摘要:

Abstract—The light emitted by adenine and thymine and the related nucleosides and nucleotides in ethylene glycol/water glass during irradiation at 77°K with X‐rays and 270 nm U.V. light has been studied. It was found that the same radiative levels were excited by both types of radiation. However, the phosphorescence to fluorescence ratios observed with X‐rays were considerably enhanced relative to those obtained with U.V. light. This observation was taken to mean that a major fraction of the excitation results from ion recombination, although direct excitation of the triplet manifold as well as intersystem crossing between upper excited levels may have contributed to the enhancement as well. The yields of the X‐ray‐induced excitation of radiative levels. which were calculated by combining the yields of X‐ray‐induced emission and the quantum yields observed with u.v.‐excitation, corresponded to:G≥ 4.0 excitations per 100 eV of dose absorbed in the solute for adenine andG≥ 1.8 for thymine. The excitation yields obtained for the nucleosides and nucleotides were somewhat smaller than those observed for the corresponding bases. It was inferred from the yields that a substantial fraction of the dose absorbed in the ribose of the nucleosides was transferred to the radiative levels of t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05972.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Ultraviolet excitation of pyrimidine derivatives in aqueous solutions containing acrylonitrile can lead to polymerisation of acrylonitrile and/or photoaddition reactions of acrylonitrile and the pyrimidine. Polymerisation of acrylonitrile induced by excitation of orotic acid occurs even in aerated solutions and is very likely due to radicals derived from excited orotic acid molecuies. Using14C‐labelied orotic acid, the polymer is shown to contain the pyrimidine. With other pyrimidine derivatives, polymerisation is observed only in deaerated solutions and its low yield did not allow us to determine whether the polymerisation is induced by radicals or by photosensitisation. The role of the lowest excited singlet and triplet states of the pyrimidine derivatives in the photoaddition reaction is discussed. In the case of orotic acid, photoaddition is shown to proceed entirely by way of the triplet st

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05973.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The pigmentsin vivoof single cells ofChlorella pyrenoidosawere studied by the microspectrophotometric technique. An accessory recording the first derivative of absorption was used to obtain fine resolution and enhanced accuracy. The results suggest that there are several long‐wavelength components of Chla in vivo.In addition, there seem to be four short‐wave forms of Chla.It is also likely that Chlbexistsin vivoin two different forms. The existence of all these forms was demonstrated at room temper

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05974.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—Saturation of optical absorption by an aqueous solution of the amylose‐iodine‐iodide complex was observed. Transmission of ruby laser radiation as a function of incident laser power density was measured and fitted to the steady‐state solution of a double‐absorption rate‐equation model. This study gave an indirect determination of the lifetime of the first excited energy level. The material behaved as a passiveQ‐switch for

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05975.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The u.v.‐induced degradation of the DNA of therecA1mutant ofEscherichia coliK‐12 has been further investigated. The extensive degradation was mostly prevented by an additional mutation in theuvrAgene. Furthermore, when amino acid‐starvedrecAbacteria were irradiated and held under a condition preventing DNA replication, the DNA was degraded very little. The mode of u.v.‐induced DNA degradation was investigated by comparing the time course of release of label from the acid‐insoluble fraction of two growing cultures of arecA uvrAdouble mutant; the one was pulse‐labeled with3H‐thymidine and the other was pulse‐labeled and chased thereafter for 12 min. It was found that, in spite of very little degradation of the bulk of DNA. the label incorporated into the former culture was lost rapidly from the acid‐insoluble fraction. while the label incorporated into the latter culture was not. It was concluded. therefore. that breakdown of the replicating point is characteristic ofrecAmutants and that degradation of the bulk of DNA is induced in some way by the function of theuvrAgene. Therefore, the degradation of the major part of DNA which follows the degradation of the replicating point appears to be a s

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05976.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The effect of relative humidity on the survival and sensitivity to radiations ofStreptococcus liquefacienshas been studied. The micro‐organism was found to be little affected by dehydration in aerosols and its sensitivity to the lethal action of 2537 Å light to be unaffected by changes in the relative humidity at which the cells were held during irradiation. The cells were more stable to the lethal action of 3200–4000 Å, however, when they were held at 70% relative humidity than at 50 or 30% relative humidity. Mutant cells unable to liquify gelatine were induced by semi‐dehydration at 50% relative humidity and their numbers were increased by concomitant irradiation with 3200–4000 Å light. This type of mutant was not observed when the cells were irradiated with 2537 Å light. Mutant cells which had a different response from that of the parent cell to the presence of oxygen in their growth medium were produced by both wavebands of light, but only when the cells were held at 50% relative humidity. It is proposed that semi‐dehydration stresses the cell membrane and damages those parts of the bacterial DNA associated with the membrane. Concomitant irradiation is suggested to enhance this pa

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05977.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Abstract—The properties of a pulsed ruby laser beam focused through a triocular microscope were studied in relation to microsurgery. Quantitative studies on ‘model tissues’ with different absorbencies at 6943 Å revealed that the spot diameter of the focused microbeam was dependent upon several factors. It decreased with (1) a decrease in the absorption by the object at 6943 Å; (2) a decrease in the energy of the microbeam; and (3) an increase in the magnification of the microscope. The existence of the ‘tube of effect’ in the optical path of the focused micro‐beam was realized by irradiating the object at different planes. The depth of the tube of effect increased with (1) increase in laser energy or (2) decrease in magnification. By employing certain plant species (Spirogyra praetensisTranseau,Ulva lactucaLinnaeus,Porphyra miniata(Lyngbye) C. Agardh andElodeasp.) the reaction of the protoplasm to the laser microbeam in terms of ‘primary damage’ and ‘secondary damage’ was defined. Based on these experimental data the concept of minimal visible spot size in laser microsurgery and its limi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05978.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05979.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05980.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1970.tb05981.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY