bluuebunny/crossref_metadata_2025_split huggingface dataset:
A SOLUBLE PROTEIN‐CHLOROPHYLL COMPLEX FROM SPINACH CHLOROPLASTS 11. THE PHYSICAL AND PHOTOCHEMICAL PROPERTIES OF THE COMPLEX*
Authors: Kahn Joseph S. , Bannister Thomas T. 
Published: January 2008

Abstract— Some physical and photochemical properties of a proteinxhlorophyll complex which can be extracted from spinach chloroplasts with dilute Triton X‐100, have been measured. The molar extinction coefficient at the red maximum (671 mμ) is 6.8 × 104. Solutions of the complex are weakly fluorescent, having a quantum yield of about 0.01. The complex undergoes photoautooxidation in the presence of oxygen with a quantum yield of about 0.2 × 10‐‐4, and sensitizes the autooxidation of p‐toluene‐diamine (quantum yield about 1×10‐‐3) and of ascorbic acid (quantum yield 0.25). The complex‐catalyzed reduction of ferricyanide, in the presence of a protein‐carotene complex, was confirmed; its quantum yield is about 8 × 10‐‐4. The protein‐chlorophyll complex does not undergo a Krasnovsky reaction, nor could sensitized reductions of dye by abscorbate be detected. When excess Triton is added to the protein‐chlorophyll complex, it is converted into a detergent colloid apparently identical to a previously described Tween colloid.The properties of the protein‐chlorophyll complex are compared with those of other states of chlorophyll in vivo and in vitro.
THYMINE DIMERIZATION IN L‐STRAIN MAMMALIAN CELLS AFTER IRRADIATION WITH ULTRAVIOLET LIGHT AND THE SEARCH FOR REPAIR MECHANISMS
Authors: Klímek Miroš 
Published: January 2008

Abstract— The formation of thymine dimers in the DNA of L‐strain mammalian cells after irradiation with ultraviolet light has been demonstrated. The amount of dimer formed rises with the dose of u.v. light.In the course of post‐irradiation incubation the thymine dimers remain in the TCA insoluble fraction and diminish as did the other thymidine‐H3 derivatives with increasing incubation time. The dimer is not found in the soluble fraction. Thus, dimer excision (i.e. its liberation into the soluble fraction) as an expression of repair of radiation damage analogous to dark repair in E. coli was not found in these experiments.
INVESTIGATION OF MAGNESIUM TETRABENZPORPHYRIN‐I.:ABSORPTION AND FLUORESCENCE IN ORGANIC SOLUTION AND AQUEOUS MEDIUM
Authors: Goedheer J. C. , Siero J. P. J. 
Published: January 2008

Abstract Absorption and fluorescence properties of a magnesium containing porphyrin pigment are described which generally resemble those of the cholorophylls.In organic solvents the absorption bands are appreciably sharper than those of the naturally occurring magnesium porphyrins, while the fluorescence yield is approximately equal. Dilution of alcoholic or other water miscible solvents with buffer or water results in the formation of non‐fluorescing “colloidal” pigment forms. Two are forms are evident which differ spectroscopically and photochemically. Addition of detergent prevents formation of such forms or may restore the “in solution” properties.
ON THE LUMINESCENCE OF L‐TRYPTOPHANE AND l‐TYROSINE IN AQUEOUS SOLUTION AT 77dK INDUCED BY X‐RAYS AND U.V.‐LIGHT
Authors: STEEN H. B. 
Published: January 2008

Abstract— The lumincscence arising from L‐tryptophane and L‐tyrosine in aqueous solutions at 77d̀K during irradiation with u.v.‐light and with X‐rays has been studied. The spectra obtained with the two types of radiation were largely similar, differing only in that the yields of phosphorescence relative to fluorescence were considerably enhanced in the case of X‐irradiation. The decay times observed for the exponentially decaying phosphorescence, being 6.6 sec and 2.7 sec for tryptophane and tyrosine respectively, were the same for both kinds of irradiation. The G‐value of the X‐ray induced luminescence was about 10 for both tryptophane and tyrosine. Thus, about 30 per cent of the total energy absorbed from X‐rays in these compounds was re‐emitted as light.It was concluded that the X‐ray induced fluorescence and phosphorescence originate from the same levels as does the luminescence caused by u.v.‐light, i.e. the lowest excited singlet and the lowest triplet level of the aromatic structure of these compounds. In the case of X‐irradiation the enhanced ratios between the yields of phosphorescence and fluorescence indicated that some process other than excitation directly from the ground state contributed considerably to the luminescence yields. Assuming this process to be a recombination between the ionized molecule and its electron, it was calculated that the contribution to the luminescence yield from excitations directly from the ground state relative to that from ionizations, was negligible for both compounds.
THE VARIATION OF RADIATION SENSITIVITY OF BACTERIA FED TETRAHYMENA PYRIFORMIS DURING THE GROWTH CYCLE AND FACTORS RELATED TO ITS ORIGIN
Authors: Calkins J. 
Published: January 2008

Abstract— Tetrahymena pyriformis shows a cyclic variation of sensitivity (for lethality) to u.v. light while the response to X‐rays is almost constant throughout the growth (division to division) cycle. It is demonstrated in this paper, and elsewhere, that survival of caffeine treated animals is higher after higher doses than after the lower doses of radiation; such a response indicates that the increased radiation dose induces a resistant state not existing at lower doses. Response of synchronized animals to postirradiation treatment with caffeine is interpreted as indicating that recovery from the lethal effect of radiation has two components as previously postulated: (1) a caffeine sensitive recovery system (termed the ‘N’ system) and, (2) an activated recovery capacity (termed the 'T’ system) which is less sensitive to caffeine.The maximum activated (T) system repair capacity only equals the repair capacity of the (N) non‐activated system for X‐ray induced lesions and, since the N system does not seem to show a cyclic variation of effectiveness for X‐ray induced lesions, the X‐ray survival remains constant throughout the growth cycle.The repair capacity of the activated (T) repair system is, throughout most of the cycle and especially during the S period, much greater than that of the N system for u.v. induced lesions. Thus the u.v. response vanes in a manner largely dependent upon the capacity of the activated system and the fraction of the population showing the activated response; in G2, a time when the activated repair system is rather ineffective, the non‐activated (N) system appears to become unusually efficient in the repair of u.v. induced lesions.
THE REACTION OF METHYLENE WITH HYDROGEN
Authors: Powell‐Wiffen J. W. , Wayne R. P. 
Published: January 2008

Abstract— An investigation has been made of the reaction between methylene, formed by the photolysis of ketene, and hydrogen. Ethane, ethylene and methane are the major hydrocarbon products, and it has been shown that the formation of these products may be adequately described by the sequence of processesCH2CO +hv→ CH2+ CO (1)CH2+ H2→ CH3+H (2)2CH3→ C2H6 (3)CH3+ H2+ CH4+ H (4)CH2+ CH2CO → C2H4+ CO (7)In particular, the relative rates of ethane and methane formation are consistent with the known rate constants for reactions (3) and (4), and it is not therefore necessary to postulate the participation of an ‘insertion’ processCH2+ H2→ CH4 (6) to account for the formation of methane.Decrease of the energy possessed by the methylene, either by increase of the wavelength of ketene photolysis, or by increase of gas pressure, is shown to result in an increase in the reactivity of the methylene towards ketene relative to its reactivity towards hydrogen (i.e. the ratio k2/k2 increases).
PHOTOPROCESSES AND MOLECULAR ASSOCIATIONS*
Authors: Leterrier F. , Douzou P. 
Published: January 2008

Abstract— The progressive reduction in temperature of hydro‐alcoholic mixtures is a way of associating aromatic molecules. It is possible to test the solute association, both by absorption and fluorescence measurements, of ‘polymerizable dyes' and solutes of biological interest. It is also possible to test the solute association by electron spin resonance of stable radicals (Wür‐ster's blue). The application of this technique to the study of photoprocesses was performed with flavin mononucleotide (FMN) by electron spin resonance and absorption spectroscopy in order to analyze the mechanism of photoreduction, and the stability of photo‐induced free radicals.The procedure of associating molecules by temperature effect in these solvents can be applied to the spectroscopic studies of the triplet state of aromatics in glassy solutions at 77°K.
THE CHEMILUMINESCENCE OF INDOLE DERIVATIVES IN DIMETHYL SULFOXIDE*
Authors: BERGER A. W. , DRISCOLL J. N. , DRISCOLL J. S. , PIROG J. A. , LINSCHITZ H. 
Published: January 2008

AbstractThe chemiluminescent autoxidation of over fifty indoles has been measured in dimethyl sulfoxide (DMSO). The 3‐alkylindole derivatives represent the brightest and most efficient members of this group.The chemiluminescence yield (per mole) of skatole is (1·5 ± 0·6) × 10‐3. The chemiluminescence spectrum of skatole is identical with the fluorescence spectrum of o‐formamidoacetophenone in the same environment Similar results for 2,3‐dimethylindole lead to the identification of the acylamide anion as the emitter in indole chemiluminescence. A peroxide ring cleavage excitation mechanism is proposed.
TRIPLET BEHAVIOR OF ORGANIC COMPOUNDS
Authors: GRIFFIN R. N. 
Published: January 2008

Abstract— The rates of phosphorescence decay of nine compounds in frozen glass were measured. Six of the nine compounds decay exponentially, indicating that previously reported non‐exponential decay of some of them may have resulted from impurities, probably in the solvent.Three compounds – acetophenone, phenanthrene, and acridine orange–have unusual decay kinetics. Acetophenone has no wavelength–dependence of rate, but the decay is non‐exponential at all observed stages. The effect is believed due to a multiplicity of metastable excited states, all of which ultimately decay through a common lowest triplet. The delayed emission of phenanthrene in frozen glass consists of phosphorescence and a P‐type delayed fluorescence in the dimer band only. The ratio of the rates of decay of phosphorescence and delayed fluorescence is nearly the same in frozen glass as it is in liquid solution. It is suggested that excimers can be formed by molecules up to 100 A apart, and that the description ‘excited dimer’ is misleading. Finally, acridine orange has a P‐Type delayed fluorescence which decays initially with second‐order kinetics. The first‐order kinetics generally observed in P‐type delayed fluorescence are merely the result of the relative importance of competitive unimolecular reactions in depopulation of the triplet state.
THYMINE‐DIMER AND ACTION‐SPECTRUM EVIDENCE FOR INDIRECT PHOTOREACTIVATION IN ESCHERICHIA COLI*
Authors: Jagger John , Stafford R. S. , Snow Jeanne M. 
Published: January 2008

Abstract— Cells of Escherichia coli B and B phr‐ were labeled with tritiated thymidine, exposed to inactivating ultraviolet radiation at 254 nm, given photoreactivation (PR) treatment immediately thereafter, and then immediately hydrolyzed and assayed for thymine‐containing dimers. It was found that (1) PR treatment of strain B phr‐ does not split thymine dimers and (2) the amount of splitting of thymine dimers in strain B at 334 nm is only 45 per cent of the amount of splitting observed at 405 nm for the same amount of biological PR. These findings show that all of the PR in E. coli B phr‐, and part of the PR at 334 nm in E. coli B, is indirect (does not use PR enzyme) and is not due to thymine‐dimer splitting.Action spectra for PR in Escherichia' coli strains Bs‐1 and B/r were obtained. At wavelengths below 366 nm (the indirect PR region), PR is relatively much more efficient in strain B/r in logarithmic phase than in strain B/r in stationary phase or in strain Bs‐l. This is consistent with the expectation that indirect PR would not be exhibited by strains, such as Bs‐1 that lack dark‐repair ability, or by certain strains in the stationary phase, such as B/r, which, upon plating, have a ‘built‐in’ growth delay that can permit optimal dark repair, but indirect PR would be exhibited by intermediate cases, such as in strain B (which is less resistant to u.v. than strain B/r) or in strain B/r in logarithmic phase. These findings support the hypothesis that indirect PR results from enhancement of dark repair.
STUDIES ON FLAVINS IN ORGANIC SOLVENTS — III. SPECTRAL BEHAVIOUR OF LUMIFLAVIN
Authors: Kozioł Jacek 
Published: January 2008

Abstract— The absorption and fluorescence emission spectra of lumiflavin have been studied in nonaqueous solvents of different polarity. The corrected emission spectra show apparent mirror symmetry to the longest wavelength absorption maximum. In view of high molar extinction coefficient of the longest wavelength maximum in absorption spectra, constant polarization of fluorescence across it in dioxane and high values of quantum yields of Buorescence, τ→τ* character of corresponding electronic transition was proposed. Roughly linear correlation was found between transition energies and quantum yields of fluorescence on the one hand, and polarity of solvents expressed in Kosower's ‘Z’ values (excepting acetic acid) on the other.In preliminary experiments it was found that lumiflavin in dioxane and in acetic acid is strongly photodecomposed by the monochromatic(436 nm) light.
EXCITED STATES OF SIX‐MEMBERED N‐HETEROCYCLES. FLUORESCENCE, PHOSPHORESCENCE AND ACID—BASE EQUILIBRIA OF ELECTRONICALLY EXCITED PHENAZINE
Authors: GRABOWSKA A. , PAKUŁA B. 
Published: January 2008

Abstract— An account of a systematic study of the acid‐base equilibria of phenazine in the two lowest excited (π,π) states is presented. Pure electronic levels of the free base and of both its protonated forms have been located by spectroscopic methods. Fluorescence, phosphorescence and corresponding absorption spectra have been measured. The O‐O energies of the free base, of the singly‐protonated species and of the doubly protonated form in the lowest triplet state (3Lα(π, π)) are: 15, 475 cm‐1, 14, 175 cm‐1 and about 9300cm‐1, respectively. This last value has been estimated from the experimentally determined S‐T splitting in the other two forms. Corresponding energies of the lowest singlet state (ILα(π,π)) are: 23,500 cm‐1, 21,250cm‐1 and 17,300 cm‐1. The fluorescence of the free base has been found in polar as well as in non‐polar solvents and has been checked by the fluorescence excitation spectrum. Fluorescence quantum yields for the free base have been measured: 8.6 times 10‐4 and 3.0 × 10‐5 in ethanol and hexane solutions, respectively. Emission in ethanol has been ascribed to (π,π), that in hexane —to (π, π). fluorescence.The changes of pKα's under excitation, calculated from the Forster's cycle, are equal: δpKa1=+2.8±0.3; δpKa11≅+10±1.5 in the lowest (π, π) triplet state and δpKa1=+4.8±0.5; δpKa11=+8.4 ± 0.5 in the lowest (π,π) singlet state. The δpKa11 in the triplet state is at least as high as that in the 1La(π, π) state. P P P calculations of the electronic levels and of the molecular diagrams have been performed. The energies obtained exceed experimental values by not more than 0.5 eV. An increase of the net charge on nitrogen δp under excitation has been found to be +50, +70 and +19 per cent in the 1La, 1Lb and 3La states, respectively. A good correlation has been found between δpKa1 and δp in both excited states, which have been studied experimentally.
PHOTOCHEMISTRY OF TOBACCO MOSAIC VIRUS RNA. EFFECT OF HCN*
Authors: EVANS NEIL A. , SAVIGE W. E. , McLAREN A. D. 
Published: January 2008

Abstract— In attempting to sort out possible mechanisms of photoreactivation of tobacco mosaic virus RNA (TMV‐RNA) inactivated by ultraviolet radiation (u.v.) in buffer of ionic strength 0.25, we have investigated the effect of HCN on the quantum yield for u.v. inactivation of TMV‐RNA and on the percent photoreactivation of inactivated TMV‐RNA. Some photo‐products produced by irradiation of model substances, polyuridylic acid (poly U) and polycytidylic acid (poly C), in the presence of HCN have also been studied.The ratio of the quantum yield for inactivation of TMV‐RNA in the presence of HCN to that in the absence of HCN is 1.5, under non‐photoreactivating conditions. By comparison, the ratio of the initial rates of loss of uracil residues in poly U under comparable conditions is 1.6; by contrast, the rate of loss of cytosine residues in poly C is unaffected by HCN. This similarity of ratios between poly U and TMV‐RNA suggests that two of the mechanisms of u.v. inactivation of TMV‐RNA at high ionic strength are akin to known reactions of uracil residues in poly U, i.e. hydrate and dimer formation.The photohydration reaction in poly U, as measured by the heat reversal of hydrated residues to uracil residues, is almost abolished by HCN, and the rate of dimerization, as measured by the appearance of dimer containing oligonucleotides following enzymatic hydrolysis of irradiated poly U, is reduced to half by HCN. HCN does not affect the rate of hydration of cytosine residues in poly C. Since photoreactivation of RNA inactivated in presence of HCN is only 60 per cent of that in absence of HCN it is suggested that uracil dimers are somehow involved in photoreactivation of TMV‐RNA inactivated at high ionic strength.
MIGRATION OF EXCITATION ENERGY FROM THIONINE TO METHYLENE BLUE IN MICELLES
Authors: SINGHAL G. S. , RABINOWITCH E. , HEVESI J. , SRINIVASAN V. 
Published: January 2008

Abstract— The main absorption bands of thionine (Th+) and methylene blue (MB+) in aqueous solution lie at 598 nm and 664 nm, respectively. This position permits excitation energy transfer from Th+ to MB+, but not vice versa. We describe here studies of such transfer between these molecules adsorbed on micelles of sodium lauryl sulfate (SLS), imitating, at least to some extent, the state of pigments in chloroplasts.The SLS concentration was varied from 3.0 to 11 × 10‐3M. In the presence of dye, aggregation to micelles, each containing 70–100 detergent molecules, begins at about 3.0 × 10‐3M SLS. Practically all dye ions are adsorbed on these micelles as soon as their formation begins.Energy transfer from adsorbed Th+ ions to adsorbed MB+ ions can be demonstrated by observing the quenching of the fluorescence of thionine and the sensitization of that of methylene blue.At [Th+] = [MB+] = 1 × 10‐5M, the most efficient energy transfer (82 per cent efficiency, as derived from measurements of the quenching of Th+ fluorescence, or 90 per cent, as derived from sensitization of MB+ fluorescence) is observed at the lowest SLS‐concentration (3.0 × 10‐3M), when the only micelles present are those formed by aggregation of dye‐carrying low molecular complexes of SLS with dye cations. Each micelle carries, under these conditions, 10–14 molecules of the two dyes, and the distance between two closest dye ions is about 16 A. Transfer becomes less efficient as the SLS‐concentration increases, causing pigment molecules to distribute themselves among a greater number of micelles.
PHOTOLYSIS OF ETHYL CHLOROACETATE IN LIQUID PHASE AT 2537 A°R
Authors: WOJTCZAK JAN , MATUSZEWSKI BOGDAN 
Published: January 2008

Abstract— Results on the photolysis of ethyl chloroacetate, CICH2COOC2H5, at A°≅ 254 nm in liquid phase are presented. GLC and i.r. methods revealed as products: hydrogen chloride and ethyl acetate; in smaller quantities–ethyl succinate and ethyl oxalate; in traces–ethyl malonate, CO2, CO and CH3CI; yet other, unidentified products with higher boiling points. Quantum yields are determined for some products. Similar studies were performed in the presence of I2 as a radical scavenger. In the present case, ethyl iodoacetate I – CH2COOC2H5 was found to arise in the system. The following primary process may be written on the basis of the experimental data:CICH2COOC2H5← CI + CH2COOC2H5Attempts to explain the production of these compounds are based mainly on the properties of the CH2COOC2H5 radical.
TRIPLET STATES OF POLYCYCLIC AROMATIC HYDROCARBONS IN FLUID SOLUTION AND IN THE SOLID STATE
Authors: SLIFKIN M. A. , WALMSLEY R. H. 
Published: January 2008

Abstract— –Triplet states of several large polycyclic aromatic hydrocarbons together with their lifetimes have been determined both in fluid solution and in the solid state using a spectrophoto‐metric technique.Excited states and lifetimes of some solid charge transfer complexes between the hydrocarbons and chloranil have been examined.The assignment of the 1Bb states of some of the hydrocarbons have been made from the energies of the triplet states.
A FLASH PHOTOLYSIS STUDY OF THE TRIPLET STATE OF ACRIDINE ORANGE IN BASIC SOLVENTS
Authors: KELLMANN A. 
Published: January 2008

Abstract— Photochemical reactions of acridine orange (AO) in basic aqueous and ethanolic solutions were studied using the flash photolysis technique. The absorption spectrum of AO was determined in detail (230–900 nm) and extinction coefficients were obtained. The decay of the triplet state is the result of a first order process, a triplet‐triplet annihilation process and a quenching by the dye in the ground state. The main part of the triplet decays to the ground state; however the observation of semi‐reduced AO shows that the decay is partly due to chemical reactions.An efficient reversible reaction is observed on flashing aqueous solutions of AO containing tetramethyl‐p‐phenylenediamine: semi‐reduced AO is formed in high yield by reaction between the triplet dye and the diamine. In addition, irreversible reactions of AO occur; these are shown to be due to the triplet state by the method of triplet energy transfer.
OBITUARY
Authors: ROE Dr. EDNA M. F. , KNOWLES AUBREY 
Published: January 2008

Edna Roe died on 31 July, 1971, in London after a long illness borne cheerfully and with great courage. This was typical of Edna, who had often given courage and hope to others in similar situations.Edna Margaret Frances Roe was born and educated in London and worked there for most of her life. Soon after graduating she joined the staff of the Research Institute of the Royal Cancer Hospital to work with W. V. Mayneord on the absorption spectra of carcinogenic hydrocarbons. This work included a study of the fluorescence of these molecules and this encounter with the excited state led to a sustained interest in the photochemistry of biologically active molecules, particularly in the fields of photodynamic action and the UV degradation of nucleic acids.
ISOLATION OF PHOTOCHEMICAL REACTION CENTERS FROM A CAROTENOIDLESS MUTANT OF RHODOSPIRILLUM RUBRUM*
Authors: WANG RICHARD T. , CLAYTON RODERICK K. 
Published: January 2008

SummaryLauryl dimethyl amine oxide was used to isolate reaction centers from a carotenoid‐less mutant, strain G‐9, of Rhodospirillum rubrum. These reaction centers have absorption spectra and light or chemically induced difference spectra very similar to those obtained from Rhodopseudomonas spheroides, strain R‐26. But, unlike those from Rps. spheroides, they are more labile to higher detergent concentrations and to ammonium sulfate. The cytochrome content was estimated to be less than one per 10 P870.
PHOTOALKYLATION OF PURINES IN DNA
Authors: BEN‐ISHAI R. , GREEN M. , GRAFF E. , ELAD D. , STEINMAUS H. , SALOMON J. 
Published: January 2008

Abstract— Ultraviolet light irradiation of DNA in the presence of alcohols such as 2‐propanol leads to hydroxyalkylation of the purine bases. The purine photoproducts were identified as C‐8 hydroxyalkyl derivatives of adenine and guanine by chromatographic mobility, co‐crystallization with authentic samples, and by photoreversal to the original purines. Experiments are reported which demonstrate that the photoalkylation reaction is dependent upon secondary structural alterations in DNA. It is suggested that the photoalkylation of purines proceeds through free‐radical intermediates.The presence of alcohols during irradiation considerably decreases pyrimidine‐dimer formation.