bluuebunny/crossref_metadata_2025 huggingface dataset:
Microenvironment Effects on the Excited State Properties of Psoralens: a Clue to Their Photobiological Activity
Authors: Sousa Cristina , Sá e Melo Teresa
Published: January 2008

Abstract— The singlet and triplet excited state parameters (φf, Tf and SpHT) of psoralen (PSO) and derivatives 4,6,4′‐trimeth‐ylangelicin (TMA) and 4,5′,8‐trimethylpsoralen (TMP) show an extreme sensitivity to solvation in dioxane/water mixtures. These effects are attributed to the variation of the Si → S0 internal conversion rate constant kic, which is the nonradiative deactivation path dominating their photophysical behavior. Depending on the compound, kic is very high, (∼1 times 1010 s_1) in nonpolar solvents and then decreases to a low value (3 times 108s−1) with increasing solvent polarity. This work shows that dioxane/water mixtures display the same solvent‐induced changes in the electronic structure of psoralens during solvation as those induced by the biological microenvironment sensed by the drug's localization. This mixture matches the photophysical parameters of psoralens observed in protic and aprotic pure solvents, in micelles, in liposomes and in human serum low‐density lipoproteins (LDL). They can be used to probe the solvating ability of the interaction site in macrocyclic hosts. A particular localization site, i.e. the more (TMA and TMP) or less (PSO) lipophilic sites found when in interaction with LDL, determines the amount of the triplet reactive state of psoralens and the molecular mechanism available for photoreac‐tion: oxic (type I and type II) or anoxic (type III) pathways.
Investigating the Red Shift between in vitro and in vivo Urocanic Acid Photoisomerization Action Spectra
Authors: Jones Christopher D. , Barton Alun K. , Crosby John , Norval Mary , Gibbs Neil K.
Published: January 2008

Abstract— Trans‐urocanic acid (UCA) is found in the upper layer of the skin and UV irradiation induces its photoisomerization to cis‐UCA. Cis‐UCA mimics some of the immunosuppressive properties of UV exposure. The wavelength dependence for in vitro photoisomerization of trans‐UCA (15 μM) over the spectral range 250 nm‐340 nm (10 nm intervals) was determined. The action spectrum revealed that maximal cis‐UCA production occurred at 280 nm, which is red‐shifted by 10‐12 nm from its absorption peak at 268 nm and differs markedly from the reported action spectra for cis‐UCA production in mouse skin in vivo, which peaks at 300‐310 nm. The reasons for the red shift between the in vitro and in vivo action spectra are not clear. There is limited evidence suggesting that the UV absorption maximum of trans‐UCA red shifts from 268 nm in vitro to 310 nm on interaction with stratum corneum proteins in vivo. This phenomenon was investigated by applying trans‐UCA (2.5 mg/cm2) in an oil emulsion to isolated human stratum corneum. After incubation at 37°C for 1 h, the absorption spectra of stratum corneum with UCA and with oil only were compared using a Xe arc source and a spectrora‐diometer. A moderate red shift in trans‐UCA absorption from ∼268 nm to 280 nm was observed. In summary, we suggest that the 10‐12 nm red shift between the UCA absorption spectrum peak and the action spectrum peak in vitro may be accounted for by the wavelength dependence of quantum yields reported over the 254‐313 nm range. The red shift between the in vitro and in vivo photoisomerization action spectra may result from the 10 to 12 nm red shift in the absorption of UCA in association with stratum corneum proteins, combined with increasing quantum yields over the 254‐313 nm range.
Structurally Controlled Porphyrin‐Aggregation Process in Phospholipid Membranes
Authors: Borovkov Victor V. , Anikin Michael , Wasa Kiyotaka , Sakata Yoshiteru
Published: January 2008

Abstract— Structurally controlled aggregation course for five porphyrins (etioporphyrin [EP], 5‐mono‐ and 5,15‐di‐[p‐tol‐yl]etioporphyrin [TP and DTP], 5,10,15,20‐tetrakis[p‐tol‐y1]porphin [TTP], and 5,10,15,20‐tetrakis[3,5‐di‐tert‐bu‐tylphenyl]porphin [TBP]) in dipalmitoyl‐phosphatidyl‐choline liposomes has been monitored by fluorescence and absorption spectroscopy. While TBP shows no tendency to aggregate in liposomes, EP, TP, DTP and TTP form a porphyrin‐enriched domain in membrane interior with time. The further aggregation steps within porphyrin clusters resulting in formation of stacked porphyrin aggregates have been observed for EP, TP and DTP.
Combined Effects of Constant Sublethal UVA Irradiation and Elevated Temperature on the Survival and General Metabolism of the Convict‐Cichlid Fish, Cichlasoma nigrofasciatum
Authors: Winckler K. , Fidhiany L.
Published: January 2008

Abstract— In a previous study we observed that a constant sublethal UVA (320‐400 nm) irradiation had a significant effect on the general metabolism in the Convict‐cichlid fish (Cichlasoma nigrofasciatum) [Winckler, K. and Fidhiany, L. (1996) J. Photochem. Photobiol. B. Biol. (In press)]. In the present study we show that sublethal UVA irradiation in combination with elevated environmental temperature has a deleterious effect on the same population. The threshold temperature for a sudden increase in mortality of fish receiving an additional sublethal UVA irradiation was 32°C. Prior to the increased mortality, the fish started to avoid the UV light source when the water temperature increased to 31.5°C. Mortality decreased when the temperature declined below 31.5°C. As soon as the temperature changed to normal (adapted) condition (27‐29°C) mortality returned to normal levels. In contrast, no changes of fish behavior or mortality were observed at elevated temperature in the nonirradiated reference population. The percentages of fish surviving the high temperature stress were 21.9% for the UVA population and 96.8% for the reference population. The specific oxygen consumption (SOC, average ± SD) of the survivors from the UVA population during temperature stress was 0.21 ± 0.05 mg O2 h‐1 g body weight (BW)‐1, while it was 0.54 ± 0.11 mg O2 h‐1 g BW‐1 in the reference population. After the environmental temperature returned below the apparent upper temperature tolerance limit, the oxygen consumption of the UVA population gradually normalized. The SOC measured at different temperature levels‐after the fish passed the temperature stress‐ showed no significant differences between the UVA population and its reference at 23, 25, 27 and 29°C. However, the SOC at 31°C was significantly (P < 0.05) lower than reference, while at 33°C it was higher (P < 0.10).
Reflective Light Properties of Tissue Layers in Beech (Fagus sylvatica L.) Leaves
Authors: Hoque Enamul , Remus Guido
Published: January 2008

Abstract— Reflective light properties of various tissue layers (adaxial epidermis, palisade and spongy parenchyma and abaxial epidermis) of beech (Fagus sylvatica L.) leaves were measured using paradermal (parallel to epidermis) and transverse sections in the visible and infrared spectral bands by a high‐resolution reflectance cytophotometer. Results showed an increment of reflectances of rest leaves following successive removal of paradermal tissue layers (adaxial epidermis, palisade parenchyma, abaxial epidermis). Reflectances of palisade parenchyma with spongy parenchyma and abaxial epidermis increased linearly in the infrared and green spectral bands with increasing chloroplast count. The enhancement of paradermal reflectances with successive removal of paradermal tissue layers was due to various optical effects of tissue/cell layers, whereby removal of paradermal tissue layers containing light absorbers, e.g. chloroplasts/chlorophyll‐protein complexes, is of importance. The parabolic relationships found between lateral reflectances and distances of various tissue/cell layers from adaxial epidermis indicated lateral reflectances of the mesophyll to be governed mainly by selective chlorophyll absorb‐ances of light according to Lambert‐Beer's law.
On the Possibility of Evanescent Wave Excitation Distal from a Solid‐Liquid Interface Using Light Quenching
Authors: Lakowicz Joseph R. , Gryczynski Zygmunt , Gryczynski Ignacy
Published: January 2008

Abstract— Evanescent wave illumination with total internal reflection is often used to provide excitation near a quartz‐water interface. We now show that evanescent illumination at one wavelength and incident angle, coupled with light quenching at a second wavelength and incident angle, can be used for selective excitation of fluorophores located up to 5000 Å into the aqueous phase. The displacement of the fluorophore population from the solid‐liquid interface depends on the angles of incidence of the excitation and quenching beams and the optical power of the quenching beam. Light quenching with an evanescent wave was demonstrated to be experimentally possible using Pyridinez and a light‐quenching wavelength of 736 nm. The use of combined evanescent wave excitation and evanescent wave quenching could provide selective excitation of fluorophores in the cytoplasmic region of cells and may provide improved response times for optical sensors based on evanescent excitation.
Photophysical and Redox Properties of a Series of Phthalocyanines: Relation with Their Photodynamic Activities on TF‐1 and Daudi Leukemic Cells
Authors: Daziano Jean‐Pierre , Steenken Steen , Chabannon Christian , Mannoni Patrice , Chanon Michel , Julliard Michel
Published: January 2008

Abstract— The photodynamic therapy (PDT) efficiency of five phthalocyanines, chloroaluminum phthalocyanine (AlPc), dichlorosilicon phthalocyanine (SiPc), bis(tri‐n‐hexylsi‐loxy)silicon phthalocyanine (PcHEX), bis(triphenyl‐siloxy)silicon phthalocyanine (PcPHE) and nickel phthalocyanine (NiPc), was assessed on two leukemic cell lines TF‐1 and erythroieukemic and B lymphoblastic cell lines, Daudi, respectively. AlPc showed the best photocytotox‐icity leading to 0.008 surviving fraction at 2 × 10−9M for TF‐1 and 4 × 10−9M for Daudi. At 5 × 10−7M, SiPc and PcHEX induced a significant photokilling, whereas NiPc and PcPHE were inactive. Laser flash photolysis and photoredox properties of the phthalocyanines were investigated to try to relate these parameters with the biological effects. AlPc showed the longest triplet lifetime: 484 fis in dimethyl sulfoxide/H2O. This value was increased up to 820 u.s when AlPc was complexed with human serum albumin used as a membrane model. Such an enhancement was not observed with the silicon phthalocyanines. Upon irradiation, all the phthalocyanines generated singlet oxygen with 0.29–0.37 quantum yield values. The reduction potentials of the excited states obtained from measurement in the ground state and energy of the excited triplets show that AlPc is the best electron acceptor. The in vitro photocytotoxicity observed and the measured parameters are in agreement with a key role of electron transfer in PDT assays involving these phthalocyanines.
Inactivation of Trypanosoma cruzi Trypomastigote Forms in Blood Components with a Psoralen and Ultraviolet A Light
Authors: Gottlieb Paul , Margolis‐Nunno Henrietta , Robinson Richard , Shen Li‐Gang , Chimezie Eleanor , Horowitz Bernard , Ben‐Hur Ehud
Published: January 2008

Inactivation of the blood‐borne parasite Trypanosoma cruzi by UVA and 4′‐aminomethyl‐4,5′,8‐trimethylpsor‐alen (AMT) was studied in the blood components fresh frozen plasma (FFP) and platelet concentrate (PC). The AMT was utilized at a concentration of 50 μg/mL and the inactivation procedure included the flavonoid rutin (at 0.35 mM), a quencher of type I and type II photo‐reactants, which we have previously found to maintain platelet integrity during this treatment regimen. Within both FFP and PC, complete inactivation of the infective form of T. cruzi, the trypomastigote, was achieved at a UVA (320–400 nm radiation) fluence of 4.2 J/cm2. We note that while the infectivity of the parasite is eliminated at 4.2 J/cmZ the trypomastigote motility continues for at least 16 h post‐treatment and is inhibited only after much higher light doses. Isolation of total DNA from the parasite cells after treatment in the presence of 3H‐AMT indicated that at the lethal UVA fluence about 0.5 AMT adducts per kilobase pairs occurred. These results suggest that this psoralen plus UVA methodology, which shows promise in enhancing the viral safety of PC, may in addition eliminate bloodborne T. cruzi, the causative agent of Chagas disease.
Book Review
Authors: Govindjee
Published: January 2008

Molecular Processes of Photosynthesis. Edited by J. Barber. Volume 10 of Advances in Molecular and Cell Biology (series editor, E. Edward Bittar). Jai Press Inc., Greenwich, CT and London, U.K. 1994; 437 pp. 97.50. ISBN 1–55938–710–6.
Enhancement of the Photolysis of Nucleic Acid Monomers by Phosphates
Authors: Wang Kong‐jiang , Pan Xian‐ming , Wu Ji‐lan , Wang Wen‐qing
Published: January 2008

Abstract— In the tentative simulation of prebiotic synthesis, it was found that the photolysis yield of nucleic acid bases, nucleosides and nucleotides (NA) undergoing UV irradiation was sharply enhanced by added orthophosphate. Filter experiments demonstrated that the enhancement is due to UV quanta of wavelength less than 215 nm in the emission spectrum of a medium pressure mercury lamp. The phosphate‐induced enhancement of the photolysis of NA constitutes an additional channel of nucleic acid monomer degradation through their interaction with photoionized phosphate radicals.
Hydroperoxynaphthalimide Derivative‐mediated Oxidation of Heme Proteins on Photoirradiation: Horseradish Peroxidase
Authors: Yamamoto Takahiro , Maeda Yasushi , Matsugo Seiichi , Kitano Hiromi
Published: January 2008

Abstract— Horseradish peroxidase (HRP) was photoirradiated in the presence of organic peroxide (1, hydroperoxynaphthalimide derivative) at around 353 nm and 0°C. This compound bound to a heme pocket of HRP as shown by its inhibitory effect on catalysis by HRP (Ki= 5.5 times 10−5 M) and subsequently it formed an intermediate in the same way as H202. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) suggested cleavage of the peptide chain of HRP on photoirradiation with 1. From CD spectra and SDS‐PAGE, it was presumed that the destruction of both secondary structure and heme of the enzyme occurred to some extent upon photoirradiation, which resulted in a decrease in the catalytic activity. The absorption spectra also suggested that the heme group of the enzyme was destroyed, and the fluorescence spectra showed that the Trp residue in the photoirradiated HRP was oxidized to N‐formylkynurenine by a hydroxyl radical generated from 1. Energy transfer from the excited naphthalimide moiety or hydrogen abstraction also seemed to make some contribution to the alteration of the heme group.
Interaction between Cytochrome b2 Core and Flavodehydrogenase from the Yeast Hansenula anomala
Authors: Albanl J. R.
Published: January 2008

Abstract— The binding of cytochrome b2 core (a monomer) to flavodehydrogenase (a tetramer), both purified from Hansenula anomala flavocytochrome b2, has been studied in the presence of 2‐p‐toluidinylnaphthalene‐6‐sulfonate (TNS). The association constant of the TNS‐flavodehy‐drogenase complex was found to be equal to 0.64 μM−1 with a stoichiometry of one TNS per tetramer. Binding of cytochrome b2 core to flavodehydrogenase was followed by monitoring changes in the TNS fluorescence. Our results indicated that the binding is cooperative, with a stoichiometry of four cytochrome b2 cores per tetramer of flavodehydrogenase.
TNO Institute of Environmental Sciences, Energy Research and Process Innovation, the Netherlands
Authors: Ma Jianzhong , Guicherit Robert
Published: January 2008

Abstract— A radiative transfer model is used to study the effect of stratospheric ozone depletion and tropospheric pollution on UVB (280‐315 nm) radiation in the troposphere at midiatitudes of the Northern Hemisphere. The difference in the vertical distribution of UVB radiation for a range of pollution conditions typical for remote clean and more polluted sites on cloudless summer days is shown. The changes in downward UVB irradiance, UVB actinic flux, DNA‐weighted UV radiation and photodissociation frequency of ozone at the earth's surface are quantified in relation to stratospheric ozone depletion and typical ranges of tropospheric pollutants (ozone [O3], sulfur dioxide [SO2] and aerosols) in nonurban polluted regions. The results show that near the earth's surface, in non‐urban polluted regions, an increase of tropospheric pollution, which occurred over the last 50‐100 years, has cancelled the effect of an increase of UVB radiation due to stratospheric ozone depletion that has occurred since the late 1970s. The results hold for summer conditions and the decrease of UVB radiation is most pronounced in the polluted boundary layer. At higher altitudes the effect of tropospheric pollution on UVB radiation is far less. Prior to 1970 it was mainly tropospheric pollution that altered UVB radiation at the surface of the earth. In addition, since the late 1970s enhanced UVB radiation reaching the top of the troposphere, due to stratospheric ozone depletion, also had an impact on UVB levels in the troposphere.
Cysteine Derivatives Protect Against UV‐lnduced Reactive Intermediates in Human Keratinocytes: The Role of Glutathione Synthesis
Authors: Steenvoorden David P. T. , van Henegouwen Gerard M. J. Beijersbergen
Published: January 2008

Abstract— Several recent studies have shown cysteine derivatives can protect against negative effects of UV exposure. In this study, an attempt was made to correlate cellular bioavailability and metabolism of cysteine derivatives with protection against UV‐induced reactive intermediates. Human keratinocytes were treated with cysteine, N‐ace‐tylcysteine(NAC), cysteine‐ethylester(CYSET) and N‐acetylcysteine‐ethylester. The uptake of the compounds and their metabolism to cysteine and eventually to glutathione(GSH) was measured. Large differences in uptake were observed, with CYSET resulting in the highest and NAC in the lowest intracellular thiol levels. The increase in intracellular GSH was similar for all derivatives with a maximum of 23‐54% over the control level. Protective efficacy of the derivatives was measured as the inhibition of binding of UV‐induced reactive intermediates from 8‐methoxypsoralen. There was only a small difference between the compounds, with maximum protection of 25‐31%. No relation was found between total intracellular thiol and protection. However, for NAC, there was a linear relation between GSH level and protective efficacy (r = 0.94). Even though this was not clear for the other derivatives(r = 0.55 for CYS; r= 0.60 for CYSET; r = 0.70 for NACET), it indicates that GSH synthesis is an important factor.

This was confirmed by experiments using cells with irreversibly inhibited GSH synthesis. Even though the total intracellular thiol level was comparable to uninhibited cells, protection was decreased. We conclude that the intracellular GSH increase is the most important factor in photoprotection by cysteine derivatives.
Physiological Doses of Ultraviolet Irradiation Induce DNA Strand Breaks in Cultured Human Melanocytes, as Detected by Means of an Immunochemical Assay
Authors: Wenczl Enikö , Pool Sacha , Timmerman Arie J. , van der Schans Govert P. , Roza Len , Schothorst Albert A.
Published: January 2008

Abstract— An immunochemical assay, i.e. sandwich enzyme‐linked immunosorbent assay, has been modified to detect UV‐induced damage in cellular DNA of monolayer‐grown human melanocytes. The method is based on the binding of a monoclonal antibody to single‐stranded DNA. The melanocytes derived from human foreskin of skin type II individuals were suspended and exposed to UVA, UVB, solar‐simulated light or γ‐rays. Following physiological doses of UVA, UVB or solar‐simulated light, a dose‐related DNA unwinding comprising a considerable number of single‐strand breaks (ssb) was observed. No correlation was found between different seeded cell densities or different culturing periods and the UVA sensitivity of the cells. After UVA irradiation, 0.07 ssb/1010 Da/kJ/m2 were detected and after UVB irradiation 1.9 ssb/1010 Da/kJ/m2 were seen. One minimal erythema dose of solar‐simulated light induced 2.25 ssb/1010 Da. Our results from melanocytes expressed in ssb/Da DNA are comparable and have the same sensitivity toward UVA as well as toward UVB as nonpigmented skin cells. As low doses of UVA have already been shown to induce detectable numbers of ssb, this assay is of great interest for further investigations about the photoprotecting and/or photosensitizing effects of melanins in human melanocytes derived from different skin types.
In vitro Fluence Rate Effects in Photodynamic Reactions with AIPcS4 as Sensitizer
Authors: Moor Anne C. E. , Lagerberg Johan W. M. , Tijssen Karmi , Foley Sarah , Truscott T. George , Kochevar Irene E. , Brand Anneke , Dubbelman Tom M. A. R. , VanSteveninck John
Published: January 2008

Abstract— It has been shown previously that the efficiency of photodynamic therapy (PDT) both in vivo and in vitro is dependent on fluence rate. In this study, different in vitro experiments showed that tetrasulfonated aluminum phthalocyanine (AlPcS4) is more efficient in photosensi‐tization if the light is delivered at low fluence rate. Erythrocyte damage, virus inactivation and photooxidation of reduced glutathione (GSH) and histidine were all enhanced if light was delivered at 100 W/m2 as compared to 500 W/m2. Bleaching did not occur under these conditions. Oxygen depletion, shown to be important in fluence rate effects observed in vivo, does not seem to be involved. On theoretical grounds saturation of the triplet state is not likely under these conditions. A possible explanation for the observed fluence rate effects might be found in different reaction pathways, that are favored under high or low fluence rate illuminations. These reactions might involve uni‐ or bimolecular reactions of intermediate products, resulting in less efficiency at higher fluence rate. It proves to be important, under all circumstances, to monitor fluence rate, because a change in fluence rate, even with similar total fluences, might influence photobiological results in an unexpected way.
Pulsed Photoacoustic Study of the Diffusion of Chromophores in Human Skin
Authors: Lahjomri F. , Puccetti G. , Leblanc R. M. , Alard V. , Denis A. , Trenchant J.‐F.
Published: January 2008

The technique of pulsed photoacoustic spectroscopy was used to investigate the diffusion of chromophores in human skin. The kinetic of diffusion has been studied for five solutions at different concentrations in a mixture of chromophores, as used in commercial sunscreens. In addition to the classical macroscopic interpretation of the diffusion process, a new method is shown to give more detailed information on chromophore presence at different depths in skin. For the first time, results are expressed in the frequency domain by means of the Fourier transform applied to the photoacoustic signal. The spectra are discussed versus the depth in skin samples and the time of diffusion kinetics. This new method of data analysis is shown to be very useful for understanding the influence of the internal structure of a medium on the penetration rate of chromophores into skin.
Synthesis and Photoreaction of a‐Methylene‐γ‐Butyrolactone‐Psoralen Heterodimers
Authors: Giménez‐Arnau Elena , Bussey Cécile , Lepoittevin Jean‐Pierre
Published: January 2008

Three double‐headed molecules were synthesized by linking a photoreactive linear (1, 2) or angular (3) furocou‐marin via a linear 10‐ or 5‐carbon chain to an electro‐philic α‐methylene‐γ‐butyrolactone. The photochemical behavior of these molecules was investigated in ethanol at 365 nm and the photocycloadducts obtained from each compound were isolated and characterized. In all cases, the photoreactivity results showed the 3,4‐pyrone double bond of the psoralen (linear or angular) to be the most reactive and [2 + 2] intramolecular photocycloadducts between the 3,4‐pyrone and the exomethylenic double bonds were obtained. With compounds 1 and 2, two kinds of intramolecular photocycloadducts were obtained, namely cissyn‐exo derivatives in 46% and 36% yield, respectively, and trans‐syn‐exo derivatives in 14% and 18% yield, respectively. With compound 3, only the trans‐syn‐exo derivative was obtained in 33% yield.
Ultraviolet Irradiation Produces Novel Endonuclease Ill‐Sensitive Cytosine Photoproducts at Dipyrimidine Sites
Authors: Jen J. , Mitchell D. L. , Cunningham R. P. , Smith C. A. , Taylor J.‐S. , Cleaver J. E.
Published: January 2008

Ultraviolet light irradiation of DNA in vitro and in vivo induces cyclobutane dimers, (6–4) pyrimidine‐pyrimi‐done photoproducts and a variety of minor products. Using a denned DNA fragment, we have identified two classes of sites that can be cleaved by Escherichia coli endonuclease III: single cytokines whose heat lability corresponds to that of cytosine hydrates and more heat‐stable dipyrimidines containing cytosine. The dipyrimidine products are induced at sites suggestive of (6–4) photoproducts but are not recognized as (6–4) photoproducts by radioimmunoassay. Use of oligonucleotides containing a single cyclobutane thymine dimer, a (6–4) photoproduct or the Dewar photoisomer of the (6–4) photoproduct also indicated that these products are not substrates for endonuclease III. We have therefore identified a minor UV photoproduct that has the same sequence specificity as the two major dipyrimidine photoproducts; it may be a minor isomer, a unique derivative or an oxidative lesion confined to dipyrimidine sites. Its biological significance is not yet known but may be masked by the preponderance of major products at the same sites. Its occurrence at the particular site in dipyrimidine sequences involved in the mutagenic action of UV photoproducts suggests that it may play a role in generating C to T transitions that are common UV‐induced mutations.
Effects of Nonpolar and Polar Solvents on the Qx and QY Energies of Bacteriochlorophyll a and Bacteriopheophytin a
Authors: Limantara Leenawaty , Sakamoto Shun , Koyama Yasushi , Nagae Hiroyoshi
Published: January 2008

The effects of nonpolar and polar solvents on the Qx and Qy energies of bacteriochlorophyll (BChl) a and bacteriopheophytin (BPhe) a were examined by electronic absorption spectroscopy. All of the four different energies exhibited a linear dependence on R(n) = (n2 ‐ l)/(n2+ 2), where n is the refractive index of the solvent, in both nonpolar and polar solvents. The energy of each state of both pigments could be expressed as v = ‐dR(n) + e (in cm‐1) where coefficient d was related to the dispersive interaction between the solute and the solvent molecules. A theory developed by Nagae showed that coefficient d originates from the quantum‐mechanical fluctuation of the multipole moments of the solute, in terms of which the following characteristics of the observed d values were explained: (1) In all of the four cases of the Qx, and Qy energies of both BChl a and BPhe a, the d values for the polar solvents were smaller than those for the non‐polar solvents. (2) In both nonpolar and polar solvents, the d value of BChl a was larger than that of BPhe a in the Qy energy, whereas the d value of BPhe a was larger than that of BChl a in the Qx energy. (3) The d value of the Qx energy was larger than that of the Qy, energy for either case of BChl a or BPhe a.
Relationship between Skin Color and Sun Exposure History: A Statistical Classification Approach
Authors: Rubegni Pietro , Cevenini Gabriele , Flori Maria Laura , Fimiani Michele , Stanghellini Elisabetta , Molinu Antonietta , Barbini Paolo , Andreassi Lucio
Published: January 2008

In this study our aim was to determine the biophysical values of constitutive skin color in Caucasians and to define the correlation between skin color and phototype assessed according to the Fitzpatrick method. Constitutive skin color was measured on the buttock, with a Minolta CR‐200 colorimeter, in a population of 557 consecutive subjects belonging to phototype categories I, II, III and IV. The colorimeter expresses the results in five different color systems. We used the “Yxy” and L*a*b* systems, which are the most widespread in dermatology. Statistical analysis of the data showed that the “Yxy” system is even more discriminant than the L*a*b* system when the Fitzpatrick classification scheme is adopted as the reference and shows a poor ability to correctly classify the intermediate phototypes (II and III). On the contrary the “Yxy” system performs well in distinguishing phototypes I and IV. To establish whether this low discriminating capacity for phototypes II and III is related to a low discriminating capacity of the method suggested by Fitzpatrick or by our procedure, an objective technique (minimal erythemal dose) should be used to evaluate the percentage errors of classification of both the Fitzpatrick method and instrumental measurement of skin color. The results of such a study are extremely important because the evaluation of skin color is objective, simple and has potential applications in dermatology and cosmetology.
Characterization of DNA Damage Inflicted by Free Radicals from a Mutagenic Sunscreen Ingredient and Its Location Using an in vitro Genetic Reversion Assay
Authors: McHugh Peter J. , Knowland John
Published: January 2008

We describe an in vitro approach to assessing the potential genotoxicity of illuminated sunscreens. The photomutagenic sunscreen Padimate‐O attacks DNA on illumination with simulated sunlight, producing strand breaks and lesions that are labile to N, N'‐dimethylethy‐lenediamine but few, if any, cyclobutane dimers or other direct photoproducts. The damage can be completely suppressed by the free radical quenchers Tris, ethanol, mannitol and dimethylsulfoxide, which is commonly used as a solvent in conventional photomutagenicity assays. Using a genetic reversion assay that depends on regenerating P‐galactosidase activity in photodamaged plas‐mids we find that GC base pairs are particularly susceptible to attack by Padimate‐O.
Interaction of UV Light‐Induced α–Tocopherol Radicals with Lipids Detected by an Electron Spin Resonance Prooxidation Effect
Authors: Walke Mathias , Beckert Dieter , Lasch Jürgen
Published: January 2008

The reaction rate constants of the interaction between light‐induced α–tocopherol radicals with unsaturated lipids in a heterogeneous system compared to a homogeneous system are of the same order of magnitude. The decay rates of compartmentalized ‐α‐tocopherol radicals were significantly reduced by using negatively charged sodium dodecyl sulfate (SDS) micelles. A partially resolved electron spin resonance (ESR) hyperfine structure was observed under the conditions of both high lipid concentrations in comparison to the α‐tocopherol concentration and of a regular distribution of α‐tocopherol molecules inside the heterogeneous lipid structures. Alphα‐to‐copherol radicals have a considerable prooxidation potential at higher concentrations. Ascorbic acid dissolved in the aqueous medium provokes very fast ‐α‐tocopherol radical recycling through the boundary layer between the aqueous medium and micelles. By contrast, very slow reactions such as those of α‐tocopherol radicals with glutathione through this boundary layer are measurable. Despite using the heterogeneous SDS micellar system, the decay kinetics of the α‐tocopherol radical ESR signal is simply compounded. In addition to the known stabilization effect of cholesterol in membrane systems, cholesterol itself acts as a target molecule attacked by free radicals, e.g. ‐α‐tocopherol radicals. Using stratum corneum extracts that contain unsaturated lipids and cholesterol the ‐α‐tocopherol radical can prooxidatively react with these compounds. Using focused UV light generates a high radical yield in a relatively short time compared to the lifetime of the ‐α‐tocopherol radicals. The decay processes after radical induction can be characterized as consecutive reactions. The compartmentalization of radicals induced in SDS micelles and the close proximity of target molecules are essential if very slow one‐electron reductions are to be measured.
Photoprotection of Mammalian Acid‐Soluble Collagen by Cuttlefish Sepia Melanin In Vitro
Authors: Menter Julian M. , Patta Abrienne M. , Hollins Thomas D. , Moore Cyril L. , Willis Isaac
Published: January 2008

Several important clinical conditions can result in close association between the pigment melanin and dermal collagen. Because melanin and its precursors can be chemically reactive in ground and excited states, it is important to know whether the resulting melanin‐collagen interaction results in photoprotection or photoaggression. Acidic and neutral air‐saturated collagen suspensions (0.033%) were irradiated with0–2.6 times 104 J/m2 UVC or with0–83 times 104 J/m2 solar‐simulating UV radiation (SSR). Photochemical destruction of a photolabile collagen fluorophore (δem 360 nm) and collagen chain degradation were monitored as functions of irradiation time in the presence and absence of added (0–100μg) sepia eumelanin. Melanin retarded collagen photodamage but did not qualitatively alter the fluorescence fading kinetics. Both H202 and 02 can be produced by UV irradiation of eumelanin. Added H202 and K02 destroyed collagen fluorescence and caused 50% chain degradation at ca10–20‐fold molar excess. Previous studies have demonstrated that eumelanins efficiently scavenge 02 . We demonstrated that eumelanin also efficiently scavenges H202 as evidenced by its ability to (a) compete with scopoletin for peroxide uptake and (b) directly take up H202 through a dialysis bag. The latter observation suggests that peroxide scavenging could occur in vivo by melanin sequestered in melanophages. Thus, neither UV‐generated 02 nor H202 are likely to be present in concentrations high enough to cause measurable collagen damage. Absorption and/or scattering of excitation radiation away from the target chromophore appears to be the primary photoprotection mechanism, although scavenging of active 02 intermediates may play an important, if subtle role.
A Comparison of the Photodynamic Effects of Temoporfin (mTHPC) and MC540 on Leukemia Cells: Efficacy and Apoptosis
Authors: Chen J. Y. , Mak N. K. , Wen J. M. , Leung W. N. , Chen S. C. , Fung M. C. , Cheung N. H.
Published: January 2008

The photodynamic effects of temoporfin (meso‐tetrahy‐droxyphenylchlorin, mTHPC) and merocyanine 540 (MC540) in murine myeloid leukemia M1 and WEHI 3B (JCS) cells were compared. The mTHPC was found to be more potent and selective. At a lethal dosage of 90% killing (LD90), only 1.3 μM of mTHPC and 4.2 kj/m2 of light irradiation was required, which was a 20‐fold lower drug concentration and 11‐fold smaller light dose than that required when using MC540. Meanwhile, three times less, or 15%, of the coincubated erythrocytes were destroyed by mTHPC than by MC540. Confocal micrographs showed that both drugs accumulated diffusely inside the cytoplasm in a very similar fashion, but mTHPC induced a more extensive apoptosis in photosensitized JCS cells. For example, at LD90, mTHPC practically killed all JCS cells via apoptosis and cleaved the DNA to extremely small 150 base‐pair fragments. In contrast, among the JCS cells killed by MC540, about 88% died via apoptosis and large DNA fragments were abundant. Relative to MC540, the ability of mTHPC to trigger large‐scale and thorough apoptosis in leukemia cells may help explain its potency and selectivity.
Transient Species in the Photochemistry of Tiaprofenic Acid and Its Decarboxylated Photoproduct*
Authors: Encinas Susana , Miranda Miguel A. , Marconi Giancarlo , Monti Sandra
Published: January 2008

Photoexcitation of tiaprofenic acid (TPA) in aqueous medium leads with almost unitary efficiency to the lowest π,π* triplet, which is detected by transient absorption. The deactivation of this state occurs in the microsecond time domain and is dominated by a thermally activated spin‐allowed process with –10 kcal/mol energy barrier. The occurrence of decarboxylation from an upper state, likely the second triplet of n, π* character, is confirmed by the study of the transients toward the final keto photoproduct, i.e. the benzoylthiophene ethyl derivative (DTPA). At neutral pH, upon adiabatic release of the CO2 fragment, long‐lived triplet biradicals and ground‐state intermediates with a protonated carbonyl oxygen are formed. Laser flash photolysis of DTPA leads almost quantitatively to the lowest π,π* triplet, with similar T‐T absorption features as those of TPA. However the DTPA triplet appears essentially unreactive in aqueous medium. In isopropanol H‐abstraction from the solvent is demonstrated by the formation of the ketyl radical.
Photobinding of Tiaprofenic Acid and Suprofen to Proteins and Cells: A Combined Study Using Radiolabeling, Antibodies and Laser Flash Photolysis of Model Bichromophores
Authors: Castell José V. , Hernández Daniel , Gómez‐Lechón María José , Lahoz Agustín , Miranda Miguel A. , Morera Isabel M. , Perez‐Prieto Julia , Sarabia Zaideth
Published: January 2008

Drug photoallergy is a matter of current concern. It involves the formation of drug‐protein photoadducts (pho‐toantigens) that may ultimately trigger an immunological response. Tyrosine residues appear to be key binding sites in proteins. The present work has investigated the photobinding of tiaprofenic and (TPA) and the closely related isomer suprofen (SUP) to proteins and cells by means of radioactive labeling and drug‐directed antibodies. To ascertain whether preassociation with the protein may play a role in photoreactivity, two model bichro‐mophoric compounds (TPA‐Tyr and SUP‐Tyr) have been prepared and studied by laser flash photolysis. The results of this work show that (a) TPA and SUP photo‐bind to proteins with similar efficiencies, (b) both drugs form photoadducts that share a basic common structure, as they are recognized by the same antibody and (c) drug‐protein preassociation must play a key role in photoreactivity, as indicated by the dramatic decrease in the triplet state lifetimes of the model bichromophores compared to the parent drugs.
Influence of Solvent Polarity and Proticity on the Photochemical Properties of Norfloxacin
Authors: Bilski P. , Martinez L. J. , Koker E. B. , Chignell C. F.
Published: January 2008

Abstract— The fluoroquinolone antibacterial norfloxacin (NF) is a moderate photosensitizer of singlet molecular oxygen (1O2). We have studied photosensitization by NF as a function of medium polarity and proticity in solvent mixtures. We have used 1,4‐dioxane and propylene carbonate mixtures to keep proticity constant while modulating polarity, and water/D2O and ethylene carbonate mixtures to alter proticity without large changes in polarity. The absorption spectrum of NF was little affected by solvent changes, as compared to the fluorescence spectrum that exhibited as much as a 50 nm blue‐shift, e.g. 1,4‐dioxane versus D2O. The quantum yield of NF fluorescence saturated at an almost 10 times higher value (?0.14) when proticity was increased by added water, up to 0.2 mol fraction, to ethylene carbonate. Less pronounced, the increasing polarity in 1,4‐dioxane/propylene carbonate mixtures affected the fluorescence yield much less. Norfloxacin produces 1O2 and is able to quench 1O2. The rate constant for 1O2 quenching is 4.5 × 107 M−1 s−1 in propylene carbonate but decreases ca four times in D2O. The quantum yield of 1O2 photogeneration was also up to five times higher in solvents that were both protic and polar than vice versa. Our data show that NF is more photochemically active in an environment that is both protic and polar. This suggests the involvement of polar excited state(s) and possible proton/hydrogen transfer during photoexcitation. Similar processes may initiate the phototoxic response reported in some patients treated with the fluoroquinolone drugs. The phototoxicity of NF and other fluoroquinolone antibiotics may strongly depend on their localization in hydrophilic or hydrophobic cell/tissue regions.
Molecular Requirement of Chlorosomal Chlorophylls. Self‐Organization of a Chlorophyll Derivative Possessing a Hydroxyl Group at Ring II
Authors: Oba Toru , Tamiaki Hitoshi
Published: January 2008

Aggregation of zinc 71‐hydroxyl‐132‐demethoxycarbonyl‐pheophytin a (Zn‐71‐OH‐Chl) was examined in relation to the structure and function of the self‐aggregates of 31‐OH‐type chlorophylls (Chi) in chlorosomes of green photosynthetic bacteria. The Zn‐71‐OH‐Chl aggregates yielded a Qy absorption band at 712 nm with a 1.2‐fold larger width (full width at half maximum, 500 cm−1) than the monomer's (420 cm−1). Infrared and NMR spectroscopies revealed that each molecule in the aggregate links together with simultaneous coordination (C71‐OH…Zn) and hydrogen bonding (C71‐OH … O=C131). A nonlinear alignment of the constituent molecules in the oligomeric structure was assumed. Despite the similar molecular linkages, linearly aligned Qy, moments in the Zn‐31‐OH‐Chl aggregate gave a chlorosome‐like broader, more redshifted Qy band (740 nm; 670 cm−1, 2.1‐fold larger than the monomer's). Because it is advantageous for efficient light harvesting and energy transfer to have several Qy, spectral components, spread over a wide spectral range, that can act as the energy gradient, it is concluded that not only the intermolecular linkages but the linear locations of OH, C=0 and Mg in the molecule are crucial for photosynthetic antenna of the self‐assembled chiorosomal Chl.
Selective Examination of Plasma Membrane–Associated Photosensitizers Using Total Internal Reflection Fluorescence Spectroscopy: Correlation between Photobleaching and Photodynamic Efficacy of Protoporphyrin IX
Authors: Strauss W. S. L. , Sailer R. , Gschwend M. H. , Emmert H. , Steiner R. , Schneckenburger H.
Published: January 2008

Fluorescence spectra, fluorescence decay kinetics, photobleaching kinetics and photodynamic efficacy of protoporphyrin IX (PP) were investigated in endothelial cells in vitro after different incubation times. Fluorescence spectra and photobleaching kinetics were determined during total internal reflection (TIR) illumination or epiillumination. Because penetration depth of the excitation light during TIR illumination was limited to about 100 nm, plasma membrane‐associated PP was almost selectively examined. Spectra obtained by TIR fluorescence spectroscopy (FS) showed a very low background, where‐as spectra obtained by epi‐illumination exhibited considerable background by autofluorescence and scattered light. For photobleaching kinetics during TIR illumination after 1 h or 24 h incubation, a biexponential fluorescence decrease was observed with a rapidly and a slowly bleaching portion. After 1 h incubation, the rapidly bleaching portion was the predominant fraction, whereas after 24 h incubation comparable relative amounts of the rapidly and slowly bleaching portion were determined. The rapidly and slowly bleaching portion were assigned to PP monomers and aggregated species in close vicinity to the plasma membrane. Fluorescence decay measurements after epi‐illumination support the decrease of PP monomers within the whole cell with increasing incubation time. In contrast to TIR illumination, photobleaching of PP during epi‐illumination was characterized by slow monoexponential fluorescence decrease after 1 h or 24 h incubation. Photodynamic efficacy of PP using epi‐illumination was found to depend strongly on incubation time. Considerable cell inactivation was determined for short incubation times (1 h or 3 h), whereas photodynamic efficacy was diminished for longer incubation times. Reduced photodynamic efficacy after long incubation times was assigned to the lower amount of photodynamically active monomers determined close to the plasma membrane as well as within the whole cell. In conclusion, TIRFS measurements are suggested to be an appropriate tool for the examination of the plasma membrane‐associated photosensitizer fraction in living cells.
Light Regulation of Phytochrome Content in Wild‐type and Aphototropic Mutants of the Moss Ceratodon purpureus
Authors: Esch Heike , Lamparter Tilman
Published: January 2008

In filaments of the moss Ceratodon purpureus, phototropism is controlled by the photoreceptor phytochrome. Thirty‐three aphototropic mutants with a proposed defect in phytochrome‐chromophore biosynthesis were isolated and analyzed. The phototropic response of those mutants was rescued with the precursor of the phytochrome chromophore, biliverdin. Phytochrome spectral activity was measured in 19 arbitrarily chosen mutants. All contained low but still measurable quantities of photoactive phytochrome; the highest level was around 15% of the wild‐type. The level of total phytochrome (apophytochrome and holophytochrome) as assayed by immunoblotting was indistinguishable from wild‐type. The content of photoactive phytochrome in Ceratodon is light‐regulated. Phytochrome of wild‐type kept for 24 h in red light was reduced to 50% as compared to dark controls but was unaffected by blue. The red‐light‐induced decrease was partially reversible by far‐red light, indicating that phytochrome itself is the photoreceptor for this response. This regulation was further analyzed with the mutant ptr114, which contains 15% photoactive phytochrome as compared to the wild‐type. In this mutant, continuous red light given for 6 days decreased the level of spectrally active phytochrome down to 25% of dark controls, whereas the amount of phytochrome found on immunoblots was hardly reduced. This indicates that the loss of phytochrome affects only the holoprotein and implies that Ceratodon phytochrome is specifically degraded as a far‐red‐absorbing phytochrome.
Novel Visible and Ultraviolet Light Photogeneration of Hydroxyl Radicals by 2‐Methyl‐4‐nitro‐quinoline‐N‐oxide (MNO) and 4, 4′‐Dinitro‐(2, 2′) bipyridinyl‐N, N′‐dioxide (DBD)
Authors: Botchway Stanley W. , Chakrabarti Subrata , Makrigiorgos G. Mike
Published: January 2008

Chemicals that upon absorption of light generate hydroxyl radicals (·OH), free of other damaging species under physiological conditions, are useful tools for the study of the biological effects of ·OH radical and for its utilization for analytical purposes. We report the novel property of 2‐methyl‐4‐nitro‐quinoline‐N‐oxide (MNO) and 4, 4′‐dinitro‐(2, 2′) bipyridinyl‐N, N′‐dioxide (DBD) to act as photogenerators of ·OH with UV and visible light. Upon irradiation with 360–400 nm light MNO and DBD generate free radicals that convert coumarin carboxylic acid (CCA) to fluorescent 7‐OH‐CCA; the ·OH radical scavengers dimethylsulfoxide (DMSO) and ethanol eliminate the induction of 7‐OH‐CCA fluorescence. Upon 400 nm illumination in the presence of MNO, supercoiled plasmid DNA is converted to circular and strand break‐age is significantly reduced in the presence of DMSO and completely absent in the absence of MNO. The conversion of CCA to 7‐OH‐CCA and of supercoiled plasmid to circular DNA are also observed in the absence of oxygen. Taken together, these data indicate that MNO and DBD constitute novel ·OH‐generating compounds. Because currently known ·OH‐photogenerating compounds require UV illumination (< 360 nm) that also damages DNA and cells directly, the property of MNO to generate ·OH upon 400 nm illumination is advantageous when studies on cells, DNA and other biomolecules are conducted.