摘要:

AbstractApplication of nearest‐neighbour band theory to the case of charges trapped on polymer chains shows that the trapping states can have an exponential energy distribution. Comparison with existing photoconduction data suggests that Fermi level in polymers is about 1eV below the conduction band, that the mobility activation energy is 0.1eV or less in commercial polymers and that the conduction bands are narro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08734.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractA variety of substances which quench the fluorescence of riboflavin decrease the rate of anaerobic photobleaching (photolysis) of the flavin at concentrations which have little effect on the fluorescence. A semi‐quantitative estimate of the yield of various products of photolysis using thin layer chromatography and autoradiography with C14‐labelled riboflavin shows that at least ten radioactive products are formed. Whereas the yield of most of these is decreased by low concentrations of quenchers, such as phenol, some are decreased only at quencher concentrations high enough to decrease the fluorescence significantly. The effects of quenchers on the phosphorescence and ESR signal induced by light were also observed. It is concluded that lumichrome arises, in part, from degradation of the excited singlet state, but that 9‐formylmethylflavin and other products arise through the triplet state. A major product of anaerobic photolysis is a substance moving just ahead of riboflavin on chromatograms and which, like 9‐formylmethylflavin, is destroyed by treatment with sodium hydroxide. Effects of varying the nature of the solvent, the flavin structure and the pH are reported, and the kinetics of processes involved in the primary photochemical acts and in quenching are di

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08735.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractAfter irradiation at 3655 Å of an aqueous frozen solution containing thymine and psoralen, a new photocompound was isolated by column chromatography. It contains a furocoumarin and a pyrimidine‐moiety linked together by the formation of a cyclobutane ring (see formulas II and III). By irradiation at 2537 Å in acetic acid solution, the photocompound breaks up again yielding psoralen and thymine. From an aqueous frozen solution containing cytosine and psoralen irradiated at 3655 Å, an analogous photocompound was obtained, which, however, consists of the addition to psoralen of a uracil molecule, instead of a cytosine one (IV, V). It has been stated that the hydrolytic deamination of the cytosine moiety to the uracil one takes place during the working up of the photocompound in aqueous solution after irradiation. Substances with properties similar to those above were obtained from bergapten (5‐methoxy‐psoralen) and thymine, from psoralen and thymidine or thymidylic acid, irradiated at 3655 Å.The new substances may be considered as model compounds in explaining the photoreactions which take place between the skin‐photosensitizing furocoumarins and DNA upon irradiatio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08736.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractThe excitation of the eosin‐human serum albumin complex has been investigated with spectral and photochemical techniques. Measurements of the changes in absorption and fluorescence spectra induced by complexing have shown that the first eosin molecule is held more strongly than the next few and that multiple binding leads to an enhanced fluorescence self‐quenching. Flash photolytic measurements indicate that dye‐dye quenching interactions enhance triplet eosin formation, and that oxygen quenching of the triplet is suppressed when the dye is singly bound. The quantum yield for aerobic photobleaching of the complex has been measured and is interpreted in terms of these fin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08737.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractThe ultraviolet (u.v.) irradiation of the 3′ isomer of cytidylic acid (Cp) produces the hydrate (Cp*) with water added across the 5–6 double bond. The yield of this photo‐product has been measured by, (a) separating the photoproduct by electrophoresis and (b) by observing the loss in absorbance. When corrections are made for reversal of the hydrate during the experiment, both methods gave the same result. Cross sections and quantum yields for the production of the hydrate were measured over the wavelength range 220 to 290 nm and over a pH range from 1 to 10. The quantum yield is markedly dependent on pH being higher by a factor of 6 to 10 for the neutral form. We have also demonstrated the existence of a very short lived photoproduct (half life 8–9 min) in both Cp3′ and Cp5′: The nature of this short lived product i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08738.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractParamecium multimicronucleatumwas irradiated with U.V. in solutions of differing osmotic pressures and ionic content. The rates of contraction and the diameters of the anterior contractile vacuoles were measured and changes in the volumes of solution entering the contractile vacuoles upon U.V. irradiation for paramecia maintained in solutions of differing ionic content were calculated. The volume of fluid entering the contractile vacuoles of paramecia irradiated (1) in standard balanced salt solution (SBSS) was regulated by a compensatory mechanism at lower U.V. doses but increased after relatively large U.V. doses; (2) in distilled water, increased after much smaller U.V. doses; (3) in isotonic balanced salt solution, showed little change upon irradiation.Increased osmotic pressure (with added sucrose) was found to reduce u.v.‐induced blistering of the pellicle, but in general U.V. damage was similar to that of paramecia in solutions of identical ionic content but lacking sucrose. Paramecia in SBSS with added sucrose to make it isomotic to the interior of the cell ruptured only after doses larger than for paramecia in SBSS lacking sucrose. Cell rupture of paramecia in solutions containing high CaCl2concentrations generally occurred later than for those in SBSS. High KCI concentration (unbalanced salt solution) in the presence of high CaCl2concentration provided some protection from U.V. irradiation to the paramecia. High NaCl concentration (unbalanced salt solution) in the presence of high CaCl2concentration appeared to increase u.v. damage to paramecia. Paramecia were most resistant to u.v. irradiation, as judged by the above criteria, when present in balanced salt solution enriched with calcium, thus simulating pond wate

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08739.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

AbstractThe quantum yield for the conversion of malachite green cyanide (MGL) to the oxidized form MG+has been measured over the wavelength range from 225 to 289 nm using a total absorption aluminium calorimeter to measure the flux of photons. The number of molecules of MGL converted was determined from the increase in absorbance of the solution at 622 nm. MG+was found to have a maximum extinction coefficient of 10.63 × 104at 622 nm. The quantum yield for the conversion of MGL to MG+is constant over the wavelength range with a value of 0.91 ± 0.01. The use of MGL as an actinometer for photochemical studies is describe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08740.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08741.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08742.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY