Identification of both preequilibrium and diffusion limits for reaction of singlet oxygen, O2(1.DELTA.g), with both physical and chemical quenchers:  variable-temperature, time-resolved infrared luminescence studies

Gorman, A. A.; Hamblett, I.; Lambert, C.; Spencer, Barry B.; Standen, M. C.

doi:10.1021/ja00232a016

Cited by 128 publications

(102 citation statements)

References 2 publications

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“…Both the effect of quencher oxidation potential and the thermodynamic parameters are consistent with the proposed mechanism for singlet oxygen quenching by phenols and amines involving reversible formation of an exciplex with considerable charge transfer character (43,44). An overall mechanism is shown in Scheme 1, emphasising the apparent paradox of 5HT being involved in both formation and quenching of singlet oxygen.…”

Section: Formation and Quenching Of Singlet Oxygen In Solutions Of 5hsupporting

confidence: 80%

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Dad¹,

Bisby²,

Clark³

et al. 2005

Journal of Photochemistry and Photobiology B: Biology

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Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence ('hyperluminescence'). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (λ max 400-420 nm) and another transient absorption with λ max 480 nm and lifetime of 2 μs in deaerated solutions. Based on quenching by oxygen and β-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with λ max 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen ( 1 O 2 *) with a quantum yield of ∼0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 × 10 8 dm 3 mol -1 s -1 . The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin.

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Section: Formation and Quenching Of Singlet Oxygen In Solutions Of 5hsupporting

confidence: 80%

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Dad¹,

Bisby²,

Clark³

et al. 2005

Journal of Photochemistry and Photobiology B: Biology

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“…47,54 As the solution viscosity is increased, however, the magnitude of the bimolecular quenching rate constant decreases indicating that the process of singlet oxygen deactivation is now determined by the rate at which singlet oxygen and NaN 3 encounter each other (i.e., the diffusion-controlled limit). Considering that the apparent intracellular diffusion coefficient for a small molecule such as oxygen can be comparatively small, [25][26][27][28] and that subcellular domains can have apparent viscosities that are comparatively large, 29 the data shown in Figure 5 provide the necessary framework to interpret data recorded upon the quenching of intracellular singlet oxygen by NaN 3 .…”

Section: Scheme 1 General Kinetic Scheme Used To Model Singlet Oxygementioning

confidence: 99%

Singlet Oxygen in a Cell: Spatially Dependent Lifetimes and Quenching Rate Constants

2008

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Singlet molecular oxygen, O 2 (a 1 ∆ g ), can be created in a single cell from ground state oxygen, O 2 (X 3 Σ g -), upon focused laser irradiation of an intracellular sensitizer. This cytotoxic species can subsequently be detected by its 1270 nm phosphorescence (a 1 ∆ g → X 3 Σ g -) with subcellular spatial resolution. The singlet oxygen lifetime determines its diffusion distance and, hence, the intracellular volume element in which singlet-oxygen-initiated perturbation of the cell occurs. In this study, the time-resolved phosphorescence of singlet oxygen produced by the sensitizers chlorin (Chl) and 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-21H,23H-porphine (TMPyP) was monitored. These molecules localize in different domains of a living cell. The data indicate that (i) the singlet oxygen lifetime and (ii) the rate constant for singlet oxygen quenching by added NaN 3 depend on whether Chl or TMPyP was the photosensitizer.These observations likely reflect differences in the chemical and physical constituency of a given subcellular domain (e.g., spatially-dependent oxygen and NaN 3 diffusion coefficients) and, as such, are evidence that singlet oxygen responds to the inherent heterogeneity of a cell.Thus, despite a relatively long intracellular lifetime, singlet oxygen does not diffuse a great distance from its site of production. This is a consequence of an apparent intracellular viscosity that is comparatively large.3

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“…; e 0,64 ± 0,04 eV através de calorimetria fotoacústica resolvida no tempo 46 . Gorman et al 47 , utilizando dados termodinâmicos obtidos através de experimentos com variação de temperatura, obtiveram o valor de 1,0 eV para a energia espectroscópica (ou vertical) do estado triplete de β-caroteno, enquanto Redmond e Lambert, utilizando calorimetria de fotoacústica pulsada e C 60 e C 70 como sensibilizadores obtiveram o valor de 0,84 ± 0,04 eV para a energia do estado triplete relaxado 45 . Para β-ionona foi demonstrado que o estado triplete espectroscópico (ou vertical) sofre relaxamento extremamente rápido para um estado triplete torcido onde acredita-se que a dupla ligação central esteja a 90 0 em relação a sua configuração inicial, neste caso a energia do estado triplete relaxado encontra-se 0,67 eV abaixo da energia do estado triplete vertical inicialmente formado 19,48 .…”

Section: O Estado Triplete De Carotenóidesunclassified

Fotofísica de carotenóides e o papel antioxidante de b-caroteno

Cardoso¹

1997

Quím. Nova

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PHOTOPHYSICS OF CAROTENOIDS AND THE ANTIOXIDANT ROLE OF β-CAROTENE.Carotenoid polyenes play a wide role in nature and their photophysical properties make of these pigments a focus of research in photochemistry, photobiology and photomedicine. Some aspects of the singlet and triplet states and, their interaction with molecular and singlet oxygen and free radicals are briefly reviewed in this article.Keywords: carotenoids; β-carotene; singlet oxygen. DIVULGAÇÃO INTRODUÇÃODe todos os pigmentos naturais, os carotenóides são provavelmente os de maior ocorrência, podendo ser encontrados em animais, plantas e microorganismos. São pigmentos altamente coloridos, insaturados e lipofílicos, apresentando uma variedade de cores desde o amarelo até o vermelho. Os carotenóides são responsáveis pela coloração apresentada por muitos insetos, pássaros, peixes e crustáceos. Por exemplo, são responsá-veis pelas cores do salmão, da truta e do peixe dourado, pela plumagem rosa dos flamingos e, pela mudança de cor da lagosta, quando submetida ao aquecimento, em função da liberação de um carotenóide,astaxantina (I), que está inicialmente associado à uma proteína.E-Mail: cardoso@iq.ufrj.br Quase todos os carotenóides são derivados de tetraterpenos (C 40 ) com o esqueleto hidrocarbônico consistindo em oito unidades isoprenóides. Na natureza, os carotenóides surgem a partir da reação de acoplamento "cauda-cauda" do análogo C20 do pirofosfato de farnesila, levando inicialmente à formação do fitoeno (Figura 1); este por sua vez, através de reações de desidrogenação, ciclização e oxidação, dará origem a uma variedade de pigmentos C 40 , como por exemplo, os abundantes β-caroteno (II) e licopeno (III). Esta classe de pigmentos também inclui certos compostos formados pelo rearranjo deste esqueleto, ou pela remoção formal de parte desta estrutura. Carotenóides formados somente por átomos de carbono e hidrogênio são chamados de carotenos, enquanto os derivados contendo um heteroátomo, como por exemplo oxigênio, são chamados de xantofilas 1 . O carotenóide mais conhecido é o β-caroteno, pigmento responsável pela cor característica da cenoura que corresponde à pró-vitamina A mais abundante e de maior atividade, sendo convertido em vitamina A 1 pela quebra oxidativa da dupla ligação central e posterior redução bioquímica do aldeído (Figura 2). Os carotenóides destacam-se em outras áreas da medicina além da nutricional, sendo utilizados no tratamento de certas doenças de pele, como por exemplo na fotoporfíria eritropoié-tica. Estudos recentes indicam uma possível atividade anticancerígena como também a provável participação como moduladores das respostas imunológicas 2,3 . Na área comercial os carotenóides já há alguns anos vêm sendo utilizados como colorantes e antioxidantes, principalmente em alimentos pois,

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Identification of both preequilibrium and diffusion limits for reaction of singlet oxygen, O2(1.DELTA.g), with both physical and chemical quenchers: variable-temperature, time-resolved infrared luminescence studies

Cited by 128 publications

References 2 publications

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Singlet Oxygen in a Cell: Spatially Dependent Lifetimes and Quenching Rate Constants

Fotofísica de carotenóides e o papel antioxidante de b-caroteno

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