bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ENERGETICS OF ELECTRON‐TRANSFER REACTIONS OF CHLOROPHYLL AND OTHER COMPOUNDS*
Authors: Seely G. R.
Published: January 2008

Abstract— Quite often the primary photochemical reaction of an excited state molecule is transfer of an electron to or from another molecule in its ground state. Rates of such reactions are closely dependent on differences between ground and excited state redox potentials of the reagents. The solvent also plays an important role in stabilizing ion pairs formed by the electron transfer. This Review discusses experimental data relating rates to electrochemical energy parameters in the context of a scheme which portrays the energy and electron transactions in a unified manner. Three consequences of reaction of a singlet excited state are distinguished: (S1) quenching without detectable products, (S2) exciplex fluorescence, (S3) transient radical ion production, and energetically necessary conditions are derived for each. Similarly, four kinds of reactions involving the triplet state are distinguished, which depend on the relation between the energy of the triplet state and that of the ion pair states: (TI) rapid quenching, (T2) slow quenching, (T3) accelerated intersystem crossing and (T4) generation by reaction between radical ions of like spin. The last may be followed by electrochemiluminescence. Classes of compounds for which data are available include chlorophylls, porphyrins and a few other molecules of biological interest, aromatic hydrocarbons and their derivatives, heterocyclic systems, carbonyl compounds, dyes, and complexes of Ru and U. A Table compiling median or selected values of ground and excited state electrochemical potentials of chlorophylls, some porphyrins, and a few other compounds is presented.
THE INVOLVEMENT OF THE HYDROXYL RADICAL IN THE DESTRUCTIVE PHOTOOXIDATION OF CHLOROPHYLLS IN VIVO AND IN VITRO*
Authors: Harbour John R. , Bolton James R.
Published: January 2008

Abstract— The photooxidation of chlorophylls in vivo and in aqueous micellar solutions has been investigated. Through spin trapping experiments, it was found that hydroxyl radicals are photo‐produced in these systems if oxygen is present. Optical studies indicate that the rate of photo‐destruction of chlorophyll is spin trap dependent. This suggests that the hydroxyl radical may play a key role in the destruction of chlorophyll.
AN FMN‐PHOTOSYSTEM I PHOTOVOLTAIC CELL
Authors: Gross Elizabeth L. , Youngman David R. , Winemiller Sandra L.
Published: January 2008

Abstract— We have made a photovoltaic cell using Photosystem I subchloroplast particles isolated according to the method of Shiozawa et al. (1974). The particles were placed on a filter between two compartments one of which contained the electron donor, K4Fe(CN)6 and the other the electron acceptor, FMN. Upon illumination with white light (I= 80 W/m2) a potential of 300 mV was observed across a 3000 Ω load resistance. Both Photosystem I photochemistry and direct photoreactions of FMN contribute to the process. A power output of 20 μW was observed for a 2 cm2 filter containing 60 μg chlorophyll. This corresponds to 0.1 W/m2. The power efficiency was 0.13%. The short circuit current was 108 μA.
LASER INTENSITY AND THE COMPARATIVE METHOD FOR DETERMINATION OF TRIPLET QUANTUM YIELDS
Authors: Bensasson R. , Goldschmidt C. R. , Land E. J. , Truscott T. G.
Published: January 2008

Abstract— In the comparative method of determining the triplet quantum yield øT by laser flash absorption spectroscopy, general equations are established (1) for describing the dependence of øT with laser intensity and (2) for absolute actionometry of a laser pulse. Applications to specific examples are discussed.
PICOSECOND TIME RESOLVED FLUORESCENCE OF CHLOROPHYLL IN VIVO
Authors: Tredwell C. J. , Synowiec J. A. , Searle G. F. W. , Porter G. , Barber J.
Published: January 2008

Abstract. The published data concerning the fluorescence kinetics of chlorophyll a in various photosynthetic species are reviewed. The effects of singlet‐singlet and singlet‐triplet annihilation induced by excessively high incident light intensities are discussed and related to the changes produced in the fluorescence lifetimes and quantum yields. We also review the fluorescence lifetimes of Chlorella pyrenoidosa and spinach chloroplast fragments under a variety of experimental conditions; these measurements were performed at single pulse excitation intensities of less than 5 × 1013 photons cm–2 where distortion due to annihilation processes is negligible. Evidence for and against a time dependent rate equation for energy migration will be discussed with reference to the authors' work on in vitro systems.
FLUORESCENCE STUDY OF THE PHYSICO‐CHEMICAL PROPERTIES OF A BENZO(A)PYRENE7,8‐DIHYDRODIOL9,10‐OXIDE DERIVATIVE BOUND COVALENTLY TO DNA
Authors: Prusik Thaddeus , Geacintov Nicholas E. , Tobiasz Christopher , Ivanovic Vesna , Weinstein I. Bernard
Published: January 2008

Abstract— Covalent complexes between7,8‐dihydrodiol 9.10‐oxide benzo(a)pyrene (BPDE) and DNA with a modification of one BPDE molecule per 1000 DNA bases were prepared in vitro. The same stereoselective and chemically homogeneous binding of BPDE to native DNA was observed, as reported earlier for human and bovine bronchial explants. The fluorescence of the pyrene‐like aromatic moiety of BPDE bound to DNA in vitro was used as a probe of the microenvironment of the BPDE molecule in order to obtain information about the structure of the BPDE‐DNA complex dissolved in aqueous solution. Fluorescence techniques, based on the quenching of the singlet excited states by metal ions such as Ag+, by iodide ions, and by molecular oxygen are described, which provide a method for differentiating between external and internal (intercalation) binding of polycyclic aromatic molecules to DNA. Silver ions, which bind specifically to DNA bases, exhibit a strong quenching effect on noncovalently bound, intercalated benzo(a)pyrene; on the other hand, there is no quenching effect on the fluorescence of BPDE in the covalent DNA adduct. Quenchers such as O2 and iodide ions, which do not specifically bind to DNA and are dissolved in the solution external to the DNA molecule, exhibit a quenching effect on the BPDE chromophore. Furthermore, the fluorescence yield of the BPDE‐DNA complex decreases with increasing DNA concentration, an effect which is not observed with non‐covalently bound intercalated benzo(a)pyrene‐DNA complexes, and which is attributed to intermolecular DNA‐DNA interactions. The results of these studies indicate that the pyrene‐like chromophore in the covalent BPDE‐DNA complex is not intercalated between the base pairs, and that it is located in an accessible region external to the DNA helix. Possible structures are discussed.
ULTRAVIOLET INACTIVATION OF THE MIDI VARIANT OF QP RNA: CHARACTERIZATION OF TEMPLATE ACTIVITY
Authors: Ryan Francis J. , O'Hara Patrick J. A. , Gordon Milton P.
Published: January 2008

Abstract— MDV‐1 RNA is a 218 nucleotide variant of bacteriophage Qβ RNA. Qβ replicase catalyzes the formation of a strand complementary to a single‐stranded (SS) MDV‐I template. Upon phenol extraction, the template and complementary strands become double‐stranded (DS). Polyacrylamide gel electrophoresis of the products of this reaction revealed SS RNA, DS RNA, and discrete intermediate bands. UV irradiation of the template caused a decrease in DS RNA production which followed single‐hit kinetics with a quantum yield of 1.6 × 10‐‐3. Concomitant with this diminished DS RNA production were increases in SS RNA and intermediate sized RNA. The latter was shown to consist of a full sized SS template annealed to a partially completed nascent strand. Upon electrophoresis, these partially completed duplexes migrated in the same positions as those found in the analysis of unirradiated template, suggesting that this RNA contains replication obstruction areas in which UV lesions cause an increase in replication inhibition.
SPECTRAL POWER DISTRIBUTION OF LIGHT SOURCES AFFECTS GROWTH AND DEVELOPMENT OF RATS
Authors: Ozaki Yoshisuke , Wurtman Richard J.
Published: January 2008

Abstract— Groups of seven timed pregnant rats were exposed to equal illuminances (75 ftcandles) from high‐pressure sodium vapor bulbs (202 μW/cm2) or sunlight‐simulating fluorescent bulbs (309 μW/cm2). Offspring raised under sodium light weighed more during early development and had larger adrenal glands at autopsy (days 26 or 28 for males; day 48 for females) than those raised under fluorescent light. These data provide further evidence that the spectral quality of artificial lighting is a major determinant of its effects on mammalian growth and development.
THE EFFECT OF CROSS‐LINKING ON PHOTOCYCLING ACTIVITY OF BACTERIORHODOPSIN
Authors: Konishi Tetsuya , Tristram Stephanie , Packer Lester
Published: January 2008

Abstract— Purple membrane preparations from Halobacterium halobium were chemically modified with imidoesters. Dimethyl adipimidate (8.3 Å chain length) amidinates about five of the six free lysine residues whereas dimethyl suberimidate (11.3 Å) under the same conditions reacts with only 2–3 residues. Gel electrophoresis showed that the shorter chain length imidoesters were less effective than dimethyl suberimidate in oligomer formation. However, dimethyl adipimidate resulted in a more marked inhibition of the photoreaction activity. Monofunctional imidates, methyl acetimidate and methyl butyrimi‐date, at comparable degrees of amidination, did not appreciably affect activity indicating that the presence of bulky groups on the exposed lysine residues does not cause the effects observed. Hence, the introduction of molecular mobility constraints by intramolecular cross‐linking slows photocycling, and, therefore, inhibits proton pumping activity of bacteriorhodopsin. This indicates that conforma‐tional changes of the protein moiety of bacteriorhodopsin occur during photocycling activity.
STUDIES ON TETRAPYRROLS PIGMENTS—I. ABSORPTION AND FLUORESCENCE OF BILIVERDIN DIMETHYL ESTERS OF THE IX SERIES
Authors: Petrier C. , Dupuy C. , Jardon P. , Gautron R.
Published: January 2008

Abstract— Each of the four isomeric biliverdin dimethyl esters of the IX series give a fluorescent spectrum at ambient temperature, the intensity of which increases considerably when these biliverdins are complexed with zinc. A systematic study of the influence of protic and aprotic solvents failed to yield significant results. In methanol. variations in the pH greatly affect the emission absorption spectra of zinc complexes of biliverdins.
QUENCHING OF THE FLUORESCENCE OF 8‐METHOXYPSORALEN BY PROTONS
Authors: Menger Eva L. , Bhattacharjee Himangshu R. , Hammond George S.
Published: January 2008

Abstract— The quenching of 8‐methoxypsoralen (8‐MOP) fluorescence by protons was observed to occur at the diffusion controlled rates in aqueous solutions at room temperature. Enhanced basicity of 8‐MOP in the excited state compared to the ground state is expected on theoretical grounds. The fluorescence yield. which we determined as 6.3 × 10‐‐4 at pH 1 is surprisingly low and indicative of extremely fast radiationless decay pathways. The fluorescence lifetime of 8‐MOP in neutral aqueous solution is on the order of 1–2 ns.
ROLE OF DYE MOLECULES REMAINING OUTSIDE THE CELL DURING PHOTODYNAMIC INACTIVATION OF ESCHERICHIA COLI IN THE PRESENCE OF ACRIFLAVINE
Authors: Bagchi B. , Basu Sreeradha
Published: January 2008

Abstract— Photodynamic inactivation of cells is caused by damage to the regions proximal to the cell envelope or to the DNA via a singlet oxygen mechanism. For penetrating dyes the possibility of either type of damage remains. The contribution of a penetrating dye. acriflavine. remaining outside E. coli B/r cells during irradiation. towards photodynamic inactivation was investigated. It was found that this contribution was either nil or negligible.
THE SINGLE CRYSTAL PHOSPHORESCENCE OF ADENINE AT 77 K
Authors: Slavík Jan , Jelínek Orakar , Pláek Jaromír
Published: January 2008

Abstract— The low temperature phosphorescence spectra of large single crystals of adenine salts (adenine sulphate, adenine hemisulphate monohydrate, adenine hydrobromide hemihydrate) were compared with the spectra of polyadenylic acid in polydlcoholic glasses compiled from literature. The results show that adenine single crystals may serve as a convenient molecular system for modeling energy levels of polyadenylic acid and energy transfer between adenine molecules, at least in the case of triplet states. The main advantage of such a model system is that their periodic molecular arrangement and the site of protonation are exactly known from the X‐ray diffraction studies.
PROTEIN‐RNA CROSSLINKS IN RIBOSOMES: ULTRAVIOLET ACTION SPECTRA. COMPARISON WITH INACTIVATION ACTION SPECTRUM
Authors: Muel B. , Giocanti N. , Ekert B.
Published: January 2008

Abstract— RNA‐protein crosslinking by UV of different wavelengths was studied in 70S E. coli ribosomes by three techniques: sucrose gradient centrifugation in the presence of sodium dodecyl sulfate (SDS), RNA solubilization in LiCI‐urea concentrated solutions and RNA adsorption on nitrocellulose filters in the presence of SDS.

The centrifugational technique shows that the crosslinking reaction occurs in two steps, the first one corresponding to the fixation of a few protein molecules on 16 or 23 s RNAs and the second one corresponding to extensive RNA‐protein crosslinking so that most protein molecules are no longer released by SDS from 30S and 50S subunits.

The initial rates for the first step of crosslinking were evaluated by the solubilization and adsorption techniques at 7 (or 6) wavelengths of irradiation between 223 and 290 mm. The action spectrum for RNA solubilization in LiCl‐urea is perturbed at 223 nm by the breakage of protein chains. The action spectrum for retention on nitrocellulose filters seems to be exempt of this defect. It corresponds at high wavelengths to a nucleic chromophore and at low wavelengths to a proteic one. This means that RNA‐protein crosslinking may occur through RNA and protein excitation. The similarity between the action spectrum for RNA retention on nitrocellulose filters and the action spectrum for inactivation of ribosomal synthesis activity suggests that RNA‐protein crosslinking may be responsible for inactivation of ribosomes by UV.
OCCURRENCE OF PYRIMIDINE‐RICH TRACTS IN ASCITES TUMOR DNA AND THE FORMATION OF UV‐INDUCED THYMINE DIMERS
Authors: Ramakrishnan Narayani , Pradhan D. S.
Published: January 2008

Abstract— Analysis of the distribution of pyrimidine‐rich tracts (up to decanucleotides) in ascites tumor DNA revealed that these tracts occur predominantly in repetitive sequence of DNA. UV irradiation of ascites DNA resulted in preferential formation of thymine dimers in the pyrimidine‐rich tracts as compared to other regions of DNA.
CORTICOSTEROID (METHYLPREDNISOLONE) MODULATION OF PHOTOPEROXIDATION BY ULTRAVIOLET LIGHT IN LIPOSOMES
Authors: Seligman M. L. , Mitamura J. , Shera N. , Demopoulos H. B.
Published: January 2008

Abstract— UV irradiation of ovolecithin liposomes produced a dose dependent wave of peroxidation which reached a peak and then fell again coincident with substrate exhaustion. This correlated well with subsequent increases in membrane permeability. There was a progressive loss of unsaturated fatty acids, and when cholesterol was incorporated into liposomes, the UV produced a progressive loss of this steroid.

Methylprednisolone sodium succinate, a synthetic corticosteroid, was found to inhibit this peroxidation in a dose dependent manner, also ameliorating membrane permeability increases when present during irradiation, but not able to compensate for pre‐existing damage. When cholesterol was present in the liposomes, methylprednisolone sodium succinate was also able to protect this steroid from UV peroxidative damage.

The rates of reaction in this system suggested that polyunsaturated fatty acids, even when present in extremely small concentrations, underwent an initial rapid wave of peroxidation, which served to initiate the slower rate of lipoperoxidation within the bulk of mono‐ and di‐“unsaturates”. At low concentrations, the corticosteroid preferentially blocked damage to mono‐ and di‐unsaturated fatty acids, affecting the polyunsaturated fatty acids as well, at higher concentrations.

This study suggests that the corticosteroid, methylprednisolone sodium succinate, possesses antioxidant properties in lipid systems subjected to free radical peroxidation.
LIGHT‐INDUCED CONFORMATIONAL CHANGES IN CATTLE RHODOPSIN AS PROBED BY MEASUREMENTS OF THE INTEFFACE POTENTIAL
Authors: Trissl H‐W.
Published: January 2008

Abstract— A novel technique of capacitative coupling of oriented rhodopsin at a polar/apolar interface allows the time resolved investigation of conformational changes following a flash. Electric signals arise as a consequence of changes of the interface potential. A signal occurring within milliseconds behaves like the R2‐phase of the “early receptor potential” (= ERP). This response is interpreted as a conformational change of rhodopsin. No correlation of this signal is found to the spectroscopically defined metarhodopsin I‐metarhodopsin II transition.

The temperature dependence of the conformational change coincides with the temperature dependence of the latency of the ‘a‐wave’ of the electroretinogram, reported by Arden and Ikeda (1968). It is suggested that the command step of visual excitation is the conformational change and not one of the spectroscopically defined photolysis steps of rhodopsin.

Analysis of slower electrical signals following the fast response is in accordance with the model of a light‐induced pore formation.
SPECTRAL PROPERTIES OF CHLOROPHYLL a MONOLAYERS: MONOLAYERS OF CHLOROPHYLL a AND PHEOPHYTIN AT A GAS‐WATER INTERFACE*
Authors: Hirsch Rhoda Elison , Brody Seymour Steven
Published: January 2008

Abstract— Surface and spectral properties of chlorophyll a monolayers were studied at a nitrogen‐water interface. Direct spectral analysis of Chl monolayers indicated that compression results in a heterogenous mixture of Chl species. Fourth derivative and difference spectra showed the presence of minor bands at 692, 726 and 748 nm. The state of compression determines the quantity and type of spectral species formed. A Chl monolayer on an acid subphase results in the formation of a long wavelength absorbing species (705 nm) similar to that of pheophytin. The half‐band width, optical density/monolayer, and extinction coefficients of Chl monolayers are given. It is concluded that in the monolayer the formation of various aggregated species of Chl can be induced.
ULTRAVIOLET EFFECTS ON KILLING, FRUITING BODY FORMATION AND THE SPORES OF DICTYOSTELIUM DISCOIDEUM
Authors: Ohnishi Takeo , Nozu Keiichi
Published: January 2008

Abstract— ‐Ultraviolet effects on amoeboid cells of three strains of Dictyosrrlium discoidruin, NC‐4. γs‐13 and γs‐18. for killing. fruiting body formation, spore formation and viability of the spores were studied.

The strain of γs‐13 was more sensitive to UV light for killing than NC‐4 at 10% survival. In addition. γs‐13 was the most sensitive strain among the three for fruiting body formation and spore formation. The developmental process of this organism, however, showed a large resistance to UV light when compared with the killing. The spores of γs‐13 formed after UV irradiation were mostly non‐viable, though those of γs‐18 and NC‐4 were fully viable
ELECTRONICALLY EXCITED SPECIES IN THE PEROXIDASE CATALYZED OXIDATION OF INDOLEACETIC ACID. EFFECT UPON DNA AND RNA
Authors: Vidigal Carmen C. C. , Faljoni‐Alário Adelaide , Durán Nelson , Zinner Klaus , Shimizu Yoshiaki , Cilento Giuseppe
Published: January 2008

Abstract— The electronically excited species generated in the peroxidase (oxidase) catalyzed oxidation of the plant hormone indole‐3‐acetic acid is an excited state of indole‐3‐carboxaldehyde.

The chemiexcited species is able to induce in DNA the same alterations as observed with light or with enzyme‐generated triplet acetone. The chemiexcited species can also alter r‐RNA.
FLUORESCENCE YIELD PROPERTIES OF A FRACTION ENRICHED IN NEWLY SYNTHESIZED BACTERIOCHLOROPHYLL U‐PROTEIN COMPLEXES FROM RHODOPSEUDOMONAS SPHAEROIDES
Authors: Hunter C. Neil , Grondelle Renk van , Holes Nigel G. , Jones Owen T. G. , Niederman Robert A.
Published: January 2008

Abstract— A membrane fraction enriched in newly synthesized bacteriochlorophyll a‐protein complexes was isolated from Rhodopseudomoms sphaeroides by rate‐zone sedimentation. An examination of the fluorescence yield properties showed that the ratio of the maximal fluorescence emission near 910 nm (with all photochemical traps closed) to that of the initial fluorescence rise (with all traps open) was 2.2 compared to 2.9 in chromatophores. The spectrum for the variable portion of the fluorescence emission (the slow rise between the initial and maximal levels) was essentially the same in both fractions, but that observed for the initial rise in the newly synthesized material showed a greater fluorescence yield with a broad peak near 865 nm. This extra emission is thought to arise from the light‐harvesting bacteriochlorophyll complex with an absorption maximum at 850 nm and suggests that this component is only partially connected to photosynthetic units. In contrast, the little extra emission observed at the longer wavelengths in this fraction indicated that energy is transferred more efficiently between the 875 nm antenna complex and photochemical reaction centers. The kinetics of the fluorescence rise suggest that photosynthetic units exist at separate sites in newly synthesized membrane regions.
PHOTOCHEMICAL REACTIONS OF CYTOSINE N‐METHYL ANALOGS IN ALCOHOLIC SOLUTION
Authors: Ekpenyong Kieran I. , Shetlar Martin D.
Published: January 2008

Abstract— –The photochemical reactions of 1‐methylcytosine (la), 1, N4‐dimethylcytosine (Ib), and 1, N4. N4‐trimethylcytosine (Ic) in isopropanol have been investigated. In all three reactions addition of isopropanol occurs across the 5,6‐double bond of the pyrimidine ring. For example, in the case of Ir photo‐reaction with isopropanol leads to formation of 5,6‐dihydro‐6–(2‐hydroxy‐2‐propyl)‐l, N4, N4‐trimethylcytosine (IIc). In all three reactions 5,6‐dihydro‐l‐methyluracil (III) was also isolated as a product; in the case of Ic, 5,6‐dihydro‐1, N4, N4‐trimethylcytosine (IV) was isolated as well. Evidence is presented that indicates cytosine, cytidine, and 2',3'‐isopropylidene cytidine also form adducts with isopropanol. Photoinduced reaction of Ic with ethanol leads to formation of 5.6‐dihydro‐6–(l‐hydroxy‐l‐ethyl)‐l, N4. N4‐trimethylcytosine (V).

Both acetone sensitization and di‐t‐butyl peroxide initiated free radical reactions of Ib with isopropanol leads to formation of an adduct identical to that formed in the unsensitized photochemical reaction of Ib with isopropanol.
FLAVIN PIGMENTS EMBEDDED IN LIPID MATRICES: A SPECTROSCOPIC AND PHOTOCHEMICAL INVESTIGATION
Authors: Heelis P. F. , Parsons B. J. , Phillips G. O. , Barghigiani C. , Colombetti G. , Lenci F. , McKellar J. F.
Published: January 2008

Abstract— –The spectroscopic properties of riboflavin tetrabutyrate have been studied in lecithin lipo‐somes and several detergent micellar systems. The results indicate that the flavin chromophore is located close to the liposome‐water interphase rather than in the hydrophobic region. By varying the number of flavins contained in each liposome and employing fluorescence spectroscopy and steady state photolysis techniques, the possible existence of two distinct environments for the flavin chromophore was demonstrated. Several basic photochemical properties of riboflavin tetrabutyrate in liposomes and micellar systems were investigated using laser flash and microsecond flash photolysis techniques.
EMISSION SPECTRUM OF THE MICROSOMAL CHEMILUMINESCENCE OF A PROXIMATE CARCINOGEN, 7,8‐DIOL‐BENZO[a]PYRENE, DETERMINED WITH A WEDGE INTERFERENCE FILTER SPECTROMETER*
Authors: Hamman J. P. , Biggley W. H. , Seliger H. H.
Published: January 2008

Abstract— The emission spectrum of the microsome‐mediated chemiluminescence of a proximate carcinogenic metabolite of benzo[a]pyrene, 7,8‐diol‐benzo[a]pyrene. has been measured with a wedge interference filter spectrometer calibrated with known chemiluminescent and bioluminescent reactions. This instrument has a noise equivalent signal at 490 nm (bandpass 24 nm) of 104 photon s‐1 at 20°C. Spectral and kinetic data indicate that the microsomal chemilurninescence of this metabolite is an exiplex chemiluminescence that proceeds through a dioxetane intermediate.
SPECTROFLUOROMETRIC DETERMINATION OF CHLOROPHYLL(IDE) a AND b AND PHEOPHYTIN (OR PHEOPHORBIDE) a AND b IN UNSEGREGATED PIGMENT MIXTURES*
Authors: Bazzaz Maarib B. , Rebeiz Constantin A.
Published: January 2008

Abstract— Simultaneous equations were derived for the determination of chlorophyllide a and b and pheophorbide a and b in unsegregated mixtures of the four tetrapyrroles. The same equations can also be used for the determination of chlorophyll a and b and pheophytin a and b in unsegregated mixtures, after separation of the phytylated tetrapyrroles from their unphytylated analogs by solvent extraction. The equations are capable of calculating the fluorescence Soret excitation amplitude contributed solely by any one of the four tetrapyrroles in the mixture, from two Soret excitation spectra recorded at emission wavelengths of 674 and 660 nm respectively. The Soret excitation amplitudes are then converted into concentrations by reference to standard calibration curves. The equations are usable with any excitation corrected spectrofluorometer. They are particularly suited for the study of Chl‡catabo‐lism with minimum generation of chemical artifacts.
BRANCHING IN THE BACTERIORHODOPSIN PHOTOCHEMICAL CYCLE
Authors: Sherman Warren V. , Eicke Robert R. , Stafford Shirley R. , Wasacz Frank M.
Published: January 2008

Abstract— Kinetics have been determined for the decay of the terminal phototransients M(410) and O(660) and the reappearance of the BR(570) chromophore in flash‐photolyzed aqueous suspensions of light‐adapted purple membrane fragments from Halobacterium halobium. The results were fitted to a linear model of
PHOTOREACTIVITY OF ISOLATED PHOTOSYSTEM I PARTICLES UPON COMBINATION WITH ARTIFICIAL LIPID MEMBRANES OR TRITON X‐100 MICELLES*
Authors: GINKEL GIJS VAN
Published: January 2008

Abstract— PS‐I particles isolated according to Shiozawa et al. (1974) show increased rates of O2‐‐ and H +‐uptake with ascorbate as electron donor upon combination with an artificial vesicular lipid membrane. The amount of increase varies depending on the reconstitution procedure used. Combination of PS‐I particles with Triton X‐100 micelles increases these photochemical activities even more. The observed proton uptake in PS‐I lipid vesicles is not caused by the well‐known proton gradient found in thylakoid membranes, since lipid vesicles containing extracted leaf Chl show the same activities and uncouplers have no effect. Because these phenomena are also caused by solubilized Chl, it is concluded that there is no obvious correlation with PS‐I activity.

Proton uptake most probably is caused by oxidation of ascorbate by either singlet oxygen, superoxide or OH‐radicals formed in the light. Experimental results are obtained which indicate that Chl in lipid catalyzes formation of superoxide and singlet oxygen. However, it is not clear whether superoxide formation is caused by direct electron transport from excited Chl to oxygen or by a secondary reaction. Diphenylcarbazone disproportionation has been reported as a specific photosystem I reaction. However, PS‐I lipid vesicles and Chl‐lipid‐Triton X‐100 mixtures oxidize DPCN at comparable rates, showing that the reaction is not specific for PS‐I. Cations stimulate DPCN disproportionation in Chl‐lipid‐Triton X‐100 mixtures but do not affect the rate of P700 photooxidation at all. Therefore it is suggested that Gross and Greniers (1978) conclusion that cation regulation of PSI electron flow (studied by DPCN disproportionation of PS‐I particles in Triton X‐100 micelles) provides a fine tuning mechanism for energy transfer, has to be reevaluated.
EFFECTS OF LIGHT AND cGMP ON MEMBRANE FLUIDITY OF FROG ROD OUTER SEGMENTS*
Authors: Wey Chang‐Lin , Cone Richard A. , Gaffney Betty J.
Published: January 2008

Abstract—We have used a spin‐labeled fatty acid to detect changes induced by light and by cGMP in isolated rod outer segment membranes. We chose a spin probe (5‐doxylstearic acid) which has the nitroxide group placed on the hydrocarbon chain, so the probe should reside somewhat inside the hydrophobic region of the membrane. We found that light exposures which bleached the rhodopsin also produced a small change in the EPR spectra. The spectral changes are consistent with a small increase in membrane fluidity. Light exposures which bleach rhodopsin are known to activate a phosphodiesterase that markedly decreases the cGMP level in rod outer segment. Therefore, we attempted to vary cGMP levels directly by adding Bu2‐cGMP, or indirectly, by adding IBMX, CDTA or ATP to try to inhibit the phosphodiesterase. In each case where the cGMP level is expected to increase, we observed spectral changes in the dark which suggested a small decrease in membrane fluidity. Thus, all of our results with this probe are consistent with the idea that changing the level of cGMP produces changes in membrane fluidity. The light‐induced spectral changes we observed required the presence of ATP, and were inhibited by 2mM Ca2+, or by the chelator of divalent cations, CDTA.
POSSIBLE IMPLICATION OF PHOTOOXIDATION REACTIONS IN RETINAL PHOTO‐DAMAGE*
Authors: Delmelle M.
Published: January 2008

Abstract—The study suggests that photosensitized reactions might constitute a trigger of the photo‐damage occurring in the visual cells. Retinal is used as a sensitizer candidate: it is shown that its illumination leads to singlet oxygen production which in turn generates membrane damage in model systems.
EFFECTS OF DIETARY VITAMIN E AND SELENIUM ON LIGHT DAMAGE TO THE RAT RETINA*,†
Authors: Stone William L. , Katz Martin L. , Lurie Mark , Marmor Michael F. , Dratz Edward A.
Published: January 2008

Abstract—In this study we have investigated effects of dietary supplementation or deficiency in α‐tocopherol (vitamin E) and selenium on acute light stress to albino rats. Selenium, which is an essential component of the enzyme glutathione peroxidase, and α‐tocopherol are thought to be important in preventing in vivo lipid peroxidation. Before light stress, sections of paraffin embedded eyes show an intense yellow autofluorescent pigment localized in the retinal pigment epithelium (RPE) of the deficient rats which is barely visible in tissue sections from the supplemented rats. The fluorescent pigment is thought to be the result of damaging lipid peroxidation reactions. In addition the dcficient rats show increased electroretinogram (ERG) thresholds and decreased ERG‐amplitudes compared to the supplemented rats. Acute 12 h light stress did not produce an increase in autofluorescent pigment in the RPE of the supplemented or deficient rats. The supplemented rats. however. showed marked light damage effects as measured by ERG‐parameters. Contrary to our expectations, the deficient rats showed a lesser amount of light damage to the ERG than the supplemented rats. Our ERG results to date fail to implicate r‐tocopherol levels or glutathione peroxidase activity as major factors in protecting the retina and pigment epithelium from damage after acute light stress.
PHOTOACOUSTIC SPECTROSCOPY AND RADIANT ENERGY CONVERSION: THEORY OF THE EFFECT WITH SPECIAL EMPHASIS ON PHOTOSYNTHESIS
Authors: Malkin Shmuel , Cahln David
Published: January 2008

Abstract—The use of photoacoustic spectroscopy in the study of photoactive samples (photochemical, luminescent, photovoltaic) is considered. After a short explanation of the parameters important in this technique and ways of measuring them, photochemical processes are considered in detail. Relations are derived for the determination of the energy stored in photochemical products and the quantum yield for the photochemical processes.

One‐ and two‐step photochemical processes are treated in detail and the dependence of the photo‐acoustically detected products on modulation frequency is considered, showing the possibility of separating reaction steps according to their rate constants. Particular attention is given to the photosynthetic process and the potential of this method for determination of energy conversion efficiencies of the different stages of photosynthesis is demonstrated. Also the use of the technique in the study of photovoltaic processes is outlined.
ENERGY RELAXATION MECHANISM IN Ni(II), Pd(II), Pt(II) and Zn(II) PORPHYRINS
Authors: Kobayashi T. , Straub K. D. , Rentzepis P. M.
Published: January 2008

Abstract—Picosecond absorption spectroscopy was used to determine the intramolecular energy relaxation processes occurring in Ni(II). Pd(II), Pt(II), and Zn(II) protoporphyrin IX dimethyl ester. Picosecond data on the rate of ground state repopulation and the kinetics of a transient intermediate made it possible to determine the lifetimes of the excited singlet state of Ni, Pd, and Zn porphyrins as 10±2ps, 19±3ps, and 2.6±0.5 ps, respectively, and<8 ps for Pt porphyrin. On the basis of these data. the nonfluorescent and nonphosphorescent property of Ni porphyrin can be interpreted in terms of internal conversion to a lower lying singlet d‐d level which is not the case for the strongly phosphorescent Pd and Pt porphyrins.
REPAIR OF NEAR (365 nm)‐ AND FAR (254 nm)‐UV DAMAGE TO BACTERIOPHAGE OF ESCHERICHIA COLI
Authors: Tyrrell Rex M.
Published: January 2008

Abstract: Intact bacteriophage have been irradiated at 365 nm or at 254 nm and then analysed for DNA photoproducts or injected into their bacterial host to test susceptibility of the damage to both phage and host‐cell mediated repair systems. Both thymine dimers and single‐strand breaks are induced in the phage DNA by 365 nm radiation. The dimers appear to be the major lethal lesion (approximately 2 dimers per lethal event) in both repair deficient bacteriophage T4 and bacteriophage λ. after irradiation with either 254 nm or 365 nm radiation. Damage induced in T4 by either wavelength is equally susceptible to x‐gene reactivation (repair sector approximately 0.5). v‐gene reactivation acts on a larger fraction of the near‐UV damage (repair sector of 0.82 at 365 nm as against 0.66 at 254 nm). The host‐cell mediated photoreactivation system is only slightly less effective for near‐UV damage but host‐cell reactivation (as measured by comparing survival of phage λ. on a uvr+ and a uvr‐ host) is effective against a far smaller sector of near‐UV damage (0.35) than far‐UV damage (0.85). Weigle‐reactivation (far‐UV induced) of near‐UV damage to phage λ is not observed. The results suggest that unless the near‐UV damaged phage DNA is repaired immediately after injection. the lesions rapidly lose their susceptibility to repair with a consequent loss of activity of the phage particles.
PHOTOBEHAVIOR OF EUGLENA GRACILIS: ACTION SPECTRUM FOR THE STEP‐DOWN PHOTOPHOBIC RESPONSE OF INDIVIDUAL CELLS
Authors: Barghigiani Corrado , Colombetti Giuliano , Franchini Barbara , Lenci Francesco
Published: January 2008

Abstract—Light‐induced behavioral responses of Euglena gracilis have been investigated in single cells by means of a video system coupled to an optical microscope. Light intensity‐effect curves at different wavelengths in the near UV and visible range have been determined. From these curves the action spectrum for the step‐down photophobic response of Euglena has been calculated. From a comparison with the results obtained using a population method by means of a phototaxigraph, it is concluded that a single photomotile reaction is responsible for cell accumulation, brought about by trapping in the light spot and possibly by phototaxis towards scattered light from organisms already in the light field.
EFFECT OF METHYL SUBSTITUENTS ON THE TRIPLET STATE PROPERTIES OF BENZ[a]ANTHRACENE
Authors: Co Tiao‐te , Kwiram Alvin L.
Published: January 2008

Abstract—Optical detection of magnetic resonance (ODMR) and phosphorescence results are reported for benz[a]anthracene and five of its methyl derivatives. Each of these compounds is well characterized by its ODMR signals.
LASER PHOTOLYSIS STUDIES OF THE REDUCTION OF PARAQUAT CATIONS IN METHANOL
Authors: Rodgers Michael A. J.
Published: January 2008

Abstract— A computer‐controlled laser photolysis apparatus has been used to investigate the results of photoexcitation of paraquat. cations (PQ2+) in methanol solution. The formation of the monoreduced species (PQ+) is shown to occur in two processes overall; one is too fast to be resolved from the laser pulse; the second shows first order kinetics with an observed rate constant which is linearly dependent on the paraquat concentration. The natural lifetime of this second precursor to PQ+ was measured at 1.4 μs. about ten times longer than the CH3O'radical which is the anticipated reductant. The identity of this precursor is possibly a radical pair.
PHOTOSENSITIZED CYCLODIMERIZATION OF 5‐FLUOROURACIL
Authors: Shim Sang Chul , Lee Seung Han
Published: January 2008

Abstract—The photosensitization by acetone or N‐methyllutidone yields a C4‐cyclodimer from 5‐fluorouracil in aqueous solution. with a quantum yield of 2 × 10‐‐3. The dimer isolated has been characterized by UV, IR. NMR, and mass spectra. The stereochemistry of the dimer has been determined to be anti head‐to‐tail configuration from the NMR spectral analysis.
PHOTOVOLTATC EFFICIENCIES OF MICROCRYSTALLINE AND ANHYDROUS CHLOROPHYLL a
Authors: Dodelet J. P. , Brich J. Le , Leblanc R. M.
Published: January 2008

Abstract— A thin layer of chlorophyll a (around 2000 Å). a p‐type organic semiconductor. was sandwiched between two different metals. aluminum and silver. We used the photovoltaic effect in order to study the efficiency of light conversion by the crystalline and anhydrous forms of Chl a. When the photovoltaic cell is illuminated through the semi‐transparent aluminum electrode. an action spectrum similar to the visible absorption spectrum of Chl a is obtained. The anhydrous form. always shows a maximum, in the red, at 672 nm and the crystalline one at 746 nm to 738 nm depending on the amount of water vapor present in the measuring area. The light conversion efficiency has been measured at the maximum absorption in the red for both forms of Chl a. For the anhydrous form, we found values as high as 0.036%, which is very significant even compared to 0.21%, the highest value found for the crystalline form. In both cases. the incident light power was approximately 10 μW on the cell. The light conversion efficiency of both forms of Chl a cells was found to depend on a combine effect of the nature of the gas (O1. N2. air. Ar. N2O. SF6, H2) and the amount of water vapor present in the measuring area. The best conversion efficiency was obtained with O2, or air saturated with water. This combined effect was very large for the crystalline form whereas the anhydrous form was only slightly affected.
INTENSITY AND TIME‐DEPENDENCE OF THE CAROTENOID TRIPLET QUENCHING UNDER LIGHT FLASHES OF RECTANGULAR SHAPE IN CHLORELLA
Authors: Maróti Peter , Lavorel Jean
Published: January 2008

Abstract— As is known the chlorophyll fluorescence of photosynthetizing plants is strongly quenched by carotenoid triplet states if the exciting light intensity is high enough (> 10 kW/m2). This light‐induced quenching process was studied by measuring the relative yield of chlorophyll fluoresccncc excited with a pulsed argon laser at 20 C in light adapted algae as function of time (within lo μs) and exciting light intensity (<400 kW/m2). The experimental yield against time and yield against intensity curves have been adequately explained by a statistical model of Photosystem 2 (PS 2) units based upon the existence of freely moving excitons according to which the carotenoid triplet quenchers are randomly distributed and are perfect traps for excitons. Accepting the hypothesis that carotenoid triplet quenching occurs only in PS 2 units. it could be concluded that the height of the true zero level of PS 2 fluorescence is somewhat lower than the half value of the fluorescence level of the dark adapted state.
LIGHT‐INDUCED PERTURBATION OF AROMATIC RESIDUES IN BOVINE RHODOPSIN AND BACTERIORHODOPSIN*
Authors: Rafferty Charles N.
Published: January 2008

Abstract—

Light‐induced changes in the UV absorption spectrum of bovine rod outer segment membranes were measured by conventional difference spectroscopy and by flash photolysis methods. Different thermal intermediates of rhodopsin (lumirhodopsin, metarhodopsin I, metarhodopsin II, and meta‐rhodopsin III) have absorption spectra in the ultraviolet which differ from the rhodopsin spectrum and from each other. The spectra associated with metarhodopsin I, metarhodopsin II, and metarhodopsin III are characteristic of perturbation of a small number of tyr. and/or trp residues, most likely one trp residue. These aromatic residues are in the neighborhood of the retinal Schiff base and undergo coordinated changes of interaction with retinal during the bleaching sequence. At the metarhodopsin II stage, the magnitude of the UV spectral changes is consistent with the exposure of a previously shielded trp residue to an aqueous environment. The present results are consistent with previous spectral studies which limit the extent of light‐induced conformational changes to regions of the protein in the neighborhood of the retinal Schiff base. An analogous study was made on light‐adapted purple membranes of Halobacterium halobium. The UV absorption spectrum associated with the deprotonated Schiff base intermediate of the trans‐bacteriorhodopsin cycle is indicative, in part, of aromatic residue perturbation. However, significant changes in the secondary and tertiary structures of the bacterio‐rhodopsin protein characteristic of a delocalized conformational change are unlikely at this intermediate stage.
ACTION SPECTRA OF PHOTOPHOSPHORYLATION–I. ATP FORMATION COUPLED TO NON‐CYCLIC ELECTRON FLOW
Authors: Ginkel Gus Van , Hammans Johan W. Kleinen
Published: January 2008

Abstract— Photophosphorylation action spectra were measured with the utmost precision to identify the different pigment forms involved in the light‐harvesting process for formation ofadenosine–5′‐triphosphate (ATP).

With ferricyanide‐ions as electron acceptor freshly prepared thylakoid membranes yield a typical photosystem 2 (PS II) action spectrum peaking at 672 nm and with pronounced shoulders at 650 and 680 nm. Because ferricyanide‐ions can be reduced by both photosystems we suggest that due to the poor accessibility of these hydrophilic ions to the PS II acceptor site, the PS II electron flow is rate‐limiting. When the thylakoid membranes are aged, the maximum of the action spectrum shifts to 675 nm and bands in the spectral region690–725 nm are observed, which are generally attributed to photosystem 1 (PS I). Obviously, as a result of the aging, the rate‐limiting effect of PS II electron flow decreases and activity of both photosystems is observed.

With nicotinamide adenine dinucleotide phosphate (NADP) and ferredoxin as electron acceptors also a typical PS II action spectrum is obtained peaking at 676 nm and with a sharp drop in activity at 695 nm. However, the spectrum shows a pronounced peak at706–707 nm, which is attributed to a pigment involved in the light‐harvesting for either of the two photosystems.

Curve‐analysis of the action spectra suggests that four forms of Chi a exist at room temperature in the spectral region660–685 nm. However, a definite conclusion about the occurrence of different pigment forms will be drawn on the basis of combined results from this and the following publication. This is done to yield a conclusion that is statistically more reliable.

ATP–adenosine‐5′‐triphosphate; BSA– bovine serum albumin; Chl–chlorophyll; DBMIB–2,5‐dibromo‐3‐methyl‐6‐isopropylbenzoquinone; DCMU–3‐(3,4)‐dichlorophenyl‐1,1‐dimethyl urea; NADP –nicotinamide adenine dinucleotide phosphate; Pi–orthophosphate‐ion; PMS–N‐methyl‐phenazonium sulphate or phenazinemethosulphate;PS–1–photosystem 1;PS–2–photosystem 2.
ACTION SPECTRA OF PHOTOPHOSPHORYLATION–II. ATP FORMATION CATALYZED BY PHENAZINEMETHOSULPHATE SUGGESTING THE INVOLVEMENT OF LONG WAVELENGTH PIGMENT FORMS IN THE LIGHT‐HARVESTING PROCESS FOR PS II AND PS I
Authors: Ginkel Gus Van , Hammans Johan W. Kleinen
Published: January 2008

Abstract— Action spectra of phenazinemethosulfate (PMS)‐catalyzed photophosphorylation, measured under aerobic conditions without added reductants, show the involvement of both photosystem 2 (PS II) and photosystem 1 (PS I). Addition of low concentrations 3‐(3,4)dichlorophenly‐l, 1‐dimethylurea (DCMU) changes the shape of the curves and causes formation of typical PS II action spectra. This can be understood by the partial inhibition of PS II electron flow by DCMU, which therefore becomes rate‐limiting. The presence of DCMU causes a strong decrease of photochemical activity in these spectra at 638, 660 and 690 nm, which we attribute to decreasing activity of PS I pigments.

Curve analysis of the action spectra suggests the presence of different Chi forms at room temperature peaking at: 641.6; 650.3; 661.2; 669.8; 677.1; 684.0 and 690.6 nm. Comparison of our data with published data from low temperature absorption spectra indicates that lowering the temperature causes a decrease in halfwidth of the absorption bands but no significant change in peak position. Our data support the hypothesis of French and co‐workers that there are four universal forms of Chi a also at 25â°C.

Careful investigation of data in literature does not give evidence that the pigment peaking at 641 nm is a second form of Chi b, as is sometimes assumed.

Because our action spectra show two small but distinct maxima at703–705 and718–720 nm when PS II is rate‐limiting, we also measured action spectra of PS I (reduced PMS + DCMU) and PS II (ferricyanide‐ions + 2,5‐dibromo‐3‐methyl‐6‐isopropylbenzoquinone) separately.

They show, in agreement with published data, that PS I is operating more efficiently in the spectral region690–725 nm than PS II. The Chi form peaking at 690 nm is absent in the PS II action spectrum, whereas this curve has two small but distinct maxima around703–705 and718–720 nm, respectively, which are also present in the PS I action spectrum.

We, therefore, suggest that light absorbed by these pigments can be transferred to either of the two photosystems, and not to PS I exclusively as is sometimes assumed.

ATP,adenosine–5′‐triphosphate; BSA, bovine serum albumin; Chi, chlorophyll; DBMIB, 2,5‐dibromo‐3‐methyl‐6‐isopropylbenzoquinone; DCMU, 3‐(3,4)‐dichlorophenyl‐1,1‐dimethyl urea; NADP, nicotinamide adenine dinucleotide phosphate; Pi orthophosphate‐ion; PMS, JV‐methylphenazonium sulphate or phenazinemethosulphate; PS I, photosystem 1; PS II, photosystem 2.
CHLORIDE ENHANCEMENT OF QUENCHING OF TRIPLET METHYLENE BLUE BY Fe(II)
Authors: Osif T. L. , Lichtin Norman N.
Published: January 2008

Abstract— The influence of chloride ion on the rate of decay of triplet methylene blue in 0.01 M acid in the absence and presence of ferrous ions was investigated by means of laser flash‐photolysis monitored by kinetic spectrophotometry. Chloride weakly accelerates decay of 3MBH2± in aqueous solution in the absence of Fe(II). Quenching of 3MBH2+ by Fe(II) is more strongly catalyzed by Cl‐ in both water and 50 v/v% aq. CH3CN. The uncatalyzed quenching constant, k5, is of the order of 1 × 106M‐1 s‐1 while in 4.8 M aqueous chloride (μ– 7.2 M) k5= (37.2 ± 1.8) × 106M‐1 s‐1. A possible role of chloride is as a bridging species in quenching via electron transfer between 3MBH2+ and Fe(II).