bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light Distributions from Point, Line and Plane Sources for Photochemical Reactions and Fluorescence in Turbid Biological Tissues
Authors: Jacques Steven L. 
Published: January 2008

ABSTRACTLight 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

ABSTRACTExperimental 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

ABSTRACTWe 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

ABSTRACTPronounced 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

ABSTRACTCovalently 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

ABSTRACTIntimal 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

ABSTRACTThe 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

ABSTRACTThe 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.
Environmental Control of the Deformability of the DNA Double Helix
Authors: Georghiou S. , Kubala Steven M. , Large Catherine C. 
Published: January 2008

ABSTRACTThe 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

ABSTRACTTwo‐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

ABSTRACTThe 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.
Singlet Oxygen Adducts of Cholesterol: Photogeneration and Reductive Turnover in Membrane Systems
Authors: Korytowski Witold , Girotti Albert W. 
Published: January 2008

AbstractIdentification of signature products provides a powerful means for establishing whether singlet molecular oxygen (1O2) is a reactive intermediate in a photodynamic process. This approach is particularly attractive for biological systems in which direct physical measurement is difficult because of the short lifetime of 1O2. Among the many possible reporter molecules in a target system, cholesterol (Ch) has the advantage of affording a limited number of readily distinguishable oxidation products, among which are the hydroperoxides 3β‐hydroxy‐5α‐cholest‐6‐ene‐5‐hydroperoxide (5α‐OOH), 3p‐hydroxy‐cholest‐4‐ene‐6a‐hydroperoxide (6α‐OOH) and 3β‐hy‐droxycholest‐4‐ene‐6β‐hydroperoxide (6β‐OOH) that derive specifically from 1O2 addition. The purpose of this study was to compare these species in terms of (1) rates of accumulation in photodynamically treated liposomal membranes; (2) susceptibility to iron‐mediated 1 e‐reduction that triggers chain peroxidative damage; (3) susceptibility to selenoperoxidase (phospholipid hydroperoxide glutathione peroxidase [PHGPX])‐mediated 2 e reduction that protects against such damage and (4) relative toxicity to mammalian cells. Our results indicate that 5α‐OOH is photogenerated at a much greater initial rate than 6α‐OOH or 6β‐OOH. Although liposomal 5α‐OOH, 6α‐OOH, and 6β‐OOH exhibit similar first‐order decay kinetics during iron/ascorbate treatment, the former decays much more slowly during GSH/PHGPX treatment, and is more toxic to L1210 cells. These and related findings suggest that 5α‐OOH is potentially the most damaging ChOOH to arise in photodynamically treated cells.
Mutation Spectrum Induced by Singlet Oxygen in Escherichia coli Deficient in Exonuclease III
Authors: Agnez‐Lima Lucymara F. , Mascio Paolo Di , Napolitano Rita L. , Fuchs Robert P. , Menck Carlos F. M. 
Published: January 2008

AbstractThe repair of singlet oxygen (1O2)‐induced DNA lesions requires several enzymes of the nucleotide and base excision repair pathways, including exonuclease III and endonucle‐ase IV that are known apurinic/apyrunidinic‐endonucleases in Escherichia coli. In order to better understand the relevance of exonuclease III on the repair of these lesions, we investigated the mutagenic events that result from the replication of a 1O2‐damaged plasmid in an exonuclease‐deflcient host (xth). The mutation spectrum in the tRNA supF gene target indicated that the absence of exonuclease III does not change the types of mutations induced by 1O2 (mostly of G:C ← T:A and G:C ← C:G transver‐sions). However, the spectrum shows that the mutations are scattered in the supF gene, which is significatively different from the one obtained in wild‐type bacteria. Thus, exonuclease III may act on the repair of 1O2‐induced lesions altering the DNA repair sequence specificity.
Bisimidazoacridones: Effect of Molecular Environment on Conformation and Photophysical Properties
Authors: Tarasov Sergey G. , Casas‐Finet Jose R. , Cholody Wieslaw M. , Michejda Christopher J. 
Published: January 2008

AbstractBisimidazoacridones (BIA) are highly selective antineoplastic and antiviral agents. Ultraviolet‐visible spectroscopy and steady‐state and time‐resolved fluorescence spectroscopy studies were carried out to probe the behavior of BIA in aqueous and nonaqueous (organic solvents, colloid micelles) solutions. Three ranges of fluorescence lifetimes were revealed: ˜0.2‐0.5 ns (presumably reflecting the chromophore–chromophore interaction), ˜1–5 ns (interpreted as linker‐perturbed chromophore decay) and ˜6–12 ns (nonperturbed chromophore decay). The pre‐exponential and steady‐state contributions of these components to the decay signal as well as the data on steady‐state fluorescence intensities, wavelength maxima and bandwidths showed that the BIA conformations in solution were sensitive to the environment and influenced strongly by their propensity to minimize hydrophobic interactions. In water, the molecules tend to adopt condensed conformations that bring the two imi‐dazoacridone moieties into close proximity (resulting in intramolecular fluorescence energy transfer), while in nonaqueous systems the conformations become more relaxed. The transfer from a polar to more lipophilic environment of macromolecules is suggested to be the main driving force for binding of BIA to biomacromolecules, such as nucleic acids.
Analysis of Fluorescence Lifetime of Protochlorophyllide and Chlorophyllide in Isolated Etioplast Membranes Measured from Multifrequency Cross‐correlation Phase Fluorometry
Authors: MySliwa‐Kurdziel Beata , Franck Fabrice , Strzatka Kazimierz 
Published: January 2008

AbstractThe fluorescence decays of protochlorophyllide (Pchlide) and of chlorophyllide (Chlide) in wheat etioplast membranes were analyzed using a multiexponential fluorescence decay model. Using different excitation wavelengths from 430 to 470 nm, we found that a triple‐exponential model at 14°C and a double‐exponential model at — 170°C were adequate to describe the Pchlide fluorescence decay. We discuss the origin of the three fluorescence lifetime components at 14°C on the basis of the dependence of their fractional intensities on the excitation wavelength and by correlating the fractional intensities with integrated fluorescence intensities of different Pchlide forms in steady‐state fluorescence spectra. The fluorescence decay of the main Pchlide form, photoactive Pchlide‐F657, is shown to have a complex character with a fast component of 0.25 ns and a slower component of about 2 ns. Two lifetime components of 2 ns and 5.5–6.0 ns are ascribed to the second photoactive form, Pchlide‐F645, and to nonphotoactive Pchlide forms, respectively. In etioplast membranes preilluminated by a short saturating light pulse, we found a single 5.0 ns component for Chlide‐F688 (the Chlide‐NADPH: protochlorophyllide oxidoreductase [PORJ‐NADP+complex) and an additional 1.6 ns component when the formation of Chlide‐F696 (the Chlide‐POR‐NADPH complex) was promoted by exogenous NADPH. From the fluorescence lifetime results we evaluated the quantum yield of the primary photoreaction by Chlide‐F696 as being 70%.