Photochemistry Research Papers - Academia.edu (original) (raw)

Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources-water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e − and H + recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O 2 that leads to reduced and unstable H 2 production. However, presently, several approaches are developed to improve the energetic efficiency to generate H 2 . This review examines the main available pathways to improve the photosynthetic H 2 production.

- by and +1
- •
- Organic Chemistry, Photochemistry, Solar Energy, Hydrogen Production

The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 µs, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (η ∆) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization.

- by Adjaci Uchoa Fernandes
- •
- Chemistry, Photochemistry, Nanoparticle, Nanoparticles

Human papilloma virus infection is increasing at an alarming rate. The ability of the virus to establish a subclinical infection and its association with malignancy of the lower genital tract make the statistics even more worrisome. Topical application of acetic acid solution provokes temporal alterations of the light-scattering properties of human papilloma virus-induced lesions of anogenital area. For the in vivo study of the phenomenon, an imaging system has been employed, which performs time-lapse imaging and enables the calculation and display of the kinetics of the provoked alterations in any point within the examined area. Confirmation of diagnosis has been established with conventional histology and polymerase chain reaction. It has been shown that the method provides early detection and staging of skin alteration or transformation due to human papilloma virus infection and enables mapping of the infected area.

- by Costas Balas
- •
- Light Scattering, Kinetics, Photochemistry, Biology

The use of bacteriorhodopsin (BR) as an active layer in write-once-read-many optical storage is presented. This novel feature of BR materials may be used on a wide variety of substrates, among them transparent substrates but also paper and plastics. The physical basis of the recording process is polarization-sensitive two-photon absorption. As an example for this new BR application, an identification card equipped with an optical recording strip is presented, which has a capacity of about 1 MB of data. The recording density currently used is 125 kB/cm 2 , which is far from the optical limits but allows operation with cheap terminals using plastic optics. In the examples given, data are stored in blocks of 10 kB each. A special optical encryption procedure allows the stored data to be protected from unauthorized reading. The molecular basis of this property is again the polarization-sensitive recording mechanism. The unique combination of optical storage, photochromism, and traceability of the BR material is combined on the single-molecule level. BR introduces a new quality of storage capability for applications with increased security and anticounterfeiting requirements.

- by Norbert Hampp
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- Optics, Biomedical Engineering, Photochemistry, Computer Security

A short synthesis of the revised structure of the marine natural product tridachiahydropyrone is described. A novel biomimetic photochemical electrocyclization was employed to construct the bicyclic carbon framework from an open-chain polyene precursor. The spectroscopic data matched that of the isolated natural product, supporting a revised structure of this complex metabolite.

- by John Moses
- •
- Photochemistry, Biomimetics, Gastropoda, CHEMICAL SCIENCES

Heat-induced changes in photosystem I (PSI) have been studied in terms of rates of oxygen consumption using various donors (DCPIPH 2 , TMPD red and DAD red ), formation of photo-oxidized P700 and changes in Chl a fluorescence emission at 77 K. Linear heating of thylakoid membranes from 35 • C to 70 • C caused an enhancement in PSI-mediated electron transfer rates (DCPIPH 2 →MV) up to 55 • C. However, no change was observed in PSI rates when other electron donors were used (TMPD red and DAD red ). Similarly, Chl a fluorescence emission spectra at 77 K of heat-treated thylakoid membranes did not show any increase in peak at 735 nm, however, a significant decrease was observed as a function of temperature in the peaks at 685 and 694 nm. In DCMU-treated control thylakoid membranes maximum photo-oxidized P700 was generated at g = 2.0025. In heat-treated thylakoid membranes maximum intensity of photo-oxidized P700 signal was observed at ∼50-55 • C without DCMU treatment. The steady-state signal of the photo-oxidized P700 was studied in the presence of DCPIPH 2 and TMPD red as electron donors in DCMU-treated control and in 50 • C treated thylakoid membranes. We present here the first of such comparative study of PSI activity in terms of the rates of oxygen consumption and re-reduction kinetics of photo-oxidized P700 in the presence of different electron donors. It appears that the formation of the P700 + signal in heat-treated thylakoid membranes is due to an inhibited electron supply from PSII and not due to spillover or antenna migration.

- by Arjun Tiwari
- •
- Kinetics, Photochemistry, Electron Transport, photosystem I

Eighteen radiative transfer models in use for calculation of UV index are compared with respect to their results for more than 100 cloud-free atmospheres, which describe present, possible future and extreme conditions. The comparison includes six multiple-scattering spectral models, eight fast spectral models and four empirical models. Averages of the results of the six participating multiple-scattering spectral models are taken as a basis for assessment. The agreement among the multiple-scattering models is within 20.5 UV index values for more than 80% of chosen atmospheric parameters. The fast spectral models have very different agreement, between +1 and up to 12 UV index values. The results of the empirical models agree reasonably well with the reference models but only for the atmospheres for which they have been developed. The data to describe the atmospheric conditions, which are used for the comparison, together with the individual results of all participating models and model descriptions are available on the Internet: http://www.meteo.physik.uni-muenchen.de/strahlunglcostl.

- by Gunther Schauberger
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- Photochemistry, Biological Sciences, Computer Simulation, Physical sciences

Abstract— Irradiation of 1,3–dimethyluracil (DMU) in 1–aminopropane (AP) with u.v. light resulted in the formation of reduced and dimeric forms of DMU and adducts between DMU and AP. The formation of these compounds may be rationalized from the activation of either DMU or AP. Irradiation of DMU and poly-l-lysine in water with u.v. light resulted in the extensive binding of DMU to poly-l-lysine. The pyrimidine is probably attached to the ε-carbon of the polypeptide at the 6–position. The biological implications of these studies are discussed.

- by philip lisagor
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- Radiation Chemistry, Photochemistry, Life Sciences, Biological Sciences

The prominent nitric oxide (NO) donor [Ru(terpy)(bdqi)NO](PF 6 ) 3 has been synthesized and evaluated with respect to noteworthy biological effects due to its NO photorelease, including vascular relaxation and melanoma cell culture toxicity. The potential for delivering NO in therapeutic quantities is tenable since the nitrosyl ruthenium complex (NRC) must first reach the "target tissue" and then release the NO upon stimulus. In this context, NRC-loaded lipid carriers were developed and characterized to further explore its topical administration for applications such as skin cancer treatment. NRC-loaded solid lipid nanoparticles (SLN) and nanostructured lipid carriers were prepared via the microemulsification method, with average diameters of 275 ± 15 nm and 211 ± 31 nm and zeta potentials of −40.7 ± 10.4 mV and −50.0 ± 7.5 mV, respectively. In vitro kinetic studies of NRC release from nanoparticles showed sustained release of NRC from the lipid carriers and illustrated the influence of the release medium and the lyophilization process. Stability studies showed that NO is released from NRC as a function of temperature and time and due to skin contact. The encapsulation of NRC in SLN followed by its lyophilization, significantly improved the complex stability. Furthermore, of particular interest was the fact that in the NO photorelease study, the NO release from the NRC-loaded SLN was approximately twice that of just NRC in solution. NRC-loaded SLN performs well enough at releasing and protecting NO degradation in vitro that it is a promising carrier for topical delivery of NO.

- by Renata Fonseca Vianna Lopez and +1
- •
- Analytical Chemistry, Kinetics, Photochemistry, Scanning Electron Microscopy

The photochemical behavior of oxyfluorfen [2-chloro-1-(3-etoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] on two Greek soils was investigated. Soils were sampled from Nea Malgara and Preveza regions, characterized by a different organic matter content. Soils were spiked with the diphenyl-ether herbicide and irradiation experiments were performed either in the laboratory with a solar simulator (xenon lamp) or outside, under natural sunlight irradiation; other soil samples were kept in the dark to control the retention reaction. Kinetic parameters of both retention and photochemical reactions were calculated using zero-, first- and second- (Langmuir-Hinshelwood) order equations, and best fit was checked through statistical analysis. The soil behaviors were qualitatively similar but quantitatively different, with the soil sampled from the Nea Malgara region much more sorbent as compared with Preveza soil. All studied reactions followed second-order kinetics and photochemical reaction...

- by Laura Scrano
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- Earth Sciences, Kinetics, Photochemistry, Statistical Analysis

A comparative investigation of configurational photoisomerization of bilirubin (Z,Z-BR) bound to human serum albumin (HSA) in vifro produced by fluorescent lamps currently employed in phototherapy of neonatal jaundice has been carried out by using a fast absorbance technique. Photoequilibrium 2, E-BR concentrations and rise-times are reported. Similar measurements effected with monochromatic laser lines in the blue-green spectral region are presented for comparison purposes.

- by Riccardo Pratesi
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- Mathematics, Photochemistry, Phototherapy, Biological Sciences
- by Hosni Takache
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- Engineering, Technology, Photochemistry, Biotechnology
- by Mireille Toebes
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- Photochemistry, Vietnam, Transgenic Mice, influenza A
- by Charles Czeisler
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- Rhythm, Photochemistry, Biology, Medicine

Electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/ MS) have been used to differentiate the 2-and 4-methylpyridyl isomers of free-base and metallated cationic ␤-vinylpyridylporphyrins. The analysis by ESI-MS/MS of the deuterated analogs and semiempirical calculations of structural and electronic parameters were also undertaken. The two free-base isomers are easily differentiated by ESI-MS/MS but the presence of a metallic center renders differentiation of the metallated isomers less effective. The data acquired show that of all the studied compounds, the free-base 2-methylpyridyl isomer, which was operative in the in vitro photoinactivation of Herpes simples virus, has a different gas-phase behavior. Local distortion of the macrocycle due to the presence of the ␤-vinylpyridyl substituent occurs for all the compounds, but a different electron density distribution can account for the observed gas-phase behavior of this potential virus photoinactivator.

- by Mariette M. Pereira
- •
- Chemistry, Analytical Chemistry, Photochemistry, Mass Spectrometry

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- by Daniel Blanco Ania
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- Chemistry, Photochemistry
- by Bhaven Patel
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- Crystallography, Photochemistry, Macromolecular X-Ray Crystallography, Temperature

Iron overload in human body causes damages to our internal organs and can be fatal if untreated. To make aware of this ill effect to the public living nearby an Iron Workshop in residential area of Ernakulam District in Kerala, a study on the iron concentrations in soil samples collected within a distance of 200 meters around a Iron Workshop was done. It was found that the iron content as Fe (II) was higher than that of the normal value expected within in this area. During the raining season, this excess iron may leach out into the nearby wells. People drinking this well water may have a chance of getting iron overload. Based on our studies we have given awareness to the public regarding the symptoms of iron overload and precautions to be taken.

- by Dileesh S
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- Organic Chemistry, Pharmacy, Phytochemistry, Photochemistry

The photocatalytic disinfection of Escherichia coli, a pathogenic micro-organism was investigated. An aqueous suspension of the micro-organism (1 × 10 8 cfu/ml) and neat TiO 2 or silver-loaded TiO 2 were irradiated with a high pressure mercury lamp for various time periods at neutral pH (7.0). Silver loading (1%, w/w) dramatically reduced the illumination time for complete degradation (less than 1-2 min) and minimum catalyst concentration was determined as 0.1 mg/ml. Possible killing mechanism and intermediate products were also determined. Occurrence of lipidperoxidation which produces malondialdehyde (MDA) was proposed but the method employed was so effective that all micro-organisms and intermediate products were further degraded to harmless products.

- by Ferda Candan
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- Engineering, High Pressure, Photochemistry, Biological Sciences

TPE-PDT has advantages over one-photon PDT, including lower collateral damage to healthy tissue and more precise delivery of PDT. As with one-photon PDT, there can be local photochemical depletion of oxygen during TPE-PDT. Here, we investigate model systems and live cells to measure local photosensitizer photobleaching and through it, infer local oxygen consumption in therapeutic volumes of the order 1 pm3. Multilamellar vesicles (MLV) and African green monkey kidney ((3-1) cells were used to study the TPE photobleaching dynamics of the photosensitizer, Verteporfin. It was found that in an oxygen-rich environment, photobleaching kinetics could not be modeled using a mono-exponential function, whereas in hypoxic conditions a mono-exponential decay was adequate to represent photobleaching. A biexponential was found to adequately model the oxygen-rich conditions and it is hypothesized that the fast part of the decay is oxygendependent, whereas the slower rate constant is largely oxygen-independent. Photobleaching recovery studies in the CV-1 cells support this hypothesis.

- by Nicole Kelly
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- Kinetics, Photochemistry, Porphyrins, Biological Sciences

It is critically important to accurately determine histidine since it is an indicator for many diseases when at an abnormal level. Here, an inexpensive and simple method using an amine-functionalized magnetic nanoparticle-based Ni 2+ −histidine affinity pair system was developed for highly sensitive and selective detection of histidine in human urine by photochemical vapor generation atomic spectrometry. Ni 2+ was first bound to the amine groups of the amine-functionalized magnetic nanoparticles and then liberated to solution via the highly specific interaction between the histidine and Ni 2+ in the presence of histidine. The liberated histidine−Ni 2+ complex was exposed to UV irradiation in the presence of formic acid to form gaseous nickel tetracarbonyl, which was separated from the sample matrix and determined by atomic absorption/fluorescence spectrometry. Compared to other methods, this approach promises high sensitivity, simplicity in design, and convenient operation. The need for organic solvents, enzymatic reactions, separation processes, chemical modification, expensive instrumentations, and sophisticated and complicated pretreatment is minimized with this strategy. A limit of detection of 1 nM was obtained and provided tens-to-hundreds of fold improvements over that achieved with conventional methods. The protocol was evaluated by analysis of several urine samples with good recoveries and showed great potential for practical application.

- by Yuan Hu
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- Chemical Engineering, Analytical Chemistry, Photochemistry, Amines

Ultraviolet irradiation of skin induces various DNA photolesions. Here we demonstrate that irradiation of human buttock skin with 300 nm UVR in situ induces thymine dimers and 6-4 photoproducts. Irradiation with 260 nm immediately followed by UVA (320 nm) induces the Dewar photoisomers of the 6-4 lesions. All three lesions can be detected in methanol-fixed paraffin sections using specific monoclonal antibodies.

- by Antony Young
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- Photochemistry, Image Analysis, Integrated Optics, Peroxidase

The hypericin analogs blepharismin (BP), oxyblepharismin (OxyBP) and stentorin (ST), the photosensing chromophores responsible for photomotile reactions in the ciliates Blepharisma japonicum (red and blue cells) and Stentor coeruleus, represent a new class of photoreceptor pigments whose chemical structures have recently been determined. In the case of ST it has been shown that the first excited singlet state can be deactivated by donation of an electron to an appropriate acceptor molecule (e.g. a quinone molecule). This charge transfer can be considered a possible mechanism for the primary photoprocess for the photomotile responses in S. coeruleus. To determine whether an electron transfer process also occurs in the deactivation of excited blepharismin, we studied the fluorescence quenching of OxyBP in dimethyl-sulfoxide (DMSO) and in ethanol using electron acceptors with different reduction potentials. Under our experimental conditions ground state and excited state complexes (like fluorescent exciplexes) are not formed between the fluorophore and the quenchers. In DMSO the bimolecular quenching constant values (k,) calculated on the basis of the best fitting procedures clearly show that the quenching efficiency decreases with the quencher negative reduction potential, E". The k, (M-l s l ) and Eo (V) values are, respectively, 7.8 X lo9 and -0.134 for 1,4-benzoquinone, 8.9 X lo9 and -0.309 for 1,4-naphthoquinone, 2.4 X 10' and -0.8 for nitrobenzene, 0.009 X 10' and -1.022 for azobenzene and 0 and -1.448 for benzophenone. These findings point to the conclusion that upon formation of the encounter complex between OxyBP and the quencher, an electron is released from excited OxyBP to the quencher, similar to what happens in ST. It is suggested that in the pigment granules such a light-induced charge transfer from excited blepharismin to a suitable electron acceptor triggers sensory transduction processes in B. japonicum.

- by Annamaria Quaranta and +2
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- Photochemistry, Biological Sciences, Electron Transfer, Physical sciences

This study evaluated the effectiveness of dual-wavelength ratio fluorescence imaging using a pH-dependent indicator (5,6-carboxyfluorescein, 5,6-CF) for in vivo pH mapping of tissue. A prototype version of a highly sensitive fluorescence imaging device consisting of a modified xenon lamp, an image-intensified camera and a digital imageprocessing system has been developed. 5,6-Carboxyfluorescein was used because its fluorescence emission increases as a function of pH in the physiological (6.0-7.4) pH range. The ratio of fluorescence intensities obtained with the imaging system has been calibrated using aqueous 5,6-CF standards at various pH values. Because the pH of interstitial fluid of malignant tumors tends to be lower than that of normal tissue and can be depressed by glucose administration, experiments were performed on 10 CDF mice bearing lymphoid leukemia P388 grafted subcutaneously. The range of linearity of the calibration curve was obtained between 5.3 and 6.7 with a measured pK, value of 5.93. Consequently the maximum sensitivity was observed in this range. The calculated pH from ratio images was 6.21 * 0.12 in tumorous tissue. This value was equivalent to those obtained at the same time using microelectrodes (6.2 k 0.3). These experiments showed that a dose of 5 mg/kg 5,6-CF and an excitation power density of 2.5 mW/cm2 are sufficient to give a fluorescent pH image of tumors. The limitation of 5,6-CF for the in vivo mapping of tissue results from its low pK, and consequent range of sensitivity. The advantages of this imaging technique compared to microelectrodes are that it (I) is noninvasive, (2) displays a two-dimensional pH image with high resolution (profile distribution of pH in tissue) and (3) can be used to monitor pH over a few hours.

- by Serge Mordon
- •
- Chemistry, Kinetics, Photochemistry, Medicine

Benzophenones (BP) and related aryl ketone photophores have become established as the photoactivatable group of choice for high-efficiency covalent modification of hydrophobic regions of binding proteins, including enzymes and receptors that recognize peptide hormones, (oligo)nucleotides and nucleosides, phosphoinositides, inosi-to1 polyphosphates and a wide variety of therapeutic molecules. This review presents the advantages of BP as photoaffinity labels and provides specific examples from the last 3 years of applications of BP-containing ligands used in biochemistry.

- by Glenn Prestwich
- •
- Photochemistry, Photobiology, Biological Sciences, Physical sciences

Fluocinolone 16,17-acetonide is a corticosteroid used topically to treat various inflammatory skin diseases. Its photoreactivity was studied under UV-A and UV-B light in aqueous buffer in the presence of oxygen. This drug is photolabile under UV-B light and, to a lesser extent, under UV-A light, which is absorbed far less. In phosphate buffer, approximately 80% of fluocinolone acetonide decomposes after 5 Jlcm' of UV-B irradiation, whereas under 30 J/cm2 of UV-A light approximately only 20% decomposes. Both the drug and its photoproducts have been evaluated through a battery of in vitro studies and found to cause photohemolysis and induce photodamage to proteins (erythrocyte ghosts, bovine serum albumin) and linoleic acid. In addition, one of the photoproducts (the 17-hydroperoxy derivative) is highly toxic in the dark. Therefore, both loss of therapeutic activity and light-induced adverse effects may be expected when patients expose themselves to sunlight after drug administration. A major mechanism for phototoxicity involves radicals forming from drug breakdown, at least under UV-B, although reactive oxygen species may play a role, particularly under UV-A.

- by Angelo Albini
- •
- Water, Free Radicals, Photochemistry, Biological Sciences

The photophysical properties of Piroxicam, a nonsteroidal anti-inflammatory drug (NSAID), were investigated at different pH ext values in reversed micelles of Aerosol-OT (AOT) in iso-octane, using both steady-state and picosecond time-resolved fluorescence spectroscopy. In contrast with the very complex data obtained in aqueous media, where several prototropic species are in equilibrium, the reversed micellar system essentially favors two species. The absorption spectra shows only one isosbestic point at ‫؍‬ 348 nm. Excited-state intramolecular proton transfer (ESIPT), also detected in water, is promoted at low water pool contents measured by 0 ‫؍‬ [H 2 O]/[AOT]. A strongly shifted ( em ‫؍‬ 470 nm) tautomeric emission is found. Upon the gradual increase of 0 , striking differences with pH ext are found. At pH ext ‫؍‬ 4, the drug preferentially locates itself in the interfacial region partitioning between a hydrophobic and a hydrophilic domain. Global analysis was applied to the decay data and the results were interpreted by the ''two-state excited-state'' formalism. At pH ext ‫؍‬ 7, the anionic species is prevalent and the probe locates itself deeper inside the water core of the reversed micelles. Thus, a strong dependence on water content is detected, approaching a behavior similar to that observed in free aqueous solutions.

