Home About us Contact
|
Home About us Contact | ||
|
|
||
Host Matrix (host + matrix)
Selected AbstractsElectrochemical Study of Anionic Ferrocene Derivatives Intercalated in Layered Double Hydroxides: Application to Glucose Amperometric BiosensorsELECTROANALYSIS, Issue 3-5 2009Christine Mousty Abstract Layered double hydroxides (Zn2Cr(OH)6X,nH2O LDH) containing (3-sulfopropyl)ferrocene-carboxylate (FcPSO3) and 1,1,-bis(3-sulfopropyl)ferrocene-carboxylate (Fc(PSO3)2) as interlayer anions (X) have been prepared by the co-precipitation method and characterized by PXRD, FTIR, SEM and XPS. The electrochemical behavior of these hybrid materials has been evaluated by cyclic voltammetry. A new amperometric biosensor based on the immobilization of glucose oxidase in ZnCr-FcPSO3 hybrid material was presented, the intercalated anions playing the role of mediators that shuttle electrons between the FAD centers in the enzyme and the electrode surface. The performance of the resulting biosensor for glucose determination under anaerobic conditions was evaluated by chronoamperometry at 0.5,V. The sensitivity (65,mA M,1 cm,2) determined in the concentration range 10,25,,M is higher than sensitivities reported for other glucose biosensors based on LDH host matrices. [source] Three-Dimensionally Ordered Gold Nanocrystal/Silica Superlattice Thin Films Synthesized via Sol,Gel Self-Assembly,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2006H. Fan Abstract Nanocrystals and their ordered arrays hold many important applications in fields such as catalysis, surface-enhanced Raman spectroscopy based sensors, memory storage, and electronic and optical nanodevices. Herein, a simple and general method to synthesize ordered, three-dimensional, transparent gold nanocrystal/silica superlattice thin films by self-assembly of gold nanocrystal micelles with silica or organosilsesquioxane by spin-coating is reported. The self-assembly process is conducted under acidic sol,gel conditions (ca.,pH,2), ensuring spin-solution homogeneity and stability and facilitating the formation of ordered and transparent gold nanocrystal/silica films. The monodisperse nanocrystals are organized within inorganic host matrices as a face-centered cubic mesostructure, and characterized by transmission electron spectroscopy and X-ray diffraction. [source] Mechanico-chemical interaction of SWNTs with different host matrices evidenced by SERS spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006Serge Lefrant Abstract Surface enhanced Raman scattering (SERS) performed with 676.4 and 1064 nm excitations were used to investigate single-walled carbon nanotubes (SWNTs) thin films prepared from platelets obtained by non-hydrostatic compression at 0.58 GPa. SWNTs were compressed alone or dispersed into chemical reactive and non-reactive host matrices. SERS spectra indicate that by compression, SWNTs break into fragments of different sizes, which in turn can react or not with the host matrix. In inorganic hosts (KI, Ag) donor-acceptor complexes are formed. The appearance of short fragments of SWNTs with a closed-shell fullerenes behaviour is revealed in SERS spectra. This typical signature appears in the Raman spectrum as a line at ca. 1460 cm,1 associated with a pentagonal pinch mode. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescent properties of PP and LDPE films and rods doped with the Eu(III)-La(III) complexPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2006Roman Pogreb Abstract The work is devoted to luminescent properties of trivalent lanthanide complexes dispersed in thermoplastic host matrices. Polyethylene films and polypropylene-rods, both doped with these complexes, were manufactured using an extrusion technique. Two kinds of dopants were used: Eu(III)-thenoyltrifluoroacetone-1,10-phenanthroline complex (1) and Eu(III)-La(III)-1,10-phenanthroline complex (2). Absorption, excitation, emission spectra and lifetime of luminescence were studied. The impact of the polymer matrix on the emission spectra was investigated. Emission spectra of the films were studied at room and helium temperatures. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) surface mapping showed that in the Eu(III)-La(III) complex europium forms islands (clusters) with a dimension of 1,µm, whereas lanthanum was dispersed more uniformly in the polymer matrix. Dependence of emission intensity on the excitation was determined. Copyright © 2006 John Wiley & Sons, Ltd. [source] Bright and Efficient, Non-Doped, Phosphorescent Organic Red-Light-Emitting Diodes,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2004Y.