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Enhanced luminescence of Tb(3+)/Eu(3+) doped tellurium oxide glass containing silver nanostructures

KASSAB, Luciana R. P.; ALMEIDA, Ricardo de; SILVA, Davinson M. da; ASSUMPCAO, Thiago A. A. de; ARAUJO, Cid B. de
Fonte: AMER INST PHYSICS Publicador: AMER INST PHYSICS
Tipo: Artigo de Revista Científica
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We report on energy transfer studies in terbium (Tb(3+))-europium (Eu(3+)) doped TeO(2)-ZnO-Na(2)O-PbO glass containing silver nanostructures. The samples excitation was made using ultraviolet radiation at 355 nm. Luminescence spectra were recorded from approximate to 480 to approximate to 700 nm. Enhanced Eu(3+) luminescence at approximate to 590 nm (transition (5)D(0)-(7)F(1)) and approximate to 614 nm (transition (5)D(0)-(7)F(2)) are observed. The large luminescence enhancement was obtained due to the simultaneous contribution of the Tb(3+)-Eu(3+) energy transfer and the contribution of the intensified local field on the Eu(3+) ions located near silver nanostructures.; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); Fundacao de Amparo a Ciencia e Tecnologia de Pernambuco (FACEPE)

Estudo da ação in vitro de nanopartícula de prata; Study of in vitro action of silver nanoparticle

Cavassin, Emerson Danguy
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/09/2013 Português
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O presente estudo avaliou a ação in vitro de diferentes nanopartículas de prata (nanoAg) sintetizadas pelo Instituto de Pesquisas Tecnológicas (IPT) e Universidade Federal de São Carlos (IFSC) e controles de sulfadiazina de prata, nitrato de prata e nanoAg comercial Sigma, frente a bactérias e leveduras. Os objetivos do estudo foram avaliar a ação in vitro de NanoAg sintetizadas no Brasil frente a bactérias sensíveis aos antimicrobianos e multirresistentes (MR), incluindo Gram positivos e negativos, além de candidas isoladas de amostras clínicas. Definir as condições de síntese que resultem em nanoAg com melhor efeito antimicrobiano in vitro frente a isolados sensíveis e MR. Foram utilizadas diferentes metodologias tais como agar well diffusion, determinação de concentração inibitória mínima CIM, concentração bactericida mínima (CBM), curva do tempo de morte e inibição da formação de biofilme. Ao todo, foram avaliados 110 isolados, sendo 37 sensíveis aos antimicrobianos, 54 MR, e 19 candidas frente a 29 nanoAg com diferentes características de síntese. Os testes de difusão em meio sólido apresentaram heterogeneidade de resultados frente aos micro-organismos avaliados. Enquanto as informações de CIM50 e CIM90 evidenciaram não existir variações no efeito inibitório frente isolados sensíveis ou resistentes aos antimicrobianos. As curvas do tempo de morte ilustraram a dinâmica de inibição dos compostos de prata e a interferência do sangue nos testes in vitro. A partir dos testes com biofilme foi possível observar efeito inibitório e de descolamento de biofilme previamente formado. Os resultados permitiram concluir a maior eficácia para nanoAg com Citrato e Quitosana...

Enhanced luminescence of Tb3+/Eu3+ doped tellurium oxide glass containing silver nanostructures

Kassab, Luciana R. P.; de Almeida, Ricardo; da Silva, Davinson M.; de Assumpcao, Thiago A. A.; de Araujo, Cid B.
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica Formato: 3
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); We report on energy transfer studies in terbium (Tb3+)-europium (Eu3+) doped TeO2-ZnO-Na2O-PbO glass containing silver nanostructures. The samples excitation was made using ultraviolet radiation at 355 nm. Luminescence spectra were recorded from approximate to 480 to approximate to 700 nm. Enhanced Eu3+ luminescence at approximate to 590 nm (transition D-5(0)-F-7(1)) and approximate to 614 nm (transition D-5(0)-F-7(2)) are observed. The large luminescence enhancement was obtained due to the simultaneous contribution of the Tb3+-Eu3+ energy transfer and the contribution of the intensified local field on the Eu3+ ions located near silver nanostructures.

Formation of silver chloride nanocrystals as a corrosion product of silver in H2SO4 solution

Picon, C. A.; Fernandes, F. A P; Machado, S. A P; Tremiliosi-Filho, G.; Casteletti, L. C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 199-202
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The purpose of this study is to characterize the corrosion product on the surface of silver, employing H2SO4 (0.5M) as electrolyte. The electrochemical parameters, Ecor, Icor, V cor and Rp were obtained after analyzing the potentiodynamic polarization curve in which two peaks were observed. The smallest (passive region) is attributed to the Cl- traces from the reference electrode, with micro-cracks. The second peak (in the transpassivation region) corresponds to the polarization curve of silver in H2SO 4 without contaminants. SEM images and EDS analysis reveal images of a surface layer on silver, consisting of structures containing sulfur, oxygen, silver and chloride, as the corrosion product. On this layer silver sulfate crystals were observed, which occurs during the formation of silver chloride nanocrystals with different morphologies, when chloride ions were added to the electrolyte medium. ©The Electrochemical Society.

Synthesis, crystal structures, antimicrobial, antifungal and antituberculosis activities of mixed ligand silver(I) complexes

Altaf, Muhammad; Stoeckli-Evans, Helen; Cuin, Alexandre; Sato, Daisy Nakamura; Pavan, Fernando Rogério; Leite, Clarice Queico Fujimura; Ahmad, Saeed; Bouakka, Mohammed; Mimouni, Mostafa; Khardli, Fatima Zahra; Hadda, Taibi Ben
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 138-147
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The biological activity of some new mixed silver-phosphane-thio-ligand complexes, with 1:1:2, 1:1:1 and 1:2:1 (Ag:phospine:ligand) compositions, have been examined. Ten compounds were prepared using a series of silver(I) salts [AgX, where X = NO3, ClO4, PF6 and Br], tertiary phosphines and the ligands thi-osemicarbazide, 2-(propan-2-ylidene) hydrazinecarbothioamide, and thiazolidine-2-thione. The syntheses were carried out under ambient conditions, and the ten complexes obtained were found to be light stable. All 10 compounds were characterized by elemental analysis, FTIR, and NMR spectroscopy, whereas nine compounds were characterized by X-ray diffraction analysis. The anti-proliferative activities were evaluated by minimum inhibitory concentration (MIC: lg/mL) in an aqueous suspension system and they all show promising potential activity against selective strains of Gram-positive and Gram-negative bacteria, fungous and Mycrobaterium tuberculosis H37Rv. © 2013 Elsevier Ltd. All rights reserved.

Desenvolvimento de curativos de quitosana e alginato contendo fosfato hidrogenado de zircônio, sódio e prata; Development of chitosan-alginate wound dressings containing silver sodium hydrogen zirconium phosphate

Ana Kelly Girata
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/04/2011 Português
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36.29%
A quitosana é um polissacarídeo obtido pela desacetilação da quitina e o alginato, um biopolímero extraído de algas. Ambos são atóxicos, biocompatíveis e facilitam a cicatrização de feridas. Por estas razões, podem ser empregados para a produção de curativos para o tratamento de lesões de pele. Além disso, muitos curativos têm incorporado compostos contendo prata para a prevenção e o controle de infecções bacterianas. Diante disso, este trabalho teve por objetivo o desenvolvimento de metodologia de produção de membranas constituídas por quitosana e alginato contendo um agente antimicrobiano à base de prata estabilizada (AlphaSan® RC2000) para aplicação na terapia de lesões de pele. As membranas produzidas foram caracterizadas quanto à morfologia de superfície, à espessura, à absorção de fluidos, à perda de massa quando em contato com diferentes fluidos, à capacidade de drenagem de água, à resistência mecânica, à citotoxicidade a fibroblastos, ao desempenho quanto à atividade antimicrobiana, à sensibilidade e irritabilidade dérmica. Os resultados mostraram que o aumento da quantidade de fármaco causa o aumento da opacidade e da espessura das membranas. A eficiência de incorporação do AlphaSan® RC2000 foi de até 99%. As membranas contendo o agente antimicrobiano foram capazes de absorver de 15 g a 42...

Detection of silver protein complex injections in the bovine udder using x-ray fluorescence: A preliminary investigation

Graham, Sean A.; O’Meara, Joanne M.; Dobson, Howard
Fonte: Canadian Veterinary Medical Association Publicador: Canadian Veterinary Medical Association
Tipo: Artigo de Revista Científica
Publicado em /04/2005 Português
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To determine the feasibility of using x-ray fluorescence (XRF) to detect the presence of silver in the mammary gland of dairy cows injected with mild silver protein suspension. The XRF spectroscopy was conducted on cadaver udders with and without mild silver protein injected. Spectral analysis was performed in order to determine the amplitude of the silver K-alpha peak that was detected. By comparing the amplitude of the K-alpha peak to the background, a minimum time of collection was determined, as a measure of the time required to observe a silver signal that is significantly non-zero. The minimum detection time required for evidence of injected silver suspension was calculated to be 2.8 ± 0.2 s. Even with an additional requirement that the net signal exceed 50 counts, the clear indication of the presence of silver will be observed within 4 min of interrogation. X-ray fluorescence spectroscopy was shown to be a viable method for the detection of injected silver protein in cadaver mammary glands of dairy cows. While these findings are promising, further studies must be conducted to investigate the time dependence of the silver signal when diffusion, absorption, and redistribution are involved, under conditions that better mimic those encountered at an exhibition. This technique...

Mechanism of Prophylaxis by Silver Compounds against Infection of Burns

Ricketts, C. R.; Lowbury, E. J. L.; Lawrence, J. C.; Hall, M.; Wilkins, M. D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 23/05/1970 Português
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To clarify tthe mechanism by which local application of silver compounds protects burns against infection, an ion-specific electrode was used to measùre the concentration of silver ions in solutions. By this method it was shown that in burn dressings silver ions were reduced to a very low level by precipitation as silver chloride. The antibacterial effect was found to depend on the availability of silver ions from solution in contact with precipitate. Between 10-5 and 10-6 molar silver nitrate solution in water was rapidly bactericidal. The minimal amount of silver nitrate causing inhibition of respiration of skin in tissue culture was about 25 times the minimal concentration of silver nitrate that inhibited growth of Pseudomonas aeruginosa.

A Pharmacological and Toxicological Profile of Silver as an Antimicrobial Agent in Medical Devices

Lansdown, Alan B. G.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
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Silver is used widely in wound dressings and medical devices as a broad-spectrum antibiotic. Metallic silver and most inorganic silver compounds ionise in moisture, body fluids, and secretions to release biologically active Ag+. The ion is absorbed into the systemic circulation from the diet and drinking water, by inhalation and through intraparenteral administration. Percutaneous absorption of Ag+ through intact or damaged skin is low. Ag+ binds strongly to metallothionein, albumins, and macroglobulins and is metabolised to all tissues other than the brain and the central nervous system. Silver sulphide or silver selenide precipitates, bound lysosomally in soft tissues, are inert and not associated with an irreversible toxic change. Argyria and argyrosis are the principle effects associated with heavy deposition of insoluble silver precipitates in the dermis and cornea/conjunctiva. Whilst these changes may be profoundly disfiguring and persistent, they are not associated with pathological damage in any tissue. The present paper discusses the mechanisms of absorption and metabolism of silver in the human body, presumed mechanisms of argyria and argyrosis, and the elimination of silver-protein complexes in the bile and urine. Minimum blood silver levels consistent with early signs of argyria or argyrosis are not known. Silver allergy does occur but the extent of the problem is not known. Reference values for silver exposure are discussed.

Engineered Escherichia coli Silver-Binding Periplasmic Protein That Promotes Silver Tolerance

Hall Sedlak, Ruth; Hnilova, Marketa; Grosh, Carolynn; Fong, Hanson; Baneyx, Francois; Schwartz, Dan; Sarikaya, Mehmet; Tamerler, Candan; Traxler, Beth
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /04/2012 Português
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Silver toxicity is a problem that microorganisms face in medical and environmental settings. Through exposure to silver compounds, some bacteria have adapted to growth in high concentrations of silver ions. Such adapted microbes may be dangerous as pathogens but, alternatively, could be potentially useful in nanomaterial-manufacturing applications. While naturally adapted isolates typically utilize efflux pumps to achieve metal resistance, we have engineered a silver-tolerant Escherichia coli strain by the use of a simple silver-binding peptide motif. A silver-binding peptide, AgBP2, was identified from a combinatorial display library and fused to the C terminus of the E. coli maltose-binding protein (MBP) to yield a silver-binding protein exhibiting nanomolar affinity for the metal. Growth experiments performed in the presence of silver nitrate showed that cells secreting MBP-AgBP2 into the periplasm exhibited silver tolerance in a batch culture, while those expressing a cytoplasmic version of the fusion protein or MBP alone did not. Transmission electron microscopy analysis of silver-tolerant cells revealed the presence of electron-dense silver nanoparticles. This is the first report of a specifically engineered metal-binding peptide exhibiting a strong in vivo phenotype...

Comparative Evaluation of Silver-Containing Antimicrobial Dressings on In Vitro and In Vivo Processes of Wound Healing

Hiro, Matthew E.; Pierpont, Yvonne N.; Ko, Francis; Wright, Terry E; Robson, Martin C.; Payne, Wyatt G.
Fonte: Open Science Company, LLC Publicador: Open Science Company, LLC
Tipo: Artigo de Revista Científica
Publicado em 11/10/2012 Português
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Objectives: To compare the in vitro and in vivo effects of silver products on wound healing. Methods: Eight silver products were compared to determine: fibroblast function using fibroblast-populated collagen lattices (FPCLs), fibroblast viability using the Trypan Blue exclusion test, and fibroblast mitochondrial activity using the MTT [yellow tetrazolium salt; 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. In vivo effects of 9 silver products were evaluated utilizing a rat model of contaminated wounds. Serial quantitative bacteriology was performed on tissue biopsies over a 10-day period and serial wound areas were obtained over 12 days. Results: Fibroblast cytotoxicity occurred for all of the silver products evaluated. Remaining viable fibroblasts were insufficient to allow FPCL contraction. Mitochondrial activity of the fibroblasts allowed a separation of the various silver compounds. Actisorb Silver and Silvercel had the greatest viable fibroblast activity, but less than the control. Despite in vitro cytotoxicity, all of the silver products except Contreet Foam and Acticoat Moisture Control accelerated wound healing. Conclusions: Silver-containing dressings appeared to benefit healing of the wounds. Just as in vitro bacterial analyses do not fully predict the effect of an antimicrobial in the in vivo setting...

New potent inhibitors of aquaporins: silver and gold compounds inhibit aquaporins of plant and human origin

Niemietz, C.; Tyerman, S.
Fonte: Elsevier Science BV Publicador: Elsevier Science BV
Tipo: Artigo de Revista Científica
Publicado em //2002 Português
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Silver and gold compounds were tested as potential inhibitors of aquaporins of plant- and human origin. Silver as AgNO₃ or silver sulfadiazine inhibited with high potency (EC₅₀ 1–10 μM) the water permeability of the peribacteroid membrane from soybean (containing Nodulin 26), the water permeability of plasma membrane from roots (containing plasma membrane integral proteins), and the water permeability of human red cells (containing aquaporin 1). Gold as HAuCl₄ was less effective but still inhibited peribacteroid membrane water permeability (EC₅₀=10 μM). Silver and gold are more potent inhibitors of aquaporins than the presently widely used mercury containing compounds.; http://www.elsevier.com/wps/find/journaldescription.cws_home/506085/description#description; Christa M. Niemietz and Stephen D. Tyerman; Copyright © 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V.

Adhesion of gold and silver nanoparticles onto urea-alkylamine inclusion compounds

Lang, Erika; Barrientos, Lorena; Jara Vergara, Paul Sebastian; Sobrados, Isabel; Muñoz, Martín; Yutronic Sáez, Nicolás Ignacio; Campos, Cristian
Fonte: Springer Publicador: Springer
Tipo: Artículo de revista
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Artículo de publicación ISI.; We report the synthesis and characterization of a new series of urea inclusion compounds containing primary alkylamine (octyl, decyl and dodecyl) as guests, as well as the deposition of gold and silver nanoparticles onto the crystalline surface of these complexes. X-ray diffraction confirms the inclusion process of the amine in the urea cavities. The structures determined for the three complexes correspond to a hexagonal channel structure with space group P6(1)22. Alkylamine-urea stoichiometric ratios in all cases satisfy the relationship 1:3n (n = 2 for octylamine and 3 for decylamine and dodecylamine), determined by elemental analysis. The deposition of gold and silver nanoparticles by the magnetron sputtering technique onto microcrystals of the complexes was analyzed by Diffuse Reflectance Spectroscopy, showing characteristic surface plasmon resonance for metal nanoparticles. Transmission electron microscopy demonstrates the presence of metal nanoparticles (MNPs) in a size range between 5 and 60 nm for gold and between 5 and 20 nm for silver, and furthermore, in some cases it shows vestiges of a hexagonal arrangement of the MNPs. X-ray diffraction and IR measurements demonstrate that the basic structure of the matrix remains unchanged after the MNPs adhesion. IR also shows increased broadening and intensity of the characteristic NH2 bending frequencies (1...

Antibacterial, kinetics and bacteriolytic properties of silver(I) pyridinedicarboxylate compounds

Velásquez, Carla; Abarca, Romina; Páez, Maritza; Gómez, Grace; Kogan, Marcelo Javier; Azócar, M. Ignacio
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo de revista
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Artículo de publicación ISI; Antibacterial properties of silver(I)-pyridinedicarboxylate compounds (with Pyridine-2,3-dicarboxylic(Lutidinic acid), pyridine-2,4-dicarboxylic (Quinolinic acid) and pyridine-2,5-dicarboxylic (Isocinchomeronic acid)) were studied against Escherichia coli, Listeria monocytogenes (ISP-65-08), Salmonella typhi and Staphylococcus aureus (ATCC 25923) using kinetics of grown inhibition, viability assays, minimuminhibitory concentration and optical microscopy. The 3 silver compounds were tested toward UV-radiation in order to characterize their light insensitivity for potential medical devices: UV-radiation curable polymers. Photophysical measurements show remarkable differences toward UV-radiation, which were explained based on their polymeric structures with multiple nature bonds between pyridinedicarboxylic ligands and Ag(I) centers. We found a bacteriolytic effect and differences in the antibacterial efficiency depending on the structure of the complexes and the nature of Ag\X (X = oxygen and nitrogen) bonds: AgQuinol N AgLutidin N AgIsocinchom.; This work was supported by FONDECYT (Grant Nos 11080133 and 1100537), CONICYT (Grant: 79090024) FONDAP 15130011 and DICYT (No 021340AG).

Optical properties of silver composite metamaterials

Orbons, Shannon; Freeman, Darren; Luther-Davies, Barry; Gibson, Brant Cameron; Huntington, Shane T; Jamieson, David Norman; Roberts, Ann
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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We present a computational and experimental study investigating the optical properties of nanoscale silver composite metamaterials fabricated by ion beam lithography. Both simulations and experimental results demonstrate high transmission efficiencies in

Highly luminescent gold(I)-silver(I) and cold(I)-copper(I) chalcogenide clusters

Crespo, Olga; Gimeno, M. Concepción; Laguna, Antonio; Larraz, Carmen; Villacampa, M. Dolores
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artículo Formato: 259768 bytes; application/pdf
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12 pages, 9 tables, 9 figures, 4 schemes.-- Supporting information for this article is available on http://www.wiley-vch.de/contents/jc_2111/2007/f600566_s.pdf or from the author.; [EN] The reactions of [AuClL] with Ag2O, where L represents the heterofunctional ligands PPh2py and PPh2CH2CH2py, give the trigoldoxonium complexes [O(AuL)3]BF4. Treatment of these compounds with thio- or selenourea affords the triply bridging sulfide or selenide derivatives [E(AuL)3]BF4 (E=S, Se). These trinuclear species react with Ag(OTf) or [Cu(NCMe)4]PF6 to give different results, depending on the phosphine and the metal. The reactions of [E(AuPPh2py)3]BF4 with silver or copper salts give [E(AuPPh2py)3M]2+ (E=O, S, Se; M=Ag, Cu) clusters that are highly luminescent. The silver complexes consist of tetrahedral Au3Ag clusters further bonded to another unit through aurophilic interactions, whereas in the copper species two coordination isomers with different metallophilic interactions were found. The first is analogous to the silver complexes and in the second, two [S(AuPPh2py)3]+ units bridge two copper atoms through one pyridine group in each unit. The reactions of [E(AuPPh2CH2CH2py)3]BF4 with silver and copper salts give complexes with [E(AuPPh2CH2CH2py)3M]2+ stoichiometry (E=O...

Mechanistic studies of a new nucleated infectious development system using pyridinium salts : Nucleation of silver halide grains by dihydropyridines

Obi, Naoki; Takeuchi, Jun; Kojima, Yasuhiko; Shigemitsu, Yasuo; DiFrancesco, A. Gary; Hailstone, Richard
Fonte: The Society for Imaging Science and Technology (IS&T) Publicador: The Society for Imaging Science and Technology (IS&T)
Tipo: Artigo de Revista Científica
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Photographic properties of 1-benzyl-1,4-dihydronicotinamide (BNAH) are studied for better understanding of the mechanism of the production of high contrast by the infectious development induced by the combination of a pyridinium salt and Metol-ascorbate developer. Treatment of silver bromide emulsion or silver chlorobromo emulsion by BNAH and redox buffer followed by development gave high fog density. It has been suggested that the oxidation product of BNAH by redox buffer nucleates silver halide grains and makes them developable. Results support the hypothesis that dihydropyridine works as an intermediate in the production of high contrast by the infectious development in the presence of a pyridinium salt.; This article may be accessed on the publisher's website (additional fees may apply) at: http://www.imaging.org/store/epub.cfm?abstrid=389

Effect of I– impurity on the efficiency of silver cluster formation on AgBr microcrystal surfaces

Hailstone, Richard
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica Formato: 68438 bytes; application/pdf
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Computer simulation is used to study the effect of iodide impurity on silver cluster formation on AgBr microcrystals. The simulation is based on a nucleation-and-growth model of silver cluster formation in competition with recombination of electrons and holes. The efficiency of silver cluster formation is calculated as a function of microcrystal size and shown to increase with size for the impurity-free control, contrary to experimental data. This behavior is due to a partitioning of the hole between free and trapped states which favors the free side as size increases. As a result, recombination decreases and efficiency increases at large microcrystal size. Iodide impurity decreases efficiency relatively more at larger sizes because it introduces an internal recombination pathway not present in the control simulation. Because of their larger volume-to-surface-area ratios, the larger microcrystals are affected more by this additional recombination pathway than smaller microcrystals.

Manufacture of wood-cement composites from Acacia Mangium: mechanistic study of compounds improving the compatability of Acacia Mangium heartwood with Portland cement

Semple, Kate; Cunningham, Ross; Evans, Philip David
Fonte: Society of Wood Science and Technology Publicador: Society of Wood Science and Technology
Tipo: Artigo de Revista Científica
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46.14%
Numerous inorganic compounds were screened to identify those capable of minimizing the inhibitory effect of Acacia mangium heartwood on the setting of cement. It was hypothesized that the most effective compounds would be ones that could accelerate the hydration of cement and form complexes with inhibitory phenolic extractives found in the heartwood of A. mangium. Our hypothesis proved correct since compounds such as SnCl4, AlCl3, and FeCl3 and/or their ionic species that were able to bond with the phenolic heartwood constituents of A. mangium as well as accelerate cement hydration were generally more effective at strengthening cement hydration in the presence of A. mangium heartwood than compounds that simply accelerated cement hydration. Compounds containing Ni2+, Ag+, Fe3+, and Co2+, that bonded to phenolic constituents of A. mangium heartwood, but lacked the ability to strongly accelerate cement hydration increased maximum hydration temperature attained in wood-cement mixes. The findings suggest that complexation of phenolic heartwood extractives may be an important mechanism by which inorganic compounds reduce the inhibitory effect of certain wood species on the hydration of cement. A combination of compounds including a cost-effective accelerator (such as CaCl2 or MgCl2) and an efficient chelating agent (containing such ions as Al3+...

p-Allyl Cation Cyclisations Initiated by Silver(I)-promoted Electrocyclic Ring Opening of Ring-fused gem-Dibromocyclopropanes Possessing Tethered Nucleophiles: The Influence of Chiral Auxiliaries on the Diastereoselectivity of Cyclisations Involving meso-Substrates

Banwell, Martin; Edwards, Alison; Harvey, Joanne; Hockless, David; Willis, Anthony
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
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46.2%
The epimeric pairs of ring-fused gem-dibromocyclopropanes 17/18 and 27/28, each of which possesses an internal plane of symmetry and has a tethered carbamate moiety with an associated chiral auxiliary, react with silver perchlorate to give, in a diastereoselective manner, the corresponding pairs of azabicyclic compounds, 19/20 and 29/30 respectively.