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Effects of Synthesis Conditions on the Nanostructure of Hybrid Sols Produced by the Hydrolytic Condensation of (3-Methacryloxypropyl)trimethoxysilane

SANTILLI, C. V.; SARMENTO, V. H. V.; DAHMOUCHE, K.; PULCINELLI, S. H.; Craievich, Aldo Felix
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
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Polysilsesquioxanes containing methacrylate pendant groups were prepared by the sol-gel process through hydrolysis and condensation of (3-methacryloxypropyl)trimethoxysilane (MPTS) dissolved in a methanol/methyl methacrylate (MMA) mixture. The effects of different water, MMA, and methanol contents, as well as of pH, on the nanoscopic and local structures of the system, at advanced stages of the condensation reaction, were studied by small-angle X-ray scattering (SAXS) and (29)Si nuclear magnetic resonance (NMR) spectroscopy, respectively. SAXS results indicate that the nanoscopic features of the hybrid sol could be described by a hierarchical model composed of two levels, namely (i) silsesquioxane (SSQO) nanoparticles Surrounded by the methacrylate pendant groups and the methanol/MMA mixture. and (ii) aggregation zones or islands containing correlated SSQO nanoparticles, embedded in the liquid medium. The (29)Si NMR results Show that the inner Structures of SSQO nanoparticles produced at pH 1 and 3 were built Up of polyhedral structures. mainly cagelike octamers and small linear oligomers, respectively. Irrespective of MMA and methanol contents, for a [H(2)O]/[MPTS] ratio higher than or equal to 1, the SSQO nailoparticles produced at pH I exhibit an average condensation degree (CD approximate to 69-87%) and average radius of gyration (R(g) approximate to 2.5 angstrom) larger than those produced at pH 3 (CD approximate to 48-67% and R(g) approximate to 1.5 angstrom). Methanol appears to act as a redispersion agent...

A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

CARMO, Devaney Ribeiro do; PAIM, Leonardo Lataro; METZKER, Gustavo; DIAS FILHO, Newton Luiz; STRADIOTTO, Nelson Ramos
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
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This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E(1/2)(ox)) = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v = 20 mV s(-1)). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 x 10(-4) to 4.0 x 10(-3) mol L(-1) for the determination of nitrite, with a detection limit of 2.1 x 10(-4) mol L(-1) and the amperometric sensitivity of 8.04 mA/mol L(-1). (C) 2010 Elsevier Ltd. All rights reserved.; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[Proc. 03/12882-6]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[Proc. 01/04494-0]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[Proc. 92/3515-3]

Estudo da imobilização de catalisadores metalocênicos sobre sílicas modificadas com silsesquioxanos

Bianchini, Daniela
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
POR
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Neste estudo, silsesquioxanos (POSS) foram empregados como suportes ou modificadores de sílica em sistemas catalíticos heterogêneos. Os silsesquioxanos são constituídos por estruturas octaédricas (T8), nonaédricas (T9(OH)) e decaédricas (T10) contendo grupos orgânicos volumosos e ramificados ligados aos átomos de silício. Os silsesquioxanos foram impregnados com catalisadores metalocênicos, os quais foram imobilizados também sobre sílicas previamente modificadas com POSS. As interações metaloceno-POSS, POSS-sílica e metaloceno-POSS-sílica foram investigadas por diversas técnicas de caracterização, tais como FT-IR-ATR, FT-IR-PAS, FT-IR-IES, DRIFTS, Raman, TGA, RMN no estado sólido, XPS e RBS.Os resultados mostraram que o catalisador metalocênico fixa-se sobre o silsesquioxano através de ligações químicas com o álcool do grupo orgânico, gerando segmentos Zr-O-C e espécies de hidrocloreto de amina. Além disso, os heteroátomos presentes nos grupos orgânicos do POSS podem se coordenar ao metaloceno. A imobilização do metaloceno sobre a sílica modificada com POSS resulta na formação de duas espécies catalíticas, uma delas imobilizada sobre o silsesquioxano e a outra imobilizada diretamente sobre a superfície da sílica. As sílicas solúveis (SS)...

An innovative series of layered nanostructured aminoalkylsilica hybrid material

Trindade, Carolina de Moraes da; Stoll, Gabriela Costa; Pereira, Altair Soria; Costa, Tania Maria Haas; Benvenutti, Edilson Valmir
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
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Uma nova série de amostras de material híbrido à base de sílica, contendo o grupo catiônico amoniopropil ligado na forma pendente, foi obtida usando-se o método sol-gel de síntese, variando-se a razão molar entre o precursor inorgânico e o precursor orgânico. A análise termogravimétrica mostrou que as amostras são termicamente estáveis até 260 °C. Os resultados obtidos por difratometria de raios X, microscopia eletrônica de transmissão, ressonância magnética nuclear de 29Si e análise elementar são compatíveis com o modelo estrutural de camadas de silsesquioxano com distâncias basais de até 5,4 nm, contendo sílica amorfa no espaço entre as camadas.; An innovative series of silica-based hybrid materials containing pendant cationic ammoniumpropyl groups was obtained using the sol-gel method, by varying the molar ratio of the inorganic and organic precursors. Thermogravimetric analysis showed that samples were thermally stable up to 260 °C. Results obtained by X-ray diffractometry, transmission electron microscopy, 29Si nuclear magnetic resonance and elemental analysis were compatible with a silsesquioxane layered structural model showing basal distances up to 5.4 nm, containing amorphous silica in the interlayer space.

Materiais híbridos à base de sílica obtidos pelo método sol-gel; Silica based hybrid materials obtained by the sol-gel method

Benvenutti, Edilson Valmir; Moro, Celso Camilo; Costa, Tania Maria Haas; Gallas, Marcia Russman
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
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This review deals with silica based hybrid materials obtained by the sol-gel method. It involves concepts, classifications and important definitions regarding the sol-gel method that allows obtaining materials with organic and inorganic components dispersed in a molecular or nanometric level. We discuss the properties and characteristics of hybrid materials related to experimental synthesis conditions. We devote a special attention to the nanostructured materials, where the self-organization is imposed by the organic component. Finally, we present some important applications of these materials based on their specific properties.

Caracterização viscosimétrica de nanocompósitos híbridos PS/POSS; Viscometric characterization of PS/POSS hybrid nanocomposites

Bianchi, Otávio; Repenning, Gustavo Borcelli; Mauler, Raquel Santos; Oliveira, Ricardo Vinicius Bof de; Canto, Leonardo Bresciani
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
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Nanocompósitos híbridos de poliestireno (PS) e poliedros oligoméricos silsesquioxanos (POSS) com diferentes composições e graus de hibridização foram obtidos por processamento reativo no estado fundido utilizando-se peróxido de dicumila (DCP) como iniciador, na presença ou não de estireno como agente de transferência de radical. Os materiais foram caracterizados viscosimetricamente por cromatografia de permeação em gel (GPC) usando detecção tripla por espalhamento de luz, viscosimetria e índice de refração. As amostras PS/POSS processadas com estireno apresentaram maiores valores de massa molar ponderal média (M) e menores valores de polidispersão (M /M), devido ao maior grau de conversão da reação de hibridização do PS-POSS (28-40%) e do menor grau de degradação (cisão) das cadeias do PS, quando comparadas com amostras PS/POSS processadas sem estireno nas quais o grau de conversão ficou em torno de 24-28%. Para os sistemas PS e PS/POSS em solução com THF, os parâmetros da equação de Mark-Houwink-Sakurada (MHS), α Ξ 0,7 e log K Ξ –3,5 a –3,9 e os valores dos parâmetros de interação polímero-solvente, χij Ξ 0,49, não apresentaram diferenças significativas com relação aos tamanhos moleculares. Por outro lado...

Uso da metodologia sol-gel na preparação de materiais amorfos e nanoestruturados à base de sílica contendo grupos orgânicos com propriedades específicas

Grando, Sílvia Regina
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
POR
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Nesse trabalho foram desenvolvidos novos materiais à base de sílica, amorfos e nanoestruturados, pelo método sol-gel de síntese e a adição de precursores com grupos funcionais específicos. Inicialmente foi investigado o comportamento fotofísico de benzazolas dispersas em xerogéis híbridos com diferentes hidrofobicidades, preparados com a adição de diferentes porcentagens molares do precursor dimetildimetoxisilano (DDMS). Nos espectros normalizados de emissão de fluorescência do corante 2-(5’-amino-2’-hidroxifenil) benzimidazol (5-AHBI) disperso nos xerogéis híbridos foram observadas duas bandas, uma delas atribuída a emissão normal (N*) e a outra atribuída a emissão pelo mecanismo de transferência protônica intramolecular no estado excitado - ESIPT (E*), com deslocamento de Stokes próximo a 150 nm. Nos híbridos contendo o corante 2-(5’-amino-2’-hidroxifenil) benzotiazol (5-AHBT), observou-se uma banda bastante alargada em que a emissão de fluorescência mostrou-se dependente da polaridade da matriz, com a emissão máxima variando de 496 para 533 nm com o aumento da porcentagem de DDMS nas sínteses. Sílicas mesoporosas ordenadas do tipo MCM-41 e SBA-15 foram sintetizadas e os resultados de difração de raios X (XRD) e das isotermas de adsorção-dessorção de N2 desses materiais mostraram organização hexagonal de poros...

Structure of copper(II) complexes adsorbed on functionalized polyhedral oligomeric silsesquioxane

Dias Filho, Newton Luiz; Costa, Reginaldo Mendonca; Schultz, Mario Sergio
Fonte: Elsevier B.V. Sa Publicador: Elsevier B.V. Sa
Tipo: Artigo de Revista Científica Formato: 2314-2320
ENG
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The 3-amino-1,2,4-triazole-modified silsesquioxane nanoplatforms have been prepared and characterized. The silsesquioxane nanocages readily react with CuX(2) in aqueous solution to form copper complex-substituted silsesquioxanes. Adsorption isotherms of CuX(2) from aqueous solution were studied at 25 degrees C. The electronic and ESR spectral parameters indicated that the copper ion is in a distorted-tetragonal symmetry field. (C) 2007 Elsevier B.V. All rights reserved.

Self-Structuring of Lamellar Bridged Silsesquioxanes with Long Side Spacers

Fernandes, Mariana; Nobre, Sonia S.; Xu Qinghong,; Carcel, Carole; Cachia, Jean Nicolas; Cattoen, Xavier; Sousa, Jose M.; Ferreira, Rute A. S.; Carlos, Luis D.; Santilli, Celso V.; Man, Michel Wong Chi; Bermudez, Veronica de Zea
Fonte: Amer Chemical Soc Publicador: Amer Chemical Soc
Tipo: Artigo de Revista Científica Formato: 10877-10891
ENG
Relevância na Pesquisa
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Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(11)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si- (CH(2))(10)-Y(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) Cm materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils)...

Adsorption of heavy metal ions and epoxidation catalysis using a new polyhedral oligomeric silsesquioxane

Soares, Isaac V.; Vieira, Eduardo G.; Filho, Newton L.D.; Bastos, Andréa C.; da Silva, Niléia C.; Garcia, Edemir F.; Lima, Lucélia Julia A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 405-414
ENG
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The objective of this research was the preparation of a silsesquioxane functionalized with eight chloropropyl chains (T8-PrCl) and of a new derivative functionalized with a pendant linear chain (2-amino-1,3,4-thiadiazole - ATD; T8-Pr-ATD). The two nanostructured materials were characterized by 13C and 29Si NMR, FTIR and elemental analysis. The new nanostructured material, octakis[3-(2-amino-1,3,4-thiadiazole)propyl] octasilsesquioxane (T8-Pr-ATD), was tested as a ligand for transition-metal ions with a special attention to adsorption isotherms. The adsorption was performed using a batchwise process and the organofunctionalized surface showed the ability to adsorb the metal ions Cu (II), Co (II), and Ni (II) from water and ethanol. The adsorption isotherms were fitted by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) model. The kinetics of adsorption of metals were performed using three models such as pseudo-first order, pseudo-second order and Elovich. The Langmuir and Elovich models were the most appropriate to describe the adsorption and kinetic data, respectively. Furthermore, the T8-Pr-ATD was successfully applied to the analysis of environmental samples (river and sea water). Subsequently, a new nanomaterial was prepared by functionalization of the T8-Pr-ATD with a Mo (II) organometallic complex (T8-Pr-ATD-Mo). Only a few works in the literature have reported this type of substitution...

Nanocompósitos baseados no sistema epoxídico DEGBA/DETA modificado com uma resina epoxídica de silsesquioxano

Rangel, Sibeli Amália
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 70 f. : il.
POR
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Ciência dos Materiais - FEIS; Polímeros epoxídicos são um dos mais importantes tipos de polímeros termorrígidos, extensivamente usados como adesivos e estruturas. Em reações epoxídicas são convertidos em um sistema termorrígido pela ação de agentes de cura. Tais reações químicas provocam uma mudança no estado físico do material, partindo de um líquido viscoso para um gel e se transformando em um material vitrificado. Os termorrígidos apresentam excelentes propriedades, tais como: alta tensão de ruptura e módulo de Young, fácil processamento, resistência térmica e química, e estabilidade dimensional. Entretanto, são quebradiços e possuem baixa resistência a propagação de trincas. Para superar estes inconvenientes, muitos tipos de compósitos de polímero com reforço foram desenvolvidos, em que as resinas epoxídicas são reforçadas com agentes modificadores, tais como enchimentos, oligômeros poliédricos de silsesquioxanos, dendrímeros, etc. Oligômeros poliédricos de silsesquioxanos (POSS), (RSiO1.5)n com n = 4, 6, 8, 10..., são nanoplataformas organo-funcionalizadas com 1 a 8 grupos reativos ou não reativos (R) ligados aos oito vértices possíveis do silsesquioxano cúbico. POSS octaédrico (n = 8) são os membros mais importantes desta família. No POSS...

Self-structuring of lamellar bridged silsesquioxanes with long side spacers

Fernandes, M.; Nobre, S. S.; Xu, Q. H.; Carcel, C.; Cachia, J. N.; Cattoen, X.; Sousa, J. M.; Ferreira, R. A. S.; Carlos, L. D.; Santilli, C. V.; Man, M. W. C.; Bermudez, V. D.
Fonte: ACS Publicador: ACS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
276.73324%
Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(11)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si- (CH(2))(10)-Y(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) Cm materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils)...

Structure–property relationships in hybrid dental nanocomposite resins containing monofunctional and multifunctional polyhedral oligomeric silsesquioxanes

Wang, Weiguo; Sun, Xiang; Huang, Li; Gao, Yu; Ban, Jinghao; Shen, Lijuan; Chen, Jihua
Fonte: Dove Medical Press Publicador: Dove Medical Press
Tipo: Artigo de Revista Científica
Publicado em 10/02/2014 EN
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Organic-inorganic hybrid materials, such as polyhedral oligomeric silsesquioxanes (POSS), have the potential to improve the mechanical properties of the methacrylate-based composites and resins used in dentistry. In this article, nanocomposites of methacryl isobutyl POSS (MI-POSS [bears only one methacrylate functional group]) and methacryl POSS (MA-POSS [bears eight methacrylate functional groups]) were investigated to determine the effect of structures on the properties of dental resin. The structures of the POSS-containing networks were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Monofunctional POSS showed a strong tendency toward aggregation and crystallization, while multifunctional POSS showed higher miscibility with the dimethacrylate monomer. The mechanical properties and wear resistance decreased with increasing amounts of MI-POSS, indicating that the MI-POSS agglomerates act as the mechanical weak point in the dental resins. The addition of small amounts of MA-POSS improved the mechanical and shrinkage properties. However, samples with a higher MA-POSS concentration showed lower flexural strength and flexural modulus, indicating that there is a limited range in which the reinforcement properties of MA-POSS can operate. This concentration dependence is attributed to phase separation at higher concentrations of POSS...

Elektrochemie von redoxaktiv modifizierten Silsesquioxanen; Electrochemistry of redox-active modified silsesquioxanes

Reißig, Thomas
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Masterarbeit
DE_DE
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Ein mit acht Ferroceneinheiten modifiziertes Silsesquioxan wurde bezüglich seines Redox-Verhalten mit Hilfe elektroanalytischer Messmethoden - Cyclovoltammetrie, Chronoamperometrie, Differentialpulsvoltammetrie – untersucht. Bei allen elektrochemischen Messungen diente Dimethylsulfoxid (DMSO) als Lösungsmittel und Ferrocen als Referenzsubstanz. Die Cyclovoltammogramme des ferrocenmodifizierten Silsesquioxans zeigten zwei Signale: ein vorgelagertes adsorptionskontrolliertes Signal und ein diffusionskontrolliertes Hauptsignal. Es werden acht Elektronen bei ähnlichen Potentialen unabhängig voneinander übertragen.; A silsesquioxane modified with eight ferrocene units was examined with respect to its redox behaviour by electroanalytical methods – cyclic voltammetry, chronoamperometry, differential pulse voltammetry. For all electrochemical measurements dimethylsulfoxid (DMSO) served as a solvent and ferrocene as a reference substance. The shape of the cyclic voltammogramms of the ferrocene-modified silsesquioxanes showed two signals: a preceding adsorption-controlled signal and a diffusion-controlled main signal. Eight electrons are transmitted independently of each other at similar potentials.

Accessibility studies of ionic and non-ionic fluorophores embedded in sol-gel materials and new functionalised polyhedral silsesquioxanes; Zugänglichkeitsstudien über in Sol-Gel-Materialien eingebundene ionische und nichtionische Fluorophore sowie neue funktionalisierte polyhedrale Silsesquioxane

Ruiz Abad, David
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
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The knowledge about the diffusion of products and educts into and out of porous materials is of high importance for the development of new porous sol-gel processed hybrid catalysts. Therefore the accessibility of active centers embedded in sol-gel materials was studied by luminescence spectroscopy. Modified tris(2,2’- bipyridine)ruthenium(II) and pyrenemethanol were co-condensed with tetramethoxysilane (TMOS) in a buffer system. The buffer enforces the pH to remain constant during the sol-gel process which keeps the hydrolysis and condensation kinetics constant. The resulting material was divided into four parts which were dried in different ways, obtaining four sol-gel materials. The functionalized materials were characterized by 29Si solid state NMR spectroscopy to provide the degree of condensation, by BET measurements that supply information about the porosity, the surface area of the material and finally by luminescence studies which offer information about the accessibility of the fluorophores. The accessibility of the fluorophores in the sol-gel materials, quenched by different compounds (oxygen, anthracene and N,N-diethylaniline) and swollen in four diverse organic solvents of various polarities (MeOH, MeCN, n-hexane and THF) are strongly reduced compared to the accessibility of the same active centers attached to the surface of 200 nm nanoparticles as well as compared to the fluorophores dissolved in diverse solvents. Moreover the accessibility of the active centers in the sol-gel material strongly depends on the size and polarity of the quenching molecule and on the solvent used. In a second project new polyhedral oligomeric silsesquioxanes (POSS) were synthesized and functionalized with active centres. The advantage of these functionalized POSS is their solubility in organic solvents which allows them to be characterized by different spectroscopic methods. Therefore they serve as model systems to gain more insight into the interaction of catalysts with the surface of silica matrices at a molecular level and the structure and reactivity of the heterogeneous catalyst.; Die Kenntnis über das Diffusionsverhalten von Edukten und Produkten in porösen Materialien ist von außerordentlicher Bedeutung für die Entwicklung neuer Sol-Gel-prozessierter Hybridkatalysatoren. Daher wurde in dieser Arbeit die Zugänglichkeit von aktiven Zentren...

Calcium(II)-sensitive and Silsesquioxane-based Contrast Agents for Magnetic Resonance Imaging - Synthesis, Characterisation and Mechanistic Studies; Calcium(II)-sensitive und Silsesquioxan-basierte Kontrastmittel für die Magnetresonanztomographie - Synthese, Charakterisierung und Mechanistische Untersuchungen

Henig, Jörg
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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The evolvement of magnetic resonance imaging (MRI) to one of the most powerful tools in medical diagnosis is strongly related to the development of paramagnetic contrast agents (CAs). Today, almost 30% of MRI investigations use a contrast agent. These are mainly gadolinium based extracellular perfusion agents which distribute non-specifically throughout plasma and interstitial spaces. The next generation of CAs is aimed at a more efficient and more specific imaging. As calcium(II) plays an important role in regulating a great variety of neuronal processes, there is a strong interest to generate gadolinium complexes which can act as calcium-sensors in functional magnetic resonance imaging (fMRI). In this work the mechanistic aspects of the calcium sensitivity of a series of DO3A-based lanthanide chelates, bearing an alkyl aminobisphosphonate group (alkyl = propyl – hexyl) as the additional coordination site, were investigated. Instead of increasing, as observed for other calcium sensitive CAs, the longitudinal relaxivity r1 (the paramagnetic longitudinal proton relaxation rate enhancement referred to one millimolar concentration of Gd3+) of these systems decreases with increasing calcium concentration. This might be an advantage in instances where a decreased ion concentration should be transformed into an image. For the investigation (time-resolved) luminescence spectroscopy as well as NMR based techniques like 1H-T1 measurements...

Silsesquioxanes and Silica Nanoparticles as Platforms for Fluorine and Gadolinium Based Contrast Agents for Magnetic Resonance Imaging; Silsesquioxane und Silika-Nanopartikel als Grundlagen für Fluor- und Gadolinium-basierte Kontrastmittel für die Magnetresonanz-Bildgebung

Kocak, Filiz
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertação
EN
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276.73324%
Magnetic resonance imaging (MRI) is an important diagnostic tool for the imaging of soft tissues. The non-invasive technique of MRI allows for the detection of tumors, infections and injuries at an early stage. New opportunities for medical diagnosis and magnetic resonance (MR) imaging techniques are offered with the use of hybrid nanomaterials. The functionalization of a nano-sized material, e.g. with paramagnetic Gd(III) chelate complexes for 1H imaging or with 19F containing molecules for 19F imaging leads to a high concentration of contrast agents, which can be obtained at low volumes. In the first part of the work T8-silsesquioxanes were functionalized with polyorganofluorinated groups (PFG). By different synthetic pathways highly symmetrical polyorganofluorinated POSS cubes (PF-POSS) which generate a sharp singlet in the 19F spectrum were obtained. The properties of the PF-POSS cubes in dependency of their PFG structures, the resulting solubility and their hydrolysis stability were investigated. Additionally, in vitro measurements as well as post mortem experiments were performed for chosen examples. In the second part of this work the size dependent properties of spherical and monodisperse silica nanoparticles (SNPs) with diameters of about 15...

Modulating the Photoluminescence of Bridged Silsesquioxanes Incorporating Eu(3+)-Complexed n,n '-Diureido-2,2 '-bipyridine Isomers: Application for Luminescent Solar Concentrators

Graffion, Julien; Cattoen, Xavier; Man, Michel Wong Chi; Fernandes, Vasco R.; Andre, Paulo S.; Ferreira, Rute A. S.; Carlos, Luis D.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Artigo de Revista Científica
ENG
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Two new urea-bipyridine derived bridged organosilanes (P5 and P6) have been synthesized and their hydrolysis-condensation under nucleophilic catalysis in the presence of Eu(3+) salts led to luminescent bridged silsesquioxanes (M5-Eu and M6-Eu). An important loading of Eu(3+) (up to 11%(w)) can be obtained for the material based on the 6,6'-isomer. Indeed the photoluminescence properties of these materials, that have been investigated in depth (photoluminescence (PL), quantum yield, lifetimes), show a significantly different complexation mode of the Eu(3+) ions for M6-Eu, compared with M4-Eu (obtained from the already-reported 4,4'-isomer) and M5-Eu. Moreover, M6-Eu exhibits the highest absolute emission quantum yield value (0.18 +/- 0.02) among these three materials. The modification of the sol composition upon the addition of a malonamide derivative led to similar luminescent features but with an increased quantum yield (026 +/- 0.03). In addition, M6-Eu can be processed as thin films by spin-coating on glass substrates, leading to plates coated by a thin layer (similar to 54 nm) of Eu(3+)-containing hybrid silica exhibiting one of the highest emission quantum yields reported so far for films of Eu(3+)-containing hybrids (0.34 +/- 0.03) and an interesting potential as new luminescent solar concentrators (LSCs) with an optical conversion efficiency of similar to 4%. The ratio between the light guided to the film edges and the one emitted by the surface of the film was quantified through the mapping of the intensity of the red pixels (in the RGB color model) from a film image. This quantification enabled a more accurate estimation of the transport losses due to the scattering of the emitted light in the film (0.40)...

Modulating the photoluminescence of bridged silsesquioxanes incorporating Eu(3+)-complexed n,n '-diureido-2,2 '-bipyridine isomers: application for luminescent solar concentrators

Graffion, Julien; Cattoën, Xavier; Man, Michel Wong Chi; Fernandes, Vasco R.; André, Paulo S.; Ferreira, Rute A. S.; Carlos, Luís D.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
276.73324%
Two new urea-bipyridine derived bridged organosilanes (P5 and P6) have been synthesized and their hydrolysis-condensation under nucleophilic catalysis in the presence of Eu(3+) salts led to luminescent bridged silsesquioxanes (M5-Eu and M6-Eu). An important loading of Eu(3+) (up to 11%(w)) can be obtained for the material based on the 6,6'-isomer. Indeed the photoluminescence properties of these materials, that have been investigated in depth (photoluminescence (PL), quantum yield, lifetimes), show a significantly different complexation mode of the Eu(3+) ions for M6-Eu, compared with M4-Eu (obtained from the already-reported 4,4'-isomer) and M5-Eu. Moreover, M6-Eu exhibits the highest absolute emission quantum yield value (0.18 +/- 0.02) among these three materials. The modification of the sol composition upon the addition of a malonamide derivative led to similar luminescent features but with an increased quantum yield (026 +/- 0.03). In addition, M6-Eu can be processed as thin films by spin-coating on glass substrates, leading to plates coated by a thin layer (similar to 54 nm) of Eu(3+)-containing hybrid silica exhibiting one of the highest emission quantum yields reported so far for films of Eu(3+)-containing hybrids (0.34 +/- 0.03) and an interesting potential as new luminescent solar concentrators (LSCs) with an optical conversion efficiency of similar to 4%. The ratio between the light guided to the film edges and the one emitted by the surface of the film was quantified through the mapping of the intensity of the red pixels (in the RGB color model) from a film image. This quantification enabled a more accurate estimation of the transport losses due to the scattering of the emitted light in the film (0.40)...

Tin Silsesquioxanes as Models for the “Open” Site in Tin-Containing Zeolite Beta

Brand, Stephen K.; Labinger, Jay A.; Davis, Mark E.
Fonte: Wiley Publicador: Wiley
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 05/11/2015
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287.69514%
The use of biomass as a resource to produce value-added products has garnered significant interest as a means of reducing reliance on fossil fuels. This task is complicated by the complex, highly functionalized nature of abundant biomass derivatives, such as glucose. Tin-containing zeolite Beta (Sn-Beta) can selectively isomerize glucose to fructose through a 1,2-intramolecular hydride shift (1,2-HS) or selectively produce mannose through a 1,2-intramolecular carbon shift (1,2-CS) by titration of the silanol groups with sodium (Na-Sn-Beta). To understand the structure–activity relationships between the conditions of the active sites in the zeolite, two molecular models (tin silsesquioxanes) of the tin sites in the zeolite were synthesized. Tin silsesquioxanes that contain an octahedral tin site with and without an adjacent silanol group selectively form fructose through a 1,2-HS and mannose through a 1,2-CS, respectively, and provide further evidence for the nature of the active sites in Sn-Beta.