-H. Song Abstract Ir(III) metal complexes with formula [(nazo)2Ir(Fppz)] (1), [(nazo)2Ir(Bppz)] (2), and [(nazo)2Ir(Fptz)] (3) [(nazo)H,= 4-phenyl quinazoline, (Fppz)H,=,3-trifluoromethyl-5-(2-pyridyl) pyrazole, (Bppz)H,=,3- t -butyl-5-(2-pyridyl) pyrazole, and (Fptz)H,=,3-trifluoromethyl-5-(2-pyridyl) triazole] were synthesized, among which the exact configuration of 1 was confirmed using single-crystal X-ray diffraction analysis. These complexes exhibited bright red phosphorescence with relatively short lifetimes of 0.4,1.05,,s in both solution and the solid-state at room temperature. Non-doped organic light-emitting diodes (OLEDs) were fabricated using complexes 1 and 2 in the absence of a host matrix. Saturated red electroluminescence was observed at ,max,=,626,nm (host-emitter complex,1) and 652,nm (host-emitter complex,2), which corresponds to coordinates (0.66,0.34) and (0.69,0.31), respectively, on the 1931 Commission Internationale de l'Eclairage (CIE) chromaticity diagram. The non-doped devices employing complex,1 showed electroluminance as high as 5780,cd,m,2, an external quantum efficiency of 5.5,% at 8,V, and a current density of 20,mA,cm,2. The short phosphorescence lifetime of 1 in the solid state, coupled with its modest ,,, stacking interactions, appear to be the determining factors for its unusual success as a non-doped host-emitter. [source] Nonblinking and Nonbleaching Upconverting Nanoparticles as an Optical Imaging Nanoprobe and T1 Magnetic Resonance Imaging Contrast AgentADVANCED MATERIALS, Issue 44 2009Yong Il Park Core/shell upconverting nanoparticles (UCNPs) of NaGdF4:Er3+,Yb3+/NaGdF4 (see figure) are shown to serve as a multimodal imaging probe that works for both background-free optical imaging and magnetic resonance imaging (MRI). The nonblinking and nonbleaching properties of UCNPs can contribute to minimization of possible artifacts in long-term imaging experiments. Owing to Gd3+ ions in the host matrix, contrast is enhanced in T1 -weighted MRI. [source] Revealing the Electron,Phonon Coupling in a Conjugated Polymer by Single-Molecule Spectroscopy,ADVANCED MATERIALS, Issue 15 2007R. Hildner Electron,phonon coupling in a ,-conjugated polymer is revealed by single-molecule spectroscopy in combination with statistical pattern recognition techniques. The technique allows to reveal the phonon-side band in the spectra of methyl-substituted ladder-type poly(para-phenylene) (see figure). For this polymer a weak electron,phonon coupling strength is found at low temperatures. The distribution of the phonon frequencies provides strong evidence that the low-energy vibrational modes, which couple to the electronic transitions, stem from vibrations of the host matrix. [source] Host collagen signal induces antigen I/II adhesin and invasin gene expression in oral Streptococcus gordoniiMOLECULAR MICROBIOLOGY, Issue 2 2003Catherine Heddle Summary Microbial interactions with host molecules, and programmed responses to host environmental stimuli, are critical for colonization and initiation of pathogenesis. Bacteria of the genus Streptococcus are primary colonizers of the human mouth. They express multiple cell-surface adhesins that bind salivary components and other oral bacteria and enable the development of polymicrobial biofilms associated with tooth decay and periodontal disease. However, the mechanisms by which streptococci invade dentine to infect the tooth pulp and periapical tissues are poorly understood. Here we show that production of the antigen I/II (AgI/II) family polypeptide adhesin and invasin SspA in Streptococcus gordonii is specifically upregulated in response to a collagen type I signal, minimally the tri-peptide Gly-Pro-Xaa (where Xaa is hydroxyproline or alanine). Increased AgI/II polypeptide expression promotes bacterial adhesion and extended growth of streptococcal cell chains along collagen type I fibrils that are characteristically found within dentinal tubules. These observations define a new model of host matrix signal-induced tissue penetration by bacteria and open the way for novel therapy opportunities for oral invasive diseases. [source] Thermoluminescence and other optical studies on RbBr:Tb3+ crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007P. K. Manimozhi Abstract Optical absorption, photoluminescence, photostimulated luminescence (PSL) and thermoluminescence (TL) studies on RbBr:Tb3+ crystals irradiated with X-rays is reported. The optical absorption in the UV region confirms the presence of terbium in the host matrix in the trivalent state. Photoluminescence of these crystals exhibits characteristic Tb3+ emissions due to transitions from the 5D3 and 5D4 levels to various levels of the 7F septet. On F-bleaching X-irradiated crystals Z3 centers are observed. The TL glow curve indicates a two-step thermal annihilation process for the radiatively created defects. The presence of the characteristic emissions due to terbium ions in the photostimulation at the F band confirms the participation of Tb ions in the defect-production process. Trap parameters for the TL process are calculated and presented. Emissions under the TL glow peaks contain the characteristic emissions of Tb3+ in addition to the emission due to the recombination of the F electron with V-type centers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanico-chemical