bluuebunny/crossref_metadata_2025_split huggingface dataset:
CHEMICAL CHANGES LEADING TO CHEMILUMINESCENCE OF LUCIGENINE (DIMETHYLBIACRIDYLIUM NITRATE) AND OF SOME PHTHALAZINEDIONE DERIVATIVES
Authors: Totter John R. , Philbrook George E. 
Published: January 2008

Abstract— Measurements of the redox potential of the chemiluminescent compound 10,10′ dimethyl‐9,9′ biacridylium nitrate (‐0.093 V) show that it is thermodynamically possible to reduce it with hydrogen peroxide or with ammonium hydroxide in alkaline solutions at equilibrium concentrations sufficiently high to account for the observed chemiluminescence. Reduction of the compound with ammonium hydroxide takes place much more slowly than the corresponding reaction with hydrogen peroxide so that when both redox couples (O2/H2O2 and N2H4/NH4OH) are present the hydrogen peroxide couple predominates if oxygen is supplied. It was shown that interference with the oxygen supply or its partial removal with nitrogen brings about an increase in chemiluminescence intensity in NH4OH while increasing the concentration of oxygen diminished the intensity.5‐amino 2,3 phthalazine 1,4 dione (luminol) also appears to undergo a reduction following a two step oxidation. This is shown by the fact that when oxygen was supplied the chemiluminescence intensity was found to be directly proportional to the OH‐ concentration while a typical titration curve with pK 11.7 is exhibited by the intensity when the oxygen supply is limited in mixtures of luminol and peroxydisulfate. The peroxide presumably arises in the first oxidation step. Amino peroxyphthalic anhydride is suggested as an intermediate which is reduced to the aminophthalate ion, the presumed emitter in the chemiluminescence.
THE ROLE OF PEROXIDES IN THE INHIBITION OF DNA SYNTHESIS IN CELLS FOLLOWING IRRIDIATION WITH A U.V. MICROBEAM
Authors: Dendy P.P. , Smith C.L. , Aebi H. E. 
Published: January 2008

Abstract Previous work had shown that the rate of DNA syntheses in mammalian cells could be reduced when a microbeam of ultraviolet light was directed into the medium surrounding the cells. The present work was designed to gather informtion on the mechanism of this effect.Results show that catalase does protect the cellualar DNA synthesis under the following conditions.(1) The microbeam must be directed into the surrounding medium—there is no protection if it strikes any part of the cell.(2) The catalase must have been in contact with the cells for at least 4 hr before irradiation.(3) At high closes of radiation the protection is only partial.The catalase was labelled with fluorescent dye to demonstrate that it was able to penetrate the cell cytoplasm but not nucleus. Morphological studies on cell exposed to medium containing hydrogen pereoxide showed that protection was provided by intracellular and not extracellular catalasse and supported the idea that the toxic product produced by ultraviolet radiation of the medium was ultimately a peroxide.
ÉTUDE EN SPECTROSCOPIE PAR ÉCLAIR DES COLORANTS THIAZINIQUES EN SOLUTION AQUEUSE
Authors: Faure Jean , Bonneau Roland , Joussot‐Dubien Jacques 
Published: January 2008

Abstract— pK values of ionisation equilibrium of thiazines dyes in their triplet state have been measured in aqueous solutions by spectroscopy. The triplet‐triplet absorption bands, in the red part of the spectrum, are given for thionine, azurs and methylene blue. It is shown that, in the pH range 4–9, the equilibria investigated correspond to a second protonation of thiazines dyes that occurs in the triplet state: 3TH++ H+→3TH22+designating by 3TH+ the thiazine cation similar to the species stable in neutral aqueous solutions.
ULTRAVIOLET PHOTOINACTIVATION STUDIES ON HYBRID VIRUSES OBTAINED BY THE CROSS‐RECONSTITUTION OF THE PROTEIN AND RNA COMPONENTS OF U(1) AND U(2) STRAINS OF TMV*
Authors: Streeter David G. , Gordon Milton P. 
Published: January 2008

ABSTRACTThe sensitivities of U(1) and U(2) TMV strains to inactivation by ultraviolet light at 253.7 nm were compared with those of hybrid viruses obtained by reconstituting the protein of either native strain with the RNA of the other. In each case, the hybrid virus was found to be virtually identical in sensitivity to the native strain which supplied the protein coat, indicating that the relative sensitivities of the two native strains to ultraviolet light are solely a function of their respective protein coats. Amino acid analysis of the U (2) protein reveals about thirteen or fourteen amino acid replacements compared with the U (1) strain, which is in agreement with earlier studies indicating that there are considerable differences in the protein subunits of the two proteins. Some of the ways in which the observed differences in proteins of the two strains may determine their respective ultraviolet sensitivities are discussed.
UN NOUVEAU MODELE DES CENTRES PHOTOCHIMIQUES DU SYSTEME II*
Authors: Joliot P. , Barbieri G. , Chabaud R. 
Published: January 2008

Abstract— The amount of oxygen evolved by Chlorella cells or by isolated chloroplasts has been measured after illumination by short saturating flashes. In all conditions, the amount of oxygen evolved by one flash is proportional to the fraction of the photochemical centers susceptible to produce oxygen.If dark adapted algae or chloroplasts are illuminated by a sene of flashes, no oxygen is produced by the first flash. This phenomenon is related to the activation process.If yn is the amount of oxygen evolved by the nth flash of the sequence, it appears that the sene yn shows large oscillations with a period 4. These oscillations are completely damped after 4–6 periods and the amount of oxygen evolved by a flash reaches a stationary value. For any value of n. the quantities yn and yn+2 are linked by a recurrent relation which is the same for Chlorella cells and spinach chloroplasts. No relation can be found between the terms yn and y(n+1).The mathematical properties of the series yn can be understood if one admits that a two memory process is involved in the photochemical reaction.The results have been interpreted in terms of a new model of the System II photochemical centers. The main characteristics of this model are:(1) Each photochemical center includes two electron donors (Z) and one electron acceptor (Q).(2) The formation of one atom of oxygen requires a two quantum process corresponding to the transfer of two electrons from the same electron donor (first memory).(3) The photochemical center acts as a switch which connects alternately each donor to the acceptor (second memory). The switch process occurs after each photoact with an efficiency of about 85 per cent.Other arguments in favor of this model are obtained from studies of the rate of oxygen production at the onset of a weak illumination.
OXIDATION‐REDUCTION REACTIONS OF P700 AND CYTOCHROME f IN FRACTION 1 PARTICLES PREPARED FROM SPINACH CHLOROPLASTS BY FRENCH PRESS TREATMENT
Authors: FORK DAVID C. , MURATA NORIO 
Published: January 2008

Abstract— –Fraction‐1 particles were prepared by passing spinach chloroplasts three times through the French pressure cell and centrifuging in a sucrose gradient.With the electron donor DAD (diaminodurol or 2,3,5,6‐tetramethyl‐p‐phenylenediamine) and ascorbate, a light‐induced difference spectrum revealed the oxidation of both cytochrome f and P700 upon illumination of these particles. The oxidation of cytochrome f was completed in less than 0.5 msec. P700 and cytochrome f thus seem to be tightly bound to each other in these particles. Addition of Triton X‐100 abolished the fast oxidation of cytochrome f but not that of P700.Artificial electron donors such as DAD, DCIP (2,6‐dichlorophenol indophenol), and PMS (N‐methylphenazonium methosulfate) were good electron donors for photoreaction 1 in these particles, while neither plastocyanin, Porphyra cytochrome 553, nor Euglena cytochrome‐552 reduced P700 efficiently. However, after treatment of fraction 1 particles with Triton X‐100 reduced DAD, DCIP and PMS were no longer efficient electron donors, while plastocyanin and the algal cytochromes were highly active in reducing P700. Mammalian cytochrome c was not a good electron donor either before or after Triton treatment.Measurements of the effectiveness of P700 reduction as a function of concentration in Triton‐treated particles showed plastocyanin to be about four times more active than Porphyra or Euglena cytochromes which in turn were about fourteen times more active than mammalian cytochrome c.Recent studies by Murata and Brown have shown that plastocyanin is not required for the reduction of NADP in these particles with DCIP and isoascorbate as electron donors. The present investigation and that of Murata and Brown indicate that disintegration of chloroplasts with the French pressure cell and centrifugation in a sucrose gradient is the best method to separate system‐1 particles having an electron‐transport system in almost the native state as in chloroplasts.
ESR STUDIES OF THE LOW TEMPERATURE IRRADIATION OF KERATIN AND ITS COMPONENT AMINO ACIDS
Authors: PAILTHORPE M. T. , NICHOLLS C. H. 
Published: January 2008

Abstract— The photoejection of electrons from the aromatic amino acids at 77°K by 290–340 nm radiation was found to involve both monophotonic and biphotonic processes. However, only monophotonic processes are involved when electrons are photoejected from cystine or cysteine. These electrons prefer to attach themselves to adjacent sulphur groups rather than the dielectric traps in the matrix, so that both anionic and cationic radicals are formed.In keratin at 77°K, the disulphide anion radicals are produced by both monophotonic and biphotonic mechanisms, indicating that the electrons captured by the disulphides are photo‐ejected from the aromatic amino acids. At room temperature the thiyl and aromatic radicals are produced only by monophotonic reactions.
PHOTOSENSITIZATION OF HUMAN DIPLOID CELL CULTURES BY INTRACELLULAR FLAVINS AND PROTECTION BY ANTIOXIDANTS
Authors: Pereira Olivia M. , Smith James R. , Packer Lester 
Published: January 2008

Abstract— The damaging effects of near ultraviolet and visible light on WI‐38 human diploid lung fibroblasts were investigated. WI‐38 cells in culture were killed by light doses ranging from 2 to 10 × 103 W/m2 h. There was an inverse correlation between culture age, i.e. population doubling level and photosensitivity. However, this effect could not be related to capacity for DNA synthesis and cell division.Flavins were clearly implicated as endogenous photosensitizers, and antioxidants such as d, l‐α‐tocopherol (vitamin E), BHT and ascorbic acid were found to afford the cells protection from light damage. Furthermore, products of lipid peroxidation could be detected in cell homogenates irradiated in the presence of ribofiavin.
PHOTOSYNTHESIS AS A RESOURCE FOR ENERGY AND MATERIALS*
Authors: Calvin Melvin 
Published: January 2008

Abstract— Photosynthesis, both natural and as a model process, is examined as a possible annually renewable resource for both material and energy. The conversion of carbohydrate from cane, beets and other sources through fermentation alcohol to hydrocarbon may again become economic in the light of improved fermentation technology. It may also be possible to produce material by direct fermentation of relatively labile carbohydrates in seaweed. Even the direct photosynthetic production of hydrocarbon from known sources (Hevea, etc.), or newly bred ones, seems possible in view of the large number of species and the new techniques of plant cell cloning which have already been successful on sugar cane.Finally, more distantly, synthetic systems constructed on the basis of our growing knowledge of the photosynthetic processes may produce fuel, fertilizer and power. Thus, from our current knowledge of the natural quantum conversion process in green plants we can envisage several photoelectron transfer processes. In a first one the excited sensitizer (chlorophyll) transfers its electron to an acceptor molecule such as an iron‐sulfur complex which, in turn, could either reduce a carbon compound or pass that electron into a hydrogen‐generating system leading to the evolution of molecular hydrogen. The remaining cation radical sensitizer would have to be neutralized through a chain of electron transfers which begins at another sensitized reaction (presumably by another kind of chlorophyll) through a quinone and other electron carriers. Finally, the last cation radical near the oxidation level of oxygen could be neutralized by electron transfer, ultimately from a water molecule (hydroxide or bicarbonate ion) involving a manganese catalyst.Some steps in this sequence of transfers have already been demonstrated in synthetic systems. However, the actual physical construction of such a complete system is a much more complex task.
RETARDATION OF ULTRAVIOLET LIGHT ACCELERATED CHLOROSIS BY VISIBLE LIGHT OR BY BENZYLADENINE IN NICOTIAN A GLUTINOSA LEAVES: CHANGES IN AMINO ACID CONTENT AND CHLOROPLAST ULTRASTRUCTURE*
Authors: Skokut Thomas A. , Wu J. H. , Daniel R. S. 
Published: January 2008

Abstract— Low doses (180–720 Jm‐2) of ultraviolet light (254 nm) are known to accelerate the chlorosis of detached leaves in darkness. The development of such chlorosis is prevented by a photoreactivation treatment. However, we found that delayed light exposure or benzyladenine treatments (which were not effective in photorepair of UV‐induced thymine dimers in cell DNA) were also effective in retarding the UV‐accelerated chlorosis.Small drops of benzyladenine solution placed on the UV irradiated leaf formed green islands which acted as strong sinks for the accumulation of free amino acids during dark incubation. To a lesser degree, non–irradiated green tissues surrounded by irradiated yellow leaf tissue also acted as sinks for amino acid accumulation.The accelerated chlorophyll loss in UV‐irradiated leaves was correlated with degradation of chloroplast ultrastructure. Visible light or benzyladenine retarded this chloroplast degradation. The accelerated senescence of UV irradiated leaf tissue, therefore, is ultrastructurally and physiologically similar to normal senescence of detached dark‐incubated leaves, but progresses at a faster rate.When the lower leaf surface was irradiated with high UV doses (3600–10,800 Jm‐2), the chloroplast ultrastructure of the spongy cells (except the envelope) was preserved for 3 days after dark incubation. However, the chloroplasts of the palisade cells were in a late stage of senescence. Since the spongy cells were dead (plasmalemma, tonoplast and chloroplast envelope disappeared), the maintenance of green color and ultrastructure of chloroplasts could have been due to inhibition of degrading enzymes normally associated with senescence.
BINDING OF GLYCOLATE OXIDASE TO PEROXISOMAL MEMBRANE AS AFFECTED BY LIGHT
Authors: Roth‐Bejerano N. , Lips S. H. 
Published: January 2008

AbstractThe stability of the bond of glycolate oxidase to the peroxisomal membrane obtained from etiolated barley leaves, (Hordeum vulgareL. var Dvir) is affected by the pH of the homogenization medium. Peroxisomes isolated at pH 4 or 10 retain glycolic oxidase, while peroxisomes isolated at pH 69 loose this enzyme during centrifugation. Preillumination of whole seedlings, detached leaves or even homogenates changes the effect of pH on the retention of glycolate oxidase‐attachment which is strengthened at pH 9–10 and becomes very loose at pH 4–7. White and red light are responsible for the effect described. Far red light reverses this effect of red light.Illumination induces a change in the isoelectric point (IpH) of peroxisomes without affecting the IpH of soluble enzymes. This red light‐induced change on IpH of microbodies is not reversed by far red light. The possible effects of light on peroxisomal membrane properties and on modulation of glycolate oxidase binding are discussed.
PHYTOCHROME ACTION: A REAPPRAISAL
Authors: Jose A. M. , Vince‐Prue D. 
Published: January 2008

AbstractStems of fully green plants show at least two types of response to light. In one, Pfr inhibits elongation. The second is a promotion of elongation which operates only in light; the effectiveness of red and far‐red wavelengths indicates that this response is also mediated through phytochrome. Studies of the de‐etiolation process also provide evidence for two modes of action of phytochrome; one is a Pfr‐dependent reaction, and the second requires continuous light (or frequent short irradiations).It is proposed that, in addition to reactions which require Pfr and proceed in darkness, an important reaction of phytochrome in green plants occurs only in light. We have termed these two modes of action of phytochrome “static” and “dynamic”. The static mode operates after a brief exposure to light which establishes Pfr; the potential responses are largely reversible by far‐red and exhibit reciprocity. The dynamic mode operates only in light and the responses do not show reciprocity. We consider that this mode operates through the transition from one bound form of phytochrome to another. The possible involvement of these two modes of action of phytochrome in photoperiodic mechanisms is discussed.
ENERGY TRANSFER STUDIES ON CRYPTOMONAD BILIPROTEINS
Authors: MacColl Robert , Berns Donald S. 
Published: January 2008

Abstract. Fluorescence techniques of various types have been used to study the light‐gathering and energy transfer modes for various cryptomonad biliproteins (phycocyanin or phycoerythrins). Analysis of fluorescence polarization and absorption data demonstrates that each cryptomonad biliprotein is composed of at least two distinct types of absorbing chromophore, each attached to the protein through covalent linkages to different polypeptide chains. Examination of the fluorescence emission spectra as a function of excitation at several wavelengths demonstrates that only one of these absorbing chromo‐phores is responsible for the fluorescence. This behavior is consistent with a known phenomenon whereby photons are gathered by more than one chromophore and then after radiationless energy transfer are emitted by only one chromophore.Application of Förster dipole‐dipole energy transfer theory is made to the study of the mode by which energy absorbed by biliproteins migrates to Chl a. The spectral overlap integral between phycocyanin (Chroomonas sp.) and Chl a is 7.13 ± 10‐10cm6mol‐1and between phycocyanin and Chl c2 0.25 ± 10‐10cm6mol‐1. This large difference in overlap suggests, although does not prove, that phycocyanin might transfer energy directly to Chl a without a Chl c2 intermediary. The cryptomonad phycoerythrins may also use this method but a Chl c2 intermediate could not be ruled out for them. Radiationless energy transfer among homogeneous biliproteins is shown to be feasible. All these calculations are based on in vitro spectra and the interpretations extrapolated to the cellular situation, and these tentative conclusions are reached without knowledge of other factors, such as chromophore‐chro‐mophore orientation and distance, which could greatly influence the energy transfer scheme.
QUENCHING OF CHLOROPHYLL FLUORESCENCE BY NITROBENZENE
Authors: Beddard G. S. , Carlin Sheena , Harris L. , Porter G. , Tredwell C. J. 
Published: January 2008

Abstract—Nitrobenzene quenching of chlorophyll fluorescence in ethanol has been investigated. Steady state relative quantum yields have been measured and fluorescence decay rates were determined using both nanosecond photon counting and picosecond pulses from a mode‐locked Nd3+ glass laser.The fluorescence decay is described by1(t)=I0 exp (‐t/τ−At1/2)the form predicted for decay governed by the kinetics of the continuum model of diffusion controlled reactions. From the parameters of the fluorescence decay, the encounter distance is 5–7 A° the mutual diffusion coefficient is 0.62 × 10‐‐5 cm2s‐1± 12%.Some of the fluorescence quenching is also attributed to static quenching by a nitrobenzene‐chlorophyll, ground‐state complex. The equilibrium constant for formation of this ground‐state complex was determined to be 4.1 M‐1. The combined dynamic and static quenching model allows calculation of quantum yields of fluorescence in good agreement with the experimentally determined quantum yields.
QUENCHING OF TRIPLET STATES OF AROMATIC KETONES BY INDOLE AND 3‐METHYL INDOLE IN BENZENE SOLUTION. EVIDENCE FOR HYDROGEN‐ATOM ABSTRACTION, FOR QUENCHING DUE TO FAVOURABLE CHARGE TRANSFER INTERACTION AND FOR THE LACK OF ELECTRONIC ENERGY TRANSFER
Authors: Wilkinson Francis , Garner Anthony 
Published: January 2008

Abstract— Quenching of the triplet states of the aromatic ketones (KCO), benzophenone, acetophenone and xanthone, by indole and 3‐methyl indole gives rise to the neutral radicals resulting from hydrogenatom transfer with variable efficiency (40–100%). Thus in addition to the reaction, 3KCO*+RH →KCOH +R.some other quenching path or paths occur. There is no evidence for any triplet energy transfer even when this is energetically favourable, and it is suggested therefore that quenching to give ground state species following favourable charge‐transfer interactions accounts for the proportion of quenching without reaction.The spectra of the indole radicals, R., were determined and the kinetics of their decay in aerated and deaerated solution were investigated and reaction schemes proposed to explain these observations.
WAVELENGTH DEPENDENCE AND KINETICS OF UV‐INDUCED FREE RADICAL FORMATION IN THE HUMAN CORNEA AND LENS
Authors: Yamanashi B. S. , Hacker H. , Klintworth G. K. 
Published: January 2008

Abstract— The wavelength dependence of free radical formation in the human lens and cornea was obtained in the ultraviolet‐visible (UV‐VIS) range with electron paramagnetic resonance. The spectral feature of having their maxima close to 290 nm, negligible intensity above 320 nm, and appreciable intensity toward 260 nm is common to both of these tissues.The kinetics of free radical formation in the lens and cornea was interpreted in terms of a two component exponential function with characteristic rate constants kl and k2, the latter of which has the same value for both the lens and cornea.
CIRCADIAN RHYTHM OF EXTRARETINAL PHOTOSENSITIVITY IN HATCHLING ALLIGATORS, ALLIGATOR MISSISSIPPIENSIS
Authors: Kavaliers Martin 
Published: January 2008

Abstract—Hatchling American alligators, Alligator mississippiensis, display a diel rhythm of extra‐retinal (non‐pineal) photosensitivity. There is a bimodal pattern in the threshold fluence rate required for initiating and effecting extra‐retinally‐mediated phototaclic responses. Significantly greater threshold fluence rates are required in the photophase than the scotophasc of a 12 h light: 12 h dark cycle. Under constant darkness there continues an endogenous, apparently circadian rhythm of extra‐retinal photosensitivity. In all cases there is a significantly greater photosensitivity at lower temperatures.
GERMICIDAL ULTRAVIOLET LIGHT INDUCES ORNITHINE DECARBOXYLASE IN MOUSE EPIDERMAL CELLS AND MODIFIES THE INDUCTION CAUSED BY PHORBOL ESTER TUMOR PROMOTERS
Authors: Lichti Ulrike , Bowden G. Timothy , Patterson Elroy , Ben Theresa , Yuspa Stuart H. 
Published: January 2008

Abstract—Germicidal ultraviolet light (UVC. 8–10 J/m2) induces ornithine decarboxylase (ODC) in mouse epidermal cells in vitro in a biphasic manner with maxima of 2–3 fold induction at 4–6 h and of 10–20 fold induction at 15–18 h after irradiation. At this dose of UVC overall protein synthesis is inhibited by 10–30% and RNA synthesis by 40–50%. Induction of both ODC peaks is prevented by actinomycin D or cycloheximide. Similar culture factors appear to influence the extent of ODC induction by UVC and by the tumor promoter, 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA), since the ratio of peak activities is approximately constant at 2, whereas absolute values vary considerably between experiments. If cells are irradiated with UVC and then exposed to TPA, the effects are additive at 10 J/m2, less than additive at higher and enhanced at lower doses of UVC.