bluuebunny/crossref_metadata_2025 huggingface dataset:
MATHEMATICAL ASPECTS OF THE ULTRAVIOLET PHOTOCHEMISTRY OF PYRIMIDINE DINUCLEOSIDE PHOSPHATES
Authors: Brown I. H. , Johns H. E.
Published: January 2008

Abstract A mathematical formulation of the Kinetics of dimner and hydrate formation in pyrimidine dinucleosides upon ultraviolet (u.v.) radiatin is presented. The formulation allows for the possibilities of forming a number of types of dimers each with different cross sections for formtion and reversal, and of forming photo‐irreversible products such as hydrates. The general differential equations descrbinjg the kinetics are solved in terms of a series of exponential terms which are functions of all the cross sections. The way in which any given species of hotoproduct is dependent upon the cross sections is illustrted in several examples. The results have been used to predict the maximum amount of dirner which may be produced for a given set of cross sections and the exposure at which this maximum is expected. The conditions under which dimers may be detected in a mixture of parent and dimer upon re‐irradiation at short wavelengths are examined in terms of the differential equations.
THE RECOVERY OF THE ALBINO RAT ELECTRORETINOGRAM AFTER PARTIAL LIGHT ADAPTATION
Authors: Buckser Stanley
Published: January 2008

Abstract— The ERG obtained from albino rats was recorded every 90 sec after the eye was exposed to an adapting white light of known energy. The normalized a‐wave regeneration curves for a constant test stimulus obtained from different rats, using different adapting light energies, were identical and superimposable, except that a delay between the time that the adapting light was turned off and the time that the a‐wave appeared was observed for the high energy adapting light experiments. This delay increased as the adapting light energy increased.
THE EFFECT OF INHIBITORS AND UNCOUPLERS OF PHOTOSYNTHETIC PHOSPHORYLATION ON THE DELAYED LIGHT EMISSION OF CHLOROPLASTS*
Authors: Mayne Berger C.
Published: January 2008

Abstract— Measurements were made of the 3.7 msec delayed light emission of chloroplasts treated with a variety of agents which affect the rate of electron transport (Hill reaction) or photosynthetic phosphorylation. The presence of the electron acceptors ferricyanide or pyocyanine increased delayed light emission. Inhibitors of electron transport (3‐(3,4‐dichlorophenyl)‐1, ‐1‐dimethylurea or 1,10(ortho)‐penanthroline) inhibited delayed light emission. The addition of a phosphate acceptor system inhibited delayed light emission. This inhibition was reversed by inhibitors of the phosphorylation reaction, e.g. Dio‐9 or phlorizin. From these results it was concluded that the 3.7 msec delayed light emission probably occurs as a result of back reactions of intermediates in the coupled electron transport and photosynthetic phosphorylation systems.
LIGHT‐INDUCED CYTOCHROME REACTIONS IN THE GREEN PHOTOSYNTHETIC BACTERIUM CHLOROPSEUDOMONAS ETHYLICUM*
Authors: Sybesma Christiaan
Published: January 2008

Abstract— Light‐induced absorbance changes in cells of the green photosynthetic bacterium choloropseudomonas ethylicum depleted of substrate show that at lest two cytochromes become oxidized upon illumination. Inhibitory effects of phenylmercuric acetate and the uncoupler carbonyl cyanide 3‐chlorophenylhydrazone (which apparently acted also as a sulfhydryl reagent) prove athat neither of the cytochromes is oxidized by the other. A provisional electron transport pathway is presentd, which is compaltible with the experimentsl data.
TEH PHOTO‐OXIDATION OF SIMPLE N‐ALKYL ANILINES STUDIED BY FLASH PHOTOLYSIS
Authors: Mckellar J. F.
Published: January 2008

Abstract— The flash‐initiated photo‐oxidation of six simple N‐alkyl tertiary, secondary and primary anilines was studied in aqueous solution by kinetic spectroscopy. Two transient species were observed with the tertiary anilines, but only one “transient” was observed with the secondary and primary anilines. Where possible, the kinetics of formation and decay of these transients was studied in detail. The formation of highly coloured products was observed on flashing the anilines in air‐saturated solution and the variation of their colour with the pH of the solution was noted. Preliminary observations on the nature of possible blue products from the tertiary anilines were made. The results for thwe tertiary anilines are interpreted in terms of the mechanism previously for the photo‐oxidation of HEMA.
LUMINESCENCE OF L‐TRYPTOPHAN IN THE DRY STATE AND IN AQUEOUS SOLUTION INDUCED BY X‐RAYS AND U.V.‐LIGHT AT 77°K
Authors: Steen H. B.
Published: January 2008

Abstract— The luminescence from tryptophan in the dry state and in aqueous glass. induced by u.v.‐light and X‐rays at 77°K, has been studied. The spectra of the luminescence from the dry material, which were identical for the two types of irradiation, were attributed to the same excited singlet level as that giving rise to the fluorescence from the aqueous sample. The strong phosphorescence exhibited by the latter. could not be detected for the dry material with either type of irradiation. This was attributed to a strong quenching of the radiative triplet level occurring upon crystallization of the substance. The yield of X‐ray induced fluorescence of tryptophan in aqueous glass was found to be similar to that observed in the dry state. It was concluded that there is no extensive transfer of energy between the solvent and the solute molecules contributing to the fluorescence yield of tryptophan in aqueous glass.
FLASH PHOTOLYSIS OF SEVERAL AROMATICS BY ULTRAVIOLET LIGHT AND VISIBLE LIGHT IN THE PRESENCE OF EOSIN Y*
Authors: Chrysochoos J. , Grossweiner L. I.
Published: January 2008

Abstract— A flash photolysis investigation was made of the photo‐oxidation of aqueous aniline, resorcinol, βnaphthol, p‐sulfanilic acid, and p‐bromophenol induced by ultraviolet and visible light irradiation in the presence of eosin Y. The transient spectra show that u.v. irradiation generates the hydrated electron (except in p‐bromophenol) and the radical products of one‐electron oxidation. The initial products of the eosin‐sensitized oxidations are the dye semi‐quinone and aromatic radicals which coincide with the u.v. photolysis products in at least several cases. The investigation of the reaction kinetics by rapid spectrophotometry with analog computer analysis shows that the aromatics quench the triplet state of eosin and also react with it in a slower electron‐transfer process, in competition with ‘dye‐dye’ quenching and electron‐transfer reactions. The u.v. and dye‐sensitized oxidations are discussed in terms of their energetics.
PHOTOSYNTHETIC EFFICIENCY OF A PHYCOCYANIN‐LESS MUTANT OF CYANIDIUM*
Authors: Volk S. L. , Bishop N. I.
Published: January 2008

Abstract— 1. R‐II is a u.v. induced mutant of cyanidium caldarium which lacks the major accessory pigment phycocyanin.

2. Loss of phycocyanin does not impair photosynthesis or the Hill reaction.

3. The action spectrum for the quantum yield indicates an efficiently operating photosynthetic mechanism which is shifted in peak efficiency toward longer wavelengths when compared to the wild‐type spectrum. The red drop is also shifted toward the far red in R‐II.

4. Although 30 per cent enhancement was obtained in wild‐type Cyanidium, no enhancement was observed when phycocyanin was absent.

5. A pigment absorbing at 720 nm has been observed and may possibly represent a chlorophyll‐phycocyanin complex.
EXCITED STATES OF FLAVINE COENZYMES‐TV. KINETICS OF THE PHOTOREDUCTION OF LUMIFLAVINE BY METHIONINE
Authors: Byrom P. , Turnbull J. H.
Published: January 2008

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 process.
DELAYED FLUORESCENCE IN PHOTOSYNTHETIC MATERIALS: TRANSIENT RESPONSE TO PULSED LIGHT IN CHLORELLA
Authors: Ruby R. H.
Published: January 2008

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 fluorescence.
ABSORPTION MAXIMA OF CATIONS RELATED TO RETINAL AND THEIR IMPLICATION TO MECHANISMS FOR BATHOCHROMIC SHIFT IN VISUAL PIGMENT*
Authors: Blatz P. E. , Pippert D. L. , Balasubramaniyan V.
Published: January 2008

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 Λmax values, 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 carbonium ion.
STRUCTURE OF DYE AGGREGATES AND THE MECHANISM(S) OF PHOTOSENSITIZATION OF AgBr*,†
Authors: Bird George R. , Zuckerman Bernard , Ames Allan E.
Published: January 2008

Abstract— This paper reports the present conclusions of an extended investigation on photo‐sensitization of silver bromide. A general molecular packing structure for dye aggregates on the AgBr (111) surface is proposed. This structure, along with the observed spectral absorption displacements of small aggregates, is used to elucidate the phenomena of antisensitization and supersensitization. Supersensitization is seen as a partitioning of large dye aggregates into small aggregates by a deliberately added second component or by gaps between the aggregates. This partitioning isolates antisensitizing dye in a small fraction of the aggregates and minimizes its effect. The smallest aggregates are least likely to contain an antisensitizer, and show the highest quantum efficiency for photoconductivity and photographic action. Photoconductivity measurements establish that supersensitization occurs before the electron appears in the AgBr phase.

The question of direct electron injection vs. energy transfer as mechanisms for AgBr photosensitization is examined in terms of radiationless transfer to surface Ag2S on AgBr. The absorption of surface Ag2S is shown to be adequate for acceptance of Förster transfer from the dye, and surface Ag2S is known to be photographically active. However, this mechanism is inefficient, and inadequate to account for observed high efficiency infrared sensitization. Direct electron injection is seen as the more probable mechanism for efficient dye sensitization of AgBr.
OPTICAL SENSITIZATION OF CHARGE CARRIER TRANSPORT IN POLY(N‐VINYL CARBAZOLE)*
Authors: Regensburger Paul J.
Published: January 2008

Abstract— The photoconductivity of thin films of poly(N‐vinyl carbazole), and poly(N‐vinyl carbazole) sensitized with a thin layer of amorphous selenium, has been measured using a ‘xerographic’ condenser discharge technique and a conventional time of flight light pulse photo‐response technique. Direct camer generation and hole mobility in the polymer was found to be strongly field dependent. There appears to be no evidence for deep trapping. Hole transport through the polymer was able to be sensitized by light absorbed in the selenium. The results indicate that the photosensitization mechanism can be thought of in terms of hole generation and transport in selenium, field‐modulated injection across the selenium polymer interface and transport through the polymer.
SENSIBILISIERTE PHOTOOXIDATION DURCH METHYLENBLAU, THIOPYRONIN UND PYRONIN‐I MITTEILUNG: FLASH‐PHOTOOXIDATION VON p‐DIAMINOTOLUOL
Authors: GOLLMICK F. A. , BERG H.
Published: January 2008

The dye (F)*sensitized photooxidation of p‐diaminotoluene (RH2) was examined by flash‐spectroscopy and the mechanism was elucidated. The first chemical reaction is the generation of two free radicals from the triplet dye and the hydrogen donor. These radicals may react in several ways without oxygen:

or additionally with oxygen:

The connection of this mechanism with photodynamic action is discussed.
A METHOD FOR THE CORRECTION OF QUANTUM YIELDS OF FLUORESCENCE IN SOLUTIONS
Authors: ROHATGI K. K. , SINGHAL G. S.
Published: January 2008

Abstract— The correction factors due to the overlap of absorption and emission spectra have been calculated for various concentrations of fluorescein dye at pH 12 by using the experimentally obtained value of apparent molar absorptivity, ε2, for the fluorescence radiation. The observed fluorescence intensities for the same‐surface detection for a given geometry have been corrected for the secondary emission effect thus calculated, and also for refraction and dilution effects, to give corrected relative quantum yields for the solutions. These have been converted to the absolute values by comparison of the integrated fluorescence quantum spectrum of a dilute solution of fluorescein with that for quinine sulphate in 0.1 N H2SO4. The corrected quantum yields compare well with values given in the literature.
PHOTOBIOLOGIE DU MESOCOTYLE D'AVOINE–IV. SPECTRES D'ACTION ET EFFICACITE QUANTIQUE DE LA LUMIERE
Authors: SANDMEIER M.
Published: January 2008

Abstract— The wavelengths most active in influencing the growth of segments of oat mesocotyl are 435 nm (blue), 665 nm (red) and 730 nm (far red). Using a high‐energy source (1.5 × 1018 quanta/cm2), an inhibition in all areas of the spectrum except the far red was obtained. The efficiency of the different radiations was studied: blue light is the most active, red and far red have about the same efficiency; green is a thousand times less active. The effect induced by blue light cannot be directly attributed to phytochrome, because the wavelength of maximum effect does not correspond with that of maximum absorption of the pigment (there is 55 nm difference); also, blue light is more active than the red radiation.
ABSOLUTE VALUES OF PHOTON EMISSION FROM THE MARINE DINOFLAGELLATES PYRODINIUM BAHAMENSE, GONYAULAX POLYEDRA AND PYROCYSTIS LUNUU*
Authors: Seliger H. H. , Biggley W. H. , Swift E.
Published: January 2008

Abstract— The total photons emitted per organism upon complete stimulation during the dark phase of their photoperiod for P. bahamense, G. polyedra and P. lunula are 2·8 × 108± 15%; 1·2 × 108± 12% and 40 × 108± 11% respectively, P. bahamense in natural populations in Jamaica. W. 1. emitted the same total stimulable light per organism as in laboratory cultures. The bioluminescent emission spectra are the same for all three species (vmax.= 20.860 cm‐1).
A KINETIC ISOTOPE EFFECT IN THE PHOTOREACTIVATION OF U.V.‐INACTIVATED TOBACCO MOSAIC VIRUS RNA*
Authors: EVANS N. A. , McLAREN A. D.
Published: January 2008

Abstract— Inactivation of tobacco mosaic virus RNA (TMV‐RNA) by u.v. radiation is slower in D2O than in H2O, and TMV‐RNA which has been inactivated in D2O is photoreactivated faster (on Pinto bean) than TMV‐RNA which has been inactivated in H2O. The maximum amount of photoreactivation is unaffected by the solvent, H2O or D2O, present during irradiation. These deuterium isotope effects for inactivation and photoreactivation suggest that pyrimidine hydrates are photoreactivable lesions on Pinto bean.
A MUTANT OF ESCHERZCHZA COLI K12 EXHIBITING VARYING ULTRAVIOLET SENSITIVITIES DEPENDING ON THE TEMPERATURE OF INCUBATION AFTER IRRADIATION*
Authors: SUZUKI KENSHl , SAlTO ETSUKO , MORIMYO MlTSUOKl
Published: January 2008

Abstract— A mutant, URT‐43, was isolated from E. coli C600 dar+. The mutant has a characteristic feature in that its sensitivity to ultraviolet (u.v.) light is greatly influenced by the temperature at which irradiated bacteria are incubated. On the basis of dose‐reduction factor, URT‐43 is approximately ten times more sensitive at 42° than at 30°C, even though unirradiated bacteria are not thenno‐sensitive, The mutant could not repair u.v.‐irradiated bacteriophage Λvir in the dark either at 30° or at 42°C, indicating that it is defective in host‐cell reactivation. In contrast, the same bacteriophage was reactivated in preirradiated URT‐43 if the host‐bacteriophage complex was plated at 30° but there was no reactivation at 42°C. Therefore u.v.reactivation was positive at 30° but negative at 42°C. The induction of prophage by URT‐43(Λh) was achieved by much lower doses of U.V. light than that required for the induction of lysogenic wild type bacteria. Experiments were performed in which irradiated URT‐43 was first incubated for various periods in liquid media and plated both at 30° and 42°C. It was found that irradiated bacteria came to be resistant to subsequent plating at 42° only when they were preincubated in the liquid medium containing necessary amino acids and at 30°C. Since this phenomenon was completely inhibited by chloramphenicol, the process seemed to require de novo protein synthesis. An hypothesis was proposed that there are at least two independent dark‐repair mechanisms in E. coli; one is responsible for host‐cell reactivation and the other is responsible for U.V. reactivation.
ULTRAVIOLET LIGHT INDUCED FREE RADICALS IN GLYCINE PEPTIDES IN THE SOLID STATE
Authors: COLLINS M. A. , GRANT R. A.
Published: January 2008

Abstract— The effect of ultraviolet radiation on glycine, diglycine, triglycine and polyglycine in the solid state has been investigated using ESR. The irradiated diglycine and tnglycine displayed signals commonly encountered when more energetic radiations are employed, but polyglycine displayed an additional signal not previously described and the signal from glycine was found to differ from those produced by other radiations.
NEAR‐U.V. PHOTOLYSIS OF PYRIMIDINE HETEROADDUCTS IN E. COLI DNA*
Authors: PATRICK M. H.
Published: January 2008

Abstract— The cytosine‐thymine precursor of the U–T adduct is not subject to enzymatic photoreactivation, but can be eliminated directly from u.v.‐irradiated E. coli DNA by exposure to wavelengths around 313 nm.
ACTION OF PHOTOREACTIVATING LIGHT ON PYRIMIDINE HETEROADDUCT IN BACTERIA*
Authors: IKENAGA M. , PATRICK M. H. , JAGGER J.
Published: January 2008

Abstract— In stationary‐phase Escherichia coli B/r, photoreactivation (PR) at 313 nm of ultraviolet (u.v.) killing is inefficient compared with PR at 405 nm, and can be explained solely by photoenzymatic reversal of pyrimidine dimers.

In Staphylococcus epidermidis, PR shows a maximum at 313 nm, suggesting that this organism shows the Type III PR proposed by Jagger et al.[5] for Streptomyces strains. Reversal of pyrimidine dimers is not sufficient to explain this PR. The mechanism of Type III PR remains unknown.

With both S. epidermidis and E. coli B/r, the amount of uracil–thymine heteroadduct in DNA hydrolysates decreases if the cells are given a post‐u.v. treatment at 313 nm, but no decrease is observed if the post‐u.v. treatment is at 405 nm. The biological significance of this adduct and of its removal is not clear. It may play a role in Type III PR.
PHYTOCHROME CONVERSION BY ULTRAVIOLET LIGHT
Authors: PRATT L. H. , BUTLER W. L.
Published: January 2008

Abstract— Light absorbed primarily by the protein of phytochrome is active in transforming both the red and far‐red absorbing forms. Pr and Pfr. The ratio of quantum yields for the conversions of Pr and Pfr by u.v. radiation (φr/φfr)u.v.= 1.5 and does not differ significantly from the ratio obtained with red and far‐red light absorbed directly by the chromophores (φr/φfr)vvis. Thus, the efficiency of energy transfer from protein to chromophore is essentially the same for both forms of the chromoprotein. The ratio of the relative quantum yields for u.v. and visible light (φr)u.v./(φr)vis was 0.32 indicating that 30–35 per cent of the light energy absorbed by the protein was transferred to the chromophore.
EXCISION OF CYTOSINE‐THYMINE ADDUCT FROM THE DNA OF ULTRAVIOLET‐IRRADIATED MICROCOCCUS RADIODURANS*
Authors: VARGHESE A. J. , DAY. RUFUS S.
Published: January 2008

Abstract— 6‐4‘‐[pyrimidin‐2’‐one]‐thymine (PO‐T), a deamination product of a cytosine–thymine adduct accounted for about 17 per cent of the total detectable thymine‐derived photoproducts in u.v.‐irradiated Micrococcus radiodurans. On incubation of the irradiated cells, oligonucleotides containing the photoproducts were released into the medium. After various periods of incubation the different photoproducts were isolated both from the cells and from the medium. Analysis of these different photoproducts showed that during the excision process the ratio of PO–T to total thymine‐derived products remained constant both in the cells and in the medium. This shows that the precursor to PO–T is excised at the same rate as the other thymine‐derived photoproducts by the dark repair mechanisms exhibited by this radiation‐resistant organism.
ELECTRON SPIN RESONANCE STUDIES OF THE EXCITED TRIPLET STATES OF DL‐5‐HYDROXY‐TRYPTOPHAN, 5‐HYDROXYINDOLE, 6‐HYDROXY‐NICOTINIC ACID, INDOLE AND HIPPURIC ACID‡,‡
Authors: CHEN TZENG‐MING
Published: January 2008

Abstract— The electron spin resonances of the metastable triplet states of DL‐5‐hydroxy‐tryptophan, 6‐hydroxynicotinic acid, and other related compounds have been observed in various glasses at 77°K. These compounds are biologically interesting in connection with photochemical processes. The Δm= 2 transitions were observed and the spin‐spin interaction parameter (D2+ 3E21/2 was determined. However, for indole, it was also able to observe the Δm= 1 transitions from which D and E were determined separately. From the values of (D2+ 3E2)1/2, D and E whenever possible and from the decay times of the triplet states, it was possible to characterize the lowest triplets as π—π* states in all cases.

Studies of the pH dependence of DL‐5‐hydroxytryptophan, 5‐hydroxyindole, and 6‐hydroxynicotinic acid indicate that the unionized molecule exhibits a resonance different from that of the related ion with a proton removed from the phenolic hydroxyl group.

The zero‐field splitting parameters D* and the lifetime of the triplet states have also been measured in various glasses and in Lucite. Both temperature and the specific nature of the host media affected the values of these parameters.
GRADIENT FORMATION OF ANTHOCYANIN IN SEEDLINGS OF FAGOPYRUM AND SINAPIS UNILATERALLY EXPOSED TO RED AND FAR‐RED LIGHT*
Authors: SHROPSHIRE W. , MOHR H.
Published: January 2008

Abstract— Anthocyanin synthesis was measured in hypocotyl halves excised from Fagopyrum and Sinapis seedlings irradiated unilaterally or equilaterally with red or far‐red light. Although no phototropic curvatures are produced by red or far‐red exposure, a significant gradient in anthocyanin formation was observed for Fagopyrum seedlings and the trend for gradient formation is present in Sinapis seedlings. The gradient production in Fagopyrurn is correlated with this tissue's greater optical density. Since the intensities used do not inhibit elongation completely (through the phytochrome system) and an intensity gradient is present in the tissue (as evidenced by anthocyanin formation) it is concluded that (a) a steeper light gradient is required to induce phototropic curvatures or (b) a diffusible material affecting elongation growth prevents any differential from being established across the tissue.
DECOMPOSITION PHOTOSENSIBILISEE DE SOLVANTS ORGANIQUES A 77°K PAR UNE AMINE AROMATIQUE, LA DIPHENYLPARAPHENYLENEDIAMINE*
Authors: CHACHATY C. , SCHOEMAKER D. , BENSASSON R.
Published: January 2008

Abstract— –By e.s.r. we have studied the photoexcitation of an aromatic amine to its triplet state at 77°K, its photoionization to a radical cation and the simultaneous formation of solvent radicals proceeding from the photosensitization of the organic glassy matrix.

