ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06952.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen (1Δgand1Σg+) were calculated for a number of conditions. For the gas phase we estimateKeq(1Δg3Σg‐) = 1.67 exp(‐94.31 KJ/RT) andKeq(1Σg+/3Σg‐) = 0.33 exp(‐157.0 KJ/RT). The calculated rate constants for the3Σg+→1Δgtransition of O2at 25°C varied from 2.5 × 10‐11s‐1in water to 4.8 × 10‐16s‐1in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06953.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06954.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The use of cyclic 1,3‐dienes and polycyclic aromatic hydrocarbons as xenobiotic substrates for the interception of electronically excited (singlet) molecular oxygen (1O2) in biological systems is reviewed and criticized, and the possibility of utilization of reactive endogenous substrates for1O2interception is considered. The common sterols, cholesterol, 5α‐cholest‐7‐en‐3β‐ol, and 5α‐lanost‐8‐en‐3β‐ol each give oxidation products with1O2different from those with ground‐state molecular oxygen that can be distinguished from one another by

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06955.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Results concerning Rose Bengal sensitized photoxidation of 2,7‐dimethyl‐2,6‐octadiene (A) are discussed. This diolefin may be considered as a model molecule of polyisoprene of polymerization number two with 1,4‐4,1 addition mode.All the mono‐ and dihydroperoxides apt to occur are actually obtained. One of the occurring hydroperoxides, 2,7‐dimethyl‐dihydroperoxy‐3,5‐octadiene, which has the structure of a conjugated diene, does not lead to an endoperoxide. This is contrary to Kaplan and Kelleher's hypothesis. On the other hand, no trihydroperoxide forms as a result of further addition of singlet oxygen (1O2).A complete kinetic study has allowed us to determine the rate constants of all the reactions which take place. The reactivity of (A) is twice that of 2‐methyl‐2‐pentene and the addition of1O2to one of the double bonds of (A) induces deactivation of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06956.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Since 1972 the protective (quenching) effect of N3‐and the enhancing effect of D2O have been used in combination to demonstrate1O2(1Δg) as the major reactive intermediate in the dye‐sensitized photooxygenation of biomolecules inin vitrosystems. Extended application toin vivosystems has recently begun, producing some results which generally support the involvement of1O2pathways in the photosensitization processes. The use of other1O2quenchers and acceptors has also been increasing. In the application of these techniques as diagnostic tests for1O2participation inin vivosystems, careful examination of the experimental conditions should be made with respect to the quenching capability and accessibility of D2O in the specified cellular environment. Furthermore, the diffusive nature of1O2, generation sites, generation efficiencies, the location and type of sensitizers, and the reactivity of1O2with presumed target structures in the cell should also be taken into account in the interpretation. Recent studies illustrating the importance of these factors are discussed. Finally, a tentative picture of the mode ofin vivophotodynamic activity of common dye sensitizers is ou

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06957.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06958.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The order of inhibition of the photooxidation of chlorophyllain ethanol and ethanol‐benzene is as follows: β‐carotene, α‐tocopherol, benzoquinone, DABCO, menadione, cholesterol and KI. The quenching of singlet oxygen by β‐carotene occurs by a collisional quenching mechanism with a diffusion‐controlled rate of 1.7 × 1010M‐1s‐1. Photodecomposition of Chiais faster in ethanol‐D2O than in ethanol‐H2O. Photoirradiation (660 nm) of the peridinin‐Chla‐protein complex, a photosynthetic light‐harvesting pigment isolated from marine dinoflagellates, did not show any photo‐decomposition of its Chiain H2O or D2O, even after an extended period (12 h) of irradiation. However, the carotenoid, peridinin, in the photosynthetic antenna pigment was photobleached (ca. 10%) during the irradiation. We conclude that the singlet oxygen formed as a result of the Chi photosensitization is immediately quenched by the low‐lying triplet state of four peridinin molecules (per Chla) bound within the same protein crevice. The carotenoid thus effectively protects Chlafrom photodynamic damage, providing a direct proof for the protective role of carotenoids in t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06959.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06960.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The photooxidation of epinephrine, sensitized by methylene blue or by chlorophylls, excited with red light, involves the reduction of two molecules of oxygen to hydrogen peroxide per molecule of epinephrine oxidized to adrenochrome. The initial rates of these reactions are not affected by low concentrations of catalase. In 99 mol % D2O, rates of methylene blue sensitized photooxidations are accelerated as much as 5.2 times over rates in ordinary water. Azide anion is a more effective inhibitor of this reaction in D2O than in H2O. Half maximal inhibitions are obtained by 1.3 mM azide in H2O and by 0.1 mAf azide in D2O. Isotope effects and azide sensitivities point to photooxidation of epinephrine in D2O primarily by a singlet oxygen pathway; in H2O, non‐singlet oxygen pathways become more predominant. Superoxide dismutase (SOD) markedly inhibits rates of the photooxidations in H2O and in D2O; about 25% at 10‐9MSOD, and 50% at 10‐6MSOD in H2O. In the photooxidation in H2O, both by non‐singlet and singlet oxygen mechanisms, the amount of superoxide produced is equivalent to the amount of O2consumed in the photooxidation of epinephrine; the superoxide thus formed participates in the oxidation of ep

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb06961.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY