the various complexes of PSII are affected in response to, for example, nutritional disorders and other environmental stress conditions. We here present, to our knowledge, a new method that allows the analysis of metal binding in intact photosynthetic complexes of barley (Hordeum vulgare) thylakoids. The method is based on size exclusion chromatography coupled to inductively coupled plasma triple-quadrupole mass spectrometry. Proper fractionation of PSII super- and subcomplexes was achieved by critical selection of elution buffers, detergents for protein solubilization, and stabilizers to maintain complex integrity. The applicability of the method was shown by quantification of Mn binding in PSII from thylakoids of two barley genotypes with contrasting Mn efficiency exposed to increasing levels of Mn deficiency. The amount of PSII supercomplexes was drastically reduced in response to Mn deficiency. The Mn efficient genotype bound significantly more Mn per unit of PSII under control and mild Mn deficiency conditions than the inefficient genotype, despite having lower or similar total leaf Mn concentrations. It is concluded that the new method facilitates studies of the internal use of Mn and other biometals in various PSII complexes as well as their relative dynamics according to changes in environmental conditions. PMID:26084923

  1. Earthworm Lumbricus rubellus MT-2: Metal Binding and Protein Folding of a True Cadmium-MT

    PubMed Central

    Kowald, Gregory R.; Stürzenbaum, Stephen R.; Blindauer, Claudia A.

    2016-01-01

    Earthworms express, as most animals, metallothioneins (MTs)—small, cysteine-rich proteins that bind d10 metal ions (Zn(II), Cd(II), or Cu(I)) in clusters. Three MT homologues are known for Lumbricus rubellus, the common red earthworm, one of which, wMT-2, is strongly induced by exposure of worms to cadmium. This study concerns composition, metal binding affinity and metal-dependent protein folding of wMT-2 expressed recombinantly and purified in the presence of Cd(II) and Zn(II). Crucially, whilst a single Cd7wMT-2 species was isolated from wMT-2-expressing E. coli cultures supplemented with Cd(II), expressions in the presence of Zn(II) yielded mixtures. The average affinities of wMT-2 determined for either Cd(II) or Zn(II) are both within normal ranges for MTs; hence, differential behaviour cannot be explained on the basis of overall affinity. Therefore, the protein folding properties of Cd- and Zn-wMT-2 were compared by 1H NMR spectroscopy. This comparison revealed that the protein fold is better defined in the presence of cadmium than in the presence of zinc. These differences in folding and dynamics may be at the root of the differential behaviour of the cadmium- and zinc-bound protein in vitro, and may ultimately also help in distinguishing zinc and cadmium in the earthworm in vivo. PMID:26742040

  2. Quantifying Pb and Cd complexation by alginates and the role of metal binding on macromolecular aggregation.

    PubMed

    Lamelas, Cristina; Avaltroni, Fabrice; Benedetti, Marc; Wilkinson, Kevin J; Slaveykova, Vera I

    2005-01-01

    The Pb and Cd binding capacity of alginates were quantified by the determination of their complex stability constants and the concentration of complexing sites using H+, Pb2+, or Cd2+ selective electrodes in both static and dynamic titrations. Centrifugation filter devices (30 kDa filter cutoff), followed by inductively coupled plasma mass spectrometry (ICP-MS) measurements of lead or cadmium in the filtrates, were used to validate the results. The influence of ionic strength, pH, and the metal-to-alginate ratio was determined for a wide range of metal concentrations. Because of their polyelectrolytic properties, alginates may adopt different conformations depending on the physicochemistry of the medium, including the presence of metals. Therefore, molecular diffusion coefficients of the alginate were determined by fluorescence correlation spectroscopy under the same conditions of pH, ionic strength, and metal-to-alginate ratios that were used for the metal binding studies. The complexation and conformational properties of the alginate were related within the framework of the nonideal competitive adsorption isotherm (NICA) combined with a Donnan approach to account for both intrinsic and electrostatic contributions.

  3. Earthworm Lumbricus rubellus MT-2: Metal Binding and Protein Folding of a True Cadmium-MT.

    PubMed

    Kowald, Gregory R; Stürzenbaum, Stephen R; Blindauer, Claudia A

    2016-01-05

    Earthworms express, as most animals, metallothioneins (MTs)-small, cysteine-rich proteins that bind d(10) metal ions (Zn(II), Cd(II), or Cu(I)) in clusters. Three MT homologues are known for Lumbricus rubellus, the common red earthworm, one of which, wMT-2, is strongly induced by exposure of worms to cadmium. This study concerns composition, metal binding affinity and metal-dependent protein folding of wMT-2 expressed recombinantly and purified in the presence of Cd(II) and Zn(II). Crucially, whilst a single Cd₇wMT-2 species was isolated from wMT-2-expressing E. coli cultures supplemented with Cd(II), expressions in the presence of Zn(II) yielded mixtures. The average affinities of wMT-2 determined for either Cd(II) or Zn(II) are both within normal ranges for MTs; hence, differential behaviour cannot be explained on the basis of overall affinity. Therefore, the protein folding properties of Cd- and Zn-wMT-2 were compared by ¹H NMR spectroscopy. This comparison revealed that the protein fold is better defined in the presence of cadmium than in the presence of zinc. These differences in folding and dynamics may be at the root of the differential behaviour of the cadmium- and zinc-bound protein in vitro, and may ultimately also help in distinguishing zinc and cadmium in the earthworm in vivo.

  4. Separation of single-walled carbon nanotubes on silica gel. Materials morphology and Raman excitation wavelength affect data interpretation.

    PubMed

    Dyke, Christopher A; Stewart, Michael P; Tour, James M

    2005-03-30

    In this report, procedures are discussed for the enrichment of single-walled carbon nanotube (SWNT) types by simple filtration of the functionalized SWNTs through silica gel. This separation uses nanotube sidewall functionalization employing two different strategies. In the first approach, a crude mixture of metallic and semiconducting SWNTs was heavily functionalized with 4-tert-butylphenyl addends to impart solubility to the entire sample of SWNTs. Two major polarity fractions were rapidly filtered through silica gel, with the solvent being removed in vacuo, heated to 700 degrees C to remove the addends, and analyzed spectroscopically. The second approach uses two different aryldiazonium salts (one with a polar grafting group and one nonpolar), appended selectively onto the different SWNTs by means of titration and monitoring by UV analysis throughout the functionalization process. The different addends accentuate the polarity differences between the band-gap-based types permitting their partial separation on silica gel. Thermal treatment regenerated pristine SWNTs in enriched fractions. The processed samples were analyzed and characterized by Raman spectroscopy. A controlled functionalization method using 4-fluorophenyl and 4-iodophenyl addends was performed, and XPS analyses yielded data on the degree of functionalization needed to affect the van Hove singularities in the UV/vis/NIR spectra. Finally, we demonstrate that relative peak intensity changes in Raman spectra can be caused by morphological changes in SWNT bundling based on differing flocculation or deposition methods. Therefore a misleading impression of separations can result, underscoring the care needed in assessing efficacies in SWNT enrichment and the prerequisite use of multiple excitation wavelengths and similar flocculation or deposition methods in comparative analyses.

  5. [Zinc-induced interactions of the metal-binding domain of beta-amyloid with nucleic acids and glycosaminoglycans].

    PubMed

    Khmeleva, S A; Kozin, S A; Kiseleva, Y Y; Mitkevich, V A; Makarov, A A; Radko, S P

    2016-01-01

    Zinc ions form complexes with β-amyloid peptides and play an important role in Alzheimer's disease pathogenesis. It has been demonstrated by turbidimetry and correlation spectroscopy that synthetic peptide Aβ16 representing the metal-binding domain of β-amyloid is able to interact with nucleic acids, chondroitin polysulfate, and dextran sulfates in the presence of zinc ions. The amino acid D7H substitution enhanced the peptide binding to polyanions, whereas the H6R and H6A-H13A substitutions abolished this interaction. It is suggested that the metal-binding domain may serve as a zinc-dependent site of β-amyloid interaction with biological polyanions including DNA, RNA, and glycosaminoglycans.

  6. Application of solid phase extraction with the use of silica modified with polyaniline film for pretreatment of samples from plant material before HPLC determination of triterpenic acids.

    PubMed

    Sowa, Ireneusz; Wójciak-Kosior, Magdalena; Rokicka, Kamila; Kocjan, Ryszard; Szymczak, Grażyna

    2014-05-01

    The new sorbent based on silica gel coated with a film of polyaniline (Si-PANI) was obtained in a process of in situ polymerization directly on carrier particles and its potential application for pretreatment of plant material samples with the use of solid phase extraction (SPE) was investigated. Parameters such as cartridge conditioning, the volume and concentration of the sample, the type and volume of the elution solvent were optimized and compared with parameters obtained for RP-18 and aminopropyl silica cartridges. The high recovery values above 97% after the SPE procedure with the use of Si-PANI cartridges proves their utility for analysis of triterpenic acids. The sorbent tested was successfully used for clean-up of extracts from Salvia officinalis L., Syzygium aromaticum (L.) Merrill., and Origanum vulgare L. prior to HPLC-DAD determination of oleanolic, ursolic and betulinic acid. The efficiency of sample purification was verified by monitoring of chromatograms in the region between 190 nm and 400 nm during the gradient elution. The fewest components or their lowest concentrations were observed for all the investigated samples after the SPE procedures.

  7. Trace metals, metal-binding proteins and histopathology of the hepatopancreas in Dungeness crab

    SciTech Connect

    Thompson, J.A.J.; Brand, D.; Yunker, M.B.

    1995-12-31

    The authors have been examining trace metals and histopathology of the hepatopancreas in the Dungeness crab, Cancer magister, from four sites in the Fraser R. estuary and at two reference sites. Animals were collected at the same time over a two-year period. Tissues were analyzed for their trace metal content using ICPS and for metal-binding protein using pulse polarography. ANOVA and principal component analysis (PCA) were performed on all data. Copper, cadmium and silver are significantly higher in areas receiving sewage discharge. Copper and silver covary in all PCA models and form a cluster distinct from all other metals. The strong covariance raises the possibility that animals are taking up Ag along with Cu. In all PCA models, Ca and Sr (and to lesser extent Ba) form a distinct cluster in the third PC. Histopathological examination of crab hepatopancreatic tissue was carried out to determine if any idiopathic differences existed among populations from the Fraser River estuary and the reference sites. Four cell types were identified in all tissues examined: E-cell (embryonic), R-cell (reserve), B-cell (basophilic) and F-cell (fibrillar). The degree of vacuolation and glycogen storage within the R-cells was significantly greater in crabs collected from the estuary. Also, a significantly higher number of crabs from this site possessed proliferative invasive granulocytes associated with the hepatopancreas. Additionally, nucleolar hypertrophy within the F-cells occurred in crabs collected from the Fraser estuary, relative to those from the reference sites. The hepatopancreas may serve as a suitable subject for further examination of contaminant effects, since cell types show a varied response to exposure.

  8. Copper(I)-α-synuclein interaction: structural description of two independent and competing metal binding sites.

    PubMed

    Camponeschi, Francesca; Valensin, Daniela; Tessari, Isabella; Bubacco, Luigi; Dell'Acqua, Simone; Casella, Luigi; Monzani, Enrico; Gaggelli, Elena; Valensin, Gianni

    2013-02-04

    The aggregation of α-synuclein (αS) is a critical step in the etiology of Parkinson's disease. Metal ions such as copper and iron have been shown to bind αS, enhancing its fibrillation rate in vitro. αS is also susceptible to copper-catalyzed oxidation that involves the reduction of Cu(II) to Cu(I) and the conversion of O(2) into reactive oxygen species. The mechanism of the reaction is highly selective and site-specific and involves interactions of the protein with both oxidation states of the copper ion. The reaction can induce oxidative modification of the protein, which generally leads to extensive protein oligomerization and precipitation. Cu(II) binding to αS has been extensively characterized, indicating the N terminus and His-50 as binding donor residues. In this study, we have investigated αS-Cu(I) interaction by means of NMR and circular dichroism analysis on the full-length protein (αS(1-140)) and on two, designed ad hoc, model peptides: αS(1-15) and αS(113-130). In order to identify and characterize the metal binding environment in full-length αS, in addition to Cu(I), we have also used Ag(I) as a probe for Cu(I) binding. Two distinct Cu(I)/Ag(I) binding domains with comparable affinities have been identified. The structural rearrangements induced by the metal ions and the metal coordination spheres of both sites have been extensively characterized.

  9. Cadmium accumulation and toxicity in the unicellular alga Pseudokirchneriella subcapitata: Influence of metal-binding exudates and exposure time.

    PubMed

    Paquet, Nathalie; Lavoie, Michel; Maloney, Frédéric; Duval, Jérôme F L; Campbell, Peter G C; Fortin, Claude

    2015-07-01

    Predicting metal availability and toxicity for chronic (several hours or days) metal exposure scenarios, even for unicellular algae, is a major challenge to existing toxicity models. This is because several factors affecting metal uptake and toxicity, such as the release of metal-binding exudates, changes in the kinetics of metal uptake and toxicity over time, and algal physiological acclimation to internalized metals, are still poorly understood. The present study assessed the influence of these factors on Cd uptake and toxicity in laboratory batch cultures of the freshwater alga Pseudokirchneriella subcapitata. To do so, changes in the free Cd(2+) concentrations caused by the release of metal-binding algal exudates were monitored, (109)Cd accumulation in algal cells was measured, and Cd-induced inhibition of algal growth as a function of exposure time (from 12 h to 96 h) was followed. Results indicate that metal-binding exudates may decrease the proportion of the free Cd(2+) ion in solution up to 2-fold, a decrease that affects Cd uptake and toxicity. Pseudokirchneriella subcapitata has the capacity to decrease net Cd uptake rate on short time scales (<24 h), but this reduction in the Cd uptake rate disappeared after 24 h, and Cd toxicity occurred at relatively high Cd concentrations in solution. These data illustrate some of the pitfalls of standard algal toxicity assays, which were designed for acute exposures, and suggest how robust chronic bioassays might be developed.

  10. Template-directed covalent conjugation of DNA to native antibodies, transferrin and other metal-binding proteins

    NASA Astrophysics Data System (ADS)

    Rosen, Christian B.; Kodal, Anne L. B.; Nielsen, Jesper S.; Schaffert, David H.; Scavenius, Carsten; Okholm, Anders H.; Voigt, Niels V.; Enghild, Jan J.; Kjems, Jørgen; Tørring, Thomas; Gothelf, Kurt V.

    2014-09-01

    DNA-protein conjugates are important in bioanalytical chemistry, molecular diagnostics and bionanotechnology, as the DNA provides a unique handle to identify, functionalize or otherwise manipulate proteins. To maintain protein activity, conjugation of a single DNA handle to a specific location on the protein is often needed. However, preparing such high-quality site-specific conjugates often requires genetically engineered proteins, which is a laborious and technically challenging approach. Here we demonstrate a simpler method to create site-selective DNA-protein conjugates. Using a guiding DNA strand modified with a metal-binding functionality, we directed a second DNA strand to the vicinity of a metal-binding site of His6-tagged or wild-type metal-binding proteins, such as serotransferrin, where it subsequently reacted with lysine residues at that site. This method, DNA-templated protein conjugation, facilitates the production of site-selective protein conjugates, and also conjugation to IgG1 antibodies via a histidine cluster in the constant domain.

  11. Enhanced bioaccumulation of heavy metal ions by bacterial cells due to surface display of short metal binding peptides

    SciTech Connect

    Kotrba, P.; Ruml, T.; Doleckova, L.; Lorenzo, V. de

    1999-03-01

    Metal binding peptides of sequences Gly-His-His-Pro-His-Gly (named HP) and Gly-Cys-Gly-Cys-Pro-Cys-Gly-Cys-Gly (named CP) were genetically engineered into LamB protein and expressed in Escherichia coli. The Cd{sup 2+}-to-HP and Cd{sup 2+}-to-CP stoichiometries of peptides were 1:1 and 3:1, respectively. Hybrid LamB proteins were found to be properly folded in the outer membrane of E. coli. Isolated cell envelopes of E. coli bearing newly added metal binding peptides showed an up to 1.8-fold increase in Cd{sup 2+} binding capacity. The bioaccumulation of Cd{sup 2+}, Cu{sup 2+}, and Zn{sup 2+} by E. coli was evaluated. Surface display of CP multiplied the ability of E. coli to bind Cd{sup 2+} from growth medium fourfold. Display of HP peptide did not contribute to an increase in the accumulation of Cu{sup 2+} and Zn{sup 2+}. However, Cu{sup 2+} ceased contribution of HP for Cd{sup 2+} accumulation, probably due to the strong binding of Cu{sup 2+} to HP. Thus, considering the cooperation of cell structures with inserted peptides, the relative affinities of metal binding peptide and, for example, the cell wall to metal ion should be taken into account in the rational design of peptide sequences possessing specificity for a particular metal.

  12. Identification and partial characterization of a low affinity metal-binding site in the light chain of tetanus toxin.

    PubMed

    Wright, J F; Pernollet, M; Reboul, A; Aude, C; Colomb, M G

    1992-05-05

    Tetanus toxin was shown to contain a metal-binding site for zinc and copper. Equilibrium dialysis binding experiments using 65Zn indicated an association constant of 9-15 microM, with one zinc-binding site/toxin molecule. The zinc-binding site was localized to the toxin light chain as determined by binding of 65Zn to the light chain but not to the heavy chain after separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transfer to Immobilon membranes. Copper was an efficient inhibitor of 65Zn binding to tetanus toxin and caused two peptide bond cleavages in the toxin light chain in the presence of ascorbate. These metal-catalyzed oxidative cleavages were inhibited by the presence of zinc. Partial characterization of metal-catalyzed oxidative modifications of a peptide based on a putative metal-binding site (HELIH) in the toxin light chain was used to map the metal-binding site in the protein.

  13. Metal binding sites of the estradiol receptor from calf uterus and their possible role in the regulation of receptor function

    SciTech Connect

    Medici, N.; Minucci, S.; Nigro, V.; Abbondanza, C.; Armetta, I.; Molinari, A.M.; Puca, G.A. )

    1989-01-10

    The existence of putative metal binding sites on the estradiol receptor (ER) molecule from calf uterus was evaluated by immobilizing various divalent metals to iminodiacetate-Sepharose. ER from both crude and highly purified preparations binds to metal-containing adsorbents complexed with Zn(II), Ni(II), Co(II), and Cu(II), but not to those complexed with Fe(II) and Cd(II). Analysis of affinity-labeled ER by ({sup 3}H)tamoxifen aziridine after elution from a column of Zn(II)-charged iminodiacetate-Sepharose showed that ER fragments obtained by extensive trypsinization were also bound. Zn(II) and the same other metals able to bind ER, when immobilized on resins, inhibit the binding of estradiol to the receptor at micromolar concentration. This inhibition is noncompetitive and can be reversed by EDTA. The inhibition of the hormone binding was still present after trypsin treatment of the cytosol, and it was abolished by preincubation with the hormone. Micromolar concentrations of these metals were able to block those chemical-physical changes occurring during the process of ER transformation in vitro. The presence of metal binding sites that modulate the ER activity in the hormone binding domain of ER is speculated. Since progesterone receptor showed the same pattern of binding and elution from metal-containing adsorbents, the presence of metal binding regulatory sites could be a property of all steroid receptors.

  14. Dehydrogenation of ethylbenzene with nitrous oxide in the presence of mesoporous silica materials modified with transition metal oxides.

    PubMed

    Kuśtrowski, Piotr; Chmielarz, Lucjan; Dziembaj, Roman; Cool, Pegie; Vansant, Etienne F

    2005-01-20

    The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites.

  15. Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation

    PubMed Central

    Lechner, Carolin C.; Becker, Christian F. W.

    2015-01-01

    Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research. An outstanding example for biomineral morphogenesis is the formation of highly elaborate, nano-patterned silica shells by diatoms. Among the organic macromolecules that have been closely linked to the tightly controlled precipitation of silica in diatoms, silaffins play an extraordinary role. These peptides typically occur as complex posttranslationally modified variants and are directly involved in the silica deposition process in diatoms. However, even in vitro silaffin-based peptides alone, with and without posttranslational modifications, can efficiently mediate biomimetic silica precipitation leading to silica material with different properties as well as with encapsulated cargo molecules of a large size range. In this review, the biomineralization process of silica in diatoms is summarized with a specific focus on silaffins and their in vitro silica precipitation properties. Applications in the area of bio- and nanotechnology as well as in diagnostics and therapy are discussed. PMID:26295401

  16. Research and Development of a New Silica-Alumina Based Cementitious Material Largely Using Coal Refuse for Mine Backfill, Mine Sealing and Waste Disposal Stabilization

    SciTech Connect

    Henghu Sun; Yuan Yao

    2012-06-29

    Coal refuse and coal combustion byproducts as industrial solid waste stockpiles have become great threats to the environment. To activate coal refuse is one practical solution to recycle this huge amount of solid waste as substitute for Ordinary Portland Cement (OPC). The central goal of this project is to investigate and develop a new silica-alumina based cementitious material largely using coal refuse as a constituent that will be ideal for durable construction, mine backfill, mine sealing and waste disposal stabilization applications. This new material is an environment-friendly alternative to Ordinary Portland Cement. The main constituents of the new material are coal refuse and other coal wastes including coal sludge and coal combustion products (CCPs). Compared with conventional cement production, successful development of this new technology could potentially save energy and reduce greenhouse gas emissions, recycle vast amount of coal wastes, and significantly reduce production cost. A systematic research has been conducted to seek for an optimal solution for enhancing pozzolanic reactivity of the relatively inert solid waste-coal refuse in order to improve the utilization efficiency and economic benefit as a construction and building material.

  17. The Role of Silica in Precious Metal Supported Titania Hybrid Mesoporous Materials for Remediation and Energy Production

    NASA Astrophysics Data System (ADS)

    Kibombo, Harrison S.

    Semiconductor photocatalysis is an advanced oxidation process (AOP) that continues to show promise for the concomitant mineralization of non--biodegradable noxious and persistent organic pollutants (POPs) to environmentally benign products, and the splitting of water. This work examined the use of sol--gel chemistry as a viable approach for the incorporation of transparent silica (SiO2) matrix and/or platinum onto titania (TiO2) so as to optimize physico-chemical properties such as charge separation, crystallinity, surface area, and particle size. It was determined that crystallinity of anatase in the mixed oxide photocatalyst can be improved by the addition of simple non-polar aromatic co-solvents in the sol-gel route, and subsequently enhance the photocatalytic degradation of phenol under UV--light irradiation. The Pt of smaller particle sizes in Pt--TiO2--SiO 2 resulted in higher phenol degradation efficiencies under solar simulated conditions, irrespective of the synthesis method employed. The presence of Pt in the lowest oxidation state, Pt0, is crucial for enhanced phenol degradation whereas PtO2 (Pt4+) serves as a mild recombination center for photogenerated charge carriers rather than demonstrating total inactivity. The production of ·OH radicals was shown to be imperative for sustaining the degradation process. In the water splitting reaction for hydrogen production, the role of the crystallinity of anatase is reaffirmed when TiO2--SiO2 is used, as the surface defects present in the silica phase seem to serve as recombination centers. However, in Pt--TiO2 photocatalysts, the presence of Pt 0 or PtO2 in close contact with TiO2 (heterojunction) allows for more efficient electron propagation and facilitates minimization of electron--hole recombination, hence improved solar simulated photocatalytic hydrogen evolution. Extensive characterization of the photocatalysts were carried out by powder X--ray Diffraction (XRD), Nitrogen Physisorption Studies, Diffuse

  18. Metal binding and antioxidant properties of chimeric tri- and tetra-domained metallothioneins.

    PubMed

    Moreau, Jean-Luc; Baudrimont, Magalie; Carrier, Patrick; Peltier, Gilles; Bourdineaud, Jean-Paul

    2008-05-01

    An unusual tri-domained (alpha-beta-beta) natural oyster metallothionein (MT) is known, and non-oxidative MT dimers occur in vivo in mollusk species and in mammals. To assess the respective role of the MT domains, two chimeric MTs were constructed: a tetra-domained oyster MT corresponding to the alpha-beta-alpha-beta structure, in order to mimic the natural non-oxidative dimeric form, and a tri-domained alpha-beta-alpha oyster MT. Metal binding and putative antioxidant properties of these two chimeric MTs were investigated using expression of the related genes in the bacteria Escherichia coli. In a wild-type strain these MTs could efficiently bind Cd. In a superoxide dismutase (sodA sodB) null mutant, the tri-domained MT was found to exacerbate Cd toxicity whereas the tetra-domained MT efficiently protected bacteria from Cd. The paradoxical toxicity displayed by the tri-domained MT upon Cd contamination was linked to the generation of superoxide radicals generated by a mechanism which most probably involves a copper-redox cycling reaction, since a Cd-contaminated sodA sodB strain expressing this MT produced 4 times more O2(-) than the control bacteria, and MT toxicity disappeared in the presence of bathocuproine disulfonic acid, a copper chelator. In contrast, the tetra-domained form did not. Interestingly, in bacteria producing superoxide dismutase but hypersensitive to oxidative stress due to either mutations in thioredoxin and glutathione reductase pathways (WM104 mutant) or to a lack of gamma-glutamylcysteine synthetase (gshA mutant), both chimeric MTs were protecting against Cd toxicity. However, an unexpected lack of antioxidant function was observed for both chimeric MTs, which were found to enhance the toxicity of hydrogen peroxide in WM104, or that of menadione in QC1726. Altogether, our results suggest that superoxide dismutase activity counteracts the potential prooxidative effect of the tri-domained MT mediated by Cu ions and that the tetra

  19. Correction: Ga[OSi(O(t)Bu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry.

    PubMed

    Dombrowski, James P; Johnson, Gregory R; Bell, Alexis T; Tilley, T Don

    2016-11-22

    Correction for 'Ga[OSi(O(t)Bu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry' by James P. Dombrowski et al., Dalton Trans., 2016, 45, 11025-11034.

  20. A study of freezing-melting hysteresis of water in different porous materials. Part II: surfactant-templated silicas.

    PubMed

    Petrov, Oleg; Furó, István

    2011-09-28

    The freezing-melting hysteresis of water in mesoporous silicas MCM-48, MCM-41 and SBA-16 has been studied by NMR cryoporometry. The hysteresis in MCM-48 was found to exhibit nearly parallel branches, matching type H1 hysteresis that had been observed earlier in controlled pore glass. The same type of hysteresis is observed in two of three different-sized MCM-41 under study (a pore diameter of 3.6 and 3 nm), superimposed with a secondary, extremely broad, type H3 hysteresis. No hysteresis was found in the smallest MCM-41 with a pore diameter < 3 nm. Finally, water in SBA-16 exhibits type H2 hysteresis with the freezing branch being essentially steeper than the melting one, which is attributed to a pore blockage upon freezing, similar to what we observed earlier in Vycor porous glass. The data were analyzed using the model of curvature-dependent metastability of a solid phase upon melting; the validity of this model has been discussed.

  1. Porous carbon-coated silica macroparticles as anode materials for lithium ion batteries: Effect of boric acid

    NASA Astrophysics Data System (ADS)

    Kim, Young-Kuk; Moon, Jong-Woo; Lee, Jung-Goo; Baek, Youn-Kyung; Hong, Seong-Hyun

    2014-12-01

    We report carbon-coated porous silica macroparticles (SiO2@C) prepared using polymeric templates and subsequent carbonization with sucrose for improved electrochemical energy storage in lithium-ion batteries (LIBs). In addition, boron is introduced to improve the stability of electrochemical cells by pyrolyzing mixtures of sucrose and boric acid (SiO2@C + B) under inert atmosphere. The initially large surface area of porous SiO2 (SBET ∼ 658 m2 g-1) is reduced to 102 m2 g-1 after carbonization and introduction of boric acid. Surface of both SiO2@C and SiO2@C + B are covered with amorphous carbon. In particular, SiO2@C + B particles containing borosilicate (Si-O-B) phase and B-O bondings and Si-C-O bondings are also detected from the X-ray photoelectron spectra. The SiO2@C + B macroparticles shows high reversible charge capacity up to 503 mAh g-1 after 103 cycles of Li intercalation/de-intercalation although initial capacity was 200 mAh g-1. The improved charge capacity of SiO2@C + B is attributed to formation of advantageous microstructures induced from boric acid.

  2. Removal of uranium(VI) ions from aqueous solutions using Schiff base functionalized SBA-15 mesoporous silica materials.

    PubMed

    Dolatyari, Leila; Yaftian, Mohammad Reza; Rostamnia, Sadegh

    2016-03-15

    Functionalized SBA-15 mesoporous silica particles, bearing N-propylsalicylaldimine and ethylenediaminepropylesalicylaldimine Schiff base ligands, abbreviated as SBA/SA and SBA/EnSA respectively, were prepared and characterized by FT-IR, elemental analysis, TGA, XRD, TEM and SEM techniques. The potentials of these adsorbents were examined by using them in solid phase extraction of U(VI) ions from water samples. It is shown that 20 mg of SBA/SA or SBA/EnSA can remove rapidly (∼15 min) and quantitatively uranium(VI) ions from 10 to 200 mL of water solutions (pH 4) containing 0.2 mg of the ions, at 25 °C. The adsorbed ions were stripped by 1 mL of dilute nitric acid solution (0.1 mol L(-1)). It means that the studied adsorbents are able to be used for removal and concentration of uranyl ions. This allowed achieving to a concentration factor of 200 for uranyl ions. The variation in the ionic strength in the range 0-1 mol L(-1) did not affect the extraction efficiencies of the adsorbents. The adsorbents showed selective separation of uranyl ions from Cd(2+), Co(2+), Ni(2+), Mn(2+), Cr(3+), Ba(2+), Fe(3+) and Eu(3+) ions. Thermodynamic investigations revealed that the adsorption of uranyl ions by the adsorbents was spontaneous and endothermic. The Langmuir model described suitably the adsorption isotherms. This model determined the maximum adsorption capacity of the adsorbents SBA/SA and SBA/EnSA as 54 and 105.3 mg uranyl/g adsorbent, respectively. The kinetics of the processes was interpreted by using Pseudo-second-order model.

  3. Ionic Liquid and Silica Sol-Gel Composite Materials Doped with N,N,N ',N '-tetra(n-octyl)diglycolamide for Extraction of La3+ and Ba2+

    SciTech Connect

    Bell, Jason R; Dai, Sheng; Yu, Bo; Luo, Huimin

    2012-01-01

    Sol-gel processed silica materials which incorporated ionic liquids and tetraoctyldiglycolamide (TODGA) were prepared and used for extraction of La3+ and Ba2+ from aqueous solution. Imidazolium-based ionic liquids, 1-alkyl-3-methylimidazolium bis(trifluoromethane)sulfonimide ([Cnmim][NTf2]) were entrapped in the monolithic composite sorbents. Extraction efficiency was found to be dependent upon both the volume of IL used in the silica matrix, and the alkyl chain length of the IL cation. The silica composite sorbent containing [C8mim][NTf2] exhibited the best extraction efficiency for La3+ and the best separation factor for La3+ / Ba 2+. The results were analyzed by both Langmuir and Freundlich adsorption isotherm models, and the Freundlich model was found to give better fit.

  4. Cellular membrane trafficking of mesoporous silica nanoparticles

    SciTech Connect

    Fang, I-Ju

    2012-01-01

    This dissertation mainly focuses on the investigation of the cellular membrane trafficking of mesoporous silica nanoparticles. We are interested in the study of endocytosis and exocytosis behaviors of mesoporous silica nanoparticles with desired surface functionality. The relationship between mesoporous silica nanoparticles and membrane trafficking of cells, either cancerous cells or normal cells was examined. Since mesoporous silica nanoparticles were applied in many drug delivery cases, the endocytotic efficiency of mesoporous silica nanoparticles needs to be investigated in more details in order to design the cellular drug delivery system in the controlled way. It is well known that cells can engulf some molecules outside of the cells through a receptor-ligand associated endocytosis. We are interested to determine if those biomolecules binding to cell surface receptors can be utilized on mesoporous silica nanoparticle materials to improve the uptake efficiency or govern the mechanism of endocytosis of mesoporous silica nanoparticles. Arginine-glycine-aspartate (RGD) is a small peptide recognized by cell integrin receptors and it was reported that avidin internalization was highly promoted by tumor lectin. Both RGD and avidin were linked to the surface of mesoporous silica nanoparticle materials to investigate the effect of receptor-associated biomolecule on cellular endocytosis efficiency. The effect of ligand types, ligand conformation and ligand density were discussed in Chapter 2 and 3. Furthermore, the exocytosis of mesoporous silica nanoparticles is very attractive for biological applications. The cellular protein sequestration study of mesoporous silica nanoparticles was examined for further information of the intracellular pathway of endocytosed mesoporous silica nanoparticle materials. The surface functionality of mesoporous silica nanoparticle materials demonstrated selectivity among the materials and cancer and normal cell lines. We aimed to determine

  5. Why iron? A spin-polarized conceptual density functional theory study on metal-binding specificity of porphyrin.

    PubMed

    Feng, Xin-Tian; Yu, Jian-Guo; Liu, Ruo-Zhuang; Lei, Ming; Fang, Wei-Hai; De Proft, Frank; Liu, Shubin

    2010-06-03

    Heme is a key cofactor of hemoproteins in which porphyrin is often found to be preferentially metalated by the iron cation. In our previous work [Feng, X. T.; Yu, J. G.; Lei, M.; Fang, W. H.; Liu, S. B. J. Phys. Chem. B 2009, 113, 13381], conceptual density functional theory (CDFT) descriptors have been applied to understand the metal-binding specificity of porphyrin. We found that the iron-porphyrin complex significantly differs in many aspects from porphyrin complexes with other metal cations except Ru, for which similar behaviors for the reactivity descriptors were discovered. In this study, we employ the spin-polarized version of CDFT to investigate the reactivity for a series of (pyridine)(n)-M(ll)-porphyrin complexes-where M = Mg, Ca, Cr, Mn, Co, Ni, Cu, Zn, Ru, and Cd, and n = 0, 1, and 2-to further appreciate the metal-binding specificity of porphyrin. Both global and local descriptors were examined within this framework. We found that, within the spin resolution, not only chemical reactivity descriptors from CDFT of the iron complex are markedly different from that of other metal complexes, but we also discovered substantial differences in reactivity descriptors between Fe and Ru complexes. These results confirm that spin properties play a highly important role in physiological functions of hemoproteins. Quantitative reactivity relationships have been revealed between global and local spin-polarized reactivity descriptors. These results contribute to our better understanding of the metal binding specificity and reactivity for heme-containing enzymes and other metalloproteins alike.

  6. A minimalist chemical model of matrix metalloproteinases--can small peptides mimic the more rigid metal binding sites of proteins?

    PubMed

    Árus, Dávid; Nagy, Nóra Veronika; Dancs, Ágnes; Jancsó, Attila; Berkecz, Róbert; Gajda, Tamás

    2013-09-01

    In order to mimic the active center of matrix metalloproteinases (MMPs), we synthesized a pentadecapeptide (Ac-KAHEFGHSLGLDHSK-NH2) corresponding to the catalytic zinc(II) binding site of human MMP-13. The multi-domain structural organization of MMPs fundamentally determines their metal binding affinity, catalytic activity and selectivity. Our potentiometric, UV-visible, CD, EPR, NMR, mass spectrometric and kinetic studies are aimed to explore the usefulness of such flexible peptides to mimic the more rigid metal binding sites of proteins, to examine the intrinsic metal binding properties of this naked sequence, as well as to contribute to the development of a minimalist, peptide-based chemical model of MMPs, including the catalytic properties. Since the multiimidazole environment is also characteristic for copper(II), and recently copper(II) containing variants of MMPs have been identified, we also studied the copper(II) complexes of the above peptide. Around pH 6-7 the peptide, similarly to MMPs, offers a {3Nim} coordination binding site for both zinc(II) and copper(II). In the case of copper(II), the formation of amide coordinated species at higher pH abolished the analogy with the copper(II) containing MMP variant. On the other hand, the zinc(II)-peptide system mimics some basic features of the MMP active sites: the main species around pH7 (ZnH2L) possesses a {3Nim,H2O} coordination environment, the deprotonation of the zinc-bound water takes place near the physiological pH, it forms relatively stable ternary complexes with hydroxamic acids, and the species ZnH2L(OH) and ZnH2L(OH)2 have notable hydrolytic activity between pH7 and 9.

  7. Structural Comparisons of Apo- and Metalated Three-Stranded Coiled Coils Clarify Metal Binding Determinants in Thiolate Containing Designed Peptides

    SciTech Connect

    Chakraborty, Saumen; Touw, Debra S.; Peacock, Anna F.A.; Stuckey, Jeanne; Pecoraro, Vincent L.

    2010-11-05

    Over the past two decades, designed metallopeptides have held the promise for understanding a variety of fundamental questions in metallobiochemistry; however, these dreams have not yet been realized because of a lack of structural data to elaborate the protein scaffolds before metal complexation and the resultant metalated structures which ultimately exist. This is because there are few reports of structural characterization of such systems either in their metalated or nonmetalated forms and no examples where an apo structure and the corresponding metalated peptide assembly have both been defined by X-ray crystallography. Herein we present X-ray structures of two de novo designed parallel three-stranded coiled coils (designed using the heptad repeat (a {yields} g)) CSL9C (CS = Coil Ser) and CSL19C in their nonmetalated forms, determined to 1.36 and 2.15 {angstrom} resolutions, respectively. Leucines from either position 9 (a site) or 19 (d site) are replaced by cysteine to generate the constructs CSL9C and CSL19C, respectively, yielding thiol-rich pockets at the hydrophobic interior of these peptides, suitable to bind heavy metals such as As(III), Hg(II), Cd(II), and Pb(II). We use these structures to understand the inherent structural differences between a and d sites to clarify the basis of the observed differential spectroscopic behavior of metal binding in these types of peptides. Cys side chains of (CSL9C){sub 3} show alternate conformations and are partially preorganized for metal binding, whereas cysteines in (CSL19C){sub 3} are present as a single conformer. Zn(II) ions, which do not coordinate or influence Cys residues at the designed metal sites but are essential for forming X-ray quality crystals, are bound to His and Glu residues at the crystal packing interfaces of both structures. These 'apo' structures are used to clarify the changes in metal site organization between metalated As(CSL9C){sub 3} and to speculate on the differential basis of Hg

  8. Silica/Polymer and Silica/Polymer/Fiber Composite Aerogels

    NASA Technical Reports Server (NTRS)

    Ou, Danny; Stepanian, Christopher J.; Hu, Xiangjun

    2010-01-01

    Aerogels that consist, variously, of neat silica/polymer alloys and silica/polymer alloy matrices reinforced with fibers have been developed as materials for flexible thermal-insulation blankets. In comparison with prior aerogel blankets, these aerogel blankets are more durable and less dusty. These blankets are also better able to resist and recover from compression . an important advantage in that maintenance of thickness is essential to maintenance of high thermal-insulation performance. These blankets are especially suitable as core materials for vacuum- insulated panels and vacuum-insulated boxes of advanced, nearly seamless design. (Inasmuch as heat leakage at seams is much greater than heat leakage elsewhere through such structures, advanced designs for high insulation performance should provide for minimization of the sizes and numbers of seams.) A silica/polymer aerogel of the present type could be characterized, somewhat more precisely, as consisting of multiply bonded, linear polymer reinforcements within a silica aerogel matrix. Thus far, several different polymethacrylates (PMAs) have been incorporated into aerogel networks to increase resistance to crushing and to improve other mechanical properties while minimally affecting thermal conductivity and density. The polymethacrylate phases are strongly linked into the silica aerogel networks in these materials. Unlike in other organic/inorganic blended aerogels, the inorganic and organic phases are chemically bonded to each other, by both covalent and hydrogen bonds. In the process for making a silica/polymer alloy aerogel, the covalent bonds are introduced by prepolymerization of the methacrylate monomer with trimethoxysilylpropylmethacrylate, which serves as a phase cross-linker in that it contains both organic and inorganic monomer functional groups and hence acts as a connector between the organic and inorganic phases. Hydrogen bonds are formed between the silanol groups of the inorganic phase and the

  9. Assessing the potential of ToF-SIMS as a complementary approach to investigate cement-based materials — Applications related to alkali–silica reaction

    SciTech Connect

    Bernard, Laetitia; Leemann, Andreas

    2015-02-15

    In this study, the potential of time-of-flight secondary ion mass spectrometry (ToF-SIMS) for the application in cement-based materials is assessed in combination and comparison with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). Mortar, concrete and samples from model systems providing products formed by the alkali–silica reaction (ASR) were studied. ToF-SIMS provides qualitative data on alkalis in cases where EDX reaches its limits in regard to detectable concentration, lateral resolution and atomic number of the elements. Due to its high in-depth resolution of a few atomic monolayers, thin layers of reaction products can be detected on the surfaces and chemically analyzed with ToF-SIMS. Additionally, it delivers information on the molecular conformation within the ASR product, its hydrogen content and its isotope ratios, information not provided by EDX. Provided the samples are carefully prepared, ToF-SIMS opens up new possibilities in the analysis of cement-based materials.

  10. Change in transmittance of fused silica as a means of detecting material sputtered from components on a 5-cm ion thruster

    NASA Technical Reports Server (NTRS)

    Weigand, A. J.; Mirtich, M. J.

    1972-01-01

    Two endurance tests of a 5-cm mercury bombardment thruster are reported. Both tests used a translational screen-grid system with the beam vectored 10 degrees. The first test lasted 141 hours and the second test operated for 2026 hours. In each test two fused silica samples (solar cell covers), 2.0 cm by 2.1 cm, were placed in shielded holders to detect materials sputtered from the thruster. Spectral optical properties between 0.398 and 2.16 microns were measured on each sample, both before and after the endurance tests. The deposition on each sample was spectrographically analyzed to determine the type of materials sputtered from the thruster. It was found that sputtering from the neutralizer is highly dependent on its position with respect to the beam edge. The sputtering from the accelerator grid of the translational screen-grid system of the 2026 hour test was sufficient to form an opaque film on the sample located in the direction opposite to the vectored beam.

  11. Silica-supported biomimetic membranes.

    PubMed

    Ariga, Katsuhiko

    2004-01-01

    The hybridization of lipid membranes with inorganic silica-based framework results in mechanically stable biomembrane mimics. This account describes three types of silica-based biomimetic membranes. As the first example, a Langmuir monolayer of dialkylalkoxysilane was polymerized and immobilized onto a porous glass plate. Permeability through the monolayer-immobilized glass was regulated by phase transition of the immobilized monolayer. In the second example, spherical vesicles covalently attached to a silica cover layer (Cerasome) were prepared. The Cerasome was stable enough to be assembled into layer-by-layer films without destruction of its vesicular structure. This material could be an example of the multicellular assembly. Mesoporous silica films densely filling peptide assemblies (Proteosilica) are introduced as the third example. The Proteosilica was synthesized as a transparent film through template sol-gel reaction using amphiphilic peptides.

  12. Does Variation of the Inter-Domain Linker Sequence Modulate the Metal Binding Behaviour of Helix pomatia Cd-Metallothionein?

    PubMed Central

    Gil-Moreno, Selene; Jiménez-Martí, Elena; Palacios, Òscar; Zerbe, Oliver; Dallinger, Reinhard; Capdevila, Mercè; Atrian, Sílvia

    2015-01-01

    Snail metallothioneins (MTs) constitute an ideal model to study structure/function relationships in these metal-binding polypeptides. Helix pomatia harbours three MT isoforms: the highly specific CdMT and CuMT, and an unspecific Cd/CuMT, which represent paralogous proteins with extremely different metal binding preferences while sharing high sequence similarity. Preceding work allowed assessing that, although, the Cys residues are responsible for metal ion coordination, metal specificity or preference is achieved by diversification of the amino acids interspersed between them. The metal-specific MT polypeptides fold into unique, energetically-optimized complexes of defined metal content, when binding their cognate metal ions, while they produce a mixture of complexes, none of them representing a clear energy minimum, with non-cognate metal ions. Another critical, and so far mostly unexplored, region is the stretch linking the individual MT domains, each of which represents an independent metal cluster. In this work, we have designed and analyzed two HpCdMT constructs with substituted linker segments, and determined their coordination behavior when exposed to both cognate and non-cognate metal ions. Results unequivocally show that neither length nor composition of the inter-domain linker alter the features of the Zn(II)- and Cd(II)-complexes, but surprisingly that they influence their ability to bind Cu(I), the non-cognate metal ion. PMID:26703589

  13. Metal-binding particles alleviate lead and zinc toxicity during seed germination of metallophyte grass Astrebla lappacea.

    PubMed

    Rossato, L; MacFarlane, J; Whittaker, M; Pudmenzky, A; Doley, D; Schmidt, S; Monteiro, M J

    2011-06-15

    Combining metal-binding particles and metal-tolerant plants (metallophytes) offers a promising new approach for rehabilitation of heavy metal contaminated sites. Three types of hydrogel metal-binding polymer particles were synthesized and their effects on metal concentrations tested in vitro using metal ion solutions. The most effective of the tested polymers was a micron-sized thiol functional cross-linked acrylamide polymer which reduced the available solution concentrations of Pb(2+) (9.65 mM), Cu(2+) (4mM) and Zn(2+) (10mM) by 86.5%, 75.5% and 63.8%, respectively, and was able to store water up to 608% of its dry mass. This polymer was not toxic to seed germination. In deionised water, it enhanced seed germination, and at otherwise phytotoxic Pb(2+) (9.65 mM) and Zn(2+) (10mM) concentrations, it allowed normal germination and root elongation of the metallophyte grass Astrebla lappacea. We conclude that the polymer has the potential to facilitate restoration of heavy metal contaminated lands by reducing the concentration of metal cations in the soil solution and improving germination rates through reduced toxicity and enhanced plant water relations.

  14. Preparation and characterization of urease-encapsulated biosensors in poly(vinyl alcohol)-modified silica sol-gel materials.

    PubMed

    Tsai, Hsiao-chung; Doong, Ruey-an

    2007-08-30

    The microenvironments of the sol-gel-derived urease biosensors in terms of elemental ratio, surface morphology, specific surface area and pore size were investigated to characterize the physicochemical properties of poly(vinyl alcohol) (PVA)-modified sol-gel materials. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and surface area analyzer were used to identify the surface species, topography and pore distribution of the organically doped sol-gel network. XPS results showed that stoichiometric ratios of oxygen-to-silicon in sol-gel materials were in the range 2.08-2.11. The sol-gel materials were partially dried and negatively charged, which retained 6-8% water content to maintain urease activity. The surface morphology of the sol-gel altered obviously when macromolecules were encapsulated, resulting in the increase in surface mean roughness from 0.207 to 2.636 nm. The specific surface area decreased dramatically after the immobilization of biomolecules and organic additives, which clearly depicts that PVA and urease were co-encapsulated into the sol-gel network. However, there still exist enough pore volumes for analytes to mass transport. The apparent Michaelis-Menten constant value (Km) of the encapsulated urease was similar to that in solution and the overall catalytic efficiency in PVA-doped sol-gel-derived glasses only decreased by a factor of 3.2 relative to the value in solution. In addition, the analytical performance of the entrapped urease in PVA-doped sol-gel materials was examined by determining the Cu(II) concentration in aqueous solution. The analytical range of Cu(II) was in the range 2x10(-6) to 2x10(-2) M with a detection limit of 1.5 microg L(-1). Results obtained in this study demonstrate a strategy for maintaining urease activity for biomedical and environmental applications.

  15. Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage

    PubMed Central

    Min, Xin; Fang, Minghao; Huang, Zhaohui; Liu, Yan’gai; Huang, Yaoting; Wen, Ruilong; Qian, Tingting; Wu, Xiaowen

    2015-01-01

    Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG. PMID:26261089

  16. Immobilizing gold nanoparticles in mesoporous silica covered reduced graphene oxide: a hybrid material for cancer cell detection through hydrogen peroxide sensing.

    PubMed

    Maji, Swarup Kumar; Sreejith, Sivaramapanicker; Mandal, Amal Kumar; Ma, Xing; Zhao, Yanli

    2014-08-27

    A new kind of two-dimensional (2-D) hybrid material (RGO-PMS@AuNPs), fabricated by the immobilization of ultrasmall gold nanoparticles (AuNPs, ∼3 nm) onto sandwich-like periodic mesopourous silica (PMS) coated reduced graphene oxide (RGO), was employed for both electrocatalytic application and cancer cell detection. The hybrid-based electrode sensor showed attractive electrochemical performance for sensitive and selective nonenzymatic detection of hydrogen peroxide (H2O2) in 0.1 M phosphate buffered saline, with wide linear detection range (0.5 μM to 50 mM), low detection limit (60 nM), and good sensitivity (39.2 μA mM(-1) cm(-2)), and without any interference by common interfering agents. In addition, the sensor exhibited a high capability for glucose sensing and H2O2 detection in human urine. More interestingly, the hybrid was found to be nontoxic, and the electrode sensor could sensitively detect a trace amount of H2O2 in a nanomolar level released from living tumor cells (HeLa and HepG2). Because the hybrid presents significant properties for the detection of bioactive species and certain cancerous cells by the synergistic effect from RGO, PMS, and AuNPs, it could be able to serve as a versatile platform for biosensing, bioanalysis, and biomedical applications.

  17. Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage.

    PubMed

    Min, Xin; Fang, Minghao; Huang, Zhaohui; Liu, Yan'gai; Huang, Yaoting; Wen, Ruilong; Qian, Tingting; Wu, Xiaowen

    2015-08-11

    Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.

  18. Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage

    NASA Astrophysics Data System (ADS)

    Min, Xin; Fang, Minghao; Huang, Zhaohui; Liu, Yan'Gai; Huang, Yaoting; Wen, Ruilong; Qian, Tingting; Wu, Xiaowen

    2015-08-01

    Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.

  19. Macrocyclic polyamine-functionalized silica as a solid-phase extraction material coupled with ionic liquid dispersive liquid-liquid extraction for the enrichment of polycyclic aromatic hydrocarbons.

    PubMed

    Liu, Longhui; He, Lijun; Jiang, Xiuming; Zhao, Wenjie; Xiang, Guoqiang; Anderson, Jared L

    2014-04-01

    In this study, silica modified with a 30-membered macrocyclic polyamine was synthesized and first used as an adsorbent material in SPE. The SPE was further combined with ionic liquid (IL) dispersive liquid-liquid microextraction (DLLME). Five polycyclic aromatic hydrocarbons were employed as model analytes to evaluate the extraction procedure and were determined by HPLC combined with UV/Vis detection. Acetone was used as the elution solvent in SPE as well as the dispersive solvent in DLLME. The enrichment of analytes was achieved using the 1,3-dibutylimidazolium bis[(trifluoromethyl)sulfonyl]imide IL/acetone/water system. Experimental conditions for the overall macrocycle-SPE-IL-DLLME method, such as the amount of adsorbent, sample solution volume, sample solution pH, type of elution solvent as well as addition of salt, were studied and optimized. The developed method could be successfully applied to the analysis of four real water samples. The macrocyclic polyamine offered higher extraction efficiency for analytes compared with commercially available C18 cartridge, and the developed method provided higher enrichment factors (2768-5409) for model analytes compared with the single DLLME. Good linearity with the correlation coefficients ranging from 0.9983 to 0.9999 and LODs as low as 0.002 μg/L were obtained in the proposed method.

  20. Silica-titania sol-gel hybrid materials: synthesis, characterization and potential application in solid phase extraction.

    PubMed

    de Moraes, Sandra V M; Passos, Joana B; Schossler, Patricia; Caramão, Elina B; Moro, Celso C; Costa, Tania M H; Benvenutti, Edilson V

    2003-04-10

    The biphenilaminepropylsilica and biphenilaminepropylsilicatitania were synthesized by sol-gel method, in two steps: (a) biphenylamine reacts with chloropropyltrimethoxysilane and (b) the product of reaction was polycondensed with tetraethylorthosilicate (TEOS) or TEOS and titanium isopropoxide. The sol-gel materials were characterized using infrared spectroscopy and N(2) adsorption-desorption isotherms and they were employed as sorbents for carcinogenic N-containing compound retention, in aqueous solution, using the SPE technique. The N-containing compounds adsorption was influenced by the titania presence and the sorption process seems to happen in the pores with higher organic density.

  1. The Hydrothermal System at Home Plate in Gusev Crater, Mars: Formation of High Silica Material by Acid-Sulfate Alteration of Basalt

    NASA Technical Reports Server (NTRS)

    Morris, R. V.; Ming, D. W.; Gellert, R.; Yen, A.; Clark, B. C.; Gnaff, T. G.; Arvidson, R. E.; Squyres, S. W.

    2008-01-01

    The Alpha Particle X-ray Spectrometer (APXS) instrument on the Mars Exploration Rover (MER) Spirit measured three targets on or adjacent to Home Plate in Gusev Crater that have unusually high SiO2 concentrations (68% to 91%), unusually low FeO concentrations (1% to 7%, with total Fe as FeO), and unusually high TiO2/FeO ratios (0.2 to 1.2 by weight) [1]. Two targets (Kenosha Comets and Lefty Ganote) are located on high albedo soil (Gertrude Weise) that was exposed by the rover wheels, and one target is a float rock called Fuzzy Smith. Kenosha Comets has the highest SiO2 concentration, lowest FeO concentration, and highest TiO2/FeO ratio. Mineralogical evidence from the MER Miniature Thermal Emission Spectrometer (Mini-TES) suggests that the SiO2 is present as amorphous (noncrystalline) SiO2 at Gertrude Weise and nearby targets [2,3]. Mini-TES data were not acquired for Fuzzy Smith. Home Plate is considered to have an explosive volcanic origin, resulting when basaltic magma came into contact with ground water or ice [4]. Within 50 m to 1 km of Home Plate are sulfate rich soil deposits (Paso Robles class soils with 22-35% SO3) which are considered to be probable fumarolic and/or hydrothermal deposits associated with the volcanism [5]. We develop the model here, suggested by [5], that the high-silica materials are another manifestation of acid-sulfate processes associated with fumarolic and hydrothermal activity at Home Plate. This is done by analogy with basaltic materials altered by acid sulfate processes on the Island of Hawaii.

  2. Improved selective cholesterol adsorption by molecularly imprinted poly(methacrylic acid)/silica (PMAA-SiO₂) hybrid material synthesized with different molar ratios.

    PubMed

    Clausen, Débora Nobile; Pires, Igor Matheus Ruiz; Tarley, César Ricardo Teixeira

    2014-11-01

    The present paper describes the synthesis of molecularly imprinted polymer - poly(methacrylic acid)/silica and reports its performance feasibility with desired adsorption capacity and selectivity for cholesterol extraction. Two imprinted hybrid materials were synthesized at different methacrylic acid (MAA)/tetraethoxysilane (TEOS) molar ratios (6:1 and 1:5) and characterized by FT-IR, TGA, SEM and textural data. Cholesterol adsorption on hybrid materials took place preferably in apolar solvent medium, especially in chloroform. From the kinetic data, the equilibrium time was reached quickly, being 12 and 20 min for the polymers synthesized at MAA/TEOS molar ratio of 6:1 and 1:5, respectively. The pseudo-second-order model provided the best fit for cholesterol adsorption on polymers, confirming the chemical nature of the adsorption process, while the dual-site Langmuir-Freundlich equation presented the best fit to the experimental data, suggesting the existence of two kinds of adsorption sites on both polymers. The maximum adsorption capacities obtained for the polymers synthesized at MAA/TEOS molar ratios of 6:1 and 1:5 were found to be 214.8 and 166.4 mg g(-1), respectively. The results from isotherm data also indicated higher adsorption capacity for both imprinted polymers regarding to corresponding non-imprinted polymers. Nevertheless, taking into account the retention parameters and selectivity of cholesterol in the presence of structurally analogue compounds (5-α-cholestane and 7-dehydrocholesterol), it was observed that the polymer synthesized at the MAA/TEOS molar ratio of 6:1 was much more selective for cholesterol than the one prepared at the ratio of 1:5, thus suggesting that selective binding sites ascribed to the carboxyl group from MAA play a central role in the imprinting effect created on MIP.

  3. X-ray absorption and diffraction studies of the metal binding sites in amyloid beta-peptide.

    PubMed

    Streltsov, Victor

    2008-03-01

    A major source of neurodegeneration observed in Alzheimer's disease is believed to be caused by the toxicity from reactive oxygen species produced in the brain mediated by the A beta protein and mainly copper species. An atomic model of an amyloid beta-peptide (A beta) Cu2+ complex or at least the structure of the metal binding site is of great interest. Accurate information about the Cu-binding site of A beta protein can facilitate simulation of redox chemistry using high level quantum mechanics. Complementary X-ray diffraction and X-ray absorption techniques can be employed to obtain such accurate information. This review provides a blend of X-ray diffraction results on amyloid structures and selected works on A beta Cu2+ binding based on spectroscopic measurements with emphasis on the X-ray absorption technique.

  4. MetalDetector: a web server for predicting metal-binding sites and disulfide bridges in proteins from sequence

    PubMed Central

    Lippi, Marco; Passerini, Andrea; Punta, Marco; Rost, Burkhard; Frasconi, Paolo

    2008-01-01

    Summary: The web server MetalDetector classifies histidine residues in proteins into one of two states (free or metal bound) and cysteines into one of three states (free, metal bound or disulfide bridged). A decision tree integrates predictions from two previously developed methods (DISULFIND and Metal Ligand Predictor). Cross-validated performance assessment indicates that our server predicts disulfide bonding state at 88.6% precision and 85.1% recall, while it identifies cysteines and histidines in transition metal-binding sites at 79.9% precision and 76.8% recall, and at 60.8% precision and 40.7% recall, respectively. Availability: Freely available at http://metaldetector.dsi.unifi.it Contact: metaldetector@dsi.unifi.it Supplementary Information: Details and data can be found at http://metaldetector.dsi.unifi.it/help.php PMID:18635571

  5. Solution structure and intermolecular interactions of the third metal-binding domain of ATP7A, the Menkes disease protein.

    PubMed

    Banci, Lucia; Bertini, Ivano; Cantini, Francesca; DellaMalva, Nunzia; Herrmann, Torsten; Rosato, Antonio; Wüthrich, Kurt

    2006-09-29

    The third metal-binding domain of the human Menkes protein (MNK3), a copper(I)-transporting ATPase, has been expressed in Escherichia coli and characterized in solution. The solution structure of MNK3, its copper(I)-binding properties, and its interaction with the physiological partner, HAH1, have been studied. MNK3 is the domain most dissimilar in structure from the other domains of the Menkes protein. This is reflected in a significant rearrangement of the last strand of the four-stranded beta-sheet when compared with the other known homologous proteins or protein domains. MNK3 is also peculiar with respect to its interaction with the copper(I) ion, as it was found to be a comparatively weak binder. Copper(I) transfer from metal-loaded HAH1 was observed experimentally, but the metal distribution was shifted toward binding by HAH1. This is at variance with what is observed for the other Menkes domains.

  6. Removal of oxyanions from aqueous systems using polymer filtration (water-soluble metal-binding polymers with ultrafiltration)

    SciTech Connect

    Rogers, Y.C.; Santos, E.C.; Robison, T.W.; Gibson, R.R.; Smith B.F.

    1997-12-31

    The group V-A and VI-A elements exist in the environment as oxyanions. They enter the environment from both agricultural and industrial sources. The Kestersen reservoir hazardous to wildlife. Arsenic and antimony are used in pesticides and as hardners in alloys, bearings, and in storage batteries. All these metals are emitted during smelting operations. We have been able to remove As(V)/Se(V) from the 100 ppm level to very low levels using water-soluble metal-binding polymers with ultrafiltration. Arsenic contaminated drinking water from Europe was treated and the As level was successfully lowered to better than drinking water standards (<0.1 ppm). We will report on the development and testing of new water-soluble polymers for binding oxyanions.

  7. Identifying cysteines and histidines in transition-metal-binding sites using support vector machines and neural networks.

    PubMed

    Passerini, Andrea; Punta, Marco; Ceroni, Alessio; Rost, Burkhard; Frasconi, Paolo

    2006-11-01

    Accurate predictions of metal-binding sites in proteins by using sequence as the only source of information can significantly help in the prediction of protein structure and function, genome annotation, and in the experimental determination of protein structure. Here, we introduce a method for identifying histidines and cysteines that participate in binding of several transition metals and iron complexes. The method predicts histidines as being in either of two states (free or metal bound) and cysteines in either of three states (free, metal bound, or in disulfide bridges). The method uses only sequence information by utilizing position-specific evolutionary profiles as well as more global descriptors such as protein length and amino acid composition. Our solution is based on a two-stage machine-learning approach. The first stage consists of a support vector machine trained to locally classify the binding state of single histidines and cysteines. The second stage consists of a bidirectional recurrent neural network trained to refine local predictions by taking into account dependencies among residues within the same protein. A simple finite state automaton is employed as a postprocessing in the second stage in order to enforce an even number of disulfide-bonded cysteines. We predict histidines and cysteines in transition-metal-binding sites at 73% precision and 61% recall. We observe significant differences in performance depending on the ligand (histidine or cysteine) and on the metal bound. We also predict cysteines participating in disulfide bridges at 86% precision and 87% recall. Results are compared to those that would be obtained by using expert information as represented by PROSITE motifs and, for disulfide bonds, to state-of-the-art methods.

  8. Silica Lubrication in Faults (Invited)

    NASA Astrophysics Data System (ADS)

    Rowe, C. D.; Rempe, M.; Lamothe, K.; Kirkpatrick, J. D.; White, J. C.; Mitchell, T. M.; Andrews, M.; Di Toro, G.

    2013-12-01

    Silica-rich rocks are common in the crust, so silica lubrication may be important for causing fault weakening during earthquakes if the phenomenon occurs in nature. In laboratory friction experiments on chert, dramatic shear weakening has been attributed to amorphization and attraction of water from atmospheric humidity to form a 'silica gel'. Few observations of the slip surfaces have been reported, and the details of weakening mechanism(s) remain enigmatic. Therefore, no criteria exist on which to make comparisons of experimental materials to natural faults. We performed a series of friction experiments, characterized the materials formed on the sliding surface, and compared these to a geological fault in the same rock type. Experiments were performed in the presence of room humidity at 2.5 MPa normal stress with 3 and 30 m total displacement for a variety of slip rates (10-4 - 10-1 m/s). The friction coefficient (μ) reduced from >0.6 to ~0.2 at 10-1 m/s, but only fell to ~0.4 at 10-2 - 10-4 m/s. The slip surfaces and wear material were observed using laser confocal Raman microscopy, electron microprobe, X-ray diffraction, and transmission electron microscopy. Experiments at 10-1 m/s formed wear material consisting of ≤1 μm powder that is aggregated into irregular 5-20 μm clumps. Some material disaggregated during analysis with electron beams and lasers, suggesting hydrous and unstable components. Compressed powder forms smooth pavements on the surface in which grains are not visible (if present, they are <100 nm). Powder contains amorphous material and as yet unidentified crystalline and non-crystalline forms of silica (not quartz), while the worn chert surface underneath shows Raman spectra consistent with a mixture of quartz and amorphous material. If silica amorphization facilitates shear weakening in natural faults, similar wear materials should be formed, and we may be able to identify them through microstructural studies. However, the sub

  9. Optothermal nonlinearity of silica aerogel

    NASA Astrophysics Data System (ADS)

    Braidotti, Maria Chiara; Gentilini, Silvia; Fleming, Adam; Samuels, Michiel C.; Di Falco, Andrea; Conti, Claudio

    2016-07-01

    We report on the characterization of silica aerogel thermal optical nonlinearity, obtained by z-scan technique. The results show that typical silica aerogels have nonlinear optical coefficient similar to that of glass (≃10-12 m2/W), with negligible optical nonlinear absorption. The nonlinear coefficient can be increased to values in the range of 10-10 m2/W by embedding an absorbing dye in the aerogel. This value is one order of magnitude higher than that observed in the pure dye and in typical highly nonlinear materials like liquid crystals.

  10. Biomimetic silica encapsultation of living cells

    NASA Astrophysics Data System (ADS)

    Jaroch, David Benjamin

    Living cells perform complex chemical processes on size and time scales that artificial systems cannot match. Cells respond dynamically to their environment, acting as biological sensors, factories, and drug delivery devices. To facilitate the use of living systems in engineered constructs, we have developed several new approaches to create stable protective microenvironments by forming bioinspired cell-membrane-specific silica-based encapsulants. These include vapor phase deposition of silica gels, use of endogenous membrane proteins and polysaccharides as a site for silica nucleation and polycondensation in a saturated environment, and protein templated ordered silica shell formation. We demonstrate silica layer formation at the surface of pluripotent stem-like cells, bacterial biofilms, and primary murine and human pancreatic islets. Materials are characterized by AFM, SEM and EDS. Viability assays confirm cell survival, and metabolite flux measurements demonstrate normal function and no major diffusion limitations. Real time PCR mRNA analysis indicates encapsulated islets express normal levels of genetic markers for β-cells and insulin production. The silica glass encapsulant produces a secondary bone like calcium phosphate mineral layer upon exposure to media. Such bioactive materials can improve device integration with surrounding tissue upon implantation. Given the favorable insulin response, bioactivity, and long-term viability observed in silica-coated islets, we are currently testing the encapsulant's ability to prevent immune system recognition of foreign transplants for the treatment of diabetes. Such hybrid silica-cellular constructs have a wide range of industrial, environmental, and medical applications.

  11. Fluorescence energy transfer between points in G-actin: the nucleotide-binding site, the metal-binding site and Cys-373 residue.

    PubMed

    Miki, M; Wahl, P

    1985-04-05

    Fluorescence energy transfers were studied in order to investigate the spatial relationships between the nucleotide-binding site, the metal-binding site and the Cys-373 residue in the G-actin molecule. When 1-N6-ethenoadenosine-5'-triphosphate (epsilon-ATP) in the nucleotide-binding site and Co2+ or Ni2+ in the metal-binding site were used as fluorescence donor and acceptor, respectively, the fluorescence intensity of epsilon-ATP was perfectly quenched by Ni2+ or Co2+. This indicated that the nucleotide-binding site is very close to the metal-binding site; the distance should be less than 10 A. When N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine (IAEDANS) bound to Cys-373 residue and Co2+ in the metal-binding site were used as a fluorescence donor and an acceptor, respectively, the transfer efficiency was equal to 5 +/- 1%. The corresponding distance was calculated to be 23-32 A, assuming a random orientation factor K2 = 2/3.

  12. Structural Biology of The sequestration & Transport of Heavy Metal Toxins: NMR Structure Determination of Proteins Containing the CYS-X-Y-Metal Binding Motif

    SciTech Connect

    Stanley J. Opella

    2004-03-10

    The support from the Department of Energy enabled us to initiate research on several proteins from the bacterial mercury detoxification system; in particular, we were able to determine the structures of MerP and related metal binding sequences. We have also worked on the membrane transport proteins MerF and MerT.

  13. Preconcentration of low levels of americium and plutonium from waste waters by synthetic water-soluble metal-binding polymers with ultrafiltration

    SciTech Connect

    Smith, B.F.; Gibson, R.R.; Jarvinen, G.D.; Robison, T.W.; Schroeder, N.C.; Stalnaker, N.D.

    1997-12-31

    A preconcentration approach to assist in the measurement of low levels of americium and plutonium in waste waters has been developed based on the concept of using water-soluble metal-binding polymers in combination with ultrafiltration. The method has been optimized to give over 90% recovery and accountability from actual waste water.

  14. Stimuli-responsive polyaniline coated silica microspheres and their electrorheology

    NASA Astrophysics Data System (ADS)

    Park, Dae Eun; Choi, Hyoung Jin; Vu, Cuong Manh

    2016-05-01

    Silica/polyaniline (PANI) core-shell structured microspheres were synthesized by coating the surface of silica micro-beads with PANI and applied as a candidate inorganic/polymer composite electrorheological (ER) material. The silica micro-beads were initially modified using N-[(3-trimethoxysilyl)-propyl] aniline to activate an aniline functional group on the silica surface for a better PANI coating. The morphology of the PANI coating on the silica surface was examined by scanning electron microscopy and the silica/PANI core-shell structure was confirmed by transmission electron microscopy. The chemical structure of the particles was confirmed by Fourier transform infrared spectroscopy. Rotational rheometry was performed to confirm the difference in the ER properties between pure silica and silica/PANI microsphere-based ER fluids when dispersed in silicone oil.

  15. Engineered Bacterial Metal-binding Proteins for Nanoscale Self-assembly and heavy Metal Tolerance

    NASA Astrophysics Data System (ADS)

    Hall Sedlak, Ruth Amanda

    Implementing biological principles in material synthesis and assembly is one way to expand our abilities to efficiently assemble nanoscale materials and devices. Specifically, recent advances in identifying peptides that bind inorganic materials with high affinity and specificity has spurred investigation of protein models for nanoscale inorganic assembly. This dissertation presents the results of my studies of several E. coli proteins engineered to bind inorganic materials through simple peptide motifs. I demonstrate that these proteins modulate the self-assembly of DNA-based nanostructures and can introduce heavy metal tolerance into metal-sensitive bacteria. Chapter 2 explores use of the engineered F plasmid DNA relaxase/helicase TraI for the self-assembly of complex DNA-protein-gold nanostructures. The full-length protein is engineered with a gold binding motif at an internal permissive site (TraI369GBP1-7x), while a truncated version of TraI is engineered with the same gold binding motif at the C-terminus (TraI361GBP1-7x). Both constructs bind gold nanoparticles while maintaining their DNA binding activity, and transmission electron microscopy reveals TraI369GBP1-7x utilizes its non-specific DNA binding activity to decorate single-stranded and double-stranded DNA with gold nanoparticles. The self assembly principles demonstrated in this work will be fundamental to constructing higher ordered hybrid nanostructures through DNA-protein-nanoparticle interactions. Chapter 3 studies the effects of expressing inorganic binding peptides within cells. I identified a silver binding peptide that, when fused to the periplasmic maltose binding protein, protects E. coli from silver toxicity in batch culture and reduces silver ions to silver nanoparticles within the bacterial periplasm. Engineered metal-ion tolerant microorganisms such as this E. coli could potentially be used in applications ranging from remediation to interrogation of biomolecule-metal interactions in vivo

  16. Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica.

    PubMed

    Bansal, Vipul; Ahmad, Absar; Sastry, Murali

    2006-11-01

    Rice husk is a cheap agro-based waste material, which harbors a substantial amount of silica in the form of amorphous hydrated silica grains. However, there have been no attempts at harnessing the enormous amount of amorphous silica present in rice husk and its room-temperature biotransformation into crystalline silica nanoparticles. In this study, we address this issue and describe how naturally deposited amorphous biosilica in rice husk can be bioleached and simultaneously biotransformed into high value crystalline silica nanoparticles. We show here that the fungus Fusarium oxysporum rapidly biotransforms the naturally occurring amorphous plant biosilica into crystalline silica and leach out silica extracellularly at room temperature in the form of 2-6 nm quasi-spherical, highly crystalline silica nanoparticles capped by stabilizing proteins; that the nanoparticles are released into solution is an advantage of this process with significant application and commercial potential. Calcination of the silica nanoparticles leads to loss of occluded protein and to an apparently porous structure often of cubic morphology. The room-temperature synthesis of oxide nanomaterials using microorganisms starting from potential cheap agro-industrial waste materials is an exciting possibility and could lead to an energy-conserving and economically viable green approach toward the large-scale synthesis of oxide nanomaterials.

  17. Carbon-Coated Silica and Silica-Coated Carbon for Elastomer Reinforcement

    NASA Astrophysics Data System (ADS)

    Kohls, D. J.; Beaucage, G.; Pratsinis, S. E.; Kammler, H.

    2000-03-01

    Recently several silica producers have introduced dual-phase grades of silica/carbon powders intended for use in elastomer reinforcement. These mass-produced, nano-structured materials have carbon content in excess of 75carbon aggregates, the intent being to enhance the strength of filler-filler networking in a nano-composite. We have recently developed pyrolytic, nano-scale silica aggregates with interfacial carbon (typically less than 3the aim of enhancing elastomer-filler interaction in green tires. Our carbon-coated silicas display improved processability in typical tire compounds and enhanced dynamic mechanical performance. We also have developed facilities to produce organically functionalized silicas using a novel, room-temperature, aerosol, chemical reactor (ASG reactor). This talk will present our results on dynamic mechanical properties of elastomer compounds with our carbon-coated silica; commercial dual-phase, silica-coated carbon; ASG-organically-modified silicas; conventional carbon black; conventional precipated and fumed silica; as well as blends of the conventional materials. The mass-fractal structure as determined by SAXS and SALS, as well as gas and DBP absorption measurements and microscopy will be presented.

  18. Incorporation of anti-inflammatory agent into mesoporous silica

    NASA Astrophysics Data System (ADS)

    Rodrigues Braz, Wilson; Lamec Rocha, Natállia; de Faria, Emerson H.; Silva, Márcio L. A. e.; Ciuffi, Katia J.; Tavares, Denise C.; Furtado, Ricardo Andrade; Rocha, Lucas A.; Nassar, Eduardo J.

    2016-09-01

    The unique properties of macroporous, mesoporous, and microporous systems, including their ability to accommodate molecules of different sizes inside their pores and to act as drug delivery systems, have been the object of extensive studies. In this work, mesoporous silica with hexagonal structure was obtained by template synthesis via the sol-gel process. The resulting material was used as support to accommodate the anti-inflammatory agent indomethacin. The alkaline route was used to prepare the mesoporous silica; cetyltrimethylammonium bromide was employed as porogenic agent. The silica particles were functionalized with 3-aminopropyltriethoxysilane alkoxide (APTES) by the sol-gel post-synthesis method. Indomethacin was incorporated into the silica functionalized with APTES and into non-functionalized silica. The resulting systems were characterized by x-ray diffraction (XRD), specific area, infrared spectroscopy, and thermal analyses (TGA). XRD attested to formation of mesoporous silica with hexagonal structure. This structure remained after silica functionalization with APTES and incorporation of indomethacin. Typical infrared spectroscopy vibrations and organic material decomposition during TGA confirmed silica functionalization and drug incorporation. The specific surface area and pore volume of the functionalized material incorporated with indomethacin decreased as compared with the specific surface area and pore volume of the non-functionalized silica containing no drug, suggesting both the functionalizing agent and the drug were present in the silica. Cytotoxicity tests conducted on normal fibroblasts (GM0479A) cells attested that the silica matrix containing indomethacin was less toxic than the free drug.

  19. Incorporation of anti-inflammatory agent into mesoporous silica.

    PubMed

    Braz, Wilson Rodrigues; Rocha, Natállia Lamec; de Faria, Emerson H; Silva, Márcio L A E; Ciuffi, Katia J; Tavares, Denise C; Furtado, Ricardo Andrade; Rocha, Lucas A; Nassar, Eduardo J

    2016-09-23

    The unique properties of macroporous, mesoporous, and microporous systems, including their ability to accommodate molecules of different sizes inside their pores and to act as drug delivery systems, have been the object of extensive studies. In this work, mesoporous silica with hexagonal structure was obtained by template synthesis via the sol-gel process. The resulting material was used as support to accommodate the anti-inflammatory agent indomethacin. The alkaline route was used to prepare the mesoporous silica; cetyltrimethylammonium bromide was employed as porogenic agent. The silica particles were functionalized with 3-aminopropyltriethoxysilane alkoxide (APTES) by the sol-gel post-synthesis method. Indomethacin was incorporated into the silica functionalized with APTES and into non-functionalized silica. The resulting systems were characterized by x-ray diffraction (XRD), specific area, infrared spectroscopy, and thermal analyses (TGA). XRD attested to formation of mesoporous silica with hexagonal structure. This structure remained after silica functionalization with APTES and incorporation of indomethacin. Typical infrared spectroscopy vibrations and organic material decomposition during TGA confirmed silica functionalization and drug incorporation. The specific surface area and pore volume of the functionalized material incorporated with indomethacin decreased as compared with the specific surface area and pore volume of the non-functionalized silica containing no drug, suggesting both the functionalizing agent and the drug were present in the silica. Cytotoxicity tests conducted on normal fibroblasts (GM0479A) cells attested that the silica matrix containing indomethacin was less toxic than the free drug.

  20. Ab initio Study of Transition metal binding to the Prion Protein

    NASA Astrophysics Data System (ADS)

    Cox, Daniel L.; Singh, Rajiv R. P.; Pan, Jianping

    2004-03-01

    Fundamental understanding of the prion protein (PrP) is of critical public health importance in view of mad cow and chronic wasting diseases. In recent years, it has been shown that the normal form (PrP^c) binds copper^1), and the structure of the copper binding domain has been elaborated. Hypotheses about toxicity associated with binding of other metals (notably manganese) have been put forward, Accordingly, using the ab initio SIESTA density functional theory code^2), we calculated the binding energy E_B(M) of M-(PrP) complexes relative to initially uncomplexed M ions, with M=Cu,Ni,Zn,Mn and (PrP)^* the minimal binding domain. The binding energy trend is E_B(Ni)>E_B(Cu)>E_B(Zn)>E_B(Mn), consistent with recent experiments apart from the surprising stability of Ni. We will also present preliminary results for binding of initially complexed M ions. *-Supported by U.S. DOE, Office of Basic Energy Sciences, Division of Materials Research 1) G.S. Jackson et al., Proc. Nat. Acad. Sci. (USA) 98, 8531 (2001). 2) P. Ordejón, et al., Phys. Rev. B53, R10441 (1996); J.M. Soler et al., J. Phys. Cond. Matt. 14, 2745 (2002).

  1. Silica extraction from geothermal water

    DOEpatents

    Bourcier, William L; Bruton, Carol J

    2014-09-23

    A method of producing silica from geothermal fluid containing low concentration of the silica of less than 275 ppm includes the steps of treating the geothermal fluid containing the silica by reverse osmosis treatment thereby producing a concentrated fluid containing the silica, seasoning the concentrated fluid thereby producing a slurry having precipitated colloids containing the silica, and separating the silica from the slurry.

  2. Metal-binding protein in the pacific oyster, Crassostrea gigas: assessment of the protein as a biochemical environmental indicator

    SciTech Connect

    Imber, B.E.; Thompson, J.A.J.; Ward, S.

    1987-04-01

    In this paper the determination of metal-binding proteins (MBP) in the Pacific Oyster (Crassostrea gigas) is reported. The objectives of this study were to employ a simple, cost-effective method for quantifying MBP and to assess this parameter for possible use as an indicator of identifiable sources of metal input to biological systems. Abnormally high quantities of zinc had been found previously in C. gigas growing in waters adjacent to the Kraft pump mill at Crofton, British Columbia. From 1971 to 1973 oysters near the effluent outfalls were found to have body-burden zinc six to ten times the zinc concentrations found in reference specimens. Zinc dithionite was used in the pulping process at the mill until 1973. Subsequent to a change to sodium dithionite, concentrations of zinc in oysters decreased steadily. A second potential source of contamination is sited directly south of the pulp mill. In this case, leaching of copper and zinc from smelter slag into Osborn Bay has been identified.

  3. Transcriptional regulation, metal binding properties and structure of Pden1597, an unusual zinc transport protein from Paracoccus denitrificans

    DOE PAGES

    Handali, Melody; Neupane, Durga P.; Roychowdhury, Hridindu; ...

    2015-03-18

    Here, ATP-binding cassette (ABC) transporters of the cluster 9 family are ubiquitous among bacteria and essential for acquiring Zn2+ and Mn2+ from the environment or, in the case of pathogens, from the host. These rely on a substrate-binding protein (SBP) to coordinate the relevant metal with high affinity and specificity and subsequently release it to a membrane permease for translocation into the cytoplasm. Although a number of cluster 9 SBP structures have been determined, the structural attributes conferring Zn2+ or Mn2+ specificity remain ambiguous. Here we describe the gene expression profile, in vitro metal binding properties, and crystal structure ofmore » a new cluster 9 SBP from Paracoccus denitrificans we have called AztC. Although all of our results strongly indicate Zn2+ over Mn2+ specificity, the Zn2+ ion is coordinated by a conserved Asp residue only observed to date as a metal ligand in Mn2+-specific SBPs. The unusual sequence properties of this protein are shared among close homologues, including members from the human pathogens Klebsiella pneumonia and Enterobacter aerogenes, and would seem to suggest a subclass of Zn2+-specific transporters among the cluster 9 family. In any case, the unusual coordination environment of AztC expands the already considerable range of those available to Zn2+-specific SBPs and highlights the presence of a His-rich loop as the most reliable indicator of Zn2+ specificity.« less

  4. Phosphorylation of Ser8 promotes zinc-induced dimerization of the amyloid-β metal-binding domain.

    PubMed

    Kulikova, Alexandra A; Tsvetkov, Philipp O; Indeykina, Maria I; Popov, Igor A; Zhokhov, Sergey S; Golovin, Andrey V; Polshakov, Vladimir I; Kozin, Sergey A; Nudler, Evgeny; Makarov, Alexander A

    2014-10-01

    Zinc-induced aggregation of the amyloid-β peptide (Aβ) is a hallmark molecular feature of Alzheimer's disease (AD). Recently it was shown that phosphorylation of Aβ at Ser8 promotes the formation of toxic aggregates. In this work, we have studied the impact of Ser8 phosphorylation on the mode of zinc interaction with the Aβ metal-binding domain 1-16 using isothermal titration calorimetry, electrospray ionization mass spectrometry and NMR spectroscopy. We have discovered a novel zinc binding site ((6)HDpS(8)) in the phosphorylated peptide, in which the zinc ion is coordinated by the imidazole ring of His6, the phosphate group attached to Ser8 and a backbone carbonyl group of His6 or Asp7. Interaction of the zinc ion with this site involves His6, thereby withdrawing it from the interaction pattern observed in the non-modified peptide. This event was found to stimulate dimerization of peptide chains through the (11)EVHH(14) site, where the zinc ion is coordinated by the two pairs of Glu11 and His14 in the two peptide subunits. The proposed molecular mechanism of zinc-induced dimerization could contribute to the understanding of initiation of pathological Aβ aggregation, and the (11)EVHH(14) tetrapeptide can be considered as a promising drug target for the prevention of amyloidogenesis.

  5. Expression and purification of recombinant proteins in Escherichia coli tagged with a small metal-binding protein from Nitrosomonas europaea.

    PubMed

    Vargas-Cortez, Teresa; Morones-Ramirez, Jose Ruben; Balderas-Renteria, Isaias; Zarate, Xristo

    2016-02-01

    Escherichia coli is still the preferred organism for large-scale production of recombinant proteins. The use of fusion proteins has helped considerably in enhancing the solubility of heterologous proteins and their purification with affinity chromatography. Here, the use of a small metal-binding protein (SmbP) from Nitrosomonas europaea is described as a new fusion protein for protein expression and purification in E. coli. Fluorescent proteins tagged at the N-terminal with SmbP showed high levels of solubility, compared with those of maltose-binding protein and glutathione S-transferase, and low formation of inclusion bodies. Using commercially available IMAC resins charged with Ni(II), highly pure recombinant proteins were obtained after just one chromatography step. Proteins may be purified from the periplasm of E. coli if SmbP contains the signal sequence at the N-terminal. After removal of the SmbP tag from the protein of interest, high-yields are obtained since SmbP is a protein of just 9.9 kDa. The results here obtained suggest that SmbP is a good alternative as a fusion protein/affinity tag for the production of soluble recombinant proteins in E. coli.

  6. Crystal structure of the hexameric catabolic ornithine transcarbamylase from Lactobacillus hilgardii: Structural insights into the oligomeric assembly and metal binding.

    PubMed

    de Las Rivas, Blanca; Fox, Gavin C; Angulo, Iván; Ripoll, Martín M; Rodríguez, Héctor; Muñoz, Rosario; Mancheño, José M

    2009-10-23

    Catabolic ornithine transcarbamylase (cOTC; EC 2.1.3.3) catalyzes the formation of ornithine (ORN) and carbamoyl phosphate from citrulline, which constitutes the second step of the degradation of arginine via the arginine deiminase pathway. Here, we report the crystal structure of cOTC from the lactic acid bacteria Lactobacillus hilgardii (Lh-cOTC) refined to 2.1 A resolution. The structure reveals that Lh-cOTC forms a hexameric assembly, which was also confirmed by gel-filtration chromatography and analytical ultracentrifugation. The homohexamer, with 32 point group symmetry, represents a new oligomeric state within the members of the ornithine transcarbamylase family that are typically homotrimeric or homododecameric. The C-terminal end from each subunit constitutes a key structural element for the stabilization of the hexameric assembly in solution. Additionally, the structure reveals, for the first time in the ornithine transcarbamylase family, a metal-binding site located at the 3-fold molecular symmetry axis of each trimer.

  7. Sulfur and selenium antioxidants: challenging radical scavenging mechanisms and developing structure-activity relationships based on metal binding.

    PubMed

    Zimmerman, Matthew T; Bayse, Craig A; Ramoutar, Ria R; Brumaghim, Julia L

    2015-04-01

    Because sulfur and selenium antioxidants can prevent oxidative damage, numerous animal and clinical trials have investigated the ability of these compounds to prevent the oxidative stress that is an underlying cause of cardiovascular disease, Alzheimer's disease, and cancer, among others. One of the most common sources of oxidative damage is metal-generated hydroxyl radical; however, very little research has focused on determining the metal-binding abilities and structural attributes that affect oxidative damage prevention by sulfur and selenium compounds. In this review, we describe our ongoing investigations into sulfur and selenium antioxidant prevention of iron- and copper-mediated oxidative DNA damage. We determined that many sulfur and selenium compounds inhibit Cu(I)-mediated DNA damage and that DNA damage prevention varies dramatically when Fe(II) is used in place of Cu(I) to generate hydroxyl radical. Oxidation potentials of the sulfur or selenium compounds do not correlate with their ability to prevent DNA damage, highlighting the importance of metal coordination rather than reactive oxygen species scavenging as an antioxidant mechanism. Additional gel electrophoresis, mass spectrometry, and UV-visible studies confirmed sulfur and selenium antioxidant binding to Cu(I) and Fe(II). Ultimately, our studies established that both the hydroxyl-radical-generating metal ion and the chemical environment of the sulfur or selenium significantly affect DNA damage prevention and that metal coordination is an essential mechanism for these antioxidants.

  8. Evaluation of synthetic water-soluble metal-binding polymers with ultrafiltration for selective concentration of americium and plutonium

    SciTech Connect

    Smith, B.F.; Gibson, R.R.; Jarvinen, G.D.; Jones, M.M.; Lu, M.T.; Robison, T.W.; Schroeder, N.C.; Stalnaker, N.

    1997-12-31

    Routine counting methods and ICP-MS are unable to directly measure the new US Department of Energy (DOE) regulatory level for discharge waters containing alpha-emitting radionuclides of 30 pCi/L total alpha or the 0.05 pCi/L regulatory level for Pu or Am activity required for surface waters at the Rocky Flats site by the State of Colorado. This inability indicates the need to develop rapid, reliable, and robust analytical techniques for measuring actinide metal ions, particularly americium and plutonium. Selective separation or preconcentration techniques would aid in this effort. Water-soluble metal-binding polymers in combination with ultrafiltration are shown to be an effective method for selectively removing dilute actinide ions from acidic solutions of high ionic strength. The actinide-binding properties of commercially available water-soluble polymers and several polymers which have been reported in the literature were evaluated. The functional groups incorporated in the polymers were pyrrolidone, amine, oxime, and carboxylic, phosphonic, or sulfonic acid. The polymer containing phosphonic acid groups gave the best results with high distribution coefficients and concentration factors for {sup 241}Am(III) and {sup 238}Pu(III)/(IV) at pH 4 to 6 and ionic strengths of 0.1 to 4.

  9. Unbound position II in MXCXXC metallochaperone model peptides impacts metal binding mode and reactivity: Distinct similarities to whole proteins.

    PubMed

    Shoshan, Michal S; Dekel, Noa; Goch, Wojciech; Shalev, Deborah E; Danieli, Tsafi; Lebendiker, Mario; Bal, Wojciech; Tshuva, Edit Y

    2016-06-01

    The effect of position II in the binding sequence of copper metallochaperones, which varies between Thr and His, was investigated through structural analysis and affinity and oxidation kinetic studies of model peptides. A first Cys-Cu(I)-Cys model obtained for the His peptide at acidic and neutral pH, correlated with higher affinity and more rapid oxidation of its complex; in contrast, the Thr peptide with the Cys-Cu(I)-Met coordination under neutral conditions demonstrated weaker and pH dependent binding. Studies with human antioxidant protein 1 (Atox1) and three of its mutants where S residues were replaced with Ala suggested that (a) the binding affinity is influenced more by the binding sequence than by the protein fold (b) pH may play a role in binding reactivity, and (c) mutating the Met impacted the affinity and oxidation rate more drastically than did mutating one of the Cys, supporting its important role in protein function. Position II thus plays a dominant role in metal binding and transport.

  10. Heavy metal-binding proteins from metal-stimulated bacteria as a novel adsorbent for metal removal technology.

    PubMed

    Sano, D; Myojo, K; Omura, T

    2006-01-01

    Water pollution with toxic heavy metals is of growing concern because heavy metals could bring about serious problems for not only ecosystems in the water environment but also human health. Some metal removal technologies have been in practical use, but much energy and troublesome treatments for chemical wastes are required to operate these conventional technologies. In this study, heavy metal-binding proteins (HMBPs) were obtained from metal-stimulated activated sludge culture with affinity chromatography using copper ion as a ligand. Two-dimensional electrophoresis revealed that a number of proteins in activated sludge culture were recovered as HMBPs for copper ion. N-termini of five HMBPs were determined, and two of them were found to be newly discovered proteins for which no amino acid sequences in protein databases were retrieved at more than 80% identities. Metal-coordinating amino acids occupied 38% of residues in one of the N-terminal sequences of the newly discovered HMBPs. Since these HMBPs were expected to be stable under conditions of water and wastewater treatments, it would be possible to utilize HMBPs as novel adsorbents for heavy metal removal if mass volume of HMBPs can be obtained with protein cloning techniques.

  11. micro-XANES and micro-XRF investigations of metal binding mechanisms in biosolids.

    PubMed

    Hettiarachchi, G M; Scheckel, K G; Ryan, J A; Sutton, S R; Newville, M

    2006-01-01

    Micro-X-ray fluorescence (micro-XRF) microprobe analysis and micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy were employed to identify Fe and Mn phases and their association with selected metals in two biosolids (limed composted [LC] and Nu-Earth) before and after treatment to remove organic carbon (OC). Spatial correlations derived from elemental mapping of XRF images showed strong correlations between Fe and Cd, Cr, Pb, or Zn (r2= 0.65-0.92) before and after removal of most of the OC. The strong correlation between Fe and Cu that was present in intact samples disappeared after OC removal, suggesting that Cu was associated with OC coatings that may have been present on Fe compounds. Except for Fe and Cr, the spatial correlations of metals with Mn were improved after treatment to remove OC, indicating that the treatment may have altered more than the OC in the system. The Fe micro-XANES spectra of the intact biosolids sample showed that every point had varying mixtures of Fe(II and III) species and no two points were identical. The lack of uniformity in Fe species in the biosolids sample illustrates the complexity of the materials and the difficulty of studying biosolids using conventional analytical tools or chemical extraction techniques. Still, these microscopic observations provide independent information supporting the previous laboratory and field hypothesis that Fe compounds play a major role in retention of environmentally important trace elements in biosolids. This could be due to co-precipitation of the metals with Fe, adsorption of metals by Fe compounds, or a combination of both mechanisms.

  12. Synthesis and Characterization of Bionanoparticle-Silica Composites and Mesoporous Silica with Large Pores

    SciTech Connect

    Niu, Z.; Yang, L.; Kabisatpathy, S.; He, J.; Lee, A.; Ron, J.; Sikha, G.; Popov, B.N.; Emrick, T.; Russell, T. P.; Wang. Q.

    2009-03-24

    A sol-gel process has been developed to incorporate bionanoparticles, such as turnip yellow mosaic virus, cowpea mosaic virus, tobacco mosaic virus, and ferritin into silica, while maintaining the integrity and morphology of the particles. The structures of the resulting materials were characterized by transmission electron microscopy, small angle X-ray scattering, and N{sub 2} adsorption-desorption analysis. The results show that the shape and surface morphology of the bionanoparticles are largely preserved after being embedded into silica. After removal of the bionanoparticles by calcination, mesoporous silica with monodisperse pores, having the shape and surface morphology of the bionanoparticles replicated inside the silica, was produced,. This study is expected to lead to both functional composite materials and mesoporous silica with structurally well-defined large pores.

  13. Health hazards due to the inhalation of amorphous silica.

    PubMed

    Merget, R; Bauer, T; Küpper, H U; Philippou, S; Bauer, H D; Breitstadt, R; Bruening, T

    2002-01-01

    Occupational exposure to crystalline silica dust is associated with an increased risk for pulmonary diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and lung cancer. This review summarizes the current knowledge about the health effects of amorphous (non-crystalline) forms of silica. The major problem in the assessment of health effects of amorphous silica is its contamination with crystalline silica. This applies particularly to well-documented pneumoconiosis among diatomaceous earth workers. Intentionally manufactured synthetic amorphous silicas are without contamination of crystalline silica. These synthetic forms may be classified as (1) wet process silica, (2) pyrogenic ("thermal" or "fumed") silica, and (3) chemically or physically modified silica. According to the different physicochemical properties, the major classes of synthetic amorphous silica are used in a variety of products, e.g. as fillers in the rubber industry, in tyre compounds, as free-flow and anti-caking agents in powder materials, and as liquid carriers, particularly in the manufacture of animal feed and agrochemicals; other uses are found in toothpaste additives, paints, silicon rubber, insulation material, liquid systems in coatings, adhesives, printing inks, plastisol car undercoats, and cosmetics. Animal inhalation studies with intentionally manufactured synthetic amorphous silica showed at least partially reversible inflammation, granuloma formation and emphysema, but no progressive fibrosis of the lungs. Epidemiological studies do not support the hypothesis that amorphous silicas have any relevant potential to induce fibrosis in workers with high occupational exposure to these substances, although one study disclosed four cases with silicosis among subjects exposed to apparently non-contaminated amorphous silica. Since the data have been limited, a risk of chronic bronchitis, COPD or emphysema cannot be excluded. There is no study

  14. Nonporous Silica Nanoparticles for Nanomedicine Application

    PubMed Central

    Tang, Li; Cheng, Jianjun

    2013-01-01

    Summary Nanomedicine, the use of nanotechnology for biomedical applications, has potential to change the landscape of the diagnosis and therapy of many diseases. In the past several decades, the advancement in nanotechnology and material science has resulted in a large number of organic and inorganic nanomedicine platforms. Silica nanoparticles (NPs), which exhibit many unique properties, offer a promising drug delivery platform to realize the potential of nanomedicine. Mesoporous silica NPs have been extensively reviewed previously. Here we review the current state of the development and application of nonporous silica NPs for drug delivery and molecular imaging. PMID:23997809

  15. Conversion of geothermal waste to commercial products including silica

    DOEpatents

    Premuzic, Eugene T.; Lin, Mow S.

    2003-01-01

    A process for the treatment of geothermal residue includes contacting the pigmented amorphous silica-containing component with a depigmenting reagent one or more times to depigment the silica and produce a mixture containing depigmented amorphous silica and depigmenting reagent containing pigment material; separating the depigmented amorphous silica and from the depigmenting reagent to yield depigmented amorphous silica. Before or after the depigmenting contacting, the geothermal residue or depigmented silica can be treated with a metal solubilizing agent to produce another mixture containing pigmented or unpigmented amorphous silica-containing component and a solubilized metal-containing component; separating these components from each other to produce an amorphous silica product substantially devoid of metals and at least partially devoid of pigment. The amorphous silica product can be neutralized and thereafter dried at a temperature from about 25.degree. C. to 300.degree. C. The morphology of the silica product can be varied through the process conditions including sequence contacting steps, pH of depigmenting reagent, neutralization and drying conditions to tailor the amorphous silica for commercial use in products including filler for paint, paper, rubber and polymers, and chromatographic material.

  16. Silver-coated dye-embedded silica beads: a core material of dual tagging sensors based on fluorescence and Raman scattering.

    PubMed

    Kim, Kwan; Lee, Hyang Bong; Choi, Jeong-Yong; Shin, Kuan Soo

    2011-02-01

    We have developed a new type of dual-tag sensor for immunoassays, operating via both fluorescence and surface-enhanced Raman scattering (SERS). A one-shot fluorescence image over the whole specimen allows us to save considerable time because any unnecessary time-consuming SERS measurements can be avoided from the signature of the fluorescence. Dye-embedded silica beads are prepared initially, and then SERS-active silver is coated onto them via a very simple electroless-plating method. The Raman markers are subsequently assembled onto the Ag-coated silica beads, after which they are stabilized by silanization via a biomimetic process in which a poly(allylamine hydrochloride) layer formed on the Raman markers by a layer-by-layer deposition method acting as a scaffold for guiding silicification. In the final stage, specific antibodies are attached to the silica surface in order to detect target antigens. The fluorescence signal of the embedded dye can be used as a fast readout system of molecular recognition, whereas the SERS signals are subsequently used as the signature of specific molecular interactions. In this way, the antibody-grafted particles were found to recognize antigens down to 1 × 10(-10) g mL(-1) solely by the SERS peaks of the Raman markers.

  17. Silica and Pyroxene in IVA Irons; Possible Formation of the IVA Magma by Impact Melting and Reduction of L-LL-Chondrite Materials Followed by Crystallization and Cooling

    NASA Technical Reports Server (NTRS)

    Wasson, John T.; Matsunami, Yoshiyuki; Rubin, Alan E.

    2006-01-01

    Group IVA is a large magmatic group of iron meteorites. The mean DELTA O-17 (= delta O-17 - 0.52(raised dot) delta O-18) of the silicates is approx. plus or minus 1.2%o, similar to the highest values in L chondrites and the lowest values in LL chondrites; delta O-18 values are also in the L/LL range. This strongly suggests that IVA irons formed by melting L-LL parental material, but the mean Ni content of IVA irons (83 mg/g) is much lower than that of a presumed L-LL parent (approx. 170 mg/g) and the low-Ca pyroxene present in two IVA meteorites is Fs13, much lower than the Fs20-29 values in L and LL chondrites. Thus, formation from L-LL precursors requires extensive addition of metallic Fe, probably produced by reduction of FeS and FeO. Group IVA also has S/Ni, Ga/Ni, and Ge/Ni ratios that are much lower than those in L-LL chondrites or any chondrite group that preserves nebular compositions, implying loss of these volatile elements during asteroidal processing. We suggest that these reduction and loss processes occurred near the surface of the asteroid during impact heating, and resulted partly from reduction by C, and partly from the thermal dissociation of FeS and FeO with loss of O and S. The hot (approx. 1770 K) low-viscosity melt quickly moved through channels in the porous asteroid to form a core. Two members of the IVA group, Sao Joao Nepomuceno (hereafter, SJN) and Steinbach, contain moderate amounts of orthopyroxene and silica, and minor amounts of low-Ca clinopyroxene. Even though SJN formed after approx. 26% crystallization and Steinbach formed after approx. 77% Crystallization of the IVA core, both could have originated within several tens of meters of the core-mantle interface if 99% of the crystallization occurred from the center outwards. Two other members of the group (Gibeon and Bishop Canyon) contain tabular tridymite, which we infer to have initially formed as veins deposited from a cooling SiO-rich vapor. The silicates were clearly introduced

  18. High purity silica reflective heat shield development

    NASA Technical Reports Server (NTRS)

    Nachtscheim, P. R.; Blome, J. C.

    1976-01-01

    A hyperpure vitreous silica material is being developed for use as a reflective and ablative heat shield for planetary entry. Various purity grades and forms of raw materials were evaluated along with various processing methods. Slip casting of high purity grain was selected as the best processing method, resulting in a highly reflective material in the wavelength bands of interest (the visible and ultraviolet regions). The selected material was characterized with respect to optical, mechanical and physical properties using a limited number of specimens. The process has been scaled up to produce a one-half scale heat shield (18 in. dia.) (45.72 cm) for a Jupiter entry vehicle. This work is now being extended to improve the structural safety factor of the heat shield by making hyperpure silica material tougher through the addition of silica fibers.

  19. Silica substrate or portion formed from oxidation of monocrystalline silicon

    DOEpatents

    Matzke, Carolyn M.; Rieger, Dennis J.; Ellis, Robert V.

    2003-07-15

    A method is disclosed for forming an inclusion-free silica substrate using a monocrystalline silicon substrate as the starting material and oxidizing the silicon substrate to convert it entirely to silica. The oxidation process is performed from both major surfaces of the silicon substrate using a conventional high-pressure oxidation system. The resulting product is an amorphous silica substrate which is expected to have superior etching characteristics for microfabrication than conventional fused silica substrates. The present invention can also be used to convert only a portion of a monocrystalline silicon substrate to silica by masking the silicon substrate and locally thinning a portion the silicon substrate prior to converting the silicon portion entirely to silica. In this case, the silica formed by oxidizing the thinned portion of the silicon substrate can be used, for example, as a window to provide optical access through the silicon substrate.

  20. The role of substrate specificity and metal binding in defining the activity and structure of an intracellular subtilisin.

    PubMed

    Gamble, Michael; Künze, Georg; Brancale, Andrea; Wilson, Keith S; Jones, D Dafydd

    2012-01-01

    The dimeric intracellular subtilisin proteases (ISPs) found throughout Gram-positive bacteria are a structurally distinct class of the subtilase family. Unlike the vast majority of subtilisin-like proteases, the ISPs function exclusively within the cell, contributing the majority of observed cellular proteolytic activity. Given that they are active within the cell, little is known about substrate specificity and the role of stress signals such as divalent metal ions in modulating ISP function. We demonstrate that both play roles in defining the proteolytic activity of Bacillus clausii ISP and propose the molecular basis of their effects. Enzyme kinetics reveal that one particular synthetic tetrapeptide substrate, Phe-Ala-Ala-Phe-pNA, is hydrolysed with a catalytic efficiency ∼100-fold higher than any other tested. Heat-denatured whole proteins were found to be better substrates for ISP than the native forms. Substrate binding simulations suggest that the S1, S2 and S4 sites form defined binding pockets. The deep S1 cavity and wide S4 site are fully occupied by the hydrophobic aromatic side-chains of Phe. Divalent metal ions, probably Ca(2+), are proposed to be important for ISP activity through structural changes. The presence of >0.01 mM EDTA inactivates ISP, with CD and SEC suggesting that the protein becomes less structured and potentially monomeric. Removal of Ca(2+) at sites close to the dimer interface and the S1 pocket are thought to be responsible for the effect. These studies provide a new insight into the potential physiological function of ISPs, by reconciling substrate specificity and divalent metal binding to associate ISP with the unfolded protein response under stress conditions.

  1. The role of substrate specificity and metal binding in defining the activity and structure of an intracellular subtilisin

    PubMed Central

    Gamble, Michael; Künze, Georg; Brancale, Andrea; Wilson, Keith S.; Jones, D. Dafydd

    2012-01-01

    The dimeric intracellular subtilisin proteases (ISPs) found throughout Gram-positive bacteria are a structurally distinct class of the subtilase family. Unlike the vast majority of subtilisin-like proteases, the ISPs function exclusively within the cell, contributing the majority of observed cellular proteolytic activity. Given that they are active within the cell, little is known about substrate specificity and the role of stress signals such as divalent metal ions in modulating ISP function. We demonstrate that both play roles in defining the proteolytic activity of Bacillus clausii ISP and propose the molecular basis of their effects. Enzyme kinetics reveal that one particular synthetic tetrapeptide substrate, Phe-Ala-Ala-Phe-pNA, is hydrolysed with a catalytic efficiency ∼100-fold higher than any other tested. Heat-denatured whole proteins were found to be better substrates for ISP than the native forms. Substrate binding simulations suggest that the S1, S2 and S4 sites form defined binding pockets. The deep S1 cavity and wide S4 site are fully occupied by the hydrophobic aromatic side-chains of Phe. Divalent metal ions, probably Ca2+, are proposed to be important for ISP activity through structural changes. The presence of >0.01 mM EDTA inactivates ISP, with CD and SEC suggesting that the protein becomes less structured and potentially monomeric. Removal of Ca2+ at sites close to the dimer interface and the S1 pocket are thought to be responsible for the effect. These studies provide a new insight into the potential physiological function of ISPs, by reconciling substrate specificity and divalent metal binding to associate ISP with the unfolded protein response under stress conditions. PMID:23650602

  2. High-resolution crystal structures reveal plasticity in the metal binding site of apurinic/apyrimidinic endonuclease I.

    PubMed

    He, Hongzhen; Chen, Qiujia; Georgiadis, Millie M

    2014-10-21

    Apurinic/apyrimidinic endonuclease I (APE1) is an essential base excision repair enzyme that catalyzes a Mg²⁺-dependent reaction in which the phosphodiester backbone is cleaved 5' of an abasic site in duplex DNA. This reaction has been proposed to involve either one or two metal ions bound to the active site. In the present study, we report crystal structures of Mg²⁺, Mn²⁺, and apo-APE1 determined at 1.4, 2.2, and 1.65 Å, respectively, representing two of the highest resolution structures yet reported for APE1. In our structures, a single well-ordered Mn²⁺ ion was observed coordinated by D70 and E96; the Mg²⁺ site exhibited disorder modeled as two closely positioned sites coordinated by D70 and E96 or E96 alone. Direct metal binding analysis of wild-type, D70A, and E96A APE1, as assessed by differential scanning fluorimetry, indicated a role for D70 and E96 in binding of Mg²⁺ or Mn²⁺ to APE1. Consistent with the disorder exhibited by Mg²⁺ bound to the active site, two different conformations of E96 were observed coordinated to Mg²⁺. A third conformation for E96 in the apo structure is similar to that observed in the APE1-DNA-Mg²⁺ complex structure. Thus, binding of Mg²⁺ in three different positions within the active site of APE1 in these crystal structures corresponds directly with three different conformations of E96. Taken together, our results are consistent with the initial capture of metal by D70 and E96 and repositioning of Mg²⁺ facilitated by the structural plasticity of E96 in the active site.

  3. Rack-induced metal binding vs. flexibility: Met121His azurin crystal structures at different pH

    PubMed Central

    Messerschmidt, Albrecht; Prade, Lars; Kroes, Sandra J.; Sanders–Loehr, Joann; Huber, Robert; Canters, Gerard W.

    1998-01-01

    The rack-induced bonding mechanism of metals to proteins is a useful concept for explaining the generation of metal sites in electron transfer proteins, such as the blue copper proteins, that are designed for rapid electron transfer. The trigonal pyramidal structure imposed by the protein with three strong equatorial ligands (one Cys and two His) provides a favorable geometry for both cuprous and cupric oxidation states. However, the crystal structures of the Met121His mutant of azurin from Alcaligenes denitrificans at pH 6.5 (1.89- and 1.91-Å resolutions) and pH 3.5 (2.45-Å resolution) show that the preformed metal binding cavity in the protein is more flexible than expected. At high pH (6.5), the Cu site retains the same three equatorial ligands as in the wild-type azurin and adds His121 as a fourth strong ligand, creating a tetrahedral copper site geometry with a green color referred to as 1.5 type. In the low pH (3.5) structure, the protonation of His121 causes a conformational change in residues 117–123, moving His121 away from the copper. The empty coordination site is occupied by an oxygen atom of a nitrate molecule of the buffer solution. This axial ligand is coordinated less strongly, generating a distorted tetrahedral copper geometry with a blue color and spectroscopic properties of a type-1 site. These crystal structures demonstrate that blue copper proteins are flexible enough to permit a range of movement of the Cu atom along the axial direction of the trigonal pyramid. PMID:9520385

  4. Rack-induced metal binding vs. flexibility: Met121His azurin crystal structures at different pH.

    PubMed

    Messerschmidt, A; Prade, L; Kroes, S J; Sanders-Loehr, J; Huber, R; Canters, G W

    1998-03-31

    The rack-induced bonding mechanism of metals to proteins is a useful concept for explaining the generation of metal sites in electron transfer proteins, such as the blue copper proteins, that are designed for rapid electron transfer. The trigonal pyramidal structure imposed by the protein with three strong equatorial ligands (one Cys and two His) provides a favorable geometry for both cuprous and cupric oxidation states. However, the crystal structures of the Met121His mutant of azurin from Alcaligenes denitrificans at pH 6.5 (1.89- and 1.91-A resolutions) and pH 3.5 (2.45-A resolution) show that the preformed metal binding cavity in the protein is more flexible than expected. At high pH (6.5), the Cu site retains the same three equatorial ligands as in the wild-type azurin and adds His121 as a fourth strong ligand, creating a tetrahedral copper site geometry with a green color referred to as 1.5 type. In the low pH (3.5) structure, the protonation of His121 causes a conformational change in residues 117-123, moving His121 away from the copper. The empty coordination site is occupied by an oxygen atom of a nitrate molecule of the buffer solution. This axial ligand is coordinated less strongly, generating a distorted tetrahedral copper geometry with a blue color and spectroscopic properties of a type-1 site. These crystal structures demonstrate that blue copper proteins are flexible enough to permit a range of movement of the Cu atom along the axial direction of the trigonal pyramid.

  5. Spectral and metal-binding properties of three single-point tryptophan mutants of the human transferrin N-lobe.

    PubMed Central

    He, Q Y; Mason, A B; Lyons, B A; Tam, B M; Nguyen, V; MacGillivray, R T; Woodworth, R C

    2001-01-01

    Human serum transferrin N-lobe (hTF/2N) contains three conserved tryptophan residues, Trp(8), Trp(128) and Trp(264), located in three different environments. The present report addresses the different contributions of the three tryptophan residues to the UV-visible, fluorescence and NMR spectra of hTF/2N and the effect of the mutations at each tryptophan residue on the iron-binding properties of the protein. Trp(8) resides in a hydrophobic box containing a cluster of three phenylalanine side chains and is H bonded through the indole N to an adjacent water cluster lying between two beta-sheets containing Trp(8) and Lys(296) respectively. The fluorescence of Trp(8) may be quenched by the benzene rings. The apparent increase in the rate of iron release from the Trp(8)-->Tyr mutant could be due to the interference of the mutation with the H-bond linkage resulting in an effect on the second shell network. The partial quenching in the fluorescence of Trp(128) results from the nearby His(119) residue. Difference-fluorescence spectra reveal that any protein containing Trp(128) shows a blue shift upon binding metal ion, and the NMR signal of Trp(128) broadens out and disappears upon the binding of paramagnetic metals to the protein. These data imply that Trp(128) is a major fluorescent and NMR reporter group for metal binding, and possibly for cleft closure in hTF/2N. Trp(264) is located on the surface of the protein and does not connect to any functional residues. This explains the facts that Trp(264) is the major contributor to both the absorbance and fluorescence spectra, has a strong NMR signal and the mutation at Trp(264) has little effect on the iron-binding and release behaviours of the protein. PMID:11171122

  6. Structure and interactions of the C-terminal metal binding domain of Archaeoglobus fulgidus CopA

    PubMed Central

    Agarwal, Sorabh; Hong, Deli; Desai, Nirav K.; Sazinsky, Matthew H.; Argüello, José M.; Rosenzweig, Amy C.

    2010-01-01

    The Cu+-ATPase CopA from Archaeoglobus fulgidus belongs to the P1B family of the P-type ATPases. These integral membrane proteins couple the energy of ATP hydrolysis to heavy metal ion translocation across membranes. A defining feature of P1B-1-type ATPases is the presence of soluble metal binding domains at the N-terminus (N-MBDs). The N-MBDs exhibit a conserved ferredoxin-like fold, similar to that of soluble copper chaperones, and bind metal ions via a conserved CXXC motif. The N-MBDs enable Cu+ regulation of turnover rates apparently through Cu-sensitive interactions with catalytic domains. A. fulgidus CopA is unusual in that it contains both an N-terminal MBD and a C-terminal MBD (C-MBD). The functional role of the unique C-MBD has not been established. Here, we report the crystal structure of the apo, oxidized C-MBD to 2.0 Å resolution. In the structure, two C-MBD monomers form a domain-swapped dimer, which has not been observed previously for similar domains. In addition, the interaction of the C-MBD with the other cytoplasmic domains of CopA, the ATP binding domain (ATPBD) and actuator domain (A-domain) has been investigated. Interestingly, the C-MBD interacts specifically with both of these domains, independent of the presence of Cu+ or nucleotides. These data reinforce the uniqueness of the C-MBD and suggest a distinct structural role for the C-MBD in CopA transport. PMID:20602459

  7. Metal binding properties of Escherichia coli YjiA, a member of the metal homeostasis-associated COG0523 family of GTPases.

    PubMed

    Sydor, Andrew M; Jost, Marco; Ryan, Katherine S; Turo, Kaitlyn E; Douglas, Colin D; Drennan, Catherine L; Zamble, Deborah B

    2013-03-12

    GTPases are critical molecular switches involved in a wide range of biological functions. Recent phylogenetic and genomic analyses of the large, mostly uncharacterized COG0523 subfamily of GTPases revealed a link between some COG0523 proteins and metal homeostasis pathways. In this report, we detail the bioinorganic characterization of YjiA, a representative member of COG0523 subgroup 9 and the only COG0523 protein to date with high-resolution structural information. We find that YjiA is capable of binding several types of transition metals with dissociation constants in the low micromolar range and that metal binding affects both the oligomeric structure and GTPase activity of the enzyme. Using a combination of X-ray crystallography and site-directed mutagenesis, we identify, among others, a metal-binding site adjacent to the nucleotide-binding site in the GTPase domain that involves a conserved cysteine and several glutamate residues. Mutations of the coordinating residues decrease the impact of metal, suggesting that metal binding to this site is responsible for modulating the GTPase activity of the protein. These findings point toward a regulatory function for these COG0523 GTPases that is responsive to their metal-bound state.

  8. Macrophages in T cell/histiocyte rich large B cell lymphoma strongly express metal-binding proteins and show a bi-activated phenotype.

    PubMed

    Hartmann, Sylvia; Tousseyn, Thomas; Döring, Claudia; Flüchter, Patricia; Hackstein, Holger; Herreman, An; Ponzoni, Maurilio; de Wolf-Peeters, Chris; Facchetti, Fabio; Gascoyne, Randy D; Küppers, Ralf; Steidl, Christian; Hansmann, Martin-Leo

    2013-12-01

    Abundant macrophage infiltration in tumors often correlates with a poor prognosis. T cell/histiocyte rich large B cell lymphoma (THRLBCL) is a distinct aggressive B cell lymphoma entity showing a high macrophage content. To further elucidate the role of tumor-associated macrophages in THRLBCL, we performed gene expression profiling of microdissected histiocyte subsets of THRLBCL, nodular lymphocyte predominant Hodgkin lymphoma (NLPHL), Piringer lymphadenitis, sarcoidosis, nonspecific lymphadenitis and monocytes from peripheral blood. In a supervised principal component analysis, histiocytes from THRLBCL were most closely related to epithelioid cells from NLPHL, with both types of cells expressing genes related to proinflammatory and regulatory macrophage activity. Moreover, histiocytes from THRLBCL strongly expressed metal-binding proteins like MT2A, by which histiocytes of THRLBCL can be distinguished from the other histiocyte subsets investigated. Interestingly, the validation at the protein level showed a strong expression of TXN, CXCL9, MT2A and SOD2 not only in macrophages of THRLBCL but also in the tumor cells of NLPHL and classical Hodgkin lymphoma (cHL). Overall, the present findings indicate that macrophages in the microenvironment of THRLBCL have acquired a distinct gene expression pattern that is characterized by a mixed M1/M2 phenotype and a strong expression of several metal binding proteins. The microenvironments in NLPHL and THRLBCL appear to have a similar influence on the macrophage phenotype. The high expression of metal binding proteins in histiocytes of THRLBCL may be diagnostically useful, but a potential pathophysiological role remains to be identified.

  9. Metal Binding Properties of Escherichia coli YjiA, a Member of the Metal Homeostasis-Associated COG0523 Family of GTPases

    PubMed Central

    2013-01-01

    GTPases are critical molecular switches involved in a wide range of biological functions. Recent phylogenetic and genomic analyses of the large, mostly uncharacterized COG0523 subfamily of GTPases revealed a link between some COG0523 proteins and metal homeostasis pathways. In this report, we detail the bioinorganic characterization of YjiA, a representative member of COG0523 subgroup 9 and the only COG0523 protein to date with high-resolution structural information. We find that YjiA is capable of binding several types of transition metals with dissociation constants in the low micromolar range and that metal binding affects both the oligomeric structure and GTPase activity of the enzyme. Using a combination of X-ray crystallography and site-directed mutagenesis, we identify, among others, a metal-binding site adjacent to the nucleotide-binding site in the GTPase domain that involves a conserved cysteine and several glutamate residues. Mutations of the coordinating residues decrease the impact of metal, suggesting that metal binding to this site is responsible for modulating the GTPase activity of the protein. These findings point toward a regulatory function for these COG0523 GTPases that is responsive to their metal-bound state. PMID:24449932

  10. Ga[OSi(O(t)Bu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry.

    PubMed

    Dombrowski, James P; Johnson, Gregory R; Bell, Alexis T; Tilley, T Don

    2016-07-05

    The molecular precursor tris[(tri-tert-butoxy)siloxy]gallium, as the tetrahydrofuran adduct Ga[OSi(O(t)Bu)3]3·THF (), was synthesized via the salt metathesis reaction of gallium trichloride with NaOSi(O(t)Bu)3. This complex serves as a model for isolated gallium in a silica framework. Complex decomposes thermally in hydrocarbon solvent, eliminating isobutylene, water, and tert-butanol to generate high surface area gallium-containing silica at low temperatures. When thermal decomposition was performed in the presence of P-123 Pluronic as a templating agent the generated material displayed uniform vermicular pores. Textural mesoporosity was evident in untemplated material. Co-thermolysis of with HOSi(O(t)Bu)3 in the presence of P-123 Pluronic led to materials with Ga : Si ratios ranging from 1 : 3 to 1 : 50, denoted UCB1-GaSi3, UCB1-GaSi10, UCB1-GaSi20 and UCB1-GaSi50. After calcination at 500 °C these materials exhibited decreasing surface areas and broadening pore distributions with increasing silicon content, indicating a loss of template effects. The position and dispersion of the gallium in UCB1-GaSi materials was investigated using (71)Ga MAS-NMR, powder XRD, and STEM/EDS elemental mapping. The results indicate a high degree of gallium dispersion in all samples, with gallium oxide clusters or oligomers present at higher gallium content.

  11. Immobilization of silver nanoparticles on silica microspheres

    NASA Astrophysics Data System (ADS)

    Huang, Chih-Kai; Chen, Chia-Yin; Han, Jin-Lin; Chen, Chii-Chang; Jiang, Meng-Dan; Hsu, Jen-Sung; Chan, Chia-Hua; Hsieh, Kuo-Huang

    2010-01-01

    The silver nanoparticles (Ag NPs) have been immobilized onto silica microspheres through the adsorption and subsequent reduction of Ag+ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared through sol-gel processing; their surfaces were then functionalized using 3-mercaptopropyltrimethoxysilane (MPTMS). The major aims of this study were to immobilize differently sized Ag particles onto the silica microspheres and to understand the mechanism of formation of the Ag nano-coatings through the self-assembly/adsorption behavior of Ag NPs/Ag+ ions on the silica spheres. The obtained Ag NP/silica microsphere conglomerates were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). Their electromagnetic wave shielding effectiveness were also tested and studied. The average particle size of the obtained Ag NPs on the silica microsphere was found that could be controllable (from 2.9 to 51.5 nm) by adjusting the ratio of MPTMS/TEOS and the amount of AgNO3.

  12. Light-Induced Surface Patterning of Silica.

    PubMed

    Kang, Hong Suk; Lee, Seungwoo; Choi, Jaeho; Lee, Hongkyung; Park, Jung-Ki; Kim, Hee-Tak

    2015-10-27

    Manipulating the size and shape of silica precursor patterns using simple far-field light irradiation and transforming such reconfigured structures into inorganic silica patterns by pyrolytic conversion are demonstrated. The key concept of our work is the use of an azobenzene incorporated silica precursor (herein, we refer to this material as azo-silane composite) as ink in a micromolding process. The moving direction of azo-silane composite is parallel to light polarization direction; in addition, the amount of azo-silane composite movement can be precisely determined by controlling light irradiation time. By exploiting this peculiar phenomenon, azo-silane composite patterns produced using the micromolding technique are arbitrarily manipulated to obtain various structural features including high-resolution size or sophisticated shape. The photoreconfigured patterns formed with azo-silane composites are then converted into pure silica patterns through pyrolytic conversion. The pyrolytic converted silica patterns are uniformly formed over a large area, ensuring crack-free formation and providing high structural fidelity. Therefore, this optical manipulation technique, in conjunction with the pyrolytic conversion process, opens a promising route to the design of silica patterns with finely tuned structural features in terms of size and shape. This platform for designing silica structures has significant value in various nanotechnology fields including micro/nanofluidic channel for lab-on-a-chip devices, transparent superhydrophobic surfaces, and optoelectronic devices.

  13. Sonochemical preparation of silica nanorods for gene delivery using single-walled carbon nanotubes as templates.

    PubMed

    Lee, Kyoung G; Min, Jung Sun; Wi, Rinbok; Kim, Jin Chul; Ahn, Jeong Keun; Kim, Do Hyun

    2011-01-01

    Silica nanorods were fabricated with single-walled carbon nanotubes (SWCNTs) via ultrasound. The diameter of the resulting SWCNT-silica particles ranged from 60 to 70 nm. The morphology of this composite material was investigated via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The individual SWCNTs are uniformly coated with silica and formed a unique nanocomposite material. The important role of ultrasound and the mechanism of silica layer formation on SWCNTs were explained via the hydrolysis of the silica source and the adsorption of the siloxane groups on the SWCNT surfaces under ultrasound irradiation. The amino-functionalized silica nanorods were demonstrated as non-viral vectors for gene delivery.

  14. Development of an improved toughness hyperpure silica reflective heat shield

    NASA Technical Reports Server (NTRS)

    Rusert, E. L.; Hackett, T. L.; Drennan, D. N.

    1979-01-01

    High purity three dimensionally woven silica-silica materials were evaluated for use as a tough reflective heat shield for planetary entry probes. A special weave design was selected to minimize light piping effects through the heat shield thickness. Various weave spacings were evaluated for densification efficiency with an 0.7 micron particle size high purity silica. Spectral hemispherical reflectance was measured from 0.2 to 2.5 microns at room temperature. Reflectance increases due to densification and purity of material were measured. Reflectance of 3D hyperpure silica was higher than 3D astroquartz silica for all wavelengths. Mechanical properties were measured in beam flexure and beam shear tests. Results indicated strengths lower than reported for slip cast fused silica. Low strengths were attributed to low densities achieved through vacuum impregnation.

  15. Method of solidifying waste materials, such as radioactive or toxic materials, contained in aqueous solutions

    SciTech Connect

    Knieper, J.; May, K.; Printz, H.

    1984-07-24

    A method is disclosed of solidifying waste materials, such as radioactive or toxic materials, which are contained in aqueous solutions. To accomplish this solidification, an inorganic, non-metallic binding agent such as gypsum is intermixed with the aqueous solution and a substance such as pumice or ceramic tile which promotes the intermixing of the binding agent and the aqueous solution.

  16. Silazine to silica

    NASA Technical Reports Server (NTRS)

    Harvey, Gale A.

    1993-01-01

    Thin film silica and/or methyl silicone were detected on most external surfaces of the retrieved LDEF. Both solar ultraviolet radiation and atomic oxygen can convert silicones to silica. Known sources of silicone in or on the LDEF appear inadequate to explain the ubiquitous presence of the silica and silicone films. Hexamethyldisilazane (HMDS) was used as the Challenger tile waterproofing compound for the Challenger/LDEF deployment mission. HMDS is both volatile and chemically reactive at STP. In addition, HMDS releases NH3 which depolymerizes silicone RTV's. Polyurethanes are also depolymerized. Experiments are reported that indicate much of the silicone and silica contamination of LDEF resulted directly or indirectly from HMDS.

  17. Grassy Silica Nanoribbons and Strong Blue Luminescence

    NASA Astrophysics Data System (ADS)

    Wang, Shengping; Xie, Shuang; Huang, Guowei; Guo, Hongxuan; Cho, Yujin; Chen, Jun; Fujita, Daisuke; Xu, Mingsheng

    2016-09-01

    Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications.

  18. Grassy Silica Nanoribbons and Strong Blue Luminescence

    PubMed Central

    Wang, Shengping; Xie, Shuang; Huang, Guowei; Guo, Hongxuan; Cho, Yujin; Chen, Jun; Fujita, Daisuke; Xu, Mingsheng

    2016-01-01

    Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications. PMID:27666663

  19. Designed synthesis of Graphene @titania @mesoporous silica hybrid material as size-exclusive metal oxide affinity chromatography platform for selective enrichment of endogenous phosphopeptides.

    PubMed

    Yao, Jizong; Sun, Nianrong; Deng, Chunhui; Zhang, Xiangming

    2016-04-01

    In this work, a novel size-exclusive metal oxide affinity chromatography (SE-MOAC) platform was built for phosphoproteome research. The operation for preparing graphene @titania @mesoporous silica nanohybrids (denoted as G@TiO2@mSiO2) was facile and easy to conduct by grafting titania nanoparticles on polydopamine (PD)-covered graphene, following a layer of mesoporous silica was coated on the outermost layer. The G@TiO2@mSiO2 nanohybrids exhibited high sensitivity with a low detection limit of 5 amol/μL (a total amount of 1 fmol) and high selectivity for phosphopeptides at a mass ratio of phosphopeptides to non-phosphopeptides (1:1000). The size-exclusive capability of the nanohybrids were also demonstrated by enriching the phosphopeptides from the mixture of Bovine Serum Albumin (BSA), α-casein, and β-casein digests with a high mass ratio (β-casein digests: α-casein: BSA, 1:500:500), which was attributed to the large surface area and ordered mesoporous channels. In addition, the G@TiO2@mSiO2 nanohybrids were employed to capture the endogenous phosphopeptides from human serum successfully.

  20. Photonic integrated circuits based on silica and polymer PLC

    NASA Astrophysics Data System (ADS)

    Izuhara, T.; Fujita, J.; Gerhardt, R.; Sui, B.; Lin, W.; Grek, B.

    2013-03-01

    Various methods of hybrid integration of photonic circuits are discussed focusing on merits and challenges. Material platforms discussed in this report are mainly polymer and silica. We categorize the hybridization methods using silica and polymer waveguides into two types, chip-to-chip and on-chip integration. General reviews of these hybridization technologies from the past works are reviewed. An example for each method is discussed in details. We also discuss current status of our silica PLC hybrid integration technology.

  1. Apoprotein Structure and Metal Binding Characterization of a de Novo Designed Peptide, α3DIV, that Sequesters Toxic Heavy Metals.

    PubMed

    Plegaria, Jefferson S; Dzul, Stephen P; Zuiderweg, Erik R P; Stemmler, Timothy L; Pecoraro, Vincent L

    2015-05-12

    De novo protein design is a biologically relevant approach that provides a novel process in elucidating protein folding and modeling the metal centers of metalloproteins in a completely unrelated or simplified fold. An integral step in de novo protein design is the establishment of a well-folded scaffold with one conformation, which is a fundamental characteristic of many native proteins. Here, we report the NMR solution structure of apo α3DIV at pH 7.0, a de novo designed three-helix bundle peptide containing a triscysteine motif (Cys18, Cys28, and Cys67) that binds toxic heavy metals. The structure comprises 1067 NOE restraints derived from multinuclear multidimensional NOESY, as well as 138 dihedral angles (ψ, φ, and χ1). The backbone and heavy atoms of the 20 lowest energy structures have a root mean square deviation from the mean structure of 0.79 (0.16) Å and 1.31 (0.15) Å, respectively. When compared to the parent structure α3D, the substitution of Leu residues to Cys enhanced the α-helical content of α3DIV while maintaining the same overall topology and fold. In addition, solution studies on the metalated species illustrated metal-induced stability. An increase in the melting temperatures was observed for Hg(II), Pb(II), or Cd(II) bound α3DIV by 18-24 °C compared to its apo counterpart. Further, the extended X-ray absorption fine structure analysis on Hg(II)-α3DIV produced an average Hg(II)-S bond length at 2.36 Å, indicating a trigonal T-shaped coordination environment. Overall, the structure of apo α3DIV reveals an asymmetric distorted triscysteine metal binding site, which offers a model for native metalloregulatory proteins with thiol-rich ligands that function in regulating toxic heavy metals, such as ArsR, CadC, MerR, and PbrR.

  2. Molecular imprinting of bulk, microporous silica

    NASA Astrophysics Data System (ADS)

    Katz, Alexander; Davis, Mark E.

    2000-01-01

    Molecular imprinting aims to create solid materials containing chemical functionalities that are spatially organized by covalent or non-covalent interactions with imprint (or template) molecules during the synthesis process. Subsequent removal of the imprint molecules leaves behind designed sites for the recognition of small molecules, making the material ideally suited for applications such as separations, chemical sensing and catalysis. Until now, the molecular imprinting of bulk polymers and polymer and silica surfaces has been reported, but the extension of these methods to a wider range of materials remains problematic. For example, the formation of substrate-specific cavities within bulk silica, while conceptually straightforward, has been difficult to accomplish experimentally. Here we describe the imprinting of bulk amorphous silicas with single aromatic rings carrying up to three 3-aminopropyltriethoxysilane side groups; this generates and occupies microporosity and attaches functional organic groups to the pore walls in a controlled fashion. The triethoxysilane part of the molecules' side groups is incorporated into the silica framework during sol-gel synthesis, and subsequent removal of the aromatic core creates a cavity with spatially organized aminopropyl groups covalently anchored to the pore walls. We find that the imprinted silicas act as shape-selective base catalysts. Our strategy can be extended to imprint other functional groups, which should give access to a wide range of functionalized materials.

  3. Silica, Silicosis, and Autoimmunity

    PubMed Central

    Pollard, Kenneth Michael

    2016-01-01

    Inhalation of dust containing crystalline silica is associated with a number of acute and chronic diseases including systemic autoimmune diseases. Evidence for the link with autoimmune disease comes from epidemiological studies linking occupational exposure to crystalline silica dust with the systemic autoimmune diseases systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Although little is known regarding the mechanism by which silica exposure leads to systemic autoimmune disease, there is a voluminous literature on silica exposure and silicosis that may help identify immune processes that precede development of autoimmunity. The pathophysiology of silicosis consists of deposition of silica particles in the alveoli of the lung. Ingestion of these particles by macrophages initiates an inflammatory response, which stimulates fibroblasts to proliferate and produce collagen. Silica particles are encased by collagen leading to fibrosis and the nodular lesions characteristic of the disease. The steps in the development of silicosis, including acute and chronic inflammation and fibrosis, have different molecular and cellular requirements, suggesting that silica-induced inflammation and fibrosis may be mechanistically separate. Significantly, it is unclear whether silica-induced inflammation and fibrosis contribute similarly to the development of autoimmunity. Nonetheless, the findings from human and animal model studies are consistent with an autoimmune pathogenesis that begins with activation of the innate immune system leading to proinflammatory cytokine production, pulmonary inflammation leading to activation of adaptive immunity, breaking of tolerance, and autoantibodies and tissue damage. The variable frequency of these immunological features following silica exposure suggests substantial genetic involvement and gene/environment interaction in silica-induced autoimmunity. However, numerous questions remain unanswered. PMID:27014276

  4. Fused silica reflecting heat shields for outer planet entry probes

    NASA Technical Reports Server (NTRS)

    Congdon, W. M.; Peterson, D. L.

    1975-01-01

    The development of slip-cast fused silica is discussed as a heat shield designed to meet the needs of outer-planet entry probes. The distinguishing feature of silica is its ability to reflect the radiation imposed by planetary-entry environments. This reflectivity is particularly sensitive to degradation by the presence of trace amounts of contaminants introduced by the starting materials or by processing. The microstructure of a silica configuration also significantly influences the reflectivity and other thermomechanical properties. The processing techniques attendant on controlling microstructure while maintaining purity are discussed. The selection of a starting material of essential purity precludes the use of purified natural quartz and requires the use of synthetic fused silica. The silica is characterized in a limited combined heating test environment. The surface mass loss is controlled by liquid runoff from a relatively low-temperature melt layer; the reflectance is basically maintained and the material achieves a surprisingly high heat of ablation.

  5. Surfactant doped silica aerogels dried at supercritical pressure

    NASA Astrophysics Data System (ADS)

    Parale, V. G.; Mahadik, D. B.; Kavale, M. S.; Rao, A. Venkateswara; Vhatkar, R. S.; Wagh, P. B.; Gupta, Satish C.

    2013-02-01

    By combining the molecular silica precursor methyltrimethoxysilane (MTMS) with methanol, water and Tween-80 solution, we get surfactant-doped silica alcogels. The wet alcogels can be exchanged with methanol and then supercritically extracted with nitrogen to produce surfactant-doped silica aerogels (SDSAs). SDSAs represent a new class of aerogels that are composed of aggregated submicron porous particles that have tunable interparticle nanoporosity. As we increased the percentage of surfactant, the physical properties of silica aerogels changes. In this study we characterized the SDSAs by SEM for morphological study, FTIR for the material composition, contact angle for hydrophobicity determination and thermal conductivity measurements are carried out for thermal insulation application.

  6. The metal-binding properties of the blue crab copper specific CuMT-2: a crustacean metallothionein with two cysteine triplets.

    PubMed

    Serra-Batiste, Montserrat; Cols, Neus; Alcaraz, Luis A; Donaire, Antonio; González-Duarte, Pilar; Vasák, Milan

    2010-06-01

    Most crustacean metallothioneins (MTs) contain 18 Cys residues and bind six divalent metal ions. The copper-specific CuMT-2 (MTC) of the blue crab Callinectes sapidus with 21 Cys residues, of which six are organized in two uncommon Cys-Cys-Cys sequences, represents an exception. However, its metal-binding properties are unknown. By spectroscopic and spectrometric techniques we show that all 21 Cys residues of recombinant MTC participate in the binding of Cu(I), Zn(II), and Cd(II) ions, indicating that both Cys triplets act as ligands. The fully metallated M(8) (II)-MTC (M is Zn, Cd) form possesses high- and low-affinity metal binding sites, as evidenced by the formation of Zn(6)-MTC and Cd(7)-MTC species from M(8) (II)-MTC after treatment with Chelex 100. The NMR characterization of Cd(7)-MTC suggests the presence of a two-domain structure, each domain containing one Cys triplet and encompassing either the three-metal or the four-metal thiolate cluster. Whereas the metal-Cys connectivities in the three-metal cluster located in the N-terminal domain (residues 1-31) reveal a Cd(3)Cys(9) cyclohexane-like structure, the presence of dynamic processes in the C-terminal domain (residues 32-64) precluded the determination of the organization of the four-metal cluster. Absorption and circular dichroism features accompanying the stepwise binding of Cu(I) to MTC suggest that all 21 Cys are involved in the binding of eight to nine Cu(I) ions (Cu(8-9)-MTC). The subsequent generation of Cu(12)-MTC involves structural changes consistent with a decrease in the Cu(I) coordination number. Overall, the metal-binding properties of MTC reported here contribute to a better understanding of the role of Cys triplets in MTs.

  7. Bifunctional mesoporous silicas with clearly distinguished localization of grafted groups

    NASA Astrophysics Data System (ADS)

    Roik, N. V.; Belyakova, L. A.

    2013-12-01

    Bifunctional mesoporous silicas with clearly distinguished localization of grafted groups on the surface of particles and inside their pores were obtained by means of sol-gel synthesis with postsynthetic vapor-phase treatment in vacuum. It was found that the synthesized materials have the hexagonally ordered porous structure typical of MCM-41 type silica.

  8. Community Geothermal Technology Program: Silica bronze project. Final report

    SciTech Connect

    Bianchini, H.

    1989-10-01

    Objective was to incorporate waste silica from the HGP-A geothermal well in Pohoiki with other refractory materials for investment casting of bronze sculpture. The best composition for casting is about 50% silica, 25% red cinders, and 25% brick dust; remaining ingredient is a binder, such as plaster and water.

  9. Water-Silica Force Field for Simulating Nanodevices

    PubMed Central

    Cruz-Chu, Eduardo R.; Aksimentiev, Aleksei; Schulten, Klaus

    2008-01-01

    Amorphous silica is an inorganic material that is central for many nanotechnology appplications, such as nanoelectronics, microfluidics, and nanopore technology. In order to use molecular dynamics (MD) simulations to study the behavior of biomolecules with silica, we developed a force field for amorphous silica surfaces based on their macroscopic wetting properties that is compatible with the CHARMM force field and TIP3P water model. The contact angle of a water droplet with silica served as a criterion to tune the intermolecular interactions. The resulting force field was used to study the permeation of water through silica nanopores, illustrating the influence of the surface topography and the intermolecular parameters on permeation kinetics. We find that minute modeling of the amorphous surface is critical for MD studies, since the particular arrangement of surface atoms controls sensitively electrostatic interactions between silica and water. PMID:17064100

  10. Pillaring effects in macroporous carrageenan-silica composite microspheres.

    PubMed

    Boissière, M; Tourrette, A; Devoisselle, J M; Di Renzo, F; Quignard, F

    2006-02-01

    The impregnation of a carrageenan gel by a silica sol is an efficient method to form a composite material which can be conveniently activated by CO2 supercritical drying. The textural properties of the solids have been characterized by nitrogen adsorption-desorption at 77 K and their composition by thermogravimetric analysis and EDX microprobe. Morphology was examined by SEM. The silica-carrageenan composites present an open macroporous structure. Silica particles retained inside the gel behaved as pillars between the polysaccharide fibrils and form a stick-and-ball network. The stiffening of the carrageenan gel by silica prevented its shrinkage upon drying. The nature of the alkali cations affected the retention of silica particles inside the gel. In the absence of silica, carrageenan fibrils rearrange under supercritical drying and form an aerogel with cavities in the mesopore range.

  11. Interactive effects of waterborne metals in binary mixtures on short-term gill-metal binding and ion uptake in rainbow trout (Oncorhynchus mykiss).

    PubMed

    Niyogi, Som; Nadella, Sunita R; Wood, Chris M

    2015-08-01

    Metal binding to fish gills forms the basis of the biotic ligand model (BLM) approach, which has emerged as a useful tool for conducting site-specific water quality assessments for metals. The current BLMs are designed to assess the toxicity of individual metals, and cannot account for the interactive effects of metal mixtures to aquatic organisms including fish. The present study was designed mainly to examine the interactive effects of waterborne metals (Cd, Zn, Cu, Ag, and Ni) in specific binary combinations on short-term (3h) gill-metal binding and essential ion (Ca(2+) and Na(+)) uptake (a physiological index of toxicity) in fish, using juvenile freshwater rainbow trout (Oncorhynchus mykiss) as the model species. We hypothesized that binary mixtures of metals that share a common mode of uptake and toxicity (e.g., Cd and Zn - Ca(2+) antagonists, Cu and Ag - Na(+) antagonists) would reduce the gill binding of each other via competitive interactions and induce less than additive effects on ion transport. In addition, the mixture of metals that have different modes of uptake and toxicity (e.g., Cd and Cu, or Cd and Ni) would not exhibit any interactive effects either on gill-metal binding or ion transport. We found that both Zn and Cu reduced gill-Cd binding and vice versa, however, Ni did not influence gill-Cd binding in fish. Surprisingly, Ag was found to stimulate gill-Cu binding especially at high exposure concentrations, whereas, Cu had no effect on gill-Ag binding. The inhibitory effect of Cd and Zn in mixture on branchial Ca(2+) uptake was significantly greater than that of Cd or Zn alone. Similarly, the inhibitory effect of Cu and Ag in mixture on branchial Na(+) uptake was significantly greater than that of Cu or Ag alone. The inhibitory effects of Cd and Zn mixture on Ca(2+) uptake as well as Cu and Ag mixture on Na(+) uptake were found to follow the principles of simple additivity. In contrast, no significant additive effect on either Ca(2+) or Na

  12. Application of silica nanoparticles for increased silica availability in maize

    NASA Astrophysics Data System (ADS)

    Suriyaprabha, R.; Karunakaran, G.; Yuvakkumar, R.; Prabu, P.; Rajendran, V.; Kannan, N.

    2013-02-01

    Silica nanoparticles were extracted from rice husk and characterised comprehensively. The synthesised silica powders were amorphous in size with 99.7% purity (20-40 nm). Nanosilica was amended with red soil at 15 kg ha-1 along with micron silica. The influence of nanoscale on silica uptake, accumulation and nutritional variations in maize roots were evaluated through the studies such as root sectioning, elemental analysis and physiological parameters (root length and silica content) and compared with micron silica and control. Nanosilica treated soil reveals enhanced silica uptake and elongated roots which make the plant to resist in stress conditions like drought.

  13. Silica biomineralization via the self-assembly of helical biomolecules.

    PubMed

    Liu, Ben; Cao, Yuanyuan; Huang, Zhehao; Duan, Yingying; Che, Shunai

    2015-01-21

    The biomimetic synthesis of relevant silica materials using biological macromolecules as templates via silica biomineralization processes attract rapidly rising attention toward natural and artificial materials. Biomimetic synthesis studies are useful for improving the understanding of the formation mechanism of the hierarchical structures found in living organisms (such as diatoms and sponges) and for promoting significant developments in the biotechnology, nanotechnology and materials chemistry fields. Chirality is a ubiquitous phenomenon in nature and is an inherent feature of biomolecular components in organisms. Helical biomolecules, one of the most important types of chiral macromolecules, can self-assemble into multiple liquid-crystal structures and be used as biotemplates for silica biomineralization, which renders them particularly useful for fabricating complex silica materials under ambient conditions. Over the past two decades, many new silica materials with hierarchical structures and complex morphologies have been created using helical biomolecules. In this review, the developments in this field are described and the recent progress in silica biomineralization templating using several classes of helical biomolecules, including DNA, polypeptides, cellulose and rod-like viruses is summarized. Particular focus is placed on the formation mechanism of biomolecule-silica materials (BSMs) with hierarchical structures. Finally, current research challenges and future developments are discussed in the conclusion.

  14. Metal-binding thermodynamics of the histidine-rich sequence from the metal-transport protein IRT1 of Arabidopsis thaliana.

    PubMed

    Grossoehme, Nicholas E; Akilesh, Shreeram; Guerinot, Mary Lou; Wilcox, Dean E

    2006-10-16

    The widespread ZIP family of transmembrane metal-transporting proteins is characterized by a large intracellular loop that contains a histidine-rich sequence whose biological role is unknown. To provide a chemical basis for this role, we prepared and studied a peptide corresponding to this sequence from the first iron-regulated transporter (IRT1) of Arabidopsis thaliana, which transports Fe2+ as well as Mn2+, Co2+, Zn2+, and Cd2+. Isothermal titration calorimetry (ITC) measurements, which required novel experiments and data analysis, and supporting spectroscopic methods were used to quantify IRT1's metal-binding affinity and associated thermodynamics. The peptide, PHGHGHGHGP, binds metal ions with 1:1 stoichiometry and stabilities that are consistent with the Irving-Williams series. Comparison of the metal-binding thermodynamics of the peptide with those of trien provides new insight about enthalpic and entropic contributions to the stability of the metal-peptide complex. Although Fe2+ and other IRT1-transported metal ions do not bind very tightly, this His-rich sequence has a very high entropy-driven affinity for Fe3+, which may have biological significance.

  15. Structure of Human J-type Co-chaperone HscB Reveals a Tetracysteine Metal-binding Domain*S⃞

    PubMed Central

    Bitto, Eduard; Bingman, Craig A.; Bittova, Lenka; Kondrashov, Dmitry A.; Bannen, Ryan M.; Fox, Brian G.; Markley, John L.; Phillips, George N.

    2008-01-01

    Iron-sulfur proteins play indispensable roles in a broad range of biochemical processes. The biogenesis of iron-sulfur proteins is a complex process that has become a subject of extensive research. The final step of iron-sulfur protein assembly involves transfer of an iron-sulfur cluster from a cluster-donor to a cluster-acceptor protein. This process is facilitated by a specialized chaperone system, which consists of a molecular chaperone from the Hsc70 family and a co-chaperone of the J-domain family. The 3.0Å crystal structure of a human mitochondrial J-type co-chaperone HscB revealed an L-shaped protein that resembles Escherichia coli HscB. The important difference between the two homologs is the presence of an auxiliary metal-binding domain at the N terminus of human HscB that coordinates a metal via the tetracysteine consensus motif CWXCX9–13FCXXCXXXQ. The domain is found in HscB homologs from animals and plants as well as in magnetotactic bacteria. The metal-binding site of the domain is structurally similar to that of rubredoxin and several zinc finger proteins containing rubredoxin-like knuckles. The normal mode analysis of HscB revealed that this L-shaped protein preferentially undergoes a scissors-like motion that correlates well with the conformational changes of human HscB observed in the crystals. PMID:18713742

  16. Crystal structure of plant ferritin reveals a novel metal binding site that functions as a transit site for metal transfer in ferritin.

    PubMed

    Masuda, Taro; Goto, Fumiyuki; Yoshihara, Toshihiro; Mikami, Bunzo

    2010-02-05

    Ferritins are important iron storage and detoxification proteins that are widely distributed in living kingdoms. Because plant ferritin possesses both a ferroxidase site and a ferrihydrite nucleation site, it is a suitable model for studying the mechanism of iron storage in ferritin. This article presents for the first time the crystal structure of a plant ferritin from soybean at 1.8-A resolution. The soybean ferritin 4 (SFER4) had a high structural similarity to vertebrate ferritin, except for the N-terminal extension region, the C-terminal short helix E, and the end of the BC-loop. Similar to the crystal structures of other ferritins, metal binding sites were observed in the iron entry channel, ferroxidase center, and nucleation site of SFER4. In addition to these conventional sites, a novel metal binding site was discovered intermediate between the iron entry channel and the ferroxidase site. This site was coordinated by the acidic side chain of Glu(173) and carbonyl oxygen of Thr(168), which correspond, respectively, to Glu(140) and Thr(135) of human H chain ferritin according to their sequences. A comparison of the ferroxidase activities of the native and the E173A mutant of SFER4 clearly showed a delay in the iron oxidation rate of the mutant. This indicated that the glutamate residue functions as a transit site of iron from the 3-fold entry channel to the ferroxidase site, which may be universal among ferritins.

  17. Rare Earth Doped Silica Nanoparticles via Thermolysis of a Single Source Metallasilsesquioxane Precursor

    PubMed Central

    Davies, Gemma-Louise; O’Brien, John; Gun’ko, Yurii K.

    2017-01-01

    Rare earth metal doped silica nanoparticles have significant advantages over traditional organic dyes and quantum dots. Silsesquioxanes are promising precursors in the production of silica nanoparticles by thermolysis, due to their structural similarities with silica materials. This manuscript describes the production of a new Eu3+-based metallasilsesquioxane species and its use as a single source precursor in the thermolytic production of luminescent rare earth metal doped silica nanoparticles with characteristic emission in the visible region of the spectrum. PMID:28378754

  18. Cellulose-silica aerogels.

    PubMed

    Demilecamps, Arnaud; Beauger, Christian; Hildenbrand, Claudia; Rigacci, Arnaud; Budtova, Tatiana

    2015-05-20

    Aerogels based on interpenetrated cellulose-silica networks were prepared and characterised. Wet coagulated cellulose was impregnated with silica phase, polyethoxydisiloxane, using two methods: (i) molecular diffusion and (ii) forced flow induced by pressure difference. The latter allowed an enormous decrease in the impregnation times, by almost three orders of magnitude, for a sample with the same geometry. In both cases, nanostructured silica gel was in situ formed inside cellulose matrix. Nitrogen adsorption analysis revealed an almost threefold increase in pores specific surface area, from cellulose aerogel alone to organic-inorganic composite. Morphology, thermal conductivity and mechanical properties under uniaxial compression were investigated. Thermal conductivity of composite aerogels was lower than that of cellulose aerogel due to the formation of superinsulating mesoporous silica inside cellulose pores. Furthermore, composite aerogels were stiffer than each of reference aerogels.

  19. Crystalline Silica Primer

    USGS Publications Warehouse

    ,

    1992-01-01

    substance and will present a nontechnical overview of the techniques used to measure crystalline silica. Because this primer is meant to be a starting point for anyone interested in learning more about crystalline silica, a list of selected readings and other resources is included. The detailed glossary, which defines many terms that are beyond the scope of this publication, is designed to help the reader move from this presentation to a more technical one, the inevitable next step.

  20. Molecular sieving silica membrane fabrication process

    DOEpatents

    Raman, Narayan K.; Brinker, Charles Jeffrey

    1998-01-01

    A process for producing a molecular sieve silica membrane comprising depositing a hybrid organic-inorganic polymer comprising at least one organic constituent and at least one inorganic constituent on a porous substrate material and removing at least a portion of the at least one organic constituent of the hybrid organic-inorganic polymer, forming a porous film.

  1. Molecular sieving silica membrane fabrication process

    DOEpatents

    Raman, N.K.; Brinker, C.J.

    1999-08-10

    A process is described for producing a molecular sieve silica membrane comprising depositing a hybrid organic-inorganic polymer comprising at least one organic constituent and at least one inorganic constituent on a porous substrate material and removing at least a portion of the at least one organic constituent of the hybrid organic-inorganic polymer, forming a porous film. 11 figs.

  2. Mesoporous silica coated silica-titania spherical particles: from impregnation to core-shell formation.

    PubMed

    Shiba, Kota; Takei, Toshiaki; Ogawa, Makoto

    2016-11-22

    The coating of solid surfaces with inorganic materials is a promising approach not only to impart various functionalities but also to modify physicochemical properties that are affected by the geometry/structure of the coating. In this study, a silica-hexadecyltrimethylammonium (silica-CTA) hybrid layer was deposited on monodispersed spherical particles composed of titania and octadecylamine (titania-ODA) by a sol-gel reaction of tetraethoxysilane in aqueous CTA/ammonia/methanol solution. The formation of the coating was confirmed by SEM and TEM observations. The coating thickness varied from a few nm to 100 nm depending on the Si/Ti ratio. We found that Si/Ti = 0.68 resulted in the formation of microporous silica-titania particles with the pore size of 0.7 nm as revealed by nitrogen adsorption/desorption measurements. Because the titania-ODA particles can be converted to mesoporous titania particles after removing ODA by acid/base treatment, the silica species can be impregnated into the titania particles and replace ODA under basic conditions. By increasing the Si/Ti molar ratio up to 1.4, silica-titania particles with non-porous structures were obtained. An amorphous to anatase transition occurred at around 800 °C, indicating the complete impregnation of silica inside the titania particles. Further increases of the Si/Ti molar ratio (to 3.4 and 6.8) led to the formation of the silica-CTA shell on the core particles, and the shell was converted to mesoporous silica layers with a pore size of 2 nm after calcination at 550 °C for 5 h. Non-linear control of the pore size/structure is presented for the first time; this will be useful for the precise design of diverse hybrid materials for optical, catalytic and biomedical applications.

  3. Structural changes in precipitated silica induced by external forces

    NASA Astrophysics Data System (ADS)

    Schneider, Gerald Johannes; Göritz, Dietmar

    2010-04-01

    The morphology of pure precipitated silica, silica filled in polydimethylsiloxane rubber, and silica filled in styrene butadiene rubber was studied by means of small-angle X-ray scattering experiments. The silica at a length scale of a few nanometers consists of primary particles, which form aggregates, and clusters with aggregates as basic units. It is evidenced that the aggregate branching, represented by the mass fractal dimension, and the aggregate diameter are different if pure silica and silica in rubber are compared. Contrary, the size of the primary particles and their surface are not influenced. It is demonstrated that the change in the aggregate morphology is due to the external mechanical forces appearing during the mixing process. This is achieved by model experiments using a pistil and a mortar and a composite with different silica fractions. By that means, a systematic change in the morphology with grinding time is observed. Then, the experiments on the composite demonstrate that the major contributions to the mass fractal dimensions are due to the external mechanical forces. In order to test reproducibility and universal validity in the case of precipitated silicas, independent experiments on one silica and further silicas are performed. Several important conclusions are obtained from the study. First, it is shown that a comparison of different pure silica samples without knowing their history may be difficult or questionable. Second, it becomes evident that it is not sufficient to provide only a description of the materials, rather than the details of the sample treatment have to be reported. Therefore, solely the characterization of the morphology of the pure silica is not sufficient to be compared to the mechanical properties of the composites.

  4. Silica, silicosis and cancer in Finland.

    PubMed

    Partanen, T; Jaakkola, J; Tossavainen, A

    1995-01-01

    Approximately 100 000 Finnish workers are currently employed in jobs and tasks that may involve exposure to airborne silica dust. The major industries involved are mining and quarrying; production of glass, ceramics, bricks and other building materials; metal industry, particularly iron and steel founding; and construction. Over 1500 cases of silicosis have occurred in Finland since 1935. Tuberculosis has been a frequent complication of silicosis. Results of studies from several countries strongly suggest that silica dust also causes lung cancer. The results of the relevant Finnish epidemiologic and industrial hygiene studies addressing cancer risk and exposure to quartz dust are summarized.

  5. High resolution patterning of silica aerogels

    SciTech Connect

    Bertino, M.F.; Hund, J.F.; Sosa, J.; Zhang, G.; Sotiriou-Leventis, C.; Leventis, N.; Tokuhiro, A.T.; Terry, J.

    2008-10-30

    Three-dimensional metallic structures are fabricated with high spatial resolution in silica aerogels. In our method, silica hydrogels are prepared with a standard base-catalyzed route, and exchanged with an aqueous solution typically containing Ag{sup +} ions (1 M) and 2-propanol (0.2 M). The metal ions are reduced photolytically with a table-top ultraviolet lamp, or radiolytically, with a focused X-ray beam. We fabricated dots and lines as small as 30 x 70 {micro}m, protruding for several mm into the bulk of the materials. The hydrogels are eventually supercritically dried to yield aerogels, without any measurable change in the shape and spatial resolution of the lithographed structures. Transmission electron microscopy shows that illuminated regions are composed by Ag clusters with a size of several {micro}m, separated by thin layers of silica.

  6. Protein Localization in Silica Nanospheres Derived via Biomimetic Mineralization (POSTPRINT)

    DTIC Science & Technology

    2010-01-01

    can be used for characterizing a wide range of mesoporous and ultrastructural materials. neutron scattering, silica, lysozyme, biomineralization U U...used for characterizing a wide range of mesoporous and ultrastructural materials. FU LL P A P ER © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv...The nitrogen adsorption isotherms of the silica-lysozyme composites show typical type IV characteristics, with hysteresis indicative of a

  7. Carbon nanomaterials in silica aerogel matrices

    SciTech Connect

    Hamilton, Christopher E; Chavez, Manuel E; Duque, Juan G; Gupta, Gautam; Doorn, Stephen K; Dattelbaum, Andrew M; Obrey, Kimberly A D

    2010-01-01

    Silica aerogels are ultra low-density, high surface area materials that are extremely good thermal insulators and have numerous technical applications. However, their mechanical properties are not ideal, as they are brittle and prone to shattering. Conversely, single-walled carbon nanotubes (SWCNTs) and graphene-based materials, such as graphene oxide, have extremely high tensile strength and possess novel electronic properties. By introducing SWCNTs or graphene-based materials into aerogel matrices, it is possible to produce composites with the desirable properties of both constituents. We have successfully dispersed SWCNTs and graphene-based materials into silica gels. Subsequent supercritical drying results in monolithic low-density composites having improved mechanical properties. These nanocomposite aerogels have great potential for use in a wide range of applications.

  8. Silica containing highly porous alumina ceramic

    NASA Astrophysics Data System (ADS)

    Svinka, R.; Svinka, V.; Zake, I.

    2011-04-01

    Porous alumina ceramic were produced by slip casting of aqueous alumina slurry with added small amount of metallic aluminium powder. Pores form in result of chemical reaction of aluminum with water by hydrogen gas evolution reaction and solidification of suspension. Porosity of such materials sintered at a temperature of 1600 - 1750°C varies from 60 to 90%. Pore size distribution and mechanical strength of these materials depend largely on the grain size of used raw materials. The major part of pores in the materials produced without additive of silica are larger than 10 ±m, but with 5 - 10 wt.% additive of silica in the raw mix pore size decreases considerably. The sintering shrinkage decreases to 2.5%. Coefficient of thermal expansion equally decreases from 8.9-10-6 K-1 to 7.1 10-6 K-1 and classification temperature increases to 1600°C, while deformation at high temperature decreases considerably.

  9. Composite Silica Aerogels Opacified with Titania

    NASA Technical Reports Server (NTRS)

    Paik, Jon-Ah; Sakamoto, Jeffrey; Jones, Steven; Fleurial, Jean-Pierre; DiStefano, Salvador; Nesmith, Bill

    2009-01-01

    A further improvement has been made to reduce the high-temperature thermal conductivities of the aerogel-matrix composite materials described in Improved Silica Aerogel Composite Materials (NPO-44287), NASA Tech Briefs, Vol. 32, No. 9 (September 2008), page 50. Because the contribution of infrared radiation to heat transfer increases sharply with temperature, the effective high-temperature thermal conductivity of a thermal-insulation material can be reduced by opacifying the material to reduce the radiative contribution. Therefore, the essence of the present improvement is to add an opacifying constituent material (specifically, TiO2 powder) to the aerogel-matrix composites.

  10. Developing a Process for Commercial Silica Production from Geothermal Brines

    SciTech Connect

    Bourcier, W; Martin, S; Viani, B; Bruton, C

    2001-04-11

    Useful mineral by-products can be produced from geothermal brines. Although silica has many commercial uses, problems remain in producing a marketable product. We are conducting laboratory and modeling studies aimed at optimizing for rubber additive use, the properties of silica precipitates from Salton Sea and Coso-like geothermal fluids, Our goal is to develop a robust technique for producing silicas that have desirable physical and chemical properties for commercial use, while developing a generic understanding of silica precipitation that will allow extraction to be extended to additional fluid types, and to be easily modified to produce new types of marketable silica. Our experiments start with an acidified geothermal fluid similar to those treated by pH modification technology. Silica precipitation is induced by adding base and/or adding Mg or Ca salts to affect the nature of the precipitate. For the analog Salton Sea fluids, adding base alone caused silica to precipitate fairly rapidly. To date, we have characterized precipitates from experiments in which the final pH varied from 4 to 8, where NaOH and Na{sub 2}C0{sub 3} were added as bases, and CaCl{sub 2} and MgCl{sub 2} were added as salts. SEM photos of the silica precipitates from the Salton Sea and Cos0 fluids show that the silica particles are clusters of smaller silica particles down to the resolution of the SEM (about 80-100 nm in diameter). The particle sizes and surface areas of silicas from the Salton Sea and Coso analog brines are similar to the properties of the Degussa silica commonly used as a rubber additive. An evaluation of the strength of the silica-organic bond as tested by dispersion in oil (polybutadiene) was inconclusive. Neither the Degussa materials nor our laboratory precipitates dispersed readily in nor dispersed down to the fundamental particle size. Preliminary NMR data indicates that the Degussa silica has a smaller degree of silica polymerization (a slightly smaller average

  11. Development of an affinity silica monolith containing human serum albumin for chiral separations.

    PubMed

    Mallik, Rangan; Hage, David S

    2008-04-14

    An affinity monolith based on silica and containing immobilized human serum albumin (HSA) was developed and evaluated in terms of its binding, efficiency and selectivity in chiral separations. The results were compared with data obtained for the same protein when used as a chiral stationary phase with HPLC-grade silica particles or a monolith based on a copolymer of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA). The surface coverage of HSA in the silica monolith was similar to values obtained with silica particles and a GMA/EDMA monolith. However, the higher surface area of the silica monolith gave a material that contained 1.3-2.2-times more immobilized HSA per unit volume when compared to silica particles or a GMA/EDMA monolith. The retention, efficiency and resolving power of the HSA silica monolith were evaluated using two chiral analytes: d/l-tryptophan and R/S-warfarin. The separation of R- and S-ibuprofen was also considered. The HSA silica monolith gave higher retention and higher or comparable resolution and efficiency when compared with HSA columns that contained silica particles or a GMA/EDMA monolith. The silica monolith also gave lower back pressures and separation impedances than these other materials. It was concluded that silica monoliths can be valuable alternatives to silica particles or GMA/EDMA monoliths when used with immobilized HSA as a chiral stationary phase.

  12. Kinetics of silica polymerization

    SciTech Connect

    Weres, O.; Yee, A.; Tsao, L.

    1980-05-01

    The polymerization of silicic acid in geothermal brine-like aqueous solutions to produce amorphous silica in colloidal form has been studied experimentally and theoretically. A large amount of high quality experimental data has been generated over the temperature rang 23 to 100{sup 0}C. Wide ranges of dissolved silica concentration, pH, and sodium chloride concentration were covered. The catalytic effects of fluoride and the reaction inhibiting effects of aluminum and boron were studied also. Two basic processes have been separately studied: the formation of new colloidal particles by the homogeneous nucleation process and the deposition of dissolved silica on pre-existing colloidal particles. A rigorous theory of the formation of colloidal particles of amorphous silica by homogeneous nucleation was developed. This theory employs the Lothe-Pound formalism, and is embodied in the computer code SILNUC which quantitatively models the homogeneous nucleation and growth of colloidal silica particles in more than enough detail for practical application. The theory and code were extensively used in planning the experimental work and analyzing the data produced. The code is now complete and running in its final form. It is capable of reproducing most of the experimental results to within experimental error. It is also capable of extrapolation to experimentally inaccessible conditions, i.e., high temperatures, rapidly varying temperature and pH, etc.

  13. Water-soluble metal-binding polymers with ultrafiltration: A technology for the removal, concentration, and recovery of metal ions from aqueous streams

    SciTech Connect

    Smith, B.F.; Robison, T.W.; Jarvinen, G.D.

    1997-12-31

    The use of water-soluble metal-binding polymers coupled with ultrafiltration (UF) is a technology under development to selectively concentrate and recover valuable or regulated metal-ions from dilute process or waste waters. The polymers have a sufficiently large molecular size that they can be separated and concentrated using commercially available UF technology. The polymers can then be reused by changing the solution conditions to release the metal-ions, which are recovered in a concentrated form for recycle or disposal. Pilot-scale demonstrations have been completed for a variety of waste streams containing low concentrations of metal ions including electroplating wastes (zinc and nickel) and nuclear waste streams (plutonium and americium). Many other potential commercial applications exist including remediation of contaminated solids. An overview of both the pilot-scale demonstrated applications and small scale testing of this technology are presented.

  14. Silica Synthesis by Sponges: Unanticipated Molecular Mechanism

    NASA Astrophysics Data System (ADS)

    Morse, D. E.; Weaver, J. C.

    2001-12-01

    Oceanic diatoms, sponges and other organisms synthesize gigatons per year of silica from silicic acid, ultimately obtained from the weathering of rock. This biogenic silica exhibits a remarkable diversity of structures, many of which reveal a precision of nanoarchitectural control that exceeds the capabilities of human engineering. In contrast to the conditions of anthropogenic and industrial manufacture, the biological synthesis of silica occurs under mild physiological conditions of low temperatures and pressures and near-neutral pH. In addition to the differentiation between biological and abiotic processes governing silica formation, the biomolecular mechanisms controlling synthesis of these materials may offer insights for the development of new, environmentally benign routes for synthesis of nanostructurally controlled silicas and high-performance polysiloxane composites. We found that the needle-like silica spicules made by the marine sponge, Tethya aurantia, each contain an occluded axial filament of protein composed predominantly of repeating assemblies of three similar subunits we named "silicateins." To our surprise, analysis of the purified protein subunits and the cloned silicatein DNAs revealed that the silicateins are highly homologous to a family of hydrolytic enzymes. As predicted from this finding, we discovered that the silicatein filaments are more than simple, passive templates; they actively catalyze and spatially direct polycondensation to form silica, (as well as the phenyl- and methyl-silsesquioxane) from the corresponding silicon alkoxides at neutral pH and low temperature. Catalytic activity also is exhibited by the silicatein subunits obtained by disaggregation of the protein filaments and those produced from recombinant DNA templates cloned in bacteria. This catalytic activity accelerates the rate-limiting hydrolysis of the silicon alkoxide precursors. Genetic engineering, used to produce variants of the silicatein molecule with

  15. The metallomics approach: use of Fe(II) and Cu(II) footprinting to examine metal binding sites on serum albumins.

    PubMed

    Duff, Michael R; Kumar, Challa V

    2009-11-01

    Metal binding to serum albumins is examined by oxidative protein-cleavage chemistry, and relative affinities of multiple metal ions to particular sites on these proteins were identified using a fast and reliable chemical footprinting approach. Fe(ii) and Cu(ii), for example, mediate protein cleavage at their respective binding sites on serum albumins, in the presence of hydrogen peroxide and ascorbate. This metal-mediated protein-cleavge reaction is used to evaluate the binding of metal ions, Na(+), Mg(2+), Ca(2+), Al(3+), Cr(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ce(3+) to albumins, and the relative affinities (selectivities) of the metal ions are rapidly evaluated by examining the extent of inhibition of protein cleavage. Four distinct systems Fe(II)/BSA, Cu(II)/BSA, Fe(II)/HSA and Cu(II)/HSA are examined using the above strategy. This metallomics approach is novel, even though the cleavage of serum albumins by Fe(II)/Cu(II) has been reported previously by this laboratory and many others. The protein cleavage products were analyzed by SDS PAGE, and the intensities of the product bands quantified to evaluate the extent of inhibition of the cleavage and thereby evaluate the relative binding affinities of specific metal ions to particular sites on albumins. The data show that Co(II) and Cr(III) showed the highest degree of inhibition, across the table, followed by Mn(II) and Ce(III). Alakali metal ions and alkaline earth metal ions showed very poor affinity for these metal sites on albumins. Thus, metal binding profiles for particular sites on proteins can be obtained quickly and accurately, using the metallomics approach.

  16. Location of high-affinity metal binding sites in the profile structure of the Ca+2-ATPase in the sarcoplasmic reticulum by resonance x-ray diffraction.

    PubMed Central

    Asturias, F J; Blasie, J K

    1991-01-01

    Resonance x-ray diffraction measurements on the lamellar diffraction from oriented multilayers of isolated sarcoplasmic reticulum (SR) membranes containing a small concentration of lanthanide (III) ions (lanthanide/protein molar ratio approximately 4) have allowed us to calculate both the electron density profile of the SR membrane and the separate electron density profile of the resonant lanthanide atoms bound to the membrane to a relatively low spatial resolution of approximately 40 A. Analysis of the membrane electron density profile and modeling of the separate low resolution lanthanide atom profile, using step-function electron density models based on the assumption that metal binding sites in the membrane profile are discrete and localized, resulted in the identification of a minimum of three such binding sites in the membrane profile. Two of these sites are low-affinity, low-occupancy sites identified with the two phospholipid polar headgroup regions of the lipid bilayer within the membrane profile. Up to 20% of the total lanthanide (III) ions bind to these low-affinity sites. The third site has relatively high affinity for lanthanide ion binding; its Ka is roughly an order of magnitude larger than that for the lower affinity polar headgroup sites. Approximately 80% of the total lanthanide ions present in the sample are bound to this high-affinity site, which is located in the "stalk" portion of the "headpiece" within the profile structure of the Ca+2 ATPase protein, approximately 12 A outside of the phospholipid polar headgroups on the extravesicular side of the membrane profile. Based on the nature of our results and on previous reports in the literature concerning the ability of lanthanide (III) ions to function as Ca+2 analogues for the Ca+2 ATPase we suggest that we have located a high-affinity metal binding site in the membrane profile which is involved in the active transport of Ca+2 ions across the SR membrane by the Ca+2 ATPase. PMID:1826221

  17. Characterization of the redox and metal binding activity of BsSco, a protein implicated in the assembly of cytochrome c oxidase.

    PubMed

    Imriskova-Sosova, Iveta; Andrews, Diann; Yam, Katherine; Davidson, David; Yachnin, Brahm; Hill, Bruce C

    2005-12-27

    Members of the Sco protein family are implicated in the assembly of the respiratory complex cytochrome c oxidase. Several possible roles have been proposed for Sco: a copper delivery agent, a site-specific thiol reductase, and an indicator of cellular redox status. Two cysteine residues (C45 and C49) in the sequence CXXXCP and a histidine (H135) approximately 90 residues toward the C-terminus are conserved in Sco from bacteria, yeast, and humans. The soluble domain of Sco has a thioredoxin fold that is suggestive of redox activity for this protein. We have characterized the soluble domain of the Sco protein from Bacillus subtilis (i.e., sBsSco) for its redox reactivity and metal binding capacity. In oxidized sBsSco, the cysteines are present as an intramolecular disulfide. Oxidized sBsSco does not bind metal, but can be reduced in vitro to a metal-binding form. Reduction of the disulfide in sBsSco is accompanied by increased intrinsic fluorescence. The reducibility of the cystine is unchanged when the conserved histidine is mutated to alanine. Tight binding by reduced sBsSco is observed for Cu(II) by electronic absorption, intrinsic fluorescence, and EPR spectroscopies, and isothermal titration calorimetry with an observed stoichiometry of one Cu(II) ion per sBsSco and a KD of approximately 50 nM. Tight binding of Cu(I) and Ag(I) is observed by quenching of intrinsic tryptophan fluorescence. Cobalt(II) exhibits weak binding, whereas Ni(II) and Zn(II) do not appear to bind. The high-affinity binding of metals by BsSco is triggered by its redox state, and this property could be important for its function in vivo.

  18. [Effect of mutations and modifications of amino acid residues on zinc-induced interaction of the metal-binding domain of β-amyloid with DNA].

    PubMed

    Khmeleva, S A; Mezentsev, Y V; Kozin, S A; Mitkevich, V A; Medvedev, A E; Ivanov, A S; Bodoev, N V; Makarov, A A; Radko, S P

    2015-01-01

    Interaction of intranuclear β-amyloid with DNA is considered to be a plausible mechanism of Alzheimer's disease pathogenesis. The interaction of single- and double-stranded DNA with synthetic peptides was analyzed using surface plasmon resonance. The peptides represent the metal-binding domain of β-amyloid (amino acids 1-16) and its variants with chemical modifications and point substitutions of amino acid residues which are associated with enhanced neurotoxicity of β-amyloid in cell tests. It has been shown that the presence of zinc ions is necessary for the interaction of the peptides with DNA in solution. H6R substitution has remarkably reduced the ability of domain 1-16 to bind DNA. This is in accordance with the supposition that the coordination of a zinc ion by amino acid residues His6, Glu11, His13, and His14 of the β-amyloid metal-binding domain results in the occurrence of an anion-binding site responsible for the interaction of the domain with DNA. Zinc-induced dimerization and oligomerization of domain 1-16 associated with phosphorylation of Ser8 and the presence of unblocked amino- and carboxy-terminal groups have resulted in a decrease of peptide concentrations required for detection of the peptide-DNA interaction. The presence of multiple anion-binding sites on the dimers and oligomers is responsible for the enhancement of the peptide-DNA interaction. A substitution of the negatively charged residue Asp7 for the neutral residue Asn in close proximity to the anion-binding site of the domain 1-16 of Aβ facilitates the electrostatic interaction between this site and phosphates of a polynucleotide chain, which enhances zinc-induced binding to DNA.

  19. Silica Precipitation and Lithium Sorption

    SciTech Connect

    Jay Renew

    2015-09-20

    This file contains silica precipitation and lithium sorption data from the project. The silica removal data is corrected from the previous submission. The previous submission did not take into account the limit of detection of the ICP-MS procedure.

  20. Abnormal behavior of silica doped with small amounts of aluminum

    PubMed Central

    Liu, Jinling; Wang, Yiguang; An, Linan

    2016-01-01

    Silica is the most abundant mineral in the crust of the Earth. It has been demonstrated that the aluminum concentration in silica plays a key role in determining many properties of silica-based components. Although the alumina-silica system has been intensely studied, the effect of very small amounts of aluminum on the structure and properties of silica remains unclear. We report results of first principles calculations showing that small amounts of aluminum could be metastable when located in the center of Si-O rings without breaking the silica network. In contrast, higher aluminum contents will result in the destruction of the Si-O bonds, leading to the formation of triclusters and a 4-, 5-, and 6-fold Al-O coordination, as observed in previous studies. Based on the silica structure obtained through geometric optimization, the properties of silica doped with small amounts of aluminum were calculated. The results can account for many ‘abnormal’ phenomena experimentally observed. The results benefit most areas such as geosciences, microelectronics, glass industry, and ceramic materials. PMID:27752133

  1. Abnormal behavior of silica doped with small amounts of aluminum

    NASA Astrophysics Data System (ADS)

    Liu, Jinling; Wang, Yiguang; An, Linan

    2016-10-01

    Silica is the most abundant mineral in the crust of the Earth. It has been demonstrated that the aluminum concentration in silica plays a key role in determining many properties of silica-based components. Although the alumina-silica system has been intensely studied, the effect of very small amounts of aluminum on the structure and properties of silica remains unclear. We report results of first principles calculations showing that small amounts of aluminum could be metastable when located in the center of Si-O rings without breaking the silica network. In contrast, higher aluminum contents will result in the destruction of the Si-O bonds, leading to the formation of triclusters and a 4-, 5-, and 6-fold Al-O coordination, as observed in previous studies. Based on the silica structure obtained through geometric optimization, the properties of silica doped with small amounts of aluminum were calculated. The results can account for many ‘abnormal’ phenomena experimentally observed. The results benefit most areas such as geosciences, microelectronics, glass industry, and ceramic materials.

  2. Fast determination of Ziziphora tenuior L. essential oil by inorganic-organic hybrid material based on ZnO nanoparticles anchored to a composite made from polythiophene and hexagonally ordered silica.

    PubMed

    Piryaei, Marzieh; Abolghasemi, Mir Mahdi; Nazemiyeh, Hossein

    2015-01-01

    In this paper, for the first time, an inorganic-organic hybrid material based on ZnO nanoparticles was anchored to a composite made from polythiophene and hexagonally ordered silica (ZnO/PT/SBA-15) for use in solid-phase fibre microextraction (SPME) of medicinal plants. A homemade SPME apparatus was used for the extraction of volatile components of Ziziphora tenuior L. A simplex method was used for optimisation of five different parameters affecting the efficiency of the extraction. The main constituents extracted by ZnO/PT/SBA-15 and PDMS fibres and hydrodistillation (HD) methods, respectively, included pulegone (51.25%, 53.64% and 56.68%), limonene (6.73%, 6.58% and 8.3%), caryophyllene oxide (5.33%, 4.31% and 4.53%) and 1,8-cineole (4.21%, 3.31% and 3.18%). In comparison with the HD method, the proposed technique could equally monitor almost all the components of the sample, in an easier way, in a shorter time and requiring a much lower amount of the sample.

  3. Fluid diffusion in porous silica

    NASA Astrophysics Data System (ADS)

    McCann, Lowell I.

    Fluid motion in porous media has received a great deal of theoretical and experimental attention due to its importance in systems as diverse as ground water aquifers, catalytic processes, and size separation schemes. Often, the motion of interest is the random thermal motion of molecules in a fluid undergoing no net flow. This diffusive motion is particularly important when the size of the pores is nearly the same as the size of the molecules. In this study, fluid diffusion is measured in several varieties of porous silica whose pore structure is determined by the process by which it is made. The samples in this study have porosities (φ, the ratio of the pore volume to the total sample volume) that vary from 0.3 to 0.75 and average pore radii that range from approximately 15 to 120 A. Determining the effect of the pore structure on the diffusion of a liquid in a porous material is complicated by the chemical interactions between the diffusing molecules and the pore surface. In this study, ions in a hydrophilic fluid are used to block the adsorption of the diffusing dye molecules to the hydroxyl groups covering the silica surface. This technique is unlike typical surface treatments of silica in that it does not permanently alter the pore geometry. In this work, fluid diffusion is measured with a transient holographic grating technique where interfering laser beams create a periodic refractive index modulation in the fluid. The diffraction of a third laser off this grating is monitored to determine how quickly the grating relaxes, thereby determining the diffusion coefficient of the molecules in the fluid. Varying the grating periodicity controls the length scale of the diffusion measurement from 1.2 to 100 μm which is much larger than the average pore sizes of the samples. Therefore, over these large scales, we measure 'normal' diffusion, where the mean squared displacement of a diffusing particle varies linearly with time. In one particular type of porous silica

  4. Epoxy Grout With Silica Thickener

    NASA Technical Reports Server (NTRS)

    Mcclung, C. E.

    1984-01-01

    Grout cures quickly, even in presence of hydraulic oil. Grout is mixture of aggregate particles, finely-divided silica, epoxy resin, and triethylenetetramine curing agent, with mixture containing about 85 percent silica and aggregate particle sand 15 percent resin and curing agent. Silica is thickening agent and keeps grout from sagging.

  5. 78 FR 14540 - Cyromazine, Silica Silicates (Silica Dioxide and Silica Gel), Glufosinate Ammonium, Dioctyl...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-06

    ... AGENCY Cyromazine, Silica Silicates (Silica Dioxide and Silica Gel), Glufosinate Ammonium, Dioctyl Sodium... ammonium, dioctyl sodium sulfosuccinate (DSS) and undecylenic acid (UDA) and opens a public comment period...-HQ-OPP-2006-0108... Kelly Ballard, (703) 305-8126, Ballard.kelly@epa.gov . Dioctyl...

  6. Nanoindentation studies of nickel zinc ferrite embedded mesoporous silica template

    NASA Astrophysics Data System (ADS)

    Banerjee, S.; Hajra, P.; Mada, M. R.; Bandopadhyay, S.; Chakravorty, D.

    2013-02-01

    Nickel zinc ferrite (NZF) embedded mesoporous silica KIT-6 nanocomposite (NZFMS) was synthesized via impregnation method. The microstructure of the samples was characterized by transmission electron microscopy (TEM). Nanoindentation (NI) studies were carried out on both mesoporous silica (MS) and the nanocomposite NZFMS. It was found that the young's modulus (E) and hardness (H) of the NZFMS were higher than that of the MS. From creep measurement it was observed that the creep-strain rate was greater for NZFMS compared to MS. This arose due to diffusion of Fe3+ ions from nickel zinc ferrite to the silica glass. The results indicate that the NZFMS material shows superplastic behaviour at room temperature.

  7. Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatography.

    PubMed

    Galarneau, Anne; Iapichella, Julien; Brunel, Daniel; Fajula, François; Bayram-Hahn, Zöfre; Unger, Klaus; Puy, Guillaume; Demesmay, Claire; Rocca, Jean-Louis

    2006-04-01

    Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (approximately 1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the micrometer scale. We developed a synthesis strategy to control the particle morphology of MTS using the concept of pseudomorphic transformation. Pseudomorphism was recognized in the mineral world to gain a mineral that presents a morphology not related to its crystallographic symmetry group. Pseudomorphic transformations have been applied to amorphous spherical silica particles usually used in chromatography as stationary phases to produce MTS with the same morphology, using alkaline solution to dissolve progressively and locally silica and reprecipitate it around surfactant micelles into ordered MTS structures. Spherical beads of MTS with hexagonal and cubic symmetries have been synthesized and successfully used in HPLC in fast separation processes. MTS with a highly connected structure (cubic symmetry), uniform pores with a diameter larger than 6 nm in the form of particles of 5 microm could compete with monolithic silica columns. Monolithic columns are receiving strong interest and represent a milestone in the area of fast separation. Their synthesis is a sol-gel process based on phase separation between silica and water, which is assisted by the presence of polymers. The control of the synthesis of monolithic silica has been systematically explored. Because of unresolved yet

  8. Tuning of the excitation wavelength in Eu(3+)-aminophenyl based polyfluorinated β-diketonate complexes: a red-emitting Eu(3+)-complex encapsulated in a silica/polymer hybrid material excited by blue light.

    PubMed

    Usha Gangan, T V; Reddy, M L P

    2015-09-28

    We describe herein the synthesis, characterization and photophysical properties of a series of europium complexes based on three aminophenyl based polyfluorinated β-diketonates, namely, 1-(4-aminophenyl)-4,4,5,5,5-pentafluoro-3-hydroxypent-2-en-1-one, 1-(4-(dimethylamino)phenyl)-4,4,5,5,5-pentafluoro-3-hydroxypent-2-en-1-one and 1-(4-(diphenylamino)phenyl)-4,4,5,5,5-pentafluoro-3-hydroxypent-2-en-1-one, and an ancillary ligand, 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide. The results demonstrated that the triphenylamine based polyfluorinated Eu(3+)-β-diketonate complexes dramatically red-shifted the excitation maximum to the visible region (λex, max = 400 nm) with an impressive quantum yield (40%) as compared to the simple Eu(3+)-aminophenyl-β-diketonate complexes (λex, max = 370 nm). This can be explained on the basis of the conjugation between nitrogen lone pair electrons and the phenyl π-electrons in the β-diketonate ligand system. On the other hand, the electron-donating dimethylamino group (Hammett constant: σp = -0.83) containing Eu(3+)-β-diketonate complexes moderately shifted the excitation maximum in the UV region from 370 to 380 nm as compared to unsubstituted aminophenyl (Hammett constant: σp = -0.66) Eu(3+) complexes. The displacement of water molecules in aminophenyl based Eu(3+)-β-diketonate binary complexes by a rigid phosphine oxide ligand richly enhances the photoluminescence quantum yields as well as the excited state lifetime values of the corresponding ternary complexes. As an integral part of this work, hybrid materials have been developed through a sol-gel route by encapsulating a ternary Eu(3+) compound in a silica/polymer hybrid for high performance luminescence applications. In addition, a bright red-emitting diode was fabricated by coating the designed hybrid material onto a 400 nm emitting InGaN chip and the photoluminescence was examined. Notably, the current study clearly shows that the developed triphenylamine

  9. Silica-Fayalite-bearing Chondrules in Ordinary Chondrites: Evidence of Oxidation in the Solar Nebula

    NASA Astrophysics Data System (ADS)

    Krot, A. N.; Wasson, J. T.

    1993-07-01

    above; the principal difference between them is the presence of fayalite-forming veins within or rims around the silica grains. The continuum between these chondrule categories implies that they are genetically related: We infer that the fayalite veins and rims formed by nebular alteration of the silica grains. Fayalite forms veins along the silica grain boundaries in granular silica-fayalite-bearing chondrules. Fragments of granular silica chondrules occur as relict clasts within two pyroxene chondrules in Sharps. These fragments were altered after chondrule solidification. Conclusions: (1) Silica-bearing chondrules have similar textures to common mafic silicate chondrules and were formed by melting silica-rich precursor material that possibly formed by nonequilibrium condensation. (2) The higher abundance of silica-bearing chondrules in H than in L and LL chondrites may indicate a greater degree of silica condensation in the H-formation region. (3) Silica-fayalite-bearing chondrules formed by alteration of silica-bearing chondrules. The common occurrence of both categories within the same chondrite suggests that oxidation and fayalite formation by nebular gas was an inefficient process.

  10. A New Model for the Structure of Silica Glass

    DTIC Science & Technology

    1989-09-20

    of Hosemann [61 suggests that really silica glass consists of a material with the connectivity of one of the SiO2 polymorphs, such as cristobalite but...Figure 1: Six-rings Both cristobalite and tridymite, two high temperature silica polymorphs contain s,1ch rings. They differ only in the stacking sequence...of sheets of tetrahedra, ABC for (cubic) cristobalite and AB for (hexagonal) tridymite. Importantly the linkages between the sheets in these dimorphs

  11. (129)Xe NMR of Mesoporous Silicas

    SciTech Connect

    Anderson, M.T.; Asink, R.A.; Kneller, J.M.; Pietrass, T.

    1999-04-23

    The porosities of three mesoporous silica materials were characterized with {sup 129}Xe NMR spectroscopy. The materials were synthesized by a sol-gel process with r = 0, 25, and 70% methanol by weight in an aqueous cetyltrimethylammonium bromide solution. Temperature dependent chemical shifts and spin lattice relaxation times reveal that xenon does not penetrate the pores of the largely disordered (r= 70%) silica. For both r = 0 and 25%, temperature dependent resonances corresponding to physisorbed xenon were observed. An additional resonance for the r = 25% sample was attributed to xenon between the disordered cylindrical pores. 2D NMR exchange experiments corroborate the spin lattice relaxation data which show that xenon is in rapid exchange between the adsorbed and the gas phase.

  12. Optical properties of polyimide/silica nanocomposite

    NASA Astrophysics Data System (ADS)

    Tommalieh, M. J.; Zihlif, A. M.

    2010-12-01

    The optical properties of thin films of polyimide/silica nanocomposites prepared via sol-gel process were investigated as a function of nanosilica particles content. Absorption and reflectance spectra were collected by a spectrophotometer giving UV-radiation of wavelength range 200-800 nm. The optical data obtained were analyzed in terms of absorption formula for non-crystalline materials. The calculated values of the optical energy gap and the width of the energy tails of the localized states exhibited silica concentration dependence. The direct optical energy gap for neat polyimide is about 1.95 eV, and decreases to a value of 1.8 eV for nanocomposite of 25 wt% nanosilica content. It was found that the calculated refractive index and dielectric constants of nanocomposites increase with silica particles content. The overall dependence of the optical and dielectrical constants on silica content in polyimide matrix is argued on the basis of the observed morphology and overlap of the localized energy sates of different color centers. The EMT model was fitted to the observed dielectric data.

  13. The synthesis and application of two mesoporous silica nanoparticles as drug delivery system with different shape

    NASA Astrophysics Data System (ADS)

    Wang, Jiayi; Wang, Zhuyuan; Chen, Hui; Zong, Shenfei; Cui, Yiping

    2015-05-01

    Mesoporous silica nanospheres(MSNSs) have been obtained utilizing the conventional reverse micelles synthesis method while the mesoporous silica nanorods(MSNRs) have been acquired by means of changing certain parameters. Afterwards, the prepared mesoporous silica nanospheres and nanorods were used as drug carriers to load and release the classical cancer therapeutic drug—DOX. According to the absorption spectra, the encapsulation efficiency of the mesoporous silica nanospheres is almost as high as that of the nanospheres. Different from the familiar encapsulation efficiency, the release characteristic curves of the mesoporous silica nanospheres and nanorods possessed certain differences during the release process. Finally incellular fluorescence imaging was achieved to observe the endocytosis of the mesoporous silica materials. Our results show that although both of the two kinds of nanoparticles possess favourable properties for loading and releasing drugs, the mesoporous silica nanospheres perform better in dispersity and controlled release than the nanorods, which probably endow them the potential as incellular drug delivery system.

  14. Using fluorescence-based microplate assay to assess DOM-metal binding in reactive materials for treatment of acid mine drainage.

    PubMed

    Neculita, Carmen Mihaela; Dudal, Yves; Zagury, Gerald J

    2011-01-01

    One potential drawback of compost-based passive bioreactors, which is a promising biotechnology for acid mine drainage (AMD) treatment, is the transport of dissolved organic matter (DOM)-metal complexes in surface waters. To address this problem, the objective of this study was to assess the maximum capacity of organic substrates to release soluble DOM-metal complexes in treated water. The reactivities of DOM in maple wood chips and sawdust, composted poultry manure, and leaf compost were quantified toward Cd2+, Ni2+, Fe2+, and Cu2+ using fluorescence quenching. The DOM showed the highest reactivity toward Fe, but a limited number of available sites for sorption, whereas DOM-Cd complexes exhibited the lowest fluorescence quenching. Overall, the DOM from a mixture of wastes formed higher concentrations of DOM-metal complexes relative to sole substrates. Among DOM-metal complexes, the concentrations of DOM-Ni complexes were the highest. After reaching steady-state, low concentrations of DOM-metal complexes were released in treated water, which is in agreement with theoretical predictions based on geochemical modeling. Therefore, in addition to physicochemical characterization, fluorescence quenching technique is recommended for the substrate selection of bioreactors.

  15. Presence of nano-sized silica during in vitro digestion of foods containing silica as a food additive.

    PubMed

    Peters, Ruud; Kramer, Evelien; Oomen, Agnes G; Rivera, Zahira E Herrera; Oegema, Gerlof; Tromp, Peter C; Fokkink, Remco; Rietveld, Anton; Marvin, Hans J P; Weigel, Stefan; Peijnenburg, Ad A C M; Bouwmeester, Hans

    2012-03-27

    The presence, dissolution, agglomeration state, and release of materials in the nano-size range from food containing engineered nanoparticles during human digestion is a key question for the safety assessment of these materials. We used an in vitro model to mimic the human digestion. Food products subjected to in vitro digestion included (i) hot water, (ii) coffee with powdered creamer, (iii) instant soup, and (iv) pancake which either contained silica as the food additive E551, or to which a form of synthetic amorphous silica or 32 nm SiO(2) particles were added. The results showed that, in the mouth stage of the digestion, nano-sized silica particles with a size range of 5-50 and 50-500 nm were present in food products containing E551 or added synthetic amorphous silica. However, during the successive gastric digestion stage, this nano-sized silica was no longer present for the food matrices coffee and instant soup, while low amounts were found for pancakes. Additional experiments showed that the absence of nano-sized silica in the gastric stage can be contributed to an effect of low pH combined with high electrolyte concentrations in the gastric digestion stage. Large silica agglomerates are formed under these conditions as determined by DLS and SEM experiments and explained theoretically by the extended DLVO theory. Importantly, in the subsequent intestinal digestion stage, the nano-sized silica particles reappeared again, even in amounts higher than in the saliva (mouth) digestion stage. These findings suggest that, upon consumption of foods containing E551, the gut epithelium is most likely exposed to nano-sized silica.

  16. Nanostructured mesoporous silica matrices in nanomedicine.

    PubMed

    Vallet-Regí, M

    2010-01-01

    In the last few years the biomedical research field has shown a growing interest towards nanostructured mesoporous silica materials, whose chemical composition is silica and present nanometric pores. These bioceramics exhibit two important features: they can regenerate osseous tissues--the bond bioactivity of these materials has been confirmed by the formation of biological-like nanoapatites on their surface when in contact with physiological fluids--and they are able to act as controlled release systems. Drugs in the nanometre scale can be loaded on those matrices and then locally released in a controlled fashion. It is possible to chemically modify the silica walls to favour the adsorption of certain biomolecules such as peptides, proteins or growth factors. It is even possible to design smart biomaterials where the drug is released under an external stimulus. Thus, looking at all those properties, a question arises: Have these bioceramics good expectations to be used in clinical medical practice? Their biocompatibility, bioactivity, capacity to regenerate bone and ability to act as controlled release systems of biologically active species have been confirmed. In fact, their preliminary in vitro and in vivo essays have been positive. Now it is the time to adequate all these properties to the actual clinical problems, and to evaluate their efficiency in comparison with materials already known and currently employed such as bioglasses.

  17. Luminescent Silica Nanoparticles for cancer diagnosis

    PubMed Central

    Montalti, Marco; Petrizza, Luca; Rampazzo, Enrico; Zaccheroni, Nelsi; Marchiò, Serena

    2015-01-01

    Fluorescence imaging techniques are becoming essential in preclinical investigations, and the research of suitable tools for in vivo measurements is gaining more and more importance and attention. Nanotechnology entered the field to try to find solutions for many limitation at the state of the art, and luminescent nanoparticles (NPs) are one of the most promising materials proposed for future diagnostic implementation. NPs constitute also a versatile platform that can allow facile multi-functionalization to perform multimodal imaging or theranostic (simultaneous diagnosis and therapy). In this contribution we have focussed our attention only on dye doped silica or silica-based NPs conjugated with targeting moieties to enable specific cancer cells imaging and differentiation, even if also a few non targeted systems have been cited and discussed for completeness. We have summarized common synthetic approaches to these materials and then surveyed the most recent imaging applications of silica-based nanoparticles in cancer. The field of theranostic is so important and stimulating that, even if it is not the central topic of this paper, we have included some significant examples. We have then concluded with short hints on systems already in clinical trials and examples of specific applications in children tumours. This review tries to describe and discuss, through focussed examples, the great potentialities of these materials in the medical field, with the aim to encourage further research to implement applications that are still rare. PMID:23458621

  18. High quality factor silica microspheres functionalized with self-assembled nanomaterials.

    PubMed

    Kandas, Ishac; Zhang, Baigang; Daengngam, Chalongrat; Ashry, Islam; Jao, Chih-Yu; Peng, Bo; Ozdemir, Sahin K; Robinson, Hans D; Heflin, James R; Yang, Lan; Xu, Yong

    2013-09-09

    With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement.

  19. Modified silica sol coatings for surface enhancement of leather.

    PubMed

    Mahltig, Boris; Vossebein, Lutz; Ehrmann, Andrea; Cheval, Nicolas; Fahmi, Amir

    2012-06-01

    The presented study reports on differently modified silica sols for coating applications on leather. Silica sols are prepared by acidic hydrolysis of tetraethoxysilane and modified by silane compounds with fluorinated and non-fluorinated alkylgroups. In contrast to many earlier investigations regarding sol-gel applications on leather, no acrylic resin is used together with the silica sols when applying on leather. The modified silica particles are supposed to aggregate after application, forming thus a modified silica coating on the leather substrate. Scanning electron microscopy investigation shows that the applied silica coatings do not fill up or close the pores of the leather substrate. However, even if the pores of the leather are not sealed by this sol-gel coating, an improvement of the water repellent and oil repellent properties of the leather substrates are observed. These improved properties of leather by application of modified silica sols can provide the opportunity to develop sol-gel products for leather materials present in daily life.

  20. Functionalization effects of single-walled carbon nanotubes as templates for the synthesis of silica nanorods and study of growing mechanism of silica.

    PubMed

    Lee, Kyoung G; Wi, Rinbok; Imran, Muhammad; Park, Tae Jung; Lee, Jaebeom; Lee, Sang Yup; Kim, Do Hyun

    2010-07-27

    Silica nanorods were successfully prepared through a sol-gel process in the presence of carboxylic-functionalized single-walled carbon nanotubes (C-SWCNTs). The effect of chemical functionalization of single-walled carbon nanotubes (SWCNTs) on the growth of the silica layer was investigated using pristine SWCNTs (P-SWCNTs) and C-SWCNTS. The C-SWCNTs served as a unique template to fabricate silica hybrid composite materials. The crystalline formation and growing mechanism of the silica layer on C-SWCNTs were explained by the hydrolysis and chemical bonding between silica precursors and carboxylated SWCNTs. The C-SWCNTs, as templates, were successfully encapsulated using silica, and used templates were removed by oxidation at high temperature. Finally, silica nanorods/nanowires were synthesized in forms of mold, and this silica fabrication mechanism could be applied for large-scale production of silica nanomaterials and highly flexible nanocomposites. The sequence of a silica encapsulation process of C-SWCNTs and removed C-SWCNTs was characterized using SEM, TEM, EDX, FT-IR and Raman spectroscopy, XRD, and electrical analysis.

  1. Crystal Structures of Apo and Metal-Bound Forms of the UreE Protein from Helicobacter pylori: Role of Multiple Metal Binding Sites

    SciTech Connect

    Shi, Rong; Munger, Christine; Asinas, Abdalin; Benoit, Stephane L.; Miller, Erica; Matte, Allan; Maier, Robert J.; Cygler, Miroslaw

    2010-10-22

    The crystal structure of the urease maturation protein UreE from Helicobacter pylori has been determined in its apo form at 2.1 {angstrom} resolution, bound to Cu{sup 2+} at 2.7 {angstrom} resolution, and bound to Ni{sup 2+} at 3.1 {angstrom} resolution. Apo UreE forms dimers, while the metal-bound enzymes are arranged as tetramers that consist of a dimer of dimers associated around the metal ion through coordination by His102 residues from each subunit of the tetramer. Comparison of independent subunits from different crystal forms indicates changes in the relative arrangement of the N- and C-terminal domains in response to metal binding. The improved ability of engineered versions of UreE containing hexahistidine sequences at either the N-terminal or C-terminal end to provide Ni{sup 2+} for the final metal sink (urease) is eliminated in the H102A version. Therefore, the ability of the improved Ni{sup 2+}-binding versions to deliver more nickel is likely an effect of an increased local concentration of metal ions that can rapidly replenish transferred ions bound to His102.

  2. Bacterial and cell-free production of APP671-726 containing amyloid precursor protein transmembrane and metal-binding domains.

    PubMed

    Bocharova, O V; Urban, A S; Nadezhdin, K D; Bocharov, E V; Arseniev, A S

    2013-11-01

    More than half of the mutations associated with familiar Alzheimer's disease have been found in the transmembrane domain of amyloid precursor protein (APP). These pathogenic mutations presumably influence the APP transmembrane domain structural and dynamic properties and result in its conformational change or/and lateral dimerization. Despite much data about the pathogenesis of Alzheimer's disease, the initial steps of the pathogenesis remain unclear so far. For the investigation of the molecular basis of Alzheimer's disease, we selected amyloid precursor protein fragment APP671-726 containing the transmembrane and metal-binding domains. This fragment is the substrate of the γ-secretase complex whose abnormal activity leads to the formation of amyloidogenic Aβ42 peptides. This work for the first time describes a highly effective cell-free APP671-726 production method and improved method of bacterial synthesis. Both methods yield milligram quantities of isotope-labeled protein for structural study by high resolution NMR spectroscopy in membrane mimicking milieus.

  3. NMR and XAS reveal an inner-sphere metal binding site in the P4 helix of the metallo-ribozyme ribonuclease P

    PubMed Central

    Koutmou, Kristin S.; Casiano-Negroni, Anette; Getz, Melissa M.; Pazicni, Samuel; Andrews, Andrew J.; Penner-Hahn, James E.; Al-Hashimi, Hashim M.; Fierke, Carol A.

    2010-01-01

    Functionally critical metals interact with RNA through complex coordination schemes that are currently difficult to visualize at the atomic level under solution conditions. Here, we report a new approach that combines NMR and XAS to resolve and characterize metal binding in the most highly conserved P4 helix of ribonuclease P (RNase P), the ribonucleoprotein that catalyzes the divalent metal ion-dependent maturation of the 5′ end of precursor tRNA. Extended X-ray absorption fine structure (EXAFS) spectroscopy reveals that the Zn2+ bound to a P4 helix mimic is six-coordinate, with an average Zn-O/N bond distance of 2.08 Å. The EXAFS data also show intense outer-shell scattering indicating that the zinc ion has inner-shell interactions with one or more RNA ligands. NMR Mn2+ paramagnetic line broadening experiments reveal strong metal localization at residues corresponding to G378 and G379 in B. subtilis RNase P. A new “metal cocktail” chemical shift perturbation strategy involving titrations with , Zn2+, and confirm an inner-sphere metal interaction with residues G378 and G379. These studies present a unique picture of how metals coordinate to the putative RNase P active site in solution, and shed light on the environment of an essential metal ion in RNase P. Our experimental approach presents a general method for identifying and characterizing inner-sphere metal ion binding sites in RNA in solution. PMID:20133747

  4. Metal ion as both a cofactor and a probe of metal-binding sites in a uranyl-specific DNAzyme: a uranyl photocleavage study.

    PubMed

    Cepeda-Plaza, Marjorie; Null, Eric L; Lu, Yi

    2013-11-01

    DNAzymes are known to bind metal ions specifically to carry out catalytic functions. Despite many studies since DNAzymes were discovered nearly two decades ago, the metal-binding sites in DNAzymes are not fully understood. Herein, we adopt uranyl photocleavage to probe specific uranyl-binding sites in the 39E DNAzyme with catalytically relevant concentrations of uranyl. The results indicate that uranyl binds between T23 and C25 in the bulge loop, G11 and T12 in the stem loop of the enzyme strand, as well as between T2.4 and G3 close to the cleavage site in the substrate strand. Control experiments using two 39E DNAzyme mutants revealed a different cleavage pattern of the mutated region. Another DNAzyme, the 8-17 DNAzyme, which has a similar secondary structure but shows no activity in the presence of uranyl, indicated a different uranyl-dependent photocleavage as well. In addition, a close correlation between the concentration-dependent photocleavage and enzymatic activities is also demonstrated. Together, these experiments suggest that uranyl photocleavage has been successfully used to probe catalytically relevant uranyl-binding sites in the 39E DNAzyme. As uranyl is the cofactor of the 39E DNAzyme as well as the probe, specific uranyl binding has now been identified without disruption of the structure.

  5. Crystal Structure of Phosphatidylglycerophosphatase (PGPase), a Putative Membrane-Bound Lipid Phosphatase, Reveals a Novel Binuclear Metal Binding Site and Two Proton Wires

    SciTech Connect

    Kumaran,D.; Bonnano, J.; Burley, S.; Swaminathan, S.

    2006-01-01

    Phosphatidylglycerophosphatase (PGPase), an enzyme involved in lipid metabolism, catalyzes formation of phosphatidylglycerol from phosphatidylglycerophosphate. Phosphatidylglycerol is a multifunctional phospholipid, found in the biological membranes of many organisms. Here, we report the crystal structure of Listeria monocytogenes PGPase at 1.8 Angstroms resolution. PGPase, an all-helical molecule, forms a homotetramer. Each protomer contains an independent active site with two metal ions, Ca{sup 2+} and Mg{sup 2+}, forming a hetero-binuclear center located in a hydrophilic cavity near the surface of the molecule. The binuclear center, conserved ligands, metal-bound water molecules, and an Asp-His dyad form the active site. The catalytic mechanism of this enzyme is likely to proceed via binuclear metal activated nucleophilic water. The binuclear metal-binding active-site environment of this structure should provide insights into substrate binding and metal-dependent catalysis. A long channel with inter-linked linear water chains, termed 'proton wires', is observed at the tetramer interface. Comparison of similar water chain structures in photosynthetic reaction centers (RCs), Cytochrome f, gramicidin, and bacteriorhodopsin, suggests that PGPase may conduct protons via proton wires.

  6. A moderate metal-binding hydrazone meets the criteria for a bioinorganic approach towards Parkinson's disease: Therapeutic potential, blood-brain barrier crossing evaluation and preliminary toxicological studies.

    PubMed

    Cukierman, Daphne Schneider; Pinheiro, Ana Beatriz; Castiñeiras-Filho, Sergio L P; da Silva, Anastácia Sá P; Miotto, Marco C; De Falco, Anna; de P Ribeiro, Thales; Maisonette, Silvia; da Cunha, Alessandra L M C; Hauser-Davis, Rachel A; Landeira-Fernandez, J; Aucélio, Ricardo Q; Outeiro, Tiago F; Pereira, Marcos D; Fernández, Claudio O; Rey, Nicolás A

    2017-02-22

    Alzheimer's and Parkinson's diseases share similar amyloidogenic mechanisms, in which metal ions might play an important role. In this last neuropathy, misfolding and aggregation of α-synuclein (α-Syn) are crucial pathological events. A moderate metal-binding compound, namely, 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INHHQ), which was previously reported as a potential 'Metal-Protein Attenuating Compound' for Alzheimer's treatment, is well-tolerated by healthy Wistar rats and does not alter their major organ weights, as well as the tissues' reduced glutathione and biometal levels, at a concentration of 200mgkg(-1). INHHQ definitively crosses the blood-brain barrier and can be detected in the brain of rats so late as 24h after intraperitoneal administration. After 48h, brain clearance is complete. INHHQ is able to disrupt, in vitro, anomalous copper-α-Syn interactions, through a mechanism probably involving metal ions sequestering. This compound is non-toxic to H4 (human neuroglioma) cells and partially inhibits intracellular α-Syn oligomerization. INHHQ, thus, shows definite potential as a therapeutic agent against Parkinson's as well.

  7. Elucidating connectivity and metal-binding structures of unlabeled paramagnetic complexes by 13C and 1H solid-state NMR under fast magic angle spinning.

    PubMed

    Wickramasinghe, Nalinda P; Shaibat, Medhat A; Ishii, Yoshitaka

    2007-08-23

    Characterizing paramagnetic complexes in solids is an essential step toward understanding their molecular functions. However, methodologies to characterize chemical and electronic structures of paramagnetic systems at the molecular level have been notably limited, particularly for noncrystalline solids. We present an approach to obtain connectivities of chemical groups and metal-binding structures for unlabeled paramagnetic complexes by 13C and 1H high-resolution solid-state NMR (SSNMR) using very fast magic angle spinning (VFMAS, spinning speed >or=20 kHz). It is experimentally shown for unlabeled Cu(II)(Ala-Thr) that 2D 13C/1H correlation SSNMR under VFMAS provides the connectivity of chemical groups and assignments for the characterization of unlabeled paramagnetic systems in solids. We demonstrate that on the basis of the assignments provided by the VFMAS approach multiple 13C-metal distances can be simultaneously elucidated by a combination of measurements of 13C anisotropic hyperfine shifts and 13C T1 relaxation due to hyperfine interactions for this peptide-Cu(II) complex. It is also shown that an analysis of 1H anisotropic hyperfine shifts allows for the determination of electron-spin states in Fe(III)-chloroprotoporphyin-IX in solid states.

  8. Conserved histidine residues at the ferroxidase centre of the Campylobacter jejuni Dps protein are not strictly required for metal binding and oxidation.

    PubMed

    Sanchuki, Heloisa B S; Valdameri, Glaucio; Moure, Vivian R; Rodriguez, Jorge A; Pedrosa, Fábio O; Souza, Emanuel M; Korolik, Victoria; Ribeiro, Ronny Rocha; Huergo, Luciano F

    2016-01-01

    Iron is an essential micronutrient for living organisms as it is involved in a broad variety of important biological processes. However, free iron inside the cell could be potentially toxic, generating hydroxyl radicals through the Fenton reaction. Dps (DNA-binding protein from starved cells) belongs to a subfamily of ferritins and can store iron atoms inside the dodecamer. The presence of a ferroxidase centre, composed of highly conserved residues, is a signature of this protein family. In this study, we analysed the role of two conserved histidine residues (H25 and H37) located at the ferroxidase centre of the Campylobacter jejuni Dps protein by replacing them with glycine residues. The C. jejuni H25G/H37G substituted variant showed reduced iron binding and ferroxidase activities in comparison with wt Dps, while DNA-binding activity remained unaffected. We also found that both CjDps wt and CjDps H25G/H37G were able to bind manganese atoms. These results indicate that the H25 and H37 residues at the ferroxidase centre of C. jejuni Dps are not strictly required for metal binding and oxidation.

  9. α-Synuclein amyloid fibrils with two entwined, asymmetrically associated protofibrils [α-Synuclein amyloid fibrils with two entwined, asymmetrically associated, protofibrils and axially stacked metal binding sites

    DOE PAGES

    Dearborn, Altaira D.; Wall, Joseph S.; Cheng, Naiqian; ...

    2015-12-07

    Parkinson disease and other progressive neurodegenerative conditions are characterized by the intracerebral presence of Lewy bodies, containing amyloid fibrils of α-synuclein. We used cryo-electron microscopy and scanning transmission electron microscopy (STEM) to study in vitro-assembled fibrils. These fibrils are highly polymorphic. Focusing on twisting fibrils with an inter-crossover spacing of 77 nm, our reconstructions showed them to consist of paired protofibrils. STEM mass per length data gave one subunit per 0.47 nm axial rise per protofibril, consistent with a superpleated β-structure. The STEM images show two thread-like densities running along each of these fibrils, which we interpret as ladders ofmore » metal ions. These threads confirmed the two-protofibril architecture of the 77-nm twisting fibrils and allowed us to identify this morphotype in STEM micrographs. Some other, but not all, fibril morphotypes also exhibit dense threads, implying that they also present a putative metal binding site. As a result, we propose a molecular model for the protofibril and suggest that polymorphic variant fibrils have different numbers of protofibrils that are associated differently.« less

  10. α-Synuclein amyloid fibrils with two entwined, asymmetrically associated protofibrils [α-Synuclein amyloid fibrils with two entwined, asymmetrically associated, protofibrils and axially stacked metal binding sites

    SciTech Connect

    Dearborn, Altaira D.; Wall, Joseph S.; Cheng, Naiqian; Heymann, J. Bernard; Kajava, Andrey V.; Varkey, Jobin; Langen, Ralf; Steven, Alasdair C.

    2015-12-07

    Parkinson disease and other progressive neurodegenerative conditions are characterized by the intracerebral presence of Lewy bodies, containing amyloid fibrils of α-synuclein. We used cryo-electron microscopy and scanning transmission electron microscopy (STEM) to study in vitro-assembled fibrils. These fibrils are highly polymorphic. Focusing on twisting fibrils with an inter-crossover spacing of 77 nm, our reconstructions showed them to consist of paired protofibrils. STEM mass per length data gave one subunit per 0.47 nm axial rise per protofibril, consistent with a superpleated β-structure. The STEM images show two thread-like densities running along each of these fibrils, which we interpret as ladders of metal ions. These threads confirmed the two-protofibril architecture of the 77-nm twisting fibrils and allowed us to identify this morphotype in STEM micrographs. Some other, but not all, fibril morphotypes also exhibit dense threads, implying that they also present a putative metal binding site. As a result, we propose a molecular model for the protofibril and suggest that polymorphic variant fibrils have different numbers of protofibrils that are associated differently.

  11. A New Type of Metal-Binding Site in Cobalt- And Zinc-Containing Adenylate Kinases Isolated From Sulfate-Reducers D. Gigas And D. Desulfuricans ATCC 27774

    SciTech Connect

    Gavel, O.Y.; Bursakov, S.A.; Rocco, G.Di; Trincao, J.; Pickering, I.J.; George, G.N.; Calvete, J.J.; Brondino, C.; Pereira, A.S.; Lampreia, J.; Tavares, P.; Moura, J.J.G.; Moura, I.

    2009-05-18

    Adenylate kinase (AK) mediates the reversible transfer of phosphate groups between the adenylate nucleotides and contributes to the maintenance of their constant cellular level, necessary for energy metabolism and nucleic acid synthesis. The AK were purified from crude extracts of two sulfate-reducing bacteria (SRB), Desulfovibrio (D.) gigas NCIB 9332 and Desulfovibrio desulfuricans ATCC 27774, and biochemically and spectroscopically characterized in the native and fully cobalt- or zinc-substituted forms. These are the first reported adenylate kinases that bind either zinc or cobalt and are related to the subgroup of metal-containing AK found, in most cases, in Gram-positive bacteria. The electronic absorption spectrum is consistent with tetrahedral coordinated cobalt, predominantly via sulfur ligands, and is supported by EPR. The involvement of three cysteines in cobalt or zinc coordination was confirmed by chemical methods. Extended X-ray absorption fine structure (EXAFS) indicate that cobalt or zinc are bound by three cysteine residues and one histidine in the metal-binding site of the 'LID' domain. The sequence {sup 129}Cys-X{sub 5}-His-X{sub 15}-Cys-X{sub 2}-Cys of the AK from D. gigas is involved in metal coordination and represents a new type of binding motif that differs from other known zinc-binding sites of AK. Cobalt and zinc play a structural role in stabilizing the LID domain.

  12. Agricultural waste as a source for the production of silica nanoparticles.

    PubMed

    Vaibhav, Vineet; Vijayalakshmi, U; Roopan, S Mohana

    2015-03-15

    The major interest of the paper deals with the extraction of silica from four natural sources such as rice husk, bamboo leaves, sugarcane bagasse and groundnut shell. These waste materials in large quantities can create a serious environmental problem. Hence, there is a need to adopt proper strategy to reduce the waste. In the present investigation, all the waste materials are subjected to moisture removal in a hot plate and sintered at 900°C for 7 h. The sintered powder was treated with 1 M NaOH to form sodium silicate and then with 6M H2SO4 to precipitate silica. The prepared silica powders were characterized by FT-IR, XRD and SEM-EDAX analysis. The silica recovered from different sources was found to vary between 52% and 78%. Magnesium substituted silica was formed from the groundnut waste and further treatment is required to precipitate silica.

  13. The world ocean silica cycle.

    PubMed

    Tréguer, Paul J; De La Rocha, Christina L

    2013-01-01

    Over the past few decades, we have realized that the silica cycle is strongly intertwined with other major biogeochemical cycles, like those of carbon and nitrogen, and as such is intimately related to marine primary production, the efficiency of carbon export to the deep sea, and the inventory of carbon dioxide in the atmosphere. For nearly 20 years, the marine silica budget compiled by Tréguer et al. (1995) , with its exploration of reservoirs, processes, sources, and sinks in the silica cycle, has provided context and information fundamental to study of the silica cycle. Today, the budget needs revisiting to incorporate advances that have notably changed estimates of river and groundwater inputs to the ocean of dissolved silicon and easily dissolvable amorphous silica, inputs from the dissolution of terrestrial lithogenic silica in ocean margin sediments, reverse weathering removal fluxes, and outputs of biogenic silica (especially on ocean margins and in the form of nondiatomaceous biogenic silica). The resulting budget recognizes significantly higher input and output fluxes and notes that the recycling of silicon occurs mostly at the sediment-water interface and not during the sinking of silica particles through deep waters.

  14. Silica burial enhanced by iron limitation in oceanic upwelling margins

    NASA Astrophysics Data System (ADS)

    Pichevin, L. E.; Ganeshram, R. S.; Geibert, W.; Thunell, R.; Hinton, R.

    2014-07-01

    In large swaths of the ocean, primary production by diatoms may be limited by the availability of silica, which in turn limits the biological uptake of carbon dioxide. The burial of biogenic silica in the form of opal is the main sink of marine silicon. Opal burial occurs in equal parts in iron-limited open-ocean provinces and upwelling margins, especially the eastern Pacific upwelling zone. However, it is unclear why opal burial is so efficient in this margin. Here we measure fluxes of biogenic material, concentrations of diatom-bound iron and silicon isotope ratios using sediment traps and a sediment core from the Gulf of California upwelling margin. In the sediment trap material, we find that periods of intense upwelling are associated with transient iron limitation that results in a high export of silica relative to organic carbon. A similar correlation between enhanced silica burial and iron limitation is evident in the sediment core, which spans the past 26,000 years. A global compilation also indicates that hotspots of silicon burial in the ocean are all characterized by high silica to organic carbon export ratios, a diagnostic trait for diatoms growing under iron stress. We therefore propose that prevailing conditions of silica limitation in the ocean are largely caused by iron deficiency imposing an indirect constraint on oceanic carbon uptake.

  15. Stable and responsive fluorescent carbon nanotube silica gels

    SciTech Connect

    Dattelbaum, Andrew M; Gupta, Gautam; Doorn, Stephen K; Duque, Juan G

    2010-05-03

    Here we report a general route to prepare silica nanocomposite gels doped with fluorescent single walled carbon nanotubes (SWNT). We show that tetramethylorthosilicate (TMOS) vapors can be used to gel an aqueous suspension of surfactant-wrapped SWNT while maintaining fluorescence from the semiconducting nanotubes. The vapor phase silica process is performed at room temperature and is simple, reproducible, relatively quick, and requires no dilution of SWNT dispersions. However, exposure of aqueous SWNT suspensions to TMOS vapors resulted in an acidification of the suspension prior to gelation that caused a decrease in the emission signal from sodium dodecylsulfate (SDS) wrapped SWNT. We also show that although the SWNT are encapsulated in silica the emission signal from the encapsulated SWNT may be attenuated by exposing the nanocomposites to small aromatic molecules known to mitigate SWNT emission. These results demonstrate a new route for the preparation of highly luminescent SWNT/silica composite materials that are potentially useful for future sensing applications.

  16. Quantification of residual stress from photonic signatures of fused silica

    NASA Astrophysics Data System (ADS)

    Cramer, K. Elliott; Hayward, Maurice; Yost, William T.

    2014-02-01

    A commercially available grey-field polariscope (GFP) instrument for photoelastic examination is used to assess impact damage inflicted upon the outer-most pane of Space Shuttle windows made from fused silica. A method and apparatus for calibration of the stress-optic coefficient using four-point bending is discussed. The results are validated on known material (acrylic) and are found to agree with literature values to within 6%. The calibration procedure is then applied to fused-silica specimens and the stress-optic coefficient is determined to be 2.43 ± 0.54 × 10-12 Pa-1. Fused silica specimens containing impacts artificially made at NASA's Hypervelocity Impact Technology Facility (HIT-F), to simulate damage typical during space flight, are examined. The damage sites are cored from fused silica window carcasses and examined with the GFP. The calibrated GFP measurements of residual stress patterns surrounding the damage sites are presented.

  17. Photoluminescence properties of silica aerogel/porous silicon nanocomposites

    NASA Astrophysics Data System (ADS)

    Karlash, A. Yu; Zakharko, Yu E.; Skryshevsky, V. A.; Tsiganova, A. I.; Kuznetsov, G. V.

    2010-08-01

    The luminescent properties of nanocomposite pellets based on silica aerogel and porous Si powder are studied depending on the ratio of chemical compounds. The photoluminescence of nanocomposites is characterized by a red-orange band related to silicon nanoparticles and a blue-green band related to silica aerogel with close values of decay time and activation energy. Remarkable tuning of nanocomposites' photoluminescence spectra in the RGB region is established allowing their use as promising phosphor materials for light-emitting diodes. The outgoing spectra of pellet photoluminescence are guided by the chemical composition ratio, porous Si and silica aerogel technology, and the storage time in ambient atmosphere. It was shown that using the silica aerogel as a dielectric matrix considerably increases the stability of photoluminescence yield of silicon nanoparticles.

  18. Adsorption of mycotoxins in beverages onto functionalized mesoporous silicas

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mycotoxins, natural toxins produced by fungi, are a global concern as contaminates of agricultural commodities. Exposure to these toxins can be reduced by the use of binding materials. Templated mesoporous silicas are promising materials with favorable adsorptive properties for dyes, ions, and toxin...

  19. Our favorite materials: silica hydride stationary phases.

    PubMed

    Pesek, Joseph J; Matyska, Maria T

    2009-12-01

    "Chance favors the prepared mind." Louis Pasteur. "Reality is merely an illusion, albeit a very persistent one". Albert Einstein. As so succinctly stated by these two famous scientists, it is sometimes necessary to step outside the bounds of traditional thinking and look at ideas that many claim to be impossible based on preconceived notions rather than experimental data. This review is dedicated to those open-minded scientists who are willing to evaluate new concepts objectively rather than dismiss new approaches with outdated theories.

  20. Mesoporous-silica films, fibers, and powders by evaporation

    DOEpatents

    Bruinsma, Paul J.; Baskaran, Suresh; Bontha, Jagannadha R.; Liu, Jun

    2008-05-06

    This invention pertains to surfactant-templated nanometer-scale porosity of a silica precursor solution and forming a mesoporous material by first forming the silica precursor solution into a preform having a high surface area to volume ratio, then rapid drying or evaporating a solvent from the silica precursor solution. The mesoporous material may be in any geometric form, but is preferably in the form of a film, fiber, powder or combinations thereof. The rapid drying or evaporation of solvent from the solution is accomplished by layer thinning, for example spin casting, liquid drawing, and liquid spraying respectively. Production of a film is by layer thinning, wherein a layer of the silica precursor solution is formed on a surface followed by removal of an amount of the silica precursor solution and leaving a geometrically thinner layer of the silica precursor solution from which the solvent quickly escapes via evaporation. Layer thinning may be by any method including but not limited to squeegeeing and/or spin casting. In powder formation by spray drying, the same conditions of fast drying exists as in spin-casting (as well as in fiber spinning) because of the high surface-area to volume ratio of the product. When a powder is produced by liquid spraying, the particles or micro-bubbles within the powder are hollow spheres with walls composed of mesoporous silica. Mesoporous fiber formation starts with a similar silica precursor solution but with an added pre-polymer making a pituitous mixture that is drawn into a thin strand from which solvent is evaporated leaving the mesoporous fiber(s).

  1. Mesoporous-silica films, fibers, and powders by evaporation

    DOEpatents

    Bruinsma, P.J.; Baskaran, S.; Bontha, J.R.; Liu, J.

    1999-07-13

    This invention pertains to surfactant-templated nanometer-scale porosity of a silica precursor solution and forming a mesoporous material by first forming the silica precursor solution into a preform having a high surface area to volume ratio, then rapid drying or evaporating a solvent from the silica precursor solution. The mesoporous material may be in any geometric form, but is preferably in the form of a film, fiber, powder or combinations thereof. The rapid drying or evaporation of solvent from the solution is accomplished by layer thinning, for example spin casting, liquid drawing, and liquid spraying respectively. Production of a film is by layer thinning, wherein a layer of the silica precursor solution is formed on a surface followed by removal of an amount of the silica precursor solution and leaving a geometrically thinner layer of the silica precursor solution from which the solvent quickly escapes via evaporation. Layer thinning may be by any method including but not limited to squeegeeing and/or spin casting. In powder formation by spray drying, the same conditions of fast drying exists as in spin-casting (as well as in fiber spinning) because of the high surface-area to volume ratio of the product. When a powder is produced by liquid spraying, the particles or micro-bubbles within the powder are hollow spheres with walls composed of mesoporous silica. Mesoporous fiber formation starts with a similar silica precursor solution but with an added pre-polymer making a pituitous mixture that is drawn into a thin strand from which solvent is evaporated leaving the mesoporous fiber(s). 24 figs.

  2. Mesoporous-silica films, fibers, and powders by evaporation

    DOEpatents

    Bruinsma, Paul J.; Baskaran, Suresh; Bontha, Jagannadha R.; Liu, Jun

    1999-01-01

    This invention pertains to surfactant-templated nanometer-scale porosity of a silica precursor solution and forming a mesoporous material by first forming the silica precursor solution into a preform having a high surface area to volume ratio, then rapid drying or evaporating a solvent from the silica precursor solution. The mesoporous material may be in any geometric form, but is preferably in the form of a film, fiber, powder or combinations thereof. The rapid drying or evaporation of solvent from the solution is accomplished by layer thinning, for example spin casting, liquid drawing, and liquid spraying respectively. Production of a film is by layer thinning, wherein a layer of the silica precursor solution is formed on a surface followed by removal of an amount of the silica precursor solution and leaving a geometrically thinner layer of the silica precursor solution from which the solvent quickly escapes via evaporation. Layer thinning may be by any method including but not limited to squeegeeing and/or spin casting. In powder formation by spray drying, the same conditions of fast drying exists as in spin-casting (as well as in fiber spinning) because of the high surface-area to volume ratio of the product. When a powder is produced by liquid spraying, the particles or micro-bubbles within the powder are hollow spheres with walls composed of mesoporous silica. Mesoporous fiber formation starts with a similar silica precursor solution but with an added pre-polymer making a pituitous mixture that is drawn into a thin strand from which solvent is evaporated leaving the mesoporous fiber(s).

  3. Water-Dispersible Silica-Coated Upconverting Liposomes: Can a Thin Silica Layer Protect TTA-UC against Oxygen Quenching?

    PubMed Central

    2017-01-01

    Light upconversion by triplet–triplet annihilation (TTA-UC) in nanoparticles has received considerable attention for bioimaging and light activation of prodrugs. However, the mechanism of TTA-UC is inherently sensitive for quenching by molecular oxygen. A potential oxygen protection strategy is the coating of TTA-UC nanoparticles with a layer of oxygen-impermeable material. In this work, we explore if (organo)silica can fulfill this protecting role. Three synthesis routes are described for preparing water-dispersible (organo)silica-coated red-to-blue upconverting liposomes. Their upconversion properties are investigated in solution and in A549 lung carcinoma cells. Although it was found that the silica offered no protection from oxygen in solution and after uptake in A549 cancer cells, upon drying of the silica-coated liposome dispersion in an excess of (organo)silica precursor, interesting liposome–silica nanocomposite materials were obtained that were capable of generating blue light upon red light excitation in air. PMID:28317022

  4. Optimization of silica silanization by 3-aminopropyltriethoxysilane.

    PubMed

    Howarter, John A; Youngblood, Jeffrey P

    2006-12-19

    Thin films of 3-aminopropyltriethoxysilane (APTES) are commonly used to promote adhesion between silica substrates and organic or metallic materials with applications ranging from advanced composites to biomolecular lab-on-a-chip. Unfortunately, there is confusion as to which reaction conditions will result in consistently aminated surfaces. A wide range of conflicting experimental methods are used with researchers often assuming the creation of smooth self-assembled monolayers. A range of film morphologies based on the film deposition conditions are presented here to establish an optimized method of APTES film formation. The effect of reaction temperature, solution concentration, and reaction time on the structure and morphology was studied for the system of APTES on silica. Three basic morphologies were observed: smooth thin film, smooth thick film, and roughened thick film.

  5. Targeted mesoporous silica nanocarriers in oncology.

    PubMed

    Baeza, Alejandro; Vallet-Regí, Maria

    2016-06-02

    Cancer is one of the major leading causes of death worldwide and its prevalence will be higher in the coming years due to the progressive aging of the population. The development of nanocarriers in oncology has provided a new hope in the fight against this terrible disease. Among the different types of nanoparticles which have been described, mesoporous silica nanoparticles (MSNs) constitute a very promising material due to their inherent properties as high loading capacity of many different drugs, excellent biocompatibility and easiness functionalization. This review presents the current state of the art related with the development of mesoporous silica nanocarriers for antitumoral therapy paying special attention on targeted MSN able to selectively destroy tumoral cells reducing the side damage in healthy ones, and the basic principles of targeting tumoral tissues and cells.

  6. Phase diagram of silica from computer simulation

    NASA Astrophysics Data System (ADS)

    Saika-Voivod, Ivan; Sciortino, Francesco; Grande, Tor; Poole, Peter H.

    2004-12-01

    We evaluate the phase diagram of the “BKS” potential [van Beest, Kramer, and van Santen, Phys. Rev. Lett. 64, 1955 (1990)], a model of silica widely used in molecular dynamics (MD) simulations. We conduct MD simulations of the liquid, and three crystals ( β -quartz, coesite, and stishovite) over wide ranges of temperature and density, and evaluate the total Gibbs free energy of each phase. The phase boundaries are determined by the intersection of these free energy surfaces. Not unexpectedly for a classical pair potential, our results reveal quantitative discrepancies between the locations of the BKS and real silica phase boundaries. At the same time, we find that the topology of the real phase diagram is reproduced, confirming that the BKS model provides a satisfactory qualitative description of a silicalike material. We also compare the phase boundaries with the locations of liquid-state thermodynamic anomalies identified in previous studies of the BKS model.

  7. Synthesis and characterization of biocomposites based on chitosan and geothermal silica

    NASA Astrophysics Data System (ADS)

    Kusumastuti, Yuni; Petrus, Himawan Tri Bayu Murti; Yohana, Fiska; Buwono, Agung Tri; Zaqina, Radinda Bian

    2017-03-01

    With the amount of about 3000 ton per year of precipitate silica, Dieng's geothermal power plant possesses potential to utilize the precipitate silica. This material is a result of silica scaling mitigation that reduces the geothermal power plant productivity to the point of 40% within a year. In this study, the precipitated silica which is mostly in the amorphous state has potential uses for biomaterial such as bone graft composite. In order to obtain best of geothermal quality, purification was conducted using dry washing method to reach 95.65% of SiO2 purity. The silica was mixed in gel phase with 17.11% of water content. The geothermal silica was mixed with composition of chitosan/gelatin/geothermal silica (C/G/GS) and chitosan/pectin/geothermal silica (C/P/GS) biocomposites with certain ratio. Those two biocomposites were characterized and compared in order to determine the effect of geothermal silica addition into the matrix. From the observation, in general, it was obtained that the swelling ratio of C/P/GS is higher than C/G/GS. However, in comparison to the sample without geothermal silica addition, the swelling ratio of silica added biocomposites at various composition is lower. In term of Young's modulus at 1:1:1 ratio, silica addition into C/P biocomposite decreased the value while addition of silica into C/G biocomposite increased Young's modulus value. In general, no interaction was observed significantly between Young's modulus and swelling ratio. The interaction between the functional group of chitosan, pectin or gelatin and geothermal silica in the composite was also revealed by FTIR spectra analysis.

  8. Mesoporous silicas with tunable morphology for the immobilization of laccase.

    PubMed

    Gascón, Victoria; Díaz, Isabel; Márquez-Álvarez, Carlos; Blanco, Rosa M

    2014-05-30

    Siliceous ordered mesoporous materials (OMM) are gaining interest as supports for enzyme immobilization due to their uniform pore size, large surface area, tunable pore network and the introduction of organic components to mesoporous structure. We used SBA-15 type silica materials, which exhibit a regular 2D hexagonal packing of cylindrical mesopores of uniform size, for non-covalent immobilization of laccase. Synthesis conditions were adjusted in order to obtain supports with different particle shape, where those with shorter channels had higher loading capacity. Despite the similar isoelectric points of silica and laccase and the close match between the size of laccase and the pore dimensions of these SBA-15 materials, immobilization was achieved with very low leaching. Surface modification of macro-/mesoporous amorphous silica by grafting of amine moieties was proved to significantly increase the isoelectric point of this support and improve the immobilization yield.

  9. Performance of Silica Gel in the Role of Residual Air Drying

    NASA Technical Reports Server (NTRS)

    Jan, Darrell L.; Hogan, John A.; Koss, Brian; Palmer, Gary H.; Richardson, Justine; Linggi, Paul

    2014-01-01

    Removal of carbon dioxide (CO2) is a necessary step in air revitalization and is often accomplished with sorbent materials. Since moisture competes with CO2 in sorbent materials, it is necessary to remove the water first. This is typically accomplished in two stages: bulk removal and residual drying. Silica gel is used as the bulk drying material in the Carbon Dioxide Removal Assembly (CDRA) in operation on ISS. There has been some speculation that silica gel may also be capable of serving as the residual drying material. This paper will describe test apparatus and procedures for determining the performance of silica gel in residual air drying.

  10. Silica Fillers for elastomer Reinforement

    SciTech Connect

    Kohls, D.J.; Schaefer, D.W.

    2009-08-26

    This article summarizes recent work on the structure of precipitated silica used in the reinforcement of elastomers. Silica has a unique morphology, consisting of multiple structural levels that can be controlled through processing. The ability to control and characterize the multiple structures of precipitated silica is an example of morphological engineering for reinforcement applications. In this summary of some recent research efforts using precipitated silica, small-angle scattering techniques are described and their usefulness for determining the morphology of silica in terms of primary particles, aggregates, and agglomerates are discussed. The structure of several different precipitated silica powders is shown as well as the mechanical properties of elastomers reinforced with these silica particles. The study of the mechanical properties of filled elastomer systems is a challenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward rule of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fillers like silica and carbon black on the reinforcement of elastomers. In general, the structure-property relationships developed for filled elastomers have evolved into the following major areas: Filler structure, hydrodynamic reinforcement, and interactions between fillers and elastomers.

  11. Silica Fillers for elastomer Reinforement

    SciTech Connect

    Kohls, D.J.; Schaefer, D.W.

    2012-09-10

    This article summarizes recent work on the structure of precipitated silica used in the reinforcement of elastomers. Silica has a unique morphology, consisting of multiple structural levels that can be controlled through processing. The ability to control and characterize the multiple structures of precipitated silica is an example of morphological engineering for reinforcement applications. In this summary of some recent research efforts using precipitated silica, small-angle scattering techniques are described and their usefulness for determining the morphology of silica in terms of primary particles, aggregates, and agglomerates are discussed. The structure of several different precipitated silica powders is shown as well as the mechanical properties of elastomers reinforced with these silica particles. The study of the mechanical properties of filled elastomer systems is a challenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward rule of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fillers like silica and carbon black on the reinforcement of elastomers. In general, the structure-property relationships developed for filled elastomers have evolved into the following major areas: Filler structure, hydrodynamic reinforcement, and interactions between fillers and elastomers.

  12. Immobilized lipid-bilayer materials

    DOEpatents

    Sasaki, Darryl Y.; Loy, Douglas A.; Yamanaka, Stacey A.

    2000-01-01

    A method for preparing encapsulated lipid-bilayer materials in a silica matrix comprising preparing a silica sol, mixing a lipid-bilayer material in the silica sol and allowing the mixture to gel to form the encapsulated lipid-bilayer material. The mild processing conditions allow quantitative entrapment of pre-formed lipid-bilayer materials without modification to the material's spectral characteristics. The method allows for the immobilization of lipid membranes to surfaces. The encapsulated lipid-bilayer materials perform as sensitive optical sensors for the detection of analytes such as heavy metal ions and can be used as drug delivery systems and as separation devices.

  13. Resistance properties of a macroporous silica-based N,N,N',N'-tetraoctyl-3-oxapentane-1,5-diamide-impregnated polymeric adsorption material against nitric acid, temperature and γ-irradiation

    NASA Astrophysics Data System (ADS)

    Zhang, Anyun; Wei, Yuezhou; Hoshi, Harutaka; Kumagai, Mikio; Kamiya, Masayoshi; Koyama, Tomozo

    2005-04-01

    The resistance of a novel silica-based N,N,N',N'-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) polymeric adsorption material (TODGA/SiO 2-P) against nitric acid, temperature and γ-irradiation had been investigated. The adsorption property of the treated TODGA/SiO 2-P was evaluated by a 3 M HNO 3 solution containing 0.01 M Nd(III). It was found that both 3 and 0.01 M HNO 3 concentrations did not decrease the stability of TODGA/SiO 2-P at 25°C. The quantity of TODGA leaked from TODGA/SiO 2-P was equivalent to its solubility in the corresponding HNO 3 aqueous solution. The effect of 3 M HNO 3 on the leakage of TODGA at 80°C was significantly higher than that in 0.01 M HNO 3 as well as in all cases at 25°C. The amount of Nd(III) adsorbed towards the treated TODGA/SiO 2-P was determined in the range of 0.143-0.148 mmol/g for the HNO 3 concentration effect and 0.142-0.0506 mmol/g for the temperature effect. γ-Irradiation showed a more noticeable destruction effect on TODGA/SiO 2-P. The content of TODGA leaked increased with an increase in the γ-irradiation dose (ID) from 1.06 to 3.72 MGy in terms of the linear equation [TODGA]=794.5ID+84.0. The amount of Nd(III) adsorbed onto the irradiated TODGA/SiO 2-P decreased rapidly from 0.134 to 0.0438 mmol/g, which was lower than 0.153 mmol/g, the adsorption of fresh TODGA/SiO 2-P for Nd(III), according to the equation QNd(III)=-0.0301ID+0.160, showing that a large quantity of TODGA leaked from TODGA/SiO 2-P. The adsorbed amount of Nd(III) decreased obviously in this order: the HNO 3 concentration effect, temperature effect and γ-irradiation.

  14. Fluoroquinolones stimulate the DNA cleavage activity of topoisomerase IV by promoting the binding of Mg2+ to the second metal binding site

    PubMed Central

    Oppegard, Lisa M.; Schwanz, Heidi A.; Towle, Tyrell R.; Kerns, Robert J.; Hiasa, Hiroshi

    2016-01-01

    Background Fluoroquinolones target bacterial type IIA topoisomerases, DNA gyrase and topoisomerase IV (Topo IV). Fluoroquinolones trap a topoisomerase-DNA covalent complex as a topoisomerase-fluoroquinolone-DNA ternary complex and ternary complex formation is critical for their cytotoxicity. A divalent metal ion is required for type IIA topoisomerase-catalyzed strand breakage and religation reactions. Recent studies have suggested that type IIA topoisomerases use two metal ions, one structural and one catalytic, to carry out the strand breakage reaction. Methods We conducted a series of DNA cleavage assays to examine the effects of fluoroquinolones and quinazolinediones on Mg2+-, Mn2+-, or Ca2+-supported DNA cleavage activity of Esherichia coli Topo IV. Results In the absence of any drug, 20–30 mM Mg2+ was required for the maximum levels of the DNA cleavage activity of Topo IV, whereas approximately 1 mM of either Mn2+ or Ca2+ was sufficient to support the maximum levels of the DNA cleavage activity of Topo IV. Fluoroquinolones promoted the Topo IV-catalyzed strand breakage reaction at low Mg2+ concentrations where Topo IV alone could not efficiently cleave DNA. Conclusions and General Significance At low Mg2+ concentrations, fluoroquinolones may stimulate the Topo IV-catalyzed strand breakage reaction by promoting Mg2+ binding to metal binding site B through the structural distortion in DNA. As Mg2+ concentration increases, fluoroquinolones may inhibit the religation reaction by either stabilizing Mg2+ at site B or inhibition the binding of Mg2+ to site A. This study provides a molecular basis of how fluoroquinolones stimulate the Topo IV-catalyzed strand breakage reaction by modulating Mg2+ binding. PMID:26723176

  15. Transcriptional regulation, metal binding properties and structure of Pden1597, an unusual zinc transport protein from Paracoccus denitrificans

    SciTech Connect

    Handali, Melody; Neupane, Durga P.; Roychowdhury, Hridindu; Yukl, Erik T.

    2015-03-18

    Here, ATP-binding cassette (ABC) transporters of the cluster 9 family are ubiquitous among bacteria and essential for acquiring Zn2+ and Mn2+ from the environment or, in the case of pathogens, from the host. These rely on a substrate-binding protein (SBP) to coordinate the relevant metal with high affinity and specificity and subsequently release it to a membrane permease for translocation into the cytoplasm. Although a number of cluster 9 SBP structures have been determined, the structural attributes conferring Zn2+ or Mn2+ specificity remain ambiguous. Here we describe the gene expression profile, in vitro metal binding properties, and crystal structure of a new cluster 9 SBP from Paracoccus denitrificans we have called AztC. Although all of our results strongly indicate Zn2+ over Mn2+ specificity, the Zn2+ ion is coordinated by a conserved Asp residue only observed to date as a metal ligand in Mn2+-specific SBPs. The unusual sequence properties of this protein are shared among close homologues, including members from the human pathogens Klebsiella pneumonia and Enterobacter aerogenes, and would seem to suggest a subclass of Zn2+-specific transporters among the cluster 9 family. In any case, the unusual coordination environment of AztC expands the already considerable range of those available to Zn2+-specific SBPs and highlights the presence of a His-rich loop as the most reliable indicator of Zn2+ specificity.

  16. Zinc-induced heterodimer formation between metal-binding domains of intact and naturally modified amyloid-beta species: implication to amyloid seeding in Alzheimer's disease?

    PubMed

    Mezentsev, Yuri V; Medvedev, Alexei E; Kechko, Olga I; Makarov, Alexander A; Ivanov, Alexis S; Mantsyzov, Alexey B; Kozin, Sergey A

    2016-11-01

    Zinc ions and modified amyloid-beta peptides (Aβ) play a critical role in the pathological aggregation of endogenous Aβ in Alzheimer's disease (AD). Zinc-induced Aβ oligomerization is mediated by the metal-binding domain (MBD) which includes N-terminal residues 1-16 (Aβ1-16). Earlier, it has been shown that Aβ1-16 as well as some of its naturally occurring variants undergoes zinc-induced homodimerization via the interface in which zinc ion is coordinated by Glu11 and His14 of the interacting subunits. In this study using surface plasmon resonance technique, we have found that in the presence of zinc ions Aβ1-16 forms heterodimers with MBDs of two Aβ species linked to AD: Aβ containing isoAsp7 (isoAβ) and Aβ containing phosphorylated Ser8 (pS8-Aβ). The heterodimers appear to possess the same interface as the homodimers. Simulation of 200 ns molecular dynamic trajectories in two constructed models of dimers ([Aβ1-16/Zn/Aβ1-16] and [isoAβ1-16/Zn/Aβ1-16]), has shown that conformational flexibility of the N-terminal fragments of the dimer subunits is controlled by the structure of corresponding sites 6-8. The data suggest that isoAβ and pS8-Aβ can be involved in the AD pathogenesis by means of their zinc-dependent interactions with endogenous Aβ resulting in the formation of heterodimeric seeds for amyloid aggregation.

  17. Peptide -- Silica Hybrid Networks

    NASA Astrophysics Data System (ADS)

    Altunbas, Aysegul; Sharma, Nikhil; Nagarkar, Radhika; Schneider, Joel; Pochan, Darrin

    2010-03-01

    In this study, a bio-inspired route was used to fabricate scaffolds that display hierarchical organization of an inorganic layer around an organic self-assembled peptide fibril template. The 20 amino acid peptide used in this study intramolecular folds into a beta-hairpin conformation on addition of a desired solution stimulus. This intramolecular folding is followed by intermolecular self-assembly of the peptides into a three dimensional network of entangled fibrils rich in beta-sheet with a high density of lysine groups exposed on the fibril-surfaces. The lysine-rich surface chemistry was utilized to create a silica shell around the fibrils. The mineralization process of the fibrils results in a rigid, porous silica network that retains the microscale and nanoscale structure of the peptide fibril network. Structural characterization via Transmission Electron Microscopy, cryogenic-Scanning Electron Microscopy, mechanical characterization via oscillatory rheology, Small Angle X-ray and Neutron Scattering of the silicified hydrogels will be presented.

  18. Synthesis and Characterization of MO[OSi(OtBu)3]4 andMO2[OSi(OtBu)3]2 (M=Mo,W): Models for Isolated Oxo-Molybdenum and-Tungsten Sites on Silica and Precursors to Molybdena- and Tungsta-SilicaMaterials

    SciTech Connect

    Jarupatrakorn, Jonggol; Coles, Martyn P.; Tilley, T. Don

    2005-01-20

    The tri(alkoxy)siloxy complexes MO[OSi(OtBu)3]4 (1, M = Mo and 2, M = W) were prepared from MOCl4 and LiOSi(OtBu)3. Similarly, reactions of MO2Cl2(DME) with LiOSi(OtBu)3 afforded the new siloxide complexes MO2[OSi(OtBu)3]2 (3, M = Mo and 4, M = W), which are thermally unstable at ambient temperature. More stable compounds were obtained by the crystallizations of 3 and 4 in a coordinating solvent, to form the ether adducts MoO2[OSi(OtBu)3]2(THF) (3a) and WO2[OSi(OtBu)3]2(DME) (4a). These compounds serve as soluble models for isolated molybdenum or tungsten atoms on a silica surface and were characterized by 1H, 13C, 29Si, 95Mo, and 183W NMR, FT-Raman, FT-IR, and UV-vis spectroscopies. Compounds 1, 2, 3a, and 4a were used to prepare metal-oxide silica composites via the thermolytic molecular precursor method. The xerogels obtained from the thermolyses of 1, 2, 3a, and 4a in toluene contained mesoporosity with surface areas of 10, 230, 106, and 270 m2 g-1, respectively. Despite the high surface areas for most samples, these xerogels contain MO3 domains. Complexes 1 and 2 were also used to introduce molybdenum and tungsten sites, respectively, onto mesoporous SBA-15 silica via displacement of the -OSi(OtBu)3 ligand for a siloxyl group from the silica surface. All molybdenum- and tungsten-containing systems were tested as catalysts for the epoxidation of cyclohexene using tert-butyl hydroperoxide (TBHP) or aqueous H2O2 as the oxidant.

  19. Control over the permeation of silica nanoshells by surface-protected etching with water.

    PubMed

    Hu, Yongxing; Zhang, Qiao; Goebl, James; Zhang, Tierui; Yin, Yadong

    2010-10-14

    We demonstrate a water-based etching strategy for converting solid silica shells into porous ones with controllable permeability. It overcomes the challenges of the alkaline-based surface-protected etching process that we previously developed for the production of porous and hollow silica nanostructures. Mild etching around the boiling point of water partially breaks the imperfectly condensed silica network and forms soluble monosilicic acid, eventually producing mesoscale pores in the silica structures. With the surface protection from poly(vinyl pyrrolidone) (PVP), it is possible to maintain the overall shape of the silica structures while at the same time to create porosity inside. By using bulky PVP molecules which only protect the near-surface region, we are able to completely remove the interior silica and produce hollow particles. Because the etching is mild and controllable, this process is particularly useful for treating small silica particles or core-shell particles with very thin silica shells for which the alkaline-based etching method has been difficult to control. We demonstrated the precise control of the permeation of the chemical species through the porous silica shells by using a model reaction which involves the etching of Ag encapsulated inside Ag@SiO(2) by a halocarbon. It is expected that the water-based surface-protected etching method can be conveniently extended to the production of various porous silica shells containing functional materials whose diffusion to outside and/or reaction with outside species can be easily controlled.

  20. Nanoporous silica and carbon thin films: Synthesis and characterizations

    NASA Astrophysics Data System (ADS)

    Song, Lingyan

    Mesoporous carbons with different symmetries and mesoporous carbon-silica composites with hexagonal symmetry have been studied previously through polymer templating; however, those studies were only limited to powder materials. Here, by using polymer as a versatile platform, multiple routes including vapor infiltration of preformed templates and cooperative self-assembly were utilized to create nanoporous silica, carbon and carbon-silica composite films with the desired morphologies. Materials of different characteristics were developed and the potential applications were discussed. First, a facile method was investigated for patterning nanoporous silica, polymer and carbon films with structures on the order of ten nanometer, hundred nanometer and micron sizes from self assembly, phase separation and lithographic patterning, respectively. The methodology developed provides a simple, etch-free route to patterning nanoporous films utilizing commercially available materials. To improve the ordering of mesoporous carbon films, mesoporous polymer/carbon films with different symmetries were explored through the evaporation induced self-assembly (EISA) approach with water soluble resol as a carbon precursor and triblock copolymers as templates. Films exhibited well-defined orthorhombic and well-ordered rectangular symmetries after template removal by using two different block copolymers, respectively. The predominant difficulties in fabricating cylindrical mesopores were proposed, and a new composition window for obtaining ordered cylindrical mesopores in carbon films was obtained. A facile approach to improve the robustness of mesoporous polymer/carbon films by the addition of silica to a carbon matrix through the reactive co-assembly of resol and tetraorthosilicate with triblock copolymer template was then explored. The pyrolysis of the resol-silica-triblock copolymer film yielded a porous film with well defined pore size. The addition of silica to the matrix impacted

  1. Materialism.

    PubMed

    Melnyk, Andrew

    2012-05-01

    Materialism is nearly universally assumed by cognitive scientists. Intuitively, materialism says that a person's mental states are nothing over and above his or her material states, while dualism denies this. Philosophers have introduced concepts (e.g., realization and supervenience) to assist in formulating the theses of materialism and dualism with more precision, and distinguished among importantly different versions of each view (e.g., eliminative materialism, substance dualism, and emergentism). They have also clarified the logic of arguments that use empirical findings to support materialism. Finally, they have devised various objections to materialism, objections that therefore serve also as arguments for dualism. These objections typically center around two features of mental states that materialism has had trouble in accommodating. The first feature is intentionality, the property of representing, or being about, objects, properties, and states of affairs external to the mental states. The second feature is phenomenal consciousness, the property possessed by many mental states of there being something it is like for the subject of the mental state to be in that mental state. WIREs Cogn Sci 2012, 3:281-292. doi: 10.1002/wcs.1174 For further resources related to this article, please visit the WIREs website.

  2. Approaches to separations using silica colloidal membranes

    NASA Astrophysics Data System (ADS)

    Ignacio-de Leon, Patricia Anne Argana

    This thesis describes the synthesis and properties of free-standing nanoporous silica colloidal membranes where the molecular transport is controlled on the basis of size, charge, and chiral selectivity. To achieve this, free-standing membranes were prepared from colloidal solutions of silica nanospheres and the nanopore size and surface functionality were varied. First, Au-coated membranes were prepared and the transport of neutral and charged small molecules through Au-coated silica colloidal membranes modified with poly(methacrylic acid) was studied. Polymer length was controlled by polymerization time to produce pH- and ion-responsive brushes inside the nanopores. By monitoring the flux of a diffusing species, it was demonstrated that the polyelectrolyte brush undergoes swelling and collapse when the pH is increased and decreased, respectively. We also observed an expansion and contraction in the absence and presence of counterions, respectively. We also studied the transport of enantiomers of a chiral dye molecule through silica colloidal membranes with attached chiral moieties. We used small molecules and polymers of amino acid derivatives and chiral calixarenes capable of chiral recognition as a result of stereochemically dependent noncovalent interactions with the diffusing molecule. We found that the selectivity remains approximately the same for membranes modified with small molecules and with polymers. This suggests that enantiopermselectivity depends primarily on the strength of noncovalent interactions rather than the availability of recognition sites. Next, the transport of various generations of dendrimers through silica colloidal membranes was studied in a proof-of-concept experiment to demonstrate the size-selectivity of our materials. Smaller dendrimers were found to diffuse faster and selectivity is improved by using smaller nanopores. Finally, the transport of proteins through silica colloidal membranes was studied as a function of nanopore size

  3. A silica gel based method for extracting insect surface hydrocarbons.

    PubMed

    Choe, Dong-Hwan; Ramírez, Santiago R; Tsutsui, Neil D

    2012-02-01

    Here, we describe a novel method for the extraction of insect cuticular hydrocarbons using silica gel, herein referred to as "silica-rubbing". This method permits the selective sampling of external hydrocarbons from insect cuticle surfaces for subsequent analysis using gas chromatography-mass spectrometry (GC-MS). The cuticular hydrocarbons are first adsorbed to silica gel particles by rubbing the cuticle of insect specimens with the materials, and then are subsequently eluted using organic solvents. We compared the cuticular hydrocarbon profiles that resulted from extractions using silica-rubbing and solvent-soaking methods in four ant and one bee species: Linepithema humile, Azteca instabilis, Camponotus floridanus, Pogonomyrmex barbatus (Hymenoptera: Formicidae), and Euglossa dilemma (Hymenoptera: Apidae). We also compared the hydrocarbon profiles of Euglossa dilemma obtained via silica-rubbing and solid phase microextraction (SPME). Comparison of hydrocarbon profiles obtained by different extraction methods indicates that silica rubbing selectively extracts the hydrocarbons that are present on the surface of the cuticular wax layer, without extracting hydrocarbons from internal glands and tissues. Due to its surface specificity, efficiency, and low cost, this new method may be useful for studying the biology of insect cuticular hydrocarbons.

  4. All-silica single-mode optical fiber with photonic crystal cladding

    NASA Astrophysics Data System (ADS)

    Knight, J. C.; Birks, T. A.; Russell, P. St. J.; Atkin, D. M.

    1996-10-01

    We report the fabrication of a new type of consists of a pure silica core surrounded by a silica-air photonic crystal material with a hexagonal symmetry. The fiber supports a single robust low-loss guided mode over a very broad spectral range of at least 458-1550 nm.

  5. Controllable in situ synthesis of magnetite coated silica-core water-dispersible hybrid nanomaterials.

    PubMed

    Qu, Haiou; Tong, Sheng; Song, Kejing; Ma, Hui; Bao, Gang; Pincus, Seth; Zhou, Weilie; O'Connor, Charles

    2013-08-20

    Magnetite nanoparticle coated silica (Fe3O4@SiO2) hybrid nanomaterials hold an important position in the fields of cell imaging and drug delivery. Here we report a large scale synthetic procedure that allows attachment of magnetite nanoparticles onto a silica surface in situ. Many different silica nanomaterials such as Stöber silica nanospheres, mesoporous silica nanoparticles, and hollow silica nanotubes have been coated with a high density layer of water-dispersible magnetite nanoparticles. The size and attachment efficiency of the magnetite nanoparticle can be well tuned by adjusting the precursor concentration and reflux time. The functionalization of Fe3O4@SiO2 nanoparticles with dye molecules and biocompatible polymers impart optical imaging modality and good colloidal stability in either buffer solution or serum. The functionalized materials also exhibited strong potential as negative contrast agents in T2 weighted magnetic resonance imaging.

  6. Recent Advances in Research on the Synthetic Fiber Based Silica Aerogel Nanocomposites

    PubMed Central

    Ślosarczyk, Agnieszka

    2017-01-01

    The presented paper contains a brief review on the synthesis and characterization of silica aerogels and its nanocomposites with nanofibers and fibers based on a literature study over the past twenty years and my own research. Particular attention is focused on carbon fiber-based silica aerogel nanocomposites. Silica aerogel is brittle in nature, therefore, it is necessary to improve this drawback, e.g., by polymer modification or fiber additives. Nevertheless, there are very few articles in the literature devoted to the synthesis of silica aerogel/fiber nanocomposites, especially those focusing on carbon fibers and nanofibers. Carbon fibers are very interesting materials, namely due to their special properties: high conductivity, high mechanical properties in relation to very low bulk densities, high thermal stability, and chemical resistance in the silica aerogel matrix, which can help enhance silica aerogel applications in the future. PMID:28336876

  7. The Optical Properties of Ion Implanted Silica

    NASA Technical Reports Server (NTRS)

    Smith, Cydale C.; Ila, D.; Sarkisov, S.; Williams, E. K.; Poker, D. B.; Hensley, D. K.

    1997-01-01

    We will present our investigation on the change in the optical properties of silica, 'suprasil', after keV through MeV implantation of copper, tin, silver and gold and after annealing. Suprasil-1, name brand of silica glass produced by Hereaus Amerisil, which is chemically pure with well known optical properties. Both linear nonlinear optical properties of the implanted silica were investigated before and after thermal annealing. All implants, except for Sn, showed strong optical absorption bands in agreement with Mie's theory. We have also used Z-scan to measure the strength of the third order nonlinear optical properties of the produced thin films, which is composed of the host material and the metallic nanoclusters. For implants with a measurable optical absorption band we used Doyle's theory and the full width half maximum of the absorption band to calculate the predicted size of the formed nanoclusters at various heat treatment temperatures. These results are compared with those obtained from direct observation using transmission electron microscopic techniques.

  8. Allyl-silica Hybrid Monoliths For Chromatographic Application

    NASA Astrophysics Data System (ADS)

    Guo, Wenjuan

    Column technology continues to be the most investigated topics in the separation world, since the column is the place where the chromatographic separation happens, making it the heart of the separation system. Allyl-silica hybrid monolithic material has been exploited as support material and potential stationary phases for liquid chromatography; the stationary phase anchored to the silica surface by Si-C bond, which is more pH stable than traditional stationary phase. First, nuclear magnetic resonance spectroscopy has been used to study the sol in the synthesis of allyl-silica hybrid monoliths. Allyl-trimethoxysilane (allyl-TrMOS), dimethyldimethoxysilane (DMDMOS) and tetramethoxysilane (TMOS) have been served as co-precursors in the sol-gel synthesis of organo-silica hybrid monolithic columns for liquid chromatography (LC). 29Si nuclear magnetic resonance (NMR) and 1H NMR spectroscopy were employed to monitor reaction profiles for the acid-catalyzed hydrolysis and initial condensation reactions of the individual precursor and the hybrid system. 29Si-NMR has also been used to identify different silane species formed during the reactions. The overall hydrolysis rate has been found to follow the trend DMDMOS > allyl-TrMOS > TMOS, if each precursor is reacted individually (homo-polymerization). Precursors show different hydrolysis rate when reacted together in the hybrid system than they are reacted individually. Cross-condensation products of TMOS and DMDMOS (QD) arise about 10 minutes of initiation of the reaction. The allyl-silica monolithic columns for capillary liquid chromatography can only be prepared in capillaries with 50 im internal diameter with acceptable performance. One of the most prominent problems related to the synthesis of silica monolithic structures is the volume shrinkage. The synthesis of allylfunctionalized silica hybrid monolithic structures has been studied in an attempt to reduce the volume shrinkage during aging, drying and heat treatment

  9. HVI Ballistic Limit Characterization of Fused Silica Thermal Panes

    NASA Technical Reports Server (NTRS)

    Miller, J. E.; Bohl, W. D.; Christiansen, E. L.; Davis, B. A.; Deighton, K. D.

    2015-01-01

    Fused silica window systems are used heavily on crewed reentry vehicles, and they are currently being used on the next generation of US crewed spacecraft, Orion. These systems improve crew situational awareness and comfort, as well as, insulating the reentry critical components of a spacecraft against the intense thermal environments of atmospheric reentry. Additionally, these materials are highly exposed to space environment hazards like solid particle impacts. This paper discusses impact studies up to 10 km/s on a fused silica window system proposed for the Orion spacecraft. A ballistic limit equation that describes the threshold of perforation of a fuse silica pane over a broad range of impact velocities, obliquities and projectile materials is discussed here.

  10. Silica heat shield sizing

    NASA Technical Reports Server (NTRS)

    Ebbesmeyer, L. H.; Christensen, H. E.

    1975-01-01

    The sensitivity of silica heat shield requirements to gap width, tile edge radius, and heat transfer distribution within tile gaps was investigated. A two-dimensional thermal model was modified and used to determine the effect of two dimensional heat transfer distributions at high temperature reusable surface insulation edges on shuttle thermal protection system (TPS) requirements. The sensitivity of TPS requirements to coating thickness, emissivity, substructure thickness, and changes in gap heating for several locations on shuttle was also studied. An inverse solution technique was applied to temperature data obtained in the Ames 20 MW turbulent duct in order to examine the effect of tile edge radius on TPS requirements. The derived heating values were then used to predict TPS requirements. Results show that increasing tile radius reduces TPS requirements.

  11. Biofunctionalization of carbon nanostructures through enzyme immobilization in colloidal silica

    NASA Astrophysics Data System (ADS)

    Goulet, Evan M.

    Multi-walled carbon nanotubes (MWNT) and carbon nanopipettes (CNP) provide interesting high aspect ratio scaffolds on which to base functionally gradient materials. In this dissertation, we present a general method for the production of an enzymatically active composite material based on MWNTs. Polyethyleneimine (PEI) was applied to purified MWNTs, generating a positive electrostatic potential on the MWNTs. This positive potential was used to apply negatively charged colloidal silica particle in the presence of a high concentration of enzyme. The silica coating continued to grow via localized condensation of silica particles driven by the buffered saline conditions, immobilizing the enzyme within the coating. The mesoporous nanostructure was characterized via transmission electron microscopy. Optical spectroscopy experiments on the material employed as an active suspension showed that the immobilized enzymes horseradish peroxidase (HRP) and tyrosinase (TV) retained their activity upon incorporation into the material. Using HRP as a model enzyme, it was determined that the MWNT-HRP-Silica material showed similar pH and temperature dependencies in activity to those of free HRP in solution. An examination of the Michaelis-Menten kinetics showed that the material had a slightly higher value of KM than did free HRP. The MWNT-HRP-Silica material was also employed as an active filter membrane, which allowed us to explore the reusable nature of the material. We were able to show the denaturation of the filter due to the loss of Ca2+ cations at low pH and then restore the activity by soaking the filter membrane in 1 mM CaCl2. The MWNT-HRP-Silica material was used to modify a carbon microelectrode and produce a functioning electrochemical sensor for H2O2 . Utilizing cyclic voltammetry, the sensor was shown to have a linear response in limiting current versus concentration of H2O2 of 4.26 pA/microM. We also determined a lower detection limit of 0.67 microM H2O2. CNPs were

  12. Quartz/fused silica chip carriers

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The primary objective of this research and development effort was to develop monolithic microwave integrated circuit (MMIC) packaging which will operate efficiently at millimeter-wave frequencies. The packages incorporated fused silica as the substrate material which was selected due to its favorable electrical properties and potential performance improvement over more conventional materials for Ka-band operation. The first step towards meeting this objective is to develop a package that meets standard mechanical and thermal requirements using fused silica and to be compatible with semiconductor devices operating up to at least 44 GHz. The second step is to modify the package design and add multilayer and multicavity capacity to allow for application specific integrated circuits (ASIC's) to control multiple phase shifters. The final step is to adapt the package design to a phased array module with integral radiating elements. The first task was a continuation of the SBIR Phase 1 work. Phase 1 identified fused silica as a viable substrate material by demonstrating various plating, machining, and adhesion properties. In Phase 2 Task 1, a package was designed and fabricated to validate these findings. Task 2 was to take the next step in packaging and fabricate a multilayer, multichip module (MCM). This package is the predecessor to the phased array module and demonstrates the ability to via fill, circuit print, laminate, and to form vertical interconnects. The final task was to build a phased array module. The radiating elements were to be incorporated into the package instead of connecting to it with wire or ribbon bonds.

  13. New porous polycaprolactone-silica composites for bone regeneration.

    PubMed

    Plazas Bonilla, Clara E; Trujillo, Sara; Demirdögen, Bermali; Perilla, Jairo E; Murat Elcin, Y; Gómez Ribelles, José L

    2014-07-01

    Polycaprolactone porous membranes were obtained by freeze extraction of dioxane from polycaprolactone-dioxane solid solutions. Porosities as high as 90% with interconnected structures were obtained by this technique. A silica phase was synthesized inside the pores of the polymer membrane by sol-gel reaction using tetraethylorthosilicate (TEOS) as a silica precursor and catalyzed in acidic and basic conditions. Two different morphologies of the inorganic phase were obtained depending on the type of catalyst. In acid catalyzed sol-gel reaction, a homogeneous layer of silica was deposited on the pores, and discrete microspheres were synthesized on the pore walls when a basic catalyst was used. The morphology of the inorganic phase influenced the mechanical and thermal behavior, as well as the hydrophilic character of the composites. Bioactivity of the porous materials was tested in vitro by measuring the deposition of hydroxyapatite on the surfaces of the porous composite membranes. Polycaprolactone/silica composites revealed a superior bioactivity performance compared with that of the pure polymer; evidenced by the characteristic cauliflower structures on the material surface, increase in weight and Ca/P ratio of the hydroxyapatite layer. Also, the acid catalyzed composites presented better bioactivity than the base catalyzed composites, evidencing the importance in the morphology of the silica phase.

  14. Site-specific interactions of Cu(II) with alpha and beta-synuclein: bridging the molecular gap between metal binding and aggregation.

    PubMed

    Binolfi, Andrés; Lamberto, Gonzalo R; Duran, Rosario; Quintanar, Liliana; Bertoncini, Carlos W; Souza, Jose M; Cerveñansky, Carlos; Zweckstetter, Markus; Griesinger, Christian; Fernández, Claudio O

    2008-09-03

    The aggregation of alpha-synuclein (AS) is a critical step in the etiology of Parkinson's disease (PD) and other neurodegenerative synucleinopathies. Protein-metal interactions play a critical role in AS aggregation and might represent the link between the pathological processes of protein aggregation and oxidative damage. Our previous studies established a hierarchy in AS-metal ion interactions, where Cu(II) binds specifically to the protein and triggers its aggregation under conditions that might be relevant for the development of PD. In this work, we have addressed unresolved structural details related to the binding specificity of Cu(II) through the design of site-directed and domain-truncated mutants of AS and by the characterization of the metal-binding features of its natural homologue beta-synuclein (BS). The structural properties of the Cu(II) complexes were determined by the combined application of nuclear magnetic resonance, electron paramagnetic resonance, UV-vis, circular dichroism spectroscopy, and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). Two independent, noninteracting copper-binding sites with significantly different affinities for the metal ion were detected in the N-terminal regions of AS and BS. MALDI MS provided unique evidence for the direct involvement of Met1 as the primary anchoring residue for Cu(II) in both proteins. Comparative spectroscopic analysis of the two proteins allowed us to deconvolute the Cu(II) binding modes and unequivocally assign the higher-affinity site to the N-terminal amino group of Met1 and the lower-affinity site to the imidazol ring of the sole His residue. Through the use of competitive chelators, the affinity of the first equivalent of bound Cu(II) was accurately determined to be in the submicromolar range for both AS and BS. Our results prove that Cu(II) binding in the C-terminal region of synucleins represents a nonspecific, very low affinity process. These new insights into the

  15. The Predicted Metal-Binding Region of the Arterivirus Helicase Protein Is Involved in Subgenomic mRNA Synthesis, Genome Replication, and Virion Biogenesis

    PubMed Central

    van Dinten, Leonie C.; van Tol, Hans; Gorbalenya, Alexander E.; Snijder, Eric J.

    2000-01-01

    Equine arteritis virus (EAV), the prototype Arterivirus, is a positive-stranded RNA virus that expresses its replicase in the form of two large polyproteins of 1,727 and 3,175 amino acids. The functional replicase subunits (nonstructural proteins), which drive EAV genome replication and subgenomic mRNA transcription, are generated by extensive proteolytic processing. Subgenomic mRNA transcription involves an unusual discontinuous step and generates the mRNAs for structural protein expression. Previously, the phenotype of mutant EAV030F, which carries a single replicase point mutation (Ser-2429→Pro), had implicated the nsp10 replicase subunit (51 kDa) in viral RNA synthesis, and in particular in subgenomic mRNA transcription. nsp10 contains an N-terminal (putative) metal-binding domain (MBD), located just upstream of the Ser-2429→Pro mutation, and a helicase activity in its C-terminal part. We have now analyzed the N-terminal domain of nsp10 in considerable detail. A total of 38 mutants, most of them carrying specific single point mutations, were tested in the context of an EAV infectious cDNA clone. Variable effects on viral genome replication and subgenomic mRNA transcription were observed. In general, our results indicated that the MBD region, and in particular a set of 13 conserved Cys and His residues that are assumed to be involved in zinc binding, is essential for viral RNA synthesis. On the basis of these data and comparative sequence analyses, we postulate that the MBD may employ a rather unusual mode of zinc binding that could result in the association of up to four zinc cations with this domain. The region containing residue Ser-2429 may play the role of “hinge spacer,” which connects the MBD to the rest of nsp10. Several mutations in this region specifically affected subgenomic mRNA synthesis. Furthermore, one of the MBD mutants was replication and transcription competent but did not produce infectious progeny virus. This suggests that nsp10 is

  16. Prediction of rigid silica based insulation conductivity

    NASA Technical Reports Server (NTRS)

    Williams, Stanley D.; Curry, Donald M.

    1993-01-01

    A method is presented for predicting the thermal conductivity of low density, silica based fibrous insulators. It is shown that the method can be used to extend data values to the upper material temperature limits from those obtained from the test data. It is demonstrated that once the conductivity is accurately determined by the analytical model the conductivity for other atmospheres can be predicted. The method is similar to that presented by previous investigators, but differs significantly in the contribution due to gas and internal radiation.

  17. Modulation of microporous/mesoporous structures in self-templated cobalt-silica

    PubMed Central

    Martens, Dana L.; Wang, David K.; Motuzas, Julius; Smart, Simon; da Costa, João C. Diniz

    2015-01-01

    Finite control of pore size distributions is a highly desired attribute when producing porous materials. While many methodologies strive to produce such materials through one-pot strategies, oftentimes the pore structure requires post-treatment modification. In this study, modulation of pore size in cobalt-silica systems was investigated by a novel, non-destructive, self-templated method. These systems were produced from two cobalt-containing silica starting materials which differed by extent of condensation. These starting materials, sol (SG′) and xerogel (XG′), were mixed with pure silica sol to produce materials containing 5–40 mol% Co. The resultant SG-series materials exhibited typical attributes for cobalt-silica systems: mesoporous characteristics developed at high cobalt concentrations, coinciding with Co3O4 formation; whereas, in the XG-series materials, these mesoporous characteristics were extensively suppressed. Based on an examination of the resultant materials a mechanism describing the pore size formation and modulation of the two systems was proposed. Pore size modulation in the XG-series was caused, in part, by the cobalt source acting as an autogenous template for the condensation of the silica network. These domains could be modified when wetted, allowing for the infiltration and subsequent condensation of silica oligomers into the pre-formed, mesoporous cages, leading to a reduction in the mesoporous content of the final product. PMID:25609189

  18. Immobilization of enzymes on porous silicas--benefits and challenges.

    PubMed

    Hartmann, Martin; Kostrov, Xenia

    2013-08-07

    Porous silica materials have extensively been used for the immobilization of enzymes aiming at their use as biocatalysts or biosensors. This tutorial review will discuss the benefits and challenges of different immobilization techniques and will provide references to recent papers for further reading. Moreover, novel trends and unsolved problems will be introduced.

  19. Toughening Mechanisms in Silica-Filled Epoxy Nanocomposites

    NASA Astrophysics Data System (ADS)

    Patel, Binay S.

    Epoxies are widely used as underfill resins throughout the microelectronics industry to mechanically couple and protect various components of flip-chip assemblies. Generally rigid materials largely surround underfill resins. Improving the mechanical and thermal properties of epoxy resins to better match those of their rigid counterparts can help extend the service lifetime of flip-chip assemblies. Recently, researchers have demonstrated that silica nanoparticles are effective toughening agents for lightly-crosslinked epoxies. Improvements in the fracture toughness of silica-filled epoxy nanocomposites have primarily been attributed to two toughening mechanisms: particle debonding with subsequent void growth and matrix shear banding. Various attempts have been made to model the contribution of these toughening mechanisms to the overall fracture energy observed in silica-filled epoxy nanocomposites. However, disparities still exist between experimental and modeled fracture energy results. In this dissertation, the thermal, rheological and mechanical behavior of eight different types of silica-filled epoxy nanocomposites was investigated. Each nanocomposite consisted of up to 10 vol% of silica nanoparticles with particle sizes ranging from 20 nm to 200 nm, with a variety of surface treatments and particle structures. Fractographical analysis was conducted with new experimental approaches in order to accurately identify morphological evidence for each proposed toughening mechanism. Overall, three major insights into the fracture behavior of real world silica-filled epoxy nanocomposites were established. First, microcracking was observed as an essential toughening mechanism in silica-filled epoxy nanocomposites. Microcracking was observed on the surface and subsurface of fractured samples in each type of silica-filled epoxy nanocomposite. The additional toughening contribution of microcracking to overall fracture energy yielded excellent agreement between experimental

  20. Silica particles cause NADPH oxidase–independent ROS generation and transient phagolysosomal leakage

    PubMed Central

    Joshi, Gaurav N.; Goetjen, Alexandra M.; Knecht, David A.

    2015-01-01

    Chronic inhalation of silica particles causes lung fibrosis and silicosis. Silica taken up by alveolar macrophages causes phagolysosomal membrane damage and leakage of lysosomal material into the cytoplasm to initiate apoptosis. We investigated the role of reactive oxygen species (ROS) in this membrane damage by studying the spatiotemporal generation of ROS. In macrophages, ROS generated by NADPH oxidase 2 (NOX2) was detected in phagolysosomes containing either silica particles or nontoxic latex particles. ROS was only detected in the cytoplasm of cells treated with silica and appeared in parallel with an increase in phagosomal ROS, as well as several hours later associated with mitochondrial production of ROS late in apoptosis. Pharmacological inhibition of NOX activity did not prevent silica-induced phagolysosomal leakage but delayed it. In Cos7 cells, which do not express NOX2, ROS was detected in silica-containing phagolysosomes that leaked. ROS was not detected in phagolysosomes containing latex particles. Leakage of silica-containing phagolysosomes in both cell types was transient, and after resealing of the membrane, endolysosomal fusion continued. These results demonstrate that silica particles can generate phagosomal ROS independent of NOX activity, and we propose that this silica-generated ROS can cause phagolysosomal leakage to initiate apoptosis. PMID:26202463

  1. Removing Dissolved Silica from Waste Water with Catechol and Active Carbon

    SciTech Connect

    Sasan, Koroush; Brady, Patrick; Krumhansl, James L.; Nenoff, Tina M.

    2017-01-01

    Fresh water scarcity is going to be a global great challenge in the near future because of the increasing population. Our water resources are limited and, hence, water treatment and recycling methods are the only alternatives for fresh water procurement in the upcoming decades. Water treatment and recycling methods serve to remove harmful or problematic constituents from ground, surface and waste waters prior to its consumption, industrial supply, or other uses. Scale formation in industrial and domestic installations is still an important problem during water treatment. In water treatment, silica scaling is a real and constant concern for plant operations. The focus of this study is on the viability of using a combination of catechol and active carbon to remove dissolved silica from concentrated cooling tower water (CCTW). Various analytical methods, such as ICP-MS and UV-vis, were used to understand the structure-property relationship between the material and the silica removal results. UV-Vis indicates that catechol can react with silica ions and form a silica-catecholate complex. The speciation calculation of catechol and silica shows that catechol and silica bind in the pH range of 8 – 10; there is no evidence of linkage between them in neutral and acidic pHs. The silica removal results indicate that using ~4g/L of catechol and 10g/L active carbon removes up to 50% of the dissolved silica from the CCTW.

  2. Pressure-Induced Transformations in Silica

    NASA Astrophysics Data System (ADS)

    Kingma, Kathleen Jane

    Polymorphic phase transitions in the silica minerals alpha-quartz and stishovite have been investigated using diamond-anvil cell techniques at room temperature. Structural and vibrational properties of these materials were monitored as a function of pressure using in situ Raman scattering, synchrotron x-ray diffraction, and optical microscopy. Pressure-quenched samples were characterized at ambient conditions using Raman spectroscopy, electron diffraction, transmission electron microscopy, backscattered and secondary electron imaging, and optical microscopy. Solid-state amorphization of alpha -quartz has been found to begin with formation of crystallographically controlled planar defects, followed by growth of amorphous silica at these defect sites. Characteristic microstructures (planar defects and amorphous lamellae) are found in quartz upon quasihydrostatic and nonhydrostatic compression and from comminution, suggesting that there is a common mechanism for solid-state amorphization of silicates in static and shock compression experiments, meteorite impact, and deformation by tectonic processes. A new crystalline-crystalline transformation has been discovered in alpha-quartz at 21 GPa, documented by abrupt changes in the synchrotron x-ray diffraction pattern and the Raman spectrum. Upon decompression, the high-pressure phase reverts to a quartz -like structure in an unusual twinned state. The Raman spectrum of samples recovered from hydrostatic compression closely resembles spectra of both dynamically shocked quartz and quartz that has experienced extensive grinding; each shows significant deviations from the spectrum of pristine quartz. The transformation from rutile-structured silica (stishovite) to the CaCl_2-structured form has been documented by high-pressure Raman scattering at 51 GPa. At this pressure, the pressure dependence of the soft B_{1rm g} vibrational mode changes sign, and the stishovite E _{rm g} mode splits, as predicted for the transformation

  3. Elastic Phase Response of Silica Nanoparticles Buried in Soft Matter

    SciTech Connect

    Tetard, Laurene; Passian, Ali; Lynch, Rachel M; Voy, Brynn H; Shekhawat, Gajendra; Dravid, Vinayak; Thundat, Thomas George

    2008-01-01

    Tracking the uptake of nanomaterials by living cells is an important component in assessing both potential toxicity and in designing future materials for use in vivo. We show that the difference in the local elasticity at the site of silica (SiO{sub 2}) nanoparticles confined within a macrophage enables functional ultrasonic interactions. By elastically exciting the cell, a phase perturbation caused by the buried SiO{sub 2} nanoparticles was detected and used to map the subsurface populations of nanoparticles. Localization and mapping of stiff chemically synthesized silica nanoparticles within the cellular structures of a macrophage are important in basic as well as applied studies.

  4. Multifunctional clickable and protein-repellent magnetic silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Estupiñán, Diego; Bannwarth, Markus B.; Mylon, Steven E.; Landfester, Katharina; Muñoz-Espí, Rafael; Crespy, Daniel

    2016-01-01

    Silica nanoparticles are versatile materials whose physicochemical surface properties can be precisely adjusted. Because it is possible to combine several functionalities in a single carrier, silica-based materials are excellent candidates for biomedical applications. However, the functionality of the nanoparticles can get lost upon exposure to biological media due to uncontrolled biomolecule adsorption. Therefore, it is important to develop strategies that reduce non-specific protein-particle interactions without losing the introduced surface functionality. Herein, organosilane chemistry is employed to produce magnetic silica nanoparticles bearing differing amounts of amino and alkene functional groups on their surface as orthogonally addressable chemical functionalities. Simultaneously, a short-chain zwitterion is added to decrease the non-specific adsorption of biomolecules on the nanoparticles surface. The multifunctional particles display reduced protein adsorption after incubation in undiluted fetal bovine serum as well as in single protein solutions (serum albumin and lysozyme). Besides, the particles retain their capacity to selectively react with biomolecules. Thus, they can be covalently bio-functionalized with an antibody by means of orthogonal click reactions. These features make the described multifunctional silica nanoparticles a promising system for the study of surface interactions with biomolecules, targeting, and bio-sensing.Silica nanoparticles are versatile materials whose physicochemical surface properties can be precisely adjusted. Because it is possible to combine several functionalities in a single carrier, silica-based materials are excellent candidates for biomedical applications. However, the functionality of the nanoparticles can get lost upon exposure to biological media due to uncontrolled biomolecule adsorption. Therefore, it is important to develop strategies that reduce non-specific protein-particle interactions without losing the

  5. Evaluation of silica nanoparticle binding to major human blood proteins

    NASA Astrophysics Data System (ADS)

    Hata, Katsutomo; Higashisaka, Kazuma; Nagano, Kazuya; Mukai, Yohei; Kamada, Haruhiko; Tsunoda, Shin-ichi; Yoshioka, Yasuo; Tsutsumi, Yasuo

    2014-12-01

    Nanomaterials are used for various biomedical applications because they are often more effective than conventional materials. Recently, however, it has become clear that the protein corona that forms on the surface of nanomaterials when they make contact with biological fluids, such as blood, influences the pharmacokinetics and biological responses induced by the nanomaterials. Therefore, when evaluating nanomaterial safety and efficacy, it is important to analyze the interaction between nanomaterials and proteins in biological fluids and to evaluate the effects of the protein corona. Here, we evaluated the interaction of silica nanoparticles, a commonly used nanomaterial, with the human blood proteins albumin, transferrin, fibrinogen, and IgG. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that the amount of albumin, transferrin, and IgG binding to the silica particles increased as the particle size decreased under conditions where the silica particle mass remained the same. However, under conditions in which the specific surface area remained constant, there were no differences in the binding of human plasma proteins to the silica particles tested, suggesting that the binding of silica particles with human plasma proteins is dependent on the specific surface area of the silica particles. Furthermore, the amount of albumin, transferrin, and IgG binding to silica nanoparticles with a diameter of 70 nm (nSP70) and a functional amino group was lower than that with unmodified nSP70, although there was no difference in the binding between nSP70 with the surface modification of a carboxyl functional group and nSP70. These results suggest that the characteristics of nanomaterials are important for binding with human blood proteins; this information may contribute to the development of safe and effective nanomaterials.

  6. Using Nucleation Theory to Understand the Dissolution Kinetics of Vitreous and Biogenic Silica: The Paradox of the Silica Polymorphs

    NASA Astrophysics Data System (ADS)

    Han, N.; de Yoreo, J. J.; Wallace, A. F.; Dove, P. M.

    2006-12-01

    Recent studies of the global biogeochemistry are refocusing on the demineralization kinetics of biogenic silicas—amorphous silicas produced by marine phytoplankton, sponges and terrestrial plants. Amorphous silica lacks the crystalline order that can be studied with classical terrace, ledge, and kink-based models of crystal growth and dissolution. Despite variations in Si-O-Si bond lengths and angles, all of these materials share the same fundamental chemical unit, silica tetrahedron. Silica tetrahedra on quartz surfaces have distinct hydration chemistries with two predominant types of sites available for reaction with water: gamma species have a higher degree of connectivity with the mineral surface via binding to three bridging oxygens while beta groups are bonded to two bridging oxygens. Surface groups of amorphous silica have the same coordinations as gamma and beta species in quartz. Support for the idea that crystalline and amorphous SiO2 exhibit similar dissolution and growth reaction pathways are found in rate data reported for the synthetic and biogenic amorphous silicas and quartz. Previous studies show that the `bulk' rate of silica production by quartz and amorphous silica is enhanced 50- 100 fold when alkaline or alkaline earth cations are introduced to otherwise pure solutions. Our recent study of quartz dissolution found this `salt effect' arises by a transition from dissolution at preexisting step edges and dislocation defects (detachment of beta species) to the homogeneous nucleation of vacancy islands across the entire surface (plucking of gamma species) in CaCl2 and NaCl solutions. This transition to homogeneous nucleation results in an exponential dependence of quartz dissolution rate on increasing chemical driving force (undersaturation) that is explained by the classical nucleation theory that was developed for crystal growth. We pose the question of why amorphous silica should also be enhanced 100-fold by electrolytes. From a mechanistic

  7. New support for high-performance liquid chromatography based on silica coated with alumina particles.

    PubMed

    Silveira, José Leandro R; Dib, Samia R; Faria, Anizio M

    2014-01-01

    A new material based on silica coated with alumina nanoparticles was proposed for use as a chromatographic support for reversed-phase high-performance liquid chromatography. Alumina nanoparticles were synthesized by a sol-gel process in reversed micelles composed of sodium bis(2-ethylhexyl)sulfosuccinate, and the support material was formed by the self-assembly of alumina layers on silica spheres. Spectroscopic and (29)Si nuclear magnetic resonance results showed evidence of chemical bonds between the alumina nanoparticles and the silica spheres, while morphological characterizations showed that the aluminized silica maintained the morphological properties of silica desired for chromatographic purposes after alumina incorporation. Stability studies indicated that bare silica showed high dissolution (~83%), while the aluminized silica remained practically unchanged (99%) after passing one liter of the alkaline mobile phase, indicating high stability under alkaline conditions. The C18 bonded aluminized silica phase showed great potential for use in high-performance liquid chromatography to separate basic molecules in the reversed-phase mode.

  8. Environmentally-Friendly Geopolymeric Binders Made with Silica

    NASA Astrophysics Data System (ADS)

    Erdogan, S. T.

    2013-12-01

    Portland cement (PC) is the ubiquitous binding material for constructions works. It is a big contributor to global warming and climate change since its production is responsible for 5-10 % of all anthropogenic CO2 emissions. Half of this emission arises from the calcination of calcareous raw materials and half from kiln fuel burning and cement clinker grinding. Recently there have been efforts to develop alternative binders with lower greenhouse gas emissions. One such class of binders is geopolymers, formed by activating natural or waste materials with suitable alkaline or acidic solutions. These binders use natural or industrial waste raw materials with a very low CO2 footprint from grinding of the starting materials, and some from the production of the activating chemicals. The total CO2 emissions from carefully formulated mixtures can be as low as 1/10th - 1/5th of those of PC concrete mixtures with comparable properties. While use of industrial wastes as raw materials is environmentally preferable, the variability of their chemical compositions over time renders their use difficult. Use of natural materials depletes resources but can have more consistent properties and can be more easily accepted. Silica sand is a natural material containing very high amounts of quartz. Silica fume is a very fine waste from silicon metal production that is mostly non-crystalline silica. This study describes the use of sodium hydroxide and sodium silicate solutions to yield mortars with mechanical properties comparable to those of portland cement mortars and with better chemical and thermal durability. Strength gain is slower than with PC mixtures at room temperature but adequate ultimate strength can be achieved with curing at slightly elevated temperatures in less than 24 h. The consistency of the chemical compositions of these materials and their abundance in several large, developing countries makes silica attractive for producing sustainable concretes with reduced carbon

  9. Characterization of Ca(2+)-binding sites in the kidney stone inhibitor glycoprotein nephrocalcin using vanadyl ions: different metal binding properties in strong and weak inhibitor proteins revealed by EPR and ENDOR.

    PubMed

    Mustafi, D; Nakagawa, Y

    1996-11-26

    Nephrocalcin (NC), a calcium-binding glycoprotein of 14,000 molecular weight as a monomer, is known to inhibit the growth of calcium oxalate monohydrate (COM) crystals in renal tubules. We have isolated NC from bovine kidney tissue and purified into four isoforms, fractions A-D. NC-A and NC-B strongly inhibit the growth of COM crystals, and NC-C and NC-D inhibit crystal growth weakly. The strongly inhibitor proteins are abundant in normal subjects, whereas stone formers excrete less of NC-A and NC-B and more of NC-C and NC-D. NC-C was characterized with respect to its metal binding sites by using vanadyl ion (VO2+) as a paramagnetic probe in electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopic studies. We demonstrated that VO2+ binds to NC-C with a stoichiometry of metal:protein binding of 4:1 and that VO2+ competes with Ca2+ in binding to NC-C. In NC-C, the metal ion is exposed to solvent water molecules and two water molecules are detected in the inner coordination sphere of the metal ion by ENDOR. In the metal binding environment of NC-A, as reported previously (Mustafi, D., & Nakagawa, Y. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 11323-11327), inner sphere coordinated water is completely excluded. Based on the results of the metal binding properties in both strong and weak inhibitor proteins, a probable mechanism of inhibition of COM crystal growth by NC has been outlined.

  10. Hierarchical control of porous silica by pH adjustment: Alkyl polyamines as surfactants for bimodal silica synthesis and its carbon replica

    SciTech Connect

    Abellan, G.; Carrillo, A.I.; Linares, N.; Serrano, E.

    2009-08-15

    Bimodal macro-mesoporous silica networks have been prepared in a simple one-pot synthesis using an inexpensive tetramine surfactant and tetraethoxysilane as a silica precursor. These novel materials show high pore volumes and templated mesopores (average pore size 3.0 nm) embedded in 20 nm thick walls forming interparticle large meso/macropores. The judicious control of the pH during the silica formation allows for the precise control of the interparticle condensation, likely due to the change in the interaction between the tetramine surfactant and the silica precursors. Finally, a highly porous carbon replica with bimodal porosity was prepared by using the bimodal silica as a hard sacrificial template. The microstructure of the silica template was accurately transferred to the carbon material obtaining high surface areas (up to 1300 m{sup 2} g{sup -1}) and total pore volumes >=2 cm{sup 3} g{sup -1}. - Graphical abstract: Hierarchical bimodal porous silica and its carbon replica prepared by nanocasting.

  11. Thermal conductivity of silica nanoparticle powder: Measurement and theoretical analysis

    NASA Astrophysics Data System (ADS)

    Huang, Congliang; Lin, Zizhen; Feng, Yanhui; Zhang, Xinxin; Wang, Ge

    2015-12-01

    The hot-wire method was applied to experimentally determine the thermal conductivity (TC) of a silica nanoparticle powder. A fitting model was further employed to analyze the experimental results and to predict the TC over a wider porosity scale. Results show that the effective TC of the silica-nanoparticle powder can be less than that of free air because of the low TC of both the silica nanoparticles and the air confined in the pore spaces; the relative contribution of the nanoparticle TC, the confined air TC, and the radiation heat transfer coefficient to the effective TC will significantly affect at which porosity the extreme value of the effective TC occurs; the porosity obtained when the contribution to the effective TC of the confined air equals that of the nanoparticles is the most favorable for constructing thermal insulation materials.

  12. Evaluating Dimethyldiethoxysilane for use in Polyurethane Crosslinked Silica Aerogels

    NASA Technical Reports Server (NTRS)

    Randall, Jason P.; Meador, Mary Ann B.; Jana, Sadhan C.

    2008-01-01

    Silica aerogels are highly porous materials which exhibit exceptionally low density and thermal conductivity. Their "pearl necklace" nanostructure, however, is inherently weak; most silica aerogels are brittle and fragile. The strength of aerogels can be improved by employing an additional crosslinking step using isocyanates. In this work, dimethyldiethoxysilane (DMDES) is evaluated for use in the silane backbone of polyurethane crosslinked aerogels. Approximately half of the resulting aerogels exhibited a core/shell morphology of hard crosslinked aerogel surrounding a softer, uncrosslinked center. Solid state NMR and scanning electron microscopy results indicate the DMDES incorporated itself as a conformal coating around the outside of the secondary silica particles, in much the same manner as isocyanate crosslinking. Response surface curves were generated from compression data, indicating levels of reinforcement comparable to that in previous literature, despite the core/shell morphology.

  13. Enhanced characteristics of fused silica fibers using laser polishing

    NASA Astrophysics Data System (ADS)

    Heptonstall, A.; Barton, M. A.; Bell, A. S.; Bohn, A.; Cagnoli, G.; Cumming, A.; Grant, A.; Gustafson, E.; Hammond, G. D.; Hough, J.; Jones, R.; Kumar, R.; Lee, K.; Martin, I. W.; Robertson, N. A.; Rowan, S.; Strain, K. A.; Tokmakov, K. V.

    2014-05-01

    The search for gravitational wave signals from astrophysical sources has led to the current work to upgrade the two largest of the long-baseline laser interferometers, the LIGO detectors. The first fused silica mirror suspensions for the Advanced LIGO gravitational wave detectors have been installed at the LIGO Hanford and Livingston sites. These quadruple pendulums use synthetic fused silica fibers produced using a CO2 laser pulling machine to reduce thermal noise in the final suspension stage. The suspension thermal noise in Advanced LIGO is predicted to be limited by internal damping in the surface layer of the fibers, damping in the weld regions, and the strength of the fibers. We present here a new method for increasing the fracture strength of fused silica fibers by laser polishing of the stock material from which they are produced. We also show measurements of mechanical loss in laser polished fibers, showing a reduction of 30% in internal damping in the surface layer.

  14. Mesoporous silica and organosilica films templated by nanocrystalline chitin.

    PubMed

    Nguyen, Thanh-Dinh; Shopsowitz, Kevin E; MacLachlan, Mark J

    2013-11-04

    Liquid crystalline phases can be used to impart order into inorganic solids, creating materials that mimic natural architectures. Herein, mesoporous silica and organosilica films with layered structures and high surface areas have been templated by nanocrystalline chitin. Aqueous suspensions of spindle-shaped chitin nanocrystals were prepared by sequential deacetylation and hydrolysis of chitin fibrils isolated from king crab shells. The nanocrystalline chitin self-assembles into a nematic liquid-crystalline phase that has been used to template silica and organosilica composites. Removal of the chitin template by either calcination or sulfuric-acid-catalyzed hydrolysis gave mesoporous silica and ethylene-bridged organosilica films. The large, crack-free mesoporous films have layered structures with features that originate from the nematic organization of the nanocrystalline chitin.

  15. High Resolution, Single-Step Patterning of Silica Aerogels

    NASA Technical Reports Server (NTRS)

    Bertino, M. F.; Hund, J. F.; Sosa, J.; Zhang, G.; Sotiriou-Leventis, C.; Leventis, N.; Tokuhiro, A. T.; Terry, J.

    2003-01-01

    Three-dimensional metallic structures are fabricated with high spatial resolution in silica aerogels. In our method, silica hydrogels are prepared with a standard base-catalyzed route, and exchanged with an aqueous solution typically containing Ag' ions (1 M) and 2-propanol (0.2 M). The metal ions are reduced photolytically with a table-top ultraviolet lamp, or radiolytically, with a focused X-ray beam. We fabricated dots and lines as small as 30 x 70 km, protruding for several mm into the bulk of the materials. The hydrogels are eventually supercritically dried to yield aerogels, without any measurable change in the shape and spatial resolution of the lithographed structures. Transmission electron microscopy shows that illuminated regions are composed of Ag clusters with a size of several pm, separated by thin layers of silica.

  16. Supercontinuum generation in non-silica fibers

    NASA Astrophysics Data System (ADS)

    Price, Jonathan H. V.; Feng, Xian; Heidt, Alexander M.; Brambilla, Gilberto; Horak, Peter; Poletti, Francesco; Ponzo, Giorgio; Petropoulos, Periklis; Petrovich, Marco; Shi, Jindan; Ibsen, Morten; Loh, Wei H.; Rutt, Harvey N.; Richardson, David J.

    2012-09-01

    The development of super continuum sources is driven by the requirements of a wide range of emerging applications. This paper points out how non-silica fibers are of benefit not only because their broad mid-IR transparency enables continuum generation in the 2-5 μm region but also since the high intrinsic nonlinearity of the glasses reduces the power-threshold for devices at wavelengths below 2 μm. For these glasses, the material zero-dispersion wavelength is typically shifted to long wavelengths compared to silica so dispersion tailoring is key to creating sources based on practical, near-IR, solid state pump lasers. We show how modeling work has produced fiber designs that provide flattened dispersion profiles with high nonlinearity coefficients and zero-dispersion wavelengths in the near-IR. Building on this flexibility, modeling of the pulse dynamics then demonstrates how coherent mid-IR supercontinuum sources could be developed. We also show the importance of the second zero-dispersion wavelength using bismuth fibers as an example. Nonlinear mode-coupling is shown to be a factor in larger core fibers for high-power applications. Demonstrations of supercontinuum in microstructured tellurite fibers, all-solid lead-silicate (SF57) fibers and in bismuth fibers and tapers are then reported to show what has been achieved experimentally using a range of materials and fiber geometries.

  17. Epoxy Crosslinked Silica Aerogels (X-Aerogels)

    NASA Technical Reports Server (NTRS)

    fabrizio, Eve; Ilhan, Faysal; Meador, Mary Ann; Johnston, Chris; Leventis, Nicholas

    2004-01-01

    NASA is interested in the development of strong lightweight materials for the dual role of thermal insulator and structural component for space vehicles; freeing more weight for useful payloads. Aerogels are very-low density materials (0.010 to 0.5 g/cc) that, due to high porosity (meso- and microporosity), can be, depending on the chemical nature of the network, ideal thermal insulators (thermal conductivity approx. 15 mW/mK). However, aerogels are extremely fragile. For practical application of aerogels, one must increase strength without compromising the physical properties attributed to low density. This has been achieved by templated growth of an epoxy polymer layer that crosslinks the "pearl necklace" network of nanoparticles: the framework of a typical silica aerogel. The requirement for conformal accumulation of the epoxy crosslinker is reaction both with the surface of silica and with itself. After cross-linking, the strength of a typical aerogel monolith increases by a factor of 200, in the expense of only a 2-fold increase in density. Strength is increased further by coupling residual unreacted epoxides with diamine.

  18. Mechanical and Thermal Characterization of Silica Nanocomposites

    NASA Astrophysics Data System (ADS)

    Cunningham, Anthony Lamar

    Polymer nanocomposites are a class of materials containing nanoparticles with a large interfacial surface area. Only a small quantity of nanoparticles are needed to provide superior multifunctional properties; such as mechanical, thermal, electrical, and moisture absorption properties in polymers. Nanoparticles tend to agglomerate, so special techniques are required for homogeneous distribution. Nanosilica is now readily available as colloidal sols, for example; Nanopox RTM F400 (supplied by Evonik Nanoresins AG, Germany). The nanoparticles are first synthesized from aqueous sodium silicate solution, and then undergo a surface modification process with organosilane and matrix exchange. F400 contains 40%wt silica nanoparticles colloidally dispersed in a DGEBA epoxy resin. The mean particle diameter is about 20 nm with a narrow distribution range of about 5 to 35 nm. The objectives of this study are to develop a reproducible processing method for nanosilica enhanced resin systems used in the manufacturing of fiber reinforced composites that will be characterized for mechanical and thermal properties. Research has concluded that shows improvements in the properties of the matrix material when processed in loading variations of 0 to 25%wt silica nanoparticles. The loadings were also used to manufacture fiberglass reinforced nanocomposite laminates and also tested for mechanical and thermal properties.

  19. Secondary emission conductivity of high purity silica fabric

    NASA Technical Reports Server (NTRS)

    Belanger, V. J.; Eagles, A. E.

    1977-01-01

    High purity silica fabrics were proposed for use as a material to control the effects of electrostatic charging of satellites at synchronous altitudes. These materials exhibited very quiet behavior when placed in simulated charging environments as opposed to other dielectrics used for passive thermal control which exhibit varying degrees of electrical arcing. Secondary emission conductivity is proposed as a mechanism for this superior behavior. Design of experiments to measure this phenomena and data taken on silica fabrics are discussed as they relate to electrostatic discharge (ESD) control on geosynchronous orbit spacecraft. Studies include the apparent change in resistivity of the material as a function of the electron beam energy, flux intensity, and the effect of varying electric fields impressed across the material under test.

  20. Oxidation and Volatilization of Silica-Formers in Water Vapor

    NASA Technical Reports Server (NTRS)

    Opila, E. J.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    At high temperatures SiC and Si3N4 react with water vapor to form a silica scale. Silica scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming silica and the other removing silica, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved, After steady state is achieved, the oxide found on the surface is a constant thickness and recession of the underlying material occurs at a linear rate. The steady state oxide thickness, the time to achieve steady state, and the steady state recession rate can all be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate can also be determined from parameters that describe a water vapor-containing environment. Accordingly, maps have been developed to show these steady state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of silica formers in water-vapor containing environments such as combustion environments. Finall