bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased Photosensitivity in HL60 Cells Expressing Wild‐Type p53
Authors: Fisher Anita M. R. , Danenberg Kathleen , Banerjee Debabrata , Bertino Joseph R. , Danenberg Peter , Gomer Charles J.
Published: January 2008

Loss of p53 function has been correlated with decreased sensitivity to chemotherapy and radiation therapy in a variety of human tumors. Comparable analysis of p53 status with sensitivity to oxidative stress induced by pho‐todynamic therapy has not been reported. In the current study we examined photosensitivity in human promye‐locytic leukemia HL60 cells exhibiting either wild‐type p53, mutated p53 or deleted p53 expression. Experiments were performed using a purpurin, tin ethyl etiopurpurin (SnET2)‐, or a porphyrin, Photofrin (PH)‐based photo‐sensitizer. Total SnET2 accumulation was comparable in all three cell lines. Uptake of PH was highest in cells expressing wild‐type p53 but incubation conditions could be adjusted to achieve equivalent cellular PH levels during experiments that analyzed photosensitivity. Survival measurements demonstrated that HL60 cells expressing wild‐type p53 were more sensitive to PH‐ and SnET2‐mediated photosensitization, as well as to UVC irradiation, when compared to HL60 cells exhibiting deleted or mutated p53 phenotypes. A rapid apoptotic response was observed following purpurin‐ and porphyrin‐induced photosensitization in all cell lines. Results of this study indicate that photosensitivity is increased in HL60 cells expressing wild‐type p53 and that photosensitizer‐medi‐ated oxidative stress can induce apoptosis through a p53‐independent mechanism in HL60 cells.
PhotochemCAD‡: A Computer‐Aided Design and Research Tool in Photochemistry
Authors: Du Hai , Fuh Ru‐Chun Amy , Li Junzhong , Corkan L. Andrew , Lindsey Jonathan S.
Published: January 2008

A database of absorption and fluorescence spectra, including molar absorption coefficients and fluorescence quantum yields, has been compiled for 125 photochemically relevant compounds. An accompanying program enables calculation of oscillator strengths, natural radiative lifetimes, transition dipole moments, Forster energy‐transfer rates, multicomponent analysis, simulations of fluorescence spectra upon energy transfer among linear arrays of pigments, calculations of blackbody radiator curves at different temperatures and Lorentzian and Gaussian peak distributions. The program runs under Windows 95 and is equipped with extensive literature references and help features.
The Origin of115–130°C Thermoluminescence Bands in Chlorophyll‐Containing Material
Authors: Vavilin Dmitrii V. , Ducruet Jean‐Marc
Published: January 2008

High‐temperature thermoluminescence (TL) emitted in the temperature region from +50 to +150°C has been studied in a variety of chlorophyll‐containing samples that were allowed to dry during the TL measurement. Analysis of the recorded traces by a multicomponent‐fit‐ting procedure revealed the existence of up to three bands of nonphotosynthetic origin with peak positions at62–75,114–128 and151–157°C and apparent activation energies of 27.0‐28.8, 14.1‐15.4 and 22.1‐23.3 kcal/mol (the bands are denoted as HT1 HT2 and HT3, respectively). Low‐temperature treatment of leaves, incubation of algae in the presence of paraquat, exposure of algae or isolated thylakoids to a strong light, all conditions known to stimulate oxidative damage to membrane lipids, caused appearance of a small HT1, band and significant rise in the intensity of the HT2 band. The increase in the HT2 component correlated positively with accumulation of conjugated dienes and malondialdehyde in thylakoids illuminated with a strong light. Different quenchers of active oxygen species and scavengers of free radicals added to preilluminated thylakoids or thylakoid lipid extracts before the TL measurements, as well as injection of argon into the TL measuring chamber, caused no changes in the intensity of the HT2 emission. The HT2 band in the thylakoids increased strongly upon addition of linoleate peroxidized by hydroxyradicals generated in the Fenton reaction but remained unchanged if the linoleate was oxidized with the use of lipoxygenase. We suggest that the HT2 band arises due to thermal decomposition of lipid cyclic peroxides present in the samples. In turn, the decomposition reaction leads to formation of carbonyls in triplet state with following migration of excitation energy toward chlorophyll. Contrary to the HT1, and HT2 bands, the HT3 band of TL cannot be associated with the thermolysis of lipid peroxidation products already present in the samples before starting the TL gradient.
Skin Necrosis due to Photodynamic Action of Benzoporphyrin Depends on Circulating Rather than Tissue Drug Levels: Implications for Control of Photodynamic Therapy
Authors: Lin Gloria C. , Tsoukas Maria L. , Lee Margaret S. , González Salvador , Vibhagool Chitralada , Anderson R. Rox , Kollias Nikiforos
Published: January 2008

In an ideal world, photodynamic therapy (PDT) of abnormal tissue would reliably spare the surrounding normal tissue. Normal tissue responses set the limits for light and drug dosimetry. The threshold fluence for necrosis (TFN) was measured in normal skin following intravenous infusion with a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD‐MA) Verteporfin as a function of drug dose (0.25‐2.0 mg/kg), wavelength of irradiation (458 and 690 nm) and time interval (0–5h) between drug administration and irradiation. The BPD‐MA levels were measured in plasma and skin tissue to elucidate the relationship between TFN, drug kinetics and biodistribution. The PDT response of normal skin was highly reproducible. The TFN for 458 and 690 nm wavelengths was nearly identical and the estimated quantum efficiency for skin response was equal at these two wavelengths. Skin phototoxicity, quantified in terms of 1/ TFN, closely correlated with the plasma pharmacokinetics rather than the tissue pharmacokinetics and was quadratically dependent on the plasma drug concentration regardless of the administered drug dose or time interval between drug and light exposure. This study strongly suggests that noninvasive measurements of the circulating drug level at the time of light treatment will be important for setting optimal light dosimetry for PDT with liposomal BPD‐MA, a vascular photosensitizer.
Characterization of the Transient Intermediates Generated from the Photoexcitation of Nabumetone: A Comparison with Naproxen
Authors: Martínez Lydia J. , Scaiano J. C.
Published: January 2008

