bluuebunny/crossref_metadata_2025 huggingface dataset:
FLUCTUATING PHOTOSYNTHETIC UNITS IN HIGHER PLANTS AND FAIRLY CONSTANT UNITS IN ALGAE*
Authors: SCHMID G. H. , GAFFRON H.
Published: January 2008

Abstract— In the present paper we define the photosynthetic unit as the number of chlorophyll molecules involved in the fixation of one molecule of CO2 during strong short flashes lasting less than 100 μsec, because this is what we have measured experimentally. These units vaned between 300 and 5000 chlorophylls per CO2 fixed per flash in all higher plants tested. The statistical frequency distribution of the unit sizes for a given plant species as analyzed by a computer showed discontinuities of the same kind as we have pointed out before. Within the overall range of 300 to 5000 chlorophylls per CO2 fixed per flash, integration of the unit size density over small increments of 50 chlorophylls per CO2 fixed per flash showed the existence of distinct subgroups of unit sizes.
THE PHOTOCHEMISTRY OF 14 C‐5‐BROMO‐2‘‐DEOXYURIDYLYL‐(3’→5‘)‐THYMIDINE DETERMINATION OF QUANTUM YIELDS AS A FUNCTION OF pH
Authors: PETER HEINRICH H. , DREWER ROBERT J.
Published: January 2008

Abstract— Quantum yields for the formation of the major photoproduct of 2‐14C‐5‐bromo‐2′‐deoxyuridylyl‐(3‘→5’)‐thymidine (BrdUpT) have been determined by irradiation of the 2‐14C‐BrU‐labeled dinucleotide at pH 2.3, 5.9, 7.05, 8.0 and 10.25 with U.V. light at 280nm. At acidic and neutral pH the quantum yield was 0.0063; the value decreased markedly above pH 8.0 to 0.0025 at pH 10.25. Some evidence of the formation of additional photoproducts at high and low pH was found. Some aspects of the mechanism of the reaction are discussed.

Consideration of pKa values calculated for singlet and triplet excited states indicates that the decrease in the quantum yield of main photoproduct at high pH is due to dissociation of the excited bromodeoxyuridine moiety. It is suggested that the formation of BrdUpT photoproduct and the debromination of bromouracil‐labeled DN A occur via different excited states.
ABSORPTION CHANGES IN THE REACTION CENTER OF PHOTOSYNTHETIC BACTERIA AND n‐ELECTRON CALCULATIONS ON BACTERIOCHLOROPHYLL, ITS MONO CATION AND ANION
Authors: OTTEN H. A.
Published: January 2008

Abstract— π‐Electron calculations of the MO‐SCF‐CI type in the PPP approximations are carried out for the tetra pyrrole ring of the bacteriochlorophyll molecule, its mono cation and anion.

According to the calculations the formation of the positive ion will be accompanied by the disappearance of the longest wavelength absorption band of the neutral system and the appearance of a new band near 1200 nm. Absorption changes of the same kind are found in the reaction center of photosynthetic bacteria upon illumination, supporting the hypothesis that the primary reaction is an expulsion of an electron from the π‐electron system of the reaction center bacteriochlorophyll.
FLASH PHOTOLYSIS STUDIES OF OROTIC ACID
Authors: HERBERT M. A. , JOHNS H. E.
Published: January 2008

Abstract— The triplet state of orotic acid has been studied by flash photolysis. The rate for dimerization has been observed to vary from 2 × 109M‐1 sec‐1 at pH 1 where both the triplet and ground state molecules are neutral, to under 108 M‐1 sec‐1 above pH 9 where both the triplet and ground state molecules are doubly ionized. The pK of the triplet state has been measured as 4.6. The rate of oxygen quenching for the triplet is 2–3 × 109 M‐1 sec‐1 while the rate of radiationless decay in solution is 0.73 × 104 sec‐1. The triplet absorption spectra have been measured for the two ionic forms of the triplet.
THE FORMATION OF LONG WAVELENGTH ABSORBING SPECIES FROM SHORT WAVELENGTH ABSORBING LINEAR CONJUGATED POLYENES*
Authors: BLATZ P. E.
Published: January 2008

Abstract— Even linear conjugated polyenes absorb at a wavelength much shorter than their odd polyene analogues. One way even polyenes can be converted into odd polyenes is by simple protonation. The odd polyene, the retinyliccation, absorbs at a wavelength long enough, 600 nm, to accommodate known visual pigments. Protonated unsymmetrical π‐systems terminating in nitrogen have the ability to absorb at intermediate and long wavelengths. The actual excitation energy is a function of the anionic radius. Consequently, the wavelength in a visual pigment can be regulated by the distance between the centers of positive and negative charges for the N‐retinylidenealkylammonium cation.
SENSITIZED PHOTOOXYGENATION ACCORDING TO TYPE I MECHANISM (RADICAL MECHANISM) — PART III. EXPERIMENTS WITH CONTINUOUS ILLUMINATION
Authors: ZÜGEL M. , FÖRSTER TH. , KRAMER H. E. A.
Published: January 2008

Abstract— The photochemical reaction in the system thionine (sensitizer), allylthiourea (ATU, acceptor), and oxygen was studied with continuous illumination. In oxygen‐free aqueous solution thionine is photoreduced to leucothionine. With oxygen, however, a photooxygenation of the acceptor takes place. At the same time the quantum yield of the bleaching reaction of thionine decreases markedly in comparison with that of the oxygen‐free solution. At about 100 sec after the beginning of illumination, the overall quantum yield of the bleaching reaction diminishes further because the leucothionine formed during the reaction now becomes transformed into thionine. The quantum yields do not change significantly over the range of oxygen concentrations studied (initial concentration 1 × 10‐5 to 5 × 10‐5M). In addition they are independent of the light intensity. The influence of the pH and the acceptor concentration were also investigated.

The sensitizer is not only bleached reductively, but is also partly destroyed by oxidation. The results are in agreement with the reaction scheme elucidated by flash photolysis measurements.

In accordance with this reaction scheme, the primary reaction (a) of the reductive bleaching of the sensitizer, (b) of the photooxygenation of the acceptor and (c) of the oxidative destruction of the sensitizer, is identical in all cases. This process is the redox reaction between the sensitizer triplet and the acceptor, where a semithionine and an ATU‐radical are formed. The reaction represents an example of a Type I photooxygenation according to the notation of Gollnick.
INFLUENCE OF ENERGY TRANSFER ON THE PHOTOIONIZATION OF TRYPTOPHAN AND TYROSINE IN BASIC MEDIA†
Authors: SANTUS R. , BAZIN M. , AUBAILLY M. , GUERMONPREZ R.
Published: January 2008

Abstract— The luminescence studies of the delayed isothermal and light stimulated recombinations of photoejected electrons with photoionized chromophores at 77°K show that in the peptide tryptophyltyrosine, where energy transfer occurs at the singlet level from tryptophan to tyrosine and at the triplet level from tyrosine to tryptophan, tryptophan photoionization is greatly enhanced. This increase in photoionization efficiency is attributed to triplet‐triplet transfer.
INHIBITION OF 3H‐THYMIDINE INCORPORATION IN PIG KIDNEY CELLS BY FAR‐RED LIGHT*
Authors: CHEN C. H. , GORDON S. A.
Published: January 2008

Exposure of pig kidney cells in monolayer culture to far‐red light (FRL), near 750 nm, was found to increase the incidence of chromatid aberrations and aberrant cells [1]. Dose–response curves for cell populations predominantly in early S reached a maximum at incident energies of ca. 50 mJ cm‐2. We show here that the incorporation of tritiated thymidine by the nuclei of pig kidney cells in monolayer also is inhibited by FRL, with a similar dose‐response maximum.
POST‐LUMINESCENCE DES CHLOROPLASTES INTACTS ET ALTERES PAR DENATURATION PARTIELLE: ETUDE EXPERIMENTALE, INTERPRETATION THEORIQUE ET CALCUL D'ENERGIES D'ACTIVATION
Authors: LAINE‐BÖSZÖRMENYI M. , PAILLOTIN G. , ROUX P. FALLOT et E.
Published: January 2008

Abstract— The authors have studied the temperature effect on the luminescence of spinach chloroplast suspension after illumination at 675 nm.

The decay of the luminescence has been followed at constant temperature (from 0°C to 40°C) or after sudden temperature jumps (0°C ≤ΔT≤ 47°C).

They have compared the results obtained with intact chloroplasts and those after mild thermal denaturation.

From these experimentally found values they have calculated the activation energies related to the radiative and non‐radiative ways of disappearence of the entity which is at the origin of the luminescence.

On the basis of the values found for these energies (0·9 eV and 0·43 eV respectively), the authors evolve the hypothesis that this entity may be an electron self‐trapped in the chloroplast structure (small polaron).
THE FLAVIN‐SENSITIZED PHOTOOXIDATION OF NUCLEOTIDES — III. THE PARTICIPATION OF OXYGEN
Authors: KNOWLES A. , MAUTNER GILLIAN N.
Published: January 2008

Abstract— Quantum yields for the lumiflavin‐sensitized oxidation of guanosine monophosphate and adenosine monophosphate in solution have been measured as functions of oxygen and nucleotide concentration. The quantum yield increases with oxygen concentration at low oxygen concentrations, but quenching of the excited flavin molecule by oxygen results in a fall in quantum yield at higher concentrations. It has also been established that the reciprocal of the quantum yield is linearly related to the reciprocal of the nucleotide concentration. A mechanism in which molecular oxygen reacts with an excited complex formed between triplet lumiflavin and the nucleotide is consistent with these observations.

A value for the second‐order rate constant for the quenching of triplet lumifiavin by oxygen of 2·65 × 109M‐1 sec‐1 has been obtained.
PHOTOREACTIVATION IN THE YEAST SCHIZOSACCHAROMYCES POMBE
Authors: FABRE F.
Published: January 2008

Abstract— Visible light (VL) illumination of u.v.‐irradiated cells of the fission yeast Schizosaccharomyces pombe does not increase the survival of wild‐type cells, but does increase the survival of some specific UVS strains. This photoreactivation has been studied in the U VS 1,1 mutant in the stationary growth phase.

It is not dependent on temperature during VL illumination.

The effect of pre‐u.v. or post‐u.v. illumination on survival is the same.

There is an overlap of photoreactivation and liquid holding recovery.

VL does increase the growth delay after irradiation.

It is concluded from these results that the photoreactivation is not due to a photoreactivating enzyme, but to an indirect process.

The existence in this yeast of two different repair pathways of u.v. lesions has been demonstrated previously. The study of indirect photoreactivation in different strains, blocked in one or the other repair pathway by mutation or by a repair inhibitor (caffeine), leads to the conclusion that the VL treatment favours only one of these two repair mechanisms, which is presumably the excision‐repair pathway. The strain UVS A, which would repair u.v. lesions by a recombinational mechanism, does not show any photoreactivation.
PHOTOREACTIVATION OF TOBACCO MOSAIC VIRUS AND POTATO VIRUS X RIBONUCLEIC ACIDS INACTIVATED BY ACETONE‐SENSITIZED PHOTOREACTION*
Authors: HUANG C. W. , GORDON M. P.
Published: January 2008

