Página 1 dos resultados de 1770 itens digitais encontrados em 0.001 segundos

Substituent effects on the photolysis of methyl 2-carboxylate substituted aliphatic 2H-azirines

Gómez-Zavaglia, Andrea; Kaczor, Agnieszka; Cardoso, Ana L.; Melo, Teresa M. V. D. Pinho e; Fausto, Rui
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
360.25836%
In this study, the UV induced photochemical reactions of two 2H-azirines - methyl 2-chloro-3-methyl-2H-azirine-2-carboxylate (MCMAC) and methyl 3-methyl-2H-azirine-2-carboxylate (MMAC) - isolated in argon matrices are compared. For both compounds, irradiation with [lambda] > 235 nm led to observation of two primary photoprocesses: (a) CC bond cleavage, with production of nitrile ylides (P1-type products), and (b) CN bond cleavage, with production of methylated ketene imines (P2-type products). However, subsequent photoprocesses were found to be different in the two cases. In MCMAC, both primary photoproducts were shown to undergo further reactions: P1-type products decarboxylate, giving [(1-chloroethylidene)imino]ethanide, which bears a CN+C- group (P3-type product); P2-type products decarbonylate, yielding a substituted ylidene methanamine (P4-type product). In MMAC, only P2-type primary photoproducts appeared to react, undergoing decarbonylation or decarboxylation (both reactions leading to P4-type products), whereas P1-type products were found to be non-reactive. The non-observation of any secondary photoproduct resulting from photolysis of P1-MMAC revealed the higher photostability of this species when compared with the corresponding photoproduct obtained from MCMAC.; http://www.sciencedirect.com/science/article/B6TGS-4MSXTBJ-2/1/00b194a96da3576f4b463ba673a96d28

Photolysis of ferric ions in the presence of sulfate or chloride ions: implications for the photo-Fenton process

MACHULEK JR., Amilcar; MORAES, Jose Ermirio F.; OKANO, Laura T.; SILVERIO, Cristina A.; QUINA, Frank H.
Fonte: ROYAL SOC CHEMISTRY Publicador: ROYAL SOC CHEMISTRY
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
364.89363%
The photo-Fenton process (Fe(2+)/Fe(3+), H(2)O(2), UV light) is one of the most efficient and advanced oxidation processes for the mineralization of the organic pollutants of industrial effluents and wastewater. The overall rate of the photo-Fenton process is controlled by the rate of the photolytic step that converts Fe(3+) back to Fe(2+). In this paper, the effect of sulfate or chloride ions on the net yield of Fe(2+) during the photolysis of Fe(3+) has been investigated in aqueous solution at pH 3.0 and 1.0 in the absence of hydrogen peroxide. A kinetic model based on the principal reactions that occur in the system fits the data for formation of Fe(2+) satisfactorily. Both experimental data and model prediction show that the availability of Fe(2+) produced by photolysis of Fe(3+) is inhibited much more in the presence of sulfate ion than in the presence of chloride ion as a function of the irradiation time at pH 3.0.; CNPq; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

Phototransients of 2-ethylaminodiphenylborinate generated by direct photolysis and photosensitization

Santos, Willy G.; Tominaga, Tania T.; Nascimento, Otaciro Rangel; Schmitt, Carla C.; Neumann, Miguel G.
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
368.03363%
Ground state interactions and excited states and transients formed after photolysis and photosensitization of 2-ethylaminodiphenylborinate (2APB) were studied by various techniques. The UV spectrum shows a large absorption band at 235 nm (epsilon = 14,500 M-1 cm(-1)) with a shoulder at 260 nm. The fluorescence spectra show increasing emission intensity with maximum at 300 nm, which shifts to the red up to 10(-3) M concentrations. At higher concentrations, the emission intensity decreases, probably due to the formation of aggregates. UV excitation in deareated solutions shows the formation of two transients at 300 and 360 nm. The latter has a lifetime of 5.7 mu s in ethanol and is totally quenched in the presence of oxygen and assigned to the triplet state of 2APB. The 300 nm peak is not affected by oxygen, has a lifetime in the order of milliseconds, and corresponds to a boron-centered radical species originated from the singlet state. A boron radical can also be obtained by electron transfer from triplet Safranine to the borinate (k(q) = 9.7 x 10(7) M-1 s(-1)) forming the semioxidized form of the dye. EPR experiments using DMPO show that dye-sensitized and direct UV-photolysis of 2ABP renders initially arylboron-centered radicals. (C) 2012 Elsevier B.V. All rights reserved.; FAPESP [Proc. 2009/15998-1]; FAPESP; CNPq [304672/2011-4...

Fotólise de brometos de orto-xilila: um estudo em solventes apolares; Benzylbromides photolysis: an investigation on apolar solvents

Rezende, Daisy de Brito
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 01/12/1994 PT
Relevância na Pesquisa
368.03363%
O presente trabalho tem por objetivo o estudo da fotólise de uma série de brometos de benzila orto-substituídos em solventes apoIares, visando contribuir para a elucidação, tanto dos mecanismos operativos após a homólise de ligações carbono., halogênio em sistemas benzílicos, como das espécies intermediárias envolvidas no processo. Assim sendo, irradiaram-se soluções benzênicas dos compostos α-bromo-o-xileno (MBX), α, α-dibromo-o-xileno (GBX), α, α-dibromo-o-xileno (DBX), α, α α'tribromo-o-xileno (TRBX) e α, α α, α-tetrabromo-o-xileno (TBX) e soluções de MBX e DBX em iso-octano, utilizando-se uma lâmpada de vapor de mercúrio de baixa pressão ( λemissão=254nm). Os produtos foram analisados e identificados por cromatografia gasosa acoplada a espectrometria de massas e confirmados por co-injeção de amostras autênticas, sintetizadas por via térmica. Os rendimentos quânticos dos produtos foram calculados, utilizando-se o leucocianeto de verde-malaquita como actinômetro. A análise dos produtos revelou que a homólise da ligação C-Br é seguida de uma série de reações de abstração de hidrogênio e recombinação de radicais resultando sempre em xilenos menos e mais bromados que o xileno de partida. Benzaldeídos...

Estudo da degradação do diclofenaco em meio aquoso: fotólise vs. fotocatálise heterogênea (TiO2/UV); Study on the degradation of aqueous diclofenac: photolysis vs. heterogeneous photocatalysis (TiO2/UV)

Pinto, Leydy Katherine Ardila
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 23/08/2013 PT
Relevância na Pesquisa
368.03363%
Os produtos farmacêuticos têm sido considerados como um problema ambiental devido à sua entrada contínua e persistência no ecossistema aquático, mesmo em baixas concentrações (µg L-1 e ng L-1). Muitos fármacos têm sido frequentemente determinados em Estações de Tratamento de Esgoto (ETEs), águas superficiais, subterrâneas e de abastecimento, devido à baixa eficiência dos sistemas convencionais de tratamento na eliminação destes compostos. O diclofenaco (DCF), é um Anti-Inflamatório Não Esteróide (AINE) comumente utilizado como analgésico, antiartrítico e antirreumático. Possui uma baixa biodegradabilidade e tem a capacidade de bioacumulação nos tecidos de seres vivos, podendo apresentar efeitos ecotóxicos. Como o DCF pode não ser eficientemente removido pelos tratamentos convencionais de água e esgoto, novos processos têm sido pesquisados para a sua remoção, entre eles os processos oxidativos avançados (POAs). O objetivo deste trabalho foi tratar o DCF sódico aquoso por fotocatálise heterogênea (TiO2/UV). Para isso foi realizado um planejamento fatorial 25 com a finalidade de se determinar os efeitos dos parâmetros reacionais -- dosagem e tipo de fotocatalisador, concentração inicial do fármaco...

Degradação de fármacos em meio aquoso por meio de fotólise e peroxidação fotoassistida.; Degradation of pharmaceuticals compounds in aqueous medium by photolysis and photoassisted peroxidation.

Katsumata, Caroline Pereira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/08/2014 PT
Relevância na Pesquisa
370.30145%
Estudou-se a degradação dos fármacos acetaminofeno (ACT), atenolol (ATL), bezafibrato (BZF), diclofenaco (DIC) e ibuprofeno (IBU) em solução aquosa através de fotólise e peroxidação fotoassistida. As soluções foram caracterizadas antes e após os processos de fotólise e UV/H₂O₂ quanto à degradação dos fármacos e à remoção de carbono orgânico total. Também foi avaliada a degradação por fotólise dos fármacos em uma matriz real (efluente de estação de tratamento de esgoto, ETE). Os experimentos foram realizados em um reator anular com lâmpada de vapor de mercúrio de baixa pressão de 36 ou 75 W e concentrações iniciais de 5 ou 20 mg L⁻¹ de cada fármaco, em mistura e individualmente, no caso dos estudos de fotólise UV. Os resultados mostraram absorção de radiação UV (254 nm) pelo ACT superior à dos demais fármacos (€=8990 L mol⁻¹ cm⁻¹), e comparativamente inferior para o ATL e IBU (€=725 e 1080 L mol⁻¹ cm⁻¹, respectivamente). Não houve degradação por hidrólise após 24h em qualquer pH. O DIC e o BZF degradaram-se mais rapidamente, independentemente do processo fotoassistido. As concentrações de DIC nos experimentos realizados com [DIC]0=5 mg L⁻¹ ficaram abaixo do limite de detecção após 20 minutos de irradiação. Na presença de H H₂O₂ as concentrações dos contaminantes ficaram abaixo do limite de detecção após 50 minutes para concentrações iniciais de 20 mg L⁻¹. Os resultados dos ensaios de toxicidade nos experimentos realizados com a mistura de fármacos mostraram valores de CE50 inferiores aos valores obtidos nos experimentos com a solução dos fármacos individuais. Os valores de TOC apresentaram redução de até 13% ao final de 120 minutos...

Photolysis at long wavelengths of amino acid ester derivatives based on 4-methyl-6-methoxy-2-oxo-2H-naphtho[1,2-b]pyrans

Piloto, Ana M.; Soares, Ana M. S.; Hungerford, Graham; Costa, Susana P. G.; Gonçalves, M. Sameiro T.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
Publicado em 27/07/2011 ENG
Relevância na Pesquisa
360.25836%
Ester derivatives of fused 4-methyl-6-methoxy-2-oxo-2H- naphtho[1,2-b]pyran, using valine and phenylalanine as model bifunctional molecules were synthesised, to assess its applicability as a photocleavable protecting group, for solution phase organic synthesis and in caging applications, at longer wavelengths. The behaviour of the corresponding derivatives towards photolysis was evaluated by irradiation in mixture of HEPES buffer and acetonitrile or methanol, in a photochemical reactor at 350 and 419 nm, followed by HPLC/UV monitoring. Time-resolved fluorescence measurements were used to elucidate the dynamics.; Fundação para a Ciência e a Tecnologia (FCT) -PTDC/QUI/69607/2006, SFRH/BD/61459/2009; Fundo Europeu de Desenvolvimento Regional (FEDER) - REDE/1517/RMN/2005

Photolysis, ozonation and chlorination of flame retardants in water treatment

Salgado, Ricardo; Chanfana, Cátia; Martins, Susana; Galhanas, Dina; Epifâneo, Lisete; Noronha, João Paulo
Fonte: Repositório Comum de Portugal Publicador: Repositório Comum de Portugal
Tipo: Conferência ou Objeto de Conferência
Publicado em /06/2015 ENG
Relevância na Pesquisa
364.89363%
Com o apoio RAADRI.; Flame retardants (FR) are added to different materials to reduce the risk of fire. They save lives, prevent injuries and property losses, and protect the environment by helping to prevent fires. In Western Europe, the average annual growth rate for 2007–2012 for all flame retardant chemicals is expected to be just over 3% in volume terms. The benefits of flame retardants must necessarily be balanced with the risks posed by these high production volume chemicals for human health and ecosystems. Several studies have determined that these compounds can lead to the emergence of several diseases as hormonal problems, neurological deficit, allergies and even cancer. These compounds are difficult to biodegrade in wastewater treatment plants (WWTP), and they can absorb to the sludge and/or be discharged by the WWTP effluent in the river basin. The dynamic of the adsorption equilibrium in the environment through the adsorption soil and sediments can promote the entrance in the urban water cycle, through the surface and groundwater and reach the drinking water system. Many studies reported the detection of FR in surface and groundwater used often for drinking water source. The degradation of triphenylphosphate (TPP), Hexabromocyclododecane (HBCD)...

Laser flash photolysis study of the phenolic hydrogen abstraction by 1,2-aceanthrylenedione triplet

Serra,Ana Cristina S.; Lucas,Nanci C. de; Netto-Ferreira,José Carlos
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2004 EN
Relevância na Pesquisa
360.25836%
The nanosecond laser flash photolysis technique has been used to study the reactivity of 1,2-aceanthrylenedione (1) triplet towards phenols. Using acetonitrile as solvent, the quenching rate constant k q ranged from 3.3 x 10(5) L mol-1s-1 (phenol) to 1.3 x 10(7) L mol-1s-1 (4hydroxyphenol). Phenols with electron donating substituents were more reactive. The kinetic isotope effect (kH/kD) observed for the quenching of 1 with 4-methoxyphenol was 1.5. The Hammett plot for the reaction of the triplet of 1 with phenols gave a reaction constant rho = 1.04 in acetonitrile solution. The low value for the quenching rate constant measured for this triplet with 1,3-cyclohexadiene (k q=2.0 x 10(4) L mol-1s-1) and the diffusion controlled quenching rate constant obtained for beta-carotene suggest that the energy of the lowest triplet state for 1,2-aceanthrylenedione is located between 88 and 219 kJ mol-1.

Laser flash photolysis study of the reaction of 1H-benz[f]indane-1,2,3-trione with olefins

Silva,Monica Teixeira da; Netto-Ferreira,José Carlos
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2004 EN
Relevância na Pesquisa
360.25836%
The photochemistry of 1H-benz[f]indane-1,2,3-trione (1) in the presence of olefins has been examined in benzene solution at room temperature by laser flash photolysis. The triplet excited state of 1 (tau = 3 mus, lambda = 460 and 490 nm, in benzene) is quenched by olefins containing allylic hydrogen with rate constants ranging from 10(5) L mol-1s-1 (for 1,5-hexadiene) to 10(9) L mol-1s-1 (for 2,5-dimethyl-2,4-hexadiene). A comparison of the reactivity of 1 with that of 1,2,3-indantrione (2) shows that a similar mechanism for the quenching by olefins is operating for the two cyclic vicinal triketones and involves essentially the lowest triplet excited state of n,pi* character.

Laser flash photolysis study of the photochemistry of thioxanthone in organic solvents

Rodrigues,Janaina F.; Silva,Francisco de Assis da; Netto-Ferreira,José Carlos
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
360.25836%
The photoreactivity of the triplet excited state of thioxanthone (TX) was investigated employing the laser flash photolysis technique. The wavelength for the absorption maximum and the lifetime of the triplet excited state are solvent dependent. When hydrogen donor solvents were employed, a new band at 410 nm was observed in the triplet absorption spectrum, which was attributed to the ketyl radical derived from thioxantone. Quenching rate constants, k q, ranged from (1.7 ± 0.1) × 10(6) L mol-1 s-1 for toluene to ca. 10(9) L mol-1 s-1 for phenol and its derivatives containing polar substituents, as well as for indole, triethylamine and DABCO.

Phenolic hydrogen abstraction by the triplet excited state of thiochromanone: a laser flash photolysis study

Ribeiro,Alessandra M.; Bertoti,Ada Ruth; Netto-Ferreira,José Carlos
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
360.25836%
Triplet ketones are known to oxidize biological substrates which can lead to damage of several biomolecules such as amino acids, nucleosides and DNA. As part of our systematic study on the interaction between carbonyl compounds and phenols, the triplet reactivity of thiochromanone (1) towards substituted phenols, in acetonitrile, was investigated employing the laser flash photolysis technique. The quenching rate constants ranged from (1.1 ± 0.1) × 10(8) L mol-1 s-1 (4-cyanophenol) to (5.8 ± 1.0) × 10(9) L mol-1 s-1 (hydroquinone). A Hammett plot for the reaction of triplet 1 with phenols containing polar substituents resulted in a reaction constant ρ = -0.90. This negative value observed for the reaction constant ρ is in accord with a mechanism in which the hydrogen transfer from phenols to the triplet carbonyl involves a coupled electron/proton transfer.

Photolysis of the novel inotropes EMD 57033 and EMD 57439: evidence that Ca2+ sensitization and phosphodiesterase inhibition depend upon the same enantiomeric site.

Lee, J. A.; Palmer, S.; Kentish, J. C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1996 EN
Relevância na Pesquisa
273.358%
1. We studied the effects of flash photolysis on the novel enantiomeric cardiac inotropes EMD 57033 (a calcium sensitizer) and EMD 57439 (a phosphodiesterase III inhibitor) in rat isolated ventricular trabeculae. 2. In skinned trabeculae, EMD 57439 had no effect on force production, consistent with lack of an active cyclic AMP system in this preparation. In contrast, EMD 57033 potentiated force at partial and maximal activation. A single flash of near u.v. light given at partial activation (30-70%) reduced force potentiation by 52.4 +/- 5.2%. No effect was produced by flashes in the presence of EMD 57439 or in the absence of either drug. 3. The time course of relaxation induced by EMD 57033 photolysis was indistinguishable from that obtained on deactivating the muscle by rapidly lowering Ca2+ using photolysis of the caged chelator of calcium, diazo-2. 4. In intact, twitching trabeculae, EMD 57033 increased diastolic and peak force and slowed relaxation. These effects were simultaneously reduced by a light flash. In these muscles EMD 57439 reduced force, without affecting the twitch time course. These effects were also reduced by a light flash. 5. The u.v. absorbance spectra of EMD 57033 and EMD 57439 were identical. After photolysis optical density decreased substantially and the peak shifted from 320 nm to 280 nm. 6. The proton n.m.r. spectra of these compounds were identical. The main change post-photolysis was a decrease in the proton signal associated with the enantiomeric carbon atom. 7. This novel manipulation of the molecular structure of EMD 57033 and EMD 57439 within an experiment thus provides direct evidence linking calcium sensitization to a particular molecular structure. The three main effects of the sensitizer on the twitch were simultaneously abolished and may be mechanistically linked. Flash photolysis may be a useful tool for further investigations of the actions of these compounds. In particular...

In Situ Investigation the Photolysis of the PAHs Adsorbed on Mangrove Leaf Surfaces by Synchronous Solid Surface Fluorimetry

Wang, Ping; Wu, Tun-Hua; Zhang, Yong
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 03/01/2014 EN
Relevância na Pesquisa
273.358%
An established synchronous solid surface fluorimetry (S-SSF) was utilized for in situ study the photolysis processes of anthracene (An) and pyrene (Py) adsorbed on the leaf surfaces of Kandelia obovata seedlings (Ko) and Aegiceras corniculata (L.) Blanco seedlings (Ac). Experimental results demonstrated that the photolysis of An and Py adsorbed on the leaf surfaces of two mangrove species under the laboratory conditions, followed first-order kinetics with their photolysis rates in the order of Ac>Ko. In addition, with the same amount of substances, the photolysis rate of An adsorbed on the same mangrove leaf surfaces was much faster than the adsorbed Py. In order to investigate further, the photolysis processes of An and Py in water were also studied for comparison. And the photolysis of An and Py in water also followed first-order kinetics. Moreover, for the same initial amount, the photolysis rate of the PAH in water was faster than that adsorbed on the leaf surfaces of two mangrove species. Therefore, photochemical behaviors of PAHs were dependent not only on their molecular structures but also the physical-chemical properties of the substrates on which they are adsorbed.

Análise da concentração de gases traço (NO NO2 O3) e da fotólise de NO2 na região amazônica na época seca; Analysis of the trace gases (NO NO2 O3) concentration ando f the NO2 photolysis in the amazon region at the dry season

Chagas, Ericka Voss
Fonte: Universidade Federal de Alagoas; BR; Processos de superfície terrestre; Programa de Pós-Graduação em Meteorologia; UFAL Publicador: Universidade Federal de Alagoas; BR; Processos de superfície terrestre; Programa de Pós-Graduação em Meteorologia; UFAL
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
368.03363%
With the objective of understanding the relationship between NO2 photolysis and solar global radiation in the Amazon region, and studying the concentration of the gases NO, NO2 and O3, the data collected from July 02 to 28th, 2001, as part of the campaign from the experiment LBA/CLAIRE-2001 (Large Scale Biosphere- Atmosphere / Cooperative LBA Airborne Regional Experiment - 2001) were analyzed. The photolytic reactions have a critical role controlling the abundance of many atmospherical pollutants, decomposing trace gases (that affect the terrestrial radiation balance) and contributing for their removal from the atmosphere. A significant increase of the NO concentration in the beginning of the morning was observed, whereas the NO2 concentration proved to be higher at night. The O3 concentration increases with the sunrise, with its peak at approximately 14h. The curve of NO2 photolysis (J(NO2)) showed similarity to the Rg curve, with the influence of cloudiness. When the NO2 photolysis begins, an inversion of the magnitude of the NO and NO2 with O3 concentration occurs. The NO2 concentration of varied greatly when analyzing the differences between the clear, partially cloudy and cloudy days.; Fundação de Amparo a Pesquisa do Estado de Alagoas; Com o objetivo de entender as relações entre fotólise de NO2 e radiação solar global na região amazônica...

Cross-bridge kinetics in the presence of MgADP investigated by photolysis of caged ATP in rabbit psoas muscle fibres.

Dantzig, J A; Hibberd, M G; Trentham, D R; Goldman, Y E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1991 EN
Relevância na Pesquisa
273.358%
1. The interaction between MgADP and rigor cross-bridges in glycerol-extracted single fibres from rabbit psoas muscle has been investigated using laser pulse photolysis of caged ATP (P3-1(2-nitrophenyl)ethyladenosine 5'-triphosphate) in the presence of MgADP and following small length changes applied to the rigor fibre. 2. Addition of 465 microM-MgADP to a rigor fibre caused rigor tension to decrease by 15.3 +/- 0.7% (S.E.M., n = 24 trials in thirteen fibres). The half-saturation value for this tension reduction was 18 +/- 4 microM (n = 23, thirteen fibres). 3. Relaxation from rigor by photolysis of caged ATP in the absence of Ca2+ was markedly slowed by inclusion of 20 microM-2 mM-MgADP in the photolysis medium. 4. Four phases of tension relaxation occurred with MgADP in the medium: at, a quick partial relaxation (in pre-stretch fibres); bt, a slowing of relaxation or a rise in tension for 50-100 ms; ct, a sudden acceleration of relaxation; and dt, a final, nearly exponential relaxation. 5. Experiments at varied MgATP and MgADP concentrations suggested that phase at is due to MgATP binding to nucleotide-free cross-bridges. 6. Phase bt was abbreviated by including 1-20 mM-orthophosphate (Pi) in the photolysis medium, or by applying quick stretches before photolysis or during phase bt. These results suggest that phases bt and ct are complex processes involving ADP dissociation...

Effects of aerosols on tropospheric photolysis rates in clear and cloudy atmospheres

Liao, Hong; Yung, Yuk L.; Seinfeld, John H.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 20/10/1999
Relevância na Pesquisa
273.358%
The effect of aerosols on 14 tropospheric photolysis reactions is examined under noncloudy and cloudy sky conditions by using a detailed one-dimensional radiative transfer model. Pure (NH_4)_2SO_4, pure soot, and internal and external mixtures of the two aerosols, as well as mineral dust aerosol, are considered. Nonabsorbing aerosol generally enhances photolysis rates above and in the upper part of the aerosol layer in both noncloudy and cloudy atmospheres, with the enhancement effect reduced in the presence of clouds. In contrast, soot aerosol reduces photolysis rates under both noncloudy and cloudy sky conditions, with the reduction accentuated by a cloud layer. Mixtures of absorbing and nonabsorbing aerosols may produce enhancement or reduction in photolysis rates under clear sky conditions, whereas they generally reduce rates when a cloud is present. In the absence of cloud, sulfate aerosol at urban levels enhances tropospheric average photolysis rates from 11 to 18% for the 14 reactions studied; soot aerosol decreases tropospheric average rates from 6 to 11%. In the presence of a 500-m-thick stratus cloud, sulfate aerosol enhances each of 14 tropospheric average photolysis rates by about 5%; soot aerosol decreases tropospheric average photolysis rates from 9 to 19%.

Direct measurements of NO2 photolysis rates for Mexico City

Castro, Telma; Ruiz-Suarez, Luis; Gay, Carlos; Helguera, Maria; Ruiz-Suarez, Jesus
Fonte: Universidad Nacional Autonoma de Mexico Publicador: Universidad Nacional Autonoma de Mexico
Tipo: Artigo de Revista Científica Formato: 491343 bytes; application/pdf
EN_US
Relevância na Pesquisa
364.89363%
Direct measurements of the rate of NO2 photolysis to NO and O(3P) are reported as photolysis frequencies J (NO2) for Mexico City. These frequencies were measured using a flow reactor, where a known concentration of NO2 was photolysed for different experimental exposure times. UV radiation was measured with an Eppley UV radiometer. Comparisons with calculated values using a radiation transfer model, and Madronich's formula are shown (Refer to PDF file for exact formulas).; The authors want to thank Alfredo Rodriguez for his help in designing and building the equipment used in this research. This work has been supported by Instituto Mexicano del Petroleo and Direccion General de Asuntos del Personal Academico, UNAM.

The d 1 Π g (v=1) Rydberg State of O 2 : Optical-optical Double-resonance and Huggins-band Ozone-photolysis, Resonance-enhanced Multiphoton-ionization Studies with a b 1 Σ + g (v=0)-state Platform

O'Keeffe, P; Ridley, T.; Sheard, H.A.; Lawley, K P; Donovan, R.J.; Lewis, Brenton
Fonte: American Institute of Physics (AIP) Publicador: American Institute of Physics (AIP)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
364.89363%
The d←←b(1,0) band of O2 following Huggins-band photolysis of O3 was explored. Analyses of these REMPI spectra yield, not only the first information on d(v=1) rotational levels with J>29, but also the first estimate of an O2(b-state fragment rotationa

Application of Photolysis in Food Research; Aplicação de Fotólise em Alimentos

Simone Stülp; Univates; Leandro M. de Carvalho; Universidade Federal de Santa Maria
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 07/01/2015 PT
Relevância na Pesquisa
364.89363%
This article aims to discuss relevant aspects related to photolysis and its relation to the food area. For this purpose, topics relating to different types of radiation are shown, the use of radiation incidence on the preparation and pre-treatment of analytical samples, the application of photolysis studies stability of foods and beverages (wine for example), and the use of photochemistry in wastewater treatment, specially effluent from the food industry. DOI: 10.5935/1984-6835.20150014; O presente artigo tem por objetivo discutir aspectos relevantes relacionados à fotólise e sua relação com a área de alimentos. Para tanto, serão apresentados tópicos relativos aos diferentes tipos de radiação, a utilização da incidência de radiação no preparo e pré-tratamento de amostras analíticas, a aplicação da fotólise em estudos de estabilidade de alimentos e bebidas, dentre estes o vinho, e a utilização da fotoquímica no tratamento de efluentes, sendo que neste artigo serão demonstrados resultados de efluentes provenientes do setor alimentício. DOI: 10.5935/1984-6835.20150014