bluuebunny/crossref_metadata_2025 huggingface dataset:
ULTRAVIOLET INACTIVATION OF THE MIDIVARIANT OF Qß RNA: THE SITES OF UV‐INDUCED REPLICATION INHIBITION
Authors: O'Hara Patrick J. A. , Gordon Milton P.
Published: January 2008

Abstract— MDV‐1 RNA is a small variant of bacteriophage Qß, and consists of complementary ‘plus’ (+) and ‘minus’ (‐) strands. It is an active template in replication reactions catalyzed by Qß replicase. Using high‐resolution polyacrylamide gel electrophoresis, we have located the sites of replication inhibition caused by irradiation of (+) and (‐) MDV‐1 template RNA with 254‐nm light. Presumably, this inhibition was caused by uridine hydrates and pyrimidine cyclobutane dimers, which previously were shown to be formed at levels of 3.5 and 0.3 per (+) MDV‐1 strand, respectively, at the dose used here (2500 Jm‐2). Each of the ten inhibition sites correspond to regions in the template which contain two or more pyrimidines, including at least one uridine. At each site, replication inhibition occurred at two or three adjacent bases. The sites of the photolesions with respect to the known primary sequence and proposed secondary structure of MDV‐1, and the implications of this work for locating the sites of lesions produced by other agents which inhibit the replication of a small RNA molecule are discussed.
PHOTOVOLTAIC ACTION SPECTRA AND EFFICIENCIES OF CHLOROPHYLL a SPECIES ABSORBING NEAR 700 nm
Authors: Dodelet J. P. , Brech J. Le , Chapados C. , Leblanc R. M.
Published: January 2008

Abstract— Alcohol vapors affect the photovoltaic properties of anhydrous chlorophyll a (Chi a). At 23°C, a photovoltaic cell of the type Allanhydrous Chi a|Ag has been successively submitted to non saturating vapors of methanol, ethanol, 1‐propanol, 2‐propanol, cyclopropyl carbinol, cyclopentanol, methyl cyclopropyl carbinol, 1‐butanol, 1‐pentanol and chloroethanol. The action spectrum of anhydrous Chi a has a maximum in the red at 672 nm. This maximum is shifted towards 700 nm under the influence of alcohol vapors. The most important changes occur for ethanol, 1‐propanol and 2‐propanol. In the same way, the conversion efficiencies of light energy into electrical energy, measured at the maximum in the red are, for the same alcohols, higher than the initial value 1.7 times 10‐2% obtained on the average for anhydrous Chi a. A maximum value of 6.3 times 10‐2% has been obtained after rehydration of Chi a solvated with 2‐propanol. The influence of alcohol vapors has been interpreted in terms of microcapillarity of anhydrous Chi a and a mean microcavity radius of 11 ± 6 Å has been deduced from the photocurrent variation with the amount of alcohol vapor present in the measuring area. Furthermore, the action spectrum shift towards 700 nm has been interpreted by the formation, at 23°C, of Chi a special aggregates whose action spectrum has been obtained by difference. Infrared spectroscopy demonstrated that anhydrous Chi a obtained from electrodeposition is an assembly of Chi a dimers and that alcohol vapors, producing the special aggregates formation at 23°C, induce a decrease of the free C=O ketone band and an increase of the associated C=O ketone. The C=O esters band is not affected by the Chi a reorganization.
PHOTOREACTIONS OF ALLOPURINOL AND HYPOXANTHINE WITH 2‐PROPANOL
Authors: Bose Samarendra N. , Davies R. Jeremy H.
Published: January 2008

Abstract— Ultraviolet irradiation of allopurinol with 2‐propanol, either in aqueous solution at 254 nm or in aqueous acetone (used as a photosensitizer) at > 290 nm, gave 2‐(3'‐hydroxy‐2',3'‐dimethylbutan‐2'‐yl)pyrazolo[3,4‐d]pyrimidin‐4(5H)‐one (3) and 6‐(2'‐hydroxypropan‐2'‐yl)pyrazolo[3,4‐d]pyrimidin‐4(5H)‐one (4) as major products. In addition, two minor photoproducts, which were not characterized, were detected by thin layer chromatography. Under similar irradiation conditions, hypoxanthine yielded 8‐(2'‐hydroxypropan‐2'‐yl)‐2‐(propan‐2'‐yl)hypoxanthine (5), 8‐(3'‐hydroxy‐2',3'‐dimethylbutan‐2'‐yl)hy‐poxanthine (6) and 8‐(2'‐hydroxypropan‐2'‐yl)hypoxanthine (7) together with two unidentified minor photoproducts. Compounds 5 and 6 appear to be secondary photoproducts derived from 7. Initiation of the reaction by photodecomposition of di‐t‐butyl peroxide led to specific formation of 4 from allopurinol and of 7 from hypoxanthine. The allopurinol and hypoxanthine photoproducts were characterized by their 1H‐NMR, UV, and mass spectra.
LIGHT‐DRIVEN REDOX PROCESSES IN FUNCTIONAL MICELLAR UNITS—III. Zn‐TETRAPHENYLPORPHYRIN SENSITIZED REACTIONS IN METHYL VIOLOGENE SURFACTANT ASSEMBLIES
Authors: Pileni Marie‐Paule , Braun A. M. , Grätzel M.
Published: January 2008

Abstract— The photoreduction of methyl viologene by ZnTPP triplet excited states was studied in mixed micelles containing the functional surfactant JV‐dodecyl, N‐methyl viologene (C12MV2+) as one and Cetyltrimethylammoniumchloride (CTAC) as the other component. Using the laser photolysis technique the kinetics of the redox reaction were studied at various CTAC/C12MV2+ ratios. The average time for the electron transfer decreases linearly with the C12MV2+ occupancy. The back transfer from C12MV2+ to ZnTPP2+ can be intercepted if a donor such as NADH is cosolubilized in the micelle. In such a system irreversible methyl viologene reduction is achieved which in the presence of a suitable redox catalyst can be used to produce hydrogen from water.
ENVIRONMENTAL EFFECTS ON THE ELECTRONIC SPECTRAL PROPERTIES OF 1‐PYRENECARBOXALDEHYDE AND THEIR APPLICATION IN PROBING BIOLOGICAL STRUCTURES
Authors: Lianos P. , Cremel G.
Published: January 2008

Abstract— The electronic spectra of 1‐pyrenecarboxaldehyde are sensitive to environmental polarity. In the fluorescence spectrum especially, an extensive loss of structure, large red shifts and an increase in the quantum yield is progressively observed on going from aliphatic to polar solvents or even mixtures between the two types of solvent. When 1‐pyrenecarboxaldehyde interacts with substances possessing an amino group its fluorescence quantum yield increases without a simultaneous spectral shift or loss of spectral structure. These phenomena are explained in terms of the effect of the solvent on the nπ*‐ππ* state coupling. The effect of temperature and the pH on the electronic spectral properties are discussed. The solvent‐sensitive photophysical properties of 1‐pyrenecarboxaldehyde can be used to probe the interior of lecithin vesicles. These properties, as well as the dynamics of the interaction of the hydrocarbon with proteins, can yield information about mitochondrial membranes.
SPECTRAL PROPERTIES OF (ISO)ALLOXAZINES IN THE VAPOUR PHASE
Authors: Eweg Jan K. , Müer Franz , Bebelaar Dick , Voorst Joop D. W. van
Published: January 2008

Abstract— Spectral properties of alloxazine and isoalloxazine derivatives were determined at high temperatures in the vapour phase. In comparison with spectra observed in solution, vapour phase spectrometry gives primary photophysical properties of the isolated chromophore. Fluorescence lifetimes in the vapour phase range from <0.5 to 18 ns. There is some indication that an intramolecular complex can exist between the isoalloxazine moiety and its aliphatic side chain carrying a polar (hydroxyl) group. Direct photodissociation of the molecule in its first electronically excited singlet state is not very probable.
PHOTOCATALYSIS, PHOTOREDUCTION, PHOTOOXIDATION AND PHOTOREDOX HYDROGEN TRANSFER REACTIONS OF METALLOPORPHYRINS
Authors: Harel Y. , Manassen J.
Published: January 2008

Abstract— Hydrogen transfer from tertiary amines to nitroaromatics is photocatalysed by SnIV and GeIV complexes of tetraphenylporphyrin. There are two photochemical steps, one involving hydrogen transfer to the catalyst, and the second being a hydrogen donation from the intermediate formed. The photoredox properties of para‐substituted tin tetraphenyl porphyrin dichlorides can be correlated with the one electron oxidation‐reduction potentials of the porphyrins and of the reduced intermediates. The steady‐state concentration of intermediate and rate of product formation depend also on the electron donor and acceptor properties of, respectively, the amine and nitro‐compound. Fluorescence results indicate that in both photochemical steps excited singlet states of porphyrins are involved and there is evidence for exciplex formation with ground state amine. Acetic anhydride has a cocatalytic effect but does not influence the quenching of porphyrin fluorescence by amine or the quertchirjg of the fluorescence of the intermediate by nitrobenzene.
THE ROLE OF PYRIMIDINE DIMERS AND NON‐DIMER DAMAGE IN THE INACTIVATION OF ESCHERICHIA COLI BY UV RADIATION
Authors: Hodges N. D. M. , Moss S. H. , Davies D. J. G.
Published: January 2008

Abstract— We have quantitated the role of pyrimidine dimers and non‐dimer damage in the inactivation of Escherichia coli by far‐UV radiation, near‐UV radiation, and triplet state sensitized near‐UV radiation. The extent of photoreactivation in vivo of an excision and postreplication repair‐deficient strain of E. coli after the different radiation treatments has been correlated with the relative proportion of pyrimidine dimers and non‐dimer lesions produced. Using an excision deficient strain of E. coli, the susceptibility to recA+ ‐dependent repair of the damage produced by the different radiation treatments has also been quantified.
SPECTROPHOTOMETRIC IDENTITY OF THE ENERGY TRANSFER CHROMOPHORES IN RENILLA AND AEQUOREA GREEN‐FLUORESCENT PROTEINS
Authors: Ward William W. , Cody Chris W. , Hart Russell C. , Cormier Milton J.
Published: January 2008

Abstract— Spectral properties of guanidine‐denaturated and pronase‐digested green‐fluorescent proteins (GFP) from two species of bioluminescent coelenterates have been investigated. Spectrophotometric titrations of Renilla and Aequorea GFP, following denaturation in 6M guanidine HCl at elevated temperature, revealed identical absorption peaks in acid (383–384 nm) and in alkali (447–448 nm) and a single isosbestic point in the visible region at 405 nm. Both proteins exhibited a spectrophotometric pK. of 8.1 in guanidine ‐HCl. Pronase digestion of the heat‐denaturated GFP's generated a methanol‐soluble blue‐fluorescent peptide with identical fluorescence emission spectra (λmax= 430 nm, uncorrected; φf1= 0.003) for both coelenterate species. These data suggest that the large absorption differences between native Renilla and Aequorea GFP molecules result from unique protein environments imported to a common chromophore.
PHOTOVOLTAGE AND PHOTOCURRENT AT TETRAPHENYLPORPHYRIN AND ZINC TETRAPHENYLPORPHYRIN ELECTRODES IN ACIDIC SOLUTIONS
Authors: Jimbo Hiroyuki , Yoneyama Hiroshi , Tamura Hideo
Published: January 2008

Abstract— Photoelectrochemical properties of tetraphenylporphyrin and zinc tetraphenylporphyrin spread on a platinum plate were investigated in acidic solutions containing a variety of electroactive species. It was found that the photovoltage measured in 0.5 M sulfuric acid solutions depended strongly on the redox potential of the electroactive species; species having a redox potential of around 1.0 V vs NHE (such as oxygen and dichromate ions) generated the largest photovoltage. A similar dependency was also observed in the photocurrent, although a little ambiguous. These phenomena are discussed from a point of semiconductor electrochemistry. The magnitude of the photocurrent was found to be influenced by solution pH, suggesting that protonation of the porphyrin film surface plays an important role in the charge transfer process.
PHOTOPHYSICS AND IONIC PHOTODISSOCIATION OF POLYESTERS WITH PENDANT 1‐PYRENYL GROUPS IN SOLUTION
Authors: Masuhara H. , Ohwada S. , Seki Y. , Mataga N. , Sato K. , Tazuke S.
Published: January 2008

Abstract—

Primary photoprocesses of polyesters with pendant pyrenyl groups in solution were studied by means of nanosecond laser flash photolysis method. The intrapolymer process of the Sl Sl annihilation was observed. Intense laser excitation brings about dense population of several fluorescent states in a polymer chain, and their mutual interaction leads to efficient deactivation. This process is confirmed by excitation intensity dependence of fluorescence spectra and fluorescence intensity. It was also confirmed that the T‐T absorption intensity decreases as the degree of polymerization increases. This low formation yield of the triplet state in the polyesters is ascribed mainly to the above Sl Sl interaction. In addition the polymer effect on the ionic photodissociation yield of the polyester‐electron acceptor was investigated. The yield decreases as the degree of polymerization increases. This effect is due to slow solvation processes, which may be due to low micropolarity and high microviscosily around the polymer chain.
THE INTERACTION OF CHLOROPHYLL‐A WITH DETERGENT MICELLES
Authors: Brown Robert G. , Evans E. Hilary
Published: January 2008

Abstract—

Absorption and fluorescence spectra of Chl‐a in ethanol, ethanol/water mixtures and aqueous sodium dodecyl sulphate are reported. Contrary to a previous report, it is found that Chl‐a is not solubilized in the anionic detergent as a microcrystalline form.
LONG‐RANGE TRIPLET‐SINGLET ENERGY TRANSFER FROM ENZYME GENERATED TRIPLET ACETONE TO XANTHENE DYES
Authors: Durán Nelson , Cilento Giuseppe
Published: January 2008

Abstract—

Enzyme‐generated and protected acetone transfers its energy to xanthene dyes by a nontrivial process. The relative populations of the S1 state are indicative of the operation of a heavy atom effect, being 1:15:100 for fluorescein, eosine and Rose Bengal. On the other hand Stern‐Volmer constants and kET0 values are similar for the three dyes and are remarkably higher than for collisional processes.

It is tentatively suggested that at least for eosine and Rose Bengal, a triplet‐triplet cxciton transfer may occur to populate an upper triplet state of the dye followed by heavy‐atom enhanced intersystem crossing to the S1 state.
DNA PHOTOREACTIVATING ENZYME FROM SILKWORM
Authors: Muraoka Noriko , Okuda Atsuyuki , Ikenaga Mituo
Published: January 2008

Abstract—

An ammonium‐sulfate‐precipitable (33–70%) fraction in extracts from eggs of silkworm Bombyx mori contains photoreactivating enzyme that reactivates the transforming activity of UV inactivated Hemophilus influenzae DNA. The action spectrum for in vitro photoreactivation with the enzyme has a broad peak around 365–385 nm, with a shoulder extending to 460 nm. This relatively higher photoreactivation efficiency at wavelengths longer than 450 nm seems to be a unique feature of DNA photoreactivating enzyme of silkworm. Using gel filtration, a mol wt of 42,000 was estimated for the enzyme. Optimum and isoionic pH of the enzyme were 7.2 and 5.4, respectively. These properties of silkworm enzyme are within the range of variations in reported biochemical characteristics of photoreactivating enzymes from different species.
EXISTENCE OF HYPSORHODOPSIN AS THE FIRST INTERMEDIATE IN THE PRIMARY PHOTOCHEMICAL PROCESS OF CATTLE RHODOPSIN
Authors: Kobayashi Takayoshi
Published: January 2008

Abstract—

It has long been believed that bathorhodopsin is the first intermediate of visual process for cattle rhodopsin. In the present paper hypsorhodopsin is shown to be the first intermediate by the use of picosecond spectropic technique. The main first intermediate, hypsorhodopsin, is formed with the time constant of 15 ± 5 ps. The time constant of the formation of bathorhodopsin from hypsorhodopsin is 50 ± 20 ps. Bathorhodopsin intermediates formed directly from excited state rhodopsin and those formed indirectly through hypsorhodopsin are 71/2#% and 93%, respectively, of total bathorhodopsin intermediates in octylglucoside buffered solution. Batho intermediates formed directly and indirectly are 0% and 100%. respectively, of total batho intermediates in LDAO buffered solution.
PHOTOCONDUCTIVITY AND PHOTOVOLTAIC EFFECTS IN LANGMUIR‐BLODGETT FILMS OF CHLOROPHYLL‐a
Authors: Jones R. , Tredgold R. H. , O'Mullane J. E.
Published: January 2008

Abstract—

The DC photoconductivity and photovoltaic effect in Langmuir films of Chlorophyll‐a (Chi a) of precisely controlled thickness formed between Al and Au electrodes have been extensively investigated. The dark conductivity and dark voltage are almost abolished in a N2 atmosphere. The action spectrum of the photocurrent closely resembles the monolayer absorption spectrum of Chl indicating that the primary event in photoconduction is the generation of singlet excited states. Thicknessdependence studies on the photoconductivity indicate that carrier generation is a surface process and that the mean diffusion length of the excited state is approximately 20 nm. In short (˜1 s) light exposures the photocurrent always increases linearly with both the applied voltage and the light intensity. In continuous light the current‐voltage characteristics are highly non‐linear and the photocurrent shows a square‐root intensity dependence at high intensities and small applied potentials. These results are interpreted in terms of second‐order recombination and charge‐trapping processes at high carrier densities. The photovoltage usually shows a logarithmic intensity dependence at high intensities and its maximum value in thick films is 800 mV with the Al electrode acquiring a negative polarity. This behaviour, together with some observations on the asymmetry of photocurrent‐voltage characteristics and the effect of substituting an aqueous top electrode for Au, further suggest that the photoactive surface is a p‐n junction between the Chl and Al2O3 layers.
INDUCED REPAIR IN ESCHERICHIA COLI: INDUCTION BY ULTRAVIOLET LIGHT AT‐79°C
Authors: Rader Mildred , Fluke D. J. , Pollard Ernest C.
Published: January 2008

Abstract—

Two of the phenomena associated with induced (S.O.S.) repair, namely induced inhibition of post radiation DNA degradation and induced radioresistance have been shown to be elicited by 245 nm radiation applied to E. coli cells in the frozen state at ‐79°C. The effect of radiation in this condition is considerably less photoreactivable than similar effects produced by exposure in the wet state. Since protein‐DNA crosslinks are believed to be formed under these conditions, such consequences of UV radiation appear to be a potent inducer of induced repair.
FLUORESCENCE PROPERTIES OF PORPHYRIN‐GLOBIN FROM HUMAN HEMOGLOBIN
Authors: Sebban Pierre , Coppey Maïté , Alpert Bernard , Lindqvist Lars , Jameson David M.
Published: January 2008

Abstract—

Fluorescence excitation and emission spectra, decays, and quantum yields are reported for the porphyrin‐globin of hemoglobin (HbdesFe) in aqueous solution of pH 8, at 4°C. A very weak fluorescence was observed in the UV (maximum at 334 nm), due to tryptophan and tyrosine residues, in addition to the strong porphyrin emission in the visible (maxima at 624 and 692 nm) reported previously. The absorption and fluorescence properties of the porphyrins of HbdesFe were compared to those for free porphyrin in organic solvents and in aqueous solution. The close similarity of the fluorescence decays and quantum yields in HbdesFe and in solution indicate the absence of stronger, specific porphyrin‐protein interactions; however, slight spectral shifts point to the existence of water molecules in the HbdesFe porphyrin environment. The fluorescence study also demonstrates the existence of efficient Trp‐porphyrin energy transfer of Förster type. The extent of transfer is in satisfactory agreement with the value expected from crystallographic data for hemoglobin. The results are discussed and compared to previous fluorescence studies of hemoglobin and apohemoglobin. An improved method for the preparation of HbdesFe is reported.
SPECTROSCOPY OF POLYENES—IV. ABSORPTION AND EMISSION SPECTRAL PROPERTIES OF POLYENE ALCOHOLS RELATED TO RETINOL AS HOMOLOGUES
Authors: Das Paritosh K. , Becker Ralph S.
Published: January 2008

Abstract—

A number of polyene alcohols related to retinol as homologues have been examined for their spectral and photophysical properties. The absorption spectra of the polyene alcohols with short polyene chainlength show an intense band system with its maximum at 3000–4000 cm‐1 above that of the main band system. The intensity of this higher‐energy band system decreases sharply as the polyene chainlength is increased. All the polyene alcohols fluoresce strongly or moderately strongly at 77 K, the intrinsic fluorescence lifetimes being significantly longer than those expected from the oscillator strengths of the main, low‐energy absorption band system. Fluorescence (relatively weak) is also observed at room temperature in the cases of polyene alcohols of long chainlength. A discussion is presented regarding the possible assignments of the various observed absorption band systems, state order and nature of the lowest excited singlet state, and aggregate formation (in 3‐methylpentane at 77 K) and its effect on spectral and photodynamical behavior.
OBSERVATIONS OF C‐S AND S‐S BOND CLEAVAGE IN THE PHOTOLYSIS OF DISULFIDES IN SOLUTION
Authors: Morine Gerald H. , Kuntz Robert R.
Published: January 2008

Abstract— A comparison of the transient absorption spectra from the photolysis of disulfides in solution suggests that C‐S bond breakage is a common primary photolytic process. This process becomes more important as the resulting carbon centered radical is stabilized by increasing alkyl substitution or resonance interaction with an aromatic system. The perthiyl radical product is characterized by λmax?380 nm,ε380?1700 M−1 cm−1 and decays by second order kinetics with k2?3.7×108M−1 s−1 in water.

In the presence of O2, the photolysis of disulfides which produce the thiyl radical give transient absorptions in the 500–600 nm region. Possible identities of these transients are discussed.
PHOTOREACTIVATION OF ULTRAVIOLET IRRADIATED NON‐DIVIDING POPULATIONS OF ICR 2A FROG CELLS
Authors: Rosenstein Barry S. , Kantor G. J.
Published: January 2008

Abstract— Ultraviolet (UV) irradiation of non‐dividing populations of ICR 2A frog cells led to their detachment from the surface of the culture dish and eventual lysis. Exposure of the cells to photoreactivating light after UV irradiation prevented cell killing and was accompanied by a loss of endonuclease sensitive sites from DNA. This photoreversal did not take place when the cells were exposed at 4°C to photoreactivating light indicating that the reversal was the result of photoenzymatic repair. As the action of photoreactivating enzyme is specific for the repair of pyrimidine dimers in DNA, these results suggest that pyrimidine dimers in DNA are the critical lesions leading to the death of non‐dividing populations of UV irradiated cells.
THE ANAEROBIC PHOTOLYSIS OF TRYPTOPHAN CONTAINING PEPTIDES—II
Authors: Ddillon J.
Published: January 2008

Abstract A number of trp–containing peptides (gly‐l‐trp, l‐ala‐l‐trp, l‐trp‐gly and N‐acetyl‐trp) have been photolyzed under anaerobic conditions. Analysis of the resultant photoproduct mixtures suggests the intermediacy of an hydrated electron in the case of trp‐gly and N‐acetyl‐trp. Amino acid trp peptides deaminate with a concomitant cyclization to the 4‐position of the indole. This appears to occur via a short‐lived radical indole complex. Little difference was detected between photoproduct mixtures using either vycor or a Corning CS‐0‐54 (cut off ca. 295 nm) as filters. Thus these reactions can occur both above and below the ionization point of trp.
A WATER‐SOLUBLE RUBRENE DERIVATIVE: SYNTHESIS, PROPERTIES AND TRAPPING OF 1O2 IN AQUEOUS SOLUTION
Authors: Aubry J. M. , Rigaudy J. , Cuong Nguyen Kim
Published: January 2008

Abstract A rubrene derivative has been synthesized as a new trap for singlet oxygen in aqueous solution. Photooxygenation and evolution of the endoperoxide under various conditions have been investigated. This trap may be used either as a colorimetric test or as a specific one by isolation of the endoperoxide.
ON THE CONSTRUCTION OF NANOSECOND TIME‐RESOLVED EMISSION SPECTRA
Authors: Meech S. R. , O'Connor D. V. , Roberts A. J. , Phillips D.
Published: January 2008

Abstract Two common methods of obtaining nanosecond time‐resolved spectra (TRES) are compared. TRES measured directly are distorted owing to convolution of the fluorescence signal with the exciting pulse but can be obtained with ease. Undistorted TRES, constructed from deconvoluted decay curves, suffer from poor spectral resolution, require much experimental and computation time to produce and may not be completely free from distortions. Nevertheless, they must be used for quantitative calculations. It is recommended that the method of obtaining TRES should be determined by the type of information required.
THE EFFECT OF CHRONIC APPLICATIONS OF TRETINOIN(RETINOIC ACID) ON ACUTE RESPONSES OF MAMMALIAN SKIN TO UVB RADIATION IN VIVO
Authors: Epstein J. H. , Grekin D. A.
Published: January 2008

Abstract The effects of long—term applications of tretinoin(retinoic acid; RA) on acute responses to UVB radiation were examined in hairless mouse skin in vivo. The skin was examined histologically and the radioactive tracer [3H]‐thymidine was used to study premitotic semiconservative DNA synthesis in the epidermal basal cells. Ten and 23 wk applications of a 0.05% RA solution (3 times a wk) induced epidermal acanthosis, hypertrophy of the individual cells and an increased number of [3H]‐thymidine‐labelled basal cells. At both time periods there was a distinct reduction in the expected inhibition of DNA synthesis at 4 h and the expected acceleration of DNA synthesis at 48 h after a single exposure to UVB radiation. In addition, the histologic morphology was unchanged at 48 h post irradiation. Thus, the repeated RA applications had a definitive influence on at least two aspects of the cutaneous response to UVB energy.
ULTRAVIOLET PHOTOIRRADIATION OF DAUNOMYCIN AND DNA–DAUNOMYCIN COMPLEXES
Authors: Gray P. J. , Phillips D. R.
Published: January 2008

Abstract— Daunomycin and daunomycin–DNA complexes have been irradiated with UV light for up to 1 h. The drug was degraded to a variety of precipitates, all of which were devoid of the sugar moiety and these precipitates were further degraded by photobleaching. The precipitates have been fractionated by HPLC. The major component (resulting from 10min irradiation of a deoxygenated drug solution) was characterized by proton NMR and field desorption mass spectrometry as a modified aglycone (ring A was aromatic and was de‐acetylated). The production of hydrogen peroxide, photobleaching and the formation of precipitate were all inhibited by the addition of DNA. All of these effects appear to depend on the free drug concentration in solution. In the absence of DNA, all of these effects were enhanced by the presence of oxygen and diminished if the solutions were deoxygenated with argon.
MAINTENANCE OF DNA REPAIR CAPACITY IN DIFFERENTIATING RAT MUSCLE CELLS IN VITRO
Authors: Koval Thomas M. , Kaufman Stephen J.
Published: January 2008

Abstract— Unscheduled DNA synthesis has been measured at several times during the differentiation of cultured rat skeletal muscle cells in response to exposures to 254nm UV light. There is no change in the amount of repair DNA synthesis as the cells fuse and differentiate from postmitotic prefusion myoblasts to multinucleated contracting myotubes.
ELECTRIC DICHROISM OF PURPLE MEMBRANE SUSPENSIONS
Authors: Kimura Yoshiaki , Ikegami Akira , Ohno Koki , Saigo Satoshi , Takeuchi Yasuaki
Published: January 2008

Abstract— Suspensions of purple membranes were exposed to reversing rectangular pulses of relatively low electric field (less than 100V/cm) at various frequencies. Orientation of the membranes was estimated by measuring linear dichroism at 565nm. In the electric field of frequency lower than about 10Hz the purple membranes tended to align perpendicular to the electric field. This orientation was induced mostly by permanent dipole which was perpendicular to the membrane surface. The value of permanent dipole moment was determined to be 140D per protein at pH 7.0, 25°C, in the presence of 5mM phosphate buffer.

In an electric field of frequency more than 100Hz the membrane tended to align parallel to the electric field. Electric polarizability parallel to the membrane surface was estimated to be 1 ± 10−12 cm3 under the same conditions.

Electric dichroism of light‐adapted and dark‐adapted purple membranes was found to coincide with each other at high frequency. From this result the angle of retinal to the membrane surface was concluded to be the same between light‐adapted and dark‐adapted bacteriorhodopsins.
FLUORESCENCE RELAXATION KINETICS AND QUANTUM YIELD FROM THE ISOLATED PHYCOBILIPROTEINS OF THE BLUE‐GREEN ALGA NOSTOC SP. MEASURED AS A FUNCTION OF SINGLE PICOSECOND PULSE INTENSITY, I
Authors: Wong D. , Pellegrino F. , Alfano R. R. , Zilinskas B. A.
Published: January 2008

Abstract— Phycobilisomes from the blue‐green alga Nostoc sp. are known to contain the phycobiliproteins: c‐phycoerythrin (c‐PE), c‐phycocyanin (c‐PC) and four forms of allophycocyanin (APC I, II, III, and B). We have made a detailed study of the effects of the intensity of a single 6 ps excitation pulse on the decay kinetics and the yield of fluorescence in the individual isolated phycobiliproteins at pH 7 and 23°C. The risetime of the fluorescence of c‐PE, c‐PC and APC was > 12 ps. We found that the decay of the fluorescence was exponential at intensities of 1014 photons/cm2 in all the phycobiliproteins; the lifetimes being 1552 ± 31ps for c‐PE, 2111 ± 83ps for c‐PC, 1932 ± 165ps for APC I, 1870 ± 90ps for APC II, 1816 ± 88ps for APC III, (1869 ± 62ps for the averaged APC's I, II, and III), and 2667 ± 233 ps for APC B. We also found that the fluorescence decay became non‐exponential in c‐PE at excitation intensities < 1014 photons/cm2, but was exponential for all the other phycobiliproteins even at a pulse intensity of 1015 photons/cm2. The relaxation times of c‐PE and c‐PC decreased with excitation intensity above 1014 photons/cm2. For c‐PE and c‐PC the relative fluorescence vs excitation intensity was readily described by a relationship derived for a model in which exciton–exciton annihilation occurs. In APC the fluorescence yield and relaxation time were only slightly dependent on the excitation intensity. The results are interpreted to indicate the occurrence of singlet–singlet annihilation intramolecularly among the several phycobilin chromophores within the individual phycobiliprotein molecules in solution. The s to f transfer time is less than 12ps in c‐PC.
THE EFFECT OF pH ON THE FLUORESCENCE OF COMPLEXES OF HUMAN SERUM ALBUMIN AND BOVINE SERUM ALBUMIN WITH BILIRUBIN
Authors: Lee J. J. , Gillispie G. D.
Published: January 2008

Abstract— Fluorescence studies as a function of pH clearly show that the environment and conformation of bilirubin bound to human serum albumin (HSA) are quite different than those for binding to bovine serum albumin (BSA). The visible fluorescence of the bilirubin‐BSA complex is maximal at the extremes of pH; in contrast, the bilirubin‐HSA complex fluorescence is at a maximum, near physiological pH.
RESPIRATION RESPONSES OF A polA1 AND A tif‐1 MUTANT OF ESCHERICHIA COLI TO FAR‐ULTRAVIOLET IRRADIATION*
Authors: Swenson Paul A.
Published: January 2008

Abstract— Cessation of respiration in Escherichia coli 60min after far‐ultraviolet (254 nm) irradiation is dependent upon the recA and lexA gene products and is regulated by cyclic 3′,5′‐adenosine monophosphate (cAMP) and its receptor protein. Respiration responses to UV irradiation were studied in two E. coli B/r mutants, polA1 and tif‐1, both of which express other rec/lex functions (such as mutagenesis) after UV irradiation. The cells were grown on glycerol minimal medium supplemented with required amino acids. After receiving a relatively high UV fluence, the polA1 mutant, deficient in DNA polymer‐ase I, showed a respiration shutoff response like the wild type cells. 5‐Fluorouracil and rifampin, an inhibitor of initiation of RNA synthesis, did not prevent respiration shutoff in the mutant cells as they did in the wild type cells. Thus, RNA synthesis is not necessary for cessation of respiration in polA1 cells and the process is not an induced one. At lower fluences which did not shut off respiration of polA1 cells, cAMP did not cause a more complete shutoff as it did for the wild type cells. The tif‐1 mutant has a modified recA protein, and when unirradiated cells are incubated at 42°C they form filaments, mutate, and show other rec/lex responses. This mutant did not shut off its respiration at either 30 or 42°C, and the response was not modified by cAMP. An E. coli K12 strain, W3110, was also tested for its respiration response to UV. At 52J/m2 respiration did not shut off and cAMP had no effect.
DYE BINDING AND PHOTODYNAMIC ACTION
Authors: Amagasa Jumpei
Published: January 2008

A variety of natural and synthetic compounds can act as effective photosensitizers in biological systems, including psoralens, flavins, porphyrins, acridines, phenothiazines, xanthenes, quinones, polyenes, haloaromatics and inorganic ions. These, in the presence of light and oxygen, inactivate and modify the integrity of important biomolecules and cellular structures, leading to cell death, mutation and other special function losses [70,118,119]. Many photosensitizers can act as mediators of photodynamic and non‐photodynamic reactions, depending on the experimental conditions. Although a great variety of photosensitized reactions may occur with different sensitizers and substrates, they can be classified into two types of reaction mechanisms, that is, Type I (radical) and Type II (singlet oxygen; 1O2) mechanisms. Type I and Type II reactions for important biomolecules have recently been reviewed [27, 119].
BIOLUMINESCENCE: BIOCHEMICAL AND PHYSIOLOGICAL ADVANCES
Authors: Ward William W.
Published: January 2008

Bioluminescent organisms are to be found among the bacteria, fungi, unicellular algae, and most of the major animal phyla, some of which contain hundreds of luminescent species. Early biochemical studies reflected this taxonomic diversity and often a primary focus of attention was the uniqueness of each newly isolated system. Relatively few in vitro cross‐reactions were discovered among unrelated species and five of the first six luciferins to be characterized proved to be structurally unrelated compounds. The functions of bioluminescence in many organisms were unknown and, while several theories arose, these theories seldom addressed the part that light production might play in the ecology of an organism or a population. Major advances on each of these fronts have been made during the past decade. Biochemical research has centered on the chemical mechanism(s) of luminescence and a single type of chemical species, a dioxetanone, has emerged as a common intermediate in several (but not all) bioluminescence and chemiluminescence systems. Likewise, in the last 10 years, numerous interphyletic cross‐reactions have been discovered and the ecological functions of bioluminescence for a large number of species have been established. Intensive studies are continuing on reaction mechanisms, especially those involving the bioluminescent bacteria, and much remains to be learned about the protein biochemistry of all luminescence systems. Amino acid sequence determinations and X‐ray crystallographic studies have been initiated in several laboratories and, in others, attempts are being made to clone the genes that code for bioluminescence proteins. Sensitized bioluminescence has been implicated in representatives of both prokaryotic and eukaryotic organisms. Low level biological chemiluminescence has been investigated in a variety of systems including liver microsomes and phagocytic leucocytes using sensitive photon counting devices. Perhaps the area of greatest growth, however, has been the application of bioluminescence and chemiluminescence techniques as tools of clinical research. The need for safe, sensitive and specific assay methods has, for example, stimulated the development of immobilized luciferases and luciferase‐linked enzyme systems. In addition, luminescence immunoassay has emerged as a reasonable alternative to the commonly used, but more troublesome, method of radioimmunoassay. This trend toward applications development has shifted the emphasis of some of the university laboratories and in general has improved the lines of communication between basic and applied research groups working in the area of bioluminescence.
LIFETIME AND ACTIVATION ENERGY OF THE PHOTOINDUCED QUINOID INTERMEDIATE IN PYRIDOXAL CATALYSIS
Authors: Ledbetter John W. , Hanckel John M. , Cornish Timothy J.
Published: January 2008

Abstract— The lifetime of the p‐quinoid intermediate of transamination was determined through photoinduction in the metal‐ion model system. From the dependence of the lifetime on temperature, the Arrhenius activation energy for proton transfer was 4.2–8.4 kJ/mol (1‐2 kcal/mol). The activation energy correlated well with the R group of the amino acid and demonstrated that native substrates have a very labile proton.
THE EFFECTS OF HIGH‐INTENSITY UV‐RADIATION ON NUCLEIC ACIDS AND THEIR COMPONENTS—I. THYMINE
Authors: Rubin Leonid B. , Menshonkova Tatiana N. , Simukova Natalia A. , Budowsky Edward I.
Published: January 2008

Abstract— The set of final products of thymine conversion induced by high‐intensity UV irradiation (λ= 266nm, intensity 1024‐5 × 1029 photons·s−1·m−2, pulse duration 10ns) of the dilute aqueous solution to the first approximation is similar to that formed with ionizing irradiation (γ‐irradiation of aqueous solution or autoradiolysis of a solid 2‐[14C]‐thymine). The data obtained suggest that high‐intensity UV‐induced photochemical conversion of thymine involves photoionization and/or photodissociation. These processes pass through the higher excited state(s) populated as a result of the second photon absorption by excited (most probably in the T1 triplet state) thymine molecules.
CHLOROPHYLL‐QUINONE PHOTOCHEMISTRY IN LIPOSOMES: MECHANISMS OF RADICAL FORMATION AND DECAY*
Authors: Hurley John K. , Castelli Francesco , Tollin Gordon
Published: January 2008

Abstract—Laser flash photolysis has been used to investigate the mechanism of formation and decay of the radical species generated by light‐induced electron transfer from chlorophylla(Chi) triplet to various quinones in egg phosphatidyl choline bilayer vesicles. Chlorophyll triplet quenching by quinone is controlled by diffusion occurring within the bilayer membrane (kq∼ 106M−1s−1. as compared to ∼ 109M−1s−1in ethanol) and reflects bilayer viscosity. Radical formation via separation of the intermediate ion pair is also inhibited by increased bilayer viscosity. Cooperativity is observed in the radical formation process due to an enhancement of radical separation by electron transfer from semiquinone anion radical to a neighboring quinone molecule. Two modes of radical decay are observed, a rapid (t1/2= 150μ) recombination between Chi and quinone radicals occurring within the bilayer and a much slower (t1/2= 1–100 ms) recombination occurring across the bilayer‐water interface. The latter is also cooperative, which accounts for at1/2which is dependent upon quinone concentration. The slow decay is only observed with quinones which are not tightly anchored into the bilayer, and is probably the result of electron transfer from semiquinone anion radical formed within the bilayer to a quinone molecule residing at the bilayer‐water interface. Direct evidence for such a process has been obtained from experiments in which both ubiquinone and benzoquinone are present simultaneously. With benzo‐quinone, approx. 60% of the radical decay occurs via the slow mode. Triplet to radical conversion efficiencies in the bilayer systems are comparable to those obtained in fluid solution (∼ 60%). However, radical recombination, at least for the slow decay mechanism, is considerably retarded.
PHOTOCHEMICAL CHARACTERIZATION OF COVALENTLY‐LINKED PORPHYRIN‐QUINONE COMPLEXES*
Authors: Kong Josephine L. Y. , Spears Kenneth G. , Loach Paul A.
Published: January 2008

Abstract— The fluorescence properties of a covalently‐linked porphyrin‐quinone complex and its zinc derivative were studied in a variety of organic solvents. The kinetics of fluorescence decay for both the quinone and hydroquinone oxidation states were measured in acetonitrile, dichloromethane, dimethyl‐formamide, and pentane. The fluorescence yield and kinetics of decay at room temperature were little affected in the porphyrin or zinc porphyrin complexes when the attached quinone was reduced. However, for these complexes the fluorescence yield and lifetimes were both substantially decreased in acetonitrile and dichloromethane when the quinone was in its oxidized state. These latter decay kinetics were not explainable by a process having a single exponential decay. On the other hand, little fluorescence quenching or lifetime shortening was observed in dimethylformamide or pentane, indicating unique solvent dependencies for the quenching process. Evidence was obtained for photoproduced charge separation from EPR measurements on the covalently‐linked zinc porphyrin‐quinone complex. The EPR data showed equivalent concentrations of a Zn porphyrin cation radical and a benzoquinone anion radical in acetonitrile or dichloromethane at both room temperature and 77 K. The charge separated state rapidly decayed at room temperature (in sub‐millisecond times) but was quite stable at 77 K. It is concluded that light‐induced charge separation in acetonitrile and dichloromethane at room temperature may occur from the excited singlet state with a high quantum efficiency. A photoproduced charge separated state also occurred when the covalently‐linked complexes were incorporated into egg yolk phosphatidylcholine liposomes. The quantum yield for radical formation in this latter system was 0.1 and the lifetimes of the radical species formed were many minutes.
EVIDENCE FOR A MAJOR STRONG BINDING SITE FOR TETRACHLOROSALICYLANILIDE ON HUMAN SERUM ALBUMIN
Authors: Rickwood Diane M. , Barratt Martin D.
Published: January 2008

Abstract— Solutions of human serum albumin(HSA) monomer were irradiated with UV light(360 nm) in the presence of [14C]‐3,3.4′S‐tetrachlorosalicylanilide([14C]‐T4CS).The [14C]‐T4 CS‐labeiled HSA was cleaved by cyanogen bromide and separated into two fractions. These fractions were reduced carboxymethylated and separated into their seven characteristic peptides and monitored for radioactivity. Tetrachlorosalicylanilide was found to bind mainly to one region of the sequence of HSA and this covalent binding site was located in residues 124 (Cys) to 298 (Met) of the molecule. The binding of 3,5‐dichlorosalicylamido‐4‐(2,2,6.6‐tetramethylpiperidine‐l‐oxyl (DCS‐TEMPO),a spin‐label analogue of T4CS, to HSA was studied by electron spin resonance spectroscopy. In the absence of UV light. DCS‐TEMPO bound non‐covalently (k = 6.1 times 106M1) to one major binding site on HSA. These results are evidence for the existence of a major strong binding site for the photochemical binding of T4CS to HSA.
A PHOTOSYNTHETIC PHOTOELECTROCHEMICAL CELL USING FLAVIN MONONUCLEOTIDE AS THE ELECTRON ACCEPTOR
Authors: Pan R. L. , Bhardwaj R. , Gross E. L.
Published: January 2008

Abstract— We have been developing a solar cell using the photochemistry of photosystem 1 particles and flavin mononucleotide. We have studied the effect of changing various parameters including the nature of the electron donor, its redox poise, the pH of the medium and the salt concentration. When we put all of the improvements together, we obtain 1900 μW of power (2.4 W/m2),15 mA short circuit current,and an open circuit potential of 640 mV. The maximum power conversion efficiency was 1%. Several light‐dark cycles could be observed. One of the important properties of this cell is that it can store energy in the form of chemical potential.
CAROTENOID TRIPLET STATES IN PHOTOSYNTHETIC BACTERIA
Authors: Frank Harry A. , Machnicki John , Felber Mary
Published: January 2008

Abstract— The triplet state spectra of anaerobically grown cells of Rhodopseudomonas sphaeroides GIC and R. sphaeroides wild type and aerobically grown cells of R. sphaeroides wild type were examined under reducing and non‐reducing conditions at 100 K. by electron paramagnetic resonance (EPR). Large differences in the zero field splitting parameters, |D| and |E| of the triplets are seen to arise in the different preparations. The spectra are assigned to the triplet states of carotenoids, some of which are closely associated with the reaction center and others are contained in the light harvesting complex. Taken together with the triplet state data on Rhodospirillum rubrum wild type previously published the trends in the zero field splitting parameters can be understood in terms of the extent of electron derealization in carotenoids of varying length.
DIKETONES AS PHOTOSENSITIZING AGENTS: APPLICATION TO αLAMINO ACIDS and ENZYMES
Authors: Maukinen Kauko K. , Makinen Pirkko‐Liisa
Published: January 2008

Abstract— 2,3‐Butanedione (biacetyl), phenylglyoxal, 1,2‐cyclohexanedione and similar carbonyl compounds have been used as specific arginyl probes in enzyme chemistry. Depending on irradiation conditions, these and other related carbonyl compounds may, however, cause extensive changes in the structure of an enzyme regardless of the essentiality or unessentiality of arginyl residue for enzyme activity. Particularly biacetyl and 2,3‐pentanedione are powerful and general photoinactivators of enzymes in the visible region. A striking result of this process is the virtually total, time‐dependent loss of tryptophan fluorescence of the enzyme, which is accompanied by other irreversible structural changes. Several ketones and ketone aldehydes photoinactivate enzymes in UV light as well; phenylglyoxal and 1,2‐cyclohexanedione effectively inactivated enzymes at 254 nm and in the far UV region. In most cases, these photosensitized inactivations of an enzyme can be prevented by keeping the reaction mixture in anoxic conditions or adding singlet oxygen quenchers to the reaction mixture. 2‐Thiol‐L‐histidine, 3‐methyl‐L‐histidine and other imidazole derivatives are more effective protectors of enzymes against photodestruction than N3‐.
MONOADDITION OF DICTAMNINE TO SYNTHETIC DOUBLE‐STRANDED POLYDEOXYRIBONUCLEOTIDES IN UVA AND THE EFFECT OF PHOTOMODIFIED DNA ON TEMPLATE ACTIVITY
Authors: Pfyffer Gaby E. , Pfyffer Bernhard U. , Towers G. H. Neil
Published: January 2008

Abstract— The photoreactivity of dictamnine, a furoquinoline alkaloid, towards different synthetic DNAs has been studied. The ratio of the photobinding of [3H]‐dictamnine to poly(dA‐dT) poly(dA‐dT): poly(dG‐dC) poly(dG‐dC): poly(dA‐dU) poly(dA‐dU): poly(dA) poly(dT), in relation to that of calf thymus DNA, is 18:1:0.5:0.3. Prior treatment of calf thymus DNA with dictamnine in light inhibits the subsequent incorporation of 8‐methoxypsoralen (8‐MOP). These results suggest that the sites in DNA for the photobinding of dictamnine are probably identical with those for monoad‐ducts of 8‐MOP. Furthermore, the template activity of photomodified DNA in the RNA polymerase reaction is considerably inhibited for poly(dA‐dT)poly(dA‐dT), to a lesser extent for calf thymus DNA, but almost not affected for the linear copolymer, poly(dA)‐poly(dT).
PHYSICAL AND CHEMICAL PROPERTIES OF CHLOROPHYLL RCI EXTRACTED FROM PHOTOSYSTEM I OF SPINACH LEAVES AND FROM GREEN ALGAE
Authors: Dornemann Dieter , Senger Horst
Published: January 2008

Abstract— A new chlorophyll, designated chlorophyll RCI (Chi RCI), with absorption and fluorescence properties different to other known chlorophylls, has been extracted from photosystem I (PSI) sub‐chloroplast particles of the green alga Scenedesmus obliquus; it was suggested that this chlorophyll is either the chromophore ofP–700 or the chromophore of another holochrome associated in a 1:1 molar ratio withP–700. We now report the extraction and isolation of a chlorophyll from PSI particle preparations from spinach leaves with properties identical to those of Chi RCI from Scenedesmus. Its molar ratio toP–700 measured in vivo is again approximately 1:1. Chlorophyll RCI is further characterized by its fluorescence characteristics and redox behaviour. Molecular weight determinations show that Chi RCI has a mol wt 35 units higher than that of chlorophyll a (Chi a).