- by Robert B Pansu
- •
- Photochemistry, Biological Sciences, Physical sciences, CHEMICAL SCIENCES

The fate of electronically excited states in DNA base stacks is of tremendous importance for subsequent photochemical damage reactions in the genome. In this study we present a femtosecond broadband pump-probe study on the adenine isomer 2-aminopurine (Ap) incorporated into trinucleotides. After selective excitation of Ap we can monitor energy delocalization between neighboring Ap moieties as well as excited state electron transfer, depending on the sequence of the trinucleotide. Our results establish the time scale for intrastand excimer formation and reveal the lifetime of the excimer state.

- by Torsten Fiebig
- •
- Photochemistry, Biological Sciences, DNA, Physical sciences
- by Bert Kohlmann
- •
- Management, Engineering, Ecological Engineering, Bioinformatics

When investigating the toxicity of individual particle sources, it is important to consider the contribution of both primary and secondary particles. In this article, we present the design of a new photochemical chamber that can be used to form secondary sulfuric acid particles from diluted coal-fired power plant emissions. The chamber is a relatively small, well-mixed flow reactor that can fit in a mobile reaction laboratory. It produces high concentrations of hydroxyl radical (OH) from the photolysis of ozone (O 3 ) in the presence of water vapor. Two chambers were built and tested. A pilot chamber was tested in the laboratory, using mixtures of NO and SO 2 in air, at concentrations that are approximately 100 times lower than those in power plant stack emissions. This chamber was able to oxidize about 20% of the SO 2 , thereby producing 1350 μg m −3 of H 2 SO 4 particles. Further tests showed that increasing O 3 concentrations and residence time increased the H 2 SO 4 production. A field chamber was built subsequently and used in a toxicological study. Diluted coal-fired power plant emissions were introduced in the chamber. Over 19 days of exposure, the chamber, on average, converted 17% of the supplied SO 2 emissions and produced an average of 350 μg m −3 of H 2 SO 4 particles. Particle losses were determined for the pilot chamber, using artificial particles whose size ranged from 50 to 1000 nm. The determined losses ranged from 21 to 42%, with no trend between the amount of particle loss and particle size. Losses for the field chamber, estimated using model calculations, were found to be similar to those of the pilot chamber.

- by Jack M Wolfson
- •
- Photochemistry, Coal, Acid Rain, Power Plant

The transmembrane glycoprotein CD44 is currently thought to be the main cell surface receptor for the glycosaminoglycan hyaluronate. We previously showed that (1) CD44 regulate keratinocyte proliferation; (2) topical retinoids dramatically increase the expression of CD44, hyaluronate and hyaluronate synthase (HAS)s in mouse epidermis; (3) topical retinaldehyde restores the epidermal thickness and CD44 expression which are correlated with clinical improvement in lichen sclerosus et atrophicus lesions; and (4) retinaldehyde-induced proliferative response of keratinocytes is a CD44-dependent phenomenon and requires the presence of HB-EGF, erbBl and matrix metalloproteinases. In this study, we analyzed the effect of UV irradiation on the levels of epidermal hyaluronate and CD44 in mice, as well as its potential prevention by topical retinoids. UVA (10 J/cm2) or UVB (1 J/cm2) irradiation significantly decreased the expression of CD44 and hyaluronate in the epidermis of hairless mice after 2 h. Expression of both epidermal CD44 and hyaluronate was reconstituted within 24 h. Topical application of retinaldehyde for 3 days prior to UVA or UVB irradiation prevented the decrease of CD44 and hyaluronate expression. Topical retinol and retinoic acid also increased the basal levels of epidermal CD44 and hyaluronate, although their preventive effect on UV-induced decrease of these molecules was less pronounced as compared to topical retinaldehyde. These data confirm the relationships between retinoid and CD44 pathways, although the primary target@) of UV leading to CD44 and hyaluronate degradation remain to be elucidated.

- by O. Sorg
- •
- Kinetics, Photochemistry, Biological Sciences, Mice

An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the

- by Michael Giersig
- •
- Microfluidics, Photochemistry, Crystallization, Nanotechnology

An amine-reactive caged rhodamine was synthesized and conjugated to aminodextran. The resulting tracer was injected into a single cell zebrafish embryo, and a portion of the tracer was photolyzed in a single cell after development. The... more

Clinical performance of light-curing composite restorations is greatly influenced by the quality of the curing light. Currently used photopolymerization units have some important drawbacks, such as decreasing light output with time and distance, which results in a relatively low degree of conversion and shallow depth of cure, particularly of darker shades. Experiments with continuous argon laser polymerization showed overheating of the composite sample, as well as increased shrinkage of the material. In this study, a pulsed laser, set at 468 nm (the maximum of the camphorquinone absorption coefficient), with 20-ns pulse duration, repetition rate of 10 Hz and energy of 10 mJ per pulse, was used as a light source. The aim of the study was to evaluate the effect of polymerization of light and dark shades of three different hybrid composites cured by pulsed laser at the surface and at 3.0 mm depth. The degree of conversion was measured by Fourier transform infrared spectroscopy (FTIR). Applying pulsed blue laser, significantly better results were obtained for both shades compared to standard polymerization values. Very weak dependence of the degree of conversion, between the surface measurements and those at 3.0 mm, were observed in the case of pulsed laser polymerization due to the piercing nanopulses and the monochromatic light at 468 nm. 0 1997 Published by Elsevier Science Limited. All rights reserved

- by Mira Ristić and +1
- •
- Biomaterials, Photochemistry, Multidisciplinary, Lasers
- by Carlos E. Crespo-Hernández and +1
- •
- Photochemistry, Chemical, Nucleic Acids, CHEMICAL SCIENCES

The photosynthetic apparatus of green sulfur bacteria, the chlorosome, is generally considered as a highly efficient natural light-harvesting system. The efficient exciton transport through chlorosomes toward the reaction centers originates from self-assembly of the bacteriochlorophyll molecules. The aim of the present work is to realize a long exciton diffusion length in an artificial light-harvesting system using the concept of self-assembled natural chlorosomal chromophores. The ability to transport excitons is studied for porphyrin derivatives with different tendencies to form molecular stacks by self-assembly. A porphyrin derivative denoted as ZnOP, containing methoxymethyl substituents ({meso-tetrakis[3,5-bis(methoxymethyl)phenyl]porphyrinato}zinc(II)) is found to form self-assembled stacks, in contrast to a derivative with tertbutyl substituents, ZnBuP ({meso-tetrakis[3,5-bis(tert-butyl)phenyl]porphyrinato}zinc(II)). Exciton transport and dissociation in a bilayer of these porphyrin derivatives and TiO2 are studied using the time-resolved microwave conductivity (TRMC) method. For ZnOP layers it is found that excitons undergo diffusive motion between the self-assembled stacks, with the exciton diffusion length being as long as 15 (1 nm, which is comparable to that in natural chlorosomes. For ZnBuP a considerably shorter exciton diffusion length of 3 (1 nm is found. Combining these exciton diffusion lengths with exciton lifetimes of 160 ps for ZnOP and 74 ps for ZnBuP yields exciton diffusion coefficients equal to 1.4 × 10-6 m 2 /s and 1 × 10-7 m 2 /s, respectively. The larger exciton diffusion coefficient for ZnOP originates from a strong excitonic coupling for interstack energy transfer. The findings show that energy transfer is strongly affected by the molecular organization. The efficient interstack energy transfer shows promising prospects for application of such self-assembled porphyrins in optoelectronics.

- by Robertus J.m. Klein Gebbink
- •
- Chemistry, Photochemistry, Self Assembly, Porphyrins

Vacuum ultraviolet (VUV) irradiation at wavelengths of λ > 160 nm of urea-h 4 (NH 2 CONH 2) and urea-d 4 (ND 2 COND 2) has been monitored by Fourier transform infrared spectroscopy in argon and xenon matrixes. Several primary photoproducts, such as HNCO:NH 3 (isocyanic acid:ammonia), CO:N 2 H 4 (carbon monoxide: hydrazine) molecular complexes, and isourea (H 2 N(OH)CdNH), which is reported for the first time, were characterized. The assignment of complexes was achieved by co-depositing the pairs of respective species, whereas the isourea identification was based on the comparison between the experimental and theoretical (B3LYP) infrared spectra. Isourea is found in the argon matrix in its most stable (s-Z)-(E) configuration. It is an intermediate in the VUV decomposition process; its dehydration leads to the NH 2 CN:H 2 O complex. In the xenon matrix, the photochemistry of urea yields the HNCO:NH 3 complex as a major product, whereas the CO:N 2 H 4 complex is observed in trace amounts. The observed differences between the argon and xenon matrixes suggest the crossing between S 1 and T 1 potential surfaces of urea to be responsible for the formation of the HNCO:NH 3 complex. A comparison is also performed with other carboxamides, such as formamide (HCONH 2) or acetamide (CH 3 CONH 2).

- by Fabrice Duvernay
- •
- Photochemistry, Ultraviolet, Urea, Xenon

UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodiurn quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands.

- by María Francisca Parrado
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- Photochemistry, Photosynthesis, Flavonoids, Biological Sciences

A database on UV-absorbing mycosporines and mycosporine-like amino acids (MAAs) has been constructed that provides information on various mycosporines and MAAs reported in fungi, cyanobacteria, macroalgae, phytoplankton and animals from aquatic and terrestrial habitats. It also contains information on biosynthetic routes of MAAs as well as on the absorption maxima and molecular structures of different mycosporines and MAAs . This database provides necessary information for scientists working in the field of photoprotective compounds in fungi, cyanobacteria, macroalgae, phytoplankton and animals ). are available online as Supplementary material in the electronic copy of the journal as well as on our server <http:

- by shailendra singh
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- Photochemistry, Cyanobacteria, Fungi, Phytoplankton

Introduction: Low level laser therapy (LLLT) has been shown to enhance collagen production and wound healing but its effect on cartilage repair from biomechanical point of view is not known yet. The aim of present study was to evaluate the biomechanical behaviour of repairing osteochondral defect in rabbits which received a pulsed low-level gallium-arsenide (Ga-As) laser irradiation. Materials and methods: Osteochondral defects with 5 mm diameter and 4 mm in depth induced by drilling in right femoral patellar grooves of 41 adolescent male rabbits. They were divided into experimental and control groups. Experimental group received pulsed Ga-As (890 nm) laser irradiation with energy density of 4.8 J/cm 2 . The rabbits in control group received placebo LLLT with shut-down equipment. The control defects were allowed to heal spontaneously. Each group were divided into three subgroups: A, B and C. Subgroups A, B and C were sacrificed on 4, 8, and 16 weeks after surgery. The knee joint were removed, and the defects were examined biomechanically by in situ-indentation method. The thickness, instantaneous and equilibrium indentation stiffness was measured during the test. Data were analysed using ANOVA and independent sample t-test. Result: While no difference was observed in the repaired cartilage biomechanical properties among 4th, 8th, 16th weeks in study groups. The equilibrium indentation stiffness of experimental group was significantly higher in 8th week in comparison with control group. Conclusion: LLLT significantly enhances the stiffness of repairing tissue in the 8th week post injury in osteochondral defects in rabbits.

- by Giti Torkaman
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- Photochemistry, Wound Healing, Femur, Low Level Laser Therapy

Excimer laser radiation at 193 nm (ArF) and 308 nm (XeCl) is being used for medical applications. Because ultraviolet radiation is absorbed by DNA and causes cell killing, mutagenesis, and carcinogenesis, the effects of 193-and 308-nm excimer laser radiation on biological material have been studied. Radiation ut 193 nm causes less cell killing than conventional 254 nm germicidal light per incident photon. Radiation at 193 nm showed very low potential for causing mutation because proteins absorb strongly at 193 nm thereby reducing the photon flwc reaching the nuclear DNA. In addition, the quantum yield of a cytotoxic and mutagenic photoproduct of DNA is lower for I93 nm than for 254 nm. Radiation at 308 nm is cytotoxic and mutagenic. Results of in vitro assays indicate that the relative abilig of excimer laser radiation to cause DNA damage decreases in the order 248 nm > 308 nm > 193 nm.

- by Irene Kochevar
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- Biomedical Engineering, Photochemistry, DNA damage, DNA

In this work we present a detailed study of the mechanism of photochemistry and thermal reactions, as well as of the kinetics of flavothione (FLT) in ethanol. Furthermore, we analyzed how the hydroxysubstitution pattern of FLT influenced both the kinetics and the mechanism relative to the parent FLT. We show that the primary photochemical reaction of FLT in the absence of oxygen is hydrogen (H)-atom abstraction from the solvent by way of the excited triplet state of FLT. Several products result from thermal reactions of the resulting semireduced FLTH radical, including more than one dimer. A full mechanism is proposed, and the relevant rate constants are evaluated. On the other hand, in the presence of oxygen and a low concentration of FLT, we found that the principal photoproduct is the parent flavone (FL). The reaction leading to photoxidation is not via 1 O 2 attacking a thione, but instead, it is via a reaction of the FLTH radical with ground state oxygen. The kinetic data also demonstrate that the relative values of concentrations of reactants and the rate constants of the reactions can control the dominance of one mechanism over others. We also have examined the photochemical mechanisms and kinetics for several hydroxyflavothiones (n-OHFLT) and compared them with FLT itself. We have found that the photochemical mechanism radically changes depending on the positions of substitution. These differences are directly related to the ordering of the excited states of the n-OHFLT. Specifically, FLT with lowest 3 n,p* states (FLT, 6-hydroxyflavothione, 7-hydroxyflavothione and 7,8-dihydroxyflavothione) efficiently abstract H atoms to give the semireduced radical of the thione. The radical can (1) dimerize to form two different dimers; (2) react with oxygen to produce the parent FL; and (3) recombine with the solvent radical to yield the original FLT. In contrast, FLT with lowest 3 p,p* states (3-hydroxyflavothione, 3,6-dihydroxyflavothione and 3,7-dihydroxyflavothione) behave as photosensitizers of oxygen to form singlet oxygen, which then reacts with the ground state of the substituted FLT. Finally, when T 2

- by Fausto Elisei
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- Kinetics, Photochemistry, Biological Sciences, Physical sciences

Marine aerosols produced by bursting bubbles at the ocean surface are highly enriched in organic matter (OM) relative to seawater. The importance of this OM in the photochemical evolution of marine aerosols and particularly as a source of reactive oxidants are unknown but likely significant. To investigate oxidant production, nascent aerosols were generated by bubbling zero air through flowing Sargasso seawater and photochemical production of OH radical and hydroperoxide were quantified in aqueous extracts exposed to solar radiation. Extrapolation to ambient conditions indicates that OM photolysis was the primary in situ source for OH (1.1 x10 -8 M s -1 ) and hydroperoxides (1.7 x 10 -8 M s -1 ) in nascent aerosols; NO 3 photolysis was the primary source in aged, acidified aerosols (1.4×10 -7 and 4.1×10 -8 M s -1 , respectively). In situ OH photoproduction was comparable to gas-phase uptake whereas H 2 O 2 photoproduction was slower.

- by Maben Net
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- Engineering, Geochemistry, Oceanography, Organic Chemistry

In spite of their great potential as therapeutic agents, most S-nitrosothiols are too unstable to isolate. We have shown that the S-nitroso adduct of N-acetylcysteine (SNAC) can be synthesized directly in aqueous and polyethylene glycol (PEG) 400 matrix by using a reactive gaseous (NO/O 2 ) mixture. Spectral monitoring of the S-N bond cleavage showed that SNAC, synthesized by this method, is relatively stable in nonbuffered aqueous solution at 25؇C in the dark and that its stability is greatly increased in PEG matrix, resulting in a 28-fold decrease in its initial rate of thermal decomposition. Irradiation with UV light ( ‫؍‬ 333 nm) accelerated the rate of decomposition of SNAC to NO in both matrices, indicating that SNAC may find use for the photogeneration of NO. The quantum yield for SNAC decomposition decreased from 0.65 ؎ 0.15 in aqueous solution to 0.047 ؎ 0.005 in PEG 400 matrix. This increased stability in PEG matrix was assigned to a cage effect promoted by the PEG microenvironment that increases the rate of geminated radical pair recombination in the homolytic S-N bond cleavage process. This effect allowed for the storage of SNAC in PEG at Ϫ20؇C in the dark for more than 10 weeks with negligible decomposition. Such stabilization may represent a viable option for the synthesis, storage and handling of S-nitrosothiol solutions for biomedical applications.

