bluuebunny/crossref_metadata_2025 huggingface dataset:
ESR STUDY OF ORIENTED TRIPLET MOLECULES GENERATED BY EXCITATION WITH POLARIZED LIGHT
Authors: Rabold Gary Paul , Piette Lawrence H.
Published: January 2008

Abstract— The lowest‐lying triplet states of a variety of aromatic molecules and complexes have been generated by the irradiation of these compounds in solvent glasses with plane‐polarized light. Measurements of the allowed (ΔM=± 1) ESR transitions clearly demonstrate that the triplets so formed are oriented with respect to the external magnetic field. By this method the triplet zero‐field splitting parameters, D and E, can be evaluated simply and reliably. Intramolecular energy transfer is postulated to explain the triplet spectra of Zn(o‐phen)2(NO3)2 and Zn(o‐phen)3(NO3)2. It was observed that in triplet‐triplet energy transfer from benzophenone to naphthalene there is no apparent orientation requirement between the donor and acceptor molecules. Further areas of significance and application of this technique are suggested.
PHOTO‐CHEMILUMINESCENT EMISSION IN OZONE
Authors: Wayne R. P.
Published: January 2008

Abstract— Photo‐chemiluminescence is the phenomenon of radiation from a chemiluminescent reaction in which one or more of the reactants are formed initially by a photochemical process. Such photo‐chemiluminest emission has been observed, using a flow apparatus designed for the purpose, in ozne prepared from cylinder oxygen. The emission is shown to be identical with that observed from the reaction of nitric oxide with ozone. The ultimate source of the emission is taken to be the activation in the ozonizer of nitrogen, present as a trace impurity in the oxygen; nitrogen pentoxide is the oxide of nitrogen expected to be formed in the presence of ozone. Photolysis of ozone forms atomic oxygen which reacts with nitrogen pentoxide to yield nitric oxide which subsequently enters into the chemiluminescent reaction with ozone. (Experiments are described which confirm that nitric oxide is one of the products of the reaction between atomic oxygen and nitrogen pentoxide). The variation of emitted intensity with total gas pressure, ozone concentration and linear flow velocity is shown to be consistent with the mechanism proposed.

No emission could be detected from either O2(1δg) or O2(1σ+g), which are possible products of the ozone photolysis. It is shown that while the absence of radiation from the 1σ+g; state indicates that O2(1σ+g) is not present in our system, yet the apparatus is not sufficiently sensitive in its present form to detect radiation from O2(lδg).
PHOTO‐DIMERIZATION AND PHTO‐REDUCTION OF ALPHA‐NAPTHOQUINONE IN DIFFERENT SOVENT MEDIA
Authors: Rennnert J. , Japar S. , Guttman M.
Published: January 2008

Abstract ‐Violet and ultravioet radiation are equally efficient in phot‐dimerizing aplhanathoquinone in benzene. The reactants yielding the dimeric photo‐product are moelcules in the ground state and excited ones. The photo‐reduction in 2‐propanol occurs with the same effciency for excitation in the n→* and →π* absorption bands. It is concluded that either reaction occurs via an n,π* excited state molecule, by direct excitation or after 100 per cent effucient internal conversion from the π,π* to the n,π* state.
PHOTOCHEMICAL AROMATIC HYDROXYLATION OF FLAVINS UNDER ANAEROBIC CONDIIONS
Authors: Nijenhuis B. Te , Berends W.
Published: January 2008

Abstract ‐Lumichrome and other flavins were found to undergo a hydroxylation in the aromatic nucleus on irradiation with visible light under anaerobic conditions at low pH's. Arguments are given that the first step is the first step is the addition of water to the flavin in its excited state.
pH‐DEPENDENCE OF RHODAMINE B SEMIQUINONE DISMUTATION RATE IN AQUEOUS ALCOHOLIC SOLUTION
Authors: Stevens B. , Sharpe R. R. , Bingham W. S. W.
Published: January 2008

Abstract— A single transient species is observed in absorption following the flash irradiation of dilute deoxygenated aqueous alcoholic solutions of rhodamine B in hte pH range 5.5–7.0 The second‐order decay constant for this semiquinone radical is an approximate linear function of the prevailing hydrogen ion concentration, the transient persisting for a period of from several seconds in neutral solution to several hours at pH = 12.

The slow rate of decay and its pH‐dependence are explained in terms of an electron or H‐atom transfer between the (unobserved) protonated and (observed) unprotonated semiquinone radical with simultaneous regeneration of hte D+> and production of the leuco‐dye DH:—

D·+ DH·+→ D++ DH

Insofar as the reactant concentrations are controlled by the acid dissociation constant Ka of DH.+ the data are consistent with a value of 5.5±1.0 for pKa and a pH‐independent rate constant Ko of 1.3±0.5×106 1. Mole‐1 sec‐1 at 20d̀C.
SPECTROCSOPIC STUDIES OF PURINES—III. PROPERTIES OF PURINES SUBSTITUTED AT THE SIXTH AND NINTH POSITIONS*
Authors: Klenwächter Vladimir , Drobnik Jaroslav , Augenstein Leroy
Published: January 2008

Abstract— We have investigated the effects of solvent and pH on the absorption and emission propertied of various 6‐ and 9‐substituted purines as a means of examining the nature of the directed not only at deteriming the relative energies of (π,π*) and (π,π*) states, but in particular, at examining the nature and energies of the two lowest‐lying (π,π*) states. For examplem, the attachment of a methyl or ribosyl group to the N9 of purine does not change the relative energies of the lowest‐lying (π,π*) and (π,π*) states; thus, the latter is the singlet of lowest energy. However, the lowest singles in derivatives formed by substitution at C6 are(π,π*) states—i.e. there is no long‐wavelength tail in the absorption spectra and florescence is comparable in intensity to phosphorescence. Further the absence of emission from neutaral adenine at room temperature is due to temperature quenching. Both lowest (π–π*) transtions. are contained under a common envelope and cannot be resolved in the absorption spectra. The shoulder observed in some of these compounds on the long‐wavelength slope of absorption envelope is vibrational in nature. Consideration of the effects of solvents on absorption and the analysis of luminescence spectra make it possible to locate the relative position of these (π–π*) transitions within the common envelope. In compounds with an ‐H on N9 and a free (aza) N1 (e.g. adenine, anionic hupoxanthine) the weaker, solvent‐sensitive (W) band has a higher energy then the more intense, solvent‐insensitive (S) band. When N1 is protonated, (e.g., in hypoxanthine or cationic adenine) and/or when methyl or ribosyl is substituted at N9, the order of these bands is inverted due ot a red shift of the W band. This shift is most apparent in the 9‐substituted hypoxanthines, where in non‐polar solvents the W band can be readily resolved in the absoption spectra. This inversion results in a red shift of both fluorescence and phophorescence and an increase of the P/F ratio. When chlorine or iodine is attached at C6 only phosphorescence having a very short lifetime appears due to heavy atom enhancement of single—triplet transitions.
STUDY OF PYRIMIDINE DIMERS IN MAMMALIAN CELLS SURVIVING LOW DOSES OF ULTRAVIOLET RADIATION*
Authors: Trosko J. E. , Kasschau M. R.
Published: January 2008

Abstract— Ultraviolet‐induced pyrimidine dimers were not found to be excided from the DNA of Chinese hamster cells in small oligounucleotides. At doses whereby many cells survive the radiation, the dimers were still associates with the large polynucleotides even after 48 hr of postirradiation incubation.
ON THE COMPLEX FORMATION OF ACRIDINE DYES WITH DNA‐IV. THE EQUILIBRIUM CONSTANTS OF SUBSTITUTED PROFLAVINE AND ACRIDINE ORANGE DERIVATIVES*
Authors: Löber G.
Published: January 2008

Abstract— The binding constants of the complex formation of several acridine dyes with calf thymus DNA are reported. The results indicate, that the binding tendency increases with the basicity of the dyes in the order acridine < 3–amino‐acridine < 3.6–bis‐monocetamino‐acridine < 3.6–diamino‐acridine ≅ 3.6–bis‐dimethylamino‐acndine < 3.6–diamino‐10–methyl‐acridine. The ring‐N alkylated amino‐acridines give in general the highest brinding constants, but there is no significant difference in the extrapolated values, K0, at diminishing dye concentration if the chain length of the alkyl groups is increased from methyl to amyl. Only substitution with phenyl seems to inhibit the binding. On the other hand, the weaker binding of the acndine itself is sensitive to the ring‐N alkylation and the binding tendency decreases in the order acridine > 10–methyl‐acridine > 10–propyl‐acridine. These findings could be explained, if the electrostatic binding involving the positively charged ring nitrogen, which seems to be more important for the more weakly interacting acridines, is complemented by other binding mechanisms, including possibly non‐electrostatic interactions in the case of those amino‐acridines having the strong binding effect.
PRIMARY PRODUCTS OF LIQUID WATER PHOTOLYSIS AT 1236, 1470 AND 1849 Å
Authors: Getoff N. , Schenck G. O.
Published: January 2008

Abstract— The yield of the primary products of the liquid water photolysis at 1236 and 1470 Å is reported. It was found that besides the dissociation of the excited water molecules into H and OH radicals probably e−aq is also formed. The H and OH radicals were scavenged by means of formate, and the e−aq together with a part of H2O* by adding carbon dioxide. The quantum yields determined at 1236 Å, are: Φ(H, OH) = 1.03 & 0.02, 0.06 <Φ(e−aq, H2O*) < 0.12 and at 1470 Å,: Φ(H, OH)=0.72±0.02, 0.037 < Φ(e−aq, H2O*) <0.075. The quantum yield of high purity water at 1849 Å in the absence of any scavengers is Φ(H, OH)=0.022. Previously published data by us for 1849 Å are also given: Φ(H, OH)=0.33 ± 0.01 and 0.02 < Φ (e−aq H2O*) < 0.04. Reaction mechanisms are proposed.
ON THE SUMMATION OF QUANTA FOR THE PHOTOIONIZATION OF TYROSINE AND TRYPTOPHAN IN ALKALINE SOLUTIONS AT 80°K
Authors: Vladimirov Yu. A. , Fesenko E. E.
Published: January 2008

Abstract— Some results of a study of the summation of quanta for the photoionization of tyrosine and tryptophan in frozen alkaline solution are presented. By means of a double‐beam irradiation method it has been shown that the photoionization of aromatic amino acids in such solutions proceeds via a triplet state intermediate.
PHOTOPHYSICAL AND PHOTOCHEMICAL EFFECTS OF DYE BINDING*
Authors: Bellin J. S.
Published: January 2008

Abstract— A discussion is given of the photophysical and photochemical consequences of the binding of dyes and of pigments of biological importance to polymeric substrates. The modification of the photochemical properties induced by dye binding can in large part be ascribed to the known changes in photophysical properties of dyes engendered by such interactions. Principally, these involve enhanced formation of metastable species of dye molecules and decreased opportunity for self‐quenching. In photochemical terms, dye binding thus enhances susceptibility to photoreduction, causes an increase in the quantum yield of photoreduction with increasing concentration of bound dye, and induces enhanced ability to act as a sensi‐tizer in photoreduction. Paradoxically, dye binding decreases the ability of the bound dye to act as a sensitizer in photoxidation.
FLASH PHOTOLYSIS OF FLAVINS‐II. QUENCHING OF THE PHOTOREACTIONS*,†
Authors: GREEN MAURICE , TOLLIN GORDON
Published: January 2008

Abstract— Quenching of the degradative photobleaching of FMN in anaerobic aqueous solution, and of the flavin‐sensitized photo‐oxidation of EDTA, alcohols, glycols, and glycerol, has been examined using flash techniques. The quenching can be produced by addition of KI, by successive flashes, and by increasing the flavin concentration (self‐quenching). It is concluded that the lowest triplet is the photoreactive species in all systems, that the successive flash effect is due to triplet quenching by a reaction product, and that the concentration quenching may be due to either triplet‐triplet annihilation or to reaction between a ground‐state flavin and a flavin triplet.
RATE CONSTANTS FOR THE DEHYDRATION OF SINGLE AND DOUBLE HYDRATES OF CYTIDYLYL (3‘‐5’)–CYTIDINE
Authors: HARIHARAN P. V. , JOHNS H. E.
Published: January 2008

Abstract— Cytidylyl (3′‐5′) cytidine (CpC) was irradiated with ultraviolet light (u.v.) to produce the single hydrate (a mixture of C*pC and CpC*) and the double hydrate C*pC* which were separated by electrophoresis. These photoproducts rapidly dehydrate to CpC and deaminate to a mixture of U*pC and CpU*. The rate constants for dehydration and deamination of the hydrates were evaluated for a range of pH values from 3 to 8 at 0°C. It is observed that the rate constants for decay of C*pC* lie between those for C*pC and CpC* for all pH values studied. Both single and double hydrates show minimum stability around pH 4·5 and maximum stability around pH 8. The maximum rate constants for dehydration of C*pC*, C*pC and CpC* are 0·26, 0·145 and 0.35 hr‐1 respectively and the minimum values are 0.024, 0.011 and 0.091 hr‐1 respectively all at 0°C. The rate constants for deamination of C*pC to U*pC for a range of pH values at 0°C were measured. The amount of deamination product varies from about 2 to 10 per cent of the hydrate depending on pH with the maximum amount being produced around pH 8.
TRANSFER OF ENERGY FROM REACTION CENTER TO LIGHT HARVESTING CHLOROPHYLL IN A PHOTOSYNTHETIC BACTERIUM*
Authors: Zankel Kenneth L.
Published: January 2008

Abstract— Previous evidence indicates that energy transfer in photosynthetic bacteria can occur from reaction center to light harvesting chlorophyll (the reverse of the usually considered flow) and that the amount of this flow depends on the strain of bacteria. The present report demonstrates that the action spectrum for fluorescence of Rhodopseudomonas spheroides, strain R26, is changed by adding the strong reductant dithionite. This change indicates that the amount of reverse flow can be altered chemically. The amount of reverse flow inferred from these measurements is consistent with the amount predicted from the absorption and fluorescence spectra of chromatophores and isolated reaction centers, and from the relative fluorescence yields of these two. The measurements permit an estimate of the transfer rates describing the energy flow from light harvesting to reaction center chlorophyll as well as the reverse flow. The spectrum for delayed fluorescence of Rps. spheroides, strain Ga, was found to be similar to that of the variable part of the fluorescence. This is a necessary, but not sufficient, condition that the energy for delayed fluorescence originates in the reaction centers.
ETUDE PAR SPECTROSCOPIE D'ECLAIRS DU TRANSFERT D'ENERGIE CHLOROPHYLLE‐CAROTENOIDE
Authors: Mathis Paul
Published: January 2008

Abstract— Energy transfer from chlorophyll A in its lowest triplet state to carotenoid pigments is demonstrated by rapid flash photolysis experiments.

Two systems are used; the first consists of chlorophyll A and p carotene in organic solvents: in diluted solutions, energy transfer is diffusion controlled. The second consists of chlorophyll A and lutein incorporated into digitonin micelles suspended in water; with this system a very rapid energy transfer is observed (< 0.4 × 10‐‐6 sec).

Energy transfer results in a carotenoid metastable state, which is supposed to be a triplet state; for lutein its half‐life is 8·9 × 10‐‐6 sec, and it has an absorption peak at 518 nm. Depopulation of lutein ground state, around 450 nm, can be observed, as well as the reactivity of oxygen towards the metastable state.

Most of these results were obtained with a Q‐switch ruby laser as exciting source (6943 Å). A 4350 Å flash can also be obtained by two successive non linear effects. Using this flash for exciting chlorophyll A alone, a strong signal is detected, due to its triplet state. By exciting directly B carotene or lutein, it is not possible to detect any metastable state with our technique.
PHOTOCHEMIE ANOMALER NUCLEINSAUREBAUSTEINE‐VI. ZUM PHOTOCHEMISCHEN REAKTIONSMECHANISMUS DES 6‐AZAURACILS†
Authors: KITTLER L. , LÖBER G.
Published: January 2008

Abstract— The photohydration reaction of 6‐azauracil has been investigated in the presence of paramagnetic ions, at different pH and in the presence of benzophenone, acetophenone and acetone as sensitizers. Paramagnetic ions inhibit photohydrate formation and there is a linear relation between the magnetic moment of the added metal ions and the half lifetime of the photoreaction. By reactivation experiments it was shown that the hydration reaction is mainly quenched. From the pH dependence of the photoreaction of 6‐azauracil and its N‐methyl‐derivatives it follows that the properties at the N3‐atom are important. Thus, the reaction was decreased strongly if the N3‐position is protonated, while methyl substitution at the same position causes an increase. The small differences between the pKs of the ground state and the photochemical ly active state as well as the quenching experiments indicate that the triplet state is involved in the hydration reaction. Strong evidence for this was also the triplet‐triplet transfer which increases in going from benzophenone to acetophenone and acetone. Thus the photochemically active state of 6‐azauracil leading to hydration differs from that of uracil where the hydrate forming reaction occurs via the excited singlet state.
POLARIZATION OF FLUORESCENCE FROM BACTERIOCHLOROPHYLL IN CASTOR OIL, IN CHROMATOPHORES AND AS P870 IN PHOTOSYNTHETIC REACTION CENTERS
Authors: EBREY T. G. , CLAYTON R. K.
Published: January 2008

Abstract— The polarization of fluorescence from isolated photosynthetic reaction centers and from light harvesting chlorophyll in photosynthetic units was measured over a wide range of exciting wavelengths. In addition, the fluorescence polarization of bacteriochlorophyll was measured. The simplest interpretation of the data is that in the bacterial reaction center, the three chlorophyll molecules closely associated with photochemical oxidation do not have their transition moments parallel to one another. Highly polarized fluorescence was also observed from the intact photosynthetic unit.
EFFECT OF DESASPIDIN AND DCMU ON PHOTOKINESIS OF BLUE‐GREEN ALGAE*
Authors: NULTSCH W.
Published: January 2008

Abstract— The effect of desaspidin and DCMU (3–(3.4‐dichlorophenyl)‐1,1‐dimethylurea) on the speed of movement in light and dark of the blue‐green alga Phormidium uncinatum has been investigated. Desaspidin, which uncouples oxidative phosphorylation and predominantly cyclic photosynthetic phosphorylations, inhibits movement in the dark and light as well, but dark movement is more sensitive. Movement in the light is more sensitive under anaerobic conditions than in air. The inhibitory effect of desaspidin is markedly increased by DCMU, which inhibits non‐cyclic electron transport and coupled phosphorylation in air as well as under argon. There is no evidence for any photodestruction of desaspidin in air, provided that no ferricyanide is present in the medium. These findings are interpreted to confirm the concept that photokinesis (i.e. a light induced acceleration of movement in microorganisms) is the result of an increased ATP production by photosynthetic phosphorylation and that both cyclic and non‐cyclic photophosphorylations supply energy for the movement in blue‐green algae.
A SPECTROSCOPIC INVESTIGATION OF AGGREGATIONS IN CHLOROPHYLL SOLUTIONS†
Authors: AMSTER R. L.
Published: January 2008

Abstract— Absorption and emission spectra are reported for polar and non‐polar solutions of chlorophyll a and chlorophyll b. These spectra can be interpreted in terms of the formation of chlorophyll dimers and more highly aggregated forms. The phosphorescence spectra of polar and non‐polar solutions of chlorophyll a are identical and are associated with emission from a π‐π‐* triplet state.
PHOTOCHEMICAL DEGRADATION OF KERATINS
Authors: LENNOX F. G. , ROWLANDS R. J.
Published: January 2008

Abstract— Twenty‐nine samples of fur, hair. wool and feathers have been irradiated with a Sunlamp (Λ max. 310 nm) and with a 2 kW mercury vapour lamp emitting mixed U.V. and visible radiation resembling sunlight. Photodegradation is accompanied by progressive yellowing when irradiated with the Sunlamp. It is accompanied by bleaching followed by yellowing, or by bleaching throughout irradiation if the initial yellowness is high, when exposed to the 2 kW lamp. A group of nine fur and hair samples, representing four different orders of mammals, are the most sensitive to yellowing, followed by a group of ten wool and hair samples from the Artiodactyla and finally by the feather keratins which are less susceptible than the α‐keratins. Amino acid analysis of the keratins before and after Sunlamp irradiation shows strong correlation of yellowing both with the initial concentration of tryptophan and with its destruction during irradiation. Similar correlations of yellowing with destruction of other amino acids are less significant. Preliminary washing with non‐ionic detergent increases susceptibility to u.v. yellowing.
A DUAL‐BEAM SOURCE OF ACTINIC LIGHT FOR PHOTOSYNTHESIS RESEARCH
Authors: MARGOZZI ANGELO PAUL , HENDERSON MILTON , WEAVER ELLEN C.
Published: January 2008

Abstract— A dual‐beam source for providing illumination of white or nearly monochromatic light for photosynthesis studies is presented. The device provides programmed, repetitive sample illumination with variable intensity, pulse duration and sequence and a means of monitoring that program. It utilizes a lamp with an integral heat rejecting reflector, and a fiber optic bundle which efficiently transmits the light, diffusely and evenly illuminating the sample.
MECHANISMS OF SENSITIZED PHOTOCHEMICAL cis‐trans‐ISOMERIZATION IN SOLUTION†
Authors: TURRO NICHOLAS J.
Published: January 2008

Abstract— The mechanisms of sensitized cis‐trans‐isomerization of olefins and polyenes are discussed. Three general mechanisms which embrace a range of interactions between the sensitizer and olefin or polyene are considered: radiationless electronic excitation transfer, chemical addition‐elimination, and energy transfer to non‐spectroscopic states.
PREPARATION AND PROPERTIES OF NEW VISUAL PIGMENT ANALOGUES FROM 5,6‐DIHYDRORETINAL AND CATTLE OPSIN*
Authors: Blatz Paul E. , Dewhurst Peter B. , Balasubramaniyan V. , Balasubramaniyan P. , Lin Mow
Published: January 2008

Abstract— On irradiation of all‐trans 5,6‐dihydroretinal (I), two opsin‐active isomers are formed. Both these isomers (believed to be the 11‐cis and 9‐cis isomers) individually couple with cattle opsin to form complexes which have maximal absorption at 465 nm. These complexes satisfy all the established criteria characteristic of synthetic visual pigments.
STUDIES ON THE PHOTO‐C4‐CYCLO‐ADDITION REACTIONS BETWEEN SKIN‐PHOTOSENSITIZING FUROCOUMARINS AND NUCLEIC ACIDS*
Authors: Musajo L. , Rodighiero G.
Published: January 2008

Abstract— Among the natural or synthetic furocoumarins (psoralens) a group exists which has interesting biological properties, the best known of which is skin‐photosensitization. The mechanism of action has remained unclarified for a long time. Furocoumarins lack photooxidative properties; they act by a mechanism that does not require oxygen and are therefore different from photodynamic substances. Photosensitizing furocoumarins when irradiated at 365 nm react with nucleic acids to give a C4‐cyclo‐addition to the 5,6‐double bond of the pyrimidine bases engaging their 3,4‐ or 4‵,5‵‐double bond. Differences exist in the behaviour of the various furocoumarins; psoralen reacts equally well with native DNA, with denatured DNA and with RNA, whereas bergapten, xanthotoxin and 8‐methylpsoralen at room temperature react to a much greater extent with native DNA than with denatured DNA and with RNA. A temperature effect has also been observed. In the case of native DNA an intercalation, occurring in the dark, of furocoumarins between two adjacent base pairs of the double helix is suggested as the first step in the reaction. The photoreaction is not accompanied by breaks in the polynucleotide chain or by conformational modifications of the macromolecule. A parallelism was observed between the order of activity of the substances of this group for photoreaction with native DNA and for skin‐photosensitization. Ehrlich ascites tumor cells lose completely their capacity of transmitting the tumor after irradiation in the presence of psoralen, bergapten and xanthotoxin. By hydrolysis of DNA extracted from Ehrlich ascites tumor cells irradiated in the presence of psoralen a photoadduct between psoralen and thymine was isolated.
RECOVERY OF HAEMOPHILUS INFLUENZAE FROM ULTRAVIOLET AND X‐RAY DAMAGE
Authors: BARNHART B. J. , COX S. H.
Published: January 2008

Abstract— Results of experiments on reactivation of ultraviolet (u.v.)‐irradiated Haemophilus influenzae and cellular reactivation of u.v.‐damaged transforming deoxyribonucleic acid (DNA) and bacteriophage are reported. Liquid‐holding recovery (LHR) is small for the u.v.‐sensitive mutant BC100 which, relative to the wild type, also has greatly reduced host‐cell reactivation (HCR) of u.v.‐inactivated phage, and competent cultures show reduced competent cell reactivation (CCR) of u.v.‐inactivated transforming DNA. BC100 cells can be transformed with DNA isolated from the wild type strain Rd to a u.v. resistance similar to that of Rd, and irradiation of the DNA reduces the transformation frequency for this marker (uvr). The u.v.‐resistant mutant BC200 displays very little LHR under the usual conditions where reactivation occurs after plating. The colony‐forming ability (cfa) of irradiated BC200 is greater than that of Rd, but HCR and CCR are the same on this mutant as on the wild type. The major difference between Rd and BC200 is the enhanced u.v. survival of cfa of the latter. It was determined that this difference reflects cell lysis of irradiated Rd and lack of lysis in BC200 cultures. That lysis is closely correlated with damage to the bacterial chromosome is suggested by the finding that the lytic response of Rd (as determined turbidimetrically) can be negated by the liquid‐holding procedure, but lysis of BC100 (which lacks comparable DNA‐repair ability) can be only partially inhibited by this procedure. LHR occurs when post‐plating dark recovery is incomplete, is temperature‐sensitive, and occurs unimpeded when post‐u.v. protein synthesis is inhibited by chloramphenicol. It is suggested that enzymatically catalyzed reactivation of DNA occurs or is initiated during liquid‐holding of u.v.‐irradiated H. influenzae Rd and that the necessary enzyme(s) exists prior to appearance of u.v. lesions in the DNA. Results are reported for X‐ray inactivation of transforming DNA as assayed on BC100, Rd and BC200 and of the cfa of the three strains.
PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS
Authors: BEN‐HUR E. , ROSENTHAL I.
Published: January 2008

Abstract— The photosensitized monomerization of cis‐syn and trans‐syn cyclobutane‐type thymine dimers, and the cis‐syn thymine‐uracil dimer, using anthraquinone derivatives as sensitizers, is described.
CHEMILUMINESCENCE IN HYDROCARBON OXIDATION IN SOLUTION. A QUANTITATIVE STUDY OF THE EXCITATION AND EMISSION STEPS†
Authors: BELYAKOV V. A. , VASSIL'EV R. F.
Published: January 2008

Abstract— Chemiluminescence in the visible region during liquid‐phase hydrocarbon oxidation is excited by peroxy radical disproportionation; a carbonyl compound, P, in the triplet state is the emitter. Several types of energy transfer from P to acceptors are considered. These provide valuable information (lifetimes, rate constants, emission yields) relevant to triplet state molecules. The excitation yields are estimated making use of this information, the absolute chemiluminescence intensities and the reaction rates. Electronic excitation of P, vibrational excitation of ground state P and reverse decomposition of an intermediate complex into initial peroxy radicals are considered as competing processes strongly dependent on transformation of chemical energy into vibrations.
PARAMETRES PHYSIQUES CARACTERISANT LE DOMMAGE THERMIQUE SELECTIF DE MITOCHONDRIES EN MICRO‐IRRADIATION PAR LASER
Authors: SALET C. , LUTZ M. , BARNES F. S.
Published: January 2008

Abstract— Laser micro‐irradiation was used to study the uptake of low levels of strain (Janus Green B) by the mitochondria of tissue culture cells and the selective lesions induced by the irradiation. A comparison of the thermal effects produced in the cells and in a stained model system (albumin), permitted the calculation of the degree of concentration of stain in the mitochondria from the staining media (approximately 500 fold). Evaluation of the various parameters of Laser irradiation, particularly thermal events, resulted in optimal irradiation times for measurement of local stain concentration, as well as for the selective destruction of the stained mitochondria. For the studies of the latter phenomenon a lower limit for irradiation duration is set by optical saturation and dielectric breakdown.
STUDIES ON THE PROTECTIVE FUNCTION OF THE CAROTENOID PIGMENTS OF SARCINA LUTEA
Authors: MATHEWS‐ROTH MICHELINE M. , KRINSKY NORMAN I.
Published: January 2008

Abstract— An investigation was made of both the composition of and mechanism of photo‐protection by the carotenoid pigments of Sarcina lutea ATCC 9341a and three induced mutants.

The wild‐type and mutants 2a and 4b were each found to contain three major pigment fractions, each fraction consisting of a single pigment having identical absorption maxima but differing from each other in chromatographic mobility. Although the mutants contain the same kinds of pigments as does the wild‐type, the mutant cells contain less pigment per cell than does the wild‐type. The third mutant, 93a, contains no colored carotenoids.

It was found that there were changes in both the absolute and relative amounts of the various pigment fractions when cultures of wild‐type, mutants 2a and 4b, grown in nutrient broth in the dark, were examined during the logarithmic and stationary phases of the growth curve. In addition, changes were observed in the pigments when the cells were exposed to light in buffer. These changes were similar in the wild‐type and in mutant 2a, but were quite different in mutant 4b. Studies of photokilling curves suggested that these changes in amounts of the various pigment fractions were not related to photoprotection, but that the important factor may be the total amount of pigment per cell.
LES CAROTENES FLUORESCENT‐ILS?*
Authors: TRIC C. , LEJEUNE V.
Published: January 2008

Abstract— –Carotenoids, with II conjugated double bonds show a lack of fluorescence. For β‐carotene, no U.V. fluorescence (300–400 nm) is observed with a quantum yield greater than 10‐4 we have observed a large hand visible fluorescence, already described by several authors, but this fluorescence remains when the β‐carotene is bleached, and must be assigned to some impurity present with β‐carotene. The fluorescence of lycopene solutions, whose quantum yield should be smaller than 10‐3, is similarly assigned to an impurity less photosensitive than lycopene. The fluorescence of canthaxanthine is also very weak (quantum yield ˜ 2. 10‐5). In the deactivation paths to the ground state, photodecomposition is quite unimportant, and probably photoisomerisation too: internal conversion appears to be extremely rapid, within a time scale comparable with the periods of vibration of the carbon atoms.
THE SPECTROSCOPY AND PHOTOCHEMISTRY OF NATURALLY OCCURRING AND SYNTHETIC CHROMENES
Authors: KOLC JAROSLAV , BECKER RALPH S.
Published: January 2008

Abstract— –All naturally occurring and synthetic chromenes studied exhibit photochromism at — 196°C and in some cases at room temperature. Chromenes containing a coumarin moiety have the least photochemistry and also exhibit the strongest emissions. Chromenes containing a hydroxyl group ortho to an acetyl group exhibit solely a phosphorescence. Lapachenole (a 7,8‐benzochromene) shows the most rapid and highest percentage conversion to the colored form and no emission. Photocolored form of evodione can be produced by a triplet energy transfer from benzophenone.
AN ANALYSIS OF FOURTH DERIVATIVE SPECTRA
Authors: BUTLER W. L. , HOPKINS D. W.
Published: January 2008

Abstract— –Fourth derivative spectra of chloroplast at – 196°C, obtained by four sequential differentiations of the absorption spectrum, were examined to determine the conditions for optimal signal‐to‐noise ratio and resolution. An appreciable improvement in the signal‐to‐noise ratio was found when the four differentiating intervals were nearly but not exactly equal. The process of differentiating digitized data with the computer was explored in order to define the rules for optimization of the fourth derivative curves.
ABSENCE OF REPAIR REPLICATION FOLLOWING ULTRAVIOLET IRRADIATION OF AN EXCISION‐DEFICIENT MUTANT OF ESCHERICHIA COLI
Authors: COOPER P. K. , HANAWALT P. C.
Published: January 2008

The excision‐repair of damaged DNA in bacteria and other systems probably requires at least three enzymes to carry out the following steps in sequence: (1) Recognition of a structural distortion in the DNA and the production of an endonucleolytic cleavage of the damaged strand near the lesion. (2) The simultaneous peeling back of the damaged strand and resynthesis of the excised region, with eventual cleavage of the damaged segment from the DNA. (3) The rejoining of the newly synthesized strand to contiguous parental DNA. Evidence for all three steps has been obtained from in vivo studies. The E. coli DNA polymerase has been shown to carry out step # 2 in vitro [1] and the polynucleotide ligase has the required specificity for step # 3[2–4]. An enzyme responsible for step # 1 has been purified from Micrococcus lysodeikticus [5,6] but not from E. coli, although a class of u.v. sensitive mutants in E. coli has been shown to be defective in this step in the repair sequence. In such mutants the release of pyrimidine dimers from the damaged DNA is not observed during post‐irradiation growth of u.v. irradiated cultures [7]. It would be predicted, as a consequence, that the next step, non‐conservative repair replication, would not be seen in these mutants. Hanawalt and Petti‐john showed this to be true for the double mutant E. coli B8‐1 that includes a deficiency in dimer excision [8]. In the present study we have looked more closely at an E. coli K‐12 strain that has only the uvrA6 deficiency that results in inability to excise pyrimidine dimers.
PHOTOREACTIVATION OF KILLING IN STREPTOMYCES‐II. KINETICS OF FORMATION AND PHOTOLYSIS OF PYRIMIDINE DIMERS AND ADDUCTS IN S. COELICOLOR AND S. GRISEUS PHR‐1*
Authors: IKENAGA M. , JAGGER J.
Published: January 2008

Abstract— A pyrimidine adduct, 6‐4‘‐[pyrimidine‐2’‐one] thymine (PO‐T)‡, observed in DNA hydrolysates of 254‐nm ultraviolet (u.v.) irradiated conidia of Streptomyces coelicolor, increases linearly with u.v. dose up to 2 × 105 ergs/mm2. Yields of thymine dimer (T○) and uracil‐thymine dimer (U○) level off at much lower doses. Initial relative rates of formation of these u.v. photoproducts are: 1:1.3:4.8 for PO‐T, T○ and U○, respectively. Similar results were obtained with a Streptomyces griseus mutant, PHR‐1.

An equation is derived to estimate the ratio of the amount of PO‐T to the total amount of thymine‐derived photoproducts at low (biological) u.v. doses. The observed PO‐T fractions compare well with the calculated values.

Rapid photolysis of the precursor of PO‐T was observed by post‐u. v. treatment at 313 nm of conidia of S. coelicolor and of S. griseus PHR‐1. The photolysis was much slower at 365 nm and did not occur at all at 405 nm. Pyrimidine dimers were not appreciably affected by post‐u. v. treatment at the above wavelengths in these Streptomyces strains. Both of these strains are phenotypically photoreactivation‐deficient, and the present results indicate that they do not possess active photoreactivating enzyme.

In earlier papers[3,4,5], the pyrimidine adduct found in acid hydrolysates of DNA was loosely referred to as “uracil‐thymine adduct (U‐T adduct)”. Such terminology is not strictly correct. The pyrimidine adduct in acid hydrolysates is PO‐T (sometimes called P2B), which could theoretically result from removal of ammonia from a C‐T adduct or removal of water from a U‐T adduct (see [6]).
CIRCULAR DICHROISM OF BOVINE RHODOPSIN
Authors: SHICHI HITOSHI
Published: January 2008

Abstract— When rhodopsin is associated with membrane particles, phospholipid may be involved in maintaining a preferred conformation of the opsin and the asymmetric structure of the chromophore of rhodopsin.
LIGHT DISTRIBUTION AND ELECTRON DONATION IN THE Z SCHEME*
Authors: BEN‐HAYYIM GOZAL , AVRON MORDHAY
Published: January 2008

Abstract— Several recent reports indicate that the photosynthetic machinery possesses a device whereby the relative distribution of absorbed light energy into the two reaction centers can be varied in response to the environment in which the photosynthesizing cells or chloro‐plasts are placed. Conditions reported which affect this distribution include the electron acceptor or electron donor system employed, the concentration of magnesium ions, and the preillumination history of the preparation. These observations are described and discussed in terms of their relevance to the interpretation of quantum yield and enhancement data.

Several laboratories have presented evidence recently that chloroplasts, after undergoing a pretreatment which destroys their capacity to evolve oxygen, can still transfer electrons via both photosystems, provided an appropriate electron donor is added. It is shown that electron donors like manganous ions and ascorbate can compete effectively with water as electron donors to Photosystem II, in untreated chloroplasts.
ISOLATION OF UNIQUE DIMER SPECTRA OF DYES FROM THE COMPOSITE SPECTRA OF AGGREGATED SOLUTIONS
Authors: ROHATGI K. K. , MUKHOPADHYAY A. K.
Published: January 2008

Abstract— Aggregation of fluorescein, eosin and rose bengal in aqueous solutions has been studied. Mathematical expressions are derived to calculate the monomer mole fractions in moderately and highly concentrated solutions. The average values of the dimer dissociation constant, Kd, for fluorescein, eosin and rose bengal in aqueous solutions at pH 12 are 0.20, 9.0×10‐3 and 40 × 10‐3 moles/l respectively. A method is developed here to isolate the dimer spectrum from the composite spectrum. The uniqueness of this method is established by comparison with other known methods. The dimer spectra of all the three dyes are reported.
SENSITIZED PHOTOOXYGENATION ACCORDING TO TYPE I MECHANISM (RADICAL MECHANISM) — PART II. FLASH PHOTOLYSIS EXPERIMENTS
Authors: KRAMER H. E. A. , MAUTE A.
Published: January 2008

Abstract— In order to gain further insight into the sensitized photooxygenation of the system thionine, allylthiourea, and oxygen, the influence of the leucothionine, which is formed during the photoreaction, was studied by flash photolysis. In the presence of leucothionine, additional thionine (Λobs= 598 nm) is reformed; i.e., leucothionine is oxidized to thionine by way of a semithionine intermediate (Λbs= 770 nm). This additional semithionine formation due to leucothionine is complete by 30 μsec after the flash. By varying the leucothionine concentration, the flash intensity and the pH it can be shown that the agent which oxidizes leucothionine to semithionine is identical to the agent which transforms semithionine to thionine.
PHOTOCHEMICAL REACTIONS OF AROMATIC KETONES WITH NUCLEIC ACIDS AND THEIR COMPONENTS I—. PURINE AND PYRIMIDINE BASES AND NUCLEOSIDES*.
Authors: CHARLIER M. , HELENE C.
Published: January 2008

Abstract— The photochemical reactions of benzophenone and acetophenone with purine and pyrimidine derivatives in aqueous solutions have been investigated by flash photolysis and steady‐state experiments.

Upon excitation of these two ketones in aqueous solutions, two transient species are observed: molecules in their triplet state and ketyl radicals. The triplet state lifetimes are 65 μsec for benzophenone and 125 μsec for acetophenone. The ketyl radicals disappear by a second order reaction, controlled by diffusion. In the presence of pyrimidine derivatives, the triplet state is quenched and the ketyl radical concentration is decreased without any change in its kinetics of disappearance. Ketone molecules in their triplet state react with purine derivatives leading to an increase in the yield of ketyl radicals due to H‐atom abstraction from the purines.

Steady‐state experiments show that benzophenone and acetophenone irradiated in aqueous solution at wavelengths longer than 290 nm undergo photochemical reactions. The rate of these photochemical reactions is increased in the presence of pyrimidine derivatives and even more in the presence of purine derivatives. Following energy transfer from the triplet state of benzophenone to diketopyrimidines, cyclobutane dimers are formed. The energy transfer rate decreases in the order orotic acid > thymine > uracil. Benzophenone molecules in their triplet state can also react chemically with pyrimidine derivatives to give addition photoproducts.

All these results are discussed with respect to photosensitized reactions in nucleic acids involving ketones as sensitizers.
CIRCULAR POLARIZATION OF FLUORESCENCE EMITTED BY AN OPTICALLY ACTIVE COMPOUND
Authors: GAFNI A. , STEINBERG I. Z.
Published: January 2008

Chiral compounds absorb circularly polarized light of opposite sense to different extents. This property, commonly known as circular dichroism, CD, is closely related to the optical rotatory dispersion of the compound under study, and has been extensively applied to the study of chiral compounds[1, 2]. On the other hand, very little information is available concerning the preferential emission of circularly polarized light of one sense over that of the opposite sense from chiral luminescent compounds. The scarcity of data about circularly polarized luminescence, CPL, is probably due to lack of suitable instrumentation for the measurement of small amounts of circularly polarized light present in a large background of unpolarized luminescence. Indeed, the only CPL data available are of a few substances which exhibit an exceptionally high degree of circular polarization in their emitted light [3, 4].
THERMOLUMINESCENCE AND TEMPERATURE EFFECTS ON DELAYED LIGHT EMISSION (CORRECTED FOR CHANGES IN QUANTUM YIELD OF FLUORESCENCE) IN DCMU‐TREATED ALGAE*
Authors: JURSINIC P. , GOVINDJEE
Published: January 2008

Abstract—

The simultaneous measurements of delayed light emission (DLE) and chlorophyll (Chl) fluorescence yield in DCMU§ treated Chlorella were made in the time range of 1 to 10 sec at various temperatures from 0 to 50°C. Similar measurements were made for DCMU treated thermophilic strain of Synechococcus in the temperature range of 0 to 75°C.

Using the basic assumption that DLE is produced by the back reaction of primary photoproducts of system II, and that two such reactions are required for it, a linear relationship between J‐1/2 (where J is energy per unit time available for DLE) and time after illumination was derived. This second‐order relationship was confirmed experimentally at several temperatures (2°, 5°, 10° and 15°C). From these analyses, reaction rate decay constants, at specific temperatures, were calculated.

An Arrhenius plot was made for these calculated rate constants. Its slope (8–10 kcal/mole) agreed well with previous reports; however, it had a region of zero slope which occurred at the physiological temperature of the organisms used.

Thermoluminescence or temperature jump delayed light emission (TDLE) was measured using various temperature conditions and it was found that not only the magnitude of the temperature jump (ΔT), but the initial and final temperatures of the sample were important. For example, a temperature jump of 8°C from 2 to 10°C gave much higher TDLE than from 12 to 20°C.

Many properties e.g., magnitude, temperature dependence and time independence of TDLE could be explained by the DLE decay data (corrected for changes in fluorescence yield) and the kinetic analysis.

It is suggested that, in addition to the back reaction of Z+ (the primary oxidized photoproduct of system II) with Q‐ (the primary reduced photoproduct of system II), a reducing entity, beyond the sites of DCMU and antimycin a action, is somehow involved in the production of slow DLE.
ENERGY TRANSFER FROM MICELLAR SODIUM PHENYLUNDECANOATE TO SOLUBILIZED NAPHTHALENE
Authors: ALMGREN M.
Published: January 2008

Abstract— Excitation energy transfer from the phenyl groups of surface active phenylundecanoate ions to naphthalene molecules has been studied under conditions such that the naphthalene molecules have been solubilized by micelles of phenylundecanoate. From measurements of the naphthalene fluorescence intensity in solutions of varying surfactant concentration the critical micelle concentration has been determined as 0·0091 M. The product of the micellar aggregation number and the efficiency of energy transfer has been obtained as 75 from measurements of both the sensitized naphthalene fluorescence and the quenching of the phenylgroup fluorescence. In the evaluation of the experimental data it has been assumed that the partition of naphthalene between the micelles and the aqueous phase may be treated as a distribution equilibrium, and that the solubilized naphthalene molecules are partitioned among the micelles according to a Poisson distribution. With this model, the naphthalene fluorescence intensities may be accounted for over the whole range of surfactant concentrations.

At high naphthalene concentrations, emission from naphthalene excimers has been observed. The possibility of self‐quenching via excimer formation is considered.

The experimental results point to a quantum efficiency near unity for the transfer of excitation energy from the phenyl groups of the surfactant ions that form a micelle to a single solubilized naphthalene molecule. The high efficiency suggests that the naphthalene molecule and the phenyl groups are present inside the micelles.
MATRIX EFFECTS ON THE RADIATIONLESS TRANSITION' S1→T1 AND T1→S0 FOR BENZENE AND N, N, N', N'‐TETRAMETHYLPARAPHENYLENE‐DIAMINE MOLECULES
Authors: BERNAS A. , TRUONG T. B.
Published: January 2008

Abstract— The present study attempts to correlate the phosphorescence life time τp at 77°K of a definite solute: tetramethylparaphenylenediamine (TMPD) with various solvents viscosity and polarity. A few experiments with benzene in the same solvents are also reported. The following results have been obtained:

The measured τp vary regularly with the sample immersion time in liquid N2, reaching a constant value after a few hours. This effect is related to the glass matrix relaxation. The rate constant Kisc (S, 1→T1) is also found to vary during relaxation of the solvent.

In the expression giving the nonradiative rate constant Knr (T1→S0), the bimolecular quenching term appears negligible for high viscosity matrices i.e. for η= 109 poises for benzene and for TMPD. Knr is found to vary linearly with log η, as well as the intersystem crossing S1→T1 rate constant Kisc.

Both Knr (T1→S0) and Kisc (S1→T1), increase with decreasing polarity of the solvent.

From our own observations and literature data[6] for C6H6 it appears that solvent viscosity does not contribute appreciably to the observed temperature effect on the solute τp when only a monomolecular triplet deactivation is operative.