bluuebunny/crossref_metadata_2025 huggingface dataset:
THEORETICAL ASPECTS OF THE U.V. INACTIVATION OF PROTEINS CONTAINING DISULFIDE BONDS
Authors: Dose Klaus
Published: January 2008

Abstract Equations are proposed for the estimation of quantum yields for cystine destruction and disulfide protein inactivation during u.v.‐irradiation in acidic and neutral solutions. The formulas permit a discussion of energy transfer from excited aromatic amino acids to cystines and/or of chemical reactions between excited tryptophans or tyrosines and cystines. The results are discussed with regard to general aspects of the photo‐biochemistry of enzymes.
SOME STABLE FLUORESCENT CONVERTER SOLUTIONS ENHANCING OPTICAL PUMPING IN THE VISIBLE REGION
Authors: Wladimiroff W. W.
Published: January 2008

Abstract A series of fluorescent converter solutions is described, increasing the radiation intensity of flash lamps in the region 4000–6000 Å with a factor RΛ1.5˜3. The converter solutions are composed for use at an optical path of 1 cm, are easy to prepare, and are stable under high intensity irradiation with u. v. and visible light.
ACTIVATION OF LUCIGENIN CHEMILUMINESCENCE BY SERRATIA MARCESCENS
Authors: Oleniacz W.S. , Pisano M. A. , Insorera R. V.
Published: January 2008

Abstract Cell–free extracts and intact cells of Serratia marcescens were found to activate lucigenin (10,10 ‐dimethy1‐9,9‐biacridylium nitrate) chemiluminescence in the absence of either added H2O2 or alkali. Light emission proceeded in alcoholic solvents and, in general, the intensity decreased with increasing length of the alcoholic carbon chain. Th e intensity of bacterially activated lucigenin chemiluminescence increased in a logarithmic linear manner with increasing methanol concentrations, maximum intensities occurring with 90% methanol. Other organic lucigenin solvents also supported the bacterially activated light emission process, although not to the same extent as 90% methanol. The addition of KOH to methanol failed to enhance chemiluminescence. The luminescent process was charaterized by the attainment of peak light emission three seconds after the initiation of the reaction, followed by rapid decay to a low constant light level. The bacterial activation of lucigening chemiluminescence was found to be enhanced by the inclusion by the inclusion of fluorescein in the neutral methanol solvent.
KINETICS OF PHOTODIMERIZATION OF OROTIC ACID IN AQUEOUS MEDIUM
Authors: Sztumpf‐Kulikowska Eva , Shugar D. , Boag J. W.
Published: January 2008

Abstract— Ultraviolet irradiation of orotic acid in aqueous medium leads to the formation of dimers with a cyclobutane ring between the 5,6 bonds of two monomers. These photodimers in turn undergo photodissociation, with the result that an equilibrium is established between photodimerization and photodissociation. The equilibrium point is independent of dose rate, but is appreciably dependent on the irradiation wavelength, pH of the medium (i.e. whether the monomer is in the neutral or anionic form), and initial monomer and oxygen concentrations; the effect of oxygen apparently being to deactivate excited monomers. The kinetics of photodimerization and photodissociation have been examined at different wavelengths and with varying oxygen concentrations at different initial monomer concentrations. The results have been compared with a theoretical model in which it is assumed that a dimer is formed between an excited monomer and second molecule in the ground state, and that oxygen can also react with, and deactivate, an excited monomer. The agreement between the proposed model and the experimental data is reasonably good, and has made possible an estimate of the lifetime of the excited state of orotic acid in aqueous medium, which is about 10‐6 sec.
SPECTROSCOPIC STUDIES OF PURINES—IV. POLATIZATION OF EMISSION FROM PURINE AND SOME OF ITS DERIVATIVES*
Authors: Drobnik Jaroslav , Kleinwächter Vladimir , Augenstein Leroy
Published: January 2008

Abstract— The polarization of fluoresecnce and phosphorescence due to the emission from (π,π*)singlet and triplet states of purine and several of its derivatives have been measured using the method of photoselection. In at least two 2‐amino substituted derivatives, the two lowest π‐π* transition moments are mutually perpendicular. The main vibrational progression of phosphorescence is negatively polarized with respect to both of them and therefore must be singlet states interact with the emitting (π.π*) triplet state. In addition a weak progression, polarized in the plane of the molecule, is found. The vibronic mixing of (n,π*) and (π,π*) triplet states is suggested to account for the mixed polarization. The halogen derivatives of purine show zero plarization of phosphorescence and their phosphorescence spectra are blurred so that it is difficult to differentiate the various interacting states.
PHOTOCHEMINE ANOMALER NUCLEINSÄUREBAUSTEINE‐I. PHOTODEGRADATION VON AZAPYRIMIDINEN UND AZAPURINEN
Authors: Kittler L. , Berg H.
Published: January 2008

Abstract— The photodegradation of Azapyrimidines and Azapurines by intensive u.v.‐irradiation has been investigated and compared with some pyrimidines and purines. The main output at 253.7 nm of our special low pressure mercury lamp which surrounded the cylindrical cell, was 6.7 times 10‐6 einstein cm‐2 min‐1. The concentrations (5 times 10‐4 M in phosphate buffer pH 7) of the irradiated substances decrease exponentially with half‐lifetimes between 2 and more than 60 min. In contrast to the very high stability of adenine, 8‐Azaadenine was degradated in a few minutes only. 6‐Azauracil also reacts rapidly in its excited state with solvent and the first stable photoproduct one can enrich is its hydratation product. By heating of the hydratation product the 6‐Azauracil was regenerated. The changes in stability:

Azauracil > Uracil

Azaadenine < Adeninc

Azaguanine < Guanine

are of great interest in the field of photomutagenis of DNA, modifies by azabases.
PREVENTION OF PHOTOREACTIVATION OF TOBACCO MOSAIC VIRUS–RIBONUCLEIC ACID BY RECONSTITUTION*
Authors: Small Gary D. , Gordon Milton P.
Published: January 2008

Abstract— The photoreactivation of TMV–RNA‡ irradiated with either 253–7 mμ or 302 mμ light can be prevented by reconstitution of the virus from TMV–protein and the ultraviolet irradiated RNA. The prevention of photoreactivation by reconstitution is not irreversible as the RNA can be extracted from the reconstituted virus and is still capable of undergoing photoreactivation.
APPARATUS FOR THE MEASUREMENT OF QUANTUM YIELDS AND RATES OF PHOTOCHEMICAL REACTIONS
Authors: Wolf Harold P. , Bohning James J. , Schnieper Peter A. , Weiss Karl
Published: January 2008

Abstract— A versatile irradiation apparatus for the quantitative study of photochemical reactions is described, which incorporates a commercial monochromator and utilizes a calibrated thermopile for the continuous measurement of light absorption during irradiation. The operating characteristics are discussed, and illustrative applications are cited. Using this apparatus, the quantum yield of the potassium ferrioxalate actinometer at 366 nm and 25d̀C was determined as 1.27 ± 0.01 for a 6.0 times 10‐3 M solution, in excellent agreement with reported values of 1.26.
PHOTOCHROMISM* IN TRIPHENYLMETHANES
Authors: Macnair Richard N.
Published: January 2008

Abstract— A critical review of photochromism in triphenylmethane derivatives and some related compounds is presented. Most of the triphenylmethane compounds reported to be photochromic as well as some of those reported as non‐photochromic are mentioned. Compounds were included only if the conditions under which the observations were made were reasonably well described. Qualitative observations of photochromism are predominant since very little quantitative data are available. Physical properties of the compounds and/or their solutions which appear to be related to photochromism are discussed including conductivity, dielectric constant and dipole moment. Among other topics discussed are mechanisms and kinetic studies.
PHOTOPRODUCT FORMATION IN DNA AT LOW TEMPERATURes.
Authors: Rahn R. O. , Hosszu J. L.
Published: January 2008

Abstract— The temperature dependence of thy mine photoproduct formation in Escherichia culi DNA dissolved either in water or in a 50 per cent ethylene glycol solution was studied at temperatures between + 25 and — 196°C. At low temperatures, the formation of thymine dimer was strongly inhibited. A dose of 1 × 104 ergs/mm2 at 280 nm converted 2 per cent of the thymine to dimer at 25°C as compared with 0.2 per cent at — 196°C. In addition, a new thymine photo‐product which was both nonphotoreversible and nonphotoreactivable was found at low temperatures. On the basis of its chromatographic mobility, this new photoproduct was assumed to be the same as that isolated from irradiated spores of Bacillus megaterium. Extensive irradiation at 254 nrn of DNA at — 120°C resulted in a yield of > 23 per cent for the ‘spore‐type’ photoproduct as compared with 6 per cent for the thymine dimer. In poly d(AT), irradiated at low temperature, no spore‐type photoproduct was found; this suggests that adjacent thymine residues are necessary for the formation of the spore‐type photoproduct.
A FLASH‐PHOTOLYSIS INVESTIGATION OF FLAVIN PHOTOSENSITIZATION OF PURINE NUCLEOTIDES
Authors: KNOWLES A. , ROE E. M. F.
Published: January 2008

Evidence for the existence of a reactive triplet excited state of lumiflavin has been obtained by the flash‐photolysis technique. The triplet state is formed in high yield on the irradiation of flavin solutions in water or chloroform by visible light, and it has been demonstrated that it can transfer its energy to a second molecular species. The flavin‐sensitised oxidation of two purine nucleotides, adenylic and guanylic acids, has been studied by flash‐photolysis and by long‐term irradiation, and the results suggest a triplet‐triplet mechanism for the transfer of energy from the excited flavin to the nucleotide.

Approximate absorption spectra of the triplet state and of a semiquinone of the flavin have been calculated from the complex transient absorption curves observed on flashing the flavin solution. The triplet decays by a first‐order process where k1= 1·1 × 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. 104 sec‐1 and the semiquinone by a second‐order process where k2= 0·75 × 109 1.m‐1 sec‐1. The rate constants and extinction coefficients obtained enable decay curves to be calculated which fit satisfactorily those measured with the kinetic‐flash apparatus.
PHOSPHORESCENCE OF AROMATIC KETONES IN LOW‐TEMPERATURE GLASSES
Authors: GRIFFIN R. N.
Published: January 2008

Abstract— Phosphorescence decay kinetics and emission spectra of some acetophenone derivatives were measured in ether/alcohol and hydrocarbon glasses. Most decay rates observed were a sum of exponentials, and different emission spectra were observed at different intervals in the decay. The observations can be explained in terms of coexistent n, π*, π, π*, and charge‐transfer triplets, but solvent shifts in the direction expected for π, π* and charge‐transfer triplets were not observed.
PHOTOBIOLOGY OF RNA BACTERIOPHAGES–II U.V.–IRRADIATION OF f2: EFFECTS ON EXTRACELLULAR STAGES OF INFECTION AND ON EARLY REPLICATION*
Authors: WERBIN HAROLD , VALENTINE RAYMOND C. , HILDALGO‐SALVATIERRA OSCAR , McLAREN A. D.
Published: January 2008

Abstract— The effect of u.v. irradiation (2537 Å) on the RNA bacteriophage f2 has been studied with respect to the adsorption of f2 to E. coli K12 (male strain), the penetration of f2‐RN A into the host cell and the conversion of the phage nucleic acid to the double‐stranded replicative intermediate. The biological parameter most sensitive to u.v. was the plaque‐forming ability of the phage. Its loss could be attributed to several factors. (1). A binding of capsid protein to phage nucleic acid interfering with host penetration by the f2‐RNA. (2). Desorption of some irradiated phage at 37° from their attachment sites on the host. (3). Molecular alterations in the RNA preventing formation of the replicative intermediate within the host.

The relationship of these factors to the lack of photoreactivability of irradiated f2 is discussed.
PHOTOCHEMISTRY OF THE MODEL PHOTOTROPIC SYSTEM INVOLVING FLAVINS AND INDOLES–I. FLUORESCENCE POLARIZATION AND MO CALCULATIONS OF THE DIRECTION OF THE ELECTRONIC TRANSITION MOMENTS IN FLAVINS*
Authors: KURTIN WILLIAM E. , SONG PILL‐SOON
Published: January 2008

Abstract— The fluorescence polarization spectra of riboflavin, lumiflavin, and alloxazine under different conditions have been obtained. It has been shown that the polarization spectrum of riboflavin is not affected significantly by media such as D2O‐glycerol (50: 50) and castor oil. Our data do not indicate the anomalous spectral shift of riboflavin in castor oil, in contrast to the previous finding described by Thomas. The electronic structures of lumiflavin and alloxazine are similar to that of riboflavin, as revealed by the fluorescence polarization measurements and the molecular orbital calculations. The Pariser‐Parr‐Pople semiempirical SCF ASMO CI computations have been performed to compare the calculated transition moments with the polarization data. The theory predicts an angle of 42° between the 450 and 365 nm transition oscillators, in reasonable agreement with the experimental angle of about 49°. It has been shown, from the comparison of the calculated and observed spectral quantities, that the pseudo‐heteroatom model for treating methyl groups in the flavin molecule is not adequate. The group orbital and inductive approximations appear to be satisfactory. Finally, the implication of the present findings has been briefly discussed in connection with phototropism.
DELAYED LUMINESCENCE OF ORGANIC MIXED CRYSTALS — IX. AMINO ACIDS AND PROTEINS*
Authors: Mccarville M. E. , Mcglynn S. P.
Published: January 2008

Abstract— This paper discusses the possibility of triplet exciton motion and triplet‐triplet annihilation in mixed crystal systems in which the hosts are phenylalanine, tyrosine and trypto‐phan and in four protein systems. Triplet‐triplet annihilation and triplet transfer are observed in certain phenylalanine‐ and tryptophan‐host systems. No evidence of either triplet transfer or energy multiplication is found in tyrosine‐host crystal systems or in any protein system.
‘UPHILL’ ENERGY TRANSFER IN A PHOTOSYNTHETIC BACTERIUM*
Authors: Zankel Kenneth L. , Clayton Roderick K.
Published: January 2008

Abstract— Detectable energy flow in the ‘uphill’ direction was demonstrated by exciting the fluorescence of a shorter wavelength band of Rhodopseudomonas spheroides with light absorbed by a longer wavelength band. A variation in the fluorescence spectrum which depends on the state of the traps was also demonstrated. This information, coupled with fluorescence data obtained with monochromatic light, leads to the conclusion that for the longest wavelength bands the ‘uphill’ transfer is about as fast as transfer to the traps; i.e. the ‘average’ rate constant is on the order of 109 sec. The ratio of the uphill to downhill rate agrees with a theoretical estimate of about 0·5. Some possible ramifications of such uphill flow are discussed.
LETTUCE SEED GERMINATION: EFFECTS OF HIGH TEMPERATURE AND OF REPEATED FAR‐RED TREATMENT IN RELATION TO PHYTOCHROME
Authors: Scheibe Joseph , Lang Anton
Published: January 2008

Abstract— At 37°C the active form of phytochrome in lettuce seed cannot function to promote subsequent germination. This effect of high temperature is distinct from thermal acceleration of dark reversion from the active form of phytochrome to the inactive form, and may be due to reversible denaturation of phytochrome.

Repeated brief irradiations with far‐red light inhibit subsequent germination in the whole seed, whereas a similar irradiation regime results in a strong enhancement of the development of growth potential (ability to expand against an externally‐imposed osmotic restraint) in the excised axial portion of the seed. A possible explanation for these two opposing results, in volving two different pigment systems with effective loci in different parts of the seed, is suggested.
PHOTOSENSITIZED BLEACHING OF β‐CAROTENE WITH LIGHT AT 632·8 nm FROM A CONTINUOUS‐WAVE GAS LASER
Authors: Hasegawa Kiyozo , Macmillan James D. , Maxwell W. A. , Chichester C. O.
Published: January 2008

Abstract— β‐Carotene was not affected when irradiated with a monochromatic beam of light (632·8 nm) from a continuous‐wave gas laser. However, β ‐carotene undenvent numerous changes when irradiated in the presence of the photosensitizing dye toluidine blue. Initially there was a considerable decrease in the absorbance of the β‐carotene, accompanied by small shifts of the absorption maxima to shorter wavelengths as well as the formation of two new peaks at 400 and 375 nm. Ultimately a complete bleaching of the solution was observed. By the use of column and thin layer chromatography up to 13 different compounds including cis‐isomers, epoxides and possibly hydroxy compounds were shown to be formed by the photosensitization of the β‐carotene. These reactions were found to be oxygen‐dependent.
DEPENDENCE OF INTERSYSTEM CROSSING ON EXCITATION ENERGY IN OROTIC ACID
Authors: WHILLANS D. W. , JOHNS H. E.
Published: January 2008

Abstract— Photochemical dimerization in orotic acid in aqueous solution has been studied as a function of oxygen concentration, orotic acid concentration and the wavelength of irradiation under two pH conditions. One dimer was detected. Analysis of the data enabled us to obtain a minimum estimate of the efficiency of intersystem crossing, øISC. from singlet to triplet levels. This efficiency increases by a factor of two with increasing energy of excitation over the wavelength range 240–302 nm, and by a similar factor between pH 3 and pH 1. The maximum value obtained was 0.15 for irradiation at 240 nm at pH 1. The relation between quantum yield and øISC is discussed and possible mechanisms to explain this variation of øISC with energy are proposed.
ENVIRONMENTAL EFFECTS ON THE FLUORESCENCE OF TYROSINE AND ITS HOMOLOGUES
Authors: FEITELSON JEHUDA
Published: January 2008

Abstract— In order to study the influence of the environment on the fluorescence of tyrosine the emission of tyrosine as well as of the related compounds p‐cresol, O‐methyltyrosine and phenylalanine in aqueous solutions of alcohol, dioxane, acetonitrile, dimethylformarnide, N‐dimethylacetamide and acetic acid was measured. It was found that the quenching of the tyrosine fluorescence by —CONH and —COOH groups proceeds apparently by direct interaction with the excited aromatic ring. The phenolic OH group does not seem to be directly involved in the process although it contributes to the quenching, probably, by increasing the electronic charge density of the excited ring. The relevant quenching constants are presented.
CHEMILUMINESCENCE AND ENERGY TRANSFER OF EXCITED ACETOPHENONE
Authors: HÖFERT MANFRED
Published: January 2008

Abstract— Further evidence is found that acetophenone in its triplet‐state is formed as the luminescent species in the autoxidation of ethylbenzene. Energy transfer from this ketone to the triplet‐states of various acceptors results in quenching of the already weak chemilumin‐escence and follows a diffusion‐controlled rate as expected. The poor resemblance between the experimentally recorded spectral distribution of this light emission and the known phosphorescence spectra of the assumed emitters is discussed.
DOSE RESPONSE BEHAVIOUR FOR POLAROTROPISM OF THE CHLORONEMA OF THE FERN DRYOPTERIS FILIX‐MAS (L.) SCHOTT
Authors: STEINER A. M.
Published: January 2008

Abstract— The dose response behaviour for polarotropism of the chloronema of the fern Dryopteris filix‐mas was studied in detail. By varying the two factors, time and intensity, dose response curves were obtained, which consisted of as many as two maxima and minima or no maxima and minima at all. Furthermore, the effects of red light and dark, given before polarotropic induction, were compared, and the influence of temperature on the dose response behaviour was examined. There are two main results: (1) Under all conditions tested, the dose response behaviour in far‐red, red, blue, and near U.V. apparently is the same. (2) In this one system, the chloronema of Dryopteris, all types of dose response curves, which have been described previously for tropic responses mediated by light, could be obtained simply by varying the conditions. The variable and complex dose response behaviour is discussed in connection with other photoresponses in lower and higher plants.
PHOTOSENSITIZED DIMERIZATION OF THYMINE
Authors: JENNINGS BOJAN HAMLIN , PASTRA STYLIANI‐CHRYSSOULA , WELLINGTON JUDITH L.
Published: January 2008

Abstract— In contrast with previous reports from other laboratories, four isomeric dimers were isolated from the photochemical reaction of thymine sensitized by either acetone or propiophenone. Product analyses, made by use of nuclear magnetic resonance spectroscopy, showed that the distribution of dimers is dependent on the character of the solvent medium. Mass spectra for all four dimers were obtained and are here presented.
ON THE PHOTODECOMPOSITION OF CHLOROPHYLL IN VITRO‐II. INTERMEDIATES AND BREAKDOWN PRODUCTS*
Authors: JEN J. J. , MACKINNEY G.
Published: January 2008

Abstract— The bleaching of chlorophyll solutions by light in the presence of oxygen can be interrupted, and red intermediates can be precipitated by the use of highly nonpolar solvents in appropriate solvent mixtures. The precipitates are more highly oxygenated but retain phytol and a N‐Mg ratio of 4:1. The NMR spectra indicate that the methine bridge and vinyl protons have been lost. Methyl ethyl maleimide is a product of chromic acid oxidation of the red precipitates. It is also found in the supernatant solution and in the fully bleached end product.
SOLID STATE PHOTOCHEMISTRY OF THYMINE, ITS N‐METHYLATED DERIVATIVES AND OROTIC ACIDS IN KBr MATRICES
Authors: LISEWSKI R. , WIERZCHOWSKI K. L.
Published: January 2008

Abstract— Photodimerization of a number of 2,4‐diketopyrimidines including thymine, 1 ‐methylthymine, 3‐methylthymine, 1,3‐dimethylthymine, orotic and 5‐methylorotic acids was studied in the solid state in KBr matrices. A technique developed for quantitative measurements of monomer and dimer concentrations under these conditions by means of u.v. and i.r. spectrophotometry is described. The absorption spectra of crystalline diketopyrimidines exhibit, in relation to the solution spectra in water, marked hypochromicity (33–69 per cent) and red shift of the long wavelength edge of the absorption (2000–3000 cm‐1) indicative of resonance intermolecular interaction and mixing of different electronic states. In most cases dimerization appeared the only photochemical reaction and the stereochemical form of main dimer corresponded with the predicted one on the basis of known crystal structure of the monomer. Initial quantum yields of monomer disappearance varied from solid to solid in the range of 0.1‐0.9 M/Einstein being, apparently, to a degree dependent on the separation between nearest‐neighbour C=C bonds. Reaction mechanism is discussed in terms of involvement of singlet excimer states.
ULTRAVIOLET PHOTOCHEMISTRY OF THYMINE IN AQUEOUS SOLUTION
Authors: FISHER G. J. , JOHNS H. E.
Published: January 2008

Abstract— We have investigated the ultraviolet photochemistry of thymine in aqueous solution. Four isomeric dimers are produced, and the yield of each has been measured as a function of thymine concentration, oxygen concentration, and temperature. At low thymine concentration, dimerization proceeds via the triplet state, while at high concentration it arises mainly from aggregates, probably from a singlet precursor. We have determined the ratios of rate constants for the triplet state mechanism and the quantum yield for dimerization from aggregates. The quantum yield for dimerization from the triplet state in thymine is smaller by a factor of about 10 than that in uracil, which in turn is smaller by another factor of 10 than that in orotic acid. It increases with the energy of the exciting radiation in a manner similar to the behaviour of uracil and orotic acid. On the other hand, dimer formation from aggregates is independent of photon energy. Dimerization from aggregates decreases with increasing temperature, while the total production of dimers from the triplet state is independent of temperature.
SOME OBSERVATIONS ON THE LETHAL EFFECTS OF NEAR‐ULTRAVIOLET LIGHT ON ESCHERICHIA COLI, COMPARED WITH THE LETHAL EFFECTS OF FAR‐ULTRAVIOLET LIGHT
Authors: PEAK M. J.
Published: January 2008

Abstract— Near‐ultraviolet light (365.5 nm) reduces the ability of Escherichia coli B/r and B8‐1, to form colonies on nutrient agar after irradiation. This lethal effect is distinct from that obtained after far‐u.v. irradiation (253.7 nm) because the far‐u.v. sensitive and resistant strains are equally susceptible to near‐u.v. Variation in susceptibility to ultraviolet light during growth is more marked for near‐u.v. than for far‐u.v. The number of survivors after near‐u.v. irradiation of log phase cells is affected by several post‐irradiation treatments; more cells survive if growth immediately after irradiation occurs at higher temperatures (unlike far‐u.v.). Also, the presence of acriflavine and caffeine in the nutrient agar decreases the number of survivors (in common with far‐u.v.).
THE DYE‐SENSITIZED PHOTO‐OXIDATION CHEMILUMINESCENCE OF LUMINOL*
Authors: MATHESON I. B. C. , LEE J.
Published: January 2008

Abstract— The chemiluminescence reaction of luminol has been investigated using conditions of methylene blue photosensitized oxidation. The quantum yields of chemiluminescence obtained were dependent upon temperature and the concentrations of luminol and base; and under the optimum conditions of high temperature and low luminol concentration, the value of the quantum yield approached that for the chemical reaction where the oxidant is hydrogen peroxide and catalyst. An analysis of the results suggests that it is not the primary species produced on photosensitization which is responsible for the chemiluminescent reaction, but a species produced by reaction of the primary species with base.
REPAIR REPLICATION IN CHINESE HAMSTER CELLS AFTER DAMAGE FROM ULTRAVIOLET LIGHT*
Authors: CLEAVER JAMES E.
Published: January 2008

Abstract— After irradiation with u.v. light, Chinese hamster cells perform repair replication of their DNA. Small numbers of nucleosides are inserted into DNA, such that when BrUdR is used there is no detectable change in density. Repair replication begins immediately after irradiation, but it decelerates steadily and at least half is complete within 4 hr. Repair replication saturates above 200 ergs/mm2 at a level which represents 0.055 per cent replacement of all thymine sites in 4 hr. Repair replication in mammalian cells, in contrast to that in microorganisms, does not appear to replace pyrimidine dimers excised from DNA in acid soluble form, and neither repair nor semiconservative replication discriminates between BrUdR and TdR.
COMPARAISON ENTRE L'EMISSION D'OXYGENE ET L'EMISSION DE LUMINESCENCE A LA SUITE D'UNE SERIE D'ECLAIRS SATURANTS
Authors: BARBIERI GERARD , DELOSME RENE , JOLIOT PIERRE
Published: January 2008

Abstract— Luminescence of Chlorella cells has been measured after illumination by a series of short saturating flashes.

The intensity of luminescence is strongly dependent upon the number of flashes; luminescence is minimum after a single flash and maximum after a double flash illumination.

Ifl/n is the intensity of luminescence measured 0.24 sec after the nth flash, the series ln shows oscillations as a function of n. The series ln is very similar to the series yn, in which y is the amount of oxygen evolved by the nth flash, the term ln corresponding to the term yn+1. To interpret the oscillations of the series yn, different models of system II photochemical centers have been proposed, one by ourselves and the other one by KOK et al. In these models the electron donor Z of photosystem 11 is supposed to have 2 or 4 levels of oxidation, the more oxidized state being the precursor of oxygen. These different oxidation states of the donor Z allow storage of the photic energy in the system. The correlation between the series yn and ln shows that at least one of the oxidized forms of the donor Z is a substrate for the luminescence reaction.
PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES—III. MECHANISM OF PHOTODAMAGE OF ALANINE PEPTIDES IN THE SOLID STATE
Authors: JOHNS R. B. , SEURET M. G.
Published: January 2008

Abstract— –The structures of the primary radicals formed by 2537 Å photolysis at —196° of alanine peptides of varying size have been determined. The conversion of the primary to stable secondary radicals on heat treatment has been followed in detail by ESR techniques and the chemical change shown to be intermolecular hydrogen atom transfer. The primary photochemical event is shown to be decarboxylation, but photodamage cannot be prevented by conversion of the carboxyl group to an acid derivative.
STUDIES ON THE RED AND BLUE FORMS OF THE PIGMENT OF BLEPHARISMA*
Authors: GIESE ARTHUR C. , GRAINGER ROBERT M.
Published: January 2008

Abstract— –The intracellular pigment of the ciliate protozoan Blepharisma in the presence of oxygen sensitizes the cells to bright visible light (2700 foot candles (fc)). Illumination of the cells with dim visible light (200 fc) changes the color of the pigment to blue‐gray; such cells are no longer sensitive to bright visible light. The pigment which exists in granules can be extruded by cold treatment and is slowly regenerated. The suspension of red cells, the extruded pigment from them and an ethanol extract of the pigment all have very similar absorption spectra. Illumination of the red pigment in ethanol converts it to the blue form of the pigment but only if oxygen is present, indicating a photooxidation. The pigment can be oxidized in darkness to the blue form by ozonation. A suspension of blue cells, the extruded pigment from them and an ethanol extract from them, all have similar absorption spectra. The pigments in red and blue form are very similar spectrophotometrically and in solubility in three species of Blepharisma studies: B. americanum, B. intermedium and B. japonicum. The purified pigment has strong absorption in the far (200–300 nm) ultraviolet (u.v.) and may serve as a screen against damaging U.V. radiation, especially as Blepharisma shows poor photoreactivation.
FLASH PHOTOLYSIS AND INACTIVATION OF AQUEOUS LYSOZYME*
Authors: GROSSWEINER L. I. , USUI Y.
Published: January 2008

Abstract— –Flash photolysis of aqueous lysozyme has shown that the initial photochemical products are photo‐oxidized tryptophan residues (Λmax= 500 nm), hydrated electrons (Λmax= 720 nm), and the cystine residue electron adduct (Λmax= 420 nm). Comparisons with mixtures of the chromophoric amino acids show that 1 to 2 tryptophan residues provide electrons at a quantum yield of 0.018 (25 per cent). Part of the ejected electrons are captured by cystine residues via a short‐range, intramolecular process with essentially unit efficiency. The remainder become hydrated and back react with oxidized tryptophan residues before 10‐4sec. The cystine residue electron adduct decays with 2 msec halftime (25°C) and 1.5 kcal/mole activation energy. The surviving oxidized tryptophan residues decay with a comparable time constant in a hydroxyl ion catalyzed process. In acid solutions the oxidized tryptophan residue and long‐lived H atom adduct are observed (Λmax= 380 nm). The quantum yield of lysozyme inactivation induced by xenon flash irradiation above 250 nm is 0.023 (20 per cent), which is not sensitive to oxygen or pH. Comparison to the primary photochemical reactions indicates that electron ejection from the essential tryptophan residues inactivates the enzyme, irrespective of the electron trap and subsequent reactions. On the basis of the structure and supporting information it is proposed that the tryptophan residues of the active site are involved. Direct disruption of cystine residues does not contribute more than 10 per cent to the inactivation quantum yield in this wavelength region. Lysozyme inactivation may differ from other enzymes because the chromophores include essential residues located in the active center.
IDENTIFICATION OF THE MAJOR ULTRAVIOLET ABSORBANCE PHOTOCHANGES IN PHOTOSYNTHETIC SYSTEMS*
Authors: LOACH P. A. , BAMBARA R. A. , RYAN F. J.
Published: January 2008

Abstract— –Measurement of the changes in the absorbance spectrum of bacteriochlorophyll upon reversible one electron oxidation in methanol have been extended into the u.v. regions of the spectrum. A striking resemblance between the oxidized minus reduced spectrum of bacteriochlorophyll and the light minus dark spectrum of chromatophore preparations from Rhodospirillum rubrum and Rhodospeudomonas spheroides is demonstrated. After subtracting from the chromatophore light minus dark spectrum changes which are the result of the photo‐oxidation of the primary electron donor molecule, no major changes remain in the u.v. which would be ascribable to quinone or pteridine photoreduction. Major photochanges which are not completely accounted for by oxidation of the primary electron donor molecule are in the spectral region between 320 and 450 nm. Possible explanations of these remaining changes are explored. Reversible oxidation of bacteriochlorophyll was also carried out in dichloromethane in order to determine the dependency of the oxidized minus reduced difference spectrum on the polarity and hydrogen bonding properties of the solvent. Although the same general features were observed as with the experiment in methanol, there were significant shifts of some of the band locations toward the u.v.
THE IN VITRO PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES—II. THE TRIPLET STATES OF β‐CAROTENE AND LYCOPENE EXCITED BY PULSE RADIOLYSIS
Authors: LAND E. J. , SYKEY A. , TRUSCOTT T. G.
Published: January 2008

Abstract— –Pulse radiolysis has been used to excite the triplet states of β‐carotene (τ# 9μ sec) and lycopene (τ= 8μsec) in hexane solution, both in the presence and absence of naphthalene as a triplet sensitiser. The absorption spectra of both triplets have been measured in the range 430–550 nm and have thus been extended into the region of the corresponding singlet absorptions. The overlap of the triplet and singlet spectra is discussed in relation to in vivo studies. Extinction coefficients of 1.3±0.1 × 105 l/mole cm for β‐carotene triplet 515 nm and 3.9±0.2 × 105 l/mole cm for lycopene triplet at 525 nm were obtained. Isomerisation of the all‐trans polyenes used was detected and preliminary measurements indicate that the yield of isomerisation was greater than the triplet yield. The rate of triplet energy transfer from naphthalene to β‐carotene was estimated to be 1.5 × 1010 l/mole sec. The corresponding value for lycopene was 1.4× 1010 l/mole sec. The measured efficient quenching of triplet β‐carotene by oxygen may occur by an energy transfer mechanism, leading to the formation of singlet oxygen (1Δg. This would suggest that the triplet energy level of β‐carotene lies between 121 and 94 kJ mole‐1.
PHOTOCHEMISTRY OF THYMIDINE AS A THIN SOLID FILM*
Authors: VARGHESE A. J.
Published: January 2008

Abstract— –Photochemistry of thymidine in the solid state has been investigated. Four isomers of the cyclobutane‐type thymidine dimer, two bimolecular addition products with u.v. absorbance maxima above 300 nm, (the formation of which involves the C=C and C=O groups of adjacent thymine residues) and 5‐thyminyl‐5.6 dihydrothymine (TDHT) (formed by the addition of a thyminyl radical at the C5 position of a thymyl radical) were isolated. TDHT was found to be the major photoproduct. The results are compared with those for thymidine irradiated in the frozen state.
PHOTOBIOLOGICAL EFFECTS OF METAL IONS. PHOTOSENSITIZING ACTION OF URANYL ACETATE ON Escherichia coli K‐12*
Authors: NEELY W. C. , ELLIS S. P. , CODY R. M.
Published: January 2008

Abstract— The Uranyl acetate sensitized killing of Escherichia coli K‐12 by a light source approximating sunlight in both intensity and wavelength distribution is demonstrated to occur at a concentration of 5.0 × 10O‐4M uranyl acetate (pH 7.0). The photosensitized killing was evident after 150 min and almost complete within 320 min. Auxotrophic mutants were isolated from cultures incubated in both light and dark for 160 min at this concentration of uranyl acetate. Binding of UO22+ to E. coli is shown to occur with 82% of the UO22+ ions in a 5 × 10‐4M solution (pH 7.0) being bound to the cell wall. In the dark as well as at other pH values the extent of binding was much less. Most of the binding occurred in a time less than 30 min. The observation of rapid binding but delayed photosensitization is attributed to the necessity for penetration of uranyl ions into the cells' interior to effect photosensitization.
CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY: LIGHT‐INDUCED ABSORBANCE CHANGES AND ESR SIGNALS FOR VARIOUS PORPHYRIN‐QUINONE AND HYDROQUINONE SYSTEMS IN ALCOHOL SOLVENTS*
Authors: WHITE ROBERT A. , TOLLIN GORDON
Published: January 2008

Abstract— Light‐dark optical difference spectra of degassed ethanol or pyridine solutions of chlorophyll and benzoquinone or hydroquinone at temperatures above — 50°C show only the semiquinone absorbance band. Decay of the signals is second order, with a rate constant in agreement with earlier ESR results.

Light‐induced optical changes due to chlorophyll can be elicited by lowering the temperature of ethanol solutions of chlorophyll and benzoquinone to a region of high viscosity. Hydroquinone is not effective in producing these optical changes.

Similar results are achieved at room temperature by using as solvent a degassed mixture of the alcohols: cyclohexanol, tert‐butanol, and ethanol (CBE). Difference spectra show bleaching of the chlorophyll bands and increased absorbance in the intermediate wavelength region (460–580 nm). Decay kinetics are first order, while the rise is complicated (probably biphasic). ESR signals have no hyperfine structure and also decay by first order kinetics, at a rate which is faster than that of the optical changes. The ESR signals reach a steady state more rapidly than the optical signals, without biphasic kinetics. These results demonstrate that at least two species are generated.

Addition of acid increases the amount of bleaching in CBE, while small amounts of base decrease it. Larger amounts of base cause chlorophyll bleaching to completely disappear and only the semiquinone anion is observed. Activation energies for the chlorophyll a‐benzoquinone photoreaction in CBE are 10–14 kcal/mole. Lower potential quinones give lower activation energies. The rate constant for quenching of the triplet state of chlorophyll a by β‐carotene in CBE is 7.5±0.5×108 (M set)‐1. β‐carotene also quenches photoproduct formation. The bimolecular rate constant for formation of the photoproduct with benzoquinone was calculated to be 7×108 (Msec)‐1.

The redox potential of the quinone affects both the magnitude of the chlorophyll absorbance changes and the rate of decay. The higher the potential, the larger the changes and the slower the decay. Other porphyrin systems show similar photoreactions only if they are chelated with a group II metal, such as Mg2+, Cd+2, or Zn+2.

The results are interpreted in terms of the formation, by a triplet‐sensitized one‐electron transfer from solvent to quinone, of a chlorophyll‐semiquinone complex which is stabilized via coordination with the chelated metal.
CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY: FLASH PHOTOLYSIS STUDIES OF THE CHLOROPHYLL‐QUINONE REACTION IN ALCOHOL SOLVENTS*
Authors: WHITE ROBERT A. , TOLLIN GORDON
Published: January 2008

Abstract— Flash photolysis of chlorophyll a alone in CBE (cyclohexanol‐t‐butanol‐ethanol) yields a difference spectrum similar to those obtained upon steady illumination of chlorophyll a‐quinone mixtures in this solvent. Decay kinetics in CBE and dimethylsulfoxide are faster at the Soret band than at 460–580 nm and red band regions. This difference is not obtained in other solvents (CHCI3, CCI4, t‐butanol, ethanol), implying that two or more species are obtained in CBE and DMSO.

β‐Carotene in CBE increases the rate of decay of the flash‐induced chlorophyll transients at 430 and 660 nm but only decreases the magnitude of the signal at 470 nm. This implies that the 470 nm absorbance is due to a product formed from the triplet state. This effect is not observed in ethanol.

Adding quinone to chlorophyll solutions results in slowly decaying species being generated by flash excitation in CBE. Three components can be distinguished: the first (t1/2˜ 0.2 msec) corresponds to the triplet state; the second (t1/2= 5–10 msec) is quinone concentration and species independent; the third (t1/2= several seconds) is dependent upon quinone concentration and species (rate is faster for higher concentrations and lower potential quinones). The ESR signal decay rate is approximately equal to the third component flash decay rate when the chlorophyll and quinone concentrations are equal. With excess quinone, the flash decay rate becomes faster, and the ESR decay rate decreases slightly. These slowly‐decaying species are not produced when quinone is added to chlorophyll a in ethanol or t‐butanol, or to pheophytin in CBE. One observes merely a decrease in signal height with no accompanying increase in decay rate.

