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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. [Silica risk in construction industry: an investigation on raw materials].

    PubMed

    Bottai, M; Cini, A; Talini, D; Dini, F; Berti, S; Vincentini, M; Cosentino, E; Taddeo, D

    2007-01-01

    Typical construction activities like demolition, excavation and sanding can expose workers to silica, but there are few investigations carried out with the aim of evaluating the silica content in raw materials used for these activities (mortars, plasters, cement...). Our intervention has been directed in looking for free crystalline silica in samples of raw materials. We have measured the silica content in these materials comparing declared and real composition found in the products. Our intent was to obtain more information about the working activities which expose workers to free crystalline silica in construction industry and to highlight the silica presence in raw materials also when the companies don't declare it, against labeling rules based on Italian law D.lgs 65/03.

  11. 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.

  12. 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.

  13. 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.

  14. Sol-Gel Synthesis of Non-Silica Monolithic Materials

    PubMed Central

    Gaweł, Bartłomiej; Gaweł, Kamila; Øye, Gisle

    2010-01-01

    Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing materials of other oxides than silica. In this review, we present different synthesis methods for inorganic, non-silica monolithic materials. Some examples of application of the materials are also included.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Biotemplated diatom silica-titania materials for air purification.

    PubMed

    Van Eynde, Erik; Tytgat, Tom; Smits, Marianne; Verbruggen, Sammy W; Hauchecorne, Birger; Lenaerts, Silvia

    2013-04-01

    We present a novel manufacture route for silica-titania photocatalysts using the diatom microalga Pinnularia sp. Diatoms self-assemble into porous silica cell walls, called frustules, with periodic micro-, meso- and macroscale features. This unique hierarchical porous structure of the diatom frustule is used as a biotemplate to incorporate titania by a sol-gel methodology. Important material characteristics of the modified diatom frustules under study are morphology, crystallinity, surface area, pore size and optical properties. The produced biosilica-titania material is evaluated towards photocatalytic activity for NOx abatement under UV radiation. This research is the first step to obtain sustainable, well-immobilised silica-titania photocatalysts using diatoms.

  20. Temperature dependent NIR emitting lanthanide-PMO/silica hybrid materials.

    PubMed

    Kaczmarek, Anna M; Esquivel, Dolores; Ouwehand, Judith; Van Der Voort, Pascal; Romero-Salguero, Francisco J; Van Deun, Rik

    2017-06-28

    Two materials - a mesoporous silica (MS) and a periodic mesoporous organosilica (PMO) functionalized with dipyridyl-pyridazine (dppz) units were grafted with near-infrared (NIR) emitting lanthanide (Nd(3+), Er(3+), Yb(3+)) complexes in an attempt to obtain hybrid NIR emitting materials. The parent materials: dppz-vSilica and dppz-ePMO were prepared by a hetero Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (dptz) and the double bonds of either ethenylene-bridged PMO (ePMO) or vinyl-silica (vSilica) and subsequent oxidation. The dppz-vSilica is reported here for the first time. The prepared lanthanide-PMO/silica hybrid materials were studied in depth for their luminescence properties at room temperature and chosen Nd(3+) and Yb(3+) samples also at low temperature (as low as 10 K). We show that both the dppz-vSilica and dppz-ePMO materials can be used as "platforms" for obtaining porous materials showing NIR luminescence. To obtain NIR emission these materials can be excited either in the UV or Vis region (into the π→π* transitions of the ligands or directly into the f-f transitions of the Ln(3+) ions). More interestingly, when functionalized with Nd(3+) or Yb(3+)β-diketonate complexes these materials showed interesting luminescence properties over a wide temperature range (10-360 K). The Yb(3+) materials were investigated for their potential use as ratiometric temperature sensors.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. Metal containing mesoporous silica materials: Synthesis, characterization, and applications

    NASA Astrophysics Data System (ADS)

    Gomez, Sinue

    The work presented here comprises the development of a new route for the incorporation of transition metals (TM = Mn, V, Cr) into the pores of mesoporous silica materials, the characterization, and the applications of the resulting materials. The mesoporous silica material used in this work is of the M41S family, known as MCM-48. The first part of the work is going to be focused on in the incorporation of manganese species. Characterization of the resulting materials will be sub-divided in two major parts: (1) Structural and textural properties and (2) Analysis of the Mn oxidation state, coordination and location in the mesoporous host. The process of incorporation of Mn into the mesoporous materials takes place by using high valence metal precursor anions. Then a mechanism to describe the process of loading the Mn species will be proposed. The method developed makes possible the incorporation of high loadings of transition metals while maintaining the properties of the host material, MCM-48. In the second part of the research the synthesis method developed in the first part is used to incorporate other transition metals such as vanadium and chromium. As in the first part, the nature of the TM species is investigated and their catalytic application in oxidation of styrene is also studied. The materials show good activity towards styrene oxidation with conversions as high as 100%. The catalysts can also be recycled without significant loss of activity. Finally, the last part of the research deals with the incorporation of tin oxide into mesoporous silica. A similar approach to the one used for transition metals was used to load tin in MCM-48, however, discrete tin oxide nanoparticles were formed on the surface of the mesoporous structure rather than inside of the pores. The sensing properties towards reducing gases such as hydrogen of these materials were tested, and the Sn containing mesoporous silica show promising properties for gas sensing applications.

  6. Silica - Boronate affinity material for quick enrichment of intracellular nucleosides.

    PubMed

    Wang, Shuxia; Li, Huihui; Guan, Xiujuan; Cheng, Ting; Zhang, Haixia

    2017-05-01

    Boronic acid modified materials have been widely used to adsorb nucleosides, but their adsorption capacities require further improvement. Most cis-diol containing biomolecules are in very low abundance along with interfering components in real samples, and need to be enriched specially. In this study, we synthesize a kind of silica absorbent modified with boronic acid derivative, using amorphous silica as raw material and obtaining high adsorption capacity for adenosine. In addition, the adsorption equilibrium can be completed within 10s and 1min for the desorption. Finally, the material was successfully applied to enrich nucleosides from cells and the spiked recoveries were found between 82.21% and 118.9%. The results showed that the prepared adsorbent has potential to effectively enrich cis-diol substances from cell samples. Copyright © 2017 Elsevier B.V. All rights reserved.

  7. 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

  8. 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.

  9. Self-Assembly in Biosilicification and Biotemplated Silica Materials.

    PubMed

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

    2014-09-04

    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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Preferred Metal Binding Site of Aniline

    NASA Astrophysics Data System (ADS)

    Kumari, Sudesh; Sohnlein, Brad; Yang, Dong-Sheng

    2012-06-01

    Group III metal-aniline complexes, M-aniline (M = Sc, Y, and La), were produced by interactions between laser-vaporized metal atoms and aniline vapor in a pulsed molecular beam source, identified by photoionization time-of-flight mass spectrometry, and studied by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and density functional theory calculations. Adiabatic ionization energies and several vibrational intervals were measured from the ZEKE spectra. Metal binding sites and electronic states were determined by combining the ZEKE measurements and theoretical calculations. Although aniline has various possible sites for metal coordination, the preferred site was determined to be phenyl ring. The metal binding with the phenyl ring yields syn and anti conformers. In these conformers, the neutral complexes are in doublet ground states and the corresponding singly charged cations in singlet states.

  18. 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.

  19. 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.

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

    SciTech Connect

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

    2016-07-25

    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: SiO{sub 2} + 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.

  1. 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

  2. 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

  3. 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.

  4. Helium ion microscopy: a new tool for imaging novel mesoporous silica and organosilica materials.

    PubMed

    Terpstra, Andrea S; Shopsowitz, Kevin E; Gregory, Camille F; Manning, Alan P; Michal, Carl A; Hamad, Wadood Y; Yang, Jijin; MacLachlan, Mark J

    2013-02-25

    Helium ion microscopy (HIM) has been used to image mesoporous silica and organosilica for the first time. Images of chiral nematic silica, ethylenesilica, and new benzenesilica reveal the structural organization, pore dimensions and connectivity of these materials on the nanometer length scale.

  5. 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.

  6. Silica materials with wall-embedded nitroxides provide efficient polarization matrices for dynamic nuclear polarization NMR.

    PubMed

    Besson, Eric; Ziarelli, Fabio; Bloch, Emily; Gerbaud, Guillaume; Queyroy, Séverine; Viel, Stéphane; Gastaldi, Stéphane

    2016-04-25

    Hybrid mesoporous silica materials with wall-embedded nitroxides are shown to efficiently polarize impregnated substrates in high-field dynamic nuclear polarization magic-angle spinning solid-state NMR experiments.

  7. 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.

  8. Study of silica sol-gel materials for sensor development

    NASA Astrophysics Data System (ADS)

    Lei, Qiong

    Silica sol-gel is a transparent, highly porous silicon oxide glass made at room temperature by sol-gel process. The name of silica sol-gel comes from the observable physical phase transition from liquid sol to solid gel during its preparation. Silica sol-gel is chemically inert, thermally stable, and photostable, it can be fabricated into different desired shapes during or after gelation, and its porous structure allows encapsulation of guest molecules either before or after gelation while still retaining their functions and sensitivities to surrounding environments. All those distinctive features make silica sol-gel ideal for sensor development. Study of guest-host interactions in silica sol-gel is important for silica-based sensor development, because it helps to tailor local environments inside sol-gel matrix so that higher guest loading, longer shelf-life, higher sensitivity and faster response of silica gel based sensors could be achieved. We focused on pore surface modification of two different types of silica sol-gel by post-grafting method, and construction of stable silica hydrogel-like thin films for sensor development. By monitoring the mobility and photostability of rhodamine 6G (R6G) molecules in silica alcogel thin films through single molecule spectroscopy (SMS), the guest-host interactions altered by post-synthesis grafting were examined. While physical confinement remains the major factor that controls mobility in modified alcogels, both R6G mobility and photostability register discernable changes after surface charges are respectively reversed and neutralized by aminopropyltriethoxysilane (APTS) and methyltriethoxysilane (MTES) grafting. The change in R6G photostability was found to be more sensitive to surface grafting than that of mobility. In addition, silica film modification by 0.4% APTS is as efficient as that by pure MTES in lowering R6G photostability, which suggests that surface charge reversal is more effective than charge neutralization

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Facile synthesis and application of poly(ionic liquid)-bonded silica hybrid materials.

    PubMed

    Bi, Wentao; Tian, Minglei; Row, Kyung Ho

    2012-05-07

    Facile methods were developed to prepare hybrid poly(ionic liquid)-bonded silica for a wide range of applications, particularly in analytical chemistry. The hybrid material obtained was evaluated by comparing its adsorption capacity with other conventional separation materials. In addition, the hybrid material has the potential for industrial scale production.

  15. 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.

  16. 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.

  17. Reversible assembly of tunable nanoporous materials from "hairy" silica nanoparticles.

    PubMed

    Khabibullin, Amir; Fullwood, Emily; Kolbay, Patrick; Zharov, Ilya

    2014-10-08

    Membranes with 1-100 nm nanopores are widely used in water purification and in biotechnology, but are prone to blockage and fouling. Reversibly assembled nanoporous membranes may be advantageous due to recyclability, cleaning, and retentate recovery, as well as the ability to tune the pore size. We report the preparation and characterization of size-selective nanoporous membranes with controlled thickness, area, and pore size via reversible assembly of polymer brush-grafted ("hairy") silica nanoparticles. We describe membranes reversibly assembled from silica particles grafted with (1) polymer brushes carrying acidic and basic groups, and (2) polymer brushes carrying neutral groups. The former are stable in most organic solvents and easily disassemble in water, whereas the latter are water-stable and disassemble in organic solvents.

  18. 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.

  19. The dynamic association processes leading from a silica precursor to a mesoporous SBA-15 material.

    PubMed

    Alfredsson, Viveka; Wennerström, Håkan

    2015-07-21

    During the last two decades, the synthesis of silica with an ordered mesoporous structure has been thoroughly explored. The basis of the synthesis is to let silica monomers polymerize in the presence of an amphiphilic template component. In the first studies, cationic surfactants were used as structure inducer. Later it was shown that pluronic copolymers also could have the role. One advantage with the pluronics copolymers is that they allow for a wider variation in the radius of pores in the resulting silica material. Another advantage lies in the higher stability resulting from the thicker walls between the pores. Mesoporous silica has a very high area to volume ratio, and the ordered structure ensures surface homogeneity. There are a number of applications of this type of material. It can be used as support for catalysts, as templates to produces other mesoporous inorganic materials, or in controlled release applications. The synthesis of mesoporous silica is, from a practical point of view, simple, but there are significant possibilities to vary synthesis conditions with a concomitant effect on the properties of the resulting material. It is clear that the structural properties on the nanometer scale are determined by the self-assembly properties of the amphiphile, and this knowledge has been used to optimize pore geometry and pore size. To have a practical functional material it is desirable to also control the structure on a micrometer scale and larger. In practice, one has largely taken an empirical approach in optimizing reaction conditions, paying less attention to underlying chemical and physicochemical mechanisms that lead from starting conditions to the final product. In this Account, we present our systematic studies of the processes involved not only in the formation of the mesoporous structure as such, but also of the formation of structures on the micrometer scale. The main point is to show how the ongoing silica polymerization triggers a sequence

  20. Applying Fused Silica and Other Transparent Window Materials in Aerospace Applications

    NASA Technical Reports Server (NTRS)

    Salem, Jon

    2017-01-01

    A variety of transparent ceramics, such as AlONs and spinels, that were developed for military applications hold promise as spacecraft windows. Window materials in spacecraft such as the Space Shuttle must meet many requirements such as maintaining cabin pressure, sustaining thermal shock, and tolerating damage from hyper-velocity impact while providing superior optical characteristics. The workhorse transparent material for space missions from Apollo to the International Space Station has been fused silica due in part to its low density, low coefficient of expansion and optical quality. Despite its successful use, fused silica exhibits lower fracture toughness and impact resistance as compared to newer materials. Can these newer transparent ceramics lighten spacecraft window systems and might they be useful for applications such as phone screens? This presentation will compare recent optical ceramics to fused silica and demonstrate how weight can be saved.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  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. Soft-Templating Synthesis of Mesoporous Silica-Based Materials for Environmental Applications

    NASA Astrophysics Data System (ADS)

    Gunathilake, Chamila Asanka

    Dissertation research is mainly focus on: 1) the development of mesoporous silica materials with organic pendant and bridging groups (isocyanurate, amidoxime, benzene) and incorporated metal (aluminum, zirconium, calcium, and magnesium) species for high temperature carbon dioxide (CO2) sorption, 2) phosphorous-hydroxy functionalized mesoporous silica materials for water treatment, and 3) amidoxime-modified ordered mesoporous silica materials for uranium sorption under seawater conditions. The goal is to design composite materials for environmental applications with desired porosity, surface area, and functionality by selecting proper metal oxide precursors, organosilanes, tetraethylorthosilicate, (TEOS), and block copolymer templates and by adjusting synthesis conditions. The first part of dissertation presents experimental studies on the merge of aluminum, zirconium, calcium, and magnesium oxides with mesoporous silica materials containing organic pendant (amidoxime) and bridging groups (isocyanurate, benzene) to obtain composite sorbents for CO2 sorption at ambient (0-25 °C) and elevated (60-120 °C) temperatures. These studies indicate that the aforementioned composite sorbents are fairly good for CO2 capture at 25 °C via physisorption mechanism and show a remarkably high affinity toward CO2 chemisorption at 60-120 °C. The second part of dissertation is devoted to silica-based materials with organic functionalities for removal of heavy metal ions such as lead from contaminated water and for recovery of metal ions such as uranium from seawater. First, ordered mesoporous organosilica (OMO) materials with diethylphosphatoethyl and hydroxyphosphatoethyl surface groups were examined for Pb2+ adsorption and showed unprecedented adsorption capacities up to 272 mg/g and 202 mg/g, respectively However, the amidoxime-modified OMO materials were explored for uranium extraction under seawater conditions and showed remarkable capacities reaching 57 mg of uranium per gram

  7. Effect of electrolytes on proteins physisorption on ordered mesoporous silica materials.

    PubMed

    Salis, Andrea; Medda, Luca; Cugia, Francesca; Monduzzi, Maura

    2016-01-01

    This short review highlights the effect of electrolytes on the performance of proteins-mesoporous silica conjugates which can open interesting perspectives in biotechnological fields, particularly nanomedicine and biocatalysis. Indeed therapeutic proteins and peptides represent a challenging innovation for several kinds of diseases, but since their self-life in biological fluids is very short, they need a stealth protective carrier. Similarly, enzymes need a solid support to improve thermal stability and to allow for recycling. Ordered mesoporous silica materials represent a valid choice as widely demonstrated. Both proteins and silica mesoporous materials possess charged surfaces, and here, the crucial role of pH, buffer, ionic strength and electrolyte type is posed in relation with loading/release of proteins onto/from the silica support through the analysis of adsorption and release processes. A delicate interplay of electrostatic and van der Waals interactions arises from considering electrolytes' effects on the two different charged surfaces. Clear outcomes concern the effect of pH and ionic strength. Protein loading onto the silica matrix is favored by an adsorbing solution having a pH close to the protein pI, and by a high ionic strength that reduces the Debye length. Release is instead favored by an adsorbing solution characterized by an intermediate ionic strength, close to the physiological values. Significant specific ions effects are shown to affect both proteins and silica matrices, as well as protein adsorption onto silica matrices. Further work is needed to quantify specific ion effects on the preservation of the biological activity, and on the release performance. Copyright © 2015 Elsevier B.V. All rights reserved.

  8. Hybrid photosynthetic materials derived from microalgae Cyanidium caldarium encapsulated within silica gel.

    PubMed

    Rooke, Joanna Claire; Léonard, Alexandre; Meunier, Christophe F; Sarmento, Hugo; Descy, Jean-Pierre; Su, Bao-Lian

    2010-04-15

    Cyanidium caldarium (Tilden) Geitler SAG 16.91 has been encapsulated within a porous silica host structure to target novel photosynthetic hybrid materials suitable for use in solar cells or CO(2) fixation. C. caldarium cells are both thermophilic and acidophilic; on account of these tolerances the hybrid materials could be employed in more extreme heat conditions. TEM highlights that the external cell membrane can remain intact after encapsulation. The images reveal an alignment of silica gel around the external membrane of the cell, providing evidence that the cell wall acts as both a nucleation and polymerisation site for silica species and that the silica scaffold formed by the aggregation of colloidal particles, generates a porosity that can facilitate the transport of nutrients towards the cell. Epifluorescence microscopy and UV-visible spectroscopy have revealed the preservation of photosynthetic apparatus post-immobilisation. Productivity studies showed how the presence of silica nanoparticles within the matrix can adversely interact with the exterior cellular structures preventing the production of oxygen through photosynthesis. 2009 Elsevier Inc. All rights reserved.

  9. Metal binding stoichiometry and isotherm choice in biosorption

    SciTech Connect

    Schiewer, S.; Wong, M.H.

    1999-11-01

    Seaweeds that possess a high metal binding capacity may be used as biosorbents for the removal of toxic heavy metals from wastewater. The binding of Cu and Ni by three brown algae (Sargassum, Colpomenia, Petalonia) and one green alga (Ulva) was investigated at pH 4.0 and pH 3.0. The greater binding strength of Cu is reflected in a binding constant that is about 10 times as high as that of Ni. The extent of metal binding followed the order Petalonia {approximately} Sargassum > Colpomenia > Ulva. This was caused by a decreasing number of binding sites and by much lower metal binding constants for Ulva as compared to the brown algae. Three different stoichiometric assumptions are compared for describing the metal binding, which assume either that each metal ion M binds to one binding site B forming a BM complex or that a divalent metal ion M binds to two monovalent sites B forming BM{sub 0.5} or B{sub 2}M complexes, respectively. Stoichiometry plots are proposed as tools to discern the relevant binding stoichiometry. The pH effect in metal binding and the change in proton binding were well predicted for the B{sub 2}M or BM{sub 0.5} stoichiometries with the former being better for Cu and the latter preferable for Ni. Overall, the BM{sub 0.5} model is recommended because it avoids iterations.

  10. 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.

  11. Fabrication and testing of engineered forms of self-assembled monolayers on mesoporous silica (SAMMS) material

    SciTech Connect

    Mattigod, S.V.; Liu, J.; Fryxell, G.E.; Baskaran, S.; Gong, M.; Nie, Z.; Feng, X.; Klasson, K.T.

    1998-09-01

    A number of engineered forms such as flexible extrudates, beads, and rods were fabricated using thiol-SAMMS (Self-Assembled Monolayers on Mesoporous Silica) and tested for their mercury adsorption capacities. The flexible extrudate form had a mercury adsorption capacity of 340 mg/g but was found to be structurally unstable. A structurally sound bead form of thiol-SAMMS was fabricated with 5, 10, 25, and 40% by weight clay binder (attapulgite) and successfully functionalized. A structurally stable but non-optimized rod form of thiol-SAMMS was also fabricated. Bench-scale processes were developed to silanize and functionalize mesoporous silica beads made with attapulgite clay binder. Contact angle measurements were conducted to assess the degree of surface coverage by functional groups on mesoporous silica materials.

  12. Preparation of polyimide-silica hybrid materials by high pressure-thermal polymerization

    SciTech Connect

    Gaw, K.; Suzuki, Hironori; Jikei, Mitsutoshi; Kakimoto, Masaaki; Imai, Yoshio

    1996-12-31

    Polyimide-silica hybrid materials were prepared via a modified sol-gel, high pressure-thermal polymerization procedure. Precursor monomer salts were made from ethanol soluble 2,5-diethoxycarboxyl terephthalic acid (p-PME) and either a disiloxanediamine, an aliphatic diamine (1,9 diaminononane) or combinations of the two. Solutions of tetramethoxysilane (TMOS) and monomer salt were transformed into a gel, dehydrated, and the resulting powders were subjected to high pressure and thermal polymerization and transformed into a polyimide-silica composite. By varying the TMOS content, and/or the siloxane to aliphatic diamine ratio, composites of 0 to 100 wt% SiO{sub 2} were made. The silica morphology changed significantly with siloxane/aliphatic PI ratio. Reaction mechanisms, thermal and physical properties and composite morphologies are discussed.

  13. Synthesis and Charaterization of Silica-Based Aldehyde Chitosan Hybrid Material for Biodiesel Purification.

    PubMed

    da Silva, Sandra Rodrigues; de Albuquerque, Nilson J A; de Almeida, Rusiene M; de Abreu, Fabiane C

    2017-09-25

    This study concerns the development and charaterization of Silica-based aldehyde Chitosan hybrid material as an adsorbent for biodiesel purification. This biocomposite was prepared by sol-gel route and oxidation with periodate, and then characterized. FTIR experiments showed that the hybrid formed presents absorption bands similar to those of Chitosan-Silica, with the exception of the vibrations at 1480 cm(-1) and 1570 cm(-1) attributed to the symmetrical angular deformation in the N-H plane, and possess large N₂ Brunauer-Emmett-Teller (BET) surface areas. Thermogravimetric analysis (TG) and scanning electron microscopy (SEM) was also carried out. Adsorption studies of bioadsorbents involving the analysis of free glycerol, soap, acidity, diglycerides, triglycerides, and fluorescence spectroscopy showed that silica-based aldehyde chitosan has a good affinity for glycerol and a good purification process.

  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. 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.

  17. Deep wet etching on fused silica material for fiber optic sensors

    NASA Astrophysics Data System (ADS)

    Chen, Xiaopei; Yu, Bing; Zhu, YiZheng; Wang, Anbo

    2004-01-01

    In this paper, deep microstructures on fused silica material, which are useful for fabrication of the fiber optic sensors, were obtained by using a wet chemical etching process. The etching solutions and the masking materials used for developing deep structure are described in this paper. The etch rate of a fused silica diaphragm in room temperature ranged from 46nm per minute to 83nm per minute with different concentrations of Buffered Hydrogen Fluoride (BHF). The etch depth of one step etching was 25μm with the surface roughness less than 20nm (peak-to-peak value). The optical reflectance from the deep etched surface was 4%, which is the same as a well-cleaved fiber end face. This result made the visibility of interference fringes from the single mode fiber optic sensors to be as high as 96%. Furthermore, two-step structures on the fused silica diaphragms with the total depth greater than 35μm are demonstrated. To the best knowledge of the authors, this is the deepest structure produced by wet etching process on fused silica material. Fiber optic pressure sensors based on deep etched diaphragms were fabricated and tested. Fabrication of microstructures on the fiber end faces by using this process is therefore possible.

  18. 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.

  19. 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.

  20. 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.

  1. 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).

  2. 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

  3. 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.

  4. 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.

  5. Evaluation of the dual retention properties of stationary phases based on silica hydride: Perfluorinated bonded material.

    PubMed

    Pesek, Joseph J; Matyska, Maria T; Natekar, Harshada

    2016-03-01

    The synthesis of a new perfluorinated stationary phase based on silica hydride using a hydrosilation reaction was investigated. The material was characterized by elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy and (13) C cross-polarization magic-angle spinning NMR spectroscopy. The retention properties of this new material were tested in the reversed-phase and normal-phase mode. Variable buffer strength experiments at two pH conditions for selected polar compounds were used to compare the new phase to hydrophilic interaction liquid chromatography retention. These results and previous data reported in the literature were used to postulate differences in the retention mechanism between hydrophilic interaction liquid chromatography and silica hydride-based stationary phases. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. A novel composite material based on antimony(III) oxide and amorphous silica

    SciTech Connect

    Zemnukhova, Ludmila A.; Panasenko, Alexander E.

    2013-05-01

    The composite material nSb₂O₃·mSiO₂·xH₂O was prepared by hydrolysis of SbCl₃ and Na₂SiO₃ in an aqueous medium. It has been shown that the composition of the material is influenced by the ratio of the initial components and the acidity of the reaction medium. The morphology of the material particles and its specific surface area have been determined. The thermal and optic properties were also investigated. - Graphical abstract: Novel composite material containing amorphous silica and crystal antimony(III) oxide has been synthesized by hydrolysis of SbCl₃ and Na₂SiO₃ in an aqueous medium. Highlights: • The composite material nSb₂O₃·mSiO₂·xH₂O was prepared in an aqueous medium. • The composition of the material is controllable by a synthesis conditions. • The morphology of the material and its optic properties have been determined.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Staphylococcal Surface Display of Metal-Binding Polyhistidyl Peptides

    PubMed Central

    Samuelson, Patrik; Wernérus, Henrik; Svedberg, Malin; Ståhl, Stefan

    2000-01-01

    Recombinant Staphylococcus xylosus and Staphylococcus carnosus strains were generated with surface-exposed chimeric proteins containing polyhistidyl peptides designed for binding to divalent metal ions. Surface accessibility of the chimeric surface proteins was demonstrated and the chimeric surface proteins were found to be functional in terms of metal binding, since the recombinant staphylococcal cells were shown to have gained Ni2+- and Cd2+-binding capacity, suggesting that such bacteria could find use in bioremediation of heavy metals. This is, to our knowledge, the first time that recombinant, surface-exposed metal-binding peptides have been expressed on gram-positive bacteria. Potential environmental or biosensor applications for such recombinant staphylococci as biosorbents are discussed. PMID:10698802

  16. 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

  17. 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.

  18. Silica Polyamine Composites: New Supramolecular Materials for Cation and Anion Recovery and Remediation

    SciTech Connect

    Hughes, Mark; Miranda, Paul; Nielsen, Daniel J.; Rosenberg, Edward; Gobetto, Roberto; Viale, Alessandra; Burton, Sarah D.

    2006-03-01

    The surface coverage of amorphous silica gels used in the synthesis of silica polyamine composites has been investigated by 29Si NMR. By diluting the polyamine anchor silane, chloropropyl trichlorosilane, with methyl trichlorosilane it was found that surface coverage could be markedly improved for a range of amine polymers after grafting to the silica surface. The commensurate decrease in the number of anchor points and increase in the number of free amines results in an increase in metal capacity and/or an improvement in capture kinetics. Solid state CPMAS-13C NMR has been employed to investigate the structure and metal ion binding of a series of these composite materials. It is reported that the highly branched polymer, poly(ethyleneimine) (PEI) exhibits much broader 13C NMR resonances than the linear polymers poly(allylamine) (PAA) and poly(vinylamine) (PVA). These results are understood in terms of the low energy conformations calculated from molecular modeling studies. Three new applications of the technology are also presented: (1) separation of lanthanides as a group from ferric ion and all other divalent ions; (2) a multi step process for recovering and concentrating the valuable metals in acid mine drainage; (3) a process for removing low level arsenic and selenium in the presence of sulfate using immobilized cations on the composite materials.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. [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.

  4. Silica nanoparticles produced by DC arc plasma from a solid raw materials

    NASA Astrophysics Data System (ADS)

    Kosmachev, P. V.; Vlasov, V. A.; Skripnikova, N. K.

    2017-05-01

    Plasma synthesis of SiO2 nanoparticles in experimental atmospheric pressure plasma reactor on the basis of DC arc plasma generator was presented in this paper. Solid high-silica raw materials such as diatomite from Kamyshlovskoye deposit in Russia, quartzite from Chupinskoye deposit in Russia and milled window glass were used. The obtained nanoparticles were characterized based on their morphology, chemical composition and size distribution. Scanning electron microscopy, laser diffractometry, nitrogen absorption (Brunauer-Emmett-Teller method), X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy were used to characterize the synthesized products. The obtained silica nanoparticles are agglomerated, have spherical shape and primary diameters between 10-300 nm. All samples of synthesized nanopowders were compared with commercial nanopowders.

  5. 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.

  6. 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.

  7. 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.

  8. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  9. 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.

  10. 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.

  11. 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.

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

    DOEpatents

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

    2017-06-06

    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.

  13. Asymmetric bioreduction of acetophenones by Baker's yeast and its cell-free extract encapsulated in sol-gel silica materials

    NASA Astrophysics Data System (ADS)

    Kato, Katsuya; Nakamura, Hitomi; Nakanishi, Kazuma

    2014-02-01

    Baker's yeast (BY) encapsulated in silica materials was synthesized using a yeast cell suspension and its cell-free extract during a sol-gel reaction of tetramethoxysilane with nitric acid as a catalyst. The synthesized samples were fully characterized using various methods, such as scanning electron microscopy, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, thermogravimetry, and differential thermal analysis. The BY cells were easily encapsulated inside silica-gel networks, and the ratio of the cells in the silica gel was approximately 75 wt%, which indicated that a large volume of BY was trapped with a small amount of silica. The enzyme activity (asymmetric reduction of prochiral ketones) of BY and its cell-free extract encapsulated in silica gel was investigated in detail. The activities and enantioselectivities of free and encapsulated BY were similar to those of acetophenone and its fluorine derivatives, which indicated that the conformation structure of BY enzymes inside silica-gel networks did not change. In addition, the encapsulated BY exhibited considerably better solvent (methanol) stability and recyclability compared to free BY solution. We expect that the development of BY encapsulated in sol-gel silica materials will significantly impact the industrial-scale advancement of high-efficiency and low-cost biocatalysts for the synthesis of valuable chiral alcohols.

  14. 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.

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

    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 C 18H 38 between 350 and 400 °C, isotopic exchanges between C 18H 38 and D 2O and between C 19D 40 and H 2O 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

  17. Compatibility enhancement of polyimide-silica hybrid sol-gel materials without incorporation of silane-coupling agent.

    PubMed

    Hung, Wei-I; Weng, Chang-Jian; Huang, Kuan-Yeh; Wu, Pei-Shan; Dai, Jiun-Kuang; Chang, Ya-Han; Tsai, Mei-Hui; Yeh, Jui-Ming; Yu, Yuan-Hsiang

    2011-04-01

    A facile route has been developed to enhance compatibility between organic polyimide matrix and dispersed phase of inorganic silica particles without addition of conventional silane-coupling agent. The as-prepared hybrid sol-gel materials having reduced size of SiO2 particle dispersed in polyimide matrix were successfully synthesized through pre-catalyzed sol-gel route using an organic diamine base. The PI-silica hybrid materials through conventional polyamic acid-catalyzed sol-gel route with/without silane-coupling agent were also prepared for comparative control studies. Morphological feature of as-prepared sol-gel materials prepared from three different approaches was also compared based on the studies of transmission electron microscopy. Effects of the material composition, in three different catalyzed routes, were investigated by thermal stability, mechanical strength, optical clarity, gas barrier and water absorption measurements of polyimide and a series of polyimide-silica hybrid sol-gel materials, respectively.

  18. 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.

  19. The structural coloration of textile materials using self-assembled silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Gao, Weihong; Rigout, Muriel; Owens, Huw

    2017-09-01

    The work presented investigates how to produce structural colours on textile materials by applying a surface coating of silica nanoparticles (SNPs). Uniform SNPs with particle diameters in a controlled micron size range (207-350 nm) were synthesized using a Stöber-based solvent varying (SV) method which has been reported previously. Photonic crystals (PCs) were formed on the surface of a piece of textile fabric through a process of natural sedimentation self-assembly of the colloidal suspension containing uniform SNPs. Due to the uniformity and a particular diameter range of the prepared SNPs, structural colours were observed from the fabric surface due to the Bragg diffraction of white light with the ordered structure of the silica PCs. By varying the mean particle diameter, a wide range of spectral colours from red to blue were obtained. The comparison of structural colours on fabrics and on glasses suggests that a smooth substrate is critical when producing materials with high colour intensity and spatial uniformity. This work suggested a promising approach to colour textile materials without the need for traditional dyes and/or pigments. [Figure not available: see fulltext.

  20. 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).

  1. 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

  2. Reflectance spectra diversity of silica-rich materials: Sensitivity to environment and implications for detections on Mars

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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 Minéralogie, l’Eau, les Glaces, et l’Activité (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 μm 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 ∼1.4 μm OH feature and the symmetry of the ∼1.9 μm feature can be used to discern between various forms of silica-rich materials, and that the ratio of the ∼2.2 μm (SiOH) and ∼1.9 μm (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 compositional diversity of

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. Simulation from the first principal theory on the effect of supporting silica on graphene and the new composite material

    NASA Astrophysics Data System (ADS)

    Kiarii, Ephraim M.; Govender, Krishna K.; Ndungu, Patrick G.; Govender, Penny P.

    2017-07-01

    Silica has been used as support material with many photocatalytic materials. In this study, silica polymorphs on graphene and epoxy graphene were studied using Density Functional Theory (DFT) to determine the interfacial and optical properties of the composite material. The powder diffraction patterns and Raman spectra for the silica polymorph structural models as well as graphene and epoxy graphene monoxide were generated using Material Studio (2016), and the GGA in PBE first principle method. The electronic and optical properties as well as work function analysis of the polymorphs with graphene and epoxy graphene monoxide starting molecules together with the layers systems were compared. In Our findings the optical properties of the layers generated were sensitive to the visible light in both epoxy-graphene monoxide and graphene composites.

  8. Structural investigation of nonionic fluorinated micelles by SANS in relation to mesoporous silica materials.

    PubMed

    Michaux, Florentin; Blin, Jean-Luc; Teixeira, José; Stébé, Marie José

    2012-01-12

    In an attempt to answer the question if there is dependence between the pore ordering of the mesoporous silica, obtained through the cooperative template mechanism, and the shape of the micellar aggregates of the surfactant solutions, the micellar structures of two nonionic fluorinated surfactant based-systems are studied by SANS. By fitting the experimental spectra with theoretical models, the structural evolution of the molecular aggregates can be described, and some important parameters can be obtained, such as the water and eventually oil penetration into the surfactant film, the aggregation number, the area per polar head of the surfactant, and the surfactant chain conformations. We have shown that for the C(8)F(17)C(2)H(4)(OC(2)H(4))(9)OH system, the micelles are prolate spheroids. The increase of the surfactant concentration in water does not change the characteristics of the interfacial film, but the aggregation number raises and the particles become more elongated. By contrast, the experimental curves of C(7)F(15)C(2)H(4)(OC(2)H(4))(8)OH cannot be fitted considering a small particle model. However, progressive incorporation of fluorocarbon induces a change of size and shape of the globules, which become smaller and more and more spherical. Regarding the material mesopore ordering, it appears that the micelles that lead to hexagonal mesoporous silica materials are described with a model of quasi-spherical globules. On the contrary, when large micelles are found, only wormhole-like structures are obtained.

  9. 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).

  10. Cellular Responses to the Metal-Binding Properties of Metformin

    PubMed Central

    Logie, Lisa; Harthill, Jean; Patel, Kashyap; Bacon, Sandra; Hamilton, D. Lee; Macrae, Katherine; McDougall, Gordon; Wang, Huan-Huan; Xue, Lin; Jiang, Hua; Sakamoto, Kei; Prescott, Alan R.; Rena, Graham

    2012-01-01

    In recent decades, the antihyperglycemic biguanide metformin has been used extensively in the treatment of type 2 diabetes, despite continuing uncertainty over its direct target. In this article, using two independent approaches, we demonstrate that cellular actions of metformin are disrupted by interference with its metal-binding properties, which have been known for over a century but little studied by biologists. We demonstrate that copper sequestration opposes known actions of metformin not only on AMP-activated protein kinase (AMPK)-dependent signaling, but also on S6 protein phosphorylation. Biguanide/metal interactions are stabilized by extensive π-electron delocalization and by investigating analogs of metformin; we provide evidence that this intrinsic property enables biguanides to regulate AMPK, glucose production, gluconeogenic gene expression, mitochondrial respiration, and mitochondrial copper binding. In contrast, regulation of S6 phosphorylation is prevented only by direct modification of the metal-liganding groups of the biguanide structure, supporting recent data that AMPK and S6 phosphorylation are regulated independently by biguanides. Additional studies with pioglitazone suggest that mitochondrial copper is targeted by both of these clinically important drugs. Together, these results suggest that cellular effects of biguanides depend on their metal-binding properties. This link may illuminate a better understanding of the molecular mechanisms enabling antihyperglycemic drug action. PMID:22492524

  11. 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

  12. 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

  13. Preparation and Electrochemical Characterization of Mesoporous Polyaniline-Silica Nanocomposites as an Electrode Material for Pseudocapacitors

    PubMed Central

    Zu, Lei; Cui, Xiuguo; Jiang, Yanhua; Hu, Zhongkai; Lian, Huiqin; Liu, Yang; Jin, Yushun; Li, Yan; Wang, Xiaodong

    2015-01-01

    Mesoporous polyaniline-silica nanocomposites with a full interpenetrating structure for pseudocapacitors were synthesized via the vapor phase approach. The morphology and structure of the nanocomposites were deeply investigated by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis and nitrogen adsorption-desorption tests. The results present that the mesoporous nanocomposites possess a uniform particle morphology and full interpenetrating structure, leading to a continuous conductive polyaniline network with a large specific surface area. The electrochemical performances of the nanocomposites were tested in a mixed solution of sulfuric acid and potassium iodide. With the merits of a large specific surface area and suitable pore size distribution, the nanocomposite showed a large specific capacitance (1702.68 farad (F)/g) due to its higher utilization of the active material. This amazing value is almost three-times larger than that of bulk polyaniline when the same mass of active material was used. PMID:28788006

  14. 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.

  15. Formation and characterization of high surface area thermally stabilized titania/silica composite materials via hydrolysis of titanium(IV) tetra-isopropoxide in sols of spherical silica particles.

    PubMed

    Khalil, Kamal M S; Elsamahy, Ahmed A; Elanany, Mohamed S

    2002-05-15

    A direct synthetic route leading to titania particles dispersed on nonporous spherical silica particles has been investigated; 5, 10, and 20% (w/w) titania/silica sols mixtures were achieved via hydrolyzation of titanium tetra-isopropxide solution in the mother liquor of a freshly prepared sol of spherical silica particles (Stöber particles). Titania/silica materials were produced by subsequent drying and calcination of the xerogels so obtained for 3 h at 400 and 600 degrees C. The materials were investigated by means of thermal analyses (TGA and DSC), FT-IR, N(2) gas adsorption-desorption, powder X-ray diffraction (XRD), and transmission electron microscopy (TEM). In spite of the low surface area (13.1 m(2)/g) of the pure spherical silica particles calcined at 400 degrees C, high surface area and mesoporous texture titania/silica materials were obtained (e.g., S(BET) ca. 293 m(2)/g for the 10% titania/silica calcined at 400 degrees C). Moreover, the materials were shown to be amorphous toward XRD up to 600 degrees C, while reasonable surface areas were preserved. It has been concluded that dispersion of titania particles onto the surface of the nonporous spherical silica particles increase their roughness, therefore leading to composite materials of less firm packing and mesoporosity.

  16. 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.

  17. Investigating the Heavy Metal Adsorption of Mesoporous Silica Materials Prepared by Microwave Synthesis

    NASA Astrophysics Data System (ADS)

    Zhu, Wenjie; Wang, Jingxuan; Wu, Di; Li, Xitong; Luo, Yongming; Han, Caiyun; Ma, Wenhui; He, Sufang

    2017-05-01

    Mesoporous silica materials (MSMs) of the MCM-41 type were rapidly synthesized by microwave heating using silica fume as silica source and evaluated as adsorbents for the removal of Cu2+, Pb2+, and Cd2+ from aqueous solutions. The effects of microwave heating times on the pore structure of the resulting MSMs were investigated as well as the effects of different acids which were employed to adjust the solution pH during the synthesis. The obtained MCM-41 samples were characterized by nitrogen adsorption-desorption analyses, X-ray powder diffraction, and transmission electron microscopy. The results indicated that microwave heating method can significantly reduce the synthesis time of MCM-41 to 40 min. The MCM-41 prepared using citric acid (c-MCM-41(40)) possessed more ordered hexagonal mesostructure, higher pore volume, and pore diameter. We also explored the ability of c-MCM-41(40) for removing heavy metal ions (Cu2+, Pb2+, and Cd2+) from aqueous solution and evaluated the influence of pH on its adsorption capacity. In addition, the adsorption isotherms were fitted by Langmuir and Freundlich models, and the adsorption kinetics were assessed using pseudo-first-order and pseudo-second-order models. The intraparticle diffusion model was studied to understand the adsorption process and mechanism. The results confirmed that the as-synthesized adsorbent could efficiently remove the heavy metal ions from aqueous solution at pH range of 5-7. The adsorption isotherms obeyed the Langmuir model, and the maximum adsorption capacities of the adsorbent for Cu2+, Pb2+, and Cd2+ were 36.3, 58.5, and 32.3 mg/g, respectively. The kinetic data were well fitted to the pseudo-second-order model, and the results of intraparticle diffusion model showed complex chemical reaction might be involved during adsorption process.

  18. A discussion on the thickness of pyrolysis layer in the ablation model for silica-phenolics composite material

    NASA Astrophysics Data System (ADS)

    Cai, Timin; Wang, Simin

    1989-02-01

    By means of the firing tests of a small experimental solid rocket motor, observing color change of the silica-phenolics composite material on the divergent section of the nozzle, and also using infrared ray spectral analysis and conductimetry for the material on that section, it is found that the thickness of the pyrolysis layer is of the same order of magnitude as the thickness of charring layer, which is up to 2.5 mm. For this reason, it is concluded that the pyrolysis layer model, rather than the pyrolysis surface model, should be adopted to calculate the ablation rate and the temperature distribution of the silica-phenolics composite nozzle.

  19. 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.

  20. 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).

  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. Magnetic and electronic properties of bimagnetic materials comprising cobalt particles within hollow silica decorated with magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Okada, T.; González-Alfaro, Y.; Espinosa, A.; Watanabe, N.; Haeiwa, T.; Sonehara, M.; Mishima, S.; Sato, T.; Muñoz-Noval, A.; Aranda, P.; Garcia-Hernández, M.; Ruiz-Hitzky, E.

    2013-09-01

    Bimagnetic materials were fabricated by decorating the external surface of rattle-type hollow silica microspheres (which themselves contain metallic cobalt nanoparticles) with magnetite nanoparticles; thus, each magnetic substance was spatially isolated by the silica shell. The amount of magnetite decoration on the co-occluded hollow silica was varied from 1 to 17 mass %. Magnetic and electronic properties of the resulting bimagnetic materials were characterized by superconducting quantum interference device measurements and X-ray absorption spectroscopy, respectively. The ferrous iron in the bimagnetic sample was slightly more oxidized than in the magnetite reference, probably from some charge-transfer because of the SiO2 surface contact, although the overall oxidation state of the samples is very similar to that of magnetite. The temperature dependence of the sample magnetization recorded with Zero Field Cooling and Field Cooling resulted in blocking temperatures for the bimagnetic materials that were close to that of magnetite nanoparticles (176 K) and were lower than that for the bare Co-occluded hollow silica (which was above room temperature). Values of coercive force and exchange bias at 300 K became quite small after decoration with only minimal amounts of magnetite nanoparticles (1-3 mass %) and were lower than those of magnetite. This is the first example of enhancing superparamagnetism by spatial separation of both Co and magnetite magnetic nanoparticles using a thin wall of diamagnetic silica.

  3. 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.

  4. 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. Published by Elsevier B.V.

  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. 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.

  7. In vitro evaluation of a silica whitening toothpaste containing blue covarine on the colour of teeth containing anterior restoration materials.

    PubMed

    Philpotts, Carole J; Cariddi, Eufemia; Spradbery, Paul S; Joiner, Andrew

    2017-08-19

    To investigate the effects of a silica-based whitening toothpaste containing blue covarine on the colour of restorations in extracted human teeth. Human extracted teeth were mounted in acrylic resin. A cavity was cut into the enamel surface and the specimen restored with either glass ionomer or composite dental materials. Following 4 weeks storage in water, specimens were treated with either water, red wine or a toothpaste containing blue covarine (n=10) for 24h followed by brushing with a silica-based toothpaste. Specimens were imaged with a digital imaging system at baseline, after 24h treatment and after brushing with a silica-based toothpaste. CIELAB colour parameters were determined for the restoration and the whole specimen and overall mean colour changes calculated (ΔE). Baseline and post-brushing images were compared subjectively for overall stain and staining around the restoration margin. Red wine produced the largest ΔE values for whole specimens and for all restoration materials and the largest subjective stain scores for whole specimens and restoration margins. The red wine stain was not completely removed by brushing with a silica-based toothpaste. Comparisons of the red wine group with either the blue covarine toothpaste group or the water group were of statistical significance for all parameters (ANOVA, Tukey-Kramer, p<0.05). Following brushing with the silica-based toothpaste, specimens from the blue covarine toothpaste group were not significantly different (p>0.05) to the water group, for all restoration material types. Exaggerated treatment with a blue covarine containing toothpaste does not significantly affect the colour of the restoration or the restoration margin of the dental materials tested versus a water alone treatment. The silica-based blue covarine containing toothpaste does not permanently stain the restorative materials tested or their margins. Copyright © 2017. Published by Elsevier Ltd.

  8. 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.

  9. 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.

  10. An overview on the role of silica-based materials in vaccine development.

    PubMed

    Navarro-Tovar, Gabriela; Palestino, Gabriela; Rosales-Mendoza, Sergio

    2016-11-01

    Although vaccination has prevented millions of deaths, the development of highly immunogenic subunit vaccines is still required. Since the number of adjuvants approved for human use is limited, the new paths for the development of delivery vehicles offered by nanotechnology are of key relevance. Areas covered: Herein, the potential of silica nanoparticles (SP) as both adjuvants and vaccine delivery vehicles is discussed based on the analysis of the current biomedical literature. Expert commentary: SP are reported not only as biodegradable and biocompatible material but also as easy to modify and with a low production cost. Additionally, several reports suggest that SP enhance the immune response. Therefore, SP are a promising delivery vehicle and/or adjuvant in vaccines. However, knowledge on the industrial production and specific aspects of immunity are still required.

  11. Photovoltaic's silica-rich waste sludge as supplementary cementitious material (SCM)

    SciTech Connect

    Quercia, G.; Putten, J.J.G. van der; Hüsken, G.; Brouwers, H.J.H.

    2013-12-15

    Waste sludge, a solid recovered from wastewater of photovoltaic-industries, composes of agglomerates of nano-particles like SiO{sub 2} and CaCO{sub 3}. This sludge deflocculates in aqueous solutions into nano-particles smaller than 1 μm. Thus, this sludge constitutes a potentially hazardous waste when it is improperly disposed. Due to its high content of amorphous SiO{sub 2}, this sludge has a potential use as supplementary cementitious material (SCM) in concrete. In this study the main properties of three different samples of photovoltaic's silica-rich waste sludge (nSS) were physically and chemically characterized. The characterization techniques included: scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nitrogen physical adsorption isotherm (BET method), density by Helium pycnometry, particle size distribution determined by laser light scattering (LLS) and zeta-potential measurements by dynamic light scattering (DLS). In addition, a dispersability study was performed to design stable slurries to be used as liquid additives for the concrete production on site. The effects on the hydration kinetics of cement pastes by the incorporation of nSS in the designed slurries were determined using an isothermal calorimeter. A compressive strength test of standard mortars with 7% of cement replacement was performed to determine the pozzolanic activity of the waste nano-silica sludge. Finally, the hardened system was fully characterized to determine the phase composition. The results demonstrate that the nSS can be utilized as SCM to replace portion of cement in mortars, thereby decreasing the CO{sub 2} footprint and the environmental impact of concrete. -- Highlights: •Three different samples of PV nano-silica sludge (nSS) were fully characterized. •nSS is composed of agglomerates of nano-particles like SiO{sub 2} and CaCO{sub 3}. •Dispersability studies demonstrated that nSS agglomerates are broken to nano

  12. 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.

  13. 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).

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. Hydrophilic surface modification of acrylic denture base material by silica coating and its influence on Candida albicans adherence.

    PubMed

    Azuma, Akinobu; Akiba, Norihisa; Minakuchi, Shunsuke

    2012-03-13

    Silica coating modifies hydrophobic denture base materials to have a hydrophilic surface. The purpose of this study was to evaluate the effect of silica coating to a denture base material on resistance to Candida albicans (C. albicans) adherence. Specimens were prepared by polymerizing an acrylic denture lining material and polished using silicon carbide paper up an abrasive grade of 1000. The specimens of a coated group were treated three times by a silica coating agent using a nonwoven cloth. The surface properties were evaluated by contact angle measurement, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). A C. albicans adherence assay was performed after 1.5, 6, and 24 h incubation. The mean contact angle of the coated group showed significantly lower than that of the non-coated group (p < 0.05). In the coated group, the surface roughness decreased in SEM images, and Si was continuously detected in EDS analysis. At 24 h incubation time, the colony forming unit of C. albicans on the coated group was significantly reduced compared to the non-coated group (p < 0.05). These results suggest that hydrophilic surface modification by the silica coating reduces C. albicans adherence and could contribute to daily denture care.

  1. 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.

  2. Formation and characterization of different ceria/silica composite materials via dispersion of ceria gel or soluble ceria precursors in silica sols.

    PubMed

    Khalil, Kamal M S; Elkabee, Leena A; Murphy, Brian

    2005-07-15

    Composite ceria/silica materials of 10 and 20% (w/w) were prepared by calcination, at 650 degrees C for 3 h, of the xerogels obtained by mixing the corresponding amount of a ceria precursor with freshly prepared sols of spherical silica particles (Stober particles) in their mother liquors. Two different ceria precursors were examined in this investigation. The first was a gel produced by the prehydrolysis of cerium(IV) isopropoxide in isopropanol medium, and the second was an aqueous solution of cerium(IV) ammonium nitrate. Different textural and morphological characteristics that developed by calcination were investigated by TGA, FTIR, XRD, SEM, and analyses of N2 adsorption isotherms. The results indicated that ceria dispersion and formation of mesoporous textural composite materials produced by the second precursor, cerium(IV) ammonium nitrate, are better than those produced by the first precursor, prehydrolyzed cerium(IV) isopropoxide. The results are discussed in terms of the effect of precursors and mixing media on nucleation and growth of ceria particles and their protection from sintering on calcination at the test temperature.

  3. Stepwise complexometric determination of aluminium, titanium and iron concentrations in silica sand and allied materials.

    PubMed

    Kayal, Nijhuma; Singh, Nahar

    2007-10-19

    This study aimed at measuring the quantities of Al, Ti and Fe in silica sand and allied materials employing a complexometric method in the same analyte and a stepwise indirect titration with EDTA. The method involves the complexation of Al, Ti and Fe with excess EDTA and the selective de-complexation of TiO-EDTA and Al-EDTA complexes with tartaric acid and NaF respectively. In addition to its simplicity, rapidity and accuracy, the proposed method does not require the use of a separation technique or any sophisticated instrumentation. Each of the test samples were analyzed five times using the proposed method. The method's accuracy was confirmed by analyzing the US National Institute of Standards and Technology's (NIST) Standard Reference Materials (SRM) 81a, 89 and IPT SRM 61 using the procedure proposed, in addition to analyzing Ti and Fe levels by spectrophotometry and that of Al by complexometry. The study shows that there is good agreement between the proposed and existing methods. The standard deviations of the measurements were calculated by analyzing five replicates of each sample, and were found to be less than 1.5% in our method.

  4. 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.

  5. Molecular dynamics simulations of stability at the early stages of silica materials preparation

    NASA Astrophysics Data System (ADS)

    Gholizadeh, Reza; Wang, Yujun; Yu, Yang-Xin

    2017-06-01

    The main objective of this article is the Molecular dynamics simulations of stability phenomenon at the early stages of silica production in a colloidal solution. The Dreiding force field used during the whole calculation for the search of all bonding, angle, dihedral, inversion potential sets for a given configuration. For studying the stability phenomenon, two scenarios are specified: (1) The diameter of silica nanoparticles in each simulation box is the same while initial distances of two silica nanoparticles are different (system I), (2) The initial distance between two silica nanoparticles in each simulation box is the same while silica nanoparticles diameters are different (system II). The charge of atoms in silica nanoparticles determined using density functional theory calculations (Dmol3). The Born repulsion forces were predominant rather than the van der Waals attraction forces. Furthermore, trajectories, mean squared displacements, radial distribution functions, and electrical charges of silica nanoparticles are determined. The displacement of silica nanoparticles was negligible which demonstrates that atoms could not approach more close. The studied colloidal solution was stable regard to the results of molecular dynamics simulations.

  6. 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.

  7. 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

  8. 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.

  9. Development of new composite materials for hydrogen storage. The AB5 type hydride alloy with silica glass support

    NASA Astrophysics Data System (ADS)

    Grinberga, L.; Kleperis, J.

    2007-12-01

    Use of the spill-over effect to enhance catalytic activity and the amount of absorbed hydrogen in a new composite material is reported. An AB5 lanthanum nickel alloy with a small number of additives serves as the catalyst and the bulk material for hydrogen storage and a silica glass powder with a developed surface serves as the support material. The amount of absorbed hydrogen in the alloy and composite is determined from thermo-gravimetric data. Structural changes in the developed composite during hydrogenation are found to confirm the synergy between the alloy and the support material.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. Quercetin conjugated silica particles as novel biofunctional hybrid materials for biological applications.

    PubMed

    Vergara-Castañeda, Hayde; Hernandez-Martinez, Angel R; Estevez, Miriam; Mendoza, Sandra; Luna-Barcenas, Gabriel; Pool, Héctor

    2016-03-15

    The aim of this work is to formulate biofunctional hybrid materials (HMs) with quercetin (QC) and silica particles (SiPs) by simple methods such as sol-gel and QC conjugation. Physicochemical characterization included particle size, zeta potential (ζ), FTIR and SEM imaging. Spherical particles with ca. 115 nm in diameter were produced, ζ and FTIR demonstrated that QC conjugation was successfully achieved. Electrochemical analyses performed by cyclic voltammetry (CV) suggested that potential binding sites between QC and SiPs may be at functional groups from A ring or C ring, affecting the transfer electron of resorcinol moiety. Iron chelating activity and lipid peroxidation assays showed that after conjugation to SiPs, QC decreased its metal chelating activity, but anti-radical properties is maintained. Our results demonstrated that our proposed method is simple and effective to obtain bio-functional HMs. Our findings prove to be useful in the design of protective approaches against lipid oxidation in food, pharmaceutical, and cosmetics fields.

  15. 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.

  16. 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.

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

    PubMed

    Atsü, Saadet; Keskın, Yasemin

    2013-01-01

    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. 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. 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. 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.

  18. The toxicological mode of action and the safety of synthetic amorphous silica-a nanostructured material.

    PubMed

    Fruijtier-Pölloth, Claudia

    2012-04-11

    Synthetic amorphous silica (SAS), in the form of pyrogenic (fumed), precipitated, gel or colloidal SAS, has been used in a wide variety of industrial and consumer applications including food, cosmetics and pharmaceutical products for many decades. Based on extensive physico-chemical, ecotoxicology, toxicology, safety and epidemiology data, no environmental or health risks have been associated with these materials if produced and used under current hygiene standards and use recommendations. With internal structures in the nanoscale size range, pyrogenic, precipitated and gel SAS are typical examples of nanostructured materials as recently defined by the International Organisation for Standardisation (ISO). The manufacturing process of these SAS materials leads to aggregates of strongly (covalently) bonded or fused primary particles. Weak interaction forces (van der Waals interactions, hydrogen bonding, physical adhesion) between aggregates lead to the formation of micrometre (μm)-sized agglomerates. Typically, isolated nanoparticles do not occur. In contrast, colloidal SAS dispersions may contain isolated primary particles in the nano-size range which can be considered nano-objects. The size of the primary particle resulted in the materials often being considered as "nanosilica" and in the inclusion of SAS in research programmes on nanomaterials. The biological activity of SAS can be related to the particle shape and surface characteristics interfacing with the biological milieu rather than to particle size. SAS adsorbs to cellular surfaces and can affect membrane structures and integrity. Toxicity is linked to mechanisms of interactions with outer and inner cell membranes, signalling responses, and vesicle trafficking pathways. Interaction with membranes may induce the release of endosomal substances, reactive oxygen species, cytokines and chemokines and thus induce inflammatory responses. None of the SAS forms, including colloidal nano-sized particles, were shown

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. Probing local pH-based precipitation processes in self-assembled silica-carbonate hybrid materials.

    PubMed

    Opel, Julian; Hecht, Mandy; Rurack, Knut; Eiblmeier, Josef; Kunz, Werner; Cölfen, Helmut; Kellermeier, Matthias

    2015-11-07

    Crystallisation of barium carbonate in the presence of silica can lead to the spontaneous assembly of highly complex superstructures, consisting of uniform and largely co-oriented BaCO3 nanocrystals that are interspersed by a matrix of amorphous silica. The formation of these biomimetic architectures (so-called silica biomorphs) is thought to be driven by a dynamic interplay between the components, in which subtle changes of conditions trigger ordered mineralisation at the nanoscale. In particular, it has been proposed that local pH gradients at growing fronts play a crucial role in the process of morphogenesis. In the present work, we have used a special pH-sensitive fluorescent dye to directly trace these presumed local fluctuations by means of confocal laser scanning microscopy. Our data demonstrate the existence of an active region near the growth front, where the pH is locally decreased with respect to the alkaline bulk solution on a length scale of few microns. This observation provides fundamental and, for the first time, direct experimental support for the current picture of the mechanism underlying the formation of these peculiar materials. On the other hand, the absence of any temporal oscillations in the local pH - another key feature of the envisaged mechanism - challenges the notion of autocatalytic phenomena in such systems and raises new questions about the actual role of silica as an additive in the crystallisation process.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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

  12. Castor oil polyurethane containing silica nanoparticles as filling material of bone defect in rats.

    PubMed

    Nacer, Renato Silva; Poppi, Rodrigo Ré; Carvalho, Paulo de Tarso Camilo de; Silva, Baldomero Antonio Kato da; Odashiro, Alexandre Nakao; Silva, Iandara Schettert; Delben, José Renato Jurkevicz; Delben, Angela Antonia Sanches Tardivo

    2012-01-01

    To evaluate the biologic behavior of the castor polymer containing silica nanoparticles as a bone substitute in diafisary defect. Twenty seven male Rattus norvegicus albinus Wistar lineage were submitted to bone defect filled with castor oil polymer. Three experimental groups had been formed with nine animals each: (1) castor oil polymer containing only calcium carbonate; (2) castor oil polymer with calcium carbonate and doped with 5% of silica nanoparticles; (3) castor polymer with calcium carbonate doped with 10% of silica nanoparticles; 3 animals of each group were submitted to euthanasia 15, 30 and 60 days after experimental procedure, and their femurs were removed to histological evaluation. there was bone growth in all the studied groups, with a greater tendency of growth in the group 1. After 30 days all the groups presented similar results. After 60 days a greater amount of fibroblasts, osteoblasts, osteocytes and osteoclasts in group 3 was observed, with integrated activity of 3 kinds of cells involved in the bone activation-reabsorption-formation. The castor polymer associated to the silica nanoparticles is biocompatible and allows osteoconduction. The presence of osteoprogenitors cells suggests silica osteoinduction capacity.

  13. 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. Copyright © 2016 Elsevier Inc. All rights reserved.

  14. Shock sensitivity of energetic material and nanometric damage mechanisms in silica glass

    NASA Astrophysics Data System (ADS)

    Nomura, Ken-Ichi

    This dissertation focuses on molecular dynamics (MD) simulations of shock sensitivity of energetic material (EM) and nanometric damage mechanisms in amorphous SiO2 (a-SiO2). A scalable parallel MD algorithm incorporating first principles-based reactive force fields (ReaxFF) has been implemented to perform multimillion-to-billion atom chemically reactive MD simulations. Mechanical stimuli in energetic materials initiate chemical reactions at shock fronts prior to detonation. Multimillion-atom ReaxFF-MD simulations are performed to investigate atomistic mechanisms of shock-induced reaction initiation in 1,3,5-trinitro-1,3,5-triazine (RDX) crystal. The simulation reveals a bi-modal molecular response against a planar shock loading, which creates a nanoscale layered-structure of molecular dipole behind a shock front. The sensitivity of energetic crystals changes with defects such as voids, grain boundaries and cracks. By performing million-atom ReaxFF-MD simulations, the effects of microstructures in crystal on shock sensitivity have been investigated. MD simulation reveals the formation of a nanojet which focuses into a narrow beam as the void collapses. By increasing particle velocity, a pinning-depinning transition of the shock wave front at the void occurs. Shock loading simulation in a nanophase RDX crystal reveals a deformation mechanism that is mediated by molecular reorientation and conformation changes. Molecular rotation and deformation significantly reduce the energy barrier for the onset of slip. In contrast to crystalline solids, damage, flow and fracture in glass are still controversial areas. We have performed multimillion-atom MD simulations to investigate initiation and growth of wing cracks in confined silica glass. Under dynamic compression, frictional sliding of precrack surfaces nucleates nanovoids which evolve into nanocrack columns at the precrack tip. Nanocrack columns merge to form a wing crack, which grows via coalescence with nanovoids in the

  15. Magnetic memory from site isolated Dy(III) on silica materials

    DOE PAGES

    Allouche, Florian; Lapadula, Giuseppe; Siddiqi, Georges; ...

    2017-02-22

    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 dehydroxylatedmore » 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. Throughout the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence.« less

  16. 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

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Solid-phase polarization matrixes for dynamic nuclear polarization from homogeneously distributed radicals in mesostructured hybrid silica materials.

    PubMed

    Gajan, David; Schwarzwälder, Martin; Conley, Matthew P; Grüning, Wolfram R; Rossini, Aaron J; Zagdoun, Alexandre; Lelli, Moreno; Yulikov, Maxim; Jeschke, Gunnar; Sauvée, Claire; Ouari, Olivier; Tordo, Paul; Veyre, Laurent; Lesage, Anne; Thieuleux, Chloé; Emsley, Lyndon; Copéret, Christophe

    2013-10-16

    Mesoporous hybrid silica-organic materials containing homogeneously distributed stable mono- or dinitroxide radicals covalently bound to the silica surface were developed as polarization matrixes for solid-state dynamic nuclear polarization (DNP) NMR experiments. For TEMPO-containing materials impregnated with water or 1,1,2,2-tetrachloroethane, enhancement factors of up to 36 were obtained at ∼100 K and 9.4 T without the need for a glass-forming additive. We show that the homogeneous radical distribution and the subtle balance between the concentration of radical in the material and the fraction of radicals at a sufficient inter-radical distance to promote the cross-effect are the main determinants for the DNP enhancements we obtain. The material, as well as an analogue containing the poorly soluble biradical bTUrea, is used as a polarizing matrix for DNP NMR experiments of solutions containing alanine and pyruvic acid. The analyte is separated from the polarization matrix by simple filtration.

  7. Development and characterization of silica and titania based nano structured materials for the removal of indoor and outdoor air pollutants

    NASA Astrophysics Data System (ADS)

    Peiris, Thelge Manindu Nirasha

    Solar energy driven catalytic systems have gained popularity in environmental remediation recently. Various photocatalytic systems have been reported in this regard and most of the photocatalysts are based on well-known semiconducting material, Titanium Dioxide, while some are based on other materials such as Silicon Dioxide and various Zeolites. However, in titania based photocatalysts, titania is actively involved in the catalytic mechanism by absorbing light and generating exitons. Because of this vast popularity of titania in the field of photocatalysis it is believed that photocatalysis mainly occurs via non-localized mechanisms and semiconductors are extremely important. Even though it is still rare, photocatalysis could be localized and possible without use of a semiconductor as well. Thus, to support localized photocatalytic systems, and to compare the activity to titania based systems, degradation of organic air pollutants by nanostructured silica, titania and mixed silica titania systems were studied. New materials were prepared using two different approaches, precipitation technique (xerogel) and aerogel preparation technique. The prepared xerogel samples were doped with both metal (silver) and non-metals (carbon and sulfur) and aerogel samples were loaded with Chromium, Cobalt and Vanadium separately, in order to achieve visible light photocatalytic activity. Characterization studies of the materials were carried out using Nova BET analysis, DR UV-vis spectrometry, powder X-ray diffraction, X-ray photoelectron Spectroscopy, FT-IR spectroscopy, Transmission Electron Microscopy, etc. Kinetics of the catalytic activities was studied using a Shimadzu GCMS-QP 5000 instrument using a closed glass reactor. All the experiments were carried out in gaseous phase using acetaldehyde as the model pollutant. Kinetic results suggest that chromium doped silica systems are good UV and visible light active photocatalysts. This is a good example for a localized

  8. 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.

  9. Quasi-continuum photoluminescence: Unusual broad spectral and temporal characteristics found in defective surfaces of silica and other materials

    SciTech Connect

    Laurence, Ted A. Bude, Jeff D.; Shen, Nan; Steele, William A.; Ly, Sonny

    2014-02-28

    We previously reported a novel photoluminescence (PL) with a distribution of fast decay times in fused silica surface flaws that is correlated with damage propensity by high fluence lasers. The source of the PL was not attributable to any known silica point defect. Due to its broad spectral and temporal features, we here give this PL the name quasi-continuum PL (QC-PL) and describe the features of QC-PL in more detail. The primary features of QC-PL include broad excitation and emission spectra, a broad distribution of PL lifetimes from 20 ps to 5 ns, continuous shifts in PL lifetime distributions with respect to emission wavelength, and a propensity to photo-bleach and photo-brighten. We found similar PL characteristics in surface flaws of other optical materials, including CaF{sub 2}, DKDP, and quartz. Based on the commonality of the features in different optical materials and the proximity of QC-PL to surfaces, we suggest that these properties arise from interactions associated with high densities of defects, rather than a distribution over a large number of types of defects and is likely found in a wide variety of structures from nano-scale composites to bulk structures as well as in both broad and narrow band materials from dielectrics to semiconductors.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. Cadmium detection by a thermally responsive elastin copolymer with metal-binding functionality.

    PubMed

    Chu, Hun Su; Ryum, Jung; Won, Jong-In

    2013-08-15

    Heavy metals are of great concern to environmental safety because of their adverse effects on the environment and human health, even at very low levels. In particular, cadmium and several cadmium-containing compounds are carcinogens and induce many types of cancer. Biological extracts of cadmium have been given greater attention recently because they are considered to be environmentally benign and economically acceptable. Among promising candidates, one emerging technology is the use of tunable, metal-binding biopolymers based on elastin-like polypeptides (ELPs). An ELP consists of the repeating pentapeptide of specific amino acids, Val-Pro-Gly-Xaa-Gly (where the "guest residue" Xaa is any amino except proline) that undergoes a reversible phase transition at a specific temperature (transition temperature, Tt). However, the ELP itself is relatively non-selective. A biopolymer with metal-binding domains that have stronger affinity, capacity, and selectivity would have distinct advantages. We investigated the use of a new generation of ELP biopolymers, EC18-ELP containing synthetic phytochelatin (EC), which is a metal-binding protein with a repetitive motif (Glu-Cys)nGly, as the metal-binding domain. In this study, an EC18-ELP fusion protein was expressed in Escherichia coli and the metal binding ability of EC to cadmium was examined quantitatively. In addition, transition temperature variation was analyzed when the fusion protein bound to cadmium. Copyright © 2013 Elsevier Inc. All rights reserved.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Hydrophilic nano-silica coating agents with platinum and diamond nanoparticles for denture base materials.

    PubMed

    Yoshizaki, Taro; Akiba, Norihisa; Inokoshi, Masanao; Shimada, Masayuki; Minakuchi, Shunsuke

    2017-05-31

    Preventing microorganisms from adhering to the denture surface is important for ensuring the systemic health of elderly denture wearers. Silica coating agents provide high hydrophilicity but lack durability. This study investigated solutions to improve the durability of the coating layer, determine an appropriate solid content concentration of SiO2 in the silica coating agent, and evaluate the effect of adding platinum (Pt) and diamond nanoparticles (ND) to the agent. Five coating agents were prepared with different SiO2 concentrations with/without Pt and ND additives. The contact angle was measured, and the brush-wear test was performed. Scanning electron microscopy was used to investigate the silica coating layer. The appropriate concentration of SiO2 was found to be 0.5-0.75 wt%. The coating agents with additives showed significantly high hydrophilicity immediately after coating and after the brush-wear test. The coating agents with/without additives formed a durable coating layer even after the brush-wear test.

  2. Double-Layer Surface Modification of Polyamide Denture Base Material by Functionalized Sol-Gel Based Silica for Adhesion Improvement.

    PubMed

    Hafezeqoran, Ali; Koodaryan, Roodabeh

    2017-09-21

    Limited surface treatments have been proposed to improve the bond strength between autopolymerizing resin and polyamide denture base materials. Still, the bond strength of autopolymerizing resins to nylon polymer is not strong enough to repair the fractured denture effectively. This study aimed to introduce a novel method to improve the adhesion of autopolymerizing resin to polyamide polymer by a double layer deposition of sol-gel silica and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (AE-APTMS). The silica sol was synthesized by acid-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) as silica precursors. Polyamide specimens were dipped in TEOS-derived sol (TS group, n = 28), and exposed to ultraviolet (UV) light under O2 flow for 30 minutes. UV-treated specimens were immersed in AE-APTMS solution and left for 24 hours at room temperature. The other specimens were either immersed in AE-APTMS solution (AP group, n = 28) or left untreated (NT group, n = 28). Surface characterization was investigated by fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Two autopolymerizing resins (subgroups G and T, n = 14) were bonded to the specimens, thermocycled, and then tested for shear bond strength with a universal testing machine. Data were analyzed with one-way ANOVA followed by Tukey's HSD (α = 0.05). FTIR spectra of treated surfaces confirmed the chemical modification and appearance of functional groups on the polymer. One-way ANOVA revealed significant differences in shear bond strength among the study groups. Tukey's HSD showed that TST and TSG groups had significantly higher shear bond strength than control groups (p = 0.001 and p < 0.001, respectively). Moreover, bond strength values of APT were statistically significant compared to controls (p = 0.017). Amino functionalized TEOS-derived silica coating is a simple and cost-effective method for improving the bond strength between the autopolymerizing resin and polyamide denture

  3. 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.

  4. 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

  5. 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.

  6. Synthesis of Bioactive Chlorogenic Acid-Silica Hybrid Materials via the Sol–Gel Route and Evaluation of Their Biocompatibility

    PubMed Central

    Pacifico, Severina

    2017-01-01

    Natural phenol compounds are gaining a great deal of attention because of their potential use as prophylactic and therapeutic agents in many diseases, as well as in applied science for their preventing role in oxidation deterioration. With the aim to synthetize new phenol-based materials, the sol–gel method was used to embed different content of the phenolic antioxidant chlorogenic acid (CGA) within silica matrices to obtain organic-inorganic hybrid materials. Fourier transform infrared (FTIR) measurements were used to characterize the prepared materials. The new materials were screened for their bioactivity and antioxidant potential. To this latter purpose, direct DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azinobis-(3-ethylbenzothiazolin-6-sulfonic acid) methods were applied: radical scavenging capability appeared strongly dependent on the phenol amount in investigated hybrids, and became pronounced, mainly toward the ABTS radical cation, when materials with CGA content equal to 15 wt% and 20 wt% were analyzed. The in vitro biocompatibility of the synthetized materials was estimated by using the MTT assay towards fibroblast NIH 3T3 cells, human keratinocyte HaCaT cells, and the neuroblastoma SH-SY5Y cell line. As cell viability and morphology of tested cell lines seemed to be unaffected by new materials, the attenuated total reflectance (ATR)-FTIR method was applied to deeply measure the effects of the hybrids in the three different cell lines. PMID:28773198

  7. Synthesis of Bioactive Chlorogenic Acid-Silica Hybrid Materials via the Sol-Gel Route and Evaluation of Their Biocompatibility.

    PubMed

    Catauro, Michelina; Pacifico, Severina

    2017-07-21

    Natural phenol compounds are gaining a great deal of attention because of their potential use as prophylactic and therapeutic agents in many diseases, as well as in applied science for their preventing role in oxidation deterioration. With the aim to synthetize new phenol-based materials, the sol-gel method was used to embed different content of the phenolic antioxidant chlorogenic acid (CGA) within silica matrices to obtain organic-inorganic hybrid materials. Fourier transform infrared (FTIR) measurements were used to characterize the prepared materials. The new materials were screened for their bioactivity and antioxidant potential. To this latter purpose, direct DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azinobis-(3-ethylbenzothiazolin-6-sulfonic acid) methods were applied: radical scavenging capability appeared strongly dependent on the phenol amount in investigated hybrids, and became pronounced, mainly toward the ABTS radical cation, when materials with CGA content equal to 15 wt% and 20 wt% were analyzed. The in vitro biocompatibility of the synthetized materials was estimated by using the MTT assay towards fibroblast NIH 3T3 cells, human keratinocyte HaCaT cells, and the neuroblastoma SH-SY5Y cell line. As cell viability and morphology of tested cell lines seemed to be unaffected by new materials, the attenuated total reflectance (ATR)-FTIR method was applied to deeply measure the effects of the hybrids in the three different cell lines.

  8. 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.

  9. Structure and Properties of Sio2 Nanopowder Obtained From High-Silica Raw Materials by Plasma Method

    NASA Astrophysics Data System (ADS)

    Kosmachev, P. V.; Vlasov, V. A.; Skripnikova, N. K.

    2017-06-01

    The paper presents a plasma-assisted generation of nanodisperse powder obtained from diatomite, a natural high-silica material. The structure and properties of the obtained material are investigated using the transmission electron microscopy, energy dispersive X-Ray spectroscopy, infrared and X-ray photoelectron spectroscopies, and Brunauer-Emmett-Teller method. It is clearly shown that the obtained SiO2 nanoparticles are spherical, polydisperse and represented in the form of agglomerates. The specific surface of this nanopowder is 32 m2/g. Thermodynamic modeling of the plasma-assisted process is used to obtain the equilibrium compositions of condensed and gaseous reaction products. The plasma process is performed within the 300-5000 K temperature range.

  10. Adsorption of transition metal ions from aqueous solutions onto a novel silica gel matrix inorganic-organic composite material.

    PubMed

    Yin, Ping; Xu, Qiang; Qu, Rongjun; Zhao, Guifang; Sun, Yanzhi

    2010-01-15

    A novel inorganic-organic composite material silica gel microspheres encapsulated by imidazole functionalized polystyrene (SG-PS-azo-IM) has been synthesized and characterized. This composite material was used to investigate the adsorption of Cr(III), Mn(II), Fe(III), Ni(II), Cu(II), Zn(II), Hg(II), Pb(II), Pd(II), Pt(II), Ag(I), and Au(III) from aqueous solutions, and the research results displayed that SG-PS-azo-IM has the highest adsorption capacity for Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data, the best interpretation for the experimental data was given by the Langmuir isotherm equation, and the maximum adsorption capacity for Au(III) is 1.700 mmol/g. The adsorption selectivity, the dynamic adsorption and desorption properties of SG-PS-azo-IM for Au(III) have also been studied. The results showed that SG-PS-azo-IM had excellent adsorption for Au(III) in four binary ions system, especially in the systems of Au(III)-Zn(II) and Au(III)-Cu(II), and almost Au(III) could be desorbed with the eluent solution of 0.5% thiourea in 1 mol/L HCl. Moreover, this novel composite material was used to preconcentrate Au(III) before its determination by flame atomic adsorption spectrometry. In the initial concentration range of 0.10-0.20 microg/mL, multiple of enrichment could reach 5.28. Thus, silica gel encapsulated by polystyrene coupling with imidazole (SG-PS-azo-IM) is favorable and useful for the removal of transition metal ions, and the high adsorption capacity makes it a good promising candidate material for Au(III) removal.

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

    PubMed

    Akhter, Parveen; Hussain, Murid; Saracco, Guido; Russo, Nunzio

    2014-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Akhter, Parveen; Hussain, Murid; Saracco, Guido; Russo, Nunzio

    2014-04-01

    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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Synthesis of monodisperse mesoporous silica hollow microcapsules and their release of loaded materials.

    PubMed

    Kato, Noritaka; Ishii, Tomohiro; Koumoto, Shouzou

    2010-09-07

    Monodisperse mesoporous silica hollow capsules (MSHCs) with sizes ranging from 570 to 75 nm were synthesized using the sol-gel method combined with the template-assisted method. Monodisperse polystyrene (PS) particles were used as templates for the hollow structure of the MSHCs, and cylindrical micelles of cationic surfactant were used to create mesopores across the shell of the MSHC. To obtain MSHCs with a degree of polydispersity in diameter comparable to that of the PS templates and spherical in shape with uniform shell thicknesses, the conditions for the synthesis were systematically examined. It was found that the ranges of the reaction conditions to obtain such MSHCs had to be narrow because (1) the colloidal stability of the particles must be maintained before and after the sol-gel reaction and (2) the rate of the silica formation during the reaction must be regulated to attain sufficient shell thickness to retain the hollow structure and to achieve smooth surfaces. The sustained release of dye molecules loaded in the MSHCs was confirmed, indicating that our MSHC is a candidate for use as a drug carrier in drug delivery systems or as a container for microreactors.

  18. Electrochemical behavior of zinc particles with silica based coatings as anode material for zinc air batteries with improved discharge capacity

    NASA Astrophysics Data System (ADS)

    Schmid, M.; Willert-Porada, M.

    2017-05-01

    Silica coatings on zinc particles as anode material for alkaline zinc air batteries are expected to reduce early formation of irreversible ZnO passivation layers during discharge by controlling zinc dissolution and precipitation of supersaturated zincates, Zn(OH)42-. Zinc particles were coated with SiO2 (thickness: 15 nm) by chemical solution deposition and with Zn2SiO4 (thickness: 20 nm) by chemical vapor deposition. These coatings formed a Si(OH)4 gel in aqueous KOH and retarded hydrogen evolution by 40%. By treatment in aqueous KOH and drying afterwards, the silica coatings were changed into ZnO-K2O·SiO2 layers. In this work, the electrochemical performance of such coated zinc particles is investigated by different electrochemical methods in order to gain a deeper understanding of the mechanisms of the coatings, which reduce zinc passivation. In particular, zinc utilization and changes in internal resistance are investigated. Moreover, methods for determination of diffusion coefficients, charge carrier numbers and activation energies for electrochemical oxidation are determined. SiO2-coated zinc particles show improved discharge capacity (CVD-coated zinc: 69% zinc utilization, CSD-coated zinc: 62% zinc utilization) as compared to as-received zinc (57% zinc utilization) at C/20 rate, by reducing supersaturation of zincates. Additionally, KOH-modified SiO2-coated zinc particles enhance rechargeability after 100% depth-of-discharge.

  19. 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.

  20. 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

  1. Metal Binding Studies and EPR Spectroscopy of the Manganese Transport Regulator MntR†

    PubMed Central

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

    2007-01-01

    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 Å) observed in some of the available crystal structures. MntR is found to have a surprisingly low binding affinity (∼160 μM) for its cognate metal ion Mn2+. Moreover, the results of DNA binding studies in the presence

  2. Luciferase and luciferin co-immobilized mesoporous silica nanoparticle materials for intracellular biocatalysis.

    PubMed

    Sun, Xiaoxing; Zhao, Yannan; Lin, Victor S-Y; Slowing, Igor I; Trewyn, Brian G

    2011-11-23

    We report a gold nanoparticle (AuNP)-capped mesoporous silica nanoparticle (Au-MSN) platform for intracellular codelivery of an enzyme and a substrate with retention of bioactivity. As a proof-of-concept demonstration, Au-MSNs are shown to release luciferin from the interior pores of MSN upon AuNP uncapping in response to disulfide-reducing antioxidants and codeliver bioactive luciferase from the PEGylated exterior surface of Au-MSN to Hela cells. The effectiveness of luciferase-catalyzed luciferin oxidation and luminescence emission in the presence of intracellular ATP was measured by a luminometer. Overall, the chemical tailorability of the Au-MSN platform to retain enzyme bioactivity, the ability to codeliver enzyme and substrate, and the potential for imaging tumor growth and metastasis afforded by intracellular ATP- and glutathione-dependent bioluminescence make this platform appealing for intracellular controlled catalysis and tumor imaging.

  3. 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

  4. 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.

  5. Novel Shape-Stabilized Phase Change Materials Composed of Polyethylene Glycol/Nonsurfactant-Templated Mesoporous Silica: Preparation and Thermal Properties

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Zhu, Yingying; Wang, Jinbao; Lv, Mengjiao; Zhang, Xiongjie; Gao, Junkai; Zhang, Zijun; Lei, Hao

    2017-09-01

    A novel shape-stabilized phase change material (PEG/TAMS), fabricated using tannic acid-templated mesoporous silica (TAMS) as a support for polyethylene glycol, was developed for thermal energy storage. The method used to synthesize TAMS was simple, cost effective, environmentally friendly, and free of surfactant. The characterization results indicated that PEG was physically absorbed to TAMS and that TAMS had no influence on the crystal structure of PEG. According to the TGA thermograms, PEG/TAMS has excellent thermal stability and can be applied over a wide temperature range. Additionally, the differential scanning calorimetry results suggested that PEG/TAMS has good thermal properties and that its fusion and solidification enthalpies reached 114.7 J/g and 102.4 J/g, respectively. The results indicated that PEG/TAMS has great potential for practical applications.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. Kinetics of the formation of 2D-hexagonal silica nanostructured materials by nonionic block copolymer templating in solution.

    PubMed

    Manet, Sabine; Schmitt, Julien; Impéror-Clerc, Marianne; Zholobenko, Vladimir; Durand, Dominique; Oliveira, Cristiano L P; Pedersen, Jan Skov; Gervais, Christel; Baccile, Niki; Babonneau, Florence; Grillo, Isabelle; Meneau, Florian; Rochas, Cyrille

    2011-10-06

    The different steps of the self-assembly in solution of several 2D-hexagonal silica nanostructured SBA-15 materials have been investigated by SAXS and SANS in situ experiments. Unique quantitative information about the shape and size evolution upon time of the micellar aggregates throughout the self-assembly process is obtained using a complete model that describes well the scattering data for the various synthesis conditions. In all cases, before the precipitation of the material, the micelles shape changes from spherical to rod-like, where the structure of the rod-like micelles is linked to the structure of the 2D-hexagonal precipitated material. In addition, the kinetics of hydrolysis of the inorganic precursor (TEOS) has been determined by in situ Raman spectroscopy. More specifically, by comparing synthesis made with different acids (HNO(3), HBr, HCl, H(2)SO(4), and H(3)PO(4)), it is found that materials prepared using the "salting-out" anions (SO(4)(2-) and H(2)PO(4)(-)) are much better ordered than with the "salting-in" anions (NO(3)(-) and Br(-)). © 2011 American Chemical Society

  11. The effects of an airborne-particle abrasion and silica-coating on the bond strength between grooved titanium alloy temporary cylinders and provisional veneering materials.

    PubMed

    Wei, Ann Yu-Chieh; Sharma, Arun B; Watanabe, Larry G; Finzen, Frederick C

    2011-03-01

    Even though mechanical retentive features, such as grooves, are incorporated into the surface of titanium alloy temporary cylinders, a reliable bond to veneering provisional materials is not always achievable for screw-retained provisional implant restorations. There is insufficient information about the effect of tribochemical silica coating on the bond strength between provisional materials and grooved titanium alloy temporary cylinders. The purpose of this study was to evaluate, in vitro, the effect of an airborne-particle abrasion and silica-coating technique on the bond strength between grooved titanium alloy temporary cylinders and provisional veneering bisphenol-A glycidyl methacrylate and polymethyl methacrylate materials. Forty grooved titanium alloy (Ti-6Al-4V) internal connection implant temporary cylinders were used. A disc of veneering material (7.1 × 3.4 mm) was created around the midsection of each cylinder. Forty specimens were divided into 4 groups (n=10): group NoTxPMMA, no surface treatment and polymethyl methacrylate veneering material; group NoTxBisGMA, no surface treatment and BisGMA veneering material; group AbPMMA, airborne-particle abrasion, silica-coating surface treatment (Rocatec), and polymethyl methacrylate; and group AbBisGMA, airborne-particle abrasion, silica-coating surface treatment (Rocatec), and BisGMA. Each specimen was subjected to ultimate shear load testing at the interface of the veneering material and the temporary cylinder in a universal testing machine at a constant crosshead speed of 5 mm/min. Data were analyzed with a 1-way ANOVA (α=.05) followed by post hoc Student-Newman-Keuls test. Each specimen underwent surface observation with a light microscope at ×40 magnification to compare fracture patterns. Airborne-particle abrasion and silica-coating surface treatment significantly lowered the shear bond strength (P<.05). The type of provisional material did not significantly affect the shear bond strength, with or

  12. Engineering ultra-flattened normal dispersion photonic crystal fiber with silica material

    NASA Astrophysics Data System (ADS)

    Ferhat, Mohamed Lamine; Cherbi, Lynda; Bahloul, Lies; Hariz, Abdelhafid

    2017-05-01

    The tailoring of the group velocity dispersion (GVD) of an optical fiber is critical in many applications, influence on the bandwidth of information transmission in optical communication systems, successful utilization of nonlinear optical properties in applications such as supercontinuum generation, wavelength conversion and harmonic generation via stimulated Raman scattering ...In this work, we propose a design of ultra-flattened photonic crystal fiber by changing the diameter of the air holes of the cladding rings. The geometry is composed of only four rings, hexagonal structure of air holes and silica as background of the solid core. As a result, we present structures with broadband flat normal dispersion on many wavelengths bands useful for several applications. We obtain flat normal dispersion over 1000 nm broadband flat normal dispersion below -7 [ps/nm.km], and ultra-flat near zero normal dispersion below -0.2 [ps/nm.km] over 150 nm. The modeled photonic crystal fiber would be valuable for the fabrication of ultra-flattened-dispersion fibers, and have potential applications in wide-band high-speed optical communication systems, supercontinuum generation and many other applications.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Development of regenerative dye impregnated mesoporous silica materials for assessing exposure to ammonia.

    PubMed

    Chang, Yu-Chang; Bai, Hsunling; Chiang, Hsueh-Shih; Karthik, Mani; Li, Shou-Nan; Hsu, Jung-Nan; Shih, Hui-Ya

    2012-07-01

    The mesostructured materials MCM-41 and SBA-15 were studied as possible supports of bromocresol green (BG) dye impregnation for the ammonia gas detection because of their large surface area, high regenerative property, and high thermal stability. X-ray diffraction, transmission electron microscopy, scanning electron microscope, and N2 adsorption analysis were used to characterize the prepared materials. These materials could sense ammonia via visible color change from yellowish-orange to blue color. The color change process of the nanostructured materials was fully reversible during 10 cyclic tests. The results indicated that the ammonia absorption responses of the two nanostructured materials were both very sensitive, and high linear correlation and high precision were achieved. As the gaseous ammonia concentrations were 50 and 5 ppmv, the response times for the SBA-15/BG were only 1 and 5 min, respectively. Moreover the BG dye-impregnated SBA-15 was less affected by the variation in the relative humidity. It also had faster response for the detection of NH3, as well as lower manufacturing price as compared to that of the dye-impregnated MCM-41. Such feature enables SBA-15/BG to be a very promising material for the detection of ammonia gas.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

    2017-10-01

    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, 105B: 1828-1839, 2017. © 2016 Wiley Periodicals, Inc.

  4. Method to prevent recession loss of silica and silicon-containing materials in combustion gas environments

    DOEpatents

    Brun, Milivoj Konstantin; Luthra, Krishan Lal

    2003-01-01

    While silicon-containing ceramics or ceramic composites are prone to material loss in combustion gas environments, this invention introduces a method to prevent or greatly reduce the thickness loss by injecting directly an effective amount, generally in the part per million level, of silicon or silicon-containing compounds into the combustion gases.

  5. Assessment of the surface areas of silica and clay in acid-leached clay materials using concepts of adsorption on heterogeneous surfaces.

    PubMed

    Nguetnkam, J P; Kamga, R; Villiéras, F; Ekodeck, G E; Razafitianamaharavo, A; Yvon, J

    2005-09-01

    Two clays of the areas of Kaélé and Kousseri (extreme North Cameroon) containing mainly smectites and minor amounts of kaolinite were activated with sulfuric acid (1 to 8 N). Crystal-chemical properties were studied using X-ray diffraction, Fourier transform infrared spectroscopy, and chemical analysis, while textural properties were analyzed by step-by-step nitrogen adsorption at 77 K and low-pressure quasi-equilibrium argon adsorption at 77 K. As is generally observed, smectite is more sensitive to acid leaching than kaolinite. As a result of smectite decomposition, amorphous Al-containing silica forms, leading to an increase in the specific surface area of the leached materials. The content of the clay minerals and amorphous silica can be estimated on the basis of changes in the chemical composition of the samples upon acid leaching. As far as adsorption energy distributions derived from low-pressure argon derivative adsorption isotherms are concerned, the main modifications occur when 1 N sulfuric acid is used, due to the replacement of calcium and sodium compensating cations by protons. When higher acid concentrations are used, variations in adsorption energy distribution can be assigned to the presence of amorphous silica. It was possible to model experimental adsorption energy distributions as weighted sums of argon adsorption energy distributions obtained on (i) 1 N samples representing protonated clays and (ii) a silica gel used as a reference aluminous silica. Using such an approach, increasing acid concentration results in an increase in the surface area of silica, whereas the surface area of the remaining clay minerals remains roughly constant.

  6. 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

  7. 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.

  8. Neutron Compton scattering investigation of sodium hydride: From bulk material to encapsulated nanoparticulates in amorphous silica gel

    NASA Astrophysics Data System (ADS)

    Seel, A. G.; Sartbaeva, A.; Mayers, J.; Ramirez-Cuesta, A. J.; Edwards, P. P.

    2011-03-01

    In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

  9. Neutron Compton scattering investigation of sodium hydride: from bulk material to encapsulated nanoparticulates in amorphous silica gel.

    PubMed

    Seel, A G; Sartbaeva, A; Mayers, J; Ramirez-Cuesta, A J; Edwards, P P

    2011-03-21

    In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Designing novel hybrid materials by one-pot co-condensation: from hydrophobic mesoporous silica nanoparticles to superamphiphobic cotton textiles.

    PubMed

    Pereira, C; Alves, C; Monteiro, A; Magén, C; Pereira, A M; Ibarra, A; Ibarra, M R; Tavares, P B; Araújo, J P; Blanco, G; Pintado, J M; Carvalho, A P; Pires, J; Pereira, M F R; Freire, C

    2011-07-01

    This work reports the synthesis and characterization of mesoporous silica nanoparticles (MSNs) functionalized with tridecafluorooctyltriethoxysilane (F13) and their in situ incorporation onto cotton textiles. The hybrid MSNs and the functional textiles were prepared by a one-pot co-condensation methodology between tetraethylorthosilicate (TEOS) and F13, with hexadecyltrimethylammonium chloride (CTAC) as the template and triethanolamine as the base. The influence of the F13 to TEOS molar ratio (1:10, 1:5 and 1:3) on the nanoparticle morphology, porosity, degree of functionalization, and hydro/oleophobic properties is discussed. The hybrid nanosilicas presented high colloidal stability and were spherical and monodispersed with average particle size of ∼45 nm. They also showed high surface areas, large pore volumes, and a wormhole-type mesoporous structure. The increase in the organosilane proportion during the co-condensation process led to a more radially branched wormhole-like mesoporosity, a decrease in the surface area, pore volume, and amount of surface silanol groups, and an enrichment of the surface with fluorocarbon moieties. These changes imparted hydrophobic and oleophobic properties to the materials, especially to that containing the highest F13 loading. Cotton textiles were coated with the F13-MSNs through an efficient and less time-consuming route. The combination between surface roughness and mesoporosity imparted by the MSNs, and the low surface energy provided by the organosilane resulted in superhydrophobic functional textiles. Moreover, the textile with the highest loading of fluorocarbon groups was superamphiphobic.

  15. 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. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. 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.

  17. 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.

  18. 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. Copyright © 2016 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

  19. Bone regeneration in the presence of a synthetic hydroxyapatite/silica oxide-based and a xenogenic hydroxyapatite-based bone substitute material.

    PubMed

    Kruse, A; Jung, R E; Nicholls, F; Zwahlen, R A; Hämmerle, C H F; Weber, F E

    2011-05-01

    A comparison of synthetic hydroxyapatite/silica oxide, xenogenic hydroxyapatite-based bone substitute materials with empty control sites in terms of bone regeneration enhancement in a rabbit calvarial four non-critical-sized defect model. In each of six rabbits, four bicortical calvarial bone defects were generated. The following four treatment modalities were randomly allocated: (1) empty control site, (2) synthetic hydroxyapatite/silica oxide-based (HA/SiO) test granules, (3) xenogenic hydroxyapatite -based granules, (4) synthetic hydroxyapatite/silica oxide -based (HA/SiO) test two granules. The results of the latter granules have not been reported due to their size being three times bigger than the other two granule types. After 4 weeks, the animals were sacrificed and un-decalcified sections were obtained for histological analyses. For statistical analysis, the Kruskal-Wallis test was applied (P<0.05). Histomorphometric analysis showed an average area fraction of newly formed bone of 12.32±10.36% for the empty control, 17.47±6.42% for the xenogenic hydroxyapatite -based granules group, and 21.2±5.32% for the group treated with synthetic hydroxyapatite/silica oxide -based granules. Based on the middle section, newly formed bone bridged the defect to 38.33±37.55% in the empty control group, 54.33±22.12% in the xenogenic hydroxyapatite -based granules group, and to 79±13.31% in the synthetic hydroxyapatite/silica oxide -based granules group. The bone-to-bone substitute contact was 46.38±18.98% for the xenogenic and 59.86±14.92% for the synthetic hydroxyapatite/silica oxide-based granules group. No significant difference in terms of bone formation and defect bridging could be detected between the two bone substitute materials or the empty defect. There is evidence that the synthetic hydroxyapatite/silica oxide granules provide comparable results with a standard xenogenic bovine mineral in terms of bone formation and defect bridging in non-critical size

  20. Selective adsorption mechanisms of antilipidemic and non-steroidal anti-inflammatory drug residues on functionalized silica-based porous materials in a mixed solute.

    PubMed

    Suriyanon, Nakorn; Permrungruang, Jutima; Kaosaiphun, Jidanan; Wongrueng, Aunnop; Ngamcharussrivichai, Chawalit; Punyapalakul, Patiparn

    2015-10-01

    The selective adsorption mechanisms of naproxen (NAP), acetaminophen (ACT), and clofibric acid (CFA) on silica-based porous materials were examined by single and mixed-batch adsorption. Effects of the types and densities of surface functional groups on adsorption capacities were determined, including the role of hydrophobic and hydrophilic dissolved organic matters (DOMs). Hexagonal mesoporous silica (HMS), superparamagnetic HMS (HMS-SP) and SBA-15 were functionalized and applied as adsorbents. Compared with powdered activated carbon (PAC), amine-functionalized HMS had a better adsorption capacity for CFA, but PAC possessed a higher adsorption capacity for the other pharmaceuticals than HMS and its two derivatives. In contrast to PAC, the adsorption capacity of the mesoporous silicas varied with the solution pH, being highest at pH 5. Electrostatic interactions and hydrogen bonding were found to be the main mechanisms. Increase in grafted amine group density on silica surfaces can enhance the CFA adsorption capacity. Further, hydrophilic DOM can decrease CFA adsorption capacities on amino-grafted adsorbents by adsorption site competition, while hydrophobic DOM can interfere with CFA adsorption by the interaction between hydrophobic DOM and CFA. Finally, in a competitive adsorption study, the adsorption capacity of hydrophilic adsorbents for acidic pharmaceuticals varied with their pKa values. Copyright © 2015 Elsevier Ltd. All rights reserved.

  1. 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.

  2. 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.

  3. 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.

  4. Ordered mesoporous silica material SBA-15: a broad-spectrum formulation platform for poorly soluble drugs.

    PubMed

    Van Speybroeck, Michiel; Barillaro, Valéry; Thi, Thao Do; Mellaerts, Randy; Martens, Johan; Van Humbeeck, Jan; Vermant, Jan; Annaert, Pieter; Van den Mooter, Guy; Augustijns, Patrick

    2009-08-01

    Encapsulating poorly soluble drugs in mesoporous silicates is an emerging strategy to improve drug dissolution. This study evaluates the applicability of the ordered mesoporous silicate SBA-15 as an excipient to enhance dissolution, for a test series of 10 poorly soluble compounds with a high degree of physicochemical diversity (carbamazepine, cinnarizine, danazol, diazepam, fenofibrate, griseofulvin, indomethacin, ketoconazole, nifedipine, and phenylbutazone). A generic solvent impregnation method was used to load all model compounds. The target drug content was 20%. The physical nature of the formulations was investigated using differential scanning calorimetry (DSC) and the pharmaceutical performance evaluated by means of in vitro dissolution. Aliquots of each formulation were stored at 25 degrees C/52% RH for 6 months, and again subjected to DSC and in vitro dissolution. The target drug content of 20% was attained in all cases. DSC data evidenced the noncrystalline state of the confined drugs. All SBA-15 formulations exhibited an enhanced dissolution as compared to their corresponding crystalline materials, and the high pharmaceutical performance of all formulations was retained during the 6 months storage period. The results of this study suggest that encapsulation in SBA-15 can be applied as a dissolution-enhancing formulation approach for a very wide variety of poorly soluble drugs. Copyright 2009 Wiley-Liss, Inc.

  5. 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

  6. 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

  7. 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

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

    PubMed

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

    2015-01-01

    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. 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. 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 components or as carrier proteins

  9. 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.

  10. Mechanism of self-assembly in the synthesis of silica mesoporous materials: in situ studies by X-ray and neutron scattering.

    PubMed

    Blin, J L; Impéror-Clerc, M

    2013-05-07

    In this review, recent progress in the understanding of the formation of various silica mesoporous materials is reported. Owing to time-resolved experiments using Small Angle X-ray or Neutron Scattering (SAXS or SANS), it is possible to follow in situ the formation of a material during its synthesis via the Cooperative Templating Mechanism (CTM). Such experiments directly provide unique information about the structural properties of the material inside the synthesis solution. One of the main findings is that phase transformations often occur in the material prior to the stabilisation of its final structure. Moreover, during the very early stages of the synthesis, it is also possible to detect the first hybrid silica-surfactant micellar aggregates, prior to the precipitation of the material, as reported in the case of the SBA-15 materials. All these experiments allow a better understanding of the formation mechanisms and of the influence of the many synthesis parameters. These results open the way to a better prediction and control of the structure of mesoporous materials.

  11. Enrichment of proteinaceous materials on a strong cation-exchange diol silica restricted access material: protein-protein displacement and interaction effects.

    PubMed

    Willemsen, Olga; Machtejevas, Egidijus; Unger, Klaus K

    2004-02-06

    A study of size exclusion and enrichment of proteins employing strong cation-exchange diol silica restricted access material (SCX-RAM) under saturation conditions is presented. Experiments were carried out with bacitracin, protamine, ribonuclease, lysozyme and bovine serum albumin as individual proteinaceous analytes as well as comprehensive binary mixtures and with human urine samples. Protein size dependent capacity features of the SCX-RAM column was observed. Bacitracin demonstrated the highest capacity followed by protamine while adsorption capacities of both ribonuclease and lysozyme were found smaller by a factor of 10. Applying binary protein samples occurring displacement effects were apparent: proteins with strong cationic properties displaced those already adsorbed by the bonded cation-exchange ligands. Bacitracin was displaced in all binary mixture experiments in particular by protamine. Furthermore, the binary mixtures displayed increased adsorption for some proteins due to complex formation. Lysozyme and ribonuclease showed double capacity values when paired with bacitracin. Both phenomena, displacement and enhanced adsorption occurred in the saturated state and led to changes in the urine composition during sample preparation. Injecting urine samples the relative proportions of fractions changed from 4 up to more than 20 times, due to the differences of the protein adsorption capacities on the SCX-RAM column. Analysing urine samples the SCX-RAM column provided extensive long-term stability.

  12. 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.

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

    PubMed Central

    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

    2016-01-01

    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 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. Our results highlight the versatility of protein scaffolds in accommodating new biochemical activities and provide unprecedented insight into the earliest stages of biomineralization. PMID:26981620

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

    PubMed

    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

    2016-03-01

    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 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. Our results highlight the versatility of protein scaffolds in accommodating new biochemical activities and provide unprecedented insight into the earliest stages of biomineralization.

  15. 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

  16. Characterization and acidic properties of Al-SBA-15 materials prepared by post-synthesis alumination of a low-cost ordered mesoporous silica

    SciTech Connect

    Gomez-Cazalilla, M.; Merida-Robles, J.M.; Gurbani, A.; Rodriguez-Castellon, E.; Jimenez-Lopez, A.

    2007-03-15

    A series of Al-containing SBA-15 type materials with different Si/Al ratio, were prepared by post-synthesis modification of a pure highly ordered mesoporous silica SBA-15 obtained by using sodium silicate as silica source, and amphiphilic block copolymer as structure-directing agent. A high level of aluminum incorporation was achieved, reaching an Si/Al ratio of up to 5.5, without any significant loss in the textural properties of SBA-15. These materials were fully characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), {sup 27}Al NMR spectroscopy, and N{sub 2} adsorption at 77 K. The acid properties of these materials have been evaluated by NH{sub 3}-TPD, adsorption of pyridine and deuterated acetonitrile coupled to FTIR spectroscopy. The effective acidity of these materials was evaluated using two catalytic reactions: 2-propanol dehydrogenation and 1-butene isomerization. The adsorption of basic probe molecules and the catalytic behavior revealed an evolution of the acid properties with the Al content. These studies have shown that the Al-SBA-15 materials contain Bronsted and Lewis acid sites with medium acidity which makes them appropriate to be used as acid catalysts in heterogeneous catalysis, catalytic supports, and adsorbents. - Graphical abstract: Al KLL spectra of Al-SBA-15 materials with different Si/Al ratios.

  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 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.

  19. 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

    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. In this paper, 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. Finally, taken together, these findings elucidate a previously unknown MBD and suggest new regulatory mechanisms for metal transport by P1B-ATPases.

  20. A new metal binding domain involved in cadmium, cobalt and zinc transport

    DOE PAGES

    Smith, Aaron T.; Barupala, Dulmini; Stemmler, Timothy L.; ...

    2015-07-20

    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. In this paper, 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 anmore » 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. Finally, taken together, these findings elucidate a previously unknown MBD and suggest new regulatory mechanisms for metal transport by P1B-ATPases.« less

  1. 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.

  2. 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.

  3. Characterization of a multi-metal binding biosorbent: Chemical modification and desorption studies.

    PubMed

    Abdolali, Atefeh; Ngo, Huu Hao; Guo, Wenshan; Zhou, John L; Du, Bin; Wei, Qin; Wang, Xiaochang C; Nguyen, Phuoc Dan

    2015-10-01

    This work attends to preparation and characterization of a novel multi-metal binding biosorbent after chemical modification and desorption studies. Biomass is a combination of tea waste, maple leaves and mandarin peels with a certain proportion to adsorb cadmium, copper, lead and zinc ions from aqueous solutions. The mechanism involved in metal removal was investigated by SEM, SEM/EDS and FTIR. SEM/EDS showed the presence of different chemicals and adsorbed heavy metal ions on the surface of biosorbent. FTIR of both unmodified and modified biosorbents revealed the important role of carboxylate groups in heavy metal biosorption. Desorption using different eluents and 0.1 M HCl showed the best desorption performance. The effectiveness of regeneration step by 1 M CaCl2 on five successive cycles of sorption and desorption displays this multi-metal binding biosorbent (MMBB) can effectively be utilized as an adsorbent to remove heavy metal ions from aqueous solutions in five cycles of sorption/desorption/regeneration. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. Generation of Metal-Binding Staphylococci through Surface Display of Combinatorially Engineered Cellulose-Binding Domains

    PubMed Central

    Wernérus, Henrik; Lehtiö, Janne; Teeri, Tuula; Nygren, Per-Åke; Ståhl, Stefan

    2001-01-01

    Ni2+-binding staphylococci were generated through surface display of combinatorially engineered variants of a fungal cellulose-binding domain (CBD) from Trichoderma reesei cellulase Cel7A. Novel CBD variants were generated by combinatorial protein engineering through the randomization of 11 amino acid positions, and eight potentially Ni2+-binding CBDs were selected by phage display technology. These new variants were subsequently genetically introduced into chimeric surface proteins for surface display on Staphylococcus carnosus cells. The expressed chimeric proteins were shown to be properly targeted to the cell wall of S. carnosus cells, since full-length proteins could be extracted and affinity purified. Surface accessibility for the chimeric proteins was demonstrated, and furthermore, the engineered CBDs, now devoid of cellulose-binding capacity, were shown to be functional with regard to metal binding, since the recombinant staphylococci had gained Ni2+-binding capacity. Potential environmental applications for such tailor-made metal-binding bacteria as bioadsorbents in biofilters or biosensors are discussed. PMID:11571172

  11. Generation of metal-binding staphylococci through surface display of combinatorially engineered cellulose-binding domains.

    PubMed

    Wernérus, H; Lehtiö, J; Teeri, T; Nygren, P A; Ståhl, S

    2001-10-01

    Ni(2+)-binding staphylococci were generated through surface display of combinatorially engineered variants of a fungal cellulose-binding domain (CBD) from Trichoderma reesei cellulase Cel7A. Novel CBD variants were generated by combinatorial protein engineering through the randomization of 11 amino acid positions, and eight potentially Ni(2+)-binding CBDs were selected by phage display technology. These new variants were subsequently genetically introduced into chimeric surface proteins for surface display on Staphylococcus carnosus cells. The expressed chimeric proteins were shown to be properly targeted to the cell wall of S. carnosus cells, since full-length proteins could be extracted and affinity purified. Surface accessibility for the chimeric proteins was demonstrated, and furthermore, the engineered CBDs, now devoid of cellulose-binding capacity, were shown to be functional with regard to metal binding, since the recombinant staphylococci had gained Ni(2+)-binding capacity. Potential environmental applications for such tailor-made metal-binding bacteria as bioadsorbents in biofilters or biosensors are discussed.

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

    PubMed

    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

  13. 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

  14. 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.

  15. 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.

  16. Double layer approach to create durable superhydrophobicity on cotton fabric using nano silica and auxiliary non fluorinated materials

    NASA Astrophysics Data System (ADS)

    Manatunga, Danushika Charyangi; de Silva, Rohini M.; de Silva, K. M. Nalin

    2016-01-01

    Creation of differential superhydrophobicity by applying different non-fluorinated hydrophobization agents on a cotton fabric roughened with silica nanoparticles was studied. Cotton fabric surface has been functionalized with silica nanoparticles and further hydrophobized with different hydrophobic agents such as hexadecyltrimethoxy silane (HDTMS), stearic acid (SA), triethoxyoctyl silane (OTES) and hybrid mixtures of HDTMS/SA and HDTMS/OTES. The cotton fabrics before and after the treatment were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM) and thermogravimetric analysis (TGA). The wetting behavior of cotton samples was investigated by water contact angle (WCA) measurement, water uptake, water repellency and soil repellency testing. The treated fabrics exhibited excellent water repellency and high water contact angles (WCA). When the mixture of two hydrophobization agents such as HDTMS/OTES and HDTMS/SA is used, the water contact angle has increased (145°⿿160°) compared to systems containing HDTMS, OTES, SA alone (130°⿿140°). It was also noted that this fabricated double layer (silica + hydrophobization agent) was robust even after applying harsh washing conditions and there is an excellent anti-soiling effect observed over different stains. Therefore superhydrophobic cotton surfaces with high WCA and soil repellency could be obtained with silica and mixture of hydrophobization agents which are cost effective and environmentally friendly when compared with the fluorosilane treatment.

  17. 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.

  18. One-step synthesis of amine-functionalized hollow mesoporous silica nanoparticles as efficient antibacterial and anticancer materials.

    PubMed

    Hao, Nanjing; Jayawardana, Kalana W; Chen, Xuan; Yan, Mingdi

    2015-01-21

    In this study, amine-functionalized hollow mesoporous silica nanoparticles with an average diameter of ∼100 nm and shell thickness of ∼20 nm were prepared by an one-step process. This new nanoparticulate system exhibited excellent killing efficiency against mycobacterial (M. smegmatis strain mc(2) 651) and cancer cells (A549).

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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... the registration review of cyromazine, silica silicates (silica dioxide and silica gel), glufosinate...). Silica silicates, silicon dioxide and silica gel, are insecticides and acaracides used in...

  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. 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.

  6. 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.

  7. 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. © Crown copyright 2014.

  8. Hybrid mesoporous-silica materials functionalized by Pt(II) complexes: correlation between the spatial distribution of the active center, photoluminescence emission, and photocatalytic activity.

    PubMed

    Mori, Kohsuke; Watanabe, Kentaro; Terai, Yoshikazu; Fujiwara, Yasufumi; Yamashita, Hiromi

    2012-09-03

    [Pt(tpy)Cl]Cl (tpy: terpyridine) was successfully anchored to a series of mesoporous-silica materials that were modified with (3-aminopropyl)triethoxysilane with the aim of developing new inorganic-organic hybrid photocatalysts. Herein, the relationship between the luminescence characteristics and photocatalytic activities of these materials is examined as a function of Pt loading to define the spatial distribution of the Pt complex in the mesoporous channel. At low Pt loading, the Pt complex is located as an isolated species and exhibits strong photoluminescence emission at room temperature owing to metal-to-ligand charge-transfer ((3)MLCT) transitions (at about 530 nm). Energy- and/or electron-transfer from (3)MLCT to O(2) generate potentially active oxygen species, which are capable of promoting the selective photooxidation of styrene derivatives. On the other hand, short Pt···Pt interactions are prominent at high loading and the metal-metal-to-ligand charge-transfer ((3)MMLCT) transition is at about 620 nm. Such Pt complexes, which are situated close to each other, efficiently catalyze H(2)-evolution reactions in aqueous media in the presence of a sacrificial electron donor (EDTA) under visible-light irradiation. This study also investigates the effect of nanoconfinement on anchored guest complexes by considering the differences between the pore dimensions and structures of mesoporous-silica materials. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  10. 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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.Silica and silica incorporated nanocomposite materials have been extensively studied for a wide range of applications. Here we demonstrate an

  11. Structural and thermodynamic characterization of metal binding in Vps29 from Entamoeba histolytica: Implication in retromer function.

    PubMed

    Srivastava, Vijay Kumar; Yadav, Rupali; Natsuki, Watanabe; Tomar, Priya; Mukherjee, Madhumita; Gourinath, Samudrala; Nakada-Tsukui, Kumiko; Nozaki, Tomoyoshi; Datta, Sunando

    2017-09-12

    Vps29 is the smallest subunit of retromer complex with metallo-phosphatase fold. Although the role of metal in Vps29 is in quest, its metal binding mutants has been reported to affect the localization of the retromer complex in human cells. In this study, we report the structural and thermodynamic consequences of these mutations in Vps29 from the protozoan parasite, Entamoeba histolytica (EhVps29). EhVps29 is a zinc binding protein as revealed by X-ray crystallography and isothermal titration calorimetry. The metal binding pocket of EhVps29 exhibits marked differences in its 3-dimensional architecture and metal coordination in comparison to its human homologs and other metallo-phosphatases. Alanine substitutions of the metal-coordinating residues showed significant alteration in the binding affinity of EhVps29 for zinc. We also determined the crystal structures of metal binding defective mutants (D62A and D62A/H86A) of EhVps29. Based on our results, we propose that the metal atoms or the bound water molecules in the metal binding site are important for maintaining the structural integrity of the protein. Further cellular studies in the amoebic trophozoites showed that the overexpression of wild type EhVps29 leads to reduction in intracellular cysteine protease activity suggesting its crucial role in secretion of the proteases. This article is protected by copyright. All rights reserved. © 2017 John Wiley & Sons Ltd.

  12. 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...

  13. 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...

  14. 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.

  15. Investigations of the uptake of transuranic radionuclides by humic and fulvic acids chemically immobilized on silica gel and their competitive release by complexing agents

    SciTech Connect

    Bulman, R.A.; Szabo, G.; Clayton, R.F.; Clayton, C.R.

    1998-07-01

    The chemistry of the interactions of transuranic elements (TUs) with humic substances needs to be understood so that humate-mediated movement of transuranic radionuclides through the environment can be predicted. This paper reports the chemical immobilization on silica gel of humic and fulvic acids and evaluates the potential of these new materials for the retention of Pu and Am. In addition to the preparation of the foregoing immobilized humic substances, other low molecular weight metal-binding ligands have also been immobilized on silica gel to investigate the binding sites for transuranic elements (TUs) in humic substances. The X-ray photoelectron spectra (XPS) of Th(IV) complexed by humic acid and the immobilized humic acid are similar thus it appears that immobilization of humic acid does not generate any configurational changes in the Th(IV)-binding sites of the macromolecule. A variety of chelating agents partly mobilize these TUs sorbed on the solid phases. A batch method was used to determine the distribution coefficients (R{sub d}) of Pu and Am between the silica gels and aqueous solutions of phosphate and citrate. The effects of the immobilized ligands, the anions and pH in the solution on sorption were assessed. Distributed coefficients (R{sub d}) for the uptake of Pu and Am by these prepared solid phases are, in some cases, of a similar order of magnitude as those determined for soil and particles suspended in terrestrial surface waters.

  16. 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

  17. 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.

  18. Effect of O-Side-Chain-Lipopolysaccharide Chemistry on Metal Binding

    PubMed Central

    Langley, S.; Beveridge, T. J.

    1999-01-01

    Pseudomonas aeruginosa PAO1 produces two chemically distinct types of lipopolysaccharides (LPSs), termed A-band LPS and B-band LPS. The A-band O-side chain is electroneutral at physiological pH, while the B-band O-side chain contains numerous negatively charged sites due to the presence of uronic acid residues in the repeat unit structure. Strain PAO1 (A+ B+) and three isogenic LPS mutants (A+ B−, A− B+, and A− B−) were studied to determine the contribution of the O-side-chain portion of LPS to metal binding by the surfaces of gram-negative cells. Transmission electron microscopy with energy-dispersive X-ray spectroscopy was used to locate and analyze sites of metal deposition, while atomic absorption spectrophotometry and inductively coupled plasma-mass spectrometry were used to perform bulk quantitation of bound metal. The results indicated that cells of all of the strains caused the precipitation of gold as intracellular, elemental crystals with a d-spacing of 2.43 Å. This type of precipitation has not been reported previously for gram-negative cells and suggests that in the organisms studied gold binding is not a surface-mediated event. All four strains bound similar amounts of copper (0.213 to 0.222 μmol/mg [dry weight] of cells) at the cell surface, suggesting that the major surface metal-binding sites reside in portions of the LPS which are common to all strains (perhaps the phosphoryl groups in the core-lipid A region). However, significant differences were observed in the abilities of strains dps89 (A− B+) and AK1401 (A+ B−) to bind iron and lanthanum, respectively. Strain dps89 caused the precipitation of iron (1.623 μmol/mg [dry weight] of cells) as an amorphous mineral phase (possibly iron hydroxide) on the cell surface, while strain AK1401 nucleated precipitation of lanthanum (0.229 μmol/mg [dry weight] of cells) as apiculate, surface-associated crystals. Neither iron nor lanthanum precipitates were observed on the cells of other

  19. 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

  20. 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.

  1. 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

  2. ETMB-RBF: discrimination of metal-binding sites in electron transporters based on RBF networks with PSSM profiles and significant amino acid pairs.

    PubMed

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

    2013-01-01

    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. 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. 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. 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.

  3. Photoluminescence profiles and fast/slow annealing effects of Eu(III)/Tb(III)-codoped silica phosphor materials.

    PubMed

    Yoon, Hee Jung; Choi, Young In; Kang, Jun-Gill; Sohn, Youngku

    2016-05-01

    A silica (SiO2) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using a modified Stöber method. The effects of fast and slow thermal annealing on photoluminescence profile imaging were examined. Slow annealing treatment suppressed more quenching sites than fast thermal annealing to further increase the photoluminescence signals. The photoluminescence signals observed between 450 and 720 nm were assigned to the (5)D(0)  → (7)F(J) (J = 0,1,2,3,4) of Eu(III) and the (5)D(4)  → (7)F(J) (J = 6,5,4,3) transitions of Tb(III). Photoluminescence was largely sensitized by indirect excitation and was much stronger than that generated by direct excitation. The Eu(III) and Tb(III) ions were doped at lower symmetry sites in the silica matrix. Copyright © 2015 John Wiley & Sons, Ltd.

  4. Metal-binding peptides: Their role in responses to metal stress

    SciTech Connect

    Rauser, W.E. )

    1989-04-01

    Excess metals are one stress that plants may encounter. The metals Cd, Cu, Ni, and Zn are considered because of concern for their entry into the foodchain of animals and man. Studies of metal tolerant plants and cell cultures suggest three types of responses: exclusion of metal from protoplasts by binding to cell walls, differential membrane transport reducing metal exposure of enzymes, and intracellular chelation of metal in innocuous forms. One group of compounds involved in the latter response are metal-binding peptides designated phytochelatins. They are a family of small peptides composed of five kinds of amino acids, including 2 to 11 cysteines which provide thiols for selective binding of metal. Metals induce the synthesis of phytochelatins through unknown enzymes involving glutathione. In plant cell cultures the peptides bind about 90% of the intracellular Cd. In roots of young plants up to half of the metal is bound by phytochelatins. Intact plants probably use a combination of responses to deal with excess metals, phytochelatins may dominate in certain cases.

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

    PubMed Central

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

    2014-01-01

    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. PMID:24778258

  6. Detection of metal binding sites on functional S-layer nanoarrays using single molecule force spectroscopy.

    PubMed

    Tang, Jilin; Ebner, Andreas; Kraxberger, Bernhard; Leitner, Michael; Hykollari, Alba; Kepplinger, Christian; Grunwald, Christian; Gruber, Hermann J; Tampé, Robert; Sleytr, Uwe B; Ilk, Nicola; Hinterdorfer, Peter

    2009-10-01

    Crystalline bacterial cell surface layers (S-layers) show the ability to recrystallize into highly regular pattern on solid supports. In this study, the genetically modified S-layer protein SbpA of Lysinibacillus sphaericus CCM 2177, carrying a hexa-histidine tag (His(6)-tag) at the C-terminus, was used to generate functionalized two-dimensional nanoarrays on a silicon surface. Atomic force microscopy (AFM) was applied to explore the topography and the functionality of the fused His(6)-tags. The accessibility of the His(6)-tags was demonstrated by in-situ anti-His-tag antibody binding to the functional S-layer array. The metal binding properties of the His(6)-tag was investigated by single molecule force microscopy. For this purpose, newly developed tris-NTA was tethered to the AFM tips via a flexible polyethylene glycol (PEG) linker. The functionalized tips showed specific interactions with S-layer containing His(6)-tags in the presence of nickel ions. Thus the His(6)-tag is located at the outer surface of the S-layer and can be used for stable but reversible attachment of functional tris-NTA derivatives.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. Heterogeneity in metal binding by individual fluorescent components in a eutrophic algae-rich lake.

    PubMed

    Xu, Huacheng; Yan, Zaisheng; Cai, Haiyuan; Yu, Guanghui; Yang, Liuyan; Jiang, Helong

    2013-12-01

    Dissolved organic matter (DOM) affects the toxicity, mobility and bioavailability of metals in aquatic environment. In this study, the interactions between two metals of environmental concern [Cu(II) and Fe(III)] with DOM in a euthrophic algae-rich lake (Lake Taihu, China), including dissolved natural organic matter (NOM) and algal extracellular polymeric substance (EPS), were studied using fluorescence excitation-emission matrix (EEM) quenching titration combined with parallel factor (PARAFAC) analysis. Obvious protein-like peaks were detected in algal EPS matrix, while both protein- and humic-like peaks can be found in NOM. PARAFAC analysis identified four fluorescent components, including one humic-, one tryptophan- and two tyrosine-like components, from 114 EEM samples. It was shown that fluorescent tyrosine- (log K(M) > 5.21) and humic-like substances (log K(M) > 4.84) in NOM fraction exhibited higher metal binding capacities than those in EPS matrix, while algal EPS was characterized with a high metal-tryptophan-like substances affinity (log K(M) > 5.08). Moreover, for the eutrophic algae-rich lakes, fluorescent tryptophan- and humic-like substances were responsible for Cu transportation, whereas the mobility of Fe would be related with the tyrosine-like substances. The results facilitate a further insight into the biogeochemical behaviors of metals in eutrophic algae-rich ecosystems as well as other related aquatic environments. © 2013 Elsevier Inc. All rights reserved.

  13. 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.

  14. Metal binding affinity and structural properties of calmodulin-like protein 14 from Arabidopsis thaliana.

    PubMed

    Vallone, Rosario; La Verde, Valentina; D'Onofrio, Mariapina; Giorgetti, Alejandro; Dominici, Paola; Astegno, Alessandra

    2016-08-01

    In addition to the well-known Ca(2+) sensor calmodulin, plants possess many calmodulin-like proteins (CMLs) that are predicted to have specific roles in the cell. Herein, we described the biochemical and biophysical characterization of recombinant Arabidopsis thaliana CML14. We applied isothermal titration calorimetry to analyze the energetics of Ca(2+) and Mg(2+) binding to CML14, and nuclear magnetic resonance spectroscopy, together with intrinsic and ANS-based fluorescence, to evaluate the structural effects of metal binding and metal-induced conformational changes. Furthermore, differential scanning calorimetry and limited proteolysis were used to characterize protein thermal and local stability. Our data demonstrate that CML14 binds one Ca(2+) ion with micromolar affinity (Kd ∼ 12 µM) and the presence of 10 mM Mg(2+) decreases the Ca(2+) affinity by ∼5-fold. Although binding of Ca(2+) to CML14 increases protein stability, it does not result in a more hydrophobic protein surface and does not induce the large conformational rearrangement typical of Ca(2+) sensors, but causes only localized structural changes in the unique functional EF-hand. Our data, together with a molecular modelling prediction, provide interesting insights into the biochemical properties of Arabidopsis CML14 and may be useful to direct additional studies aimed at understanding its physiological role. © 2016 The Protein Society.

  15. Multiple metal binding cores are required for metalloregulation by M-box riboswitch RNAs

    PubMed Central

    Wakeman, Catherine A.; Ramesh, Arati; Winkler, Wade C.

    2009-01-01

    Riboswitches are regulatory RNAs that control downstream gene expression in response to direct association with intracellular metabolites or metals. Typically, riboswitch aptamer domains bind to a single small molecule metabolite. In contrast, an X-ray crystallographic structural model for the M-box riboswitch aptamer revealed the absence of an organic metabolite ligand but the presence of at least six tightly associated magnesiums. This observation agrees well with the proposed role of the M-box riboswitch in functioning as a sensor of intracellular magnesium, although additional nonspecific metal interactions are also undoubtedly required for these purposes. To gain greater functional insight into the metalloregulatory capabilities of M-box RNAs we sought to determine whether all or a subset of the RNA-chelated magnesium ions were required for riboswitch function. To accomplish this task, each magnesium binding site was simultaneously yet individually perturbed through random incorporation of phosphorothioate nucleotide analogues and RNA molecules were investigated for their ability to fold in varying levels of magnesium. These data revealed that all of the magnesium ions observed in the structural model are important for magnesium-dependent tertiary structure formation. Additionally, these functional data revealed a new core of potential metal binding sites that are likely to assist formation of key tertiary interactions and were previously unobserved in the structural model. It is clear from these data that–M-box RNAs require specific binding of a network of metal ions for partial fulfillment of their metalloregulatory functions. PMID:19619558

  16. Creation of a putative third metal binding site in type II dihydroorotases significantly enhances enzyme activity.

    PubMed

    Huang, Yen-Hua; Huang, Cheng-Yang

    2015-01-01

    Dihydroorotase (DHOase) is the third enzyme in the de novo biosynthesis pathway of pyrimidine nucleotides. DHOase is divided into two types (I and II). Type II DHOase generally contains a binuclear metal center in its active site. Recently, the crystal structure of DHOase domain in human CAD protein (huDHOase) has revealed three metal ions in the protein's active site. However, whether type II DHOase can have the critical third metal ion, as observed in huDHOase, remains unknown. In the present study, the putative third metal binding site in type II enzymes, such as the prokaryotic Salmonella enterica serovar Typhimurium LT2 DHOase (StDHOase) and the eukaryotic Saccharomyces cerevisiae DHOase (ScDHOase), was created and identified. StDHOase T198E and ScDHOase T208E mutants had higher activities compared with their wild-type enzymes. The need for a higher DHOase stability and activity may drive creation of the third metal ion binding site in huDHOase, which can be achieved by mutating a highly conserved position T in type II dihydroorotases to E, similar to that in huDHOase.

  17. 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.

  18. 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.

  19. 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.

  20. High strength and low friction of a PAA-alginate-silica hydrogel as potential material for artificial soft tissues.

    PubMed

    Lin, Hong-Ru; Ling, Ming-Hung; Lin, Yiu-Jiuan

    2009-01-01

    In this study, a series of poly(acrylic) acid (PAA)-based hydrogels was prepared by UV polymerization. Hydrogels with an interpenetrating network structure were formed by combining PAA and alginate (Alg) solutions. The incorporation of nano-silica into these gel solutions significantly increased their compressive strength and fracture toughness but lowered their cross-linking density and friction coefficient. The prepared hydrogels were considerably hydrophilic for water content greater than 98%, which is in accordance with the nature of soft tissues such as cartilage. The preliminary cell culture of adipose stem cells (ADSCs) on PAA-Alg-Si hydrogels results in good biological safety. These features suggest that the PAA-Alg-Si hydrogels prepared in this study can be used as artificial soft tissues.

  1. 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

  2. [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.

  3. Direct Measurement of the Nanomechanical Stability of a Redox Protein Active Site and Its Dependence upon Metal Binding.

    PubMed

    Giannotti, Marina I; Cabeza de Vaca, Israel; Artés, Juan M; Sanz, Fausto; Guallar, Victor; Gorostiza, Pau

    2015-09-10

    The structural basis of the low reorganization energy of cupredoxins has long been debated. These proteins reconcile a conformationally heterogeneous and exposed metal-chelating site with the highly rigid copper center required for efficient electron transfer. Here we combine single-molecule mechanical unfolding experiments with statistical analysis and computer simulations to show that the metal-binding region of apo-azurin is mechanically flexible and that high mechanical stability is imparted by copper binding. The unfolding pathway of the metal site depends on the pulling residue and suggests that partial unfolding of the metal-binding site could be facilitated by the physical interaction with certain regions of the redox protein.

  4. 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.

  5. Synthesis of Hierarchically Structured Hybrid Materials by Controlled Self-Assembly of Metal-Organic Framework with Mesoporous Silica for CO2 Adsorption.

    PubMed

    Chen, Chong; Li, Bingxue; Zhou, Lijin; Xia, Zefeng; Feng, Nengjie; Ding, Jing; Wang, Lei; Wan, Hui; Guan, Guofeng

    2017-07-12

    The HKUST-1@SBA-15 composites with hierarchical pore structure were constructed by in situ self-assembly of metal-organic framework (MOF) with mesoporous silica. The structure directing role of SBA-15 had an obvious impact on the growth of MOF crystals, which in turn affected the morphologies and structural properties of the composites. The pristine HKUST-1 and the composites with different content of SBA-15 were characterized by XRD, N2 adsorption-desorption, SEM, TEM, FT-IR, TG, XPS, and CO2-TPD techniques. It was found that the composites were assembled by oriented growth of MOF nanocrystals on the surfaces of SBA-15 matrix. The interactions between surface silanol groups and metal centers induced structural changes and resulted in the increases in surface areas as well as micropore volumes of hybrid materials. Besides, the additional constraints from SBA-15 also restrained the expansion of HKUST-1, contributing to their smaller crystal sizes in the composites. The adsorption isotherms of CO2 on the materials were measured and applied to calculate the isosteric heats of adsorption. The HS-1 composite exhibited an increase of 15.9% in CO2 uptake capacity compared with that of HKUST-1. Moreover, its higher isosteric heats of CO2 adsorption indicated the stronger interactions between the surfaces and CO2 molecules. The adsorption rate of the composite was also improved due to the introduction of mesopores. Ten cycles of CO2 adsorption-desorption experiments implied that the HS-1 had excellent reversibility of CO2 adsorption. This study was intended to provide the possibility of assembling new composites with tailored properties based on MOF and mesoporous silica to satisfy the requirements of various applications.

  6. 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.

  7. Mutagenicity of mercury chloride and mechanisms of cellular defence: the role of metal-binding proteins.

    PubMed

    Schurz, F; Sabater-Vilar, M; Fink-Gremmels, J

    2000-11-01

    The mechanisms of toxicity and, particularly, the potential carcinogenicity of inorganic mercury are still under debate. Results of mutagenicity and genotoxicity testing with mercury have been inconsistent: mercury induces DNA single-strand breaks at low concentrations in mammalian cells but has not proved mutagenic in several bacterial mutagenicity assays. We investigated the mutagenicity of subtoxic concentrations of inorganic mercury and the role of metal-binding proteins and free radicals in this process. A mutagenicity assay using NIH 3T3 cells, transfected with a vector containing lacZ' as a reporter for mutational events, was applied. In this model, inorganic mercury significantly increased the mutation frequency in the lacZ gene, even at the lowest concentration tested. The mutation frequency was greatest at an Hg(2+) concentration of 0.5 microM. To identify the mechanisms involved, different cellular responses to non-cytotoxic concentrations of HgCl(2) were measured. Hg(2+) increased the intracellular amount of reactive oxygen species. This induction of oxidative stress was observed, although the intracellular glutathione (GSH) and metallothionein (MT) concentrations were increased significantly. Mercury-induced MT expression was even more pronounced after GSH depletion. Correspondingly, radical formation was more evident in the presence of the GSH-depleting agent L-buthioneine-[S:,R:]-sulfoximine. These findings suggest that the observed mutations might be a consequence of oxidative processes, rather than due to a direct interaction of mercury with nuclear DNA. The results also indicate that the auto-induction of MT by Hg(2+) fails to prevent these mutational events.

  8. Isolation and characterization of iron chelators from turmeric (Curcuma longa): selective metal binding by curcuminoids.

    PubMed

    Messner, Donald J; Surrago, Christine; Fiordalisi, Celia; Chung, Wing Yin; Kowdley, Kris V

    2017-08-11

    Iron overload disorders may be treated by chelation therapy. This study describes a novel method for isolating iron chelators from complex mixtures including plant extracts. We demonstrate the one-step isolation of curcuminoids from turmeric, the medicinal food spice derived from Curcuma longa. The method uses iron-nitrilotriacetic acid (NTA)-agarose, to which curcumin binds rapidly, specifically, and reversibly. Curcumin, demethoxycurcumin, and bisdemethoxycurcumin each bound iron-NTA-agarose with comparable affinities and a stoichiometry near 1. Analyses of binding efficiencies and purity demonstrated that curcuminoids comprise the primary iron binding compounds recovered from a crude turmeric extract. Competition of curcuminoid binding to the iron resin was used to characterize the metal binding site on curcumin and to detect iron binding by added chelators. Curcumin-Iron-NTA-agarose binding was inhibited by other metals with relative potency: (>90% inhibition) Cu(2+) ~ Al(3+) > Zn(2+) ≥ Ca(2+) ~ Mg(2+) ~ Mn(2+) (<20% inhibition). Binding was also inhibited by pharmaceutical iron chelators (desferoxamine or EDTA) or by higher concentrations of weak iron chelators (citrate or silibinin). Investigation of the physiological effects of iron binding by curcumin revealed that curcumin uptake by cultured cells was reduced >80% by addition of iron to the media; uptake was completely restored by desferoxamine. Ranking of metals by relative potencies for blocking curcumin uptake agreed with their relative potencies in blocking curcumin binding to iron-NTA-agarose. We conclude that curcumin can selectively bind toxic metals including iron in a physiological setting, and propose inhibition of curcumin binding to iron-NTA-agarose for iron chelator screening.

  9. 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.

  10. Metal binding of metallothioneins in human astrocytomas (U87 MG, IPDDC-2A).

    PubMed

    Znidaric, Magda Tusek; Pucer, Anja; Fatur, Tanja; Filipic, Metka; Scancar, Janez; Falnoga, Ingrid

    2007-10-01

    Astroglia cells structurally and nutritionally support neurons in the central nervous system. They play an important role in guiding the construction of the nervous system and controlling the chemical and ionic environment of neurons. They also represent the major sites for accumulation and immobilisation of toxic metal ions most probably connected with metallothioneins. For this reason astroglia cells possess high cytosolic levels of metallothioneins I, II and III (MT-I,II,III). Our aim was to establish the inducibility and metal binding of MTs in two human astrocytoma cell lines, U87 MG (astrocytoma-glioblastoma, grade IV) and IPDDC-2A (astrocytoma, grade II), on exposure to cadmium chloride (1 microM). MTs were identified by molecular weight (size exclusion chromatography) and their metal content (Cd, Zn and Cu) to follow the interactions between metals. We showed that MTs are constitutively expressed in both human astrocytoma cell lines. In accordance with the higher malignancy grade of U87 MG, the amount of MTs was higher in U87 MG than in IPDDC-2A cells. After 24 hours of exposure to Cd their expression greatly increased in both cell lines and they were capable of immobilising almost all water soluble Cd. Induction of MTs in U87 MG cells was additionally followed up to 48 hours with exposure to different concentrations of CdCl(2) (1, 10 microM). Induction was a time dependent process throughout the period. Isoform III (identified by chromatographic separation of isoform III from I/II) was present at all exposure times, but only in traces with respect to the prevailing amounts of MT-I/II isoforms. So induction can be attributed to isoform I/II only.

  11. A Conserved Metal Binding Motif in the Bacillus subtilis Competence Protein ComFA Enhances Transformation.

    PubMed

    Chilton, Scott S; Falbel, Tanya G; Hromada, Susan; Burton, Briana M

    2017-08-01

    Genetic competence is a process in which cells are able to take up DNA from their environment, resulting in horizontal gene transfer, a major mechanism for generating diversity in bacteria. Many bacteria carry homologs of the central DNA uptake machinery that has been well characterized in Bacillus subtilis It has been postulated that the B. subtilis competence helicase ComFA belongs to the DEAD box family of helicases/translocases. Here, we made a series of mutants to analyze conserved amino acid motifs in several regions of B. subtilis ComFA. First, we confirmed that ComFA activity requires amino acid residues conserved among the DEAD box helicases, and second, we show that a zinc finger-like motif consisting of four cysteines is required for efficient transformation. Each cysteine in the motif is important, and mutation of at least two of the cysteines dramatically reduces transformation efficiency. Further, combining multiple cysteine mutations with the helicase mutations shows an additive phenotype. Our results suggest that the helicase and metal binding functions are two distinct activities important for ComFA function during transformation.IMPORTANCE ComFA is a highly conserved protein that has a role in DNA uptake during natural competence, a mechanism for horizontal gene transfer observed in many bacteria. Investigation of the details of the DNA uptake mechanism is important for understanding the ways in which bacteria gain new traits from their environment, such as drug resistance. To dissect the role of ComFA in the DNA uptake machinery, we introduced point mutations into several motifs in the protein sequence. We demonstrate that several amino acid motifs conserved among ComFA proteins are important for efficient transformation. This report is the first to demonstrate the functional requirement of an amino-terminal cysteine motif in ComFA. Copyright © 2017 American Society for Microbiology.

  12. Hepatic cadmium, metal-binding proteins and bioaccumulation in bluegills exposed to aqueous cadmium

    USGS Publications Warehouse

    Cope, W.G.; Atchison, G.J.; Wiener, J.G.

    1994-01-01

    We examined sublethal responses of juvenile bluegills Lepomis macrochirus to aqueous cadmium in two 28-d tests (test I, 0.0-8.4 μg Cd per liter; test II, 0.0-32.3 μg Cd per liter) in an intermittent-flow diluter. The experimental design was completely randomized, with two replicates in each of eight treatments (seven Cd exposures and one water control with 25 fish per replicate). Cadmium did not affect the growth of test fish. The mean whole-body concentrations of Cd in exposed fish were 1.8- to 44-fold those in controls in the two tests. Mean concentrations of hepatic nonthionein cytosolic Cd (not bound by metal-binding proteins, MBP) in all Cd treatments greatly exceeded those in controls, and mean concentrations of hepatic MBP in all treatments except one (0.8 μg Cd per liter in test I) exceeded those in controls. Nonthionein cytosolic Cd, hepatic MBP, and whole-body Cd in bluegills were linearly related to exposure concentrations within the range 0 to 20 μg Cd per liter. Much of the total Cd-binding capacity of hepatic MBP per fish was occupied by Cd after the 28-d exposures, although additional Cd-binding capacity remained unoccupied by Cd in fish in all treatments. The mean total Cd-binding capacity of hepatic MBP per fish, which ranged from 1.7 to 14 nmol Cd in test I and from 0.8 to 24 nmol Cd in test II, increased in a concentration-response manner at exposure concentrations below 13 μg/L. Nonthionein cytosolic Cd was the most sensitive indicator of Cd exposure, based on an LOEC of 0.8 μg Cd per liter.

  13. Exposure to crystalline silica in abrasive blasting operations where silica and non-silica abrasives are used.

    PubMed

    Radnoff, Diane L; Kutz, Michelle K

    2014-01-01

    Exposure to respirable crystalline silica is a hazard common to many industries in Alberta but particularly so in abrasive blasting. Alberta occupational health and safety legislation requires the consideration of silica substitutes when conducting abrasive blasting, where reasonably practicable. In this study, exposure to crystalline silica during abrasive blasting was evaluated when both silica and non-silica products were used. The crystalline silica content of non-silica abrasives was also measured. The facilities evaluated were preparing metal products for the application of coatings, so the substrate should not have had a significant contribution to worker exposure to crystalline silica. The occupational sampling results indicate that two-thirds of the workers assessed were potentially over-exposed to respirable crystalline silica. About one-third of the measurements over the exposure limit were at the work sites using silica substitutes at the time of the assessment. The use of the silica substitute, by itself, did not appear to have a large effect on the mean airborne exposure levels. There are a number of factors that may contribute to over-exposures, including the isolation of the blasting area, housekeeping, and inappropriate use of respiratory protective equipment. However, the non-silica abrasives themselves also contain silica. Bulk analysis results for non-silica abrasives commercially available in Alberta indicate that many contain crystalline silica above the legislated disclosure limit of 0.1% weight of silica per weight of product (w/w) and this information may not be accurately disclosed on the material safety data sheet for the product. The employer may still have to evaluate the potential for exposure to crystalline silica at their work site, even when silica substitutes are used. Limited tests on recycled non-silica abrasive indicated that the silica content had increased. Further study is required to evaluate the impact of product recycling

  14. 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.

  15. 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. © 2015 SETAC.

  16. 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.

  17. 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.

  18. 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.

  19. Overexpression and divalent metal binding properties of the methionyl aminopeptidase from Pyrococcus furiosus.

    PubMed

    Meng, Lu; Ruebush, Shane; D'souza, Ventris M; Copik, Alicja J; Tsunasawa, Susumu; Holz, Richard C

    2002-06-11

    The gene encoding for the methionyl aminopeptidase from the hyperthermophilic archaeon Pyrococcus furiosus (PfMetAP-II; EC 3.4.11.18) has been inserted into a pET 27b(+) vector and overexpressed in Escherichia coli. The new expression system resulted in a 5-fold increase in purified enzyme obtained from a 5 L fermentor growth. The as-purified PfMetAP-II enzyme, to which no exogenous metal ions or EDTA was added, was found to have 1.2 equiv of zinc and 0.1 equiv of iron present by ICP-AES analysis. This enzyme had a specific activity of 5 units/mg, a 60-fold decrease from the fully loaded Fe(II) enzymes. When an additional 2 equiv of Zn(II) was added to the as-purified PfMetAP-II, no activity could be detected. The combination of these data with previously reported whole cell studies on EcMetAP-I further supports the suggestion that the in vivo metal ion for all MetAP's is Fe(II). Both Co(II)- and Fe(II)-loaded PfMetAP-II showed similar substrate specificities to EcMetAP-I. Substrate binding was largely affected by the amino acid in the P1 position and the length of the polypeptide. The substrates MSSHRWDW and MP-p-NA showed the smallest K(m) values while the substrates MGMM and MP-p-NA provided the highest turnover. The catalytic efficiency (k(cat)/K(m)) of PfMetAP-II for MP-p-NA at 30 degrees C was 799 500 and 340 930 M(-1) s(-1) for Co(II)- and Fe(II)-loaded PfMetAP-II, respectively. Maximum catalytic activity was obtained with 1 equiv of Co(II) or Fe(II), and the dissociation constants (K(d)) for the first metal binding site were found to be 50 +/- 15 and 20 +/- 15 nM for Co(II)- and Fe(II)-substituted PfMetAP-II, respectively. Electronic absorption spectral titration of a 1 mM sample of apo-PfMetAP-II with Co(II) provided a dissociation constant of 0.35 +/- 0.02 mM for the second metal binding site, a 17500-fold increase compared to the first metal binding site. The electronic absorption data also indicated that both Co(II) ions reside in a pentacoordinate

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. RAFT Polymerization of N-[3-(Trimethoxysilyl)-propyl]acrylamide and Its Versatile Use in Silica Hybrid Materials.

    PubMed

    Maçon, Anthony L B; Greasley, Sarah L; Becer, C Remzi; Jones, Julian R

    2015-12-01

    Reversible addition-fragmentation chain transfer (RAFT) polymerization and characterization of an alkoxysilane acrylamide monomer using a trithiocarbonate chain transfer agent are described. Poly(N-[3-(trimethoxysilyl)propyl]acrylamide) (PTMSPAA) homopolymers are obtained with good control over the polymerization. A linear increase in the molecular weight is observed whereas the polydispersity values do not exceed 1.2 regardless of the monomer conversion. Moreover, PTMSPAA is used as a macro-RAFT agent to polymerize N-isopropylacrylamide (NIPAM). By varying the degree of polymerization of NIPAM within the block copolymer, different sizes of thermoresponsive particles are obtained. These particles are stabilized by the condensation of the alkoxysilane moieties of the polymers. Furthermore, a co-network of silica and PTMSPAA is prepared using the sol-gel process. After drying, transparent mesoporous hybrids are obtained with a surface area of up to 400 m(2) g(-1). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. A novel and facile strategy for highly flame retardant polymer foam composite materials: Transforming silicone resin coating into silica self-extinguishing layer.

    PubMed

    Wu, Qian; Zhang, Qian; Zhao, Li; Li, Shi-Neng; Wu, Lian-Bin; Jiang, Jian-Xiong; Tang, Long-Cheng

    2017-08-15

    In this study, a novel strategy was developed to fabricate highly flame retardant polymer foam composite materials coated by synthesized silicone resin (SiR) polymer via a facile dip-coating processing. Applying the SiR polymer coating, the mechanical property and thermal stability of SiR-coated polymer foam (PSiR) composites are greatly enhanced without significantly altering their structure and morphology. The minimum oxygen concentration to support the combustion of foam materials is greatly increased, i.e. from LOI 14.6% for pure foam to LOI 26-29% for the PSiR composites studied. Especially, adjusting pendant group to SiOSi group ratio (R/Si ratio) of SiRs produces highly flame retardant PSiR composites with low smoke toxicity. Cone calorimetry results demonstrate that 44-68% reduction in the peak heat release rate for the PSiR composites containing different R/Si ratios over pure foam is achieved by the presence of appropriate SiR coating. Digital and SEM images of post-burn chars indicate that the SiR polymer coating can be transformed into silica self-extinguishing porous layer as effective inorganic barrier effect, thus preserving the polymer foam structure from fire. Our results show that the SiR dip-coating technique is a promising strategy for producing flame retardant polymer foam composite materials with improved mechanical properties. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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.

  12. Enhanced Thermal Properties of Novel Latent Heat Thermal Storage Material Through Confinement of Stearic Acid in Meso-Structured Onion-Like Silica

    NASA Astrophysics Data System (ADS)

    Gao, Junkai; Lv, Mengjiao; Lu, Jinshu; Chen, Yan; Zhang, Zijun; Zhang, Xiongjie; Zhu, Yingying

    2017-08-01

    Meso-structured onion-like silica (MOS), which had a highly ordered, onion-like multilayer; large surface area and pore volume; and highly curved mesopores, were synthesized as a support for stearic acid (SA) to develop a novel shape-stabilized phase change material (SA/MOS). The characterizations of SA/MOS were studied by the analysis technique of scanning electron microscope, infrared spectroscopy, x-ray diffraction, differential scanning calorimeter (DSC), and thermal gravimetry analysis (TGA). The results showed that the interaction between the SA and the MOS was physical adsorption and that the MOS had no effect on the crystal structure of the SA. The DSC results suggested that the melting and solidifying temperature of the SA/MOS were 72.7°C and 63.9°C with a melting latent heat of 108.0 J/g and a solidifying latent heat of 126.0 J/g, respectively, and the TGA results indicated that the SA/MOS had a good thermal stability. All of the results demonstrated that the SA/MOS was a promising thermal energy storage material candidate for practical applications.

  13. 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.

  14. 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.

  15. Fast characterization of functionalized silica materials by silicon-29 surface-enhanced NMR spectroscopy using dynamic nuclear polarization.

    PubMed

    Lelli, Moreno; Gajan, David; Lesage, Anne; Caporini, Marc A; Vitzthum, Veronika; Miéville, Pascal; Héroguel, Florent; Rascón, Fernando; Roussey, Arthur; Thieuleux, Chloé; Boualleg, Malika; Veyre, Laurent; Bodenhausen, Geoffrey; Copéret, Christophe; Emsley, Lyndon

    2011-02-23

    We demonstrate fast characterization of the distribution of surface bonding modes and interactions in a series of functionalized materials via surface-enhanced nuclear magnetic resonance spectroscopy using dynamic nuclear polarization (DNP). Surface-enhanced silicon-29 DNP NMR spectra were obtained by using incipient wetness impregnation of the sample with a solution containing a polarizing radical (TOTAPOL). We identify and compare the bonding topology of functional groups in materials obtained via a sol-gel process and in materials prepared by post-grafting reactions. Furthermore, the remarkable gain in time provided by surface-enhanced silicon-29 DNP NMR spectroscopy (typically on the order of a factor 400) allows the facile acquisition of two-dimensional correlation spectra.

  16. 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.

  17. 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.

  18. Spectroscopic and metal-binding properties of DF3: an artificial protein able to accommodate different metal ions

    PubMed Central

    Torres Martin de Rosales, Rafael; Faiella, Marina; Farquhar, Erik; Que, Lawrence; Andreozzi, Concetta; Pavone, Vincenzo; Maglio, Ornella; Nastri, Flavia

    2010-01-01

    The design, synthesis, and metal-binding properties of DF3, a new de novo designed di-iron protein model are described (“DF” represents due ferri, Italian for “two iron,” “di-iron”). DF3 is the latest member of the DF family of synthetic proteins. They consist of helix–loop–helix hairpins, designed to dimerize and form an antiparallel four-helix bundle that encompasses a metal-binding site similar to those of non-heme carboxylate-bridged di-iron proteins. Unlike previous DF proteins, DF3 is highly soluble in water (up to 3 mM) and forms stable complexes with several metal ions (Zn, Co, and Mn), with the desired secondary structure and the expected stoichiometry of two ions per protein. UV–vis studies of Co(II) and Fe(III) complexes confirm a metal-binding environment similar to previous di-Co(II)- and di-Fe(III)-DF proteins, including the presence of a µ-oxo-di-Fe(III) unit. Interestingly, UV–vis, EPR, and resonance Raman studies suggest the interaction of a tyro-sine adjacent to the di-Fe(III) center. The design of DF3 was aimed at increasing the accessibility of small molecules to the active site of the four-helix bundle. Indeed, binding of azide to the di-Fe(III) site demonstrates a more accessible metal site compared with previous DFs. In fact, fitting of the binding curve to the Hill equation allows us to quantify a 150% accessibility enhancement, with respect to DF2. All these results represent a significant step towards the development of a functional synthetic DF metalloprotein. PMID:20225070

  19. Organic-inorganic hybrid silica material derived from a monosilylated Grubbs-Hoveyda ruthenium carbene as a recyclable metathesis catalyst.

    PubMed

    Borja, Guadalupe; Pleixats, Roser; Alibés, Ramón; Cattoën, Xavier; Man, Michel Wong Chi

    2010-08-23

    The synthesis of a monosilylated Grubbs-Hoveyda ruthenium alkylidene complex is described, as well as the preparation and characterization of the corresponding material by sol-gel cogelification with tetraethoxysilane (TEOS) and the assay of this recyclable supported catalyst in ring-closing diene and enyne metathesis reactions under thermal and microwave conditions.

  20. Granulated activated carbon modified with hydrophobic silica aerogel-potential composite materials for the removal of uranium from aqueous solutions.

    PubMed

    Coleman, Sabre J; Coronado, Paul R; Maxwell, Robert S; Reynolds, John G

    2003-05-15

    Aqueous solutions of 100 parts per billion (ppb) uranium at pH 7 were treated with granulated activated carbon (GAC) that had been modified with various formulations of hydrophobic aerogels. The composite materials were found to be superior in removing uranium from a stock solution compared to GAC alone evaluated by a modified ASTM D 3860-98 method for batch testing. The testing results were evaluated using a Freundlich adsorption model. The best performing material has parameters of n = 287 and Kf = 1169 compared to n = 1.00, and Kf = 20 for GAC alone. The composite materials were formed by mixing (CH3O)4Si with the hydrophobic sol-gel precursor, (CH3O)3SiCH2CH2CF3 and with specified modifiers, such as H3PO4, Ca(NO3)2, and (C2H5O)3SiCH2CH2P(O)(OC2H5)2, elation catalysts, and GAC in a supercritical reactor system. After gelation, supercritical extraction, and sieving, the composites were tested. Characterization by FTIR and 31P NMR indicate the formation of phosphate in the case of the H3PO4 and Ca(NO3)2 composites and phosphonic acid related compounds in the phosphonate composite. These composite materials have potential application in the clean up of groundwater at DOE and other facilities.

  1. 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

  2. Hints for Metal-Preference Protein Sequence Determinants: Different Metal Binding Features of the Five Tetrahymena thermophila Metallothioneins

    PubMed Central

    Espart, Anna; Marín, Maribel; Gil-Moreno, Selene; Palacios, Òscar; Amaro, Francisco; Martín-González, Ana; Gutiérrez, Juan C.; Capdevila, Mercè; Atrian, Sílvia

    2015-01-01

    The metal binding preference of metallothioneins (MTs) groups them in two extreme subsets, the Zn/Cd- and the Cu-thioneins. Ciliates harbor the largest MT gene/protein family reported so far, including 5 paralogs that exhibit relatively low sequence similarity, excepting MTT2 and MTT4. In Tetrahymena thermophila, three MTs (MTT1, MTT3 and MTT5) were considered Cd-thioneins and two (MTT2 and MTT4) Cu-thioneins, according to gene expression inducibility and phylogenetic analysis. In this study, the metal-binding abilities of the five MTT proteins were characterized, to obtain information about the folding and stability of their cognate- and non-cognate metal complexes, and to characterize the T. thermophila MT system at protein level. Hence, the five MTTs were recombinantly synthesized as Zn2+-, Cd2+- or Cu+-complexes, which were analyzed by electrospray mass spectrometry (ESI-MS), circular dichroism (CD), and UV-vis spectrophotometry. Among the Cd-thioneins, MTT1 and MTT5 were optimal for Cd2+ coordination, yielding unique Cd17- and Cd8- complexes, respectively. When binding Zn2+, they rendered a mixture of Zn-species. Only MTT5 was capable to coordinate Cu+, although yielding heteronuclear Zn-, Cu-species or highly unstable Cu-homometallic species. MTT3 exhibited poor binding abilities both for Cd2+ and for Cu+, and although not optimally, it yielded the best result when coordinating Zn2+. The two Cu-thioneins, MTT2 and MTT4 isoforms formed homometallic Cu-complexes (major Cu20-MTT) upon synthesis in Cu-supplemented hosts. Contrarily, they were unable to fold into stable Cd-complexes, while Zn-MTT species were only recovered for MTT4 (major Zn10-MTT4). Thus, the metal binding preferences of the five T. thermophila MTs correlate well with their previous classification as Cd- and Cu-thioneins, and globally, they can be classified from Zn/Cd- to Cu-thioneins according to the gradation: MTT1>MTT5>MTT3>MTT4>MTT2. The main mechanisms underlying the evolution and

  3. 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.

  4. Application of the restricted-access precolumn packing material alkyl-diol silica in a column-switching system for the determination of ketoprofen enantiomers in horse plasma.

    PubMed

    Baeyens, W R; Van der Weken, G; Haustraete, J; Aboul-Enein, H Y; Corveleyn, S; Remon, J P; García-Campaña, A M; Deprez, P

    2000-02-25

    The group of LiChrospher ADS (alkyl-diol silica) sorbents that make part of a unique family of restricted-access materials, have been developed as special packings for precolumns used in the LC-integrated sample processing of biofluids. The advantage of these sorbents lies in the direct injection of untreated biological fluids, that is without sample clean-up, the elimination of the protein matrix with a quantitative recovery together with an on-column enrichment. The present method is based on previous work applying UV detection at 260 nm for ketoprofen determinations. Plasma samples introduced to the ADS precolumn using a 0.1 M phosphate buffer, pH 7.0. After washing with the buffer the ADS column was backflushed with the mobile phase 0.01 M phosphate buffer-6% (v/v) 2-propanol-5 mM octanoic acid at a pH of 5.5, thus transporting the analytes to the chiral-HSA (human serum albumin) (100x4.0 mm) column where the separation of the ketoprofen enantiomers was achieved with a resolution factor of 1.4. The developed column-switching method was fully applicable to plasma injections.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. Al-promoted increase of surface area and adsorption capacity in ordered mesoporous silica materials with a cubic structure.

    PubMed

    Carmona, Daniel; Balas, Francisco; Mayoral, Álvaro; Luque, Rafael; Urriolabeitia, Esteban P; Santamaría, Jesús

    2011-12-07

    The structure of ordered mesoporous materials presenting a cubic structure undergoes a strong modification after adding aluminium alkoxides to the synthesis gel. As a result, an outstanding increase in the surface area and pore volume is observed, together with changes in the mesopore ordering. Hydrated aluminium species influence the chemical environment of the micelles during synthesis, which seems to induce the accumulation of stacking faults in the mesopore framework, and give rise to closer structural packing. The adsorption and release of ibuprofen as a test molecule correlates well with the textural changes observed.

  11. High purity silica reflecting heat shield development

    NASA Technical Reports Server (NTRS)

    Congdon, W.

    1974-01-01

    A reflecting heat shield composed of fused silica in which the scattering results from the refractive index mismatch between silica particles and the voids introduced during the fabrication process is developed. Major considerations and conclusions of the development are: the best material to use is Type A, which is capable of ultra-high-purity and which does not show the 0.243 micrometer absorption band; the reflection efficiency of fused silica is decreased at higher temperatures due to the bathochromic shift of the ultraviolet cut-off; for a given silica material, over the wavelength region and particle sizes tested, the monodisperse particle size configurations produce higher reflectances than continuous particle size configurations; and the smaller monodisperse particle size configurations give higher reflectance than the larger ones. A reflecting silica configuration that is an efficient reflector of shock layer radiation at high ablation temperatures is achieved by tailoring the matrix for optimum scattering and using an ultra-high-purity material.

  12. Functional metal-binding proteins by metal-stimulated bacteria for the development of an innovative metal removal technology.

    PubMed

    Antsuki, T; Sano, D; Omura, T

    2003-01-01

    Heavy metal pollution has become an environmental problem throughout the world because heavy metal can be accumulated into the food chain and bring about serious problems, not only for ecosystems but also for human health. In this study, functional metal-binding proteins (FMBPs) were isolated from a metal-stimulated activated sludge culture with the aim of applying them to an innovative metal removal technology. Activated sludge bacteria was cultured in growth media including copper ion, and the stimulation of protein production by copper ion led to the 14% increase in a quantity of extracted crude proteins per 1 g of bacterial cell pellet (wet). In order to isolate FMBPs, extracted crude proteins were applied to the immobilized metal affinity column in which each of copper, nickel and zinc was used as a ligand. Several FMBPs were succesfully isolated from copper-stimulated bacteria. One of FMBPs (molecular weight of about 40 kDa) exhibited an ability to adsorb all three metals. The multi metal-binding property of this FMBP could be applied to an innovative metal removal technology. Furthermore, isolated FMBPs that could capture only one kind of heavy metal would also be attractive as a metal adsorbent in recovering a specific metal as a resource from wastewater, including several heavy metals.

  13. Structure of Human J-type Co-chaperone HscB Reveals a Tetracysteine Metal-binding Domain

    SciTech Connect

    Bitto, Eduard; Bingman, Craig A.; Bittova, Lenka; Kondrashov, Dmitry A.; Bannen, Ryan M.; Fox, Brian G.; Markley, John L.; Phillips, Jr., George N.

    2008-11-24

    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 3.0 A 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 CWXCX(9-13)FCXXCXXXQ. 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.

  14. The CXXC motifs in the metal binding domains are required for ATP7B to mediate resistance to cisplatin☆

    PubMed Central

    Safaei, Roohangiz; Adams, Preston L.; Maktabi, Mohammad H.; Mathews, Ryan A.; Howell, Stephen B.

    2013-01-01

    The copper (Cu) exporter ATP7B mediates resistance to cisplatin (cDDP) but details of the mechanism are unknown. We explored the role of the CXXC motifs in the metal binding domains (MBDs) of ATP7B by investigating binding of cDDP to the sixth metal binding domain (MBD6) or a variant in which the CXXC motif was converted to SXXS. Platinum measurement showed that cDDP bound to wild type MBD6 but not to the SXXS variant. Wild type ATP7B rendered ovarian 2008 cells resistant to cDDP. In 2008 and in HEK293T cells, wild type ATP7B trafficked from TGN to peripheral locations in response to Cu or cDDP. A variant in which the CXXC motifs in all 6 MBDs were converted to SXXS localized correctly to the TGN but failed to traffic when exposed to either Cu or cDDP. Deletion of either the first 5 MBDs or all 6 MBDs resulted in failure to localize to the TGN. Neither the SXXS variant nor the deletion variant was able to mediate resistance to cDDP. We conclude that cDDP binds to the CXXC motifs of ATP7B and that this interaction is essential to the trafficking of ATP7B and to its ability to mediate resistance to cDDP. PMID:22459168

  15. The CXXC motifs in the metal binding domains are required for ATP7B to mediate resistance to cisplatin.

    PubMed

    Safaei, Roohangiz; Adams, Preston L; Maktabi, Mohammad H; Mathews, Ryan A; Howell, Stephen B

    2012-05-01

    The copper (Cu) exporter ATP7B mediates resistance to cisplatin (cDDP) but details of the mechanism are unknown. We explored the role of the CXXC motifs in the metal binding domains (MBDs) of ATP7B by investigating binding of cDDP to the sixth metal binding domain (MBD6) or a variant in which the CXXC motif was converted to SXXS. Platinum measurement showed that cDDP bound to wild type MBD6 but not to the SXXS variant. Wild type ATP7B rendered ovarian 2008 cells resistant to cDDP. In 2008 and in HEK293T cells, wild type ATP7B trafficked from TGN to peripheral locations in response to Cu or cDDP. A variant in which the CXXC motifs in all 6 MBDs were converted to SXXS localized correctly to the TGN but failed to traffic when exposed to either Cu or cDDP. Deletion of either the first 5 MBDs or all 6 MBDs resulted in failure to localize to the TGN. Neither the SXXS variant nor the deletion variant was able to mediate resistance to cDDP. We conclude that cDDP binds to the CXXC motifs of ATP7B and that this interaction is essential to the trafficking of ATP7B and to its ability to mediate resistance to cDDP. Copyright © 2012 Elsevier Inc. All rights reserved.

  16. 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

  17. The enthalpy of the alanine peptide helix measured by isothermal titration calorimetry using metal-binding to induce helix formation.

    PubMed

    Lopez, Maria M; Chin, Der-Hang; Baldwin, Robert L; Makhatadze, George I

    2002-02-05

    The goal of this study is to use the model system described earlier to make direct measurements of the enthalpy of helix formation at different temperatures. For this we studied model alanine peptides in which helix formation can be triggered by metal (La(3+)) binding. The heat of La(3+) interaction with the peptides at different temperatures is measured by isothermal titration calorimetry. Circular dichroism spectroscopy is used to follow helix formation. Peptides of increasing length (12-, 16-, and 19-aa residues) that contain a La(3+)-binding loop followed by helices of increasing length, are used to separate the heat of metal binding from the enthalpy of helix formation. We demonstrate that (i) the enthalpy of helix formation is -0.9 +/- 0.1 kcal/mol; (ii) the enthalpy of helix formation is independent of the peptide length; (iii) the enthalpy of helix formation does not depend significantly on temperature in the range from 5 to 45 degrees C, suggesting that the heat capacity change on helix formation is very small. Thus, the use of metal binding to induce helix formation has an enormous potential for measuring various thermodynamic properties of alpha-helices.

  18. claMP Tag: a versatile inline metal-binding platform based on the metal abstraction peptide.

    PubMed

    Mills, Brittney J; Mu, Qingxin; Krause, Mary E; Laurence, Jennifer S

    2014-06-18

    Molecularly targeted research and diagnostic tools are essential to advancing understanding and detection of many diseases. Metals often impart the desired functionality to these tools, and conjugation of high-affinity chelators to proteins is carried out to enable targeted delivery of the metal. This approach has been much more effective with large lanthanide series metals than smaller transition metals. Because chemical conjugation requires additional processing and purification steps and yields a heterogeneous mixture of products, inline incorporation of a peptide tag capable of metal binding is a highly preferable alternative. Development of a transition metal binding tag would provide opportunity to greatly expand metal-based analyses. The metal abstraction peptide (MAP) sequence was genetically engineered into recombinant protein to generate the claMP Tag. The effects of this tag on recombinant epidermal growth factor (EGF) protein expression, disulfide bond formation, tertiary structural integrity, and transition metal incorporation using nickel were examined to confirm the viability of utilizing the MAP sequence to generate linker-less metal conjugates.

  19. 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.

  20. 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.

  1. 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.

  2. Coumarin-based fluorescence hybrid silica material used for selective detection and absorption of Hg2+ in aqueous media

    NASA Astrophysics Data System (ADS)

    Meng, Qingtao; Jia, Hongmin; Wang, Cuiping; Zhao, Hongbin; Lu, Gonghao; Hu, Zhizhi; Zhang, Zhiqiang; Duan, Chunying

    2014-11-01

    An inorganic-organic hybrid fluorescence material (C-SBA-15) was prepared by covalent immobilization of a coumarin derivative within the channels of SBA-15. The characterization results of XRD, TEM micrographs, FT-IR and UV-vis demonstrate that coumarin is successfully grafted onto the inner surface of SBA-15 and its organized structure is preserved. C-SBA-15 can detect Hg2+ with high selectivity to Pb2+, Zn2+, Cu2+, Mn2+, Cd2+, Co2+, Ag+, Fe3+, Ni2+, K+, Na+, Ca2+, Mg2+ and Li+ in water. Furthermore, the fluorogenical response is reversible by treating with EDTA and do not vary over a broad pH range (5.0-10.5). C-SBA-15 features more outstanding absorbing capacity for Hg2+ among other HTM ions in water.

  3. 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

  4. Crystal structure of YegS, a homologue to the mammalian diacylglycerol kinases, reveals a novel regulatory metal binding site.

    PubMed

    Bakali, H M Amin; Herman, Maria Dolores; Johnson, Kenneth A; Kelly, Amélie A; Wieslander, Ake; Hallberg, B Martin; Nordlund, Pär

    2007-07-06

    The human lipid kinase family controls cell proliferation, differentiation, and tumorigenesis and includes diacylglycerol kinases, sphingosine kinases, and ceramide kinases. YegS is an Escherichia coli protein with significant sequence homology to the catalytic domain of the human lipid kinases. We have solved the crystal structure of YegS and shown that it is a lipid kinase with phosphatidylglycerol kinase activity. The crystal structure reveals a two-domain protein with significant structural similarity to a family of NAD kinases. The active site is located in the interdomain cleft formed by four conserved sequence motifs. Surprisingly, the structure reveals a novel metal binding site composed of residues conserved in most lipid kinases.

  5. 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.

  6. 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

  7. 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.

  8. Design of a novel metal binding peptide by molecular dynamics simulation to sequester Cu and Zn ions

    PubMed Central

    Mahnam, K.; Saffar, B.; Mobini-Dehkordi, M.; Fassihi, A.; Mohammadi, A.

    2014-01-01

    Heavy metal toxicity has serious adverse effects on the environment. The metal sequestering characteristics of a novel metal binding peptide (Glu-Cys)11 Gly+linker+hexahistidine (EC11:His6) was investigated to determine if it can absorb Cu2+ or Zn2+ cations. Molecular dynamics simulations were carried out using a model of 6 Cu2+ or Zn2+ and other ions enclosed in a fully hydrated simulation box with the designed peptide. Totally, 240 nano second (ns) simulations were done in three phases. Results showed that the selected linker is able to separate two domains of this peptide and that the carboxyl oxygens of Glu residues of EC11 in the designed peptide can absorb these ions. Sequestration of Cu2+ or Zn2+ ions by the designed peptide does not change overall tertiary and secondary structures of peptide. PMID:25598801

  9. Interplay between metal binding and cis/trans isomerization in legume lectins: structural and thermodynamic study of P. angolensis lectin.

    PubMed

    Garcia-Pino, Abel; Buts, Lieven; Wyns, Lode; Loris, Remy

    2006-08-04

    The interplay between metal binding, carbohydrate binding activity, stability and structure of the lectin from Pterocarpus angolensis was investigated. Removal of the metals leads to a more flexible form of the protein with significantly less conformational stability. Crystal structures of this metal-free form show significant structural rearrangements, although some structural features that allow the binding of sugars are retained. We propose that substitution of an asparagine residue at the start of the C-terminal beta-strand of the legume lectin monomer hinders the trans-isomerization of the cis-peptide bond upon demetallization and constitutes an intramolecular switch governing the isomer state of the non-proline bond and ultimately the lectin phenotype.

  10. 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.

  11. 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.

  12. The sea urchin metallothionein system: Comparative evaluation of the SpMTA and SpMTB metal-binding preferences☆

    PubMed Central

    Tomas, Mireia; Domènech, Jordi; Capdevila, Mercè; Bofill, Roger; Atrian, Sílvia

    2013-01-01

    Metallothioneins (MTs) constitute a superfamily of ubiquitous metal-binding proteins of low molecular weight and high Cys content. They are involved in metal homeostasis and detoxification, amongst other proposed biological functions. Two MT isoforms (SpMTA and SpMTB) have been reported in the echinoderm Strongylocentrotus purpuratus (sea urchin), both containing 20 Cys residues and presenting extremely similar sequences, although showing distinct tissular and ontogenic expression patterns. Although exhaustive information is available for the Cd(II)-SpMTA complex, this including the full resolution of its 3D structure, no data has been reported concerning either SpMTA Zn(II) and Cu(I) binding properties, or the characterization of SpMTB at protein level. In this work, both the SpMTA and SpMTB isoforms, as well as their separate α and β domains, have been recombinantly synthesized in the presence of Zn(II), Cd(II) or Cu(II), and the corresponding metal complexes have been analyzed using electrospray mass spectrometry, and CD, ICP-AES and UV–vis spectroscopies. The results clearly show a better performance of isoform A when binding Zn(II) and Cd(II), and of isoform B when coordinating Cu(I). Thus, our results confirm the differential metal binding preference of SpMTA and SpMTB, which, together with the reported induction pattern of the respective genes, highlights how also in Echinodermata the MT polymorphism may be linked to the evolution of different physiological roles. PMID:23847757

  13. 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.

  14. Copper-transfer mechanism from the human chaperone Atox1 to a metal-binding domain of Wilson disease protein.

    PubMed

    Rodriguez-Granillo, Agustina; Crespo, Alejandro; Estrin, Dario A; Wittung-Stafshede, Pernilla

    2010-03-18

    The molecular details of how copper (Cu) is transferred from the human Cu chaperone Atox1 to metal-binding domains (MBDs) of P(1B)-type ATPases are still unclear. Here, we use a computational approach, employing quantum mechanics/molecular mechanics (QM/MM) methods, to shed light on the reaction mechanism [probable intermediates, Cu(I) coordination geometries, activation barriers, and energetics] of Cu(I) transfer from Atox1 to the fourth MBD of Wilson disease protein (WD4). Both Atox1 and WD4 have solvent-exposed metal-binding motifs with two Cys residues that coordinate Cu(I). After assessing the existence of all possible 2-, 3- and 4-coordinate Cu-intermediate species, one dominant reaction path emerged. First, without activation barrier, WD4's Cys1 binds Cu(I) in Atox1 to form a 3-coordinated intermediate. Next, with an activation barrier of about 9.5 kcal/mol, a second 3-coordinated intermediate forms that involves both of the Cys residues in WD4 and Cys1 of Atox1. This species can then form the product by decoordination of Atox1's Cys1 (barrier of about 8 kcal/mol). Overall, the Cu-transfer reaction from Atox1 to WD4 appears to be kinetically accessible but less energetically favorable (DeltaE = 7.7 kcal/mol). Our results provide unique insights into the molecular mechanism of protein-mediated Cu(I) transfer in the secretory pathway and are in agreement with existing experimental data.

  15. Crystal structure of Yersinia pestis virulence factor YfeA reveals two polyspecific metal-binding sites

    PubMed Central

    Perry, Robert D.

    2017-01-01

    Gram-negative bacteria use siderophores, outer membrane receptors, inner membrane transporters and substrate-binding proteins (SBPs) to transport transition metals through the periplasm. The SBPs share a similar protein fold that has undergone significant structural evolution to communicate with a variety of differentially regulated transporters in the cell. In Yersinia pestis, the causative agent of plague, YfeA (YPO2439, y1897), an SBP, is important for full virulence during mammalian infection. To better understand the role of YfeA in infection, crystal structures were determined under several environmental conditions with respect to transition-metal levels. Energy-dispersive X-ray spectroscopy and anomalous X-ray scattering data show that YfeA is polyspecific and can alter its substrate specificity. In minimal-media experiments, YfeA crystals grown after iron supplementation showed a threefold increase in iron fluorescence emission over the iron fluorescence emission from YfeA crystals grown from nutrient-rich conditions, and YfeA crystals grown after manganese supplementation during overexpression showed a fivefold increase in manganese fluorescence emission over the manganese fluorescence emission from YfeA crystals grown from nutrient-rich conditions. In all experiments, the YfeA crystals produced the strongest fluorescence emission from zinc and could not be manipulated otherwise. Additionally, this report documents the discovery of a novel surface metal-binding site that prefers to chelate zinc but can also bind manganese. Flexibility across YfeA crystal forms in three loops and a helix near the buried metal-binding site suggest that a structural rearrangement is required for metal loading and unloading. PMID:28695856

  16. Metagenomics analysis reveals a new metallothionein family: Sequence and metal-binding features of new environmental cysteine-rich proteins.

    PubMed

    Ziller, Antoine; Yadav, Rajiv Kumar; Capdevila, Mercè; Reddy, Mondem Sudhakara; Vallon, Laurent; Marmeisse, Roland; Atrian, Silvia; Palacios, Òscar; Fraissinet-Tachet, Laurence

    2017-02-01

    Metallothioneins are cysteine-rich proteins, which function as (i) metal carriers in basal cell metabolism and (ii) protective metal chelators in conditions of metal excess. Metallothioneins have been characterized from different eukaryotic model and cultivable species. Presently, they are categorized in 15 families but evolutionary relationships between these metallothionein families remain unresolved. Several cysteine-rich protein encoding genes that conferred Cd-tolerance in Cd-sensitive yeast mutants have previously been isolated from soil eukaryotic metatranscriptomes. They were called CRPs for "cysteine-rich proteins". These proteins, of unknown taxonomic origins, share conserved cysteine motifs and could be considered as metallothioneins. In the present work, we analyzed these CRPs with respect to their amino acid sequence features and their metal-binding abilities towards Cd, Zn and Cu metal ions. Sequence analysis revealed that they share common features with different known metallothionein families, but also exhibit unique specific features. Noticeably, CRPs display two separate cysteine-rich domains which, when expressed separately in yeast, confer Cd-tolerance. The N-terminal domain contains some conserved atypical Cys motifs, such as one CCC and two CXCC ones. Five CRPs were expressed and purified as recombinant proteins and their metal-binding characteristics were studied. All these CRPs chelated Cd(II), Zn(II) and Cu(I), although displaying a better capacity for Zn(II) coordination. All CRPs are able to confer Cd-tolerance, and four of them confer Zn-tolerance in the Zn-sensitive zrc1Δ yeast mutant. We designated these CRPs as environmental metallothioneins belonging to a new formerly undescribed metallothionein family. Copyright © 2016 Elsevier Inc. All rights reserved.

  17. Dissociation and metal-binding characteristics of yellow lichen substances suggest a relationship with site preferences of lichens

    PubMed Central

    Hauck, Markus; Jürgens, Sascha-René; Willenbruch, Karen; Huneck, Siegfried; Leuschner, Christoph

    2009-01-01

    Background and Aims Many species of lichen-forming fungi contain yellow or orange extracellular pigments belonging to the dibenzofurans (usnic acid), anthraquinones (e.g. parietin) or pulvinic acid group. These pigments are all equally efficient light screens, leading us to question the potential ecological and evolutionary significance of diversity in yellow and orange lichen substances. Here the hypothesis is tested that the different pigments differ in metal-binding characteristics, which suggest that they may contribute to adaptation to sites differing in pH and metal availability. Methods UV spectroscopy was used to study the dissociation and the pH dependence of the metal-binding behaviour of seven isolated lichen substances in methanol. Metals applied were selected macro- and micro-nutrients (Cu2+, Fe2+, Fe3+, Mg2+, Mn2+ and Zn2+). Key Results All the pigments studied are strong to moderate acids with pKa1 values between 2·8 and 4·5. Metal complexation is common in the lichen substances studied. Complexation takes place under acidic conditions with usnic acid, but under alkaline conditions with parietin and most compounds of the pulvinic acid group. The pulvinic acid derivative rhizocarpic acid forms metal complexes both in the acidic and the alkaline range. Conclusions Metal complexation by lichen substances could be a prerequisite for lichen substance-mediated control of metal uptake. Assuming such an effect at pH values where the affinity of the metal for the lichen substance is intermediate would explain the strong preference of lichens with usnic or rhizocarpic acids to acidic substrata. Moreover, it would explain the preference of lichens with parietin and some lichens with compounds of the pulvinic acid group either for nutrient-rich substrata at low pH or for calcareous substrata. PMID:18977765

  18. 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.

  19. Precipitated silica as flow regulator.

    PubMed

    Müller, Anne-Kathrin; Ruppel, Joanna; Drexel, Claus-Peter; Zimmermann, Ingfried

    2008-08-07

    Flow regulators are added to solid pharmaceutical formulations to improve the flow properties of the powder mixtures. The primary particles of the flow regulators exist in the form of huge agglomerates which are broken down into smaller aggregates during the blending process. These smaller aggregates adsorb at the surface of the solid's grains and thus diminish attractive Van-der-Waals-forces by increasing the roughness of the host's surface. In most cases amorphous silica is used as flow additive but material properties like particle size or bond strength influence the desagglomeration tendency of the agglomerates and thus the flow regulating potency of each silica. For some silica types we will show that the differences in their flow regulating potency are due to the rate and extent by which they are able to cover the surface of the host particles. Binary powder mixtures consisting of a pharmaceutical excipient and an added flow regulator were blended in a Turbula mixer for a defined period of time. As pharmaceutical excipient corn starch was used. The flow regulators were represented by a selection of amorphous silicon dioxide types like a commercial fumed silica and various types of SIPERNAT precipitated silica provided by Evonik-Degussa GmbH, Hanau, Germany. Flowability parameters of the mixtures were characterized by means of a tensile strength tester. The reduction of tensile strength with the blending time can be correlated with an increase in fragmentation of the flow regulator.

  20. 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.

  1. Antimicrobial Properties of a Novel Silver-Silica Nanocomposite Material▿

    PubMed Central

    Egger, Salome; Lehmann, Rainer P.; Height, Murray J.; Loessner, Martin J.; Schuppler, Markus

    2009-01-01

    Nanotechnology enables development and production of novel silver-based composite materials. We used in vitro tests to demonstrate the antimicrobial activity of a silver-silica nanocomposite compared to the activities of conventional materials, such as silver nitrate and silver zeolite. A silver-silica-containing polystyrene material was manufactured and shown to possess strong antimicrobial properties. PMID:19270121

  2. 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.

  3. 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.

  4. 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.

  5. Metal binding to the N-terminal cytoplasmic domain of the PIB ATPase HMA4 is required for metal transport in Arabidopsis.

    PubMed

    Laurent, Clémentine; Lekeux, Gilles; Ukuwela, Ashwinie A; Xiao, Zhiguang; Charlier, Jean-Benoit; Bosman, Bernard; Carnol, Monique; Motte, Patrick; Damblon, Christian; Galleni, Moreno; Hanikenne, Marc

    2016-03-01

    PIB ATPases are metal cation pumps that transport metals across membranes. These proteins possess N- and C-terminal cytoplasmic extensions that contain Cys- and His-rich high affinity metal binding domains, which may be involved in metal sensing, metal ion selectivity and/or in regulation of the pump activity. The PIB ATPase HMA4 (Heavy Metal ATPase 4) plays a central role in metal homeostasis in Arabidopsis thaliana and has a key function in zinc and cadmium hypertolerance and hyperaccumulation in the extremophile plant species Arabidopsis halleri. Here, we examined the function and structure of the N-terminal cytoplasmic metal-binding domain of HMA4. We mutagenized a conserved CCTSE metal-binding motif in the domain and assessed the impact of the mutations on protein function and localization in planta, on metal-binding properties in vitro and on protein structure by Nuclear Magnetic Resonance spectroscopy. The two Cys residues of the motif are essential for the function, but not for localization, of HMA4 in planta, whereas the Glu residue is important but not essential. These residues also determine zinc coordination and affinity. Zinc binding to the N-terminal domain is thus crucial for HMA4 protein function, whereas it is not required to maintain the protein structure. Altogether, combining in vivo and in vitro approaches in our study provides insights towards the molecular understanding of metal transport and specificity of metal P-type ATPases.

  6. 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.

  7. 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.

  8. Arabidopsis AtNaKR1 is a phloem mobile metal-binding protein necessary for phloem function and root meristem maintenance

    USDA-ARS?s Scientific Manuscript database

    The SODIUM POTASSIUM ROOT DEFECTIVE 1 (NaKR1) encodes a soluble metal binding protein that is specifically expressed in companion cells of the phloem. The nakr1-1 mutant phenotype includes high Na+, K+, and Rb+ accumulation in leaves, short roots, and late flowering. Starch accumulation in the leave...

  9. [Biosynthesis of human calcitonin and mini-proinsulin in bacterial cells in the form of hybrid proteins with corresponding antisense peptides and a metal-binding peptide].

    PubMed

    Efimov, V A; Buriakova, A A; Fradkov, A F; Chakhmakhcheva, O G

    1996-07-01

    To verify experimentally the molecular recognition theory, plasmids were constructed that provided the efficient synthesis of hybrid proteins composed of human calcitonin or miniproinsulin, the corresponding antisense peptides, and a histidine-rich metal-binding peptide. A method for isolation of the hybrid proteins by metal-chelating chromatography, cleavage, and renaturation was developed.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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).

  18. Chemical and enzymatic extraction of heavy metal binding polymers from isolated cell walls of Saccharomyces cerevisiae

    SciTech Connect

    Brady, D.; Stoll, A.D.; Starke, L.; Duncan, J.R. . Dept. of Biochemistry and Microbiology)

    1994-07-01

    Isolated cell walls of the yeast Saccharomyces cerevisiae were treated by either chemical (alkali and acid) or enzymatic (protease, mannanase or [beta]-glucuronidase) processes to yield partially purified products. These products were partially characterized by infrared analysis. They were subsequently reacted with heavy metal cation solutions and the quantity of metal accumulated by the cell wall material determined. The Cu[sup 2+] ion (0.24, 0.36, 1.12, and 0.60 [mu]mol/mg) was accumulated to a greater extent than either Co[sup 2+] (0.13, 0.32, 0.43, and 0.32 [mu]mol/mg) or Cd[sup 2+] (0.17, 0.34, 0.39, and 0.46 [mu]mol/mg) by yeast cell walls, glucan, mannan, and chitin, respectively. The isolated components each accumulated greater quantities of the cations than the intact cell wall. Removal of the protein component of the yeast cell wall by Pronase caused a 29.5% decrease in metal accumulation by yeast cell walls per mass, indicating that protein is a heavy metal accumulating component. The data indicate that the outer mannan-protein layer of the yeast cell wall is more important than the inner glucan-chitin layer in heavy metal cation accumulation.

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Metal binding and substrate positioning by evolutionarily invariant U6 sequences in catalytically active protein-free snRNAs

    PubMed Central

    Lee, Caroline; Jaladat, Yasaman; Mohammadi, Afshin; Sharifi, Armin; Geisler, Sarah; Valadkhan, Saba

    2010-01-01

    We have previously shown that a base-paired complex formed by two of the spliceosomal RNA components, U6 and U2 small nuclear RNAs (snRNAs), can catalyze a two-step splicing reaction that depended on an evolutionarily invariant region in U6, the ACAGAGA box. Here we further analyze this RNA-catalyzed reaction and show that while the 5′ and 3′ splice site substrates are juxtaposed and positioned near the ACAGAGA sequence in U6, the role of the snRNAs in the reaction is beyond mere juxtaposition of the substrates and likely involves the formation of a sophisticated active site. Interestingly, the snRNA-catalyzed reaction is metal dependent, as is the case with other known splicing RNA enzymes, and terbium(III) cleavage reactions indicate metal binding by the U6/U2 complex within the evolutionarily conserved regions of U6. The above results, combined with the structural similarities between U6 and catalytically critical domains in group II self-splicing introns, suggest that the base-paired complex of U6 and U2 snRNAs is a vestigial ribozyme and a likely descendant of a group II-like self-splicing intron. PMID:20826700

  6. 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.

  7. Transcriptional Regulation, Metal Binding Properties and Structure of Pden1597, an Unusual Zinc Transport Protein from Paracoccus denitrificans*

    PubMed Central

    Handali, Melody; Neupane, Durga P.; Roychowdhury, Hridindu; Yukl, Erik T.

    2015-01-01

    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. PMID:25787075

  8. Determination of the heavy metal binding capacity of aquatic samples using MetPLATE: a preliminary study.

    PubMed

    Huang, F; Bitton, G; Kong, I C

    1999-08-30

    MetPLATE, a microbial toxicity test which is specific for heavy metal toxicity, was used to rapidly determine the heavy metal binding capacity (HMBC) of a wide range of surface waters from Florida and Georgia. HMBC determines the impact of physicochemical factors on metal bioavailability and toxicity. The new developed protocol, using MetPLATE as the toxicity assay, showed that HMBC varied from 1.7 to 39.2 for Cd whereas the ranges for Cu and Ag were < 1-11.9 and < 1-2.1, respectively. The effect of seasons on HMBC was determined using samples from the Hogtown Creek, Gainesville, FL, and from the St John's river in Jacksonville, FL. Both surface waters displayed the highest HMBC during the Fall season. Preliminary examination of the limited data set confirms that HMBC may be influenced by the concentration of dissolved organic carbon (DOC). These preliminary data show that the impact of physical and chemical parameters on the toxicity of metals in aquatic environments can be rapidly assessed using rapid and low-cost microbiotests.

  9. Dynamics of the metal binding domains and regulation of the human copper transporters ATP7B and ATP7A.

    PubMed

    Yu, Corey H; Dolgova, Natalia V; Dmitriev, Oleg Y

    2017-04-01

    Copper transporters ATP7A and ATP7B regulate copper levels in the human cells and deliver copper to the biosynthetic pathways. ATP7A and ATP7B belong to the P-type ATPases and share much of the domain architecture and the mechanism of ATP hydrolysis with the other, well-studied, enzymes of this type. A unique structural feature of the copper ATPases is the chain of six cytosolic metal-binding domains (MBDs), which are believed to be involved in copper-dependent regulation of the activity and intracellular localization of these enzymes. Although the structures of all the MBDs have been solved, the mechanism of copper-dependent regulation of ATP7B and ATP7A, the roles of individual MBDs, and the relationship between the regulatory and catalytic copper binding are still unknown. We describe the structure and dynamics of the MBDs, review the current knowledge about their functional roles and propose a mechanism of regulation of ATP7B by copper-dependent changes in the dynamics and conformation of the MBD chain. Transient interactions between the MBDs, rather than transitions between distinct static conformations are likely to form the structural basis of regulation of the ATP-dependent copper transporters in human cells. © 2016 IUBMB Life, 69(4):226-235, 2017. © 2017 International Union of Biochemistry and Molecular Biology.

  10. 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

  11. 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.

  12. 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.

  13. 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, S