Abstract— Acetone‐sensitized photoinactivation and subsequent in vivo photoreactivation of tobacco mosaic virus (TMV) and potato virus X (PVX) ribonucleic acids (RNA's) were demonstrated. The photoreactivable sectors were comparable to those obtained for the same RNA's irradiated at 253·7 nm. Only dimers were detected in these RNA's. Irradiation of E. coli rRNA at a higher dose indicated that photoreversible pyrimidine dimers were the main photoproducts detected in the sensitized reaction, whereas pyrimidine hydrates were formed only in negligible amounts. These results have led us to conclude that photoreversible pyrimidine dimers constitute both a lethal and photorepairable type of lesion in u.v.‐damaged viral RNA.
NANOSECOND IRRADIATION STUDIES OF BIOLOGICAL MOLECULES‐I. COENZYME Q 6 (UBIQUINONE‐30)
Authors: BENSASSON R. , CHACHATY C. , LAND E. J. , SALET C.
Published: January 2008

Abstract— The coenzyme ubiquinone, an isoprenoid benzoquinone present in the electron‐transport chain of mitochondria, has been studied using nanosecond laser flash photolysis and pulse radiolysis. The hitherto undetected triplet excited state of the coenzyme has been identified and some of the physico‐chemical properties determined. These measurements may assist the understanding in molecular terms of the degradative action of light upon biological materials, photophosphorylation and the possible initiation of biological electron transport via quinone light absorption.

Laser photolysis of ubiquinone in cyclohexane and pulse radiolysis of ubiquinone in benzene results in the formation of a transient absorption with maximum around 440 nm and a half‐life of 650 nsec in cyclohexane and 450 nsec in benzene. Energy transfer sensitisation of the β‐carotene triplet absorption by ubiquinone in cyclohexane at a rate consistent with the life‐time of the 440 nm transient absorption, yields strong evidence that this transient species is triplet ubiquinone. The triplet reacts with oxygen with a rate constant of 2 × 10‐‐9 mole‐1 sec‐1.

Photolysis studies of ubiquinone in ethanol and isopropanol and addition of ethanol to ubiquinone in cyclohexane show that little ubisemiquinone is formed by reaction of the triplet with alcohols. Electron spin resonance studies support this conclusion, and also show that some ubisemiquinone is however formed on photolysis of solutions of ubiquinone in methylcyclohexane.

Energy transfer experiments in the presence of various triplet energy donors and acceptors suggest that the triplet energy of ubiquinone lies between 176 and 123 W mole‐1, and that the triplet extinction coefficient at 440 nrn is 19,000 mole‐1 cm‐1 in cyclohexane and 13,000 mole‐1 cm‐1 in benzene (at 430 nm).

The singlet to triplet crossover efficiency for ubiquinone in cyclohexane was estimated to be 0.04. The low triplet energy level, crossover efficiency and abnormal type of reaction with alcohols are reflections of the profound influence of the isoprenoid chain upon excited states of this quinone.
PHOTOCHEMIE ANOMALER NUCLEINSÄUREBAUSTEINE‐VIII. ZUR PHOTOCHEMIE DES 6–AZACYTOSINS UND 6–AZACYTIDINS
Authors: KITTLER L.
Published: January 2008

Abstract— The photochemical behavior of 6–azacytosine and 6–azacytidine has been investigated by spectrophotometric, polarographic, and chromatographic methods. Both compounds form photohydration products, similar to cytosine and cytidine, but their photosensitivity is about ten fold higher. The greatest stability against u.v. light was found in strong acid and alkaline medium, indicating that under these conditions the electronic density at the reaction center is decreased.

For estimation of the photochemically active excited state triplet‐triplet‐transfer, experiments and measurements in the presence of paramagnetic metal ions were done. The results show that the photohydration reaction involves the first excited singlet state and the corresponding triplet state probably as well.

The photoproducts of both substances can be reactivated by heat. This reaction in acidic medium is strongly overlapped by a deamination reaction which yields 6–azauracil as a final product. In alkaline solution the ring system of the photohydration product is disrupted in the dark. The kinetic parameters of the heat‐reversible reaction of 6–azacytosine and 6–azacytidine are completely identical. This is in contrast to the published results with cytosine and cytidine where the back reaction is lowered for the latter. The differences in the behavior of the normal bases and their azaanalogues can be explained by means of an intramolecular hydrogen bond stabilization of the cytidine photoproduct. An analogous stabilization effect in the case of the 6–azacytidine photoproduct seems to be improbable for sterical reasons.
SENSIBILISIERTE PHOTOOXYDATION DURCH METHYLENBLAU THIOPYRONIN UND PYRONIN‐III. MITTEILUNG: ÜBER DEN MECHANISMUS DER PHOTOSENSIBILISIERTEN OXYDATION DES GUANOSINS DURCH THIOPYRONIN
Authors: GOLLMICK F. A. , BERG H.
Published: January 2008

Abstract— The thiopyronin‐sensitized photooxidation of guanosine was investigated, using flash photolysis techniques. The reaction kinetics of three short‐lived intermediates (the triplet state, the reduced radical, and the oxidized radical) were followed by spectroscopy. The influence of guanosine concentration on the reaction rate shows that only the oxidized radical (reaction 7) of thiopyronin is affected by guanosine. This suggests that the primary step in the photodynamic destruction of DNA is the oxidation of guanosine by the oxidized radical of thiopyronin (reaction 9). This mechanism is discussed in terms of the redox potentials of the donor and the acceptor for three different cases: (1) where the oxidation potential of the donor is more negative than that of the triplet state, the acceptor being the triplet state (FT); (2) where the oxidation potential of the donor is between the potentials of the triplet state and the oxidized radical, the acceptor being the oxidized radical (Fox); and (3) where the oxidation potential of the donor is more positive than the reduction potential of both the triplet state and the oxidized radical; in this case no electron exchange takes place. The thiopyronin‐guanosine system is an example of the second case.
THE PHOTOCHEMICAL REACTIONS OF 1,3–DIMETHYLURACIL WITH 1–AMINOPROPANE AND POLY‐l‐LYSINE*
Authors: GORELIC LESTER S. , LISAGOR PHILIP , YANG N. C.
Published: January 2008

Abstract— Irradiation of 1,3–dimethyluracil (DMU) in 1–aminopropane (AP) with u.v. light resulted in the formation of reduced and dimeric forms of DMU and adducts between DMU and AP. The formation of these compounds may be rationalized from the activation of either DMU or AP. Irradiation of DMU and poly‐l‐lysine in water with u.v. light resulted in the extensive binding of DMU to poly‐l‐lysine. The pyrimidine is probably attached to the ε‐carbon of the polypeptide at the 6–position. The biological implications of these studies are discussed.
MECHANISM OF THE REACTION BETWEEN LUMINOL AND MOLECULAR OXYGEN
Authors: BECK MI. T. , JOÓ F.
Published: January 2008

Abstract— The oxidation of luminol by molecular oxygen in dimethylsulfoxide was studied by following the intensity of emitted light. The results indicate that the reaction takes place through reversible formation of an oxygen‐containing intermediate. The stability constant of this compound has been determined in IDMSO: ethanol (4:1) mixed solvent. The effects of different parameters were investigated and a quantitative relationship established between the intensity of emitted light and the concentrations of the reactants.

New methods for determining (oxygen concentrations in gases and for demonstrating cold light emission are suggested.
PHOTODICHROISM OF RHODOPSIN SOLUTIONS AT ‐196°C
Authors: STRACKEE L.
Published: January 2008

Abstract— The photodichroism of a system of randomly oriented, bleachable pigment molecules, rigidly fixed in an inert transparent matrix was investigated theoretically. A formula was derived for the photochemical equilibrium reaction between three pigments, N1⇆N2⇆N3 in the case that the absorption ellipsoids of the pigments are rotationally symmetric and their symmetry axes coincide. The formula was applied to the dichroism induced by plane polarized light of different wavelengths in an aqueous rhodopsin‐glycerol mixture at –196°C. It was found that the absorption ellipsoids of this visual pigment, its analogue, isorhodopsin, and its first bleaching product, prelumirhodopsin, are elongated with an apparent axial ratio of about 5. It was concluded that the light absorbing properties of these pigments cannot be described by a single transition moment vector (linear absorber). The absolute value of the quantum efficiency of the conversion of rhodopsin to prelumirhodopsin was shown to be approximately equal to the quantum efficiency of bleaching rhodopsin at room temperature. Some evidence was obtained that indicates that the relative quantum efficiencies of the rhodopsin system at – 196°C may be wavelength dependent.
PHOTOCHEMICAL OXIDATIONS — VI. THE NATURE OF THE DONOR SITE IN THE OXYGEN‐HYDROCARBON CONTACT CHARGE‐TRANSFER COMPLEX
Authors: STENBERG V. I. , SNEERINGER P. V. , NIU C. , KULEVSKY N.
Published: January 2008

Abstract— Two sets of experiments, designed to determine whether the C—C or C—H bonds of hydrocarbons act as the donor site in the contact charge‐transfer complex between oxygen and hydrocarbons, were performed. It was found that the rates of oxygen uptake during the photooxidation increase with decreasing ‘s character’ of the C—H bond. Also, the rates of product accumulation during the induction period were shown to increase with basicity of the C—H bond, i.e., tertiary C—H > secondary C—H > primary C—H. The conclusion from these data is that the C—H bond is the donor site.
GROUND AND LOWEST EXCITED TRIPLET STATE DISSOCIATION CONSTANTS OF THE 5‐, 6‐ AND 7‐MONONITRO‐8‐QUINOLINOLS. SPECTROSCOPIC EVIDENCE FOR INTRAMOLECULAR HYDROGEN BONDING IN THE LOWEST TRIPLET STATE OF 7‐NITRO‐8‐QUINOLINOL*
Authors: AARON J. J. , WINEFORDNER J. D. , SCHULMAN S. G. , GERSHON H.
Published: January 2008

Abstract— The dissociation constants of 5‐nitro‐8‐quinoIinol, 6‐nitro‐8‐quinolinol and 7‐nitro‐8‐quinolinol have been determined for the ground states of the molecules by potentio‐metric titration, and for the lowest triplet states from the shifts of the O—O bands of phosphorescence occurring upon dissociation. The ground‐state dissociation constants of the phenolic groups are found to be typical of ortho, meta, and para nitro phenols. The phosphorescences of all prototropic species derived from the 6‐isomer appear to be anomalous and their origin is unknown. The anomalously low acidity of the neutral species of the 7‐isomer in its triplet state, relative to that of the neutral species of the 5‐isomer in its triplet state, is attributed to intramolecular hydrogen bonding in the lowest triplet sfate of the 7‐isorner, between the phenolic proton and the 7‐nitro group. The magnitudes of the two triplet‐state disSociation constants of both the 5 and 7 isomers suggest that the predominant uncharged species in fluid solutions containing the triplet‐state molecules are the excited zwitterions.
KINETIC PROPERTIES OF THE TRIPLET STATES OF METHYLENE BLUE AND OTHER PHOTOSENSITIZING DYES
Authors: NILSSON R. , MERKEL P. B. , KEARNS D. R.
Published: January 2008

Abstract— The long‐lived (> 1 μsec) transients formed in the flash excitation of the representative photosensitizers methylene blue, eosin Y and pyrene have been investigated and various criteria have been used to distinguish between triplet state intermediates and chemical intermediates. Previous assignments of the triplet transients of methylene blue appeared less secure in view of the photochemical reactivity of this dye and its lack of phosphorescence. Earlier assignments of monomeric and dimeric triplet transients of methylene blue are substantiated, however, by the observations that the rate constant for quenching by oxygen is approximately 1/9th diffusion controlled and the formation rates are commensurate with singlet decay rates and by the observation of triplet‐triplet annihilation. Additional evidence in support of monomer triplet assignments for methylene blue and eosin Y is provided by the effect of heavy atom quenchers Cs+, Hg2+ and T1+ on decay rates. Due to chemical reactivity, quenching by I−appears less suitable as a diagnostic test for triplet state intermediates. The effect of N3−, which is known to quench singlet oxygen molecules and to alter the course of photosensitized oxidations, on the triplet decay of methylene blue, eosin Y and pyrene is also investigated.
A NEW APPROACH TO SPECTRAL RECORDING APPLIED TO THE STUDY OF LOW‐TEMPERATURE THERMOLUMINESCENCE
Authors: HOLM CHR. , KOLBERG S. , SEIM T. O. , PRYDZ S.
Published: January 2008

Abstract— A circularly wedged optical interference filter covering about one octave of frequencies, in our particular case corresponding to the wavelength range of 390–740 nm, is used as a broad‐band, high‐transmission monochromator. The filter wheel is mounted in front of a photomultiplier, and the current signal from the latter is fed to the Y axis of an oscilloscope. Coupling of the filter rotation to the triggering of the oscilloscope rendered the emission spectrum under investigation permanently available as a trace on the screen of the oscilloscope. Single scan photography of the scope trace, using a Polaroid camera, is one instance where the method proves to be well suited to the study of rapidly varying sources or of systems showing a rapidly changing spectral transmittance. Applications of the instrument's particular combination of qualities are demonstrated, using tyrosine, which is thermoluminescent upon low temperature irradiation with X rays, as a test system.
PHOTOSENSITIZATION AND COMPLEX FORMATION IN A MODEL SYSTEM: 2‐AMINO‐PYRIMIDINE IN ETHANOL
Authors: NEUBACHER H. , LENCI F.
Published: January 2008

Abstract— In the presence of 2‐amino‐pyrimidine, ethanol free radicals are produced in rigid glasses at 77°K by light not absorbed by the alcohol. ESR measurements indicate that a photo‐sensitization occurs following a step‐wise biphotonic process via triplet‐triplet absorption. Absorption, fluorescence and phosphorescence measurements show that the photosensitization quenching effect at high sensitizer concentration is correlated with formation of a molecular complex, probably generated from an excited state of 2‐amino‐pyrimidine.
FLASH PHOTOLYSIS OF RIBONUCLEASE A
Authors: VOLKERT W. A. , GROSSWEINER L. I.
Published: January 2008

Abstract— Flash photolysis spectra show that ultraviolet irradiation of RNase (Λ > 250 nm) at pH 11.5 generates the hydrated electron and a long‐lived transient with absorption maxima at 390 nm and 410 nm, attributed to the phenoxyl type radical from tyrosyl residues. Comparison of the initial yields with flash photolysis spectra obtained from aqueous tyrosine and mixtures of the chromophoric amino acids indicates that 3–4 tyrosyl residues are photoionized in the primary act. This process is almost completely quenched at pH 1–9, even though the p‐alanylphenoxyl radical is obtained with tyrosine over this pH range and the accompanying electron is observed at pH 7. The negative result is not altered by denaturation of RNase with 8M urea or heating to 70°C, suggesting that a primary chain interaction is responsible for the suppression of tyrosyl residue photolysis. This mechanism is supported by flash photolysis spectra of small peptides, showing that the initial radical yield from tyrosylglycylglycine is strongly quenched compared to tyrosine when the phenolic group is protonated. Comparion of this work with published results on fluorescence and inactivation quantum yields indicates that photochemical electron ejection from RNase in alkaline solutions takes place in the dissociable residues and does not contribute to loss of enzymic activity.
ACTION DE LA TEMPERATURE SUR LA DUREE DE VIE DE FLUORESCENCE ET LE RENDEMENT DE FLUORESCENCE DE LA C‐PHYCOCYANINE EN SOLUTION
Authors: VERNOTTE C. , MOYA I.
Published: January 2008

Abstract— The influence of temperature on the fluorescence yield and lifetime (measured by a phase fluorimeter) of C‐hycocyanin in various forms of polymerization in solution, was studied over the temperature range 0–75°C. The temperature dependence of φ and φ below 50°C may be ascribed to an effect on internal conversion, with activation energy of 0.45. eV. Above 50°C, a large enhancement of is observed which may be due to the appearance of direct fluorescence from the sensitizer chromophores, the transfer efficiency between the two different chromo‐phores present in each monomer being decreased by protein denaturation. At room temperature, there is almost no difference between the lifetimes of the different polymers, whereas large differences between their fluorescence yields are observed. Therefore, a static quenching of the fluorescence of the chromophores by the solvent molecules may occur.
ENERGY TRANSFER BETWEEN PHOTOSYNTHETIC UNITS ANALYZED BY FLASH OXYGEN YIELD vs. FLASH INTENSITY*
Authors: WANG RICHARD T. , MYERS JACK
Published: January 2008

Abstract— Relative yield of O2 (Y) was measured in Chlorella pyrenoidosa in response to varied intensity (l) of single 10μsec flashes on a constant low background of 710 nm light. Analysis is based on the proposition that the photochemical event leading to O2 evolution occurs at a reaction center or trap which requires a time much longer than the flash for regeneration by dark reactions. Hence O2, flash yield measures the number of traps ‘killed’ and allows treatment in terms of target theory. Data for Y vs. l were analyzed by computer fitting to four models. The first three models supposed that each unit (aggregate of light‐harvesting pigment molecules) contains one, two, and three traps, respectively, and allows no transfer of excitation energy out of the unit. The last model supposed only one trap per unit and a probability of transfer out of a unit with closed trap. Among the first three models, the data best fit the one with two traps per unit. A slightly better fit for two traps per unit was obtained by introducing a trapping efficiency less than unity. An equally good fit was also obtained with the model of the Joliots with a probability of 0.3 that excitation energy in a unit with closed trap is transferred to another unit. Uncertainties in analysis arose from the necessity of treating maximum flash yield as an estimated parameter and by the possible inhomogeneity in units and traps.
THE FATE OF PYRIMIDINE DIMERS IN ULTRAVIOLET‐IRRADIATED CHLAMYDOMONAS
Authors: SWINTON DAVID C. , HANAWALT PHILIP C.
Published: January 2008

Abstract— We have developed a chromatographic technique for the separation of 32P‐labeled pyrimidine nucleotide dimers of the form PypPy from 32P‐phosphate in enzymatic hydroly sates of ultraviolet‐irradiated DNA. Application of this technique to 32P‐labeled Chlamydomonas reinhardii shows that ultraviolet irradiation of this organism induces pyrimidine dimers in both nuclear and chloroplast DNA. We have found no evidence that these dimers are excised from either DNA species after several hours incubation under non‐photoreactivating conditions. A function has been derived to permit the pyrimidine‐dimer content determined from radioactive‐thymine‐labeled cells to be conveniently compared to that obtained from 32P‐phosphate‐labeled cells.
ULTRAVIOLET‐LIGHT‐INDUCED CONFORMATIONAL CHANGES IN DNA
Authors: LANG H. , LUCK G.
Published: January 2008

Abstract— Irradiation of DNA at 254 nm produces alterations in the secondary structure leading to changes in the circular‐dichroism (CD) spectrum. A new Cotton effect around 320 nm, and a change in the rotatory strength of the CD maximum at 275 nm, was observed. Whereas the new negative maximum at 320 nm generally increases with increasing radiation dose, the maximum at 275 nm is enhanced at lower UV doses but is diminished at higher doses. Thus we suppose that there are two different DNA conformations, the transition between which occurs at 15times104 ergs/mm2. Below this dose, the DNA is in a partially closed and twisted state, but above it the DNA has a C‐like conformation.

It is possible that those regions of the DNA containing altered conformation may act as recognition sites for repair.

UV‐Bestrahlung von DNS mit 254 nm UV‐Licht führt zu Strukturänder‐ungen in der DNS, die sich in einem veränderten CD‐Spektrum manifestieren. So kann erstens ein neuer Cotton‐Effekt bei 320 nm und zweitens eine Veränderung der Rotatorstärke des positiven Maximums bei 275 beobachtet werden. Während der neue Übergang bei 320 nm sukzessive mit steigender Bestrahlungsdosis zunimmt, wird das Maximum bei 275 nm erst vergrößert um bei höheren UV‐Dosen wieder abzufallen. Es wird angenommen, daß die DNS somit in zwei verschiedenen Konformationen vorliegt, deren Übergang bei einer Bestrahlungsdosis von etwa 15times104 erg/mm2 erfolgt. Während bei niedrigen UV‐Dosen die DNS in einem teilweise ringförmigen, verdrillten Zustand vorliegen soll, müßte bei höheren Bestrahlungsdosen vorwiegend ein C‐konformationsähnlicher Zustand existieren. Es wäre denkbar, daß die konformativ veränderten Bereiche im DNS‐Molekül als Erkennungsorte für die Reparaturenzyme fungieren und somit die Reparatur initiieren.
ULTRAVIOLET IRRADIATION OF POTATO VIRUS X, ITS RNA, AND A HYBRID VIRUS PARTICLE: PHOTOREACTIVATION, KINETIC ISOTOPE EFFECTS, AND QUANTUM YIELD OF INACTIVATION*
Authors: McCleary Leila O. , Gordon Milton P.
Published: January 2008

Abstract— Studies have been made of the inactivation of potato virus X (PVX), free PVX‐RNA, and a phenotypically mixed virus particle composed of PVX‐RNA and tobacco mosiac virus (U‐1 strain) protein (PVXRNA: TMVPRO) by ultraviolet radiation of 254, 280 and 302 nm wavelengths. Rate constants and quantum yields of inactivation have been determined under conditions of photoreactivation and non‐photoreactivation in H2O and D2O. The ratios of the rate constants in H2O to those in D2O obtained for PVX‐RNA were greater than unity at the above three wavelengths, as was the case for PVX at 254 and 302 nm. The ratios of the rate constants were, within experimental error, equal to unity for PVXRNA:TMVPRO at all three wavelengths and for PVX at 280 nm. It is concluded that, in contrast to the situation observed with TMV and PVXRNA:TMVPRO, the behavior of the intact PVX viron upon irradiation closely approximates the behavior of free RNA in solution, on the basis of quantum yields of inactivation, photoreactivated sector, and the ratio of kinetic isotope effects in H2O and D2O.
A COMPARATIVE STUDY OF PHOTODYNAMIC OXIDATION AND RADIOFREQUENCY‐DISCHARGE‐GENERATED 1O2 OXIDATION OF GUANOSINE
Authors: Kornhauser A. , Krinsky N. I. , Huang P.‐K. C. , Clagett D. C.
Published: January 2008

Abstract— Guanosine‐2‐14C and guanosine‐8‐14C were subjected, under similar environmental conditions, to oxidation either by radiofrequency‐discharge‐generated singlet oxygen or by a methylene‐blue‐sensitized photodynamic reaction. The reaction products in both cases were compared chromatographically. The product distributions were not identical, indicating differing modes of oxidation in these two systems. It is suggested that both Type I and Type II oxidation mechanisms are operative in the photodynamic system, whereas only Type II‐like reactions occur in the radio‐frequency‐discharge system.
LOWEST EXCITED TRIPLET‐STATE DISSOCIATION CONSTANTS OF PURINES IN AQUEOUS SOLUTION. SUBSTITUENT EFFECTS*
Authors: Aaron J. J. , Winefordner J. D.
Published: January 2008

Abstract— Lowest triplet‐state dissociation constants of purine and eight of its derivatives have been determined from the shifts of the 0–0 bands of phosphorescence occurring upon protonation and deprotonation (dissociation), in rigid aqueous solutions at 77°K. Triplet‐state dissociation constants (pKaτ) are found to be significantly different from the corresponding ground–state pKa‐values, differences ranging from 0.6 to 3.8 pK units. In the equilibria between neutral and anion species, purines are more acidic in the triplet state, due to derealization of the negative charge of the triplet‐state anion. In the equilibria between cation and neutral species, the basicity of purine, amino, methyl, and benzyl‐amino derivatives is increased in the triplet state compared to the ground state. The anomalously low basicity of the halogeno‐ and methylmercapto‐derivatives in their triplet state is attributed to the increased interactions of dir orbitals of halogens and sulfur atoms with π orbitals in the triplet state. In general, substituent effects on the pKa of purines appear to be parallel in the ground and excited triplet states.
PHOTOREGULATION OF α‐CHYMOTRYPSIN ACTIVITY BY ISOMERIZABLE INHIBITORS. STUDY OF THE ACTION MECHANISM*
Authors: Fournier M. , Bourdon J.
Published: January 2008

Abstract— The N‐p‐phenylazophenyl‐N‐phenylcarbamyl chloride (PAPC) in its cis form is five times more active as inhibitor of α‐chymotrypsin than in the trans form. In the present work, derivatives of PAPC have been synthesized. Each of these new compounds is photoisomerizable and is an inhibitor (in the cis and in the trans form) of α‐chymotrypsin. The cis isomer is always more active than the trans. The m‐methyl derivative is 17.5 times more active in the cis form than in the trans, whereas, for the para‐substituted compound, this ratio is only 3.5.

Several hypotheses can explain this difference of activity between the cis and trans isomers: (1) steric hindrance towards the trans isomer, (2) lower affinity of the enzyme for the trans isomer, (3) higher reactivity of the complex formed between the enzyme and the cis form of the inhibitor. These hypotheses are discussed.
PRIMARY PHOTOCHEMICAL PRODUCTS OF DITHIOGLYCOLIC ACID IN AQUEOUS SOLUTION
Authors: Feitelson Jehuda , Shafferman Avigdor , Stein Gabriel
Published: January 2008

Abstract— The photochemistry of dithioglycolic acid at 254 nm was investigated in deaerated aqueous solutions in the pH range 1.4–7.3. Initial yields of the primary photochemical products H2S,–SH and aldehyde‐(probably glyoxylic acid) were determined. The complex pH dependence of these simultaneously formed first stable products is interpreted in terms of the ground‐state ionic equilibria, and in addition pH‐dependent processes occurring in the excited state and labile intermediate sequence.

It is suggested that the photochemical mechanism involves two parallel pathways: one a hydrolytic splitting of S ‐ S leading to H2S formation (unaffected by the presence of O2 or isopropanol), the other a free radical mechanism via C–S breakage, which is affected by the presence of O2 or isopropanol.
PHYTOCHROME INTERMEDIATES IN VIVO–II. CHARACTERISATION OF INTERMEDIATES BY DIFFERENCE SPECTROPHOTOMETRY
Authors: Spruit C. J. P. , Kendrick R. E.
Published: January 2008

Abstract— In epicotyl tissue of Pisum, irradiation of Pr at – 196°C forms a stable product P698, whereas Pfr forms a stable product P650. On warming P698, dark transformation to Pr predominates. On warming P650 to – 70°C an intermediate P690 is formed which bleaches on further warming to –10°C. When tissue is cooled to –196°C during actinic irradiation, difference spectra for subsequent warming to –10°C indicate that Pr, Pfr and an intermediate P710 are formed from weakly absorbing intermediates. Complete photoconversion of Pr to Pfr is not possible at temperatures below –5°C. As the temperature is reduced, the amount of Pfr produced from Pr decreases, while P710 increases. P710 can be photoconverted at –20°C and above, ultimately forming Pr, but in contrast to Pfr it is not photoconvertible at –196°C.
FREE RADICALS INDUCED BY PHOTOLYSIS OF FROZEN SOLUTIONS OF THYMIDINE‐5'‐MONOPHOSPHATE: AN ESR STUDY
Authors: Lion Yves , Vorst Albert van de
Published: January 2008

Abstract— The photolysis (Δ < 220 nm) of thymidine‐5'‐monophosphate was studied by electron‐spin resonance (ESR) in acidic and alkaline phases. In both cases, the H–addition radical at the C6 position is detected at 77°K. At 225°K, a triplet 1:2:1 is observed, which suggests a H abstraction radical from the CH3 group. When oxygen is present during irradiation, a peroxide–type radical is observed, which results partly from a reaction like R + O2→ ROO and partly from an energy transfer from thymidine‐5′‐monophosphate to oxygen, probably in the 1π0 state.
SENSITIZED PHOTODEGRADATION OF CELLULOSE AND CELLULOSIC WASTES
Authors: Eskins K. , Bucher B. L. , Sloneker J. H.
Published: January 2008

Abstract— The photodegradation of cellulose and cellulose–containing waste sensitized by a variety of dyes was measured by means of viscosity, tensile strength, and scanning electron microscopy. Anthraquinone‐2‐sulfonate and proflavin dihydrochloride were both more effective than either rose bengal or methylene blue for degradation. Samples degraded by these dyes were similar in appearance to enzyme‐degraded ones, but were less susceptible to further degradative action by enzymes.
INHIBITION OF ETHYL BENZENE OXIDATION BY STABLE IMINOXY RADICALS, STUDIED BY CHEMILUMINESCENCE
Authors: Matisová‐Rychlá L. , Karpukhin O. N. , Pochalok T. O.
Published: January 2008

Abstract— The inhibition by stable radicals having the structure (X‐O)2NO of the initiated oxidation of ethyl benzene was studied. According to a formal kinetic scheme, verified by both theoretical computer calculations and an experimental chemiluminescence method, the rate constants of the interaction of peroxyradicals with iminoxy radicals were estimated at 60°C to be: 2.4 times 105 litres mol‐1 s‐1 for X = OCH3 and 3.4 times 105 litres mol‐1 s‐1 for X = OCH2CH3.
NEGATIVE PHOTO‐PHOBOTACTIC REACTIONS IN PHORMIDIUM UNCINATUM*
Authors: Haeder Donat P. , Nultsch Wilhelm
Published: January 2008

Abstract— The photo‐phobotaxis of Phormidium uncinatum has been studied by means of a double‐beam arrangement for simultaneous irradiation with two wavelengths in trap and background. Under these conditions the photo‐phobotactic reaction depends on whether one or both photosynthetic photosystems are excited by the two wavelengths. If far red or infrared is used as trap light, negative reactions occur under ail background wavelengths investigated. Furthermore, negative reactions are not as sensitive to 3‐(3,4‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU) as positive ones. These results suggest that negative photo‐phobotactic reactions might be caused by light absorbed mainly by photosystem I, while both photosystems I and II can participate in mediating positive phobotactic reactions. In the range in which the absorption spectra of both photosystems overlap, the type of response depends on the photosystem with the stronger absorption.
CONSTANCY OF THE UV SENSITIVITY OF E. COLI DURING THE CELL CYCLE*
Authors: Kubitschek Herbert E. , Finney Ann C. , Krisch Robert E.
Published: January 2008

Abstract— Cells from slowly growing glucose‐limited chemostat cultures of two different strains of Escherichia coli were separated by size on sucrose gradients, and 254‐nm ultraviolet (UV) survival curves were obtained for samples of the different cell sizes. With the repair‐deficient strain Bs‐1 there was no observable change in survival curve during the cell cycle. With the repair‐proficient strain 15 THU, there was no observable change in the final slope, but y‐axis intercepts increased slightly for the older cells. Our results provide further evidence for the approximate independence of UV sensitivity, k, upon cell age within the division cycle and upon the presence or absence of DNA synthesis. They are consistent with a model in which UV lesions in newly replicated strands of DNA do not contribute to lethality.
PROMPT AND DELAYED FLUORESCENCE OF SOME DNA ADSORBATES
Authors: Parker C. A. , Joyce Thelma A.
Published: January 2008

Abstract— The absorption and prompt fluorescence spectra of twelve cationic compounds in the free and bound states were surveyed, and four compounds selected for detailed study, viz: proflavine, benzoflavine, acridine orange and thioflavine T. The absorption spectra, prompt fluorescence spectra and delayed fluorescence and phosphorescence spectra of these four compounds in fluid solutions in the free and bound states were measured. The shifts in the promp fluorescence bands of the diaminoacridines on adsorption were found to differ significantly from those of the other compounds, and the behaviour of acridine orange was found to be different from that of the other two diaminoacridines. All three diaminoacridines gave E‐type delayed fluorescence in the free and bound states. The ordered structure of the strongly binding adsorption sites in native DNA is associated with a higher intensity of delayed fluorescence than is observed from the diaminoacridines in the free state or adsorbed on denatured DNA. Quenching experiments with proflavine indicated that, in the weakly binding sites, its triplet is easily quenched by unadsorbed quenchers, but in the strongly binding sites its triplet is quenched only with great difficulty.
ULTRAVIOLET AND γ‐RAY‐INDUCED REACTIONS OF NUCLEIC ACID CONSTITUENTS. REACTIONS OF PURINES WITH AMINES
Authors: Salomon J. , Elad D.
Published: January 2008

Abstract— Photochemical and γ‐ray‐induced reactions of purines with amines are described. These lead to the appropriate 8‐substituted purines. The photoproducts were obtained in yields of up to 100% by the use of a variety of photosensitizers, including peroxides. A free radical mechanism is proposed for these reactions.

Such reactions may be relevant to the problem of the nature of DNA‐protein cross‐links induced by ultraviolet radiation.
PHOTODYNAMIC INACTIVATION OF SARCOPLASMIC RETICULUM VESICLE MEMBRANES BY XANTHENE DYES
Authors: Kondo Mitsuo , Kasai Michiki
Published: January 2008

Abstract— Photosensitized oxidation of sarcoplasmic reticulum (SR) vesicle membranes by a series of xanthene dyes was investigated. With increasing dye concentration and illumination time, the calcium ion uptake, ATPase activity and UV fluorescence intensity of SR decreased, and the absorbance at 241 nm increased. In xanthene dyes, the order of inactivation of the calcium uptake and ATPase activity of SR was in accord with decreasing order, of fluorescence intensity and increasing order of absorbance at 241 nm. Some regular relationships exist between the molecular structures of xanthene dyes and the photodynamic inactivation of SR membranes.
SELECTIVE PHOTOSENSITIZED OXIDATION OF THE METHIONYL RESIDUES IN ELASTASE
Authors: Jori Giulio , Gennari Giorgio , Folin Marcella
Published: January 2008

In recent years, significant advances have clarified the mechanism of photosensitized oxidations (see, for example, Foote, 1968), especially as regards the nature of the reactive oxidizing agents. This fact stimulated the development of reaction systems which allow selective photooxidation of specific components of biological macromolecules (Spikes and Livingston, 1969; Spikes and MacKnight, 1970). In the field of proteins, the selective conversion of the methionyl residues to the sulfoxide can be achieved by irradiation with visible light in the presence of hematoporphyrin at neutral or acid pH (Jori et al., 1969).