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Replacement Reaction (replacement + reaction)
Kinds of Replacement Reaction Selected AbstractsGold Nanocages for Biomedical Applications,ADVANCED MATERIALS, Issue 20 2007E. Skrabalak Abstract Nanostructured materials provide a promising platform for early cancer detection and treatment. Here we highlight recent advances in the synthesis and use of Au nanocages for such biomedical applications. Gold nanocages represent a novel class of nanostructures, which can be prepared via a remarkably simple route based on the galvanic replacement reaction between Ag nanocubes and HAuCl4. The Au nanocages have a tunable surface plasmon resonance peak that extends into the near-infrared, where the optical attenuation caused by blood and soft tissue is essentially negligible. They are also biocompatible and present a well-established surface for easy functionalization. We have tailored the scattering and absorption cross-sections of Au nanocages for use in optical coherence tomography and photothermal treatment, respectively. Our preliminary studies show greatly improved spectroscopic image contrast for tissue phantoms containing Au nanocages. Our most recent results also demonstrate the photothermal destruction of breast cancer cells in vitro by using immuno-targeted Au nanocages as an effective photo-thermal transducer. These experiments suggest that Au nanocages may be a new class of nanometer-sized agents for cancer diagnosis and therapy. [source] Phlogopite and quartz lamellae in diamond-bearing diopside from marbles of the Kokchetav massif, Kazakhstan: exsolution or replacement reaction?JOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2009L. F. DOBRZHINETSKAYA Abstract Exsolution lamellae of pyroxene in garnet (grt), coesite in titanite and omphacite from UHPM terranes are widely accepted as products of decompression. However, interpretation of oriented lamellae of phyllosilicates, framework silicates and oxides as a product of decompression of pyroxene is very often under debate. Results are presented here of FIB-TEM, FEG-EMP and synchrotron-assisted infrared (IR) spectroscopy studies of phlogopite (Phlog) and phlogopite + quartz (Qtz) lamellae in diamond-bearing clinopyroxene (Cpx) from ultra-high pressure (UHP) marble. These techniques allowed collection of three-dimensional information from the grain boundaries of both the single (phlogopite), two-phase lamellae (phlogopite + quartz), and fluid inclusions inside of diamond included in K-rich Cpx and understanding their relationships and mechanisms of formation. The Cpx grains contain in their cores lamellae-I, which are represented by topotactically oriented extremely thin lamellae of phlogopite (that generally are two units cell wide but locally can be seen to be somewhat broader) and microdiamond. The core composition is: (Ca0.94K0.04Na0.02) (Al0.06Fe0.08Mg0.88) (Si1.98Al0.02)O6.00. Fluid inclusions rich in K and Si are recognized in the core of the Cpx, having no visible connections to the lamellae-I. Lamellar-II inclusions consist of micron-size single laths of phlogopite and lens-like quartz or slightly elongated phlogopite + quartz intergrowths; all are situated in the rim zone of the Cpx. The composition of the rim is (Ca0.95Fe0.03Na0.02) (Al0.05Fe0.05Mg0.90)Si2O6, and the rim contains more Ca, Mg then the core, with no K there. Such chemical tests support our microstructural observations and conclusion that the phlogopite lamellae-I are exsolved from the K-rich Cpx-precursor during decompression. It is assumed that Cpx-precursor was also enriched in H2O, because diamond included in the core of this Cpx contains fluid inclusions. The synchrotron IR spectra of such diamond record the presence of OH, stretching and H2O bending motion regions. Lamellar-II inclusions are interpreted as forming partly because of modification of the lamellae-I in the presence of fluid enriched in K, Fe and Si during deformation of the host diopside; the latter is probably related to the shallower stage of exhumation of the UHP marble. This study emphasizes that in each case to understand the mechanism of lamellar inclusion formation more detailed studies are needed combining both compositional, structural and three-dimensional textural features of lamellar inclusions and their host. [source] The role of Bi3+ -complex ion as the stabilizer in electroless nickel plating processAICHE JOURNAL, Issue 4 2009K. Wang Abstract Bi3+ -complex ion is presented here as a less toxic stabilizer for use in electroless nickel plating (ENP) to replace the existing Pb2+ ion stabilizer. The asymmetric derivatives of EDTA are identified to be a type of coordination ligands that can combine with Bi3+ ions to form soluble complexes in the acidic ENP solution. In the ENP system studied the Bi3+ -complex ion displays a critical stabilizer concentration of about 10,5 mol/L, that is, the percolation concentration over which the ENP rate drops sharply. Besides the experimental measurement, deposition rates of both Ni and P are also simulated by using a kinetic model that has been derived from the double electric layer theory. The Bi3+ -complex ion, behaving like conventional Pb2+ ion, stabilizes ENP bath through the chemical replacement reaction at the surface of Ni deposition layer and results in a passive plating surface. This investigation also verifies the properties of the EN deposit, which are insignificantly affected by the length of service time of the plating solution by employing Bi3+ -complex ion stabilizer. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Characterization of chitin,metal silicates as binding superdisintegrantsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2009Iyad Rashid Abstract When chitin is used in pharmaceutical formulations, processing of chitin with metal silicates is advantageous, from both an industrial and pharmaceutical perspective, compared to processing using silicon dioxide. Unlike the use of acidic and basic reagents for the industrial preparation of chitin,silica particles, coprecipitation of metal silicates is dependent upon a simple replacement reaction between sodium silicate and metal chlorides. When coprecipitated onto chitin particles, aluminum, magnesium, or calcium silicates result in nonhygroscopic, highly compactable/disintegrable compacts. Disintegration and hardness parameters for coprocessed chitin compacts were investigated and found to be independent of the particle size. Capillary action appears to be the major contributor to both water uptake and the driving force for disintegration of compacts. The good compaction and compression properties shown by the chitin,metal silicates were found to be strongly dependent upon the type of metal silicate coprecipitated onto chitin. In addition, the inherent binding and disintegration abilities of chitin,metal silicates are useful in pharmaceutical applications when poorly compressible and/or highly nonpolar drugs need to be formulated. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4887,4901, 2009 [source] A New Photothermal Therapeutic Agent: Core-Free Nanostructured AuxAg1,x DendritesCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2008Kuo-Wei Hu Abstract A new class of AuxAg1,x nanostructures with dendrite morphology and a hollow interior were synthesized by using a replacement reaction between Ag dendrites and an aqueous solution of HAuCl4. The Ag nanostructured dendrites were generated by the reaction of AgNO3 with ascorbic acid in a methanol/water system. The dendrites resemble a coral shape and are built up of many stems with an asymmetric arrangement. Each stem is approximately 400,nm in length and 65,nm in diameter. The bimetallic composition of AuxAg1,x can be tuned by the addition of different amounts of HAuCl4 to the Ag dendritic solution. The hollowing process resulted in tubular structures with a wall thickness of 10.5,nm in Au0.3Ag0.7 dendrites. The UV/Vis spectra indicate that the strongest NIR absorption among the resulting hollow AuxAg1,x dendrites was in Au0.3Ag0.7. The MTT assay was conducted to evaluate the cytotoxicity of Ag dendrites, hollow Au0.06Ag0.94 and Au0.3Ag0.7 dendrites, and Au nanorods. It was found that hollow Au0.06Ag0.94 and Au0.3Ag0.7 dendrites exhibited good biocompatibility, while both Ag dendrites and Au nanorods showed dose-dependent toxicity. Because of absorption in the NIR region, hollow Au0.3Ag0.7 dendrites were used as photothermal absorbers for destroying A549 lung cancer cells. Their photothermal performance was compared to that of Au nanorod photothermal therapeutic agents. As a result, the particle concentration and laser power required for efficient cancer cell damage were significantly reduced for hollow Au0.3Ag0.7 dendrites relative to those used for Au nanorods. The hollow Au0.3Ag0.7 nanostructured dendrites show potential in photothermolysis for killing cancer cells. [source] From Ag Nanoprisms to Triangular AuAg NanoboxesADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Damian Aherne Abstract In recent years, galvanic replacement reactions have been successfully employed to produce hollow bimetallic nanostructures of a range of shapes, yet to date there has been no example of the formation of hollow triangular AuAg nanostructures from a Ag nanoprism template. In this manuscript the first example of the synthesis of enclosed triangular AuAg nanostructures (triangular nanoboxes) via galvanic replacement reactions from Ag nanoprisms is reported. These triangular nanoboxes are studied by TEM and HAADF-STEM imaging to elucidate their structure. These studies show that the nanostructures are hollow and do not consist of a Ag core surrounded by a Au shell. Discrete dipole approximation calculations for the extinction spectra are carried out and provide additional evidence that the nanostructures are hollow. These new triangular nanoboxes are very attractive candidates for encapsulation and transport of materials of interest such as drugs, radioisotopes, or magnetic materials. [source] Synthesis and Characterization of Noble-Metal Nanostructures Containing Gold Nanorods in the CenterADVANCED MATERIALS, Issue 6 2010Eun Chul Cho Noble-metal nanostructures containing gold (Au) nanorods in the center were synthesized by employing Au nanorods as templates for epitaxial growth of silver (Ag). The immediate products, Au@Ag core,shell nanocrystals with an octahedral shape, were transformed into noble-metal (Au, Pd, and Pt) hollow nanostructures containing Au nanorods in the center, via galvanic replacement reactions (see figure). [source] "Remote" Fabrication via Three-Dimensional Reaction-Diffusion: Making Complex Core-and-Shell Particles and Assembling Them into Open-Lattice CrystalsADVANCED MATERIALS, Issue 19 2009Paul J. Wesson Reaction-diffusion (RD) processes initiated from the surfaces of mesoscopic particles can fabricate complex core-and-shell structures. The propagation of a sharp RD front selectively removes metal colloids or nanoparticles from the supporting gel or polymer matrix. Once fabricated, the core structures can be processed "remotely" via galvanic replacement reactions, and the composite particles can be assembled into open-lattice crystals. [source] Reaction localization and softening of texturally hardened mylonites in a reactivated fault zone, central ArgentinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2005S. J. WHITMEYER Abstract The Tres Arboles ductile fault zone in the Eastern Sierras Pampeanas, central Argentina, experienced multiple ductile deformation and faulting events that involved a variety of textural and reaction hardening and softening processes. Much of the fault zone is characterized by a (D2) ultramylonite, composed of fine-grained biotite + plagioclase, that lacks a well-defined preferred orientation. The D2 fabric consists of a strong network of intergrown and interlocking grains that show little textural evidence for dislocation or dissolution creep. These ultramylonites contain gneissic rock fragments and porphyroclasts of plagioclase, sillimanite and garnet inherited from the gneissic and migmatitic protolith (D1) of the hangingwall. The assemblage of garnet + sillimanite + biotite suggests that D1-related fabrics developed under upper amphibolite facies conditions, and the persistence of biotite + garnet + sillimanite + plagioclase suggests that the ultramylonite of D2 developed under middle amphibolite facies conditions. Greenschist facies, mylonitic shear bands (D3) locally overprint D2 ultramylonites. Fine-grained folia of muscovite + chlorite ± biotite truncate earlier biotite + plagioclase textures, and coarser-grained muscovite partially replaces relic sillimanite grains. Anorthite content of shear band (D3) plagioclase is c. An30, distinct from D1 and D2 plagioclase (c. An35). The anorthite content of D3 plagioclase is consistent with a pervasive grain boundary fluid that facilitated partial replacement of plagioclase by muscovite. Biotite is partially replaced by muscovite and/or chlorite, particularly in areas of inferred high strain. Quartz precipitated in porphyroclast pressure shadows and ribbons that help define the mylonitic fabric. All D3 reactions require the introduction of H+ and/or H2O, indicating an open system, and typically result in a volume decrease. Syntectonic D3 muscovite + quartz + chlorite preferentially grew in an orientation favourable for strain localization, which produced a strong textural softening. Strain localization occurred only where reactions progressed with the infiltration of aqueous fluids, on a scale of hundreds of micrometre. Local fracturing and microseismicity may have induced reactivation of the fault zone and the initial introduction of fluids. However, the predominant greenschist facies deformation (D3) along discrete shear bands was primarily a consequence of the localization of replacement reactions in a partially open system. [source] On the origin of rim textures surrounding anhydrous silicate grains in CM carbonaceous chondritesMETEORITICS & PLANETARY SCIENCE, Issue 5 2000Lauren BROWNING Bulk chemical analyses and observations of these rims indicate the presence of phyllosilicates and disseminated opaques. Because phyllosilicates could not have survived the chondrule formation process, chondrule silicate rims must have formed entirely by late-state aqueous reactions. As such, these textures provide a useful benchmark for isolating alteration features from more complex CM matrix materials. Both chondrule silicate and matrix silicate rims exhibit morphological features commonly associated with advancing stages of replacement reactions in terrestrial serpentinites. Contacts between many matrix silicate rims and the adjacent matrix materials suggest that these rims formed entirely by aqueous reactions in a parent-body setting. This contrasts with previous assertions that rim textures can only form by the accretion of nebular dust but does not imply an origin for the rims surrounding other types of CM core components, such as chondrules. [source] | |||||||||||||