Mechanisms to account for all of these phenomena are presented which involve an initial chlorophyll triplet‐solvent reaction with the subsequent formation of several species of chloro‐phyll‐quinone radical complexes.
DELAYED‐LIGHT STUDIES ON PHOTOSYNTHETIC ENERGY CONVERSION‐III. EFFECT OF 3‐(3,4‐DICHLOROPHENYL)‐1,1 ‐DIMETHYL UREA ON THE MILLISECOND EMISSION FROM CHLOROPLASTS PERFORMING PHOTOREDUCTION OF FERRICYANIDE*
Authors: BERTSCH W. , WEST JANET , HILL R.
Published: January 2008

Abstract— How does a plant convert electronic excitation of chlorophyll into stable chemical potential? The time scales of fluorescence (10‐‐9 sec) and steady‐state enzymatic turnover (10–2 sec) indicate that energy storage must be involved. Millisecond delayed singlet emission from chlorophyll allows measurement of metastable energy storage at Photoreaction II. Activation of noncyclic electron transport results in more rapid decay and in increase of emission at 10‐‐3 sec, both effects being inhibited by the poison DCMU. These results can be explained by at least three different models of the reaction center: the oxidized chlorophyll model, the chlorophyll triplet model, and the two‐quantum electron‐hole model.
INHIBITION OF ELECTRON TRANSPORT IN CHLOROPLASTS BY CHAOTROPIC AGENTS AND THE USE OF MANGANESE AS AN ELECTRON DONOR TO PHOTOSYSTEM II*
Authors: LOZIER R. , BAGINSKY M. , BUTLER W. L.
Published: January 2008

Abstract— Incubating spinach chloroplasts with various chaotropic agents results in inhibition of photosynthetic electron transport between water and Photosystem II similar to the inhibition caused by washing chloroplasts with a high concentration of Tris buffer. Partial restoration of NADP photoreduction and fluorescence of variable yield is achieved by adding hydroquinone or Mn2+, either of which donates electrons to Photosystem II in the inhibited chloroplasts. The inhibitory treatments cause the release of Mn from its bound state in the chloroplast, thus allowing the measurement of the ESR signal of Mn2+. The ESR measurement is used to follow the photooxidation of Mn2+ as it donates electrons to photosystem II.
KINETIC STUDIES ON CHEMILUMINESCENCE OF CHLOROPLASTS INDUCED BY CHANGES IN ION CONCENTRATION
Authors: HARDT H. , MALKIN S.
Published: January 2008

Abstract— Acid‐base, acid‐, and salt‐induced chemiluminescences of chloroplasts were investigated in relation to their dependences upon several time parameters:

The dependence of the three chemiluminescences on the preillumination time was similar; the luminescences rose to a maximum and then decayed to a steady‐state This behaviour depends on the preillumination level and the length of the dark time following the preillumination. Analysis of the above indicates the formation of quenching entities during the preillumination which react with the luminescence precursors mainly in the dark.

In contrast, the delayed light measured after 22 msec from the preillumination, showed a much slower but smooth rise to the steady‐state with no subsequent drop.

During the dark period following preillumination the ability of the system to chemi‐luminescence decayed with a first order rate.

During emission the above chemiluminescences decayed with a first order law. The total emission in different experiments was also proportional to the maximum emission, in agreement with a first order law of decay.

The comparison of the kinetic behaviour of the three types of chemiluminescence indicates common precursors of luminescence for at least the acid‐base and the salt types. The delayed emission at 22 msec however, seems to have separate precursors than the three chemiluminescences.
PROFLAVINE‐SENSITIZED SELECTIVE PHOTOOXXDATION OF THE TRYPTOPHYL RESIDUES IN PAPAIN
Authors: JORI G. , GALIAZZO G.
Published: January 2008

Abstract— A detailed analysis of the effects of acidic pH values and of temperature on the ultraviolet absorption spectrum of papain demonstrated that the protein can exist in several more or less denatured conformations depending on the surrounding medium. Proflavine‐sensitized photooxidation of papain, under experimental conditions corresponding to the spectroscopically detected conformational states, allowed us to modify separately the five tryptophyl residues. Tryptophan‐7 and 69 appear to be at least partially exposed to the aqueous environment in native papain; however, the former becomes inaccessible to the photooxidizing agent at temperatures lower than 15°C. The photooxidative conversion of these residues to formyl‐kynurenine has no appreciable effect on the tertiary structure as well as on the enzymic activity of papain. On the other hand, tryptophan‐177. which appears to be largely buried, can also be modified with minor variations in the spatial geometry of the protein, but its indole moiety must be critically involved in the enzyme‐substrate interaction, since its conversion to formyl‐kynurenine almost completely inhibits the catalytic activity. Finally, tryptophan‐181 and ‐26 are deeply buried in internal hydrophobic clusters and become available to photooxidation only after the protein molecule has been extensively disorganized. Our results suggest that the solution conformation of some areas of the papain molecule may be different from that in the crystal state as deduced from X‐ray diffraction studies.
PHOTODYNAMIC OXIDATION OF IODIDE ION AND AROMATIC AMINO ACIDS BY EOSIN*
Authors: KEPKA A. G. , GROSSWEINER L. I.
Published: January 2008

Abstract— The photosensitized oxidation of I‐, tyrosine, and tryptophan by aqueous eosin has been investigated with a photostationary technique, in which the system is irradiated with sinusoidally modulated light and phase sensitive detection is used to measure the spectra of short‐lived intermediates and their rate constants. It has been shown that the principal oxidizing agent for I‐ is semi‐oxidized eosin (X) produced by the reduction of oxygen by triplet state eosin. The same mechanism obtains when femcyanide ion is substitued for oxygen. A second oxidizing agent is effective in oxygenated solutions at high I‐ concentrations, attributed to O2‐. The X mechanism controls when tyrosine or tryptophan are irradiated at low substrate concentrations in the presence of oxygen or femcyanide. However, at high substrate concentrations, or in the absence of the electron accepting agents, the mechanism switches to the ‘dye‐substrate’ process where triplet state eosin oxidizes the aromatic substrate and is reduced to the semiquinone. The conversion quantum yields agree with the predictions based on the measured quenching and reaction rate constants.