The photochemical and photophysical properties of nabumetone (4‐[6‐methoxy‐2‐naphthyl]‐2‐butanone) were examined employing conventional and time‐resolved spectroscopic techniques. The naphthalene‐like nabumetone triplet is formed with 29% efficiency in acetonitrile. Singlet oxygen formation was also detected in this solvent with a φA value of 0.19. A naphthalene‐like radical cation absorption, formed via biphotonic processes, was also detected. The reactivity of both the triplet and radical cation of nabumetone toward different substrates was examined. The photochemical properties of nabumetone are compared with those of naproxen, a structurally related acidic nonsteroidal anti‐inflammatory drug. For these two anti‐inflammatory agents, a type II photosen‐sitization process is most likely responsible for their phototoxicity.
Structure and Medium‐Dependent Photodecomposition of Fluoroquinolone Antibiotics
Authors: Fasani Elisa , Profumo Antonella , Albini Angelo
Published: January 2008

The photochemical reactivity of four fluoroquinolone antibiotics is examined. For norfloxacin (NOR), enoxacin (ENX) and lomefloxacin (LOM), the only process occurring is defluorination (from position 6 for the first two drugs, from position 8 for the last one). The quantum efficiency is both structure and medium dependent (4 close to 0.5 both in water and in 0.1 M phosphate buffer for LOM,‐ 0.01 for ENX and 0.004 for NOR in buffer, but more than an order of magnitude higher in neat water). Ofloxacin (OFL) is less light sensitive φ 0.001) and undergoes, in part, reactions different from defluorination. The photoreaction involves heterolytic C‐F bond fragmentation and its efficiency is determined by the internal charge‐transfer character of the excited state (increasing in the series OFL < NOR < ENX < LOM according to the electronegativity of the substituent in position 8) and by the stabilization of the resulting aryl cation (larger for the 8‐cation than for the 6‐cation). The relevance of these data for the rationalization of the known phototoxicity of these drugs is discussed.
Light Dose and Time Dependency of Photodynamic Cell Membrane Damage
Authors: Saito Takashi , Hartell Nick A. , Muguruma Hitoshi , Hotta Shu , Sasaki Satoshi , Ito Masao , Karube Isao
Published: January 2008

We have investigated the light dose and time dependency of photodynamic cell membrane damage using electrophysiological methods. This study controls the level of cell membrane damage by precisely administration of the light dose. The photosensitizer used was 5′,5″‐bis(aminomethyl)‐2,2′:5′,2″‐terthiophene dihydrochloride (BAT). A confocal laser scanning microscope was used to provide rapid light activation (<1 s) and the subsequent membrane damage was monitored using standard patch clamp techniques. In the presence of 49 μM BAT, light levels less than 0.94 J/cm2 led to a reversible depolarization (20 mV) and reduction of resistance (10%) within 3 s of illumination. Higher intensities of illumination (1.57 J/cm2) caused a complete and irreversible loss of membrane potential and cell membrane resistance within 8 s of illumination. The threshold dose of light required to induce cell death by illumination in the presence of BAT was increased in the presence of the antioxidant Trolox‐C.
The Complexity of the Prto PfrPhototransformation Kinetics Is an Intrinsic Property of Native Phytochrome*
Authors: Schmidt Peter , Gertsch Thomas , Remberg Anja , Gärtner Wolfgang , Braslavsky Silvia E. , Schaffner Kurt
Published: January 2008

Several possible origins of the complex phytochrome red to far‐red light‐absorbing phytochrome (PrPfr) phototransformation kinetics in the nanosecond‐to‐second time range have been examined. Heterogeneity based on protein sequence is ruled out as an origin of the multi‐component kinetics because recombinant 124 kDa oat phytochrome A apoprotein reconstituted with phytochro‐mobilin and the native protein are very similar in this regard throughout this time range. The Prforms of native 124 kDa oat phytochrome A and of a homogeneous recombinant 65 kDa chromoprotein fragment exhibit thermochromic properties interpreted as arising in each case from the presence of two Prspecies in thermal equilibrium. They exhibit identical photochemical properties. The complex kinetics therefore cannot result from Prheterogeneity either. Thus, the presence of two Prforms in equilibrium (Pr,675and Pr,655) and the complex multiex‐ponential PrPfrphototransformation kinetics observed in all time ranges are intrinsic properties of the homogeneous holoprotein of oat phytochrome A.
The Photobiological Differences of Gilvocarcins V and M Are not Related to their Transient Intermediates and Triplet Yields
Authors: Arce Rafael , Oyola Rolando , Alegría Antonio E.
Published: January 2008

Abstract—The transient absorption spectra of the intermediates produced by the 355 nm laser excitation of gilvocarcin derivatives have been investigated in various solvents. The spectra consist of a triplet‐triplet absorption in the visible region and a residual absorption observed between 340 and 700 nm due to a long‐lived species, assigned to the radical cation. A broad‐fast decaying band with a maximum at around 700 nm attributed to the solvated electron is also seen in solutions containing a low DMSO/water volume ratio and at 266 nm irradiation of a 50% methanol/water solvent mixture. The molar absorption coefficient of the triplet state of gilvocarcin V (GV) and gilvocarcin M (GM), determined by the energy transfer method, is independent of the solvent properties and has a value of 3.0 × 104/Mcm. The triplet decay rate constants for both drugs are between 1 and 5 × 104/s. A similar initial yield and triplet decay rate constant of GV were observed in the presence of 3.4 mMthymine. Thus, a quenching rate constant of the GV's triplet state by thymine is estimated to be lower than 106/Ms. The triplet quantum yields of both antibiotics determined by using the comparative method are higher in dimethylsulfoxide (DMSO) (0.18) than are those corresponding to 25% DMSO/water (0.06). The decrease in φTin the presence of water could be attributed to an enhanced internal conversion rate constant from the S1state or to an increase in the photoionization yield. The similarity of the transient intermediates and their yields for GV and GM suggest that their photobiological differences are due to other factors such as DNA binding constants, preferential localization of the drugs in the cell or the enhanced reactivity of the vinyl group toward cellular components.
An Analysis of UVA Emissions from Sunlamps and the Potential Importance for Melanoma
Authors: Miller Sharon A. , Hamilton Scott L. , Wester Ulf G. , Cyr W. Howard
Published: January 2008

Abstract— Exposure to solar UV radiation is a risk factor for cutaneous malignant melanoma (CMM). Epidemiologic studies have also considered the use of sunlamps as a possible contributor to CMM. We measured and analyzed the emission spectra of six different currently marketed sunlamps and a historical sunlamp, the UVB‐emitting FS lamp, and compared the results to solar exposure. For a typical tanner (20 sessions @ 2 minimal erythema doses (MED)/session), the annual UVA doses from commonly used fluorescent sunlamps were 0.3‐1.2 times that received from the sun. For a frequent tanner (100 sessions @ 4 MED/session), the annual UVA doses from fluorescent sunlamps were 1.2‐4.7 times that received from the sun and 12 times for recently available, high‐pressure sunlamps. To determine biologically effective doses, action spectra for squamous cell carcinoma (SCC) in humans and for melanoma in the Xiphophorus fish (XFM) were applied to the sunlamps' emission spectra. The results for the effective doses using the SCC action spectrum tracked the UVB doses, while the results using the XFM action spectrum tracked the UVA doses. When combined with UV exposure received from the sun, typical sunlamp use results in an approximate doubling of annual effective dose, if the XFM action spectrum is applied. Frequent use, however, can increase the annual effective XFM dose by as much as 6 times what would be received from the sun alone for fluorescent sunlamps and as much as 12 times for newer, high‐pressure sunlamps.
Effects of Supplementary Ultraviolet‐B Radiation on Photosynthetic Transcripts at Different Stages of Leaf Development and Light Levels in Pea (Pisum sativum L.): Role of Active Oxygen Species and Antioxidant Enzymes.
Authors: A.‐H.‐Mackerness Soheila , Surplus S. Lynn , Jordan Brian. R. , Thomas Brian
Published: January 2008

Abstract— Supplementary UVB radiation caused the down‐regulation of transcripts of the photosynthetic genes Lhcb and psbA in fully expanded pea leaves. This response was less marked in apical buds and was ameliorated by high light. The effect of UVB on leaves was mimicked by free radical generators and prevented by antioxidant feeding. Under UVB, active oxygen species levels, determined by level of lipid peroxides, was highest in leaves under low light and lower under high light and in buds. Activities of ascorbate peroxidase, glutathione reductase and superoxide dismutase were increased in response to UVB irradiation and were higher under high light and in buds. These results indicate that active oxygen species are involved in the UVB signal pathway leading to the down‐regulation of photosynthetic genes. Furthermore, they suggest that the antioxidant capacity of plant tissue determines the susceptibility of these transcripts to UVB radiation.
Effects of the Subcellular Redistribution of Two Nile Blue Derivatives on Photodynamic Oxygen Consumption
Authors: Georgakoudi Irene , Foster Thomas H.
Published: January 2008

Abstract— We present experimental evidence that demonstrates directly how the subcellular localization and redistribution of two nile blue derivatives, 5‐ethylamino‐9‐diethyl‐ami‐nobenzo[α]phenothiazinium chloride (EtNBS) and 5‐ethylamino‐9‐diethyl‐aminobenzo[α]phenoselenazinium chloride (EtNBSe), affect oxygen consumption during irradiation of sensitized multicell EMT6 spheroids. Specifically, two well‐defined phases of oxygen consumption are observed during treatment, with the onset of the second phase being a fluence‐dependent event. Fluorescence microscopy during irradiation of EtNBS‐sensitized EMT6 monolayer cultures indicates that sensitizer redistribution from intracellular organelles, presumably lysosomes, to the cytosol can explain the onset of the second oxygen consumption phase. This event requires eight times fewer photons for EtNBSe than for EtNBS, consistent with the higher singlet oxygen yield of the former dye. The existence of a second oxygen consumption phase suggests that the aggregated form of the dye is a less efficient photodynamic agent. Moreover, we present evidence suggesting that damage to the primary sites of localization might be less significant than damage incurred by the sites to which the sensitizer redistributes during irradiation.
Light Distributions from Point, Line and Plane Sources for Photochemical Reactions and Fluorescence in Turbid Biological Tissues
Authors: Jacques Steven L.
Published: January 2008

Light distributions in biological tissues are summarized in simple expressions for sphewrical, cylindrical and planar geometries due to point sources, line sources and planar sources. The goal is to provide workable tools for computing light distributions that govern the amount and distribution of photochemical reactions in experimental solutions, films and biological tissues. Diffusion theory expressions are compared with Monte Carlo simulations. Analytic expressions that mimic accurate Monte Carlo simulations are presented. Application to fluorescence measurements and prediction of necrotic zones in photodynamic therapy are outlined.
Photodynamic Synovectomy Using Benzoporphyrin Derivative in an Antigen‐induced Arthritis Model for Rheumatoid Arthritis
Authors: Trauner Kenneth B. , Gandour‐Edwards Regina , Bamberg Mike , Shortkroff Sonya , Sledge Clement , Hasan Tayyaba
Published: January 2008

Experimental photodynamic therapy (PDT) has recently been adapted for the treatment of inflammatory and rheumatoid arthritis. The biodistribution of benzoporphyrin derivative monoacid ring A (BPD‐MA) and the effect of percutaneous light activation via intra‐articular bare cleaved optical fibers was investigated using a rabbit‐antigen‐induced arthritis model. Qualitative evaluation of intra‐articular photosensitizer clearance was performed with laser‐induced fluorescence from 0 to 6 h following intravenous injection. The compound was rapidly taken up within the joint and then cleared steadily over the 6 h interval. Biodistribution was determined by fluorescence microscopy and spectrofluoroscopic extraction techniques 3 h following intravenous injection of 2 mg/kg BPD‐MA. The biodistribution study demonstrated elevated levels of BPD‐MA in synovium (0.35 μg/g) and muscle (0.35μg/g). Fluorescence microscopy demonstrated presence of the compound within pathologic synovium but absence of the photosensitizer within meniscus, ligament, bone and articular cartilage. Tissue effects were evaluated histologically at 2 and 4 weeks posttreatment. BPD‐MA‐mediated PDT caused synovial necrosis in the region of light activation in 50% of treatment knees at 2 weeks and 43% at 4 weeks. No damage to nonpathologic tissues was observed. These studies indicate that selective destruction of synovium can be achieved by the light‐activated photosensitizing agent BPD‐MA without damage to articular cartilage or periarticular soft tissues. PDT needs to be further evaluated to optimize treatment parameters to provide for a new minimally invasive synovectomy technique.
Control of NO Concentration in Solutions of Nitrosothiol Compounds by Light
Authors: Zhelyaskov Valentin R. , Gee Kyle R. , Godwin Dwayne W.
Published: January 2008

We studied the thermal and photolytic decomposition of two S‐nitrosothiols, S‐nitrosoglutathione (GSNO) and S‐nitroso‐N‐acetylpenicillamine (SNAP), in water or propanol solutions. A "concentration clamp" (relatively constant concentration of NO as a function of time) could be implemented in a closed volume by varying the pH, concentration of nitrovasodilator and intensity of the light source. Depending on the conditions, the light either stimulated NO release or sharply decreased NO concentration in the test solutions. Changes in the absorption spectra of GSNO solutions were monitored as a function of light exposure. Generation of superoxide as a product of a photolytic decomposition reaction of S‐nitrosothiols and further oxidation of NO is the most likely mechanism for light suppression of NO concentration.
Aggregation of the Light‐Harvesting Complex in Intact Leaves of Tobacco Plants Stressed by CO2Deficit
Authors: Šiffel Pavel , Vácha František
Published: January 2008

Pronounced aggregation of the photosystem II light‐harvesting complex (LHC II) was observed in low‐lightgrown tobacco plants stressed with a strong CO2deficit for 2–3 days. The LHC II aggregates showed a typical band at 697–700 nm (F699) in low‐temperature emission spectra. Its excitation spectrum corresponded to that of detergent‐solubilized LHC II. Formation of F699in stressed plants was not reversed in the dark and leaves did not contain any zeaxanthin showing that neither a light‐induced transthylakoid pH gradient nor zeaxanthin was required for LHC II aggregation. The CO2‐stressed plants showed clear signs of photodamage: depression of the potential yield of photosystem II photochemistry (F,/FM) by 50–70% and a decline in chlorophyll content by 10–15%. Therefore, we propose that the photodamage to the photosynthetic apparatus is the cause of the LHC II aggregation in plants. The F699exhibited a reversible decrease of its intensity upon irradiation of leaves with intensive light. There was no or only slight decrease around 700 nm in unstressed plants. The nonphotochemical quenching of chlorophyll fluorescence showed the opposite relation, being higher before than after the strong CO2deficit. This discrepancy was likely related to the different LHC II aggregation state in control and stressed plants.
Synthesis and Crystal Structures of Cofacial Bisoctaethylchlorins as Structural Models for the Special Pair*
Authors: Kalisch Werner W. , Senge Mathias O. , Ruhlandt‐Senge Karin
Published: January 2008

Covalently linked bistetrapyrrole systems can be used to mimic structurally the arrangement of the two special pair bacteriochlorophylls in the bacterial photosynthetic reaction center. Such models require a cofacial arrangement of the two tetrapyrrole units with some overlap of the It systems and intramolecular stabilization by aggregation of the two macrocycles. Using the McMurry re‐action for the coupling of metallo formyloctaethylchlorins, covalently linked cofacial bischlorins were prepared and characterized by spectroscopy and single crystal X‐ray crystallography. Coupling of NI(II)5‐formyloctaethylchlorin yielded a (Z)‐ethene‐bridged bischlorin with cofacial orientation of the subunits stabilized by intramolecular π‐π interactions that structurally resembles the situation found for the special pair in bacterial reaction centers. In addition, two different atropisomers of the respective (E)‐ethene‐bridged bischlorin were formed. Use of Cu(II)5‐formyloctaethylchlorin yielded similar products, however a crystal structure showed a (Z)‐ethene‐bridged bischlorin without intramolecular stabilization via aggregation effects. The bischlorins are easily oxidized to mixed chlorin‐porphyrin species.
Importance of the Treatment Field for the Application of Vascular Photodynamic Therapy to Inhibit Intimal Hyperplasia
Authors: van Eps Randolph G. Statius , ChandraSekar N. R. , Hasan Tayyaba , LaMuraglia Glenn M.
Published: January 2008

Intimal hyperplasia (IH) plays a dominant role in the development of restenosis. In previous studies, photodynamic therapy (PDT) prevented IH induced by segmental balloon injury of the rat carotid. The critical elements required to control IH effectively with this technique are not fully understood. This study assessed the importance of the treatment field by studying the repair process of injured vessels, in which the PDT‐treatment field did not target the entire injured area. The entire rat common carotid artery was balloon‐injured to induce IH, whereas only the cervical segment below the bifurcation was subjected to PDT by external light irradiation after administration of the photosensitizer chloroaluminum sulfonated phthalocyanine. Light irradiation of injured arteries without photosensitizer served as control for PDT, and PDT of uninjured arteries was included as a control group for the balloon injury. Histologic characterization of the repair process was sequentially assessed. Balloon‐injured arteries without PDT displayed rapid IH development with a peak at 2 weeks. Photodynamic therapy of balloon‐injured arteries resulted in complete local depletion of medial smooth muscle cells (SMC), which was associated with a lack of IH until 2 weeks. However, at 4 and 16 weeks there was significant IH in PDT‐treated arteries despite a lack of medial SMC repopulation. A wave of IH progression over the acellular media was observed in these arteries, migrating from the injured non‐PDT‐treated area. The PDT of uninjured arteries did not result in IH and was also associated with a persistent acellular media. Delayed IH development after PDT of injured vessels can result from IH progression from an injured site not included in the treatment field. This also indicated that the source of cells developing the intimal hyperplasia lesion can originate from an area remote from the lesion. Together with previous results and the determination that PDT itself does not induce IH, it can be reasoned that inclusion of the whole injured artery or a section of an uninjured margin in the treatment field is essential for effective PDT prevention of IH.
Sulfonated Chloroaluminum Phthalocyanine Incorporates into Human Plasma Lipoproteins: Photooxidation of Low‐Density Lipoproteins
Authors: Santos Armanda E. , Laranjinha João A. N. , Almeida Leonor M.
Published: January 2008

The interactions of sulfonated chloroaluminum phthalocyanine (AlPcSn) with human low‐density lipoproteins (LDL) were studied in vitro in human plasma and in an isolated LDL fraction, in order to understand the potential effects of the sensitizer against LDL. The AlPcSn added to plasma distributes in all lipoproteins as observed by the drastic color changes of the separated fractions by ultracentrifugation. In isolated LDL, incubation with AlPcSn causes fluorescence quenching of the apoprotein tryptophan residues. Furthermore, AlPcSn incorporates in liposomes, with a lipid composition similar to the external monolayer of human LDL, as indicated by absorbance spectroscopy. The photosensitizing properties of AlPcSn in LDL particles were studied on the basis of the fluorescence quenching of previously incorporated cis‐parinaric acid (PnA), used as an oxidation probe, and of O2 consumption. The photooxidation of either PnA or LDL lipids is highly dependent on irradiation time and on the dye concentration. Moreover, photooxidation of LDL proceeds only during the illumination period. After stopping the illumination and upon addition of Cu2+ to the LDL solution, the oxidative rate is resumed, probably due to hydroperoxide cleavage and formation of species able to propagate the oxidative reaction. Thus, our data indicate that AlPcSn distributes in human plasma lipoproteins and, in isolated LDL, it can interact either with the lipid phase or the apoprotein. The photooxidation of LDL induced by AlPcSn seems to involve singlet oxygen as the main reactive species in the degradative process.
Triplet Photoreactivity of the Diaryl Ketone Tiaprofenic Acid and Its Decarboxylated Photoproduct. Photobiological Implications
Authors: Encinas Susana , Miranda Miguel A. , Marconi Giancarlo , Monti Sandra
Published: January 2008

The 2‐benzoylthiophene chromophore of the photosensitizing drug tiaprofenic acid and of its decarboxylated derivative is characterized by a unusually high energy gap between the T1 (π,π*) and T2 (n,π*) excited states, which makes this a unique system to study the intrinsic photo‐reactivity of the two states. Weak fluorescence and phosporescence emission were detected at room temperature. Tiaprofenic acid undergoes photodecarboxylation from the triplet manifold as the main reaction. The photoprocess is temperature dependent with activation energy of 7–10 kcal/mol, close to the energy gap between T1 and T2. The decarboxylated product abstracts hydrogen in type I reactions. The involvement of T2 in the above processes is proposed. Moreover the decarboxylated derivative exhibits reactivity toward phenols, consistent with a participation of the T1 state as electron acceptor. The observed photoprocesses can account for biological photosensitization reactions, like membrane damage and protein modification.
Excited‐State Energy Level Does Not Determine the Differential Effect of Violaxanthin and Zeaxanthin on Chlorophyll Fluorescence Quenching in the Isolated Light‐Harvesting Complex of Photosystem II
Authors: Ruban Alexander V. , Phillip Denise , Young Andrew J. , Horton Peter
Published: January 2008

Abstract— The mechanism of action of xanthophyll cycle carotenoids in controlling the quenching of chlorophyll fluorescence in the major light‐harvesting complex of photosystem II (LHCIIb) has been investigated. Auroxanthin, a diepoxy carotenoid with 7 conjugated carbon double bonds, violaxanthin (9 conjugated double bonds) and zeaxanthin (11 conjugated double bonds) have been compared with regard to their effects in vitro on fluorescence quenching and LHCIIb oligomerization. It was found that auroxanthin stimulated fluorescence quenching, similar to the effect of zeaxanthin and in contrast to the inhibition caused by violaxanthin. Auroxanthin caused an increase in the oligomerization of LHCIIb and an increase in relative emission of long‐wavelength fluorescence at 77 K. It is concluded that auroxanthin can mimic the effect of zeaxanthin on LHCII, strongly suggesting that the xanthophyll cycle carotenoids control quenching in vitro by an indirect structural effect and not by direct quenching of chlorophyll excited states.
Environmental Control of the Deformability of the DNA Double Helix
Authors: Georghiou S. , Kubala Steven M. , Large Catherine C.
Published: January 2008

The deformability of DNA is of crucial importance in a number of processes and interactions, such as its enzymatic recognition, its packaging into chromosomes, its interactions with drugs, and the formation of photodimers in it. Here we have studied this property by following the formation of excited‐state molecular complexes (excimers) between adjacent bases of poly(dA‐dT).poly(dA‐dT) at 20°C. The force that drives the helix distortion appears to stem mainly from charge–resonance interaction. The results indicate that the deformability of the helix on the nanosecond time scale is considerable at normal solvent viscosities, whereas it is greatly reduced by frictional forces at high viscosities (attained through sucrose addition) at which the excimer has a much less favorable geometry: the difference in the interaction energies between 1 cP and 58 cP is about 6 kcal/mol, a value that is similar to the base stacking energies for the undistorted helix. This behavior parallels the modulation by the solvent viscosity of the thermally driven motions of the bases of poly(dA) poly(dT), which we recently reported on the basis of time‐resolved intrinsic fluorescence anisotropy measurements (S. Georghiou et al., Biophys. J., 70, 1909–1922, 1996). It is inferred that environmental impediments to molecular motion can modulate the conformation and dynamics of DNA. Such modulation might play a role in gene regulation: particular base configurations, which can be enzymatically recognized, may be attained as dictated by the prevailing viscosity conditions and/or geometric constraints. By contrast, up to 3 M NaCl or 0.1 M MgCl2 do not significantly reduce the deformability of the helix. The considerable plasticity of this polynucleotide is probably linked to the significant flexibility of the TA step that may account for the wide‐spread use of the TATA sequence in transcription, site‐specific recombination and the initiation of DNA replication.
The Origin of the Wavelength‐Dependent Photoreactivity of Trans‐Urocanic Acid
Authors: Hanson Kerry M. , Simon John D.
Published: January 2008

Two‐color, pulsed‐laser photoacoustic calorimetry is used to distinguish between multiple rotamer or electronic state contributions to the absorption spectrum of the epidermal chromophore trans‐urocanic acid. The data definitively show that the wavelength‐dependent photochemistry of trans‐urocanic acid results from the presence of two distinct, weakly coupled electronic states absorbing between 264 nm and 310 nm.
Postadministration Protective Effect of Magnesium‐L‐ascorbyl‐phosphate on the Development of UVB‐induced Cutaneous Damage in Mice
Authors: Kobayashi Shizuko , Takehana Makoto , Kanke Motoko , Itoh Shinobu , Ogata Eiichi
Published: January 2008

The effects of stable vitamin C, magnesium‐L‐ascorbyl‐2‐phosphate (MAP), administered after acute and chronic exposure to UVB irradiation were investigated using hairless mice. Intraperitoneal administration of 100 mg/kg of MAP immediately after acute exposure to 15 kJ/m2 of UVB significantly prevented increases of UVB‐induced lipid peroxidation in skin and sialic acid in serum, an inflammation marker. Administration of 50 mg/kg of MAP immediately after each exposure significantly delayed skin tumor formation and hyperplasia induced by chronic exposure to 2 kJ/m2 of UVB. Intraperitoneal administration of 200 mg/kg of MAP produced an increase in ascorbic acid (As) levels in the serum, liver and skin within 15 min. Serum As levels quickly returned to normal, but hepatic and cutaneous levels remained elevated before returning to normal after 24 h, suggesting that MAP was converted to As in the serum and in those tissues. Ultraviolet B‐induced hydroxyl radical generation in murine skin homogenates was scavenged by As‐Na addition, which was directly detected by electron spin resonance (ESR). These results suggest that postadministration of MAP delays progression of skin damage induced by UVB irradiation. It is presumed that MAP, once converted to As, exhibits such inhibitory effects by scavenging hydroxyl and lipid radicals generated as a direct or indirect result of UVB exposure.
Fluorescent Dimers of Merocyanine 540 (MC540) in the Gel Phase of Phosphatidylcholine Liposomes
Authors: Bernik Delia , Tymczyszyn Elizabeth , Daraio Marta Edit , Negri R. Martín
Published: January 2008

Abstract— Fluorescence emission from merocyanine 540 (MC540) dimers was observed in dipalmitoylphosphatidylcholine (DPPC) vesicles. This unusual behavior was observed only for vesicles in the gel‐phase state. No dimer fluorescence was observed either in monopalmitoylphosphati‐dylcholine (C16PC) micelles or in liquid‐crystalline DPPC vesicles, indicating that dimer fluorescence efficiency increases in highly packed interfaces. The excitonic theory of Kasha was used to interpret the spectral features. The overall fluorescence quantum yield (φr) decreases with decreasing lipid: probe ratio, not only because of the presence of a weakly fluorescent dimer that absorbs a high fraction of the total absorbed light but also due to quenching of monomer emission. This suggests the existence of probe domains. The dimer fluorescence quantum yields (φm) were estimated in DPPC large unilamellar vesicles (LUV) and DPPC multilamellar vesicles. The dependence of φr with probe concentration is compatible with values of φm lower than 0.05. The dimerization equilibrium of MC540 in C16PC micelles and DPPC‐LUV was also studied. Apparent dimerization equilibrium constants, Kdapp and dimer absorption spectrum were calculated in C16PC micelles for the first time. The dimerization equilibrium constant in DPPC‐LUV was calculated and discussed in terms of the fraction of volume occupied by the lipid phase.
A Model‐Derived Global Climatology of UV Irradiation at the Earth's Surface
Authors: Sabziparvar All A. , Shine Keith P. , Forster Piers M. de F.
Published: January 2008

Abstract— We present calculations of the geographical distribution of the dose rate at the surface of UVB (280–320 nm), UVA (320–400 nm) and, using biological action spectra, the effective radiation for erythema, cataracts and keratitis. A multistream radiative transfer model is used in conjunction with a multiyear climatology of ozone, cloud, surface pressure, surface albedo, temperature and a rudimentary representation of aerosols to calculate the clear‐sky and all‐sky irradiances. Model outputs are evaluated using daily UV measurements and found to be accurate to about ±10% for clear skies and ±20% for all‐sky conditions. The effects of UV‐weighted surface albedo, surface altitude, sun‐earth separation and the vertical distribution of ozone and temperature are included. The results show that the sun's position is the most important factor in determining the geographical pattern of global daily UV rather than column ozone, cloud, surface pressure, daylength or surface albedo. Over elevated regions, the effect of the differences in surface pressure on daily doses was found to be more significant than the effect of the differences in column ozone. Clouds reduce the clear‐sky UV dose from a few percent over arid and semiarid regions to 45% in regions with frequent midlatitude depressions.
Thermally Induced Chemiluminescence of Barley Leaves
Authors: Skotnica Jirí , Fiala Jiři , Ilík Petr , Dvořk Lubomír
Published: January 2008

Abstract—An unconventional band in the thermoluminescence glow curve of barley leaves at about +50°C was examined. In contrast to bands usually observed around +50°C, this band (designated as CL) is not related to photosynthetic electron transport in photosystem II. The appearance of the CL band (1) requires previous freezing of the sample, (2) is not influenced by light excitation and (3) depends on the presence of oxygen. In pure oxygen the glow curves for both leaves and chloroplast suspension exhibit three maxima at about +40°C, +65°C and +90°C. Based on the emission spectra of the CL band and measurements with etiolated leaves, we suppose that the majority of emission corresponding to the CL band originates from chlorophyll. A lipoxygenase inhibitor, butylated hydroxytoluene, and sodium azide decrease the intensity of the CL band. We propose that the mechanism leading to emission of the CL band involves thermally stimulated production of an active oxygen species that results in lipid peroxidation.
Merocyanine 540 Solubilized as an Ion Pair with Cationic Surfactant in Nonpolar Solvents: Spectral and Photochemical Properties
Authors: Bilski Piotr , McDevitt Todd , Chignell Colin F.
Published: January 2008

Abstract— Merocyanine 540 (MC) is an anionic dye that is used to photopurge the bone marrow of leukemia cells. Under these conditions it is localized mostly in cell membranes, which may affect its photochemical reactivity. We investigated the photochemistry of MC dissolved as a hydro‐phobic ion pair with a hexadecyltrioctadecylammonium cation in cyclohexane, trimethylpentane and toluene as well as in propylene carbonate, CH3CN, C2H5OH and D2O. In organic solvents, the absorption and fluorescence spectra of MC were strongly red‐shifted compared with aqueous solutions. The fluorescence was also more intense despite aggregation that occurred in some solvents. Aggregation strongly affects the spectral and photochemical properties of MC, especially in aliphatic hydrocarbons in which distinctive H‐type aggregates are formed. Hydrophobic MC is a moderate photosensitizer of singlet molecular oxygen (1O2). The following values for 1O2 quantum yields were calculated based on 1O2 phosphorescence relative to 1O2 generation by Rose Bengal: ∼0.12 in trimethylpenthane, ∼0.13 in cyclohexane, 0.045 in EtOH, 0.039 in toluene, 0.007 in CH3CN and ∼3 × 10–4 in D2O. The H‐aggregates of MC in cyclohexane and trimethylpentane are better 1O2 producers than monomeric MC. The above 1O2 quantum yields are corrected for self‐quenching because MC is an efficient 1O2 quencher (17 × 107M−1 s−1 in CH3CN, 6.8 × 107M−1 s−1 in D2O, 5.2 × 107M−1 s−1 in EtOH, and 1.4 × 107M−1 s−1 in toluene). Merocyanine undergoes photodegradation, a solvent‐dependent process that proceeds faster when the dye is aggregated. The initial photodegradation rate is much slower in organic solvents than in water, but photodegradation products accumulated during longer irradiation may increase the rate in most solvents. Higher photostability and better photosensitization by MC in hydrophobic nonpolar solvents suggest that the killing of leukemia cells via a photodynamic mechanism may operate mostly in cell membranes. In contrast, any cytotoxic products from photodecomposition may be important in hydrophilic cell compartments. Our data show the spectral and photochemical properties of MC in a pure hydrophobic environment.
Attenuation of Biologically Effective UV Radiation in Tropical Atlantic Waters Measured with a Biochemical DNA Dosimeter
Authors: Boelen Peter , Obernostere Ingrid , Vink Arie A. , Buma Anita G. J.
Published: January 2008

Abstract— A biochemical dosimeter was developed to study the attenuation of biologically effective UV radiation in marine tropical waters. Small quartz vials were used containing a solution of DNA molecules; the vials were incubated at discrete water depths. Subsequently, DNA damage was determined in these samples, using an antibody directed against thymine dimers followed by chemiluminescent detection. Measurements of DNA damage were compared with calculated biologically effective doses, as derived from spectroradiometer measurements. The biodosimeter was found to be a reliable and easy tool to determine levels of harmful UV radiation in marine waters. The highest attenuation coefficient (1.60 m‐l) measured with the biochemical dosimeter was found in eutrophic waters, at a coastal station off Curabcao, Netherlands Antilles. At the other stations attenuation coefficients ranged from 0.18 m‐1 in central Atlantic waters to 0.43 m‐1 close to the Curapcao coast line. Latter results indicate that biologically effective UV radiation may easily reach ecologically significant depths, e.g. coral reef communities.
A Third Member of the Photolyase/Blue‐light Photoreceptor Family in Drosophila: A Putative Circadian Photoreceptor
Authors: Selby Christopher P. , Sancar Aziz
Published: January 2008

Abstract— Two photolyases, specific for cyclobutane pyrimidine dimers and (6–4) photoproducts, have been reported in Drosophila. These enzymes share extensive sequence homologies with the plant blue‐light photoreceptor. We have now identified a third gene in Drosophila melanogaster with extensive sequence homology to the photolyase gene. The newly identified gene, which we named dCRY, was expressed as a recombinant protein and tested for photolyase activity. The recombinant protein exhibited photochemical properties similar to those of Drosophila pyrimidine dimer and (6–4) photolyases but lacked photolyase activity. In light of recent evidence that blue‐light photoreceptors regulate the circadian clock in mammals, we propose that dCRY is the circadian photoreceptor in this organism.
A Putative Blue‐Light Receptor From Drosophila melanogaster
Authors: Okano Satoshi , Kanno Shin‐ichiro , Takao Masashi , Eker Andre P. M. , Lsono Kunio , Tsukahara Yasuo , Yasui Akira
Published: January 2008

Abstract— A gene encoding a 62.5 kDa homolog of Drosophila melanogaster photolyase was isolated. Purified recombinant protein contained a flavin adenine dinucleotide chromophore. The recombinant protein did not show photolyase activity for either cyclobutane pyrimidine dimers or 6–4 photoproducts in vitro as well as in vivo in Escherichia coli host cells, suggesting that the protein is not a DNA repair enzyme but a blue‐light photoreceptor. Reverse transcription polymerase chain reaction analysis showed that the gene is more expressed in head than in body and that it is more expressed in antennae than in legs, wings and mouth appendages. In a phylogenetic tree of the photolyase family, the Drosophila photolyase homolog is located in a cluster containing 6–4 photolyases and mammalian photolyase homologs, which is only distantly related to the clade of higher plant blue‐light photoreceptors. The mammalian photolyase homologs are more closely related to Drosophila 6–4 photolyase than to the Drosophila photolyase homolog, suggesting different roles of the photolyase homologs.
Singlet Oxygen Generation by Metallotexaphyrins
Authors: Grossweiner Leonard I. , Bilgin Mehmet D. , Berdusis Peter , Mody Tarak D.
Published: January 2008

Abstract. Metallotexaphyrins have clinical applications as photo‐sensitizers of photodynamic therapy (PDT). The singlet oxygen quantum yield (φ>Δ) was determined for a series of metallotexaphyrin derivatives (Lu [III], Y [III], Cd [II], In [III] and Gd [in]) under conditions where the agents are believed to exist in monomeric form. The results show φΔ of metallotexaphyrins vary with the medium and the metal cation. Measurements on the Lu (III) texaphyrin led to φΔ= 0.38 in unbuffered 5% Tween 20 and φΔ= 0.58 in pH 7.4 phosphate buffer plus 1% Triton X‐100 (±10%). The in vitro photodynamic efficiency calculated from φΔ is compared to in vivo PDT efficacy in an animal tumor model.
Femtosecond Two‐photon Excited Fluorescence of Melanin*
Authors: Teuchner Klaus , Freyer Wolfgang , Leupold Dieter , Volkmer Andreas , Birch David J. S. , Altmeyer Peter , Stucker Markus , Hoffmann Klaus
Published: January 2008

Abstract. Fluorescence of synthetic melanin in dimethyl sulfoxide has been excited by two‐photon absorption at 800 run, using 120 fs pulses with photon flux densities 1027 cm 2 s1. The shortest main component of the three‐exponential decay of fluorescence is 200 ± 2 ps. The overall spectral shape is red‐shifted with respect to the 400 nm excited fluorescence. Two‐photon excited melanin fluorescence also has been measured from excised samples of healthy human skin tissue. Because of the selectivity of melanin excitation via resonant two‐photon absorption, it is hypothesized that fluorescence excited in this way may yield information on malignant transformation.
Cloning and Molecular Characterization of the cDNA for the Brazilian Larval Click‐beetle Pyrearinus termitilluminans Luciferase
Authors: Viviani V. R. , Silva A. C. R. , Perez G. L. O. , Santelli R. V. , Bechara E. J. H. , Reinach F. C.
Published: January 2008

Abstract. The larval click‐beetle Pyrearinus termitilluminans elicits the phenomenon of luminous termite mounds in the central‐west region of Brazil. The bioluminescence (BL) spectrum of this larva (Λmax= 534 run) is one of the most blue‐shifted reported among known luminescent Cole‐optera. We have isolated mRNA from larval thoracic lanterns and constructed a cDNA library into a δZAP II vector. An expression library was obtained after excision of the pBluescript plasmid. This library was screened by photodetection and one clone that emitted green BL (Δmax= 538 nm) was isolated. The 2.2 kb cDNA insert includes a 543 residue open reading frame showing 82% homology with the luciferase isoenzymes of Pyrophorus pla‐giophthalamus (Coleoptera: Elateridae). As expected, the region between residues 223 and 247 that contains the putative active site for BL color determination showed a higher degree of homology among click‐beetle luciferases that elicit closer BL colors. The in vitro BL spectrum of recombinant P. termitilluminans luciferase also peaks at 538 nm and, as in the case of native enzyme, does not show any bathochromic shift upon decreasing the pH.