bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOCHEMISTRY AND PHOTOBIOLOGY OF PSORALENS
Authors: Song Pill‐Soon , Tapley Kenneth J.
Published: January 2008

Abstract— The photochemistry and photobiology of psoralens have been rcvicwed on the basis of selected literature. In addition to the well establishcd photoaddition of psoralens to DNA. photoreac‐tions involving RNA. tRNA and proteins warrant further studies. Although thymine seems to be one of the predominant bases for the psoralen photocycloaddition in DNA. photoreactions of other bases such as adenine and the mechanisms other than cycloaddition should also be investigated in order to fully assess the specificity of psoralen photoreactions and their application BS a probe for biopolymer structure and as a tool for photobiological studies of microorganisms. The relativc photobiological importance of monoaddition vs crosslinking of psoralens to nucleic acids also remains to be fully elucidated.
AN ULTRAVIOLET RADIATION DOSIMETER BASED ON THE PHOTOSENSITISING DRUG, NALIDIXIC ACID
Authors: Tate T. J. , Diffey B. L. , Davis A.
Published: January 2008

Abstract— The optical properties of a polymer film which incorporates the photosensitising drug, nalidixic acid, as the chromophore are described. The film is shown to be suitable as a UV dosimeter in the wavelength range 280–350 nm. It is suggested that the film could be used as a biological monitor in subjects photosensitised with 8‐methoxypsoralen. as in the photochemotherapy of psoriasis.
DNA DAMAGE AND REPAIR: INDUCTION AND REMOVAL OF THYMINE DIMERS IN ULTRAVIOLET LIGHT IRRADIATED INTACT WATER PLANTS
Authors: Degani N. , Ben‐Hur E. , Riklis E.
Published: January 2008

Abstract— The production of UV‐induced thymine dimers and their fate upon post‐irradiation incubation in the dark was studied in DNA of the intact water plants Wolffia microscopica and Spirodela polyrhiza. The results demonstrate production of thymine dimers, and the ability of the plant cells to remove the dimers from their DNA. The rate of removal is rapid during the first few h of post‐irradiation incubation in the dark. It continues at a slower rate for the next 24–48 h, at which time it is essentially complete. The disappearance of thymine dimers in light or in the dark is analogous to the well‐known processes in other biological systems, namely, photoreactivation and dark excision.
ACTION SPECTRA FOR KILLING NON‐DIVIDING NORMAL HUMAN AND XERODERMA PIGMENTOSUM CELLS
Authors: Kantor G. J. , Sutherland J. C. , Setlow R. B.
Published: January 2008

Abstract— Non‐dividing human cells degenerate and eventually detach from a culture vessel surface when exposed to UV light. Action spectra for this kind of cell inactivation were determined using eight monochromatic wavelengths from 240 to 313 nm and both a normal DNA excision‐repair‐proficient strain and a repair‐deficient Xeroderma pigmentosum (XP12BE) strain. The action spectra for both strains have similar shapes with a broad peak between 254 and 280 nm followed by a steep decline at wavelengths greater than 280 nm. The relative action spectra are similar to those for inactivation of reproductive capacity and pyrimidine dimer formation in rodent cells suggesting that the critical target and critical damage for inactivation of non‐dividing human cells is DNA and damage to DNA, respectively. Normal repair‐proficient cells are 5–7 times more resistant at all wavelengths, based on a comparison of Do values, than repair‐deficient XP12BE cells, supporting the conclusion that the inactivating damage at all wavelengths is to DNA.
DECREASED PHOTO‐INDUCED MUTAGENICITY OF MONO‐FUNCTIONAL AS OPPOSED TO BI‐FUNCTIONAL FUROCOUMARINS IN YEAST
Authors: Averbeck D. , Moustacchi E.
Published: January 2008

Abstract— The photoaddition of mono‐functional furocoumarins such as 5,7‐dimethoxycoumarin, angelicin and 3‐carbethoxypsoralen induces as a function of dose or of survival a much lower frequency of reverse mutations in Saccharomyces cerevisiae than the two bi‐functional furocoumarins, psoralen and 8‐methoxypsoralen. From this, it is suggested that bi‐functional lesions, i.e. DNA interstrand cross‐links, may be repaired in yeast by an error‐prone process.
KINETIC AND SPECTROSCOPIC FEATURES OF SOME CAROTENOID TRIPLET STATES: SENSITIZATION BY SINGLET OXYGEN
Authors: Rodgers Michael A. J. , Bates Anne L.
Published: January 2008

Abstract— Triplet‐triplet absorption spectra of a series of carotenoid pigments in benzene solution have been determined by pulse radiolysis experiments. The natural lifetimes in deaerated solution have also been measured. They fall in the range 2–10 µs as found for other carotenoids under similar conditions. Pulsed laser (337 nm) excitation of benzene solutions containing oxygen, carotenoid and a photosensitized molecule (anthracene) showed the generation of absorption spectra of the triplet states. These absorptions decayed by first order kinetics in such a way as to indicate that they were formed in reactions with singlet oxygen, itself generated by interaction with the anthracene triplet state. Bimolecular rate constants for energy transfer from O*2 (1△g), to carotenoid have been evaluated.
EXCITATION AND ADAPTATION IN LIMULUS VENTRAL PHOTORECEPTORS
Authors: Brown Joel E.
Published: January 2008

Abstract— Currents induced by illumination can be recorded from Limulus ventral photoreceptors by a voltage‐clamp technique. Several assumptions underlying the analysis of these currents are discussed and recent experiments designed to examine these assumptions are reviewed.
HETEROEXCIMER SYSTEMS IN AQUEOUS MICELLAR SOLUTIONS
Authors: Waka Yasuhiro , Hamamoto Kimihiko , Mataga Noboru
Published: January 2008

Abstract—

Fluorescence quenching due to charge transfer interactions in the excited state has been studied in aqueous micellar solutions. Fluorescers used were pyrene, various pyrene derivatives and several other conjugated π‐electronic systems, and quenchers were N, N‐dimethylaniline, N. N‐dimethylaniline sulfonate, dicyanobenzenes and cyanopyridine. Strong quenching of the aromatic hydrocarbon fluorescence with dimethylanilines as well as dicyanobenzenes was observed, while no heteroexcimer emission was detected. The dependences of relative fluorescence yield and fluorescence decay curve upon the quencher concentration have been explained with equations derived on the basis of a simple model. Based on the obtained results, some discussions were given on the nature of micelle ‘interior’ and micelle ‘surface’.
ACTINIC EFFECTS OF LIGHT AND BIOLOGICAL IMPLICATIONS*
Authors: Thorington Luke
Published: January 2008

Abstract—

Illumination is not the only, nor even the most important, benefit of the earth's complement of solar optical radiation; life itself is physically and chemically balanced between effects of too much and too little of it. Chemically, the effects range from the synthesis of ozone in the stratosphere and biochemicals in the biosphere, to the influence or control of complete living organisms, including humans. This actinism depends upon the spectrum, irradiancc and modulation, or SIAM. of the natural optical radiation environment. By manipulating the SIAM of artificially produced actinic optical radiation, profound effects are now routinely induced in people, animals and plants. The next logical application for this SIAM technology is in the environments where people themselves live and work. Meanwhile, it should be recognized that artificial illumination, as presently prescribed for these environments, is actinic.
TEMPERATURE‐SENSITIVITY OF LIGHT‐INDUCED PHASE SHIFTING OF THE CIRCADIAN CLOCK OF NEUROSPORA
Authors: Nakashima Hideaki , Feldman Jerry F.
Published: January 2008

Abstract—

Two new mutants of Neurospora craasa, designated hth‐1 and hth‐2, have been isolated which allow clear expression of the circadian conidiation rhythm at high temperature (36°C). Both strains showed single‐gene segregation and produced similar phenotypes but mapped to different genetic loci. These mutants allowed an analysis of the effect of temperature on (1) light‐induced phase‐shifting of the circadian rhythm, (2) period length of rhythm, and (3) growth rate. The amplitude of the phase response curve to light was drastically reduced as the temperature was increased from 25°C to 34°C. Phase advances were decreased more than phase delays. As previously reported (Sargent et al., 1966), the period length of the rhythm is temperature‐compensated below 30°C (Q10˜ 1) but not well‐compensated above 30°C (Q10 1.3–1.7). The decrease in amplitude of the light phase response curve occurred in both temperature ranges. Furthermore, the Q10 value was lowered by addition of yeast extract in the high temperature range but not in the low range. Q10 values for growth rate also differed in these strains both in the low temperature range (25–30°C) and the high temperature range (30–34°C).
ON THE STATE OF CHROMOPHORE PROTONATION IN RHODOPSIN: IMPLICATION FOR PRIMARY PHOTOCHEMISTRY IN VISUAL PIGMENTS
Authors: Narva D. , Callender R. H.
Published: January 2008

Abstract—

Resonance Raman multicomponent spectra of bovine rhodopsin, isorhodopsin, and bathorhodopsin are obtained at low temperature. Application of the double beam, ‘pump‐probe’ technique allows an extraction of the rhodopsin and bathorhodopsin spectra in both protonated and deuterated media. Our results show that the Schiff bases of both rhodopsin and bathorhodopsin are fully protonated and the degree of protonation is unaffected by the rhodopsin‐bathorhodopsin transformation. Further, the data support the concept or cis‐trans isomerization as occurring in this transition. The effect of these results on various models for the primary photochemical event in vision is discussed.
LIGHT INDUCED INTERACTIONS OF BENZO[a]PYRENE WITH CARBOXYLIC ACIDS*
Authors: Logani Mahendra K. , Austin Willodene A. , Davies Ronald E.
Published: January 2008

Abstract The in vitro photochemical behaviour of benzo[a]pyrene (BP) in presence of short and long chain carboxylic acids is studied. The direct irradiation (295–400 or 320–400 nm) of BP in solution in the presence of saturated carboxylic acids destroys more than 70% of this carcinogen in 72 h with a 150 W Xe arc lamp. Consumption of BP alone under similar conditions is less than 10%. The principal product resulting from direct interaction of BP with carboxylic acids is characterized as 6‐acyloxybenzo[a]pyrene by means of UV, IR, NMR and mass spectroscopy. The other pathways of destruction may involve polymerization. Saturated fatty acids are shown to favour photoacyloxyation, while unsaturated fatty acids appear to facilitate polymerization of BP. The effect of different factors, such as the carboxylic acid involved, solvent, and wavelength on photoacyloxylation reaction as well as on the consumption of BP is discussed. Photoinduced interaction of BP with carboxylic acids seems to involve radical cation as well as free radicals of the hydrocarbon. Biological properties of BP esters in terms of primary irritancy and carcinogenic activity have also been tested by mouse skin assay. Both long and short chain esters do not show any carcinogenic activity; conversely, long chain esters are shown to be more severe irritants as compared to short chain esters or BP.
9‐CIS, 11‐CIS‐RETINAL* FROM DIRECT IRRADIATION OF ALL‐TRANS‐RETINAL. NEW GEOMETRIC ISOMERS OF VITAMIN A AND CAROTENOIDS 9
Authors: Denny Marlene , Chun Melissa , Liu R. S. H.
Published: January 2008

Abstract The irradiation mixture of all‐trans‐retinal in acetonitrile was shown to contain four cis,cis isomers as well as the four cis isomers reported earlier. The relatively new 9‐cis, 11‐cis‐retinal was isolated and characterized.
VARIATIONS IN THE ERYTHEMAL RESPONSE OF GUINEA–PIG SKIN†
Authors: Morison Warwick L. , Parrish John A. , Anderson R. Rox , Harrist Terence J.
Published: January 2008

Abstract In albino guinea‐pigs marked differences were found in the erythemal responses at different sites of the back. The minimal erythemal dose (MED) to UVB (290‐320 nm) radiation of the upper part of the back was less than 20% of the MED of the lower part of the back. This difference was not due to variations in the thickness of the skin or optical transmission by the epidermis.
DNA DAMAGE IN RAT 9L CELLS TREATED WITH 8‐METHOXYPSORALEN AND NEAR‐UV LIGHT ASSAYED BY VISCOELASTOMETRY AND S1 NUCLEASE
Authors: Shafer Richard H. , Chase Eric S. , Wun Kai‐Lam W.
Published: January 2008

–The techniques of viscoelastometry and S1 nuclease digestion were applied to the analysis of DNA damage in rat 9L cells treated with the combination of 8‐MOP (8‐methoxysporalen) and near‐UV light. Treatment of cells with near‐UV light alone resulted in a decrease in the viscoelastic retardation time under both denaturing and nondenaturing conditons. Exposure of cells to 8‐MOP alone yielded a maximum in the plot of retardation time vs dose under nondenaturing conditions, similar to that found with ionizing radition. This observation suggests that treatment with 8‐MOP alone leads to DNA strand breaks. Viscoelastic analysis of cell lysates under denaturing conditions demonstrated that treatment of cells with 8‐MOP and UV radiation led to substantial increases in both the viscoelastic retardation time and recoil, consistent with formation of DNA interstrand cross‐links. Viscoelastic analysis of cell lysates under nondenaturing conditions showed that exposure to long wavelength UV light in the presence of 8‐MOP produced a decrease in retardation time. This decrease reflects the combined effect of strand breaks and interstrand cross‐links. Results from the S1 nuclease assay confirmed these observations and permitted quantitation of DNA damage arising from single‐strand breaks and DNA interstrand crosslinks. The importance of including the effect of strand breaks in the quantitation of cross‐link formation is discussed.
ENERGY TRANSFER FROM CHLOROPHYLL b TO CHLOROPHYLL a IN A HYDROPHOBIC MODEL SYSTEM
Authors: Eissler R. L. , Dutton H. J.
Published: January 2008

Abstract— Chlorophyll a and chlorophyll b purified by high‐performance liquid chromatography (HPLC) were subsequently adsorbed on the surface of a pellicular reverse phase packing normally used in HPLC. The granule surface is reacted with octadecyl groups and furnishes an hydrophobic substrate for pigment adsorption. Reflectance spectra of chlorophyll a and chlorophyll b, each adsorbed at average spacings of about 11 nm2 per molecule, had red region maxima at 664 and 643nm respectively. Fluorescence excitation spectra for 740nm emission from these surfaces peaked at about 420nm for chlorophyll a and 460nm for chlorophyll b. Adsorbed pigments excited at either of the two wave lengths had a single fluorescence emission peak at 683nm for chlorophyll a and at 664nm for chlorophyll b. A surface having both pigments adsorbed in approximately equal amounts with an overall average spacing of about 5.6nm2 per molecule also had peaks at 420 and 460nm in the excitation spectrum. However, excitation of adsorbed molecules on this (latter) surface, at either 420 or 460nm, produced emission with the single chlorophyll a peak at 683nm. It is concluded that, under the conditions of our experiment, exciting adsorbed chlorophyll b contributes strongly to emission from adsorbed chlorophyll a.
SPONTANEOUS AGGREGATION OF BACTERIORHODOPSIN IN BROWN MEMBRANE
Authors: Hwang S.‐B. , Tseng Y.‐W. , Stoeckenius W.
Published: January 2008

Abstract— Halobacterium halobium cells grown in nicotine‐containing medium synthesize bacterio‐opsin (bO) but little bacteriorhod‐opsin (bR) because nicotine inhibits retinal synthesis. In nicotine‐grown cells, bacterio‐opsin is found in a specific cell membrane fraction, the brown membrane (b.m.), which consists mainly of small round sheets. Freeze‐fracture of isolated brown membrane reveals a dense particle population on its cytoplasmic fracture face, with few particles on the external face. There is no apparent order in the particle distribution and the fracture faces are practically indistinguishable from those of red membrane (r.m.). The absorbance spectrum of b.m. shows peaks at 550 and 410nm, the circular dichroism (CD) spectrum a positive band around 540nm and positive and negative bands around 410nm with a cross‐over at 412nm. The photoreaction cycle of bR in b.m. has the same intermediates found in purple membrane (p.m.), but the apparent kinetics resemble those of bR monomers.

Addition of 13‐cis‐, or all‐trans‐retinal to b.m. induces a rapid 5‐ to 10‐fold increase in the visible absorbance band, and the absorbance maximum shifts to 560nm in the dark. Kinetic analysis of the absorbance increase shows three first order kinetic constants with t½= 0.5 min, 6 min and 100 min, with most of the increase contributed by the fastest component. The CD bilobal pattern typical for purple membrane appears together with the strong negative band at 320nm. Ellipticity change at 590nm is nearly as rapid as the absorbance increase; within 5 min, 85% of the negative band is formed. Electron microscopy after addition of retinal reveals structurally distinct domains in the b.m. sheets which have the characteristic appearance of p.m. However, X‐ray reflections are more diffuse compared to p.m. Flash spectroscopy of reconstituted b.m. detects the same photocycle intermediates as in b.m. or p.m., but with apparent kinetics closer to those of purple membrane than before reconstitution. These results show that bO in the b.m. binds retinal to form bR which spontaneously aggregates into a lattice. However, the reconstituted bR lattice is not as well‐ordered as in p.m. and some bR is still present in the form of monomers and/or small aggregates.
BIOSYNTHESIS AND ASSEMBLY OF PURPLE MEMBRANE OF HALOBACTERIUM HALOBIUM S9: LIGHT STIMULATION OF BACTERIORHODOPSIN FORMATION
Authors: Konishi Tetsuya , Seki Mayumi
Published: January 2008

Abstract— The effect of light on purple membrane biogenesis in Halobacterium halobium S9 strain was investigated. When bacteria were grown in the dark, the 570nm absorption due to bacteriorhodopsin increased more slowly than under illumination, but eventually after longer incubation, reached the same level as that seen in the illuminated culture.

Analysis of membrane fractions by sucrose density gradient centrifugation revealed that two different membrane fractions, containing purple and brown membrane could be detected in the exponential growth phase. Another fraction whose density was higher than that of purple membrane, disappeared concomitantly with the increase in purple membrane and brown membrane, indicating that it may be related to purple membrane formation.

HPLC analysis of membrane proteins showed that there was no significant difference in de novo synthesis of bacterio–opsin between dark and illuminated cultures. This led us to conclude that light stimulated retinal binding to bacterio–opsin and/or retinal biosynthesis rather than bacterio–opsin synthesis. Bacteriorhodopsin seemed to form the brown membrane fraction first, which then spontaneously reorganized into purple membrane.

When incorporated in liposomes, bacteriorhodopsin in brown membrane was found to have rather higher proton pump activity than that in purple membrane. The H+ pumping activity was quite heat labile. This and the CD spectra indicated that bacteriorhodopsin in brown membrane might exist without forming normal timer unit.
PURPLE MEMBRANE ANALOGS SYNTHESIZED FROM C17 ALDEHYDE
Authors: Tokunaga Fumio , Ebrey Thomas G. , Crouch Rosalie
Published: January 2008

Abstract— All‐trans, 11‐cis and 9‐cis isomers of the C17 aldehyde analogs of retinal bound with purple membrane apoprotein, probably through a Schiff base linkage at the normal retinal binding site. The complex formed from C17 aldehyde and purple membrane apoprotein was slowly decomposed by 10mM hydroxylamine. The C17 aldehyde competitively inhibited the regeneration of purple membrane from all‐trans‐retinal and purple membrane apoprotein. The differential ability of the different isomers to inhibit the regeneration suggests that purple membrane has a binding site for the side chain of retinal in addition to the Schiff base binding site.
THE EFFECT OF VISCOSITY ON THE PHOTOCYCLE OF BACTERIORHODOPSIN
Authors: Beece D. , Bowne S. F. , Czégé J. , Eisenstein L. , Frauenfelder H. , Good D. , Marden M. C. , Marque J. , Ormos P. , Reinisch L. , Yue K. T.
Published: January 2008

Abstract— We study the effect of solvent viscosity on the kinetics of the photocycle of bacteriorhodopsin (bR) from Halobacterium halobium. Solvent viscosity is altered by changing the glycerol concentration from 20 to 80% glycerol by volume. The kinetics of the photocycle are observed after flash photolysis at four wavelengths at several temperatures between 240 and 315 K. Assuming a sequential model, bR → K ‐→ L → M → O → bR, Arrhenius plots of the rate coefficients determine the activation enthalpies and frequency factors for each step. Kinetic data from all solvents are considered together and studied as a function of temperature for fixed solvent viscosities. The early steps of the cycle are insensitive to solvent viscosity, →; the later steps are retarded with increasing viscosity. Activation enthalpies are independent of viscosity; the frequency factors are proportional to η−K, where the exponent k 0.25 for the transition K → L, 0.0 for L → M, 0.8 for M → O and 0.5 for O → bR.
LOW TEMPERATURE RESONANCE RAMAN STUDY OF THE L INTERMEDIATE OF BACTERIORHODOPSIN
Authors: Narva D. L. , Callender R. H. , Ebrey T. G.
Published: January 2008

Abstract— Resonance Raman spectra of photostationary state mixtures at — 80°C of bR568, L, L′, and M for light‐adapted bacteriorhodopsin were obtained. The approximate Raman spectrum of L + L’ was obtained by computer, subtracting the known Raman spectra of bR568 and M from the photostationary state spectra. Several new species not previously observed with the bacteriorhodopsin photocycle have been proposed recently. We compare our results to these studies in order to investigate the photoreaction scheme of bacteriorhodopsin.
THE 3‐METHYLINDOLE/n‐BUTANOL EXCIPLEXES: EVIDENCE FOR TWO EXCIPLEX SITES IN INDOLE COMPOUNDS
Authors: Hershberger Martin V. , Lumry Rufus , Verrall Ronald
Published: January 2008

Abstract— The 1‐butanol concentration dependence of fluorescence emission intensities and spectra from 3‐methylindole/1‐butanol exciplexes in 1‐heptane reveals a 1:1 stoichimetry near the isoemissive point increasing to 1:2 at higher concentrations. The large increase in stability of the 1:1 complex relative to indole itself is attributed to its relatively low dissociation rate with an activation energy of 36.8 kJ/mol. Each step of exciplex formation shifts the emission maximum about 15 nm to the red. The stronger combining site is the negative C‐3. The weaker site is the positive N‐1. Stabilization due to charge transfer between excited indole and electrophilic or nucleophilic partners is small relative to dipole‐dipole interactions. There is no indication of significant orbital‐overlap. The detection of both positive and negative centers for exciplex formation on indole, 1‐methyl indole and electronically similar derivatives resolves some long‐standing problems and extends the basis of knowledge necessary to use tryptophanyl‐residue fluorescence as a quantitative probe for protein conformational character and its changes.
ELECTRON TRANSFER FROM CHLOROPHYLL a TO QUINONE IN MONO‐ AND MULTILAYER ARRAYS
Authors: Dodelet J.‐P. , Lawrence M. F. , Ringuet M. , Leblanc R. M.
Published: January 2008

Abstract— Mono‐ and multilayers of chlorophyll a (Chl a)– lecithin have been prepared on quartz slides, by means of the Blodgett‐Langmuir technique, for fluorescence studies. Self‐quenching of the Chl a fluorescence has been observed in Chl a‐lecithin single layer excited with a laser light at 632.8 nm. The fluorescence yield is reduced by 50% at a concentration of 7 ± 1012 Chl a molecules cm−2. Chl a fluorescence quenching, by adding N,N‐distearoyl‐1,4‐diaminoanthraquinone (SAQ), has been studied. in a single layer, in pure Chl a and also at various dilutions of Chl a in lecithin. The results are explained in terms of a dynamic quenching rather than in terms of a permanent complex formation, at the ground state, between Chl a and SAQ. The fluorescence quenching has been interpreted as the result of an electron transfer from excited Chl a to SAQ, and rate constants of 8.3 ± 10−5 cm2 molecule−1 S−1 and 2.4 ± 10−4 cm2 molecule−1 s−1 have been found for pure diluted Chl a, respectively. Ten per cent of the diluted Chl a fluorescence always remains unquenchable and independent of the quinone concentration. In multilayers, where SAQ and Chl a are in different layers, there is no fluorescence quenching for pure or diluted Chl a even when the chromophores are in two adjacent layers. This happens only if SAQ is not able to diffuse from one layer to another. A minimum value of 22.4 nm has been found for the singlet exciton diffusion length in pure Chl a multilayers.
SOLID PHASE PHOTOREDUCTION OF METHYLVIOLOGEN ON CELLULOSE SENSITIZED BY TRIS(2,2′‐BIPYRIDYL)RUTHENIUM COMPLEX
Authors: Kaneko Masao , Yamada Akira
Published: January 2008

–Methylviologen (MV2+) adsorbed on cellulose could be reduced photochemically in the solid phase sensitized by tris(2,2′‐bipyridyl)ruthenium(II) complex, [Ru(II)(bpy)3], using disodium ethylene‐diaminetetraacetic acid (Na2EDTA) as a reducing agent. Formation of the cation radical (MV +.) was confirmed by visible and EPR spectra. The MV+. formed on cellulose was remarkably stable against air oxidation and rapidly accumulated even by the irradiation under air. Water adsorbed on the cellulose greatly retarded the photoreaction. Action spectrum showed that the excitation of Ru(II)(byp)3 is responsible for the photochemical reaction. The quenching of the emission from Ru(II)(bpy)*3 by MV2+. indicated that a primary photochemical reaction occurs between Ru(II)(bpy)*3 and MV2+. The main reaction path is the reduction of MV2+ by Ru(II)(bpy)3, giving MV+. and Ru(III)(bpy)3, followed by the reduction of Ru(III)(bpy)3 to Ru(II)(bpy)3 with Na2EDTA, which in turn is oxidized to give carbon dioxide.
UPON THE OPTIMAL GRAPHICAL REPRESENTATION OF FLASH DATA FROM PHOTOCHEMICAL SYSTEMS OBEYING FIRST ORDER KINETICS
Authors: Nagle John F.
Published: January 2008

Abstract— It is recommended that plots of absorbance change vs. log time be considered as a way to represent many decades of flash spectroscopy data when several separate decays are present. The values of the rate constants k, for the decays are easily revealed by nearly linear portions of the plots centered near tj=k−1j, which are inflection points in the graphs. The amplitudes of the decays are easily seen because they are proportional to the slopes of the linear portions of the plots. Such plots introduce no spurious singularities and they are easy to construct using semi‐log paper. Examples, including one from bacteriorhodopsin, are presented. A simple mathematical proof of these features is provided.
TRIPLET ENERGY MIGRATION BETWEEN CARBONYL CHROMOPHORES IN MICELLAR SOLUTION*
Authors: Scaiano J. C. , Selwyn J. C.
Published: January 2008

Abstract— Triplet energy transfer from acetophenone, propiophenone and isobutyrophenone to γ‐methylvalerophenone has been examined in micellar solution using laser flash photolysis techniques. The kinetics of the processes are controlled by the rates of sensitizer exit from the micelle and by the distribution of energy acceptors in the micellar phase. The photosensitized Norrish Type II cleavage in sodium dodecyl sulfate micelles provides an example of efficient quantum harvesting; the biradical produced in the reaction has a lifetime of 92 ns, which suggests that the biradical resides in a polar hydroxylic environment.
OPTICAL ABSORPTION AND ELECTRON SPIN RESONANCE SPECTRA OF CATION RADICALS OF DIMERIC CHLOROPHYLL a IN LOW‐TEMPERATURE MATRICES
Authors: Hoshino Mikio , Ikehara Kiyoshi , Imamura Masashi , Seki Hiroshi , Hama Yoshimasa
Published: January 2008

Abstract— A chlorophyll (Chl) a solution in 3‐methylpentane at 77 K exhibits an absorption spectrum with a distinct peak at 706 nm in the red‐band region. The formation of the 706 nm absorbing species (S706) was reversible with respect to temperature change; no chemical change was observed. γ‐Irradiation of the rigid 3‐methylpentane solution at 77 K yields an absorption spectrum which can be ascribed to S706+ and S706−. When carbon tetrachloride, an electron scavenger, was added to the solution, the absorption of S706+ survived, which has peaks at 850 and 956 nm. It is assumed that the S706 is hydrogen‐bonded dimeric Chi a, which may be regarded as a model of P700 in photosynthesis. Cation radicals of monomeric Chi a were formed in a γ‐irradiated sec‐butyl chloride solution at 77 K, and an absorption spectrum with peaks at 730 and 813 nm was recorded. ESR spectra of the cation radicals of S706 and monomeric Chi a are of a similar shape but their linewidths are 7.5 and 11.0 Gauss, respectively. The linewidth narrowing observed for S706+ is clear evidence for the assumption that S706 is dimeric Chi a. Comparison was made of the absorption spectrum of S706+ with the light‐induced spectrum of P700 reported earlier.
BIPHASIC PHOTOCHEMISTRY: THE FIRST ACTINOMETRIC REACTION ON A SOLID SUPPORT
Authors: Lazare S. , Mayo P. de , Ware W. R.
Published: January 2008

Abstract— An apparatus is described and an actinometric standard proposed (the intramolecular cycloaddition of the tricyclic dienedione 1) for the determination of quantum yields of reaction of substances adsorbed on silica gel.
THE EFFECT OF ULTRAVIOLET LIGHT ON THE CYCLIC NUCLEOTIDE SYSTEM OF HUMAN FIBROBLASTS
Authors: Fertel Richard H. , Tejwani Gopi A. , Albrightson Christine R. , Hart Ronald W.
Published: January 2008

Abstract— The concentrations of cyclic AMP and cyclic GMP in human skin fibroblasts in culture were determined after exposing the cells to varying fluences of UV (254 nm) light. The cyclic nucleotide concentrations of cells irradiated in the log phase of growth were unchanged relative to controls. In contrast, there was a rise in the concentration of cyclic AMP in cells irradiated after they reached confluency. The increase in concentration was observed as early as 30 min after irradiation, reached a maximum of about 200% of control at 4 to 6 h after exposure, and returned to control values by 24 h after irradiation. The effect was proportional to a UV fluence from 5 to 20 J/m2, and was blocked by the addition of the UV absorbing agent para‐aminobenzoic acid. In contrast, our results indicated that UV light had no effect on the concentration of cyclic GMP in human fibroblast cell cultures. Because of the importance of cyclic nucleotides in the regulation of cellular function, it is reasonable to hypothesize that changes in cyclic AMP induced by UV light may affect the extranuclear functions of irradiated cells.
COMPETITION BETWEEN THE SINGLET OXYGEN AND ELECTRON TRANSFER MECHANISMS IN THE PORPHYRIN‐SENSITIZED PHOTOOXIDATION OF l‐TRYPTOPHAN AND TRYPTAMINE IN AQUEOUS MICELLAR DISPERSIONS
Authors: Rossi Eliana , Van de Vorst Albert , Jori Giulio
Published: January 2008

Abstract— Kinetic studies of the hematoporphyrin–sensitized photooxidation of l‐tryptophan and tryptamine at pH 10 in either homogeneous aqueous solutions or in aqueous dispersions of Triton X–100 and cetyltrimethylammonium bromide micelles indicate that the indole substrates are attacked via a mixed type I (electron transfer from triplet dye)/type II (1O2‐involving) mechanism. Both reactive intermediates, generated by micelle‐solubilized hematoporphyrin, can diffuse to attack substrate molecules located in either the bulk aqueous phase or a different micelle. In particular, incorporation of the substrate into a micelle has only minor effects on its reactivity toward1O2, although the 1O2—indole interaction appears to be more efficient in cationic micelles owing to a favourable orientation of the target with respect to the attacking species. On the other hand, the electron transfer from triplet porphyrin to a micellized substrate is virtually non‐operative when the latter is located in an anionic micelle, whereas in neutral or cationic micelles, the efficiency of the process is again controlled by the substrate orientation. Studies of tryptamine photooxidation sensitized by meso‐tetra‐(4‐sulfonato‐phenyl) porphine in the presence of sodium dodecylsulphate micelles lend further support to the abovementioned conclusions.
AN EPR STUDY ON THE TRIPLET STATE OF PURINE FREE BASE IN AQUEOUS GLASSES AT 77 K
Authors: Arce R. , Rivera M.
Published: January 2008

Abstract— Since purine free base in aqueous solution exists in different ionic forms at different pHs and most of its photoreactions are likely to involve the triplet excited states of these different ionic forms, electron paramagnetic resonance studies (EPR) have been performed in order to determine intersystem crossing quantum yields and other characteristic parameters of the excited triplet state of these forms. Intersystem crossing yields decrease with a decrease in pH, being 0.62, 0.37 and 0.10 in 8 M NaOH, 8 M NaCIO4 and 6M H3P04 glasses, respectively. Differences in triplet decay lifetimes 3.4, 2.5 and 3.1 s, as well as in root mean‐square zero‐field splitting (ZFS) parameter, D*, (0,1304, 0.1512 and 0.1353 cm‐1) are also observed for the anionic, neutral and cationic species of purine free base. The EPR signals of the triplet state of the neutral and anionic forms have been observed simultaneously in the pH range of7–10.
THE QUANTUM YIELD FOR BILIRUBIN PHOTOISOMERISATION
Authors: Sloper R. W. , Truscott T. G.
Published: January 2008

Abstract— The difference extinction coefficient, dL500, for the photoisomerisation of bilirubin (BR) bound to human serum albumin is determined, by isolation of the product, as 4000 1000 mol‐1 dm3 cm‐1, This value is used with laser flash photolysis data to calculate the quantum yield for photoisomerisation as 0.2 +‐ 0.05 which allows the quantitative demonstration of the much higher efficiency of photoisomerisation compared with self sensitised photooxidation. Similar findings were made for BR in organic solvents and suggest that photoisomerising action is the major relaxation path for excited BR under a variety of conditions.
THE EFFECT OF MONOCHROMATIC LIGHT ONTRANS‐HEXADECENOIC ACID and CHLOROPHYLL ACCUMULATION IN ETIOLATED LEAVES OFVIGNA SINENSISL.*
Authors: Guët C. , Tremolieres A. , Lecharny A.
Published: January 2008

Abstract—Spectral sensitivities for C16 rranshexadecenoic acid accumulation in etiolated leaves ofVigna sinensisL. show two maxima, one in the blue and one in the far red, indicating a control by the high irradiance reaction. Spectral sensitivities are different for rranshexadecenoic acid and chlorophyll accumulation indicating that the biosynthesis of these compounds must not be obligatory linked.
EFFECT OF BLUE/UV LIGHT ON ANTHOCYANIN SYNTHESIS IN TOMATO SEEDLINGS IN THE ABSENCE OF BULK CAROTENOIDS
Authors: Drumm‐Herrel H. , Mohr H.
Published: January 2008

Abstract Anthocyanin synthesis in the hypocotyl of tomato (Lycopersicon esculentum) seedlings responds strongly and specifically to blue/UV light while the response to red and far‐red light, operating through phytochrome, is weak. The herbicide Norflurazon (SAN 9789) was used to inhibit synthesis of colored carotenoids almost completely without affecting growth and development measurably. Even though carotenoid content was reduced to less than 2% of normal and the fluence rate response function for blue and UV light was linear within the experimental range, Norflurazon treatment did not reduce seedling sensitivity toward blue/UV light. It was concluded that at least‘bulk’carotenoids are not the photoreceptor chromophore of the blue/UV photoreceptor pigment.
THEORETICAL STUDIES OF BILIPROTEIN CHROMOPHORES AND RELATED BILE PIGMENTS BY MOLECULAR ORBITAL AND RAMACHANDRAN TYPE CALCULATIONS
Authors: Scheer H. , Formanek H. , Schneider S.
Published: January 2008

Abstract Ramachandran calculations have been used to gain insight into steric hindrance in bile pigments related to biliprotein chromophores. The high optical activity of denatured phycocyanin, as compared to phycoerythrin, has been related to the asymmetric substitution at ring A, which shifts the equilibrium towards the P‐helical form of the chromophore. Geometric effects on the electronic structures and transitions have then been studied by molecular orbital calculations for several conjugation systems including the chromophores of phycocyanin, phytochrome Pr, cations, cation radicals and tautomeric forms. For these different chromophores some general trends can be deduced. For instance, for a given change in the gross shape (e.g. either unfolding of the molecule from a cyclic‐helical to a fully extended geometry, or upon out‐of‐plane twists of the pyrrole ring A) of the molecules under study, the predicted absorption spectra all change in a similar way. Nonetheless, there are characteristic distinctions between the different n‐systems, both in the transition energies and the charge distribution, which can be related to their known differences in spectroscopic properties and their reactivity.
THE USE OF A COMPUTERIZED SPECTRORADIOMETER TO PREDICT PHYTOCHROME PHOTOEQUILIBRIA UNDER POLYCHROMATIC IRRADIATION
Authors: Gardner Gary , Graceffo Michael A.
Published: January 2008

Abstract A method is described for predicting the effect of polychromatic irradiation upon the photo‐stationary equilibrium of the plant photoreceptor phytochrome. This method follows from the rate equations for phototransformation and utilizes the in vivo action spectra for phytochrome phototransformation (Pratt and Briggs, 1966). A scanning spectroradiometer interfaced with a microcomputer is used to determine a spectral photon distribution from 360 to 800 nm. The products of the photon fluence rate and the relative quantum efficiencies at 2‐nm intervals are summed over the entire visible range to yield a predicted percentage of the pigment in the Pfr form. This value was determined under eight different polychromatic light sources and was generally within 7% Pfr of the value measured in etiolated corn coleoptiles under the same light sources.
A STUDY OF THE PHOTOCHEMICAL PROPERTIES OF SOME CINNAMATE SUNSCREENS BY STEADY STATE AND LASER FLASH PHOTOLYSIS
Authors: Morlière P. , Avice O. , Melo T. Sa E , Dubertret L. , Giraud M. , Santus R.
Published: January 2008

The E⇄ Z photoisomerization of 4′‐methoxycinnamates, used as sunscreens in cosmetics, has been studied by steady state and laser flash photolysis, in aqueous and organic solutions. Photoisomerization quantum yields are found to be fairly high (˜0.5‐1), although no intermediate is detected upon laser flash photolysis. Cinnamates are not photodynamic sensitizers but are able to quench the 8‐methoxy‐psoralen and 5‐methoxypsoralen triplets which produces E → Z isomerization.
LASER FLASH PHOTOLYSIS AND PHOTOINACTIVATION OF SUBTILISIN BPN'
Authors: Blum Aleksander , Grossweiner Leonard I.
Published: January 2008

Abstract— Laser flash photolysis of subtilisin BPN’at 265 nm has shown that photoionization of tryptophanyl (Trp) and tyrosinyl (Tyr) residues are the principal initial photochemical reactions. The initial products are the corresponding oxidized radicals. Trp and Tyr, and hydrated electrons (eaq) which react with the enzyme at: k(eaq+ subt. BPN') = 2.1 × 1010 M−1 s−1. The photoionization quantum yield was 0.032 ± 0.005 at 265 nm, which was enhanced 3.5‐fold by simultaneous excitation at 265 and 530 nm. The photoionization yields were unchanged by 3 M bromide ion and 8 M urea. which did affect the enzyme fluorescence excited at 265 and 295 nm. A similar lack of correlation between the effects of perturbants on the photionization yields and fluorescence yields was found for subtilisin Carlsherg. The results indicate that the monophotonic and biphotonic ionization of the Trp residues does not involve the thermally‐equilibrated. lowest excited singlet state and that singlet energy transfer from Tyr to Trp does not contribute to Trp photoionization. The photoinactivation quantum yield was 0.014 for 265 nm laser excitation. which was not changed by simultaneous 530 nm excitation. The corresponding quantum yield was 0.009 for low intensity 254 nm radiation, indicative of a biphotonic contribution to photoinactivation. The results are explained by postulating that photolysis of Trp‐113 leads to disruption of hydrogen bonding to Asn‐117 and a shift in the primary chain sequence associated with the aromatic substrate binding sites. The photoionization quantum yields in subtilisin BPN’and subtilisin Carlsberg agree with a model based on the assumption that exposed Trp and Tyr residues contribute independently at intrinsic photoionization efficiencies characteristic of the chromophores.
EFFECT OF PHYTOCHROME ON THE BIOSYNTHESIS OF ACYCLIC AND CYCLIC CAROTENOIDS IN HIGHER PLANTS
Authors: Grumbach Karl H.
Published: January 2008

Abstract—

Radish plants were grown in the presence of three different herbicides that interfere with the formation of the normal range of cyclic carotenoids, leading to an accumulation of acyclic biosynthetic intermediates, mainly phytoene (SAN 6706 and amitrole) and zeta‐carotene (3852). Plants were then irradiated by four different light programs in order to gain more insight into the first steps of carotenoid biosynthesis and their control by light and phytochrome. In all cases, herbicide‐treated and control, carotenoid biosynthesis was greatly enhanced by red light consistent with an effect of phytochrome on the early steps of the pathway. However, similar enhancement was also obtained after treatment with far‐red light. Indeed with SAN 6706‐treated plants synthesis of phytoene was stimulated to a much greater extent by far‐red light given alone, than by red light. The involvement of phytochrome in the regulation of carotenoid biosynthesis appears not to be as simple as previously supposed.
ACTION SPECTRUM FOR THE PHOTOPERIODIC INDUCTION OF BULB FORMATION IN Allium cepa L.
Authors: Lercari Bartolomeo
Published: January 2008

Abstract— The action spectrum for the induction of bulb formation in Allium cepa L. was determined by continuous irradiation with monochromatic light for 3 h in the middle of the daily light period of the inductive photoperiod (18 h). The resultant action spectrum showed a single peak at 714 nm. Daily 3 h dark interruptions in the middle of inductive long photoperiods do not permit bulb formation. Bulb formation was inhibited also by monochromatic far red light (758 nm) applied at the beginning of the 3 h dark interruptions. The results of dichromatic irradiations indicate that phytochrome is the only photoreceptor involved in the photoperiodic regulation of bulbing in onion plants. The effect of far red light exhibits the characteristics (action spectrum and fluence rate dependency) of a classical “HIR” response.
LIQUID PHASE ELECTRON SPIN‐ECHO STUDIES: DIRECT DETECTION OF THE TRANSVERSE RELAXATION TIME OF PHOTOPRODUCED TETRAMETHYLBENZIDINE CATION IN AQUEOUS MICELLAR SOLUTIONS OF SODIUM DODECYLSULFATE
Authors: Narayana P. A. , Kevan Larry
Published: January 2008

Electron spin echo detection of laser photogenerated tetramethylbenzidine cation in liquid sodium dodecylsulfate micellar solutions at room temperature is reported. The phase memory time is 180 ns which can be identified with the transverse relaxation time. Deuteration effects on the phase memory time indicate that the cation interacts more strongly with surfactant molecules than with water molecules.
PICOSECOND FLUORESCENCE STUDIES OF P700‐ENRICHED PARTICLES OF SPINACH CHLOROPLASTS
Authors: Kamogawa Keui , Morris John M. , Takagi Yoshihiro , Nakashima Nobuaki , Yoshihara Keitaro , Ikegami Isamu
Published: January 2008

Dynamic properties of the picosecond fluorescence of highly enriched reaction‐center particles of photosystem I (8 ‐ 10 chlorophylls/P700) prepared from spinach have been investigated. The number (N) of photons used to excite chlorophyll molecules per reaction center was controlled between 0.06 and 80. The 1/e lifetime was ca. 25 ps for N1. which is much shorter than previously measured lifetimes of photosystem I particles. The initial fluorescence intensity saturated at higher excitation intensities (N≲ 1). This was interpreted in terms of interaction and annihilation among excited chlorophyll molecules which occur almost entirely within the duration of a laser flash. The spectrum‐resolved fluorescence decay was faster at 690 than at 680 nm. This implies that two kinds of antenna chlorophylls, apart from and in close proximity to P700, have different lifetimes. Upon heat treatment a component with a much longer fluorescence decay time was observed. The growth of this component upon heat treatment at increasing temperatures showed a correlation with a decrease in the amount of P700 that could be photooxidized.
CHEMICAL ACTINOMETRY IN THE VISIBLE (475 ‐ 610 nm) BY meso‐DIPHENYLHELIANTHRENE
Authors: Brauer H.‐ D. , Schmidt R. , Gauglitz G. , HUBIG S.
Published: January 2008

Abstract The self‐sensitized photooxidation of meso‐diphenylhelianthrene to its endoperoxide was kincticallv examined. It is recommendable as a convenient, reliable, and wavelength independent actinometer for the visible wavelength range. The calibration values, the actinometric procedure and the evaluation method are given in detail.
SV40 INDUCTION FROM A MAMMALIAN CELL LINE BY ULTRAVIOLET RADIATION and THE PHOTOSENSITIZERS 8‐METHOXYPSORALEN and ANGELICIN
Authors: Moore Sharon P. , Blount Howard , Coohill Thomas P.
Published: January 2008

Abstract SV40‐transformed weanling Syrian hamster kidney cells were exposed to long wavelength ultraviolet radiation in the presence of 8‐methoxypsoralen or angelicin. The number of viruses induced as a result of this treatment was quantitated on CV‐1P cells. The results indicate that angelicin, which is generally believed to form only monoadducts, is a potent viral inducing agent even when compared with 8‐methoxypsoralen (8‐MOP), which forms both monoadducts and crosslinks. At low radiation exposures 8‐MOP is more effective than angelicin; as the radiation exposure is increased angelicin is capable of inducing the same peak level of virus expression as was 8‐MOP. It appears that the induction of SV40 is a phenomenon possibly related to the repair of monoadducts.
SENSITIZED PHOTOREDUCTION OF CO(EDTA)‐ IN AERATED AQUEOUS SOLUTION. ITS PHOTO‐ELECTROCHEMICAL AND PHOTOBIOLOGICAL APPLICATIONS
Authors: Takakubo M.
Published: January 2008

Abstract— The reduction of Co(edta)‐ in aerated aqueous solution containing 1‐hydroxy‐5‐oxo‐5H‐pyrido[3,2a]phenoxazine‐3‐calboxylic acid (HPPC) as sensitizer and ethylenediaminetetraacetate ion(EDTA) as electron donor was studied. Semireduced HPPC, formed in a reaction between triplet HPPC and EDTA, was shown to reduce Co(edta)‐ to Co(edta)2‐. The ratio of the rate constant for oxidation of semireduced HPPC by oxygen to that by Co(edta)‐ was determined to be 0.45± 0.01 from competition reaction kinetics. A (concentration)half‐cell (oxidation‐reduction electrode) based on the photoreduction of Co(edta)‐ was found to give an electrode potential decrease of 100 mV. Co(edta)‐ was also found to be reduced during illumination in aerated suspension of chloroplasts. The rate of oxygen evolution for the Co(edta)‐ ‐chloroplast system was nearly the same as that for the Fe(CN)63‐ ‐chloroplast system both in the absence and presence of ammonium ions.