摘要:

Abstract–The use of absorption and fluorescence spectroscopy for following the progress of the photo‐reaction between DNA and 4′‐aminomethyl‐4,5′,8‐trimethylpsoralen (AMT) has been investigated. Absorption at long wavelengths and fluorescence both decline upon intercalation of AMT into the DNA helix. The loss of fluorescence from AMT and the accompanying appearance of monoadduct fluorescence upon irradiation by UV light can be easily followed by using the excitation beam of a spectro‐fluorometer as the source of irradiation and monitoring the changing emission spectrum. Where cross‐link formation is possible, the subsequent decline of monoadduct fluorescence is seen as well. This suggests that the 4,5‐tnonoadduct is a precursor of cross‐links. Both monoaddition and cross‐linking are more rapid with poly d(A·T) than with calf thymus DNA or poly d(A·T). Excitation spectra can be helpful in resolving the levels of AMT and 4′,5′‐monoadduct when both are contributing to the emission spectrum. Some changes are observed in the emission spectrum of AMT–poly d(A·T) monoadducts after prolonged irradiation wh

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05493.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract–Methylviologen (MV2+) adsorbed on cellulose could be reduced photochemically in the solid phase sensitized by tris(2,2′‐bipyridyl)ruthenium(II) complex, [Ru(II)(bpy)3], using disodium ethylene‐diaminetetraacetic acid (Na2EDTA) as a reducing agent. Formation of the cation radical (MV+.) was confirmed by visible and EPR spectra. The MV+. formed on cellulose was remarkably stable against air oxidation and rapidly accumulated even by the irradiation under air. Water adsorbed on the cellulose greatly retarded the photoreaction. Action spectrum showed that the excitation of Ru(II)(byp)3is responsible for the photochemical reaction. The quenching of the emission from Ru(II)(bpy)*3by MV2+. indicated that a primary photochemical reaction occurs between Ru(II)(bpy)*3and MV2+. The main reaction path is the reduction of MV2+by Ru(II)(bpy)3, giving MV+. and Ru(III)(bpy)3, followed by the reduction of Ru(III)(bpy)3to Ru(II)(bpy)3with Na2EDTA, which in turn is oxidized to give carbon

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05494.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—A previous study on the electronic spectroscopy ofp‐N,N‐dialkylaminobenzylidenemalononitrile, 1, has been extended to a larger variety of organic solvents and to micelles of ionic and nonionic surfactants. By comparing the fluorescence emission (λFand φ∫) of 1 in micelles and in homogeneous organic solvents, the effective polarity and the microviscosity of the micellar environments of potassium dodecanoate, sodium dodecyl sulfate, cetyltrimethylammonium bromide and Triton X‐100 micelles have been determined to be 40, 40, 36 and 28, respectively and 23, 31, 34 and 28 cP, respectively. These results indicate that the fluorescence probe is located in the micelle–water interface of a micelle and this region of a micelle is polar and viscous. 1 has also been studied in different surfactants with varying surfactant concentrations. The φ∫of 1, a microviscosity gauge for micellar aggregates, remains unchanged at the critical micelle concentrations of various surfactants, but decreases at much lower surfactant concentrations. This is attributable to the formation of premicellar aggregates of surfactant molecules below their critical micell

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05495.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Flavin photochemistry as well as biochemistry consists of competitive 1e−‐ and 2e−‐reduction pathways, depending on the nature of the substrate. We show that cyanide ion is a photosubstrate which suppresses 1e−‐oxidoreduction and leads to exclusive formation of 6‐ and 9‐cyano‐1,5‐dihydroflavin. The photoreduction mechanism is thus revealed as a nucleophilic addition of cyanide ion at the excited flavin triplet. Preparative photochemistry and isolation and characterization of cyanoflavins have been done, as well as thorough mechanistic studies by conventional flash photolysis. In contrast, nitrite ion is shown to be a normal photosubstrate for flavins leading to exclusive 1e−‐transfer

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05496.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—The production of singlet oxygen (1O2) by a series of furocoumarins with different skin sensitizing abilities has been investigated with methods already proven to be suitable to establish the ability of 8‐methoxypsoralen (8‐MOP) to generate1O2.The following compounds: 5‐methoxypsoralen (5‐MOP), psoralen, 4,5′,8‐trimethylpsoralen (TMP) and 5,8–dimethoxypsoralen (5,8–DMOP), are able to generate1O2when irradiated with long–wave ultraviolet light. With the photobiologically inactive angelicin no1O2production has been found. The relative extent of1O2formation has been determined for the various furocoumarins and has been compared with literature data for the skin photosensitizing effect. The observed relation between experimental data on the one side and the literature data on the othe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05497.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—The photosensitizing activity of α‐terthienyl, a naturally occurring compound fromTageteshas been studied. Fluence‐response curves for the effect of α‐terthienyl and near‐UV radiation onEscherichia colihave been prepared. Photosensitization ofE. coliwas enhanced in aerobic as compared to anaerobic conditions and exogenous superoxide dismutase had a slight protective effect. Sodium azide, a quencher of1O2, protected yeast cells from photosensitization with α‐terthienyl. The available evidence suggests that α‐terthienyl acts as a photodynamic

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05498.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Photoprotection is a reduction in response to far‐UV (190–300. nm) radiation in cells that have been previously exposed to longer wavelengths. It has been proposed that photoprotection operates by means of a growth delay that permits more time for dark repair. Growth delay inEscherichia coliutilizes 4‐thiouridine (4Srd) in transfer RNA as a chromophore and it requires therel+gene, which exerts a stringent control upon RNA synthesis. Mutants that were eitherrelor4Srd−were isolated fromE. coliB, utilizing a near‐UV‐induced growth‐delay selection technique. Therelmutants, which undergo little growth delay after near‐UV irradiation, show only 50% as much photoprotection as wild types, while4Srd−mutants show no photoprotection at all. Thus, photoprotection appears to utilize4Srd as its sole chromophore inE. coliB and B/r, and no more than 50% of photoprotection in these strains can be a result of near‐UV

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05499.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—The mechanism of inactivating action of high‐power picosecond laser UV radiation (λ= 266 nm) on the λ and φX174 bacteriophages and the pBR 322 plasmid has been studied. It has been shown that at UV radiation intensities from 1011to 1013W/m2, inactivation of viruses and bacterial plasmids occurs mainly on account of single‐strand breaks in the DNA chain unlike the case of less powerful UV radiation where the inactivation is associated with the formation of pyrimidin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05500.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—This paper considers mechanisms of near‐UV (334nm) induced photoprotection as well as potentiation of far‐UV (254 nm) lethality inCandida guilliermondii.Using exogenous precursors of serotonin, it appears that the above two mechanisms involve photoactivated synthesis of serotonin. It has been postulated that the serotonin effect could take place by binding t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05501.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—UV‐enhanced reactivation of minute‐virus‐of‐mice (MVM), an autonomous parvovirus, was studied in parasynchronous mouse A9 cells. The survival of UV‐irradiated MVM is increased in cells which have been UV‐irradiated prior to infection. UV‐enhanced reactivation can be explained neither by facilitated plaque detection on UV‐treated indicator cells, nor by altered kinetics of virus production by UV‐irradiated cells. No effect of the multiplicity of infection on virus survival was detected in unirra‐diated or irradiated cells. The magnitude of UV‐enhanced reactivation is a direct exponential function of the UV dose administered to the virus while virus survival is inversely proportional to the UV dosage. The expression of UV‐enhanced reactivation can be activated in cells arrested in G0, it requiresde novoprotein synthesis and it is maximal when cells are irradiated 30 h before the onset of viral DNA replication. Early phases of the viral cycle, such as adsorption to cellular receptors, migration to the nucleus and uncoating, were not affected by cell irradiation and are unlikely targets of the UV‐enhanced reactivation function(s). These results, together with the single‐strandedness of the viral genome, strongly suggest that the step stimulated in UV‐irradiated cells functions concomitant with, or subse

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb05502.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY