ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04266.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Laser flash photolysis oftrans‐[Rh(dppe)2X2][PF6] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH2Cl2or CH3CN produces the d7Rh(II) radicals, [Rh(dppe)2X]+, and halogen atoms. The kinetics of the disappearance of [Rh(dppe)2X]+radicals in CH2Cl2or CH3CN were mixed order: H‐atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)2X][PF6], and Rh/X recombination. In the poor H‐atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H‐atom abstraction. The hydride complexes [RhH(dppe)2X][PF6], formed by H‐atom abstraction were completely characterized by31P{1H}‐NMR,1H‐NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3‐bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04267.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The purpose of this study was to assess the mechanism of merocyanine 540 (MC540) photobleaching in a liposomal system. Broad based visible irradiation of MC540 in unilamellar dilauroylphosphatidylcholine (DLPC) vesicles resulted in dye bleaching that was strictly O2dependent. The rate of self‐sensitized photobleaching was enhanced in D2O and inhibited by both azide and histidine, consistent with1O2intermediacy (Type II chemistry). Supportive evidence for this mechanism was obtained by using a Type II sensitizer, aluminum phthalocyanine tetrasulfonate (AIPcS Λmax, = 678 nm). Irradiation of AIPcS and MC540 in DLPC with Λ>630 nm (absorbed only by AIPcS) light resulted in rapid bleaching of MC540, which was stimulated by D2O and inhibited by azide. A rate constant of 107M‐1s‐1was determined for the chemical quenching of1O2by MC540. The rate constant for physical quenching of1O2by MC540 was estimated to beca

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04268.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—A photoacoustic (PA) effect theory taking into account two heat sources corresponding to the radiationless relaxation processes of two states of different lifetimes and to the heat diffusion across the sample is herewith presented. Results obtained demonstrate that the amplitude and the phase of the PA signal depend on the sample's thermal properties, on its optical absorption coefficient, on the lifetime of the long‐lived excited state, and on the ratio of the two heat sources. This ratio can be expressed as a function of the product of the energy of the excited state times the quantum yield of its production. Simulations of PA amplitude and phase variationsvslight modulation frequency exhibit new features of the PA signal: phase inversion and fast decrease of the amplitude. Experimental verifications were carried out on solutions and gels. Fitting of the amplitude and phase variations allow us to measure the lifetime and conversion yield of the intermediate state which can be a triplet state or singlet oxygen, O2(1Δg). The addition of an acceptor, specific to O2(1Δg), induces changes in the amplitude of the PA signal which can be used to study the production and deactivation of this excited form of oxygen. This work demonstrates the usefullness of PA in the detection of metastable excited states such as the triplet state and singlet oxygen and in their quantitative ana

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04269.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Photoluminescence and quenching of 4,4'‐dicarboxy‐2,2'‐bipyridinebis(2,2'‐bipyridine)‐ruthenium(II) complex (Ru(DCbpy)(bpy)22+) in an aqueous solution as well as in a silk fibroin membrane were studied. Emission quenching by oxygen in an aqueous solution showed a linear relationship with respect to oxygen concentration. When the complex was incorporated into a silk fibroin membrane by adsorption from an aqueous solution into a preformed membrane, the photoexcited state of the complex was not quenched by oxygen in an aqueous phase. However, when the complex was incorporated into a silk fibroin membrane by casting a mixture of the complex and silk fibroin, the photoexcited complex was quenched by oxygen in an aqueous phase. In this case the Stern‐Volmer plots showed a downward‐deviating curve indicating heterogeneity of the probe site. Emission intensity decreased with an increase of the water content in the silk f

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04270.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Novel synthetic polyene polyketones and new synthetic capsorubin isomers were examined for their ability to quench singlet molecular oxygen (1O2) generated by the thermodissociation of the endoperoxide of 3,3'‐(l,4‐naphthylene) dipropionate (NDPO2). C28‐polyene‐tetrone (1) exhibits the highest physical quenching rate constant with1O2(kq= 16 × 109M‐1s‐1). For comparison, the rate constant for the most efficient biological carotenoid, lycopene (3) is kq= 9 × 109M‐1s‐1that of β‐carotene (5) kq= 5 × 109M‐1s‐1. The presence of two oxalyl chromophores at the ends of the polyene chain seems to enhance the1O2quenching ability in the C28‐polyene‐tetrone (1). C28‐polyene‐tetrone‐diacetal (2) (kq= 9 × 109M‐1s‐1) and C40‐epiisocapsorubin (4) (kq= 8 × 109M‐1s‐1) also have high1O2quenching abilities. Two carotenoids from plants, phytoene and phytofluene, were much less efficient, kqvalues being below 107M‐1s‐1. Due to the very high singlet oxygen quenching abilities, C28‐polyene‐tetrone (1), C28‐polyene‐tetrone‐diacetal (2) and C40‐epiisocapsorubin (4) may have potential use in prev

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04271.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Reflectance spectrophotometry from 420 to 780 nm on 31 primary melanoma and 31 benign nevi has been performed by using an external integrating sphere coupled to a spectrophotometer. Measurements show that reflectance spectra of melanoma and nevi manifest dissimilar patterns. From these spectra four variables, whose physical and/or physiological meanings remain to be investigated, have been derived. All of them are significantly different when compared between melanoma and nevi. A discriminant function between the two groups of lesions has been determined by using a stepwise discriminant analysis, resulting in a test with a sensitivity of 90.3% and a specificity of 77.4%. This method of discrimination between melanoma and nevi seems to have a discriminating power almost equal to that of a clinical judgement from a specialized medical doctor, thus suggesting a new method for screening skin pigmented lesion

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04272.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Singlet oxygen lifetimes for detergent‐dispersed L1210 leukemia cells in deuterium oxide buffer were measured by following the decay of 1270 nm phosphorescence. Four photosensitizers and two detergents were studied. Stern‐Volmer plots were linear over the cell concentration range studied (0–107cells/mL). The singlet‐oxygen quenching constants obtained depended somewhat upon the specific combination of detergent and photosensitizer used. Extrapolation of the singlet‐oxygen lifetime data to “100%” cell concentration (1.39 ± 0.04 × 109cells/mL) and correction for the contribution of the water solvent gave a singlet‐oxygen lifetime between 0.17 and 0.32 us for the L1210 leukemia cell. The theoretical contributions of various types of biological molecules within the L1210 cell to the total singlet‐oxygen quenching were calculated from their concentrations and their quenching constants. These calculations suggest that proteins will quench most of the singlet‐oxygen. Only about 7% of the singlet‐ox

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04273.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—5‐geranoxypsoralen (Bergamottin) does not photosensitize bacteria or a bacterial virus. It does, however, photosensitize mammalian cells in tissue culture. Irradiation with either black light (300–400 nm) or fluorescent ceiling lights produced at least four photobiologically active degradation products, the chemical nature of which still remains to be elucidated. Prolonged exposure to black light resulted in the formation of inactive molecu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04274.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The photochemistry of benzanthrone (7H‐benz[de]‐anthracene‐7‐one) has been studied using electron paramagnetic resonance (EPR) in conjunction with the spin trapping technique and the direct detection of singlet molecular oxygen luminescence. Irradiation (Λcx= 394 nm) of benzanthrone (BA) in aerated ethanol, dimethylsulfoxide or benzene resulted in the generation of superoxide (O−2) which was trapped by 5,5‐dimethyl‐1‐pyrroline‐N‐oxide. The ethoxyl radical was also detected in ethanol. Photolysis of BA in deaerated basic ethanol led to the formation of BA anion radical, BA, which was detected directly by ESR. This radical anion decayed back to BA with a unimolecular rate constant of 1.5 × 10‐3s‐1. The1O2quantum yields (Λex>345 nm) for BA in ethanol, 90% ethanol and basic ethanol (0.1NNaOH) were 0.89, 0.88 and 0.28 respectively relative to Rose Bengal. The lower yield of1O2in basic ethanol may be attributable to the reaction of oxygen with BA (which is generated in higher yield at alkaline pH) to give O−2. These findings suggest that on exposure to light BA can generate active oxygen species which may be responsible for the photocontact dermatitis caused by BA in industrial wo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb04275.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY