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Sample records for iron oxide cross-linked

  1. Magnetic Characterization of Iron Oxide Cross Linked Hydro gels

    NASA Astrophysics Data System (ADS)

    Senaratne, U.; Powell, N.; Kroll, E.; Tsoi, G.; Naik, R.; Naik, V.; Vaishnava, P. P.; Wenger, L. E.

    2004-03-01

    Magnetic hydro gels have potential applications in drug delivery, cells sorting, sensors, and actuating technologies. Iron oxide alginate nanocomposites were synthesized following the method of Kroll et al^1 by cross linking sodium alginate with Fe^2+ and Fe^3+ in methanol: water. The ion-cross linked alginate hydro gels are oxidized in an alkaline solution. The resulting hydro gel consists of iron oxide cross linked alginate. The alginate hydro gels are inert to the reaction conditions and therefore the reaction sequence can be repeated. The multiple loadings result in an increase in the amount of iron oxide and the size of the iron oxide nanoparticles in the cross linked hydro gels. The third and sixth loaded iron oxide alginate hydro gels were dried and characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and Superconducting Quantum Interference Device (SQUID) magnetometry. The XRD patterns have characteristic features of γ- Fe_2O3 or Fe_3O4 phases. The average particle size, calculated from the XRD peaks, for third loaded iron oxide alginate was 2 nm. The zero-field-cooled and field-cooled SQUID measurements show the iron oxide nanoparticles are superparamagnetic with blocking temperature (T_B) of approximately 35 K. Above the blocking temperature, the inverse susceptibility versus temperature relationship does not follow the Curie-Weiss law, indicating strong inter-particle interactions. The M vs. H data above the blocking temperature was fitted with a modified Langevin function to obtain additional information about the iron oxide particle size. Details of the relationship between coercive field and temperature as well as the particle size distribution obtained from XRD and TEM measurements will be presented. *Research supported by NSF grant # DGE ˜980720 **Supported by NSF REU grant # EEC-0097736 ^1E. Kroll, F.M. Winnik, and R.F. Ziolo, Chem. Mater, 8, 1594 (1996).

  2. Block Copolymer Cross-linked Nanoassemblies Improve Particle Stability and Biocompatibility of Superparamagnetic Iron Oxide Nanoparticles

    PubMed Central

    Dan, Mo; Scott, Daniel F.; Hardy, Peter A.; Wydra, Robert J.; Hilt, J. Zach; Yokel, Robert A.; Bae, Younsoo

    2014-01-01

    Purpose To develop cross-linked nanoassemblies (CNAs) as carriers for superparamagnetic iron oxide nanoparticles (IONPs). Methods Ferric and ferrous ions were co-precipitated inside core-shell type nanoparticles prepared by cross-linking poly(ethylene glycol)-poly(aspartate) block copolymers to prepare CNAs entrapping Fe3O4 IONPs (CNA-IONPs). Particle stability and biocompatibility of CNA-IONPs were characterized in comparison to citrate-coated Fe3O4 IONPs (Citrate-IONPs). Results CNA-IONPs, approximately 30 nm in diameter, showed no precipitation in water, PBS, or a cell culture medium after 3 or 30 h, at 22, 37, and 43 °C, and 1, 2.5, and 5 mg/mL, whereas Citrate-IONPs agglomerated rapidly (> 400 nm) in all aqueous media tested. No cytotoxicity was observed in a mouse brain endothelial-derived cell line (bEnd.3) exposed to CNA-IONPs up to 10 mg/mL for 30 h. Citrate-IONPs (> 0.05 mg/mL) reduced cell viability after 3 h. CNA-IONPs retained the superparamagnetic properties of entrapped IONPs, enhancing T2-weighted magnetic resonance images (MRI) at 0.02 mg/mL, and generating heat at a mild hyperthermic level (40 ~ 42 °C) with an alternating magnetic field (AMF). Conclusion Compared to citric acid coating, CNAs with a cross-linked anionic core improved particle stability and biocompatibility of IONPs, which would be beneficial for future MRI and AMF-induced remote hyperthermia applications. PMID:23080062

  3. Enhancement of irradiation effects on cancer cells by cross-linked dextran-coated iron oxide (CLIO) nanoparticles

    NASA Astrophysics Data System (ADS)

    Huang, Fu-Kuo; Chen, Wen-Chang; Lai, Sheng-Feng; Liu, Chi-Jen; Wang, Cheng-Liang; Wang, Chang-Hai; Chen, Hsiang-Hsin; Hua, Tzu-En; Cheng, Yi-Yun; Wu, M. K.; Hwu, Y.; Yang, Chung-Shi; Margaritondo, G.

    2010-01-01

    We investigated iron oxide nanoparticles with two different surface modifications, dextran coating and cross-linked dextran coating, showing that their different internalization affects their capability to enhance radiation damage to cancer cells. The internalization was monitored with an ultrahigh resolution transmission x-ray microscope (TXM), indicating that the differences in the particle surface charge play an essential role and dominate the particle-cell interaction. We found that dextran-coated iron oxide nanoparticles cannot be internalized by HeLa and EMT-6 cells without being functionalized with amino groups (the cross-linked dextran coating) that modify the surface potential from -18 mV to 13.4 mV. The amount of cross-linked dextran-coated iron oxide nanoparticles uptaken by cancer cells reached its maximum, 1.33 × 109 per HeLa cell, when the co-culture concentration was 40 µg Fe mL-1 or more. Standard tests indicated that these internalized nanoparticles increased the damaging effects of x-ray irradiation, whereas they are by themselves biocompatible. These results could lead to interesting therapy applications; furthermore, iron oxide also produces high contrast for magnetic resonance imaging (MRI) in the diagnosis and therapy stages.

  4. Polyethylene glycol modified, cross-linked starch-coated iron oxide nanoparticles for enhanced magnetic tumor targeting.

    PubMed

    Cole, Adam J; David, Allan E; Wang, Jianxin; Galbán, Craig J; Hill, Hannah L; Yang, Victor C

    2011-03-01

    While successful magnetic tumor targeting of iron oxide nanoparticles has been achieved in a number of models, the rapid blood clearance of magnetically suitable particles by the reticuloendothelial system (RES) limits their availability for targeting. This work aimed to develop a long-circulating magnetic iron oxide nanoparticle (MNP) platform capable of sustained tumor exposure via the circulation and, thus, potentially enhanced magnetic tumor targeting. Aminated, cross-linked starch (DN) and aminosilane (A) coated MNPs were successfully modified with 5 kDa (A5, D5) or 20 kDa (A20, D20) polyethylene glycol (PEG) chains using simple N-Hydroxysuccinimide (NHS) chemistry and characterized. Identical PEG-weight analogues between platforms (A5 & D5, A20 & D20) were similar in size (140-190 nm) and relative PEG labeling (1.5% of surface amines - A5/D5, 0.4% - A20/D20), with all PEG-MNPs possessing magnetization properties suitable for magnetic targeting. Candidate PEG-MNPs were studied in RES simulations in vitro to predict long-circulating character. D5 and D20 performed best showing sustained size stability in cell culture medium at 37 °C and 7 (D20) to 10 (D5) fold less uptake in RAW264.7 macrophages when compared to previously targeted, unmodified starch MNPs (D). Observations in vitro were validated in vivo, with D5 (7.29 h) and D20 (11.75 h) showing much longer half-lives than D (0.12 h). Improved plasma stability enhanced tumor MNP exposure 100 (D5) to 150 (D20) fold as measured by plasma AUC(0-∞). Sustained tumor exposure over 24 h was visually confirmed in a 9L-glioma rat model (12 mg Fe/kg) using magnetic resonance imaging (MRI). Findings indicate that a polyethylene glycol modified, cross-linked starch-coated MNP is a promising platform for enhanced magnetic tumor targeting, warranting further study in tumor models.

  5. Distribution and accumulation of Cy5.5-labeled thermally cross-linked superparamagnetic iron oxide nanoparticles in the tissues of ICR mice

    PubMed Central

    Hue, Jin Joo; Lee, Hu-Jang; Jon, Sangyong; Nam, Sang Yoon; Yun, Young Won; Kim, Jong-Soo

    2013-01-01

    Free Cy5.5 dye and Cy5.5-labeled thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION) have been routinely used for in vivo optical imaging. However, there is little information about the distribution and accumulation of free Cy5.5 dye and Cy5.5-labeled TCL-SPION in the tissues of mice. Free Cy5.5 dye (0.1 mg/kg body weight) and Cy5.5-labeled TCL-SPION (15 mg/kg body weight) were intravenously injected into the tail vein of ICR mice. The biodistribution and accumulation of the TCL-SPION and Cy5.5 were observed by ex vivo optical imaging and fluorescence signal generation at various time points over 28 days. Cy5.5 dye fluorescence in various organs was rapidly eliminated from 0.5 to 24 h post-injection. Fluorescence intensity of Cy5.5 dye in the liver, lung, kidney, and stomach was fairly strong at the early time points within 1 day post-injection. Cy5.5-labeled TCL-SPION had the highest fluorescence density in the lung at 0.5 h post-injection and decreased rapidly over time. Fluorescence density in liver and spleen was maintained over 28 days. These results suggest that TCL-SPION can be useful as a carrier of therapeutic reagents to treat diseases by persisting for long periods of time in the body. PMID:24366671

  6. Biologically relevant oxidants cause bound proteins to readily oxidatively cross-link at Guanine.

    PubMed

    Solivio, Morwena J; Nemera, Dessalegn B; Sallans, Larry; Merino, Edward J

    2012-02-20

    Oxidative DNA-protein cross-links have received less attention than other types of DNA damage and remain as one of the least understood types of oxidative lesion. A model system using ribonuclease A and a 27-nucleotide DNA was used to determine the propensity of oxidative cross-linking to occur in the presence of oxidants. Cross-link formation was examined using four different oxidation systems that generate singlet oxygen, superoxide, and metal-based Fenton reactions. It is shown that oxidative cross-linking occurs in yields ranging from 14% to a maximal yield of 61% in all oxidative systems when equivalent concentrations of DNA and protein are present. Because singlet oxygen is the most efficient oxidation system in generating DNA-protein cross-links, it was chosen for further analyses. Cross-linking occurred with single-stranded DNA binding protein and not with bovine serum albumin. Addition of salt lowered nonspecific binding affinity and lowered cross-link yield by up to 59%. The yield of cross-linking increased with increased ratios of protein compared with DNA. Cross-linking was highly dependent on the number of guanines in a DNA sequence. Loss of guanine content on the 27-nucleotide DNA led to nearly complete loss in cross-linking, while primer extension studies showed cross-links to predominantly occur at guanine base on a 100-nucleotide DNA. The chemical species generated were examined using two peptides derived from the ribonuclease A sequence, N-acetyl-AAAKF and N-acetyl-AYKTT, which were cross-linked to 2'-deoxyguanosine. The cross-link products were spiroiminodihydantoin, guanidinohydantoin, and tyrosyl-based adducts. Formation of tyrosine-based adducts may be competitive with the more well-studied lysine-based cross-links. We conclude that oxidative cross-links may be present at high levels in cells since the propensity to oxidatively cross-link is high and so much of the genomic DNA is coated with protein.

  7. In Vivo Oxidative Stability Changes of Highly Cross-Linked Polyethylene Bearings: An Ex Vivo Investigation.

    PubMed

    Rowell, Shannon L; Reyes, Christopher R; Malchau, Henrik; Muratoglu, Orhun K

    2015-10-01

    The development of highly cross-linked UHMWPEs focused on stabilizing radiation-induced free radicals as the sole precursor to oxidative degradation. However, secondary in vivo oxidation mechanisms have been discovered. After a preliminary post-operative analysis, we subjected highly cross-linked retrievals with 1-4 years in vivo durations and never-implanted controls to accelerated aging to predict the extent to which their oxidative stability was compromised in vivo. Lipid absorption, oxidation, and hydroperoxides were measured using infrared spectroscopy. Gravimetric swelling was used to measure cross-link density. After aging, all retrievals, except vitamin E-stabilized components, regardless of initial lipid levels or oxidation, showed significant oxidative degradation, demonstrated by subsurface oxidative peaks, increased hydroperoxides and decreased cross-link density, compared to their post-operative material properties and never-implanted counterparts, confirming oxidative stability changes.

  8. The relative contribution of calcium, zinc and oxidation-based cross-links to the stiffness of Arion subfuscus glue.

    PubMed

    Braun, M; Menges, M; Opoku, F; Smith, A M

    2013-04-15

    Metal ions are present in many different biological materials, and are capable of forming strong cross-links in aqueous environments. The relative contribution of different metal-based cross-links was measured in the defensive glue produced by the terrestrial slug Arion subfuscus. This glue contains calcium, magnesium, zinc, manganese, iron and copper. These metals are essential to the integrity of the glue and to gel stiffening. Removal of all metals caused at least a 15-fold decrease in the storage modulus of the glue. Selectively disrupting cross-links involving hard Lewis acids such as calcium reduced the stiffness of the glue, while disrupting cross-links involving borderline Lewis acids such as zinc did not. Calcium is the most common cation bound to the glue (40 mmol l(-1)), and its charge is balanced primarily by sulphate at 82-84 mmol l(-1). Thus these ions probably play a primary role in bringing polymers together directly. Imine bonds formed as a result of protein oxidation also contribute substantially to the stiffness of the glue. Disrupting these bonds with hydroxylamine caused a 33% decrease in storage modulus of the glue, while stabilizing them by reduction with sodium borohydride increased the storage modulus by 40%. Thus a combination of metal-based bonds operates in this glue. Most likely, cross-links directly involving calcium play a primary role in bringing together and stabilizing the polymer network, followed by imine bond formation and possible iron coordination.

  9. Electrospun gelatin nanofibers: a facile cross-linking approach using oxidized sucrose.

    PubMed

    Jalaja, K; James, Nirmala R

    2015-02-01

    Gelatin nanofibers were fabricated via electrospinning with minimal toxicity from solvents and cross-linking agents. Electrospinning was carried out using a solvent system based on water and acetic acid (8:2, v/v). Acetic acid concentration was kept as minimum as possible to reduce the toxic effects. Electrospun gelatin nanofibers were cross-linked with oxidized sucrose. Sucrose was oxidized by periodate oxidation to introduce aldehyde functionality. Cross-linking with oxidized sucrose could be achieved without compromising the nanofibrous architecture. Cross-linked gelatin nanofibers maintained the fibrous morphology even after keeping in contact with aqueous medium. The morphology of the cross-linked nanofibrous mats was examined by scanning electron microscopy (SEM). Oxidized sucrose cross-linked gelatin nanofibers exhibited improved thermal and mechanical properties. The nanofibrous mats were evaluated for cytotoxicity and cell viability using L-929 fibroblast cells. The results confirmed that oxidized sucrose cross-linked gelatin nanofibers were non-cytotoxic towards L-929 cells with good cell viability.

  10. Feruloylated arabinoxylans are oxidatively cross-linked by extracellular maize peroxidase but not by horseradish peroxidase.

    PubMed

    Burr, Sally J; Fry, Stephen C

    2009-09-01

    Covalent cross-linking of soluble extracellular arabinoxylans in living maize cultures, which models the cross-linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H2O2/peroxidase, O2/laccase, or reactive oxygen species acting non-enzymically. To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extracellular, feruloylated [pentosyl-3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Cross-linking was suppressed by iodide, an H2O2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H2O2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [3H]arabinoxylans in vitro only if H2O2 was also added, indicating a peroxidase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases (assayed on o-dianisidine) were also present. Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylan-cross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [3H]arabinoxylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.

  11. Cross-linking proteins by laccase-catalyzed oxidation: importance relative to other modifications.

    PubMed

    Steffensen, Charlotte L; Andersen, Mogens L; Degn, Peter E; Nielsen, Jacob H

    2008-12-24

    Laccase-catalyzed oxidation was able to induce intermolecular cross-links in beta-lactoglobulin, and ferulic acid-mediated laccase-catalyzed oxidation was able to induce intermolecular cross-links in alpha-casein, whereas transglutaminase cross-linked only alpha-casein. In addition, different patterns of laccase-induced oxidative modifications were detected, including dityrosine formation, formation of fluorescent tryptophan oxidation products, and carbonyls derived from histidine, tryptophan, and methionine. Laccase-catalyzed oxidation as well as transglutaminase induced only minor changes in surface tension of the proteins, and the changes could not be correlated to protein cross-linking. The presence of ferulic acid was found to influence the effect of laccase, allowing laccase to form irreducible intermolecular cross-links in beta-lactoglobulin and resulting in proteins exercising higher surface tensions due to cross-linking as well as other oxidative modifications. The outcome of using ferulic acid-mediated laccase-catalyzed oxidation to modify the functional properties of proteinaceous food components or other biosystems is expected to be highly dependent on the protein composition, resulting in different changes of the functional properties.

  12. Oxidation increases mucin polymer cross-links to stiffen airway mucus gels.

    PubMed

    Yuan, Shaopeng; Hollinger, Martin; Lachowicz-Scroggins, Marrah E; Kerr, Sheena C; Dunican, Eleanor M; Daniel, Brian M; Ghosh, Sudakshina; Erzurum, Serpel C; Willard, Belinda; Hazen, Stanley L; Huang, Xiaozhu; Carrington, Stephen D; Oscarson, Stefan; Fahy, John V

    2015-02-25

    Airway mucus in cystic fibrosis (CF) is highly elastic, but the mechanism behind this pathology is unclear. We hypothesized that the biophysical properties of CF mucus are altered because of neutrophilic oxidative stress. Using confocal imaging, rheology, and biochemical measures of inflammation and oxidation, we found that CF airway mucus gels have a molecular architecture characterized by a core of mucin covered by a web of DNA and a rheological profile characterized by high elasticity that can be normalized by chemical reduction. We also found that high levels of reactive oxygen species in CF mucus correlated positively and significantly with high concentrations of the oxidized products of cysteine (disulfide cross-links). To directly determine whether oxidation can cross-link mucins to increase mucus elasticity, we exposed induced sputum from healthy subjects to oxidizing stimuli and found a marked and thiol-dependent increase in sputum elasticity. Targeting mucin disulfide cross-links using current thiol-amino structures such as N-acetylcysteine (NAC) requires high drug concentrations to have mucolytic effects. We therefore synthesized a thiol-carbohydrate structure (methyl 6-thio-6-deoxy-α-D-galactopyranoside) and found that it had stronger reducing activity than NAC and more potent and fast-acting mucolytic activity in CF sputum. Thus, oxidation arising from airway inflammation or environmental exposure contributes to pathologic mucus gel formation in the lung, which suggests that it can be targeted by thiol-modified carbohydrates.

  13. Identification of dityrosine cross-linked sites in oxidized human serum albumin.

    PubMed

    Annibal, Andrea; Colombo, Graziano; Milzani, Aldo; Dalle-Donne, Isabella; Fedorova, Maria; Hoffmann, Ralf

    2016-04-15

    Reactive oxygen species (ROS) can oxidize virtually all cellular components. In proteins cysteine, methionine, tryptophan, and tyrosine residues are most prone to oxidation and their oxidized forms are thus considered as biomarkers of oxidative protein damages. Ultraviolet radiation and some endogenous ROS can produce tyrosine radicals reacting with other tyrosine residues yielding intra- or intermolecular cross-links in proteins. These 3,3'-dityrosines can be quantified by their characteristic fluorescence, but analytical methods to identify the modification sites in proteins are still missing. Although mass spectrometry (MS) is routinely used to map other post-translational modifications, the analysis of dityrosines is challenged by simultaneous fragmentations of both cross-linked peptide chains producing complex tandem mass spectra. Additionally, the fragmentation patterns differ from linear peptides. Here, we studied the fragmentation behavior of dityrosine cross-linked peptides obtained by incubating three peptides (AAVYHHFISDGVR, TEVSSNHVLIYLDK, and LVAYYTLIGASGQR) with horseradish peroxidase in the presence of hydrogen peroxide. Homo- and hetero-dimerization via dityrosine was monitored by fluorescence spectroscopy and MS. The fragmentation characteristics of dityrosine-linked peptides were studied on an ESI-LTQ-Orbitrap-MS using collision induced dissociation, which allowed localizing the cross-linked positions and provided generic rules to identify this oxidative modification. When human serum albumin oxidized with 50-fold molar excess of HOCl in phosphate buffer saline was analyzed by nanoRPC-ESI-MS/MS, an automatic database search considering all possible (in-silico generated) tyrosine-containing peptides as dynamic modifications revealed four different types of oxidatively modified tyrosine residues including dityrosines linking ten different Tyr residues. The automatic database search was confirmed by manual interpretation of each tandem mass spectrum.

  14. Preparation and characterization of electrospun in-situ cross-linked gelatin-graphite oxide nanofibers.

    PubMed

    Zhan, Jianchao; Morsi, Yosry; Ei-Hamshary, Hany; Al-Deyab, Salem S; Mo, Xiumei

    2016-01-01

    Electrospun gelatin(Gel) nanofibers scaffold has such defects as poor mechanical property and quick degradation due to high solubility. In this study, the in situ cross-linked electrospinning technique was used for the production of gelatin nanofibers. Deionized water was chosen as the spinning solvent and graphite oxide (GO) was chosen as the enhancer. The morphological structure, porosity, thermal property, moisture absorption, and moisture retention performance, hydrolysis resistance, mechanical property, and biocompatibility of the produced nanofibers were investigated. Compared with in situ cross-linked gelatin nanofibers scaffold, in situ cross-linked Gel-GO nanofibers scaffold has the following features: (1) the hydrophilicity, moisture absorption, and moisture retention performance slightly reduce, while the hydrolysis resistance is improved; (2) the breaking strength, breaking elongation, and Young's modulus are significantly improved; (3) the porosity slightly reduces while the biocompatibility considerably increases. The in situ cross-linked Gel-GO nanofibers scaffold is likely to be applied in such fields as drug delivery and scaffold for skin tissue engineering.

  15. A strong integrated strength and toughness artificial nacre based on dopamine cross-linked graphene oxide.

    PubMed

    Cui, Wei; Li, Mingzhu; Liu, Jiyang; Wang, Ben; Zhang, Chuck; Jiang, Lei; Cheng, Qunfeng

    2014-09-23

    Demands of the strong integrated materials have substantially increased across various industries. Inspired by the relationship of excellent integration of mechanical properties and hierarchical nano/microscale structure of the natural nacre, we have developed a strategy for fabricating the strong integrated artificial nacre based on graphene oxide (GO) sheets by dopamine cross-linking via evaporation-induced assembly process. The tensile strength and toughness simultaneously show 1.5 and 2 times higher than that of natural nacre. Meanwhile, the artificial nacre shows high electrical conductivity. This type of strong integrated artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.

  16. New Aptes Cross-linked Polymers from Poly(ethylene oxide)s and Cyanuric Chloride for Lithium Batteries

    NASA Technical Reports Server (NTRS)

    Tigelaar, Dean M.; Meador, Mary Ann B.; Kinder, James D.; Bennett, William R.

    2005-01-01

    A new series of polymer electrolytes for use as membranes for lithium batteries are described. Electrolytes were made by polymerization between cyanuric chloride and diamino-terminated poly(ethylene oxide)s, followed by cross-linking via a sol-gel process. Thermal analysis and lithium conductivity of freestanding polymer films were studied. The effects of several variables on conductivity were investigated, such as length of backbone PEO chain, length of branching PEO chain, extent of branching, extent of cross-linking, salt content, and salt counterion. Polymer films with the highest percentage of PEO were found to be the most conductive, with a maximum lithium conductivity of 3.9 x 10(exp -5) S/cm at 25 C. Addition of plasticizer to the dry polymers increased conductivity by an order of magnitude.

  17. Physiologically relevant oxidative degradation of oligo(proline) cross-linked polymeric scaffolds.

    PubMed

    Yu, Shann S; Koblin, Rachel L; Zachman, Angela L; Perrien, Daniel S; Hofmeister, Lucas H; Giorgio, Todd D; Sung, Hak-Joon

    2011-12-12

    Chronic inflammation-mediated oxidative stress is a common mechanism of implant rejection and failure. Therefore, polymer scaffolds that can degrade slowly in response to this environment may provide a viable platform for implant site-specific, sustained release of immunomodulatory agents over a long time period. In this work, proline oligomers of varying lengths (P(n)) were synthesized and exposed to oxidative environments, and their accelerated degradation under oxidative conditions was verified via high performance liquid chromatography and gel permeation chromatography. Next, diblock copolymers of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL) were carboxylated to form 100 kDa terpolymers of 4%PEG-86%PCL-10%cPCL (cPCL = poly(carboxyl-ε-caprolactone); i% indicates molar ratio). The polymers were then cross-linked with biaminated PEG-P(n)-PEG chains, where P(n) indicates the length of the proline oligomer flanked by PEG chains. Salt-leaching of the polymeric matrices created scaffolds of macroporous and microporous architecture, as observed by scanning electron microscopy. The degradation of scaffolds was accelerated under oxidative conditions, as evidenced by mass loss and differential scanning calorimetry measurements. Immortalized murine bone-marrow-derived macrophages were then seeded on the scaffolds and activated through the addition of γ-interferon and lipopolysaccharide throughout the 9-day study period. This treatment promoted the release of H(2)O(2) by the macrophages and the degradation of proline-containing scaffolds compared to the control scaffolds. The accelerated degradation was evidenced by increased scaffold porosity, as visualized through scanning electron microscopy and X-ray microtomography imaging. The current study provides insight into the development of scaffolds that respond to oxidative environments through gradual degradation for the controlled release of therapeutics targeted to diseases that feature chronic

  18. Self-Powered Electrochemistry for the Oxidation of Organic Molecules by a Cross-Linked Triboelectric Nanogenerator.

    PubMed

    Zheng, Xin; Su, Jingzhen; Wei, Xianjun; Jiang, Tao; Gao, Shuyan; Wang, Zhong Lin

    2016-07-01

    A cross-linked triboelectric nanogenerator with high performance is designed for the first time, which harvests vibrational energy to self-power the electrochemical oxidation of organic molecules. This system lays the groundwork for applications to an environmentally friendly production of important organic molecules and the waste treatment of organic pollutants.

  19. Inhibition of DNA cross-linking by mitomycin C by peroxidase-mediated oxidation of mitomycin C hydroquinone.

    PubMed

    Penketh, P G; Hodnick, W F; Belcourt, M F; Shyam, K; Sherman, D H; Sartorelli, A C

    2001-09-14

    Mitomycin C requires reductive activation to cross-link DNA and express anticancer activity. Reduction of mitomycin C (40 microm) by sodium borohydride (200 microm) in 20 mm Tris-HCl, 1 mm EDTA at 37 degrees C, pH 7.4, gives a 50-60% yield of the reactive intermediate mitomycin C hydroquinone. The hydroquinone decays with first order kinetics or pseudo first order kinetics with a t(12) of approximately 15 s under these conditions. The cross-linking of T7 DNA in this system followed matching kinetics, with the conversion of mitomycin C hydroquinone to leuco-aziridinomitosene appearing to be the rate-determining step. Several peroxidases were found to oxidize mitomycin C hydroquinone to mitomycin C and to block DNA cross-linking to various degrees. Concentrations of the various peroxidases that largely blocked DNA cross-linking, regenerated 10-70% mitomycin C from the reduced material. Thus, significant quantities of products other than mitomycin C were produced by the peroxidase-mediated oxidation of mitomycin C hydroquinone or products derived therefrom. Variations in the sensitivity of cells to mitomycin C have been attributed to differing levels of activating enzymes, export pumps, and DNA repair. Mitomycin C hydroquinone-oxidizing enzymes give rise to a new mechanism by which oxic/hypoxic toxicity differentials and resistance can occur.

  20. Improved stability and cell response by intrinsic cross-linking of multilayers from collagen I and oxidized glycosaminoglycans.

    PubMed

    Zhao, Mingyan; Li, Lihua; Zhou, Changren; Heyroth, Frank; Fuhrmann, Bodo; Maeder, Karsten; Groth, Thomas

    2014-11-10

    Stability of surface coatings against environmental stress, such as pH, high ionic strength, mechanical forces, and so forth, is crucial for biomedical application of implants. Here, a novel extracellular-matrix-like polyelectrolyte multilayer (PEM) system composed of collagen I (Col I) and oxidized glycosaminoglycans (oGAGs) was stabilized by intrinsic cross-linking due to formation of imine bonds between aldehydes of oxidized chondroitin sulfate (oCS) or hyaluronan (oHA) and amino groups of Col I. It was also found that Col I contributed significantly more to overall mass in CS-Col I than in HA-Col I multilayer systems and fibrillized particularly in the presence of native and oxidized CS. Adhesion and proliferation studies with murine C3H10T1/2 embryonic fibroblasts demonstrated that covalent cross-linking of oGAG with Col I had no adverse effects on cell behavior. By contrast, it was found that cell size and polarization was more pronounced on oGAG-based multilayer systems, which corresponded also to the higher stiffness of cross-linked multilayers as observed by studies with quartz crystal microbalance (QCM). Overall, PEMs prepared from oGAG and Col I give rise to stable PEM constructs due to intrinsic cross-linking that may be useful for making bioactive coatings of implants and tissue engineering scaffolds.

  1. Oxidation of Second Generation Sequentially Irradiated and Annealed Highly Cross-Linked X3™ Polyethylene Tibial Bearings.

    PubMed

    Kop, Alan M; Pabbruwe, Moreica B; Keogh, Catherine; Swarts, Eric

    2015-10-01

    Since the first use of ultra-high-molecular-weight polyethylene as a bearing material, research and development efforts have sought to improve wear resistance, increase longevity and lessen the potential for debris mediated adverse tissue responses. A series of second generation sequentially cross-linked and annealed tibial bearings were analysed after several bearings sent for routine retrieval analysis showed oxidative degradation including subsurface whitening, cracking and gross material loss. Evaluation incorporated visual and white banding assessment, mechanical testing and spectroscopy analysis. Whilst visual observation and white banding assessment confirmed oxidative changes, a decrease in mechanical properties and increasing ketone oxidation index as a function of time in vivo suggest time dependent oxidative degradation. Clinically relevant degradation of the sequentially cross-linked and annealed tibial bearings was observed.

  2. Study of the Photo-oxidation and Photolysis of Unsaturated and Cross-linked Polyesters (UP) in the Presence of Photoactive or not Inorganic Fillers

    NASA Astrophysics Data System (ADS)

    Khalil, Zahi; Koubaissy, Bachar; Akil, Mariam

    Disturbances of the photochemical evolution involved in the photolysis and in the photo-oxidation at long wavelengths (ë?300 nm) of poly(propylene glycol-maleatophtalate cross-linked by the styrene (UP),caused by the addition of photo-active pigment such as zinc sulphide or black iron oxides,and no photoactive inorganic fillers such as calcium carbonate have been analysed by means of FTIR and U.V. spectrophotometry. The photo-oxidation observed by FTIR of the polymer UP in the presence of inorganic fillers leads to the same photoproducts such as ones of the photo-oxidation of the virgin polymer, but the oxidation rate is greatly affected by the nature and the percentage of the inorganic filler. Zinc sulfide and black iron are incorporated in the film of polymers, the absorption spectra of ZnS reveals that this pigment is not as absorbent as titanium oxide in a more limited field. On the other hand, with a very low inner filter effect, black iron oxides promote the formation of absorbing photoproducts. The addition of Calcium carbonate non- absorbing filler to the UP, causes a slight decrease in the evolution of the I.R

  3. Furan-oxidation-triggered inducible DNA cross-linking: acyclic versus cyclic furan-containing building blocks--on the benefit of restoring the cyclic sugar backbone.

    PubMed

    Stevens, Kristof; Claeys, Diederica D; Catak, Saron; Figaroli, Sara; Hocek, Michal; Tromp, Jan M; Schürch, Stefan; Van Speybroeck, Veronique; Madder, Annemieke

    2011-06-14

    Oligodeoxynucleotides incorporating a reactive functionality can cause irreversible cross-linking to the target sequence and have been widely studied for their potential in inhibition of gene expression or development of diagnostic probes for gene analysis. Reactive oligonucleotides further show potential in a supramolecular context for the construction of nanometer-sized DNA-based objects. Inspired by the cytochrome P450 catalyzed transformation of furan into a reactive enal species, we recently introduced a furan-oxidation-based methodology for cross-linking of nucleic acids. Previous experiments using a simple acyclic building block equipped with a furan moiety for incorporation into oligodeoxynucleotides have shown that cross-linking occurs in a very fast and efficient way and that substantial amounts of stable, site-selectively cross-linked species can be isolated. Given the destabilization of duplexes observed upon introduction of the initially designed furan-modified building block into DNA duplexes, we explore here the potential benefits of two new building blocks featuring an extended aromatic system and a restored cyclic backbone. Thorough experimental analysis of cross-linking reactions in a series of contexts, combined with theoretical calculations, permit structural characterization of the formed species and allow assessment of the origin of the enhanced cross-link selectivity. Our experiments clearly show that the modular nature of the furan-modified building blocks used in the current cross-linking strategy allow for fine tuning of both yield and selectivity of the interstrand cross-linking reaction.

  4. Thiol oxidation and protein cross-link formation during chill storage of pork patties added essential oil of oregano, rosemary, or garlic.

    PubMed

    Nieto, Gema; Jongberg, Sisse; Andersen, Mogens L; Skibsted, Leif H

    2013-10-01

    The effect of two levels (0.05% and 0.4%) of essential oil of rosemary, oregano, or garlic on protein oxidation in pork patties was studied during storage under modified atmosphere (MAP: 70% O2: 20% CO2: 10% N2) or under aerobic conditions (AE) at 4°C. The oxidative stability of the meat proteins was evaluated as loss of thiols for up to 9 days of storage, and as formation of myosin cross-links analyzed by SDS-PAGE after 12 days of storage. Protein thiols were lost during storage to yield myosin disulfide cross-links. Essential oils of rosemary and oregano were found to retard the loss of thiols otherwise resulting in myosin cross-links. Garlic essential oil, on the contrary, was found to promote protein oxidation, as seen by an extreme loss in thiol groups, and elevated myosin cross-link formation compared to control.

  5. Mussel-inspired new approach for polymerization and cross-linking of peptides and proteins containing tyrosines by Fremy's salt oxidation.

    PubMed

    Wilchek, Meir; Miron, Talia

    2015-03-18

    Our objective was to develop a method mimicking the natural process of coherence in marine mollusks, by direct chemical conversion of protein tyrosine residues to DOPA-o-quinones, which consequently generates polymerization and cross-linking. Fremy's salt, (ON(SO3K)2, was used to convert tyrosine residues in peptides and proteins to reactive o-quinones. The conversion of tyrosines to DOPA-o-quinones, and their ability to polymerize or cross-link, was tested on tyramine, peptides, and proteins. The peptides tested were as follows: biotin-PEG4-tyramine (PEG-BT), and two decapeptides (identical to the repeating units comprising the mussel's adhesive protein). The proteins tested were as follows: bovine pancreatic ribonuclease A (RNase), lysozyme, IgG, avidin, and streptavidin. The oxidized peptides and proteins were all shown to incorporate oxygen atoms and undergo polymerization and cross-linking, depending on the availability of nucleophiles, mostly lysine amino groups of proteins. All the peptides and the noninteracting proteins such as RNase and lysozyme underwent homopolymerization upon Fremy's salt oxidation. When Fremy's salt oxidaized PEG-BT was mixed with the above proteins, it did not react with any of these proteins because PEG-BT underwent fast self-polymerization. Conversely, streptavidin or avidin cross-linked with PEG-BT after preincubation, thus showing that biorecognition is a prerequisite for cross-linking. Polymerization and cross-linking also occurred, following Fremy's salt oxidation of interacting proteins such as avidin and strepavidin with biotinyilated lysozyme or biotinylated RNase. This indicates that only proteins in very close proximity readily cross-link and polymerize via tyrosine residues. Attempts to convert DOPA-quinone to DOPA by reduction with sodium dithionite (Na2S2O4), was successful as far as small peptides were used. Fremy's salt oxidation can serve as an easy and useful tool to polymerize and cross-link proteins, for

  6. A hydrated phospholipid polymer-grafted layer prevents lipid-related oxidative degradation of cross-linked polyethylene.

    PubMed

    Kyomoto, Masayuki; Moro, Toru; Yamane, Shihori; Takatori, Yoshio; Tanaka, Sakae; Ishihara, Kazuhiko

    2017-01-01

    The surface and substrate of a cross-linked polyethylene (CLPE) liner are designed to achieve resistance against oxidative degradation in the construction of hip joint replacements. In this study, we aimed to evaluate the oxidative degradation caused by lipid absorption of a highly hydrophilic nanometer-scaled thickness layer prepared by grafting a poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) layer and a high-dose gamma-ray irradiated CLPE with vitamin E blending (HD-CLPE[VE]). The HD-CLPE(VE) and PMPC-grafted HD-CLPE(VE) exhibited extremely high oxidation resistance regardless of lipid absorption, even though residual-free radical levels were detectable. The water wettability of the PMPC-grafted CLPE and PMPC-grafted HD-CLPE(VE) surfaces was considerably greater than that of untreated surfaces. The hydrated PMPC-grafted layer also exhibited extremely low solubility for squalene. Lipids such as squalene and cholesterol esters diminished the oxidation resistance of CLPE despite the vitamin E improvement. Notably, the PMPC-grafted surface was resistant to lipid absorption and diffusion as well as subsequent lipid-related oxidative degradation, likely because of the presence of the hydrated PMPC-grafted layer. Together, these results provide preliminary evidence that the resistance against lipid absorption and diffusion of a hydrated PMPC-grafted layer might positively affect the extent of resistance to the in vivo oxidation of orthopedic implants.

  7. Flour mill stream blending affects sugar snap cookie and Japanese sponge cake quality and oxidative cross-linking potential of soft white wheat.

    PubMed

    Ramseyer, Daniel D; Bettge, Arthur D; Morris, Craig F

    2011-01-01

    The purpose of this research was to study the functional differences between straight grade (75% extraction rate) and patent (60% extraction rate) flour blends from 28 genetically pure soft white and club wheat grain lots, as evidenced by variation in sugar snap cookie and Japanese sponge cake quality. Functional differences were examined relative to arabinoxylan content, protein content, and oxidative cross-linking potential of flour slurries. Oxidative cross-linking measurements were obtained on flour slurries with a low shear Bostwick consistometer and considered endogenous oxidative cross-linking potential (water alone) or enhanced oxidative cross-linking potential (with added hydrogen peroxide-peroxidase). A 2-way ANOVA indicated that flour blend was the greater source of variation compared to grain lot for all response variables except water-extractable arabinoxylan content. Patent flours produced larger sugar snap cookies and Japanese sponge cakes, and contained significantly less total and water-unextractable arabinoxylans, protein, and ash than did straight grade flours. Patent flours produced more viscous slurries for endogenous and enhanced cross-linking measurements compared to the straight grade flours. The functional differences between patent and straight grade flours appear to be related to the particular mill streams that were utilized in the formulation of the 2 flour blends and compositional differences among those streams.

  8. Photoinduced Cross-Linking of Dynamic Poly(disulfide) Films via Thiol Oxidative Coupling.

    PubMed

    Feillée, Noémi; Chemtob, Abraham; Ley, Christian; Croutxé-Barghorn, Céline; Allonas, Xavier; Ponche, Arnaud; Le Nouen, Didier; Majjad, Hicham; Jacomine, Léandro

    2016-01-01

    Initially developed as an elastomer with an excellent record of barrier and chemical resistance properties, poly(disulfide) has experienced a revival linked to the dynamic nature of the S-S covalent bond. A novel photobase-catalyzed oxidative polymerization of multifunctional thiols to poly(disulfide) network is reported. Based solely on air oxidation, the single-step process is triggered by the photodecarboxylation of a xanthone acetic acid liberating a strong bicyclic guanidine base. Starting with a 1 μm thick film based on trithiol poly(ethylene oxide) oligomer, the UV-mediated oxidation of thiols to disulfides occurs in a matter of minutes both selectively, i.e., without overoxidation, and quantitatively as assessed by a range of spectroscopic techniques. Thiolate formation and film thickness determine the reaction rates and yield. Spatial control of the photopolymerization serves to generate robust micropatterns, while the reductive cleavage of S-S bridges allows the recycling of 40% of the initial thiol groups.

  9. Enzymatically cross-linked hyaluronic acid/graphene oxide nanocomposite hydrogel with pH-responsive release.

    PubMed

    Song, Fangfang; Hu, Weikang; Xiao, Longqiang; Cao, Zheng; Li, Xiaoqiong; Zhang, Chao; Liao, Liqiong; Liu, Lijian

    2015-01-01

    Hyaluronic acid (HA) is made up of repeating disaccharide units (β-1,4-d-glucuronic acid and β-1,3-N-acetyl-d-glucosamine) and is a major constituent of the extracellular matrix. HA and its derivatives which possess excellent biocompatibility and physiochemical properties have been studied in drug delivery and tissue engineering applications. Tyramine-based HA hydrogel with good compatibility to cell and tissue has been reported recently. However, inferior mechanical property may limit the biomedical application of the HA hydrogel. In this study, HA/graphene oxide (GO) nanocomposite (NC) hydrogel was prepared through a horseradish peroxidase catalyzed in situ cross-linking process. As compared with pure HA hydrogels, incorporation of GO to the HA matrix could significantly enhance the mechanical properties (storage moduli 1800 Pa) of the hydrogel and prolong the release of rhodamine B (RB) as the model drug from the hydrogel (33 h) as well. In addition, due to the multiple interactions between GO and RB, the NC hydrogels showed excellent pH-responsive release behavior. The release of RB from the NC hydrogel was prolonged at low pH (pH 4.0) in the presence of GO, which could be attributed to the enhanced interactions between GO and HA as well as with RB. In situ three-dimensional encapsulation of mouse embryonic fibroblasts (BALB 3T3 cells) in the NC hydrogels and cytotoxicity results indicated the cytocompatibility of both the enzymatic cross-linking process and HA/GO NC hydrogels (cell viability 90.6 ± 4.25%). The enzymatically catalyzed fabrication of NC hydrogels proved to be an easy and mild approach, and had great potential in the construction of both tissue engineering scaffolds and stimuli-responsive drug release matrices.

  10. Oxidation resistant peroxide cross-linked UHMWPE produced by blending and surface diffusion

    NASA Astrophysics Data System (ADS)

    Gul, Rizwan M.; Oral, Ebru; Muratoglu, Orhun K.

    2014-06-01

    Ultra-high molecular weight polyethylene (UHMWPE) has been widely used as acetabular cup in total hip replacement (THR) and tibial component in total knee replacement (TKR). Crosslinking of UHMWPE has been successful used to improve its wear performance leading to longer life of orthopedic implants. Crosslinking can be performed by radiation or organic peroxides. Peroxide crosslinking is a convenient process as it does not require specialized equipment and the level of crosslinking can be manipulated by changing the amount of peroxide added. However, there is concern about the long-term stability of these materials due to possible presence of by-products. Vitamin E has been successfully used to promote long-term oxidative stability of UHMWPE. In this study, UHMWPE has been crosslinked using organic peroxide in the presence of Vitamin E to produce an oxidation resistant peroxide crosslinked material. Crosslinking was performed both in bulk by mixing peroxide and resin, and only on the surface using diffusion of peroxides.The results show that UHMWPE can be crosslinked using organic peroxides in the presence of vitamin E by both methods. However, the level of crosslinking decreases with the increase in vitamin E content. The wear resistance increases with the increase in crosslink density, and oxidation resistance significantly increases due to the presence of vitamin E.

  11. Borate cross-linked graphene oxide-chitosan as robust and high gas barrier films

    NASA Astrophysics Data System (ADS)

    Yan, Ning; Capezzuto, Filomena; Lavorgna, Marino; Buonocore, Giovanna G.; Tescione, Fabiana; Xia, Hesheng; Ambrosio, Luigi

    2016-05-01

    Chitosan (CS) is one of the most promising polymers due to its biocompatibility, biodegradability, and natural abundance. However, its poor mechanical and barrier properties make it difficult to satisfy a wide range of applications. Herein, borate ions, originating from the hydrolysis of sodium tetraborate decahydrate (borax), have been used to crosslink chitosan and graphene oxide (GO) nanocomposites. Chitosan films consisting of 1.0 wt% boron and 1.0 wt% GO exhibit a significant improvement in both the toughness and oxygen barrier properties compared to pristine chitosan. In particular the tensile strength of the samples after thermal treatment increases by ~160% compared to pristine chitosan, whereas their oxygen permeability reduces by ~90%. This is ascribed to the chemical crosslinking between chitosan and GO nanoplatelets through borate ions, as well as the formation of a layered morphology with graphene nanoplatelets oriented parallel to the sample surface. The exceptional robust and high gas barrier film has promising application in the packaging industry. The borate-crosslinking chemistry represents the potential strategy for improving properties of other polymer nanocomposites.Chitosan (CS) is one of the most promising polymers due to its biocompatibility, biodegradability, and natural abundance. However, its poor mechanical and barrier properties make it difficult to satisfy a wide range of applications. Herein, borate ions, originating from the hydrolysis of sodium tetraborate decahydrate (borax), have been used to crosslink chitosan and graphene oxide (GO) nanocomposites. Chitosan films consisting of 1.0 wt% boron and 1.0 wt% GO exhibit a significant improvement in both the toughness and oxygen barrier properties compared to pristine chitosan. In particular the tensile strength of the samples after thermal treatment increases by ~160% compared to pristine chitosan, whereas their oxygen permeability reduces by ~90%. This is ascribed to the chemical

  12. Reverse osmosis desalination of chitosan cross-linked graphene oxide/titania hybrid lamellar membranes

    NASA Astrophysics Data System (ADS)

    Deng, Hui; Sun, Penzhan; Zhang, Yingjiu; Zhu, Hongwei

    2016-07-01

    With excellent mass transport properties, graphene oxide (GO)-based lamellar membranes are believed to have great potential in water desalination. In order to quantify whether GO-based membranes are indeed suitable for reverse osmosis (RO) desalination, three sub-micrometer thick GO-based lamellar membranes: GO-only, reduced GO (RGO)/titania (TO) nanosheets and RGO/TO/chitosan (CTS) are prepared, and their RO desalination performances are evaluated in a home-made RO test apparatus. The photoreduction of GO by TO improves the salt rejection, which increases slowly with the membrane thickness. The RGO/TO/CTS hybrid membranes exhibit higher rejection rates of only about 30% (greater than threefold improvement compared with a GO-only membrane) which is still inferior compared to other commercial RO membranes. The low rejection rates mainly arise from the pressure-induced weakening of the ion-GO interlayer interactions. Despite the advantages of simple, low-cost preparation, high permeability and selectivity of GO-based lamellar membranes, as the current desalination performances are not high enough to afford practical application, there still remains a great challenge to realize high performance separation membranes for water desalination applications.

  13. Reverse osmosis desalination of chitosan cross-linked graphene oxide/titania hybrid lamellar membranes.

    PubMed

    Deng, Hui; Sun, Penzhan; Zhang, Yingjiu; Zhu, Hongwei

    2016-07-08

    With excellent mass transport properties, graphene oxide (GO)-based lamellar membranes are believed to have great potential in water desalination. In order to quantify whether GO-based membranes are indeed suitable for reverse osmosis (RO) desalination, three sub-micrometer thick GO-based lamellar membranes: GO-only, reduced GO (RGO)/titania (TO) nanosheets and RGO/TO/chitosan (CTS) are prepared, and their RO desalination performances are evaluated in a home-made RO test apparatus. The photoreduction of GO by TO improves the salt rejection, which increases slowly with the membrane thickness. The RGO/TO/CTS hybrid membranes exhibit higher rejection rates of only about 30% (greater than threefold improvement compared with a GO-only membrane) which is still inferior compared to other commercial RO membranes. The low rejection rates mainly arise from the pressure-induced weakening of the ion-GO interlayer interactions. Despite the advantages of simple, low-cost preparation, high permeability and selectivity of GO-based lamellar membranes, as the current desalination performances are not high enough to afford practical application, there still remains a great challenge to realize high performance separation membranes for water desalination applications.

  14. pH-dependent cross-linking of catechols through oxidation via Fe(3+) and potential implications for mussel adhesion.

    PubMed

    Fullenkamp, Dominic E; Barrett, Devin G; Miller, Dusty R; Kurutz, Josh W; Messersmith, Phillip B

    2014-01-01

    The mussel byssus is a remarkable attachment structure that is formed by injection molding and rapid in-situ hardening of concentrated solutions of proteins enriched in the catecholic amino acid 3,4-dihydroxy-L-phenylalanine (DOPA). Fe(3+), found in high concentrations in the byssus, has been speculated to participate in redox reactions with DOPA that lead to protein polymerization, however direct evidence to support this hypothesis has been lacking. Using small molecule catechols, DOPA-containing peptides, and native mussel foot proteins, we report the first direct observation of catechol oxidation and polymerization accompanied by reduction of Fe(3+) to Fe(2+). In the case of the small molecule catechol, we identified two dominant dimer species and characterized their connectivities by nuclear magnetic resonance (NMR), with the C6-C6 and C5-C6 linked species as the major and minor products, respectively. For the DOPA-containing peptide, we studied the pH dependence of the reaction and demonstrated that catechol polymerization occurs readily at low pH, but is increasingly diminished in favor of metal-catechol coordination interactions at higher pH. Finally, we demonstrate that Fe(3+) can induce cross-links in native byssal mussel proteins mefp-1 and mcfp-1 at acidic pH. Based on these findings, we discuss the potential implications to the chemistry of mussel adhesion.

  15. Cross-linked gelatin/nanoparticles composite coating on micro-arc oxidation film for corrosion and drug release

    NASA Astrophysics Data System (ADS)

    Xu, Xinhua; Lu, Ping; Guo, Meiqing; Fang, Mingzhong

    2010-02-01

    A composite coating which could control drug release and biocorrosion of magnesium alloy stent materials WE42 was prepared. This composite coating was fabricated on the surface of the micro-arc oxidation (MAO) film of the magnesium alloy, WE42, by mixing different degrees of cross-linked gelatin with well-dispersed poly( DL-lactide-co-glycolide) (PLGA) nanoparticles. The PLGA nanoparticles were prepared by emulsion solvent evaporation/extraction technique. Nano ZS laser diffraction particle size analyzer detected that the size of the nanoparticles to be 150-300 nm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) was used to analyze the morphology of the nanoparticles and the composite coating. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior of the composite coating. Drug release was determined by ultraviolet-visible (UV-vis) spectrophotometer. The corrosion resistance of the composite coating was improved by preventing the corrosive ions from diffusing to the MAO films. The drug release rate of paclitaxel (PTX) exhibited a nearly linear sustained-release profile with no significant burst releases.

  16. Iron Oxides

    SciTech Connect

    Qafoku, Nikolla; Amonette, James E.

    2016-09-19

    Abstract: Fe oxides are common clay-sized oxide, oxyhydroxide and hydroxide soil minerals. They are compounds of Fe, O, and H that have structures based on close-packed arrays of O. The octahedral and tetrahedral cavities within these arrays are filled with either Fe3+ or Fe2+ to form Fe(O/OH)6, FeO6, or FeO4 structural units. All of the naturally occurring Fe oxide minerals usually undergo some degree of isomorphous substitution of other metal ions for Fe in their structures. Relatively simple techniques may be used to identify Fe oxides in the field based on their typical colors and magnetic properties. In the laboratory, a variety of instrumental techniques can be used to confirm phase identity and to quantify amount. Of these, X-ray diffraction, infrared spectroscopy, electron microscopy, thermal analysis, and Mössbauer spectroscopy are the most commonly used techniques. As oxides, the functional groups on their surfaces may have positive, negative, or no charge depending on pH and on the concentration and nature of other ions in the contact solution. A net positive surface charge usually is observed in soils because Fe oxides have a point-of-zero-charge in the neutral or slightly basic pHs. The functional groups on the surface form complexes with cations and anions from the aqueous phase. Their sorption and electron-buffering properties significantly affect the geochemical cycles of almost all elements having agronomic or environmental significance.

  17. Ionic liquids in a poly ethylene oxide cross-linked gel polymer as an electrolyte for electrical double layer capacitor

    NASA Astrophysics Data System (ADS)

    Chaudoy, V.; Tran Van, F.; Deschamps, M.; Ghamouss, F.

    2017-02-01

    In the present work, we developed a gel polymer electrolyte via the incorporation of a room temperature ionic liquid into a cross-linked polymer matrix. The cross-linked gel electrolyte was prepared using a free radical polymerization of methacrylate and dimethacrylate oligomers dissolved in 1-propyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide. Combining the advantages of the ionic liquids and of conventional polymers, the cross-linked gel polymer electrolyte was used both as a separator and as an electrolyte for a leakage-free and non-flammable EDLC supercapacitor. The quasi-all solid-state supercapacitors showed rather good capacitance, power and energy densities by comparison to a liquid electrolyte-based EDLC.

  18. Theoretical Study of Oxidation of Guanine by Singlet Oxygen (¹Δg) and Formation of Guanine:Lysine Cross-Links.

    PubMed

    Thapa, Bishnu; Munk, Barbara H; Burrows, Cynthia J; Schlegel, H Bernhard

    2017-03-01

    Oxidation of guanine in the presence of lysine can lead to guanine-lysine cross-links. The ratio of the C-4, C-5 and C-8 crosslinks depends on the manner of oxidation. Type II photosensitizers such as Rose Bengal and methylene blue can generate singlet oxygen, which leads to a different ratio of products than oxidation by type I photosensitizers or by one electron oxidants. Modeling reactions of singlet oxygen can be quite challenging. Reactions have been explored using CASSCF, NEVPT2, DFT, CCSD(T), BD(T) calculations with SMD implicit solvation. The spin contaminations in open-shell calculations were corrected by Yamaguchi's approximate spin projection method. The addition of singlet oxygen to guanine to form guanine endoperoxide proceeds step-wise via a zwitterionic peroxyl intermediate. The subsequent barrier for ring closure is smaller than the initial barrier for singlet oxygen addition. Ring opening of the endoperoxide by protonation at C4-O is followed by loss of a proton from C-8 and dehydration to produce 8-oxoGox. The addition of lysine (modelled by methylamine) or water across the C5-N7 double bond of 8-oxoGox is followed by acyl migration to form the final spiro products. The barrier for methylamine addition is significantly lower than for water addition and should be the dominant reaction channel. These results are in good agreement with the experimental results for the formation of guanine-lysine cross-links via oxidation by type II photosensitizers.

  19. Tryptophan hydroxylase 2 aggregates through disulfide cross-linking upon oxidation: Possible link to serotonin deficits and non-motor symptoms in Parkinson's disease

    PubMed Central

    Kuhn, Donald M.; Sykes, Catherine E.; Geddes, Timothy J.; Jaunarajs, Karen L. Eskow; Bishop, Christopher

    2010-01-01

    Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopamine neurons of the nigrostriatal system, resulting in severe motor disturbances. Although much less appreciated, non-motor symptoms are also very common in PD and many can be traced to serotonin neuronal deficits. Tryptophan hydroxylase 2 (TPH2), the rate-limiting enzyme in the serotonin biosynthesis, is a phenotypic marker for serotonin neurons and is known to be extremely labile to oxidation. Therefore, the oxidative processes that prevail in PD could cause TPH2 misfolding and modify 5HT neuronal function much as is seen in dopamine neurons. Oxidation of TPH2 inhibits enzyme activity and leads to the formation of high molecular weight aggregates in a dithiothreitol-reversible manner. Cysteine-scanning mutagenesis shows that as long as a single cysteine residue (out of a total of 13 per monomer) remains in TPH2, it cross-links upon oxidation and only cysteine-less mutants are resistant to this effect. The effects of oxidants on TPH2 catalytic function and cross-linking are also observed in intact TPH2-expressing HEK293 cells. Oxidation shifts TPH2 from the soluble compartment into membrane fractions and large inclusion bodies. Sequential non-reducing/reducing two-dimensional SDS-PAGE and immunoblotting confirmed that TPH2 was one of a small number of cytosolic proteins that form disulfide-bonded aggregates. The propensity of TPH2 to misfold upon oxidation of its cysteine residues is responsible for its catalytic lability and may be related to loss of serotonin neuronal function in PD and the emergence of non-motor (psychiatric) symptoms. PMID:21105877

  20. Oxidation in ultrahigh molecular weight polyethylene and cross-linked polyethylene acetabular cups tested against roughened femoral heads in a hip joint simulator.

    PubMed

    Taddei, Paola; Affatato, Saverio; Fagnano, Concezio; Toni, Aldo

    2006-06-01

    This study was aimed at comparing the oxidative degradation of commercial acetabular cups made of cross-linked polyethylene (XLPE) and conventional ultrahigh molecular weight polyethylene (UHMWPE). After testing against deliberately scratched CoCrMo femoral heads in a hip joint simulator, the cups, microtomed parallel to the articulating surface, were analyzed by IR spectroscopy. Due to the potential for artifacts caused by absorbed contaminants, the IR spectra were compared only after hexane extraction; actually, XLPE was found to absorb more serum than UHMWPE. The two sets of unworn acetabular cups showed different oxidation patterns with consequently different distributions of carbonyl species; unworn XLPE was characterized by lower contents of carbonyl species and hydrogen-bonded alcohols and higher contents of trans-vinylene species than unworn UHMWPE. Upon simulator testing, UHMWPE showed more significant changes in oxidation indexes and distribution of carbonyl compounds than XLPE, confirming a better wear behavior for XLPE under the adopted testing conditions.

  1. Oxidatively Generated Guanine(C8)-Thymine(N3) Intrastrand Cross-links in Double-stranded DNA Are Repaired by Base Excision Repair Pathways.

    PubMed

    Talhaoui, Ibtissam; Shafirovich, Vladimir; Liu, Zhi; Saint-Pierre, Christine; Akishev, Zhiger; Matkarimov, Bakhyt T; Gasparutto, Didier; Geacintov, Nicholas E; Saparbaev, Murat

    2015-06-05

    Oxidatively generated guanine radical cations in DNA can undergo various nucleophilic reactions including the formation of C8-guanine cross-links with adjacent or nearby N3-thymines in DNA in the presence of O2. The G*[C8-N3]T* lesions have been identified in the DNA of human cells exposed to oxidative stress, and are most likely genotoxic if not removed by cellular defense mechanisms. It has been shown that the G*[C8-N3]T* lesions are substrates of nucleotide excision repair in human cell extracts. Cleavage at the sites of the lesions was also observed but not further investigated (Ding et al. (2012) Nucleic Acids Res. 40, 2506-2517). Using a panel of eukaryotic and prokaryotic bifunctional DNA glycosylases/lyases (NEIL1, Nei, Fpg, Nth, and NTH1) and apurinic/apyrimidinic (AP) endonucleases (Apn1, APE1, and Nfo), the analysis of cleavage fragments by PAGE and MALDI-TOF/MS show that the G*[C8-N3]T* lesions in 17-mer duplexes are incised on either side of G*, that none of the recovered cleavage fragments contain G*, and that T* is converted to a normal T in the 3'-fragment cleavage products. The abilities of the DNA glycosylases to incise the DNA strand adjacent to G*, while this base is initially cross-linked with T*, is a surprising observation and an indication of the versatility of these base excision repair proteins.

  2. The human oxidative DNA glycosylase NEIL1 excises psoralen-induced interstrand DNA cross-links in a three-stranded DNA structure.

    PubMed

    Couvé, Sophie; Macé-Aimé, Gaëtane; Rosselli, Filippo; Saparbaev, Murat K

    2009-05-01

    Previously, we have demonstrated that human oxidative DNA glycosylase NEIL1 excises photoactivated psoralen-induced monoadducts but not genuine interstrand cross-links (ICLs) in duplex DNA. It has been postulated that the repair of ICLs in mammalian cells is mainly linked to DNA replication and proceeds via dual incisions in one DNA strand that bracket the cross-linked site. This process, known as "unhooking," enables strand separation and translesion DNA synthesis through the gap, yielding a three-stranded DNA repair intermediate composed of a short unhooked oligomer covalently bound to the duplex. At present, the detailed molecular mechanism of ICL repair in mammalian cells remains unclear. Here, we constructed and characterized three-stranded DNA structures containing a single ICL as substrates for the base excision repair proteins. We show that NEIL1 excises with high efficiency the unhooked ICL fragment within a three-stranded DNA structure. Complete reconstitution of the repair of unhooked ICL shows that it can be processed in a short patch base excision repair pathway. The new substrate specificity of NEIL1 points to a preferential involvement in the replication-associated repair of ICLs. Based on these data, we propose a model for the mechanism of ICL repair in mammalian cells that implicates the DNA glycosylase activity of NEIL1 downstream of Xeroderma Pigmentosum group F/Excision Repair Cross-Complementing 1 endonuclease complex (XPF/ERCC1) and translesion DNA synthesis repair steps. Finally, our data demonstrate that Nei-like proteins from Escherichia coli to human cells can excise bulky unhooked psoralen-induced ICLs via hydrolysis of glycosidic bond between cross-linked base and deoxyribose sugar, thus providing an alternative heuristic solution for the removal of complex DNA lesions.

  3. Chemical modification of wheat protein-based natural polymers: grafting and cross-linking reactions with poly(ethylene oxide) diglycidyl ether and ethyl diamine.

    PubMed

    Kurniawan, Lusiana; Qiao, Greg G; Zhang, Xiaoqing

    2007-09-01

    Mobile poly(ethylene oxide) diglycidyl ether (PEODGE) segments were chemically grafted onto a soluble wheat protein (WP), and different network structures were formed via coupling reactions with ethyl diamine (EDA) in different PEODGE/EDA (PE) ratios. When the PE ratio was 1:1, linear PEs were the predominant segments grafted onto WP chains and the whole WP-PEODGE-EDA (WPE) system was still soluble with an increased molecular weight. Reducing the amount of EDA in the systems produced insoluble cross-linked WPE networks. The broad distribution of network structures and chain mobility resulted in a broad glass transition for the WPE materials. However, the glass transition started at lower temperatures, and the materials became flexible at room temperature. The PE segments were present in all rigid, intermediate, and mobile phases in WPE networks, while the proportion of mobile WP chains was increased as a result of the plasticization effect from the mobile PE segments. The mobility of the most mobile component lipid was also restricted to some extent when forming the cross-linked WPE networks. The study demonstrated that the formation of different network structures with PE segments could significantly improve the flexibility of WP materials, vary the solubility, and modify the mechanical performance of WP-based natural polymer materials.

  4. Intrastrand G-U cross-links generated by the oxidation of guanine in 5'-d(GCU) and 5'-r(GCU).

    PubMed

    Crean, Conor; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-10-15

    It has been suggested that carbonate radical anions are biologically important because they may be produced during the inflammatory response. The carbonate radicals can selectively oxidize guanine in DNA and RNA by one-electron transfer mechanisms and the guanine radicals thus formed decay by diverse competing pathways with other free radicals or nucleophiles. Using a photochemical method to generate CO(3)(-) radicals in vitro, we compare the distributions of products initiated by the one-electron oxidation of guanine in the trinucleotides 5'-r(GpCpU) and 5'-d(GpCpU) in aqueous buffer solutions (pH 7.5). Similar distributions of stable end products identified by LC-MS/MS methods were found in both cases. The guanine oxidation products include the diastereomeric pair of spiroiminodihydantoin (Sp) and 2,5-diamino-4H-imidazolone (Iz). In addition, intrastrand cross-linked products involving covalent bonds between the G and the U bases (GCU) were also found, although with different relative yields in the 2'-deoxy- and the ribotrinucleotides. The positive-ion MS/MS spectra of the 5'-r(GpCpU) and 5'-d(GpCpU) products clearly indicate the presence of covalently linked G-U products that have a mass smaller by 2 Da than the sum of the G and U bases in both types of trinucleotides. The 5'-d(GCU) cross-linked product was further characterized by 1D and 2D NMR methods that confirm its cyclic structure in which the guanine C8 atom is covalently linked to the uracil N3 atom.

  5. Enhanced Phosphate Removal by Nanosized Hydrated La(III) Oxide Confined in Cross-linked Polystyrene Networks.

    PubMed

    Zhang, Yanyang; Pan, Bingcai; Shan, Chao; Gao, Xiang

    2016-02-02

    A new nanocomposite adsorbent La-201 of extremely high capacity and specific affinity toward phosphate was fabricated and well characterized, where hydrated La(III) oxide (HLO) nanoclusters were immobilized inside the networking pores of the polystyrene anion exchanger D-201. La-201 exhibited enhanced phosphate adsorption in the presence of competing anions (chloride, sulfate, nitrate, bicarbonate, and silicate) at greater levels (up to molar ratio of 20), with working capacity 2-4 times higher than a commercial Fe(III) oxide-based nanocomposite HFO-201 in batch runs. Column adsorption runs by using La-201 could effectively treat ∼6500 bed volumes (BV) of a synthetic feeding solution before breakthrough occurred (from 2.5 mg P/L in influent to <0.5 mg P/L in effluent), approximately 11 times higher magnitude than that of HFO-201. The exhausted La-201 could be regenerated with NaOH-NaCl binary solution at 60 °C for repeated use without any significant capacity loss. The underlying mechanism for the specific sorption of phosphate by La-201 was revealed with the aid of STEM-EDS, XPS, XRD, and SSNMR analysis, and the formation of LaPO4·xH2O is verified to be the dominant pathway for selective phosphate adsorption by the immobilized nano-HLO. The results indicated that La-201 was very promising in highly efficient removal of phosphate from contaminated waters.

  6. Borate cross-linking chitosan/graphene oxide films: Toward the simultaneous enhancement of gases barrier and mechanical properties

    NASA Astrophysics Data System (ADS)

    Yan, Ning; Capezzuto, Filomena; Buonocore, Giovanna G.; Tescione, Fabiana; Lavorgna, Marino; Xia, Hesheng; Ambrosio, Luigi

    2015-12-01

    Borate adducts, originated from hydrolysis of sodium tetraborate decahydrate (borax), have been used to crosslink chitosan (CS) and graphene oxide (GO) nanosheets for the production of innovative composite sustainable materials. CS/GO film consisting of 10wt% borax and 1wt% GO exhibits a significant improvement of both toughness and oxygen barrier properties in comparison to pristine chitosan. In particular the tensile strength increases by about 100% and 150% after thermal annealing of samples at 90°C for 50min whereas the oxygen permeability reduces of about 90% compared to pristine chitosan. The enhancement of both mechanical and barrier properties is ascribed to the formation of a resistant network due to the chemical crosslinking, including borate orthoester bonds and hydroxyl moieties complexes, formed among borate ions, chitosan, and GO nanoplatelets. The crosslinked graphene-based chitosan material with its enhanced mechanical and barrier properties may significantly broad the range of applications of chitosan based-materials which presently are very limited and addressed only to packaging.

  7. Iron oxide surfaces

    NASA Astrophysics Data System (ADS)

    Parkinson, Gareth S.

    2016-03-01

    The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe3O4), maghemite (γ-Fe2O3), haematite (α-Fe2O3), and wüstite (Fe1-xO) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. Fe diffuses in and out from the bulk in response to the O2 chemical potential, forming sometimes complex intermediate phases at the surface. For example, α-Fe2O3 adopts Fe3O4-like surfaces in reducing conditions, and Fe3O4 adopts Fe1-xO-like structures in further reducing conditions still. It is argued that known bulk defect structures are an excellent starting point in building models for iron oxide surfaces. The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe3O4 is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment. It is also an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed. The best understood iron oxide surface at present is probably Fe3O4(100); the structure is

  8. Enhanced Lithium Ion Transport in Poly(ethylene glycol) Diacrylate-Supported Solvate Ionogel Electrolytes via Chemically Cross-linked Ethylene Oxide Pathways.

    PubMed

    D'Angelo, Anthony J; Panzer, Matthew J

    2017-02-02

    Lithium-ion solvate ionic liquids (SILs), consisting of complexed Li(+) cations and a weakly basic anion, represent an emergent class of nonvolatile liquid electrolytes suitable for lithium-based electrochemical energy storage. In this report, solid-state, flexible solvate ionogel electrolytes are synthesized via UV-initiated free radical polymerization/cross-linking of poly(ethylene glycol) diacrylate (PEGDA) in situ within the [Li(G4)][TFSI] electrolyte, which is formed by an equimolar mixture of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and tetraglyme (G4). Ion diffusivity measurements reveal enhanced Li(+) diffusion in PEGDA-supported solvate ionogels, as compared to poly(methyl methacrylate)-supported gels that lack ethylene oxide chains. At 21 vol% PEGDA, a maximum Li(+) transport number of 0.58 and a room temperature ionic conductivity of 0.43 mS/cm have been achieved in a solvate ionogel electrolyte that exhibits an elastic modulus of 0.47 MPa. These results demonstrate the importance of polymer scaffold selection on solvate ionogel electrolyte performance for advanced lithium-based batteries.

  9. Iron oxide nanoparticle synthesis in aqueous and membrane systems for oxidative degradation of trichloroethylene from water

    NASA Astrophysics Data System (ADS)

    Gui, Minghui; Smuleac, Vasile; Ormsbee, Lindell E.; Sedlak, David L.; Bhattacharyya, Dibakar

    2012-05-01

    The potential for using hydroxyl radical (OH•) reactions catalyzed by iron oxide nanoparticles (NPs) to remediate toxic organic compounds was investigated. Iron oxide NPs were synthesized by controlled oxidation of iron NPs prior to their use for contaminant oxidation (by H2O2 addition) at near-neutral pH values. Cross-linked polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) microfiltration membranes were prepared by in situ polymerization of acrylic acid inside the membrane pores. Iron and iron oxide NPs (80-100 nm) were directly synthesized in the polymer matrix of PAA/PVDF membranes, which prevented the agglomeration of particles and controlled the particle size. The conversion of iron to iron oxide in aqueous solution with air oxidation was studied based on X-ray diffraction, Mössbauer spectroscopy and BET surface area test methods. Trichloroethylene (TCE) was selected as the model contaminant because of its environmental importance. Degradations of TCE and H2O2 by NP surface generated OH• were investigated. Depending on the ratio of iron and H2O2, TCE conversions as high as 100 % (with about 91 % dechlorination) were obtained. TCE dechlorination was also achieved in real groundwater samples with the reactive membranes.

  10. Corneal Collagen Cross-Linking

    PubMed Central

    Jankov II, Mirko R.; Jovanovic, Vesna; Nikolic, Ljubisa; Lake, Jonathan C.; Kymionis, Georgos; Coskunseven, Efekan

    2010-01-01

    Corneal collagen cross-linking (CXL) with riboflavin and ultraviolet-A (UVA) is a new technique of corneal tissue strengthening by using riboflavin as a photosensitizer and UVA to increase the formation of intra and interfibrillar covalent bonds by photosensitized oxidation. Keratocyte apoptosis in the anterior segment of the corneal stroma all the way down to a depth of about 300 microns has been described and a demarcation line between the treated and untreated cornea has been clearly shown. It is important to ensure that the cytotoxic threshold for the endothelium has not been exceeded by strictly respecting the minimal corneal thickness. Confocal microscopy studies show that repopulation of keratocytes is already visible 1 month after the treatment, reaching its pre-operative quantity and quality in terms of functional morphology within 6 months after the treatment. The major indication for the use of CXL is to inhibit the progression of corneal ectasias, such as keratoconus and pellucid marginal degeneration. CXL may also be effective in the treatment and prophylaxis of iatrogenic keratectasia, resulting from excessively aggressive photoablation. This treatment has also been used to treat infectious corneal ulcers with apparent favorable results. Combination with other treatments, such as intracorneal ring segment implantation, limited topography-guided photoablation and conductive keratoplasty have been used with different levels of success. PMID:20543933

  11. Fabrication of patterned calcium cross-linked alginate hydrogel films and coatings through reductive cation exchange.

    PubMed

    Bruchet, Marion; Melman, Artem

    2015-10-20

    Calcium cross-linked alginate hydrogels are widely used in targeted drug delivery, tissue engineering, wound treatment, and other biomedical applications. We developed a method for preparing homogeneous alginate hydrogels cross-linked with Ca(2+) cations using reductive cation exchange in homogeneous iron(III) cross-linked alginate hydrogels. Treatment of iron(III) cross-linked alginate hydrogels with calcium salts and sodium ascorbate results in reduction of iron(III) cations to iron(II) that are instantaneously replaced with Ca(2+) cations, producing homogeneous ionically cross-linking hydrogels. Alternatively, the cation exchange can be performed by photochemical reduction in the presence of calcium chloride using a sacrificial photoreductant. This approach allows fabrication of patterned calcium alginate hydrogels through photochemical patterning of iron(III) cross-linked alginate hydrogel followed by the photochemical reductive exchange of iron cations to calcium.

  12. 21 CFR 186.1374 - Iron oxides.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Iron oxides. 186.1374 Section 186.1374 Food and... Substances Affirmed as GRAS § 186.1374 Iron oxides. (a) Iron oxides (oxides of iron, CAS Reg. No. 1332-37-2) are undefined mixtures of iron (II) oxide (CAS Reg. No. 1345-25-1, black cubic crystals) and iron...

  13. 21 CFR 73.2250 - Iron oxides.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Iron oxides. 73.2250 Section 73.2250 Food and... ADDITIVES EXEMPT FROM CERTIFICATION Cosmetics § 73.2250 Iron oxides. (a) Identity. The color additives iron oxides consist of any one or any combination of synthetically prepared iron oxides, including...

  14. Cross-linked polyvinyl alcohol films as alkaline battery separators

    NASA Technical Reports Server (NTRS)

    Sheibley, D. W.; Manzo, M. A.; Gonzalez-Sanabria, O. D.

    1983-01-01

    Cross-linking methods have been investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: (1) PVA-dialdehyde blends post-treated with an acid or acid periodate solution (two-step method) and (2) PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid functionality (one-step method). Laboratory samples of each cross-linked type of film were prepared and evaluated in standard separator screening tests. Then pilot-plant batches of films were prepared and compared to measure differences due to the cross-linking method. The pilot-plant materials were then tested in nickel oxide-zinc cells to compare the two methods with respect to performance characteristics and cycle life. Cell test results are compared with those from tests with Celgard.

  15. Cross-linked polyvinyl alcohol films as alkaline battery separators

    NASA Technical Reports Server (NTRS)

    Sheibley, D. W.; Manzo, M. A.; Gonzalez-Sanabria, O. D.

    1982-01-01

    Cross-linking methods were investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: (1) PVA-dialdehyde blends post-treated with an acid or acid periodate solution (two-step method) and (2) PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid functionality (one-step method). Laboratory samples of each cross-linked type of film were prepared and evaluated in standard separator screening tests. The pilot-plant batches of films were prepared and compared to measure differences due to the cross-linking method. The pilot-plant materials were then tested in nickel oxide - zinc cells to compare the two methods with respect to performance characteristics and cycle life. Cell test results are compared with those from tests with Celgard.

  16. Low temperature cross linking polyimides

    NASA Technical Reports Server (NTRS)

    Serafini, T. T.; Delvigs, P. (Inventor)

    1982-01-01

    A polyimide is formed by cross linking a prepolymer formed by reacting a polyfunctional ester, a polyfunctional amine, and an end-capping unit. By providing an end-capping unit, the prepolymer is curable at a relatively low temperature of about 175 to 245 C.

  17. Water oxidation: High five iron

    NASA Astrophysics Data System (ADS)

    Lloret-Fillol, Julio; Costas, Miquel

    2016-03-01

    The oxidation of water is essential to the sustainable production of fuels using sunlight or electricity, but designing active, stable and earth-abundant catalysts for the reaction is challenging. Now, a complex containing five iron atoms is shown to efficiently oxidize water by mimicking key features of the oxygen-evolving complex in green plants.

  18. Molecular Structures of Isolevuglandin-Protein Cross-Links.

    PubMed

    Bi, Wenzhao; Jang, Geeng-Fu; Zhang, Lei; Crabb, John W; Laird, James; Linetsky, Mikhail; Salomon, Robert G

    2016-10-17

    Isolevuglandins (isoLGs) are stereo and structurally isomeric γ-ketoaldehydes produced through free radical-induced oxidation of arachidonates. Some isoLG isomers are also generated through enzymatic cyclooxygenation. Post-translational modification of proteins by isoLGs is associated with loss-of-function, cross-linking and aggregation. We now report that a low level of modification by one or two molecules of isoLG has a profound effect on the activity of a multi subunit protease, calpain-1. Modification of one or two key lysyl residues apparently suffices to abolish catalytic activity. Covalent modification of calpain-1 led to intersubunit cross-linking. Hetero- and homo-oligomers of the catalytic and regulatory subunits of calpain-1 were detected by SDS-PAGE with Western blotting. N-Acetyl-glycyl-lysine methyl ester and β-amyloid(11-17) peptide EVHHQKL were used as models for characterizing the cross-linking of protein lysyl residues resulting from adduction of iso[4]LGE2. Aminal, bispyrrole, and trispyrrole cross-links of these two peptides were identified and fully characterized by mass spectrometry. Aminal and bispyrrole dimers were both detected. Furthermore, a complex mixture of derivatives of the bispyrrole cross-link containing one or more additional atoms of oxygen was found. Interesting differences are evident in the predominant cross-link type generated in the reaction of iso[4]LGE2 with these peptides. More aminal cross-links versus bispyrrole are formed during the reaction of the dipeptide with iso[4]LGE2. In contrast, more bispyrrole versus aminal cross-links are formed during the reaction of EVHHQKL with iso[4]LGE2. It is tempting to speculate that the EVHHQKL peptide-pyrrole modification forms noncovalent aggregates that favor the production of covalent bispyrrole cross-links because β-amyloid(11-17) tends to spontaneously oligomerize.

  19. Well-Constructed Single-Layer Molybdenum Disulfide Nanorose Cross-Linked by Three Dimensional-Reduced Graphene Oxide Network for Superior Water Splitting and Lithium Storage Property

    PubMed Central

    Zhao, Yanyan; Kuai, Long; Liu, Yanguo; Wang, Pengpeng; Arandiyan, Hamidreza; Cao, Sufeng; Zhang, Jie; Li, Fengyun; Wang, Qing; Geng, Baoyou; Sun, Hongyu

    2015-01-01

    A facile one-step solution reaction route for growth of novel MoS2 nanorose cross-linked by 3D rGO network, in which the MoS2 nanorose is constructed by single-layered or few-layered MoS2 nanosheets, is presented. Due to the 3D assembled hierarchical architecture of the ultrathin MoS2 nanosheets and the interconnection of 3D rGO network, as well as the synergetic effects of MoS2 and rGO, the as-prepared MoS2-NR/rGO nanohybrids delivered high specific capacity, excellent cycling and good rate performance when evaluated as an anode material for lithium-ion batteries. Moreover, the nanohybrids also show excellent hydrogen-evolution catalytic activity and durability in an acidic medium, which is superior to MoS2 nanorose and their nanoparticles counterparts. PMID:25735416

  20. 21 CFR 186.1374 - Iron oxides.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...) are undefined mixtures of iron (II) oxide (CAS Reg. No. 1345-25-1, black cubic crystals) and iron (III) oxide (CAS Reg. No. 1309-37-1, red-brown to black trigonal crystals). (b) In accordance with §...

  1. 21 CFR 186.1374 - Iron oxides.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...) are undefined mixtures of iron (II) oxide (CAS Reg. No. 1345-25-1, black cubic crystals) and iron (III) oxide (CAS Reg. No. 1309-37-1, red-brown to black trigonal crystals). (b) In accordance with §...

  2. 21 CFR 186.1374 - Iron oxides.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...) are undefined mixtures of iron (II) oxide (CAS Reg. No. 1345-25-1, black cubic crystals) and iron (III) oxide (CAS Reg. No. 1309-37-1, red-brown to black trigonal crystals). (b) In accordance with §...

  3. 46 CFR 148.275 - Iron oxide, spent; iron sponge, spent.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Iron oxide, spent; iron sponge, spent. 148.275 Section... § 148.275 Iron oxide, spent; iron sponge, spent. (a) Before spent iron oxide or spent iron sponge is... been cooled and weathered for at least eight weeks. (b) Both spent iron oxide and spent iron sponge...

  4. 46 CFR 148.275 - Iron oxide, spent; iron sponge, spent.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Iron oxide, spent; iron sponge, spent. 148.275 Section... § 148.275 Iron oxide, spent; iron sponge, spent. (a) Before spent iron oxide or spent iron sponge is... been cooled and weathered for at least eight weeks. (b) Both spent iron oxide and spent iron sponge...

  5. 46 CFR 148.275 - Iron oxide, spent; iron sponge, spent.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Iron oxide, spent; iron sponge, spent. 148.275 Section... § 148.275 Iron oxide, spent; iron sponge, spent. (a) Before spent iron oxide or spent iron sponge is... been cooled and weathered for at least eight weeks. (b) Both spent iron oxide and spent iron sponge...

  6. 46 CFR 148.275 - Iron oxide, spent; iron sponge, spent.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Iron oxide, spent; iron sponge, spent. 148.275 Section... § 148.275 Iron oxide, spent; iron sponge, spent. (a) Before spent iron oxide or spent iron sponge is... been cooled and weathered for at least eight weeks. (b) Both spent iron oxide and spent iron sponge...

  7. Electrospinning formaldehyde cross-linked zein solutions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In order to develop zein fibers with improved physical properties and solvent resistance, formaldehyde was used as the cross-linking reagent before spinning. The cross-linking reaction was carried out in either acetic acid or ethanolic-HCl where the amount of cross-linking reagent was between 1 and...

  8. 21 CFR 73.3125 - Iron oxides.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Iron oxides. 73.3125 Section 73.3125 Food and... ADDITIVES EXEMPT FROM CERTIFICATION Medical Devices § 73.3125 Iron oxides. (a) Identity and specifications. The color additive iron oxides (CAS Reg. No. 1332-37-2), Color Index No. 77491, shall conform...

  9. Effects of polymerization on the oxygen carrying and redox properties of diaspirin cross-linked hemoglobin.

    PubMed

    Rogers, M S; Ryan, B B; Cashon, R E; Alayash, A I

    1995-04-27

    Human hemoglobin site specifically cross-linked with bis(3,5-dibromosalicyl)fumarate results in a low oxygen affinity hemoglobin-based red cell substitute (alpha-DBBF). Polymerization of alpha-DBBF by bis(maleoylglycylamide) polyethylene glycol (BMAA-PEG) yields poly alpha-DBBF which offers the added benefits of reduced renal clearance and increased retention in the vascular circulation. Oxygen equilibrium curves for poly alpha-DBBF are slightly left-shifted (higher O2 affinity) compared to those of alpha-DBBF; with a diminished cooperativity and a reduced Bohr effect. In rapid mixing experiments (oxygen dissociation and carbon monoxide binding), poly alpha-DBBF exhibits a several fold increase in the overall rate of deoxygenation and carbon monoxide binding kinetics over its cross-linked counterpart. The rate of nitric oxide binding to the oxidized form of poly alpha-DBBF shows little or no change compared to the intramolecularly cross-linked derivative. The reduction of cyanomet poly alpha-DBBF by dithionite is several fold faster than that of HbA0 and alpha-DBBF whereas the slow subsequent cyanide dissociation from the ferrous iron remained unchanged among all proteins. The propensity of poly alpha-DBBF for auto-oxidation is slightly enhanced over alpha-DBBF whereas the extent of oxidative modification by hydrogen peroxide is very similar. Polymerization appears to selectively modify ligand interactions and redox kinetics of the tetrameric cross-linked form which reflects a possibly more open heme pocket. The data suggests that changes in oxygenation properties of hemoglobin brought about by a given modification are not necessarily predictive of other functional changes.

  10. A copper-hydrogen peroxide redox system induces dityrosine cross-links and chemokine oligomerisation.

    PubMed

    MacGregor, Helen J; Kato, Yoji; Marshall, Lindsay J; Nevell, Thomas G; Shute, Janis K

    2011-12-01

    The activity of the chemoattractant cytokines, the chemokines, in vivo is enhanced by oligomerisation and aggregation on glycosaminoglycan (GAG), particularly heparan sulphate, side chains of proteoglycans. The chemokine RANTES (CCL5) is a T-lymphocyte and monocyte chemoattractant, which has a minimum tetrameric structure for in vivo activity and a propensity to form higher order oligomers. RANTES is unusual among the chemokines in having five tyrosine residues, an amino acid susceptible to oxidative cross-linking. Using fluorescence emission spectroscopy, Western blot analysis and LCMS-MS, we show that a copper/H2O2 redox system induces the formation of covalent dityrosine cross-links and RANTES oligomerisation with the formation of tetramers, as well as higher order oligomers. Amongst the transition metals tested, namely copper, nickel, mercury, iron and zinc, copper appeared unique in this respect. At high (400 μM) concentrations of H2O2, RANTES monomers, dimers and oligomers are destroyed, but heparan sulphate protects the chemokine from oxidative damage, promoting dityrosine cross-links and multimer formation under oxidative conditions. Low levels of dityrosine cross-links were detected in copper/H2O2-treated IL-8 (CXCL8), which has one tyrosine residue, and none were detected in ENA-78 (CXCL5), which has none. Redox-treated RANTES was fully functional in Boyden chamber assays of T-cell migration and receptor usage on activated T-cells following RANTES oligomerisation was not altered. Our results point to a protective, anti-oxidant, role for heparan sulphate and a previously unrecognised role for copper in chemokine oligomerisation that may offer an explanation for the known anti-inflammatory effect of copper-chelators such as penicillamine and tobramycin.

  11. Electrospun cross linked rosin fibers

    NASA Astrophysics Data System (ADS)

    Baek, Woo-il; Nirmala, R.; Barakat, Nasser A. M.; El-Newehy, Mohamed H.; Al-Deyab, Salem S.; Kim, Hak Yong

    2011-12-01

    In this study, we describe the first reported preparation of rosin in fiber form through use of an electrospinning technique utilizing various solvent systems. The polymer concentration of the formed fiber was studied by using various solvents such as chloroform, ethanol, N-N dimethylformamide (DMF), tetrahydrofuran (THF), acetone, and methylene chloride (MC). An electrospray of the solution resulted in the beaded form of the rosin. By varying the polymer concentration with MC, we were then able to obtain uniform fibers. However, the fibers exhibited large diameter. We believe that it is possible to reduce the diameter of the rosin fibers through appropriate selection of electrospinning parameters. In addition, the morphological transitions from beads, to beaded fiber, to fiber were studied at different polymer concentrations. We propose a possible physical cross linking mechanism for the formation of rosin fibers during the electrospinning process. Our results demonstrate the feasibility of producing fiber nanostructures of rosin by using an electrospinning technique.

  12. 21 CFR 73.2250 - Iron oxides.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... ADDITIVES EXEMPT FROM CERTIFICATION Cosmetics § 73.2250 Iron oxides. (a) Identity. The color additives iron... per million. (c) Uses and restrictions. Iron oxides are safe for use in coloring cosmetics generally, including cosmetics applied to the area of the eye, in amounts consistent with good manufacturing...

  13. 21 CFR 73.2250 - Iron oxides.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... ADDITIVES EXEMPT FROM CERTIFICATION Cosmetics § 73.2250 Iron oxides. (a) Identity. The color additives iron... per million. (c) Uses and restrictions. Iron oxides are safe for use in coloring cosmetics generally, including cosmetics applied to the area of the eye, in amounts consistent with good manufacturing...

  14. 21 CFR 73.2250 - Iron oxides.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... ADDITIVES EXEMPT FROM CERTIFICATION Cosmetics § 73.2250 Iron oxides. (a) Identity. The color additives iron... per million. (c) Uses and restrictions. Iron oxides are safe for use in coloring cosmetics generally, including cosmetics applied to the area of the eye, in amounts consistent with good manufacturing...

  15. 21 CFR 73.2250 - Iron oxides.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... ADDITIVES EXEMPT FROM CERTIFICATION Cosmetics § 73.2250 Iron oxides. (a) Identity. The color additives iron... per million. (c) Uses and restrictions. Iron oxides are safe for use in coloring cosmetics generally, including cosmetics applied to the area of the eye, in amounts consistent with good manufacturing...

  16. High-Relaxivity Superparamagnetic Iron Oxide Nanoworms with Decreased Immune Recognition and Long-Circulating Properties

    PubMed Central

    Wang, Guankui; Inturi, Swetha; Serkova, Natalie J.; Merkulov, Sergey; McCrae, Keith; Russek, Stephen E.; Banda, Nirmal K.; Simberg, Dmitri

    2015-01-01

    One of the core issues of nanotechnology involves masking the foreignness of nanomaterials to enable in vivo longevity and long-term immune evasion. Dextran-coated superparamagnetic iron oxide nanoparticles are very effective magnetic resonance imaging (MRI) contrast agents, and strategies to prevent immune recognition are critical for their clinical translation. Here we prepared 20 kDa dextran-coated SPIO nanoworms (NWs) of 250 nm diameter and a high molar transverse relaxivity rate R2 (~400 mM−1 s−1) to study the effect of cross-linking-hydrogelation with 1-chloro-2,3-epoxypropane (epichlorohydrin) on the immune evasion both in vitro and in vivo. Cross-linking was performed in the presence of different concentrations of NaOH (0.5 to 10 N) and different temperatures (23 and 37 °C). Increasing NaOH concentration and temperature significantly decrease the binding of anti-dextran antibody and dextran-binding lectin conconavalin A to the NWs. The decrease in dextran immunoreactivity correlated with the decrease in opsonization by complement component 3 (C3) and with the decrease in the binding of the lectin pathway factor MASP-2 in mouse serum, suggesting that cross-linking blocks the lectin pathway of complement. The decrease in C3 opsonization correlated with the decrease in NW uptake by murine peritoneal macrophages. Optimized NWs demonstrated up to 10 h circulation half-life in mice and minimal uptake by the liver, while maintaining the large 250 nm size in the blood. We demonstrate that immune recognition of large iron oxide nanoparticles can be efficiently blocked by chemical cross-linking-hydrogelation, which is a promising strategy to improve safety and bioinertness of MRI contrast agents. PMID:25419856

  17. Indium Sorption to Iron Oxides

    NASA Astrophysics Data System (ADS)

    White, S. J.; Sacco, S. A.; Hemond, H.; Hussain, F. A.; Runkel, R. L.; Walton-Day, K. E.; Kimball, B. A.; Shine, J. P.

    2014-12-01

    Indium is an increasingly important metal in semiconductors and electronics, and its use is growing rapidly as a semiconductive coating (as indium tin oxide) for liquid crystal displays (LCDs) and flat panel displays. It also has uses in important energy technologies such as light emitting diodes (LEDs) and photovoltaic cells. Despite its rapid increase in use, very little is known about the environmental behavior of indium, and concerns are being raised over the potential health effects of this emerging metal contaminant. One source of indium to the environment is acid mine drainage from the mining of lead, zinc, and copper sulfides. In our previous studies of a stream in Colorado influenced by acid mine drainage from lead and zinc mining activities, indium concentrations were found to be 10,000 times those found in uncontaminated rivers. However, the speciation and mobility of indium could not be reliably modeled because sorption constants to environmental sorbents have not been determined. In this study, we generate sorption constants for indium to ferrihydrite in the laboratory over a range of pHs, sorbent to sorbate ratios, and ionic strengths. Ferrihydrite is one of the most important sorbents in natural systems, and sorption to amorphous iron oxides such as ferrihydrite is thought to be one of the main removal mechanisms of metals from the dissolved phase in aqueous environments. Because of its relatively low solubility, we also find that indium hydroxide precipitation can dominate indium's partitioning at micromolar concentrations of indium. This precipitation may be important in describing indium's behavior in our study stream in Colorado, where modeling sorption to iron-oxides does not explain the complete removal of indium from the dissolved phase when the pH of the system is artificially raised to above 8. This study contributes much-needed data about indium's aqueous behavior, in order to better understand its fate, transport, and impacts in the

  18. Tannin biosynthesis of iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Herrera-Becerra, R.; Rius, J. L.; Zorrilla, C.

    2010-08-01

    In this work, iron oxide nanoparticles synthesized with gallic acid and tannic acid are characterized using High-Resolution Transmission Electron Microscopy (HRTEM). Its size, form, and structure are compared with nanoparticles obtained previously using alfalfa biomass in order to find a simpler, consistent, and environmentally friendly method in the production of iron oxide nanoparticles.

  19. 21 CFR 186.1374 - Iron oxides.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... iron (II) oxide (CAS Reg. No. 1345-25-1, black cubic crystals) and iron (III) oxide (CAS Reg. No. 1309-37-1, red-brown to black trigonal crystals). (b) In accordance with § 186.1(b)(1), the ingredient...

  20. Porous Cross-Linked Polyimide Networks

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B. (Inventor); Guo, Haiquan (Inventor)

    2015-01-01

    Porous cross-linked polyimide networks are provided. The networks comprise an anhydride end-capped polyamic acid oligomer. The oligomer (i) comprises a repeating unit of a dianhydride and a diamine and terminal anhydride groups, (ii) has an average degree of polymerization of 10 to 50, (iii) has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups, and (iv) has been chemically imidized to yield the porous cross-linked polyimide network. Also provided are porous cross-linked polyimide aerogels comprising a cross-linked and imidized anhydride end-capped polyamic acid oligomer, wherein the oligomer comprises a repeating unit of a dianhydride and a diamine, and the aerogel has a density of 0.10 to 0.333 g/cm.sup.3 and a Young's modulus of 1.7 to 102 MPa. Also provided are thin films comprising aerogels, and methods of making porous cross-linked polyimide networks.

  1. The effect of cross-link distributions in axially-ordered, cross-linked networks

    NASA Astrophysics Data System (ADS)

    Bennett, C. Brad; Kruczek, James; Rabson, D. A.; Matthews, W. Garrett; Pandit, Sagar A.

    2013-07-01

    Cross-linking between the constituent chains of biopolymers has a marked effect on their materials’ properties. In certain of these materials, such as fibrillar collagen, increases in cross-linking lead to an increase in the melting temperature. Fibrillar collagen is an axially-ordered network of cross-linked polymer chains exhibiting a broadened denaturation transition, which has been explained in terms of the successive denaturation with temperature of multiple species. We model axially-ordered, cross-linked materials as stiff chains with distinct arrangements of cross-link-forming sites. Simulations suggest that systems composed of chains with identical arrangements of cross-link-forming sites exhibit critical behavior. In contrast, systems composed of non-identical chains undergo a crossover. This model suggests that the arrangement of cross-link-forming sites may contribute to the broadening of the denaturation transition in fibrillar collagen.

  2. Gas-Barrier Hybrid Coatings by the Assembly of Novel Poly(vinyl alcohol) and Reduced Graphene Oxide Layers through Cross-Linking with Zirconium Adducts.

    PubMed

    Yan, Ning; Capezzuto, Filomena; Buonocore, Giovanna G; Lavorgna, Marino; Xia, Hesheng; Ambrosio, Luigi

    2015-10-14

    Gas-barrier materials obtained by coating poly(ethylene terephthalate) (PET) substrates have already been studied in the recent literature. However, because of the benefits of using cheaper, biodegradable, and nonpolar polymers, multilayered hybrid coatings consisting of alternate layers of reduced graphene oxide (rGO) nanosheets and a novel high amorphous vinyl alcohol (HAVOH) with zirconium (Zr) adducts as binders were successfully fabricated through a layer-by-layer (LbL) assembly approach. Atomic force microscopy analysis showed that rGO nanoplatelets were uniformly dispersed over the HAVOH polymer substrate. Scanning and transmission electron microscopies revealed that multilayer (HAVOH/Zr/rGO)n hybrid coatings exhibited a brick-wall structure with HAVOH and rGO as buildings blocks. It has been shown that 40 layers of HAVOH/Zr/rGO ultrathin films deposited on PET substrates lead to a decrease of 1 order of magnitude of oxygen permeability with respect to the pristine PET substrate. This is attributed to the effect of zirconium polymeric adducts, which enhance the assembling efficiency of rGO and compact the layers, as confirmed by NMR characterization, resulting in a significant increment of the oxygen-transport pathways. Because of their high barrier properties and high flexibility, these films are promising candidates in a variety of applications such as packaging, selective gas films, and protection of flexible electronics.

  3. Platinum Attachments on Iron Oxide Nanoparticle Surfaces

    SciTech Connect

    Palchoudhury, Soubantika; Xu, Yaolin; An, Wei; Turner, C. H.; Bao, Yuping

    2010-04-30

    Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.

  4. Highly cross-linked nanoporous polymers

    DOEpatents

    Steckle, Jr., Warren P.; Apen, Paul G.; Mitchell, Michael A.

    1998-01-01

    Condensation polymerization followed by a supercritical extraction step can be used to obtain highly cross-linked nanoporous polymers with high surface area, controlled pore sizes and rigid structural integrity. The invention polymers are useful for applications requiring separation membranes.

  5. Highly cross-linked nanoporous polymers

    DOEpatents

    Steckle, Jr., Warren P.; Apen, Paul G.; Mitchell, Michael A.

    1997-01-01

    Condensation polymerization followed by a supercritical extraction step can be used to obtain highly cross-linked nanoporous polymers with high surface area, controlled pore sizes and rigid structural integrity. The invention polymers are useful for applications requiring separation membranes.

  6. Cross-linked biopolymer bundles: Cross-link reversibility leads to cooperative binding/unbinding phenomena

    NASA Astrophysics Data System (ADS)

    Vink, Richard L. C.; Heussinger, Claus

    2012-01-01

    We consider a biopolymer bundle consisting of filaments that are cross-linked together. The cross-links are reversible: they can dynamically bind and unbind adjacent filament pairs as controlled by a binding enthalpy. The bundle is subjected to a bending deformation and the corresponding distribution of cross-links is measured. For a bundle consisting of two filaments, upon increasing the bending amplitude, a first-order transition is observed. The transition is from a state where the filaments are tightly coupled by many bound cross-links, to a state of nearly independent filaments with only a few bound cross-links. For a bundle consisting of more than two filaments, a series of first-order transitions is observed. The transitions are connected with the formation of an interface between regions of low and high cross-link densities. Combining umbrella sampling Monte Carlo simulations with analytical calculations, we present a detailed picture of how the competition between cross-link shearing and filament stretching drives the transitions. We also find that, when the cross-links become soft, collective behavior is not observed: the cross-links then unbind one after the other leading to a smooth decrease of the average cross-link density.

  7. When Density Functional Approximations Meet Iron Oxides.

    PubMed

    Meng, Yu; Liu, Xing-Wu; Huo, Chun-Fang; Guo, Wen-Ping; Cao, Dong-Bo; Peng, Qing; Dearden, Albert; Gonze, Xavier; Yang, Yong; Wang, Jianguo; Jiao, Haijun; Li, Yongwang; Wen, Xiao-Dong

    2016-10-11

    Three density functional approximations (DFAs), PBE, PBE+U, and Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE), were employed to investigate the geometric, electronic, magnetic, and thermodynamic properties of four iron oxides, namely, α-FeOOH, α-Fe2O3, Fe3O4, and FeO. Comparing our calculated results with available experimental data, we found that HSE (a = 0.15) (containing 15% "screened" Hartree-Fock exchange) can provide reliable values of lattice constants, Fe magnetic moments, band gaps, and formation energies of all four iron oxides, while standard HSE (a = 0.25) seriously overestimates the band gaps and formation energies. For PBE+U, a suitable U value can give quite good results for the electronic properties of each iron oxide, but it is challenging to accurately get other properties of the four iron oxides using the same U value. Subsequently, we calculated the Gibbs free energies of transformation reactions among iron oxides using the HSE (a = 0.15) functional and plotted the equilibrium phase diagrams of the iron oxide system under various conditions, which provide reliable theoretical insight into the phase transformations of iron oxides.

  8. Oxidation of guanine by carbonate radicals derived from photolysis of carbonatotetramminecobalt(III) complexes and the pH dependence of intrastrand DNA cross-links mediated by guanine radical reactions.

    PubMed

    Crean, Conor; Lee, Young Ae; Yun, Byeong Hwa; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-08-11

    The carbonate radical anion CO(3)(*-) is a decomposition product of nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite, an important biological byproduct of the inflammatory response. The selective oxidation of guanine in DNA by CO(3)(*-) radicals is known to yield spiroiminodihydantoin (Sp) and guanidinohydantoin (Gh) products, and also a novel intrastrand cross-linked product: 5'-d(CCATCG*CT*ACC), featuring a linkage between guanine C8 (G*) and thymine N3 (T*) atoms in the oligonucleotide (Crean et al., Nucleic Acids Res. 2008, 36, 742-755). Involvement of the T-N3 (pK(a) of N3-H is 9.67) suggests that the formation of 5'-d(CCATCG*CT*ACC) might be pH-dependent. This hypothesis was tested by generating CO(3)(*-) radicals through the photodissociation of carbonatotetramminecobalt(III) complexes by steady-state UV irradiation, which allowed for studies of product yields in the pH 5.0-10.0 range. The yield of 5'-d(CCATCG*CT*ACC) at pH 10.0 is approximately 45 times greater than at pH 5.0; this is consistent with the proposed mechanism, which requires N3(H) thymine proton dissociation followed by nucleophilic addition to the C8 guanine radical.

  9. Modified gum arabic cross-linked gelatin scaffold for biomedical applications.

    PubMed

    Sarika, P R; Cinthya, Kuriakose; Jayakrishnan, A; Anilkumar, P R; James, Nirmala Rachel

    2014-10-01

    The present work deals with development of modified gum arabic cross-linked gelatin scaffold for cell culture. A new biocompatible scaffold was developed by cross-linking gelatin (Gel) with gum arabic, a polysaccharide. Gum arabic was subjected to periodate oxidation to obtain gum arabic aldehyde (GAA). GAA was reacted with gelatin under appropriate pH to prepare the cross-linked hydrogel. Cross-linking occurred due to Schiff's base reaction between aldehyde groups of oxidized gum arabic and amino groups of gelatin. The scaffold prepared from the hydrogel was characterized by swelling properties, degree of cross-linking, in vitro degradation and scanning electron microscopy (SEM). Cytocompatibility evaluation using L-929 and HepG2 cells confirmed non-cytotoxic and non-adherent nature of the scaffold. These properties are essential for generating multicellular spheroids and hence the scaffold is proposed to be a suitable candidate for spheroid cell culture.

  10. On the formation of iron(III) oxides via oxidation of iron(II)

    SciTech Connect

    Bongiovanni, R.; Pelizzetti, E.; Borgarello, E.; Meisel, D.

    1994-09-01

    Formation of iron oxides in aqueous salt solutions is reviewed. The discussion is focused on the oxidation of iron(II) and the following hydrolysis process that leads to the formation of a solid phase from homogeneous solutions. Results from our own studies on the kinetics of the oxidation reactions and the ensuing growth processes are presented.

  11. DNA interstrand cross-linking by epichlorohydrin.

    PubMed

    Romano, Keith P; Newman, Adam G; Zahran, Rami W; Millard, Julie T

    2007-05-01

    Epichlorohydrin (ECH), an important industrial chemical, is a bifunctional alkylating agent with the potential to form DNA cross-links. Occupational exposure to this suspect carcinogen leads to chromosomal aberrations, and ECH has been shown previously to undergo reaction with DNA in vivo and in vitro. We used denaturing polyacrylamide gel electrophoresis to monitor the possible formation of interstrand cross-links within DNA oligomers by ECH and the related compound, epibromohydrin (EBH). Although both compounds did indeed form cross-links between deoxyguanosine residues, EBH was a more efficient cross-linker than ECH. The optimal pH for cross-linking also varied, with ECH more efficient at pH 5.0 and EBH more efficient at pH 7.0. Both agents were relatively flexible in the sequences targeted, with comparable efficiencies for 5'-GGC and 5'GC sites. Furthermore, interstrand cross-linking by the two optical isomers of ECH correlated with their relative cytotoxicities, with R-ECH about twice as potent as S-ECH.

  12. Cross-linking chemistry of squid beak.

    PubMed

    Miserez, Ali; Rubin, Daniel; Waite, J Herbert

    2010-12-03

    In stark contrast to most aggressive predators, Dosidicus gigas (jumbo squids) do not use minerals in their powerful mouthparts known as beaks. Their beaks instead consist of a highly sclerotized chitinous composite with incremental hydration from the tip to the base. We previously reported l-3,4-dihydroxyphenylalanine (dopa)-histidine (dopa-His) as an important covalent cross-link providing mechanical strengthening to the beak material. Here, we present a more complete characterization of the sclerotization chemistry and describe additional cross-links from D. gigas beak. All cross-links presented in this report share common building blocks, a family of di-, tri-, and tetra-histidine-catecholic adducts, that were separated by affinity chromatography and high performance liquid chromatography (HPLC) and identified by tandem mass spectroscopy and proton nuclear magnetic resonance ((1)H NMR). The data provide additional insights into the unusually high cross-link density found in mature beaks. Furthermore, we propose both a low molecular weight catechol, and peptidyl-dopa, to be sclerotization agents of squid beak. This appears to represent a new strategy for forming hard tissue in animals. The interplay between covalent cross-linking and dehydration on the graded properties of the beaks is discussed.

  13. Water soluble dendronized iron oxide nanoparticles.

    PubMed

    Daou, T J; Pourroy, G; Greneche, J M; Bertin, A; Felder-Flesch, D; Begin-Colin, S

    2009-06-21

    The grafting of pegylated dendrons on 9(2) nm and 39(5) nm iron oxide nanoparticles in water, through a phosphonate group as coupling agent has been successfully achieved and its mechanism investigated, with a view to produce biocompatible magnetic nano-objects for biomedical applications. Grafting has been demonstrated to occur by interaction of negatively charged phosphonate groups with positively charged groups and hydroxyl at the iron oxide surface. The isoelectric point of the suspension of dendronized iron oxide nanoparticles is shifted towards lower pH as the amount of dendron increases. It reaches 4.7 for the higher grafting rate and for both particle size. Thus, the grafting of molecules using a phosphonate group allows stabilizing electrostatically the suspensions at physiological pH, a prerequisite for biomedical applications. Moreover the grafting step has been shown to preserve the magnetic properties of iron oxide nanoparticles due to super-super exchange interactions through the phosphonate group.

  14. In situ cross-linking of stimuli-responsive hemicellulose microgels during spray drying.

    PubMed

    Zhao, Weifeng; Nugroho, Robertus Wahyu N; Odelius, Karin; Edlund, Ulrica; Zhao, Changsheng; Albertsson, Ann-Christine

    2015-02-25

    Chemical cross-linking during spray drying offers the potential for green fabrication of microgels with a rapid stimuli response and good blood compatibility and provides a platform for stimuli-responsive hemicellulose microgels (SRHMGs). The cross-linking reaction occurs rapidly in situ at elevated temperature during spray drying, enabling the production of microgels in a large scale within a few minutes. The SRHMGs with an average size range of ∼ 1-4 μm contain O-acetyl-galactoglucomannan as a matrix and poly(acrylic acid), aniline pentamer (AP), and iron as functional additives, which are responsive to external changes in pH, electrochemical stimuli, magnetic field, or dual-stimuli. The surface morphologies, chemical compositions, charge, pH, and mechanical properties of these smart microgels were evaluated using scanning electron microscopy, IR, zeta potential measurements, pH evaluation, and quantitative nanomechanical mapping, respectively. Different oxidation states were observed when AP was introduced, as confirmed by UV spectroscopy and cyclic voltammetry. Systematic blood compatibility evaluations revealed that the SRHMGs have good blood compatibility. This bottom-up strategy to synthesize SRHMGs enables a new route to the production of smart microgels for biomedical applications.

  15. In Situ Cross-Linking of Stimuli-Responsive Hemicellulose Microgels during Spray Drying

    PubMed Central

    2015-01-01

    Chemical cross-linking during spray drying offers the potential for green fabrication of microgels with a rapid stimuli response and good blood compatibility and provides a platform for stimuli-responsive hemicellulose microgels (SRHMGs). The cross-linking reaction occurs rapidly in situ at elevated temperature during spray drying, enabling the production of microgels in a large scale within a few minutes. The SRHMGs with an average size range of ∼1–4 μm contain O-acetyl-galactoglucomannan as a matrix and poly(acrylic acid), aniline pentamer (AP), and iron as functional additives, which are responsive to external changes in pH, electrochemical stimuli, magnetic field, or dual-stimuli. The surface morphologies, chemical compositions, charge, pH, and mechanical properties of these smart microgels were evaluated using scanning electron microscopy, IR, zeta potential measurements, pH evaluation, and quantitative nanomechanical mapping, respectively. Different oxidation states were observed when AP was introduced, as confirmed by UV spectroscopy and cyclic voltammetry. Systematic blood compatibility evaluations revealed that the SRHMGs have good blood compatibility. This bottom-up strategy to synthesize SRHMGs enables a new route to the production of smart microgels for biomedical applications. PMID:25630464

  16. Probing structural elements in RNA using engineered disulfide cross-links.

    PubMed Central

    Maglott, E J; Glick, G D

    1998-01-01

    Three analogs of unmodified yeast tRNAPhe, each possessing a single disulfide cross-link, have been designed and synthesized. One cross-link is between G1 and C72 in the amino acid acceptor stem, a second cross-link is in the central D region of yeast tRNAPhe between C11 and C25 and the third cross-link bridges U16 and C60 at the D loop/T loop interface. Air oxidation to form the cross-links is quantitative and analysis of the cross-linked products by native and denaturing PAGE, RNase T1 mapping, Pb(II) cleavage, UV cross-linking and thermal denaturation demonstrates that the disulfide bridges do not alter folding of the modified tRNAs relative to the parent sequence. The finding that cross-link formation between thiol-derivatized residues correlates with the position of these groups in the crystal structure of native yeast tRNAPhe and that the modifications do not significantly perturb native structure suggests that this methodology should be applicable to the study of RNA structure, conformational dynamics and folding pathways. PMID:9469841

  17. In vivo protein cross-linking.

    PubMed

    Agou, Fabrice; Ye, Fei; Véron, Michel

    2004-01-01

    In the cell, homo- and heteroassociations of polypeptide chains evolve and take place within subcellular compartments that are crowded with many other cellular macromolecules. In vivo chemical cross-linking of proteins is a powerful method to examine changes in protein oligomerization and protein-protein interactions upon cellular events such as signal transduction. This chapter is intended to provide a guide to the selection of the cell-membrane-permeable cross-linkers, the optimization of in vivo cross-linking conditions, and the identification of specific cross-links in a cellular context where the frequency of random collisions is high. By combining the chemoselectivity of the homo-bifunctional cross-linker and the length of its spacer arm with knowledge on the protein structure, we show that selective cross-links can be introduced specifically on either the dimer or the hexamer form of the same polypeptide in vitro as well as in vivo, using the human type B nucleoside diphosphate kinase as a protein model.

  18. Cross-linked structure of network evolution

    SciTech Connect

    Bassett, Danielle S.; Wymbs, Nicholas F.; Grafton, Scott T.; Porter, Mason A.; Mucha, Peter J.

    2014-03-15

    We study the temporal co-variation of network co-evolution via the cross-link structure of networks, for which we take advantage of the formalism of hypergraphs to map cross-link structures back to network nodes. We investigate two sets of temporal network data in detail. In a network of coupled nonlinear oscillators, hyperedges that consist of network edges with temporally co-varying weights uncover the driving co-evolution patterns of edge weight dynamics both within and between oscillator communities. In the human brain, networks that represent temporal changes in brain activity during learning exhibit early co-evolution that then settles down with practice. Subsequent decreases in hyperedge size are consistent with emergence of an autonomous subgraph whose dynamics no longer depends on other parts of the network. Our results on real and synthetic networks give a poignant demonstration of the ability of cross-link structure to uncover unexpected co-evolution attributes in both real and synthetic dynamical systems. This, in turn, illustrates the utility of analyzing cross-links for investigating the structure of temporal networks.

  19. Highly cross-linked nanoporous polymers

    DOEpatents

    Steckle, W.P. Jr.; Apen, P.G.; Mitchell, M.A.

    1998-01-20

    Condensation polymerization followed by a supercritical extraction step can be used to obtain highly cross-linked nanoporous polymers with high surface area, controlled pore sizes and rigid structural integrity. The invention polymers are useful for applications requiring separation membranes. 1 fig.

  20. The Irony of Iron – Biogenic Iron Oxides as an Iron Source to the Ocean

    PubMed Central

    Emerson, David

    2016-01-01

    Primary productivity in at least a third of the sunlit open ocean is thought to be iron-limited. Primary sources of dissolved iron (dFe) to the ocean are hydrothermal venting, flux from the sediments along continental margins, and airborne dust. This article provides a general review of sources of hydrothermal and sedimentary iron to the ocean, and speculates upon the role that iron-cycling microbes play in controlling iron dynamics from these sources. Special attention is paid to iron-oxidizing bacteria (FeOB) that live by oxidizing iron and producing biogenic iron oxides as waste products. The presence and ubiquity of FeOB both at hydrothermal systems and in sediments is only beginning to be appreciated. The biogenic oxides they produce have unique properties that could contribute significantly to the dynamics of dFe in the ocean. Changes in the physical and chemical characteristics of the ocean due to climate change and ocean acidification will undoubtedly impact the microbial iron cycle. A better understanding of the contemporary role of microbes in the iron cycle will help in predicting how these changes could ultimately influence marine primary productivity. PMID:26779157

  1. The Irony of Iron - Biogenic Iron Oxides as an Iron Source to the Ocean.

    PubMed

    Emerson, David

    2015-01-01

    Primary productivity in at least a third of the sunlit open ocean is thought to be iron-limited. Primary sources of dissolved iron (dFe) to the ocean are hydrothermal venting, flux from the sediments along continental margins, and airborne dust. This article provides a general review of sources of hydrothermal and sedimentary iron to the ocean, and speculates upon the role that iron-cycling microbes play in controlling iron dynamics from these sources. Special attention is paid to iron-oxidizing bacteria (FeOB) that live by oxidizing iron and producing biogenic iron oxides as waste products. The presence and ubiquity of FeOB both at hydrothermal systems and in sediments is only beginning to be appreciated. The biogenic oxides they produce have unique properties that could contribute significantly to the dynamics of dFe in the ocean. Changes in the physical and chemical characteristics of the ocean due to climate change and ocean acidification will undoubtedly impact the microbial iron cycle. A better understanding of the contemporary role of microbes in the iron cycle will help in predicting how these changes could ultimately influence marine primary productivity.

  2. A novel method for immobilization of proteins via entrapment of magnetic nanoparticles through epoxy cross-linking.

    PubMed

    Iype, Tessy; Thomas, Jaiby; Mohan, Sangeetha; Johnson, Kochurani K; George, Ligi E; Ambattu, Lizebona A; Bhati, Aniruddha; Ailsworth, Kristen; Menon, Bindu; Rayabandla, Sunayana M; Jesudasan, Rachel A; Santhosh, Sam; Ramchand, Chaniyilparampu N

    2017-02-15

    A method for immobilization of functional proteins by chemical cross-linking of the protein of interest and uncoated iron oxide nanoparticles in the presence of Epichlorohydrin is described. As a result of the cross-linking, the proteins form a matrix in which the particles get entrapped. The optimum concentration of Epichlorohydrin that facilitates immobilization of protein without affecting the functional properties of the protein was determined. This method was used to immobilize several functional proteins and the development and functional activity of Protein A-magnetic nanoparticles (MNPs) is described here in detail. The Protein A-MNPs possess high binding capacity due to the increased surface area of uncoated nanoparticles and robust magnetic separation due to the absence of polymeric coating materials. Protein A-MNPs were successfully used for purification of antibodies and also for immunoprecipitation. We also immobilized enzymes such as horse radish peroxidase and esterase and found that by providing the optimum incubation time, temperature and protein to nanoparticle ratio, we can retain the activity and improve the stability of the enzyme. This study is the first demonstration that Epichlorohydrin can be used to entrap nanoparticles in a cross-linked matrix of protein without impairing the activity of immobilized protein.

  3. Exploring Microbial Iron Oxidation in Wetland Soils

    NASA Astrophysics Data System (ADS)

    Wang, J.; Muyzer, G.; Bodelier, P. L. E.; den Oudsten, F.; Laanbroek, H. J.

    2009-04-01

    Iron is one of the most abundant elements on earth and is essential for life. Because of its importance, iron cycling and its interaction with other chemical and microbial processes has been the focus of many studies. Iron-oxidizing bacteria (FeOB) have been detected in a wide variety of environments. Among those is the rhizosphere of wetland plants roots which release oxygen into the soil creating suboxic conditions required by these organisms. It has been reported that in these rhizosphere microbial iron oxidation proceeds up to four orders of magnitude faster than strictly abiotic oxidation. On the roots of these wetland plants iron plaques are formed by microbial iron oxidation which are involved in the sequestering of heavy metals as well organic pollutants, which of great environmental significance.Despite their important role being catalysts of iron-cycling in wetland environments, little is known about the diversity and distribution of iron-oxidizing bacteria in various environments. This study aimed at developing a PCR-DGGE assay enabling the detection of iron oxidizers in wetland habitats. Gradient tubes were used to enrich iron-oxidizing bacteria. From these enrichments, a clone library was established based on the almost complete 16s rRNA gene using the universal bacterial primers 27f and 1492r. This clone library consisted of mainly α- and β-Proteobacteria, among which two major clusters were closely related to Gallionella spp. Specific probes and primers were developed on the basis of this 16S rRNA gene clone library. The newly designed Gallionella-specific 16S rRNA gene primer set 122f/998r was applied to community DNA obtained from three contrasting wetland environments, and the PCR products were used in denaturing gradient gel electrophoresis (DGGE) analysis. A second 16S rRNA gene clone library was constructed using the PCR products from one of our sampling sites amplified with the newly developed primer set 122f/998r. The cloned 16S rRNA gene

  4. Cross-Linking Studies of Lysozyme Nucleation

    NASA Technical Reports Server (NTRS)

    Forsythe, Elizabeth; Pusey, Marc

    2000-01-01

    Tetragonal chicken egg white crystals consist of 4(sub 3) helices running in alternating directions, the helix rows having a two fold symmetry with each other. The unit cell consists of one complete tetrameric turn from each of two adjacent helices (an octamer). PBC analysis indicates that the helix intermolecular bonds are the strongest in the crystal, therefore likely formed first. AFM analysis of the (110) surface shows only complete helices, no half steps or bisected helices being found, while AFM line scans to measure the growth step increments show that they are multiples of the 4(sub 3) helix tetramer dimensions. This supports our thesis that the growth units are in fact multiples of the four molecule 4(sub 3) helix unit, the "average" growth unit size for the (110) face being an octamer (two turns about the helix) and the (101) growth unit averaging about the size of a hexamer. In an effort to better understand the species involved in the crystal nucleation and growth process, we have initiated an experimental program to study the species formed in solution compared to what is found in the crystal through covalent cross-linking studies. These experiments use the heterobifunctional cross-linking agent aminoethyl-4-azidonitroanaline (AEANA). An aliphatic amine at one end is covalently attached to the protein by a carbodiimide-mediated reaction, and a photo reactive group at the other can be used to initiate crosslinking. Modifications to the parent structure can be used to alter the distance between the two reactive groups and thus the cross-linking agents "reach". In practice, the cross-linking agent is first coupled to the asp101 side chain through the amine group. Asp101 lies within the active site cleft, and previous work with fluorescent probes had shown that derivatives at this site still crystallize in the tetragonal space group. This was also found to be the case with the AEANA derivative, which gave red tetragonal crystals. The protein now has a

  5. Chitosan-cross-linked osmium polymer composites as an efficient platform for electrochemical biosensors.

    PubMed

    Jirimali, Harishchandra Digambar; Nagarale, Rajaram Krishna; Lee, Jong Myung; Saravanakumar, Durai; Shin, Woonsup

    2013-07-22

    A new family of chitosan-cross-linked osmium polymer composites was prepared and its electrochemical properties were examined. The composites were prepared by quaternization of the poly(4-vinylpyridine) osmium bipyridyl polymer (PVP-Os) which was then cross-linked with chitosan, yielding PVP-Os/chitosan. Films made of the composites showed improved mass and electron transport owing to the porous and hydrophilic structure which is derived from the cross-links between the Os polymer and chitosan. The rate for glucose oxidation was enhanced four times when glucose oxidase (GOx) was immobilized on PVP-Os/chitosan compared immobilization on PVP-Os.

  6. Enzymatically cross-linked hyperbranched polyglycerol hydrogels as scaffolds for living cells.

    PubMed

    Wu, Changzhu; Strehmel, Christine; Achazi, Katharina; Chiappisi, Leonardo; Dernedde, Jens; Lensen, Marga C; Gradzielski, Michael; Ansorge-Schumacher, Marion B; Haag, Rainer

    2014-11-10

    Although several strategies are now available to enzymatically cross-link linear polymers to hydrogels for biomedical use, little progress has been reported on the use of dendritic polymers for the same purpose. Herein, we demonstrate that horseradish peroxidase (HRP) successfully catalyzes the oxidative cross-linking of a hyperbranched polyglycerol (hPG) functionalized with phenol groups to hydrogels. The tunable cross-linking results in adjustable hydrogel properties. Because the obtained materials are cytocompatible, they have great potential for encapsulating living cells for regenerative therapy. The gel formation can be triggered by glucose and controlled well under various environmental conditions.

  7. Metal ion binding to iron oxides

    NASA Astrophysics Data System (ADS)

    Ponthieu, M.; Juillot, F.; Hiemstra, T.; van Riemsdijk, W. H.; Benedetti, M. F.

    2006-06-01

    The biogeochemistry of trace elements (TE) is largely dependent upon their interaction with heterogeneous ligands including metal oxides and hydrous oxides of iron. The modeling of TE interactions with iron oxides has been pursued using a variety of chemical models. The objective of this work is to show that it is possible to model the adsorption of protons and TE on a crystallized oxide (i.e., goethite) and on an amorphous oxide (HFO) in an identical way. Here, we use the CD-MUSIC approach in combination with valuable and reliable surface spectroscopy information about the nature of surface complexes of the TE. The other objective of this work is to obtain generic parameters to describe the binding of the following elements (Cd, Co, Cu, Ni, Pb, and Zn) onto both iron oxides for the CD-MUSIC approach. The results show that a consistent description of proton and metal ion binding is possible for goethite and HFO with the same set of model parameters. In general a good prediction of almost all the collected experimental data sets corresponding to metal ion binding to HFO is obtained. Moreover, dominant surface species are in agreement with the recently published surface complexes derived from X-ray absorption spectroscopy (XAS) data. Until more detailed information on the structure of the two iron oxides is available, the present option seems a reasonable approximation and can be used to describe complex geochemical systems. To improve our understanding and modeling of multi-component systems we need more data obtained at much lower metal ion to iron oxide ratios in order to be able to account eventually for sites that are not always characterized in spectroscopic studies.

  8. DNA Gel with dynamic cross-links

    NASA Astrophysics Data System (ADS)

    Park, Chang-Young; Fygenson, Deborah; Saleh, Omar

    2014-03-01

    The mechanical properties of a living cell are strongly related to the cytoskeletal network, which is comprised of diverse protein filaments connected by cross-linking proteins, some of which are dynamic. Gels comprised of dynamic cross-linkers exhibit unique mechanical properties not seen in those using permanent cross-linkers. To investigate the effect of a dynamic cross-linker on mechanical properties of a material, we have synthesized biopolymer gels with a well-known semi-flexible biopolymer, DNA, and probed the mechanics of the system using microrheological techniques. We discuss these results in comparison to cytoskeletal systems, and seek to establish universal principles of dynamic cross-link based gels. This work was supported by the NSF-funded UCSB MRSEC program, Award No. DMR-0520415.

  9. Positive tone cross-linked resists based on photoacid inhibition of cross linking

    NASA Astrophysics Data System (ADS)

    Lawson, Richard A.; Chun, Jun Sung; Neisser, Mark; Tolbert, Laren M.; Henderson, Clifford L.

    2014-03-01

    A resist imaging design that utilizes photoacid inhibition of cationic polymerization and cross-linking during a postexposure bake step has been studied. The key to the design approach is the use of two different polymerization catalysts/initiators: (1) a photoacid produced from a photoacid generator (PAG) upon exposure of the resist that can result in polymerization and cross-linking of the resist matrix and (2) a thermal cross-linking catalyst (TCC) designed to thermally catalyze epoxide-phenol cross-linking. The TCC can be chosen from a variety of compounds such as triphenylphosphine (TPP) or imidazole. When only one of these catalysts (e.g TPP or photoacid) is present in an epoxide and phenol containing resist matrix, it will individually catalyze cross-linking. When they are present together, they effectively quench one another and little to no cross-linking occurs. This approach can be used to switch the tone of a resist from negative (photoacid catalyzed) to positive (TCC catalyzed and photoacid inhibited). The effect of the ratio of TCC:PAG was examined and the optimal ratio for positive tone behavior was determined. Resist contrast can be modified by optimization of epoxide:phenol ratio in the formulation. Dual tone behavior with positive tone at low dose and negative tone at higher doses can be observed in certain formulation conditions. Initial EUV patterning shows poor results, but the source of the poor imaging is not yet understood.

  10. Iron oxides in human spleen.

    PubMed

    Kopáni, Martin; Miglierini, Marcel; Lančok, Adriana; Dekan, Július; Čaplovicová, Mária; Jakubovský, Ján; Boča, Roman; Mrazova, Hedviga

    2015-10-01

    Iron is an essential element for fundamental cell functions and a catalyst for chemical reactions. Three samples extracted from the human spleen were investigated by scanning (SEM) and transmission electron microscopy (TEM), Mössbauer spectrometry (MS), and SQUID magnetometry. The sample with diagnosis of hemosiderosis (H) differs from that referring to hereditary spherocytosis and the reference sample. SEM reveals iron-rich micrometer-sized aggregate of various structures-tiny fibrils in hereditary spherocytosis sample and no fibrils in hemochromatosis. Hematite and magnetite particles from 2 to 6 μm in TEM with diffraction in all samples were shown. The SQUID magnetometry shows different amount of diamagnetic, paramagnetic and ferrimagnetic structures in the tissues. The MS results indicate contribution of ferromagnetically split sextets for all investigated samples. Their occurrence indicates that at least part of the sample is magnetically ordered below the critical temperature. The iron accumulation process is different in hereditary spherocytosis and hemosiderosis. This fact may be the reason of different iron crystallization.

  11. Iron-catalysed oxidation intermediates captured in a DNA repair dioxygenase

    SciTech Connect

    Yi, Chengqi; Jia, Guifang; Hou, Guanhua; Dai, Qing; Zhang, Wen; Zheng, Guanqun; Jian, Xing; Yang, Cai-Guang; Cui, Qiang; He, Chuan

    2010-11-19

    Mononuclear iron-containing oxygenases conduct a diverse variety of oxidation functions in biology, including the oxidative demethylation of methylated nucleic acids and histones. Escherichia coli AlkB is the first such enzyme that was discovered to repair methylated nucleic acids, which are otherwise cytotoxic and/or mutagenic. AlkB human homologues are known to play pivotal roles in various processes. Here we present structural characterization of oxidation intermediates for these demethylases. Using a chemical cross-linking strategy, complexes of AlkB-double stranded DNA (dsDNA) containing 1,N{sup 6}-etheno adenine ({var_epsilon}A), N{sup 3}-methyl thymine (3-meT) and N{sup 3}-methyl cytosine (3-meC) are stabilized and crystallized, respectively. Exposing these crystals, grown under anaerobic conditions containing iron(II) and {alpha}-ketoglutarate ({alpha}KG), to dioxygen initiates oxidation in crystallo. Glycol (from {var_epsilon}A) and hemiaminal (from 3-meT) intermediates are captured; a zwitterionic intermediate (from 3-meC) is also proposed, based on crystallographic observations and computational analysis. The observation of these unprecedented intermediates provides direct support for the oxidative demethylation mechanism for these demethylases. This study also depicts a general mechanistic view of how a methyl group is oxidatively removed from different biological substrates.

  12. Catalytic iron oxide for lime regeneration in carbonaceous fuel combustion

    DOEpatents

    Shen, Ming-Shing; Yang, Ralph T.

    1980-01-01

    Lime utilization for sulfurous oxides absorption in fluidized combustion of carbonaceous fuels is improved by impregnation of porous lime particulates with iron oxide. The impregnation is achieved by spraying an aqueous solution of mixed iron sulfate and sulfite on the limestone before transfer to the fluidized bed combustor, whereby the iron compounds react with the limestone substrate to form iron oxide at the limestone surface. It is found that iron oxide present in the spent limestone acts as a catalyst to regenerate the spent limestone in a reducing environment. With only small quantities of iron oxide the calcium can be recycled at a significantly increased rate.

  13. DNA cross-linking by intermediates in the mitomycin activation cascade

    SciTech Connect

    Cera, C.; Egbertson, M.; Teng, S.P.; Crothers, D.M.; Danishefsky, S.J. )

    1989-06-27

    The authors have assayed the cross-linking of oligonucleotides containing repeated mitomycin-reactive CpG sites in order to assess the factors that enhance activation of the carbamoyl function at C{sub 10}, yielding efficient mitomycin cross-linking. Drugs studied include mitomycin C (MC), N-methylmitomycin A (NMA), and the aziridinomitosene of NMA (MS). Drugs were reduced both by catalytic hydrogenation and by dithionite. They find that cross-linking by fully reduced NMA can be increased severalfold by addition of either excess dithionite reductant or the oxidant FeCl{sub 3}. Enhancement by FeCl{sub 3} is not seen with MC or MS, but excess dithionite increases cross-linking by all three compounds. They explain the action of Fe{sup 3+} by postulating production of the semiquinone of the monoadduct of mitomycin reacted at the C{sub 1}-position; according to this mechanism, departure of the carbamate from C{sub 10} is more efficient for the semiquinone than for the hydroquinone. However, the results imply that the hydroquinone can also function as a cross-linking agent. Excess dithionite beyond that required for stoichiometric reduction, activates the carbamate 2-3-fold for cross-linking. They find that the fully reduced leucoaziridinomitosene is highly unstable in solution, yet it produces efficient cross-linking. Hence, this compound is highly reactive in DNA alkylation and a good candidate for the role of primary alkylating agent.

  14. Synthesis and Characterization of Cross-linked Polymer Electrolyte Membranes for Supercapacitor

    NASA Astrophysics Data System (ADS)

    Rosi, Memoria; Ekaputra, Muhamad Prama; Abdullah, Mikrajuddin; Khairurrijal

    2010-10-01

    Cross-linked polyvinyl alcohol (PVA) electrolyte membranes have been synthesized by using a solution casting method. In this study, PVA was blended with oxidative cross-linked agent (zinc acetate) and nano-sized silica as filler to stabilize PVA matrix and enhance conductivity. The cross-linked membranes were immersed into lithium hydroxide (LiOH) aqueous solution to increase their ionic conductivity. Two techniques were used to characterize the resulted membranes including Fourier transform infra red (FTIR) and AC impedance spectroscopies. The results showed that absorption peaks of C-O-C group and Si-O-Si are presence in the FTIR spectra attributed to the cross-linking process. Impedance spectra indicated that the contribution of ionic dopant (LiOH) to enhance conductivity is insignificant. The highest conductivity of the studied cross-linked PVA membrane is 1.34×10-3 S cm-1 corresponding to 5% LiOH dopant concentration of cross-linked PVA-zinc acetate-nano silica membrane. The present study also suggested that the solution casting is appropriate for cross-linked membrane synthesis.

  15. The Iron-Catalyzed Oxidation of Hydrazine by Nitric Acid

    SciTech Connect

    Karraker, D.G.

    2001-07-17

    To assess the importance of iron to hydrazine stability, the study of hydrazine oxidation by nitric acid has been extended to investigate the iron-catalyzed oxidation. This report describes those results.

  16. Defluoridation by Bacteriogenic Iron Oxides: Sorption Studies

    NASA Astrophysics Data System (ADS)

    Evans, K.; Ferris, F.

    2009-05-01

    At concentrations above 1 mg/L, fluoride in drinking water can lead to dental and skeletal fluorosis, a disease that causes mottling of the teeth, calcification of ligaments, crippling bone deformities and many other physiological disorders that can, ultimately, lead to death. Conservative estimates are that fluorosis afflicts tens of millions of people worldwide. As there is no treatment for fluorosis, prevention is the only means of controlling the disease. While numerous defluoridation techniques have been explored, no single method has been found to be both effective and inexpensive enough to implement widely. Our research began in India, with a large-scale geochemical study of the groundwater in a fluoride-contaminated region of Orissa. Having developed a better understanding of the geochemical relationships that exist between fluoride and other parameters present in an affected area, as well as the complex relationships that arise among those parameters that can impact the presence of fluoride, we began investigating certain remediation scenarios involving iron oxides. A common approach to remediation involves the partitioning of fluoride from groundwater by sorption onto a variety of materials, one of the most effective of which is iron oxide whose surface area acts as a scavenger for fluoride. In the presence of iron oxidizing bacteria, the oxidation rate of iron has been shown to be ˜6 times greater than in their absence; fluoride should, therefore, be removed from an aqueous environment by bacteriogenic iron oxides (BIOS) much more quickly than by abiotic iron oxides. Most recently, sorption studies have been conducted using both BIOS and synthetic hydrous ferric oxides in order to compare the behavior between biotic and abiotic sorbents. These studies have provided sorption isotherms that allow comparison of fluoride removed by sorption to BIOS versus synthetic iron oxides. Sorption affinity constants have also been determined, which allow for the

  17. 21 CFR 73.3125 - Iron oxides.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 1 2013-04-01 2013-04-01 false Iron oxides. 73.3125 Section 73.3125 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL LISTING OF COLOR... effect. (2) Authorization and compliance with this use shall not be construed as waiving any of...

  18. 21 CFR 73.3125 - Iron oxides.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 1 2012-04-01 2012-04-01 false Iron oxides. 73.3125 Section 73.3125 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL LISTING OF COLOR... effect. (2) Authorization and compliance with this use shall not be construed as waiving any of...

  19. Novel chitosan-based films cross-linked by genipin with improved physical properties.

    PubMed

    Jin, J; Song, M; Hourston, D J

    2004-01-01

    Novel cross-linked chitosan-based films were prepared using the solution casting technique. A naturally occurring and nontoxic cross-linking agent, genipin, was used to form the chitosan and chitosan/poly(ethylene oxide) (PEO) blend networks, where two types of PEO were used, one with a molecular weight of 20 000 g/mol (HPEO) and the other of 600 g/mol (LPEO). Genipin is used in traditional Chinese medicine and extracted from gardenia fruit. Importantly, it overcomes the problem of physiological toxicity inherent in the use of some common synthetic chemicals as cross-linking agents. The mechanical properties and the stability in water of cross-linked and un-crosslinked chitosan and chitosan/PEO blend films were investigated. It was shown that, compared to the transparent yellow, un-cross-linked chitosan/PEO blend films, the genipin-cross-linked chitosan-based film, blue in color, was more elastic, was more stable, and had better mechanical properties. Genipin-cross-linking produced chitosan networks that were insoluble in acidic and alkaline solutions but were able to swell in these aqueous media. The swelling characteristics of the films exhibit sensitivity to the environmental pH and temperature. The surface properties of the films were also examined by contact angle measurements using water and mixtures of water/ethanol. The results showed that, with the one exception of cross-linked pure chitosan in 100% water, the cross-linked chitosan and chitosan/PEO blends were more hydrophobic than un-crosslinked ones.

  20. Maturation of Collagen Ketoimine Cross-links by an Alternative Mechanism to Pyridinoline Formation in Cartilage*

    PubMed Central

    Eyre, David R.; Weis, Mary Ann; Wu, Jiann-Jiu

    2010-01-01

    The tensile strength of fibrillar collagens depends on stable intermolecular cross-links formed through the lysyl oxidase mechanism. Such cross-links based on hydroxylysine aldehydes are particularly important in cartilage, bone, and other skeletal tissues. In adult cartilages, the mature cross-linking structures are trivalent pyridinolines, which form spontaneously from the initial divalent ketoimines. We examined whether this was the complete story or whether other ketoimine maturation products also form, as the latter are known to disappear almost completely from mature tissues. Denatured, insoluble, bovine articular cartilage collagen was digested with trypsin, and cross-linked peptides were isolated by copper chelation chromatography, which selects for their histidine-containing sequence motifs. The results showed that in addition to the naturally fluorescent pyridinoline peptides, a second set of cross-linked peptides was recoverable at a high yield from mature articular cartilage. Sequencing and mass spectral analysis identified their origin from the same molecular sites as the initial ketoimine cross-links, but the latter peptides did not fluoresce and were nonreducible with NaBH4. On the basis of their mass spectra, they were identical to their precursor ketoimine cross-linked peptides, but the cross-linking residue had an M+188 adduct. Considering the properties of an analogous adduct of identical added mass on a glycated lysine-containing peptide from type II collagen, we predicted that similar dihydroxyimidazolidine structures would form from their ketoimine groups by spontaneous oxidation and free arginine addition. We proposed the trivial name arginoline for the ketoimine cross-link derivative. Mature bovine articular cartilage contains about equimolar amounts of arginoline and hydroxylysyl pyridinoline based on peptide yields. PMID:20363745

  1. Chemical design of biocompatible iron oxide nanoparticles for medical applications.

    PubMed

    Ling, Daishun; Hyeon, Taeghwan

    2013-05-27

    Iron oxide nanoparticles are one of the most versatile and safe nanomaterials used in medicine. Recent progress in nanochemistry enables fine control of the size, crystallinity, uniformity, and surface properties of iron oxide nanoparticles. In this review, the synthesis of chemically designed biocompatible iron oxide nanoparticles with improved quality and reduced toxicity is discussed for use in diverse biomedical applications.

  2. 21 CFR 73.1200 - Synthetic iron oxide.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 1 2014-04-01 2014-04-01 false Synthetic iron oxide. 73.1200 Section 73.1200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  3. 21 CFR 73.1200 - Synthetic iron oxide.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 1 2011-04-01 2011-04-01 false Synthetic iron oxide. 73.1200 Section 73.1200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  4. 21 CFR 73.200 - Synthetic iron oxide.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 1 2011-04-01 2011-04-01 false Synthetic iron oxide. 73.200 Section 73.200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Foods § 73.200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  5. 21 CFR 73.1200 - Synthetic iron oxide.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 1 2012-04-01 2012-04-01 false Synthetic iron oxide. 73.1200 Section 73.1200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  6. 21 CFR 73.1200 - Synthetic iron oxide.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 1 2013-04-01 2013-04-01 false Synthetic iron oxide. 73.1200 Section 73.1200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  7. 21 CFR 73.1200 - Synthetic iron oxide.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Synthetic iron oxide. 73.1200 Section 73.1200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  8. 21 CFR 73.200 - Synthetic iron oxide.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Synthetic iron oxide. 73.200 Section 73.200 Food... COLOR ADDITIVES EXEMPT FROM CERTIFICATION Foods § 73.200 Synthetic iron oxide. (a) Identity. (1) The color additive synthetic iron oxide consists of any one or any combination of synthetically...

  9. Ferrous iron oxidation by anoxygenic phototrophic bacteria

    NASA Astrophysics Data System (ADS)

    Widdel, Friedrich; Schnell, Sylvia; Heising, Silke; Ehrenreich, Armin; Assmus, Bernhard; Schink, Bernhard

    1993-04-01

    NATURAL oxidation of ferrous to ferric iron by bacteria such as Thiobacillus ferrooxidans or Gallionella ferruginea1, or by chemical oxidation2,3 has previously been thought always to involve molecular oxygen as the electron acceptor. Anoxic photochemical reactions4-6 or a photobiological process involving two photosystems7-9 have also been discussed as mechanisms of ferrous iron oxidation. The knowledge of such processes has implications that bear on our understanding of the origin of Precambrian banded iron formations10-14. The reducing power of ferrous iron increases dramatically at pH values higher than 2-3 owing to the formation of ferric hydroxy and oxyhydroxy compounds1,2,15 (Fig. 1). The standard redox potential of Fe3+/Fe2+ (E0 = +0.77 V) is relevant only under acidic conditions. At pH 7.0, the couples Fe(OH)3/Fe2+ (E'0 = -0.236V) or Fe(OH)3 + HCO-3FeCO3 (E'0 = +0.200 V) prevail, matching redox potentials measured in natural sediments9,16,17. It should thus be possible for Fe(n) around pH 7.0 to function as an electron donor for anoxygenic photosynthesis. The midpoint potential of the reaction centre in purple bacteria is around +0.45 V (ref. 18). Here we describe purple, non-sulphur bacteria that can indeed oxidize colourless Fe(u) to brown Fe(in) and reduce CO2 to cell material, implying that oxygen-independent biological iron oxidation was possible before the evolution of oxygenic photosynthesis.

  10. Cross-linked carbon nanotube heat spreader

    NASA Astrophysics Data System (ADS)

    Konesky, Gregory

    2014-09-01

    Isolated individual carbon nanotubes (CNTs) have shown exceptional thermal conductivity along their axis, but have poor thermal transfer between adjacent CNTs. Thick bundles of aligned CNTs have been used as heat pipes, but the thermal input and output areas are the same, providing no heat spreading effect. Energetic argon ion beams are used to join, or cross-link overlapping CNTs in a thick film to form an interpenetrating network with an isotropic thermal conductivity of 2150 W/m-K. Such thick films may be used as heat spreaders to enlarge the thermal footprint of various electronic and semiconductor devices, laser diodes and CPU chips, for example, to enhance cooling.

  11. Inverted bulk-heterojunction solar cell with cross-linked hole-blocking layer

    PubMed Central

    Udum, Yasemin; Denk, Patrick; Adam, Getachew; Apaydin, Dogukan H.; Nevosad, Andreas; Teichert, Christian; S. White, Matthew.; S. Sariciftci, Niyazi.; Scharber, Markus C.

    2014-01-01

    We have developed a hole-blocking layer for bulk-heterojunction solar cells based on cross-linked polyethylenimine (PEI). We tested five different ether-based cross-linkers and found that all of them give comparable solar cell efficiencies. The initial idea that a cross-linked layer is more solvent resistant compared to a pristine PEI layer could not be confirmed. With and without cross-linking, the PEI layer sticks very well to the surface of the indium–tin–oxide electrode and cannot be removed by solvents used to process PEI or common organic semiconductors. The cross-linked PEI hole-blocking layer functions for multiple donor–acceptor blends. We found that using cross-linkers improves the reproducibility of the device fabrication process. PMID:24817837

  12. Bifunctional Electrophiles Cross-Link Thioredoxins with Redox Relay Partners in Cells

    PubMed Central

    Naticchia, Matthew R.; Brown, Haley A.; Garcia, Francisco J.; Lamade, Andrew M.; Justice, Samantha L.; Herrin, Rachelle P.; Morano, Kevin A.; West, James D.

    2013-01-01

    Thioredoxin protects cells against oxidative damage by reducing disulfide bonds in improperly oxidized proteins. Previously, we found that the baker's yeast cytosolic thioredoxin Trx2 undergoes cross-linking to form several protein-protein complexes in cells treated with the bifunctional electrophile divinyl sulfone (DVSF). Here, we report that the peroxiredoxin Tsa1 and the thioredoxin reductase Trr1, both of which function in a redox relay network with thioredoxin, become cross-linked in complexes with Trx2 upon DVSF treatment. Treatment of yeast with other bifunctional electrophiles, including diethyl acetylenedicarboxylate (DAD), mechlorethamine (HN2), and 1,2,3,4-diepoxybutane (DEB), resulted in the formation of similar cross-linked complexes. Cross-linking of Trx2 and Tsa1 to other proteins by DVSF and DAD is dependent on modification of the active site Cys residues within these proteins. In addition, the human cytosolic thioredoxin, cytosolic thioredoxin reductase, and peroxiredoxin 2 form cross-linked complexes to other proteins in the presence of DVSF, although each protein shows different susceptibilities to modification by DAD, HN2, and DEB. Taken together, our results indicate that bifunctional electrophiles potentially disrupt redox homeostasis in yeast and human cells by forming cross-linked complexes between thioredoxins and their redox partners. PMID:23414292

  13. Nitric oxide and plant iron homeostasis.

    PubMed

    Buet, Agustina; Simontacchi, Marcela

    2015-03-01

    Like all living organisms, plants demand iron (Fe) for important biochemical and metabolic processes. Internal imbalances, as a consequence of insufficient or excess Fe in the environment, lead to growth restriction and affect crop yield. Knowledge of signals and factors affecting each step in Fe uptake from the soil and distribution (long-distance transport, remobilization from old to young leaves, and storage in seeds) is necessary to improve our understanding of plant mineral nutrition. In this context, the role of nitric oxide (NO) is discussed as a key player in maintaining Fe homeostasis through its cross talk with hormones, ferritin, and frataxin and the ability to form nitrosyl-iron complexes.

  14. Formulations for iron oxides dissolution

    DOEpatents

    Horwitz, Earl P.; Chiarizia, Renato

    1992-01-01

    A mixture of a di- or polyphosphonic acid and a reductant wherein each is present in a sufficient amount to provide a synergistic effect with respect to the dissolution of metal oxides and optionally containing corrosion inhibitors and pH adjusting agents.

  15. Corneal collagen cross-linking: a review.

    PubMed

    O'Brart, David P S

    2014-01-01

    The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4-6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation.

  16. Corneal Collagen Cross-Linking Outcomes: Review

    PubMed Central

    Jankov II, Mirko R; Jovanovic, Vesna; Delevic, Sladjana; Coskunseven, Efekan

    2011-01-01

    Keratoconus is a condition characterized by biomechanical instability of the cornea, presenting in a progressive, asymmetric and bilateral way. Corneal collagen cross-linking with riboflavin and UVA (CXL) is a new technique of corneal tissue strengthening that combines the use of riboflavin as a photo sensitizer and UVA irradiation. The studies showed that CXL was effective in halting the progression of keratoconus over a period of up to four years. The published studies also revealed a reduction of max K readings by more than 2 D, while the postoperative SEQ was reduced by an average of more than 1 D, and refractive cylinder decreased by about 1 D. No eyes lost any line of BCDVA. Moreover, there was no significant decrease in endothelial cell density. It was also found that CXL treatment was effective with reducing corneal and total wavefront aberrations. Corneal cross-linking has also led to an arrest and/or even a partial reversal of keratectasia in the treatment of iatrogenic ectasia after excimer laser ablation. A primary intervention such as CXL should be considered to potentially increase the biomechanical stability of the corneal tissue and postpone the need of lamellar or penetrating keratoplasty. PMID:21448301

  17. Corneal collagen cross-linking: A review

    PubMed Central

    O’Brart, David P.S.

    2014-01-01

    The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4–6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation. PMID:25000866

  18. To Cross-Link or Not to Cross-Link? Cross-Linking Associated Foreign Body Response of Collagen-Based Devices

    PubMed Central

    Delgado, Luis M.; Bayon, Yves; Pandit, Abhay

    2015-01-01

    Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling. PMID:25517923

  19. Modification of the surface of superparamagnetic iron oxide nanoparticles to enable their safe application in humans

    PubMed Central

    Strehl, Cindy; Maurizi, Lionel; Gaber, Timo; Hoff, Paula; Broschard, Thomas; Poole, A Robin; Hofmann, Heinrich; Buttgereit, Frank

    2016-01-01

    Combined individually tailored methods for diagnosis and therapy (theragnostics) could be beneficial in destructive diseases, such as rheumatoid arthritis. Nanoparticles are promising candidates for theragnostics due to their excellent biocompatibility. Nanoparticle modifications, such as improved surface coating, are in development to meet various requirements, although safety concerns mean that modified nanoparticles require further review before their use in medical applications is permitted. We have previously demonstrated that iron oxide nanoparticles with amino-polyvinyl alcohol (a-PVA) adsorbed on their surfaces have the unwanted effect of increasing human immune cell cytokine secretion. We hypothesized that this immune response was caused by free-floating PVA. The aim of the present study was to prevent unwanted immune reactions by further surface modification of the a-PVA nanoparticles. After cross-linking of PVA to nanoparticles to produce PVA-grafted nanoparticles, and reduction of their zeta potential, the effects on cell viability and cytokine secretion were analyzed. PVA-grafted nanoparticles still stimulated elevated cytokine secretion from human immune cells; however, this was inhibited after reduction of the zeta potential. In conclusion, covalent cross-linking of PVA to nanoparticles and adjustment of the surface charge rendered them nontoxic to immune cells, nonimmunogenic, and potentially suitable for use as theragnostic agents. PMID:27877036

  20. Method of Cross-Linking Aerogels Using a One-Pot Reaction Scheme

    NASA Technical Reports Server (NTRS)

    Meador, Ann B.; Capadona, Lynn A.

    2008-01-01

    A document discusses a new, simplified method for cross-linking silica and other oxide aerogels, with a polymeric material to increase strength of such materials without adversely affecting porosity or low density. This innovation introduces the polymer precursor into the sol before gelation either as an agent, which co-reacts with the oxide gel, or as soluble polymer precursors, which do not interact with the oxide gel in any way. Subsequent exposure to heat, light, catalyst or other method of promoting polymerization causes cross-linking without any additional infiltration steps.

  1. Oxidation Potentials in Iron and Steel Making

    NASA Astrophysics Data System (ADS)

    Matousek, J. W.

    2013-11-01

    The state of oxidation of a pyrometallurgical process given by the partial pressure of oxygen and the temperature (the oxidation potential) is one of the important properties monitored and controlled in the smelting and refining of iron and the nonferrous metals. Solid electrolyte sensors based on ZrO2 and a reference electrode such as Cr/Cr2O3 to measure the oxygen pressure found early application in the steel industry, followed soon after in copper, nickel, lead, and zinc smelting. Similar devices are installed in automobile postcombustion/exhaust trains as part of emission control systems. The current discussion reviews this technology as applied in the primary steps of iron and steel making and refining.

  2. Method for preparing hydrous iron oxide gels and spherules

    DOEpatents

    Collins, Jack L.; Lauf, Robert J.; Anderson, Kimberly K.

    2003-07-29

    The present invention is directed to methods for preparing hydrous iron oxide spherules, hydrous iron oxide gels such as gel slabs, films, capillary and electrophoresis gels, iron monohydrogen phosphate spherules, hydrous iron oxide spherules having suspendable particles homogeneously embedded within to form composite sorbents and catalysts, iron monohydrogen phosphate spherules having suspendable particles of at least one different sorbent homogeneously embedded within to form a composite sorbent, iron oxide spherules having suspendable particles homogeneously embedded within to form a composite of hydrous iron oxide fiber materials, iron oxide fiber materials, hydrous iron oxide fiber materials having suspendable particles homogeneously embedded within to form a composite, iron oxide fiber materials having suspendable particles homogeneously embedded within to form a composite, dielectric spherules of barium, strontium, and lead ferrites and mixtures thereof, and composite catalytic spherules of barium or strontium ferrite embedded with oxides of Mg, Zn, Pb, Ce and mixtures thereof. These variations of hydrous iron oxide spherules and gel forms prepared by the gel-sphere, internal gelation process offer more useful forms of inorganic ion exchangers, catalysts, getters, dielectrics, and ceramics.

  3. Optical properties of iron oxides

    NASA Astrophysics Data System (ADS)

    Musfeldt, Janice

    2012-02-01

    Magnetoelectric coupling in materials like multiferroics, dilute magnetic semiconductors, and topological insulators has attracted a great deal of attention, although most work has been done in the static limit. Optical spectroscopy offers a way to investigate the dynamics of charge-spin coupling, an area where there has been much less effort. Using these techniques, we discovered that charge fluctuation in LuFe2O4, the prototypical charge ordered multiferroic, has an onset well below the charge ordering transition, supporting the ``order by fluctuation'' mechanism for the development of charge order superstructure. Bragg splitting and large magneto-optical contrast suggest a low temperature monoclinic distortion that can be driven by both temperature and magnetic field. At the same time, dramatic splitting of the LuO2 layer phonon mode is attributed to charge-rich/poor proximity effects, and its temperature dependence reveals the antipolar nature of the W layer pattern. Using optical techniques, we also discovered that α-Fe2O3, a chemically-similar parent compound and one of the world's oldest and most iconic antiferromagnetic materials, appears more red in applied magnetic field than in zero field conditions. This effect is driven by a field-induced reorientation of magnetic order. The oscillator strength lost in the color band is partially transferred to the magnon side band, a process that also reveals a new exciton pattern induced by the modified exchange coupling. Analysis of the exciton pattern exposes C2/c monoclinic symmetry in the high field phase of hematite. Taken together, these findings advance our understanding of iron-based materials under extreme conditions. [4pt] Collaborators include: X. S. Xu, P. Chen, Q. -C. Sun, T. V. Brinzari (Tennessee); S. McGill (NHMFL); J. De Groot, M. Angst, R. P. Hermann (Julich); A. D. Christianson, B. C. Sales, D. Mandrus (ORNL); A. P. Litvinchuk (Houston); J. -W. Kim (Ames); Z. Islam (Argonne); N. Lee, S. -W. Cheong

  4. Fibromodulin Interacts with Collagen Cross-linking Sites and Activates Lysyl Oxidase*

    PubMed Central

    Bihan, Dominique; Bonna, Arkadiusz; Rubin, Kristofer; Farndale, Richard W.

    2016-01-01

    The hallmark of fibrotic disorders is a highly cross-linked and dense collagen matrix, a property driven by the oxidative action of lysyl oxidase. Other fibrosis-associated proteins also contribute to the final collagen matrix properties, one of which is fibromodulin. Its interactions with collagen affect collagen cross-linking, packing, and fibril diameter. We investigated the possibility that a specific relationship exists between fibromodulin and lysyl oxidase, potentially imparting a specific collagen matrix phenotype. We mapped the fibromodulin-collagen interaction sites using the collagen II and III Toolkit peptide libraries. Fibromodulin interacted with the peptides containing the known collagen cross-linking sites and the MMP-1 cleavage site in collagens I and II. Interestingly, the interaction sites are closely aligned within the quarter-staggered collagen fibril, suggesting a multivalent interaction between fibromodulin and several collagen helices. Furthermore, we detected an interaction between fibromodulin and lysyl oxidase (a major collagen cross-linking enzyme) and mapped the interaction site to 12 N-terminal amino acids on fibromodulin. This interaction also increases the activity of lysyl oxidase. Together, the data suggest a fibromodulin-modulated collagen cross-linking mechanism where fibromodulin binds to a specific part of the collagen domain and also forms a complex with lysyl oxidase, targeting the enzyme toward specific cross-linking sites. PMID:26893379

  5. Fibromodulin Interacts with Collagen Cross-linking Sites and Activates Lysyl Oxidase.

    PubMed

    Kalamajski, Sebastian; Bihan, Dominique; Bonna, Arkadiusz; Rubin, Kristofer; Farndale, Richard W

    2016-04-08

    The hallmark of fibrotic disorders is a highly cross-linked and dense collagen matrix, a property driven by the oxidative action of lysyl oxidase. Other fibrosis-associated proteins also contribute to the final collagen matrix properties, one of which is fibromodulin. Its interactions with collagen affect collagen cross-linking, packing, and fibril diameter. We investigated the possibility that a specific relationship exists between fibromodulin and lysyl oxidase, potentially imparting a specific collagen matrix phenotype. We mapped the fibromodulin-collagen interaction sites using the collagen II and III Toolkit peptide libraries. Fibromodulin interacted with the peptides containing the known collagen cross-linking sites and the MMP-1 cleavage site in collagens I and II. Interestingly, the interaction sites are closely aligned within the quarter-staggered collagen fibril, suggesting a multivalent interaction between fibromodulin and several collagen helices. Furthermore, we detected an interaction between fibromodulin and lysyl oxidase (a major collagen cross-linking enzyme) and mapped the interaction site to 12 N-terminal amino acids on fibromodulin. This interaction also increases the activity of lysyl oxidase. Together, the data suggest a fibromodulin-modulated collagen cross-linking mechanism where fibromodulin binds to a specific part of the collagen domain and also forms a complex with lysyl oxidase, targeting the enzyme toward specific cross-linking sites.

  6. Cross-linking cellulose nanofibrils for potential elastic cryo-structured gels

    NASA Astrophysics Data System (ADS)

    Syverud, Kristin; Kirsebom, Harald; Hajizadeh, Solmaz; Chinga-Carrasco, Gary

    2011-12-01

    Cellulose nanofibrils were produced from P. radiata kraft pulp fibers. The nanofibrillation was facilitated by applying 2,2,6,6-tetramethylpiperidinyl-1-oxyl-mediated oxidation as pretreatment. The oxidized nanofibrils were cross-linked with polyethyleneimine and poly N-isopropylacrylamide- co-allylamine- co-methylenebisacrylamide particles and were frozen to form cryo-structured gels. Samples of the gels were critical-point dried, and the corresponding structures were assessed with scanning electron microscopy. It appears that the aldehyde groups in the oxidized nanofibrils are suitable reaction sites for cross-linking. The cryo-structured materials were spongy, elastic, and thus capable of regaining their shape after a given pressure was released, indicating a successful cross-linking. These novel types of gels are considered potential candidates in biomedical and biotechnological applications.

  7. Kojak: Efficient analysis of chemically cross-linked protein complexes

    PubMed Central

    Hoopmann, Michael R.; Zelter, Alex; Johnson, Richard S.; Riffle, Michael; MacCoss, Michael J.; Davis, Trisha N.; Moritz, Robert L.

    2015-01-01

    Protein chemical cross-linking and mass spectrometry enable the analysis of protein-protein interactions and protein topologies, however complicated cross-linked peptide spectra require specialized algorithms to identify interacting sites. The Kojak cross-linking software application is a new, efficient approach to identify cross-linked peptides, enabling large-scale analysis of protein-protein interactions by chemical cross-linking techniques. The algorithm integrates spectral processing and scoring schemes adopted from traditional database search algorithms, and can identify cross-linked peptides using many different chemical cross-linkers, with or without heavy isotope labels. Kojak was used to analyze both novel and existing datasets, and was compared with existing cross-linking algorithms. The algorithm provided increased cross-link identifications over existing algorithms, and equally importantly, the results in a fraction of computational time. The Kojak algorithm is open-source, cross-platform, and freely available. This software provides both existing and new cross-linking researchers alike an effective way to derive additional cross-link identifications from new or existing datasets. For new users, it provides a simple analytical resource resulting in more cross-link identifications than other methods. PMID:25812159

  8. Corneal cross-linking treatment of keratoconus

    PubMed Central

    Farjadnia, Mahgol; Naderan, Mohammad

    2015-01-01

    Keratoconus as the most common cause of ectasia is one of the leading cause of corneal transplants worldwide. The current available therapies do not modify the underlying pathogenesis of the disease, and none of the available approaches but corneal transplant hinder the ongoing ectasia. Several studies document Crosslink defect between collagen fibrils in the pathogenesis of keratoconus. Collagen cross link is a relatively new approach that with the application of the riboflavin and ultraviolet A, new covalent bands reform. Subjective and objective results following this method seem to be promising. Endothelial damage besides other deep structural injury, which is the major concern of this technique have not yet been reported, when applying the standard method. PMID:26622134

  9. Glutaraldehyde cross-linked magnetic chitosan nanocomposites: Reduction precipitation synthesis, characterization, and application for removal of hazardous textile dyes.

    PubMed

    Kadam, Avinash A; Lee, Dae Sung

    2015-10-01

    Magnetic chitosan nanocomposites (MCNCs) were synthesized by an inexpensive reduction precipitation technique using a glutaraldehyde cross-linking agent at room temperature. Successful chitosan coating of iron oxide nanoparticles was confirmed by X-ray photoemission spectroscopy. X-ray diffraction data revealed crystalline particle sizes for the iron oxide and MCNCs to be around 6-7 and 8-9 nm, respectively. In addition, the MCNCs exhibited supermagnetic properties having magnetic saturation of 17.5 emu/g. The synthesized MCNCs showed 91.60% absorption of Acid Red 2, while iron oxide 16.40% absorption; enhanced performance in MCNCs was resulted from presence of free amino and hydroxyl groups. Furthermore, the optimum pH and adsorbent concentration were 3 and 1.0 g/L, respectively. The Redlich-Peterson isotherm fit experimental data better than Langmuir and Freundlich models, based on non-linear regression. Finally, MCNCs showed 96% American Dye Manufacturing Institute (ADMI) value removal and gave recovery efficiency of 100%, making them attractive for further practical applications.

  10. Chemistry of the collagen cross-links. Origin and partial characterization of a putative mature cross-link of collagen.

    PubMed Central

    Barnard, K; Light, N D; Sims, T J; Bailey, A J

    1987-01-01

    The conversion of the reducible divalent cross-links in collagen to non-reducible multivalent cross-links in mature collagen has resulted in the identification of several new amino acids as the putative mature cross-link. None of these compounds has completely satisfied the necessary criteria. We have now isolated an amino acid of high Mr, derived from lysine, that is only present in high-Mr peptides derived from mature collagen. Its increase with age of the tissue correlates with the decrease in the reducible cross-links, and it is present both in mature skin and bone, which are initially cross-linked through the aldimine and oxo-imine divalent cross-link respectively. We propose that this amino acid, as yet incompletely characterized and designated compound M, is a major cross-link of mature collagen. PMID:3117039

  11. Encapsulation of cobalt nanoparticles in cross-linked-polymer cages

    NASA Astrophysics Data System (ADS)

    Hatamie, Shadie; Dhole, S. D.; Ding, J.; Kale, S. N.

    2009-07-01

    Nanoparticles embedded in polymeric cages give rise to interesting applications ranging from nanocatalysis to drug-delivery systems. In this context, we report on synthesis of cobalt (Co) nanoparticles trapped in polyvinyl alcohol (PVA) matrix to yield self-supporting magnetic films in PVA slime. A 20 nm, Co formed in FCC geometry encapsulated with a weak citrate coat when caged in PVA matrix exhibited persistence of magnetism and good radio-frequency response. Cross-linking of PVA chains to form cage-like structures to arrest Co nanoparticles therein, is believed to be the reason for oxide-free nature of Co, promising applications in biomedicine as well as in radio-frequency shielding.

  12. Ice templated and cross-linked xylan/nanocrystalline cellulose hydrogels.

    PubMed

    Köhnke, Tobias; Elder, Thomas; Theliander, Hans; Ragauskas, Arthur J

    2014-01-16

    Structured xylan-based hydrogels, reinforced with cellulose nanocrystals (CNCs), have successfully been prepared from water suspensions by cross-linking during freeze-casting. In order to induce cross-linking during the solidification/sublimation operation, xylan was first oxidized using sodium periodate to introduce dialdehydes. The oxidized xylan was then mixed with CNCs after which the suspension was frozen unidirectionally in order to control the ice crystal formation and by that the pore morphology of the material. Finally the ice crystal templates were removed by freeze-drying. During the freeze-casting process hemiacetal bonds are formed between the aldehyde groups and hydroxyl groups, either on other xylan molecules or on CNCs, which cross-links the system. The proposed cross-linking reaction was confirmed by using cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The pore morphology of the obtained materials was analyzed by scanning electron microscopy (SEM). The materials were also tested for compressive strength properties, both in dry and water swollen state. All together this study describes a novel combined freeze-casting/cross-linking process which enables fabrication of nanoreinforced biopolymer-based hydrogels with controlled porosity and 3-D architecture.

  13. Photocontrolled Cargo Release from Dual Cross-Linked Polymer Particles.

    PubMed

    Tan, Shereen; Cui, Jiwei; Fu, Qiang; Nam, Eunhyung; Ladewig, Katharina; Ren, Jing M; Wong, Edgar H H; Caruso, Frank; Blencowe, Anton; Qiao, Greg G

    2016-03-09

    Burst release of a payload from polymeric particles upon photoirradiation was engineered by altering the cross-linking density. This was achieved via a dual cross-linking concept whereby noncovalent cross-linking was provided by cyclodextrin host-guest interactions, and irreversible covalent cross-linking was mediated by continuous assembly of polymers (CAP). The dual cross-linked particles (DCPs) were efficiently infiltrated (∼80-93%) by the biomacromolecule dextran (molecular weight up to 500 kDa) to provide high loadings (70-75%). Upon short exposure (5 s) to UV light, the noncovalent cross-links were disrupted resulting in increased permeability and burst release of the cargo (50 mol % within 1 s) as visualized by time-lapse fluorescence microscopy. As sunlight contains UV light at low intensities, the particles can potentially be incorporated into systems used in agriculture, environmental control, and food packaging, whereby sunlight could control the release of nutrients and antimicrobial agents.

  14. Synthesis and properties of reprocessable sulfonated polyimides cross-linked via acid stimulation for use as proton exchange membranes

    NASA Astrophysics Data System (ADS)

    Zhang, Boping; Ni, Jiangpeng; Xiang, Xiongzhi; Wang, Lei; Chen, Yongming

    2017-01-01

    Cross-linked sulfonated polyimides are one of the most promising materials for proton exchange membrane (PEM) applications. However, these cross-linked membranes are difficult to reprocess because they are insoluble. In this study, a series of cross-linkable sulfonated polyimides with flexible pendant alkyl side chains containing trimethoxysilyl groups is successfully synthesized. The cross-linkable polymers are highly soluble in common solvents and can be used to prepare tough and smooth films. Before the cross-linking reaction is complete, the membranes can be reprocessed, and the recovery rate of the prepared films falls within an acceptable range. The cross-linked membranes are obtained rapidly when the cross-linkable membranes are immersed in an acid solution, yielding a cross-linking density of the gel fraction of greater than 90%. The cross-linked membranes exhibit high proton conductivities and tensile strengths under hydrous conditions. Compared with those of pristine membranes, the oxidative and hydrolytic stabilities of the cross-linked membranes are significantly higher. The CSPI-70 membrane shows considerable power density in a direct methanol fuel cell (DMFC) test. All of these results suggest that the prepared cross-linked membranes have great potential for applications in proton exchange membrane fuel cells.

  15. Phase Formation Behavior in Ultrathin Iron Oxide.

    PubMed

    Jõgi, Indrek; Jacobsson, T Jesper; Fondell, Mattis; Wätjen, Timo; Carlsson, Jan-Otto; Boman, Mats; Edvinsson, Tomas

    2015-11-17

    Nanostructured iron oxides, and especially hematite, are interesting for a wide range of applications ranging from gas sensors to renewable solar hydrogen production. A promising method for deposition of low-dimensional films is atomic layer deposition (ALD). Although a potent technique, ALD of ultrathin films is critically sensitive to the substrate and temperature conditions where initial formation of islands and crystallites influences the properties of the films. In this work, deposition at the border of the ALD window forming a hybrid ALD/pulsed CVD (pCVD) deposition is utilized to obtain a deposition less sensitive to the substrate. A thorough analysis of iron oxide phases formation on two different substrates, Si(100) and SiO2, was performed. Films between 3 and 50 nm were deposited and analyzed with diffraction techniques, high-resolution Raman spectroscopy, and optical spectroscopy. Below 10 nm nominal film thickness, island formation and phase dependent particle crystallization impose constraints for deposition of phase pure iron oxides on non-lattice-matching substrates. Films between 10 and 20 nm thickness on SiO2 could effectively be recrystallized into hematite whereas for the corresponding films on Si(100), no recrystallization occurred. For films thicker than 20 nm, phase pure hematite can be formed directly with ALD/pCVD with very low influence of the substrate on either Si or SiO2. For more lattice matched substrates such as SnO2:F, Raman spectroscopy indicated formation of the hematite phase already for films with 3 nm nominal thickness and clearly for 6 nm films. Analysis of the optical properties corroborated the analysis and showed a quantum confined blue-shift of the absorption edge for the thinnest films.

  16. Mineral resource of the month: iron oxide pigments

    USGS Publications Warehouse

    ,

    2008-01-01

    The article discusses iron oxide pigments, which have been used as colorants since human began painting as they resist color change due to sunlight exposure, have good chemical resistance and are stable under normal ambient conditions. Cyprus, Italy and Spain are among the countries that are known for the production of iron oxide pigments. Granular forms of iron oxides and nano-sized materials are cited as developments in the synthetic iron oxide pigment industry which are being used in computer disk drives and nuclear magnetic resonance imaging.

  17. Suspension Hydrogen Reduction of Iron Oxide Concentrates

    SciTech Connect

    H.Y. Sohn

    2008-03-31

    The objective of the project is to develop a new ironmaking technology based on hydrogen and fine iron oxide concentrates in a suspension reduction process. The ultimate objective of the new technology is to replace the blast furnace and to drastically reduce CO2 emissions in the steel industry. The goals of this phase of development are; the performance of detailed material and energy balances, thermochemical and equilibrium calculations for sulfur and phosphorus impurities, the determination of the complete kinetics of hydrogen reduction and bench-scale testing of the suspension reduction process using a large laboratory flash reactor.

  18. Modified iron oxide nanomaterials: Functionalization and application

    NASA Astrophysics Data System (ADS)

    Bagheri, Samira; Julkapli, Nurhidayatullaili Muhd

    2016-10-01

    Iron oxide magnetic nanoparticles have aroused the interest of researchers of materials' chemistry due to its exceptional properties such as decent magnetic, electric, catalytic, biocompatibility, and low toxicity. However, these magnetic nanoparticles are predisposed towards aggregation and forming larger particles, due to its strong anisotropic dipolar interactions, particularly in the aqueous phase, consequently depriving them of dispersibility and particular properties, ultimately degrading their performance. Hence, this review focuses on modified magnetic nanoparticles that are stable, easily synthesized, possess a high surface area and could be facile-separated via magnetic forces, and are of low toxicity and costs for applications such as catalyst/catalyst support, food security, biomedical, and pollutant remediation.

  19. Different effect of hydrogelation on antifouling and circulation properties of dextran-iron oxide nanoparticles.

    PubMed

    Karmali, Priya Prakash; Chao, Ying; Park, Ji-Ho; Sailor, Michael J; Ruoslahti, Erkki; Esener, Sadik C; Simberg, Dmitri

    2012-03-05

    Premature recognition and clearance of nanoparticulate imaging and therapeutic agents by macrophages in the tissues can dramatically reduce both the nanoparticle half-life and delivery to the diseased tissue. Grafting nanoparticles with hydrogels prevents nanoparticulate recognition by liver and spleen macrophages and greatly prolongs circulation times in vivo. Understanding the mechanisms by which hydrogels achieve this "stealth" effect has implications for the design of long-circulating nanoparticles. Thus, the role of plasma protein absorption in the hydrogel effect is not yet understood. Short-circulating dextran-coated iron oxide nanoparticles could be converted into stealth hydrogel nanoparticles by cross-linking with 1-chloro-2,3-epoxypropane. We show that hydrogelation did not affect the size, shape and zeta potential, but completely prevented the recognition and clearance by liver macrophages in vivo. Hydrogelation decreased the number of hydroxyl groups on the nanoparticle surface and reduced the binding of the anti-dextran antibody. At the same time, hydrogelation did not reduce the absorption of cationic proteins on the nanoparticle surface. Specifically, there was no effect on the binding of kininogen, histidine-rich glycoprotein, and protamine sulfate to the anionic nanoparticle surface. In addition, hydrogelation did not prevent activation of plasma kallikrein on the metal oxide surface. These data suggest that (a) a stealth hydrogel coating does not mask charge interactions with iron oxide surface and (b) the total blockade of plasma protein absorption is not required for maintaining iron oxide nanoparticles' long-circulating stealth properties. These data illustrate a novel, clinically promising property of long-circulating stealth nanoparticles.

  20. Inhibition of bacterial growth by iron oxide nanoparticles with and without attached drug: Have we conquered the antibiotic resistance problem?

    NASA Astrophysics Data System (ADS)

    Armijo, Leisha M.; Jain, Priyanka; Malagodi, Angelina; Fornelli, F. Zuly; Hayat, Allison; Rivera, Antonio C.; French, Michael; Smyth, Hugh D. C.; Osiński, Marek

    2015-03-01

    Pseudomonas aeruginosa is among the top three leading causative opportunistic human pathogens, possessing one of the largest bacterial genomes and an exceptionally large proportion of regulatory genes therein. It has been known for more than a decade that the size and complexity of the P. aeruginosa genome is responsible for the adaptability and resilience of the bacteria to include its ability to resist many disinfectants and antibiotics. We have investigated the susceptibility of P. aeruginosa bacterial biofilms to iron oxide (magnetite) nanoparticles (NPs) with and without attached drug (tobramycin). We also characterized the susceptibility of zero-valent iron NPs, which are known to inactivate microbes. The particles, having an average diameter of 16 nm were capped with natural alginate, thus doubling the hydrodynamic size. Nanoparticle-drug conjugates were produced via cross-linking drug and alginate functional groups. Drug conjugates were investigated in the interest of determining dosage, during these dosage-curve experiments, NPs unbound to drug were tested in cultures as a negative control. Surprisingly, we found that the iron oxide NPs inhibited bacterial growth, and thus, biofilm formation without the addition of antibiotic drug. The inhibitory dosages of iron oxide NPs were investigated and the minimum inhibitory concentrations are presented. These findings suggest that NP-drug conjugates may overcome the antibiotic drug resistance common in P. aeruginosa infections.

  1. A Diatom Ferritin Optimized for Iron Oxidation but Not Iron Storage*

    PubMed Central

    Pfaffen, Stephanie; Bradley, Justin M.; Abdulqadir, Raz; Firme, Marlo R.; Moore, Geoffrey R.; Le Brun, Nick E.; Murphy, Michael E. P.

    2015-01-01

    Ferritin from the marine pennate diatom Pseudo-nitzschia multiseries (PmFTN) plays a key role in sustaining growth in iron-limited ocean environments. The di-iron catalytic ferroxidase center of PmFTN (sites A and B) has a nearby third iron site (site C) in an arrangement typically observed in prokaryotic ferritins. Here we demonstrate that Glu-44, a site C ligand, and Glu-130, a residue that bridges iron bound at sites B and C, limit the rate of post-oxidation reorganization of iron coordination and the rate at which Fe3+ exits the ferroxidase center for storage within the mineral core. The latter, in particular, severely limits the overall rate of iron mineralization. Thus, the diatom ferritin is optimized for initial Fe2+ oxidation but not for mineralization, pointing to a role for this protein in buffering iron availability and facilitating iron-sparing rather than only long-term iron storage. PMID:26396187

  2. Effect of mineral particles containing iron on primary cultures of rabbit tracheal epithelial cells: possible implication of oxidative stress.

    PubMed Central

    Guilianelli, C; Baeza-Squiban, A; Boisvieux-Ulrich, E; Houcine, O; Zalma, R; Guennou, C; Pezerat, H; Marano, F

    1993-01-01

    Environmental mineral particles such as asbestos are responsible for numerous respiratory diseases. In addition to effects related to their geometry, particles are now assumed to act by triggering an oxidative stress process. Iron-containing particles, in particular, can produce oxygen-activated species by oxidizing their iron. To evaluate the involvement of iron-containing particles in respiratory diseases, three mineral particles (chrysotile, nemalite, and hematite) were tested in primary cultures of tracheal epithelium. Because of the ciliary beat, the three mineral particles were quickly concentrated at the periphery of the mucociliary epithelium, reconstituted in vitro where they induced cellular lesions. Endocytosis of the three types of particles was observed. Cytotoxicity studies have indicated that among the tested particles, the most cytostatic after 24 hr of treatment was the one that contained more Fe2+ available on the surface, nemalite. Moreover, the effect of nemalite was reduced by pretreatment with desferrioxamine. As mineral particles, especially asbestos, are suspected to induce squamous metaplasia, we chose to study two specific transformations of the epithelium: the expression of cytokeratin-13 and the formation of cross-linked envelopes. Under our culture conditions, nemalite and chrysotile increased the expression of the cytokeratin-13, a specific marker of squamous metaplasia, whereas nemalite was the only particle able to strongly induce the formation of cross-linked envelopes. Nemalite was the most cytostatic particle and the most efficient at inducing squamous metaplasia. Measures of oxidizing power by electron-spin resonance revealed that nemalite produced the most oxygen-activated species.(ABSTRACT TRUNCATED AT 250 WORDS) Images Figure 1. Figure 2. a Figure 2. b Figure 2. c Figure 2. d Figure 2. e Figure 2. f Figure 3. a Figure 3. b Figure 3. c Figure 3. d Figure 4. Figure 5. a Figure 5. b Figure 5. c Figure 5. d Figure 6. PMID:8119255

  3. Protein Interactions Captured by Chemical Cross-linking: Simple Cross-linking Screen Using Sulfo-MBS.

    PubMed

    Nadeau, Owen W; Carlson, Gerald M

    2007-04-01

    INTRODUCTIONThis protocol describes a method for chemical cross-linking of proteins using sulfo-MBS (m-maleimidobenzoyl-N-hydroxysulfo-succinimide ester). Optimal conditions for cross-linking can be determined rapidly for a fixed concentration of a protein complex by varying the time of cross-linking, pH of the reaction, and concentration of sulfo-MBS. Typically, these screens require only small amounts of target proteins and can be carried out in less than a day.

  4. Insight into the evolution of the iron oxidation pathways.

    PubMed

    Ilbert, Marianne; Bonnefoy, Violaine

    2013-02-01

    Iron is a ubiquitous element in the universe. Ferrous iron (Fe(II)) was abundant in the primordial ocean until the oxygenation of the Earth's atmosphere led to its widespread oxidation and precipitation. This change of iron bioavailability likely put selective pressure on the evolution of life. This element is essential to most extant life forms and is an important cofactor in many redox-active proteins involved in a number of vital pathways. In addition, iron plays a central role in many environments as an energy source for some microorganisms. This review is focused on Fe(II) oxidation. The fact that the ability to oxidize Fe(II) is widely distributed in Bacteria and Archaea and in a number of quite different biotopes suggests that the dissimilatory Fe(II) oxidation is an ancient energy metabolism. Based on what is known today about Fe(II) oxidation pathways, we propose that they arose independently more than once in evolution and evolved convergently. The iron paleochemistry, the phylogeny, the physiology of the iron oxidizers, and the nature of the cofactors of the redox proteins involved in these pathways suggest a possible scenario for the timescale in which each type of Fe(II) oxidation pathways evolved. The nitrate dependent anoxic iron oxidizers are likely the most ancient iron oxidizers. We suggest that the phototrophic anoxic iron oxidizers arose in surface waters after the Archaea/Bacteria-split but before the Great Oxidation Event. The neutrophilic oxic iron oxidizers possibly appeared in microaerobic marine environments prior to the Great Oxidation Event while the acidophilic ones emerged likely after the advent of atmospheric O(2). This article is part of a Special Issue entitled: The evolutionary aspects of bioenergetic systems.

  5. Improving the mechanical and thermal properties of gelatin hydrogels cross-linked by cellulose nanowhiskers.

    PubMed

    Dash, Rajalaxmi; Foston, Marcus; Ragauskas, Arthur J

    2013-01-16

    This study demonstrates the preparation of a renewable and biocompatible hydrogel with superior mechanical properties consisting of a gelatin matrix cross-linked with oxidized cellulose nanowhiskers. We found an increased degree of chemical cross-linking (0.14-17%) between gelatin and nanowhiskers with the increased amount of aldehyde contents (0.062-0.230mmolg(-1)). (1)H nuclear magnetic resonance (NMR) T(2) relaxation experiments on D(2)O swollen hydrogels demonstrated systems consisting of both gelatin and cellulose nanowhiskers displayed a higher percentage of "ridge" protons, attributed in part to increasing chemical cross-linking junction points between gelatin and nanowhiskers. This increase in hydrogel rigidity not only modified local chain dynamics but also influenced gel swelling, showing relatively reduced water uptake ability than that of the neat gelatin. Rheological measurements confirmed a 150% improvement in storage modulus (G') of the cross-linked hydrogels compared to neat gelatin. Chemical cross-linking also increased the resistance of the gels towards thermal degradation above the melting temperature of gelatin as observed by thermal scanning experiments.

  6. Multi-Scale Modeling of Cross-Linked Nanotube Materials

    NASA Technical Reports Server (NTRS)

    Frankland, S. J. V.; Odegard, G. M.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

    2005-01-01

    The effect of cross-linking single-walled carbon nanotubes on the Young's modulus of a nanotube-reinforced composite is modeled with a multi-scale method. The Young's modulus is predicted as a function of nanotube volume fraction and cross-link density. In this method, the constitutive properties of molecular representative volume elements are determined using molecular dynamics simulation and equivalent-continuum modeling. The Young's modulus is subsequently calculated for cross-linked nanotubes in a matrix which consists of the unreacted cross-linking agent. Two different cross-linking agents are used in this study, one that is short and rigid (Molecule A), and one that is long and flexible (Molecule B). Direct comparisons between the predicted elastic constants are made for the models in which the nanotubes are either covalently bonded or not chemically bonded to the cross-linking agent. At a nanotube volume fraction of 10%, the Young's modulus of Material A is not affected by nanotube crosslinking, while the Young's modulus of Material B is reduced by 64% when the nanotubes are cross-linked relative to the non-cross-linked material with the same matrix.

  7. TRACE ELEMENT BINDING DURING STRUCTURAL TRANSFORMATION IN IRON OXIDES

    EPA Science Inventory

    Iron (hydr)oxides often control the mobility of inorganic contaminants in soils and sediments. A poorly ordered form of ferrihydrite is commonly produced during rapid oxidation of ferrous iron at sharp redox fronts encountered during discharge of anoxic/suboxic waters into terre...

  8. Modified Nanoemulsions with Iron Oxide for Magnetic Resonance Imaging

    PubMed Central

    Fan, Yongyi; Guo, Rui; Shi, Xiangyang; Allen, Steven; Cao, Zhengyi; Baker, James R.; Wang, Su He

    2016-01-01

    A nanoemulsion (NE) is a surfactant-based, oil-in-water, nanoscale, high-energy emulsion with a mean droplet diameter of 400–600 nm. When mixed with antigen and applied nasally, a NE acts as a mucosal adjuvant and induces mucosal immune responses. One possible mechanism for the adjuvant effect of this material is that it augments antigen uptake and distribution to lymphoid tissues, where the immune response is generated. Biocompatible iron oxide nanoparticles have been used as a unique imaging approach to study the dynamics of cells or molecular migration. To study the uptake of NEs and track them in vivo, iron oxide nanoparticles were synthesized and dispersed in soybean oil to make iron oxide-modified NEs. Our results show that iron oxide nanoparticles can be stabilized in the oil phase of the nanoemulsion at a concentration of 30 µg/μL and the iron oxide-modified NEs have a mean diameter of 521 nm. In vitro experiments demonstrated that iron oxide-modified NEs can affect uptake by TC-1 cells (a murine epithelial cell line) and reduce the intensity of magnetic resonance (MR) images by shortening the T2 time. Most importantly, in vivo studies demonstrated that iron oxide-modified NE could be detected in mouse nasal septum by both transmission electron microscopy and MR imaging. Altogether these experiments demonstrate that iron oxide-modified NE is a unique tool that can be used to study uptake and distribution of NEs after nasal application. PMID:28335351

  9. Uptake And Intracellular Distribution Of Functionalized Iron Oxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Panariti, A.; Lettiero, B.; Morjan, I.; Alexandreascu, R.; Wang, D.; Bucci, C.; Miserocchi, G.; Rivolta, I.

    2010-10-01

    Iron oxide Nanoparticles represents promising nanocarrier for magnetic resonance imaging (MRI), targeted drug and gene delivery. In our study we investigated the interaction between lung alveolar epithelial cells and iron oxide NPs coated with L-Dihydroxyphenylalanina (L-Dopa)-TRITC. Our data suggest that particles crossed the plasma membrane with an energy-dependent process.

  10. Cross-linked polyvinyl alcohol and method of making same

    NASA Technical Reports Server (NTRS)

    Hsu, L. C.; Sheibley, D. W.; Philipp, W. H. (Inventor)

    1981-01-01

    A film-forming polyvinyl alcohol polymer is mixed with a polyaldehyde-polysaccharide cross-linking agent having at least two monosaccharide units and a plurality of aldehyde groups per molecule, perferably an average of at least one aldehyde group per monosaccharide units. The cross-linking agent, such as a polydialdehyde starch, is used in an amount of about 2.5 to 20% of the theoretical amount required to cross-link all of the available hydroxyl groups of the polyvinyl alcohol polymer. Reaction between the polymer and cross-linking agent is effected in aqueous acidic solution to produce the cross-linked polymer. The polymer product has low electrical resistivity and other properties rendering it suitable for making separators for alkaline batteries.

  11. Ecological succession among iron-oxidizing bacteria.

    PubMed

    Fleming, Emily J; Cetinić, Ivona; Chan, Clara S; Whitney King, D; Emerson, David

    2014-04-01

    Despite over 125 years of study, the factors that dictate species dominance in neutrophilic iron-oxidizing bacterial (FeOB) communities remain unknown. In a freshwater wetland, we documented a clear ecological succession coupled with niche separation between the helical stalk-forming Gallionellales (for example, Gallionella ferruginea) and tubular sheath-forming Leptothrix ochracea. Changes in the iron-seep community were documented using microscopy and cultivation-independent methods. Quantification of Fe-oxyhydroxide morphotypes by light microscopy was coupled with species-specific fluorescent in situ hybridization (FISH) probes using a protocol that minimized background fluorescence caused by the Fe-oxyhydroxides. Together with scanning electron microscopy, these techniques all indicated that Gallionellales dominated during early spring, with L. ochracea becoming more abundant for the remainder of the year. Analysis of tagged pyrosequencing reads of the small subunit ribosomal RNA gene (SSU rRNA) collected during seasonal progression supported a clear Gallionellales to L. ochracea transition, and community structure grouped according to observed dominant FeOB forms. Axis of redundancy analysis of physicochemical parameters collected from iron mats during the season, plotted with FeOB abundance, corroborated several field and microscopy-based observations and uncovered several unanticipated relationships. On the basis of these relationships, we conclude that the ecological niche of the stalk-forming Gallionellales is in waters with low organic carbon and steep redoxclines, and the sheath-forming L. ochracea is abundant in waters that contain high concentrations of complex organic carbon, high Fe and Mn content and gentle redoxclines. Finally, these findings identify a largely unexplored relationship between FeOB and organic carbon.

  12. Ecological succession among iron-oxidizing bacteria

    PubMed Central

    Fleming, Emily J; Cetinić, Ivona; Chan, Clara S; Whitney King, D; Emerson, David

    2014-01-01

    Despite over 125 years of study, the factors that dictate species dominance in neutrophilic iron-oxidizing bacterial (FeOB) communities remain unknown. In a freshwater wetland, we documented a clear ecological succession coupled with niche separation between the helical stalk-forming Gallionellales (for example, Gallionella ferruginea) and tubular sheath-forming Leptothrix ochracea. Changes in the iron-seep community were documented using microscopy and cultivation-independent methods. Quantification of Fe-oxyhydroxide morphotypes by light microscopy was coupled with species-specific fluorescent in situ hybridization (FISH) probes using a protocol that minimized background fluorescence caused by the Fe-oxyhydroxides. Together with scanning electron microscopy, these techniques all indicated that Gallionellales dominated during early spring, with L. ochracea becoming more abundant for the remainder of the year. Analysis of tagged pyrosequencing reads of the small subunit ribosomal RNA gene (SSU rRNA) collected during seasonal progression supported a clear Gallionellales to L. ochracea transition, and community structure grouped according to observed dominant FeOB forms. Axis of redundancy analysis of physicochemical parameters collected from iron mats during the season, plotted with FeOB abundance, corroborated several field and microscopy-based observations and uncovered several unanticipated relationships. On the basis of these relationships, we conclude that the ecological niche of the stalk-forming Gallionellales is in waters with low organic carbon and steep redoxclines, and the sheath-forming L. ochracea is abundant in waters that contain high concentrations of complex organic carbon, high Fe and Mn content and gentle redoxclines. Finally, these findings identify a largely unexplored relationship between FeOB and organic carbon. PMID:24225888

  13. Bio-inspired Iron Catalysts for Hydrocarbon Oxidations

    SciTech Connect

    Que, Jr., Lawrence

    2016-03-22

    Stereoselective oxidation of C–H and C=C bonds are catalyzed by nonheme iron enzymes. Inspired by these bioinorganic systems, our group has been exploring the use of nonheme iron complexes as catalysts for the oxidation of hydrocarbons using H2O2 as an environmentally friendly and atom-efficient oxidant in order to gain mechanistic insights into these novel transformations. In particular, we have focused on clarifying the nature of the high-valent iron oxidants likely to be involved in these transformations.

  14. Iron oxide nanoparticle enhancement of radiation cytotoxicity

    NASA Astrophysics Data System (ADS)

    Mazur, Courtney M.; Tate, Jennifer A.; Strawbridge, Rendall R.; Gladstone, David J.; Hoopes, P. Jack

    2013-02-01

    Iron oxide nanoparticles (IONPs) have been investigated as a promising means for inducing tumor cell-specific hyperthermia. Although the ability to generate and use nanoparticles that are biocompatible, tumor specific, and have the ability to produce adequate cytotoxic heat is very promising, significant preclinical and clinical development will be required for clinical efficacy. At this time it appears using IONP-induced hyperthermia as an adjunct to conventional cancer therapeutics, rather than as an independent treatment, will provide the initial IONP clinical treatment. Due to their high-Z characteristics, another option is to use intracellular IONPs to enhance radiation therapy without excitation with AMF (production of heat). To test this concept IONPs were added to cell culture media at a concentration of 0.2 mg Fe/mL and incubated with murine breast adenocarcinoma (MTG-B) cells for either 48 or 72 hours. Extracellular iron was then removed and all cells were irradiated at 4 Gy. Although samples incubated with IONPs for 48 hrs did not demonstrate enhanced post-irradiation cytotoxicity as compared to the non-IONP-containing cells, cells incubated with IONPs for 72 hours, which contained 40% more Fe than 48 hr incubated cells, showed a 25% decrease in clonogenic survival compared to their non-IONP-containing counterparts. These results suggest that a critical concentration of intracellular IONPs is necessary for enhancing radiation cytotoxicity.

  15. Oxidation inhibits iron-induced blood coagulation.

    PubMed

    Pretorius, Etheresia; Bester, Janette; Vermeulen, Natasha; Lipinski, Boguslaw

    2013-01-01

    Blood coagulation under physiological conditions is activated by thrombin, which converts soluble plasma fibrinogen (FBG) into an insoluble clot. The structure of the enzymatically-generated clot is very characteristic being composed of thick fibrin fibers susceptible to the fibrinolytic degradation. However, in chronic degenerative diseases, such as atherosclerosis, diabetes mellitus, cancer, and neurological disorders, fibrin clots are very different forming dense matted deposits (DMD) that are not effectively removed and thus create a condition known as thrombosis. We have recently shown that trivalent iron (ferric ions) generates hydroxyl radicals, which subsequently convert FBG into abnormal fibrin clots in the form of DMDs. A characteristic feature of DMDs is their remarkable and permanent resistance to the enzymatic degradation. Therefore, in order to prevent thrombotic incidences in the degenerative diseases it is essential to inhibit the iron-induced generation of hydroxyl radicals. This can be achieved by the pretreatment with a direct free radical scavenger (e.g. salicylate), and as shown in this paper by the treatment with oxidizing agents such as hydrogen peroxide, methylene blue, and sodium selenite. Although the actual mechanism of this phenomenon is not yet known, it is possible that hydroxyl radicals are neutralized by their conversion to the molecular oxygen and water, thus inhibiting the formation of dense matted fibrin deposits in human blood.

  16. Microbially Induced Iron Oxidation: What, Where, How

    SciTech Connect

    SCHIERMEYER,ELISA M.; PROVENCIO,PAULA P.; NORTHUP,DIANA E.

    2000-08-15

    From the results of the different bacterial cells seen, it is fairly certain that Gallionella is present because of the bean-shaped cells and twisted stalks found with the TEM. The authors cannot confirm, though, what other iron-oxidizing genera exist in the tubes, since the media was only preferential and not one that isolated a specific genus of bacteria. Based on the environment in which they live and the source of the water, they believe their cultures contain Gallionella, Leptothrix, and possibly Crenothrix and Sphaerotilus. They believe the genus Leptothrix rather than Sphaerotilus exist in the tubes because the water source was fresh, unlike the polluted water in which Sphaerotilus are usually found. The TEM preparations worked well. The cryogenic method rapidly froze the cells in place and allowed them to view their morphology. The FAA method, as stated previously, was the best of the three methods because it gave the best contrast. The gluteraldehyde samples did not come out as well. It is possible that the gluteraldehyde the authors prepared was still too concentrated and did not mix well. Although these bacteria were collected from springs and then cultured in an environment containing a presumably pure iron-bearing metal, it seems the tube already containing Manganese Gradient Medium could be used with a piece of metal containing these bacteria. A small piece of corroding metal could then be inserted into the test tube and cultured to study the bacteria.

  17. Multifunctional iron oxide nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Bloemen, M.; Denis, C.; Van Stappen, T.; De Meester, L.; Geukens, N.; Gils, A.; Verbiest, T.

    2015-03-01

    Multifunctional nanoparticles have attracted a lot of attention since they can combine interesting properties like magnetism, fluorescence or plasmonic effects. As a core material, iron oxide nanoparticles have been the subject of intensive research. These cost-effective and non-toxic particles are used nowadays in many applications. We developed a heterobifunctional PEG ligand that can be used to introduce functional groups (carboxylic acids) onto the surface of the NP. Via click chemistry, a siloxane functionality was added to this ligand, for a subsequent covalent ligand exchange reaction. The functionalized nanoparticles have an excellent colloidal stability in complex environments like buffers and serum or plasma. Antibodies were coupled to the introduced carboxylic acids and these NP-antibody bioconjugates were brought into contact with Legionella bacteria for magnetic separation experiments.

  18. Biocompatible multishell architecture for iron oxide nanoparticles.

    PubMed

    Wotschadlo, Jana; Liebert, Tim; Clement, Joachim H; Anspach, Nils; Höppener, Stephanie; Rudolph, Tobias; Müller, Robert; Schacher, Felix H; Schubert, Ulrich S; Heinze, Thomas

    2013-01-01

    The coating of super-paramagnetic iron oxide nanoparticles (SPIONs) with multiple shells is demonstrated by building a layer assembled from carboxymethyldextran and poly(diallydimethylammonium chloride). Three shells are produced stepwise around aggregates of SPIONs by the formation of a polyelectrolyte complex. A growing particle size from 96 to 327 nm and a zeta potential in the range of +39 to -51 mV are measured. Microscopic techniques such as TEM, SEM, and AFM exemplify the core-shell structures. Magnetic force microscopy and vibrating sample magnetometer measurements confirm the architecture of the multishell particles. Cell culture experiments show that even nanoparticles with three shells are still taken up by cells.

  19. Multiple hearth furnace for reducing iron oxide

    DOEpatents

    Brandon, Mark M [Charlotte, NC; True, Bradford G [Charlotte, NC

    2012-03-13

    A multiple moving hearth furnace (10) having a furnace housing (11) with at least two moving hearths (20) positioned laterally within the furnace housing, the hearths moving in opposite directions and each moving hearth (20) capable of being charged with at least one layer of iron oxide and carbon bearing material at one end, and being capable of discharging reduced material at the other end. A heat insulating partition (92) is positioned between adjacent moving hearths of at least portions of the conversion zones (13), and is capable of communicating gases between the atmospheres of the conversion zones of adjacent moving hearths. A drying/preheat zone (12), a conversion zone (13), and optionally a cooling zone (15) are sequentially positioned along each moving hearth (30) in the furnace housing (11).

  20. Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions

    NASA Astrophysics Data System (ADS)

    Scholz, Florian; Löscher, Carolin R.; Fiskal, Annika; Sommer, Stefan; Hensen, Christian; Lomnitz, Ulrike; Wuttig, Kathrin; Göttlicher, Jörg; Kossel, Elke; Steininger, Ralph; Canfield, Donald E.

    2016-11-01

    Iron is an essential element for life on Earth and limits primary production in large parts of the ocean. Oxygen-free continental margin sediments represent an important source of bioavailable iron to the ocean, yet little of the iron released from the seabed reaches the productive sea surface. Even in the anoxic water of oxygen minimum zones, where iron solubility should be enhanced, most of the iron is rapidly re-precipitated. To constrain the mechanism(s) of iron removal in anoxic ocean regions we explored the sediment and water in the oxygen minimum zone off Peru. During our sampling campaign the water column featured two distinct redox boundaries separating oxic from nitrate-reducing (i.e., nitrogenous) water and nitrogenous from weakly sulfidic water. The sulfidic water mass in contact with the shelf sediment contained elevated iron concentrations >300 nM. At the boundary between sulfidic and nitrogenous conditions, iron concentrations dropped sharply to <20 nM coincident with a maximum in particulate iron concentration. Within the iron gradient, we found an increased expression of the key functional marker gene for nitrate reduction (narG). Part of this upregulation was related to the activity of known iron-oxidizing bacteria. Collectively, our data suggest that iron oxidation and removal is induced by nitrate-reducing microbes, either enzymatically through anaerobic iron oxidation or by providing nitrite for an abiotic reaction. Given the important role that iron plays in nitrogen fixation, photosynthesis and respiration, nitrate-dependent iron oxidation likely represents a key-link between the marine biogeochemical cycles of nitrogen, oxygen and carbon.

  1. Elasticity of cross-linked semiflexible biopolymers under tension.

    PubMed

    von der Heydt, Alice; Wilkin, Daniel; Benetatos, Panayotis; Zippelius, Annette

    2013-09-01

    Aiming at the mechanical properties of cross-linked biopolymers, we set up and analyze a model of two weakly bending wormlike chains subjected to a tensile force, with regularly spaced inter-chain bonds (cross-links) represented by harmonic springs. Within this model, we compute the force-extension curve and the differential stiffness exactly and discuss several limiting cases. Cross-links effectively stiffen the chain pair by reducing thermal fluctuations transverse to the force and alignment direction. The extra alignment due to cross-links increases both with growing number and with growing strength of the cross-links, and is most prominent for small force f. For large f, the additional, cross-link-induced extension is subdominant except for the case of linking the chains rigidly and continuously along their contour. In this combined limit, we recover asymptotically the elasticity of a weakly bending wormlike chain without constraints, stiffened by a factor of 4. The increase in differential stiffness can be as large as 100% for small f or large numbers of cross-links.

  2. Effects of iron chelators, iron salts, and iron oxide nanoparticles on the proliferation and the iron content of oligodendroglial OLN-93 cells.

    PubMed

    Hohnholt, Michaela; Geppert, Mark; Dringen, Ralf

    2010-08-01

    The oligodendroglial cell line OLN-93 was used as model system to investigate the consequences of iron deprivation or iron excess on cell proliferation. Presence of ferric or ferrous iron chelators inhibited the proliferation of OLN-93 cells in a time and concentration dependent manner, while the application of a molar excess of ferric ammonium citrate (FAC) prevented the inhibition of proliferation by the chelator deferoxamine. Proliferation of OLN-93 cells was not affected by incubation with 300 microM iron that was applied in the form of FAC, FeCl(2), ferrous ammonium sulfate or iron oxide nanoparticles, although the cells efficiently accumulated iron during exposure to each of these iron sources. The highest specific iron content was observed for cells that were exposed to the nanoparticles. These data demonstrate that the proliferation of OLN-93 cells depends strongly on the availability of iron and that these cells efficiently accumulate iron from various extracellular iron sources.

  3. Kinetics of enzyme-catalyzed cross-linking of feruloylated arabinan from sugar beet.

    PubMed

    Zaidel, Dayang Norulfairuz Abang; Arnous, Anis; Holck, Jesper; Meyer, Anne S

    2011-11-09

    Ferulic acid (FA) groups esterified to the arabinan side chains of pectic polysaccharides can be oxidatively cross-linked in vitro by horseradish peroxidase (HRP) catalysis in the presence of hydrogen peroxide (H(2)O(2)) to form ferulic acid dehydrodimers (diFAs). The present work investigated whether the kinetics of HRP catalyzed cross-linking of FA esterified to α-(1,5)-linked arabinans are affected by the length of the arabinan chains carrying the feruloyl substitutions. The kinetics of the HRP-catalyzed cross-linking of four sets of arabinan samples from sugar beet pulp, having different molecular weights and hence different degrees of polymerization, were monitored by the disappearance of FA absorbance at 316 nm. MALDI-TOF/TOF-MS analysis confirmed that the sugar beet arabinans were feruloyl-substituted, and HPLC analysis verified that the amounts of diFAs increased when FA levels decreased as a result of the enzymatic oxidation treatment with HRP and H(2)O(2). At equimolar levels of FA (0.0025-0.05 mM) in the arabinan samples, the initial rates of the HRP-catalyzed cross-linking of the longer chain arabinans were slower than those of the shorter chain arabinans. The lower initial rates may be the result of the slower movement of larger molecules coupled with steric phenomena, making the required initial reaction of two FAs on longer chain arabinans slower than on shorter arabinans.

  4. Iron Oxide as an MRI Contrast Agent for Cell Tracking

    PubMed Central

    Korchinski, Daniel J.; Taha, May; Yang, Runze; Nathoo, Nabeela; Dunn, Jeff F.

    2015-01-01

    Iron oxide contrast agents have been combined with magnetic resonance imaging for cell tracking. In this review, we discuss coating properties and provide an overview of ex vivo and in vivo labeling of different cell types, including stem cells, red blood cells, and monocytes/macrophages. Furthermore, we provide examples of applications of cell tracking with iron contrast agents in stroke, multiple sclerosis, cancer, arteriovenous malformations, and aortic and cerebral aneurysms. Attempts at quantifying iron oxide concentrations and other vascular properties are examined. We advise on designing studies using iron contrast agents including methods for validation. PMID:26483609

  5. “Zero-length” cross-linking in solid state as an approach for analysis of protein–protein interactions

    PubMed Central

    El-Shafey, Ahmed; Tolic, Nikola; Young, Malin M.; Sale, Kenneth; Smith, Richard D.; Kery, Vladimir

    2006-01-01

    We have developed a new approach for the analysis of interacting interfaces in protein complexes and protein quaternary structure based on cross-linking in the solid state. Protein complexes are freeze-dried under vacuum, and cross-links are introduced in the solid phase by dehydrating the protein in a nonaqueous solvent creating peptide bonds between amino and carboxyl groups of the interacting peptides. Cross-linked proteins are digested into peptides with trypsin in both H216O and H218O and then readily distinguished in mass spectra by characteristic 8 atomic mass unit (amu) shifts reflecting incorporation of two 18O atoms into each C terminus of proteolytic peptides. Computer analysis of mass spectrometry (MS) and MS/MS data is used to identify the cross-linked peptides. We demonstrated specificity and reproducibility of our method by cross-linking homo-oligomeric protein complexes of glutathione-S-transferase (GST) from Schistosoma japonicum alone or in a mixture of many other proteins. Identified cross-links were predominantly of amide origin, but six esters and thioesters were also found. The cross-linked peptides were validated against the GST monomer and dimer X-ray structures and by experimental (MS/MS) analyses. Some of the identified cross-links matched interacting peptides in the native 3D structure of GST, indicating that the structure of GST and its oligomeric complex remained primarily intact after freeze-drying. The pattern of oligomeric GST obtained in solid state was the same as that obtained in solution by Ru (II) Bpy32+ catalyzed, oxidative “zero-length” cross-linking, confirming that it is feasible to use our strategy for analyzing the molecular interfaces of interacting proteins or peptides. PMID:16501223

  6. Studies of the kinetics and mechanisms of perfluoroether reactions on iron and oxidized iron surfaces

    NASA Technical Reports Server (NTRS)

    Napier, Mary E.; Stair, Peter C.

    1992-01-01

    Polymeric perfluoroalkylethers are being considered for use as lubricants in high temperature applications, but have been observed to catalytically decompose in the presence of metals. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) were used to explore the decomposition of three model fluorinated ethers on clean polycrystalline iron surfaces and iron surfaces chemically modified with oxygen. Low temperature adsorption of the model fluorinated ethers on the clean, oxygen modified and oxidized iron surfaces was molecular. Thermally activated defluorination of the three model compounds was observed on the clean iron surface at remarkably low temperatures, 155 K and below, with formation of iron fluoride. Preferential C-F bond scission occurred at the terminal fluoromethoxy, CF3O, of perfluoro-1-methoxy-2-ethoxy ethane and perfluoro-1-methoxy-2-ethoxy propane and at CF3/CF2O of perfluoro-1,3-diethoxy propane. The reactivity of the clean iron toward perfluoroalkylether decomposition when compared to other metals is due to the strength of the iron fluoride bond and the strong electron donating ability of the metallic iron. Chemisorption of an oxygen overlayer lowered the reactivity of the iron surface to the adsorption and decomposition of the three model fluorinated ethers by blocking active sites on the metal surface. Incomplete coverage of the iron surface with chemisorbed oxygen results in a reaction which resembles the defluorination reaction observed on the clean iron surface. Perfluoro-1-methoxy-2-ethoxy ethane reacts on the oxidized iron surface at 138 K, through a Lewis acid assisted cleavage of the carbon oxygen bond, with preferential attack at the terminal fluoromethoxy, CF3O. The oxidized iron surface did not passivate, but became more reactive with time. Perfluoro-1-methoxy-2-ethoxy propane and perfluoro-1,3-diethoxy propane desorbed prior to the observation of decomposition on the oxidized iron surface.

  7. Magnetization measurements and XMCD studies on ion irradiated iron oxide and core-shell iron/iron-oxide nanomaterials

    SciTech Connect

    Kaur, Maninder; Qiang, You; Jiang, Weilin; Pearce, Carolyn; McCloy, John S.

    2014-12-02

    Magnetite (Fe3O4) and core-shell iron/iron-oxide (Fe/Fe3O4) nanomaterials prepared by a cluster deposition system were irradiated with 5.5 MeV Si2+ ions and the structures determined by x-ray diffraction as consisting of 100% magnetite and 36/64 wt% Fe/FeO, respectively. However, x-ray magnetic circular dichroism (XMCD) indicates similar surfaces in the two samples, slightly oxidized and so having more Fe3+ than the expected magnetite structure, with XMCD intensity much lower for the irradiated core-shell samples indicating weaker magnetism. X-ray absorption spectroscopy (XAS) data lack the signature for FeO, but the irradiated core-shell system consists of Fe-cores with ~13 nm of separating oxide crystallite, so it is likely that FeO exists deeper than the probe depth of the XAS (~5 nm). Exchange bias (Hex) for both samples becomes increasingly negative as temperature is lowered, but the irradiated Fe3O4 sample shows greater sensitivity of cooling field on Hex. Loop asymmetries and Hex sensitivities of the irradiated Fe3O4 sample are due to interfaces and interactions between grains which were not present in samples before irradiation as well as surface oxidation. Asymmetries in the hysteresis curves of the irradiated core/shell sample are related to the reversal mechanism of the antiferromagnetic FeO and possibly some near surface oxidation.

  8. Investigation of oxidation process of mechanically activated ultrafine iron powders

    NASA Astrophysics Data System (ADS)

    Lysenko, E. N.; Nikolaev, E. V.; Vlasov, V. A.; Zhuravkov, S. P.

    2016-02-01

    The oxidation of mechanically activated ultrafine iron powders was studied using X- ray powder diffraction and thermogravimetric analyzes. The powders with average particles size of 100 nm were made by the electric explosion of wire, and were subjected to mechanical activation in planetary ball mill for 15 and 40 minutes. It was shown that a certain amount of FeO phase is formed during mechanical activation of ultrafine iron powders. According to thermogravimetric analysis, the oxidation process of non-milled ultrafine iron powders is a complex process and occurs in three stages. The preliminary mechanical activation of powders considerably changes the nature of the iron powders oxidation, leads to increasing in the temperature of oxidation onset and shifts the reaction to higher temperatures. For the milled powders, the oxidation is more simple process and occurs in a single step.

  9. Nitric Oxide Improves Internal Iron Availability in Plants1

    PubMed Central

    Graziano, Magdalena; Beligni, María Verónica; Lamattina, Lorenzo

    2002-01-01

    Iron deficiency impairs chlorophyll biosynthesis and chloroplast development. In leaves, most of the iron must cross several biological membranes to reach the chloroplast. The components involved in the complex internal iron transport are largely unknown. Nitric oxide (NO), a bioactive free radical, can react with transition metals to form metal-nitrosyl complexes. Sodium nitroprusside, an NO donor, completely prevented leaf interveinal chlorosis in maize (Zea mays) plants growing with an iron concentration as low as 10 μm Fe-EDTA in the nutrient solution. S-Nitroso-N-acetylpenicillamine, another NO donor, as well as gaseous NO supply in a translucent chamber were also able to revert the iron deficiency symptoms. A specific NO scavenger, 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, blocked the effect of the NO donors. The effect of NO treatment on the photosynthetic apparatus of iron-deficient plants was also studied. Electron micrographs of mesophyll cells from iron-deficient maize plants revealed plastids with few photosynthetic lamellae and rudimentary grana. In contrast, in NO-treated maize plants, mesophyll chloroplast appeared completely developed. NO treatment did not increase iron content in plant organs, when expressed in a fresh matter basis, suggesting that root iron uptake was not enhanced. NO scavengers 2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and methylene blue promoted interveinal chlorosis in iron-replete maize plants (growing in 250 μm Fe-EDTA). Even though results support a role for endogenous NO in iron nutrition, experiments did not establish an essential role. NO was also able to revert the chlorotic phenotype of the iron-inefficient maize mutants yellow stripe1 and yellow stripe3, both impaired in the iron uptake mechanisms. All together, these results support a biological action of NO on the availability and/or delivery of metabolically active iron within the plant. PMID:12481068

  10. Cross-linking of bovine and caprine caseins by microbial transglutaminase and their use as microencapsulating agents for n-3 fatty acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Bovine and caprine caseins were cross-linked with microbial transglutaminase (mTG). The mTG-cross-linked bovine or caprine casein dispersion, mixed with 14.5% maltodextrin (DE = 40), was used to prepare emulsions with 10.5% algae oil. Oxidative stability of emulsions was evaluated by peroxide valu...

  11. Gelation threshold of cross-linked polymer brushes.

    PubMed

    Hoffmann, Max; Lang, Michael; Sommer, Jens-Uwe

    2011-02-01

    The cross-linking of polymer brushes is studied using the bond-fluctuation model. By mapping the cross-linking process into a two-dimensional (2D) percolation problem within the lattice of grafting points, we investigate the gelation transition in detail. We show that the particular properties of cross-linked polymer brushes can be reduced to the distribution of bonds which are formed between the grafted chains, and we propose scaling arguments to relate the gelation threshold to the chain length and the grafting density. The gelation threshold is lower than the percolation threshold for 2D bond percolation because of the longer range and broad distribution of bonds formed by the cross-linking process. We term this type of percolation problem star percolation. We observe a broad crossover from mean-field to critical percolation behavior by analyzing the cluster size distribution near the gelation threshold.

  12. Photoreactivities and thermal properties of psoralen cross-links

    SciTech Connect

    Yeung, A.T.; Jones, B.K.; Chu, C.T.

    1988-05-03

    The authors have studied the photoreaction of 8-methoxypsoralen (8-MOP), 4,5',8-trimethylpsoralen (TMP), and 4'-(hydroxymethyl)-4,5',8-trimethylpsoralen (HMT) with a pair of 18-base-long oligonucleotides in which a 14-base region is complementary. Only one 5'TpA site, favored for both monoadduct and cross-link formation with psoralen, is present in this oligonucleotide pair. They have used this model system to demonstrate, for the first time, strand specificity in the photoreaction of psoralen with DNA. They found that the two types of cross-links which form at this site have large differences in thermal stabilities. In addition, the denaturation of each cross-links isomer duplex occurred in at least three stages, which can be visualized as three bands in thermal equilibrium under the conditions of a denaturing polyacrylamide gel. This novel observation suggests that there are several domains differing in thermal stability in a psoralen cross-link.

  13. Application of novel iron core/iron oxide shell nanoparticles to sentinel lymph node identification

    NASA Astrophysics Data System (ADS)

    Cousins, Aidan; Howard, Douglas; Henning, Anna M.; Nelson, Melanie R. M.; Tilley, Richard D.; Thierry, Benjamin

    2015-12-01

    Current `gold standard' staging of breast cancer and melanoma relies on accurate in vivo identification of the sentinel lymph node. By replacing conventional tracers (dyes and radiocolloids) with magnetic nanoparticles and using a handheld magnetometer probe for in vivo identification, it is believed the accuracy of sentinel node identification in nonsuperficial cancers can be improved due to increased spatial resolution of magnetometer probes and additional anatomical information afforded by MRI road-mapping. By using novel iron core/iron oxide shell nanoparticles, the sensitivity of sentinel node mapping via MRI can be increased due to an increased magnetic saturation compared to traditional iron oxide nanoparticles. A series of in vitro magnetic phantoms (iron core vs. iron oxide nanoparticles) were prepared to simulate magnetic particle accumulation in the sentinel lymph node. A novel handheld magnetometer probe was used to measure the relative signals of each phantom, and determine if clinical application of iron core particles can improve in vivo detection of the sentinel node compared to traditional iron oxide nanoparticles. The findings indicate that novel iron core nanoparticles above a certain size possess high magnetic saturation, but can also be produced with low coercivity and high susceptibility. While some modification to the design of handheld magnetometer probes may be required for particles with large coercivity, use of iron core particles could improve MRI and magnetometer probe detection sensitivity by up to 330 %.

  14. Diepoxybutane cross-links DNA at 5'-GNC sequences.

    PubMed

    Millard, J T; White, M M

    1993-03-02

    Epoxides are cancer-causing agents chemically analogous to the nitrogen mustards, a family of powerful antitumor drugs. We found that the DNA interstrand cross-linking sequence preference of diepoxybutane is the same as that of the mustard mechlorethamine: 5'-GNC. Therefore, the genomic site of cross-linking alone cannot explain why some interstrand cross-linkers act as antitumor agents whereas others are deadly toxins.

  15. Large Scale Chemical Cross-linking Mass Spectrometry Perspectives

    PubMed Central

    Zybailov, Boris L.; Glazko, Galina V.; Jaiswal, Mihir; Raney, Kevin D.

    2014-01-01

    The spectacular heterogeneity of a complex protein mixture from biological samples becomes even more difficult to tackle when one’s attention is shifted towards different protein complex topologies, transient interactions, or localization of PPIs. Meticulous protein-by-protein affinity pull-downs and yeast-two-hybrid screens are the two approaches currently used to decipher proteome-wide interaction networks. Another method is to employ chemical cross-linking, which gives not only identities of interactors, but could also provide information on the sites of interactions and interaction interfaces. Despite significant advances in mass spectrometry instrumentation over the last decade, mapping Protein-Protein Interactions (PPIs) using chemical cross-linking remains time consuming and requires substantial expertise, even in the simplest of systems. While robust methodologies and software exist for the analysis of binary PPIs and also for the single protein structure refinement using cross-linking-derived constraints, undertaking a proteome-wide cross-linking study is highly complex. Difficulties include i) identifying cross-linkers of the right length and selectivity that could capture interactions of interest; ii) enrichment of the cross-linked species; iii) identification and validation of the cross-linked peptides and cross-linked sites. In this review we examine existing literature aimed at the large-scale protein cross-linking and discuss possible paths for improvement. We also discuss short-length cross-linkers of broad specificity such as formaldehyde and diazirine-based photo-cross-linkers. These cross-linkers could potentially capture many types of interactions, without strict requirement for a particular amino-acid to be present at a given protein-protein interface. How these shortlength, broad specificity cross-linkers be applied to proteome-wide studies? We will suggest specific advances in methodology, instrumentation and software that are needed to

  16. Neohemoglobins and Cross-Linked Hemoglobins as Blood Substitute.

    DTIC Science & Technology

    1982-12-01

    normal SFH. For bovine hemoglobi, cross-linking of the oxy and carboxy derivatives increased substantially the oxygen affinity and eliminated the oxygen...hemoglobins were prepared by the filtration method. The respective heme-free proteins (apohemoglobins) were prepared by extraction with methyl ...protein. Recombined neohemoglogins and cross-linked hemoglobins were purified by chromatography on CM cellulose using a linear gradient formed by equal

  17. A New Cross-Link for an Old Cross-Linking Drug: The Nitrogen Mustard Anticancer Agent Mechlorethamine Generates Cross-Links Derived from Abasic Sites in Addition to the Expected Drug-Bridged Cross-Links.

    PubMed

    Nejad, Maryam Imani; Johnson, Kevin M; Price, Nathan E; Gates, Kent S

    2016-12-20

    Nitrogen mustard anticancer drugs generate highly reactive aziridinium ions that alkylate DNA. Monoadducts arising from reaction with position N7 of guanine residues are the major DNA adducts generated by these agents. Interstrand cross-links in which the drug bridges position N7 of two guanine residues are formed in low yields relative to those of the monoadducts but are generally thought to be central to medicinal activity. The N7-alkylguanine residues generated by nitrogen mustards are depurinated to yield abasic (Ap) sites in duplex DNA. Here, we show that Ap sites generated by the nitrogen mustard mechlorethamine lead to interstrand cross-links of a type not previously associated with this drug. Gel electrophoretic data were consistent with early evolution of the expected drug-bridged cross-links, followed by the appearance of Ap-derived cross-links. The evidence is further consistent with a reaction pathway involving alkylation of a guanine residue in a 5'-GT sequence, followed by depurination to generate the Ap site, and cross-link formation via reaction of the Ap aldehyde residue with the opposing adenine residue at this site [Price, N. E., Johnson, K. M., Wang, J., Fekry, M. I., Wang, Y., and Gates, K. S. (2014) J. Am. Chem. Soc. 136, 3483-3490]. The monofunctional DNA-alkylating agents 2-chloro-N,N-diethylethanamine 5, (2-chloroethyl)ethylsulfide 6, and natural product leinamycin similarly were found to induce the formation of Ap-derived cross-links in duplex DNA. This work provides the first characterization of Ap-derived cross-links at sequences in which a cytosine residue is located directly opposing the Ap site. Cross-linking processes of this type could be relevant in medicine and biology because Ap sites with directly opposing cytosine residues occur frequently in genomic DNA via spontaneous or enzymatic depurination of guanine and N7-alkylguanine residues.

  18. Oxidative Stress and the Homeodynamics of Iron Metabolism

    PubMed Central

    Bresgen, Nikolaus; Eckl, Peter M.

    2015-01-01

    Iron and oxygen share a delicate partnership since both are indispensable for survival, but if the partnership becomes inadequate, this may rapidly terminate life. Virtually all cell components are directly or indirectly affected by cellular iron metabolism, which represents a complex, redox-based machinery that is controlled by, and essential to, metabolic requirements. Under conditions of increased oxidative stress—i.e., enhanced formation of reactive oxygen species (ROS)—however, this machinery may turn into a potential threat, the continued requirement for iron promoting adverse reactions such as the iron/H2O2-based formation of hydroxyl radicals, which exacerbate the initial pro-oxidant condition. This review will discuss the multifaceted homeodynamics of cellular iron management under normal conditions as well as in the context of oxidative stress. PMID:25970586

  19. Cross-linked polyelectrolyte multilayers for marine antifouling applications.

    PubMed

    Zhu, Xiaoying; Jańczewski, Dominik; Lee, Serina Siew Chen; Teo, Serena Lay-Ming; Vancso, G Julius

    2013-07-10

    A polyionic multilayer film was fabricated by layer-by-layer (LbL) sequential deposition followed by cross-linking under mild conditions on a substrate surface to inhibit marine fouling. A novel polyanion, featuring methyl ester groups for an easy cross-linking was used as a generic solution for stabilization of LbL films in a harsh environment. Covalent cross-linking was confirmed by FTIR and XPS spectroscopy. AFM was used to observe film morphology and its variation because of cross-linking, as well as to measure the thickness of the LbL films. Cross-linking improved the stability of the LbL film when it was immersed in artificial seawater, natural seawater, and in a polar organic solvent (DMSO). No changes in the thickness and topography of the film were observed in these media. The LbL films prevented settlement of Amphibalanus amphitrite barnacle cyprids and reduced adhesion of the benthic diatom Amphora coffeaeformis. Assay results indicated that the cross-linking process did not weaken the antifouling effect of LbL films. The high stability and low degree of fouling make these coatings potentially promising candidates in marine applications.

  20. Functional synergy of actin filament cross-linking proteins.

    PubMed

    Tseng, Yiider; Schafer, Benjamin W; Almo, Steven C; Wirtz, Denis

    2002-07-12

    The organization of filamentous actin (F-actin) in resilient networks is coordinated by various F-actin cross-linking proteins. The relative tolerance of cells to null mutations of genes that code for a single actin cross-linking protein suggests that the functions of those proteins are highly redundant. This apparent functional redundancy may, however, reflect the limited resolution of available assays in assessing the mechanical role of F-actin cross-linking/bundling proteins. Using reconstituted F-actin networks and rheological methods, we demonstrate how alpha-actinin and fascin, two F-actin cross-linking/bundling proteins that co-localize along stress fibers and in lamellipodia, could synergistically enhance the resilience of F-actin networks in vitro. These two proteins can generate microfilament arrays that "yield" at a strain amplitude that is much larger than each one of the proteins separately. F-actin/alpha-actinin/fascin networks display strain-induced hardening, whereby the network "stiffens" under shear deformations, a phenomenon that is non-existent in F-actin/fascin networks and much weaker in F-actin/alpha-actinin networks. Strain-hardening is further enhanced at high rates of deformation and high concentrations of actin cross-linking proteins. A simplified model suggests that the optimum results of the competition between the increased stiffness of bundles and their decreased density of cross-links. Our studies support a re-evaluation of the notion of functional redundancy among cytoskeletal regulatory proteins.

  1. Cross-linking and the molecular packing of corneal collagen

    NASA Technical Reports Server (NTRS)

    Yamauchi, M.; Chandler, G. S.; Tanzawa, H.; Katz, E. P.

    1996-01-01

    We have quantitatively characterized, for the first time, the cross-linking in bovine cornea collagen as a function of age. The major iminium reducible cross-links were dehydro-hydroxylysinonorleucine (deH-HLNL) and dehydro-histidinohydroxymerodesmosine (deH-HHMD). The former rapidly diminished after birth; however, the latter persisted in mature animals at a level of 0.3 - 0.4 moles/mole of collagen. A nonreducible cross-link, histidinohydroxylysinonorleucine (HHL), previously found only in skin, was also found to be a major mature cross-link in cornea. The presence of HHL indicates that cornea fibrils have a molecular packing similar to skin collagen. However, like deH-HHMD, the HHL content in corneal fibrils only reaches a maximum value with time about half that of skin. These data suggest that the corneal fibrils are comprised of discrete filaments that are internally stabilized by HHL and deH-HHMD cross-links. This pattern of intermolecular cross-linking would facilitate the special collagen swelling property required for corneal transparency.

  2. Oxidation state of iron in plagioclase from lunar basalts.

    NASA Technical Reports Server (NTRS)

    Hafner, S. S.; Virgo, D.; Warburton, D.

    1971-01-01

    Determination of the oxidation state of iron in the plagioclase from the coarse-grained basalts 10044 and 12021, using Mossbauer spectroscopy. The location of iron in the crystal structure was also investigated. The spectra show that iron is in the high-spin ferrous state, and they located at least two distinct positions with different coordination numbers. Some excess resonant absorption is probably due to Fe(3+), although the Fe(3+) doublet could not be positively resolved.

  3. Mitochondrial protein interactome elucidated by chemical cross-linking mass spectrometry.

    PubMed

    Schweppe, Devin K; Chavez, Juan D; Lee, Chi Fung; Caudal, Arianne; Kruse, Shane E; Stuppard, Rudy; Marcinek, David J; Shadel, Gerald S; Tian, Rong; Bruce, James E

    2017-02-14

    Mitochondrial protein interactions and complexes facilitate mitochondrial function. These complexes range from simple dimers to the respirasome supercomplex consisting of oxidative phosphorylation complexes I, III, and IV. To improve understanding of mitochondrial function, we used chemical cross-linking mass spectrometry to identify 2,427 cross-linked peptide pairs from 327 mitochondrial proteins in whole, respiring murine mitochondria. In situ interactions were observed in proteins throughout the electron transport chain membrane complexes, ATP synthase, and the mitochondrial contact site and cristae organizing system (MICOS) complex. Cross-linked sites showed excellent agreement with empirical protein structures and delivered complementary constraints for in silico protein docking. These data established direct physical evidence of the assembly of the complex I-III respirasome and enabled prediction of in situ interfacial regions of the complexes. Finally, we established a database and tools to harness the cross-linked interactions we observed as molecular probes, allowing quantification of conformation-dependent protein interfaces and dynamic protein complex assembly.

  4. Effect of cross-linking ultrahigh molecular weight polyethylene: Surface molecular orientation and wear characteristics

    SciTech Connect

    Sambasivan, Sharadha; Fischer, Daniel A.; Hsu, Stephen M.

    2007-07-15

    Molecular orientation at the surface layer of cross-linked ultrahigh molecular weight polyethylene (UHMWPE) has been examined. Molecular orientation has been shown to affect the wear resistance and surface mechanical properties of UHMWPE under biomechanical loading conditions. This study utilizes a nondestructive synchrotron based soft x-ray technique; near edge x-ray absorption fine structure at the carbon K-edge to examine the degree of surface molecular orientation of UHMWPE subjected to various cross-linking/sterilization techniques as a function of stress and wear. UHMWPE samples prepared under gamma irradiation, ethylene-oxide (EtO) treatment, and electron beam irradiation were worn in a wear tester systematically. Results suggest that the cross-linking resists surface orientation when the samples were under tensile and biomechanical stresses. The molecular orientation in the C-C chains in the polymer showed a monotonic decrease with an increase in gamma irradiation dosage levels. EtO sterilized samples showed more C-C chain orientation than the electron beam irradiated samples, but lower than the 30 kGy gamma irradiated samples. Ordered C-C chains in UHMWPE samples have been associated with more crystallinity or large strain plastic deformation of the polymer. Higher levels of gamma irradiation appear to induce cross-linking of C-C chains and render a polymer with more amorphous phase which resists orientation after wear and imparts wear resistance to the polymer.

  5. Immobilisation of arsenic by iron(II)-oxidizing bacteria

    NASA Astrophysics Data System (ADS)

    Kappler, A.; Hohmann, C.; Winkler, E.; Muehe, M.; Morin, G.

    2008-12-01

    Arsenic-contaminated groundwater is an environmental problem that affects about 1-2% of the world's population. As arsenic-contaminated water is also used for irrigating rice fields, the uptake of arsenic via rice is in some cases even higher than via drinking water. Arsenic is often of geogenic origin and in many cases bound to iron(III) minerals. Microbial iron(III) reduction leads to dissolution of Fe(III) minerals and thus the arsenic bound to these minerals is released to the environment. In turn, iron(II)-oxidizing bacteria have the potential to co-precipitate or sorb arsenic during iron(II) oxidation followed by iron(III) mineral formation. Here, we present work on arsenic co-precipitation and immobilization by anaerobic and aerobic iron(II)-oxidizing bacteria. Co-precipitation batch experiments with pure cultures of nitrate-dependent, phototrophic, and microaerophilic Fe(II)-oxidizing bacteria are used to quantify the amount of arsenic that can be immobilized during microbial iron mineral precipitation. Iron and arsenic speciation and redox state are determined by X- ray diffraction and synchrotron-based X-ray absorption methods (EXAFS, XANES). Microcosm experiments are set-up either with liquid media or with rice paddy soil amended with arsenic. Rice paddy soil from arsenic contaminated rice fields in China that include a natural population of Fe(II)-oxidizing microorganisms is used as inoculum. Dissolved and solid-phase arsenic and iron are quantified, Arsenic speciation is determined and the iron minerals are identified. Additionally, Arsenic uptake into the rice plant is quantified and a gene expression pattern in rice (Oryza sativa cv Gladia) is determined by microarrays as a response to the presence of Fe(II)-oxidizing bacteria.

  6. Biogenic Fabrication of Iron/Iron Oxide Nanoparticles and Their Application

    NASA Astrophysics Data System (ADS)

    Siddiqi, Khwaja Salahuddin; ur Rahman, Aziz; Tajuddin; Husen, Azamal

    2016-11-01

    Enshrined in this review are the biogenic fabrication and applications of coated and uncoated iron and iron oxide nanoparticles. Depending on their magnetic properties, they have been used in the treatment of cancer, drug delivery system, MRI, and catalysis and removal of pesticides from potable water. The polymer-coated iron and iron oxide nanoparticles are made biocompatible, and their slow release makes them more effective and lasting. Their cytotoxicity against microbes under aerobic/anaerobic conditions has also been discussed. The magnetic moment of superparamagnetic iron oxide nanoparticles changes with their interaction with biomolecules as a consequence of which their size decreases. Their biological efficacy has been found to be dependent on the shape, size, and concentration of these nanoparticles.

  7. Influence of cross-linking degree of a biodegradable genipin-cross-linked gelatin guide on peripheral nerve regeneration.

    PubMed

    Lu, Ming-Chin; Hsiang, Shih-Wei; Lai, Tung-Yuan; Yao, Chun-Hsu; Lin, Li-Yu; Chen, Yueh-Sheng

    2007-01-01

    We evaluated peripheral nerve regeneration using biodegradable genipin-cross-linked gelatin nerve conduits (GGCs) with three different cross-linking degrees, 24, 36 and 51%. Biocompatibility and biodegradability of the GGC and its efficiency as a guidance channel were examined based on the repair process of a 10-mm gap in the rat sciatic nerve. From this pilot study we concluded that GGCs with a mean cross-linking degree of 36% can ensure nerve regeneration with a more mature structure, as demonstrated by better developed epineural and perineural organisation and axonal development, as well as better-recovered electrophysiology with a relatively positive sciatic functional index and a shorter latency of the muscle action potential curve. Regenerated nerves in the GGCs with mean cross-linking degrees of 24 and 51% were less favourable, due to irritation caused by degradation material and compression by the remaining tube walls, respectively.

  8. Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

    PubMed Central

    2008-01-01

    Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed. PMID:21749733

  9. Stem cell tracking using iron oxide nanoparticles.

    PubMed

    Bull, Elizabeth; Madani, Seyed Yazdan; Sheth, Roosey; Seifalian, Amelia; Green, Mark; Seifalian, Alexander M

    2014-01-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) are an exciting advancement in the field of nanotechnology. They expand the possibilities of noninvasive analysis and have many useful properties, making them potential candidates for numerous novel applications. Notably, they have been shown that they can be tracked by magnetic resonance imaging (MRI) and are capable of conjugation with various cell types, including stem cells. In-depth research has been undertaken to establish these benefits, so that a deeper level of understanding of stem cell migratory pathways and differentiation, tumor migration, and improved drug delivery can be achieved. Stem cells have the ability to treat and cure many debilitating diseases with limited side effects, but a main problem that arises is in the noninvasive tracking and analysis of these stem cells. Recently, researchers have acknowledged the use of SPIONs for this purpose and have set out to establish suitable protocols for coating and attachment, so as to bring MRI tracking of SPION-labeled stem cells into common practice. This review paper explains the manner in which SPIONs are produced, conjugated, and tracked using MRI, as well as a discussion on their limitations. A concise summary of recently researched magnetic particle coatings is provided, and the effects of SPIONs on stem cells are evaluated, while animal and human studies investigating the role of SPIONs in stem cell tracking will be explored.

  10. Iron Oxide Nanocrystals for Magnetic Hyperthermia Applications

    PubMed Central

    Armijo, Leisha M.; Brandt, Yekaterina I.; Mathew, Dimple; Yadav, Surabhi; Maestas, Salomon; Rivera, Antonio C.; Cook, Nathaniel C.; Withers, Nathan J.; Smolyakov, Gennady A.; Adolphi, Natalie; Monson, Todd C.; Huber, Dale L.; Smyth, Hugh D. C.; Osiński, Marek

    2012-01-01

    Magnetic nanocrystals have been investigated extensively in the past several years for several potential applications, such as information technology, MRI contrast agents, and for drug conjugation and delivery. A specific property of interest in biomedicine is magnetic hyperthermia—an increase in temperature resulting from the thermal energy released by magnetic nanocrystals in an external alternating magnetic field. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field strengths of 9 and 25 mT. Polymorphous nanocrystals as well as spherical nanocrystals and nanowires in paramagnetic to ferromagnetic size range exhibited good heating power. A remarkable 30 °C temperature increase was observed in a nanowire sample at 111 kHz and magnetic field of 25 mT (19.6 kA/m), which is very close to the typical values of 100 kHz and 20 mT used in medical treatments.

  11. Synthesis and heating effect of iron/iron oxide composite and iron oxide nanoparticles

    PubMed Central

    Zeng, Q.; Baker, I.; Loudis, J. A.; Liao, Y.F.; Hoopes, P.J.

    2014-01-01

    Fe/Fe oxide nanoparticles, in which the core consists of metallic Fe and the shell is composed of Fe oxides, were obtained by reduction of an aqueous solution of FeCl3 within a NaBH4 solution, or, using a water-in-oil micro-emulsion with CTAB as the surfactant. The reduction was performed either in an inert atmosphere or in air, and passivation with air was performed to produce the Fe/Fe3O4 core/shell composite. Phase identification and particle size were determined by X-ray diffraction and TEM. Thermal analysis was performed using a differential scanning calorimeter. The quasistatic magnetic properties were measured using a VSM, and the specific absorption rates (SARs) of both Fe oxide and Fe/Fe3O4 composite nanoparticles either dispersed in methanol or in an epoxy resin were measured by Luxtron fiber temperature sensors in an alternating magnetic field of 150 Oe at 250 kHz. It was found that the preparation conditions, including the concentrations of solutions, the mixing procedure and the heat treatment, influence the particle size, the crystal structure and consequently the magnetic properties of the particles. Compared with Fe oxides, the saturation magnetization (MS) of Fe/Fe3O4 particles (100–190 emu/g) can be twice as high, and the coercivity (HC) can be tunable from several Oe to several hundred Oe. Hence, the SAR of Fe/Fe3O4 composite nanoparticles can be much higher than that of Fe oxides, with a maximum SAR of 345 W/g. The heating behavior is related to the magnetic behavior of the nanoparticles. PMID:25301983

  12. Iron oxide-based nanomagnets in nanomedicine: fabrication and applications

    PubMed Central

    Meng Lin, Meng; Kim, Hyung-Hwan; Kim, Hyuck; Muhammed, Mamoun; Kyung Kim, Do

    2010-01-01

    Iron oxide-based nanomagnets have attracted a great deal of attention in nanomedicine over the past decade. Down to the nanoscale, superparamagnetic iron oxide nanoparticles can only be magnetized in the presence of an external magnetic field, which makes them capable of forming stable colloids in a physio-biological medium. Their superparamagnetic property, together with other intrinsic properties, such as low cytotoxicity, colloidal stability, and bioactive molecule conjugation capability, makes such nanomagnets ideal in both in-vitro and in-vivo biomedical applications. In this review, a chemical, physical, and biological synthetic approach to prepare iron oxide-based nanomagnets with different physicochemical properties was illustrated and compared. The growing interest in iron oxide-based nanomagnets with multifunctionalities was explored in cancer diagnostics and treatment, focusing on their combined roles in a magnetic resonance contrast agent, hyperthermia, and magnetic force assisted drug delivery. Iron oxides as magnetic carriers in gene therapy were reviewed with a focus on the sophisticated design and construction of magnetic vectors. Finally, the iron oxide-based nanomagnet also represents a very promising tool in particle/cell interfacing in controlling cellular functionalities, such as adhesion, proliferation, differentiation, and cell patterning, in stem cell therapy and tissue engineering applications. PMID:22110854

  13. Wear measurement of highly cross-linked UHMWPE using a 7Be tracer implantation technique.

    PubMed

    Wimmer, Markus A; Laurent, Michel P; Dwiwedi, Yasha; Gallardo, Luis A; Chipps, Kelly A; Blackmon, Jeffery C; Kozub, Raymond L; Bardayan, Daniel W; Gross, Carl J; Stracener, Daniel W; Smith, Michael S; Nesaraja, Caroline D; Erikson, Luke; Patel, Nidhi; Rehm, Karl E; Ahmad, Irshad; Greene, John P; Greife, Uwe

    2013-04-01

    The very low wear rates achieved with the current highly cross-linked ultrahigh molecular weight polyethylenes (UHMWPE) used in joint prostheses have proven to be difficult to measure accurately by gravimetry. Tracer methods are therefore being explored. The purpose of this study was to perform a proof-of-concept experiment on the use of the radioactive tracer beryllium-7 ((7)Be) for the determination of in vitro wear in a highly cross-linked orthopedic UHMWPE. Three cross-linked and four conventional UHMWPE pins made from compression-molded GUR 1050, were activated with 10(9) to 10(10) (7)Be nuclei using a new implantation setup that produced a homogenous distribution of implanted nuclei up to 8.5 μm below the surface. The pins were tested for wear in a six-station pin-on-flat apparatus for up to 7.1 million cycles (178 km). A Germanium gamma detector was employed to determine activity loss of the UHMWPE pins at preset intervals during the wear test. The wear of the cross-linked UHMWPE pins was readily detected and estimated to be 17 ± 3 μg per million cycles. The conventional-to-cross-linked ratio of the wear rates was 13.1 ± 0.8, in the expected range for these materials. Oxidative degradation damage from implantation was negligible; however, a weak dependence of wear on implantation dose was observed limiting the number of radioactive tracer atoms that can be introduced. Future applications of this tracer technology may include the analysis of location-specific wear, such as loss of material in the post or backside of a tibial insert.

  14. Iron, oxidative stress, and redox signaling in the cardiovascular system.

    PubMed

    Gudjoncik, Aurélie; Guenancia, Charles; Zeller, Marianne; Cottin, Yves; Vergely, Catherine; Rochette, Luc

    2014-08-01

    The redox state of the cell is predominantly dependent on an iron redox couple and is maintained within strict physiological limits. Iron is an essential metal for hemoglobin synthesis in erythrocytes, for oxidation-reduction reactions, and for cellular proliferation. The maintenance of stable iron concentrations requires the coordinated regulation of iron transport into plasma from dietary sources in the duodenum, from recycled senescent red cells in macrophages, and from storage in hepatocytes. The absorption of dietary iron, which is present in heme or nonheme form, is carried out by mature villus enterocytes of the duodenum and proximal jejunum. Multiple physiological processes are involved in maintaining iron homeostasis. These include its storage at the intracellular and extracellular level. Control of iron balance in the whole organism requires communication between sites of uptake, utilization, and storage. Key protein transporters and the molecules that regulate their activities have been identified. In this field, ferritins and hepcidin are the major regulator proteins. A variety of transcription factors may be activated depending on the level of oxidative stress, leading to the expression of different genes. Major preclinical and clinical trials have shown advances in iron-chelation therapy for the treatment of iron-overload disease as well as cardiovascular and chronic inflammatory diseases.

  15. Sustained release of Avastin® from polysaccharides cross-linked hydrogels for ocular drug delivery.

    PubMed

    Xu, Xu; Weng, Yuhua; Xu, Lu; Chen, Hao

    2013-09-01

    Avastin(®) was the first choice drug for the treatment of age related macular degeneration (AMD) and proliferative diabetic retinopathy in clinic. Due to its short half-time in intraocular, it was required repeat administration. In this paper, an in situ injectable polysaccharides cross-linked hydrogel was developed for potential ocular drug delivery of avastin. The polysaccharide cross-linked hydrogel was first synthesized by simple mixing of glycol chitosan and oxidized alginate aqueous solution, and then characterized by scanning electron microscopy (SEM) and rheometer. In vitro degradation test indicated that the degradation rate of hydrogels could be controlled by the varying the content of oxidized alginate in hydrogels. In vitro release study showed that the encapsulated avastin had an initial burst release at early stage (within 4 h) followed by a sustained release manner in period of 3 days. With the increase of oxidized alginate concentration in the hydrogel, the release rate of avastin from hydrogels declined accordingly. Meanwhile, the structure stability of avastin released from hydrogels at specific time intervals did not show apparent changes as compared with native avastin based on the analysis of SDS-polyacrylamide gel electrophoresis (SDS-PAEG). As a result, the developed in situ injectable polysaccharides cross-linked hydrogel with controllable degradation rate and drug release might be a versatile carrier for avastin to apply in ocular drug delivery.

  16. Synthesis and enzymatic degradation of epichlorohydrin cross-linked pectins.

    PubMed

    Semdé, Rasmané; Moës, André J; Devleeschouwer, Michel J; Amighi, Karim

    2003-02-01

    The water solubility of pectin was successfully decreased by cross-linking with increasing amounts of epichlorohydrin in the reaction media. The initial molar ratios of epichlorohydrin/ galacturonic acid monomer in the reaction mixtures were 0, 0.37, 0.56, 0.74, 1.00, 1.47, and 2.44. The resulting epichlorohydrin cross-linked pectins were thus referred to as C-LP0, C-LP37, C-LP56, C-LP75, C-LP100, C-LP150, and C-LP250, respectively. Methoxylation degrees ranged from 60.5 +/- 0.9% to 68.0 +/- 0.6%, and the effective cross-linking degrees, determined by quantification of the hydroxyl anions consumed during the reaction, were 0, 17.8, 26.0, 38.3, 46.5, 53.5, and 58.7%. respectively. After incubating the different cross-linked pectins (0.5% w/v) in 25 mL of 0.05 M acetate-phosphate buffer (pH 4.5), containing 50 microL of Pectinex Ultra SP-L (pectinolytic enzymes), between 60 and 80% of the pectin osidic bounds were broken in less than 1 hr. Moreover, increasing the cross-linking degree only resulted in a weak slowing on the enzymatic degradation velocity.

  17. Mapping of psoralen cross-linked nucleotides in RNA.

    PubMed Central

    Garrett-Wheeler, E; Lockard, R E; Kumar, A

    1984-01-01

    A method is described for using the cross-linking reagent 4'-(hydroxy-methyl)-4,5',8-trimethylpsoralen (HMT) to map base paired regions and higher-order structure within RNA molecules. Applying this method to yeast tRNAPhe, we have specifically identified cross-links within the acceptor stem between U6 X U68, in the D-stem between C11 X C25, and in the T psi-stem between U50 X C63 and U52 X C63. We have also identified a unique cross-link between U8 X C48 which are trans pyrimidines in the core region due to tertiary interactions between U8:A14 and C48:G15. The precise point of cross-linking was deduced in every case by using purine-specific U2 ribonuclease along with cytidine-specific CL3 ribonuclease which will anomalously cleave after photoreversed pyrimidines. The ability to map the precise point of cross-linking should prove invaluable in identifying nucleotides in close proximity within the tertiary structure of other RNA molecules. Images PMID:6425802

  18. Spectroscopic characterization of collagen cross-links in bone

    NASA Technical Reports Server (NTRS)

    Paschalis, E. P.; Verdelis, K.; Doty, S. B.; Boskey, A. L.; Mendelsohn, R.; Yamauchi, M.

    2001-01-01

    Collagen is the most abundant protein of the organic matrix in mineralizing tissues. One of its most critical properties is its cross-linking pattern. The intermolecular cross-linking provides the fibrillar matrices with mechanical properties such as tensile strength and viscoelasticity. In this study, Fourier transform infrared (FTIR) spectroscopy and FTIR imaging (FTIRI) analyses were performed in a series of biochemically characterized samples including purified collagen cross-linked peptides, demineralized bovine bone collagen from animals of different ages, collagen from vitamin B6-deficient chick homogenized bone and their age- and sex-matched controls, and histologically stained thin sections from normal human iliac crest biopsy specimens. One region of the FTIR spectrum of particular interest (the amide I spectral region) was resolved into its underlying components. Of these components, the relative percent area ratio of two subbands at approximately 1660 cm(-1) and approximately 1690 cm(-1) was related to collagen cross-links that are abundant in mineralized tissues (i.e., pyridinoline [Pyr] and dehydrodihydroxylysinonorleucine [deH-DHLNL]). This study shows that it is feasible to monitor Pyr and DHLNL collagen cross-links spatial distribution in mineralized tissues. The spectroscopic parameter established in this study may be used in FTIRI analyses, thus enabling the calculation of relative Pyr/DHLNL amounts in thin (approximately 5 microm) calcified tissue sections with a spatial resolution of approximately 7 microm.

  19. Slow down of actin depolymerization by cross-linking molecules.

    PubMed

    Schmoller, Kurt M; Semmrich, Christine; Bausch, Andreas R

    2011-02-01

    The ability to control the assembly and disassembly dynamics of actin filaments is an essential property of the cellular cytoskeleton. While many different proteins are known which accelerate the polymerization of monomers into filaments or promote their disintegration, much less is known on mechanisms which guarantee the kinetic stability of the cytoskeletal filaments. Previous studies indicate that cross-linking molecules might fulfill these stabilizing tasks, which in addition facilitates their ability to regulate the organization of cytoskeletal structures in vivo. The effect of depolymerization factors on such structures or the mechanism which leads finally to their disintegration remain unknown. Here, we use multiple depolymerization methods in order to directly demonstrate that cross-linking and bundling proteins effectively suppress the actin depolymerization in a concentration dependent manner. Even the actin depolymerizing factor cofilin is not sufficient to facilitate a fast disintegration of highly cross-linked actin networks unless molecular motors are used simultaneously. The drastic modification of actin kinetics by cross-linking molecules can be expected to have wide-ranging implications for our understanding of the cytoskeleton, where cross-linking molecules are omnipresent and essential.

  20. Oxidation-Induced Degradable Nanogels for Iron Chelation

    NASA Astrophysics Data System (ADS)

    Liu, Zhi; Wang, Yan; Purro, Max; Xiong, May P.

    2016-02-01

    Iron overload can increase cellular oxidative stress levels due to formation of reactive oxygen species (ROS); untreated, it can be extremely destructive to organs and fatal to patients. Since elevated oxidative stress levels are inherent to the condition in such patients, oxidation-induced degradable nanogels for iron chelation were rationally designed by simultaneously polymerizing oxidation-sensitive host-guest crosslinkers between β-cyclodextrin (β-CD) and ferrocene (Fc) and iron chelating moieties composed of deferoxamine (DFO) into the final gel scaffold in reverse emulsion reaction chambers. UV-Vis absorption and atomic absorption spectroscopy (AAS) was used to verify iron chelating capability of nanogels. These materials can degrade into smaller chelating fragments at rates proportional to the level of oxidative stress present. Conjugating DFO reduces the cytotoxicity of the chelator in the macrophage cells. Importantly, the nanogel can effectively reduce cellular ferritin expression in iron overloaded cells and regulate intracellular iron levels at the same time, which is important for maintaining a homeostatic level of this critical metal in cells.

  1. Oxidation-Induced Degradable Nanogels for Iron Chelation

    PubMed Central

    Liu, Zhi; Wang, Yan; Purro, Max; Xiong, May P.

    2016-01-01

    Iron overload can increase cellular oxidative stress levels due to formation of reactive oxygen species (ROS); untreated, it can be extremely destructive to organs and fatal to patients. Since elevated oxidative stress levels are inherent to the condition in such patients, oxidation-induced degradable nanogels for iron chelation were rationally designed by simultaneously polymerizing oxidation-sensitive host-guest crosslinkers between β-cyclodextrin (β-CD) and ferrocene (Fc) and iron chelating moieties composed of deferoxamine (DFO) into the final gel scaffold in reverse emulsion reaction chambers. UV-Vis absorption and atomic absorption spectroscopy (AAS) was used to verify iron chelating capability of nanogels. These materials can degrade into smaller chelating fragments at rates proportional to the level of oxidative stress present. Conjugating DFO reduces the cytotoxicity of the chelator in the macrophage cells. Importantly, the nanogel can effectively reduce cellular ferritin expression in iron overloaded cells and regulate intracellular iron levels at the same time, which is important for maintaining a homeostatic level of this critical metal in cells. PMID:26868174

  2. Photocatalysis over titania on iron oxide

    NASA Astrophysics Data System (ADS)

    Kim, Kwi Cheol; Han, Chong Soo

    2006-03-01

    Photocatalytic activity of TiO{2} deposited on spherical sub micron-sized Fe{2}O{3} particle was investigated under ultraviolet or visible light. The Fe{2}O{3} particles were prepared using a spray pyrolysis of aqueous Fe(NO{3})3 solution in air flow. TiO{2} was deposited on Fe{2}O{3} particle by irradiation of ultraviolet or visible light to the suspension of Fe{2}O{3} particle and a TiO{2} precursor. When TiO{2} was formed under visible light (TiO{2}/Fe{2}O{3}-VIS), there were reasonable trends in the phase shift of PAS signal and EDX signal of Ti. However, there was no trend for the case of ultra violet irradiation (TiO{2}/Fe{2}O{3}-UV). TiO{2}/Fe{2}O{3}-VIS showed higher rates of decomposition of organic compound, of decrease in contact angle of water drop, and of decrease in the number of E. coli under visible light than TiO{2}/Fe{2}O{3}-UV or TiO{2} film. From the results, it was suggested that TiO{2}/Fe{2}O{3}-VIS had a regular thin layer of TiO{2} compared to TiO{2}/Fe{2}O{3}-UV and the photo-generated carrier(s) in iron oxide migrated to the surface of TiO{2} in the case of TiO{2}/Fe{2}O{3}-VIS.

  3. Stabilization and functionalization of iron oxide nanoparticles for biomedical applications

    NASA Astrophysics Data System (ADS)

    Amstad, Esther; Textor, Marcus; Reimhult, Erik

    2011-07-01

    Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface presentation of functionalities. This review is focused on different aspects of the stability of superparamagnetic iron oxide NPs, from its practical definition to its implementation by molecular design of the dispersant shell around the iron oxide core and further on to its influence on the magnetic properties of the superparamagnetic iron oxide NPs. Special attention is given to the selection of molecular anchors for the dispersant shell, because of their importance to ensure colloidal and functional stability of sterically stabilized superparamagnetic iron oxide NPs. We further detail how dispersants have been optimized to gain close control over iron oxide NP stability, size and functionalities by independently considering the influences of anchors and the attached sterically repulsive polymer brushes. A critical evaluation of different strategies to stabilize and functionalize core-shell superparamagnetic iron oxide NPs as well as a brief introduction to characterization methods to compare those strategies is given.Superparamagnetic iron oxide nanoparticles (NPs) are used in a rapidly expanding number of research and practical applications in the biomedical field, including magnetic cell labeling separation and tracking, for therapeutic purposes in hyperthermia and drug delivery, and for diagnostic purposes, e.g., as contrast agents for magnetic resonance imaging. These applications require good NP stability at physiological conditions, close control over NP size and controlled surface

  4. Extreme dryness and DNA-protein cross-links

    NASA Astrophysics Data System (ADS)

    Bieger-Dose, A.; Dose, K.; Meffert, R.; Mehler, M.; Risi, S.

    Exposure of fungal conidia (Aspergillus ochraceus) or spores of Bacillus subtilis to extreme dryness or vacuum induces DNA lesions, including strand breaks and the formation of DNA-protein cross-links. In wet cells only a small amount of protein is bound to DNA, but exposure to conditions of lowered water activity results in an increasing number of cross-links between DNA and proteins. In fungal conidia these cross-links are detected after selective iodination (125J) of the DNA-bound proteins followed by gel electrophoresis and subsequent autoradiography. Another approach is the labelling of DNA with 32p by means of nick translation and the detection of differences in the electrophoretic mobility of DNA before and after digestion with proteinase K of proteins bound to DNA.

  5. Functional polymer laminates from hyperthermal hydrogen induced cross-linking.

    PubMed

    Thompson, David B; Trebicky, Tomas; Crewdson, Patrick; McEachran, Matthew J; Stojcevic, Goran; Arsenault, Gilles; Lau, Woon M; Gillies, Elizabeth R

    2011-12-20

    The use of a hyperthermal hydrogen induced cross-linking process to prepare laminates comprising polypropylene, poly(isobutylene-co-isoprene), and poly(vinyl acetate) is described. In this new, milder alternative to conventional plasma techniques, neutral molecular hydrogen projectiles were used to create carbon radicals on impacted surfaces by collision-induced dissociation of C-H bonds, and this process was used to cross-link polymers on a polypropylene surface. It was demonstrated that multiple layers of cross-linked materials could be added, creating polymer laminates with each layer introducing new functionalities and properties. In particular, the present work shows that the process is largely nondestructive toward ester functionalities. First, the esters were grafted to become nonleachable. Then, the esters were subsequently hydrolyzed to convert the surface from hydrophobic to hydrophilic. Afterward, the esters could be recovered by simple esterification demonstrating that further chemical transformations were possible.

  6. Controlled oxidation of iron nanoparticles in chemical vapour synthesis

    NASA Astrophysics Data System (ADS)

    Ruusunen, Jarno; Ihalainen, Mika; Koponen, Tarmo; Torvela, Tiina; Tenho, Mikko; Salonen, Jarno; Sippula, Olli; Joutsensaari, Jorma; Jokiniemi, Jorma; Lähde, Anna

    2014-02-01

    In the present study, iron oxide nanoparticles (primary particle size of 80-90 nm) with controlled oxidation state were prepared via an atmospheric pressure chemical vapour synthesis (APCVS) method. Iron pentacarbonyl [Fe(CO)5], a precursor material, was thermally decomposed to iron in the APCVS reactor. Subsequently, the iron was oxidized with controlled amount of oxygen in the reactor to produce nearly pure magnetite or haematite particles depending on the oxygen concentration. Size, morphology and crystal structure of the synthesized nanoparticles were studied with scanning mobility particle sizer (SMPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). In addition, thermodynamic equilibrium calculations and computational fluid dynamics model were used to predict the oxidation state of the iron oxides and the reaction conditions during mixing. Aggregates of crystalline particles were formed, determined as magnetite at the oxygen volumetric fraction of 0.1 % and haematite at volumetric fraction of 0.5 %, according to the XRD. The geometric mean electrical mobility diameter of the aggregates increased from 110 to 155 nm when the volumetric fraction of oxygen increased from 0.1 to 0.5 %, determined using the SMPS. The aggregates were highly sintered based on TEM analyses. As a conclusion, APCVS method can be used to produce nearly pure crystalline magnetite or haematite nanoparticles with controlled oxidation in a continuous one-stage gas-phase process.

  7. Synthesis of phase pure praseodymium barium copper iron oxide.

    PubMed

    Konne, Joshua L; Davis, Sean A; Glatzel, Stefan; Hall, Simon R

    2013-06-18

    The control of crystallization of praseodymium barium copper iron oxide, an intermediate temperature solid oxide fuel cell cathode material, has been demonstrated for the first time using a biotemplated sol-gel synthesis technique. The results obtained showed significant improvement in purity, synthesis time, surface area and simplicity over that previously reported.

  8. The Oxidation Of Iron In A Gel Using Consumer Chemicals

    ERIC Educational Resources Information Center

    Wright, Stephen W.; Folger, Marsha R.; Quinn, Ryan P.; Sauls, Frederick C.; Krone, Diane

    2005-01-01

    An experiment is conducted for the oxidation of iron in a gel using consumer chemicals, which is pertinent to the students' understanding of redox chemistry and of the relative oxidation potentials of various metals. The experiment can be carried out with consumer chemicals that might be purchased at a supermarket and commonly found in the home.

  9. FTIR Spectroscopic Studies on Cross Linking of SU-8 Photoresist

    NASA Astrophysics Data System (ADS)

    Kalaiselvi, S. M. P.; Tan, T. L.; Rawat, R. S.; Lee, P.; Heussler, S. P.; Breese, M. B. H.

    2013-11-01

    The usage of chemically-amplified, negative tone SU-8 photoresist is numerous, spanning industrial, scientific and medical fields. Hence, in this study, some preliminary studies were conducted to understand the dosage and heat treatment requirements of the SU-8 photoresist essential for pattern generation using X-ray lithography. In this work, using Synchrotron as the X-ray source, SU-8 photoresist was characterized for X-ray lithography in terms of its process parameters such as X-ray exposure dose, post exposure bake (PEB) time and temperature for various photoresist thicknesses which is considered worthwhile in view of applications of SU-8 for the fabrication of very high aspect ratio micro structures. The process parameters were varied and the resultant cross linking of the molecular chains of the photoresist was accurately monitored using a Fourier Transform Infra-Red (FTIR) spectrometer and the results are discussed. The infrared absorption peak at 914 cm-1 in the spectrum of the SU-8 photoresist was found to be a useful indicator for the completion of cross linking in the SU-8 photoresist. Results show that the cross linking of the SU-8 photoresist is at a higher rate from 0 J/cm3 to 30 J/cm3 after which the peak almost saturates regardless of the PEB time. It is a good evidence for the validation of dosage requirement of SU-8 photoresist for effective completion of cross linking, which in turn is a requirement for efficient fabrication of micro and nano structures. An analogous behavior was also observed between the extent of cross linking and the PEB time and temperature. The rate of cross linking declines after a certain period of PEB time regardless of PEB temperature. The obtained results also show a definite relation between variation of the absorbance area of the peak at 914 cm-1 and the X-ray exposure dose.

  10. Appearance of cross linked proteins in human atheroma and rat pre-fibrotic liver detected by a new monoclonal antibody.

    PubMed

    Itabe, H; Jimi, S; Kamimura, S; Suzuki, K; Uesugi, N; Imanaka, T; Shijo, H; Takano, T

    1998-02-27

    A new monoclonal antibody against malondialdehyde (MDA)-treated low density lipoprotein (LDL) was raised using homogenate of human atheroma as immunogen. This antibody, DLH2, was obtained by selecting the clones which did not react to native LDL but did react to copper-induced oxidized LDL (OxLDL). DLH2 showed a greater reactivity to MDA-LDL than to OxLDL. When LDL was treated with various aldehyde containing reagents, treatment of LDL with glutaraldehyde or MDA greatly increased the reactivity to the antibody, while LDL treated with 2,4-hexadienal or 4-hydroxynonenal was not reactive. Among many proteins tested, high density lipoprotein, bovine serum albumin and hemoglobin showed significant reactivity to DLH2 after they were treated with MDA or glutaraldehyde. When low density and high density lipoproteins treated with MDA were subjected to immunoblot analysis, newly formed products larger than the original apolipoproteins were detected with the antibody, suggesting that this antibody recognizes aggregated proteins with divalent short chain cross linkers. The antigenic materials were shown by immunohistochemical analysis to be present in foamy macrophages in human atheromatous lesions. DLH2 antigen did not colocalize either with apolipoprotein B. Furthermore, we found a massive accumulation of the antigenic material in Kupffer cells in the liver of rats treated with alcohol and carbonyl iron, a model of hepatic fibrosis due to oxidative stress. These results suggest the presence of cross linked proteins in damaged tissues.

  11. Positronium yields in amorphous, cross-linked and conductive polystyrene

    NASA Astrophysics Data System (ADS)

    Procházka, Ivan; Čížek, Jakub; Motyčka, Václav

    2007-02-01

    Variations in positronium yields due to positron irradiation of specimens during experiment were investigated on the three commercially available modifications of polystyrene (Goodfellow): amorphous, cross-linked and conductive. Positron lifetime technique was employed. The variations of the positronium yields were expressed as changes of the ortho-positronium intensity as functions of the irradiation time. It was found that the positronium yield curves obtained for the amorphous and cross-linked polystyrene cannot be represented as a simple single-exponential relaxation towards a steady state and at least one additional component or a modified shape of the relaxation curve should be considered.

  12. Cross-Linked Nanotube Materials with Variable Stiffness Tethers

    NASA Technical Reports Server (NTRS)

    Frankland, Sarah-Jane V.; Odegard, Gregory M.; Herzog, Matthew N.; Gates, Thomas S.; Fay, Catherine C.

    2004-01-01

    The constitutive properties of a cross-linked single-walled carbon nanotube material are predicted with a multi-scale model. The material is modeled as a transversely isotropic solid using concepts from equivalent-continuum modeling. The elastic constants are determined using molecular dynamics simulation. Some parameters of the molecular force field are determined specifically for the cross-linker from ab initio calculations. A demonstration of how the cross-linked nanotubes may affect the properties of a nanotube/polyimide composite is included using a micromechanical analysis.

  13. Does vitamin E-stabilized ultrahigh-molecular-weight polyethylene address concerns of cross-linked polyethylene in total knee arthroplasty?

    PubMed

    Haider, Hani; Weisenburger, Joel N; Kurtz, Steven M; Rimnac, Clare M; Freedman, Jordan; Schroeder, David W; Garvin, Kevin L

    2012-03-01

    Concerns about reduced strength, fatigue resistance, and oxidative stability of highly cross-linked and remelted ultrahigh-molecular-weight polyethylene (UHMWPE) have limited its clinical acceptance for total knee arthroplasty. We hypothesized that a highly cross-linked UHMWPE stabilized with vitamin E would have less oxidation and loss of mechanical properties. We compared the oxidation, in vitro strength, fatigue-crack propagation resistance, and wear of highly cross-linked UHMWPE doped with vitamin E to γ-inert-sterilized direct compression-molded UHMWPE (control). After accelerated aging, the control material showed elevated oxidation, loss of small-punch mechanical properties, and loss of fatigue-crack propagation resistance. In contrast, the vitamin E-stabilized material had minimal changes and exhibited 73% to 86% reduction in wear for both cruciate-retaining and posterior-stabilized total knee arthroplasty designs. Highly cross-linked vitamin E-stabilized UHMWPE performed well in vitro.

  14. Self-cross-linking biopolymers as injectable in situ forming biodegradable scaffolds.

    PubMed

    Balakrishnan, Biji; Jayakrishnan, A

    2005-06-01

    The injectable polymer scaffolds which are biocompatible and biodegradable are important biomaterials for tissue engineering and drug delivery. Hydrogels derived from natural proteins and polysaccharides are ideal scaffolds for tissue engineering since they resemble the extracellular matrices of the tissue comprised of various amino acids and sugar-based macromolecules. Here, we report a new class of hydrogels derived from oxidized alginate and gelatin. We show that periodate-oxidized sodium alginate having appropriate molecular weight and degree of oxidation rapidly cross-links proteins such as gelatin in the presence of small concentrations of sodium tetraborate (borax) to give injectable systems for tissue engineering, drug delivery and other medical applications. The rapid gelation in the presence of borax is attributed to the slightly alkaline pH of the medium as well as the ability of borax to complex with hydroxyl groups of polysaccharides. The effect of degree of oxidation and concentration of alginate dialdehyde, gelatin and borax on the speed of gelation was examined. As a general rule, the gelling time decreased with increase in concentration of oxidized alginate, gelatin and borax and increase in the degree of oxidation of alginate. Cross-linking parameters of the gel matrix were studied by swelling measurements and trinitrobenzene sulphonic acid (TNBS) assay. In general, the degree of cross-linking was found to increase with increase in the degree of oxidation of alginate, whereas the swelling ratio and the degree of swelling decreased. The gel was found to be biocompatible and biodegradable. The potential of the system as an injectable drug delivery vehicle and as a tissue-engineering scaffold is demonstrated by using primaquine as a model drug and by encapsulation of hepatocytes inside the gel matrix, respectively.

  15. Thermally Conductive-Silicone Composites with Thermally Reversible Cross-links.

    PubMed

    Wertz, J T; Kuczynski, J P; Boday, D J

    2016-06-08

    Thermally conductive-silicone composites that contain thermally reversible cross-links were prepared by blending diene- and dienophile-functionalized polydimethylsiloxane (PDMS) with an aluminum oxide conductive filler. This class of thermally conductive-silicones are useful as thermal interface materials (TIMs) within Information Technology (IT) hardware applications to allow rework of valuable components. The composites were rendered reworkable via retro Diels-Alder cross-links when temperatures were elevated above 130 °C and required little mechanical force to remove, making them advantageous over other TIM materials. Results show high thermal conductivity (0.4 W/m·K) at low filler loadings (45 wt %) compared to other TIM solutions (>45 wt %). Additionally, the adhesion of the material was found to be ∼7 times greater at lower temperatures (25 °C) and ∼2 times greater at higher temperatures (120 °C) than commercially available TIMs.

  16. Effect of green tea on iron status and oxidative stress in iron-loaded rats.

    PubMed

    Ounjaijean, S; Thephinlap, C; Khansuwan, U; Phisalapong, C; Fucharoen, S; Porter, J B; Srichairatanakool, S

    2008-07-01

    Plasma non-transferrin bound iron (NTBI) is potentially toxic and contributes to the generation of reactive oxygen species (ROS), consequently leading to tissue damage and organ dysfunction. Iron chelators and antioxidants are used for treatment of thalassemia patients. Green tea (GT) contains catechins derivatives that have many biological activities. The purpose of this study was to investigate the iron-chelating and free-radical scavenging capacities of green tea extract in vivo. Rats were injected ip with ferric citrate together with orally administered GT extract (GTE) for 4 months. Blood was collected monthly for measurement of iron overload and oxidative stress indicators. Plasma iron (PI) and total iron-binding capacity (TIBC) were quantified using bathophenanthroline method. Plasma NTBI was assayed with NTA chelation/HPLC. Plasma malonyldialdehyde (MDA) was determined by using the TBARS method. Erythrocyte oxidative stress was assessed using flow cytometry. Levels of PI, TIBC, NTBI and MDA, and erythrocyte ROS increased in the iron-loaded rats. Intervention with GT extract markedly decreased the PI and TIBC concentrations. It also lowered the transferrin saturation and effectively inhibited formation of NTBI. It also decreased the levels of erythrocyte ROS in week 4, 12 and 16. Therefore, green tea extract can decrease iron in plasma as well as eliminate lipid peroxidation in plasma, and destroy formation of erythrocyte ROS in the rats challenged with iron. The bifunctional effects could be beneficial in alleviating the iron and oxidative stress toxicity. In prospective, these GTE activities should be further examined in thalassemic animals or humans.

  17. A chameleon catalyst for nonheme iron-promoted olefin oxidation.

    PubMed

    Iyer, Shyam R; Javadi, Maedeh Moshref; Feng, Yan; Hyun, Min Young; Oloo, Williamson N; Kim, Cheal; Que, Lawrence

    2014-11-18

    We report the chameleonic reactivity of two nonheme iron catalysts for olefin oxidation with H2O2 that switch from nearly exclusive cis-dihydroxylation of electron-poor olefins to the exclusive epoxidation of electron-rich olefins upon addition of acetic acid. This switching suggests a common precursor to the nucleophilic oxidant proposed to Fe(III)-η(2)-OOH and electrophilic oxidant proposed to Fe(V)(O)(OAc), and reversible coordination of acetic acid as a switching pathway.

  18. Iron oxide and gold nanoparticles in cancer therapy

    NASA Astrophysics Data System (ADS)

    Gotman, Irena; Psakhie, Sergey G.; Lozhkomoev, Aleksandr S.; Gutmanas, Elazar Y.

    2016-08-01

    Continuous research activities in the field of nanomedicine in the past decade have, to a great extent, been focused on nanoparticle technologies for cancer therapy. Gold and iron oxide nanoparticles (NP) are two of the most studied inorganic nanomaterials due to their unique optical and magnetic properties. Both types of NPs are emerging as promising systems for anti-tumor drug delivery and for nanoparticle-mediated thermal therapy of cancer. In thermal therapy, localized heating inside tumors or in proximity of tumor cells can be induced, for example, with Au NPs by radiofrequency ablation heating or conversion of photon energy (photothermal therapy) and in iron oxide magnetic NPs by heat generation through relaxation in an alternating magnetic field (magnetic hyperthermia). Furthermore, the superparamagnetic properties of iron oxide nanoparticles have led to their use as potent MRI (magnetic resonance imaging) contrast agents. Surface modification/coating can produce NPs with tailored and desired properties, such as enhanced blood circulation time, stability, biocompatibility and water solubility. To target nanoparticles to specific tumor cells, NPs should be conjugated with targeting moieties on the surface which bind to receptors or other molecular structures on the cell surface. The article presents several approaches to enhancing the specificity of Au and iron oxide nanoparticles for tumor tissue by appropriate surface modification/functionalization, as well as the effect of these treatments on the saturation magnetization value of iron oxide NPs. The use of other nanoparticles and nanostructures in cancer treatment is also briefly reviewed.

  19. Haem-assisted dityrosine-cross-linking of fibrinogen under non-thermal plasma exposure: one important mechanism of facilitated blood coagulation

    PubMed Central

    Ke, Zhigang; Huang, Qing

    2016-01-01

    Although blood coagulation facilitated by non-thermal plasma has been reported several years ago, the insight to the involved mechanisms is still rather limited. In this work, we report our discovery of a new mechanism for the haem-promoted blood-coagulation caused by non-thermal plasma treatment. The reason for the haem role is due to that its oxidized form, namely, hematin, can promote the dityrosine cross-linking of fibrinogen, the most important coagulation protein, to form a membrane-like layer on the surface of the treated blood with plasma exposure. Both haem and non-thermal-plasma generated hydrogen peroxide are requisite for the cross-linking process. We confirmed that fibrinogen can coordinate with the haem iron to form a protein-haem complex which shows pseudo-peroxidase activity, and in the presence of hydrogen peroxide, the complex can induce the dityrosine formation between fibrinogen molecules, leading to the fibrin network necessary for the blood coagulation. Understanding of such an underlying mechanism can be useful to guide more efficient application of non-thermal plasma in the management of hemostasis, thrombosis and etc. PMID:27229173

  20. Development and use of iron oxide nanoparticles (Part 1): Synthesis of iron oxide nanoparticles for MRI

    PubMed Central

    Lodhia, J; Mandarano, G; Ferris, NJ; Eu, P; Cowell, SF

    2010-01-01

    Contrast agents, such as iron oxide, enhance MR images by altering the relaxation times of tissues in which the agent is present. They can also be used to label targeted molecular imaging probes. Unfortunately, no molecular imaging probe is currently available on the clinical MRI market. A promising platform for MRI contrast agent development is nanotechnology, where superparamagnetic iron oxide nanoparticles (SPIONS) are tailored for MR contrast enhancement, and/or for molecular imaging. SPIONs can be produced using a range of methods and the choice of method will be influenced by the characteristics most important for a particular application. In addition, the ability to attach molecular markers to SPIONS heralds their application in molecular imaging. There are many reviews on SPION synthesis for MRI; however, these tend to be targeted to a chemistry audience. The development of MRI contrast agents attracts experienced researchers from many fields including some researchers with little knowledge of medical imaging or MRI. This situation presents medical radiation practitioners with opportunities for involvement, collaboration or leadership in research depending on their level of commitment and their ability to learn. Medical radiation practitioners already possess a large portion of the understanding, knowledge and skills necessary for involvement in MRI development and molecular imaging. Their expertise in imaging technology, patient care and radiation safety provides them with skills that are directly applicable to research on the development and application of SPIONs and MRI. In this paper we argue that MRI SPIONs, currently limited to major research centres, will have widespread clinical use in the future. We believe that knowledge about this growing area of research provides an opportunity for medical radiation practitioners to enhance their specialised expertise to ensure best practice in a truly multi-disciplinary environment. This review outlines how and

  1. A pentanuclear iron catalyst designed for water oxidation.

    PubMed

    Okamura, Masaya; Kondo, Mio; Kuga, Reiko; Kurashige, Yuki; Yanai, Takeshi; Hayami, Shinya; Praneeth, Vijayendran K K; Yoshida, Masaki; Yoneda, Ko; Kawata, Satoshi; Masaoka, Shigeyuki

    2016-02-25

    Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth's crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between Fe(II)5 and Fe(III)5; the Fe(III)5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.

  2. A pentanuclear iron catalyst designed for water oxidation

    NASA Astrophysics Data System (ADS)

    Okamura, Masaya; Kondo, Mio; Kuga, Reiko; Kurashige, Yuki; Yanai, Takeshi; Hayami, Shinya; Praneeth, Vijayendran K. K.; Yoshida, Masaki; Yoneda, Ko; Kawata, Satoshi; Masaoka, Shigeyuki

    2016-02-01

    Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth’s crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between FeII5 and FeIII5; the FeIII5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.

  3. Polyimide Aerogels with Three-Dimensional Cross-Linked Structure

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B. (Inventor)

    2016-01-01

    A method for creating a three dimensional cross-linked polyimide structure includes dissolving a diamine, a dianhydride, and a triamine in a solvent, imidizing a polyamic acid gel by heating the gel, extracting the gel in a second solvent, supercritically drying the gel, and removing the solvent to create a polyimide aerogel.

  4. Porous Cross-Linked Polyimide-Urea Networks

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B. (Inventor); Nguyen, Baochau N. (Inventor)

    2015-01-01

    Porous cross-linked polyimide-urea networks are provided. The networks comprise a subunit comprising two anhydride end-capped polyamic acid oligomers in direct connection via a urea linkage. The oligomers (a) each comprise a repeating unit of a dianhydride and a diamine and a terminal anhydride group and (b) are formulated with 2 to 15 of the repeating units. The subunit was formed by reaction of the diamine and a diisocyanate to form a diamine-urea linkage-diamine group, followed by reaction of the diamine-urea linkage-diamine group with the dianhydride and the diamine to form the subunit. The subunit has been cross-linked via a cross-linking agent, comprising three or more amine groups, at a balanced stoichiometry of the amine groups to the terminal anhydride groups. The subunit has been chemically imidized to yield the porous cross-linked polyimide-urea network. Also provided are wet gels, aerogels, and thin films comprising the networks, and methods of making the networks.

  5. Potential Effects of Corneal Cross-Linking upon the Limbus

    PubMed Central

    2016-01-01

    Corneal cross-linking is nowadays the most used strategy for the treatment of keratoconus and recently it has been exploited for an increasing number of different corneal pathologies, from other ectatic disorders to keratitis. The safety of this technique has been widely assessed, but clinical complications still occur. The potential effects of cross-linking treatment upon the limbus are incompletely understood; it is important therefore to investigate the effect of UV exposure upon the limbal niche, particularly as UV is known to be mutagenic to cellular DNA and the limbus is where ocular surface tumors can develop. The risk of early induction of ocular surface cancer is undoubtedly rare and has to date not been published other than in one case after cross-linking. Nevertheless it is important to further assess, understand, and reduce where possible any potential risk. The aim of this review is to summarize all the reported cases of a pathological consequence for the limbal cells, possibly induced by cross-linking UV exposure, the studies done in vitro or ex vivo, the theoretical bases for the risks due to UV exposure, and which aspects of the clinical treatment may produce higher risk, along with what possible mechanisms could be utilized to protect the limbus and the delicate stem cells present within it. PMID:27689081

  6. Cross-linking of dithiols by mitomycin C.

    PubMed

    Paz, Manuel M

    2010-08-16

    Upon reduction, the antitumor drug mitomycin C undergoes a cascade of reactions to give a bis-electrophile that alkylates cellular nucleophiles. We recently reported that dithiols activate mitomycin C by reduction, and we report here that dithiols, after executing the reductive activation of mitomycin C, are bis-alkylated by the activated drug to form S,S'-cross-links as the predominant end products. The diastereomeric pair of adducts formed by 1,3-propanedithiol has been fully characterized by UV, HRMS, CD, and NMR experiments. Racemic dithiol (+/-)-dithiothreitol gave four diastereomeric cross-links, and (+/-)-dihydrolipoic acid gave eight cross-links (two regioisomers with four diastereomers each) that were partially characterized by UV and MS. The observed dependence of cross-link formation on dithiol concentration indicated the requirement of a second reduction step by dithiol, prior to the alkylation of the second arm of the dithiol. The existence of unidentified reaction pathways was manifested by the formation of unexpected intermediates during the course of the reaction of mitomycin C with dithiols and by the formation of unsoluble mitosene derivatives in the reaction between equimolar amounts of dithiol and mitomycin C. Mechanistic details of the reaction are addressed in light of these results. Finally, we discuss the potential relevance of our findings for the interaction of mitomycin C with dithiol-containing proteins.

  7. Citric-acid-derived photo-cross-linked biodegradable elastomers.

    PubMed

    Gyawali, Dipendra; Tran, Richard T; Guleserian, Kristine J; Tang, Liping; Yang, Jian

    2010-01-01

    Citric-acid-derived thermally cross-linked biodegradable elastomers (CABEs) have recently received significant attention in various biomedical applications, including tissue-engineering orthopedic devices, bioimaging and implant coatings. However, citric-acid-derived photo-cross-linked biodegradable elastomers are rarely reported. Herein, we report a novel photo-cross-linked biodegradable elastomer, referred to as poly(octamethylene maleate citrate) (POMC), which preserves pendant hydroxyl and carboxylic functionalities after cross-linking for the potential conjugation of biologically active molecules. Pre-POMC is a low-molecular-mass pre-polymer with an average molecular mass between 701 and 1291 Da. POMC networks are soft and elastic with an initial modulus of 0.07 to 1.3 MPa and an elongation-at-break between 38 and 382%. FT-IR-ATR results confirmed the successful surface immobilization of type-I collagen onto POMC films, which enhanced in vitro cellular attachment and proliferation. Photo-polymerized POMC films implanted subcutaneously into Sprague-Dawley rats demonstrated minimal in vivo inflammatory responses. The development of POMC enriches the family of citric-acid-derived biodegradable elastomers and expands the available biodegradable polymers for versatile needs in biomedical applications.

  8. Viscoelastic Nanomechanics of Ionically Cross-linked Polyelectrolyte Networks

    NASA Astrophysics Data System (ADS)

    Han, Biao; Lee, Daeyeon; Han, Lin

    2015-03-01

    Understanding the mechanics of ionic polyelectrolyte networks is critical for applications where nm-to-um mechanics is the key to success. This study aims to reveal the roles of ionic cross-links and fixed charges in the viscoelasticity of layer-by-layer poly(allylamine hydrochloride)/poly(acrylic acid) microfilms, PAH/PAA, a complex held by pH-sensitive amine-carboxyl links. AFM-nanoindentation and force relaxation (tip R =12.5um) was performed at ionic strength(IS) =0.01-1.0M, pH =5.5-2.0 (pKa of PAA =2.3). When pH changes from 5.5 to 2.0, the films swell for 4x from densely linked, net neutral state to loosely linked, positively charged one. A >100x reduction in indentation modulus was observed at all IS, suggesting the dominance of decrease in cross-link density. In most states, more than 90% force relaxation was observed, where cross-link breaking/reformation likely dominates viscoelasticity. However, at pH =2.5 and IS =0.01M, when electrical double layer repulsion is important (Debye length =3nm), relaxation was about 60%, highlighting the contribution of fixed charges. In summary, this study revealed unique viscoelastic behaviors of PAH/PAA due to the pH- and IS-dependent cross-link and charge densities.

  9. Femtosecond laser collagen cross-linking without traditional photosensitizers

    NASA Astrophysics Data System (ADS)

    Guo, Yizang; Wang, Chao; Celi, Nicola; Vukelic, Sinisa

    2015-03-01

    Collagen cross-linking in cornea has the capability of enhancing its mechanical properties and thereby providing an alternative treatment for eye diseases such as keratoconus. Currently, riboflavin assisted UVA light irradiation is a method of choice for cross-link induction in eyes. However, ultrafast pulsed laser interactions may be a powerful alternative enabling in-depth treatment while simultaneously diminishing harmful side effects such as, keratocyte apoptosis. In this study, femtosecond laser is utilized for treatment of bovine cornea slices. It is hypothesized that nonlinear absorption of femtosecond laser pulses plays a major role in the maturation of immature cross-links and the promotion of their growth. Targeted irradiation with tightly focused laser pulses allows for the absence of a photosensitizing agent. Inflation test was conducted on half treated porcine cornea to identify the changes of mechanical properties due to laser treatment. Raman spectroscopy was utilized to study subtle changes in the chemical composition of treated cornea. The effects of treatment are analyzed by observing shifts in Amide I and Amide III bands, which suggest deformation of the collagen structure in cornea due to presence of newly formed cross-links.

  10. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  11. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram of... grafted copolymer of cross-linked sodium polyacrylate identified as 2-propenoic acid, polymers with N,N-di-2-propenyl-2-propen-1-amine and hydrolyzed polyvinyl acetate, sodium salts, graft (CAS Reg....

  12. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  13. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  14. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  15. Simulation of Fracture Nucleation in Cross-Linked Polymer Networks

    NASA Astrophysics Data System (ADS)

    Moller, J. C.; Barr, S. A.; Schultz, E. J.; Breitzman, T. D.; Berry, R. J.

    2013-02-01

    A novel atomistic simulation method is developed whereby polymer systems can undergo strain-rate-controlled deformation while bond scission is enabled. The aim is to provide insight into the nanoscale origins of fracture. Various highly cross-linked epoxy systems including various resin chain lengths and levels of nonreactive dilution were examined. Consistent with the results of physical experiments, cured resin strength increased and ductility decreased with increasing cross-link density. An analysis of dihedral angle activity shows the locations in the molecular network that are most absorptive of mechanical energy. Bond scission occurred principally at cross-link sites as well as between phenyl rings in the bisphenol moiety. Scissions typically occurred well after yield and were accompanied by steady increases in void size and dihedral angle motion between bisphenol moieties and at cross-link sites. The methods developed here could be more broadly applied to explore and compare the atomistic nature of deformation for various polymers such that mechanical and fracture properties could be tuned in a rational way. This method and its results could become part of a solution system that spans multiple length and time scales and that could more completely represent such mechanical events as fracture.

  16. Clinical fracture of cross-linked UHMWPE acetabular liners.

    PubMed

    Furmanski, Jevan; Anderson, Martin; Bal, Sonny; Greenwald, A Seth; Halley, David; Penenberg, Brad; Ries, Michael; Pruitt, Lisa

    2009-10-01

    Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is increasingly used as a bearing material in total hip replacements. Cross-linking of UHMWPE has been shown to increase wear resistance but decrease its fracture resistance. We analyzed the clinical fracture failure of four cross-linked UHMWPE total hip replacement components of four different designs via microscopic observation of the fracture surfaces, and found that in all cases fractures initiated at stress concentrations in an unsupported region of the component (termed the elevated rim). Finite element analyses (FEA) of each individual implant design were then conducted. Results from this analysis demonstrated that the predicted magnitude and orientation of maximum principal stress due to mechanical loading of the elevated rim was sufficient to propagate initiated fatigue cracks in each case. FEA also predicted that cracks may arrest after some amount of growth due to a steep stress gradient near the initiation site. Further, while anatomical positioning of the implant and material properties affect the risk of fracture, we examined whether these failures are strongly related to the notched elevated rim design feature that is common to the four failed cases presented here. We believe that cross-linked UHMWPE remains an excellent bearing material for total hip replacements but that designs employing this material should mitigate stress concentrations or other design features that increase the risk of fracture.

  17. Cross-Linked Protein Crystals for Vaccine Delivery

    NASA Astrophysics Data System (ADS)

    St. Clair, Nancy; Shenoy, Bhami; Jacob, Lawrence D.; Margolin, Alexey L.

    1999-08-01

    The progress toward subunit vaccines has been limited by their poor immunogenicity and limited stability. To enhance the immune response, subunit vaccines universally require improved adjuvants and delivery vehicles. In the present paper, we propose the use of cross-linked protein crystals (CLPCs) as antigens. We compare the immunogenicity of CLPCs of human serum albumin with that of soluble protein and conclude that there are marked differences in the immune response to the different forms of human serum albumin. Relative to the soluble protein, crystalline forms induce and sustain over almost a 6-month study a 6- to 10-fold increase in antibody titer for highly cross-linked crystals and an approximately 30-fold increase for lightly cross-linked crystals. We hypothesize that the depot effect, the particulate structure of CLPCs, and highly repetitive nature of protein crystals may play roles in the enhanced production of circulating antibodies. Several features of CLPCs, such as their remarkable stability, purity, biodegradability, and ease of manufacturing, make them highly attractive for vaccine formulations. This work paves the way for a systematic study of protein crystallinity and cross-linking on enhancement of humoral and T cell responses.

  18. Molecular mechanisms in deformation of cross-linked hydrogel nanocomposite.

    PubMed

    Mathesan, Santhosh; Rath, Amrita; Ghosh, Pijush

    2016-02-01

    The self-folding behavior in response to external stimuli observed in hydrogels is potentially used in biomedical applications. However, the use of hydrogels is limited because of its reduced mechanical properties. These properties are enhanced when the hydrogels are cross-linked and reinforced with nanoparticles. In this work, molecular dynamics (MD) simulation is applied to perform uniaxial tension and pull out tests to understand the mechanism contributing towards the enhanced mechanical properties. Also, nanomechanical characterization is performed using quasi static nanoindentation experiments to determine the Young's modulus of hydrogels in the presence of nanoparticles. The stress-strain responses for chitosan (CS), chitosan reinforced with hydroxyapatite (HAP) and cross-linked chitosan are obtained from uniaxial tension test. It is observed that the Young's modulus and maximum stress increase as the HAP content increases and also with cross-linking process. Load displacement plot from pullout test is compared for uncross-linked and cross-linked chitosan chains on hydroxyapatite surface. MD simulation reveals that the variation in the dihedral conformation of chitosan chains and the evolution of internal structural variables are associated with mechanical properties. Additional results reveal that the formation of hydrogen bonds and electrostatic interactions is responsible for the above variations in different systems.

  19. Cross-linked protein crystals for vaccine delivery

    PubMed Central

    St. Clair, Nancy; Shenoy, Bhami; Jacob, Lawrence D.; Margolin, Alexey L.

    1999-01-01

    The progress toward subunit vaccines has been limited by their poor immunogenicity and limited stability. To enhance the immune response, subunit vaccines universally require improved adjuvants and delivery vehicles. In the present paper, we propose the use of cross-linked protein crystals (CLPCs) as antigens. We compare the immunogenicity of CLPCs of human serum albumin with that of soluble protein and conclude that there are marked differences in the immune response to the different forms of human serum albumin. Relative to the soluble protein, crystalline forms induce and sustain over almost a 6-month study a 6- to 10-fold increase in antibody titer for highly cross-linked crystals and an approximately 30-fold increase for lightly cross-linked crystals. We hypothesize that the depot effect, the particulate structure of CLPCs, and highly repetitive nature of protein crystals may play roles in the enhanced production of circulating antibodies. Several features of CLPCs, such as their remarkable stability, purity, biodegradability, and ease of manufacturing, make them highly attractive for vaccine formulations. This work paves the way for a systematic study of protein crystallinity and cross-linking on enhancement of humoral and T cell responses. PMID:10449716

  20. Safety assessment of chronic oral exposure to iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Chamorro, Susana; Gutiérrez, Lucía; Vaquero, María Pilar; Verdoy, Dolores; Salas, Gorka; Luengo, Yurena; Brenes, Agustín; José Teran, Francisco

    2015-05-01

    Iron oxide nanoparticles with engineered physical and biochemical properties are finding a rapidly increasing number of biomedical applications. However, a wide variety of safety concerns, especially those related to oral exposure, still need to be addressed for iron oxide nanoparticles in order to reach clinical practice. Here, we report on the effects of chronic oral exposure to low doses of γ-Fe2O3 nanoparticles in growing chickens. Animal observation, weight, and diet intake reveal no adverse signs, symptoms, or mortality. No nanoparticle accumulation was observed in liver, spleen, and duodenum, with feces as the main excretion route. Liver iron level and duodenal villi morphology reflect the bioavailability of the iron released from the partial transformation of γ-Fe2O3 nanoparticles in the acid gastric environment. Duodenal gene expression studies related to the absorption of iron from γ-Fe2O3 nanoparticles indicate the enhancement of a ferric over ferrous pathway supporting the role of mucins. Our findings reveal that oral administration of iron oxide nanoparticles is a safe route for drug delivery at low nanoparticle doses.

  1. Characterization of iron oxide layers using Auger electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Bizjak, Milan; Zalar, Anton; Panjan, Peter; Zorko, Benjamin; Praček, Borut

    2007-02-01

    Metals can form several kinds of oxides. Iron forms wustite (FeO), magnetite (FeO + Fe 2O 3 or Fe 3O 4) and haematite (Fe 2O 3). Iron oxides, especially magnetite, are used for insulation between the lamellas of an electromotor made of electromagnetic sheet. In this work, iron oxide layers were characterized on industrial samples of electromagnetic sheet by AES depth profile analysis, and iron oxides with known chemical composition were used as reference samples, i.e. a magnetite mineral and a standard haematite reference sample. The magnetite mineral was chosen because it can be found in nature in a very pure form. The selection of reference samples was also verified on samples with an oxide layer of known composition, which were prepared by sputter deposition. The composition of the sputtered oxide layers was analysed by the weight-gain method and Rutherford backscattering without the use of standard reference materials (SRM), and the results were then compared with those obtained by AES depth profile analysis.

  2. Virus-Templated Near-Amorphous Iron Oxide Nanotubes.

    PubMed

    Shah, Sachin N; Khan, Abid A; Espinosa, Ana; Garcia, Miguel A; Nuansing, Wiwat; Ungureanu, Mariana; Heddle, Jonathan G; Chuvilin, Andrey L; Wege, Christina; Bittner, Alexander M

    2016-06-14

    We present a simple synthesis of iron oxide nanotubes, grown under very mild conditions from a solution containing Fe(II) and Fe(III), on rod-shaped tobacco mosaic virus templates. Their well-defined shape and surface chemistry suggest that these robust bionanoparticles are a versatile platform for synthesis of small, thin mineral tubes, which was achieved efficiently. Various characterization tools were used to explore the iron oxide in detail: Electron microscopy (SEM, TEM), magnetometry (SQUID-VSM), diffraction (XRD, TEM-SAED), electron spectroscopies (EELS, EDX, XPS), and X-ray absorption (XANES with EXAFS analysis). They allowed determination of the structure, crystallinity, magnetic properties, and composition of the tubes. The protein surface of the viral templates was crucial to nucleate iron oxide, exhibiting analogies to biomineralization in natural compartments such as ferritin cages.

  3. Manganese- and iron-dependent marine methane oxidation.

    PubMed

    Beal, Emily J; House, Christopher H; Orphan, Victoria J

    2009-07-10

    Anaerobic methanotrophs help regulate Earth's climate and may have been an important part of the microbial ecosystem on the early Earth. The anaerobic oxidation of methane (AOM) is often thought of as a sulfate-dependent process, despite the fact that other electron acceptors are more energetically favorable. Here, we show that microorganisms from marine methane-seep sediment in the Eel River Basin in California are capable of using manganese (birnessite) and iron (ferrihydrite) to oxidize methane, revealing that marine AOM is coupled, either directly or indirectly, to a larger variety of oxidants than previously thought. Large amounts of manganese and iron are provided to oceans from rivers, indicating that manganese- and iron-dependent AOM have the potential to be globally important.

  4. Arsenate adsorption onto iron oxide amended rice husk char.

    PubMed

    Cope, Christopher O; Webster, Damon S; Sabatini, David A

    2014-08-01

    In this study, rice husks were charred at 550 °C in a partially sealed ceramic vessel for 30minutes to create a high specific surface area (SSA) rice husk char (RHC). The RHC was then amended with iron oxides using dissolved ferric nitrate, Fe(NO3)3⋅9H2O, to provide a surface chemistry conducive to arsenic adsorption. The 550 °C iron oxide amended rice husk char's (550 IOA-RHC's) SSA was nearly 2.5 orders of magnitude higher and the arsenate adsorptive level was nearly 2 orders of magnitude higher than those reported for iron oxide amended sand, thus indicating a positive relationship between post-amendment SSA and arsenate adsorptive levels. Rice husks were then charred at temperatures ranging from 450 °C to 1050 °C to create an even higher SSA material, which might further increase arsenate adsorptive levels. The 950 °C RHC was chosen for amendment due to its high SSA and feasibility of being produced in the field. Once amended, the 950 °C iron oxide amended rice husk char (950 IOA-RHC) improved the arsenate adsorption capacity by thus confirming a positive relationship, though not a linear relationship, between post-amendment SSA and arsenic adsorptive capacity. Further study demonstrated that post-amendment mesoporous volume and mesoporous surface area appear to be better indicators of arsenic adsorptive capacity than SSA or iron content.

  5. The effect of an additional phosphite stabilizer on the properties of radiation cross-linked vitamin E blends of UHMWPE.

    PubMed

    Oral, Ebru; Neils, Andrew; Yabannavar, Pooja; Muratoglu, Orhun K

    2014-06-01

    Antioxidant stabilization of radiation cross-linked ultrahigh molecular weight polyethylene (UHMWPE) has been introduced to improve the oxidative stability of total joint implant bearing surfaces. Blending of an antioxidant with UHMWPE resin powder followed by consolidation and radiation cross-linking has been cleared by the FDA for use in both total hips and total knees for designs incorporating two antioxidants, namely vitamin E and Covernox™ (a medical grade version of Irganox™ 1010). The antioxidants in the polymer are expected to protect the polymer during consolidation, during radiation cross-linking, on the shelf before implantation, and in vivo after implantation. To maximize the protection of the polymer afforded by the antioxidant in vivo, a novel approach may be the use of multiple antioxidants, especially to protect the primary antioxidant for a longer period of time. We hypothesized that the addition of a phosphite stabilizer (Irgafos 168™) commonly used in conjunction with hindered phenolic antioxidants in polymer processing could improve the oxidative stability of radiation cross-linked blends of vitamin E. To test our hypothesis, we prepared UHMWPE blends with 0.05 wt% Irgafos and 0.05 wt% vitamin E and compared its cross-link density, wear resistance, tensile properties, and impact strength to control blends containing only vitamin E. Our hypothesis was not supported; the cross-link density of UHMWPE was significantly decreased by the additive without additional benefit to oxidative stability. To our knowledge, this was the first attempt at using multiple stabilizers in medical grade UHMWPE.

  6. Electrolytic photodissociation of chemical compounds by iron oxide electrodes

    SciTech Connect

    Somorjai, G.A.; Leygraf, C.H.

    1984-07-17

    Chemical compounds can be dissociated by contacting the same with a p/n type semi-conductor diode having visible light as its sole source of energy. The diode consists of low cost, readily available materials, specifically polycrystalline iron oxide doped with silicon in the case of the n-type semi-conductor electrode, and polycrystalline iron oxide doped with magnesium in the case of the p-type electrode. So long as the light source has an energy greater than 2.2 electron volts, no added energy source is needed to achieve dissociation.

  7. Multifunctional Iron Oxide Nanoparticles for Diagnostics, Therapy and Macromolecule Delivery

    PubMed Central

    Yen, Swee Kuan; Padmanabhan, Parasuraman; Selvan, Subramanian Tamil

    2013-01-01

    In recent years, multifunctional nanoparticles (NPs) consisting of either metal (e.g. Au), or magnetic NP (e.g. iron oxide) with other fluorescent components such as quantum dots (QDs) or organic dyes have been emerging as versatile candidate systems for cancer diagnosis, therapy, and macromolecule delivery such as micro ribonucleic acid (microRNA). This review intends to highlight the recent advances in the synthesis and application of multifunctional NPs (mainly iron oxide) in theranostics, an area used to combine therapeutics and diagnostics. The recent applications of NPs in miRNA delivery are also reviewed. PMID:24396508

  8. Electrolytic photodissociation of chemical compounds by iron oxide photochemical diodes

    DOEpatents

    Somorjai, Gabor A.; Leygraf, Christofer H.

    1985-01-01

    Chemical compounds can be dissociated by contacting the same with a p/n type semi-conductor photochemical diode having visible light as its sole source of energy. The photochemical diode consists of low cost, readily available materials, specifically polycrystalline iron oxide doped with silicon in the case of the n-type semi-conductor electrode, and polycrystalline iron oxide doped with magnesium in the case of the p-type electrode. So long as the light source has an energy greater than 2.2 electron volts, no added energy source is needed to achieve dissociation.

  9. Structural changes in iron-cobalt oxide nanosystems

    NASA Astrophysics Data System (ADS)

    Nishchev, K. N.; Golub'ev, M. A.; Maksimov, Yu. V.; Beglov, V. I.; Kyashkin, V. M.; Panov, A. A.

    2015-05-01

    The structure of binary iron-cobalt oxide nanosystems—precursors of bimetallic catalysts—is studied by Mössbauer spectroscopy, X-ray diffraction, and small-angle X-ray scattering. The oxide system under study represents a promising material for creating new metallic nanocatalysts for ammonia synthesis. The structural evolution in the composition range 100Fe/0Co-5Fe/95Co is found to correspond to the transition from fine-grained α-Fe2O3 to mixed iron-cobalt spinels of various compositions and degrees of dispersity.

  10. Recovery of iron oxide from coal fly ash

    DOEpatents

    Dobbins, Michael S.; Murtha, Marlyn J.

    1983-05-31

    A high quality iron oxide concentrate, suitable as a feed for blast and electric reduction furnaces is recovered from pulverized coal fly ash. The magnetic portion of the fly ash is separated and treated with a hot strong alkali solution which dissolves most of the silica and alumina in the fly ash, leaving a solid residue and forming a precipitate which is an acid soluble salt of aluminosilicate hydrate. The residue and precipitate are then treated with a strong mineral acid to dissolve the precipitate leaving a solid residue containing at least 90 weight percent iron oxide.

  11. Electrolytic photodissociation of chemical compounds by iron oxide electrodes

    DOEpatents

    Somorjai, Gabor A.; Leygraf, Christofer H.

    1984-01-01

    Chemical compounds can be dissociated by contacting the same with a p/n type semi-conductor diode having visible light as its sole source of energy. The diode consists of low cost, readily available materials, specifically polycrystalline iron oxide doped with silicon in the case of the n-type semi-conductor electrode, and polycrystalline iron oxide doped with magnesium in the case of the p-type electrode. So long as the light source has an energy greater than 2.2 electron volts, no added energy source is needed to achieve dissociation.

  12. Multifunctional superparamagnetic iron oxide nanoparticles: promising tools in cancer theranostics.

    PubMed

    Santhosh, Poornima Budime; Ulrih, Nataša Poklar

    2013-08-09

    Iron-oxide nanoparticles of small dimensions that have superparamagnetic properties show immense potential to revolutionize the future of cancer theranostics, the combinatorial diagnosis and therapeutic approach towards cancer. Superparamagnetic iron-oxide nanoparticles (SPIONs) have unique magnetic properties, due to which they show excellent tumor-targeting efficiency, and this paves the way for effective personalized cancer treatment. The aim of this review is to focus on the ability of SPIONs to perform multiple roles in the field of cancer biology, such as in diagnosis, monitoring, targeting and therapy. Also, other topics are discussed, including the synthesis of SPIONs, the challenges and recent advances.

  13. Magnetic fluid hyperthermia: focus on superparamagnetic iron oxide nanoparticles.

    PubMed

    Laurent, Sophie; Dutz, Silvio; Häfeli, Urs O; Mahmoudi, Morteza

    2011-08-10

    Due to their unique magnetic properties, excellent biocompatibility as well as multi-purpose biomedical potential (e.g., applications in cancer therapy and general drug delivery), superparamagnetic iron oxide nanoparticles (SPIONs) are attracting increasing attention in both pharmaceutical and industrial communities. The precise control of the physiochemical properties of these magnetic systems is crucial for hyperthermia applications, as the induced heat is highly dependent on these properties. In this review, the limitations and recent advances in the development of superparamagnetic iron oxide nanoparticles for hyperthermia are presented.

  14. Cross-linked polystyrene sulfonic acid and polyethylene glycol as a low-fouling material.

    PubMed

    Alghunaim, Abdullah; Zhang Newby, Bi-min

    2016-04-01

    A negatively charged hydrophilic low fouling film was prepared by thermally cross-linking a blend consisting of polystyrene sulfonic acid (PSS) and polyethylene glycol (PEG). The film was found to be stable by dip-washing. The fouling resistance of this material toward bacterial (Escherichia coli) and colloidal (polystyrene particles) attachment, non-specific protein (fibronectin) adsorption and cell (3T3 NIH) adhesion was evaluated and was compared with glass slides modified with polyethylene glycol (PEG) brushes, oxidized 3-mercaptopropyltrimethoxysilane (sulfonic acid, SA), and n-octadecyltrichlorosilane (OTS). The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and thermodynamic models based on surface energy were used to explain the interaction behaviors of E. coli/polystyrene particles-substrate and protein-substrate interactions, respectively. The cross-linked PSS-PEG film was found to be slightly better than SA and PEG toward resisting non-specific protein adsorption, and showed comparable low attachment results as those of PEG toward particle, bacterial and NIH-3T3 cells adhesion. The low-fouling performance of PSS-PEG, a cross-linked film by a simple thermal curing process, could allow this material to be used for applications in aqueous environments, where most low fouling hydrophilic polymers, such as PSS or PEG, could not be easily retained.

  15. Structural Analysis and Mechanical Characterization of Hyaluronic Acid-Based Doubly Cross-Linked Networks

    PubMed Central

    Jha, Amit K.; Hule, Rohan A.; Jiao, Tong; Teller, Sean S.; Clifton, Rodney J.; Duncan, Randall L.; Pochan, Darrin J.; Jia, Xinqiao

    2009-01-01

    We have created a new class of hyaluronic acid (HA)-based hydrogel materials with HA hydrogel particles (HGPs) embedded in and covalently cross-linked to a secondary network. HA HGPs with an average diameter of ∼900 nm and narrow particle size distribution were synthesized using a refined reverse micelle polymerization technique. The average mesh size of the HGPs was estimated to be approximately 5.5 to 7.0 nm by a protein uptake experiment. Sodium periodate oxidation not only introduced aldehyde groups to the particles but also reduced the average particle size. The aldehyde groups generated were used as reactive handles for subsequent cross-linking with an HA derivative containing hydrazide groups. The resulting macroscopic gels contain two distinct hierarchical networks (doubly cross-linked networks, DXNs): one within individual particles and another among different particles. Bulk gels (BGs) formed by direct mixing of HA derivatives with mutually reactive groups were included for comparison. The hydrogel microstructures were collectively characterized by microscopy and neutron scattering techniques. Their viscoelasticity was quantified at low frequencies (0.1−10 Hz) using a controlled stress rheometer and at high frequencies (up to 200 Hz) with a home-built torsional wave apparatus. Both BGs and DXNs are stable elastic gels that become stiffer at higher frequencies. The HA-based DXN offers unique structural hierarchy and mechanical properties that are suitable for soft tissue regeneration. PMID:20046226

  16. Macromolecular cross-linked enzyme aggregates (M-CLEAs) of α-amylase.

    PubMed

    Nadar, Shamraja S; Muley, Abhijeet B; Ladole, Mayur R; Joshi, Pranoti U

    2016-03-01

    Macromolecular cross-linked enzyme aggregates (M-CLEAs) of α-amylase were prepared by precipitation and subsequent cross-linking. The non-toxic, biodegradable, biocompatible, renewable polysaccharide based macromolecular cross-linkers viz. agar, chitosan, dextran, and gum arabic were used as a substitute for traditional glutaraldehyde to augment activity recovery toward macromolecular substrate. Macromolecular cross-linkers were prepared by periodate mediated controlled oxidation of polysaccharides. The effects of precipitating agent, concentration and different cross-linkers on activity recovery of α-amylase CLEAs were investigated. α-Amylase aggregated with ammonium sulphate and cross-linked by dextran showed 91% activity recovery, whereas glutaraldehyde CLEAs (G-CLEAs) exhibited 42% activity recovery. M-CLEAs exhibited higher thermal stability in correlation with α-amylase and G-CLEAs. Moreover, dextran and chitosan M-CLEAs showed same affinity for starch hydrolysis as of free α-amylase. The changes in secondary structures revealed the enhancements in structural and conformational rigidity attributed by cross-linkers. Finally, after five consecutive cycles dextran M-CLEAs retained 1.25 times higher initial activity than G-CLEAs.

  17. Size-dependent magnetic properties of iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Patsula, Vitalii; Moskvin, Maksym; Dutz, Silvio; Horák, Daniel

    2016-01-01

    Uniform iron oxide nanoparticles in the size range from 10 to 24 nm and polydisperse 14 nm iron oxide particles were prepared by thermal decomposition of Fe(III) carboxylates in the presence of oleic acid and co-precipitation of Fe(II) and Fe(III) chlorides by ammonium hydroxide followed by oxidation, respectively. While the first method produced hydrophobic oleic acid coated particles, the second one formed hydrophilic, but uncoated, nanoparticles. To make the iron oxide particles water dispersible and colloidally stable, their surface was modified with poly(ethylene glycol) and sucrose, respectively. Size and size distribution of the nanoparticles was determined by transmission electron microscopy, dynamic light scattering and X-ray diffraction. Surface of the PEG-functionalized and sucrose-modified iron oxide particles was characterized by Fourier transform infrared (FT-IR) and Raman spectroscopy and thermogravimetric analysis (TGA). Magnetic properties were measured by means of vibration sample magnetometry and specific absorption rate in alternating magnetic fields was determined calorimetrically. It was found, that larger ferrimagnetic particles showed higher heating performance than smaller superparamagnetic ones. In the transition range between superparamagnetism and ferrimagnetism, samples with a broader size distribution provided higher heating power than narrow size distributed particles of comparable mean size. Here presented particles showed promising properties for a possible application in magnetic hyperthermia.

  18. Corneal Cross-Linking: Evaluating the Potential for a Lower Power, Shorter Duration Treatment

    PubMed Central

    Caruso, Ciro; Barbaro, Gaetano; Tronino, Diana; Ostacolo, Carmine; Sacchi, Antonia; Pacente, Luigi; Del Prete, Antonio; Sala, Marina; Troisi, Salvatore

    2016-01-01

    Purpose: To determine the cross-linking effect of a riboflavin ultraviolet-A (UV-A) corneal cross-linking treatment that is both shorter and has lower energy than the Dresden protocol. Methods: In a first experiment, 12 human corneas were presoaked with riboflavin and then irradiated with UV-A at 3 mW/cm2 after clearing the surface of riboflavin, with no added riboflavin during irradiation. Percent UV-A transmission through the corneas was measured at intervals up to 30 minutes. A second experiment involved 24 porcine corneas. Eight were de-epithelialized, presoaked in riboflavin for 30 minutes, and irradiated at 1.5 mW/cm2 for 10 minutes. An additional 8 were riboflavin treated and similarly irradiated, but with epithelium intact and a final 8 corneas were not treated. Young modulus was measured in all 24 corneas at the end of the experiment. Results: The first experiment showed essentially complete riboflavin oxidation after only 10 minutes. Based on these results, a shortened UV-A exposure cross-linking experiment was designed using a reduced UV-A fluence of 1.5 mW/cm2, an endothelial exposure within safety limits in humans. With this protocol Young modulus was the same in the irradiated porcine corneas but with epithelium intact as in the untreated corneas. In contrast, Young modulus increased by a factor of 1.99 in the UV-A cross-linked corneas at 1.5 mW/cm2 for 10 minutes with the epithelium removed. Conclusions: A shorter, lower energy protocol than the Dresden protocol seems to provide a significant increase in Young modulus, similar to published results with higher energy, longer exposure protocols. PMID:26989958

  19. Unprecedented Selective Oxidation of Styrene Derivatives using a Supported Iron Oxide Nanocatalyst in Aqueous Medium

    EPA Science Inventory

    Iron oxide nanoparticles supported on mesoporous silica-type materials have been successfully utilized in the aqueous selective oxidation of alkenes under mild conditions using hydrogen peroxide as a green oxidant. Catalysts could be easily recovered after completion of the reac...

  20. Iron oxides, dissolved silica, and regulation of marine phosphate concentration

    NASA Astrophysics Data System (ADS)

    Planavsky, N.; Reinhard, C.; Lyons, T.

    2008-12-01

    Phosphorous concentrations in iron oxide-rich sediments reflect orthophosphate levels in the water column from which iron oxides precipitated. Sediment P/Fe ratios are also strongly influenced by the concentrations of dissolved species that inhibit orthophosphate-to-ferrihydrite sorption, most notably silica. It may, therefore, be possible to use P/Fe ratios in iron oxide-rich sediments to estimate past dissolved P concentrations, if one considers the evolution of the silica cycle. A compilation of Fe and P data in iron oxide-rich sediments through time reveals an increase in P/Fe ratios after the Jurassic. We propose that this trend indicates evolution of the iron-oxide phosphate removal mechanism caused by decreasing levels of sorption inhibition by dissolved silica. The large difference in P/Fe ratios in Cenozoic versus older iron-oxide rich sediments can be linked with Si drawdown caused by the proliferation of siliceous plankton in the Cretaceous. There is also a late Mesozoic or Cenozoic increase in V/Fe ratios, which provides additional evidence for lower ferrihydrite anion sorption efficiency prior to diatom radiation. P/Fe ratios in iron oxide-rich sediments from the early and middle Phanerozoic are comparable to the ratios in iron formations previously presented as evidence for an early Precambrian phosphate crisis (Bjerrum and Canfield, 2002, Nature, 417:159-162). Given the compelling evidence for higher Si concentrations in the Precambrian compared to the Phanerozoic and dissolved P concentrations comparable to modern levels throughout the Phanerozoic, the presented trend of P/Fe ratios suggests dissolved P concentrations were higher in Precambrian than Phanerozoic oceans. High dissolved P levels in the Precambrian may have been linked to inhibited carbonate fluorapatite (CFA) formation as a result of persistently high levels of carbonate supersaturation. Carbonate ion substitution into CFA scales with the ambient carbonate ion activity and increases

  1. Deposition rates of oxidized iron on Mars

    NASA Technical Reports Server (NTRS)

    Burns, R. G.

    1993-01-01

    The reddened oxidized surface of Mars is indicative of temporal interactions between the Martian atmosphere and its surface. During the evolution of the Martian regolith, primary ferromagnesian silicate and sulfide minerals in basaltic rocks apparently have been oxidized to secondary ferric-bearing assemblages. To evaluate how and when such oxidized deposits were formed on Mars, information about the mechanisms and rates of chemical weathering of Fe(2+)-bearing minerals has been determined. In this paper, mechanisms and rates of deposition of ferric oxide phases on the Martian surface are discussed.

  2. Magnetic resonance imaging contrast of iron oxide nanoparticles developed for hyperthermia is dominated by iron content

    PubMed Central

    Wabler, Michele; Zhu, Wenlian; Hedayati, Mohammad; Attaluri, Anilchandra; Zhou, Haoming; Mihalic, Jana; Geyh, Alison; DeWeese, Theodore L.; Ivkov, Robert; Artemov, Dmitri

    2015-01-01

    Purpose Magnetic iron oxide nanoparticles (MNPs) are used as contrast agents for magnetic resonance imaging (MRI) and hyperthermia for cancer treatment. The relationship between MRI signal intensity and cellular iron concentration for many new formulations, particularly MNPs having magnetic properties designed for heating in hyperthermia, is lacking. In this study, we examine the correlation between MRI T2 relaxation time and iron content in cancer cells loaded with various MNP formulations. Materials and methods Human prostate carcinoma DU-145 cells were loaded with starch-coated bionised nanoferrite (BNF), iron oxide (Nanomag® D-SPIO), Feridex™, and dextran-coated Johns Hopkins University (JHU) particles at a target concentration of 50 pg Fe/cell using poly-D-lysine transfection reagent. T2-weighted MRI of serial dilutions of these labelled cells was performed at 9.4 T and iron content quantification was performed using inductively coupled plasma mass spectrometry (ICP-MS). Clonogenic assay was used to characterise cytotoxicity. Results No cytotoxicity was observed at twice the target intracellular iron concentration (~100 pg Fe/cell). ICP-MS revealed highest iron uptake efficiency with BNF and JHU particles, followed by Feridex and Nanomag-D-SPIO, respectively. Imaging data showed a linear correlation between increased intracellular iron concentration and decreased T2 times, with no apparent correlation among MNP magnetic properties. Conclusions This study demonstrates that for the range of nanoparticle concentrations internalised by cancer cells the signal intensity of T2-weighted MRI correlates closely with absolute iron concentration associated with the cells. This correlation may benefit applications for cell-based cancer imaging and therapy including nanoparticle-mediated drug delivery and hyperthermia. PMID:24773041

  3. Nitric oxide ameliorates the damaging effects of oxidative stress induced by iron deficiency in cyanobacterium Anabaena 7120.

    PubMed

    Kaushik, Manish Singh; Srivastava, Meenakshi; Srivastava, Alka; Singh, Anumeha; Mishra, Arun Kumar

    2016-11-01

    In cyanobacterium Anabaena 7120, iron deficiency leads to oxidative stress with unavoidable consequences. Nitric oxide reduces pigment damage and supported the growth of Anabaena 7120 in iron-deficient conditions. Elevation in nitric oxide accumulation and reduced superoxide radical production justified the role of nitric oxide in alleviating oxidative stress in iron deficiency. Increased activities of antioxidative enzymes and higher levels of ROS scavengers (ascorbate, glutathione and thiol) in iron deficiency were also observed in the presence of nitric oxide. Nitric oxide also supported the membrane integrity of Anabaena cells and reduces protein and DNA damage caused by oxidative stress induced by iron deficiency. Results suggested that nitric oxide alleviates the damaging effects of oxidative stress induced by iron deficiency in cyanobacterium Anabaena 7120.

  4. Generation of guanine-thymidine cross-links in DNA by peroxynitrite/carbon dioxide.

    PubMed

    Yun, Byeong Hwa; Geacintov, Nicholas E; Shafirovich, Vladimir

    2011-07-18

    Nitrosoperoxycarbonate derived from the combination of carbon dioxide and peroxynitrite is an important chemical mediator of inflammation. In aqueous solutions, it rapidly decomposes to the reactive species CO(3)(•-) and (•)NO(2) radicals that are known to initiate the selective oxidation and nitration of guanine in DNA. We have previously demonstrated that the reactions of carbonate radical anions with guanine in 2'-deoxyoligoribonucleotides generate a previously unknown intrastrand cross-linked guanine-thymine product G*-T* with a covalent bond between the C8 (G*) and the thymine N3 (T*) atoms (Crean Nucleic Acids Res. 2008, 36, 742-755). In this work, we demonstrate that G*-T* cross-linked products are also formed when peroxynitrite (0.1 mM) reacts with native DNA in aqueous solutions (pH 7.5-7.7) containing 25 mM carbon dioxide/bicarbonate, in addition to the well-known nitration/oxidation products of guanine such as 8-nitroguanine (8-nitro-G), 5-guanidino-4-nitroimidazole (NIm), 8-oxo-7,8-dehydroguanine (8-oxo-G), and spiroiminodihydantoin (Sp). The yields of these products, after enzymatic digestion with P1 nuclease and alkaline phosphatase to the nucleotide level and reversed phase HPLC separation, were compared with those obtained with the uniformly, isotopically labeled (15)N,(13)C-labeled 2'-deoxy oligoribonucleotides 5'-dGpT and 5'-dGpCpT. The d(G*pT*) and d(G*-T*) cross-linked products derived from the di- and trioligonucleotides, respectively, were used as standards for identifying the analogous lesions in calf thymus DNA by isotope dilution LC-MS/MS methods in the selected reaction monitoring mode. The NIm and 8-nitro-G are the major products formed (∼0.05% each), and lesser amounts of 8-oxo-G (∼0.02%) and d(G*pT*) and d(G*-T*) enzymatic digestion products (∼0.002% each) were found. It is shown that the formation of d(G*pT*) enzyme digestion product can arise only from intrastrand cross-links, whereas d(G*-T*) can arise from both interstrand

  5. A Facile and Efficient Approach for the Production of Reversible Disulfide Cross-linked Micelles.

    PubMed

    Li, Yuanpei; Bharadwaj, Gaurav; Lee, Joyce S

    2016-12-23

    Nanomedicine is an emerging form of therapy that harnesses the unique properties of particles that are nanometers in scale for biomedical application. Improving drug delivery to maximize therapeutic outcomes and to reduce drug-associated side effects are some of the cornerstones of present-day nanomedicine. Nanoparticles in particular have found a wide application in cancer treatment. Nanoparticles that offer a high degree of flexibility in design, application, and production based on the tumor microenvironment are projected to be more effective with rapid translation into clinical practice. The polymeric micellar nano-carrier is a popular choice for drug delivery applications. In this article, we describe a simple and effective protocol for synthesizing drug-loaded, disulfide cross-linked micelles based on the self-assembly of a well-defined amphiphilic linear-dendritic copolymer (telodendrimer, TD). TD is composed of polyethylene glycol (PEG) as the hydrophilic segment and a thiolated cholic acid cluster as the core-forming hydrophobic moiety attached stepwise to an amine-terminated PEG using solution-based peptide chemistry. Chemotherapy drugs, such as paclitaxel (PTX), can be loaded using a standard solvent evaporation method. The O2-mediated oxidation was previously utilized to form intra-micellar disulfide cross-links from free thiol groups on the TDs. However, the reaction was slow and not feasible for large-scale production. Recently, an H2O2-mediated oxidation method was explored as a more feasible and efficient approach, and it was 96 times faster than the previously reported method. Using this approach, 50 g of PTX-loaded, disulfide cross-linked nanoparticles have been successfully produced with narrow particle size distribution and high drug loading efficiency. The stability of the resulting micelle solution is analyzed using disrupting conditions such as co-incubation with a detergent, sodium dodecyl sulfate, with or without a reducing agent. The drug

  6. Synthesis, characterization, applications, and challenges of iron oxide nanoparticles

    PubMed Central

    Ali, Attarad; Zafar, Hira; Zia, Muhammad; ul Haq, Ihsan; Phull, Abdul Rehman; Ali, Joham Sarfraz; Hussain, Altaf

    2016-01-01

    Recently, iron oxide nanoparticles (NPs) have attracted much consideration due to their unique properties, such as superparamagnetism, surface-to-volume ratio, greater surface area, and easy separation methodology. Various physical, chemical, and biological methods have been adopted to synthesize magnetic NPs with suitable surface chemistry. This review summarizes the methods for the preparation of iron oxide NPs, size and morphology control, and magnetic properties with recent bioengineering, commercial, and industrial applications. Iron oxides exhibit great potential in the fields of life sciences such as biomedicine, agriculture, and environment. Nontoxic conduct and biocompatible applications of magnetic NPs can be enriched further by special surface coating with organic or inorganic molecules, including surfactants, drugs, proteins, starches, enzymes, antibodies, nucleotides, nonionic detergents, and polyelectrolytes. Magnetic NPs can also be directed to an organ, tissue, or tumor using an external magnetic field for hyperthermic treatment of patients. Keeping in mind the current interest in iron NPs, this review is designed to report recent information from synthesis to characterization, and applications of iron NPs. PMID:27578966

  7. Iron as a catalyst of human low-density lipoprotein oxidation: Critical factors involved in its oxidant properties.

    PubMed

    Lapenna, Domenico; Ciofani, Giuliano; Obletter, Gabriele

    2017-05-01

    Iron-induced human LDL oxidation, which is relevant to atherosclerosis, has not yet been properly investigated. We addressed such issue using iron(II) and (III) basically in the presence of phosphates, which are present in vivo and influence iron oxidative properties, at pH 4.5 and 7.4, representative, respectively, of the lysosomal and plasma environment. In 10mM phosphate buffered saline (PBS), iron(II) induces substantial LDL oxidation at pH 4.5 at low micromolar concentrations, while at pH 7.4 has low oxidative effects; iron(III) promotes small LDL oxidation only at pH 4.5. In 10mM sodium acetate/NaCl buffer, pH 4.5, iron-induced LDL oxidation is far higher than in PBS, highlighting the relevance of phosphates in the inhibitory modulation of iron-induced LDL oxidation. LDL oxidation is related to iron binding to the protein and lipid moiety of LDL, and requires the presence of iron(II) bound to LDL together with iron(III). Chemical modification of LDL carboxyl groups, which could bind iron especially at pH 4.5, decreases significantly iron binding to LDL and iron-induced LDL oxidation. Hydroxyl radical scavengers are ineffective on iron-induced LDL oxidation, which is inhibited by metal chelation, scavengers of alkoxyl/peroxyl radicals, or removal of LDL lipid hydroperoxides (LOOH). Overall, substantial human LDL oxidation is induced LOOH-dependently by iron(II) at pH 4.5 even in the presence of phosphates, suggesting the occurrence of iron(II)-induced LDL oxidation in vivo within lysosomes, where pH is about 4.5, iron(II) and phosphates coexist, plasma with its antioxidants is absent, and glutathione peroxidase is poorly expressed resulting in LOOH accumulation.

  8. Distribution Behavior of Phosphorus and Metallization of Iron Oxide in Carbothermic Reduction of High-Phosphorus Iron Ore

    NASA Astrophysics Data System (ADS)

    Cha, Ji-Whoe; Kim, Dong-Yuk; Jung, Sung-Mo

    2015-10-01

    Distribution behavior of phosphorus and metallization of iron ore in the carbothermic reduction of high-phosphorus iron ore were investigated. Reduction degree of the iron oxide was evaluated by quadruple mass spectrometry connected to thermogravimetric analysis. The distribution of some elements including phosphorus was examined by electron probe micro-analyzer mapping analyses. The reduction behavior of high-phosphorus iron ore was evaluated as a function of reduction temperature, C/O molar ratio, and CaO addition. High reduction temperature accelerated the reduction of both iron oxide and hydroxylapatite, and high C/O molar ratio also promotes both of them. Those were contradictory to the targets of higher reduction degree of iron oxide and of lower one of hydroxylapatite. It was confirmed that appropriate amount of CaO addition could enhance the reduction of iron oxide, and regulate the reduction of hydroxylapatite.

  9. Iron Partitioning and Oxidation State in Earth's Lower Mantle

    NASA Astrophysics Data System (ADS)

    Piet, H.; Badro, J.; Nabiei, F.; Dennenwaldt, T.; Shim, S. H. D.; Cantoni, M.; Hébert, C.; Gillet, P.

    2015-12-01

    Valence state and concentrations of iron in lower mantle phases have strong effects on their chemical and physical properties. Experimental studies have reported stark differences in iron partitioning between bridgmanite (Brg) and ferropericlase (Fp) for San Carlos olivine [1] and pyrolite [2] systems. We recently performed experiments at lower mantle conditions for an Al-rich olivine system [3] and observed an iron enrichment of the silicate phase very similar to that in pyrolite. Mössbauer studies [4] have shown that in the presence of aluminum non negligible amounts of Fe3+ could be incorporated in bridgmanite explaining the observed iron enrichment. Non negligible amounts of Fe3+ in the lower mantle could influence transport properties of the phases [5]. The evaluation of ferrous and ferric iron concentrations in lower mantle mineral assemblages is then key to a thorough understanding of geophysical observations and associated mantle dynamics. We used electron energy loss spectroscopy technique to quantify the proportions of Fe2+ and Fe3+ iron in Brg and Fp phases previously synthesized from Al-rich olivine composition [3]. The oxidation state of iron in the lower mantle will be discussed as well as ensuing implications on transport properties for relevant lower mantle compositions. References [1] Sakai et al., 2009 [2] Prescher et al., 2014 [3] Piet et al., submitted [4] McCammon et al., 1996 [5] Xu et al., 1998

  10. Uptake and metabolism of iron oxide nanoparticles in brain cells.

    PubMed

    Petters, Charlotte; Irrsack, Ellen; Koch, Michael; Dringen, Ralf

    2014-09-01

    Magnetic iron oxide nanoparticles (IONPs) are used for various applications in biomedicine, for example as contrast agents in magnetic resonance imaging, for cell tracking and for anti-tumor treatment. However, IONPs are also known for their toxic effects on cells and tissues which are at least in part caused by iron-mediated radical formation and oxidative stress. The potential toxicity of IONPs is especially important concerning the use of IONPs for neurobiological applications as alterations in brain iron homeostasis are strongly connected with human neurodegenerative diseases. Since IONPs are able to enter the brain, potential adverse consequences of an exposure of brain cells to IONPs have to be considered. This article describes the pathways that allow IONPs to enter the brain and summarizes the current knowledge on the uptake, the metabolism and the toxicity of IONPs for the different types of brain cells in vitro and in vivo.

  11. From iron coordination compounds to metal oxide nanoparticles

    PubMed Central

    Iacob, Mihail; Racles, Carmen; Tugui, Codrin; Stiubianu, George; Bele, Adrian; Sacarescu, Liviu; Timpu, Daniel

    2016-01-01

    Various types, shapes and sizes of iron oxide nanoparticles were obtained depending on the nature of the precursor, preparation method and reaction conditions. The mixed valence trinuclear iron acetate, [Fe2 IIIFeIIO(CH3COO)6(H2O)3]·2H2O (FeAc1), μ3-oxo trinuclear iron(III) acetate, [Fe3O(CH3COO)6(H2O)3]NO3∙4H2O (FeAc2), iron furoate, [Fe3O(C4H3OCOO)6(CH3OH)3]NO3∙2CH3OH (FeF), iron chromium furoate, FeCr2O(C4H3OCOO)6(CH3OH)3]NO3∙2CH3OH (FeCrF), and an iron complex with an original macromolecular ligand (FePAZ) were used as precursors for the corresponding oxide nanoparticles. Five series of nanoparticle samples were prepared employing either a classical thermal pathway (i.e., thermal decomposition in solution, solvothermal method, dry thermal decomposition/calcination) or using a nonconventional energy source (i.e., microwave or ultrasonic treatment) to convert precursors into iron oxides. The resulting materials were structurally characterized by wide-angle X-ray diffraction and Fourier transform infrared, Raman, energy-dispersive X-ray, and X-ray fluorescence spectroscopies, as well as thermogravimetric analysis. The morphology was characterized by transmission electron microscopy, atomic force microscopy and dynamic light scattering. The parameters were varied within each route to fine tune the size and shape of the formed nanoparticles. PMID:28144555

  12. Model selection for athermal cross-linked fiber networks.

    PubMed

    Shahsavari, A; Picu, R C

    2012-07-01

    Athermal random fiber networks are usually modeled by representing each fiber as a truss, a Euler-Bernoulli or a Timoshenko beam, and, in the case of cross-linked networks, each cross-link as a pinned, rotating, or welded joint. In this work we study the effect of these various modeling options on the dependence of the overall network stiffness on system parameters. We conclude that Timoshenko beams can be used for the entire range of density and beam stiffness parameters, while the Euler-Bernoulli model can be used only at relatively low network densities. In the high density-high bending stiffness range, strain energy is stored predominantly in the axial and shear deformation modes, while in the other extreme range of parameters, the energy is stored in the bending mode. The effect of the model size on the network stiffness is also discussed.

  13. Transparent Humidity Sensor Using Cross-Linked Polyelectrolyte Membrane

    SciTech Connect

    Zhang, Q.; Smith, James R.; Saraf, Laxmikant V.; Hua, Feng

    2009-07-02

    This paper describes the fabrication of a porous cross-linked polyelectrolyte membrane and the characterization of its humidity sensitivity performance. Electrostatic self-assembly, combined with acid treatment, and post-deposition annealing produced the membrane. The fabrication process offers the ability to control the thickness of the membrane, as well as enabling the engineering of the humidity sensitivity properties. A transparent humidity sensor was fabricated by integrating the membrane between two parallel electrodes. In order to improve the moisture absorption and diffusion, both the polyelectrolyte layer and the electrode were made porous. The membrane was cross-linked to enhance the durability in high humid environments. Such a polyelectrolyte membrane showed high sensitivity to relative humidity variation over a range of 25%–99%. The see-through property of the structure adds extra features and benefits to the sensor.

  14. Cross-linking reveals laminin coiled-coil architecture

    PubMed Central

    Armony, Gad; Jacob, Etai; Moran, Toot; Levin, Yishai; Mehlman, Tevie; Levy, Yaakov; Fass, Deborah

    2016-01-01

    Laminin, an ∼800-kDa heterotrimeric protein, is a major functional component of the extracellular matrix, contributing to tissue development and maintenance. The unique architecture of laminin is not currently amenable to determination at high resolution, as its flexible and narrow segments complicate both crystallization and single-particle reconstruction by electron microscopy. Therefore, we used cross-linking and MS, evaluated using computational methods, to address key questions regarding laminin quaternary structure. This approach was particularly well suited to the ∼750-Å coiled coil that mediates trimer assembly, and our results support revision of the subunit order typically presented in laminin schematics. Furthermore, information on the subunit register in the coiled coil and cross-links to downstream domains provide insights into the self-assembly required for interaction with other extracellular matrix and cell surface proteins. PMID:27815530

  15. Behavior of iron aluminides in oxidizing and sulfidizing environments

    SciTech Connect

    Tortorelli, P.F.; DeVan, J.H.; DiStefano, J.R.

    1989-01-01

    To date, use of iron aluminides based on Fe/sub 3/Al (less than or equal to30 at. % Al) or FeAl (30--50 at. % Al) for structural applications has been limited by their low ductility and poor fracture toughness at room temperature and inadequate strength above 600/degree/C. However, in recent years, a renewed effort has been devoted to the development of ductile iron aluminides with increased strength, particularly in view of their good potential for use in hostile environments. While it is expected that such aluminides will be able to form oxide scales for corrosion protection in oxidizing high temperature environments, resistance to degradation in oxidizing salt or oxidizing/sulfidizing gas environments has not been adequately addressed as a function of compositional and microstructural changes. This paper reviews and extends results for iron aluminides exposed to an oxidizing/sulfidizing gas and presents the first data for corrosion of this class of materials by an aggressive oxidizing molten nitrate salt of 48.5NaNO/sub 3/--50.5KNO/sub 3/--1Na/sub 2/O/sub 2/. 14 refs., 11 figs.

  16. Reversible PH Lability of Cross-Linked Vault Nanocapsules

    SciTech Connect

    Yu, M.; Ng, B.C.; Rome, L.H.; Tolbert, S.H.; Monbouquette, H.G.

    2009-05-28

    Vaults are ubiquitous, self-assembled protein nanocapsules with dimension in the sub-100 nm range that are conserved across diverse phyla from worms to humans. Their normal presence in humans at a copy number of over 10 000/cell makes them attractive as potential drug delivery vehicles. Toward this goal, bifunctional amine-reactive reagents are shown to be useful for the reversible cross-linking of recombinant vaults such that they may be closed and opened in a controllable manner.

  17. Estimating the Degree of Cross-Linking in Rubber

    NASA Technical Reports Server (NTRS)

    Fedors, R. F.

    1983-01-01

    Degree of cross-linking or network chain concentration of rubber estimated with aid of new method. Quantity is needed in studies of mechanical behavior of rubber. New method is based on finding rubber follows different stress/ strain relationships in extension and retraction. When rubber specimen is stretched to given extension ration and released. Stress-vs-strain curve follows two paths: one for extension and other for retraction.

  18. Cytokines and growth factors cross-link heparan sulfate

    PubMed Central

    Migliorini, Elisa; Thakar, Dhruv; Kühnle, Jens; Sadir, Rabia; Dyer, Douglas P.; Li, Yong; Sun, Changye; Volkman, Brian F.; Handel, Tracy M.; Coche-Guerente, Liliane; Fernig, David G.; Lortat-Jacob, Hugues; Richter, Ralf P.

    2015-01-01

    The glycosaminoglycan heparan sulfate (HS), present at the surface of most cells and ubiquitous in extracellular matrix, binds many soluble extracellular signalling molecules such as chemokines and growth factors, and regulates their transport and effector functions. It is, however, unknown whether upon binding HS these proteins can affect the long-range structure of HS. To test this idea, we interrogated a supramolecular model system, in which HS chains grafted to streptavidin-functionalized oligoethylene glycol monolayers or supported lipid bilayers mimic the HS-rich pericellular or extracellular matrix, with the biophysical techniques quartz crystal microbalance (QCM-D) and fluorescence recovery after photobleaching (FRAP). We were able to control and characterize the supramolecular presentation of HS chains—their local density, orientation, conformation and lateral mobility—and their interaction with proteins. The chemokine CXCL12α (or SDF-1α) rigidified the HS film, and this effect was due to protein-mediated cross-linking of HS chains. Complementary measurements with CXCL12α mutants and the CXCL12γ isoform provided insight into the molecular mechanism underlying cross-linking. Fibroblast growth factor 2 (FGF-2), which has three HS binding sites, was also found to cross-link HS, but FGF-9, which has just one binding site, did not. Based on these data, we propose that the ability to cross-link HS is a generic feature of many cytokines and growth factors, which depends on the architecture of their HS binding sites. The ability to change matrix organization and physico-chemical properties (e.g. permeability and rigidification) implies that the functions of cytokines and growth factors may not simply be confined to the activation of cognate cellular receptors. PMID:26269427

  19. Physicochemical properties of collagen solutions cross-linked by glutaraldehyde.

    PubMed

    Tian, Zhenhua; Li, Conghu; Duan, Lian; Li, Guoying

    2014-06-01

    The physicochemical properties of collagen solutions (5 mg/ml) cross-linked by various amounts of glutaraldehyde (GTA) [GTA/collagen (w/w) = 0-0.5] under acidic condition (pH 4.00) were examined. Based on the results of the determination of residual amino group content, sodium dodecyl sulphate-polyacrylamide gel electrophoresis, dynamic rheological measurements, differential scanning calorimetry and atomic force microscopy (AFM), it was proved that the collagen solutions possessed strikingly different physicochemical properties depending on the amount of GTA. At low GTA amounts [GTA/collagen (w/w) ≤ 0.1], the residual amino group contents of the cross-linked collagens decreased largely from 100% to 32.76%, accompanied by an increase in the molecular weight. Additionally, increases of the fiber diameter and the values of G', G″ and η* were measured, while the thermal denaturation temperature (Td) did not change visibly and the fluidity of collagen samples was still retained with increasing the GTA amount. When the ratio of GTA to collagen exceeded 0.1, although the residual amino group content only decreased by ~8.2%, the cross-linked collagen solution [GTA/collagen (w/w) = 0.3] displayed a clear loss of flow and a sudden rise (~2.0 °C) of the Td value compared to the uncross-linked collagen solution, probably illustrating that the collagen solution was converted into a gel with mature network structure-containing nuclei observed in AFM image. It was conjectured that the physicochemical properties of the collagen solutions might be in connection with the cross-linking between collagen molecules from the same aggregate or different aggregates.

  20. Late failure of annealed highly cross-linked polyethylene acetabular liner.

    PubMed

    Hara, Daisuke; Nakashima, Yasuharu; Yamamoto, Takuaki; Higashihara, Shinshichiro; Todo, Mitsugu; Hirata, Masanobu; Akiyama, Mio; Iwamoto, Yukihide

    2013-12-01

    Highly cross-linked polyethylene (HXPE) in total hip arthroplasty (THA) has been shown to significantly decrease wear rates compared with conventional polyethylene (CPE). However, crosslinking, thermal treatment and oxidation can decrease the mechanical properties of PE, and several cases of fracture of remelted HXPE liners were reported. We present, for the first time, unexpected failures of THA with the use of annealed HXPE liners in two patients occurring at 7 and 8 years after operation. Operative findings revealed dislocated liners from the metal shell and a fracture of the superior rim at the rim-dome junction in both liners. Scanning electron microscopy showed that the cracks initiated at the rim and propagated toward the articular surface. Both liners showed generally a low amount of oxidation (less than 1.00) at the articular surface and low wear rates; however, oxidation at the rim was relatively higher (mean 1.55). These findings suggested that decreased mechanical properties at the rim-dome junction due to cross-linking, annealing and oxidation might have been caused breakage of the HXPE liners after a long implantation time, although the annealed HXPE achieved low degree of wear.

  1. Induction and repair of DNA cross-links induced by sulfur mustard in the A-549 cell line followed by a comet assay.

    PubMed

    Jost, Petr; Svobodova, Hana; Stetina, Rudolf

    2015-07-25

    Sulfur mustard is a highly toxic chemical warfare agent with devastating impact on intoxicated tissues. DNA cross-links are probably the most toxic DNA lesions induced in the cell by sulfur mustard. The comet assay is a very sensitive method for measuring DNA damage. In the present study using the A-549 lung cell line, the comet assay protocol was optimized for indirect detection of DNA cross-links induced by sulfur mustard. The method is based on the additional treatment of the assayed cells containing cross-links with the chemical mutagen, styrene oxide. Alkali-labile adducts of styrene oxide cause DNA breaks leading to the formation of comets. A significant dose-dependent reduction of DNA migration of the comet's tail was found after exposing cells to sulfur mustard, indicative of the amount of sulfur mustard induced cross-links. The remarkable decrease of % tail DNA could be observed as early as 5min following exposure to sulfur mustard and the maximal effect was found after 30min, when DNA migration was reduced to the minimum. Sulfur mustard preincubated in culture medium without cells lost its ability to induce cross-links and had a half-life of about 15min. Pre-incubation longer than 30min does not lead to a significant increase in cross-links when applied to cells. However, the amount of cross-links is decreased during further incubation due to repair. The current modification of the comet assay provides a useful tool for detecting DNA cross-links induced by sulfur mustard and could be used for detection of other DNA cross-linking agents such as chemotherapeutic drugs.

  2. Magnetic macromolecular cross linked enzyme aggregates (CLEAs) of glucoamylase.

    PubMed

    Nadar, Shamraja S; Rathod, Virendra K

    2016-02-01

    This work illustrates the preparation of magnetic macromolecular glucoamylase CLEAs using dialdehydic pectin, as a cross linker instead of traditional glutaraldehyde. The effect of precipitators type and amount, cross linker concentration, cross linking time and amount of amino functionalized magnetic nanoparticles (AFMNs) on glucoamylase activity was studied. Glucoamylase magnetic macromolecular CLEAs prepared by precipitation in presence of AFMNs by ammonium sulfate were subsequently cross linked by dialdehydic pectin. After cross-linked by pectin, 95.4% activity recovery was achieved in magnetic macromolecular CLEAs, whereas in case of glutaraldehyde cross linker, 85.3% activity recovery was achieved. Magnetic macromolecular CLEAs showed 2.91 and 1.27 folds higher thermal stability as compared to free and magnetic glutaraldehyde CLEAs. In kinetics study, magnetic macromolecular CLEAs retained same Km values, whereas magnetic glutaraldehyde CLEAs showed higher Km value than free enzyme. The porous structure of magnetic macromolecular CLEAs was not only enhanced mass transfer toward macromolecular substrates, but also showed compression resistance for 5 consecutive cycles which was checked in terms of effectiveness factor. At the end, in reusability study; magnetic macromolecular CLEAs were retained 84% activity after 10(th) cycle without leaching of enzyme which is 22% higher than traditional magnetic CLEAs.

  3. Homogeneous UVA system for corneal cross-linking treatment

    NASA Astrophysics Data System (ADS)

    Ayres Pereira, Fernando R.; Stefani, Mario A.; Otoboni, José A.; Richter, Eduardo H.; Ventura, Liliane

    2010-02-01

    The treatment of keratoconus and corneal ulcers by collagen cross-linking using ultraviolet type A irradiation, combined with photo-sensitizer Riboflavin (vitamin B2), is a promising technique. The standard protocol suggests instilling Riboflavin in the pre-scratched cornea every 5min for 30min, during the UVA irradiation of the cornea at 3mW/cm2 for 30 min. This process leads to an increase of the biomechanical strength of the cornea, stopping the progression, or sometimes, even reversing Keratoconus. The collagen cross-linking can be achieved by many methods, but the utilization of UVA light, for this purpose, is ideal because of its possibility of a homogeneous treatment leading to an equal result along the treated area. We have developed a system, to be clinically used for treatment of unhealthy corneas using the cross-linking technique, which consists of an UVA emitting delivery device controlled by a closed loop system with high homogeneity. The system is tunable and delivers 3-5 mW/cm2, at 365nm, for three spots (6mm, 8mm and 10mm in diameter). The electronics close loop presents 1% of precision, leading to an overall error, after the calibration, of less than 10% and approximately 96% of homogeneity.

  4. Ion exchange selectivity for cross-linked polyacrylic acid

    NASA Technical Reports Server (NTRS)

    May, C. E.; Philipp, W. H.

    1983-01-01

    The ion separation factors for 21 common metal ions with cross-linked polyacrylic acid were determined as a function of pH and the percent of the cross-linked polyacrylic acid neutralized. The calcium ion was used as a reference. At a pH of 5 the decreasing order of affinity of the ions for the cross-linked polyacrylic acid was found to be: Hg++, Fe+++, Pb++, Cr+++, Cu++, Cd++, Al+++, Ag+, Zn++, Ni++, Mn++, Co++, Ca++, Sr++, Ba++, Mg++, K+, Rb+, Cs+, Na+, and Li+. Members of a chemical family exhibited similar selectivities. The Hg++ ion appeared to be about a million times more strongly bound than the alkali metal ions. The relative binding of most of the metal ions varied with pH; the very tightly and very weakly bound ions showed the largest variations with pH. The calcium ion-hydrogen ion equilibrium was perturbed very little by the presence of the other ions. The separation factors and selectivity coefficients are discussed in terms of equilibrium and thermodynamic significance.

  5. Fiber optic immunosensor for cross-linked fibrin concentration

    NASA Astrophysics Data System (ADS)

    Moskowitz, Samuel E.

    2000-08-01

    Working with calcium ions in the blood, platelets produce thromboplastin which transforms prothrombin into thrombin. Removing peptides, thrombin changes fibrinogen into fibrin. Cross-linked insoluble fibrin polymers are solubilized by enzyme plasmin found in blood plasma. Resulting D-dimers are elevated in patients with intravascular coagulation, deep venous thrombosis, pulmonary embolism, myocardial infarction, multiple trauma, cancer, impaired renal and liver functions, and sepsis. Consisting principally of a NIR 780 nm GaAlAs laser diode and a 800 nm avalanche photodiode (APD), the fiber-optic immunosensor can determined D-dimer concentration to levels <0.1 ng/ml. A capture monoclonal antibody to the antigen soluble cross-linked fibrin is employed. Immobilized at the tip of an optical fiber by avidin-biotin, the captured antigen is detected by a second antibody which is labeled with NN 382 fluorescent dye. An evanescent wave traveling on an excitation optical fiber excites the antibody-antigen fluorophore complex. Concentration of cross-linked fibrin is directly proportional to the APD measured intensity of fluorescence. NIR fluorescence has advantages of low background interference, short fluorescence lifetime, and large difference between excitation and emission peaks. Competitive ELISA test for D-dimer concentration requires trained personnel performing a time consuming operation.

  6. Electrochemical Characterization of Ultrathin Cross-Linked Metal Nanoparticle Films.

    PubMed

    Han, Chu; Percival, Stephen J; Zhang, Bo

    2016-09-06

    Here we report the preparation, characterization, and electrochemical study of conductive, ultrathin films of cross-linked metal nanoparticles (NPs). Nanoporous films ranging from 40 to 200 nm in thickness composed of gold and platinum NPs of ∼5 nm were fabricated via a powerful layer-by-layer spin coating process. This process allows preparation of uniform NP films as large as 2 × 2 cm(2) with precise control over thickness, structure, and electrochemical and electrocatalytic properties. Gold, platinum, and bimetallic NP films were fabricated and characterized using cyclic voltammetry, scanning electron microscopy, and conductance measurements. Their electrocatalytic activity toward the oxygen reduction reaction (ORR) was investigated. Our results show that the electrochemical activity of such NP films is initially hindered by the presence of dense thiolate cross-linking ligands. Both electrochemical cycling and oxygen plasma cleaning are effective means in restoring their electrochemical activity. Gold NP films have higher electric conductivity than platinum possibly due to more uniform film structure and closer particle-particle distance. The electrochemical and electrocatalytic performance of platinum NP films can be greatly enhanced by the incorporation of gold NPs. This work focuses on electrochemical characterization of cross-linked NP films and demonstrates several unique properties. These include quick and easy preparation, ultrathin and uniform film thickness, tunable structure and composition, and transferability to many other substrates.

  7. Supersaturated lysozyme solution structure studied by chemical cross-linking.

    PubMed

    Hall, Clayton L; Clemens, John R; Brown, Amanda M; Wilson, Lori J

    2005-06-01

    Glutaraldehyde cross-linking followed by separation has been used to detect aggregates of chicken egg-white lysozyme (CEWL) in supersaturated solutions. In solutions of varying NaCl content, the number of aggregates was found to be related to the ionic strength of the solution. Separation by SDS-PAGE showed that percentage of dimer in solution ranged from 25.3% for no NaCl to 27.1% at 15% NaCl, and the aggregates larger than dimer increased from 1.9% for no NaCl to 36.8% at 15% NaCl. Conversely, the percentage of monomers decreased from 72.8% without NaCl to 36.1% at 15% NaCl. Molecular weights by capillary electrophoresis (SDS-CE) were found to be multiples of the monomer molecular weights, with the exception of trimer, which indicates a very compact structure. Native separation was accomplished using size-exclusion chromatography (SEC) and gave a lower monomer concentration and higher aggregate concentration than SDS-CE, which is a denaturing separation method. Most noticeably, trimers were absent in the SEC separation. The number of aggregates did not change with increased time between addition of NaCl and addition of cross-linking agent when separated by gel electrophoresis (SDS-PAGE). The results suggest that high ionic strength CEWL solutions are highly aggregated and that denaturing separation methods disrupt cross-linked products.

  8. 40 CFR 721.10529 - Cobalt iron manganese oxide, carboxylic acid-modified (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Cobalt iron manganese oxide... Significant New Uses for Specific Chemical Substances § 721.10529 Cobalt iron manganese oxide, carboxylic acid... substance identified generically as cobalt iron manganese oxide, carboxylic acid-modified (PMN P-12-35)...

  9. 40 CFR 721.10529 - Cobalt iron manganese oxide, carboxylic acid-modified (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Cobalt iron manganese oxide... Significant New Uses for Specific Chemical Substances § 721.10529 Cobalt iron manganese oxide, carboxylic acid... substance identified generically as cobalt iron manganese oxide, carboxylic acid-modified (PMN P-12-35)...

  10. Simultaneous reductive dissolution of iron oxide and oxidation of iodide in ice.

    NASA Astrophysics Data System (ADS)

    Kim, Kitae; Choi, Wonyong

    2015-04-01

    Iron is an important trace element controlling the metabolism and growth of all kinds of living species. Especially, the bio-availability of iron has been regarded as the limiting factor for primary productivity in HNLC (High Nutrients Low Chlorophyll) regions including Southern ocean. The dissolution of iron oxide provides enhanced the bio-availability of iron for phytoplankton growth. The halogen chemistry in polar regions is related to various important environmental processes such as Antarctic Ozone Depletion Event(ODE), mercury depletion, oxidative processes in atmosphere, and the formation of CCN (Cloud Condensation Nuclei). In this study, we investigated the reductive dissolution of iron oxide particles to produce Fe(II)aq and simultaneous oxidation of I- (iodide) to I3- (tri-iodide) in ice phase under UV irradiation or dark condition. The reductive generation of Fe(II)aq from iron oxides and oxidation of iodide to I3- were negligible in water but significantly accelerated in frozen solution both in the presence and absence of light. The enhanced reductive generation of Fe(II)aq and oxidative formation of I3- in ice were observed regardless of the various types of iron oxides [hematite (α-Fe2O3) maghemite (γ- Fe2O3), goethite (α-FeOOH), lepidocrocite (γ-FeOOH) and, magnetite (Fe3O4)]. We explained that the enhanced redox production of Fe(II)aq and I3- in ice is contributed to the freeze concentration of iodides, protons, and dissolved oxygen in the unfrozen solution. When the concentration of both iodides and protons were raised by 10-fold each, the formation of Fe(II)aq in water under UV irradiation was approached to those in ice. The outdoor experiments were carried out under ambient solar radiation in winter season of mid-latitude (Pohang, Korea: 36°N latitude) and also confirmed that the production of Fe(II)aq via reductive dissolution of iron oxide and I3- generation via I- oxidation were enhanced in frozen solution. These results suggest that iron

  11. Cross linking molecular systems to form ultrathin dielectric layers

    NASA Astrophysics Data System (ADS)

    Feng, Danqin

    Dehydrogenation leads to cross linking of polymer or polymer like formation in very different systems: self-assembled monolayers and in closo -carboranes leading to the formation of semiconducting and dielectric boron carbide. We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1';4',1"-terphenyl]-4,4"-dimethanethiol, from the dispersion of the molecular orbitals with changing the wave vector k and from the changes with temperature. With the formation self assembled molecular (SAM) layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. Although organic adsorbates and thin films are generally regarded as "soft" materials, the effective Debye temperature, indicative of the dynamic motion of the lattice normal to the surface, can be very high, e.g. in the multilayer film formed from [1,1'-biphenyl]-4,4'-dimethanethiol (BPDMT). Depending on molecular orientation, the effective Debye temperature can be comparable to that of graphite due to the 'stiffness' of the benzene rings, but follows the expected Debye-Waller behavior for the core level photoemission intensities with temperature. This is not always the case. We find that a monomolecular film formed from [1,1';4',1"-terphenyl]-4,4"-dimethanethiol deviates from Debye-Waller temperature behavior and is likely caused by temperature dependent changes in molecular orientation. We also find evidence for the increase in dielectric character with polymerization (cross-linking) in spite of the decrease in the HOMO-LUMO gap upon irradiation of TPDMT. The changes in the HOMO-LUMO gap, with cross-linking, are roughly consistent with the band dispersion. The decomposition and cross-linking processes are also accompanied by changes in molecular orientation. The energetics of the three isomeric carborane cage compounds [ closo-1,2-orthocarborane, closo-1

  12. Towards aging mechanisms of cross-linked polyethylene (XLPE) cable insulation materials in nuclear power plants

    SciTech Connect

    Liu, Shuaishuai; Fifield, Leonard S.; Bowler, Nicola

    2016-12-19

    Cross-linked polyethylene (XLPE) cable insulation material undergoes simultaneous, accelerated thermal and gamma-radiation aging to simulate the long-term aging environment within nuclear power plants (NPPs). A variety of materials characterization tests, including scanning electron microscopy, thermo-gravimetric analysis, differential scanning calorimetry, oxidation induction time, gel-fraction and dielectric properties measurement, are conducted on pristine and differently aged XLPE samples. A preliminary model of one possible aging mechanism of XLPE cable insulation material under gamma radiation at elevated temperature of 115 °C is suggested.

  13. Effects of chebulic acid on advanced glycation endproducts-induced collagen cross-links.

    PubMed

    Lee, Ji-Young; Oh, Jun-Gu; Kim, Jin Sook; Lee, Kwang-Won

    2014-01-01

    Advanced glycation end-products (AGEs) have been implicated in the development of diabetic complications. We report the antiglycating activity of chebulic acid (CA), isolated from Terminalia chebula on breaking the cross-links of proteins induced by AGEs and inhibiting the formation of AGEs. Aminoguanidine (AG) reduced 50% of glycated bovine serum albumin (BSA) with glycolaldehyde (glycol-BSA)-induced cross-links of collagen at a concentration of 67.8 ± 2.5 mM, the level of CA required for exerting a similar antiglycating activity was 38.8 ± 0.5 µM. Also, the breaking activity on collagen cross-links induced by glycol-BSA was potent with CA (IC50=1.46 ± 0.05 mM), exhibiting 50-fold stronger breaking activity than with ALT-711, a well-known cross-link breaker (IC50=72.2 ± 2.4 mM). IC50 values of DPPH· scavenging activity for CA and ascorbic acid (AA) were 39.2 ± 4.9 and 19.0 ± 1.2 µg dry matter (DM) mL(-1), respectively, and ferric reducing and antioxidant power (FRAP) activities for CA and AA were 4.70 ± 0.06 and 11.4 ± 0.1 mmol/FeSO4·7H2O/g DM, respectively. The chelating activities of CA, AG and ALT711 on copper-catalyzed oxidation of AA were compared, and in increasing order, ALT-711 (IC50 of 1.92 ± 0.20 mM)cross-linking, the activity of which may be explained in large part by its chelating and antioxidant activities, suggesting that CA may constitute a promising antiglycating candidate in intervening AGE-mediated diabetic complications.

  14. Oxidation, carburization and/or sulfidation resistant iron aluminide alloy

    DOEpatents

    Sikka, Vinod K.; Deevi, Seetharama C.; Fleischhauer, Grier S.; Hajaligol, Mohammad R.; Lilly, Jr., A. Clifton

    2003-08-19

    The invention relates generally to aluminum containing iron-base alloys useful as electrical resistance heating elements. The aluminum containing iron-base alloys have improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The alloy has an entirely ferritic microstructure which is free of austenite and includes, in weight %, over 4% Al, .ltoreq.1% Cr and either .gtoreq.0.05% Zr or Zro.sub.2 stringers extending perpendicular to an exposed surface of the heating element or .gtoreq.0.1% oxide dispersoid particles. The alloy can contain 14-32% Al, .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Zr, .ltoreq.1% C, .ltoreq.0.1% B. .ltoreq.30% oxide dispersoid and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, .ltoreq.1% oxygen, .ltoreq.3% Cu, balance Fe.

  15. Deep reduction behavior of iron oxide and its effect on direct CO oxidation

    NASA Astrophysics Data System (ADS)

    Dong, Changqing; Liu, Xinglei; Qin, Wu; Lu, Qiang; Wang, Xiaoqiang; Shi, Simo; Yang, Yongping

    2012-01-01

    Reduction of metal oxide oxygen carrier has been attractive for direct CO oxidation and CO2 separation. To investigate the reduction behaviors of iron oxide prepared by supporting Fe2O3 on γ-Al2O3 and its effect on CO oxidation, fluidized-bed combustion experiments, thermogravimetric analyzer (TGA) experiments, and density functional theory (DFT) calculations were carried out. Gas yield (γCO2) increases significantly with the increase of temperature from 693 K to 1203 K, while carbon deposition decreases with the increase of temperature from 743 K to 1203 K, where temperature is a very important factor for CO oxidation by iron oxide. Further, it were quantitatively detected that the interaction between CO and Fe2O3, breakage of O-Fe bonds and formation of new C-O bonds, and effect of reduction degree were quantitatively detected. Based on adsorptions under different temperatures and reducing processes from Fe3+ into Fe2+, Fe+ and then into Fe, it was found that Fe2+ → Fe+ was the reaction-controlling step and the high oxidation state of iron is active for CO oxidation, where efficient partial reduction of Fe2O3 into FeO rather than complete reduction into iron may be more energy-saving for CO oxidation.

  16. Effect of cross-linking on the microstructure and mechanical properties of ultra-high molecular weight polyethylene.

    PubMed

    Ries, Michael D; Pruitt, Lisa

    2005-11-01

    Ultra-high molecular weight polyethylene is a semicrystalline polymer, which means that a portion of the molecules is in a solid crystalline phase and the remaining portion is in a rubbery amorphous phase. Varying the polymer chemistry in the two phases can alter the mechanical properties of the material. When highly cross-linked polyethylene is formed, the cross-links occur in the amorphous but not the crystalline region. Remelting after irradiation-induced cross-linking neutralizes the free radicals that are caused by irradiation but also decreases the amount of crystallinity. Decreased crystallinity can contribute to a decrease in mechanical properties. Annealing below the melt temperature after irradiation retains a higher level of crystallinity. However, heating below the melt temperature does not neutralize irradiation-induced free radicals that can then react with oxygen, causing oxidative degradation. Newer "second-generation" highly cross-linked polyethylenes have been developed that are annealed below the melt temperature, but use either a pharmacologic antioxidant, mechanical deformation, or sequential low-dose irradiation and annealing treatments rather than heating above the melt point to neutralize residual free radicals. High-pressure treatment at elevated temperatures also can increase crystallinity. However, increased crystallinity is associated with an increase in modulus and contact stress, which can increase wear. Although cross-linking ultra-high molecular weight polyethylene can reduce wear, currently available highly cross-linked polyethylenes also decrease mechanical properties when compared with conventional ultra-high molecular weight polyethylene, so that use of these materials in total knee arthroplasty may contribute to mechanical failure of the bearing surface.

  17. Oxide Dispersion Strengthened Iron Aluminide by CVD Coated Powders

    SciTech Connect

    Asit Biswas Andrew J. Sherman

    2006-09-25

    This I &I Category2 program developed chemical vapor deposition (CVD) of iron, aluminum and aluminum oxide coated iron powders and the availability of high temperature oxidation, corrosion and erosion resistant coating for future power generation equipment and can be used for retrofitting existing fossil-fired power plant equipment. This coating will provide enhanced life and performance of Coal-Fired Boilers components such as fire side corrosion on the outer diameter (OD) of the water wall and superheater tubing as well as on the inner diameter (ID) and OD of larger diameter headers. The program also developed a manufacturing route for readily available thermal spray powders for iron aluminide coating and fabrication of net shape component by powder metallurgy route using this CVD coated powders. This coating can also be applid on jet engine compressor blade and housing, industrial heat treating furnace fixtures, magnetic electronic parts, heating element, piping and tubing for fossil energy application and automotive application, chemical processing equipment , heat exchanger, and structural member of aircraft. The program also resulted in developing a new fabrication route of thermal spray coating and oxide dispersion strengthened (ODS) iron aluminide composites enabling more precise control over material microstructures.

  18. Covalent Immobilization of Catalase onto Regenerated Silk Fibroins via Tyrosinase-Catalyzed Cross-Linking.

    PubMed

    Wang, Ping; Qi, Chenglong; Yu, Yuanyuan; Yuan, Jiugang; Cui, Li; Tang, Gengtie; Wang, Qiang; Fan, Xuerong

    2015-09-01

    Regenerated silk fibroins could be used as medical scaffolds and carrier materials for enzyme immobilization. In the present work, tyrosinase enzyme was used for enzymatic oxidation of silk fibroins, followed by immobilization of catalase onto the fibroin surfaces through physical adsorption and covalent cross-linking as well. Spectrophotometry, SDS-PAGE, and Fourier transform infrared spectroscopy (FTIR) were used to examine the efficiency of enzymatic oxidation and catalase immobilization, respectively. The results indicate that tyrosine residues in silk fibroins could be oxidized and converted to the active o-quinones. Incubating silk fibroins with catalase and tyrosinase led to a noticeable change of molecular weight distribution, indicating the occurrence of the cross-links between silk fibroins and catalase molecules. Two different pathways were proposed for the catalase immobilizations, and the method based on grafting of catalase onto the freeze-dried fibroin membrane is more acceptable. The residual enzyme activity for the immobilized catalase exhibited higher than that of the control after repeated washing cycles. Meanwhile, the thermal stability and alkali resistance were also slightly improved as compared to free catalase. The mechanisms of enzymatic immobilization are also concerned.

  19. Binding and Internalization of Iron Oxide Nanoparticles Targeted to Nuclear Oncoprotein

    PubMed Central

    Knight, Linda C.; Romano, Jan E.; Krynska, Barbara; Faro, Scott; Mohamed, Feroze B.; Gordon, Jennifer

    2013-01-01

    A targeted nanoconjugate is being developed for non-invasive detection of gene expression in cells expressing the JC virus oncoprotein, T-antigen, which has been associated with medulloblastoma and other cancers. JC virus T-antigen localizes predominantly to the nucleus via a classical monopartite nuclear localization signal (NLS). An antibody fragment which recognizes JC virus T-antigen was attached to cross-linked dextran coated iron oxide nanoparticles. Radiolabeled conjugates were added to mouse medulloblastoma cells expressing the target T-antigen to test their ability to bind to tumor cells and be internalized by the cells. All conjugates containing targeting antibody bound to cells and were internalized, with increasing levels over time. There was no difference in cell binding or internalization among conjugates containing 2, 4, 6 or 8 antibody fragments per nanoparticle. Conjugates with only nonspecific antibody on nanoparticles, or unconjugated nonspecific antibody, had significantly lower total binding and internalization than conjugates with targeting antibody. Unconjugated targeting antibody had equivalent or lower cell uptake compared with targeted nanoparticle conjugates. Specificity of uptake was demonstrated by >80% reduction of nanoconjugate uptake in the presence of 100 fold excess of unconjugated antibody. The presence of a membrane translocation peptide (Tat) on the nanoparticles in addition to targeting antibody did not improve nanoconjugate internalization over the internalization caused by the antibody alone. This antibody nanoconjugate demonstrates feasibility of targeting a nuclear protein and suggests that a minimum number of antibody fragments per nanoparticle are sufficient for achieving binding specificity and efficient uptake into living cells. PMID:23487404

  20. Intratumoral iron oxide nanoparticle hyperthermia and radiation cancer treatment

    NASA Astrophysics Data System (ADS)

    Hoopes, P. J.; Strawbridge, R. R.; Gibson, U. J.; Zeng, Q.; Pierce, Z. E.; Savellano, M.; Tate, J. A.; Ogden, J. A.; Baker, I.; Ivkov, R.; Foreman, A. R.

    2007-02-01

    The potential synergism and benefit of combined hyperthermia and radiation for cancer treatment is well established, but has yet to be optimized clinically. Specifically, the delivery of heat via external arrays /applicators or interstitial antennas has not demonstrated the spatial precision or specificity necessary to achieve appropriate a highly positive therapeutic ratio. Recently, antibody directed and possibly even non-antibody directed iron oxide nanoparticle hyperthermia has shown significant promise as a tumor treatment modality. Our studies are designed to determine the effects (safety and efficacy) of iron oxide nanoparticle hyperthermia and external beam radiation in a murine breast cancer model. Methods: MTG-B murine breast cancer cells (1 x 106) were implanted subcutaneous in 7 week-old female C3H/HeJ mice and grown to a treatment size of 150 mm3 +/- 50 mm3. Tumors were then injected locally with iron oxide nanoparticles and heated via an alternating magnetic field (AMF) generator operated at approximately 160 kHz and 400 - 550 Oe. Tumor growth was monitored daily using standard 3-D caliper measurement technique and formula. specific Mouse tumors were heated using a cooled, 36 mm diameter square copper tube induction coil which provided optimal heating in a 1 cm wide region in the center of the coil. Double dextran coated 80 nm iron oxide nanoparticles (Triton Biosystems) were used in all studies. Intra-tumor, peri-tumor and rectal (core body) temperatures were continually measured throughout the treatment period. Results: Preliminary in vivo nanoparticle-AMF hyperthermia (167 KHz and 400 or 550 Oe) studies demonstrated dose responsive cytotoxicity which enhanced the effects of external beam radiation. AMF associated eddy currents resulted in nonspecific temperature increases in exposed tissues which did not contain nanoparticles, however these effects were minor and not injurious to the mice. These studies also suggest that iron oxide nanoparticle

  1. Niobian iron oxides as heterogeneous Fenton catalysts for environmental remediation

    NASA Astrophysics Data System (ADS)

    Oliveira, Diana Q. L.; Oliveira, Luiz C. A.; Murad, Enver; Fabris, José D.; Silva, Adilson C.; de Menezes, Lucas Morais

    2010-01-01

    Heterogeneous Fenton or Fenton-like reagents consist of a mixture of an iron-containing solid matrix and a liquid medium with H2O2. The Fenton system is based on the reaction between Fe2 + and H2O2 to produce highly reactive intermediate hydroxyl radicals ( • OH), which are able to oxidize organic contaminants, whereas the Fenton-like reaction is based on the reaction between Fe3 + and H2O2. These heterogeneous systems offer several advantages over their homogeneous counterparts, such as no sludge formation, operation at near-neutral pH and the possibility of recycling the iron promoter. Some doping transition cations in the iron oxide structure are believed to enhance the catalytic efficiency for the oxidation of organic substrates in water. In this work, goethites synthesized in presence of niobium served as precursors for the preparation of magnetites (niobian magnetites) via chemical reduction with hydrogen at 400°C. These materials were used as Fenton-like catalysts. Both groups of (Nb, Fe)-oxide samples were characterized by 57Fe Mössbauer spectroscopy at 298 K. The results show that increasing niobium contents raise the catalytic potential for decomposition of methylene blue, which was, in this work, used as a model molecule for organic substrates in water.

  2. Oxidative effect of several intravenous iron complexes in the rat.

    PubMed

    Bailie, George R; Schuler, Catherine; Leggett, Robert E; Li, Hsin; Li, Hsin-Dat; Patadia, Hiten; Levin, Robert

    2013-06-01

    The objective of this study was to compare the oxidative stress induced in rat internal organs by the administration of the following clinically used intravenous (IV) iron (Fe) containing compounds: iron sucrose (IS), iron dextran (ID), ferric carboxymaltose and ferumoxytol. Groups of six adult rats received 1 mg/kg of each compound weekly for 5 doses. Seven days following the last dose, animals were euthanized and tissue samples of heart, lung, liver, and kidney were obtained, washed in warmed saline and frozen under liquid nitrogen and stored at -80 °C for analysis for nitrotyrosine (NT) and dinitro phenyl (DNP) as markers of oxidative stress. All tissues showed a similar pattern of oxidative stress. All Fe products stimulated an increase in the tissue concentration of both NT and DNP. In general, DNP was stimulated significantly less than NT except for IS. DNP was stimulated to an equal degree except for ID where NT was significantly higher than the NT concentrations in all other Fe compounds. ID produced over 10-fold the concentration of NT than any other Fe. IV Fe compounds present a risk of oxidative stress to a variety of internal organs. However, we found that IS was the least damaging and ID was the worst.

  3. Autoclavable highly cross-linked polyurethane networks in ophthalmology.

    PubMed

    Bruin, P; Meeuwsen, E A; van Andel, M V; Worst, J G; Pennings, A J

    1993-11-01

    Highly cross-linked aliphatic polyurethane networks have been prepared by the bulk step reaction of low molecular weight polyols and hexamethylenediisocyanate (HDI). These polyurethane networks are optically transparent, colourless and autoclavable amorphous glassy thermosets, which are suited for use in ophthalmic applications such as intraocular lenses and keratoprostheses. The properties of these glassy polyurethanes, obtained from the reaction of the low molecular weight polyols triisopropanolamine (TIPA) or tetrakis (2-hydroxypropyl)ethylenediamine (Quadrol) and HDI in stoichiometric proportions, have been investigated in more detail. The glassy Quadrol/HDI-based polyurethane exhibits a reduction in ultimate glass transition temperature from 85 to 48 degrees C by uptake of 1% of water, and good ultimate mechanical properties (tensile strength 80-85 MPa, elongation at break ca 15%, modulus ca 1.5 GPa). IR spectra of these hydrophobic polyurethane networks revealed the absence of an isocyanate absorption, indicating that all isocyanates, apparently, had reacted during the cross-linking reaction. The biocompatibility could be increased by grafting tethered polyacrylamide chains onto the surface during network formation. These transparent cross-linked polyurethanes did not transmit UV light up to 400 nm, by incorporation of a small amount of the UV absorbing chromophore Coumarin 102, and could be sterilized simply by autoclaving. They were implanted in rabbit eyes, either in the form of small circular disks or in the form of a keratoprosthesis (artificial cornea). It was shown that the material was well tolerated by the rabbit eyes. Serious opacification of the cornea, a direct result of an adverse reaction to the implant, was never seen. Even 1 yr after implantation of a polyurethane keratoprosthesis the eye was still 'quiet'.

  4. Macrophage response to cross-linked and conventional UHMWPE.

    PubMed

    Sethi, Rajiv K; Neavyn, Mark J; Rubash, Harry E; Shanbhag, Arun S

    2003-07-01

    To prevent wear debris-induced osteolysis and aseptic loosening, cross-linked ultra-high molecular weight polyethylene's (UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked UHMWPE (XLPE) and compared it to conventional UHMWPE (CPE) as well as other clinically used orthopaedic materials such as titanium-alloy (TiAlV) and cobalt-chrome alloy (CoCr). Human peripheral blood monocytes and murine macrophages, as surrogates for cells mediating peri-implant inflammation, were cultured onto custom designed lipped disks fabricated from the test materials to isolate cells. Culture supernatants were collected at 24 and 48h and analyzed for cytokines such as IL-1alpha, IL-1beta, TNF-alpha and IL-6. Total RNA was extracted from adherent cells and gene expression was analyzed using qualitative RT-PCR. In both in vitro models, macrophages cultured on cross-linked and conventional polyethylene released similar levels of cytokines, which were also similar to levels on control tissue culture dishes. Macrophages cultured on TiAlV and CoCr-alloy released significantly higher levels of cytokines. Human monocytes from all donors varied in the magnitude of cytokines released when cultured on identical surfaces. The variability in individual donor responses to TiAlV and CoCr surfaces may reflect how individuals respond differently to similar stimuli and perhaps reveal a predisposed sensitivity to particular materials.

  5. Polyimide Aerogels with Three-Dimensional Cross-Linked Structure

    NASA Technical Reports Server (NTRS)

    Panek, John

    2010-01-01

    Polyimide aerogels with three-dimensional cross-linked structure are made using linear oligomeric segments of polyimide, and linked with one of the following into a 3D structure: trifunctional aliphatic or aromatic amines, latent reactive end caps such as nadic anhydride or phenylethynylphenyl amine, and silica or silsesquioxane cage structures decorated with amine. Drying the gels supercritically maintains the solid structure of the gel, creating a polyimide aerogel with improved mechanical properties over linear polyimide aerogels. Lightweight, low-density structures are desired for acoustic and thermal insulation for aerospace structures, habitats, astronaut equipment, and aeronautic applications. Aerogels are a unique material for providing such properties because of their extremely low density and small pore sizes. However, plain silica aerogels are brittle. Reinforcing the aerogel structure with a polymer (X-Aerogel) provides vast improvements in strength while maintaining low density and pore structure. However, degradation of polymers used in cross-linking tends to limit use temperatures to below 150 C. Organic aerogels made from linear polyimide have been demonstrated, but gels shrink substantially during supercritical fluid extraction and may have lower use temperature due to lower glass transition temperatures. The purpose of this innovation is to raise the glass transition temperature of all organic polyimide aerogel by use of tri-, tetra-, or poly-functional units in the structure to create a 3D covalently bonded network. Such cross-linked polyimides typically have higher glass transition temperatures in excess of 300 400 C. In addition, the reinforcement provided by a 3D network should improve mechanical stability, and prevent shrinkage on supercritical fluid extraction. The use of tri-functional aromatic or aliphatic amine groups in the polyimide backbone will provide such a 3D structure.

  6. Curcumin Attenuates Iron Accumulation and Oxidative Stress in the Liver and Spleen of Chronic Iron-Overloaded Rats

    PubMed Central

    Badria, Farid A.; Ibrahim, Ahmed S.; Badria, Adel F.; Elmarakby, Ahmed A.

    2015-01-01

    Objectives Iron overload is now recognized as a health problem in industrialized countries, as excessive iron is highly toxic for liver and spleen. The potential use of curcumin as an iron chelator has not been clearly identified experimentally in iron overload condition. Here, we evaluate the efficacy of curcumin to alleviate iron overload-induced hepatic and splenic abnormalities and to gain insight into the underlying mechanisms. Design and Methods Three groups of male adult rats were treated as follows: control rats, rats treated with iron in a drinking water for 2 months followed by either vehicle or curcumin treatment for 2 more months. Thereafter, we studied the effects of curcumin on iron overload-induced lipid peroxidation and anti-oxidant depletion. Results Treatment of iron-overloaded rats with curcumin resulted in marked decreases in iron accumulation within liver and spleen. Iron-overloaded rats had significant increases in malonyldialdehyde (MDA), a marker of lipid peroxidation and nitric oxide (NO) in liver and spleen when compared to control group. The effects of iron overload on lipid peroxidation and NO levels were significantly reduced by the intervention treatment with curcumin (P<0.05). Furthermore, the endogenous anti-oxidant activities/levels in liver and spleen were also significantly decreased in chronic iron overload and administration of curcumin restored the decrease in the hepatic and splenic antioxidant activities/levels. Conclusion Our study suggests that curcumin may represent a new horizon in managing iron overload-induced toxicity as well as in pathological diseases characterized by hepatic iron accumulation such as thalassemia, sickle cell anemia, and myelodysplastic syndromes possibly via iron chelation, reduced oxidative stress derived lipid peroxidation and improving the body endogenous antioxidant defense mechanism. PMID:26230491

  7. Iron-mediated anaerobic oxidation of methane in brackish coastal sediments.

    PubMed

    Egger, Matthias; Rasigraf, Olivia; Sapart, Célia J; Jilbert, Tom; Jetten, Mike S M; Röckmann, Thomas; van der Veen, Carina; Bândă, Narcisa; Kartal, Boran; Ettwig, Katharina F; Slomp, Caroline P

    2015-01-06

    Methane is a powerful greenhouse gas and its biological conversion in marine sediments, largely controlled by anaerobic oxidation of methane (AOM), is a crucial part of the global carbon cycle. However, little is known about the role of iron oxides as an oxidant for AOM. Here we provide the first field evidence for iron-dependent AOM in brackish coastal surface sediments and show that methane produced in Bothnian Sea sediments is oxidized in distinct zones of iron- and sulfate-dependent AOM. At our study site, anthropogenic eutrophication over recent decades has led to an upward migration of the sulfate/methane transition zone in the sediment. Abundant iron oxides and high dissolved ferrous iron indicate iron reduction in the methanogenic sediments below the newly established sulfate/methane transition. Laboratory incubation studies of these sediments strongly suggest that the in situ microbial community is capable of linking methane oxidation to iron oxide reduction. Eutrophication of coastal environments may therefore create geochemical conditions favorable for iron-mediated AOM and thus increase the relevance of iron-dependent methane oxidation in the future. Besides its role in mitigating methane emissions, iron-dependent AOM strongly impacts sedimentary iron cycling and related biogeochemical processes through the reduction of large quantities of iron oxides.

  8. Low Temperature CO oxidation over Iron Oxide Nanoparticles Decorating Internal Structures of a Mesoporous Alumina

    PubMed Central

    Kim, Il Hee; Seo, Hyun Ook; Park, Eun Ji; Han, Sang Wook; Kim, Young Dok

    2017-01-01

    Using a chemical vapor deposition method with regulated sample temperatures under ambient pressure conditions, we were able to fully decorate the internal structure of a mesoporous Al2O3 bead (~1 mm in particle diameter) with iron oxide nanoparticles (with a mean lateral size of less than 1 nm). The iron oxide-decorated Al2O3 showed a high CO oxidation reactivity, even at room temperature. Very little deactivation of the CO oxidation activity was observed with increasing reaction time at ~100 °C. Additionally, this catalyst showed high CO oxidation activity, even after annealing at ~900 °C under atmospheric conditions (i.e., the structure of the catalysts could be maintained under very harsh treatment conditions). We show that our catalysts have potential for application as oxidation catalysts in industrial processes due to the simplicity of their fabrication process as well as the high and stable catalytic performance. PMID:28091561

  9. Low Temperature CO oxidation over Iron Oxide Nanoparticles Decorating Internal Structures of a Mesoporous Alumina

    NASA Astrophysics Data System (ADS)

    Kim, Il Hee; Seo, Hyun Ook; Park, Eun Ji; Han, Sang Wook; Kim, Young Dok

    2017-01-01

    Using a chemical vapor deposition method with regulated sample temperatures under ambient pressure conditions, we were able to fully decorate the internal structure of a mesoporous Al2O3 bead (~1 mm in particle diameter) with iron oxide nanoparticles (with a mean lateral size of less than 1 nm). The iron oxide-decorated Al2O3 showed a high CO oxidation reactivity, even at room temperature. Very little deactivation of the CO oxidation activity was observed with increasing reaction time at ~100 °C. Additionally, this catalyst showed high CO oxidation activity, even after annealing at ~900 °C under atmospheric conditions (i.e., the structure of the catalysts could be maintained under very harsh treatment conditions). We show that our catalysts have potential for application as oxidation catalysts in industrial processes due to the simplicity of their fabrication process as well as the high and stable catalytic performance.

  10. Novel magnetic cross-linked lipase aggregates for improving the resolution of (R, S)-2-octanol.

    PubMed

    Liu, Ying; Guo, Chen; Liu, Chun-Zhao

    2015-03-01

    Novel magnetic cross-linked lipase aggregates were fabricated by immobilizing the cross-linked lipase aggregates onto magnetic particles with a high number of -NH2 terminal groups using p-benzoquinone as the cross-linking agent. At the optimal fabrication conditions, 100% of immobilization efficiency and 139% of activity recovery of the magnetic cross-linked lipase aggregates were achieved. The magnetic cross-linked lipase aggregates were able to efficiently resolve (R, S)-2-octanol, and retained 100% activity and 100% enantioselectivity after 10 cycles of reuse, whereas the cross-linked lipase aggregates only retained about 50% activity and 70% enantioselectivity due to insufficient cross-linking. These results provide a great potential for industrial applications of the magnetic cross-linked lipase aggregates.

  11. Iron oxide and iron carbide particles produced by the polyol method

    NASA Astrophysics Data System (ADS)

    Yamada, Y.; Shimizu, R.; Kobayashi, Y.

    2016-12-01

    Iron oxide ( γ-Fe2O3) and iron carbide (Fe3C) particles were produced by the polyol method. Ferrocene, which was employed as an iron source, was decomposed in a mixture of 1,2-hexadecandiol, oleylamine, and 1-octadecene. Particles were characterized using Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. It was found that oleylamine acted as a capping reagent, leading to uniform-sized (12-16 nm) particles consisting of γ-Fe 2O3. On the other hand, 1-octadecene acted as a non-coordinating solvent and a carbon source, which led to particles consisting of Fe3C and α-Fe with various sizes.

  12. Iron aluminide alloy container for solid oxide fuel cells

    DOEpatents

    Judkins, Roddie Reagan; Singh, Prabhakar; Sikka, Vinod Kumar

    2000-01-01

    A container for fuel cells is made from an iron aluminide alloy. The container alloy preferably includes from about 13 to about 22 weight percent Al, from about 2 to about 8 weight percent Cr, from about 0.1 to about 4 weight percent M selected from Zr and Hf, from about 0.005 to about 0.5 weight percent B or from about 0.001 to about 1 weight percent C, and the balance Fe and incidental impurities. The iron aluminide container alloy is extremely resistant to corrosion and metal loss when exposed to dual reducing and oxidizing atmospheres at elevated temperatures. The alloy is particularly useful for containment vessels for solid oxide fuel cells, as a replacement for stainless steel alloys which are currently used.

  13. Exchange Bias Effects in Iron Oxide-Based Nanoparticle Systems

    PubMed Central

    Phan, Manh-Huong; Alonso, Javier; Khurshid, Hafsa; Lampen-Kelley, Paula; Chandra, Sayan; Stojak Repa, Kristen; Nemati, Zohreh; Das, Raja; Iglesias, Óscar; Srikanth, Hariharan

    2016-01-01

    The exploration of exchange bias (EB) on the nanoscale provides a novel approach to improving the anisotropic properties of magnetic nanoparticles for prospective applications in nanospintronics and nanomedicine. However, the physical origin of EB is not fully understood. Recent advances in chemical synthesis provide a unique opportunity to explore EB in a variety of iron oxide-based nanostructures ranging from core/shell to hollow and hybrid composite nanoparticles. Experimental and atomistic Monte Carlo studies have shed light on the roles of interface and surface spins in these nanosystems. This review paper aims to provide a thorough understanding of the EB and related phenomena in iron oxide-based nanoparticle systems, knowledge of which is essential to tune the anisotropic magnetic properties of exchange-coupled nanoparticle systems for potential applications. PMID:28335349

  14. Noble Metal-Iron Oxide Hybrid Nanomaterials: Emerging Applications.

    PubMed

    Leung, Ken Cham-Fai; Xuan, Shouhu

    2016-02-01

    This account provides an overview of current research activities that focus on the synthesis and applications of nanomaterials from noble metal (e.g., Au, Ag, Pd) and iron oxide (Fe3O4) hybrids. An introduction to the synthetic strategies that have been developed for generating M-Fe3O4 nanomaterials with different novel structures is presented. Surface functionalization and bioconjugation of these hybrid nanoparticles and nanocomposites are also reviewed. The utilization of the advantageous properties of both noble metals and iron oxide for a variety of applications, such as theranostics, gene delivery, biosensing, cell sorting, bioseparation, and catalysis, is discussed and highlighted. Finally, future trends and perspectives of these sophisticated nanocomposites are outlined. The fundamental requirements underpinning the effective preparation of M-Fex Oy hybrid nanomaterials shed light on the future development of heterogeneous catalysts, nanotheranostics, nanomedicines, and other chemical technologies.

  15. Porous Iron oxide nanorods and their photothermal applications

    NASA Astrophysics Data System (ADS)

    Larsen, George; Huang, Weijie; Zhao, Yiping; Hunyadi Murph, Simona E.

    2016-09-01

    Iron oxide is a unique semiconductor material, either as a single nanoparticle, or as a component of multifunctional nanoparticles. Its desirable properties, abundance, non-toxicity, and excellent magnetic properties make it a valuable for many applications. Porous iron oxide nanorods are able to transduce light into heat through the photothermal effect. Photothermal heating arises from the energy dissipated during light absorption leading to rapid temperature rise in close proximity to the surface of the nanoparticle. The heating effect can be efficiently harnessed to drive/promote different physical phenomena. In this report, we describe the synthesis and properties of porous Fe3O4 for photothermal applications. We then demonstrate their use as photothermally enhanced and recyclable materials for environmental remediation through sorption processes.

  16. Dendronized iron oxide colloids for imaging the sentinel lymph node

    NASA Astrophysics Data System (ADS)

    Jouhannaud, J.; Garofalo, A.; Felder-Flesch, D.; Pourroy, G.

    2015-03-01

    Various methods have been used in medicine for more than one century to explore the lymphatic system. Radioactive colloids (RuS labelled with 99mTc) or/and Vital Blue dye are injected around the primary tumour and detected by means of nuclear probe or visual colour inspection respectively. The simultaneous clinical use of both markers (dye and radionuclide) improves the sensitivity of detection close to 100%. Superparamagnetic iron oxides (SPIOs) are currently receiving much attention as strong T2 weighted magnetic resonance imaging contrast agents that can be potentially used for preoperative localization of sentinel nodes, but also for peroperative detection of sentinel node using hand-held probes. In that context, we present the elaboration of dendronized iron oxide nanoparticles elaborated at the Institute of Physics and Chemistry of Materials of Strasbourg.

  17. Reflection spectra and magnetochemistry of iron oxides and natural surfaces

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1978-01-01

    The magnetic properties and spectral characteristics of iron oxides are distinctive. Diagnostic features in reflectance spectra (0.5 to 2.4 micron) for alpha Fe2O3, gamma Fe2O3, and FeOOH include location of Fe3(+) absorption features, intensity ratios at various wavelengths, and the curve shape between 1.2 micron and 2.4 micron. The reflection spectrum of natural rock surfaces are seldom those of the bulk rock because of weathering effects. Coatings are found to be dominated by iron oxides and clay. A simple macroscopic model of rock spectra (based on concepts of stains and coatings) is considered adequate for interpretation of LANDSAT data. The magnetic properties of materials associated with specific spectral types and systematic changes in both spectra and magnetic properties are considered.

  18. Promising iron oxide-based magnetic nanoparticles in biomedical engineering.

    PubMed

    Tran, Phuong Ha-Lien; Tran, Thao Truong-Dinh; Vo, Toi Van; Lee, Beom-Jin

    2012-12-01

    For the past few decades biomedical engineering has imprinted its significant impact on the map of science through its wide applications on many other fields. An important example obviously proving this fact is the versatile application of magnetic nanoparticles in theranostics. Due to preferable properties such as biocompatibility, non-toxicity compared to other metal derivations, iron oxide-based magnetic nanoparticles was chosen to be addressed in this review. Aim of this review is to give the readers a whole working window of these magnetic nanoparticles in the current context of science. Thus, preparation of magnetic iron oxide nanoparticles with the so-far techniques, methods of characterizing the nanoparticles as well as their most recent biomedical applications will be stated.

  19. Copper Iron Conversion Coating for Solid Oxide Fuel Cell Interconnects

    NASA Astrophysics Data System (ADS)

    Grolig, Jan Gustav; Alnegren, Patrik; Froitzheim, Jan; Svensson, Jan-Erik

    2015-11-01

    A conversion coating of iron and copper was investigated with the purpose of increasing the performance of Sanergy HT as a potential SOFC interconnect material. Samples were exposed to a simulated cathode atmosphere (air, 3 % H2O) for durations of up to 1000 h at 850 °C. Their performance in terms of corrosion, chromium evaporation and electrical resistance (ASR) was monitored and compared to uncoated and cobalt-coated Sanergy HT samples. The copper iron coating had no negative effects on corrosion protection and decreased chromium evaporation by about 80%. An Area Specific Resistance (ASR) of 10 mΩcm2 was reached after 1000 h of exposure. Scanning Electron Microscopy revealed well adherent oxide layers comprised of an inner chromia layer and an outer spinel oxide layer.

  20. Nanovectors for anticancer agents based on superparamagnetic iron oxide nanoparticles

    PubMed Central

    Douziech-Eyrolles, Laurence; Marchais, Hervé; Hervé, Katel; Munnier, Emilie; Soucé, Martin; Linassier, Claude; Dubois, Pierre; Chourpa, Igor

    2007-01-01

    During the last decade, the application of nanotechnologies for anticancer drug delivery has been extensively explored, hoping to improve the efficacy and to reduce side effects of chemotherapy. The present review is dedicated to a certain kind of anticancer drug nanovectors developed to target tumors with the help of an external magnetic field. More particularly, this work treats anticancer drug nanoformulations based on superparamagnetic iron oxide nanoparticles coated with biocompatible polymers. The major purpose is to focus on the specific requirements and technological difficulties related to controlled delivery of antitumoral agents. We attempt to state the problem and its possible perspectives by considering the three major constituents of the magnetic therapeutic vectors: iron oxide nanoparticles, polymeric coating and anticancer drug. PMID:18203422

  1. Kinetics of copper ion absorption by cross-linked calcium polyacrylate membranes

    NASA Technical Reports Server (NTRS)

    Philipp, W. H.; May, C. E.

    1983-01-01

    The absorption of copper ions from aqueous copper acetate solutions by cross-linked calcium acrylate membranes was found to obey parabolic kinetics similar to that found for oxidation of metals that form protective oxide layers. For pure calcium polyacrylate membranes the rate constant was essentially independent of copper acetate concentration and film thickness. For a cross-linked copolymer film of polyvinyl alcohol and calcium polyacrylate, the rate constant was much greater and dependent on the concentration of copper acetate. The proposed mechanism in each case involves the formation of a copper polyacrylate phase on the surface of the membrane. The diffusion of the copper ion through this phase appears to be the rate controlling step for the copolymer film. The diffusion of the calcium ion is apparently the rate controlling step for the calcium polyacrylate. At low pH, the copper polyacrylate phase consists of the normal copper salt; at higher pH, the phase appears to be the basic copper salt.

  2. CLC CI-/H+ Transporters Constrained by Covalent Cross-Linking

    SciTech Connect

    Nguitragool,W.; Miller, C.

    2007-01-01

    CLC Cl-/H+ exchangers are homodimers with Cl--binding and H+-coupling residues contained within each subunit. It is not known whether the transport mechanism requires conformational rearrangement between subunits or whether each subunit operates as a separate exchanger. We designed various cysteine substitution mutants on a cysteine-less background of CLC-ec1, a bacterial CLC exchanger of known structure, with the aim of covalently linking the subunits. The constructs were cross-linked in air or with exogenous oxidant, and the cross-linked proteins were reconstituted to assess their function. In addition to conventional disulfides, a cysteine-lysine cross-bridge was formed with I2 as an oxidant. The constructs, all of which contained one, two, or four cross-bridges, were functionally active and kinetically competent with respect to Cl- turnover rate, Cl-/H+ exchange stoichiometry, and H+ pumping driven by a Cl- gradient. These results imply that large quaternary rearrangements, such as those known to occur for 'common gating' in CLC channels, are not necessary for the ion transport cycle and that it is therefore likely that the transport mechanism is carried out by the subunits working individually, as with 'fast gating' of the CLC channels.

  3. Iron oxide particles as a catalyst in chemical oxidation of organic contaminants

    SciTech Connect

    Gurol, M.D.; Lin, S.S.; Bhat, N.

    1995-12-31

    This research addresses the use of ozone and hydrogen peroxide in the presence of iron oxide particles which provide a catalytic surface for conversion to hydroxyl free radical. N-butylchloride (BuCl) and monochlorobenzene (MCB) were oxidized using goethite as the catalyst. The effect of varying the dosage of hydrogen peroxide or ozone, the mass and the size of the geothite particles, the mixing speed, and the gas flow rate for ozonation was investigated. The effect of water quality in terms of pH, carbonate alkalinity and initial organic concentration on reaction rates was addressed as well. Experimental observations showed that varying the stirring speed in the reactor or the size of the iron oxide particles did not have any significant effect on the oxidation rates, indicating that the rate was controlled by the intrinsic reaction rates on iron oxide surfaces. The presence of hydrogen peroxide significantly increased the removal of BuCl, and higher dosages caused considerably higher removal. Results also demonstrated a strong dependence of BuCl removal on the iron oxide dosage. MCB adsorbed strongly on goethite, but was oxidized effectively by ozone. Hydrogen peroxide decomposed rapidly in the presence of goethite at a rate directly proportional to the rate of BuCl oxidation. These results indicate that the interaction of hydrogen peroxide with goethite particles leads to the formation of hydroxyl free radical, which is responsible for oxidation of BuCl. Similarly, ozone decomposed in the presence of goethite. The oxidation efficiency for hydrogen peroxide/goethite remained unaffected when the pH and the alkalinity were varied. Furthermore, the ozone/goethite system provided mineralization as measured by the removal of the total organic carbon. Hence, both of these oxidation processes promise to be effective in oxidation of organic compounds, and may not suffer from the limitations of other radical processes.

  4. Damage and fatigue in cross-linked rubbers

    NASA Astrophysics Data System (ADS)

    Melnikov, Alexei

    Damage and fatigue of elastomers have not been fundamentally understood because of the complex nature of these materials. All currently existing models are completely phenomenological. Therefore two problems have been investigated in this research to address those fundamental issues. The first problem was creating an innovative concept with a mathematical modeling, which would be able to describe the damage using molecular characteristics of elastomers. The second problem is developing new approaches to study fatigue, and especially impact fatigue of elastomers. The following results have been obtained in this research. A theoretical model of damage has been developed which involves the basic molecular characteristics of cross-linked elastomers and takes into account the effects of viscoelasticity and stress-induced crystallization. This model was found very reliable and successful in description of numerous quasi-static simple extension experiments for monotonous and repeating loadings. It also roughly predicts in molecular terms the failure of elastomers with various degrees of cross-linking. Quasi-impact fatigue tests with different geometry of an indenter have also been performed. Some microscopic features of rubber damage have been investigated using optical microscopy and SEM. In particular, the accumulation of a completely de-vulcanized, liquid-like substance was observed under intense, multi-cycle impacts. All the findings discovered in quasi-impact experiments are consistent with the damage model predictions.

  5. Tea Derived Galloylated Polyphenols Cross-Link Purified Gastrointestinal Mucins

    PubMed Central

    Georgiades, Pantelis; Pudney, Paul D. A.; Rogers, Sarah; Thornton, David J.; Waigh, Thomas A.

    2014-01-01

    Polyphenols derived from tea are thought to be important for human health. We show using a combination of particle tracking microrheology and small-angle neutron scattering that polyphenols acts as cross-linkers for purified gastrointestinal mucin, derived from the stomach and the duodenum. Both naturally derived purified polyphenols, and green and black tea extracts are shown to act as cross-linkers. The main active cross-linking component is found to be the galloylated forms of catechins. The viscosity, elasticity and relaxation time of the mucin solutions experience an order of magnitude change in value upon addition of the polyphenol cross-linkers. Similarly small-angle neutron scattering experiments demonstrate a sol-gel transition with the addition of polyphenols, with a large increase in the scattering at low angles, which is attributed to the formation of large scale (>10 nm) heterogeneities during gelation. Cross-linking of mucins by polyphenols is thus expected to have an impact on the physicochemical environment of both the stomach and duodenum; polyphenols are expected to modulate the barrier properties of mucus, nutrient absorption through mucus and the viscoelastic microenvironments of intestinal bacteria. PMID:25162539

  6. Supermacroporous chemically cross-linked poly(aspartic acid) hydrogels.

    PubMed

    Gyarmati, Benjámin; Mészár, E Zsuzsanna; Kiss, Lóránd; Deli, Mária A; László, Krisztina; Szilágyi, András

    2015-08-01

    Chemically cross-linked poly(aspartic acid) (PASP) gels were prepared by a solid-liquid phase separation technique, cryogelation, to achieve a supermacroporous interconnected pore structure. The precursor polymer of PASP, polysuccinimide (PSI) was cross-linked below the freezing point of the solvent and the forming crystals acted as templates for the pores. Dimethyl sulfoxide was chosen as solvent instead of the more commonly used water. Thus larger temperatures could be utilized for the preparation and the drawback of increase in specific volume of water upon freezing could be eliminated. The morphology of the hydrogels was characterized by scanning electron microscopy and interconnectivity of the pores was proven by the small flow resistance of the gels. Compression tests also confirmed the interconnected porous structure and the complete re-swelling and shape recovery of the supermacroporous PASP hydrogels. The prepared hydrogels are of interest for several biomedical applications as scaffolding materials because of their cytocompatibility, controllable morphology and pH-responsive character.

  7. Preparation and characterization of cross-linked composite polymer electrolytes

    SciTech Connect

    Hou, J.; Baker, G.L.

    1998-11-01

    Cross-linkable composite electrolytes were prepared from poly(ethylene glycol) dimethyl ether (PEGDME)-500, LiClO{sub 4}, fumed silica, and 10 wt % methyl, butyl, or octyl methacrylate. The silicas used were chemically modified by attaching methacrylate groups to the silica surface through C{sub 8} and C{sub 3} tethers. Before cross-linking, the electrolytes were thixotropic and had ionic conductivities of >2 {times} 10{sup {minus}4} S/cm. After ultraviolet (UV)-induced cross-linking, the electrolytes were rubbery and dimensionally stable, and the conductivities were unchanged. Conductivity, extraction, and thermal analysis data all support a model where the added methacrylate monomer and growing polymer chains phase separate from the electrolyte phase during photopolymerization to yield a methacrylate-rich silica/polymer phase and little or no polymer in the PEGDME-500 phase. Thus, the mechanical properties of the composite electrolyte and its ionic conductivity are decoupled and can be optimized independently.

  8. Iron oxide magnetic nanoparticles synthesized by atmospheric microplasmas

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Kaur, Parvin; Tan, Augustine Tuck Lee; Singh, Rajveer; Lee, Paul Choon Keat; Springham, Stuart Victor; Ramanujan, Raju V.; Rawat, R. S.

    2014-08-01

    This paper presents the synthesis of iron oxide nanoparticles using the atmospheric microplasma (AMP). The properties of iron oxide nanoparticles synthesized using AMP are compared with particles (i) formed in as-prepared solution and (ii) prepared using thermal decomposition method. Iron oxide nanoparticles prepared by all the 3 treatment methods exhibit quite soft ferromagnetic properties with coercivities less than 10 G. The AMP synthesis technique was found to be more efficient and better than thermal decomposition method due to ultra-shorter experiment time (around 2.5 min) as compared to 90 min required for thermal decomposition method. Moreover, AMP synthesized nanoparticles are better isolated and of smaller size than thermal decomposition ones. The effect of plasma discharge timings on synthesized nanoparticles has also been studied in this work. Coercivity of synthesized nanoparticles decreases with the increasing plasma discharge timings from 3 to 10 min. The nanoparticles synthesized using plasma discharge timing of 10 min exhibit the smallest coercivity of around 3 G. This suggests a high possibility of achieving super-paramagnetic nanoparticles by optimizing the plasma discharge timings of AMP.

  9. Modulated self-reversed magnetic hysteresis in iron oxides

    PubMed Central

    Ma, Ji; Chen, Kezheng

    2017-01-01

    The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe3+ cations due to their negative enough surface zeta potentials. These iron oxides@Fe3+ core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe3+ shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe3+ concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields. PMID:28220793

  10. Modulated self-reversed magnetic hysteresis in iron oxides.

    PubMed

    Ma, Ji; Chen, Kezheng

    2017-02-21

    The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe(3+) cations due to their negative enough surface zeta potentials. These iron oxides@Fe(3+) core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe(3+) shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe(3+) concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields.

  11. Modulated self-reversed magnetic hysteresis in iron oxides

    NASA Astrophysics Data System (ADS)

    Ma, Ji; Chen, Kezheng

    2017-02-01

    The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe3+ cations due to their negative enough surface zeta potentials. These iron oxides@Fe3+ core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe3+ shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe3+ concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields.

  12. Reducing arsenic accumulation in rice grain through iron oxide amendment.

    PubMed

    Farrow, Eric M; Wang, Jianmin; Burken, Joel G; Shi, Honglan; Yan, Wengui; Yang, John; Hua, Bin; Deng, Baolin

    2015-08-01

    Effects of soil-arsenic (As), phosphorus and iron oxide on As accumulation in rice grain were investigated. Cultivars that have significantly different sensitivity to As, straighthead-resistant Zhe 733 and straighthead-susceptible Cocodrie, were used to represent different cultivar varieties. The grain accumulation of other elements of concern, selenium (Se), molybdenum (Mo), and cadmium (Cd) was also monitored. Results demonstrated that high soil-As not only resulted in high grain-As, but could also result in high grain-Se, and Zhe 733 had significantly less grain-As than Cocodrie did. However, soil-As did not impact grain-Mo and Cd. Among all elements monitored, iron oxide amendment significantly reduced grain-As for both cultivars, while the phosphate application only reduced grain-Se for Zhe 733. Results also indicated that cultivar type significantly impacted grain accumulation of all monitored trace elements. Therefore, applying iron oxide to As-contaminated land, in addition to choosing appropriate rice cultivar, can effectively reduce the grain accumulation of As.

  13. Evidence for an oxygen evolving iron-oxo-cerium intermediate in iron-catalysed water oxidation.

    PubMed

    Codolà, Zoel; Gómez, Laura; Kleespies, Scott T; Que, Lawrence; Costas, Miquel; Lloret-Fillol, Julio

    2015-01-22

    The non-haem iron complex α-[Fe(II)(CF3SO3)2(mcp)] (mcp=(N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-cis-diaminocyclohexane) reacts with Ce(IV) to oxidize water to O2, representing an iron-based functional model for the oxygen evolving complex of photosystem II. Here we trap an intermediate, characterized by cryospray ionization high resolution mass spectrometry and resonance Raman spectroscopy, and formulated as [(mcp)Fe(IV)(O)(μ-O)Ce(IV)(NO3)3](+), the first example of a well-characterized inner-sphere complex to be formed in cerium(IV)-mediated water oxidation. The identification of this reactive Fe(IV)-O-Ce(IV) adduct may open new pathways to validate mechanistic notions of an analogous Mn(V)-O-Ca(II) unit in the oxygen evolving complex that is responsible for carrying out the key O-O bond forming step.

  14. Cross-linked network development in compatibilized alkyd/acrylic hybrid latex films for the creation of hard coatings.

    PubMed

    Wang, Tao; de las Heras Alarcón, Carolina; Goikoetxea, Monika; Beristain, Itxaso; Paulis, Maria; Barandiaran, Maria J; Asua, José M; Keddie, Joseph L

    2010-09-07

    Hybrids made from an alkyd resin and an acrylic copolymer can potentially combine the desired properties of each component. Alkyd/acrylic hybrid latex particles were synthesized via miniemulsion polymerization and used to create films at room temperature. Comparisons of the alkyd auto-oxidative cross-linking rates and the associated network development are made between two alkyd resins (with differing levels of hydrophilicity as measured by their acid numbers). The effects of increasing the compatibilization between the alkyd and the acrylic phase via functionalization with glycidyl methacrylate (GMA) are investigated. Magnetic resonance profiling and microindentation measurements reveal that film hardening occurs much faster in a GMA-functionalized alkyd hybrid than in the standard hybrid. The film's hardness increases by a factor of 4 over a 5-day period. The rate of cross-linking is significantly slower in nonfunctionalized alkyd hybrid films and when the more hydrophilic alkyd resin is used. Tensile deformation of the hybrid latex films reveals the effects of GMA functionalization and drier concentration in creating a denser cross-linked network. Modeling of the tensile deformation behavior of the hybrid films used a combination of the upper convected Maxwell model (to describe the viscoelastic component) and the Gent model (to describe the elastic component). The modeling provides a correlation between the cross-linked network formation and the resulting mechanical properties.

  15. Characterization and detection of lysine-arginine cross-links derived from dehydroascorbic acid.

    PubMed

    Reihl, Oliver; Lederer, Markus O; Schwack, Wolfgang

    2004-02-25

    Covalently cross-linked proteins are among the major modifications caused by the advanced Maillard reaction. So far, the chemical nature of these aggregates is largely unknown. L-dehydroascorbic acid (DHA, 5), the oxidation product of L-ascorbic acid (vitamin C), is known as a potent glycation agent. Identification is reported for the lysine-arginine cross-links N6-[2-[(4-amino-4-carboxybutyl)amino]-5-(2-hydroxyethyl)-3,5-dihydro-4H-imidazol-4-ylidene]-L-lysine (9), N6-[2-[(4-amino-4-carboxybutyl)amino]-5-(1,2-dihydroxyethyl)-3,5-dihydro-4H-imidazol-4-ylidene]-L-lysine (11), and N6-[2-[(4-amino-4-carboxybutyl)amino]-5-[(1S,2S)-1,2,3-trihydroxypropyl]-3,5-dihydro-4H-imidazol-4-ylidene]-L-lysine (13). The formation pathways could be established starting from dehydroascorbic acid (5), the degradation products 1,3,4-trihydroxybutan-2-one (7, L-erythrulose), 3,4-dihydroxy-2-oxobutanal (10, L-threosone), and L-threo-pentos-2-ulose (12, L-xylosone) were proven as precursors of the lysine-arginine cross-links 9, 11, and 13. Products 9 and 11 were synthesized starting from DHA 5, compound N6-[2-[(4-amino-4-carboxybutyl)amino]-5-[(1S,2R)-1,2,3-trihydroxypropyl]-3,5-dihydro-4H-imidazol-4-ylidene]-L-lysine (16) via the precursor D-erythro-pentos-2-ulose (15). The present study revealed that the modification of lysine and arginine side chains by DHA 5 is a complex process and could involve a number of reactive carbonyl species.

  16. Effects of green tea on iron accumulation and oxidative stress in livers of iron-challenged thalassemic mice.

    PubMed

    Saewong, T; Ounjaijean, S; Mundee, Y; Pattanapanyasat, K; Fucharoen, S; Porter, J B; Srichairatanakool, S

    2010-03-01

    Liver is affected by secondary iron overload in transfusions dependent b-thalassemia patients. The redox iron can generate reactive oxidants that damage biomolecules, leading to liver fibrosis and cirrhosis. Iron chelators are used to treat thalassemias to achieve negative iron balance and relieve oxidant-induced organ dysfunctions. Green tea (GT) (Camellia sinensis) catechins exhibit anti-oxidation, the inhibition of carcinogenesis, the detoxification of CYP2E1-catalyzed HepG2 cells and iron chelation. The purpose of this study was to investigate the effectiveness of GT in iron-challenged thalassemic mice. Heterozygous BKO type-thalassemia (BKO) mice (C57BL/6) experienced induced iron overload by being fed a ferrocene-supplemented diet (Fe diet) for 8 weeks, and by orally being given GT extract (300 mg/kg) and deferiprone (DFP) (50 mg/kg) for a further 8 weeks. Liver iron content (LIC) was analyzed by TPTZ colorimetric and Perl's staining techniques. Concentrations of liver reduced glutathione (GSH), collagen and malondialdehyde (MDA) were also measured. Dosages of the GT extract and DFP lowered LIC in the Fe diet-fed BKO mice effectively. The extract did not change any concentrations of liver glutathione, collagen and MDA in the BKO mice. Histochemical examination showed leukocyte infiltration in the near by hepatic portal vein and high iron accumulation in the livers of the iron-loaded BKO mice, however GT treatment lowered the elevated iron deposition. In conclusion, green tea inhibits or delays the deposition of hepatic iron in regularly iron-loaded thalassemic mice effectively. This will prevent the iron-induced generation of free radicals via Haber-Weiss and Fenton reactions, and consequently liver damage and fibrosis. Combined chelation with green tea would be investigated in beta-thalassemia patients with iron overload.

  17. Evaluation of iron oxide nanoparticle biocompatibility.

    PubMed

    Hanini, Amel; Schmitt, Alain; Kacem, Kamel; Chau, François; Ammar, Souad; Gavard, Julie

    2011-01-01

    Nanotechnology is an exciting field of investigation for the development of new treatments for many human diseases. However, it is necessary to assess the biocompatibility of nanoparticles in vitro and in vivo before considering clinical applications. Our characterization of polyol-produced maghemite γ-Fe(2)O(3) nanoparticles showed high structural quality. The particles showed a homogeneous spherical size around 10 nm and could form aggregates depending on the dispersion conditions. Such nanoparticles were efficiently taken up in vitro by human endothelial cells, which represent the first biological barrier to nanoparticles in vivo. However, γ-Fe(2)O(3) can cause cell death within 24 hours of exposure, most likely through oxidative stress. Further in vivo exploration suggests that although γ-Fe(2)O(3) nanoparticles are rapidly cleared through the urine, they can lead to toxicity in the liver, kidneys and lungs, while the brain and heart remain unaffected. In conclusion, γ-Fe(2)O(3) could exhibit harmful properties and therefore surface coating, cellular targeting, and local exposure should be considered before developing clinical applications.

  18. Evaluation of Characterization Techniques for Iron Pipe Corrosion Products and Iron Oxide Thin Films

    SciTech Connect

    Borch, Thomas; Camper, Anne K.; Biederman, Joel A.; Butterfield, Phillip; Gerlach, Robin; Amonette, James E.

    2008-10-01

    A common problem faced by drinking water studies is that of properly characterizing the corrosion products (CP) in iron pipescor synthetic Fe (hydr)oxides used to simulate the iron pipe used in municipal drinking-water systems. The present work compares the relative applicability of a suite of imaging and analytical techniques for the characterization of CPs and synthetic Fe oxide thin films and provide an overview of the type of data that each instrument can provide as well as their limitations to help researchers and consultants choose the best technique for a given task. Crushed CP from a water distribution system and synthetic Fe oxide thin films formed on glass surfaces were chosen as test samples for this evaluation. The CP and synthetic Fe oxide thin films were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray powder diffractometry (XRD), grazing incident diffractometry (GID), transmission electron microscopy (TEM), selected area electron diffraction, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared, Mössbauer spectroscopy, Brunauer-Emmett-Teller N2 adsorption and Fe concentration was determined by the ferrozine method. XRD and GID were found to be the most suitable techniques for identification of the mineralogical composition of CP and synthetic Fe oxide thin films, respectively. AFM and a combined ToF-SIMS-AFM approach proved excellent for roughness and depth profiling analysis of synthetic Fe oxide thin films, respectively. Corrosion products were difficult to study by AFM due to their surface roughness, while synthetic Fe oxide thin films resisted most spectroscopic methods due to their limited thickness (118 nm). XPS analysis is not recommended for mixtures of Fe (hydr)oxides due to their spectral similarities. SEM and TEM provided great detail on mineralogical morphology.

  19. Alleviation of iron induced oxidative stress by the grape fruit flavanone naringin in vitro.

    PubMed

    Jagetia, Ganesh Chandra; Reddy, Tiyagura Koti

    2011-04-25

    Iron is an essential element that participates in several metabolic activities of cells; however, excess iron is a major cause of iron-induced oxidative stress and several human diseases. The protective effect of naringin, a grape fruit flavanone, was studied in iron overloaded isolated mouse liver mitochondria, where the isolated mitochondrial fraction was incubated with various concentrations of naringin before ferric ion loading. Iron overloading of mitochondrial fraction resulted in an increase in lipid peroxidation, protein oxidation, and DNA damage, whereas iron overload reduced the glutathione (GSH) concentration, glutathione-S-transferase (GST), glutathione peroxidase (GSHPx), catalase and superoxide dismutase (SOD) activities. Pretreatment of mitochondrial fraction with naringin inhibited iron-induced lipid peroxidation, protein oxidation, and DNA damage. Conversely, naringin supplementation arrested iron-induced depletion in the GSH contents, GSHPx, GST, SOD and catalase activities significantly. Ferric iron reduction assay revealed that naringin could not reduce ferric iron into ferrous iron indicating that it did not exhibit prooxidant activity. Iron free coordination site assay indicated that naringin was unable to occupy all the active sites of iron indicating that naringin did not completely chelate iron. Our study demonstrates that naringin was able to share the burden of endogenous oxidants by inhibiting the iron-induced depletion of all important antioxidant enzymes as well as GSH and may act as a good antioxidant.

  20. Iron isotope fractionation during photo-oxidation of aqueous ferrous iron

    NASA Astrophysics Data System (ADS)

    Staton, S.; Amskold, L.; Gordon, G.; Anbar, A.; Konhauser, K.

    2006-05-01

    The classic interpretation of banded iron formations (BIFs) presumes the presence of dissolved O2 in the surface ocean to oxidize ferrous Fe. However, at least two alternative oxidation mechanisms are possible: UV photo-oxidation; and the activity of anaerobic Fe(II)-oxidizing photosynthetic bacteria. We are investigating Fe isotope fractionation as a means of differentiating amongst these mechanisms. Photo-oxidation has been examined at pH ~ 3 and 41°C in the absence of ligands other than H2O, OH-, and Cl- using UVA (316-400 nm) and UVC (200-280 nm) light sources. In these experiments, ferrous Fe was oxidized and precipitated as ferric oxyhydroxide. We find that isotopically heavy Fe was preferentially removed from solution. The fractionation factor (α) for the overall reaction is ~ 1.0025. This value is comparable to the α between Fe2+ and Fe3+ hexaquo complexes, but larger than the effect seen during the overall process of ferrous Fe oxidation and precipitation at near-neutral pH. The magnitude of isotope fractionation is likely to change at higher pH for two reasons. First, ferric oxyhydroxide precipitation, which may impart a kinetic isotope effect, is faster at higher pH. Second, the major UV-absorbing ferrous species in the ocean is the ferrous hydroxide ion [Fe(OH)+], the concentration of which is strongly pH dependent. Photo-oxidation experiments at realistic seawater pH are under current investigation.

  1. New Insight into Microbial Iron Oxidation as Revealed by the Proteomic Profile of an Obligate Iron-Oxidizing Chemolithoautotroph.

    PubMed

    Barco, Roman A; Emerson, David; Sylvan, Jason B; Orcutt, Beth N; Jacobson Meyers, Myrna E; Ramírez, Gustavo A; Zhong, John D; Edwards, Katrina J

    2015-09-01

    Microaerophilic, neutrophilic, iron-oxidizing bacteria (FeOB) grow via the oxidation of reduced Fe(II) at or near neutral pH, in the presence of oxygen, making them relevant in numerous environments with elevated Fe(II) concentrations. However, the biochemical mechanisms for Fe(II) oxidation by these neutrophilic FeOB are unknown, and genetic markers for this process are unavailable. In the ocean, microaerophilic microorganisms in the genus Mariprofundus of the class Zetaproteobacteria are the only organisms known to chemolithoautotrophically oxidize Fe and concurrently biomineralize it in the form of twisted stalks of iron oxyhydroxides. The aim of this study was to identify highly expressed proteins associated with the electron transport chain of microaerophilic, neutrophilic FeOB. To this end, Mariprofundus ferrooxydans PV-1 was cultivated, and its proteins were extracted, assayed for redox activity, and analyzed via liquid chromatography-tandem mass spectrometry for identification of peptides. The results indicate that a cytochrome c4, cbb3-type cytochrome oxidase subunits, and an outer membrane cytochrome c were among the most highly expressed proteins and suggest an involvement in the process of aerobic, neutrophilic bacterial Fe oxidation. Proteins associated with alternative complex III, phosphate transport, carbon fixation, and biofilm formation were abundant, consistent with the lifestyle of Mariprofundus.

  2. New Insight into Microbial Iron Oxidation as Revealed by the Proteomic Profile of an Obligate Iron-Oxidizing Chemolithoautotroph

    PubMed Central

    Emerson, David; Sylvan, Jason B.; Orcutt, Beth N.; Jacobson Meyers, Myrna E.; Ramírez, Gustavo A.; Zhong, John D.; Edwards, Katrina J.

    2015-01-01

    Microaerophilic, neutrophilic, iron-oxidizing bacteria (FeOB) grow via the oxidation of reduced Fe(II) at or near neutral pH, in the presence of oxygen, making them relevant in numerous environments with elevated Fe(II) concentrations. However, the biochemical mechanisms for Fe(II) oxidation by these neutrophilic FeOB are unknown, and genetic markers for this process are unavailable. In the ocean, microaerophilic microorganisms in the genus Mariprofundus of the class Zetaproteobacteria are the only organisms known to chemolithoautotrophically oxidize Fe and concurrently biomineralize it in the form of twisted stalks of iron oxyhydroxides. The aim of this study was to identify highly expressed proteins associated with the electron transport chain of microaerophilic, neutrophilic FeOB. To this end, Mariprofundus ferrooxydans PV-1 was cultivated, and its proteins were extracted, assayed for redox activity, and analyzed via liquid chromatography-tandem mass spectrometry for identification of peptides. The results indicate that a cytochrome c4, cbb3-type cytochrome oxidase subunits, and an outer membrane cytochrome c were among the most highly expressed proteins and suggest an involvement in the process of aerobic, neutrophilic bacterial Fe oxidation. Proteins associated with alternative complex III, phosphate transport, carbon fixation, and biofilm formation were abundant, consistent with the lifestyle of Mariprofundus. PMID:26092463

  3. Comparison of the Effects of Iron Oxide, as a New Form of Iron Supplement, and Ferrous Sulfate on the Blood Levels of Iron and Total Iron-Binding Globulin in the Rabbit.

    PubMed

    Kheiri, Reyhaneh; Koohi, Mohammad Kazem; Sadeghi-Hashjin, Goudarz; Nouri, Hadiseh; Khezli, Noushin; Hassan, Mohsen Aghamohammad; Hoomani, Fatemeh; Shams, Gholamreza; Rasouli, Ali; Motaghinejad, Majid

    2017-01-01

    Iron oxide is an important biological agent that has a key role in medical processes; however, the mechanism whereby it provides iron for human and animal cells and its biological uses remains unclear. We aimed to evaluate the effects of oral iron oxide on serum iron status and compare the results with those of iron sulfate as a reference salt. Fifteen adult rabbits were divided into 3 groups of 5 each: control group, iron sulfate group, and iron oxide group. The groups received doses of 3.3, 10, and 33 mg/kg in 3 experiments. Venous blood samples were obtained just before the oral administration of iron sulfate and iron oxide (3.3 mg/kg). More blood samples were taken 3 times at the time points of 1, 6, and 12 hours after the administration of the solutions. Serum was separated for the measurement of iron (Fe) and total iron-binding globulin (TIBG) with routine methods. One week later, the same experiment was repeated with 10 mg/kg of iron sulfate and iron oxide; and 1 week later after the second experiment, again the same experiment was repeated with 33 mg/kg of iron sulfate and iron oxide. The results showed that 33 mg/kg of iron sulfate 1 hour after treatment caused a significant difference in the Fe and TIBG levels between all the groups (P=0.014 for Fe and P=0.027 for TIBG). Our data showed that the absorption of iron oxide was similar to that of ferrous sulfate and in high doses was as useful as iron supplement.

  4. Comparison of the Effects of Iron Oxide, as a New Form of Iron Supplement, and Ferrous Sulfate on the Blood Levels of Iron and Total Iron-Binding Globulin in the Rabbit

    PubMed Central

    Kheiri, Reyhaneh; Koohi, Mohammad Kazem; Sadeghi-Hashjin, Goudarz; Nouri, Hadiseh; Khezli, Noushin; Hassan, Mohsen Aghamohammad; Hoomani, Fatemeh; Shams, Gholamreza; Rasouli, Ali; Motaghinejad, Majid

    2017-01-01

    Iron oxide is an important biological agent that has a key role in medical processes; however, the mechanism whereby it provides iron for human and animal cells and its biological uses remains unclear. We aimed to evaluate the effects of oral iron oxide on serum iron status and compare the results with those of iron sulfate as a reference salt. Fifteen adult rabbits were divided into 3 groups of 5 each: control group, iron sulfate group, and iron oxide group. The groups received doses of 3.3, 10, and 33 mg/kg in 3 experiments. Venous blood samples were obtained just before the oral administration of iron sulfate and iron oxide (3.3 mg/kg). More blood samples were taken 3 times at the time points of 1, 6, and 12 hours after the administration of the solutions. Serum was separated for the measurement of iron (Fe) and total iron-binding globulin (TIBG) with routine methods. One week later, the same experiment was repeated with 10 mg/kg of iron sulfate and iron oxide; and 1 week later after the second experiment, again the same experiment was repeated with 33 mg/kg of iron sulfate and iron oxide. The results showed that 33 mg/kg of iron sulfate 1 hour after treatment caused a significant difference in the Fe and TIBG levels between all the groups (P=0.014 for Fe and P=0.027 for TIBG). Our data showed that the absorption of iron oxide was similar to that of ferrous sulfate and in high doses was as useful as iron supplement. PMID:28293054

  5. 3-Hydroxykynurenine and 3-hydroxyanthranilic acid generate hydrogen peroxide and promote alpha-crystallin cross-linking by metal ion reduction.

    PubMed

    Goldstein, L E; Leopold, M C; Huang, X; Atwood, C S; Saunders, A J; Hartshorn, M; Lim, J T; Faget, K Y; Muffat, J A; Scarpa, R C; Chylack, L T; Bowden, E F; Tanzi, R E; Bush, A I

    2000-06-20

    The kynurenine pathway catabolite 3-hydroxykynurenine (3HK) and redox-active metals such as copper and iron are implicated in cataractogenesis. Here we investigate the reaction of kynurenine pathway catabolites with copper and iron, as well as interactions with the major lenticular structural proteins, the alpha-crystallins. The o-aminophenol kynurenine catabolites 3HK and 3-hydroxyanthranilic acid (3HAA) reduced Cu(II)>Fe(III) to Cu(I) and Fe(II), respectively, whereas quinolinic acid and the nonphenolic kynurenine catabolites kynurenine and anthranilic acid did not reduce either metal. Both 3HK and 3HAA generated superoxide and hydrogen peroxide in a copper-dependent manner. In addition, 3HK and 3HAA fostered copper-dependent alpha-crystallin cross-linking. 3HK- or 3HAA-modifed alpha-crystallin showed enhanced redox activity in comparison to unmodified alpha-crystallin or ascorbate-modified alpha-crystallin. These data support the possibility that 3HK and 3HAA may be cofactors in the oxidative damage of proteins, such as alpha-crystallin, through interactions with redox-active metals and especially copper. These findings may have relevance for understanding cataractogenesis and other degenerative conditions in which the kynurenine pathway is activated.

  6. Ceruloplasmin protects injured spinal cord from iron-mediated oxidative damage.

    PubMed

    Rathore, Khizr I; Kerr, Bradley J; Redensek, Adriana; López-Vales, Rubèn; Jeong, Suh Young; Ponka, Prem; David, Samuel

    2008-11-26

    CNS injury-induced hemorrhage and tissue damage leads to excess iron, which can cause secondary degeneration. The mechanisms that handle this excess iron are not fully understood. We report that spinal cord contusion injury (SCI) in mice induces an "iron homeostatic response" that partially limits iron-catalyzed oxidative damage. We show that ceruloplasmin (Cp), a ferroxidase that oxidizes toxic ferrous iron, is important for this process. SCI in Cp-deficient mice demonstrates that Cp detoxifies and mobilizes iron and reduces secondary tissue degeneration and functional loss. Our results provide new insights into how astrocytes and macrophages handle iron after SCI. Importantly, we show that iron chelator treatment has a delayed effect in improving locomotor recovery between 3 and 6 weeks after SCI. These data reveal important aspects of the molecular control of CNS iron homeostasis after SCI and suggest that iron chelator therapy may improve functional recovery after CNS trauma and hemorrhagic stroke.

  7. Pulmonary toxicity and kinetic study of Cy5.5-conjugated superparamagnetic iron oxide nanoparticles by optical imaging

    SciTech Connect

    Cho, Wan-Seob; Park, Sue Nie; Yu, Mi Kyung; Jon, Sangyong; Jeong, Jayoung

    2009-08-15

    Recent advances in the development of nanotechnology and devices now make it possible to accurately deliver drugs or genes to the lung. Magnetic nanoparticles can be used as contrast agents, thermal therapy for cancer, and be made to concentrate to target sites through an external magnetic field. However, these advantages may also become problematic when taking into account safety and toxicological factors. This study demonstrated the pulmonary toxicity and kinetic profile of anti-biofouling polymer coated, Cy5.5-conjugated thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION) by optical imaging. Negatively charged, 36 nm-sized, Cy5.5-conjugated TCL-SPION was prepared for optical imaging probe. Cy5.5-conjugated TCL-SPION was intratracheally instilled into the lung by a non-surgical method. Cy5.5-conjugated TCL-SPION slightly induced pulmonary inflammation. The instilled nanoparticles were distributed mainly in the lung and excreted in the urine via glomerular filtration. Urinary excretion was peaked at 3 h after instillation. No toxicity was found under the concentration of 1.8 mg/kg and the half-lives of nanoparticles in the lung and urine were estimated to be about 14.4 {+-} 0.54 h and 24.7 {+-} 1.02 h, respectively. Although further studies are required, our results showed that Cy5.5-conjugated TCL-SPION can be a good candidate for use in pulmonary delivery vehicles and diagnostic probes.

  8. Using a magnetic field to redirect an oncolytic adenovirus complexed with iron oxide augments gene therapy efficacy.

    PubMed

    Choi, Joung-Woo; Park, Ji Won; Na, Youjin; Jung, Soo-Jung; Hwang, June Kyu; Choi, Dongho; Lee, Kyeong Geun; Yun, Chae-Ok

    2015-10-01

    Adenovirus (Ad) is a widely used vector for cancer gene therapy but its therapeutic efficacy is limited by low coxsackievirus and adenovirus receptor (CAR) expression in tumors and non-specifically targeted infection. Ad infectivity and specificity can be markedly improved by creating Ad-magnetic nanoparticles cluster complexes and directing their migration with an external magnetic field (MGF). We electrostatically complexed GFP-expressing, replication-incompetent Ad (dAd) with PEGylated and cross-linked iron oxide nanoparticles (PCION), generating dAd-PCION complexes. The dAd-PCION showed increased transduction efficiency, independent of CAR expression, in the absence or presence of an MGF. Cancer cell killing and intracellular oncolytic Ad (HmT)-PCION replication significantly increased with MGF exposure. Site-directed, magnetically-targeted delivery of the HmT-PCION elicited significantly greater therapeutic efficacy versus treatment with naked HmT or HmT-PCION without MGF in CAR-negative MCF7 tumors. Immunohistochemical tumor analysis showed increased oncolytic Ad replication in tumors following infection by HmT-PCION using an MGF. Whole-body bioluminescence imaging of tumor-bearing mice showed a 450-fold increased tumor-to-liver ratio for HmT-PCION with, versus without, MGF. These results demonstrate the feasibility and potential of external MGF-responsive PCION-coated oncolytic Ads as smart hybrid vectors for cancer gene therapy.

  9. Reductive dechlorination of chlorinated solvents by zero-valent iron, iron oxide and iron sulfide minerals

    SciTech Connect

    Sivavec, T.M.; Horney, D.P.

    1996-10-01

    The degradation of chlorinated solvents by reduction at the surface of zero-valent metals and bimetallic systems has emerged as an important approach to the in-situ remediation of ground water. Reduction by iron metal was studied in batch and column systems to develop a mechanistic understanding of the reaction chemistry and to determine the factors that affect dechlorination rate and long term performance in field applications.

  10. Mercury removal in wastewater by iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Vélez, E.; Campillo, G. E.; Morales, G.; Hincapié, C.; Osorio, J.; Arnache, O.; Uribe, J. I.; Jaramillo, F.

    2016-02-01

    Mercury is one of the persistent pollutants in wastewater; it is becoming a severe environmental and public health problem, this is why nowadays its removal is an obligation. Iron oxide nanoparticles are receiving much attention due to their properties, such as: great biocompatibility, ease of separation, high relation of surface-area to volume, surface modifiability, reusability, excellent magnetic properties and relative low cost. In this experiment, Fe3O4 and γ-Fe2O3 nanoparticles were synthesized using iron salts and NaOH as precipitation agents, and Aloe Vera as stabilizing agent; then these nanoparticles were characterized by three different measurements: first, using a Zetasizer Nano ZS for their size estimation, secondly UV-visible spectroscopy which showed the existence of resonance of plasmon at λmax∼360 nm, and lastly by Scanning Electron Microscopy (SEM) to determine nanoparticles form. The results of this characterization showed that the obtained Iron oxides nanoparticles have a narrow size distribution (∼100nm). Mercury removal of 70% approximately was confirmed by atomic absorption spectroscopy measurements.

  11. Crystal structure of iron-oxide nanoparticles synthesized from ferritin

    NASA Astrophysics Data System (ADS)

    Krispin, Michael; Ullrich, Aladin; Horn, Siegfried

    2012-02-01

    We have investigated the crystal structure of nanosized iron-oxide by X-ray diffraction (XRD), extended X-ray absorption fine structure measurements at the iron K-edge as well as by transmission electron microscopy (TEM). Iron-oxide nanoparticles were produced by thermal treatment of horse spleen ferritin molecules. The structure of these particles was compared to α-Fe2O3 and γ-Fe2O3 nanopowder references. The thermal treatment of a submonolayer film of ferritin molecules results in pure γ-Fe2O3 nanoparticles, while for films above a certain thickness α-Fe2O3 and γ-Fe2O3 coexist, exhibiting two different crystallite sizes. TEM shows a characteristic particle diameter of 7 nm for γ-Fe2O3 resulting from thermal treatment of monolayers, consistent with the crystallite size of the γ-phase as obtained from XRD measurements on multi-layered samples. XRD shows the α-Fe2O3 phase to be characterized by a crystallite size of 34 nm.

  12. Isodityrosine cross-linking mediates insolubilization of cell walls in Chlamydomonas.

    PubMed

    Waffenschmidt, S; Woessner, J P; Beer, K; Goodenough, U W

    1993-07-01

    Enzymatic removal of the cell wall induces vegetative Chlamydomonas reinhardtii cells to transcribe wall genes and synthesize new hydroxyproline-rich glycoproteins (HRGPs) related to the extensins found in higher plant cell walls. A cDNA expression library made from such induced cells was screened with antibodies to an oligopeptide containing the (SP)x repetitive domains found in Chlamydomonas wall proteins. One of the selected cDNAs encodes an (SP)x-rich polypeptide that also displays a repeated YGG motif. Ascorbate, a peroxidase inhibitor, and tyrosine derivatives were shown to inhibit insolubilization of both the vegetative and zygotic cell walls of Chlamydomonas, suggesting that oxidative cross-linking of tyrosines is occurring. Moreover, insolubilization of both walls was concomitant with a burst in H2O2 production and in extracellular peroxidase activity. Finally, both isodityrosine and dityrosine were found in hydrolysates of the insolubilized vegetative wall layer. We propose that the formation of tyrosine cross-links is essential to Chlamydomonas HRGP insolubilization.

  13. Isodityrosine cross-linking mediates insolubilization of cell walls in Chlamydomonas.

    PubMed Central

    Waffenschmidt, S; Woessner, J P; Beer, K; Goodenough, U W

    1993-01-01

    Enzymatic removal of the cell wall induces vegetative Chlamydomonas reinhardtii cells to transcribe wall genes and synthesize new hydroxyproline-rich glycoproteins (HRGPs) related to the extensins found in higher plant cell walls. A cDNA expression library made from such induced cells was screened with antibodies to an oligopeptide containing the (SP)x repetitive domains found in Chlamydomonas wall proteins. One of the selected cDNAs encodes an (SP)x-rich polypeptide that also displays a repeated YGG motif. Ascorbate, a peroxidase inhibitor, and tyrosine derivatives were shown to inhibit insolubilization of both the vegetative and zygotic cell walls of Chlamydomonas, suggesting that oxidative cross-linking of tyrosines is occurring. Moreover, insolubilization of both walls was concomitant with a burst in H2O2 production and in extracellular peroxidase activity. Finally, both isodityrosine and dityrosine were found in hydrolysates of the insolubilized vegetative wall layer. We propose that the formation of tyrosine cross-links is essential to Chlamydomonas HRGP insolubilization. PMID:7689882

  14. Cross-linked chitosan/liposome hybrid system for the intestinal delivery of quercetin.

    PubMed

    Caddeo, Carla; Díez-Sales, Octavio; Pons, Ramon; Carbone, Claudia; Ennas, Guido; Puglisi, Giovanni; Fadda, Anna Maria; Manconi, Maria

    2016-01-01

    Quercetin is a flavonoid with antioxidant/anti-inflammatory properties, poorly absorbed when administered orally. To increase its bioavailability and optimize its release in the intestine, a hybrid system made of liposomes coated with cross-linked chitosan, named TPP-chitosomes, was developed and characterized by light scattering, transmission electron microscopy, differential scanning calorimetry, X-ray powder diffraction and Turbiscan® technology. The TPP-chitosomes were nanosized (∼180 nm), fairly spherical in shape and unilamellar. The actual coating of the surface of liposomes with the cross-linked chitosan was demonstrated by Small-Angle X-ray Scattering. The release of quercetin in simulated gastric and intestinal pH was investigated, the results showing that the system provided resistance to acidic conditions, and promoted the release in alkaline pH, mimicking the intestinal environment. The proposed hybrid system represents a promising combination of nanovesicles and chitosan for the delivery of quercetin to the intestine in the therapy of oxidative stress/inflammation related disorders.

  15. Wear Measurement of Highly Cross-linked UHMWPE using a 7Be Tracer Implantation Technique

    SciTech Connect

    Wimmer, Markus A.; Laurent, Michael P.; Dwivedi, Yasha; Gallardo, Luis A.; Chipps, K.; Blackmon, Jeffery C; Kozub, R. L.; Bardayan, Daniel W; Gross, Carl J; Stracener, Daniel W; Smith, Michael Scott; Nesaraja, Caroline D; Erikson, Luke; Patel, Nidhi; Rehm, Karl E.; Ahmad, Irshad; Greene, John P.; Greife, Uwe

    2013-01-01

    The very low wear rates achieved with the current highly cross-linked ultrahigh molecular weight polyethylenes (UHMWPE) used in joint prostheses have proven to be difficult to measure accurately by gravimetry. Tracer methods are there- fore being explored. The purpose of this study was to perform a proof-of-concept experiment on the use of the radioactive tracer beryllium-7 (7Be) for the determination of in vitro wear in a highly cross-linked orthopedic UHMWPE. Three cross-linked and four conventional UHMWPE pins made from compression- molded GUR 1050, were activated with 109 to 1010 7Be nuclei using a new implantation setup that produced a homogenous distribution of implanted nuclei up to 8.5 lm below the surface. The pins were tested for wear in a six-station pin-on-flat appara- tus for up to 7.1 million cycles (178 km). A Germanium gamma detector was employed to determine activity loss of the UHMWPE pins at preset intervals during the wear test. The wear of the cross-linked UHMWPE pins was readily detected and esti- mated to be 17 6 3 lg per million cycles. The conventional-to- cross-linked ratio of the wear rates was 13.1 6 0.8, in the expected range for these materials. Oxidative degradation dam- age from implantation was negligible; however, a weak depend- ence of wear on implantation dose was observed limiting the number of radioactive tracer atoms that can be introduced. Future applications of this tracer technology may include the analysis of location-specific wear, such as loss of material in the post or backside of a tibial insert.

  16. Yield and Failure Behavior Investigated for Cross-Linked Phenolic Resins Using Molecular Dynamics

    NASA Technical Reports Server (NTRS)

    Monk, Joshua D.; Lawson, John W.

    2016-01-01

    Molecular dynamics simulations were conducted to fundamentally evaluate the yield and failure behavior of cross-linked phenolic resins at temperatures below the glass transition. Yield stress was investigated at various temperatures, strain rates, and degrees of cross-linking. The onset of non-linear behavior in the cross-linked phenolic structures was caused by localized irreversible molecular rearrangements through the rotation of methylene linkers followed by the formation or annihilation of neighboring hydrogen bonds. The yield stress results, with respect to temperature and strain rate, could be fit by existing models used to describe yield behavior of amorphous glasses. The degree of cross-linking only indirectly influences the maximum yield stress through its influence on glass transition temperature (Tg), however there is a strong relationship between the degree of cross-linking and the failure mechanism. Low cross-linked samples were able to separate through void formation, whereas the highly cross-linked structures exhibited bond scission.

  17. Liquid behavior of cross-linked actin bundles.

    PubMed

    Weirich, Kimberly L; Banerjee, Shiladitya; Dasbiswas, Kinjal; Witten, Thomas A; Vaikuntanathan, Suriyanarayanan; Gardel, Margaret L

    2017-02-28

    The actin cytoskeleton is a critical regulator of cytoplasmic architecture and mechanics, essential in a myriad of physiological processes. Here we demonstrate a liquid phase of actin filaments in the presence of the physiological cross-linker, filamin. Filamin condenses short actin filaments into spindle-shaped droplets, or tactoids, with shape dynamics consistent with a continuum model of anisotropic liquids. We find that cross-linker density controls the droplet shape and deformation timescales, consistent with a variable interfacial tension and viscosity. Near the liquid-solid transition, cross-linked actin bundles show behaviors reminiscent of fluid threads, including capillary instabilities and contraction. These data reveal a liquid droplet phase of actin, demixed from the surrounding solution and dominated by interfacial tension. These results suggest a mechanism to control organization, morphology, and dynamics of the actin cytoskeleton.

  18. Adding chemical cross-links to a physical hydrogel.

    PubMed

    Paradossi, Gaio; Finelli, Ivana; Cerroni, Barbara; Chiessi, Ester

    2009-09-17

    Synergistic hydrogels are often encountered in polysaccharide mixtures widely used in food and biopharma products. The xanthan and konjac glucomannan pair provides one of the most studied synergistic hydrogels. Recently we showed that the junction zones stabilizing the 3D structure of this gel are present as macromolecular complexes in solution formed by the partially depolymerised polysaccharidic chains. The non-covalent interactions stabilizing the structure of the polysaccharidic complex cause the melting of the ordered structure of the complex in the solution and of the hydrogels. Introduction of chemical cross-links in the 3D structure of the synergistic hydrogel removes this behaviour, adding new features to the swelling and to the viscoelastic properties of the cured hydrogel. The use of epichlorohydrin as low molecular weight cross-linker does not impact unfavourably on the viability of NIH 3T3 fibroblasts.

  19. Photoinduced Plasticity in Cross-Linked Liquid Crystalline Networks.

    PubMed

    McBride, Matthew K; Hendrikx, Matthew; Liu, Danqing; Worrell, Brady T; Broer, Dirk J; Bowman, Christopher N

    2017-02-24

    Photoactivated reversible addition fragmentation chain transfer (RAFT)-based dynamic covalent chemistry is incorporated into liquid crystalline networks (LCNs) to facilitate spatiotemporal control of alignment, domain structure, and birefringence. The RAFT-based bond exchange process, which leads to stress relaxation, is used in a variety of conditions, to enable the LCN to achieve a near-equilibrium structure and orientation upon irradiation. Once formed, and in the absence of subsequent triggering of the RAFT process, the (dis)order in the LCN and its associated birefringence are evidenced at all temperatures. Using this approach, the birefringence, including the formation of spatially patterned birefringent elements and surface-active topographical features, is selectively tuned by adjusting the light dose, temperature, and cross-linking density.

  20. Conventional Versus Cross-Linked Polyethylene for Total Hip Arthroplasty.

    PubMed

    Surace, Michele F; Monestier, Luca; Vulcano, Ettore; Harwin, Steven F; Cherubino, Paolo

    2015-09-01

    The clinical and radiographic outcomes of 88 patients who underwent primary total hip arthroplasty with either conventional polyethylene or cross-linked polyethylene (XLPE) from the same manufacturer were compared. There were no significant differences between the 2 subpopulations regarding average age, gender, side affected, or prosthetic stem and cup size. The average follow-up was 104 months (range, 55 to 131 months). To the authors' knowledge, this is the longest follow-up for this particular insert. Clinical and radiographic evaluations were performed at 1, 3, 6, and 12 months and then annually. Results showed that XLPE has a significantly greater wear reduction than that of standard polyethylene in primary total hip arthroplasty. At the longest available follow-up for these specific inserts, XLPE proved to be effective in reducing wear.

  1. Synthesis and Reactive Properties of Iron Oxide-Coated Nanoaluminum

    NASA Astrophysics Data System (ADS)

    Kaplowitz, Daniel A.; Jian, Guoqiang; Gaskell, Karen; Jacob, Rohit; Zachariah, Michael R.

    2014-04-01

    A homogeneous coating of Fe3O4 on in situ-generated nanoaluminum was accomplished by thermal decomposition of Fe(CO)5 in an aluminum aerosol stream and subsequent oxidation of iron by air bleed. X-ray photoelectron spectroscopy (XPS) investigation revealed that oxygen penetrated through this coating, and Fe3O4 facilitated the formation of an expanded aluminum oxide layer compared to an uncoated aluminum case. Closed cell combustion tests displayed a minor decrease in pressure response for the coated product, which was attributed to the increased aluminum oxide layer. The critical ignition temperature was reduced for the coated product in T-jump fine-wire combustion tests.

  2. Low-temperature formation of magnetic iron oxides

    NASA Technical Reports Server (NTRS)

    Koch, Chr. Bender; Madsen, M. B.

    1992-01-01

    Elemental analysis and magnetic measurements of the surface of Mars have indicated the presence of an iron oxide with a considerable magnetic moment. Identification of the oxide phase(s) is an important subject as this may be used to identify the process of weathering on the martian surface as well as the composition of the Mars regolith itself. Consequently, interest was in evidence of new formation of strongly magnetic phases (e.g., magnetite, maghemite, feroxyhyte) in terrestrially derived Mars sample analogs. Within the group of Mars sample analogs derived from low-temperature weathering of basalts in Arctic regions, evidence of magnetic oxides formed at the outermost weathering rind was never observed. However, in one instance where the weathering products accumulating in a crack of a basaltic stone were investigated, evidence of magnetite was found. The experimental details are presented.

  3. Grass Cell Walls: A Story of Cross-Linking

    PubMed Central

    Hatfield, Ronald D.; Rancour, David M.; Marita, Jane M.

    2017-01-01

    Cell wall matrices are complex composites mainly of polysaccharides, phenolics (monomers and polymers), and protein. We are beginning to understand the synthesis of these major wall components individually, but still have a poor understanding of how cell walls are assembled into complex matrices. Valuable insight has been gained by examining intact components to understand the individual elements that make up plant cell walls. Grasses are a prominent group within the plant kingdom, not only for their important roles in global agriculture, but also for the complexity of their cell walls. Ferulate incorporation into grass cell wall matrices (C3 and C4 types) leads to a cross-linked matrix that plays a prominent role in the structure and utilization of grass biomass compared to dicot species. Incorporation of p-coumarates as part of the lignin structure also adds to the complexity of grass cell walls. Feruoylation results in a wall with individual hemicellulosic polysaccharides (arabinoxylans) covalently linked to each other and to lignin. Evidence strongly suggests that ferulates not only cross-link arabinoxylans, but may be important factors in lignification of the cell wall. Therefore, the distribution of ferulates on arabinoxylans could provide a means of structuring regions of the matrix with the incorporation of lignin and have a significant impact upon localized cell wall organization. The role of other phenolics in cell wall formation such as p-coumarates (which can have concentrations higher than ferulates) remains unknown. It is possible that p-coumarates assist in the formation of lignin, especially syringyl rich lignin. The uniqueness of the grass cell wall compared to dicot sepcies may not be so much in the gross composition of the wall, but how the distinctive individual components are organized into a functional wall matrix. These features are discussed and working models are provided to illustrate how changing the organization of feruoylation and p

  4. The wear of cross-linked polyethylene against itself.

    PubMed

    Joyce, T J; Ash, H E; Unsworth, A

    1996-01-01

    Cross-linked polyethylene (XLPE) may have an application as a material for an all-plastic surface replacement finger joint. It is inexpensive, biocompatible and can be injection-moulded into the complex shapes that are found on the ends of the finger bones. Further, the cross-linking of polyethylene has significantly improved its mechanical properties. Therefore, the opportunity exists for an all-XLPE joint, and so the wear characteristics of XLPE sliding against itself have been investigated. Wear tests were carried out on both reciprocating pin-on-plate machines and a finger function simulator. The reciprocating pin-on-plate machines had pins loaded at 10 N and 40 N. All pin-on-plate tests show wear factors from the plates very much greater than those of the pins. After 349 km of sliding, a mean wear factor of 0.46 x 10(-6) mm3/N m was found for the plates compared with 0.021 x 10(-6) mm3/N m for the pins. A fatigue mechanism may be causing this phenomenon of greater plate wear. Tests using the finger function simulator give an average wear rate of 0.22 x 10(-6) mm3/N m after 368 km. This sliding distance is equivalent to 12.5 years of use in vivo. The wear factors found were comparable with those of ultra-high molecular weight polyethylene (UHMWPE) against a metallic counterface and, therefore, as the loads across the finger joint are much less than those across the knee or the hip, it is probable that an all-XLPE finger joint will be viable from a wear point of view.

  5. Synthesis and Evaluation of Nanostructured Gold-Iron Oxide Catalysts for the Oxidative Dehydrogenation of Cyclohexane

    NASA Astrophysics Data System (ADS)

    Wu, Peng

    Shape-controlled iron oxide and gold-iron oxide catalysts with a cubic inverse spinel structure were studied in this thesis for the oxidative dehydrogenation of cyclohexane. The structure of iron oxide and gold-iron oxide catalysts has no major impact on their oxidative dehydrogenation activity. However, the product selectivity is influenced. Both cyclohexene and benzene are formed on bare iron oxide nanoshapes, while benzene is the only dehydrogenation product in the presence of gold. The selectivity of benzene over CO2 depends strongly on the stability of the iron oxide support and the gold-support interaction. The highest benzene yield has been observed on gold-iron oxide octahedra. {111}-bound nanooctahedra are highly stable in reaction conditions at 300 °C, while {100}-bound nanocubes start to sinter above 250 °C. The highest benzene yield has been observed on gold-iron oxide nanooctahedra, which are likely to have gold atoms, and few-atom gold clusters strongly-bound on their surface. Cationic gold appears to be the active site for benzene formation. An all-organic method to prepare Au-FeOx nano-catalysts is needed due to the inconvenience of the half-organic, half-inorganic synthesis process discussed above. Several methods from the literature to prepare gold-iron oxide nanocomposites completely in organic solvents were reviewed and followed. FeOx Au synthesis procedures in literatures are initially designed for a Au content of over 70%. This approach was tried here to prepare composites with a much lower Au content (2-5 atom. %). Heat treatment is required to bond Au and FeOx NPs in the organic-phase syntheses. Au-FeOx-4 was obtained as a selective catalyst for the ODH of cyclohexane. A Audelta+ peak is observed in the UV-Vis spectrum of sample Au-FeOx-4. This different Au delta+ form may be cationic Au nano-clusters interacting with the FeOx support. It has been demonstrated that cationic gold is responsible for dehydrogenation behavior. Furthermore, the

  6. GAS-PHASE FLAME SYNTHESIS AND PROPERTIES OF MAGNETIC IRON OXIDE NANOPARTICLES WITH REDUCED OXIDATION STATE

    PubMed Central

    Kumfer, Benjamin M; Shinoda, Kozo; Jeyadevan, Balachandran; Kennedy, Ian M

    2010-01-01

    Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane. PMID:20228941

  7. In Vivo Clearance and Toxicity of Monodisperse Iron Oxide Nanocrystals

    PubMed Central

    Gu, Luo; Fang, Ronnie H.; Sailor, Michael J.; Park, Ji-Ho

    2012-01-01

    Thermal decomposition of organometallic precursors have been found to generate highly crystalline iron oxide (IO) nanocrystals that display superior MR contrast and lower polydispersity than IO nanocrystals synthesized by aqueous precipitation. In the present study, the in vivo characteristics of IO nanocrystals prepared by the thermal decomposition route and then coated with a phospholipid containing a pendant poly(ethylene glycol) chain are examined. The size and surface chemistry of the IO nanocrystal influences the biodistibution, the rate of biodegradation and bioclearance, and the biodegradation products. We conclude that the in vivo fate of PEGylated monodisperse IO nanocrystals and the iron, phospholipid, and oleic acid biodegradation products may influence the cellular environments in the organs and blood that can determine their safety in the body. PMID:22646927

  8. Hydrophilic Packaging of Iron Oxide Nanoclusters for Highly Sensitive Imaging

    PubMed Central

    Smith, Cartney E.; Ernenwein, Dawn; Shkumatov, Artem; Clay, Nicholas; Lee, JuYeon; Melhem, Molly; Misra, Sanjay; Zimmerman, Steven C.; Kong, Hyunjoon

    2015-01-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) are used as imaging probes to provide contrast in magnetic resonance images. Successful use of SPIONs in targeted applications greatly depends on their ability to generate contrast, even at low levels of accumulation, in the tissue of interest. In the present study, we report that SPION nanoclusters packaged to a controlled size by a hyperbranched polyglycerol (HPG) can target tissue defects and have a high relaxivity of 719 mM−1s−1, which was close to their theoretical maximal limit. The resulting nanoclusters were able to identify regions of defective vasculature in an ischemic murine hindlimb using MRI with iron doses that were 5–10 fold lower than those typically used in preclinical studies. Such high relaxivity was attributed to the molecular architecture of HPG, which mimics that of the water retentive polysaccharide, glycogen. The results of this study will be broadly useful in sensitive imaging applications. PMID:26291408

  9. Study of nanocomposites based on iron oxides and pectin

    SciTech Connect

    Chistyakova, Nataliya I. Shapkin, Alexey A. Sirazhdinov, Ruslan R. Gubaidulina, Tatiana V. Kiseleva, Tatiana Yu. Kazakov, Alexander P. Rusakov, Vyacheslav S.

    2014-10-27

    Mössbauer and X-ray diffraction study of nanocomposites based on iron oxides and pectin (PC) was carried out involving magnetization measurements. The concentrations of PC in nanocomposites varied from 0 to 10%. Mössbauer investigations of nanocomposites were carried out in the temperature range from 5 to 300 K. Many-state superparamagnetic relaxation model was used for spectra fitting. The magnetization, M(T,H), was measured in the temperature interval of 80-300 K and magnetic field up to 10 kOe. Formation of the 'iron-polymer' interface was not observed. Particle sizes were estimated using the Mössbauer and X-ray powder diffraction data.

  10. Study of nanocomposites based on iron oxides and pectin

    NASA Astrophysics Data System (ADS)

    Chistyakova, Nataliya I.; Shapkin, Alexey A.; Sirazhdinov, Ruslan R.; Gubaidulina, Tatiana V.; Kiseleva, Tatiana Yu.; Kazakov, Alexander P.; Rusakov, Vyacheslav S.

    2014-10-01

    Mössbauer and X-ray diffraction study of nanocomposites based on iron oxides and pectin (PC) was carried out involving magnetization measurements. The concentrations of PC in nanocomposites varied from 0 to 10%. Mössbauer investigations of nanocomposites were carried out in the temperature range from 5 to 300 K. Many-state superparamagnetic relaxation model was used for spectra fitting. The magnetization, M(T,H), was measured in the temperature interval of 80-300 K and magnetic field up to 10 kOe. Formation of the "iron-polymer" interface was not observed. Particle sizes were estimated using the Mössbauer and X-ray powder diffraction data.

  11. Magnetic characteristics of iron-modified oxide layers on titanium

    NASA Astrophysics Data System (ADS)

    Rudnev, V. S.; Adigamova, M. V.; Lukiyanchuk, I. V.; Tkachenko, I. A.; Morozova, V. P.; Ustinov, A. Yu.; Kharitonskii, P. V.; Frolov, A. M.

    2014-12-01

    Iron-modified TiO2 coatings on titanium exhibiting ferromagnetic properties are formed by combining plasma electrolytic oxidation (PEO) and impregnation with subsequent annealing. It is found that iron is contained in the composition of dispersed particles with sizes of 1-10 μm distributed over the surface of the coatings. It is shown that the coercive force of the coating on titanium samples is 20-70 Oe. The composition, structure, and magnetic properties of the samples with coatings prepared via direct PEO and by combining PEO and impregnation are compared. It is concluded that impregnation and annealing procedures can be used to impart ferromagnetic properties to PEO coatings with different compositions, e.g., protective coatings and coatings applied in catalysis or medicine.

  12. RGD-conjugated iron oxide magnetic nanoparticles for magnetic resonance imaging contrast enhancement and hyperthermia.

    PubMed

    Zheng, S W; Huang, M; Hong, R Y; Deng, S M; Cheng, L F; Gao, B; Badami, D

    2014-03-01

    The purpose of this study was to develop a specific targeting magnetic nanoparticle probe for magnetic resonance imaging and therapy in the form of local hyperthermia. Carboxymethyl dextran-coated ultrasmall superparamagnetic iron oxide nanoparticles with carboxyl groups were coupled to cyclic arginine-glycine-aspartic peptides for integrin α(v)β₃ targeting. The particle size, magnetic properties, heating effect, and stability of the arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide were measured. The arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide demonstrates excellent stability and fast magneto-temperature response. Magnetic resonance imaging signal intensity of Bcap37 cells incubated with arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide was significantly decreased compared with that incubated with plain ultrasmall superparamagnetic iron oxide. The preferential uptake of arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide by target cells was further confirmed by Prussian blue staining and confocal laser scanning microscopy.

  13. Selective Inhibition of the Oxidation of Ferrous Iron or Sulfur in Thiobacillus ferrooxidans

    PubMed Central

    Harahuc, Lesia; Lizama, Hector M.; Suzuki, Isamu

    2000-01-01

    The oxidation of either ferrous iron or sulfur by Thiobacillus ferrooxidans was selectively inhibited or controlled by various anions, inhibitors, and osmotic pressure. Iron oxidation was more sensitive than sulfur oxidation to inhibition by chloride, phosphate, and nitrate at low concentrations (below 0.1 M) and also to inhibition by azide and cyanide. Sulfur oxidation was more sensitive than iron oxidation to the inhibitory effect of high osmotic pressure. These differences were evident not only between iron oxidation by iron-grown cells and sulfur oxidation by sulfur-grown cells but also between the iron and sulfur oxidation activities of the same iron-grown cells. Growth experiments with ferrous iron or sulfur as an oxidizable substrate confirmed the higher sensitivity of iron oxidation to inhibition by phosphate, chloride, azide, and cyanide. Sulfur oxidation was actually stimulated by 50 mM phosphate or chloride. Leaching of Fe and Zn from pyrite (FeS2) and sphalerite (ZnS) by T. ferrooxidans was differentially affected by phosphate and chloride, which inhibited the solubilization of Fe without significantly affecting the solubilization of Zn. PMID:10698768

  14. Biological iron oxidation by Gallionella spp. in drinking water production under fully aerated conditions.

    PubMed

    de Vet, W W J M; Dinkla, I J T; Rietveld, L C; van Loosdrecht, M C M

    2011-11-01

    Iron oxidation under neutral conditions (pH 6.5-8) may be a homo- or heterogeneous chemically- or a biologically-mediated process. The chemical oxidation is supposed to outpace the biological process under slightly alkaline conditions (pH 7-8). The iron oxidation kinetics and growth of Gallionella spp. - obligatory chemolithotrophic iron oxidizers - were assessed in natural, organic carbon-containing water, in continuous lab-scale reactors and full-scale groundwater trickling filters in the Netherlands. From Gallionella cell numbers determined by qPCR, balances were made for all systems. The homogeneous chemical iron oxidation occurred in accordance with the literature, but was retarded by a low water temperature (13 °C). The contribution of the heterogeneous chemical oxidation was, despite the presence of freshly formed iron oxyhydroxides, much lower than in previous studies in ultrapure water. This could be caused by the adsorption of natural organic matter (NOM) on the iron oxide surfaces. In the oxygen-saturated natural water with a pH ranging from 6.5 to 7.7, Gallionella spp. grew uninhibited and biological iron oxidation was an important, and probably the dominant, process. Gallionella growth was not even inhibited in a full-scale filter after plate aeration. From this we conclude that Gallionella spp. can grow under neutral pH and fully aerated conditions when the chemical iron oxidation is retarded by low water temperature and inhibition of the autocatalytic iron oxidation.

  15. Nitric oxide, nitrosyl iron complexes, ferritin and frataxin: a well equipped team to preserve plant iron homeostasis.

    PubMed

    Ramirez, Leonor; Simontacchi, Marcela; Murgia, Irene; Zabaleta, Eduardo; Lamattina, Lorenzo

    2011-11-01

    Iron is a key element in plant nutrition. Iron deficiency as well as iron overload results in serious metabolic disorders that affect photosynthesis, respiration and general plant fitness with direct consequences on crop production. More than 25% of the cultivable land possesses low iron availability due to high pH (calcareous soils). Plant biologists are challenged by this concern and aimed to find new avenues to ameliorate plant responses and keep iron homeostasis under control even at wide range of iron availability in various soils. For this purpose, detailed knowledge of iron uptake, transport, storage and interactions with cellular compounds will help to construct a more complete picture of its role as essential nutrient. In this review, we summarize and describe the recent findings involving four central players involved in keeping cellular iron homeostasis in plants: nitric oxide, ferritin, frataxin and nitrosyl iron complexes. We attempt to highlight the interactions among these actors in different scenarios occurring under iron deficiency or iron overload, and discuss their counteracting and/or coordinating actions leading to the control of iron homeostasis.

  16. Iron oxides stimulate sulfate-driven anaerobic methane oxidation in seeps

    PubMed Central

    Sivan, Orit; Antler, Gilad; Turchyn, Alexandra V.; Marlow, Jeffrey J.; Orphan, Victoria J.

    2014-01-01

    Seep sediments are dominated by intensive microbial sulfate reduction coupled to the anaerobic oxidation of methane (AOM). Through geochemical measurements of incubation experiments with methane seep sediments collected from Hydrate Ridge, we provide insight into the role of iron oxides in sulfate-driven AOM. Seep sediments incubated with 13C-labeled methane showed co-occurring sulfate reduction, AOM, and methanogenesis. The isotope fractionation factors for sulfur and oxygen isotopes in sulfate were about 40‰ and 22‰, respectively, reinforcing the difference between microbial sulfate reduction in methane seeps versus other sedimentary environments (for example, sulfur isotope fractionation above 60‰ in sulfate reduction coupled to organic carbon oxidation or in diffusive sedimentary sulfate–methane transition zone). The addition of hematite to these microcosm experiments resulted in significant microbial iron reduction as well as enhancing sulfate-driven AOM. The magnitude of the isotope fractionation of sulfur and oxygen isotopes in sulfate from these incubations was lowered by about 50%, indicating the involvement of iron oxides during sulfate reduction in methane seeps. The similar relative change between the oxygen versus sulfur isotopes of sulfate in all experiments (with and without hematite addition) suggests that oxidized forms of iron, naturally present in the sediment incubations, were involved in sulfate reduction, with hematite addition increasing the sulfate recycling or the activity of sulfur-cycling microorganisms by about 40%. These results highlight a role for natural iron oxides during bacterial sulfate reduction in methane seeps not only as nutrient but also as stimulator of sulfur recycling. PMID:25246590

  17. VEGF-Iron Oxide Conjugate for Dual MR and PET Imaging of Breast Cancer Angiogenesis

    DTIC Science & Technology

    2007-09-01

    iron oxide nanoparticles conjugated with macrocyclic chelating agent DOTA for 64Cu-labeling and cyclic RGD peptide for integrin alpha (v)beta(3...Nanoparticles We have developed two types of novel superparamagentic iron oxide nanoparticles (USPIO), namely, PVP -IO and PASP-IO...Polyvinylpyrrolidone ( PVP )-coated iron oxide ( PVP -IO) nanoparticles were synthesized by a one-step thermal decomposition method (Fig. 3). The overall size of the

  18. Arsenic Bioremediation by Biogenic Iron Oxides and Sulfides

    PubMed Central

    Couture, Raoul-Marie; Van Cappellen, Philippe; Corkhill, Claire L.; Charnock, John M.; Polya, David A.; Vaughan, David; Vanbroekhoven, Karolien; Lloyd, Jonathan R.

    2013-01-01

    Microcosms containing sediment from an aquifer in Cambodia with naturally elevated levels of arsenic in the associated groundwater were used to evaluate the effectiveness of microbially mediated production of iron minerals for in situ As remediation. The microcosms were first incubated without amendments for 28 days, and the release of As and other geogenic chemicals from the sediments into the aqueous phase was monitored. Nitrate or a mixture of sulfate and lactate was then added to stimulate biological Fe(II) oxidation or sulfate reduction, respectively. Without treatment, soluble As concentrations reached 3.9 ± 0.9 μM at the end of the 143-day experiment. However, in the nitrate- and sulfate-plus-lactate-amended microcosms, soluble As levels decreased to 0.01 and 0.41 ± 0.13 μM, respectively, by the end of the experiment. Analyses using a range of biogeochemical and mineralogical tools indicated that sorption onto freshly formed hydrous ferric oxide (HFO) and iron sulfide mineral phases are the likely mechanisms for As removal in the respective treatments. Incorporation of the experimental results into a one-dimensional transport-reaction model suggests that, under conditions representative of the Cambodian aquifer, the in situ precipitation of HFO would be effective in bringing groundwater into compliance with the World Health Organization (WHO) provisional guideline value for As (10 ppb or 0.13 μM), although soluble Mn release accompanying microbial Fe(II) oxidation presents a potential health concern. In contrast, production of biogenic iron sulfide minerals would not remediate the groundwater As concentration below the recommended WHO limit. PMID:23666325

  19. Nanocrystalline iron oxide aerogels as mesoporous magnetic architectures.

    PubMed

    Long, Jeffrey W; Logan, Michael S; Rhodes, Christopher P; Carpenter, Everett E; Stroud, Rhonda M; Rolison, Debra R

    2004-12-29

    We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties.

  20. Superparamagnetic iron oxide nanoparticles: magnetic nanoplatforms as drug carriers

    PubMed Central

    Wahajuddin; Arora, Sumit

    2012-01-01

    A targeted drug delivery system is the need of the hour. Guiding magnetic iron oxide nanoparticles with the help of an external magnetic field to its target is the principle behind the development of superparamagnetic iron oxide nanoparticles (SPIONs) as novel drug delivery vehicles. SPIONs are small synthetic γ-Fe2O3 (maghemite) or Fe3O4 (magnetite) particles with a core ranging between 10 nm and 100 nm in diameter. These magnetic particles are coated with certain biocompatible polymers, such as dextran or polyethylene glycol, which provide chemical handles for the conjugation of therapeutic agents and also improve their blood distribution profile. The current research on SPIONs is opening up wide horizons for their use as diagnostic agents in magnetic resonance imaging as well as for drug delivery vehicles. Delivery of anticancer drugs by coupling with functionalized SPIONs to their targeted site is one of the most pursued areas of research in the development of cancer treatment strategies. SPIONs have also demonstrated their efficiency as nonviral gene vectors that facilitate the introduction of plasmids into the nucleus at rates multifold those of routinely available standard technologies. SPION-induced hyperthermia has also been utilized for localized killing of cancerous cells. Despite their potential biomedical application, alteration in gene expression profiles, disturbance in iron homeostasis, oxidative stress, and altered cellular responses are some SPION-related toxicological aspects which require due consideration. This review provides a comprehensive understanding of SPIONs with regard to their method of preparation, their utility as drug delivery vehicles, and some concerns which need to be resolved before they can be moved from bench top to bedside. PMID:22848170

  1. AN EFFICIENT AND ECOFRIENDLY OXIDATION OF ALKENES USING IRON NITRATE AND MOLECULAR OXYGEN

    EPA Science Inventory

    An environmentally friendly solventless oxidation of alkenes is accomplished efficiently using relatively benign iron nitrate as catalyst in the pressence of molecular oxygen under pressurized conditions.

  2. Biomechanical Analysis of a Pedicle Screw-Rod System with a Novel Cross-Link Configuration

    PubMed Central

    Hara, Masahito; Umebayashi, Daisuke; Haimoto, Shoichi; Yamamoto, Yu; Nishimura, Yusuke; Wakabayashi, Toshihiko

    2016-01-01

    Study Design The strength effects of a pedicle screw-rod system supplemented with a novel cross-link configuration were biomechanically evaluated in porcine spines. Purpose To assess the biomechanical differences between a conventional cross-link pedicle screw-rod system versus a novel cross-link instrumentation, and to determine the effect of the cross-links. Overview of Literature Transverse cross-link systems affect torsional rigidity, but are thought to have little impact on the sagittal motion of spinal constructs. We tested the strength effects in pullout and flexion-compression tests of novel cross-link pedicle screw constructs using porcine thoracic and lumbar vertebrae. Methods Five matched thoracic and lumbar vertebral segments from 15 porcine spines were instrumented with 5.0-mm pedicle screws, which were then connected with 6.0-mm rods after partial corpectomy in the middle vertebral body. The forces required for construct failure in pullout and flexion-compression tests were examined in a randomized manner for three different cross-link configurations: un-cross-link control, conventional cross-link, and cross-link passing through the base of the spinous process. Statistical comparisons of strength data were analyzed using Student's t-tests. Results The spinous process group required a significantly greater pullout force for construct failure than the control group (p=0.036). No difference was found between the control and cross-link groups, or the cross-link and spinous process groups in pullout testing. In flexion-compression testing, the spinous processes group required significantly greater forces for construct failure than the control and cross-link groups (p<0.001 and p=0.003, respectively). However, there was no difference between the control and cross-link groups. Conclusions A novel cross-link configuration that features cross-link devices passing through the base of the spinous processes increased the mechanical resistance in pullout and

  3. Enriched Iron(III)-Reducing Bacterial Communities are Shaped by Carbon Substrate and Iron Oxide Mineralogy.

    PubMed

    Lentini, Christopher J; Wankel, Scott D; Hansel, Colleen M

    2012-01-01

    Iron (Fe) oxides exist in a spectrum of structures in the environment, with ferrihydrite widely considered the most bioavailable phase. Yet, ferrihydrite is unstable and rapidly transforms to more crystalline Fe(III) oxides (e.g., goethite, hematite), which are poorly reduced by model dissimilatory Fe(III)-reducing microorganisms. This begs the question, what processes and microbial groups are responsible for reduction of crystalline Fe(III) oxides within sedimentary environments? Further, how do changes in Fe mineralogy shape oxide-hosted microbial populations? To address these questions, we conducted a large-scale cultivation effort using various Fe(III) oxides (ferrihydrite, goethite, hematite) and carbon substrates (glucose, lactate, acetate) along a dilution gradient to enrich for microbial populations capable of reducing Fe oxides spanning a wide range of crystallinities and reduction potentials. While carbon source was the most important variable shaping community composition within Fe(III)-reducing enrichments, both Fe oxide type and sediment dilution also had a substantial influence. For instance, with acetate as the carbon source, only ferrihydrite enrichments displayed a significant amount of Fe(III) reduction and the well-known dissimilatory metal reducer Geobacter sp. was the dominant organism enriched. In contrast, when glucose and lactate were provided, all three Fe oxides were reduced and reduction coincided with the presence of fermentative (e.g., Enterobacter spp.) and sulfate-reducing bacteria (e.g., Desulfovibrio spp.). Thus, changes in Fe oxide structure and resource availability may shift Fe(III)-reducing communities between dominantly metal-respiring to fermenting and/or sulfate-reducing organisms which are capable of reducing more recalcitrant Fe phases. These findings highlight the need for further targeted investigations into the composition and activity of speciation-directed metal-reducing populations within natural environments.

  4. Iron oxide hydroxide nanoflower assisted removal of arsenic from water

    SciTech Connect

    Raul, Prasanta Kumar; Devi, Rashmi Rekha; Umlong, Iohborlang M.; Thakur, Ashim Jyoti; Banerjee, Saumen; Veer, Vijay

    2014-01-01

    Graphical abstract: Non-magnetic polycrystalline iron oxide hydroxide nanoparticle with flower like morphology is found to play as an effective adsorbent media to remove As(III) from 300 μg L{sup −1} to less than 10 μg L{sup −1} from drinking water over wide range of pH. TEM image clearly reveals that the nanoparticle looks flower like morphology with average particle size less than 20 nm. The maximum sorption capacity of the sorbent is found to be 475 μg g{sup −1} for arsenic at room temperature and the data fitted to different isotherm models indicate the heterogeneity of the adsorbent surface. The material can be regenerated up to 70% using dilute hydrochloric acid and it would be utilized for de-arsenification purposes. - Highlights: • The work includes synthesis of iron oxide hydroxide nanoflower and its applicability for the removal of arsenic from water. • The nanoparticle was characterized using modern instrumental methods like FESEM, TEM, BET, XRD, etc. • The maximum sorption capacity of the sorbent is found to be 475 μg g{sup −1} for arsenic at room temperature. • The sorption is multilayered on the heterogeneous surface of the nano adsorbent. • The mechanism of arsenic removal of IOH nanoflower follows both adsorption and ion-exchange. - Abstract: Non-magnetic polycrystalline iron oxide hydroxide nanoparticle with flower like morphology is found to play as an effective adsorbent media to remove As(III) from 300 μg L{sup −1} to less than 10 μg L{sup −1} from drinking water over wide range of pH. The nanoparticle was characterized by X-ray powder diffraction analysis (XRD), BET surface area, FTIR, FESEM and TEM images. TEM image clearly reveals flower like morphology with average particle size less than 20 nm. The nanoflower morphology is also supported by FESEM images. The maximum sorption capacity of the sorbent is found to be 475 μg g{sup −1} for arsenic and the data fitted to different isotherm models indicate the

  5. Resistive switching in iron-oxide-filled carbon nanotubes.

    PubMed

    Cava, Carlos E; Persson, Clas; Zarbin, Aldo J G; Roman, Lucimara S

    2014-01-07

    Iron-oxide-filled carbon nanotubes exhibit an intriguing charge bipolarization behavior which allows the material to be applied in resistive memory devices. Raman analysis conducted with an electric field applied in situ shows the Kohn anomalies and a strong modification of the electronic properties related to the applied voltage intensity. In addition, the I(D)/I(G) ratio indicated the reversibility of this process. The electrical characterization indicated an electronic transport governed by two main kinds of charge hopping, one between the filling and the nanotube and the other between the nanotube shells.

  6. Synthesis of a novel supermagnetic iron oxide nanocomposite hydrogel based on graft copolymerization of poly((2-dimethylamino)ethyl methacrylate) onto salep for controlled release of drug.

    PubMed

    Bardajee, Ghasem Rezanejade; Hooshyar, Zari; Asli, Maryam Jahanbakhsh; Shahidi, Fatemeh Emamjome; Dianatnejad, Nastaran

    2014-03-01

    In this research, a novel supermagnetic iron oxide nanocomposite hydrogel was prepared using simultaneous in situ formation of iron oxide nanoparticles (IONs) and three-dimensional cross-linked polymer networks based on graft copolymerization of poly((2-dimethylamino)ethyl methacrylate) (PDMA) onto salep (PDMA-g-salep). The prepared ION-PDMA-g-salep hydrogel was systematically characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDAX), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). In addition, the ION-PDMA-g-salep hydrogel exhibits favorable swelling properties that are sensitive to temperature, pH, and external magnetic field (EMF). The drug release behavior of the prepared hydrogel under EMF, different temperatures and pHs was also studied for the evaluation of the release mechanism and determination of diffusion coefficients. Finally, the antibacterial activity and cytotoxicity studies of the prepared hydrogel were examined. These results suggested that the ION-PDMA-g-salep hydrogel could be a promising candidate for biological dressing applications.

  7. Catalytic effect of free iron ions and heme-iron on chromophore oxidation of a polyene antibiotic amphotericin B

    NASA Astrophysics Data System (ADS)

    Czernel, Grzegorz; Typek, Rafał; Klimek, Katarzyna; Czuryło, Aleksandra; Dawidowicz, Andrzej L.; Gagoś, Mariusz

    2016-05-01

    Owing to the presence of a chromophore in the amphotericin B (AmB) structure, the molecule can undergo the oxidation process. In this research, AmB chromophore oxidation was catalysed by iron ions (iron(III) chloride (FeCl3), pH 2.5) and by heme-iron (methemoglobin (HbFe(III)), and hemin (heme-Fe(III)) at pH 7.0). Additionally, we compared oxidation processes induced by the aforementioned oxidizing agents with autoxidation by dioxygen (O2) naturally occurring in a sample. The effects of the interaction of the oxidizing agents with AmB were analysed using molecular spectroscopies (electronic absorption (UV-Vis), fluorescence) and LC-MS. The use of a 1,10-phenanthroline (phen) chelator facilitated unambiguous determination of the oxidative effect of free iron(III) ions (FeIII) in an acidic solution on the AmB molecules. Also, the changes in the spectra of fluorescence emission centred at ∼470 nm indicate iron-catalysed processes of AmB chromophore oxidation. Unexpectedly, we found a similar spectroscopic effect for AmB induced by methemoglobin and hemin at pH 7.0. Methemoglobin and hemin at a concentration of 8 × 10-7 M (physiological) significantly increases the rate of the processes of AmB chromophore oxidation relative to the process of autoxidation.

  8. Evidence for equilibrium iron isotope fractionation by nitrate-reducing iron(II)-oxidizing bacteria

    PubMed Central

    Kappler, A.; Johnson, C.M.; Crosby, H.A.; Beard, B.L.; Newman, D.K.

    2010-01-01

    Iron isotope fractionations produced during chemical and biological Fe(II) oxidation are sensitive to the proportions and nature of dissolved and solid-phase Fe species present, as well as the extent of isotopic exchange between precipitates and aqueous Fe. Iron isotopes therefore potentially constrain the mechanisms and pathways of Fe redox transformations in modern and ancient environments. In the present study, we followed in batch experiments Fe isotope fractionations between Fe(II)aq and Fe(III) oxide/hydroxide precipitates produced by the Fe(III) mineral encrusting, nitrate-reducing, Fe(II)-oxidizing Acidovorax sp. strain BoFeN1. Isotopic fractionation in 56Fe/54Fe approached that expected for equilibrium conditions, assuming an equilibrium Δ56FeFe(OH)3 – Fe(II)aq fractionation factor of +3.0 ‰. Previous studies have shown that Fe(II) oxidation by this Acidovorax strain occurs in the periplasm, and we propose that Fe isotope equilibrium is maintained through redox cycling via coupled electron and atom exchange between Fe(II)aq and Fe(III) precipitates in the contained environment of the periplasm. In addition to the apparent equilibrium isotopic fractionation, these experiments also record the kinetic effects of initial rapid oxidation, and possible phase transformations of the Fe(III) precipitates. Attainment of Fe isotope equilibrium between Fe(III) oxide/hydroxide precipitates and Fe(II)aq by neutrophilic, Fe(II)-oxidizing bacteria or through abiologic Fe(II)aq oxidation is generally not expected or observed, because the poor solubility of their metabolic product, i.e. Fe(III), usually leads to rapid precipitation of Fe(III) minerals, and hence expression of a kinetic fractionation upon precipitation; in the absence of redox cycling between Fe(II)aq and precipitate, kinetic isotope fractionations are likely to be retained. These results highlight the distinct Fe isotope fractionations that are produced by different pathways of biological and

  9. Reactions of metal ions at surfaces of hydrous iron oxide

    USGS Publications Warehouse

    Hem, J.D.

    1977-01-01

    Cu, Ag and Cr concentrations in natural water may be lowered by mild chemical reduction involving ferric hydroxide-ferrous ion redox processes. V and Mo solubilities may be controlled by precipitation of ferrous vanadate or molybdate. Concentrations as low as 10-8.00 or 10-9.00 M are readily attainable for all these metals in oxygen-depleted systems that are relatively rich in Fe. Deposition of manganese oxides such as Mn3O4 can be catalyzed in oxygenated water by coupling to ferrous-ferric redox reactions. Once formed, these oxides may disproportionate, giving Mn4+ oxides. This reaction produces strongly oxidizing conditions at manganese oxide surfaces. The solubility of As is significantly influenced by ferric iron only at low pH. Spinel structures such as chromite or ferrites of Cu, Ni, and Zn, are very stable and if locally developed on ferric hydroxide surfaces could bring about solubilities much below 10-9.00 M for divalent metals near neutral pH. Solubilities calculated from thermodynamic data are shown graphically and compared with observed concentrations in some natural systems. ?? 1977.

  10. Mediated glucose enzyme electrodes by cross-linking films of osmium redox complexes and glucose oxidase on electrodes.

    PubMed

    Ó Conghaile, Peter; Kamireddy, Sirisha; MacAodha, Domhnall; Kavanagh, Paul; Leech, Dónal

    2013-04-01

    Here, we report on a novel, versatile approach for the preparation of mediated enzyme electrodes, demonstrated using cross-linked films of glucose oxidase and a range of functionalised osmium complexes on graphite electrodes. Response of enzyme electrodes are optimised by evaluation of glucose response as a function of variation in ratios of [Os(2,2'-bipyridine)2(4-aminomethyl pyridine)Cl](+) redox mediator, polyallylamine support and glucose oxidase enzyme cross-linked using a di-epoxide reagent in films on graphite. Lowering of the redox potential required to mediate glucose oxidation is achieved by synthesis of complexes using (4,4'-dimethyl-2,2'-bipyridine) or (4,4'-dimethoxy-2,2'-bipyridine) as a ligand instead of (2,2'-bipyridine). Enzyme electrodes prepared using the complexes based on dimethoxy- or dimethyl-substituted bipyridines provide glucose oxidation current densities of 30 and 70 μA cm(-2) at 0.2 and 0.35 V applied potential compared to 120 μA cm(-2) at 0.45 V for the initial enzyme electrode, under pseudo-physiological conditions in 5 mM glucose, with stability of signals proving inadequate for long-term operation. Current output and stability may be improved by selection of alternate anchoring and cross-linking methodology, to provide enzyme electrodes capable for application to long-term glucose biosensors and anodes in enzymatic fuel cells.

  11. Macroscopic and microscopic biodistribution of intravenously administered iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Misra, Adwiteeya; Petryk, Alicia A.; Strawbridge, Rendall R.; Hoopes, P. Jack

    2015-03-01

    Iron oxide nanoparticles (IONP) are being developed for use as a cancer treatment. They have demonstrated efficacy when used either as a monotherapy or in conjunction with conventional chemotherapy and radiation. The success of IONP as a therapeutic tool depends on the delivery of a safe and controlled cytotoxic thermal dose to tumor tissue following activation with an alternating magnetic field (AMF). Prior to clinical approval, knowledge of IONP toxicity, biodistribution and physiological clearance is essential. This preliminary time-course study determines the acute toxicity and biodistribution of 110 nm dextran-coated IONP (iron) in mice, 7 days post systemic, at doses of 0.4, 0.6, and 1.0 mg Fe/ g mouse bodyweight. Acute toxicity, manifested as changes in the behavior of mice, was only observed temporarily at 1.0 mg Fe/ g mouse bodyweight, the highest dose administered. Regardless of dose, mass spectrometry and histological analysis demonstrated over 3 mg Fe/g tissue in organs within the reticuloendotheilial system (i.e. liver, spleen, and lymph nodes). Other organs (brain, heart, lungs, and kidney) had less than 0.5 mg Fe/g tissue with iron predominantly confined to the organ vasculature.

  12. Intracellular degradation of functionalized carbon nanotube/iron oxide hybrids is modulated by iron via Nrf2 pathway

    PubMed Central

    Elgrabli, Dan; Dachraoui, Walid; Marmier, Hélène de; Ménard-Moyon, Cécilia; Bégin, Dominique; Bégin-Colin, Sylvie; Bianco, Alberto; Alloyeau, Damien; Gazeau, Florence

    2017-01-01

    The in vivo fate and biodegradability of carbon nanotubes is still a matter of debate despite tremendous applications. In this paper we describe a molecular pathway by which macrophages degrade functionalized multi-walled carbon nanotubes (CNTs) designed for biomedical applications and containing, or not, iron oxide nanoparticles in their inner cavity. Electron microscopy and Raman spectroscopy show that intracellularly-induced structural damages appear more rapidly for iron-free CNTs in comparison to iron-loaded ones, suggesting a role of iron in the degradation mechanism. By comparing the molecular responses of macrophages derived from THP1 monocytes to both types of CNTs, we highlight a molecular mechanism regulated by Nrf2/Bach1 signaling pathways to induce CNT degradation via NOX2 complex activation and O2•−, H2O2 and OH• production. CNT exposure activates an oxidative stress-dependent production of iron via Nrf2 nuclear translocation, Ferritin H and Heme oxygenase 1 translation. Conversely, Bach1 was translocated to the nucleus of cells exposed to iron-loaded CNTs to recycle embedded iron. Our results provide new information on the role of oxidative stress, iron metabolism and Nrf2-mediated host defence for regulating CNT fate in macrophages. PMID:28120861

  13. Engineered Iron/Iron Oxide Functionalized Membranes for Selenium and Other Toxic Metal Removal from Power Plant Scrubber Water.

    PubMed

    Gui, Minghui; Papp, Joseph K; Colburn, Andrew S; Meeks, Noah D; Weaver, Benjamin; Wilf, Ilan; Bhattacharyya, Dibakar

    2015-08-15

    The remediation of toxic metals from water with high concentrations of salt has been an emerging area for membrane separation. Cost-effective nanomaterials such as iron and iron oxide nanoparticles have been widely used in reductive and oxidative degradation of toxic organics. Similar procedures can be used for redox transformations of metal species (e.g. metal oxyanions to elemental metal), and/or adsorption of species on iron oxide surface. In this study, iron-functionalized membranes were developed for reduction and adsorption of selenium from coal-fired power plant scrubber water. Iron-functionalized membranes have advantages over iron suspension as the membrane prevents particle aggregation and dissolution. Both lab-scale and full-scale membranes were prepared first by coating polyvinylidene fluoride (PVDF) membranes with polyacrylic acid (PAA), followed by ion exchange of ferrous ions and subsequent reduction to zero-valent iron nanoparticles. Water permeability of membrane decreased as the percent PAA functionalization increased, and the highest ion exchange capacity (IEC) was obtained at 20% PAA with highly pH responsive pores. Although high concentrations of sulfate and chloride in scrubber water decreased the reaction rate of selenium reduction, this was shown to be overcome by integration of nanofiltration (NF) and iron-functionalized membranes, and selenium concentration below 10 μg/L was achieved.

  14. Enhancing the Performance of the Rechargeable Iron Electrode in Alkaline Batteries with Bismuth Oxide and Iron Sulfide Additives

    SciTech Connect

    Manohar, AK; Yang, CG; Malkhandi, S; Prakash, GKS; Narayanan, SR

    2013-09-07

    Iron-based alkaline rechargeable batteries have the potential of meeting the needs of large-scale electrical energy storage because of their low-cost, robustness and eco-friendliness. However, the widespread commercial deployment of iron-based batteries has been limited by the low charging efficiency and the poor discharge rate capability of the iron electrode. In this study, we have demonstrated iron electrodes containing bismuth oxide and iron sulfide with a charging efficiency of 92% and capable of being discharged at the 3C rate. Such a high value of charging efficiency combined with the ability to discharge at high rates is being reported for the first time. The bismuth oxide additive led to the in situ formation of elemental bismuth and a consequent increase in the overpotential for the hydrogen evolution reaction leading to an increase in the charging efficiency. We observed that the sulfide ions added to the electrolyte and iron sulfide added to the electrode mitigated-electrode passivation and allowed for continuous discharge at high rates. At the 3C discharge rate, a utilization of 0.2 Ah/g was achieved. The performance level of the rechargeable iron electrode demonstrated here is attractive for designing economically-viable large-scale energy storage systems based on alkaline nickel-iron and iron-air batteries. (C) 2013 The Electrochemical Society. All rights reserved.

  15. Morphology of biogenic iron oxides records microbial physiology and environmental conditions: toward interpreting iron microfossils.

    PubMed

    Krepski, S T; Emerson, D; Hredzak-Showalter, P L; Luther, G W; Chan, C S

    2013-09-01

    Despite the abundance of Fe and its significance in Earth history, there are no established robust biosignatures for Fe(II)-oxidizing micro-organisms. This limits our ability to piece together the history of Fe biogeochemical cycling and, in particular, to determine whether Fe(II)-oxidizers played a role in depositing ancient iron formations. A promising candidate for Fe(II)-oxidizer biosignatures is the distinctive morphology and texture of extracellular Fe(III)-oxyhydroxide stalks produced by mat-forming microaerophilic Fe(II)-oxidizing micro-organisms. To establish the stalk morphology as a biosignature, morphologic parameters must be quantified and linked to the microaerophilic Fe(II)-oxidizing metabolism and environmental conditions. Toward this end, we studied an extant model organism, the marine stalk-forming Fe(II)-oxidizing bacterium, Mariprofundus ferrooxydans PV-1. We grew cultures in flat glass microslide chambers, with FeS substrate, creating opposing oxygen/Fe(II) concentration gradients. We used solid-state voltammetric microelectrodes to measure chemical gradients in situ while using light microscopy to image microbial growth, motility, and mineral formation. In low-oxygen (2.7-28 μm) zones of redox gradients, the bacteria converge into a narrow (100 μm-1 mm) growth band. As cells oxidize Fe(II), they deposit Fe(III)-oxyhydroxide stalks in this band; the stalks orient directionally, elongating toward higher oxygen concentrations. M. ferrooxydans stalks display a narrow range of widths and uniquely biogenic branching patterns, which result from cell division. Together with filament composition, these features (width, branching, and directional orientation) form a physical record unique to microaerophilic Fe(II)-oxidizer physiology; therefore, stalk morphology is a biosignature, as well as an indicator of local oxygen concentration at the time of formation. Observations of filamentous Fe(III)-oxyhydroxide microfossils from a ~170 Ma marine Fe

  16. Iron and oxygen isotope fractionation during iron UV photo-oxidation: Implications for early Earth and Mars

    NASA Astrophysics Data System (ADS)

    Nie, Nicole X.; Dauphas, Nicolas; Greenwood, Richard C.

    2017-01-01

    Banded iron formations (BIFs) contain appreciable amounts of ferric iron (Fe3+). The mechanism by which ferrous iron (Fe2+) was oxidized into Fe3+ in an atmosphere that was globally anoxic is highly debated. Of the three scenarios that have been proposed to explain BIF formation, photo-oxidation by UV photons is the only one that does not involve life (the other two are oxidation by O2 produced by photosynthesis, and anoxygenic photosynthesis whereby Fe2+ is directly used as electron donor in place of water). We experimentally investigated iron and oxygen isotope fractionation imparted by iron photo-oxidation at a pH of 7.3. The iron isotope fractionation between precipitated Fe3+-bearing lepidocrocite and dissolved Fe2+ follows a Rayleigh distillation with an instantaneous 56Fe/54Fe fractionation factor of + 1.2 ‰. Such enrichment in the heavy isotopes of iron is consistent with the values measured in BIFs. We also investigated the nature of the mass-fractionation law that governs iron isotope fractionation in the photo-oxidation experiments (i.e., the slope of the δ56Fe-δ57Fe relationship). The experimental run products follow a mass-dependent law corresponding to the high-T equilibrium limit. The fact that a ∼3.8 Gyr old BIF sample (IF-G) from Isua (Greenland) falls on the same fractionation line confirms that iron photo-oxidation in the surface layers of the oceans was a viable pathway to BIF formation in the Archean, when the atmosphere was largely transparent to UV photons. Our experiments allow us to estimate the quantum yield of the photo-oxidation process (∼0.07 iron atom oxidized per photon absorbed). This yield is used to model iron oxidation on early Mars. As the photo-oxidation proceeds, the aqueous medium becomes more acidic, which slows down the reaction by changing the speciation of iron to species that are less efficient at absorbing UV-photons. Iron photo-oxidation in centimeter to meter-deep water ponds would take months to years to

  17. Iron and manganese oxide mineralization in the Pacific

    USGS Publications Warehouse

    Hein, J.R.; Koschinsky, A.; Halbach, P.; Manheim, F. T.; Bau, M.; Kang, J.-K.; Lubick, N.

    1997-01-01

    Iron, manganese, and iron-manganese deposits occur in nearly all geomorphologic and tectonic environments in the ocean basins and form by one or more of four processes: (1) hydrogenetic precipitation from cold ambient seawater, (2) precipitation from hydrothermal fluids, (3) precipitation from sediment pore waters that have been modified from bottom water compositions by diagenetic reactions in the sediment column and (4) replacement of rocks and sediment. Iron and manganese deposits occur in five forms: nodules, crusts, cements, mounds and sediment-hosted stratabound layers. Seafloor oxides show a wide range of compositions from nearly pure iron to nearly pure manganese end members. Fe/Mn ratios vary from about 24 000 (up to 58% elemental Fe) for hydrothermal seamount ironstones to about 0.001 (up to 52% Mn) for hydrothermal stratabound manganese oxides from active volcanic arcs. Hydrogenetic Fe-Mn crusts that occur on most seamounts in the ocean basins have a mean Fe/Mn ratio of 0.7 for open-ocean seamount crusts and 1.2 for continental margin seamount crusts. Fe-Mn nodules of potential economic interest from the Clarion-Clipperton Zone have a mean Fe/Mn ratio of 0.3, whereas the mean ratio for nodules from elsewhere in the Pacific is about 0.7. Crusts are enriched in Co, Ni and Pt and nodules in Cu and Ni, and both have significant concentrations of Pb, Zn, Ba, Mo, V and other elements. In contrast, hydrothermal deposits commonly contain only minor trace metal contents, although there are many exceptions, for example, with Ni contents up to 0.66%, Cr to 1.2%, and Zn to 1.4%. Chondrite-normalized REE patterns generally show a positive Ce anomaly and abundant ??REEs for hydrogenetic and mixed hydrogenetic-diagenetic deposits, whereas the Ce anomaly is negative for hydrothermal deposits and ??REE contents are low. However, the Ce anomaly in crusts may vary from strongly positive in East Pacific crusts to slightly negative in West Pacific crusts, which may reflect

  18. Disulfide cross-linking influences symbiotic activities of nodule peptide NCR247.

    PubMed

    Shabab, Mohammed; Arnold, Markus F F; Penterman, Jon; Wommack, Andrew J; Bocker, Hartmut T; Price, Paul A; Griffitts, Joel S; Nolan, Elizabeth M; Walker, Graham C

    2016-09-06

    Interactions of rhizobia with legumes establish the chronic intracellular infection that underlies symbiosis. Within nodules of inverted repeat-lacking clade (IRLC) legumes, rhizobia differentiate into nitrogen-fixing bacteroids. This terminal differentiation is driven by host nodule-specific cysteine-rich (NCR) peptides that orchestrate the adaptation of free-living bacteria into intracellular residents. Medicago truncatula encodes a family of >700 NCR peptides that have conserved cysteine motifs. NCR247 is a cationic peptide with four cysteines that can form two intramolecular disulfide bonds in the oxidized forms. This peptide affects Sinorhizobium meliloti transcription, translation, and cell division at low concentrations and is antimicrobial at higher concentrations. By preparing the three possible disulfide-cross-linked NCR247 regioisomers, the reduced peptide, and a variant lacking cysteines, we performed a systematic study of the effects of intramolecular disulfide cross-linking and cysteines on the activities of an NCR peptide. The relative activities of the five NCR247 variants differed strikingly among the various bioassays, suggesting that the NCR peptide-based language used by plants to control the development of their bacterial partners during symbiosis is even greater than previously recognized. These patterns indicate that certain NCR bioactivities require cysteines whereas others do not. The results also suggest that NCR247 may exert some of its effects within the cell envelope whereas other activities occur in the cytoplasm. BacA, a membrane protein that is critical for symbiosis, provides protection against all bactericidal forms of NCR247. Oxidative folding protects NCR247 from degradation by the symbiotically relevant metalloprotease HrrP (host range restriction peptidase), suggesting that disulfide bond formation may additionally stabilize NCR peptides during symbiosis.

  19. Disulfide cross-linking influences symbiotic activities of nodule peptide NCR247

    PubMed Central

    Shabab, Mohammed; Arnold, Markus F. F.; Penterman, Jon; Wommack, Andrew J.; Bocker, Hartmut T.; Price, Paul A.; Griffitts, Joel S.; Nolan, Elizabeth M.; Walker, Graham C.

    2016-01-01

    Interactions of rhizobia with legumes establish the chronic intracellular infection that underlies symbiosis. Within nodules of inverted repeat-lacking clade (IRLC) legumes, rhizobia differentiate into nitrogen-fixing bacteroids. This terminal differentiation is driven by host nodule-specific cysteine-rich (NCR) peptides that orchestrate the adaptation of free-living bacteria into intracellular residents. Medicago truncatula encodes a family of >700 NCR peptides that have conserved cysteine motifs. NCR247 is a cationic peptide with four cysteines that can form two intramolecular disulfide bonds in the oxidized forms. This peptide affects Sinorhizobium meliloti transcription, translation, and cell division at low concentrations and is antimicrobial at higher concentrations. By preparing the three possible disulfide–cross-linked NCR247 regioisomers, the reduced peptide, and a variant lacking cysteines, we performed a systematic study of the effects of intramolecular disulfide cross-linking and cysteines on the activities of an NCR peptide. The relative activities of the five NCR247 variants differed strikingly among the various bioassays, suggesting that the NCR peptide-based language used by plants to control the development of their bacterial partners during symbiosis is even greater than previously recognized. These patterns indicate that certain NCR bioactivities require cysteines whereas others do not. The results also suggest that NCR247 may exert some of its effects within the cell envelope whereas other activities occur in the cytoplasm. BacA, a membrane protein that is critical for symbiosis, provides protection against all bactericidal forms of NCR247. Oxidative folding protects NCR247 from degradation by the symbiotically relevant metalloprotease HrrP (host range restriction peptidase), suggesting that disulfide bond formation may additionally stabilize NCR peptides during symbiosis. PMID:27551097

  20. Cerebral Blood Volume MRI with Intravascular Superparamagentic Iron Oxide Nanoparticles

    PubMed Central

    Kim, Seong-Gi; Harel, Noam; Jin, Tao; Kim, Tae; Lee, Phil; Zhao, Fuqiang

    2013-01-01

    Cerebral blood volume (CBV) is a crucial physiological indicator of tissue viability and vascular reactivity. Thus, non-invasive CBV mapping has been of great interest. For this, ultrasmall superparamagnetic iron oxide nanoparticles (USPIO) including monocrystalline iron oxide nanoparticles (MION) can be used as long half-life, intravascular susceptibility agents of CBV MRI measurements. Also, CBV-weighted fMRI with USPIO provides enhanced sensitivity, reduced large vessel contribution, and improved spatial specificity compared to conventional blood oxygenation-level dependent (BOLD) fMRI, and measures a single physiological parameter that is easily interpretable. We review physiochemical and magnetic properties as well as pharmacokinetics of USPIO in brief. We then extensively discuss quantifications of baseline CBV, vessel size index, and functional CBV change. We also provide reviews of dose-dependent sensitivity, vascular filter function, specificity, characteristics, and impulse response function of CBV fMRI. Examples of CBV fMRI specificity at the laminar and columnar resolution are provided. Finally, we briefly review application of CBV measurements to functional and pharmacological studies in animals. Overall, the use of USPIO can determine baseline CBV and its changes induced by functional activity and pharmacological interventions. PMID:23208650

  1. Tuning the structure and habit of iron oxide mesocrystals

    SciTech Connect

    Wetterskog, Erik; Klapper, Alice; Disch, Sabrina; Josten, Elisabeth; Hermann, Raphaël P.; Rücker, Ulrich; Brückel, Thomas; Bergström, Lennart; Salazar-Alvarez, German

    2016-07-11

    A precise control over the meso- and microstructure of ordered and aligned nanoparticle assemblies, i.e., mesocrystals, is essential in the quest for exploiting the collective material properties for potential applications. In this work, we produced evaporation-induced self-assembled mesocrystals with different mesostructures and crystal habits based on iron oxide nanocubes by varying the nanocube size and shape and by applying magnetic fields. A full 3D characterization of the mesocrystals was performed using image analysis, high-resolution scanning electron microscopy and Grazing Incidence Small Angle X-ray Scattering (GISAXS). This enabled the structural determination of e.g. multi-domain mesocrystals with complex crystal habits and the quantification of interparticle distances with sub-nm precision. Mesocrystals of small nanocubes (l = 8.6 12.6 nm) are isostructural with a body centred tetragonal (bct ) lattice whereas assemblies of the largest nanocubes in this study (l = 13.6 nm) additionally form a simple cubic (sc) lattice. The mesocrystal habit can be tuned from a square, hexagonal to star-like and pillar shapes depending on the particle size and shape and the strength of the applied magnetic field. Finally, we outline a qualitative phase diagram of the evaporation-induced self-assembled superparamagnetic iron oxide nanocube mesocrystals based on nanocube edge length and magnetic field strength.

  2. Tuning the structure and habit of iron oxide mesocrystals

    DOE PAGES

    Wetterskog, Erik; Klapper, Alice; Disch, Sabrina; ...

    2016-07-11

    A precise control over the meso- and microstructure of ordered and aligned nanoparticle assemblies, i.e., mesocrystals, is essential in the quest for exploiting the collective material properties for potential applications. In this work, we produced evaporation-induced self-assembled mesocrystals with different mesostructures and crystal habits based on iron oxide nanocubes by varying the nanocube size and shape and by applying magnetic fields. A full 3D characterization of the mesocrystals was performed using image analysis, high-resolution scanning electron microscopy and Grazing Incidence Small Angle X-ray Scattering (GISAXS). This enabled the structural determination of e.g. multi-domain mesocrystals with complex crystal habits and themore » quantification of interparticle distances with sub-nm precision. Mesocrystals of small nanocubes (l = 8.6 12.6 nm) are isostructural with a body centred tetragonal (bct ) lattice whereas assemblies of the largest nanocubes in this study (l = 13.6 nm) additionally form a simple cubic (sc) lattice. The mesocrystal habit can be tuned from a square, hexagonal to star-like and pillar shapes depending on the particle size and shape and the strength of the applied magnetic field. Finally, we outline a qualitative phase diagram of the evaporation-induced self-assembled superparamagnetic iron oxide nanocube mesocrystals based on nanocube edge length and magnetic field strength.« less

  3. Iron release and membrane damage in erythrocytes exposed to oxidizing agents, phenylhydrazine, divicine and isouramil.

    PubMed Central

    Ferrali, M; Signorini, C; Ciccoli, L; Comporti, M

    1992-01-01

    Mouse erythrocytes were incubated with oxidizing agents, phenylhydrazine, divicine and isouramil. With all the oxidants a rapid release of iron in a desferrioxamine (DFO)-chelatable form was seen and it was accompanied by methaemoglobin formation. If the erythrocytes were depleted of GSH by a short preincubation with diethyl maleate, the release of iron was accompanied by lipid peroxidation and, subsequently, haemolysis. GSH depletion by itself did not induce iron release, methaemoglobin formation, lipid peroxidation or haemolysis. Rather, the fate of the cell in which iron is released depended on the intracellular availability of GSH. In addition, iron release was higher in depleted cells than in native ones, suggesting a role for GSH in preventing iron release when oxidative stress is imposed by the oxidants. Iron release preceded lipid peroxidation. The latter was prevented when the erythrocytes were preloaded with DFO in such a way (preincubation with 10 mM-DFO) that the intracellular concentration was equivalent to that of the released iron, but not when the intracellular DFO was lower (preincubation with 0.1 mM-DFO). Extracellular DFO did not affect lipid peroxidation and haemolysis, suggesting again that the observed events occur intracellularly (intracellular chelation of released iron). The relevance of iron release from iron complexes in the mechanisms of cellular damage induced by oxidative stress is discussed. PMID:1637315

  4. Characterization of the deoxyguanosine-lysine cross-link of methylglyoxal.

    PubMed

    Petrova, Katya V; Millsap, Amy D; Stec, Donald F; Rizzo, Carmelo J

    2014-06-16

    Methylglyoxal is a mutagenic bis-electrophile that is produced endogenously from carbohydrate precursors. Methylglyoxal has been reported to induce DNA-protein cross-links (DPCs) in vitro and in cultured cells. Previous work suggests that these cross-links are formed between guanine and either lysine or cysteine side chains. However, the chemical nature of the methylglyoxal induced DPC have not been determined. We have examined the reaction of methylglyoxal, deoxyguanosine (dGuo), and Nα-acetyllysine (AcLys) and determined the structure of the cross-link to be the N2-ethyl-1-carboxamide with the lysine side chain amino group (1). The cross-link was identified by mass spectrometry and the structure confirmed by comparison to a synthetic sample. Further, the cross-link between methylglyoxal, dGuo, and a peptide (AcAVAGKAGAR) was also characterized. The mechanism of cross-link formation is likely to involve an Amadori rearrangement.

  5. Flanking sequences modulate diepoxide and mustard cross-linking efficiencies at the 5'-GNC site.

    PubMed

    Sawyer, Gregory A; Frederick, Elizabeth D; Millard, Julie T

    2004-08-01

    Diepoxybutane, diepoxyoctane, and mechlorethamine are cytotoxic agents that induce interstrand cross-links between the N7 positions of deoxyguanosine residues on opposite strands of the DNA duplex preferentially at 5'-GNC sequences. We have systematically varied the identity of either the base 5' to the cross-linked deoxyguanosine residues or the intervening base pair to determine flanking sequence effects on cross-linking efficiency. We used synthetic DNA oligomers containing four 5'-N(1)GN(2)C sites that varied either N(1) or N(2). Interstrand cross-links were purified through denaturing polyacrylamide gel electrophoresis and then subjected to piperidine cleavage. The amount of cleavage at each deoxyguanosine residue, representative of cross-linking efficiency at that site, was determined by sequencing gel analysis. Our data suggest that cross-linking efficiency varies with the identity of N(1) similarly (purines > pyrimidines) for diepoxybutane, diepoxyoctane, and mechlorethamine but that the effects of N(2) differ for the three compounds.

  6. Strain hardening, avalanches, and strain softening in dense cross-linked actin networks

    NASA Astrophysics Data System (ADS)

    Åström, Jan A.; Kumar, P. B. Sunil; Vattulainen, Ilpo; Karttunen, Mikko

    2008-05-01

    Actin filament networks enable the cytoskeleton to adjust to internal and external forcing. These dynamic networks can adapt to changes by dynamically adjusting their cross-links. Here, we model actin filaments as cross-linked elastic fibers of finite dimensions, with the cross-links being approximately 1μm apart, and employ a full three-dimensional model to study their elastic properties by computer simulations. The results show compelling evidence that dense actin networks are characterized by (a) strain hardening without entropic elasticity, (b) avalanches of cross-link slippage leading to strain softening in the case of breakable cross-links, and (c) spontaneous formation of stress fibers in the case of dynamic cross-link formation and destruction.

  7. Effect of glucose content on thermally cross-linked fibrous gelatin scaffolds for tissue engineering.

    PubMed

    Siimon, Kaido; Reemann, Paula; Põder, Annika; Pook, Martin; Kangur, Triin; Kingo, Külli; Jaks, Viljar; Mäeorg, Uno; Järvekülg, Martin

    2014-09-01

    Thermally cross-linked glucose-containing electrospun gelatin meshes were studied as possible cell substrate materials. FTIR analysis was used to study the effect of glucose on cross-linking reactions. It was found that the presence of glucose increases the extent of cross-linking of fibrous gelatin scaffolds, which in return determines scaffold properties and their usability in tissue engineering applications. Easy to handle fabric-like scaffolds were obtained from blends containing up to 15% glucose. Maximum extent of cross-linking was reached at nearly 20% glucose content. Cross-linking effectively resulted in decreased solubility and increased resistance to enzymatic degradation. Preliminary short-term cell culture experiments indicate that such thermally cross-linked gelatin-glucose scaffolds are suitable for tissue engineering applications.

  8. An Open Data Format for Visualization and Analysis of Cross-Linked Mass Spectrometry Results.

    PubMed

    Hoopmann, Michael R; Mendoza, Luis; Deutsch, Eric W; Shteynberg, David; Moritz, Robert L

    2016-11-01

    Protein-protein interactions are an important element in the understanding of protein function, and chemical cross-linking shotgun mass spectrometry is rapidly becoming a routine approach to identify these specific interfaces and topographical interactions. Protein cross-link data analysis is aided by dozens of algorithm choices, but hindered by a lack of a common format for representing results. Consequently, interoperability between algorithms and pipelines utilizing chemical cross-linking remains a challenge. pepXML is an open, widely-used format for representing spectral search algorithm results that has facilitated information exchange and pipeline development for typical shotgun mass spectrometry analyses. We describe an extension of this format to incorporate cross-linking spectral search results. We demonstrate application of the extension by representing results of multiple cross-linking search algorithms. In addition, we demonstrate adapting existing pepXML-supporting software pipelines to analyze protein cross-linking results formatted in pepXML. Graphical Abstract ᅟ.

  9. Energy harvesting from vibration with cross-linked polypropylene piezoelectrets

    SciTech Connect

    Zhang, Xiaoqing; Wu, Liming; Sessler, Gerhard M.

    2015-07-15

    Piezoelectret films are prepared by modification of the microstructure of polypropylene foam sheets cross-linked by electronic irradiation (IXPP), followed by proper corona charging. Young’s modulus, relative permittivity, and electromechanical coupling coefficient of the fabricated films, determined by dielectric resonance spectra, are about 0.7 MPa, 1.6, and 0.08, respectively. Dynamic piezoelectric d{sub 33} coefficients up to 650 pC/N at 200 Hz are achieved. The figure of merit (FOM, d{sub 33} ⋅ g{sub 33}) for a more typical d{sub 33} value of 400 pC/N is about 11.2 GPa{sup −1}. Vibration-based energy harvesting with one-layer and two-layer stacks of these films is investigated at various frequencies and load resistances. At an optimum load resistance of 9 MΩ and a resonance frequency of 800 Hz, a maximum output power of 120 μW, referred to the acceleration g due to gravity, is obtained for an energy harvester consisting of a one-layer IXPP film with an area of 3.14 cm{sup 2} and a seismic mass of 33.7 g. The output power can be further improved by using two-layer stacks of IXPP films in electric series. IXPP energy harvesters could be used to energize low-power electronic devices, such as wireless sensors and LED lights.

  10. Zinc cross-linked hydroxamated alginates for pulsed drug release

    PubMed Central

    Raut, Neha S; Deshmukh, Prasad R; Umekar, Milind J; Kotagale, Nandkishor R

    2013-01-01

    Introduction: Alginates can be tailored chemically to improve solubility, physicochemical, and biological properties and its complexation with metal ion is useful for controlling the drug release. Materials And Methods: Synthesized N,O-dimethyl, N-methyl, or N-Benzyl hydroxylamine derivatives of sodium alginate were subsequently complexed with zinc to form beads. Hydroxamation of sodium alginate was confirmed by Fourier transform infra-red spectroscopy (FTIR) and differential scanning calorimetry (DSC). Results: The synthesized polymeric material exhibited reduced aqueous, HCl and NaOH solubility. The hydroxamated derivatives demonstrated pulsed release where change in pH of the dissolution medium stimulated the atenolol release. Conclusion: Atenolol loaded Zn cross-linked polymeric beads demonstrated the sustained the plasma drug levels with increased half-life. Although the synthesized derivatives greatly altered the aqueous solubility of sodium alginate, no significant differences in in vitro and in vivo atenolol release behavior amongst the N,O-dimethyl, N-methyl, or N-Benzyl hydroxylamine derivatives of sodium alginate were observed. PMID:24350039

  11. Photosensitive cross-linked block copolymers with controllable release.

    PubMed

    Yu, Lili; Lv, Cong; Wu, LiZhu; Tung, ChenHo; Lv, WanLiang; Li, ZhongJin; Tang, XinJing

    2011-01-01

    We intend to form photosensitive block copolymer micelles for controllable release of encapsulated substances. Here, we designed and synthesized a new photocleavable cross-linker (2-nitrophenyl ethylene glycol dimethacrylate) for methyl methacrylate (MMA) atom transfer radical polymerization. Four different ratios (0:1, 1:26, 1:16, 1:8.8) of the photocleavable cross-linker to MMA monomer were used and four block copolymers (P0, P1, P2, P3) were synthesized with PEO-Br as the macroinitiator. Gel permeation chromatography and (1) H NMR studies showed that linear polymer molecules could be cross-linked by the photocleavable linker. The fluorescence studies of the encapsulated Nile Red (NR) showed that there were lower critical micelle concentrations for the polymer P1, P2 and P3 than polymer P0. And dynamic light scattering and SEM confirmed the formation of polymer micelles. Photolysis experiments demonstrated that NR encapsulated in the polymer micelles could be released upon UV irradiation (365 nm, 11 mW cm(-2)) due to the breakage of the photocleavable linker and the generation of more hydrophilic acid moieties, which destabilized polymer micelles. Our study shows a new strategy for the possibility of photocontrollable drug release for hydrophobic drugs.

  12. Synthesis and Properties of Cross-Linked Polyamide Aerogels

    NASA Technical Reports Server (NTRS)

    Williams, Jarrod C.; Meador, Mary Ann; McCorkle, Linda

    2015-01-01

    We report the first synthesis of cross-linked polyamide aerogels through step growth polymerization using a combination of diamines, diacid chloride and triacid chloride. Polyamide oligomers endcapped with amines are prepared as stable solutions in N-methylpyrrolidinone from several different diamine precursors and 1,3-benzenedicarbonyl dichloride. Addition of 1,3,5-benzenetricarbonyl trichloride yields gels which form in under five minutes according to the scheme shown. Solvent exchange of the gels into ethanol, followed by drying using supercritical CO2 extraction gives colorless aerogels with densities around 0.1 to 0.2 gcm3. Thicker monolithes of the polyamide aerogels are stiff and strong, while thin films of certain formulations are highly flexible, durable, and even translucent. These materials may have use as insulation for deployable space structures, rovers, habitats or extravehicular activity suits as well as in many terrestrial applications. Strucure property relationships of the aerogels, including surface area, mechanical properties, and thermal conductivity will be discussed.

  13. Automated determination of cross-linked fibrin derivatives in plasma.

    PubMed

    Elms, M J; Bundesen, P G; Rowbury, D; Goodall, S; Wakeham, N; Rowell, J A; Hillyard, C J; Rylatt, D B

    1993-02-01

    Automated assays for the measurement of cross-linked fibrin derivatives in plasma (XL-FbDP) have been developed utilizing latex beads coated with anti-D dimer monoclonal antibody (DD-3B6/22) for both the Cobas Fara Chemistry Centrifugal and the Cobas Mira analysers (Roche, Basle, Switzerland). The analysers were programmed to mix plasma and latex reagent simultaneously and analyse absorbance changes over a 10-15 min period. Results were interpolated by the analyser from a standard curve derived from a polymer of D-dimer. Both assays had high precision (< 5% CV) for values between 100 and 1000 ng/ml and provided clear discrimination between normal samples and samples from patients suffering from the thrombotic diseases, DVT/PE and DIC. The results obtained for XL-FbDP determination with both methods compared well with established methods: a high correlation was obtained with a semi-quantitative manual latex method for both the Fara (r = 0.92) and Mira (r = 0.83) and correlations (r) of 0.81 (Fara) and 0.84 (Mira) were obtained with an enzyme immunoassay (EIA). Correlation between the two automated procedures was high (r = 0.96). The automated method will enable laboratories to provide a rapid and accurate quantitation of XL-FbDP.

  14. Pyridinium cross-links in heritable disorders of collagen

    SciTech Connect

    Pasquali, M.; Still, M.J.; Dembure, P.P.

    1995-12-01

    Ehlers-Danlos syndrome (EDS) is a heterogeneous group of inherited disorders of collagen that is characterized by skin fragility, skin hyperextensibility, and joint hypermobility. EDS type VI is caused by impaired collagen lysyl hydroxylase (procollagen-lysine, 2-oxoglutarate 5-dioxygenase; E.C.1.14.11.4), the ascorbate-dependent enzyme that hydroxylates lysyl residues on collagen neopeptides. Different alterations in the gene for collagen lysyl hydroxylase have been reported in families with EDS type VI. In EDS type VI, impairment of collagen lysyl hydroxylase results in a low hydroxylysine content in mature collagen. Hydroxylysine is a precursor of the stable, covalent, intermolecular cross-links of collagen, pyridinoline (Pyr), and deoxypyridinoline (Dpyr). Elsewhere we reported in preliminary form that patients with EDS type VI had a distinctive alteration in the urinary excretion of Pyr and Dpyr. In the present study, we confirm that the increased Dpyr/Pyr ratio is specific for EDS type VI and is not observed in other inherited or acquired collagen disorders. In addition, we find that skin from patients with EDS type VI has reduced Pyr and increased Dpyr, which could account for the organ pathology. 19 refs., 1 tab.

  15. Nickel aluminides and nickel-iron aluminides for use in oxidizing environments

    DOEpatents

    Liu, Chain T.

    1988-03-15

    Nickel aluminides and nickel-iron aluminides treated with hafnium or zirconium, boron and cerium to which have been added chromium to significantly improve high temperature ductility, creep resistance and oxidation properties in oxidizing environments.

  16. Mapping the Iron Oxidation State in Martian Meteorites

    NASA Technical Reports Server (NTRS)

    Martin, A. M.; Treimann, A. H.; Righter, K.

    2017-01-01

    Several types of Martian igneous meteorites have been identified: clinopyroxenites (nakhlites), basaltic shergottites, peridotitic shergottites, dunites (chassignites) and orthopyroxenites [1,2]. In order to constrain the heterogeneity of the Martian mantle and crust, and their evolution through time, numerous studies have been performed on the iron oxidation state of these meteorites [3,4,5,6,7,8,9]. The calculated fO2 values all lie within the FMQ-5 to FMQ+0.5 range (FMQ representing the Fayalite = Magnetite + Quartz buffer); however, discrepancies appear between the various studies, which are either attributed to the choice of the minerals/melts used, or to the precision of the analytical/calculation method. The redox record in volcanic samples is primarily related to the oxidation state in the mantle source(s). However, it is also influenced by several deep processes: melting, crystallization, magma mixing [10], assimilation and degassing [11]. In addition, the oxidation state in Martian meteorites is potentially affected by several surface processes: assimilation of sediment/ crust during lava flowing at Mars' surface, low temperature micro-crystallization [10], weathering at the surface of Mars and low temperature reequilibration, impact processes (i.e. high pressure phase transitions, mechanical mixing, shock degassing and melting), space weathering, and weathering on Earth (at atmospheric conditions different from Mars). Decoding the redox record of Martian meteorites, therefore, requires large-scale quantitative analysis methods, as well as a perfect understanding of oxidation processes.

  17. Atomistic simulations of uranium incorporation into iron (hydr)oxides.

    PubMed

    Kerisit, Sebastien; Felmy, Andrew R; Ilton, Eugene S

    2011-04-01

    Atomistic simulations were carried out to characterize the coordination environments of U incorporated in three Fe-(hydr)oxide minerals: goethite, magnetite, and hematite. The simulations provided information on U-O and U-Fe distances, coordination numbers, and lattice distortion for U incorporated in different sites (e.g., unoccupied versus occupied sites, octahedral versus tetrahedral) as a function of the oxidation state of U and charge compensation mechanisms (i.e., deprotonation, vacancy formation, or reduction of Fe(III) to Fe(II)). For goethite, deprotonation of first shell hydroxyls enables substitution of U for Fe(III) with a minimal amount of lattice distortion, whereas substitution in unoccupied octahedral sites induced appreciable distortion to 7-fold coordination regardless of U oxidation states and charge compensation mechanisms. Importantly, U-Fe distances of ∼3.6 Å were associated with structural incorporation of U and cannot be considered diagnostic of simple adsorption to goethite surfaces. For magnetite, the octahedral site accommodates U(V) or U(VI) with little lattice distortion. U substituted for Fe(III) in hematite maintained octahedral coordination in most cases. In general, comparison of the simulations with available experimental data provides further evidence for the structural incorporation of U in iron (hydr)oxide minerals.

  18. Atomistic Simulations of Uranium Incorporation into Iron (Hydr)Oxides

    SciTech Connect

    Kerisit, Sebastien N.; Felmy, Andrew R.; Ilton, Eugene S.

    2011-04-29

    Atomistic simulations were carried out to characterize the coordination environments of U incorporated in three Fe-(hydr)oxide minerals: goethite, magnetite, and hematite. The simulations provided information on U-O and U-Fe distances, coordination numbers, and lattice distortion for U incorporated in different sites (e.g., unoccupied versus occupied sites, octahedral versus tetrahedral) as a function of the oxidation state of U and charge compensation mechanisms (i.e., deprotonation, vacancy formation, or reduction of Fe(III) to Fe(II)). For goethite, deprotonation of first shell hydroxyls enables substitution of U for Fe(III) with a minimal amount of lattice distortion, whereas substitution in unoccupied octahedral sites induced appreciable distortion to 7-fold coordination regardless of U oxidation states and charge compensation mechanisms. Importantly, U-Fe distances of ~3.6 Å were associated with structural incorporation of U and cannot be considered diagnostic of simple adsorption to goethite surfaces. For magnetite, the octahedral site accommodates U(V) or U(VI) with little lattice distortion. U substituted for Fe(III) in hematite maintained octahedral coordination in most cases. In general, comparison of the simulations with available experimental data provides further evidence for the structural incorporation of U in iron (hydr)oxide minerals.

  19. Clinical efficacy of two forms of intravenous iron--saccharated ferric oxide and cideferron--for iron deficiency anemia.

    PubMed

    Araki, T; Takaai, M; Miyazaki, A; Ohshima, S; Shibamiya, T; Nakamura, T; Yamamoto, K

    2012-12-01

    Over 90% of iron deficiency anemia cases are due to iron deficiency associated with depletion of stored iron or inadequate intake. Parenteral iron supplementation is an important part of the management of anemia, and some kinds of intravenous iron are used. However, few studies have evaluated the clinical efficacy of these drugs. The purpose of this study was to compare and assess the clinical efficacy of two types of intravenous iron injection, saccharated ferric oxide (SFO) and cideferron (CF). Medical records were obtained for 91 unrelated Japanese anemia patients treated with SFO (n = 37) or CF (n = 54) from May 2005 to May 2010 at Gunma University Hospital. Patients treated with blood transfusion, erythropoietin or oral iron were excluded. Hemoglobin (Hb) values measured on day 0, 7 and 14 were used to assess the efficacy of intravenous irons. A significant increase was observed in the mean Hb value by day 14 of administration in both the CF group and SFO group, and the mean Hb increase due to administration of CF for 7 days was comparable to that of SFO for 14 days. Age and sex did not affect improvement of Hb value. CF is fast acting and highly effective compared with SFO for the treatment of iron deficiency anemia. The use of CF may shorten a therapeutic period for iron deficiency anemia, and CF may be feasible for reducing the hospitalization period.

  20. Effect of dietary iron and copper on performance and oxidative stability in broiler leg meat.

    PubMed

    Ruiz, J A; Pérez-Vendrell, A M; Esteve-Garcia, E

    2000-05-01

    1. An experiment was carried out to determine the effect of removal of supplemental iron and copper from broiler diets during the last 3 weeks before slaughter on broiler performance, tissue vitamin E concentrations and oxidation values in raw; cooked and stored broiler leg meat. 2. Removal of supplemental iron and copper from the diet slightly decreased food efficiency; the differences were significant only when both minerals were removed simultaneously 3. Effect of iron withdrawal on iron concentration in tissue was low. However, total copper concentration in tissue was reduced in animals deprived of iron or both minerals simultaneously. 4. Removal of dietary iron and copper did not affect vitamin E concentration in raw and cooked meat, while stored meat showed lower concentrations in animals deprived of iron and copper simultaneously. 5. The removal of iron and copper from the diet reduced oxidation values in cooked broiler leg meat as measured by the thiobarbituric acid-reacting substances method (TBARS).

  1. Potential for microbial oxidation of ferrous iron in basaltic glass.

    PubMed

    Xiong, Mai Yia; Shelobolina, Evgenya S; Roden, Eric E

    2015-05-01

    Basaltic glass (BG) is an amorphous ferrous iron [Fe(II)]-containing material present in basaltic rocks, which are abundant on rocky planets such as Earth and Mars. Previous research has suggested that Fe(II) in BG can serve as an energy source for chemolithotrophic microbial metabolism, which has important ramifications for potential past and present microbial life on Mars. However, to date there has been no direct demonstration of microbially catalyzed oxidation of Fe(II) in BG. In this study, three different culture systems were used to investigate the potential for microbial oxidation of Fe(II) in BG, including (1) the chemolithoautotrophic Fe(II)-oxidizing, nitrate-reducing "Straub culture"; (2) the mixotrophic Fe(II)-oxidizing, nitrate-reducing organism Desulfitobacterium frappieri strain G2; and (3) indigenous microorganisms from a streambed Fe seep in Wisconsin. The BG employed consisted of clay and silt-sized particles of freshly quenched lava from the TEB flow in Kilauea, Hawaii. Soluble Fe(II) or chemically reduced NAu-2 smectite (RS) were employed as positive controls to verify Fe(II) oxidation activity in the culture systems. All three systems demonstrated oxidation of soluble Fe(II) and/or structural Fe(II) in RS, whereas no oxidation of Fe(II) in BG material was observed. The inability of the Straub culture to oxidize Fe(II) in BG was particularly surprising, as this culture can oxidize other insoluble Fe(II)-bearing minerals such as biotite, magnetite, and siderite. Although the reason for the resistance of the BG toward enzymatic oxidation remains unknown, it seems possible that the absence of distinct crystal faces or edge sites in the amorphous glass renders the material resistant to such attack. These findings have implications with regard to the idea that Fe(II)-Si-rich phases in basalt rocks could provide a basis for chemolithotrophic microbial life on Mars, specifically in neutral-pH environments where acid-promoted mineral dissolution and

  2. Methylglyoxal-induced DNA-protein cross-links and cytotoxicity in Chinese hamster ovary cells.

    PubMed

    Brambilla, G; Sciabà, L; Faggin, P; Finollo, R; Bassi, A M; Ferro, M; Marinari, U M

    1985-05-01

    The technique of alkaline elution was applied to study the capacity of methylglyoxal to induce DNA damage and repair in Chinese hamster ovary cells. DNA cross-linking was observed after a 90-min exposure to a subtoxic dose (1.5 mM), and the cross-links were fully repaired by 24 h. The cross-linking appeared to be DNA-protein in nature, since proteinase treatment removed the effect. When the same cells were exposed to methylglyoxal in the presence of a rat liver metabolic system, both cytotoxicity and cross-linking frequency were significantly reduced.

  3. Effect of cross-linking and enzymatic hydrolysis composite modification on the properties of rice starches.

    PubMed

    Xiao, Huaxi; Lin, Qinlu; Liu, Gao-Qiang

    2012-07-06

    Native rice starch lacks the versatility necessary to function adequately under rigorous industrial processing, so modified starches are needed to meet the functional properties required in food products. This work investigated the impact of enzymatic hydrolysis and cross-linking composite modification on the properties of rice starches. Rice starch was cross-linked with epichlorohydrin (EPI) with different concentrations (0.5%, 0.7%, 0.9% w/w, on a dry starch basis), affording cross-linked rice starches with the three different levels of cross-linking that were named R₁, R₂, and R₃, respectively. The cross-linked rice starches were hydrolyzed by α-amylase and native, hydrolyzed, and hydrolyzed cross-linked rice starches were comparatively studied. It was found that hydrolyzed cross-linked rice starches showed a lower the degree of amylase hydrolysis compared with hydrolyzed rice starch. The higher the degree of cross-linking, the higher the capacity to resist enzyme hydrolysis. Hydrolyzed cross-linked rice starches further increased the adsorptive capacities of starches for liquids and decreased the trend of retrogradation, and it also strengthened the capacity to resist shear compared to native and hydrolyzed rice starches.

  4. Xilmass: A New Approach toward the Identification of Cross-Linked Peptides.

    PubMed

    Yılmaz, Şule; Drepper, Friedel; Hulstaert, Niels; Černič, Maša; Gevaert, Kris; Economou, Anastassios; Warscheid, Bettina; Martens, Lennart; Vandermarliere, Elien

    2016-10-18

    Chemical cross-linking coupled with mass spectrometry plays an important role in unravelling protein interactions, especially weak and transient ones. Moreover, cross-linking complements several structural determination approaches such as cryo-EM. Although several computational approaches are available for the annotation of spectra obtained from cross-linked peptides, there remains room for improvement. Here, we present Xilmass, a novel algorithm to identify cross-linked peptides that introduces two new concepts: (i) the cross-linked peptides are represented in the search database such that the cross-linking sites are explicitly encoded, and (ii) the scoring function derived from the Andromeda algorithm was adapted to score against a theoretical tandem mass spectrometry (MS/MS) spectrum that contains the peaks from all possible fragment ions of a cross-linked peptide pair. The performance of Xilmass was evaluated against the recently published Kojak and the popular pLink algorithms on a calmodulin-plectin complex data set, as well as three additional, published data sets. The results show that Xilmass typically had the highest number of identified distinct cross-linked sites and also the highest number of predicted cross-linked sites.

  5. Effect of radiation cross-linking on the abrasive wear behaviour of polyethylenes

    NASA Astrophysics Data System (ADS)

    Gul, Rizwan M.; Khan, Tahir I.

    2014-06-01

    This study explores the differences in the dry abrasive wear behavior of different polyethylenes, and compares the effect of radiation cross-linking on the wear behavior. Four different types of polyethylenes: LDPE, LLDPE, HDPE and UHMWPE were studied. Cross-linking was carried out by high energy electron beam with radiation dose of 200 kGy. The results show that in unirradiated state UHMWPE has excellent wear resistance, with HDPE showing comparable wear properties; both LDPE and LLDPE exhibit high wear rate. Cross-linking improves wear rate of LDPE and UHMWPE, however, the wear rate of HDPE and LLDPE increases with cross-linking.

  6. Structural features of covalently cross-linked hydroxylase and reductase proteins of soluble methane monooxygenase as revealed by mass spectrometric analysis.

    PubMed

    Kopp, Daniel A; Berg, Eric A; Costello, Catherine E; Lippard, Stephen J

    2003-06-06

    Soluble methane monooxygenase requires complexes between its three component proteins for efficient catalysis. The hydroxylase (MMOH) must bind both to the reductase (MMOR) and to the regulatory protein (MMOB) to facilitate oxidation of methane to methanol. Although structures of MMOH, MMOB, and one domain of MMOR have been determined, less geometric information is available for the complexes. To address this deficiency, MMOH and MMOR were cross-linked by a carbodiimide reagent and analyzed by specific proteolysis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and capillary high performance liquid chromatography mass spectrometry. Tandem mass spectra conclusively identified two amine-to-carboxylate cross-linked sites involving the alpha subunit of MMOH and the [2Fe-2S] domain of MMOR (MMOR-Fd). In particular, the N terminus of the MMOH alpha subunit forms cross-links to the side chains of MMOR-Fd residues Glu-56 and Glu-91. These Glu residues are close to one another on the surface of MMOR-Fd and >25 A from the [2Fe-2S] cluster. Because the N terminus of the alpha subunit of MMOH was not located in the crystal structure of MMOH, a detailed structural model of the complex based on the cross-link was precluded; however, a previously proposed binding site for MMOR on MMOH could be ruled out. Based on the cross-linking results, a MMOR E56Q/E91Q double mutant was generated. The mutant retains >80% of MMOR NADH oxidase activity but reduces sMMO activity to approximately 65% of the level supported by the wild type reductase. Cross-linking to MMOH was diminished but not abolished in the double mutant, indicating that other residues of MMOR also form cross-links to MMOH.

  7. Iron oxide reduction in deep Baltic Sea sediments: the potential role of anaerobic oxidation of methane

    NASA Astrophysics Data System (ADS)

    Egger, Matthias; Slomp, Caroline P.; Dijkstra, Nikki; Sapart, Célia J.; Risgaard-Petersen, Nils; Kasten, Sabine; Riedinger, Natascha; Barker Jørgensen, Bo

    2015-04-01

    Methane is a powerful greenhouse gas and its emission from marine sediments to the atmosphere is largely controlled by anaerobic oxidation of methane (AOM). Traditionally, sulfate is considered to be the most important electron acceptor for AOM in marine sediments. However, recent studies have shown that AOM may also be coupled to the reduction of iron (Fe) oxides (Beal et al., 2009; Riedinger et al., 2014; Egger et al., 2014). In the Baltic Sea, the transition from the Ancylus freshwater phase to the Littorina brackish/marine phase (A/L-transition) ca. 9-7 ka ago (Zillén et al., 2008) resulted in the accumulation of methanogenic brackish/marine sediments overlying Fe-oxide rich lacustrine deposits. The downward diffusion of methane from the brackish/marine sediments into the lake sediments leads to an ideal diagenetic system to study a potential coupling between Fe oxide reduction and methane oxidation. Here, we use porewater and sediment geochemical data obtained at sites M0063 and M0065 during the IODP Baltic Sea Paleoenvironment Expedition 347 in 2013 to identify the potential mechanisms responsible for the apparent Fe oxide reduction in the non-sulfidic limnic sediments below the A/L transition. In this presentation, we will review the various explanations for the elevated ferrous Fe in the porewater in the lake sediments and we will specifically address the potential role of the reaction of methane with Fe-oxides. References: Beal E. J., House C. H. and Orphan V. J. (2009) Manganese- and iron-dependent marine methane oxidation. Science 325, 184-187. Egger M., Rasigraf O., Sapart C. J., Jilbert T., Jetten M. S. M., Röckmann T., van der Veen C., Banda N., Kartal B., Ettwig K. F. and Slomp C. P. (2014) Iron-mediated anaerobic oxidation of methane in brackish coastal sediments. Environ. Sci. Technol. 49, 277-283. Riedinger N., Formolo M. J., Lyons T. W., Henkel S., Beck A. and Kasten S. (2014) An inorganic geochemical argument for coupled anaerobic oxidation of

  8. Chemical characterization of iron oxide precipitates from wetlands constructed to treat polluted mine drainage

    SciTech Connect

    Fish, C.L.; Partezana, J.M.; Hedin, R.S.

    1996-12-31

    The passive treatment of abandoned mine drainage using wetlands will produce a significant amount of iron rich sludge which will require costly removal and disposal. An alternative to disposal may be the use of this iron oxide material as pigments which could defray some of these costs. In this research, iron deposits from five alkaline mine drainage wetlands were collected and a series of standard tests were run. The tests included loss on ignition, moisture, pH, acid soluble metals, oil absorption, and water soluble matter. The results of these tests were compared to those achieved using commercially available natural and synthetic iron oxides. The results indicate that iron oxides from constructed wetlands have chemical properties that are intermediate to those of natural and synthetic iron oxide products.

  9. Oxygen vacancy promoted methane partial oxidation over iron oxide oxygen carriers in the chemical looping process.

    PubMed

    Cheng, Zhuo; Qin, Lang; Guo, Mengqing; Xu, Mingyuan; Fan, Jonathan A; Fan, Liang-Shih

    2016-11-30

    We perform ab initio DFT+U calculations and experimental studies of the partial oxidation of methane to syngas on iron oxide oxygen carriers to elucidate the role of oxygen vacancies in oxygen carrier reactivity. In particular, we explore the effect of oxygen vacancy concentration on sequential processes of methane dehydrogenation, and oxidation with lattice oxygen. We find that when CH4 adsorbs onto Fe atop sites without neighboring oxygen vacancies, it dehydrogenates with CHx radicals remaining on the same site and evolves into CO2via the complete oxidation pathway. In the presence of oxygen vacancies, on the other hand, the formed methyl (CH3) prefers to migrate onto the vacancy site while the H from CH4 dehydrogenation remains on the original Fe atop site, and evolves into CO via the partial oxidation pathway. The oxygen vacancies created in the oxidation process can be healed by lattice oxygen diffusion from the subsurface to the surface vacancy sites, and it is found that the outward diffusion of lattice oxygen atoms is more favorable than the horizontal diffusion on the same layer. Based on the proposed mechanism and energy profile, we identify the rate-limiting steps of the partial oxidation and complete oxidation pathways. Also, we find that increasing the oxygen vacancy concentration not only lowers the barriers of CH4 dehydrogenation but also the cleavage energy of Fe-C bonds. However, the barrier of the rate-limiting step cannot further decrease when the oxygen vacancy concentration reaches 2.5%. The fundamental insight into the oxygen vacancy effect on CH4 oxidation with iron oxide oxygen carriers can help guide the design and development of more efficient oxygen carriers and CLPO processes.

  10. Maleimide cross-linked bioactive PEG hydrogel exhibits improved reaction kinetics and cross-linking for cell encapsulation and in-situ delivery

    PubMed Central

    Phelps, Edward A.; Enemchukwu, Nduka O.; Fiore, Vincent F.; Sy, Jay C.; Murthy, Niren; Sulchek, Todd A.; Barker, Thomas H.

    2012-01-01

    Engineered polyethylene glycol-maleimide matrices for regenerative medicine exhibit improved reaction efficiency and wider range of Young’s moduli by utilizing maleimide cross-linking chemistry. This hydrogel chemistry is advantageous for cell delivery due to the mild reaction that occurs rapidly enough for in situ delivery, while easily lending itself to “plug-and-play” design variations such as incorporation of enzyme-cleavable cross-links and cell-adhesion peptides. PMID:22174081

  11. Alkaline battery containing a separator of a cross-linked copolymer of vinyl alcohol and unsaturated carboxylic acid

    NASA Technical Reports Server (NTRS)

    Hsu, L. C.; Philipp, W. H.; Sheibley, D. W.; Gonzalez-Sanabria, O. D. (Inventor)

    1985-01-01

    A battery separator for an alkaline battery is described. The separator comprises a cross linked copolymer of vinyl alcohol units and unsaturated carboxylic acid units. The cross linked copolymer is insoluble in water, has excellent zincate diffusion and oxygen gas barrier properties and a low electrical resistivity. Cross linking with a polyaldehyde cross linking agent is preferred.

  12. Green tea extract impairs meat emulsion properties by disturbing protein disulfide cross-linking.

    PubMed

    Jongberg, Sisse; Terkelsen, Linda de S; Miklos, Rikke; Lund, Marianne N

    2015-02-01

    The dose-dependent effects of green tea extract (100, 500, or 1500ppm) on the textural and oxidative stability of meat emulsions were investigated, and compared to a control meat emulsion without extract. All levels of green tea extract inhibited formation of TBARS as a measure for lipid oxidation. Overall protein thiol oxidation and myosin heavy chain (MHC) cross-linking were inhibited by 100ppm green tea extract without jeopardizing the textural stability, while increasing concentrations of extract resulted in reduced thiol concentration and elevated levels of non-reducible protein modifications. Addition of 1500ppm green tea extract was found to modify MHC as evaluated by SDS-PAGE combining both protein staining and specific thiol staining, indicating that protein modifications generated through reactions of green tea phenolic compounds with protein thiols, disrupted the meat emulsion properties leading to reduced water holding capacity and textural stability. Hence, a low dose of green tea extract preserves both the textural and the oxidative stability of the meat proteins.

  13. Iron-oxide minerals affect extracellular electron-transfer paths of Geobacter spp.

    PubMed

    Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

    2013-01-01

    Some bacteria utilize (semi)conductive iron-oxide minerals as conduits for extracellular electron transfer (EET) to distant, insoluble electron acceptors. A previous study demonstrated that microbe/mineral conductive networks are constructed in soil ecosystems, in which Geobacter spp. share dominant populations. In order to examine how (semi)conductive iron-oxide minerals affect EET paths of Geobacter spp., the present study grew five representative Geobacter strains on electrodes as the sole electron acceptors in the absence or presence of (semi)conductive iron oxides. It was found that iron-oxide minerals enhanced current generation by three Geobacter strains, while no effect was observed in another strain. Geobacter sulfurreducens was the only strain that generated substantial amounts of currents both in the presence and absence of the iron oxides. Microscopic, electrochemical and transcriptomic analyses of G. sulfurreducens disclosed that this strain constructed two distinct types of EET path; in the absence of iron-oxide minerals, bacterial biofilms rich in extracellular polymeric substances were constructed, while composite networks made of mineral particles and microbial cells (without polymeric substances) were developed in the presence of iron oxides. It was also found that uncharacterized c-type cytochromes were up-regulated in the presence of iron oxides that were different from those found in conductive biofilms. These results suggest the possibility that natural (semi)conductive minerals confer energetic and ecological advantages on Geobacter, facilitating their growth and survival in the natural environment.

  14. Dopamine Serves as a Stable Surface Modifier for Iron Oxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Chi, Xiaoqin; Wang, Xiaomin; Hu, Juan; Wang, Lirong; Gao, Jinhao; Zhang, Bei; Zhang, Xixiang

    2013-03-01

    Iron oxide nanoparticles are an important class of nanomaterials in a broad range of biomedical applications because of their superparamagnetism and biocompatibility. The success of biomedical applications of iron oxide nanoparticles relies on the particles' surface functionalization, which requires robust and versatile surface anchors. Here, we report on a detailed examination of the dopamine-based surface modification of iron oxide nanoparticles. We used dopamine (2-(3,4-dihydroxyphenyl)ethylamine) and L-dopa (3,4-dihydroxy-L-phenylalanine) as two surface modifiers and chose Fe2O3 hollow nanoparticles and Fe3O4 nanoparticles as two representative substrates. Optical and TEM images showed that iron oxide nanoparticles dispersed very well in water after surface modification. The analysis of the UV-Vis spectra indicated that dopamine and L-dopa are stable after being immobilized on the surface of iron oxide nanoparticles when the pH value of the environment is about 7. The magnetic properties analysis further showed that the blocking temperature of the dopamine- or L-dopa-decorated iron oxide nanoparticles hardly changed over 20 days, confirming long-term stability of these surface modified nanoparticles. Cell assay indicated that these dopamine- or L-dopa-modified iron oxide nanoparticles were biocompatible. These results confirm that dopamine serves as a stable modifier and a robust anchor to functionalize iron oxide nanoparticles in biomedical applications.

  15. Genome Sequence of the Acidophilic Iron Oxidizer Ferrimicrobium acidiphilum Strain T23T.

    PubMed

    Eisen, Sebastian; Poehlein, Anja; Johnson, D Barrie; Daniel, Rolf; Schlömann, Michael; Mühling, Martin

    2015-04-30

    Extremely acidophilic iron-oxidizing bacteria have largely been characterized for the phyla Proteobacteria and Nitrospira. Here, we report the draft genome of an iron-oxidizing and -reducing heterotrophic mesophile of the Actinobacteria, Ferrimicrobium acidiphilum, which was isolated from an abandoned pyrite mine. The genome sequence comprises 3.08 Mb.

  16. Iron-Oxide Minerals Affect Extracellular Electron-Transfer Paths of Geobacter spp

    PubMed Central

    Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

    2013-01-01

    Some bacteria utilize (semi)conductive iron-oxide minerals as conduits for extracellular electron transfer (EET) to distant, insoluble electron acceptors. A previous study demonstrated that microbe/mineral conductive networks are constructed in soil ecosystems, in which Geobacter spp. share dominant populations. In order to examine how (semi)conductive iron-oxide minerals affect EET paths of Geobacter spp., the present study grew five representative Geobacter strains on electrodes as the sole electron acceptors in the absence or presence of (semi)conductive iron oxides. It was found that iron-oxide minerals enhanced current generation by three Geobacter strains, while no effect was observed in another strain. Geobacter sulfurreducens was the only strain that generated substantial amounts of currents both in the presence and absence of the iron oxides. Microscopic, electrochemical and transcriptomic analyses of G. sulfurreducens disclosed that this strain constructed two distinct types of EET path; in the absence of iron-oxide minerals, bacterial biofilms rich in extracellular polymeric substances were constructed, while composite networks made of mineral particles and microbial cells (without polymeric substances) were developed in the presence of iron oxides. It was also found that uncharacterized c-type cytochromes were up-regulated in the presence of iron oxides that were different from those found in conductive biofilms. These results suggest the possibility that natural (semi)conductive minerals confer energetic and ecological advantages on Geobacter, facilitating their growth and survival in the natural environment. PMID:23363619

  17. Collagen Cross-Linking Using Riboflavin and Ultraviolet-A for Corneal Thinning Disorders

    PubMed Central

    Pron, G; Ieraci, L; Kaulback, K

    2011-01-01

    reports not involving outcome events such as safety, effectiveness, durability, vision quality or patient satisfaction following an intervention with corneal implants reports not involving corneal thinning disorders and an intervention involving CXL Summary of Evidence Findings In the Medical Advisory Secretariat evidence review on corneal cross-linking, 65 reports (16 case reports) involving 1403 patients were identified on the use of CXL for managing corneal thinning disorders. The reports were summarized according to their primary clinical indication, whether or not secondary interventions were used in conjunction with CXL (referred to as CXL-Plus) and whether or not it was a safety-related report. The safety review was based on information from the cohort studies evaluating effectiveness, clinical studies evaluating safety, treatment response or recovery, and published case reports of complications. Complications, such as infection and noninfectious keratitis (inflammatory response), reported in case reports, generally occurred in the first week and were successfully treated with topical antibiotics and steroids. Other complications, such as the cytotoxic effects on the targeted corneal stroma, occurred as side effects of the photo-oxidative process generated by riboflavin and ultraviolet-A and were usually reversible. The reports on treatment effectiveness involved 15 pre-post longitudinal cohort follow-up studies ranging from follow-up of patients’ treated eye only, follow-up in both the treated and untreated fellow-eye; and follow-up in the treated eye only and a control group not receiving treatment. One study was a 3-arm randomized control study (RCT) involving 2 comparators: one comparator was a sham treatment in which one eye was treated with riboflavin only; and the other comparator was the untreated fellow-eye. The outcomes reported across the studies involved statistically significant and clinically relevant improvements in corneal topography and

  18. Integrated Cryogenic Satellite Communications Cross-Link Receiver Experiment

    NASA Technical Reports Server (NTRS)

    Romanofsky, R. R.; Bhasin, K. B.; Downey, A. N.; Jackson, C. J.; Silver, A. H.; Javadi, H. H. S.

    1995-01-01

    An experiment has been devised which will validate, in space, a miniature, high-performance receiver. The receiver blends three complementary technologies; high temperature superconductivity (HTS), pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuits (MMIC), and a miniature pulse tube cryogenic cooler. Specifically, an HTS band pass filter, InP MMIC low noise amplifier, HTS-sapphire resonator stabilized local oscillator (LO), and a miniature pulse tube cooler will be integrated into a complete 20 GHz receiver downconverter. This cooled downconverter will be interfaced with customized signal processing electronics and integrated onto the space shuttle's 'HitchHiker' carrier. A pseudorandom data sequence will be transmitted to the receiver, which is in low Earth orbit (LEO), via the Advanced Communication Technology Satellite (ACTS) on a 20 GHz carrier. The modulation format is QPSK and the data rate is 2.048 Mbps. The bit error rate (BER) will be measured in situ. The receiver is also equipped with a radiometer mode so that experiment success is not totally contingent upon the BER measurement. In this mode, the receiver uses the Earth and deep space as a hot and cold calibration source, respectively. The experiment closely simulates an actual cross-link scenario. Since the receiver performance depends on channel conditions, its true characteristics would be masked in a terrestrial measurement by atmospheric absorption and background radiation. Furthermore, the receiver's performance depends on its physical temperature, which is a sensitive function of platform environment, thermal design, and cryocooler performance. This empirical data is important for building confidence in the technology.

  19. Encoding Hydrogel Mechanics via Network Cross-Linking Structure

    PubMed Central

    2015-01-01

    The effects of mechanical cues on cell behaviors in 3D remain difficult to characterize as the ability to tune hydrogel mechanics often requires changes in the polymer density, potentially altering the material’s biochemical and physical characteristics. Additionally, with most PEG diacrylate (PEGDA) hydrogels, forming materials with compressive moduli less than ∼10 kPa has been virtually impossible. Here, we present a new method of controlling the mechanical properties of PEGDA hydrogels independent of polymer chain density through the incorporation of additional vinyl group moieties that interfere with the cross-linking of the network. This modification can tune hydrogel mechanics in a concentration dependent manner from <1 to 17 kPa, a more physiologically relevant range than previously possible with PEG-based hydrogels, without altering the hydrogel’s degradation and permeability. Across this range of mechanical properties, endothelial cells (ECs) encapsulated within MMP-2/MMP-9 degradable hydrogels with RGDS adhesive peptides revealed increased cell spreading as hydrogel stiffness decreased in contrast to behavior typically observed for cells on 2D surfaces. EC-pericyte cocultures exhibited vessel-like networks within 3 days in highly compliant hydrogels as compared to a week in stiffer hydrogels. These vessel networks persisted for at least 4 weeks and deposited laminin and collagen IV perivascularly. These results indicate that EC morphogenesis can be regulated using mechanical cues in 3D. Furthermore, controlling hydrogel compliance independent of density allows for the attainment of highly compliant mechanical regimes in materials that can act as customizable cell microenvironments. PMID:26082943

  20. Corneal cross-linking in 9 horses with ulcerative keratitis

    PubMed Central

    2013-01-01

    Background Corneal ulcers are one of the most common eye problems in the horse and can cause varying degrees of visual impairment. Secondary infection and protease activity causing melting of the corneal stroma are always concerns in patients with corneal ulcers. Corneal collagen cross-linking (CXL), induced by illumination of the corneal stroma with ultraviolet light (UVA) after instillation of riboflavin (vitamin B2) eye drops, introduces crosslinks which stabilize melting corneas, and has been used to successfully treat infectious ulcerative keratitis in human patients. Therefore we decided to study if CXL can be performed in sedated, standing horses with ulcerative keratitis with or without stromal melting. Results Nine horses, aged 1 month to 16 years (median 5 years) were treated with a combination of CXL and medical therapy. Two horses were diagnosed with mycotic, 5 with bacterial and 2 with aseptic ulcerative keratitis. A modified Dresden-protocol for CXL could readily be performed in all 9 horses after sedation. Stromal melting, diagnosed in 4 horses, stopped within 24 h. Eight of nine eyes became fluorescein negative in 13.5 days (median time; range 4–26 days) days after CXL. One horse developed a bacterial conjunctivitis the day after CXL, which was successfully treated with topical antibiotics. One horse with fungal ulcerative keratitis and severe uveitis was enucleated 4 days after treatment due to panophthalmitis. Conclusions CXL can be performed in standing, sedated horses. We did not observe any deleterious effects attributed to riboflavin or UVA irradiation per se during the follow-up, neither in horses with infectious nor aseptic ulcerative keratitis. These data support that CXL can be performed in the standing horse, but further studies are required to compare CXL to conventional medical treatment in equine keratitis and to optimize the CXL protocol in this species. PMID:23803176

  1. Porous Iron Oxide Ribbons Grown on Graphene for High-Performance Lithium Storage

    PubMed Central

    Yang, Shubin; Sun, Yi; Chen, Long; Hernandez, Yenny; Feng, Xinliang; Müllen, Klaus

    2012-01-01

    A well-designed nanostructure of transition metal oxides has been regarded as a key to solve their problems of large volume changes during lithium insertion-desertion processes which are associated with pulverization of the electrodes and rapid capacity decay. Here we report an effective approach for the fabrication of porous iron oxide ribbons by controlling the nucleation and growth of iron precursor onto the graphene surface and followed by an annealing treatment. The resultant iron oxide ribbons possess large aspect ratio, porous structure, thin feature and enhanced open-edges. These characteristics are favorable for the fast diffusion of lithium ions and electrons, and meanwhile can effectively accommodate the volume change of iron oxides during the cycling processes. As a consequence, the graphene-induced porous iron oxide ribbons exhibit a high reversible capacity and excellent cycle stability for lithium storage. PMID:22645643

  2. Designed synthesis and surface engineering strategies of magnetic iron oxide nanoparticles for biomedical applications.

    PubMed

    Wu, Wei; Jiang, Chang Zhong; Roy, Vellaisamy A L

    2016-12-01

    Iron oxide nanoparticles (NPs) hold great promise for future biomedical applications because of their magnetic properties as well as other intrinsic properties such as low toxicity, colloidal stability, and surface engineering capability. Numerous related studies on iron oxide NPs have been conducted. Recent progress in nanochemistry has enabled fine control over the size, crystallinity, uniformity, and surface properties of iron oxide NPs. This review examines various synthetic approaches and surface engineering strategies for preparing naked and functional iron oxide NPs with different physicochemical properties. Growing interest in designed and surface-engineered iron oxide NPs with multifunctionalities was explored in in vitro/in vivo biomedical applications, focusing on their combined roles in bioseparation, as a biosensor, targeted-drug delivery, MR contrast agents, and magnetic fluid hyperthermia. This review outlines the limitations of extant surface engineering strategies and several developing strategies that may overcome these limitations. This study also details the promising future directions of this active research field.

  3. The concept of delayed nucleation in nanocrystal growthdemonstrated for the case of iron oxide nanodisks

    SciTech Connect

    Casula, Maria F.; Jun, Young-wook; Zaziski, David J.; Chan, EmoryM.; Corrias, Anna; Alivisatos, Paul A.

    2005-09-09

    A comprehensive study of iron oxide nanocrystal growth through non-hydrolitic, surfactant-mediated thermal reaction of iron pentacarbonyl and an oxidizer has been conducted, which includes size control, anisotropic shape evolution, and crystallographic phase transition of monodisperse iron oxide colloidal nanocrystals. The reaction was monitored by in situ UV-Vis spectroscopy taking advantage of the color change accompanying the iron oxide colloid formation allowing measurement of the induction time for nucleation. Features of the synthesis such as the size control and reproducibility are related to the occurrence of the observed delayed nucleation process. As a separate source of iron and oxygen is adopted, phase control could also be achieved by sequential injections of oxidizer.

  4. Photosensitized UVA-Induced Cross-Linking between Human DNA Repair and Replication Proteins and DNA Revealed by Proteomic Analysis

    PubMed Central

    2016-01-01

    Long wavelength ultraviolet radiation (UVA, 320–400 nm) interacts with chromophores present in human cells to induce reactive oxygen species (ROS) that damage both DNA and proteins. ROS levels are amplified, and the damaging effects of UVA are exacerbated if the cells are irradiated in the presence of UVA photosensitizers such as 6-thioguanine (6-TG), a strong UVA chromophore that is extensively incorporated into the DNA of dividing cells, or the fluoroquinolone antibiotic ciprofloxacin. Both DNA-embedded 6-TG and ciprofloxacin combine synergistically with UVA to generate high levels of ROS. Importantly, the extensive protein damage induced by these photosensitizer+UVA combinations inhibits DNA repair. DNA is maintained in intimate contact with the proteins that effect its replication, transcription, and repair, and DNA–protein cross-links (DPCs) are a recognized reaction product of ROS. Cross-linking of DNA metabolizing proteins would compromise these processes by introducing physical blocks and by depleting active proteins. We describe a sensitive and statistically rigorous method to analyze DPCs in cultured human cells. Application of this proteomics-based analysis to cells treated with 6-TG+UVA and ciprofloxacin+UVA identified proteins involved in DNA repair, replication, and gene expression among those most vulnerable to cross-linking under oxidative conditions. PMID:27654267

  5. Iron(3) oxide-based nanoparticles as catalysts in advanced organic aqueous oxidation.

    PubMed

    Zelmanov, Grigory; Semiat, Raphael

    2008-01-01

    Water contaminated with dissolved organic matter is an important issue to resolve for all-purpose uses. The catalytic behavior of iron-based nanocatalysts was investigated for the treatment of contaminated water in the advanced chemical oxidation process. In this study, typical organic contaminants, such as ethylene glycol and phenol, were chosen to simulate common contaminants. It was shown that the two substances are efficiently destroyed by the Fenton-like reaction using iron(3) oxide-based nanocatalysts in the presence of hydrogen peroxide without the need for UV or visible radiation sources at room temperature. A strong effect of nanocatalyst concentration on reaction rate was shown. The kinetic reaction was found and the reaction rate coefficient k was calculated.

  6. Iron oxidation in Mops buffer. Effect of EDTA, hydrogen peroxide and FeCl3.

    PubMed

    Tadolini, B

    1987-01-01

    The effect of EDTA and H2O2 on iron autoxidation in Mops buffer depends on the pH of the solution. At acidic pH, EDTA caused the oxidation of a stoichiometric amount of iron. At neutral and alkaline pH, EDTA and H2O2 not only oxidizes a stoichiometric amount of iron but also causes the oxidation of the Fe2+ exceeding the concentration of these compounds. In the presence of EDTA, oxidation of Fe2+ in exceeding the concentration of these compounds has a shorter lag phase and an increased rate compared with that in the absence. The solution develops a yellow colour whose intensity is proportional to the amount of Fe2+ exceeding the concentration of these compounds in solution. When the reaction is conducted in the presence of NBT, formazan formation is greatly reduced compared to the control without EDTA and H2O2. The Fe3+-EDTA complex and Fe3+ affected iron oxidation, development of the yellow colour and NBT reduction in a similar fashion. In all these experimental conditions, iron oxidation is greatly reduced in the presence of mannitol, sorbitol and catalase. In phosphate buffer, EDTA oxidized a stoichiometric amount of iron without affecting free Fe2+ oxidation. Fe3+ has no effect on iron oxidation in this buffer.

  7. J-integral fracture toughness and tearing modulus measurement of radiation cross-linked UHMWPE.

    PubMed

    Gomoll, A; Wanich, T; Bellare, A

    2002-11-01

    Radiation and chemical cross-linking of medical grade ultrahigh molecular weight polyethylene (UHMWPE) has recently been utilized in an effort to improve wear performance of total joint replacement components. However, reductions in mechanical properties with cross-linking are cause for concern regarding the use of cross-linked UHMWPE for high-stress applications such as in total knee replacement prostheses. In this study, the fracture behavior of radiation cross-linked UHMWPE was compared to that of uncross-linked UHMWPE. The Rice and Sorensen model that utilizes mechanical parameters obtained from uniaxial tensile and compact tension tests was used to calculate the steady state J-integral fracture toughness, Jss, for radiation cross-linked UHMWPE. Jss decreased monotonically with increase in radiation dose. UHMWPE exhibited tough, ductile tearing behavior with stable crack growth when it was cross-linked using a gamma radiation dose of 0-50 kGy. However, in cross-linked UHMWPE irradiated to a dose of 100 and 200 kGy, unstable fracture occurred spontaneously upon attaining the initial crack driving force, J1c. This indicates that a high degree of cross-linking is less desirable for high-stress applications in orthopaedic implants. However, a substantial increase in J1c, even at a low degree of cross-linking, suggests that a low degree of cross-linking may be beneficial for resistance to delamination and catastrophic failure, both of which require an initiation step for the fracture to propagate in the material. This mechanical test should, however, be considered along with fatigue tests and joint simulator testing before determination of an appropriate amount of cross-linking for total joint replacement prostheses that experience high stresses.

  8. Killing mechanism of stable N-halamine cross-linked polymethacrylamide nanoparticles that selectively target bacteria.

    PubMed

    Natan, Michal; Gutman, Ori; Lavi, Ronit; Margel, Shlomo; Banin, Ehud

    2015-02-24

    Increased resistance of bacteria to disinfection and antimicrobial treatment poses a serious public health threat worldwide. This has prompted the search for agents that can inhibit both bacterial growth and withstand harsh conditions (e.g., high organic loads). In the current study, N-halamine-derivatized cross-linked polymethacrylamide nanoparticles (NPs) were synthesized by copolymerization of the monomer methacrylamide (MAA) and the cross-linker monomer N,N-methylenebis(acrylamide) (MBAA) and were subsequently loaded with oxidative chlorine using sodium hypochlorite (NaOCl). The chlorinated NPs demonstrated remarkable stability and durability to organic reagents and to repetitive bacterial loading cycles as compared with the common disinfectant NaOCl (bleach), which was extremely labile under these conditions. The antibacterial mechanism of the cross-linked P(MAA-MBAA)-Cl NPs was found to involve generation of reactive oxygen species (ROS) only upon exposure to organic media. Importantly, ROS were not generated upon suspension in water, revealing that the mode of action is target-specific. Further, a unique and specific interaction of the chlorinated NPs with Staphylococcus aureus was discovered, whereby these microorganisms were all specifically targeted and marked for destruction. This bacterial encircling was achieved without using a targeting module (e.g., an antibody or a ligand) and represents a highly beneficial, natural property of the P(MAA-MBAA)-Cl nanostructures. Our findings provide insights into the mechanism of action of P(MAA-MBAA)-Cl NPs and demonstrate the superior efficacy of the NPs over bleach (i.e., stability, specificity, and targeting). This work underscores the potential of developing sustainable P(MAA-MBAA)-Cl NP-based devices for inhibiting bacterial colonization and growth.

  9. Processing, Microstructure, and Oxidation Behavior of Iron Foams

    NASA Astrophysics Data System (ADS)

    Park, Hyeji; Noh, Yoonsook; Choi, Hyelim; Hong, Kicheol; Kwon, Kyungjung; Choe, Heeman

    2016-09-01

    With its historically long popularity in major structural applications, the use of iron (Fe) has also recently begun to be explored as an advanced functional material. For this purpose, it is more advantageous to use Fe as a porous structure, simply because it can provide a greater surface area and a higher reaction rate. This study uses a freeze-casting method, which consists of simple and low-cost processing steps, to produce Fe foam with a mean pore size of 10 μm. We examine the influences of various parameters ( i.e., mold bottom temperature, powder content, and sintering time) on the processing of Fe foam, along with its oxidation kinetics at 823 K (550 °C) with various heat-treatment times. We confirm that Fe2O3 and Fe3O4 oxide layers are successfully formed on the surface of Fe foam. With the Fe oxide layers as an active anode material, the Fe foam can potentially be used as a three-dimensional anode current collector for an advanced lithium-ion battery.

  10. Solution voltammetry of 4 nm magnetite iron oxide nanoparticles.

    PubMed

    Roberts, Joseph J P; Westgard, John A; Cooper, Laura M; Murray, Royce W

    2014-07-30

    The voltammetry of solution-dispersed magnetite iron oxide Fe3O4 nanoparticles is described. Their currents are controlled by nanoparticle transport rates, as shown with potential step chronoamperometry and rotated disk voltammetry. In pH 2 citrate buffer with added NaClO4 electrolyte, solution cyclic voltammetry of these nanoparticles (average diameter 4.4 ± 0.9 nm, each containing ca. 30 Fe sites) displays an electrochemically irreversible oxidation with E(PEAK) at ca. +0.52 V and an irreversible reduction with E(PEAK) at ca. +0.2 V vs Ag/AgCl reference electrode. These processes are presumed to correspond to the formal potentials for one-electron oxidation of Fe(II) and reduction of Fe(III) at their different sites in the magnetite nanoparticle structure. The heterogeneous electrode reaction rates of the nanoparticles are very slow, in the 10(-5) cm/s range. The nanoparticles are additionally characterized by a variety of tools, e.g., TEM, UV/vis, and XPS spectroscopies.

  11. Iron oxide nanoparticles for magnetically assisted patterned coatings

    NASA Astrophysics Data System (ADS)

    Dodi, Gianina; Hritcu, Doina; Draganescu, Dan; Popa, Marcel I.

    2015-08-01

    Iron oxide nanoparticles able to magnetically assemble during the curing stage of a polymeric support to create micro-scale surface protuberances in a controlled manner were prepared and characterized. The bare Fe3O4 particles were obtained by two methods: co-precipitation from an aqueous solution containing Fe3+/Fe2+ ions with a molar ratio of 2:1 and partial oxidation of ferrous ions in alkaline conditions. The products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and magnetization measurement. They were subsequently functionalized using oleic acid, sodium oleate, or non-ionic surfactant mixtures with various hydrophilic to lipophilic balance (HLB) values. Composite nanoparticle-polymer films prepared by spraying were deposited and cured by drying on glass slides under a static magnetic field in the range of 1.5-5.5 mT. Magnetic field generated surface roughness was evidenced by optical and scanning electron microscopy. The optimum hierarchical patterning was obtained with the nanoparticles produced by partial oxidation and functionalized with hydrophobic surfactants. Possible applications may include ice-phobic composite coatings.

  12. Three methods for in situ cross-linking of polyvinyl alcohol films for application as ion-conducting membranes in potassium hydroxide electrolyte. [battery separators

    NASA Technical Reports Server (NTRS)

    Philipp, W. H.; Hsu, L. C.

    1979-01-01

    Three methods of in situ cross-linking polyvinyl alcohol films are presented. They are: (1) acetalization with a dialdehyde such as glutaraldehyde, (2) acetalization with aldehyde groups formed by selective oxidative cleaving of the few percent of 1,2 diol units present in polyvinyl alcohol, and (3) cross-linking by hydrogen abstraction by reaction with hydrogen atoms and hydroxyl radicals from irradiated water. For the third method, improvement in film conductivity in KOH solution at the expense of mechanical strength is obtained by the presence of polyacrylic acid in the polyvinyl alcohol films. Resistivities in 45 percent KOH are given for in situ cross-linked films prepared by each of the three methods.

  13. Identification of a membrane cytochrome c from neutrophilic, iron-oxidizing Mariprofundus ferrooxydans, strain PV-1

    NASA Astrophysics Data System (ADS)

    Barco, R. A.; Zhong, J.; Ramirez, G. A.; Reese, B. K.; Edwards, K. J.

    2012-12-01

    Neutrophilic-iron oxidizing bacteria (FeOB) are a group of bacteria that can oxidize iron at -or near neutral pH, making them relevant in habitats with naturally high levels of reduced iron (i.e. Fe2+) such as hydrothermal vents. In the ocean, microorganisms in the Mariprofundus genus (zeta- Proteobacteria) are the only known organisms to chemolithoautotrophically oxidize iron. In order to identify the active bacterial oxidation of iron in the environment (i.e. in the deep biosphere), biomarkers for this functionality are needed. The aim of this study is to confirm the expression of potential functional biomarkers that are diagnostic of neutrophilic bacterial iron-oxidation. To this end, Mariprofundus ferrooxydans, strain PV-1 was cultivated in large batches and its proteins extracted via a methodology to circumvent protein binding to filamentous material. Proteins were assayed for redox-activity and for iron-oxidation activity. The bands of the gel that showed activity were analyzed via LC-MS/MS for identification of peptides and subsequently protein-matched to the M. ferrooxydans proteome database. The results indicate that a membrane cytochrome c with homology to the iron-oxidizing Cyt572 from Leptospirillum Group II is expressed in M. ferrooxydans when it is active. Other proteins associated with the electron transport chain of M. ferroxydans such as cbb3-type cytochrome oxidase subunits were identified and validated separately through reverse transcription followed by PCR amplification.

  14. Iron and carbon metabolism by a mineral-oxidizing Alicyclobacillus-like bacterium.

    PubMed

    Yahya, Adibah; Hallberg, Kevin B; Johnson, D Barrie

    2008-04-01

    A novel iron-oxidizing, moderately thermophilic, acidophilic bacterium (strain "GSM") was isolated from mineral spoil taken from a gold mine in Montana. Biomolecular analysis showed that it was most closely related to Alicyclobacillus tolerans, although the two bacteria differed in some key respects, including the absence (in strain GSM) of varpi-alicyclic fatty acids and in their chromosomal base compositions. Isolate GSM was able to grow in oxygen-free media using ferric iron as terminal electron acceptor confirming that it was a facultative anaerobe, a trait not previously described in Alicyclobacillus spp.. The acidophile used both organic and inorganic sources of energy and carbon, although growth and iron oxidation by isolate GSM was uncoupled in media that contained both fructose and ferrous iron. Fructose utilization suppressed iron oxidation, and oxidation of ferrous iron occurred only when fructose was depleted. In contrast, fructose catabolism was suppressed when bacteria were harvested while actively oxidizing iron, suggesting that both ferrous iron- and fructose-oxidation are inducible in this acidophile. Isolate GSM accelerated the oxidative dissolution of pyrite in liquid media either free of, or amended with, organic carbon, although redox potentials were significantly different in these media. The potential of this isolate for commercial mineral processing is discussed.

  15. Physical properties of new iron arsenide oxide with thick perovskite-type oxide layer

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Naoto; Ogino, Hiraku; Kishio, Koji; Shimoyama, Junichi

    2010-03-01

    Since the discovery of high-Tc superconductivity in LaFeAsO, a large number of layered compounds having anti-fluorite type Fe- or Ni-pnictide layer have been discovered. Among them, a series of pnictide oxides having perovskite-type oxide layersfootnotetextH. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008 are attractive because of their chemical flexibility particularly at the perovskite-type oxide layer, which may results in new compounds. In the present study, various physical properties have been investigated for the new iron pnictide oxides with thick perovskite-type blocking layers, i.e., large interlayer distance between Fe-layers more than 1.7 nm. These samples showed metallic and paramagnetic behaviors in resistivity and magnetization measurements, respectively, down to 2 K without any signs of superconductivity and other anomalies. Relationship among crystal structure, constituent elements and physical properties will be discussed for the newly discovered system.

  16. Efficient Low-pH Iron Removal by a Microbial Iron Oxide Mound Ecosystem at Scalp Level Run.

    PubMed

    Grettenberger, Christen L; Pearce, Alexandra R; Bibby, Kyle J; Jones, Daniel S; Burgos, William D; Macalady, Jennifer L

    2017-04-01

    Acid mine drainage (AMD) is a major environmental problem affecting tens of thousands of kilometers of waterways worldwide. Passive bioremediation of AMD relies on microbial communities to oxidize and remove iron from the system; however, iron oxidation rates in AMD environments are highly variable among sites. At Scalp Level Run (Cambria County, PA), first-order iron oxidation rates are 10 times greater than at other coal-associated iron mounds in the Appalachians. We examined the bacterial community at Scalp Level Run to determine whether a unique community is responsible for the rapid iron oxidation rate. Despite strong geochemical gradients, including a >10-fold change in the concentration of ferrous iron from 57.3 mg/liter at the emergence to 2.5 mg/liter at the base of the coal tailings pile, the bacterial community composition was nearly constant with distance from the spring outflow. Scalp Level Run contains many of the same taxa present in other AMD sites, but the community is dominated by two strains of Ferrovum myxofaciens, a species that is associated with high rates of Fe(II) oxidation in laboratory studies.IMPORTANCE Acid mine drainage pollutes more than 19,300 km of rivers and streams and 72,000 ha of lakes worldwide. Remediation is frequently ineffective and costly, upwards of $100 billion globally and nearly $5 billion in Pennsylvania alone. Microbial Fe(II) oxidation is more efficient than abiotic Fe(II) oxidation at low pH (P. C. Singer and W. Stumm, Science 167:1121-1123, 1970, https://doi.org/10.1126/science.167.3921.1121). Therefore, AMD bioremediation could harness microbial Fe(II) oxidation to fuel more-cost-effective treatments. Advances will require a deeper understanding of the ecology of Fe(II)-oxidizing microbial communities and the factors that control their distribution and rates of Fe(II) oxidation. We investigated bacterial communities that inhabit an AMD site with rapid Fe(II) oxidation and found that they were dominated by two

  17. Genotoxicity of Superparamagnetic Iron Oxide Nanoparticles in Granulosa Cells

    PubMed Central

    Pöttler, Marina; Staicu, Andreas; Zaloga, Jan; Unterweger, Harald; Weigel, Bianca; Schreiber, Eveline; Hofmann, Simone; Wiest, Irmi; Jeschke, Udo; Alexiou, Christoph; Janko, Christina

    2015-01-01

    Nanoparticles that are aimed at targeting cancer cells, but sparing healthy tissue provide an attractive platform of implementation for hyperthermia or as carriers of chemotherapeutics. According to the literature, diverse effects of nanoparticles relating to mammalian reproductive tissue are described. To address the impact of nanoparticles on cyto- and genotoxicity concerning the reproductive system, we examined the effect of superparamagnetic iron oxide nanoparticles (SPIONs) on granulosa cells, which are very important for ovarian function and female fertility. Human granulosa cells (HLG-5) were treated with SPIONs, either coated with lauric acid (SEONLA) only, or additionally with a protein corona of bovine serum albumin (BSA; SEONLA-BSA), or with dextran (SEONDEX). Both micronuclei testing and the detection of γH2A.X revealed no genotoxic effects of SEONLA-BSA, SEONDEX or SEONLA. Thus, it was demonstrated that different coatings of SPIONs improve biocompatibility, especially in terms of genotoxicity towards cells of the reproductive system. PMID:26540051

  18. Magnetic iron oxide nanoclusters with tunable optical response

    NASA Astrophysics Data System (ADS)

    Kostopoulou, Athanasia; Tsiaoussis, Ioannis; Lappas, Alexandros

    2011-04-01

    We have developed a modified synthetic protocol for the growth of monodispersed, superparamagnetic, flower-like colloidal nanoclusters (CNCs), which are consisted of smaller iron oxide nanocrystals with adjustable size. We show that their optical properties can be tuned by applying an external magnetic field. The latter controls the subtle balance of the CNCs’ mutual interactions (magnetic versus electrostatic) and drives their assembly in aqueous media. Spectrophotometric measurements reveal that a diffuse reflectance maximum, in the visible range, is related to the CNCs organization. As the strength of the external magnetic field increases, in the range 160-600 G, the spectral weight of this feature shifts towards the blue region of the spectrum. The induced photonic crystal-like response entails a remarkable magneto-optical behavior, closely associated with the size-dependent characteristics of the CNCs ensemble. Such materials pave the way for promising technological implementations in photonics.

  19. Magneto-optical Properties of Iron Oxide Nanoclusters

    NASA Astrophysics Data System (ADS)

    Kostopoulou, Athanasia; Tsiaoussis, Ioannis; Lappas, Alexandros

    2010-11-01

    We have developed a modified synthetic protocol for the growth of monodispersed, superparamagnetic, flower-like colloidal nanoclusters (CNCs) with 40-120 nm average diameters. Importantly, these are consisted of smaller iron oxide nanocrystals, also with adjustable size (12.2-7.7 nm). We show that their optical properties can be tuned by applying an external magnetic field. Spectrophotometric measurements under these conditions reveal a diffuse reflectance maximum in the visible range, which is related to the CNCs assembly in ordered structures. The increasing field strength leads to a blue shift in the spectral weight when the size of the CNCs is above a critical diameter. The size-dependent characteristics of the CNCs determine their magneto-optical behavior and their potential in photonic crystal based technologies.

  20. System for recycling char in iron oxide reducing kilns

    SciTech Connect

    Baker, A.C.; Keran, V.P.

    1983-03-08

    A method and means for improving the efficiency of the process for directly reducing ore containing iron oxide in a rotary kiln using a solid carbonaceous reducing agent, such as coal, introduced from the ore feed and discharge ends of the kiln, as both fuel and reductant, is disclosed wherein the charred coal or char found in the discharge product is recycled into the process at the discharge end of the kiln rather than the feed end as in the prior art. In particular, the recovered char, both coarse and finer particles, are transported to a recycle bin from which they are returned at a preselected rate to the kiln process by being injected along with the coal blown into the discharge end of the kiln. Alternatively, the recycle char alone may be fed without any coal at the discharge end of the kiln.

  1. Colloidal stability of iron oxide nanoparticles with multivalent polymer surfactants.

    PubMed

    Choi, Young-Wook; Lee, Hoik; Song, Youngjun; Sohn, Daewon

    2015-04-01

    This paper introduces a new approach for preparing magnetic colloidal suspensions with electrostatic repulsion between particles and polyelectrolyte surfactants. The surface charge of the iron oxide particles was positive in acidic aqueous conditions; however the surface charge of the colloid was negative in basic aqueous conditions due to the amphoteric property of Fe2O3. The long-term colloidal stability and particle distribution of the multivalent charged polymers, Poly(4-vinylbenzenesulfonate sodium salt) (PSS), Poly(acrylic acid) (PAA), and Poly(allylamine hydrochloride) (PAH) were compared with the monovalent surfactant sodium dodecyl sulfate (SDS). Both mono- and multivalent surfactant molecules showed good colloidal stability for extended periods of time. However, the particle distribution was dependent on the hydrophobicity of the surfactants' functional groups. Polyelectrolytes with a negatively charged functional group showed good long-term stability of particles and a narrow particle distribution regardless of the acid dissociation constant (pKa) of the polymer.

  2. Transformation of iron oxides on PI electrospun membranes

    NASA Astrophysics Data System (ADS)

    Li, Penggang; Lv, Fengzhu; Liu, Leipeng; Ding, Ling; Zhang, Yihe

    2016-09-01

    Iron oxides/PI fiber membranes, especially magnetic PI membranes, are important flexible porous materials available application in the field of wave absorption, magnetic recording, membrane separation and catalysts. Therefore, α-Fe2O3 loaded PI composite fibers were prepared by electrospinning of poly(amic acid) PAA solution followed by loading Fe3+ on the PAA membrane by ion-exchange and then imidization. Then the α-Fe2O3 on PI membrane were reduced by H2 to give magnetic PI membranes. The content of α-Fe2O3 and Fe3O4 on PI can be controlled by adjustment the ion-exchange time. The saturation magnetization of the composite membranes can reach up to 4 emu/g and the final composite membranes have magnetic response ability.

  3. Superparamagnetic iron oxide nanoparticles (SPIONs) for targeted drug delivery

    NASA Astrophysics Data System (ADS)

    Garg, Vijayendra K.; Kuzmann, Erno; Sharma, Virender K.; Kumar, Arun; Oliveira, Aderbal C.

    2016-10-01

    Studies of superparamagnetic iron oxide nanoparticles (SPIONs) have been extensively carried out. Since the earlier work on Mössbauer studies on SPIONs in 1970s, many biomedical applications and their uses in innovative methods to produce new materials with improved performance have appeared. Applications of SPIONs in environmental remediation are also forthcoming. Several different methods of synthesis and coating of the magnetic particles have been described in the literature, and Mössbauer spectroscopy has been an important tool in the characterization of these materials. It is quite possible that the interpretation of the Mössbauer spectra might not be entirely correct because the possible presence of maghemite in the end product of SPIONs might not have been taken into consideration. Nanotechnology is an emerging field that covers a wide range of new technologies under development in nanoscale (1 to 100 nano meters) to produce new products and methodology.

  4. Iron (Oxyhydr)Oxide Biosignatures in the Brushy Basin Member of the Jurassic Morrison Formation, Colorado Plateau, USA: Analog for Martian Diagenetic Iron

    NASA Astrophysics Data System (ADS)

    Potter-McIntyre, S. L.; Chan, M. A.; McPherson, B. J.

    2012-03-01

    Iron precipitates in modern microbial mats compared with iron cements in Jurassic alkaline saline lake sediments show that morphological and chemical biosignatures are present and preserved in oxidized, evaporative environments analogous to Mars.

  5. Pilot scale application of nanosized iron oxides as electron acceptors for bioremediation

    NASA Astrophysics Data System (ADS)

    Bosch, Julian; Fritzsche, Andreas; Frank-Fahle, Beatrice; Lüders, Tilmann; Höss, Sebastian; Eisenmann, Heinrich; Held, Thomas; Totsche, Kai U.; Meckenstock, Rainer U.

    2014-05-01

    Microbial reduction of ferric iron is a major biogeochemical process in groundwater aquifer ecosystems and often associated with the degradation of organic contaminants, as bacteria couple iron reduction to the oxidation reduced carbon like e.g. BTEX. Yet in general the low bioavailability of natural iron oxides limits microbial reduction rates. However, nanosized iron oxides have an unequally enhanced bioavailability and reactivity compared to their respective bulk, macro-sized, and more crystalline materials. At the same time, nanosized iron oxides can be produced in stable colloidal suspensions, permitting efficient injections into contaminated aquifers. We examined the reactivity of nanosized synthetic colloidal iron oxides in microbial iron reduction. Application of colloidal nanoparticles led to a strong and sustainable enhancement of microbial reaction rates in batch experiments and sediment columns. Toluene oxidation was increased five-fold as compared to bulk, non-colloidal ferrihydrite as electron acceptor. Furthermore, we developed a unique approach for custom-tailoring the subsurface mobility of these particles after being injected into a contaminant plume. In a field pilot application, we injected 18 m3 of an iron oxide nanoparticle solution into a BTEX contaminated aquifer with a maximum excess pressure as low as 0.2 bar. The applied suspension showed a superior subsurface mobility, creating a reactive zone of 4 m height (corresponding to the height of the confined aquifer) and 6 m in diameter. Subsequent monitoring of BTEX, microbial BTEX degradation metabolites, ferrous iron generation, stable isotopes fractionation, microbial populations, and methanogenesis demonstrated the strong impact of our approach. Mathematic processed X-ray diffractograms and FTIR spectra provided a semi-quantitatively estimate of the long-term fate of the iron oxide colloids in the aquifer. Potential environmental risks of the injection itself were monitored with

  6. Mutagenic Effects of Iron Oxide Nanoparticles on Biological Cells.

    PubMed

    Dissanayake, Niluka M; Current, Kelley M; Obare, Sherine O

    2015-09-30

    In recent years, there has been an increased interest in the design and use of iron oxide materials with nanoscale dimensions for magnetic, catalytic, biomedical, and electronic applications. The increased manufacture and use of iron oxide nanoparticles (IONPs) in consumer products as well as industrial processes is expected to lead to the unintentional release of IONPs into the environment. The impact of IONPs on the environment and on biological species is not well understood but remains a concern due to the increased chemical reactivity of nanoparticles relative to their bulk counterparts. This review article describes the impact of IONPs on cellular genetic components. The mutagenic impact of IONPs may damage an organism's ability to develop or reproduce. To date, there has been experimental evidence of IONPs having mutagenic interactions on human cell lines including lymphoblastoids, fibroblasts, microvascular endothelial cells, bone marrow cells, lung epithelial cells, alveolar type II like epithelial cells, bronchial fibroblasts, skin epithelial cells, hepatocytes, cerebral endothelial cells, fibrosarcoma cells, breast carcinoma cells, lung carcinoma cells, and cervix carcinoma cells. Other cell lines including the Chinese hamster ovary cells, mouse fibroblast cells, murine fibroblast cells, Mytilus galloprovincialis sperm cells, mice lung cells, murine alveolar macrophages, mice hepatic and renal tissue cells, and vero cells have also shown mutagenic effects upon exposure to IONPs. We further show the influence of IONPs on microorganisms in the presence and absence of dissolved organic carbon. The results shed light on the OPEN ACCESS Int. J. Mol. Sci. 2015, 16 23483 transformations IONPs undergo in the environment and the nature of the potential mutagenic impact on biological cells.

  7. Mutagenic Effects of Iron Oxide Nanoparticles on Biological Cells

    PubMed Central

    Dissanayake, Niluka M.; Current, Kelley M.; Obare, Sherine O.

    2015-01-01

    In recent years, there has been an increased interest in the design and use of iron oxide materials with nanoscale dimensions for magnetic, catalytic, biomedical, and electronic applications. The increased manufacture and use of iron oxide nanoparticles (IONPs) in consumer products as well as industrial processes is expected to lead to the unintentional release of IONPs into the environment. The impact of IONPs on the environment and on biological species is not well understood but remains a concern due to the increased chemical reactivity of nanoparticles relative to their bulk counterparts. This review article describes the impact of IONPs on cellular genetic components. The mutagenic impact of IONPs may damage an organism’s ability to develop or reproduce. To date, there has been experimental evidence of IONPs having mutagenic interactions on human cell lines including lymphoblastoids, fibroblasts, microvascular endothelial cells, bone marrow cells, lung epithelial cells, alveolar type II like epithelial cells, bronchial fibroblasts, skin epithelial cells, hepatocytes, cerebral endothelial cells, fibrosarcoma cells, breast carcinoma cells, lung carcinoma cells, and cervix carcinoma cells. Other cell lines including the Chinese hamster ovary cells, mouse fibroblast cells, murine fibroblast cells, Mytilus galloprovincialis sperm cells, mice lung cells, murine alveolar macrophages, mice hepatic and renal tissue cells, and vero cells have also shown mutagenic effects upon exposure to IONPs. We further show the influence of IONPs on microorganisms in the presence and absence of dissolved organic carbon. The results shed light on the transformations IONPs undergo in the environment and the nature of the potential mutagenic impact on biological cells. PMID:26437397

  8. The role of antioxidants and iron chelators in the treatment of oxidative