bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alkyl Ether Analogs of Chlorophyll‐a Derivatives: Part 1. Synthesis, Photophysical Properties and Photodynamic Efficacy
Authors: Pandey Ravindra K. , Sumlin Adam B. , Constantine Scott , Aoudia Mohamed , Potter William R. , Bellnier David A. , Henderson Barbara W. , Rodgers Michael A. , Smith Kevin M. , Dougherty Thomas J. 
Published: January 2008

AbstractThe synthesis, preliminary in vivo biological activity, singlet oxygen and fluorescence yields of a series of alkyl ether derivatives of chlorophyll‐a analogs are described. For short‐chain carbon ethers (1–7carbon units), it was observed that the biological activity increased by increasing the length of the carbon chain, being maximum in compounds with n‐hexyl and n‐heptyl chains. Related sensitizers prepared by reacting 2‐(1‐bromoethyl)‐2‐devinylpyropheophorbide‐a with (sec)alcohols were found to be less effective. Under similar treatment conditions, photosensitizers containing cis‐ and trans‐ 3‐hexenyl side chains were ineffective. Thus, both stereochemical and steric factors caused differences in sensitizing activity. In general, pyropheophorbide‐a analogs were found to be more active than related chlorin e6 derivatives, in which the isocyclic ring (ring “E”) was cleaved. Related photosensitizers in the 9‐deoxy‐ series were found to be as effective as the corresponding pyropheophorbide‐a analogs. The photosensitizers prepared from pyropheophorbide‐a methyl ester and chlorin e6 trimethyl ester have long wavelength absorption at 660 nm (ε 45000 to 50000). Reduction of the carbonyl group in the pyropheophorbide‐a to methylene (ring E) resulted in a blue shift to 648 nm (ε 38000).
Medical UV Exposures and HIV Activation
Authors: Zmudzka Barbara Z. , Miller Sharon A. , Jacobs Mary E. , Beer Janusz Z. 
Published: January 2008

AbstractThis paper presents the first attempt to evaluate the potential of clinical UV exposures to induce the human immunodeficiency (HIV) promoter and, thus, to upregulate HIV growth in those skin cells that are directly affected by the exposure. Using the data for HIV promoter activationin vitro, we computed UVB and psoralen plus UVA (PUVA) doses that produce 50% of the maximal promoter activation (AD50). Then, using (a) literature data for UV transmittance in the human skin, (b) a composite action spectrum for HIV promoter and pyrimidine dimer induction by UVB and (c) an action spectrum for DNA synthesis inhibition by PUVA, we estimated the distribution of medical UVB and PUVA doses in the skin. This allowed us to estimate how deep into the skin the HIV‐activating doses might penetrate in an initial and an advanced stage of UVB or PUVA therapy. Such analysis was done for normal type II skin and for single exposures. The results allow us to predict where in the skin the HIV promoter may be induced by selected small and large therapeutic UVB or PUVA doses. To accommodate changes in skin topography due to disease and UV therapy, our considerations would require further refinements. For UVB we found that, when the incident dose on the surface of the skin is 500 J/m2(290–320nm) (initial stage of the therapy), the dose producing 50% of the maximal HIV promoter activation (ADUVB50) is limited to the stratum corneum. However, with an incident dose of 5000 J/m2(an advanced stage of the therapy), ADUVB50may be delivered as far as the living cells of the epidermis and even to some parts of the upper dermis. For PUVA we found that, when the incident UVA doses are 25 or 100 kJ/m2(320–400nm) (an initial and an advanced stage of therapy, respectively), and the 8‐methoxypsoralen concentration in the blood is 0.1 μg/mL (the desired level), the combined doses to the mid epidermis (and some areas of the upper dermis) are well below the 50% HIV promoter‐activating PUVA dose (ADPUVA50). Only under the worst scenario conditions,i. e.an exceptionally high drug concentration in the patient's tissues and localization of HIV in the nearest proximity to the skin surface, would the combined PUVA dose expected during photochemotherapy exceed ADPUVA50. These results suggest that the probability of HIV activation in the epidermis by direct mechanisms is higher for UVB than for PUVA treatment. However, complexities of the UV‐inducible HIV activation and immunomodulatory phenomena are such that our results by themselves should not be taken as an indication that UVB therapy carries a higher risk than PUVA therapy when administered to HIV‐infected patients.
Quantitative Determination of Cyclobutane Thymine Dimers in DNA by Stable Isotope‐Dilution Mass Spectrometry
Authors: Podmore Ian D. , Cooke Marcus S. , Herbert Karl E. , Lunec Joseph 
Published: January 2008

AbstractIn order to understand the role of UV‐induced DNA lesions in biological processes such as mutagenesis and carcinogenesis, it is essential to detect and quantify DNA damage in cells. In this paper we present a novel and both highly selective and sensitive assay using capillary gas chromatography (GC) combined with mass spectrometry (MS) for the detection and accurate quantitation of a major product of UV‐induced DNA damage (cissyn cyclobutadithymine). Quantitation of the cyclobutane thymine dimer was achieved by the use of an internal standard in the form of a stable 2H‐labeled analogue. Both isotopically labeled and nonlabeled dimers were prepared directly from their corresponding monomers. Each was identified as their trimethylsilyl ether derivative by GC‐MS. Calibration plots were obtained for known quantities of both nonlabeled analyte and internal standard. Quantitation of cis‐syn cyclobutadithymine was demonstrated in DNA exposed to UVC radiation over a dose range of 0 to 3500 J m−2. Under the conditions used, the limit of detection was found to be 20–50 fmol on column (equivalent to 0.02–0.05 nmol dimer per mg DNA). The results of the present study indicate that capillary GC‐MS is an ideally suited technique for selective and sensitive quantification of cis‐syn cyclobutadithymine in DNA and hence UV‐induced DNA damage.
UVB Shielding Role of FeCI3 and Certain Cyanobacterial Pigments
Authors: Kumar Ashok , Tyagi Madhu B. , Srinivas Ganna , Singh Nilima , Kumar Har D. , Sinha Rajeshwar P. , Häder Donat‐P. 
Published: January 2008

AbstractThe shielding role of ferric iron (FeCl3) and certain cyanobacterial pigments (a brown‐colored pigment from Scytonema hofmanii culture filtrate and a pink extract from Nostoc spongiaeforme) against UVB‐induced damage in the filamentous, nitrogen‐fixing cyanobacterium Nostoc muscorum has been demonstrated. Addition of these colored compounds to agarose gels (1–3 mm thick) resulted in a considerable decrease in UVB transmittance through the gels. The lowest UVB transmittance (15%) occurred through a 3 mm gel containing 0.01% FeCl3 followed by S. hofmanii culture filtrate (40%) and N. spongiaeforme extract (50%). These substances appear to act as very efficient UVB‐absorbing screens. Percent survival and 14CO2 uptake of N. muscorum increased significantly if UVB exposure was given on gels containing FeCl3 or other UVB‐shielding substances. The highest protection of N. muscorum was recorded with FeCl3, followed by S. hofmanii culture filtrate and N. spongiaeforme extract. Such UV‐shielding substances if present in required concentration range may enhance the survival of cyanobacteria exposed to high levels of UVB.
Flow Cytometric Technique for Quantitating Cytotoxic Response to Photodynamic Therapy
Authors: Campbell D. L. , Fisher M. E. , Johnson J. G. , Rossi F. M. , Campling B. G. , Pottier R. H. , Kennedy J. C. 
Published: January 2008

Abstract— A simple flow cytometric technique for rapid measurement of multilog cytotoxic responses to photosensitization of cellular systems is described. This technique is particularly useful for cell lines with a low colony‐forming efficiency, for which a nonclonogenic assay is required. The assay separates cell‐sized objects from cellular debris by gating on forward scatter versus side scatter, identifies viable cells by positive calcein AM and negative ethidium homodimer‐1 staining and measures cell concentration relative to an internal standard of polystyrene beads. Large numbers of cells can be analyzed rapidly.Two patient‐derived small cell lung cancer cell lines, NCI‐H209 and SV‐E, were used to test the technique. Photoradiation survival curves of the response of these cell lines to 5‐aminolevulinic acid‐induced protoporphyrin IX photosensitization correlated with the extent of photosensitizer accumulation. There was good agreement between the results obtained using the tritiated thymidine incorporation assay and the flow cytometric cytotoxicity assay. The technique can be used to measure cytotoxic responses to photosensitization of cell lines regardless of their plating efficiencies.
Fluence‐Dependent Induction of Micronuclei by Aluminum Phthalocyanine Tetrasulfonate‐Mediated Photodynamic Therapy
Authors: Hahn Kevin A. , Panjehpour Masoud , Lu Xiaochen 
Published: January 2008

