摘要:

Abstract—Semiconductors with a sufficiently large energy gap, in contact with an electrolyte, can be used as electrodes for the study of electrochemical reactions of excited molecules. The behavior of excited chlorophyll molecules at single crystal ZnO‐electrodes has been investigated. These molecules inject electrons from excited levels into the conduction band of the electrode, thus giving rise to an anodic photocurrent. The influence of various agents on this electron transfer has been studied. In the presence of suitable electron donors (e.g., hydroquinone, phenylhydrazine) in the electrolyte chlorophyll molecules, absorbing quanta, mediate the pumping of electrons from levels of the reducing agents into the conduction band of the semiconductor‐electron acceptor. The electron capture by the semiconductor electrode is irreversible, when an adequate electrochemical gradient is provided in the electrode surface. Some properties of excited chlorophyll at semiconductor electrodes (unidirectional electron transfer, highly efficient charge separation, chlorophyll as electron pump and able to convert electronic excitation into electric energy) show similarity to the behavior of chlorophyll in photosynthetic reaction ce

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06156.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—(1) By excitation at 295 nm tryptophan fluorescence from 17 proteins was examined free of contributions from tyrosine. The tryptophan quantum yields for native proteins were both higher and lower than that of the free amino acid and spanned a 5‐fold range. No simple relationship was apparent between ‘exposure’ of tryptophyl side chains in proteins and the magnitude of the quantum yield or of the position of the emission maximum. (2) Denaturation of these proteins in 6Mguanidine hydrochloride considerably narrowed the range of values of yields (ca0.1 to 0.17). While reduction of the disulfide bridges altered the yield of several proteins, it appeared to have no general effect on narrowing the range observed with a group of proteins, suggesting that either: (a) the amino acid sequence around a tryptophan in a disrupted peptide chain influences the yield, or (b) ‘residual’ three dimensional structure persists in reduced denatured proteins. (3) It was possible to demonstrate using both 280 and 295 nm excited spectra that tyrosine fluorescence, while weak, is generally present in proteins. These data also showed that transfer of the excited state from tyrosine to tryptophan is a common occurrence in native proteins and occurs with very high efficiency in a numb

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06157.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—By comparing the photochemical behaviour of tryptophan and N'‐methyl tryptophan, both in the free state and protein bound, evidence has been obtained which indicates that indole N—H bond fission is a primary photochemical reaction during the photolysis of tryptophan with 300–360 nm radiation. ESR evidence suggests that immediately following N—H bond fission, rearrangement of the indole nucleus occurs to form the 3‐indolyl free radical. This radical was found to be quite stable in a frozen matrix at 150°K, but has a lifetime of only 50

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06158.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Rate constants for both radiative and non‐radiative relaxation of the fluorescent state of indole and several methyl‐indoles in solution have been calculated from fluorescence lifetime and quantum yield values.Radiative relaxation for indoles is solvent dependent while non‐radiative relaxation is attributed to at least two processes, one of which is both solvent and temperature dependent. The latter process measured in aqueous solvents manifests a pattern of compensation of activation enthalpy by activation entropy with an isokinetic temperature for indole of 283°K.A quantitatively consistent description of the excited‐state behavior of 1‐Me‐indole in both free and exciplex state is provided. Small deviations in fluorescence parameters for indole suggest a more complicated

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06159.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Monomer, trimer and hexamer states of C. Phycocyanin chromophore protein have been isolated. Owing to a very slow approach to equilibrium mixing, it has been possible to estimate the number of each type of the two chromophores ‘s’; and‘f’present, using a fluoros‐cence polorization method. It is found that there is one s chromophore and onefchromophore per protein monomer of molecular weight 30,000, a value in agreement with the monomer mol. wt. determined by Bernset aland by thermodynamic measurements in this laboratory. Absorption and fluorescence spectra of hexamer and monomer solutions have been compared. The hexamer solution shows greater fluorescence than the monomer solution, a phenomenon that may be attributable to a change in environment of chromophore following polymerization, with consequent change of fluorescence yield of each chromophore type and/or variation in energy transfer b

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06160.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Photolysis of tritium‐labelled thymine‐derived photoproducts by 254‐nm ultraviolet radiation (u.v.) in conidia ofStreptomyces griseuswas measured by chromatography of cell hydrolysates. The relative photolysis cross‐sections of uracilthymine dimer (UT○) at various wavelengths are the same as those of thymine‐thymine dimer (TT○), and their ratios at 313, 365, 405 and 436 nm are 2:1:2:3. Except at 436 nm, these relative values agree very well with cross‐sections previously reported for photoreactivation of u.v. killing in this organism, leading to the conclusion that photoreactivation in the wild type is due to repair of cyclobutane‐type pyrimidine dimers. In a mutant showing restricted photoreactivation (S. griseusPHR‐1), post‐u.v. treatments at the above wavelengths did not affect UT○ and TT○ in the conidia, supporting the earlier suggestion that this organism does not contain active PR enzyme. Another u.v. photoproduct, the precursor of a pyrimidine adduct (PO‐T) that appears in cell hydrolysates, was removed from both wild‐type and mutant cells very efficiently at 313 nm. This is presumably a direct photochemical reaction. In addition, in wild‐type cells, the precursor of PO‐T appeared to be inefficiently removed photoenzymatically at all wavelengths. Removal of the precursor of PO‐T appears to be biologically sig

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06161.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Absorption and emission spectra of several N‐arylbenzamides have been measured. The quantum yields for their fluorescence were found to be dependent on matrix viscosity and temperature. Singlet‐triplet splittings for these compounds were determined from their emission spectra and found to be abnormally small forπ. π*states (˜ 1500 cm‐1). Indeed, the phosphorescencemaximaof N‐arylbenzamides occur slightly to the blue relative to their fluorescence maxima. Intersystem crossing efficiencies were determined for several of these compounds and are consistent with S1→S0radia

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06162.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The time dependence of the delayed light in the green algaChlorella pyrenoidosahas been examined quantitatively in the 1 to 12 msec range after excitation with light pulses (A = 6328 Å) of 100 μsec and 4.5 msec duration. We have confirmed the data of Tollin, Ruby, and Bertschet al., on the time course of the delayed light in the msec range. New experiments, with 100 μsec flash excitation, on the time dependence of the delayed light emitted byChlorellatreated with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DMU), hydroxylamine, methyl violgen, and various combinations of these chemicals are presented. Also, data on the dependence of the delayed light intensity on the intensity of the excitation light in the 1.5 and 5.0 msec range are reported. The square law dependence, reported by Jones, in the 140 and 250 msec range is confirmed in the 1.5 and 5.0 msec range at very low light levels.The experimental data on delayed light has been analyzed in terms of a model which incorporates triplet exciton fusion. The following major points result from this analysis: (1) A triplet exciton kinetic model can explain both the time dependence and the excitation intensity dependence of the delayed light emitted byChlorella. (2) The density of triplet excitons predicted by the model from the observed delayed light intensity is much less than that which can be detected by flash photolysis measurements. Therefore, the failure of such measurements to detect triplet statesin vivodoes not disprove the model. (3) The possibility of changes in the rate of electron transfer reactions of photosynthesis is included in the kinetic model. The predictions from the model are compared with the effects of chemical additives on the time dependence of the delayed light decay. (4) The proposed triplet exciton model predicts that the delayed light intensity may, under certain specific conditions, be affected by a magnetic field. The negative result of an attempt to observe this effect is reported and discussed. (5) It is concluded that the proposed triplet ‘fusion’ model is a valid alternative to the electron‐hole r

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06163.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06164.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06165.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY