bluuebunny/crossref_metadata_2025 huggingface dataset:
ON THE FLUORESCENCE OF KETONES OF THE ANDROSTANE SERIES
Authors: WEINREB A. , WERNER A.
Published: January 2008

Abstract— The fluorescence spectrum and relative intensity of several ketoandrostanes is investigated as a function of the position of the carbonyl group on the steroid skeleton. The fluorescence intensity, though very low, depends rather strongly on the position. No dependence on solvent, excitation wavelength (in the vicinity of the first absorption peak), cooling or presence of oxygen was found. No phosphorescence was observed. The fluorescence decay time of the strongest fluorescing compound was measured to be 4·4 ± 0·2 nsec. For diketoandrostanes deactivation interactions between the carbonyl groups were found, depending on the position of the groups. The results are considered to be closely related to the vibrational pattern of the steroid frame.
TRANSFERTS D'ENERGIE INTRAMOLECULAIRES DANS LES SPIROPYRANNES PHOTOCHROMIQUES
Authors: BALNY C. , GUGLIELMETTI R. , MOSSÉ M. , METZGER J.
Published: January 2008

Abstract— The spectroluminescence of some new benzoheterospiropyrans has been investigated. The results are compared with the known luminescent properties of indolinospiropyrans. The phosphorescent properties are discussed in terms of intramolecular energy transfer and a correlation with colorability is suggested. The role of substituents on the chromene ring is also discussed.
PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES‐IV. GASEOUS PRODUCTS FROM THE PHOTOLYSIS OF ALANINE PEPTIDES IN THE SOLID STATE
Authors: JOHNS R. B. , SEURET M. G.
Published: January 2008

Abstract— Earlier studies based on ESR measurements of the photodamage induced by 254 nm irradiation of solid state alanine peptides have been supplemented by a new mechanistic probe involving mass spectrometric and gas‐solid‐chromatographic analyses of the gaseous products viz., carbon monoxide, carbon dioxide, hydrogen, methane and ethane. Decarboxylation, a major reaction, is temperature sensitive and independent of carbon monoxide formation. Carbon monoxide does not arise from the carboxyl group but rather by peptide bond rupture, which may lead to the generation of at least some of the hydrogen gas detected. The use of N‐deuterated‐DL‐alanyl‐DL‐alanine shows that the methyl radicals generated can abstract hydrogen atoms from the solid state peptide, and the formation of H2 and HD implicate an imine intermediate in the photodegradation.
ELECTRONICALLY EXCITED PRODUCTS IN THE PHOTODISSOCIATION OF Di‐9‐METHYLANTHRACENE
Authors: MENTER J. , FORSTER TH.
Published: January 2008

Abstract— Although the vast majority of photochemical reactions in condensed phase lead directly to product molecules in the ground states it might be expected that in favorable cases a certain fraction of the reacting species would escape deactivation long enough to attain the product configuration adiabatically in an electronically excited state. In this communication, we report that di‐9‐methylanthracene, in addition to its normal diabatic course, also leads to small but finite amounts of both excited singlet monomer and excimer species. Oxygen quenching experiments seem to indicate that the monomer and excimer are derived from excited di‐9‐methylanthracene with little mutual interconversion. The fluorescence yields were determined for these processes in aerated solution at room temperature to be φ1= 0·00040 ± 0·00005 and φ2= 0·00037 ± 0·00005 for monomer and excimer species, respectively.
THE IN VITRO PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES‐III. ABSORPTION SPECTRA, LIFETIMES AND RATES OF OXYGEN QUENCHING OF THE TRIPLET STATES OF β‐CAROTENE, RETINAL AND RELATED POLYENES
Authors: TRUSCOTT T. O. , LAND E. J. , SYKES A.
Published: January 2008

Abstract— The triplet‐triplet absorption spectra of six polyenes have been characterised using flash photolysis, in the presence of anthracene as sensitizer, and pulse radiolysis, in the absence of a sensitizer. The polyenes include several which contain carbonyl groups whose triplet states, unlike retinal, could not be detected unsensitized by flash photolysis. The triplet lifetimes appear to be a function of the number of conjugated double bonds, and vary between 7 and 14 μ sec. In general, the longer the polyene, the shorter the lifetime. An empirical linear relation was found between the frequencies of the polyene triplet‐triplet absorption maxima, and the frequencies of the corresponding ground singlet‐singlet maxima. The rate constants for quenching by oxygen of nine polyene triplet states were determined to lie in the range 2–7 × 109M‐1 sec‐1. The possible mechanisms for oxygen quenching of triplet states are discussed and analogies between the results for oxygen quenching of polyenes and of polyacenes are drawn. The rate constant for oxygen quenching of all‐trans‐β‐carotene triplet was the same in benzene and hexane.
EFFECT OF DIPICOLINIC ACID ON THE ULTRAVIOLET RADIATION RESISTANCE OF BACILLUS CEREUS SPORES
Authors: GERMAINE G. R. , MURRELL W. G.
Published: January 2008

Abstract— The ultraviolet radiation (UV) resistance of B. cereus spores was shown to depend on their content of dipicolinic acid (DPA). Wild‐type spores with decreasing amounts of DPA exhibited increased UV resistance. Similarly, spores devoid of DPA (DPA‐minus), produced by a mutant strain of B. cereus unable to synthesize DPA, were more resistant to UV than mutant spores (DPA‐plus) produced in the presence of exogenously supplied DPA. Resistance of both the wild type and mutant strains to ionizing radiation, however, was unaffected by DPA content. Comparison of the resistance of DPA‐minus and DPA‐plus mutant spores to UV of various wavelengths showed that the greater sensitivity of the latter DPA‐plus spores appeared at wavelengths corresponding to the region of the first molecular absorption band of the calcium chelate of DPA. In the wild type and mutant, thymine photoproducts were produced at a greater rate and to a greater extent in spores with high levels of DPA than in spores with low DPA.

The data indicate that DPA transfers energy to DN A in vivo, which leads to the conclusion that DPA occurs in the spore protoplast.
PHOTOLYSIS OF AQUEOUS SOLUTIONS OF POTASSIUM CIS‐DIAQUOBIS (OXALATO) CHROMATE (III)
Authors: ROPHAEL M. W. , MALATI M. A.
Published: January 2008

Abstract— The photolysis of aqueous solutions of cis‐[Cr(C2O4)2(H2O)2]‐ at 254 nm and pH 4 produced CO2 and H2 in nearly equal yields. The quantum yield of hydrogen, φ2, increased by 9% and the yield of carbon dioxide, φ, by 65% as the pH was lowered from 4 to I. The total gas yield, φgas, decreased in the presence of added oxalate or chromium (II) ions and when the light intensity was lowered. The gas yield in D2O was appreciably higher than in H2O. The variation of φgas with pH (D) and with added oxalate ion was roughly parallel in the two liquid media. The gas yield increased in the series:

A tentative mechanism is suggested to explain the results.
OSCILLATIONS OF THE TRIGGERED LUMINESCENCES OF ISOLATED CHLOROPLASTS PREILLUMINATED BY SHORT FLASHES*
Authors: HARDT HAIM , MALKIN SHMUEL
Published: January 2008

Abstract— Four types of triggered luminescence of isolated lettuce chloroplast (HCl‐induced, methanol‐induced, sodium benzoate‐induced and T‐jump‐induced) were examined after preillumination by a series (from 1 to 10) of short flashes. Oscillations were observed in the luminescence peaks, with a period of four flashes. These oscillations had maxima after the second and the sixth flash, similar to those of delayed light emission. The maxima were shifted forward two flashes by 50 μM hydroxylamine, as in oxygen evolution, and were abolished by 5 μM DCMU, as for delayed light. These results may show that the mechanism of triggered luminescence is influenced directly by the oxidation states (S1) on the donor side of photo‐system II.
EXCITED STATES IN PHOTODIMERIZATION OF AQUEOUS TYROSINE AT ROOM TEMPERATURE
Authors: Shimizu Okiyasu
Published: January 2008

Abstract— The photoionization of tyrosine in aqueous solution in the liquid state was studied at room temperature by analyzing the kinetics of formation of bityrosine upon irradiation of tyrosine, and the external heavy‐atom effect on the formation of bityrosine. The relative number of bityrosine molecules was determined by measuring the fluorescence intensity at 400 nm. A kinetic model for the formation of bityrosine was formulated on the assumption that the rate constants were first‐order for production of radicals and for recombination with ejected electrons. The applicability of this model to the present case was confirmed by the experimental data. On the basis of the model, we found that the electronic process of photoionization of tyrosine at room temperature is different in acidic and alkaline media. In acidic media a tyrosine molecule absorbs one light quantum and photoionizes through a singlet excited state, while in alkaline media a tyrosinate ion photoionizes after absorption of two light quanta. The intermediate product that absorbs the second photon is in a triplet excited state.
PHYTOCHROME INTERMEDIATES IN VIVO‐I. EFFECTS OF TEMPERATURE, LIGHT INTENSITY, WAVELENGTH AND OXYGEN ON INTERMEDIATE ACCUMULATION
Authors: Kendrick R. E. , Spruit C. J. P.
Published: January 2008

Abstract— Accumulation of weakly absorbing phytochrome intermediates has been demonstrated in Pisum epicotyl tissue under conditions of pigment cycling using a quasi‐continuous measuring spectrophotometer. An action spectrum shows 690–700 nm to be the most efficient wavelength range in this process. Difference spectra for the decay of intermediates maintained by 690 nm light show that, if the experiment is done at 0°C, only Pfr is formed. At – 11°C, intermediates decaying to Pr can also be observed. At – 20°C, Pr is produced as well as a pigment with peak absorption at 710nm. Kinetic analysis of intermediate decay at – 11°C reveals that at least two intermediates are maintained by 690 nm light. The level of intermediate maintained by incandescent light at 0°C was 25% higher in air than in nitrogen.
OPTICALLY DETECTED MAGNETIC RESONANCE OF THE TRYPTOPHAN PHOSPHORESCENT STATE IN NATIVE PROTEINS*
Authors: Zuclich J. , Schweitzer D. , Maki A. H.
Published: January 2008

Abstract— The phosphorescent triplet state of tryptophan has been studied by the method of optically detected magnetic resonance (ODMR) at pumped helium temperatures in zero magnetic field. Only one of the triplet sublevels is found to be significantly radiative; the other two decay radiationlessly. Although the phosphorescence and ODMR decay lifetimes are influenced by spin–lattice relaxation processes at T= 1.3°K, the lifetime of the radiative level can be estimated as approximately 2 s, whereas the lifetimes of the non–radiative levels are in excess of 10 s. Comparison of the ODMR signals and the phosphorescence spectra has been made for tryptophans in native proteins with the following results: the ODMR signals of the two types of tryptophan sites in horse liver alcohol dehydrogenase can be resolved due to a shift in the D and E values of the respective triplet states; binding of the substrate tri‐N‐acetylglucosamine to hen lysozyme leads to a considerable narrowing of the phosphorescence peaks and ODMR signals as well as to a shift in the E value of the triplet state.

The following tentative conclusions can be reached: the tryptophan triplet D and E values are measurably affected by the environment of the chromophore in the protein, as are the linewidths of the magnetic resonance transitions. The |E| value is reduced and the magnetic resonance linewidth is increased with increasing exposure of the tryptophan to hydroxylic solvent. Although a considerable part of the width of the magnetic resonance transition can be ascribed to a heterogeneity of environments in the sample, there appears to exist an intrinsic line–broadening process which at present is not understood.
LOW RESOLUTION OPTICAL SPECTROSCOPY OF RETINYL POLYENES: LOW LYING ELECTRONIC LEVELS AND SPECTRAL BROADNESS*
Authors: Christensen Ronald L. , Kohler Bryan E.
Published: January 2008

Abstract— Optical absorption and emission spectra of retinal, axerophtene, anhydrovitamin A, and 2,10‐dimethylundecapentaene in rigid glass matrixes at 77°K are presented. An interpretation of the observed spectra which provides a rationalization on the basis of electronic structure for the diffuse nature of the retinal spectrum is discussed. For the undecapentaene a weakly absorbing 1Ag state was found 3250 cm‐1 lower in energy than the level responsible for the strong visible absorption.
THERMAL REACTIVATION OF ULTRAVIOLET‐IRRADIATED ESCHERICHIA COLI: RELATIONSHIP TO RESPIRATION*
Authors: Swenson P. A. , Boyle J. M. , Schenley R. L.
Published: January 2008

Abstract— The effects of postirradiation incubation at 42°C on respiration and viability were studied in cells of ultraviolet (UV)‐irradiated Escherichia coli strains B/r and B. Prior to UV irradiation (52 J/m2 at 254 nm), the cells were grown in minimal liquid medium containing glycerol. When incubated in this liquid medium at 37°C, respiration of both strains is known to cease about an hour after UV irradiation, but is found to be continuous upon incubation at 42°C. In both strains, continuance of respiration is accompanied by an early increase in viability (‘liquid thermal reactivation’), but the increase for B/r (30‐fold) is 3 times that for strain B. The kinetic pattern of viability for B/r at 42°C is the same as that previously obtained for B/r and B when respiration is maintained by 5‐fluorouracil (FU) treatment. A different pattern is seen for Strain B at 42°C, but when FU and thermal treatments are given together, the FU type response dominates and the amount of reactivation obtained is about the same as with FU alone. This result suggests that in the absence of FU liquid thermal treatment prevents division of a potentially reactivable group of filaments in this lon‐ strain. The amount of liquid thermal reactivation (where plates are incubated at 37°C) is about equal to the amount of plate thermal reactivation (where irradiated cells, plated immediately after UV irradiation are incubated at 42°C). We infer that liquid and plate thermal reactivation involves the same group of cells.
PHOTOINDUCED ONE‐ELECTRON TRANSFER BETWEEN BACTERIOCHLOROPHYLL AND QUINONE IN ACETONE*
Authors: Harbour John R. , Tollin Gordon
Published: January 2008

Abstract— Illumination with red light of a degassed solution of bacteriochlorophyll and benzoquinone or ubiquinone in dry acetone at low temperatures (< ‐ 105°C) leads to the formation of the bacteriochlorophyll cation radical and the quinone anion radical, as detected by ESR spectroscopy. At temperatures around ‐ 110°C, the quinone radical signal corresponds to an emission of microwave radiation. These results are interpreted in terms of a one‐electron transfer from a spin‐polarized bacteriochlorophyll triplet state to the quinone, producing an anion radical which is predominantly in the upper spin state.
ABSORPTION AND EMISSION SPECTRAL PROPERTIES OF SOME 2‐PHENYLQUINOLINES AND RELATED FUSED SYSTEMS
Authors: Thorsett E. D. , Stermitz F. R. , O‘donnell C. M.
Published: January 2008

Abstract— A series of modified 2‐phenylquinolines were synthesized and their absorption and emission spectral properties measured in order to determine the effect of structural modifications on excited states. It was hoped that modifications would sufficiently change excited‐state properties so that similar structural modifications in 2‐phenylquinolinemethanols would negate the phototoxicity of these compounds. The excited states of 2‐(o‐hydroxyphenyl)quinoline, 11 H‐indeno[1,2‐b]quinoline, and l,4‐dimethyl‐5,6‐dihydrobenz[c]acridine proved to have properties different from those of normal 2‐phenylquinolines, and this effect was shown to be reflected in simple photochemistry of the dihydrobenzacridine. Absorption spectra provided information on conformational preferences for several of the derivatives.
ELECTRON AND ENERGY TRANSFER IN ILLUMINATED POROUS VYCOR GLASS
Authors: Wong P. K.
Published: January 2008

Abstract— Porous Vycor glass samples containing adsorbed molecules were illuminated at 77 K by a mercury lamp jacketed by a filter cutting off wavelengths below 250 nm. Oxygen or carbon dioxide on Vycor produces an asymmetric electron paramagnetic resonance (EPR) signal best described as holes trapped in the glass. Methyl bromide produces an identical EPR signal plus four other lines due to methyl radicals. Evidence is presented that the products result from excitonic energy transfer from the Vycor to the adsorbed materials. Triphenylamine (TPA) adsorbed on Vycor can also be photoionized by similar illumination, and the cation radical TPA+ can be stabilized at 77 K if an electron acceptor is also adsorbed. Attachment of the photoejected electron by carbon dioxide forms CO2‐, and that by methyl bromide leads to methyl radicals. The CH3 radical yield is dependent on the surface separation between the electron donor (TPA) and the acceptor (CH3Br). By monitoring the relative quantum yield of the methyl radicals as a function of distance separating the TPA and CH3Br, it is shown that the photoelectron is capable of migrating on the Vycor glass surface.
A STUDY OF LIGHT‐INDUCED ELECTRON PARAMAGNETIC RESONANCE SIGNALS IN WALLS OF MOSS SPORES AND POLLEN GRAINS
Authors: Chevallier Daniel
Published: January 2008

Abstract—Light‐induced EPR signals can be observed in moss spores and pollen grains. Their characteristics are studied in this paper. The modification of these signals during spore maturation or various physical and chemical treatments shows that they probably originate in the spore or pollen grain wall. This hypothesis is confirmed by the similarity between the spore (or isolated spore wall) absorption spectrum and the light‐induced signal action spectrum.
LASER PHOTOLYSIS OF 3‐METHYLLUMIFLAVIN
Authors: Visser A. J. W. G. , Ommen G. J. van , Ark G. van , Müller F. , Voorst J. D. W. van
Published: January 2008

Abstract—The pH dependence of the transient absorptions of 3‐methyllumiflavin has been investigated with laser photolysis in the nanosecond time range. Three different transient species (I, II and III) can be observed. The analysis of the decay curves shows that I and II can be ascribed to the optical absorption spectra of the lowest excited singlet and triplet states, respectively. Their appearance is not affected by a change of pH of the solution. The transient spectra due to species III have a decay which is dependent on pH. By comparison of these results with spectral data obtained with flavin dissolved in polymethylmethacrylate and with photochemical data reported in the literature, a structure for III is proposed which might explain the observed pH dependence.
PHYTOCHROME‐STIMULATED REGENERATION OF PROTOCHLOROPHYLL IN COTYLEDONS OF THE MUSTARD SEEDLING
Authors: Jabben M. , Masoner M. , Kasemir H. , Mohr H.
Published: January 2008

Abstract—It has been shown [Kasemir, H., U. Oberdorfer and H. Mohr, Photochem. Photobiol. (1973) 18, 481–486] that elimination of the lag phase of chlorophyll a (Chl) accumulation in continuous white light is due exclusively to the action of phytochrome (Pfr). In the present paper we show that the action of Pfr on the lag phase of Chl accumulation can be understood quantitatively as a consequence of the action of Pfr on the initial rate of protochlorophyll (PChl) regeneration. Disappearance of PChl (or formation of Chl) can be excluded as a control signal for the light‐mediated changes in rate of PChl regeneration. The Pfr control of PChl regeneration does not discriminate between PChl 650 and PChl 637. The action of Pfr on the PChl regeneration is a relatively fast process (time lag < 3 h). On the other hand, the effect remains stable over long periods (at least 24 h) in darkness.
INDUCTION OF SINGLE‐STRAND BREAKS (ALKALI‐LABILE BONDS) IN BACTERIAL AND PHAGE DNA BY NEAR UV (365 nm) RADIATION*
Authors: Tyrrell Rex M. , Ley Ronald D. , Webb Robert B.
Published: January 2008

Abstract—Irradiation at 365 nm results in the induction of approximately 2–4 times 10‐6 and 1‐2times 10‐6 single‐strand breaks (alkali‐labile bonds) per 108 daltons per J m‐2 in extracted phage T4 DNA and in Escherichia coli bacterial DNA, respectively. The rate of break induction in DNA of intact phage is approximately one‐fourth that for extracted phage DNA. 2‐aminoethylisothiouronium bromide‐HBr protects against break induction in both phage systems. No breaks are induced in the DNA of bacteria irradiated under anaerobic conditions over the dose range tested. Possible induction mechanisms are suggested. Consideration is given to the relative importance of pyrimidine dimers and single‐strand breaks in the bactericidal action of 365 nm radiation.
INDUCTION OF FREE RADICALS IN DNA BY PROFLAVINE AND VISIBLE LIGHT: INFLUENCE OF OXYGEN AND IONIC STRENGTH
Authors: Claire‐M  , Calberg‐Bacq  , Van de Vorst Albert
Published: January 2008

Abstract—The photosensitization of native DNA is observed as an induction of free radicals in the DNA moiety of proflavine‐DNA complexes. The intensity of the electron paramagnetic resonance spectra (at 77 K) is a measure of the number of free radicals present in frozen solutions of DNA‐proflavine complexes after irradiation with visible light (Λ > 320 nm). In the absence of O2, the photosensitization is significant but very low; it increases slightly with increasing NaCl ionic strength; it appears to be due to intercalated dye molecules and the qualitative analysis of the spectra obtained shows that mainly thymidine is involved. The reaction measured after saturation with O2 is the same as the reaction in air but is quantitatively higher; the free radicals observed are peroxides. This induction of free radicals appears to be due to the intercalated dye molecules, each molecule acting independently. The important observation is a very sharp and large (around a hundred‐fold) increase in the photosensitizing efficiency of the bound dye molecules occurring in NaCl between μ, # 0–25 and μ= 0–5 and in MgCl2 between μ# 0–01 and μ=0–1.
SIMPLE EXPLANATION OF THE MISSES IN THE COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION
Authors: Delrieu Marie‐Jose
Published: January 2008

Abstract—In the model of Forbush et at. (1971) the observed damping of the flash yield sequence of photosynthetic O2 evolution was related to a certain percentage of ‘misses’ (α; i.e. centers not converted). The possibility of a miss was supposed to be equal for all states S0.1,2,3. We propose a new model and a new recurrence law that gives better quantitative agreement with the O2 yield oscillations observed in Chlorella during a sequence of flashes. We find a better fit with all experimental results by assuming very unequal misses; the misses occur nearly exclusively on S2 (and also sometimes on S3). In the simpler case of only one miss on one state, half of S2 exists as an inactive form S2+‐ because it is in apparent equilibrium with pool A. The active form of S2 is converted to S3 in a flash and the unchanged inactive form S2+‐ explains the miss:

S
1
hv→S2+‐=S2hv→S3

(S2+‐ is a transition state between S1 to S2 associated with Q‐).

In the dark, the apparent equilibrium constant KA between pool A and Q (i.e. S0, S1 in the dark) is very large; this explains why there is no miss on these states. In light, the experimental value of KA between pool A and Q (i.e. S2, S3 in the light) is 1, and this explains why the misses are large for states S2, S3; i.e., S2+‐/S2‐ 1 and sometimes S3+‐/S3˜0–1.

This new model predicts that the total number of active states ΣSi=S0+S1+S2+S3 is an oscillating function of the flash number. This sum 2S, is also the number of trapping centers for excitons. As fluorescence is proportional to excitons that are not trapped, our model explains why the fluorescence oscillates as a function of the flash number. We find also that the initial rates of O2 evolution after (n ‐ 1) flashes vs the 02 yield of the nth flash are not exactly on a straight line, which also favors our model.
PHOTOREACTIVATION OF THYMINE‐STARVED ESCHERICHIA COLIBs‐1
Authors: Ghosh Nandini , Bhattacharjee Sukhendu B.
Published: January 2008

Abstract—Thymine starvation prior to 254 nm ultraviolet light (UV) exposures has been found to decrease the level of maximum photoreactivation in Escherichia coliBs‐1. The dark equilibrium level of photoreactivating enzyme‐substrate complexes was determined from the levels of photoreactivation obtained with exposures to single flashes of high‐intensity light. The kinetics indicate that photoreactivating enzyme concentration does not decrease as a result of thymine starvation. The UV sensitivities of normal and thymine‐starved cells are found to be the same. Photoreactivation by sequential flashes shows a lesser number of total photorepairable lesions in starved cells. It is concluded that thymine starvation renders a portion of the dimers inaccessible to the photoreactivating enzyme, thus lowering the level of maximum photoreactivation.
PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS IN DNA BY INDOLE DERIVATIVES AND TRYPTOPHAN‐CONTAINING PEPTIDES
Authors: Charlier Michel , Hélène Claude
Published: January 2008

Abstract—Indole derivatives, such as serotonin or the oligopeptide Lys‐Trp‐Lys, are able to photosensitize the splitting of thymine dimers in DNA. These indole derivatives have to be bound to DNA in order to efficiently photosensitize the splitting reaction. Serotonin may also induce the photosensitized formation of thymine‐containing dimers in native DNA. In this case, an equilibrium is reached when 5 per cent of the total thymines are dimerized. In both cases (splitting and dimer formation), the formation of electron donor‐acceptor complexes between either dimers or two adjacent thymine monomers, and excited indole rings, could be an intermediate step in the reactions. Thymine‐dimer splitting would then result from an electron transfer reaction involving the indole ring as the electron donor. These results are discussed with respect to the mechanism of action of the photoreactivating enzyme.
DERIVATION OF PHOTOCHROME ABSORPTION SPECTRA FROM ABSORBANCE DIFFERENCE MEASUREMENTS
Authors: Stavenga D. G.
Published: January 2008

Abstract— A method is presented with the aid of which the absorption spectrum of at least one of the two states of a photochrome can be calculated from experimental difference spectra. It is shown that the method can be applied to (biological) photochromes contained in inhomogeneous media together with absorbing, non‐photochromic impurities. This medium may have the properties of an optical waveguide.
LUMINESCENCE PROPERTIES AND RELATED PHOTOCHEMISTRY OF 4‐AMINO‐2‐METHOXYPYRIMIDINE
Authors: Szabo A. G. , Berens K. B.
Published: January 2008

Abstract— The luminescence properties of 4‐amino‐2‐methoxypyrimidine, I, have been studied in several solvents. These studies indicate that the photochemical reaction of I with dihydrogen phosphate buffer proceeds via an intermediate derived from the fluorescent singlet excited state of I.
THE QUENCHING OF SINGLET OXYGEN BY AMINO ACIDS AND PROTEINS
Authors: Matheson I. B. C. , Etheridge R. D. , Kratowich Nancy R. , Lee John
Published: January 2008

Abstract— The physical quenching of singlet molecular oxygen (1Δg) by amino acids and proteins in D2O solution has been measured by their inhibition of the rate of singlet oxygen oxidation of the bilirubin anion. Steady‐state singlet oxygen concentrations are produced by irradiating the oxygenated solution with the 1–06 μm output of a Nd‐YAG laser, which absorbs directly in the electronic transition 1Δg+ 1v→3Σg‐. The rate of quenching by most of the proteins studied is approximated by the sum of the quenching rates of their amino acids histidine, tryptophan and methionine, which implies that these amino acids in the protein structure are all about equally accessible to the singlet oxygen. The quenching constants differ from those obtained by the ruby‐laser methylene‐blue‐photosensitized method of generating singlet oxygen, or from the results of steady‐state methylene‐blue‐photosensitized oxidation, where singlet oxygen is assumed to be the main reactive species. The singlet oxygen quenching rates in D2O, pD 8, are (107? mol‐1 s‐1): alanine 0–2, methionine 3, tryptophan 9, histidine 17, carbonic anhydrase 85, lysozyme 150, superoxide dismutase 260, aposuperoxide dismutase 250.
MECHANISM OF PHOTOREDUCTION OF THIAZINE DYES BY EDTA STUDIED BY FLASH PHOTOLYSIS—III CONSEQUENCES OF A NEWLY FOUND pKT OF THIONINE ON THE MECHANISM IN BASIC SOLUTIONS
Authors: Bonneau Roland , Pereyre Josette
Published: January 2008

Abstract— Evidence for an acid‐base equilibrium between the neutral and monocationic forms of the triplet state of thionine, 3T and 3TH+ (pKT# 8–9) has been found. This equilibrium, which has no counterpart in the methylene blue system can explain the different behaviours of these two similar dyes concerning their photoreduction by ethylene diamine tetracetic acid (EDTA) in basic solutions. With reasonable assumptions about the reactivity of the various species present in solution, it is now possible to calculate over the whole pH range the quantum yield of semireduced dye formation φs, which, according to the previously proposed mechanism, must be proportional to the overall photoreduction quantum yield φR. The very good fit between the calculated curve φs =f(pH) and the experimental one φR =f(pH) for both dyes strongly supports the proposed mechanism.
ANALYSIS OF THE BINDING OF PHYTOCHROME TO PARTICULATE FRACTIONS
Authors: Schäfer Eberhard
Published: January 2008

Abstract— The binding of phytochrome to receptor sites in a particulate fraction of maize coleoptiles has been studied as a function of the level of far‐red‐absorbing phytochrome (Pfr) offered in vivo and in vitro. Evidence is presented that the binding is cooperative. The degree of cooperativity expressed by the Hill coefficient of the binding function is the same (1–6) both in vivo and in vitro, whereas the Hill coefficient of the state function in vivo is significantly higher (2‐1). The highest Hill coefficient (3–5) was found for the in vitro binding function in squash hooks.
PHYTOENE AS A PROTECTIVE AGENT AGAINST SUNBURN (>280nm) RADIATION IN GUINEA PIGS
Authors: Mathews‐Roth Micheline M. , Pathak Madhu A.
Published: January 2008

Abstract— Phytoene, the colorless triene precursor of β‐carotene (17 mg/g body weight) or a placebo was given to guinea pigs by daily intraperitoneal injection for 14 days, after which the animals were exposed to radiation (> 280 nm). It was found that the animals receiving phytoene developed significantly less erythema to the radiation than did the animals receiving placebo.
INDUCED DEACTIVATION OF NAPHTHALENE TRIPLETS BY CIS‐PIPERYLENE
Authors: Kelly John R. , Gupta Amitava , Hammond George S.
Published: January 2008

Abstract— Interaction of naphthalene triplets with trans‐piperylene leads to triplet energy transfer with unit efficiency. When cis‐piperylene is used as a quencher of naphthalene triplets, the efficiency of triplet energy transfer is found to be 0–76 ± 004. The rest of the quenching encounters in this case lead to deactivation of naphthalene triplets, without energy transfer.
VISUAL PIGMENTS‐V. GROUND AND EXCITED‐STATE ACID DISSOCIATION CONSTANTS OF PROTONATED ALL‐TRANS RETINAL SCHIFF BASE AND CORRELATION WITH THEORY*
Authors: Schaffer Arnold M. , Yamaoka Tsuguo , Becker Ralph S.
Published: January 2008

Abstract— The acid dissociation constants of protonated all‐trans retinal Schiff base (SB‐H+) in a 50% water‐methanol solution at 0°C is 6–95 for the ground state and nominally 16–65 for the first excited singlet state, with a potential range of ˜ 12–21. These values are in qualitative agreement with the results of semiempirical MO calculations, which indicate that the total charge density on nitrogen is greater in the first excited singlet than in the ground state (QN* > QN). However, pertinent to vision, CNDO/2 calculations on all‐trans and 11‐cis Schiff base and SB‐H+ indicate that, for torsional angles of approximately 80–100° around the 11–12 double bond, QN* < QN. This result suggests that it may be possible for the proton to come off the imine nitrogen during isomerization from 11 ‐cis SB‐H+ to all‐trans SB‐H+. The potential consequence of this during isomerization of rhodopsin is the initiation of unfolding of the protein opsin.
STIMULATION OF THE SHIBATA SHIFT BY PHOTOCHROME IN THE COTYLEDONS OF THE MUSTARD SEEDLING SINAPIS ALBA L.
Authors: Jabben M. , Mohr H.
Published: January 2008

Abstract— In the cotyledons of the mustard seedling Sinapis alba L. the duration of the Shibata shift can be greatly shortened by a pretreatment with light pulses prior to the protochlorophyllide– chloro‐phyllide a photoconversion. It was shown that the light pulses act through photochrome (Pfr). Since reversibility of a red light pulse induction by a far‐red light pulse is rapidly lost (within 2 min) it is concluded that at least the initial action of Pfr occurs rapidly in this response. On the other hand, the effect of a red light pulse on the rate of protochlorophyll regeneration in the mustard seedling cotyledons is fully reversible by a far‐red light pulse for more than 5 min. It is concluded that control of protochlorophyll regeneration and control of the Shibata shift by phytochrome cannot be consequences of the same initial action of Pfr Apparently Pfr controls both phenomena independently.
CHLOROPHYLL SENSITIZED CHARGE SEPARATION IN PHOSPHOLIPID VESICLES
Authors: Tomkiewicz M. , Corker G. A.
Published: January 2008

Abstract— Chlorophyll (chl) a in sonicated egg yolk lecithin vesicles, even with local concentrations of 0.1 M, exists in its monomeric form as is evident by the absorption, circular dichroic and EPR spectra of such suspensions. With the water soluble oxidants, K3Fe(CN)6 or SmCl3, it is possible to photoproduce the chl cation radical. With K3Fe(CN)6 as acceptor the formation and decay kinetics can be explained by a second order process influenced by diffusion of the water soluble components in this heterogenous system. With the exception of an iron‐sulfur protein isolated from Rhodospirillum ruhrum, we have not detected a photochemical reaction of chl with various iron‐sulfur proteins or ubiquinone.
THE EFFECT OF POTASSIUM IODIDE ON PHOTOPHOBIC RESPONSES IN EUGLENA: EVIDENCE FOR TWO PHOTORECEPTOR PIGMENTS*
Authors: Mikolajczyk Ewa , Diehn Bodo
Published: January 2008

Abstract— Potassium iodide, a quencher of flavin fluorescence, inhibits the shock reaction which Euglena experiences upon a sudden decrease in light intensity (inverse photophobic response) completely at a concentration of 150 mM. The rate of swimming of the cells at the same concentration of KI is reduced to 30% of the control. The direct photophobic response, a shock reaction which appears identical but occurs upon an increase in light intensity, is unaffected by KI as is negative phototaxis of Euglena. It is concluded that a non‐flavin pigment system mediates photoreception for the direct photophobic response and negative phototaxis.
ON THE PHYSIOLOGICAL SIGNIFICANCE OF DARK REVERSION OF PHYTOCHROME IN THE MUSTARD SEEDLING
Authors: Oelze‐Karow H. , Scháfer E. , Mohr H.
Published: January 2008

Abstract—We present physiological evidence using the threshold control of lipoxygenase synthesis† by Pfr in the mustard seedling (LOG response) that there is no dark reversion of phytochrome

which would be relevant for this response. Such Ptr which can be detected with the lipoxygenase response disappears exclusively through degradation with a half‐life of 45 min at 25°C. De novo synthesis of P*r in the hypocotylar hook takes place at a constant rate (zero order rate constant) irrespective of the level of Pr or P*tot, i.e. there is no detectable feedback control of Pr synthesis during the period of experimentation. The data of the present paper are consistent with a quantitative phytochrome model (Scheme 1) which has been advanced and treated quantitatively in the companion paper (Oelze‐Karow and Mohr, 1976).
INTERACTION OF DISULFIDE GROUPS WITH NUCLEIC ACID BASES
Authors: Montenay‐Garestier Thérèse , Brun Francine , Hélène Claude
Published: January 2008

Abstract— Low temperature luminescence studies have provided evidence for interactions between the disulfide group of cystamine and adenine bases in cystamine‐poly(A) complexes and in cystamine‐adenosine aggregates. A quenching of adenine phosphorescence by cystamine was observed. At room temperature complex formation between cystamine and poly(A) was followed by proton magnetic resonance, absorption spectrophotometry and fluorescence using competition with a fluorescent peptide to monitor the binding process. These base‐disulfide interactions could be involved in the photochemistry of protein‐nucleic acid complexes.
Pfr PHYTOCHROME AND SUCROSE REQUIREMENT FOR RHYTHMIC LEAFLET MOVEMENT IN ALBIZZIA
Authors: Satter Ruth L. , Applewhite Philip B. , Chaudhri Javade , Galston Arthur W.
Published: January 2008

Abstract— Albizzia leaflets open and close with a circadian periodicity without damping during extended dark periods if supplied with sucrose and irradiated with red each rhythmic cycle. In the absence of a carbohydrate source, the rhythm damps irrespective of phytochrome status and the differential effects of red and far‐red light treatments tend to disappear after 2 or 3 cycles. The rhythm also damps if leaflets are exposed to red only once, or if they are exposed to far‐red once or cyclically. Sucrose does not prevent such damping but affects the stable angle assumed; the rhythm damps in the closed position in the presence of sucrose, and in the partially open position in its absence. Sucrose appears to have two distinct effects; it interacts with Pfr to promote manifestation of the rhythm and it reduces the average angle, whether the Pfr level is low or high.
DEVELOPMENT OF THERMOLUMINESCENCE BANDS DURING GREENING OF WHEAT LEAVES UNDER CONTINUOUS AND INTERMITTENT ILLUMINATION
Authors: Inoue Yorinao , Ichikawa Tetsuo , Shibata Kazuo
Published: January 2008

Abstract— Mature wheat leaves excited by 1‐min illumination at a low temperature of ‐60° C showed five thermoluminescence bands at ‐45, ‐10, +25, +40 and +55° C (denoted as Zu, A, B1 B2 and C bands, respectively). The development of these bands during greening of etiolated wheat leaves under continuous and intermittent illumination was investigated, and the following results were obtained. (1) Etiolated leaves showed only the C band. When these leaves were greened under continuous light, the B1 and B2 bands appeared at 3 h and the Zu band appeared at 10 h. The B1 and B2 bands were intensified during prolonged greening under continuous illumination to be the strong bands observed for mature leaves. The A band and the group of B1 and B2 bands were alternative: Similar experiments by excitation of thermoluminescence at ‐20° C showed the development of the A band instead of these B1 and B1 bands. (2) When the etiolated leaves were greened under intermittent illumination (1‐ms light + 5‐min dark), the Zu band first appeared after 5 h of illumination (60 flashes) and was gradually intensified during further illumination with 340 flashes but, interestingly, neither the B1 nor the B2 band appeared even after 24–28 h of illumination with 280–340 flashes. (3) On exposure of such leaves greened under intermittent illumination to continuous light, the B1 and B2 bands were rapidly developed. The appearance of these bands was accompanied by the generation of the Hill activity (DCIP photoreduction with water as electron donor). (4) These results were discussed in relation to the previous study on photoactivation of the latent water‐splitting system accumulated in the leaves greened under intermittent illumination. It was deduced that the structure responsible for the A band or the group of B1 and B2 bands is involved in the evolution of oxygen in chloroplasts, and probably involves cations of the Mn2+ catalyst generated by the action of light.
THE ROLE OF SOLAR ULTRAVIOLET RADIATION IN ‘NATURAL’ WATER PURIFICATION
Authors: Calkins John , Buckles James D. , Moeller John R.
Published: January 2008

Abstract— The concentration of Escherichia coli in the input and output of a tertiary wastewater system (4 lagoons) has been monitored over an 11 month period. The integrated flux of biologically active solar ultraviolet (UV) radiation was measured during this period. By also determining (1) the effective temperature in the system, (2) the growth rate of E. coli at the effective temperature, (3) the penetration of the solar UV into the lagoons, (4) the dose‐response relation for killing of E. coli by UV and (5) the retention time of water in the system, it is possible to compare the ‘die off’ expected from solar UV exposure to the actual ‘die off’ observed for different batches of water.

The observed killing of E. coli was quite close to the values calculated, considering the numerous factors involved. Solar UV light would thus seem to be a very important factor in the natural purification of water. Because each successful species must possess characteristics (physiological or behavioral) which provide adequate resistance to solar UV, the ecological role of solar UV radiation has not been widely appreciated.
LIGHT‐INDUCED ABSORBANCE CHANGES IN CELL‐FREE EXTRACTS OF NEUROSPORA CRASSA*
Authors: Schmidt W. , Butler W. L.
Published: January 2008

Abstract— The mycelium of Neurospora crassa was ground and extracted with buffer and separated into a soluble supernatant fraction and a particulate fraction by centrifugation. Both fractions were examined for light‐induced absorbance changes. Irradiation of the supernatant fraction caused a reversible photooxidation of cytochrome c which was inhibited by sodium azide or by dialysis. The action spectrum for the photooxidation showed that the response was mediated by an endogenous flavin. The photooxidation of cytochrome c, lost by dialysis, could be restored by adding flavin mononucleotide. Irradiation of the particulate fraction with blue light caused a reversible photoreduction of cytochrome c and cytochrome oxidase and, in some samples, of cytochrome b as well. The supernatant fraction showed photooxidation of cytochrome c rather than the more usual photoreductive changes because of the presence of super‐oxide dismutase activity.
ELECTRONIC PROCESSES AND PHOTOELECTRIC ASPECTS OF BILAYER LIPID MEMBRANES
Authors: Tien H. Ti
Published: January 2008

Abstract— Owing to the complexity of biological membranes, many model systems have been studied in order to gain insight into the molecular mechanism of specific functions. One such model membrane extensively investigated in the past decade is the so‐called bilayer lipid membrane (BLM). With suitable modifications, a BLM less than 100 A thick separating two aqueous solutions has been used as a model for a variety of biological membranes. This paper is devoted to a review of the properties and electronic processes of modified BLM.

Recent experiments using these membranes which contain photosynthetic pigments or dyes have demonstrated that, upon illumination, an EMF and a current can be generated. The connection between the photoelectric BLM and light‐sensitive biological membranes and the rationale for this work are described.

Additionally, the effects of physical chemical parameters such as electric field, temperature, light intensity, duration of illumination and chemical agents (electron acceptors, donors, uncouplers, etc.) on the photoresponses of BLM are discussed. Other results indicate that BLM containing photoactive compounds behave similar to that of a silicon solar cell with one side of the membrane reducing and the other side oxidizing. The transverse pathway for the electron across the BLM could be provided by carotenoids such as β‐carotene. Photoelectric BLM of this type represents a unique kind of energy transducing system and may well be useful in the conversion of solar energy into electricity and/or other forms of energy.
PHOTOSENSITIVE BILAYER MEMBRANES AS MODEL SYSTEMS FOR PHOTOBIOLOGICAL PROCESSES
Authors: Berns Donald S.
Published: January 2008

Abstract— Photobiological processes such as photosynthesis, photomorphogenesis, photomovement, and photoreception are all associated with the membranous portions of cells. The unique properties of membrane surfaces are apparently required to achieve biologically relevant energy transduction and photocontrol phenomena and consequently the use of model membrane systems is suggested as an advantageous approach to elucidation of the important physical and chemical processes involved. Black lipid membrane (BLM) and liposome techniques are critically reviewed as preferred techniques for constructing and manipulating lipid bilayers. The lipid bilayer is considered to be the basic foundation for biological membrane models, and specific physical phenomena observed with the bilayers and their biological ramifications are analyzed. Light‐stimulated polarization of the membrane and electron transfer across the bilayer are viewed as appropriate analogs of vision and photosynthesis, respectively. Bilayer‐adsorbed dye experiments are the simplest systems explored that exhibit polarization and charge transfer across the membrane. Chloroplast extract BLM experiments are cited as an example of the light‐stimulated transfer of electrons across the membrane under the influence of a preexisting redox gradient. Biliprotein (phycocyanin or phycoerythrin) on one side of the chloroplast extract membrane permits the direction of electron flow across the membrane so that a redox gradient is created in a manner truly analogous to photosynthesis. The potential for solar energy conversion from such membranes is explicitly considered utilizing a schematic photoelectrochemical cell. Model membranes containing bacterial rhodopsin and phytochrome represent examples of ionic gradients that result in biological energy transduction. Studies of membranes that exhibit transient photoeffects are considered potentially relevant for the elucidation of phototaxis. The analysis of many properties of photosensitive membranes is greatly aided by the use of appropriate theoretical models. It is apparent that there is a great potential for the application of photosensitive model membranes in many research areas involving complex photobiological phenomena and novel methods for solar energy conversion.
EXCITED STATE INTERACTIONS OF 7‐AZAINDOLE WITH ALCOHOL AND WATER
Authors: Avouris Phaedon , Yang Li L. , El‐Bayoumi M. Ashraf
Published: January 2008

Abstract— The fluorescence spectrum of 7‐azaindole in alcohol is composed of two fluorescence bands. Effects of pH, temperature and solvent deuteration on the fluorescence spectra and quantum yields of 7‐azaindole and other model compounds in ethanol and in water are reported. The long wavelength band arises from a tautomeric species formed in an adiabatic photoreaction involving double proton transfer between one molecule of 7‐azaindole and one molecule of alcohol.

The fluorescence spectrum of 7‐azaindole in water is composed of only one band, but the emission is weak and shows a large solvent isotope effect. The possibility of a double proton transfer reaction between 7‐azaindole and water is discussed.
ULTRAVIOLET RADIATION AND SKIN CANCER: IN MICE AND MEN*
Authors: Blum Harold F.
Published: January 2008

Abstract— In both mice and men the effects of repeated exposures to UVR accumulate. Unresolvable uncertainty pertains in both cases. Incidence of skin cancer in human populations may be influenced by various factors that cannot be separately evaluated. Uncertainty of predictions regarding the effect of increased UVR due to diminution of stratospheric ozone cover is discussed.