interaction of SWNTs with different host matrices evidenced by SERS spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006Serge Lefrant Abstract Surface enhanced Raman scattering (SERS) performed with 676.4 and 1064 nm excitations were used to investigate single-walled carbon nanotubes (SWNTs) thin films prepared from platelets obtained by non-hydrostatic compression at 0.58 GPa. SWNTs were compressed alone or dispersed into chemical reactive and non-reactive host matrices. SERS spectra indicate that by compression, SWNTs break into fragments of different sizes, which in turn can react or not with the host matrix. In inorganic hosts (KI, Ag) donor-acceptor complexes are formed. The appearance of short fragments of SWNTs with a closed-shell fullerenes behaviour is revealed in SERS spectra. This typical signature appears in the Raman spectrum as a line at ca. 1460 cm,1 associated with a pentagonal pinch mode. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal precipitation of self-organized PbTe quantum dots in CdTe host matrixPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008K. Koike Abstract This paper describes a selective growth of PbTe/CdTe quantum wells (QWs) and quantum dots (QDs) in CdTe host matrix by molecular beam epitaxy. These two tellurides possess almost identical lattice constants, but differ fundamentally in their lattice structure. Owing to a strong phase separation by the lattice-type mismatch, insertion of a PbTe thin layer in CdTe matrix at higher temperatures than 280 °C was resulted in a self-organized growth of coherent and three-dimensionally isotropic QDs. The same growth procedure at lower temperatures, on the other hand, yielded a conventional QW structure with sharp heterointerface. This QW structure, however, was found to precipitate well-ordered QD-array by a postgrowth annealing, indicating that the QD formation is induced by the minimization of interface energy between the inmiscible two tellurides. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of non-random incorporation of Mn ions on the magnetotransport properties of Ga1,xMnxAs alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008C. Michel Abstract We study theoretically the influence of a spatially nonrandom incorporation of Mn ions on the magnetotransport in paramagnetic Ga1,xMnxAs alloys. Such a nonrandomness may be introduced during post-growth annealing treatment. We use a resistor-network model for describing the electrical transport of this disordered semiconductor system as a function of temperature and external magnetic field. The model is founded on classical semiconductor band-transport and neglects many-body interactions. The peculiarities of paramagnetic dilute magnetic semiconductors, in particular, the magnetic-field induced changes of the density of states, the broad acceptor-energy distribution, and the interplay of magnetic field independent disorder (due to the alloying of GaAs with Mn) and magnetic field dependent disorder (due to the the Giant Zeeman splitting) are accounted for in a mean-field fashion. We have previously shown that this empirical transport model based on reasonable assumptions and realistic material parameters yields a satisfactory quantitative description of the experimentally obtained temperature and magnetic-field dependence of the resistivity of Ga0.98Mn0.02As samples annealed at different temperatures. For Ga1,xMnxAs alloys annealed at temperatures above 500 °C where structural changes lead to the formation of MnAs clusters, the transport is dominated by the paramagnetic GaAs:Mn host matrix as the cluster density is below the percolation threshold. We will show that in this situation the transport results can only be explained accounting for a nonrandom Mn distribution. Thus the analysis shown here provides further understanding of the annealing-induced changes of the transport properties in dilute magnetic III-Mn-V semiconductors. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Impact of Annealing on the Conductivity of Amorphous Carbon Films Incorporating Copper and Gold Nanoparticles Deposited by Pulsed Dual Cathodic ArcPLASMA PROCESSES AND POLYMERS, Issue S1 2009Jose Luis Endrino Abstract The influence of annealing in argon at 300,°C on the conductivity, phase stability and electronic structure of hydrogen-free amorphous carbon (a-C) films containing copper (a-C:Cu) and gold (a-C:Au) nanoclusters was investigated. The motivation of this work is twofold: (1) to study the thermal stability of a-C:Cu and a-C:Au films and (2) to point out the relevance of X-ray absorption near edge structure (XANES) technique to study the structural evolution of metal-doped a-C nanocomposites. The films were produced at room temperature using a selective-bias pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas grazing incidence X-ray diffraction (GIXRD) was used to monitor phase transformation and identify the dispersion or agglomeration of the crystallites within the carbon matrix. XANES spectra at the C-K was used to investigate the effect of annealing in argon on the electronic structure of the a-C matrix, while Cu K and Au L-edges were investigated on a-C:Cu and a-C:Au samples, respectively, to study the nanocluster evolution. XANES showed that the a-C host matrix increased its graphitic character and that stress was relieved upon annealing. No relevant changes were observed in the Au arrangements in a-C:Au films. In the case of the a-C:Cu samples, the Cu-K XANES spectra indicated the formation of Cu2O crystals which correlated well with GIXRD spectra and the decrease in conductivity. [source] Structural, thermal, micromechanical and electrical study of polyimide composite thin films incorporating indium tin oxidePOLYMER INTERNATIONAL, Issue 9 2010Anand Kumar Gupta Abstract Studies of composite films incorporating inorganic materials are of immense importance for current technological applications. Polyimide (PI) composite thin films incorporating indium tin oxide (ITO) at various weight ratios were processed using an in situ generation approach. The resultant product was imidized up to 350 °C to test the ability of the material to endure high temperatures without affecting the host matrix. The morphological behaviour of the PI/ITO composite films was investigated using Fourier transform infrared, scanning electron microscopy and atomic force microscopy characterization techniques. The degrees of crystallinity and ITO particle size within the PI matrix were studied using X-ray diffraction. The thermal, structural and electrical properties were analysed using thermogravimetric analysis, differential scanning calorimetry, UV-visible spectroscopy and the four-probe technique. The micromechanical properties of the composites were evaluated in terms of tensile strength, tensile modulus and elongation. An overall improvement in the properties of the composite films was observed in comparison to those of pure PI. The synergistic improvement in the composite films is associated with the interaction mechanism between ITO and PI, where ITO becomes dispersed and interacts within the PI matrix. This leads to a decrease in available free-space volume and increases the surface enrichment providing reinforcement to the matrix. Copyright © 2010 Society of Chemical Industry [source] Bioencapsulation of apomyoglobin in nanoporous organosilica sol,gel glasses: Influence of the siloxane network on the conformation and stability of a model proteinBIOPOLYMERS, Issue 11 2009Bouzid Menaa Abstract Nanoporous sol,gel glasses were used as host materials for the encapsulation of apomyoglobin, a model protein employed to probe in a rational manner the important factors that influence the protein conformation and stability in silica-based materials. The transparent glasses were prepared from tetramethoxysilane (TMOS) and modified with a series of mono-, di- and tri-substituted alkoxysilanes, RnSi(OCH3)4,n (R = methyl-, n = 1; 2; 3) of different molar content (5, 10, 15%) to obtain the decrease of the siloxane linkage (SiOSi). The conformation and thermal stability of apomyoglobin characterized by circular dichroism spectroscopy (CD) was related to the structure of the silica host matrix characterized by 29Si MAS NMR and N2 adsorption. We observed that the protein transits from an unfolded state in unmodified glass (TMOS) to a native-like helical state in the organically modified glasses, but also that the secondary structure of the protein was enhanced by the decrease of the siloxane network with the methyl modification (n = 0 < n = 1 < n = 2 < n = 3; 0 < 5 < 10 < 15 mol %). In 15% trimethyl-modified glass, the protein even reached a maximum molar helicity (,24,000 deg. cm2 mol,1) comparable to the stable folded heme-bound holoprotein in solution. The protein conformation and stability induced by the change of its microlocal environment (surface hydration, crowding effects, microstructure of the host matrix) were discussed owing to this trend dependency. These results can have an important impact for the design of new efficient biomaterials (sensors or implanted devices) in which properly folded protein is necessary. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 895,906, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Thermally Driven AFM for NanoenergeticsIMAGING & MICROSCOPY (ELECTRONIC), Issue 2 2009A Method to Investigate the Decomposition on the Nanoscale Abstract A fundamental understanding of the decomposition of energetic nanocompounds infiltrated in porous host matrixes requires the investigation of their behavior on a nanoscale during a thermal stress. Up to now, the decomposition of pure energetic nanomaterials has only been observed on a macroscopic scale. Thermally driven AFM revealed that the decomposition of the energetic material present in the pores of a Cr2O3 matrix induces a spatial expansion of the oxide on the nanometric scale. [source] | ||||||||||||||||||||||||||||