bluuebunny/crossref_metadata_2025 huggingface dataset:
A PHOTOCHEMICAL MID‐ULTRAVIOLET DOSIMETER FOR PRACTICAL USE AS A SUNBURN DOSIMETER
Authors: Zweig A. , Henderson W. A.
Published: January 2008

Abstract— A mid‐UV dosimeter has been developed based on the irreversible photochemical conversion of 3′‐[p‐(dimethylamino)‐phenyl] spiro‐[fluorene–9,4′‐oxazolidine]–2′,5′‐dione (1) to p‐dimethylamino‐N‐fluoren‐9‐ylidine aniline (2), carbon monoxide and carbon dioxide. Formulations of 1 in a polycarbonate film matrix are colorless, thermally stable, and undergo photolysis only when exposed to wavelengths of less than 350 nm. The red photoproduct 2 is both thermally and photochemically stable under dosimeter use conditions. The depth of red color developed depends solely on the degree of exposure to mid‐UV radiation. In outdoor studies color intensity steadily developed during an initial 2 h of exposure to noontime Miami June sunshine. Color comparators representing consecutive 15–20 min exposure increments of this sunshine were readily distinguishable from each other by visual inspection. The comparators could be visually matched to colors generated by the dosimeter film formulation, and covered the exposure range of interest for avoidance of sunburn. This photochemical mid‐UV dosimeter is seen to fulfill all the requirements of a practical sunburn dosimeter.
INTERACTION OF IONIZING RADIATION AND ULTRAVIOLET‐LIGHT IN DIPLOID YEAST STRAINS OF DIFFERENT SENSITIVITY*
Authors: Schneider E. , Kiefer J.
Published: January 2008

Abstract— The interaction of ionizing radiation and UV‐light regarding colony forming ability in 3 diploid yeast strains of Saccharomyces cerevisiae was investigated. A wild type and two radiation sensitive mutants were used. No difference in the response of the three strains could be detected when the UV dose was given first, but when ionizing radiation was applied shortly before UV, there were essential differences depending on the kind of mutation. The involvement of repair mechanisms in the interaction is discussed.
TRIPLET STATES OF CAROTENOIDS FROM PHOTOSYNTHETIC BACTERIA STUDIED BY NANOSECOND ULTRAVIOLET AND ELECTRON PULSE IRRADIATION
Authors: Bensasson R. , Land E. J. , Maudinas B.
Published: January 2008

Abstract— Absorptions of the triplet excited states of five carotenoids (15,15'‐ds phytoene, all‐trans phytoene, C‐carotene, spheroidene and spirilloxanthin), extracted from the photosynthetic bacteria Rhodopseudomonas spheroides and Rhodospirillum rubrum, have been detected in solution using pulse radiolysis and laser flash photolysis. Triplet lifetimes, extinction coefficients, lowest energy levels and quantum efficiencies of formation have been determined. Comparison of the carotenoid triplet energy levels with that of O2('Δg) suggests that spirilloxanthin, spheroidene and possibly alsoζ‐carotene, would be expected to protect against photodynamic action caused by O2 ('Δg), but not cis or trans phytoene. The S→T intersystem crossing efficiences of all five polyenes were found to be low, being a few per cent or less. In their protective role these triplet states can only therefore be effectively reached via energy transfer from another triplet, except in the case of O2 ('Δg). The low crossover efficiencies also mean that light absorbed by such carotenoids in their possible role as accessory pigments would not be wasted in crossing over to the triplet state.
EXTRARETINAL PHOTORECEPTION IN ENTRAINMENT OF CRUSTACEAN ORCADIAN RHYTHMS*
Authors: Page Terry L. , Larimer James L.
Published: January 2008

Abstract— An attempt was made to determine whether entrainment of the circadian rhythms of locomotor activity and ERG amplitude of the crayfish involved extraretinal photoreception. The results of a variety of experiments involving surgical lesions and localized illumination provided evidence that both rhythms can be entrained via an extraretinal pathway. The data also demonstrate that the caudal photoreceptor is unnecessary for entrainment. Our evidence to date suggests that the extraretinal photoreceptor is located in the supraesophageal ganglion; however, the possibility of photoreceptive input from other regions of the CNS, particularly the optic lobe, has not been eliminated. It is also tentatively concluded that the circadian oscillators for both the locomotor and the ERG amplitude rhythms are located within the supraesophageal ganglion, but more data are needed to confirm this conclusion.
PICOSECOND AND NANOSECOND TSOMERIZATION KINETICS OF PROTONATED 11‐CIS RETINYLIDENE SCHIFF BASES
Authors: Huppert D. , Rentzepis P. M. , Kliger D. S.
Published: January 2008

Abstract— Picosecond and nonosecond spectroscopy has been used to study the isomerization mechanism of protonated 11‐cis retinylidene Schiff bases. The formation and bleaching of absorption bands within 10 ps and corresponding decay and recovery within 11 ns indicate that the isomerization mechanism of the protonated Schiff bases is not identical to rhodopsin in which the primary photophysical event is probably due to electron transfer or partial isomerization of the chromophore to a nonplanar conformation.
THE EFFECT OF CHEMICAL STRUCTURE ON THE PHOTOSENSITIZING EFFICIENCIES OF PORPHYRINS
Authors: Cauzzo Giulio , Gennari Ciorgio , Jori Giulio , Spikes John D.
Published: January 2008

Abstract— A kinetic investigation was performed on the photooxidation of methionine sensitized by various porphyrins at different oxygen concentrations. The rate of photooxidation was found to be strongly dependent on the nature of the sensitizer. In the case of hematoporphyrin, chelation of Mg2+ and Zn2+ and especially of Cu2+ and Fe2+ caused a significant decrease of the photosensitizing efficiency. Fluorescence and/or flash photolysis studies showed that such a decrease is ascribed to an enhancement of the non‐radiative decay of the first excited singlet state as well as to a reduction of the triplet lifetime. The sensitizing efficiency is also dependent on the nature of the porphyrin side chains. A reaction mechanism involving 1O2 as the oxidizing agent is proposed.
PHOTOSYNTHETIC ACTION SPECTRA AND LIGHT‐HARVESTING IN GRIFFITHSIA MONILIS (RHODOPHYTA)
Authors: Larkum A. W. D. , Weyrauch S. K.
Published: January 2008

Abstract— In cells of the red alga Griffithsia monilis the action spectrum of photosynthetic oxygen production at low light intensity shows that the phycobilins (including allophycocyanin) are the major light‐harvesting pigments. As the light intensity is increased carotenoids and chlorophyll a contribute proportionately more to the spectrum, since the phycobilin activity becomes light‐saturated. When action spectra are performed against a background light of various monochromatic wavelengths it can be shown that chlorophyll a increases in its light‐harvesting activity. Nevertheless light absorbed at a single wavelength (487 nm) by phycoerythrin (and possibly a carotenoid) still shows the highest photosynthetic activity. Fluorescence measurements at 77K indicate that a chlorophyll a fluorescence is small and that the amount of chlorophyll all (f 693) is very low. A model is proposed in which the phycobilins, in phycobilisomes, pass on absorbed light energy to either photosystem, whereas light absorbed by chlorophyll is passed on mainly to photosystem I.
FLASH PHOTOLYSIS OF TRYPTOPHAN AND N‐ACETYL‐L‐TRYPTOPHANAMIDE; THE EFFECT OF BROMIDE ON TRANSIENT YIELDS
Authors: Volkert W. A. , Kuntz R. R. , Ghiron C. A. , Evans R. F. , Santus R. , Bazin M.
Published: January 2008

Abstract— The initial yields of the cation and neutral radicals and the triplet are greatly enhanced when high concentrations of Br‐ are present during the flash photolysis of aqueous solutions containing either tryptophan or N‐acetyl‐L‐trytophanamide. The present study is an attempt to elucidate the mechanism by which Br‐ induces these effects. The results obtained indicate that the initial event involves an interaction between the fluorescent state and Br‐ to promote the formation of a long‐lived radical precursor that may be the triplet. It is shown that all of the Br‐‐induced neutral and cation radical formation originate from this long‐lived state. Furthermore, it was found that the mechanism of radical production from the Br‐‐induced long‐lived precursor does not involve hydrated electron formation.
DELAYED FLUORESCENCE FROM CHLORELLA: II. EFFECTS OF ELECTRON TRANSPORT INHIBITORS DCMU AND NH2OH
Authors: Ruby R. H.
Published: January 2008

Abstract. –Steady state and transient effects of two electron transport inhibitors (NH2OH˙HCl and DCMU) and one uncoupler (FCCP) upon the emission of delayed fluorescence have been studied in whole cells of Chlorella pyrenoidosa. Observations were made on changes in the delayed fluorescence emitted 0.5 ms after a brief flash and 60 ms after the extinction of steady illumination and on changes in the induction effects caused by preillumination. Patterns in the time course of events after inhibitor addition occur which have different characteristics for each of the additives. The observations are consistent with a model of delayed fluorescence production based on the recombination of charges.
ACID‐BASE EQUILIBRIA OF ELECTRONICALLY EXCITED PHENAZINE
Authors: Chalvet O. , Jaffé H. H. , Rayez J. C.
Published: January 2008

Abstract. Using the CNDO/S method, we have studied the lowest singlet ← singlet and triplet ← singlet transition energies of phenazine and its two conjugate acids. The spectra of the conjugate acids are not well reproduced by the calculations unless a water molecule is introduced to hydrogen bond to each < N+H group. The pattern of the pK's for the acid‐base equilibria in the excited states is shown to conform with previously derived general patterns.
THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT–V. SEASONAL CHANGES IN RADIANT ENERGY QUALITY IN WOODLANDS
Authors: Tasker R. , Smith Harry
Published: January 2008

Abstract. The spectral distribution of radiant energy on the floor of three typical English woodlands (birch, beech and oak) has been monitored throughout the whole growing season. The results are presented in terms of the changes in the ratio of the photon fluxes at 660 nm and 730 nm (τ) and in the photosynthetically active radiation (PAR). The results are discussed in relation to the hypothesis that the role of phytochrome is to detect changed light quality due to mutual shading and to direct development accordingly.
ENHANCEMENT OF THE NON‐TRYPTOPHAN FLUORESCENCE OF HUMAN LENS PROTEINS AFTER NEAR‐UV LIGHT EXPOSURE*
Authors: Zigman Seymour , Groff Jeannine , Yulo Teresa
Published: January 2008

Abstract. In this work, the non‐tryptophan fluorescence (360 nm excited; 440 nm emitted) of human lens proteins was found to be intensified by exposing whole lens homogenates to near‐UV light in the presence of tryptophan photoproducts. The induced fluorescence accumulates mainly in the soluble phase proteins, whereas in aging and brown cataractous lenses, the major fluorescence is found in the insoluble proteins. Using SDS‐polyacrylamide gel electrophoresis with densitometric and fluorescence scanning techniques, the polypeptide chains of the three major protein fractions were analyzed for their specific non‐tryptophan fluorescences. The same chains were found in all fractions. Two chains (11,000 and 45,000 daltons) were found to accumulate most of the induced fluorescence. These also contained the greatest intrinsic fluorescence initially. The data indicates that specific polypeptide chains in the lens proteins are most sensitive to modifications due to their exposure to near‐UV light in the presence of tryptophan photoproducts.
EFFECTS OF 2,5‐DIBROMO‐3‐METHYL‐6‐ISOPROPYL BENZOQUINONE (DBMIB) ON PHOTOCHEMICAL EVENTS IN RHODOSPIRILLUM RUBRUM*
Authors: Bering Charles L. , Loach Paul A.
Published: January 2008

Abstract. The quinone antagonist dibromothymoquinone (2,5‐dibromo‐3‐methyl‐6‐isopropyl benzoquinone, DBMIB)‡ was used to inhibit early photochemical changes in chromatophores of the photo‐synthetic bacterium, Rhodospirillum rubrum. With continuous illumination with near infrared light, we observed an approximately threefold decrease in efficiency of P865+ formation at 100–200 μM DBMIB as measured by absorbance changes at 605 or 430 nm. However, with continuous illumination of several seconds duration, maximal absorbance changes were observed. At low concentrations (1–10 μM) of DBMIB, a decrease in the decay rate of the ΔA430 or ΔA605 was observed. Using a short (2–10 μs), low intensity light pulse for excitation, we observed that DBMIB inhibits P865+ formation. The concentration dependency of this inhibition corresponds to that seen with continuous illumination. We tested the possibility that DBMIB was displacing the first stable electron acceptor, which has been shown to be a tightly bound ubiquinone (UQ) in R. rubrum. Chromatophores prepared from cells grown with 14C‐p‐hydroxybenzoic acid in their media provided a sample in which the benzoquinones were labelled specifically with 14C. These labelled chromatophores were first extracted with petroleum ether to remove the loosely bound ubiquinone pool and then were treated with DBMIB. DBMIB displaced about 1/2 of the remaining tightly‐bound UQ present. The DBMIB inhibition was tested for reversibility by adding an excess of UQ to DBMIB‐treated samples. In these cases, restoration to 80% could be achieved from samples which were only 20% active relative to the untreated samples. A similar inhibitory effect by DBMIB was also demonstrated in whole cells of Rhodospirillum rubrum, the G‐9 mutant of Rhodospirillum rubrum, Rhodopseudomoms sphaeroides, Rhodopseudomonas capsulata, and Chromatium vinosum. The mechanism for inhibition is most consistent with displacement of, or interference with the first stable electron acceptor (ubiquinone) rather than by random quenching of excited states at the level of antenna bacteriochlorophyll.
TEMPERATURE DEPENDENCE OF DELAYED LIGHT EMISSION IN THE 6 to 340 MICROSECOND RANGE AFTER A SINGLE FLASH IN CHLOROPLASTS
Authors: Jursinic P. , Govindjee
Published: January 2008

Abstract. The delayed light emission decay rate (up to 120 μs) and the rise in chlorophyll a fluorescence yield (from 3 to 35 μs) in isolated chloroplasts from several species, following a saturating 10 ns flash, are temperature independent in the 0–35°C range. However, delayed light in the 120–340 μs range is temperature dependent. Arrhenius plots of the exponential decay constants are: (a) linear for lettuce and pea chloroplasts but discontinuous for bush bean (12–17°C) and spinach (12–20°C) chloroplasts; (b) unaffected by 3‐(3,4 dichlorophenyl)‐1,1‐dimethylurea (inhibitor of electron flow), gramicidin D (which eliminates light‐induced membrane potential) and glutaraldehyde fixation (which stops gross structural changes).

The discontinuities, noted above for bush bean and spinach chloroplasts, are correlated with abrupt changes in (a) the thylakoid membrane lipid fluidity (monitored by EPR spectra of 12 nixtroxide stearate, 12NS) and (b) the fluidity of extracted lipids (monitored by differential calorimetry and EPR spectra of 12 NS). However, no such discontinuity was observed in (a) chlorophyll a fluorescence intensity of thylakoids and (b) fluorescence of tryptophan residues of delipidated chloroplasts.

Microsecond delayed light is linearly dependent on light intensity at flash intensities as low as one quantum per 2 times 104 chlorophyll molecules. We suggest that this delayed light could originate from a one quantum process in agreement with the hypothesis that recombination of primary charges leads to this light emission. A working hypothesis for the energy levels of Photosystem II components is proposed involving a charge stabilization step on the primary acceptor side, which is in a lipid environment.

Finally, the redox potential of P680 (the reaction center for chlorophyll of system II) is calculated to be close to 1.0–1.3 V.
ENERGY TRANSFER IN THE ACCESSORY PIGMENTS R‐PHYCOERYTHRIN AND C‐PHYCOCYANIN
Authors: Barber D. J. W. , Richards J. T.
Published: January 2008

Abstract— The photosynthetic accessory pigments R‐phycoerythrin and C‐phycocyanin were extracted from a red sea‐weed and a filamentous blue‐green alga. Investigation of quenching of phycoerythrin fluorescence by phycocyanin at room and liquid nitrogen temperatures yielded rates for the SternVolmer quenching constants (Kq From these values, rate constants k(D–A) were calculated for the transfer of energy from phycoerythrin to phycocyanin.

The transfer rate constants obtained were such that a collisional transfer mechanism was ruled out, and were of similar order of magnitude as the rate constants for transfer of electronic energy in mixed organic crystals.
INHIBITION AND UNCOUPLING OF ELECTRON TRANSPORT IN ISOLATED CHLOROPLASTS BY THE HERBICIDE 4,6‐DINITRO‐O‐CRESOL
Authors: Rensen J. J. S. van , van der Vet W. , Vliet W. P. A. van
Published: January 2008

Abstract— Dinitrophenols are known to affect photosynthetic electron transfer. It is shown that the widely used herbicide 4,6‐dinitro‐o‐cresol is a potent inhibitor of the Hill reaction in isolated chloroplasts. By studying different parts of Photosystem II dependent electron transport it is indicated that this herbicide inhibits at the same site as 3‐(3.4‐dichlorophenyl)‐l,1‐dimethylurea.

However, the Photosystem I dependent Mehler reaction ascorbate/dichlorophenolindophenol→ diquat is stimulated at higher concentrations of the herbicide. This stimulation does not occur when an uncoupler is added to the reaction medium. There is also no stimulation of the ascorbatep‐tetra‐methyl‐p‐phenylene diamine → diquat Mehler reaction. This suggests that 4,6‐dinitro‐o‐cresol uncouples electron transport in the Photosystem I dependent Mehler reaction, when added at higher
PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS BY INDOLE DERIVATIVES AND BY TRYPTOPHAN‐CONTAINING OLIGOPEPTIDES AND PROTEINS
Authors: Hèléne Claude , Charlier Michel
Published: January 2008

Abstract— Indole derivatives including tryptophan can be used as photosensitizers of the splitting of pyrimidine dimers. The reaction can take place in frozen aqueous solutions as well as in fluid medium. Electron transfer from the indole ring to the dimer appears to be involved in the photosensitized reaction. Solvated electrons produced by flash photolysis in the presence of indoles or by pulse radiolysis are also able to split thymine dimers.

The splitting of pyrimidine dimers in DNA can be photosensitized by indole derivatives such as serotonin and by tryptophan‐containing oligopeptides. Several methods including fluorescence and nuclear magnetic resonance have been used to show that the indole ring of these oligopeptides is able to stack with bases in nucleic acids. These stacked complexes are involved in the photosensitized reaction.

The splitting of pyrimidine dimers in DNA has also been photosensitized by the protein coded by gene 32 of phage T4 which binds strongly and cooperatively to single‐stranded DNA. The mechanism of the splitting reaction as well as the possible use of this reaction to investigate the role of tryptophan residues in the binding of proteins to nucleic acids are discussed.
EXCITATION ENERGY MIGRATION IN PHYCOBILISOMES: COMPARISON OF EXPERIMENTAL RESULTS AND THEORETICAL PREDICTIONS
Authors: Grabowski J. , Gantt E.
Published: January 2008

Abstract— Quantum yield and fluorescence polarization determinations on phycobilisomes and their constituent phycobiliproteins show that phycobilisomes are energetically effective macromolecular structures. Energy migration within the phycobilisome to allophycocyanin, the longest wavelength absorbing and emitting phycobiliprotein, was indicated by the predominant allophycocyanin fluorescence emission which was independent of the phycobiliprotein being excited. The high efficiency of the energy migration inside the phycobilisome was reflected by the low polarized fluorescence. Excitation of phycobilisomes in the region of major absorption (500–650 nm) resulted in degrees of fluorescence polarization between +0.02 and –0.02, whereas in isolated phycobiliproteins the values were 2 to 12 times greater. Furthermore, 94–98° of the excitation energy of phycoerythrin was transferred to phycocyanin and allophycocyanin as determined from comparisons of fluorescence spectra of intact and dissociated phycobilisomes. The fluorescence quantum yields of phycobilisomes were about 0.60–0.68, very similar to that of pure allophycocyanin in solution (0.68). Phycobilisomes isolated from Fremyella diplosiphon and Nostoc sp. (blue‐gree algae) have respective quantum yields of 0.68 and 0. 65, and those isolated from Porphyridium cruentum (red alga), about 0.60. In Fremyella diplosiphon and Nostoc sp., which showed a striking adaptation to different wavelengths, the phycobilisome quantum yields only varied from 0.68 to 0.67 and from 0.65 to 0. 60, respectively. The mean transfer time, calculated on the basis of experimental results, was about 280 ± 40 ps for transfer of excitation from the phycoerythrin to the phycocyanin layer in phycobilisomes. This time corresponds to the mean number of jumps, about 28, of the excitation in the phycoerythrin layer before it is captured by phycocyanin. These values are in reasonable agreement with the values of 250 ± 30 ps and 25 jumps, calculated on the basis of a phycobilisome model (of Porphyridium cruentum) and Pearlstein's theory of energy migration devised for a three‐dimensional photosynthetic unit. It was also shown that Paillotin's theory of energy migration predicts similar values for mean transfer time and mean number of jumps, if one assumes that phycocyanin is a perfect sink for phycoerythrin excitation.
SINGLET OXYGEN REACTIONS WITH 2,7‐DIMETHYL‐2,6‐OCTADIENE
Authors: Tanielian Charles , Chaineaux Jacques
Published: January 2008

Abstract— Results concerning Rose Bengal sensitized photoxidation of 2,7‐dimethyl‐2,6‐octadiene (A) are discussed. This diolefin may be considered as a model molecule of polyisoprene of polymerization number two with 1,4‐4,1 addition mode.

All the mono‐ and dihydroperoxides apt to occur are actually obtained. One of the occurring hydroperoxides, 2,7‐dimethyl‐dihydroperoxy‐3,5‐octadiene, which has the structure of a conjugated diene, does not lead to an endoperoxide. This is contrary to Kaplan and Kelleher's hypothesis. On the other hand, no trihydroperoxide forms as a result of further addition of singlet oxygen (1O2).

A complete kinetic study has allowed us to determine the rate constants of all the reactions which take place. The reactivity of (A) is twice that of 2‐methyl‐2‐pentene and the addition of 1O2 to one of the double bonds of (A) induces deactivation of the remaining double bond.
CELLULAR AND SUBCELLULAR MECHANISMS OF PHOTODYNAMIC ACTION: THE 1O2 HYPOTHESIS AS A DRIVING FORCE IN RECENT RESEARCH
Authors: Ito Takashi
Published: January 2008

Abstract— Since 1972 the protective (quenching) effect of N3‐ and the enhancing effect of D2O have been used in combination to demonstrate 1O2 (1Δg) as the major reactive intermediate in the dye‐sensitized photooxygenation of biomolecules in in vitro systems. Extended application to in vivo systems has recently begun, producing some results which generally support the involvement of 1O2 pathways in the photosensitization processes. The use of other 1O2 quenchers and acceptors has also been increasing. In the application of these techniques as diagnostic tests for 1O2 participation in in vivo systems, careful examination of the experimental conditions should be made with respect to the quenching capability and accessibility of D2O in the specified cellular environment. Furthermore, the diffusive nature of 1O2, generation sites, generation efficiencies, the location and type of sensitizers, and the reactivity of 1O2 with presumed target structures in the cell should also be taken into account in the interpretation. Recent studies illustrating the importance of these factors are discussed. Finally, a tentative picture of the mode of in vivo photodynamic activity of common dye sensitizers is outlined.
A NEW METHOD FOR THE DETECTION OF SINGLET OXYGEN IN AQUEOUS SOLUTIONS
Authors: Kraljić I. , Mohsni S. El
Published: January 2008

Abstract— In experiments on the interception of reactive intermediates of strongly oxidizing character in dye (S) sensitized photooxidations using p‐nitrosodimethylaniline (RNO) as a selective scavenger, it has been observed that some substrates (A) or 1O2 acceptors (like imidazole derivatives) induce the bleaching of RNO as followed spectrophotometrically at 440 nm. Since singlet oxygen (1O2) does not react chemically with RNO, this bleaching is a consequence of 1O2 capture by the imidazole ring which results in the formation of a trans‐annular peroxide intermediate [1O2] capable of inducing the bleaching of RNO (‐RNO). In the absence of RNO, [1O2] decomposes or rearranges into the final oxygenation product 1O2: 1Δg Thus, the system imidazole plus RNO can be used as a sensitive and selective test for the presence of 1O2 in aqueous solutions. The method can also be applied in the presence of sensitizing dyes which, under visible irradiation, can partially bleach RNO even in the absence of imidazole derivatives. In such a case, the bleaching of RNO is strongly increased by the presence of imidazoles with a characteristic dependence on their concentration. The separation of the product of RNO bleaching by thin layer chromatography can serve as additional proof of the presence of 1O2 in the system. The imidazole plus RNO method has been applied to a number of sensitizing and non‐sensitizing dyes.
PHOTOCHEMICAL REACTIONS OF CHLORPROMAZINE; CHEMICAL AND BIOCHEMICAL IMPLICATIONS
Authors: Rosenthal I. , Ben‐Hur E. , Prager A. , Riklis E.
Published: January 2008

Abstract— The photoexcited chlorpromazine reacts with methanol to yield promazine and 2‐methoxypromazine by two different reaction pathways: hydrogen atom abstraction and nucleophilic attack. respectively. When the photoexcitation of chlorpromazine is performed in the presence of protein or nucleic acids, chlorpromazine binds to the biopolymer. This binding is drastically pH‐dependent and correlates to the phototoxic effect exhibited in chlorpromazine—photosensitization of E. coli. No photodynamic damage of E. coli attributed to CPZ‐sensitization of molecular oxygen could be detected.
ACTIVATED OXYGEN: SINGLET MOLECULAR OXYGEN AND SUPEROXIDE ANION
Authors: Khan Ahsan U.
Published: January 2008

Abstract— Elusive processes associated with molecular oxygen in chemical and biological systems are interpreted in terms of two activated oxygen species, singlet molecular oxygen (1Σ+g/1Δg) and superoxide anion (X2πg). The generation and deactivation of singlet oxygen by interaction with organic triplet states are discussed within a comprehensive theoretical framework. Experimental results indicate the anomalous molecular oxygen enhanced luminescence from organic chromophores in polymer matrices results from the deactivation of singlet (1Δg) oxygen by energy transfer to electronically excited states of the chromophore, and three types of oxygen enhanced luminescence have been identified in these systems. Properties of the superoxide anion relevant to its solution chemistry are briefly discussed. Electron transfer theory is used to theoretically examine the generation of singlet oxygen in disproportionation reactions of the superoxide anion, predicting that, depending on the number of water molecules present, the disproportionation reaction is a proficient source of singlet oxygen. A competing quenching process imposes a limit to the steady state concentration of singlet oxygen in most chemical systems. Available experimental results on the quenching of singlet oxygen by superoxide anion are in good agreement with theoretical results obtained via application of electron transfer theory.
REEVALUATION OF THE SPECTRAL AND KINETIC PROPERTIES OF HO2 AND O2‐ FREE RADICALS
Authors: Bielski Benon H. J.
Published: January 2008

Abstract— The spectra and molar absorbances of the HO2 and O2‐ free radicals have been redetermined in aqueous formate solutions by pulse and stopped‐flow radiolysis as well as by 60Co gamma‐ray studies. The extinction coefficients at the corresponding maxima and 23°C are 225= 1400 ± 80 M‐1 cm‐1 and 225= 2350 ± 120 M‐1 cm‐1 respectively. Reevaluation of earlier published rate data in terms of the new extinction coefficients yielded the following rate constants for the spontaneous decay of HO2 and O2‐: KHo2+HO2= (8.60 ± 0.62) × 105M‐1 s‐1; KHo2+O2‐= (1.02 ± 0.49) × 108M‐1 s‐1; KHo2+O2‐ < 0.35 M‐1 s‐1. For the equilibrium HO2→ O2‐+ H+ the dissociation constant is KHo2= (2.05 ± 0.39) × 10‐5M or pKHO2= 4.69 ± 0.08. G(O2‐) has been evaluated as a function of formate concentration.
CHEMICAL REACTIONS OF SUPEROXIDE ANION RADICAL IN APROTIC SOLVENTS
Authors: Frimer Aryeh A. , Rosenthal Ionel
Published: January 2008

Abstract— While superoxide anion radical does not normally react with olefins, it does react with activated double bonds. Thus O‐2 oxidatively cleaves certain α,β‐unsaturated ketones such as chalcones and tetracyclone and electron poor olefins such as 1,1‐dicyano and 1,1‐dinitro olefins. Similarly O‐2 can react with substituted nitrobenzenes to yield the corresponding nitrophenols. EPR and oxygen labeling (KO362) experiments confirm an electron transfer mechanism.
SUPEROXIDE RADICALS, SUPEROXIDE DISMUTASES AND THE AEROBIC LIFESTYLE
Authors: Fridovich Irwin
Published: January 2008

Abstract— The superoxide radical (O‐2) is a commonplace product of the biological reduction of molecular oxygen and plays an important role in oxygen toxicity. Superoxide dismutases (SOD) catalytically scavenge this radical and are the primary defense against its cytotoxicity. The data which support these statements have been briefly reviewed. Oxygen enhances the lethality of certain antibiotics, such as streptonigrin, and of ionizing radiation as well. The role of O‐2 in the enhancements is presented and the basis of the radioprotective effects of SOD discussed. Several more recent developments are presented in detail including: (a) The induction of the MnSOD of E. coli upon exposure to very low levels of oxygen, (b) The changes in SOD in E. coli as a function of nutritional state, during culture in a chemostat. (c) A convenient new assay and activity stain for SOD.
SPIN TRAPPING OF FREE RADICALS PRODUCED FROM NITROSOAMINE CARCINOGENS
Authors: Floyd Robert A. , Soong Lailing M. , Stuart Melissa A. , Reigh Darryel L.
Published: January 2008

Abstract— Using the spin trap 5,5‐dimethylpyrroline‐1‐oxide we have demonstrated that the nitrosoamine carcinogen, 1‐nitrosopiperidine, upon incubation with rat liver microsomes and nuclei produces two trapped free radical species. One trapped species is the hydroxyl free radical whereas the other is a free radical of unknown structure of the carcinogen itself. Three other nitrosoamine carcinogens tested, including diethylnitrosoamine, dimethylnitrosoamine and 1‐nitrosopyrroline yielded similar results with the exception that the trapped carcinogen radical differs dependent upon the compound used. Oxygen was required to produce the hydroxyl free radical but its presence decreased the yield of the carcinogen radical. Both cyanide and α‐tocopherol acetate caused a decrease in the yield of the carcinogen free radical. Some heat‐labile inhibitor(s) of radical production was/were present in the cytosol. The amount of radical produced was not proportional to the P450 content.
FLUORIMETRIC DETERMINATION OF 4‘,5’‐CYCLOADDUCTS IN THE DNA‐PSORALEN PHOTOREACTION
Authors: Dall‘Acqua F. , Caffieri S. , Rodighiero G.
Published: January 2008

Abstract— 4′,5′‐Photocycloadducts of psoralen with pyrimidine bases of DNA have been quantitatively determined by fluorescence measurements on the acid hydrolysate of DNA‐psoralen photoadducts.
THE PHOTOMORPHOGENETIC CONTROL OF THE DEVELOPMENT OF PLASTID GLYCERALDEHYDE‐PHOSPHATE DEHYDROGENASE AND PHOSPHORIBULOKINASE ACTIVITIES IN COTYLEDONS OF MUSTARD SEEDLINGS
Authors: Bradbeer J. W. , Hargrave D. F. , Langman L.
Published: January 2008

The plastid glyceraldehyde‐phosphate dehydrogenase and phosphoribulokinase of mustard cotyledon extracts were activated by preincubation with ATP and with ATP and dithiothreitol respectively. By in vitro activation prior to assay, it was possible to determine the potential activities, which appear to have been directly proportional to the amount of each enzyme protein present. In this way it was possible to deduce the net synthesis of these two enzymes. The induction of synthesis of glyceraldehyde‐phosphate dehydrogenase and phosphoribulokinase, by continuous far red or white light were similar hut net synthesis in continuous far red continued longer for glyceraldehyde‐phosphate dehydrogenase than for phosphoribulokinase. The kinetics of the development of the glyceraldehyde‐phosphate dehydrogenase potential activity were very close to those reported by Bruning et al. (1975) for this enzyme. The data do not permit elimination of either the single switch or multiple switches hypotheses for the action of phytochrome.

Continuous white illumination gave results similar to those for continous far red for the net synthesis of the two enzymes but it was more effective than far‐red in bringing about enzyme activation in vivo.
SOLVENT EFFECT ON PHOTOSENSITIZED OXIDATION OF IODIDE ION BY ANTHRACENE SULPHONATES
Authors: Gupta Anindya K. , Rohatgi‐Mukherjee K. K.
Published: January 2008

Abstract— Iodide ion oxidation by singlet oxygen is found to be influenced by two properties of the solvent. One is the polarity of the solvent and the other is the availability of protons in the solvent. By suitable choice of solvents and solvent mixtures both kinds of effects have been studied. In water‐methanol mixtures the reaction is found to be facilitated in more polar medium. In isodielectric media as obtained by mixtures of acetonitrile and methanol the reaction is repressed with increase in the aprotic component (CH3CN) in the solvent. The same effect is observed in the DMSO‐H, O mixtures. In heavy water the reaction rate is doubled and the effect fits well into the proposed kinetic scheme involving singlet oxygen for photosensitized oxidation of I‐ by anthracene sulphonates.
PHOTOCHEMICAL INTERACTION OF FUROCOUMARINS WITH BROMODEOXYURIDINE AND POLYDEOXY‐NUCLEOTIDES CONTAINING BROMODEOXYURIDINE: ITS BIOLOGICAL IMPLICATIONS
Authors: Ben‐Hur E. , Riklis E.
Published: January 2008

Abstract— The photoreaction of 5‐bromodeoxyuridine (BUdR) exposed to 360 nm light in the presence of the furocoumarins, 4,5′,8‐trimethylpsoralen (TMP) and 8‐methoxypsoralen (&MOP), was studied and compared to those of thymidine. BUdR reacted with furocoumarins, producing cyclobutane‐containing adducts, as does thymidine. Furocoumarins reacted also with BUdR‐containing polymer, poly(dA‐BUdR) in the double stranded form, at a rate similar to that of thymidine‐containing polymer, poly(dA‐dT). Polyamines, which slow the photoreactions of TMP with DNA, had no effect on its binding to the two former polynucleotides. It is suggested that because of the similar photoreactions of BUdR and thymidine with furocoumarins, this combination could be used to elucidate the mechanism by which BUdR sensitizes biological systems. In Escherichia coli some sensitization by BUdR of TMP plus 360 nm light killing was observed. It is therefore concluded that at least part of the sensitization of bacteria by BUdR to UV and ionizing radiation is caused by interference with the repair processes. Since no such sensitization was observed in a uvr B mutant, BUdR apparently impairs the efficiency of the excision resynthesis pathway of repair.
SOLAR DOSIMETRY WITH REPAIR DEFICIENT BACTERIAL SPORES: ACTION SPECTRA, PHOTOPRODUCT MEASUREMENTS AND A COMPARISON WITH OTHER BIOLOGICAL SYSTEMS
Authors: Tyrrell Rex M.
Published: January 2008

Abstract— Populations of radiation sensitive spores (Bacillus subtilis UVSSP), vegetative bacteria (E. coli K12‐AB2480) and bacteriophage (E. coli phage T4vx) have been considered as possible biological dosimeters to integrate DNA‐absorbed solar energy incident on the Earth's surface.

Irradiation of spores of B. subtilis UVSSP with monochromatic far‐ and near‐UV radiation and solar radiation have indicated that these radiations have a similar efficiency in inducing spore photoproducts per lethal event. Action spectra for lethality taken with the three radiation sensitive biological systems show a similar pattern in each case with a broad shoulder in the 334–365 nm wavelength region. This finding indicates a relatively high susceptibility of the DNA to chemical alteration in this wavelength range. Although less sensitive to sunlight than the other biological systems tested, the B. subtilis UVSSP spore mutant has the advantage of temperature independence of inactivation, stability between irradiation and assay and a simple, reproducible irradiation and assay procedure. Field measurements have supported the utility of this mutant as a sunlight dosimeter.
ZINC TETRAPHENYLPORPHYRIN‐SENSITIZED PHOTOREDUCTION OF ANTHRAQUINONESULFONATE IN AQUEOUS MICELLAR SOLUTIONS*
Authors: Kano Koji , Takuma Keisuke , Ikeda Tsuyoshi , Nakajima Daisuke , Tsutsui Yashuhiro , Matsuo Taku
Published: January 2008

Abstract— Zn‐tetraphenylporphyrin (ZnTPP), solubilized in non‐ionic surfactant micelles, was found to sensitize photoreductions of some sodium anthraquinonesulfonatesz in the presence of ascorbic acid under anaerobic conditions. The reaction rate was increased by the addition of an anionic surfactant, while retardation was observed with a cationic surfactant. The pH‐reaction rate profiles showed maxima located in the order corresponding to pKa‐values for the semiquinone of each anthraquinone‐sulfonate. A reaction scheme involving the formation of ZnTPP+ at the primary step, followed by back‐reduction with ascorbic acid, is proposed. The reaction scheme is in good agreement with the results of flash photolysis. The surfactant micelles are suggested to aid the charge‐separation between the ionic species just after the redox reaction involving the photoexcited ZnTPP and anthraquinonesulfonates.
STUDIES OF CHLOROPHYLL‐CHLOROPHYLL AND CHLOROPHYLL‐LIGAND INTERACTIONS BY VISIBLE ABSORPTION AND INFRARED SPECTROSCOPY AT LOW TEMPERATURES
Authors: Cotton T. M. , Loach P. A. , Katz J. J. , Ballschmiter K.
Published: January 2008

Abstract— A comparison of the visible absorption and infrared spectra of various chlorophyll‐chlorophyll (Chl) and Chi‐nucleophile aggregates at room temperature and at low temperatures has been made. The IR data provide structural information indispensable for the interpretation of the visible spectra. As a necessary preliminary, it is shown that Chl a solutions in nonpolar solvents can be prepared by appropriate drying techniques that contain at a conservative estimate ≤ 3 mol % of water (i.e. Chl a/H2O > 30:1). Very dry solutions of Chl a or Pyrochl a(≥ 10 mM) in toluene or methylcyclohexane‐isopentane solution show only slight changes in visible spectra on cooling to 77 K. From IR, additional Chl‐Chl aggregation occurs on cooling in methylcyclohexane‐isopentane but not to a significant extent in toluene. Dilute (10 μM) solutions of Chl a or Pyrochl a in nonpolar solvents form a new absorption peak near 700 nm at low temperatures, which we attribute to traces of water in the solvent or other residual nucleophiles not removed during the Chl purification. Addition of stoichiometric amounts of water increases the size of the ˜700 nm peak even in dilute Chl solutions. Chlorophyll a, Pyrochl a, but not pheophytin a are shown to interact with nucleophiles of the general type RXH (where R= H or alkyl, and X = O, N, or S). Such nucleophiles can coordinate to the Mg atom of one Chl molecule by lone pairs on O, N, or S, and hydrogen bond to oxygen donor functions in another Chl molecule. A ˜0.1 M solution of Chl a or Pyrochl a in toluene containing 1.5 equivalents of ethanol is converted almost entirely to a species absorbing at ˜700 nm at 77 K. Infrared spectroscopy shows conclusively that it is the keto C=O function that is involved in the cross‐linking by hydrogen bonding, a conclusion supported by the observation that Pyrochl a forms a very similar red‐shifted species at low temperatures, despite the absence of a carbomethoxy C=O function. n‐Butylamine and ethanethiol interact in much the same way as does ethanol to form species red shifted to ˜700 nm. A variety of possible structures for the low temperature forms is discussed, and the use of these red shifted species as paradigms for photoreaction center Chl is described.
KINETICS OF PHYTOCHROME PELLETABILITY*
Authors: Lehmann U. , Schäfer E.
Published: January 2008

Abstract— The pelletability of Pr from maize coleoptiles was studied as a function of the delay time between a red and a far‐red light pulse given in vivo. The obtained curve can be resolved into three parts. The two slowest reactions have half lives of 40 s and 3.6 min at 0°C. Furthermore, a break in the Arrhenius plot from the slowest reaction of the curve indicates that either the phytochrome “receptor” or the phytochrome molecule itself undergoes a jump in the Arrhenius activation energy at 20°C. These data are in good agreement with kinetic studies of phytochrome pelletability also discussed in this paper.
MUTATIONS IN SACCHAROMYCES CEREVISIAE AFFECTING SENSITIVITY TO PHOTODYNAMIC INACTIVATION
Authors: Roth R. , Papierniak K. J. , Anderson J. M.
Published: January 2008

Abstract— Mutants of Saccharomyces cerevisiae with varying photodynamic sensitivities were isolated in an attempt to help identify the cytoplasmic targets of photodynamic action in yeast.
RELATIONSHIP BETWEEN MUTAGENESIS AND CARCINOGENESIS*
Authors: Trosko James E. , Chang Chia‐cheng
Published: January 2008

Abstract— Since the neoplastic condition is a phenotypic expression of the genome of the tumor cells, it is reasonable to assume that the neoplastic state can be the result of the alteration of gene activity by either mutagenesis or gene modulation. The review of the literature seems to support the hypothesis that both mutations and epigenetic processes are components to carcinogenesis. Consistent with the mutation theory of cancer are: (1) the clonal nature of tumors; (2) the mutagenicity of most (but not all) carcinogens; (3) correlation of high mutation frequencies in cells of cancer‐prone human fibro‐ blasts lacking DNA repair enzymes; (4) correlation of in vitro DNA damage, in vitro mutation and transformation frequencies with in vivo tumorigenesis; (5) age‐related incidences of various hereditary tumors; and (6) the correlation between photoreactivation of DNA damage and the biological amelioration of UV‐induced neoplasms. Supporting the epigenetic theory of carcinogenesis is the reversion of certain types of neoplastic cells to a state allowing normal development. These latter studies demonstrate the totipotency of the genes in some types of malignant cells.

An integrative theory of carcinogenesis is presented that synthesizes the mutation and epigenetic theories with Comings' general theory of carcinogenesis and the 2‐stage theory of carcinogenesis. Data are presented that test the predictions of the 2‐stage theory of carcinogenesis, and that support the hypothesis that mutagenesis plays a major role in carcinogenesis (initiation phase) and that gene modulation of repressed mutations is responsible for tumor promotion.
A LASER FLASH PHOTOLYSIS STUDY OF THE NATURE OF FLAVIN MONONUCLEOTIDE TRIPLET STATES AND THE REACTIONS OF THE NEUTRAL FORM WITH AMINO ACIDS
Authors: Heelis P. F. , Parsons B. J. , Phillips G. O. , McKellar J. F.
Published: January 2008

Abstract— Primary photochemical processes in aqueous solution have been characterised for FMN. The influence of pH on these processes is attributed to protonation of the neutral triplet and not to the presence of a dimeric species as postulated earlier. Second order rate constants for reaction between the neutral triplet and some naturally occurring amino acids are reported.
PROTOPORPHYRIN‐SENSITIZED PHOTODYNAMIC MODIFICATION OF PROTEINS IN ISOLATED HUMAN RED BLOOD CELL MEMBRANES
Authors: Dubbelman T. M. A. R. , Goeij A. F. P. M. de , Steveninck J. van
Published: January 2008

Abstract— The photodynamic action of protoporphyrin on red cell ghosts is reflected by extensive cross‐linking of membrane proteins to very high molecular weight protein aggregates. This process was studied with sepharose gel chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis.

Most sensitive to this photodynamic effect are spectrin and band 2. 1, 2. 2, 2.3 and 4.1. polypeptides, which are cross‐linked after very brief illumination periods, with a concomitant loss of spectrin‐associated ATPase activity. Band 6 protein, representing the monomeric form of glyceraldehyde‐3‐phosphate dehydrogenase, is also very sensitive to protoporphyrin‐induced cross‐linking. The enzymatic activity decreased even faster than the amount of band 6 polypeptides, suggesting that modification(s) of the enzyme other than cross‐linking, possibly by rapid photooxidation of a thiol group, may be responsible for inactivation.

Extracted and purified spectrin was cross‐linked with about the same velocity as membrane‐bound spectrin, reinforcing our previously drawn conclusion that membrane lipids are not involved in the cross‐linking reaction. Eluted band 6 polypeptides on the other hand exhibited a relatively fast photo‐oxidative modification but a much slower cross‐linking to dimers and tetramers. This suggests that the membrane structure, e.g. the spectrin matrix may play an essential role in the incorporation of membrane‐bound band 6 polypeptides in the high molecular weight cross‐linked complex.
KINETIC FACTORS GOVERNING SENSITIZED PHOTOOXIDATION OF EXCITABLE CELL MEMBRANES
Authors: Pooler J. P. , Valenzeno Dennis P.
Published: January 2008

Abstract— The kinetic factors which determine the rate at which Na+ channels in nerve membranes become photochemically modified were studied on giant axons from lobsters using the double sucrose gap voltage clamp technique. Axons were bathed in artificial sea water containing sensitizing dyes and illuminated from a Xe are source with light in the visible region while being repetitively step depolarized. Successive values of peak Na+ current and time‐to‐peak were monitored and rate constants for their change served as the assay for magnitude of modification. Action spectra for four sensitizers in the fluorescein series exhibited red shifts of roughly 17nm demonstrating that sensitizing species are not simply free in solution. Eosin Y diffuses to its sensitization sites with a half time of 70s indicating the existence of a major diffusion barrier which may mean that dye must penetrate to the interior of the membrane to be effective. Eosin Y is removed from sensitization sites by rinse with the same half time but shows two fractions: a faster fraction comprising 80% of sensitizing effectiveness and a slower fraction comprising 20%. The concentration dependence for Eosin Y is linear below 10 μM and shows a progressive saturation at higher values, where the relationship is difficult to determine because of shielding. Different sensitizers vary in their ability to sensitize block of channels vs disruption of inactivation, demonstrating separate processes for the two modifications. It is suggested that both modifications proceed from single photon absorption events by individual sensitizer molecules bound or located close to the modification sites on the channels.