bluuebunny/crossref_metadata_2025 huggingface dataset:
Photooxidation of Troglitazone, a New Antidiabetic Drug *
Authors: Fu Yulan , Sheu Chimin , Fujita Takashi , Foote C. S.
Published: January 2008

Troglitazone (CS‐045) is a new oral antidiabetic drug reported to be effective in insulin‐resistant diabetes and to show antihypertensive effects. Photooxidation of troglitazone gave the quinone and quinone epoxide as the major final stable products. An intermediate observed by NMR spectroscopy was shown to be the hydroperoxydi‐enone, which is moderately stable at room temperature. The rate constant of singlet oxygen quenching by troglitazone is 2.14 × 108M−1s−1 and the reaction rate constant in acetone‐d, is 8.64 × 10, M−1 s−1. Only the chroman ring of troglitazone reacts with and quenches singlet oxygen significantly, and its reactivity and products are analogous to those of a‐tocopherol. The reactivity of CS‐045 toward singlet oxygen is much larger than that of the related compounds lacking the chroman ring.
Time‐Resolved Infrared Spectroscopy in Studies of Organometallic Excited States and Reactive Intermediates
Authors: Ford Peter C. , Bridgewater Jon S. , Lee Brian
Published: January 2008

Abstract— This article provides a brief overview of time‐resolved infrared spectroscopy (TRIR) applied to the investigation of organometallic photochemistry in solution. In this context, some fundamental problems where flash photolysis TRIR techniques may provide information relevant to photochemical pathways and to certain thermal reaction mechanisms are described. Different approaches to obtaining TRIR spectral information are summarized and illustrated with specific applications.
Steric Hindrance between Chromophore Substituents as the Driving Force of Rhodopsin Photoisomerization: 10‐Methyl‐13‐Demethyl Retinal Containing Rhodopsin
Authors: Koch Daniel , Gärtner Wolfgang
Published: January 2008

Abstract— A visual chromophore analogue, 10‐methyl‐13‐demethyl (dm) retinal, was synthesized and reconstituted with bleached bovine rhodopsin to form a visual pigment derivative with absorbance maximum at 505 nm. The investigations with this new compound were stimulated from recent results using 13‐dm retinal as a chromophore that revealed a remarkable loss in quantum efficiency (φ of 13‐dm retinal‐containing rhodopsin: 0.30, Ternieden and Gartner, J. Photochem. Photobiol. B Biol. 33, 83–86, 1996). The quantum efficiency of the new pigment was determined as 0.59 by quantitative bleaching using reconstituted rhodopsin as a reference. The very similar quantum efficiencies of rhodopsin and the new pigment give experimental support for the recently presented hypothesis that a steric hindrance between the substituents at positions 10 and 13 in 11‐cis‐retinal is elevated during the photoisomerization and thus facilitates the rapid photoisomerization of the visual chromophore (Peteanu et al., Proc. Natl. Acad. Sci. USA 90, 11762–11766, 1993). Such steric hindrance is removed from the molecule by the elimination of the methyl group from position 13 and can be re‐established via a rearrangement of the substitution pattern by introducing a methyl group at position 10 of 13‐dm retinal.
Irradiation of DNA with 193 nm Light Yields Formamidopyrimidine‐DNA Glycosylase (Fpg) Protein‐Sensitive Lesions
Authors: Melvin T. , Cunniffe S. , Papworth D. , Roldan‐Arjona T. , O'Neill P.
Published: January 2008

Abstract— Irradiation of aqueous solutions of plasmid DNA (pUC18) at pH 7.6 with 193 nm laser light results in low yields of prompt single strand breakage (air‐saturated sample φssb= [1.5 ± 0.1] ± 10−4, argon‐saturated sample φssb= [0.9 ± 0.1] ± 10−4). Treatment of the irradiated DNA samples with Escherichia coli formamidopyrimi‐dine‐DNA glycosylase (Fpg) protein results in an approximate 20‐fold increase in the yield of single strand breakage (air‐saturated sample φfpg= [33.1 ± 3.1] ± 10−4, argon‐saturated sample φfpg= [23.8 ± 2.6] × 10 4). This result indicates that 193 nm light induces other modification) (most likely of the purine moieties) that are 20 times more abundant than prompt strand breakage within the DNA matrix.
Effects of a Single Exposure to UVB Radiation on the Activities and Protein Levels of Copper‐Zinc and Manganese Superoxide Dismutase in Cultured Human Keratinocytes
Authors: Sasaki Hiroko , Akamatsu Hirohiko , Horio Takeshi
Published: January 2008

Abstract— Ultraviolet B irradiation has been believed to decrease or impair the activity of reactive oxygen species (ROS) scavenging enzymes such as superoxide dismutase (SOD) in the skin. It has been recently reported that two isozymes of SOD, namely copper‐zinc SOD (Cu‐Zn SOD) and manganese SOD (Mn SOD), exist in mammalian cells and that the two enzymes play different roles in living systems. The aim of this study was to investigate changes in SOD activities and protein levels in cultured human keratinocytes after acute UVB irradiation. In addition, the protein levels of Cu‐Zn SOD and Mn SOD were quantified separately. A single exposure to UVB irradiation produced an increase in SOD activity and protein level that peaked immediately after UVB irradiation, after which a decline was observed, with subsequent recovery to baseline levels 24 h after irradiation. In individual assays of Mn SOD and Cu‐Zn SOD, the amount of Mn SOD protein decreased and then gradually recovered 24 h after irradiation. In contrast, the amount of Cu‐Zn SOD protein increased immediately after UVB irradiation, and then gradually declined. To evaluate the mechanisms of these changes, we examined the effects of the cytokines, interleukin‐1α (IL‐1α) and tumor necrosis factor‐α (TNF‐α), which can be secreted from keratinocytes after UVB irradiation, on the SOD activity and protein levels in keratinocytes. Interleukin‐la and TNF‐α enhanced both the SOD activity and protein level of Mn SOD, while these cytokines had no effect on Cu‐Zn SOD protein levels in cultured human keratinocytes after incubation for 24 h. Furthermore, when neutralizing antibodies against IL‐1α and TNF‐α were added separately or together to the culture medium before UVB irradiation, the recovery of total SOD activity and Mn SOD protein level were markedly inhibited 24 h after irradiation. Our results suggest that significant increases in SOD activity and protein level occur as a cutaneous antioxidant defense mechanism that protects against the cytotoxicity as a result of UVB irradiation, and that this increase in SOD is attributed to Cu‐Zn SOD. The Cu‐Zn SOD and Mn SOD protein levels changed in a different manner after UVB irradiation. The former may participate in an early phase and the latter in a late phase defense mechanism directed against oxidant cytotoxicity through UVB irradiation. In addition, the recovery of Mn SOD to baseline levels 24 h after UVB irradiation seems to be mediated through cytokines such as IL‐1α and TNF‐α, which are secreted from keratinocytes.
Halogenated Squaraine Dyes as Potential Photochemotherapeutic Agents. Synthesis and Study of Photophysical Properties and Quantum Efficiencies of Singlet Oxygen Generation*
Authors: Ramaiah Danaboyina , Joy Abraham , Chandrasekhar Nese , Eldho Nadukkudy V. , Das Suresh , George Manapurathu V.
Published: January 2008

Abstract— We describe the synthesis and photophysical studies, including measurements of quantum yields of triplet excited states and singlet oxygen generation of bis(3,5‐dibromo‐2,4,6‐trihydroxyphenyl)squaraine (2) and bis(3,5‐diiodo‐2,4,6‐trihydroxyphenyl)squaraine (3). These dyes exist in solution in the protonated, neutral, single and double depro‐tonated forms, depending on pH. The pKa values of these dyes were found to be relatively lower than those of the parent bis(2,4,6‐trihydroxyphenyl)squaraine (1). Only the single deprotonated forms (Sq) of 2 and 3 showed measurable fluorescence. In microheterogeneous media such as in the presence of β‐cyclodextrin, cetyltrunethylammonium bromide and polyvinylpyrrolidone), bathochromic shifts in the absorption and emission spectra of Sq were observed with a substantial enhancement in their fluorescence yields. Triplet excited states are the main transient intermediates obtained upon 532 nm laser excitation of the various forms of 2 and 3 in methanol. These triplets have lifetimes in the range from 0.061 to 132 μs. The triplet quantum yields of double deprotonated forms are low (φT = <0.01), whereas the neutral and Sq−forms of 2 (φr = 0.12 and 0.22) and 3 (φT= 0.24 and 0.5), respectively, exhibited significant triplet yields. Quantum yields of singlet oxygen generation by Sq−forms of 2 and 3 were determined in methanol and were found to be 0.13 and 0.47, respectively, which are in good agreement with the triplet yields obtained in these systems.
Gene Expression in Skin Tumors Induced in Hairless Mice by Chronic Exposure to Ultraviolet B Irradiation
Authors: Sato Hiromi , Suzuki Junko S. , Tanaka Misao , Ogiso Manabu , Tohyama Chiharu , Kobayashi Shizuko
Published: January 2008

Abstract— We investigated the expressions of c‐Ha‐ras, c‐jun, c‐fos, c‐myc genes and p53 protein in the development of skin tumors induced by chronic exposure to UVB without a photosensitizer using hairless mice. When mice were exposed to UVB at a dose of 2 kJ/m2three times a week, increased c‐Ha‐ras and c‐myc transcripts were detected after only 5 weeks of exposure, while no tumor appeared on the exposed skin. The increase in gene expression continued until 25 weeks, when tumors, identified pathologically as mainly squamous cell carcinomas (SCC), developed in the dorsal skin. In these SCC, overexpression of c‐fos mRNA was also observed along with the increases in c‐Ha‐ras and c‐myc. A single dose of UVB (2 kJ/m2) applied to the backs of hairless mice transiently induced overexpression of the early event genes c‐fos, c‐jun and c‐myc, but not c‐Ha‐ras, in the exposed area of skin. Accumulation of p53 protein was determined by Western blotting analysis or immunobJstochemistry using monoclonal antibodies PAb 240 or 246, which recognize mutant or wild type, respectively. In the SCC., a mutant p53 protein accumulated in the cytoplasm and nucleus. After single‐dose irradiation, the increased wild‐type p53 protein was observed in the nuclei of epidermal cells. The present results suggest that overexpression of the c‐fos, c‐myc and c‐Ha‐ras genes, and the mutational changes in p53 protein might be associated with skin photocarcinogenesis. Moreover, overexpression of the c‐Ha‐ras and c‐myc genes might be an early event in the development of UVB‐induced skin tumors in mice.
UVB DNA Dosimeters Analyzed by Polymerase Chain Reactions
Authors: Yoshida Hiroko , Regan James D.
Published: January 2008

Abstract— Purified bacteriophage Λ DNA was dried on a UV‐tran‐sparent polymer film and served as a UVB dosimeter for personal and ecological applications. Bacteriophage Λ. DNA was chosen because it is commercially available and inexpensive, and its entire sequence is known. Each dosimeter contained two sets of DNA sandwiched between UV‐transparent polymer films, one exposed to solar radiation (experimental) and another protected from UV radiation by black paper (control). The DNA dosimeter was then analyzed by a polymerase chain reaction (PCR) that amplifies a 500 base pair specific region of Λ DNA. Photoinduced damage in DNA blocks polymerase from synthesizing a new strand; therefore, the amount of amplified product in UV‐exposed DNA was reduced from that found in control DNA. The average lesion frequency per 500 base pair per strand at 16 PCR cycles was –1.22, 1.00, 0.70 and 0.50 for 30 ng, 50 ng, 100 ng and 150 ng of dried DNA, respectively, after a total dose of 60 kj m 2 delivered with a solar UVB simulator. Although the average lesion frequency increases linearly with increasing doses for four different amounts of template DNA, the lesion frequency seems to be averaged by the amplified products from the protected Λ DNA molecules below the top few layers. The average daily dose, equivalent to the UV dose applied with the solar UVB simulator, was 10.2±0.4 kj m2 with the 50 ng containing DNA dosimeter in September 1995 in Melbourne, FL. Both 50 ng and 150 ng containing DNA dosimeters produced the same average daily dose within experimental error in January 1996, which was 5.2±0.3 kj m 2 at the same location. The dried Λ DNA dosimeter is compact, robust, safe and transportable, stable over long storage times and provides the total UVB dose integrated over the exposure time.
Effect of Photodynamic Pretreatment on the Susceptibility of Murine Tumor Cells To Macrophage Antitumor Mechanisms
Authors: Reiter Isabella , Schwamberger Giinter , Krammer Barbara
Published: January 2008

Abstract— In vitro photodynamic treatment of YAC‐1 murine T‐lymphoma cells with the hematoporphyrin derivative Photosan 3 and red light resulted in dose‐dependent phototoxicity. Photodynamic pretreatment, however, did not render these cells more susceptible to macrophage‐me‐diated tumor cytotoxicity or the cytotoxic effects of mac‐rophage‐derived antitumor mediators like tumor necrosis factor aL (TNF‐aL) or interferon bT (IFN‐bT). Independent of the degree of photosensitization used, the cytotoxicity values obtained with macrophages or the different mediators were shifted by the respective values for phototoxicity, suggesting these effects to be additive and thus not interdependent. These data show that while higher overall tumor cytotoxicity can be achieved by a combination of photodynamic treatment and macro‐phage‐mediated tumor destruction, this apparently is not a result of enhanced sensitivity of photodynamically treated tumor cells to macrophage antitumor mechanisms in general
Electron Spin Resonance Evidence of the Generation of Superoxide Anion, Hydroxyl Radical and Singlet Oxygen during the Photohemolysis of Human Erythrocytes with Bacteriochlorin a
Authors: Hoebeke Maryse , Schuitmaker Hans J. , Jannink Lies E. , Dubbelman Tom M. A. R. , Jakobs Andreas , Van de Vorst Albert
Published: January 2008

Abstract— Photodynamic therapy with bacteriochlorin a (BCA) as sensitizer induces damage to red blood cells in vivo. To assess the extent of the contributuion of reactive oxygen species (ROS) and to determine a possible reaction mechanism, competition experiments with assorted ROS quenching or/and enhancing agents were performed in human erythrocytes as model system and in phosphate buffer. In the erythrocyte experiments, a 2% suspension was incubated with BCA for 1 h, washed with phosphate‐buffered saline, resuspended and subsequently illuminated with a diode laser using a fluence rate of 2.65 mW/cm2. Potassium leakage and hemolysis were light and BCA dose dependent. Adding tryptophan (3.3 mM), azide (1 mM) or histidine (10 mM) to the erythrocyte suspension before illumination delayed the onset of K‐leakage and hemolysis suggesting a type II mechanism. The D2O did not affect K‐leakage nor photohemolysis. Adding mannitol (13.3 mM) or glycerol (300 nM) also caused a delay in the onset of K‐leakage and hemolysis, suggesting the involvement of radicals. In phosphate buffer experiments, it was shown using electron spin resonance (ESR) associated with spin‐trapping techniques that BCA is able to generate 02∼* and OH* radicals without production of aqueous electron. Visible or UV irradiation of the dye in the presence of the spin trap 5,5‐dimethyl‐1‐pyrroline‐iV‐oxide (DMPO) gave an ESR spectrum characteristic of the DMPO‐hydroxyl radical spin adduct DMPO‐OH. Addition of ethanol or sodium formate produced supplementary hyperfine splittings due to the respective CH3CHOH * and CO2‐1 radical adducts, indicating the presence of free OH*. Production of DMPO‐OH was partly inhibited by superoxide dismutase (SOD), catalase and desferoxamine, suggesting that the iron‐catalyzed decomposition of H2O2 was partly involved in the formation of one part of the observed OH *. The complementary inhibition of DMPO‐OH production by azide and 9,10‐anthracenedipropionic acid (ADPA) was consistent with 1O2 production by BCA followed by reaction of 1O2 with DMPO and decay of the intermediate complex to form DMPO‐OH and free OH*. All our results seem to indicate that BCA is a 50%/50% type 1/type 2 sensitizer in buffered aqueous solutions and confirmed that the dye‐induced hemolysis of erythrocytes was well caused by a mixed type 1/type 2 mechanism.
Color Changes Induced by Pigment Granule Aggregation in Chromatophores: A Quantitative Model Based on Beer's Law
Authors: Masthay Mark B.
Published: January 2008

Abstract— A model is presented that quantitatively relates changes in the Beer's Law absorbance of light‐absorbing chromatophores (melanophores, erythrophores and xanthophores) of cephalopods to changes in the extent of pigment granule aggregation in these cells. Assuming a circular chromatophore of uniform thickness is initially in its dispersed state, and using a pigment granule aggregation index (PGAI) that specifies the extent of pigment granule aggregation, we find that for a given PGAI, the increase in the photon flux through the chromatophore induced by pigment granule aggregation is directly proportional to the dispersed state absorbance. That is, for a given PGAI, darkly colored chromatophores experience greater clearing responses than weakly colored chromatophores. Color changes are also found to be induced as effectively by a small number of large chromatophores or a large number of small chromatophores provided the total skin surface area covered by pigment in the dispersed states are equivalent in the two cases. These results are related to the morphologies and pigment aggregation behaviors of melanophores, erythrophores and xanthophores, based on the light absorption properties of the melanin, pteridine and carotenoid pigments found in these cells. The relative utility and limitations of this model for studying cephalopod (nonden‐dritic) and vertebrate (dendritic) chromatophores are also discussed.
Solar UVB Dosimetry by Amplification of Short and Long Segments in Phage LD DNA
Authors: Yoshida Hiroko , Regan James D.
Published: January 2008

Abstract— DNA UVB dosimeters, consisting of minidots of dried bacteriophage DNA placed on a UV‐transparent polymer film, were analyzed by polymerase chain reactions (PCR). Ultraviolet‐B dosimetry obtained with amplification of phage LD DNA of segments of 1.08 kilobase pairs (kbp) and 2.24 kbp was compared with that obtained with amplification of a 0.5 kbp segment (H. Yoshida and J. D. Regan, 66, 82‐88, Photochem. Photobiol 1997). The number of lesions in each segment induced by UV radiation is proportional to the size of the amplified segments; thus, the average lesion frequency per unit dose was greatest in the 2.24 kbp and least in the 0.5 kbp segment. The average lesion frequency per unit dose was 3.5 times 10‐2 and 11.9 times 10‐2 m2 kJ‐1 for 1.08 kbp and 2.24 kpb, respectively, compared to that for 0.5 kbp of 1.7 times 10‐2 m2 kJ‐1 at 50 ng DNA. Dependability of DNA dosimeters, containing 50 ng and 100 ng, was tested by placing the DNA dosimeters for a time period of either 1 or 2 days outdoors on 8‐12 January at Melbourne, FL. The daily dose was obtained directly with amplification of the 2.24 kbp segment and the 2 day continuous dose was obtained with amplification of the 1.08 kbp segment. Although the average lesion frequencies were different, both 50 ng and 100 ng DNA dosimeters provided about the same UVB dose, equivalent to the dose applied with a solar UVB simulator. The total UVB dose for 4 days obtained by amplification of the 1.08 and 2.24 kbp segments was 19.4‐20.8 kJ m‐2, which is within experimental error with the 4 day continuous dose obtained with 0.5 kbp segments. The average daily dose obtained by 0.5 kbp and 1.08 kbp agreed with the average daily dose directly obtained with 2.24 kbp.
Erythemal UV Irradiances at Lauder, New Zealand: Relationship between Horizontal and Normal Incidence
Authors: McKenzie R. L. , Paulin K. J. , Kotkamp M.
Published: January 2008

Abstract— Measurements from sensors designed to measure erythemal UV irradiance were used to relate the UV incident on a horizontal surface to that incident on a surface maintained normal to the sun throughout the day at Lauder, New Zealand. These UV measurements were also related to variations in global radiation, total column ozone and atmospheric pressure at the surface. Strong correlations were found between these variables over the 37 day observation period in the summer of 1995/1996. Results from these cross‐calibrated UV sensors show that the irradiance incident on a surface normal to the sun can be significantly different from that on a horizontal surface. On clear days, the normal‐incidence signal can be 30‐40% greater for solar zenith angles in the range 60‐70Ao. Consequently, the risk of UV damage can be greater than reported by measurements or models that assume horizontal incidence (e.g. UV index). On cloudy days the normal‐incidence UV can be less than 50% of the horizontal‐incidence UV. Averaged over a day, any enhancements in normal‐incidence UV over horizontal‐incidence UV are smaller. The effects were strongly dependent on cloud conditions. Under clear skies the enhancements are generally less than 10%, and the integrated excess over horizontal‐incidence UV is usually less than 5%. However, under cloudy skies the reductions can still be large.
Mutagenicity of Photodynamic Therapy as Compared to UVC and Ionizing Radiation in Human and Murine Lymphoblast Cell Lines
Authors: Evans Helen H. , Horng Min‐Fen , Ricanati Marlene , Deahl J. Thorn , Oleinick Nancy L.
Published: January 2008

Abstract— The mutagenicity of photodynamic therapy (PDT) using red light and either Photofrin® (porfimer sodium) (PF) or aluminum phthalocyanine (AIPc) as the photosensitizer was determined at the thymidine kinase (TK) locus in the human lymphoblastic cell lines, TK6 and WTK1, and was compared to the mutagenicity of UVC and X‐radia‐tion in these cells as well as the mutagenicity of PDT in murine L5178Y lymphoblastic cell lines. Photodynamic therapy was found not to be mutagenic in TK6 cells, which possess an active p53 gene and which are relatively deficient in recombination and repair of DNA double‐strand breaks. In contrast, PDT with either sensitizer was significantly mutagenic in WTK1 cells, which harbor an inactivating mutation in the p53 gene and are relatively efficient in recombination and double‐strand break repair as compared to TK6 cells. The induced mutant frequency in WTK1 cells with PF as the photosensitizer was similar to that induced by UVC radiation but lower than that induced by X‐radiation at equitoxic faiences/ doses. The mutant frequency induced by PDT in WTK1 cells with either photosensitizer was much lower than that induced in murine lymphoblasts at equitoxic fluences. The TK6 and WTK1 cells did not differ in their sensitivity to the cytotoxic effects of PDT, but the level of PDT‐induced apoptosis was greater in TK6 than in WTK1 cells. These results indicate that the mutagenicity of PDT varies in different types of cells and may be related to the repair capabilities as well as the p53 status of the cells.
Absorbance Changes by Aromatic Amino Acid Side Chains in Early Rhodopsin Photointermediates
Authors: Lewis James W. , Jäger Stefan , Kliger David S.
Published: January 2008

Abstract—Absorbance changes were monitored from 250 to 650 nm during the first microsecond after photolysis of detergent suspensions of bovine rhodopsin at 20°C. Global analysis of the resulting data produced difference spectra for bathorhodopsin, BSI and lumirhodopsin which give the change in absorbance of the aromatic amino acid side chains in these photointermediates relative to rhodopsin. These spectra show that the significant bleaching of absorbance near 280 nm, which has been seen previously for the lumirhodopsin, metarhodopsin I and metarhodopsin II intermediates, extends to times as early as bathorhodopsin. Because no corresponding absorbance increase is observed in the 250‐275 nm region, the earliest bleaching of the 280 nm absorbance in rhodopsin is attributed to disruption of a hyperchromic interaction affecting Trp265. Partial decay of this 280 nm bleaching as bathorhodopsin converts to BSI takes place maximally near 290 nm, where Trp265has been shown to absorb, and could be due to the ring of the retinylidene chromophore resuming a position at the BSI stage that reestablishes the hyperchromic interaction with Trp265. A subsequent change in the 250‐300 nm region, which has no counterpart in the visible chromophore bands, indicates the possible presence of a protein‐localized process as lumirhodopsin is formed.
Historical Aspects of Ultraviolet Action Spectroscopy*
Authors: Coohill Thomas P.
Published: January 2008

One of the fundamental methods for analysis of an organism's responses to UV radiation is the construction of the wavelength dependence for a given bioeffect, termed an action spectrum. At minimum, this demonstrates the organism's response to different spectral regions; in some cases, it points to the target chromophore for the effect. The historical importance of certain action spectra and the development of refined techniques for their construction is the subject of this review. Wherever possible, I have kept to the original spellings, terms and identification of wavelengths. This includes using angstroms and nanometers (but not millimicrons) as the authors did. I preferred to reference papers with the most complete set of data rather than the earliest reports.
Far‐UV‐lnduced Dimeric Photoproducts in Short Oligonucleotides: Sequence Effects
Authors: Douki Thierry , Zalizniak Tatiana , Cadet Jean
Published: January 2008

Cyclobutane pyrimidine dimers and pyrimidine(6‐4)pyrimidone adducts represent the two major classes of far‐UV‐induced DNA photoproducts. Because of the lack of appropriate detection methods for each individual photoproduct, little is known about the effect of the sequence on their formation. In the present work, the photoproduct distribution obtained upon exposure of a series of dinucleoside monophosphates to 254 nm light was determined. In the latter model compounds, the presence of a cytosine, located at either the 5′‐ or the 3′‐ side of a thymine moiety, led to the preferential formation of (6‐4) adducts, whereas the cis‐syn cyclobutane dimer was the main thymine‐thymine photoproduct. In contrast, the yield of dimeric photoproducts, and particularly of (6‐4) photoadducts, was very low upon irradiation of the cytosine–cytosine dinucleoside monophosphate. However, substitution of cytosine by uracil led to an increase in the yield of (6‐4) photoproduct. It was also shown that the presence of a phosphate group at the 5′‐ end of a thymine‐thymine dinucleoside monophosphate does not modify the photoproduct distribution. As an extension of the studies on dinucleoside monophosphates, the trinucleotide TpdCpT was used as a more relevant DNA model. The yields of formation of the thymine‐cytosine and cytosine–thymine (6‐4) photoproducts were in a 5:1 ratio, very close to the value obtained upon photolysis of the related dinucleoside monophosphates. The characterization of the two TpdCpT (6‐4) adducts was based on H NMR, UV and mass spectroscopy analyses. Additional evidence for the structures was inferred from the analysis of the enzymatic digestion products of the (6‐4) adducts of TpdCpT with phosphodiesterases. The latter enzymes were shown to induce the quantitative release of the photoproduct as a modified dinucleoside monophosphate in a highly sequence‐specific manner.
Iodouracil as a Personal Dosimeter for Solar UVB
Authors: Rahn Ronald , Lee Mark Andrew
Published: January 2008

A solution of iodouracil (0.2 mg/mL) and KI (0.1 M) in 0.23 M borate buffer (pH 7) forms triiodide upon exposure to UVB. In the presence of thyodene, the blue starch‐iodine complex is formed, the intensity of which is proportional to the amount of UVB exposure. Studies were conducted using either a sunlamp or solar irradiation to generate the triiodide endpoint. Samples (1 mL each) were placed in a plastic 24 well sample holder for exposure, and the intensity of the light at each well was controlled by placing a template over the holder with apertures of various sizes (0.4‐1.5 cm) to vary the amount of light incident on each sample. The endpoint was measured using a spectrometer to monitor the absorbance increase at 400 nm of each sample or a densitometer to monitor the optical density of a photograph of the resulting solutions. The selectivity for UVB was demonstrated by irradiating through a UVB cutoff filter that reduced the sunlamp yield by 98.5% and the solar radiation yield by 94%. The correlation between the observed absorbance changes at 400 nm and the amount of absorbed energy was shown to be approximately the same for both types of radiation and the resulting quantum yield calculated to be ˜1%, consistent with the value obtained previously for 5‐iododeoxyuridine using monochromatic radiation. It is proposed that this system be incorporated into a personal dosimeter for monitoring solar UVB exposures, where the degree of exposure can be estimated either by visual inspection or, for more quantitative analysis, by UV spectroscopy.

The preliminary results presented here demonstrate that the IU actinometer has the potential to be developed as a personal dosimeter for monitoring exposures to solar UVB. The value of this system is that it can provide a visual response to solar radiation with a spectral sensitivity confined mainly to the UVB portion of the sun's spectrum. It responds to exposures within the maximal erythemal range and is easily prepared from available materials.
Ultraviolet Radiation at Sites on the Antarctic Coast
Authors: Frederick John E. , Qu Zheng , Booth C. Rocky
Published: January 2008

Ground‐based measurements of solar UV irradiance combined with calculations using satellite‐based ozone data are able to define the variability in UV sunlight at Palmer Station and McMurdo Station, Antarctica over time scales of years. Special attention focuses on the spring and summer seasons. Satellite data show that the annual ozone loss that occurs during October was greater in1991–1992 than in1979–1980. This led to average noontime UVB irradiances computed for clear skies in the latter period that exceeded those in the earlier time by50–65%. However, a biologically weighted irradiance for suppression of photosynthesis in phytoplankton indigenous to the area near McMurdo Station increased by at most 5% over this period in response to the change in ozone owing to an important contribution from the UVA. At Palmer Station the behavior of ozone and cloudiness can mesh so as to produce the largest noontime UVB irradiances of the year in October as opposed to near summer solstice in December and January. Interannual variability in UVB irradiance during October, the month of the major ozone loss, is larger at Palmer than at McMurdo during the time spanned by ground‐based irradiance measurements, being1990–1994. However, interannual variations in cloudiness were more important than changes in ozone in causing the observed year‐to‐year variability at Palmer Station. The opposite situation prevailed at McMurdo during October, where interannual variations in ozone were responsible for most of the year‐to‐year differences in UVB received at the ground.
Salt‐induced Charge Separation in Photoinduced Electron Transfer Reactions. The Effect of Ion Size*
Authors: Grosso Viviana N. , Previtali Carlos M. , Chesta Carlos A.
Published: January 2008

The effect of added salts on the efficiency for photoinduced charge separation in two typical electron acceptor (A)/electron donor (D) systems was studied by the technique of laser flash photolysis. We investigate the exciplex‐forming pyrene/p‐dicyanobenzene (Py/DCB) and pyrene/N,N‐dimethylaniline (Py/DMA) systems in ethyl acetate. The salts selected for this study are tetrabutylammonium chloride, tetrahexylammonium chloride, lithium perchlorate, sodium perchlorate, tetrabutylammonium perchlorate, sodium tetraphenylborate and tetrabutylammonium tetraphenyl‐borate. In most cases, the salts quench the emission of the exciplexes with rate constants near the diffusional rate limit in ethyl acetate. An apparent red shift of the fluorescence maximum of the exciplexes with increasing salt concentration is also generally observed. Laser flash photolysis experiments showed that in the absence of the salts both A/D systems yield exclusively the triplet excited state of the polyaromatic. However, in the presence of many of the electrolytes studied, induced free radical ion formation is observed. The experimental efficiencies for induced charge separation (n) depend on the A/D system and on the nature of the salt. The measured n values vary between 0 and 0.5. The most striking variation corresponds to the lithium and sodium perchlorates. These salts are almost totally inefficient in quenching the Py/DCB exciplex, while they quench and induce charge separation from the Py/DMA exciplex with a high yield. The effect of the different salts on both exciplexes may be rationalized by using the concept of the soft/hard character of the interacting ions.
Association of Ceramide Accumulation with Photodynamic Treatment‐Induced Cell Death
Authors: Separovic Duska , Mann Karl J. , Oleinick Nancy L.
Published: January 2008

Abstract— Ceramide, a stress‐induced second messenger, has been associated with apoptosis in several malignant and non‐malignant cell lines. We have shown that photodynamic treatment (PDT), using the phthalocyanine photosensitiz‐er Pc 4 (HOSiPcOSi[CH3]2[CH2]3N[CH3]2), causes increased ceramide generation and subsequent induction of apoptosis in L5178Y‐R (LY‐R) mouse lymphoma cells. To test further if ceramide generation accompanies photocytotoxicity, we treated various cell lines with a PDT dose producing a 99‐99.9% loss of clonogenicity. Like LY‐R cells, human leukemia (U937) cells underwent rapid DNA fragmentation initiating within 1 h after PDT. Similarly, Chinese hamster ovary (CHO) cells showed rapid DNA laddering, beginning 1 h following the treatment. In contrast, mouse radiation‐induced fibrosarcoma (RIF‐1) cells showed no apoptosis within 24 h post‐PDT, as judged by the absence of 50 kbp and oligonucleosome‐size DNA fragments, as well as no annexin V binding to cells with preserved membrane integrity. Using the same doses of PDT, we observed a time‐dependent ceramide accumulation in all three cell lines. While a significant increase in ceramide levels was reached within 1 and 10 min in U937 and CHO cells, respectively, elevated ceramide production was measured only after 30 min in RIF‐1 cells. In addition, exogenous N‐acetyl‐sphingosine was able to mimic PDT‐induced apoptosis in U937 and CHO cells. We suggest that ceramide accumulation is associated with PDT‐induced apoptosis and photocytotox‐icity.
Photocycloaddition Reactions of Pyrazinopsoralen with Simple Olefins
Authors: Han Gyu Seok , Shim Sang Chul
Published: January 2008

Direct photolyses of pyrazinopsoralen (PzPs) with excess olefins such as dimethyl fumarate (DMFu), dimethyl maleate (DMMa) and dimethyl ethylidenemalonate (DMEM) gave C4‐photocycloadducts. The photoproducts were determined to be 1:1 C4‐cycloadducts formed through the addition of 4′,5′‐furan double bond of the excited PzPsto the olefins. The fluorescence of PzPswas quenched by olefins with rate constants on the order of 109–1010M‐1/s. The appearance of the long‐lived fluorescence component implies a singlet exciplex mechanism for the photocycloaddition reaction of PzPs with excess olefins.
The Effect of Biological Substrates on the Ultrafast Excited‐state Dynamics of Zinc Phthalocyanine Tetrasulfonate in Solution
Authors: Howe L. , Zhang J. Z.
Published: January 2008

Zinc phthalocyanine tetrasulfonate (ZnPcS4), a potential photosensitizer for photodynamic therapy (PDT), has been studied using femtosecond laser spectroscopy. The excited‐state dynamics in water have been found to be fast (<80 ps) and dominated by intermolecular aggregation. Since the proposed mechanism for PDT is energy transfer from the triplet excited state of the photosensitizer to triplet O2creating singlet O2, the short lifetime is expected to be unfavorable for producing singlet O2. This leads to the suggestion that the presence of biological substrates may have an effect on the excited‐state dynamics. To test this hypothesis, the lifetimes of the ex‐cited states of ZnPcS4have been directly measured in the presence of a model membrane, n‐hexadecyltrimethylammonium bromide (CTAB). The excited‐state dynamics of ZnPcS4in buffer solutions and with human serum albumin (HSA) have also been measured. The presence of HSA and CTAB increases the excited‐state lifetime significantly relative to that observed in water. The longer lifetime of ZnPcS4 in CTAB (>1 ns) indicates that the micellar surface favors monomer formation. By increasing the excited‐state lifetime, the surface substantially in‐creases the photosensitizing potential of ZnPcS4.
Identification of the Flavonoid Glycosides that Accumulate in Brassica napus L. cv. Topas Specifically in Response to Ultraviolet B Radiation
Authors: Wilson Kenneth E. , Wilson Michael I. , Greenberg Bruce M.
Published: January 2008

We have shown in previous work that Brassica napus synthesizes epidermal flavonoids in response to UVB radiation (290–320 nm) and that these compounds are effective at screening the leaf mesophyll from UVB (Wilson and Greenberg, Photochem. Photobiol. 57, 556–563, 1993). This route of acclimation is common to many plant species. However, flavonoids are a highly diverse group of compounds that vary greatly from species to species, and little is known about the specific flavonoids synthesized in response to UVB. To address this, we extracted flavonoids from the leaves of B. napus plants exposed to photosynthetically active radiation (PAR: 400–700 nm), PAR + UVA (320–400 nm) and PAR + UVA + UVB. The compounds were resolved by HPLC and their structures were elucidated. Twelve distinct flavonoid glucosides with quercetin and kaempferol backbones were found. In some cases, a hydroxycinnamic acid moiety was linked via an ester bridge to a glucose. Of the 12 compounds identified, the leaf concentrations of 6 increased in response to UVB: kaempferol‐3‐O‐sophoroside (K2), kaempferol‐3‐O‐sophoroside‐7‐O‐glucoside (Q3), quercetin‐3‐O‐sophoroside (Q2), quercetin‐3‐O‐sophoroside‐7‐O‐glucoside (Q3), K3‐coumaroyl ester and Q3‐caffeoyl ester. Of these six compounds, K2, K3, Q2 and Q3 accumulated to high enough concentrations to contribute to UVB screening. Interestingly, the extractable amounts of the other six compounds identified were lower in the plants exposed to UVA or UVA + UVB compared to plants exposed only to PAR. Thus, in B. napus UV exposure seems to cause a shift in the population of flavonoid glycosides, with four of the UVB‐induced flavonoids being generated in high concentrations.
Assessment of DNA Damage Induced by Broadband and Narrowband UVB in Cultured Lymphoblasts and Keratinocytes Using the Comet Assay
Authors: Tzung Tien‐Yi , Rünger Thomas M.
Published: January 2008

Phototherapy with broadband UVB is an effective treatment for inflammatory dermatoses. A newly developed fluorescent UVB lamp (Philips TL01) that emits a narrowband UVB around 311 nm was shown to be superior for the phototherapy of psoriasis. In order to contribute to the knowledge about the carcinogenic potential of this UVB source, we measured the DNA damage in lymphoblasts and keratinocytes induced by narrowband UVB and compared it with that by conventional broadband UVB using the single cell gel electrophoresis (comet as‐say). At equal doses, broadband UVB produced more DNA damage than narrowband UVB. However, in phototherapy of psoriasis, up to 10‐fold higher doses are used with TLO1. When therapeutically equivalent doses were compared (10‐fold correction for narrowband UVB), we found only slight differences in the amount of DNA damage produced by broadband and narrowband UVB. This supports the already existing evidence that for phototherapy narrowband UVB is not more carcinogenic than broadband UVB.
Effect of Membrane Potential on the Binding of Merocyanine 540 to Human Erythrocytes
Authors: Lagerberg Johan W. M. , VanSteveninck John , Dubbelman Tom M. A. R.
Published: January 2008

Illumination of erythrocytes in the presence of merocyanine 540 (MC540) resulted in changed binding characteristics of MC540, i.e. a red shift in the emission maximum of bound dye with an increase in the relative fluorescence quantum yield. Aluminum phthalocyanine tetrasulfonate‐mediated photodynamic treatment, before addition of MC540, resulted in a comparable change in the MC540‐binding characteristics with, in addition, an increase in the concentration of MC540 in the membrane. Both photodynamic treatments induce depolarization of the red cell membrane, with a dose dependency comparable to that of changed MC540 binding. Also depolarization, induced by incubation of the cells with A23187 in the presence of Ca2+ in high [K+] buffer, resulted in similar changes in the MC540 binding characteristics. These results indicate a relation between photodynamically induced membrane depolarization and changed MC540‐binding characteristics. Hyperpolarization induced by incubation with A23187 in low [K+] buffer resulted in decreased binding of MC540. In accordance, the MC540‐mediated photodamage to red cells decreased upon hyperpolarization of the cells. The results indicate that the binding of MC540 to erythrocytes is strongly dependent on the membrane potential and that hyperpolarization of the membrane could be a possible protection mechanism for erythrocytes against MC540‐mediated photodynamic damage.
Reconstruction of the Water‐Oxidizing Complex in Manganese‐Depleted Photosystem II Preparations Using Mononuclear Manganese Complexes
Authors: Allakhverdiev S. I. , Ozdemir U. , Harnois J. , Karacan N. , Hotchandani S. , Klimov V. V. , Murata N. , Carpentier R.
Published: January 2008

Abstract—The water‐oxidizing complex of chloroplast photosystem II is composed of a cluster of four manganese atoms that can accumulate four oxidizing redox equivalents. Depletion of manganese from the water‐oxidizing complex fully inhibits oxygen evolution. However, the complex can be reconstituted in the presence of exogenous manganese in a process called photoactivation. In the present study, mononuclear manganese complexes with ligands derived from either nitrosonaphthol and ethylenediamine (Niten) or from diaminohexane and salicylaldehyde (Salhxn) are used in photoactivation experiments. Measurements of photoinduced changes of chlorophyll fluorescence yield, thermal dissipation using photoacoustic spectroscopy, photoreduction of 2,6‐dichorophenolindophenol and oxygen evolution in manganese‐depleted and in reconstituted photosystem II preparations demonstrate that photoactivation is more efficient when Niten and Salhxn complexes are used instead of MnCl2. It is inferred that the aromatic ligands facilitate the interaction of the manganese atoms with photosystem II. The addition of CaCl2and of the extrinsic polypeptide of 33 kDa known as the manganese‐stabilizing protein during photoactivation further enhances the recovery of electron transport and oxygen evolution activities. It is proposed that mononuclear manganese complexes are able to contribute to re‐constitution of the water‐oxidizing complex by sequential addition of single ions similarly to the current model for assembly of the tetranuclear manganese cluster and that these complexes constitute suitable model systems to study the assembly of the water‐oxidizing complex.
Direct Comparison of DMA Damage, Isomerization of Urocanic Acid and Edema in the Mouse Produced by Three Commonly Used Artificial UV Light Sources
Authors: Yarosh Daniel B. , Kibitel Jeannie , Ullrich Stephen E. , Kim Tae‐Heung , Ananthaswamy Honnavara N. , Krien Paul , Fourtanier Anny , Kripke Margaret L.
Published: January 2008

Abstract— Exposure to sunlight can result in a number of harmful effects, including sunburn, erythema, premature aging of the skin, immune suppression and skin cancer. Studies designed to understand the underlying mechanisms often depend upon the use of artificial sources of UV radiation. Unfortunately, conclusions from different laboratories using different lamps often conflict, and it is entirely possible that the different spectra of sunlights used in each may be a source of conflict. To minimize confounding variables, we employed two of the more commonly used UY light sources, fluorescent sunlamps, such as the FS‐40 and Kodacel‐filtered FS‐40 sunlamps, and a xenon arc solar simulator and compared, in one series of standardized experiments, the effects of each light source on DNA damage, urocanic acid isomerization and edema formation. The dose‐response curves, calculated by linear regression or curve fitting were compared. The data indicate that DNA damage and urocanic acid isomerization were more sensitive to shorter wavelengths of UV than longer wavelengths, and the biological endpoint of edema most closely correlated with the induction of DNA damage. The results emphasize the dominance of shorter wavelengths within the UV spectrum in damaging biological tissues, even when the solar simulator, which contains significant amounts of UVA, was used and demonstrate that each light source has a characteristic pattern of induction of biochemical and biological endpoints.
Photobleaching of Arterial Fluorescent Compounds: Characterization of Elastin, Collagen and Cholesterol Time‐resolved Spectra during Prolonged Ultraviolet Irradiation
Authors: Marcu Laura , Grundfest Warren S. , Maarek Jean‐Michel I.
Published: January 2008

Abstract— To study the photobleaching of the main fluorescent compounds of the arterial wall, we repeatedly measured the time‐resolved fluorescence of elastin, collagen and cholesterol during 560 s of excitation with nitrogen laser pulses. Three fluence rate levels were used: 0.72, 7.25 and 21.75 μW/mm2. The irradiation‐related changes of the fluorescence intensity and of the time‐resolved fluorescence decay constants were characterized for the emission at 390, 430 and 470 nm. The fluorescence intensity at 390 nm decreased by 25–35% when the fluence delivered was 4 mJ/mm2 a common value in fluorescence studies of the arterial wall. Cholesterol fluorescence photobleached the most, and elastin fluorescence photobleached the least. Photobleaching was most intense at 390 nm and least intense at 470 nm such that the emission spectra of the three compounds were markedly distorted by photobleaching. The time‐resolved decay constants and the fluorescence lifetime were not altered by irradiation when the fluence was below 4 mJ/mm2. The spectral distortions associated with photobleaching complicate the interpretation of arterial wall fluorescence in terms of tissue content in elastin, collagen and cholesterol. Use of the time‐dependent features of the emission that are not altered by photobleaching should increase the accuracy of arterial wall analysis by fluorescence spectroscopy.