In the case of methanol and ethanol matrix we observe approximately one solvent radical per solute radical cation. In the case of isopropanol and methyltetrahydrofuran we find respectively three and two solvent radicals per solute radical cation. The results suggest two possible processes of photosensitization. By successive absorption of two photons, the amine reaches an excited triplet state which is able either to dissociate giving one electron and one cation radical or to transfer its energy to the solvent, this last being decomposed.

It is assumed that in the case of methanol and ethanol, the radicals from the solvent are only formed by reaction on the matrix by the released electron, whereas in the case of isopropanol and methyltetrahydrofuran, the second process is prevalent or exclusive.
PHOTOCHEMICAL OXIDATIONS—IV. THE PHOTOOXIDATION OF CYCLOHEXANE WITH OXYGEN
Authors: KULEVSKY NORMAN , SNEERINGER PAUL V. , GRINA LARRY D. , STENBERG VIRGIL I.
Published: January 2008

Abstract— –For the photooxidation of cyclohexane, data on the rates of formation of cyclohexanol (I), cyclohexanone (II), and cyclohexylhydroperoxide (III) are presented. There are induction periods for the formation of I and II but not for III. The alcohol (I) is not the precursor of II in this reaction. The photooxidation does not occur when optical filters eliminate wavelengths of 260 nm or less from the incident light, and therefore the contact charge transfer absorption is responsible for the initiation of the reaction. Ozone is not involved to any significant extent in this reaction. The photodecomposition of III produces I and II, and this decomposition is first order during the initial stages. An overall 11 step mechanism is suggested for the photooxidation.
PHOTOLYSIS AND RADIOLYSIS OF PHENYL‐ALANYLGLYCINE
Authors: WHEELER OWEN H. , JULIÁN DOLORES A. , RIBOT ROSA AMPARO
Published: January 2008

The Photolysis of glycine and alanine containing peptides in oxygenated solution has been shown to result in the formation of glyoxylic and pyruvic acids, through oxidative cleavage of the peptide bond[1]. The same products were formed in the radiolysis of such peptides in the presence of oxygen[2]. In a peptide containing aromatic amino‐acids the absorption of light results in the excitation of the aromatic ring and it has been postulated[3] that energy is transferred to the peptide bond, resulting in the formation of a radical on the carbon atom adjacent to the peptide bond. Radiolysis, however, involves the attack of hydroxyl radicals and other reactive species formed in the absorption of radiation by water[2]. This study compares the behavior of phenylalanylglycine to photolysis and radiolysis in aerated aqueous solution in relation to a possible energy transfer in photolysis.
A THEORETICAL TREATMENT OF THE ELECTRONIC STATES OF THIONINE AND RELATED MOLECULES
Authors: SOMMER U. , KRAMER H. E. A.
Published: January 2008

Abstract— –Problems associated with the protolytic equilibria of thionine and related molecules in their lowest excited electronic states were investigated. The theoretical arguments are based on semi‐empirical SCF MO (CI) calculations for the π‐electronic system of these molecules; all singly excited configurations were included in the CI. The results indicate that the basic form of thionine in its ground, first excited singlet and lowest triplet state is protonated at the heterocyclic N atom. The difference of the pK values of these three states can be explained in terms of the calculated charge densities. The photochemical reactivity of the lowest triplet of the acidic form of thionine (3TH22+) differs greatly from that of the lowest triplet of the basic form (3TH+). Some arguments for the assignment of nπ* character to 3TH22+ and ππ* character to 3TH+ are advanced.
THE PHOTOOXYGENATION OF MAGNESIUM‐OCTAETHYLPORPHIN*
Authors: FUHRHOP J.‐H. , MAUZERALL D.
Published: January 2008

Abstract— Octaethylporphinato‐magnesium (MgOEP) has been photooxygenated in quantitative yield to a brown compound with its main absorption peaks at 825 and 408 nm. The product has been isolated and evidence suggests that it is 4‐formyl‐5‐oxa‐octaethylporphinato‐magnesium II. II is very labile to hydrolysis, the main isolated decomposition product being 1, γ‐dioxo‐8‘‐formyl‐octaethyl violin III. The absorption, i.r., PMR and mass spectra of II and III are reported and possible paths to their formation are discussed.
ELECTROCHEMISTRY OF EXCITED MOLECULES: PHOTO‐ELECTROCHEMICAL REACTIONS OF CHLOROPHYLLS*
Authors: TRIBUTSCH H. , CALVIN M.
Published: January 2008

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 centers.
EXCIPLEX STUDIES‐IV. RADIATIVE AND NON‐RADIATIVE RELAXATION OF THE FLUORESCENT STATE OF INDOLE†
Authors: WALKER M. S. , BEDNAR T. W. , LUMRY R. , HUMPHRIES F.
Published: January 2008

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 set of events.
THE MECHANISM OF DELAYED LIGHT PRODUCTION BY PHOTOSYNTHETIC ORGANISMS AND A NEW EFFECT OF ELECTRIC FIELDS ON CHLOROPLASTS*,‡
Authors: ARNOLD WILLIAM , AZZI JIM
Published: January 2008

Abstract— Green plants, after illumination, emit light at times far too long to be fluorescence. This delayed light is closely connected with the process of photosynthesis and seems to be one of the few ways of studying the first steps in that process. In this paper we argue that there are at least 3 or maybe 4 mechanisms producing delayed light. (1) The delayed light in the range of 1–100 msec seems to come from the recombination of electrons and holes. The photosynthetic unit must absorb 2 quanta for this process. (2) At longer times the delayed light can come from thermal fluctuations lifting an electron from the level of ferredoxin to that of chlorophyll. The unit need only absorb 1 light quantum for this kind of delayed light. (3) Similarly, a part of the long‐time delayed light comes from the untrapping of holes. (4) A part of the delayed light emitted at times longer than a few minutes seems to involve molecular oxygen. Finally, we shall describe a new phenomenon involving the effect of electric fields on chloroplasts, that we feel will be helpful in understanding the untrapping mechanisms of delayed light production.
CHLOROPHYLL‐PROTEINS AND REACTION CENTER PREPARATIONS FROM PHOTOSYNTHETIC BACTERIA, ALGAE AND HIGHER PLANTS*,‡
Authors: THORNBER J. PHILIP , OLSON JOHN M.
Published: January 2008

Abstract— The use of sodium dodecyl sulfate to dissociate photosynthetic membranes followed by standard fractionation techniques yields chlorophyll‐proteins and reaction center complexes with molecular weights of 500,000 or less. Much about the structure and function of photo‐synthetic units in vivo can be deduced from the properties of the isolated complexes. The Bchl‐protein from green bacteria is approximated by an incompletely filled sphere ˜ 80 Â in diameter consisting of four identical subunits. The five Bchl molecules in each subunit are 14 to 20Â apart. The related Chl a‐proteins from a blue‐green alga and various eukaryotic plants may have similar structural characteristics. The Chl a‐protein from a blue‐green alga contains one molecule of P700 per 60–90 Chl a molecules. The quantum requirement for P700 oxidation is 2.6 or less. The midpoint potential in various preparations ranges from 0.38 V to 0.42 V. Green algae and higher plants yield a Chl a‐protein similar to that from the blue‐green alga; in addition they yield another Chl‐protein (mol. wt. = 2–3×104) which contains an equal amount of Chl a and Chl b. These two Chl‐proteins account for most of the chlorophyll in these organisms. Two photosynthetic bacteria (Rhodopseudomonas viridis and Chromatium) yield protein complexes containing Bchl, carotenoid, and bound cytochromes. The reaction center complex from R. viridis contains P960 (Em, 8= 0.39 to 0.42 V), cytochrome 558 (Em,8= 0.33 V) and cytochrome 553 (Em,7=— 0.02 V). Quantum requirements for P960 and C558 oxidation are ˜2.2 and 3.0, respectively. Complex A from Chromatium contains Bchl 890, P883, cytochrome 556 (Em,8= 0.34 V) and cytochrome 552 (Em,7=˜0.04 V). The quantum requirement for C556 oxidation is about 15. Both high‐ and low‐potential cytochromes can donate electrons to the reaction center chlorophyll present in either complex. This fact supports the idea that only one kind of photochemical reaction center functions in photosynthetic bacteria. An hypothesis about the nature of the photosynthetic unit in purple bacteria is outlined.
ON THE INTERACTION OF PHOTOSYSTEMS I AND II IN ALGAL CELLS*,†
Authors: HOCH GEORGE E. , RANDLES JOAN
Published: January 2008

Abstract— Steady‐state relaxation spectrophotometry was applied to intact algal cells. The results indicated System I operates in a cyclic manner, only indirectly affected by the presence or absence of oxygen evolution. This action in whole cells is distinct from that occurring in chloroplasts, where System I appears tightly coupled to System II. No evidence was found for the oxidation of cytochrome by P700. Fluorescence emission measurements on intact cells emphasized the role of membrane permeability agents in controlling the emission yield. Large changes in the yield caused by Systems I and II could be observed in the presence of these agents. In sum, the results proved complex and were difficult to resolve in any simple scheme but emphasized the possible role of protons (or membrane potential) in controlling fluorescence yield.
WAVELENGTH REGULATION IN VISUAL PIGMENT CHROMOPHORE: LARGE INDUCED BATHOCHROMIC SHIFTS IN RETINOL AND RELATED POLYENES.*
Authors: BLATZ P. E. , BAUMGARTNER N. , BALASUBRAMANIYAN V. , BALASUBRAMANIYAN P. , STEDMAN E.
Published: January 2008

Abstract— Low temperature techniques are used to record spectra of long wavelength absorbing electrochromic species formed from retinol and related compounds. Formation of these electrochromic species is induced either by iodine or trichloroacetic acid which merely act as acids. The electrochromic species are the corresponding carbonium ions of the respective polyenes. The resulting carbonium ions of a given polyene are identical regardless of whether they are formed by iodine or trichloroacetic acid. The molecular structures of the carbonium ions can be written with certainty. Consequently, the exact nature of the π‐electron system in the polyene and its carbonium ion may be elucidated.
PHOTOCHEMICAL COUPLING OF BENZO[a]PYRENE WITH 1‐METHYLCYTOSINE; PHOTOENHANCEMENT OF CARCINOGENICITY
Authors: CAVALIERI E. , CALVIN M.
Published: January 2008

Abstract— Irradiation of the carcinogenic benzo[a]pyrene(I) with 1‐methylcytosine hydro‐chloride(II) (molar ratio 1:10) at 3500 Å in methanol‐acetone produces the 6‐(1‐methylcytos‐5‐yl)‐benzo[a]pyrene(III). The structure of the product shows the hydrocarbon bound through the most active 6‐carbon atom to the nucleophilic 5‐position of the base. In the second part, the possibility of observing carcinogenic effects on the mouse skin from non‐carcinogenic hydrocarbons under the action of u.v. light is investigated. Both experiments provide evidence that the 4,5‐double bond (K region) of I presumably does not play a role in triggering the cancer process.
EXCITATION AND FLUORESCENCE SPECTRA OF THE CHROMOPHORE ASSOCIATED WITH THE DNA‐PHOTOREACTIVATING ENZYME FROM THE BLUE–GREEN ALGA ANACYSTIS NIDULANS
Authors: MINATO S. , WERBIN H.
Published: January 2008

DNA‐PHOTOREACTIVATING enzymes can be classified as deoxyribonucleate cyclobutane dipyrimidine photolyases*. Such an enzyme was recently purified 3760‐fold from the blue‐green alga Anacystis niduluns [8]. The absorption spectrum of the enzyme revealed a small peak at 418 nm that was attributed to an impurity. The enzyme has now been purified further, by affinity chromatography on far‐ultraviolet (far‐u.v.) irradiated DNA non‐covalently bonded to cellulose, and its excitation and fluorescence spectra measured. These spectra reveal the presence of a non protein chromophore associated with the algal photolyase. The peak wavelengths in the excitation and absorption spectra in the visible region are almost identical and close to that observed in the in vitro photoreactivation action spectrum [8], observations supporting the view that this chromophore is involved as a cofactor in DNA photo reactivation.
PHOTOCHEMICAL REACTIONS OF AROMATIC KETONES WITH NUCLEIC ACIDS AND THEIR COMPONENTS–III. CHAIN BREAKAGE AND THYMINE DIMERIZATION IN BENZOPHENONE PHOTOSENSITIZED DNA*
Authors: CHARLIER M. , HELENE C. , CARRIER W. L.
Published: January 2008

Abstract— Excitation of benzophenone in the presence of calf thymus and E. coli DNA leads to photosensitized damages to the macromolecule. Two main reactions are observed: thymine dimerization and chain break formation. Benzophenone photosensitized chain breaks are also observed in polyadenylic acid.

The melting temperature of DNA decreases with the duration of irradiation.

Under our experimental conditions, the ratio of the yields of dimers and single‐chain breaks produced in DNA is about 1. Photosensitized damage to deoxyribose residues leading to chain breakage is shown to be similar to that produced by X or γ ray irradiation. The oxygen effect upon chain break production is studied and discussed in relation with its effect upon intermediate species.

Thymine dimers are formed following energy transfer from benzophenone in its triplet state. In previous flash‐photolysis studies we showed that benzophenone in its triplet state reacts with water molecules to give ketyl and OH radicals. Ketyl radicals are not involved in reactions with DNA. It is proposed that OH radicals produced in the above reaction are responsible for the production of single‐chain breaks by attack on the deoxyribose residues.
CHANGES IN TOTAL DIFFUSE SPECTRAL REFLECTANCE OF AMINO ACIDS AND PROTEINS AFTER ULTRAVIOLET IRRADIATION
Authors: ANGLIN J. H. , SAYRE R. M. , BATTEN W. H.
Published: January 2008

Abstract— Total diffuse reflectance spectra of air‐dried surfaces of free and neutralized amino acid preparations before and after irradiation in vitro are reported. It was found that some free or neutralized amino acid surfaces underwent modification which resulted in changes in the diffuse reflectance spectra after U.V. exposure. It is suggested that these reflectance changes result from transformations in the side chains of the amino acids and that the transformations may differ from those occurring when amino acids in solution are irradiated. Histidine, cystine, hydroxyproline and some protein surfaces showed changes in reflectance of 330–400 nm light similar to those reported in skin after U.V. irradiation in viuo.
AUTOMATIC SCANNING SPECTROPHOTOMETER WITH PUNCH TAPE OUTPUT FOR BIO‐APPLICATIONS
Authors: SEIM T. , PRYDZ S. , HOLTSMARK T.
Published: January 2008

Abstract— An automated scanning spectrophotometer has been constructed for the measurement of color‐vision test stimuli and various types of luminescence. Recorder and paper tape output data have been provided. Processing of the spectral information is performed on a CDC 3300 computer.

Photoelectric detection is employed. An inexpensive Jarrel‐Ash 0.25 m,f/3.6 Ebert type monochromator is employed with two gratings, blazed for 300 and 600 nm, respectively.

The spectral sweep range can be easily set by electromechanical registers, as can the number of sweeps required. Photon numbers are integrated by a counter over 5 nm blocks, and this procedure sets the limit of resolution. At present the spectral range is from 400 to 800 nm. By calibration against an ultraviolet‐emitting standard lamp the useful range can easily be extended downwards to 250 nm.

Computer programs have been written which add several spectra when these are faint and produce a mean spectrum in the form of listed and plotted output. The mean noise level is subtracted. Subprograms have been made for the smoothing of poor spectral data where noise predominates and for the correction for stray light and grating ‘ghosts’ in the monochromator. A program has been made which performs colorimetric analyses of light sources, spectral filters, and pigmented surfaces. The dominant wavelength and the excitation purity are computed and given in CIE chromaticity coordinates and three‐stimulus values.
PHOTOLYSIS OF POLYRIBOBROMOURIDYLIC ACID
Authors: EHRLICH MELANIE , RILEY MONICA
Published: January 2008

Abstract—Photolysis of polyribobromouridylic acid with 313 nm light at neutral pH caused extensive debromination and a loss of A280(280–nm absorbance) without comparable increase in A260. At an exposure of 190μE/cm2, strand breakage occurred on the average of one break every 170 BrU residues. Little if any pyrimidine hydrate was produced. Exhaustive RNase hydrolysis of photolysed polymer gave a mixture of mononucleotides and oligonucleotides. The mononucleotide fraction was found to be composed of unaltered BrUMP and contained little if any UMP. Irradiation of the polymer at alkaline pH caused little or no debromination or spectral change.
ACTION SPECTRA FOR ULTRAVIOLET KILLING AND PHOTOREACTIVATION IN THE BLUE‐GREEN ALGA AGMENELLUM QUADRUPLICATUM
Authors: BAALEN C. VAN , O'DONNELL R.
Published: January 2008

Abstract— The action spectrum for photoreactivation has been determined in a coccoid blue‐green alga, Agmenellum quadruplicatum. The spectrum is rather similar to that recorded for Streptomyces griseus conidia, with some suggestion of a little more structure. The action spectrum suggests possible carotenoid involvement; however, no other evidence for this could be found. The action spectrum for u.v. killing is also broad with some evidence of fine structure. The possible implication of tetrahydropteridines or c‐phycocyanin as chromophores in the region 240–300 nm, along with DNA, is pointed out.
SIMULTANEOUS GROWTH AND DECAY OF FREE RADICALS IN IRRADIATED PROTEINS
Authors: SHATKAY ADAM
Published: January 2008

Abstract— The electron paramagnetic resonance signals due to free radicals created in illuminated keratin have been studied during illumination and also during the decay of the signal in the dark. A number of mechanisms suggested to account for the simultaneous growth and decay of radicals during illumination is considered but only one of these is capable of accounting for the experimental results.
EFFECTS OF PHOTOSYSTEM II INHIBITORS ON ELECTRON PARAMAGNETIC RESONANCE SIGNAL II OF SPINACH CHLOROPLASTS
Authors: LOZIER RICHARD H. , BUTLER WARREN L.
Published: January 2008

Abstract— In isolated spinach chloroplasts the light‐induced electron paramagnetic resonance signal (signal II) associated with the oxygen evolving photosystem (photosystem II) decays slowly and incompletely in the dark. Tris‐washing, hydroxylamine, or carbonylcyanide m‐chlorophenylhydrazone (CCCP) enhance the decay of signal II, which can still be induced by red (645 nm) but not by far‐red (735 nm) radiation. Although 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) alone has no effect on signal II, it blocks the induction of signal II in the presence of hydroxylamine or CCCP. These data suggest that signal II is an indicator of an oxidized intermediate on the water‐splitting side of photosystem II.
PRIMARY PHOTOCHEMISTRY OF PHOTOSYNTHESIS Report on a Conference held at Argonne National Laboratory, November 1971
Authors: LOACH PAUL , KATZ JOSEPH J.
Published: January 2008

In conclusion, the conference was judged to be extremely useful for the 230 persons who attended, and all departed with an optimistic enthusiasm about the certainty of progress in this field over the next 5 to 10 years. A statistic that perhaps represents a new record and should be shared to underscore the significance of the meeting to researchers in this area of photosynthesis is that out of 59 scheduled speakers all were in attendance and only one had to be replaced because of a commitment to take part in ceremonies for the 150th anniversary of a famous university in the East. From our experience with the form of the meeting, we feel that the open attendance but limited subject concept is a highly desirable meeting form and should be used for most scientific meetings.
PHOTOCHIMIE DES ACIDES AMINES AROMATIQUES EN SOLUTION ‐ I. dl‐PHENYLALANINE, dl‐TYROSINE ET l‐DOPA
Authors: HASSELMANN C. , LAUSTRIAT G.
Published: January 2008

Abstract— The action of ultraviolet radiation on dl‐phenyldanine, dl‐tyrosine and l‐dopa has been studied in dilute aqueous solutions (10‐2M–5 × 10‐3M). Irradiation was performed in nitrogen or in air, at a wavelength of 254nm. The photoproducts of low molecular weight (amino acids, carboxylic acids, amines) were isolated either by chromatography on an ion exchange column or by thin‐layer chromatography and identified mainly by ultraviolet absorption and staining with ninhydrin. The isolation of photopolymers was carried out by chromatography on a Biogel column; identification of these photoproducts was mainly achieved by ultraviolet and infrared spectroscopy.

With phenylalanine, which is the most photosensitive amino acid, the principal reaction results in splitting of the side chain, giving alanine, glycine, and four other amine compounds whose structure has not been determined. In air, additional minor products resulting from photooxydation are obtained: ortho, meta and paratyrosine. Traces of phenylethylamine were isolated after irradiation in an inert atmosphere. The polymers produced under air and nitrogen are similar. They probably result from rearrangement of aromatic radicals formed by splitting of the side chain.

Tyrosine and dopa, irradiated in air, yield mainly melanin; before polymerization, tyrosine is first converted into dopa. In a inert atmosphere, these aromatic aminoacids also polymerize, giving monophenolic and biphenolic compounds with structure close to that of melanin. The biphenolic polymer (thus obtained from dopa) shows the properties of a leuco derivative of melanin. The monophenolic polymer can be converted into melanin by the combined action of oxygen and ultraviolet radiation. Other reactions give only minor products: parahydroxy‐phenyllactic acid and 3,4‐dihydroxyphenyllactic acid by deamination‐hydroxylation of tyrosine and dopa (in air): meta and paratyrosine by dehydroxylation of dopa, either in air or in nitrogen.