Abstract— The purpose of the study was to determine if aluminum phthalocyanine tetrasulfonate (A1PcS4) photodynamic therapy (PDT) induced the formation of micronuclei in vitro and whether micronuclei formation was dependent on fiuence or cell type. NIH‐3T3 and EMT‐6 monolayer cultures were incubated in AlPcS4 (0 or 1 μg/mL) for 24 h, received 0.0, 0.5,1.0 or 1.5 J/cm 2 of 675 nm light, then reincubated and harvested at either 24, 48 or 72 h. The micronucleus frequency was determined in binucleated cells using the cytochalasin‐block method. Cytotoxicity was assessed by using the 3(4,5‐dimenthylthiazoyl‐2‐yl)2,5(diphenyl‐tetrazolium bromide) (MTT) method. The effect of treatment on cell cycle progression was determined by calculating a proliferative index.Aluminum phthalocyanine tetrasulfonate PDT induced a fluence‐dependent increase in the frequency of micro‐nuclei in NIH‐3T3 and EMT‐6 cells. The maximal effect of PDT was obtained in both cell lines 24 h after treatment. NIH‐3T3 and EMT‐6 cells exposed to a low fiuence of 0.5 J/cm2 had a significantly lower number of micro‐nuclei per cell 48 h following PDT treatment compared to the number of micronuclei per cell observed 24 h following treatment; however, when cells were exposed to a fluence (1.0 or 1.5 J/cm2) the number of micronuclei per cell did not diminish until 72 h after PDT treatment. The results obtained from the micronucleus assay paralleled those results obtained from the MTT assay.
Photooxidation of Troglitazone, a New Antidiabetic Drug *
Authors: Fu Yulan , Sheu Chimin , Fujita Takashi , Foote C. S. 
Published: January 2008

ABSTRACTTroglitazone (CS‐045) is a new oral antidiabetic drug reported to be effective in insulin‐resistant diabetes and to show antihypertensive effects. Photooxidation of troglitazone gave the quinone and quinone epoxide as the major final stable products. An intermediate observed by NMR spectroscopy was shown to be the hydroperoxydi‐enone, which is moderately stable at room temperature. The rate constant of singlet oxygen quenching by troglitazone is 2.14 × 108M−1s−1 and the reaction rate constant in acetone‐d, is 8.64 × 10, M−1 s−1. Only the chroman ring of troglitazone reacts with and quenches singlet oxygen significantly, and its reactivity and products are analogous to those of a‐tocopherol. The reactivity of CS‐045 toward singlet oxygen is much larger than that of the related compounds lacking the chroman ring.
Historical Aspects of Ultraviolet Action Spectroscopy*
Authors: Coohill Thomas P. 
Published: January 2008

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

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

AbstractA solution of iodouracil (0.2 mg/mL) and KI (0.1 M) in 0.23 M borate buffer (pH 7) forms triiodide upon exposure to UVB. In the presence of thyodene, the blue starch‐iodine complex is formed, the intensity of which is proportional to the amount of UVB exposure. Studies were conducted using either a sunlamp or solar irradiation to generate the triiodide endpoint. Samples (1 mL each) were placed in a plastic 24 well sample holder for exposure, and the intensity of the light at each well was controlled by placing a template over the holder with apertures of various sizes (0.4‐1.5 cm) to vary the amount of light incident on each sample. The endpoint was measured using a spectrometer to monitor the absorbance increase at 400 nm of each sample or a densitometer to monitor the optical density of a photograph of the resulting solutions. The selectivity for UVB was demonstrated by irradiating through a UVB cutoff filter that reduced the sunlamp yield by 98.5% and the solar radiation yield by 94%. The correlation between the observed absorbance changes at 400 nm and the amount of absorbed energy was shown to be approximately the same for both types of radiation and the resulting quantum yield calculated to be ˜1%, consistent with the value obtained previously for 5‐iododeoxyuridine using monochromatic radiation. It is proposed that this system be incorporated into a personal dosimeter for monitoring solar UVB exposures, where the degree of exposure can be estimated either by visual inspection or, for more quantitative analysis, by UV spectroscopy.SummaryThe preliminary results presented here demonstrate that the IU actinometer has the potential to be developed as a personal dosimeter for monitoring exposures to solar UVB. The value of this system is that it can provide a visual response to solar radiation with a spectral sensitivity confined mainly to the UVB portion of the sun's spectrum. It responds to exposures within the maximal erythemal range and is easily prepared from available materials.
Ultraviolet Radiation at Sites on the Antarctic Coast
Authors: Frederick John E. , Qu Zheng , Booth C. Rocky 
Published: January 2008

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

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

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

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

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