ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07555.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Photolysis of synthetic estrogen dienestrol resulted in formation of a 4a,4b‐dihydrophenanthrene, a rare example of a stable intermediate of the classical stilbene → phenanthrene photocyclization. Time‐lapse spectrometric investigation suggested an initialcis‐transisomerization in the dimethylbuta‐dime moiety of dienestrol followed by a photochemical [1, 51 sigmatropic proton transfer which converted the two cross‐conjugatedp‐hydroxystyrene halves into a vinyl‐stilbene. A subsequent electrocyclic ring‐closure in an electronically excited state generated a cyclic nonaromatic heptenediol. This last photoproduct tautomerized rapidly in the dark to a stable, crystalline, tricyclic pentenedione. The final diketone product is an example of a 4a.4b‐dihydrophenanthrene self‐stabilized by a double ketoenol tautomerism. The three sequential photoisomerizations of dienestrol are made possible by a fortuitous coincidence of steric and orbita

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07556.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Experiments on the photooxidation ofN‐allylthiourea, thiourea, and N‐allylurea sensitized by the dye phenosafranine show that inN‐allylthiourea the thiourea group is the site of singlet oxygen attack, while the allyl moiety neither reacts with nor quenches this metastable form of O2(in neutral aqueous solutions). Low concentrations of N‐3(a known quencher of singlet oxygen) strongly reduce the photooxidation of allylthiourea by a mechanism which apparently obeys simple competition kinetics. From these results the rate constant of the reaction between allylthiourea and singlet oxygen is obtained (k= 4 × 106M‐1s

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07557.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—An imidazole ring photodegradation induced by indole derivatives in oxygen‐free aqueous solutions (Λexc= 254 nm) was demonstrated and studied in various systems at low concentration (0.2 mM). The degradation rate was maximal in the indole‐imidazole system and decreased when a substituent was present on either or both rings. The degradation rate also depended on pH (maximal at pH ˜ 6) and on imidazole concentration. Results obtained under N2O atmosphere, in the presence and absence of 1M t‐butanol, indicate that the imidazole degradation is promoted by hydrated electrons photogenerated by the indole chromophore. Kinetic analysis of the data confirms this

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07558.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—On treatment with 8‐methoxypsoralen plus near UV light, an excisionless (uvrB‐) strain ofEscherichia colishowed about 3– and 10 times higher sensitivities to killing and mutation, respectively, than its parental strain. On re‐irradiation with near UV in the absence of unbound psoralen, theuvrB‐strain pretreated with psoralen plus near UV showed a decrease in both survival and mutation. After treatment with psoralen plus near UV, re‐irradiation of T7 DNA in the absence of unbound psoralen caused an increase in the cross‐linked fraction with an equivalent decrease in the non‐cross‐linked fraction. From these and previous results, we conclude that monoadducts produced by treatment with psoralen plus near UV are converted to cross‐links by further irradiation and that, inE. coli, monoadducts are responsible for the mutation induced by psoralen‐plus‐light whereas cross‐links are the major

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07559.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—5,7‐DimethoxJtcoumarin (DMC) dimerizes through the C4‐photo‐cycloaddition of 3,4‐double bonds to form asynhead‐to‐tail dimer on direct irradiation (Λ≥300 nm) in acetonitrile or benzene solution. The quantum yield of the photocyclodimerization in acetonitrile is 0.068 which is greater than that of coumarin.In the presence of triplet sensitizers such as benzophenone, 5,7‐dimethoxycoumarin forms anantidimer with the quantum yield greater than 0.08. The structure of the photodimers has been elucidated by IR, UV, NMR, and mass spectrometry. The results of luminescence studies, triplet quenching and sensitization revealed that thesynhead‐to‐tail dimer was formed via an excited singlet precursor, while theantidimer was formed via the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07560.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The photoreactivity of psoralen and 8‐methylpsoralen towards various samples of DNA having different base‐pair compositions has been studied. The total photobinding capacity shown by the two furocoumarins increases by increasing the content of A‐T, confirming the data previously obtained using synthetic polynucleotides.The amount of monofunctional fluorescent 4′,5′‐cycloadducts and of the cross‐linkages formed during the photoreaction is not parallel to the content of A‐T, but is highest when the A‐T content is between 50 and 60%, while it decreases as the content of A‐T is lowered or increased. The possible binding site for the formation of 4′,5′‐monofunctional cycloadducts as well as of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07561.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Rabbits immunized with sonicated DNA UV‐irradiated (365 nm) in the presence of 8‐methoxypsoralen (8‐MOP) produced a specific antiserum directed against DNA‐8‐MOP‐photoadduct. None of the long chain DNA preparations modified photochemically in the same way elicited an immunological response, although all of them gave a positive immunodiffusion test on agarose with the antiserum directed against DNA‐8‐MOP‐photoadduct. A positive reaction has also been demonstrated in the indirect immunofluorescence test, using as a source of cellular native DNACrithidia luciliaecells treated with 8‐MOP and irradiated at 365 nm (UVA). A possible use of the specific antiserum for detecting the formation of DNA‐8‐MOP‐photoadduct, in the skin and/or lymphocytes of patients with psoriasis treated by combination of 8‐MOP and

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07562.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Rabbit muscle aldolase, modified by azo groups covalently bound to cysteinyl residues 237 and 287, shows activation of the fructose‐1,6 diphosphate cleavage reaction at 30T, after preirradiation with visible light. When the light treatment is carried out under an atmosphere of Ar to avoid oxidation, there is a reversible diminution of the Michaelis‐Menten constant, with no change in the turnover number. The direct effect of the light is theE →Z geometric isomerization of the azochromophore; thereafter the Z isomer is thermally converted to the more stableEisomer. Both regulation at the level of the enzyme‐substrate interaction and the involvement of the geometry of the chromophore have been demonstrated. The substrate, added to azoaldolase in the dark, causesEto Z isomerization of part of the extrinsic protein chromophores leading to a different isomeric composition at the thermal equilibrium. This result is consistent with higher binding energy of the enzymesubstrate complex when the modified enzyme contains azo chromophores in the Z configuration, as compared with the same chromophores in theEconfiguration. Azoaldolase has been discussed as a model for direct photoregulation of enzyme activity at the level of enzyme‐substrate

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07563.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Linear dichroism measurements using magnetic field oriented bovine visual rod outer segments have been made in the UV and visible spectral regions. The results indicate that the planes of the aromatic amino acid residues of rhodopsin tend to be oriented normal to the membrane plane both before and after bleaching. In contrast, the retinal chromophore which tends to be oriented with its absorption oscillator parallel to the membrane plane before bleaching is randomly oriented about 10min after bleaching whereas the membranes remain oriented. Estimates of the anisotropy in the diamagnetic susceptibility of rhodopsin aromatic residues indicate that the anisotropic magnetic properties of these protein residues are sufficient to account for the observed orientation of visual rod outer segments in a homogenous magnetic fiel

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07564.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY