Reaction Kinetics at Dispersed-Colloid/Solution Interfaces:  Benzophenone Triplet-State Quenching by Methylated Silica Particles

and, Stephanie R. Shield; Harris, Joel M.

doi:10.1021/jp0014420

Cited by 16 publications

(31 citation statements)

References 45 publications

(105 reference statements)

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“…There can be several reasons for the change of the rate constant at an interface, which may be classified in energetic and geometric reasons (relative arrangement, accessibility, and orientation of reactants and the dimensionality of space of their motion) (44,45). The rate constant of the elementary reaction between reactant A in solution and reactant B immobilized at the surface of a spherical particle S , as derived from the Smoluchowski equation (44,46,47), is given by .…”

Section: Discussionmentioning

confidence: 99%

Water/Silica Nanoparticle Interfacial Kinetics of Sulfate, Hydrogen Phosphate, and Dithiocyanate Radicals

Caregnato

Bertolotti

González

et al. 2005

Photochem & Photobiology

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The values of the rate constants for the reactions of the sulfate (2.5 x 10(9) M(-1) s(-1)) and hydrogen phosphate (2.2 x 10(8) M(-1) s(-1)) radicals with silica nanoparticles are obtained by flash photolysis experiments with silica suspensions containing S(2)O(8)(2-) or P(2)O(8)(4-), respectively. The interaction of these radicals with the silica nanoparticles leads to formation of transients, probably adsorbed sulfate and hydrogen phosphate radicals, with absorption maxima at around 320 and 350 nm, respectively. A different mechanism takes place for the interaction of the less oxidizing dithiocyanate radicals with the silica nanoparticles. These radicals selectively react with the dissociated silanol groups of the nanoparticles with a rate constant at 298.2K of 7 x 10(7) M(-1) s(-1) (per mol of SiO(-) groups), and there is no evidence for their adsorption at the surface. All the results are discussed in terms of the Smoluchowski equation and redox potential of the inorganic radicals.

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Section: Discussionmentioning

confidence: 99%

Water/Silica Nanoparticle Interfacial Kinetics of Sulfate, Hydrogen Phosphate, and Dithiocyanate Radicals

Caregnato

Bertolotti

González

et al. 2005

Photochem & Photobiology

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“…The rate constant of the elementary reaction between reactant A in solution and reactant B immobilized at the surface of a spherical particle S as derived from the Smoluchowski equation, is given by Eq. (4) (10,31). …”

Section: Resultsmentioning

confidence: 99%

“…Preparation of the suspensions. To reduce colloidal aggregation (10), 2.5 mL of an aqueous phosphate buffer solution of pH = 6.4 was mixed with the same volume of acetonitrile and used as the solvent for the time‐resolved experiments. The samples were bubbled for 15 min with Ar before the experiments and mixed every 2–3 min during the laser irradiation process.…”

mentioning

confidence: 99%

Generation of Chemisorbed Benzyl Radicals on Silica Nanoparticles

Arce

Rosso

Oliveira

et al. 2010

Photochem & Photobiology

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Functionalized silica nanoparticles (NP) were obtained by esterification of the silanol groups of fumed silica nanoparticles with benzyl alcohol. These particles were characterized by Fourier transform infrared spectroscopy, (13)C and (29)Si NMR spectroscopy, thermogravimetry, total organic carbon, Brunauer-Emmett-Teller analysis, UV-visible spectroscopy, and transmission electron microscopy. NP suspensions in water/acetonitrile mixtures were used as quenchers of benzophenone (BP) phosphorescence in time-resolved experiments at the excitation wavelength of 266 nm. The phosphorescence signals obtained in the presence of the nanoparticles were fitted to biexponential decays. Both decays were accelerated in the presence of increasing amounts of NP. A model, including the reversible adsorption of BP on the NP, which was supported by computer simulations accounts for the observed results. Laser flash-photolysis experiments with excitation at 266 nm of NP suspensions in water/acetonitrile in the presence of BP generated benzyl radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (320 nm) by transient optical techniques.

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“…Assim, a quantificação luminescente de analitos, como filtros solares orgânicos, ácido p-metocinâmico, 2-etil-metil-p-metoxicinamato 182 e derivados da benzofenona; [183][184][185][186][187][188][189][190][191] substâncias estrogênicas, como os derivados do estradiol; e antiinflamatórios não-esteróides (AINEs) como a indometacina, acetamicina, ibuprofeno, e muitos outros fármacos, será plausível dependendo apenas da habilidade do pesquisador para investigar e/ou explorar novas rotas alternativas que permitam quantificar esses analitos através da espectroscopia de luminescência.…”

Section: Considerações Finais E Conclusõesunclassified

Aplicação e avanços da espectroscopia de luminescência em análises farmacêuticas

et al. 2008

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Recebido em 20/10/06; aceito em 30/11/07; publicado na web em 4/9/08 APPLICATION AND ADVANCES IN THE LUMINESCENCE SPECTROSCOPY IN PHARMACEUTICAL ANALYSES. This paper provides a review on the latest advances and applications of the luminescence spectroscopy for the development of pharmaceuticals analyses methods, basically based on the photo-and chemiluminescence. The different forms of the drugs determination on pharmaceuticals through the fluorescence and chemiluminescence are discussed. The analyses include the drugs native fluorescence (liquid and solid-phases); the fluorescence from the oxidizing or reducing forms of the drug; the fluorescence from the chemical derivatization and their photochemistry and hydrolysis reactions. The quenching of luminescence and chemiluminescence generation for the pharmaceutical quantification are also shown. Finally, the trends and future perspectives of the luminescence spectroscopy in the field of the pharmaceutical research are discussed.Keywords: luminescence spectroscopy; drugs; cosmetics analysis; introdução Devido ao progresso contínuo em técnicas e instrumentos, a indústria farmacêutica busca o emprego de metodologias que ofereçam maior sensibilidade, seletividade, robustez, precisão, exatidão e rapidez. Neste sentido, um grande número de equipamentos de cromatografia líquida de alta eficiência (CLAE) com diversos tipos de detecção domina este ramo industrial. Contudo, o advento da sofisticação de instrumentação automatizada de espectrômetros de luminescência poderá resultar em um substancial aumento de aplicações desta técnica instrumental na indústria farmacêutica, principalmente, no que se refere à análise diretamente na matriz do medicamento.A espectroscopia de luminescência é uma ferramenta analítica extremamente sensível e tem sido amplamente aplicada na resolução de problemas que requerem baixos limites de detecção, podendo ser facilmente encontrados na literatura muitos trabalhos mostrando análises ao nível de traços.1-6 A sensibilidade inerente a esta técnica é consideravelmente maior em comparação a outras metodologias, entre elas a espectrofotometria UV/visível, apresentando limites de detecção de até três ordens de grandeza menores, os quais normalmente se encontram na faixa de ng mL -1 , sendo conseqüência do baixo sinal de fundo que as medidas fluorescentes apresentam. Diferentemente do que ocorre no fenômeno da luminescência, nas medidas de absorbância o sinal está associado à atenuação da intensidade de um feixe de radiação por uma espécie absorvente. Nos casos onde a quantidade da espécie é pequena, esta atenuação é menor, tornando assim a detecção da espécie difícil. Outra característica importante da luminescência diz respeito à seletividade, porque espécies com rendimentos quânticos de fluorescência apreciáveis são menos comuns do que substâncias cuja fluorescência não pode ser detectada. Desta forma, moléculas fluorescentes apresentam comprimento de onda característico de excitação e/ou emissão. Adicionalmente, o comprimento de onda de excitação d...

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Reaction Kinetics at Dispersed-Colloid/Solution Interfaces: Benzophenone Triplet-State Quenching by Methylated Silica Particles

Cited by 16 publications

References 45 publications

Water/Silica Nanoparticle Interfacial Kinetics of Sulfate, Hydrogen Phosphate, and Dithiocyanate Radicals

Water/Silica Nanoparticle Interfacial Kinetics of Sulfate, Hydrogen Phosphate, and Dithiocyanate Radicals

Generation of Chemisorbed Benzyl Radicals on Silica Nanoparticles

Aplicação e avanços da espectroscopia de luminescência em análises farmacêuticas

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