摘要:

Abstract—Kinetics of fluorescence quenching and photoreduction of lumiflavine by methionine in anaerobic aqueous solution show that the flavine reacts in the excited triplet state at a diffusion controlled rate. Individual rate constants and activation energies are determined for the proces

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05868.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—Duroquinone shows no or only very slight dehydrogenation of solvents on flashing or irradiating (Λ>330 nm) solutions in ethanol, isopropanol,tert.‐butanol, cyclohexane or paraffin. Reversible reactions of excited duroquinone occur with its photochemical reaction products durohydroquinone and duroquinone dimer in preirradiated solutions. The results show the photochemical behaviour of duroquinone to be quite different from that of other quin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05869.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The absorption and fluorescence spectra of acridine, phenazine, their cations and phenazine‐di‐N‐oxide are studied in several polymer matrices. There is a one‐to‐one correspondence between previously measured spectra in fluid media and those reported here for plastic media. The matrix‐induced spectral shifts are dependent upon the polarity and hydrogen‐bonding ability of the polymer substrate. Environmental perturbations are also produced by high pressures (0–27 kbar) applied to the polymer matrix. Specific interactions between polymer substrate and the electronically excited solutes are evident from pressure‐induced red shifts of the fluorescence and changes in quantum yields under pressure. These interactions between solute and its microscopic environment are subtle and varied for this group of nitrogen hetero‐cyclics, although their effects are smaller than those encountered in the adsor

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05870.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—Ultraviolet irradiation of14C‐uracil in aqueous solution results in the formation of hydrate and dimer photoproducts. The rate of dimerization increases with increasing uracil concentration, and decreases with increasing concentration of oxygen in solution. The kinetics are in agreement with a model previously proposed to account for the reactions, in which dimerization occurs by a reaction involving the triplet state of uracil, but hydration occurs from an excited singlet state. Oxygen reduces dimer formation by quenching the triplet. The quantum yield for intersystem crossing (ISC) to the triplet depends on the irradiation wavelength, increasing from 0.0014 at 280 nm to 0.016 at 230 nm. The ratio of rate constants for reaction of the triplet with oxygen and for dimerization is 1.1; the ratio of rate constants for triplet decay and for dimerization is 5.9 × 10‐5M. The increase in ISC with photon energy suggests that ISC is favoured from excited vibrational levels. The quantum yield for hydration is about 0.002 at pH 4.5 for all wavelengths, but increases as the pH is dec

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05871.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—Delayed light emission (measured 4 msec after excitation) and the light‐induced red shifts of the bacteriochlorophyll and carotenoid absorption bands of chromatophores ofRhodopseudomonas spheroideswere inhibited by a variety of reagents. These included anti‐mycin A, NQNO, CCCP, desaspidin, quinacrine, chlorpromazine, 2,4‐dinitrophenol, gramicidin D, Triton X‐100 and valinomycin in the presence of potassium, cesium or ammonium ions. Delayed light emission was enhanced by orthophenanthroline, ethanol, succinate and glutathione.Delayed light emission from chromatophores ofRhodospirillum rubrumwas attenuated during photophosphorylation but restored approximately to its initial value in the presence of oligomycin. Since the delayed light and band shifts are inhibited under conditions which tend to deplete or block the formation of high energy phosphorylation intermediate, it is suggested that the presence of a high energy intermediate is a prerequisite for the appearance of each of the three

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05872.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The decay of the delayed fluorescence intensity of Chlorella cells following a brief flash of light is investigated in the region of time from 1 msec to 1 sec with greater accuracy than previous investigations. It is found that the best mathematical description for this decay is the sum of several exponential decays and is thought to be evidence for the existence of several distinct components in the production of delayed fluorescenc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05873.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The cations resulting from eleven retinal‐related polyenes by placing the latter in n‐butanol‐sulfuric acid were examined spectroscopically in an effort to explain the batho‐chromic effect observed in visual pigments. A comparison of the Λmaxvalues, intensities and 1/2‐band widths of the model carbonium ions with those of the visual pigments does not seem to justify the representation of the chromophore in visual pigments as a pure c

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05874.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—ESR studies have been made of the kinetics of semiquinone radical formation and disappearance resulting from the reversible photosensitization by chlorophyll of hydroquinone oxidation in a pyridine‐water solvent. The rate of radical decay was found to be second order with respect to the radical concentration, with a rate constant of 6.7 × 105l./mole sec at ‐30°C and an activation energy of 6900 cal/mole. The rate of radical formation was recombination‐limited and, through the use of β‐carotene as a quencher, the rate constant was determined to be 8.81 × 105l./mole sec at ‐30°C. The effect of light intensity and hydroquinone concentration on the rate of semiquinone radical formation and on the steady state radical concentration was also investigated and possible mechanisms to explain the resul

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05875.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05876.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05877.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY