摘要:

Abstract—When [3H]‐cyclic adenosine 3′,5′‐monophosphate and [3H]‐cyclic guanosine 3′,5′‐monophos‐phate are irradiated at varying UV wavelengths in the presence of cyclic nucleotide receptor proteins, photo‐incorporation is maximal in the region of 280 nm. This suggests that covalent coupling occurs by means of photo‐activation of an entity other than the ligand cyclic nucleotide. The action spectra more closely resemble the absorbtion spectrum of the reacting protein, making it likely that absorhtion of radiant energy by components of the protein receptor leads to

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07637.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Methylvinylmaleimide, a product of the photooxidation of bilirubin, exhibits a broad luminescence band at approximately 450 nm on filter paper at room temperature. In methanol solvent, at 77 K, a broad phosphorescence band centered at 465 nm is observed. The experimental and theoretical spectroscopic properties of this compound are compared to those of the related molecules maleimide and phthalimide. Methylvinylmaleimide is photodegraded at pH 7.6 in a self‐sensitized reaction that in part involves singlet oxy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07638.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The flash photolysis of N‐acetyl‐L‐tryptophanamide (NATA) in the presence of the fluorescence quenchers, imidazole, acrylamide and trichloroethanol, has been investigated. Imadazole and acrylamide induce a decrease in the NATA radical yield which correlates with their NATA fluorescence quenching action. These observations suggest that the fluorescent state is primarily responsible for the monophotonic photoionization processes. The acrylamide data also suggest that 40–65% of the NATA radicals arise from a long‐lived state (τ˜μs) which must originate from the fluorescent state. Unlike imidazole and acrylamide, trichloroethanol enhances the radical yield by reaction with excited state precursors. Mechanisms for the quenching of fluorescence and the long‐lived stat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07639.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The low spin hemin derivative di‐cyan‐hemin can sensitize the photooxidation of amino acids. The efficiency of this dye as a photosensitizer is generally lower than that of other porphyrins such as hematoporphyrin in aqueous solution, but it is significantly enhanced by addition of ethanol. On the basis of the identified photooxidation end‐products of some amino acids, photooxidation kinetic data and EPR measurements, it appears that methionine is quantitatively converted to methionine sulfoxide by a pure Type II (singlet oxygen) mechanism, whereas in the case of cysteine and tryptophan a mixed Type ILType II mechanism is probably op

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07640.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Phosphorescence of organic molecules in fluid solutions may be conveniently and readily observed under certain conditions. Ifkp(radiative phosphorescence rate constant) is 10s‐1, then (in the absence of photoreaction) phosphorescence is observable upon N2purging. For example, nitrogen purged, acetonitrile solutions of bromo and dibromonaphthalene display readily observable phosphorescence as a result of internal heavy atom enhancement of πS, andkp. External heavy atom enhancement of k, (CH2BrCH2Br solvent) of aromatic hydrocarbons even allows observation of phosphorescence from these compounds in N2purged fluid solutions. Although bromonaphthalenes are not significantly phosphorescent in N2purged aqueous solution, phosphorescence is readily observed in N2purged detergent (HDTBr, HDTCl, and SDS) solutions above the critical micelle concentration. The general factors which determine whether phosphorescence is “readily” obervable in fluid solution are briefly discussed and the results are interpreted in light of these

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07641.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—A kinetic method for the identification of primary reactions in sensitized photooxidations is described. It is based on the calculation of Fractions of primary reactions of triplet sensitizer (3S) and singlet oxygen (1O2) as a function of substrate concentration (A) and on the comparison of experimental and theoretical curves. The theoretical curve that coincides with the experimental one indicates the mechanism of the chemical change observed. Only the quenching rate constants of3S and1O2are needed for this calculation. The method enables one to distinguish the free radical and1O2mechanism. Applications of the method with 3‐indole acetic acid, 1‐histidine and N‐3using phenosafranine as the sensitizing dye (aqueous solutions, pH 7.C7.2) are described. The chemical change followed in these experiments is the bleaching ofp‐nitrosodimethylaniline (RNO) which gives precise and reproducible results. The bleaching of RNO is induced by the presence of some substrates which produce reactive intermediates with an oxidizing character. The kinetic method can be applied to any chemical change observed in different systems of sensitized photooxidations. The quantum yield of3S and1O2formation need not

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07642.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Iodide ion oxidation by singlet oxygen is found to be influenced by two properties of the solvent. One is the polarity of the solvent and the other is the availability of protons in the solvent. By suitable choice of solvents and solvent mixtures both kinds of effects have been studied. In water‐methanol mixtures the reaction is found to be facilitated in more polar medium. In isodielectric media as obtained by mixtures of acetonitrile and methanol the reaction is repressed with increase in the aprotic component (CH3CN) in the solvent. The same effect is observed in the DMSO‐H, O mixtures. In heavy water the reaction rate is doubled and the effect fits well into the proposed kinetic scheme involving singlet oxygen for photosensitized oxidation of I‐by anthracene sulp

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07643.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The DNA precursor3H‐thymidine incorporation rate (dpm/pg DNA) in mouse L‐929 cells decreases immediately after exposure to UV light. This decrease is initially dose dependent, but at exposures greater than 22.5 J/m2appears to be radio‐resistant. This was not explained by measurements of uptake of3H‐thymidine into the acid soluble pool (dpm/pg DNA). The radio‐resistant incorporation amounted to approximately 35% of the control rate. DNA reassociation (“C0T”) studies were performed with DNA labeled with3H‐thymidine immediately after exposure of L‐929 cells with a dose of UV resulting in radio‐resistant incorporation to determine whether this radio‐resistant incorporation was occurring in sequences of a particular repetitious frequency. These studies, performed in the highly repetitive to intermediate range, showed that the radio‐resistant incorporation was occurring in DNA of all classes of repetitious frequency. DNA synthesized at different times after UV exposure, during the period when post‐replication repair can occur, was similarly labeled for short intervals and isolated. The DNA reassociation studies showed that this DNA synthesis was also of all class

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07644.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—The photoreaction of 5‐bromodeoxyuridine (BUdR) exposed to 360 nm light in the presence of the furocoumarins, 4,5′,8‐trimethylpsoralen (TMP) and 8‐methoxypsoralen (&MOP), was studied and compared to those of thymidine. BUdR reacted with furocoumarins, producing cyclobutane‐containing adducts, as does thymidine. Furocoumarins reacted also with BUdR‐containing polymer, poly(dA‐BUdR) in the double stranded form, at a rate similar to that of thymidine‐containing polymer, poly(dA‐dT). Polyamines, which slow the photoreactions of TMP with DNA, had no effect on its binding to the two former polynucleotides. It is suggested that because of the similar photoreactions of BUdR and thymidine with furocoumarins, this combination could be used to elucidate the mechanism by which BUdR sensitizes biological systems. InEscherichia colisome sensitization by BUdR of TMP plus 360 nm light killing was observed. It is therefore concluded that at least part of the sensitization of bacteria by BUdR to UV and ionizing radiation is caused by interference with the repair processes. Since no such sensitization was observed in auvrB mutant, BUdR apparently impairs the efficiency of the excision resynthesi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07645.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract—Exposure of BrdUrd‐substitutedE. colicells to 360 nm light in the presence of the bisbenzimi‐dazole dye 33258 Hoechst increases their sensitivity dramatically. Mutant cells deficient in excision repair of DNA damage (uurB) are more sensitive than wild type cells, indicating that the cells are able to repair this type of damage. However, they perform only a limited amount of liquid holding recovery (LHR). Exposure of the dye with BrdUrd to near UV light in solution results in the appearance of two BrdUrd derived photoproducts. One appears to be deoxyuridine, and the other — an adduct of BrdUrd‐dye. The adduct is acid labile and as a result only uracil is observed in acid‐hydrolyzates of DNA after exposure of BrdUrd‐substituted cells to 360 nm light in the presence of 33258 Hoechst. The production of uracil is linearly dependent on light exposure. Cells in which 85% of thymidine was replaced by BrdUrd are unable to remove more than 5–10% of uracil from their DNA during postirradiation incubation. However, when only 4% of thymidine is replaced, about 50% of the uracil is removed during 30min incubation after exposure. The results are consistent with our previous work, indicating that BrdUrd interferes with repair via excision‐resynthesis. A working hypothesis is suggested to explain

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07646.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY