摘要:

Abstract—The photolytic and radiolytic product formation of the complex benzene‐fumaronitrile are compared. The equilibrium constants for the complexes of benzene‐fumaronitrile and benzene‐maleonitrile determined by UV and NMR spectroscopy are given. The products which were found in both photolysis and radiolysis of the system benzene‐fumaronitrile were biphenyl. phenylsuccinodinitrile and maleonitrile. The production of a 2:1 adduct of fumaronitrile and benzene in very small yields could only be confirmed in the case of photolysis. Additional products in radiolysis were phenylcyclohexadienes and benzonitrile. Experiments using filtered light proved that isomerisation of fumaronitrile to maleonitrile and production of phenylsuccinodinitrile proceed via the excited charge‐transfer complex. There are indications that the excited charge transfer complex is likewise an intermediate in the radiolytic formation of these nitriles. The addition of fumaronitrile to benzene reduces the yield of biphenyl in both photolysis and

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06830.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Photoexcited 1,3‐dimethyluracil (DMU) reacts with methanol to give 1,3‐dimethyl‐6‐hydroxymethyl‐5‐hydrouracil (1a) in addition to cyclobutane type dimers and 1,3‐dimethyl‐6‐methoxy‐5‐hydrouracil (2a). Free radical induced reaction, initiated by photodecomposition of di‐t‐butyl peroxide with light of wavelength greater than 290nm, leads to1a, 5,6‐dihydroxymethyl‐5,6‐dihydro‐1,3‐dimethyl‐uracil (1d) and 6‐hydroxy

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06831.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The odd nucleoside 4‐thiouridine, which is present in position 8 of 70% ofE. colitRNAs, possesses unusual spectroscopic properties which make it suitable for intramolecular energy transfer studies. Both its luminescence excitation spectrum and the action spectrum (230–380 nm) for the 8–13 link formation have been established in nativeE. colitRNA at room temperature. The spectra are identical and present a new unexpected peak around 260 nm. At this wavelength, they are amplified by a factor of nine as compared with the absorption and excitation spectra of the free nucleoside in aqueous solution.The origin of this new peak is discussed and it is concluded that energy transfer does occur from the common nucleosides to the 4‐thiouridine residue. Using the values of the nucleosides to 4‐thiouridine distances inferred from the sets of atomic coordinates obtained on yeast tRNAphecrystals, a satisfactory account of our finding can be obtained assuming singlet‐singlet energy transfer. The efficiency of the mechanism is probably favoured by a good overlap between the emission spectra of the common nucleosides and the absorption spectrum of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06832.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—In UV‐irradiated vegetative cultures of the cellular slime moldDictyostelium discoideumNC‐4, single strand breaks appeared in the DNA very rapidly and at low temperatures (0–4°C). However, when these cells were incubated, prior to UV irradiation, in the presence of 2 mM2,4‐dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, breaks did not appear in the DNA. Extracts prepared from cells that had been incubated either in the presence or absence of DNP were tested for endonucleolytic activities on a UV‐irradiated exogenous DNA template (φX‐174 RF I). Results suggested that DNP might mediate its effect by interfering with the action of a UV‐spec

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06833.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Action spectra for lethality of both stationary and exponentially growing cells of recombinationless (recA) mutants ofSalmonella typhimuriumandEscherichia coliwere obtained. Maximum sensitivity was observed at 260nm which corresponds to the maximum absorbance of DNA. However, a shoulder occurred in the 280–300 nm range that departed significantly from the absorption spectrum of DNA. At wavelengths longer than 320nm, the shapes of inactivation curves departed significantly from those at wavelengths shorter than 320nm and survival curves at wavelengths longer than 320nm had a large shoulder. A small peak or shoulder occurred in the 330–340nm region of the action spectra. The special sensitivity ofrecAmutants to broad spectrum near‐UV radiation may be due to synergistic effects of different wavelengths. Parallels between the inactivation ofrecAmutants and the induction of a photoproduct ofl‐tryptophan toxic forrecAmutants (now known to be H2O2) suggest that H2O2photoproduct from endogenous tryptophan may be involved in the high sensitivity of these strains to broad spectrum near‐U

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06834.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—The lethal interaction of far ultraviolet (254nm), near ultraviolet (334 and 365nm) and violet visible (405nm) radiation treatment with mild heat treatment was studied. Except at 254nm, a strong positive radiation dose‐dependent interaction (synergism) was always observed. The efficiency of sensitisation to heat, as a function of dose at each wavelength, was found to be directly correlated with the dose necessary to eliminate the shoulder from the survival curve of a repair proficient strain but was apparently unrelated to the relative near‐ultraviolet sensitivities of a repair deficient strain. The interaction was independent of the order of treatments. A radiation dose of 106Jm‐2at 365nm slightly sensitised a cell population to 45°C incubation (normally non‐lethal) and strongly sensitised the cells to 48°C treatment (normally 80 percent survival after 2 hours). It is proposed that in addition to DNA damage, both heat treatment and near ultraviolet treatment interfere with DNA recovery mechanisms so that the combination of the two agents inevitably leads to a strong positive

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06835.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—We correlate annual ultraviolet dose estimates with age specific and age adjusted incidence data for non‐melanoma skin cancer in the United States, United Kingdom, Canada and Australia. We first examine (1) a reciprocity or photographic model in which incidence rates (R) are related to exposure (E) which is the product of age (T) and annual dose (D). We also test several models which violate reciprocity including models identified by the labels: (2) Dose potency; (3) Double cause; (4) Age‐exposure and (5) separable. Our analyses together with the recent National Cancer Institute study favors the age‐exposure model and/or the double cause models. All models lead to biological amplification factors (defined as the ratio of the percent increase in skin cancer incidence due to a 1% increase in dose) greater than unity. For the U.S. we find the biological amplification to be approximately 1.8 for the population center but greater in regions of higher UV annual dose, and less in regions of lower annual

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06836.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—A structure is proposed for the prosthetic group of the visual pigments rhodopsin, prelumirhodopsin (bathorhodopsin) and lumirhodopsin. The intrinsic photochemical step in this model is tautomerization of the prosthetic group of rhodopsin to a hexaeneamine retrotautomer with an exomethylene group for prelumirhodopsin. Based on the proposed structures, molecular orbital calculations were carried out; the absorption maxima calculated snowed the same trends as the Λmaxvalues observed. An exact fit was not obtained because many interactions had to be neglected. Essential information of the laser Raman resonance spectrum of prelumirhodopsin can be interpreted based on the structures proposed by our model.The model elucidates why some retinal derivates can and others cannot form visual pigments with opsin and visual pigments having vastly differing absorption maxima yet employ the same mechanism for their photoreacti

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06837.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Dose‐response curves were measured for the delay phase shift of pupae emergence ofDrosophila pseudoobscura.From these curves an action spectrum was determined for this process; it suggests a flavin to be the photoreceptor pigm

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06838.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Abstract—Fluorometric evidence suggesting the presence of flavins in isolated eyespots ofEuglena gracilisvar.bacillarisis reported for the first time. Fluorescence spectra of eyespots and flavin standards show maxima at 540nm and 530nm, respectively. Excitation spectra show matching major peaks at 360–370 nm and at 450nm. The addition of riboflavin standard to eyespot samples increases fluorescence intensity without major corresponding shifts in wavelength maxima. Photolysis of eyespot samples in the presence of EDTA effects a decrease in the fluorescence intensity; the fluorescence is quantitatively restored to its initial value by bubbling the photolyzed solution with air. Preliminary quantitative data, obtained by fluorescence measurements, indicate the presence ofca.5 × 10‐4μg flavin/ml eyespot sample. While flavins have been hypothesized to be components of the photoreceptor system, they have been reported previously only in the paraflagellar bodies of intact cells. Emission and excitation data obtained by us for eyespots are similar to those previously reported by other investigators for paraflagellar bodies, but our studies now suggest the presence of flavins also inEuglenae

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1976.tb06839.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY