bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOCHEMISTRY OF BENZOTHIAZOLE MODELS OF PHEOMELANIN
Authors: LAMBERT CHRIS , SINCLAIR ROY S. , TRUSCOTT T. GEORGE , LAND EDWARD J. , MILES R. , LIU CHUNG‐TSING
Published: January 2008

Abstract— The photochemistry of several 4‐hydroxy‐ and 4‐methoxybenzothiazoles has been investigated by laser flash photolysis. In aqueous solutions of pH3–12, the 4‐hydroxybenzothiazole chromophore undergoes monophotonic photoionization to afford e‐aq with quantum yields on the order of 0.06; no evidence for triplet species was obtained. The spectra and stability of the resultant free radicals were determined using pulse radiolysis. In contrast, triplet transients with life‐times on the order of 8 mUs are readily observable upon irradiation of the 4‐methoxybenzothiazole analog. Triplet sensitization experiments with the water‐soluble carotenoid crocetin were employed to obtain the triplet extinction coefficients and subsequently the triplet quantum yields. The significance of these differences in photochemical behavior is discussed in relationship to the photochemistry and photobiology of the epidermal melanin pigment pheomelanin.
SPECTROSCOPIC AND DYNAMIC CHARACTERIZATION OF FMN IN REVERSED MICELLES ENTRAPPED WATER POOLS
Authors: VISSER A. J. W. G. , SANTEMA J. S. , VAN HOEK A.
Published: January 2008

Abstract—The encapsulation of FMN in surfactant entrapped water pools resulted into specific interactions of FMN with the polar head groups, the entrapped water molecules and the outer apolar solvent. Two positively charged surfactant/solvent systems were employed: dodecyl ammonium propionate (DAP) in toluene and hexadecyltrimethylammonium bromide (CTAB) in chloroform/n‐octane (6:5, vol/vol). Also a surfactant with a negatively charged polar head group, sodiumbis(2‐ethylhexyl) sulfosuccinate (AOT) inn‐octane, was used. In CTAB and especially DAP reversed micellar systems the light absorption spectra revealed the localization of the flavin in a more apolar environment, while in AOT reversed micelles FMN appeared to reside mainly in the core of the water pool. The fluorescence spectra showed unresolved bands, which were blue‐shifted in DAP and CTAB reversed micelles as compared to the spectra of aqueous FMN solutions. The fluorescence decay kinetics of FMN in enclosed water droplets is non‐exponential. The heterogeneity can be explained assuming incomplete relaxation of partly immobilized water molecules during the lifetime of the excited singlet state. The relatively high anisotropy of the fluorescence of FMN in encapsulated water indicated a higher viscosity than in bulk water. This was confirmed by anisotropy decay measurements of FMN in DAP and AOT entrapped water, for which the rotational correlation times were much longer than for FMN in plain water.
VACUUM UV LASER INDUCED SCISSION OF SIMIAN VIRUS 40 DNA*
Authors: JOHNSON‐THOMPSON MARIAN , HALPERN JOSHUA B. , JACKSONS WILLIAM M. , GEORGE JAY
Published: January 2008

Abstract— The effect of vacuum UV‐laser irradiation on Simian virus 40 (SV40) DNA I was studied in vitro. Following exposure of SV40 DNA I to an argon fluoride (ArF) laser (LD = 193 nm), single‐strand breaks occur in either strand of the double‐stranded superhelical molecule (DNA I) and convert it to the DNA II conformation. Upon increased irradiation times, additional breaks occur in already scissioned strands resulting in the production of smaller fragments as analyzed by alkaline sucrose centrifugation. These results suggest that short periods of irradiation lead to conformational alterations of SV40 DNA I.
THE MODIFICATION OF RIBONUCLEASE‐A BY NEARULTRAVIOLET IRRADIATION IN THE PRESENCE OF PSORALEN
Authors: SCHIAVON O. , SIMONIC R. , RONCHI S. , BEVILACQUA R. , VERONESE F. M.
Published: January 2008

Abstract— Ribonuclease A is inactivated when irradiated under oxygen by UV‐A light in the presence of psoralen. The rate of inactivation is greatly reduced by sodium azide. ascorbate or nitrogen, whereas the substrate gives only very limited protection. A ribonuclease sample modified to 40% remaining activity presented a significant modification of amino acid residues known to be sensitive to oxidation and 1.4 mol of bound psoralen per mol of protein. The secondary structure of the enzyme, as assessed by circular dicroism was not changed by irradiation; neither was aggregation of the enzyme to a higher mol wt evident. Studies on the tryptic peptides fractionated by high performance liquid chromatography showed that the photomodification occurs with very low selectivity. All the five peptides containing hystidine, tyrosine and methionine residues were greatly modified, although two, those containing histidine residues 12 and 119 in the sequence, amino acids known to be involved in the catalytic activity of ribonuclease. are modified to a greater extent. The protein bound psoralen. revealed by radioactivity in the HPLC eluate, was not found associated to only one or few peptide peaks but spread on a large zone of elution.
PHOTOSENSITIZATION BY DRUGS: NALIDIXIC AND OXOLINIC ACIDS
Authors: MOORE DOUGLAS E. , HEMMENS VIOLET J. , YIP HELEN
Published: January 2008

Abstract— The antibacterial drugs, nalidixic acid and oxolinic acid, have been tested as photosensitizers in aqueous solution using 365 nm UV light. Absorption and fluorescence spectra indicate that intramolecular hydrogen bonding stabilizes the unionized form of these compounds in the pH region2–4. The ability of the unionized species to sensitize photooxidation by the type II (singlet oxygen) mechanism was found to be lower than when these drugs were ionized. Comparison withquinoline–3‐carboxylic acid and the methyl esters of nalidixic and oxolinic acids emphasised the significance of the hydrogen bonding in relation to the excited state properties. Unionized nalidixic acid undergoes photolysis more readily than the ionized form, apparently by a free radical mechanism, while oxolinic acid is more stable.
COMPARISON OF THE EFFICACY OF PULSED AND CONTINUOUS‐WAVE RED LASER LIGHT IN INDUCTION OF PHOTOCYTOTOXICITY BY HAEMATOPORPHYRIN DERIVATIVE
Authors: COWLED P. A. , GRACE J. R. , FORBES I. J.
Published: January 2008

Abstract—The efficiency of pulsed and continuous wave laser light to induce photodynamic activity in haematoporphyrin derivative (Hpd) was compared in two systems, a tissue culture assay and a transplantable mouse tumour. No difference was found.
THERMAL DENATURATION OF MONOMERIC AND TRIMERIC PHYCOCYANINS STUDIED BY STATIC AND POLARIZED TIME‐RESOLVED FLUORESCENCE SPECTROSCOPY
Authors: HEFFERLE P. , JOHN W. , SCHEER H. , SCHNEIDER S.
Published: January 2008

C. Phycocyanin (PC) and allophycocyanin (APC). as well as the α‐subunit of PC. have been isolated from the blue‐green alga (cyanobacterium).Spirulina platensis. The effects of partial thermal denaturation of PC and of its state of aggregation have been studied by ps time‐resolved, polarized fluorescence spectroscopy. All measurements have been performed under low photon fluxes(1013photons/pulse cm2) to minimize singlet‐singlet annihilation processes. A complex decay is obtained under most conditions, which can be fitted satisfactorily with a bi‐exponential (T1=70–400 ps, T2‐1000–3000 ps) for both the isotropic and the polarized part, but with different intensities and time constants for the two decay curves. The data are interpreted in the framework of the model first developed byTealeandDale[Biochem. J.116, 161 (1970)], which divides the spectroscopically different chromophores in (predominantly) sensitizing (s) and fluorescing (f), ones. If one assumes temperature dependent losses in the energy transfer from thesto thefand betweenfchromophores. both the biexponential nature of the isotropic fluorescence decay and the polarization data can be rationalized. In the isotropic emission (corresponding to the population of excited states) the short lifetime is related to thesftransfer. the longer one to the “free” decay of the final acceptor(s) (=f). The polarized part is dominated by an extremely short decay time. which is related tosftransfer,as well asto resonance transfer between thef‐chromophores.
PHOTOREDUCTION OF NAD TO NADH IN SEMICONDUCTOR DISPERSIONS
Authors: Cuendet Pierre , GrÄTZEL Michael
Published: January 2008

Abstract— Band gap illumination of TiO2 (anatase) dispersions in weakly alkaline solutions of nicotinamide‐adenine‐dinucleotide (NAD+) leads in the presence of rhodium trisbipyridyl complex [Rh(bipy)3+3], to continuous generation of biologically active cofactor NADH. Effects of pH, NAD+ and Rh(bipy)3+3 concentration on the efficiency of this photoconversion process are investigated. The reaction proceeds already in aqueous solution in the absence of external electron donors but it is enhanced significantly in the presence of 10% methanol.
PEPTIDE MODELS FOR THE BACTERIORHODOPSIN CHROMOPHORE. RETINYLIDENE‐LYSINE SYSTEMS CONTAINING ASPARTIC ACID AND SERINE RESIDUES
Authors: Vijayakumar E. K. S. , Balaram P.
Published: January 2008

Abstract— The retinylidene Schiff base derivative of seven lysine containing peptides have been prepared in order to investigate solvent and neighboring group effects, on the absorption maximum of the protonated Schiff base chromophore. The peptides studied are Boc‐Aib‐Lys‐Aib‐OMe (1), Boc‐Ala‐Aib‐Lys‐OMe (2), Boc‐Ala‐Aib‐Lys‐Aib‐OMe (3), Boc‐Aib‐Asp‐Aib‐Aib‐Lys‐Aib‐OMe (4), Boc‐Aib‐Asp‐Aib‐Ala‐Aib‐Lys‐Aib‐OMe (5), Boc‐Lys‐Val‐Gly‐Phe‐OMe (6) and Boc‐Ser‐Ala‐Lys‐Val‐Gly‐Phe‐OMe (7). In all cases protonation shifts the absorption maxima to the red by 3150–8450 cm‐1. For peptides 1–3 the protonation shifts are significantly larger in nonhydrogen bonding solvents like CHCl3 or CH2Cl2 as compared to hydrogen bonding solvents like CH3OH. The presence of a proximal Asp residue in 4 and 5 results in pronounced blue shift of the absorption maximum of the protonated Schiff base in CHCl3, relative to peptides lacking this residue. Peptides 6 and 7 represent small segments of the bacteriorhodopsin sequence in the vicinity of Lys‐216. The presence of Ser reduces the magnitude of the protonation shift.
ALKALINE ELUTION STUDIES OF HEMATOPORPHYRIN‐DERIVATIVE PHOTOSENSITIZED DNA DAMAGE AND REPAIR IN CHINESE HAMSTER OVARY CELLS
Authors: Blazek E. R. , Hariharan P. V.
Published: January 2008

AbstractWe have used alkaline elution to study DNA damage produced by the photosensitizer hematoporphyrin derivative (HPD) in cultured Chinese hamster cells. Dosimetry was performed by measuring fluence and calculating photon absorption by intracellular HPD. HPD photosensitization causes DNA strand breakage. These breaks are repaired by the cell, although their fractional rate of repair is smaller than that for X‐ray induced strand breaks at equivalent levels of strand breakage. The combined DNA polymerase inhibitors cytosine arabinoside and hydroxyurea suppress the repair of HPD‐photosensitized breaks more strongly than they suppress repair of X‐ray induced breaks. Addition of novobiocin to the aforementioned inhibitors causes almost total suppression of photosensitized break repair. A nucleotide excision repair system with inhibitor susceptibility similar to that of the system which removes pyrimidine dimers thus does not act upon HPD‐photosensitized damage. The repair rate and inhibitor sensitivity findings together suggest biologically important differences in the chemical nature of X‐ray induced and HPD‐photosensitized strand breaks. In addition to strand breaks, HPD photosensitization produces covalent DNA‐protein crosslinks, some of which persist through at least 90 min incubation, but which are repaired within 180 min.
EFFICIENT FORMATION OF A CROSSLINKABLE HMT MONOADDUCT AT THE Kpn I RECOGNITION SITE
Authors: Gamper Howard , Piette Jacques , Hearst John E.
Published: January 2008

Abstract The double‐stranded Kpn I linker, CGGTACCG, is readily crosslinked by 4′‐hydroxymethyl‐4,5′,8‐trimethylpsoralen (HMT). Under identical conditions, the corresponding Bam HI linker, CGGATCCG, is resistant to modification. The differential reactivity of HMT towards the two sequences is also observed with SV40 DNA where the Kpn I restriction site is ten‐fold more susceptible to HMT modification than the Bam HI site. Selective reaction with the Kpn I site is attributed to preferential intercalation of HMT into the TpA sequence. The availability of crosslinked Kpn I linker has allowed us to characterize the kinetics of photoreversal. Upon irradiation at 254 nm, the diadduct reverses at a faster rate than the monoadduct, leading to an accumulation of the latter. The resultant monoadduct reforms crosslink rapidly upon irradiation at 365 nm. DNA oligomers like the Kpn I linker, which can be modified by the above protocol to contain a crosslinkable HMT monoadduct, could he exploited as photoreactive sequence‐specific probes.
LYSIS OF EGG PHOSPHATIDYLCHOLINE LIPOSOMES BY SINGLET OXYGEN GENERATED IN THE GAS PHASE
Authors: Eisenberg Walter C. , Taylor Kevin , Grossweiner Leonard I.
Published: January 2008

Abstract Singlet molecular oxygen was generated in the gas phase by heterogeneous energy transfer from a film of dry Rose Bengal and bubbled into suspensions of egg phosphatidylcholine liposomes, leading to membrane lysis and lipid peroxidation. The analysis based on large target diffusion kinetics indicates that approximately 3000 interactions were required for lysis of 1.5 μm liposomes. This experimental method makes it possible to measure the reactivity of gas phase singlet oxygen with aqueous biological systems.
A WAVE‐OPTICS EFFECT WHICH ENHANCES LIGHT ABSORPTION BY CHLOROPHYLL IN VIVO
Authors: Latimer Paul
Published: January 2008

Abstract Light is widely thought to move through cells and tissues as rays. Actually light is inherently wave‐like; ray motion is a special simple case of wave motion. To determine how well rays simulate light propagation and gradients within cells, absorption and scattering by particles were calculated with two sets of equations: one based on wave propagation within the particle and the other based on ray propagation. The ray model is found to substantially describe absorption at all particle size levels; however, it does not correctly describe scattering. Furthermore, for biological cells and structures larger than λ, the wave equations predict absorption cross sections which are 8–10% larger than expected on the basis of ray optics and extraction data: i.e. absorption is increased by a peculiar wave optics effect. This effect must enhance the efficiency with which the plants collect light energy for photosynthesis. The effect should be accounted for in corrections for the sieve effect.
SPECTRAL EVIDENCE FOR PHOTO‐INDUCED ISOMERIZATION OF CAROTENOIDS IN BACTERIAL PHOTOREACTION CENTER
Authors: Boucher François , Gingras Gabriel
Published: January 2008

Abstract The aim of this work was to determine whether spirilloxanthin and sphaeroidene bound to the same site of the photoreaction center isolated from Rhodospirillum rubrum can display cis–trans isomerization under conditions that lead to formation of triplet state PR of the primary electron donor. To this end, we monitored changes in the absorption spectrum of these bound carotenoids as induced by red light at low redox potentials. This experiment was performed both with the intact photoreaction center isolated from strain Sl and with the photoreaction center isolated from carotenoidless strain G9 reconstituted with either spirilloxanthin or sphaeroidene. In both preparations, spirilloxanthin exhibited light‐induced absorption changes that can be interpreted as a cis–trans isomerization. Under our experimental conditions, the absorption changes attained their full extent in about 1 min and were not or were only partially reversed when the light was switched off. Under our experimental conditions, the extent of these changes indicate that about 15% of the bound spirilloxanthin undergoes isomerization. Sphaeroidene artificially attached to the G9 photoreaction center also undergoes light‐induced absorbance changes, but these cannot easily be interpreted as a cis–trans isomerization.
INFLUENCE OF THE LOCATION OF TRYPTOPHANYL RESIDUES IN PROTEINS ON THEIR PHOTOSENSITIVITY
Authors: Pigault Claire , Gerard Dominique
Published: January 2008

The environmental effect on Trp residues photolysis was investigated on four proteins containing a single Trp residue in environments of various polarities: glucagon (exposed residue), nuclease (partially buried residue), RNase T1 (fully buried residue) and melittin (exposed or partially buried residue depending on the salt concentration). Direct photolysis was performed in neutral N2‐saturated phosphate solution at 20°C using 302 nm monochromatic light. Tryptophan loss was monitored by both absorption and fluorescence spectroscopy and by amino acid analysis. The results suggest that tryptophan photodegradation depends on the location of the residue in the protein, with regard to the exposure to the aqueous medium and to the neighbouring amino acids in the primary amino acid sequence and in the three dimensional structure. Photochemical products were not analysed but fluorescence spectra indicate that they vary with protein.
CHANGES IN TERTIARY STRUCTURE OF CALF‐LENS α‐CRYSTALLIN BY NEAR‐UV IRRADIATION: ROLE OF HYDROGEN PEROXIDE
Authors: Andley Usha P. , Sutherland Philip , Liang Jack N. , Chakrabarti B.
Published: January 2008

The effect of 300 nm irradiation on the three lens crystallins, α‐, β‐, and γ‐, was studied by using fluorescence and circular dichroism techniques. α‐Crystallin showed a pronounced change in tertiary structure as manifested in fluorescence and circular dichroism measurements. This finding is in agreement with our earlier findings that the tryptophan residues of α‐crystallin are more exposed than those of the other two crystallins. The results of studies using inhibitors specific for the different active species of oxygen suggest that H2O2‐mediated damage is involved in the change of tertiary structure of the proteins. Analyses of circular dichroism spectra indicate that, upon irradiation, the secondary structure of α‐crystallin remains virtually unaltered, and that the change in tertiary structure results primarily from photoinduced damage to the tryptophan residues.
FLAVIN‐MEDIATED PRODUCTION OF HYDROGEN PEROXIDE IN PHOTOELECTROCHEMICAL CELLS
Authors: Roncel Mercedes , Navarro José A. , Rosa Francisco F. De la , Rosa Miguel A. De la
Published: January 2008

A photoelectrochemical cell for hydrogen peroxide production using flavin photosystems is described. The anodic solution, which is kept free of oxygen by passing an Ar stream through it, contains the photoreceptor (flavin mononucleotide or lumiflavin) and the electron donor (EDTA, semicarbazide or hydroxylamine), while the peroxide is formed at the electrode of the cathodic solution, whose oxygen content is increased by bubbling with pure oxygen. Among several electrode metals that have been tested (Ag, Pt and Hg), Hg is the most efficient. The pH of the anodic and cathodic solutions should be adjusted to 14 and 1, respectively, for optimum results.
PHOTOCHEMICAL‐LIKE DESTRUCTION OF TRYPTOPHAN IN SERUM ALBUMINS INDUCED BY ENZYME‐GENERATED TRIPLET SPECIES
Authors: Rivas Edy I. , Paladini Alejandro , Cilento Giuseppe
Published: January 2008

Abstract —Human and bovine serum albumin quench enzyme‐generated acetone phosphorescence (Ksv=ca. 104M1). Concomitantly, these proteins are altered as shown by diminished tryptophan absorption at 280 nm, appearance of products of the formylkynurenine type (max=ca. 320 nm) and disappearance of tryptophan fluorescence. These alterations—which are similar to those induced photochemically—were also observed with serum albumins exposed to enzyme‐generated triplet acetaldehyde. On the other hand, triplet acetone generated by the thermolysis of tetramethyldioxetane failed to induce alterations. Presumably energy transfer occurs from the enzyme‐generated triplet species to tryptophan group(s) in the serum albumin associated with the acting enzyme. The detailed mechanism is, however, not yet understood.
PHOTOREDUCTION OF THIONINE BY WATER
Authors: Somer Güler , Temizer Aytekin
Published: January 2008

Abstract —The photoreduction of thionine by water has been studied, using a technique applied in earlier work on photoreduction of methylene blue. It is found for thionine as for methylene blue, that a long‐lived excited intermediate is formed, and that two such intermediates react to produce a single reduced molecule, thus providing adequate energy for the reaction. The mechanism proposed for methylene blue photoreduction is shown to be applicable to thionine photoreduction as well, indicating the unimportance of the amine methyl groups. Although in previous work it was suggested that H2O was the reducing agent, none of them, however, could determine the H2O2 formed. The formation of H2O2 is confirmed in this work, and the kinetics of its formation are shown to be in accordance with the mechanism.
PHOTO‐OXIDATION OF THYMINE SENSITIZED BY 2‐METHYL‐1,4‐NAPHTHOQUINONE: ANALYSIS OF PRODUCTS INCLUDING THREE NOVEL PHOTO‐DIMERS
Authors: WAGNER J. R. , CADET J. , FISHER G. J.
Published: January 2008

Abstract —The near‐UV photosensitization of thymine by 2‐methyl‐1,4‐naphthoquinone in oxygenated aqueous solution leads to the formation of nine major thymine‐derived products. Six of the photoproducts, representing 70% of the initial thymine loss, are also known to be formed by γ‐ray or X‐ray irradiation of oxygenated water solutions of thymine. They include the cis and trans isomers of 5‐hydroperoxy‐6‐hydroxy‐5,6‐dihydrothymine, the cis and trans thymine glycols, 5‐hydroxy‐5‐methylhydantoin, and N‐formyl‐N′‐pyruvylurea. The three remaining major products, accounting for a further 25% of the initial thymine loss, are thymine di‐adducts of a type not previously reported. Preliminary characterization of these novel photoproducts, based on their UV absorption, mass spectra, and proton and carbon‐13 nuclear magnetic resonance spectra, suggests that in each of the three, the thymine moieties are linked by an N(1)‐C(5) or N(1)‐C(6) bond. A thymine cation radical is implicated as the common precursor of all 9 products. Accordingly. pyrimidine photosensitization by 2‐methyl‐1,4‐naphthoquinone serves as a model system for studying the chemical consequences of radiation‐induced ionization of the DNA bases.
TARGETED MUTAGENESIS OF M13 DNA INDUCED BY PHOTOSENSITIZED REACTION
Authors: Piette Jacques , Van De Vorst Albert
Published: January 2008

Abstract —Inactivation and mutagenesis of M13 mp10 DNA either on a double‐stranded or a single‐stranded form have been induced after photosensitization mediated by proflavine. Both the rate of inactivation and the frequency of the induction of mutations in the Lac gene are at least ten times more important when the double‐stranded DNA has been used as substrate for the photosensitization reaction. Promazine has also been able to promote photomutagenesis in the Lac gene but less efficiently than proflavine. Numerous clones coming from E. cali K12 JM103 transfection by photosensitized single‐ or double‐stranded M13 mp10 DNA have been purified and amplified. The DNA of each individual clone has been extracted and sequenced in the Lac gene using two different primers. An important hot spot for photosensitized mutagenesis has been localized at position ‐65 from the start of the Lac gene transcription and corresponds to a transition pattern G → A. Other minor base sequence modifications have also been recorded in the Lac gene.
ACTION SPECTRUM (620–640 nm) FOR HEMATOPORPHYRIN DERIVATIVE INDUCED CELL KILLING
Authors: GOMER CHARLES J. , DOIRON DANIEL R. , RUCKER NATALIE , RAZUM NICHOLAS J. , FOUNTAIN STANLEY W.
Published: January 2008

Abstract— Monochromatic red light generated by a tunable dye laser is currently being utilized for the treatment of solid tumors with hematoporphyrin derivative (HpD) photoradiation therapy (PRT). Experiments were performed using mammalian cells to determine the most efficient wavelength of red light (620 to 640 nm range) for HpD induced cellular photoinactivation. Decrease in the clonogenic potential of Chinese hamster ovary (CHO) cells was examined following both short (I h) and extended (12 h) HpD incubation times. Maximal photosensitization was observed with wavelengths ranging from 630 to 632.5 nm and the action spectra for cell killing matched the absorption spectra for HpD bound to cells. Similar observations were obtained following both short and extended HpD‐cell incubation times. The potential relevance of these results as they relate to clinical HpD PRT are discussed.
THE PHOTOCHEMISTRY OF 5‐METHYLCYTOSINE AND 5‐METHYL‐2′‐DEOXYCYTIDINE IN AQUEOUS SOLUTION
Authors: Celewicz Lech , Sheilar Martin D.
Published: January 2008

Abstract

The nucleobase 5‐methylcytosine (I) is a minor component of eukaryotic DNA thought to be important in regulation of gene expression. The photochemical reactions of this nucleobase and its 2′‐deoxyribonucleoside, 5‐methyl‐2′‐deoxycytidine (II), in water have been studied. These reactions lead, respectively, to 3‐amino‐2‐methylacrylamidine (Ib) and 3‐(2‐erythro‐d‐pentopyranos‐1‐yl) amino‐2‐methylacrylamidine (IIb) as the main photoproducts. The structure of the photoproducts was established by spectroscopic methods (1H and13C NMR, UV spectroscopy, electron impact and liquid secondary ion mass spectrometry); in the case ofIb, confirmatory evidence was obtained by chemical methods (photolysis of 5‐methyl[2–13C]cytosine, hydrolysis ofN‐carbomethoxy‐3‐amino‐2‐methylacryl‐amidine and reaction ofIbwith 1,1′‐carbonyldiimidazole to giveI). The quantum yield for formation ofIbwas determined to be 1.8 × 10‐3at pH 7.5 while the quantum yield for formation ofIIbhas a lower value of 0.2 × 10‐3at pH 7.5. These quantum yields depend strongly on pH and reach maximum values of 2.0 × 10‐3at pH 7.0 (Ib) and 0.6 × 10‐3at pH 5.0 (IIb). The mechanism of formation ofIb(orIIb) is proposed to involve nucleophilic attack of water on the C‐2 position of photoexcitedI(orII), followed by ring opening and decarboxylation of an intermediate carbamic acid.
HEMATOPORPHYRIN‐SENSITIZED PHOTOINACTIVATION OF Streptococcus faecalis
Authors: Bertoloni Giulio , Salvato Benedetto , Dall‘Acqua Marina , Vazzoler Marina , Jori Giulio
Published: January 2008

Abstract— The photosensitizing action of hematoporphyrin (HP) on the cells of some bacterial strains belonging to the species Streptococcus faecalis, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae, as well as of strains of yeast Candida albicans, was studied in air‐equilibrated aqueous media at pH 7.2. All Gram‐negative strains appeared to be resistant even to prolonged irradiation both in the presence and in the absence of EDTA. On the other hand. Gram‐positive and yeast strains were photosensitive. In the case of Str. faecalis, whose strains displayed a particularly high photosensitivity, the efficiency of the photoprocess was mainly controlled by the HP concentration in the incubation medium (0.1‐1 μg/ml) and by the irradiation time (0–10 min); temperature (18–37oC) exerted a minor effect, whereas the incubation time (6–30 min) had no detectable influence. The photolability of Str. faecalis cells was only slightly different in the logarithmic and stationary phase of growth. The type of photoinduced ultrastructural modifications and the largely preferential binding of HP to the cytoplasmic membrane, as observed by cell fractionation studies, suggest that one important target of the HP‐photosensitized process is represented by membrane components.
PHOTOSENSITIZED INACTIVATION OF CHINESE HAMSTER CELLS BY PHTHALOCYANINES
Authors: Ben‐Hur E. , Rosenthal I.
Published: January 2008

Chloroaluminum phthalocyanine was found to sensitize cultured Chinese hamster cells upon exposure to white fluorescent light. Elimination of wavelengths below 370 nm did not reduce the effect significantly, indicating that the effective wavelengths were those absorbed by the Q band (600–700 nm) of phthalocyanine. The magnitude of the photosensitizing effect increased with the dye concentration and the time of its contact with the cells prior to light exposure. Although photosensitization was drastically reduced in the absence of oxygen, the lack of effect of glycerol and D20 during exposure suggests that neither hydroxyl radicals nor 1O2 are responsible for the cytotoxic response. The efficiency of the photosensitized induced cell killing did not vary with the position of the cells in the cell cycle, in contrast to exposure to X‐rays. The improved spectral properties, the reported low toxicity and the selective retention by neoplasms, make phthalocyanines promising candidates for use in photodynamic therapy of cancer.
PHOTO ACOUSTIC SPECTRA OF PHYCOBILIPROTEINS and CHLOROPHYLLIN IN ISOTROPIC and ANISOTROPIC POLYVINYL ALCOHOL FILMS
Authors: Frackowiak Danuta , Hotchandani Surat , Leblanc Roger M.
Published: January 2008

Abstract—Photoacoustic spectra (PAS) of biliproteins: R‐phycoerythrin (PE) with R‐phycocyanin (PC) admixture in isotropic and anisotropic polyvinyl‐alcohol (PVA) films were measured. The mixtures of biliproteins and chlorophyllin (Chllin) in PVA were also investigated. In order to establish the influence of PVA anisotropy on PAS amplitude, the stretched and unstretched PVA films colored by Congo red were studied. The films with PE and Chllin mixture when illuminated in the region of PE absorption, show higher PAS signals than the films with PE alone. This is explained by the excitation energy transfer from efficiently fluorescent PE to Chllin that has much lower yield of fluorescence. The stretched films always show a higher PAS signal than isotropic films because of the increase in the thermal conductivity of PVA. But normalized PAS of Congo red and Chllin in stretched PVA are similar to those in unstretched films.

Pigment molecules oriented parallel to the direction of film stretching have a lower rate of thermal deactivation compared to that of unoriented molecules as has been found by comparing PAS of differently oriented Congo red molecules using photoselection by polarized light. The same result was obtained for various PE chromophores which are differently oriented in anisotropic films.
ENZYMATIC GENERATION OF ELECTRONICALLY EXCITED STATES BY ELECTRON TRANSFER
Authors: Villablanca Miguel , Cilento Giuseppe
Published: January 2008

Abstract— The catechol oxidase promoted oxidation of catechols produces electronically excited states readily detected by chlorophyll sensitized fluorescence. Both the chemiexcitation step and the transfer step are efficient. The use of chlorophyll has confirmed that the peroxidase catalyzed oxidation of dihydroxyfumarate also generates electronically excited species. It is concluded that efficient enzymatic generation of electronic energy can occur not only through the dioxetane/dioxetanone route, but also via electron transfer processes.
SPECTRAL PROPERTIES, PHOTOTRANSFORMATION KINETICS AND PELLETABILITY OF PHYTOCHROME IN Pharbitis nil Chois*
Authors: Lee Helen S. J. , Kendrick Richard E. , Vince‐Prue Daphne
Published: January 2008

Abstract— An examination has been made of the involvement of phytochrome in the circadian rhythm of flowering in Pharbitis nil Chois. The peak position of Pfr absorption changes with time after a red light pulse. The shortest absorption wavelength of Pfr occurs at the same time as flowering is inhibited by red light in dark grown, red light pretreated plants. Pelletable and supernatant phytochrome show a similar trend with lowest values found at the time of flower inhibition. Neither phototransformation kinetics nor intermediates of phytochrome which accumulate in white light show such a relationship to the circadian rhythm found in flowering of dark grown P. nil.
PHYTOCHROME SYNTHESIS DURING IMBIBITION IN EMBRYONIC AXES OF Pisum sativum L.*
Authors: Konomi Koji , Nagatani Akira , Furuya Masaki
Published: January 2008

Abstract— The exact quantity of phytochrome in crude homogenates (2kS) prepared from embryonic axes of Pisum sativum during imbibition at 25°C on 0,2% agar was estimated optically. The problem of the scattering factor was solved by using highly purified phytochrome as an internal standard. The content of phytochrome protein moiety in diluted samples of the crude homogenates of the axes was also determined by an enzyme‐linked immunosorbent assay (ELISA). Phytochrome was not detectable either spectropho‐tometrically or immunochemically in 2kS of dormant dry axes. Embryonic axes quickly absorbed water during the first1–2 h after the start of imbibition, after which the fresh weight stayed at a constant level for a further 10 h. The content of spectrophotometrically detectable phytochrome increased during imbibition in the dark, reaching about 0.2 μ.g/axis after 12 h. The amount of phytochrome in 2kS of axes in the light was so small that only about 0.05 μg/axis was detected after 12 h. The content of immunochemically detectable phytochrome greatly increased up to ca. 0.5 μg/axis after 12 h of dark incubation. In 2kS of the light‐grown axes the content of the phytochrome protein was ca. one fourth lower than in dark‐grown axes. We conclude that the appearance and increase of phytochrome in fragments of imbibed embryonic axes were caused by de novo synthesis and that the contents of both photometrically detectable phytochrome and its protein moiety in the light‐grown samples were lower than those in the dark throughout the early germination process.
PLANT PROTECTIVE RESPONSE TO ENHANCED UV‐B RADIATION UNDER FIELD CONDITIONS: LEAF OPTICAL PROPERTIES and PHOTOSYNTHESIS
Authors: Flint Stephan D. , Jordan Peter W. , Caldwell Martyn M.
Published: January 2008

Abstract— Plants of Vicia faba were grown in the field during early to midsummer while receiving two levels of supplemental UV‐B radiation. Light‐saturated photosynthesis and stomatal diffusive conductance of intact leaves did not show any indications of UV‐radiation damage. Supplemental UV treatment did cause increased concentrations of UV‐absorbing flavonoid pigments in leaf tissues and decreased epidermal transmittance of UV radiation. While epidermal transmittance was reduced 30% under the low‐UV treatment, the high‐UV treatment failed to elicit as large a change. However, total amounts of flavonoids in other leaf tissues did increase in response to the high‐UV treatment (up to 12% greater per unit leaf area than for control plants). This may have been a major factor protecting underlying photosynthetic tissues.
INTERACTION OF HYDROXYLAMINE WITH THE WATER‐OXIDIZING ENZYME INVESTIGATED VIA PROTON RELEASE*
Authors: Förster Verena , Junge Wolfgang
Published: January 2008

Abstract— Photosynthetic water oxidation is a four‐step redox process which is driven by a one‐quantum‐one‐electron reaction center. Stepwise electron Abstract—ion from the water‐oxidizing enzyme is accompanied by stepwise proton release with the following stoichiometric pattern at given half‐rise times: 1 H+ (250 μs, S0→ S1):0 H+(S1→ S2): 1 H+ (200 μs, S2→ S3): 2 H+ (1.2 ms, S3→ S4→ S0). (Förster and Junge, 1985, preceding article in this issue). Hydroxylamine at low concentrations (≲100 μ M) appears to compete with water at the active site of the water‐ oxidizing enzyme. Its interference shifts the dark state of the water‐oxidizing enzyme by two steps backwards (Bouges, 1971). We found that the hydroxylamine‐induced shift was also reflected in the stoichiometric pattern and in the kinetics of proton‐release. In the presence of hydroxylamine, two protons per reaction center were released with a half‐rise time of ≅ 2 ms upon the first exciting flash given to dark adapted thylakoids. This was slower than observed for each of the protons released during unperturbed water oxidation. One proton was released upon the second flash. The half‐rise time of the main component observed upon the second flash in hydroxylamine‐treated samples agreed with the one observed upon the fourth flash in the absence of hydroxylamine, which had been attributed to the S0→ S1 transition. The two protons which were observed upon the first flash in hydroxylamine‐treated thylakoids may be due to hydroxylamine oxidation or to the association of water to the catalytic manganese center after detachment of oxidized hydroxylamine from its binding site.
INDUCTION OF DNA‐PROTEIN CROSSLINKS IN HUMAN CELLS BY ULTRAVIOLET and VISIBLE RADIATIONS: ACTION SPECTRUM
Authors: Peak J. G. , Peak M. J. , Sikorski R. S. , Jones C. A.
Published: January 2008

Abstract— DNA‐protein crosslinking was induced in cultured human P3 teratocarcinoma cells by irradiation with monochromatic radiation with wavelengths in the range254–434 nm (far‐UV, near‐UV, and blue light). Wavelength 545 nm green light did not induce these crosslinks, using the method of alkaline elution of the DNA from membrane filters. The action spectrum for the formation of DNA‐protein crosslinks revealed two maxima, one in the far‐UV spectrum that closely coincided with the relative spectrum of DNA at 254 and 290 nm, and one in the visible light spectrum at 405 nm, which has no counterpart in the DNA spectrum. The primary events for the formation of DNA‐protein crosslinks by such long‐wavelength radiation probably involve photosensitizers. This dual mechanism for DNA‐protein crosslink formation is in strong contrast to the single mechanism for pyrimidine dimer formation in DNA, which apparently has no component in the visible light spectrum.
THERMALLY STIMULATED LUMINESCENCE OF UV‐AND X‐IRRADIATED CAFFEINE
Authors: Jahan M. S. , Cooke D. W.
Published: January 2008

Abstract— Thermally stimulated luminescence studies of UV‐ and X‐irradiated caffeine have been conducted in the interval77–300 K. The X‐ray‐induced glow curve exhibits peaks at 102, 128, 158, and 198 K, whereas the UV‐induced curve is characterized by peaks with maxima at 120 and 208 K. Analysis of the X‐ray‐induced glow peaks revealed that the 102 and 128 K peaks obeyed first‐order kinetics, while the 158 and 198 K ones followed orders of 1.3 and 1.8, respectively. Trapping parameters associated with the peaks were also elucidated. Concomitant emission spectra of each glow peak (both UV and X‐ray induced) were identical and consisted of a band with well‐defined maxima at 405 and 480 nm which are attributed to singlet (S1→ S0+ hv) and triplet (T1→ S0+ hv) transitions, respectively. At elevated temperatures the triplet transition is not observed due to quenching of the triplet state or to triplet‐triplet interactions. An energy‐level diagram depicting the thermally stimulated processes in irradiated caffeine is presented.
DYE LASER INTRACAVITY ABSORPTION AS AN OPTICAL PROBE IN CONDENSED PHASE AND BIOLOGICAL SYSTEMS
Authors: Giniger Rina , Gutman Menachem
Published: January 2008

Abstract— A sensitive optical method to monitor local environmental changes in biological systems is described. It utilizes the high optical amplification typical to any dye laser cavity by installing the investigated system inside the laser resonator. Very small changes in the optical density of a probe dye can be detected and related to the dye's state of aggregation or in another demonstration to its adsorption on differently charged micelles and liposomes. When further developed, this technique can prove to be a very sensitive method to measure membrane potentials, changes in molecular environment and molecular dynamics. The pulsed laser used is advantageous to a continuous source used in fluorescence and absorption methods reducing photodynamic damage.
FLUORESCENCE SPECTRAL CHANGES OF HEMATOPORPHYRIN DERIVATIVE UPON BINDING TO LIPID VESICLES, Staphylococcus aureus AND Escherichia coli CELLS
Authors: Ehrenberg Benjamin , Malik Zvi , Nitzan Yeshayahu
Published: January 2008

Abstract—The binding of hematoporphyrin derivated (Hpd) to lipid vesicles and bacterial membranes was determined by fluorescence spectroscopy. The fluorescence measurements of Hpd in aqueous solutions showed two bands at 613 and 677 nm. In lipid environments of lecithin vesicles the fluorescence spectrum was shifted to 631 and 692 nm, respectively. Hpd was rapidly bound to the cell membrane ofStaphylococcus aureuswhile much less binding occurred in the presence ofEscherichia coli.At the same time, spheroplasts of both bacteria were shown to bind Hpd to a similar extent. These results are well correlated with the photoinactivation of the gram positive bacteria with Hpd while the gram negative cells were shown to be resistant. The pH dependence of both Hpd binding toS. aureusas well as the photodynamic inhibitory effect of the same bacteria are similar. It is concluded that the segregation of Hpd to the cell membrane is a prerequisite for its photodynamic effect.
PICOSECOND FLUORESCENCE STUDY OF PHOTOSYNTHETIC MUTANTS OF Chlamydomonas reinhardii: ORIGIN OF THE FLUORESCENCE DECAY KINETICS OF CHLOROPLASTS
Authors: Gulotty Robert J. , Mets Laurens , Alberte Randall S. , Fleming Graham R.
Published: January 2008

Abstract— The fluorescence decay kinetics of photosynthetic mutants of Chlamydomonas reinhardii which lack photosystem II (PS II), photosystem I (PS I), and both PS II and PS I have been measured. The PS II mutant strain8–36C exhibits fluorescence decay lifetime components of 53, 424 and 2197 ps. The fluorescence decay of a PS I mutant strain12–7 contains two major fluorescence decay components with lifetimes of 152 and 424 ps. The fluorescence decay of mutant strain C2, which lacks both PS II and PS I, is nearly single exponential with a lifetime of 2561 ± 222 ps. In simulations in which it is assumed that wild‐type decays are a simple sum of the major decay components of the isolated parts of the photosynthetic unit as measured in the mutants, curves are obtained that fit the wild‐type C. reinhardii fluorescence decay data when the absorption cross‐sections of PS II and PS I are weighted approximately equally. The 89 ps lifetime component in the wild‐type is an average of 53 and 152 ps components arising from excitation transfer to and trapping in PS I and PS II. The single step transfer time in PS I is estimated to be between 100 and 700 fs depending on assumptions about array size. We find that between two and four visits to the PS I reaction center are required before final trapping.
TRIPLET EXCITATION TRANSFER INVOLVING β‐IONONE. A KINETIC STUDY BY LASER FLASH PHOTOLYSIS
Authors: Chattopadhyay S. K. , Kumar C. V. , Das P. K.
Published: January 2008

Abstract— Employing nanosecond laser flash photolysis, β‐ionone (BI) has been examined as an acceptor and as a donor of triplet excitation. In the limit of diffusion‐control as well as below it, the rate constants for the quenching of a series of sensitizer triplets by BI are2–3 times smaller than those by 2,4‐hexadienal (HD), although the triplet energies (spectroscopic) of the two carbonyl‐containing dienes are estimated to be the same (∼55 kcal mol‐1). We attribute the difference to a steric effect arising from ground‐state geometric distortion and heavy alkyl‐substitution in BI. In spite of possible exothermic energy transfer, BI triplet is nearly nonquenchable by azulene and ferrocene; this is explainable by torsional relaxation to an equilibrium geometry at which the vertical energy gap is smaller than 40 kcal mol‐1. The singlet oxygen yield from the interaction of BI triplet with oxygen in benzene is estimated to be 0.5, suggesting that spin‐exchange and energy‐transfer may be involved to the same extent in the oxygen quenching process.
SITE‐SELECTION and SHPOLSKII SPECTROSCOPY OF MODEL PHOTOSYNTHETIC SYSTEMS
Authors: Hala J. , Pelant I. , Ambroz M. , Pancoska P. , VACEK K.
Published: January 2008

Abstract—

Low temperature (T= 10 K) site‐selection fluorescence and excitation spectra of both isolated pheophorbide‐a molecules (I PHEO) and pheophorbide covalently bonded to the synthetic l‐lysyl‐l‐alanyl‐l.‐alanine polypeptide (B PHEO) were measured in dimethylformamide (DMF) matrices. The fluorescence spectra display sharp vibronic lines at different wavenumbers for different dye laser excitation wavelengths, superimposed on a broad band background. Spectral analysis provides frequencies of normal vibrations (FNV) and site distribution functions (SDF). The FNV and SDF of I PHEO in DMF have been found to show good agreement with other chlorophyll‐like molecules. A covalent binding between the polypeptide and PHEO molecules produces only slight changes in FNV but significant broadenings and shifts to lower energies in SDF. The fluorescence spectra of I PHEO in a typical Shpolskii matrix (n‐octane) were also measured and found to exhibit sharp non‐shifting vibronic lines for all wavelengths and kinds of excitation. A general model explaining both site‐selection and Shpolskii spectroscopy is presented.
TYROSYL FLUORESCENCE SPECTRA OF PROTEINS LACKING TRYPTOPHAN: EFFECTS OF INTRAMOLECULAR INTERACTIONS
Authors: Lux Béatrice , Baudier Jacques , Gerard Dominique
Published: January 2008

Abstract— The fluorescence spectra of class A proteins which lack tryptophanyl residues were examined in detail, and revealed some differences in the position of maximum and half‐width of the tyrosine emission band between proteins and tyrosine itself. These parameters were affected by conformational changes in protein molecules (denaturation, thermal effects, ion binding) which also induced variations in absorption spectra and fluorescence quantum yields. These observations are thought to be related to the formation of hydrogen bonds between the hydroxyl group of the tyrosyl residues and proton acceptor groups in the protein.
PHOTOREACTIVATING ENZYME FROM Streptomyces griseus—VI. ACTION SPECTRUM AND KINETICS OF PHOTOREACTIVATION
Authors: Eker A. P. M. , Hessels J. K. C. , Dekker R. H.
Published: January 2008

Abstract— A high resolution action spectrum for photoreactivation was determined using purified photoreactivating enzyme from Streptomyces griseus. Conversion of pyrimidine dimers in UV‐irradiated DNA, the substrate for photoreactivating enzyme, was measured with a Haemophilus influenzae transformation assay. A high similarity was found between action spectrum (max. at 445 nm) and the long wavelength absorption band (max. at 443 nm)of photoreactivating enzyme. In addition to the400–470 nm region considerable photoreactivation was found with wavelengths between 280 and 320 nm. No evidence was obtained for the presence of nonenzymatic photoreactivation. Comparison of in vitro and in vivo action spectra revealed that the sharp peak at 313 nm found in vivo is probably the result of counteracting photoreactivation and inactivation effects. Comparison of the action spectrum with the absorption spectrum of 8‐hydroxy‐10‐methyl‐5‐deazaisoalloxazine in an aprotic dipolar solvent (which serves as a model for the 8‐hydroxy‐5‐deazaflavin chromophore in photoreactivating enzyme) indicates the possible presence of other chromophore(s) involved in the photorepair process. From kinetic measurements and flash experiments values were obtained for the rate constants of the photoreactivation reaction. The quantum yield of photoreactivation was estimated to be approximately 1.