- by Marcelo Oliveira
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- Photochemistry, Biological Sciences, Nitric oxide, Physical sciences
- by Assaf Anderson
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- Engineering, Water, Electrochemistry, Photochemistry

The aim of this paper was to gain further insight into the effect of the clay pretreatment process on photofermentative hydrogen production. This two-stage process involved a clay pretreatment step followed by photofermentation which was performed under anaerobic conditions with the illumination by Tungsten lamps. Rhodobacter sphaeroides O.U.001 was used for photofermentation. Higher amounts of color (65%), total phenol (81%) and chemical oxygen demand (31%) removal efficiencies were achieved after clay pretreatment process. During photofermentative hydrogen production with the effluent of clay pretreatment process, the main organic compounds resulting higher hydrogen production rates were found to be acetic, lactic, propionic, and butyric acids. Compared to photofermentation using raw olive mill wastewater (16 L H 2 =L OMW ), the amount of photofermentative hydrogen production was doubled by using the effluent of the clay pretreatment process (31:5 L H 2 =L OMW ). The reasons for the improvement of hydrogen production by clay treatment can be attributed to the high removal of the hardly biodegradable compounds such as phenols; minor removal of organic acids, sugars and amino acids that are known to enhance photofermentative hydrogen production; and the color depletion of raw OMW which might cause a shadowing effect on the photosynthetic bacteria.

- by Ufuk Gündüz
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- Production, Hydrogen, Photochemistry, Multidisciplinary

A method was developed for the determination of aflatoxin B1 in medical herbs (senna pods, botanical name Cassia angustifolia; devil's claw, botanical name Harpagophytum procumbens; and ginger roots, botanical name Zingiber officinale). The method, which was tested in a mini-collaborative study by 4 laboratories, is based on an immunoaffinity cleanup followed by reversed-phase high-performance liquid chromatography separation and fluorescence detection after post-column derivatization. It allows the quantitation of aflatoxin B1 at levels lower than 2 ng/g. A second extractant (acetone-water) was tested and compared to the proposed methanol-water extractant. Several post-column derivatization options (electrochemically generated bromine, photochemical reaction, and chemical bromination) as well as different integration modes (height versus area) were also investigated. No differences were found depending on the choice of derivatization system or the signal integration mode used. ...

- by Katy Kroeger and +1
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- Analytical Chemistry, Photochemistry, Calibration, Methanol

Radiographers process X-ray films using developer and fixer solutions that contain chemicals known to cause or exacerbate asthma. In a study in British Columbia, Canada, radiographers' personal exposures to glutaraldehyde (a constituent of the developer chemistry), acetic acid (a constituent of the fixer chemistry), and sulfur dioxide (a byproduct of sulfites, present in both developer and fixer solutions) were measured. Average full-shift exposures to glutaraldehyde, acetic acid, and sulfur dioxide were 0.0009 mg/m3, 0.09 mg/m3, and 0.08 mg/m3, respectively, all more than one order of magnitude lower than current occupational exposure limits. Local exhaust ventilation of the processing machines and use of silver recovery units lowered exposures, whereas the number of films processed per machine and the time spent near the machines increased exposures. Personnel in clinic facilities had higher exposures than those in hospitals. Private clinics were less likely to have local exha...

- by Michael Brauer and +1
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- Photochemistry, Environmental Monitoring, Ventilation, British Columbia

Synthesis and processing techniques have now been established for obtaining high quality monodisperse nanocrystals of various metallic and semiconducting materials, fullerenes of distinct properties, single-and multi-wall carbon nanotubes, polymeric dendrimers with tailored functionalities, as well as other nanophase constructs. The next key step towards novel applications of nanostructured materials concerns their positioning, arrangement, and connection into functional networks without mutual aggregation. In this review, we highlight the recent progress of using anthraceneand pyrene-based self-assembling molecules with tunable energetic (-interactions, hydrogen bonding, dipole-dipole interactions) and variable geometries to create stable, highly ordered, and rigid self-assembled monolayer (SAM) templates with adjustable superlattices on crystalline substrates. Based on aromatic SAM templates, stable and highly ordered self-assembled structures of optoelectronically active C 60 have been obtained and shown to exhibit desirable electrical and optoelectronic properties, such as nonlinear transporting effect for molecular electronics and efficient photocurrent generation for mimicking photosynthesis in nature. By using genetically engineered polypeptides with surface recognition for specific inorganics, selective integration of nanoparticles onto aromatic SAM templates have also been realized. Through a combination of spatially confined surface chemical reaction and microcontact printing, sub-micron arrays of peptide-organic hybrid conjugates were successfully generated to serve as templates to achieve the patterned assembly of nanoparticles.

- by Hadi Zareie
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- Engineering, Organic Chemistry, Technology, Electronics