摘要:

Abstract.The quantum yields of HCI (φHC1) formation have been measured for the photolysis ofN‐methyldiphenylamine (MeDPA), triphenylamine (TPA) and diphenylamine (DPA) in the presence of CCl4in polar solvents. The quantum yields of N‐methylcarbazole formation (φmφca) have also been determined for the system MeDPA‐CCl4. With increasing CCl4concentration, φHClincreases as φMeCAdecreases, and φHClreaches maximum values 2.7 at 1MCCl4. Using laser photolysis, transient spectra have been recorded for MeDPA in the absence and presence of CCl4in polar and non‐polar solvents, and for TPA. Transient absorption due to the triplet states and photocyclization products (without CCU), exciplexes, the (C6H5)2NCHi radical, the MeDPA+cation radical, the (TPA+., CCl4) ion pair, and the TPA+cation radical have been identified. The mechanistic implications of these results

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07712.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The role of protein synthesis in liquid‐holding recovery from ultra‐violet radiation damage in synchronizedSaccharomyces cerevisiaecells has been studied using cycloheximide as a specific inhibitor of cytoplasmic protein synthesis. Liquid‐holding recovery from UV‐induced budding delay is completed within a few hours and is not inhibited by the presence of cycloheximide. Liquid‐holding recovery from lethal UV damage is unaffected by cycloheximide for liquid‐holding times less than about 12 h. For longer times recovery is inhibited, with survival enhancement eliminated after about 48 h. Periods greater than 48 h of liquid‐holding in the presence of cycloheximide result in survival less than that obtained with immediate plating, but the same concentration of cycloheximide is not toxic to unirr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07713.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The photodynamic inactivation ofE. coliby visible light and O2was found to occur in the presence of the sensitizer rose bengal, immobilized by covalent bonding to polystyrene beads. The demonstrated absence of significant amounts of dissolved rose bengal indicated that an inactivation mechanism based on penetration of sensitizer molecules into the cell's interior could not be operating. Survival curves typically exhibited induction periods followed by rapid exponential death, with 99.99% kill requiring 1–2 h depending on conditions. A mechanism involving the participation of photo‐generated singlet excited oxygen O2(1δ) in inactivation ofE. coliis proposed. The photodynamic inactivation rate increased significantly in H2O compared with H2O, which is evidence supporting singlet oxygen as an active intermediate, since O2(1δ) has a much longer lifetime in H2O than in H2O. H2O did not act as a short term poison in the absence of sensi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07714.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Illumination of single‐stranded φ×174 phage DNA with visible lightλ>500 nm) in the presence of the sensitizer thiopyronine results in both chain scissions detectable by velocity sedimentation in neutral medium and in alkali‐labile bonds which yield secondary strand breaks after alkaline treatment. Compared with the generation of primary strand breaks, the formation of alkali‐labile sites seems to be the predominant reaction.Photodynamic treatment of homogeneous double‐stranded Ta, phage DNA leads to changes in the overall conformation of DNA as revealed by an initial increase of the sedimentation coefficient. The simultaneous occurrence of different effects (decrease of molecular weight, increase of effective DNA flexibility) is particularly evident from changes in the sedimentation coefficient distribution. The fact that both processes influence the sedimentation behaviour questions the common procedure of calculating double‐strand break numbers from sedimentation coefficient distributions on the basis of s#‐M relations which are valid for intact DNA only.Photooxidized double‐stranded DNA exhibits an increased sensitivity agai

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07715.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The photooxidation of tetracyclone yielding dibenzoyl stilbene was studied by means of an18O labelling method recently used to study heme catabolism. Unlike heme degrading systems, the photooxidation of tetracyclone was found to proceed by a one‐molecule mechanism whereby both oxygen atoms in dibenzoyl stilbene are derived from the same molecule of molecular oxygen. This is evidence for a dioxobridged intermediat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07716.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.A new model is presented for the calculation of the increased incidence of non‐melanoma skin cancer in Caucasians resulting from ozone reduction. The model postulates that the probability of first incidence of such skin cancer is distributed log‐normally as a function of total accumulated lifetime dose of harmful ultraviolet radiation. The effect on skin cancer incidence of an increase in harmful ultraviolet radiation due to ozone reduction can then be calculated directly from the extent to which each individual's lifetime accumulated dose is thereby increased. The result of such a perturbation, on average, would be to cause skin cancer to appear at a slightly earlier age. Since skin cancer is predominantly a disease of the elderly, this shift to younger ages has the effect, when integrated over the entire population, of increasing the overall total incidence of skin can

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07717.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Alltrans‐retinal has been introduced (2 mol %) into artificial membranes made up of egg lecithin, cholesterol and dicetyl phosphate. Illumination of retinal‐enriched liposomes at 365 nm induced photodynamic damages; it triggered the sensitized oxidation of the lipids measured by the appearance of a 233 nm absorption band or by the formation of malonyl dialdehyde. Illumination produced an increase of the membrane fluidity detected with the spin label technique and led also to the lysis of the liposomes as revealed by the release of entrapped chromate ions or by changes in light scattering. Singlet oxygen is involved in these photodynamic effects. The results have been discussed in connection with the light damage phenomena which may afflict the rod outer segment membra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07718.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Continuous far‐red light operating through phytochrome reduces the rate of hypocotyl lengthening by a factor of 8. Consonant with this was a reduction of up to 12% in the proportion of total cytoplasmic ribosomes present as polysomes. A 2% reduction was elicited by brief red light. Evidence is presented which argues against these changes arising from a change in extractability or nucleolytic activity. The speed of the response (1.5 h) is much slower than that for inhibition of lengthening (15 min). The data therefore indicate that phytochrome is unlikely to act by controlling the general rate of translation in this instanc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07719.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.The efficiency of singlet‐singlet energy transfer was studied in bilayer lipid membrane vesicles (liposomes) for the following donor‐acceptor systems: (1)p‐terphenyl (TP) and diphenyloctatetraene (DPO); (2) DPO and chlorophylla(Chla); and (3) β‐carotene and Chla.The energy transfer efficiency φDAwas measured by sensitized fluorescence of the acceptor. Fractional quenching of the donor φQwas found from the donor fluorescence in absence and presence of the acceptor. For TP‐DPO and for DPO‐Chla, the transfer efficiency increased with increasing acceptor concentration but was essentially independent of the donor concentration. No energy transfer from β‐carotene to Chlacould be detected. In liposomes, φDAdiffered only slightly from φQat all donor and acceptor concentrations, thus demonstrating the absence of any appreciable energy losses. For solutions of the same donor‐acceptor pairs in cyclohexane φQwas considerably larger than φDA. The difference represents energy lost, principally by internal conversion, due to collisional quenching. The principal function of the lipid membrane appears to be the suppression of such losses. In addition, the rate of energy transfer in lipid membranes is about double that in solutions (at the same intermolecular distance) due to mor

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07720.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Abstract.Polarized absorption and fluorescence of chlorophyllaand bacteriochlorophyll solutions in nematic liquid crystal mixtures have been studied in the presence of an external electric field.The electric field caused a reorientation of the pigment molecules as concluded from changes in the polarized absorption. However, no correlation was found between the change in the polarized absorption and the change in the polarized fluorescence as a function of the field strength. The field influence was much stronger than expected only from the molecular orientation. The fluorescence polarized parallel to the direction of the liquid crystal was found to increase, whereas the similarly polarized absorption decreases. As a whole, the fluorescence yield significantly increased. It is suggested that the additional electric field is reinforced by a local field, most probably due to a protonation of the liquid crystal molecules.Charged solvent molecules are reoriented in an external electric field which changes the local electric field acting on chlorophylls. Similar changes in CHI fluorescence yield due to local electric field can be createdin vivoby the shift of charged molecules present in surrounding pigments. Such effects can be at least partially responsible for slow induction of fluorescence phenomena.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1978.tb07721.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY