摘要:

Abstract—The fluorescence quenching of 3,4‐benzoquinoline, 5,6‐benzoquinoline and 7,8‐benzoquino‐Iine by dimethylmercury was examined inn‐hexane and acetonitrile between ‐ 30 and + 50°C. The data were obtained under conditions of continuous and pulsed irradiation.It is shown that the temperature effect observed on the Stern‐Volmer constant of fluorescence quenching of 3,4‐benzoquinoline is the result of a strong temperature dependent S1state lifetime.Furthermore, it appears that dimethylmercury does not form stronger exciplexes with aza‐aromatics than with the other hydrocarbons. Thus, complexation involves the π‐electronic system of the heterocyclic species which is consistent with the soft acid ch

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08952.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—On the basis of corrected fluorescence excitation and emission spectra, flavin photo‐processes in anisotropically vesicle‐bound flavins have been studied. By means of aliphatic C18H37‐chains at positions 3, 7 and 10, the flavin nucleus can be variously anchored within the membrane/water interface (amphiflavin), thereby mimicking the various positions and microenvironments of the isoalloxazine ring in flavoproteins. From polarization spectra, the angles between the different electronic transition moments of isotropically dissolved or membrane‐bound flavins have been obtained. Polarization and angle spectra of isotropically and various anisotropically embedded flavins exhibit strong differences, reflecting the specific interaction with the matrices. Based on a slightly modified theory, originally developed by Perrin and Weber, using the concentration dependence of fluorescence polarization, it is found that the radiative flavin‐flavin interaction (selfcontact) on the membrane is by a factor of 25 to 54 smaller than in isotropic solution. This is taken as further justification to study anisotropic flavin chemistry on the basis of flavin‐lo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08953.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—We have characterized the spectra, acidity constants and decay kinetics of the triplet and semireduced radical species of Safranin‐O. Between pH 3.0 and 10.6, there are three triplet species denoted3DH2 +2,3DH+and3D, the pKas being 7.5 and 9.2. All three triplet species exhibit first order decay, the rate constant for3DH+beingca.5‐fold lower than the rate constants of3DH+and3D. Ascorbic acid and ethylenediaminetetraacetic acid (EDTA) quench the triplet state under appropriate pH conditions and the pH dependencies of the yield of semireduced dye indicate that3DH+is more reactive than3DH+or3D. With EDTA as the reducing agent, there is the additional requirement that at least one of the amino nitrogens be deprotonated to obtain a significant yield of semireduced dye. In these reactions, ascorbic acid is oxidized reversibly, but EDTA is oxidized irreversibly, so that with the latter reducing agent photolysis causes buildup of the leucodye, which on subsequent photolysis can reduce triplet state dye. With ascorbic acid as the reducing agent, the regeneration of the ground state dye is reversible, the decay of the semireduced radical being second order. In general, the transient photochemistry of Safranin‐O resembles that of Thionine, the major difference being that the lifetimes of3DH2 +2and3DH+are much longer for Safranin‐O than for

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08954.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—The fluorescence decay of tryptophan‐25 in monomeric glucagon at pH 8.2 was measured at a series of emission wavelengths using pulsed laser excitation and single photon counting techniques. Double exponential kinetics were consistently observed, with time constants 3.26 and 1.11 ns. This allowed the steady‐state emission spectrum to be resolved into two components with differing intensities but similar emission maxima near 350 nm. Decay parameters were almost unchanged in the presence of 5.5Mguanidinium chloride. The dual emission is thought to reflect different conformers of the indole ring or of the peptide

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08955.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Triplet energy transfer from acetophenone, propiophenone and isobutyrophenone to γ‐methylvalerophenone has been examined in micellar solution using laser flash photolysis techniques. The kinetics of the processes are controlled by the rates of sensitizer exit from the micelle and by the distribution of energy acceptors in the micellar phase. The photosensitized Norrish Type II cleavage in sodium dodecyl sulfate micelles provides an example of efficient quantum harvesting; the biradical produced in the reaction has a lifetime of 92 ns, which suggests that the biradical resides in a polar hydroxylic environ

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08956.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—An important regulator of numerous physiological processes in higher plants is abscisic acid (ABA), which is photoisomerized from the more biologically activecisisomer to the nearly inactivetransisomer by natural sunlight. It is possible that this photoisomerization is a UV control mechanism in functions regulated by ABA.The quantum yields of both thecistotransandtranstocisphotoisomerizations were measured by an initial velocities method under various conditions of pH and oxygen concentration at room temperature. The yield for photoisomerization of cis‐ABA ranged from 0.25 at pH 3.0 to 0.11 at pH 7.0. Oxygen partially quenched the process. The quantum yield varies only slightly with wavelength.The quantum yield of photolysis of cis‐ABA is reported for pH 3.0 as 0.06. This yield also varies slightly with wavelength and is relatively insensitive to oxygen. This relatively high yield explains the loss of potency of ABA during UV irradiation.Phosphorescence ofcis‐ andtrans‐ABAis observed in methanol at 77 K. Onset of the emission is at 350 nm. The emission spectra is the same for both isomers.From these results a mechanism of UV action on plants based on the photoisomerization of the inactive trans‐ABA to the biologically activecisisomer

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08957.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—A general model is proposed to explain certain phenomena observed upon the near‐UV irradiation of biological materials. The model states that the ratio of two action spectra (e.g. in the presence or absence of histidine) does not accurately portray the absorption spectrum of the underlying chromophore. Rather, such a ratio is dictated by the relative amounts of two photoproducts. Both photoproducts are induced most efficiently at or below 300 nm. One photoproduct, sensitive to the presence of the variable agent (e.g. histidine), has a broader production spectrum than the other, which is induced independently of the variable agent. The first photoproduct is quantitatively more important at shorter wavelengths while the second dominates at longer wavelengths. An equation has been derived which defines the model in mathematical terms. Such a model might explain: (1) increased phage and bacterial inactivation in the presence of sublethal hydrogen peroxide concentrations; (2) the discrepancy between the inactivation action spectrum and absorption spectrum of psoralen; (3) histidine protection of transforming DNA inactivation; (4) phage T7 inactivation; (5) bacterial inactivation under anoxic conditions; (6) inactivation of DNA repair enzymes; and (7) photomutagenesis at low fiuence ra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08958.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Diazobicyclo (2.2.2) octane (DABCO) protects the genetic activity of purified transformingBacillus subtilisDNA against inactivation by near‐, but not far‐, UV light. The maximum dose‐modifying factor is 0.4, at 0.1MDABCO. Maximal protection is at about 350 nm and no protection occurs below 313 nm. The spectrum for protection is similar to that described for 2‐aminoethylisothiouronium bromide hydrobromide. The relevance of these observations with regard to the role of singlet oxygen in near‐UV effects i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08959.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—The induction of sister chromatid exchanges (SCE) and cell sensitivity in mouse myeloma cells (66.2 subclone of MPC11) by irradiation with monochromatic near‐UV (365 nm) light were studied under aerobic and anaerobic conditions. Sister chromatid exchanges were studied using the fluorescence‐plus‐Giemsa technique, and sensitivity was determined by the ability of irradiated and nonirradiated control cells to form colonies in soft agar. Cells were found to be 16 times more sensitive to near‐UV light under aerobic exposure, producing an F37value of 7 × 104J/m2compared to the F37value of 11.5 × 105J/m2under anaerobic conditions. The induction of SCE was also 12 times more efficient for aerobic irradiation than for anaerobic irradiation. The data suggest that the SCE‐inducing potential of DNA lesions differs when near‐UV irradiation is performed in the presence or absence of air. In addition, the DNA lesions responsible for lethality and also those lesions leading to SCE induction may differ under the two irradia

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08960.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Sets of G1, S, and G2 phaseXenopuscells were exposed to 15.0 Jm−2UV and their ability to photoreactivate the induced cell killing (loss of colony forming ability) and chromosomal aberrations was determined as a function of time following the UV exposure. Most of the lesions induced in G1 cells that lead to cell death were converted to a non‐photoreactivable state before the cells entered the S phase, while lesions leading to chromosomal aberrations were converted to a non‐photoreactivable state as the cells entered the S phase. In S phase cells the UV‐induced lesions leading to aberrations appeared to be converted to a non‐photoreactivable state at a much faster rate than those leading to cell death. A significant fraction of the lesions induced in G2 cells, that lead to cell death, were converted to a non‐photoreactivable state before the progeny of the exposed cells reached the next succeeding S phase. Few, if any, lesions were induced in G2 cells that were expressed as aberrations at the first mitosis following exposure. Some of the lesions induced in the G2 cells led to aberrations that were observable in the progeny that progressed to the second mitosis following exposure. These lesions were converted to a non‐photoreactivable state as the progeny of the exposed G2 cells progressed through the first S phase following exposure. These results suggest that the intracellular mechanism which expresses photoreactivable UV‐induced lesions as cell death is not identical to the mechanism which expresses such lesions as chromosomal aberrations, and the two mechanisms operate with different efficiencies in different phases

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb08961.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY