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Chemical Stability (chemical + stability)
Selected AbstractsChemical Stability of an Admixture Combining Ziconotide and Bupivacaine During Simulated Intrathecal AdministrationNEUROMODULATION, Issue 2007David Shields PhD ABSTRACT Objective., To determine the stability of an admixture combining ziconotide with bupivacaine hydrochloride during simulated intrathecal infusion under laboratory conditions at 37°. Materials and Methods., An admixture containing ziconotide (25 µg/mL) and bupivacaine hydrochloride (5 mg/mL) was stored in SynchroMed® II pumps at 37° and in control vials at either 37° or 5°. Using high-performance liquid chromatography, drug concentrations were determined from samples obtained at varying intervals during the 30-day study. Results., After 30 days, pump ziconotide and bupivacaine hydrochloride concentrations measured an average of 86.9% and 99.4% of their initial concentrations, respectively. Control vials displayed similar degradation rates for both drugs. Statistical evaluation of the ziconotide 95% confidence interval indicated that the ziconotide concentration would meet or exceed 90% and 80% of initial concentration for 22 days and 45 days, respectively. Conclusions., An admixture containing 25 µg/mL ziconotide and 5 mg/mL bupivacaine hydrochloride was 90% stable for 22 days and 80% stable for 45 days (extrapolated) in SynchroMed® II infusion pumps. [source] Chemical Stability of Ziconotide-Clonidine Hydrochloride Admixtures With and Without Morphine Sulfate During Simulated Intrathecal AdministrationNEUROMODULATION, Issue 2007David Shields PhD ABSTRACT Objective., To determine the stability of ziconotide,clonidine hydrochloride admixtures with and without morphine sulfate during simulated intrathecal infusion under laboratory conditions at 37°. Materials and Methods., Admixtures of ziconotide (25 µg/mL) and clonidine hydrochloride (2 mg/mL) with and without morphine sulfate (35 mg/mL) were stored in Medtronic SynchroMed® II pumps at 37°. Pumps were sampled immediately after filling and at four additional time points over the course of 28 (ziconotide,clonidine hydrochloride admixture) or 20 (ziconotide,clonidine hydrochloride,morphine sulfate admixture) days. Drug concentrations were determined using high-performance liquid chromatography. Results., Ziconotide concentration exceeded 97% of initial at all time points when combined with clonidine alone; statistical evaluation indicated that both ziconotide and clonidine concentrations would remain above 90% of initial for more than 60 days. When compounded with both clonidine and morphine, ziconotide and clonidine concentrations declined; statistical evaluation indicated that the ziconotide concentration was 70% of initial after 20 days, and that clonidine would remain 90% stable for 42 days. Morphine was stable in the presence of ziconotide and clonidine. Conclusions., A ziconotide-clonidine admixture was 90% stable for 60 days (extrapolated), and a ziconotide-clonidine-morphine admixture was 70% stable for 20 days. [source] Long-Term Structural and Chemical Stability of DNA in Hydrated Ionic Liquids,ANGEWANDTE CHEMIE, Issue 9 2010Ranganathan Vijayaraghavan Dr. Sicher aufbewahrt: Es wurde gezeigt, dass DNA in einer Vielzahl Cholin-basierter hydratisierter ionischer Flüssigkeiten (ILs) löslich ist (siehe Bild). Die gelöste DNA ist außergewöhnlich langzeitstabil und liegt auch nach über einem Jahr unverändert vor. [source] Oxide Ion Conductivity and Chemical Stability of Lanthanum Fluorides Doped with Oxygen, La(Sr,Na)F3-2xOx.CHEMINFORM, Issue 51 2004Masaki Ando Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Doubly Strapped meso,meso -Linked Porphyrin Arrays and Triply Linked Conjugated Porphyrin TapesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Toshiaki Ikeda Abstract 1,10-Dioxydecamethylene doubly strapped ZnII -porphyrin S1 was prepared and treated with AgPF6 to give meso,meso -linked porphyrin oligomers Sn (n = 2, 3, 4, 6, 8, and 12), which were converted to triply linked porphyrin tapes TSn by meso,meso, -dibromo meso,meso -linked porphyrin arrays BSn and meso,meso, -diphenyl meso,meso -linked porphyrin arrays PSn. The structures of S1 and S2 have been determined by single-crystal X-ray diffraction analysis. Characteristically, Sn exhibit sharp Q(0,0) absorption and fluorescence bands. Low energy Q-band-like absorption bands of TSn are progressively red-shifted with an increase in the number of porphyrins without saturation behavior of conjugation. The double straps suppress ,,, stacking to some extent as seen from partial preservation of vibration structures in the Q-band-like bands of TS4 and TS6 and improve the chemical stabilities of longer tapes such as TS8 and TS12. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The Properties of Covalently Immobilized Trypsin on Soap-Free P(MMA-EA-AA) Latex ParticlesMACROMOLECULAR BIOSCIENCE, Issue 4 2005Kai Kang Abstract Summary: The covalent immobilization of trypsin onto poly[(methyl methacrylate)- co -(ethyl acrylate)- co -(acrylic acid)] latex particles, produced by a soap-free emulsion polymerization technique, was carried out using the carbodiimide method. The catalytic properties and kinetic parameters, as well as the stability of the immobilized enzyme were compared to those of the free enzyme. Results showed that the optimum temperature and pH for the immobilized trypsin in the hydrolysis of casein were 55,°C and 8.5, both of which were higher than that of the free form. It was found that Km (Michaelis constant) was 45.7 mg,·,ml,1 and Vmax (maximal reaction rate) was 793.0 ,g,·,min,1 for immobilized trypsin, compared to a Km of 30.0 mg,·,ml,1 and a Vmax of 5,467.5 ,g,·,min,1 for free trypsin. The immobilized trypsin exhibited much better thermal and chemical stabilities than its free counterpart and maintained over 63% of its initial activity after reusing ten times. TEM photograph of latex particles after trypsin immobilization. [source] Camouflaged Carborarods Derived from B -Permethyl-1,12-diethynyl- para - and B -Octamethyl-1,7-diethylnyl- meta -carborane ModulesCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2005Axel Herzog Dr. Abstract Rigid camouflaged carborarods constructed from the corresponding C,C,-diethynyl derivatives of B -decamethyl-1,12-dicarbadodecaborane(12) (6) and B -octamethyl-1,7-dicarbadodecaborane(12) (48) have been synthesized by largely conventional organic transformations. These carborarods are the longest discrete rod species available by this method in which B-methylated p -carborane and m- carborane cages are linked through their carbon vertices by using butadiynylene moieties. They exhibit enhanced solubility in common organic solvents relative to all other presently known carborane-based rigid-rod molecules. The oxidative coupling of bis(ethynyl) derivatives of 6 generates oligomers containing, on average, 16 carborane modules. The structural characterization of the corresponding dimeric species revealed that the carborarods possess a sinusoidal chain distortion in the solid state. The stereoelectronic properties of these and related model carborarods were evaluated by using molecular dimensions as a monitor for the comparison of computational and experimental methods. In addition, the effect of exhaustive B-methylation of 12- and 10-vertex para -carborane cages in a series of model C,C,-diethynyl derivatives was similarly investigated by computational and structural studies. As expected, a correlation of intercage CC bond lengths with cage size was observed and was attributed to hybridization effects. B-Permethylation had no significant structural effect with either 10- or 12-vertex cage derivatives. Relative to unsubstituted compounds, thermal and chemical stabilities of B-permethylated derivatives were increased through the operation of a steric "bumper-car" process, and solubilities in organic solvents were enhanced. The formation of linear, sterically encumbered platina,carborarods using ethynyl derivatives of 6 as precursors is described. [source] Thinnest Two-Dimensional Nanomaterial,Graphene for Solar EnergyCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 7 2010Yun Hang Hu Prof. Abstract Graphene is a rapidly rising star in materials science. This two-dimensional material exhibits unique properties, such as low resistance, excellent optical transmittance, and high mechanical and chemical stabilities. These exceptional advantages possess great promise for its potential applications in photovoltaic devices. In this Review, we present the status of graphene research for solar energy with emphasis on solar cells. Firstly, the preparation and properties of graphene are described. Secondly, applications of graphene as transparent conductive electrodes and counter electrodes are presented. Thirdly, graphene-based electron- (or hole) accepting materials for solar energy conversion are evaluated. Fourthly, the promoting effect of graphene on photovoltaic devices and the photocatalytic property of graphene,semiconductor composites are discussed. Finally, the challenges to increase the power conversion efficiency of graphene-based solar cells are explored. [source] Oxidative stability of Echium plantagineum seed oil bodiesEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7 2010David A. Gray Abstract Echium plantagineum seed contains a highly polyunsaturated oil (approximately 14% linoleic acid, 10% ,-linolenic acid, 33% ,-linolenic acid and 14% stearidonic acid); almost half of the fatty acids are omega-3 fatty acids, so there is an interest in the possible health benefits of this oil, which, once extracted, is prone to oxidation. For the first time in reported literature, oil bodies (OBs), the organelles that store the oil in mature seed, were recovered from E. plantagineum seeds. The oxidative stability of these organelles ex vivo, dispersed in an aqueous continuous phase, was tested against processed E. plantagineum oil emulsions stabilised with either SDS or Tween 20. For both primary and secondary oxidation products the OBs were the most stable form of dispersed oil, and the dispersed systems were all more stable than bulk E. plantagineum oil after incubating at 40°C for 7 days. The possible reasons for the enhanced chemical stability of E. plantagineum OBs are explored in this paper. Practical applications: OBs, the natural store of oil in oilseeds, can be recovered from seeds intact and are relatively stable to oxidation ex vivo. Echium seed OBs, enriched in physiologically active omega-3 fatty acids, therefore offer an attractive alternative to traditional oil extraction methods and overcome the need to encapsulate the omega-3 rich oil. [source] Apatite Deposition on NaOH-Treated PEEK and UHMWPE Films for Sclera Materials in Artificial Cornea Implants,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Monica Pino Abstract Cornea implants consist of a clear optic portion with a surrounding ring known as the skirt, which needs to integrate with the sclera. However, currently used skirt materials lead to poor tissue integration. Improvements in this respect may be achieved by using a bioactive skirt material that adapts to the metabolic activity of the cornea. Polyether etherketone (PEEK) and ultra-high molecular weight polyethylene (UHMWPE) might provide interesting alternatives, if they can be rendered bioactive. We, therefore, investigated the potential of surface-modifying PEEK and UHMWPE films through the use of a two-step treatment. This process involved a suitable chemical surface modification (via immersion in NaOH), with subsequent formation of apatite layers on the polymers' surfaces through exposure to supersaturated simulated body fluid (1.5 SBF). In the present work the effect of 5 and 10,M NaOH on formation of the apatite layer has been investigated with regard to wettability and topography features. In addition, the chemical stability of the apatite layer formed has been analyzed. Our data demonstrate that with an increase in NaOH concentration the wettability of the polymer increased, whilst some changes to the polymer film topography (increase/decrease in roughness) were observed. Most beneficially, the apatite layer that subsequently was grown on pre-treated PEEK and UHMWPE films through immersion in 1.5 SBF contained phosphate and carbonate ions, in similar ratios to those found in the apatite in dentine, thus, promising good in vivo bioactivity of these polymer films,a necessity if they are to be integrated into artificial cornea. [source] Green tea extract reduces induction of p53 and apoptosis in UVB-irradiated human skin independent of transcriptional controlsEXPERIMENTAL DERMATOLOGY, Issue 1 2009Christian D. Mnich Abstract:, Ultraviolet (UV) irradiation plays a pivotal role in human skin carcinongenesis. Preclinically, systemically and topically applied green tea extract (GTE) has shown reduction of UV-induced (i) erythema, (ii) DNA damage, (iii) formation of radical oxygen species and (iv) downregulation of numerous factors related to apoptosis, inflammation, differentiation and carcinogenesis. In humans, topical GTE has so far only been tested in limited studies, with usually very high GTE concentrations and over short periods of time. Both chemical stability of GTE and staining properties of highly concentrated green tea polyphenols limit the usability of highly concentrated green tea extracts in cosmetic products. The present study tested the utility of stabilized low-dose GTE as photochemopreventive agents under everyday conditions. We irradiated with up to 100 mJ/cm2 of UVB light skin patches which were pretreated with either OM24® -containing lotion or a placebo lotion. Biopsies were taken from both irradiated and un-irradiated skin for both immunohistochemistry and DNA microarray analysis. We found that while OM24® treatment did not significantly affect UV-induced erythema and thymidine dimer formation, OM24® treatment significantly reduced UV-induced p53 expression in keratinocytes. We also found that OM24® treatment significantly reduced the number of apoptotic keratinocytes (sunburn cells and TUNEL-positive cells). Carefully controlled DNA microarray analyses showed that OM24® treatment does not induce off-target changes in gene expression, reducing the likelihood of unwanted side-effects. Topical GTE (OM24®) reduces UVB-mediated epithelial damage already at low, cosmetically usable concentrations, without tachyphylaxis over 5 weeks, suggesting GTE as suitable everyday photochemopreventive agents. [source] Squaraine-Doped Functional Nanoprobes: Lipophilically Protected Near-Infrared Fluorescence for BioimagingADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Yong-Deok Lee Abstract Hydrophobically stabilized near-IR fluorescence from self-assembled nanoprobes composed of amphiphilic poly(maleic anhydride- alt -octadec-1-ene) (PMAO) and lipophilized squaraine dopants is reported. From comparative studies with varying lipophilicity of squaraine dyes as well as of nanoparticulate polymer matrices, it is found that dual protection by simultaneous lipophilization of the dye-polymer pair greatly improves the chemical stability of labile squaraine dyes, to produce efficient NIR fluorescence in physiological aqueous milieux. The surface properties of negatively charged PMAO nanoparticles are readily modified by coating with an amine-rich cationic glycol chitosan with biofunctionality. Efficient cellular imaging and in vivo sentinel lymph node mapping with size and surface-controlled nanoprobes demonstrate that lipophilic dual protection of NIR fluorescence and the underlying functional nanoprobe approach hold great potential for bioimaging applications. [source] High thermal and chemical stability of Thermus thermophilus seven-iron ferredoxinFEBS JOURNAL, Issue 23 2003Linear clusters form at high pH on polypeptide unfolding To probe the stability of the seven-iron ferredoxin from Thermus thermophilus (FdTt), we investigated its chemical and thermal denaturation processes in solution. As predicted from the crystal structure, FdTt is extremely resistant to perturbation. The guanidine hydrochloride-induced unfolding transition shows a midpoint at 6.5 m (pH 7, 20 °C), and the thermal midpoint is above boiling, at 114 °C. The stability of FdTt is much lower at acidic pH, suggesting that electrostatic interactions are important for the high stability at higher pH. On FdTt unfolding at alkaline pH, new absorption bands at 520 nm and 610 nm appear transiently, resulting from rearrangement of the cubic clusters into linear three-iron species. A range of iron,sulfur proteins has been found to accommodate these novel clusters in vitro, although no biological function has yet been assigned. [source] Surface-Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal NanocatalystsADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Qiao Zhang Abstract Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk,shell and core,satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability of the metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework. [source] Nanolithography: Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-Objects (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Mater. On page 3696, Wang et al. report on the nanoscale chemical surface patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns by the iterative application of thermochemical nanolithography. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for the selective attachment of nanometer-sized objects, such as proteins or DNA, using standard chemical protocols. [source] Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-ObjectsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Debin Wang Abstract Nanoscale chemical patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns is achieved by the iterative application of thermochemical nanolithography (TCNL) to inscribe amine patterns followed by their chemical conversion to other functional groups. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for covalent and molecular-recognition-based attachment of nano-objects using standard chemical protocols. In particular, the ability of this method to attach proteins and DNA to the chemical nanopatterns and to create co-patterns of two distinctive bioactive proteins is demonstrated. [source] Barium Non-Stoichiometry Role on the Properties of Ba1+xCe0.65Zr0.20Y0.15O3,, Proton Conductors for IT-SOFCsFUEL CELLS, Issue 5 2008S. Barison Abstract Proton conducting perovskite oxides have been widely investigated because of their potential as electrolytes for intermediate temperature solid oxide fuel cells. Among them, BaCeO3 - based materials exhibit good proton conductivity under a humidified hydrogen-containing atmosphere, but rather poor chemical stability in CO2 atmosphere. The substitution with Zr for Ce improves the chemical stability but reduces proton conductivity due to difficulties in fabricating dense materials. In the present work, single phase nanostructured powders of Ba1+xCe0.65Zr0.20Y0.15O3,, (x,=,0, 0.05, 0.10) solid solutions have been prepared by a modified sol,gel Pechini method with the final aim of evaluating the role of barium on their chemical and electrical properties. A significant influence of barium excess on the preparation and on properties of these materials has been demonstrated. In fact, density measurements evidenced that a 5 or 10,mol% nominal barium excess sensibly favoured the sintering process. Impedance analyses of sintered pellets confirmed the necessity of barium excess in order to avoid the lowering of proton conductivity, which has been evidenced for samples having stoichiometric barium content. Moreover, an unforeseen increase in chemical stability in CO2 -containing atmosphere with the growth of the barium excess was detected by thermogravimetric analyses. [source] Radiation Grafted Membranes for Polymer Electrolyte Fuel Cells,FUEL CELLS, Issue 3 2005L. Gubler Abstract The cost of polymer electrolyte fuel cell (PEFC) components is crucial to the commercial viability of the technology. Proton exchange membranes fabricated via the method of radiation grafting offer a cost-competitive option, because starting materials are inexpensive commodity products and the preparation procedure is based on established industrial processes. Radiation grafted membranes have been used with commercial success in membrane separation technology. This review focuses on the application of radiation grafted membranes in fuel cells, in particular the identification of fuel cell relevant membrane properties, aspects of membrane electrode assembly (MEA) fabrication, electrochemical performance and durability obtained in cell or stack tests, and investigation of failure modes and post mortem analysis. The application in hydrogen and methanol fuelled cells is treated separately. Optimized styrene,/,crosslinker grafted and sulfonated membranes show performance comparable to perfluorinated membranes. Some properties, such as methanol permeability, can be tailored to be superior. Durability of several thousand hours at practical operating conditions has been demonstrated. Alternative styrene derived monomers with higher chemical stability offer the prospect of enhanced durability or higher operating temperature. [source] Novel Polymer Electrolyte Membranes for Automotive Applications , Requirements and Benefits,FUEL CELLS, Issue 4 2004C. Wieser Abstract During the past few years, the feasibility of using polymer electrolyte fuel cells in automotive power trains at an impressive performance level has been proven repeatedly. However, current fuel cell stacks are still largely based on decade-old polymer electrolyte membrane technology thus limiting performance, durability, reliability, and cost of the fuel cell systems. The major challenge for membrane R&D constitutes the demand for polymer electrolytes that allow for system operation at higher temperatures and lower water management requirements without increased conduction losses. None the less, demanding automotive requirements will not compromise on other properties such as mechanical and chemical stability and gas permeability. [source] Ionic-Liquid-Doped Polyaniline Inverse Opals: Preparation, Characterization, and Application for the Electrochemical Impedance Immunoassay of Hepatitis B Surface AntigenADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Xing-Hua Li Abstract A 3D ordered macroporous (3DOM) ionic-liquid-doped polyaniline (IL-PANI) inverse opaline film is fabricated with an electropolymerization method and gold nanoparticles (AuNPs) are assembled on the film by electrostatic adsorption, which offers a promising basis for biomolecular immobilization due to its satisfactory chemical stability, good electronic conductivity, and excellent biocompatibility. The AuNP/IL-PANI inverse opaline film could be used to fabricate an electrochemical impedance spectroscopy (EIS) immunosensor for the determination of Hepatitis B surface antigen (HBsAg). The concentration of HBsAg is measured using the EIS technique by monitoring the corresponding specific binding between HBsAg and HBsAb (surface antibody). The increased electron transfer resistance (Ret) values are proportional to the logarithmic value of the concentration of HBsAg. This novel immunoassay displays a linear response range between 0.032,pg mL,1 and 31.6,pg mL,1 with a detection limit of 0.001,pg mL,1. The detection of HBsAg levels in several sera showed satisfactory agreement with those using a commercial turbidimetric method. [source] Proton Transport from Dendritic Helical-Pore-Incorporated PolymersomesADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Anthony J. Kim Abstract The ability to add synthetic channels to polymersome (polymer vesicle) membranes could lead to novel membrane composites with unique selectivity and permeability. Proton transport through two different synthetic pores, self-assembled from either a dendritic dipeptide, (6Nf-3,4-3,5)12G2-CH2 -Boc-L-Tyr-L-Ala-OMe, or a dendritic ester, (R)-4Bp-3,4-dm8G1-COOMe, incorporated into polymersome membranes are studied. Polymersomes provide an excellent platform for studying such transport processes due to their robustness and mechanical and chemical stability compared to liposomes. It is found that the incorporated dendritic dipeptide and dendritic ester assemble into stable helical pores in the poly(ethylene oxide)-polybutadiene (PEO-PBD) polymersomes but not in the poly(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyl oxazoline) (PMOX-PDMS-PMOX) polymersomes. The incorporation is confirmed by circular dichroism (CD), changes in purely synthetic mechanical strength (e.g., areal expansion modulus) as assessed by micropipette aspiration, and cryo-TEM. In addition to the structural analyses, a transport measurement shows the incorporated dendritic helical pores allow facile transport of protons across the polymersome membranes after up to one month of storage. This integration of synthetic porous channels with polymersome substrates could provide a valuable tool for studying active transport processes in a composite membrane. These composites will ultimately expand the family of biologically inspired porous-membrane mimics. [source] Biofunctionalization of Vertically Aligned Diamond NanowiresADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Nianjun Yang Abstract Vertically aligned diamond nanowires are biofunctionalized using aminophenyl linker molecules to bond nucleic acid molecules with a well-defined nanometer-sized spacing to the transducer. This novel DNA biosensor combines the outstanding electrochemical properties of diamond as a transducer with the controlled bonding of DNA molecules to the tips of nanowires by use of an electrochemical attachment scheme. Nucleic acid molecules are bonded in this way and dispersed to the transducer, giving rise to optimized hybridization kinetics of DNA. Negatively charged redox mediator molecules (Fe(CN)63,/4,) are applied for DNA-hybridization sensing. Voltammetric detection of DNA hybridization by differential pulse voltammetry is performed with respect to its sensitivity and reproducibility. On a sensor area of 0.03,cm2, a detection limit of 2.0 pM is achieved. As for the chemical stability of the DNA bonding to the diamond nanowires, no degradation over 30 hybridization/denaturation cycles could be detected. By use of this dilute DNA arrangement, single-base mismatch discrimination is achieved. Under the same conditions, smooth diamond modified with phenyl is not suitable for amperometric DNA sensing. [source] MEL-type Pure-Silica Zeolite Nanocrystals Prepared by an Evaporation-Assisted Two-Stage Synthesis Method as Ultra-Low- k Materials,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008Yan Liu Abstract A MEL-type pure-silica zeolite (PSZ), prepared by spin-on of nanoparticle suspensions, has been shown to be a promising ultra-low-dielectric-constant (k) material because of its high mechanical strength, hydrophobicity, and chemical stability. In our previous works, a two-stage synthesis method was used to synthesize a MEL-zeolite nanoparticle suspension, in which both nanocrystal yield and particle size of the zeolite suspension increased with increasing synthesis time. For instance, at a crystal yield of 63%, the particle size is 80,nm, which has proved to be too large because it introduces a number of problems for the spin-on films, including large surface roughness, surface striations, and large mesopores. In the current study, the two-stage synthesis method is modified into an evaporation-assisted two-stage method by adding a solvent-evaporation process between the two thermal-treatment steps. The modified method can yield much smaller particle sizes (e.g., 14,vs. 80,nm) while maintaining the same nanocrystal yields as the two-stage synthesis. Furthermore, the nanoparticle suspensions from the evaporation-assisted two-stage synthesis show a bimodal particle size distribution. The primary nanoparticles are around 14,nm in size and are stable in the final suspension with 60% solvent evaporation. The factors that affect nanocrystal synthesis are discussed, including the concentration, pH value, and viscosity. Spin-on films prepared by using suspensions synthesized this way have no striations and improved elastic modulus (9.67,±,1.48,GPa vs. 7.82,±,1.30,GPa), as well as a similar k value (1.91,±,0.09 vs. 1.89,±,0.08) to the previous two-stage synthesized films. [source] Research on Advanced Materials for Li-ion BatteriesADVANCED MATERIALS, Issue 45 2009Hong Li Abstract In order to address power and energy demands of mobile electronics and electric cars, Li-ion technology is urgently being optimized by using alternative materials. This article presents a review of our recent progress dedicated to the anode and cathode materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density. Nanostructured inorganic compounds have been extensively investigated. Size effects revealed in the storage of lithium through micropores (hard carbon spheres), alloys (Si, SnSb), and conversion reactions (Cr2O3, MnO) are studied. The formation of nano/micro core,shell, dispersed composite, and surface pinning structures can improve their cycling performance. Surface coating on LiCoO2 and LiMn2O4 was found to be an effective way to enhance their thermal and chemical stability and the mechanisms are discussed. Theoretical simulations and experiments on LiFePO4 reveal that alkali metal ions and nitrogen doping into the LiFePO4 lattice are possible approaches to increase its electronic conductivity and does not block transport of lithium ion along the 1D channel. [source] Properties of Porous Si3N4/BN Composites Fabricated by RBSN TechniqueINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2010Ji-Xuan Liu Reaction bonding of silicon nitride (RBSN) technique combined with slip-casting shaping process was used to fabricate porous Si3N4/BN ceramic composites. Si/BN slurry with chemical stability, good dispersibility, and viscosity was prepared using glycerol trioleate (GTO) covering on Si surface and poly(acrylic acid) (PAA) as dispersant. The hydrolysis of Si was strongly prevented by GTO coating. The dispersibility of covered Si and BN suspensions were improved by PAA dispersant. Twenty volume percent covered Si/BN slurries with low viscosity were successfully casted. The cast bodies were dried at room temperature, debindered at 750°C and nitrided below 1450°C. The nitrided samples mainly consist of ,-Si3N4, ,-Si3N4, and h-BN. The composites exhibit homogeneous microstructure consisting of faceted particles, ,-Si3N4 nanowires and a large amount of pores. The porosity is 52.64% and the pore size is in the range of 60,300 nm. The composites show compressive strength of 16.6±1.5 MPa. The dielectric constant of the composite is about 3.1 and the dielectric loss is below 0.5% under different frequencies. [source] Lanthanum Chromite-Based Interconnects as Key Materials for SOFC Stack DevelopmentINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2004Natsuko Sakai The historical investigations on the physicochemical and transport properties of lanthanum chromite-based perovskite oxides are reviewed to evaluate the compatibility as interconnects in solid oxide fuel cells. These materials improve sinterability in air. This has led to investigations on other physicochemical properties of these materials, such as thermal expansion, mechanical strength, and chemical stability. Lanthanum and chromium ion can be substituted by alkaline earths or transition metals, and this translates into a large flexibility in physicochemical properties. However, the formation of oxygen vacancies in a reducing atmosphere can result in an undesirable isothermal expansion or oxygen permeation. The chemical stability of these materials is governed by the fast cation diffusion at the grain boundary of the polycrystals. [source] Protein-Modified Porous Silicon NanostructuresADVANCED MATERIALS, Issue 8 2008Luca De Stefano Biological passivation of porous silicon (PSi)-based optical devices is demonstrated. Infiltration by small amphiphilic fungal proteins called HFBs changes the wettability of the PSi surface (see figure) and protects the sponge-like structure against dissolution by basic solutions. This protein membrane leaves the sensing ability of an optical transducer unchanged, adding chemical stability that can be the key in biomolecular experiments. [source] Synthesis and Assembly of Monodisperse High-Coercivity Silica-Capped FePt Nanomagnets of Tunable Size, Composition, and Thermal Stability from Microemulsions,ADVANCED MATERIALS, Issue 19 2006Q. Yan A microemulsion approach to obtain high - coercivity (850 mT) FePt nanomagnets capped with a nanoscopic silica shell is reported (see figure). This versatile method allows the easy tuning of particle size and composition. The silica shell inhibits agglomeration and preserves the chemical stability of the particles up to 650,°C, and facilitates surface functionalization and particle assembly. These attributes are attractive for harnessing the nanomagnets for realizing novel devices and composites. [source] Human synthetic sebum formulation and stability under conditions of use and storageINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1 2009P. W. Wertz Synopsis The human skin surface and hair are generally coated with a thin film of liquid phase sebaceous lipids. This surface lipid film contributes to the cosmetic properties of the skin. Synthetic sebum has been used for studies on properties of skin and hair. However, there has been no standardized formulation of synthetic sebum and many of the synthetic sebum formulations that have been used do not closely resemble actual sebum. In this study, a formulation for a standardized and inexpensive synthetic sebum is proposed, and the chemical stability of this lipid mixture is demonstrated under conditions of use and storage. The proposed synthetic sebum consists of 17% fatty acid, 44.7% triglyceride, 25% wax monoester (jojoba oil) and 12.4% squalene. This lipid mixture takes up approximately 6% of its weight in water when equilibrated in an atmosphere saturated with water vapour. It is stable on exposure to the atmosphere at 32°C for at least 48 h, and it is also stable on storage at 4 or ,20°C, either dry or in chloroform : methanol solution for at least 6 months. This synthetic sebum could be useful in studies on cosmetic properties of the skin surface or hair, on penetration of chemicals into the skin or in development of standardized tests of laundry detergent performance. Résumé La surface de la peau et les poils de l'être humain sont généralement enduits d'un mince film de lipides sébacés en phase liquide. Ce film lipidique de surface contribue aux propriétés esthétiques de la peau. Bien que du sébum synthétique ait été employéà des fins d'études sur les propriétés de la peau et des poils, il n'en éxiste pas de formulation standardisée. Plusieurs des formulations utilisées ne ressemblent pas au sébum naturel. La présente étude propose une formulation standardisée et peu coûteuse d'un sébum synthétique; elle vise aussi à démontrer sa stabilité chimique dans des conditions d'utilization et de stockage. Le sébum synthétique tel que proposé est composé de 17% d'acides gras, de 44.7% de triglycérides, de 25% d'un mono ester de cire (huile de jojoba) et de 12.4% de squalène. Ce mélange lipidique prend environ 6% de son poids dans l'eau lorsqu'il est équilibré dans une atmoshpère saturée en vapeur d'eau. Le mélange demeure stable pendant au moins 48 heures lorsque éxposéà une atmoshpère de 32o. Il le demeure également dans des conditions de stockage de 4oà,20oà sec ou en solution de chloroforme:méthanol pendant au moins 6 mois. Ce sébum synthétique pourrait être utile àétudier les propriétés esthétiques de la surface de la peau et des poils ou de la pénétration cutanée de produits chimiques. Il pourrait aussi servir àélaborer des tests standardisés de rendement des détergents de lessive. [source] Polymer Electrolyte Membranes with a Pore-Filling Structure for a Direct Methanol Fuel Cell,ADVANCED MATERIALS, Issue 14 2003T. Yamaguchi Pore-filling membranes that are composed of a porous substrate and a filling polymer electrolyte have been developed. These polyelectrolyte membranes demonstrate low permeation with respect to methanol, high proton conductivity, good mechanical strength, chemical stability, and low cost, making them ideal for use in direct methanol fuel cells. The necessary characteristics can also be controlled by changing the substrate and the filling polymer electrolyte. [source] | ||||||||||||||||||||||||||||||||||