bluuebunny/crossref_metadata_2025 huggingface dataset:
CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY: FLASH PHOTOLYSIS STUDIES OF THE CHLOROPHYLL‐QUINONE REACTION IN PYRIDINE
Authors: RAMAN R. , TOLLIN GORDON
Published: January 2008

Abstract— –Analysis of the effect of β‐carotene and benzoquinone on the decay curves of flash‐induced transients in chlorophyll a solutions in pyridine and isooctane indicates that the formation of quinone radicals proceeds via a ternary complex of solvent, chlorophyll and quinone. It is suggested that the solvent is the source of electrons for this process.
PHOTO ACTIVATION OF UROCANASE IN PSEUDOMONAS PUTIDA: FACTORS INFLUENCING ACTIVATION
Authors: HUG DANIEL H. , HUNTER JOHN K. , ROTH DENNIS E.
Published: January 2008

Abstract— –When washed cells of histidine‐grown Pseudomonas putida were incubated at 8°C in darkness, urocanase activity diminished after several days; most of this lost activity could be restored by treatment of cell extracts with near‐u.v. light. Sunlight and daylight were also effective for activation. Non‐irradiated extract, when added to the active preparation, did not inhibit the enzyme activity. Heated and boiled extracts with or without irradiation did not catalyze the urocanase reaction nor did they change the activity of an activated extract when added to it. Photoactivation of cell extracts did not require oxygen, was not dependent on temperature and was not prevented by dialysis. Urocanase purified by gel electrophoresis was capable of light activation. It is suggested that the photoreceptor is closely associated with urocanase since it is not separated from the enzyme by dialysis or electrophoresis.
FLUORESCENCE AND THE STRUCTURE OF PROTEIN—XX. FLUORESCENCE OF 3‐AMINOTYROSINE AND OTHER AMINOPHENOLS
Authors: COWGILL ROBERT W.
Published: January 2008

Abstract— –The fluorescence of 3‐NH2 tyrosine and of simpler isomeric aminophenols was observed in aqueous solution at room temperature. Marked changes in both emission spectrum and fluorescence efficiency were observed upon change of pH and solvent composition. An explanation for the observed behavior is offered on the basis of two effects. First, peculiarities in the emission spectra were accountable in terms of proton dissociation from the cationic amino group in the excited singlet state so that emission characteristic of the free base was observed even in acidic solutions. Second, the unexpectedly low fluorescence efficiency from the free base was shown to result from quenching by the aqueous solvent. The relevance of these studies for the fluorescence of 3‐NH2 tyrosyl groups in proteins is discussed briefly.
THE FLAVIN‐SENSITIZED PHOTOOXIDATION OF NUCLEOTIDES—II. THE PARTICIPATION OF THE FLAVIN TRIPLET STATE
Authors: KNOWLES A.
Published: January 2008

Abstract— –A study has been made of the effects of a series of nucleotides upon the electronic excited states of lumiflavin in order to determine the mechanism of their flavin‐sensitized oxidation. A hydrogen‐abstraction mechanism is ruled out, because if the nucleotide acts as a reducing agent for the excited dye molecules, it should increase the rate of reduction of the dye when the irradiation is carried out in the absence of oxygen. However, each of the nucleotides studied was found to reduce the rate of anaerobic photoreduction. While oxidation by an intermediate species such as the dye ‘moloxide’ or singlet oxygen is not entirely ruled out, our evidence suggests that the initial reaction is between the nucleotide and the flavin triplet. This results in a loss of the triplet excitation energy and is a very efficient reaction, guanosine monophosphate shewing 36 per cent of the triplet quenching efficiency of potassium iodide. The relative rates of reaction of the nucleotides with the flavin triplet exactly parallels their quantum yields of sensitized photo‐oxidation. The formation of ground‐state complexes between flavin and nucleotide and the participation of the singlet excited state of the flavin are not considered to be important.
EFFECT OF SOLUTION ENVIRONMENT ON THE ABSORPTION MAXIMA OF SCHIFF BASES OF RETINAL*
Authors: BLATZ P. E. , JOHNSON R. H. , MOHLER J. H. , Al‐DILAIMI S. K. , DEWHURST S. , ERICKSON J. O.
Published: January 2008

Abstract— –Preliminary examination of the effect of solution environment on the electronic absorption spectrum of N‐retinylidene‐n‐butylamine(I) is reported. It is established that small amounts of CO2 dissolved in certain solvents cause the formation of the conjugate acid of I. This reaction is shown to be dependent on temperature and the concentration of CO2. The pKb of I in aqueous buffer was measured spectrophotometrically and found to be 8.71. Salts of I were prepared in a number of ways and their spectra were determined in selected solvents. The Λmax varies with method of preparation, and only one method gives reproducible results. The Λmnx is a function of the solvent in which the spectrum is determined. It was also found that the absorption maximum in wavenumbers is proportional to the negative logarithm of acid concentration.
PHOTODEGRADATION OF HEXACHLOROPHENE AND RELATED POLYCHLORINATED PHENOLS
Authors: SHAFFER G. W. , NIKAWITZ E. , MANOWITZ M. , DAENIKER H. U.
Published: January 2008

Abstract— –Irradiation of hexachlorophene in absolute ethanol yields a series of dechlorinated bisphenols resulting from loss of chlorine at the ortho and para positions relative to the hydroxy groups. The two primary photoproducts. 2.2′‐dihydroxy‐3,3′, 5,6,6′‐pentachlorodiphenylmethane and 2,2′‐dihydroxy‐3,5,5′, 6,6′‐pentachlorodiphenylmethane were identified by independent syntheses.
PHOTOSENSITIZED DEGRADATION OF C‐PHYCOCYANIN*
Authors: BELLIN JUDITH S. , GERGEL CAROL A.
Published: January 2008

Abstract— –Irradiation with visible light in the presence of allylthiourea causes the transformation of phycocyanin into a ‘purple’ chromoprotein absorbing maximally at 565 and 605 nm. This reaction is irreversible, and not affected by the presence of oxygen. The product is homogeneous on electrophoresis, ultracentrifugation and chromatography, and has a molecular weight one third that of the starting material. Although apparently physically homogeneous, the action spectrum for fluorescence suggests that the ‘purple’ compound may consist of two two chromophores associated with protein moieties that are indistinguishable.
CHEMILUMINESCENCE IN THE PROCESS OF OXIDATIVE RING‐OPENING OF PURPUROGALLINQUINONES
Authors: SLAWINSKI JANUSZ
Published: January 2008

Abstract— The oxidation of purpurogalline (PPG) by alkaline solution of H2O2 pH 9–11 at 298°K is accompanied by chemiluminescence (CL) in the spectral range 400–600 nm with the maximum at 500 nm and quantum yield about 10‐6. The optimal concentrations of reactants with respect to maximal intensity are: 2 × 10‐4M PPG, 10‐2M NaOH, 1M H2O2. Activation energy calculated from the maximum intensity of CL is 8.1×0.4 kcal/mole. Light emission occurs only when OH‐groups of the phenolic ring of PPG undergo oxidation and the blue anion of o‐PPG‐quinone is formed. The rate that determines step in the reaction associated with luminescence is the nucleophilic attack of OOH‐ ion on the blue anion of o‐PPG‐quinone. In this exergonic step (‐ΔH = 63 to 230kcal/mole) the o‐ and/or p‐quinone ring is opened and carbonyl derivatives of α‐tropolone are produced. They display fluorescence in the region 400–600 nm. The fluorescence spectrum of the reaction mixture after oxidation of PPG is very close to that of CL. It is likely that carbonyl derivatives of α‐tropolone are emitters of CL.
SEPARATION ET CARACTERISATION SPECTROSCOPIQUE DU MONOMERE ET DES POLYMERES DE LA C. PHYCOCYANINE.*
Authors: VERNOTTE C.
Published: January 2008

Abstract— Monomer, trimer and hexamer states of C. Phycocyanin chromophore protein have been isolated. Owing to a very slow approach to equilibrium mixing, it has been possible to estimate the number of each type of the two chromophores ‘s’; and ‘f’ present, using a fluoros‐cence polorization method. It is found that there is one s chromophore and one f chromophore per protein monomer of molecular weight 30,000, a value in agreement with the monomer mol. wt. determined by Berns et al and by thermodynamic measurements in this laboratory. Absorption and fluorescence spectra of hexamer and monomer solutions have been compared. The hexamer solution shows greater fluorescence than the monomer solution, a phenomenon that may be attributable to a change in environment of chromophore following polymerization, with consequent change of fluorescence yield of each chromophore type and/or variation in energy transfer between them.
DELAYED‐LIGHT STUDIES ON PHOTOSYNTHETIC ENERGY CONVERSION‐IV. EFFECT OF TRIS POISONING, AND OF ITS REVERSAL BY HYDROGEN DONORS, ON THE MILLISECOND EMISSION FROM CHLOROPLASTS*
Authors: BERTSCH W. , LURIE SUSAN
Published: January 2008

Abstract— Destruction of the oxygen‐evolving activity of chloroplasts by treatment with 0.8 M Tris‐HC1 results in an extremely rapid dark decay of millisecond delayed light. Addition of electron acceptors such K3Fe(CN)6 or NADP+ does not change the decay characteristics of this msec delayed light. Artificial electron donors such as DPC partially restore the msec delayed emission to the slowly decaying situation which is found in control chloroplasts. Addition of electron acceptors to this photochemically competent system results in more rapid decay and in an increase of emission at 1 msec, as in control chloroplasts. We suggest on the basis of the delayed light data that Tris treatment induces a rapid side reaction which uselessly dissipates the oxidizing and reducing power which is stored by Photoreaction II. Artificial electron donors allow the Tris‐poisoned photoreaction to store energy long enough for utilization of the energy by normal photosynthetic reactions, as shown by the flattening of the delayed light curves. In the restored system the normal reactions of electron transport are thus able to compete with the Tris‐induced side reaction. This interpretation is supported by the finding that the restored system requires higher exciting intensities for saturation of NADP+ reduction than the control system.
COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION‐II. DAMPING OF FLASH YIELD OSCILLATION, DEACTIVATION*
Authors: FORBUSH BLISS , KOK BESSEL , McGLOIN MARION P.
Published: January 2008

Abstract— A quantitative analysis is made of a linear 4‐step model for photosynthetic O2 evolution in which each photochemical trapping center or an associated enzyme cycles through 5 oxidation states (S0, S1, S2, S3, S4). The overall reaction is: S0→ S4, S4→ S0+ O2, where kd= rate of dark reaction. Based on data obtained with isolated chloroplasts, four aspects were considered: (1) The two perturbations which damp the oscillation of the O2 flash yield in a flash sequence given after a dark period‐(a) a failure rate (α) of the trapping centers in the photochemical conversion (‘misses’) and (b) double effective excitations in a fraction (8) of the centers which are in the S0 and S1 states (‘double hits’). Best fit with the experimental data is obtained for α= 0.1, β=0.05. (2) The kinetics and the mechanism of deactivation—the loss of + charges (O2 precursors) in the dark. The momentary distribution of the four oxidation states (S0‐‐S3) in a sample can be computed from the O2 yields of four consecutive flashes with corrections for a and β. The time course of the various states in the dark following specific preilluminations reveals that deactivation proceeds in single equivalent steps: S3→S2, S2,→S1. S1, itself stable in the dark, is the end product of deactivation. The ground state S0 cannot be formed by deactivation in the dark but is only formed during illumination. (3) The various ratios [S0]/[S1] which can be observed in a sample after deactivation following different preilluminations with flashes or continuous light. (4) The transients of the O2 evolution rate in weak continuous light as observed after deactivation with or without flash preillumination. In all instances satisfactory agreement is found between the observations and the predictions of the model.
DISTRIBUTIONS OF FREE RADICALS AMONG AMINO ACIDS FROM LYOPHILIZED ULTRAVIOLET‐IRRADIATED PROTEINS
Authors: MILLER J. H. , WHITE F. H. , RIESZ P. , KON H.
Published: January 2008

Abstract— The effects of u.v.‐irradiation at 254 nm upon lyophilized ribonuclease, lysozyme, insulin, and chymotrypsinogen have been investigated by electron spin resonance (ESR). enzymatic assay, and labeling of free radical sites with tritiated hydrogen sulfide (HST). The ESR signal of the irradiated protein diminishes on exposure to HST, and tritium becomes covalently bound to carbon. The distribution of tritium among the amino acids of each protein. studied as an indicator of the carbon free radical distribution, differs markedly from those observed previously to result from exposure to gamma radiation, electrical discharge. or hydrogen atoms. However, the earlier observation that the tritium distribution is influenced by protein conformation holds true as well for u.v.‐irradiation. Moreover, the distributions of tritium among the amino acids of u.v.‐irradiated proteins indicate a broad scattering of free radicals. Tyrosine and phenylalanine, residues that absorb light energy in the region of the wavelength employed, are not particularly important as radical carriers. Thus, for ribonuclease, these residues incorporated 3.8 and 1.5 per cent of the total tritium, but they absorb 51 and 12 per cent of the light, respectively. These results, together with the observed low recoveries of methionine, an amino acid that does not absorb at 254 nm, add weight to the concept that a migration of energy ensues after the initial absorption of light energy and that photolytic damage may thus be due to destruction of amino acids other than those initially absorbing the u.v.‐radiation.
THE ACTION OF U.V. LIGHT OF VARIOUS WAVELENGTHS ON PAPAIN
Authors: DOSE K. , RISI S.
Published: January 2008

Abstract— Papain, prepared according to Kimmel and Smith is activated by irradiation with u.v. light of 254, 280 and 313 nm (φA= 0·022 ± 10 per cent). This activation is caused by the reductive splitting of a mixed disulfide in position 25. This disulfide is split with higher probability than any of the three structural disulfide links. This selectivity is likely caused by specific reduction of the mixed disulfide by thiol groups produced elsewhere in the molecule, although specific reduction by direct photochemical processes cannot be completely excluded on the basis of the data available. The quantum yields for destruction of structural cystine residues at the three wavelengths are comparable with the yields of cystine destruction in other proteins. The data also confirm that quanta absorbed by aromatic amino acid residues contribute to cystine destruction. In contrast to other enzymes with structural disulfide bonds, however, no correlation was found between the destruction of disulfide links and loss in activity. The results suggest that the mechanism of papain inactivation is not only dependent on the wavelength, but also on the dose.
ACETONE‐SENSITIZED DIMERIZATION OF CYTOSINE DERIVATIVES*
Authors: VARGHESE A. J.
Published: January 2008

Abstract— Irradiation of cytosine derivatives in aqueous solution in the presence of acetone with light of wavelength > 290 nm results in the formation of cyclobutane‐type dimers. A mixture of cis‐syn, cis‐anti and trans‐anti isomers are formed, the trans‐anti dimer being the major product. The trans‐anti isomers have been isolated as crystalline products and are found to be fairly stable in the solid state. These dimeric products undergo deamination in neutral aqueous solution. In acidic solution monomerization is an important reaction whereas in alkaline solution ring opening is the major mode of degradation. The results of analysis of the photo‐products are compared with those of sensitized irradiation of uracil and undine.
EPR STUDY OF WOOL IRRADIATED WITH BLUE LIGHT
Authors: SHATKAY A. , MICHAELI I.
Published: January 2008

Abstract— Wool fibres were exposed to visible light in the blue range. The free radicals created by the illumination were studied using electron paramagnetic resonance. It is shown that by control of the light intensity and frequency it is possible to get considerable insight into the mechanism of the creation and the decay of the free radicals. The radical population under the above conditions appears to consist of an initial stable radical insensitive to radiation, and three other radicals, two of which follow decay kinetics considerably different from that of the remaining free radical. All the latter three radicals are probably caused by N–H or C–H bond scission.

The kinetics of radicals in irradiated proteins is discussed. It is shown that the mechanisms previously suggested in the literature are inadequate to account for the form of the experimental curve describing the number of radicals vs. time in irradiated protein. A new mechanism is suggested in which the decayed radicals form sites immune to further irradiation. Such a mechanism is shown to be consistent with the experimental curves. The kinetics of the decay of radicals after the cessation of illumination is examined in detail. It is found that in the case of irradiated keratin the mechanisms assuming first order decay are inconsistent with the experimental results, while the assumption of second order decay for two different species of radicals yields results consistent with the experimental evidence.
SINGLE‐STRAND BREAKS INDUCED IN DNA BY VACUUM‐ULTRAVIOLET RADIATION
Authors: WIRTHS A. , JUNG H.
Published: January 2008

Abstract— The efficiency of vacuum u.v. for producing single‐strand breaks in DNA was determined for wavelengths between 58 and 254 nm (corresponding to photon energies of 21·2 and 4·9 eV, respectively) by using the supertwisted RF‐DNA of bacteriophage φX174. The cross‐section for production of single‐strand breaks increases continuously by about 5 orders of magnitude between 5 and 10 eV photon energy, whereas from 11 to 21 eV the number of strand breaks produced per unit of incident radiation energy is approximately constant. Thus, absorption of a 10‐eV photon causes DNA strand breaks with maximum efficiency. In addition, the number of electrons liberated from DNA by photons below 10 eV is one or two orders of magnitude higher than the frequency of strand breaks, demonstrating that in this energy range only a small fraction of the ionizations leads to strand breakage in DNA.
THE NATURE OF ULTRAVIOLET LIGHT‐INDUCED STRAND BREAKAGE IN DNA CONTAINING BROMOURACIL
Authors: DODSON M. L. , HEWITT R. , MANDEL M.
Published: January 2008

Abstract— Single‐strand breaks are produced in the phosphodiester backbone of ultraviolet‐light‐irradiated 5–bromodeoxyuridine‐containing DNA (BU‐DNA) after treatment with alkali. No radiation dependent breakage is observed in thymine‐containing DNA (thy‐DNA). The relative yields of breaks terminated by 5′‐hydroxyl and 5′‐phosphate groups was determined by measuring the rate of phosphorylation achieved with polynucleotide kinase in BU‐DNA single strands before and after treatment with alkaline phosphatase. The ratio of 5′‐phosphate to 5′ hydroxyl groups ranged from 2.3 to 2.9 in different experiments. When cysteamine was present during irradiation no new end groups were produced.

In order to identify the nucleoside(s) at the 5′‐termini, phosphate groups were removed with alkaline phosphatase and the 5′‐hydroxyl groups were phosphorylated with polynucleotide kinase. Electrophoresis of enzymatic digests showed a single 32P‐labeled component migrating more rapidly than any of the four usual 5′‐mononucleotides. Upon column chromatography this component resolved into a major peak coincident with 5′‐dUMP and a lesser unidentified constituent. No 5′‐dBUM32P was observed among these nucleotides.
POLARIZATION OF FLUORESCENCE OF RIBOFLAVIN IN ANISOTROPIC MEDIUM
Authors: SIÓDMIAK J. , FRACKOWIAK D.
Published: January 2008

Abstract— The dichroism and anisotropy of emission of polyvinyl alcohol (PVA) film with riboflavin (RF) were measured. The short axis of the RF molecule seems to be oriented in the direction of stretching of the film. The transition moment of the weak absorption band at 300 nm is also parallel to this direction, but it forms an angle greater than 50° with the emission oscillator. The transition moments of absorption bands at 440, 360 and 270 nm are intermediate in direction between long and short axes of the RF molecule. The extinction at 360 nm probably involves more than one electronic transition. Angles between absorption oscillators are very close to those obtained by Song and Kurtin. The mode of orientation of RF molecules suggests appearance of some type of binding between RF and the PVA matrix.
PHOTOREDUCTION OF CRYSTAL VIOLET IN SOLUTION AND IN POLY(VINYL ALCOHOL) FILMS
Authors: LEAVER I. H.
Published: January 2008

Abstract— The photolysis of crystal violet oxalate has been studied in aqueous and non‐aqueous solutions and in films of poly(viny1 alcohol) at room temperature. Evidence has been obtained from electron‐spin‐resonance, absorption and fluorescence spectroscopy for the formation of the semireduced dye radical, tri‐(p‐dimethylaminophenyl)methyl, both in solution and in the solid state. Electron spin resonance and luminescence spectra of the radical produced by electrolytic reduction of the dye are also reported.
PHOTOREACTION OF FMN‐TRICINE AND ITS PARTICIPATION IN PHOTOPHOSPHORYLATION*
Authors: NELSON N. , NELSON H. , RACKER E.
Published: January 2008

Abstract— In the presence of light, Tricine efficiently reduced flavin. Under aerobic conditions, oxygen uptake was observed. Inhibition studies with superoxide dismutase, with cytochrome c as electron acceptor, suggested that about 50% of the reduced oxygen was superoxide anion. Oxygen uptake by this system was markedly inhibited by 2.5 mM phenol or salicyl aldehyde.

A rapid and convenient assay for superoxide dismutase was developed based on the light‐induced reduction of cytochrome c by flavin mononucleotide (FMN) and Tricine.

Reduction of cytochrome c in chloroplasts without addition of ferredoxin appears to be mediated by superoxide anions, as indicated by inhibition of this reaction by superoxide dismutase.

Loss of photophosphorylation by sonication of chloroplasts could be partially prevented by the presence of Tricine and FMN during sonication. Phosphorylation under these conditions was dependent on white light, but no evidence for the participation of superoxide anion could be obtained with internal or external superoxide dismutase.
A STUDY OF THE METHYLENE BLUE‐SENSITIZED OXIDATION OF AMINO ACIDS
Authors: KNOWLES A. , GURNANI S.
Published: January 2008

Abstract— A study has been made of the effects of eight amino acids and a group of compounds related to tryptophan upon the photofading of methylene blue under anaerobic conditions and upon the excited species generated by flash photolysis of the dye. These effects are discussed in relation to the ease of sensitized photooxidation of the amino acids by methylene blue, in order to test the hydrogen‐abstraction mechanism proposed for this reaction.

In general, amino acids susceptible to sensitized oxidation also act as reducing agents in the photoreduction of methylene blue, while the insensitive compounds do not reduce the light‐excited dye molecule. Methionine, histidine and tyrosine are exceptions, but this is probably due to our choice of pH for the photofading experiments.

The flash‐photolysis experiments give no clear‐cut evidence for a reaction between amino acid and dye triplet excited state leading to an enhanced yield of the semi‐reduced radical, thought to be an intermediate of the photofading reaction. The lifetime of the semi‐oxidized radical is reduced by many of the amino acids, and this may be the reactive intermediate in their oxidation.
CIRCULAR DICHROISM SPECTRA OF SYSTEM I PARTICLES FROM NORMAL CHLOROPLASTS AND CAROTENOID‐DEFICIENT MUTANTS OF MAIZE
Authors: GARAY A. , DEMETER S. , KOVÁCS K. , HORVÁTH G. , FALUDI‐DÁNIEL ÁGNES
Published: January 2008

Abstract— Circular dichroism (CD) spectra were studied in System I particles prepared by digitonin fragmentation of chloroplasts of normal maize and carotenoid‐deficient mutants. CD bands of pigment molecules were found to be higher in particles than in solutions. This phenomenon was most pronounced for the particles containing the carotenoid composition of normal chloroplast lamellae. The CD signal of chlorophylls bound to particles of carotenoid‐deficient chloroplasts was closer to that found in solutions. This indicates that aggregation and/or binding of chlorophylls in carotenoid‐deficient mutants may be less extensive than in normal chloroplasts.
DYE‐SENSITIZED PHOTOREDUCTION OF METHYL VIOLOGEN
Authors: BELLIN JUDITH S. , ALEXANDER RICHARD , MAHONEY ROBERT D.
Published: January 2008

Abstract— The kinetics of the proflavine‐sensitized photoreduction of methyl viologen (MV2+) to the blue radical cation (MV.+) are presented. The triplet excited state of proflavine accepts an electron from EDTA to form the singly‐reduced species of proflavine (PH.); this species donates an electron to either the oxidized (MV.+) or the singly–reduced (MV.+) species of the bipyridyl. MV2+ can be reoxidized by oxygen to MV2+ but is decomposed by H2O2. The doubly‐reduced form can not be reoxidized either by oxygen or by peroxide. Potassium iodide inhibits the photoreduction of MV2+ by competing with it as reactant for the singly‐reduced form of proflavine (PH.). The mechanism presented may be analogous to that occurring in the reduction of MV2+ by illuminated spinach chloroplasts; its herbicidal action can not be ascribed to the formation of peroxides.
KINETICS OF REVERSIBLE PHOTOCHROMIC REACTIONS IN THE SERIES OF 1,5‐DISUBSTITUTED 3,3‐DIMETHYL‐6'‐NITRO‐8'‐BROMOSPIRO‐[(2'H, 1 ‐BENZOPYRAN)–2,2‘‐INDOLINES]
Authors: HALBERSTAM M. A. , GORDIN M. B.
Published: January 2008

Abstract— A method has been worked out for finding parameters that characterize the photochromism of spiropyrans. It involves statistical processing of the experimental results. The method is programmable. The fact that discoloration does exist has been verified through mathematical modelling. The result agrees with data reported in the literature. Coloration and discoloration quantum yields have been found for a number of novel spiropyrans. An attempt was made to rationalize the photochromism kinetics as a function of effects displayed by the substituents attached to positions 1 and 5 of the indoline site.
MEASUREMENT OF THE TEMPERATURE DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF ORGANIC MOLECULES IN SOLUTION
Authors: MANTULIN W. W. , HUBER J. R.
Published: January 2008

A DETAILED investigation of the temperature dependence of the fluorescence quantum yield φf can yield–directly or indirectly–significant information about behavior of excited states of organic molecules, such as the temperature effect on radiationless transitions and on photochemical reactivity. Variation of the temperature changes the viscosity of the solvent and, in conjunction with measurements of φf(T), allows investigations of diffusion‐controlled processes. For example, energy transfer and quenching processes as well as excimer or exciplex formation fall into this category. Recent review articles by Weller (1962) and Birks (1970) deal with this topic. Moreover, Huber and Mantulin (1972) have suggested that restraints placed upon geometric modifications of the excited molecule by temperature‐induced changes in the solvent cage (variation of site structure) are reflected in a varying φf.

The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10‐diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion‐controlled quenching by oxygen measured over a wide temperature range.
ACETONE‐SENSITIZED PHOTOINACTIVATION OF TRANSFORMING DNA
Authors: Pons F. W. , Mennigmann H. D.
Published: January 2008

Abstract— Irradiation of Haemophilus influenzae transforming DNA with 313 nm radiation in the presence of acetone leads to inactivation of transforming activity. Some of the lesions produced are substrate for photoreactivating enzyme and the dark‐repair mechanism. In addition, other lesions are produced which, if their production is not prevented by the presence of EDTA during irradiation, render the DNA less photoreactivable. The possibility is discussed that, among others, single‐strand breaks are responsible for this loss in photoreactivability.
THYMINE HYDRATE FORMED BY ULTRAVIOLET AND GAMMA IRRADIATION OF AQUEOUS SOLUTIONS
Authors: Fisher Gordon J. , Johns Harold E.
Published: January 2008

Abstract— Evidence is presented for the formation of a thymine hydrate upon ultraviolet (UV) or gamma irradiation of aqueous solutions. The UV quantum efficiency exhibits a dependence on pH similar to that shown for uracil hydration, but the yield is three orders of magnitude smaller than for uracil. Hydration is not affected by wavelength, oxygen, or concentration of thymine. The reversal rate of the photohydrate to thymine is similar to the reversal rates of both isomers of the thymine hydrate formed by γ radiolysis, and depends on pH in the same way as the rate for the uracil photohydrate. The photohydrate of thymine is chromatographically identical to the cis isomer of 6‐hydroxy‐5, 6‐dihydrothymine.
EPR INVESTIGATIONS CONCERNING THE STRUCTURE OF THE ASCORBIC ACID RADICAL IN WATER, ALCOHOL, AND DIMETHYLSULFOXIDE
Authors: Steenken S. , Olbrich G.
Published: January 2008

Abstract—Electron paramagnetic resonance (EPR) spectra of the ascorbic acid radical in water, methanol, ethanol,n‐propanol, and dimethylsulfoxide are reported. The radical was produced by photolyzing ascorbic acid solutions containing acetone. Lines from13C in natural abundance are observed. Four different13C‐coupling constants can be distinguished. A comparison of the experimental1H‐coupling constants with values calculated by the INDO method allows assignment to specific protons in the radical. An effect of solvent on the spectrum is observed and is interpreted in terms of intramolecular hydrogen bonding. Data are presented which indicate that ascorbic acid is able to scavenge alcohol radicals by H‐atom transfer.
POSTREPLICATION REPAIR IN AN EXCISION‐DEFECTIVE MUTANT OF ESCHERICHIA COLI: ULTRAVIOLET LIGHT‐INDUCED INCORPORATION OF BROMODEOXYURIDINE INTO PARENTAL DNA*
Authors: Ley Ronald D.
Published: January 2008

Abstract— Ultraviolet (UV) light‐induced incorporation of bromodeoxyuridine (BrdUrd) into parental DNA of an excision‐defective mutant of Escherichia coli has been observed by selective photolysis of bromouracil (BrUra)‐containing regions in the parental DNA. It appears that the BrUra‐containing regions occur only in that DNA which has served as a template for normal semiconservative replication. After an exposure at 254 nm which results in one pyrimidine dimer per 45times 106 daltons, incubation in BrdUrd resulted in BrUra–containing regions ˜ 1.5 times 104 nucleotides in length at intervals of ˜ 55 times 106 daltons in the parental DNA. Thus approximately one BrUra‐containing region has occurred for every 1.2 pyrimidine dimers in the parental DNA. The observed incorporation of BrdUrd is interpreted in terms of a proposed model for postreplication repair in which genetic exchanges produce single‐strand gaps in the parental DNA.
DESTRUCTION OF PHOTOREACTIVATING ENZYME BY 365 nm RADIATION*
Authors: Webb Robert B. , Brown Mickey S.
Published: January 2008

Abstract— Following the observation that in vivo photoreactivation of 365‐nm‐induced pyrimidine dimers could not be observed chemically, a study was made of the inactivation of photoreactivating enzyme activity by this near‐ultraviolet wavelength. It was observed that: (1) Dimers induced in extracted bacterial DNA by 365 nm radiation are completely photoreactivable and are monomerized as an exponential function of the photoreactivation time. (2) Photoreactivability of 254‐nm‐induced damage in Escherichia coli B/r Hcr is progressively destroyed in vivo as a function of the dose of 365 nm radiation. (3) The ability of the yeast photoreactivating enzyme to monomerize dimers induced at 365 nm in bacterial DNA is destroyed in vitro as a function of the dose of 365 nm radiation, and at a rate comparable to killing of E. coli. These results are consistent with biological measurements which indicate that photoreactivability of ultraviolet (near and far) lethal damage is reduced by exposure of the bacteria to 365 nm radiation.
ROLE OF THE TRYPTOPHAN FLUORESCENT STATE IN THE ULTRAVIOLET‐INDUCED INACTIVATION OF β‐TRYPSIN*
Authors: Sellers D. R. , Ghiron C. A.
Published: January 2008

Abstract— Stern‐Volmer quenching constants for β‐trypsin at pH 3 were determined for fluorescence quenching by histidine, acrylamide, and nitrate ion. A modified Stern‐Volmer plot (Lehrer, 1971) was employed to show that all of the fluorescent tryptophanyl residues of β‐trypsin were equally susceptible to quenching by acrylamide at pH 3 when the enzyme was either in its native conformation or denatured in 6 M guanidine hydrochloride (GuHCl). Fluorescence lifetime measurements indicated that acrylamide quenched β‐trypsin fluorescence by a purely collisional mechanism. Solvation of tryptophanyl residues of the protein was maximal at 2.5 M GuHCl, as monitored by fluorescence emission wavelength.

Investigations of the ultraviolet‐induced inactivation of β‐trypsin at 295 nm were performed in the presence of acrylamide at pH 3. The quantum yields for enzyme inactivation and indole destruction (determined using the PDAB reagent) were unchanged upon depopulation of the fluorescent state by 65 per cent, whether the enzyme was in its native conformation or denatured by 6 M GuHCl. It is concluded that the fluorescent state of tryptophanyl residues of β‐trypsin is not involved in enzyme inactivation or tryptophan destruction.
PROTECTIVE ACTION OF CAROTENOID PIGMENTS AGAINST PHOTODYNAMIC DAMAGE TO LIPOSOMES*
Authors: Anderson Susan M. , Krinsky Norman I.
Published: January 2008

Abstract—When liposomes (a model membrane system) are subjected to a dye‐sensitized photo‐oxidation, lysis, as measured by glucose leakage or a change in light scattering, results. Before lysis occurs, the membrane lipids undergo peroxidative damage, as determined by the appearance of malondialdehyde. Carotenoids incorporated into the liposomal membrane protect against both lipid peroxidation and liposomal lysis. Other1O2quenchers and free radical absorbers also protect liposomes from photodynamic damage.
THE ROLE OF O2‐ IN THE CHEMILUMINESCENCE OF LUMINOL*
Authors: Hodgson E. K. , Fridovich I.
Published: January 2008

Abstract— The chemiluminescence of luminol in buffered aqueous solutions is inhibited by superoxide dismutase. This occurs whether the luminescence is induced by ferricyanide, persulfate, hypochlorite, or by the action of xanthine oxidase on xanthine. Since superoxide dismutase inhibits reactions which involve O2‐, we conclude that this radical is a constant factor in the chemiluminescence of luminol in aqueous solutions. The kinetics of light production are discussed in terms of hypothetical mechanisms that fit the available data. The strong luminescence of luminol in aprotic solvents or in aqueous systems containing relatively high concentrations of H2O2 could not be explored in this way, because superoxide dismutase is inactive under such conditions.
COMPARISON OF PHOTOTRAP COMPLEXES FROM CHROMATOPHORES OF RHODOSPIRILLUM RUBRUM, RHODOPSEUDOMONAS SPHEROIDES, AND THE R‐26 MUTANT OF RHODOPSEUDOMONAS SPHEROIDES*
Authors: HALL R. L. , Kung M. Chu , Fu M. , Hales B. J. , Loach P. A.
Published: January 2008

Abstract— After dissolution of the membrane structure of chromatophores from Rhodospirillum rubrum, Rhodopseudomonas spheroides, and the R‐26 mutant of Rhodopseudomonas spheroides, active phototrap complexes from each have been purified by a column electrophoresis procedure. Phospholipids and transition metals were well separated from the phototrap complex in all three systems. The purified R. rubrum phototrap complex retained a full complement of antenna bacteriochlorophyll and carotenoid pigments which had nearly the same absorbance spectra as in the intact cell, and which delivered absorbed light energy to the phototrap with just as high efficiency as in the intact cell. Sodium dodecyl sulfate (SDS) disc gel electrophoresis using Tris buffer showed that these preparations often contained only two prominent polypeptides of 30,000 ± 2000 and 12,000 ± 4000 mol. wt., and a lesser amount of a third polypeptide of 21,000 ± 2000 mol. wt.

The phototrap complexes prepared from the wild type and the R‐26 mutant of R. spheroides were similar, in that a partial separation from antenna pigments occurred during column electrophoresis. Both complexes had prominent polypeptides of 24,000 ± 2000 and 21,000 ± 2000 mol. wt., but no polypeptide of 30,000 mol. wt remained after electrophoresis. A third major polypeptide occurred with a mol. wt. of about 12,000 but seemed identifiable with an incompletely separated antenna pigment fraction. The phototrap complex prepared from the R‐26 mutant had a typical reaction center spectrum.

In the case of wild type R. spheroides purification, two distinct protein‐pigment complexes separated. Although the absorbance of the bacteriochlorophyll and carotenoid pigments were little changed from those of the in vivo system, different polypeptides in the two fractions were observed by SDS disc gel electrophoresis; only one fraction seemed to be intimately related with the phototrap complex.
ACTION SPECTRUM FOR ENZYMATIC PHOTOREACTIVATION IN MAIZE*
Authors: Ikenaoa M. , Kondo S. , Fujii T.
Published: January 2008

Abstract— An ammonium‐sulfate‐precipitable (35–70 per cent) fraction in extracts of Zea mays pollen contains photoreactivating enzyme that reactivates the transforming ability of ultraviolet‐inactivated Hemophilus influenzae DNA. The action spectrum of in vitro photoreactivation with the enzyme has a broad single maximum at 385 nm. Parallel to the in vitro response, in vivo photo‐reactivation of ultraviolet‐induced premutational damage in pollen of this plant is more efficient at 405 nm than at 334 nm. From these results we conclude that photoreactivation of ultraviolet‐induced mutational damage in maize pollen is chiefly of the direct enzymatic type.
PHOTOREGULATION OF POLYMER CONFORMATION BY PHOTOCHROMIC MOIETIES–I. ANIONIC LIGAND TO AN ANIONIC POLYMER*
Authors: Veen G. van der , Prins W.
Published: January 2008

Abstract— Photoregulated biological processes appear to make use of membrane‐bound photochromic macromolecules. In order to elucidate various physicochemical pathways by which these processes can be triggered, model studies have been undertaken employing photochromic moieties bound to synthetic macromolecules with a labile fold structure. Inspired by Lovrien's 1967 work, attention was first focused on the anionic dis‐azo stilbene dye chrysophenine (CHP) and poly(methacrylic acid) (PMA) in aqueous solution. This ligand is found to bind to and unfold PMA only if the degree of ionization of the polymer is below 0·75. Viscosity as well as equilibrium dialysis data indicate that maximally one CHP per ten monomer units PMA is bound. The apparent degree of ionization conferred to PMA by the ionic CHP ligand leading to polymer unfolding is the same as the known real degree of ionization leading to polymer unfolding in the absence of CHP. Upon trans→cis photoisomerization, the ligand either desorbs or creates a higher local dielectric constant because of the large cis‐azo dipole moments. As a result some refolding to a more compact hydrodynamic volume occurs, as deduced from the viscosity measurements at a low degree of ionization. Simultaneously a lowering of the pKapp by 0·1 pK unit is observed at degrees of ionization below 0·075. Photoregulation of conformation as well as of pKapp indicates two possible pathways for the regulation of ionic fluxes such as have been postulated for photobiological transducers.
PHOTOREDUCTION OF HORSE HEART CYTOCHROME c
Authors: Vorkink W. P. , Cusanovich M. A.
Published: January 2008

Abstract— During the course of studies on the mechanism of electron transport as catalyzed by cytochrome c, we have found that ferri‐horse heart cytochrome c will undergo photoreduction. We have characterized the photoreduction of horse heart cytochrome c in regard to the photochemistry, the nature of the electron donor, and effect of solvent (pH, solvent perturbation, ionic strength). We conclude that ferri‐horse heart cytochrome c undergoes photoreduction mediated by a light‐induced heme excited state. Further, the protein moiety of cytochrome c serves in part to quench the formation of the excited state, and also to control the interaction of the electron donor and photo‐excited cytochrome.
PHOTOOXIDATIVE AND SPECTRAL STUDIES ON CYTOCHROME c. CONFORMATIONAL CHANGES INDUCED BY BINDING OF CARDIOLIPIN
Authors: Jori Giulio , Tamburro Antonio Mario , Azzi Angelo
Published: January 2008

Abstract— Binding of cardiolipin to ferrocytochrome c, to form a 4:1 molar complex, results in an approximately sixfold increase of the tryptophan fluorescence emission. Furthermore, appreciable perturbations of the circular dichroism spectrum occur in the Soret and in the far‐ultraviolet regions. The irradiation of the ferrocytochrome–cardiolipin complex at pH 8·8 with visible light leads to the photooxidative modification of histidine‐18, tyrosine‐48 and methionine‐80. Comparison of the above findings with those concerning unbound ferrocytochrome c suggests that the interaction between cardiolipin and ferrocytochrome c provokes a perturbation of the protein conformation, which possibly involves the disruption of the hydrogen bonds linking the aromatic rings of tryptophan‐59 and tyrosine‐48 with one propionic side chain of the heme.
PHOTOCONTROL OF ANTHOCYANIN SYNTHESIS: PHYTOCHROME, CHLOROPHYLL AND ANTHOCYANIN SYNTHESIS*
Authors: Mancinelli A. L. , Tai Ping‐Kaung Ku , Susinno R.
Published: January 2008

Abstract—Anthocyanin synthesis in cabbage and mustard seedlings depends upon duration and irradiance of the light treatment. The relative effectiveness of radiation in various spectral regions depends upon the length of the irradiation and decreases with increasing dose. In intermittent light treatments, far‐red light can reverse the promoting action of red light if the dark interval between successive irradiations is longer than one hour. If the length of the dark interval is less than one hour, far‐red applied immediately after each red irradiation, enhances anthocyanin accumulation. Anthocyanin accumulation under various light treatments seems to correlate, to some extent, with the rate of phytochrome decay, but not with chlorophyll production. Anthocyanin accumulation is inhibited by 2,4‐dinitrophenol and by the ammonium ion, but not by DCMU. The ammonium ion inhibits anthocyanin accumulation induced by a single, short red irradiation. This suggest that the ammonium ion may have a wider spectrum of action in vivo than in chloroplast preparations where it acts as a specific uncoupler of photophosphorylation. Streptomycin inhibits chlorophyll synthesis and enhances anthocyanin accumulation. These results suggest that there is very little, if any, interaction between photosynthesis and ‘high‐irradiance‐reaction’ anthocyanin synthesis in cabbage and mustard seedlings.
ULTRAVIOLET INACTIVATION OF THE ABILITY OF E. COLI TO SUPPORT THE GROWTH OF PHAGE T7: AN ACTION SPECTRUM
Authors: Day Rufus S. , Muel Bernard
Published: January 2008

Abstract—The action spectrum for inactivation of the capacity of stationary‐phase Escherichia coli B to support the growth of T7 bacteriophage was measured, using radiation 240–405 nm in wavelength. The action spectrum has a minimum at 254 nm, a maximum at 267 nm, and a shoulder between 313 and 334 nm, followed by a decrease at longer wavelengths, indicating that nucleic acid is probably not the target for capacity inactivation. Deoxycytidine, cytidine, thiamine, and some proteins have absorption spectra similar to the far‐ultraviolet (240–300 nm) portion of this action spectrum.
RELATIONSHIP BETWEEN SURVIVAL, PHOTOPRODUCT PRODUCTION AND REPAIR CAPACITY IN A VARIANT OF BACILLUS CEREUS
Authors: Johnston Gerald C. , Young I. Elizabeth
Published: January 2008

Abstract—As sporulation progresses, there is an increased resistance to UV irradiation of the cells of Bacillus cereus var. alesti. This progressive increase is independent of post‐irradiation treatment and appears to be a property of the stage of sporulation. In addition, the proportion of photoproducts formed is different for each stage of sporulation. Cells irradiated at Stage I (axial filament) of sporulation display relatively large amounts of spore photoproduct ‘c’ and less of photoproduct ‘b’. As sporulation proceeds, UV irradiation results in the production of more spore photoproduct ‘b’ and less ‘c’, suggesting a progressive change in configuration of the DNA within the sporulating cell. If irradiated early in the process (Stage II), large amounts of cyclobutane‐type dimers are also produced which, with the ‘spore‐specific’ photoproducts, may be retained in the resultant spore. Although no excision‐repair was detectable during germination of these spores, both vegetative and ‘spore‐specific’ damage is reduced during this period. The ‘spore‐specific’ repair mechanism may be able to remove vegetative damage from germinating spores.
EXCITED STATES AND PHOTOBIOLOGICAL PROPERTIES OF POTENTIAL DNA CROSS‐LINKING AGENTS, THE BENZODIPYRONES
Authors: Harter Marian L. , Felkner Ira C. , Mantulin William W. , McInturff Dyna L. , Marx John N. , Song Pill‐Soon
Published: January 2008

Abstract—Potential DNA cross‐linking agents, benzo{1,2‐b:4,5‐b'}dipyran‐2,8‐dione (cis‐benzodipyrone) and benzo{1,2‐b:4,5‐b'}dipyran‐2,7‐dione (trans‐benzodipyrone), have been synthesized. The excited triplet states of these reagents resemble those of other coumaryl derivatives in their spectroscopic assignments and characteristics and thus their reactivites. In particular, trans ‐benzodipyrone is significantly more reactive toward pyrimidine bases in solution than the other coumaryl derivatives examined, by virtue of its possessing two reactive pyrone C=C bonds within the molecular framework. The unique reactivity of trans ‐benzodipyrone, with its two reactive pyrone bonds across the long molecular axis, appears to be reflected in its ability to photoinduce mutation in certain Bacillus subtilis strains. This preliminary study provides data that will be useful in designing experiments to elucidate the molecular mechanisms for the biological activities of these compounds.
A CLIMATOLOGY OF SOLAR ERYTHEMA DOSE*
Authors: Mo T. , Green A. E. S.
Published: January 2008

Abstract—Semi‐empirical formulas for the ultraviolet erythema dose derived in an earlier paper are used to deduce an ultraviolet photoclimatology. We calculate the climatology of daily erythema radiation doses for the northern hemisphere at 5d̀ latitude intervals. Similar dose calculations are also performed specifically for ten metropolitan areas. Effects of seasonal and geographic variations of ozone, turbidity, and cloudiness on the local erythema doses are also investigated. We present a simple approximate analytic formula for the annual erythema dose as a function of latitude, cloud cover, and ground albedo for use in connection with studies of the epidemiology of skin cancer. The implications of possible ozone depletion due to a future fleet of supersonic aircraft in the stratosphere are discussed. These calculations are made for a normal ozone thickness of 0.32 cm and for a 5, 10, 20, and 50 per cent ozone reduction.